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Revision 1.399 by root, Mon Apr 2 23:14:41 2012 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		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);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_run (loop, 0);
		62
		63	// break was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
10		92
11	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	95	these event sources and provide your program with events.
14		96
15	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	104	watcher.
23		105
24	=head1 FEATURES	106	=head2 FEATURES
25		107
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		113	timers (C<ev_timer>), absolute timers with customised rescheduling
		114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	115	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
		119
		120	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	122	for example).
33		123
34	=head1 CONVENTIONS	124	=head2 CONVENTIONS
35		125
36	Libev is very configurable. In this manual the default configuration	126	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	127	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	128	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	129	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	130	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	132	this argument.
43		133
44	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
45		135
46	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
48	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the C<double> type in C, and when you need to do any calculations on	140	too. It usually aliases to the C<double> type in C. When you need to do
51	it, you should treat it as such.	141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
52		165
53		166
54	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
55		168
56	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
…		…
60		173
61	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
62		175
63	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked
		184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
		188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
66		192
67	=item int ev_version_major ()	193	=item int ev_version_major ()
68		194
69	=item int ev_version_minor ()	195	=item int ev_version_minor ()
70		196
71	You can find out the major and minor version numbers of the library	197	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	198	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	199	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	200	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	201	version of the library your program was compiled against.
76		202
		203	These version numbers refer to the ABI version of the library, not the
		204	release version.
		205
77	Usually, it's a good idea to terminate if the major versions mismatch,	206	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	209	not a problem.
81		210
82	Example: make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
84		214
85	assert (("libev version mismatch",	215	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
88		218
89	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
90		220
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	224	a description of the set values.
95		225
96	Example: make sure we have the epoll method, because yeah this is cool and	226	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	227	a must have and can we have a torrent of it please!!!11
98		228
99	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
101		231
102	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
103		233
104	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
105	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
107	most BSDs and will not be autodetected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
108	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
109	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
110		241
111	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
112		243
113	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
114	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
115	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
117	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
118		249
119	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
120		251
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
122		253
123	Sets the allocation function to use (the prototype is similar to the	254	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	256	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	257	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	258	or take some potentially destructive action.
		259
		260	Since some systems (at least OpenBSD and Darwin) fail to implement
		261	correct C<realloc> semantics, libev will use a wrapper around the system
		262	C<realloc> and C<free> functions by default.
128		263
129	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	265	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	266	or even to sleep a while and retry until some memory is available.
132		267
133	Example: replace the libev allocator with one that waits a bit and then	268	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	269	retries (example requires a standards-compliant C<realloc>).
135		270
136	static void *	271	static void *
137	persistent_realloc (void *ptr, long size)	272	persistent_realloc (void *ptr, size_t size)
138	{	273	{
139	for (;;)	274	for (;;)
140	{	275	{
141	void *newptr = realloc (ptr, size);	276	void *newptr = realloc (ptr, size);
142		277
…		…
148	}	283	}
149		284
150	...	285	...
151	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
152		287
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
154		289
155	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	293	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	294	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	295	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	296	(such as abort).
162		297
163	Example: do the same thing as libev does internally:	298	Example: This is basically the same thing that libev does internally, too.
164		299
165	static void	300	static void
166	fatal_error (const char *msg)	301	fatal_error (const char *msg)
167	{	302	{
168	perror (msg);	303	perror (msg);
…		…
170	}	305	}
171		306
172	...	307	...
173	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
174		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
175	=back	323	=back
176		324
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
178		326
179	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
180	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
181	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
182		330
183	If you use threads, a common model is to run the default event loop	331	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	332	supports child process events, and dynamically created event loops which
185	create, you also create another event loop. Libev itself does no locking	333	do not.
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		334
190	=over 4	335	=over 4
191		336
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		338
194	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
195	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
196	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
198		349
199	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
200	function.	351	function (or via the C<EV_DEFAULT> macro).
		352
		353	Note that this function is I<not> thread-safe, so if you want to use it
		354	from multiple threads, you have to employ some kind of mutex (note also
		355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
		357
		358	The default loop is the only loop that can handle C<ev_child> watchers,
		359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		360	a problem for your application you can either create a dynamic loop with
		361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
201		382
202	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		385
205	The following flags are supported:	386	The following flags are supported:
…		…
211	The default flags value. Use this if you have no clue (it's the right	392	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	393	thing, believe me).
213		394
214	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
215		396
216	If this flag bit is ored into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, or to work
221	around bugs.	402	around bugs.
222		403
		404	=item C<EVFLAG_FORKCHECK>
		405
		406	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		407	make libev check for a fork in each iteration by enabling this flag.
		408
		409	This works by calling C<getpid ()> on every iteration of the loop,
		410	and thus this might slow down your event loop if you do a lot of loop
		411	iterations and little real work, but is usually not noticeable (on my
		412	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		413	without a system call and thus I<very> fast, but my GNU/Linux system also has
		414	C<pthread_atfork> which is even faster).
		415
		416	The big advantage of this flag is that you can forget about fork (and
		417	forget about forgetting to tell libev about forking) when you use this
		418	flag.
		419
		420	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		421	environment variable.
		422
		423	=item C<EVFLAG_NOINOTIFY>
		424
		425	When this flag is specified, then libev will not attempt to use the
		426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		427	testing, this flag can be useful to conserve inotify file descriptors, as
		428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		429
		430	=item C<EVFLAG_SIGNALFD>
		431
		432	When this flag is specified, then libev will attempt to use the
		433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		434	delivers signals synchronously, which makes it both faster and might make
		435	it possible to get the queued signal data. It can also simplify signal
		436	handling with threads, as long as you properly block signals in your
		437	threads that are not interested in handling them.
		438
		439	Signalfd will not be used by default as this changes your signal mask, and
		440	there are a lot of shoddy libraries and programs (glib's threadpool for
		441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
		457
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		459
225	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	462	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
		465
		466	To get good performance out of this backend you need a high amount of
		467	parallelism (most of the file descriptors should be busy). If you are
		468	writing a server, you should C<accept ()> in a loop to accept as many
		469	connections as possible during one iteration. You might also want to have
		470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
230		476
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	477	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		478
233	And this is your standard poll(2) backend. It's more complicated than	479	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	480	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	481	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	482	considerably with a lot of inactive fds). It scales similarly to select,
		483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		484	performance tips.
		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		488
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
240	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
241	but it scales phenomenally better. While poll and select usually scale like	495	it scales phenomenally better. While poll and select usually scale like
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	496	O(total_fds) where total_fds is the total number of fds (or the highest
243	either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
244		498
		499	The epoll mechanism deserves honorable mention as the most misdesigned
		500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
		526
245	While stopping and starting an I/O watcher in the same iteration will	527	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	529	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
		532	file descriptors.
250		533
251	Please note that epoll sometimes generates spurious notifications, so you	534	Best performance from this backend is achieved by not unregistering all
252	need to use non-blocking I/O or other means to avoid blocking when no data	535	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
		546	While nominally embeddable in other event loops, this feature is broken in
		547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
254		551
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		553
257	Kqueue deserves special mention, as at the time of this writing, it	554	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	556	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	560	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		562	system like NetBSD.
		563
		564	You still can embed kqueue into a normal poll or select backend and use it
		565	only for sockets (after having made sure that sockets work with kqueue on
		566	the target platform). See C<ev_embed> watchers for more info.
263		567
264	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	570	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	572	two event changes per incident. Support for C<fork ()> is very bad (you
		573	might have to leak fd's on fork, but it's more sane than epoll) and it
		574	drops fds silently in similarly hard-to-detect cases
		575
		576	This backend usually performs well under most conditions.
		577
		578	While nominally embeddable in other event loops, this doesn't work
		579	everywhere, so you might need to test for this. And since it is broken
		580	almost everywhere, you should only use it when you have a lot of sockets
		581	(for which it usually works), by embedding it into another event loop
		582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
269		588
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		590
272	This is not implemented yet (and might never be).	591	This is not implemented yet (and might never be, unless you send me an
		592	implementation). According to reports, C</dev/poll> only supports sockets
		593	and is not embeddable, which would limit the usefulness of this backend
		594	immensely.
273		595
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		597
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
278		600
279	Please note that solaris ports can result in a lot of spurious	601	While this backend scales well, it requires one system call per active
280	notifications, so you need to use non-blocking I/O or other means to avoid	602	file descriptor per loop iteration. For small and medium numbers of file
281	blocking when no data (or space) is available.	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		604	might perform better.
		605
		606	On the positive side, this backend actually performed fully to
		607	specification in all tests and is fully embeddable, which is a rare feat
		608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
282		623
283	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
284		625
285	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		629
		630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		639
289	=back	640	=back
290		641
291	If one or more of these are ored into the flags value, then only these	642	If one or more of the backend flags are or'ed into the flags value,
292	backends will be tried (in the reverse order as given here). If none are	643	then only these backends will be tried (in the reverse order as listed
293	specified, most compiled-in backend will be tried, usually in reverse	644	here). If none are specified, all backends in C<ev_recommended_backends
294	order of their flag values :)	645	()> will be tried.
295		646
296	The most typical usage is like this:
297
298	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300
301	Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:
303
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305
306	Use whatever libev has to offer, but make sure that kqueue is used if
307	available (warning, breaks stuff, best use only with your own private
308	event loop and only if you know the OS supports your types of fds):
309
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311
312	=item struct ev_loop *ev_loop_new (unsigned int flags)
313
314	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).
318
319	Example: try to create a event loop that uses epoll and nothing else.	647	Example: Try to create a event loop that uses epoll and nothing else.
320		648
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	650	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
324		652
		653	Example: Use whatever libev has to offer, but make sure that kqueue is
		654	used if available.
		655
		656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		657
325	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
326		659
327	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
328	etc.). None of the active event watchers will be stopped in the normal	661	etc.). None of the active event watchers will be stopped in the normal
329	sense, so e.g. C<ev_is_active> might still return true. It is your	662	sense, so e.g. C<ev_is_active> might still return true. It is your
330	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
331	calling this function, or cope with the fact afterwards (which is usually	664	calling this function, or cope with the fact afterwards (which is usually
332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
333	for example).	666	for example).
334		667
		668	Note that certain global state, such as signal state (and installed signal
		669	handlers), will not be freed by this function, and related watchers (such
		670	as signal and child watchers) would need to be stopped manually.
		671
		672	This function is normally used on loop objects allocated by
		673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
		678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		679	and C<ev_loop_destroy>.
		680
335	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
336		682
337	Like C<ev_default_destroy>, but destroys an event loop created by an	683	This function sets a flag that causes subsequent C<ev_run> iterations to
338	earlier call to C<ev_loop_new>.
339
340	=item ev_default_fork ()
341
342	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
343	one. Despite the name, you can call it anytime, but it makes most sense	685	name, you can call it anytime, but it makes most sense after forking, in
344	after forking, in either the parent or child process (or both, but that	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
345	again makes little sense).	687	child before resuming or calling C<ev_run>.
346		688
347	You I<must> call this function in the child process after forking if and	689	Again, you I<have> to call it on I<any> loop that you want to re-use after
348	only if you want to use the event library in both processes. If you just	690	a fork, I<even if you do not plan to use the loop in the parent>. This is
349	fork+exec, you don't have to call it.	691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
		693
		694	On the other hand, you only need to call this function in the child
		695	process if and only if you want to use the event loop in the child. If
		696	you just fork+exec or create a new loop in the child, you don't have to
		697	call it at all (in fact, C<epoll> is so badly broken that it makes a
		698	difference, but libev will usually detect this case on its own and do a
		699	costly reset of the backend).
350		700
351	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
352	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
353	quite nicely into a call to C<pthread_atfork>:
354		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
355	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
356		715
357	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	716	=item int ev_is_default_loop (loop)
358	without calling this function, so if you force one of those backends you
359	do not need to care.
360		717
361	=item ev_loop_fork (loop)	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
362		720
363	Like C<ev_default_fork>, but acts on an event loop created by	721	=item unsigned int ev_iteration (loop)
364	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	722
365	after fork, and how you do this is entirely your own problem.	723	Returns the current iteration count for the event loop, which is identical
		724	to the number of times libev did poll for new events. It starts at C<0>
		725	and happily wraps around with enough iterations.
		726
		727	This value can sometimes be useful as a generation counter of sorts (it
		728	"ticks" the number of loop iterations), as it roughly corresponds with
		729	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		730	prepare and check phases.
		731
		732	=item unsigned int ev_depth (loop)
		733
		734	Returns the number of times C<ev_run> was entered minus the number of
		735	times C<ev_run> was exited normally, in other words, the recursion depth.
		736
		737	Outside C<ev_run>, this number is zero. In a callback, this number is
		738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		739	in which case it is higher.
		740
		741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		742	throwing an exception etc.), doesn't count as "exit" - consider this
		743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
366		745
367	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
368		747
369	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
370	use.	749	use.
…		…
373		752
374	Returns the current "event loop time", which is the time the event loop	753	Returns the current "event loop time", which is the time the event loop
375	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
376	change as long as callbacks are being processed, and this is also the base	755	change as long as callbacks are being processed, and this is also the base
377	time used for relative timers. You can treat it as the timestamp of the	756	time used for relative timers. You can treat it as the timestamp of the
378	event occuring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
379		758
		759	=item ev_now_update (loop)
		760
		761	Establishes the current time by querying the kernel, updating the time
		762	returned by C<ev_now ()> in the progress. This is a costly operation and
		763	is usually done automatically within C<ev_run ()>.
		764
		765	This function is rarely useful, but when some event callback runs for a
		766	very long time without entering the event loop, updating libev's idea of
		767	the current time is a good idea.
		768
		769	See also L<The special problem of time updates> in the C<ev_timer> section.
		770
		771	=item ev_suspend (loop)
		772
		773	=item ev_resume (loop)
		774
		775	These two functions suspend and resume an event loop, for use when the
		776	loop is not used for a while and timeouts should not be processed.
		777
		778	A typical use case would be an interactive program such as a game: When
		779	the user presses C<^Z> to suspend the game and resumes it an hour later it
		780	would be best to handle timeouts as if no time had actually passed while
		781	the program was suspended. This can be achieved by calling C<ev_suspend>
		782	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		783	C<ev_resume> directly afterwards to resume timer processing.
		784
		785	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		786	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		787	will be rescheduled (that is, they will lose any events that would have
		788	occurred while suspended).
		789
		790	After calling C<ev_suspend> you B<must not> call I<any> function on the
		791	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		792	without a previous call to C<ev_suspend>.
		793
		794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		795	event loop time (see C<ev_now_update>).
		796
380	=item ev_loop (loop, int flags)	797	=item bool ev_run (loop, int flags)
381		798
382	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
383	after you initialised all your watchers and you want to start handling	800	after you have initialised all your watchers and you want to start
384	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, and then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
385		804
386	If the flags argument is specified as C<0>, it will not return until	805	If the flags argument is specified as C<0>, it will keep handling events
387	either no event watchers are active anymore or C<ev_unloop> was called.	806	until either no event watchers are active anymore or C<ev_break> was
		807	called.
388		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
		812
389	Please note that an explicit C<ev_unloop> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
390	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
391	finished (especially in interactive programs), but having a program that	815	finished (especially in interactive programs), but having a program
392	automatically loops as long as it has to and no longer by virtue of	816	that automatically loops as long as it has to and no longer by virtue
393	relying on its watchers stopping correctly is a thing of beauty.	817	of relying on its watchers stopping correctly, that is truly a thing of
		818	beauty.
394		819
		820	This function is I<mostly> exception-safe - you can break out of a
		821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		822	exception and so on. This does not decrement the C<ev_depth> value, nor
		823	will it clear any outstanding C<EVBREAK_ONE> breaks.
		824
395	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
396	those events and any outstanding ones, but will not block your process in	826	those events and any already outstanding ones, but will not wait and
397	case there are no events and will return after one iteration of the loop.	827	block your process in case there are no events and will return after one
		828	iteration of the loop. This is sometimes useful to poll and handle new
		829	events while doing lengthy calculations, to keep the program responsive.
398		830
399	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	831	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
400	neccessary) and will handle those and any outstanding ones. It will block	832	necessary) and will handle those and any already outstanding ones. It
401	your process until at least one new event arrives, and will return after	833	will block your process until at least one new event arrives (which could
402	one iteration of the loop. This is useful if you are waiting for some	834	be an event internal to libev itself, so there is no guarantee that a
403	external event in conjunction with something not expressible using other	835	user-registered callback will be called), and will return after one
		836	iteration of the loop.
		837
		838	This is useful if you are waiting for some external event in conjunction
		839	with something not expressible using other libev watchers (i.e. "roll your
404	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
405	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
406		842
407	Here are the gory details of what C<ev_loop> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
408		846
409	* If there are no active watchers (reference count is zero), return.	847	- Increment loop depth.
410	- Queue prepare watchers and then call all outstanding watchers.	848	- Reset the ev_break status.
		849	- Before the first iteration, call any pending watchers.
		850	LOOP:
		851	- If EVFLAG_FORKCHECK was used, check for a fork.
		852	- If a fork was detected (by any means), queue and call all fork watchers.
		853	- Queue and call all prepare watchers.
		854	- If ev_break was called, goto FINISH.
411	- If we have been forked, recreate the kernel state.	855	- If we have been forked, detach and recreate the kernel state
		856	as to not disturb the other process.
412	- Update the kernel state with all outstanding changes.	857	- Update the kernel state with all outstanding changes.
413	- Update the "event loop time".	858	- Update the "event loop time" (ev_now ()).
414	- Calculate for how long to block.	859	- Calculate for how long to sleep or block, if at all
		860	(active idle watchers, EVRUN_NOWAIT or not having
		861	any active watchers at all will result in not sleeping).
		862	- Sleep if the I/O and timer collect interval say so.
		863	- Increment loop iteration counter.
415	- Block the process, waiting for any events.	864	- Block the process, waiting for any events.
416	- Queue all outstanding I/O (fd) events.	865	- Queue all outstanding I/O (fd) events.
417	- Update the "event loop time" and do time jump handling.	866	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
418	- Queue all outstanding timers.	867	- Queue all expired timers.
419	- Queue all outstanding periodics.	868	- Queue all expired periodics.
420	- If no events are pending now, queue all idle watchers.	869	- Queue all idle watchers with priority higher than that of pending events.
421	- Queue all check watchers.	870	- Queue all check watchers.
422	- Call all queued watchers in reverse order (i.e. check watchers first).	871	- Call all queued watchers in reverse order (i.e. check watchers first).
423	Signals and child watchers are implemented as I/O watchers, and will	872	Signals and child watchers are implemented as I/O watchers, and will
424	be handled here by queueing them when their watcher gets executed.	873	be handled here by queueing them when their watcher gets executed.
425	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	874	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
426	were used, return, otherwise continue with step *.	875	were used, or there are no active watchers, goto FINISH, otherwise
		876	continue with step LOOP.
		877	FINISH:
		878	- Reset the ev_break status iff it was EVBREAK_ONE.
		879	- Decrement the loop depth.
		880	- Return.
427		881
428	Example: queue some jobs and then loop until no events are outsanding	882	Example: Queue some jobs and then loop until no events are outstanding
429	anymore.	883	anymore.
430		884
431	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
432	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
433	ev_loop (my_loop, 0);	887	ev_run (my_loop, 0);
434	... jobs done. yeah!	888	... jobs done or somebody called break. yeah!
435		889
436	=item ev_unloop (loop, how)	890	=item ev_break (loop, how)
437		891
438	Can be used to make a call to C<ev_loop> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
439	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
440	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	894	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
441	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	895	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		896
		897	This "break state" will be cleared on the next call to C<ev_run>.
		898
		899	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		900	which case it will have no effect.
442		901
443	=item ev_ref (loop)	902	=item ev_ref (loop)
444		903
445	=item ev_unref (loop)	904	=item ev_unref (loop)
446		905
447	Ref/unref can be used to add or remove a reference count on the event	906	Ref/unref can be used to add or remove a reference count on the event
448	loop: Every watcher keeps one reference, and as long as the reference	907	loop: Every watcher keeps one reference, and as long as the reference
449	count is nonzero, C<ev_loop> will not return on its own. If you have	908	count is nonzero, C<ev_run> will not return on its own.
450	a watcher you never unregister that should not keep C<ev_loop> from	909
451	returning, ev_unref() after starting, and ev_ref() before stopping it. For	910	This is useful when you have a watcher that you never intend to
		911	unregister, but that nevertheless should not keep C<ev_run> from
		912	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		913	before stopping it.
		914
452	example, libev itself uses this for its internal signal pipe: It is not	915	As an example, libev itself uses this for its internal signal pipe: It
453	visible to the libev user and should not keep C<ev_loop> from exiting if	916	is not visible to the libev user and should not keep C<ev_run> from
454	no event watchers registered by it are active. It is also an excellent	917	exiting if no event watchers registered by it are active. It is also an
455	way to do this for generic recurring timers or from within third-party	918	excellent way to do this for generic recurring timers or from within
456	libraries. Just remember to I<unref after start> and I<ref before stop>.	919	third-party libraries. Just remember to I<unref after start> and I<ref
		920	before stop> (but only if the watcher wasn't active before, or was active
		921	before, respectively. Note also that libev might stop watchers itself
		922	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		923	in the callback).
457		924
458	Example: create a signal watcher, but keep it from keeping C<ev_loop>	925	Example: Create a signal watcher, but keep it from keeping C<ev_run>
459	running when nothing else is active.	926	running when nothing else is active.
460		927
461	struct dv_signal exitsig;	928	ev_signal exitsig;
462	ev_signal_init (&exitsig, sig_cb, SIGINT);	929	ev_signal_init (&exitsig, sig_cb, SIGINT);
463	ev_signal_start (myloop, &exitsig);	930	ev_signal_start (loop, &exitsig);
464	evf_unref (myloop);	931	ev_unref (loop);
465		932
466	Example: for some weird reason, unregister the above signal handler again.	933	Example: For some weird reason, unregister the above signal handler again.
467		934
468	ev_ref (myloop);	935	ev_ref (loop);
469	ev_signal_stop (myloop, &exitsig);	936	ev_signal_stop (loop, &exitsig);
		937
		938	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		939
		940	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		941
		942	These advanced functions influence the time that libev will spend waiting
		943	for events. Both time intervals are by default C<0>, meaning that libev
		944	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		945	latency.
		946
		947	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		948	allows libev to delay invocation of I/O and timer/periodic callbacks
		949	to increase efficiency of loop iterations (or to increase power-saving
		950	opportunities).
		951
		952	The idea is that sometimes your program runs just fast enough to handle
		953	one (or very few) event(s) per loop iteration. While this makes the
		954	program responsive, it also wastes a lot of CPU time to poll for new
		955	events, especially with backends like C<select ()> which have a high
		956	overhead for the actual polling but can deliver many events at once.
		957
		958	By setting a higher I<io collect interval> you allow libev to spend more
		959	time collecting I/O events, so you can handle more events per iteration,
		960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		961	C<ev_timer>) will not be affected. Setting this to a non-null value will
		962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		963	sleep time ensures that libev will not poll for I/O events more often then
		964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
		966
		967	Likewise, by setting a higher I<timeout collect interval> you allow libev
		968	to spend more time collecting timeouts, at the expense of increased
		969	latency/jitter/inexactness (the watcher callback will be called
		970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		971	value will not introduce any overhead in libev.
		972
		973	Many (busy) programs can usually benefit by setting the I/O collect
		974	interval to a value near C<0.1> or so, which is often enough for
		975	interactive servers (of course not for games), likewise for timeouts. It
		976	usually doesn't make much sense to set it to a lower value than C<0.01>,
		977	as this approaches the timing granularity of most systems. Note that if
		978	you do transactions with the outside world and you can't increase the
		979	parallelity, then this setting will limit your transaction rate (if you
		980	need to poll once per transaction and the I/O collect interval is 0.01,
		981	then you can't do more than 100 transactions per second).
		982
		983	Setting the I<timeout collect interval> can improve the opportunity for
		984	saving power, as the program will "bundle" timer callback invocations that
		985	are "near" in time together, by delaying some, thus reducing the number of
		986	times the process sleeps and wakes up again. Another useful technique to
		987	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		988	they fire on, say, one-second boundaries only.
		989
		990	Example: we only need 0.1s timeout granularity, and we wish not to poll
		991	more often than 100 times per second:
		992
		993	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		994	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		995
		996	=item ev_invoke_pending (loop)
		997
		998	This call will simply invoke all pending watchers while resetting their
		999	pending state. Normally, C<ev_run> does this automatically when required,
		1000	but when overriding the invoke callback this call comes handy. This
		1001	function can be invoked from a watcher - this can be useful for example
		1002	when you want to do some lengthy calculation and want to pass further
		1003	event handling to another thread (you still have to make sure only one
		1004	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1005
		1006	=item int ev_pending_count (loop)
		1007
		1008	Returns the number of pending watchers - zero indicates that no watchers
		1009	are pending.
		1010
		1011	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1012
		1013	This overrides the invoke pending functionality of the loop: Instead of
		1014	invoking all pending watchers when there are any, C<ev_run> will call
		1015	this callback instead. This is useful, for example, when you want to
		1016	invoke the actual watchers inside another context (another thread etc.).
		1017
		1018	If you want to reset the callback, use C<ev_invoke_pending> as new
		1019	callback.
		1020
		1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1022
		1023	Sometimes you want to share the same loop between multiple threads. This
		1024	can be done relatively simply by putting mutex_lock/unlock calls around
		1025	each call to a libev function.
		1026
		1027	However, C<ev_run> can run an indefinite time, so it is not feasible
		1028	to wait for it to return. One way around this is to wake up the event
		1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1030	I<release> and I<acquire> callbacks on the loop.
		1031
		1032	When set, then C<release> will be called just before the thread is
		1033	suspended waiting for new events, and C<acquire> is called just
		1034	afterwards.
		1035
		1036	Ideally, C<release> will just call your mutex_unlock function, and
		1037	C<acquire> will just call the mutex_lock function again.
		1038
		1039	While event loop modifications are allowed between invocations of
		1040	C<release> and C<acquire> (that's their only purpose after all), no
		1041	modifications done will affect the event loop, i.e. adding watchers will
		1042	have no effect on the set of file descriptors being watched, or the time
		1043	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1044	to take note of any changes you made.
		1045
		1046	In theory, threads executing C<ev_run> will be async-cancel safe between
		1047	invocations of C<release> and C<acquire>.
		1048
		1049	See also the locking example in the C<THREADS> section later in this
		1050	document.
		1051
		1052	=item ev_set_userdata (loop, void *data)
		1053
		1054	=item void *ev_userdata (loop)
		1055
		1056	Set and retrieve a single C<void *> associated with a loop. When
		1057	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1058	C<0>.
		1059
		1060	These two functions can be used to associate arbitrary data with a loop,
		1061	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1062	C<acquire> callbacks described above, but of course can be (ab-)used for
		1063	any other purpose as well.
