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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head1 DESCRIPTION	11	=head2 EXAMPLE PROGRAM
		12
		13	// a single header file is required
		14	#include <ev.h>
		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
		20	ev_io stdin_watcher;
		21	ev_timer timeout_watcher;
		22
		23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
		25	static void
		26	stdin_cb (EV_P_ ev_io *w, int revents)
		27	{
		28	puts ("stdin ready");
		29	// for one-shot events, one must manually stop the watcher
		30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
		35	}
		36
		37	// another callback, this time for a time-out
		38	static void
		39	timeout_cb (EV_P_ ev_timer *w, int revents)
		40	{
		41	puts ("timeout");
		42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
		44	}
		45
		46	int
		47	main (void)
		48	{
		49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
		51
		52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
		54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		55	ev_io_start (loop, &stdin_watcher);
		56
		57	// initialise a timer watcher, then start it
		58	// simple non-repeating 5.5 second timeout
		59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		60	ev_timer_start (loop, &timeout_watcher);
		61
		62	// now wait for events to arrive
		63	ev_run (loop, 0);
		64
		65	// break was called, so exit
		66	return 0;
		67	}
		68
		69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
		72
		73	The newest version of this document is also available as an html-formatted
		74	web page you might find easier to navigate when reading it for the first
		75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
10		94
11	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	97	these event sources and provide your program with events.
14		98
15	To do this, it must take more or less complete control over your process	99	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	100	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	101	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	103	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	104	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	105	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	106	watcher.
23		107
24	=head1 FEATURES	108	=head2 FEATURES
25		109
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	110	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	111	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	112	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		113	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		115	timers (C<ev_timer>), absolute timers with customised rescheduling
		116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	117	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	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
		121
		122	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	124	for example).
33		125
34	=head1 CONVENTIONS	126	=head2 CONVENTIONS
35		127
36	Libev is very configurable. In this manual the default configuration	128	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	129	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	130	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	131	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	132	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 *>)	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	134	this argument.
43		135
44	=head1 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
45		137
46	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	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	140	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	141	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the double type in C.	142	too. It usually aliases to the C<double> type in C. When you need to do
		143	any calculations on it, you should treat it as some floating point value.
		144
		145	Unlike the name component C<stamp> might indicate, it is also used for
		146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Libev also has a few internal error-checking C<assert>ions, and also has
		165	extensive consistency checking code. These do not trigger under normal
		166	circumstances, as they indicate either a bug in libev or worse.
		167
51		168
52	=head1 GLOBAL FUNCTIONS	169	=head1 GLOBAL FUNCTIONS
53		170
54	These functions can be called anytime, even before initialising the	171	These functions can be called anytime, even before initialising the
55	library in any way.	172	library in any way.
…		…
58		175
59	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
60		177
61	Returns the current time as libev would use it. Please note that the	178	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	179	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
		182
		183	=item ev_sleep (ev_tstamp interval)
		184
		185	Sleep for the given interval: The current thread will be blocked
		186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
		190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
64		194
65	=item int ev_version_major ()	195	=item int ev_version_major ()
66		196
67	=item int ev_version_minor ()	197	=item int ev_version_minor ()
68		198
69	You can find out the major and minor version numbers of the library	199	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	200	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	201	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	202	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	203	version of the library your program was compiled against.
74		204
		205	These version numbers refer to the ABI version of the library, not the
		206	release version.
		207
75	Usually, it's a good idea to terminate if the major versions mismatch,	208	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	211	not a problem.
79		212
		213	Example: Make sure we haven't accidentally been linked against the wrong
		214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
		216
		217	assert (("libev version mismatch",
		218	ev_version_major () == EV_VERSION_MAJOR
		219	&& ev_version_minor () >= EV_VERSION_MINOR));
		220
		221	=item unsigned int ev_supported_backends ()
		222
		223	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		224	value) compiled into this binary of libev (independent of their
		225	availability on the system you are running on). See C<ev_default_loop> for
		226	a description of the set values.
		227
		228	Example: make sure we have the epoll method, because yeah this is cool and
		229	a must have and can we have a torrent of it please!!!11
		230
		231	assert (("sorry, no epoll, no sex",
		232	ev_supported_backends () & EVBACKEND_EPOLL));
		233
		234	=item unsigned int ev_recommended_backends ()
		235
		236	Return the set of all backends compiled into this binary of libev and
		237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
		239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
		240	and will not be auto-detected unless you explicitly request it (assuming
		241	you know what you are doing). This is the set of backends that libev will
		242	probe for if you specify no backends explicitly.
		243
		244	=item unsigned int ev_embeddable_backends ()
		245
		246	Returns the set of backends that are embeddable in other event loops. This
		247	value is platform-specific but can include backends not available on the
		248	current system. To find which embeddable backends might be supported on
		249	the current system, you would need to look at C<ev_embeddable_backends ()
		250	& ev_supported_backends ()>, likewise for recommended ones.
		251
		252	See the description of C<ev_embed> watchers for more info.
		253
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
81		255
82	Sets the allocation function to use (the prototype is similar to the	256	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	257	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	258	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	259	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	260	or take some potentially destructive action.
		261
		262	Since some systems (at least OpenBSD and Darwin) fail to implement
		263	correct C<realloc> semantics, libev will use a wrapper around the system
		264	C<realloc> and C<free> functions by default.
87		265
88	You could override this function in high-availability programs to, say,	266	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,	267	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.	268	or even to sleep a while and retry until some memory is available.
91		269
		270	Example: Replace the libev allocator with one that waits a bit and then
		271	retries (example requires a standards-compliant C<realloc>).
		272
		273	static void *
		274	persistent_realloc (void *ptr, size_t size)
		275	{
		276	for (;;)
		277	{
		278	void *newptr = realloc (ptr, size);
		279
		280	if (newptr)
		281	return newptr;
		282
		283	sleep (60);
		284	}
		285	}
		286
		287	...
		288	ev_set_allocator (persistent_realloc);
		289
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
93		291
94	Set the callback function to call on a retryable syscall error (such	292	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	293	as failed select, poll, epoll_wait). The message is a printable string
96	indicating the system call or subsystem causing the problem. If this	294	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	295	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	296	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	297	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	298	(such as abort).
101		299
		300	Example: This is basically the same thing that libev does internally, too.
		301
		302	static void
		303	fatal_error (const char *msg)
		304	{
		305	perror (msg);
		306	abort ();
		307	}
		308
		309	...
		310	ev_set_syserr_cb (fatal_error);
		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
102	=back	325	=back
103		326
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
105		328
106	An event loop is described by a C<struct ev_loop *>. The library knows two	329	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	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
108	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
109		332
110	If you use threads, a common model is to run the default event loop	333	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	334	supports child process events, and dynamically created event loops which
112	create, you also create another event loop. Libev itself does no locking	335	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		336
117	=over 4	337	=over 4
118		338
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		340
121	This will initialise the default event loop if it hasn't been initialised	341	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	342	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	343	the C<flags> parameter are described in more detail in the entry for
124	flags).	344	C<ev_loop_new>.
		345
		346	If the default loop is already initialised then this function simply
		347	returns it (and ignores the flags. If that is troubling you, check
		348	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		349	flags, which should almost always be C<0>, unless the caller is also the
		350	one calling C<ev_run> or otherwise qualifies as "the main program".
125		351
126	If you don't know what event loop to use, use the one returned from this	352	If you don't know what event loop to use, use the one returned from this
127	function.	353	function (or via the C<EV_DEFAULT> macro).
		354
		355	Note that this function is I<not> thread-safe, so if you want to use it
		356	from multiple threads, you have to employ some kind of mutex (note also
		357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
		359
		360	The default loop is the only loop that can handle C<ev_child> watchers,
		361	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		362	a problem for your application you can either create a dynamic loop with
		363	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		364	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		365
		366	Example: This is the most typical usage.
		367
		368	if (!ev_default_loop (0))
		369	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		370
		371	Example: Restrict libev to the select and poll backends, and do not allow
		372	environment settings to be taken into account:
		373
		374	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		375
		376	=item struct ev_loop *ev_loop_new (unsigned int flags)
		377
		378	This will create and initialise a new event loop object. If the loop
		379	could not be initialised, returns false.
		380
		381	This function is thread-safe, and one common way to use libev with
		382	threads is indeed to create one loop per thread, and using the default
		383	loop in the "main" or "initial" thread.
128		384
129	The flags argument can be used to specify special behaviour or specific	385	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).	386	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		387
132	It supports the following flags:	388	The following flags are supported:
133		389
134	=over 4	390	=over 4
135		391
136	=item C<EVFLAG_AUTO>	392	=item C<EVFLAG_AUTO>
137		393
138	The default flags value. Use this if you have no clue (it's the right	394	The default flags value. Use this if you have no clue (it's the right
139	thing, believe me).	395	thing, believe me).
140		396
141	=item C<EVFLAG_NOENV>	397	=item C<EVFLAG_NOENV>
142		398
143	If this flag bit is ored into the flag value (or the program runs setuid	399	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	400	or setgid) then libev will I<not> look at the environment variable
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	402	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	403	useful to try out specific backends to test their performance, to work
148	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
149		407
		408	=item C<EVFLAG_FORKCHECK>
		409
		410	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		411	make libev check for a fork in each iteration by enabling this flag.
		412
		413	This works by calling C<getpid ()> on every iteration of the loop,
		414	and thus this might slow down your event loop if you do a lot of loop
		415	iterations and little real work, but is usually not noticeable (on my
		416	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
		417	sequence without a system call and thus I<very> fast, but my GNU/Linux
		418	system also has C<pthread_atfork> which is even faster). (Update: glibc
		419	versions 2.25 apparently removed the C<getpid> optimisation again).
		420
		421	The big advantage of this flag is that you can forget about fork (and
		422	forget about forgetting to tell libev about forking, although you still
		423	have to ignore C<SIGPIPE>) when you use this flag.
		424
		425	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		426	environment variable.
		427
		428	=item C<EVFLAG_NOINOTIFY>
		429
		430	When this flag is specified, then libev will not attempt to use the
		431	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		432	testing, this flag can be useful to conserve inotify file descriptors, as
		433	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		434
		435	=item C<EVFLAG_SIGNALFD>
		436
		437	When this flag is specified, then libev will attempt to use the
		438	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		439	delivers signals synchronously, which makes it both faster and might make
		440	it possible to get the queued signal data. It can also simplify signal
		441	handling with threads, as long as you properly block signals in your
		442	threads that are not interested in handling them.
		443
		444	Signalfd will not be used by default as this changes your signal mask, and
		445	there are a lot of shoddy libraries and programs (glib's threadpool for
		446	example) that can't properly initialise their signal masks.
		447
		448	=item C<EVFLAG_NOSIGMASK>
		449
		450	When this flag is specified, then libev will avoid to modify the signal
		451	mask. Specifically, this means you have to make sure signals are unblocked
		452	when you want to receive them.
		453
		454	This behaviour is useful when you want to do your own signal handling, or
		455	want to handle signals only in specific threads and want to avoid libev
		456	unblocking the signals.
