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Revision 1.322 by root, Sun Oct 24 17:58:41 2010 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	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	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
…		…
70	=head2 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	104	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	105	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(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	107	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	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
82		111
83	It also is quite fast (see this	112	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	114	for example).
86		115
87	=head2 CONVENTIONS	116	=head2 CONVENTIONS
88		117
89	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	121	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>	122	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.	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		124	this argument.
95		125
96	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
97		127
98	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	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	130	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	131	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	132	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	133	any calculations on it, you should treat it as some floating point value.
		134
104	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
		157
106		158
107	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
108		160
109	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
110	library in any way.	162	library in any way.
…		…
113		165
114	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
115		167
116	Returns the current time as libev would use it. Please note that the	168	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	169	C<ev_now> function is usually faster and also often returns the timestamp
118	you actually want to know.	170	you actually want to know. Also interesting is the combination of
		171	C<ev_update_now> and C<ev_now>.
119		172
120	=item ev_sleep (ev_tstamp interval)	173	=item ev_sleep (ev_tstamp interval)
121		174
122	Sleep for the given interval: The current thread will be blocked until	175	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	176	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	177	this is a sub-second-resolution C<sleep ()>.
125		178
126	=item int ev_version_major ()	179	=item int ev_version_major ()
127		180
128	=item int ev_version_minor ()	181	=item int ev_version_minor ()
129		182
…		…
140	as this indicates an incompatible change. Minor versions are usually	193	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	194	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	195	not a problem.
143		196
144	Example: Make sure we haven't accidentally been linked against the wrong	197	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	198	version (note, however, that this will not detect other ABI mismatches,
		199	such as LFS or reentrancy).
146		200
147	assert (("libev version mismatch",	201	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	202	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	203	&& ev_version_minor () >= EV_VERSION_MINOR));
150		204
151	=item unsigned int ev_supported_backends ()	205	=item unsigned int ev_supported_backends ()
152		206
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	207	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	208	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	210	a description of the set values.
157		211
158	Example: make sure we have the epoll method, because yeah this is cool and	212	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	213	a must have and can we have a torrent of it please!!!11
160		214
161	assert (("sorry, no epoll, no sex",	215	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	216	ev_supported_backends () & EVBACKEND_EPOLL));
163		217
164	=item unsigned int ev_recommended_backends ()	218	=item unsigned int ev_recommended_backends ()
165		219
166	Return the set of all backends compiled into this binary of libev and also	220	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	221	also recommended for this platform, meaning it will work for most file
		222	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	223	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	224	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	225	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.	226	probe for if you specify no backends explicitly.
172		227
173	=item unsigned int ev_embeddable_backends ()	228	=item unsigned int ev_embeddable_backends ()
174		229
175	Returns the set of backends that are embeddable in other event loops. This	230	Returns the set of backends that are embeddable in other event loops. This
176	is the theoretical, all-platform, value. To find which backends	231	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	232	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	233	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	234	& ev_supported_backends ()>, likewise for recommended ones.
180		235
181	See the description of C<ev_embed> watchers for more info.	236	See the description of C<ev_embed> watchers for more info.
182		237
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		239
185	Sets the allocation function to use (the prototype is similar - the	240	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	241	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	242	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	243	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	244	or take some potentially destructive action.
190	function.	245
		246	Since some systems (at least OpenBSD and Darwin) fail to implement
		247	correct C<realloc> semantics, libev will use a wrapper around the system
		248	C<realloc> and C<free> functions by default.
191		249
192	You could override this function in high-availability programs to, say,	250	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,	251	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.	252	or even to sleep a while and retry until some memory is available.
195		253
196	Example: Replace the libev allocator with one that waits a bit and then	254	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	255	retries (example requires a standards-compliant C<realloc>).
198		256
199	static void *	257	static void *
200	persistent_realloc (void *ptr, size_t size)	258	persistent_realloc (void *ptr, size_t size)
201	{	259	{
202	for (;;)	260	for (;;)
…		…
211	}	269	}
212		270
213	...	271	...
214	ev_set_allocator (persistent_realloc);	272	ev_set_allocator (persistent_realloc);
215		273
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		275
218	Set the callback function to call on a retryable syscall error (such	276	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	277	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	278	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	279	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	280	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	281	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	282	(such as abort).
225		283
226	Example: This is basically the same thing that libev does internally, too.	284	Example: This is basically the same thing that libev does internally, too.
…		…
235	...	293	...
236	ev_set_syserr_cb (fatal_error);	294	ev_set_syserr_cb (fatal_error);
237		295
238	=back	296	=back
239		297
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		299
242	An event loop is described by a C<struct ev_loop *>. The library knows two	300	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	301	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	302	libev 3 had an C<ev_loop> function colliding with the struct name).
245		303
246	If you use threads, a common model is to run the default event loop	304	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	305	supports signals and child events, and dynamically created event loops
248	create, you also create another event loop. Libev itself does no locking	306	which 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		307
253	=over 4	308	=over 4
254		309
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	310	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		311
257	This will initialise the default event loop if it hasn't been initialised	312	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	313	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	314	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).	315	C<ev_loop_new>.
		316
		317	If the default loop is already initialised then this function simply
		318	returns it (and ignores the flags. If that is troubling you, check
		319	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		320	flags, which should almost always be C<0>, unless the caller is also the
		321	one calling C<ev_run> or otherwise qualifies as "the main program".
261		322
262	If you don't know what event loop to use, use the one returned from this	323	If you don't know what event loop to use, use the one returned from this
263	function.	324	function (or via the C<EV_DEFAULT> macro).
264		325
		326	Note that this function is I<not> thread-safe, so if you want to use it
		327	from multiple threads, you have to employ some kind of mutex (note also
		328	that this case is unlikely, as loops cannot be shared easily between
		329	threads anyway).
		330
265	The default loop is the only loop that can handle C<ev_signal> and	331	The default loop is the only loop that can handle C<ev_child> watchers,
266	C<ev_child> watchers, and to do this, it always registers a handler	332	and to do this, it always registers a handler for C<SIGCHLD>. If this is
267	for C<SIGCHLD>. If this is a problem for your app you can either	333	a problem for your application you can either create a dynamic loop with
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	334	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	335	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
270	C<ev_default_init>.	336
		337	Example: This is the most typical usage.
		338
		339	if (!ev_default_loop (0))
		340	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		341
		342	Example: Restrict libev to the select and poll backends, and do not allow
		343	environment settings to be taken into account:
		344
		345	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		346
		347	Example: Use whatever libev has to offer, but make sure that kqueue is
		348	used if available (warning, breaks stuff, best use only with your own
		349	private event loop and only if you know the OS supports your types of
		350	fds):
		351
		352	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
		353
		354	=item struct ev_loop *ev_loop_new (unsigned int flags)
		355
		356	This will create and initialise a new event loop object. If the loop
		357	could not be initialised, returns false.
		358
		359	Note that this function I<is> thread-safe, and one common way to use
		360	libev with threads is indeed to create one loop per thread, and using the
		361	default loop in the "main" or "initial" thread.
271		362
272	The flags argument can be used to specify special behaviour or specific	363	The flags argument can be used to specify special behaviour or specific
273	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	364	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
274		365
275	The following flags are supported:	366	The following flags are supported:
…		…
281	The default flags value. Use this if you have no clue (it's the right	372	The default flags value. Use this if you have no clue (it's the right
282	thing, believe me).	373	thing, believe me).
283		374
284	=item C<EVFLAG_NOENV>	375	=item C<EVFLAG_NOENV>
285		376
286	If this flag bit is ored into the flag value (or the program runs setuid	377	If this flag bit is or'ed into the flag value (or the program runs setuid
287	or setgid) then libev will I<not> look at the environment variable	378	or setgid) then libev will I<not> look at the environment variable
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	379	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	override the flags completely if it is found in the environment. This is	380	override the flags completely if it is found in the environment. This is
290	useful to try out specific backends to test their performance, or to work	381	useful to try out specific backends to test their performance, or to work
291	around bugs.	382	around bugs.
292		383
293	=item C<EVFLAG_FORKCHECK>	384	=item C<EVFLAG_FORKCHECK>
294		385
295	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	386	Instead of calling C<ev_loop_fork> manually after a fork, you can also
296	a fork, you can also make libev check for a fork in each iteration by	387	make libev check for a fork in each iteration by enabling this flag.
297	enabling this flag.
298		388
299	This works by calling C<getpid ()> on every iteration of the loop,	389	This works by calling C<getpid ()> on every iteration of the loop,
300	and thus this might slow down your event loop if you do a lot of loop	390	and thus this might slow down your event loop if you do a lot of loop
301	iterations and little real work, but is usually not noticeable (on my	391	iterations and little real work, but is usually not noticeable (on my
302	Linux system for example, C<getpid> is actually a simple 5-insn sequence	392	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
303	without a syscall and thus I<very> fast, but my Linux system also has	393	without a system call and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	394	C<pthread_atfork> which is even faster).
305		395
306	The big advantage of this flag is that you can forget about fork (and	396	The big advantage of this flag is that you can forget about fork (and
307	forget about forgetting to tell libev about forking) when you use this	397	forget about forgetting to tell libev about forking) when you use this
308	flag.	398	flag.
309		399
310	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	400	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
311	environment variable.	401	environment variable.
		402
		403	=item C<EVFLAG_NOINOTIFY>
		404
		405	When this flag is specified, then libev will not attempt to use the
		406	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		407	testing, this flag can be useful to conserve inotify file descriptors, as
		408	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		409
		410	=item C<EVFLAG_SIGNALFD>
		411
		412	When this flag is specified, then libev will attempt to use the
		413	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		414	delivers signals synchronously, which makes it both faster and might make
		415	it possible to get the queued signal data. It can also simplify signal
		416	handling with threads, as long as you properly block signals in your
		417	threads that are not interested in handling them.
		418
		419	Signalfd will not be used by default as this changes your signal mask, and
		420	there are a lot of shoddy libraries and programs (glib's threadpool for
		421	example) that can't properly initialise their signal masks.
312		422
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	423	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		424
315	This is your standard select(2) backend. Not I<completely> standard, as	425	This is your standard select(2) backend. Not I<completely> standard, as
316	libev tries to roll its own fd_set with no limits on the number of fds,	426	libev tries to roll its own fd_set with no limits on the number of fds,
317	but if that fails, expect a fairly low limit on the number of fds when	427	but if that fails, expect a fairly low limit on the number of fds when
318	using this backend. It doesn't scale too well (O(highest_fd)), but its	428	using this backend. It doesn't scale too well (O(highest_fd)), but its
319	usually the fastest backend for a low number of (low-numbered :) fds.	429	usually the fastest backend for a low number of (low-numbered :) fds.
320		430
321	To get good performance out of this backend you need a high amount of	431	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	432	parallelism (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	433	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	434	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	435	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	436	readiness notifications you get per iteration.
		437
		438	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		439	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		440	C<exceptfds> set on that platform).
327		441
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	442	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		443
330	And this is your standard poll(2) backend. It's more complicated	444	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	445	than select, but handles sparse fds better and has no artificial
332	limit on the number of fds you can use (except it will slow down	446	limit on the number of fds you can use (except it will slow down
333	considerably with a lot of inactive fds). It scales similarly to select,	447	considerably with a lot of inactive fds). It scales similarly to select,
334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	448	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	449	performance tips.
336		450
		451	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		452	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		453
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	454	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		455
		456	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		457	kernels).
338		458
339	For few fds, this backend is a bit little slower than poll and select,	459	For few fds, this backend is a bit little slower than poll and select,
340	but it scales phenomenally better. While poll and select usually scale	460	but it scales phenomenally better. While poll and select usually scale
341	like O(total_fds) where n is the total number of fds (or the highest fd),	461	like O(total_fds) where n is the total number of fds (or the highest fd),
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	462	epoll scales either O(1) or O(active_fds).
343	of shortcomings, such as silently dropping events in some hard-to-detect	463
344	cases and rewiring a syscall per fd change, no fork support and bad	464	The epoll mechanism deserves honorable mention as the most misdesigned
345	support for dup.	465	of the more advanced event mechanisms: mere annoyances include silently
		466	dropping file descriptors, requiring a system call per change per file
		467	descriptor (and unnecessary guessing of parameters), problems with dup and
		468	so on. The biggest issue is fork races, however - if a program forks then
		469	I<both> parent and child process have to recreate the epoll set, which can
		470	take considerable time (one syscall per file descriptor) and is of course
		471	hard to detect.
		472
		473	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		474	of course I<doesn't>, and epoll just loves to report events for totally
		475	I<different> file descriptors (even already closed ones, so one cannot
		476	even remove them from the set) than registered in the set (especially
		477	on SMP systems). Libev tries to counter these spurious notifications by
		478	employing an additional generation counter and comparing that against the
		479	events to filter out spurious ones, recreating the set when required. Last
		480	not least, it also refuses to work with some file descriptors which work
		481	perfectly fine with C<select> (files, many character devices...).
346		482
347	While stopping, setting and starting an I/O watcher in the same iteration	483	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	484	will result in some caching, there is still a system call per such
349	(because the fd could point to a different file description now), so its	485	incident (because the same I<file descriptor> could point to a different
350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	486	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
351	very well if you register events for both fds.	487	file descriptors might not work very well if you register events for both
352		488	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		489
357	Best performance from this backend is achieved by not unregistering all	490	Best performance from this backend is achieved by not unregistering all
358	watchers for a file descriptor until it has been closed, if possible, i.e.	491	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	492	i.e. keep at least one watcher active per fd at all times. Stopping and
		493	starting a watcher (without re-setting it) also usually doesn't cause
		494	extra overhead. A fork can both result in spurious notifications as well
		495	as in libev having to destroy and recreate the epoll object, which can
		496	take considerable time and thus should be avoided.
360		497
		498	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		499	faster than epoll for maybe up to a hundred file descriptors, depending on
		500	the usage. So sad.
		501
361	While nominally embeddeble in other event loops, this feature is broken in	502	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	503	all kernel versions tested so far.
		504
		505	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		506	C<EVBACKEND_POLL>.
363		507
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	508	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		509
366	Kqueue deserves special mention, as at the time of this writing, it	510	Kqueue deserves special mention, as at the time of this writing, it
367	was broken on all BSDs except NetBSD (usually it doesn't work reliably	511	was broken on all BSDs except NetBSD (usually it doesn't work reliably
368	with anything but sockets and pipes, except on Darwin, where of course	512	with anything but sockets and pipes, except on Darwin, where of course
369	it's completely useless). For this reason it's not being "autodetected"	513	it's completely useless). Unlike epoll, however, whose brokenness
		514	is by design, these kqueue bugs can (and eventually will) be fixed
		515	without API changes to existing programs. For this reason it's not being
370	unless you explicitly specify it explicitly in the flags (i.e. using	516	"auto-detected" unless you explicitly specify it in the flags (i.e. using
371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	517	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
372	system like NetBSD.	518	system like NetBSD.
373		519
374	You still can embed kqueue into a normal poll or select backend and use it	520	You still can embed kqueue into a normal poll or select backend and use it
375	only for sockets (after having made sure that sockets work with kqueue on	521	only for sockets (after having made sure that sockets work with kqueue on
376	the target platform). See C<ev_embed> watchers for more info.	522	the target platform). See C<ev_embed> watchers for more info.
377		523
378	It scales in the same way as the epoll backend, but the interface to the	524	It scales in the same way as the epoll backend, but the interface to the
379	kernel is more efficient (which says nothing about its actual speed, of	525	kernel is more efficient (which says nothing about its actual speed, of
380	course). While stopping, setting and starting an I/O watcher does never	526	course). While stopping, setting and starting an I/O watcher does never
381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	527	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
382	two event changes per incident, support for C<fork ()> is very bad and it	528	two event changes per incident. Support for C<fork ()> is very bad (but
383	drops fds silently in similarly hard-to-detect cases.	529	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		530	cases
384		531
385	This backend usually performs well under most conditions.	532	This backend usually performs well under most conditions.
386		533
387	While nominally embeddable in other event loops, this doesn't work	534	While nominally embeddable in other event loops, this doesn't work
388	everywhere, so you might need to test for this. And since it is broken	535	everywhere, so you might need to test for this. And since it is broken
389	almost everywhere, you should only use it when you have a lot of sockets	536	almost everywhere, you should only use it when you have a lot of sockets
390	(for which it usually works), by embedding it into another event loop	537	(for which it usually works), by embedding it into another event loop
391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	538	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	539	also broken on OS X)) and, did I mention it, using it only for sockets.
		540
		541	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		542	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		543	C<NOTE_EOF>.
393		544
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	545	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		546
396	This is not implemented yet (and might never be, unless you send me an	547	This is not implemented yet (and might never be, unless you send me an
397	implementation). According to reports, C</dev/poll> only supports sockets	548	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	552	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		553
403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	554	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
404	it's really slow, but it still scales very well (O(active_fds)).	555	it's really slow, but it still scales very well (O(active_fds)).
405		556
406	Please note that solaris event ports can deliver a lot of spurious	557	Please note that Solaris event ports can deliver a lot of spurious
407	notifications, so you need to use non-blocking I/O or other means to avoid	558	notifications, so you need to use non-blocking I/O or other means to avoid
408	blocking when no data (or space) is available.	559	blocking when no data (or space) is available.
409		560
410	While this backend scales well, it requires one system call per active	561	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	562	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	563	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	564	might perform better.
414		565
415	On the positive side, ignoring the spurious readyness notifications, this	566	On the positive side, with the exception of the spurious readiness
416	backend actually performed to specification in all tests and is fully	567	notifications, this backend actually performed fully to specification
417	embeddable, which is a rare feat among the OS-specific backends.	568	in all tests and is fully embeddable, which is a rare feat among the
		569	OS-specific backends (I vastly prefer correctness over speed hacks).
		570
		571	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		572	C<EVBACKEND_POLL>.
418		573
419	=item C<EVBACKEND_ALL>	574	=item C<EVBACKEND_ALL>
420		575
421	Try all backends (even potentially broken ones that wouldn't be tried	576	Try all backends (even potentially broken ones that wouldn't be tried
422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	577	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
424		579
425	It is definitely not recommended to use this flag.	580	It is definitely not recommended to use this flag.
426		581
427	=back	582	=back
428		583
429	If one or more of these are ored into the flags value, then only these	584	If one or more of the backend flags are or'ed into the flags value,
430	backends will be tried (in the reverse order as listed here). If none are	585	then only these backends will be tried (in the reverse order as listed
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	586	here). If none are specified, all backends in C<ev_recommended_backends
432		587	()> will be tried.
433	The most typical usage is like this:
434
435	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437
438	Restrict libev to the select and poll backends, and do not allow
439	environment settings to be taken into account:
440
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442
443	Use whatever libev has to offer, but make sure that kqueue is used if
444	available (warning, breaks stuff, best use only with your own private
445	event loop and only if you know the OS supports your types of fds):
446
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448
449	=item struct ev_loop *ev_loop_new (unsigned int flags)
450
451	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).
455		588
456	Example: Try to create a event loop that uses epoll and nothing else.	589	Example: Try to create a event loop that uses epoll and nothing else.
457		590
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	591	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	592	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	593	fatal ("no epoll found here, maybe it hides under your chair");
461		594
462	=item ev_default_destroy ()	595	=item ev_loop_destroy (loop)
463		596
464	Destroys the default loop again (frees all memory and kernel state	597	Destroys an event loop object (frees all memory and kernel state
465	etc.). None of the active event watchers will be stopped in the normal	598	etc.). None of the active event watchers will be stopped in the normal
466	sense, so e.g. C<ev_is_active> might still return true. It is your	599	sense, so e.g. C<ev_is_active> might still return true. It is your
467	responsibility to either stop all watchers cleanly yoursef I<before>	600	responsibility to either stop all watchers cleanly yourself I<before>
468	calling this function, or cope with the fact afterwards (which is usually	601	calling this function, or cope with the fact afterwards (which is usually
469	the easiest thing, you can just ignore the watchers and/or C<free ()> them	602	the easiest thing, you can just ignore the watchers and/or C<free ()> them
470	for example).	603	for example).
471		604
472	Note that certain global state, such as signal state, will not be freed by	605	Note that certain global state, such as signal state (and installed signal
473	this function, and related watchers (such as signal and child watchers)	606	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	607	as signal and child watchers) would need to be stopped manually.
475		608
476	In general it is not advisable to call this function except in the	609	This function is normally used on loop objects allocated by
477	rare occasion where you really need to free e.g. the signal handling	610	C<ev_loop_new>, but it can also be used on the default loop returned by
		611	C<ev_default_loop>, in which case it is not thread-safe.
		612
		613	Note that it is not advisable to call this function on the default loop
		614	except in the rare occasion where you really need to free it's resources.
478	pipe fds. If you need dynamically allocated loops it is better to use	615	If you need dynamically allocated loops it is better to use C<ev_loop_new>
479	C<ev_loop_new> and C<ev_loop_destroy>).	616	and C<ev_loop_destroy>.
480		617
481	=item ev_loop_destroy (loop)	618	=item ev_loop_fork (loop)
482		619
483	Like C<ev_default_destroy>, but destroys an event loop created by an
484	earlier call to C<ev_loop_new>.
485
486	=item ev_default_fork ()
487
488	This function sets a flag that causes subsequent C<ev_loop> iterations	620	This function sets a flag that causes subsequent C<ev_run> iterations to
489	to reinitialise the kernel state for backends that have one. Despite the	621	reinitialise the kernel state for backends that have one. Despite the
490	name, you can call it anytime, but it makes most sense after forking, in	622	name, you can call it anytime, but it makes most sense after forking, in
491	the child process (or both child and parent, but that again makes little	623	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
492	sense). You I<must> call it in the child before using any of the libev	624	child before resuming or calling C<ev_run>.
493	functions, and it will only take effect at the next C<ev_loop> iteration.	625
		626	Again, you I<have> to call it on I<any> loop that you want to re-use after
		627	a fork, I<even if you do not plan to use the loop in the parent>. This is
		628	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		629	during fork.
494		630
495	On the other hand, you only need to call this function in the child	631	On the other hand, you only need to call this function in the child
496	process if and only if you want to use the event library in the child. If	632	process if and only if you want to use the event loop in the child. If
497	you just fork+exec, you don't have to call it at all.	633	you just fork+exec or create a new loop in the child, you don't have to
		634	call it at all (in fact, C<epoll> is so badly broken that it makes a
		635	difference, but libev will usually detect this case on its own and do a
		636	costly reset of the backend).
498		637
499	The function itself is quite fast and it's usually not a problem to call	638	The function itself is quite fast and it's usually not a problem to call
500	it just in case after a fork. To make this easy, the function will fit in	639	it just in case after a fork.
501	quite nicely into a call to C<pthread_atfork>:
502		640
		641	Example: Automate calling C<ev_loop_fork> on the default loop when
		642	using pthreads.
		643
		644	static void
		645	post_fork_child (void)
		646	{
		647	ev_loop_fork (EV_DEFAULT);
		648	}
		649
		650	...
503	pthread_atfork (0, 0, ev_default_fork);	651	pthread_atfork (0, 0, post_fork_child);
504		652
505	=item ev_loop_fork (loop)	653	=item int ev_is_default_loop (loop)
506		654
507	Like C<ev_default_fork>, but acts on an event loop created by	655	Returns true when the given loop is, in fact, the default loop, and false
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	656	otherwise.
509	after fork, and how you do this is entirely your own problem.
510		657
511	=item unsigned int ev_loop_count (loop)	658	=item unsigned int ev_iteration (loop)
512		659
513	Returns the count of loop iterations for the loop, which is identical to	660	Returns the current iteration count for the event loop, which is identical
514	the number of times libev did poll for new events. It starts at C<0> and	661	to the number of times libev did poll for new events. It starts at C<0>
515	happily wraps around with enough iterations.	662	and happily wraps around with enough iterations.
516		663
517	This value can sometimes be useful as a generation counter of sorts (it	664	This value can sometimes be useful as a generation counter of sorts (it
518	"ticks" the number of loop iterations), as it roughly corresponds with	665	"ticks" the number of loop iterations), as it roughly corresponds with
519	C<ev_prepare> and C<ev_check> calls.	666	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		667	prepare and check phases.
		668
		669	=item unsigned int ev_depth (loop)
		670
		671	Returns the number of times C<ev_run> was entered minus the number of
		672	times C<ev_run> was exited, in other words, the recursion depth.
		673
		674	Outside C<ev_run>, this number is zero. In a callback, this number is
		675	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		676	in which case it is higher.
		677
		678	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		679	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		680	ungentleman-like behaviour unless it's really convenient.
520		681
521	=item unsigned int ev_backend (loop)	682	=item unsigned int ev_backend (loop)
522		683
523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	684	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
524	use.	685	use.
…		…
529	received events and started processing them. This timestamp does not	690	received events and started processing them. This timestamp does not
530	change as long as callbacks are being processed, and this is also the base	691	change as long as callbacks are being processed, and this is also the base
531	time used for relative timers. You can treat it as the timestamp of the	692	time used for relative timers. You can treat it as the timestamp of the
532	event occurring (or more correctly, libev finding out about it).	693	event occurring (or more correctly, libev finding out about it).
533		694
		695	=item ev_now_update (loop)
		696
		697	Establishes the current time by querying the kernel, updating the time
		698	returned by C<ev_now ()> in the progress. This is a costly operation and
		699	is usually done automatically within C<ev_run ()>.
		700
		701	This function is rarely useful, but when some event callback runs for a
		702	very long time without entering the event loop, updating libev's idea of
		703	the current time is a good idea.
		704
		705	See also L<The special problem of time updates> in the C<ev_timer> section.
		706
		707	=item ev_suspend (loop)
		708
		709	=item ev_resume (loop)
		710
		711	These two functions suspend and resume an event loop, for use when the
		712	loop is not used for a while and timeouts should not be processed.
		713
		714	A typical use case would be an interactive program such as a game: When
		715	the user presses C<^Z> to suspend the game and resumes it an hour later it
		716	would be best to handle timeouts as if no time had actually passed while
		717	the program was suspended. This can be achieved by calling C<ev_suspend>
		718	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		719	C<ev_resume> directly afterwards to resume timer processing.
		720
		721	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		722	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		723	will be rescheduled (that is, they will lose any events that would have
		724	occurred while suspended).
		725
		726	After calling C<ev_suspend> you B<must not> call I<any> function on the
		727	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		728	without a previous call to C<ev_suspend>.
		729
		730	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		731	event loop time (see C<ev_now_update>).
		732
534	=item ev_loop (loop, int flags)	733	=item ev_run (loop, int flags)
535		734
536	Finally, this is it, the event handler. This function usually is called	735	Finally, this is it, the event handler. This function usually is called
537	after you initialised all your watchers and you want to start handling	736	after you have initialised all your watchers and you want to start
538	events.	737	handling events. It will ask the operating system for any new events, call
		738	the watcher callbacks, an then repeat the whole process indefinitely: This
		739	is why event loops are called I<loops>.
539		740
540	If the flags argument is specified as C<0>, it will not return until	741	If the flags argument is specified as C<0>, it will keep handling events
541	either no event watchers are active anymore or C<ev_unloop> was called.	742	until either no event watchers are active anymore or C<ev_break> was
		743	called.
542		744
543	Please note that an explicit C<ev_unloop> is usually better than	745	Please note that an explicit C<ev_break> is usually better than
544	relying on all watchers to be stopped when deciding when a program has	746	relying on all watchers to be stopped when deciding when a program has
545	finished (especially in interactive programs), but having a program that	747	finished (especially in interactive programs), but having a program
546	automatically loops as long as it has to and no longer by virtue of	748	that automatically loops as long as it has to and no longer by virtue
547	relying on its watchers stopping correctly is a thing of beauty.	749	of relying on its watchers stopping correctly, that is truly a thing of
		750	beauty.
548		751
549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	752	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
550	those events and any outstanding ones, but will not block your process in	753	those events and any already outstanding ones, but will not wait and
551	case there are no events and will return after one iteration of the loop.	754	block your process in case there are no events and will return after one
		755	iteration of the loop. This is sometimes useful to poll and handle new
		756	events while doing lengthy calculations, to keep the program responsive.
