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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
		13	// a single header file is required
11	#include <ev.h>	14	#include <ev.h>
12		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
13	ev_io stdin_watcher;	20	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
15		22
16	/* called when data readable on stdin */	23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
17	static void	25	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	27	{
20	/* puts ("stdin ready"); */	28	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	29	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
23	}	35	}
24		36
		37	// another callback, this time for a time-out
25	static void	38	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	40	{
28	/* puts ("timeout"); */	41	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
30	}	44	}
31		45
32	int	46	int
33	main (void)	47	main (void)
34	{	48	{
35	struct ev_loop *loop = ev_default_loop (0);	49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
36		51
37	/* initialise an io watcher, then start it */	52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
40		56
		57	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	58	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
44		61
45	/* loop till timeout or data ready */	62	// now wait for events to arrive
46	ev_loop (loop, 0);	63	ev_run (loop, 0);
47		64
		65	// break was called, so exit
48	return 0;	66	return 0;
49	}	67	}
50		68
51	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
52		70
		71	This document documents the libev software package.
		72
53	The newest version of this document is also available as a html-formatted	73	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	74	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
56		94
57	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	97	these event sources and provide your program with events.
60		98
…		…
67	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	106	watcher.
69		107
70	=head2 FEATURES	108	=head2 FEATURES
71		109
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	114	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	115	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(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	117	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	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
82		121
83	It also is quite fast (see this	122	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	124	for example).
86		125
87	=head2 CONVENTIONS	126	=head2 CONVENTIONS
88		127
89	Libev is very configurable. In this manual the default configuration will	128	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	129	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	130	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	131	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>	132	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.	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		134	this argument.
95		135
96	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
97		137
98	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	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	140	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	141	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	142	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as some floatingpoint value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
104	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
		168	Libev also has a few internal error-checking C<assert>ions. These do not
		169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
		171
106		172
107	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
108		174
109	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
110	library in any way.	176	library in any way.
…		…
113		179
114	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
115		181
116	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
117	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
118	you actually want to know.	184	you actually want to know. Also interesting is the combination of
		185	C<ev_now_update> and C<ev_now>.
119		186
120	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
121		188
122	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
123	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
124	this is a subsecond-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
125		198
126	=item int ev_version_major ()	199	=item int ev_version_major ()
127		200
128	=item int ev_version_minor ()	201	=item int ev_version_minor ()
129		202
…		…
140	as this indicates an incompatible change. Minor versions are usually	213	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	214	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	215	not a problem.
143		216
144	Example: Make sure we haven't accidentally been linked against the wrong	217	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	218	version (note, however, that this will not detect other ABI mismatches,
		219	such as LFS or reentrancy).
146		220
147	assert (("libev version mismatch",	221	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	222	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	223	&& ev_version_minor () >= EV_VERSION_MINOR));
150		224
151	=item unsigned int ev_supported_backends ()	225	=item unsigned int ev_supported_backends ()
152		226
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	227	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	228	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	230	a description of the set values.
157		231
158	Example: make sure we have the epoll method, because yeah this is cool and	232	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	233	a must have and can we have a torrent of it please!!!11
160		234
161	assert (("sorry, no epoll, no sex",	235	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	236	ev_supported_backends () & EVBACKEND_EPOLL));
163		237
164	=item unsigned int ev_recommended_backends ()	238	=item unsigned int ev_recommended_backends ()
165		239
166	Return the set of all backends compiled into this binary of libev and also	240	Return the set of all backends compiled into this binary of libev and
167	recommended for this platform. This set is often smaller than the one	241	also recommended for this platform, meaning it will work for most file
		242	descriptor types. This set is often smaller than the one returned by
168	returned by C<ev_supported_backends>, as for example kqueue is broken on	243	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
169	most BSDs and will not be autodetected unless you explicitly request it	244	and will not be auto-detected unless you explicitly request it (assuming
170	(assuming you know what you are doing). This is the set of backends that	245	you know what you are doing). This is the set of backends that libev will
171	libev will probe for if you specify no backends explicitly.	246	probe for if you specify no backends explicitly.
172		247
173	=item unsigned int ev_embeddable_backends ()	248	=item unsigned int ev_embeddable_backends ()
174		249
175	Returns the set of backends that are embeddable in other event loops. This	250	Returns the set of backends that are embeddable in other event loops. This
176	is the theoretical, all-platform, value. To find which backends	251	value is platform-specific but can include backends not available on the
177	might be supported on the current system, you would need to look at	252	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	253	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
180		255
181	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
182		257
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
184		259
185	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	262	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	263	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	264	or take some potentially destructive action.
190	function.	265
		266	Since some systems (at least OpenBSD and Darwin) fail to implement
		267	correct C<realloc> semantics, libev will use a wrapper around the system
		268	C<realloc> and C<free> functions by default.
191		269
192	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
195		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
196	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	289	retries.
198		290
199	static void *	291	static void *
200	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
201	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
202	for (;;)	300	for (;;)
203	{	301	{
204	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
205		303
206	if (newptr)	304	if (newptr)
…		…
211	}	309	}
212		310
213	...	311	...
214	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
215		313
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
217		315
218	Set the callback function to call on a retryable syscall error (such	316	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	319	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	320	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	321	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	322	(such as abort).
225		323
226	Example: This is basically the same thing that libev does internally, too.	324	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	331	}
234		332
235	...	333	...
236	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
237		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
238	=back	349	=back
239		350
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		352
242	An event loop is described by a C<struct ev_loop *>. The library knows two	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
243	types of such loops, the I<default> loop, which supports signals and child	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	355	libev 3 had an C<ev_loop> function colliding with the struct name).
245		356
246	If you use threads, a common model is to run the default event loop	357	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	358	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	359	do not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		360
253	=over 4	361	=over 4
254		362
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		364
257	This will initialise the default event loop if it hasn't been initialised	365	This returns the "default" event loop object, which is what you should
258	yet and return it. If the default loop could not be initialised, returns	366	normally use when you just need "the event loop". Event loop objects and
259	false. If it already was initialised it simply returns it (and ignores the	367	the C<flags> parameter are described in more detail in the entry for
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	368	C<ev_loop_new>.
		369
		370	If the default loop is already initialised then this function simply
		371	returns it (and ignores the flags. If that is troubling you, check
		372	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		373	flags, which should almost always be C<0>, unless the caller is also the
		374	one calling C<ev_run> or otherwise qualifies as "the main program".
261		375
262	If you don't know what event loop to use, use the one returned from this	376	If you don't know what event loop to use, use the one returned from this
263	function.	377	function (or via the C<EV_DEFAULT> macro).
		378
		379	Note that this function is I<not> thread-safe, so if you want to use it
		380	from multiple threads, you have to employ some kind of mutex (note also
		381	that this case is unlikely, as loops cannot be shared easily between
		382	threads anyway).
		383
		384	The default loop is the only loop that can handle C<ev_child> watchers,
		385	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		386	a problem for your application you can either create a dynamic loop with
		387	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		388	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		389
		390	Example: This is the most typical usage.
		391
		392	if (!ev_default_loop (0))
		393	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		394
		395	Example: Restrict libev to the select and poll backends, and do not allow
		396	environment settings to be taken into account:
		397
		398	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		399
		400	=item struct ev_loop *ev_loop_new (unsigned int flags)
		401
		402	This will create and initialise a new event loop object. If the loop
		403	could not be initialised, returns false.
		404
		405	This function is thread-safe, and one common way to use libev with
		406	threads is indeed to create one loop per thread, and using the default
		407	loop in the "main" or "initial" thread.
264		408
265	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		411
268	The following flags are supported:	412	The following flags are supported:
…		…
274	The default flags value. Use this if you have no clue (it's the right	418	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	419	thing, believe me).
276		420
277	=item C<EVFLAG_NOENV>	421	=item C<EVFLAG_NOENV>
278		422
279	If this flag bit is ored into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
284	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
285		431
286	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
287		433
288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
289	a fork, you can also make libev check for a fork in each iteration by	435	make libev check for a fork in each iteration by enabling this flag.
290	enabling this flag.
291		436
292	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
296	without a syscall and thus I<very> fast, but my Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
297	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
298		444
299	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
301	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
302		448
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	450	environment variable.
		451
		452	=item C<EVFLAG_NOINOTIFY>
		453
		454	When this flag is specified, then libev will not attempt to use the
		455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		456	testing, this flag can be useful to conserve inotify file descriptors, as
		457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		458
		459	=item C<EVFLAG_SIGNALFD>
		460
		461	When this flag is specified, then libev will attempt to use the
		462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		463	delivers signals synchronously, which makes it both faster and might make
		464	it possible to get the queued signal data. It can also simplify signal
		465	handling with threads, as long as you properly block signals in your
		466	threads that are not interested in handling them.
		467
		468	Signalfd will not be used by default as this changes your signal mask, and
		469	there are a lot of shoddy libraries and programs (glib's threadpool for
		470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	=item C<EVFLAG_NOTIMERFD>
		486
		487	When this flag is specified, the libev will avoid using a C<timerfd> to
		488	detect time jumps. It will still be able to detect time jumps, but takes
		489	longer and has a lower accuracy in doing so, but saves a file descriptor
		490	per loop.
		491
		492	The current implementation only tries to use a C<timerfd> when the first
		493	C<ev_periodic> watcher is started and falls back on other methods if it
		494	cannot be created, but this behaviour might change in the future.
305		495
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		497
308	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	500	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its	501	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	usually the fastest backend for a low number of (low-numbered :) fds.	502	usually the fastest backend for a low number of (low-numbered :) fds.
313		503
314	To get good performance out of this backend you need a high amount of	504	To get good performance out of this backend you need a high amount of
315	parallelity (most of the file descriptors should be busy). If you are	505	parallelism (most of the file descriptors should be busy). If you are
316	writing a server, you should C<accept ()> in a loop to accept as many	506	writing a server, you should C<accept ()> in a loop to accept as many
317	connections as possible during one iteration. You might also want to have	507	connections as possible during one iteration. You might also want to have
318	a look at C<ev_set_io_collect_interval ()> to increase the amount of	508	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	509	readiness notifications you get per iteration.
		510
		511	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		512	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		513	C<exceptfds> set on that platform).
320		514
321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	515	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
322		516
323	And this is your standard poll(2) backend. It's more complicated	517	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	518	than select, but handles sparse fds better and has no artificial
325	limit on the number of fds you can use (except it will slow down	519	limit on the number of fds you can use (except it will slow down
326	considerably with a lot of inactive fds). It scales similarly to select,	520	considerably with a lot of inactive fds). It scales similarly to select,
327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	521	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	522	performance tips.
329		523
		524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		526
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
331		528
		529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
		530	kernels).
		531
332	For few fds, this backend is a bit little slower than poll and select,	532	For few fds, this backend is a bit little slower than poll and select, but
333	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
334	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
335	epoll scales either O(1) or O(active_fds). The epoll design has a number	535	fd), epoll scales either O(1) or O(active_fds).
336	of shortcomings, such as silently dropping events in some hard-to-detect	536
337	cases and rewiring a syscall per fd change, no fork support and bad	537	The epoll mechanism deserves honorable mention as the most misdesigned
338	support for dup.	538	of the more advanced event mechanisms: mere annoyances include silently
		539	dropping file descriptors, requiring a system call per change per file
		540	descriptor (and unnecessary guessing of parameters), problems with dup,
		541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
		543	0.1ms) and so on. The biggest issue is fork races, however - if a program
		544	forks then I<both> parent and child process have to recreate the epoll
		545	set, which can take considerable time (one syscall per file descriptor)
		546	and is of course hard to detect.
		547
		548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		549	but of course I<doesn't>, and epoll just loves to report events for
		550	totally I<different> file descriptors (even already closed ones, so
		551	one cannot even remove them from the set) than registered in the set
		552	(especially on SMP systems). Libev tries to counter these spurious
		553	notifications by employing an additional generation counter and comparing
		554	that against the events to filter out spurious ones, recreating the set
		555	when required. Epoll also erroneously rounds down timeouts, but gives you
		556	no way to know when and by how much, so sometimes you have to busy-wait
		557	because epoll returns immediately despite a nonzero timeout. And last
		558	not least, it also refuses to work with some file descriptors which work
		559	perfectly fine with C<select> (files, many character devices...).
		560
		561	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		562	cobbled together in a hurry, no thought to design or interaction with
		563	others. Oh, the pain, will it ever stop...
339		564
340	While stopping, setting and starting an I/O watcher in the same iteration	565	While stopping, setting and starting an I/O watcher in the same iteration
341	will result in some caching, there is still a syscall per such incident	566	will result in some caching, there is still a system call per such
342	(because the fd could point to a different file description now), so its	567	incident (because the same I<file descriptor> could point to a different
343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	568	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
344	very well if you register events for both fds.	569	file descriptors might not work very well if you register events for both
345		570	file descriptors.
346	Please note that epoll sometimes generates spurious notifications, so you
347	need to use non-blocking I/O or other means to avoid blocking when no data
348	(or space) is available.
349		571
350	Best performance from this backend is achieved by not unregistering all	572	Best performance from this backend is achieved by not unregistering all
351	watchers for a file descriptor until it has been closed, if possible, i.e.	573	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	574	i.e. keep at least one watcher active per fd at all times. Stopping and
		575	starting a watcher (without re-setting it) also usually doesn't cause
		576	extra overhead. A fork can both result in spurious notifications as well
		577	as in libev having to destroy and recreate the epoll object, which can
		578	take considerable time and thus should be avoided.
353		579
		580	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		581	faster than epoll for maybe up to a hundred file descriptors, depending on
		582	the usage. So sad.
		583
354	While nominally embeddeble in other event loops, this feature is broken in	584	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
		586
		587	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		588	C<EVBACKEND_POLL>.
		589
		590	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		591
		592	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		593	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		594	only tries to use it in 4.19+).
		595
		596	This is another Linux train wreck of an event interface.
		597
		598	If this backend works for you (as of this writing, it was very
		599	experimental), it is the best event interface available on Linux and might
		600	be well worth enabling it - if it isn't available in your kernel this will
		601	be detected and this backend will be skipped.
		602
		603	This backend can batch oneshot requests and supports a user-space ring
		604	buffer to receive events. It also doesn't suffer from most of the design
		605	problems of epoll (such as not being able to remove event sources from
		606	the epoll set), and generally sounds too good to be true. Because, this
		607	being the Linux kernel, of course it suffers from a whole new set of
		608	limitations, forcing you to fall back to epoll, inheriting all its design
		609	issues.
		610
		611	For one, it is not easily embeddable (but probably could be done using
		612	an event fd at some extra overhead). It also is subject to a system wide
		613	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		614	requests are left, this backend will be skipped during initialisation, and
		615	will switch to epoll when the loop is active.
		616
		617	Most problematic in practice, however, is that not all file descriptors
		618	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		619	files, F</dev/null> and many others are supported, but ttys do not work
		620	properly (a known bug that the kernel developers don't care about, see
		621	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		622	(yet?) a generic event polling interface.
		623
		624	Overall, it seems the Linux developers just don't want it to have a
		625	generic event handling mechanism other than C<select> or C<poll>.
		626
		627	To work around all these problem, the current version of libev uses its
		628	epoll backend as a fallback for file descriptor types that do not work. Or
		629	falls back completely to epoll if the kernel acts up.
		630
		631	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		632	C<EVBACKEND_POLL>.
356		633
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		635
359	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
360	was broken on all BSDs except NetBSD (usually it doesn't work reliably	637	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
361	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
362	it's completely useless). For this reason it's not being "autodetected"	639	where of course it's completely useless). Unlike epoll, however, whose
363	unless you explicitly specify it explicitly in the flags (i.e. using	640	brokenness is by design, these kqueue bugs can be (and mostly have been)
364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	641	fixed without API changes to existing programs. For this reason it's not
365	system like NetBSD.	642	being "auto-detected" on all platforms unless you explicitly specify it
		643	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
		644	known-to-be-good (-enough) system like NetBSD.
366		645
367	You still can embed kqueue into a normal poll or select backend and use it	646	You still can embed kqueue into a normal poll or select backend and use it
368	only for sockets (after having made sure that sockets work with kqueue on	647	only for sockets (after having made sure that sockets work with kqueue on
369	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
370		649
371	It scales in the same way as the epoll backend, but the interface to the	650	It scales in the same way as the epoll backend, but the interface to the
372	kernel is more efficient (which says nothing about its actual speed, of	651	kernel is more efficient (which says nothing about its actual speed, of
373	course). While stopping, setting and starting an I/O watcher does never	652	course). While stopping, setting and starting an I/O watcher does never
374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	653	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
375	two event changes per incident, support for C<fork ()> is very bad and it	654	two event changes per incident. Support for C<fork ()> is very bad (you
		655	might have to leak fds on fork, but it's more sane than epoll) and it
376	drops fds silently in similarly hard-to-detect cases.	656	drops fds silently in similarly hard-to-detect cases.
377		657
378	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
379		659
380	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
381	everywhere, so you might need to test for this. And since it is broken	661	everywhere, so you might need to test for this. And since it is broken
382	almost everywhere, you should only use it when you have a lot of sockets	662	almost everywhere, you should only use it when you have a lot of sockets
383	(for which it usually works), by embedding it into another event loop	663	(for which it usually works), by embedding it into another event loop
384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	664	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
385	sockets.	665	also broken on OS X)) and, did I mention it, using it only for sockets.
		666
		667	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		668	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		669	C<NOTE_EOF>.
386		670
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	671	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		672
389	This is not implemented yet (and might never be, unless you send me an	673	This is not implemented yet (and might never be, unless you send me an
390	implementation). According to reports, C</dev/poll> only supports sockets	674	implementation). According to reports, C</dev/poll> only supports sockets
391	and is not embeddable, which would limit the usefulness of this backend	675	and is not embeddable, which would limit the usefulness of this backend
392	immensely.	676	immensely.
393		677
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		679
396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	680	This uses the Solaris 10 event port mechanism. As with everything on
397	it's really slow, but it still scales very well (O(active_fds)).	681	Solaris, it's really slow, but it still scales very well (O(active_fds)).
398
399	Please note that solaris event ports can deliver a lot of spurious
400	notifications, so you need to use non-blocking I/O or other means to avoid
401	blocking when no data (or space) is available.
402		682
403	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
404	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	686	might perform better.
407		687
		688	On the positive side, this backend actually performed fully to
		689	specification in all tests and is fully embeddable, which is a rare feat
		690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
		702
		703	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		704	C<EVBACKEND_POLL>.
		705
408	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
409		707
410	Try all backends (even potentially broken ones that wouldn't be tried	708	Try all backends (even potentially broken ones that wouldn't be tried
411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	709	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413		711
414	It is definitely not recommended to use this flag.	712	It is definitely not recommended to use this flag, use whatever
		713	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		714	at all.
		715
		716	=item C<EVBACKEND_MASK>
		717
		718	Not a backend at all, but a mask to select all backend bits from a
		719	C<flags> value, in case you want to mask out any backends from a flags
		720	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
415		721
416	=back	722	=back
417		723
418	If one or more of these are ored into the flags value, then only these	724	If one or more of the backend flags are or'ed into the flags value,
419	backends will be tried (in the reverse order as given here). If none are	725	then only these backends will be tried (in the reverse order as listed
420	specified, most compiled-in backend will be tried, usually in reverse	726	here). If none are specified, all backends in C<ev_recommended_backends
421	order of their flag values :)	727	()> will be tried.
422
423	The most typical usage is like this:
424
425	if (!ev_default_loop (0))
426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
427
428	Restrict libev to the select and poll backends, and do not allow
429	environment settings to be taken into account:
430
431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
432
433	Use whatever libev has to offer, but make sure that kqueue is used if
434	available (warning, breaks stuff, best use only with your own private
435	event loop and only if you know the OS supports your types of fds):
436
437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
438
439	=item struct ev_loop *ev_loop_new (unsigned int flags)
440
441	Similar to C<ev_default_loop>, but always creates a new event loop that is
442	always distinct from the default loop. Unlike the default loop, it cannot
443	handle signal and child watchers, and attempts to do so will be greeted by
444	undefined behaviour (or a failed assertion if assertions are enabled).
445		728
446	Example: Try to create a event loop that uses epoll and nothing else.	729	Example: Try to create a event loop that uses epoll and nothing else.
447		730
448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	731	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
449	if (!epoller)	732	if (!epoller)
450	fatal ("no epoll found here, maybe it hides under your chair");	733	fatal ("no epoll found here, maybe it hides under your chair");
451		734
		735	Example: Use whatever libev has to offer, but make sure that kqueue is
		736	used if available.
		737
		738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		745
452	=item ev_default_destroy ()	746	=item ev_loop_destroy (loop)
453		747
454	Destroys the default loop again (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
455	etc.). None of the active event watchers will be stopped in the normal	749	etc.). None of the active event watchers will be stopped in the normal
456	sense, so e.g. C<ev_is_active> might still return true. It is your	750	sense, so e.g. C<ev_is_active> might still return true. It is your
457	responsibility to either stop all watchers cleanly yoursef I<before>	751	responsibility to either stop all watchers cleanly yourself I<before>
458	calling this function, or cope with the fact afterwards (which is usually	752	calling this function, or cope with the fact afterwards (which is usually
459	the easiest thing, you can just ignore the watchers and/or C<free ()> them	753	the easiest thing, you can just ignore the watchers and/or C<free ()> them
460	for example).	754	for example).
461		755
462	Note that certain global state, such as signal state, will not be freed by	756	Note that certain global state, such as signal state (and installed signal
463	this function, and related watchers (such as signal and child watchers)	757	handlers), will not be freed by this function, and related watchers (such
464	would need to be stopped manually.	758	as signal and child watchers) would need to be stopped manually.
465		759
466	In general it is not advisable to call this function except in the	760	This function is normally used on loop objects allocated by
467	rare occasion where you really need to free e.g. the signal handling	761	C<ev_loop_new>, but it can also be used on the default loop returned by
		762	C<ev_default_loop>, in which case it is not thread-safe.
		763
		764	Note that it is not advisable to call this function on the default loop
		765	except in the rare occasion where you really need to free its resources.
468	pipe fds. If you need dynamically allocated loops it is better to use	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
469	C<ev_loop_new> and C<ev_loop_destroy>).	767	and C<ev_loop_destroy>.
470		768
471	=item ev_loop_destroy (loop)	769	=item ev_loop_fork (loop)
472		770
473	Like C<ev_default_destroy>, but destroys an event loop created by an	771	This function sets a flag that causes subsequent C<ev_run> iterations
474	earlier call to C<ev_loop_new>.
475
476	=item ev_default_fork ()
477
478	This function reinitialises the kernel state for backends that have	772	to reinitialise the kernel state for backends that have one. Despite
479	one. Despite the name, you can call it anytime, but it makes most sense	773	the name, you can call it anytime you are allowed to start or stop
480	after forking, in either the parent or child process (or both, but that	774	watchers (except inside an C<ev_prepare> callback), but it makes most
481	again makes little sense).	775	sense after forking, in the child process. You I<must> call it (or use
		776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
482		777
483	You I<must> call this function in the child process after forking if and	778	In addition, if you want to reuse a loop (via this function or
484	only if you want to use the event library in both processes. If you just	779	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
485	fork+exec, you don't have to call it.	780
		781	Again, you I<have> to call it on I<any> loop that you want to re-use after
		782	a fork, I<even if you do not plan to use the loop in the parent>. This is
		783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		784	during fork.
		785
		786	On the other hand, you only need to call this function in the child
		787	process if and only if you want to use the event loop in the child. If
		788	you just fork+exec or create a new loop in the child, you don't have to
		789	call it at all (in fact, C<epoll> is so badly broken that it makes a
		790	difference, but libev will usually detect this case on its own and do a
		791	costly reset of the backend).
486		792
487	The function itself is quite fast and it's usually not a problem to call	793	The function itself is quite fast and it's usually not a problem to call
488	it just in case after a fork. To make this easy, the function will fit in	794	it just in case after a fork.
489	quite nicely into a call to C<pthread_atfork>:
490		795
		796	Example: Automate calling C<ev_loop_fork> on the default loop when
		797	using pthreads.
		798
		799	static void
		800	post_fork_child (void)
		801	{
		802	ev_loop_fork (EV_DEFAULT);
		803	}
		804
		805	...
491	pthread_atfork (0, 0, ev_default_fork);	806	pthread_atfork (0, 0, post_fork_child);
492		807
493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	808	=item int ev_is_default_loop (loop)
494	without calling this function, so if you force one of those backends you
495	do not need to care.
496		809
497	=item ev_loop_fork (loop)	810	Returns true when the given loop is, in fact, the default loop, and false
		811	otherwise.
498		812
499	Like C<ev_default_fork>, but acts on an event loop created by
500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
501	after fork, and how you do this is entirely your own problem.
502
503	=item unsigned int ev_loop_count (loop)	813	=item unsigned int ev_iteration (loop)
504		814
505	Returns the count of loop iterations for the loop, which is identical to	815	Returns the current iteration count for the event loop, which is identical
506	the number of times libev did poll for new events. It starts at C<0> and	816	to the number of times libev did poll for new events. It starts at C<0>
507	happily wraps around with enough iterations.	817	and happily wraps around with enough iterations.
508		818
509	This value can sometimes be useful as a generation counter of sorts (it	819	This value can sometimes be useful as a generation counter of sorts (it
510	"ticks" the number of loop iterations), as it roughly corresponds with	820	"ticks" the number of loop iterations), as it roughly corresponds with
511	C<ev_prepare> and C<ev_check> calls.	821	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		822	prepare and check phases.
		823
		824	=item unsigned int ev_depth (loop)
		825
		826	Returns the number of times C<ev_run> was entered minus the number of
		827	times C<ev_run> was exited normally, in other words, the recursion depth.
		828
		829	Outside C<ev_run>, this number is zero. In a callback, this number is
		830	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		831	in which case it is higher.
		832
		833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		834	throwing an exception etc.), doesn't count as "exit" - consider this
		835	as a hint to avoid such ungentleman-like behaviour unless it's really
		836	convenient, in which case it is fully supported.
512		837
513	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
514		839
515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	840	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
516	use.	841	use.
…		…
521	received events and started processing them. This timestamp does not	846	received events and started processing them. This timestamp does not
522	change as long as callbacks are being processed, and this is also the base	847	change as long as callbacks are being processed, and this is also the base
523	time used for relative timers. You can treat it as the timestamp of the	848	time used for relative timers. You can treat it as the timestamp of the
524	event occurring (or more correctly, libev finding out about it).	849	event occurring (or more correctly, libev finding out about it).
525		850
		851	=item ev_now_update (loop)
		852
		853	Establishes the current time by querying the kernel, updating the time
		854	returned by C<ev_now ()> in the progress. This is a costly operation and
		855	is usually done automatically within C<ev_run ()>.
		856
		857	This function is rarely useful, but when some event callback runs for a
		858	very long time without entering the event loop, updating libev's idea of
		859	the current time is a good idea.
		860
		861	See also L</The special problem of time updates> in the C<ev_timer> section.
		862
		863	=item ev_suspend (loop)
		864
		865	=item ev_resume (loop)
		866
		867	These two functions suspend and resume an event loop, for use when the
		868	loop is not used for a while and timeouts should not be processed.
		869
		870	A typical use case would be an interactive program such as a game: When
		871	the user presses C<^Z> to suspend the game and resumes it an hour later it
		872	would be best to handle timeouts as if no time had actually passed while
		873	the program was suspended. This can be achieved by calling C<ev_suspend>
		874	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		875	C<ev_resume> directly afterwards to resume timer processing.
		876
		877	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		878	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		879	will be rescheduled (that is, they will lose any events that would have
		880	occurred while suspended).
		881
		882	After calling C<ev_suspend> you B<must not> call I<any> function on the
		883	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		884	without a previous call to C<ev_suspend>.
		885
		886	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		887	event loop time (see C<ev_now_update>).
		888
526	=item ev_loop (loop, int flags)	889	=item bool ev_run (loop, int flags)
527		890
528	Finally, this is it, the event handler. This function usually is called	891	Finally, this is it, the event handler. This function usually is called
529	after you initialised all your watchers and you want to start handling	892	after you have initialised all your watchers and you want to start
530	events.	893	handling events. It will ask the operating system for any new events, call
		894	the watcher callbacks, and then repeat the whole process indefinitely: This
		895	is why event loops are called I<loops>.
531		896
532	If the flags argument is specified as C<0>, it will not return until	897	If the flags argument is specified as C<0>, it will keep handling events
533	either no event watchers are active anymore or C<ev_unloop> was called.	898	until either no event watchers are active anymore or C<ev_break> was
		899	called.
534		900
		901	The return value is false if there are no more active watchers (which
		902	usually means "all jobs done" or "deadlock"), and true in all other cases
		903	(which usually means " you should call C<ev_run> again").
		904
535	Please note that an explicit C<ev_unloop> is usually better than	905	Please note that an explicit C<ev_break> is usually better than
536	relying on all watchers to be stopped when deciding when a program has	906	relying on all watchers to be stopped when deciding when a program has
537	finished (especially in interactive programs), but having a program that	907	finished (especially in interactive programs), but having a program
538	automatically loops as long as it has to and no longer by virtue of	908	that automatically loops as long as it has to and no longer by virtue
539	relying on its watchers stopping correctly is a thing of beauty.	909	of relying on its watchers stopping correctly, that is truly a thing of
		910	beauty.
540		911
		912	This function is I<mostly> exception-safe - you can break out of a
		913	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		914	exception and so on. This does not decrement the C<ev_depth> value, nor
		915	will it clear any outstanding C<EVBREAK_ONE> breaks.
		916
541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	917	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
542	those events and any outstanding ones, but will not block your process in	918	those events and any already outstanding ones, but will not wait and
543	case there are no events and will return after one iteration of the loop.	919	block your process in case there are no events and will return after one
		920	iteration of the loop. This is sometimes useful to poll and handle new
		921	events while doing lengthy calculations, to keep the program responsive.
544		922
545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	923	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
546	neccessary) and will handle those and any outstanding ones. It will block	924	necessary) and will handle those and any already outstanding ones. It
547	your process until at least one new event arrives, and will return after	925	will block your process until at least one new event arrives (which could
548	one iteration of the loop. This is useful if you are waiting for some	926	be an event internal to libev itself, so there is no guarantee that a
549	external event in conjunction with something not expressible using other	927	user-registered callback will be called), and will return after one
		928	iteration of the loop.
		929
		930	This is useful if you are waiting for some external event in conjunction
		931	with something not expressible using other libev watchers (i.e. "roll your
550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	932	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
551	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
552		934
553	Here are the gory details of what C<ev_loop> does:	935	Here are the gory details of what C<ev_run> does (this is for your
		936	understanding, not a guarantee that things will work exactly like this in
		937	future versions):
554		938
		939	- Increment loop depth.
		940	- Reset the ev_break status.
555	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
		942	LOOP:
556	* If EVFLAG_FORKCHECK was used, check for a fork.	943	- If EVFLAG_FORKCHECK was used, check for a fork.
557	- If a fork was detected, queue and call all fork watchers.	944	- If a fork was detected (by any means), queue and call all fork watchers.
558	- Queue and call all prepare watchers.	945	- Queue and call all prepare watchers.
		946	- If ev_break was called, goto FINISH.
559	- If we have been forked, recreate the kernel state.	947	- If we have been forked, detach and recreate the kernel state
		948	as to not disturb the other process.
560	- Update the kernel state with all outstanding changes.	949	- Update the kernel state with all outstanding changes.
561	- Update the "event loop time".	950	- Update the "event loop time" (ev_now ()).
562	- Calculate for how long to sleep or block, if at all	951	- Calculate for how long to sleep or block, if at all
563	(active idle watchers, EVLOOP_NONBLOCK or not having	952	(active idle watchers, EVRUN_NOWAIT or not having
564	any active watchers at all will result in not sleeping).	953	any active watchers at all will result in not sleeping).
565	- Sleep if the I/O and timer collect interval say so.	954	- Sleep if the I/O and timer collect interval say so.
		955	- Increment loop iteration counter.
566	- Block the process, waiting for any events.	956	- Block the process, waiting for any events.
567	- Queue all outstanding I/O (fd) events.	957	- Queue all outstanding I/O (fd) events.
568	- Update the "event loop time" and do time jump handling.	958	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
569	- Queue all outstanding timers.	959	- Queue all expired timers.
570	- Queue all outstanding periodics.	960	- Queue all expired periodics.
571	- If no events are pending now, queue all idle watchers.	961	- Queue all idle watchers with priority higher than that of pending events.