		457
		458	It's also required by POSIX in a threaded program, as libev calls
		459	C<sigprocmask>, whose behaviour is officially unspecified.
		460
		461	This flag's behaviour will become the default in future versions of libev.
		462
150	=item C<EVMETHOD_SELECT> (portable select backend)	463	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		464
		465	This is your standard select(2) backend. Not I<completely> standard, as
		466	libev tries to roll its own fd_set with no limits on the number of fds,
		467	but if that fails, expect a fairly low limit on the number of fds when
		468	using this backend. It doesn't scale too well (O(highest_fd)), but its
		469	usually the fastest backend for a low number of (low-numbered :) fds.
		470
		471	To get good performance out of this backend you need a high amount of
		472	parallelism (most of the file descriptors should be busy). If you are
		473	writing a server, you should C<accept ()> in a loop to accept as many
		474	connections as possible during one iteration. You might also want to have
		475	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		476	readiness notifications you get per iteration.
		477
		478	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		479	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		480	C<exceptfds> set on that platform).
		481
152	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	482	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
153		483
154	=item C<EVMETHOD_EPOLL> (linux only)	484	And this is your standard poll(2) backend. It's more complicated
		485	than select, but handles sparse fds better and has no artificial
		486	limit on the number of fds you can use (except it will slow down
		487	considerably with a lot of inactive fds). It scales similarly to select,
		488	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		489	performance tips.
155		490
156	=item C<EVMETHOD_KQUEUE> (some bsds only)	491	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		492	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
157		493
158	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	494	=item C<EVBACKEND_EPOLL> (value 4, Linux)
159		495
160	=item C<EVMETHOD_PORT> (solaris 10 only)	496	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		497	kernels).
161		498
162	If one or more of these are ored into the flags value, then only these	499	For few fds, this backend is a bit little slower than poll and select, but
163	backends will be tried (in the reverse order as given here). If one are	500	it scales phenomenally better. While poll and select usually scale like
164	specified, any backend will do.	501	O(total_fds) where total_fds is the total number of fds (or the highest
		502	fd), epoll scales either O(1) or O(active_fds).
		503
		504	The epoll mechanism deserves honorable mention as the most misdesigned
		505	of the more advanced event mechanisms: mere annoyances include silently
		506	dropping file descriptors, requiring a system call per change per file
		507	descriptor (and unnecessary guessing of parameters), problems with dup,
		508	returning before the timeout value, resulting in additional iterations
		509	(and only giving 5ms accuracy while select on the same platform gives
		510	0.1ms) and so on. The biggest issue is fork races, however - if a program
		511	forks then I<both> parent and child process have to recreate the epoll
		512	set, which can take considerable time (one syscall per file descriptor)
		513	and is of course hard to detect.
		514
		515	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		516	but of course I<doesn't>, and epoll just loves to report events for
		517	totally I<different> file descriptors (even already closed ones, so
		518	one cannot even remove them from the set) than registered in the set
		519	(especially on SMP systems). Libev tries to counter these spurious
		520	notifications by employing an additional generation counter and comparing
		521	that against the events to filter out spurious ones, recreating the set
		522	when required. Epoll also erroneously rounds down timeouts, but gives you
		523	no way to know when and by how much, so sometimes you have to busy-wait
		524	because epoll returns immediately despite a nonzero timeout. And last
		525	not least, it also refuses to work with some file descriptors which work
		526	perfectly fine with C<select> (files, many character devices...).
		527
		528	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		529	cobbled together in a hurry, no thought to design or interaction with
		530	others. Oh, the pain, will it ever stop...
		531
		532	While stopping, setting and starting an I/O watcher in the same iteration
		533	will result in some caching, there is still a system call per such
		534	incident (because the same I<file descriptor> could point to a different
		535	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		536	file descriptors might not work very well if you register events for both
		537	file descriptors.
		538
		539	Best performance from this backend is achieved by not unregistering all
		540	watchers for a file descriptor until it has been closed, if possible,
		541	i.e. keep at least one watcher active per fd at all times. Stopping and
		542	starting a watcher (without re-setting it) also usually doesn't cause
		543	extra overhead. A fork can both result in spurious notifications as well
		544	as in libev having to destroy and recreate the epoll object, which can
		545	take considerable time and thus should be avoided.
		546
		547	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		548	faster than epoll for maybe up to a hundred file descriptors, depending on
		549	the usage. So sad.
		550
		551	While nominally embeddable in other event loops, this feature is broken in
		552	all kernel versions tested so far.
		553
		554	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		555	C<EVBACKEND_POLL>.
		556
		557	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		558
		559	Kqueue deserves special mention, as at the time of this writing, it
		560	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		561	with anything but sockets and pipes, except on Darwin, where of course
		562	it's completely useless). Unlike epoll, however, whose brokenness
		563	is by design, these kqueue bugs can (and eventually will) be fixed
		564	without API changes to existing programs. For this reason it's not being
		565	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		566	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		567	system like NetBSD.
		568
		569	You still can embed kqueue into a normal poll or select backend and use it
		570	only for sockets (after having made sure that sockets work with kqueue on
		571	the target platform). See C<ev_embed> watchers for more info.
		572
		573	It scales in the same way as the epoll backend, but the interface to the
		574	kernel is more efficient (which says nothing about its actual speed, of
		575	course). While stopping, setting and starting an I/O watcher does never
		576	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		577	two event changes per incident. Support for C<fork ()> is very bad (you
		578	might have to leak fd's on fork, but it's more sane than epoll) and it
		579	drops fds silently in similarly hard-to-detect cases.
		580
		581	This backend usually performs well under most conditions.
		582
		583	While nominally embeddable in other event loops, this doesn't work
		584	everywhere, so you might need to test for this. And since it is broken
		585	almost everywhere, you should only use it when you have a lot of sockets
		586	(for which it usually works), by embedding it into another event loop
		587	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		588	also broken on OS X)) and, did I mention it, using it only for sockets.
		589
		590	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		591	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		592	C<NOTE_EOF>.
		593
		594	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		595
		596	This is not implemented yet (and might never be, unless you send me an
		597	implementation). According to reports, C</dev/poll> only supports sockets
		598	and is not embeddable, which would limit the usefulness of this backend
		599	immensely.
		600
		601	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		602
		603	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		604	it's really slow, but it still scales very well (O(active_fds)).
		605
		606	While this backend scales well, it requires one system call per active
		607	file descriptor per loop iteration. For small and medium numbers of file
		608	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		609	might perform better.
		610
		611	On the positive side, this backend actually performed fully to
		612	specification in all tests and is fully embeddable, which is a rare feat
		613	among the OS-specific backends (I vastly prefer correctness over speed
		614	hacks).
		615
		616	On the negative side, the interface is I<bizarre> - so bizarre that
		617	even sun itself gets it wrong in their code examples: The event polling
		618	function sometimes returns events to the caller even though an error
		619	occurred, but with no indication whether it has done so or not (yes, it's
		620	even documented that way) - deadly for edge-triggered interfaces where you
		621	absolutely have to know whether an event occurred or not because you have
		622	to re-arm the watcher.
		623
		624	Fortunately libev seems to be able to work around these idiocies.
		625
		626	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		627	C<EVBACKEND_POLL>.
		628
		629	=item C<EVBACKEND_ALL>
		630
		631	Try all backends (even potentially broken ones that wouldn't be tried
		632	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		633	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		634
		635	It is definitely not recommended to use this flag, use whatever
		636	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		637	at all.
		638
		639	=item C<EVBACKEND_MASK>
		640
		641	Not a backend at all, but a mask to select all backend bits from a
		642	C<flags> value, in case you want to mask out any backends from a flags
		643	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
165		644
166	=back	645	=back
167		646
168	=item struct ev_loop *ev_loop_new (unsigned int flags)	647	If one or more of the backend flags are or'ed into the flags value,
		648	then only these backends will be tried (in the reverse order as listed
		649	here). If none are specified, all backends in C<ev_recommended_backends
		650	()> will be tried.
169		651
170	Similar to C<ev_default_loop>, but always creates a new event loop that is	652	Example: Try to create a event loop that uses epoll and nothing else.
171	always distinct from the default loop. Unlike the default loop, it cannot
172	handle signal and child watchers, and attempts to do so will be greeted by
173	undefined behaviour (or a failed assertion if assertions are enabled).
174		653
175	=item ev_default_destroy ()	654	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		655	if (!epoller)
		656	fatal ("no epoll found here, maybe it hides under your chair");
176		657
177	Destroys the default loop again (frees all memory and kernel state	658	Example: Use whatever libev has to offer, but make sure that kqueue is
178	etc.). This stops all registered event watchers (by not touching them in	659	used if available.
179	any way whatsoever, although you cannot rely on this :).	660
		661	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
180		662
181	=item ev_loop_destroy (loop)	663	=item ev_loop_destroy (loop)
182		664
183	Like C<ev_default_destroy>, but destroys an event loop created by an	665	Destroys an event loop object (frees all memory and kernel state
184	earlier call to C<ev_loop_new>.	666	etc.). None of the active event watchers will be stopped in the normal
		667	sense, so e.g. C<ev_is_active> might still return true. It is your
		668	responsibility to either stop all watchers cleanly yourself I<before>
		669	calling this function, or cope with the fact afterwards (which is usually
		670	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		671	for example).
185		672
186	=item ev_default_fork ()	673	Note that certain global state, such as signal state (and installed signal
		674	handlers), will not be freed by this function, and related watchers (such
		675	as signal and child watchers) would need to be stopped manually.
187		676
		677	This function is normally used on loop objects allocated by
		678	C<ev_loop_new>, but it can also be used on the default loop returned by
		679	C<ev_default_loop>, in which case it is not thread-safe.
		680
		681	Note that it is not advisable to call this function on the default loop
		682	except in the rare occasion where you really need to free its resources.
		683	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		684	and C<ev_loop_destroy>.
		685
		686	=item ev_loop_fork (loop)
		687
		688	This function sets a flag that causes subsequent C<ev_run> iterations
188	This function reinitialises the kernel state for backends that have	689	to reinitialise the kernel state for backends that have one. Despite
189	one. Despite the name, you can call it anytime, but it makes most sense	690	the name, you can call it anytime you are allowed to start or stop
190	after forking, in either the parent or child process (or both, but that	691	watchers (except inside an C<ev_prepare> callback), but it makes most
191	again makes little sense).	692	sense after forking, in the child process. You I<must> call it (or use
		693	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
192		694
193	You I<must> call this function after forking if and only if you want to	695	In addition, if you want to reuse a loop (via this function or
194	use the event library in both processes. If you just fork+exec, you don't	696	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
195	have to call it.	697
		698	Again, you I<have> to call it on I<any> loop that you want to re-use after
		699	a fork, I<even if you do not plan to use the loop in the parent>. This is
		700	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		701	during fork.
		702
		703	On the other hand, you only need to call this function in the child
		704	process if and only if you want to use the event loop in the child. If
		705	you just fork+exec or create a new loop in the child, you don't have to
		706	call it at all (in fact, C<epoll> is so badly broken that it makes a
		707	difference, but libev will usually detect this case on its own and do a
		708	costly reset of the backend).
196		709
197	The function itself is quite fast and it's usually not a problem to call	710	The function itself is quite fast and it's usually not a problem to call
198	it just in case after a fork. To make this easy, the function will fit in	711	it just in case after a fork.
