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Revision 1.351 by root, Mon Jan 10 14:24:26 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 double type in C.	140	too. It usually aliases to the C<double> type in C. When you need to do
		141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
51		166
52	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
53		168
54	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
55	library in any way.	170	library in any way.
…		…
58		173
59	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
60		175
61	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
62	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
63	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 ()>.
64		186
65	=item int ev_version_major ()	187	=item int ev_version_major ()
66		188
67	=item int ev_version_minor ()	189	=item int ev_version_minor ()
68		190
69	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
70	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
71	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
72	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
73	version of the library your program was compiled against.	195	version of the library your program was compiled against.
74		196
		197	These version numbers refer to the ABI version of the library, not the
		198	release version.
		199
75	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,
76	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
77	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
78	not a problem.	203	not a problem.
79		204
		205	Example: Make sure we haven't accidentally been linked against the wrong
		206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
		208
		209	assert (("libev version mismatch",
		210	ev_version_major () == EV_VERSION_MAJOR
		211	&& ev_version_minor () >= EV_VERSION_MINOR));
		212
		213	=item unsigned int ev_supported_backends ()
		214
		215	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		216	value) compiled into this binary of libev (independent of their
		217	availability on the system you are running on). See C<ev_default_loop> for
		218	a description of the set values.
		219
		220	Example: make sure we have the epoll method, because yeah this is cool and
		221	a must have and can we have a torrent of it please!!!11
		222
		223	assert (("sorry, no epoll, no sex",
		224	ev_supported_backends () & EVBACKEND_EPOLL));
		225
		226	=item unsigned int ev_recommended_backends ()
		227
		228	Return the set of all backends compiled into this binary of libev and
		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
		231	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
		232	and will not be auto-detected unless you explicitly request it (assuming
		233	you know what you are doing). This is the set of backends that libev will
		234	probe for if you specify no backends explicitly.
		235
		236	=item unsigned int ev_embeddable_backends ()
		237
		238	Returns the set of backends that are embeddable in other event loops. This
		239	value is platform-specific but can include backends not available on the
		240	current system. To find which embeddable backends might be supported on
		241	the current system, you would need to look at C<ev_embeddable_backends ()
		242	& ev_supported_backends ()>, likewise for recommended ones.
		243
		244	See the description of C<ev_embed> watchers for more info.
		245
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		247
82	Sets the allocation function to use (the prototype is similar to the	248	Sets the allocation function to use (the prototype is similar - the
83	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
84	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
85	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
86	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.
87		257
88	You could override this function in high-availability programs to, say,	258	You could override this function in high-availability programs to, say,
89	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,
90	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.
91		261
		262	Example: Replace the libev allocator with one that waits a bit and then
		263	retries (example requires a standards-compliant C<realloc>).
		264
		265	static void *
		266	persistent_realloc (void *ptr, size_t size)
		267	{
		268	for (;;)
		269	{
		270	void *newptr = realloc (ptr, size);
		271
		272	if (newptr)
		273	return newptr;
		274
		275	sleep (60);
		276	}
		277	}
		278
		279	...
		280	ev_set_allocator (persistent_realloc);
		281
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
93		283
94	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
95	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
96	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
97	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
98	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
99	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
100	(such as abort).	290	(such as abort).
101		291
		292	Example: This is basically the same thing that libev does internally, too.
		293
		294	static void
		295	fatal_error (const char *msg)
		296	{
		297	perror (msg);
		298	abort ();
		299	}
		300
		301	...
		302	ev_set_syserr_cb (fatal_error);
		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
102	=back	317	=back
103		318
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
105		320
106	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
107	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
108	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
109		324
110	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
111	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
112	create, you also create another event loop. Libev itself does no locking	327	do not.
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116		328
117	=over 4	329	=over 4
118		330
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		332
121	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
122	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
123	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
124	flags).	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".
125		343
126	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
127	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.
128		376
129	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
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		379
132	It supports the following flags:	380	The following flags are supported:
133		381
134	=over 4	382	=over 4
135		383
136	=item C<EVFLAG_AUTO>	384	=item C<EVFLAG_AUTO>
137		385
138	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
139	thing, believe me).	387	thing, believe me).
140		388
141	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
142		390
143	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
144	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
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	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
147	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
148	around bugs.	396	around bugs.
149		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
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		450
152	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
153	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,
154	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
155	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
156	the fastest backend for a low number of fds.	455	usually the fastest backend for a low number of (low-numbered :) fds.
157		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).
		467
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	468	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		469
160	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
161	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
162	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
163	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.
164		476
		477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		479
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	480	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		481
		482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		483	kernels).
166		484
167	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,
168	but it scales phenomenally better. While poll and select usually scale like	486	but it scales phenomenally better. While poll and select usually scale
169	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),
170	either O(1) or O(active_fds).	488	epoll scales either O(1) or O(active_fds).
171		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
172	While stopping and starting an I/O watcher in the same iteration will	513	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	514	will result in some caching, there is still a system call per such
174	(because the fd could point to a different file description now), so its	515	incident (because the same I<file descriptor> could point to a different
175	best to avoid that. Also, dup()ed file descriptors might not work very	516	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
176	well if you register events for both fds.	517	file descriptors might not work very well if you register events for both
		518	file descriptors.
177		519
		520	Best performance from this backend is achieved by not unregistering all
		521	watchers for a file descriptor until it has been closed, if possible,
		522	i.e. keep at least one watcher active per fd at all times. Stopping and
		523	starting a watcher (without re-setting it) also usually doesn't cause
		524	extra overhead. A fork can both result in spurious notifications as well
		525	as in libev having to destroy and recreate the epoll object, which can
		526	take considerable time and thus should be avoided.
		527
		528	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		529	faster than epoll for maybe up to a hundred file descriptors, depending on
		530	the usage. So sad.
		531
		532	While nominally embeddable in other event loops, this feature is broken in
		533	all kernel versions tested so far.
		534
		535	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		536	C<EVBACKEND_POLL>.
		537
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	538	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		539
180	Kqueue deserves special mention, as at the time of this writing, it	540	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	541	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	542	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	543	it's completely useless). Unlike epoll, however, whose brokenness
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	544	is by design, these kqueue bugs can (and eventually will) be fixed
		545	without API changes to existing programs. For this reason it's not being
		546	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		547	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		548	system like NetBSD.
		549
		550	You still can embed kqueue into a normal poll or select backend and use it
		551	only for sockets (after having made sure that sockets work with kqueue on
		552	the target platform). See C<ev_embed> watchers for more info.
185		553
186	It scales in the same way as the epoll backend, but the interface to the	554	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	555	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	556	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	557	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	558	two event changes per incident. Support for C<fork ()> is very bad (but
		559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		560	cases
191		561
		562	This backend usually performs well under most conditions.
		563
		564	While nominally embeddable in other event loops, this doesn't work
		565	everywhere, so you might need to test for this. And since it is broken
		566	almost everywhere, you should only use it when you have a lot of sockets
		567	(for which it usually works), by embedding it into another event loop
		568	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		569	also broken on OS X)) and, did I mention it, using it only for sockets.
		570
		571	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		572	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		573	C<NOTE_EOF>.
		574
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	575	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		576
194	This is not implemented yet (and might never be).	577	This is not implemented yet (and might never be, unless you send me an
		578	implementation). According to reports, C</dev/poll> only supports sockets
		579	and is not embeddable, which would limit the usefulness of this backend
		580	immensely.
195		581
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		583
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	584	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	585	it's really slow, but it still scales very well (O(active_fds)).
200		586
		587	While this backend scales well, it requires one system call per active
		588	file descriptor per loop iteration. For small and medium numbers of file
		589	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		590	might perform better.
		591
		592	On the positive side, this backend actually performed fully to
		593	specification in all tests and is fully embeddable, which is a rare feat
		594	among the OS-specific backends (I vastly prefer correctness over speed
		595	hacks).
		596
		597	On the negative side, the interface is I<bizarre>, with the event polling
		598	function sometimes returning events to the caller even though an error
		599	occured, but with no indication whether it has done so or not (yes, it's
		600	even documented that way) - deadly for edge-triggered interfaces, but
		601	fortunately libev seems to be able to work around it.
		602
		603	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		604	C<EVBACKEND_POLL>.
		605
201	=item C<EVMETHOD_ALL>	606	=item C<EVBACKEND_ALL>
202		607
203	Try all backends (even potentially broken ones that wouldn't be tried	608	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	609	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	610	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		611
		612	It is definitely not recommended to use this flag, use whatever
		613	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		614	at all.
		615
		616	=item C<EVBACKEND_MASK>
		617
		618	Not a backend at all, but a mask to select all backend bits from a
		619	C<flags> value, in case you want to mask out any backends from a flags
		620	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
206		621
207	=back	622	=back
208		623
209	If one or more of these are ored into the flags value, then only these	624	If one or more of the backend flags are or'ed into the flags value,
210	backends will be tried (in the reverse order as given here). If none are	625	then only these backends will be tried (in the reverse order as listed
211	specified, most compiled-in backend will be tried, usually in reverse	626	here). If none are specified, all backends in C<ev_recommended_backends
212	order of their flag values :)	627	()> will be tried.
213		628
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	629	Example: Try to create a event loop that uses epoll and nothing else.
215		630
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	631	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
217	always distinct from the default loop. Unlike the default loop, it cannot	632	if (!epoller)
218	handle signal and child watchers, and attempts to do so will be greeted by	633	fatal ("no epoll found here, maybe it hides under your chair");
219	undefined behaviour (or a failed assertion if assertions are enabled).
220		634
221	=item ev_default_destroy ()	635	Example: Use whatever libev has to offer, but make sure that kqueue is
		636	used if available.
222		637
223	Destroys the default loop again (frees all memory and kernel state	638	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
224	etc.). This stops all registered event watchers (by not touching them in
225	any way whatsoever, although you cannot rely on this :).
226		639
227	=item ev_loop_destroy (loop)	640	=item ev_loop_destroy (loop)
228		641
229	Like C<ev_default_destroy>, but destroys an event loop created by an	642	Destroys an event loop object (frees all memory and kernel state
230	earlier call to C<ev_loop_new>.	643	etc.). None of the active event watchers will be stopped in the normal
		644	sense, so e.g. C<ev_is_active> might still return true. It is your
		645	responsibility to either stop all watchers cleanly yourself I<before>
		646	calling this function, or cope with the fact afterwards (which is usually
		647	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		648	for example).
231		649
232	=item ev_default_fork ()	650	Note that certain global state, such as signal state (and installed signal
		651	handlers), will not be freed by this function, and related watchers (such
		652	as signal and child watchers) would need to be stopped manually.
233		653
		654	This function is normally used on loop objects allocated by
		655	C<ev_loop_new>, but it can also be used on the default loop returned by
		656	C<ev_default_loop>, in which case it is not thread-safe.
		657
		658	Note that it is not advisable to call this function on the default loop
		659	except in the rare occasion where you really need to free its resources.
		660	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		661	and C<ev_loop_destroy>.
		662
		663	=item ev_loop_fork (loop)
		664
		665	This function sets a flag that causes subsequent C<ev_run> iterations to
234	This function reinitialises the kernel state for backends that have	666	reinitialise the kernel state for backends that have one. Despite the
235	one. Despite the name, you can call it anytime, but it makes most sense	667	name, you can call it anytime, but it makes most sense after forking, in
236	after forking, in either the parent or child process (or both, but that	668	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
237	again makes little sense).	669	child before resuming or calling C<ev_run>.
238		670
239	You I<must> call this function in the child process after forking if and	671	Again, you I<have> to call it on I<any> loop that you want to re-use after
240	only if you want to use the event library in both processes. If you just	672	a fork, I<even if you do not plan to use the loop in the parent>. This is
241	fork+exec, you don't have to call it.	673	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		674	during fork.
		675
		676	On the other hand, you only need to call this function in the child
		677	process if and only if you want to use the event loop in the child. If
		678	you just fork+exec or create a new loop in the child, you don't have to
		679	call it at all (in fact, C<epoll> is so badly broken that it makes a
		680	difference, but libev will usually detect this case on its own and do a
		681	costly reset of the backend).
242		682
243	The function itself is quite fast and it's usually not a problem to call	683	The function itself is quite fast and it's usually not a problem to call
244	it just in case after a fork. To make this easy, the function will fit in	684	it just in case after a fork.
245	quite nicely into a call to C<pthread_atfork>:
246		685
		686	Example: Automate calling C<ev_loop_fork> on the default loop when
		687	using pthreads.
		688
		689	static void
		690	post_fork_child (void)
		691	{
		692	ev_loop_fork (EV_DEFAULT);
		693	}
		694
		695	...
247	pthread_atfork (0, 0, ev_default_fork);	696	pthread_atfork (0, 0, post_fork_child);
248		697
249	=item ev_loop_fork (loop)	698	=item int ev_is_default_loop (loop)
250		699
251	Like C<ev_default_fork>, but acts on an event loop created by	700	Returns true when the given loop is, in fact, the default loop, and false
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	701	otherwise.
253	after fork, and how you do this is entirely your own problem.
254		702
		703	=item unsigned int ev_iteration (loop)
		704
		705	Returns the current iteration count for the event loop, which is identical
		706	to the number of times libev did poll for new events. It starts at C<0>
		707	and happily wraps around with enough iterations.
		708
		709	This value can sometimes be useful as a generation counter of sorts (it
		710	"ticks" the number of loop iterations), as it roughly corresponds with
		711	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		712	prepare and check phases.
		713
255	=item unsigned int ev_method (loop)	714	=item unsigned int ev_depth (loop)
256		715
		716	Returns the number of times C<ev_run> was entered minus the number of
		717	times C<ev_run> was exited normally, in other words, the recursion depth.
		718
		719	Outside C<ev_run>, this number is zero. In a callback, this number is
		720	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		721	in which case it is higher.
		722
		723	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		724	throwing an exception etc.), doesn't count as "exit" - consider this
		725	as a hint to avoid such ungentleman-like behaviour unless it's really
		726	convenient, in which case it is fully supported.
		727
		728	=item unsigned int ev_backend (loop)
		729
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	730	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	731	use.
259		732
260	=item ev_tstamp ev_now (loop)	733	=item ev_tstamp ev_now (loop)
261		734
262	Returns the current "event loop time", which is the time the event loop	735	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	736	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	737	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	738	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	739	event occurring (or more correctly, libev finding out about it).
267		740
		741	=item ev_now_update (loop)
		742
		743	Establishes the current time by querying the kernel, updating the time
		744	returned by C<ev_now ()> in the progress. This is a costly operation and
		745	is usually done automatically within C<ev_run ()>.
		746
		747	This function is rarely useful, but when some event callback runs for a
		748	very long time without entering the event loop, updating libev's idea of
		749	the current time is a good idea.
		750
		751	See also L<The special problem of time updates> in the C<ev_timer> section.
		752
		753	=item ev_suspend (loop)
		754
		755	=item ev_resume (loop)
		756
		757	These two functions suspend and resume an event loop, for use when the
		758	loop is not used for a while and timeouts should not be processed.
		759
		760	A typical use case would be an interactive program such as a game: When
		761	the user presses C<^Z> to suspend the game and resumes it an hour later it
		762	would be best to handle timeouts as if no time had actually passed while
		763	the program was suspended. This can be achieved by calling C<ev_suspend>
		764	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		765	C<ev_resume> directly afterwards to resume timer processing.
		766
		767	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		768	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		769	will be rescheduled (that is, they will lose any events that would have
		770	occurred while suspended).
		771
		772	After calling C<ev_suspend> you B<must not> call I<any> function on the
		773	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		774	without a previous call to C<ev_suspend>.
		775
		776	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		777	event loop time (see C<ev_now_update>).
		778
268	=item ev_loop (loop, int flags)	779	=item ev_run (loop, int flags)
269		780
270	Finally, this is it, the event handler. This function usually is called	781	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	782	after you have initialised all your watchers and you want to start
272	events.	783	handling events. It will ask the operating system for any new events, call
		784	the watcher callbacks, an then repeat the whole process indefinitely: This
		785	is why event loops are called I<loops>.
273		786
274	If the flags argument is specified as 0, it will not return until either	787	If the flags argument is specified as C<0>, it will keep handling events
275	no event watchers are active anymore or C<ev_unloop> was called.	788	until either no event watchers are active anymore or C<ev_break> was
		789	called.
276		790
		791	Please note that an explicit C<ev_break> is usually better than
		792	relying on all watchers to be stopped when deciding when a program has
		793	finished (especially in interactive programs), but having a program
		794	that automatically loops as long as it has to and no longer by virtue
		795	of relying on its watchers stopping correctly, that is truly a thing of
		796	beauty.
		797
		798	This function is also I<mostly> exception-safe - you can break out of
		799	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		800	exception and so on. This does not decrement the C<ev_depth> value, nor
		801	will it clear any outstanding C<EVBREAK_ONE> breaks.
		802
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	803	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	804	those events and any already outstanding ones, but will not wait and
279	case there are no events and will return after one iteration of the loop.	805	block your process in case there are no events and will return after one
		806	iteration of the loop. This is sometimes useful to poll and handle new
		807	events while doing lengthy calculations, to keep the program responsive.
280		808
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	809	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	810	necessary) and will handle those and any already outstanding ones. It
283	your process until at least one new event arrives, and will return after	811	will block your process until at least one new event arrives (which could
		812	be an event internal to libev itself, so there is no guarantee that a
		813	user-registered callback will be called), and will return after one
284	one iteration of the loop.	814	iteration of the loop.
285		815
286	This flags value could be used to implement alternative looping	816	This is useful if you are waiting for some external event in conjunction
287	constructs, but the C<prepare> and C<check> watchers provide a better and	817	with something not expressible using other libev watchers (i.e. "roll your
288	more generic mechanism.	818	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		819	usually a better approach for this kind of thing.
289		820
290	Here are the gory details of what ev_loop does:	821	Here are the gory details of what C<ev_run> does:
291		822
292	1. If there are no active watchers (reference count is zero), return.	823	- Increment loop depth.
		824	- Reset the ev_break status.
		825	- Before the first iteration, call any pending watchers.
		826	LOOP:
		827	- If EVFLAG_FORKCHECK was used, check for a fork.
		828	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	829	- Queue and call all prepare watchers.
		830	- If ev_break was called, goto FINISH.
294	3. If we have been forked, recreate the kernel state.	831	- If we have been forked, detach and recreate the kernel state
		832	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	833	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	834	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	835	- Calculate for how long to sleep or block, if at all
		836	(active idle watchers, EVRUN_NOWAIT or not having
		837	any active watchers at all will result in not sleeping).
		838	- Sleep if the I/O and timer collect interval say so.
		839	- Increment loop iteration counter.
298	7. Block the process, waiting for events.	840	- Block the process, waiting for any events.
		841	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	842	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	843	- Queue all expired timers.
301	10. Queue all outstanding periodics.	844	- Queue all expired periodics.
302	11. If no events are pending now, queue all idle watchers.	845	- Queue all idle watchers with priority higher than that of pending events.
303	12. Queue all check watchers.	846	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	847	- Call all queued watchers in reverse order (i.e. check watchers first).
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	848	Signals and child watchers are implemented as I/O watchers, and will
306	was used, return, otherwise continue with step #1.	849	be handled here by queueing them when their watcher gets executed.
		850	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		851	were used, or there are no active watchers, goto FINISH, otherwise
		852	continue with step LOOP.
		853	FINISH:
		854	- Reset the ev_break status iff it was EVBREAK_ONE.
		855	- Decrement the loop depth.
		856	- Return.
307		857
		858	Example: Queue some jobs and then loop until no events are outstanding
		859	anymore.
		860
		861	... queue jobs here, make sure they register event watchers as long
		862	... as they still have work to do (even an idle watcher will do..)
		863	ev_run (my_loop, 0);
		864	... jobs done or somebody called unloop. yeah!
		865
308	=item ev_unloop (loop, how)	866	=item ev_break (loop, how)
309		867
310	Can be used to make a call to C<ev_loop> return early (but only after it	868	Can be used to make a call to C<ev_run> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	869	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	870	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	871	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		872
		873	This "break state" will be cleared on the next call to C<ev_run>.
		874
		875	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		876	which case it will have no effect.
314		877
315	=item ev_ref (loop)	878	=item ev_ref (loop)
316		879
317	=item ev_unref (loop)	880	=item ev_unref (loop)
318		881
319	Ref/unref can be used to add or remove a reference count on the event	882	Ref/unref can be used to add or remove a reference count on the event
320	loop: Every watcher keeps one reference, and as long as the reference	883	loop: Every watcher keeps one reference, and as long as the reference
321	count is nonzero, C<ev_loop> will not return on its own. If you have	884	count is nonzero, C<ev_run> will not return on its own.
322	a watcher you never unregister that should not keep C<ev_loop> from	885
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	886	This is useful when you have a watcher that you never intend to
		887	unregister, but that nevertheless should not keep C<ev_run> from
		888	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		889	before stopping it.
		890
324	example, libev itself uses this for its internal signal pipe: It is not	891	As an example, libev itself uses this for its internal signal pipe: It
325	visible to the libev user and should not keep C<ev_loop> from exiting if	892	is not visible to the libev user and should not keep C<ev_run> from
326	no event watchers registered by it are active. It is also an excellent	893	exiting if no event watchers registered by it are active. It is also an
327	way to do this for generic recurring timers or from within third-party	894	excellent way to do this for generic recurring timers or from within
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	895	third-party libraries. Just remember to I<unref after start> and I<ref
		896	before stop> (but only if the watcher wasn't active before, or was active
		897	before, respectively. Note also that libev might stop watchers itself
		898	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		899	in the callback).
		900
		901	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		902	running when nothing else is active.