572	- Queue all check watchers.	962	- Queue all check watchers.
573	- Call all queued watchers in reverse order (i.e. check watchers first).	963	- Call all queued watchers in reverse order (i.e. check watchers first).
574	Signals and child watchers are implemented as I/O watchers, and will	964	Signals, async and child watchers are implemented as I/O watchers, and
575	be handled here by queueing them when their watcher gets executed.	965	will be handled here by queueing them when their watcher gets executed.
576	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	966	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
577	were used, or there are no active watchers, return, otherwise	967	were used, or there are no active watchers, goto FINISH, otherwise
578	continue with step *.	968	continue with step LOOP.
		969	FINISH:
		970	- Reset the ev_break status iff it was EVBREAK_ONE.
		971	- Decrement the loop depth.
		972	- Return.
579		973
580	Example: Queue some jobs and then loop until no events are outsanding	974	Example: Queue some jobs and then loop until no events are outstanding
581	anymore.	975	anymore.
582		976
583	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
584	... as they still have work to do (even an idle watcher will do..)	978	... as they still have work to do (even an idle watcher will do..)
585	ev_loop (my_loop, 0);	979	ev_run (my_loop, 0);
586	... jobs done. yeah!	980	... jobs done or somebody called break. yeah!
587		981
588	=item ev_unloop (loop, how)	982	=item ev_break (loop, how)
589		983
590	Can be used to make a call to C<ev_loop> return early (but only after it	984	Can be used to make a call to C<ev_run> return early (but only after it
591	has processed all outstanding events). The C<how> argument must be either	985	has processed all outstanding events). The C<how> argument must be either
592	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	986	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
593	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	987	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		988
		989	This "break state" will be cleared on the next call to C<ev_run>.
		990
		991	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		992	which case it will have no effect.
594		993
595	=item ev_ref (loop)	994	=item ev_ref (loop)
596		995
597	=item ev_unref (loop)	996	=item ev_unref (loop)
598		997
599	Ref/unref can be used to add or remove a reference count on the event	998	Ref/unref can be used to add or remove a reference count on the event
600	loop: Every watcher keeps one reference, and as long as the reference	999	loop: Every watcher keeps one reference, and as long as the reference
601	count is nonzero, C<ev_loop> will not return on its own. If you have	1000	count is nonzero, C<ev_run> will not return on its own.
602	a watcher you never unregister that should not keep C<ev_loop> from	1001
603	returning, ev_unref() after starting, and ev_ref() before stopping it. For	1002	This is useful when you have a watcher that you never intend to
		1003	unregister, but that nevertheless should not keep C<ev_run> from
		1004	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		1005	before stopping it.
		1006
604	example, libev itself uses this for its internal signal pipe: It is not	1007	As an example, libev itself uses this for its internal signal pipe: It
605	visible to the libev user and should not keep C<ev_loop> from exiting if	1008	is not visible to the libev user and should not keep C<ev_run> from
606	no event watchers registered by it are active. It is also an excellent	1009	exiting if no event watchers registered by it are active. It is also an
607	way to do this for generic recurring timers or from within third-party	1010	excellent way to do this for generic recurring timers or from within
608	libraries. Just remember to I<unref after start> and I<ref before stop>.	1011	third-party libraries. Just remember to I<unref after start> and I<ref
		1012	before stop> (but only if the watcher wasn't active before, or was active
		1013	before, respectively. Note also that libev might stop watchers itself
		1014	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		1015	in the callback).
609		1016
610	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	1017	Example: Create a signal watcher, but keep it from keeping C<ev_run>
611	running when nothing else is active.	1018	running when nothing else is active.
612		1019
613	struct ev_signal exitsig;	1020	ev_signal exitsig;
614	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
615	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
616	evf_unref (loop);	1023	ev_unref (loop);
617		1024
618	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
619		1026
620	ev_ref (loop);	1027	ev_ref (loop);
621	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
622		1029
623	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	1030	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
624		1031
625	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	1032	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
626		1033
627	These advanced functions influence the time that libev will spend waiting	1034	These advanced functions influence the time that libev will spend waiting
628	for events. Both are by default C<0>, meaning that libev will try to	1035	for events. Both time intervals are by default C<0>, meaning that libev
629	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	1036	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		1037	latency.
630		1038
631	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	1039	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
632	allows libev to delay invocation of I/O and timer/periodic callbacks to	1040	allows libev to delay invocation of I/O and timer/periodic callbacks
633	increase efficiency of loop iterations.	1041	to increase efficiency of loop iterations (or to increase power-saving
		1042	opportunities).
634		1043
635	The background is that sometimes your program runs just fast enough to	1044	The idea is that sometimes your program runs just fast enough to handle
636	handle one (or very few) event(s) per loop iteration. While this makes	1045	one (or very few) event(s) per loop iteration. While this makes the
637	the program responsive, it also wastes a lot of CPU time to poll for new	1046	program responsive, it also wastes a lot of CPU time to poll for new
638	events, especially with backends like C<select ()> which have a high	1047	events, especially with backends like C<select ()> which have a high
639	overhead for the actual polling but can deliver many events at once.	1048	overhead for the actual polling but can deliver many events at once.
640		1049
641	By setting a higher I<io collect interval> you allow libev to spend more	1050	By setting a higher I<io collect interval> you allow libev to spend more
642	time collecting I/O events, so you can handle more events per iteration,	1051	time collecting I/O events, so you can handle more events per iteration,
643	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1052	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
644	C<ev_timer>) will be not affected. Setting this to a non-null value will	1053	C<ev_timer>) will not be affected. Setting this to a non-null value will
645	introduce an additional C<ev_sleep ()> call into most loop iterations.	1054	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1055	sleep time ensures that libev will not poll for I/O events more often then
		1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
646		1058
647	Likewise, by setting a higher I<timeout collect interval> you allow libev	1059	Likewise, by setting a higher I<timeout collect interval> you allow libev
648	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
649	latency (the watcher callback will be called later). C<ev_io> watchers	1061	latency/jitter/inexactness (the watcher callback will be called
650	will not be affected. Setting this to a non-null value will not introduce	1062	later). C<ev_io> watchers will not be affected. Setting this to a non-null
651	any overhead in libev.	1063	value will not introduce any overhead in libev.
652		1064
653	Many (busy) programs can usually benefit by setting the io collect	1065	Many (busy) programs can usually benefit by setting the I/O collect
654	interval to a value near C<0.1> or so, which is often enough for	1066	interval to a value near C<0.1> or so, which is often enough for
655	interactive servers (of course not for games), likewise for timeouts. It	1067	interactive servers (of course not for games), likewise for timeouts. It
656	usually doesn't make much sense to set it to a lower value than C<0.01>,	1068	usually doesn't make much sense to set it to a lower value than C<0.01>,
657	as this approsaches the timing granularity of most systems.	1069	as this approaches the timing granularity of most systems. Note that if
		1070	you do transactions with the outside world and you can't increase the
		1071	parallelity, then this setting will limit your transaction rate (if you
		1072	need to poll once per transaction and the I/O collect interval is 0.01,
		1073	then you can't do more than 100 transactions per second).
		1074
		1075	Setting the I<timeout collect interval> can improve the opportunity for
		1076	saving power, as the program will "bundle" timer callback invocations that
		1077	are "near" in time together, by delaying some, thus reducing the number of
		1078	times the process sleeps and wakes up again. Another useful technique to
		1079	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		1080	they fire on, say, one-second boundaries only.
		1081
		1082	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1083	more often than 100 times per second:
		1084
		1085	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1086	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1087
		1088	=item ev_invoke_pending (loop)
		1089
		1090	This call will simply invoke all pending watchers while resetting their
		1091	pending state. Normally, C<ev_run> does this automatically when required,
		1092	but when overriding the invoke callback this call comes handy. This
		1093	function can be invoked from a watcher - this can be useful for example
		1094	when you want to do some lengthy calculation and want to pass further
		1095	event handling to another thread (you still have to make sure only one
		1096	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1097
		1098	=item int ev_pending_count (loop)
		1099
		1100	Returns the number of pending watchers - zero indicates that no watchers
		1101	are pending.
		1102
		1103	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1104
		1105	This overrides the invoke pending functionality of the loop: Instead of
		1106	invoking all pending watchers when there are any, C<ev_run> will call
		1107	this callback instead. This is useful, for example, when you want to
		1108	invoke the actual watchers inside another context (another thread etc.).
		1109
		1110	If you want to reset the callback, use C<ev_invoke_pending> as new
		1111	callback.
		1112
		1113	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1114
		1115	Sometimes you want to share the same loop between multiple threads. This
		1116	can be done relatively simply by putting mutex_lock/unlock calls around
		1117	each call to a libev function.
		1118
		1119	However, C<ev_run> can run an indefinite time, so it is not feasible
		1120	to wait for it to return. One way around this is to wake up the event
		1121	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1122	I<release> and I<acquire> callbacks on the loop.
		1123
		1124	When set, then C<release> will be called just before the thread is
		1125	suspended waiting for new events, and C<acquire> is called just
		1126	afterwards.
		1127
		1128	Ideally, C<release> will just call your mutex_unlock function, and
		1129	C<acquire> will just call the mutex_lock function again.
		1130
		1131	While event loop modifications are allowed between invocations of
		1132	C<release> and C<acquire> (that's their only purpose after all), no
		1133	modifications done will affect the event loop, i.e. adding watchers will
		1134	have no effect on the set of file descriptors being watched, or the time
		1135	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1136	to take note of any changes you made.
		1137
		1138	In theory, threads executing C<ev_run> will be async-cancel safe between
		1139	invocations of C<release> and C<acquire>.
		1140
		1141	See also the locking example in the C<THREADS> section later in this
		1142	document.
		1143
		1144	=item ev_set_userdata (loop, void *data)
		1145
		1146	=item void *ev_userdata (loop)
		1147
		1148	Set and retrieve a single C<void *> associated with a loop. When
		1149	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1150	C<0>.
		1151
		1152	These two functions can be used to associate arbitrary data with a loop,
		1153	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1154	C<acquire> callbacks described above, but of course can be (ab-)used for
		1155	any other purpose as well.
		1156
		1157	=item ev_verify (loop)
		1158
		1159	This function only does something when C<EV_VERIFY> support has been
		1160	compiled in, which is the default for non-minimal builds. It tries to go
		1161	through all internal structures and checks them for validity. If anything
		1162	is found to be inconsistent, it will print an error message to standard
		1163	error and call C<abort ()>.
		1164
		1165	This can be used to catch bugs inside libev itself: under normal
		1166	circumstances, this function will never abort as of course libev keeps its
		1167	data structures consistent.
658		1168
659	=back	1169	=back
660		1170
661		1171
662	=head1 ANATOMY OF A WATCHER	1172	=head1 ANATOMY OF A WATCHER
663		1173
		1174	In the following description, uppercase C<TYPE> in names stands for the
		1175	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1176	watchers and C<ev_io_start> for I/O watchers.
		1177
664	A watcher is a structure that you create and register to record your	1178	A watcher is an opaque structure that you allocate and register to record
665	interest in some event. For instance, if you want to wait for STDIN to	1179	your interest in some event. To make a concrete example, imagine you want
666	become readable, you would create an C<ev_io> watcher for that:	1180	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1181	for that:
667		1182
668	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
669	{	1184	{
670	ev_io_stop (w);	1185	ev_io_stop (w);
671	ev_unloop (loop, EVUNLOOP_ALL);	1186	ev_break (loop, EVBREAK_ALL);
672	}	1187	}
673		1188
674	struct ev_loop *loop = ev_default_loop (0);	1189	struct ev_loop *loop = ev_default_loop (0);
		1190
675	struct ev_io stdin_watcher;	1191	ev_io stdin_watcher;
		1192
676	ev_init (&stdin_watcher, my_cb);	1193	ev_init (&stdin_watcher, my_cb);
677	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1194	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
678	ev_io_start (loop, &stdin_watcher);	1195	ev_io_start (loop, &stdin_watcher);
		1196
679	ev_loop (loop, 0);	1197	ev_run (loop, 0);
680		1198
681	As you can see, you are responsible for allocating the memory for your	1199	As you can see, you are responsible for allocating the memory for your
682	watcher structures (and it is usually a bad idea to do this on the stack,	1200	watcher structures (and it is I<usually> a bad idea to do this on the
683	although this can sometimes be quite valid).	1201	stack).
684		1202
		1203	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1204	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1205
685	Each watcher structure must be initialised by a call to C<ev_init	1206	Each watcher structure must be initialised by a call to C<ev_init (watcher
686	(watcher *, callback)>, which expects a callback to be provided. This	1207	*, callback)>, which expects a callback to be provided. This callback is
687	callback gets invoked each time the event occurs (or, in the case of io	1208	invoked each time the event occurs (or, in the case of I/O watchers, each
688	watchers, each time the event loop detects that the file descriptor given	1209	time the event loop detects that the file descriptor given is readable
689	is readable and/or writable).	1210	and/or writable).
690		1211
691	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1212	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
692	with arguments specific to this watcher type. There is also a macro	1213	macro to configure it, with arguments specific to the watcher type. There
693	to combine initialisation and setting in one call: C<< ev_<type>_init	1214	is also a macro to combine initialisation and setting in one call: C<<
694	(watcher *, callback, ...) >>.	1215	ev_TYPE_init (watcher *, callback, ...) >>.
695		1216
696	To make the watcher actually watch out for events, you have to start it	1217	To make the watcher actually watch out for events, you have to start it
697	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1218	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
698	*) >>), and you can stop watching for events at any time by calling the	1219	*) >>), and you can stop watching for events at any time by calling the
699	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
700		1221
701	As long as your watcher is active (has been started but not stopped) you	1222	As long as your watcher is active (has been started but not stopped) you
702	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it except when explicitly documented
703	reinitialise it or call its C<set> macro.	1224	otherwise. Most specifically you must never reinitialise it or call its
		1225	C<ev_TYPE_set> macro.
704		1226
705	Each and every callback receives the event loop pointer as first, the	1227	Each and every callback receives the event loop pointer as first, the
706	registered watcher structure as second, and a bitset of received events as	1228	registered watcher structure as second, and a bitset of received events as
707	third argument.	1229	third argument.
708		1230
…		…
717	=item C<EV_WRITE>	1239	=item C<EV_WRITE>
718		1240
719	The file descriptor in the C<ev_io> watcher has become readable and/or	1241	The file descriptor in the C<ev_io> watcher has become readable and/or
720	writable.	1242	writable.
721		1243
722	=item C<EV_TIMEOUT>	1244	=item C<EV_TIMER>
723		1245
724	The C<ev_timer> watcher has timed out.	1246	The C<ev_timer> watcher has timed out.
725		1247
726	=item C<EV_PERIODIC>	1248	=item C<EV_PERIODIC>
727		1249
…		…
745		1267
746	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
747		1269
748	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
749		1271
750	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1272	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
751	to gather new events, and all C<ev_check> watchers are invoked just after	1273	gather new events, and all C<ev_check> watchers are queued (not invoked)
752	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1274	just after C<ev_run> has gathered them, but before it queues any callbacks
		1275	for any received events. That means C<ev_prepare> watchers are the last
		1276	watchers invoked before the event loop sleeps or polls for new events, and
		1277	C<ev_check> watchers will be invoked before any other watchers of the same
		1278	or lower priority within an event loop iteration.
		1279
753	received events. Callbacks of both watcher types can start and stop as	1280	Callbacks of both watcher types can start and stop as many watchers as
754	many watchers as they want, and all of them will be taken into account	1281	they want, and all of them will be taken into account (for example, a
755	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1282	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
756	C<ev_loop> from blocking).	1283	blocking).
757		1284
758	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
759		1286
760	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1287	The embedded event loop specified in the C<ev_embed> watcher needs attention.
761		1288
762	=item C<EV_FORK>	1289	=item C<EV_FORK>
763		1290
764	The event loop has been resumed in the child process after fork (see	1291	The event loop has been resumed in the child process after fork (see
765	C<ev_fork>).	1292	C<ev_fork>).
766		1293
		1294	=item C<EV_CLEANUP>
		1295
		1296	The event loop is about to be destroyed (see C<ev_cleanup>).
		1297
		1298	=item C<EV_ASYNC>
		1299
		1300	The given async watcher has been asynchronously notified (see C<ev_async>).
		1301
		1302	=item C<EV_CUSTOM>
		1303
		1304	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1305	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1306
767	=item C<EV_ERROR>	1307	=item C<EV_ERROR>
768		1308
769	An unspecified error has occured, the watcher has been stopped. This might	1309	An unspecified error has occurred, the watcher has been stopped. This might
770	happen because the watcher could not be properly started because libev	1310	happen because the watcher could not be properly started because libev
771	ran out of memory, a file descriptor was found to be closed or any other	1311	ran out of memory, a file descriptor was found to be closed or any other
		1312	problem. Libev considers these application bugs.
		1313
772	problem. You best act on it by reporting the problem and somehow coping	1314	You best act on it by reporting the problem and somehow coping with the
773	with the watcher being stopped.	1315	watcher being stopped. Note that well-written programs should not receive
		1316	an error ever, so when your watcher receives it, this usually indicates a
		1317	bug in your program.
774		1318
775	Libev will usually signal a few "dummy" events together with an error,	1319	Libev will usually signal a few "dummy" events together with an error, for
776	for example it might indicate that a fd is readable or writable, and if	1320	example it might indicate that a fd is readable or writable, and if your
777	your callbacks is well-written it can just attempt the operation and cope	1321	callbacks is well-written it can just attempt the operation and cope with
778	with the error from read() or write(). This will not work in multithreaded	1322	the error from read() or write(). This will not work in multi-threaded
779	programs, though, so beware.	1323	programs, though, as the fd could already be closed and reused for another
		1324	thing, so beware.
780		1325
781	=back	1326	=back
782		1327
783	=head2 GENERIC WATCHER FUNCTIONS	1328	=head2 GENERIC WATCHER FUNCTIONS
784
785	In the following description, C<TYPE> stands for the watcher type,
786	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
787		1329
788	=over 4	1330	=over 4
789		1331
790	=item C<ev_init> (ev_TYPE *watcher, callback)	1332	=item C<ev_init> (ev_TYPE *watcher, callback)
791		1333
…		…
797	which rolls both calls into one.	1339	which rolls both calls into one.
798		1340
799	You can reinitialise a watcher at any time as long as it has been stopped	1341	You can reinitialise a watcher at any time as long as it has been stopped
800	(or never started) and there are no pending events outstanding.	1342	(or never started) and there are no pending events outstanding.
801		1343
802	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1344	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
803	int revents)>.	1345	int revents)>.
804		1346
		1347	Example: Initialise an C<ev_io> watcher in two steps.
		1348
		1349	ev_io w;
		1350	ev_init (&w, my_cb);
		1351	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1352
805	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1353	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
806		1354
807	This macro initialises the type-specific parts of a watcher. You need to	1355	This macro initialises the type-specific parts of a watcher. You need to
808	call C<ev_init> at least once before you call this macro, but you can	1356	call C<ev_init> at least once before you call this macro, but you can
809	call C<ev_TYPE_set> any number of times. You must not, however, call this	1357	call C<ev_TYPE_set> any number of times. You must not, however, call this
810	macro on a watcher that is active (it can be pending, however, which is a	1358	macro on a watcher that is active (it can be pending, however, which is a
811	difference to the C<ev_init> macro).	1359	difference to the C<ev_init> macro).
812		1360
813	Although some watcher types do not have type-specific arguments	1361	Although some watcher types do not have type-specific arguments
814	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1362	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
815		1363
		1364	See C<ev_init>, above, for an example.
		1365
816	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1366	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
817		1367
818	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1368	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
819	calls into a single call. This is the most convinient method to initialise	1369	calls into a single call. This is the most convenient method to initialise
820	a watcher. The same limitations apply, of course.	1370	a watcher. The same limitations apply, of course.
821		1371
		1372	Example: Initialise and set an C<ev_io> watcher in one step.
		1373
		1374	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1375
822	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1376	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
823		1377
824	Starts (activates) the given watcher. Only active watchers will receive	1378	Starts (activates) the given watcher. Only active watchers will receive
825	events. If the watcher is already active nothing will happen.	1379	events. If the watcher is already active nothing will happen.
826		1380
		1381	Example: Start the C<ev_io> watcher that is being abused as example in this
		1382	whole section.
		1383
		1384	ev_io_start (EV_DEFAULT_UC, &w);
		1385
827	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1386	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
828		1387
829	Stops the given watcher again (if active) and clears the pending	1388	Stops the given watcher if active, and clears the pending status (whether
		1389	the watcher was active or not).
		1390
830	status. It is possible that stopped watchers are pending (for example,	1391	It is possible that stopped watchers are pending - for example,
831	non-repeating timers are being stopped when they become pending), but	1392	non-repeating timers are being stopped when they become pending - but
832	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1393	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
833	you want to free or reuse the memory used by the watcher it is therefore a	1394	pending. If you want to free or reuse the memory used by the watcher it is
834	good idea to always call its C<ev_TYPE_stop> function.	1395	therefore a good idea to always call its C<ev_TYPE_stop> function.
835		1396
836	=item bool ev_is_active (ev_TYPE *watcher)	1397	=item bool ev_is_active (ev_TYPE *watcher)
837		1398
838	Returns a true value iff the watcher is active (i.e. it has been started	1399	Returns a true value iff the watcher is active (i.e. it has been started
839	and not yet been stopped). As long as a watcher is active you must not modify	1400	and not yet been stopped). As long as a watcher is active you must not modify
840	it.	1401	it unless documented otherwise.
		1402
		1403	Obviously, it is safe to call this on an active watcher, or actually any
		1404	watcher that is initialised.
841		1405
842	=item bool ev_is_pending (ev_TYPE *watcher)	1406	=item bool ev_is_pending (ev_TYPE *watcher)
843		1407
844	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1408	Returns a true value iff the watcher is pending, (i.e. it has outstanding
845	events but its callback has not yet been invoked). As long as a watcher	1409	events but its callback has not yet been invoked). As long as a watcher
846	is pending (but not active) you must not call an init function on it (but	1410	is pending (but not active) you must not call an init function on it (but
847	C<ev_TYPE_set> is safe), you must not change its priority, and you must	1411	C<ev_TYPE_set> is safe), you must not change its priority, and you must
848	make sure the watcher is available to libev (e.g. you cannot C<free ()>	1412	make sure the watcher is available to libev (e.g. you cannot C<free ()>
849	it).	1413	it).
850		1414
		1415	It is safe to call this on any watcher in any state as long as it is
		1416	initialised.
		1417
851	=item callback ev_cb (ev_TYPE *watcher)	1418	=item callback ev_cb (ev_TYPE *watcher)
852		1419
853	Returns the callback currently set on the watcher.	1420	Returns the callback currently set on the watcher.
854		1421
855	=item ev_cb_set (ev_TYPE *watcher, callback)	1422	=item ev_set_cb (ev_TYPE *watcher, callback)
856		1423
857	Change the callback. You can change the callback at virtually any time	1424	Change the callback. You can change the callback at virtually any time
858	(modulo threads).	1425	(modulo threads).
859		1426
860	=item ev_set_priority (ev_TYPE *watcher, priority)	1427	=item ev_set_priority (ev_TYPE *watcher, int priority)
861		1428
862	=item int ev_priority (ev_TYPE *watcher)	1429	=item int ev_priority (ev_TYPE *watcher)
863		1430
864	Set and query the priority of the watcher. The priority is a small	1431	Set and query the priority of the watcher. The priority is a small
865	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1432	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
866	(default: C<-2>). Pending watchers with higher priority will be invoked	1433	(default: C<-2>). Pending watchers with higher priority will be invoked
867	before watchers with lower priority, but priority will not keep watchers	1434	before watchers with lower priority, but priority will not keep watchers
868	from being executed (except for C<ev_idle> watchers).	1435	from being executed (except for C<ev_idle> watchers).
869		1436
870	This means that priorities are I<only> used for ordering callback
871	invocation after new events have been received. This is useful, for
872	example, to reduce latency after idling, or more often, to bind two
873	watchers on the same event and make sure one is called first.
874
875	If you need to suppress invocation when higher priority events are pending	1437	If you need to suppress invocation when higher priority events are pending
876	you need to look at C<ev_idle> watchers, which provide this functionality.	1438	you need to look at C<ev_idle> watchers, which provide this functionality.
877		1439
878	You I<must not> change the priority of a watcher as long as it is active or	1440	You I<must not> change the priority of a watcher as long as it is active
879	pending.	1441	or pending. Reading the priority with C<ev_priority> is fine in any state.
		1442
		1443	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1444	fine, as long as you do not mind that the priority value you query might
		1445	or might not have been clamped to the valid range.
880		1446
881	The default priority used by watchers when no priority has been set is	1447	The default priority used by watchers when no priority has been set is
882	always C<0>, which is supposed to not be too high and not be too low :).	1448	always C<0>, which is supposed to not be too high and not be too low :).
883		1449
884	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1450	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
885	fine, as long as you do not mind that the priority value you query might	1451	priorities.
886	or might not have been adjusted to be within valid range.
887		1452
888	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1453	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
889		1454
890	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1455	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
891	C<loop> nor C<revents> need to be valid as long as the watcher callback	1456	C<loop> nor C<revents> need to be valid as long as the watcher callback
892	can deal with that fact.	1457	can deal with that fact, as both are simply passed through to the
		1458	callback.
893		1459
894	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1460	=item int ev_clear_pending (loop, ev_TYPE *watcher)
895		1461
896	If the watcher is pending, this function returns clears its pending status	1462	If the watcher is pending, this function clears its pending status and
897	and returns its C<revents> bitset (as if its callback was invoked). If the	1463	returns its C<revents> bitset (as if its callback was invoked). If the
898	watcher isn't pending it does nothing and returns C<0>.	1464	watcher isn't pending it does nothing and returns C<0>.
899		1465
		1466	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1467	callback to be invoked, which can be accomplished with this function.
		1468
		1469	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1470
		1471	Feeds the given event set into the event loop, as if the specified event
		1472	had happened for the specified watcher (which must be a pointer to an
		1473	initialised but not necessarily started event watcher, though it can be
		1474	active). Obviously you must not free the watcher as long as it has pending
		1475	events.
		1476
		1477	Stopping the watcher, letting libev invoke it, or calling
		1478	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1479	not started in the first place.
		1480
		1481	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1482	functions that do not need a watcher.
		1483
900	=back	1484	=back
901		1485
		1486	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1487	OWN COMPOSITE WATCHERS> idioms.
902		1488
903	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1489	=head2 WATCHER STATES
904		1490
905	Each watcher has, by default, a member C<void *data> that you can change	1491	There are various watcher states mentioned throughout this manual -
906	and read at any time, libev will completely ignore it. This can be used	1492	active, pending and so on. In this section these states and the rules to
907	to associate arbitrary data with your watcher. If you need more data and	1493	transition between them will be described in more detail - and while these
908	don't want to allocate memory and store a pointer to it in that data	1494	rules might look complicated, they usually do "the right thing".
909	member, you can also "subclass" the watcher type and provide your own
910	data:
911		1495
912	struct my_io	1496	=over 4
913	{
914	struct ev_io io;
915	int otherfd;
916	void *somedata;
917	struct whatever *mostinteresting;
918	}
919		1497
920	And since your callback will be called with a pointer to the watcher, you	1498	=item initialised
921	can cast it back to your own type:
922		1499
923	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1500	Before a watcher can be registered with the event loop it has to be
924	{	1501	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
925	struct my_io *w = (struct my_io *)w_;	1502	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
926	...
927	}
928		1503
929	More interesting and less C-conformant ways of casting your callback type	1504	In this state it is simply some block of memory that is suitable for
930	instead have been omitted.	1505	use in an event loop. It can be moved around, freed, reused etc. at
		1506	will - as long as you either keep the memory contents intact, or call
		1507	C<ev_TYPE_init> again.
931		1508
932	Another common scenario is having some data structure with multiple	1509	=item started/running/active
933	watchers:
934		1510
935	struct my_biggy	1511	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
936	{	1512	property of the event loop, and is actively waiting for events. While in
937	int some_data;	1513	this state it cannot be accessed (except in a few documented ways, such as
938	ev_timer t1;	1514	stoping it), moved, freed or anything else - the only legal thing is to
939	ev_timer t2;	1515	keep a pointer to it, and call libev functions on it that are documented
940	}	1516	to work on active watchers.
941		1517
942	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1518	As a rule of thumb, before accessing a member or calling any function on
943	you need to use C<offsetof>:	1519	a watcher, it should be stopped (or freshly initialised). If that is not
		1520	convenient, you can check the documentation for that function or member to
		1521	see if it is safe to use on an active watcher.
944		1522
945	#include <stddef.h>	1523	=item pending
946		1524
		1525	If a watcher is active and libev determines that an event it is interested
		1526	in has occurred (such as a timer expiring), it will become pending. It
		1527	will stay in this pending state until either it is explicitly stopped or
		1528	its callback is about to be invoked, so it is not normally pending inside
		1529	the watcher callback.
		1530
		1531	Generally, the watcher might or might not be active while it is pending
		1532	(for example, an expired non-repeating timer can be pending but no longer
		1533	active). If it is pending but not active, it can be freely accessed (e.g.
		1534	by calling C<ev_TYPE_set>), but it is still property of the event loop at
		1535	this time, so cannot be moved, freed or reused. And if it is active the
		1536	rules described in the previous item still apply.
		1537
		1538	Explicitly stopping a watcher will also clear the pending state
		1539	unconditionally, so it is safe to stop a watcher and then free it.
		1540
		1541	It is also possible to feed an event on a watcher that is not active (e.g.
		1542	via C<ev_feed_event>), in which case it becomes pending without being
		1543	active.
		1544
		1545	=item stopped
		1546
		1547	A watcher can be stopped implicitly by libev (in which case it might still
		1548	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1549	latter will clear any pending state the watcher might be in, regardless
		1550	of whether it was active or not, so stopping a watcher explicitly before
		1551	freeing it is often a good idea.
		1552
		1553	While stopped (and not pending) the watcher is essentially in the
		1554	initialised state, that is, it can be reused, moved, modified in any way
		1555	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1556	it again).
		1557
		1558	=back
		1559
		1560	=head2 WATCHER PRIORITY MODELS
		1561
		1562	Many event loops support I<watcher priorities>, which are usually small
		1563	integers that influence the ordering of event callback invocation
		1564	between watchers in some way, all else being equal.
		1565
		1566	In libev, watcher priorities can be set using C<ev_set_priority>. See its
		1567	description for the more technical details such as the actual priority
		1568	range.
		1569
		1570	There are two common ways how these these priorities are being interpreted
		1571	by event loops:
		1572
		1573	In the more common lock-out model, higher priorities "lock out" invocation
		1574	of lower priority watchers, which means as long as higher priority
		1575	watchers receive events, lower priority watchers are not being invoked.
		1576
		1577	The less common only-for-ordering model uses priorities solely to order
		1578	callback invocation within a single event loop iteration: Higher priority
		1579	watchers are invoked before lower priority ones, but they all get invoked
		1580	before polling for new events.
		1581
		1582	Libev uses the second (only-for-ordering) model for all its watchers
		1583	except for idle watchers (which use the lock-out model).
		1584
		1585	The rationale behind this is that implementing the lock-out model for
		1586	watchers is not well supported by most kernel interfaces, and most event
		1587	libraries will just poll for the same events again and again as long as
		1588	their callbacks have not been executed, which is very inefficient in the
		1589	common case of one high-priority watcher locking out a mass of lower
		1590	priority ones.
		1591
		1592	Static (ordering) priorities are most useful when you have two or more
		1593	watchers handling the same resource: a typical usage example is having an
		1594	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1595	timeouts. Under load, data might be received while the program handles
		1596	other jobs, but since timers normally get invoked first, the timeout
		1597	handler will be executed before checking for data. In that case, giving
		1598	the timer a lower priority than the I/O watcher ensures that I/O will be
		1599	handled first even under adverse conditions (which is usually, but not
		1600	always, what you want).
		1601
		1602	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1603	will only be executed when no same or higher priority watchers have
		1604	received events, they can be used to implement the "lock-out" model when
		1605	required.
		1606
		1607	For example, to emulate how many other event libraries handle priorities,
		1608	you can associate an C<ev_idle> watcher to each such watcher, and in
		1609	the normal watcher callback, you just start the idle watcher. The real
		1610	processing is done in the idle watcher callback. This causes libev to
		1611	continuously poll and process kernel event data for the watcher, but when
		1612	the lock-out case is known to be rare (which in turn is rare :), this is
		1613	workable.