199	quite nicely into a call to C<pthread_atfork>:
200		712
		713	Example: Automate calling C<ev_loop_fork> on the default loop when
		714	using pthreads.
		715
		716	static void
		717	post_fork_child (void)
		718	{
		719	ev_loop_fork (EV_DEFAULT);
		720	}
		721
		722	...
201	pthread_atfork (0, 0, ev_default_fork);	723	pthread_atfork (0, 0, post_fork_child);
202		724
203	=item ev_loop_fork (loop)	725	=item int ev_is_default_loop (loop)
204		726
205	Like C<ev_default_fork>, but acts on an event loop created by	727	Returns true when the given loop is, in fact, the default loop, and false
206	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	728	otherwise.
207	after fork, and how you do this is entirely your own problem.
208		729
		730	=item unsigned int ev_iteration (loop)
		731
		732	Returns the current iteration count for the event loop, which is identical
		733	to the number of times libev did poll for new events. It starts at C<0>
		734	and happily wraps around with enough iterations.
		735
		736	This value can sometimes be useful as a generation counter of sorts (it
		737	"ticks" the number of loop iterations), as it roughly corresponds with
		738	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		739	prepare and check phases.
		740
209	=item unsigned int ev_method (loop)	741	=item unsigned int ev_depth (loop)
210		742
		743	Returns the number of times C<ev_run> was entered minus the number of
		744	times C<ev_run> was exited normally, in other words, the recursion depth.
		745
		746	Outside C<ev_run>, this number is zero. In a callback, this number is
		747	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		748	in which case it is higher.
		749
		750	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		751	throwing an exception etc.), doesn't count as "exit" - consider this
		752	as a hint to avoid such ungentleman-like behaviour unless it's really
		753	convenient, in which case it is fully supported.
		754
		755	=item unsigned int ev_backend (loop)
		756
211	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	757	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
212	use.	758	use.
213		759
214	=item ev_tstamp ev_now (loop)	760	=item ev_tstamp ev_now (loop)
215		761
216	Returns the current "event loop time", which is the time the event loop	762	Returns the current "event loop time", which is the time the event loop
217	got events and started processing them. This timestamp does not change	763	received events and started processing them. This timestamp does not
218	as long as callbacks are being processed, and this is also the base time	764	change as long as callbacks are being processed, and this is also the base
219	used for relative timers. You can treat it as the timestamp of the event	765	time used for relative timers. You can treat it as the timestamp of the
220	occuring (or more correctly, the mainloop finding out about it).	766	event occurring (or more correctly, libev finding out about it).
221		767
		768	=item ev_now_update (loop)
		769
		770	Establishes the current time by querying the kernel, updating the time
		771	returned by C<ev_now ()> in the progress. This is a costly operation and
		772	is usually done automatically within C<ev_run ()>.
		773
		774	This function is rarely useful, but when some event callback runs for a
		775	very long time without entering the event loop, updating libev's idea of
		776	the current time is a good idea.
		777
		778	See also L</The special problem of time updates> in the C<ev_timer> section.
		779
		780	=item ev_suspend (loop)
		781
		782	=item ev_resume (loop)
		783
		784	These two functions suspend and resume an event loop, for use when the
		785	loop is not used for a while and timeouts should not be processed.
		786
		787	A typical use case would be an interactive program such as a game: When
		788	the user presses C<^Z> to suspend the game and resumes it an hour later it
		789	would be best to handle timeouts as if no time had actually passed while
		790	the program was suspended. This can be achieved by calling C<ev_suspend>
		791	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		792	C<ev_resume> directly afterwards to resume timer processing.
		793
		794	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		795	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		796	will be rescheduled (that is, they will lose any events that would have
		797	occurred while suspended).
		798
		799	After calling C<ev_suspend> you B<must not> call I<any> function on the
		800	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		801	without a previous call to C<ev_suspend>.
		802
		803	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		804	event loop time (see C<ev_now_update>).
		805
222	=item ev_loop (loop, int flags)	806	=item bool ev_run (loop, int flags)
223		807
224	Finally, this is it, the event handler. This function usually is called	808	Finally, this is it, the event handler. This function usually is called
225	after you initialised all your watchers and you want to start handling	809	after you have initialised all your watchers and you want to start
226	events.	810	handling events. It will ask the operating system for any new events, call
		811	the watcher callbacks, and then repeat the whole process indefinitely: This
		812	is why event loops are called I<loops>.
227		813
228	If the flags argument is specified as 0, it will not return until either	814	If the flags argument is specified as C<0>, it will keep handling events
229	no event watchers are active anymore or C<ev_unloop> was called.	815	until either no event watchers are active anymore or C<ev_break> was
		816	called.
230		817
		818	The return value is false if there are no more active watchers (which
		819	usually means "all jobs done" or "deadlock"), and true in all other cases
		820	(which usually means " you should call C<ev_run> again").
		821
		822	Please note that an explicit C<ev_break> is usually better than
		823	relying on all watchers to be stopped when deciding when a program has
		824	finished (especially in interactive programs), but having a program
		825	that automatically loops as long as it has to and no longer by virtue
		826	of relying on its watchers stopping correctly, that is truly a thing of
		827	beauty.
		828
		829	This function is I<mostly> exception-safe - you can break out of a
		830	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		831	exception and so on. This does not decrement the C<ev_depth> value, nor
		832	will it clear any outstanding C<EVBREAK_ONE> breaks.
		833
231	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	834	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
232	those events and any outstanding ones, but will not block your process in	835	those events and any already outstanding ones, but will not wait and
233	case there are no events and will return after one iteration of the loop.	836	block your process in case there are no events and will return after one
		837	iteration of the loop. This is sometimes useful to poll and handle new
		838	events while doing lengthy calculations, to keep the program responsive.
234		839
235	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	840	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
236	neccessary) and will handle those and any outstanding ones. It will block	841	necessary) and will handle those and any already outstanding ones. It
237	your process until at least one new event arrives, and will return after	842	will block your process until at least one new event arrives (which could
		843	be an event internal to libev itself, so there is no guarantee that a
		844	user-registered callback will be called), and will return after one
238	one iteration of the loop.	845	iteration of the loop.
239		846
240	This flags value could be used to implement alternative looping	847	This is useful if you are waiting for some external event in conjunction
241	constructs, but the C<prepare> and C<check> watchers provide a better and	848	with something not expressible using other libev watchers (i.e. "roll your
242	more generic mechanism.	849	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		850	usually a better approach for this kind of thing.
243		851
244	Here are the gory details of what ev_loop does:	852	Here are the gory details of what C<ev_run> does (this is for your
		853	understanding, not a guarantee that things will work exactly like this in
		854	future versions):
245		855
246	1. If there are no active watchers (reference count is zero), return.	856	- Increment loop depth.
		857	- Reset the ev_break status.
		858	- Before the first iteration, call any pending watchers.
		859	LOOP:
		860	- If EVFLAG_FORKCHECK was used, check for a fork.
		861	- If a fork was detected (by any means), queue and call all fork watchers.
247	2. Queue and immediately call all prepare watchers.	862	- Queue and call all prepare watchers.
		863	- If ev_break was called, goto FINISH.
248	3. If we have been forked, recreate the kernel state.	864	- If we have been forked, detach and recreate the kernel state
		865	as to not disturb the other process.
249	4. Update the kernel state with all outstanding changes.	866	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	867	- Update the "event loop time" (ev_now ()).
251	6. Calculate for how long to block.	868	- Calculate for how long to sleep or block, if at all
		869	(active idle watchers, EVRUN_NOWAIT or not having
		870	any active watchers at all will result in not sleeping).
		871	- Sleep if the I/O and timer collect interval say so.
		872	- Increment loop iteration counter.
252	7. Block the process, waiting for events.	873	- Block the process, waiting for any events.
		874	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	875	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
254	9. Queue all outstanding timers.	876	- Queue all expired timers.
255	10. Queue all outstanding periodics.	877	- Queue all expired periodics.
256	11. If no events are pending now, queue all idle watchers.	878	- Queue all idle watchers with priority higher than that of pending events.
257	12. Queue all check watchers.	879	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	880	- Call all queued watchers in reverse order (i.e. check watchers first).
259	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	881	Signals and child watchers are implemented as I/O watchers, and will
260	was used, return, otherwise continue with step #1.	882	be handled here by queueing them when their watcher gets executed.
		883	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		884	were used, or there are no active watchers, goto FINISH, otherwise
		885	continue with step LOOP.
		886	FINISH:
		887	- Reset the ev_break status iff it was EVBREAK_ONE.
		888	- Decrement the loop depth.
		889	- Return.
261		890
		891	Example: Queue some jobs and then loop until no events are outstanding
		892	anymore.
		893
		894	... queue jobs here, make sure they register event watchers as long
		895	... as they still have work to do (even an idle watcher will do..)
		896	ev_run (my_loop, 0);
		897	... jobs done or somebody called break. yeah!
		898
262	=item ev_unloop (loop, how)	899	=item ev_break (loop, how)
263		900
264	Can be used to make a call to C<ev_loop> return early (but only after it	901	Can be used to make a call to C<ev_run> return early (but only after it
265	has processed all outstanding events). The C<how> argument must be either	902	has processed all outstanding events). The C<how> argument must be either
266	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	903	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
267	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	904	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		905
		906	This "break state" will be cleared on the next call to C<ev_run>.
		907
		908	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		909	which case it will have no effect.
268		910
269	=item ev_ref (loop)	911	=item ev_ref (loop)
270		912
271	=item ev_unref (loop)	913	=item ev_unref (loop)
272		914
273	Ref/unref can be used to add or remove a reference count on the event	915	Ref/unref can be used to add or remove a reference count on the event
274	loop: Every watcher keeps one reference, and as long as the reference	916	loop: Every watcher keeps one reference, and as long as the reference
275	count is nonzero, C<ev_loop> will not return on its own. If you have	917	count is nonzero, C<ev_run> will not return on its own.
276	a watcher you never unregister that should not keep C<ev_loop> from	918
277	returning, ev_unref() after starting, and ev_ref() before stopping it. For	919	This is useful when you have a watcher that you never intend to
		920	unregister, but that nevertheless should not keep C<ev_run> from
		921	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		922	before stopping it.
		923
278	example, libev itself uses this for its internal signal pipe: It is not	924	As an example, libev itself uses this for its internal signal pipe: It
279	visible to the libev user and should not keep C<ev_loop> from exiting if	925	is not visible to the libev user and should not keep C<ev_run> from
280	no event watchers registered by it are active. It is also an excellent	926	exiting if no event watchers registered by it are active. It is also an
281	way to do this for generic recurring timers or from within third-party	927	excellent way to do this for generic recurring timers or from within
282	libraries. Just remember to I<unref after start> and I<ref before stop>.	928	third-party libraries. Just remember to I<unref after start> and I<ref
		929	before stop> (but only if the watcher wasn't active before, or was active
		930	before, respectively. Note also that libev might stop watchers itself
		931	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		932	in the callback).
		933
		934	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		935	running when nothing else is active.