		903
		904	ev_signal exitsig;
		905	ev_signal_init (&exitsig, sig_cb, SIGINT);
		906	ev_signal_start (loop, &exitsig);
		907	ev_unref (loop);
		908
		909	Example: For some weird reason, unregister the above signal handler again.
		910
		911	ev_ref (loop);
		912	ev_signal_stop (loop, &exitsig);
		913
		914	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		915
		916	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		917
		918	These advanced functions influence the time that libev will spend waiting
		919	for events. Both time intervals are by default C<0>, meaning that libev
		920	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		921	latency.
		922
		923	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		924	allows libev to delay invocation of I/O and timer/periodic callbacks
		925	to increase efficiency of loop iterations (or to increase power-saving
		926	opportunities).
		927
		928	The idea is that sometimes your program runs just fast enough to handle
		929	one (or very few) event(s) per loop iteration. While this makes the
		930	program responsive, it also wastes a lot of CPU time to poll for new
		931	events, especially with backends like C<select ()> which have a high
		932	overhead for the actual polling but can deliver many events at once.
		933
		934	By setting a higher I<io collect interval> you allow libev to spend more
		935	time collecting I/O events, so you can handle more events per iteration,
		936	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		937	C<ev_timer>) will be not affected. Setting this to a non-null value will
		938	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		939	sleep time ensures that libev will not poll for I/O events more often then
		940	once per this interval, on average.
		941
		942	Likewise, by setting a higher I<timeout collect interval> you allow libev
		943	to spend more time collecting timeouts, at the expense of increased
		944	latency/jitter/inexactness (the watcher callback will be called
		945	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		946	value will not introduce any overhead in libev.
		947
		948	Many (busy) programs can usually benefit by setting the I/O collect
		949	interval to a value near C<0.1> or so, which is often enough for
		950	interactive servers (of course not for games), likewise for timeouts. It
		951	usually doesn't make much sense to set it to a lower value than C<0.01>,
		952	as this approaches the timing granularity of most systems. Note that if
		953	you do transactions with the outside world and you can't increase the
		954	parallelity, then this setting will limit your transaction rate (if you
		955	need to poll once per transaction and the I/O collect interval is 0.01,
		956	then you can't do more than 100 transactions per second).
		957
		958	Setting the I<timeout collect interval> can improve the opportunity for
		959	saving power, as the program will "bundle" timer callback invocations that
		960	are "near" in time together, by delaying some, thus reducing the number of
		961	times the process sleeps and wakes up again. Another useful technique to
		962	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		963	they fire on, say, one-second boundaries only.
		964
		965	Example: we only need 0.1s timeout granularity, and we wish not to poll
		966	more often than 100 times per second:
		967
		968	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		969	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		970
		971	=item ev_invoke_pending (loop)
		972
		973	This call will simply invoke all pending watchers while resetting their
		974	pending state. Normally, C<ev_run> does this automatically when required,
		975	but when overriding the invoke callback this call comes handy. This
		976	function can be invoked from a watcher - this can be useful for example
		977	when you want to do some lengthy calculation and want to pass further
		978	event handling to another thread (you still have to make sure only one
		979	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		980
		981	=item int ev_pending_count (loop)
		982
		983	Returns the number of pending watchers - zero indicates that no watchers
		984	are pending.
		985
		986	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		987
		988	This overrides the invoke pending functionality of the loop: Instead of
		989	invoking all pending watchers when there are any, C<ev_run> will call
		990	this callback instead. This is useful, for example, when you want to
		991	invoke the actual watchers inside another context (another thread etc.).
		992
		993	If you want to reset the callback, use C<ev_invoke_pending> as new
		994	callback.
		995
		996	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		997
		998	Sometimes you want to share the same loop between multiple threads. This
		999	can be done relatively simply by putting mutex_lock/unlock calls around
		1000	each call to a libev function.
		1001
		1002	However, C<ev_run> can run an indefinite time, so it is not feasible
		1003	to wait for it to return. One way around this is to wake up the event
		1004	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1005	I<release> and I<acquire> callbacks on the loop.
		1006
		1007	When set, then C<release> will be called just before the thread is
		1008	suspended waiting for new events, and C<acquire> is called just
		1009	afterwards.
		1010
		1011	Ideally, C<release> will just call your mutex_unlock function, and
		1012	C<acquire> will just call the mutex_lock function again.
		1013
		1014	While event loop modifications are allowed between invocations of
		1015	C<release> and C<acquire> (that's their only purpose after all), no
		1016	modifications done will affect the event loop, i.e. adding watchers will
		1017	have no effect on the set of file descriptors being watched, or the time
		1018	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1019	to take note of any changes you made.
		1020
		1021	In theory, threads executing C<ev_run> will be async-cancel safe between
		1022	invocations of C<release> and C<acquire>.
		1023
		1024	See also the locking example in the C<THREADS> section later in this
		1025	document.
		1026
		1027	=item ev_set_userdata (loop, void *data)
		1028
		1029	=item void *ev_userdata (loop)
		1030
		1031	Set and retrieve a single C<void *> associated with a loop. When
		1032	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1033	C<0>.
		1034
		1035	These two functions can be used to associate arbitrary data with a loop,
		1036	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1037	C<acquire> callbacks described above, but of course can be (ab-)used for
		1038	any other purpose as well.
		1039
		1040	=item ev_verify (loop)
		1041
		1042	This function only does something when C<EV_VERIFY> support has been
		1043	compiled in, which is the default for non-minimal builds. It tries to go
		1044	through all internal structures and checks them for validity. If anything
		1045	is found to be inconsistent, it will print an error message to standard
		1046	error and call C<abort ()>.
		1047
		1048	This can be used to catch bugs inside libev itself: under normal
		1049	circumstances, this function will never abort as of course libev keeps its
		1050	data structures consistent.
329		1051
330	=back	1052	=back
331		1053
		1054
332	=head1 ANATOMY OF A WATCHER	1055	=head1 ANATOMY OF A WATCHER
333		1056
		1057	In the following description, uppercase C<TYPE> in names stands for the
		1058	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1059	watchers and C<ev_io_start> for I/O watchers.
		1060
334	A watcher is a structure that you create and register to record your	1061	A watcher is an opaque structure that you allocate and register to record
335	interest in some event. For instance, if you want to wait for STDIN to	1062	your interest in some event. To make a concrete example, imagine you want
336	become readable, you would create an C<ev_io> watcher for that:	1063	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1064	for that:
337		1065
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1066	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
339	{	1067	{
340	ev_io_stop (w);	1068	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	1069	ev_break (loop, EVBREAK_ALL);
342	}	1070	}
343		1071
344	struct ev_loop *loop = ev_default_loop (0);	1072	struct ev_loop *loop = ev_default_loop (0);
		1073
345	struct ev_io stdin_watcher;	1074	ev_io stdin_watcher;
		1075
346	ev_init (&stdin_watcher, my_cb);	1076	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1077	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	1078	ev_io_start (loop, &stdin_watcher);
		1079
349	ev_loop (loop, 0);	1080	ev_run (loop, 0);
350		1081
351	As you can see, you are responsible for allocating the memory for your	1082	As you can see, you are responsible for allocating the memory for your
352	watcher structures (and it is usually a bad idea to do this on the stack,	1083	watcher structures (and it is I<usually> a bad idea to do this on the
353	although this can sometimes be quite valid).	1084	stack).
354		1085
		1086	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1087	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1088
355	Each watcher structure must be initialised by a call to C<ev_init	1089	Each watcher structure must be initialised by a call to C<ev_init (watcher
356	(watcher *, callback)>, which expects a callback to be provided. This	1090	*, callback)>, which expects a callback to be provided. This callback is
357	callback gets invoked each time the event occurs (or, in the case of io	1091	invoked each time the event occurs (or, in the case of I/O watchers, each
358	watchers, each time the event loop detects that the file descriptor given	1092	time the event loop detects that the file descriptor given is readable
359	is readable and/or writable).	1093	and/or writable).
360		1094
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1095	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
362	with arguments specific to this watcher type. There is also a macro	1096	macro to configure it, with arguments specific to the watcher type. There
363	to combine initialisation and setting in one call: C<< ev_<type>_init	1097	is also a macro to combine initialisation and setting in one call: C<<
364	(watcher *, callback, ...) >>.	1098	ev_TYPE_init (watcher *, callback, ...) >>.
365		1099
366	To make the watcher actually watch out for events, you have to start it	1100	To make the watcher actually watch out for events, you have to start it
367	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1101	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
368	*) >>), and you can stop watching for events at any time by calling the	1102	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1103	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
370		1104
371	As long as your watcher is active (has been started but not stopped) you	1105	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	1106	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	1107	reinitialise it or call its C<ev_TYPE_set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		1108
380	Each and every callback receives the event loop pointer as first, the	1109	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	1110	registered watcher structure as second, and a bitset of received events as
382	third argument.	1111	third argument.
383		1112
…		…
392	=item C<EV_WRITE>	1121	=item C<EV_WRITE>
393		1122
394	The file descriptor in the C<ev_io> watcher has become readable and/or	1123	The file descriptor in the C<ev_io> watcher has become readable and/or
395	writable.	1124	writable.
396		1125
397	=item C<EV_TIMEOUT>	1126	=item C<EV_TIMER>
398		1127
399	The C<ev_timer> watcher has timed out.	1128	The C<ev_timer> watcher has timed out.
400		1129
401	=item C<EV_PERIODIC>	1130	=item C<EV_PERIODIC>
402		1131
…		…
408		1137
409	=item C<EV_CHILD>	1138	=item C<EV_CHILD>
410		1139
411	The pid specified in the C<ev_child> watcher has received a status change.	1140	The pid specified in the C<ev_child> watcher has received a status change.
412		1141
		1142	=item C<EV_STAT>
		1143
		1144	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1145
413	=item C<EV_IDLE>	1146	=item C<EV_IDLE>
414		1147
415	The C<ev_idle> watcher has determined that you have nothing better to do.	1148	The C<ev_idle> watcher has determined that you have nothing better to do.
416		1149
417	=item C<EV_PREPARE>	1150	=item C<EV_PREPARE>
418		1151
419	=item C<EV_CHECK>	1152	=item C<EV_CHECK>
420		1153
421	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1154	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
422	to gather new events, and all C<ev_check> watchers are invoked just after	1155	to gather new events, and all C<ev_check> watchers are invoked just after
423	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1156	C<ev_run> has gathered them, but before it invokes any callbacks for any
424	received events. Callbacks of both watcher types can start and stop as	1157	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	1158	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1159	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	1160	C<ev_run> from blocking).
		1161
		1162	=item C<EV_EMBED>
		1163
		1164	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1165
		1166	=item C<EV_FORK>
		1167
		1168	The event loop has been resumed in the child process after fork (see
		1169	C<ev_fork>).
		1170
		1171	=item C<EV_CLEANUP>
		1172
		1173	The event loop is about to be destroyed (see C<ev_cleanup>).
		1174
		1175	=item C<EV_ASYNC>
		1176
		1177	The given async watcher has been asynchronously notified (see C<ev_async>).
		1178
		1179	=item C<EV_CUSTOM>
		1180
		1181	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1182	by libev users to signal watchers (e.g. via C<ev_feed_event>).
428		1183
429	=item C<EV_ERROR>	1184	=item C<EV_ERROR>
430		1185
431	An unspecified error has occured, the watcher has been stopped. This might	1186	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	1187	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	1188	ran out of memory, a file descriptor was found to be closed or any other
		1189	problem. Libev considers these application bugs.
		1190
434	problem. You best act on it by reporting the problem and somehow coping	1191	You best act on it by reporting the problem and somehow coping with the
435	with the watcher being stopped.	1192	watcher being stopped. Note that well-written programs should not receive
		1193	an error ever, so when your watcher receives it, this usually indicates a
		1194	bug in your program.
436		1195
437	Libev will usually signal a few "dummy" events together with an error,	1196	Libev will usually signal a few "dummy" events together with an error, for
438	for example it might indicate that a fd is readable or writable, and if	1197	example it might indicate that a fd is readable or writable, and if your
439	your callbacks is well-written it can just attempt the operation and cope	1198	callbacks is well-written it can just attempt the operation and cope with
440	with the error from read() or write(). This will not work in multithreaded	1199	the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	1200	programs, though, as the fd could already be closed and reused for another
		1201	thing, so beware.
442		1202
443	=back	1203	=back
444		1204
		1205	=head2 GENERIC WATCHER FUNCTIONS
		1206
		1207	=over 4
		1208
		1209	=item C<ev_init> (ev_TYPE *watcher, callback)
		1210
		1211	This macro initialises the generic portion of a watcher. The contents
		1212	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1213	the generic parts of the watcher are initialised, you I<need> to call
		1214	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1215	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1216	which rolls both calls into one.
		1217
		1218	You can reinitialise a watcher at any time as long as it has been stopped
		1219	(or never started) and there are no pending events outstanding.
		1220
		1221	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1222	int revents)>.
		1223
		1224	Example: Initialise an C<ev_io> watcher in two steps.
		1225
		1226	ev_io w;
		1227	ev_init (&w, my_cb);
		1228	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1229
		1230	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1231
		1232	This macro initialises the type-specific parts of a watcher. You need to
		1233	call C<ev_init> at least once before you call this macro, but you can
		1234	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1235	macro on a watcher that is active (it can be pending, however, which is a
		1236	difference to the C<ev_init> macro).
		1237
		1238	Although some watcher types do not have type-specific arguments
		1239	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1240
		1241	See C<ev_init>, above, for an example.
		1242
		1243	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1244
		1245	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1246	calls into a single call. This is the most convenient method to initialise
		1247	a watcher. The same limitations apply, of course.
		1248
		1249	Example: Initialise and set an C<ev_io> watcher in one step.
		1250
		1251	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1252
		1253	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1254
		1255	Starts (activates) the given watcher. Only active watchers will receive
		1256	events. If the watcher is already active nothing will happen.
		1257
		1258	Example: Start the C<ev_io> watcher that is being abused as example in this
		1259	whole section.
		1260
		1261	ev_io_start (EV_DEFAULT_UC, &w);
		1262
		1263	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1264
		1265	Stops the given watcher if active, and clears the pending status (whether
		1266	the watcher was active or not).
		1267
		1268	It is possible that stopped watchers are pending - for example,
		1269	non-repeating timers are being stopped when they become pending - but
		1270	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1271	pending. If you want to free or reuse the memory used by the watcher it is
		1272	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1273
		1274	=item bool ev_is_active (ev_TYPE *watcher)
		1275
		1276	Returns a true value iff the watcher is active (i.e. it has been started
		1277	and not yet been stopped). As long as a watcher is active you must not modify
		1278	it.
		1279
		1280	=item bool ev_is_pending (ev_TYPE *watcher)
		1281
		1282	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1283	events but its callback has not yet been invoked). As long as a watcher
		1284	is pending (but not active) you must not call an init function on it (but
		1285	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1286	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1287	it).
		1288
		1289	=item callback ev_cb (ev_TYPE *watcher)
		1290
		1291	Returns the callback currently set on the watcher.
		1292
		1293	=item ev_cb_set (ev_TYPE *watcher, callback)
		1294
		1295	Change the callback. You can change the callback at virtually any time
		1296	(modulo threads).
		1297
		1298	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1299
		1300	=item int ev_priority (ev_TYPE *watcher)
		1301
		1302	Set and query the priority of the watcher. The priority is a small
		1303	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1304	(default: C<-2>). Pending watchers with higher priority will be invoked
		1305	before watchers with lower priority, but priority will not keep watchers
		1306	from being executed (except for C<ev_idle> watchers).
		1307
		1308	If you need to suppress invocation when higher priority events are pending
		1309	you need to look at C<ev_idle> watchers, which provide this functionality.
		1310
		1311	You I<must not> change the priority of a watcher as long as it is active or
		1312	pending.
		1313
		1314	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1315	fine, as long as you do not mind that the priority value you query might
		1316	or might not have been clamped to the valid range.
		1317
		1318	The default priority used by watchers when no priority has been set is
		1319	always C<0>, which is supposed to not be too high and not be too low :).
		1320
		1321	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1322	priorities.
		1323
		1324	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1325
		1326	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1327	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1328	can deal with that fact, as both are simply passed through to the
		1329	callback.
		1330
		1331	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1332
		1333	If the watcher is pending, this function clears its pending status and
		1334	returns its C<revents> bitset (as if its callback was invoked). If the
		1335	watcher isn't pending it does nothing and returns C<0>.
		1336
		1337	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1338	callback to be invoked, which can be accomplished with this function.
		1339
		1340	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1341
		1342	Feeds the given event set into the event loop, as if the specified event
		1343	had happened for the specified watcher (which must be a pointer to an
		1344	initialised but not necessarily started event watcher). Obviously you must
		1345	not free the watcher as long as it has pending events.
		1346
		1347	Stopping the watcher, letting libev invoke it, or calling
		1348	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1349	not started in the first place.
		1350
		1351	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1352	functions that do not need a watcher.
		1353
		1354	=back
		1355
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1356	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		1357
447	Each watcher has, by default, a member C<void *data> that you can change	1358	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	1359	and read at any time: libev will completely ignore it. This can be used
449	to associate arbitrary data with your watcher. If you need more data and	1360	to associate arbitrary data with your watcher. If you need more data and
450	don't want to allocate memory and store a pointer to it in that data	1361	don't want to allocate memory and store a pointer to it in that data
451	member, you can also "subclass" the watcher type and provide your own	1362	member, you can also "subclass" the watcher type and provide your own
452	data:	1363	data:
453		1364
454	struct my_io	1365	struct my_io
455	{	1366	{
456	struct ev_io io;	1367	ev_io io;
457	int otherfd;	1368	int otherfd;
458	void *somedata;	1369	void *somedata;
459	struct whatever *mostinteresting;	1370	struct whatever *mostinteresting;
460	}	1371	};
		1372
		1373	...
		1374	struct my_io w;
		1375	ev_io_init (&w.io, my_cb, fd, EV_READ);
461		1376
462	And since your callback will be called with a pointer to the watcher, you	1377	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1378	can cast it back to your own type:
464		1379
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1380	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
466	{	1381	{
467	struct my_io *w = (struct my_io *)w_;	1382	struct my_io *w = (struct my_io *)w_;
468	...	1383	...
469	}	1384	}
470		1385
471	More interesting and less C-conformant ways of catsing your callback type	1386	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1387	instead have been omitted.
		1388
		1389	Another common scenario is to use some data structure with multiple
		1390	embedded watchers:
		1391
		1392	struct my_biggy
		1393	{
		1394	int some_data;
		1395	ev_timer t1;
		1396	ev_timer t2;
		1397	}
		1398
		1399	In this case getting the pointer to C<my_biggy> is a bit more
		1400	complicated: Either you store the address of your C<my_biggy> struct
		1401	in the C<data> member of the watcher (for woozies), or you need to use
		1402	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1403	programmers):
		1404
		1405	#include <stddef.h>
		1406
		1407	static void
		1408	t1_cb (EV_P_ ev_timer *w, int revents)
		1409	{
		1410	struct my_biggy big = (struct my_biggy *)
		1411	(((char *)w) - offsetof (struct my_biggy, t1));
		1412	}
		1413
		1414	static void
		1415	t2_cb (EV_P_ ev_timer *w, int revents)
		1416	{
		1417	struct my_biggy big = (struct my_biggy *)
		1418	(((char *)w) - offsetof (struct my_biggy, t2));
		1419	}
		1420
		1421	=head2 WATCHER STATES
		1422
		1423	There are various watcher states mentioned throughout this manual -
		1424	active, pending and so on. In this section these states and the rules to
		1425	transition between them will be described in more detail - and while these
		1426	rules might look complicated, they usually do "the right thing".
		1427
		1428	=over 4
		1429
		1430	=item initialiased
		1431
		1432	Before a watcher can be registered with the event looop it has to be
		1433	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1434	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1435
		1436	In this state it is simply some block of memory that is suitable for use
		1437	in an event loop. It can be moved around, freed, reused etc. at will.
		1438
		1439	=item started/running/active
		1440
		1441	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1442	property of the event loop, and is actively waiting for events. While in
		1443	this state it cannot be accessed (except in a few documented ways), moved,
		1444	freed or anything else - the only legal thing is to keep a pointer to it,
		1445	and call libev functions on it that are documented to work on active watchers.
		1446
		1447	=item pending
		1448
		1449	If a watcher is active and libev determines that an event it is interested
		1450	in has occurred (such as a timer expiring), it will become pending. It will
		1451	stay in this pending state until either it is stopped or its callback is
		1452	about to be invoked, so it is not normally pending inside the watcher
		1453	callback.
		1454
		1455	The watcher might or might not be active while it is pending (for example,
		1456	an expired non-repeating timer can be pending but no longer active). If it
		1457	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1458	but it is still property of the event loop at this time, so cannot be
		1459	moved, freed or reused. And if it is active the rules described in the
		1460	previous item still apply.
		1461
		1462	It is also possible to feed an event on a watcher that is not active (e.g.
		1463	via C<ev_feed_event>), in which case it becomes pending without being
		1464	active.
		1465
		1466	=item stopped
		1467
		1468	A watcher can be stopped implicitly by libev (in which case it might still
		1469	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1470	latter will clear any pending state the watcher might be in, regardless
		1471	of whether it was active or not, so stopping a watcher explicitly before
		1472	freeing it is often a good idea.
		1473
		1474	While stopped (and not pending) the watcher is essentially in the
		1475	initialised state, that is it can be reused, moved, modified in any way
		1476	you wish.
		1477
		1478	=back
		1479
		1480	=head2 WATCHER PRIORITY MODELS
		1481
		1482	Many event loops support I<watcher priorities>, which are usually small
		1483	integers that influence the ordering of event callback invocation
		1484	between watchers in some way, all else being equal.
		1485
		1486	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1487	description for the more technical details such as the actual priority
		1488	range.
		1489
		1490	There are two common ways how these these priorities are being interpreted
		1491	by event loops:
		1492
		1493	In the more common lock-out model, higher priorities "lock out" invocation
		1494	of lower priority watchers, which means as long as higher priority
		1495	watchers receive events, lower priority watchers are not being invoked.