		1614
		1615	Usually, however, the lock-out model implemented that way will perform
		1616	miserably under the type of load it was designed to handle. In that case,
		1617	it might be preferable to stop the real watcher before starting the
		1618	idle watcher, so the kernel will not have to process the event in case
		1619	the actual processing will be delayed for considerable time.
		1620
		1621	Here is an example of an I/O watcher that should run at a strictly lower
		1622	priority than the default, and which should only process data when no
		1623	other events are pending:
		1624
		1625	ev_idle idle; // actual processing watcher
		1626	ev_io io; // actual event watcher
		1627
947	static void	1628	static void
948	t1_cb (EV_P_ struct ev_timer *w, int revents)	1629	io_cb (EV_P_ ev_io *w, int revents)
949	{	1630	{
950	struct my_biggy big = (struct my_biggy *	1631	// stop the I/O watcher, we received the event, but
951	(((char *)w) - offsetof (struct my_biggy, t1));	1632	// are not yet ready to handle it.
		1633	ev_io_stop (EV_A_ w);
		1634
		1635	// start the idle watcher to handle the actual event.
		1636	// it will not be executed as long as other watchers
		1637	// with the default priority are receiving events.
		1638	ev_idle_start (EV_A_ &idle);
952	}	1639	}
953		1640
954	static void	1641	static void
955	t2_cb (EV_P_ struct ev_timer *w, int revents)	1642	idle_cb (EV_P_ ev_idle *w, int revents)
956	{	1643	{
957	struct my_biggy big = (struct my_biggy *	1644	// actual processing
958	(((char *)w) - offsetof (struct my_biggy, t2));	1645	read (STDIN_FILENO, ...);
		1646
		1647	// have to start the I/O watcher again, as
		1648	// we have handled the event
		1649	ev_io_start (EV_P_ &io);
959	}	1650	}
		1651
		1652	// initialisation
		1653	ev_idle_init (&idle, idle_cb);
		1654	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1655	ev_io_start (EV_DEFAULT_ &io);
		1656
		1657	In the "real" world, it might also be beneficial to start a timer, so that
		1658	low-priority connections can not be locked out forever under load. This
		1659	enables your program to keep a lower latency for important connections
		1660	during short periods of high load, while not completely locking out less
		1661	important ones.
960		1662
961		1663
962	=head1 WATCHER TYPES	1664	=head1 WATCHER TYPES
963		1665
964	This section describes each watcher in detail, but will not repeat	1666	This section describes each watcher in detail, but will not repeat
965	information given in the last section. Any initialisation/set macros,	1667	information given in the last section. Any initialisation/set macros,
966	functions and members specific to the watcher type are explained.	1668	functions and members specific to the watcher type are explained.
967		1669
968	Members are additionally marked with either I<[read-only]>, meaning that,	1670	Most members are additionally marked with either I<[read-only]>, meaning
969	while the watcher is active, you can look at the member and expect some	1671	that, while the watcher is active, you can look at the member and expect
970	sensible content, but you must not modify it (you can modify it while the	1672	some sensible content, but you must not modify it (you can modify it while
971	watcher is stopped to your hearts content), or I<[read-write]>, which	1673	the watcher is stopped to your hearts content), or I<[read-write]>, which
972	means you can expect it to have some sensible content while the watcher	1674	means you can expect it to have some sensible content while the watcher is
973	is active, but you can also modify it. Modifying it may not do something	1675	active, but you can also modify it (within the same thread as the event
		1676	loop, i.e. without creating data races). Modifying it may not do something
974	sensible or take immediate effect (or do anything at all), but libev will	1677	sensible or take immediate effect (or do anything at all), but libev will
975	not crash or malfunction in any way.	1678	not crash or malfunction in any way.
976		1679
		1680	In any case, the documentation for each member will explain what the
		1681	effects are, and if there are any additional access restrictions.
977		1682
978	=head2 C<ev_io> - is this file descriptor readable or writable?	1683	=head2 C<ev_io> - is this file descriptor readable or writable?
979		1684
980	I/O watchers check whether a file descriptor is readable or writable	1685	I/O watchers check whether a file descriptor is readable or writable
981	in each iteration of the event loop, or, more precisely, when reading	1686	in each iteration of the event loop, or, more precisely, when reading
…		…
988	In general you can register as many read and/or write event watchers per	1693	In general you can register as many read and/or write event watchers per
989	fd as you want (as long as you don't confuse yourself). Setting all file	1694	fd as you want (as long as you don't confuse yourself). Setting all file
990	descriptors to non-blocking mode is also usually a good idea (but not	1695	descriptors to non-blocking mode is also usually a good idea (but not
991	required if you know what you are doing).	1696	required if you know what you are doing).
992		1697
993	If you must do this, then force the use of a known-to-be-good backend
994	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
995	C<EVBACKEND_POLL>).
996
997	Another thing you have to watch out for is that it is quite easy to	1698	Another thing you have to watch out for is that it is quite easy to
998	receive "spurious" readyness notifications, that is your callback might	1699	receive "spurious" readiness notifications, that is, your callback might
999	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1700	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1000	because there is no data. Not only are some backends known to create a	1701	because there is no data. It is very easy to get into this situation even
1001	lot of those (for example solaris ports), it is very easy to get into	1702	with a relatively standard program structure. Thus it is best to always
1002	this situation even with a relatively standard program structure. Thus	1703	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1003	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1004	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1704	preferable to a program hanging until some data arrives.
1005		1705
1006	If you cannot run the fd in non-blocking mode (for example you should not	1706	If you cannot run the fd in non-blocking mode (for example you should
1007	play around with an Xlib connection), then you have to seperately re-test	1707	not play around with an Xlib connection), then you have to separately
1008	whether a file descriptor is really ready with a known-to-be good interface	1708	re-test whether a file descriptor is really ready with a known-to-be good
1009	such as poll (fortunately in our Xlib example, Xlib already does this on	1709	interface such as poll (fortunately in the case of Xlib, it already does
1010	its own, so its quite safe to use).	1710	this on its own, so its quite safe to use). Some people additionally
		1711	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1712	indefinitely.
		1713
		1714	But really, best use non-blocking mode.
1011		1715
1012	=head3 The special problem of disappearing file descriptors	1716	=head3 The special problem of disappearing file descriptors
1013		1717
1014	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1718	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1015	descriptor (either by calling C<close> explicitly or by any other means,	1719	a file descriptor (either due to calling C<close> explicitly or any other
1016	such as C<dup>). The reason is that you register interest in some file	1720	means, such as C<dup2>). The reason is that you register interest in some
1017	descriptor, but when it goes away, the operating system will silently drop	1721	file descriptor, but when it goes away, the operating system will silently
1018	this interest. If another file descriptor with the same number then is	1722	drop this interest. If another file descriptor with the same number then
1019	registered with libev, there is no efficient way to see that this is, in	1723	is registered with libev, there is no efficient way to see that this is,
1020	fact, a different file descriptor.	1724	in fact, a different file descriptor.
1021		1725
1022	To avoid having to explicitly tell libev about such cases, libev follows	1726	To avoid having to explicitly tell libev about such cases, libev follows
1023	the following policy: Each time C<ev_io_set> is being called, libev	1727	the following policy: Each time C<ev_io_set> is being called, libev
1024	will assume that this is potentially a new file descriptor, otherwise	1728	will assume that this is potentially a new file descriptor, otherwise
1025	it is assumed that the file descriptor stays the same. That means that	1729	it is assumed that the file descriptor stays the same. That means that
…		…
1039		1743
1040	There is no workaround possible except not registering events	1744	There is no workaround possible except not registering events
1041	for potentially C<dup ()>'ed file descriptors, or to resort to	1745	for potentially C<dup ()>'ed file descriptors, or to resort to
1042	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1746	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1043		1747
		1748	=head3 The special problem of files
		1749
		1750	Many people try to use C<select> (or libev) on file descriptors
		1751	representing files, and expect it to become ready when their program
		1752	doesn't block on disk accesses (which can take a long time on their own).
		1753
		1754	However, this cannot ever work in the "expected" way - you get a readiness
		1755	notification as soon as the kernel knows whether and how much data is
		1756	there, and in the case of open files, that's always the case, so you
		1757	always get a readiness notification instantly, and your read (or possibly
		1758	write) will still block on the disk I/O.
		1759
		1760	Another way to view it is that in the case of sockets, pipes, character
		1761	devices and so on, there is another party (the sender) that delivers data
		1762	on its own, but in the case of files, there is no such thing: the disk
		1763	will not send data on its own, simply because it doesn't know what you
		1764	wish to read - you would first have to request some data.
		1765
		1766	Since files are typically not-so-well supported by advanced notification
		1767	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1768	to files, even though you should not use it. The reason for this is
		1769	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1770	usually a tty, often a pipe, but also sometimes files or special devices
		1771	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1772	F</dev/urandom>), and even though the file might better be served with
		1773	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1774	it "just works" instead of freezing.
		1775
		1776	So avoid file descriptors pointing to files when you know it (e.g. use
		1777	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1778	when you rarely read from a file instead of from a socket, and want to
		1779	reuse the same code path.
		1780
1044	=head3 The special problem of fork	1781	=head3 The special problem of fork
1045		1782
1046	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1783	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1047	useless behaviour. Libev fully supports fork, but needs to be told about	1784	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1048	it in the child.	1785	to be told about it in the child if you want to continue to use it in the
		1786	child.
1049		1787
1050	To support fork in your programs, you either have to call	1788	To support fork in your child processes, you have to call C<ev_loop_fork
1051	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1789	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1052	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1790	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1053	C<EVBACKEND_POLL>.
1054		1791
		1792	=head3 The special problem of SIGPIPE
		1793
		1794	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1795	when writing to a pipe whose other end has been closed, your program gets
		1796	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1797	this is sensible behaviour, for daemons, this is usually undesirable.
		1798
		1799	So when you encounter spurious, unexplained daemon exits, make sure you
		1800	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1801	somewhere, as that would have given you a big clue).
		1802
		1803	=head3 The special problem of accept()ing when you can't
		1804
		1805	Many implementations of the POSIX C<accept> function (for example,
		1806	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1807	connection from the pending queue in all error cases.
		1808
		1809	For example, larger servers often run out of file descriptors (because
		1810	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1811	rejecting the connection, leading to libev signalling readiness on
		1812	the next iteration again (the connection still exists after all), and
		1813	typically causing the program to loop at 100% CPU usage.
		1814
		1815	Unfortunately, the set of errors that cause this issue differs between
		1816	operating systems, there is usually little the app can do to remedy the
		1817	situation, and no known thread-safe method of removing the connection to
		1818	cope with overload is known (to me).
		1819
		1820	One of the easiest ways to handle this situation is to just ignore it
		1821	- when the program encounters an overload, it will just loop until the
		1822	situation is over. While this is a form of busy waiting, no OS offers an
		1823	event-based way to handle this situation, so it's the best one can do.
		1824
		1825	A better way to handle the situation is to log any errors other than
		1826	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1827	messages, and continue as usual, which at least gives the user an idea of
		1828	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1829	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1830	usage.
		1831
		1832	If your program is single-threaded, then you could also keep a dummy file
		1833	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1834	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1835	close that fd, and create a new dummy fd. This will gracefully refuse
		1836	clients under typical overload conditions.
		1837
		1838	The last way to handle it is to simply log the error and C<exit>, as
		1839	is often done with C<malloc> failures, but this results in an easy
		1840	opportunity for a DoS attack.
1055		1841
1056	=head3 Watcher-Specific Functions	1842	=head3 Watcher-Specific Functions
1057		1843
1058	=over 4	1844	=over 4
1059		1845
1060	=item ev_io_init (ev_io *, callback, int fd, int events)	1846	=item ev_io_init (ev_io *, callback, int fd, int events)
1061		1847
1062	=item ev_io_set (ev_io *, int fd, int events)	1848	=item ev_io_set (ev_io *, int fd, int events)
1063		1849
1064	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1850	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1065	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1851	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE>, both
1066	C<EV_READ | EV_WRITE> to receive the given events.	1852	C<EV_READ | EV_WRITE> or C<0>, to express the desire to receive the given
		1853	events.
1067		1854
1068	=item int fd [read-only]	1855	Note that setting the C<events> to C<0> and starting the watcher is
		1856	supported, but not specially optimized - if your program sometimes happens
		1857	to generate this combination this is fine, but if it is easy to avoid
		1858	starting an io watcher watching for no events you should do so.
1069		1859
1070	The file descriptor being watched.	1860	=item ev_io_modify (ev_io *, int events)
1071		1861
		1862	Similar to C<ev_io_set>, but only changes the requested events. Using this
		1863	might be faster with some backends, as libev can assume that the C<fd>
		1864	still refers to the same underlying file description, something it cannot
		1865	do when using C<ev_io_set>.
		1866
		1867	=item int fd [no-modify]
		1868
		1869	The file descriptor being watched. While it can be read at any time, you
		1870	must not modify this member even when the watcher is stopped - always use
		1871	C<ev_io_set> for that.
		1872
1072	=item int events [read-only]	1873	=item int events [no-modify]
1073		1874
1074	The events being watched.	1875	The set of events the fd is being watched for, among other flags. Remember
		1876	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1877	EV_READ >>, and similarly for C<EV_WRITE>.
		1878
		1879	As with C<fd>, you must not modify this member even when the watcher is
		1880	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1075		1881
1076	=back	1882	=back
1077		1883
1078	=head3 Examples	1884	=head3 Examples
1079		1885
1080	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1886	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1081	readable, but only once. Since it is likely line-buffered, you could	1887	readable, but only once. Since it is likely line-buffered, you could
1082	attempt to read a whole line in the callback.	1888	attempt to read a whole line in the callback.
1083		1889
1084	static void	1890	static void
1085	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1891	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1086	{	1892	{
1087	ev_io_stop (loop, w);	1893	ev_io_stop (loop, w);
1088	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1894	.. read from stdin here (or from w->fd) and handle any I/O errors
1089	}	1895	}
1090		1896
1091	...	1897	...
1092	struct ev_loop *loop = ev_default_init (0);	1898	struct ev_loop *loop = ev_default_init (0);
1093	struct ev_io stdin_readable;	1899	ev_io stdin_readable;
1094	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1900	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1095	ev_io_start (loop, &stdin_readable);	1901	ev_io_start (loop, &stdin_readable);
1096	ev_loop (loop, 0);	1902	ev_run (loop, 0);
1097		1903
1098		1904
1099	=head2 C<ev_timer> - relative and optionally repeating timeouts	1905	=head2 C<ev_timer> - relative and optionally repeating timeouts
1100		1906
1101	Timer watchers are simple relative timers that generate an event after a	1907	Timer watchers are simple relative timers that generate an event after a
1102	given time, and optionally repeating in regular intervals after that.	1908	given time, and optionally repeating in regular intervals after that.
1103		1909
1104	The timers are based on real time, that is, if you register an event that	1910	The timers are based on real time, that is, if you register an event that
1105	times out after an hour and you reset your system clock to last years	1911	times out after an hour and you reset your system clock to January last
1106	time, it will still time out after (roughly) and hour. "Roughly" because	1912	year, it will still time out after (roughly) one hour. "Roughly" because
1107	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1913	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1108	monotonic clock option helps a lot here).	1914	monotonic clock option helps a lot here).
		1915
		1916	The callback is guaranteed to be invoked only I<after> its timeout has
		1917	passed (not I<at>, so on systems with very low-resolution clocks this
		1918	might introduce a small delay, see "the special problem of being too
		1919	early", below). If multiple timers become ready during the same loop
		1920	iteration then the ones with earlier time-out values are invoked before
		1921	ones of the same priority with later time-out values (but this is no
		1922	longer true when a callback calls C<ev_run> recursively).
		1923
		1924	=head3 Be smart about timeouts
		1925
		1926	Many real-world problems involve some kind of timeout, usually for error
		1927	recovery. A typical example is an HTTP request - if the other side hangs,
		1928	you want to raise some error after a while.
		1929
		1930	What follows are some ways to handle this problem, from obvious and
		1931	inefficient to smart and efficient.
		1932
		1933	In the following, a 60 second activity timeout is assumed - a timeout that
		1934	gets reset to 60 seconds each time there is activity (e.g. each time some
		1935	data or other life sign was received).
		1936
		1937	=over 4
		1938
		1939	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1940
		1941	This is the most obvious, but not the most simple way: In the beginning,
		1942	start the watcher:
		1943
		1944	ev_timer_init (timer, callback, 60., 0.);
		1945	ev_timer_start (loop, timer);
		1946
		1947	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1948	and start it again:
		1949
		1950	ev_timer_stop (loop, timer);
		1951	ev_timer_set (timer, 60., 0.);
		1952	ev_timer_start (loop, timer);
		1953
		1954	This is relatively simple to implement, but means that each time there is
		1955	some activity, libev will first have to remove the timer from its internal
		1956	data structure and then add it again. Libev tries to be fast, but it's
		1957	still not a constant-time operation.
		1958
		1959	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1960
		1961	This is the easiest way, and involves using C<ev_timer_again> instead of
		1962	C<ev_timer_start>.
		1963
		1964	To implement this, configure an C<ev_timer> with a C<repeat> value
		1965	of C<60> and then call C<ev_timer_again> at start and each time you
		1966	successfully read or write some data. If you go into an idle state where
		1967	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1968	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1969
		1970	That means you can ignore both the C<ev_timer_start> function and the
		1971	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1972	member and C<ev_timer_again>.
		1973
		1974	At start:
		1975
		1976	ev_init (timer, callback);
		1977	timer->repeat = 60.;
		1978	ev_timer_again (loop, timer);
		1979
		1980	Each time there is some activity:
		1981
		1982	ev_timer_again (loop, timer);
		1983
		1984	It is even possible to change the time-out on the fly, regardless of
		1985	whether the watcher is active or not:
		1986
		1987	timer->repeat = 30.;
		1988	ev_timer_again (loop, timer);
		1989
		1990	This is slightly more efficient then stopping/starting the timer each time
		1991	you want to modify its timeout value, as libev does not have to completely
		1992	remove and re-insert the timer from/into its internal data structure.
		1993
		1994	It is, however, even simpler than the "obvious" way to do it.
		1995
		1996	=item 3. Let the timer time out, but then re-arm it as required.
		1997
		1998	This method is more tricky, but usually most efficient: Most timeouts are
		1999	relatively long compared to the intervals between other activity - in
		2000	our example, within 60 seconds, there are usually many I/O events with
		2001	associated activity resets.
		2002
		2003	In this case, it would be more efficient to leave the C<ev_timer> alone,
		2004	but remember the time of last activity, and check for a real timeout only
		2005	within the callback:
		2006
		2007	ev_tstamp timeout = 60.;
		2008	ev_tstamp last_activity; // time of last activity
		2009	ev_timer timer;
		2010
		2011	static void
		2012	callback (EV_P_ ev_timer *w, int revents)
		2013	{
		2014	// calculate when the timeout would happen
		2015	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		2016
		2017	// if negative, it means we the timeout already occurred
		2018	if (after < 0.)
		2019	{
		2020	// timeout occurred, take action
		2021	}
		2022	else
		2023	{
		2024	// callback was invoked, but there was some recent
		2025	// activity. simply restart the timer to time out
		2026	// after "after" seconds, which is the earliest time
		2027	// the timeout can occur.
		2028	ev_timer_set (w, after, 0.);
		2029	ev_timer_start (EV_A_ w);
		2030	}
		2031	}
		2032
		2033	To summarise the callback: first calculate in how many seconds the
		2034	timeout will occur (by calculating the absolute time when it would occur,
		2035	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		2036	(EV_A)> from that).
		2037
		2038	If this value is negative, then we are already past the timeout, i.e. we
		2039	timed out, and need to do whatever is needed in this case.
		2040
		2041	Otherwise, we now the earliest time at which the timeout would trigger,
		2042	and simply start the timer with this timeout value.
		2043
		2044	In other words, each time the callback is invoked it will check whether
		2045	the timeout occurred. If not, it will simply reschedule itself to check
		2046	again at the earliest time it could time out. Rinse. Repeat.
		2047
		2048	This scheme causes more callback invocations (about one every 60 seconds
		2049	minus half the average time between activity), but virtually no calls to
		2050	libev to change the timeout.
		2051
		2052	To start the machinery, simply initialise the watcher and set
		2053	C<last_activity> to the current time (meaning there was some activity just
		2054	now), then call the callback, which will "do the right thing" and start
		2055	the timer:
		2056
		2057	last_activity = ev_now (EV_A);
		2058	ev_init (&timer, callback);
		2059	callback (EV_A_ &timer, 0);
		2060
		2061	When there is some activity, simply store the current time in
		2062	C<last_activity>, no libev calls at all:
		2063
		2064	if (activity detected)
		2065	last_activity = ev_now (EV_A);
		2066
		2067	When your timeout value changes, then the timeout can be changed by simply
		2068	providing a new value, stopping the timer and calling the callback, which
		2069	will again do the right thing (for example, time out immediately :).
		2070
		2071	timeout = new_value;
		2072	ev_timer_stop (EV_A_ &timer);
		2073	callback (EV_A_ &timer, 0);
		2074
		2075	This technique is slightly more complex, but in most cases where the
		2076	time-out is unlikely to be triggered, much more efficient.
		2077
		2078	=item 4. Wee, just use a double-linked list for your timeouts.
		2079
		2080	If there is not one request, but many thousands (millions...), all
		2081	employing some kind of timeout with the same timeout value, then one can
		2082	do even better:
		2083
		2084	When starting the timeout, calculate the timeout value and put the timeout
		2085	at the I<end> of the list.
		2086
		2087	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2088	the list is expected to fire (for example, using the technique #3).
		2089
		2090	When there is some activity, remove the timer from the list, recalculate
		2091	the timeout, append it to the end of the list again, and make sure to
		2092	update the C<ev_timer> if it was taken from the beginning of the list.
		2093
		2094	This way, one can manage an unlimited number of timeouts in O(1) time for
		2095	starting, stopping and updating the timers, at the expense of a major
		2096	complication, and having to use a constant timeout. The constant timeout
		2097	ensures that the list stays sorted.
		2098
		2099	=back
		2100
		2101	So which method the best?
		2102
		2103	Method #2 is a simple no-brain-required solution that is adequate in most
		2104	situations. Method #3 requires a bit more thinking, but handles many cases
		2105	better, and isn't very complicated either. In most case, choosing either
		2106	one is fine, with #3 being better in typical situations.
		2107
		2108	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2109	rather complicated, but extremely efficient, something that really pays
		2110	off after the first million or so of active timers, i.e. it's usually
		2111	overkill :)
		2112
		2113	=head3 The special problem of being too early
		2114
		2115	If you ask a timer to call your callback after three seconds, then
		2116	you expect it to be invoked after three seconds - but of course, this
		2117	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2118	guaranteed to any precision by libev - imagine somebody suspending the
		2119	process with a STOP signal for a few hours for example.
		2120
		2121	So, libev tries to invoke your callback as soon as possible I<after> the
		2122	delay has occurred, but cannot guarantee this.
		2123
		2124	A less obvious failure mode is calling your callback too early: many event
		2125	loops compare timestamps with a "elapsed delay >= requested delay", but
		2126	this can cause your callback to be invoked much earlier than you would
		2127	expect.
		2128
		2129	To see why, imagine a system with a clock that only offers full second
		2130	resolution (think windows if you can't come up with a broken enough OS
		2131	yourself). If you schedule a one-second timer at the time 500.9, then the
		2132	event loop will schedule your timeout to elapse at a system time of 500
		2133	(500.9 truncated to the resolution) + 1, or 501.
		2134
		2135	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2136	501" and invoke the callback 0.1s after it was started, even though a
		2137	one-second delay was requested - this is being "too early", despite best
		2138	intentions.
		2139
		2140	This is the reason why libev will never invoke the callback if the elapsed
		2141	delay equals the requested delay, but only when the elapsed delay is
		2142	larger than the requested delay. In the example above, libev would only invoke
		2143	the callback at system time 502, or 1.1s after the timer was started.
		2144
		2145	So, while libev cannot guarantee that your callback will be invoked
		2146	exactly when requested, it I<can> and I<does> guarantee that the requested
		2147	delay has actually elapsed, or in other words, it always errs on the "too
		2148	late" side of things.
		2149
		2150	=head3 The special problem of time updates
		2151
		2152	Establishing the current time is a costly operation (it usually takes
		2153	at least one system call): EV therefore updates its idea of the current
		2154	time only before and after C<ev_run> collects new events, which causes a
		2155	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2156	lots of events in one iteration.
1109		2157
1110	The relative timeouts are calculated relative to the C<ev_now ()>	2158	The relative timeouts are calculated relative to the C<ev_now ()>
1111	time. This is usually the right thing as this timestamp refers to the time	2159	time. This is usually the right thing as this timestamp refers to the time
1112	of the event triggering whatever timeout you are modifying/starting. If	2160	of the event triggering whatever timeout you are modifying/starting. If
1113	you suspect event processing to be delayed and you I<need> to base the timeout	2161	you suspect event processing to be delayed and you I<need> to base the
1114	on the current time, use something like this to adjust for this:	2162	timeout on the current time, use something like the following to adjust
		2163	for it:
1115		2164
1116	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2165	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1117		2166
1118	The callback is guarenteed to be invoked only when its timeout has passed,	2167	If the event loop is suspended for a long time, you can also force an
1119	but if multiple timers become ready during the same loop iteration then	2168	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1120	order of execution is undefined.	2169	()>, although that will push the event time of all outstanding events
		2170	further into the future.
		2171
		2172	=head3 The special problem of unsynchronised clocks
		2173
		2174	Modern systems have a variety of clocks - libev itself uses the normal
		2175	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2176	jumps).
		2177
		2178	Neither of these clocks is synchronised with each other or any other clock
		2179	on the system, so C<ev_time ()> might return a considerably different time
		2180	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2181	a call to C<gettimeofday> might return a second count that is one higher
		2182	than a directly following call to C<time>.
		2183
		2184	The moral of this is to only compare libev-related timestamps with
		2185	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2186	a second or so.
		2187
		2188	One more problem arises due to this lack of synchronisation: if libev uses
		2189	the system monotonic clock and you compare timestamps from C<ev_time>
		2190	or C<ev_now> from when you started your timer and when your callback is
		2191	invoked, you will find that sometimes the callback is a bit "early".
		2192
		2193	This is because C<ev_timer>s work in real time, not wall clock time, so
		2194	libev makes sure your callback is not invoked before the delay happened,
		2195	I<measured according to the real time>, not the system clock.
		2196
		2197	If your timeouts are based on a physical timescale (e.g. "time out this
		2198	connection after 100 seconds") then this shouldn't bother you as it is
		2199	exactly the right behaviour.
		2200
		2201	If you want to compare wall clock/system timestamps to your timers, then
		2202	you need to use C<ev_periodic>s, as these are based on the wall clock
		2203	time, where your comparisons will always generate correct results.
		2204
		2205	=head3 The special problems of suspended animation
		2206
		2207	When you leave the server world it is quite customary to hit machines that
		2208	can suspend/hibernate - what happens to the clocks during such a suspend?
		2209
		2210	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2211	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2212	to run until the system is suspended, but they will not advance while the
		2213	system is suspended. That means, on resume, it will be as if the program
		2214	was frozen for a few seconds, but the suspend time will not be counted
		2215	towards C<ev_timer> when a monotonic clock source is used. The real time
		2216	clock advanced as expected, but if it is used as sole clocksource, then a
		2217	long suspend would be detected as a time jump by libev, and timers would
		2218	be adjusted accordingly.
		2219
		2220	I would not be surprised to see different behaviour in different between
		2221	operating systems, OS versions or even different hardware.
		2222
		2223	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2224	time jump in the monotonic clocks and the realtime clock. If the program
		2225	is suspended for a very long time, and monotonic clock sources are in use,
		2226	then you can expect C<ev_timer>s to expire as the full suspension time
		2227	will be counted towards the timers. When no monotonic clock source is in
		2228	use, then libev will again assume a timejump and adjust accordingly.
		2229
		2230	It might be beneficial for this latter case to call C<ev_suspend>
		2231	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2232	deterministic behaviour in this case (you can do nothing against
		2233	C<SIGSTOP>).
1121		2234
1122	=head3 Watcher-Specific Functions and Data Members	2235	=head3 Watcher-Specific Functions and Data Members
1123		2236
1124	=over 4	2237	=over 4
1125		2238
1126	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2239	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1127		2240
1128	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2241	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1129		2242
1130	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2243	Configure the timer to trigger after C<after> seconds (fractional and
1131	C<0.>, then it will automatically be stopped. If it is positive, then the	2244	negative values are supported). If C<repeat> is C<0.>, then it will
		2245	automatically be stopped once the timeout is reached. If it is positive,
1132	timer will automatically be configured to trigger again C<repeat> seconds	2246	then the timer will automatically be configured to trigger again C<repeat>
1133	later, again, and again, until stopped manually.	2247	seconds later, again, and again, until stopped manually.
1134		2248
1135	The timer itself will do a best-effort at avoiding drift, that is, if you	2249	The timer itself will do a best-effort at avoiding drift, that is, if
1136	configure a timer to trigger every 10 seconds, then it will trigger at	2250	you configure a timer to trigger every 10 seconds, then it will normally
1137	exactly 10 second intervals. If, however, your program cannot keep up with	2251	trigger at exactly 10 second intervals. If, however, your program cannot
1138	the timer (because it takes longer than those 10 seconds to do stuff) the	2252	keep up with the timer (because it takes longer than those 10 seconds to
1139	timer will not fire more than once per event loop iteration.	2253	do stuff) the timer will not fire more than once per event loop iteration.
1140		2254
1141	=item ev_timer_again (loop)	2255	=item ev_timer_again (loop, ev_timer *)
1142		2256
1143	This will act as if the timer timed out and restart it again if it is	2257	This will act as if the timer timed out, and restarts it again if it is
1144	repeating. The exact semantics are:	2258	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2259	timeout to the C<repeat> value and calling C<ev_timer_start>.
1145		2260
		2261	The exact semantics are as in the following rules, all of which will be
		2262	applied to the watcher:
		2263
		2264	=over 4
		2265
1146	If the timer is pending, its pending status is cleared.	2266	=item If the timer is pending, the pending status is always cleared.
1147		2267
1148	If the timer is started but nonrepeating, stop it (as if it timed out).	2268	=item If the timer is started but non-repeating, stop it (as if it timed
		2269	out, without invoking it).
1149		2270
1150	If the timer is repeating, either start it if necessary (with the	2271	=item If the timer is repeating, make the C<repeat> value the new timeout
1151	C<repeat> value), or reset the running timer to the C<repeat> value.	2272	and start the timer, if necessary.
1152		2273
1153	This sounds a bit complicated, but here is a useful and typical	2274	=back
1154	example: Imagine you have a tcp connection and you want a so-called idle
1155	timeout, that is, you want to be called when there have been, say, 60
1156	seconds of inactivity on the socket. The easiest way to do this is to
1157	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1158	C<ev_timer_again> each time you successfully read or write some data. If
1159	you go into an idle state where you do not expect data to travel on the
1160	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1161	automatically restart it if need be.
1162		2275
1163	That means you can ignore the C<after> value and C<ev_timer_start>	2276	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1164	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2277	usage example.
1165		2278
1166	ev_timer_init (timer, callback, 0., 5.);	2279	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1167	ev_timer_again (loop, timer);
1168	...
1169	timer->again = 17.;
1170	ev_timer_again (loop, timer);
1171	...
1172	timer->again = 10.;
1173	ev_timer_again (loop, timer);
1174		2280
1175	This is more slightly efficient then stopping/starting the timer each time	2281	Returns the remaining time until a timer fires. If the timer is active,
1176	you want to modify its timeout value.	2282	then this time is relative to the current event loop time, otherwise it's
		2283	the timeout value currently configured.
		2284
		2285	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2286	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2287	will return C<4>. When the timer expires and is restarted, it will return
		2288	roughly C<7> (likely slightly less as callback invocation takes some time,
		2289	too), and so on.
1177		2290
1178	=item ev_tstamp repeat [read-write]	2291	=item ev_tstamp repeat [read-write]
1179		2292
1180	The current C<repeat> value. Will be used each time the watcher times out	2293	The current C<repeat> value. Will be used each time the watcher times out
1181	or C<ev_timer_again> is called and determines the next timeout (if any),	2294	or C<ev_timer_again> is called, and determines the next timeout (if any),
1182	which is also when any modifications are taken into account.	2295	which is also when any modifications are taken into account.