		1064
		1065	=item ev_verify (loop)
		1066
		1067	This function only does something when C<EV_VERIFY> support has been
		1068	compiled in, which is the default for non-minimal builds. It tries to go
		1069	through all internal structures and checks them for validity. If anything
		1070	is found to be inconsistent, it will print an error message to standard
		1071	error and call C<abort ()>.
		1072
		1073	This can be used to catch bugs inside libev itself: under normal
		1074	circumstances, this function will never abort as of course libev keeps its
		1075	data structures consistent.
470		1076
471	=back	1077	=back
472		1078
473		1079
474	=head1 ANATOMY OF A WATCHER	1080	=head1 ANATOMY OF A WATCHER
475		1081
		1082	In the following description, uppercase C<TYPE> in names stands for the
		1083	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1084	watchers and C<ev_io_start> for I/O watchers.
		1085
476	A watcher is a structure that you create and register to record your	1086	A watcher is an opaque structure that you allocate and register to record
477	interest in some event. For instance, if you want to wait for STDIN to	1087	your interest in some event. To make a concrete example, imagine you want
478	become readable, you would create an C<ev_io> watcher for that:	1088	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1089	for that:
479		1090
480	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1091	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
481	{	1092	{
482	ev_io_stop (w);	1093	ev_io_stop (w);
483	ev_unloop (loop, EVUNLOOP_ALL);	1094	ev_break (loop, EVBREAK_ALL);
484	}	1095	}
485		1096
486	struct ev_loop *loop = ev_default_loop (0);	1097	struct ev_loop *loop = ev_default_loop (0);
		1098
487	struct ev_io stdin_watcher;	1099	ev_io stdin_watcher;
		1100
488	ev_init (&stdin_watcher, my_cb);	1101	ev_init (&stdin_watcher, my_cb);
489	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1102	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
490	ev_io_start (loop, &stdin_watcher);	1103	ev_io_start (loop, &stdin_watcher);
		1104
491	ev_loop (loop, 0);	1105	ev_run (loop, 0);
492		1106
493	As you can see, you are responsible for allocating the memory for your	1107	As you can see, you are responsible for allocating the memory for your
494	watcher structures (and it is usually a bad idea to do this on the stack,	1108	watcher structures (and it is I<usually> a bad idea to do this on the
495	although this can sometimes be quite valid).	1109	stack).
496		1110
		1111	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1112	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1113
497	Each watcher structure must be initialised by a call to C<ev_init	1114	Each watcher structure must be initialised by a call to C<ev_init (watcher
498	(watcher *, callback)>, which expects a callback to be provided. This	1115	*, callback)>, which expects a callback to be provided. This callback is
499	callback gets invoked each time the event occurs (or, in the case of io	1116	invoked each time the event occurs (or, in the case of I/O watchers, each
500	watchers, each time the event loop detects that the file descriptor given	1117	time the event loop detects that the file descriptor given is readable
501	is readable and/or writable).	1118	and/or writable).
502		1119
503	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1120	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
504	with arguments specific to this watcher type. There is also a macro	1121	macro to configure it, with arguments specific to the watcher type. There
505	to combine initialisation and setting in one call: C<< ev_<type>_init	1122	is also a macro to combine initialisation and setting in one call: C<<
506	(watcher *, callback, ...) >>.	1123	ev_TYPE_init (watcher *, callback, ...) >>.
507		1124
508	To make the watcher actually watch out for events, you have to start it	1125	To make the watcher actually watch out for events, you have to start it
509	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1126	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
510	*) >>), and you can stop watching for events at any time by calling the	1127	*) >>), and you can stop watching for events at any time by calling the
511	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1128	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
512		1129
513	As long as your watcher is active (has been started but not stopped) you	1130	As long as your watcher is active (has been started but not stopped) you
514	must not touch the values stored in it. Most specifically you must never	1131	must not touch the values stored in it. Most specifically you must never
515	reinitialise it or call its C<set> macro.	1132	reinitialise it or call its C<ev_TYPE_set> macro.
516		1133
517	Each and every callback receives the event loop pointer as first, the	1134	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	1135	registered watcher structure as second, and a bitset of received events as
519	third argument.	1136	third argument.
520		1137
…		…
529	=item C<EV_WRITE>	1146	=item C<EV_WRITE>
530		1147
531	The file descriptor in the C<ev_io> watcher has become readable and/or	1148	The file descriptor in the C<ev_io> watcher has become readable and/or
532	writable.	1149	writable.
533		1150
534	=item C<EV_TIMEOUT>	1151	=item C<EV_TIMER>
535		1152
536	The C<ev_timer> watcher has timed out.	1153	The C<ev_timer> watcher has timed out.
537		1154
538	=item C<EV_PERIODIC>	1155	=item C<EV_PERIODIC>
539		1156
…		…
545		1162
546	=item C<EV_CHILD>	1163	=item C<EV_CHILD>
547		1164
548	The pid specified in the C<ev_child> watcher has received a status change.	1165	The pid specified in the C<ev_child> watcher has received a status change.
549		1166
		1167	=item C<EV_STAT>
		1168
		1169	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1170
550	=item C<EV_IDLE>	1171	=item C<EV_IDLE>
551		1172
552	The C<ev_idle> watcher has determined that you have nothing better to do.	1173	The C<ev_idle> watcher has determined that you have nothing better to do.
553		1174
554	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
555		1176
556	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
557		1178
558	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
559	to gather new events, and all C<ev_check> watchers are invoked just after	1180	to gather new events, and all C<ev_check> watchers are invoked just after
560	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1181	C<ev_run> has gathered them, but before it invokes any callbacks for any
561	received events. Callbacks of both watcher types can start and stop as	1182	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	1183	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1184	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	1185	C<ev_run> from blocking).
		1186
		1187	=item C<EV_EMBED>
		1188
		1189	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1190
		1191	=item C<EV_FORK>
		1192
		1193	The event loop has been resumed in the child process after fork (see
		1194	C<ev_fork>).
		1195
		1196	=item C<EV_CLEANUP>
		1197
		1198	The event loop is about to be destroyed (see C<ev_cleanup>).
		1199
		1200	=item C<EV_ASYNC>
		1201
		1202	The given async watcher has been asynchronously notified (see C<ev_async>).
		1203
		1204	=item C<EV_CUSTOM>
		1205
		1206	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1207	by libev users to signal watchers (e.g. via C<ev_feed_event>).
565		1208
566	=item C<EV_ERROR>	1209	=item C<EV_ERROR>
567		1210
568	An unspecified error has occured, the watcher has been stopped. This might	1211	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	1212	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	1213	ran out of memory, a file descriptor was found to be closed or any other
		1214	problem. Libev considers these application bugs.
		1215
571	problem. You best act on it by reporting the problem and somehow coping	1216	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	1217	watcher being stopped. Note that well-written programs should not receive
		1218	an error ever, so when your watcher receives it, this usually indicates a
		1219	bug in your program.
573		1220
574	Libev will usually signal a few "dummy" events together with an error,	1221	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	1222	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	1223	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	1224	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	1225	programs, though, as the fd could already be closed and reused for another
		1226	thing, so beware.
579		1227
580	=back	1228	=back
581		1229
582	=head2 GENERIC WATCHER FUNCTIONS	1230	=head2 GENERIC WATCHER FUNCTIONS
583
584	In the following description, C<TYPE> stands for the watcher type,
585	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
586		1231
587	=over 4	1232	=over 4
588		1233
589	=item C<ev_init> (ev_TYPE *watcher, callback)	1234	=item C<ev_init> (ev_TYPE *watcher, callback)
590		1235
…		…
596	which rolls both calls into one.	1241	which rolls both calls into one.
597		1242
598	You can reinitialise a watcher at any time as long as it has been stopped	1243	You can reinitialise a watcher at any time as long as it has been stopped
599	(or never started) and there are no pending events outstanding.	1244	(or never started) and there are no pending events outstanding.
600		1245
601	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1246	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
602	int revents)>.	1247	int revents)>.
603		1248
		1249	Example: Initialise an C<ev_io> watcher in two steps.
		1250
		1251	ev_io w;
		1252	ev_init (&w, my_cb);
		1253	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1254
604	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1255	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
605		1256
606	This macro initialises the type-specific parts of a watcher. You need to	1257	This macro initialises the type-specific parts of a watcher. You need to
607	call C<ev_init> at least once before you call this macro, but you can	1258	call C<ev_init> at least once before you call this macro, but you can
608	call C<ev_TYPE_set> any number of times. You must not, however, call this	1259	call C<ev_TYPE_set> any number of times. You must not, however, call this
609	macro on a watcher that is active (it can be pending, however, which is a	1260	macro on a watcher that is active (it can be pending, however, which is a
610	difference to the C<ev_init> macro).	1261	difference to the C<ev_init> macro).
611		1262
612	Although some watcher types do not have type-specific arguments	1263	Although some watcher types do not have type-specific arguments
613	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1264	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
614		1265
		1266	See C<ev_init>, above, for an example.
		1267
615	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1268	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
616		1269
617	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1270	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
618	calls into a single call. This is the most convinient method to initialise	1271	calls into a single call. This is the most convenient method to initialise
619	a watcher. The same limitations apply, of course.	1272	a watcher. The same limitations apply, of course.
620		1273
		1274	Example: Initialise and set an C<ev_io> watcher in one step.
		1275
		1276	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1277
621	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1278	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
622		1279
623	Starts (activates) the given watcher. Only active watchers will receive	1280	Starts (activates) the given watcher. Only active watchers will receive
624	events. If the watcher is already active nothing will happen.	1281	events. If the watcher is already active nothing will happen.
625		1282
		1283	Example: Start the C<ev_io> watcher that is being abused as example in this
		1284	whole section.
		1285
		1286	ev_io_start (EV_DEFAULT_UC, &w);
		1287
626	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1288	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
627		1289
628	Stops the given watcher again (if active) and clears the pending	1290	Stops the given watcher if active, and clears the pending status (whether
		1291	the watcher was active or not).
		1292
629	status. It is possible that stopped watchers are pending (for example,	1293	It is possible that stopped watchers are pending - for example,
630	non-repeating timers are being stopped when they become pending), but	1294	non-repeating timers are being stopped when they become pending - but
631	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1295	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
632	you want to free or reuse the memory used by the watcher it is therefore a	1296	pending. If you want to free or reuse the memory used by the watcher it is
633	good idea to always call its C<ev_TYPE_stop> function.	1297	therefore a good idea to always call its C<ev_TYPE_stop> function.
634		1298
635	=item bool ev_is_active (ev_TYPE *watcher)	1299	=item bool ev_is_active (ev_TYPE *watcher)
636		1300
637	Returns a true value iff the watcher is active (i.e. it has been started	1301	Returns a true value iff the watcher is active (i.e. it has been started
638	and not yet been stopped). As long as a watcher is active you must not modify	1302	and not yet been stopped). As long as a watcher is active you must not modify
…		…
641	=item bool ev_is_pending (ev_TYPE *watcher)	1305	=item bool ev_is_pending (ev_TYPE *watcher)
642		1306
643	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1307	Returns a true value iff the watcher is pending, (i.e. it has outstanding
644	events but its callback has not yet been invoked). As long as a watcher	1308	events but its callback has not yet been invoked). As long as a watcher
645	is pending (but not active) you must not call an init function on it (but	1309	is pending (but not active) you must not call an init function on it (but
646	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1310	C<ev_TYPE_set> is safe), you must not change its priority, and you must
647	libev (e.g. you cnanot C<free ()> it).	1311	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1312	it).
648		1313
649	=item callback = ev_cb (ev_TYPE *watcher)	1314	=item callback ev_cb (ev_TYPE *watcher)
650		1315
651	Returns the callback currently set on the watcher.	1316	Returns the callback currently set on the watcher.
652		1317
653	=item ev_cb_set (ev_TYPE *watcher, callback)	1318	=item ev_cb_set (ev_TYPE *watcher, callback)
654		1319
655	Change the callback. You can change the callback at virtually any time	1320	Change the callback. You can change the callback at virtually any time
656	(modulo threads).	1321	(modulo threads).
657		1322
		1323	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1324
		1325	=item int ev_priority (ev_TYPE *watcher)
		1326
		1327	Set and query the priority of the watcher. The priority is a small
		1328	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1329	(default: C<-2>). Pending watchers with higher priority will be invoked
		1330	before watchers with lower priority, but priority will not keep watchers
		1331	from being executed (except for C<ev_idle> watchers).
		1332
		1333	If you need to suppress invocation when higher priority events are pending
		1334	you need to look at C<ev_idle> watchers, which provide this functionality.
		1335
		1336	You I<must not> change the priority of a watcher as long as it is active or
		1337	pending.
		1338
		1339	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1340	fine, as long as you do not mind that the priority value you query might
		1341	or might not have been clamped to the valid range.
		1342
		1343	The default priority used by watchers when no priority has been set is
		1344	always C<0>, which is supposed to not be too high and not be too low :).
		1345
		1346	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1347	priorities.
		1348
		1349	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1350
		1351	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1352	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1353	can deal with that fact, as both are simply passed through to the
		1354	callback.
		1355
		1356	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1357
		1358	If the watcher is pending, this function clears its pending status and
		1359	returns its C<revents> bitset (as if its callback was invoked). If the
		1360	watcher isn't pending it does nothing and returns C<0>.
		1361
		1362	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1363	callback to be invoked, which can be accomplished with this function.
		1364
		1365	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1366
		1367	Feeds the given event set into the event loop, as if the specified event
		1368	had happened for the specified watcher (which must be a pointer to an
		1369	initialised but not necessarily started event watcher). Obviously you must
		1370	not free the watcher as long as it has pending events.
		1371
		1372	Stopping the watcher, letting libev invoke it, or calling
		1373	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1374	not started in the first place.
		1375
		1376	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1377	functions that do not need a watcher.
		1378
658	=back	1379	=back
659		1380
		1381	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1382	OWN COMPOSITE WATCHERS> idioms.
660		1383
661	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1384	=head2 WATCHER STATES
662		1385
663	Each watcher has, by default, a member C<void *data> that you can change	1386	There are various watcher states mentioned throughout this manual -
664	and read at any time, libev will completely ignore it. This can be used	1387	active, pending and so on. In this section these states and the rules to
665	to associate arbitrary data with your watcher. If you need more data and	1388	transition between them will be described in more detail - and while these
666	don't want to allocate memory and store a pointer to it in that data	1389	rules might look complicated, they usually do "the right thing".
667	member, you can also "subclass" the watcher type and provide your own
668	data:
669		1390
670	struct my_io	1391	=over 4
		1392
		1393	=item initialiased
		1394
		1395	Before a watcher can be registered with the event loop it has to be
		1396	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1397	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1398
		1399	In this state it is simply some block of memory that is suitable for
		1400	use in an event loop. It can be moved around, freed, reused etc. at
		1401	will - as long as you either keep the memory contents intact, or call
		1402	C<ev_TYPE_init> again.
		1403
		1404	=item started/running/active
		1405
		1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1407	property of the event loop, and is actively waiting for events. While in
		1408	this state it cannot be accessed (except in a few documented ways), moved,
		1409	freed or anything else - the only legal thing is to keep a pointer to it,
		1410	and call libev functions on it that are documented to work on active watchers.
		1411
		1412	=item pending
		1413
		1414	If a watcher is active and libev determines that an event it is interested
		1415	in has occurred (such as a timer expiring), it will become pending. It will
		1416	stay in this pending state until either it is stopped or its callback is
		1417	about to be invoked, so it is not normally pending inside the watcher
		1418	callback.
		1419
		1420	The watcher might or might not be active while it is pending (for example,
		1421	an expired non-repeating timer can be pending but no longer active). If it
		1422	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1423	but it is still property of the event loop at this time, so cannot be
		1424	moved, freed or reused. And if it is active the rules described in the
		1425	previous item still apply.
		1426
		1427	It is also possible to feed an event on a watcher that is not active (e.g.
		1428	via C<ev_feed_event>), in which case it becomes pending without being
		1429	active.
		1430
		1431	=item stopped
		1432
		1433	A watcher can be stopped implicitly by libev (in which case it might still
		1434	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1435	latter will clear any pending state the watcher might be in, regardless
		1436	of whether it was active or not, so stopping a watcher explicitly before
		1437	freeing it is often a good idea.
		1438
		1439	While stopped (and not pending) the watcher is essentially in the
		1440	initialised state, that is, it can be reused, moved, modified in any way
		1441	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1442	it again).
		1443
		1444	=back
		1445
		1446	=head2 WATCHER PRIORITY MODELS
		1447
		1448	Many event loops support I<watcher priorities>, which are usually small
		1449	integers that influence the ordering of event callback invocation
		1450	between watchers in some way, all else being equal.
		1451
		1452	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1453	description for the more technical details such as the actual priority
		1454	range.
		1455
		1456	There are two common ways how these these priorities are being interpreted
		1457	by event loops:
		1458
		1459	In the more common lock-out model, higher priorities "lock out" invocation
		1460	of lower priority watchers, which means as long as higher priority
		1461	watchers receive events, lower priority watchers are not being invoked.
		1462
		1463	The less common only-for-ordering model uses priorities solely to order
		1464	callback invocation within a single event loop iteration: Higher priority
		1465	watchers are invoked before lower priority ones, but they all get invoked
		1466	before polling for new events.
		1467
		1468	Libev uses the second (only-for-ordering) model for all its watchers
		1469	except for idle watchers (which use the lock-out model).
		1470
		1471	The rationale behind this is that implementing the lock-out model for
		1472	watchers is not well supported by most kernel interfaces, and most event
		1473	libraries will just poll for the same events again and again as long as
		1474	their callbacks have not been executed, which is very inefficient in the
		1475	common case of one high-priority watcher locking out a mass of lower
		1476	priority ones.
		1477
		1478	Static (ordering) priorities are most useful when you have two or more
		1479	watchers handling the same resource: a typical usage example is having an
		1480	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1481	timeouts. Under load, data might be received while the program handles
		1482	other jobs, but since timers normally get invoked first, the timeout
		1483	handler will be executed before checking for data. In that case, giving
		1484	the timer a lower priority than the I/O watcher ensures that I/O will be
		1485	handled first even under adverse conditions (which is usually, but not
		1486	always, what you want).
		1487
		1488	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1489	will only be executed when no same or higher priority watchers have
		1490	received events, they can be used to implement the "lock-out" model when
		1491	required.
		1492
		1493	For example, to emulate how many other event libraries handle priorities,
		1494	you can associate an C<ev_idle> watcher to each such watcher, and in
		1495	the normal watcher callback, you just start the idle watcher. The real
		1496	processing is done in the idle watcher callback. This causes libev to
		1497	continuously poll and process kernel event data for the watcher, but when
		1498	the lock-out case is known to be rare (which in turn is rare :), this is
		1499	workable.
		1500
		1501	Usually, however, the lock-out model implemented that way will perform
		1502	miserably under the type of load it was designed to handle. In that case,
		1503	it might be preferable to stop the real watcher before starting the
		1504	idle watcher, so the kernel will not have to process the event in case
		1505	the actual processing will be delayed for considerable time.
		1506
		1507	Here is an example of an I/O watcher that should run at a strictly lower
		1508	priority than the default, and which should only process data when no
		1509	other events are pending:
		1510
		1511	ev_idle idle; // actual processing watcher
		1512	ev_io io; // actual event watcher
		1513
		1514	static void
		1515	io_cb (EV_P_ ev_io *w, int revents)
671	{	1516	{
672	struct ev_io io;	1517	// stop the I/O watcher, we received the event, but
673	int otherfd;	1518	// are not yet ready to handle it.
674	void *somedata;	1519	ev_io_stop (EV_A_ w);
675	struct whatever *mostinteresting;	1520
		1521	// start the idle watcher to handle the actual event.
		1522	// it will not be executed as long as other watchers
		1523	// with the default priority are receiving events.
		1524	ev_idle_start (EV_A_ &idle);
676	}	1525	}
677		1526
678	And since your callback will be called with a pointer to the watcher, you	1527	static void
679	can cast it back to your own type:	1528	idle_cb (EV_P_ ev_idle *w, int revents)
680
681	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
682	{	1529	{
683	struct my_io *w = (struct my_io *)w_;	1530	// actual processing
684	...	1531	read (STDIN_FILENO, ...);
		1532
		1533	// have to start the I/O watcher again, as
		1534	// we have handled the event
		1535	ev_io_start (EV_P_ &io);
685	}	1536	}
686		1537
687	More interesting and less C-conformant ways of catsing your callback type	1538	// initialisation
688	have been omitted....	1539	ev_idle_init (&idle, idle_cb);
		1540	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1541	ev_io_start (EV_DEFAULT_ &io);
		1542
		1543	In the "real" world, it might also be beneficial to start a timer, so that
		1544	low-priority connections can not be locked out forever under load. This
		1545	enables your program to keep a lower latency for important connections
		1546	during short periods of high load, while not completely locking out less
		1547	important ones.
689		1548
690		1549
691	=head1 WATCHER TYPES	1550	=head1 WATCHER TYPES
692		1551
693	This section describes each watcher in detail, but will not repeat	1552	This section describes each watcher in detail, but will not repeat
694	information given in the last section.	1553	information given in the last section. Any initialisation/set macros,
		1554	functions and members specific to the watcher type are explained.
		1555
		1556	Members are additionally marked with either I<[read-only]>, meaning that,
		1557	while the watcher is active, you can look at the member and expect some
		1558	sensible content, but you must not modify it (you can modify it while the
		1559	watcher is stopped to your hearts content), or I<[read-write]>, which
		1560	means you can expect it to have some sensible content while the watcher
		1561	is active, but you can also modify it. Modifying it may not do something
		1562	sensible or take immediate effect (or do anything at all), but libev will
		1563	not crash or malfunction in any way.
695		1564
696		1565
697	=head2 C<ev_io> - is this file descriptor readable or writable?	1566	=head2 C<ev_io> - is this file descriptor readable or writable?
698		1567
699	I/O watchers check whether a file descriptor is readable or writable	1568	I/O watchers check whether a file descriptor is readable or writable
…		…
707	In general you can register as many read and/or write event watchers per	1576	In general you can register as many read and/or write event watchers per
708	fd as you want (as long as you don't confuse yourself). Setting all file	1577	fd as you want (as long as you don't confuse yourself). Setting all file
709	descriptors to non-blocking mode is also usually a good idea (but not	1578	descriptors to non-blocking mode is also usually a good idea (but not
710	required if you know what you are doing).	1579	required if you know what you are doing).
711		1580
712	You have to be careful with dup'ed file descriptors, though. Some backends
713	(the linux epoll backend is a notable example) cannot handle dup'ed file
714	descriptors correctly if you register interest in two or more fds pointing
715	to the same underlying file/socket/etc. description (that is, they share
716	the same underlying "file open").
717
718	If you must do this, then force the use of a known-to-be-good backend
719	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
720	C<EVBACKEND_POLL>).
721
722	Another thing you have to watch out for is that it is quite easy to	1581	Another thing you have to watch out for is that it is quite easy to
723	receive "spurious" readyness notifications, that is your callback might	1582	receive "spurious" readiness notifications, that is, your callback might
724	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1583	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
725	because there is no data. Not only are some backends known to create a	1584	because there is no data. It is very easy to get into this situation even
726	lot of those (for example solaris ports), it is very easy to get into	1585	with a relatively standard program structure. Thus it is best to always
727	this situation even with a relatively standard program structure. Thus	1586	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
728	it is best to always use non-blocking I/O: An extra C<read>(2) returning
729	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1587	preferable to a program hanging until some data arrives.
730		1588
731	If you cannot run the fd in non-blocking mode (for example you should not	1589	If you cannot run the fd in non-blocking mode (for example you should
732	play around with an Xlib connection), then you have to seperately re-test	1590	not play around with an Xlib connection), then you have to separately
733	wether a file descriptor is really ready with a known-to-be good interface	1591	re-test whether a file descriptor is really ready with a known-to-be good
734	such as poll (fortunately in our Xlib example, Xlib already does this on	1592	interface such as poll (fortunately in the case of Xlib, it already does
735	its own, so its quite safe to use).	1593	this on its own, so its quite safe to use). Some people additionally
		1594	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1595	indefinitely.
		1596
		1597	But really, best use non-blocking mode.
		1598
		1599	=head3 The special problem of disappearing file descriptors
		1600
		1601	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1602	descriptor (either due to calling C<close> explicitly or any other means,
		1603	such as C<dup2>). The reason is that you register interest in some file
		1604	descriptor, but when it goes away, the operating system will silently drop
		1605	this interest. If another file descriptor with the same number then is
		1606	registered with libev, there is no efficient way to see that this is, in
		1607	fact, a different file descriptor.
		1608
		1609	To avoid having to explicitly tell libev about such cases, libev follows
		1610	the following policy: Each time C<ev_io_set> is being called, libev
		1611	will assume that this is potentially a new file descriptor, otherwise
		1612	it is assumed that the file descriptor stays the same. That means that
		1613	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1614	descriptor even if the file descriptor number itself did not change.
		1615
		1616	This is how one would do it normally anyway, the important point is that
		1617	the libev application should not optimise around libev but should leave
		1618	optimisations to libev.
		1619
		1620	=head3 The special problem of dup'ed file descriptors
		1621
		1622	Some backends (e.g. epoll), cannot register events for file descriptors,
		1623	but only events for the underlying file descriptions. That means when you
		1624	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1625	events for them, only one file descriptor might actually receive events.
		1626
		1627	There is no workaround possible except not registering events
		1628	for potentially C<dup ()>'ed file descriptors, or to resort to
		1629	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1630
		1631	=head3 The special problem of files
		1632
		1633	Many people try to use C<select> (or libev) on file descriptors
		1634	representing files, and expect it to become ready when their program
		1635	doesn't block on disk accesses (which can take a long time on their own).
		1636
		1637	However, this cannot ever work in the "expected" way - you get a readiness
		1638	notification as soon as the kernel knows whether and how much data is
		1639	there, and in the case of open files, that's always the case, so you
		1640	always get a readiness notification instantly, and your read (or possibly
		1641	write) will still block on the disk I/O.
		1642
		1643	Another way to view it is that in the case of sockets, pipes, character
		1644	devices and so on, there is another party (the sender) that delivers data
		1645	on its own, but in the case of files, there is no such thing: the disk
		1646	will not send data on its own, simply because it doesn't know what you
		1647	wish to read - you would first have to request some data.
		1648
		1649	Since files are typically not-so-well supported by advanced notification
		1650	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1651	to files, even though you should not use it. The reason for this is
		1652	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1653	usually a tty, often a pipe, but also sometimes files or special devices
		1654	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1655	F</dev/urandom>), and even though the file might better be served with
		1656	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1657	it "just works" instead of freezing.
		1658
		1659	So avoid file descriptors pointing to files when you know it (e.g. use
		1660	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1661	when you rarely read from a file instead of from a socket, and want to
		1662	reuse the same code path.
		1663
		1664	=head3 The special problem of fork
		1665
		1666	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1667	useless behaviour. Libev fully supports fork, but needs to be told about
		1668	it in the child if you want to continue to use it in the child.