		1496
		1497	The less common only-for-ordering model uses priorities solely to order
		1498	callback invocation within a single event loop iteration: Higher priority
		1499	watchers are invoked before lower priority ones, but they all get invoked
		1500	before polling for new events.
		1501
		1502	Libev uses the second (only-for-ordering) model for all its watchers
		1503	except for idle watchers (which use the lock-out model).
		1504
		1505	The rationale behind this is that implementing the lock-out model for
		1506	watchers is not well supported by most kernel interfaces, and most event
		1507	libraries will just poll for the same events again and again as long as
		1508	their callbacks have not been executed, which is very inefficient in the
		1509	common case of one high-priority watcher locking out a mass of lower
		1510	priority ones.
		1511
		1512	Static (ordering) priorities are most useful when you have two or more
		1513	watchers handling the same resource: a typical usage example is having an
		1514	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1515	timeouts. Under load, data might be received while the program handles
		1516	other jobs, but since timers normally get invoked first, the timeout
		1517	handler will be executed before checking for data. In that case, giving
		1518	the timer a lower priority than the I/O watcher ensures that I/O will be
		1519	handled first even under adverse conditions (which is usually, but not
		1520	always, what you want).
		1521
		1522	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1523	will only be executed when no same or higher priority watchers have
		1524	received events, they can be used to implement the "lock-out" model when
		1525	required.
		1526
		1527	For example, to emulate how many other event libraries handle priorities,
		1528	you can associate an C<ev_idle> watcher to each such watcher, and in
		1529	the normal watcher callback, you just start the idle watcher. The real
		1530	processing is done in the idle watcher callback. This causes libev to
		1531	continuously poll and process kernel event data for the watcher, but when
		1532	the lock-out case is known to be rare (which in turn is rare :), this is
		1533	workable.
		1534
		1535	Usually, however, the lock-out model implemented that way will perform
		1536	miserably under the type of load it was designed to handle. In that case,
		1537	it might be preferable to stop the real watcher before starting the
		1538	idle watcher, so the kernel will not have to process the event in case
		1539	the actual processing will be delayed for considerable time.
		1540
		1541	Here is an example of an I/O watcher that should run at a strictly lower
		1542	priority than the default, and which should only process data when no
		1543	other events are pending:
		1544
		1545	ev_idle idle; // actual processing watcher
		1546	ev_io io; // actual event watcher
		1547
		1548	static void
		1549	io_cb (EV_P_ ev_io *w, int revents)
		1550	{
		1551	// stop the I/O watcher, we received the event, but
		1552	// are not yet ready to handle it.
		1553	ev_io_stop (EV_A_ w);
		1554
		1555	// start the idle watcher to handle the actual event.
		1556	// it will not be executed as long as other watchers
		1557	// with the default priority are receiving events.
		1558	ev_idle_start (EV_A_ &idle);
		1559	}
		1560
		1561	static void
		1562	idle_cb (EV_P_ ev_idle *w, int revents)
		1563	{
		1564	// actual processing
		1565	read (STDIN_FILENO, ...);
		1566
		1567	// have to start the I/O watcher again, as
		1568	// we have handled the event
		1569	ev_io_start (EV_P_ &io);
		1570	}
		1571
		1572	// initialisation
		1573	ev_idle_init (&idle, idle_cb);
		1574	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1575	ev_io_start (EV_DEFAULT_ &io);
		1576
		1577	In the "real" world, it might also be beneficial to start a timer, so that
		1578	low-priority connections can not be locked out forever under load. This
		1579	enables your program to keep a lower latency for important connections
		1580	during short periods of high load, while not completely locking out less
		1581	important ones.
473		1582
474		1583
475	=head1 WATCHER TYPES	1584	=head1 WATCHER TYPES
476		1585
477	This section describes each watcher in detail, but will not repeat	1586	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1587	information given in the last section. Any initialisation/set macros,
		1588	functions and members specific to the watcher type are explained.
479		1589
		1590	Members are additionally marked with either I<[read-only]>, meaning that,
		1591	while the watcher is active, you can look at the member and expect some
		1592	sensible content, but you must not modify it (you can modify it while the
		1593	watcher is stopped to your hearts content), or I<[read-write]>, which
		1594	means you can expect it to have some sensible content while the watcher
		1595	is active, but you can also modify it. Modifying it may not do something
		1596	sensible or take immediate effect (or do anything at all), but libev will
		1597	not crash or malfunction in any way.
		1598
		1599
480	=head2 C<ev_io> - is this file descriptor readable or writable	1600	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1601
482	I/O watchers check whether a file descriptor is readable or writable	1602	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1603	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1604	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1605	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1606	receiving events as long as the condition persists. Remember you can stop
		1607	the watcher if you don't want to act on the event and neither want to
		1608	receive future events.
487		1609
488	In general you can register as many read and/or write event watchers per	1610	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1611	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1612	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1613	required if you know what you are doing).
492		1614
493	You have to be careful with dup'ed file descriptors, though. Some backends	1615	If you cannot use non-blocking mode, then force the use of a
494	(the linux epoll backend is a notable example) cannot handle dup'ed file	1616	known-to-be-good backend (at the time of this writing, this includes only
495	descriptors correctly if you register interest in two or more fds pointing	1617	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
496	to the same underlying file/socket etc. description (that is, they share	1618	descriptors for which non-blocking operation makes no sense (such as
497	the same underlying "file open").	1619	files) - libev doesn't guarantee any specific behaviour in that case.
498		1620
499	If you must do this, then force the use of a known-to-be-good backend	1621	Another thing you have to watch out for is that it is quite easy to
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1622	receive "spurious" readiness notifications, that is your callback might
501	EVMETHOD_POLL).	1623	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1624	because there is no data. Not only are some backends known to create a
		1625	lot of those (for example Solaris ports), it is very easy to get into
		1626	this situation even with a relatively standard program structure. Thus
		1627	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1628	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1629
		1630	If you cannot run the fd in non-blocking mode (for example you should
		1631	not play around with an Xlib connection), then you have to separately
		1632	re-test whether a file descriptor is really ready with a known-to-be good
		1633	interface such as poll (fortunately in our Xlib example, Xlib already
		1634	does this on its own, so its quite safe to use). Some people additionally
		1635	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1636	indefinitely.
		1637
		1638	But really, best use non-blocking mode.
		1639
		1640	=head3 The special problem of disappearing file descriptors
		1641
		1642	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1643	descriptor (either due to calling C<close> explicitly or any other means,
		1644	such as C<dup2>). The reason is that you register interest in some file
		1645	descriptor, but when it goes away, the operating system will silently drop
		1646	this interest. If another file descriptor with the same number then is
		1647	registered with libev, there is no efficient way to see that this is, in
		1648	fact, a different file descriptor.
		1649
		1650	To avoid having to explicitly tell libev about such cases, libev follows
		1651	the following policy: Each time C<ev_io_set> is being called, libev
		1652	will assume that this is potentially a new file descriptor, otherwise
		1653	it is assumed that the file descriptor stays the same. That means that
		1654	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1655	descriptor even if the file descriptor number itself did not change.
		1656
		1657	This is how one would do it normally anyway, the important point is that
		1658	the libev application should not optimise around libev but should leave
		1659	optimisations to libev.
		1660
		1661	=head3 The special problem of dup'ed file descriptors
		1662
		1663	Some backends (e.g. epoll), cannot register events for file descriptors,
		1664	but only events for the underlying file descriptions. That means when you
		1665	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1666	events for them, only one file descriptor might actually receive events.
		1667
		1668	There is no workaround possible except not registering events
		1669	for potentially C<dup ()>'ed file descriptors, or to resort to
		1670	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1671
		1672	=head3 The special problem of fork
		1673
		1674	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1675	useless behaviour. Libev fully supports fork, but needs to be told about
		1676	it in the child.
		1677
		1678	To support fork in your programs, you either have to call
		1679	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1680	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1681	C<EVBACKEND_POLL>.
		1682
		1683	=head3 The special problem of SIGPIPE
		1684
		1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1686	when writing to a pipe whose other end has been closed, your program gets
		1687	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1688	this is sensible behaviour, for daemons, this is usually undesirable.
		1689
		1690	So when you encounter spurious, unexplained daemon exits, make sure you
		1691	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1692	somewhere, as that would have given you a big clue).
		1693
		1694	=head3 The special problem of accept()ing when you can't
		1695
		1696	Many implementations of the POSIX C<accept> function (for example,
		1697	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1698	connection from the pending queue in all error cases.
		1699
		1700	For example, larger servers often run out of file descriptors (because
		1701	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1702	rejecting the connection, leading to libev signalling readiness on
		1703	the next iteration again (the connection still exists after all), and
		1704	typically causing the program to loop at 100% CPU usage.
		1705
		1706	Unfortunately, the set of errors that cause this issue differs between
		1707	operating systems, there is usually little the app can do to remedy the
		1708	situation, and no known thread-safe method of removing the connection to
		1709	cope with overload is known (to me).
		1710
		1711	One of the easiest ways to handle this situation is to just ignore it
		1712	- when the program encounters an overload, it will just loop until the
		1713	situation is over. While this is a form of busy waiting, no OS offers an
		1714	event-based way to handle this situation, so it's the best one can do.
		1715
		1716	A better way to handle the situation is to log any errors other than
		1717	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1718	messages, and continue as usual, which at least gives the user an idea of
		1719	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1720	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1721	usage.
		1722
		1723	If your program is single-threaded, then you could also keep a dummy file
		1724	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1725	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1726	close that fd, and create a new dummy fd. This will gracefully refuse
		1727	clients under typical overload conditions.
		1728
		1729	The last way to handle it is to simply log the error and C<exit>, as
		1730	is often done with C<malloc> failures, but this results in an easy
		1731	opportunity for a DoS attack.
		1732
		1733	=head3 Watcher-Specific Functions
502		1734
503	=over 4	1735	=over 4
504		1736
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1737	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1738
507	=item ev_io_set (ev_io *, int fd, int events)	1739	=item ev_io_set (ev_io *, int fd, int events)
508		1740
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1741	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1742	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1743	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1744
		1745	=item int fd [read-only]
		1746
		1747	The file descriptor being watched.
		1748
		1749	=item int events [read-only]
		1750
		1751	The events being watched.
512		1752
513	=back	1753	=back
514		1754
		1755	=head3 Examples
		1756
		1757	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1758	readable, but only once. Since it is likely line-buffered, you could
		1759	attempt to read a whole line in the callback.
		1760
		1761	static void
		1762	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1763	{
		1764	ev_io_stop (loop, w);
		1765	.. read from stdin here (or from w->fd) and handle any I/O errors
		1766	}
		1767
		1768	...
		1769	struct ev_loop *loop = ev_default_init (0);
		1770	ev_io stdin_readable;
		1771	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1772	ev_io_start (loop, &stdin_readable);
		1773	ev_run (loop, 0);
		1774
		1775
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1776	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1777
517	Timer watchers are simple relative timers that generate an event after a	1778	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1779	given time, and optionally repeating in regular intervals after that.
519		1780
520	The timers are based on real time, that is, if you register an event that	1781	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1782	times out after an hour and you reset your system clock to January last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1783	year, it will still time out after (roughly) one hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1784	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1785	monotonic clock option helps a lot here).
		1786
		1787	The callback is guaranteed to be invoked only I<after> its timeout has
		1788	passed (not I<at>, so on systems with very low-resolution clocks this
		1789	might introduce a small delay). If multiple timers become ready during the
		1790	same loop iteration then the ones with earlier time-out values are invoked
		1791	before ones of the same priority with later time-out values (but this is
		1792	no longer true when a callback calls C<ev_run> recursively).
		1793
		1794	=head3 Be smart about timeouts
		1795
		1796	Many real-world problems involve some kind of timeout, usually for error
		1797	recovery. A typical example is an HTTP request - if the other side hangs,
		1798	you want to raise some error after a while.
		1799
		1800	What follows are some ways to handle this problem, from obvious and
		1801	inefficient to smart and efficient.
		1802
		1803	In the following, a 60 second activity timeout is assumed - a timeout that
		1804	gets reset to 60 seconds each time there is activity (e.g. each time some
		1805	data or other life sign was received).
		1806
		1807	=over 4
		1808
		1809	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1810
		1811	This is the most obvious, but not the most simple way: In the beginning,
		1812	start the watcher:
		1813
		1814	ev_timer_init (timer, callback, 60., 0.);
		1815	ev_timer_start (loop, timer);
		1816
		1817	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1818	and start it again:
		1819
		1820	ev_timer_stop (loop, timer);
		1821	ev_timer_set (timer, 60., 0.);
		1822	ev_timer_start (loop, timer);
		1823
		1824	This is relatively simple to implement, but means that each time there is
		1825	some activity, libev will first have to remove the timer from its internal
		1826	data structure and then add it again. Libev tries to be fast, but it's
		1827	still not a constant-time operation.
		1828
		1829	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1830
		1831	This is the easiest way, and involves using C<ev_timer_again> instead of
		1832	C<ev_timer_start>.
		1833
		1834	To implement this, configure an C<ev_timer> with a C<repeat> value
		1835	of C<60> and then call C<ev_timer_again> at start and each time you
		1836	successfully read or write some data. If you go into an idle state where
		1837	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1838	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1839
		1840	That means you can ignore both the C<ev_timer_start> function and the
		1841	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1842	member and C<ev_timer_again>.
		1843
		1844	At start:
		1845
		1846	ev_init (timer, callback);
		1847	timer->repeat = 60.;
		1848	ev_timer_again (loop, timer);
		1849
		1850	Each time there is some activity:
		1851
		1852	ev_timer_again (loop, timer);
		1853
		1854	It is even possible to change the time-out on the fly, regardless of
		1855	whether the watcher is active or not:
		1856
		1857	timer->repeat = 30.;
		1858	ev_timer_again (loop, timer);
		1859
		1860	This is slightly more efficient then stopping/starting the timer each time
		1861	you want to modify its timeout value, as libev does not have to completely
		1862	remove and re-insert the timer from/into its internal data structure.
		1863
		1864	It is, however, even simpler than the "obvious" way to do it.
		1865
		1866	=item 3. Let the timer time out, but then re-arm it as required.
		1867
		1868	This method is more tricky, but usually most efficient: Most timeouts are
		1869	relatively long compared to the intervals between other activity - in
		1870	our example, within 60 seconds, there are usually many I/O events with
		1871	associated activity resets.
		1872
		1873	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1874	but remember the time of last activity, and check for a real timeout only
		1875	within the callback:
		1876
		1877	ev_tstamp last_activity; // time of last activity
		1878
		1879	static void
		1880	callback (EV_P_ ev_timer *w, int revents)
		1881	{
		1882	ev_tstamp now = ev_now (EV_A);
		1883	ev_tstamp timeout = last_activity + 60.;
		1884
		1885	// if last_activity + 60. is older than now, we did time out
		1886	if (timeout < now)
		1887	{
		1888	// timeout occurred, take action
		1889	}
		1890	else
		1891	{
		1892	// callback was invoked, but there was some activity, re-arm
		1893	// the watcher to fire in last_activity + 60, which is
		1894	// guaranteed to be in the future, so "again" is positive:
		1895	w->repeat = timeout - now;
		1896	ev_timer_again (EV_A_ w);
		1897	}
		1898	}
		1899
		1900	To summarise the callback: first calculate the real timeout (defined
		1901	as "60 seconds after the last activity"), then check if that time has
		1902	been reached, which means something I<did>, in fact, time out. Otherwise
		1903	the callback was invoked too early (C<timeout> is in the future), so
		1904	re-schedule the timer to fire at that future time, to see if maybe we have
		1905	a timeout then.
		1906
		1907	Note how C<ev_timer_again> is used, taking advantage of the
		1908	C<ev_timer_again> optimisation when the timer is already running.
		1909
		1910	This scheme causes more callback invocations (about one every 60 seconds
		1911	minus half the average time between activity), but virtually no calls to
		1912	libev to change the timeout.
		1913
		1914	To start the timer, simply initialise the watcher and set C<last_activity>
		1915	to the current time (meaning we just have some activity :), then call the
		1916	callback, which will "do the right thing" and start the timer:
		1917
		1918	ev_init (timer, callback);
		1919	last_activity = ev_now (loop);
		1920	callback (loop, timer, EV_TIMER);
		1921
		1922	And when there is some activity, simply store the current time in
		1923	C<last_activity>, no libev calls at all:
		1924
		1925	last_activity = ev_now (loop);
		1926
		1927	This technique is slightly more complex, but in most cases where the
		1928	time-out is unlikely to be triggered, much more efficient.
		1929
		1930	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1931	callback :) - just change the timeout and invoke the callback, which will
		1932	fix things for you.
		1933
		1934	=item 4. Wee, just use a double-linked list for your timeouts.
		1935
		1936	If there is not one request, but many thousands (millions...), all
		1937	employing some kind of timeout with the same timeout value, then one can
		1938	do even better:
		1939
		1940	When starting the timeout, calculate the timeout value and put the timeout
		1941	at the I<end> of the list.
		1942
		1943	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1944	the list is expected to fire (for example, using the technique #3).
		1945
		1946	When there is some activity, remove the timer from the list, recalculate
		1947	the timeout, append it to the end of the list again, and make sure to
		1948	update the C<ev_timer> if it was taken from the beginning of the list.
		1949
		1950	This way, one can manage an unlimited number of timeouts in O(1) time for
		1951	starting, stopping and updating the timers, at the expense of a major
		1952	complication, and having to use a constant timeout. The constant timeout
		1953	ensures that the list stays sorted.
		1954
		1955	=back
		1956
		1957	So which method the best?
		1958
		1959	Method #2 is a simple no-brain-required solution that is adequate in most
		1960	situations. Method #3 requires a bit more thinking, but handles many cases
		1961	better, and isn't very complicated either. In most case, choosing either
		1962	one is fine, with #3 being better in typical situations.
		1963
		1964	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1965	rather complicated, but extremely efficient, something that really pays
		1966	off after the first million or so of active timers, i.e. it's usually
		1967	overkill :)
		1968
		1969	=head3 The special problem of time updates
		1970
		1971	Establishing the current time is a costly operation (it usually takes at
		1972	least two system calls): EV therefore updates its idea of the current
		1973	time only before and after C<ev_run> collects new events, which causes a
		1974	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1975	lots of events in one iteration.
525		1976
526	The relative timeouts are calculated relative to the C<ev_now ()>	1977	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1978	time. This is usually the right thing as this timestamp refers to the time
528	of the event triggering whatever timeout you are modifying/starting. If	1979	of the event triggering whatever timeout you are modifying/starting. If
529	you suspect event processing to be delayed and you I<need> to base the timeout	1980	you suspect event processing to be delayed and you I<need> to base the
530	on the current time, use something like this to adjust for this:	1981	timeout on the current time, use something like this to adjust for this:
531		1982
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1983	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1984
534	The callback is guarenteed to be invoked only when its timeout has passed,	1985	If the event loop is suspended for a long time, you can also force an
535	but if multiple timers become ready during the same loop iteration then	1986	update of the time returned by C<ev_now ()> by calling C<ev_now_update
536	order of execution is undefined.	1987	()>.
		1988
		1989	=head3 The special problems of suspended animation
		1990
		1991	When you leave the server world it is quite customary to hit machines that
		1992	can suspend/hibernate - what happens to the clocks during such a suspend?
		1993
		1994	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1995	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1996	to run until the system is suspended, but they will not advance while the
		1997	system is suspended. That means, on resume, it will be as if the program
		1998	was frozen for a few seconds, but the suspend time will not be counted
		1999	towards C<ev_timer> when a monotonic clock source is used. The real time
		2000	clock advanced as expected, but if it is used as sole clocksource, then a
		2001	long suspend would be detected as a time jump by libev, and timers would
		2002	be adjusted accordingly.
		2003
		2004	I would not be surprised to see different behaviour in different between
		2005	operating systems, OS versions or even different hardware.
		2006
		2007	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2008	time jump in the monotonic clocks and the realtime clock. If the program
		2009	is suspended for a very long time, and monotonic clock sources are in use,
		2010	then you can expect C<ev_timer>s to expire as the full suspension time
		2011	will be counted towards the timers. When no monotonic clock source is in
		2012	use, then libev will again assume a timejump and adjust accordingly.
		2013
		2014	It might be beneficial for this latter case to call C<ev_suspend>
		2015	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2016	deterministic behaviour in this case (you can do nothing against
		2017	C<SIGSTOP>).
		2018
		2019	=head3 Watcher-Specific Functions and Data Members
537		2020
538	=over 4	2021	=over 4
539		2022
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2023	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		2024
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2025	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		2026
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2027	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	2028	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	2029	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	2030	configured to trigger again C<repeat> seconds later, again, and again,
		2031	until stopped manually.
548		2032
549	The timer itself will do a best-effort at avoiding drift, that is, if you	2033	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	2034	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	2035	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	2036	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	2037	do stuff) the timer will not fire more than once per event loop iteration.
554		2038
555	=item ev_timer_again (loop)	2039	=item ev_timer_again (loop, ev_timer *)
556		2040
557	This will act as if the timer timed out and restart it again if it is	2041	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	2042	repeating. The exact semantics are:
559		2043
		2044	If the timer is pending, its pending status is cleared.
		2045
560	If the timer is started but nonrepeating, stop it.	2046	If the timer is started but non-repeating, stop it (as if it timed out).
561		2047
562	If the timer is repeating, either start it if necessary (with the repeat	2048	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	2049	C<repeat> value), or reset the running timer to the C<repeat> value.
564		2050
565	This sounds a bit complicated, but here is a useful and typical	2051	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
566	example: Imagine you have a tcp connection and you want a so-called idle	2052	usage example.
567	timeout, that is, you want to be called when there have been, say, 60	2053
568	seconds of inactivity on the socket. The easiest way to do this is to	2054	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	2055
570	time you successfully read or write some data. If you go into an idle	2056	Returns the remaining time until a timer fires. If the timer is active,
571	state where you do not expect data to travel on the socket, you can stop	2057	then this time is relative to the current event loop time, otherwise it's
572	the timer, and again will automatically restart it if need be.	2058	the timeout value currently configured.