1183		2296
1184	=back	2297	=back
1185		2298
1186	=head3 Examples	2299	=head3 Examples
1187		2300
1188	Example: Create a timer that fires after 60 seconds.	2301	Example: Create a timer that fires after 60 seconds.
1189		2302
1190	static void	2303	static void
1191	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2304	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1192	{	2305	{
1193	.. one minute over, w is actually stopped right here	2306	.. one minute over, w is actually stopped right here
1194	}	2307	}
1195		2308
1196	struct ev_timer mytimer;	2309	ev_timer mytimer;
1197	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2310	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1198	ev_timer_start (loop, &mytimer);	2311	ev_timer_start (loop, &mytimer);
1199		2312
1200	Example: Create a timeout timer that times out after 10 seconds of	2313	Example: Create a timeout timer that times out after 10 seconds of
1201	inactivity.	2314	inactivity.
1202		2315
1203	static void	2316	static void
1204	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2317	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1205	{	2318	{
1206	.. ten seconds without any activity	2319	.. ten seconds without any activity
1207	}	2320	}
1208		2321
1209	struct ev_timer mytimer;	2322	ev_timer mytimer;
1210	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2323	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1211	ev_timer_again (&mytimer); /* start timer */	2324	ev_timer_again (&mytimer); /* start timer */
1212	ev_loop (loop, 0);	2325	ev_run (loop, 0);
1213		2326
1214	// and in some piece of code that gets executed on any "activity":	2327	// and in some piece of code that gets executed on any "activity":
1215	// reset the timeout to start ticking again at 10 seconds	2328	// reset the timeout to start ticking again at 10 seconds
1216	ev_timer_again (&mytimer);	2329	ev_timer_again (&mytimer);
1217		2330
1218		2331
1219	=head2 C<ev_periodic> - to cron or not to cron?	2332	=head2 C<ev_periodic> - to cron or not to cron?
1220		2333
1221	Periodic watchers are also timers of a kind, but they are very versatile	2334	Periodic watchers are also timers of a kind, but they are very versatile
1222	(and unfortunately a bit complex).	2335	(and unfortunately a bit complex).
1223		2336
1224	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2337	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1225	but on wallclock time (absolute time). You can tell a periodic watcher	2338	relative time, the physical time that passes) but on wall clock time
1226	to trigger "at" some specific point in time. For example, if you tell a	2339	(absolute time, the thing you can read on your calendar or clock). The
1227	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2340	difference is that wall clock time can run faster or slower than real
1228	+ 10.>) and then reset your system clock to the last year, then it will	2341	time, and time jumps are not uncommon (e.g. when you adjust your
1229	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2342	wrist-watch).
1230	roughly 10 seconds later).
1231		2343
1232	They can also be used to implement vastly more complex timers, such as	2344	You can tell a periodic watcher to trigger after some specific point
1233	triggering an event on each midnight, local time or other, complicated,	2345	in time: for example, if you tell a periodic watcher to trigger "in 10
1234	rules.	2346	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2347	not a delay) and then reset your system clock to January of the previous
		2348	year, then it will take a year or more to trigger the event (unlike an
		2349	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2350	it, as it uses a relative timeout).
1235		2351
		2352	C<ev_periodic> watchers can also be used to implement vastly more complex
		2353	timers, such as triggering an event on each "midnight, local time", or
		2354	other complicated rules. This cannot easily be done with C<ev_timer>
		2355	watchers, as those cannot react to time jumps.
		2356
1236	As with timers, the callback is guarenteed to be invoked only when the	2357	As with timers, the callback is guaranteed to be invoked only when the
1237	time (C<at>) has been passed, but if multiple periodic timers become ready	2358	point in time where it is supposed to trigger has passed. If multiple
1238	during the same loop iteration then order of execution is undefined.	2359	timers become ready during the same loop iteration then the ones with
		2360	earlier time-out values are invoked before ones with later time-out values
		2361	(but this is no longer true when a callback calls C<ev_run> recursively).
1239		2362
1240	=head3 Watcher-Specific Functions and Data Members	2363	=head3 Watcher-Specific Functions and Data Members
1241		2364
1242	=over 4	2365	=over 4
1243		2366
1244	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2367	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1245		2368
1246	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2369	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1247		2370
1248	Lots of arguments, lets sort it out... There are basically three modes of	2371	Lots of arguments, let's sort it out... There are basically three modes of
1249	operation, and we will explain them from simplest to complex:	2372	operation, and we will explain them from simplest to most complex:
1250		2373
1251	=over 4	2374	=over 4
1252		2375
1253	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2376	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1254		2377
1255	In this configuration the watcher triggers an event at the wallclock time	2378	In this configuration the watcher triggers an event after the wall clock
1256	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2379	time C<offset> has passed. It will not repeat and will not adjust when a
1257	that is, if it is to be run at January 1st 2011 then it will run when the	2380	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1258	system time reaches or surpasses this time.	2381	will be stopped and invoked when the system clock reaches or surpasses
		2382	this point in time.
1259		2383
1260	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2384	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1261		2385
1262	In this mode the watcher will always be scheduled to time out at the next	2386	In this mode the watcher will always be scheduled to time out at the next
1263	C<at + N * interval> time (for some integer N, which can also be negative)	2387	C<offset + N * interval> time (for some integer N, which can also be
1264	and then repeat, regardless of any time jumps.	2388	negative) and then repeat, regardless of any time jumps. The C<offset>
		2389	argument is merely an offset into the C<interval> periods.
1265		2390
1266	This can be used to create timers that do not drift with respect to system	2391	This can be used to create timers that do not drift with respect to the
1267	time:	2392	system clock, for example, here is an C<ev_periodic> that triggers each
		2393	hour, on the hour (with respect to UTC):
1268		2394
1269	ev_periodic_set (&periodic, 0., 3600., 0);	2395	ev_periodic_set (&periodic, 0., 3600., 0);
1270		2396
1271	This doesn't mean there will always be 3600 seconds in between triggers,	2397	This doesn't mean there will always be 3600 seconds in between triggers,
1272	but only that the the callback will be called when the system time shows a	2398	but only that the callback will be called when the system time shows a
1273	full hour (UTC), or more correctly, when the system time is evenly divisible	2399	full hour (UTC), or more correctly, when the system time is evenly divisible
1274	by 3600.	2400	by 3600.
1275		2401
1276	Another way to think about it (for the mathematically inclined) is that	2402	Another way to think about it (for the mathematically inclined) is that
1277	C<ev_periodic> will try to run the callback in this mode at the next possible	2403	C<ev_periodic> will try to run the callback in this mode at the next possible
1278	time where C<time = at (mod interval)>, regardless of any time jumps.	2404	time where C<time = offset (mod interval)>, regardless of any time jumps.
1279		2405
1280	For numerical stability it is preferable that the C<at> value is near	2406	The C<interval> I<MUST> be positive, and for numerical stability, the
1281	C<ev_now ()> (the current time), but there is no range requirement for	2407	interval value should be higher than C<1/8192> (which is around 100
1282	this value.	2408	microseconds) and C<offset> should be higher than C<0> and should have
		2409	at most a similar magnitude as the current time (say, within a factor of
		2410	ten). Typical values for offset are, in fact, C<0> or something between
		2411	C<0> and C<interval>, which is also the recommended range.
1283		2412
		2413	Note also that there is an upper limit to how often a timer can fire (CPU
		2414	speed for example), so if C<interval> is very small then timing stability
		2415	will of course deteriorate. Libev itself tries to be exact to be about one
		2416	millisecond (if the OS supports it and the machine is fast enough).
		2417
1284	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2418	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1285		2419
1286	In this mode the values for C<interval> and C<at> are both being	2420	In this mode the values for C<interval> and C<offset> are both being
1287	ignored. Instead, each time the periodic watcher gets scheduled, the	2421	ignored. Instead, each time the periodic watcher gets scheduled, the
1288	reschedule callback will be called with the watcher as first, and the	2422	reschedule callback will be called with the watcher as first, and the
1289	current time as second argument.	2423	current time as second argument.
1290		2424
1291	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2425	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1292	ever, or make any event loop modifications>. If you need to stop it,	2426	or make ANY other event loop modifications whatsoever, unless explicitly
1293	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2427	allowed by documentation here>.
1294	starting an C<ev_prepare> watcher, which is legal).
1295		2428
		2429	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2430	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2431	only event loop modification you are allowed to do).
		2432
1296	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2433	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1297	ev_tstamp now)>, e.g.:	2434	*w, ev_tstamp now)>, e.g.:
1298		2435
		2436	static ev_tstamp
1299	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2437	my_rescheduler (ev_periodic *w, ev_tstamp now)
1300	{	2438	{
1301	return now + 60.;	2439	return now + 60.;
1302	}	2440	}
1303		2441
1304	It must return the next time to trigger, based on the passed time value	2442	It must return the next time to trigger, based on the passed time value
1305	(that is, the lowest time value larger than to the second argument). It	2443	(that is, the lowest time value larger than to the second argument). It
1306	will usually be called just before the callback will be triggered, but	2444	will usually be called just before the callback will be triggered, but
1307	might be called at other times, too.	2445	might be called at other times, too.
1308		2446
1309	NOTE: I<< This callback must always return a time that is later than the	2447	NOTE: I<< This callback must always return a time that is higher than or
1310	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2448	equal to the passed C<now> value >>.
1311		2449
1312	This can be used to create very complex timers, such as a timer that	2450	This can be used to create very complex timers, such as a timer that
1313	triggers on each midnight, local time. To do this, you would calculate the	2451	triggers on "next midnight, local time". To do this, you would calculate
1314	next midnight after C<now> and return the timestamp value for this. How	2452	the next midnight after C<now> and return the timestamp value for
1315	you do this is, again, up to you (but it is not trivial, which is the main	2453	this. Here is a (completely untested, no error checking) example on how to
1316	reason I omitted it as an example).	2454	do this:
		2455
		2456	#include <time.h>
		2457
		2458	static ev_tstamp
		2459	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2460	{
		2461	time_t tnow = (time_t)now;
		2462	struct tm tm;
		2463	localtime_r (&tnow, &tm);
		2464
		2465	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2466	++tm.tm_mday; // midnight next day
		2467
		2468	return mktime (&tm);
		2469	}
		2470
		2471	Note: this code might run into trouble on days that have more then two
		2472	midnights (beginning and end).
1317		2473
1318	=back	2474	=back
1319		2475
1320	=item ev_periodic_again (loop, ev_periodic *)	2476	=item ev_periodic_again (loop, ev_periodic *)
1321		2477
1322	Simply stops and restarts the periodic watcher again. This is only useful	2478	Simply stops and restarts the periodic watcher again. This is only useful
1323	when you changed some parameters or the reschedule callback would return	2479	when you changed some parameters or the reschedule callback would return
1324	a different time than the last time it was called (e.g. in a crond like	2480	a different time than the last time it was called (e.g. in a crond like
1325	program when the crontabs have changed).	2481	program when the crontabs have changed).
1326		2482
		2483	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2484
		2485	When active, returns the absolute time that the watcher is supposed
		2486	to trigger next. This is not the same as the C<offset> argument to
		2487	C<ev_periodic_set>, but indeed works even in interval and manual
		2488	rescheduling modes.
		2489
1327	=item ev_tstamp offset [read-write]	2490	=item ev_tstamp offset [read-write]
1328		2491
1329	When repeating, this contains the offset value, otherwise this is the	2492	When repeating, this contains the offset value, otherwise this is the
1330	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2493	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2494	although libev might modify this value for better numerical stability).
1331		2495
1332	Can be modified any time, but changes only take effect when the periodic	2496	Can be modified any time, but changes only take effect when the periodic
1333	timer fires or C<ev_periodic_again> is being called.	2497	timer fires or C<ev_periodic_again> is being called.
1334		2498
1335	=item ev_tstamp interval [read-write]	2499	=item ev_tstamp interval [read-write]
1336		2500
1337	The current interval value. Can be modified any time, but changes only	2501	The current interval value. Can be modified any time, but changes only
1338	take effect when the periodic timer fires or C<ev_periodic_again> is being	2502	take effect when the periodic timer fires or C<ev_periodic_again> is being
1339	called.	2503	called.
1340		2504
1341	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2505	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1342		2506
1343	The current reschedule callback, or C<0>, if this functionality is	2507	The current reschedule callback, or C<0>, if this functionality is
1344	switched off. Can be changed any time, but changes only take effect when	2508	switched off. Can be changed any time, but changes only take effect when
1345	the periodic timer fires or C<ev_periodic_again> is being called.	2509	the periodic timer fires or C<ev_periodic_again> is being called.
1346		2510
1347	=item ev_tstamp at [read-only]
1348
1349	When active, contains the absolute time that the watcher is supposed to
1350	trigger next.
1351
1352	=back	2511	=back
1353		2512
1354	=head3 Examples	2513	=head3 Examples
1355		2514
1356	Example: Call a callback every hour, or, more precisely, whenever the	2515	Example: Call a callback every hour, or, more precisely, whenever the
1357	system clock is divisible by 3600. The callback invocation times have	2516	system time is divisible by 3600. The callback invocation times have
1358	potentially a lot of jittering, but good long-term stability.	2517	potentially a lot of jitter, but good long-term stability.
1359		2518
1360	static void	2519	static void
1361	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2520	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1362	{	2521	{
1363	... its now a full hour (UTC, or TAI or whatever your clock follows)	2522	... its now a full hour (UTC, or TAI or whatever your clock follows)
1364	}	2523	}
1365		2524
1366	struct ev_periodic hourly_tick;	2525	ev_periodic hourly_tick;
1367	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2526	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1368	ev_periodic_start (loop, &hourly_tick);	2527	ev_periodic_start (loop, &hourly_tick);
1369		2528
1370	Example: The same as above, but use a reschedule callback to do it:	2529	Example: The same as above, but use a reschedule callback to do it:
1371		2530
1372	#include <math.h>	2531	#include <math.h>
1373		2532
1374	static ev_tstamp	2533	static ev_tstamp
1375	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2534	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1376	{	2535	{
1377	return fmod (now, 3600.) + 3600.;	2536	return now + (3600. - fmod (now, 3600.));
1378	}	2537	}
1379		2538
1380	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2539	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1381		2540
1382	Example: Call a callback every hour, starting now:	2541	Example: Call a callback every hour, starting now:
1383		2542
1384	struct ev_periodic hourly_tick;	2543	ev_periodic hourly_tick;
1385	ev_periodic_init (&hourly_tick, clock_cb,	2544	ev_periodic_init (&hourly_tick, clock_cb,
1386	fmod (ev_now (loop), 3600.), 3600., 0);	2545	fmod (ev_now (loop), 3600.), 3600., 0);
1387	ev_periodic_start (loop, &hourly_tick);	2546	ev_periodic_start (loop, &hourly_tick);
1388		2547
1389		2548
1390	=head2 C<ev_signal> - signal me when a signal gets signalled!	2549	=head2 C<ev_signal> - signal me when a signal gets signalled!
1391		2550
1392	Signal watchers will trigger an event when the process receives a specific	2551	Signal watchers will trigger an event when the process receives a specific
1393	signal one or more times. Even though signals are very asynchronous, libev	2552	signal one or more times. Even though signals are very asynchronous, libev
1394	will try it's best to deliver signals synchronously, i.e. as part of the	2553	will try its best to deliver signals synchronously, i.e. as part of the
1395	normal event processing, like any other event.	2554	normal event processing, like any other event.
1396		2555
		2556	If you want signals to be delivered truly asynchronously, just use
		2557	C<sigaction> as you would do without libev and forget about sharing
		2558	the signal. You can even use C<ev_async> from a signal handler to
		2559	synchronously wake up an event loop.
		2560
1397	You can configure as many watchers as you like per signal. Only when the	2561	You can configure as many watchers as you like for the same signal, but
1398	first watcher gets started will libev actually register a signal watcher	2562	only within the same loop, i.e. you can watch for C<SIGINT> in your
1399	with the kernel (thus it coexists with your own signal handlers as long	2563	default loop and for C<SIGIO> in another loop, but you cannot watch for
1400	as you don't register any with libev). Similarly, when the last signal	2564	C<SIGINT> in both the default loop and another loop at the same time. At
1401	watcher for a signal is stopped libev will reset the signal handler to	2565	the moment, C<SIGCHLD> is permanently tied to the default loop.
1402	SIG_DFL (regardless of what it was set to before).	2566
		2567	Only after the first watcher for a signal is started will libev actually
		2568	register something with the kernel. It thus coexists with your own signal
		2569	handlers as long as you don't register any with libev for the same signal.
		2570
		2571	If possible and supported, libev will install its handlers with
		2572	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2573	not be unduly interrupted. If you have a problem with system calls getting
		2574	interrupted by signals you can block all signals in an C<ev_check> watcher
		2575	and unblock them in an C<ev_prepare> watcher.
		2576
		2577	=head3 The special problem of inheritance over fork/execve/pthread_create
		2578
		2579	Both the signal mask (C<sigprocmask>) and the signal disposition
		2580	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2581	stopping it again), that is, libev might or might not block the signal,
		2582	and might or might not set or restore the installed signal handler (but
		2583	see C<EVFLAG_NOSIGMASK>).
		2584
		2585	While this does not matter for the signal disposition (libev never
		2586	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2587	C<execve>), this matters for the signal mask: many programs do not expect
		2588	certain signals to be blocked.
		2589
		2590	This means that before calling C<exec> (from the child) you should reset
		2591	the signal mask to whatever "default" you expect (all clear is a good
		2592	choice usually).
		2593
		2594	The simplest way to ensure that the signal mask is reset in the child is
		2595	to install a fork handler with C<pthread_atfork> that resets it. That will
		2596	catch fork calls done by libraries (such as the libc) as well.
		2597
		2598	In current versions of libev, the signal will not be blocked indefinitely
		2599	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2600	the window of opportunity for problems, it will not go away, as libev
		2601	I<has> to modify the signal mask, at least temporarily.
		2602
		2603	So I can't stress this enough: I<If you do not reset your signal mask when
		2604	you expect it to be empty, you have a race condition in your code>. This
		2605	is not a libev-specific thing, this is true for most event libraries.
		2606
		2607	=head3 The special problem of threads signal handling
		2608
		2609	POSIX threads has problematic signal handling semantics, specifically,
		2610	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2611	threads in a process block signals, which is hard to achieve.
		2612
		2613	When you want to use sigwait (or mix libev signal handling with your own
		2614	for the same signals), you can tackle this problem by globally blocking
		2615	all signals before creating any threads (or creating them with a fully set
		2616	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2617	loops. Then designate one thread as "signal receiver thread" which handles
		2618	these signals. You can pass on any signals that libev might be interested
		2619	in by calling C<ev_feed_signal>.
1403		2620
1404	=head3 Watcher-Specific Functions and Data Members	2621	=head3 Watcher-Specific Functions and Data Members
1405		2622
1406	=over 4	2623	=over 4
1407		2624
…		…
1416		2633
1417	The signal the watcher watches out for.	2634	The signal the watcher watches out for.
1418		2635
1419	=back	2636	=back
1420		2637
		2638	=head3 Examples
		2639
		2640	Example: Try to exit cleanly on SIGINT.
		2641
		2642	static void
		2643	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2644	{
		2645	ev_break (loop, EVBREAK_ALL);
		2646	}
		2647
		2648	ev_signal signal_watcher;
		2649	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2650	ev_signal_start (loop, &signal_watcher);
		2651
1421		2652
1422	=head2 C<ev_child> - watch out for process status changes	2653	=head2 C<ev_child> - watch out for process status changes
1423		2654
1424	Child watchers trigger when your process receives a SIGCHLD in response to	2655	Child watchers trigger when your process receives a SIGCHLD in response to
1425	some child status changes (most typically when a child of yours dies).	2656	some child status changes (most typically when a child of yours dies or
		2657	exits). It is permissible to install a child watcher I<after> the child
		2658	has been forked (which implies it might have already exited), as long
		2659	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2660	forking and then immediately registering a watcher for the child is fine,
		2661	but forking and registering a watcher a few event loop iterations later or
		2662	in the next callback invocation is not.
		2663
		2664	Only the default event loop is capable of handling signals, and therefore
		2665	you can only register child watchers in the default event loop.
		2666
		2667	Due to some design glitches inside libev, child watchers will always be
		2668	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2669	libev)
		2670
		2671	=head3 Process Interaction
		2672
		2673	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2674	initialised. This is necessary to guarantee proper behaviour even if the
		2675	first child watcher is started after the child exits. The occurrence
		2676	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2677	synchronously as part of the event loop processing. Libev always reaps all
		2678	children, even ones not watched.
		2679
		2680	=head3 Overriding the Built-In Processing
		2681
		2682	Libev offers no special support for overriding the built-in child
		2683	processing, but if your application collides with libev's default child
		2684	handler, you can override it easily by installing your own handler for
		2685	C<SIGCHLD> after initialising the default loop, and making sure the
		2686	default loop never gets destroyed. You are encouraged, however, to use an
		2687	event-based approach to child reaping and thus use libev's support for
		2688	that, so other libev users can use C<ev_child> watchers freely.
		2689
		2690	=head3 Stopping the Child Watcher
		2691
		2692	Currently, the child watcher never gets stopped, even when the
		2693	child terminates, so normally one needs to stop the watcher in the
		2694	callback. Future versions of libev might stop the watcher automatically
		2695	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2696	problem).
1426		2697
1427	=head3 Watcher-Specific Functions and Data Members	2698	=head3 Watcher-Specific Functions and Data Members
1428		2699
1429	=over 4	2700	=over 4
1430		2701
1431	=item ev_child_init (ev_child *, callback, int pid)	2702	=item ev_child_init (ev_child *, callback, int pid, int trace)
1432		2703
1433	=item ev_child_set (ev_child *, int pid)	2704	=item ev_child_set (ev_child *, int pid, int trace)
1434		2705
1435	Configures the watcher to wait for status changes of process C<pid> (or	2706	Configures the watcher to wait for status changes of process C<pid> (or
1436	I<any> process if C<pid> is specified as C<0>). The callback can look	2707	I<any> process if C<pid> is specified as C<0>). The callback can look
1437	at the C<rstatus> member of the C<ev_child> watcher structure to see	2708	at the C<rstatus> member of the C<ev_child> watcher structure to see
1438	the status word (use the macros from C<sys/wait.h> and see your systems	2709	the status word (use the macros from C<sys/wait.h> and see your systems
1439	C<waitpid> documentation). The C<rpid> member contains the pid of the	2710	C<waitpid> documentation). The C<rpid> member contains the pid of the
1440	process causing the status change.	2711	process causing the status change. C<trace> must be either C<0> (only
		2712	activate the watcher when the process terminates) or C<1> (additionally
		2713	activate the watcher when the process is stopped or continued).
1441		2714
1442	=item int pid [read-only]	2715	=item int pid [read-only]
1443		2716
1444	The process id this watcher watches out for, or C<0>, meaning any process id.	2717	The process id this watcher watches out for, or C<0>, meaning any process id.
1445		2718
…		…
1454		2727
1455	=back	2728	=back
1456		2729
1457	=head3 Examples	2730	=head3 Examples
1458		2731
1459	Example: Try to exit cleanly on SIGINT and SIGTERM.	2732	Example: C<fork()> a new process and install a child handler to wait for
		2733	its completion.
1460		2734
		2735	ev_child cw;
		2736
1461	static void	2737	static void
1462	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2738	child_cb (EV_P_ ev_child *w, int revents)
1463	{	2739	{
1464	ev_unloop (loop, EVUNLOOP_ALL);	2740	ev_child_stop (EV_A_ w);
		2741	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1465	}	2742	}
1466		2743
1467	struct ev_signal signal_watcher;	2744	pid_t pid = fork ();
1468	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2745
1469	ev_signal_start (loop, &sigint_cb);	2746	if (pid < 0)
		2747	// error
		2748	else if (pid == 0)
		2749	{
		2750	// the forked child executes here
		2751	exit (1);
		2752	}
		2753	else
		2754	{
		2755	ev_child_init (&cw, child_cb, pid, 0);
		2756	ev_child_start (EV_DEFAULT_ &cw);
		2757	}
1470		2758
1471		2759
1472	=head2 C<ev_stat> - did the file attributes just change?	2760	=head2 C<ev_stat> - did the file attributes just change?
1473		2761
1474	This watches a filesystem path for attribute changes. That is, it calls	2762	This watches a file system path for attribute changes. That is, it calls
1475	C<stat> regularly (or when the OS says it changed) and sees if it changed	2763	C<stat> on that path in regular intervals (or when the OS says it changed)
1476	compared to the last time, invoking the callback if it did.	2764	and sees if it changed compared to the last time, invoking the callback
		2765	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2766	happen after the watcher has been started will be reported.
1477		2767
1478	The path does not need to exist: changing from "path exists" to "path does	2768	The path does not need to exist: changing from "path exists" to "path does
1479	not exist" is a status change like any other. The condition "path does	2769	not exist" is a status change like any other. The condition "path does not
1480	not exist" is signified by the C<st_nlink> field being zero (which is	2770	exist" (or more correctly "path cannot be stat'ed") is signified by the
1481	otherwise always forced to be at least one) and all the other fields of	2771	C<st_nlink> field being zero (which is otherwise always forced to be at
1482	the stat buffer having unspecified contents.	2772	least one) and all the other fields of the stat buffer having unspecified
		2773	contents.
1483		2774
1484	The path I<should> be absolute and I<must not> end in a slash. If it is	2775	The path I<must not> end in a slash or contain special components such as
		2776	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1485	relative and your working directory changes, the behaviour is undefined.	2777	your working directory changes, then the behaviour is undefined.
1486		2778
1487	Since there is no standard to do this, the portable implementation simply	2779	Since there is no portable change notification interface available, the
1488	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2780	portable implementation simply calls C<stat(2)> regularly on the path
1489	can specify a recommended polling interval for this case. If you specify	2781	to see if it changed somehow. You can specify a recommended polling
1490	a polling interval of C<0> (highly recommended!) then a I<suitable,	2782	interval for this case. If you specify a polling interval of C<0> (highly
1491	unspecified default> value will be used (which you can expect to be around	2783	recommended!) then a I<suitable, unspecified default> value will be used
1492	five seconds, although this might change dynamically). Libev will also	2784	(which you can expect to be around five seconds, although this might
1493	impose a minimum interval which is currently around C<0.1>, but thats	2785	change dynamically). Libev will also impose a minimum interval which is
1494	usually overkill.	2786	currently around C<0.1>, but that's usually overkill.
1495		2787
1496	This watcher type is not meant for massive numbers of stat watchers,	2788	This watcher type is not meant for massive numbers of stat watchers,
1497	as even with OS-supported change notifications, this can be	2789	as even with OS-supported change notifications, this can be
1498	resource-intensive.	2790	resource-intensive.
1499		2791
1500	At the time of this writing, only the Linux inotify interface is	2792	At the time of this writing, the only OS-specific interface implemented
1501	implemented (implementing kqueue support is left as an exercise for the	2793	is the Linux inotify interface (implementing kqueue support is left as an
1502	reader). Inotify will be used to give hints only and should not change the	2794	exercise for the reader. Note, however, that the author sees no way of
1503	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2795	implementing C<ev_stat> semantics with kqueue, except as a hint).
1504	to fall back to regular polling again even with inotify, but changes are
1505	usually detected immediately, and if the file exists there will be no
1506	polling.
1507		2796
1508	=head3 Inotify	2797	=head3 ABI Issues (Largefile Support)
1509		2798
		2799	Libev by default (unless the user overrides this) uses the default
		2800	compilation environment, which means that on systems with large file
		2801	support disabled by default, you get the 32 bit version of the stat
		2802	structure. When using the library from programs that change the ABI to
		2803	use 64 bit file offsets the programs will fail. In that case you have to
		2804	compile libev with the same flags to get binary compatibility. This is
		2805	obviously the case with any flags that change the ABI, but the problem is
		2806	most noticeably displayed with ev_stat and large file support.
		2807
		2808	The solution for this is to lobby your distribution maker to make large
		2809	file interfaces available by default (as e.g. FreeBSD does) and not
		2810	optional. Libev cannot simply switch on large file support because it has
		2811	to exchange stat structures with application programs compiled using the
		2812	default compilation environment.
		2813
		2814	=head3 Inotify and Kqueue
		2815
1510	When C<inotify (7)> support has been compiled into libev (generally only	2816	When C<inotify (7)> support has been compiled into libev and present at
1511	available on Linux) and present at runtime, it will be used to speed up	2817	runtime, it will be used to speed up change detection where possible. The
1512	change detection where possible. The inotify descriptor will be created lazily	2818	inotify descriptor will be created lazily when the first C<ev_stat>
1513	when the first C<ev_stat> watcher is being started.	2819	watcher is being started.
1514		2820
1515	Inotify presense does not change the semantics of C<ev_stat> watchers	2821	Inotify presence does not change the semantics of C<ev_stat> watchers
1516	except that changes might be detected earlier, and in some cases, to avoid	2822	except that changes might be detected earlier, and in some cases, to avoid
1517	making regular C<stat> calls. Even in the presense of inotify support	2823	making regular C<stat> calls. Even in the presence of inotify support
1518	there are many cases where libev has to resort to regular C<stat> polling.	2824	there are many cases where libev has to resort to regular C<stat> polling,
		2825	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2826	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2827	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2828	xfs are fully working) libev usually gets away without polling.
1519		2829
1520	(There is no support for kqueue, as apparently it cannot be used to	2830	There is no support for kqueue, as apparently it cannot be used to
1521	implement this functionality, due to the requirement of having a file	2831	implement this functionality, due to the requirement of having a file
1522	descriptor open on the object at all times).	2832	descriptor open on the object at all times, and detecting renames, unlinks
		2833	etc. is difficult.
		2834
		2835	=head3 C<stat ()> is a synchronous operation
		2836
		2837	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2838	the process. The exception are C<ev_stat> watchers - those call C<stat
		2839	()>, which is a synchronous operation.
		2840
		2841	For local paths, this usually doesn't matter: unless the system is very
		2842	busy or the intervals between stat's are large, a stat call will be fast,
		2843	as the path data is usually in memory already (except when starting the
		2844	watcher).
		2845
		2846	For networked file systems, calling C<stat ()> can block an indefinite
		2847	time due to network issues, and even under good conditions, a stat call
		2848	often takes multiple milliseconds.
		2849
		2850	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2851	paths, although this is fully supported by libev.
1523		2852
1524	=head3 The special problem of stat time resolution	2853	=head3 The special problem of stat time resolution
1525		2854
1526	The C<stat ()> syscall only supports full-second resolution portably, and	2855	The C<stat ()> system call only supports full-second resolution portably,
1527	even on systems where the resolution is higher, many filesystems still	2856	and even on systems where the resolution is higher, most file systems
1528	only support whole seconds.	2857	still only support whole seconds.
1529		2858
1530	That means that, if the time is the only thing that changes, you might	2859	That means that, if the time is the only thing that changes, you can
1531	miss updates: on the first update, C<ev_stat> detects a change and calls	2860	easily miss updates: on the first update, C<ev_stat> detects a change and
1532	your callback, which does something. When there is another update within	2861	calls your callback, which does something. When there is another update
1533	the same second, C<ev_stat> will be unable to detect it.	2862	within the same second, C<ev_stat> will be unable to detect unless the
		2863	stat data does change in other ways (e.g. file size).
1534		2864
1535	The solution to this is to delay acting on a change for a second (or till	2865	The solution to this is to delay acting on a change for slightly more
1536	the next second boundary), using a roughly one-second delay C<ev_timer>	2866	than a second (or till slightly after the next full second boundary), using
1537	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2867	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1538	is added to work around small timing inconsistencies of some operating	2868	ev_timer_again (loop, w)>).
1539	systems.	2869
		2870	The C<.02> offset is added to work around small timing inconsistencies
		2871	of some operating systems (where the second counter of the current time
		2872	might be be delayed. One such system is the Linux kernel, where a call to
		2873	C<gettimeofday> might return a timestamp with a full second later than
		2874	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2875	update file times then there will be a small window where the kernel uses
		2876	the previous second to update file times but libev might already execute
		2877	the timer callback).