		936
		937	ev_signal exitsig;
		938	ev_signal_init (&exitsig, sig_cb, SIGINT);
		939	ev_signal_start (loop, &exitsig);
		940	ev_unref (loop);
		941
		942	Example: For some weird reason, unregister the above signal handler again.
		943
		944	ev_ref (loop);
		945	ev_signal_stop (loop, &exitsig);
		946
		947	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		948
		949	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		950
		951	These advanced functions influence the time that libev will spend waiting
		952	for events. Both time intervals are by default C<0>, meaning that libev
		953	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		954	latency.
		955
		956	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		957	allows libev to delay invocation of I/O and timer/periodic callbacks
		958	to increase efficiency of loop iterations (or to increase power-saving
		959	opportunities).
		960
		961	The idea is that sometimes your program runs just fast enough to handle
		962	one (or very few) event(s) per loop iteration. While this makes the
		963	program responsive, it also wastes a lot of CPU time to poll for new
		964	events, especially with backends like C<select ()> which have a high
		965	overhead for the actual polling but can deliver many events at once.
		966
		967	By setting a higher I<io collect interval> you allow libev to spend more
		968	time collecting I/O events, so you can handle more events per iteration,
		969	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		970	C<ev_timer>) will not be affected. Setting this to a non-null value will
		971	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		972	sleep time ensures that libev will not poll for I/O events more often then
		973	once per this interval, on average (as long as the host time resolution is
		974	good enough).
		975
		976	Likewise, by setting a higher I<timeout collect interval> you allow libev
		977	to spend more time collecting timeouts, at the expense of increased
		978	latency/jitter/inexactness (the watcher callback will be called
		979	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		980	value will not introduce any overhead in libev.
		981
		982	Many (busy) programs can usually benefit by setting the I/O collect
		983	interval to a value near C<0.1> or so, which is often enough for
		984	interactive servers (of course not for games), likewise for timeouts. It
		985	usually doesn't make much sense to set it to a lower value than C<0.01>,
		986	as this approaches the timing granularity of most systems. Note that if
		987	you do transactions with the outside world and you can't increase the
		988	parallelity, then this setting will limit your transaction rate (if you
		989	need to poll once per transaction and the I/O collect interval is 0.01,
		990	then you can't do more than 100 transactions per second).
		991
		992	Setting the I<timeout collect interval> can improve the opportunity for
		993	saving power, as the program will "bundle" timer callback invocations that
		994	are "near" in time together, by delaying some, thus reducing the number of
		995	times the process sleeps and wakes up again. Another useful technique to
		996	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		997	they fire on, say, one-second boundaries only.
		998
		999	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1000	more often than 100 times per second:
		1001
		1002	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1003	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1004
		1005	=item ev_invoke_pending (loop)
		1006
		1007	This call will simply invoke all pending watchers while resetting their
		1008	pending state. Normally, C<ev_run> does this automatically when required,
		1009	but when overriding the invoke callback this call comes handy. This
		1010	function can be invoked from a watcher - this can be useful for example
		1011	when you want to do some lengthy calculation and want to pass further
		1012	event handling to another thread (you still have to make sure only one
		1013	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1014
		1015	=item int ev_pending_count (loop)
		1016
		1017	Returns the number of pending watchers - zero indicates that no watchers
		1018	are pending.
		1019
		1020	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1021
		1022	This overrides the invoke pending functionality of the loop: Instead of
		1023	invoking all pending watchers when there are any, C<ev_run> will call
		1024	this callback instead. This is useful, for example, when you want to
		1025	invoke the actual watchers inside another context (another thread etc.).
		1026
		1027	If you want to reset the callback, use C<ev_invoke_pending> as new
		1028	callback.
		1029
		1030	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1031
		1032	Sometimes you want to share the same loop between multiple threads. This
		1033	can be done relatively simply by putting mutex_lock/unlock calls around
		1034	each call to a libev function.
		1035
		1036	However, C<ev_run> can run an indefinite time, so it is not feasible
		1037	to wait for it to return. One way around this is to wake up the event
		1038	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1039	I<release> and I<acquire> callbacks on the loop.
		1040
		1041	When set, then C<release> will be called just before the thread is
		1042	suspended waiting for new events, and C<acquire> is called just
		1043	afterwards.
		1044
		1045	Ideally, C<release> will just call your mutex_unlock function, and
		1046	C<acquire> will just call the mutex_lock function again.
		1047
		1048	While event loop modifications are allowed between invocations of
		1049	C<release> and C<acquire> (that's their only purpose after all), no
		1050	modifications done will affect the event loop, i.e. adding watchers will
		1051	have no effect on the set of file descriptors being watched, or the time
		1052	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1053	to take note of any changes you made.
		1054
		1055	In theory, threads executing C<ev_run> will be async-cancel safe between
		1056	invocations of C<release> and C<acquire>.
		1057
		1058	See also the locking example in the C<THREADS> section later in this
		1059	document.
		1060
		1061	=item ev_set_userdata (loop, void *data)
		1062
		1063	=item void *ev_userdata (loop)
		1064
		1065	Set and retrieve a single C<void *> associated with a loop. When
		1066	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1067	C<0>.
		1068
		1069	These two functions can be used to associate arbitrary data with a loop,
		1070	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1071	C<acquire> callbacks described above, but of course can be (ab-)used for
		1072	any other purpose as well.
		1073
		1074	=item ev_verify (loop)
		1075
		1076	This function only does something when C<EV_VERIFY> support has been
		1077	compiled in, which is the default for non-minimal builds. It tries to go
		1078	through all internal structures and checks them for validity. If anything
		1079	is found to be inconsistent, it will print an error message to standard
		1080	error and call C<abort ()>.
		1081
		1082	This can be used to catch bugs inside libev itself: under normal
		1083	circumstances, this function will never abort as of course libev keeps its
		1084	data structures consistent.
283		1085
284	=back	1086	=back
285		1087
		1088
286	=head1 ANATOMY OF A WATCHER	1089	=head1 ANATOMY OF A WATCHER
287		1090
		1091	In the following description, uppercase C<TYPE> in names stands for the
		1092	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1093	watchers and C<ev_io_start> for I/O watchers.
		1094
288	A watcher is a structure that you create and register to record your	1095	A watcher is an opaque structure that you allocate and register to record
289	interest in some event. For instance, if you want to wait for STDIN to	1096	your interest in some event. To make a concrete example, imagine you want
290	become readable, you would create an C<ev_io> watcher for that:	1097	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1098	for that:
291		1099
292	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1100	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
293	{	1101	{
294	ev_io_stop (w);	1102	ev_io_stop (w);
295	ev_unloop (loop, EVUNLOOP_ALL);	1103	ev_break (loop, EVBREAK_ALL);
296	}	1104	}
297		1105
298	struct ev_loop *loop = ev_default_loop (0);	1106	struct ev_loop *loop = ev_default_loop (0);
		1107
299	struct ev_io stdin_watcher;	1108	ev_io stdin_watcher;
		1109
300	ev_init (&stdin_watcher, my_cb);	1110	ev_init (&stdin_watcher, my_cb);
301	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1111	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
302	ev_io_start (loop, &stdin_watcher);	1112	ev_io_start (loop, &stdin_watcher);
		1113
303	ev_loop (loop, 0);	1114	ev_run (loop, 0);
304		1115
305	As you can see, you are responsible for allocating the memory for your	1116	As you can see, you are responsible for allocating the memory for your
306	watcher structures (and it is usually a bad idea to do this on the stack,	1117	watcher structures (and it is I<usually> a bad idea to do this on the
307	although this can sometimes be quite valid).	1118	stack).
308		1119
		1120	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1121	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1122
309	Each watcher structure must be initialised by a call to C<ev_init	1123	Each watcher structure must be initialised by a call to C<ev_init (watcher
310	(watcher *, callback)>, which expects a callback to be provided. This	1124	*, callback)>, which expects a callback to be provided. This callback is
311	callback gets invoked each time the event occurs (or, in the case of io	1125	invoked each time the event occurs (or, in the case of I/O watchers, each
312	watchers, each time the event loop detects that the file descriptor given	1126	time the event loop detects that the file descriptor given is readable
313	is readable and/or writable).	1127	and/or writable).
314		1128
315	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1129	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
316	with arguments specific to this watcher type. There is also a macro	1130	macro to configure it, with arguments specific to the watcher type. There
317	to combine initialisation and setting in one call: C<< ev_<type>_init	1131	is also a macro to combine initialisation and setting in one call: C<<
318	(watcher *, callback, ...) >>.	1132	ev_TYPE_init (watcher *, callback, ...) >>.
319		1133
320	To make the watcher actually watch out for events, you have to start it	1134	To make the watcher actually watch out for events, you have to start it
321	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1135	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
322	*) >>), and you can stop watching for events at any time by calling the	1136	*) >>), and you can stop watching for events at any time by calling the
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1137	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
324		1138
325	As long as your watcher is active (has been started but not stopped) you	1139	As long as your watcher is active (has been started but not stopped) you
326	must not touch the values stored in it. Most specifically you must never	1140	must not touch the values stored in it. Most specifically you must never
327	reinitialise it or call its set method.	1141	reinitialise it or call its C<ev_TYPE_set> macro.
328
329	You can check whether an event is active by calling the C<ev_is_active
330	(watcher *)> macro. To see whether an event is outstanding (but the
331	callback for it has not been called yet) you can use the C<ev_is_pending
332	(watcher *)> macro.
333		1142
334	Each and every callback receives the event loop pointer as first, the	1143	Each and every callback receives the event loop pointer as first, the
335	registered watcher structure as second, and a bitset of received events as	1144	registered watcher structure as second, and a bitset of received events as
336	third argument.	1145	third argument.
337		1146
…		…
346	=item C<EV_WRITE>	1155	=item C<EV_WRITE>
347		1156
348	The file descriptor in the C<ev_io> watcher has become readable and/or	1157	The file descriptor in the C<ev_io> watcher has become readable and/or
349	writable.	1158	writable.
350		1159
351	=item C<EV_TIMEOUT>	1160	=item C<EV_TIMER>
352		1161
353	The C<ev_timer> watcher has timed out.	1162	The C<ev_timer> watcher has timed out.
354		1163
355	=item C<EV_PERIODIC>	1164	=item C<EV_PERIODIC>
356		1165
…		…
362		1171
363	=item C<EV_CHILD>	1172	=item C<EV_CHILD>
364		1173
365	The pid specified in the C<ev_child> watcher has received a status change.	1174	The pid specified in the C<ev_child> watcher has received a status change.
366		1175
		1176	=item C<EV_STAT>
		1177
		1178	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1179
367	=item C<EV_IDLE>	1180	=item C<EV_IDLE>
368		1181
369	The C<ev_idle> watcher has determined that you have nothing better to do.	1182	The C<ev_idle> watcher has determined that you have nothing better to do.
370		1183
371	=item C<EV_PREPARE>	1184	=item C<EV_PREPARE>
372		1185
373	=item C<EV_CHECK>	1186	=item C<EV_CHECK>
374		1187
375	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1188	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
376	to gather new events, and all C<ev_check> watchers are invoked just after	1189	gather new events, and all C<ev_check> watchers are queued (not invoked)
377	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1190	just after C<ev_run> has gathered them, but before it queues any callbacks
		1191	for any received events. That means C<ev_prepare> watchers are the last
		1192	watchers invoked before the event loop sleeps or polls for new events, and
		1193	C<ev_check> watchers will be invoked before any other watchers of the same
		1194	or lower priority within an event loop iteration.