		1669
		1670	To support fork in your child processes, you have to call C<ev_loop_fork
		1671	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1672	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1673
		1674	=head3 The special problem of SIGPIPE
		1675
		1676	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1677	when writing to a pipe whose other end has been closed, your program gets
		1678	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1679	this is sensible behaviour, for daemons, this is usually undesirable.
		1680
		1681	So when you encounter spurious, unexplained daemon exits, make sure you
		1682	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1683	somewhere, as that would have given you a big clue).
		1684
		1685	=head3 The special problem of accept()ing when you can't
		1686
		1687	Many implementations of the POSIX C<accept> function (for example,
		1688	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1689	connection from the pending queue in all error cases.
		1690
		1691	For example, larger servers often run out of file descriptors (because
		1692	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1693	rejecting the connection, leading to libev signalling readiness on
		1694	the next iteration again (the connection still exists after all), and
		1695	typically causing the program to loop at 100% CPU usage.
		1696
		1697	Unfortunately, the set of errors that cause this issue differs between
		1698	operating systems, there is usually little the app can do to remedy the
		1699	situation, and no known thread-safe method of removing the connection to
		1700	cope with overload is known (to me).
		1701
		1702	One of the easiest ways to handle this situation is to just ignore it
		1703	- when the program encounters an overload, it will just loop until the
		1704	situation is over. While this is a form of busy waiting, no OS offers an
		1705	event-based way to handle this situation, so it's the best one can do.
		1706
		1707	A better way to handle the situation is to log any errors other than
		1708	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1709	messages, and continue as usual, which at least gives the user an idea of
		1710	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1711	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1712	usage.
		1713
		1714	If your program is single-threaded, then you could also keep a dummy file
		1715	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1716	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1717	close that fd, and create a new dummy fd. This will gracefully refuse
		1718	clients under typical overload conditions.
		1719
		1720	The last way to handle it is to simply log the error and C<exit>, as
		1721	is often done with C<malloc> failures, but this results in an easy
		1722	opportunity for a DoS attack.
		1723
		1724	=head3 Watcher-Specific Functions
736		1725
737	=over 4	1726	=over 4
738		1727
739	=item ev_io_init (ev_io *, callback, int fd, int events)	1728	=item ev_io_init (ev_io *, callback, int fd, int events)
740		1729
741	=item ev_io_set (ev_io *, int fd, int events)	1730	=item ev_io_set (ev_io *, int fd, int events)
742		1731
743	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1732	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
744	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1733	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
745	C<EV_READ | EV_WRITE> to receive the given events.	1734	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1735
		1736	=item int fd [read-only]
		1737
		1738	The file descriptor being watched.
		1739
		1740	=item int events [read-only]
		1741
		1742	The events being watched.
746		1743
747	=back	1744	=back
748		1745
		1746	=head3 Examples
		1747
749	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1748	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
750	readable, but only once. Since it is likely line-buffered, you could	1749	readable, but only once. Since it is likely line-buffered, you could
751	attempt to read a whole line in the callback:	1750	attempt to read a whole line in the callback.
752		1751
753	static void	1752	static void
754	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1753	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
755	{	1754	{
756	ev_io_stop (loop, w);	1755	ev_io_stop (loop, w);
757	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1756	.. read from stdin here (or from w->fd) and handle any I/O errors
758	}	1757	}
759		1758
760	...	1759	...
761	struct ev_loop *loop = ev_default_init (0);	1760	struct ev_loop *loop = ev_default_init (0);
762	struct ev_io stdin_readable;	1761	ev_io stdin_readable;
763	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1762	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
764	ev_io_start (loop, &stdin_readable);	1763	ev_io_start (loop, &stdin_readable);
765	ev_loop (loop, 0);	1764	ev_run (loop, 0);
766		1765
767		1766
768	=head2 C<ev_timer> - relative and optionally repeating timeouts	1767	=head2 C<ev_timer> - relative and optionally repeating timeouts
769		1768
770	Timer watchers are simple relative timers that generate an event after a	1769	Timer watchers are simple relative timers that generate an event after a
771	given time, and optionally repeating in regular intervals after that.	1770	given time, and optionally repeating in regular intervals after that.
772		1771
773	The timers are based on real time, that is, if you register an event that	1772	The timers are based on real time, that is, if you register an event that
774	times out after an hour and you reset your system clock to last years	1773	times out after an hour and you reset your system clock to January last
775	time, it will still time out after (roughly) and hour. "Roughly" because	1774	year, it will still time out after (roughly) one hour. "Roughly" because
776	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1775	detecting time jumps is hard, and some inaccuracies are unavoidable (the
777	monotonic clock option helps a lot here).	1776	monotonic clock option helps a lot here).
		1777
		1778	The callback is guaranteed to be invoked only I<after> its timeout has
		1779	passed (not I<at>, so on systems with very low-resolution clocks this
		1780	might introduce a small delay, see "the special problem of being too
		1781	early", below). If multiple timers become ready during the same loop
		1782	iteration then the ones with earlier time-out values are invoked before
		1783	ones of the same priority with later time-out values (but this is no
		1784	longer true when a callback calls C<ev_run> recursively).
		1785
		1786	=head3 Be smart about timeouts
		1787
		1788	Many real-world problems involve some kind of timeout, usually for error
		1789	recovery. A typical example is an HTTP request - if the other side hangs,
		1790	you want to raise some error after a while.
		1791
		1792	What follows are some ways to handle this problem, from obvious and
		1793	inefficient to smart and efficient.
		1794
		1795	In the following, a 60 second activity timeout is assumed - a timeout that
		1796	gets reset to 60 seconds each time there is activity (e.g. each time some
		1797	data or other life sign was received).
		1798
		1799	=over 4
		1800
		1801	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1802
		1803	This is the most obvious, but not the most simple way: In the beginning,
		1804	start the watcher:
		1805
		1806	ev_timer_init (timer, callback, 60., 0.);
		1807	ev_timer_start (loop, timer);
		1808
		1809	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1810	and start it again:
		1811
		1812	ev_timer_stop (loop, timer);
		1813	ev_timer_set (timer, 60., 0.);
		1814	ev_timer_start (loop, timer);
		1815
		1816	This is relatively simple to implement, but means that each time there is
		1817	some activity, libev will first have to remove the timer from its internal
		1818	data structure and then add it again. Libev tries to be fast, but it's
		1819	still not a constant-time operation.
		1820
		1821	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1822
		1823	This is the easiest way, and involves using C<ev_timer_again> instead of
		1824	C<ev_timer_start>.
		1825
		1826	To implement this, configure an C<ev_timer> with a C<repeat> value
		1827	of C<60> and then call C<ev_timer_again> at start and each time you
		1828	successfully read or write some data. If you go into an idle state where
		1829	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1830	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1831
		1832	That means you can ignore both the C<ev_timer_start> function and the
		1833	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1834	member and C<ev_timer_again>.
		1835
		1836	At start:
		1837
		1838	ev_init (timer, callback);
		1839	timer->repeat = 60.;
		1840	ev_timer_again (loop, timer);
		1841
		1842	Each time there is some activity:
		1843
		1844	ev_timer_again (loop, timer);
		1845
		1846	It is even possible to change the time-out on the fly, regardless of
		1847	whether the watcher is active or not:
		1848
		1849	timer->repeat = 30.;
		1850	ev_timer_again (loop, timer);
		1851
		1852	This is slightly more efficient then stopping/starting the timer each time
		1853	you want to modify its timeout value, as libev does not have to completely
		1854	remove and re-insert the timer from/into its internal data structure.
		1855
		1856	It is, however, even simpler than the "obvious" way to do it.
		1857
		1858	=item 3. Let the timer time out, but then re-arm it as required.
		1859
		1860	This method is more tricky, but usually most efficient: Most timeouts are
		1861	relatively long compared to the intervals between other activity - in
		1862	our example, within 60 seconds, there are usually many I/O events with
		1863	associated activity resets.
		1864
		1865	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1866	but remember the time of last activity, and check for a real timeout only
		1867	within the callback:
		1868
		1869	ev_tstamp timeout = 60.;
		1870	ev_tstamp last_activity; // time of last activity
		1871	ev_timer timer;
		1872
		1873	static void
		1874	callback (EV_P_ ev_timer *w, int revents)
		1875	{
		1876	// calculate when the timeout would happen
		1877	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1878
		1879	// if negative, it means we the timeout already occured
		1880	if (after < 0.)
		1881	{
		1882	// timeout occurred, take action
		1883	}
		1884	else
		1885	{
		1886	// callback was invoked, but there was some recent
		1887	// activity. simply restart the timer to time out
		1888	// after "after" seconds, which is the earliest time
		1889	// the timeout can occur.
		1890	ev_timer_set (w, after, 0.);
		1891	ev_timer_start (EV_A_ w);
		1892	}
		1893	}
		1894
		1895	To summarise the callback: first calculate in how many seconds the
		1896	timeout will occur (by calculating the absolute time when it would occur,
		1897	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1898	(EV_A)> from that).
		1899
		1900	If this value is negative, then we are already past the timeout, i.e. we
		1901	timed out, and need to do whatever is needed in this case.
		1902
		1903	Otherwise, we now the earliest time at which the timeout would trigger,
		1904	and simply start the timer with this timeout value.
		1905
		1906	In other words, each time the callback is invoked it will check whether
		1907	the timeout cocured. If not, it will simply reschedule itself to check
		1908	again at the earliest time it could time out. Rinse. Repeat.
		1909
		1910	This scheme causes more callback invocations (about one every 60 seconds
		1911	minus half the average time between activity), but virtually no calls to
		1912	libev to change the timeout.
		1913
		1914	To start the machinery, simply initialise the watcher and set
		1915	C<last_activity> to the current time (meaning there was some activity just
		1916	now), then call the callback, which will "do the right thing" and start
		1917	the timer:
		1918
		1919	last_activity = ev_now (EV_A);
		1920	ev_init (&timer, callback);
		1921	callback (EV_A_ &timer, 0);
		1922
		1923	When there is some activity, simply store the current time in
		1924	C<last_activity>, no libev calls at all:
		1925
		1926	if (activity detected)
		1927	last_activity = ev_now (EV_A);
		1928
		1929	When your timeout value changes, then the timeout can be changed by simply
		1930	providing a new value, stopping the timer and calling the callback, which
		1931	will agaion do the right thing (for example, time out immediately :).
		1932
		1933	timeout = new_value;
		1934	ev_timer_stop (EV_A_ &timer);
		1935	callback (EV_A_ &timer, 0);
		1936
		1937	This technique is slightly more complex, but in most cases where the
		1938	time-out is unlikely to be triggered, much more efficient.
		1939
		1940	=item 4. Wee, just use a double-linked list for your timeouts.
		1941
		1942	If there is not one request, but many thousands (millions...), all
		1943	employing some kind of timeout with the same timeout value, then one can
		1944	do even better:
		1945
		1946	When starting the timeout, calculate the timeout value and put the timeout
		1947	at the I<end> of the list.
		1948
		1949	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1950	the list is expected to fire (for example, using the technique #3).
		1951
		1952	When there is some activity, remove the timer from the list, recalculate
		1953	the timeout, append it to the end of the list again, and make sure to
		1954	update the C<ev_timer> if it was taken from the beginning of the list.
		1955
		1956	This way, one can manage an unlimited number of timeouts in O(1) time for
		1957	starting, stopping and updating the timers, at the expense of a major
		1958	complication, and having to use a constant timeout. The constant timeout
		1959	ensures that the list stays sorted.
		1960
		1961	=back
		1962
		1963	So which method the best?
		1964
		1965	Method #2 is a simple no-brain-required solution that is adequate in most
		1966	situations. Method #3 requires a bit more thinking, but handles many cases
		1967	better, and isn't very complicated either. In most case, choosing either
		1968	one is fine, with #3 being better in typical situations.
		1969
		1970	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1971	rather complicated, but extremely efficient, something that really pays
		1972	off after the first million or so of active timers, i.e. it's usually
		1973	overkill :)
		1974
		1975	=head3 The special problem of being too early
		1976
		1977	If you ask a timer to call your callback after three seconds, then
		1978	you expect it to be invoked after three seconds - but of course, this
		1979	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1980	guaranteed to any precision by libev - imagine somebody suspending the
		1981	process with a STOP signal for a few hours for example.
		1982
		1983	So, libev tries to invoke your callback as soon as possible I<after> the
		1984	delay has occurred, but cannot guarantee this.
		1985
		1986	A less obvious failure mode is calling your callback too early: many event
		1987	loops compare timestamps with a "elapsed delay >= requested delay", but
		1988	this can cause your callback to be invoked much earlier than you would
		1989	expect.
		1990
		1991	To see why, imagine a system with a clock that only offers full second
		1992	resolution (think windows if you can't come up with a broken enough OS
		1993	yourself). If you schedule a one-second timer at the time 500.9, then the
		1994	event loop will schedule your timeout to elapse at a system time of 500
		1995	(500.9 truncated to the resolution) + 1, or 501.
		1996
		1997	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1998	501" and invoke the callback 0.1s after it was started, even though a
		1999	one-second delay was requested - this is being "too early", despite best
		2000	intentions.
		2001
		2002	This is the reason why libev will never invoke the callback if the elapsed
		2003	delay equals the requested delay, but only when the elapsed delay is
		2004	larger than the requested delay. In the example above, libev would only invoke
		2005	the callback at system time 502, or 1.1s after the timer was started.
		2006
		2007	So, while libev cannot guarantee that your callback will be invoked
		2008	exactly when requested, it I<can> and I<does> guarantee that the requested
		2009	delay has actually elapsed, or in other words, it always errs on the "too
		2010	late" side of things.
		2011
		2012	=head3 The special problem of time updates
		2013
		2014	Establishing the current time is a costly operation (it usually takes
		2015	at least one system call): EV therefore updates its idea of the current
		2016	time only before and after C<ev_run> collects new events, which causes a
		2017	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2018	lots of events in one iteration.
778		2019
779	The relative timeouts are calculated relative to the C<ev_now ()>	2020	The relative timeouts are calculated relative to the C<ev_now ()>
780	time. This is usually the right thing as this timestamp refers to the time	2021	time. This is usually the right thing as this timestamp refers to the time
781	of the event triggering whatever timeout you are modifying/starting. If	2022	of the event triggering whatever timeout you are modifying/starting. If
782	you suspect event processing to be delayed and you I<need> to base the timeout	2023	you suspect event processing to be delayed and you I<need> to base the
783	on the current time, use something like this to adjust for this:	2024	timeout on the current time, use something like this to adjust for this:
784		2025
785	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2026	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
786		2027
787	The callback is guarenteed to be invoked only when its timeout has passed,	2028	If the event loop is suspended for a long time, you can also force an
788	but if multiple timers become ready during the same loop iteration then	2029	update of the time returned by C<ev_now ()> by calling C<ev_now_update
789	order of execution is undefined.	2030	()>.
		2031
		2032	=head3 The special problem of unsynchronised clocks
		2033
		2034	Modern systems have a variety of clocks - libev itself uses the normal
		2035	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2036	jumps).
		2037
		2038	Neither of these clocks is synchronised with each other or any other clock
		2039	on the system, so C<ev_time ()> might return a considerably different time
		2040	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2041	a call to C<gettimeofday> might return a second count that is one higher
		2042	than a directly following call to C<time>.
		2043
		2044	The moral of this is to only compare libev-related timestamps with
		2045	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2046	a second or so.
		2047
		2048	One more problem arises due to this lack of synchronisation: if libev uses
		2049	the system monotonic clock and you compare timestamps from C<ev_time>
		2050	or C<ev_now> from when you started your timer and when your callback is
		2051	invoked, you will find that sometimes the callback is a bit "early".
		2052
		2053	This is because C<ev_timer>s work in real time, not wall clock time, so
		2054	libev makes sure your callback is not invoked before the delay happened,
		2055	I<measured according to the real time>, not the system clock.
		2056
		2057	If your timeouts are based on a physical timescale (e.g. "time out this
		2058	connection after 100 seconds") then this shouldn't bother you as it is
		2059	exactly the right behaviour.
		2060
		2061	If you want to compare wall clock/system timestamps to your timers, then
		2062	you need to use C<ev_periodic>s, as these are based on the wall clock
		2063	time, where your comparisons will always generate correct results.
		2064
		2065	=head3 The special problems of suspended animation
		2066
		2067	When you leave the server world it is quite customary to hit machines that
		2068	can suspend/hibernate - what happens to the clocks during such a suspend?
		2069
		2070	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2071	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2072	to run until the system is suspended, but they will not advance while the
		2073	system is suspended. That means, on resume, it will be as if the program
		2074	was frozen for a few seconds, but the suspend time will not be counted
		2075	towards C<ev_timer> when a monotonic clock source is used. The real time
		2076	clock advanced as expected, but if it is used as sole clocksource, then a
		2077	long suspend would be detected as a time jump by libev, and timers would
		2078	be adjusted accordingly.
		2079
		2080	I would not be surprised to see different behaviour in different between
		2081	operating systems, OS versions or even different hardware.
		2082
		2083	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2084	time jump in the monotonic clocks and the realtime clock. If the program
		2085	is suspended for a very long time, and monotonic clock sources are in use,
		2086	then you can expect C<ev_timer>s to expire as the full suspension time
		2087	will be counted towards the timers. When no monotonic clock source is in
		2088	use, then libev will again assume a timejump and adjust accordingly.
		2089
		2090	It might be beneficial for this latter case to call C<ev_suspend>
		2091	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2092	deterministic behaviour in this case (you can do nothing against
		2093	C<SIGSTOP>).
		2094
		2095	=head3 Watcher-Specific Functions and Data Members
790		2096
791	=over 4	2097	=over 4
792		2098
793	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2099	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
794		2100
795	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2101	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
796		2102
797	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2103	Configure the timer to trigger after C<after> seconds. If C<repeat>
798	C<0.>, then it will automatically be stopped. If it is positive, then the	2104	is C<0.>, then it will automatically be stopped once the timeout is
799	timer will automatically be configured to trigger again C<repeat> seconds	2105	reached. If it is positive, then the timer will automatically be
800	later, again, and again, until stopped manually.	2106	configured to trigger again C<repeat> seconds later, again, and again,
		2107	until stopped manually.
801		2108
802	The timer itself will do a best-effort at avoiding drift, that is, if you	2109	The timer itself will do a best-effort at avoiding drift, that is, if
803	configure a timer to trigger every 10 seconds, then it will trigger at	2110	you configure a timer to trigger every 10 seconds, then it will normally
804	exactly 10 second intervals. If, however, your program cannot keep up with	2111	trigger at exactly 10 second intervals. If, however, your program cannot
805	the timer (because it takes longer than those 10 seconds to do stuff) the	2112	keep up with the timer (because it takes longer than those 10 seconds to
806	timer will not fire more than once per event loop iteration.	2113	do stuff) the timer will not fire more than once per event loop iteration.
807		2114
808	=item ev_timer_again (loop)	2115	=item ev_timer_again (loop, ev_timer *)
809		2116
810	This will act as if the timer timed out and restart it again if it is	2117	This will act as if the timer timed out, and restarts it again if it is
811	repeating. The exact semantics are:	2118	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2119	timeout to the C<repeat> value and calling C<ev_timer_start>.
812		2120
		2121	The exact semantics are as in the following rules, all of which will be
		2122	applied to the watcher:
		2123
		2124	=over 4
		2125
		2126	=item If the timer is pending, the pending status is always cleared.
		2127
813	If the timer is started but nonrepeating, stop it.	2128	=item If the timer is started but non-repeating, stop it (as if it timed
		2129	out, without invoking it).
814		2130
815	If the timer is repeating, either start it if necessary (with the repeat	2131	=item If the timer is repeating, make the C<repeat> value the new timeout
816	value), or reset the running timer to the repeat value.	2132	and start the timer, if necessary.
817
818	This sounds a bit complicated, but here is a useful and typical
819	example: Imagine you have a tcp connection and you want a so-called idle
820	timeout, that is, you want to be called when there have been, say, 60
821	seconds of inactivity on the socket. The easiest way to do this is to
822	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
823	time you successfully read or write some data. If you go into an idle
824	state where you do not expect data to travel on the socket, you can stop
825	the timer, and again will automatically restart it if need be.
826		2133
827	=back	2134	=back
828		2135
		2136	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
		2137	usage example.
		2138
		2139	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2140
		2141	Returns the remaining time until a timer fires. If the timer is active,
		2142	then this time is relative to the current event loop time, otherwise it's
		2143	the timeout value currently configured.
		2144
		2145	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2146	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2147	will return C<4>. When the timer expires and is restarted, it will return
		2148	roughly C<7> (likely slightly less as callback invocation takes some time,
		2149	too), and so on.
		2150
		2151	=item ev_tstamp repeat [read-write]
		2152
		2153	The current C<repeat> value. Will be used each time the watcher times out
		2154	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2155	which is also when any modifications are taken into account.
		2156
		2157	=back
		2158
		2159	=head3 Examples
		2160
829	Example: create a timer that fires after 60 seconds.	2161	Example: Create a timer that fires after 60 seconds.
830		2162
831	static void	2163	static void
832	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2164	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
833	{	2165	{
834	.. one minute over, w is actually stopped right here	2166	.. one minute over, w is actually stopped right here
835	}	2167	}
836		2168
837	struct ev_timer mytimer;	2169	ev_timer mytimer;
838	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2170	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
839	ev_timer_start (loop, &mytimer);	2171	ev_timer_start (loop, &mytimer);
840		2172
841	Example: create a timeout timer that times out after 10 seconds of	2173	Example: Create a timeout timer that times out after 10 seconds of
842	inactivity.	2174	inactivity.
843		2175
844	static void	2176	static void
845	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2177	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
846	{	2178	{
847	.. ten seconds without any activity	2179	.. ten seconds without any activity
848	}	2180	}
849		2181
850	struct ev_timer mytimer;	2182	ev_timer mytimer;
851	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2183	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
852	ev_timer_again (&mytimer); /* start timer */	2184	ev_timer_again (&mytimer); /* start timer */
853	ev_loop (loop, 0);	2185	ev_run (loop, 0);
854		2186
855	// and in some piece of code that gets executed on any "activity":	2187	// and in some piece of code that gets executed on any "activity":
856	// reset the timeout to start ticking again at 10 seconds	2188	// reset the timeout to start ticking again at 10 seconds
857	ev_timer_again (&mytimer);	2189	ev_timer_again (&mytimer);
858		2190
859		2191
860	=head2 C<ev_periodic> - to cron or not to cron?	2192	=head2 C<ev_periodic> - to cron or not to cron?
861		2193
862	Periodic watchers are also timers of a kind, but they are very versatile	2194	Periodic watchers are also timers of a kind, but they are very versatile
863	(and unfortunately a bit complex).	2195	(and unfortunately a bit complex).
864		2196
865	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2197	Unlike C<ev_timer>, periodic watchers are not based on real time (or
866	but on wallclock time (absolute time). You can tell a periodic watcher	2198	relative time, the physical time that passes) but on wall clock time
867	to trigger "at" some specific point in time. For example, if you tell a	2199	(absolute time, the thing you can read on your calender or clock). The
868	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2200	difference is that wall clock time can run faster or slower than real
869	+ 10.>) and then reset your system clock to the last year, then it will	2201	time, and time jumps are not uncommon (e.g. when you adjust your
870	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2202	wrist-watch).
871	roughly 10 seconds later and of course not if you reset your system time
872	again).
873		2203
874	They can also be used to implement vastly more complex timers, such as	2204	You can tell a periodic watcher to trigger after some specific point
		2205	in time: for example, if you tell a periodic watcher to trigger "in 10
		2206	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2207	not a delay) and then reset your system clock to January of the previous
		2208	year, then it will take a year or more to trigger the event (unlike an
		2209	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2210	it, as it uses a relative timeout).
		2211
		2212	C<ev_periodic> watchers can also be used to implement vastly more complex
875	triggering an event on eahc midnight, local time.	2213	timers, such as triggering an event on each "midnight, local time", or
		2214	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2215	those cannot react to time jumps.
876		2216
877	As with timers, the callback is guarenteed to be invoked only when the	2217	As with timers, the callback is guaranteed to be invoked only when the
878	time (C<at>) has been passed, but if multiple periodic timers become ready	2218	point in time where it is supposed to trigger has passed. If multiple
879	during the same loop iteration then order of execution is undefined.	2219	timers become ready during the same loop iteration then the ones with
		2220	earlier time-out values are invoked before ones with later time-out values
		2221	(but this is no longer true when a callback calls C<ev_run> recursively).
		2222
		2223	=head3 Watcher-Specific Functions and Data Members
880		2224
881	=over 4	2225	=over 4
882		2226
883	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2227	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
884		2228
885	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2229	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
886		2230
887	Lots of arguments, lets sort it out... There are basically three modes of	2231	Lots of arguments, let's sort it out... There are basically three modes of
888	operation, and we will explain them from simplest to complex:	2232	operation, and we will explain them from simplest to most complex:
889		2233
890	=over 4	2234	=over 4
891		2235
892	=item * absolute timer (interval = reschedule_cb = 0)	2236	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
893		2237
894	In this configuration the watcher triggers an event at the wallclock time	2238	In this configuration the watcher triggers an event after the wall clock
895	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2239	time C<offset> has passed. It will not repeat and will not adjust when a
896	that is, if it is to be run at January 1st 2011 then it will run when the	2240	time jump occurs, that is, if it is to be run at January 1st 2011 then it
897	system time reaches or surpasses this time.	2241	will be stopped and invoked when the system clock reaches or surpasses
		2242	this point in time.
898		2243
899	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2244	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
900		2245
901	In this mode the watcher will always be scheduled to time out at the next	2246	In this mode the watcher will always be scheduled to time out at the next
902	C<at + N * interval> time (for some integer N) and then repeat, regardless	2247	C<offset + N * interval> time (for some integer N, which can also be
903	of any time jumps.	2248	negative) and then repeat, regardless of any time jumps. The C<offset>
		2249	argument is merely an offset into the C<interval> periods.
904		2250
905	This can be used to create timers that do not drift with respect to system	2251	This can be used to create timers that do not drift with respect to the
906	time:	2252	system clock, for example, here is an C<ev_periodic> that triggers each
		2253	hour, on the hour (with respect to UTC):
907		2254
908	ev_periodic_set (&periodic, 0., 3600., 0);	2255	ev_periodic_set (&periodic, 0., 3600., 0);
909		2256
910	This doesn't mean there will always be 3600 seconds in between triggers,	2257	This doesn't mean there will always be 3600 seconds in between triggers,
911	but only that the the callback will be called when the system time shows a	2258	but only that the callback will be called when the system time shows a
912	full hour (UTC), or more correctly, when the system time is evenly divisible	2259	full hour (UTC), or more correctly, when the system time is evenly divisible
913	by 3600.	2260	by 3600.
