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Revision 1.355 by root, Tue Jan 11 01:41:56 2011 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 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	// unloop 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_update_now> and C<ev_now>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked until
		184	either it is interrupted or the given time interval has passed. Basically
		185	this is a sub-second-resolution C<sleep ()>.
66		186
67	=item int ev_version_major ()	187	=item int ev_version_major ()
68		188
69	=item int ev_version_minor ()	189	=item int ev_version_minor ()
70		190
71	You can find out the major and minor version numbers of the library	191	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	192	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	193	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	194	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	195	version of the library your program was compiled against.
76		196
		197	These version numbers refer to the ABI version of the library, not the
		198	release version.
		199
77	Usually, it's a good idea to terminate if the major versions mismatch,	200	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	203	not a problem.
81		204
82	Example: make sure we haven't accidentally been linked against the wrong	205	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
84		208
85	assert (("libev version mismatch",	209	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
88		212
89	=item unsigned int ev_supported_backends ()	213	=item unsigned int ev_supported_backends ()
90		214
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	215	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	216	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	218	a description of the set values.
95		219
96	Example: make sure we have the epoll method, because yeah this is cool and	220	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	221	a must have and can we have a torrent of it please!!!11
98		222
99	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
101		225
102	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
103		227
104	Return the set of all backends compiled into this binary of libev and also	228	Return the set of all backends compiled into this binary of libev and
105	recommended for this platform. This set is often smaller than the one	229	also recommended for this platform, meaning it will work for most file
		230	descriptor types. This set is often smaller than the one returned by
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	231	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
107	most BSDs and will not be autodetected unless you explicitly request it	232	and will not be auto-detected unless you explicitly request it (assuming
108	(assuming you know what you are doing). This is the set of backends that	233	you know what you are doing). This is the set of backends that libev will
109	libev will probe for if you specify no backends explicitly.	234	probe for if you specify no backends explicitly.
110		235
111	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
112		237
113	Returns the set of backends that are embeddable in other event loops. This	238	Returns the set of backends that are embeddable in other event loops. This
114	is the theoretical, all-platform, value. To find which backends	239	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	240	current system. To find which embeddable backends might be supported on
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
117	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
118		243
119	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
120		245
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
122		247
123	Sets the allocation function to use (the prototype is similar to the	248	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	249	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	250	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	251	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	252	or take some potentially destructive action.
		253
		254	Since some systems (at least OpenBSD and Darwin) fail to implement
		255	correct C<realloc> semantics, libev will use a wrapper around the system
		256	C<realloc> and C<free> functions by default.
128		257
129	You could override this function in high-availability programs to, say,	258	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,	259	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.	260	or even to sleep a while and retry until some memory is available.
132		261
133	Example: replace the libev allocator with one that waits a bit and then	262	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	263	retries (example requires a standards-compliant C<realloc>).
135		264
136	static void *	265	static void *
137	persistent_realloc (void *ptr, long size)	266	persistent_realloc (void *ptr, size_t size)
138	{	267	{
139	for (;;)	268	for (;;)
140	{	269	{
141	void *newptr = realloc (ptr, size);	270	void *newptr = realloc (ptr, size);
142		271
…		…
148	}	277	}
149		278
150	...	279	...
151	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
152		281
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
154		283
155	Set the callback function to call on a retryable syscall error (such	284	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	285	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	286	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	287	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	288	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	289	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	290	(such as abort).
162		291
163	Example: do the same thing as libev does internally:	292	Example: This is basically the same thing that libev does internally, too.
164		293
165	static void	294	static void
166	fatal_error (const char *msg)	295	fatal_error (const char *msg)
167	{	296	{
168	perror (msg);	297	perror (msg);
…		…
170	}	299	}
171		300
172	...	301	...
173	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
174		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
175	=back	317	=back
176		318
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
178		320
179	An event loop is described by a C<struct ev_loop *>. The library knows two	321	An event loop is described by a C<struct ev_loop *> (the C<struct> is
180	types of such loops, the I<default> loop, which supports signals and child	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
181	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
182		324
183	If you use threads, a common model is to run the default event loop	325	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	326	supports child process events, and dynamically created event loops which
185	create, you also create another event loop. Libev itself does no locking	327	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		328
190	=over 4	329	=over 4
191		330
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		332
194	This will initialise the default event loop if it hasn't been initialised	333	This returns the "default" event loop object, which is what you should
195	yet and return it. If the default loop could not be initialised, returns	334	normally use when you just need "the event loop". Event loop objects and
196	false. If it already was initialised it simply returns it (and ignores the	335	the C<flags> parameter are described in more detail in the entry for
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
198		343
199	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
200	function.	345	function (or via the C<EV_DEFAULT> macro).
		346
		347	Note that this function is I<not> thread-safe, so if you want to use it
		348	from multiple threads, you have to employ some kind of mutex (note also
		349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
		351
		352	The default loop is the only loop that can handle C<ev_child> watchers,
		353	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		354	a problem for your application you can either create a dynamic loop with
		355	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
201		376
202	The flags argument can be used to specify special behaviour or specific	377	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		379
205	The following flags are supported:	380	The following flags are supported:
…		…
211	The default flags value. Use this if you have no clue (it's the right	386	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	387	thing, believe me).
213		388
214	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
215		390
216	If this flag bit is ored into the flag value (or the program runs setuid	391	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	392	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	394	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	395	useful to try out specific backends to test their performance, or to work
221	around bugs.	396	around bugs.
222		397
		398	=item C<EVFLAG_FORKCHECK>
		399
		400	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		401	make libev check for a fork in each iteration by enabling this flag.
		402
		403	This works by calling C<getpid ()> on every iteration of the loop,
		404	and thus this might slow down your event loop if you do a lot of loop
		405	iterations and little real work, but is usually not noticeable (on my
		406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		407	without a system call and thus I<very> fast, but my GNU/Linux system also has
		408	C<pthread_atfork> which is even faster).
		409
		410	The big advantage of this flag is that you can forget about fork (and
		411	forget about forgetting to tell libev about forking) when you use this
		412	flag.
		413
		414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		415	environment variable.
		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	This flag's behaviour will become the default in future versions of libev.
		448
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		450
225	This is your standard select(2) backend. Not I<completely> standard, as	451	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	452	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	453	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	454	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	455	usually the fastest backend for a low number of (low-numbered :) fds.
		456
		457	To get good performance out of this backend you need a high amount of
		458	parallelism (most of the file descriptors should be busy). If you are
		459	writing a server, you should C<accept ()> in a loop to accept as many
		460	connections as possible during one iteration. You might also want to have
		461	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		462	readiness notifications you get per iteration.
		463
		464	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		465	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		466	C<exceptfds> set on that platform).
230		467
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	468	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		469
233	And this is your standard poll(2) backend. It's more complicated than	470	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	471	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	472	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	473	considerably with a lot of inactive fds). It scales similarly to select,
		474	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		475	performance tips.
		476
		477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		479
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	480	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		481
		482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		483	kernels).
		484
240	For few fds, this backend is a bit little slower than poll and select,	485	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	486	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	487	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	488	epoll scales either O(1) or O(active_fds).
244		489
		490	The epoll mechanism deserves honorable mention as the most misdesigned
		491	of the more advanced event mechanisms: mere annoyances include silently
		492	dropping file descriptors, requiring a system call per change per file
		493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(and only giving 5ms accuracy while select on the same platform gives
		496	0.1ms) and so on. The biggest issue is fork races, however - if a program
		497	forks then I<both> parent and child process have to recreate the epoll
		498	set, which can take considerable time (one syscall per file descriptor)
		499	and is of course hard to detect.
		500
		501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		502	of course I<doesn't>, and epoll just loves to report events for totally
		503	I<different> file descriptors (even already closed ones, so one cannot
		504	even remove them from the set) than registered in the set (especially
		505	on SMP systems). Libev tries to counter these spurious notifications by
		506	employing an additional generation counter and comparing that against the
		507	events to filter out spurious ones, recreating the set when required. Last
		508	not least, it also refuses to work with some file descriptors which work
		509	perfectly fine with C<select> (files, many character devices...).
		510
		511	Epoll is truly the train wreck analog among event poll mechanisms,
		512	a frankenpoll, cobbled together in a hurry, no thought to design or
		513	interaction with others.
		514
245	While stopping and starting an I/O watcher in the same iteration will	515	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	516	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	517	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	519	file descriptors might not work very well if you register events for both
		520	file descriptors.
250		521
251	Please note that epoll sometimes generates spurious notifications, so you	522	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	523	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	524	i.e. keep at least one watcher active per fd at all times. Stopping and
		525	starting a watcher (without re-setting it) also usually doesn't cause
		526	extra overhead. A fork can both result in spurious notifications as well
		527	as in libev having to destroy and recreate the epoll object, which can
		528	take considerable time and thus should be avoided.
		529
		530	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		531	faster than epoll for maybe up to a hundred file descriptors, depending on
		532	the usage. So sad.
		533
		534	While nominally embeddable in other event loops, this feature is broken in
		535	all kernel versions tested so far.
		536
		537	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		538	C<EVBACKEND_POLL>.
254		539
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	540	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		541
257	Kqueue deserves special mention, as at the time of this writing, it	542	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	543	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	544	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	545	it's completely useless). Unlike epoll, however, whose brokenness
		546	is by design, these kqueue bugs can (and eventually will) be fixed
		547	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	548	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	549	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		550	system like NetBSD.
		551
		552	You still can embed kqueue into a normal poll or select backend and use it
		553	only for sockets (after having made sure that sockets work with kqueue on
		554	the target platform). See C<ev_embed> watchers for more info.
263		555
264	It scales in the same way as the epoll backend, but the interface to the	556	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	557	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	558	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	559	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	560	two event changes per incident. Support for C<fork ()> is very bad (but
		561	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		562	cases
		563
		564	This backend usually performs well under most conditions.
		565
		566	While nominally embeddable in other event loops, this doesn't work
		567	everywhere, so you might need to test for this. And since it is broken
		568	almost everywhere, you should only use it when you have a lot of sockets
		569	(for which it usually works), by embedding it into another event loop
		570	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		571	also broken on OS X)) and, did I mention it, using it only for sockets.
		572
		573	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		574	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		575	C<NOTE_EOF>.
269		576
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	577	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		578
272	This is not implemented yet (and might never be).	579	This is not implemented yet (and might never be, unless you send me an
		580	implementation). According to reports, C</dev/poll> only supports sockets
		581	and is not embeddable, which would limit the usefulness of this backend
		582	immensely.
273		583
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	584	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		585
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	586	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	587	it's really slow, but it still scales very well (O(active_fds)).
278		588
279	Please note that solaris ports can result in a lot of spurious	589	While this backend scales well, it requires one system call per active
280	notifications, so you need to use non-blocking I/O or other means to avoid	590	file descriptor per loop iteration. For small and medium numbers of file
281	blocking when no data (or space) is available.	591	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		592	might perform better.
		593
		594	On the positive side, this backend actually performed fully to
		595	specification in all tests and is fully embeddable, which is a rare feat
		596	among the OS-specific backends (I vastly prefer correctness over speed
		597	hacks).
		598
		599	On the negative side, the interface is I<bizarre> - so bizarre that
		600	even sun itself gets it wrong in their code examples: The event polling
		601	function sometimes returning events to the caller even though an error
		602	occurred, but with no indication whether it has done so or not (yes, it's
		603	even documented that way) - deadly for edge-triggered interfaces where
		604	you absolutely have to know whether an event occurred or not because you
		605	have to re-arm the watcher.
		606
		607	Fortunately libev seems to be able to work around these idiocies.
		608
		609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		610	C<EVBACKEND_POLL>.
282		611
283	=item C<EVBACKEND_ALL>	612	=item C<EVBACKEND_ALL>
284		613
285	Try all backends (even potentially broken ones that wouldn't be tried	614	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	615	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	616	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		617
		618	It is definitely not recommended to use this flag, use whatever
		619	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		620	at all.
		621
		622	=item C<EVBACKEND_MASK>
		623
		624	Not a backend at all, but a mask to select all backend bits from a
		625	C<flags> value, in case you want to mask out any backends from a flags
		626	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		627
289	=back	628	=back
290		629
291	If one or more of these are ored into the flags value, then only these	630	If one or more of the backend flags are or'ed into the flags value,
292	backends will be tried (in the reverse order as given here). If none are	631	then only these backends will be tried (in the reverse order as listed
293	specified, most compiled-in backend will be tried, usually in reverse	632	here). If none are specified, all backends in C<ev_recommended_backends
294	order of their flag values :)	633	()> will be tried.
295		634
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.	635	Example: Try to create a event loop that uses epoll and nothing else.
320		636
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	637	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	638	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	639	fatal ("no epoll found here, maybe it hides under your chair");
324		640
		641	Example: Use whatever libev has to offer, but make sure that kqueue is
		642	used if available.
		643
		644	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		645
325	=item ev_default_destroy ()	646	=item ev_loop_destroy (loop)
326		647
327	Destroys the default loop again (frees all memory and kernel state	648	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	649	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	650	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>	651	responsibility to either stop all watchers cleanly yourself I<before>
331	calling this function, or cope with the fact afterwards (which is usually	652	calling this function, or cope with the fact afterwards (which is usually
332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	653	the easiest thing, you can just ignore the watchers and/or C<free ()> them
333	for example).	654	for example).
334		655
		656	Note that certain global state, such as signal state (and installed signal
		657	handlers), will not be freed by this function, and related watchers (such
		658	as signal and child watchers) would need to be stopped manually.
		659
		660	This function is normally used on loop objects allocated by
		661	C<ev_loop_new>, but it can also be used on the default loop returned by
		662	C<ev_default_loop>, in which case it is not thread-safe.
		663
		664	Note that it is not advisable to call this function on the default loop
		665	except in the rare occasion where you really need to free its resources.
		666	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		667	and C<ev_loop_destroy>.
		668
335	=item ev_loop_destroy (loop)	669	=item ev_loop_fork (loop)
336		670
337	Like C<ev_default_destroy>, but destroys an event loop created by an	671	This function sets a flag that causes subsequent C<ev_run> iterations to
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	672	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	673	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	674	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
345	again makes little sense).	675	child before resuming or calling C<ev_run>.
346		676
347	You I<must> call this function in the child process after forking if and	677	Again, you I<have> to call it on I<any> loop that you want to re-use after
348	only if you want to use the event library in both processes. If you just	678	a fork, I<even if you do not plan to use the loop in the parent>. This is
349	fork+exec, you don't have to call it.	679	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		680	during fork.
		681
		682	On the other hand, you only need to call this function in the child
		683	process if and only if you want to use the event loop in the child. If
		684	you just fork+exec or create a new loop in the child, you don't have to
		685	call it at all (in fact, C<epoll> is so badly broken that it makes a
		686	difference, but libev will usually detect this case on its own and do a
		687	costly reset of the backend).
350		688
351	The function itself is quite fast and it's usually not a problem to call	689	The function itself is quite fast and it's usually not a problem to call
352	it just in case after a fork. To make this easy, the function will fit in	690	it just in case after a fork.
353	quite nicely into a call to C<pthread_atfork>:
354		691
		692	Example: Automate calling C<ev_loop_fork> on the default loop when
		693	using pthreads.
		694
		695	static void
		696	post_fork_child (void)
		697	{
		698	ev_loop_fork (EV_DEFAULT);
		699	}
		700
		701	...
355	pthread_atfork (0, 0, ev_default_fork);	702	pthread_atfork (0, 0, post_fork_child);
356		703
357	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	704	=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		705
361	=item ev_loop_fork (loop)	706	Returns true when the given loop is, in fact, the default loop, and false
		707	otherwise.
362		708
363	Like C<ev_default_fork>, but acts on an event loop created by	709	=item unsigned int ev_iteration (loop)
364	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	710
365	after fork, and how you do this is entirely your own problem.	711	Returns the current iteration count for the event loop, which is identical
		712	to the number of times libev did poll for new events. It starts at C<0>
		713	and happily wraps around with enough iterations.
		714
		715	This value can sometimes be useful as a generation counter of sorts (it
		716	"ticks" the number of loop iterations), as it roughly corresponds with
		717	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		718	prepare and check phases.
		719
		720	=item unsigned int ev_depth (loop)
		721
		722	Returns the number of times C<ev_run> was entered minus the number of
		723	times C<ev_run> was exited normally, in other words, the recursion depth.
		724
		725	Outside C<ev_run>, this number is zero. In a callback, this number is
		726	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		727	in which case it is higher.
		728
		729	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		730	throwing an exception etc.), doesn't count as "exit" - consider this
		731	as a hint to avoid such ungentleman-like behaviour unless it's really
		732	convenient, in which case it is fully supported.
366		733
367	=item unsigned int ev_backend (loop)	734	=item unsigned int ev_backend (loop)
368		735
369	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	736	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
370	use.	737	use.
…		…
373		740
374	Returns the current "event loop time", which is the time the event loop	741	Returns the current "event loop time", which is the time the event loop
375	received events and started processing them. This timestamp does not	742	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	743	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	744	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).	745	event occurring (or more correctly, libev finding out about it).
379		746
		747	=item ev_now_update (loop)
		748
		749	Establishes the current time by querying the kernel, updating the time
		750	returned by C<ev_now ()> in the progress. This is a costly operation and
		751	is usually done automatically within C<ev_run ()>.
		752
		753	This function is rarely useful, but when some event callback runs for a
		754	very long time without entering the event loop, updating libev's idea of
		755	the current time is a good idea.
		756
		757	See also L<The special problem of time updates> in the C<ev_timer> section.
		758
		759	=item ev_suspend (loop)
		760
		761	=item ev_resume (loop)
		762
		763	These two functions suspend and resume an event loop, for use when the
		764	loop is not used for a while and timeouts should not be processed.
		765
		766	A typical use case would be an interactive program such as a game: When
		767	the user presses C<^Z> to suspend the game and resumes it an hour later it
		768	would be best to handle timeouts as if no time had actually passed while
		769	the program was suspended. This can be achieved by calling C<ev_suspend>
		770	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		771	C<ev_resume> directly afterwards to resume timer processing.
		772
		773	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		774	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		775	will be rescheduled (that is, they will lose any events that would have
		776	occurred while suspended).
		777
		778	After calling C<ev_suspend> you B<must not> call I<any> function on the
		779	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		780	without a previous call to C<ev_suspend>.
		781
		782	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		783	event loop time (see C<ev_now_update>).
		784
380	=item ev_loop (loop, int flags)	785	=item ev_run (loop, int flags)
381		786
382	Finally, this is it, the event handler. This function usually is called	787	Finally, this is it, the event handler. This function usually is called
383	after you initialised all your watchers and you want to start handling	788	after you have initialised all your watchers and you want to start
384	events.	789	handling events. It will ask the operating system for any new events, call
		790	the watcher callbacks, an then repeat the whole process indefinitely: This
		791	is why event loops are called I<loops>.
385		792
386	If the flags argument is specified as C<0>, it will not return until	793	If the flags argument is specified as C<0>, it will keep handling events
387	either no event watchers are active anymore or C<ev_unloop> was called.	794	until either no event watchers are active anymore or C<ev_break> was
		795	called.
388		796
389	Please note that an explicit C<ev_unloop> is usually better than	797	Please note that an explicit C<ev_break> is usually better than
390	relying on all watchers to be stopped when deciding when a program has	798	relying on all watchers to be stopped when deciding when a program has
391	finished (especially in interactive programs), but having a program that	799	finished (especially in interactive programs), but having a program
392	automatically loops as long as it has to and no longer by virtue of	800	that automatically loops as long as it has to and no longer by virtue
393	relying on its watchers stopping correctly is a thing of beauty.	801	of relying on its watchers stopping correctly, that is truly a thing of
		802	beauty.
394		803
		804	This function is also I<mostly> exception-safe - you can break out of
		805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		806	exception and so on. This does not decrement the C<ev_depth> value, nor
		807	will it clear any outstanding C<EVBREAK_ONE> breaks.
		808
395	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	809	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
396	those events and any outstanding ones, but will not block your process in	810	those events and any already outstanding ones, but will not wait and
397	case there are no events and will return after one iteration of the loop.	811	block your process in case there are no events and will return after one
		812	iteration of the loop. This is sometimes useful to poll and handle new
		813	events while doing lengthy calculations, to keep the program responsive.
398		814
399	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	815	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
400	neccessary) and will handle those and any outstanding ones. It will block	816	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	817	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	818	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	819	user-registered callback will be called), and will return after one
		820	iteration of the loop.
		821
		822	This is useful if you are waiting for some external event in conjunction
		823	with something not expressible using other libev watchers (i.e. "roll your
404	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	824	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
405	usually a better approach for this kind of thing.	825	usually a better approach for this kind of thing.
406		826
407	Here are the gory details of what C<ev_loop> does:	827	Here are the gory details of what C<ev_run> does:
408		828
409	* If there are no active watchers (reference count is zero), return.	829	- Increment loop depth.
410	- Queue prepare watchers and then call all outstanding watchers.	830	- Reset the ev_break status.
		831	- Before the first iteration, call any pending watchers.
		832	LOOP:
		833	- If EVFLAG_FORKCHECK was used, check for a fork.
		834	- If a fork was detected (by any means), queue and call all fork watchers.
		835	- Queue and call all prepare watchers.
		836	- If ev_break was called, goto FINISH.
411	- If we have been forked, recreate the kernel state.	837	- If we have been forked, detach and recreate the kernel state
		838	as to not disturb the other process.
412	- Update the kernel state with all outstanding changes.	839	- Update the kernel state with all outstanding changes.
413	- Update the "event loop time".	840	- Update the "event loop time" (ev_now ()).
414	- Calculate for how long to block.	841	- Calculate for how long to sleep or block, if at all
		842	(active idle watchers, EVRUN_NOWAIT or not having
		843	any active watchers at all will result in not sleeping).
		844	- Sleep if the I/O and timer collect interval say so.
		845	- Increment loop iteration counter.
415	- Block the process, waiting for any events.	846	- Block the process, waiting for any events.
416	- Queue all outstanding I/O (fd) events.	847	- Queue all outstanding I/O (fd) events.
417	- Update the "event loop time" and do time jump handling.	848	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
418	- Queue all outstanding timers.	849	- Queue all expired timers.
419	- Queue all outstanding periodics.	850	- Queue all expired periodics.
420	- If no events are pending now, queue all idle watchers.	851	- Queue all idle watchers with priority higher than that of pending events.
421	- Queue all check watchers.	852	- Queue all check watchers.
422	- Call all queued watchers in reverse order (i.e. check watchers first).	853	- Call all queued watchers in reverse order (i.e. check watchers first).
423	Signals and child watchers are implemented as I/O watchers, and will	854	Signals and child watchers are implemented as I/O watchers, and will
424	be handled here by queueing them when their watcher gets executed.	855	be handled here by queueing them when their watcher gets executed.
425	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	856	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
426	were used, return, otherwise continue with step *.	857	were used, or there are no active watchers, goto FINISH, otherwise
		858	continue with step LOOP.
		859	FINISH:
		860	- Reset the ev_break status iff it was EVBREAK_ONE.
		861	- Decrement the loop depth.
		862	- Return.
427		863
428	Example: queue some jobs and then loop until no events are outsanding	864	Example: Queue some jobs and then loop until no events are outstanding
429	anymore.	865	anymore.
430		866
431	... queue jobs here, make sure they register event watchers as long	867	... 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..)	868	... as they still have work to do (even an idle watcher will do..)
433	ev_loop (my_loop, 0);	869	ev_run (my_loop, 0);
434	... jobs done. yeah!	870	... jobs done or somebody called unloop. yeah!
435		871
436	=item ev_unloop (loop, how)	872	=item ev_break (loop, how)
437		873
438	Can be used to make a call to C<ev_loop> return early (but only after it	874	Can be used to make a call to C<ev_run> return early (but only after it
439	has processed all outstanding events). The C<how> argument must be either	875	has processed all outstanding events). The C<how> argument must be either
440	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	876	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
441	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	877	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		878
		879	This "break state" will be cleared on the next call to C<ev_run>.
		880
		881	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		882	which case it will have no effect.
442		883
443	=item ev_ref (loop)	884	=item ev_ref (loop)
444		885
445	=item ev_unref (loop)	886	=item ev_unref (loop)
446		887
447	Ref/unref can be used to add or remove a reference count on the event	888	Ref/unref can be used to add or remove a reference count on the event
448	loop: Every watcher keeps one reference, and as long as the reference	889	loop: Every watcher keeps one reference, and as long as the reference
449	count is nonzero, C<ev_loop> will not return on its own. If you have	890	count is nonzero, C<ev_run> will not return on its own.
450	a watcher you never unregister that should not keep C<ev_loop> from	891
451	returning, ev_unref() after starting, and ev_ref() before stopping it. For	892	This is useful when you have a watcher that you never intend to
		893	unregister, but that nevertheless should not keep C<ev_run> from
		894	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		895	before stopping it.