		1195
378	received events. Callbacks of both watcher types can start and stop as	1196	Callbacks of both watcher types can start and stop as many watchers as
379	many watchers as they want, and all of them will be taken into account	1197	they want, and all of them will be taken into account (for example, a
380	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1198	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
381	C<ev_loop> from blocking).	1199	blocking).
		1200
		1201	=item C<EV_EMBED>
		1202
		1203	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1204
		1205	=item C<EV_FORK>
		1206
		1207	The event loop has been resumed in the child process after fork (see
		1208	C<ev_fork>).
		1209
		1210	=item C<EV_CLEANUP>
		1211
		1212	The event loop is about to be destroyed (see C<ev_cleanup>).
		1213
		1214	=item C<EV_ASYNC>
		1215
		1216	The given async watcher has been asynchronously notified (see C<ev_async>).
		1217
		1218	=item C<EV_CUSTOM>
		1219
		1220	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1221	by libev users to signal watchers (e.g. via C<ev_feed_event>).
382		1222
383	=item C<EV_ERROR>	1223	=item C<EV_ERROR>
384		1224
385	An unspecified error has occured, the watcher has been stopped. This might	1225	An unspecified error has occurred, the watcher has been stopped. This might
386	happen because the watcher could not be properly started because libev	1226	happen because the watcher could not be properly started because libev
387	ran out of memory, a file descriptor was found to be closed or any other	1227	ran out of memory, a file descriptor was found to be closed or any other
		1228	problem. Libev considers these application bugs.
		1229
388	problem. You best act on it by reporting the problem and somehow coping	1230	You best act on it by reporting the problem and somehow coping with the
389	with the watcher being stopped.	1231	watcher being stopped. Note that well-written programs should not receive
		1232	an error ever, so when your watcher receives it, this usually indicates a
		1233	bug in your program.
390		1234
391	Libev will usually signal a few "dummy" events together with an error,	1235	Libev will usually signal a few "dummy" events together with an error, for
392	for example it might indicate that a fd is readable or writable, and if	1236	example it might indicate that a fd is readable or writable, and if your
393	your callbacks is well-written it can just attempt the operation and cope	1237	callbacks is well-written it can just attempt the operation and cope with
394	with the error from read() or write(). This will not work in multithreaded	1238	the error from read() or write(). This will not work in multi-threaded
395	programs, though, so beware.	1239	programs, though, as the fd could already be closed and reused for another
		1240	thing, so beware.
396		1241
397	=back	1242	=back
398		1243
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1244	=head2 GENERIC WATCHER FUNCTIONS
400		1245
401	Each watcher has, by default, a member C<void *data> that you can change	1246	=over 4
402	and read at any time, libev will completely ignore it. This can be used
403	to associate arbitrary data with your watcher. If you need more data and
404	don't want to allocate memory and store a pointer to it in that data
405	member, you can also "subclass" the watcher type and provide your own
406	data:
407		1247
408	struct my_io	1248	=item C<ev_init> (ev_TYPE *watcher, callback)
		1249
		1250	This macro initialises the generic portion of a watcher. The contents
		1251	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1252	the generic parts of the watcher are initialised, you I<need> to call
		1253	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1254	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1255	which rolls both calls into one.
		1256
		1257	You can reinitialise a watcher at any time as long as it has been stopped
		1258	(or never started) and there are no pending events outstanding.
		1259
		1260	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1261	int revents)>.
		1262
		1263	Example: Initialise an C<ev_io> watcher in two steps.
		1264
		1265	ev_io w;
		1266	ev_init (&w, my_cb);
		1267	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1268
		1269	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1270
		1271	This macro initialises the type-specific parts of a watcher. You need to
		1272	call C<ev_init> at least once before you call this macro, but you can
		1273	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1274	macro on a watcher that is active (it can be pending, however, which is a
		1275	difference to the C<ev_init> macro).
		1276
		1277	Although some watcher types do not have type-specific arguments
		1278	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1279
		1280	See C<ev_init>, above, for an example.
		1281
		1282	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1283
		1284	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1285	calls into a single call. This is the most convenient method to initialise
		1286	a watcher. The same limitations apply, of course.
		1287
		1288	Example: Initialise and set an C<ev_io> watcher in one step.
		1289
		1290	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1291
		1292	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1293
		1294	Starts (activates) the given watcher. Only active watchers will receive
		1295	events. If the watcher is already active nothing will happen.
		1296
		1297	Example: Start the C<ev_io> watcher that is being abused as example in this
		1298	whole section.
		1299
		1300	ev_io_start (EV_DEFAULT_UC, &w);
		1301
		1302	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1303
		1304	Stops the given watcher if active, and clears the pending status (whether
		1305	the watcher was active or not).
		1306
		1307	It is possible that stopped watchers are pending - for example,
		1308	non-repeating timers are being stopped when they become pending - but
		1309	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1310	pending. If you want to free or reuse the memory used by the watcher it is
		1311	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1312
		1313	=item bool ev_is_active (ev_TYPE *watcher)
		1314
		1315	Returns a true value iff the watcher is active (i.e. it has been started
		1316	and not yet been stopped). As long as a watcher is active you must not modify
		1317	it.
		1318
		1319	=item bool ev_is_pending (ev_TYPE *watcher)
		1320
		1321	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1322	events but its callback has not yet been invoked). As long as a watcher
		1323	is pending (but not active) you must not call an init function on it (but
		1324	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1325	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1326	it).
		1327
		1328	=item callback ev_cb (ev_TYPE *watcher)
		1329
		1330	Returns the callback currently set on the watcher.
		1331
		1332	=item ev_set_cb (ev_TYPE *watcher, callback)
		1333
		1334	Change the callback. You can change the callback at virtually any time
		1335	(modulo threads).
		1336
		1337	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1338
		1339	=item int ev_priority (ev_TYPE *watcher)
		1340
		1341	Set and query the priority of the watcher. The priority is a small
		1342	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1343	(default: C<-2>). Pending watchers with higher priority will be invoked
		1344	before watchers with lower priority, but priority will not keep watchers
		1345	from being executed (except for C<ev_idle> watchers).
		1346
		1347	If you need to suppress invocation when higher priority events are pending
		1348	you need to look at C<ev_idle> watchers, which provide this functionality.
		1349
		1350	You I<must not> change the priority of a watcher as long as it is active or
		1351	pending.
		1352
		1353	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1354	fine, as long as you do not mind that the priority value you query might
		1355	or might not have been clamped to the valid range.
		1356
		1357	The default priority used by watchers when no priority has been set is
		1358	always C<0>, which is supposed to not be too high and not be too low :).
		1359
		1360	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1361	priorities.
		1362
		1363	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1364
		1365	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1366	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1367	can deal with that fact, as both are simply passed through to the
		1368	callback.
		1369
		1370	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1371
		1372	If the watcher is pending, this function clears its pending status and
		1373	returns its C<revents> bitset (as if its callback was invoked). If the
		1374	watcher isn't pending it does nothing and returns C<0>.
		1375
		1376	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1377	callback to be invoked, which can be accomplished with this function.
		1378
		1379	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1380
		1381	Feeds the given event set into the event loop, as if the specified event
		1382	had happened for the specified watcher (which must be a pointer to an
		1383	initialised but not necessarily started event watcher). Obviously you must
		1384	not free the watcher as long as it has pending events.
		1385
		1386	Stopping the watcher, letting libev invoke it, or calling
		1387	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1388	not started in the first place.
		1389
		1390	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1391	functions that do not need a watcher.
		1392
		1393	=back
		1394
		1395	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1396	OWN COMPOSITE WATCHERS> idioms.
		1397
		1398	=head2 WATCHER STATES
		1399
		1400	There are various watcher states mentioned throughout this manual -
		1401	active, pending and so on. In this section these states and the rules to
		1402	transition between them will be described in more detail - and while these
		1403	rules might look complicated, they usually do "the right thing".
		1404
		1405	=over 4
		1406
		1407	=item initialised
		1408
		1409	Before a watcher can be registered with the event loop it has to be
		1410	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1411	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1412
		1413	In this state it is simply some block of memory that is suitable for
		1414	use in an event loop. It can be moved around, freed, reused etc. at
		1415	will - as long as you either keep the memory contents intact, or call
		1416	C<ev_TYPE_init> again.
		1417
		1418	=item started/running/active
		1419
		1420	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1421	property of the event loop, and is actively waiting for events. While in
		1422	this state it cannot be accessed (except in a few documented ways), moved,
		1423	freed or anything else - the only legal thing is to keep a pointer to it,
		1424	and call libev functions on it that are documented to work on active watchers.
		1425
		1426	=item pending
		1427
		1428	If a watcher is active and libev determines that an event it is interested
		1429	in has occurred (such as a timer expiring), it will become pending. It will
		1430	stay in this pending state until either it is stopped or its callback is
		1431	about to be invoked, so it is not normally pending inside the watcher
		1432	callback.
		1433
		1434	The watcher might or might not be active while it is pending (for example,
		1435	an expired non-repeating timer can be pending but no longer active). If it
		1436	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1437	but it is still property of the event loop at this time, so cannot be
		1438	moved, freed or reused. And if it is active the rules described in the
		1439	previous item still apply.
		1440
		1441	It is also possible to feed an event on a watcher that is not active (e.g.
		1442	via C<ev_feed_event>), in which case it becomes pending without being
		1443	active.
		1444
		1445	=item stopped
		1446
		1447	A watcher can be stopped implicitly by libev (in which case it might still
		1448	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1449	latter will clear any pending state the watcher might be in, regardless
		1450	of whether it was active or not, so stopping a watcher explicitly before
		1451	freeing it is often a good idea.
		1452
		1453	While stopped (and not pending) the watcher is essentially in the
		1454	initialised state, that is, it can be reused, moved, modified in any way
		1455	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1456	it again).
		1457
		1458	=back
		1459
		1460	=head2 WATCHER PRIORITY MODELS
		1461
		1462	Many event loops support I<watcher priorities>, which are usually small
		1463	integers that influence the ordering of event callback invocation
		1464	between watchers in some way, all else being equal.
		1465
		1466	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1467	description for the more technical details such as the actual priority
		1468	range.
		1469
		1470	There are two common ways how these these priorities are being interpreted
		1471	by event loops:
		1472
		1473	In the more common lock-out model, higher priorities "lock out" invocation
		1474	of lower priority watchers, which means as long as higher priority
		1475	watchers receive events, lower priority watchers are not being invoked.
		1476
		1477	The less common only-for-ordering model uses priorities solely to order
		1478	callback invocation within a single event loop iteration: Higher priority
		1479	watchers are invoked before lower priority ones, but they all get invoked
		1480	before polling for new events.
		1481
		1482	Libev uses the second (only-for-ordering) model for all its watchers
		1483	except for idle watchers (which use the lock-out model).
		1484
		1485	The rationale behind this is that implementing the lock-out model for
		1486	watchers is not well supported by most kernel interfaces, and most event
		1487	libraries will just poll for the same events again and again as long as
		1488	their callbacks have not been executed, which is very inefficient in the
		1489	common case of one high-priority watcher locking out a mass of lower
		1490	priority ones.