914		2261
915	Another way to think about it (for the mathematically inclined) is that	2262	Another way to think about it (for the mathematically inclined) is that
916	C<ev_periodic> will try to run the callback in this mode at the next possible	2263	C<ev_periodic> will try to run the callback in this mode at the next possible
917	time where C<time = at (mod interval)>, regardless of any time jumps.	2264	time where C<time = offset (mod interval)>, regardless of any time jumps.
918		2265
		2266	The C<interval> I<MUST> be positive, and for numerical stability, the
		2267	interval value should be higher than C<1/8192> (which is around 100
		2268	microseconds) and C<offset> should be higher than C<0> and should have
		2269	at most a similar magnitude as the current time (say, within a factor of
		2270	ten). Typical values for offset are, in fact, C<0> or something between
		2271	C<0> and C<interval>, which is also the recommended range.
		2272
		2273	Note also that there is an upper limit to how often a timer can fire (CPU
		2274	speed for example), so if C<interval> is very small then timing stability
		2275	will of course deteriorate. Libev itself tries to be exact to be about one
		2276	millisecond (if the OS supports it and the machine is fast enough).
		2277
919	=item * manual reschedule mode (reschedule_cb = callback)	2278	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
920		2279
921	In this mode the values for C<interval> and C<at> are both being	2280	In this mode the values for C<interval> and C<offset> are both being
922	ignored. Instead, each time the periodic watcher gets scheduled, the	2281	ignored. Instead, each time the periodic watcher gets scheduled, the
923	reschedule callback will be called with the watcher as first, and the	2282	reschedule callback will be called with the watcher as first, and the
924	current time as second argument.	2283	current time as second argument.
925		2284
926	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2285	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
927	ever, or make any event loop modifications>. If you need to stop it,	2286	or make ANY other event loop modifications whatsoever, unless explicitly
928	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2287	allowed by documentation here>.
929	starting a prepare watcher).
930		2288
		2289	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2290	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2291	only event loop modification you are allowed to do).
		2292
931	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2293	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
932	ev_tstamp now)>, e.g.:	2294	*w, ev_tstamp now)>, e.g.:
933		2295
		2296	static ev_tstamp
934	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2297	my_rescheduler (ev_periodic *w, ev_tstamp now)
935	{	2298	{
936	return now + 60.;	2299	return now + 60.;
937	}	2300	}
938		2301
939	It must return the next time to trigger, based on the passed time value	2302	It must return the next time to trigger, based on the passed time value
940	(that is, the lowest time value larger than to the second argument). It	2303	(that is, the lowest time value larger than to the second argument). It
941	will usually be called just before the callback will be triggered, but	2304	will usually be called just before the callback will be triggered, but
942	might be called at other times, too.	2305	might be called at other times, too.
943		2306
944	NOTE: I<< This callback must always return a time that is later than the	2307	NOTE: I<< This callback must always return a time that is higher than or
945	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2308	equal to the passed C<now> value >>.
946		2309
947	This can be used to create very complex timers, such as a timer that	2310	This can be used to create very complex timers, such as a timer that
948	triggers on each midnight, local time. To do this, you would calculate the	2311	triggers on "next midnight, local time". To do this, you would calculate the
949	next midnight after C<now> and return the timestamp value for this. How	2312	next midnight after C<now> and return the timestamp value for this. How
950	you do this is, again, up to you (but it is not trivial, which is the main	2313	you do this is, again, up to you (but it is not trivial, which is the main
951	reason I omitted it as an example).	2314	reason I omitted it as an example).
952		2315
953	=back	2316	=back
…		…
957	Simply stops and restarts the periodic watcher again. This is only useful	2320	Simply stops and restarts the periodic watcher again. This is only useful
958	when you changed some parameters or the reschedule callback would return	2321	when you changed some parameters or the reschedule callback would return
959	a different time than the last time it was called (e.g. in a crond like	2322	a different time than the last time it was called (e.g. in a crond like
960	program when the crontabs have changed).	2323	program when the crontabs have changed).
961		2324
		2325	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2326
		2327	When active, returns the absolute time that the watcher is supposed
		2328	to trigger next. This is not the same as the C<offset> argument to
		2329	C<ev_periodic_set>, but indeed works even in interval and manual
		2330	rescheduling modes.
		2331
		2332	=item ev_tstamp offset [read-write]
		2333
		2334	When repeating, this contains the offset value, otherwise this is the
		2335	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2336	although libev might modify this value for better numerical stability).
		2337
		2338	Can be modified any time, but changes only take effect when the periodic
		2339	timer fires or C<ev_periodic_again> is being called.
		2340
		2341	=item ev_tstamp interval [read-write]
		2342
		2343	The current interval value. Can be modified any time, but changes only
		2344	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2345	called.
		2346
		2347	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2348
		2349	The current reschedule callback, or C<0>, if this functionality is
		2350	switched off. Can be changed any time, but changes only take effect when
		2351	the periodic timer fires or C<ev_periodic_again> is being called.
		2352
962	=back	2353	=back
963		2354
		2355	=head3 Examples
		2356
964	Example: call a callback every hour, or, more precisely, whenever the	2357	Example: Call a callback every hour, or, more precisely, whenever the
965	system clock is divisible by 3600. The callback invocation times have	2358	system time is divisible by 3600. The callback invocation times have
966	potentially a lot of jittering, but good long-term stability.	2359	potentially a lot of jitter, but good long-term stability.
967		2360
968	static void	2361	static void
969	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2362	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
970	{	2363	{
971	... its now a full hour (UTC, or TAI or whatever your clock follows)	2364	... its now a full hour (UTC, or TAI or whatever your clock follows)
972	}	2365	}
973		2366
974	struct ev_periodic hourly_tick;	2367	ev_periodic hourly_tick;
975	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2368	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
976	ev_periodic_start (loop, &hourly_tick);	2369	ev_periodic_start (loop, &hourly_tick);
977		2370
978	Example: the same as above, but use a reschedule callback to do it:	2371	Example: The same as above, but use a reschedule callback to do it:
979		2372
980	#include <math.h>	2373	#include <math.h>
981		2374
982	static ev_tstamp	2375	static ev_tstamp
983	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2376	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
984	{	2377	{
985	return fmod (now, 3600.) + 3600.;	2378	return now + (3600. - fmod (now, 3600.));
986	}	2379	}
987		2380
988	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2381	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
989		2382
990	Example: call a callback every hour, starting now:	2383	Example: Call a callback every hour, starting now:
991		2384
992	struct ev_periodic hourly_tick;	2385	ev_periodic hourly_tick;
993	ev_periodic_init (&hourly_tick, clock_cb,	2386	ev_periodic_init (&hourly_tick, clock_cb,
994	fmod (ev_now (loop), 3600.), 3600., 0);	2387	fmod (ev_now (loop), 3600.), 3600., 0);
995	ev_periodic_start (loop, &hourly_tick);	2388	ev_periodic_start (loop, &hourly_tick);
996		2389
997		2390
998	=head2 C<ev_signal> - signal me when a signal gets signalled!	2391	=head2 C<ev_signal> - signal me when a signal gets signalled!
999		2392
1000	Signal watchers will trigger an event when the process receives a specific	2393	Signal watchers will trigger an event when the process receives a specific
1001	signal one or more times. Even though signals are very asynchronous, libev	2394	signal one or more times. Even though signals are very asynchronous, libev
1002	will try it's best to deliver signals synchronously, i.e. as part of the	2395	will try its best to deliver signals synchronously, i.e. as part of the
1003	normal event processing, like any other event.	2396	normal event processing, like any other event.
1004		2397
		2398	If you want signals to be delivered truly asynchronously, just use
		2399	C<sigaction> as you would do without libev and forget about sharing
		2400	the signal. You can even use C<ev_async> from a signal handler to
		2401	synchronously wake up an event loop.
		2402
1005	You can configure as many watchers as you like per signal. Only when the	2403	You can configure as many watchers as you like for the same signal, but
		2404	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2405	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2406	C<SIGINT> in both the default loop and another loop at the same time. At
		2407	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2408
1006	first watcher gets started will libev actually register a signal watcher	2409	When the first watcher gets started will libev actually register something
1007	with the kernel (thus it coexists with your own signal handlers as long	2410	with the kernel (thus it coexists with your own signal handlers as long as
1008	as you don't register any with libev). Similarly, when the last signal	2411	you don't register any with libev for the same signal).
1009	watcher for a signal is stopped libev will reset the signal handler to	2412
1010	SIG_DFL (regardless of what it was set to before).	2413	If possible and supported, libev will install its handlers with
		2414	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2415	not be unduly interrupted. If you have a problem with system calls getting
		2416	interrupted by signals you can block all signals in an C<ev_check> watcher
		2417	and unblock them in an C<ev_prepare> watcher.
		2418
		2419	=head3 The special problem of inheritance over fork/execve/pthread_create
		2420
		2421	Both the signal mask (C<sigprocmask>) and the signal disposition
		2422	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2423	stopping it again), that is, libev might or might not block the signal,
		2424	and might or might not set or restore the installed signal handler (but
		2425	see C<EVFLAG_NOSIGMASK>).
		2426
		2427	While this does not matter for the signal disposition (libev never
		2428	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2429	C<execve>), this matters for the signal mask: many programs do not expect
		2430	certain signals to be blocked.
		2431
		2432	This means that before calling C<exec> (from the child) you should reset
		2433	the signal mask to whatever "default" you expect (all clear is a good
		2434	choice usually).
		2435
		2436	The simplest way to ensure that the signal mask is reset in the child is
		2437	to install a fork handler with C<pthread_atfork> that resets it. That will
		2438	catch fork calls done by libraries (such as the libc) as well.
		2439
		2440	In current versions of libev, the signal will not be blocked indefinitely
		2441	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2442	the window of opportunity for problems, it will not go away, as libev
		2443	I<has> to modify the signal mask, at least temporarily.
		2444
		2445	So I can't stress this enough: I<If you do not reset your signal mask when
		2446	you expect it to be empty, you have a race condition in your code>. This
		2447	is not a libev-specific thing, this is true for most event libraries.
		2448
		2449	=head3 The special problem of threads signal handling
		2450
		2451	POSIX threads has problematic signal handling semantics, specifically,
		2452	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2453	threads in a process block signals, which is hard to achieve.
		2454
		2455	When you want to use sigwait (or mix libev signal handling with your own
		2456	for the same signals), you can tackle this problem by globally blocking
		2457	all signals before creating any threads (or creating them with a fully set
		2458	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2459	loops. Then designate one thread as "signal receiver thread" which handles
		2460	these signals. You can pass on any signals that libev might be interested
		2461	in by calling C<ev_feed_signal>.
		2462
		2463	=head3 Watcher-Specific Functions and Data Members
1011		2464
1012	=over 4	2465	=over 4
1013		2466
1014	=item ev_signal_init (ev_signal *, callback, int signum)	2467	=item ev_signal_init (ev_signal *, callback, int signum)
1015		2468
1016	=item ev_signal_set (ev_signal *, int signum)	2469	=item ev_signal_set (ev_signal *, int signum)
1017		2470
1018	Configures the watcher to trigger on the given signal number (usually one	2471	Configures the watcher to trigger on the given signal number (usually one
1019	of the C<SIGxxx> constants).	2472	of the C<SIGxxx> constants).
1020		2473
		2474	=item int signum [read-only]
		2475
		2476	The signal the watcher watches out for.
		2477
1021	=back	2478	=back
1022		2479
		2480	=head3 Examples
		2481
		2482	Example: Try to exit cleanly on SIGINT.
		2483
		2484	static void
		2485	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2486	{
		2487	ev_break (loop, EVBREAK_ALL);
		2488	}
		2489
		2490	ev_signal signal_watcher;
		2491	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2492	ev_signal_start (loop, &signal_watcher);
		2493
1023		2494
1024	=head2 C<ev_child> - watch out for process status changes	2495	=head2 C<ev_child> - watch out for process status changes
1025		2496
1026	Child watchers trigger when your process receives a SIGCHLD in response to	2497	Child watchers trigger when your process receives a SIGCHLD in response to
1027	some child status changes (most typically when a child of yours dies).	2498	some child status changes (most typically when a child of yours dies or
		2499	exits). It is permissible to install a child watcher I<after> the child
		2500	has been forked (which implies it might have already exited), as long
		2501	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2502	forking and then immediately registering a watcher for the child is fine,
		2503	but forking and registering a watcher a few event loop iterations later or
		2504	in the next callback invocation is not.
		2505
		2506	Only the default event loop is capable of handling signals, and therefore
		2507	you can only register child watchers in the default event loop.
		2508
		2509	Due to some design glitches inside libev, child watchers will always be
		2510	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2511	libev)
		2512
		2513	=head3 Process Interaction
		2514
		2515	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2516	initialised. This is necessary to guarantee proper behaviour even if the
		2517	first child watcher is started after the child exits. The occurrence
		2518	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2519	synchronously as part of the event loop processing. Libev always reaps all
		2520	children, even ones not watched.
		2521
		2522	=head3 Overriding the Built-In Processing
		2523
		2524	Libev offers no special support for overriding the built-in child
		2525	processing, but if your application collides with libev's default child
		2526	handler, you can override it easily by installing your own handler for
		2527	C<SIGCHLD> after initialising the default loop, and making sure the
		2528	default loop never gets destroyed. You are encouraged, however, to use an
		2529	event-based approach to child reaping and thus use libev's support for
		2530	that, so other libev users can use C<ev_child> watchers freely.
		2531
		2532	=head3 Stopping the Child Watcher
		2533
		2534	Currently, the child watcher never gets stopped, even when the
		2535	child terminates, so normally one needs to stop the watcher in the
		2536	callback. Future versions of libev might stop the watcher automatically
		2537	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2538	problem).
		2539
		2540	=head3 Watcher-Specific Functions and Data Members
1028		2541
1029	=over 4	2542	=over 4
1030		2543
1031	=item ev_child_init (ev_child *, callback, int pid)	2544	=item ev_child_init (ev_child *, callback, int pid, int trace)
1032		2545
1033	=item ev_child_set (ev_child *, int pid)	2546	=item ev_child_set (ev_child *, int pid, int trace)
1034		2547
1035	Configures the watcher to wait for status changes of process C<pid> (or	2548	Configures the watcher to wait for status changes of process C<pid> (or
1036	I<any> process if C<pid> is specified as C<0>). The callback can look	2549	I<any> process if C<pid> is specified as C<0>). The callback can look
1037	at the C<rstatus> member of the C<ev_child> watcher structure to see	2550	at the C<rstatus> member of the C<ev_child> watcher structure to see
1038	the status word (use the macros from C<sys/wait.h> and see your systems	2551	the status word (use the macros from C<sys/wait.h> and see your systems
1039	C<waitpid> documentation). The C<rpid> member contains the pid of the	2552	C<waitpid> documentation). The C<rpid> member contains the pid of the
1040	process causing the status change.	2553	process causing the status change. C<trace> must be either C<0> (only
		2554	activate the watcher when the process terminates) or C<1> (additionally
		2555	activate the watcher when the process is stopped or continued).
		2556
		2557	=item int pid [read-only]
		2558
		2559	The process id this watcher watches out for, or C<0>, meaning any process id.
		2560
		2561	=item int rpid [read-write]
		2562
		2563	The process id that detected a status change.
		2564
		2565	=item int rstatus [read-write]
		2566
		2567	The process exit/trace status caused by C<rpid> (see your systems
		2568	C<waitpid> and C<sys/wait.h> documentation for details).
1041		2569
1042	=back	2570	=back
1043		2571
1044	Example: try to exit cleanly on SIGINT and SIGTERM.	2572	=head3 Examples
1045		2573
		2574	Example: C<fork()> a new process and install a child handler to wait for
		2575	its completion.
		2576
		2577	ev_child cw;
		2578
1046	static void	2579	static void
1047	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2580	child_cb (EV_P_ ev_child *w, int revents)
1048	{	2581	{
1049	ev_unloop (loop, EVUNLOOP_ALL);	2582	ev_child_stop (EV_A_ w);
		2583	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1050	}	2584	}
1051		2585
1052	struct ev_signal signal_watcher;	2586	pid_t pid = fork ();
1053	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2587
1054	ev_signal_start (loop, &sigint_cb);	2588	if (pid < 0)
		2589	// error
		2590	else if (pid == 0)
		2591	{
		2592	// the forked child executes here
		2593	exit (1);
		2594	}
		2595	else
		2596	{
		2597	ev_child_init (&cw, child_cb, pid, 0);
		2598	ev_child_start (EV_DEFAULT_ &cw);
		2599	}
		2600
		2601
		2602	=head2 C<ev_stat> - did the file attributes just change?
		2603
		2604	This watches a file system path for attribute changes. That is, it calls
		2605	C<stat> on that path in regular intervals (or when the OS says it changed)
		2606	and sees if it changed compared to the last time, invoking the callback if
		2607	it did.
		2608
		2609	The path does not need to exist: changing from "path exists" to "path does
		2610	not exist" is a status change like any other. The condition "path does not
		2611	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2612	C<st_nlink> field being zero (which is otherwise always forced to be at
		2613	least one) and all the other fields of the stat buffer having unspecified
		2614	contents.
		2615
		2616	The path I<must not> end in a slash or contain special components such as
		2617	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2618	your working directory changes, then the behaviour is undefined.
		2619
		2620	Since there is no portable change notification interface available, the
		2621	portable implementation simply calls C<stat(2)> regularly on the path
		2622	to see if it changed somehow. You can specify a recommended polling
		2623	interval for this case. If you specify a polling interval of C<0> (highly
		2624	recommended!) then a I<suitable, unspecified default> value will be used
		2625	(which you can expect to be around five seconds, although this might
		2626	change dynamically). Libev will also impose a minimum interval which is
		2627	currently around C<0.1>, but that's usually overkill.
		2628
		2629	This watcher type is not meant for massive numbers of stat watchers,
		2630	as even with OS-supported change notifications, this can be
		2631	resource-intensive.
		2632
		2633	At the time of this writing, the only OS-specific interface implemented
		2634	is the Linux inotify interface (implementing kqueue support is left as an
		2635	exercise for the reader. Note, however, that the author sees no way of
		2636	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2637
		2638	=head3 ABI Issues (Largefile Support)
		2639
		2640	Libev by default (unless the user overrides this) uses the default
		2641	compilation environment, which means that on systems with large file
		2642	support disabled by default, you get the 32 bit version of the stat
		2643	structure. When using the library from programs that change the ABI to
		2644	use 64 bit file offsets the programs will fail. In that case you have to
		2645	compile libev with the same flags to get binary compatibility. This is
		2646	obviously the case with any flags that change the ABI, but the problem is
		2647	most noticeably displayed with ev_stat and large file support.
		2648
		2649	The solution for this is to lobby your distribution maker to make large
		2650	file interfaces available by default (as e.g. FreeBSD does) and not
		2651	optional. Libev cannot simply switch on large file support because it has
		2652	to exchange stat structures with application programs compiled using the
		2653	default compilation environment.
		2654
		2655	=head3 Inotify and Kqueue
		2656
		2657	When C<inotify (7)> support has been compiled into libev and present at
		2658	runtime, it will be used to speed up change detection where possible. The
		2659	inotify descriptor will be created lazily when the first C<ev_stat>
		2660	watcher is being started.
		2661
		2662	Inotify presence does not change the semantics of C<ev_stat> watchers
		2663	except that changes might be detected earlier, and in some cases, to avoid
		2664	making regular C<stat> calls. Even in the presence of inotify support
		2665	there are many cases where libev has to resort to regular C<stat> polling,
		2666	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2667	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2668	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2669	xfs are fully working) libev usually gets away without polling.
		2670
		2671	There is no support for kqueue, as apparently it cannot be used to
		2672	implement this functionality, due to the requirement of having a file
		2673	descriptor open on the object at all times, and detecting renames, unlinks
		2674	etc. is difficult.
		2675
		2676	=head3 C<stat ()> is a synchronous operation
		2677
		2678	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2679	the process. The exception are C<ev_stat> watchers - those call C<stat
		2680	()>, which is a synchronous operation.
		2681
		2682	For local paths, this usually doesn't matter: unless the system is very
		2683	busy or the intervals between stat's are large, a stat call will be fast,
		2684	as the path data is usually in memory already (except when starting the
		2685	watcher).
		2686
		2687	For networked file systems, calling C<stat ()> can block an indefinite
		2688	time due to network issues, and even under good conditions, a stat call
		2689	often takes multiple milliseconds.
		2690
		2691	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2692	paths, although this is fully supported by libev.
		2693
		2694	=head3 The special problem of stat time resolution
		2695
		2696	The C<stat ()> system call only supports full-second resolution portably,
		2697	and even on systems where the resolution is higher, most file systems
		2698	still only support whole seconds.
		2699
		2700	That means that, if the time is the only thing that changes, you can
		2701	easily miss updates: on the first update, C<ev_stat> detects a change and
		2702	calls your callback, which does something. When there is another update
		2703	within the same second, C<ev_stat> will be unable to detect unless the
		2704	stat data does change in other ways (e.g. file size).
		2705
		2706	The solution to this is to delay acting on a change for slightly more
		2707	than a second (or till slightly after the next full second boundary), using
		2708	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2709	ev_timer_again (loop, w)>).
		2710
		2711	The C<.02> offset is added to work around small timing inconsistencies
		2712	of some operating systems (where the second counter of the current time
		2713	might be be delayed. One such system is the Linux kernel, where a call to
		2714	C<gettimeofday> might return a timestamp with a full second later than
		2715	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2716	update file times then there will be a small window where the kernel uses
		2717	the previous second to update file times but libev might already execute
		2718	the timer callback).
		2719
		2720	=head3 Watcher-Specific Functions and Data Members
		2721
		2722	=over 4
		2723
		2724	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2725
		2726	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2727
		2728	Configures the watcher to wait for status changes of the given
		2729	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2730	be detected and should normally be specified as C<0> to let libev choose
		2731	a suitable value. The memory pointed to by C<path> must point to the same
		2732	path for as long as the watcher is active.
		2733
		2734	The callback will receive an C<EV_STAT> event when a change was detected,
		2735	relative to the attributes at the time the watcher was started (or the
		2736	last change was detected).
		2737
		2738	=item ev_stat_stat (loop, ev_stat *)
		2739
		2740	Updates the stat buffer immediately with new values. If you change the
		2741	watched path in your callback, you could call this function to avoid
		2742	detecting this change (while introducing a race condition if you are not
		2743	the only one changing the path). Can also be useful simply to find out the
		2744	new values.
		2745
		2746	=item ev_statdata attr [read-only]
		2747
		2748	The most-recently detected attributes of the file. Although the type is
		2749	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2750	suitable for your system, but you can only rely on the POSIX-standardised
		2751	members to be present. If the C<st_nlink> member is C<0>, then there was
		2752	some error while C<stat>ing the file.
		2753
		2754	=item ev_statdata prev [read-only]
		2755
		2756	The previous attributes of the file. The callback gets invoked whenever
		2757	C<prev> != C<attr>, or, more precisely, one or more of these members
		2758	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2759	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2760
		2761	=item ev_tstamp interval [read-only]
		2762
		2763	The specified interval.
		2764
		2765	=item const char *path [read-only]
		2766
		2767	The file system path that is being watched.
		2768
		2769	=back
		2770
		2771	=head3 Examples
		2772
		2773	Example: Watch C</etc/passwd> for attribute changes.
		2774
		2775	static void
		2776	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2777	{
		2778	/* /etc/passwd changed in some way */
		2779	if (w->attr.st_nlink)
		2780	{
		2781	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2782	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2783	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2784	}
		2785	else
		2786	/* you shalt not abuse printf for puts */
		2787	puts ("wow, /etc/passwd is not there, expect problems. "
		2788	"if this is windows, they already arrived\n");
		2789	}
		2790
		2791	...
		2792	ev_stat passwd;
		2793
		2794	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2795	ev_stat_start (loop, &passwd);
		2796
		2797	Example: Like above, but additionally use a one-second delay so we do not
		2798	miss updates (however, frequent updates will delay processing, too, so
		2799	one might do the work both on C<ev_stat> callback invocation I<and> on
		2800	C<ev_timer> callback invocation).
		2801
		2802	static ev_stat passwd;
		2803	static ev_timer timer;
		2804
		2805	static void
		2806	timer_cb (EV_P_ ev_timer *w, int revents)
		2807	{
		2808	ev_timer_stop (EV_A_ w);
		2809
		2810	/* now it's one second after the most recent passwd change */
		2811	}
		2812
		2813	static void
		2814	stat_cb (EV_P_ ev_stat *w, int revents)
		2815	{
		2816	/* reset the one-second timer */
		2817	ev_timer_again (EV_A_ &timer);
		2818	}
		2819
		2820	...
		2821	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2822	ev_stat_start (loop, &passwd);
		2823	ev_timer_init (&timer, timer_cb, 0., 1.02);
1055		2824
1056		2825
1057	=head2 C<ev_idle> - when you've got nothing better to do...	2826	=head2 C<ev_idle> - when you've got nothing better to do...
1058		2827
1059	Idle watchers trigger events when there are no other events are pending	2828	Idle watchers trigger events when no other events of the same or higher
1060	(prepare, check and other idle watchers do not count). That is, as long	2829	priority are pending (prepare, check and other idle watchers do not count
1061	as your process is busy handling sockets or timeouts (or even signals,	2830	as receiving "events").
1062	imagine) it will not be triggered. But when your process is idle all idle	2831
1063	watchers are being called again and again, once per event loop iteration -	2832	That is, as long as your process is busy handling sockets or timeouts
		2833	(or even signals, imagine) of the same or higher priority it will not be
		2834	triggered. But when your process is idle (or only lower-priority watchers
		2835	are pending), the idle watchers are being called once per event loop
1064	until stopped, that is, or your process receives more events and becomes	2836	iteration - until stopped, that is, or your process receives more events
1065	busy.	2837	and becomes busy again with higher priority stuff.
1066		2838
1067	The most noteworthy effect is that as long as any idle watchers are	2839	The most noteworthy effect is that as long as any idle watchers are
1068	active, the process will not block when waiting for new events.	2840	active, the process will not block when waiting for new events.
1069		2841
1070	Apart from keeping your process non-blocking (which is a useful	2842	Apart from keeping your process non-blocking (which is a useful
1071	effect on its own sometimes), idle watchers are a good place to do	2843	effect on its own sometimes), idle watchers are a good place to do
1072	"pseudo-background processing", or delay processing stuff to after the	2844	"pseudo-background processing", or delay processing stuff to after the
1073	event loop has handled all outstanding events.	2845	event loop has handled all outstanding events.
1074		2846
		2847	=head3 Watcher-Specific Functions and Data Members
		2848
1075	=over 4	2849	=over 4
1076		2850
1077	=item ev_idle_init (ev_signal *, callback)	2851	=item ev_idle_init (ev_idle *, callback)
1078		2852
1079	Initialises and configures the idle watcher - it has no parameters of any	2853	Initialises and configures the idle watcher - it has no parameters of any
1080	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2854	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1081	believe me.	2855	believe me.