		896
452	example, libev itself uses this for its internal signal pipe: It is not	897	As an example, libev itself uses this for its internal signal pipe: It
453	visible to the libev user and should not keep C<ev_loop> from exiting if	898	is not visible to the libev user and should not keep C<ev_run> from
454	no event watchers registered by it are active. It is also an excellent	899	exiting if no event watchers registered by it are active. It is also an
455	way to do this for generic recurring timers or from within third-party	900	excellent way to do this for generic recurring timers or from within
456	libraries. Just remember to I<unref after start> and I<ref before stop>.	901	third-party libraries. Just remember to I<unref after start> and I<ref
		902	before stop> (but only if the watcher wasn't active before, or was active
		903	before, respectively. Note also that libev might stop watchers itself
		904	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		905	in the callback).
457		906
458	Example: create a signal watcher, but keep it from keeping C<ev_loop>	907	Example: Create a signal watcher, but keep it from keeping C<ev_run>
459	running when nothing else is active.	908	running when nothing else is active.
460		909
461	struct dv_signal exitsig;	910	ev_signal exitsig;
462	ev_signal_init (&exitsig, sig_cb, SIGINT);	911	ev_signal_init (&exitsig, sig_cb, SIGINT);
463	ev_signal_start (myloop, &exitsig);	912	ev_signal_start (loop, &exitsig);
464	evf_unref (myloop);	913	ev_unref (loop);
465		914
466	Example: for some weird reason, unregister the above signal handler again.	915	Example: For some weird reason, unregister the above signal handler again.
467		916
468	ev_ref (myloop);	917	ev_ref (loop);
469	ev_signal_stop (myloop, &exitsig);	918	ev_signal_stop (loop, &exitsig);
		919
		920	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		921
		922	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		923
		924	These advanced functions influence the time that libev will spend waiting
		925	for events. Both time intervals are by default C<0>, meaning that libev
		926	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		927	latency.
		928
		929	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		930	allows libev to delay invocation of I/O and timer/periodic callbacks
		931	to increase efficiency of loop iterations (or to increase power-saving
		932	opportunities).
		933
		934	The idea is that sometimes your program runs just fast enough to handle
		935	one (or very few) event(s) per loop iteration. While this makes the
		936	program responsive, it also wastes a lot of CPU time to poll for new
		937	events, especially with backends like C<select ()> which have a high
		938	overhead for the actual polling but can deliver many events at once.
		939
		940	By setting a higher I<io collect interval> you allow libev to spend more
		941	time collecting I/O events, so you can handle more events per iteration,
		942	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		943	C<ev_timer>) will be not affected. Setting this to a non-null value will
		944	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		945	sleep time ensures that libev will not poll for I/O events more often then
		946	once per this interval, on average.
		947
		948	Likewise, by setting a higher I<timeout collect interval> you allow libev
		949	to spend more time collecting timeouts, at the expense of increased
		950	latency/jitter/inexactness (the watcher callback will be called
		951	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		952	value will not introduce any overhead in libev.
		953
		954	Many (busy) programs can usually benefit by setting the I/O collect
		955	interval to a value near C<0.1> or so, which is often enough for
		956	interactive servers (of course not for games), likewise for timeouts. It
		957	usually doesn't make much sense to set it to a lower value than C<0.01>,
		958	as this approaches the timing granularity of most systems. Note that if
		959	you do transactions with the outside world and you can't increase the
		960	parallelity, then this setting will limit your transaction rate (if you
		961	need to poll once per transaction and the I/O collect interval is 0.01,
		962	then you can't do more than 100 transactions per second).
		963
		964	Setting the I<timeout collect interval> can improve the opportunity for
		965	saving power, as the program will "bundle" timer callback invocations that
		966	are "near" in time together, by delaying some, thus reducing the number of
		967	times the process sleeps and wakes up again. Another useful technique to
		968	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		969	they fire on, say, one-second boundaries only.
		970
		971	Example: we only need 0.1s timeout granularity, and we wish not to poll
		972	more often than 100 times per second:
		973
		974	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		975	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		976
		977	=item ev_invoke_pending (loop)
		978
		979	This call will simply invoke all pending watchers while resetting their
		980	pending state. Normally, C<ev_run> does this automatically when required,
		981	but when overriding the invoke callback this call comes handy. This
		982	function can be invoked from a watcher - this can be useful for example
		983	when you want to do some lengthy calculation and want to pass further
		984	event handling to another thread (you still have to make sure only one
		985	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		986
		987	=item int ev_pending_count (loop)
		988
		989	Returns the number of pending watchers - zero indicates that no watchers
		990	are pending.
		991
		992	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		993
		994	This overrides the invoke pending functionality of the loop: Instead of
		995	invoking all pending watchers when there are any, C<ev_run> will call
		996	this callback instead. This is useful, for example, when you want to
		997	invoke the actual watchers inside another context (another thread etc.).
		998
		999	If you want to reset the callback, use C<ev_invoke_pending> as new
		1000	callback.
		1001
		1002	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1003
		1004	Sometimes you want to share the same loop between multiple threads. This
		1005	can be done relatively simply by putting mutex_lock/unlock calls around
		1006	each call to a libev function.
		1007
		1008	However, C<ev_run> can run an indefinite time, so it is not feasible
		1009	to wait for it to return. One way around this is to wake up the event
		1010	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1011	I<release> and I<acquire> callbacks on the loop.
		1012
		1013	When set, then C<release> will be called just before the thread is
		1014	suspended waiting for new events, and C<acquire> is called just
		1015	afterwards.
		1016
		1017	Ideally, C<release> will just call your mutex_unlock function, and
		1018	C<acquire> will just call the mutex_lock function again.
		1019
		1020	While event loop modifications are allowed between invocations of
		1021	C<release> and C<acquire> (that's their only purpose after all), no
		1022	modifications done will affect the event loop, i.e. adding watchers will
		1023	have no effect on the set of file descriptors being watched, or the time
		1024	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1025	to take note of any changes you made.
		1026
		1027	In theory, threads executing C<ev_run> will be async-cancel safe between
		1028	invocations of C<release> and C<acquire>.
		1029
		1030	See also the locking example in the C<THREADS> section later in this
		1031	document.
		1032
		1033	=item ev_set_userdata (loop, void *data)
		1034
		1035	=item void *ev_userdata (loop)
		1036
		1037	Set and retrieve a single C<void *> associated with a loop. When
		1038	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1039	C<0>.
		1040
		1041	These two functions can be used to associate arbitrary data with a loop,
		1042	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1043	C<acquire> callbacks described above, but of course can be (ab-)used for
		1044	any other purpose as well.
		1045
		1046	=item ev_verify (loop)
		1047
		1048	This function only does something when C<EV_VERIFY> support has been
		1049	compiled in, which is the default for non-minimal builds. It tries to go
		1050	through all internal structures and checks them for validity. If anything
		1051	is found to be inconsistent, it will print an error message to standard
		1052	error and call C<abort ()>.
		1053
		1054	This can be used to catch bugs inside libev itself: under normal
		1055	circumstances, this function will never abort as of course libev keeps its
		1056	data structures consistent.
470		1057
471	=back	1058	=back
472		1059
473		1060
474	=head1 ANATOMY OF A WATCHER	1061	=head1 ANATOMY OF A WATCHER
475		1062
		1063	In the following description, uppercase C<TYPE> in names stands for the
		1064	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1065	watchers and C<ev_io_start> for I/O watchers.
		1066
476	A watcher is a structure that you create and register to record your	1067	A watcher is an opaque structure that you allocate and register to record
477	interest in some event. For instance, if you want to wait for STDIN to	1068	your interest in some event. To make a concrete example, imagine you want
478	become readable, you would create an C<ev_io> watcher for that:	1069	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1070	for that:
479		1071
480	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1072	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
481	{	1073	{
482	ev_io_stop (w);	1074	ev_io_stop (w);
483	ev_unloop (loop, EVUNLOOP_ALL);	1075	ev_break (loop, EVBREAK_ALL);
484	}	1076	}
485		1077
486	struct ev_loop *loop = ev_default_loop (0);	1078	struct ev_loop *loop = ev_default_loop (0);
		1079
487	struct ev_io stdin_watcher;	1080	ev_io stdin_watcher;
		1081
488	ev_init (&stdin_watcher, my_cb);	1082	ev_init (&stdin_watcher, my_cb);
489	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1083	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
490	ev_io_start (loop, &stdin_watcher);	1084	ev_io_start (loop, &stdin_watcher);
		1085
491	ev_loop (loop, 0);	1086	ev_run (loop, 0);
492		1087
493	As you can see, you are responsible for allocating the memory for your	1088	As you can see, you are responsible for allocating the memory for your
494	watcher structures (and it is usually a bad idea to do this on the stack,	1089	watcher structures (and it is I<usually> a bad idea to do this on the
495	although this can sometimes be quite valid).	1090	stack).
496		1091
		1092	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1093	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1094
497	Each watcher structure must be initialised by a call to C<ev_init	1095	Each watcher structure must be initialised by a call to C<ev_init (watcher
498	(watcher *, callback)>, which expects a callback to be provided. This	1096	*, 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	1097	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	1098	time the event loop detects that the file descriptor given is readable
501	is readable and/or writable).	1099	and/or writable).
502		1100
503	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1101	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
504	with arguments specific to this watcher type. There is also a macro	1102	macro to configure it, with arguments specific to the watcher type. There
505	to combine initialisation and setting in one call: C<< ev_<type>_init	1103	is also a macro to combine initialisation and setting in one call: C<<
506	(watcher *, callback, ...) >>.	1104	ev_TYPE_init (watcher *, callback, ...) >>.
507		1105
508	To make the watcher actually watch out for events, you have to start it	1106	To make the watcher actually watch out for events, you have to start it
509	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1107	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
510	*) >>), and you can stop watching for events at any time by calling the	1108	*) >>), and you can stop watching for events at any time by calling the
511	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1109	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
512		1110
513	As long as your watcher is active (has been started but not stopped) you	1111	As long as your watcher is active (has been started but not stopped) you
514	must not touch the values stored in it. Most specifically you must never	1112	must not touch the values stored in it. Most specifically you must never
515	reinitialise it or call its C<set> macro.	1113	reinitialise it or call its C<ev_TYPE_set> macro.
516		1114
517	Each and every callback receives the event loop pointer as first, the	1115	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	1116	registered watcher structure as second, and a bitset of received events as
519	third argument.	1117	third argument.
520		1118
…		…
529	=item C<EV_WRITE>	1127	=item C<EV_WRITE>
530		1128
531	The file descriptor in the C<ev_io> watcher has become readable and/or	1129	The file descriptor in the C<ev_io> watcher has become readable and/or
532	writable.	1130	writable.
533		1131
534	=item C<EV_TIMEOUT>	1132	=item C<EV_TIMER>
535		1133
536	The C<ev_timer> watcher has timed out.	1134	The C<ev_timer> watcher has timed out.
537		1135
538	=item C<EV_PERIODIC>	1136	=item C<EV_PERIODIC>
539		1137
…		…
545		1143
546	=item C<EV_CHILD>	1144	=item C<EV_CHILD>
547		1145
548	The pid specified in the C<ev_child> watcher has received a status change.	1146	The pid specified in the C<ev_child> watcher has received a status change.
549		1147
		1148	=item C<EV_STAT>
		1149
		1150	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1151
550	=item C<EV_IDLE>	1152	=item C<EV_IDLE>
551		1153
552	The C<ev_idle> watcher has determined that you have nothing better to do.	1154	The C<ev_idle> watcher has determined that you have nothing better to do.
553		1155
554	=item C<EV_PREPARE>	1156	=item C<EV_PREPARE>
555		1157
556	=item C<EV_CHECK>	1158	=item C<EV_CHECK>
557		1159
558	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1160	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
559	to gather new events, and all C<ev_check> watchers are invoked just after	1161	to gather new events, and all C<ev_check> watchers are invoked just after
560	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1162	C<ev_run> has gathered them, but before it invokes any callbacks for any
561	received events. Callbacks of both watcher types can start and stop as	1163	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	1164	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1165	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	1166	C<ev_run> from blocking).
		1167
		1168	=item C<EV_EMBED>
		1169
		1170	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1171
		1172	=item C<EV_FORK>
		1173
		1174	The event loop has been resumed in the child process after fork (see
		1175	C<ev_fork>).
		1176
		1177	=item C<EV_CLEANUP>
		1178
		1179	The event loop is about to be destroyed (see C<ev_cleanup>).
		1180
		1181	=item C<EV_ASYNC>
		1182
		1183	The given async watcher has been asynchronously notified (see C<ev_async>).
		1184
		1185	=item C<EV_CUSTOM>
		1186
		1187	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1188	by libev users to signal watchers (e.g. via C<ev_feed_event>).
565		1189
566	=item C<EV_ERROR>	1190	=item C<EV_ERROR>
567		1191
568	An unspecified error has occured, the watcher has been stopped. This might	1192	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	1193	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	1194	ran out of memory, a file descriptor was found to be closed or any other
		1195	problem. Libev considers these application bugs.
		1196
571	problem. You best act on it by reporting the problem and somehow coping	1197	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	1198	watcher being stopped. Note that well-written programs should not receive
		1199	an error ever, so when your watcher receives it, this usually indicates a
		1200	bug in your program.
573		1201
574	Libev will usually signal a few "dummy" events together with an error,	1202	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	1203	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	1204	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	1205	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	1206	programs, though, as the fd could already be closed and reused for another
		1207	thing, so beware.
579		1208
580	=back	1209	=back
581		1210
582	=head2 GENERIC WATCHER FUNCTIONS	1211	=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		1212
587	=over 4	1213	=over 4
588		1214
589	=item C<ev_init> (ev_TYPE *watcher, callback)	1215	=item C<ev_init> (ev_TYPE *watcher, callback)
590		1216
…		…
596	which rolls both calls into one.	1222	which rolls both calls into one.
597		1223
598	You can reinitialise a watcher at any time as long as it has been stopped	1224	You can reinitialise a watcher at any time as long as it has been stopped
599	(or never started) and there are no pending events outstanding.	1225	(or never started) and there are no pending events outstanding.
600		1226
601	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1227	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
602	int revents)>.	1228	int revents)>.
603		1229
		1230	Example: Initialise an C<ev_io> watcher in two steps.
		1231
		1232	ev_io w;
		1233	ev_init (&w, my_cb);
		1234	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1235
604	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1236	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
605		1237
606	This macro initialises the type-specific parts of a watcher. You need to	1238	This macro initialises the type-specific parts of a watcher. You need to
607	call C<ev_init> at least once before you call this macro, but you can	1239	call C<ev_init> at least once before you call this macro, but you can
608	call C<ev_TYPE_set> any number of times. You must not, however, call this	1240	call C<ev_TYPE_set> any number of times. You must not, however, call this
609	macro on a watcher that is active (it can be pending, however, which is a	1241	macro on a watcher that is active (it can be pending, however, which is a
610	difference to the C<ev_init> macro).	1242	difference to the C<ev_init> macro).
611		1243
612	Although some watcher types do not have type-specific arguments	1244	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.	1245	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
614		1246
		1247	See C<ev_init>, above, for an example.
		1248
615	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1249	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
616		1250
617	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1251	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
618	calls into a single call. This is the most convinient method to initialise	1252	calls into a single call. This is the most convenient method to initialise
619	a watcher. The same limitations apply, of course.	1253	a watcher. The same limitations apply, of course.
620		1254
		1255	Example: Initialise and set an C<ev_io> watcher in one step.
		1256
		1257	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1258
621	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1259	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
622		1260
623	Starts (activates) the given watcher. Only active watchers will receive	1261	Starts (activates) the given watcher. Only active watchers will receive
624	events. If the watcher is already active nothing will happen.	1262	events. If the watcher is already active nothing will happen.
625		1263
		1264	Example: Start the C<ev_io> watcher that is being abused as example in this
		1265	whole section.
		1266
		1267	ev_io_start (EV_DEFAULT_UC, &w);
		1268
626	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1269	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
627		1270
628	Stops the given watcher again (if active) and clears the pending	1271	Stops the given watcher if active, and clears the pending status (whether
		1272	the watcher was active or not).
		1273
629	status. It is possible that stopped watchers are pending (for example,	1274	It is possible that stopped watchers are pending - for example,
630	non-repeating timers are being stopped when they become pending), but	1275	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	1276	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	1277	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.	1278	therefore a good idea to always call its C<ev_TYPE_stop> function.
634		1279
635	=item bool ev_is_active (ev_TYPE *watcher)	1280	=item bool ev_is_active (ev_TYPE *watcher)
636		1281
637	Returns a true value iff the watcher is active (i.e. it has been started	1282	Returns a true value iff the watcher is active (i.e. it has been started
638	and not yet been stopped). As long as a watcher is active you must not modify	1283	and not yet been stopped). As long as a watcher is active you must not modify
…		…
641	=item bool ev_is_pending (ev_TYPE *watcher)	1286	=item bool ev_is_pending (ev_TYPE *watcher)
642		1287
643	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1288	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	1289	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	1290	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	1291	C<ev_TYPE_set> is safe), you must not change its priority, and you must
647	libev (e.g. you cnanot C<free ()> it).	1292	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1293	it).
648		1294
649	=item callback = ev_cb (ev_TYPE *watcher)	1295	=item callback ev_cb (ev_TYPE *watcher)
650		1296
651	Returns the callback currently set on the watcher.	1297	Returns the callback currently set on the watcher.
652		1298
653	=item ev_cb_set (ev_TYPE *watcher, callback)	1299	=item ev_cb_set (ev_TYPE *watcher, callback)
654		1300
655	Change the callback. You can change the callback at virtually any time	1301	Change the callback. You can change the callback at virtually any time
656	(modulo threads).	1302	(modulo threads).
657		1303
		1304	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1305
		1306	=item int ev_priority (ev_TYPE *watcher)
		1307
		1308	Set and query the priority of the watcher. The priority is a small
		1309	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1310	(default: C<-2>). Pending watchers with higher priority will be invoked
		1311	before watchers with lower priority, but priority will not keep watchers
		1312	from being executed (except for C<ev_idle> watchers).
		1313
		1314	If you need to suppress invocation when higher priority events are pending
		1315	you need to look at C<ev_idle> watchers, which provide this functionality.
		1316
		1317	You I<must not> change the priority of a watcher as long as it is active or
		1318	pending.
		1319
		1320	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1321	fine, as long as you do not mind that the priority value you query might
		1322	or might not have been clamped to the valid range.
		1323
		1324	The default priority used by watchers when no priority has been set is
		1325	always C<0>, which is supposed to not be too high and not be too low :).
		1326
		1327	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1328	priorities.
		1329
		1330	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1331
		1332	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1333	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1334	can deal with that fact, as both are simply passed through to the
		1335	callback.
		1336
		1337	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1338
		1339	If the watcher is pending, this function clears its pending status and
		1340	returns its C<revents> bitset (as if its callback was invoked). If the
		1341	watcher isn't pending it does nothing and returns C<0>.
		1342
		1343	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1344	callback to be invoked, which can be accomplished with this function.
		1345
		1346	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1347
		1348	Feeds the given event set into the event loop, as if the specified event
		1349	had happened for the specified watcher (which must be a pointer to an
		1350	initialised but not necessarily started event watcher). Obviously you must
		1351	not free the watcher as long as it has pending events.
		1352
		1353	Stopping the watcher, letting libev invoke it, or calling
		1354	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1355	not started in the first place.
		1356
		1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1358	functions that do not need a watcher.
		1359
658	=back	1360	=back
659		1361
660
661	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
662		1363
663	Each watcher has, by default, a member C<void *data> that you can change	1364	Each watcher has, by default, a member C<void *data> that you can change
664	and read at any time, libev will completely ignore it. This can be used	1365	and read at any time: libev will completely ignore it. This can be used
665	to associate arbitrary data with your watcher. If you need more data and	1366	to associate arbitrary data with your watcher. If you need more data and
666	don't want to allocate memory and store a pointer to it in that data	1367	don't want to allocate memory and store a pointer to it in that data
667	member, you can also "subclass" the watcher type and provide your own	1368	member, you can also "subclass" the watcher type and provide your own
668	data:	1369	data:
669		1370
670	struct my_io	1371	struct my_io
671	{	1372	{
672	struct ev_io io;	1373	ev_io io;
673	int otherfd;	1374	int otherfd;
674	void *somedata;	1375	void *somedata;
675	struct whatever *mostinteresting;	1376	struct whatever *mostinteresting;
676	}	1377	};
		1378
		1379	...
		1380	struct my_io w;
		1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
677		1382
678	And since your callback will be called with a pointer to the watcher, you	1383	And since your callback will be called with a pointer to the watcher, you
679	can cast it back to your own type:	1384	can cast it back to your own type:
680		1385
681	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
682	{	1387	{
683	struct my_io *w = (struct my_io *)w_;	1388	struct my_io *w = (struct my_io *)w_;
684	...	1389	...
685	}	1390	}
686		1391
687	More interesting and less C-conformant ways of catsing your callback type	1392	More interesting and less C-conformant ways of casting your callback type
688	have been omitted....	1393	instead have been omitted.
		1394
		1395	Another common scenario is to use some data structure with multiple
		1396	embedded watchers:
		1397
		1398	struct my_biggy
		1399	{
		1400	int some_data;
		1401	ev_timer t1;
		1402	ev_timer t2;
		1403	}
		1404
		1405	In this case getting the pointer to C<my_biggy> is a bit more
		1406	complicated: Either you store the address of your C<my_biggy> struct
		1407	in the C<data> member of the watcher (for woozies), or you need to use
		1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1409	programmers):
		1410
		1411	#include <stddef.h>
		1412
		1413	static void
		1414	t1_cb (EV_P_ ev_timer *w, int revents)
		1415	{
		1416	struct my_biggy big = (struct my_biggy *)
		1417	(((char *)w) - offsetof (struct my_biggy, t1));
		1418	}
		1419
		1420	static void
		1421	t2_cb (EV_P_ ev_timer *w, int revents)
		1422	{
		1423	struct my_biggy big = (struct my_biggy *)
		1424	(((char *)w) - offsetof (struct my_biggy, t2));
		1425	}
		1426
		1427	=head2 WATCHER STATES
		1428
		1429	There are various watcher states mentioned throughout this manual -
		1430	active, pending and so on. In this section these states and the rules to
		1431	transition between them will be described in more detail - and while these
		1432	rules might look complicated, they usually do "the right thing".
		1433
		1434	=over 4
		1435
		1436	=item initialiased
		1437
		1438	Before a watcher can be registered with the event looop it has to be
		1439	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1440	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1441
		1442	In this state it is simply some block of memory that is suitable for use
		1443	in an event loop. It can be moved around, freed, reused etc. at will.
		1444
		1445	=item started/running/active
		1446
		1447	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1448	property of the event loop, and is actively waiting for events. While in
		1449	this state it cannot be accessed (except in a few documented ways), moved,
		1450	freed or anything else - the only legal thing is to keep a pointer to it,
		1451	and call libev functions on it that are documented to work on active watchers.
		1452
		1453	=item pending
		1454
		1455	If a watcher is active and libev determines that an event it is interested
		1456	in has occurred (such as a timer expiring), it will become pending. It will
		1457	stay in this pending state until either it is stopped or its callback is
		1458	about to be invoked, so it is not normally pending inside the watcher
		1459	callback.
		1460
		1461	The watcher might or might not be active while it is pending (for example,
		1462	an expired non-repeating timer can be pending but no longer active). If it
		1463	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1464	but it is still property of the event loop at this time, so cannot be
		1465	moved, freed or reused. And if it is active the rules described in the
		1466	previous item still apply.
		1467
		1468	It is also possible to feed an event on a watcher that is not active (e.g.
		1469	via C<ev_feed_event>), in which case it becomes pending without being
		1470	active.
		1471
		1472	=item stopped
		1473
		1474	A watcher can be stopped implicitly by libev (in which case it might still
		1475	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1476	latter will clear any pending state the watcher might be in, regardless
		1477	of whether it was active or not, so stopping a watcher explicitly before
		1478	freeing it is often a good idea.
		1479
		1480	While stopped (and not pending) the watcher is essentially in the
		1481	initialised state, that is it can be reused, moved, modified in any way
		1482	you wish.
		1483
		1484	=back
		1485
		1486	=head2 WATCHER PRIORITY MODELS
		1487
		1488	Many event loops support I<watcher priorities>, which are usually small
		1489	integers that influence the ordering of event callback invocation
		1490	between watchers in some way, all else being equal.
		1491
		1492	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1493	description for the more technical details such as the actual priority
		1494	range.
		1495
		1496	There are two common ways how these these priorities are being interpreted
		1497	by event loops:
		1498
		1499	In the more common lock-out model, higher priorities "lock out" invocation
		1500	of lower priority watchers, which means as long as higher priority
		1501	watchers receive events, lower priority watchers are not being invoked.
		1502
		1503	The less common only-for-ordering model uses priorities solely to order
		1504	callback invocation within a single event loop iteration: Higher priority
		1505	watchers are invoked before lower priority ones, but they all get invoked
		1506	before polling for new events.