		2059
		2060	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2061	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2062	will return C<4>. When the timer expires and is restarted, it will return
		2063	roughly C<7> (likely slightly less as callback invocation takes some time,
		2064	too), and so on.
		2065
		2066	=item ev_tstamp repeat [read-write]
		2067
		2068	The current C<repeat> value. Will be used each time the watcher times out
		2069	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2070	which is also when any modifications are taken into account.
573		2071
574	=back	2072	=back
575		2073
		2074	=head3 Examples
		2075
		2076	Example: Create a timer that fires after 60 seconds.
		2077
		2078	static void
		2079	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2080	{
		2081	.. one minute over, w is actually stopped right here
		2082	}
		2083
		2084	ev_timer mytimer;
		2085	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2086	ev_timer_start (loop, &mytimer);
		2087
		2088	Example: Create a timeout timer that times out after 10 seconds of
		2089	inactivity.
		2090
		2091	static void
		2092	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2093	{
		2094	.. ten seconds without any activity
		2095	}
		2096
		2097	ev_timer mytimer;
		2098	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2099	ev_timer_again (&mytimer); /* start timer */
		2100	ev_run (loop, 0);
		2101
		2102	// and in some piece of code that gets executed on any "activity":
		2103	// reset the timeout to start ticking again at 10 seconds
		2104	ev_timer_again (&mytimer);
		2105
		2106
576	=head2 C<ev_periodic> - to cron or not to cron	2107	=head2 C<ev_periodic> - to cron or not to cron?
577		2108
578	Periodic watchers are also timers of a kind, but they are very versatile	2109	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	2110	(and unfortunately a bit complex).
580		2111
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2112	Unlike C<ev_timer>, periodic watchers are not based on real time (or
582	but on wallclock time (absolute time). You can tell a periodic watcher	2113	relative time, the physical time that passes) but on wall clock time
583	to trigger "at" some specific point in time. For example, if you tell a	2114	(absolute time, the thing you can read on your calender or clock). The
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2115	difference is that wall clock time can run faster or slower than real
585	+ 10.>) and then reset your system clock to the last year, then it will	2116	time, and time jumps are not uncommon (e.g. when you adjust your
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2117	wrist-watch).
587	roughly 10 seconds later and of course not if you reset your system time
588	again).
589		2118
590	They can also be used to implement vastly more complex timers, such as	2119	You can tell a periodic watcher to trigger after some specific point
		2120	in time: for example, if you tell a periodic watcher to trigger "in 10
		2121	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2122	not a delay) and then reset your system clock to January of the previous
		2123	year, then it will take a year or more to trigger the event (unlike an
		2124	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2125	it, as it uses a relative timeout).
		2126
		2127	C<ev_periodic> watchers can also be used to implement vastly more complex
591	triggering an event on eahc midnight, local time.	2128	timers, such as triggering an event on each "midnight, local time", or
		2129	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2130	those cannot react to time jumps.
592		2131
593	As with timers, the callback is guarenteed to be invoked only when the	2132	As with timers, the callback is guaranteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	2133	point in time where it is supposed to trigger has passed. If multiple
595	during the same loop iteration then order of execution is undefined.	2134	timers become ready during the same loop iteration then the ones with
		2135	earlier time-out values are invoked before ones with later time-out values
		2136	(but this is no longer true when a callback calls C<ev_run> recursively).
		2137
		2138	=head3 Watcher-Specific Functions and Data Members
596		2139
597	=over 4	2140	=over 4
598		2141
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2142	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
600		2143
601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2144	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
602		2145
603	Lots of arguments, lets sort it out... There are basically three modes of	2146	Lots of arguments, let's sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	2147	operation, and we will explain them from simplest to most complex:
605		2148
606	=over 4	2149	=over 4
607		2150
608	=item * absolute timer (interval = reschedule_cb = 0)	2151	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
609		2152
610	In this configuration the watcher triggers an event at the wallclock time	2153	In this configuration the watcher triggers an event after the wall clock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2154	time C<offset> has passed. It will not repeat and will not adjust when a
612	that is, if it is to be run at January 1st 2011 then it will run when the	2155	time jump occurs, that is, if it is to be run at January 1st 2011 then it
613	system time reaches or surpasses this time.	2156	will be stopped and invoked when the system clock reaches or surpasses
		2157	this point in time.
614		2158
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2159	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
616		2160
617	In this mode the watcher will always be scheduled to time out at the next	2161	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	2162	C<offset + N * interval> time (for some integer N, which can also be
619	of any time jumps.	2163	negative) and then repeat, regardless of any time jumps. The C<offset>
		2164	argument is merely an offset into the C<interval> periods.
620		2165
621	This can be used to create timers that do not drift with respect to system	2166	This can be used to create timers that do not drift with respect to the
622	time:	2167	system clock, for example, here is an C<ev_periodic> that triggers each
		2168	hour, on the hour (with respect to UTC):
623		2169
624	ev_periodic_set (&periodic, 0., 3600., 0);	2170	ev_periodic_set (&periodic, 0., 3600., 0);
625		2171
626	This doesn't mean there will always be 3600 seconds in between triggers,	2172	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	2173	but only that the callback will be called when the system time shows a
628	full hour (UTC), or more correctly, when the system time is evenly divisible	2174	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	2175	by 3600.
630		2176
631	Another way to think about it (for the mathematically inclined) is that	2177	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	2178	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	2179	time where C<time = offset (mod interval)>, regardless of any time jumps.
634		2180
		2181	For numerical stability it is preferable that the C<offset> value is near
		2182	C<ev_now ()> (the current time), but there is no range requirement for
		2183	this value, and in fact is often specified as zero.
		2184
		2185	Note also that there is an upper limit to how often a timer can fire (CPU
		2186	speed for example), so if C<interval> is very small then timing stability
		2187	will of course deteriorate. Libev itself tries to be exact to be about one
		2188	millisecond (if the OS supports it and the machine is fast enough).
		2189
635	=item * manual reschedule mode (reschedule_cb = callback)	2190	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
636		2191
637	In this mode the values for C<interval> and C<at> are both being	2192	In this mode the values for C<interval> and C<offset> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	2193	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	2194	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	2195	current time as second argument.
641		2196
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2197	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
643	ever, or make any event loop modifications>. If you need to stop it,	2198	or make ANY other event loop modifications whatsoever, unless explicitly
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2199	allowed by documentation here>.
645	starting a prepare watcher).
646		2200
		2201	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2202	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2203	only event loop modification you are allowed to do).
		2204
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2205	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
648	ev_tstamp now)>, e.g.:	2206	*w, ev_tstamp now)>, e.g.:
649		2207
		2208	static ev_tstamp
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2209	my_rescheduler (ev_periodic *w, ev_tstamp now)
651	{	2210	{
652	return now + 60.;	2211	return now + 60.;
653	}	2212	}
654		2213
655	It must return the next time to trigger, based on the passed time value	2214	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	2215	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	2216	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	2217	might be called at other times, too.
659		2218
660	NOTE: I<< This callback must always return a time that is later than the	2219	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2220	equal to the passed C<now> value >>.
662		2221
663	This can be used to create very complex timers, such as a timer that	2222	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	2223	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	2224	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	2225	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	2226	reason I omitted it as an example).
668		2227
669	=back	2228	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	2232	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	2233	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	2234	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	2235	program when the crontabs have changed).
677		2236
		2237	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2238
		2239	When active, returns the absolute time that the watcher is supposed
		2240	to trigger next. This is not the same as the C<offset> argument to
		2241	C<ev_periodic_set>, but indeed works even in interval and manual
		2242	rescheduling modes.
		2243
		2244	=item ev_tstamp offset [read-write]
		2245
		2246	When repeating, this contains the offset value, otherwise this is the
		2247	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2248	although libev might modify this value for better numerical stability).
		2249
		2250	Can be modified any time, but changes only take effect when the periodic
		2251	timer fires or C<ev_periodic_again> is being called.
		2252
		2253	=item ev_tstamp interval [read-write]
		2254
		2255	The current interval value. Can be modified any time, but changes only
		2256	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2257	called.
		2258
		2259	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2260
		2261	The current reschedule callback, or C<0>, if this functionality is
		2262	switched off. Can be changed any time, but changes only take effect when
		2263	the periodic timer fires or C<ev_periodic_again> is being called.
		2264
678	=back	2265	=back
679		2266
		2267	=head3 Examples
		2268
		2269	Example: Call a callback every hour, or, more precisely, whenever the
		2270	system time is divisible by 3600. The callback invocation times have
		2271	potentially a lot of jitter, but good long-term stability.
		2272
		2273	static void
		2274	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2275	{
		2276	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2277	}
		2278
		2279	ev_periodic hourly_tick;
		2280	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2281	ev_periodic_start (loop, &hourly_tick);
		2282
		2283	Example: The same as above, but use a reschedule callback to do it:
		2284
		2285	#include <math.h>
		2286
		2287	static ev_tstamp
		2288	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2289	{
		2290	return now + (3600. - fmod (now, 3600.));
		2291	}
		2292
		2293	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2294
		2295	Example: Call a callback every hour, starting now:
		2296
		2297	ev_periodic hourly_tick;
		2298	ev_periodic_init (&hourly_tick, clock_cb,
		2299	fmod (ev_now (loop), 3600.), 3600., 0);
		2300	ev_periodic_start (loop, &hourly_tick);
		2301
		2302
680	=head2 C<ev_signal> - signal me when a signal gets signalled	2303	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		2304
682	Signal watchers will trigger an event when the process receives a specific	2305	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	2306	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	2307	will try its best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	2308	normal event processing, like any other event.
686		2309
		2310	If you want signals to be delivered truly asynchronously, just use
		2311	C<sigaction> as you would do without libev and forget about sharing
		2312	the signal. You can even use C<ev_async> from a signal handler to
		2313	synchronously wake up an event loop.
		2314
687	You can configure as many watchers as you like per signal. Only when the	2315	You can configure as many watchers as you like for the same signal, but
		2316	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2317	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2318	C<SIGINT> in both the default loop and another loop at the same time. At
		2319	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2320
688	first watcher gets started will libev actually register a signal watcher	2321	When the first watcher gets started will libev actually register something
689	with the kernel (thus it coexists with your own signal handlers as long	2322	with the kernel (thus it coexists with your own signal handlers as long as
690	as you don't register any with libev). Similarly, when the last signal	2323	you don't register any with libev for the same signal).
691	watcher for a signal is stopped libev will reset the signal handler to	2324
692	SIG_DFL (regardless of what it was set to before).	2325	If possible and supported, libev will install its handlers with
		2326	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2327	not be unduly interrupted. If you have a problem with system calls getting
		2328	interrupted by signals you can block all signals in an C<ev_check> watcher
		2329	and unblock them in an C<ev_prepare> watcher.
		2330
		2331	=head3 The special problem of inheritance over fork/execve/pthread_create
		2332
		2333	Both the signal mask (C<sigprocmask>) and the signal disposition
		2334	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2335	stopping it again), that is, libev might or might not block the signal,
		2336	and might or might not set or restore the installed signal handler.
		2337
		2338	While this does not matter for the signal disposition (libev never
		2339	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2340	C<execve>), this matters for the signal mask: many programs do not expect
		2341	certain signals to be blocked.
		2342
		2343	This means that before calling C<exec> (from the child) you should reset
		2344	the signal mask to whatever "default" you expect (all clear is a good
		2345	choice usually).
		2346
		2347	The simplest way to ensure that the signal mask is reset in the child is
		2348	to install a fork handler with C<pthread_atfork> that resets it. That will
		2349	catch fork calls done by libraries (such as the libc) as well.
		2350
		2351	In current versions of libev, the signal will not be blocked indefinitely
		2352	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2353	the window of opportunity for problems, it will not go away, as libev
		2354	I<has> to modify the signal mask, at least temporarily.
		2355
		2356	So I can't stress this enough: I<If you do not reset your signal mask when
		2357	you expect it to be empty, you have a race condition in your code>. This
		2358	is not a libev-specific thing, this is true for most event libraries.
		2359
		2360	=head3 The special problem of threads signal handling
		2361
		2362	POSIX threads has problematic signal handling semantics, specifically,
		2363	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2364	threads in a process block signals, which is hard to achieve.
		2365
		2366	When you want to use sigwait (or mix libev signal handling with your own
		2367	for the same signals), you can tackle this problem by globally blocking
		2368	all signals before creating any threads (or creating them with a fully set
		2369	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2370	loops. Then designate one thread as "signal receiver thread" which handles
		2371	these signals. You can pass on any signals that libev might be interested
		2372	in by calling C<ev_feed_signal>.
		2373
		2374	=head3 Watcher-Specific Functions and Data Members
693		2375
694	=over 4	2376	=over 4
695		2377
696	=item ev_signal_init (ev_signal *, callback, int signum)	2378	=item ev_signal_init (ev_signal *, callback, int signum)
697		2379
698	=item ev_signal_set (ev_signal *, int signum)	2380	=item ev_signal_set (ev_signal *, int signum)
699		2381
700	Configures the watcher to trigger on the given signal number (usually one	2382	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	2383	of the C<SIGxxx> constants).
702		2384
		2385	=item int signum [read-only]
		2386
		2387	The signal the watcher watches out for.
		2388
703	=back	2389	=back
704		2390
		2391	=head3 Examples
		2392
		2393	Example: Try to exit cleanly on SIGINT.
		2394
		2395	static void
		2396	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2397	{
		2398	ev_break (loop, EVBREAK_ALL);
		2399	}
		2400
		2401	ev_signal signal_watcher;
		2402	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2403	ev_signal_start (loop, &signal_watcher);
		2404
		2405
705	=head2 C<ev_child> - wait for pid status changes	2406	=head2 C<ev_child> - watch out for process status changes
706		2407
707	Child watchers trigger when your process receives a SIGCHLD in response to	2408	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	2409	some child status changes (most typically when a child of yours dies or
		2410	exits). It is permissible to install a child watcher I<after> the child
		2411	has been forked (which implies it might have already exited), as long
		2412	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2413	forking and then immediately registering a watcher for the child is fine,
		2414	but forking and registering a watcher a few event loop iterations later or
		2415	in the next callback invocation is not.
		2416
		2417	Only the default event loop is capable of handling signals, and therefore
		2418	you can only register child watchers in the default event loop.
		2419
		2420	Due to some design glitches inside libev, child watchers will always be
		2421	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2422	libev)
		2423
		2424	=head3 Process Interaction
		2425
		2426	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2427	initialised. This is necessary to guarantee proper behaviour even if the
		2428	first child watcher is started after the child exits. The occurrence
		2429	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2430	synchronously as part of the event loop processing. Libev always reaps all
		2431	children, even ones not watched.
		2432
		2433	=head3 Overriding the Built-In Processing
		2434
		2435	Libev offers no special support for overriding the built-in child
		2436	processing, but if your application collides with libev's default child
		2437	handler, you can override it easily by installing your own handler for
		2438	C<SIGCHLD> after initialising the default loop, and making sure the
		2439	default loop never gets destroyed. You are encouraged, however, to use an
		2440	event-based approach to child reaping and thus use libev's support for
		2441	that, so other libev users can use C<ev_child> watchers freely.
		2442
		2443	=head3 Stopping the Child Watcher
		2444
		2445	Currently, the child watcher never gets stopped, even when the
		2446	child terminates, so normally one needs to stop the watcher in the
		2447	callback. Future versions of libev might stop the watcher automatically
		2448	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2449	problem).
		2450
		2451	=head3 Watcher-Specific Functions and Data Members
709		2452
710	=over 4	2453	=over 4
711		2454
712	=item ev_child_init (ev_child *, callback, int pid)	2455	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		2456
714	=item ev_child_set (ev_child *, int pid)	2457	=item ev_child_set (ev_child *, int pid, int trace)
715		2458
716	Configures the watcher to wait for status changes of process C<pid> (or	2459	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	2460	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	2461	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	2462	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	2463	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	2464	process causing the status change. C<trace> must be either C<0> (only
		2465	activate the watcher when the process terminates) or C<1> (additionally
		2466	activate the watcher when the process is stopped or continued).
		2467
		2468	=item int pid [read-only]
		2469
		2470	The process id this watcher watches out for, or C<0>, meaning any process id.
		2471
		2472	=item int rpid [read-write]
		2473
		2474	The process id that detected a status change.
		2475
		2476	=item int rstatus [read-write]
		2477
		2478	The process exit/trace status caused by C<rpid> (see your systems
		2479	C<waitpid> and C<sys/wait.h> documentation for details).
722		2480
723	=back	2481	=back
724		2482
		2483	=head3 Examples
		2484
		2485	Example: C<fork()> a new process and install a child handler to wait for
		2486	its completion.
		2487
		2488	ev_child cw;
		2489
		2490	static void
		2491	child_cb (EV_P_ ev_child *w, int revents)
		2492	{
		2493	ev_child_stop (EV_A_ w);
		2494	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2495	}
		2496
		2497	pid_t pid = fork ();
		2498
		2499	if (pid < 0)
		2500	// error
		2501	else if (pid == 0)
		2502	{
		2503	// the forked child executes here
		2504	exit (1);
		2505	}
		2506	else
		2507	{
		2508	ev_child_init (&cw, child_cb, pid, 0);
		2509	ev_child_start (EV_DEFAULT_ &cw);
		2510	}
		2511
		2512
		2513	=head2 C<ev_stat> - did the file attributes just change?
		2514
		2515	This watches a file system path for attribute changes. That is, it calls
		2516	C<stat> on that path in regular intervals (or when the OS says it changed)
		2517	and sees if it changed compared to the last time, invoking the callback if
		2518	it did.
		2519
		2520	The path does not need to exist: changing from "path exists" to "path does
		2521	not exist" is a status change like any other. The condition "path does not
		2522	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2523	C<st_nlink> field being zero (which is otherwise always forced to be at
		2524	least one) and all the other fields of the stat buffer having unspecified
		2525	contents.
		2526
		2527	The path I<must not> end in a slash or contain special components such as
		2528	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2529	your working directory changes, then the behaviour is undefined.
		2530
		2531	Since there is no portable change notification interface available, the
		2532	portable implementation simply calls C<stat(2)> regularly on the path
		2533	to see if it changed somehow. You can specify a recommended polling
		2534	interval for this case. If you specify a polling interval of C<0> (highly
		2535	recommended!) then a I<suitable, unspecified default> value will be used
		2536	(which you can expect to be around five seconds, although this might
		2537	change dynamically). Libev will also impose a minimum interval which is
		2538	currently around C<0.1>, but that's usually overkill.
		2539
		2540	This watcher type is not meant for massive numbers of stat watchers,
		2541	as even with OS-supported change notifications, this can be
		2542	resource-intensive.
		2543
		2544	At the time of this writing, the only OS-specific interface implemented
		2545	is the Linux inotify interface (implementing kqueue support is left as an
		2546	exercise for the reader. Note, however, that the author sees no way of
		2547	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2548
		2549	=head3 ABI Issues (Largefile Support)
		2550
		2551	Libev by default (unless the user overrides this) uses the default
		2552	compilation environment, which means that on systems with large file
		2553	support disabled by default, you get the 32 bit version of the stat
		2554	structure. When using the library from programs that change the ABI to
		2555	use 64 bit file offsets the programs will fail. In that case you have to
		2556	compile libev with the same flags to get binary compatibility. This is
		2557	obviously the case with any flags that change the ABI, but the problem is
		2558	most noticeably displayed with ev_stat and large file support.
		2559
		2560	The solution for this is to lobby your distribution maker to make large
		2561	file interfaces available by default (as e.g. FreeBSD does) and not
		2562	optional. Libev cannot simply switch on large file support because it has
		2563	to exchange stat structures with application programs compiled using the
		2564	default compilation environment.
		2565
		2566	=head3 Inotify and Kqueue
		2567
		2568	When C<inotify (7)> support has been compiled into libev and present at
		2569	runtime, it will be used to speed up change detection where possible. The
		2570	inotify descriptor will be created lazily when the first C<ev_stat>
		2571	watcher is being started.
		2572
		2573	Inotify presence does not change the semantics of C<ev_stat> watchers
		2574	except that changes might be detected earlier, and in some cases, to avoid
		2575	making regular C<stat> calls. Even in the presence of inotify support
		2576	there are many cases where libev has to resort to regular C<stat> polling,
		2577	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2578	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2579	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2580	xfs are fully working) libev usually gets away without polling.
		2581
		2582	There is no support for kqueue, as apparently it cannot be used to
		2583	implement this functionality, due to the requirement of having a file
		2584	descriptor open on the object at all times, and detecting renames, unlinks
		2585	etc. is difficult.
		2586
		2587	=head3 C<stat ()> is a synchronous operation
		2588
		2589	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2590	the process. The exception are C<ev_stat> watchers - those call C<stat
		2591	()>, which is a synchronous operation.
		2592
		2593	For local paths, this usually doesn't matter: unless the system is very
		2594	busy or the intervals between stat's are large, a stat call will be fast,
		2595	as the path data is usually in memory already (except when starting the
		2596	watcher).
		2597
		2598	For networked file systems, calling C<stat ()> can block an indefinite
		2599	time due to network issues, and even under good conditions, a stat call
		2600	often takes multiple milliseconds.
		2601
		2602	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2603	paths, although this is fully supported by libev.
		2604
		2605	=head3 The special problem of stat time resolution
		2606
		2607	The C<stat ()> system call only supports full-second resolution portably,
		2608	and even on systems where the resolution is higher, most file systems
		2609	still only support whole seconds.
		2610
		2611	That means that, if the time is the only thing that changes, you can
		2612	easily miss updates: on the first update, C<ev_stat> detects a change and
		2613	calls your callback, which does something. When there is another update
		2614	within the same second, C<ev_stat> will be unable to detect unless the
		2615	stat data does change in other ways (e.g. file size).