1082		2856
1083	=back	2857	=back
1084		2858
		2859	=head3 Examples
		2860
1085	Example: dynamically allocate an C<ev_idle>, start it, and in the	2861	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1086	callback, free it. Alos, use no error checking, as usual.	2862	callback, free it. Also, use no error checking, as usual.
1087		2863
1088	static void	2864	static void
1089	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2865	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1090	{	2866	{
1091	free (w);	2867	free (w);
1092	// now do something you wanted to do when the program has	2868	// now do something you wanted to do when the program has
1093	// no longer asnything immediate to do.	2869	// no longer anything immediate to do.
1094	}	2870	}
1095		2871
1096	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2872	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1097	ev_idle_init (idle_watcher, idle_cb);	2873	ev_idle_init (idle_watcher, idle_cb);
1098	ev_idle_start (loop, idle_cb);	2874	ev_idle_start (loop, idle_watcher);
1099		2875
1100		2876
1101	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2877	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1102		2878
1103	Prepare and check watchers are usually (but not always) used in tandem:	2879	Prepare and check watchers are usually (but not always) used in pairs:
1104	prepare watchers get invoked before the process blocks and check watchers	2880	prepare watchers get invoked before the process blocks and check watchers
1105	afterwards.	2881	afterwards.
1106		2882
1107	You I<must not> call C<ev_loop> or similar functions that enter	2883	You I<must not> call C<ev_run> or similar functions that enter
1108	the current event loop from either C<ev_prepare> or C<ev_check>	2884	the current event loop from either C<ev_prepare> or C<ev_check>
1109	watchers. Other loops than the current one are fine, however. The	2885	watchers. Other loops than the current one are fine, however. The
1110	rationale behind this is that you do not need to check for recursion in	2886	rationale behind this is that you do not need to check for recursion in
1111	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2887	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1112	C<ev_check> so if you have one watcher of each kind they will always be	2888	C<ev_check> so if you have one watcher of each kind they will always be
1113	called in pairs bracketing the blocking call.	2889	called in pairs bracketing the blocking call.
1114		2890
1115	Their main purpose is to integrate other event mechanisms into libev and	2891	Their main purpose is to integrate other event mechanisms into libev and
1116	their use is somewhat advanced. This could be used, for example, to track	2892	their use is somewhat advanced. They could be used, for example, to track
1117	variable changes, implement your own watchers, integrate net-snmp or a	2893	variable changes, implement your own watchers, integrate net-snmp or a
1118	coroutine library and lots more. They are also occasionally useful if	2894	coroutine library and lots more. They are also occasionally useful if
1119	you cache some data and want to flush it before blocking (for example,	2895	you cache some data and want to flush it before blocking (for example,
1120	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2896	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1121	watcher).	2897	watcher).
1122		2898
1123	This is done by examining in each prepare call which file descriptors need	2899	This is done by examining in each prepare call which file descriptors
1124	to be watched by the other library, registering C<ev_io> watchers for	2900	need to be watched by the other library, registering C<ev_io> watchers
1125	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2901	for them and starting an C<ev_timer> watcher for any timeouts (many
1126	provide just this functionality). Then, in the check watcher you check for	2902	libraries provide exactly this functionality). Then, in the check watcher,
1127	any events that occured (by checking the pending status of all watchers	2903	you check for any events that occurred (by checking the pending status
1128	and stopping them) and call back into the library. The I/O and timer	2904	of all watchers and stopping them) and call back into the library. The
1129	callbacks will never actually be called (but must be valid nevertheless,	2905	I/O and timer callbacks will never actually be called (but must be valid
1130	because you never know, you know?).	2906	nevertheless, because you never know, you know?).
1131		2907
1132	As another example, the Perl Coro module uses these hooks to integrate	2908	As another example, the Perl Coro module uses these hooks to integrate
1133	coroutines into libev programs, by yielding to other active coroutines	2909	coroutines into libev programs, by yielding to other active coroutines
1134	during each prepare and only letting the process block if no coroutines	2910	during each prepare and only letting the process block if no coroutines
1135	are ready to run (it's actually more complicated: it only runs coroutines	2911	are ready to run (it's actually more complicated: it only runs coroutines
1136	with priority higher than or equal to the event loop and one coroutine	2912	with priority higher than or equal to the event loop and one coroutine
1137	of lower priority, but only once, using idle watchers to keep the event	2913	of lower priority, but only once, using idle watchers to keep the event
1138	loop from blocking if lower-priority coroutines are active, thus mapping	2914	loop from blocking if lower-priority coroutines are active, thus mapping
1139	low-priority coroutines to idle/background tasks).	2915	low-priority coroutines to idle/background tasks).
1140		2916
		2917	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2918	priority, to ensure that they are being run before any other watchers
		2919	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2920
		2921	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2922	activate ("feed") events into libev. While libev fully supports this, they
		2923	might get executed before other C<ev_check> watchers did their job. As
		2924	C<ev_check> watchers are often used to embed other (non-libev) event
		2925	loops those other event loops might be in an unusable state until their
		2926	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2927	others).
		2928
		2929	=head3 Watcher-Specific Functions and Data Members
		2930
1141	=over 4	2931	=over 4
1142		2932
1143	=item ev_prepare_init (ev_prepare *, callback)	2933	=item ev_prepare_init (ev_prepare *, callback)
1144		2934
1145	=item ev_check_init (ev_check *, callback)	2935	=item ev_check_init (ev_check *, callback)
1146		2936
1147	Initialises and configures the prepare or check watcher - they have no	2937	Initialises and configures the prepare or check watcher - they have no
1148	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2938	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1149	macros, but using them is utterly, utterly and completely pointless.	2939	macros, but using them is utterly, utterly, utterly and completely
		2940	pointless.
1150		2941
1151	=back	2942	=back
1152		2943
1153	Example: To include a library such as adns, you would add IO watchers	2944	=head3 Examples
1154	and a timeout watcher in a prepare handler, as required by libadns, and	2945
		2946	There are a number of principal ways to embed other event loops or modules
		2947	into libev. Here are some ideas on how to include libadns into libev
		2948	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2949	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2950	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2951	Glib event loop).
		2952
		2953	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1155	in a check watcher, destroy them and call into libadns. What follows is	2954	and in a check watcher, destroy them and call into libadns. What follows
1156	pseudo-code only of course:	2955	is pseudo-code only of course. This requires you to either use a low
		2956	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2957	the callbacks for the IO/timeout watchers might not have been called yet.
1157		2958
1158	static ev_io iow [nfd];	2959	static ev_io iow [nfd];
1159	static ev_timer tw;	2960	static ev_timer tw;
1160		2961
1161	static void	2962	static void
1162	io_cb (ev_loop *loop, ev_io *w, int revents)	2963	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1163	{	2964	{
1164	// set the relevant poll flags
1165	// could also call adns_processreadable etc. here
1166	struct pollfd *fd = (struct pollfd *)w->data;
1167	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1168	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1169	}	2965	}
1170		2966
1171	// create io watchers for each fd and a timer before blocking	2967	// create io watchers for each fd and a timer before blocking
1172	static void	2968	static void
1173	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2969	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1174	{	2970	{
1175	int timeout = 3600000;truct pollfd fds [nfd];	2971	int timeout = 3600000;
		2972	struct pollfd fds [nfd];
1176	// actual code will need to loop here and realloc etc.	2973	// actual code will need to loop here and realloc etc.
1177	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2974	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1178		2975
1179	/* the callback is illegal, but won't be called as we stop during check */	2976	/* the callback is illegal, but won't be called as we stop during check */
1180	ev_timer_init (&tw, 0, timeout * 1e-3);	2977	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1181	ev_timer_start (loop, &tw);	2978	ev_timer_start (loop, &tw);
1182		2979
1183	// create on ev_io per pollfd	2980	// create one ev_io per pollfd
1184	for (int i = 0; i < nfd; ++i)	2981	for (int i = 0; i < nfd; ++i)
1185	{	2982	{
1186	ev_io_init (iow + i, io_cb, fds [i].fd,	2983	ev_io_init (iow + i, io_cb, fds [i].fd,
1187	((fds [i].events & POLLIN ? EV_READ : 0)	2984	((fds [i].events & POLLIN ? EV_READ : 0)
1188	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2985	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1189		2986
1190	fds [i].revents = 0;	2987	fds [i].revents = 0;
1191	iow [i].data = fds + i;
1192	ev_io_start (loop, iow + i);	2988	ev_io_start (loop, iow + i);
1193	}	2989	}
1194	}	2990	}
1195		2991
1196	// stop all watchers after blocking	2992	// stop all watchers after blocking
1197	static void	2993	static void
1198	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2994	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1199	{	2995	{
1200	ev_timer_stop (loop, &tw);	2996	ev_timer_stop (loop, &tw);
1201		2997
1202	for (int i = 0; i < nfd; ++i)	2998	for (int i = 0; i < nfd; ++i)
		2999	{
		3000	// set the relevant poll flags
		3001	// could also call adns_processreadable etc. here
		3002	struct pollfd *fd = fds + i;
		3003	int revents = ev_clear_pending (iow + i);
		3004	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3005	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3006
		3007	// now stop the watcher
1203	ev_io_stop (loop, iow + i);	3008	ev_io_stop (loop, iow + i);
		3009	}
1204		3010
1205	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3011	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1206	}	3012	}
		3013
		3014	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3015	in the prepare watcher and would dispose of the check watcher.
		3016
		3017	Method 3: If the module to be embedded supports explicit event
		3018	notification (libadns does), you can also make use of the actual watcher
		3019	callbacks, and only destroy/create the watchers in the prepare watcher.
		3020
		3021	static void
		3022	timer_cb (EV_P_ ev_timer *w, int revents)
		3023	{
		3024	adns_state ads = (adns_state)w->data;
		3025	update_now (EV_A);
		3026
		3027	adns_processtimeouts (ads, &tv_now);
		3028	}
		3029
		3030	static void
		3031	io_cb (EV_P_ ev_io *w, int revents)
		3032	{
		3033	adns_state ads = (adns_state)w->data;
		3034	update_now (EV_A);
		3035
		3036	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3037	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3038	}
		3039
		3040	// do not ever call adns_afterpoll
		3041
		3042	Method 4: Do not use a prepare or check watcher because the module you
		3043	want to embed is not flexible enough to support it. Instead, you can
		3044	override their poll function. The drawback with this solution is that the
		3045	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3046	this approach, effectively embedding EV as a client into the horrible
		3047	libglib event loop.
		3048
		3049	static gint
		3050	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3051	{
		3052	int got_events = 0;
		3053
		3054	for (n = 0; n < nfds; ++n)
		3055	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3056
		3057	if (timeout >= 0)
		3058	// create/start timer
		3059
		3060	// poll
		3061	ev_run (EV_A_ 0);
		3062
		3063	// stop timer again
		3064	if (timeout >= 0)
		3065	ev_timer_stop (EV_A_ &to);
		3066
		3067	// stop io watchers again - their callbacks should have set
		3068	for (n = 0; n < nfds; ++n)
		3069	ev_io_stop (EV_A_ iow [n]);
		3070
		3071	return got_events;
		3072	}
1207		3073
1208		3074
1209	=head2 C<ev_embed> - when one backend isn't enough...	3075	=head2 C<ev_embed> - when one backend isn't enough...
1210		3076
1211	This is a rather advanced watcher type that lets you embed one event loop	3077	This is a rather advanced watcher type that lets you embed one event loop
…		…
1217	prioritise I/O.	3083	prioritise I/O.
1218		3084
1219	As an example for a bug workaround, the kqueue backend might only support	3085	As an example for a bug workaround, the kqueue backend might only support
1220	sockets on some platform, so it is unusable as generic backend, but you	3086	sockets on some platform, so it is unusable as generic backend, but you
1221	still want to make use of it because you have many sockets and it scales	3087	still want to make use of it because you have many sockets and it scales
1222	so nicely. In this case, you would create a kqueue-based loop and embed it	3088	so nicely. In this case, you would create a kqueue-based loop and embed
1223	into your default loop (which might use e.g. poll). Overall operation will	3089	it into your default loop (which might use e.g. poll). Overall operation
1224	be a bit slower because first libev has to poll and then call kevent, but	3090	will be a bit slower because first libev has to call C<poll> and then
1225	at least you can use both at what they are best.	3091	C<kevent>, but at least you can use both mechanisms for what they are
		3092	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1226		3093
1227	As for prioritising I/O: rarely you have the case where some fds have	3094	As for prioritising I/O: under rare circumstances you have the case where
1228	to be watched and handled very quickly (with low latency), and even	3095	some fds have to be watched and handled very quickly (with low latency),
1229	priorities and idle watchers might have too much overhead. In this case	3096	and even priorities and idle watchers might have too much overhead. In
1230	you would put all the high priority stuff in one loop and all the rest in	3097	this case you would put all the high priority stuff in one loop and all
1231	a second one, and embed the second one in the first.	3098	the rest in a second one, and embed the second one in the first.
1232		3099
1233	As long as the watcher is active, the callback will be invoked every time	3100	As long as the watcher is active, the callback will be invoked every
1234	there might be events pending in the embedded loop. The callback must then	3101	time there might be events pending in the embedded loop. The callback
1235	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3102	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1236	their callbacks (you could also start an idle watcher to give the embedded	3103	sweep and invoke their callbacks (the callback doesn't need to invoke the
1237	loop strictly lower priority for example). You can also set the callback	3104	C<ev_embed_sweep> function directly, it could also start an idle watcher
1238	to C<0>, in which case the embed watcher will automatically execute the	3105	to give the embedded loop strictly lower priority for example).
1239	embedded loop sweep.
1240		3106
1241	As long as the watcher is started it will automatically handle events. The	3107	You can also set the callback to C<0>, in which case the embed watcher
1242	callback will be invoked whenever some events have been handled. You can	3108	will automatically execute the embedded loop sweep whenever necessary.
1243	set the callback to C<0> to avoid having to specify one if you are not
1244	interested in that.
1245		3109
1246	Also, there have not currently been made special provisions for forking:	3110	Fork detection will be handled transparently while the C<ev_embed> watcher
1247	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3111	is active, i.e., the embedded loop will automatically be forked when the
1248	but you will also have to stop and restart any C<ev_embed> watchers	3112	embedding loop forks. In other cases, the user is responsible for calling
1249	yourself.	3113	C<ev_loop_fork> on the embedded loop.
1250		3114
1251	Unfortunately, not all backends are embeddable, only the ones returned by	3115	Unfortunately, not all backends are embeddable: only the ones returned by
1252	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3116	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1253	portable one.	3117	portable one.
1254		3118
1255	So when you want to use this feature you will always have to be prepared	3119	So when you want to use this feature you will always have to be prepared
1256	that you cannot get an embeddable loop. The recommended way to get around	3120	that you cannot get an embeddable loop. The recommended way to get around
1257	this is to have a separate variables for your embeddable loop, try to	3121	this is to have a separate variables for your embeddable loop, try to
1258	create it, and if that fails, use the normal loop for everything:	3122	create it, and if that fails, use the normal loop for everything.
1259		3123
1260	struct ev_loop *loop_hi = ev_default_init (0);	3124	=head3 C<ev_embed> and fork
1261	struct ev_loop *loop_lo = 0;
1262	struct ev_embed embed;
1263
1264	// see if there is a chance of getting one that works
1265	// (remember that a flags value of 0 means autodetection)
1266	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1267	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1268	: 0;
1269		3125
1270	// if we got one, then embed it, otherwise default to loop_hi	3126	While the C<ev_embed> watcher is running, forks in the embedding loop will
1271	if (loop_lo)	3127	automatically be applied to the embedded loop as well, so no special
1272	{	3128	fork handling is required in that case. When the watcher is not running,
1273	ev_embed_init (&embed, 0, loop_lo);	3129	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1274	ev_embed_start (loop_hi, &embed);	3130	as applicable.
1275	}	3131
1276	else	3132	=head3 Watcher-Specific Functions and Data Members
1277	loop_lo = loop_hi;
1278		3133
1279	=over 4	3134	=over 4
1280		3135
1281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3136	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1282		3137
…		…
1284		3139
1285	Configures the watcher to embed the given loop, which must be	3140	Configures the watcher to embed the given loop, which must be
1286	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3141	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1287	invoked automatically, otherwise it is the responsibility of the callback	3142	invoked automatically, otherwise it is the responsibility of the callback
1288	to invoke it (it will continue to be called until the sweep has been done,	3143	to invoke it (it will continue to be called until the sweep has been done,
1289	if you do not want thta, you need to temporarily stop the embed watcher).	3144	if you do not want that, you need to temporarily stop the embed watcher).
1290		3145
1291	=item ev_embed_sweep (loop, ev_embed *)	3146	=item ev_embed_sweep (loop, ev_embed *)
1292		3147
1293	Make a single, non-blocking sweep over the embedded loop. This works	3148	Make a single, non-blocking sweep over the embedded loop. This works
1294	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3149	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1295	apropriate way for embedded loops.	3150	appropriate way for embedded loops.
		3151
		3152	=item struct ev_loop *other [read-only]
		3153
		3154	The embedded event loop.
1296		3155
1297	=back	3156	=back
1298		3157
		3158	=head3 Examples
		3159
		3160	Example: Try to get an embeddable event loop and embed it into the default
		3161	event loop. If that is not possible, use the default loop. The default
		3162	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3163	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3164	used).
		3165
		3166	struct ev_loop *loop_hi = ev_default_init (0);
		3167	struct ev_loop *loop_lo = 0;
		3168	ev_embed embed;
		3169
		3170	// see if there is a chance of getting one that works
		3171	// (remember that a flags value of 0 means autodetection)
		3172	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3173	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3174	: 0;
		3175
		3176	// if we got one, then embed it, otherwise default to loop_hi
		3177	if (loop_lo)
		3178	{
		3179	ev_embed_init (&embed, 0, loop_lo);
		3180	ev_embed_start (loop_hi, &embed);
		3181	}
		3182	else
		3183	loop_lo = loop_hi;
		3184
		3185	Example: Check if kqueue is available but not recommended and create
		3186	a kqueue backend for use with sockets (which usually work with any
		3187	kqueue implementation). Store the kqueue/socket-only event loop in
		3188	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3189
		3190	struct ev_loop *loop = ev_default_init (0);
		3191	struct ev_loop *loop_socket = 0;
		3192	ev_embed embed;
		3193
		3194	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3195	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3196	{
		3197	ev_embed_init (&embed, 0, loop_socket);
		3198	ev_embed_start (loop, &embed);
		3199	}
		3200
		3201	if (!loop_socket)
		3202	loop_socket = loop;
		3203
		3204	// now use loop_socket for all sockets, and loop for everything else
		3205
		3206
		3207	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3208
		3209	Fork watchers are called when a C<fork ()> was detected (usually because
		3210	whoever is a good citizen cared to tell libev about it by calling
		3211	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3212	event loop blocks next and before C<ev_check> watchers are being called,
		3213	and only in the child after the fork. If whoever good citizen calling
		3214	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3215	handlers will be invoked, too, of course.
		3216
		3217	=head3 The special problem of life after fork - how is it possible?
		3218
		3219	Most uses of C<fork()> consist of forking, then some simple calls to set
		3220	up/change the process environment, followed by a call to C<exec()>. This
		3221	sequence should be handled by libev without any problems.
		3222
		3223	This changes when the application actually wants to do event handling
		3224	in the child, or both parent in child, in effect "continuing" after the
		3225	fork.
		3226
		3227	The default mode of operation (for libev, with application help to detect
		3228	forks) is to duplicate all the state in the child, as would be expected
		3229	when I<either> the parent I<or> the child process continues.
		3230
		3231	When both processes want to continue using libev, then this is usually the
		3232	wrong result. In that case, usually one process (typically the parent) is
		3233	supposed to continue with all watchers in place as before, while the other
		3234	process typically wants to start fresh, i.e. without any active watchers.
		3235
		3236	The cleanest and most efficient way to achieve that with libev is to
		3237	simply create a new event loop, which of course will be "empty", and
		3238	use that for new watchers. This has the advantage of not touching more
		3239	memory than necessary, and thus avoiding the copy-on-write, and the
		3240	disadvantage of having to use multiple event loops (which do not support
		3241	signal watchers).
		3242
		3243	When this is not possible, or you want to use the default loop for
		3244	other reasons, then in the process that wants to start "fresh", call
		3245	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3246	Destroying the default loop will "orphan" (not stop) all registered
		3247	watchers, so you have to be careful not to execute code that modifies
		3248	those watchers. Note also that in that case, you have to re-register any
		3249	signal watchers.
		3250
		3251	=head3 Watcher-Specific Functions and Data Members
		3252
		3253	=over 4
		3254
		3255	=item ev_fork_init (ev_fork *, callback)
		3256
		3257	Initialises and configures the fork watcher - it has no parameters of any
		3258	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3259	really.
		3260
		3261	=back
		3262
		3263
		3264	=head2 C<ev_cleanup> - even the best things end
		3265
		3266	Cleanup watchers are called just before the event loop is being destroyed
		3267	by a call to C<ev_loop_destroy>.
		3268
		3269	While there is no guarantee that the event loop gets destroyed, cleanup
		3270	watchers provide a convenient method to install cleanup hooks for your
		3271	program, worker threads and so on - you just to make sure to destroy the
		3272	loop when you want them to be invoked.
		3273
		3274	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3275	all other watchers, they do not keep a reference to the event loop (which
		3276	makes a lot of sense if you think about it). Like all other watchers, you
		3277	can call libev functions in the callback, except C<ev_cleanup_start>.
		3278
		3279	=head3 Watcher-Specific Functions and Data Members
		3280
		3281	=over 4
		3282
		3283	=item ev_cleanup_init (ev_cleanup *, callback)
		3284
		3285	Initialises and configures the cleanup watcher - it has no parameters of
		3286	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3287	pointless, I assure you.
		3288
		3289	=back
		3290
		3291	Example: Register an atexit handler to destroy the default loop, so any
		3292	cleanup functions are called.
		3293
		3294	static void
		3295	program_exits (void)
		3296	{
		3297	ev_loop_destroy (EV_DEFAULT_UC);
		3298	}
		3299
		3300	...
		3301	atexit (program_exits);
		3302
		3303
		3304	=head2 C<ev_async> - how to wake up an event loop
		3305
		3306	In general, you cannot use an C<ev_loop> from multiple threads or other
		3307	asynchronous sources such as signal handlers (as opposed to multiple event
		3308	loops - those are of course safe to use in different threads).
		3309
		3310	Sometimes, however, you need to wake up an event loop you do not control,
		3311	for example because it belongs to another thread. This is what C<ev_async>
		3312	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3313	it by calling C<ev_async_send>, which is thread- and signal safe.
		3314
		3315	This functionality is very similar to C<ev_signal> watchers, as signals,
		3316	too, are asynchronous in nature, and signals, too, will be compressed
		3317	(i.e. the number of callback invocations may be less than the number of
		3318	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3319	of "global async watchers" by using a watcher on an otherwise unused
		3320	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3321	even without knowing which loop owns the signal.
		3322
		3323	=head3 Queueing
		3324
		3325	C<ev_async> does not support queueing of data in any way. The reason
		3326	is that the author does not know of a simple (or any) algorithm for a
		3327	multiple-writer-single-reader queue that works in all cases and doesn't
		3328	need elaborate support such as pthreads or unportable memory access
		3329	semantics.
		3330
		3331	That means that if you want to queue data, you have to provide your own
		3332	queue. But at least I can tell you how to implement locking around your
		3333	queue:
		3334
		3335	=over 4
		3336
		3337	=item queueing from a signal handler context
		3338
		3339	To implement race-free queueing, you simply add to the queue in the signal
		3340	handler but you block the signal handler in the watcher callback. Here is
		3341	an example that does that for some fictitious SIGUSR1 handler:
		3342
		3343	static ev_async mysig;
		3344
		3345	static void
		3346	sigusr1_handler (void)
		3347	{
		3348	sometype data;
		3349
		3350	// no locking etc.
		3351	queue_put (data);
		3352	ev_async_send (EV_DEFAULT_ &mysig);
		3353	}
		3354
		3355	static void
		3356	mysig_cb (EV_P_ ev_async *w, int revents)
		3357	{
		3358	sometype data;
		3359	sigset_t block, prev;
		3360
		3361	sigemptyset (&block);
		3362	sigaddset (&block, SIGUSR1);
		3363	sigprocmask (SIG_BLOCK, &block, &prev);
		3364
		3365	while (queue_get (&data))
		3366	process (data);
		3367
		3368	if (sigismember (&prev, SIGUSR1)
		3369	sigprocmask (SIG_UNBLOCK, &block, 0);
		3370	}
		3371
		3372	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3373	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3374	either...).
		3375
		3376	=item queueing from a thread context
		3377
		3378	The strategy for threads is different, as you cannot (easily) block
		3379	threads but you can easily preempt them, so to queue safely you need to
		3380	employ a traditional mutex lock, such as in this pthread example:
		3381
		3382	static ev_async mysig;
		3383	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3384
		3385	static void
		3386	otherthread (void)
		3387	{
		3388	// only need to lock the actual queueing operation
		3389	pthread_mutex_lock (&mymutex);
		3390	queue_put (data);
		3391	pthread_mutex_unlock (&mymutex);
		3392
		3393	ev_async_send (EV_DEFAULT_ &mysig);
		3394	}
		3395
		3396	static void
		3397	mysig_cb (EV_P_ ev_async *w, int revents)
		3398	{
		3399	pthread_mutex_lock (&mymutex);
		3400
		3401	while (queue_get (&data))
		3402	process (data);
		3403
		3404	pthread_mutex_unlock (&mymutex);
		3405	}
		3406
		3407	=back
		3408
		3409
		3410	=head3 Watcher-Specific Functions and Data Members
		3411
		3412	=over 4
		3413
		3414	=item ev_async_init (ev_async *, callback)
		3415
		3416	Initialises and configures the async watcher - it has no parameters of any
		3417	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3418	trust me.
		3419
		3420	=item ev_async_send (loop, ev_async *)
		3421
		3422	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3423	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3424	returns.
		3425
		3426	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3427	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3428	embedding section below on what exactly this means).
		3429
		3430	Note that, as with other watchers in libev, multiple events might get
		3431	compressed into a single callback invocation (another way to look at
		3432	this is that C<ev_async> watchers are level-triggered: they are set on
		3433	C<ev_async_send>, reset when the event loop detects that).
		3434
		3435	This call incurs the overhead of at most one extra system call per event
		3436	loop iteration, if the event loop is blocked, and no syscall at all if
		3437	the event loop (or your program) is processing events. That means that
		3438	repeated calls are basically free (there is no need to avoid calls for
		3439	performance reasons) and that the overhead becomes smaller (typically
		3440	zero) under load.
		3441
		3442	=item bool = ev_async_pending (ev_async *)
		3443
		3444	Returns a non-zero value when C<ev_async_send> has been called on the
		3445	watcher but the event has not yet been processed (or even noted) by the
		3446	event loop.
		3447
		3448	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3449	the loop iterates next and checks for the watcher to have become active,
		3450	it will reset the flag again. C<ev_async_pending> can be used to very
		3451	quickly check whether invoking the loop might be a good idea.