		1507
		1508	Libev uses the second (only-for-ordering) model for all its watchers
		1509	except for idle watchers (which use the lock-out model).
		1510
		1511	The rationale behind this is that implementing the lock-out model for
		1512	watchers is not well supported by most kernel interfaces, and most event
		1513	libraries will just poll for the same events again and again as long as
		1514	their callbacks have not been executed, which is very inefficient in the
		1515	common case of one high-priority watcher locking out a mass of lower
		1516	priority ones.
		1517
		1518	Static (ordering) priorities are most useful when you have two or more
		1519	watchers handling the same resource: a typical usage example is having an
		1520	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1521	timeouts. Under load, data might be received while the program handles
		1522	other jobs, but since timers normally get invoked first, the timeout
		1523	handler will be executed before checking for data. In that case, giving
		1524	the timer a lower priority than the I/O watcher ensures that I/O will be
		1525	handled first even under adverse conditions (which is usually, but not
		1526	always, what you want).
		1527
		1528	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1529	will only be executed when no same or higher priority watchers have
		1530	received events, they can be used to implement the "lock-out" model when
		1531	required.
		1532
		1533	For example, to emulate how many other event libraries handle priorities,
		1534	you can associate an C<ev_idle> watcher to each such watcher, and in
		1535	the normal watcher callback, you just start the idle watcher. The real
		1536	processing is done in the idle watcher callback. This causes libev to
		1537	continuously poll and process kernel event data for the watcher, but when
		1538	the lock-out case is known to be rare (which in turn is rare :), this is
		1539	workable.
		1540
		1541	Usually, however, the lock-out model implemented that way will perform
		1542	miserably under the type of load it was designed to handle. In that case,
		1543	it might be preferable to stop the real watcher before starting the
		1544	idle watcher, so the kernel will not have to process the event in case
		1545	the actual processing will be delayed for considerable time.
		1546
		1547	Here is an example of an I/O watcher that should run at a strictly lower
		1548	priority than the default, and which should only process data when no
		1549	other events are pending:
		1550
		1551	ev_idle idle; // actual processing watcher
		1552	ev_io io; // actual event watcher
		1553
		1554	static void
		1555	io_cb (EV_P_ ev_io *w, int revents)
		1556	{
		1557	// stop the I/O watcher, we received the event, but
		1558	// are not yet ready to handle it.
		1559	ev_io_stop (EV_A_ w);
		1560
		1561	// start the idle watcher to handle the actual event.
		1562	// it will not be executed as long as other watchers
		1563	// with the default priority are receiving events.
		1564	ev_idle_start (EV_A_ &idle);
		1565	}
		1566
		1567	static void
		1568	idle_cb (EV_P_ ev_idle *w, int revents)
		1569	{
		1570	// actual processing
		1571	read (STDIN_FILENO, ...);
		1572
		1573	// have to start the I/O watcher again, as
		1574	// we have handled the event
		1575	ev_io_start (EV_P_ &io);
		1576	}
		1577
		1578	// initialisation
		1579	ev_idle_init (&idle, idle_cb);
		1580	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1581	ev_io_start (EV_DEFAULT_ &io);
		1582
		1583	In the "real" world, it might also be beneficial to start a timer, so that
		1584	low-priority connections can not be locked out forever under load. This
		1585	enables your program to keep a lower latency for important connections
		1586	during short periods of high load, while not completely locking out less
		1587	important ones.
689		1588
690		1589
691	=head1 WATCHER TYPES	1590	=head1 WATCHER TYPES
692		1591
693	This section describes each watcher in detail, but will not repeat	1592	This section describes each watcher in detail, but will not repeat
694	information given in the last section.	1593	information given in the last section. Any initialisation/set macros,
		1594	functions and members specific to the watcher type are explained.
		1595
		1596	Members are additionally marked with either I<[read-only]>, meaning that,
		1597	while the watcher is active, you can look at the member and expect some
		1598	sensible content, but you must not modify it (you can modify it while the
		1599	watcher is stopped to your hearts content), or I<[read-write]>, which
		1600	means you can expect it to have some sensible content while the watcher
		1601	is active, but you can also modify it. Modifying it may not do something
		1602	sensible or take immediate effect (or do anything at all), but libev will
		1603	not crash or malfunction in any way.
695		1604
696		1605
697	=head2 C<ev_io> - is this file descriptor readable or writable?	1606	=head2 C<ev_io> - is this file descriptor readable or writable?
698		1607
699	I/O watchers check whether a file descriptor is readable or writable	1608	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	1616	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	1617	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	1618	descriptors to non-blocking mode is also usually a good idea (but not
710	required if you know what you are doing).	1619	required if you know what you are doing).
711		1620
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	1621	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	1622	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	1623	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	1624	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	1625	with a relatively standard program structure. Thus it is best to always
727	this situation even with a relatively standard program structure. Thus	1626	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
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.	1627	preferable to a program hanging until some data arrives.
730		1628
731	If you cannot run the fd in non-blocking mode (for example you should not	1629	If you cannot run the fd in non-blocking mode (for example you should
732	play around with an Xlib connection), then you have to seperately re-test	1630	not play around with an Xlib connection), then you have to separately
733	wether a file descriptor is really ready with a known-to-be good interface	1631	re-test whether a file descriptor is really ready with a known-to-be good
734	such as poll (fortunately in our Xlib example, Xlib already does this on	1632	interface such as poll (fortunately in the case of Xlib, it already does
735	its own, so its quite safe to use).	1633	this on its own, so its quite safe to use). Some people additionally
		1634	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1635	indefinitely.
		1636
		1637	But really, best use non-blocking mode.
		1638
		1639	=head3 The special problem of disappearing file descriptors
		1640
		1641	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1642	descriptor (either due to calling C<close> explicitly or any other means,
		1643	such as C<dup2>). The reason is that you register interest in some file
		1644	descriptor, but when it goes away, the operating system will silently drop
		1645	this interest. If another file descriptor with the same number then is
		1646	registered with libev, there is no efficient way to see that this is, in
		1647	fact, a different file descriptor.
		1648
		1649	To avoid having to explicitly tell libev about such cases, libev follows
		1650	the following policy: Each time C<ev_io_set> is being called, libev
		1651	will assume that this is potentially a new file descriptor, otherwise
		1652	it is assumed that the file descriptor stays the same. That means that
		1653	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1654	descriptor even if the file descriptor number itself did not change.
		1655
		1656	This is how one would do it normally anyway, the important point is that
		1657	the libev application should not optimise around libev but should leave
		1658	optimisations to libev.
		1659
		1660	=head3 The special problem of dup'ed file descriptors
		1661
		1662	Some backends (e.g. epoll), cannot register events for file descriptors,
		1663	but only events for the underlying file descriptions. That means when you
		1664	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1665	events for them, only one file descriptor might actually receive events.
		1666
		1667	There is no workaround possible except not registering events
		1668	for potentially C<dup ()>'ed file descriptors, or to resort to
		1669	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1670
		1671	=head3 The special problem of files
		1672
		1673	Many people try to use C<select> (or libev) on file descriptors
		1674	representing files, and expect it to become ready when their program
		1675	doesn't block on disk accesses (which can take a long time on their own).
		1676
		1677	However, this cannot ever work in the "expected" way - you get a readiness
		1678	notification as soon as the kernel knows whether and how much data is
		1679	there, and in the case of open files, that's always the case, so you
		1680	always get a readiness notification instantly, and your read (or possibly
		1681	write) will still block on the disk I/O.
		1682
		1683	Another way to view it is that in the case of sockets, pipes, character
		1684	devices and so on, there is another party (the sender) that delivers data
		1685	on it's own, but in the case of files, there is no such thing: the disk
		1686	will not send data on it's own, simply because it doesn't know what you
		1687	wish to read - you would first have to request some data.
		1688
		1689	Since files are typically not-so-well supported by advanced notification
		1690	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1691	to files, even though you should not use it. The reason for this is
		1692	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1693	usually a tty, often a pipe, but also sometimes files or special devices
		1694	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1695	F</dev/urandom>), and even though the file might better be served with
		1696	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1697	it "just works" instead of freezing.
		1698
		1699	So avoid file descriptors pointing to files when you know it (e.g. use
		1700	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1701	when you rarely read from a file instead of from a socket, and want to
		1702	reuse the same code path.
		1703
		1704	=head3 The special problem of fork
		1705
		1706	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1707	useless behaviour. Libev fully supports fork, but needs to be told about
		1708	it in the child if you want to continue to use it in the child.
		1709
		1710	To support fork in your child processes, you have to call C<ev_loop_fork
		1711	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1712	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1713
		1714	=head3 The special problem of SIGPIPE
		1715
		1716	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1717	when writing to a pipe whose other end has been closed, your program gets
		1718	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1719	this is sensible behaviour, for daemons, this is usually undesirable.
		1720
		1721	So when you encounter spurious, unexplained daemon exits, make sure you
		1722	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1723	somewhere, as that would have given you a big clue).
		1724
		1725	=head3 The special problem of accept()ing when you can't
		1726
		1727	Many implementations of the POSIX C<accept> function (for example,
		1728	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1729	connection from the pending queue in all error cases.
		1730
		1731	For example, larger servers often run out of file descriptors (because
		1732	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1733	rejecting the connection, leading to libev signalling readiness on
		1734	the next iteration again (the connection still exists after all), and
		1735	typically causing the program to loop at 100% CPU usage.
		1736
		1737	Unfortunately, the set of errors that cause this issue differs between
		1738	operating systems, there is usually little the app can do to remedy the
		1739	situation, and no known thread-safe method of removing the connection to
		1740	cope with overload is known (to me).
		1741
		1742	One of the easiest ways to handle this situation is to just ignore it
		1743	- when the program encounters an overload, it will just loop until the
		1744	situation is over. While this is a form of busy waiting, no OS offers an
		1745	event-based way to handle this situation, so it's the best one can do.
		1746
		1747	A better way to handle the situation is to log any errors other than
		1748	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1749	messages, and continue as usual, which at least gives the user an idea of
		1750	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1751	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1752	usage.
		1753
		1754	If your program is single-threaded, then you could also keep a dummy file
		1755	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1756	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1757	close that fd, and create a new dummy fd. This will gracefully refuse
		1758	clients under typical overload conditions.
		1759
		1760	The last way to handle it is to simply log the error and C<exit>, as
		1761	is often done with C<malloc> failures, but this results in an easy
		1762	opportunity for a DoS attack.
		1763
		1764	=head3 Watcher-Specific Functions
736		1765
737	=over 4	1766	=over 4
738		1767
739	=item ev_io_init (ev_io *, callback, int fd, int events)	1768	=item ev_io_init (ev_io *, callback, int fd, int events)
740		1769
741	=item ev_io_set (ev_io *, int fd, int events)	1770	=item ev_io_set (ev_io *, int fd, int events)
742		1771
743	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1772	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
744	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1773	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
745	C<EV_READ | EV_WRITE> to receive the given events.	1774	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1775
		1776	=item int fd [read-only]
		1777
		1778	The file descriptor being watched.
		1779
		1780	=item int events [read-only]
		1781
		1782	The events being watched.
746		1783
747	=back	1784	=back
748		1785
		1786	=head3 Examples
		1787
749	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1788	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
750	readable, but only once. Since it is likely line-buffered, you could	1789	readable, but only once. Since it is likely line-buffered, you could
751	attempt to read a whole line in the callback:	1790	attempt to read a whole line in the callback.
752		1791
753	static void	1792	static void
754	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1793	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
755	{	1794	{
756	ev_io_stop (loop, w);	1795	ev_io_stop (loop, w);
757	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1796	.. read from stdin here (or from w->fd) and handle any I/O errors
758	}	1797	}
759		1798
760	...	1799	...
761	struct ev_loop *loop = ev_default_init (0);	1800	struct ev_loop *loop = ev_default_init (0);
762	struct ev_io stdin_readable;	1801	ev_io stdin_readable;
763	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1802	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
764	ev_io_start (loop, &stdin_readable);	1803	ev_io_start (loop, &stdin_readable);
765	ev_loop (loop, 0);	1804	ev_run (loop, 0);
766		1805
767		1806
768	=head2 C<ev_timer> - relative and optionally repeating timeouts	1807	=head2 C<ev_timer> - relative and optionally repeating timeouts
769		1808
770	Timer watchers are simple relative timers that generate an event after a	1809	Timer watchers are simple relative timers that generate an event after a
771	given time, and optionally repeating in regular intervals after that.	1810	given time, and optionally repeating in regular intervals after that.
772		1811
773	The timers are based on real time, that is, if you register an event that	1812	The timers are based on real time, that is, if you register an event that
774	times out after an hour and you reset your system clock to last years	1813	times out after an hour and you reset your system clock to January last
775	time, it will still time out after (roughly) and hour. "Roughly" because	1814	year, it will still time out after (roughly) one hour. "Roughly" because
776	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1815	detecting time jumps is hard, and some inaccuracies are unavoidable (the
777	monotonic clock option helps a lot here).	1816	monotonic clock option helps a lot here).
		1817
		1818	The callback is guaranteed to be invoked only I<after> its timeout has
		1819	passed (not I<at>, so on systems with very low-resolution clocks this
		1820	might introduce a small delay). If multiple timers become ready during the
		1821	same loop iteration then the ones with earlier time-out values are invoked
		1822	before ones of the same priority with later time-out values (but this is
		1823	no longer true when a callback calls C<ev_run> recursively).
		1824
		1825	=head3 Be smart about timeouts
		1826
		1827	Many real-world problems involve some kind of timeout, usually for error
		1828	recovery. A typical example is an HTTP request - if the other side hangs,
		1829	you want to raise some error after a while.
		1830
		1831	What follows are some ways to handle this problem, from obvious and
		1832	inefficient to smart and efficient.
		1833
		1834	In the following, a 60 second activity timeout is assumed - a timeout that
		1835	gets reset to 60 seconds each time there is activity (e.g. each time some
		1836	data or other life sign was received).
		1837
		1838	=over 4
		1839
		1840	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1841
		1842	This is the most obvious, but not the most simple way: In the beginning,
		1843	start the watcher:
		1844
		1845	ev_timer_init (timer, callback, 60., 0.);
		1846	ev_timer_start (loop, timer);
		1847
		1848	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1849	and start it again:
		1850
		1851	ev_timer_stop (loop, timer);
		1852	ev_timer_set (timer, 60., 0.);
		1853	ev_timer_start (loop, timer);
		1854
		1855	This is relatively simple to implement, but means that each time there is
		1856	some activity, libev will first have to remove the timer from its internal
		1857	data structure and then add it again. Libev tries to be fast, but it's
		1858	still not a constant-time operation.
		1859
		1860	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1861
		1862	This is the easiest way, and involves using C<ev_timer_again> instead of
		1863	C<ev_timer_start>.
		1864
		1865	To implement this, configure an C<ev_timer> with a C<repeat> value
		1866	of C<60> and then call C<ev_timer_again> at start and each time you
		1867	successfully read or write some data. If you go into an idle state where
		1868	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1869	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1870
		1871	That means you can ignore both the C<ev_timer_start> function and the
		1872	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1873	member and C<ev_timer_again>.
		1874
		1875	At start:
		1876
		1877	ev_init (timer, callback);
		1878	timer->repeat = 60.;
		1879	ev_timer_again (loop, timer);
		1880
		1881	Each time there is some activity:
		1882
		1883	ev_timer_again (loop, timer);
		1884
		1885	It is even possible to change the time-out on the fly, regardless of
		1886	whether the watcher is active or not:
		1887
		1888	timer->repeat = 30.;
		1889	ev_timer_again (loop, timer);
		1890
		1891	This is slightly more efficient then stopping/starting the timer each time
		1892	you want to modify its timeout value, as libev does not have to completely
		1893	remove and re-insert the timer from/into its internal data structure.
		1894
		1895	It is, however, even simpler than the "obvious" way to do it.
		1896
		1897	=item 3. Let the timer time out, but then re-arm it as required.
		1898
		1899	This method is more tricky, but usually most efficient: Most timeouts are
		1900	relatively long compared to the intervals between other activity - in
		1901	our example, within 60 seconds, there are usually many I/O events with
		1902	associated activity resets.
		1903
		1904	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1905	but remember the time of last activity, and check for a real timeout only
		1906	within the callback:
		1907
		1908	ev_tstamp last_activity; // time of last activity
		1909
		1910	static void
		1911	callback (EV_P_ ev_timer *w, int revents)
		1912	{
		1913	ev_tstamp now = ev_now (EV_A);
		1914	ev_tstamp timeout = last_activity + 60.;
		1915
		1916	// if last_activity + 60. is older than now, we did time out
		1917	if (timeout < now)
		1918	{
		1919	// timeout occurred, take action
		1920	}
		1921	else
		1922	{
		1923	// callback was invoked, but there was some activity, re-arm
		1924	// the watcher to fire in last_activity + 60, which is
		1925	// guaranteed to be in the future, so "again" is positive:
		1926	w->repeat = timeout - now;
		1927	ev_timer_again (EV_A_ w);
		1928	}
		1929	}
		1930
		1931	To summarise the callback: first calculate the real timeout (defined
		1932	as "60 seconds after the last activity"), then check if that time has
		1933	been reached, which means something I<did>, in fact, time out. Otherwise
		1934	the callback was invoked too early (C<timeout> is in the future), so
		1935	re-schedule the timer to fire at that future time, to see if maybe we have
		1936	a timeout then.
		1937
		1938	Note how C<ev_timer_again> is used, taking advantage of the
		1939	C<ev_timer_again> optimisation when the timer is already running.
		1940
		1941	This scheme causes more callback invocations (about one every 60 seconds
		1942	minus half the average time between activity), but virtually no calls to
		1943	libev to change the timeout.
		1944
		1945	To start the timer, simply initialise the watcher and set C<last_activity>
		1946	to the current time (meaning we just have some activity :), then call the
		1947	callback, which will "do the right thing" and start the timer:
		1948
		1949	ev_init (timer, callback);
		1950	last_activity = ev_now (loop);
		1951	callback (loop, timer, EV_TIMER);
		1952
		1953	And when there is some activity, simply store the current time in
		1954	C<last_activity>, no libev calls at all:
		1955
		1956	last_activity = ev_now (loop);
		1957
		1958	This technique is slightly more complex, but in most cases where the
		1959	time-out is unlikely to be triggered, much more efficient.
		1960
		1961	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1962	callback :) - just change the timeout and invoke the callback, which will
		1963	fix things for you.
		1964
		1965	=item 4. Wee, just use a double-linked list for your timeouts.
		1966
		1967	If there is not one request, but many thousands (millions...), all
		1968	employing some kind of timeout with the same timeout value, then one can
		1969	do even better:
		1970
		1971	When starting the timeout, calculate the timeout value and put the timeout
		1972	at the I<end> of the list.
		1973
		1974	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1975	the list is expected to fire (for example, using the technique #3).
		1976
		1977	When there is some activity, remove the timer from the list, recalculate
		1978	the timeout, append it to the end of the list again, and make sure to
		1979	update the C<ev_timer> if it was taken from the beginning of the list.
		1980
		1981	This way, one can manage an unlimited number of timeouts in O(1) time for
		1982	starting, stopping and updating the timers, at the expense of a major
		1983	complication, and having to use a constant timeout. The constant timeout
		1984	ensures that the list stays sorted.
		1985
		1986	=back
		1987
		1988	So which method the best?
		1989
		1990	Method #2 is a simple no-brain-required solution that is adequate in most
		1991	situations. Method #3 requires a bit more thinking, but handles many cases
		1992	better, and isn't very complicated either. In most case, choosing either
		1993	one is fine, with #3 being better in typical situations.
		1994
		1995	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1996	rather complicated, but extremely efficient, something that really pays
		1997	off after the first million or so of active timers, i.e. it's usually
		1998	overkill :)
		1999
		2000	=head3 The special problem of time updates
		2001
		2002	Establishing the current time is a costly operation (it usually takes at
		2003	least two system calls): EV therefore updates its idea of the current
		2004	time only before and after C<ev_run> collects new events, which causes a
		2005	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2006	lots of events in one iteration.
778		2007
779	The relative timeouts are calculated relative to the C<ev_now ()>	2008	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	2009	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	2010	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	2011	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:	2012	timeout on the current time, use something like this to adjust for this:
784		2013
785	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2014	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
786		2015
787	The callback is guarenteed to be invoked only when its timeout has passed,	2016	If the event loop is suspended for a long time, you can also force an
788	but if multiple timers become ready during the same loop iteration then	2017	update of the time returned by C<ev_now ()> by calling C<ev_now_update
789	order of execution is undefined.	2018	()>.
		2019
		2020	=head3 The special problems of suspended animation
		2021
		2022	When you leave the server world it is quite customary to hit machines that
		2023	can suspend/hibernate - what happens to the clocks during such a suspend?
		2024
		2025	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2026	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2027	to run until the system is suspended, but they will not advance while the
		2028	system is suspended. That means, on resume, it will be as if the program
		2029	was frozen for a few seconds, but the suspend time will not be counted
		2030	towards C<ev_timer> when a monotonic clock source is used. The real time
		2031	clock advanced as expected, but if it is used as sole clocksource, then a
		2032	long suspend would be detected as a time jump by libev, and timers would
		2033	be adjusted accordingly.
		2034
		2035	I would not be surprised to see different behaviour in different between
		2036	operating systems, OS versions or even different hardware.
		2037
		2038	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2039	time jump in the monotonic clocks and the realtime clock. If the program
		2040	is suspended for a very long time, and monotonic clock sources are in use,
		2041	then you can expect C<ev_timer>s to expire as the full suspension time
		2042	will be counted towards the timers. When no monotonic clock source is in
		2043	use, then libev will again assume a timejump and adjust accordingly.
		2044
		2045	It might be beneficial for this latter case to call C<ev_suspend>
		2046	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2047	deterministic behaviour in this case (you can do nothing against
		2048	C<SIGSTOP>).
		2049
		2050	=head3 Watcher-Specific Functions and Data Members
790		2051
791	=over 4	2052	=over 4
792		2053
793	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2054	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
794		2055
795	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2056	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
796		2057
797	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2058	Configure the timer to trigger after C<after> seconds. If C<repeat>
798	C<0.>, then it will automatically be stopped. If it is positive, then the	2059	is C<0.>, then it will automatically be stopped once the timeout is
799	timer will automatically be configured to trigger again C<repeat> seconds	2060	reached. If it is positive, then the timer will automatically be
800	later, again, and again, until stopped manually.	2061	configured to trigger again C<repeat> seconds later, again, and again,
		2062	until stopped manually.
801		2063
802	The timer itself will do a best-effort at avoiding drift, that is, if you	2064	The timer itself will do a best-effort at avoiding drift, that is, if
803	configure a timer to trigger every 10 seconds, then it will trigger at	2065	you configure a timer to trigger every 10 seconds, then it will normally
804	exactly 10 second intervals. If, however, your program cannot keep up with	2066	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	2067	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.	2068	do stuff) the timer will not fire more than once per event loop iteration.
807		2069
808	=item ev_timer_again (loop)	2070	=item ev_timer_again (loop, ev_timer *)
809		2071
810	This will act as if the timer timed out and restart it again if it is	2072	This will act as if the timer timed out and restart it again if it is
811	repeating. The exact semantics are:	2073	repeating. The exact semantics are:
812		2074
		2075	If the timer is pending, its pending status is cleared.
		2076
813	If the timer is started but nonrepeating, stop it.	2077	If the timer is started but non-repeating, stop it (as if it timed out).
814		2078
815	If the timer is repeating, either start it if necessary (with the repeat	2079	If the timer is repeating, either start it if necessary (with the
816	value), or reset the running timer to the repeat value.	2080	C<repeat> value), or reset the running timer to the C<repeat> value.
817		2081
818	This sounds a bit complicated, but here is a useful and typical	2082	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
819	example: Imagine you have a tcp connection and you want a so-called idle	2083	usage example.
820	timeout, that is, you want to be called when there have been, say, 60	2084
821	seconds of inactivity on the socket. The easiest way to do this is to	2085	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
822	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	2086
823	time you successfully read or write some data. If you go into an idle	2087	Returns the remaining time until a timer fires. If the timer is active,
824	state where you do not expect data to travel on the socket, you can stop	2088	then this time is relative to the current event loop time, otherwise it's
825	the timer, and again will automatically restart it if need be.	2089	the timeout value currently configured.
		2090
		2091	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2092	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2093	will return C<4>. When the timer expires and is restarted, it will return
		2094	roughly C<7> (likely slightly less as callback invocation takes some time,
		2095	too), and so on.
		2096
		2097	=item ev_tstamp repeat [read-write]
		2098
		2099	The current C<repeat> value. Will be used each time the watcher times out
		2100	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2101	which is also when any modifications are taken into account.