		2616
		2617	The solution to this is to delay acting on a change for slightly more
		2618	than a second (or till slightly after the next full second boundary), using
		2619	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2620	ev_timer_again (loop, w)>).
		2621
		2622	The C<.02> offset is added to work around small timing inconsistencies
		2623	of some operating systems (where the second counter of the current time
		2624	might be be delayed. One such system is the Linux kernel, where a call to
		2625	C<gettimeofday> might return a timestamp with a full second later than
		2626	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2627	update file times then there will be a small window where the kernel uses
		2628	the previous second to update file times but libev might already execute
		2629	the timer callback).
		2630
		2631	=head3 Watcher-Specific Functions and Data Members
		2632
		2633	=over 4
		2634
		2635	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2636
		2637	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2638
		2639	Configures the watcher to wait for status changes of the given
		2640	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2641	be detected and should normally be specified as C<0> to let libev choose
		2642	a suitable value. The memory pointed to by C<path> must point to the same
		2643	path for as long as the watcher is active.
		2644
		2645	The callback will receive an C<EV_STAT> event when a change was detected,
		2646	relative to the attributes at the time the watcher was started (or the
		2647	last change was detected).
		2648
		2649	=item ev_stat_stat (loop, ev_stat *)
		2650
		2651	Updates the stat buffer immediately with new values. If you change the
		2652	watched path in your callback, you could call this function to avoid
		2653	detecting this change (while introducing a race condition if you are not
		2654	the only one changing the path). Can also be useful simply to find out the
		2655	new values.
		2656
		2657	=item ev_statdata attr [read-only]
		2658
		2659	The most-recently detected attributes of the file. Although the type is
		2660	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2661	suitable for your system, but you can only rely on the POSIX-standardised
		2662	members to be present. If the C<st_nlink> member is C<0>, then there was
		2663	some error while C<stat>ing the file.
		2664
		2665	=item ev_statdata prev [read-only]
		2666
		2667	The previous attributes of the file. The callback gets invoked whenever
		2668	C<prev> != C<attr>, or, more precisely, one or more of these members
		2669	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2670	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2671
		2672	=item ev_tstamp interval [read-only]
		2673
		2674	The specified interval.
		2675
		2676	=item const char *path [read-only]
		2677
		2678	The file system path that is being watched.
		2679
		2680	=back
		2681
		2682	=head3 Examples
		2683
		2684	Example: Watch C</etc/passwd> for attribute changes.
		2685
		2686	static void
		2687	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2688	{
		2689	/* /etc/passwd changed in some way */
		2690	if (w->attr.st_nlink)
		2691	{
		2692	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2693	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2694	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2695	}
		2696	else
		2697	/* you shalt not abuse printf for puts */
		2698	puts ("wow, /etc/passwd is not there, expect problems. "
		2699	"if this is windows, they already arrived\n");
		2700	}
		2701
		2702	...
		2703	ev_stat passwd;
		2704
		2705	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2706	ev_stat_start (loop, &passwd);
		2707
		2708	Example: Like above, but additionally use a one-second delay so we do not
		2709	miss updates (however, frequent updates will delay processing, too, so
		2710	one might do the work both on C<ev_stat> callback invocation I<and> on
		2711	C<ev_timer> callback invocation).
		2712
		2713	static ev_stat passwd;
		2714	static ev_timer timer;
		2715
		2716	static void
		2717	timer_cb (EV_P_ ev_timer *w, int revents)
		2718	{
		2719	ev_timer_stop (EV_A_ w);
		2720
		2721	/* now it's one second after the most recent passwd change */
		2722	}
		2723
		2724	static void
		2725	stat_cb (EV_P_ ev_stat *w, int revents)
		2726	{
		2727	/* reset the one-second timer */
		2728	ev_timer_again (EV_A_ &timer);
		2729	}
		2730
		2731	...
		2732	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2733	ev_stat_start (loop, &passwd);
		2734	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2735
		2736
725	=head2 C<ev_idle> - when you've got nothing better to do	2737	=head2 C<ev_idle> - when you've got nothing better to do...
726		2738
727	Idle watchers trigger events when there are no other events are pending	2739	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	2740	priority are pending (prepare, check and other idle watchers do not count
729	as your process is busy handling sockets or timeouts (or even signals,	2741	as receiving "events").
730	imagine) it will not be triggered. But when your process is idle all idle	2742
731	watchers are being called again and again, once per event loop iteration -	2743	That is, as long as your process is busy handling sockets or timeouts
		2744	(or even signals, imagine) of the same or higher priority it will not be
		2745	triggered. But when your process is idle (or only lower-priority watchers
		2746	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	2747	iteration - until stopped, that is, or your process receives more events
733	busy.	2748	and becomes busy again with higher priority stuff.
734		2749
735	The most noteworthy effect is that as long as any idle watchers are	2750	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	2751	active, the process will not block when waiting for new events.
737		2752
738	Apart from keeping your process non-blocking (which is a useful	2753	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	2754	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	2755	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	2756	event loop has handled all outstanding events.
742		2757
		2758	=head3 Watcher-Specific Functions and Data Members
		2759
743	=over 4	2760	=over 4
744		2761
745	=item ev_idle_init (ev_signal *, callback)	2762	=item ev_idle_init (ev_idle *, callback)
746		2763
747	Initialises and configures the idle watcher - it has no parameters of any	2764	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2765	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	2766	believe me.
750		2767
751	=back	2768	=back
752		2769
		2770	=head3 Examples
		2771
		2772	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2773	callback, free it. Also, use no error checking, as usual.
		2774
		2775	static void
		2776	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2777	{
		2778	free (w);
		2779	// now do something you wanted to do when the program has
		2780	// no longer anything immediate to do.
		2781	}
		2782
		2783	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2784	ev_idle_init (idle_watcher, idle_cb);
		2785	ev_idle_start (loop, idle_watcher);
		2786
		2787
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2788	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		2789
755	Prepare and check watchers are usually (but not always) used in tandem:	2790	Prepare and check watchers are usually (but not always) used in pairs:
756	prepare watchers get invoked before the process blocks and check watchers	2791	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	2792	afterwards.
758		2793
		2794	You I<must not> call C<ev_run> or similar functions that enter
		2795	the current event loop from either C<ev_prepare> or C<ev_check>
		2796	watchers. Other loops than the current one are fine, however. The
		2797	rationale behind this is that you do not need to check for recursion in
		2798	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2799	C<ev_check> so if you have one watcher of each kind they will always be
		2800	called in pairs bracketing the blocking call.
		2801
759	Their main purpose is to integrate other event mechanisms into libev. This	2802	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	2803	their use is somewhat advanced. They could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	2804	variable changes, implement your own watchers, integrate net-snmp or a
		2805	coroutine library and lots more. They are also occasionally useful if
		2806	you cache some data and want to flush it before blocking (for example,
		2807	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2808	watcher).
762		2809
763	This is done by examining in each prepare call which file descriptors need	2810	This is done by examining in each prepare call which file descriptors
764	to be watched by the other library, registering C<ev_io> watchers for	2811	need to be watched by the other library, registering C<ev_io> watchers
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2812	for them and starting an C<ev_timer> watcher for any timeouts (many
766	provide just this functionality). Then, in the check watcher you check for	2813	libraries provide exactly this functionality). Then, in the check watcher,
767	any events that occured (by checking the pending status of all watchers	2814	you check for any events that occurred (by checking the pending status
768	and stopping them) and call back into the library. The I/O and timer	2815	of all watchers and stopping them) and call back into the library. The
769	callbacks will never actually be called (but must be valid nevertheless,	2816	I/O and timer callbacks will never actually be called (but must be valid
770	because you never know, you know?).	2817	nevertheless, because you never know, you know?).
771		2818
772	As another example, the Perl Coro module uses these hooks to integrate	2819	As another example, the Perl Coro module uses these hooks to integrate
773	coroutines into libev programs, by yielding to other active coroutines	2820	coroutines into libev programs, by yielding to other active coroutines
774	during each prepare and only letting the process block if no coroutines	2821	during each prepare and only letting the process block if no coroutines
775	are ready to run (it's actually more complicated: it only runs coroutines	2822	are ready to run (it's actually more complicated: it only runs coroutines
776	with priority higher than or equal to the event loop and one coroutine	2823	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	2824	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	2825	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	2826	low-priority coroutines to idle/background tasks).
780		2827
		2828	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2829	priority, to ensure that they are being run before any other watchers
		2830	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2831
		2832	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2833	activate ("feed") events into libev. While libev fully supports this, they
		2834	might get executed before other C<ev_check> watchers did their job. As
		2835	C<ev_check> watchers are often used to embed other (non-libev) event
		2836	loops those other event loops might be in an unusable state until their
		2837	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2838	others).
		2839
		2840	=head3 Watcher-Specific Functions and Data Members
		2841
781	=over 4	2842	=over 4
782		2843
783	=item ev_prepare_init (ev_prepare *, callback)	2844	=item ev_prepare_init (ev_prepare *, callback)
784		2845
785	=item ev_check_init (ev_check *, callback)	2846	=item ev_check_init (ev_check *, callback)
786		2847
787	Initialises and configures the prepare or check watcher - they have no	2848	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2849	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	2850	macros, but using them is utterly, utterly, utterly and completely
		2851	pointless.
790		2852
791	=back	2853	=back
792		2854
		2855	=head3 Examples
		2856
		2857	There are a number of principal ways to embed other event loops or modules
		2858	into libev. Here are some ideas on how to include libadns into libev
		2859	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2860	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2861	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2862	Glib event loop).
		2863
		2864	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2865	and in a check watcher, destroy them and call into libadns. What follows
		2866	is pseudo-code only of course. This requires you to either use a low
		2867	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2868	the callbacks for the IO/timeout watchers might not have been called yet.
		2869
		2870	static ev_io iow [nfd];
		2871	static ev_timer tw;
		2872
		2873	static void
		2874	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2875	{
		2876	}
		2877
		2878	// create io watchers for each fd and a timer before blocking
		2879	static void
		2880	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2881	{
		2882	int timeout = 3600000;
		2883	struct pollfd fds [nfd];
		2884	// actual code will need to loop here and realloc etc.
		2885	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2886
		2887	/* the callback is illegal, but won't be called as we stop during check */
		2888	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2889	ev_timer_start (loop, &tw);
		2890
		2891	// create one ev_io per pollfd
		2892	for (int i = 0; i < nfd; ++i)
		2893	{
		2894	ev_io_init (iow + i, io_cb, fds [i].fd,
		2895	((fds [i].events & POLLIN ? EV_READ : 0)
		2896	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2897
		2898	fds [i].revents = 0;
		2899	ev_io_start (loop, iow + i);
		2900	}
		2901	}
		2902
		2903	// stop all watchers after blocking
		2904	static void
		2905	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2906	{
		2907	ev_timer_stop (loop, &tw);
		2908
		2909	for (int i = 0; i < nfd; ++i)
		2910	{
		2911	// set the relevant poll flags
		2912	// could also call adns_processreadable etc. here
		2913	struct pollfd *fd = fds + i;
		2914	int revents = ev_clear_pending (iow + i);
		2915	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2916	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2917
		2918	// now stop the watcher
		2919	ev_io_stop (loop, iow + i);
		2920	}
		2921
		2922	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2923	}
		2924
		2925	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2926	in the prepare watcher and would dispose of the check watcher.
		2927
		2928	Method 3: If the module to be embedded supports explicit event
		2929	notification (libadns does), you can also make use of the actual watcher
		2930	callbacks, and only destroy/create the watchers in the prepare watcher.
		2931
		2932	static void
		2933	timer_cb (EV_P_ ev_timer *w, int revents)
		2934	{
		2935	adns_state ads = (adns_state)w->data;
		2936	update_now (EV_A);
		2937
		2938	adns_processtimeouts (ads, &tv_now);
		2939	}
		2940
		2941	static void
		2942	io_cb (EV_P_ ev_io *w, int revents)
		2943	{
		2944	adns_state ads = (adns_state)w->data;
		2945	update_now (EV_A);
		2946
		2947	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2948	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2949	}
		2950
		2951	// do not ever call adns_afterpoll
		2952
		2953	Method 4: Do not use a prepare or check watcher because the module you
		2954	want to embed is not flexible enough to support it. Instead, you can
		2955	override their poll function. The drawback with this solution is that the
		2956	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2957	this approach, effectively embedding EV as a client into the horrible
		2958	libglib event loop.
		2959
		2960	static gint
		2961	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2962	{
		2963	int got_events = 0;
		2964
		2965	for (n = 0; n < nfds; ++n)
		2966	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2967
		2968	if (timeout >= 0)
		2969	// create/start timer
		2970
		2971	// poll
		2972	ev_run (EV_A_ 0);
		2973
		2974	// stop timer again
		2975	if (timeout >= 0)
		2976	ev_timer_stop (EV_A_ &to);
		2977
		2978	// stop io watchers again - their callbacks should have set
		2979	for (n = 0; n < nfds; ++n)
		2980	ev_io_stop (EV_A_ iow [n]);
		2981
		2982	return got_events;
		2983	}
		2984
		2985
		2986	=head2 C<ev_embed> - when one backend isn't enough...
		2987
		2988	This is a rather advanced watcher type that lets you embed one event loop
		2989	into another (currently only C<ev_io> events are supported in the embedded
		2990	loop, other types of watchers might be handled in a delayed or incorrect
		2991	fashion and must not be used).
		2992
		2993	There are primarily two reasons you would want that: work around bugs and
		2994	prioritise I/O.
		2995
		2996	As an example for a bug workaround, the kqueue backend might only support
		2997	sockets on some platform, so it is unusable as generic backend, but you
		2998	still want to make use of it because you have many sockets and it scales
		2999	so nicely. In this case, you would create a kqueue-based loop and embed
		3000	it into your default loop (which might use e.g. poll). Overall operation
		3001	will be a bit slower because first libev has to call C<poll> and then
		3002	C<kevent>, but at least you can use both mechanisms for what they are
		3003	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3004
		3005	As for prioritising I/O: under rare circumstances you have the case where
		3006	some fds have to be watched and handled very quickly (with low latency),
		3007	and even priorities and idle watchers might have too much overhead. In
		3008	this case you would put all the high priority stuff in one loop and all
		3009	the rest in a second one, and embed the second one in the first.
		3010
		3011	As long as the watcher is active, the callback will be invoked every
		3012	time there might be events pending in the embedded loop. The callback
		3013	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3014	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3015	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3016	to give the embedded loop strictly lower priority for example).
		3017
		3018	You can also set the callback to C<0>, in which case the embed watcher
		3019	will automatically execute the embedded loop sweep whenever necessary.
		3020
		3021	Fork detection will be handled transparently while the C<ev_embed> watcher
		3022	is active, i.e., the embedded loop will automatically be forked when the
		3023	embedding loop forks. In other cases, the user is responsible for calling
		3024	C<ev_loop_fork> on the embedded loop.
		3025
		3026	Unfortunately, not all backends are embeddable: only the ones returned by
		3027	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3028	portable one.
		3029
		3030	So when you want to use this feature you will always have to be prepared
		3031	that you cannot get an embeddable loop. The recommended way to get around
		3032	this is to have a separate variables for your embeddable loop, try to
		3033	create it, and if that fails, use the normal loop for everything.
		3034
		3035	=head3 C<ev_embed> and fork
		3036
		3037	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3038	automatically be applied to the embedded loop as well, so no special
		3039	fork handling is required in that case. When the watcher is not running,
		3040	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3041	as applicable.
		3042
		3043	=head3 Watcher-Specific Functions and Data Members
		3044
		3045	=over 4
		3046
		3047	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3048
		3049	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		3050
		3051	Configures the watcher to embed the given loop, which must be
		3052	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3053	invoked automatically, otherwise it is the responsibility of the callback
		3054	to invoke it (it will continue to be called until the sweep has been done,
		3055	if you do not want that, you need to temporarily stop the embed watcher).
		3056
		3057	=item ev_embed_sweep (loop, ev_embed *)
		3058
		3059	Make a single, non-blocking sweep over the embedded loop. This works
		3060	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3061	appropriate way for embedded loops.
		3062
		3063	=item struct ev_loop *other [read-only]
		3064
		3065	The embedded event loop.
		3066
		3067	=back
		3068
		3069	=head3 Examples
		3070
		3071	Example: Try to get an embeddable event loop and embed it into the default
		3072	event loop. If that is not possible, use the default loop. The default
		3073	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3074	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3075	used).
		3076
		3077	struct ev_loop *loop_hi = ev_default_init (0);
		3078	struct ev_loop *loop_lo = 0;
		3079	ev_embed embed;
		3080
		3081	// see if there is a chance of getting one that works
		3082	// (remember that a flags value of 0 means autodetection)
		3083	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3084	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3085	: 0;
		3086
		3087	// if we got one, then embed it, otherwise default to loop_hi
		3088	if (loop_lo)
		3089	{
		3090	ev_embed_init (&embed, 0, loop_lo);
		3091	ev_embed_start (loop_hi, &embed);
		3092	}
		3093	else
		3094	loop_lo = loop_hi;
		3095
		3096	Example: Check if kqueue is available but not recommended and create
		3097	a kqueue backend for use with sockets (which usually work with any
		3098	kqueue implementation). Store the kqueue/socket-only event loop in
		3099	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3100
		3101	struct ev_loop *loop = ev_default_init (0);
		3102	struct ev_loop *loop_socket = 0;
		3103	ev_embed embed;
		3104
		3105	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3106	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3107	{
		3108	ev_embed_init (&embed, 0, loop_socket);
		3109	ev_embed_start (loop, &embed);
		3110	}
		3111
		3112	if (!loop_socket)
		3113	loop_socket = loop;
		3114
		3115	// now use loop_socket for all sockets, and loop for everything else
		3116
		3117
		3118	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3119
		3120	Fork watchers are called when a C<fork ()> was detected (usually because
		3121	whoever is a good citizen cared to tell libev about it by calling
		3122	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3123	event loop blocks next and before C<ev_check> watchers are being called,
		3124	and only in the child after the fork. If whoever good citizen calling
		3125	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3126	handlers will be invoked, too, of course.
		3127
		3128	=head3 The special problem of life after fork - how is it possible?
		3129
		3130	Most uses of C<fork()> consist of forking, then some simple calls to set
		3131	up/change the process environment, followed by a call to C<exec()>. This
		3132	sequence should be handled by libev without any problems.
		3133
		3134	This changes when the application actually wants to do event handling
		3135	in the child, or both parent in child, in effect "continuing" after the
		3136	fork.
		3137
		3138	The default mode of operation (for libev, with application help to detect
		3139	forks) is to duplicate all the state in the child, as would be expected
		3140	when I<either> the parent I<or> the child process continues.
		3141
		3142	When both processes want to continue using libev, then this is usually the
		3143	wrong result. In that case, usually one process (typically the parent) is
		3144	supposed to continue with all watchers in place as before, while the other
		3145	process typically wants to start fresh, i.e. without any active watchers.
		3146
		3147	The cleanest and most efficient way to achieve that with libev is to
		3148	simply create a new event loop, which of course will be "empty", and
		3149	use that for new watchers. This has the advantage of not touching more
		3150	memory than necessary, and thus avoiding the copy-on-write, and the
		3151	disadvantage of having to use multiple event loops (which do not support
		3152	signal watchers).
		3153
		3154	When this is not possible, or you want to use the default loop for
		3155	other reasons, then in the process that wants to start "fresh", call
		3156	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3157	Destroying the default loop will "orphan" (not stop) all registered
		3158	watchers, so you have to be careful not to execute code that modifies
		3159	those watchers. Note also that in that case, you have to re-register any
		3160	signal watchers.
		3161
		3162	=head3 Watcher-Specific Functions and Data Members
		3163
		3164	=over 4
		3165
		3166	=item ev_fork_init (ev_fork *, callback)
		3167
		3168	Initialises and configures the fork watcher - it has no parameters of any
		3169	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3170	really.
		3171
		3172	=back
		3173
		3174
		3175	=head2 C<ev_cleanup> - even the best things end
		3176
		3177	Cleanup watchers are called just before the event loop is being destroyed
		3178	by a call to C<ev_loop_destroy>.
		3179
		3180	While there is no guarantee that the event loop gets destroyed, cleanup
		3181	watchers provide a convenient method to install cleanup hooks for your
		3182	program, worker threads and so on - you just to make sure to destroy the
		3183	loop when you want them to be invoked.
		3184
		3185	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3186	all other watchers, they do not keep a reference to the event loop (which
		3187	makes a lot of sense if you think about it). Like all other watchers, you
		3188	can call libev functions in the callback, except C<ev_cleanup_start>.
		3189
		3190	=head3 Watcher-Specific Functions and Data Members
		3191
		3192	=over 4
		3193
		3194	=item ev_cleanup_init (ev_cleanup *, callback)
		3195
		3196	Initialises and configures the cleanup watcher - it has no parameters of
		3197	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3198	pointless, I assure you.
		3199
		3200	=back
		3201
		3202	Example: Register an atexit handler to destroy the default loop, so any
		3203	cleanup functions are called.
		3204
		3205	static void
		3206	program_exits (void)
		3207	{
		3208	ev_loop_destroy (EV_DEFAULT_UC);
		3209	}
		3210
		3211	...
		3212	atexit (program_exits);
		3213
		3214
		3215	=head2 C<ev_async> - how to wake up an event loop
		3216
		3217	In general, you cannot use an C<ev_run> from multiple threads or other
		3218	asynchronous sources such as signal handlers (as opposed to multiple event
		3219	loops - those are of course safe to use in different threads).
		3220
		3221	Sometimes, however, you need to wake up an event loop you do not control,
		3222	for example because it belongs to another thread. This is what C<ev_async>
		3223	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3224	it by calling C<ev_async_send>, which is thread- and signal safe.