		1491
		1492	Static (ordering) priorities are most useful when you have two or more
		1493	watchers handling the same resource: a typical usage example is having an
		1494	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1495	timeouts. Under load, data might be received while the program handles
		1496	other jobs, but since timers normally get invoked first, the timeout
		1497	handler will be executed before checking for data. In that case, giving
		1498	the timer a lower priority than the I/O watcher ensures that I/O will be
		1499	handled first even under adverse conditions (which is usually, but not
		1500	always, what you want).
		1501
		1502	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1503	will only be executed when no same or higher priority watchers have
		1504	received events, they can be used to implement the "lock-out" model when
		1505	required.
		1506
		1507	For example, to emulate how many other event libraries handle priorities,
		1508	you can associate an C<ev_idle> watcher to each such watcher, and in
		1509	the normal watcher callback, you just start the idle watcher. The real
		1510	processing is done in the idle watcher callback. This causes libev to
		1511	continuously poll and process kernel event data for the watcher, but when
		1512	the lock-out case is known to be rare (which in turn is rare :), this is
		1513	workable.
		1514
		1515	Usually, however, the lock-out model implemented that way will perform
		1516	miserably under the type of load it was designed to handle. In that case,
		1517	it might be preferable to stop the real watcher before starting the
		1518	idle watcher, so the kernel will not have to process the event in case
		1519	the actual processing will be delayed for considerable time.
		1520
		1521	Here is an example of an I/O watcher that should run at a strictly lower
		1522	priority than the default, and which should only process data when no
		1523	other events are pending:
		1524
		1525	ev_idle idle; // actual processing watcher
		1526	ev_io io; // actual event watcher
		1527
		1528	static void
		1529	io_cb (EV_P_ ev_io *w, int revents)
409	{	1530	{
410	struct ev_io io;	1531	// stop the I/O watcher, we received the event, but
411	int otherfd;	1532	// are not yet ready to handle it.
412	void *somedata;	1533	ev_io_stop (EV_A_ w);
413	struct whatever *mostinteresting;	1534
		1535	// start the idle watcher to handle the actual event.
		1536	// it will not be executed as long as other watchers
		1537	// with the default priority are receiving events.
		1538	ev_idle_start (EV_A_ &idle);
414	}	1539	}
415		1540
416	And since your callback will be called with a pointer to the watcher, you	1541	static void
417	can cast it back to your own type:	1542	idle_cb (EV_P_ ev_idle *w, int revents)
418
419	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
420	{	1543	{
421	struct my_io *w = (struct my_io *)w_;	1544	// actual processing
422	...	1545	read (STDIN_FILENO, ...);
		1546
		1547	// have to start the I/O watcher again, as
		1548	// we have handled the event
		1549	ev_io_start (EV_P_ &io);
423	}	1550	}
424		1551
425	More interesting and less C-conformant ways of catsing your callback type	1552	// initialisation
426	have been omitted....	1553	ev_idle_init (&idle, idle_cb);
		1554	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1555	ev_io_start (EV_DEFAULT_ &io);
		1556
		1557	In the "real" world, it might also be beneficial to start a timer, so that
		1558	low-priority connections can not be locked out forever under load. This
		1559	enables your program to keep a lower latency for important connections
		1560	during short periods of high load, while not completely locking out less
		1561	important ones.
427		1562
428		1563
429	=head1 WATCHER TYPES	1564	=head1 WATCHER TYPES
430		1565
431	This section describes each watcher in detail, but will not repeat	1566	This section describes each watcher in detail, but will not repeat
432	information given in the last section.	1567	information given in the last section. Any initialisation/set macros,
		1568	functions and members specific to the watcher type are explained.
433		1569
		1570	Members are additionally marked with either I<[read-only]>, meaning that,
		1571	while the watcher is active, you can look at the member and expect some
		1572	sensible content, but you must not modify it (you can modify it while the
		1573	watcher is stopped to your hearts content), or I<[read-write]>, which
		1574	means you can expect it to have some sensible content while the watcher
		1575	is active, but you can also modify it. Modifying it may not do something
		1576	sensible or take immediate effect (or do anything at all), but libev will
		1577	not crash or malfunction in any way.
		1578
		1579
434	=head2 C<ev_io> - is this file descriptor readable or writable	1580	=head2 C<ev_io> - is this file descriptor readable or writable?
435		1581
436	I/O watchers check whether a file descriptor is readable or writable	1582	I/O watchers check whether a file descriptor is readable or writable
437	in each iteration of the event loop (This behaviour is called	1583	in each iteration of the event loop, or, more precisely, when reading
438	level-triggering because you keep receiving events as long as the	1584	would not block the process and writing would at least be able to write
439	condition persists. Remember you can stop the watcher if you don't want to	1585	some data. This behaviour is called level-triggering because you keep
440	act on the event and neither want to receive future events).	1586	receiving events as long as the condition persists. Remember you can stop
		1587	the watcher if you don't want to act on the event and neither want to
		1588	receive future events.
441		1589
442	In general you can register as many read and/or write event watchers per	1590	In general you can register as many read and/or write event watchers per
443	fd as you want (as long as you don't confuse yourself). Setting all file	1591	fd as you want (as long as you don't confuse yourself). Setting all file
444	descriptors to non-blocking mode is also usually a good idea (but not	1592	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	1593	required if you know what you are doing).
446		1594
447	You have to be careful with dup'ed file descriptors, though. Some backends	1595	Another thing you have to watch out for is that it is quite easy to
448	(the linux epoll backend is a notable example) cannot handle dup'ed file	1596	receive "spurious" readiness notifications, that is, your callback might
449	descriptors correctly if you register interest in two or more fds pointing	1597	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
450	to the same underlying file/socket etc. description (that is, they share	1598	because there is no data. It is very easy to get into this situation even
451	the same underlying "file open").	1599	with a relatively standard program structure. Thus it is best to always
		1600	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
		1601	preferable to a program hanging until some data arrives.
452		1602
453	If you must do this, then force the use of a known-to-be-good backend	1603	If you cannot run the fd in non-blocking mode (for example you should
454	(at the time of this writing, this includes only EVMETHOD_SELECT and	1604	not play around with an Xlib connection), then you have to separately
455	EVMETHOD_POLL).	1605	re-test whether a file descriptor is really ready with a known-to-be good
		1606	interface such as poll (fortunately in the case of Xlib, it already does
		1607	this on its own, so its quite safe to use). Some people additionally
		1608	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1609	indefinitely.
		1610
		1611	But really, best use non-blocking mode.
		1612
		1613	=head3 The special problem of disappearing file descriptors
		1614
		1615	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1616	descriptor (either due to calling C<close> explicitly or any other means,
		1617	such as C<dup2>). The reason is that you register interest in some file
		1618	descriptor, but when it goes away, the operating system will silently drop
		1619	this interest. If another file descriptor with the same number then is
		1620	registered with libev, there is no efficient way to see that this is, in
		1621	fact, a different file descriptor.
		1622
		1623	To avoid having to explicitly tell libev about such cases, libev follows
		1624	the following policy: Each time C<ev_io_set> is being called, libev
		1625	will assume that this is potentially a new file descriptor, otherwise
		1626	it is assumed that the file descriptor stays the same. That means that
		1627	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1628	descriptor even if the file descriptor number itself did not change.
		1629
		1630	This is how one would do it normally anyway, the important point is that
		1631	the libev application should not optimise around libev but should leave
		1632	optimisations to libev.
		1633
		1634	=head3 The special problem of dup'ed file descriptors
		1635
		1636	Some backends (e.g. epoll), cannot register events for file descriptors,
		1637	but only events for the underlying file descriptions. That means when you
		1638	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1639	events for them, only one file descriptor might actually receive events.
		1640
		1641	There is no workaround possible except not registering events
		1642	for potentially C<dup ()>'ed file descriptors, or to resort to
		1643	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1644
		1645	=head3 The special problem of files
		1646
		1647	Many people try to use C<select> (or libev) on file descriptors
		1648	representing files, and expect it to become ready when their program
		1649	doesn't block on disk accesses (which can take a long time on their own).
		1650
		1651	However, this cannot ever work in the "expected" way - you get a readiness
		1652	notification as soon as the kernel knows whether and how much data is
		1653	there, and in the case of open files, that's always the case, so you
		1654	always get a readiness notification instantly, and your read (or possibly
		1655	write) will still block on the disk I/O.
		1656
		1657	Another way to view it is that in the case of sockets, pipes, character
		1658	devices and so on, there is another party (the sender) that delivers data
		1659	on its own, but in the case of files, there is no such thing: the disk
		1660	will not send data on its own, simply because it doesn't know what you
		1661	wish to read - you would first have to request some data.
		1662
		1663	Since files are typically not-so-well supported by advanced notification
		1664	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1665	to files, even though you should not use it. The reason for this is
		1666	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1667	usually a tty, often a pipe, but also sometimes files or special devices
		1668	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1669	F</dev/urandom>), and even though the file might better be served with
		1670	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1671	it "just works" instead of freezing.
		1672
		1673	So avoid file descriptors pointing to files when you know it (e.g. use
		1674	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1675	when you rarely read from a file instead of from a socket, and want to
		1676	reuse the same code path.
		1677
		1678	=head3 The special problem of fork
		1679
		1680	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1681	useless behaviour. Libev fully supports fork, but needs to be told about
		1682	it in the child if you want to continue to use it in the child.
		1683
		1684	To support fork in your child processes, you have to call C<ev_loop_fork
		1685	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1686	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1687
		1688	=head3 The special problem of SIGPIPE
		1689
		1690	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1691	when writing to a pipe whose other end has been closed, your program gets
		1692	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1693	this is sensible behaviour, for daemons, this is usually undesirable.
		1694
		1695	So when you encounter spurious, unexplained daemon exits, make sure you
		1696	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1697	somewhere, as that would have given you a big clue).
		1698
		1699	=head3 The special problem of accept()ing when you can't
		1700
		1701	Many implementations of the POSIX C<accept> function (for example,
		1702	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1703	connection from the pending queue in all error cases.
		1704
		1705	For example, larger servers often run out of file descriptors (because
		1706	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1707	rejecting the connection, leading to libev signalling readiness on
		1708	the next iteration again (the connection still exists after all), and
		1709	typically causing the program to loop at 100% CPU usage.
		1710
		1711	Unfortunately, the set of errors that cause this issue differs between
		1712	operating systems, there is usually little the app can do to remedy the
		1713	situation, and no known thread-safe method of removing the connection to
		1714	cope with overload is known (to me).
		1715
		1716	One of the easiest ways to handle this situation is to just ignore it
		1717	- when the program encounters an overload, it will just loop until the
		1718	situation is over. While this is a form of busy waiting, no OS offers an
		1719	event-based way to handle this situation, so it's the best one can do.
		1720
		1721	A better way to handle the situation is to log any errors other than
		1722	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1723	messages, and continue as usual, which at least gives the user an idea of
		1724	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1725	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1726	usage.
		1727
		1728	If your program is single-threaded, then you could also keep a dummy file
		1729	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1730	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1731	close that fd, and create a new dummy fd. This will gracefully refuse
		1732	clients under typical overload conditions.
		1733
		1734	The last way to handle it is to simply log the error and C<exit>, as
		1735	is often done with C<malloc> failures, but this results in an easy
		1736	opportunity for a DoS attack.