552		757
553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	758	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
554	neccessary) and will handle those and any outstanding ones. It will block	759	necessary) and will handle those and any already outstanding ones. It
555	your process until at least one new event arrives, and will return after	760	will block your process until at least one new event arrives (which could
556	one iteration of the loop. This is useful if you are waiting for some	761	be an event internal to libev itself, so there is no guarantee that a
557	external event in conjunction with something not expressible using other	762	user-registered callback will be called), and will return after one
		763	iteration of the loop.
		764
		765	This is useful if you are waiting for some external event in conjunction
		766	with something not expressible using other libev watchers (i.e. "roll your
558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	767	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
559	usually a better approach for this kind of thing.	768	usually a better approach for this kind of thing.
560		769
561	Here are the gory details of what C<ev_loop> does:	770	Here are the gory details of what C<ev_run> does:
562		771
		772	- Increment loop depth.
		773	- Reset the ev_break status.
563	- Before the first iteration, call any pending watchers.	774	- Before the first iteration, call any pending watchers.
		775	LOOP:
564	* If EVFLAG_FORKCHECK was used, check for a fork.	776	- If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	777	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	778	- Queue and call all prepare watchers.
		779	- If ev_break was called, goto FINISH.
567	- If we have been forked, recreate the kernel state.	780	- If we have been forked, detach and recreate the kernel state
		781	as to not disturb the other process.
568	- Update the kernel state with all outstanding changes.	782	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	783	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	784	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	785	(active idle watchers, EVRUN_NOWAIT or not having
572	any active watchers at all will result in not sleeping).	786	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	787	- Sleep if the I/O and timer collect interval say so.
		788	- Increment loop iteration counter.
574	- Block the process, waiting for any events.	789	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	790	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	791	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	792	- Queue all expired timers.
578	- Queue all outstanding periodics.	793	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	794	- Queue all idle watchers with priority higher than that of pending events.
580	- Queue all check watchers.	795	- Queue all check watchers.
581	- Call all queued watchers in reverse order (i.e. check watchers first).	796	- Call all queued watchers in reverse order (i.e. check watchers first).
582	Signals and child watchers are implemented as I/O watchers, and will	797	Signals and child watchers are implemented as I/O watchers, and will
583	be handled here by queueing them when their watcher gets executed.	798	be handled here by queueing them when their watcher gets executed.
584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	799	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
585	were used, or there are no active watchers, return, otherwise	800	were used, or there are no active watchers, goto FINISH, otherwise
586	continue with step *.	801	continue with step LOOP.
		802	FINISH:
		803	- Reset the ev_break status iff it was EVBREAK_ONE.
		804	- Decrement the loop depth.
		805	- Return.
587		806
588	Example: Queue some jobs and then loop until no events are outstanding	807	Example: Queue some jobs and then loop until no events are outstanding
589	anymore.	808	anymore.
590		809
591	... queue jobs here, make sure they register event watchers as long	810	... queue jobs here, make sure they register event watchers as long
592	... as they still have work to do (even an idle watcher will do..)	811	... as they still have work to do (even an idle watcher will do..)
593	ev_loop (my_loop, 0);	812	ev_run (my_loop, 0);
594	... jobs done. yeah!	813	... jobs done or somebody called unloop. yeah!
595		814
596	=item ev_unloop (loop, how)	815	=item ev_break (loop, how)
597		816
598	Can be used to make a call to C<ev_loop> return early (but only after it	817	Can be used to make a call to C<ev_run> return early (but only after it
599	has processed all outstanding events). The C<how> argument must be either	818	has processed all outstanding events). The C<how> argument must be either
600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	819	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	820	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
602		821
603	This "unloop state" will be cleared when entering C<ev_loop> again.	822	This "unloop state" will be cleared when entering C<ev_run> again.
		823
		824	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
604		825
605	=item ev_ref (loop)	826	=item ev_ref (loop)
606		827
607	=item ev_unref (loop)	828	=item ev_unref (loop)
608		829
609	Ref/unref can be used to add or remove a reference count on the event	830	Ref/unref can be used to add or remove a reference count on the event
610	loop: Every watcher keeps one reference, and as long as the reference	831	loop: Every watcher keeps one reference, and as long as the reference
611	count is nonzero, C<ev_loop> will not return on its own. If you have	832	count is nonzero, C<ev_run> will not return on its own.
612	a watcher you never unregister that should not keep C<ev_loop> from	833
613	returning, ev_unref() after starting, and ev_ref() before stopping it. For	834	This is useful when you have a watcher that you never intend to
		835	unregister, but that nevertheless should not keep C<ev_run> from
		836	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		837	before stopping it.
		838
614	example, libev itself uses this for its internal signal pipe: It is not	839	As an example, libev itself uses this for its internal signal pipe: It
615	visible to the libev user and should not keep C<ev_loop> from exiting if	840	is not visible to the libev user and should not keep C<ev_run> from
616	no event watchers registered by it are active. It is also an excellent	841	exiting if no event watchers registered by it are active. It is also an
617	way to do this for generic recurring timers or from within third-party	842	excellent way to do this for generic recurring timers or from within
618	libraries. Just remember to I<unref after start> and I<ref before stop>	843	third-party libraries. Just remember to I<unref after start> and I<ref
619	(but only if the watcher wasn't active before, or was active before,	844	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	845	before, respectively. Note also that libev might stop watchers itself
		846	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		847	in the callback).
621		848
622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	849	Example: Create a signal watcher, but keep it from keeping C<ev_run>
623	running when nothing else is active.	850	running when nothing else is active.
624		851
625	struct ev_signal exitsig;	852	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	853	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	854	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	855	evf_unref (loop);
629		856
630	Example: For some weird reason, unregister the above signal handler again.	857	Example: For some weird reason, unregister the above signal handler again.
631		858
632	ev_ref (loop);	859	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	860	ev_signal_stop (loop, &exitsig);
634		861
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	862	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		863
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	864	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		865
639	These advanced functions influence the time that libev will spend waiting	866	These advanced functions influence the time that libev will spend waiting
640	for events. Both are by default C<0>, meaning that libev will try to	867	for events. Both time intervals are by default C<0>, meaning that libev
641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	868	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		869	latency.
642		870
643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	871	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
644	allows libev to delay invocation of I/O and timer/periodic callbacks to	872	allows libev to delay invocation of I/O and timer/periodic callbacks
645	increase efficiency of loop iterations.	873	to increase efficiency of loop iterations (or to increase power-saving
		874	opportunities).
646		875
647	The background is that sometimes your program runs just fast enough to	876	The idea is that sometimes your program runs just fast enough to handle
648	handle one (or very few) event(s) per loop iteration. While this makes	877	one (or very few) event(s) per loop iteration. While this makes the
649	the program responsive, it also wastes a lot of CPU time to poll for new	878	program responsive, it also wastes a lot of CPU time to poll for new
650	events, especially with backends like C<select ()> which have a high	879	events, especially with backends like C<select ()> which have a high
651	overhead for the actual polling but can deliver many events at once.	880	overhead for the actual polling but can deliver many events at once.
652		881
653	By setting a higher I<io collect interval> you allow libev to spend more	882	By setting a higher I<io collect interval> you allow libev to spend more
654	time collecting I/O events, so you can handle more events per iteration,	883	time collecting I/O events, so you can handle more events per iteration,
655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	884	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
656	C<ev_timer>) will be not affected. Setting this to a non-null value will	885	C<ev_timer>) will be not affected. Setting this to a non-null value will
657	introduce an additional C<ev_sleep ()> call into most loop iterations.	886	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		887	sleep time ensures that libev will not poll for I/O events more often then
		888	once per this interval, on average.
658		889
659	Likewise, by setting a higher I<timeout collect interval> you allow libev	890	Likewise, by setting a higher I<timeout collect interval> you allow libev
660	to spend more time collecting timeouts, at the expense of increased	891	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	892	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	893	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	894	value will not introduce any overhead in libev.
664		895
665	Many (busy) programs can usually benefit by setting the io collect	896	Many (busy) programs can usually benefit by setting the I/O collect
666	interval to a value near C<0.1> or so, which is often enough for	897	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	898	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	899	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches the timing granularity of most systems.	900	as this approaches the timing granularity of most systems. Note that if
		901	you do transactions with the outside world and you can't increase the
		902	parallelity, then this setting will limit your transaction rate (if you
		903	need to poll once per transaction and the I/O collect interval is 0.01,
		904	then you can't do more than 100 transactions per second).
		905
		906	Setting the I<timeout collect interval> can improve the opportunity for
		907	saving power, as the program will "bundle" timer callback invocations that
		908	are "near" in time together, by delaying some, thus reducing the number of
		909	times the process sleeps and wakes up again. Another useful technique to
		910	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		911	they fire on, say, one-second boundaries only.
		912
		913	Example: we only need 0.1s timeout granularity, and we wish not to poll
		914	more often than 100 times per second:
		915
		916	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		917	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		918
		919	=item ev_invoke_pending (loop)
		920
		921	This call will simply invoke all pending watchers while resetting their
		922	pending state. Normally, C<ev_run> does this automatically when required,
		923	but when overriding the invoke callback this call comes handy. This
		924	function can be invoked from a watcher - this can be useful for example
		925	when you want to do some lengthy calculation and want to pass further
		926	event handling to another thread (you still have to make sure only one
		927	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		928
		929	=item int ev_pending_count (loop)
		930
		931	Returns the number of pending watchers - zero indicates that no watchers
		932	are pending.
		933
		934	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		935
		936	This overrides the invoke pending functionality of the loop: Instead of
		937	invoking all pending watchers when there are any, C<ev_run> will call
		938	this callback instead. This is useful, for example, when you want to
		939	invoke the actual watchers inside another context (another thread etc.).
		940
		941	If you want to reset the callback, use C<ev_invoke_pending> as new
		942	callback.
		943
		944	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		945
		946	Sometimes you want to share the same loop between multiple threads. This
		947	can be done relatively simply by putting mutex_lock/unlock calls around
		948	each call to a libev function.
		949
		950	However, C<ev_run> can run an indefinite time, so it is not feasible
		951	to wait for it to return. One way around this is to wake up the event
		952	loop via C<ev_break> and C<av_async_send>, another way is to set these
		953	I<release> and I<acquire> callbacks on the loop.
		954
		955	When set, then C<release> will be called just before the thread is
		956	suspended waiting for new events, and C<acquire> is called just
		957	afterwards.
		958
		959	Ideally, C<release> will just call your mutex_unlock function, and
		960	C<acquire> will just call the mutex_lock function again.
		961
		962	While event loop modifications are allowed between invocations of
		963	C<release> and C<acquire> (that's their only purpose after all), no
		964	modifications done will affect the event loop, i.e. adding watchers will
		965	have no effect on the set of file descriptors being watched, or the time
		966	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		967	to take note of any changes you made.
		968
		969	In theory, threads executing C<ev_run> will be async-cancel safe between
		970	invocations of C<release> and C<acquire>.
		971
		972	See also the locking example in the C<THREADS> section later in this
		973	document.
		974
		975	=item ev_set_userdata (loop, void *data)
		976
		977	=item ev_userdata (loop)
		978
		979	Set and retrieve a single C<void *> associated with a loop. When
		980	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		981	C<0.>
		982
		983	These two functions can be used to associate arbitrary data with a loop,
		984	and are intended solely for the C<invoke_pending_cb>, C<release> and
		985	C<acquire> callbacks described above, but of course can be (ab-)used for
		986	any other purpose as well.
		987
		988	=item ev_verify (loop)
		989
		990	This function only does something when C<EV_VERIFY> support has been
		991	compiled in, which is the default for non-minimal builds. It tries to go
		992	through all internal structures and checks them for validity. If anything
		993	is found to be inconsistent, it will print an error message to standard
		994	error and call C<abort ()>.
		995
		996	This can be used to catch bugs inside libev itself: under normal
		997	circumstances, this function will never abort as of course libev keeps its
		998	data structures consistent.
670		999
671	=back	1000	=back
672		1001
673		1002
674	=head1 ANATOMY OF A WATCHER	1003	=head1 ANATOMY OF A WATCHER
675		1004
		1005	In the following description, uppercase C<TYPE> in names stands for the
		1006	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1007	watchers and C<ev_io_start> for I/O watchers.
		1008
676	A watcher is a structure that you create and register to record your	1009	A watcher is an opaque structure that you allocate and register to record
677	interest in some event. For instance, if you want to wait for STDIN to	1010	your interest in some event. To make a concrete example, imagine you want
678	become readable, you would create an C<ev_io> watcher for that:	1011	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1012	for that:
679		1013
680	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1014	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
681	{	1015	{
682	ev_io_stop (w);	1016	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	1017	ev_break (loop, EVBREAK_ALL);
684	}	1018	}
685		1019
686	struct ev_loop *loop = ev_default_loop (0);	1020	struct ev_loop *loop = ev_default_loop (0);
		1021
687	struct ev_io stdin_watcher;	1022	ev_io stdin_watcher;
		1023
688	ev_init (&stdin_watcher, my_cb);	1024	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1025	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	1026	ev_io_start (loop, &stdin_watcher);
		1027
691	ev_loop (loop, 0);	1028	ev_run (loop, 0);
692		1029
693	As you can see, you are responsible for allocating the memory for your	1030	As you can see, you are responsible for allocating the memory for your
694	watcher structures (and it is usually a bad idea to do this on the stack,	1031	watcher structures (and it is I<usually> a bad idea to do this on the
695	although this can sometimes be quite valid).	1032	stack).
696		1033
		1034	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1035	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1036
697	Each watcher structure must be initialised by a call to C<ev_init	1037	Each watcher structure must be initialised by a call to C<ev_init (watcher
698	(watcher *, callback)>, which expects a callback to be provided. This	1038	*, callback)>, which expects a callback to be provided. This callback is
699	callback gets invoked each time the event occurs (or, in the case of io	1039	invoked each time the event occurs (or, in the case of I/O watchers, each
700	watchers, each time the event loop detects that the file descriptor given	1040	time the event loop detects that the file descriptor given is readable
701	is readable and/or writable).	1041	and/or writable).
702		1042
703	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1043	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
704	with arguments specific to this watcher type. There is also a macro	1044	macro to configure it, with arguments specific to the watcher type. There
705	to combine initialisation and setting in one call: C<< ev_<type>_init	1045	is also a macro to combine initialisation and setting in one call: C<<
706	(watcher *, callback, ...) >>.	1046	ev_TYPE_init (watcher *, callback, ...) >>.
707		1047
708	To make the watcher actually watch out for events, you have to start it	1048	To make the watcher actually watch out for events, you have to start it
709	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1049	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
710	*) >>), and you can stop watching for events at any time by calling the	1050	*) >>), and you can stop watching for events at any time by calling the
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1051	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		1052
713	As long as your watcher is active (has been started but not stopped) you	1053	As long as your watcher is active (has been started but not stopped) you
714	must not touch the values stored in it. Most specifically you must never	1054	must not touch the values stored in it. Most specifically you must never
715	reinitialise it or call its C<set> macro.	1055	reinitialise it or call its C<ev_TYPE_set> macro.
716		1056
717	Each and every callback receives the event loop pointer as first, the	1057	Each and every callback receives the event loop pointer as first, the
718	registered watcher structure as second, and a bitset of received events as	1058	registered watcher structure as second, and a bitset of received events as
719	third argument.	1059	third argument.
720		1060
…		…
729	=item C<EV_WRITE>	1069	=item C<EV_WRITE>
730		1070
731	The file descriptor in the C<ev_io> watcher has become readable and/or	1071	The file descriptor in the C<ev_io> watcher has become readable and/or
732	writable.	1072	writable.
733		1073
734	=item C<EV_TIMEOUT>	1074	=item C<EV_TIMER>
735		1075
736	The C<ev_timer> watcher has timed out.	1076	The C<ev_timer> watcher has timed out.
737		1077
738	=item C<EV_PERIODIC>	1078	=item C<EV_PERIODIC>
739		1079
…		…
757		1097
758	=item C<EV_PREPARE>	1098	=item C<EV_PREPARE>
759		1099
760	=item C<EV_CHECK>	1100	=item C<EV_CHECK>
761		1101
762	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1102	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
763	to gather new events, and all C<ev_check> watchers are invoked just after	1103	to gather new events, and all C<ev_check> watchers are invoked just after
764	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1104	C<ev_run> has gathered them, but before it invokes any callbacks for any
765	received events. Callbacks of both watcher types can start and stop as	1105	received events. Callbacks of both watcher types can start and stop as
766	many watchers as they want, and all of them will be taken into account	1106	many watchers as they want, and all of them will be taken into account
767	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1107	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
768	C<ev_loop> from blocking).	1108	C<ev_run> from blocking).
769		1109
770	=item C<EV_EMBED>	1110	=item C<EV_EMBED>
771		1111
772	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1112	The embedded event loop specified in the C<ev_embed> watcher needs attention.
773		1113
…		…
778		1118
779	=item C<EV_ASYNC>	1119	=item C<EV_ASYNC>
780		1120
781	The given async watcher has been asynchronously notified (see C<ev_async>).	1121	The given async watcher has been asynchronously notified (see C<ev_async>).
782		1122
		1123	=item C<EV_CUSTOM>
		1124
		1125	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1126	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1127
783	=item C<EV_ERROR>	1128	=item C<EV_ERROR>
784		1129
785	An unspecified error has occured, the watcher has been stopped. This might	1130	An unspecified error has occurred, the watcher has been stopped. This might
786	happen because the watcher could not be properly started because libev	1131	happen because the watcher could not be properly started because libev
787	ran out of memory, a file descriptor was found to be closed or any other	1132	ran out of memory, a file descriptor was found to be closed or any other
		1133	problem. Libev considers these application bugs.
		1134
788	problem. You best act on it by reporting the problem and somehow coping	1135	You best act on it by reporting the problem and somehow coping with the
789	with the watcher being stopped.	1136	watcher being stopped. Note that well-written programs should not receive
		1137	an error ever, so when your watcher receives it, this usually indicates a
		1138	bug in your program.
790		1139
791	Libev will usually signal a few "dummy" events together with an error,	1140	Libev will usually signal a few "dummy" events together with an error, for
792	for example it might indicate that a fd is readable or writable, and if	1141	example it might indicate that a fd is readable or writable, and if your
793	your callbacks is well-written it can just attempt the operation and cope	1142	callbacks is well-written it can just attempt the operation and cope with
794	with the error from read() or write(). This will not work in multithreaded	1143	the error from read() or write(). This will not work in multi-threaded
795	programs, though, so beware.	1144	programs, though, as the fd could already be closed and reused for another
		1145	thing, so beware.
796		1146
797	=back	1147	=back
798		1148
		1149	=head2 WATCHER STATES
		1150
		1151	There are various watcher states mentioned throughout this manual -
		1152	active, pending and so on. In this section these states and the rules to
		1153	transition between them will be described in more detail - and while these
		1154	rules might look complicated, they usually do "the right thing".
		1155
		1156	=over 4
		1157
		1158	=item initialiased
		1159
		1160	Before a watcher can be registered with the event looop it has to be
		1161	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1162	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1163
		1164	In this state it is simply some block of memory that is suitable for use
		1165	in an event loop. It can be moved around, freed, reused etc. at will.
		1166
		1167	=item started/running/active
		1168
		1169	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1170	property of the event loop, and is actively waiting for events. While in
		1171	this state it cannot be accessed (except in a few documented ways), moved,
		1172	freed or anything else - the only legal thing is to keep a pointer to it,
		1173	and call libev functions on it that are documented to work on active watchers.
		1174
		1175	=item pending
		1176
		1177	If a watcher is active and libev determines that an event it is interested
		1178	in has occurred (such as a timer expiring), it will become pending. It will
		1179	stay in this pending state until either it is stopped or its callback is
		1180	about to be invoked, so it is not normally pending inside the watcher
		1181	callback.
		1182
		1183	The watcher might or might not be active while it is pending (for example,
		1184	an expired non-repeating timer can be pending but no longer active). If it
		1185	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1186	but it is still property of the event loop at this time, so cannot be
		1187	moved, freed or reused. And if it is active the rules described in the
		1188	previous item still apply.
		1189
		1190	It is also possible to feed an event on a watcher that is not active (e.g.
		1191	via C<ev_feed_event>), in which case it becomes pending without being
		1192	active.
		1193
		1194	=item stopped
		1195
		1196	A watcher can be stopped implicitly by libev (in which case it might still
		1197	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1198	latter will clear any pending state the watcher might be in, regardless
		1199	of whether it was active or not, so stopping a watcher explicitly before
		1200	freeing it is often a good idea.
		1201
		1202	While stopped (and not pending) the watcher is essentially in the
		1203	initialised state, that is it can be reused, moved, modified in any way
		1204	you wish.
		1205
		1206	=back
		1207
799	=head2 GENERIC WATCHER FUNCTIONS	1208	=head2 GENERIC WATCHER FUNCTIONS
800
801	In the following description, C<TYPE> stands for the watcher type,
802	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
803		1209
804	=over 4	1210	=over 4
805		1211
806	=item C<ev_init> (ev_TYPE *watcher, callback)	1212	=item C<ev_init> (ev_TYPE *watcher, callback)
807		1213
…		…
813	which rolls both calls into one.	1219	which rolls both calls into one.
814		1220
815	You can reinitialise a watcher at any time as long as it has been stopped	1221	You can reinitialise a watcher at any time as long as it has been stopped
816	(or never started) and there are no pending events outstanding.	1222	(or never started) and there are no pending events outstanding.
817		1223
818	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1224	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
819	int revents)>.	1225	int revents)>.
820		1226
		1227	Example: Initialise an C<ev_io> watcher in two steps.
		1228
		1229	ev_io w;
		1230	ev_init (&w, my_cb);
		1231	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1232
821	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1233	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
822		1234
823	This macro initialises the type-specific parts of a watcher. You need to	1235	This macro initialises the type-specific parts of a watcher. You need to
824	call C<ev_init> at least once before you call this macro, but you can	1236	call C<ev_init> at least once before you call this macro, but you can
825	call C<ev_TYPE_set> any number of times. You must not, however, call this	1237	call C<ev_TYPE_set> any number of times. You must not, however, call this
826	macro on a watcher that is active (it can be pending, however, which is a	1238	macro on a watcher that is active (it can be pending, however, which is a
827	difference to the C<ev_init> macro).	1239	difference to the C<ev_init> macro).
828		1240
829	Although some watcher types do not have type-specific arguments	1241	Although some watcher types do not have type-specific arguments
830	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1242	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
831		1243
		1244	See C<ev_init>, above, for an example.
		1245
832	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1246	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
833		1247
834	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1248	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
835	calls into a single call. This is the most convinient method to initialise	1249	calls into a single call. This is the most convenient method to initialise
836	a watcher. The same limitations apply, of course.	1250	a watcher. The same limitations apply, of course.
837		1251
		1252	Example: Initialise and set an C<ev_io> watcher in one step.
		1253
		1254	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1255
838	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1256	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
839		1257
840	Starts (activates) the given watcher. Only active watchers will receive	1258	Starts (activates) the given watcher. Only active watchers will receive
841	events. If the watcher is already active nothing will happen.	1259	events. If the watcher is already active nothing will happen.
842		1260
		1261	Example: Start the C<ev_io> watcher that is being abused as example in this
		1262	whole section.
		1263
		1264	ev_io_start (EV_DEFAULT_UC, &w);
		1265
843	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1266	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
844		1267
845	Stops the given watcher again (if active) and clears the pending	1268	Stops the given watcher if active, and clears the pending status (whether
		1269	the watcher was active or not).
		1270
846	status. It is possible that stopped watchers are pending (for example,	1271	It is possible that stopped watchers are pending - for example,
847	non-repeating timers are being stopped when they become pending), but	1272	non-repeating timers are being stopped when they become pending - but
848	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1273	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
849	you want to free or reuse the memory used by the watcher it is therefore a	1274	pending. If you want to free or reuse the memory used by the watcher it is
850	good idea to always call its C<ev_TYPE_stop> function.	1275	therefore a good idea to always call its C<ev_TYPE_stop> function.
851		1276
852	=item bool ev_is_active (ev_TYPE *watcher)	1277	=item bool ev_is_active (ev_TYPE *watcher)
853		1278
854	Returns a true value iff the watcher is active (i.e. it has been started	1279	Returns a true value iff the watcher is active (i.e. it has been started
855	and not yet been stopped). As long as a watcher is active you must not modify	1280	and not yet been stopped). As long as a watcher is active you must not modify
…		…
871	=item ev_cb_set (ev_TYPE *watcher, callback)	1296	=item ev_cb_set (ev_TYPE *watcher, callback)
872		1297
873	Change the callback. You can change the callback at virtually any time	1298	Change the callback. You can change the callback at virtually any time
874	(modulo threads).	1299	(modulo threads).
875		1300
876	=item ev_set_priority (ev_TYPE *watcher, priority)	1301	=item ev_set_priority (ev_TYPE *watcher, int priority)
877		1302
878	=item int ev_priority (ev_TYPE *watcher)	1303	=item int ev_priority (ev_TYPE *watcher)
879		1304
880	Set and query the priority of the watcher. The priority is a small	1305	Set and query the priority of the watcher. The priority is a small
881	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1306	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
882	(default: C<-2>). Pending watchers with higher priority will be invoked	1307	(default: C<-2>). Pending watchers with higher priority will be invoked
883	before watchers with lower priority, but priority will not keep watchers	1308	before watchers with lower priority, but priority will not keep watchers
884	from being executed (except for C<ev_idle> watchers).	1309	from being executed (except for C<ev_idle> watchers).
885		1310
886	This means that priorities are I<only> used for ordering callback
887	invocation after new events have been received. This is useful, for
888	example, to reduce latency after idling, or more often, to bind two
889	watchers on the same event and make sure one is called first.
890
891	If you need to suppress invocation when higher priority events are pending	1311	If you need to suppress invocation when higher priority events are pending
892	you need to look at C<ev_idle> watchers, which provide this functionality.	1312	you need to look at C<ev_idle> watchers, which provide this functionality.
893		1313
894	You I<must not> change the priority of a watcher as long as it is active or	1314	You I<must not> change the priority of a watcher as long as it is active or
895	pending.	1315	pending.
896		1316
		1317	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1318	fine, as long as you do not mind that the priority value you query might
		1319	or might not have been clamped to the valid range.
		1320
897	The default priority used by watchers when no priority has been set is	1321	The default priority used by watchers when no priority has been set is
898	always C<0>, which is supposed to not be too high and not be too low :).	1322	always C<0>, which is supposed to not be too high and not be too low :).
899		1323
900	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1324	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
901	fine, as long as you do not mind that the priority value you query might	1325	priorities.
902	or might not have been adjusted to be within valid range.
903		1326
904	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1327	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
905		1328
906	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1329	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
907	C<loop> nor C<revents> need to be valid as long as the watcher callback	1330	C<loop> nor C<revents> need to be valid as long as the watcher callback
908	can deal with that fact.	1331	can deal with that fact, as both are simply passed through to the
		1332	callback.
909		1333
910	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1334	=item int ev_clear_pending (loop, ev_TYPE *watcher)
911		1335
912	If the watcher is pending, this function returns clears its pending status	1336	If the watcher is pending, this function clears its pending status and
913	and returns its C<revents> bitset (as if its callback was invoked). If the	1337	returns its C<revents> bitset (as if its callback was invoked). If the
914	watcher isn't pending it does nothing and returns C<0>.	1338	watcher isn't pending it does nothing and returns C<0>.
915		1339
		1340	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1341	callback to be invoked, which can be accomplished with this function.
		1342
		1343	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1344
		1345	Feeds the given event set into the event loop, as if the specified event
		1346	had happened for the specified watcher (which must be a pointer to an
		1347	initialised but not necessarily started event watcher). Obviously you must
		1348	not free the watcher as long as it has pending events.
		1349
		1350	Stopping the watcher, letting libev invoke it, or calling
		1351	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1352	not started in the first place.
		1353
		1354	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1355	functions that do not need a watcher.