826		2102
827	=back	2103	=back
828		2104
		2105	=head3 Examples
		2106
829	Example: create a timer that fires after 60 seconds.	2107	Example: Create a timer that fires after 60 seconds.
830		2108
831	static void	2109	static void
832	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2110	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
833	{	2111	{
834	.. one minute over, w is actually stopped right here	2112	.. one minute over, w is actually stopped right here
835	}	2113	}
836		2114
837	struct ev_timer mytimer;	2115	ev_timer mytimer;
838	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2116	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
839	ev_timer_start (loop, &mytimer);	2117	ev_timer_start (loop, &mytimer);
840		2118
841	Example: create a timeout timer that times out after 10 seconds of	2119	Example: Create a timeout timer that times out after 10 seconds of
842	inactivity.	2120	inactivity.
843		2121
844	static void	2122	static void
845	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2123	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
846	{	2124	{
847	.. ten seconds without any activity	2125	.. ten seconds without any activity
848	}	2126	}
849		2127
850	struct ev_timer mytimer;	2128	ev_timer mytimer;
851	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2129	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
852	ev_timer_again (&mytimer); /* start timer */	2130	ev_timer_again (&mytimer); /* start timer */
853	ev_loop (loop, 0);	2131	ev_run (loop, 0);
854		2132
855	// and in some piece of code that gets executed on any "activity":	2133	// and in some piece of code that gets executed on any "activity":
856	// reset the timeout to start ticking again at 10 seconds	2134	// reset the timeout to start ticking again at 10 seconds
857	ev_timer_again (&mytimer);	2135	ev_timer_again (&mytimer);
858		2136
859		2137
860	=head2 C<ev_periodic> - to cron or not to cron?	2138	=head2 C<ev_periodic> - to cron or not to cron?
861		2139
862	Periodic watchers are also timers of a kind, but they are very versatile	2140	Periodic watchers are also timers of a kind, but they are very versatile
863	(and unfortunately a bit complex).	2141	(and unfortunately a bit complex).
864		2142
865	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2143	Unlike C<ev_timer>, periodic watchers are not based on real time (or
866	but on wallclock time (absolute time). You can tell a periodic watcher	2144	relative time, the physical time that passes) but on wall clock time
867	to trigger "at" some specific point in time. For example, if you tell a	2145	(absolute time, the thing you can read on your calender or clock). The
868	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2146	difference is that wall clock time can run faster or slower than real
869	+ 10.>) and then reset your system clock to the last year, then it will	2147	time, and time jumps are not uncommon (e.g. when you adjust your
870	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2148	wrist-watch).
871	roughly 10 seconds later and of course not if you reset your system time
872	again).
873		2149
874	They can also be used to implement vastly more complex timers, such as	2150	You can tell a periodic watcher to trigger after some specific point
		2151	in time: for example, if you tell a periodic watcher to trigger "in 10
		2152	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2153	not a delay) and then reset your system clock to January of the previous
		2154	year, then it will take a year or more to trigger the event (unlike an
		2155	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2156	it, as it uses a relative timeout).
		2157
		2158	C<ev_periodic> watchers can also be used to implement vastly more complex
875	triggering an event on eahc midnight, local time.	2159	timers, such as triggering an event on each "midnight, local time", or
		2160	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2161	those cannot react to time jumps.
876		2162
877	As with timers, the callback is guarenteed to be invoked only when the	2163	As with timers, the callback is guaranteed to be invoked only when the
878	time (C<at>) has been passed, but if multiple periodic timers become ready	2164	point in time where it is supposed to trigger has passed. If multiple
879	during the same loop iteration then order of execution is undefined.	2165	timers become ready during the same loop iteration then the ones with
		2166	earlier time-out values are invoked before ones with later time-out values
		2167	(but this is no longer true when a callback calls C<ev_run> recursively).
		2168
		2169	=head3 Watcher-Specific Functions and Data Members
880		2170
881	=over 4	2171	=over 4
882		2172
883	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2173	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
884		2174
885	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2175	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
886		2176
887	Lots of arguments, lets sort it out... There are basically three modes of	2177	Lots of arguments, let's sort it out... There are basically three modes of
888	operation, and we will explain them from simplest to complex:	2178	operation, and we will explain them from simplest to most complex:
889		2179
890	=over 4	2180	=over 4
891		2181
892	=item * absolute timer (interval = reschedule_cb = 0)	2182	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
893		2183
894	In this configuration the watcher triggers an event at the wallclock time	2184	In this configuration the watcher triggers an event after the wall clock
895	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2185	time C<offset> has passed. It will not repeat and will not adjust when a
896	that is, if it is to be run at January 1st 2011 then it will run when the	2186	time jump occurs, that is, if it is to be run at January 1st 2011 then it
897	system time reaches or surpasses this time.	2187	will be stopped and invoked when the system clock reaches or surpasses
		2188	this point in time.
898		2189
899	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2190	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
900		2191
901	In this mode the watcher will always be scheduled to time out at the next	2192	In this mode the watcher will always be scheduled to time out at the next
902	C<at + N * interval> time (for some integer N) and then repeat, regardless	2193	C<offset + N * interval> time (for some integer N, which can also be
903	of any time jumps.	2194	negative) and then repeat, regardless of any time jumps. The C<offset>
		2195	argument is merely an offset into the C<interval> periods.
904		2196
905	This can be used to create timers that do not drift with respect to system	2197	This can be used to create timers that do not drift with respect to the
906	time:	2198	system clock, for example, here is an C<ev_periodic> that triggers each
		2199	hour, on the hour (with respect to UTC):
907		2200
908	ev_periodic_set (&periodic, 0., 3600., 0);	2201	ev_periodic_set (&periodic, 0., 3600., 0);
909		2202
910	This doesn't mean there will always be 3600 seconds in between triggers,	2203	This doesn't mean there will always be 3600 seconds in between triggers,
911	but only that the the callback will be called when the system time shows a	2204	but only that the callback will be called when the system time shows a
912	full hour (UTC), or more correctly, when the system time is evenly divisible	2205	full hour (UTC), or more correctly, when the system time is evenly divisible
913	by 3600.	2206	by 3600.
914		2207
915	Another way to think about it (for the mathematically inclined) is that	2208	Another way to think about it (for the mathematically inclined) is that
916	C<ev_periodic> will try to run the callback in this mode at the next possible	2209	C<ev_periodic> will try to run the callback in this mode at the next possible
917	time where C<time = at (mod interval)>, regardless of any time jumps.	2210	time where C<time = offset (mod interval)>, regardless of any time jumps.
918		2211
		2212	For numerical stability it is preferable that the C<offset> value is near
		2213	C<ev_now ()> (the current time), but there is no range requirement for
		2214	this value, and in fact is often specified as zero.
		2215
		2216	Note also that there is an upper limit to how often a timer can fire (CPU
		2217	speed for example), so if C<interval> is very small then timing stability
		2218	will of course deteriorate. Libev itself tries to be exact to be about one
		2219	millisecond (if the OS supports it and the machine is fast enough).
		2220
919	=item * manual reschedule mode (reschedule_cb = callback)	2221	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
920		2222
921	In this mode the values for C<interval> and C<at> are both being	2223	In this mode the values for C<interval> and C<offset> are both being
922	ignored. Instead, each time the periodic watcher gets scheduled, the	2224	ignored. Instead, each time the periodic watcher gets scheduled, the
923	reschedule callback will be called with the watcher as first, and the	2225	reschedule callback will be called with the watcher as first, and the
924	current time as second argument.	2226	current time as second argument.
925		2227
926	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2228	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
927	ever, or make any event loop modifications>. If you need to stop it,	2229	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	2230	allowed by documentation here>.
929	starting a prepare watcher).
930		2231
		2232	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2233	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2234	only event loop modification you are allowed to do).
		2235
931	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2236	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
932	ev_tstamp now)>, e.g.:	2237	*w, ev_tstamp now)>, e.g.:
933		2238
		2239	static ev_tstamp
934	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2240	my_rescheduler (ev_periodic *w, ev_tstamp now)
935	{	2241	{
936	return now + 60.;	2242	return now + 60.;
937	}	2243	}
938		2244
939	It must return the next time to trigger, based on the passed time value	2245	It must return the next time to trigger, based on the passed time value
940	(that is, the lowest time value larger than to the second argument). It	2246	(that is, the lowest time value larger than to the second argument). It
941	will usually be called just before the callback will be triggered, but	2247	will usually be called just before the callback will be triggered, but
942	might be called at other times, too.	2248	might be called at other times, too.
943		2249
944	NOTE: I<< This callback must always return a time that is later than the	2250	NOTE: I<< This callback must always return a time that is higher than or
945	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2251	equal to the passed C<now> value >>.
946		2252
947	This can be used to create very complex timers, such as a timer that	2253	This can be used to create very complex timers, such as a timer that
948	triggers on each midnight, local time. To do this, you would calculate the	2254	triggers on "next midnight, local time". To do this, you would calculate the
949	next midnight after C<now> and return the timestamp value for this. How	2255	next midnight after C<now> and return the timestamp value for this. How
950	you do this is, again, up to you (but it is not trivial, which is the main	2256	you do this is, again, up to you (but it is not trivial, which is the main
951	reason I omitted it as an example).	2257	reason I omitted it as an example).
952		2258
953	=back	2259	=back
…		…
957	Simply stops and restarts the periodic watcher again. This is only useful	2263	Simply stops and restarts the periodic watcher again. This is only useful
958	when you changed some parameters or the reschedule callback would return	2264	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	2265	a different time than the last time it was called (e.g. in a crond like
960	program when the crontabs have changed).	2266	program when the crontabs have changed).
961		2267
		2268	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2269
		2270	When active, returns the absolute time that the watcher is supposed
		2271	to trigger next. This is not the same as the C<offset> argument to
		2272	C<ev_periodic_set>, but indeed works even in interval and manual
		2273	rescheduling modes.
		2274
		2275	=item ev_tstamp offset [read-write]
		2276
		2277	When repeating, this contains the offset value, otherwise this is the
		2278	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2279	although libev might modify this value for better numerical stability).
		2280
		2281	Can be modified any time, but changes only take effect when the periodic
		2282	timer fires or C<ev_periodic_again> is being called.
		2283
		2284	=item ev_tstamp interval [read-write]
		2285
		2286	The current interval value. Can be modified any time, but changes only
		2287	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2288	called.
		2289
		2290	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2291
		2292	The current reschedule callback, or C<0>, if this functionality is
		2293	switched off. Can be changed any time, but changes only take effect when
		2294	the periodic timer fires or C<ev_periodic_again> is being called.
		2295
962	=back	2296	=back
963		2297
		2298	=head3 Examples
		2299
964	Example: call a callback every hour, or, more precisely, whenever the	2300	Example: Call a callback every hour, or, more precisely, whenever the
965	system clock is divisible by 3600. The callback invocation times have	2301	system time is divisible by 3600. The callback invocation times have
966	potentially a lot of jittering, but good long-term stability.	2302	potentially a lot of jitter, but good long-term stability.
967		2303
968	static void	2304	static void
969	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2305	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
970	{	2306	{
971	... its now a full hour (UTC, or TAI or whatever your clock follows)	2307	... its now a full hour (UTC, or TAI or whatever your clock follows)
972	}	2308	}
973		2309
974	struct ev_periodic hourly_tick;	2310	ev_periodic hourly_tick;
975	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2311	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
976	ev_periodic_start (loop, &hourly_tick);	2312	ev_periodic_start (loop, &hourly_tick);
977		2313
978	Example: the same as above, but use a reschedule callback to do it:	2314	Example: The same as above, but use a reschedule callback to do it:
979		2315
980	#include <math.h>	2316	#include <math.h>
981		2317
982	static ev_tstamp	2318	static ev_tstamp
983	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2319	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
984	{	2320	{
985	return fmod (now, 3600.) + 3600.;	2321	return now + (3600. - fmod (now, 3600.));
986	}	2322	}
987		2323
988	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2324	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
989		2325
990	Example: call a callback every hour, starting now:	2326	Example: Call a callback every hour, starting now:
991		2327
992	struct ev_periodic hourly_tick;	2328	ev_periodic hourly_tick;
993	ev_periodic_init (&hourly_tick, clock_cb,	2329	ev_periodic_init (&hourly_tick, clock_cb,
994	fmod (ev_now (loop), 3600.), 3600., 0);	2330	fmod (ev_now (loop), 3600.), 3600., 0);
995	ev_periodic_start (loop, &hourly_tick);	2331	ev_periodic_start (loop, &hourly_tick);
996		2332
997		2333
998	=head2 C<ev_signal> - signal me when a signal gets signalled!	2334	=head2 C<ev_signal> - signal me when a signal gets signalled!
999		2335
1000	Signal watchers will trigger an event when the process receives a specific	2336	Signal watchers will trigger an event when the process receives a specific
1001	signal one or more times. Even though signals are very asynchronous, libev	2337	signal one or more times. Even though signals are very asynchronous, libev
1002	will try it's best to deliver signals synchronously, i.e. as part of the	2338	will try its best to deliver signals synchronously, i.e. as part of the
1003	normal event processing, like any other event.	2339	normal event processing, like any other event.
1004		2340
		2341	If you want signals to be delivered truly asynchronously, just use
		2342	C<sigaction> as you would do without libev and forget about sharing
		2343	the signal. You can even use C<ev_async> from a signal handler to
		2344	synchronously wake up an event loop.
		2345
1005	You can configure as many watchers as you like per signal. Only when the	2346	You can configure as many watchers as you like for the same signal, but
		2347	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2348	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2349	C<SIGINT> in both the default loop and another loop at the same time. At
		2350	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2351
1006	first watcher gets started will libev actually register a signal watcher	2352	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	2353	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	2354	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	2355
1010	SIG_DFL (regardless of what it was set to before).	2356	If possible and supported, libev will install its handlers with
		2357	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2358	not be unduly interrupted. If you have a problem with system calls getting
		2359	interrupted by signals you can block all signals in an C<ev_check> watcher
		2360	and unblock them in an C<ev_prepare> watcher.
		2361
		2362	=head3 The special problem of inheritance over fork/execve/pthread_create
		2363
		2364	Both the signal mask (C<sigprocmask>) and the signal disposition
		2365	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2366	stopping it again), that is, libev might or might not block the signal,
		2367	and might or might not set or restore the installed signal handler.
		2368
		2369	While this does not matter for the signal disposition (libev never
		2370	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2371	C<execve>), this matters for the signal mask: many programs do not expect
		2372	certain signals to be blocked.
		2373
		2374	This means that before calling C<exec> (from the child) you should reset
		2375	the signal mask to whatever "default" you expect (all clear is a good
		2376	choice usually).
		2377
		2378	The simplest way to ensure that the signal mask is reset in the child is
		2379	to install a fork handler with C<pthread_atfork> that resets it. That will
		2380	catch fork calls done by libraries (such as the libc) as well.
		2381
		2382	In current versions of libev, the signal will not be blocked indefinitely
		2383	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2384	the window of opportunity for problems, it will not go away, as libev
		2385	I<has> to modify the signal mask, at least temporarily.
		2386
		2387	So I can't stress this enough: I<If you do not reset your signal mask when
		2388	you expect it to be empty, you have a race condition in your code>. This
		2389	is not a libev-specific thing, this is true for most event libraries.
		2390
		2391	=head3 The special problem of threads signal handling
		2392
		2393	POSIX threads has problematic signal handling semantics, specifically,
		2394	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2395	threads in a process block signals, which is hard to achieve.
		2396
		2397	When you want to use sigwait (or mix libev signal handling with your own
		2398	for the same signals), you can tackle this problem by globally blocking
		2399	all signals before creating any threads (or creating them with a fully set
		2400	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2401	loops. Then designate one thread as "signal receiver thread" which handles
		2402	these signals. You can pass on any signals that libev might be interested
		2403	in by calling C<ev_feed_signal>.
		2404
		2405	=head3 Watcher-Specific Functions and Data Members
1011		2406
1012	=over 4	2407	=over 4
1013		2408
1014	=item ev_signal_init (ev_signal *, callback, int signum)	2409	=item ev_signal_init (ev_signal *, callback, int signum)
1015		2410
1016	=item ev_signal_set (ev_signal *, int signum)	2411	=item ev_signal_set (ev_signal *, int signum)
1017		2412
1018	Configures the watcher to trigger on the given signal number (usually one	2413	Configures the watcher to trigger on the given signal number (usually one
1019	of the C<SIGxxx> constants).	2414	of the C<SIGxxx> constants).
1020		2415
		2416	=item int signum [read-only]
		2417
		2418	The signal the watcher watches out for.
		2419
1021	=back	2420	=back
1022		2421
		2422	=head3 Examples
		2423
		2424	Example: Try to exit cleanly on SIGINT.
		2425
		2426	static void
		2427	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2428	{
		2429	ev_break (loop, EVBREAK_ALL);
		2430	}
		2431
		2432	ev_signal signal_watcher;
		2433	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2434	ev_signal_start (loop, &signal_watcher);
		2435
1023		2436
1024	=head2 C<ev_child> - watch out for process status changes	2437	=head2 C<ev_child> - watch out for process status changes
1025		2438
1026	Child watchers trigger when your process receives a SIGCHLD in response to	2439	Child watchers trigger when your process receives a SIGCHLD in response to
1027	some child status changes (most typically when a child of yours dies).	2440	some child status changes (most typically when a child of yours dies or
		2441	exits). It is permissible to install a child watcher I<after> the child
		2442	has been forked (which implies it might have already exited), as long
		2443	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2444	forking and then immediately registering a watcher for the child is fine,
		2445	but forking and registering a watcher a few event loop iterations later or
		2446	in the next callback invocation is not.
		2447
		2448	Only the default event loop is capable of handling signals, and therefore
		2449	you can only register child watchers in the default event loop.
		2450
		2451	Due to some design glitches inside libev, child watchers will always be
		2452	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2453	libev)
		2454
		2455	=head3 Process Interaction
		2456
		2457	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2458	initialised. This is necessary to guarantee proper behaviour even if the
		2459	first child watcher is started after the child exits. The occurrence
		2460	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2461	synchronously as part of the event loop processing. Libev always reaps all
		2462	children, even ones not watched.
		2463
		2464	=head3 Overriding the Built-In Processing
		2465
		2466	Libev offers no special support for overriding the built-in child
		2467	processing, but if your application collides with libev's default child
		2468	handler, you can override it easily by installing your own handler for
		2469	C<SIGCHLD> after initialising the default loop, and making sure the
		2470	default loop never gets destroyed. You are encouraged, however, to use an
		2471	event-based approach to child reaping and thus use libev's support for
		2472	that, so other libev users can use C<ev_child> watchers freely.
		2473
		2474	=head3 Stopping the Child Watcher
		2475
		2476	Currently, the child watcher never gets stopped, even when the
		2477	child terminates, so normally one needs to stop the watcher in the
		2478	callback. Future versions of libev might stop the watcher automatically
		2479	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2480	problem).
		2481
		2482	=head3 Watcher-Specific Functions and Data Members
1028		2483
1029	=over 4	2484	=over 4
1030		2485
1031	=item ev_child_init (ev_child *, callback, int pid)	2486	=item ev_child_init (ev_child *, callback, int pid, int trace)
1032		2487
1033	=item ev_child_set (ev_child *, int pid)	2488	=item ev_child_set (ev_child *, int pid, int trace)
1034		2489
1035	Configures the watcher to wait for status changes of process C<pid> (or	2490	Configures the watcher to wait for status changes of process C<pid> (or
1036	I<any> process if C<pid> is specified as C<0>). The callback can look	2491	I<any> process if C<pid> is specified as C<0>). The callback can look
1037	at the C<rstatus> member of the C<ev_child> watcher structure to see	2492	at the C<rstatus> member of the C<ev_child> watcher structure to see
1038	the status word (use the macros from C<sys/wait.h> and see your systems	2493	the status word (use the macros from C<sys/wait.h> and see your systems
1039	C<waitpid> documentation). The C<rpid> member contains the pid of the	2494	C<waitpid> documentation). The C<rpid> member contains the pid of the
1040	process causing the status change.	2495	process causing the status change. C<trace> must be either C<0> (only
		2496	activate the watcher when the process terminates) or C<1> (additionally
		2497	activate the watcher when the process is stopped or continued).
		2498
		2499	=item int pid [read-only]
		2500
		2501	The process id this watcher watches out for, or C<0>, meaning any process id.
		2502
		2503	=item int rpid [read-write]
		2504
		2505	The process id that detected a status change.
		2506
		2507	=item int rstatus [read-write]
		2508
		2509	The process exit/trace status caused by C<rpid> (see your systems
		2510	C<waitpid> and C<sys/wait.h> documentation for details).
1041		2511
1042	=back	2512	=back
1043		2513
1044	Example: try to exit cleanly on SIGINT and SIGTERM.	2514	=head3 Examples
1045		2515
		2516	Example: C<fork()> a new process and install a child handler to wait for
		2517	its completion.
		2518
		2519	ev_child cw;
		2520
1046	static void	2521	static void
1047	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2522	child_cb (EV_P_ ev_child *w, int revents)
1048	{	2523	{
1049	ev_unloop (loop, EVUNLOOP_ALL);	2524	ev_child_stop (EV_A_ w);
		2525	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1050	}	2526	}
1051		2527
1052	struct ev_signal signal_watcher;	2528	pid_t pid = fork ();
1053	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2529
1054	ev_signal_start (loop, &sigint_cb);	2530	if (pid < 0)
		2531	// error
		2532	else if (pid == 0)
		2533	{
		2534	// the forked child executes here
		2535	exit (1);
		2536	}
		2537	else
		2538	{
		2539	ev_child_init (&cw, child_cb, pid, 0);
		2540	ev_child_start (EV_DEFAULT_ &cw);
		2541	}
		2542
		2543
		2544	=head2 C<ev_stat> - did the file attributes just change?
		2545
		2546	This watches a file system path for attribute changes. That is, it calls
		2547	C<stat> on that path in regular intervals (or when the OS says it changed)
		2548	and sees if it changed compared to the last time, invoking the callback if
		2549	it did.
		2550
		2551	The path does not need to exist: changing from "path exists" to "path does
		2552	not exist" is a status change like any other. The condition "path does not
		2553	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2554	C<st_nlink> field being zero (which is otherwise always forced to be at
		2555	least one) and all the other fields of the stat buffer having unspecified
		2556	contents.
		2557
		2558	The path I<must not> end in a slash or contain special components such as
		2559	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2560	your working directory changes, then the behaviour is undefined.
		2561
		2562	Since there is no portable change notification interface available, the
		2563	portable implementation simply calls C<stat(2)> regularly on the path
		2564	to see if it changed somehow. You can specify a recommended polling
		2565	interval for this case. If you specify a polling interval of C<0> (highly
		2566	recommended!) then a I<suitable, unspecified default> value will be used
		2567	(which you can expect to be around five seconds, although this might
		2568	change dynamically). Libev will also impose a minimum interval which is
		2569	currently around C<0.1>, but that's usually overkill.
		2570
		2571	This watcher type is not meant for massive numbers of stat watchers,
		2572	as even with OS-supported change notifications, this can be
		2573	resource-intensive.
		2574
		2575	At the time of this writing, the only OS-specific interface implemented
		2576	is the Linux inotify interface (implementing kqueue support is left as an
		2577	exercise for the reader. Note, however, that the author sees no way of
		2578	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2579
		2580	=head3 ABI Issues (Largefile Support)
		2581
		2582	Libev by default (unless the user overrides this) uses the default
		2583	compilation environment, which means that on systems with large file
		2584	support disabled by default, you get the 32 bit version of the stat
		2585	structure. When using the library from programs that change the ABI to
		2586	use 64 bit file offsets the programs will fail. In that case you have to
		2587	compile libev with the same flags to get binary compatibility. This is
		2588	obviously the case with any flags that change the ABI, but the problem is
		2589	most noticeably displayed with ev_stat and large file support.
		2590
		2591	The solution for this is to lobby your distribution maker to make large
		2592	file interfaces available by default (as e.g. FreeBSD does) and not
		2593	optional. Libev cannot simply switch on large file support because it has
		2594	to exchange stat structures with application programs compiled using the
		2595	default compilation environment.
		2596
		2597	=head3 Inotify and Kqueue
		2598
		2599	When C<inotify (7)> support has been compiled into libev and present at
		2600	runtime, it will be used to speed up change detection where possible. The
		2601	inotify descriptor will be created lazily when the first C<ev_stat>
		2602	watcher is being started.
		2603
		2604	Inotify presence does not change the semantics of C<ev_stat> watchers
		2605	except that changes might be detected earlier, and in some cases, to avoid
		2606	making regular C<stat> calls. Even in the presence of inotify support
		2607	there are many cases where libev has to resort to regular C<stat> polling,
		2608	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2609	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2610	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2611	xfs are fully working) libev usually gets away without polling.
		2612
		2613	There is no support for kqueue, as apparently it cannot be used to
		2614	implement this functionality, due to the requirement of having a file
		2615	descriptor open on the object at all times, and detecting renames, unlinks
		2616	etc. is difficult.