1540		2878
1541	=head3 Watcher-Specific Functions and Data Members	2879	=head3 Watcher-Specific Functions and Data Members
1542		2880
1543	=over 4	2881	=over 4
1544		2882
…		…
1550	C<path>. The C<interval> is a hint on how quickly a change is expected to	2888	C<path>. The C<interval> is a hint on how quickly a change is expected to
1551	be detected and should normally be specified as C<0> to let libev choose	2889	be detected and should normally be specified as C<0> to let libev choose
1552	a suitable value. The memory pointed to by C<path> must point to the same	2890	a suitable value. The memory pointed to by C<path> must point to the same
1553	path for as long as the watcher is active.	2891	path for as long as the watcher is active.
1554		2892
1555	The callback will be receive C<EV_STAT> when a change was detected,	2893	The callback will receive an C<EV_STAT> event when a change was detected,
1556	relative to the attributes at the time the watcher was started (or the	2894	relative to the attributes at the time the watcher was started (or the
1557	last change was detected).	2895	last change was detected).
1558		2896
1559	=item ev_stat_stat (ev_stat *)	2897	=item ev_stat_stat (loop, ev_stat *)
1560		2898
1561	Updates the stat buffer immediately with new values. If you change the	2899	Updates the stat buffer immediately with new values. If you change the
1562	watched path in your callback, you could call this fucntion to avoid	2900	watched path in your callback, you could call this function to avoid
1563	detecting this change (while introducing a race condition). Can also be	2901	detecting this change (while introducing a race condition if you are not
1564	useful simply to find out the new values.	2902	the only one changing the path). Can also be useful simply to find out the
		2903	new values.
1565		2904
1566	=item ev_statdata attr [read-only]	2905	=item ev_statdata attr [read-only]
1567		2906
1568	The most-recently detected attributes of the file. Although the type is of	2907	The most-recently detected attributes of the file. Although the type is
1569	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2908	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1570	suitable for your system. If the C<st_nlink> member is C<0>, then there	2909	suitable for your system, but you can only rely on the POSIX-standardised
		2910	members to be present. If the C<st_nlink> member is C<0>, then there was
1571	was some error while C<stat>ing the file.	2911	some error while C<stat>ing the file.
1572		2912
1573	=item ev_statdata prev [read-only]	2913	=item ev_statdata prev [read-only]
1574		2914
1575	The previous attributes of the file. The callback gets invoked whenever	2915	The previous attributes of the file. The callback gets invoked whenever
1576	C<prev> != C<attr>.	2916	C<prev> != C<attr>, or, more precisely, one or more of these members
		2917	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2918	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1577		2919
1578	=item ev_tstamp interval [read-only]	2920	=item ev_tstamp interval [read-only]
1579		2921
1580	The specified interval.	2922	The specified interval.
1581		2923
1582	=item const char *path [read-only]	2924	=item const char *path [read-only]
1583		2925
1584	The filesystem path that is being watched.	2926	The file system path that is being watched.
1585		2927
1586	=back	2928	=back
1587		2929
1588	=head3 Examples	2930	=head3 Examples
1589		2931
1590	Example: Watch C</etc/passwd> for attribute changes.	2932	Example: Watch C</etc/passwd> for attribute changes.
1591		2933
1592	static void	2934	static void
1593	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2935	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1594	{	2936	{
1595	/* /etc/passwd changed in some way */	2937	/* /etc/passwd changed in some way */
1596	if (w->attr.st_nlink)	2938	if (w->attr.st_nlink)
1597	{	2939	{
1598	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2940	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1599	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2941	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1600	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2942	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1601	}	2943	}
1602	else	2944	else
1603	/* you shalt not abuse printf for puts */	2945	/* you shalt not abuse printf for puts */
1604	puts ("wow, /etc/passwd is not there, expect problems. "	2946	puts ("wow, /etc/passwd is not there, expect problems. "
1605	"if this is windows, they already arrived\n");	2947	"if this is windows, they already arrived\n");
1606	}	2948	}
1607		2949
1608	...	2950	...
1609	ev_stat passwd;	2951	ev_stat passwd;
1610		2952
1611	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2953	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1612	ev_stat_start (loop, &passwd);	2954	ev_stat_start (loop, &passwd);
1613		2955
1614	Example: Like above, but additionally use a one-second delay so we do not	2956	Example: Like above, but additionally use a one-second delay so we do not
1615	miss updates (however, frequent updates will delay processing, too, so	2957	miss updates (however, frequent updates will delay processing, too, so
1616	one might do the work both on C<ev_stat> callback invocation I<and> on	2958	one might do the work both on C<ev_stat> callback invocation I<and> on
1617	C<ev_timer> callback invocation).	2959	C<ev_timer> callback invocation).
1618		2960
1619	static ev_stat passwd;	2961	static ev_stat passwd;
1620	static ev_timer timer;	2962	static ev_timer timer;
1621		2963
1622	static void	2964	static void
1623	timer_cb (EV_P_ ev_timer *w, int revents)	2965	timer_cb (EV_P_ ev_timer *w, int revents)
1624	{	2966	{
1625	ev_timer_stop (EV_A_ w);	2967	ev_timer_stop (EV_A_ w);
1626		2968
1627	/* now it's one second after the most recent passwd change */	2969	/* now it's one second after the most recent passwd change */
1628	}	2970	}
1629		2971
1630	static void	2972	static void
1631	stat_cb (EV_P_ ev_stat *w, int revents)	2973	stat_cb (EV_P_ ev_stat *w, int revents)
1632	{	2974	{
1633	/* reset the one-second timer */	2975	/* reset the one-second timer */
1634	ev_timer_again (EV_A_ &timer);	2976	ev_timer_again (EV_A_ &timer);
1635	}	2977	}
1636		2978
1637	...	2979	...
1638	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2980	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1639	ev_stat_start (loop, &passwd);	2981	ev_stat_start (loop, &passwd);
1640	ev_timer_init (&timer, timer_cb, 0., 1.01);	2982	ev_timer_init (&timer, timer_cb, 0., 1.02);
1641		2983
1642		2984
1643	=head2 C<ev_idle> - when you've got nothing better to do...	2985	=head2 C<ev_idle> - when you've got nothing better to do...
1644		2986
1645	Idle watchers trigger events when no other events of the same or higher	2987	Idle watchers trigger events when no other events of the same or higher
1646	priority are pending (prepare, check and other idle watchers do not	2988	priority are pending (prepare, check and other idle watchers do not count
1647	count).	2989	as receiving "events").
1648		2990
1649	That is, as long as your process is busy handling sockets or timeouts	2991	That is, as long as your process is busy handling sockets or timeouts
1650	(or even signals, imagine) of the same or higher priority it will not be	2992	(or even signals, imagine) of the same or higher priority it will not be
1651	triggered. But when your process is idle (or only lower-priority watchers	2993	triggered. But when your process is idle (or only lower-priority watchers
1652	are pending), the idle watchers are being called once per event loop	2994	are pending), the idle watchers are being called once per event loop
…		…
1659	Apart from keeping your process non-blocking (which is a useful	3001	Apart from keeping your process non-blocking (which is a useful
1660	effect on its own sometimes), idle watchers are a good place to do	3002	effect on its own sometimes), idle watchers are a good place to do
1661	"pseudo-background processing", or delay processing stuff to after the	3003	"pseudo-background processing", or delay processing stuff to after the
1662	event loop has handled all outstanding events.	3004	event loop has handled all outstanding events.
1663		3005
		3006	=head3 Abusing an C<ev_idle> watcher for its side-effect
		3007
		3008	As long as there is at least one active idle watcher, libev will never
		3009	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		3010	For this to work, the idle watcher doesn't need to be invoked at all - the
		3011	lowest priority will do.
		3012
		3013	This mode of operation can be useful together with an C<ev_check> watcher,
		3014	to do something on each event loop iteration - for example to balance load
		3015	between different connections.
		3016
		3017	See L</Abusing an ev_check watcher for its side-effect> for a longer
		3018	example.
		3019
1664	=head3 Watcher-Specific Functions and Data Members	3020	=head3 Watcher-Specific Functions and Data Members
1665		3021
1666	=over 4	3022	=over 4
1667		3023
1668	=item ev_idle_init (ev_signal *, callback)	3024	=item ev_idle_init (ev_idle *, callback)
1669		3025
1670	Initialises and configures the idle watcher - it has no parameters of any	3026	Initialises and configures the idle watcher - it has no parameters of any
1671	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	3027	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1672	believe me.	3028	believe me.
1673		3029
…		…
1676	=head3 Examples	3032	=head3 Examples
1677		3033
1678	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	3034	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1679	callback, free it. Also, use no error checking, as usual.	3035	callback, free it. Also, use no error checking, as usual.
1680		3036
1681	static void	3037	static void
1682	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	3038	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1683	{	3039	{
		3040	// stop the watcher
		3041	ev_idle_stop (loop, w);
		3042
		3043	// now we can free it
1684	free (w);	3044	free (w);
		3045
1685	// now do something you wanted to do when the program has	3046	// now do something you wanted to do when the program has
1686	// no longer asnything immediate to do.	3047	// no longer anything immediate to do.
1687	}	3048	}
1688		3049
1689	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	3050	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1690	ev_idle_init (idle_watcher, idle_cb);	3051	ev_idle_init (idle_watcher, idle_cb);
1691	ev_idle_start (loop, idle_cb);	3052	ev_idle_start (loop, idle_watcher);
1692		3053
1693		3054
1694	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3055	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1695		3056
1696	Prepare and check watchers are usually (but not always) used in tandem:	3057	Prepare and check watchers are often (but not always) used in pairs:
1697	prepare watchers get invoked before the process blocks and check watchers	3058	prepare watchers get invoked before the process blocks and check watchers
1698	afterwards.	3059	afterwards.
1699		3060
1700	You I<must not> call C<ev_loop> or similar functions that enter	3061	You I<must not> call C<ev_run> (or similar functions that enter the
1701	the current event loop from either C<ev_prepare> or C<ev_check>	3062	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1702	watchers. Other loops than the current one are fine, however. The	3063	C<ev_check> watchers. Other loops than the current one are fine,
1703	rationale behind this is that you do not need to check for recursion in	3064	however. The rationale behind this is that you do not need to check
1704	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3065	for recursion in those watchers, i.e. the sequence will always be
1705	C<ev_check> so if you have one watcher of each kind they will always be	3066	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1706	called in pairs bracketing the blocking call.	3067	kind they will always be called in pairs bracketing the blocking call.
1707		3068
1708	Their main purpose is to integrate other event mechanisms into libev and	3069	Their main purpose is to integrate other event mechanisms into libev and
1709	their use is somewhat advanced. This could be used, for example, to track	3070	their use is somewhat advanced. They could be used, for example, to track
1710	variable changes, implement your own watchers, integrate net-snmp or a	3071	variable changes, implement your own watchers, integrate net-snmp or a
1711	coroutine library and lots more. They are also occasionally useful if	3072	coroutine library and lots more. They are also occasionally useful if
1712	you cache some data and want to flush it before blocking (for example,	3073	you cache some data and want to flush it before blocking (for example,
1713	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	3074	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1714	watcher).	3075	watcher).
1715		3076
1716	This is done by examining in each prepare call which file descriptors need	3077	This is done by examining in each prepare call which file descriptors
1717	to be watched by the other library, registering C<ev_io> watchers for	3078	need to be watched by the other library, registering C<ev_io> watchers
1718	them and starting an C<ev_timer> watcher for any timeouts (many libraries	3079	for them and starting an C<ev_timer> watcher for any timeouts (many
1719	provide just this functionality). Then, in the check watcher you check for	3080	libraries provide exactly this functionality). Then, in the check watcher,
1720	any events that occured (by checking the pending status of all watchers	3081	you check for any events that occurred (by checking the pending status
1721	and stopping them) and call back into the library. The I/O and timer	3082	of all watchers and stopping them) and call back into the library. The
1722	callbacks will never actually be called (but must be valid nevertheless,	3083	I/O and timer callbacks will never actually be called (but must be valid
1723	because you never know, you know?).	3084	nevertheless, because you never know, you know?).
1724		3085
1725	As another example, the Perl Coro module uses these hooks to integrate	3086	As another example, the Perl Coro module uses these hooks to integrate
1726	coroutines into libev programs, by yielding to other active coroutines	3087	coroutines into libev programs, by yielding to other active coroutines
1727	during each prepare and only letting the process block if no coroutines	3088	during each prepare and only letting the process block if no coroutines
1728	are ready to run (it's actually more complicated: it only runs coroutines	3089	are ready to run (it's actually more complicated: it only runs coroutines
1729	with priority higher than or equal to the event loop and one coroutine	3090	with priority higher than or equal to the event loop and one coroutine
1730	of lower priority, but only once, using idle watchers to keep the event	3091	of lower priority, but only once, using idle watchers to keep the event
1731	loop from blocking if lower-priority coroutines are active, thus mapping	3092	loop from blocking if lower-priority coroutines are active, thus mapping
1732	low-priority coroutines to idle/background tasks).	3093	low-priority coroutines to idle/background tasks).
1733		3094
1734	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3095	When used for this purpose, it is recommended to give C<ev_check> watchers
1735	priority, to ensure that they are being run before any other watchers	3096	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		3097	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3098	watchers).
		3099
1736	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	3100	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1737	too) should not activate ("feed") events into libev. While libev fully	3101	activate ("feed") events into libev. While libev fully supports this, they
1738	supports this, they will be called before other C<ev_check> watchers	3102	might get executed before other C<ev_check> watchers did their job. As
1739	did their job. As C<ev_check> watchers are often used to embed other	3103	C<ev_check> watchers are often used to embed other (non-libev) event
1740	(non-libev) event loops those other event loops might be in an unusable	3104	loops those other event loops might be in an unusable state until their
1741	state until their C<ev_check> watcher ran (always remind yourself to	3105	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1742	coexist peacefully with others).	3106	others).
		3107
		3108	=head3 Abusing an C<ev_check> watcher for its side-effect
		3109
		3110	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3111	useful because they are called once per event loop iteration. For
		3112	example, if you want to handle a large number of connections fairly, you
		3113	normally only do a bit of work for each active connection, and if there
		3114	is more work to do, you wait for the next event loop iteration, so other
		3115	connections have a chance of making progress.
		3116
		3117	Using an C<ev_check> watcher is almost enough: it will be called on the
		3118	next event loop iteration. However, that isn't as soon as possible -
		3119	without external events, your C<ev_check> watcher will not be invoked.
		3120
		3121	This is where C<ev_idle> watchers come in handy - all you need is a
		3122	single global idle watcher that is active as long as you have one active
		3123	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3124	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3125	invoked. Neither watcher alone can do that.
1743		3126
1744	=head3 Watcher-Specific Functions and Data Members	3127	=head3 Watcher-Specific Functions and Data Members
1745		3128
1746	=over 4	3129	=over 4
1747		3130
…		…
1749		3132
1750	=item ev_check_init (ev_check *, callback)	3133	=item ev_check_init (ev_check *, callback)
1751		3134
1752	Initialises and configures the prepare or check watcher - they have no	3135	Initialises and configures the prepare or check watcher - they have no
1753	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3136	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1754	macros, but using them is utterly, utterly and completely pointless.	3137	macros, but using them is utterly, utterly, utterly and completely
		3138	pointless.
1755		3139
1756	=back	3140	=back
1757		3141
1758	=head3 Examples	3142	=head3 Examples
1759		3143
1760	There are a number of principal ways to embed other event loops or modules	3144	There are a number of principal ways to embed other event loops or modules
1761	into libev. Here are some ideas on how to include libadns into libev	3145	into libev. Here are some ideas on how to include libadns into libev
1762	(there is a Perl module named C<EV::ADNS> that does this, which you could	3146	(there is a Perl module named C<EV::ADNS> that does this, which you could
1763	use for an actually working example. Another Perl module named C<EV::Glib>	3147	use as a working example. Another Perl module named C<EV::Glib> embeds a
1764	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	3148	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1765	into the Glib event loop).	3149	Glib event loop).
1766		3150
1767	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	3151	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1768	and in a check watcher, destroy them and call into libadns. What follows	3152	and in a check watcher, destroy them and call into libadns. What follows
1769	is pseudo-code only of course. This requires you to either use a low	3153	is pseudo-code only of course. This requires you to either use a low
1770	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3154	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1771	the callbacks for the IO/timeout watchers might not have been called yet.	3155	the callbacks for the IO/timeout watchers might not have been called yet.
1772		3156
1773	static ev_io iow [nfd];	3157	static ev_io iow [nfd];
1774	static ev_timer tw;	3158	static ev_timer tw;
1775		3159
1776	static void	3160	static void
1777	io_cb (ev_loop *loop, ev_io *w, int revents)	3161	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1778	{	3162	{
1779	}	3163	}
1780		3164
1781	// create io watchers for each fd and a timer before blocking	3165	// create io watchers for each fd and a timer before blocking
1782	static void	3166	static void
1783	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3167	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1784	{	3168	{
1785	int timeout = 3600000;	3169	int timeout = 3600000;
1786	struct pollfd fds [nfd];	3170	struct pollfd fds [nfd];
1787	// actual code will need to loop here and realloc etc.	3171	// actual code will need to loop here and realloc etc.
1788	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3172	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1789		3173
1790	/* the callback is illegal, but won't be called as we stop during check */	3174	/* the callback is illegal, but won't be called as we stop during check */
1791	ev_timer_init (&tw, 0, timeout * 1e-3);	3175	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1792	ev_timer_start (loop, &tw);	3176	ev_timer_start (loop, &tw);
1793		3177
1794	// create one ev_io per pollfd	3178	// create one ev_io per pollfd
1795	for (int i = 0; i < nfd; ++i)	3179	for (int i = 0; i < nfd; ++i)
1796	{	3180	{
1797	ev_io_init (iow + i, io_cb, fds [i].fd,	3181	ev_io_init (iow + i, io_cb, fds [i].fd,
1798	((fds [i].events & POLLIN ? EV_READ : 0)	3182	((fds [i].events & POLLIN ? EV_READ : 0)
1799	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3183	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1800		3184
1801	fds [i].revents = 0;	3185	fds [i].revents = 0;
1802	ev_io_start (loop, iow + i);	3186	ev_io_start (loop, iow + i);
1803	}	3187	}
1804	}	3188	}
1805		3189
1806	// stop all watchers after blocking	3190	// stop all watchers after blocking
1807	static void	3191	static void
1808	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3192	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1809	{	3193	{
1810	ev_timer_stop (loop, &tw);	3194	ev_timer_stop (loop, &tw);
1811		3195
1812	for (int i = 0; i < nfd; ++i)	3196	for (int i = 0; i < nfd; ++i)
1813	{	3197	{
1814	// set the relevant poll flags	3198	// set the relevant poll flags
1815	// could also call adns_processreadable etc. here	3199	// could also call adns_processreadable etc. here
1816	struct pollfd *fd = fds + i;	3200	struct pollfd *fd = fds + i;
1817	int revents = ev_clear_pending (iow + i);	3201	int revents = ev_clear_pending (iow + i);
1818	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3202	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1819	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3203	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1820		3204
1821	// now stop the watcher	3205	// now stop the watcher
1822	ev_io_stop (loop, iow + i);	3206	ev_io_stop (loop, iow + i);
1823	}	3207	}
1824		3208
1825	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3209	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1826	}	3210	}
1827		3211
1828	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3212	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1829	in the prepare watcher and would dispose of the check watcher.	3213	in the prepare watcher and would dispose of the check watcher.
1830		3214
1831	Method 3: If the module to be embedded supports explicit event	3215	Method 3: If the module to be embedded supports explicit event
1832	notification (adns does), you can also make use of the actual watcher	3216	notification (libadns does), you can also make use of the actual watcher
1833	callbacks, and only destroy/create the watchers in the prepare watcher.	3217	callbacks, and only destroy/create the watchers in the prepare watcher.
1834		3218
1835	static void	3219	static void
1836	timer_cb (EV_P_ ev_timer *w, int revents)	3220	timer_cb (EV_P_ ev_timer *w, int revents)
1837	{	3221	{
1838	adns_state ads = (adns_state)w->data;	3222	adns_state ads = (adns_state)w->data;
1839	update_now (EV_A);	3223	update_now (EV_A);
1840		3224
1841	adns_processtimeouts (ads, &tv_now);	3225	adns_processtimeouts (ads, &tv_now);
1842	}	3226	}
1843		3227
1844	static void	3228	static void
1845	io_cb (EV_P_ ev_io *w, int revents)	3229	io_cb (EV_P_ ev_io *w, int revents)
1846	{	3230	{
1847	adns_state ads = (adns_state)w->data;	3231	adns_state ads = (adns_state)w->data;
1848	update_now (EV_A);	3232	update_now (EV_A);
1849		3233
1850	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3234	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1851	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3235	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1852	}	3236	}
1853		3237
1854	// do not ever call adns_afterpoll	3238	// do not ever call adns_afterpoll
1855		3239
1856	Method 4: Do not use a prepare or check watcher because the module you	3240	Method 4: Do not use a prepare or check watcher because the module you
1857	want to embed is too inflexible to support it. Instead, youc na override	3241	want to embed is not flexible enough to support it. Instead, you can
1858	their poll function. The drawback with this solution is that the main	3242	override their poll function. The drawback with this solution is that the
1859	loop is now no longer controllable by EV. The C<Glib::EV> module does	3243	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1860	this.	3244	this approach, effectively embedding EV as a client into the horrible
		3245	libglib event loop.
1861		3246
1862	static gint	3247	static gint
1863	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3248	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1864	{	3249	{
1865	int got_events = 0;	3250	int got_events = 0;
1866		3251
1867	for (n = 0; n < nfds; ++n)	3252	for (n = 0; n < nfds; ++n)
1868	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3253	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1869		3254
1870	if (timeout >= 0)	3255	if (timeout >= 0)
1871	// create/start timer	3256	// create/start timer
1872		3257
1873	// poll	3258	// poll
1874	ev_loop (EV_A_ 0);	3259	ev_run (EV_A_ 0);
1875		3260
1876	// stop timer again	3261	// stop timer again
1877	if (timeout >= 0)	3262	if (timeout >= 0)
1878	ev_timer_stop (EV_A_ &to);	3263	ev_timer_stop (EV_A_ &to);
1879		3264
1880	// stop io watchers again - their callbacks should have set	3265	// stop io watchers again - their callbacks should have set
1881	for (n = 0; n < nfds; ++n)	3266	for (n = 0; n < nfds; ++n)
1882	ev_io_stop (EV_A_ iow [n]);	3267	ev_io_stop (EV_A_ iow [n]);
1883		3268
1884	return got_events;	3269	return got_events;
1885	}	3270	}
1886		3271
1887		3272
1888	=head2 C<ev_embed> - when one backend isn't enough...	3273	=head2 C<ev_embed> - when one backend isn't enough...
1889		3274
1890	This is a rather advanced watcher type that lets you embed one event loop	3275	This is a rather advanced watcher type that lets you embed one event loop
…		…
1896	prioritise I/O.	3281	prioritise I/O.
1897		3282
1898	As an example for a bug workaround, the kqueue backend might only support	3283	As an example for a bug workaround, the kqueue backend might only support
1899	sockets on some platform, so it is unusable as generic backend, but you	3284	sockets on some platform, so it is unusable as generic backend, but you
1900	still want to make use of it because you have many sockets and it scales	3285	still want to make use of it because you have many sockets and it scales
1901	so nicely. In this case, you would create a kqueue-based loop and embed it	3286	so nicely. In this case, you would create a kqueue-based loop and embed
1902	into your default loop (which might use e.g. poll). Overall operation will	3287	it into your default loop (which might use e.g. poll). Overall operation
1903	be a bit slower because first libev has to poll and then call kevent, but	3288	will be a bit slower because first libev has to call C<poll> and then
1904	at least you can use both at what they are best.	3289	C<kevent>, but at least you can use both mechanisms for what they are
		3290	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1905		3291
1906	As for prioritising I/O: rarely you have the case where some fds have	3292	As for prioritising I/O: under rare circumstances you have the case where
1907	to be watched and handled very quickly (with low latency), and even	3293	some fds have to be watched and handled very quickly (with low latency),
1908	priorities and idle watchers might have too much overhead. In this case	3294	and even priorities and idle watchers might have too much overhead. In
1909	you would put all the high priority stuff in one loop and all the rest in	3295	this case you would put all the high priority stuff in one loop and all
1910	a second one, and embed the second one in the first.	3296	the rest in a second one, and embed the second one in the first.
1911		3297
1912	As long as the watcher is active, the callback will be invoked every time	3298	As long as the watcher is active, the callback will be invoked every
1913	there might be events pending in the embedded loop. The callback must then	3299	time there might be events pending in the embedded loop. The callback
1914	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3300	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1915	their callbacks (you could also start an idle watcher to give the embedded	3301	sweep and invoke their callbacks (the callback doesn't need to invoke the
1916	loop strictly lower priority for example). You can also set the callback	3302	C<ev_embed_sweep> function directly, it could also start an idle watcher
1917	to C<0>, in which case the embed watcher will automatically execute the	3303	to give the embedded loop strictly lower priority for example).
1918	embedded loop sweep.
1919		3304
1920	As long as the watcher is started it will automatically handle events. The	3305	You can also set the callback to C<0>, in which case the embed watcher
1921	callback will be invoked whenever some events have been handled. You can	3306	will automatically execute the embedded loop sweep whenever necessary.
1922	set the callback to C<0> to avoid having to specify one if you are not
1923	interested in that.
1924		3307
1925	Also, there have not currently been made special provisions for forking:	3308	Fork detection will be handled transparently while the C<ev_embed> watcher
1926	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3309	is active, i.e., the embedded loop will automatically be forked when the
1927	but you will also have to stop and restart any C<ev_embed> watchers	3310	embedding loop forks. In other cases, the user is responsible for calling
1928	yourself.	3311	C<ev_loop_fork> on the embedded loop.
1929		3312
1930	Unfortunately, not all backends are embeddable, only the ones returned by	3313	Unfortunately, not all backends are embeddable: only the ones returned by
1931	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3314	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1932	portable one.	3315	portable one.
1933		3316
1934	So when you want to use this feature you will always have to be prepared	3317	So when you want to use this feature you will always have to be prepared
1935	that you cannot get an embeddable loop. The recommended way to get around	3318	that you cannot get an embeddable loop. The recommended way to get around
1936	this is to have a separate variables for your embeddable loop, try to	3319	this is to have a separate variables for your embeddable loop, try to
1937	create it, and if that fails, use the normal loop for everything.	3320	create it, and if that fails, use the normal loop for everything.
1938		3321
		3322	=head3 C<ev_embed> and fork
		3323
		3324	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3325	automatically be applied to the embedded loop as well, so no special
		3326	fork handling is required in that case. When the watcher is not running,
		3327	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3328	as applicable.
		3329
1939	=head3 Watcher-Specific Functions and Data Members	3330	=head3 Watcher-Specific Functions and Data Members
1940		3331
1941	=over 4	3332	=over 4
1942		3333
1943	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3334	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1944		3335
1945	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3336	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
1946		3337
1947	Configures the watcher to embed the given loop, which must be	3338	Configures the watcher to embed the given loop, which must be
1948	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3339	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1949	invoked automatically, otherwise it is the responsibility of the callback	3340	invoked automatically, otherwise it is the responsibility of the callback
1950	to invoke it (it will continue to be called until the sweep has been done,	3341	to invoke it (it will continue to be called until the sweep has been done,
1951	if you do not want thta, you need to temporarily stop the embed watcher).	3342	if you do not want that, you need to temporarily stop the embed watcher).
1952		3343
1953	=item ev_embed_sweep (loop, ev_embed *)	3344	=item ev_embed_sweep (loop, ev_embed *)
1954		3345
1955	Make a single, non-blocking sweep over the embedded loop. This works	3346	Make a single, non-blocking sweep over the embedded loop. This works
1956	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3347	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1957	apropriate way for embedded loops.	3348	appropriate way for embedded loops.
1958		3349
1959	=item struct ev_loop *other [read-only]	3350	=item struct ev_loop *other [read-only]
1960		3351
1961	The embedded event loop.	3352	The embedded event loop.
1962		3353
…		…
1964		3355
1965	=head3 Examples	3356	=head3 Examples
1966		3357
1967	Example: Try to get an embeddable event loop and embed it into the default	3358	Example: Try to get an embeddable event loop and embed it into the default
1968	event loop. If that is not possible, use the default loop. The default	3359	event loop. If that is not possible, use the default loop. The default
1969	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3360	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1970	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3361	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1971	used).	3362	used).
1972		3363
1973	struct ev_loop *loop_hi = ev_default_init (0);	3364	struct ev_loop *loop_hi = ev_default_init (0);
1974	struct ev_loop *loop_lo = 0;	3365	struct ev_loop *loop_lo = 0;
1975	struct ev_embed embed;	3366	ev_embed embed;
1976		3367
1977	// see if there is a chance of getting one that works	3368	// see if there is a chance of getting one that works
1978	// (remember that a flags value of 0 means autodetection)	3369	// (remember that a flags value of 0 means autodetection)
1979	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3370	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1980	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3371	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1981	: 0;	3372	: 0;
1982		3373
1983	// if we got one, then embed it, otherwise default to loop_hi	3374	// if we got one, then embed it, otherwise default to loop_hi
1984	if (loop_lo)	3375	if (loop_lo)
1985	{	3376	{
1986	ev_embed_init (&embed, 0, loop_lo);	3377	ev_embed_init (&embed, 0, loop_lo);
1987	ev_embed_start (loop_hi, &embed);	3378	ev_embed_start (loop_hi, &embed);
1988	}	3379	}
1989	else	3380	else
1990	loop_lo = loop_hi;	3381	loop_lo = loop_hi;
1991		3382
1992	Example: Check if kqueue is available but not recommended and create	3383	Example: Check if kqueue is available but not recommended and create
1993	a kqueue backend for use with sockets (which usually work with any	3384	a kqueue backend for use with sockets (which usually work with any
1994	kqueue implementation). Store the kqueue/socket-only event loop in	3385	kqueue implementation). Store the kqueue/socket-only event loop in
1995	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3386	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1996		3387
1997	struct ev_loop *loop = ev_default_init (0);	3388	struct ev_loop *loop = ev_default_init (0);
1998	struct ev_loop *loop_socket = 0;	3389	struct ev_loop *loop_socket = 0;
1999	struct ev_embed embed;	3390	ev_embed embed;
2000		3391
2001	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3392	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2002	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3393	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2003	{	3394	{
2004	ev_embed_init (&embed, 0, loop_socket);	3395	ev_embed_init (&embed, 0, loop_socket);
2005	ev_embed_start (loop, &embed);	3396	ev_embed_start (loop, &embed);
2006	}	3397	}
2007		3398
2008	if (!loop_socket)	3399	if (!loop_socket)
2009	loop_socket = loop;	3400	loop_socket = loop;
2010		3401
2011	// now use loop_socket for all sockets, and loop for everything else	3402	// now use loop_socket for all sockets, and loop for everything else
2012		3403
2013		3404
2014	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3405	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2015		3406
2016	Fork watchers are called when a C<fork ()> was detected (usually because	3407	Fork watchers are called when a C<fork ()> was detected (usually because
2017	whoever is a good citizen cared to tell libev about it by calling	3408	whoever is a good citizen cared to tell libev about it by calling
2018	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3409	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2019	event loop blocks next and before C<ev_check> watchers are being called,	3410	and before C<ev_check> watchers are being called, and only in the child
2020	and only in the child after the fork. If whoever good citizen calling	3411	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2021	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3412	and calls it in the wrong process, the fork handlers will be invoked, too,
2022	handlers will be invoked, too, of course.	3413	of course.
		3414
		3415	=head3 The special problem of life after fork - how is it possible?
		3416
		3417	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3418	up/change the process environment, followed by a call to C<exec()>. This
		3419	sequence should be handled by libev without any problems.
		3420
		3421	This changes when the application actually wants to do event handling
		3422	in the child, or both parent in child, in effect "continuing" after the
		3423	fork.
		3424
		3425	The default mode of operation (for libev, with application help to detect
		3426	forks) is to duplicate all the state in the child, as would be expected
		3427	when I<either> the parent I<or> the child process continues.
		3428
		3429	When both processes want to continue using libev, then this is usually the
		3430	wrong result. In that case, usually one process (typically the parent) is
		3431	supposed to continue with all watchers in place as before, while the other
		3432	process typically wants to start fresh, i.e. without any active watchers.
		3433
		3434	The cleanest and most efficient way to achieve that with libev is to
		3435	simply create a new event loop, which of course will be "empty", and
		3436	use that for new watchers. This has the advantage of not touching more
		3437	memory than necessary, and thus avoiding the copy-on-write, and the
		3438	disadvantage of having to use multiple event loops (which do not support
		3439	signal watchers).