		1356
916	=back	1357	=back
917		1358
918		1359
919	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
920		1361
921	Each watcher has, by default, a member C<void *data> that you can change	1362	Each watcher has, by default, a member C<void *data> that you can change
922	and read at any time, libev will completely ignore it. This can be used	1363	and read at any time: libev will completely ignore it. This can be used
923	to associate arbitrary data with your watcher. If you need more data and	1364	to associate arbitrary data with your watcher. If you need more data and
924	don't want to allocate memory and store a pointer to it in that data	1365	don't want to allocate memory and store a pointer to it in that data
925	member, you can also "subclass" the watcher type and provide your own	1366	member, you can also "subclass" the watcher type and provide your own
926	data:	1367	data:
927		1368
928	struct my_io	1369	struct my_io
929	{	1370	{
930	struct ev_io io;	1371	ev_io io;
931	int otherfd;	1372	int otherfd;
932	void *somedata;	1373	void *somedata;
933	struct whatever *mostinteresting;	1374	struct whatever *mostinteresting;
934	}	1375	};
		1376
		1377	...
		1378	struct my_io w;
		1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
935		1380
936	And since your callback will be called with a pointer to the watcher, you	1381	And since your callback will be called with a pointer to the watcher, you
937	can cast it back to your own type:	1382	can cast it back to your own type:
938		1383
939	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
940	{	1385	{
941	struct my_io *w = (struct my_io *)w_;	1386	struct my_io *w = (struct my_io *)w_;
942	...	1387	...
943	}	1388	}
944		1389
945	More interesting and less C-conformant ways of casting your callback type	1390	More interesting and less C-conformant ways of casting your callback type
946	instead have been omitted.	1391	instead have been omitted.
947		1392
948	Another common scenario is having some data structure with multiple	1393	Another common scenario is to use some data structure with multiple
949	watchers:	1394	embedded watchers:
950		1395
951	struct my_biggy	1396	struct my_biggy
952	{	1397	{
953	int some_data;	1398	int some_data;
954	ev_timer t1;	1399	ev_timer t1;
955	ev_timer t2;	1400	ev_timer t2;
956	}	1401	}
957		1402
958	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1403	In this case getting the pointer to C<my_biggy> is a bit more
959	you need to use C<offsetof>:	1404	complicated: Either you store the address of your C<my_biggy> struct
		1405	in the C<data> member of the watcher (for woozies), or you need to use
		1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1407	programmers):
960		1408
961	#include <stddef.h>	1409	#include <stddef.h>
962		1410
963	static void	1411	static void
964	t1_cb (EV_P_ struct ev_timer *w, int revents)	1412	t1_cb (EV_P_ ev_timer *w, int revents)
965	{	1413	{
966	struct my_biggy big = (struct my_biggy *	1414	struct my_biggy big = (struct my_biggy *)
967	(((char *)w) - offsetof (struct my_biggy, t1));	1415	(((char *)w) - offsetof (struct my_biggy, t1));
968	}	1416	}
969		1417
970	static void	1418	static void
971	t2_cb (EV_P_ struct ev_timer *w, int revents)	1419	t2_cb (EV_P_ ev_timer *w, int revents)
972	{	1420	{
973	struct my_biggy big = (struct my_biggy *	1421	struct my_biggy big = (struct my_biggy *)
974	(((char *)w) - offsetof (struct my_biggy, t2));	1422	(((char *)w) - offsetof (struct my_biggy, t2));
975	}	1423	}
		1424
		1425	=head2 WATCHER PRIORITY MODELS
		1426
		1427	Many event loops support I<watcher priorities>, which are usually small
		1428	integers that influence the ordering of event callback invocation
		1429	between watchers in some way, all else being equal.
		1430
		1431	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1432	description for the more technical details such as the actual priority
		1433	range.
		1434
		1435	There are two common ways how these these priorities are being interpreted
		1436	by event loops:
		1437
		1438	In the more common lock-out model, higher priorities "lock out" invocation
		1439	of lower priority watchers, which means as long as higher priority
		1440	watchers receive events, lower priority watchers are not being invoked.
		1441
		1442	The less common only-for-ordering model uses priorities solely to order
		1443	callback invocation within a single event loop iteration: Higher priority
		1444	watchers are invoked before lower priority ones, but they all get invoked
		1445	before polling for new events.
		1446
		1447	Libev uses the second (only-for-ordering) model for all its watchers
		1448	except for idle watchers (which use the lock-out model).
		1449
		1450	The rationale behind this is that implementing the lock-out model for
		1451	watchers is not well supported by most kernel interfaces, and most event
		1452	libraries will just poll for the same events again and again as long as
		1453	their callbacks have not been executed, which is very inefficient in the
		1454	common case of one high-priority watcher locking out a mass of lower
		1455	priority ones.
		1456
		1457	Static (ordering) priorities are most useful when you have two or more
		1458	watchers handling the same resource: a typical usage example is having an
		1459	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1460	timeouts. Under load, data might be received while the program handles
		1461	other jobs, but since timers normally get invoked first, the timeout
		1462	handler will be executed before checking for data. In that case, giving
		1463	the timer a lower priority than the I/O watcher ensures that I/O will be
		1464	handled first even under adverse conditions (which is usually, but not
		1465	always, what you want).
		1466
		1467	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1468	will only be executed when no same or higher priority watchers have
		1469	received events, they can be used to implement the "lock-out" model when
		1470	required.
		1471
		1472	For example, to emulate how many other event libraries handle priorities,
		1473	you can associate an C<ev_idle> watcher to each such watcher, and in
		1474	the normal watcher callback, you just start the idle watcher. The real
		1475	processing is done in the idle watcher callback. This causes libev to
		1476	continuously poll and process kernel event data for the watcher, but when
		1477	the lock-out case is known to be rare (which in turn is rare :), this is
		1478	workable.
		1479
		1480	Usually, however, the lock-out model implemented that way will perform
		1481	miserably under the type of load it was designed to handle. In that case,
		1482	it might be preferable to stop the real watcher before starting the
		1483	idle watcher, so the kernel will not have to process the event in case
		1484	the actual processing will be delayed for considerable time.
		1485
		1486	Here is an example of an I/O watcher that should run at a strictly lower
		1487	priority than the default, and which should only process data when no
		1488	other events are pending:
		1489
		1490	ev_idle idle; // actual processing watcher
		1491	ev_io io; // actual event watcher
		1492
		1493	static void
		1494	io_cb (EV_P_ ev_io *w, int revents)
		1495	{
		1496	// stop the I/O watcher, we received the event, but
		1497	// are not yet ready to handle it.
		1498	ev_io_stop (EV_A_ w);
		1499
		1500	// start the idle watcher to handle the actual event.
		1501	// it will not be executed as long as other watchers
		1502	// with the default priority are receiving events.
		1503	ev_idle_start (EV_A_ &idle);
		1504	}
		1505
		1506	static void
		1507	idle_cb (EV_P_ ev_idle *w, int revents)
		1508	{
		1509	// actual processing
		1510	read (STDIN_FILENO, ...);
		1511
		1512	// have to start the I/O watcher again, as
		1513	// we have handled the event
		1514	ev_io_start (EV_P_ &io);
		1515	}
		1516
		1517	// initialisation
		1518	ev_idle_init (&idle, idle_cb);
		1519	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1520	ev_io_start (EV_DEFAULT_ &io);
		1521
		1522	In the "real" world, it might also be beneficial to start a timer, so that
		1523	low-priority connections can not be locked out forever under load. This
		1524	enables your program to keep a lower latency for important connections
		1525	during short periods of high load, while not completely locking out less
		1526	important ones.
976		1527
977		1528
978	=head1 WATCHER TYPES	1529	=head1 WATCHER TYPES
979		1530
980	This section describes each watcher in detail, but will not repeat	1531	This section describes each watcher in detail, but will not repeat
…		…
1004	In general you can register as many read and/or write event watchers per	1555	In general you can register as many read and/or write event watchers per
1005	fd as you want (as long as you don't confuse yourself). Setting all file	1556	fd as you want (as long as you don't confuse yourself). Setting all file
1006	descriptors to non-blocking mode is also usually a good idea (but not	1557	descriptors to non-blocking mode is also usually a good idea (but not
1007	required if you know what you are doing).	1558	required if you know what you are doing).
1008		1559
1009	If you must do this, then force the use of a known-to-be-good backend	1560	If you cannot use non-blocking mode, then force the use of a
1010	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1561	known-to-be-good backend (at the time of this writing, this includes only
1011	C<EVBACKEND_POLL>).	1562	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1563	descriptors for which non-blocking operation makes no sense (such as
		1564	files) - libev doesn't guarantee any specific behaviour in that case.
1012		1565
1013	Another thing you have to watch out for is that it is quite easy to	1566	Another thing you have to watch out for is that it is quite easy to
1014	receive "spurious" readyness notifications, that is your callback might	1567	receive "spurious" readiness notifications, that is your callback might
1015	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1568	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1016	because there is no data. Not only are some backends known to create a	1569	because there is no data. Not only are some backends known to create a
1017	lot of those (for example solaris ports), it is very easy to get into	1570	lot of those (for example Solaris ports), it is very easy to get into
1018	this situation even with a relatively standard program structure. Thus	1571	this situation even with a relatively standard program structure. Thus
1019	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1572	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1020	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1573	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1021		1574
1022	If you cannot run the fd in non-blocking mode (for example you should not	1575	If you cannot run the fd in non-blocking mode (for example you should
1023	play around with an Xlib connection), then you have to seperately re-test	1576	not play around with an Xlib connection), then you have to separately
1024	whether a file descriptor is really ready with a known-to-be good interface	1577	re-test whether a file descriptor is really ready with a known-to-be good
1025	such as poll (fortunately in our Xlib example, Xlib already does this on	1578	interface such as poll (fortunately in our Xlib example, Xlib already
1026	its own, so its quite safe to use).	1579	does this on its own, so its quite safe to use). Some people additionally
		1580	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1581	indefinitely.
		1582
		1583	But really, best use non-blocking mode.
1027		1584
1028	=head3 The special problem of disappearing file descriptors	1585	=head3 The special problem of disappearing file descriptors
1029		1586
1030	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1587	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1031	descriptor (either by calling C<close> explicitly or by any other means,	1588	descriptor (either due to calling C<close> explicitly or any other means,
1032	such as C<dup>). The reason is that you register interest in some file	1589	such as C<dup2>). The reason is that you register interest in some file
1033	descriptor, but when it goes away, the operating system will silently drop	1590	descriptor, but when it goes away, the operating system will silently drop
1034	this interest. If another file descriptor with the same number then is	1591	this interest. If another file descriptor with the same number then is
1035	registered with libev, there is no efficient way to see that this is, in	1592	registered with libev, there is no efficient way to see that this is, in
1036	fact, a different file descriptor.	1593	fact, a different file descriptor.
1037		1594
…		…
1066	To support fork in your programs, you either have to call	1623	To support fork in your programs, you either have to call
1067	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1624	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1068	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1625	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1069	C<EVBACKEND_POLL>.	1626	C<EVBACKEND_POLL>.
1070		1627
		1628	=head3 The special problem of SIGPIPE
		1629
		1630	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1631	when writing to a pipe whose other end has been closed, your program gets
		1632	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1633	this is sensible behaviour, for daemons, this is usually undesirable.
		1634
		1635	So when you encounter spurious, unexplained daemon exits, make sure you
		1636	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1637	somewhere, as that would have given you a big clue).
		1638
		1639	=head3 The special problem of accept()ing when you can't
		1640
		1641	Many implementations of the POSIX C<accept> function (for example,
		1642	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1643	connection from the pending queue in all error cases.
		1644
		1645	For example, larger servers often run out of file descriptors (because
		1646	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1647	rejecting the connection, leading to libev signalling readiness on
		1648	the next iteration again (the connection still exists after all), and
		1649	typically causing the program to loop at 100% CPU usage.
		1650
		1651	Unfortunately, the set of errors that cause this issue differs between
		1652	operating systems, there is usually little the app can do to remedy the
		1653	situation, and no known thread-safe method of removing the connection to
		1654	cope with overload is known (to me).
		1655
		1656	One of the easiest ways to handle this situation is to just ignore it
		1657	- when the program encounters an overload, it will just loop until the
		1658	situation is over. While this is a form of busy waiting, no OS offers an
		1659	event-based way to handle this situation, so it's the best one can do.
		1660
		1661	A better way to handle the situation is to log any errors other than
		1662	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1663	messages, and continue as usual, which at least gives the user an idea of
		1664	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1665	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1666	usage.
		1667
		1668	If your program is single-threaded, then you could also keep a dummy file
		1669	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1670	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1671	close that fd, and create a new dummy fd. This will gracefully refuse
		1672	clients under typical overload conditions.
		1673
		1674	The last way to handle it is to simply log the error and C<exit>, as
		1675	is often done with C<malloc> failures, but this results in an easy
		1676	opportunity for a DoS attack.
1071		1677
1072	=head3 Watcher-Specific Functions	1678	=head3 Watcher-Specific Functions
1073		1679
1074	=over 4	1680	=over 4
1075		1681
1076	=item ev_io_init (ev_io *, callback, int fd, int events)	1682	=item ev_io_init (ev_io *, callback, int fd, int events)
1077		1683
1078	=item ev_io_set (ev_io *, int fd, int events)	1684	=item ev_io_set (ev_io *, int fd, int events)
1079		1685
1080	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1686	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1081	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1687	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1082	C<EV_READ | EV_WRITE> to receive the given events.	1688	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1083		1689
1084	=item int fd [read-only]	1690	=item int fd [read-only]
1085		1691
1086	The file descriptor being watched.	1692	The file descriptor being watched.
1087		1693
…		…
1095		1701
1096	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1702	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1097	readable, but only once. Since it is likely line-buffered, you could	1703	readable, but only once. Since it is likely line-buffered, you could
1098	attempt to read a whole line in the callback.	1704	attempt to read a whole line in the callback.
1099		1705
1100	static void	1706	static void
1101	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1707	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1102	{	1708	{
1103	ev_io_stop (loop, w);	1709	ev_io_stop (loop, w);
1104	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1710	.. read from stdin here (or from w->fd) and handle any I/O errors
1105	}	1711	}
1106		1712
1107	...	1713	...
1108	struct ev_loop *loop = ev_default_init (0);	1714	struct ev_loop *loop = ev_default_init (0);
1109	struct ev_io stdin_readable;	1715	ev_io stdin_readable;
1110	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1716	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1111	ev_io_start (loop, &stdin_readable);	1717	ev_io_start (loop, &stdin_readable);
1112	ev_loop (loop, 0);	1718	ev_run (loop, 0);
1113		1719
1114		1720
1115	=head2 C<ev_timer> - relative and optionally repeating timeouts	1721	=head2 C<ev_timer> - relative and optionally repeating timeouts
1116		1722
1117	Timer watchers are simple relative timers that generate an event after a	1723	Timer watchers are simple relative timers that generate an event after a
1118	given time, and optionally repeating in regular intervals after that.	1724	given time, and optionally repeating in regular intervals after that.
1119		1725
1120	The timers are based on real time, that is, if you register an event that	1726	The timers are based on real time, that is, if you register an event that
1121	times out after an hour and you reset your system clock to last years	1727	times out after an hour and you reset your system clock to January last
1122	time, it will still time out after (roughly) and hour. "Roughly" because	1728	year, it will still time out after (roughly) one hour. "Roughly" because
1123	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1729	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1124	monotonic clock option helps a lot here).	1730	monotonic clock option helps a lot here).
		1731
		1732	The callback is guaranteed to be invoked only I<after> its timeout has
		1733	passed (not I<at>, so on systems with very low-resolution clocks this
		1734	might introduce a small delay). If multiple timers become ready during the
		1735	same loop iteration then the ones with earlier time-out values are invoked
		1736	before ones of the same priority with later time-out values (but this is
		1737	no longer true when a callback calls C<ev_run> recursively).
		1738
		1739	=head3 Be smart about timeouts
		1740
		1741	Many real-world problems involve some kind of timeout, usually for error
		1742	recovery. A typical example is an HTTP request - if the other side hangs,
		1743	you want to raise some error after a while.
		1744
		1745	What follows are some ways to handle this problem, from obvious and
		1746	inefficient to smart and efficient.
		1747
		1748	In the following, a 60 second activity timeout is assumed - a timeout that
		1749	gets reset to 60 seconds each time there is activity (e.g. each time some
		1750	data or other life sign was received).
		1751
		1752	=over 4
		1753
		1754	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1755
		1756	This is the most obvious, but not the most simple way: In the beginning,
		1757	start the watcher:
		1758
		1759	ev_timer_init (timer, callback, 60., 0.);
		1760	ev_timer_start (loop, timer);
		1761
		1762	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1763	and start it again:
		1764
		1765	ev_timer_stop (loop, timer);
		1766	ev_timer_set (timer, 60., 0.);
		1767	ev_timer_start (loop, timer);
		1768
		1769	This is relatively simple to implement, but means that each time there is
		1770	some activity, libev will first have to remove the timer from its internal
		1771	data structure and then add it again. Libev tries to be fast, but it's
		1772	still not a constant-time operation.
		1773
		1774	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1775
		1776	This is the easiest way, and involves using C<ev_timer_again> instead of
		1777	C<ev_timer_start>.
		1778
		1779	To implement this, configure an C<ev_timer> with a C<repeat> value
		1780	of C<60> and then call C<ev_timer_again> at start and each time you
		1781	successfully read or write some data. If you go into an idle state where
		1782	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1783	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1784
		1785	That means you can ignore both the C<ev_timer_start> function and the
		1786	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1787	member and C<ev_timer_again>.
		1788
		1789	At start:
		1790
		1791	ev_init (timer, callback);
		1792	timer->repeat = 60.;
		1793	ev_timer_again (loop, timer);
		1794
		1795	Each time there is some activity:
		1796
		1797	ev_timer_again (loop, timer);
		1798
		1799	It is even possible to change the time-out on the fly, regardless of
		1800	whether the watcher is active or not:
		1801
		1802	timer->repeat = 30.;
		1803	ev_timer_again (loop, timer);
		1804
		1805	This is slightly more efficient then stopping/starting the timer each time
		1806	you want to modify its timeout value, as libev does not have to completely
		1807	remove and re-insert the timer from/into its internal data structure.
		1808
		1809	It is, however, even simpler than the "obvious" way to do it.
		1810
		1811	=item 3. Let the timer time out, but then re-arm it as required.
		1812
		1813	This method is more tricky, but usually most efficient: Most timeouts are
		1814	relatively long compared to the intervals between other activity - in
		1815	our example, within 60 seconds, there are usually many I/O events with
		1816	associated activity resets.
		1817
		1818	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1819	but remember the time of last activity, and check for a real timeout only
		1820	within the callback:
		1821
		1822	ev_tstamp last_activity; // time of last activity
		1823
		1824	static void
		1825	callback (EV_P_ ev_timer *w, int revents)
		1826	{
		1827	ev_tstamp now = ev_now (EV_A);
		1828	ev_tstamp timeout = last_activity + 60.;
		1829
		1830	// if last_activity + 60. is older than now, we did time out
		1831	if (timeout < now)
		1832	{
		1833	// timeout occurred, take action
		1834	}
		1835	else
		1836	{
		1837	// callback was invoked, but there was some activity, re-arm
		1838	// the watcher to fire in last_activity + 60, which is
		1839	// guaranteed to be in the future, so "again" is positive:
		1840	w->repeat = timeout - now;
		1841	ev_timer_again (EV_A_ w);
		1842	}
		1843	}
		1844
		1845	To summarise the callback: first calculate the real timeout (defined
		1846	as "60 seconds after the last activity"), then check if that time has
		1847	been reached, which means something I<did>, in fact, time out. Otherwise
		1848	the callback was invoked too early (C<timeout> is in the future), so
		1849	re-schedule the timer to fire at that future time, to see if maybe we have
		1850	a timeout then.
		1851
		1852	Note how C<ev_timer_again> is used, taking advantage of the
		1853	C<ev_timer_again> optimisation when the timer is already running.
		1854
		1855	This scheme causes more callback invocations (about one every 60 seconds
		1856	minus half the average time between activity), but virtually no calls to
		1857	libev to change the timeout.
		1858
		1859	To start the timer, simply initialise the watcher and set C<last_activity>
		1860	to the current time (meaning we just have some activity :), then call the
		1861	callback, which will "do the right thing" and start the timer:
		1862
		1863	ev_init (timer, callback);
		1864	last_activity = ev_now (loop);
		1865	callback (loop, timer, EV_TIMER);
		1866
		1867	And when there is some activity, simply store the current time in
		1868	C<last_activity>, no libev calls at all:
		1869
		1870	last_activity = ev_now (loop);
		1871
		1872	This technique is slightly more complex, but in most cases where the
		1873	time-out is unlikely to be triggered, much more efficient.
		1874
		1875	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1876	callback :) - just change the timeout and invoke the callback, which will
		1877	fix things for you.
		1878
		1879	=item 4. Wee, just use a double-linked list for your timeouts.
		1880
		1881	If there is not one request, but many thousands (millions...), all
		1882	employing some kind of timeout with the same timeout value, then one can
		1883	do even better:
		1884
		1885	When starting the timeout, calculate the timeout value and put the timeout
		1886	at the I<end> of the list.
		1887
		1888	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1889	the list is expected to fire (for example, using the technique #3).
		1890
		1891	When there is some activity, remove the timer from the list, recalculate
		1892	the timeout, append it to the end of the list again, and make sure to
		1893	update the C<ev_timer> if it was taken from the beginning of the list.
		1894
		1895	This way, one can manage an unlimited number of timeouts in O(1) time for
		1896	starting, stopping and updating the timers, at the expense of a major
		1897	complication, and having to use a constant timeout. The constant timeout
		1898	ensures that the list stays sorted.
		1899
		1900	=back
		1901
		1902	So which method the best?
		1903
		1904	Method #2 is a simple no-brain-required solution that is adequate in most
		1905	situations. Method #3 requires a bit more thinking, but handles many cases
		1906	better, and isn't very complicated either. In most case, choosing either
		1907	one is fine, with #3 being better in typical situations.
		1908
		1909	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1910	rather complicated, but extremely efficient, something that really pays
		1911	off after the first million or so of active timers, i.e. it's usually
		1912	overkill :)
		1913
		1914	=head3 The special problem of time updates
		1915
		1916	Establishing the current time is a costly operation (it usually takes at
		1917	least two system calls): EV therefore updates its idea of the current
		1918	time only before and after C<ev_run> collects new events, which causes a
		1919	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1920	lots of events in one iteration.
1125		1921
1126	The relative timeouts are calculated relative to the C<ev_now ()>	1922	The relative timeouts are calculated relative to the C<ev_now ()>
1127	time. This is usually the right thing as this timestamp refers to the time	1923	time. This is usually the right thing as this timestamp refers to the time
1128	of the event triggering whatever timeout you are modifying/starting. If	1924	of the event triggering whatever timeout you are modifying/starting. If
1129	you suspect event processing to be delayed and you I<need> to base the timeout	1925	you suspect event processing to be delayed and you I<need> to base the
1130	on the current time, use something like this to adjust for this:	1926	timeout on the current time, use something like this to adjust for this:
1131		1927
1132	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1928	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1133		1929
1134	The callback is guarenteed to be invoked only when its timeout has passed,	1930	If the event loop is suspended for a long time, you can also force an
1135	but if multiple timers become ready during the same loop iteration then	1931	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1136	order of execution is undefined.	1932	()>.
		1933
		1934	=head3 The special problems of suspended animation
		1935
		1936	When you leave the server world it is quite customary to hit machines that
		1937	can suspend/hibernate - what happens to the clocks during such a suspend?
		1938
		1939	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1940	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1941	to run until the system is suspended, but they will not advance while the
		1942	system is suspended. That means, on resume, it will be as if the program
		1943	was frozen for a few seconds, but the suspend time will not be counted
		1944	towards C<ev_timer> when a monotonic clock source is used. The real time
		1945	clock advanced as expected, but if it is used as sole clocksource, then a
		1946	long suspend would be detected as a time jump by libev, and timers would
		1947	be adjusted accordingly.
		1948
		1949	I would not be surprised to see different behaviour in different between
		1950	operating systems, OS versions or even different hardware.
		1951
		1952	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1953	time jump in the monotonic clocks and the realtime clock. If the program
		1954	is suspended for a very long time, and monotonic clock sources are in use,
		1955	then you can expect C<ev_timer>s to expire as the full suspension time
		1956	will be counted towards the timers. When no monotonic clock source is in
		1957	use, then libev will again assume a timejump and adjust accordingly.
		1958
		1959	It might be beneficial for this latter case to call C<ev_suspend>
		1960	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1961	deterministic behaviour in this case (you can do nothing against
		1962	C<SIGSTOP>).
1137		1963
1138	=head3 Watcher-Specific Functions and Data Members	1964	=head3 Watcher-Specific Functions and Data Members
1139		1965
1140	=over 4	1966	=over 4
1141		1967
1142	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1968	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1143		1969
1144	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1970	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1145		1971
1146	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1972	Configure the timer to trigger after C<after> seconds. If C<repeat>
1147	C<0.>, then it will automatically be stopped. If it is positive, then the	1973	is C<0.>, then it will automatically be stopped once the timeout is
1148	timer will automatically be configured to trigger again C<repeat> seconds	1974	reached. If it is positive, then the timer will automatically be
1149	later, again, and again, until stopped manually.	1975	configured to trigger again C<repeat> seconds later, again, and again,
		1976	until stopped manually.
1150		1977
1151	The timer itself will do a best-effort at avoiding drift, that is, if you	1978	The timer itself will do a best-effort at avoiding drift, that is, if
1152	configure a timer to trigger every 10 seconds, then it will trigger at	1979	you configure a timer to trigger every 10 seconds, then it will normally
1153	exactly 10 second intervals. If, however, your program cannot keep up with	1980	trigger at exactly 10 second intervals. If, however, your program cannot
1154	the timer (because it takes longer than those 10 seconds to do stuff) the	1981	keep up with the timer (because it takes longer than those 10 seconds to
1155	timer will not fire more than once per event loop iteration.	1982	do stuff) the timer will not fire more than once per event loop iteration.
1156		1983
1157	=item ev_timer_again (loop)	1984	=item ev_timer_again (loop, ev_timer *)
1158		1985
1159	This will act as if the timer timed out and restart it again if it is	1986	This will act as if the timer timed out and restart it again if it is
1160	repeating. The exact semantics are:	1987	repeating. The exact semantics are:
1161		1988
1162	If the timer is pending, its pending status is cleared.	1989	If the timer is pending, its pending status is cleared.
1163		1990
1164	If the timer is started but nonrepeating, stop it (as if it timed out).	1991	If the timer is started but non-repeating, stop it (as if it timed out).
1165		1992
1166	If the timer is repeating, either start it if necessary (with the	1993	If the timer is repeating, either start it if necessary (with the
1167	C<repeat> value), or reset the running timer to the C<repeat> value.	1994	C<repeat> value), or reset the running timer to the C<repeat> value.
1168		1995
1169	This sounds a bit complicated, but here is a useful and typical	1996	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1170	example: Imagine you have a tcp connection and you want a so-called idle	1997	usage example.
1171	timeout, that is, you want to be called when there have been, say, 60
1172	seconds of inactivity on the socket. The easiest way to do this is to
1173	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1174	C<ev_timer_again> each time you successfully read or write some data. If
1175	you go into an idle state where you do not expect data to travel on the
1176	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1177	automatically restart it if need be.
1178		1998
1179	That means you can ignore the C<after> value and C<ev_timer_start>	1999	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1180	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1181		2000
1182	ev_timer_init (timer, callback, 0., 5.);	2001	Returns the remaining time until a timer fires. If the timer is active,
1183	ev_timer_again (loop, timer);	2002	then this time is relative to the current event loop time, otherwise it's
1184	...	2003	the timeout value currently configured.
1185	timer->again = 17.;
1186	ev_timer_again (loop, timer);
1187	...
1188	timer->again = 10.;
1189	ev_timer_again (loop, timer);
1190		2004
1191	This is more slightly efficient then stopping/starting the timer each time	2005	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1192	you want to modify its timeout value.	2006	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2007	will return C<4>. When the timer expires and is restarted, it will return
		2008	roughly C<7> (likely slightly less as callback invocation takes some time,
		2009	too), and so on.
1193		2010
1194	=item ev_tstamp repeat [read-write]	2011	=item ev_tstamp repeat [read-write]
1195		2012
1196	The current C<repeat> value. Will be used each time the watcher times out	2013	The current C<repeat> value. Will be used each time the watcher times out
1197	or C<ev_timer_again> is called and determines the next timeout (if any),	2014	or C<ev_timer_again> is called, and determines the next timeout (if any),
1198	which is also when any modifications are taken into account.	2015	which is also when any modifications are taken into account.