		3452
		3453	Not that this does I<not> check whether the watcher itself is pending,
		3454	only whether it has been requested to make this watcher pending: there
		3455	is a time window between the event loop checking and resetting the async
		3456	notification, and the callback being invoked.
		3457
		3458	=back
		3459
1299		3460
1300	=head1 OTHER FUNCTIONS	3461	=head1 OTHER FUNCTIONS
1301		3462
1302	There are some other functions of possible interest. Described. Here. Now.	3463	There are some other functions of possible interest. Described. Here. Now.
1303		3464
1304	=over 4	3465	=over 4
1305		3466
1306	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3467	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1307		3468
1308	This function combines a simple timer and an I/O watcher, calls your	3469	This function combines a simple timer and an I/O watcher, calls your
1309	callback on whichever event happens first and automatically stop both	3470	callback on whichever event happens first and automatically stops both
1310	watchers. This is useful if you want to wait for a single event on an fd	3471	watchers. This is useful if you want to wait for a single event on an fd
1311	or timeout without having to allocate/configure/start/stop/free one or	3472	or timeout without having to allocate/configure/start/stop/free one or
1312	more watchers yourself.	3473	more watchers yourself.
1313		3474
1314	If C<fd> is less than 0, then no I/O watcher will be started and events	3475	If C<fd> is less than 0, then no I/O watcher will be started and the
1315	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3476	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1316	C<events> set will be craeted and started.	3477	the given C<fd> and C<events> set will be created and started.
1317		3478
1318	If C<timeout> is less than 0, then no timeout watcher will be	3479	If C<timeout> is less than 0, then no timeout watcher will be
1319	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3480	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1320	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3481	repeat = 0) will be started. C<0> is a valid timeout.
1321	dubious value.
1322		3482
1323	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3483	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1324	passed an C<revents> set like normal event callbacks (a combination of	3484	passed an C<revents> set like normal event callbacks (a combination of
1325	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3485	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1326	value passed to C<ev_once>:	3486	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3487	a timeout and an io event at the same time - you probably should give io
		3488	events precedence.
1327		3489
		3490	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3491
1328	static void stdin_ready (int revents, void *arg)	3492	static void stdin_ready (int revents, void *arg)
		3493	{
		3494	if (revents & EV_READ)
		3495	/* stdin might have data for us, joy! */;
		3496	else if (revents & EV_TIMER)
		3497	/* doh, nothing entered */;
		3498	}
		3499
		3500	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3501
		3502	=item ev_feed_fd_event (loop, int fd, int revents)
		3503
		3504	Feed an event on the given fd, as if a file descriptor backend detected
		3505	the given events.
		3506
		3507	=item ev_feed_signal_event (loop, int signum)
		3508
		3509	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3510	which is async-safe.
		3511
		3512	=back
		3513
		3514
		3515	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3516
		3517	This section explains some common idioms that are not immediately
		3518	obvious. Note that examples are sprinkled over the whole manual, and this
		3519	section only contains stuff that wouldn't fit anywhere else.
		3520
		3521	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3522
		3523	Each watcher has, by default, a C<void *data> member that you can read
		3524	or modify at any time: libev will completely ignore it. This can be used
		3525	to associate arbitrary data with your watcher. If you need more data and
		3526	don't want to allocate memory separately and store a pointer to it in that
		3527	data member, you can also "subclass" the watcher type and provide your own
		3528	data:
		3529
		3530	struct my_io
		3531	{
		3532	ev_io io;
		3533	int otherfd;
		3534	void *somedata;
		3535	struct whatever *mostinteresting;
		3536	};
		3537
		3538	...
		3539	struct my_io w;
		3540	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3541
		3542	And since your callback will be called with a pointer to the watcher, you
		3543	can cast it back to your own type:
		3544
		3545	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3546	{
		3547	struct my_io *w = (struct my_io *)w_;
		3548	...
		3549	}
		3550
		3551	More interesting and less C-conformant ways of casting your callback
		3552	function type instead have been omitted.
		3553
		3554	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3555
		3556	Another common scenario is to use some data structure with multiple
		3557	embedded watchers, in effect creating your own watcher that combines
		3558	multiple libev event sources into one "super-watcher":
		3559
		3560	struct my_biggy
		3561	{
		3562	int some_data;
		3563	ev_timer t1;
		3564	ev_timer t2;
		3565	}
		3566
		3567	In this case getting the pointer to C<my_biggy> is a bit more
		3568	complicated: Either you store the address of your C<my_biggy> struct in
		3569	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3570	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3571	real programmers):
		3572
		3573	#include <stddef.h>
		3574
		3575	static void
		3576	t1_cb (EV_P_ ev_timer *w, int revents)
		3577	{
		3578	struct my_biggy big = (struct my_biggy *)
		3579	(((char *)w) - offsetof (struct my_biggy, t1));
		3580	}
		3581
		3582	static void
		3583	t2_cb (EV_P_ ev_timer *w, int revents)
		3584	{
		3585	struct my_biggy big = (struct my_biggy *)
		3586	(((char *)w) - offsetof (struct my_biggy, t2));
		3587	}
		3588
		3589	=head2 AVOIDING FINISHING BEFORE RETURNING
		3590
		3591	Often you have structures like this in event-based programs:
		3592
		3593	callback ()
1329	{	3594	{
1330	if (revents & EV_TIMEOUT)	3595	free (request);
1331	/* doh, nothing entered */;
1332	else if (revents & EV_READ)
1333	/* stdin might have data for us, joy! */;
1334	}	3596	}
1335		3597
1336	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3598	request = start_new_request (..., callback);
1337		3599
1338	=item ev_feed_event (ev_loop *, watcher *, int revents)	3600	The intent is to start some "lengthy" operation. The C<request> could be
		3601	used to cancel the operation, or do other things with it.
1339		3602
1340	Feeds the given event set into the event loop, as if the specified event	3603	It's not uncommon to have code paths in C<start_new_request> that
1341	had happened for the specified watcher (which must be a pointer to an	3604	immediately invoke the callback, for example, to report errors. Or you add
1342	initialised but not necessarily started event watcher).	3605	some caching layer that finds that it can skip the lengthy aspects of the
		3606	operation and simply invoke the callback with the result.
1343		3607
1344	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3608	The problem here is that this will happen I<before> C<start_new_request>
		3609	has returned, so C<request> is not set.
1345		3610
1346	Feed an event on the given fd, as if a file descriptor backend detected	3611	Even if you pass the request by some safer means to the callback, you
1347	the given events it.	3612	might want to do something to the request after starting it, such as
		3613	canceling it, which probably isn't working so well when the callback has
		3614	already been invoked.
1348		3615
1349	=item ev_feed_signal_event (ev_loop *loop, int signum)	3616	A common way around all these issues is to make sure that
		3617	C<start_new_request> I<always> returns before the callback is invoked. If
		3618	C<start_new_request> immediately knows the result, it can artificially
		3619	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3620	for example, or more sneakily, by reusing an existing (stopped) watcher
		3621	and pushing it into the pending queue:
1350		3622
1351	Feed an event as if the given signal occured (C<loop> must be the default	3623	ev_set_cb (watcher, callback);
1352	loop!).	3624	ev_feed_event (EV_A_ watcher, 0);
1353		3625
1354	=back	3626	This way, C<start_new_request> can safely return before the callback is
		3627	invoked, while not delaying callback invocation too much.
		3628
		3629	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3630
		3631	Often (especially in GUI toolkits) there are places where you have
		3632	I<modal> interaction, which is most easily implemented by recursively
		3633	invoking C<ev_run>.
		3634
		3635	This brings the problem of exiting - a callback might want to finish the
		3636	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3637	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3638	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3639	other combination: In these cases, C<ev_break> will not work alone.
		3640
		3641	The solution is to maintain "break this loop" variable for each C<ev_run>
		3642	invocation, and use a loop around C<ev_run> until the condition is
		3643	triggered, using C<EVRUN_ONCE>:
		3644
		3645	// main loop
		3646	int exit_main_loop = 0;
		3647
		3648	while (!exit_main_loop)
		3649	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3650
		3651	// in a modal watcher
		3652	int exit_nested_loop = 0;
		3653
		3654	while (!exit_nested_loop)
		3655	ev_run (EV_A_ EVRUN_ONCE);
		3656
		3657	To exit from any of these loops, just set the corresponding exit variable:
		3658
		3659	// exit modal loop
		3660	exit_nested_loop = 1;
		3661
		3662	// exit main program, after modal loop is finished
		3663	exit_main_loop = 1;
		3664
		3665	// exit both
		3666	exit_main_loop = exit_nested_loop = 1;
		3667
		3668	=head2 THREAD LOCKING EXAMPLE
		3669
		3670	Here is a fictitious example of how to run an event loop in a different
		3671	thread from where callbacks are being invoked and watchers are
		3672	created/added/removed.
		3673
		3674	For a real-world example, see the C<EV::Loop::Async> perl module,
		3675	which uses exactly this technique (which is suited for many high-level
		3676	languages).
		3677
		3678	The example uses a pthread mutex to protect the loop data, a condition
		3679	variable to wait for callback invocations, an async watcher to notify the
		3680	event loop thread and an unspecified mechanism to wake up the main thread.
		3681
		3682	First, you need to associate some data with the event loop:
		3683
		3684	typedef struct {
		3685	mutex_t lock; /* global loop lock */
		3686	ev_async async_w;
		3687	thread_t tid;
		3688	cond_t invoke_cv;
		3689	} userdata;
		3690
		3691	void prepare_loop (EV_P)
		3692	{
		3693	// for simplicity, we use a static userdata struct.
		3694	static userdata u;
		3695
		3696	ev_async_init (&u->async_w, async_cb);
		3697	ev_async_start (EV_A_ &u->async_w);
		3698
		3699	pthread_mutex_init (&u->lock, 0);
		3700	pthread_cond_init (&u->invoke_cv, 0);
		3701
		3702	// now associate this with the loop
		3703	ev_set_userdata (EV_A_ u);
		3704	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3705	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3706
		3707	// then create the thread running ev_run
		3708	pthread_create (&u->tid, 0, l_run, EV_A);
		3709	}
		3710
		3711	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3712	solely to wake up the event loop so it takes notice of any new watchers
		3713	that might have been added:
		3714
		3715	static void
		3716	async_cb (EV_P_ ev_async *w, int revents)
		3717	{
		3718	// just used for the side effects
		3719	}
		3720
		3721	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3722	protecting the loop data, respectively.
		3723
		3724	static void
		3725	l_release (EV_P)
		3726	{
		3727	userdata *u = ev_userdata (EV_A);
		3728	pthread_mutex_unlock (&u->lock);
		3729	}
		3730
		3731	static void
		3732	l_acquire (EV_P)
		3733	{
		3734	userdata *u = ev_userdata (EV_A);
		3735	pthread_mutex_lock (&u->lock);
		3736	}
		3737
		3738	The event loop thread first acquires the mutex, and then jumps straight
		3739	into C<ev_run>:
		3740
		3741	void *
		3742	l_run (void *thr_arg)
		3743	{
		3744	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3745
		3746	l_acquire (EV_A);
		3747	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3748	ev_run (EV_A_ 0);
		3749	l_release (EV_A);
		3750
		3751	return 0;
		3752	}
		3753
		3754	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3755	signal the main thread via some unspecified mechanism (signals? pipe
		3756	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3757	have been called (in a while loop because a) spurious wakeups are possible
		3758	and b) skipping inter-thread-communication when there are no pending
		3759	watchers is very beneficial):
		3760
		3761	static void
		3762	l_invoke (EV_P)
		3763	{
		3764	userdata *u = ev_userdata (EV_A);
		3765
		3766	while (ev_pending_count (EV_A))
		3767	{
		3768	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3769	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3770	}
		3771	}
		3772
		3773	Now, whenever the main thread gets told to invoke pending watchers, it
		3774	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3775	thread to continue:
		3776
		3777	static void
		3778	real_invoke_pending (EV_P)
		3779	{
		3780	userdata *u = ev_userdata (EV_A);
		3781
		3782	pthread_mutex_lock (&u->lock);
		3783	ev_invoke_pending (EV_A);
		3784	pthread_cond_signal (&u->invoke_cv);
		3785	pthread_mutex_unlock (&u->lock);
		3786	}
		3787
		3788	Whenever you want to start/stop a watcher or do other modifications to an
		3789	event loop, you will now have to lock:
		3790
		3791	ev_timer timeout_watcher;
		3792	userdata *u = ev_userdata (EV_A);
		3793
		3794	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3795
		3796	pthread_mutex_lock (&u->lock);
		3797	ev_timer_start (EV_A_ &timeout_watcher);
		3798	ev_async_send (EV_A_ &u->async_w);
		3799	pthread_mutex_unlock (&u->lock);
		3800
		3801	Note that sending the C<ev_async> watcher is required because otherwise
		3802	an event loop currently blocking in the kernel will have no knowledge
		3803	about the newly added timer. By waking up the loop it will pick up any new
		3804	watchers in the next event loop iteration.
		3805
		3806	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3807
		3808	While the overhead of a callback that e.g. schedules a thread is small, it
		3809	is still an overhead. If you embed libev, and your main usage is with some
		3810	kind of threads or coroutines, you might want to customise libev so that
		3811	doesn't need callbacks anymore.
		3812
		3813	Imagine you have coroutines that you can switch to using a function
		3814	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3815	and that due to some magic, the currently active coroutine is stored in a
		3816	global called C<current_coro>. Then you can build your own "wait for libev
		3817	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3818	the differing C<;> conventions):
		3819
		3820	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3821	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3822
		3823	That means instead of having a C callback function, you store the
		3824	coroutine to switch to in each watcher, and instead of having libev call
		3825	your callback, you instead have it switch to that coroutine.
		3826
		3827	A coroutine might now wait for an event with a function called
		3828	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3829	matter when, or whether the watcher is active or not when this function is
		3830	called):
		3831
		3832	void
		3833	wait_for_event (ev_watcher *w)
		3834	{
		3835	ev_cb_set (w) = current_coro;
		3836	switch_to (libev_coro);
		3837	}
		3838
		3839	That basically suspends the coroutine inside C<wait_for_event> and
		3840	continues the libev coroutine, which, when appropriate, switches back to
		3841	this or any other coroutine.
		3842
		3843	You can do similar tricks if you have, say, threads with an event queue -
		3844	instead of storing a coroutine, you store the queue object and instead of
		3845	switching to a coroutine, you push the watcher onto the queue and notify
		3846	any waiters.
		3847
		3848	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3849	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3850
		3851	// my_ev.h
		3852	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3853	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3854	#include "../libev/ev.h"
		3855
		3856	// my_ev.c
		3857	#define EV_H "my_ev.h"
		3858	#include "../libev/ev.c"
		3859
		3860	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3861	F<my_ev.c> into your project. When properly specifying include paths, you
		3862	can even use F<ev.h> as header file name directly.
1355		3863
1356		3864
1357	=head1 LIBEVENT EMULATION	3865	=head1 LIBEVENT EMULATION
1358		3866
1359	Libev offers a compatibility emulation layer for libevent. It cannot	3867	Libev offers a compatibility emulation layer for libevent. It cannot
1360	emulate the internals of libevent, so here are some usage hints:	3868	emulate the internals of libevent, so here are some usage hints:
1361		3869
1362	=over 4	3870	=over 4
		3871
		3872	=item * Only the libevent-1.4.1-beta API is being emulated.
		3873
		3874	This was the newest libevent version available when libev was implemented,
		3875	and is still mostly unchanged in 2010.
1363		3876
1364	=item * Use it by including <event.h>, as usual.	3877	=item * Use it by including <event.h>, as usual.
1365		3878
1366	=item * The following members are fully supported: ev_base, ev_callback,	3879	=item * The following members are fully supported: ev_base, ev_callback,
1367	ev_arg, ev_fd, ev_res, ev_events.	3880	ev_arg, ev_fd, ev_res, ev_events.
…		…
1372		3885
1373	=item * Priorities are not currently supported. Initialising priorities	3886	=item * Priorities are not currently supported. Initialising priorities
1374	will fail and all watchers will have the same priority, even though there	3887	will fail and all watchers will have the same priority, even though there
1375	is an ev_pri field.	3888	is an ev_pri field.
1376		3889
		3890	=item * In libevent, the last base created gets the signals, in libev, the
		3891	base that registered the signal gets the signals.
		3892
1377	=item * Other members are not supported.	3893	=item * Other members are not supported.
1378		3894
1379	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3895	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1380	to use the libev header file and library.	3896	to use the libev header file and library.
1381		3897
1382	=back	3898	=back
1383		3899
1384	=head1 C++ SUPPORT	3900	=head1 C++ SUPPORT
1385		3901
1386	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3902	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1387	you to use some convinience methods to start/stop watchers and also change	3903	you to use some convenience methods to start/stop watchers and also change
1388	the callback model to a model using method callbacks on objects.	3904	the callback model to a model using method callbacks on objects.
1389		3905
1390	To use it,	3906	To use it,
1391		3907
1392	#include <ev++.h>	3908	#include <ev++.h>
1393		3909
1394	(it is not installed by default). This automatically includes F<ev.h>	3910	This automatically includes F<ev.h> and puts all of its definitions (many
1395	and puts all of its definitions (many of them macros) into the global	3911	of them macros) into the global namespace. All C++ specific things are
1396	namespace. All C++ specific things are put into the C<ev> namespace.	3912	put into the C<ev> namespace. It should support all the same embedding
		3913	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1397		3914
1398	It should support all the same embedding options as F<ev.h>, most notably	3915	Care has been taken to keep the overhead low. The only data member the C++
1399	C<EV_MULTIPLICITY>.	3916	classes add (compared to plain C-style watchers) is the event loop pointer
		3917	that the watcher is associated with (or no additional members at all if
		3918	you disable C<EV_MULTIPLICITY> when embedding libev).
		3919
		3920	Currently, functions, static and non-static member functions and classes
		3921	with C<operator ()> can be used as callbacks. Other types should be easy
		3922	to add as long as they only need one additional pointer for context. If
		3923	you need support for other types of functors please contact the author
		3924	(preferably after implementing it).
		3925
		3926	For all this to work, your C++ compiler either has to use the same calling
		3927	conventions as your C compiler (for static member functions), or you have
		3928	to embed libev and compile libev itself as C++.
1400		3929
1401	Here is a list of things available in the C<ev> namespace:	3930	Here is a list of things available in the C<ev> namespace:
1402		3931
1403	=over 4	3932	=over 4
1404		3933
…		…
1414	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3943	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
1415		3944
1416	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3945	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
1417	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3946	the same name in the C<ev> namespace, with the exception of C<ev_signal>
1418	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3947	which is called C<ev::sig> to avoid clashes with the C<signal> macro
1419	defines by many implementations.	3948	defined by many implementations.
1420		3949
1421	All of those classes have these methods:	3950	All of those classes have these methods:
1422		3951
1423	=over 4	3952	=over 4
1424		3953
1425	=item ev::TYPE::TYPE (object *, object::method *)	3954	=item ev::TYPE::TYPE ()
1426		3955
1427	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3956	=item ev::TYPE::TYPE (loop)
1428		3957
1429	=item ev::TYPE::~TYPE	3958	=item ev::TYPE::~TYPE
1430		3959
1431	The constructor takes a pointer to an object and a method pointer to	3960	The constructor (optionally) takes an event loop to associate the watcher
1432	the event handler callback to call in this class. The constructor calls	3961	with. If it is omitted, it will use C<EV_DEFAULT>.
1433	C<ev_init> for you, which means you have to call the C<set> method	3962
1434	before starting it. If you do not specify a loop then the constructor	3963	The constructor calls C<ev_init> for you, which means you have to call the
1435	automatically associates the default loop with this watcher.	3964	C<set> method before starting it.
		3965
		3966	It will not set a callback, however: You have to call the templated C<set>
		3967	method to set a callback before you can start the watcher.
		3968
		3969	(The reason why you have to use a method is a limitation in C++ which does
		3970	not allow explicit template arguments for constructors).
1436		3971
1437	The destructor automatically stops the watcher if it is active.	3972	The destructor automatically stops the watcher if it is active.
1438		3973
		3974	=item w->set<class, &class::method> (object *)
		3975
		3976	This method sets the callback method to call. The method has to have a
		3977	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3978	first argument and the C<revents> as second. The object must be given as
		3979	parameter and is stored in the C<data> member of the watcher.
		3980
		3981	This method synthesizes efficient thunking code to call your method from
		3982	the C callback that libev requires. If your compiler can inline your
		3983	callback (i.e. it is visible to it at the place of the C<set> call and
		3984	your compiler is good :), then the method will be fully inlined into the
		3985	thunking function, making it as fast as a direct C callback.
		3986
		3987	Example: simple class declaration and watcher initialisation
		3988
		3989	struct myclass
		3990	{
		3991	void io_cb (ev::io &w, int revents) { }
		3992	}
		3993
		3994	myclass obj;
		3995	ev::io iow;
		3996	iow.set <myclass, &myclass::io_cb> (&obj);
		3997
		3998	=item w->set (object *)
		3999
		4000	This is a variation of a method callback - leaving out the method to call
		4001	will default the method to C<operator ()>, which makes it possible to use
		4002	functor objects without having to manually specify the C<operator ()> all
		4003	the time. Incidentally, you can then also leave out the template argument
		4004	list.
		4005
		4006	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4007	int revents)>.
		4008
		4009	See the method-C<set> above for more details.
		4010
		4011	Example: use a functor object as callback.
		4012
		4013	struct myfunctor
		4014	{
		4015	void operator() (ev::io &w, int revents)
		4016	{
		4017	...
		4018	}
		4019	}
		4020
		4021	myfunctor f;
		4022
		4023	ev::io w;
		4024	w.set (&f);
		4025
		4026	=item w->set<function> (void *data = 0)
		4027
		4028	Also sets a callback, but uses a static method or plain function as
		4029	callback. The optional C<data> argument will be stored in the watcher's
		4030	C<data> member and is free for you to use.
		4031
		4032	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4033
		4034	See the method-C<set> above for more details.
		4035
		4036	Example: Use a plain function as callback.
		4037
		4038	static void io_cb (ev::io &w, int revents) { }
		4039	iow.set <io_cb> ();
		4040
1439	=item w->set (struct ev_loop *)	4041	=item w->set (loop)
1440		4042
1441	Associates a different C<struct ev_loop> with this watcher. You can only	4043	Associates a different C<struct ev_loop> with this watcher. You can only
1442	do this when the watcher is inactive (and not pending either).	4044	do this when the watcher is inactive (and not pending either).
1443		4045
1444	=item w->set ([args])	4046	=item w->set ([arguments])
1445		4047
1446	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4048	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
1447	called at least once. Unlike the C counterpart, an active watcher gets	4049	method or a suitable start method must be called at least once. Unlike the
1448	automatically stopped and restarted.	4050	C counterpart, an active watcher gets automatically stopped and restarted
		4051	when reconfiguring it with this method.
1449		4052
1450	=item w->start ()	4053	=item w->start ()
1451		4054
1452	Starts the watcher. Note that there is no C<loop> argument as the	4055	Starts the watcher. Note that there is no C<loop> argument, as the
1453	constructor already takes the loop.	4056	constructor already stores the event loop.
		4057
		4058	=item w->start ([arguments])
		4059
		4060	Instead of calling C<set> and C<start> methods separately, it is often
		4061	convenient to wrap them in one call. Uses the same type of arguments as
		4062	the configure C<set> method of the watcher.
1454		4063
1455	=item w->stop ()	4064	=item w->stop ()
1456		4065
1457	Stops the watcher if it is active. Again, no C<loop> argument.	4066	Stops the watcher if it is active. Again, no C<loop> argument.
1458		4067
1459	=item w->again () C<ev::timer>, C<ev::periodic> only	4068	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1460		4069
1461	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	4070	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1462	C<ev_TYPE_again> function.	4071	C<ev_TYPE_again> function.
1463		4072
1464	=item w->sweep () C<ev::embed> only	4073	=item w->sweep () (C<ev::embed> only)
1465		4074
1466	Invokes C<ev_embed_sweep>.	4075	Invokes C<ev_embed_sweep>.
1467		4076
		4077	=item w->update () (C<ev::stat> only)
		4078
		4079	Invokes C<ev_stat_stat>.
		4080
1468	=back	4081	=back
1469		4082
1470	=back	4083	=back
1471		4084
1472	Example: Define a class with an IO and idle watcher, start one of them in	4085	Example: Define a class with two I/O and idle watchers, start the I/O
1473	the constructor.	4086	watchers in the constructor.
1474		4087
1475	class myclass	4088	class myclass
1476	{	4089	{
1477	ev_io io; void io_cb (ev::io &w, int revents);	4090	ev::io io ; void io_cb (ev::io &w, int revents);
		4091	ev::io io2 ; void io2_cb (ev::io &w, int revents);
1478	ev_idle idle void idle_cb (ev::idle &w, int revents);	4092	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1479		4093
1480	myclass ();	4094	myclass (int fd)
		4095	{
		4096	io .set <myclass, &myclass::io_cb > (this);
		4097	io2 .set <myclass, &myclass::io2_cb > (this);
		4098	idle.set <myclass, &myclass::idle_cb> (this);
		4099
		4100	io.set (fd, ev::WRITE); // configure the watcher
		4101	io.start (); // start it whenever convenient
		4102
		4103	io2.start (fd, ev::READ); // set + start in one call
		4104	}
1481	}	4105	};
1482		4106
1483	myclass::myclass (int fd)	4107
1484	: io (this, &myclass::io_cb),	4108	=head1 OTHER LANGUAGE BINDINGS
1485	idle (this, &myclass::idle_cb)	4109
		4110	Libev does not offer other language bindings itself, but bindings for a
		4111	number of languages exist in the form of third-party packages. If you know
		4112	any interesting language binding in addition to the ones listed here, drop
		4113	me a note.
		4114
		4115	=over 4
		4116
		4117	=item Perl
		4118
		4119	The EV module implements the full libev API and is actually used to test
		4120	libev. EV is developed together with libev. Apart from the EV core module,
		4121	there are additional modules that implement libev-compatible interfaces
		4122	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4123	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4124	and C<EV::Glib>).
		4125
		4126	It can be found and installed via CPAN, its homepage is at
		4127	L<http://software.schmorp.de/pkg/EV>.
		4128
		4129	=item Python
		4130
		4131	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4132	seems to be quite complete and well-documented.
		4133
		4134	=item Ruby
		4135
		4136	Tony Arcieri has written a ruby extension that offers access to a subset
		4137	of the libev API and adds file handle abstractions, asynchronous DNS and
		4138	more on top of it. It can be found via gem servers. Its homepage is at
		4139	L<http://rev.rubyforge.org/>.
		4140
		4141	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4142	makes rev work even on mingw.