		3440
		3441	When this is not possible, or you want to use the default loop for
		3442	other reasons, then in the process that wants to start "fresh", call
		3443	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3444	Destroying the default loop will "orphan" (not stop) all registered
		3445	watchers, so you have to be careful not to execute code that modifies
		3446	those watchers. Note also that in that case, you have to re-register any
		3447	signal watchers.
2023		3448
2024	=head3 Watcher-Specific Functions and Data Members	3449	=head3 Watcher-Specific Functions and Data Members
2025		3450
2026	=over 4	3451	=over 4
2027		3452
2028	=item ev_fork_init (ev_signal *, callback)	3453	=item ev_fork_init (ev_fork *, callback)
2029		3454
2030	Initialises and configures the fork watcher - it has no parameters of any	3455	Initialises and configures the fork watcher - it has no parameters of any
2031	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3456	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2032	believe me.	3457	really.
2033		3458
2034	=back	3459	=back
2035		3460
2036		3461
		3462	=head2 C<ev_cleanup> - even the best things end
		3463
		3464	Cleanup watchers are called just before the event loop is being destroyed
		3465	by a call to C<ev_loop_destroy>.
		3466
		3467	While there is no guarantee that the event loop gets destroyed, cleanup
		3468	watchers provide a convenient method to install cleanup hooks for your
		3469	program, worker threads and so on - you just to make sure to destroy the
		3470	loop when you want them to be invoked.
		3471
		3472	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3473	all other watchers, they do not keep a reference to the event loop (which
		3474	makes a lot of sense if you think about it). Like all other watchers, you
		3475	can call libev functions in the callback, except C<ev_cleanup_start>.
		3476
		3477	=head3 Watcher-Specific Functions and Data Members
		3478
		3479	=over 4
		3480
		3481	=item ev_cleanup_init (ev_cleanup *, callback)
		3482
		3483	Initialises and configures the cleanup watcher - it has no parameters of
		3484	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3485	pointless, I assure you.
		3486
		3487	=back
		3488
		3489	Example: Register an atexit handler to destroy the default loop, so any
		3490	cleanup functions are called.
		3491
		3492	static void
		3493	program_exits (void)
		3494	{
		3495	ev_loop_destroy (EV_DEFAULT_UC);
		3496	}
		3497
		3498	...
		3499	atexit (program_exits);
		3500
		3501
		3502	=head2 C<ev_async> - how to wake up an event loop
		3503
		3504	In general, you cannot use an C<ev_loop> from multiple threads or other
		3505	asynchronous sources such as signal handlers (as opposed to multiple event
		3506	loops - those are of course safe to use in different threads).
		3507
		3508	Sometimes, however, you need to wake up an event loop you do not control,
		3509	for example because it belongs to another thread. This is what C<ev_async>
		3510	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3511	it by calling C<ev_async_send>, which is thread- and signal safe.
		3512
		3513	This functionality is very similar to C<ev_signal> watchers, as signals,
		3514	too, are asynchronous in nature, and signals, too, will be compressed
		3515	(i.e. the number of callback invocations may be less than the number of
		3516	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3517	of "global async watchers" by using a watcher on an otherwise unused
		3518	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3519	even without knowing which loop owns the signal.
		3520
		3521	=head3 Queueing
		3522
		3523	C<ev_async> does not support queueing of data in any way. The reason
		3524	is that the author does not know of a simple (or any) algorithm for a
		3525	multiple-writer-single-reader queue that works in all cases and doesn't
		3526	need elaborate support such as pthreads or unportable memory access
		3527	semantics.
		3528
		3529	That means that if you want to queue data, you have to provide your own
		3530	queue. But at least I can tell you how to implement locking around your
		3531	queue:
		3532
		3533	=over 4
		3534
		3535	=item queueing from a signal handler context
		3536
		3537	To implement race-free queueing, you simply add to the queue in the signal
		3538	handler but you block the signal handler in the watcher callback. Here is
		3539	an example that does that for some fictitious SIGUSR1 handler:
		3540
		3541	static ev_async mysig;
		3542
		3543	static void
		3544	sigusr1_handler (void)
		3545	{
		3546	sometype data;
		3547
		3548	// no locking etc.
		3549	queue_put (data);
		3550	ev_async_send (EV_DEFAULT_ &mysig);
		3551	}
		3552
		3553	static void
		3554	mysig_cb (EV_P_ ev_async *w, int revents)
		3555	{
		3556	sometype data;
		3557	sigset_t block, prev;
		3558
		3559	sigemptyset (&block);
		3560	sigaddset (&block, SIGUSR1);
		3561	sigprocmask (SIG_BLOCK, &block, &prev);
		3562
		3563	while (queue_get (&data))
		3564	process (data);
		3565
		3566	if (sigismember (&prev, SIGUSR1)
		3567	sigprocmask (SIG_UNBLOCK, &block, 0);
		3568	}
		3569
		3570	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3571	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3572	either...).
		3573
		3574	=item queueing from a thread context
		3575
		3576	The strategy for threads is different, as you cannot (easily) block
		3577	threads but you can easily preempt them, so to queue safely you need to
		3578	employ a traditional mutex lock, such as in this pthread example:
		3579
		3580	static ev_async mysig;
		3581	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3582
		3583	static void
		3584	otherthread (void)
		3585	{
		3586	// only need to lock the actual queueing operation
		3587	pthread_mutex_lock (&mymutex);
		3588	queue_put (data);
		3589	pthread_mutex_unlock (&mymutex);
		3590
		3591	ev_async_send (EV_DEFAULT_ &mysig);
		3592	}
		3593
		3594	static void
		3595	mysig_cb (EV_P_ ev_async *w, int revents)
		3596	{
		3597	pthread_mutex_lock (&mymutex);
		3598
		3599	while (queue_get (&data))
		3600	process (data);
		3601
		3602	pthread_mutex_unlock (&mymutex);
		3603	}
		3604
		3605	=back
		3606
		3607
		3608	=head3 Watcher-Specific Functions and Data Members
		3609
		3610	=over 4
		3611
		3612	=item ev_async_init (ev_async *, callback)
		3613
		3614	Initialises and configures the async watcher - it has no parameters of any
		3615	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3616	trust me.
		3617
		3618	=item ev_async_send (loop, ev_async *)
		3619
		3620	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3621	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3622	returns.
		3623
		3624	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3625	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3626	embedding section below on what exactly this means).
		3627
		3628	Note that, as with other watchers in libev, multiple events might get
		3629	compressed into a single callback invocation (another way to look at
		3630	this is that C<ev_async> watchers are level-triggered: they are set on
		3631	C<ev_async_send>, reset when the event loop detects that).
		3632
		3633	This call incurs the overhead of at most one extra system call per event
		3634	loop iteration, if the event loop is blocked, and no syscall at all if
		3635	the event loop (or your program) is processing events. That means that
		3636	repeated calls are basically free (there is no need to avoid calls for
		3637	performance reasons) and that the overhead becomes smaller (typically
		3638	zero) under load.
		3639
		3640	=item bool = ev_async_pending (ev_async *)
		3641
		3642	Returns a non-zero value when C<ev_async_send> has been called on the
		3643	watcher but the event has not yet been processed (or even noted) by the
		3644	event loop.
		3645
		3646	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3647	the loop iterates next and checks for the watcher to have become active,
		3648	it will reset the flag again. C<ev_async_pending> can be used to very
		3649	quickly check whether invoking the loop might be a good idea.
		3650
		3651	Not that this does I<not> check whether the watcher itself is pending,
		3652	only whether it has been requested to make this watcher pending: there
		3653	is a time window between the event loop checking and resetting the async
		3654	notification, and the callback being invoked.
		3655
		3656	=back
		3657
		3658
2037	=head1 OTHER FUNCTIONS	3659	=head1 OTHER FUNCTIONS
2038		3660
2039	There are some other functions of possible interest. Described. Here. Now.	3661	There are some other functions of possible interest. Described. Here. Now.
2040		3662
2041	=over 4	3663	=over 4
2042		3664
2043	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3665	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2044		3666
2045	This function combines a simple timer and an I/O watcher, calls your	3667	This function combines a simple timer and an I/O watcher, calls your
2046	callback on whichever event happens first and automatically stop both	3668	callback on whichever event happens first and automatically stops both
2047	watchers. This is useful if you want to wait for a single event on an fd	3669	watchers. This is useful if you want to wait for a single event on an fd
2048	or timeout without having to allocate/configure/start/stop/free one or	3670	or timeout without having to allocate/configure/start/stop/free one or
2049	more watchers yourself.	3671	more watchers yourself.
2050		3672
2051	If C<fd> is less than 0, then no I/O watcher will be started and events	3673	If C<fd> is less than 0, then no I/O watcher will be started and the
2052	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3674	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2053	C<events> set will be craeted and started.	3675	the given C<fd> and C<events> set will be created and started.
2054		3676
2055	If C<timeout> is less than 0, then no timeout watcher will be	3677	If C<timeout> is less than 0, then no timeout watcher will be
2056	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3678	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2057	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3679	repeat = 0) will be started. C<0> is a valid timeout.
2058	dubious value.
2059		3680
2060	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3681	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2061	passed an C<revents> set like normal event callbacks (a combination of	3682	passed an C<revents> set like normal event callbacks (a combination of
2062	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3683	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2063	value passed to C<ev_once>:	3684	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3685	a timeout and an io event at the same time - you probably should give io
		3686	events precedence.
2064		3687
		3688	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3689
2065	static void stdin_ready (int revents, void *arg)	3690	static void stdin_ready (int revents, void *arg)
		3691	{
		3692	if (revents & EV_READ)
		3693	/* stdin might have data for us, joy! */;
		3694	else if (revents & EV_TIMER)
		3695	/* doh, nothing entered */;
		3696	}
		3697
		3698	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3699
		3700	=item ev_feed_fd_event (loop, int fd, int revents)
		3701
		3702	Feed an event on the given fd, as if a file descriptor backend detected
		3703	the given events.
		3704
		3705	=item ev_feed_signal_event (loop, int signum)
		3706
		3707	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3708	which is async-safe.
		3709
		3710	=back
		3711
		3712
		3713	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3714
		3715	This section explains some common idioms that are not immediately
		3716	obvious. Note that examples are sprinkled over the whole manual, and this
		3717	section only contains stuff that wouldn't fit anywhere else.
		3718
		3719	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3720
		3721	Each watcher has, by default, a C<void *data> member that you can read
		3722	or modify at any time: libev will completely ignore it. This can be used
		3723	to associate arbitrary data with your watcher. If you need more data and
		3724	don't want to allocate memory separately and store a pointer to it in that
		3725	data member, you can also "subclass" the watcher type and provide your own
		3726	data:
		3727
		3728	struct my_io
		3729	{
		3730	ev_io io;
		3731	int otherfd;
		3732	void *somedata;
		3733	struct whatever *mostinteresting;
		3734	};
		3735
		3736	...
		3737	struct my_io w;
		3738	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3739
		3740	And since your callback will be called with a pointer to the watcher, you
		3741	can cast it back to your own type:
		3742
		3743	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3744	{
		3745	struct my_io *w = (struct my_io *)w_;
		3746	...
		3747	}
		3748
		3749	More interesting and less C-conformant ways of casting your callback
		3750	function type instead have been omitted.
		3751
		3752	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3753
		3754	Another common scenario is to use some data structure with multiple
		3755	embedded watchers, in effect creating your own watcher that combines
		3756	multiple libev event sources into one "super-watcher":
		3757
		3758	struct my_biggy
		3759	{
		3760	int some_data;
		3761	ev_timer t1;
		3762	ev_timer t2;
		3763	}
		3764
		3765	In this case getting the pointer to C<my_biggy> is a bit more
		3766	complicated: Either you store the address of your C<my_biggy> struct in
		3767	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3768	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3769	real programmers):
		3770
		3771	#include <stddef.h>
		3772
		3773	static void
		3774	t1_cb (EV_P_ ev_timer *w, int revents)
		3775	{
		3776	struct my_biggy big = (struct my_biggy *)
		3777	(((char *)w) - offsetof (struct my_biggy, t1));
		3778	}
		3779
		3780	static void
		3781	t2_cb (EV_P_ ev_timer *w, int revents)
		3782	{
		3783	struct my_biggy big = (struct my_biggy *)
		3784	(((char *)w) - offsetof (struct my_biggy, t2));
		3785	}
		3786
		3787	=head2 AVOIDING FINISHING BEFORE RETURNING
		3788
		3789	Often you have structures like this in event-based programs:
		3790
		3791	callback ()
2066	{	3792	{
2067	if (revents & EV_TIMEOUT)	3793	free (request);
2068	/* doh, nothing entered */;
2069	else if (revents & EV_READ)
2070	/* stdin might have data for us, joy! */;
2071	}	3794	}
2072		3795
2073	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3796	request = start_new_request (..., callback);
2074		3797
2075	=item ev_feed_event (ev_loop *, watcher *, int revents)	3798	The intent is to start some "lengthy" operation. The C<request> could be
		3799	used to cancel the operation, or do other things with it.
2076		3800
2077	Feeds the given event set into the event loop, as if the specified event	3801	It's not uncommon to have code paths in C<start_new_request> that
2078	had happened for the specified watcher (which must be a pointer to an	3802	immediately invoke the callback, for example, to report errors. Or you add
2079	initialised but not necessarily started event watcher).	3803	some caching layer that finds that it can skip the lengthy aspects of the
		3804	operation and simply invoke the callback with the result.
2080		3805
2081	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3806	The problem here is that this will happen I<before> C<start_new_request>
		3807	has returned, so C<request> is not set.
2082		3808
2083	Feed an event on the given fd, as if a file descriptor backend detected	3809	Even if you pass the request by some safer means to the callback, you
2084	the given events it.	3810	might want to do something to the request after starting it, such as
		3811	canceling it, which probably isn't working so well when the callback has
		3812	already been invoked.
2085		3813
2086	=item ev_feed_signal_event (ev_loop *loop, int signum)	3814	A common way around all these issues is to make sure that
		3815	C<start_new_request> I<always> returns before the callback is invoked. If
		3816	C<start_new_request> immediately knows the result, it can artificially
		3817	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3818	example, or more sneakily, by reusing an existing (stopped) watcher and
		3819	pushing it into the pending queue:
2087		3820
2088	Feed an event as if the given signal occured (C<loop> must be the default	3821	ev_set_cb (watcher, callback);
2089	loop!).	3822	ev_feed_event (EV_A_ watcher, 0);
2090		3823
2091	=back	3824	This way, C<start_new_request> can safely return before the callback is
		3825	invoked, while not delaying callback invocation too much.
		3826
		3827	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3828
		3829	Often (especially in GUI toolkits) there are places where you have
		3830	I<modal> interaction, which is most easily implemented by recursively
		3831	invoking C<ev_run>.
		3832
		3833	This brings the problem of exiting - a callback might want to finish the
		3834	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3835	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3836	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3837	other combination: In these cases, a simple C<ev_break> will not work.
		3838
		3839	The solution is to maintain "break this loop" variable for each C<ev_run>
		3840	invocation, and use a loop around C<ev_run> until the condition is
		3841	triggered, using C<EVRUN_ONCE>:
		3842
		3843	// main loop
		3844	int exit_main_loop = 0;
		3845
		3846	while (!exit_main_loop)
		3847	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3848
		3849	// in a modal watcher
		3850	int exit_nested_loop = 0;
		3851
		3852	while (!exit_nested_loop)
		3853	ev_run (EV_A_ EVRUN_ONCE);
		3854
		3855	To exit from any of these loops, just set the corresponding exit variable:
		3856
		3857	// exit modal loop
		3858	exit_nested_loop = 1;
		3859
		3860	// exit main program, after modal loop is finished
		3861	exit_main_loop = 1;
		3862
		3863	// exit both
		3864	exit_main_loop = exit_nested_loop = 1;
		3865
		3866	=head2 THREAD LOCKING EXAMPLE
		3867
		3868	Here is a fictitious example of how to run an event loop in a different
		3869	thread from where callbacks are being invoked and watchers are
		3870	created/added/removed.
		3871
		3872	For a real-world example, see the C<EV::Loop::Async> perl module,
		3873	which uses exactly this technique (which is suited for many high-level
		3874	languages).
		3875
		3876	The example uses a pthread mutex to protect the loop data, a condition
		3877	variable to wait for callback invocations, an async watcher to notify the
		3878	event loop thread and an unspecified mechanism to wake up the main thread.
		3879
		3880	First, you need to associate some data with the event loop:
		3881
		3882	typedef struct {
		3883	pthread_mutex_t lock; /* global loop lock */
		3884	pthread_t tid;
		3885	pthread_cond_t invoke_cv;
		3886	ev_async async_w;
		3887	} userdata;
		3888
		3889	void prepare_loop (EV_P)
		3890	{
		3891	// for simplicity, we use a static userdata struct.
		3892	static userdata u;
		3893
		3894	ev_async_init (&u.async_w, async_cb);
		3895	ev_async_start (EV_A_ &u.async_w);
		3896
		3897	pthread_mutex_init (&u.lock, 0);
		3898	pthread_cond_init (&u.invoke_cv, 0);
		3899
		3900	// now associate this with the loop
		3901	ev_set_userdata (EV_A_ &u);
		3902	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3903	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3904
		3905	// then create the thread running ev_run
		3906	pthread_create (&u.tid, 0, l_run, EV_A);
		3907	}
		3908
		3909	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3910	solely to wake up the event loop so it takes notice of any new watchers
		3911	that might have been added:
		3912
		3913	static void
		3914	async_cb (EV_P_ ev_async *w, int revents)
		3915	{
		3916	// just used for the side effects
		3917	}
		3918
		3919	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3920	protecting the loop data, respectively.
		3921
		3922	static void
		3923	l_release (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	static void
		3930	l_acquire (EV_P)
		3931	{
		3932	userdata *u = ev_userdata (EV_A);
		3933	pthread_mutex_lock (&u->lock);
		3934	}
		3935
		3936	The event loop thread first acquires the mutex, and then jumps straight
		3937	into C<ev_run>:
		3938
		3939	void *
		3940	l_run (void *thr_arg)
		3941	{
		3942	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3943
		3944	l_acquire (EV_A);
		3945	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3946	ev_run (EV_A_ 0);
		3947	l_release (EV_A);
		3948
		3949	return 0;
		3950	}
		3951
		3952	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3953	signal the main thread via some unspecified mechanism (signals? pipe
		3954	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3955	have been called (in a while loop because a) spurious wakeups are possible
		3956	and b) skipping inter-thread-communication when there are no pending
		3957	watchers is very beneficial):
		3958
		3959	static void
		3960	l_invoke (EV_P)
		3961	{
		3962	userdata *u = ev_userdata (EV_A);
		3963
		3964	while (ev_pending_count (EV_A))
		3965	{
		3966	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3967	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3968	}
		3969	}
		3970
		3971	Now, whenever the main thread gets told to invoke pending watchers, it
		3972	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3973	thread to continue:
		3974
		3975	static void
		3976	real_invoke_pending (EV_P)
		3977	{
		3978	userdata *u = ev_userdata (EV_A);
		3979
		3980	pthread_mutex_lock (&u->lock);
		3981	ev_invoke_pending (EV_A);
		3982	pthread_cond_signal (&u->invoke_cv);
		3983	pthread_mutex_unlock (&u->lock);
		3984	}
		3985
		3986	Whenever you want to start/stop a watcher or do other modifications to an
		3987	event loop, you will now have to lock:
		3988
		3989	ev_timer timeout_watcher;
		3990	userdata *u = ev_userdata (EV_A);
		3991
		3992	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3993
		3994	pthread_mutex_lock (&u->lock);
		3995	ev_timer_start (EV_A_ &timeout_watcher);
		3996	ev_async_send (EV_A_ &u->async_w);
		3997	pthread_mutex_unlock (&u->lock);
		3998
		3999	Note that sending the C<ev_async> watcher is required because otherwise
		4000	an event loop currently blocking in the kernel will have no knowledge
		4001	about the newly added timer. By waking up the loop it will pick up any new
		4002	watchers in the next event loop iteration.
		4003
		4004	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		4005
		4006	While the overhead of a callback that e.g. schedules a thread is small, it
		4007	is still an overhead. If you embed libev, and your main usage is with some
		4008	kind of threads or coroutines, you might want to customise libev so that
		4009	doesn't need callbacks anymore.
		4010
		4011	Imagine you have coroutines that you can switch to using a function
		4012	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		4013	and that due to some magic, the currently active coroutine is stored in a
		4014	global called C<current_coro>. Then you can build your own "wait for libev
		4015	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		4016	the differing C<;> conventions):
		4017
		4018	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4019	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4020
		4021	That means instead of having a C callback function, you store the
		4022	coroutine to switch to in each watcher, and instead of having libev call
		4023	your callback, you instead have it switch to that coroutine.
		4024
		4025	A coroutine might now wait for an event with a function called
		4026	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4027	matter when, or whether the watcher is active or not when this function is
		4028	called):
		4029
		4030	void
		4031	wait_for_event (ev_watcher *w)
		4032	{
		4033	ev_set_cb (w, current_coro);
		4034	switch_to (libev_coro);
		4035	}
		4036
		4037	That basically suspends the coroutine inside C<wait_for_event> and
		4038	continues the libev coroutine, which, when appropriate, switches back to
		4039	this or any other coroutine.
		4040
		4041	You can do similar tricks if you have, say, threads with an event queue -
		4042	instead of storing a coroutine, you store the queue object and instead of
		4043	switching to a coroutine, you push the watcher onto the queue and notify
		4044	any waiters.
		4045
		4046	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4047	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4048
		4049	// my_ev.h
		4050	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4051	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4052	#include "../libev/ev.h"
		4053
		4054	// my_ev.c
		4055	#define EV_H "my_ev.h"
		4056	#include "../libev/ev.c"
		4057
		4058	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4059	F<my_ev.c> into your project. When properly specifying include paths, you
		4060	can even use F<ev.h> as header file name directly.
2092		4061
2093		4062
2094	=head1 LIBEVENT EMULATION	4063	=head1 LIBEVENT EMULATION
2095		4064
2096	Libev offers a compatibility emulation layer for libevent. It cannot	4065	Libev offers a compatibility emulation layer for libevent. It cannot
2097	emulate the internals of libevent, so here are some usage hints:	4066	emulate the internals of libevent, so here are some usage hints:
2098		4067
2099	=over 4	4068	=over 4
		4069
		4070	=item * Only the libevent-1.4.1-beta API is being emulated.
		4071
		4072	This was the newest libevent version available when libev was implemented,
		4073	and is still mostly unchanged in 2010.
2100		4074
2101	=item * Use it by including <event.h>, as usual.	4075	=item * Use it by including <event.h>, as usual.
2102		4076
2103	=item * The following members are fully supported: ev_base, ev_callback,	4077	=item * The following members are fully supported: ev_base, ev_callback,
2104	ev_arg, ev_fd, ev_res, ev_events.	4078	ev_arg, ev_fd, ev_res, ev_events.
…		…
2109		4083
2110	=item * Priorities are not currently supported. Initialising priorities	4084	=item * Priorities are not currently supported. Initialising priorities
2111	will fail and all watchers will have the same priority, even though there	4085	will fail and all watchers will have the same priority, even though there
2112	is an ev_pri field.	4086	is an ev_pri field.
2113		4087
		4088	=item * In libevent, the last base created gets the signals, in libev, the
		4089	base that registered the signal gets the signals.
		4090
2114	=item * Other members are not supported.	4091	=item * Other members are not supported.
2115		4092
2116	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4093	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2117	to use the libev header file and library.	4094	to use the libev header file and library.
2118		4095
2119	=back	4096	=back
2120		4097
2121	=head1 C++ SUPPORT	4098	=head1 C++ SUPPORT
2122		4099
		4100	=head2 C API
		4101
		4102	The normal C API should work fine when used from C++: both ev.h and the
		4103	libev sources can be compiled as C++. Therefore, code that uses the C API
		4104	will work fine.
		4105
		4106	Proper exception specifications might have to be added to callbacks passed
		4107	to libev: exceptions may be thrown only from watcher callbacks, all other
		4108	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4109	callbacks) must not throw exceptions, and might need a C<noexcept>
		4110	specification. If you have code that needs to be compiled as both C and
		4111	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4112
		4113	static void
		4114	fatal_error (const char *msg) EV_NOEXCEPT
		4115	{
		4116	perror (msg);
		4117	abort ();
		4118	}
		4119
		4120	...
		4121	ev_set_syserr_cb (fatal_error);
		4122
		4123	The only API functions that can currently throw exceptions are C<ev_run>,
		4124	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4125	because it runs cleanup watchers).
		4126
		4127	Throwing exceptions in watcher callbacks is only supported if libev itself
		4128	is compiled with a C++ compiler or your C and C++ environments allow
		4129	throwing exceptions through C libraries (most do).
		4130
		4131	=head2 C++ API
		4132
2123	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4133	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2124	you to use some convinience methods to start/stop watchers and also change	4134	you to use some convenience methods to start/stop watchers and also change
2125	the callback model to a model using method callbacks on objects.	4135	the callback model to a model using method callbacks on objects.
2126		4136
2127	To use it,	4137	To use it,
2128		4138
2129	#include <ev++.h>	4139	#include <ev++.h>
2130		4140
2131	This automatically includes F<ev.h> and puts all of its definitions (many	4141	This automatically includes F<ev.h> and puts all of its definitions (many
2132	of them macros) into the global namespace. All C++ specific things are	4142	of them macros) into the global namespace. All C++ specific things are
2133	put into the C<ev> namespace. It should support all the same embedding	4143	put into the C<ev> namespace. It should support all the same embedding
2134	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	4144	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2136	Care has been taken to keep the overhead low. The only data member the C++	4146	Care has been taken to keep the overhead low. The only data member the C++
2137	classes add (compared to plain C-style watchers) is the event loop pointer	4147	classes add (compared to plain C-style watchers) is the event loop pointer
2138	that the watcher is associated with (or no additional members at all if	4148	that the watcher is associated with (or no additional members at all if
2139	you disable C<EV_MULTIPLICITY> when embedding libev).	4149	you disable C<EV_MULTIPLICITY> when embedding libev).
2140		4150
2141	Currently, functions, and static and non-static member functions can be	4151	Currently, functions, static and non-static member functions and classes
2142	used as callbacks. Other types should be easy to add as long as they only	4152	with C<operator ()> can be used as callbacks. Other types should be easy
2143	need one additional pointer for context. If you need support for other	4153	to add as long as they only need one additional pointer for context. If
2144	types of functors please contact the author (preferably after implementing	4154	you need support for other types of functors please contact the author
2145	it).	4155	(preferably after implementing it).
		4156
		4157	For all this to work, your C++ compiler either has to use the same calling
		4158	conventions as your C compiler (for static member functions), or you have
		4159	to embed libev and compile libev itself as C++.
2146		4160
2147	Here is a list of things available in the C<ev> namespace:	4161	Here is a list of things available in the C<ev> namespace:
2148		4162
2149	=over 4	4163	=over 4
2150		4164
…		…
2160	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4174	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2161		4175
2162	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4176	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2163	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4177	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2164	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4178	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2165	defines by many implementations.	4179	defined by many implementations.
2166		4180
2167	All of those classes have these methods:	4181	All of those classes have these methods:
2168		4182
2169	=over 4	4183	=over 4
2170		4184
2171	=item ev::TYPE::TYPE ()	4185	=item ev::TYPE::TYPE ()
2172		4186
2173	=item ev::TYPE::TYPE (struct ev_loop *)	4187	=item ev::TYPE::TYPE (loop)
2174		4188
2175	=item ev::TYPE::~TYPE	4189	=item ev::TYPE::~TYPE
2176		4190
2177	The constructor (optionally) takes an event loop to associate the watcher	4191	The constructor (optionally) takes an event loop to associate the watcher
2178	with. If it is omitted, it will use C<EV_DEFAULT>.	4192	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2201	your compiler is good :), then the method will be fully inlined into the	4215	your compiler is good :), then the method will be fully inlined into the
2202	thunking function, making it as fast as a direct C callback.	4216	thunking function, making it as fast as a direct C callback.
2203		4217
2204	Example: simple class declaration and watcher initialisation	4218	Example: simple class declaration and watcher initialisation
2205		4219
2206	struct myclass	4220	struct myclass
2207	{	4221	{
2208	void io_cb (ev::io &w, int revents) { }	4222	void io_cb (ev::io &w, int revents) { }
2209	}	4223	}
2210		4224
2211	myclass obj;	4225	myclass obj;
2212	ev::io iow;	4226	ev::io iow;
2213	iow.set <myclass, &myclass::io_cb> (&obj);	4227	iow.set <myclass, &myclass::io_cb> (&obj);
		4228
		4229	=item w->set (object *)
		4230
		4231	This is a variation of a method callback - leaving out the method to call
		4232	will default the method to C<operator ()>, which makes it possible to use
		4233	functor objects without having to manually specify the C<operator ()> all
		4234	the time. Incidentally, you can then also leave out the template argument
		4235	list.
		4236
		4237	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4238	int revents)>.
		4239
		4240	See the method-C<set> above for more details.
		4241
		4242	Example: use a functor object as callback.
		4243
		4244	struct myfunctor
		4245	{
		4246	void operator() (ev::io &w, int revents)
		4247	{
		4248	...
		4249	}
		4250	}
		4251
		4252	myfunctor f;
		4253
		4254	ev::io w;
		4255	w.set (&f);
2214		4256
2215	=item w->set<function> (void *data = 0)	4257	=item w->set<function> (void *data = 0)
2216		4258
2217	Also sets a callback, but uses a static method or plain function as	4259	Also sets a callback, but uses a static method or plain function as
2218	callback. The optional C<data> argument will be stored in the watcher's	4260	callback. The optional C<data> argument will be stored in the watcher's
…		…
2220		4262
2221	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4263	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2222		4264
2223	See the method-C<set> above for more details.	4265	See the method-C<set> above for more details.
2224		4266
2225	Example:	4267	Example: Use a plain function as callback.
2226		4268
2227	static void io_cb (ev::io &w, int revents) { }	4269	static void io_cb (ev::io &w, int revents) { }
2228	iow.set <io_cb> ();	4270	iow.set <io_cb> ();
2229		4271
2230	=item w->set (struct ev_loop *)	4272	=item w->set (loop)
2231		4273
2232	Associates a different C<struct ev_loop> with this watcher. You can only	4274	Associates a different C<struct ev_loop> with this watcher. You can only
2233	do this when the watcher is inactive (and not pending either).	4275	do this when the watcher is inactive (and not pending either).
2234		4276
2235	=item w->set ([args])	4277	=item w->set ([arguments])
2236		4278
2237	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4279	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4280	with the same arguments. Either this method or a suitable start method
2238	called at least once. Unlike the C counterpart, an active watcher gets	4281	must be called at least once. Unlike the C counterpart, an active watcher
2239	automatically stopped and restarted when reconfiguring it with this	4282	gets automatically stopped and restarted when reconfiguring it with this
2240	method.	4283	method.
		4284
		4285	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4286	clashing with the C<set (loop)> method.
		4287
		4288	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4289	new event mask only, and internally calls C<ev_io_modify>.
2241		4290
2242	=item w->start ()	4291	=item w->start ()
2243		4292
2244	Starts the watcher. Note that there is no C<loop> argument, as the	4293	Starts the watcher. Note that there is no C<loop> argument, as the
2245	constructor already stores the event loop.	4294	constructor already stores the event loop.
2246		4295
		4296	=item w->start ([arguments])
		4297
		4298	Instead of calling C<set> and C<start> methods separately, it is often
		4299	convenient to wrap them in one call. Uses the same type of arguments as
		4300	the configure C<set> method of the watcher.
		4301
2247	=item w->stop ()	4302	=item w->stop ()
2248		4303
2249	Stops the watcher if it is active. Again, no C<loop> argument.	4304	Stops the watcher if it is active. Again, no C<loop> argument.
2250		4305
2251	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4306	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2263		4318
2264	=back	4319	=back
2265		4320
2266	=back	4321	=back
2267		4322
2268	Example: Define a class with an IO and idle watcher, start one of them in	4323	Example: Define a class with two I/O and idle watchers, start the I/O
2269	the constructor.	4324	watchers in the constructor.