1199		2016
1200	=back	2017	=back
1201		2018
1202	=head3 Examples	2019	=head3 Examples
1203		2020
1204	Example: Create a timer that fires after 60 seconds.	2021	Example: Create a timer that fires after 60 seconds.
1205		2022
1206	static void	2023	static void
1207	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2024	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1208	{	2025	{
1209	.. one minute over, w is actually stopped right here	2026	.. one minute over, w is actually stopped right here
1210	}	2027	}
1211		2028
1212	struct ev_timer mytimer;	2029	ev_timer mytimer;
1213	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2030	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1214	ev_timer_start (loop, &mytimer);	2031	ev_timer_start (loop, &mytimer);
1215		2032
1216	Example: Create a timeout timer that times out after 10 seconds of	2033	Example: Create a timeout timer that times out after 10 seconds of
1217	inactivity.	2034	inactivity.
1218		2035
1219	static void	2036	static void
1220	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2037	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1221	{	2038	{
1222	.. ten seconds without any activity	2039	.. ten seconds without any activity
1223	}	2040	}
1224		2041
1225	struct ev_timer mytimer;	2042	ev_timer mytimer;
1226	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2043	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1227	ev_timer_again (&mytimer); /* start timer */	2044	ev_timer_again (&mytimer); /* start timer */
1228	ev_loop (loop, 0);	2045	ev_run (loop, 0);
1229		2046
1230	// and in some piece of code that gets executed on any "activity":	2047	// and in some piece of code that gets executed on any "activity":
1231	// reset the timeout to start ticking again at 10 seconds	2048	// reset the timeout to start ticking again at 10 seconds
1232	ev_timer_again (&mytimer);	2049	ev_timer_again (&mytimer);
1233		2050
1234		2051
1235	=head2 C<ev_periodic> - to cron or not to cron?	2052	=head2 C<ev_periodic> - to cron or not to cron?
1236		2053
1237	Periodic watchers are also timers of a kind, but they are very versatile	2054	Periodic watchers are also timers of a kind, but they are very versatile
1238	(and unfortunately a bit complex).	2055	(and unfortunately a bit complex).
1239		2056
1240	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2057	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1241	but on wallclock time (absolute time). You can tell a periodic watcher	2058	relative time, the physical time that passes) but on wall clock time
1242	to trigger "at" some specific point in time. For example, if you tell a	2059	(absolute time, the thing you can read on your calender or clock). The
1243	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2060	difference is that wall clock time can run faster or slower than real
1244	+ 10.>) and then reset your system clock to the last year, then it will	2061	time, and time jumps are not uncommon (e.g. when you adjust your
1245	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2062	wrist-watch).
1246	roughly 10 seconds later).
1247		2063
1248	They can also be used to implement vastly more complex timers, such as	2064	You can tell a periodic watcher to trigger after some specific point
1249	triggering an event on each midnight, local time or other, complicated,	2065	in time: for example, if you tell a periodic watcher to trigger "in 10
1250	rules.	2066	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2067	not a delay) and then reset your system clock to January of the previous
		2068	year, then it will take a year or more to trigger the event (unlike an
		2069	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2070	it, as it uses a relative timeout).
1251		2071
		2072	C<ev_periodic> watchers can also be used to implement vastly more complex
		2073	timers, such as triggering an event on each "midnight, local time", or
		2074	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2075	those cannot react to time jumps.
		2076
1252	As with timers, the callback is guarenteed to be invoked only when the	2077	As with timers, the callback is guaranteed to be invoked only when the
1253	time (C<at>) has been passed, but if multiple periodic timers become ready	2078	point in time where it is supposed to trigger has passed. If multiple
1254	during the same loop iteration then order of execution is undefined.	2079	timers become ready during the same loop iteration then the ones with
		2080	earlier time-out values are invoked before ones with later time-out values
		2081	(but this is no longer true when a callback calls C<ev_run> recursively).
1255		2082
1256	=head3 Watcher-Specific Functions and Data Members	2083	=head3 Watcher-Specific Functions and Data Members
1257		2084
1258	=over 4	2085	=over 4
1259		2086
1260	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2087	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1261		2088
1262	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2089	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1263		2090
1264	Lots of arguments, lets sort it out... There are basically three modes of	2091	Lots of arguments, let's sort it out... There are basically three modes of
1265	operation, and we will explain them from simplest to complex:	2092	operation, and we will explain them from simplest to most complex:
1266		2093
1267	=over 4	2094	=over 4
1268		2095
1269	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2096	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1270		2097
1271	In this configuration the watcher triggers an event at the wallclock time	2098	In this configuration the watcher triggers an event after the wall clock
1272	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2099	time C<offset> has passed. It will not repeat and will not adjust when a
1273	that is, if it is to be run at January 1st 2011 then it will run when the	2100	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1274	system time reaches or surpasses this time.	2101	will be stopped and invoked when the system clock reaches or surpasses
		2102	this point in time.
1275		2103
1276	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2104	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1277		2105
1278	In this mode the watcher will always be scheduled to time out at the next	2106	In this mode the watcher will always be scheduled to time out at the next
1279	C<at + N * interval> time (for some integer N, which can also be negative)	2107	C<offset + N * interval> time (for some integer N, which can also be
1280	and then repeat, regardless of any time jumps.	2108	negative) and then repeat, regardless of any time jumps. The C<offset>
		2109	argument is merely an offset into the C<interval> periods.
1281		2110
1282	This can be used to create timers that do not drift with respect to system	2111	This can be used to create timers that do not drift with respect to the
1283	time:	2112	system clock, for example, here is an C<ev_periodic> that triggers each
		2113	hour, on the hour (with respect to UTC):
1284		2114
1285	ev_periodic_set (&periodic, 0., 3600., 0);	2115	ev_periodic_set (&periodic, 0., 3600., 0);
1286		2116
1287	This doesn't mean there will always be 3600 seconds in between triggers,	2117	This doesn't mean there will always be 3600 seconds in between triggers,
1288	but only that the the callback will be called when the system time shows a	2118	but only that the callback will be called when the system time shows a
1289	full hour (UTC), or more correctly, when the system time is evenly divisible	2119	full hour (UTC), or more correctly, when the system time is evenly divisible
1290	by 3600.	2120	by 3600.
1291		2121
1292	Another way to think about it (for the mathematically inclined) is that	2122	Another way to think about it (for the mathematically inclined) is that
1293	C<ev_periodic> will try to run the callback in this mode at the next possible	2123	C<ev_periodic> will try to run the callback in this mode at the next possible
1294	time where C<time = at (mod interval)>, regardless of any time jumps.	2124	time where C<time = offset (mod interval)>, regardless of any time jumps.
1295		2125
1296	For numerical stability it is preferable that the C<at> value is near	2126	For numerical stability it is preferable that the C<offset> value is near
1297	C<ev_now ()> (the current time), but there is no range requirement for	2127	C<ev_now ()> (the current time), but there is no range requirement for
1298	this value.	2128	this value, and in fact is often specified as zero.
1299		2129
		2130	Note also that there is an upper limit to how often a timer can fire (CPU
		2131	speed for example), so if C<interval> is very small then timing stability
		2132	will of course deteriorate. Libev itself tries to be exact to be about one
		2133	millisecond (if the OS supports it and the machine is fast enough).
		2134
1300	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2135	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1301		2136
1302	In this mode the values for C<interval> and C<at> are both being	2137	In this mode the values for C<interval> and C<offset> are both being
1303	ignored. Instead, each time the periodic watcher gets scheduled, the	2138	ignored. Instead, each time the periodic watcher gets scheduled, the
1304	reschedule callback will be called with the watcher as first, and the	2139	reschedule callback will be called with the watcher as first, and the
1305	current time as second argument.	2140	current time as second argument.
1306		2141
1307	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2142	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1308	ever, or make any event loop modifications>. If you need to stop it,	2143	or make ANY other event loop modifications whatsoever, unless explicitly
1309	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2144	allowed by documentation here>.
1310	starting an C<ev_prepare> watcher, which is legal).
1311		2145
		2146	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2147	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2148	only event loop modification you are allowed to do).
		2149
1312	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2150	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1313	ev_tstamp now)>, e.g.:	2151	*w, ev_tstamp now)>, e.g.:
1314		2152
		2153	static ev_tstamp
1315	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2154	my_rescheduler (ev_periodic *w, ev_tstamp now)
1316	{	2155	{
1317	return now + 60.;	2156	return now + 60.;
1318	}	2157	}
1319		2158
1320	It must return the next time to trigger, based on the passed time value	2159	It must return the next time to trigger, based on the passed time value
1321	(that is, the lowest time value larger than to the second argument). It	2160	(that is, the lowest time value larger than to the second argument). It
1322	will usually be called just before the callback will be triggered, but	2161	will usually be called just before the callback will be triggered, but
1323	might be called at other times, too.	2162	might be called at other times, too.
1324		2163
1325	NOTE: I<< This callback must always return a time that is later than the	2164	NOTE: I<< This callback must always return a time that is higher than or
1326	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2165	equal to the passed C<now> value >>.
1327		2166
1328	This can be used to create very complex timers, such as a timer that	2167	This can be used to create very complex timers, such as a timer that
1329	triggers on each midnight, local time. To do this, you would calculate the	2168	triggers on "next midnight, local time". To do this, you would calculate the
1330	next midnight after C<now> and return the timestamp value for this. How	2169	next midnight after C<now> and return the timestamp value for this. How
1331	you do this is, again, up to you (but it is not trivial, which is the main	2170	you do this is, again, up to you (but it is not trivial, which is the main
1332	reason I omitted it as an example).	2171	reason I omitted it as an example).
1333		2172
1334	=back	2173	=back
…		…
1338	Simply stops and restarts the periodic watcher again. This is only useful	2177	Simply stops and restarts the periodic watcher again. This is only useful
1339	when you changed some parameters or the reschedule callback would return	2178	when you changed some parameters or the reschedule callback would return
1340	a different time than the last time it was called (e.g. in a crond like	2179	a different time than the last time it was called (e.g. in a crond like
1341	program when the crontabs have changed).	2180	program when the crontabs have changed).
1342		2181
		2182	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2183
		2184	When active, returns the absolute time that the watcher is supposed
		2185	to trigger next. This is not the same as the C<offset> argument to
		2186	C<ev_periodic_set>, but indeed works even in interval and manual
		2187	rescheduling modes.
		2188
1343	=item ev_tstamp offset [read-write]	2189	=item ev_tstamp offset [read-write]
1344		2190
1345	When repeating, this contains the offset value, otherwise this is the	2191	When repeating, this contains the offset value, otherwise this is the
1346	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2192	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2193	although libev might modify this value for better numerical stability).
1347		2194
1348	Can be modified any time, but changes only take effect when the periodic	2195	Can be modified any time, but changes only take effect when the periodic
1349	timer fires or C<ev_periodic_again> is being called.	2196	timer fires or C<ev_periodic_again> is being called.
1350		2197
1351	=item ev_tstamp interval [read-write]	2198	=item ev_tstamp interval [read-write]
1352		2199
1353	The current interval value. Can be modified any time, but changes only	2200	The current interval value. Can be modified any time, but changes only
1354	take effect when the periodic timer fires or C<ev_periodic_again> is being	2201	take effect when the periodic timer fires or C<ev_periodic_again> is being
1355	called.	2202	called.
1356		2203
1357	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2204	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1358		2205
1359	The current reschedule callback, or C<0>, if this functionality is	2206	The current reschedule callback, or C<0>, if this functionality is
1360	switched off. Can be changed any time, but changes only take effect when	2207	switched off. Can be changed any time, but changes only take effect when
1361	the periodic timer fires or C<ev_periodic_again> is being called.	2208	the periodic timer fires or C<ev_periodic_again> is being called.
1362		2209
1363	=item ev_tstamp at [read-only]
1364
1365	When active, contains the absolute time that the watcher is supposed to
1366	trigger next.
1367
1368	=back	2210	=back
1369		2211
1370	=head3 Examples	2212	=head3 Examples
1371		2213
1372	Example: Call a callback every hour, or, more precisely, whenever the	2214	Example: Call a callback every hour, or, more precisely, whenever the
1373	system clock is divisible by 3600. The callback invocation times have	2215	system time is divisible by 3600. The callback invocation times have
1374	potentially a lot of jittering, but good long-term stability.	2216	potentially a lot of jitter, but good long-term stability.
1375		2217
1376	static void	2218	static void
1377	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2219	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1378	{	2220	{
1379	... its now a full hour (UTC, or TAI or whatever your clock follows)	2221	... its now a full hour (UTC, or TAI or whatever your clock follows)
1380	}	2222	}
1381		2223
1382	struct ev_periodic hourly_tick;	2224	ev_periodic hourly_tick;
1383	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2225	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1384	ev_periodic_start (loop, &hourly_tick);	2226	ev_periodic_start (loop, &hourly_tick);
1385		2227
1386	Example: The same as above, but use a reschedule callback to do it:	2228	Example: The same as above, but use a reschedule callback to do it:
1387		2229
1388	#include <math.h>	2230	#include <math.h>
1389		2231
1390	static ev_tstamp	2232	static ev_tstamp
1391	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2233	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1392	{	2234	{
1393	return fmod (now, 3600.) + 3600.;	2235	return now + (3600. - fmod (now, 3600.));
1394	}	2236	}
1395		2237
1396	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2238	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1397		2239
1398	Example: Call a callback every hour, starting now:	2240	Example: Call a callback every hour, starting now:
1399		2241
1400	struct ev_periodic hourly_tick;	2242	ev_periodic hourly_tick;
1401	ev_periodic_init (&hourly_tick, clock_cb,	2243	ev_periodic_init (&hourly_tick, clock_cb,
1402	fmod (ev_now (loop), 3600.), 3600., 0);	2244	fmod (ev_now (loop), 3600.), 3600., 0);
1403	ev_periodic_start (loop, &hourly_tick);	2245	ev_periodic_start (loop, &hourly_tick);
1404		2246
1405		2247
1406	=head2 C<ev_signal> - signal me when a signal gets signalled!	2248	=head2 C<ev_signal> - signal me when a signal gets signalled!
1407		2249
1408	Signal watchers will trigger an event when the process receives a specific	2250	Signal watchers will trigger an event when the process receives a specific
1409	signal one or more times. Even though signals are very asynchronous, libev	2251	signal one or more times. Even though signals are very asynchronous, libev
1410	will try it's best to deliver signals synchronously, i.e. as part of the	2252	will try it's best to deliver signals synchronously, i.e. as part of the
1411	normal event processing, like any other event.	2253	normal event processing, like any other event.
1412		2254
		2255	If you want signals to be delivered truly asynchronously, just use
		2256	C<sigaction> as you would do without libev and forget about sharing
		2257	the signal. You can even use C<ev_async> from a signal handler to
		2258	synchronously wake up an event loop.
		2259
1413	You can configure as many watchers as you like per signal. Only when the	2260	You can configure as many watchers as you like for the same signal, but
		2261	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2262	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2263	C<SIGINT> in both the default loop and another loop at the same time. At
		2264	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2265
1414	first watcher gets started will libev actually register a signal watcher	2266	When the first watcher gets started will libev actually register something
1415	with the kernel (thus it coexists with your own signal handlers as long	2267	with the kernel (thus it coexists with your own signal handlers as long as
1416	as you don't register any with libev). Similarly, when the last signal	2268	you don't register any with libev for the same signal).
1417	watcher for a signal is stopped libev will reset the signal handler to	2269
1418	SIG_DFL (regardless of what it was set to before).	2270	If possible and supported, libev will install its handlers with
		2271	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2272	not be unduly interrupted. If you have a problem with system calls getting
		2273	interrupted by signals you can block all signals in an C<ev_check> watcher
		2274	and unblock them in an C<ev_prepare> watcher.
		2275
		2276	=head3 The special problem of inheritance over fork/execve/pthread_create
		2277
		2278	Both the signal mask (C<sigprocmask>) and the signal disposition
		2279	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2280	stopping it again), that is, libev might or might not block the signal,
		2281	and might or might not set or restore the installed signal handler.
		2282
		2283	While this does not matter for the signal disposition (libev never
		2284	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2285	C<execve>), this matters for the signal mask: many programs do not expect
		2286	certain signals to be blocked.
		2287
		2288	This means that before calling C<exec> (from the child) you should reset
		2289	the signal mask to whatever "default" you expect (all clear is a good
		2290	choice usually).
		2291
		2292	The simplest way to ensure that the signal mask is reset in the child is
		2293	to install a fork handler with C<pthread_atfork> that resets it. That will
		2294	catch fork calls done by libraries (such as the libc) as well.
		2295
		2296	In current versions of libev, the signal will not be blocked indefinitely
		2297	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2298	the window of opportunity for problems, it will not go away, as libev
		2299	I<has> to modify the signal mask, at least temporarily.
		2300
		2301	So I can't stress this enough: I<If you do not reset your signal mask when
		2302	you expect it to be empty, you have a race condition in your code>. This
		2303	is not a libev-specific thing, this is true for most event libraries.
1419		2304
1420	=head3 Watcher-Specific Functions and Data Members	2305	=head3 Watcher-Specific Functions and Data Members
1421		2306
1422	=over 4	2307	=over 4
1423		2308
…		…
1432		2317
1433	The signal the watcher watches out for.	2318	The signal the watcher watches out for.
1434		2319
1435	=back	2320	=back
1436		2321
		2322	=head3 Examples
		2323
		2324	Example: Try to exit cleanly on SIGINT.
		2325
		2326	static void
		2327	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2328	{
		2329	ev_break (loop, EVBREAK_ALL);
		2330	}
		2331
		2332	ev_signal signal_watcher;
		2333	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2334	ev_signal_start (loop, &signal_watcher);
		2335
1437		2336
1438	=head2 C<ev_child> - watch out for process status changes	2337	=head2 C<ev_child> - watch out for process status changes
1439		2338
1440	Child watchers trigger when your process receives a SIGCHLD in response to	2339	Child watchers trigger when your process receives a SIGCHLD in response to
1441	some child status changes (most typically when a child of yours dies).	2340	some child status changes (most typically when a child of yours dies or
		2341	exits). It is permissible to install a child watcher I<after> the child
		2342	has been forked (which implies it might have already exited), as long
		2343	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2344	forking and then immediately registering a watcher for the child is fine,
		2345	but forking and registering a watcher a few event loop iterations later or
		2346	in the next callback invocation is not.
		2347
		2348	Only the default event loop is capable of handling signals, and therefore
		2349	you can only register child watchers in the default event loop.
		2350
		2351	Due to some design glitches inside libev, child watchers will always be
		2352	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2353	libev)
		2354
		2355	=head3 Process Interaction
		2356
		2357	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2358	initialised. This is necessary to guarantee proper behaviour even if the
		2359	first child watcher is started after the child exits. The occurrence
		2360	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2361	synchronously as part of the event loop processing. Libev always reaps all
		2362	children, even ones not watched.
		2363
		2364	=head3 Overriding the Built-In Processing
		2365
		2366	Libev offers no special support for overriding the built-in child
		2367	processing, but if your application collides with libev's default child
		2368	handler, you can override it easily by installing your own handler for
		2369	C<SIGCHLD> after initialising the default loop, and making sure the
		2370	default loop never gets destroyed. You are encouraged, however, to use an
		2371	event-based approach to child reaping and thus use libev's support for
		2372	that, so other libev users can use C<ev_child> watchers freely.
		2373
		2374	=head3 Stopping the Child Watcher
		2375
		2376	Currently, the child watcher never gets stopped, even when the
		2377	child terminates, so normally one needs to stop the watcher in the
		2378	callback. Future versions of libev might stop the watcher automatically
		2379	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2380	problem).
1442		2381
1443	=head3 Watcher-Specific Functions and Data Members	2382	=head3 Watcher-Specific Functions and Data Members
1444		2383
1445	=over 4	2384	=over 4
1446		2385
…		…
1472		2411
1473	=back	2412	=back
1474		2413
1475	=head3 Examples	2414	=head3 Examples
1476		2415
1477	Example: Try to exit cleanly on SIGINT and SIGTERM.	2416	Example: C<fork()> a new process and install a child handler to wait for
		2417	its completion.
1478		2418
		2419	ev_child cw;
		2420
1479	static void	2421	static void
1480	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2422	child_cb (EV_P_ ev_child *w, int revents)
1481	{	2423	{
1482	ev_unloop (loop, EVUNLOOP_ALL);	2424	ev_child_stop (EV_A_ w);
		2425	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1483	}	2426	}
1484		2427
1485	struct ev_signal signal_watcher;	2428	pid_t pid = fork ();
1486	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2429
1487	ev_signal_start (loop, &sigint_cb);	2430	if (pid < 0)
		2431	// error
		2432	else if (pid == 0)
		2433	{
		2434	// the forked child executes here
		2435	exit (1);
		2436	}
		2437	else
		2438	{
		2439	ev_child_init (&cw, child_cb, pid, 0);
		2440	ev_child_start (EV_DEFAULT_ &cw);
		2441	}
1488		2442
1489		2443
1490	=head2 C<ev_stat> - did the file attributes just change?	2444	=head2 C<ev_stat> - did the file attributes just change?
1491		2445
1492	This watches a filesystem path for attribute changes. That is, it calls	2446	This watches a file system path for attribute changes. That is, it calls
1493	C<stat> regularly (or when the OS says it changed) and sees if it changed	2447	C<stat> on that path in regular intervals (or when the OS says it changed)
1494	compared to the last time, invoking the callback if it did.	2448	and sees if it changed compared to the last time, invoking the callback if
		2449	it did.
1495		2450
1496	The path does not need to exist: changing from "path exists" to "path does	2451	The path does not need to exist: changing from "path exists" to "path does
1497	not exist" is a status change like any other. The condition "path does	2452	not exist" is a status change like any other. The condition "path does not
1498	not exist" is signified by the C<st_nlink> field being zero (which is	2453	exist" (or more correctly "path cannot be stat'ed") is signified by the
1499	otherwise always forced to be at least one) and all the other fields of	2454	C<st_nlink> field being zero (which is otherwise always forced to be at
1500	the stat buffer having unspecified contents.	2455	least one) and all the other fields of the stat buffer having unspecified
		2456	contents.
1501		2457
1502	The path I<should> be absolute and I<must not> end in a slash. If it is	2458	The path I<must not> end in a slash or contain special components such as
		2459	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1503	relative and your working directory changes, the behaviour is undefined.	2460	your working directory changes, then the behaviour is undefined.
1504		2461
1505	Since there is no standard to do this, the portable implementation simply	2462	Since there is no portable change notification interface available, the
1506	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2463	portable implementation simply calls C<stat(2)> regularly on the path
1507	can specify a recommended polling interval for this case. If you specify	2464	to see if it changed somehow. You can specify a recommended polling
1508	a polling interval of C<0> (highly recommended!) then a I<suitable,	2465	interval for this case. If you specify a polling interval of C<0> (highly
1509	unspecified default> value will be used (which you can expect to be around	2466	recommended!) then a I<suitable, unspecified default> value will be used
1510	five seconds, although this might change dynamically). Libev will also	2467	(which you can expect to be around five seconds, although this might
1511	impose a minimum interval which is currently around C<0.1>, but thats	2468	change dynamically). Libev will also impose a minimum interval which is
1512	usually overkill.	2469	currently around C<0.1>, but that's usually overkill.
1513		2470
1514	This watcher type is not meant for massive numbers of stat watchers,	2471	This watcher type is not meant for massive numbers of stat watchers,
1515	as even with OS-supported change notifications, this can be	2472	as even with OS-supported change notifications, this can be
1516	resource-intensive.	2473	resource-intensive.
1517		2474
1518	At the time of this writing, only the Linux inotify interface is	2475	At the time of this writing, the only OS-specific interface implemented
1519	implemented (implementing kqueue support is left as an exercise for the	2476	is the Linux inotify interface (implementing kqueue support is left as an
1520	reader). Inotify will be used to give hints only and should not change the	2477	exercise for the reader. Note, however, that the author sees no way of
1521	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2478	implementing C<ev_stat> semantics with kqueue, except as a hint).
1522	to fall back to regular polling again even with inotify, but changes are
1523	usually detected immediately, and if the file exists there will be no
1524	polling.
1525		2479
1526	=head3 Inotify	2480	=head3 ABI Issues (Largefile Support)
1527		2481
		2482	Libev by default (unless the user overrides this) uses the default
		2483	compilation environment, which means that on systems with large file
		2484	support disabled by default, you get the 32 bit version of the stat
		2485	structure. When using the library from programs that change the ABI to
		2486	use 64 bit file offsets the programs will fail. In that case you have to
		2487	compile libev with the same flags to get binary compatibility. This is
		2488	obviously the case with any flags that change the ABI, but the problem is
		2489	most noticeably displayed with ev_stat and large file support.
		2490
		2491	The solution for this is to lobby your distribution maker to make large
		2492	file interfaces available by default (as e.g. FreeBSD does) and not
		2493	optional. Libev cannot simply switch on large file support because it has
		2494	to exchange stat structures with application programs compiled using the
		2495	default compilation environment.
		2496
		2497	=head3 Inotify and Kqueue
		2498
1528	When C<inotify (7)> support has been compiled into libev (generally only	2499	When C<inotify (7)> support has been compiled into libev and present at
1529	available on Linux) and present at runtime, it will be used to speed up	2500	runtime, it will be used to speed up change detection where possible. The
1530	change detection where possible. The inotify descriptor will be created lazily	2501	inotify descriptor will be created lazily when the first C<ev_stat>
1531	when the first C<ev_stat> watcher is being started.	2502	watcher is being started.
1532		2503
1533	Inotify presense does not change the semantics of C<ev_stat> watchers	2504	Inotify presence does not change the semantics of C<ev_stat> watchers
1534	except that changes might be detected earlier, and in some cases, to avoid	2505	except that changes might be detected earlier, and in some cases, to avoid
1535	making regular C<stat> calls. Even in the presense of inotify support	2506	making regular C<stat> calls. Even in the presence of inotify support
1536	there are many cases where libev has to resort to regular C<stat> polling.	2507	there are many cases where libev has to resort to regular C<stat> polling,
		2508	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2509	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2510	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2511	xfs are fully working) libev usually gets away without polling.
1537		2512
1538	(There is no support for kqueue, as apparently it cannot be used to	2513	There is no support for kqueue, as apparently it cannot be used to
1539	implement this functionality, due to the requirement of having a file	2514	implement this functionality, due to the requirement of having a file
1540	descriptor open on the object at all times).	2515	descriptor open on the object at all times, and detecting renames, unlinks
		2516	etc. is difficult.
		2517
		2518	=head3 C<stat ()> is a synchronous operation
		2519
		2520	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2521	the process. The exception are C<ev_stat> watchers - those call C<stat
		2522	()>, which is a synchronous operation.
		2523
		2524	For local paths, this usually doesn't matter: unless the system is very
		2525	busy or the intervals between stat's are large, a stat call will be fast,
		2526	as the path data is usually in memory already (except when starting the
		2527	watcher).
		2528
		2529	For networked file systems, calling C<stat ()> can block an indefinite
		2530	time due to network issues, and even under good conditions, a stat call
		2531	often takes multiple milliseconds.
		2532
		2533	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2534	paths, although this is fully supported by libev.
1541		2535
1542	=head3 The special problem of stat time resolution	2536	=head3 The special problem of stat time resolution
1543		2537
1544	The C<stat ()> syscall only supports full-second resolution portably, and	2538	The C<stat ()> system call only supports full-second resolution portably,
1545	even on systems where the resolution is higher, many filesystems still	2539	and even on systems where the resolution is higher, most file systems
1546	only support whole seconds.	2540	still only support whole seconds.
1547		2541
1548	That means that, if the time is the only thing that changes, you might	2542	That means that, if the time is the only thing that changes, you can
1549	miss updates: on the first update, C<ev_stat> detects a change and calls	2543	easily miss updates: on the first update, C<ev_stat> detects a change and
1550	your callback, which does something. When there is another update within	2544	calls your callback, which does something. When there is another update
1551	the same second, C<ev_stat> will be unable to detect it.	2545	within the same second, C<ev_stat> will be unable to detect unless the
		2546	stat data does change in other ways (e.g. file size).