		3225
		3226	This functionality is very similar to C<ev_signal> watchers, as signals,
		3227	too, are asynchronous in nature, and signals, too, will be compressed
		3228	(i.e. the number of callback invocations may be less than the number of
		3229	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3230	of "global async watchers" by using a watcher on an otherwise unused
		3231	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3232	even without knowing which loop owns the signal.
		3233
		3234	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3235	just the default loop.
		3236
		3237	=head3 Queueing
		3238
		3239	C<ev_async> does not support queueing of data in any way. The reason
		3240	is that the author does not know of a simple (or any) algorithm for a
		3241	multiple-writer-single-reader queue that works in all cases and doesn't
		3242	need elaborate support such as pthreads or unportable memory access
		3243	semantics.
		3244
		3245	That means that if you want to queue data, you have to provide your own
		3246	queue. But at least I can tell you how to implement locking around your
		3247	queue:
		3248
		3249	=over 4
		3250
		3251	=item queueing from a signal handler context
		3252
		3253	To implement race-free queueing, you simply add to the queue in the signal
		3254	handler but you block the signal handler in the watcher callback. Here is
		3255	an example that does that for some fictitious SIGUSR1 handler:
		3256
		3257	static ev_async mysig;
		3258
		3259	static void
		3260	sigusr1_handler (void)
		3261	{
		3262	sometype data;
		3263
		3264	// no locking etc.
		3265	queue_put (data);
		3266	ev_async_send (EV_DEFAULT_ &mysig);
		3267	}
		3268
		3269	static void
		3270	mysig_cb (EV_P_ ev_async *w, int revents)
		3271	{
		3272	sometype data;
		3273	sigset_t block, prev;
		3274
		3275	sigemptyset (&block);
		3276	sigaddset (&block, SIGUSR1);
		3277	sigprocmask (SIG_BLOCK, &block, &prev);
		3278
		3279	while (queue_get (&data))
		3280	process (data);
		3281
		3282	if (sigismember (&prev, SIGUSR1)
		3283	sigprocmask (SIG_UNBLOCK, &block, 0);
		3284	}
		3285
		3286	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3287	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3288	either...).
		3289
		3290	=item queueing from a thread context
		3291
		3292	The strategy for threads is different, as you cannot (easily) block
		3293	threads but you can easily preempt them, so to queue safely you need to
		3294	employ a traditional mutex lock, such as in this pthread example:
		3295
		3296	static ev_async mysig;
		3297	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3298
		3299	static void
		3300	otherthread (void)
		3301	{
		3302	// only need to lock the actual queueing operation
		3303	pthread_mutex_lock (&mymutex);
		3304	queue_put (data);
		3305	pthread_mutex_unlock (&mymutex);
		3306
		3307	ev_async_send (EV_DEFAULT_ &mysig);
		3308	}
		3309
		3310	static void
		3311	mysig_cb (EV_P_ ev_async *w, int revents)
		3312	{
		3313	pthread_mutex_lock (&mymutex);
		3314
		3315	while (queue_get (&data))
		3316	process (data);
		3317
		3318	pthread_mutex_unlock (&mymutex);
		3319	}
		3320
		3321	=back
		3322
		3323
		3324	=head3 Watcher-Specific Functions and Data Members
		3325
		3326	=over 4
		3327
		3328	=item ev_async_init (ev_async *, callback)
		3329
		3330	Initialises and configures the async watcher - it has no parameters of any
		3331	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3332	trust me.
		3333
		3334	=item ev_async_send (loop, ev_async *)
		3335
		3336	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3337	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3338	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3339	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3340	section below on what exactly this means).
		3341
		3342	Note that, as with other watchers in libev, multiple events might get
		3343	compressed into a single callback invocation (another way to look at this
		3344	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3345	reset when the event loop detects that).
		3346
		3347	This call incurs the overhead of a system call only once per event loop
		3348	iteration, so while the overhead might be noticeable, it doesn't apply to
		3349	repeated calls to C<ev_async_send> for the same event loop.
		3350
		3351	=item bool = ev_async_pending (ev_async *)
		3352
		3353	Returns a non-zero value when C<ev_async_send> has been called on the
		3354	watcher but the event has not yet been processed (or even noted) by the
		3355	event loop.
		3356
		3357	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3358	the loop iterates next and checks for the watcher to have become active,
		3359	it will reset the flag again. C<ev_async_pending> can be used to very
		3360	quickly check whether invoking the loop might be a good idea.
		3361
		3362	Not that this does I<not> check whether the watcher itself is pending,
		3363	only whether it has been requested to make this watcher pending: there
		3364	is a time window between the event loop checking and resetting the async
		3365	notification, and the callback being invoked.
		3366
		3367	=back
		3368
		3369
793	=head1 OTHER FUNCTIONS	3370	=head1 OTHER FUNCTIONS
794		3371
795	There are some other functions of possible interest. Described. Here. Now.	3372	There are some other functions of possible interest. Described. Here. Now.
796		3373
797	=over 4	3374	=over 4
798		3375
799	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3376	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
800		3377
801	This function combines a simple timer and an I/O watcher, calls your	3378	This function combines a simple timer and an I/O watcher, calls your
802	callback on whichever event happens first and automatically stop both	3379	callback on whichever event happens first and automatically stops both
803	watchers. This is useful if you want to wait for a single event on an fd	3380	watchers. This is useful if you want to wait for a single event on an fd
804	or timeout without having to allocate/configure/start/stop/free one or	3381	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	3382	more watchers yourself.
806		3383
807	If C<fd> is less than 0, then no I/O watcher will be started and events	3384	If C<fd> is less than 0, then no I/O watcher will be started and the
808	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3385	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
809	C<events> set will be craeted and started.	3386	the given C<fd> and C<events> set will be created and started.
810		3387
811	If C<timeout> is less than 0, then no timeout watcher will be	3388	If C<timeout> is less than 0, then no timeout watcher will be
812	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3389	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
813	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3390	repeat = 0) will be started. C<0> is a valid timeout.
814	dubious value.
815		3391
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3392	The callback has the type C<void (*cb)(int revents, void *arg)> and is
817	passed an C<revents> set like normal event callbacks (a combination of	3393	passed an C<revents> set like normal event callbacks (a combination of
818	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3394	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
819	value passed to C<ev_once>:	3395	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3396	a timeout and an io event at the same time - you probably should give io
		3397	events precedence.
820		3398
		3399	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3400
821	static void stdin_ready (int revents, void *arg)	3401	static void stdin_ready (int revents, void *arg)
822	{	3402	{
823	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;
825	else if (revents & EV_READ)	3403	if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	3404	/* stdin might have data for us, joy! */;
		3405	else if (revents & EV_TIMER)
		3406	/* doh, nothing entered */;
827	}	3407	}
828		3408
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3409	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830
831	=item ev_feed_event (loop, watcher, int events)
832
833	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).
836		3410
837	=item ev_feed_fd_event (loop, int fd, int revents)	3411	=item ev_feed_fd_event (loop, int fd, int revents)
838		3412
839	Feed an event on the given fd, as if a file descriptor backend detected	3413	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	3414	the given events it.
841		3415
842	=item ev_feed_signal_event (loop, int signum)	3416	=item ev_feed_signal_event (loop, int signum)
843		3417
844	Feed an event as if the given signal occured (loop must be the default loop!).	3418	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3419	which is async-safe.
845		3420
846	=back	3421	=back
		3422
		3423
		3424	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3425
		3426	This section explains some common idioms that are not immediately
		3427	obvious. Note that examples are sprinkled over the whole manual, and this
		3428	section only contains stuff that wouldn't fit anywhere else.
		3429
		3430	=over 4
		3431
		3432	=item Model/nested event loop invocations and exit conditions.
		3433
		3434	Often (especially in GUI toolkits) there are places where you have
		3435	I<modal> interaction, which is most easily implemented by recursively
		3436	invoking C<ev_run>.
		3437
		3438	This brings the problem of exiting - a callback might want to finish the
		3439	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3440	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3441	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3442	other combination: In these cases, C<ev_break> will not work alone.
		3443
		3444	The solution is to maintain "break this loop" variable for each C<ev_run>
		3445	invocation, and use a loop around C<ev_run> until the condition is
		3446	triggered, using C<EVRUN_ONCE>:
		3447
		3448	// main loop
		3449	int exit_main_loop = 0;
		3450
		3451	while (!exit_main_loop)
		3452	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3453
		3454	// in a model watcher
		3455	int exit_nested_loop = 0;
		3456
		3457	while (!exit_nested_loop)
		3458	ev_run (EV_A_ EVRUN_ONCE);
		3459
		3460	To exit from any of these loops, just set the corresponding exit variable:
		3461
		3462	// exit modal loop
		3463	exit_nested_loop = 1;
		3464
		3465	// exit main program, after modal loop is finished
		3466	exit_main_loop = 1;
		3467
		3468	// exit both
		3469	exit_main_loop = exit_nested_loop = 1;
		3470
		3471	=back
		3472
847		3473
848	=head1 LIBEVENT EMULATION	3474	=head1 LIBEVENT EMULATION
849		3475
850	Libev offers a compatibility emulation layer for libevent. It cannot	3476	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	3477	emulate the internals of libevent, so here are some usage hints:
852		3478
853	=over 4	3479	=over 4
		3480
		3481	=item * Only the libevent-1.4.1-beta API is being emulated.
		3482
		3483	This was the newest libevent version available when libev was implemented,
		3484	and is still mostly unchanged in 2010.
854		3485
855	=item * Use it by including <event.h>, as usual.	3486	=item * Use it by including <event.h>, as usual.
856		3487
857	=item * The following members are fully supported: ev_base, ev_callback,	3488	=item * The following members are fully supported: ev_base, ev_callback,
858	ev_arg, ev_fd, ev_res, ev_events.	3489	ev_arg, ev_fd, ev_res, ev_events.
…		…
863		3494
864	=item * Priorities are not currently supported. Initialising priorities	3495	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	3496	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	3497	is an ev_pri field.
867		3498
		3499	=item * In libevent, the last base created gets the signals, in libev, the
		3500	base that registered the signal gets the signals.
		3501
868	=item * Other members are not supported.	3502	=item * Other members are not supported.
869		3503
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3504	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	3505	to use the libev header file and library.
872		3506
873	=back	3507	=back
874		3508
875	=head1 C++ SUPPORT	3509	=head1 C++ SUPPORT
876		3510
877	TBD.	3511	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3512	you to use some convenience methods to start/stop watchers and also change
		3513	the callback model to a model using method callbacks on objects.
		3514
		3515	To use it,
		3516
		3517	#include <ev++.h>
		3518
		3519	This automatically includes F<ev.h> and puts all of its definitions (many
		3520	of them macros) into the global namespace. All C++ specific things are
		3521	put into the C<ev> namespace. It should support all the same embedding
		3522	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3523
		3524	Care has been taken to keep the overhead low. The only data member the C++
		3525	classes add (compared to plain C-style watchers) is the event loop pointer
		3526	that the watcher is associated with (or no additional members at all if
		3527	you disable C<EV_MULTIPLICITY> when embedding libev).
		3528
		3529	Currently, functions, static and non-static member functions and classes
		3530	with C<operator ()> can be used as callbacks. Other types should be easy
		3531	to add as long as they only need one additional pointer for context. If
		3532	you need support for other types of functors please contact the author
		3533	(preferably after implementing it).
		3534
		3535	Here is a list of things available in the C<ev> namespace:
		3536
		3537	=over 4
		3538
		3539	=item C<ev::READ>, C<ev::WRITE> etc.
		3540
		3541	These are just enum values with the same values as the C<EV_READ> etc.
		3542	macros from F<ev.h>.
		3543
		3544	=item C<ev::tstamp>, C<ev::now>
		3545
		3546	Aliases to the same types/functions as with the C<ev_> prefix.
		3547
		3548	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3549
		3550	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3551	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3552	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3553	defines by many implementations.
		3554
		3555	All of those classes have these methods:
		3556
		3557	=over 4
		3558
		3559	=item ev::TYPE::TYPE ()
		3560
		3561	=item ev::TYPE::TYPE (loop)
		3562
		3563	=item ev::TYPE::~TYPE
		3564
		3565	The constructor (optionally) takes an event loop to associate the watcher
		3566	with. If it is omitted, it will use C<EV_DEFAULT>.
		3567
		3568	The constructor calls C<ev_init> for you, which means you have to call the
		3569	C<set> method before starting it.
		3570
		3571	It will not set a callback, however: You have to call the templated C<set>
		3572	method to set a callback before you can start the watcher.
		3573
		3574	(The reason why you have to use a method is a limitation in C++ which does
		3575	not allow explicit template arguments for constructors).
		3576
		3577	The destructor automatically stops the watcher if it is active.
		3578
		3579	=item w->set<class, &class::method> (object *)
		3580
		3581	This method sets the callback method to call. The method has to have a
		3582	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3583	first argument and the C<revents> as second. The object must be given as
		3584	parameter and is stored in the C<data> member of the watcher.
		3585
		3586	This method synthesizes efficient thunking code to call your method from
		3587	the C callback that libev requires. If your compiler can inline your
		3588	callback (i.e. it is visible to it at the place of the C<set> call and
		3589	your compiler is good :), then the method will be fully inlined into the
		3590	thunking function, making it as fast as a direct C callback.
		3591
		3592	Example: simple class declaration and watcher initialisation
		3593
		3594	struct myclass
		3595	{
		3596	void io_cb (ev::io &w, int revents) { }
		3597	}
		3598
		3599	myclass obj;
		3600	ev::io iow;
		3601	iow.set <myclass, &myclass::io_cb> (&obj);
		3602
		3603	=item w->set (object *)
		3604
		3605	This is a variation of a method callback - leaving out the method to call
		3606	will default the method to C<operator ()>, which makes it possible to use
		3607	functor objects without having to manually specify the C<operator ()> all
		3608	the time. Incidentally, you can then also leave out the template argument
		3609	list.
		3610
		3611	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3612	int revents)>.
		3613
		3614	See the method-C<set> above for more details.
		3615
		3616	Example: use a functor object as callback.
		3617
		3618	struct myfunctor
		3619	{
		3620	void operator() (ev::io &w, int revents)
		3621	{
		3622	...
		3623	}
		3624	}
		3625
		3626	myfunctor f;
		3627
		3628	ev::io w;
		3629	w.set (&f);
		3630
		3631	=item w->set<function> (void *data = 0)
		3632
		3633	Also sets a callback, but uses a static method or plain function as
		3634	callback. The optional C<data> argument will be stored in the watcher's
		3635	C<data> member and is free for you to use.
		3636
		3637	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3638
		3639	See the method-C<set> above for more details.
		3640
		3641	Example: Use a plain function as callback.
		3642
		3643	static void io_cb (ev::io &w, int revents) { }
		3644	iow.set <io_cb> ();
		3645
		3646	=item w->set (loop)
		3647
		3648	Associates a different C<struct ev_loop> with this watcher. You can only
		3649	do this when the watcher is inactive (and not pending either).
		3650
		3651	=item w->set ([arguments])
		3652
		3653	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
		3654	method or a suitable start method must be called at least once. Unlike the
		3655	C counterpart, an active watcher gets automatically stopped and restarted
		3656	when reconfiguring it with this method.
		3657
		3658	=item w->start ()
		3659
		3660	Starts the watcher. Note that there is no C<loop> argument, as the
		3661	constructor already stores the event loop.
		3662
		3663	=item w->start ([arguments])
		3664
		3665	Instead of calling C<set> and C<start> methods separately, it is often
		3666	convenient to wrap them in one call. Uses the same type of arguments as
		3667	the configure C<set> method of the watcher.
		3668
		3669	=item w->stop ()
		3670
		3671	Stops the watcher if it is active. Again, no C<loop> argument.
		3672
		3673	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3674
		3675	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3676	C<ev_TYPE_again> function.
		3677
		3678	=item w->sweep () (C<ev::embed> only)
		3679
		3680	Invokes C<ev_embed_sweep>.
		3681
		3682	=item w->update () (C<ev::stat> only)
		3683
		3684	Invokes C<ev_stat_stat>.
		3685
		3686	=back
		3687
		3688	=back
		3689
		3690	Example: Define a class with two I/O and idle watchers, start the I/O
		3691	watchers in the constructor.
		3692
		3693	class myclass
		3694	{
		3695	ev::io io ; void io_cb (ev::io &w, int revents);
		3696	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
		3697	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3698
		3699	myclass (int fd)
		3700	{
		3701	io .set <myclass, &myclass::io_cb > (this);
		3702	io2 .set <myclass, &myclass::io2_cb > (this);
		3703	idle.set <myclass, &myclass::idle_cb> (this);
		3704
		3705	io.set (fd, ev::WRITE); // configure the watcher
		3706	io.start (); // start it whenever convenient
		3707
		3708	io2.start (fd, ev::READ); // set + start in one call
		3709	}
		3710	};
		3711
		3712
		3713	=head1 OTHER LANGUAGE BINDINGS
		3714
		3715	Libev does not offer other language bindings itself, but bindings for a
		3716	number of languages exist in the form of third-party packages. If you know
		3717	any interesting language binding in addition to the ones listed here, drop
		3718	me a note.
		3719
		3720	=over 4
		3721
		3722	=item Perl
		3723
		3724	The EV module implements the full libev API and is actually used to test
		3725	libev. EV is developed together with libev. Apart from the EV core module,
		3726	there are additional modules that implement libev-compatible interfaces
		3727	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3728	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3729	and C<EV::Glib>).
		3730
		3731	It can be found and installed via CPAN, its homepage is at
		3732	L<http://software.schmorp.de/pkg/EV>.
		3733
		3734	=item Python
		3735
		3736	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3737	seems to be quite complete and well-documented.
		3738
		3739	=item Ruby
		3740
		3741	Tony Arcieri has written a ruby extension that offers access to a subset
		3742	of the libev API and adds file handle abstractions, asynchronous DNS and
		3743	more on top of it. It can be found via gem servers. Its homepage is at
		3744	L<http://rev.rubyforge.org/>.
		3745
		3746	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3747	makes rev work even on mingw.
		3748
		3749	=item Haskell
		3750
		3751	A haskell binding to libev is available at
		3752	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3753
		3754	=item D
		3755
		3756	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3757	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3758
		3759	=item Ocaml
		3760
		3761	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3762	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3763
		3764	=item Lua
		3765
		3766	Brian Maher has written a partial interface to libev for lua (at the
		3767	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3768	L<http://github.com/brimworks/lua-ev>.
		3769
		3770	=back
		3771
		3772
		3773	=head1 MACRO MAGIC
		3774
		3775	Libev can be compiled with a variety of options, the most fundamental
		3776	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3777	functions and callbacks have an initial C<struct ev_loop *> argument.
		3778
		3779	To make it easier to write programs that cope with either variant, the
		3780	following macros are defined:
		3781
		3782	=over 4
		3783
		3784	=item C<EV_A>, C<EV_A_>
		3785
		3786	This provides the loop I<argument> for functions, if one is required ("ev
		3787	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3788	C<EV_A_> is used when other arguments are following. Example:
		3789
		3790	ev_unref (EV_A);
		3791	ev_timer_add (EV_A_ watcher);
		3792	ev_run (EV_A_ 0);
		3793
		3794	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3795	which is often provided by the following macro.
		3796
		3797	=item C<EV_P>, C<EV_P_>
		3798
		3799	This provides the loop I<parameter> for functions, if one is required ("ev
		3800	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3801	C<EV_P_> is used when other parameters are following. Example:
		3802
		3803	// this is how ev_unref is being declared
		3804	static void ev_unref (EV_P);
		3805
		3806	// this is how you can declare your typical callback
		3807	static void cb (EV_P_ ev_timer *w, int revents)
		3808
		3809	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3810	suitable for use with C<EV_A>.
		3811
		3812	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3813
		3814	Similar to the other two macros, this gives you the value of the default
		3815	loop, if multiple loops are supported ("ev loop default").
		3816
		3817	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3818
		3819	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3820	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3821	is undefined when the default loop has not been initialised by a previous
		3822	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3823
		3824	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3825	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3826
		3827	=back
		3828
		3829	Example: Declare and initialise a check watcher, utilising the above
		3830	macros so it will work regardless of whether multiple loops are supported
		3831	or not.
		3832
		3833	static void
		3834	check_cb (EV_P_ ev_timer *w, int revents)
		3835	{
		3836	ev_check_stop (EV_A_ w);
		3837	}
		3838
		3839	ev_check check;
		3840	ev_check_init (&check, check_cb);
		3841	ev_check_start (EV_DEFAULT_ &check);
		3842	ev_run (EV_DEFAULT_ 0);
		3843
		3844	=head1 EMBEDDING
		3845
		3846	Libev can (and often is) directly embedded into host
		3847	applications. Examples of applications that embed it include the Deliantra
		3848	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3849	and rxvt-unicode.
		3850
		3851	The goal is to enable you to just copy the necessary files into your
		3852	source directory without having to change even a single line in them, so
		3853	you can easily upgrade by simply copying (or having a checked-out copy of
		3854	libev somewhere in your source tree).
		3855
		3856	=head2 FILESETS
		3857
		3858	Depending on what features you need you need to include one or more sets of files
		3859	in your application.
		3860
		3861	=head3 CORE EVENT LOOP
		3862
		3863	To include only the libev core (all the C<ev_*> functions), with manual
		3864	configuration (no autoconf):
		3865
		3866	#define EV_STANDALONE 1
		3867	#include "ev.c"
		3868
		3869	This will automatically include F<ev.h>, too, and should be done in a
		3870	single C source file only to provide the function implementations. To use
		3871	it, do the same for F<ev.h> in all files wishing to use this API (best
		3872	done by writing a wrapper around F<ev.h> that you can include instead and
		3873	where you can put other configuration options):
		3874
		3875	#define EV_STANDALONE 1
		3876	#include "ev.h"
		3877
		3878	Both header files and implementation files can be compiled with a C++
		3879	compiler (at least, that's a stated goal, and breakage will be treated
		3880	as a bug).