2270		4325
2271	class myclass	4326	class myclass
2272	{	4327	{
2273	ev_io io; void io_cb (ev::io &w, int revents);	4328	ev::io io ; void io_cb (ev::io &w, int revents);
		4329	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2274	ev_idle idle void idle_cb (ev::idle &w, int revents);	4330	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2275		4331
2276	myclass ();	4332	myclass (int fd)
2277	}	4333	{
2278
2279	myclass::myclass (int fd)
2280	{
2281	io .set <myclass, &myclass::io_cb > (this);	4334	io .set <myclass, &myclass::io_cb > (this);
		4335	io2 .set <myclass, &myclass::io2_cb > (this);
2282	idle.set <myclass, &myclass::idle_cb> (this);	4336	idle.set <myclass, &myclass::idle_cb> (this);
2283		4337
2284	io.start (fd, ev::READ);	4338	io.set (fd, ev::WRITE); // configure the watcher
		4339	io.start (); // start it whenever convenient
		4340
		4341	io2.start (fd, ev::READ); // set + start in one call
		4342	}
2285	}	4343	};
		4344
		4345
		4346	=head1 OTHER LANGUAGE BINDINGS
		4347
		4348	Libev does not offer other language bindings itself, but bindings for a
		4349	number of languages exist in the form of third-party packages. If you know
		4350	any interesting language binding in addition to the ones listed here, drop
		4351	me a note.
		4352
		4353	=over 4
		4354
		4355	=item Perl
		4356
		4357	The EV module implements the full libev API and is actually used to test
		4358	libev. EV is developed together with libev. Apart from the EV core module,
		4359	there are additional modules that implement libev-compatible interfaces
		4360	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4361	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4362	and C<EV::Glib>).
		4363
		4364	It can be found and installed via CPAN, its homepage is at
		4365	L<http://software.schmorp.de/pkg/EV>.
		4366
		4367	=item Python
		4368
		4369	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4370	seems to be quite complete and well-documented.
		4371
		4372	=item Ruby
		4373
		4374	Tony Arcieri has written a ruby extension that offers access to a subset
		4375	of the libev API and adds file handle abstractions, asynchronous DNS and
		4376	more on top of it. It can be found via gem servers. Its homepage is at
		4377	L<http://rev.rubyforge.org/>.
		4378
		4379	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4380	makes rev work even on mingw.
		4381
		4382	=item Haskell
		4383
		4384	A haskell binding to libev is available at
		4385	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4386
		4387	=item D
		4388
		4389	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4390	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4391
		4392	=item Ocaml
		4393
		4394	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4395	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4396
		4397	=item Lua
		4398
		4399	Brian Maher has written a partial interface to libev for lua (at the
		4400	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4401	L<http://github.com/brimworks/lua-ev>.
		4402
		4403	=item Javascript
		4404
		4405	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4406
		4407	=item Others
		4408
		4409	There are others, and I stopped counting.
		4410
		4411	=back
2286		4412
2287		4413
2288	=head1 MACRO MAGIC	4414	=head1 MACRO MAGIC
2289		4415
2290	Libev can be compiled with a variety of options, the most fundamantal	4416	Libev can be compiled with a variety of options, the most fundamental
2291	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4417	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2292	functions and callbacks have an initial C<struct ev_loop *> argument.	4418	functions and callbacks have an initial C<struct ev_loop *> argument.
2293		4419
2294	To make it easier to write programs that cope with either variant, the	4420	To make it easier to write programs that cope with either variant, the
2295	following macros are defined:	4421	following macros are defined:
…		…
2300		4426
2301	This provides the loop I<argument> for functions, if one is required ("ev	4427	This provides the loop I<argument> for functions, if one is required ("ev
2302	loop argument"). The C<EV_A> form is used when this is the sole argument,	4428	loop argument"). The C<EV_A> form is used when this is the sole argument,
2303	C<EV_A_> is used when other arguments are following. Example:	4429	C<EV_A_> is used when other arguments are following. Example:
2304		4430
2305	ev_unref (EV_A);	4431	ev_unref (EV_A);
2306	ev_timer_add (EV_A_ watcher);	4432	ev_timer_add (EV_A_ watcher);
2307	ev_loop (EV_A_ 0);	4433	ev_run (EV_A_ 0);
2308		4434
2309	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4435	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2310	which is often provided by the following macro.	4436	which is often provided by the following macro.
2311		4437
2312	=item C<EV_P>, C<EV_P_>	4438	=item C<EV_P>, C<EV_P_>
2313		4439
2314	This provides the loop I<parameter> for functions, if one is required ("ev	4440	This provides the loop I<parameter> for functions, if one is required ("ev
2315	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4441	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2316	C<EV_P_> is used when other parameters are following. Example:	4442	C<EV_P_> is used when other parameters are following. Example:
2317		4443
2318	// this is how ev_unref is being declared	4444	// this is how ev_unref is being declared
2319	static void ev_unref (EV_P);	4445	static void ev_unref (EV_P);
2320		4446
2321	// this is how you can declare your typical callback	4447	// this is how you can declare your typical callback
2322	static void cb (EV_P_ ev_timer *w, int revents)	4448	static void cb (EV_P_ ev_timer *w, int revents)
2323		4449
2324	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4450	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2325	suitable for use with C<EV_A>.	4451	suitable for use with C<EV_A>.
2326		4452
2327	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4453	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2328		4454
2329	Similar to the other two macros, this gives you the value of the default	4455	Similar to the other two macros, this gives you the value of the default
2330	loop, if multiple loops are supported ("ev loop default").	4456	loop, if multiple loops are supported ("ev loop default"). The default loop
		4457	will be initialised if it isn't already initialised.
		4458
		4459	For non-multiplicity builds, these macros do nothing, so you always have
		4460	to initialise the loop somewhere.
		4461
		4462	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4463
		4464	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4465	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4466	is undefined when the default loop has not been initialised by a previous
		4467	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4468
		4469	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4470	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2331		4471
2332	=back	4472	=back
2333		4473
2334	Example: Declare and initialise a check watcher, utilising the above	4474	Example: Declare and initialise a check watcher, utilising the above
2335	macros so it will work regardless of whether multiple loops are supported	4475	macros so it will work regardless of whether multiple loops are supported
2336	or not.	4476	or not.
2337		4477
2338	static void	4478	static void
2339	check_cb (EV_P_ ev_timer *w, int revents)	4479	check_cb (EV_P_ ev_timer *w, int revents)
2340	{	4480	{
2341	ev_check_stop (EV_A_ w);	4481	ev_check_stop (EV_A_ w);
2342	}	4482	}
2343		4483
2344	ev_check check;	4484	ev_check check;
2345	ev_check_init (&check, check_cb);	4485	ev_check_init (&check, check_cb);
2346	ev_check_start (EV_DEFAULT_ &check);	4486	ev_check_start (EV_DEFAULT_ &check);
2347	ev_loop (EV_DEFAULT_ 0);	4487	ev_run (EV_DEFAULT_ 0);
2348		4488
2349	=head1 EMBEDDING	4489	=head1 EMBEDDING
2350		4490
2351	Libev can (and often is) directly embedded into host	4491	Libev can (and often is) directly embedded into host
2352	applications. Examples of applications that embed it include the Deliantra	4492	applications. Examples of applications that embed it include the Deliantra
…		…
2359	libev somewhere in your source tree).	4499	libev somewhere in your source tree).
2360		4500
2361	=head2 FILESETS	4501	=head2 FILESETS
2362		4502
2363	Depending on what features you need you need to include one or more sets of files	4503	Depending on what features you need you need to include one or more sets of files
2364	in your app.	4504	in your application.
2365		4505
2366	=head3 CORE EVENT LOOP	4506	=head3 CORE EVENT LOOP
2367		4507
2368	To include only the libev core (all the C<ev_*> functions), with manual	4508	To include only the libev core (all the C<ev_*> functions), with manual
2369	configuration (no autoconf):	4509	configuration (no autoconf):
2370		4510
2371	#define EV_STANDALONE 1	4511	#define EV_STANDALONE 1
2372	#include "ev.c"	4512	#include "ev.c"
2373		4513
2374	This will automatically include F<ev.h>, too, and should be done in a	4514	This will automatically include F<ev.h>, too, and should be done in a
2375	single C source file only to provide the function implementations. To use	4515	single C source file only to provide the function implementations. To use
2376	it, do the same for F<ev.h> in all files wishing to use this API (best	4516	it, do the same for F<ev.h> in all files wishing to use this API (best
2377	done by writing a wrapper around F<ev.h> that you can include instead and	4517	done by writing a wrapper around F<ev.h> that you can include instead and
2378	where you can put other configuration options):	4518	where you can put other configuration options):
2379		4519
2380	#define EV_STANDALONE 1	4520	#define EV_STANDALONE 1
2381	#include "ev.h"	4521	#include "ev.h"
2382		4522
2383	Both header files and implementation files can be compiled with a C++	4523	Both header files and implementation files can be compiled with a C++
2384	compiler (at least, thats a stated goal, and breakage will be treated	4524	compiler (at least, that's a stated goal, and breakage will be treated
2385	as a bug).	4525	as a bug).
2386		4526
2387	You need the following files in your source tree, or in a directory	4527	You need the following files in your source tree, or in a directory
2388	in your include path (e.g. in libev/ when using -Ilibev):	4528	in your include path (e.g. in libev/ when using -Ilibev):
2389		4529
2390	ev.h	4530	ev.h
2391	ev.c	4531	ev.c
2392	ev_vars.h	4532	ev_vars.h
2393	ev_wrap.h	4533	ev_wrap.h
2394		4534
2395	ev_win32.c required on win32 platforms only	4535	ev_win32.c required on win32 platforms only
2396		4536
2397	ev_select.c only when select backend is enabled (which is enabled by default)	4537	ev_select.c only when select backend is enabled
2398	ev_poll.c only when poll backend is enabled (disabled by default)	4538	ev_poll.c only when poll backend is enabled
2399	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4539	ev_epoll.c only when the epoll backend is enabled
		4540	ev_linuxaio.c only when the linux aio backend is enabled
		4541	ev_iouring.c only when the linux io_uring backend is enabled
2400	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4542	ev_kqueue.c only when the kqueue backend is enabled
2401	ev_port.c only when the solaris port backend is enabled (disabled by default)	4543	ev_port.c only when the solaris port backend is enabled
2402		4544
2403	F<ev.c> includes the backend files directly when enabled, so you only need	4545	F<ev.c> includes the backend files directly when enabled, so you only need
2404	to compile this single file.	4546	to compile this single file.
2405		4547
2406	=head3 LIBEVENT COMPATIBILITY API	4548	=head3 LIBEVENT COMPATIBILITY API
2407		4549
2408	To include the libevent compatibility API, also include:	4550	To include the libevent compatibility API, also include:
2409		4551
2410	#include "event.c"	4552	#include "event.c"
2411		4553
2412	in the file including F<ev.c>, and:	4554	in the file including F<ev.c>, and:
2413		4555
2414	#include "event.h"	4556	#include "event.h"
2415		4557
2416	in the files that want to use the libevent API. This also includes F<ev.h>.	4558	in the files that want to use the libevent API. This also includes F<ev.h>.
2417		4559
2418	You need the following additional files for this:	4560	You need the following additional files for this:
2419		4561
2420	event.h	4562	event.h
2421	event.c	4563	event.c
2422		4564
2423	=head3 AUTOCONF SUPPORT	4565	=head3 AUTOCONF SUPPORT
2424		4566
2425	Instead of using C<EV_STANDALONE=1> and providing your config in	4567	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2426	whatever way you want, you can also C<m4_include([libev.m4])> in your	4568	whatever way you want, you can also C<m4_include([libev.m4])> in your
2427	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4569	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2428	include F<config.h> and configure itself accordingly.	4570	include F<config.h> and configure itself accordingly.
2429		4571
2430	For this of course you need the m4 file:	4572	For this of course you need the m4 file:
2431		4573
2432	libev.m4	4574	libev.m4
2433		4575
2434	=head2 PREPROCESSOR SYMBOLS/MACROS	4576	=head2 PREPROCESSOR SYMBOLS/MACROS
2435		4577
2436	Libev can be configured via a variety of preprocessor symbols you have to define	4578	Libev can be configured via a variety of preprocessor symbols you have to
2437	before including any of its files. The default is not to build for multiplicity	4579	define before including (or compiling) any of its files. The default in
2438	and only include the select backend.	4580	the absence of autoconf is documented for every option.
		4581
		4582	Symbols marked with "(h)" do not change the ABI, and can have different
		4583	values when compiling libev vs. including F<ev.h>, so it is permissible
		4584	to redefine them before including F<ev.h> without breaking compatibility
		4585	to a compiled library. All other symbols change the ABI, which means all
		4586	users of libev and the libev code itself must be compiled with compatible
		4587	settings.
2439		4588
2440	=over 4	4589	=over 4
2441		4590
		4591	=item EV_COMPAT3 (h)
		4592
		4593	Backwards compatibility is a major concern for libev. This is why this
		4594	release of libev comes with wrappers for the functions and symbols that
		4595	have been renamed between libev version 3 and 4.
		4596
		4597	You can disable these wrappers (to test compatibility with future
		4598	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4599	sources. This has the additional advantage that you can drop the C<struct>
		4600	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4601	typedef in that case.
		4602
		4603	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4604	and in some even more future version the compatibility code will be
		4605	removed completely.
		4606
2442	=item EV_STANDALONE	4607	=item EV_STANDALONE (h)
2443		4608
2444	Must always be C<1> if you do not use autoconf configuration, which	4609	Must always be C<1> if you do not use autoconf configuration, which
2445	keeps libev from including F<config.h>, and it also defines dummy	4610	keeps libev from including F<config.h>, and it also defines dummy
2446	implementations for some libevent functions (such as logging, which is not	4611	implementations for some libevent functions (such as logging, which is not
2447	supported). It will also not define any of the structs usually found in	4612	supported). It will also not define any of the structs usually found in
2448	F<event.h> that are not directly supported by the libev core alone.	4613	F<event.h> that are not directly supported by the libev core alone.
2449		4614
		4615	In standalone mode, libev will still try to automatically deduce the
		4616	configuration, but has to be more conservative.
		4617
		4618	=item EV_USE_FLOOR
		4619
		4620	If defined to be C<1>, libev will use the C<floor ()> function for its
		4621	periodic reschedule calculations, otherwise libev will fall back on a
		4622	portable (slower) implementation. If you enable this, you usually have to
		4623	link against libm or something equivalent. Enabling this when the C<floor>
		4624	function is not available will fail, so the safe default is to not enable
		4625	this.
		4626
2450	=item EV_USE_MONOTONIC	4627	=item EV_USE_MONOTONIC
2451		4628
2452	If defined to be C<1>, libev will try to detect the availability of the	4629	If defined to be C<1>, libev will try to detect the availability of the
2453	monotonic clock option at both compiletime and runtime. Otherwise no use	4630	monotonic clock option at both compile time and runtime. Otherwise no
2454	of the monotonic clock option will be attempted. If you enable this, you	4631	use of the monotonic clock option will be attempted. If you enable this,
2455	usually have to link against librt or something similar. Enabling it when	4632	you usually have to link against librt or something similar. Enabling it
2456	the functionality isn't available is safe, though, although you have	4633	when the functionality isn't available is safe, though, although you have
2457	to make sure you link against any libraries where the C<clock_gettime>	4634	to make sure you link against any libraries where the C<clock_gettime>
2458	function is hiding in (often F<-lrt>).	4635	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2459		4636
2460	=item EV_USE_REALTIME	4637	=item EV_USE_REALTIME
2461		4638
2462	If defined to be C<1>, libev will try to detect the availability of the	4639	If defined to be C<1>, libev will try to detect the availability of the
2463	realtime clock option at compiletime (and assume its availability at	4640	real-time clock option at compile time (and assume its availability
2464	runtime if successful). Otherwise no use of the realtime clock option will	4641	at runtime if successful). Otherwise no use of the real-time clock
2465	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4642	option will be attempted. This effectively replaces C<gettimeofday>
2466	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4643	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2467	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4644	correctness. See the note about libraries in the description of
		4645	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4646	C<EV_USE_CLOCK_SYSCALL>.
		4647
		4648	=item EV_USE_CLOCK_SYSCALL
		4649
		4650	If defined to be C<1>, libev will try to use a direct syscall instead
		4651	of calling the system-provided C<clock_gettime> function. This option
		4652	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4653	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4654	programs needlessly. Using a direct syscall is slightly slower (in
		4655	theory), because no optimised vdso implementation can be used, but avoids
		4656	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4657	higher, as it simplifies linking (no need for C<-lrt>).
2468		4658
2469	=item EV_USE_NANOSLEEP	4659	=item EV_USE_NANOSLEEP
2470		4660
2471	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4661	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2472	and will use it for delays. Otherwise it will use C<select ()>.	4662	and will use it for delays. Otherwise it will use C<select ()>.
2473		4663
		4664	=item EV_USE_EVENTFD
		4665
		4666	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4667	available and will probe for kernel support at runtime. This will improve
		4668	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4669	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4670	2.7 or newer, otherwise disabled.
		4671
		4672	=item EV_USE_SIGNALFD
		4673
		4674	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4675	available and will probe for kernel support at runtime. This enables
		4676	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4677	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4678	2.7 or newer, otherwise disabled.
		4679
		4680	=item EV_USE_TIMERFD
		4681
		4682	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4683	available and will probe for kernel support at runtime. This allows
		4684	libev to detect time jumps accurately. If undefined, it will be enabled
		4685	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4686	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4687
		4688	=item EV_USE_EVENTFD
		4689
		4690	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4691	available and will probe for kernel support at runtime. This will improve
		4692	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4693	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4694	2.7 or newer, otherwise disabled.
		4695
2474	=item EV_USE_SELECT	4696	=item EV_USE_SELECT
2475		4697
2476	If undefined or defined to be C<1>, libev will compile in support for the	4698	If undefined or defined to be C<1>, libev will compile in support for the
2477	C<select>(2) backend. No attempt at autodetection will be done: if no	4699	C<select>(2) backend. No attempt at auto-detection will be done: if no
2478	other method takes over, select will be it. Otherwise the select backend	4700	other method takes over, select will be it. Otherwise the select backend
2479	will not be compiled in.	4701	will not be compiled in.
2480		4702
2481	=item EV_SELECT_USE_FD_SET	4703	=item EV_SELECT_USE_FD_SET
2482		4704
2483	If defined to C<1>, then the select backend will use the system C<fd_set>	4705	If defined to C<1>, then the select backend will use the system C<fd_set>
2484	structure. This is useful if libev doesn't compile due to a missing	4706	structure. This is useful if libev doesn't compile due to a missing
2485	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4707	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2486	exotic systems. This usually limits the range of file descriptors to some	4708	on exotic systems. This usually limits the range of file descriptors to
2487	low limit such as 1024 or might have other limitations (winsocket only	4709	some low limit such as 1024 or might have other limitations (winsocket
2488	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4710	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2489	influence the size of the C<fd_set> used.	4711	configures the maximum size of the C<fd_set>.
2490		4712
2491	=item EV_SELECT_IS_WINSOCKET	4713	=item EV_SELECT_IS_WINSOCKET
2492		4714
2493	When defined to C<1>, the select backend will assume that	4715	When defined to C<1>, the select backend will assume that
2494	select/socket/connect etc. don't understand file descriptors but	4716	select/socket/connect etc. don't understand file descriptors but
…		…
2496	be used is the winsock select). This means that it will call	4718	be used is the winsock select). This means that it will call
2497	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4719	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2498	it is assumed that all these functions actually work on fds, even	4720	it is assumed that all these functions actually work on fds, even
2499	on win32. Should not be defined on non-win32 platforms.	4721	on win32. Should not be defined on non-win32 platforms.
2500		4722
2501	=item EV_FD_TO_WIN32_HANDLE	4723	=item EV_FD_TO_WIN32_HANDLE(fd)
2502		4724
2503	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4725	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2504	file descriptors to socket handles. When not defining this symbol (the	4726	file descriptors to socket handles. When not defining this symbol (the
2505	default), then libev will call C<_get_osfhandle>, which is usually	4727	default), then libev will call C<_get_osfhandle>, which is usually
2506	correct. In some cases, programs use their own file descriptor management,	4728	correct. In some cases, programs use their own file descriptor management,
2507	in which case they can provide this function to map fds to socket handles.	4729	in which case they can provide this function to map fds to socket handles.
2508		4730
		4731	=item EV_WIN32_HANDLE_TO_FD(handle)
		4732
		4733	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4734	using the standard C<_open_osfhandle> function. For programs implementing
		4735	their own fd to handle mapping, overwriting this function makes it easier
		4736	to do so. This can be done by defining this macro to an appropriate value.
		4737
		4738	=item EV_WIN32_CLOSE_FD(fd)
		4739
		4740	If programs implement their own fd to handle mapping on win32, then this
		4741	macro can be used to override the C<close> function, useful to unregister
		4742	file descriptors again. Note that the replacement function has to close
		4743	the underlying OS handle.
		4744
		4745	=item EV_USE_WSASOCKET
		4746
		4747	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4748	communication socket, which works better in some environments. Otherwise,
		4749	the normal C<socket> function will be used, which works better in other
		4750	environments.
		4751
2509	=item EV_USE_POLL	4752	=item EV_USE_POLL
2510		4753
2511	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4754	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2512	backend. Otherwise it will be enabled on non-win32 platforms. It	4755	backend. Otherwise it will be enabled on non-win32 platforms. It
2513	takes precedence over select.	4756	takes precedence over select.
2514		4757
2515	=item EV_USE_EPOLL	4758	=item EV_USE_EPOLL
2516		4759
2517	If defined to be C<1>, libev will compile in support for the Linux	4760	If defined to be C<1>, libev will compile in support for the Linux
2518	C<epoll>(7) backend. Its availability will be detected at runtime,	4761	C<epoll>(7) backend. Its availability will be detected at runtime,
2519	otherwise another method will be used as fallback. This is the	4762	otherwise another method will be used as fallback. This is the preferred
2520	preferred backend for GNU/Linux systems.	4763	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4764	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4765
		4766	=item EV_USE_LINUXAIO
		4767
		4768	If defined to be C<1>, libev will compile in support for the Linux aio
		4769	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4770	enabled on linux, otherwise disabled.
		4771
		4772	=item EV_USE_IOURING
		4773
		4774	If defined to be C<1>, libev will compile in support for the Linux
		4775	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4776	current limitations it has to be requested explicitly. If undefined, it
		4777	will be enabled on linux, otherwise disabled.
2521		4778
2522	=item EV_USE_KQUEUE	4779	=item EV_USE_KQUEUE
2523		4780
2524	If defined to be C<1>, libev will compile in support for the BSD style	4781	If defined to be C<1>, libev will compile in support for the BSD style
2525	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4782	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2538	otherwise another method will be used as fallback. This is the preferred	4795	otherwise another method will be used as fallback. This is the preferred
2539	backend for Solaris 10 systems.	4796	backend for Solaris 10 systems.
2540		4797
2541	=item EV_USE_DEVPOLL	4798	=item EV_USE_DEVPOLL
2542		4799
2543	reserved for future expansion, works like the USE symbols above.	4800	Reserved for future expansion, works like the USE symbols above.
2544		4801
2545	=item EV_USE_INOTIFY	4802	=item EV_USE_INOTIFY
2546		4803
2547	If defined to be C<1>, libev will compile in support for the Linux inotify	4804	If defined to be C<1>, libev will compile in support for the Linux inotify
2548	interface to speed up C<ev_stat> watchers. Its actual availability will	4805	interface to speed up C<ev_stat> watchers. Its actual availability will
2549	be detected at runtime.	4806	be detected at runtime. If undefined, it will be enabled if the headers
		4807	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2550		4808
		4809	=item EV_NO_SMP
		4810
		4811	If defined to be C<1>, libev will assume that memory is always coherent
		4812	between threads, that is, threads can be used, but threads never run on
		4813	different cpus (or different cpu cores). This reduces dependencies
		4814	and makes libev faster.
		4815
		4816	=item EV_NO_THREADS
		4817
		4818	If defined to be C<1>, libev will assume that it will never be called from
		4819	different threads (that includes signal handlers), which is a stronger
		4820	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4821	libev faster.
		4822
		4823	=item EV_ATOMIC_T
		4824
		4825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4826	access is atomic with respect to other threads or signal contexts. No
		4827	such type is easily found in the C language, so you can provide your own
		4828	type that you know is safe for your purposes. It is used both for signal
		4829	handler "locking" as well as for signal and thread safety in C<ev_async>
		4830	watchers.
		4831
		4832	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4833	(from F<signal.h>), which is usually good enough on most platforms.
		4834
2551	=item EV_H	4835	=item EV_H (h)
2552		4836
2553	The name of the F<ev.h> header file used to include it. The default if	4837	The name of the F<ev.h> header file used to include it. The default if
2554	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to	4838	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2555	virtually rename the F<ev.h> header file in case of conflicts.	4839	used to virtually rename the F<ev.h> header file in case of conflicts.
2556		4840
2557	=item EV_CONFIG_H	4841	=item EV_CONFIG_H (h)
2558		4842
2559	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4843	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2560	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4844	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2561	C<EV_H>, above.	4845	C<EV_H>, above.
2562		4846
2563	=item EV_EVENT_H	4847	=item EV_EVENT_H (h)
2564		4848
2565	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4849	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2566	of how the F<event.h> header can be found, the dfeault is C<"event.h">.	4850	of how the F<event.h> header can be found, the default is C<"event.h">.
2567		4851
2568	=item EV_PROTOTYPES	4852	=item EV_PROTOTYPES (h)
2569		4853
2570	If defined to be C<0>, then F<ev.h> will not define any function	4854	If defined to be C<0>, then F<ev.h> will not define any function
2571	prototypes, but still define all the structs and other symbols. This is	4855	prototypes, but still define all the structs and other symbols. This is
2572	occasionally useful if you want to provide your own wrapper functions	4856	occasionally useful if you want to provide your own wrapper functions
2573	around libev functions.	4857	around libev functions.
…		…
2578	will have the C<struct ev_loop *> as first argument, and you can create	4862	will have the C<struct ev_loop *> as first argument, and you can create
2579	additional independent event loops. Otherwise there will be no support	4863	additional independent event loops. Otherwise there will be no support
2580	for multiple event loops and there is no first event loop pointer	4864	for multiple event loops and there is no first event loop pointer
2581	argument. Instead, all functions act on the single default loop.	4865	argument. Instead, all functions act on the single default loop.
2582		4866
		4867	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4868	default loop when multiplicity is switched off - you always have to
		4869	initialise the loop manually in this case.
		4870
2583	=item EV_MINPRI	4871	=item EV_MINPRI
2584		4872
2585	=item EV_MAXPRI	4873	=item EV_MAXPRI
2586		4874
2587	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4875	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2592	When doing priority-based operations, libev usually has to linearly search	4880	When doing priority-based operations, libev usually has to linearly search
2593	all the priorities, so having many of them (hundreds) uses a lot of space	4881	all the priorities, so having many of them (hundreds) uses a lot of space
2594	and time, so using the defaults of five priorities (-2 .. +2) is usually	4882	and time, so using the defaults of five priorities (-2 .. +2) is usually
2595	fine.	4883	fine.
2596		4884
2597	If your embedding app does not need any priorities, defining these both to	4885	If your embedding application does not need any priorities, defining these
2598	C<0> will save some memory and cpu.	4886	both to C<0> will save some memory and CPU.
2599		4887
2600	=item EV_PERIODIC_ENABLE	4888	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4889	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4890	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2601		4891
2602	If undefined or defined to be C<1>, then periodic timers are supported. If	4892	If undefined or defined to be C<1> (and the platform supports it), then
2603	defined to be C<0>, then they are not. Disabling them saves a few kB of	4893	the respective watcher type is supported. If defined to be C<0>, then it
2604	code.	4894	is not. Disabling watcher types mainly saves code size.
2605		4895
2606	=item EV_IDLE_ENABLE	4896	=item EV_FEATURES
2607
2608	If undefined or defined to be C<1>, then idle watchers are supported. If
2609	defined to be C<0>, then they are not. Disabling them saves a few kB of
2610	code.
2611
2612	=item EV_EMBED_ENABLE
2613
2614	If undefined or defined to be C<1>, then embed watchers are supported. If
2615	defined to be C<0>, then they are not.
2616
2617	=item EV_STAT_ENABLE
2618
2619	If undefined or defined to be C<1>, then stat watchers are supported. If
2620	defined to be C<0>, then they are not.
2621
2622	=item EV_FORK_ENABLE
2623
2624	If undefined or defined to be C<1>, then fork watchers are supported. If
2625	defined to be C<0>, then they are not.
2626
2627	=item EV_MINIMAL
2628		4897
2629	If you need to shave off some kilobytes of code at the expense of some	4898	If you need to shave off some kilobytes of code at the expense of some
2630	speed, define this symbol to C<1>. Currently only used for gcc to override	4899	speed (but with the full API), you can define this symbol to request
2631	some inlining decisions, saves roughly 30% codesize of amd64.	4900	certain subsets of functionality. The default is to enable all features
		4901	that can be enabled on the platform.
		4902
		4903	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4904	with some broad features you want) and then selectively re-enable
		4905	additional parts you want, for example if you want everything minimal,
		4906	but multiple event loop support, async and child watchers and the poll
		4907	backend, use this:
		4908
		4909	#define EV_FEATURES 0
		4910	#define EV_MULTIPLICITY 1
		4911	#define EV_USE_POLL 1
		4912	#define EV_CHILD_ENABLE 1
		4913	#define EV_ASYNC_ENABLE 1
		4914
		4915	The actual value is a bitset, it can be a combination of the following
		4916	values (by default, all of these are enabled):
		4917
		4918	=over 4
		4919
		4920	=item C<1> - faster/larger code
		4921
		4922	Use larger code to speed up some operations.
		4923
		4924	Currently this is used to override some inlining decisions (enlarging the
		4925	code size by roughly 30% on amd64).
		4926
		4927	When optimising for size, use of compiler flags such as C<-Os> with
		4928	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4929	assertions.
		4930
		4931	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4932	(e.g. gcc with C<-Os>).
		4933
		4934	=item C<2> - faster/larger data structures
		4935
		4936	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4937	hash table sizes and so on. This will usually further increase code size
		4938	and can additionally have an effect on the size of data structures at
		4939	runtime.
		4940
		4941	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4942	(e.g. gcc with C<-Os>).
		4943
		4944	=item C<4> - full API configuration
		4945
		4946	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4947	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4948
		4949	=item C<8> - full API
		4950
		4951	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4952	details on which parts of the API are still available without this
		4953	feature, and do not complain if this subset changes over time.
		4954
		4955	=item C<16> - enable all optional watcher types
		4956
		4957	Enables all optional watcher types. If you want to selectively enable
		4958	only some watcher types other than I/O and timers (e.g. prepare,
		4959	embed, async, child...) you can enable them manually by defining
		4960	C<EV_watchertype_ENABLE> to C<1> instead.
		4961
		4962	=item C<32> - enable all backends
		4963
		4964	This enables all backends - without this feature, you need to enable at
		4965	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4966
		4967	=item C<64> - enable OS-specific "helper" APIs
		4968
		4969	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4970	default.
		4971
		4972	=back
		4973
		4974	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4975	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4976	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4977	watchers, timers and monotonic clock support.
		4978
		4979	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4980	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4981	your program might be left out as well - a binary starting a timer and an
		4982	I/O watcher then might come out at only 5Kb.
		4983
		4984	=item EV_API_STATIC
		4985
		4986	If this symbol is defined (by default it is not), then all identifiers
		4987	will have static linkage. This means that libev will not export any
		4988	identifiers, and you cannot link against libev anymore. This can be useful
		4989	when you embed libev, only want to use libev functions in a single file,
		4990	and do not want its identifiers to be visible.
		4991
		4992	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4993	wants to use libev.
		4994
		4995	This option only works when libev is compiled with a C compiler, as C++
		4996	doesn't support the required declaration syntax.
		4997
		4998	=item EV_AVOID_STDIO
		4999
		5000	If this is set to C<1> at compiletime, then libev will avoid using stdio
		5001	functions (printf, scanf, perror etc.). This will increase the code size
		5002	somewhat, but if your program doesn't otherwise depend on stdio and your
		5003	libc allows it, this avoids linking in the stdio library which is quite
		5004	big.
		5005
		5006	Note that error messages might become less precise when this option is
		5007	enabled.
		5008
		5009	=item EV_NSIG
		5010
		5011	The highest supported signal number, +1 (or, the number of
		5012	signals): Normally, libev tries to deduce the maximum number of signals
		5013	automatically, but sometimes this fails, in which case it can be
		5014	specified. Also, using a lower number than detected (C<32> should be
		5015	good for about any system in existence) can save some memory, as libev
		5016	statically allocates some 12-24 bytes per signal number.