		4143
		4144	=item Haskell
		4145
		4146	A haskell binding to libev is available at
		4147	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4148
		4149	=item D
		4150
		4151	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4152	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4153
		4154	=item Ocaml
		4155
		4156	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4157	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4158
		4159	=item Lua
		4160
		4161	Brian Maher has written a partial interface to libev for lua (at the
		4162	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4163	L<http://github.com/brimworks/lua-ev>.
		4164
		4165	=back
		4166
		4167
		4168	=head1 MACRO MAGIC
		4169
		4170	Libev can be compiled with a variety of options, the most fundamental
		4171	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4172	functions and callbacks have an initial C<struct ev_loop *> argument.
		4173
		4174	To make it easier to write programs that cope with either variant, the
		4175	following macros are defined:
		4176
		4177	=over 4
		4178
		4179	=item C<EV_A>, C<EV_A_>
		4180
		4181	This provides the loop I<argument> for functions, if one is required ("ev
		4182	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4183	C<EV_A_> is used when other arguments are following. Example:
		4184
		4185	ev_unref (EV_A);
		4186	ev_timer_add (EV_A_ watcher);
		4187	ev_run (EV_A_ 0);
		4188
		4189	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4190	which is often provided by the following macro.
		4191
		4192	=item C<EV_P>, C<EV_P_>
		4193
		4194	This provides the loop I<parameter> for functions, if one is required ("ev
		4195	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4196	C<EV_P_> is used when other parameters are following. Example:
		4197
		4198	// this is how ev_unref is being declared
		4199	static void ev_unref (EV_P);
		4200
		4201	// this is how you can declare your typical callback
		4202	static void cb (EV_P_ ev_timer *w, int revents)
		4203
		4204	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4205	suitable for use with C<EV_A>.
		4206
		4207	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4208
		4209	Similar to the other two macros, this gives you the value of the default
		4210	loop, if multiple loops are supported ("ev loop default"). The default loop
		4211	will be initialised if it isn't already initialised.
		4212
		4213	For non-multiplicity builds, these macros do nothing, so you always have
		4214	to initialise the loop somewhere.
		4215
		4216	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4217
		4218	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4219	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4220	is undefined when the default loop has not been initialised by a previous
		4221	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4222
		4223	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4224	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4225
		4226	=back
		4227
		4228	Example: Declare and initialise a check watcher, utilising the above
		4229	macros so it will work regardless of whether multiple loops are supported
		4230	or not.
		4231
		4232	static void
		4233	check_cb (EV_P_ ev_timer *w, int revents)
1486	{	4234	{
1487	io.start (fd, ev::READ);	4235	ev_check_stop (EV_A_ w);
1488	}	4236	}
		4237
		4238	ev_check check;
		4239	ev_check_init (&check, check_cb);
		4240	ev_check_start (EV_DEFAULT_ &check);
		4241	ev_run (EV_DEFAULT_ 0);
1489		4242
1490	=head1 EMBEDDING	4243	=head1 EMBEDDING
1491		4244
1492	Libev can (and often is) directly embedded into host	4245	Libev can (and often is) directly embedded into host
1493	applications. Examples of applications that embed it include the Deliantra	4246	applications. Examples of applications that embed it include the Deliantra
1494	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4247	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1495	and rxvt-unicode.	4248	and rxvt-unicode.
1496		4249
1497	The goal is to enable you to just copy the neecssary files into your	4250	The goal is to enable you to just copy the necessary files into your
1498	source directory without having to change even a single line in them, so	4251	source directory without having to change even a single line in them, so
1499	you can easily upgrade by simply copying (or having a checked-out copy of	4252	you can easily upgrade by simply copying (or having a checked-out copy of
1500	libev somewhere in your source tree).	4253	libev somewhere in your source tree).
1501		4254
1502	=head2 FILESETS	4255	=head2 FILESETS
1503		4256
1504	Depending on what features you need you need to include one or more sets of files	4257	Depending on what features you need you need to include one or more sets of files
1505	in your app.	4258	in your application.
1506		4259
1507	=head3 CORE EVENT LOOP	4260	=head3 CORE EVENT LOOP
1508		4261
1509	To include only the libev core (all the C<ev_*> functions), with manual	4262	To include only the libev core (all the C<ev_*> functions), with manual
1510	configuration (no autoconf):	4263	configuration (no autoconf):
1511		4264
1512	#define EV_STANDALONE 1	4265	#define EV_STANDALONE 1
1513	#include "ev.c"	4266	#include "ev.c"
1514		4267
1515	This will automatically include F<ev.h>, too, and should be done in a	4268	This will automatically include F<ev.h>, too, and should be done in a
1516	single C source file only to provide the function implementations. To use	4269	single C source file only to provide the function implementations. To use
1517	it, do the same for F<ev.h> in all files wishing to use this API (best	4270	it, do the same for F<ev.h> in all files wishing to use this API (best
1518	done by writing a wrapper around F<ev.h> that you can include instead and	4271	done by writing a wrapper around F<ev.h> that you can include instead and
1519	where you can put other configuration options):	4272	where you can put other configuration options):
1520		4273
1521	#define EV_STANDALONE 1	4274	#define EV_STANDALONE 1
1522	#include "ev.h"	4275	#include "ev.h"
1523		4276
1524	Both header files and implementation files can be compiled with a C++	4277	Both header files and implementation files can be compiled with a C++
1525	compiler (at least, thats a stated goal, and breakage will be treated	4278	compiler (at least, that's a stated goal, and breakage will be treated
1526	as a bug).	4279	as a bug).
1527		4280
1528	You need the following files in your source tree, or in a directory	4281	You need the following files in your source tree, or in a directory
1529	in your include path (e.g. in libev/ when using -Ilibev):	4282	in your include path (e.g. in libev/ when using -Ilibev):
1530		4283
1531	ev.h	4284	ev.h
1532	ev.c	4285	ev.c
1533	ev_vars.h	4286	ev_vars.h
1534	ev_wrap.h	4287	ev_wrap.h
1535		4288
1536	ev_win32.c required on win32 platforms only	4289	ev_win32.c required on win32 platforms only
1537		4290
1538	ev_select.c only when select backend is enabled (which is by default)	4291	ev_select.c only when select backend is enabled (which is enabled by default)
1539	ev_poll.c only when poll backend is enabled (disabled by default)	4292	ev_poll.c only when poll backend is enabled (disabled by default)
1540	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4293	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1541	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4294	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1542	ev_port.c only when the solaris port backend is enabled (disabled by default)	4295	ev_port.c only when the solaris port backend is enabled (disabled by default)
1543		4296
1544	F<ev.c> includes the backend files directly when enabled, so you only need	4297	F<ev.c> includes the backend files directly when enabled, so you only need
1545	to compile this single file.	4298	to compile this single file.
1546		4299
1547	=head3 LIBEVENT COMPATIBILITY API	4300	=head3 LIBEVENT COMPATIBILITY API
1548		4301
1549	To include the libevent compatibility API, also include:	4302	To include the libevent compatibility API, also include:
1550		4303
1551	#include "event.c"	4304	#include "event.c"
1552		4305
1553	in the file including F<ev.c>, and:	4306	in the file including F<ev.c>, and:
1554		4307
1555	#include "event.h"	4308	#include "event.h"
1556		4309
1557	in the files that want to use the libevent API. This also includes F<ev.h>.	4310	in the files that want to use the libevent API. This also includes F<ev.h>.
1558		4311
1559	You need the following additional files for this:	4312	You need the following additional files for this:
1560		4313
1561	event.h	4314	event.h
1562	event.c	4315	event.c
1563		4316
1564	=head3 AUTOCONF SUPPORT	4317	=head3 AUTOCONF SUPPORT
1565		4318
1566	Instead of using C<EV_STANDALONE=1> and providing your config in	4319	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1567	whatever way you want, you can also C<m4_include([libev.m4])> in your	4320	whatever way you want, you can also C<m4_include([libev.m4])> in your
1568	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4321	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1569	include F<config.h> and configure itself accordingly.	4322	include F<config.h> and configure itself accordingly.
1570		4323
1571	For this of course you need the m4 file:	4324	For this of course you need the m4 file:
1572		4325
1573	libev.m4	4326	libev.m4
1574		4327
1575	=head2 PREPROCESSOR SYMBOLS/MACROS	4328	=head2 PREPROCESSOR SYMBOLS/MACROS
1576		4329
1577	Libev can be configured via a variety of preprocessor symbols you have to define	4330	Libev can be configured via a variety of preprocessor symbols you have to
1578	before including any of its files. The default is not to build for multiplicity	4331	define before including (or compiling) any of its files. The default in
1579	and only include the select backend.	4332	the absence of autoconf is documented for every option.
		4333
		4334	Symbols marked with "(h)" do not change the ABI, and can have different
		4335	values when compiling libev vs. including F<ev.h>, so it is permissible
		4336	to redefine them before including F<ev.h> without breaking compatibility
		4337	to a compiled library. All other symbols change the ABI, which means all
		4338	users of libev and the libev code itself must be compiled with compatible
		4339	settings.
1580		4340
1581	=over 4	4341	=over 4
1582		4342
		4343	=item EV_COMPAT3 (h)
		4344
		4345	Backwards compatibility is a major concern for libev. This is why this
		4346	release of libev comes with wrappers for the functions and symbols that
		4347	have been renamed between libev version 3 and 4.
		4348
		4349	You can disable these wrappers (to test compatibility with future
		4350	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4351	sources. This has the additional advantage that you can drop the C<struct>
		4352	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4353	typedef in that case.
		4354
		4355	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4356	and in some even more future version the compatibility code will be
		4357	removed completely.
		4358
1583	=item EV_STANDALONE	4359	=item EV_STANDALONE (h)
1584		4360
1585	Must always be C<1> if you do not use autoconf configuration, which	4361	Must always be C<1> if you do not use autoconf configuration, which
1586	keeps libev from including F<config.h>, and it also defines dummy	4362	keeps libev from including F<config.h>, and it also defines dummy
1587	implementations for some libevent functions (such as logging, which is not	4363	implementations for some libevent functions (such as logging, which is not
1588	supported). It will also not define any of the structs usually found in	4364	supported). It will also not define any of the structs usually found in
1589	F<event.h> that are not directly supported by the libev core alone.	4365	F<event.h> that are not directly supported by the libev core alone.
1590		4366
		4367	In standalone mode, libev will still try to automatically deduce the
		4368	configuration, but has to be more conservative.
		4369
		4370	=item EV_USE_FLOOR
		4371
		4372	If defined to be C<1>, libev will use the C<floor ()> function for its
		4373	periodic reschedule calculations, otherwise libev will fall back on a
		4374	portable (slower) implementation. If you enable this, you usually have to
		4375	link against libm or something equivalent. Enabling this when the C<floor>
		4376	function is not available will fail, so the safe default is to not enable
		4377	this.
		4378
1591	=item EV_USE_MONOTONIC	4379	=item EV_USE_MONOTONIC
1592		4380
1593	If defined to be C<1>, libev will try to detect the availability of the	4381	If defined to be C<1>, libev will try to detect the availability of the
1594	monotonic clock option at both compiletime and runtime. Otherwise no use	4382	monotonic clock option at both compile time and runtime. Otherwise no
1595	of the monotonic clock option will be attempted. If you enable this, you	4383	use of the monotonic clock option will be attempted. If you enable this,
1596	usually have to link against librt or something similar. Enabling it when	4384	you usually have to link against librt or something similar. Enabling it
1597	the functionality isn't available is safe, though, althoguh you have	4385	when the functionality isn't available is safe, though, although you have
1598	to make sure you link against any libraries where the C<clock_gettime>	4386	to make sure you link against any libraries where the C<clock_gettime>
1599	function is hiding in (often F<-lrt>).	4387	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1600		4388
1601	=item EV_USE_REALTIME	4389	=item EV_USE_REALTIME
1602		4390
1603	If defined to be C<1>, libev will try to detect the availability of the	4391	If defined to be C<1>, libev will try to detect the availability of the
1604	realtime clock option at compiletime (and assume its availability at	4392	real-time clock option at compile time (and assume its availability
1605	runtime if successful). Otherwise no use of the realtime clock option will	4393	at runtime if successful). Otherwise no use of the real-time clock
1606	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4394	option will be attempted. This effectively replaces C<gettimeofday>
1607	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4395	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1608	in the description of C<EV_USE_MONOTONIC>, though.	4396	correctness. See the note about libraries in the description of
		4397	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4398	C<EV_USE_CLOCK_SYSCALL>.
		4399
		4400	=item EV_USE_CLOCK_SYSCALL
		4401
		4402	If defined to be C<1>, libev will try to use a direct syscall instead
		4403	of calling the system-provided C<clock_gettime> function. This option
		4404	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4405	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4406	programs needlessly. Using a direct syscall is slightly slower (in
		4407	theory), because no optimised vdso implementation can be used, but avoids
		4408	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4409	higher, as it simplifies linking (no need for C<-lrt>).
		4410
		4411	=item EV_USE_NANOSLEEP
		4412
		4413	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4414	and will use it for delays. Otherwise it will use C<select ()>.
		4415
		4416	=item EV_USE_EVENTFD
		4417
		4418	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4419	available and will probe for kernel support at runtime. This will improve
		4420	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4421	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4422	2.7 or newer, otherwise disabled.
1609		4423
1610	=item EV_USE_SELECT	4424	=item EV_USE_SELECT
1611		4425
1612	If undefined or defined to be C<1>, libev will compile in support for the	4426	If undefined or defined to be C<1>, libev will compile in support for the
1613	C<select>(2) backend. No attempt at autodetection will be done: if no	4427	C<select>(2) backend. No attempt at auto-detection will be done: if no
1614	other method takes over, select will be it. Otherwise the select backend	4428	other method takes over, select will be it. Otherwise the select backend
1615	will not be compiled in.	4429	will not be compiled in.
1616		4430
1617	=item EV_SELECT_USE_FD_SET	4431	=item EV_SELECT_USE_FD_SET
1618		4432
1619	If defined to C<1>, then the select backend will use the system C<fd_set>	4433	If defined to C<1>, then the select backend will use the system C<fd_set>
1620	structure. This is useful if libev doesn't compile due to a missing	4434	structure. This is useful if libev doesn't compile due to a missing
1621	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4435	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1622	exotic systems. This usually limits the range of file descriptors to some	4436	on exotic systems. This usually limits the range of file descriptors to
1623	low limit such as 1024 or might have other limitations (winsocket only	4437	some low limit such as 1024 or might have other limitations (winsocket
1624	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4438	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1625	influence the size of the C<fd_set> used.	4439	configures the maximum size of the C<fd_set>.
1626		4440
1627	=item EV_SELECT_IS_WINSOCKET	4441	=item EV_SELECT_IS_WINSOCKET
1628		4442
1629	When defined to C<1>, the select backend will assume that	4443	When defined to C<1>, the select backend will assume that
1630	select/socket/connect etc. don't understand file descriptors but	4444	select/socket/connect etc. don't understand file descriptors but
…		…
1632	be used is the winsock select). This means that it will call	4446	be used is the winsock select). This means that it will call
1633	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4447	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1634	it is assumed that all these functions actually work on fds, even	4448	it is assumed that all these functions actually work on fds, even
1635	on win32. Should not be defined on non-win32 platforms.	4449	on win32. Should not be defined on non-win32 platforms.
1636		4450
		4451	=item EV_FD_TO_WIN32_HANDLE(fd)
		4452
		4453	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4454	file descriptors to socket handles. When not defining this symbol (the
		4455	default), then libev will call C<_get_osfhandle>, which is usually
		4456	correct. In some cases, programs use their own file descriptor management,
		4457	in which case they can provide this function to map fds to socket handles.
		4458
		4459	=item EV_WIN32_HANDLE_TO_FD(handle)
		4460
		4461	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4462	using the standard C<_open_osfhandle> function. For programs implementing
		4463	their own fd to handle mapping, overwriting this function makes it easier
		4464	to do so. This can be done by defining this macro to an appropriate value.
		4465
		4466	=item EV_WIN32_CLOSE_FD(fd)
		4467
		4468	If programs implement their own fd to handle mapping on win32, then this
		4469	macro can be used to override the C<close> function, useful to unregister
		4470	file descriptors again. Note that the replacement function has to close
		4471	the underlying OS handle.
		4472
1637	=item EV_USE_POLL	4473	=item EV_USE_POLL
1638		4474
1639	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4475	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1640	backend. Otherwise it will be enabled on non-win32 platforms. It	4476	backend. Otherwise it will be enabled on non-win32 platforms. It
1641	takes precedence over select.	4477	takes precedence over select.
1642		4478
1643	=item EV_USE_EPOLL	4479	=item EV_USE_EPOLL
1644		4480
1645	If defined to be C<1>, libev will compile in support for the Linux	4481	If defined to be C<1>, libev will compile in support for the Linux
1646	C<epoll>(7) backend. Its availability will be detected at runtime,	4482	C<epoll>(7) backend. Its availability will be detected at runtime,
1647	otherwise another method will be used as fallback. This is the	4483	otherwise another method will be used as fallback. This is the preferred
1648	preferred backend for GNU/Linux systems.	4484	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4485	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1649		4486
1650	=item EV_USE_KQUEUE	4487	=item EV_USE_KQUEUE
1651		4488
1652	If defined to be C<1>, libev will compile in support for the BSD style	4489	If defined to be C<1>, libev will compile in support for the BSD style
1653	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4490	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
1666	otherwise another method will be used as fallback. This is the preferred	4503	otherwise another method will be used as fallback. This is the preferred
1667	backend for Solaris 10 systems.	4504	backend for Solaris 10 systems.
1668		4505
1669	=item EV_USE_DEVPOLL	4506	=item EV_USE_DEVPOLL
1670		4507
1671	reserved for future expansion, works like the USE symbols above.	4508	Reserved for future expansion, works like the USE symbols above.
1672		4509
		4510	=item EV_USE_INOTIFY
		4511
		4512	If defined to be C<1>, libev will compile in support for the Linux inotify
		4513	interface to speed up C<ev_stat> watchers. Its actual availability will
		4514	be detected at runtime. If undefined, it will be enabled if the headers
		4515	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4516
		4517	=item EV_NO_SMP
		4518
		4519	If defined to be C<1>, libev will assume that memory is always coherent
		4520	between threads, that is, threads can be used, but threads never run on
		4521	different cpus (or different cpu cores). This reduces dependencies
		4522	and makes libev faster.
		4523
		4524	=item EV_NO_THREADS
		4525
		4526	If defined to be C<1>, libev will assume that it will never be called
		4527	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4528	above. This reduces dependencies and makes libev faster.
		4529
		4530	=item EV_ATOMIC_T
		4531
		4532	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4533	access is atomic and serialised with respect to other threads or signal
		4534	contexts. No such type is easily found in the C language, so you can
		4535	provide your own type that you know is safe for your purposes. It is used
		4536	both for signal handler "locking" as well as for signal and thread safety
		4537	in C<ev_async> watchers.
		4538
		4539	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4540	(from F<signal.h>), which is usually good enough on most platforms,
		4541	although strictly speaking using a type that also implies a memory fence
		4542	is required.
		4543
1673	=item EV_H	4544	=item EV_H (h)
1674		4545
1675	The name of the F<ev.h> header file used to include it. The default if	4546	The name of the F<ev.h> header file used to include it. The default if
1676	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4547	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1677	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4548	used to virtually rename the F<ev.h> header file in case of conflicts.
1678		4549
1679	=item EV_CONFIG_H	4550	=item EV_CONFIG_H (h)
1680		4551
1681	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4552	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1682	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4553	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1683	C<EV_H>, above.	4554	C<EV_H>, above.
1684		4555
1685	=item EV_EVENT_H	4556	=item EV_EVENT_H (h)
1686		4557
1687	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4558	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
1688	of how the F<event.h> header can be found.	4559	of how the F<event.h> header can be found, the default is C<"event.h">.
1689		4560
1690	=item EV_PROTOTYPES	4561	=item EV_PROTOTYPES (h)
1691		4562
1692	If defined to be C<0>, then F<ev.h> will not define any function	4563	If defined to be C<0>, then F<ev.h> will not define any function
1693	prototypes, but still define all the structs and other symbols. This is	4564	prototypes, but still define all the structs and other symbols. This is
1694	occasionally useful if you want to provide your own wrapper functions	4565	occasionally useful if you want to provide your own wrapper functions
1695	around libev functions.	4566	around libev functions.
…		…
1700	will have the C<struct ev_loop *> as first argument, and you can create	4571	will have the C<struct ev_loop *> as first argument, and you can create
1701	additional independent event loops. Otherwise there will be no support	4572	additional independent event loops. Otherwise there will be no support
1702	for multiple event loops and there is no first event loop pointer	4573	for multiple event loops and there is no first event loop pointer
1703	argument. Instead, all functions act on the single default loop.	4574	argument. Instead, all functions act on the single default loop.
1704		4575
1705	=item EV_PERIODIC_ENABLE	4576	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4577	default loop when multiplicity is switched off - you always have to
		4578	initialise the loop manually in this case.
1706		4579
1707	If undefined or defined to be C<1>, then periodic timers are supported. If
1708	defined to be C<0>, then they are not. Disabling them saves a few kB of
1709	code.
1710
1711	=item EV_EMBED_ENABLE
1712
1713	If undefined or defined to be C<1>, then embed watchers are supported. If
1714	defined to be C<0>, then they are not.
1715
1716	=item EV_STAT_ENABLE
1717
1718	If undefined or defined to be C<1>, then stat watchers are supported. If
1719	defined to be C<0>, then they are not.
1720
1721	=item EV_MINIMAL	4580	=item EV_MINPRI
		4581
		4582	=item EV_MAXPRI
		4583
		4584	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4585	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4586	provide for more priorities by overriding those symbols (usually defined
		4587	to be C<-2> and C<2>, respectively).
		4588
		4589	When doing priority-based operations, libev usually has to linearly search
		4590	all the priorities, so having many of them (hundreds) uses a lot of space
		4591	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4592	fine.
		4593
		4594	If your embedding application does not need any priorities, defining these
		4595	both to C<0> will save some memory and CPU.
		4596
		4597	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4598	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4599	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4600
		4601	If undefined or defined to be C<1> (and the platform supports it), then
		4602	the respective watcher type is supported. If defined to be C<0>, then it
		4603	is not. Disabling watcher types mainly saves code size.
		4604
		4605	=item EV_FEATURES
1722		4606
1723	If you need to shave off some kilobytes of code at the expense of some	4607	If you need to shave off some kilobytes of code at the expense of some
1724	speed, define this symbol to C<1>. Currently only used for gcc to override	4608	speed (but with the full API), you can define this symbol to request
1725	some inlining decisions, saves roughly 30% codesize of amd64.	4609	certain subsets of functionality. The default is to enable all features
		4610	that can be enabled on the platform.
		4611
		4612	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4613	with some broad features you want) and then selectively re-enable
		4614	additional parts you want, for example if you want everything minimal,
		4615	but multiple event loop support, async and child watchers and the poll
		4616	backend, use this:
		4617
		4618	#define EV_FEATURES 0
		4619	#define EV_MULTIPLICITY 1
		4620	#define EV_USE_POLL 1
		4621	#define EV_CHILD_ENABLE 1
		4622	#define EV_ASYNC_ENABLE 1
		4623
		4624	The actual value is a bitset, it can be a combination of the following
		4625	values:
		4626
		4627	=over 4
		4628
		4629	=item C<1> - faster/larger code
		4630
		4631	Use larger code to speed up some operations.
		4632
		4633	Currently this is used to override some inlining decisions (enlarging the
		4634	code size by roughly 30% on amd64).
		4635
		4636	When optimising for size, use of compiler flags such as C<-Os> with
		4637	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4638	assertions.
		4639
		4640	=item C<2> - faster/larger data structures
		4641
		4642	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4643	hash table sizes and so on. This will usually further increase code size
		4644	and can additionally have an effect on the size of data structures at
		4645	runtime.
		4646
		4647	=item C<4> - full API configuration
		4648
		4649	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4650	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4651
		4652	=item C<8> - full API
		4653
		4654	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4655	details on which parts of the API are still available without this
		4656	feature, and do not complain if this subset changes over time.
		4657
		4658	=item C<16> - enable all optional watcher types
		4659
		4660	Enables all optional watcher types. If you want to selectively enable
		4661	only some watcher types other than I/O and timers (e.g. prepare,
		4662	embed, async, child...) you can enable them manually by defining
		4663	C<EV_watchertype_ENABLE> to C<1> instead.
		4664
		4665	=item C<32> - enable all backends
		4666
		4667	This enables all backends - without this feature, you need to enable at
		4668	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4669
		4670	=item C<64> - enable OS-specific "helper" APIs
		4671
		4672	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4673	default.
		4674
		4675	=back
		4676
		4677	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4678	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4679	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4680	watchers, timers and monotonic clock support.
		4681
		4682	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4683	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4684	your program might be left out as well - a binary starting a timer and an
		4685	I/O watcher then might come out at only 5Kb.
		4686
		4687	=item EV_API_STATIC
		4688
		4689	If this symbol is defined (by default it is not), then all identifiers
		4690	will have static linkage. This means that libev will not export any
		4691	identifiers, and you cannot link against libev anymore. This can be useful
		4692	when you embed libev, only want to use libev functions in a single file,
		4693	and do not want its identifiers to be visible.
		4694
		4695	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4696	wants to use libev.
		4697
		4698	This option only works when libev is compiled with a C compiler, as C++
		4699	doesn't support the required declaration syntax.
		4700
		4701	=item EV_AVOID_STDIO
		4702
		4703	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4704	functions (printf, scanf, perror etc.). This will increase the code size
		4705	somewhat, but if your program doesn't otherwise depend on stdio and your
		4706	libc allows it, this avoids linking in the stdio library which is quite
		4707	big.
		4708
		4709	Note that error messages might become less precise when this option is
		4710	enabled.
		4711
		4712	=item EV_NSIG
		4713
		4714	The highest supported signal number, +1 (or, the number of
		4715	signals): Normally, libev tries to deduce the maximum number of signals
		4716	automatically, but sometimes this fails, in which case it can be
		4717	specified. Also, using a lower number than detected (C<32> should be
		4718	good for about any system in existence) can save some memory, as libev
		4719	statically allocates some 12-24 bytes per signal number.
		4720
		4721	=item EV_PID_HASHSIZE
		4722
		4723	C<ev_child> watchers use a small hash table to distribute workload by
		4724	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4725	usually more than enough. If you need to manage thousands of children you
		4726	might want to increase this value (I<must> be a power of two).
		4727
		4728	=item EV_INOTIFY_HASHSIZE
		4729
		4730	C<ev_stat> watchers use a small hash table to distribute workload by
		4731	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4732	disabled), usually more than enough. If you need to manage thousands of
		4733	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4734	power of two).
		4735
		4736	=item EV_USE_4HEAP
		4737
		4738	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4739	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4740	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4741	faster performance with many (thousands) of watchers.
		4742
		4743	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4744	will be C<0>.
		4745
		4746	=item EV_HEAP_CACHE_AT
		4747
		4748	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4749	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4750	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4751	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4752	but avoids random read accesses on heap changes. This improves performance
		4753	noticeably with many (hundreds) of watchers.