		2617
		2618	=head3 C<stat ()> is a synchronous operation
		2619
		2620	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2621	the process. The exception are C<ev_stat> watchers - those call C<stat
		2622	()>, which is a synchronous operation.
		2623
		2624	For local paths, this usually doesn't matter: unless the system is very
		2625	busy or the intervals between stat's are large, a stat call will be fast,
		2626	as the path data is usually in memory already (except when starting the
		2627	watcher).
		2628
		2629	For networked file systems, calling C<stat ()> can block an indefinite
		2630	time due to network issues, and even under good conditions, a stat call
		2631	often takes multiple milliseconds.
		2632
		2633	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2634	paths, although this is fully supported by libev.
		2635
		2636	=head3 The special problem of stat time resolution
		2637
		2638	The C<stat ()> system call only supports full-second resolution portably,
		2639	and even on systems where the resolution is higher, most file systems
		2640	still only support whole seconds.
		2641
		2642	That means that, if the time is the only thing that changes, you can
		2643	easily miss updates: on the first update, C<ev_stat> detects a change and
		2644	calls your callback, which does something. When there is another update
		2645	within the same second, C<ev_stat> will be unable to detect unless the
		2646	stat data does change in other ways (e.g. file size).
		2647
		2648	The solution to this is to delay acting on a change for slightly more
		2649	than a second (or till slightly after the next full second boundary), using
		2650	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2651	ev_timer_again (loop, w)>).
		2652
		2653	The C<.02> offset is added to work around small timing inconsistencies
		2654	of some operating systems (where the second counter of the current time
		2655	might be be delayed. One such system is the Linux kernel, where a call to
		2656	C<gettimeofday> might return a timestamp with a full second later than
		2657	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2658	update file times then there will be a small window where the kernel uses
		2659	the previous second to update file times but libev might already execute
		2660	the timer callback).
		2661
		2662	=head3 Watcher-Specific Functions and Data Members
		2663
		2664	=over 4
		2665
		2666	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2667
		2668	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2669
		2670	Configures the watcher to wait for status changes of the given
		2671	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2672	be detected and should normally be specified as C<0> to let libev choose
		2673	a suitable value. The memory pointed to by C<path> must point to the same
		2674	path for as long as the watcher is active.
		2675
		2676	The callback will receive an C<EV_STAT> event when a change was detected,
		2677	relative to the attributes at the time the watcher was started (or the
		2678	last change was detected).
		2679
		2680	=item ev_stat_stat (loop, ev_stat *)
		2681
		2682	Updates the stat buffer immediately with new values. If you change the
		2683	watched path in your callback, you could call this function to avoid
		2684	detecting this change (while introducing a race condition if you are not
		2685	the only one changing the path). Can also be useful simply to find out the
		2686	new values.
		2687
		2688	=item ev_statdata attr [read-only]
		2689
		2690	The most-recently detected attributes of the file. Although the type is
		2691	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2692	suitable for your system, but you can only rely on the POSIX-standardised
		2693	members to be present. If the C<st_nlink> member is C<0>, then there was
		2694	some error while C<stat>ing the file.
		2695
		2696	=item ev_statdata prev [read-only]
		2697
		2698	The previous attributes of the file. The callback gets invoked whenever
		2699	C<prev> != C<attr>, or, more precisely, one or more of these members
		2700	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2701	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2702
		2703	=item ev_tstamp interval [read-only]
		2704
		2705	The specified interval.
		2706
		2707	=item const char *path [read-only]
		2708
		2709	The file system path that is being watched.
		2710
		2711	=back
		2712
		2713	=head3 Examples
		2714
		2715	Example: Watch C</etc/passwd> for attribute changes.
		2716
		2717	static void
		2718	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2719	{
		2720	/* /etc/passwd changed in some way */
		2721	if (w->attr.st_nlink)
		2722	{
		2723	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2724	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2725	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2726	}
		2727	else
		2728	/* you shalt not abuse printf for puts */
		2729	puts ("wow, /etc/passwd is not there, expect problems. "
		2730	"if this is windows, they already arrived\n");
		2731	}
		2732
		2733	...
		2734	ev_stat passwd;
		2735
		2736	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2737	ev_stat_start (loop, &passwd);
		2738
		2739	Example: Like above, but additionally use a one-second delay so we do not
		2740	miss updates (however, frequent updates will delay processing, too, so
		2741	one might do the work both on C<ev_stat> callback invocation I<and> on
		2742	C<ev_timer> callback invocation).
		2743
		2744	static ev_stat passwd;
		2745	static ev_timer timer;
		2746
		2747	static void
		2748	timer_cb (EV_P_ ev_timer *w, int revents)
		2749	{
		2750	ev_timer_stop (EV_A_ w);
		2751
		2752	/* now it's one second after the most recent passwd change */
		2753	}
		2754
		2755	static void
		2756	stat_cb (EV_P_ ev_stat *w, int revents)
		2757	{
		2758	/* reset the one-second timer */
		2759	ev_timer_again (EV_A_ &timer);
		2760	}
		2761
		2762	...
		2763	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2764	ev_stat_start (loop, &passwd);
		2765	ev_timer_init (&timer, timer_cb, 0., 1.02);
1055		2766
1056		2767
1057	=head2 C<ev_idle> - when you've got nothing better to do...	2768	=head2 C<ev_idle> - when you've got nothing better to do...
1058		2769
1059	Idle watchers trigger events when there are no other events are pending	2770	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	2771	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,	2772	as receiving "events").
1062	imagine) it will not be triggered. But when your process is idle all idle	2773
1063	watchers are being called again and again, once per event loop iteration -	2774	That is, as long as your process is busy handling sockets or timeouts
		2775	(or even signals, imagine) of the same or higher priority it will not be
		2776	triggered. But when your process is idle (or only lower-priority watchers
		2777	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	2778	iteration - until stopped, that is, or your process receives more events
1065	busy.	2779	and becomes busy again with higher priority stuff.
1066		2780
1067	The most noteworthy effect is that as long as any idle watchers are	2781	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.	2782	active, the process will not block when waiting for new events.
1069		2783
1070	Apart from keeping your process non-blocking (which is a useful	2784	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	2785	effect on its own sometimes), idle watchers are a good place to do
1072	"pseudo-background processing", or delay processing stuff to after the	2786	"pseudo-background processing", or delay processing stuff to after the
1073	event loop has handled all outstanding events.	2787	event loop has handled all outstanding events.
1074		2788
		2789	=head3 Watcher-Specific Functions and Data Members
		2790
1075	=over 4	2791	=over 4
1076		2792
1077	=item ev_idle_init (ev_signal *, callback)	2793	=item ev_idle_init (ev_idle *, callback)
1078		2794
1079	Initialises and configures the idle watcher - it has no parameters of any	2795	Initialises and configures the idle watcher - it has no parameters of any
1080	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2796	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1081	believe me.	2797	believe me.
1082		2798
1083	=back	2799	=back
1084		2800
		2801	=head3 Examples
		2802
1085	Example: dynamically allocate an C<ev_idle>, start it, and in the	2803	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1086	callback, free it. Alos, use no error checking, as usual.	2804	callback, free it. Also, use no error checking, as usual.
1087		2805
1088	static void	2806	static void
1089	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2807	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1090	{	2808	{
1091	free (w);	2809	free (w);
1092	// now do something you wanted to do when the program has	2810	// now do something you wanted to do when the program has
1093	// no longer asnything immediate to do.	2811	// no longer anything immediate to do.
1094	}	2812	}
1095		2813
1096	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2814	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1097	ev_idle_init (idle_watcher, idle_cb);	2815	ev_idle_init (idle_watcher, idle_cb);
1098	ev_idle_start (loop, idle_cb);	2816	ev_idle_start (loop, idle_watcher);
1099		2817
1100		2818
1101	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2819	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1102		2820
1103	Prepare and check watchers are usually (but not always) used in tandem:	2821	Prepare and check watchers are usually (but not always) used in pairs:
1104	prepare watchers get invoked before the process blocks and check watchers	2822	prepare watchers get invoked before the process blocks and check watchers
1105	afterwards.	2823	afterwards.
1106		2824
1107	You I<must not> call C<ev_loop> or similar functions that enter	2825	You I<must not> call C<ev_run> or similar functions that enter
1108	the current event loop from either C<ev_prepare> or C<ev_check>	2826	the current event loop from either C<ev_prepare> or C<ev_check>
1109	watchers. Other loops than the current one are fine, however. The	2827	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	2828	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,	2829	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	2830	C<ev_check> so if you have one watcher of each kind they will always be
1113	called in pairs bracketing the blocking call.	2831	called in pairs bracketing the blocking call.
1114		2832
1115	Their main purpose is to integrate other event mechanisms into libev and	2833	Their main purpose is to integrate other event mechanisms into libev and
1116	their use is somewhat advanced. This could be used, for example, to track	2834	their use is somewhat advanced. They could be used, for example, to track
1117	variable changes, implement your own watchers, integrate net-snmp or a	2835	variable changes, implement your own watchers, integrate net-snmp or a
1118	coroutine library and lots more. They are also occasionally useful if	2836	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,	2837	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>	2838	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1121	watcher).	2839	watcher).
1122		2840
1123	This is done by examining in each prepare call which file descriptors need	2841	This is done by examining in each prepare call which file descriptors
1124	to be watched by the other library, registering C<ev_io> watchers for	2842	need to be watched by the other library, registering C<ev_io> watchers
1125	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2843	for them and starting an C<ev_timer> watcher for any timeouts (many
1126	provide just this functionality). Then, in the check watcher you check for	2844	libraries provide exactly this functionality). Then, in the check watcher,
1127	any events that occured (by checking the pending status of all watchers	2845	you check for any events that occurred (by checking the pending status
1128	and stopping them) and call back into the library. The I/O and timer	2846	of all watchers and stopping them) and call back into the library. The
1129	callbacks will never actually be called (but must be valid nevertheless,	2847	I/O and timer callbacks will never actually be called (but must be valid
1130	because you never know, you know?).	2848	nevertheless, because you never know, you know?).
1131		2849
1132	As another example, the Perl Coro module uses these hooks to integrate	2850	As another example, the Perl Coro module uses these hooks to integrate
1133	coroutines into libev programs, by yielding to other active coroutines	2851	coroutines into libev programs, by yielding to other active coroutines
1134	during each prepare and only letting the process block if no coroutines	2852	during each prepare and only letting the process block if no coroutines
1135	are ready to run (it's actually more complicated: it only runs coroutines	2853	are ready to run (it's actually more complicated: it only runs coroutines
1136	with priority higher than or equal to the event loop and one coroutine	2854	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	2855	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	2856	loop from blocking if lower-priority coroutines are active, thus mapping
1139	low-priority coroutines to idle/background tasks).	2857	low-priority coroutines to idle/background tasks).
1140		2858
		2859	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2860	priority, to ensure that they are being run before any other watchers
		2861	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2862
		2863	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2864	activate ("feed") events into libev. While libev fully supports this, they
		2865	might get executed before other C<ev_check> watchers did their job. As
		2866	C<ev_check> watchers are often used to embed other (non-libev) event
		2867	loops those other event loops might be in an unusable state until their
		2868	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2869	others).
		2870
		2871	=head3 Watcher-Specific Functions and Data Members
		2872
1141	=over 4	2873	=over 4
1142		2874
1143	=item ev_prepare_init (ev_prepare *, callback)	2875	=item ev_prepare_init (ev_prepare *, callback)
1144		2876
1145	=item ev_check_init (ev_check *, callback)	2877	=item ev_check_init (ev_check *, callback)
1146		2878
1147	Initialises and configures the prepare or check watcher - they have no	2879	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>	2880	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.	2881	macros, but using them is utterly, utterly, utterly and completely
		2882	pointless.
1150		2883
1151	=back	2884	=back
1152		2885
1153	Example: To include a library such as adns, you would add IO watchers	2886	=head3 Examples
1154	and a timeout watcher in a prepare handler, as required by libadns, and	2887
		2888	There are a number of principal ways to embed other event loops or modules
		2889	into libev. Here are some ideas on how to include libadns into libev
		2890	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2891	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2892	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2893	Glib event loop).
		2894
		2895	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	2896	and in a check watcher, destroy them and call into libadns. What follows
1156	pseudo-code only of course:	2897	is pseudo-code only of course. This requires you to either use a low
		2898	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2899	the callbacks for the IO/timeout watchers might not have been called yet.
1157		2900
1158	static ev_io iow [nfd];	2901	static ev_io iow [nfd];
1159	static ev_timer tw;	2902	static ev_timer tw;
1160		2903
1161	static void	2904	static void
1162	io_cb (ev_loop *loop, ev_io *w, int revents)	2905	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1163	{	2906	{
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	}	2907	}
1170		2908
1171	// create io watchers for each fd and a timer before blocking	2909	// create io watchers for each fd and a timer before blocking
1172	static void	2910	static void
1173	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2911	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1174	{	2912	{
1175	int timeout = 3600000;truct pollfd fds [nfd];	2913	int timeout = 3600000;
		2914	struct pollfd fds [nfd];
1176	// actual code will need to loop here and realloc etc.	2915	// actual code will need to loop here and realloc etc.
1177	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2916	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1178		2917
1179	/* the callback is illegal, but won't be called as we stop during check */	2918	/* the callback is illegal, but won't be called as we stop during check */
1180	ev_timer_init (&tw, 0, timeout * 1e-3);	2919	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1181	ev_timer_start (loop, &tw);	2920	ev_timer_start (loop, &tw);
1182		2921
1183	// create on ev_io per pollfd	2922	// create one ev_io per pollfd
1184	for (int i = 0; i < nfd; ++i)	2923	for (int i = 0; i < nfd; ++i)
1185	{	2924	{
1186	ev_io_init (iow + i, io_cb, fds [i].fd,	2925	ev_io_init (iow + i, io_cb, fds [i].fd,
1187	((fds [i].events & POLLIN ? EV_READ : 0)	2926	((fds [i].events & POLLIN ? EV_READ : 0)
1188	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2927	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1189		2928
1190	fds [i].revents = 0;	2929	fds [i].revents = 0;
1191	iow [i].data = fds + i;
1192	ev_io_start (loop, iow + i);	2930	ev_io_start (loop, iow + i);
1193	}	2931	}
1194	}	2932	}
1195		2933
1196	// stop all watchers after blocking	2934	// stop all watchers after blocking
1197	static void	2935	static void
1198	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2936	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1199	{	2937	{
1200	ev_timer_stop (loop, &tw);	2938	ev_timer_stop (loop, &tw);
1201		2939
1202	for (int i = 0; i < nfd; ++i)	2940	for (int i = 0; i < nfd; ++i)
		2941	{
		2942	// set the relevant poll flags
		2943	// could also call adns_processreadable etc. here
		2944	struct pollfd *fd = fds + i;
		2945	int revents = ev_clear_pending (iow + i);
		2946	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2947	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2948
		2949	// now stop the watcher
1203	ev_io_stop (loop, iow + i);	2950	ev_io_stop (loop, iow + i);
		2951	}
1204		2952
1205	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2953	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1206	}	2954	}
		2955
		2956	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2957	in the prepare watcher and would dispose of the check watcher.
		2958
		2959	Method 3: If the module to be embedded supports explicit event
		2960	notification (libadns does), you can also make use of the actual watcher
		2961	callbacks, and only destroy/create the watchers in the prepare watcher.
		2962
		2963	static void
		2964	timer_cb (EV_P_ ev_timer *w, int revents)
		2965	{
		2966	adns_state ads = (adns_state)w->data;
		2967	update_now (EV_A);
		2968
		2969	adns_processtimeouts (ads, &tv_now);
		2970	}
		2971
		2972	static void
		2973	io_cb (EV_P_ ev_io *w, int revents)
		2974	{
		2975	adns_state ads = (adns_state)w->data;
		2976	update_now (EV_A);
		2977
		2978	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2979	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2980	}
		2981
		2982	// do not ever call adns_afterpoll
		2983
		2984	Method 4: Do not use a prepare or check watcher because the module you
		2985	want to embed is not flexible enough to support it. Instead, you can
		2986	override their poll function. The drawback with this solution is that the
		2987	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2988	this approach, effectively embedding EV as a client into the horrible
		2989	libglib event loop.
		2990
		2991	static gint
		2992	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2993	{
		2994	int got_events = 0;
		2995
		2996	for (n = 0; n < nfds; ++n)
		2997	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2998
		2999	if (timeout >= 0)
		3000	// create/start timer
		3001
		3002	// poll
		3003	ev_run (EV_A_ 0);
		3004
		3005	// stop timer again
		3006	if (timeout >= 0)
		3007	ev_timer_stop (EV_A_ &to);
		3008
		3009	// stop io watchers again - their callbacks should have set
		3010	for (n = 0; n < nfds; ++n)
		3011	ev_io_stop (EV_A_ iow [n]);
		3012
		3013	return got_events;
		3014	}
1207		3015
1208		3016
1209	=head2 C<ev_embed> - when one backend isn't enough...	3017	=head2 C<ev_embed> - when one backend isn't enough...
1210		3018
1211	This is a rather advanced watcher type that lets you embed one event loop	3019	This is a rather advanced watcher type that lets you embed one event loop
…		…
1217	prioritise I/O.	3025	prioritise I/O.
1218		3026
1219	As an example for a bug workaround, the kqueue backend might only support	3027	As an example for a bug workaround, the kqueue backend might only support
1220	sockets on some platform, so it is unusable as generic backend, but you	3028	sockets on some platform, so it is unusable as generic backend, but you
1221	still want to make use of it because you have many sockets and it scales	3029	still want to make use of it because you have many sockets and it scales
1222	so nicely. In this case, you would create a kqueue-based loop and embed it	3030	so nicely. In this case, you would create a kqueue-based loop and embed
1223	into your default loop (which might use e.g. poll). Overall operation will	3031	it into your default loop (which might use e.g. poll). Overall operation
1224	be a bit slower because first libev has to poll and then call kevent, but	3032	will be a bit slower because first libev has to call C<poll> and then
1225	at least you can use both at what they are best.	3033	C<kevent>, but at least you can use both mechanisms for what they are
		3034	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1226		3035
1227	As for prioritising I/O: rarely you have the case where some fds have	3036	As for prioritising I/O: under rare circumstances you have the case where
1228	to be watched and handled very quickly (with low latency), and even	3037	some fds have to be watched and handled very quickly (with low latency),
1229	priorities and idle watchers might have too much overhead. In this case	3038	and even priorities and idle watchers might have too much overhead. In
1230	you would put all the high priority stuff in one loop and all the rest in	3039	this case you would put all the high priority stuff in one loop and all
1231	a second one, and embed the second one in the first.	3040	the rest in a second one, and embed the second one in the first.
1232		3041
1233	As long as the watcher is active, the callback will be invoked every time	3042	As long as the watcher is active, the callback will be invoked every
1234	there might be events pending in the embedded loop. The callback must then	3043	time there might be events pending in the embedded loop. The callback
1235	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3044	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1236	their callbacks (you could also start an idle watcher to give the embedded	3045	sweep and invoke their callbacks (the callback doesn't need to invoke the
1237	loop strictly lower priority for example). You can also set the callback	3046	C<ev_embed_sweep> function directly, it could also start an idle watcher
1238	to C<0>, in which case the embed watcher will automatically execute the	3047	to give the embedded loop strictly lower priority for example).
1239	embedded loop sweep.
1240		3048
1241	As long as the watcher is started it will automatically handle events. The	3049	You can also set the callback to C<0>, in which case the embed watcher
1242	callback will be invoked whenever some events have been handled. You can	3050	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		3051
1246	Also, there have not currently been made special provisions for forking:	3052	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,	3053	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	3054	embedding loop forks. In other cases, the user is responsible for calling
1249	yourself.	3055	C<ev_loop_fork> on the embedded loop.
1250		3056
1251	Unfortunately, not all backends are embeddable, only the ones returned by	3057	Unfortunately, not all backends are embeddable: only the ones returned by
1252	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3058	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1253	portable one.	3059	portable one.
1254		3060
1255	So when you want to use this feature you will always have to be prepared	3061	So when you want to use this feature you will always have to be prepared
1256	that you cannot get an embeddable loop. The recommended way to get around	3062	that you cannot get an embeddable loop. The recommended way to get around
1257	this is to have a separate variables for your embeddable loop, try to	3063	this is to have a separate variables for your embeddable loop, try to
1258	create it, and if that fails, use the normal loop for everything:	3064	create it, and if that fails, use the normal loop for everything.
1259		3065
1260	struct ev_loop *loop_hi = ev_default_init (0);	3066	=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		3067
1270	// if we got one, then embed it, otherwise default to loop_hi	3068	While the C<ev_embed> watcher is running, forks in the embedding loop will
1271	if (loop_lo)	3069	automatically be applied to the embedded loop as well, so no special
1272	{	3070	fork handling is required in that case. When the watcher is not running,
1273	ev_embed_init (&embed, 0, loop_lo);	3071	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1274	ev_embed_start (loop_hi, &embed);	3072	as applicable.
1275	}	3073
1276	else	3074	=head3 Watcher-Specific Functions and Data Members
1277	loop_lo = loop_hi;
1278		3075
1279	=over 4	3076	=over 4
1280		3077
1281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3078	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1282		3079
…		…
1284		3081
1285	Configures the watcher to embed the given loop, which must be	3082	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	3083	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	3084	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,	3085	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).	3086	if you do not want that, you need to temporarily stop the embed watcher).
1290		3087
1291	=item ev_embed_sweep (loop, ev_embed *)	3088	=item ev_embed_sweep (loop, ev_embed *)
1292		3089
1293	Make a single, non-blocking sweep over the embedded loop. This works	3090	Make a single, non-blocking sweep over the embedded loop. This works
1294	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3091	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1295	apropriate way for embedded loops.	3092	appropriate way for embedded loops.
		3093
		3094	=item struct ev_loop *other [read-only]
		3095
		3096	The embedded event loop.
1296		3097
1297	=back	3098	=back
1298		3099
		3100	=head3 Examples
		3101
		3102	Example: Try to get an embeddable event loop and embed it into the default
		3103	event loop. If that is not possible, use the default loop. The default
		3104	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3105	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3106	used).
		3107
		3108	struct ev_loop *loop_hi = ev_default_init (0);
		3109	struct ev_loop *loop_lo = 0;
		3110	ev_embed embed;
		3111
		3112	// see if there is a chance of getting one that works
		3113	// (remember that a flags value of 0 means autodetection)
		3114	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3115	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3116	: 0;
		3117
		3118	// if we got one, then embed it, otherwise default to loop_hi
		3119	if (loop_lo)
		3120	{
		3121	ev_embed_init (&embed, 0, loop_lo);
		3122	ev_embed_start (loop_hi, &embed);
		3123	}
		3124	else
		3125	loop_lo = loop_hi;
		3126
		3127	Example: Check if kqueue is available but not recommended and create
		3128	a kqueue backend for use with sockets (which usually work with any
		3129	kqueue implementation). Store the kqueue/socket-only event loop in
		3130	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3131
		3132	struct ev_loop *loop = ev_default_init (0);
		3133	struct ev_loop *loop_socket = 0;
		3134	ev_embed embed;
		3135
		3136	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3137	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3138	{
		3139	ev_embed_init (&embed, 0, loop_socket);
		3140	ev_embed_start (loop, &embed);
		3141	}
		3142
		3143	if (!loop_socket)
		3144	loop_socket = loop;
		3145
		3146	// now use loop_socket for all sockets, and loop for everything else
		3147
		3148
		3149	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3150
		3151	Fork watchers are called when a C<fork ()> was detected (usually because
		3152	whoever is a good citizen cared to tell libev about it by calling
		3153	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3154	event loop blocks next and before C<ev_check> watchers are being called,
		3155	and only in the child after the fork. If whoever good citizen calling
		3156	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3157	handlers will be invoked, too, of course.
		3158
		3159	=head3 The special problem of life after fork - how is it possible?
		3160
		3161	Most uses of C<fork()> consist of forking, then some simple calls to set
		3162	up/change the process environment, followed by a call to C<exec()>. This
		3163	sequence should be handled by libev without any problems.
		3164
		3165	This changes when the application actually wants to do event handling
		3166	in the child, or both parent in child, in effect "continuing" after the
		3167	fork.
		3168
		3169	The default mode of operation (for libev, with application help to detect
		3170	forks) is to duplicate all the state in the child, as would be expected
		3171	when I<either> the parent I<or> the child process continues.
		3172
		3173	When both processes want to continue using libev, then this is usually the
		3174	wrong result. In that case, usually one process (typically the parent) is
		3175	supposed to continue with all watchers in place as before, while the other
		3176	process typically wants to start fresh, i.e. without any active watchers.
		3177
		3178	The cleanest and most efficient way to achieve that with libev is to
		3179	simply create a new event loop, which of course will be "empty", and
		3180	use that for new watchers. This has the advantage of not touching more
		3181	memory than necessary, and thus avoiding the copy-on-write, and the
		3182	disadvantage of having to use multiple event loops (which do not support
		3183	signal watchers).