		1737
		1738	=head3 Watcher-Specific Functions
456		1739
457	=over 4	1740	=over 4
458		1741
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1742	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1743
461	=item ev_io_set (ev_io *, int fd, int events)	1744	=item ev_io_set (ev_io *, int fd, int events)
462		1745
463	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1746	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
464	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1747	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
465	EV_WRITE> to receive the given events.	1748	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1749
		1750	=item int fd [read-only]
		1751
		1752	The file descriptor being watched.
		1753
		1754	=item int events [read-only]
		1755
		1756	The events being watched.
466		1757
467	=back	1758	=back
468		1759
		1760	=head3 Examples
		1761
		1762	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1763	readable, but only once. Since it is likely line-buffered, you could
		1764	attempt to read a whole line in the callback.
		1765
		1766	static void
		1767	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1768	{
		1769	ev_io_stop (loop, w);
		1770	.. read from stdin here (or from w->fd) and handle any I/O errors
		1771	}
		1772
		1773	...
		1774	struct ev_loop *loop = ev_default_init (0);
		1775	ev_io stdin_readable;
		1776	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1777	ev_io_start (loop, &stdin_readable);
		1778	ev_run (loop, 0);
		1779
		1780
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1781	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1782
471	Timer watchers are simple relative timers that generate an event after a	1783	Timer watchers are simple relative timers that generate an event after a
472	given time, and optionally repeating in regular intervals after that.	1784	given time, and optionally repeating in regular intervals after that.
473		1785
474	The timers are based on real time, that is, if you register an event that	1786	The timers are based on real time, that is, if you register an event that
475	times out after an hour and you reset your system clock to last years	1787	times out after an hour and you reset your system clock to January last
476	time, it will still time out after (roughly) and hour. "Roughly" because	1788	year, it will still time out after (roughly) one hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1789	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1790	monotonic clock option helps a lot here).
		1791
		1792	The callback is guaranteed to be invoked only I<after> its timeout has
		1793	passed (not I<at>, so on systems with very low-resolution clocks this
		1794	might introduce a small delay, see "the special problem of being too
		1795	early", below). If multiple timers become ready during the same loop
		1796	iteration then the ones with earlier time-out values are invoked before
		1797	ones of the same priority with later time-out values (but this is no
		1798	longer true when a callback calls C<ev_run> recursively).
		1799
		1800	=head3 Be smart about timeouts
		1801
		1802	Many real-world problems involve some kind of timeout, usually for error
		1803	recovery. A typical example is an HTTP request - if the other side hangs,
		1804	you want to raise some error after a while.
		1805
		1806	What follows are some ways to handle this problem, from obvious and
		1807	inefficient to smart and efficient.
		1808
		1809	In the following, a 60 second activity timeout is assumed - a timeout that
		1810	gets reset to 60 seconds each time there is activity (e.g. each time some
		1811	data or other life sign was received).
		1812
		1813	=over 4
		1814
		1815	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1816
		1817	This is the most obvious, but not the most simple way: In the beginning,
		1818	start the watcher:
		1819
		1820	ev_timer_init (timer, callback, 60., 0.);
		1821	ev_timer_start (loop, timer);
		1822
		1823	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1824	and start it again:
		1825
		1826	ev_timer_stop (loop, timer);
		1827	ev_timer_set (timer, 60., 0.);
		1828	ev_timer_start (loop, timer);
		1829
		1830	This is relatively simple to implement, but means that each time there is
		1831	some activity, libev will first have to remove the timer from its internal
		1832	data structure and then add it again. Libev tries to be fast, but it's
		1833	still not a constant-time operation.
		1834
		1835	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1836
		1837	This is the easiest way, and involves using C<ev_timer_again> instead of
		1838	C<ev_timer_start>.
		1839
		1840	To implement this, configure an C<ev_timer> with a C<repeat> value
		1841	of C<60> and then call C<ev_timer_again> at start and each time you
		1842	successfully read or write some data. If you go into an idle state where
		1843	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1844	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1845
		1846	That means you can ignore both the C<ev_timer_start> function and the
		1847	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1848	member and C<ev_timer_again>.
		1849
		1850	At start:
		1851
		1852	ev_init (timer, callback);
		1853	timer->repeat = 60.;
		1854	ev_timer_again (loop, timer);
		1855
		1856	Each time there is some activity:
		1857
		1858	ev_timer_again (loop, timer);
		1859
		1860	It is even possible to change the time-out on the fly, regardless of
		1861	whether the watcher is active or not:
		1862
		1863	timer->repeat = 30.;
		1864	ev_timer_again (loop, timer);
		1865
		1866	This is slightly more efficient then stopping/starting the timer each time
		1867	you want to modify its timeout value, as libev does not have to completely
		1868	remove and re-insert the timer from/into its internal data structure.
		1869
		1870	It is, however, even simpler than the "obvious" way to do it.
		1871
		1872	=item 3. Let the timer time out, but then re-arm it as required.
		1873
		1874	This method is more tricky, but usually most efficient: Most timeouts are
		1875	relatively long compared to the intervals between other activity - in
		1876	our example, within 60 seconds, there are usually many I/O events with
		1877	associated activity resets.
		1878
		1879	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1880	but remember the time of last activity, and check for a real timeout only
		1881	within the callback:
		1882
		1883	ev_tstamp timeout = 60.;
		1884	ev_tstamp last_activity; // time of last activity
		1885	ev_timer timer;
		1886
		1887	static void
		1888	callback (EV_P_ ev_timer *w, int revents)
		1889	{
		1890	// calculate when the timeout would happen
		1891	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1892
		1893	// if negative, it means we the timeout already occurred
		1894	if (after < 0.)
		1895	{
		1896	// timeout occurred, take action
		1897	}
		1898	else
		1899	{
		1900	// callback was invoked, but there was some recent
		1901	// activity. simply restart the timer to time out
		1902	// after "after" seconds, which is the earliest time
		1903	// the timeout can occur.
		1904	ev_timer_set (w, after, 0.);
		1905	ev_timer_start (EV_A_ w);
		1906	}
		1907	}
		1908
		1909	To summarise the callback: first calculate in how many seconds the
		1910	timeout will occur (by calculating the absolute time when it would occur,
		1911	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1912	(EV_A)> from that).
		1913
		1914	If this value is negative, then we are already past the timeout, i.e. we
		1915	timed out, and need to do whatever is needed in this case.
		1916
		1917	Otherwise, we now the earliest time at which the timeout would trigger,
		1918	and simply start the timer with this timeout value.
		1919
		1920	In other words, each time the callback is invoked it will check whether
		1921	the timeout occurred. If not, it will simply reschedule itself to check
		1922	again at the earliest time it could time out. Rinse. Repeat.
		1923
		1924	This scheme causes more callback invocations (about one every 60 seconds
		1925	minus half the average time between activity), but virtually no calls to
		1926	libev to change the timeout.
		1927
		1928	To start the machinery, simply initialise the watcher and set
		1929	C<last_activity> to the current time (meaning there was some activity just
		1930	now), then call the callback, which will "do the right thing" and start
		1931	the timer:
		1932
		1933	last_activity = ev_now (EV_A);
		1934	ev_init (&timer, callback);
		1935	callback (EV_A_ &timer, 0);
		1936
		1937	When there is some activity, simply store the current time in
		1938	C<last_activity>, no libev calls at all:
		1939
		1940	if (activity detected)
		1941	last_activity = ev_now (EV_A);
		1942
		1943	When your timeout value changes, then the timeout can be changed by simply
		1944	providing a new value, stopping the timer and calling the callback, which
		1945	will again do the right thing (for example, time out immediately :).
		1946
		1947	timeout = new_value;
		1948	ev_timer_stop (EV_A_ &timer);
		1949	callback (EV_A_ &timer, 0);
		1950
		1951	This technique is slightly more complex, but in most cases where the
		1952	time-out is unlikely to be triggered, much more efficient.
		1953
		1954	=item 4. Wee, just use a double-linked list for your timeouts.
		1955
		1956	If there is not one request, but many thousands (millions...), all
		1957	employing some kind of timeout with the same timeout value, then one can
		1958	do even better:
		1959
		1960	When starting the timeout, calculate the timeout value and put the timeout
		1961	at the I<end> of the list.
		1962
		1963	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1964	the list is expected to fire (for example, using the technique #3).
		1965
		1966	When there is some activity, remove the timer from the list, recalculate
		1967	the timeout, append it to the end of the list again, and make sure to
		1968	update the C<ev_timer> if it was taken from the beginning of the list.
		1969
		1970	This way, one can manage an unlimited number of timeouts in O(1) time for
		1971	starting, stopping and updating the timers, at the expense of a major
		1972	complication, and having to use a constant timeout. The constant timeout
		1973	ensures that the list stays sorted.
		1974
		1975	=back
		1976
		1977	So which method the best?
		1978
		1979	Method #2 is a simple no-brain-required solution that is adequate in most
		1980	situations. Method #3 requires a bit more thinking, but handles many cases
		1981	better, and isn't very complicated either. In most case, choosing either
		1982	one is fine, with #3 being better in typical situations.
		1983
		1984	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1985	rather complicated, but extremely efficient, something that really pays
		1986	off after the first million or so of active timers, i.e. it's usually
		1987	overkill :)
		1988
		1989	=head3 The special problem of being too early
		1990
		1991	If you ask a timer to call your callback after three seconds, then
		1992	you expect it to be invoked after three seconds - but of course, this
		1993	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1994	guaranteed to any precision by libev - imagine somebody suspending the
		1995	process with a STOP signal for a few hours for example.
		1996
		1997	So, libev tries to invoke your callback as soon as possible I<after> the
		1998	delay has occurred, but cannot guarantee this.
		1999
		2000	A less obvious failure mode is calling your callback too early: many event
		2001	loops compare timestamps with a "elapsed delay >= requested delay", but
		2002	this can cause your callback to be invoked much earlier than you would
		2003	expect.
		2004
		2005	To see why, imagine a system with a clock that only offers full second
		2006	resolution (think windows if you can't come up with a broken enough OS
		2007	yourself). If you schedule a one-second timer at the time 500.9, then the
		2008	event loop will schedule your timeout to elapse at a system time of 500
		2009	(500.9 truncated to the resolution) + 1, or 501.
		2010
		2011	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2012	501" and invoke the callback 0.1s after it was started, even though a
		2013	one-second delay was requested - this is being "too early", despite best
		2014	intentions.
		2015
		2016	This is the reason why libev will never invoke the callback if the elapsed
		2017	delay equals the requested delay, but only when the elapsed delay is
		2018	larger than the requested delay. In the example above, libev would only invoke
		2019	the callback at system time 502, or 1.1s after the timer was started.
		2020
		2021	So, while libev cannot guarantee that your callback will be invoked
		2022	exactly when requested, it I<can> and I<does> guarantee that the requested
		2023	delay has actually elapsed, or in other words, it always errs on the "too
		2024	late" side of things.
		2025
		2026	=head3 The special problem of time updates
		2027
		2028	Establishing the current time is a costly operation (it usually takes
		2029	at least one system call): EV therefore updates its idea of the current
		2030	time only before and after C<ev_run> collects new events, which causes a
		2031	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2032	lots of events in one iteration.