		4754
		4755	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4756	will be C<0>.
		4757
		4758	=item EV_VERIFY
		4759
		4760	Controls how much internal verification (see C<ev_verify ()>) will
		4761	be done: If set to C<0>, no internal verification code will be compiled
		4762	in. If set to C<1>, then verification code will be compiled in, but not
		4763	called. If set to C<2>, then the internal verification code will be
		4764	called once per loop, which can slow down libev. If set to C<3>, then the
		4765	verification code will be called very frequently, which will slow down
		4766	libev considerably.
		4767
		4768	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4769	will be C<0>.
1726		4770
1727	=item EV_COMMON	4771	=item EV_COMMON
1728		4772
1729	By default, all watchers have a C<void *data> member. By redefining	4773	By default, all watchers have a C<void *data> member. By redefining
1730	this macro to a something else you can include more and other types of	4774	this macro to something else you can include more and other types of
1731	members. You have to define it each time you include one of the files,	4775	members. You have to define it each time you include one of the files,
1732	though, and it must be identical each time.	4776	though, and it must be identical each time.
1733		4777
1734	For example, the perl EV module uses something like this:	4778	For example, the perl EV module uses something like this:
1735		4779
1736	#define EV_COMMON \	4780	#define EV_COMMON \
1737	SV *self; /* contains this struct */ \	4781	SV *self; /* contains this struct */ \
1738	SV *cb_sv, *fh /* note no trailing ";" */	4782	SV *cb_sv, *fh /* note no trailing ";" */
1739		4783
1740	=item EV_CB_DECLARE (type)	4784	=item EV_CB_DECLARE (type)
1741		4785
1742	=item EV_CB_INVOKE (watcher, revents)	4786	=item EV_CB_INVOKE (watcher, revents)
1743		4787
1744	=item ev_set_cb (ev, cb)	4788	=item ev_set_cb (ev, cb)
1745		4789
1746	Can be used to change the callback member declaration in each watcher,	4790	Can be used to change the callback member declaration in each watcher,
1747	and the way callbacks are invoked and set. Must expand to a struct member	4791	and the way callbacks are invoked and set. Must expand to a struct member
1748	definition and a statement, respectively. See the F<ev.v> header file for	4792	definition and a statement, respectively. See the F<ev.h> header file for
1749	their default definitions. One possible use for overriding these is to	4793	their default definitions. One possible use for overriding these is to
1750	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4794	avoid the C<struct ev_loop *> as first argument in all cases, or to use
1751	method calls instead of plain function calls in C++.	4795	method calls instead of plain function calls in C++.
		4796
		4797	=back
		4798
		4799	=head2 EXPORTED API SYMBOLS
		4800
		4801	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4802	exported symbols, you can use the provided F<Symbol.*> files which list
		4803	all public symbols, one per line:
		4804
		4805	Symbols.ev for libev proper
		4806	Symbols.event for the libevent emulation
		4807
		4808	This can also be used to rename all public symbols to avoid clashes with
		4809	multiple versions of libev linked together (which is obviously bad in
		4810	itself, but sometimes it is inconvenient to avoid this).
		4811
		4812	A sed command like this will create wrapper C<#define>'s that you need to
		4813	include before including F<ev.h>:
		4814
		4815	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4816
		4817	This would create a file F<wrap.h> which essentially looks like this:
		4818
		4819	#define ev_backend myprefix_ev_backend
		4820	#define ev_check_start myprefix_ev_check_start
		4821	#define ev_check_stop myprefix_ev_check_stop
		4822	...
1752		4823
1753	=head2 EXAMPLES	4824	=head2 EXAMPLES
1754		4825
1755	For a real-world example of a program the includes libev	4826	For a real-world example of a program the includes libev
1756	verbatim, you can have a look at the EV perl module	4827	verbatim, you can have a look at the EV perl module
…		…
1759	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	4830	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
1760	will be compiled. It is pretty complex because it provides its own header	4831	will be compiled. It is pretty complex because it provides its own header
1761	file.	4832	file.
1762		4833
1763	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4834	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
1764	that everybody includes and which overrides some autoconf choices:	4835	that everybody includes and which overrides some configure choices:
1765		4836
		4837	#define EV_FEATURES 8
		4838	#define EV_USE_SELECT 1
		4839	#define EV_PREPARE_ENABLE 1
		4840	#define EV_IDLE_ENABLE 1
		4841	#define EV_SIGNAL_ENABLE 1
		4842	#define EV_CHILD_ENABLE 1
1766	#define EV_USE_POLL 0	4843	#define EV_USE_STDEXCEPT 0
1767	#define EV_MULTIPLICITY 0
1768	#define EV_PERIODICS 0
1769	#define EV_CONFIG_H <config.h>	4844	#define EV_CONFIG_H <config.h>
1770		4845
1771	#include "ev++.h"	4846	#include "ev++.h"
1772		4847
1773	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4848	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
1774		4849
1775	#include "ev_cpp.h"	4850	#include "ev_cpp.h"
1776	#include "ev.c"	4851	#include "ev.c"
1777		4852
		4853	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
1778		4854
		4855	=head2 THREADS AND COROUTINES
		4856
		4857	=head3 THREADS
		4858
		4859	All libev functions are reentrant and thread-safe unless explicitly
		4860	documented otherwise, but libev implements no locking itself. This means
		4861	that you can use as many loops as you want in parallel, as long as there
		4862	are no concurrent calls into any libev function with the same loop
		4863	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4864	of course): libev guarantees that different event loops share no data
		4865	structures that need any locking.
		4866
		4867	Or to put it differently: calls with different loop parameters can be done
		4868	concurrently from multiple threads, calls with the same loop parameter
		4869	must be done serially (but can be done from different threads, as long as
		4870	only one thread ever is inside a call at any point in time, e.g. by using
		4871	a mutex per loop).
		4872
		4873	Specifically to support threads (and signal handlers), libev implements
		4874	so-called C<ev_async> watchers, which allow some limited form of
		4875	concurrency on the same event loop, namely waking it up "from the
		4876	outside".
		4877
		4878	If you want to know which design (one loop, locking, or multiple loops
		4879	without or something else still) is best for your problem, then I cannot
		4880	help you, but here is some generic advice:
		4881
		4882	=over 4
		4883
		4884	=item * most applications have a main thread: use the default libev loop
		4885	in that thread, or create a separate thread running only the default loop.
		4886
		4887	This helps integrating other libraries or software modules that use libev
		4888	themselves and don't care/know about threading.
		4889
		4890	=item * one loop per thread is usually a good model.
		4891
		4892	Doing this is almost never wrong, sometimes a better-performance model
		4893	exists, but it is always a good start.
		4894
		4895	=item * other models exist, such as the leader/follower pattern, where one
		4896	loop is handed through multiple threads in a kind of round-robin fashion.
		4897
		4898	Choosing a model is hard - look around, learn, know that usually you can do
		4899	better than you currently do :-)
		4900
		4901	=item * often you need to talk to some other thread which blocks in the
		4902	event loop.
		4903
		4904	C<ev_async> watchers can be used to wake them up from other threads safely
		4905	(or from signal contexts...).
		4906
		4907	An example use would be to communicate signals or other events that only
		4908	work in the default loop by registering the signal watcher with the
		4909	default loop and triggering an C<ev_async> watcher from the default loop
		4910	watcher callback into the event loop interested in the signal.
		4911
		4912	=back
		4913
		4914	See also L<THREAD LOCKING EXAMPLE>.
		4915
		4916	=head3 COROUTINES
		4917
		4918	Libev is very accommodating to coroutines ("cooperative threads"):
		4919	libev fully supports nesting calls to its functions from different
		4920	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4921	different coroutines, and switch freely between both coroutines running
		4922	the loop, as long as you don't confuse yourself). The only exception is
		4923	that you must not do this from C<ev_periodic> reschedule callbacks.
		4924
		4925	Care has been taken to ensure that libev does not keep local state inside
		4926	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4927	they do not call any callbacks.
		4928
		4929	=head2 COMPILER WARNINGS
		4930
		4931	Depending on your compiler and compiler settings, you might get no or a
		4932	lot of warnings when compiling libev code. Some people are apparently
		4933	scared by this.
		4934
		4935	However, these are unavoidable for many reasons. For one, each compiler
		4936	has different warnings, and each user has different tastes regarding
		4937	warning options. "Warn-free" code therefore cannot be a goal except when
		4938	targeting a specific compiler and compiler-version.
		4939
		4940	Another reason is that some compiler warnings require elaborate
		4941	workarounds, or other changes to the code that make it less clear and less
		4942	maintainable.
		4943
		4944	And of course, some compiler warnings are just plain stupid, or simply
		4945	wrong (because they don't actually warn about the condition their message
		4946	seems to warn about). For example, certain older gcc versions had some
		4947	warnings that resulted in an extreme number of false positives. These have
		4948	been fixed, but some people still insist on making code warn-free with
		4949	such buggy versions.
		4950
		4951	While libev is written to generate as few warnings as possible,
		4952	"warn-free" code is not a goal, and it is recommended not to build libev
		4953	with any compiler warnings enabled unless you are prepared to cope with
		4954	them (e.g. by ignoring them). Remember that warnings are just that:
		4955	warnings, not errors, or proof of bugs.
		4956
		4957
		4958	=head2 VALGRIND
		4959
		4960	Valgrind has a special section here because it is a popular tool that is
		4961	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4962
		4963	If you think you found a bug (memory leak, uninitialised data access etc.)
		4964	in libev, then check twice: If valgrind reports something like:
		4965
		4966	==2274== definitely lost: 0 bytes in 0 blocks.
		4967	==2274== possibly lost: 0 bytes in 0 blocks.
		4968	==2274== still reachable: 256 bytes in 1 blocks.
		4969
		4970	Then there is no memory leak, just as memory accounted to global variables
		4971	is not a memleak - the memory is still being referenced, and didn't leak.
		4972
		4973	Similarly, under some circumstances, valgrind might report kernel bugs
		4974	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4975	although an acceptable workaround has been found here), or it might be
		4976	confused.
		4977
		4978	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4979	make it into some kind of religion.
		4980
		4981	If you are unsure about something, feel free to contact the mailing list
		4982	with the full valgrind report and an explanation on why you think this
		4983	is a bug in libev (best check the archives, too :). However, don't be
		4984	annoyed when you get a brisk "this is no bug" answer and take the chance
		4985	of learning how to interpret valgrind properly.
		4986
		4987	If you need, for some reason, empty reports from valgrind for your project
		4988	I suggest using suppression lists.
		4989
		4990
		4991	=head1 PORTABILITY NOTES
		4992
		4993	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4994
		4995	GNU/Linux is the only common platform that supports 64 bit file/large file
		4996	interfaces but I<disables> them by default.
		4997
		4998	That means that libev compiled in the default environment doesn't support
		4999	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5000
		5001	Unfortunately, many programs try to work around this GNU/Linux issue
		5002	by enabling the large file API, which makes them incompatible with the
		5003	standard libev compiled for their system.
		5004
		5005	Likewise, libev cannot enable the large file API itself as this would
		5006	suddenly make it incompatible to the default compile time environment,
		5007	i.e. all programs not using special compile switches.
		5008
		5009	=head2 OS/X AND DARWIN BUGS
		5010
		5011	The whole thing is a bug if you ask me - basically any system interface
		5012	you touch is broken, whether it is locales, poll, kqueue or even the
		5013	OpenGL drivers.
		5014
		5015	=head3 C<kqueue> is buggy
		5016
		5017	The kqueue syscall is broken in all known versions - most versions support
		5018	only sockets, many support pipes.
		5019
		5020	Libev tries to work around this by not using C<kqueue> by default on this
		5021	rotten platform, but of course you can still ask for it when creating a
		5022	loop - embedding a socket-only kqueue loop into a select-based one is
		5023	probably going to work well.
		5024
		5025	=head3 C<poll> is buggy
		5026
		5027	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5028	implementation by something calling C<kqueue> internally around the 10.5.6
		5029	release, so now C<kqueue> I<and> C<poll> are broken.
		5030
		5031	Libev tries to work around this by not using C<poll> by default on
		5032	this rotten platform, but of course you can still ask for it when creating
		5033	a loop.
		5034
		5035	=head3 C<select> is buggy
		5036
		5037	All that's left is C<select>, and of course Apple found a way to fuck this
		5038	one up as well: On OS/X, C<select> actively limits the number of file
		5039	descriptors you can pass in to 1024 - your program suddenly crashes when
		5040	you use more.
		5041
		5042	There is an undocumented "workaround" for this - defining
		5043	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5044	work on OS/X.
		5045
		5046	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5047
		5048	=head3 C<errno> reentrancy
		5049
		5050	The default compile environment on Solaris is unfortunately so
		5051	thread-unsafe that you can't even use components/libraries compiled
		5052	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5053	defined by default. A valid, if stupid, implementation choice.
		5054
		5055	If you want to use libev in threaded environments you have to make sure
		5056	it's compiled with C<_REENTRANT> defined.
		5057
		5058	=head3 Event port backend
		5059
		5060	The scalable event interface for Solaris is called "event
		5061	ports". Unfortunately, this mechanism is very buggy in all major
		5062	releases. If you run into high CPU usage, your program freezes or you get
		5063	a large number of spurious wakeups, make sure you have all the relevant
		5064	and latest kernel patches applied. No, I don't know which ones, but there
		5065	are multiple ones to apply, and afterwards, event ports actually work
		5066	great.
		5067
		5068	If you can't get it to work, you can try running the program by setting
		5069	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5070	C<select> backends.
		5071
		5072	=head2 AIX POLL BUG
		5073
		5074	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5075	this by trying to avoid the poll backend altogether (i.e. it's not even
		5076	compiled in), which normally isn't a big problem as C<select> works fine
		5077	with large bitsets on AIX, and AIX is dead anyway.
		5078
		5079	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5080
		5081	=head3 General issues
		5082
		5083	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5084	requires, and its I/O model is fundamentally incompatible with the POSIX
		5085	model. Libev still offers limited functionality on this platform in
		5086	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5087	descriptors. This only applies when using Win32 natively, not when using
		5088	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5089	as every compiler comes with a slightly differently broken/incompatible
		5090	environment.
		5091
		5092	Lifting these limitations would basically require the full
		5093	re-implementation of the I/O system. If you are into this kind of thing,
		5094	then note that glib does exactly that for you in a very portable way (note
		5095	also that glib is the slowest event library known to man).
		5096
		5097	There is no supported compilation method available on windows except
		5098	embedding it into other applications.
		5099
		5100	Sensible signal handling is officially unsupported by Microsoft - libev
		5101	tries its best, but under most conditions, signals will simply not work.
		5102
		5103	Not a libev limitation but worth mentioning: windows apparently doesn't
		5104	accept large writes: instead of resulting in a partial write, windows will
		5105	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5106	so make sure you only write small amounts into your sockets (less than a
		5107	megabyte seems safe, but this apparently depends on the amount of memory
		5108	available).
		5109
		5110	Due to the many, low, and arbitrary limits on the win32 platform and
		5111	the abysmal performance of winsockets, using a large number of sockets
		5112	is not recommended (and not reasonable). If your program needs to use
		5113	more than a hundred or so sockets, then likely it needs to use a totally
		5114	different implementation for windows, as libev offers the POSIX readiness
		5115	notification model, which cannot be implemented efficiently on windows
		5116	(due to Microsoft monopoly games).
		5117
		5118	A typical way to use libev under windows is to embed it (see the embedding
		5119	section for details) and use the following F<evwrap.h> header file instead
		5120	of F<ev.h>:
		5121
		5122	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5123	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5124
		5125	#include "ev.h"
		5126
		5127	And compile the following F<evwrap.c> file into your project (make sure
		5128	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5129
		5130	#include "evwrap.h"
		5131	#include "ev.c"
		5132
		5133	=head3 The winsocket C<select> function
		5134
		5135	The winsocket C<select> function doesn't follow POSIX in that it
		5136	requires socket I<handles> and not socket I<file descriptors> (it is
		5137	also extremely buggy). This makes select very inefficient, and also
		5138	requires a mapping from file descriptors to socket handles (the Microsoft
		5139	C runtime provides the function C<_open_osfhandle> for this). See the
		5140	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5141	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5142
		5143	The configuration for a "naked" win32 using the Microsoft runtime
		5144	libraries and raw winsocket select is:
		5145
		5146	#define EV_USE_SELECT 1
		5147	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5148
		5149	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5150	complexity in the O(n²) range when using win32.
		5151
		5152	=head3 Limited number of file descriptors
		5153
		5154	Windows has numerous arbitrary (and low) limits on things.
		5155
		5156	Early versions of winsocket's select only supported waiting for a maximum
		5157	of C<64> handles (probably owning to the fact that all windows kernels
		5158	can only wait for C<64> things at the same time internally; Microsoft
		5159	recommends spawning a chain of threads and wait for 63 handles and the
		5160	previous thread in each. Sounds great!).
		5161
		5162	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5163	to some high number (e.g. C<2048>) before compiling the winsocket select
		5164	call (which might be in libev or elsewhere, for example, perl and many
		5165	other interpreters do their own select emulation on windows).
		5166
		5167	Another limit is the number of file descriptors in the Microsoft runtime
		5168	libraries, which by default is C<64> (there must be a hidden I<64>
		5169	fetish or something like this inside Microsoft). You can increase this
		5170	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5171	(another arbitrary limit), but is broken in many versions of the Microsoft
		5172	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5173	(depending on windows version and/or the phase of the moon). To get more,
		5174	you need to wrap all I/O functions and provide your own fd management, but
		5175	the cost of calling select (O(n²)) will likely make this unworkable.
		5176
		5177	=head2 PORTABILITY REQUIREMENTS
		5178
		5179	In addition to a working ISO-C implementation and of course the
		5180	backend-specific APIs, libev relies on a few additional extensions:
		5181
		5182	=over 4
		5183
		5184	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5185	calling conventions regardless of C<ev_watcher_type *>.
		5186
		5187	Libev assumes not only that all watcher pointers have the same internal
		5188	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5189	assumes that the same (machine) code can be used to call any watcher
		5190	callback: The watcher callbacks have different type signatures, but libev
		5191	calls them using an C<ev_watcher *> internally.
		5192
		5193	=item pointer accesses must be thread-atomic
		5194
		5195	Accessing a pointer value must be atomic, it must both be readable and
		5196	writable in one piece - this is the case on all current architectures.
		5197
		5198	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5199
		5200	The type C<sig_atomic_t volatile> (or whatever is defined as
		5201	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5202	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5203	believed to be sufficiently portable.
		5204
		5205	=item C<sigprocmask> must work in a threaded environment
		5206
		5207	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5208	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5209	pthread implementations will either allow C<sigprocmask> in the "main
		5210	thread" or will block signals process-wide, both behaviours would
		5211	be compatible with libev. Interaction between C<sigprocmask> and
		5212	C<pthread_sigmask> could complicate things, however.
		5213
		5214	The most portable way to handle signals is to block signals in all threads
		5215	except the initial one, and run the default loop in the initial thread as
		5216	well.
		5217
		5218	=item C<long> must be large enough for common memory allocation sizes
		5219
		5220	To improve portability and simplify its API, libev uses C<long> internally
		5221	instead of C<size_t> when allocating its data structures. On non-POSIX
		5222	systems (Microsoft...) this might be unexpectedly low, but is still at
		5223	least 31 bits everywhere, which is enough for hundreds of millions of
		5224	watchers.
		5225
		5226	=item C<double> must hold a time value in seconds with enough accuracy
		5227
		5228	The type C<double> is used to represent timestamps. It is required to
		5229	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5230	good enough for at least into the year 4000 with millisecond accuracy
		5231	(the design goal for libev). This requirement is overfulfilled by
		5232	implementations using IEEE 754, which is basically all existing ones.
		5233
		5234	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5235	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5236	is either obsolete or somebody patched it to use C<long double> or
		5237	something like that, just kidding).
		5238
		5239	=back
		5240
		5241	If you know of other additional requirements drop me a note.
		5242
		5243
1779	=head1 COMPLEXITIES	5244	=head1 ALGORITHMIC COMPLEXITIES
1780		5245
1781	In this section the complexities of (many of) the algorithms used inside	5246	In this section the complexities of (many of) the algorithms used inside
1782	libev will be explained. For complexity discussions about backends see the	5247	libev will be documented. For complexity discussions about backends see
1783	documentation for C<ev_default_init>.	5248	the documentation for C<ev_default_init>.
		5249
		5250	All of the following are about amortised time: If an array needs to be
		5251	extended, libev needs to realloc and move the whole array, but this
		5252	happens asymptotically rarer with higher number of elements, so O(1) might
		5253	mean that libev does a lengthy realloc operation in rare cases, but on
		5254	average it is much faster and asymptotically approaches constant time.
1784		5255
1785	=over 4	5256	=over 4
1786		5257
1787	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5258	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
1788		5259
		5260	This means that, when you have a watcher that triggers in one hour and
		5261	there are 100 watchers that would trigger before that, then inserting will
		5262	have to skip roughly seven (C<ld 100>) of these watchers.
		5263
1789	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5264	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
1790		5265
		5266	That means that changing a timer costs less than removing/adding them,
		5267	as only the relative motion in the event queue has to be paid for.
		5268
1791	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5269	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
1792		5270
		5271	These just add the watcher into an array or at the head of a list.
		5272
1793	=item Stopping check/prepare/idle watchers: O(1)	5273	=item Stopping check/prepare/idle/fork/async watchers: O(1)
1794		5274
1795	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	5275	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
1796		5276
		5277	These watchers are stored in lists, so they need to be walked to find the
		5278	correct watcher to remove. The lists are usually short (you don't usually
		5279	have many watchers waiting for the same fd or signal: one is typical, two
		5280	is rare).
		5281
1797	=item Finding the next timer per loop iteration: O(1)	5282	=item Finding the next timer in each loop iteration: O(1)
		5283
		5284	By virtue of using a binary or 4-heap, the next timer is always found at a
		5285	fixed position in the storage array.
1798		5286
1799	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5287	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
1800		5288
1801	=item Activating one watcher: O(1)	5289	A change means an I/O watcher gets started or stopped, which requires
		5290	libev to recalculate its status (and possibly tell the kernel, depending
		5291	on backend and whether C<ev_io_set> was used).
		5292
		5293	=item Activating one watcher (putting it into the pending state): O(1)
		5294
		5295	=item Priority handling: O(number_of_priorities)
		5296
		5297	Priorities are implemented by allocating some space for each
		5298	priority. When doing priority-based operations, libev usually has to
		5299	linearly search all the priorities, but starting/stopping and activating
		5300	watchers becomes O(1) with respect to priority handling.
		5301
		5302	=item Sending an ev_async: O(1)
		5303
		5304	=item Processing ev_async_send: O(number_of_async_watchers)
		5305
		5306	=item Processing signals: O(max_signal_number)
		5307
		5308	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5309	calls in the current loop iteration and the loop is currently
		5310	blocked. Checking for async and signal events involves iterating over all
		5311	running async watchers or all signal numbers.
1802		5312
1803	=back	5313	=back
1804		5314
1805		5315
		5316	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5317
		5318	The major version 4 introduced some incompatible changes to the API.
		5319
		5320	At the moment, the C<ev.h> header file provides compatibility definitions
		5321	for all changes, so most programs should still compile. The compatibility
		5322	layer might be removed in later versions of libev, so better update to the
		5323	new API early than late.
		5324
		5325	=over 4
		5326
		5327	=item C<EV_COMPAT3> backwards compatibility mechanism
		5328
		5329	The backward compatibility mechanism can be controlled by
		5330	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5331	section.
		5332
		5333	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5334
		5335	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5336
		5337	ev_loop_destroy (EV_DEFAULT_UC);
		5338	ev_loop_fork (EV_DEFAULT);
		5339
		5340	=item function/symbol renames
		5341
		5342	A number of functions and symbols have been renamed:
		5343
		5344	ev_loop => ev_run
		5345	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5346	EVLOOP_ONESHOT => EVRUN_ONCE
		5347
		5348	ev_unloop => ev_break
		5349	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5350	EVUNLOOP_ONE => EVBREAK_ONE
		5351	EVUNLOOP_ALL => EVBREAK_ALL
		5352
		5353	EV_TIMEOUT => EV_TIMER
		5354
		5355	ev_loop_count => ev_iteration
		5356	ev_loop_depth => ev_depth
		5357	ev_loop_verify => ev_verify
		5358
		5359	Most functions working on C<struct ev_loop> objects don't have an
		5360	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5361	associated constants have been renamed to not collide with the C<struct
		5362	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5363	as all other watcher types. Note that C<ev_loop_fork> is still called
		5364	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5365	typedef.
		5366
		5367	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5368
		5369	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5370	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5371	and work, but the library code will of course be larger.
		5372
		5373	=back
		5374
		5375
		5376	=head1 GLOSSARY
		5377
		5378	=over 4
		5379
		5380	=item active
		5381
		5382	A watcher is active as long as it has been started and not yet stopped.
		5383	See L<WATCHER STATES> for details.
		5384
		5385	=item application
		5386
		5387	In this document, an application is whatever is using libev.
		5388
		5389	=item backend
		5390
		5391	The part of the code dealing with the operating system interfaces.
		5392
		5393	=item callback
		5394
		5395	The address of a function that is called when some event has been
		5396	detected. Callbacks are being passed the event loop, the watcher that
		5397	received the event, and the actual event bitset.
		5398
		5399	=item callback/watcher invocation
		5400
		5401	The act of calling the callback associated with a watcher.
		5402
		5403	=item event
		5404
		5405	A change of state of some external event, such as data now being available
		5406	for reading on a file descriptor, time having passed or simply not having
		5407	any other events happening anymore.
		5408
		5409	In libev, events are represented as single bits (such as C<EV_READ> or
		5410	C<EV_TIMER>).
		5411
		5412	=item event library
		5413
		5414	A software package implementing an event model and loop.
		5415
		5416	=item event loop
		5417
		5418	An entity that handles and processes external events and converts them
		5419	into callback invocations.
		5420
		5421	=item event model
		5422
		5423	The model used to describe how an event loop handles and processes
		5424	watchers and events.
		5425
		5426	=item pending
		5427
		5428	A watcher is pending as soon as the corresponding event has been
		5429	detected. See L<WATCHER STATES> for details.
		5430
		5431	=item real time
		5432
		5433	The physical time that is observed. It is apparently strictly monotonic :)
		5434
		5435	=item wall-clock time
		5436
		5437	The time and date as shown on clocks. Unlike real time, it can actually
		5438	be wrong and jump forwards and backwards, e.g. when you adjust your
		5439	clock.
		5440
		5441	=item watcher
		5442
		5443	A data structure that describes interest in certain events. Watchers need
		5444	to be started (attached to an event loop) before they can receive events.
		5445
		5446	=back
		5447
1806	=head1 AUTHOR	5448	=head1 AUTHOR
1807		5449
1808	Marc Lehmann <libev@schmorp.de>.	5450	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5451	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
1809		5452

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