		3184
		3185	When this is not possible, or you want to use the default loop for
		3186	other reasons, then in the process that wants to start "fresh", call
		3187	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3188	Destroying the default loop will "orphan" (not stop) all registered
		3189	watchers, so you have to be careful not to execute code that modifies
		3190	those watchers. Note also that in that case, you have to re-register any
		3191	signal watchers.
		3192
		3193	=head3 Watcher-Specific Functions and Data Members
		3194
		3195	=over 4
		3196
		3197	=item ev_fork_init (ev_fork *, callback)
		3198
		3199	Initialises and configures the fork watcher - it has no parameters of any
		3200	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3201	really.
		3202
		3203	=back
		3204
		3205
		3206	=head2 C<ev_cleanup> - even the best things end
		3207
		3208	Cleanup watchers are called just before the event loop is being destroyed
		3209	by a call to C<ev_loop_destroy>.
		3210
		3211	While there is no guarantee that the event loop gets destroyed, cleanup
		3212	watchers provide a convenient method to install cleanup hooks for your
		3213	program, worker threads and so on - you just to make sure to destroy the
		3214	loop when you want them to be invoked.
		3215
		3216	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3217	all other watchers, they do not keep a reference to the event loop (which
		3218	makes a lot of sense if you think about it). Like all other watchers, you
		3219	can call libev functions in the callback, except C<ev_cleanup_start>.
		3220
		3221	=head3 Watcher-Specific Functions and Data Members
		3222
		3223	=over 4
		3224
		3225	=item ev_cleanup_init (ev_cleanup *, callback)
		3226
		3227	Initialises and configures the cleanup watcher - it has no parameters of
		3228	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3229	pointless, I assure you.
		3230
		3231	=back
		3232
		3233	Example: Register an atexit handler to destroy the default loop, so any
		3234	cleanup functions are called.
		3235
		3236	static void
		3237	program_exits (void)
		3238	{
		3239	ev_loop_destroy (EV_DEFAULT_UC);
		3240	}
		3241
		3242	...
		3243	atexit (program_exits);
		3244
		3245
		3246	=head2 C<ev_async> - how to wake up an event loop
		3247
		3248	In general, you cannot use an C<ev_run> from multiple threads or other
		3249	asynchronous sources such as signal handlers (as opposed to multiple event
		3250	loops - those are of course safe to use in different threads).
		3251
		3252	Sometimes, however, you need to wake up an event loop you do not control,
		3253	for example because it belongs to another thread. This is what C<ev_async>
		3254	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3255	it by calling C<ev_async_send>, which is thread- and signal safe.
		3256
		3257	This functionality is very similar to C<ev_signal> watchers, as signals,
		3258	too, are asynchronous in nature, and signals, too, will be compressed
		3259	(i.e. the number of callback invocations may be less than the number of
		3260	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3261	of "global async watchers" by using a watcher on an otherwise unused
		3262	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3263	even without knowing which loop owns the signal.
		3264
		3265	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3266	just the default loop.
		3267
		3268	=head3 Queueing
		3269
		3270	C<ev_async> does not support queueing of data in any way. The reason
		3271	is that the author does not know of a simple (or any) algorithm for a
		3272	multiple-writer-single-reader queue that works in all cases and doesn't
		3273	need elaborate support such as pthreads or unportable memory access
		3274	semantics.
		3275
		3276	That means that if you want to queue data, you have to provide your own
		3277	queue. But at least I can tell you how to implement locking around your
		3278	queue:
		3279
		3280	=over 4
		3281
		3282	=item queueing from a signal handler context
		3283
		3284	To implement race-free queueing, you simply add to the queue in the signal
		3285	handler but you block the signal handler in the watcher callback. Here is
		3286	an example that does that for some fictitious SIGUSR1 handler:
		3287
		3288	static ev_async mysig;
		3289
		3290	static void
		3291	sigusr1_handler (void)
		3292	{
		3293	sometype data;
		3294
		3295	// no locking etc.
		3296	queue_put (data);
		3297	ev_async_send (EV_DEFAULT_ &mysig);
		3298	}
		3299
		3300	static void
		3301	mysig_cb (EV_P_ ev_async *w, int revents)
		3302	{
		3303	sometype data;
		3304	sigset_t block, prev;
		3305
		3306	sigemptyset (&block);
		3307	sigaddset (&block, SIGUSR1);
		3308	sigprocmask (SIG_BLOCK, &block, &prev);
		3309
		3310	while (queue_get (&data))
		3311	process (data);
		3312
		3313	if (sigismember (&prev, SIGUSR1)
		3314	sigprocmask (SIG_UNBLOCK, &block, 0);
		3315	}
		3316
		3317	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3318	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3319	either...).
		3320
		3321	=item queueing from a thread context
		3322
		3323	The strategy for threads is different, as you cannot (easily) block
		3324	threads but you can easily preempt them, so to queue safely you need to
		3325	employ a traditional mutex lock, such as in this pthread example:
		3326
		3327	static ev_async mysig;
		3328	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3329
		3330	static void
		3331	otherthread (void)
		3332	{
		3333	// only need to lock the actual queueing operation
		3334	pthread_mutex_lock (&mymutex);
		3335	queue_put (data);
		3336	pthread_mutex_unlock (&mymutex);
		3337
		3338	ev_async_send (EV_DEFAULT_ &mysig);
		3339	}
		3340
		3341	static void
		3342	mysig_cb (EV_P_ ev_async *w, int revents)
		3343	{
		3344	pthread_mutex_lock (&mymutex);
		3345
		3346	while (queue_get (&data))
		3347	process (data);
		3348
		3349	pthread_mutex_unlock (&mymutex);
		3350	}
		3351
		3352	=back
		3353
		3354
		3355	=head3 Watcher-Specific Functions and Data Members
		3356
		3357	=over 4
		3358
		3359	=item ev_async_init (ev_async *, callback)
		3360
		3361	Initialises and configures the async watcher - it has no parameters of any
		3362	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3363	trust me.
		3364
		3365	=item ev_async_send (loop, ev_async *)
		3366
		3367	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3368	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3369	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3370	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3371	section below on what exactly this means).
		3372
		3373	Note that, as with other watchers in libev, multiple events might get
		3374	compressed into a single callback invocation (another way to look at this
		3375	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3376	reset when the event loop detects that).
		3377
		3378	This call incurs the overhead of a system call only once per event loop
		3379	iteration, so while the overhead might be noticeable, it doesn't apply to
		3380	repeated calls to C<ev_async_send> for the same event loop.
		3381
		3382	=item bool = ev_async_pending (ev_async *)
		3383
		3384	Returns a non-zero value when C<ev_async_send> has been called on the
		3385	watcher but the event has not yet been processed (or even noted) by the
		3386	event loop.
		3387
		3388	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3389	the loop iterates next and checks for the watcher to have become active,
		3390	it will reset the flag again. C<ev_async_pending> can be used to very
		3391	quickly check whether invoking the loop might be a good idea.
		3392
		3393	Not that this does I<not> check whether the watcher itself is pending,
		3394	only whether it has been requested to make this watcher pending: there
		3395	is a time window between the event loop checking and resetting the async
		3396	notification, and the callback being invoked.
		3397
		3398	=back
		3399
1299		3400
1300	=head1 OTHER FUNCTIONS	3401	=head1 OTHER FUNCTIONS
1301		3402
1302	There are some other functions of possible interest. Described. Here. Now.	3403	There are some other functions of possible interest. Described. Here. Now.
1303		3404
1304	=over 4	3405	=over 4
1305		3406
1306	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3407	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1307		3408
1308	This function combines a simple timer and an I/O watcher, calls your	3409	This function combines a simple timer and an I/O watcher, calls your
1309	callback on whichever event happens first and automatically stop both	3410	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	3411	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	3412	or timeout without having to allocate/configure/start/stop/free one or
1312	more watchers yourself.	3413	more watchers yourself.
1313		3414
1314	If C<fd> is less than 0, then no I/O watcher will be started and events	3415	If C<fd> is less than 0, then no I/O watcher will be started and the
1315	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3416	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1316	C<events> set will be craeted and started.	3417	the given C<fd> and C<events> set will be created and started.
1317		3418
1318	If C<timeout> is less than 0, then no timeout watcher will be	3419	If C<timeout> is less than 0, then no timeout watcher will be
1319	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3420	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1320	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3421	repeat = 0) will be started. C<0> is a valid timeout.
1321	dubious value.
1322		3422
1323	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3423	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1324	passed an C<revents> set like normal event callbacks (a combination of	3424	passed an C<revents> set like normal event callbacks (a combination of
1325	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3425	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1326	value passed to C<ev_once>:	3426	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3427	a timeout and an io event at the same time - you probably should give io
		3428	events precedence.
1327		3429
		3430	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3431
1328	static void stdin_ready (int revents, void *arg)	3432	static void stdin_ready (int revents, void *arg)
1329	{	3433	{
1330	if (revents & EV_TIMEOUT)
1331	/* doh, nothing entered */;
1332	else if (revents & EV_READ)	3434	if (revents & EV_READ)
1333	/* stdin might have data for us, joy! */;	3435	/* stdin might have data for us, joy! */;
		3436	else if (revents & EV_TIMER)
		3437	/* doh, nothing entered */;
1334	}	3438	}
1335		3439
1336	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3440	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1337		3441
1338	=item ev_feed_event (ev_loop *, watcher *, int revents)
1339
1340	Feeds the given event set into the event loop, as if the specified event
1341	had happened for the specified watcher (which must be a pointer to an
1342	initialised but not necessarily started event watcher).
1343
1344	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3442	=item ev_feed_fd_event (loop, int fd, int revents)
1345		3443
1346	Feed an event on the given fd, as if a file descriptor backend detected	3444	Feed an event on the given fd, as if a file descriptor backend detected
1347	the given events it.	3445	the given events it.
1348		3446
1349	=item ev_feed_signal_event (ev_loop *loop, int signum)	3447	=item ev_feed_signal_event (loop, int signum)
1350		3448
1351	Feed an event as if the given signal occured (C<loop> must be the default	3449	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
1352	loop!).	3450	which is async-safe.
		3451
		3452	=back
		3453
		3454
		3455	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3456
		3457	This section explains some common idioms that are not immediately
		3458	obvious. Note that examples are sprinkled over the whole manual, and this
		3459	section only contains stuff that wouldn't fit anywhere else.
		3460
		3461	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3462
		3463	Often (especially in GUI toolkits) there are places where you have
		3464	I<modal> interaction, which is most easily implemented by recursively
		3465	invoking C<ev_run>.
		3466
		3467	This brings the problem of exiting - a callback might want to finish the
		3468	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3469	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3470	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3471	other combination: In these cases, C<ev_break> will not work alone.
		3472
		3473	The solution is to maintain "break this loop" variable for each C<ev_run>
		3474	invocation, and use a loop around C<ev_run> until the condition is
		3475	triggered, using C<EVRUN_ONCE>:
		3476
		3477	// main loop
		3478	int exit_main_loop = 0;
		3479
		3480	while (!exit_main_loop)
		3481	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3482
		3483	// in a model watcher
		3484	int exit_nested_loop = 0;
		3485
		3486	while (!exit_nested_loop)
		3487	ev_run (EV_A_ EVRUN_ONCE);
		3488
		3489	To exit from any of these loops, just set the corresponding exit variable:
		3490
		3491	// exit modal loop
		3492	exit_nested_loop = 1;
		3493
		3494	// exit main program, after modal loop is finished
		3495	exit_main_loop = 1;
		3496
		3497	// exit both
		3498	exit_main_loop = exit_nested_loop = 1;
		3499
		3500	=head2 THREAD LOCKING EXAMPLE
		3501
		3502	Here is a fictitious example of how to run an event loop in a different
		3503	thread than where callbacks are being invoked and watchers are
		3504	created/added/removed.
		3505
		3506	For a real-world example, see the C<EV::Loop::Async> perl module,
		3507	which uses exactly this technique (which is suited for many high-level
		3508	languages).
		3509
		3510	The example uses a pthread mutex to protect the loop data, a condition
		3511	variable to wait for callback invocations, an async watcher to notify the
		3512	event loop thread and an unspecified mechanism to wake up the main thread.
		3513
		3514	First, you need to associate some data with the event loop:
		3515
		3516	typedef struct {
		3517	mutex_t lock; /* global loop lock */
		3518	ev_async async_w;
		3519	thread_t tid;
		3520	cond_t invoke_cv;
		3521	} userdata;
		3522
		3523	void prepare_loop (EV_P)
		3524	{
		3525	// for simplicity, we use a static userdata struct.
		3526	static userdata u;
		3527
		3528	ev_async_init (&u->async_w, async_cb);
		3529	ev_async_start (EV_A_ &u->async_w);
		3530
		3531	pthread_mutex_init (&u->lock, 0);
		3532	pthread_cond_init (&u->invoke_cv, 0);
		3533
		3534	// now associate this with the loop
		3535	ev_set_userdata (EV_A_ u);
		3536	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3537	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3538
		3539	// then create the thread running ev_loop
		3540	pthread_create (&u->tid, 0, l_run, EV_A);
		3541	}
		3542
		3543	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3544	solely to wake up the event loop so it takes notice of any new watchers
		3545	that might have been added:
		3546
		3547	static void
		3548	async_cb (EV_P_ ev_async *w, int revents)
		3549	{
		3550	// just used for the side effects
		3551	}
		3552
		3553	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3554	protecting the loop data, respectively.
		3555
		3556	static void
		3557	l_release (EV_P)
		3558	{
		3559	userdata *u = ev_userdata (EV_A);
		3560	pthread_mutex_unlock (&u->lock);
		3561	}
		3562
		3563	static void
		3564	l_acquire (EV_P)
		3565	{
		3566	userdata *u = ev_userdata (EV_A);
		3567	pthread_mutex_lock (&u->lock);
		3568	}
		3569
		3570	The event loop thread first acquires the mutex, and then jumps straight
		3571	into C<ev_run>:
		3572
		3573	void *
		3574	l_run (void *thr_arg)
		3575	{
		3576	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3577
		3578	l_acquire (EV_A);
		3579	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3580	ev_run (EV_A_ 0);
		3581	l_release (EV_A);
		3582
		3583	return 0;
		3584	}
		3585
		3586	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3587	signal the main thread via some unspecified mechanism (signals? pipe
		3588	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3589	have been called (in a while loop because a) spurious wakeups are possible
		3590	and b) skipping inter-thread-communication when there are no pending
		3591	watchers is very beneficial):
		3592
		3593	static void
		3594	l_invoke (EV_P)
		3595	{
		3596	userdata *u = ev_userdata (EV_A);
		3597
		3598	while (ev_pending_count (EV_A))
		3599	{
		3600	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3601	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3602	}
		3603	}
		3604
		3605	Now, whenever the main thread gets told to invoke pending watchers, it
		3606	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3607	thread to continue:
		3608
		3609	static void
		3610	real_invoke_pending (EV_P)
		3611	{
		3612	userdata *u = ev_userdata (EV_A);
		3613
		3614	pthread_mutex_lock (&u->lock);
		3615	ev_invoke_pending (EV_A);
		3616	pthread_cond_signal (&u->invoke_cv);
		3617	pthread_mutex_unlock (&u->lock);
		3618	}
		3619
		3620	Whenever you want to start/stop a watcher or do other modifications to an
		3621	event loop, you will now have to lock:
		3622
		3623	ev_timer timeout_watcher;
		3624	userdata *u = ev_userdata (EV_A);
		3625
		3626	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3627
		3628	pthread_mutex_lock (&u->lock);
		3629	ev_timer_start (EV_A_ &timeout_watcher);
		3630	ev_async_send (EV_A_ &u->async_w);
		3631	pthread_mutex_unlock (&u->lock);
		3632
		3633	Note that sending the C<ev_async> watcher is required because otherwise
		3634	an event loop currently blocking in the kernel will have no knowledge
		3635	about the newly added timer. By waking up the loop it will pick up any new
		3636	watchers in the next event loop iteration.
1353		3637
1354	=back	3638	=back
1355		3639
1356		3640
1357	=head1 LIBEVENT EMULATION	3641	=head1 LIBEVENT EMULATION
1358		3642
1359	Libev offers a compatibility emulation layer for libevent. It cannot	3643	Libev offers a compatibility emulation layer for libevent. It cannot
1360	emulate the internals of libevent, so here are some usage hints:	3644	emulate the internals of libevent, so here are some usage hints:
1361		3645
1362	=over 4	3646	=over 4
		3647
		3648	=item * Only the libevent-1.4.1-beta API is being emulated.
		3649
		3650	This was the newest libevent version available when libev was implemented,
		3651	and is still mostly unchanged in 2010.
1363		3652
1364	=item * Use it by including <event.h>, as usual.	3653	=item * Use it by including <event.h>, as usual.
1365		3654
1366	=item * The following members are fully supported: ev_base, ev_callback,	3655	=item * The following members are fully supported: ev_base, ev_callback,
1367	ev_arg, ev_fd, ev_res, ev_events.	3656	ev_arg, ev_fd, ev_res, ev_events.
…		…
1372		3661
1373	=item * Priorities are not currently supported. Initialising priorities	3662	=item * Priorities are not currently supported. Initialising priorities
1374	will fail and all watchers will have the same priority, even though there	3663	will fail and all watchers will have the same priority, even though there
1375	is an ev_pri field.	3664	is an ev_pri field.
1376		3665
		3666	=item * In libevent, the last base created gets the signals, in libev, the
		3667	base that registered the signal gets the signals.
		3668
1377	=item * Other members are not supported.	3669	=item * Other members are not supported.
1378		3670
1379	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3671	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1380	to use the libev header file and library.	3672	to use the libev header file and library.
1381		3673
1382	=back	3674	=back
1383		3675
1384	=head1 C++ SUPPORT	3676	=head1 C++ SUPPORT
1385		3677
1386	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3678	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	3679	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.	3680	the callback model to a model using method callbacks on objects.
1389		3681
1390	To use it,	3682	To use it,
1391		3683
1392	#include <ev++.h>	3684	#include <ev++.h>
1393		3685
1394	(it is not installed by default). This automatically includes F<ev.h>	3686	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	3687	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.	3688	put into the C<ev> namespace. It should support all the same embedding
		3689	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1397		3690
1398	It should support all the same embedding options as F<ev.h>, most notably	3691	Care has been taken to keep the overhead low. The only data member the C++
1399	C<EV_MULTIPLICITY>.	3692	classes add (compared to plain C-style watchers) is the event loop pointer
		3693	that the watcher is associated with (or no additional members at all if
		3694	you disable C<EV_MULTIPLICITY> when embedding libev).
		3695
		3696	Currently, functions, static and non-static member functions and classes
		3697	with C<operator ()> can be used as callbacks. Other types should be easy
		3698	to add as long as they only need one additional pointer for context. If
		3699	you need support for other types of functors please contact the author
		3700	(preferably after implementing it).
1400		3701
1401	Here is a list of things available in the C<ev> namespace:	3702	Here is a list of things available in the C<ev> namespace:
1402		3703
1403	=over 4	3704	=over 4
1404		3705
…		…
1420		3721
1421	All of those classes have these methods:	3722	All of those classes have these methods:
1422		3723
1423	=over 4	3724	=over 4
1424		3725
1425	=item ev::TYPE::TYPE (object *, object::method *)	3726	=item ev::TYPE::TYPE ()
1426		3727
1427	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3728	=item ev::TYPE::TYPE (loop)
1428		3729
1429	=item ev::TYPE::~TYPE	3730	=item ev::TYPE::~TYPE
1430		3731
1431	The constructor takes a pointer to an object and a method pointer to	3732	The constructor (optionally) takes an event loop to associate the watcher
1432	the event handler callback to call in this class. The constructor calls	3733	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	3734
1434	before starting it. If you do not specify a loop then the constructor	3735	The constructor calls C<ev_init> for you, which means you have to call the
1435	automatically associates the default loop with this watcher.	3736	C<set> method before starting it.
		3737
		3738	It will not set a callback, however: You have to call the templated C<set>
		3739	method to set a callback before you can start the watcher.
		3740
		3741	(The reason why you have to use a method is a limitation in C++ which does
		3742	not allow explicit template arguments for constructors).
1436		3743
1437	The destructor automatically stops the watcher if it is active.	3744	The destructor automatically stops the watcher if it is active.
1438		3745
		3746	=item w->set<class, &class::method> (object *)
		3747
		3748	This method sets the callback method to call. The method has to have a
		3749	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3750	first argument and the C<revents> as second. The object must be given as
		3751	parameter and is stored in the C<data> member of the watcher.
		3752
		3753	This method synthesizes efficient thunking code to call your method from
		3754	the C callback that libev requires. If your compiler can inline your
		3755	callback (i.e. it is visible to it at the place of the C<set> call and
		3756	your compiler is good :), then the method will be fully inlined into the
		3757	thunking function, making it as fast as a direct C callback.
		3758
		3759	Example: simple class declaration and watcher initialisation
		3760
		3761	struct myclass
		3762	{
		3763	void io_cb (ev::io &w, int revents) { }
		3764	}
		3765
		3766	myclass obj;
		3767	ev::io iow;
		3768	iow.set <myclass, &myclass::io_cb> (&obj);
		3769
		3770	=item w->set (object *)
		3771
		3772	This is a variation of a method callback - leaving out the method to call
		3773	will default the method to C<operator ()>, which makes it possible to use
		3774	functor objects without having to manually specify the C<operator ()> all
		3775	the time. Incidentally, you can then also leave out the template argument
		3776	list.
		3777
		3778	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3779	int revents)>.
		3780
		3781	See the method-C<set> above for more details.
		3782
		3783	Example: use a functor object as callback.
		3784
		3785	struct myfunctor
		3786	{
		3787	void operator() (ev::io &w, int revents)
		3788	{
		3789	...
		3790	}
		3791	}
		3792
		3793	myfunctor f;
		3794
		3795	ev::io w;
		3796	w.set (&f);
		3797
		3798	=item w->set<function> (void *data = 0)
		3799
		3800	Also sets a callback, but uses a static method or plain function as
		3801	callback. The optional C<data> argument will be stored in the watcher's
		3802	C<data> member and is free for you to use.
		3803
		3804	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3805
		3806	See the method-C<set> above for more details.
		3807
		3808	Example: Use a plain function as callback.
		3809
		3810	static void io_cb (ev::io &w, int revents) { }
		3811	iow.set <io_cb> ();
		3812
1439	=item w->set (struct ev_loop *)	3813	=item w->set (loop)
1440		3814
1441	Associates a different C<struct ev_loop> with this watcher. You can only	3815	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).	3816	do this when the watcher is inactive (and not pending either).
1443		3817
1444	=item w->set ([args])	3818	=item w->set ([arguments])
1445		3819
1446	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3820	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	3821	method or a suitable start method must be called at least once. Unlike the
1448	automatically stopped and restarted.	3822	C counterpart, an active watcher gets automatically stopped and restarted
		3823	when reconfiguring it with this method.
1449		3824
1450	=item w->start ()	3825	=item w->start ()
1451		3826
1452	Starts the watcher. Note that there is no C<loop> argument as the	3827	Starts the watcher. Note that there is no C<loop> argument, as the
1453	constructor already takes the loop.	3828	constructor already stores the event loop.
		3829
		3830	=item w->start ([arguments])
		3831
		3832	Instead of calling C<set> and C<start> methods separately, it is often
		3833	convenient to wrap them in one call. Uses the same type of arguments as
		3834	the configure C<set> method of the watcher.
1454		3835
1455	=item w->stop ()	3836	=item w->stop ()
1456		3837
1457	Stops the watcher if it is active. Again, no C<loop> argument.	3838	Stops the watcher if it is active. Again, no C<loop> argument.
1458		3839
1459	=item w->again () C<ev::timer>, C<ev::periodic> only	3840	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1460		3841
1461	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3842	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1462	C<ev_TYPE_again> function.	3843	C<ev_TYPE_again> function.
1463		3844
1464	=item w->sweep () C<ev::embed> only	3845	=item w->sweep () (C<ev::embed> only)
1465		3846
1466	Invokes C<ev_embed_sweep>.	3847	Invokes C<ev_embed_sweep>.
1467		3848
		3849	=item w->update () (C<ev::stat> only)
		3850
		3851	Invokes C<ev_stat_stat>.
		3852
1468	=back	3853	=back
1469		3854
1470	=back	3855	=back
1471		3856
1472	Example: Define a class with an IO and idle watcher, start one of them in	3857	Example: Define a class with two I/O and idle watchers, start the I/O
1473	the constructor.	3858	watchers in the constructor.