1552		2547
1553	The solution to this is to delay acting on a change for a second (or till	2548	The solution to this is to delay acting on a change for slightly more
1554	the next second boundary), using a roughly one-second delay C<ev_timer>	2549	than a second (or till slightly after the next full second boundary), using
1555	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2550	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1556	is added to work around small timing inconsistencies of some operating	2551	ev_timer_again (loop, w)>).
1557	systems.	2552
		2553	The C<.02> offset is added to work around small timing inconsistencies
		2554	of some operating systems (where the second counter of the current time
		2555	might be be delayed. One such system is the Linux kernel, where a call to
		2556	C<gettimeofday> might return a timestamp with a full second later than
		2557	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2558	update file times then there will be a small window where the kernel uses
		2559	the previous second to update file times but libev might already execute
		2560	the timer callback).
1558		2561
1559	=head3 Watcher-Specific Functions and Data Members	2562	=head3 Watcher-Specific Functions and Data Members
1560		2563
1561	=over 4	2564	=over 4
1562		2565
…		…
1568	C<path>. The C<interval> is a hint on how quickly a change is expected to	2571	C<path>. The C<interval> is a hint on how quickly a change is expected to
1569	be detected and should normally be specified as C<0> to let libev choose	2572	be detected and should normally be specified as C<0> to let libev choose
1570	a suitable value. The memory pointed to by C<path> must point to the same	2573	a suitable value. The memory pointed to by C<path> must point to the same
1571	path for as long as the watcher is active.	2574	path for as long as the watcher is active.
1572		2575
1573	The callback will be receive C<EV_STAT> when a change was detected,	2576	The callback will receive an C<EV_STAT> event when a change was detected,
1574	relative to the attributes at the time the watcher was started (or the	2577	relative to the attributes at the time the watcher was started (or the
1575	last change was detected).	2578	last change was detected).
1576		2579
1577	=item ev_stat_stat (ev_stat *)	2580	=item ev_stat_stat (loop, ev_stat *)
1578		2581
1579	Updates the stat buffer immediately with new values. If you change the	2582	Updates the stat buffer immediately with new values. If you change the
1580	watched path in your callback, you could call this fucntion to avoid	2583	watched path in your callback, you could call this function to avoid
1581	detecting this change (while introducing a race condition). Can also be	2584	detecting this change (while introducing a race condition if you are not
1582	useful simply to find out the new values.	2585	the only one changing the path). Can also be useful simply to find out the
		2586	new values.
1583		2587
1584	=item ev_statdata attr [read-only]	2588	=item ev_statdata attr [read-only]
1585		2589
1586	The most-recently detected attributes of the file. Although the type is of	2590	The most-recently detected attributes of the file. Although the type is
1587	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2591	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1588	suitable for your system. If the C<st_nlink> member is C<0>, then there	2592	suitable for your system, but you can only rely on the POSIX-standardised
		2593	members to be present. If the C<st_nlink> member is C<0>, then there was
1589	was some error while C<stat>ing the file.	2594	some error while C<stat>ing the file.
1590		2595
1591	=item ev_statdata prev [read-only]	2596	=item ev_statdata prev [read-only]
1592		2597
1593	The previous attributes of the file. The callback gets invoked whenever	2598	The previous attributes of the file. The callback gets invoked whenever
1594	C<prev> != C<attr>.	2599	C<prev> != C<attr>, or, more precisely, one or more of these members
		2600	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2601	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1595		2602
1596	=item ev_tstamp interval [read-only]	2603	=item ev_tstamp interval [read-only]
1597		2604
1598	The specified interval.	2605	The specified interval.
1599		2606
1600	=item const char *path [read-only]	2607	=item const char *path [read-only]
1601		2608
1602	The filesystem path that is being watched.	2609	The file system path that is being watched.
1603		2610
1604	=back	2611	=back
1605		2612
1606	=head3 Examples	2613	=head3 Examples
1607		2614
1608	Example: Watch C</etc/passwd> for attribute changes.	2615	Example: Watch C</etc/passwd> for attribute changes.
1609		2616
1610	static void	2617	static void
1611	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2618	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1612	{	2619	{
1613	/* /etc/passwd changed in some way */	2620	/* /etc/passwd changed in some way */
1614	if (w->attr.st_nlink)	2621	if (w->attr.st_nlink)
1615	{	2622	{
1616	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2623	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1617	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2624	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1618	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2625	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1619	}	2626	}
1620	else	2627	else
1621	/* you shalt not abuse printf for puts */	2628	/* you shalt not abuse printf for puts */
1622	puts ("wow, /etc/passwd is not there, expect problems. "	2629	puts ("wow, /etc/passwd is not there, expect problems. "
1623	"if this is windows, they already arrived\n");	2630	"if this is windows, they already arrived\n");
1624	}	2631	}
1625		2632
1626	...	2633	...
1627	ev_stat passwd;	2634	ev_stat passwd;
1628		2635
1629	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2636	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1630	ev_stat_start (loop, &passwd);	2637	ev_stat_start (loop, &passwd);
1631		2638
1632	Example: Like above, but additionally use a one-second delay so we do not	2639	Example: Like above, but additionally use a one-second delay so we do not
1633	miss updates (however, frequent updates will delay processing, too, so	2640	miss updates (however, frequent updates will delay processing, too, so
1634	one might do the work both on C<ev_stat> callback invocation I<and> on	2641	one might do the work both on C<ev_stat> callback invocation I<and> on
1635	C<ev_timer> callback invocation).	2642	C<ev_timer> callback invocation).
1636		2643
1637	static ev_stat passwd;	2644	static ev_stat passwd;
1638	static ev_timer timer;	2645	static ev_timer timer;
1639		2646
1640	static void	2647	static void
1641	timer_cb (EV_P_ ev_timer *w, int revents)	2648	timer_cb (EV_P_ ev_timer *w, int revents)
1642	{	2649	{
1643	ev_timer_stop (EV_A_ w);	2650	ev_timer_stop (EV_A_ w);
1644		2651
1645	/* now it's one second after the most recent passwd change */	2652	/* now it's one second after the most recent passwd change */
1646	}	2653	}
1647		2654
1648	static void	2655	static void
1649	stat_cb (EV_P_ ev_stat *w, int revents)	2656	stat_cb (EV_P_ ev_stat *w, int revents)
1650	{	2657	{
1651	/* reset the one-second timer */	2658	/* reset the one-second timer */
1652	ev_timer_again (EV_A_ &timer);	2659	ev_timer_again (EV_A_ &timer);
1653	}	2660	}
1654		2661
1655	...	2662	...
1656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2663	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1657	ev_stat_start (loop, &passwd);	2664	ev_stat_start (loop, &passwd);
1658	ev_timer_init (&timer, timer_cb, 0., 1.01);	2665	ev_timer_init (&timer, timer_cb, 0., 1.02);
1659		2666
1660		2667
1661	=head2 C<ev_idle> - when you've got nothing better to do...	2668	=head2 C<ev_idle> - when you've got nothing better to do...
1662		2669
1663	Idle watchers trigger events when no other events of the same or higher	2670	Idle watchers trigger events when no other events of the same or higher
1664	priority are pending (prepare, check and other idle watchers do not	2671	priority are pending (prepare, check and other idle watchers do not count
1665	count).	2672	as receiving "events").
1666		2673
1667	That is, as long as your process is busy handling sockets or timeouts	2674	That is, as long as your process is busy handling sockets or timeouts
1668	(or even signals, imagine) of the same or higher priority it will not be	2675	(or even signals, imagine) of the same or higher priority it will not be
1669	triggered. But when your process is idle (or only lower-priority watchers	2676	triggered. But when your process is idle (or only lower-priority watchers
1670	are pending), the idle watchers are being called once per event loop	2677	are pending), the idle watchers are being called once per event loop
…		…
1681		2688
1682	=head3 Watcher-Specific Functions and Data Members	2689	=head3 Watcher-Specific Functions and Data Members
1683		2690
1684	=over 4	2691	=over 4
1685		2692
1686	=item ev_idle_init (ev_signal *, callback)	2693	=item ev_idle_init (ev_idle *, callback)
1687		2694
1688	Initialises and configures the idle watcher - it has no parameters of any	2695	Initialises and configures the idle watcher - it has no parameters of any
1689	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2696	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1690	believe me.	2697	believe me.
1691		2698
…		…
1694	=head3 Examples	2701	=head3 Examples
1695		2702
1696	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2703	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1697	callback, free it. Also, use no error checking, as usual.	2704	callback, free it. Also, use no error checking, as usual.
1698		2705
1699	static void	2706	static void
1700	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2707	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1701	{	2708	{
1702	free (w);	2709	free (w);
1703	// now do something you wanted to do when the program has	2710	// now do something you wanted to do when the program has
1704	// no longer anything immediate to do.	2711	// no longer anything immediate to do.
1705	}	2712	}
1706		2713
1707	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2714	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1708	ev_idle_init (idle_watcher, idle_cb);	2715	ev_idle_init (idle_watcher, idle_cb);
1709	ev_idle_start (loop, idle_cb);	2716	ev_idle_start (loop, idle_watcher);
1710		2717
1711		2718
1712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2719	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1713		2720
1714	Prepare and check watchers are usually (but not always) used in tandem:	2721	Prepare and check watchers are usually (but not always) used in pairs:
1715	prepare watchers get invoked before the process blocks and check watchers	2722	prepare watchers get invoked before the process blocks and check watchers
1716	afterwards.	2723	afterwards.
1717		2724
1718	You I<must not> call C<ev_loop> or similar functions that enter	2725	You I<must not> call C<ev_run> or similar functions that enter
1719	the current event loop from either C<ev_prepare> or C<ev_check>	2726	the current event loop from either C<ev_prepare> or C<ev_check>
1720	watchers. Other loops than the current one are fine, however. The	2727	watchers. Other loops than the current one are fine, however. The
1721	rationale behind this is that you do not need to check for recursion in	2728	rationale behind this is that you do not need to check for recursion in
1722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2729	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1723	C<ev_check> so if you have one watcher of each kind they will always be	2730	C<ev_check> so if you have one watcher of each kind they will always be
1724	called in pairs bracketing the blocking call.	2731	called in pairs bracketing the blocking call.
1725		2732
1726	Their main purpose is to integrate other event mechanisms into libev and	2733	Their main purpose is to integrate other event mechanisms into libev and
1727	their use is somewhat advanced. This could be used, for example, to track	2734	their use is somewhat advanced. They could be used, for example, to track
1728	variable changes, implement your own watchers, integrate net-snmp or a	2735	variable changes, implement your own watchers, integrate net-snmp or a
1729	coroutine library and lots more. They are also occasionally useful if	2736	coroutine library and lots more. They are also occasionally useful if
1730	you cache some data and want to flush it before blocking (for example,	2737	you cache some data and want to flush it before blocking (for example,
1731	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2738	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1732	watcher).	2739	watcher).
1733		2740
1734	This is done by examining in each prepare call which file descriptors need	2741	This is done by examining in each prepare call which file descriptors
1735	to be watched by the other library, registering C<ev_io> watchers for	2742	need to be watched by the other library, registering C<ev_io> watchers
1736	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2743	for them and starting an C<ev_timer> watcher for any timeouts (many
1737	provide just this functionality). Then, in the check watcher you check for	2744	libraries provide exactly this functionality). Then, in the check watcher,
1738	any events that occured (by checking the pending status of all watchers	2745	you check for any events that occurred (by checking the pending status
1739	and stopping them) and call back into the library. The I/O and timer	2746	of all watchers and stopping them) and call back into the library. The
1740	callbacks will never actually be called (but must be valid nevertheless,	2747	I/O and timer callbacks will never actually be called (but must be valid
1741	because you never know, you know?).	2748	nevertheless, because you never know, you know?).
1742		2749
1743	As another example, the Perl Coro module uses these hooks to integrate	2750	As another example, the Perl Coro module uses these hooks to integrate
1744	coroutines into libev programs, by yielding to other active coroutines	2751	coroutines into libev programs, by yielding to other active coroutines
1745	during each prepare and only letting the process block if no coroutines	2752	during each prepare and only letting the process block if no coroutines
1746	are ready to run (it's actually more complicated: it only runs coroutines	2753	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1749	loop from blocking if lower-priority coroutines are active, thus mapping	2756	loop from blocking if lower-priority coroutines are active, thus mapping
1750	low-priority coroutines to idle/background tasks).	2757	low-priority coroutines to idle/background tasks).
1751		2758
1752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2759	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1753	priority, to ensure that they are being run before any other watchers	2760	priority, to ensure that they are being run before any other watchers
		2761	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2762
1754	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2763	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1755	too) should not activate ("feed") events into libev. While libev fully	2764	activate ("feed") events into libev. While libev fully supports this, they
1756	supports this, they will be called before other C<ev_check> watchers	2765	might get executed before other C<ev_check> watchers did their job. As
1757	did their job. As C<ev_check> watchers are often used to embed other	2766	C<ev_check> watchers are often used to embed other (non-libev) event
1758	(non-libev) event loops those other event loops might be in an unusable	2767	loops those other event loops might be in an unusable state until their
1759	state until their C<ev_check> watcher ran (always remind yourself to	2768	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1760	coexist peacefully with others).	2769	others).
1761		2770
1762	=head3 Watcher-Specific Functions and Data Members	2771	=head3 Watcher-Specific Functions and Data Members
1763		2772
1764	=over 4	2773	=over 4
1765		2774
…		…
1767		2776
1768	=item ev_check_init (ev_check *, callback)	2777	=item ev_check_init (ev_check *, callback)
1769		2778
1770	Initialises and configures the prepare or check watcher - they have no	2779	Initialises and configures the prepare or check watcher - they have no
1771	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2780	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1772	macros, but using them is utterly, utterly and completely pointless.	2781	macros, but using them is utterly, utterly, utterly and completely
		2782	pointless.
1773		2783
1774	=back	2784	=back
1775		2785
1776	=head3 Examples	2786	=head3 Examples
1777		2787
1778	There are a number of principal ways to embed other event loops or modules	2788	There are a number of principal ways to embed other event loops or modules
1779	into libev. Here are some ideas on how to include libadns into libev	2789	into libev. Here are some ideas on how to include libadns into libev
1780	(there is a Perl module named C<EV::ADNS> that does this, which you could	2790	(there is a Perl module named C<EV::ADNS> that does this, which you could
1781	use for an actually working example. Another Perl module named C<EV::Glib>	2791	use as a working example. Another Perl module named C<EV::Glib> embeds a
1782	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2792	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1783	into the Glib event loop).	2793	Glib event loop).
1784		2794
1785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2795	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1786	and in a check watcher, destroy them and call into libadns. What follows	2796	and in a check watcher, destroy them and call into libadns. What follows
1787	is pseudo-code only of course. This requires you to either use a low	2797	is pseudo-code only of course. This requires you to either use a low
1788	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2798	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1789	the callbacks for the IO/timeout watchers might not have been called yet.	2799	the callbacks for the IO/timeout watchers might not have been called yet.
1790		2800
1791	static ev_io iow [nfd];	2801	static ev_io iow [nfd];
1792	static ev_timer tw;	2802	static ev_timer tw;
1793		2803
1794	static void	2804	static void
1795	io_cb (ev_loop *loop, ev_io *w, int revents)	2805	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1796	{	2806	{
1797	}	2807	}
1798		2808
1799	// create io watchers for each fd and a timer before blocking	2809	// create io watchers for each fd and a timer before blocking
1800	static void	2810	static void
1801	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2811	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1802	{	2812	{
1803	int timeout = 3600000;	2813	int timeout = 3600000;
1804	struct pollfd fds [nfd];	2814	struct pollfd fds [nfd];
1805	// actual code will need to loop here and realloc etc.	2815	// actual code will need to loop here and realloc etc.
1806	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2816	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1807		2817
1808	/* the callback is illegal, but won't be called as we stop during check */	2818	/* the callback is illegal, but won't be called as we stop during check */
1809	ev_timer_init (&tw, 0, timeout * 1e-3);	2819	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1810	ev_timer_start (loop, &tw);	2820	ev_timer_start (loop, &tw);
1811		2821
1812	// create one ev_io per pollfd	2822	// create one ev_io per pollfd
1813	for (int i = 0; i < nfd; ++i)	2823	for (int i = 0; i < nfd; ++i)
1814	{	2824	{
1815	ev_io_init (iow + i, io_cb, fds [i].fd,	2825	ev_io_init (iow + i, io_cb, fds [i].fd,
1816	((fds [i].events & POLLIN ? EV_READ : 0)	2826	((fds [i].events & POLLIN ? EV_READ : 0)
1817	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2827	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1818		2828
1819	fds [i].revents = 0;	2829	fds [i].revents = 0;
1820	ev_io_start (loop, iow + i);	2830	ev_io_start (loop, iow + i);
1821	}	2831	}
1822	}	2832	}
1823		2833
1824	// stop all watchers after blocking	2834	// stop all watchers after blocking
1825	static void	2835	static void
1826	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2836	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1827	{	2837	{
1828	ev_timer_stop (loop, &tw);	2838	ev_timer_stop (loop, &tw);
1829		2839
1830	for (int i = 0; i < nfd; ++i)	2840	for (int i = 0; i < nfd; ++i)
1831	{	2841	{
1832	// set the relevant poll flags	2842	// set the relevant poll flags
1833	// could also call adns_processreadable etc. here	2843	// could also call adns_processreadable etc. here
1834	struct pollfd *fd = fds + i;	2844	struct pollfd *fd = fds + i;
1835	int revents = ev_clear_pending (iow + i);	2845	int revents = ev_clear_pending (iow + i);
1836	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2846	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1837	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2847	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1838		2848
1839	// now stop the watcher	2849	// now stop the watcher
1840	ev_io_stop (loop, iow + i);	2850	ev_io_stop (loop, iow + i);
1841	}	2851	}
1842		2852
1843	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2853	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1844	}	2854	}
1845		2855
1846	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2856	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1847	in the prepare watcher and would dispose of the check watcher.	2857	in the prepare watcher and would dispose of the check watcher.
1848		2858
1849	Method 3: If the module to be embedded supports explicit event	2859	Method 3: If the module to be embedded supports explicit event
1850	notification (adns does), you can also make use of the actual watcher	2860	notification (libadns does), you can also make use of the actual watcher
1851	callbacks, and only destroy/create the watchers in the prepare watcher.	2861	callbacks, and only destroy/create the watchers in the prepare watcher.
1852		2862
1853	static void	2863	static void
1854	timer_cb (EV_P_ ev_timer *w, int revents)	2864	timer_cb (EV_P_ ev_timer *w, int revents)
1855	{	2865	{
1856	adns_state ads = (adns_state)w->data;	2866	adns_state ads = (adns_state)w->data;
1857	update_now (EV_A);	2867	update_now (EV_A);
1858		2868
1859	adns_processtimeouts (ads, &tv_now);	2869	adns_processtimeouts (ads, &tv_now);
1860	}	2870	}
1861		2871
1862	static void	2872	static void
1863	io_cb (EV_P_ ev_io *w, int revents)	2873	io_cb (EV_P_ ev_io *w, int revents)
1864	{	2874	{
1865	adns_state ads = (adns_state)w->data;	2875	adns_state ads = (adns_state)w->data;
1866	update_now (EV_A);	2876	update_now (EV_A);
1867		2877
1868	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2878	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1869	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2879	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1870	}	2880	}
1871		2881
1872	// do not ever call adns_afterpoll	2882	// do not ever call adns_afterpoll
1873		2883
1874	Method 4: Do not use a prepare or check watcher because the module you	2884	Method 4: Do not use a prepare or check watcher because the module you
1875	want to embed is too inflexible to support it. Instead, youc na override	2885	want to embed is not flexible enough to support it. Instead, you can
1876	their poll function. The drawback with this solution is that the main	2886	override their poll function. The drawback with this solution is that the
1877	loop is now no longer controllable by EV. The C<Glib::EV> module does	2887	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1878	this.	2888	this approach, effectively embedding EV as a client into the horrible
		2889	libglib event loop.
1879		2890
1880	static gint	2891	static gint
1881	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2892	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1882	{	2893	{
1883	int got_events = 0;	2894	int got_events = 0;
1884		2895
1885	for (n = 0; n < nfds; ++n)	2896	for (n = 0; n < nfds; ++n)
1886	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2897	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1887		2898
1888	if (timeout >= 0)	2899	if (timeout >= 0)
1889	// create/start timer	2900	// create/start timer
1890		2901
1891	// poll	2902	// poll
1892	ev_loop (EV_A_ 0);	2903	ev_run (EV_A_ 0);
1893		2904
1894	// stop timer again	2905	// stop timer again
1895	if (timeout >= 0)	2906	if (timeout >= 0)
1896	ev_timer_stop (EV_A_ &to);	2907	ev_timer_stop (EV_A_ &to);
1897		2908
1898	// stop io watchers again - their callbacks should have set	2909	// stop io watchers again - their callbacks should have set
1899	for (n = 0; n < nfds; ++n)	2910	for (n = 0; n < nfds; ++n)
1900	ev_io_stop (EV_A_ iow [n]);	2911	ev_io_stop (EV_A_ iow [n]);
1901		2912
1902	return got_events;	2913	return got_events;
1903	}	2914	}
1904		2915
1905		2916
1906	=head2 C<ev_embed> - when one backend isn't enough...	2917	=head2 C<ev_embed> - when one backend isn't enough...
1907		2918
1908	This is a rather advanced watcher type that lets you embed one event loop	2919	This is a rather advanced watcher type that lets you embed one event loop
…		…
1914	prioritise I/O.	2925	prioritise I/O.
1915		2926
1916	As an example for a bug workaround, the kqueue backend might only support	2927	As an example for a bug workaround, the kqueue backend might only support
1917	sockets on some platform, so it is unusable as generic backend, but you	2928	sockets on some platform, so it is unusable as generic backend, but you
1918	still want to make use of it because you have many sockets and it scales	2929	still want to make use of it because you have many sockets and it scales
1919	so nicely. In this case, you would create a kqueue-based loop and embed it	2930	so nicely. In this case, you would create a kqueue-based loop and embed
1920	into your default loop (which might use e.g. poll). Overall operation will	2931	it into your default loop (which might use e.g. poll). Overall operation
1921	be a bit slower because first libev has to poll and then call kevent, but	2932	will be a bit slower because first libev has to call C<poll> and then
1922	at least you can use both at what they are best.	2933	C<kevent>, but at least you can use both mechanisms for what they are
		2934	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1923		2935
1924	As for prioritising I/O: rarely you have the case where some fds have	2936	As for prioritising I/O: under rare circumstances you have the case where
1925	to be watched and handled very quickly (with low latency), and even	2937	some fds have to be watched and handled very quickly (with low latency),
1926	priorities and idle watchers might have too much overhead. In this case	2938	and even priorities and idle watchers might have too much overhead. In
1927	you would put all the high priority stuff in one loop and all the rest in	2939	this case you would put all the high priority stuff in one loop and all
1928	a second one, and embed the second one in the first.	2940	the rest in a second one, and embed the second one in the first.
1929		2941
1930	As long as the watcher is active, the callback will be invoked every time	2942	As long as the watcher is active, the callback will be invoked every
1931	there might be events pending in the embedded loop. The callback must then	2943	time there might be events pending in the embedded loop. The callback
1932	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2944	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1933	their callbacks (you could also start an idle watcher to give the embedded	2945	sweep and invoke their callbacks (the callback doesn't need to invoke the
1934	loop strictly lower priority for example). You can also set the callback	2946	C<ev_embed_sweep> function directly, it could also start an idle watcher
1935	to C<0>, in which case the embed watcher will automatically execute the	2947	to give the embedded loop strictly lower priority for example).
1936	embedded loop sweep.
1937		2948
1938	As long as the watcher is started it will automatically handle events. The	2949	You can also set the callback to C<0>, in which case the embed watcher
1939	callback will be invoked whenever some events have been handled. You can	2950	will automatically execute the embedded loop sweep whenever necessary.
1940	set the callback to C<0> to avoid having to specify one if you are not
1941	interested in that.
1942		2951
1943	Also, there have not currently been made special provisions for forking:	2952	Fork detection will be handled transparently while the C<ev_embed> watcher
1944	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2953	is active, i.e., the embedded loop will automatically be forked when the
1945	but you will also have to stop and restart any C<ev_embed> watchers	2954	embedding loop forks. In other cases, the user is responsible for calling
1946	yourself.	2955	C<ev_loop_fork> on the embedded loop.
1947		2956
1948	Unfortunately, not all backends are embeddable, only the ones returned by	2957	Unfortunately, not all backends are embeddable: only the ones returned by
1949	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2958	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1950	portable one.	2959	portable one.
1951		2960
1952	So when you want to use this feature you will always have to be prepared	2961	So when you want to use this feature you will always have to be prepared
1953	that you cannot get an embeddable loop. The recommended way to get around	2962	that you cannot get an embeddable loop. The recommended way to get around
1954	this is to have a separate variables for your embeddable loop, try to	2963	this is to have a separate variables for your embeddable loop, try to
1955	create it, and if that fails, use the normal loop for everything.	2964	create it, and if that fails, use the normal loop for everything.
1956		2965
		2966	=head3 C<ev_embed> and fork
		2967
		2968	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2969	automatically be applied to the embedded loop as well, so no special
		2970	fork handling is required in that case. When the watcher is not running,
		2971	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2972	as applicable.
		2973
1957	=head3 Watcher-Specific Functions and Data Members	2974	=head3 Watcher-Specific Functions and Data Members
1958		2975
1959	=over 4	2976	=over 4
1960		2977
1961	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2978	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1964		2981
1965	Configures the watcher to embed the given loop, which must be	2982	Configures the watcher to embed the given loop, which must be
1966	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2983	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1967	invoked automatically, otherwise it is the responsibility of the callback	2984	invoked automatically, otherwise it is the responsibility of the callback
1968	to invoke it (it will continue to be called until the sweep has been done,	2985	to invoke it (it will continue to be called until the sweep has been done,
1969	if you do not want thta, you need to temporarily stop the embed watcher).	2986	if you do not want that, you need to temporarily stop the embed watcher).
1970		2987
1971	=item ev_embed_sweep (loop, ev_embed *)	2988	=item ev_embed_sweep (loop, ev_embed *)
1972		2989
1973	Make a single, non-blocking sweep over the embedded loop. This works	2990	Make a single, non-blocking sweep over the embedded loop. This works
1974	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2991	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1975	apropriate way for embedded loops.	2992	appropriate way for embedded loops.
1976		2993
1977	=item struct ev_loop *other [read-only]	2994	=item struct ev_loop *other [read-only]
1978		2995
1979	The embedded event loop.	2996	The embedded event loop.
1980		2997
…		…
1982		2999
1983	=head3 Examples	3000	=head3 Examples
1984		3001
1985	Example: Try to get an embeddable event loop and embed it into the default	3002	Example: Try to get an embeddable event loop and embed it into the default
1986	event loop. If that is not possible, use the default loop. The default	3003	event loop. If that is not possible, use the default loop. The default
1987	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3004	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1988	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3005	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1989	used).	3006	used).