		3881
		3882	You need the following files in your source tree, or in a directory
		3883	in your include path (e.g. in libev/ when using -Ilibev):
		3884
		3885	ev.h
		3886	ev.c
		3887	ev_vars.h
		3888	ev_wrap.h
		3889
		3890	ev_win32.c required on win32 platforms only
		3891
		3892	ev_select.c only when select backend is enabled (which is enabled by default)
		3893	ev_poll.c only when poll backend is enabled (disabled by default)
		3894	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3895	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3896	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3897
		3898	F<ev.c> includes the backend files directly when enabled, so you only need
		3899	to compile this single file.
		3900
		3901	=head3 LIBEVENT COMPATIBILITY API
		3902
		3903	To include the libevent compatibility API, also include:
		3904
		3905	#include "event.c"
		3906
		3907	in the file including F<ev.c>, and:
		3908
		3909	#include "event.h"
		3910
		3911	in the files that want to use the libevent API. This also includes F<ev.h>.
		3912
		3913	You need the following additional files for this:
		3914
		3915	event.h
		3916	event.c
		3917
		3918	=head3 AUTOCONF SUPPORT
		3919
		3920	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3921	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3922	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3923	include F<config.h> and configure itself accordingly.
		3924
		3925	For this of course you need the m4 file:
		3926
		3927	libev.m4
		3928
		3929	=head2 PREPROCESSOR SYMBOLS/MACROS
		3930
		3931	Libev can be configured via a variety of preprocessor symbols you have to
		3932	define before including (or compiling) any of its files. The default in
		3933	the absence of autoconf is documented for every option.
		3934
		3935	Symbols marked with "(h)" do not change the ABI, and can have different
		3936	values when compiling libev vs. including F<ev.h>, so it is permissible
		3937	to redefine them before including F<ev.h> without breaking compatibility
		3938	to a compiled library. All other symbols change the ABI, which means all
		3939	users of libev and the libev code itself must be compiled with compatible
		3940	settings.
		3941
		3942	=over 4
		3943
		3944	=item EV_COMPAT3 (h)
		3945
		3946	Backwards compatibility is a major concern for libev. This is why this
		3947	release of libev comes with wrappers for the functions and symbols that
		3948	have been renamed between libev version 3 and 4.
		3949
		3950	You can disable these wrappers (to test compatibility with future
		3951	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3952	sources. This has the additional advantage that you can drop the C<struct>
		3953	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3954	typedef in that case.
		3955
		3956	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3957	and in some even more future version the compatibility code will be
		3958	removed completely.
		3959
		3960	=item EV_STANDALONE (h)
		3961
		3962	Must always be C<1> if you do not use autoconf configuration, which
		3963	keeps libev from including F<config.h>, and it also defines dummy
		3964	implementations for some libevent functions (such as logging, which is not
		3965	supported). It will also not define any of the structs usually found in
		3966	F<event.h> that are not directly supported by the libev core alone.
		3967
		3968	In standalone mode, libev will still try to automatically deduce the
		3969	configuration, but has to be more conservative.
		3970
		3971	=item EV_USE_MONOTONIC
		3972
		3973	If defined to be C<1>, libev will try to detect the availability of the
		3974	monotonic clock option at both compile time and runtime. Otherwise no
		3975	use of the monotonic clock option will be attempted. If you enable this,
		3976	you usually have to link against librt or something similar. Enabling it
		3977	when the functionality isn't available is safe, though, although you have
		3978	to make sure you link against any libraries where the C<clock_gettime>
		3979	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3980
		3981	=item EV_USE_REALTIME
		3982
		3983	If defined to be C<1>, libev will try to detect the availability of the
		3984	real-time clock option at compile time (and assume its availability
		3985	at runtime if successful). Otherwise no use of the real-time clock
		3986	option will be attempted. This effectively replaces C<gettimeofday>
		3987	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3988	correctness. See the note about libraries in the description of
		3989	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3990	C<EV_USE_CLOCK_SYSCALL>.
		3991
		3992	=item EV_USE_CLOCK_SYSCALL
		3993
		3994	If defined to be C<1>, libev will try to use a direct syscall instead
		3995	of calling the system-provided C<clock_gettime> function. This option
		3996	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3997	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3998	programs needlessly. Using a direct syscall is slightly slower (in
		3999	theory), because no optimised vdso implementation can be used, but avoids
		4000	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4001	higher, as it simplifies linking (no need for C<-lrt>).
		4002
		4003	=item EV_USE_NANOSLEEP
		4004
		4005	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4006	and will use it for delays. Otherwise it will use C<select ()>.
		4007
		4008	=item EV_USE_EVENTFD
		4009
		4010	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4011	available and will probe for kernel support at runtime. This will improve
		4012	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4013	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4014	2.7 or newer, otherwise disabled.
		4015
		4016	=item EV_USE_SELECT
		4017
		4018	If undefined or defined to be C<1>, libev will compile in support for the
		4019	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4020	other method takes over, select will be it. Otherwise the select backend
		4021	will not be compiled in.
		4022
		4023	=item EV_SELECT_USE_FD_SET
		4024
		4025	If defined to C<1>, then the select backend will use the system C<fd_set>
		4026	structure. This is useful if libev doesn't compile due to a missing
		4027	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4028	on exotic systems. This usually limits the range of file descriptors to
		4029	some low limit such as 1024 or might have other limitations (winsocket
		4030	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4031	configures the maximum size of the C<fd_set>.
		4032
		4033	=item EV_SELECT_IS_WINSOCKET
		4034
		4035	When defined to C<1>, the select backend will assume that
		4036	select/socket/connect etc. don't understand file descriptors but
		4037	wants osf handles on win32 (this is the case when the select to
		4038	be used is the winsock select). This means that it will call
		4039	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4040	it is assumed that all these functions actually work on fds, even
		4041	on win32. Should not be defined on non-win32 platforms.
		4042
		4043	=item EV_FD_TO_WIN32_HANDLE(fd)
		4044
		4045	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4046	file descriptors to socket handles. When not defining this symbol (the
		4047	default), then libev will call C<_get_osfhandle>, which is usually
		4048	correct. In some cases, programs use their own file descriptor management,
		4049	in which case they can provide this function to map fds to socket handles.
		4050
		4051	=item EV_WIN32_HANDLE_TO_FD(handle)
		4052
		4053	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4054	using the standard C<_open_osfhandle> function. For programs implementing
		4055	their own fd to handle mapping, overwriting this function makes it easier
		4056	to do so. This can be done by defining this macro to an appropriate value.
		4057
		4058	=item EV_WIN32_CLOSE_FD(fd)
		4059
		4060	If programs implement their own fd to handle mapping on win32, then this
		4061	macro can be used to override the C<close> function, useful to unregister
		4062	file descriptors again. Note that the replacement function has to close
		4063	the underlying OS handle.
		4064
		4065	=item EV_USE_POLL
		4066
		4067	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4068	backend. Otherwise it will be enabled on non-win32 platforms. It
		4069	takes precedence over select.
		4070
		4071	=item EV_USE_EPOLL
		4072
		4073	If defined to be C<1>, libev will compile in support for the Linux
		4074	C<epoll>(7) backend. Its availability will be detected at runtime,
		4075	otherwise another method will be used as fallback. This is the preferred
		4076	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4077	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4078
		4079	=item EV_USE_KQUEUE
		4080
		4081	If defined to be C<1>, libev will compile in support for the BSD style
		4082	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4083	otherwise another method will be used as fallback. This is the preferred
		4084	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4085	supports some types of fds correctly (the only platform we found that
		4086	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4087	not be used unless explicitly requested. The best way to use it is to find
		4088	out whether kqueue supports your type of fd properly and use an embedded
		4089	kqueue loop.
		4090
		4091	=item EV_USE_PORT
		4092
		4093	If defined to be C<1>, libev will compile in support for the Solaris
		4094	10 port style backend. Its availability will be detected at runtime,
		4095	otherwise another method will be used as fallback. This is the preferred
		4096	backend for Solaris 10 systems.
		4097
		4098	=item EV_USE_DEVPOLL
		4099
		4100	Reserved for future expansion, works like the USE symbols above.
		4101
		4102	=item EV_USE_INOTIFY
		4103
		4104	If defined to be C<1>, libev will compile in support for the Linux inotify
		4105	interface to speed up C<ev_stat> watchers. Its actual availability will
		4106	be detected at runtime. If undefined, it will be enabled if the headers
		4107	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4108
		4109	=item EV_ATOMIC_T
		4110
		4111	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4112	access is atomic with respect to other threads or signal contexts. No such
		4113	type is easily found in the C language, so you can provide your own type
		4114	that you know is safe for your purposes. It is used both for signal handler "locking"
		4115	as well as for signal and thread safety in C<ev_async> watchers.
		4116
		4117	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4118	(from F<signal.h>), which is usually good enough on most platforms.
		4119
		4120	=item EV_H (h)
		4121
		4122	The name of the F<ev.h> header file used to include it. The default if
		4123	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4124	used to virtually rename the F<ev.h> header file in case of conflicts.
		4125
		4126	=item EV_CONFIG_H (h)
		4127
		4128	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4129	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4130	C<EV_H>, above.
		4131
		4132	=item EV_EVENT_H (h)
		4133
		4134	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4135	of how the F<event.h> header can be found, the default is C<"event.h">.
		4136
		4137	=item EV_PROTOTYPES (h)
		4138
		4139	If defined to be C<0>, then F<ev.h> will not define any function
		4140	prototypes, but still define all the structs and other symbols. This is
		4141	occasionally useful if you want to provide your own wrapper functions
		4142	around libev functions.
		4143
		4144	=item EV_MULTIPLICITY
		4145
		4146	If undefined or defined to C<1>, then all event-loop-specific functions
		4147	will have the C<struct ev_loop *> as first argument, and you can create
		4148	additional independent event loops. Otherwise there will be no support
		4149	for multiple event loops and there is no first event loop pointer
		4150	argument. Instead, all functions act on the single default loop.
		4151
		4152	=item EV_MINPRI
		4153
		4154	=item EV_MAXPRI
		4155
		4156	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4157	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4158	provide for more priorities by overriding those symbols (usually defined
		4159	to be C<-2> and C<2>, respectively).
		4160
		4161	When doing priority-based operations, libev usually has to linearly search
		4162	all the priorities, so having many of them (hundreds) uses a lot of space
		4163	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4164	fine.
		4165
		4166	If your embedding application does not need any priorities, defining these
		4167	both to C<0> will save some memory and CPU.
		4168
		4169	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4170	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4171	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4172
		4173	If undefined or defined to be C<1> (and the platform supports it), then
		4174	the respective watcher type is supported. If defined to be C<0>, then it
		4175	is not. Disabling watcher types mainly saves code size.
		4176
		4177	=item EV_FEATURES
		4178
		4179	If you need to shave off some kilobytes of code at the expense of some
		4180	speed (but with the full API), you can define this symbol to request
		4181	certain subsets of functionality. The default is to enable all features
		4182	that can be enabled on the platform.
		4183
		4184	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4185	with some broad features you want) and then selectively re-enable
		4186	additional parts you want, for example if you want everything minimal,
		4187	but multiple event loop support, async and child watchers and the poll
		4188	backend, use this:
		4189
		4190	#define EV_FEATURES 0
		4191	#define EV_MULTIPLICITY 1
		4192	#define EV_USE_POLL 1
		4193	#define EV_CHILD_ENABLE 1
		4194	#define EV_ASYNC_ENABLE 1
		4195
		4196	The actual value is a bitset, it can be a combination of the following
		4197	values:
		4198
		4199	=over 4
		4200
		4201	=item C<1> - faster/larger code
		4202
		4203	Use larger code to speed up some operations.
		4204
		4205	Currently this is used to override some inlining decisions (enlarging the
		4206	code size by roughly 30% on amd64).
		4207
		4208	When optimising for size, use of compiler flags such as C<-Os> with
		4209	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4210	assertions.
		4211
		4212	=item C<2> - faster/larger data structures
		4213
		4214	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4215	hash table sizes and so on. This will usually further increase code size
		4216	and can additionally have an effect on the size of data structures at
		4217	runtime.
		4218
		4219	=item C<4> - full API configuration
		4220
		4221	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4222	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4223
		4224	=item C<8> - full API
		4225
		4226	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4227	details on which parts of the API are still available without this
		4228	feature, and do not complain if this subset changes over time.
		4229
		4230	=item C<16> - enable all optional watcher types
		4231
		4232	Enables all optional watcher types. If you want to selectively enable
		4233	only some watcher types other than I/O and timers (e.g. prepare,
		4234	embed, async, child...) you can enable them manually by defining
		4235	C<EV_watchertype_ENABLE> to C<1> instead.
		4236
		4237	=item C<32> - enable all backends
		4238
		4239	This enables all backends - without this feature, you need to enable at
		4240	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4241
		4242	=item C<64> - enable OS-specific "helper" APIs
		4243
		4244	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4245	default.
		4246
		4247	=back
		4248
		4249	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4250	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4251	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4252	watchers, timers and monotonic clock support.
		4253
		4254	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4255	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4256	your program might be left out as well - a binary starting a timer and an
		4257	I/O watcher then might come out at only 5Kb.
		4258
		4259	=item EV_AVOID_STDIO
		4260
		4261	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4262	functions (printf, scanf, perror etc.). This will increase the code size
		4263	somewhat, but if your program doesn't otherwise depend on stdio and your
		4264	libc allows it, this avoids linking in the stdio library which is quite
		4265	big.
		4266
		4267	Note that error messages might become less precise when this option is
		4268	enabled.
		4269
		4270	=item EV_NSIG
		4271
		4272	The highest supported signal number, +1 (or, the number of
		4273	signals): Normally, libev tries to deduce the maximum number of signals
		4274	automatically, but sometimes this fails, in which case it can be
		4275	specified. Also, using a lower number than detected (C<32> should be
		4276	good for about any system in existence) can save some memory, as libev
		4277	statically allocates some 12-24 bytes per signal number.
		4278
		4279	=item EV_PID_HASHSIZE
		4280
		4281	C<ev_child> watchers use a small hash table to distribute workload by
		4282	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4283	usually more than enough. If you need to manage thousands of children you
		4284	might want to increase this value (I<must> be a power of two).
		4285
		4286	=item EV_INOTIFY_HASHSIZE
		4287
		4288	C<ev_stat> watchers use a small hash table to distribute workload by
		4289	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4290	disabled), usually more than enough. If you need to manage thousands of
		4291	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4292	power of two).
		4293
		4294	=item EV_USE_4HEAP
		4295
		4296	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4297	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4298	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4299	faster performance with many (thousands) of watchers.
		4300
		4301	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4302	will be C<0>.
		4303
		4304	=item EV_HEAP_CACHE_AT
		4305
		4306	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4307	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4308	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4309	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4310	but avoids random read accesses on heap changes. This improves performance
		4311	noticeably with many (hundreds) of watchers.
		4312
		4313	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4314	will be C<0>.
		4315
		4316	=item EV_VERIFY
		4317
		4318	Controls how much internal verification (see C<ev_verify ()>) will
		4319	be done: If set to C<0>, no internal verification code will be compiled
		4320	in. If set to C<1>, then verification code will be compiled in, but not
		4321	called. If set to C<2>, then the internal verification code will be
		4322	called once per loop, which can slow down libev. If set to C<3>, then the
		4323	verification code will be called very frequently, which will slow down
		4324	libev considerably.
		4325
		4326	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4327	will be C<0>.
		4328
		4329	=item EV_COMMON
		4330
		4331	By default, all watchers have a C<void *data> member. By redefining
		4332	this macro to something else you can include more and other types of
		4333	members. You have to define it each time you include one of the files,
		4334	though, and it must be identical each time.
		4335
		4336	For example, the perl EV module uses something like this:
		4337
		4338	#define EV_COMMON \
		4339	SV *self; /* contains this struct */ \
		4340	SV *cb_sv, *fh /* note no trailing ";" */
		4341
		4342	=item EV_CB_DECLARE (type)
		4343
		4344	=item EV_CB_INVOKE (watcher, revents)
		4345
		4346	=item ev_set_cb (ev, cb)
		4347
		4348	Can be used to change the callback member declaration in each watcher,
		4349	and the way callbacks are invoked and set. Must expand to a struct member
		4350	definition and a statement, respectively. See the F<ev.h> header file for
		4351	their default definitions. One possible use for overriding these is to
		4352	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4353	method calls instead of plain function calls in C++.
		4354
		4355	=back
		4356
		4357	=head2 EXPORTED API SYMBOLS
		4358
		4359	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4360	exported symbols, you can use the provided F<Symbol.*> files which list
		4361	all public symbols, one per line:
		4362
		4363	Symbols.ev for libev proper
		4364	Symbols.event for the libevent emulation
		4365
		4366	This can also be used to rename all public symbols to avoid clashes with
		4367	multiple versions of libev linked together (which is obviously bad in
		4368	itself, but sometimes it is inconvenient to avoid this).
		4369
		4370	A sed command like this will create wrapper C<#define>'s that you need to
		4371	include before including F<ev.h>:
		4372
		4373	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4374
		4375	This would create a file F<wrap.h> which essentially looks like this:
		4376
		4377	#define ev_backend myprefix_ev_backend
		4378	#define ev_check_start myprefix_ev_check_start
		4379	#define ev_check_stop myprefix_ev_check_stop
		4380	...
		4381
		4382	=head2 EXAMPLES
		4383
		4384	For a real-world example of a program the includes libev
		4385	verbatim, you can have a look at the EV perl module
		4386	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4387	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4388	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4389	will be compiled. It is pretty complex because it provides its own header
		4390	file.
		4391
		4392	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4393	that everybody includes and which overrides some configure choices:
		4394
		4395	#define EV_FEATURES 8
		4396	#define EV_USE_SELECT 1
		4397	#define EV_PREPARE_ENABLE 1
		4398	#define EV_IDLE_ENABLE 1
		4399	#define EV_SIGNAL_ENABLE 1
		4400	#define EV_CHILD_ENABLE 1
		4401	#define EV_USE_STDEXCEPT 0
		4402	#define EV_CONFIG_H <config.h>
		4403
		4404	#include "ev++.h"
		4405
		4406	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4407
		4408	#include "ev_cpp.h"
		4409	#include "ev.c"
		4410
		4411	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		4412
		4413	=head2 THREADS AND COROUTINES
		4414
		4415	=head3 THREADS
		4416
		4417	All libev functions are reentrant and thread-safe unless explicitly
		4418	documented otherwise, but libev implements no locking itself. This means
		4419	that you can use as many loops as you want in parallel, as long as there
		4420	are no concurrent calls into any libev function with the same loop
		4421	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4422	of course): libev guarantees that different event loops share no data
		4423	structures that need any locking.
		4424
		4425	Or to put it differently: calls with different loop parameters can be done
		4426	concurrently from multiple threads, calls with the same loop parameter
		4427	must be done serially (but can be done from different threads, as long as
		4428	only one thread ever is inside a call at any point in time, e.g. by using
		4429	a mutex per loop).
		4430
		4431	Specifically to support threads (and signal handlers), libev implements
		4432	so-called C<ev_async> watchers, which allow some limited form of
		4433	concurrency on the same event loop, namely waking it up "from the
		4434	outside".
		4435
		4436	If you want to know which design (one loop, locking, or multiple loops
		4437	without or something else still) is best for your problem, then I cannot
		4438	help you, but here is some generic advice:
		4439
		4440	=over 4
		4441
		4442	=item * most applications have a main thread: use the default libev loop
		4443	in that thread, or create a separate thread running only the default loop.
		4444
		4445	This helps integrating other libraries or software modules that use libev
		4446	themselves and don't care/know about threading.
		4447
		4448	=item * one loop per thread is usually a good model.
		4449
		4450	Doing this is almost never wrong, sometimes a better-performance model
		4451	exists, but it is always a good start.
		4452
		4453	=item * other models exist, such as the leader/follower pattern, where one
		4454	loop is handed through multiple threads in a kind of round-robin fashion.
		4455
		4456	Choosing a model is hard - look around, learn, know that usually you can do
		4457	better than you currently do :-)
		4458
		4459	=item * often you need to talk to some other thread which blocks in the
		4460	event loop.
		4461
		4462	C<ev_async> watchers can be used to wake them up from other threads safely
		4463	(or from signal contexts...).
		4464
		4465	An example use would be to communicate signals or other events that only
		4466	work in the default loop by registering the signal watcher with the
		4467	default loop and triggering an C<ev_async> watcher from the default loop
		4468	watcher callback into the event loop interested in the signal.
		4469
		4470	=back
		4471
		4472	=head4 THREAD LOCKING EXAMPLE
		4473
		4474	Here is a fictitious example of how to run an event loop in a different
		4475	thread than where callbacks are being invoked and watchers are
		4476	created/added/removed.
		4477
		4478	For a real-world example, see the C<EV::Loop::Async> perl module,
		4479	which uses exactly this technique (which is suited for many high-level
		4480	languages).
		4481
		4482	The example uses a pthread mutex to protect the loop data, a condition
		4483	variable to wait for callback invocations, an async watcher to notify the
		4484	event loop thread and an unspecified mechanism to wake up the main thread.
		4485
		4486	First, you need to associate some data with the event loop:
		4487
		4488	typedef struct {
		4489	mutex_t lock; /* global loop lock */
		4490	ev_async async_w;
		4491	thread_t tid;
		4492	cond_t invoke_cv;
		4493	} userdata;
		4494
		4495	void prepare_loop (EV_P)
		4496	{
		4497	// for simplicity, we use a static userdata struct.
		4498	static userdata u;
		4499
		4500	ev_async_init (&u->async_w, async_cb);
		4501	ev_async_start (EV_A_ &u->async_w);
		4502
		4503	pthread_mutex_init (&u->lock, 0);
		4504	pthread_cond_init (&u->invoke_cv, 0);
		4505
		4506	// now associate this with the loop
		4507	ev_set_userdata (EV_A_ u);
		4508	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4509	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4510
		4511	// then create the thread running ev_loop
		4512	pthread_create (&u->tid, 0, l_run, EV_A);
		4513	}
		4514
		4515	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4516	solely to wake up the event loop so it takes notice of any new watchers
		4517	that might have been added:
		4518
		4519	static void
		4520	async_cb (EV_P_ ev_async *w, int revents)
		4521	{
		4522	// just used for the side effects
		4523	}
		4524
		4525	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4526	protecting the loop data, respectively.