1474		3859
1475	class myclass	3860	class myclass
1476	{	3861	{
1477	ev_io io; void io_cb (ev::io &w, int revents);	3862	ev::io io ; void io_cb (ev::io &w, int revents);
		3863	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1478	ev_idle idle void idle_cb (ev::idle &w, int revents);	3864	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1479		3865
1480	myclass ();	3866	myclass (int fd)
		3867	{
		3868	io .set <myclass, &myclass::io_cb > (this);
		3869	io2 .set <myclass, &myclass::io2_cb > (this);
		3870	idle.set <myclass, &myclass::idle_cb> (this);
		3871
		3872	io.set (fd, ev::WRITE); // configure the watcher
		3873	io.start (); // start it whenever convenient
		3874
		3875	io2.start (fd, ev::READ); // set + start in one call
		3876	}
1481	}	3877	};
1482		3878
1483	myclass::myclass (int fd)	3879
1484	: io (this, &myclass::io_cb),	3880	=head1 OTHER LANGUAGE BINDINGS
1485	idle (this, &myclass::idle_cb)	3881
		3882	Libev does not offer other language bindings itself, but bindings for a
		3883	number of languages exist in the form of third-party packages. If you know
		3884	any interesting language binding in addition to the ones listed here, drop
		3885	me a note.
		3886
		3887	=over 4
		3888
		3889	=item Perl
		3890
		3891	The EV module implements the full libev API and is actually used to test
		3892	libev. EV is developed together with libev. Apart from the EV core module,
		3893	there are additional modules that implement libev-compatible interfaces
		3894	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3895	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3896	and C<EV::Glib>).
		3897
		3898	It can be found and installed via CPAN, its homepage is at
		3899	L<http://software.schmorp.de/pkg/EV>.
		3900
		3901	=item Python
		3902
		3903	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3904	seems to be quite complete and well-documented.
		3905
		3906	=item Ruby
		3907
		3908	Tony Arcieri has written a ruby extension that offers access to a subset
		3909	of the libev API and adds file handle abstractions, asynchronous DNS and
		3910	more on top of it. It can be found via gem servers. Its homepage is at
		3911	L<http://rev.rubyforge.org/>.
		3912
		3913	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3914	makes rev work even on mingw.
		3915
		3916	=item Haskell
		3917
		3918	A haskell binding to libev is available at
		3919	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3920
		3921	=item D
		3922
		3923	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3924	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3925
		3926	=item Ocaml
		3927
		3928	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3929	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3930
		3931	=item Lua
		3932
		3933	Brian Maher has written a partial interface to libev for lua (at the
		3934	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3935	L<http://github.com/brimworks/lua-ev>.
		3936
		3937	=back
		3938
		3939
		3940	=head1 MACRO MAGIC
		3941
		3942	Libev can be compiled with a variety of options, the most fundamental
		3943	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3944	functions and callbacks have an initial C<struct ev_loop *> argument.
		3945
		3946	To make it easier to write programs that cope with either variant, the
		3947	following macros are defined:
		3948
		3949	=over 4
		3950
		3951	=item C<EV_A>, C<EV_A_>
		3952
		3953	This provides the loop I<argument> for functions, if one is required ("ev
		3954	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3955	C<EV_A_> is used when other arguments are following. Example:
		3956
		3957	ev_unref (EV_A);
		3958	ev_timer_add (EV_A_ watcher);
		3959	ev_run (EV_A_ 0);
		3960
		3961	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3962	which is often provided by the following macro.
		3963
		3964	=item C<EV_P>, C<EV_P_>
		3965
		3966	This provides the loop I<parameter> for functions, if one is required ("ev
		3967	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3968	C<EV_P_> is used when other parameters are following. Example:
		3969
		3970	// this is how ev_unref is being declared
		3971	static void ev_unref (EV_P);
		3972
		3973	// this is how you can declare your typical callback
		3974	static void cb (EV_P_ ev_timer *w, int revents)
		3975
		3976	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3977	suitable for use with C<EV_A>.
		3978
		3979	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3980
		3981	Similar to the other two macros, this gives you the value of the default
		3982	loop, if multiple loops are supported ("ev loop default").
		3983
		3984	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3985
		3986	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3987	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3988	is undefined when the default loop has not been initialised by a previous
		3989	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3990
		3991	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3992	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3993
		3994	=back
		3995
		3996	Example: Declare and initialise a check watcher, utilising the above
		3997	macros so it will work regardless of whether multiple loops are supported
		3998	or not.
		3999
		4000	static void
		4001	check_cb (EV_P_ ev_timer *w, int revents)
1486	{	4002	{
1487	io.start (fd, ev::READ);	4003	ev_check_stop (EV_A_ w);
1488	}	4004	}
		4005
		4006	ev_check check;
		4007	ev_check_init (&check, check_cb);
		4008	ev_check_start (EV_DEFAULT_ &check);
		4009	ev_run (EV_DEFAULT_ 0);
1489		4010
1490	=head1 EMBEDDING	4011	=head1 EMBEDDING
1491		4012
1492	Libev can (and often is) directly embedded into host	4013	Libev can (and often is) directly embedded into host
1493	applications. Examples of applications that embed it include the Deliantra	4014	applications. Examples of applications that embed it include the Deliantra
1494	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4015	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1495	and rxvt-unicode.	4016	and rxvt-unicode.
1496		4017
1497	The goal is to enable you to just copy the neecssary files into your	4018	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	4019	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	4020	you can easily upgrade by simply copying (or having a checked-out copy of
1500	libev somewhere in your source tree).	4021	libev somewhere in your source tree).
1501		4022
1502	=head2 FILESETS	4023	=head2 FILESETS
1503		4024
1504	Depending on what features you need you need to include one or more sets of files	4025	Depending on what features you need you need to include one or more sets of files
1505	in your app.	4026	in your application.
1506		4027
1507	=head3 CORE EVENT LOOP	4028	=head3 CORE EVENT LOOP
1508		4029
1509	To include only the libev core (all the C<ev_*> functions), with manual	4030	To include only the libev core (all the C<ev_*> functions), with manual
1510	configuration (no autoconf):	4031	configuration (no autoconf):
1511		4032
1512	#define EV_STANDALONE 1	4033	#define EV_STANDALONE 1
1513	#include "ev.c"	4034	#include "ev.c"
1514		4035
1515	This will automatically include F<ev.h>, too, and should be done in a	4036	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	4037	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	4038	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	4039	done by writing a wrapper around F<ev.h> that you can include instead and
1519	where you can put other configuration options):	4040	where you can put other configuration options):
1520		4041
1521	#define EV_STANDALONE 1	4042	#define EV_STANDALONE 1
1522	#include "ev.h"	4043	#include "ev.h"
1523		4044
1524	Both header files and implementation files can be compiled with a C++	4045	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	4046	compiler (at least, that's a stated goal, and breakage will be treated
1526	as a bug).	4047	as a bug).
1527		4048
1528	You need the following files in your source tree, or in a directory	4049	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):	4050	in your include path (e.g. in libev/ when using -Ilibev):
1530		4051
1531	ev.h	4052	ev.h
1532	ev.c	4053	ev.c
1533	ev_vars.h	4054	ev_vars.h
1534	ev_wrap.h	4055	ev_wrap.h
1535		4056
1536	ev_win32.c required on win32 platforms only	4057	ev_win32.c required on win32 platforms only
1537		4058
1538	ev_select.c only when select backend is enabled (which is by default)	4059	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)	4060	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)	4061	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)	4062	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)	4063	ev_port.c only when the solaris port backend is enabled (disabled by default)
1543		4064
1544	F<ev.c> includes the backend files directly when enabled, so you only need	4065	F<ev.c> includes the backend files directly when enabled, so you only need
1545	to compile this single file.	4066	to compile this single file.
1546		4067
1547	=head3 LIBEVENT COMPATIBILITY API	4068	=head3 LIBEVENT COMPATIBILITY API
1548		4069
1549	To include the libevent compatibility API, also include:	4070	To include the libevent compatibility API, also include:
1550		4071
1551	#include "event.c"	4072	#include "event.c"
1552		4073
1553	in the file including F<ev.c>, and:	4074	in the file including F<ev.c>, and:
1554		4075
1555	#include "event.h"	4076	#include "event.h"
1556		4077
1557	in the files that want to use the libevent API. This also includes F<ev.h>.	4078	in the files that want to use the libevent API. This also includes F<ev.h>.
1558		4079
1559	You need the following additional files for this:	4080	You need the following additional files for this:
1560		4081
1561	event.h	4082	event.h
1562	event.c	4083	event.c
1563		4084
1564	=head3 AUTOCONF SUPPORT	4085	=head3 AUTOCONF SUPPORT
1565		4086
1566	Instead of using C<EV_STANDALONE=1> and providing your config in	4087	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	4088	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	4089	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1569	include F<config.h> and configure itself accordingly.	4090	include F<config.h> and configure itself accordingly.
1570		4091
1571	For this of course you need the m4 file:	4092	For this of course you need the m4 file:
1572		4093
1573	libev.m4	4094	libev.m4
1574		4095
1575	=head2 PREPROCESSOR SYMBOLS/MACROS	4096	=head2 PREPROCESSOR SYMBOLS/MACROS
1576		4097
1577	Libev can be configured via a variety of preprocessor symbols you have to define	4098	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	4099	define before including (or compiling) any of its files. The default in
1579	and only include the select backend.	4100	the absence of autoconf is documented for every option.
		4101
		4102	Symbols marked with "(h)" do not change the ABI, and can have different
		4103	values when compiling libev vs. including F<ev.h>, so it is permissible
		4104	to redefine them before including F<ev.h> without breaking compatibility
		4105	to a compiled library. All other symbols change the ABI, which means all
		4106	users of libev and the libev code itself must be compiled with compatible
		4107	settings.
1580		4108
1581	=over 4	4109	=over 4
1582		4110
		4111	=item EV_COMPAT3 (h)
		4112
		4113	Backwards compatibility is a major concern for libev. This is why this
		4114	release of libev comes with wrappers for the functions and symbols that
		4115	have been renamed between libev version 3 and 4.
		4116
		4117	You can disable these wrappers (to test compatibility with future
		4118	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4119	sources. This has the additional advantage that you can drop the C<struct>
		4120	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4121	typedef in that case.
		4122
		4123	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4124	and in some even more future version the compatibility code will be
		4125	removed completely.
		4126
1583	=item EV_STANDALONE	4127	=item EV_STANDALONE (h)
1584		4128
1585	Must always be C<1> if you do not use autoconf configuration, which	4129	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	4130	keeps libev from including F<config.h>, and it also defines dummy
1587	implementations for some libevent functions (such as logging, which is not	4131	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	4132	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.	4133	F<event.h> that are not directly supported by the libev core alone.
1590		4134
		4135	In standalone mode, libev will still try to automatically deduce the
		4136	configuration, but has to be more conservative.
		4137
1591	=item EV_USE_MONOTONIC	4138	=item EV_USE_MONOTONIC
1592		4139
1593	If defined to be C<1>, libev will try to detect the availability of the	4140	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	4141	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	4142	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	4143	you usually have to link against librt or something similar. Enabling it
1597	the functionality isn't available is safe, though, althoguh you have	4144	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>	4145	to make sure you link against any libraries where the C<clock_gettime>
1599	function is hiding in (often F<-lrt>).	4146	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1600		4147
1601	=item EV_USE_REALTIME	4148	=item EV_USE_REALTIME
1602		4149
1603	If defined to be C<1>, libev will try to detect the availability of the	4150	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	4151	real-time clock option at compile time (and assume its availability
1605	runtime if successful). Otherwise no use of the realtime clock option will	4152	at runtime if successful). Otherwise no use of the real-time clock
1606	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4153	option will be attempted. This effectively replaces C<gettimeofday>
1607	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4154	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1608	in the description of C<EV_USE_MONOTONIC>, though.	4155	correctness. See the note about libraries in the description of
		4156	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4157	C<EV_USE_CLOCK_SYSCALL>.
		4158
		4159	=item EV_USE_CLOCK_SYSCALL
		4160
		4161	If defined to be C<1>, libev will try to use a direct syscall instead
		4162	of calling the system-provided C<clock_gettime> function. This option
		4163	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4164	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4165	programs needlessly. Using a direct syscall is slightly slower (in
		4166	theory), because no optimised vdso implementation can be used, but avoids
		4167	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4168	higher, as it simplifies linking (no need for C<-lrt>).
		4169
		4170	=item EV_USE_NANOSLEEP
		4171
		4172	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4173	and will use it for delays. Otherwise it will use C<select ()>.
		4174
		4175	=item EV_USE_EVENTFD
		4176
		4177	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4178	available and will probe for kernel support at runtime. This will improve
		4179	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4180	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4181	2.7 or newer, otherwise disabled.
1609		4182
1610	=item EV_USE_SELECT	4183	=item EV_USE_SELECT
1611		4184
1612	If undefined or defined to be C<1>, libev will compile in support for the	4185	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	4186	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	4187	other method takes over, select will be it. Otherwise the select backend
1615	will not be compiled in.	4188	will not be compiled in.
1616		4189
1617	=item EV_SELECT_USE_FD_SET	4190	=item EV_SELECT_USE_FD_SET
1618		4191
1619	If defined to C<1>, then the select backend will use the system C<fd_set>	4192	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	4193	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	4194	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	4195	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	4196	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	4197	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1625	influence the size of the C<fd_set> used.	4198	configures the maximum size of the C<fd_set>.
1626		4199
1627	=item EV_SELECT_IS_WINSOCKET	4200	=item EV_SELECT_IS_WINSOCKET
1628		4201
1629	When defined to C<1>, the select backend will assume that	4202	When defined to C<1>, the select backend will assume that
1630	select/socket/connect etc. don't understand file descriptors but	4203	select/socket/connect etc. don't understand file descriptors but
…		…
1632	be used is the winsock select). This means that it will call	4205	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,	4206	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	4207	it is assumed that all these functions actually work on fds, even
1635	on win32. Should not be defined on non-win32 platforms.	4208	on win32. Should not be defined on non-win32 platforms.
1636		4209
		4210	=item EV_FD_TO_WIN32_HANDLE(fd)
		4211
		4212	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4213	file descriptors to socket handles. When not defining this symbol (the
		4214	default), then libev will call C<_get_osfhandle>, which is usually
		4215	correct. In some cases, programs use their own file descriptor management,
		4216	in which case they can provide this function to map fds to socket handles.
		4217
		4218	=item EV_WIN32_HANDLE_TO_FD(handle)
		4219
		4220	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4221	using the standard C<_open_osfhandle> function. For programs implementing
		4222	their own fd to handle mapping, overwriting this function makes it easier
		4223	to do so. This can be done by defining this macro to an appropriate value.
		4224
		4225	=item EV_WIN32_CLOSE_FD(fd)
		4226
		4227	If programs implement their own fd to handle mapping on win32, then this
		4228	macro can be used to override the C<close> function, useful to unregister
		4229	file descriptors again. Note that the replacement function has to close
		4230	the underlying OS handle.
		4231
1637	=item EV_USE_POLL	4232	=item EV_USE_POLL
1638		4233
1639	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4234	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	4235	backend. Otherwise it will be enabled on non-win32 platforms. It
1641	takes precedence over select.	4236	takes precedence over select.
1642		4237
1643	=item EV_USE_EPOLL	4238	=item EV_USE_EPOLL
1644		4239
1645	If defined to be C<1>, libev will compile in support for the Linux	4240	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,	4241	C<epoll>(7) backend. Its availability will be detected at runtime,
1647	otherwise another method will be used as fallback. This is the	4242	otherwise another method will be used as fallback. This is the preferred
1648	preferred backend for GNU/Linux systems.	4243	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4244	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1649		4245
1650	=item EV_USE_KQUEUE	4246	=item EV_USE_KQUEUE
1651		4247
1652	If defined to be C<1>, libev will compile in support for the BSD style	4248	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,	4249	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	4262	otherwise another method will be used as fallback. This is the preferred
1667	backend for Solaris 10 systems.	4263	backend for Solaris 10 systems.
1668		4264
1669	=item EV_USE_DEVPOLL	4265	=item EV_USE_DEVPOLL
1670		4266
1671	reserved for future expansion, works like the USE symbols above.	4267	Reserved for future expansion, works like the USE symbols above.
1672		4268
		4269	=item EV_USE_INOTIFY
		4270
		4271	If defined to be C<1>, libev will compile in support for the Linux inotify
		4272	interface to speed up C<ev_stat> watchers. Its actual availability will
		4273	be detected at runtime. If undefined, it will be enabled if the headers
		4274	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4275
		4276	=item EV_ATOMIC_T
		4277
		4278	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4279	access is atomic with respect to other threads or signal contexts. No such
		4280	type is easily found in the C language, so you can provide your own type
		4281	that you know is safe for your purposes. It is used both for signal handler "locking"
		4282	as well as for signal and thread safety in C<ev_async> watchers.
		4283
		4284	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4285	(from F<signal.h>), which is usually good enough on most platforms.
		4286
1673	=item EV_H	4287	=item EV_H (h)
1674		4288
1675	The name of the F<ev.h> header file used to include it. The default if	4289	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	4290	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.	4291	used to virtually rename the F<ev.h> header file in case of conflicts.
1678		4292
1679	=item EV_CONFIG_H	4293	=item EV_CONFIG_H (h)
1680		4294
1681	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4295	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	4296	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1683	C<EV_H>, above.	4297	C<EV_H>, above.
1684		4298
1685	=item EV_EVENT_H	4299	=item EV_EVENT_H (h)
1686		4300
1687	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4301	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.	4302	of how the F<event.h> header can be found, the default is C<"event.h">.
1689		4303
1690	=item EV_PROTOTYPES	4304	=item EV_PROTOTYPES (h)
1691		4305
1692	If defined to be C<0>, then F<ev.h> will not define any function	4306	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	4307	prototypes, but still define all the structs and other symbols. This is
1694	occasionally useful if you want to provide your own wrapper functions	4308	occasionally useful if you want to provide your own wrapper functions
1695	around libev functions.	4309	around libev functions.
…		…
1700	will have the C<struct ev_loop *> as first argument, and you can create	4314	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	4315	additional independent event loops. Otherwise there will be no support
1702	for multiple event loops and there is no first event loop pointer	4316	for multiple event loops and there is no first event loop pointer
1703	argument. Instead, all functions act on the single default loop.	4317	argument. Instead, all functions act on the single default loop.
1704		4318
1705	=item EV_PERIODICS	4319	=item EV_MINPRI
1706		4320
1707	If undefined or defined to be C<1>, then periodic timers are supported,	4321	=item EV_MAXPRI
1708	otherwise not. This saves a few kb of code.	4322
		4323	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4324	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4325	provide for more priorities by overriding those symbols (usually defined
		4326	to be C<-2> and C<2>, respectively).
		4327
		4328	When doing priority-based operations, libev usually has to linearly search
		4329	all the priorities, so having many of them (hundreds) uses a lot of space
		4330	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4331	fine.
		4332
		4333	If your embedding application does not need any priorities, defining these
		4334	both to C<0> will save some memory and CPU.
		4335
		4336	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4337	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4338	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4339
		4340	If undefined or defined to be C<1> (and the platform supports it), then
		4341	the respective watcher type is supported. If defined to be C<0>, then it
		4342	is not. Disabling watcher types mainly saves code size.
		4343
		4344	=item EV_FEATURES
		4345
		4346	If you need to shave off some kilobytes of code at the expense of some
		4347	speed (but with the full API), you can define this symbol to request
		4348	certain subsets of functionality. The default is to enable all features
		4349	that can be enabled on the platform.
		4350
		4351	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4352	with some broad features you want) and then selectively re-enable
		4353	additional parts you want, for example if you want everything minimal,
		4354	but multiple event loop support, async and child watchers and the poll
		4355	backend, use this:
		4356
		4357	#define EV_FEATURES 0
		4358	#define EV_MULTIPLICITY 1
		4359	#define EV_USE_POLL 1
		4360	#define EV_CHILD_ENABLE 1
		4361	#define EV_ASYNC_ENABLE 1
		4362
		4363	The actual value is a bitset, it can be a combination of the following
		4364	values:
		4365
		4366	=over 4
		4367
		4368	=item C<1> - faster/larger code
		4369
		4370	Use larger code to speed up some operations.
		4371
		4372	Currently this is used to override some inlining decisions (enlarging the
		4373	code size by roughly 30% on amd64).
		4374
		4375	When optimising for size, use of compiler flags such as C<-Os> with
		4376	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4377	assertions.
		4378
		4379	=item C<2> - faster/larger data structures
		4380
		4381	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4382	hash table sizes and so on. This will usually further increase code size
		4383	and can additionally have an effect on the size of data structures at
		4384	runtime.
		4385
		4386	=item C<4> - full API configuration
		4387
		4388	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4389	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4390
		4391	=item C<8> - full API
		4392
		4393	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4394	details on which parts of the API are still available without this
		4395	feature, and do not complain if this subset changes over time.
		4396
		4397	=item C<16> - enable all optional watcher types
		4398
		4399	Enables all optional watcher types. If you want to selectively enable
		4400	only some watcher types other than I/O and timers (e.g. prepare,
		4401	embed, async, child...) you can enable them manually by defining
		4402	C<EV_watchertype_ENABLE> to C<1> instead.
		4403
		4404	=item C<32> - enable all backends
		4405
		4406	This enables all backends - without this feature, you need to enable at
		4407	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4408
		4409	=item C<64> - enable OS-specific "helper" APIs
		4410
		4411	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4412	default.
		4413
		4414	=back
		4415
		4416	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4417	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4418	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4419	watchers, timers and monotonic clock support.
		4420
		4421	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4422	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4423	your program might be left out as well - a binary starting a timer and an
		4424	I/O watcher then might come out at only 5Kb.
		4425
		4426	=item EV_AVOID_STDIO
		4427
		4428	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4429	functions (printf, scanf, perror etc.). This will increase the code size
		4430	somewhat, but if your program doesn't otherwise depend on stdio and your
		4431	libc allows it, this avoids linking in the stdio library which is quite
		4432	big.
		4433
		4434	Note that error messages might become less precise when this option is
		4435	enabled.
		4436
		4437	=item EV_NSIG
		4438
		4439	The highest supported signal number, +1 (or, the number of
		4440	signals): Normally, libev tries to deduce the maximum number of signals
		4441	automatically, but sometimes this fails, in which case it can be
		4442	specified. Also, using a lower number than detected (C<32> should be
		4443	good for about any system in existence) can save some memory, as libev
		4444	statically allocates some 12-24 bytes per signal number.
		4445
		4446	=item EV_PID_HASHSIZE
		4447
		4448	C<ev_child> watchers use a small hash table to distribute workload by
		4449	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4450	usually more than enough. If you need to manage thousands of children you
		4451	might want to increase this value (I<must> be a power of two).
		4452
		4453	=item EV_INOTIFY_HASHSIZE
		4454
		4455	C<ev_stat> watchers use a small hash table to distribute workload by
		4456	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4457	disabled), usually more than enough. If you need to manage thousands of
		4458	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4459	power of two).
		4460
		4461	=item EV_USE_4HEAP
		4462
		4463	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4464	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4465	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4466	faster performance with many (thousands) of watchers.
		4467
		4468	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4469	will be C<0>.
		4470
		4471	=item EV_HEAP_CACHE_AT
		4472
		4473	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4474	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4475	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4476	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4477	but avoids random read accesses on heap changes. This improves performance
		4478	noticeably with many (hundreds) of watchers.
		4479
		4480	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4481	will be C<0>.
		4482
		4483	=item EV_VERIFY
		4484
		4485	Controls how much internal verification (see C<ev_verify ()>) will
		4486	be done: If set to C<0>, no internal verification code will be compiled
		4487	in. If set to C<1>, then verification code will be compiled in, but not
		4488	called. If set to C<2>, then the internal verification code will be
		4489	called once per loop, which can slow down libev. If set to C<3>, then the
		4490	verification code will be called very frequently, which will slow down
		4491	libev considerably.
		4492
		4493	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4494	will be C<0>.
1709		4495
1710	=item EV_COMMON	4496	=item EV_COMMON
1711		4497
1712	By default, all watchers have a C<void *data> member. By redefining	4498	By default, all watchers have a C<void *data> member. By redefining
1713	this macro to a something else you can include more and other types of	4499	this macro to something else you can include more and other types of
1714	members. You have to define it each time you include one of the files,	4500	members. You have to define it each time you include one of the files,
1715	though, and it must be identical each time.	4501	though, and it must be identical each time.
1716		4502
1717	For example, the perl EV module uses something like this:	4503	For example, the perl EV module uses something like this:
1718		4504
1719	#define EV_COMMON \	4505	#define EV_COMMON \
1720	SV *self; /* contains this struct */ \	4506	SV *self; /* contains this struct */ \
1721	SV *cb_sv, *fh /* note no trailing ";" */	4507	SV *cb_sv, *fh /* note no trailing ";" */
1722		4508
1723	=item EV_CB_DECLARE (type)	4509	=item EV_CB_DECLARE (type)
1724		4510
1725	=item EV_CB_INVOKE (watcher, revents)	4511	=item EV_CB_INVOKE (watcher, revents)
1726		4512
1727	=item ev_set_cb (ev, cb)	4513	=item ev_set_cb (ev, cb)
1728		4514
1729	Can be used to change the callback member declaration in each watcher,	4515	Can be used to change the callback member declaration in each watcher,
1730	and the way callbacks are invoked and set. Must expand to a struct member	4516	and the way callbacks are invoked and set. Must expand to a struct member
1731	definition and a statement, respectively. See the F<ev.v> header file for	4517	definition and a statement, respectively. See the F<ev.h> header file for
1732	their default definitions. One possible use for overriding these is to	4518	their default definitions. One possible use for overriding these is to
1733	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4519	avoid the C<struct ev_loop *> as first argument in all cases, or to use
1734	method calls instead of plain function calls in C++.	4520	method calls instead of plain function calls in C++.