1990		3007
1991	struct ev_loop *loop_hi = ev_default_init (0);	3008	struct ev_loop *loop_hi = ev_default_init (0);
1992	struct ev_loop *loop_lo = 0;	3009	struct ev_loop *loop_lo = 0;
1993	struct ev_embed embed;	3010	ev_embed embed;
1994		3011
1995	// see if there is a chance of getting one that works	3012	// see if there is a chance of getting one that works
1996	// (remember that a flags value of 0 means autodetection)	3013	// (remember that a flags value of 0 means autodetection)
1997	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3014	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1998	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3015	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1999	: 0;	3016	: 0;
2000		3017
2001	// if we got one, then embed it, otherwise default to loop_hi	3018	// if we got one, then embed it, otherwise default to loop_hi
2002	if (loop_lo)	3019	if (loop_lo)
2003	{	3020	{
2004	ev_embed_init (&embed, 0, loop_lo);	3021	ev_embed_init (&embed, 0, loop_lo);
2005	ev_embed_start (loop_hi, &embed);	3022	ev_embed_start (loop_hi, &embed);
2006	}	3023	}
2007	else	3024	else
2008	loop_lo = loop_hi;	3025	loop_lo = loop_hi;
2009		3026
2010	Example: Check if kqueue is available but not recommended and create	3027	Example: Check if kqueue is available but not recommended and create
2011	a kqueue backend for use with sockets (which usually work with any	3028	a kqueue backend for use with sockets (which usually work with any
2012	kqueue implementation). Store the kqueue/socket-only event loop in	3029	kqueue implementation). Store the kqueue/socket-only event loop in
2013	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3030	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2014		3031
2015	struct ev_loop *loop = ev_default_init (0);	3032	struct ev_loop *loop = ev_default_init (0);
2016	struct ev_loop *loop_socket = 0;	3033	struct ev_loop *loop_socket = 0;
2017	struct ev_embed embed;	3034	ev_embed embed;
2018		3035
2019	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3036	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2020	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3037	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2021	{	3038	{
2022	ev_embed_init (&embed, 0, loop_socket);	3039	ev_embed_init (&embed, 0, loop_socket);
2023	ev_embed_start (loop, &embed);	3040	ev_embed_start (loop, &embed);
2024	}	3041	}
2025		3042
2026	if (!loop_socket)	3043	if (!loop_socket)
2027	loop_socket = loop;	3044	loop_socket = loop;
2028		3045
2029	// now use loop_socket for all sockets, and loop for everything else	3046	// now use loop_socket for all sockets, and loop for everything else
2030		3047
2031		3048
2032	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3049	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2033		3050
2034	Fork watchers are called when a C<fork ()> was detected (usually because	3051	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2037	event loop blocks next and before C<ev_check> watchers are being called,	3054	event loop blocks next and before C<ev_check> watchers are being called,
2038	and only in the child after the fork. If whoever good citizen calling	3055	and only in the child after the fork. If whoever good citizen calling
2039	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3056	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2040	handlers will be invoked, too, of course.	3057	handlers will be invoked, too, of course.
2041		3058
		3059	=head3 The special problem of life after fork - how is it possible?
		3060
		3061	Most uses of C<fork()> consist of forking, then some simple calls to set
		3062	up/change the process environment, followed by a call to C<exec()>. This
		3063	sequence should be handled by libev without any problems.
		3064
		3065	This changes when the application actually wants to do event handling
		3066	in the child, or both parent in child, in effect "continuing" after the
		3067	fork.
		3068
		3069	The default mode of operation (for libev, with application help to detect
		3070	forks) is to duplicate all the state in the child, as would be expected
		3071	when I<either> the parent I<or> the child process continues.
		3072
		3073	When both processes want to continue using libev, then this is usually the
		3074	wrong result. In that case, usually one process (typically the parent) is
		3075	supposed to continue with all watchers in place as before, while the other
		3076	process typically wants to start fresh, i.e. without any active watchers.
		3077
		3078	The cleanest and most efficient way to achieve that with libev is to
		3079	simply create a new event loop, which of course will be "empty", and
		3080	use that for new watchers. This has the advantage of not touching more
		3081	memory than necessary, and thus avoiding the copy-on-write, and the
		3082	disadvantage of having to use multiple event loops (which do not support
		3083	signal watchers).
		3084
		3085	When this is not possible, or you want to use the default loop for
		3086	other reasons, then in the process that wants to start "fresh", call
		3087	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3088	Destroying the default loop will "orphan" (not stop) all registered
		3089	watchers, so you have to be careful not to execute code that modifies
		3090	those watchers. Note also that in that case, you have to re-register any
		3091	signal watchers.
		3092
2042	=head3 Watcher-Specific Functions and Data Members	3093	=head3 Watcher-Specific Functions and Data Members
2043		3094
2044	=over 4	3095	=over 4
2045		3096
2046	=item ev_fork_init (ev_signal *, callback)	3097	=item ev_fork_init (ev_signal *, callback)
…		…
2050	believe me.	3101	believe me.
2051		3102
2052	=back	3103	=back
2053		3104
2054		3105
2055	=head2 C<ev_async> - how to wake up another event loop	3106	=head2 C<ev_async> - how to wake up an event loop
2056		3107
2057	In general, you cannot use an C<ev_loop> from multiple threads or other	3108	In general, you cannot use an C<ev_run> from multiple threads or other
2058	asynchronous sources such as signal handlers (as opposed to multiple event	3109	asynchronous sources such as signal handlers (as opposed to multiple event
2059	loops - those are of course safe to use in different threads).	3110	loops - those are of course safe to use in different threads).
2060		3111
2061	Sometimes, however, you need to wake up another event loop you do not	3112	Sometimes, however, you need to wake up an event loop you do not control,
2062	control, for example because it belongs to another thread. This is what	3113	for example because it belongs to another thread. This is what C<ev_async>
2063	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3114	watchers do: as long as the C<ev_async> watcher is active, you can signal
2064	can signal it by calling C<ev_async_send>, which is thread- and signal	3115	it by calling C<ev_async_send>, which is thread- and signal safe.
2065	safe.
2066		3116
2067	This functionality is very similar to C<ev_signal> watchers, as signals,	3117	This functionality is very similar to C<ev_signal> watchers, as signals,
2068	too, are asynchronous in nature, and signals, too, will be compressed	3118	too, are asynchronous in nature, and signals, too, will be compressed
2069	(i.e. the number of callback invocations may be less than the number of	3119	(i.e. the number of callback invocations may be less than the number of
2070	C<ev_async_sent> calls).	3120	C<ev_async_sent> calls).
…		…
2075	=head3 Queueing	3125	=head3 Queueing
2076		3126
2077	C<ev_async> does not support queueing of data in any way. The reason	3127	C<ev_async> does not support queueing of data in any way. The reason
2078	is that the author does not know of a simple (or any) algorithm for a	3128	is that the author does not know of a simple (or any) algorithm for a
2079	multiple-writer-single-reader queue that works in all cases and doesn't	3129	multiple-writer-single-reader queue that works in all cases and doesn't
2080	need elaborate support such as pthreads.	3130	need elaborate support such as pthreads or unportable memory access
		3131	semantics.
2081		3132
2082	That means that if you want to queue data, you have to provide your own	3133	That means that if you want to queue data, you have to provide your own
2083	queue. But at least I can tell you would implement locking around your	3134	queue. But at least I can tell you how to implement locking around your
2084	queue:	3135	queue:
2085		3136
2086	=over 4	3137	=over 4
2087		3138
2088	=item queueing from a signal handler context	3139	=item queueing from a signal handler context
2089		3140
2090	To implement race-free queueing, you simply add to the queue in the signal	3141	To implement race-free queueing, you simply add to the queue in the signal
2091	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3142	handler but you block the signal handler in the watcher callback. Here is
2092	some fictitiuous SIGUSR1 handler:	3143	an example that does that for some fictitious SIGUSR1 handler:
2093		3144
2094	static ev_async mysig;	3145	static ev_async mysig;
2095		3146
2096	static void	3147	static void
2097	sigusr1_handler (void)	3148	sigusr1_handler (void)
2098	{	3149	{
2099	sometype data;	3150	sometype data;
2100		3151
2101	// no locking etc.	3152	// no locking etc.
2102	queue_put (data);	3153	queue_put (data);
2103	ev_async_send (DEFAULT_ &mysig);	3154	ev_async_send (EV_DEFAULT_ &mysig);
2104	}	3155	}
2105		3156
2106	static void	3157	static void
2107	mysig_cb (EV_P_ ev_async *w, int revents)	3158	mysig_cb (EV_P_ ev_async *w, int revents)
2108	{	3159	{
…		…
2139	// only need to lock the actual queueing operation	3190	// only need to lock the actual queueing operation
2140	pthread_mutex_lock (&mymutex);	3191	pthread_mutex_lock (&mymutex);
2141	queue_put (data);	3192	queue_put (data);
2142	pthread_mutex_unlock (&mymutex);	3193	pthread_mutex_unlock (&mymutex);
2143		3194
2144	ev_async_send (DEFAULT_ &mysig);	3195	ev_async_send (EV_DEFAULT_ &mysig);
2145	}	3196	}
2146		3197
2147	static void	3198	static void
2148	mysig_cb (EV_P_ ev_async *w, int revents)	3199	mysig_cb (EV_P_ ev_async *w, int revents)
2149	{	3200	{
…		…
2163	=over 4	3214	=over 4
2164		3215
2165	=item ev_async_init (ev_async *, callback)	3216	=item ev_async_init (ev_async *, callback)
2166		3217
2167	Initialises and configures the async watcher - it has no parameters of any	3218	Initialises and configures the async watcher - it has no parameters of any
2168	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3219	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2169	believe me.	3220	trust me.
2170		3221
2171	=item ev_async_send (loop, ev_async *)	3222	=item ev_async_send (loop, ev_async *)
2172		3223
2173	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3224	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2174	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3225	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2175	C<ev_feed_event>, this call is safe to do in other threads, signal or	3226	C<ev_feed_event>, this call is safe to do from other threads, signal or
2176	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3227	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2177	section below on what exactly this means).	3228	section below on what exactly this means).
2178		3229
		3230	Note that, as with other watchers in libev, multiple events might get
		3231	compressed into a single callback invocation (another way to look at this
		3232	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3233	reset when the event loop detects that).
		3234
2179	This call incurs the overhead of a syscall only once per loop iteration,	3235	This call incurs the overhead of a system call only once per event loop
2180	so while the overhead might be noticable, it doesn't apply to repeated	3236	iteration, so while the overhead might be noticeable, it doesn't apply to
2181	calls to C<ev_async_send>.	3237	repeated calls to C<ev_async_send> for the same event loop.
		3238
		3239	=item bool = ev_async_pending (ev_async *)
		3240
		3241	Returns a non-zero value when C<ev_async_send> has been called on the
		3242	watcher but the event has not yet been processed (or even noted) by the
		3243	event loop.
		3244
		3245	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3246	the loop iterates next and checks for the watcher to have become active,
		3247	it will reset the flag again. C<ev_async_pending> can be used to very
		3248	quickly check whether invoking the loop might be a good idea.
		3249
		3250	Not that this does I<not> check whether the watcher itself is pending,
		3251	only whether it has been requested to make this watcher pending: there
		3252	is a time window between the event loop checking and resetting the async
		3253	notification, and the callback being invoked.
2182		3254
2183	=back	3255	=back
2184		3256
2185		3257
2186	=head1 OTHER FUNCTIONS	3258	=head1 OTHER FUNCTIONS
…		…
2190	=over 4	3262	=over 4
2191		3263
2192	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3264	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2193		3265
2194	This function combines a simple timer and an I/O watcher, calls your	3266	This function combines a simple timer and an I/O watcher, calls your
2195	callback on whichever event happens first and automatically stop both	3267	callback on whichever event happens first and automatically stops both
2196	watchers. This is useful if you want to wait for a single event on an fd	3268	watchers. This is useful if you want to wait for a single event on an fd
2197	or timeout without having to allocate/configure/start/stop/free one or	3269	or timeout without having to allocate/configure/start/stop/free one or
2198	more watchers yourself.	3270	more watchers yourself.
2199		3271
2200	If C<fd> is less than 0, then no I/O watcher will be started and events	3272	If C<fd> is less than 0, then no I/O watcher will be started and the
2201	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3273	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2202	C<events> set will be craeted and started.	3274	the given C<fd> and C<events> set will be created and started.
2203		3275
2204	If C<timeout> is less than 0, then no timeout watcher will be	3276	If C<timeout> is less than 0, then no timeout watcher will be
2205	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3277	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2206	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3278	repeat = 0) will be started. C<0> is a valid timeout.
2207	dubious value.
2208		3279
2209	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3280	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2210	passed an C<revents> set like normal event callbacks (a combination of	3281	passed an C<revents> set like normal event callbacks (a combination of
2211	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3282	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2212	value passed to C<ev_once>:	3283	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3284	a timeout and an io event at the same time - you probably should give io
		3285	events precedence.
2213		3286
		3287	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3288
2214	static void stdin_ready (int revents, void *arg)	3289	static void stdin_ready (int revents, void *arg)
2215	{	3290	{
2216	if (revents & EV_TIMEOUT)
2217	/* doh, nothing entered */;
2218	else if (revents & EV_READ)	3291	if (revents & EV_READ)
2219	/* stdin might have data for us, joy! */;	3292	/* stdin might have data for us, joy! */;
		3293	else if (revents & EV_TIMER)
		3294	/* doh, nothing entered */;
2220	}	3295	}
2221		3296
2222	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3297	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2223		3298
2224	=item ev_feed_event (ev_loop *, watcher *, int revents)
2225
2226	Feeds the given event set into the event loop, as if the specified event
2227	had happened for the specified watcher (which must be a pointer to an
2228	initialised but not necessarily started event watcher).
2229
2230	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3299	=item ev_feed_fd_event (loop, int fd, int revents)
2231		3300
2232	Feed an event on the given fd, as if a file descriptor backend detected	3301	Feed an event on the given fd, as if a file descriptor backend detected
2233	the given events it.	3302	the given events it.
2234		3303
2235	=item ev_feed_signal_event (ev_loop *loop, int signum)	3304	=item ev_feed_signal_event (loop, int signum)
2236		3305
2237	Feed an event as if the given signal occured (C<loop> must be the default	3306	Feed an event as if the given signal occurred (C<loop> must be the default
2238	loop!).	3307	loop!).
2239		3308
2240	=back	3309	=back
2241		3310
2242		3311
…		…
2258		3327
2259	=item * Priorities are not currently supported. Initialising priorities	3328	=item * Priorities are not currently supported. Initialising priorities
2260	will fail and all watchers will have the same priority, even though there	3329	will fail and all watchers will have the same priority, even though there
2261	is an ev_pri field.	3330	is an ev_pri field.
2262		3331
		3332	=item * In libevent, the last base created gets the signals, in libev, the
		3333	first base created (== the default loop) gets the signals.
		3334
2263	=item * Other members are not supported.	3335	=item * Other members are not supported.
2264		3336
2265	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3337	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2266	to use the libev header file and library.	3338	to use the libev header file and library.
2267		3339
2268	=back	3340	=back
2269		3341
2270	=head1 C++ SUPPORT	3342	=head1 C++ SUPPORT
2271		3343
2272	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3344	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2273	you to use some convinience methods to start/stop watchers and also change	3345	you to use some convenience methods to start/stop watchers and also change
2274	the callback model to a model using method callbacks on objects.	3346	the callback model to a model using method callbacks on objects.
2275		3347
2276	To use it,	3348	To use it,
2277		3349
2278	#include <ev++.h>	3350	#include <ev++.h>
2279		3351
2280	This automatically includes F<ev.h> and puts all of its definitions (many	3352	This automatically includes F<ev.h> and puts all of its definitions (many
2281	of them macros) into the global namespace. All C++ specific things are	3353	of them macros) into the global namespace. All C++ specific things are
2282	put into the C<ev> namespace. It should support all the same embedding	3354	put into the C<ev> namespace. It should support all the same embedding
2283	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3355	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2317		3389
2318	=over 4	3390	=over 4
2319		3391
2320	=item ev::TYPE::TYPE ()	3392	=item ev::TYPE::TYPE ()
2321		3393
2322	=item ev::TYPE::TYPE (struct ev_loop *)	3394	=item ev::TYPE::TYPE (loop)
2323		3395
2324	=item ev::TYPE::~TYPE	3396	=item ev::TYPE::~TYPE
2325		3397
2326	The constructor (optionally) takes an event loop to associate the watcher	3398	The constructor (optionally) takes an event loop to associate the watcher
2327	with. If it is omitted, it will use C<EV_DEFAULT>.	3399	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2350	your compiler is good :), then the method will be fully inlined into the	3422	your compiler is good :), then the method will be fully inlined into the
2351	thunking function, making it as fast as a direct C callback.	3423	thunking function, making it as fast as a direct C callback.
2352		3424
2353	Example: simple class declaration and watcher initialisation	3425	Example: simple class declaration and watcher initialisation
2354		3426
2355	struct myclass	3427	struct myclass
2356	{	3428	{
2357	void io_cb (ev::io &w, int revents) { }	3429	void io_cb (ev::io &w, int revents) { }
2358	}	3430	}
2359		3431
2360	myclass obj;	3432	myclass obj;
2361	ev::io iow;	3433	ev::io iow;
2362	iow.set <myclass, &myclass::io_cb> (&obj);	3434	iow.set <myclass, &myclass::io_cb> (&obj);
		3435
		3436	=item w->set (object *)
		3437
		3438	This is a variation of a method callback - leaving out the method to call
		3439	will default the method to C<operator ()>, which makes it possible to use
		3440	functor objects without having to manually specify the C<operator ()> all
		3441	the time. Incidentally, you can then also leave out the template argument
		3442	list.
		3443
		3444	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3445	int revents)>.
		3446
		3447	See the method-C<set> above for more details.
		3448
		3449	Example: use a functor object as callback.
		3450
		3451	struct myfunctor
		3452	{
		3453	void operator() (ev::io &w, int revents)
		3454	{
		3455	...
		3456	}
		3457	}
		3458
		3459	myfunctor f;
		3460
		3461	ev::io w;
		3462	w.set (&f);
2363		3463
2364	=item w->set<function> (void *data = 0)	3464	=item w->set<function> (void *data = 0)
2365		3465
2366	Also sets a callback, but uses a static method or plain function as	3466	Also sets a callback, but uses a static method or plain function as
2367	callback. The optional C<data> argument will be stored in the watcher's	3467	callback. The optional C<data> argument will be stored in the watcher's
…		…
2369		3469
2370	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3470	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2371		3471
2372	See the method-C<set> above for more details.	3472	See the method-C<set> above for more details.
2373		3473
2374	Example:	3474	Example: Use a plain function as callback.
2375		3475
2376	static void io_cb (ev::io &w, int revents) { }	3476	static void io_cb (ev::io &w, int revents) { }
2377	iow.set <io_cb> ();	3477	iow.set <io_cb> ();
2378		3478
2379	=item w->set (struct ev_loop *)	3479	=item w->set (loop)
2380		3480
2381	Associates a different C<struct ev_loop> with this watcher. You can only	3481	Associates a different C<struct ev_loop> with this watcher. You can only
2382	do this when the watcher is inactive (and not pending either).	3482	do this when the watcher is inactive (and not pending either).
2383		3483
2384	=item w->set ([args])	3484	=item w->set ([arguments])
2385		3485
2386	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3486	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2387	called at least once. Unlike the C counterpart, an active watcher gets	3487	method or a suitable start method must be called at least once. Unlike the
2388	automatically stopped and restarted when reconfiguring it with this	3488	C counterpart, an active watcher gets automatically stopped and restarted
2389	method.	3489	when reconfiguring it with this method.
2390		3490
2391	=item w->start ()	3491	=item w->start ()
2392		3492
2393	Starts the watcher. Note that there is no C<loop> argument, as the	3493	Starts the watcher. Note that there is no C<loop> argument, as the
2394	constructor already stores the event loop.	3494	constructor already stores the event loop.
2395		3495
		3496	=item w->start ([arguments])
		3497
		3498	Instead of calling C<set> and C<start> methods separately, it is often
		3499	convenient to wrap them in one call. Uses the same type of arguments as
		3500	the configure C<set> method of the watcher.
		3501
2396	=item w->stop ()	3502	=item w->stop ()
2397		3503
2398	Stops the watcher if it is active. Again, no C<loop> argument.	3504	Stops the watcher if it is active. Again, no C<loop> argument.
2399		3505
2400	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3506	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2412		3518
2413	=back	3519	=back
2414		3520
2415	=back	3521	=back
2416		3522
2417	Example: Define a class with an IO and idle watcher, start one of them in	3523	Example: Define a class with two I/O and idle watchers, start the I/O
2418	the constructor.	3524	watchers in the constructor.
2419		3525
2420	class myclass	3526	class myclass
2421	{	3527	{
2422	ev::io io; void io_cb (ev::io &w, int revents);	3528	ev::io io ; void io_cb (ev::io &w, int revents);
		3529	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2423	ev:idle idle void idle_cb (ev::idle &w, int revents);	3530	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2424		3531
2425	myclass (int fd)	3532	myclass (int fd)
2426	{	3533	{
2427	io .set <myclass, &myclass::io_cb > (this);	3534	io .set <myclass, &myclass::io_cb > (this);
		3535	io2 .set <myclass, &myclass::io2_cb > (this);
2428	idle.set <myclass, &myclass::idle_cb> (this);	3536	idle.set <myclass, &myclass::idle_cb> (this);
2429		3537
2430	io.start (fd, ev::READ);	3538	io.set (fd, ev::WRITE); // configure the watcher
		3539	io.start (); // start it whenever convenient
		3540
		3541	io2.start (fd, ev::READ); // set + start in one call
2431	}	3542	}
2432	};	3543	};
		3544
		3545
		3546	=head1 OTHER LANGUAGE BINDINGS
		3547
		3548	Libev does not offer other language bindings itself, but bindings for a
		3549	number of languages exist in the form of third-party packages. If you know
		3550	any interesting language binding in addition to the ones listed here, drop
		3551	me a note.
		3552
		3553	=over 4
		3554
		3555	=item Perl
		3556
		3557	The EV module implements the full libev API and is actually used to test
		3558	libev. EV is developed together with libev. Apart from the EV core module,
		3559	there are additional modules that implement libev-compatible interfaces
		3560	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3561	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3562	and C<EV::Glib>).
		3563
		3564	It can be found and installed via CPAN, its homepage is at
		3565	L<http://software.schmorp.de/pkg/EV>.
		3566
		3567	=item Python
		3568
		3569	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3570	seems to be quite complete and well-documented.
		3571
		3572	=item Ruby
		3573
		3574	Tony Arcieri has written a ruby extension that offers access to a subset
		3575	of the libev API and adds file handle abstractions, asynchronous DNS and
		3576	more on top of it. It can be found via gem servers. Its homepage is at
		3577	L<http://rev.rubyforge.org/>.
		3578
		3579	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3580	makes rev work even on mingw.
		3581
		3582	=item Haskell
		3583
		3584	A haskell binding to libev is available at
		3585	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3586
		3587	=item D
		3588
		3589	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3590	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3591
		3592	=item Ocaml
		3593
		3594	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3595	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3596
		3597	=item Lua
		3598
		3599	Brian Maher has written a partial interface to libev for lua (at the
		3600	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3601	L<http://github.com/brimworks/lua-ev>.
		3602
		3603	=back
2433		3604
2434		3605
2435	=head1 MACRO MAGIC	3606	=head1 MACRO MAGIC
2436		3607
2437	Libev can be compiled with a variety of options, the most fundamantal	3608	Libev can be compiled with a variety of options, the most fundamental
2438	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3609	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2439	functions and callbacks have an initial C<struct ev_loop *> argument.	3610	functions and callbacks have an initial C<struct ev_loop *> argument.
2440		3611
2441	To make it easier to write programs that cope with either variant, the	3612	To make it easier to write programs that cope with either variant, the
2442	following macros are defined:	3613	following macros are defined:
…		…
2447		3618
2448	This provides the loop I<argument> for functions, if one is required ("ev	3619	This provides the loop I<argument> for functions, if one is required ("ev
2449	loop argument"). The C<EV_A> form is used when this is the sole argument,	3620	loop argument"). The C<EV_A> form is used when this is the sole argument,
2450	C<EV_A_> is used when other arguments are following. Example:	3621	C<EV_A_> is used when other arguments are following. Example:
2451		3622
2452	ev_unref (EV_A);	3623	ev_unref (EV_A);
2453	ev_timer_add (EV_A_ watcher);	3624	ev_timer_add (EV_A_ watcher);
2454	ev_loop (EV_A_ 0);	3625	ev_run (EV_A_ 0);
2455		3626
2456	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3627	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2457	which is often provided by the following macro.	3628	which is often provided by the following macro.
2458		3629
2459	=item C<EV_P>, C<EV_P_>	3630	=item C<EV_P>, C<EV_P_>
2460		3631
2461	This provides the loop I<parameter> for functions, if one is required ("ev	3632	This provides the loop I<parameter> for functions, if one is required ("ev
2462	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3633	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2463	C<EV_P_> is used when other parameters are following. Example:	3634	C<EV_P_> is used when other parameters are following. Example:
2464		3635
2465	// this is how ev_unref is being declared	3636	// this is how ev_unref is being declared
2466	static void ev_unref (EV_P);	3637	static void ev_unref (EV_P);
2467		3638
2468	// this is how you can declare your typical callback	3639	// this is how you can declare your typical callback
2469	static void cb (EV_P_ ev_timer *w, int revents)	3640	static void cb (EV_P_ ev_timer *w, int revents)
2470		3641
2471	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3642	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2472	suitable for use with C<EV_A>.	3643	suitable for use with C<EV_A>.
2473		3644
2474	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3645	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2475		3646
2476	Similar to the other two macros, this gives you the value of the default	3647	Similar to the other two macros, this gives you the value of the default
2477	loop, if multiple loops are supported ("ev loop default").	3648	loop, if multiple loops are supported ("ev loop default").
		3649
		3650	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3651
		3652	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3653	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3654	is undefined when the default loop has not been initialised by a previous
		3655	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3656
		3657	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3658	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2478		3659
2479	=back	3660	=back
2480		3661
2481	Example: Declare and initialise a check watcher, utilising the above	3662	Example: Declare and initialise a check watcher, utilising the above
2482	macros so it will work regardless of whether multiple loops are supported	3663	macros so it will work regardless of whether multiple loops are supported
2483	or not.	3664	or not.
2484		3665
2485	static void	3666	static void
2486	check_cb (EV_P_ ev_timer *w, int revents)	3667	check_cb (EV_P_ ev_timer *w, int revents)
2487	{	3668	{
2488	ev_check_stop (EV_A_ w);	3669	ev_check_stop (EV_A_ w);
2489	}	3670	}
2490		3671
2491	ev_check check;	3672	ev_check check;
2492	ev_check_init (&check, check_cb);	3673	ev_check_init (&check, check_cb);
2493	ev_check_start (EV_DEFAULT_ &check);	3674	ev_check_start (EV_DEFAULT_ &check);
2494	ev_loop (EV_DEFAULT_ 0);	3675	ev_run (EV_DEFAULT_ 0);
2495		3676
2496	=head1 EMBEDDING	3677	=head1 EMBEDDING
2497		3678
2498	Libev can (and often is) directly embedded into host	3679	Libev can (and often is) directly embedded into host
2499	applications. Examples of applications that embed it include the Deliantra	3680	applications. Examples of applications that embed it include the Deliantra
…		…
2506	libev somewhere in your source tree).	3687	libev somewhere in your source tree).
2507		3688
2508	=head2 FILESETS	3689	=head2 FILESETS
2509		3690
2510	Depending on what features you need you need to include one or more sets of files	3691	Depending on what features you need you need to include one or more sets of files
2511	in your app.	3692	in your application.
2512		3693
2513	=head3 CORE EVENT LOOP	3694	=head3 CORE EVENT LOOP
2514		3695
2515	To include only the libev core (all the C<ev_*> functions), with manual	3696	To include only the libev core (all the C<ev_*> functions), with manual
2516	configuration (no autoconf):	3697	configuration (no autoconf):
2517		3698
2518	#define EV_STANDALONE 1	3699	#define EV_STANDALONE 1
2519	#include "ev.c"	3700	#include "ev.c"
2520		3701
2521	This will automatically include F<ev.h>, too, and should be done in a	3702	This will automatically include F<ev.h>, too, and should be done in a
2522	single C source file only to provide the function implementations. To use	3703	single C source file only to provide the function implementations. To use
2523	it, do the same for F<ev.h> in all files wishing to use this API (best	3704	it, do the same for F<ev.h> in all files wishing to use this API (best
2524	done by writing a wrapper around F<ev.h> that you can include instead and	3705	done by writing a wrapper around F<ev.h> that you can include instead and
2525	where you can put other configuration options):	3706	where you can put other configuration options):
2526		3707
2527	#define EV_STANDALONE 1	3708	#define EV_STANDALONE 1
2528	#include "ev.h"	3709	#include "ev.h"
2529		3710
2530	Both header files and implementation files can be compiled with a C++	3711	Both header files and implementation files can be compiled with a C++
2531	compiler (at least, thats a stated goal, and breakage will be treated	3712	compiler (at least, that's a stated goal, and breakage will be treated
2532	as a bug).	3713	as a bug).