2632		5017
2633	=item EV_PID_HASHSIZE	5018	=item EV_PID_HASHSIZE
2634		5019
2635	C<ev_child> watchers use a small hash table to distribute workload by	5020	C<ev_child> watchers use a small hash table to distribute workload by
2636	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	5021	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2637	than enough. If you need to manage thousands of children you might want to	5022	usually more than enough. If you need to manage thousands of children you
2638	increase this value (I<must> be a power of two).	5023	might want to increase this value (I<must> be a power of two).
2639		5024
2640	=item EV_INOTIFY_HASHSIZE	5025	=item EV_INOTIFY_HASHSIZE
2641		5026
2642	C<ev_stat> watchers use a small hash table to distribute workload by	5027	C<ev_stat> watchers use a small hash table to distribute workload by
2643	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	5028	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2644	usually more than enough. If you need to manage thousands of C<ev_stat>	5029	disabled), usually more than enough. If you need to manage thousands of
2645	watchers you might want to increase this value (I<must> be a power of	5030	C<ev_stat> watchers you might want to increase this value (I<must> be a
2646	two).	5031	power of two).
		5032
		5033	=item EV_USE_4HEAP
		5034
		5035	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		5036	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		5037	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		5038	faster performance with many (thousands) of watchers.
		5039
		5040	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		5041	will be C<0>.
		5042
		5043	=item EV_HEAP_CACHE_AT
		5044
		5045	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		5046	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		5047	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		5048	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		5049	but avoids random read accesses on heap changes. This improves performance
		5050	noticeably with many (hundreds) of watchers.
		5051
		5052	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		5053	will be C<0>.
		5054
		5055	=item EV_VERIFY
		5056
		5057	Controls how much internal verification (see C<ev_verify ()>) will
		5058	be done: If set to C<0>, no internal verification code will be compiled
		5059	in. If set to C<1>, then verification code will be compiled in, but not
		5060	called. If set to C<2>, then the internal verification code will be
		5061	called once per loop, which can slow down libev. If set to C<3>, then the
		5062	verification code will be called very frequently, which will slow down
		5063	libev considerably.
		5064
		5065	Verification errors are reported via C's C<assert> mechanism, so if you
		5066	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
		5067
		5068	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		5069	will be C<0>.
2647		5070
2648	=item EV_COMMON	5071	=item EV_COMMON
2649		5072
2650	By default, all watchers have a C<void *data> member. By redefining	5073	By default, all watchers have a C<void *data> member. By redefining
2651	this macro to a something else you can include more and other types of	5074	this macro to something else you can include more and other types of
2652	members. You have to define it each time you include one of the files,	5075	members. You have to define it each time you include one of the files,
2653	though, and it must be identical each time.	5076	though, and it must be identical each time.
2654		5077
2655	For example, the perl EV module uses something like this:	5078	For example, the perl EV module uses something like this:
2656		5079
2657	#define EV_COMMON \	5080	#define EV_COMMON \
2658	SV *self; /* contains this struct */ \	5081	SV *self; /* contains this struct */ \
2659	SV *cb_sv, *fh /* note no trailing ";" */	5082	SV *cb_sv, *fh /* note no trailing ";" */
2660		5083
2661	=item EV_CB_DECLARE (type)	5084	=item EV_CB_DECLARE (type)
2662		5085
2663	=item EV_CB_INVOKE (watcher, revents)	5086	=item EV_CB_INVOKE (watcher, revents)
2664		5087
…		…
2669	definition and a statement, respectively. See the F<ev.h> header file for	5092	definition and a statement, respectively. See the F<ev.h> header file for
2670	their default definitions. One possible use for overriding these is to	5093	their default definitions. One possible use for overriding these is to
2671	avoid the C<struct ev_loop *> as first argument in all cases, or to use	5094	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2672	method calls instead of plain function calls in C++.	5095	method calls instead of plain function calls in C++.
2673		5096
		5097	=back
		5098
2674	=head2 EXPORTED API SYMBOLS	5099	=head2 EXPORTED API SYMBOLS
2675		5100
2676	If you need to re-export the API (e.g. via a dll) and you need a list of	5101	If you need to re-export the API (e.g. via a DLL) and you need a list of
2677	exported symbols, you can use the provided F<Symbol.*> files which list	5102	exported symbols, you can use the provided F<Symbol.*> files which list
2678	all public symbols, one per line:	5103	all public symbols, one per line:
2679		5104
2680	Symbols.ev for libev proper	5105	Symbols.ev for libev proper
2681	Symbols.event for the libevent emulation	5106	Symbols.event for the libevent emulation
2682		5107
2683	This can also be used to rename all public symbols to avoid clashes with	5108	This can also be used to rename all public symbols to avoid clashes with
2684	multiple versions of libev linked together (which is obviously bad in	5109	multiple versions of libev linked together (which is obviously bad in
2685	itself, but sometimes it is inconvinient to avoid this).	5110	itself, but sometimes it is inconvenient to avoid this).
2686		5111
2687	A sed command like this will create wrapper C<#define>'s that you need to	5112	A sed command like this will create wrapper C<#define>'s that you need to
2688	include before including F<ev.h>:	5113	include before including F<ev.h>:
2689		5114
2690	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	5115	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2707	file.	5132	file.
2708		5133
2709	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5134	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2710	that everybody includes and which overrides some configure choices:	5135	that everybody includes and which overrides some configure choices:
2711		5136
2712	#define EV_MINIMAL 1	5137	#define EV_FEATURES 8
2713	#define EV_USE_POLL 0	5138	#define EV_USE_SELECT 1
2714	#define EV_MULTIPLICITY 0
2715	#define EV_PERIODIC_ENABLE 0	5139	#define EV_PREPARE_ENABLE 1
		5140	#define EV_IDLE_ENABLE 1
2716	#define EV_STAT_ENABLE 0	5141	#define EV_SIGNAL_ENABLE 1
2717	#define EV_FORK_ENABLE 0	5142	#define EV_CHILD_ENABLE 1
		5143	#define EV_USE_STDEXCEPT 0
2718	#define EV_CONFIG_H <config.h>	5144	#define EV_CONFIG_H <config.h>
2719	#define EV_MINPRI 0
2720	#define EV_MAXPRI 0
2721		5145
2722	#include "ev++.h"	5146	#include "ev++.h"
2723		5147
2724	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5148	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2725		5149
2726	#include "ev_cpp.h"	5150	#include "ev_cpp.h"
2727	#include "ev.c"	5151	#include "ev.c"
2728		5152
		5153	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2729		5154
2730	=head1 COMPLEXITIES	5155	=head2 THREADS AND COROUTINES
2731		5156
2732	In this section the complexities of (many of) the algorithms used inside	5157	=head3 THREADS
2733	libev will be explained. For complexity discussions about backends see the
2734	documentation for C<ev_default_init>.
2735		5158
2736	All of the following are about amortised time: If an array needs to be	5159	All libev functions are reentrant and thread-safe unless explicitly
2737	extended, libev needs to realloc and move the whole array, but this	5160	documented otherwise, but libev implements no locking itself. This means
2738	happens asymptotically never with higher number of elements, so O(1) might	5161	that you can use as many loops as you want in parallel, as long as there
2739	mean it might do a lengthy realloc operation in rare cases, but on average	5162	are no concurrent calls into any libev function with the same loop
2740	it is much faster and asymptotically approaches constant time.	5163	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5164	of course): libev guarantees that different event loops share no data
		5165	structures that need any locking.
		5166
		5167	Or to put it differently: calls with different loop parameters can be done
		5168	concurrently from multiple threads, calls with the same loop parameter
		5169	must be done serially (but can be done from different threads, as long as
		5170	only one thread ever is inside a call at any point in time, e.g. by using
		5171	a mutex per loop).
		5172
		5173	Specifically to support threads (and signal handlers), libev implements
		5174	so-called C<ev_async> watchers, which allow some limited form of
		5175	concurrency on the same event loop, namely waking it up "from the
		5176	outside".
		5177
		5178	If you want to know which design (one loop, locking, or multiple loops
		5179	without or something else still) is best for your problem, then I cannot
		5180	help you, but here is some generic advice:
2741		5181
2742	=over 4	5182	=over 4
2743		5183
2744	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5184	=item * most applications have a main thread: use the default libev loop
		5185	in that thread, or create a separate thread running only the default loop.
2745		5186
2746	This means that, when you have a watcher that triggers in one hour and	5187	This helps integrating other libraries or software modules that use libev
2747	there are 100 watchers that would trigger before that then inserting will	5188	themselves and don't care/know about threading.
2748	have to skip roughly seven (C<ld 100>) of these watchers.
2749		5189
2750	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5190	=item * one loop per thread is usually a good model.
2751		5191
2752	That means that changing a timer costs less than removing/adding them	5192	Doing this is almost never wrong, sometimes a better-performance model
2753	as only the relative motion in the event queue has to be paid for.	5193	exists, but it is always a good start.
2754		5194
2755	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5195	=item * other models exist, such as the leader/follower pattern, where one
		5196	loop is handed through multiple threads in a kind of round-robin fashion.
2756		5197
2757	These just add the watcher into an array or at the head of a list.	5198	Choosing a model is hard - look around, learn, know that usually you can do
		5199	better than you currently do :-)
2758		5200
2759	=item Stopping check/prepare/idle watchers: O(1)	5201	=item * often you need to talk to some other thread which blocks in the
		5202	event loop.
2760		5203
2761	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5204	C<ev_async> watchers can be used to wake them up from other threads safely
		5205	(or from signal contexts...).
2762		5206
2763	These watchers are stored in lists then need to be walked to find the	5207	An example use would be to communicate signals or other events that only
2764	correct watcher to remove. The lists are usually short (you don't usually	5208	work in the default loop by registering the signal watcher with the
2765	have many watchers waiting for the same fd or signal).	5209	default loop and triggering an C<ev_async> watcher from the default loop
2766		5210	watcher callback into the event loop interested in the signal.
2767	=item Finding the next timer in each loop iteration: O(1)
2768
2769	By virtue of using a binary heap, the next timer is always found at the
2770	beginning of the storage array.
2771
2772	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2773
2774	A change means an I/O watcher gets started or stopped, which requires
2775	libev to recalculate its status (and possibly tell the kernel, depending
2776	on backend and wether C<ev_io_set> was used).
2777
2778	=item Activating one watcher (putting it into the pending state): O(1)
2779
2780	=item Priority handling: O(number_of_priorities)
2781
2782	Priorities are implemented by allocating some space for each
2783	priority. When doing priority-based operations, libev usually has to
2784	linearly search all the priorities, but starting/stopping and activating
2785	watchers becomes O(1) w.r.t. prioritiy handling.
2786		5211
2787	=back	5212	=back
2788		5213
		5214	See also L</THREAD LOCKING EXAMPLE>.
2789		5215
2790	=head1 Win32 platform limitations and workarounds	5216	=head3 COROUTINES
		5217
		5218	Libev is very accommodating to coroutines ("cooperative threads"):
		5219	libev fully supports nesting calls to its functions from different
		5220	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5221	different coroutines, and switch freely between both coroutines running
		5222	the loop, as long as you don't confuse yourself). The only exception is
		5223	that you must not do this from C<ev_periodic> reschedule callbacks.
		5224
		5225	Care has been taken to ensure that libev does not keep local state inside
		5226	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5227	they do not call any callbacks.
		5228
		5229	=head2 COMPILER WARNINGS
		5230
		5231	Depending on your compiler and compiler settings, you might get no or a
		5232	lot of warnings when compiling libev code. Some people are apparently
		5233	scared by this.
		5234
		5235	However, these are unavoidable for many reasons. For one, each compiler
		5236	has different warnings, and each user has different tastes regarding
		5237	warning options. "Warn-free" code therefore cannot be a goal except when
		5238	targeting a specific compiler and compiler-version.
		5239
		5240	Another reason is that some compiler warnings require elaborate
		5241	workarounds, or other changes to the code that make it less clear and less
		5242	maintainable.
		5243
		5244	And of course, some compiler warnings are just plain stupid, or simply
		5245	wrong (because they don't actually warn about the condition their message
		5246	seems to warn about). For example, certain older gcc versions had some
		5247	warnings that resulted in an extreme number of false positives. These have
		5248	been fixed, but some people still insist on making code warn-free with
		5249	such buggy versions.
		5250
		5251	While libev is written to generate as few warnings as possible,
		5252	"warn-free" code is not a goal, and it is recommended not to build libev
		5253	with any compiler warnings enabled unless you are prepared to cope with
		5254	them (e.g. by ignoring them). Remember that warnings are just that:
		5255	warnings, not errors, or proof of bugs.
		5256
		5257
		5258	=head2 VALGRIND
		5259
		5260	Valgrind has a special section here because it is a popular tool that is
		5261	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5262
		5263	If you think you found a bug (memory leak, uninitialised data access etc.)
		5264	in libev, then check twice: If valgrind reports something like:
		5265
		5266	==2274== definitely lost: 0 bytes in 0 blocks.
		5267	==2274== possibly lost: 0 bytes in 0 blocks.
		5268	==2274== still reachable: 256 bytes in 1 blocks.
		5269
		5270	Then there is no memory leak, just as memory accounted to global variables
		5271	is not a memleak - the memory is still being referenced, and didn't leak.
		5272
		5273	Similarly, under some circumstances, valgrind might report kernel bugs
		5274	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5275	although an acceptable workaround has been found here), or it might be
		5276	confused.
		5277
		5278	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5279	make it into some kind of religion.
		5280
		5281	If you are unsure about something, feel free to contact the mailing list
		5282	with the full valgrind report and an explanation on why you think this
		5283	is a bug in libev (best check the archives, too :). However, don't be
		5284	annoyed when you get a brisk "this is no bug" answer and take the chance
		5285	of learning how to interpret valgrind properly.
		5286
		5287	If you need, for some reason, empty reports from valgrind for your project
		5288	I suggest using suppression lists.
		5289
		5290
		5291	=head1 PORTABILITY NOTES
		5292
		5293	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5294
		5295	GNU/Linux is the only common platform that supports 64 bit file/large file
		5296	interfaces but I<disables> them by default.
		5297
		5298	That means that libev compiled in the default environment doesn't support
		5299	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5300
		5301	Unfortunately, many programs try to work around this GNU/Linux issue
		5302	by enabling the large file API, which makes them incompatible with the
		5303	standard libev compiled for their system.
		5304
		5305	Likewise, libev cannot enable the large file API itself as this would
		5306	suddenly make it incompatible to the default compile time environment,
		5307	i.e. all programs not using special compile switches.
		5308
		5309	=head2 OS/X AND DARWIN BUGS
		5310
		5311	The whole thing is a bug if you ask me - basically any system interface
		5312	you touch is broken, whether it is locales, poll, kqueue or even the
		5313	OpenGL drivers.
		5314
		5315	=head3 C<kqueue> is buggy
		5316
		5317	The kqueue syscall is broken in all known versions - most versions support
		5318	only sockets, many support pipes.
		5319
		5320	Libev tries to work around this by not using C<kqueue> by default on this
		5321	rotten platform, but of course you can still ask for it when creating a
		5322	loop - embedding a socket-only kqueue loop into a select-based one is
		5323	probably going to work well.
		5324
		5325	=head3 C<poll> is buggy
		5326
		5327	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5328	implementation by something calling C<kqueue> internally around the 10.5.6
		5329	release, so now C<kqueue> I<and> C<poll> are broken.
		5330
		5331	Libev tries to work around this by not using C<poll> by default on
		5332	this rotten platform, but of course you can still ask for it when creating
		5333	a loop.
		5334
		5335	=head3 C<select> is buggy
		5336
		5337	All that's left is C<select>, and of course Apple found a way to fuck this
		5338	one up as well: On OS/X, C<select> actively limits the number of file
		5339	descriptors you can pass in to 1024 - your program suddenly crashes when
		5340	you use more.
		5341
		5342	There is an undocumented "workaround" for this - defining
		5343	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5344	work on OS/X.
		5345
		5346	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5347
		5348	=head3 C<errno> reentrancy
		5349
		5350	The default compile environment on Solaris is unfortunately so
		5351	thread-unsafe that you can't even use components/libraries compiled
		5352	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5353	defined by default. A valid, if stupid, implementation choice.
		5354
		5355	If you want to use libev in threaded environments you have to make sure
		5356	it's compiled with C<_REENTRANT> defined.
		5357
		5358	=head3 Event port backend
		5359
		5360	The scalable event interface for Solaris is called "event
		5361	ports". Unfortunately, this mechanism is very buggy in all major
		5362	releases. If you run into high CPU usage, your program freezes or you get
		5363	a large number of spurious wakeups, make sure you have all the relevant
		5364	and latest kernel patches applied. No, I don't know which ones, but there
		5365	are multiple ones to apply, and afterwards, event ports actually work
		5366	great.
		5367
		5368	If you can't get it to work, you can try running the program by setting
		5369	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5370	C<select> backends.
		5371
		5372	=head2 AIX POLL BUG
		5373
		5374	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5375	this by trying to avoid the poll backend altogether (i.e. it's not even
		5376	compiled in), which normally isn't a big problem as C<select> works fine
		5377	with large bitsets on AIX, and AIX is dead anyway.
		5378
		5379	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5380
		5381	=head3 General issues
2791		5382
2792	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5383	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2793	requires, and its I/O model is fundamentally incompatible with the POSIX	5384	requires, and its I/O model is fundamentally incompatible with the POSIX
2794	model. Libev still offers limited functionality on this platform in	5385	model. Libev still offers limited functionality on this platform in
2795	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5386	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2796	descriptors. This only applies when using Win32 natively, not when using	5387	descriptors. This only applies when using Win32 natively, not when using
2797	e.g. cygwin.	5388	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5389	as every compiler comes with a slightly differently broken/incompatible
		5390	environment.
		5391
		5392	Lifting these limitations would basically require the full
		5393	re-implementation of the I/O system. If you are into this kind of thing,
		5394	then note that glib does exactly that for you in a very portable way (note
		5395	also that glib is the slowest event library known to man).
2798		5396
2799	There is no supported compilation method available on windows except	5397	There is no supported compilation method available on windows except
2800	embedding it into other applications.	5398	embedding it into other applications.
2801		5399
		5400	Sensible signal handling is officially unsupported by Microsoft - libev
		5401	tries its best, but under most conditions, signals will simply not work.
		5402
		5403	Not a libev limitation but worth mentioning: windows apparently doesn't
		5404	accept large writes: instead of resulting in a partial write, windows will
		5405	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5406	so make sure you only write small amounts into your sockets (less than a
		5407	megabyte seems safe, but this apparently depends on the amount of memory
		5408	available).
		5409
2802	Due to the many, low, and arbitrary limits on the win32 platform and the	5410	Due to the many, low, and arbitrary limits on the win32 platform and
2803	abysmal performance of winsockets, using a large number of sockets is not	5411	the abysmal performance of winsockets, using a large number of sockets
2804	recommended (and not reasonable). If your program needs to use more than	5412	is not recommended (and not reasonable). If your program needs to use
2805	a hundred or so sockets, then likely it needs to use a totally different	5413	more than a hundred or so sockets, then likely it needs to use a totally
2806	implementation for windows, as libev offers the POSIX model, which cannot	5414	different implementation for windows, as libev offers the POSIX readiness
2807	be implemented efficiently on windows (microsoft monopoly games).	5415	notification model, which cannot be implemented efficiently on windows
		5416	(due to Microsoft monopoly games).
2808		5417
2809	=over 4	5418	A typical way to use libev under windows is to embed it (see the embedding
		5419	section for details) and use the following F<evwrap.h> header file instead
		5420	of F<ev.h>:
2810		5421
		5422	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5423	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5424
		5425	#include "ev.h"
		5426
		5427	And compile the following F<evwrap.c> file into your project (make sure
		5428	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5429
		5430	#include "evwrap.h"
		5431	#include "ev.c"
		5432
2811	=item The winsocket select function	5433	=head3 The winsocket C<select> function
2812		5434
2813	The winsocket C<select> function doesn't follow POSIX in that it requires	5435	The winsocket C<select> function doesn't follow POSIX in that it
2814	socket I<handles> and not socket I<file descriptors>. This makes select	5436	requires socket I<handles> and not socket I<file descriptors> (it is
2815	very inefficient, and also requires a mapping from file descriptors	5437	also extremely buggy). This makes select very inefficient, and also
2816	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	5438	requires a mapping from file descriptors to socket handles (the Microsoft
2817	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	5439	C runtime provides the function C<_open_osfhandle> for this). See the
2818	symbols for more info.	5440	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5441	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2819		5442
2820	The configuration for a "naked" win32 using the microsoft runtime	5443	The configuration for a "naked" win32 using the Microsoft runtime
2821	libraries and raw winsocket select is:	5444	libraries and raw winsocket select is:
2822		5445
2823	#define EV_USE_SELECT 1	5446	#define EV_USE_SELECT 1
2824	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5447	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2825		5448
2826	Note that winsockets handling of fd sets is O(n), so you can easily get a	5449	Note that winsockets handling of fd sets is O(n), so you can easily get a
2827	complexity in the O(n²) range when using win32.	5450	complexity in the O(n²) range when using win32.
2828		5451
2829	=item Limited number of file descriptors	5452	=head3 Limited number of file descriptors
2830		5453
2831	Windows has numerous arbitrary (and low) limits on things. Early versions	5454	Windows has numerous arbitrary (and low) limits on things.
2832	of winsocket's select only supported waiting for a max. of C<64> handles	5455
		5456	Early versions of winsocket's select only supported waiting for a maximum
2833	(probably owning to the fact that all windows kernels can only wait for	5457	of C<64> handles (probably owning to the fact that all windows kernels
2834	C<64> things at the same time internally; microsoft recommends spawning a	5458	can only wait for C<64> things at the same time internally; Microsoft
2835	chain of threads and wait for 63 handles and the previous thread in each).	5459	recommends spawning a chain of threads and wait for 63 handles and the
		5460	previous thread in each. Sounds great!).
2836		5461
2837	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5462	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2838	to some high number (e.g. C<2048>) before compiling the winsocket select	5463	to some high number (e.g. C<2048>) before compiling the winsocket select
2839	call (which might be in libev or elsewhere, for example, perl does its own	5464	call (which might be in libev or elsewhere, for example, perl and many
2840	select emulation on windows).	5465	other interpreters do their own select emulation on windows).
2841		5466
2842	Another limit is the number of file descriptors in the microsoft runtime	5467	Another limit is the number of file descriptors in the Microsoft runtime
2843	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5468	libraries, which by default is C<64> (there must be a hidden I<64>
2844	or something like this inside microsoft). You can increase this by calling	5469	fetish or something like this inside Microsoft). You can increase this
2845	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5470	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2846	arbitrary limit), but is broken in many versions of the microsoft runtime	5471	(another arbitrary limit), but is broken in many versions of the Microsoft
2847	libraries.
2848
2849	This might get you to about C<512> or C<2048> sockets (depending on	5472	runtime libraries. This might get you to about C<512> or C<2048> sockets
2850	windows version and/or the phase of the moon). To get more, you need to	5473	(depending on windows version and/or the phase of the moon). To get more,
2851	wrap all I/O functions and provide your own fd management, but the cost of	5474	you need to wrap all I/O functions and provide your own fd management, but
2852	calling select (O(n²)) will likely make this unworkable.	5475	the cost of calling select (O(n²)) will likely make this unworkable.
		5476
		5477	=head2 PORTABILITY REQUIREMENTS
		5478
		5479	In addition to a working ISO-C implementation and of course the
		5480	backend-specific APIs, libev relies on a few additional extensions:
		5481
		5482	=over 4
		5483
		5484	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5485	calling conventions regardless of C<ev_watcher_type *>.
		5486
		5487	Libev assumes not only that all watcher pointers have the same internal
		5488	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5489	assumes that the same (machine) code can be used to call any watcher
		5490	callback: The watcher callbacks have different type signatures, but libev
		5491	calls them using an C<ev_watcher *> internally.
		5492
		5493	=item null pointers and integer zero are represented by 0 bytes
		5494
		5495	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5496	relies on this setting pointers and integers to null.
		5497
		5498	=item pointer accesses must be thread-atomic
		5499
		5500	Accessing a pointer value must be atomic, it must both be readable and
		5501	writable in one piece - this is the case on all current architectures.
		5502
		5503	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5504
		5505	The type C<sig_atomic_t volatile> (or whatever is defined as
		5506	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5507	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5508	believed to be sufficiently portable.
		5509
		5510	=item C<sigprocmask> must work in a threaded environment
		5511
		5512	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5513	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5514	pthread implementations will either allow C<sigprocmask> in the "main
		5515	thread" or will block signals process-wide, both behaviours would
		5516	be compatible with libev. Interaction between C<sigprocmask> and
		5517	C<pthread_sigmask> could complicate things, however.
		5518
		5519	The most portable way to handle signals is to block signals in all threads
		5520	except the initial one, and run the signal handling loop in the initial
		5521	thread as well.
		5522
		5523	=item C<long> must be large enough for common memory allocation sizes
		5524
		5525	To improve portability and simplify its API, libev uses C<long> internally
		5526	instead of C<size_t> when allocating its data structures. On non-POSIX
		5527	systems (Microsoft...) this might be unexpectedly low, but is still at
		5528	least 31 bits everywhere, which is enough for hundreds of millions of
		5529	watchers.
		5530
		5531	=item C<double> must hold a time value in seconds with enough accuracy
		5532
		5533	The type C<double> is used to represent timestamps. It is required to
		5534	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5535	good enough for at least into the year 4000 with millisecond accuracy
		5536	(the design goal for libev). This requirement is overfulfilled by
		5537	implementations using IEEE 754, which is basically all existing ones.
		5538
		5539	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5540	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5541	is either obsolete or somebody patched it to use C<long double> or
		5542	something like that, just kidding).
2853		5543
2854	=back	5544	=back
2855		5545
		5546	If you know of other additional requirements drop me a note.
		5547
		5548
		5549	=head1 ALGORITHMIC COMPLEXITIES
		5550
		5551	In this section the complexities of (many of) the algorithms used inside
		5552	libev will be documented. For complexity discussions about backends see
		5553	the documentation for C<ev_default_init>.
		5554
		5555	All of the following are about amortised time: If an array needs to be
		5556	extended, libev needs to realloc and move the whole array, but this
		5557	happens asymptotically rarer with higher number of elements, so O(1) might
		5558	mean that libev does a lengthy realloc operation in rare cases, but on
		5559	average it is much faster and asymptotically approaches constant time.
		5560
		5561	=over 4
		5562
		5563	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5564
		5565	This means that, when you have a watcher that triggers in one hour and
		5566	there are 100 watchers that would trigger before that, then inserting will
		5567	have to skip roughly seven (C<ld 100>) of these watchers.
		5568
		5569	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5570
		5571	That means that changing a timer costs less than removing/adding them,
		5572	as only the relative motion in the event queue has to be paid for.
		5573
		5574	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5575
		5576	These just add the watcher into an array or at the head of a list.
		5577
		5578	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5579
		5580	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5581
		5582	These watchers are stored in lists, so they need to be walked to find the
		5583	correct watcher to remove. The lists are usually short (you don't usually
		5584	have many watchers waiting for the same fd or signal: one is typical, two
		5585	is rare).
		5586
		5587	=item Finding the next timer in each loop iteration: O(1)
		5588
		5589	By virtue of using a binary or 4-heap, the next timer is always found at a
		5590	fixed position in the storage array.
		5591
		5592	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5593
		5594	A change means an I/O watcher gets started or stopped, which requires
		5595	libev to recalculate its status (and possibly tell the kernel, depending
		5596	on backend and whether C<ev_io_set> was used).
		5597
		5598	=item Activating one watcher (putting it into the pending state): O(1)
		5599
		5600	=item Priority handling: O(number_of_priorities)
		5601
		5602	Priorities are implemented by allocating some space for each
		5603	priority. When doing priority-based operations, libev usually has to
		5604	linearly search all the priorities, but starting/stopping and activating
		5605	watchers becomes O(1) with respect to priority handling.
		5606
		5607	=item Sending an ev_async: O(1)
		5608
		5609	=item Processing ev_async_send: O(number_of_async_watchers)
		5610
		5611	=item Processing signals: O(max_signal_number)
		5612
		5613	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5614	calls in the current loop iteration and the loop is currently
		5615	blocked. Checking for async and signal events involves iterating over all
		5616	running async watchers or all signal numbers.
		5617
		5618	=back
		5619
		5620
		5621	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5622
		5623	The major version 4 introduced some incompatible changes to the API.
		5624
		5625	At the moment, the C<ev.h> header file provides compatibility definitions
		5626	for all changes, so most programs should still compile. The compatibility
		5627	layer might be removed in later versions of libev, so better update to the
		5628	new API early than late.
		5629
		5630	=over 4
		5631
		5632	=item C<EV_COMPAT3> backwards compatibility mechanism
		5633
		5634	The backward compatibility mechanism can be controlled by
		5635	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5636	section.
		5637
		5638	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5639
		5640	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5641
		5642	ev_loop_destroy (EV_DEFAULT_UC);
		5643	ev_loop_fork (EV_DEFAULT);
		5644
		5645	=item function/symbol renames
		5646
		5647	A number of functions and symbols have been renamed:
		5648
		5649	ev_loop => ev_run
		5650	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5651	EVLOOP_ONESHOT => EVRUN_ONCE
		5652
		5653	ev_unloop => ev_break
		5654	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5655	EVUNLOOP_ONE => EVBREAK_ONE
		5656	EVUNLOOP_ALL => EVBREAK_ALL
		5657
		5658	EV_TIMEOUT => EV_TIMER
		5659
		5660	ev_loop_count => ev_iteration
		5661	ev_loop_depth => ev_depth
		5662	ev_loop_verify => ev_verify
		5663
		5664	Most functions working on C<struct ev_loop> objects don't have an
		5665	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5666	associated constants have been renamed to not collide with the C<struct
		5667	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5668	as all other watcher types. Note that C<ev_loop_fork> is still called
		5669	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5670	typedef.
		5671
		5672	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5673
		5674	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5675	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5676	and work, but the library code will of course be larger.
		5677
		5678	=back
		5679
		5680
		5681	=head1 GLOSSARY
		5682
		5683	=over 4
		5684
		5685	=item active
		5686
		5687	A watcher is active as long as it has been started and not yet stopped.
		5688	See L</WATCHER STATES> for details.
		5689
		5690	=item application
		5691
		5692	In this document, an application is whatever is using libev.
		5693
		5694	=item backend
		5695
		5696	The part of the code dealing with the operating system interfaces.
		5697
		5698	=item callback
		5699
		5700	The address of a function that is called when some event has been
		5701	detected. Callbacks are being passed the event loop, the watcher that
		5702	received the event, and the actual event bitset.
		5703
		5704	=item callback/watcher invocation
		5705
		5706	The act of calling the callback associated with a watcher.
		5707
		5708	=item event
		5709
		5710	A change of state of some external event, such as data now being available
		5711	for reading on a file descriptor, time having passed or simply not having
		5712	any other events happening anymore.
		5713
		5714	In libev, events are represented as single bits (such as C<EV_READ> or
		5715	C<EV_TIMER>).
		5716
		5717	=item event library
		5718
		5719	A software package implementing an event model and loop.
		5720
		5721	=item event loop
		5722
		5723	An entity that handles and processes external events and converts them
		5724	into callback invocations.
		5725
		5726	=item event model
		5727
		5728	The model used to describe how an event loop handles and processes
		5729	watchers and events.
		5730
		5731	=item pending
		5732
		5733	A watcher is pending as soon as the corresponding event has been
		5734	detected. See L</WATCHER STATES> for details.
		5735
		5736	=item real time
		5737
		5738	The physical time that is observed. It is apparently strictly monotonic :)
		5739
		5740	=item wall-clock time
		5741
		5742	The time and date as shown on clocks. Unlike real time, it can actually
		5743	be wrong and jump forwards and backwards, e.g. when you adjust your
		5744	clock.
		5745
		5746	=item watcher
		5747
		5748	A data structure that describes interest in certain events. Watchers need
		5749	to be started (attached to an event loop) before they can receive events.
		5750
		5751	=back
2856		5752
2857	=head1 AUTHOR	5753	=head1 AUTHOR
2858		5754
2859	Marc Lehmann <libev@schmorp.de>.	5755	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5756	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2860		5757

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