		4521
		4522	=back
		4523
		4524	=head2 EXPORTED API SYMBOLS
		4525
		4526	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4527	exported symbols, you can use the provided F<Symbol.*> files which list
		4528	all public symbols, one per line:
		4529
		4530	Symbols.ev for libev proper
		4531	Symbols.event for the libevent emulation
		4532
		4533	This can also be used to rename all public symbols to avoid clashes with
		4534	multiple versions of libev linked together (which is obviously bad in
		4535	itself, but sometimes it is inconvenient to avoid this).
		4536
		4537	A sed command like this will create wrapper C<#define>'s that you need to
		4538	include before including F<ev.h>:
		4539
		4540	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4541
		4542	This would create a file F<wrap.h> which essentially looks like this:
		4543
		4544	#define ev_backend myprefix_ev_backend
		4545	#define ev_check_start myprefix_ev_check_start
		4546	#define ev_check_stop myprefix_ev_check_stop
		4547	...
1735		4548
1736	=head2 EXAMPLES	4549	=head2 EXAMPLES
1737		4550
1738	For a real-world example of a program the includes libev	4551	For a real-world example of a program the includes libev
1739	verbatim, you can have a look at the EV perl module	4552	verbatim, you can have a look at the EV perl module
…		…
1742	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	4555	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
1743	will be compiled. It is pretty complex because it provides its own header	4556	will be compiled. It is pretty complex because it provides its own header
1744	file.	4557	file.
1745		4558
1746	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4559	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
1747	that everybody includes and which overrides some autoconf choices:	4560	that everybody includes and which overrides some configure choices:
1748		4561
		4562	#define EV_FEATURES 8
		4563	#define EV_USE_SELECT 1
		4564	#define EV_PREPARE_ENABLE 1
		4565	#define EV_IDLE_ENABLE 1
		4566	#define EV_SIGNAL_ENABLE 1
		4567	#define EV_CHILD_ENABLE 1
1749	#define EV_USE_POLL 0	4568	#define EV_USE_STDEXCEPT 0
1750	#define EV_MULTIPLICITY 0
1751	#define EV_PERIODICS 0
1752	#define EV_CONFIG_H <config.h>	4569	#define EV_CONFIG_H <config.h>
1753		4570
1754	#include "ev++.h"	4571	#include "ev++.h"
1755		4572
1756	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4573	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
1757		4574
1758	#include "ev_cpp.h"	4575	#include "ev_cpp.h"
1759	#include "ev.c"	4576	#include "ev.c"
1760		4577
		4578	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
1761		4579
		4580	=head2 THREADS AND COROUTINES
		4581
		4582	=head3 THREADS
		4583
		4584	All libev functions are reentrant and thread-safe unless explicitly
		4585	documented otherwise, but libev implements no locking itself. This means
		4586	that you can use as many loops as you want in parallel, as long as there
		4587	are no concurrent calls into any libev function with the same loop
		4588	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4589	of course): libev guarantees that different event loops share no data
		4590	structures that need any locking.
		4591
		4592	Or to put it differently: calls with different loop parameters can be done
		4593	concurrently from multiple threads, calls with the same loop parameter
		4594	must be done serially (but can be done from different threads, as long as
		4595	only one thread ever is inside a call at any point in time, e.g. by using
		4596	a mutex per loop).
		4597
		4598	Specifically to support threads (and signal handlers), libev implements
		4599	so-called C<ev_async> watchers, which allow some limited form of
		4600	concurrency on the same event loop, namely waking it up "from the
		4601	outside".
		4602
		4603	If you want to know which design (one loop, locking, or multiple loops
		4604	without or something else still) is best for your problem, then I cannot
		4605	help you, but here is some generic advice:
		4606
		4607	=over 4
		4608
		4609	=item * most applications have a main thread: use the default libev loop
		4610	in that thread, or create a separate thread running only the default loop.
		4611
		4612	This helps integrating other libraries or software modules that use libev
		4613	themselves and don't care/know about threading.
		4614
		4615	=item * one loop per thread is usually a good model.
		4616
		4617	Doing this is almost never wrong, sometimes a better-performance model
		4618	exists, but it is always a good start.
		4619
		4620	=item * other models exist, such as the leader/follower pattern, where one
		4621	loop is handed through multiple threads in a kind of round-robin fashion.
		4622
		4623	Choosing a model is hard - look around, learn, know that usually you can do
		4624	better than you currently do :-)
		4625
		4626	=item * often you need to talk to some other thread which blocks in the
		4627	event loop.
		4628
		4629	C<ev_async> watchers can be used to wake them up from other threads safely
		4630	(or from signal contexts...).
		4631
		4632	An example use would be to communicate signals or other events that only
		4633	work in the default loop by registering the signal watcher with the
		4634	default loop and triggering an C<ev_async> watcher from the default loop
		4635	watcher callback into the event loop interested in the signal.
		4636
		4637	=back
		4638
		4639	See also L<THREAD LOCKING EXAMPLE>.
		4640
		4641	=head3 COROUTINES
		4642
		4643	Libev is very accommodating to coroutines ("cooperative threads"):
		4644	libev fully supports nesting calls to its functions from different
		4645	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4646	different coroutines, and switch freely between both coroutines running
		4647	the loop, as long as you don't confuse yourself). The only exception is
		4648	that you must not do this from C<ev_periodic> reschedule callbacks.
		4649
		4650	Care has been taken to ensure that libev does not keep local state inside
		4651	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4652	they do not call any callbacks.
		4653
		4654	=head2 COMPILER WARNINGS
		4655
		4656	Depending on your compiler and compiler settings, you might get no or a
		4657	lot of warnings when compiling libev code. Some people are apparently
		4658	scared by this.
		4659
		4660	However, these are unavoidable for many reasons. For one, each compiler
		4661	has different warnings, and each user has different tastes regarding
		4662	warning options. "Warn-free" code therefore cannot be a goal except when
		4663	targeting a specific compiler and compiler-version.
		4664
		4665	Another reason is that some compiler warnings require elaborate
		4666	workarounds, or other changes to the code that make it less clear and less
		4667	maintainable.
		4668
		4669	And of course, some compiler warnings are just plain stupid, or simply
		4670	wrong (because they don't actually warn about the condition their message
		4671	seems to warn about). For example, certain older gcc versions had some
		4672	warnings that resulted in an extreme number of false positives. These have
		4673	been fixed, but some people still insist on making code warn-free with
		4674	such buggy versions.
		4675
		4676	While libev is written to generate as few warnings as possible,
		4677	"warn-free" code is not a goal, and it is recommended not to build libev
		4678	with any compiler warnings enabled unless you are prepared to cope with
		4679	them (e.g. by ignoring them). Remember that warnings are just that:
		4680	warnings, not errors, or proof of bugs.
		4681
		4682
		4683	=head2 VALGRIND
		4684
		4685	Valgrind has a special section here because it is a popular tool that is
		4686	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4687
		4688	If you think you found a bug (memory leak, uninitialised data access etc.)
		4689	in libev, then check twice: If valgrind reports something like:
		4690
		4691	==2274== definitely lost: 0 bytes in 0 blocks.
		4692	==2274== possibly lost: 0 bytes in 0 blocks.
		4693	==2274== still reachable: 256 bytes in 1 blocks.
		4694
		4695	Then there is no memory leak, just as memory accounted to global variables
		4696	is not a memleak - the memory is still being referenced, and didn't leak.
		4697
		4698	Similarly, under some circumstances, valgrind might report kernel bugs
		4699	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4700	although an acceptable workaround has been found here), or it might be
		4701	confused.
		4702
		4703	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4704	make it into some kind of religion.
		4705
		4706	If you are unsure about something, feel free to contact the mailing list
		4707	with the full valgrind report and an explanation on why you think this
		4708	is a bug in libev (best check the archives, too :). However, don't be
		4709	annoyed when you get a brisk "this is no bug" answer and take the chance
		4710	of learning how to interpret valgrind properly.
		4711
		4712	If you need, for some reason, empty reports from valgrind for your project
		4713	I suggest using suppression lists.
		4714
		4715
		4716	=head1 PORTABILITY NOTES
		4717
		4718	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4719
		4720	GNU/Linux is the only common platform that supports 64 bit file/large file
		4721	interfaces but I<disables> them by default.
		4722
		4723	That means that libev compiled in the default environment doesn't support
		4724	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4725
		4726	Unfortunately, many programs try to work around this GNU/Linux issue
		4727	by enabling the large file API, which makes them incompatible with the
		4728	standard libev compiled for their system.
		4729
		4730	Likewise, libev cannot enable the large file API itself as this would
		4731	suddenly make it incompatible to the default compile time environment,
		4732	i.e. all programs not using special compile switches.
		4733
		4734	=head2 OS/X AND DARWIN BUGS
		4735
		4736	The whole thing is a bug if you ask me - basically any system interface
		4737	you touch is broken, whether it is locales, poll, kqueue or even the
		4738	OpenGL drivers.
		4739
		4740	=head3 C<kqueue> is buggy
		4741
		4742	The kqueue syscall is broken in all known versions - most versions support
		4743	only sockets, many support pipes.
		4744
		4745	Libev tries to work around this by not using C<kqueue> by default on this
		4746	rotten platform, but of course you can still ask for it when creating a
		4747	loop - embedding a socket-only kqueue loop into a select-based one is
		4748	probably going to work well.
		4749
		4750	=head3 C<poll> is buggy
		4751
		4752	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4753	implementation by something calling C<kqueue> internally around the 10.5.6
		4754	release, so now C<kqueue> I<and> C<poll> are broken.
		4755
		4756	Libev tries to work around this by not using C<poll> by default on
		4757	this rotten platform, but of course you can still ask for it when creating
		4758	a loop.
		4759
		4760	=head3 C<select> is buggy
		4761
		4762	All that's left is C<select>, and of course Apple found a way to fuck this
		4763	one up as well: On OS/X, C<select> actively limits the number of file
		4764	descriptors you can pass in to 1024 - your program suddenly crashes when
		4765	you use more.
		4766
		4767	There is an undocumented "workaround" for this - defining
		4768	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4769	work on OS/X.
		4770
		4771	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4772
		4773	=head3 C<errno> reentrancy
		4774
		4775	The default compile environment on Solaris is unfortunately so
		4776	thread-unsafe that you can't even use components/libraries compiled
		4777	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4778	defined by default. A valid, if stupid, implementation choice.
		4779
		4780	If you want to use libev in threaded environments you have to make sure
		4781	it's compiled with C<_REENTRANT> defined.
		4782
		4783	=head3 Event port backend
		4784
		4785	The scalable event interface for Solaris is called "event
		4786	ports". Unfortunately, this mechanism is very buggy in all major
		4787	releases. If you run into high CPU usage, your program freezes or you get
		4788	a large number of spurious wakeups, make sure you have all the relevant
		4789	and latest kernel patches applied. No, I don't know which ones, but there
		4790	are multiple ones to apply, and afterwards, event ports actually work
		4791	great.
		4792
		4793	If you can't get it to work, you can try running the program by setting
		4794	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4795	C<select> backends.
		4796
		4797	=head2 AIX POLL BUG
		4798
		4799	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4800	this by trying to avoid the poll backend altogether (i.e. it's not even
		4801	compiled in), which normally isn't a big problem as C<select> works fine
		4802	with large bitsets on AIX, and AIX is dead anyway.
		4803
		4804	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4805
		4806	=head3 General issues
		4807
		4808	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4809	requires, and its I/O model is fundamentally incompatible with the POSIX
		4810	model. Libev still offers limited functionality on this platform in
		4811	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4812	descriptors. This only applies when using Win32 natively, not when using
		4813	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4814	as every compielr comes with a slightly differently broken/incompatible
		4815	environment.
		4816
		4817	Lifting these limitations would basically require the full
		4818	re-implementation of the I/O system. If you are into this kind of thing,
		4819	then note that glib does exactly that for you in a very portable way (note
		4820	also that glib is the slowest event library known to man).
		4821
		4822	There is no supported compilation method available on windows except
		4823	embedding it into other applications.
		4824
		4825	Sensible signal handling is officially unsupported by Microsoft - libev
		4826	tries its best, but under most conditions, signals will simply not work.
		4827
		4828	Not a libev limitation but worth mentioning: windows apparently doesn't
		4829	accept large writes: instead of resulting in a partial write, windows will
		4830	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4831	so make sure you only write small amounts into your sockets (less than a
		4832	megabyte seems safe, but this apparently depends on the amount of memory
		4833	available).
		4834
		4835	Due to the many, low, and arbitrary limits on the win32 platform and
		4836	the abysmal performance of winsockets, using a large number of sockets
		4837	is not recommended (and not reasonable). If your program needs to use
		4838	more than a hundred or so sockets, then likely it needs to use a totally
		4839	different implementation for windows, as libev offers the POSIX readiness
		4840	notification model, which cannot be implemented efficiently on windows
		4841	(due to Microsoft monopoly games).
		4842
		4843	A typical way to use libev under windows is to embed it (see the embedding
		4844	section for details) and use the following F<evwrap.h> header file instead
		4845	of F<ev.h>:
		4846
		4847	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4848	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4849
		4850	#include "ev.h"
		4851
		4852	And compile the following F<evwrap.c> file into your project (make sure
		4853	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4854
		4855	#include "evwrap.h"
		4856	#include "ev.c"
		4857
		4858	=head3 The winsocket C<select> function
		4859
		4860	The winsocket C<select> function doesn't follow POSIX in that it
		4861	requires socket I<handles> and not socket I<file descriptors> (it is
		4862	also extremely buggy). This makes select very inefficient, and also
		4863	requires a mapping from file descriptors to socket handles (the Microsoft
		4864	C runtime provides the function C<_open_osfhandle> for this). See the
		4865	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4866	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4867
		4868	The configuration for a "naked" win32 using the Microsoft runtime
		4869	libraries and raw winsocket select is:
		4870
		4871	#define EV_USE_SELECT 1
		4872	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4873
		4874	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4875	complexity in the O(n²) range when using win32.
		4876
		4877	=head3 Limited number of file descriptors
		4878
		4879	Windows has numerous arbitrary (and low) limits on things.
		4880
		4881	Early versions of winsocket's select only supported waiting for a maximum
		4882	of C<64> handles (probably owning to the fact that all windows kernels
		4883	can only wait for C<64> things at the same time internally; Microsoft
		4884	recommends spawning a chain of threads and wait for 63 handles and the
		4885	previous thread in each. Sounds great!).
		4886
		4887	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4888	to some high number (e.g. C<2048>) before compiling the winsocket select
		4889	call (which might be in libev or elsewhere, for example, perl and many
		4890	other interpreters do their own select emulation on windows).
		4891
		4892	Another limit is the number of file descriptors in the Microsoft runtime
		4893	libraries, which by default is C<64> (there must be a hidden I<64>
		4894	fetish or something like this inside Microsoft). You can increase this
		4895	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4896	(another arbitrary limit), but is broken in many versions of the Microsoft
		4897	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4898	(depending on windows version and/or the phase of the moon). To get more,
		4899	you need to wrap all I/O functions and provide your own fd management, but
		4900	the cost of calling select (O(n²)) will likely make this unworkable.
		4901
		4902	=head2 PORTABILITY REQUIREMENTS
		4903
		4904	In addition to a working ISO-C implementation and of course the
		4905	backend-specific APIs, libev relies on a few additional extensions:
		4906
		4907	=over 4
		4908
		4909	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4910	calling conventions regardless of C<ev_watcher_type *>.
		4911
		4912	Libev assumes not only that all watcher pointers have the same internal
		4913	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4914	assumes that the same (machine) code can be used to call any watcher
		4915	callback: The watcher callbacks have different type signatures, but libev
		4916	calls them using an C<ev_watcher *> internally.
		4917
		4918	=item pointer accesses must be thread-atomic
		4919
		4920	Accessing a pointer value must be atomic, it must both be readable and
		4921	writable in one piece - this is the case on all current architectures.
		4922
		4923	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4924
		4925	The type C<sig_atomic_t volatile> (or whatever is defined as
		4926	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4927	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4928	believed to be sufficiently portable.
		4929
		4930	=item C<sigprocmask> must work in a threaded environment
		4931
		4932	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4933	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4934	pthread implementations will either allow C<sigprocmask> in the "main
		4935	thread" or will block signals process-wide, both behaviours would
		4936	be compatible with libev. Interaction between C<sigprocmask> and
		4937	C<pthread_sigmask> could complicate things, however.
		4938
		4939	The most portable way to handle signals is to block signals in all threads
		4940	except the initial one, and run the default loop in the initial thread as
		4941	well.
		4942
		4943	=item C<long> must be large enough for common memory allocation sizes
		4944
		4945	To improve portability and simplify its API, libev uses C<long> internally
		4946	instead of C<size_t> when allocating its data structures. On non-POSIX
		4947	systems (Microsoft...) this might be unexpectedly low, but is still at
		4948	least 31 bits everywhere, which is enough for hundreds of millions of
		4949	watchers.
		4950
		4951	=item C<double> must hold a time value in seconds with enough accuracy
		4952
		4953	The type C<double> is used to represent timestamps. It is required to
		4954	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4955	good enough for at least into the year 4000 with millisecond accuracy
		4956	(the design goal for libev). This requirement is overfulfilled by
		4957	implementations using IEEE 754, which is basically all existing ones. With
		4958	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4959
		4960	=back
		4961
		4962	If you know of other additional requirements drop me a note.
		4963
		4964
1762	=head1 COMPLEXITIES	4965	=head1 ALGORITHMIC COMPLEXITIES
1763		4966
1764	In this section the complexities of (many of) the algorithms used inside	4967	In this section the complexities of (many of) the algorithms used inside
1765	libev will be explained. For complexity discussions about backends see the	4968	libev will be documented. For complexity discussions about backends see
1766	documentation for C<ev_default_init>.	4969	the documentation for C<ev_default_init>.
		4970
		4971	All of the following are about amortised time: If an array needs to be
		4972	extended, libev needs to realloc and move the whole array, but this
		4973	happens asymptotically rarer with higher number of elements, so O(1) might
		4974	mean that libev does a lengthy realloc operation in rare cases, but on
		4975	average it is much faster and asymptotically approaches constant time.
1767		4976
1768	=over 4	4977	=over 4
1769		4978
1770	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4979	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
1771		4980
		4981	This means that, when you have a watcher that triggers in one hour and
		4982	there are 100 watchers that would trigger before that, then inserting will
		4983	have to skip roughly seven (C<ld 100>) of these watchers.
		4984
1772	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4985	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
1773		4986
		4987	That means that changing a timer costs less than removing/adding them,
		4988	as only the relative motion in the event queue has to be paid for.
		4989
1774	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4990	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
1775		4991
		4992	These just add the watcher into an array or at the head of a list.
		4993
1776	=item Stopping check/prepare/idle watchers: O(1)	4994	=item Stopping check/prepare/idle/fork/async watchers: O(1)
1777		4995
1778	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	4996	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
1779		4997
		4998	These watchers are stored in lists, so they need to be walked to find the
		4999	correct watcher to remove. The lists are usually short (you don't usually
		5000	have many watchers waiting for the same fd or signal: one is typical, two
		5001	is rare).
		5002
1780	=item Finding the next timer per loop iteration: O(1)	5003	=item Finding the next timer in each loop iteration: O(1)
		5004
		5005	By virtue of using a binary or 4-heap, the next timer is always found at a
		5006	fixed position in the storage array.
1781		5007
1782	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5008	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
1783		5009
1784	=item Activating one watcher: O(1)	5010	A change means an I/O watcher gets started or stopped, which requires
		5011	libev to recalculate its status (and possibly tell the kernel, depending
		5012	on backend and whether C<ev_io_set> was used).
		5013
		5014	=item Activating one watcher (putting it into the pending state): O(1)
		5015
		5016	=item Priority handling: O(number_of_priorities)
		5017
		5018	Priorities are implemented by allocating some space for each
		5019	priority. When doing priority-based operations, libev usually has to
		5020	linearly search all the priorities, but starting/stopping and activating
		5021	watchers becomes O(1) with respect to priority handling.
		5022
		5023	=item Sending an ev_async: O(1)
		5024
		5025	=item Processing ev_async_send: O(number_of_async_watchers)
		5026
		5027	=item Processing signals: O(max_signal_number)
		5028
		5029	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5030	calls in the current loop iteration. Checking for async and signal events
		5031	involves iterating over all running async watchers or all signal numbers.
1785		5032
1786	=back	5033	=back
1787		5034
1788		5035
		5036	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5037
		5038	The major version 4 introduced some incompatible changes to the API.
		5039
		5040	At the moment, the C<ev.h> header file provides compatibility definitions
		5041	for all changes, so most programs should still compile. The compatibility
		5042	layer might be removed in later versions of libev, so better update to the
		5043	new API early than late.
		5044
		5045	=over 4
		5046
		5047	=item C<EV_COMPAT3> backwards compatibility mechanism
		5048
		5049	The backward compatibility mechanism can be controlled by
		5050	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5051	section.
		5052
		5053	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5054
		5055	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5056
		5057	ev_loop_destroy (EV_DEFAULT_UC);
		5058	ev_loop_fork (EV_DEFAULT);
		5059
		5060	=item function/symbol renames
		5061
		5062	A number of functions and symbols have been renamed:
		5063
		5064	ev_loop => ev_run
		5065	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5066	EVLOOP_ONESHOT => EVRUN_ONCE
		5067
		5068	ev_unloop => ev_break
		5069	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5070	EVUNLOOP_ONE => EVBREAK_ONE
		5071	EVUNLOOP_ALL => EVBREAK_ALL
		5072
		5073	EV_TIMEOUT => EV_TIMER
		5074
		5075	ev_loop_count => ev_iteration
		5076	ev_loop_depth => ev_depth
		5077	ev_loop_verify => ev_verify
		5078
		5079	Most functions working on C<struct ev_loop> objects don't have an
		5080	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5081	associated constants have been renamed to not collide with the C<struct
		5082	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5083	as all other watcher types. Note that C<ev_loop_fork> is still called
		5084	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5085	typedef.
		5086
		5087	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5088
		5089	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5090	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5091	and work, but the library code will of course be larger.
		5092
		5093	=back
		5094
		5095
		5096	=head1 GLOSSARY
		5097
		5098	=over 4
		5099
		5100	=item active
		5101
		5102	A watcher is active as long as it has been started and not yet stopped.
		5103	See L<WATCHER STATES> for details.
		5104
		5105	=item application
		5106
		5107	In this document, an application is whatever is using libev.
		5108
		5109	=item backend
		5110
		5111	The part of the code dealing with the operating system interfaces.
		5112
		5113	=item callback
		5114
		5115	The address of a function that is called when some event has been
		5116	detected. Callbacks are being passed the event loop, the watcher that
		5117	received the event, and the actual event bitset.
		5118
		5119	=item callback/watcher invocation
		5120
		5121	The act of calling the callback associated with a watcher.
		5122
		5123	=item event
		5124
		5125	A change of state of some external event, such as data now being available
		5126	for reading on a file descriptor, time having passed or simply not having
		5127	any other events happening anymore.
		5128
		5129	In libev, events are represented as single bits (such as C<EV_READ> or
		5130	C<EV_TIMER>).
		5131
		5132	=item event library
		5133
		5134	A software package implementing an event model and loop.
		5135
		5136	=item event loop
		5137
		5138	An entity that handles and processes external events and converts them
		5139	into callback invocations.
		5140
		5141	=item event model
		5142
		5143	The model used to describe how an event loop handles and processes
		5144	watchers and events.
		5145
		5146	=item pending
		5147
		5148	A watcher is pending as soon as the corresponding event has been
		5149	detected. See L<WATCHER STATES> for details.
		5150
		5151	=item real time
		5152
		5153	The physical time that is observed. It is apparently strictly monotonic :)
		5154
		5155	=item wall-clock time
		5156
		5157	The time and date as shown on clocks. Unlike real time, it can actually
		5158	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5159	clock.
		5160
		5161	=item watcher
		5162
		5163	A data structure that describes interest in certain events. Watchers need
		5164	to be started (attached to an event loop) before they can receive events.
		5165
		5166	=back
		5167
1789	=head1 AUTHOR	5168	=head1 AUTHOR
1790		5169
1791	Marc Lehmann <libev@schmorp.de>.	5170	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5171	Magnusson and Emanuele Giaquinta.
1792		5172

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