2533		3714
2534	You need the following files in your source tree, or in a directory	3715	You need the following files in your source tree, or in a directory
2535	in your include path (e.g. in libev/ when using -Ilibev):	3716	in your include path (e.g. in libev/ when using -Ilibev):
2536		3717
2537	ev.h	3718	ev.h
2538	ev.c	3719	ev.c
2539	ev_vars.h	3720	ev_vars.h
2540	ev_wrap.h	3721	ev_wrap.h
2541		3722
2542	ev_win32.c required on win32 platforms only	3723	ev_win32.c required on win32 platforms only
2543		3724
2544	ev_select.c only when select backend is enabled (which is enabled by default)	3725	ev_select.c only when select backend is enabled (which is enabled by default)
2545	ev_poll.c only when poll backend is enabled (disabled by default)	3726	ev_poll.c only when poll backend is enabled (disabled by default)
2546	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3727	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2547	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3728	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2548	ev_port.c only when the solaris port backend is enabled (disabled by default)	3729	ev_port.c only when the solaris port backend is enabled (disabled by default)
2549		3730
2550	F<ev.c> includes the backend files directly when enabled, so you only need	3731	F<ev.c> includes the backend files directly when enabled, so you only need
2551	to compile this single file.	3732	to compile this single file.
2552		3733
2553	=head3 LIBEVENT COMPATIBILITY API	3734	=head3 LIBEVENT COMPATIBILITY API
2554		3735
2555	To include the libevent compatibility API, also include:	3736	To include the libevent compatibility API, also include:
2556		3737
2557	#include "event.c"	3738	#include "event.c"
2558		3739
2559	in the file including F<ev.c>, and:	3740	in the file including F<ev.c>, and:
2560		3741
2561	#include "event.h"	3742	#include "event.h"
2562		3743
2563	in the files that want to use the libevent API. This also includes F<ev.h>.	3744	in the files that want to use the libevent API. This also includes F<ev.h>.
2564		3745
2565	You need the following additional files for this:	3746	You need the following additional files for this:
2566		3747
2567	event.h	3748	event.h
2568	event.c	3749	event.c
2569		3750
2570	=head3 AUTOCONF SUPPORT	3751	=head3 AUTOCONF SUPPORT
2571		3752
2572	Instead of using C<EV_STANDALONE=1> and providing your config in	3753	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2573	whatever way you want, you can also C<m4_include([libev.m4])> in your	3754	whatever way you want, you can also C<m4_include([libev.m4])> in your
2574	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3755	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2575	include F<config.h> and configure itself accordingly.	3756	include F<config.h> and configure itself accordingly.
2576		3757
2577	For this of course you need the m4 file:	3758	For this of course you need the m4 file:
2578		3759
2579	libev.m4	3760	libev.m4
2580		3761
2581	=head2 PREPROCESSOR SYMBOLS/MACROS	3762	=head2 PREPROCESSOR SYMBOLS/MACROS
2582		3763
2583	Libev can be configured via a variety of preprocessor symbols you have to define	3764	Libev can be configured via a variety of preprocessor symbols you have to
2584	before including any of its files. The default is not to build for multiplicity	3765	define before including (or compiling) any of its files. The default in
2585	and only include the select backend.	3766	the absence of autoconf is documented for every option.
		3767
		3768	Symbols marked with "(h)" do not change the ABI, and can have different
		3769	values when compiling libev vs. including F<ev.h>, so it is permissible
		3770	to redefine them before including F<ev.h> without breaking compatibility
		3771	to a compiled library. All other symbols change the ABI, which means all
		3772	users of libev and the libev code itself must be compiled with compatible
		3773	settings.
2586		3774
2587	=over 4	3775	=over 4
2588		3776
		3777	=item EV_COMPAT3 (h)
		3778
		3779	Backwards compatibility is a major concern for libev. This is why this
		3780	release of libev comes with wrappers for the functions and symbols that
		3781	have been renamed between libev version 3 and 4.
		3782
		3783	You can disable these wrappers (to test compatibility with future
		3784	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3785	sources. This has the additional advantage that you can drop the C<struct>
		3786	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3787	typedef in that case.
		3788
		3789	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3790	and in some even more future version the compatibility code will be
		3791	removed completely.
		3792
2589	=item EV_STANDALONE	3793	=item EV_STANDALONE (h)
2590		3794
2591	Must always be C<1> if you do not use autoconf configuration, which	3795	Must always be C<1> if you do not use autoconf configuration, which
2592	keeps libev from including F<config.h>, and it also defines dummy	3796	keeps libev from including F<config.h>, and it also defines dummy
2593	implementations for some libevent functions (such as logging, which is not	3797	implementations for some libevent functions (such as logging, which is not
2594	supported). It will also not define any of the structs usually found in	3798	supported). It will also not define any of the structs usually found in
2595	F<event.h> that are not directly supported by the libev core alone.	3799	F<event.h> that are not directly supported by the libev core alone.
2596		3800
		3801	In standalone mode, libev will still try to automatically deduce the
		3802	configuration, but has to be more conservative.
		3803
2597	=item EV_USE_MONOTONIC	3804	=item EV_USE_MONOTONIC
2598		3805
2599	If defined to be C<1>, libev will try to detect the availability of the	3806	If defined to be C<1>, libev will try to detect the availability of the
2600	monotonic clock option at both compiletime and runtime. Otherwise no use	3807	monotonic clock option at both compile time and runtime. Otherwise no
2601	of the monotonic clock option will be attempted. If you enable this, you	3808	use of the monotonic clock option will be attempted. If you enable this,
2602	usually have to link against librt or something similar. Enabling it when	3809	you usually have to link against librt or something similar. Enabling it
2603	the functionality isn't available is safe, though, although you have	3810	when the functionality isn't available is safe, though, although you have
2604	to make sure you link against any libraries where the C<clock_gettime>	3811	to make sure you link against any libraries where the C<clock_gettime>
2605	function is hiding in (often F<-lrt>).	3812	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2606		3813
2607	=item EV_USE_REALTIME	3814	=item EV_USE_REALTIME
2608		3815
2609	If defined to be C<1>, libev will try to detect the availability of the	3816	If defined to be C<1>, libev will try to detect the availability of the
2610	realtime clock option at compiletime (and assume its availability at	3817	real-time clock option at compile time (and assume its availability
2611	runtime if successful). Otherwise no use of the realtime clock option will	3818	at runtime if successful). Otherwise no use of the real-time clock
2612	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3819	option will be attempted. This effectively replaces C<gettimeofday>
2613	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3820	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2614	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3821	correctness. See the note about libraries in the description of
		3822	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3823	C<EV_USE_CLOCK_SYSCALL>.
		3824
		3825	=item EV_USE_CLOCK_SYSCALL
		3826
		3827	If defined to be C<1>, libev will try to use a direct syscall instead
		3828	of calling the system-provided C<clock_gettime> function. This option
		3829	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3830	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3831	programs needlessly. Using a direct syscall is slightly slower (in
		3832	theory), because no optimised vdso implementation can be used, but avoids
		3833	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3834	higher, as it simplifies linking (no need for C<-lrt>).
2615		3835
2616	=item EV_USE_NANOSLEEP	3836	=item EV_USE_NANOSLEEP
2617		3837
2618	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3838	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2619	and will use it for delays. Otherwise it will use C<select ()>.	3839	and will use it for delays. Otherwise it will use C<select ()>.
2620		3840
		3841	=item EV_USE_EVENTFD
		3842
		3843	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3844	available and will probe for kernel support at runtime. This will improve
		3845	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3846	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3847	2.7 or newer, otherwise disabled.
		3848
2621	=item EV_USE_SELECT	3849	=item EV_USE_SELECT
2622		3850
2623	If undefined or defined to be C<1>, libev will compile in support for the	3851	If undefined or defined to be C<1>, libev will compile in support for the
2624	C<select>(2) backend. No attempt at autodetection will be done: if no	3852	C<select>(2) backend. No attempt at auto-detection will be done: if no
2625	other method takes over, select will be it. Otherwise the select backend	3853	other method takes over, select will be it. Otherwise the select backend
2626	will not be compiled in.	3854	will not be compiled in.
2627		3855
2628	=item EV_SELECT_USE_FD_SET	3856	=item EV_SELECT_USE_FD_SET
2629		3857
2630	If defined to C<1>, then the select backend will use the system C<fd_set>	3858	If defined to C<1>, then the select backend will use the system C<fd_set>
2631	structure. This is useful if libev doesn't compile due to a missing	3859	structure. This is useful if libev doesn't compile due to a missing
2632	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3860	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2633	exotic systems. This usually limits the range of file descriptors to some	3861	on exotic systems. This usually limits the range of file descriptors to
2634	low limit such as 1024 or might have other limitations (winsocket only	3862	some low limit such as 1024 or might have other limitations (winsocket
2635	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3863	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2636	influence the size of the C<fd_set> used.	3864	configures the maximum size of the C<fd_set>.
2637		3865
2638	=item EV_SELECT_IS_WINSOCKET	3866	=item EV_SELECT_IS_WINSOCKET
2639		3867
2640	When defined to C<1>, the select backend will assume that	3868	When defined to C<1>, the select backend will assume that
2641	select/socket/connect etc. don't understand file descriptors but	3869	select/socket/connect etc. don't understand file descriptors but
…		…
2643	be used is the winsock select). This means that it will call	3871	be used is the winsock select). This means that it will call
2644	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3872	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2645	it is assumed that all these functions actually work on fds, even	3873	it is assumed that all these functions actually work on fds, even
2646	on win32. Should not be defined on non-win32 platforms.	3874	on win32. Should not be defined on non-win32 platforms.
2647		3875
2648	=item EV_FD_TO_WIN32_HANDLE	3876	=item EV_FD_TO_WIN32_HANDLE(fd)
2649		3877
2650	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3878	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2651	file descriptors to socket handles. When not defining this symbol (the	3879	file descriptors to socket handles. When not defining this symbol (the
2652	default), then libev will call C<_get_osfhandle>, which is usually	3880	default), then libev will call C<_get_osfhandle>, which is usually
2653	correct. In some cases, programs use their own file descriptor management,	3881	correct. In some cases, programs use their own file descriptor management,
2654	in which case they can provide this function to map fds to socket handles.	3882	in which case they can provide this function to map fds to socket handles.
2655		3883
		3884	=item EV_WIN32_HANDLE_TO_FD(handle)
		3885
		3886	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3887	using the standard C<_open_osfhandle> function. For programs implementing
		3888	their own fd to handle mapping, overwriting this function makes it easier
		3889	to do so. This can be done by defining this macro to an appropriate value.
		3890
		3891	=item EV_WIN32_CLOSE_FD(fd)
		3892
		3893	If programs implement their own fd to handle mapping on win32, then this
		3894	macro can be used to override the C<close> function, useful to unregister
		3895	file descriptors again. Note that the replacement function has to close
		3896	the underlying OS handle.
		3897
2656	=item EV_USE_POLL	3898	=item EV_USE_POLL
2657		3899
2658	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3900	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2659	backend. Otherwise it will be enabled on non-win32 platforms. It	3901	backend. Otherwise it will be enabled on non-win32 platforms. It
2660	takes precedence over select.	3902	takes precedence over select.
2661		3903
2662	=item EV_USE_EPOLL	3904	=item EV_USE_EPOLL
2663		3905
2664	If defined to be C<1>, libev will compile in support for the Linux	3906	If defined to be C<1>, libev will compile in support for the Linux
2665	C<epoll>(7) backend. Its availability will be detected at runtime,	3907	C<epoll>(7) backend. Its availability will be detected at runtime,
2666	otherwise another method will be used as fallback. This is the	3908	otherwise another method will be used as fallback. This is the preferred
2667	preferred backend for GNU/Linux systems.	3909	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3910	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2668		3911
2669	=item EV_USE_KQUEUE	3912	=item EV_USE_KQUEUE
2670		3913
2671	If defined to be C<1>, libev will compile in support for the BSD style	3914	If defined to be C<1>, libev will compile in support for the BSD style
2672	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3915	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2685	otherwise another method will be used as fallback. This is the preferred	3928	otherwise another method will be used as fallback. This is the preferred
2686	backend for Solaris 10 systems.	3929	backend for Solaris 10 systems.
2687		3930
2688	=item EV_USE_DEVPOLL	3931	=item EV_USE_DEVPOLL
2689		3932
2690	reserved for future expansion, works like the USE symbols above.	3933	Reserved for future expansion, works like the USE symbols above.
2691		3934
2692	=item EV_USE_INOTIFY	3935	=item EV_USE_INOTIFY
2693		3936
2694	If defined to be C<1>, libev will compile in support for the Linux inotify	3937	If defined to be C<1>, libev will compile in support for the Linux inotify
2695	interface to speed up C<ev_stat> watchers. Its actual availability will	3938	interface to speed up C<ev_stat> watchers. Its actual availability will
2696	be detected at runtime.	3939	be detected at runtime. If undefined, it will be enabled if the headers
		3940	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2697		3941
2698	=item EV_ATOMIC_T	3942	=item EV_ATOMIC_T
2699		3943
2700	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	3944	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2701	access is atomic with respect to other threads or signal contexts. No such	3945	access is atomic with respect to other threads or signal contexts. No such
2702	type is easily found in the C language, so you can provide your own type	3946	type is easily found in the C language, so you can provide your own type
2703	that you know is safe for your purposes. It is used both for signal handler "locking"	3947	that you know is safe for your purposes. It is used both for signal handler "locking"
2704	as well as for signal and thread safety in C<ev_async> watchers.	3948	as well as for signal and thread safety in C<ev_async> watchers.
2705		3949
2706	In the absense of this define, libev will use C<sig_atomic_t volatile>	3950	In the absence of this define, libev will use C<sig_atomic_t volatile>
2707	(from F<signal.h>), which is usually good enough on most platforms.	3951	(from F<signal.h>), which is usually good enough on most platforms.
2708		3952
2709	=item EV_H	3953	=item EV_H (h)
2710		3954
2711	The name of the F<ev.h> header file used to include it. The default if	3955	The name of the F<ev.h> header file used to include it. The default if
2712	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3956	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2713	used to virtually rename the F<ev.h> header file in case of conflicts.	3957	used to virtually rename the F<ev.h> header file in case of conflicts.
2714		3958
2715	=item EV_CONFIG_H	3959	=item EV_CONFIG_H (h)
2716		3960
2717	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3961	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2718	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3962	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2719	C<EV_H>, above.	3963	C<EV_H>, above.
2720		3964
2721	=item EV_EVENT_H	3965	=item EV_EVENT_H (h)
2722		3966
2723	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3967	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2724	of how the F<event.h> header can be found, the default is C<"event.h">.	3968	of how the F<event.h> header can be found, the default is C<"event.h">.
2725		3969
2726	=item EV_PROTOTYPES	3970	=item EV_PROTOTYPES (h)
2727		3971
2728	If defined to be C<0>, then F<ev.h> will not define any function	3972	If defined to be C<0>, then F<ev.h> will not define any function
2729	prototypes, but still define all the structs and other symbols. This is	3973	prototypes, but still define all the structs and other symbols. This is
2730	occasionally useful if you want to provide your own wrapper functions	3974	occasionally useful if you want to provide your own wrapper functions
2731	around libev functions.	3975	around libev functions.
…		…
2750	When doing priority-based operations, libev usually has to linearly search	3994	When doing priority-based operations, libev usually has to linearly search
2751	all the priorities, so having many of them (hundreds) uses a lot of space	3995	all the priorities, so having many of them (hundreds) uses a lot of space
2752	and time, so using the defaults of five priorities (-2 .. +2) is usually	3996	and time, so using the defaults of five priorities (-2 .. +2) is usually
2753	fine.	3997	fine.
2754		3998
2755	If your embedding app does not need any priorities, defining these both to	3999	If your embedding application does not need any priorities, defining these
2756	C<0> will save some memory and cpu.	4000	both to C<0> will save some memory and CPU.
2757		4001
2758	=item EV_PERIODIC_ENABLE	4002	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4003	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4004	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2759		4005
2760	If undefined or defined to be C<1>, then periodic timers are supported. If	4006	If undefined or defined to be C<1> (and the platform supports it), then
2761	defined to be C<0>, then they are not. Disabling them saves a few kB of	4007	the respective watcher type is supported. If defined to be C<0>, then it
2762	code.	4008	is not. Disabling watcher types mainly saves code size.
2763		4009
2764	=item EV_IDLE_ENABLE	4010	=item EV_FEATURES
2765
2766	If undefined or defined to be C<1>, then idle watchers are supported. If
2767	defined to be C<0>, then they are not. Disabling them saves a few kB of
2768	code.
2769
2770	=item EV_EMBED_ENABLE
2771
2772	If undefined or defined to be C<1>, then embed watchers are supported. If
2773	defined to be C<0>, then they are not.
2774
2775	=item EV_STAT_ENABLE
2776
2777	If undefined or defined to be C<1>, then stat watchers are supported. If
2778	defined to be C<0>, then they are not.
2779
2780	=item EV_FORK_ENABLE
2781
2782	If undefined or defined to be C<1>, then fork watchers are supported. If
2783	defined to be C<0>, then they are not.
2784
2785	=item EV_ASYNC_ENABLE
2786
2787	If undefined or defined to be C<1>, then async watchers are supported. If
2788	defined to be C<0>, then they are not.
2789
2790	=item EV_MINIMAL
2791		4011
2792	If you need to shave off some kilobytes of code at the expense of some	4012	If you need to shave off some kilobytes of code at the expense of some
2793	speed, define this symbol to C<1>. Currently only used for gcc to override	4013	speed (but with the full API), you can define this symbol to request
2794	some inlining decisions, saves roughly 30% codesize of amd64.	4014	certain subsets of functionality. The default is to enable all features
		4015	that can be enabled on the platform.
		4016
		4017	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4018	with some broad features you want) and then selectively re-enable
		4019	additional parts you want, for example if you want everything minimal,
		4020	but multiple event loop support, async and child watchers and the poll
		4021	backend, use this:
		4022
		4023	#define EV_FEATURES 0
		4024	#define EV_MULTIPLICITY 1
		4025	#define EV_USE_POLL 1
		4026	#define EV_CHILD_ENABLE 1
		4027	#define EV_ASYNC_ENABLE 1
		4028
		4029	The actual value is a bitset, it can be a combination of the following
		4030	values:
		4031
		4032	=over 4
		4033
		4034	=item C<1> - faster/larger code
		4035
		4036	Use larger code to speed up some operations.
		4037
		4038	Currently this is used to override some inlining decisions (enlarging the
		4039	code size by roughly 30% on amd64).
		4040
		4041	When optimising for size, use of compiler flags such as C<-Os> with
		4042	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4043	assertions.
		4044
		4045	=item C<2> - faster/larger data structures
		4046
		4047	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4048	hash table sizes and so on. This will usually further increase code size
		4049	and can additionally have an effect on the size of data structures at
		4050	runtime.
		4051
		4052	=item C<4> - full API configuration
		4053
		4054	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4055	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4056
		4057	=item C<8> - full API
		4058
		4059	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4060	details on which parts of the API are still available without this
		4061	feature, and do not complain if this subset changes over time.
		4062
		4063	=item C<16> - enable all optional watcher types
		4064
		4065	Enables all optional watcher types. If you want to selectively enable
		4066	only some watcher types other than I/O and timers (e.g. prepare,
		4067	embed, async, child...) you can enable them manually by defining
		4068	C<EV_watchertype_ENABLE> to C<1> instead.
		4069
		4070	=item C<32> - enable all backends
		4071
		4072	This enables all backends - without this feature, you need to enable at
		4073	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4074
		4075	=item C<64> - enable OS-specific "helper" APIs
		4076
		4077	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4078	default.
		4079
		4080	=back
		4081
		4082	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4083	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4084	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4085	watchers, timers and monotonic clock support.
		4086
		4087	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4088	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4089	your program might be left out as well - a binary starting a timer and an
		4090	I/O watcher then might come out at only 5Kb.
		4091
		4092	=item EV_AVOID_STDIO
		4093
		4094	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4095	functions (printf, scanf, perror etc.). This will increase the code size
		4096	somewhat, but if your program doesn't otherwise depend on stdio and your
		4097	libc allows it, this avoids linking in the stdio library which is quite
		4098	big.
		4099
		4100	Note that error messages might become less precise when this option is
		4101	enabled.
		4102
		4103	=item EV_NSIG
		4104
		4105	The highest supported signal number, +1 (or, the number of
		4106	signals): Normally, libev tries to deduce the maximum number of signals
		4107	automatically, but sometimes this fails, in which case it can be
		4108	specified. Also, using a lower number than detected (C<32> should be
		4109	good for about any system in existence) can save some memory, as libev
		4110	statically allocates some 12-24 bytes per signal number.
2795		4111
2796	=item EV_PID_HASHSIZE	4112	=item EV_PID_HASHSIZE
2797		4113
2798	C<ev_child> watchers use a small hash table to distribute workload by	4114	C<ev_child> watchers use a small hash table to distribute workload by
2799	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4115	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2800	than enough. If you need to manage thousands of children you might want to	4116	usually more than enough. If you need to manage thousands of children you
2801	increase this value (I<must> be a power of two).	4117	might want to increase this value (I<must> be a power of two).
2802		4118
2803	=item EV_INOTIFY_HASHSIZE	4119	=item EV_INOTIFY_HASHSIZE
2804		4120
2805	C<ev_stat> watchers use a small hash table to distribute workload by	4121	C<ev_stat> watchers use a small hash table to distribute workload by
2806	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4122	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2807	usually more than enough. If you need to manage thousands of C<ev_stat>	4123	disabled), usually more than enough. If you need to manage thousands of
2808	watchers you might want to increase this value (I<must> be a power of	4124	C<ev_stat> watchers you might want to increase this value (I<must> be a
2809	two).	4125	power of two).
		4126
		4127	=item EV_USE_4HEAP
		4128
		4129	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4130	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4131	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4132	faster performance with many (thousands) of watchers.
		4133
		4134	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4135	will be C<0>.
		4136
		4137	=item EV_HEAP_CACHE_AT
		4138
		4139	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4140	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4141	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4142	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4143	but avoids random read accesses on heap changes. This improves performance
		4144	noticeably with many (hundreds) of watchers.
		4145
		4146	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4147	will be C<0>.
		4148
		4149	=item EV_VERIFY
		4150
		4151	Controls how much internal verification (see C<ev_verify ()>) will
		4152	be done: If set to C<0>, no internal verification code will be compiled
		4153	in. If set to C<1>, then verification code will be compiled in, but not
		4154	called. If set to C<2>, then the internal verification code will be
		4155	called once per loop, which can slow down libev. If set to C<3>, then the
		4156	verification code will be called very frequently, which will slow down
		4157	libev considerably.
		4158
		4159	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4160	will be C<0>.
2810		4161
2811	=item EV_COMMON	4162	=item EV_COMMON
2812		4163
2813	By default, all watchers have a C<void *data> member. By redefining	4164	By default, all watchers have a C<void *data> member. By redefining
2814	this macro to a something else you can include more and other types of	4165	this macro to something else you can include more and other types of
2815	members. You have to define it each time you include one of the files,	4166	members. You have to define it each time you include one of the files,
2816	though, and it must be identical each time.	4167	though, and it must be identical each time.
2817		4168
2818	For example, the perl EV module uses something like this:	4169	For example, the perl EV module uses something like this:
2819		4170
2820	#define EV_COMMON \	4171	#define EV_COMMON \
2821	SV *self; /* contains this struct */ \	4172	SV *self; /* contains this struct */ \
2822	SV *cb_sv, *fh /* note no trailing ";" */	4173	SV *cb_sv, *fh /* note no trailing ";" */
2823		4174
2824	=item EV_CB_DECLARE (type)	4175	=item EV_CB_DECLARE (type)
2825		4176
2826	=item EV_CB_INVOKE (watcher, revents)	4177	=item EV_CB_INVOKE (watcher, revents)
2827		4178
…		…
2832	definition and a statement, respectively. See the F<ev.h> header file for	4183	definition and a statement, respectively. See the F<ev.h> header file for
2833	their default definitions. One possible use for overriding these is to	4184	their default definitions. One possible use for overriding these is to
2834	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4185	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2835	method calls instead of plain function calls in C++.	4186	method calls instead of plain function calls in C++.
2836		4187
		4188	=back
		4189
2837	=head2 EXPORTED API SYMBOLS	4190	=head2 EXPORTED API SYMBOLS
2838		4191
2839	If you need to re-export the API (e.g. via a dll) and you need a list of	4192	If you need to re-export the API (e.g. via a DLL) and you need a list of
2840	exported symbols, you can use the provided F<Symbol.*> files which list	4193	exported symbols, you can use the provided F<Symbol.*> files which list
2841	all public symbols, one per line:	4194	all public symbols, one per line:
2842		4195
2843	Symbols.ev for libev proper	4196	Symbols.ev for libev proper
2844	Symbols.event for the libevent emulation	4197	Symbols.event for the libevent emulation
2845		4198
2846	This can also be used to rename all public symbols to avoid clashes with	4199	This can also be used to rename all public symbols to avoid clashes with
2847	multiple versions of libev linked together (which is obviously bad in	4200	multiple versions of libev linked together (which is obviously bad in
2848	itself, but sometimes it is inconvinient to avoid this).	4201	itself, but sometimes it is inconvenient to avoid this).
2849		4202
2850	A sed command like this will create wrapper C<#define>'s that you need to	4203	A sed command like this will create wrapper C<#define>'s that you need to
2851	include before including F<ev.h>:	4204	include before including F<ev.h>:
2852		4205
2853	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4206	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2870	file.	4223	file.
2871		4224
2872	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4225	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2873	that everybody includes and which overrides some configure choices:	4226	that everybody includes and which overrides some configure choices:
2874		4227
2875	#define EV_MINIMAL 1	4228	#define EV_FEATURES 8
2876	#define EV_USE_POLL 0	4229	#define EV_USE_SELECT 1
2877	#define EV_MULTIPLICITY 0
2878	#define EV_PERIODIC_ENABLE 0	4230	#define EV_PREPARE_ENABLE 1
		4231	#define EV_IDLE_ENABLE 1
2879	#define EV_STAT_ENABLE 0	4232	#define EV_SIGNAL_ENABLE 1
2880	#define EV_FORK_ENABLE 0	4233	#define EV_CHILD_ENABLE 1
		4234	#define EV_USE_STDEXCEPT 0
2881	#define EV_CONFIG_H <config.h>	4235	#define EV_CONFIG_H <config.h>
2882	#define EV_MINPRI 0
2883	#define EV_MAXPRI 0
2884		4236
2885	#include "ev++.h"	4237	#include "ev++.h"
2886		4238
2887	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4239	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2888		4240
2889	#include "ev_cpp.h"	4241	#include "ev_cpp.h"
2890	#include "ev.c"	4242	#include "ev.c"
2891		4243
		4244	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2892		4245
2893	=head1 COMPLEXITIES	4246	=head2 THREADS AND COROUTINES
2894		4247
2895	In this section the complexities of (many of) the algorithms used inside	4248	=head3 THREADS
2896	libev will be explained. For complexity discussions about backends see the
2897	documentation for C<ev_default_init>.
2898		4249
2899	All of the following are about amortised time: If an array needs to be	4250	All libev functions are reentrant and thread-safe unless explicitly
2900	extended, libev needs to realloc and move the whole array, but this	4251	documented otherwise, but libev implements no locking itself. This means
2901	happens asymptotically never with higher number of elements, so O(1) might	4252	that you can use as many loops as you want in parallel, as long as there
2902	mean it might do a lengthy realloc operation in rare cases, but on average	4253	are no concurrent calls into any libev function with the same loop
2903	it is much faster and asymptotically approaches constant time.	4254	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4255	of course): libev guarantees that different event loops share no data
		4256	structures that need any locking.
		4257
		4258	Or to put it differently: calls with different loop parameters can be done
		4259	concurrently from multiple threads, calls with the same loop parameter
		4260	must be done serially (but can be done from different threads, as long as
		4261	only one thread ever is inside a call at any point in time, e.g. by using
		4262	a mutex per loop).
		4263
		4264	Specifically to support threads (and signal handlers), libev implements
		4265	so-called C<ev_async> watchers, which allow some limited form of
		4266	concurrency on the same event loop, namely waking it up "from the
		4267	outside".
		4268
		4269	If you want to know which design (one loop, locking, or multiple loops
		4270	without or something else still) is best for your problem, then I cannot
		4271	help you, but here is some generic advice:
2904		4272
2905	=over 4	4273	=over 4
2906		4274
2907	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4275	=item * most applications have a main thread: use the default libev loop
		4276	in that thread, or create a separate thread running only the default loop.