		4527
		4528	static void
		4529	l_release (EV_P)
		4530	{
		4531	userdata *u = ev_userdata (EV_A);
		4532	pthread_mutex_unlock (&u->lock);
		4533	}
		4534
		4535	static void
		4536	l_acquire (EV_P)
		4537	{
		4538	userdata *u = ev_userdata (EV_A);
		4539	pthread_mutex_lock (&u->lock);
		4540	}
		4541
		4542	The event loop thread first acquires the mutex, and then jumps straight
		4543	into C<ev_run>:
		4544
		4545	void *
		4546	l_run (void *thr_arg)
		4547	{
		4548	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4549
		4550	l_acquire (EV_A);
		4551	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4552	ev_run (EV_A_ 0);
		4553	l_release (EV_A);
		4554
		4555	return 0;
		4556	}
		4557
		4558	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4559	signal the main thread via some unspecified mechanism (signals? pipe
		4560	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4561	have been called (in a while loop because a) spurious wakeups are possible
		4562	and b) skipping inter-thread-communication when there are no pending
		4563	watchers is very beneficial):
		4564
		4565	static void
		4566	l_invoke (EV_P)
		4567	{
		4568	userdata *u = ev_userdata (EV_A);
		4569
		4570	while (ev_pending_count (EV_A))
		4571	{
		4572	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4573	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4574	}
		4575	}
		4576
		4577	Now, whenever the main thread gets told to invoke pending watchers, it
		4578	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4579	thread to continue:
		4580
		4581	static void
		4582	real_invoke_pending (EV_P)
		4583	{
		4584	userdata *u = ev_userdata (EV_A);
		4585
		4586	pthread_mutex_lock (&u->lock);
		4587	ev_invoke_pending (EV_A);
		4588	pthread_cond_signal (&u->invoke_cv);
		4589	pthread_mutex_unlock (&u->lock);
		4590	}
		4591
		4592	Whenever you want to start/stop a watcher or do other modifications to an
		4593	event loop, you will now have to lock:
		4594
		4595	ev_timer timeout_watcher;
		4596	userdata *u = ev_userdata (EV_A);
		4597
		4598	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4599
		4600	pthread_mutex_lock (&u->lock);
		4601	ev_timer_start (EV_A_ &timeout_watcher);
		4602	ev_async_send (EV_A_ &u->async_w);
		4603	pthread_mutex_unlock (&u->lock);
		4604
		4605	Note that sending the C<ev_async> watcher is required because otherwise
		4606	an event loop currently blocking in the kernel will have no knowledge
		4607	about the newly added timer. By waking up the loop it will pick up any new
		4608	watchers in the next event loop iteration.
		4609
		4610	=head3 COROUTINES
		4611
		4612	Libev is very accommodating to coroutines ("cooperative threads"):
		4613	libev fully supports nesting calls to its functions from different
		4614	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4615	different coroutines, and switch freely between both coroutines running
		4616	the loop, as long as you don't confuse yourself). The only exception is
		4617	that you must not do this from C<ev_periodic> reschedule callbacks.
		4618
		4619	Care has been taken to ensure that libev does not keep local state inside
		4620	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4621	they do not call any callbacks.
		4622
		4623	=head2 COMPILER WARNINGS
		4624
		4625	Depending on your compiler and compiler settings, you might get no or a
		4626	lot of warnings when compiling libev code. Some people are apparently
		4627	scared by this.
		4628
		4629	However, these are unavoidable for many reasons. For one, each compiler
		4630	has different warnings, and each user has different tastes regarding
		4631	warning options. "Warn-free" code therefore cannot be a goal except when
		4632	targeting a specific compiler and compiler-version.
		4633
		4634	Another reason is that some compiler warnings require elaborate
		4635	workarounds, or other changes to the code that make it less clear and less
		4636	maintainable.
		4637
		4638	And of course, some compiler warnings are just plain stupid, or simply
		4639	wrong (because they don't actually warn about the condition their message
		4640	seems to warn about). For example, certain older gcc versions had some
		4641	warnings that resulted in an extreme number of false positives. These have
		4642	been fixed, but some people still insist on making code warn-free with
		4643	such buggy versions.
		4644
		4645	While libev is written to generate as few warnings as possible,
		4646	"warn-free" code is not a goal, and it is recommended not to build libev
		4647	with any compiler warnings enabled unless you are prepared to cope with
		4648	them (e.g. by ignoring them). Remember that warnings are just that:
		4649	warnings, not errors, or proof of bugs.
		4650
		4651
		4652	=head2 VALGRIND
		4653
		4654	Valgrind has a special section here because it is a popular tool that is
		4655	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4656
		4657	If you think you found a bug (memory leak, uninitialised data access etc.)
		4658	in libev, then check twice: If valgrind reports something like:
		4659
		4660	==2274== definitely lost: 0 bytes in 0 blocks.
		4661	==2274== possibly lost: 0 bytes in 0 blocks.
		4662	==2274== still reachable: 256 bytes in 1 blocks.
		4663
		4664	Then there is no memory leak, just as memory accounted to global variables
		4665	is not a memleak - the memory is still being referenced, and didn't leak.
		4666
		4667	Similarly, under some circumstances, valgrind might report kernel bugs
		4668	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4669	although an acceptable workaround has been found here), or it might be
		4670	confused.
		4671
		4672	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4673	make it into some kind of religion.
		4674
		4675	If you are unsure about something, feel free to contact the mailing list
		4676	with the full valgrind report and an explanation on why you think this
		4677	is a bug in libev (best check the archives, too :). However, don't be
		4678	annoyed when you get a brisk "this is no bug" answer and take the chance
		4679	of learning how to interpret valgrind properly.
		4680
		4681	If you need, for some reason, empty reports from valgrind for your project
		4682	I suggest using suppression lists.
		4683
		4684
		4685	=head1 PORTABILITY NOTES
		4686
		4687	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4688
		4689	GNU/Linux is the only common platform that supports 64 bit file/large file
		4690	interfaces but I<disables> them by default.
		4691
		4692	That means that libev compiled in the default environment doesn't support
		4693	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4694
		4695	Unfortunately, many programs try to work around this GNU/Linux issue
		4696	by enabling the large file API, which makes them incompatible with the
		4697	standard libev compiled for their system.
		4698
		4699	Likewise, libev cannot enable the large file API itself as this would
		4700	suddenly make it incompatible to the default compile time environment,
		4701	i.e. all programs not using special compile switches.
		4702
		4703	=head2 OS/X AND DARWIN BUGS
		4704
		4705	The whole thing is a bug if you ask me - basically any system interface
		4706	you touch is broken, whether it is locales, poll, kqueue or even the
		4707	OpenGL drivers.
		4708
		4709	=head3 C<kqueue> is buggy
		4710
		4711	The kqueue syscall is broken in all known versions - most versions support
		4712	only sockets, many support pipes.
		4713
		4714	Libev tries to work around this by not using C<kqueue> by default on this
		4715	rotten platform, but of course you can still ask for it when creating a
		4716	loop - embedding a socket-only kqueue loop into a select-based one is
		4717	probably going to work well.
		4718
		4719	=head3 C<poll> is buggy
		4720
		4721	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4722	implementation by something calling C<kqueue> internally around the 10.5.6
		4723	release, so now C<kqueue> I<and> C<poll> are broken.
		4724
		4725	Libev tries to work around this by not using C<poll> by default on
		4726	this rotten platform, but of course you can still ask for it when creating
		4727	a loop.
		4728
		4729	=head3 C<select> is buggy
		4730
		4731	All that's left is C<select>, and of course Apple found a way to fuck this
		4732	one up as well: On OS/X, C<select> actively limits the number of file
		4733	descriptors you can pass in to 1024 - your program suddenly crashes when
		4734	you use more.
		4735
		4736	There is an undocumented "workaround" for this - defining
		4737	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4738	work on OS/X.
		4739
		4740	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4741
		4742	=head3 C<errno> reentrancy
		4743
		4744	The default compile environment on Solaris is unfortunately so
		4745	thread-unsafe that you can't even use components/libraries compiled
		4746	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4747	defined by default. A valid, if stupid, implementation choice.
		4748
		4749	If you want to use libev in threaded environments you have to make sure
		4750	it's compiled with C<_REENTRANT> defined.
		4751
		4752	=head3 Event port backend
		4753
		4754	The scalable event interface for Solaris is called "event
		4755	ports". Unfortunately, this mechanism is very buggy in all major
		4756	releases. If you run into high CPU usage, your program freezes or you get
		4757	a large number of spurious wakeups, make sure you have all the relevant
		4758	and latest kernel patches applied. No, I don't know which ones, but there
		4759	are multiple ones to apply, and afterwards, event ports actually work
		4760	great.
		4761
		4762	If you can't get it to work, you can try running the program by setting
		4763	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4764	C<select> backends.
		4765
		4766	=head2 AIX POLL BUG
		4767
		4768	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4769	this by trying to avoid the poll backend altogether (i.e. it's not even
		4770	compiled in), which normally isn't a big problem as C<select> works fine
		4771	with large bitsets on AIX, and AIX is dead anyway.
		4772
		4773	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4774
		4775	=head3 General issues
		4776
		4777	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4778	requires, and its I/O model is fundamentally incompatible with the POSIX
		4779	model. Libev still offers limited functionality on this platform in
		4780	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4781	descriptors. This only applies when using Win32 natively, not when using
		4782	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4783	as every compielr comes with a slightly differently broken/incompatible
		4784	environment.
		4785
		4786	Lifting these limitations would basically require the full
		4787	re-implementation of the I/O system. If you are into this kind of thing,
		4788	then note that glib does exactly that for you in a very portable way (note
		4789	also that glib is the slowest event library known to man).
		4790
		4791	There is no supported compilation method available on windows except
		4792	embedding it into other applications.
		4793
		4794	Sensible signal handling is officially unsupported by Microsoft - libev
		4795	tries its best, but under most conditions, signals will simply not work.
		4796
		4797	Not a libev limitation but worth mentioning: windows apparently doesn't
		4798	accept large writes: instead of resulting in a partial write, windows will
		4799	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4800	so make sure you only write small amounts into your sockets (less than a
		4801	megabyte seems safe, but this apparently depends on the amount of memory
		4802	available).
		4803
		4804	Due to the many, low, and arbitrary limits on the win32 platform and
		4805	the abysmal performance of winsockets, using a large number of sockets
		4806	is not recommended (and not reasonable). If your program needs to use
		4807	more than a hundred or so sockets, then likely it needs to use a totally
		4808	different implementation for windows, as libev offers the POSIX readiness
		4809	notification model, which cannot be implemented efficiently on windows
		4810	(due to Microsoft monopoly games).
		4811
		4812	A typical way to use libev under windows is to embed it (see the embedding
		4813	section for details) and use the following F<evwrap.h> header file instead
		4814	of F<ev.h>:
		4815
		4816	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4817	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4818
		4819	#include "ev.h"
		4820
		4821	And compile the following F<evwrap.c> file into your project (make sure
		4822	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4823
		4824	#include "evwrap.h"
		4825	#include "ev.c"
		4826
		4827	=head3 The winsocket C<select> function
		4828
		4829	The winsocket C<select> function doesn't follow POSIX in that it
		4830	requires socket I<handles> and not socket I<file descriptors> (it is
		4831	also extremely buggy). This makes select very inefficient, and also
		4832	requires a mapping from file descriptors to socket handles (the Microsoft
		4833	C runtime provides the function C<_open_osfhandle> for this). See the
		4834	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4835	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4836
		4837	The configuration for a "naked" win32 using the Microsoft runtime
		4838	libraries and raw winsocket select is:
		4839
		4840	#define EV_USE_SELECT 1
		4841	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4842
		4843	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4844	complexity in the O(n²) range when using win32.
		4845
		4846	=head3 Limited number of file descriptors
		4847
		4848	Windows has numerous arbitrary (and low) limits on things.
		4849
		4850	Early versions of winsocket's select only supported waiting for a maximum
		4851	of C<64> handles (probably owning to the fact that all windows kernels
		4852	can only wait for C<64> things at the same time internally; Microsoft
		4853	recommends spawning a chain of threads and wait for 63 handles and the
		4854	previous thread in each. Sounds great!).
		4855
		4856	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4857	to some high number (e.g. C<2048>) before compiling the winsocket select
		4858	call (which might be in libev or elsewhere, for example, perl and many
		4859	other interpreters do their own select emulation on windows).
		4860
		4861	Another limit is the number of file descriptors in the Microsoft runtime
		4862	libraries, which by default is C<64> (there must be a hidden I<64>
		4863	fetish or something like this inside Microsoft). You can increase this
		4864	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4865	(another arbitrary limit), but is broken in many versions of the Microsoft
		4866	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4867	(depending on windows version and/or the phase of the moon). To get more,
		4868	you need to wrap all I/O functions and provide your own fd management, but
		4869	the cost of calling select (O(n²)) will likely make this unworkable.
		4870
		4871	=head2 PORTABILITY REQUIREMENTS
		4872
		4873	In addition to a working ISO-C implementation and of course the
		4874	backend-specific APIs, libev relies on a few additional extensions:
		4875
		4876	=over 4
		4877
		4878	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4879	calling conventions regardless of C<ev_watcher_type *>.
		4880
		4881	Libev assumes not only that all watcher pointers have the same internal
		4882	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4883	assumes that the same (machine) code can be used to call any watcher
		4884	callback: The watcher callbacks have different type signatures, but libev
		4885	calls them using an C<ev_watcher *> internally.
		4886
		4887	=item pointer accesses must be thread-atomic
		4888
		4889	Accessing a pointer value must be atomic, it must both be readable and
		4890	writable in one piece - this is the case on all current architectures.
		4891
		4892	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4893
		4894	The type C<sig_atomic_t volatile> (or whatever is defined as
		4895	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4896	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4897	believed to be sufficiently portable.
		4898
		4899	=item C<sigprocmask> must work in a threaded environment
		4900
		4901	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4902	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4903	pthread implementations will either allow C<sigprocmask> in the "main
		4904	thread" or will block signals process-wide, both behaviours would
		4905	be compatible with libev. Interaction between C<sigprocmask> and
		4906	C<pthread_sigmask> could complicate things, however.
		4907
		4908	The most portable way to handle signals is to block signals in all threads
		4909	except the initial one, and run the default loop in the initial thread as
		4910	well.
		4911
		4912	=item C<long> must be large enough for common memory allocation sizes
		4913
		4914	To improve portability and simplify its API, libev uses C<long> internally
		4915	instead of C<size_t> when allocating its data structures. On non-POSIX
		4916	systems (Microsoft...) this might be unexpectedly low, but is still at
		4917	least 31 bits everywhere, which is enough for hundreds of millions of
		4918	watchers.
		4919
		4920	=item C<double> must hold a time value in seconds with enough accuracy
		4921
		4922	The type C<double> is used to represent timestamps. It is required to
		4923	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4924	good enough for at least into the year 4000 with millisecond accuracy
		4925	(the design goal for libev). This requirement is overfulfilled by
		4926	implementations using IEEE 754, which is basically all existing ones. With
		4927	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4928
		4929	=back
		4930
		4931	If you know of other additional requirements drop me a note.
		4932
		4933
		4934	=head1 ALGORITHMIC COMPLEXITIES
		4935
		4936	In this section the complexities of (many of) the algorithms used inside
		4937	libev will be documented. For complexity discussions about backends see
		4938	the documentation for C<ev_default_init>.
		4939
		4940	All of the following are about amortised time: If an array needs to be
		4941	extended, libev needs to realloc and move the whole array, but this
		4942	happens asymptotically rarer with higher number of elements, so O(1) might
		4943	mean that libev does a lengthy realloc operation in rare cases, but on
		4944	average it is much faster and asymptotically approaches constant time.
		4945
		4946	=over 4
		4947
		4948	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4949
		4950	This means that, when you have a watcher that triggers in one hour and
		4951	there are 100 watchers that would trigger before that, then inserting will
		4952	have to skip roughly seven (C<ld 100>) of these watchers.
		4953
		4954	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4955
		4956	That means that changing a timer costs less than removing/adding them,
		4957	as only the relative motion in the event queue has to be paid for.
		4958
		4959	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4960
		4961	These just add the watcher into an array or at the head of a list.
		4962
		4963	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4964
		4965	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4966
		4967	These watchers are stored in lists, so they need to be walked to find the
		4968	correct watcher to remove. The lists are usually short (you don't usually
		4969	have many watchers waiting for the same fd or signal: one is typical, two
		4970	is rare).
		4971
		4972	=item Finding the next timer in each loop iteration: O(1)
		4973
		4974	By virtue of using a binary or 4-heap, the next timer is always found at a
		4975	fixed position in the storage array.
		4976
		4977	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4978
		4979	A change means an I/O watcher gets started or stopped, which requires
		4980	libev to recalculate its status (and possibly tell the kernel, depending
		4981	on backend and whether C<ev_io_set> was used).
		4982
		4983	=item Activating one watcher (putting it into the pending state): O(1)
		4984
		4985	=item Priority handling: O(number_of_priorities)
		4986
		4987	Priorities are implemented by allocating some space for each
		4988	priority. When doing priority-based operations, libev usually has to
		4989	linearly search all the priorities, but starting/stopping and activating
		4990	watchers becomes O(1) with respect to priority handling.
		4991
		4992	=item Sending an ev_async: O(1)
		4993
		4994	=item Processing ev_async_send: O(number_of_async_watchers)
		4995
		4996	=item Processing signals: O(max_signal_number)
		4997
		4998	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4999	calls in the current loop iteration. Checking for async and signal events
		5000	involves iterating over all running async watchers or all signal numbers.
		5001
		5002	=back
		5003
		5004
		5005	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5006
		5007	The major version 4 introduced some incompatible changes to the API.
		5008
		5009	At the moment, the C<ev.h> header file provides compatibility definitions
		5010	for all changes, so most programs should still compile. The compatibility
		5011	layer might be removed in later versions of libev, so better update to the
		5012	new API early than late.
		5013
		5014	=over 4
		5015
		5016	=item C<EV_COMPAT3> backwards compatibility mechanism
		5017
		5018	The backward compatibility mechanism can be controlled by
		5019	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5020	section.
		5021
		5022	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5023
		5024	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5025
		5026	ev_loop_destroy (EV_DEFAULT_UC);
		5027	ev_loop_fork (EV_DEFAULT);
		5028
		5029	=item function/symbol renames
		5030
		5031	A number of functions and symbols have been renamed:
		5032
		5033	ev_loop => ev_run
		5034	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5035	EVLOOP_ONESHOT => EVRUN_ONCE
		5036
		5037	ev_unloop => ev_break
		5038	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5039	EVUNLOOP_ONE => EVBREAK_ONE
		5040	EVUNLOOP_ALL => EVBREAK_ALL
		5041
		5042	EV_TIMEOUT => EV_TIMER
		5043
		5044	ev_loop_count => ev_iteration
		5045	ev_loop_depth => ev_depth
		5046	ev_loop_verify => ev_verify
		5047
		5048	Most functions working on C<struct ev_loop> objects don't have an
		5049	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5050	associated constants have been renamed to not collide with the C<struct
		5051	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5052	as all other watcher types. Note that C<ev_loop_fork> is still called
		5053	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5054	typedef.
		5055
		5056	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5057
		5058	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5059	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5060	and work, but the library code will of course be larger.
		5061
		5062	=back
		5063
		5064
		5065	=head1 GLOSSARY
		5066
		5067	=over 4
		5068
		5069	=item active
		5070
		5071	A watcher is active as long as it has been started and not yet stopped.
		5072	See L<WATCHER STATES> for details.
		5073
		5074	=item application
		5075
		5076	In this document, an application is whatever is using libev.
		5077
		5078	=item backend
		5079
		5080	The part of the code dealing with the operating system interfaces.
		5081
		5082	=item callback
		5083
		5084	The address of a function that is called when some event has been
		5085	detected. Callbacks are being passed the event loop, the watcher that
		5086	received the event, and the actual event bitset.
		5087
		5088	=item callback/watcher invocation
		5089
		5090	The act of calling the callback associated with a watcher.
		5091
		5092	=item event
		5093
		5094	A change of state of some external event, such as data now being available
		5095	for reading on a file descriptor, time having passed or simply not having
		5096	any other events happening anymore.
		5097
		5098	In libev, events are represented as single bits (such as C<EV_READ> or
		5099	C<EV_TIMER>).
		5100
		5101	=item event library
		5102
		5103	A software package implementing an event model and loop.
		5104
		5105	=item event loop
		5106
		5107	An entity that handles and processes external events and converts them
		5108	into callback invocations.
		5109
		5110	=item event model
		5111
		5112	The model used to describe how an event loop handles and processes
		5113	watchers and events.
		5114
		5115	=item pending
		5116
		5117	A watcher is pending as soon as the corresponding event has been
		5118	detected. See L<WATCHER STATES> for details.
		5119
		5120	=item real time
		5121
		5122	The physical time that is observed. It is apparently strictly monotonic :)
		5123
		5124	=item wall-clock time
		5125
		5126	The time and date as shown on clocks. Unlike real time, it can actually
		5127	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5128	clock.
		5129
		5130	=item watcher
		5131
		5132	A data structure that describes interest in certain events. Watchers need
		5133	to be started (attached to an event loop) before they can receive events.
		5134
		5135	=back
878		5136
879	=head1 AUTHOR	5137	=head1 AUTHOR
880		5138
881	Marc Lehmann <libev@schmorp.de>.	5139	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5140	Magnusson and Emanuele Giaquinta.
882		5141

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