2908		4277
2909	This means that, when you have a watcher that triggers in one hour and	4278	This helps integrating other libraries or software modules that use libev
2910	there are 100 watchers that would trigger before that then inserting will	4279	themselves and don't care/know about threading.
2911	have to skip roughly seven (C<ld 100>) of these watchers.
2912		4280
2913	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4281	=item * one loop per thread is usually a good model.
2914		4282
2915	That means that changing a timer costs less than removing/adding them	4283	Doing this is almost never wrong, sometimes a better-performance model
2916	as only the relative motion in the event queue has to be paid for.	4284	exists, but it is always a good start.
2917		4285
2918	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4286	=item * other models exist, such as the leader/follower pattern, where one
		4287	loop is handed through multiple threads in a kind of round-robin fashion.
2919		4288
2920	These just add the watcher into an array or at the head of a list.	4289	Choosing a model is hard - look around, learn, know that usually you can do
		4290	better than you currently do :-)
2921		4291
2922	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4292	=item * often you need to talk to some other thread which blocks in the
		4293	event loop.
2923		4294
2924	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4295	C<ev_async> watchers can be used to wake them up from other threads safely
		4296	(or from signal contexts...).
2925		4297
2926	These watchers are stored in lists then need to be walked to find the	4298	An example use would be to communicate signals or other events that only
2927	correct watcher to remove. The lists are usually short (you don't usually	4299	work in the default loop by registering the signal watcher with the
2928	have many watchers waiting for the same fd or signal).	4300	default loop and triggering an C<ev_async> watcher from the default loop
2929		4301	watcher callback into the event loop interested in the signal.
2930	=item Finding the next timer in each loop iteration: O(1)
2931
2932	By virtue of using a binary heap, the next timer is always found at the
2933	beginning of the storage array.
2934
2935	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2936
2937	A change means an I/O watcher gets started or stopped, which requires
2938	libev to recalculate its status (and possibly tell the kernel, depending
2939	on backend and wether C<ev_io_set> was used).
2940
2941	=item Activating one watcher (putting it into the pending state): O(1)
2942
2943	=item Priority handling: O(number_of_priorities)
2944
2945	Priorities are implemented by allocating some space for each
2946	priority. When doing priority-based operations, libev usually has to
2947	linearly search all the priorities, but starting/stopping and activating
2948	watchers becomes O(1) w.r.t. priority handling.
2949
2950	=item Sending an ev_async: O(1)
2951
2952	=item Processing ev_async_send: O(number_of_async_watchers)
2953
2954	=item Processing signals: O(max_signal_number)
2955
2956	Sending involves a syscall I<iff> there were no other C<ev_async_send>
2957	calls in the current loop iteration. Checking for async and signal events
2958	involves iterating over all running async watchers or all signal numbers.
2959		4302
2960	=back	4303	=back
2961		4304
		4305	=head4 THREAD LOCKING EXAMPLE
2962		4306
2963	=head1 Win32 platform limitations and workarounds	4307	Here is a fictitious example of how to run an event loop in a different
		4308	thread than where callbacks are being invoked and watchers are
		4309	created/added/removed.
		4310
		4311	For a real-world example, see the C<EV::Loop::Async> perl module,
		4312	which uses exactly this technique (which is suited for many high-level
		4313	languages).
		4314
		4315	The example uses a pthread mutex to protect the loop data, a condition
		4316	variable to wait for callback invocations, an async watcher to notify the
		4317	event loop thread and an unspecified mechanism to wake up the main thread.
		4318
		4319	First, you need to associate some data with the event loop:
		4320
		4321	typedef struct {
		4322	mutex_t lock; /* global loop lock */
		4323	ev_async async_w;
		4324	thread_t tid;
		4325	cond_t invoke_cv;
		4326	} userdata;
		4327
		4328	void prepare_loop (EV_P)
		4329	{
		4330	// for simplicity, we use a static userdata struct.
		4331	static userdata u;
		4332
		4333	ev_async_init (&u->async_w, async_cb);
		4334	ev_async_start (EV_A_ &u->async_w);
		4335
		4336	pthread_mutex_init (&u->lock, 0);
		4337	pthread_cond_init (&u->invoke_cv, 0);
		4338
		4339	// now associate this with the loop
		4340	ev_set_userdata (EV_A_ u);
		4341	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4342	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4343
		4344	// then create the thread running ev_loop
		4345	pthread_create (&u->tid, 0, l_run, EV_A);
		4346	}
		4347
		4348	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4349	solely to wake up the event loop so it takes notice of any new watchers
		4350	that might have been added:
		4351
		4352	static void
		4353	async_cb (EV_P_ ev_async *w, int revents)
		4354	{
		4355	// just used for the side effects
		4356	}
		4357
		4358	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4359	protecting the loop data, respectively.
		4360
		4361	static void
		4362	l_release (EV_P)
		4363	{
		4364	userdata *u = ev_userdata (EV_A);
		4365	pthread_mutex_unlock (&u->lock);
		4366	}
		4367
		4368	static void
		4369	l_acquire (EV_P)
		4370	{
		4371	userdata *u = ev_userdata (EV_A);
		4372	pthread_mutex_lock (&u->lock);
		4373	}
		4374
		4375	The event loop thread first acquires the mutex, and then jumps straight
		4376	into C<ev_run>:
		4377
		4378	void *
		4379	l_run (void *thr_arg)
		4380	{
		4381	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4382
		4383	l_acquire (EV_A);
		4384	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4385	ev_run (EV_A_ 0);
		4386	l_release (EV_A);
		4387
		4388	return 0;
		4389	}
		4390
		4391	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4392	signal the main thread via some unspecified mechanism (signals? pipe
		4393	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4394	have been called (in a while loop because a) spurious wakeups are possible
		4395	and b) skipping inter-thread-communication when there are no pending
		4396	watchers is very beneficial):
		4397
		4398	static void
		4399	l_invoke (EV_P)
		4400	{
		4401	userdata *u = ev_userdata (EV_A);
		4402
		4403	while (ev_pending_count (EV_A))
		4404	{
		4405	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4406	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4407	}
		4408	}
		4409
		4410	Now, whenever the main thread gets told to invoke pending watchers, it
		4411	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4412	thread to continue:
		4413
		4414	static void
		4415	real_invoke_pending (EV_P)
		4416	{
		4417	userdata *u = ev_userdata (EV_A);
		4418
		4419	pthread_mutex_lock (&u->lock);
		4420	ev_invoke_pending (EV_A);
		4421	pthread_cond_signal (&u->invoke_cv);
		4422	pthread_mutex_unlock (&u->lock);
		4423	}
		4424
		4425	Whenever you want to start/stop a watcher or do other modifications to an
		4426	event loop, you will now have to lock:
		4427
		4428	ev_timer timeout_watcher;
		4429	userdata *u = ev_userdata (EV_A);
		4430
		4431	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4432
		4433	pthread_mutex_lock (&u->lock);
		4434	ev_timer_start (EV_A_ &timeout_watcher);
		4435	ev_async_send (EV_A_ &u->async_w);
		4436	pthread_mutex_unlock (&u->lock);
		4437
		4438	Note that sending the C<ev_async> watcher is required because otherwise
		4439	an event loop currently blocking in the kernel will have no knowledge
		4440	about the newly added timer. By waking up the loop it will pick up any new
		4441	watchers in the next event loop iteration.
		4442
		4443	=head3 COROUTINES
		4444
		4445	Libev is very accommodating to coroutines ("cooperative threads"):
		4446	libev fully supports nesting calls to its functions from different
		4447	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4448	different coroutines, and switch freely between both coroutines running
		4449	the loop, as long as you don't confuse yourself). The only exception is
		4450	that you must not do this from C<ev_periodic> reschedule callbacks.
		4451
		4452	Care has been taken to ensure that libev does not keep local state inside
		4453	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4454	they do not call any callbacks.
		4455
		4456	=head2 COMPILER WARNINGS
		4457
		4458	Depending on your compiler and compiler settings, you might get no or a
		4459	lot of warnings when compiling libev code. Some people are apparently
		4460	scared by this.
		4461
		4462	However, these are unavoidable for many reasons. For one, each compiler
		4463	has different warnings, and each user has different tastes regarding
		4464	warning options. "Warn-free" code therefore cannot be a goal except when
		4465	targeting a specific compiler and compiler-version.
		4466
		4467	Another reason is that some compiler warnings require elaborate
		4468	workarounds, or other changes to the code that make it less clear and less
		4469	maintainable.
		4470
		4471	And of course, some compiler warnings are just plain stupid, or simply
		4472	wrong (because they don't actually warn about the condition their message
		4473	seems to warn about). For example, certain older gcc versions had some
		4474	warnings that resulted in an extreme number of false positives. These have
		4475	been fixed, but some people still insist on making code warn-free with
		4476	such buggy versions.
		4477
		4478	While libev is written to generate as few warnings as possible,
		4479	"warn-free" code is not a goal, and it is recommended not to build libev
		4480	with any compiler warnings enabled unless you are prepared to cope with
		4481	them (e.g. by ignoring them). Remember that warnings are just that:
		4482	warnings, not errors, or proof of bugs.
		4483
		4484
		4485	=head2 VALGRIND
		4486
		4487	Valgrind has a special section here because it is a popular tool that is
		4488	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4489
		4490	If you think you found a bug (memory leak, uninitialised data access etc.)
		4491	in libev, then check twice: If valgrind reports something like:
		4492
		4493	==2274== definitely lost: 0 bytes in 0 blocks.
		4494	==2274== possibly lost: 0 bytes in 0 blocks.
		4495	==2274== still reachable: 256 bytes in 1 blocks.
		4496
		4497	Then there is no memory leak, just as memory accounted to global variables
		4498	is not a memleak - the memory is still being referenced, and didn't leak.
		4499
		4500	Similarly, under some circumstances, valgrind might report kernel bugs
		4501	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4502	although an acceptable workaround has been found here), or it might be
		4503	confused.
		4504
		4505	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4506	make it into some kind of religion.
		4507
		4508	If you are unsure about something, feel free to contact the mailing list
		4509	with the full valgrind report and an explanation on why you think this
		4510	is a bug in libev (best check the archives, too :). However, don't be
		4511	annoyed when you get a brisk "this is no bug" answer and take the chance
		4512	of learning how to interpret valgrind properly.
		4513
		4514	If you need, for some reason, empty reports from valgrind for your project
		4515	I suggest using suppression lists.
		4516
		4517
		4518	=head1 PORTABILITY NOTES
		4519
		4520	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4521
		4522	GNU/Linux is the only common platform that supports 64 bit file/large file
		4523	interfaces but I<disables> them by default.
		4524
		4525	That means that libev compiled in the default environment doesn't support
		4526	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4527
		4528	Unfortunately, many programs try to work around this GNU/Linux issue
		4529	by enabling the large file API, which makes them incompatible with the
		4530	standard libev compiled for their system.
		4531
		4532	Likewise, libev cannot enable the large file API itself as this would
		4533	suddenly make it incompatible to the default compile time environment,
		4534	i.e. all programs not using special compile switches.
		4535
		4536	=head2 OS/X AND DARWIN BUGS
		4537
		4538	The whole thing is a bug if you ask me - basically any system interface
		4539	you touch is broken, whether it is locales, poll, kqueue or even the
		4540	OpenGL drivers.
		4541
		4542	=head3 C<kqueue> is buggy
		4543
		4544	The kqueue syscall is broken in all known versions - most versions support
		4545	only sockets, many support pipes.
		4546
		4547	Libev tries to work around this by not using C<kqueue> by default on this
		4548	rotten platform, but of course you can still ask for it when creating a
		4549	loop - embedding a socket-only kqueue loop into a select-based one is
		4550	probably going to work well.
		4551
		4552	=head3 C<poll> is buggy
		4553
		4554	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4555	implementation by something calling C<kqueue> internally around the 10.5.6
		4556	release, so now C<kqueue> I<and> C<poll> are broken.
		4557
		4558	Libev tries to work around this by not using C<poll> by default on
		4559	this rotten platform, but of course you can still ask for it when creating
		4560	a loop.
		4561
		4562	=head3 C<select> is buggy
		4563
		4564	All that's left is C<select>, and of course Apple found a way to fuck this
		4565	one up as well: On OS/X, C<select> actively limits the number of file
		4566	descriptors you can pass in to 1024 - your program suddenly crashes when
		4567	you use more.
		4568
		4569	There is an undocumented "workaround" for this - defining
		4570	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4571	work on OS/X.
		4572
		4573	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4574
		4575	=head3 C<errno> reentrancy
		4576
		4577	The default compile environment on Solaris is unfortunately so
		4578	thread-unsafe that you can't even use components/libraries compiled
		4579	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4580	defined by default. A valid, if stupid, implementation choice.
		4581
		4582	If you want to use libev in threaded environments you have to make sure
		4583	it's compiled with C<_REENTRANT> defined.
		4584
		4585	=head3 Event port backend
		4586
		4587	The scalable event interface for Solaris is called "event
		4588	ports". Unfortunately, this mechanism is very buggy in all major
		4589	releases. If you run into high CPU usage, your program freezes or you get
		4590	a large number of spurious wakeups, make sure you have all the relevant
		4591	and latest kernel patches applied. No, I don't know which ones, but there
		4592	are multiple ones to apply, and afterwards, event ports actually work
		4593	great.
		4594
		4595	If you can't get it to work, you can try running the program by setting
		4596	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4597	C<select> backends.
		4598
		4599	=head2 AIX POLL BUG
		4600
		4601	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4602	this by trying to avoid the poll backend altogether (i.e. it's not even
		4603	compiled in), which normally isn't a big problem as C<select> works fine
		4604	with large bitsets on AIX, and AIX is dead anyway.
		4605
		4606	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4607
		4608	=head3 General issues
2964		4609
2965	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4610	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2966	requires, and its I/O model is fundamentally incompatible with the POSIX	4611	requires, and its I/O model is fundamentally incompatible with the POSIX
2967	model. Libev still offers limited functionality on this platform in	4612	model. Libev still offers limited functionality on this platform in
2968	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4613	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2969	descriptors. This only applies when using Win32 natively, not when using	4614	descriptors. This only applies when using Win32 natively, not when using
2970	e.g. cygwin.	4615	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4616	as every compielr comes with a slightly differently broken/incompatible
		4617	environment.
		4618
		4619	Lifting these limitations would basically require the full
		4620	re-implementation of the I/O system. If you are into this kind of thing,
		4621	then note that glib does exactly that for you in a very portable way (note
		4622	also that glib is the slowest event library known to man).
2971		4623
2972	There is no supported compilation method available on windows except	4624	There is no supported compilation method available on windows except
2973	embedding it into other applications.	4625	embedding it into other applications.
2974		4626
		4627	Sensible signal handling is officially unsupported by Microsoft - libev
		4628	tries its best, but under most conditions, signals will simply not work.
		4629
		4630	Not a libev limitation but worth mentioning: windows apparently doesn't
		4631	accept large writes: instead of resulting in a partial write, windows will
		4632	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4633	so make sure you only write small amounts into your sockets (less than a
		4634	megabyte seems safe, but this apparently depends on the amount of memory
		4635	available).
		4636
2975	Due to the many, low, and arbitrary limits on the win32 platform and the	4637	Due to the many, low, and arbitrary limits on the win32 platform and
2976	abysmal performance of winsockets, using a large number of sockets is not	4638	the abysmal performance of winsockets, using a large number of sockets
2977	recommended (and not reasonable). If your program needs to use more than	4639	is not recommended (and not reasonable). If your program needs to use
2978	a hundred or so sockets, then likely it needs to use a totally different	4640	more than a hundred or so sockets, then likely it needs to use a totally
2979	implementation for windows, as libev offers the POSIX model, which cannot	4641	different implementation for windows, as libev offers the POSIX readiness
2980	be implemented efficiently on windows (microsoft monopoly games).	4642	notification model, which cannot be implemented efficiently on windows
		4643	(due to Microsoft monopoly games).
2981		4644
2982	=over 4	4645	A typical way to use libev under windows is to embed it (see the embedding
		4646	section for details) and use the following F<evwrap.h> header file instead
		4647	of F<ev.h>:
2983		4648
		4649	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4650	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4651
		4652	#include "ev.h"
		4653
		4654	And compile the following F<evwrap.c> file into your project (make sure
		4655	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4656
		4657	#include "evwrap.h"
		4658	#include "ev.c"
		4659
2984	=item The winsocket select function	4660	=head3 The winsocket C<select> function
2985		4661
2986	The winsocket C<select> function doesn't follow POSIX in that it requires	4662	The winsocket C<select> function doesn't follow POSIX in that it
2987	socket I<handles> and not socket I<file descriptors>. This makes select	4663	requires socket I<handles> and not socket I<file descriptors> (it is
2988	very inefficient, and also requires a mapping from file descriptors	4664	also extremely buggy). This makes select very inefficient, and also
2989	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4665	requires a mapping from file descriptors to socket handles (the Microsoft
2990	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4666	C runtime provides the function C<_open_osfhandle> for this). See the
2991	symbols for more info.	4667	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4668	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2992		4669
2993	The configuration for a "naked" win32 using the microsoft runtime	4670	The configuration for a "naked" win32 using the Microsoft runtime
2994	libraries and raw winsocket select is:	4671	libraries and raw winsocket select is:
2995		4672
2996	#define EV_USE_SELECT 1	4673	#define EV_USE_SELECT 1
2997	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4674	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2998		4675
2999	Note that winsockets handling of fd sets is O(n), so you can easily get a	4676	Note that winsockets handling of fd sets is O(n), so you can easily get a
3000	complexity in the O(n²) range when using win32.	4677	complexity in the O(n²) range when using win32.
3001		4678
3002	=item Limited number of file descriptors	4679	=head3 Limited number of file descriptors
3003		4680
3004	Windows has numerous arbitrary (and low) limits on things. Early versions	4681	Windows has numerous arbitrary (and low) limits on things.
3005	of winsocket's select only supported waiting for a max. of C<64> handles	4682
		4683	Early versions of winsocket's select only supported waiting for a maximum
3006	(probably owning to the fact that all windows kernels can only wait for	4684	of C<64> handles (probably owning to the fact that all windows kernels
3007	C<64> things at the same time internally; microsoft recommends spawning a	4685	can only wait for C<64> things at the same time internally; Microsoft
3008	chain of threads and wait for 63 handles and the previous thread in each).	4686	recommends spawning a chain of threads and wait for 63 handles and the
		4687	previous thread in each. Sounds great!).
3009		4688
3010	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4689	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3011	to some high number (e.g. C<2048>) before compiling the winsocket select	4690	to some high number (e.g. C<2048>) before compiling the winsocket select
3012	call (which might be in libev or elsewhere, for example, perl does its own	4691	call (which might be in libev or elsewhere, for example, perl and many
3013	select emulation on windows).	4692	other interpreters do their own select emulation on windows).
3014		4693
3015	Another limit is the number of file descriptors in the microsoft runtime	4694	Another limit is the number of file descriptors in the Microsoft runtime
3016	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4695	libraries, which by default is C<64> (there must be a hidden I<64>
3017	or something like this inside microsoft). You can increase this by calling	4696	fetish or something like this inside Microsoft). You can increase this
3018	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4697	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3019	arbitrary limit), but is broken in many versions of the microsoft runtime	4698	(another arbitrary limit), but is broken in many versions of the Microsoft
3020	libraries.
3021
3022	This might get you to about C<512> or C<2048> sockets (depending on	4699	runtime libraries. This might get you to about C<512> or C<2048> sockets
3023	windows version and/or the phase of the moon). To get more, you need to	4700	(depending on windows version and/or the phase of the moon). To get more,
3024	wrap all I/O functions and provide your own fd management, but the cost of	4701	you need to wrap all I/O functions and provide your own fd management, but
3025	calling select (O(n²)) will likely make this unworkable.	4702	the cost of calling select (O(n²)) will likely make this unworkable.
		4703
		4704	=head2 PORTABILITY REQUIREMENTS
		4705
		4706	In addition to a working ISO-C implementation and of course the
		4707	backend-specific APIs, libev relies on a few additional extensions:
		4708
		4709	=over 4
		4710
		4711	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4712	calling conventions regardless of C<ev_watcher_type *>.
		4713
		4714	Libev assumes not only that all watcher pointers have the same internal
		4715	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4716	assumes that the same (machine) code can be used to call any watcher
		4717	callback: The watcher callbacks have different type signatures, but libev
		4718	calls them using an C<ev_watcher *> internally.
		4719
		4720	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4721
		4722	The type C<sig_atomic_t volatile> (or whatever is defined as
		4723	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4724	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4725	believed to be sufficiently portable.
		4726
		4727	=item C<sigprocmask> must work in a threaded environment
		4728
		4729	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4730	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4731	pthread implementations will either allow C<sigprocmask> in the "main
		4732	thread" or will block signals process-wide, both behaviours would
		4733	be compatible with libev. Interaction between C<sigprocmask> and
		4734	C<pthread_sigmask> could complicate things, however.
		4735
		4736	The most portable way to handle signals is to block signals in all threads
		4737	except the initial one, and run the default loop in the initial thread as
		4738	well.
		4739
		4740	=item C<long> must be large enough for common memory allocation sizes
		4741
		4742	To improve portability and simplify its API, libev uses C<long> internally
		4743	instead of C<size_t> when allocating its data structures. On non-POSIX
		4744	systems (Microsoft...) this might be unexpectedly low, but is still at
		4745	least 31 bits everywhere, which is enough for hundreds of millions of
		4746	watchers.
		4747
		4748	=item C<double> must hold a time value in seconds with enough accuracy
		4749
		4750	The type C<double> is used to represent timestamps. It is required to
		4751	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4752	good enough for at least into the year 4000 with millisecond accuracy
		4753	(the design goal for libev). This requirement is overfulfilled by
		4754	implementations using IEEE 754, which is basically all existing ones. With
		4755	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3026		4756
3027	=back	4757	=back
3028		4758
		4759	If you know of other additional requirements drop me a note.
		4760
		4761
		4762	=head1 ALGORITHMIC COMPLEXITIES
		4763
		4764	In this section the complexities of (many of) the algorithms used inside
		4765	libev will be documented. For complexity discussions about backends see
		4766	the documentation for C<ev_default_init>.
		4767
		4768	All of the following are about amortised time: If an array needs to be
		4769	extended, libev needs to realloc and move the whole array, but this
		4770	happens asymptotically rarer with higher number of elements, so O(1) might
		4771	mean that libev does a lengthy realloc operation in rare cases, but on
		4772	average it is much faster and asymptotically approaches constant time.
		4773
		4774	=over 4
		4775
		4776	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4777
		4778	This means that, when you have a watcher that triggers in one hour and
		4779	there are 100 watchers that would trigger before that, then inserting will
		4780	have to skip roughly seven (C<ld 100>) of these watchers.
		4781
		4782	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4783
		4784	That means that changing a timer costs less than removing/adding them,
		4785	as only the relative motion in the event queue has to be paid for.
		4786
		4787	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4788
		4789	These just add the watcher into an array or at the head of a list.
		4790
		4791	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4792
		4793	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4794
		4795	These watchers are stored in lists, so they need to be walked to find the
		4796	correct watcher to remove. The lists are usually short (you don't usually
		4797	have many watchers waiting for the same fd or signal: one is typical, two
		4798	is rare).
		4799
		4800	=item Finding the next timer in each loop iteration: O(1)
		4801
		4802	By virtue of using a binary or 4-heap, the next timer is always found at a
		4803	fixed position in the storage array.
		4804
		4805	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4806
		4807	A change means an I/O watcher gets started or stopped, which requires
		4808	libev to recalculate its status (and possibly tell the kernel, depending
		4809	on backend and whether C<ev_io_set> was used).
		4810
		4811	=item Activating one watcher (putting it into the pending state): O(1)
		4812
		4813	=item Priority handling: O(number_of_priorities)
		4814
		4815	Priorities are implemented by allocating some space for each
		4816	priority. When doing priority-based operations, libev usually has to
		4817	linearly search all the priorities, but starting/stopping and activating
		4818	watchers becomes O(1) with respect to priority handling.
		4819
		4820	=item Sending an ev_async: O(1)
		4821
		4822	=item Processing ev_async_send: O(number_of_async_watchers)
		4823
		4824	=item Processing signals: O(max_signal_number)
		4825
		4826	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4827	calls in the current loop iteration. Checking for async and signal events
		4828	involves iterating over all running async watchers or all signal numbers.
		4829
		4830	=back
		4831
		4832
		4833	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4834
		4835	The major version 4 introduced some minor incompatible changes to the API.
		4836
		4837	At the moment, the C<ev.h> header file tries to implement superficial
		4838	compatibility, so most programs should still compile. Those might be
		4839	removed in later versions of libev, so better update early than late.
		4840
		4841	=over 4
		4842
		4843	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4844
		4845	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4846
		4847	ev_loop_destroy (EV_DEFAULT);
		4848	ev_loop_fork (EV_DEFAULT);
		4849
		4850	=item function/symbol renames
		4851
		4852	A number of functions and symbols have been renamed:
		4853
		4854	ev_loop => ev_run
		4855	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4856	EVLOOP_ONESHOT => EVRUN_ONCE
		4857
		4858	ev_unloop => ev_break
		4859	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4860	EVUNLOOP_ONE => EVBREAK_ONE
		4861	EVUNLOOP_ALL => EVBREAK_ALL
		4862
		4863	EV_TIMEOUT => EV_TIMER
		4864
		4865	ev_loop_count => ev_iteration
		4866	ev_loop_depth => ev_depth
		4867	ev_loop_verify => ev_verify
		4868
		4869	Most functions working on C<struct ev_loop> objects don't have an
		4870	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4871	associated constants have been renamed to not collide with the C<struct
		4872	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4873	as all other watcher types. Note that C<ev_loop_fork> is still called
		4874	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4875	typedef.
		4876
		4877	=item C<EV_COMPAT3> backwards compatibility mechanism
		4878
		4879	The backward compatibility mechanism can be controlled by
		4880	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4881	section.
		4882
		4883	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4884
		4885	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4886	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4887	and work, but the library code will of course be larger.
		4888
		4889	=back
		4890
		4891
		4892	=head1 GLOSSARY
		4893
		4894	=over 4
		4895
		4896	=item active
		4897
		4898	A watcher is active as long as it has been started and not yet stopped.
		4899	See L<WATCHER STATES> for details.
		4900
		4901	=item application
		4902
		4903	In this document, an application is whatever is using libev.
		4904
		4905	=item backend
		4906
		4907	The part of the code dealing with the operating system interfaces.
		4908
		4909	=item callback
		4910
		4911	The address of a function that is called when some event has been
		4912	detected. Callbacks are being passed the event loop, the watcher that
		4913	received the event, and the actual event bitset.
		4914
		4915	=item callback/watcher invocation
		4916
		4917	The act of calling the callback associated with a watcher.
		4918
		4919	=item event
		4920
		4921	A change of state of some external event, such as data now being available
		4922	for reading on a file descriptor, time having passed or simply not having
		4923	any other events happening anymore.
		4924
		4925	In libev, events are represented as single bits (such as C<EV_READ> or
		4926	C<EV_TIMER>).
		4927
		4928	=item event library
		4929
		4930	A software package implementing an event model and loop.
		4931
		4932	=item event loop
		4933
		4934	An entity that handles and processes external events and converts them
		4935	into callback invocations.
		4936
		4937	=item event model
		4938
		4939	The model used to describe how an event loop handles and processes
		4940	watchers and events.
		4941
		4942	=item pending
		4943
		4944	A watcher is pending as soon as the corresponding event has been
		4945	detected. See L<WATCHER STATES> for details.
		4946
		4947	=item real time
		4948
		4949	The physical time that is observed. It is apparently strictly monotonic :)
		4950
		4951	=item wall-clock time
		4952
		4953	The time and date as shown on clocks. Unlike real time, it can actually
		4954	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4955	clock.
		4956
		4957	=item watcher
		4958
		4959	A data structure that describes interest in certain events. Watchers need
		4960	to be started (attached to an event loop) before they can receive events.
		4961
		4962	=back
3029		4963
3030	=head1 AUTHOR	4964	=head1 AUTHOR
3031		4965
3032	Marc Lehmann <libev@schmorp.de>.	4966	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3033		4967

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