479		2033
480	The relative timeouts are calculated relative to the C<ev_now ()>	2034	The relative timeouts are calculated relative to the C<ev_now ()>
481	time. This is usually the right thing as this timestamp refers to the time	2035	time. This is usually the right thing as this timestamp refers to the time
482	of the event triggering whatever timeout you are modifying/starting. If	2036	of the event triggering whatever timeout you are modifying/starting. If
483	you suspect event processing to be delayed and you *need* to base the timeout	2037	you suspect event processing to be delayed and you I<need> to base the
484	on the current time, use something like this to adjust for this:	2038	timeout on the current time, use something like the following to adjust
		2039	for it:
485		2040
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2041	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
		2042
		2043	If the event loop is suspended for a long time, you can also force an
		2044	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		2045	()>, although that will push the event time of all outstanding events
		2046	further into the future.
		2047
		2048	=head3 The special problem of unsynchronised clocks
		2049
		2050	Modern systems have a variety of clocks - libev itself uses the normal
		2051	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2052	jumps).
		2053
		2054	Neither of these clocks is synchronised with each other or any other clock
		2055	on the system, so C<ev_time ()> might return a considerably different time
		2056	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2057	a call to C<gettimeofday> might return a second count that is one higher
		2058	than a directly following call to C<time>.
		2059
		2060	The moral of this is to only compare libev-related timestamps with
		2061	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2062	a second or so.
		2063
		2064	One more problem arises due to this lack of synchronisation: if libev uses
		2065	the system monotonic clock and you compare timestamps from C<ev_time>
		2066	or C<ev_now> from when you started your timer and when your callback is
		2067	invoked, you will find that sometimes the callback is a bit "early".
		2068
		2069	This is because C<ev_timer>s work in real time, not wall clock time, so
		2070	libev makes sure your callback is not invoked before the delay happened,
		2071	I<measured according to the real time>, not the system clock.
		2072
		2073	If your timeouts are based on a physical timescale (e.g. "time out this
		2074	connection after 100 seconds") then this shouldn't bother you as it is
		2075	exactly the right behaviour.
		2076
		2077	If you want to compare wall clock/system timestamps to your timers, then
		2078	you need to use C<ev_periodic>s, as these are based on the wall clock
		2079	time, where your comparisons will always generate correct results.
		2080
		2081	=head3 The special problems of suspended animation
		2082
		2083	When you leave the server world it is quite customary to hit machines that
		2084	can suspend/hibernate - what happens to the clocks during such a suspend?
		2085
		2086	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2087	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2088	to run until the system is suspended, but they will not advance while the
		2089	system is suspended. That means, on resume, it will be as if the program
		2090	was frozen for a few seconds, but the suspend time will not be counted
		2091	towards C<ev_timer> when a monotonic clock source is used. The real time
		2092	clock advanced as expected, but if it is used as sole clocksource, then a
		2093	long suspend would be detected as a time jump by libev, and timers would
		2094	be adjusted accordingly.
		2095
		2096	I would not be surprised to see different behaviour in different between
		2097	operating systems, OS versions or even different hardware.
		2098
		2099	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2100	time jump in the monotonic clocks and the realtime clock. If the program
		2101	is suspended for a very long time, and monotonic clock sources are in use,
		2102	then you can expect C<ev_timer>s to expire as the full suspension time
		2103	will be counted towards the timers. When no monotonic clock source is in
		2104	use, then libev will again assume a timejump and adjust accordingly.
		2105
		2106	It might be beneficial for this latter case to call C<ev_suspend>
		2107	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2108	deterministic behaviour in this case (you can do nothing against
		2109	C<SIGSTOP>).
		2110
		2111	=head3 Watcher-Specific Functions and Data Members
487		2112
488	=over 4	2113	=over 4
489		2114
490	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2115	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
491		2116
492	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2117	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
493		2118
494	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2119	Configure the timer to trigger after C<after> seconds. If C<repeat>
495	C<0.>, then it will automatically be stopped. If it is positive, then the	2120	is C<0.>, then it will automatically be stopped once the timeout is
496	timer will automatically be configured to trigger again C<repeat> seconds	2121	reached. If it is positive, then the timer will automatically be
497	later, again, and again, until stopped manually.	2122	configured to trigger again C<repeat> seconds later, again, and again,
		2123	until stopped manually.
498		2124
499	The timer itself will do a best-effort at avoiding drift, that is, if you	2125	The timer itself will do a best-effort at avoiding drift, that is, if
500	configure a timer to trigger every 10 seconds, then it will trigger at	2126	you configure a timer to trigger every 10 seconds, then it will normally
501	exactly 10 second intervals. If, however, your program cannot keep up with	2127	trigger at exactly 10 second intervals. If, however, your program cannot
502	the timer (because it takes longer than those 10 seconds to do stuff) the	2128	keep up with the timer (because it takes longer than those 10 seconds to
503	timer will not fire more than once per event loop iteration.	2129	do stuff) the timer will not fire more than once per event loop iteration.
504		2130
505	=item ev_timer_again (loop)	2131	=item ev_timer_again (loop, ev_timer *)
506		2132
507	This will act as if the timer timed out and restart it again if it is	2133	This will act as if the timer timed out, and restarts it again if it is
508	repeating. The exact semantics are:	2134	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2135	timeout to the C<repeat> value and calling C<ev_timer_start>.
509		2136
		2137	The exact semantics are as in the following rules, all of which will be
		2138	applied to the watcher:
		2139
		2140	=over 4
		2141
		2142	=item If the timer is pending, the pending status is always cleared.
		2143
510	If the timer is started but nonrepeating, stop it.	2144	=item If the timer is started but non-repeating, stop it (as if it timed
		2145	out, without invoking it).
511		2146
512	If the timer is repeating, either start it if necessary (with the repeat	2147	=item If the timer is repeating, make the C<repeat> value the new timeout
513	value), or reset the running timer to the repeat value.	2148	and start the timer, if necessary.
514
515	This sounds a bit complicated, but here is a useful and typical
516	example: Imagine you have a tcp connection and you want a so-called idle
517	timeout, that is, you want to be called when there have been, say, 60
518	seconds of inactivity on the socket. The easiest way to do this is to
519	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
520	time you successfully read or write some data. If you go into an idle
521	state where you do not expect data to travel on the socket, you can stop
522	the timer, and again will automatically restart it if need be.
523		2149
524	=back	2150	=back
525		2151
		2152	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
		2153	usage example.
		2154
		2155	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2156
		2157	Returns the remaining time until a timer fires. If the timer is active,
		2158	then this time is relative to the current event loop time, otherwise it's
		2159	the timeout value currently configured.
		2160
		2161	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2162	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2163	will return C<4>. When the timer expires and is restarted, it will return
		2164	roughly C<7> (likely slightly less as callback invocation takes some time,
		2165	too), and so on.
		2166
		2167	=item ev_tstamp repeat [read-write]
		2168
		2169	The current C<repeat> value. Will be used each time the watcher times out
		2170	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2171	which is also when any modifications are taken into account.
		2172
		2173	=back
		2174
		2175	=head3 Examples
		2176
		2177	Example: Create a timer that fires after 60 seconds.
		2178
		2179	static void
		2180	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2181	{
		2182	.. one minute over, w is actually stopped right here
		2183	}
		2184
		2185	ev_timer mytimer;
		2186	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2187	ev_timer_start (loop, &mytimer);
		2188
		2189	Example: Create a timeout timer that times out after 10 seconds of
		2190	inactivity.
		2191
		2192	static void
		2193	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2194	{
		2195	.. ten seconds without any activity
		2196	}
		2197
		2198	ev_timer mytimer;
		2199	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2200	ev_timer_again (&mytimer); /* start timer */
		2201	ev_run (loop, 0);
		2202
		2203	// and in some piece of code that gets executed on any "activity":
		2204	// reset the timeout to start ticking again at 10 seconds
		2205	ev_timer_again (&mytimer);
		2206
		2207
526	=head2 C<ev_periodic> - to cron or not to cron	2208	=head2 C<ev_periodic> - to cron or not to cron?
527		2209
528	Periodic watchers are also timers of a kind, but they are very versatile	2210	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	2211	(and unfortunately a bit complex).
530		2212
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2213	Unlike C<ev_timer>, periodic watchers are not based on real time (or
532	but on wallclock time (absolute time). You can tell a periodic watcher	2214	relative time, the physical time that passes) but on wall clock time
533	to trigger "at" some specific point in time. For example, if you tell a	2215	(absolute time, the thing you can read on your calendar or clock). The
534	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2216	difference is that wall clock time can run faster or slower than real
535	+ 10.>) and then reset your system clock to the last year, then it will	2217	time, and time jumps are not uncommon (e.g. when you adjust your
536	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2218	wrist-watch).
537	roughly 10 seconds later and of course not if you reset your system time
538	again).
539		2219
540	They can also be used to implement vastly more complex timers, such as	2220	You can tell a periodic watcher to trigger after some specific point
		2221	in time: for example, if you tell a periodic watcher to trigger "in 10
		2222	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2223	not a delay) and then reset your system clock to January of the previous
		2224	year, then it will take a year or more to trigger the event (unlike an
		2225	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2226	it, as it uses a relative timeout).
		2227
		2228	C<ev_periodic> watchers can also be used to implement vastly more complex
541	triggering an event on eahc midnight, local time.	2229	timers, such as triggering an event on each "midnight, local time", or
		2230	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2231	those cannot react to time jumps.
		2232
		2233	As with timers, the callback is guaranteed to be invoked only when the
		2234	point in time where it is supposed to trigger has passed. If multiple
		2235	timers become ready during the same loop iteration then the ones with
		2236	earlier time-out values are invoked before ones with later time-out values
		2237	(but this is no longer true when a callback calls C<ev_run> recursively).
		2238
		2239	=head3 Watcher-Specific Functions and Data Members
542		2240
543	=over 4	2241	=over 4
544		2242
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2243	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
546		2244
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2245	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
548		2246
549	Lots of arguments, lets sort it out... There are basically three modes of	2247	Lots of arguments, let's sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	2248	operation, and we will explain them from simplest to most complex:
551
552		2249
553	=over 4	2250	=over 4
554		2251
555	=item * absolute timer (interval = reschedule_cb = 0)	2252	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
556		2253
557	In this configuration the watcher triggers an event at the wallclock time	2254	In this configuration the watcher triggers an event after the wall clock
558	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2255	time C<offset> has passed. It will not repeat and will not adjust when a
559	that is, if it is to be run at January 1st 2011 then it will run when the	2256	time jump occurs, that is, if it is to be run at January 1st 2011 then it
560	system time reaches or surpasses this time.	2257	will be stopped and invoked when the system clock reaches or surpasses
		2258	this point in time.
561		2259
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2260	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
563		2261
564	In this mode the watcher will always be scheduled to time out at the next	2262	In this mode the watcher will always be scheduled to time out at the next
565	C<at + N * interval> time (for some integer N) and then repeat, regardless	2263	C<offset + N * interval> time (for some integer N, which can also be
566	of any time jumps.	2264	negative) and then repeat, regardless of any time jumps. The C<offset>
		2265	argument is merely an offset into the C<interval> periods.
567		2266
568	This can be used to create timers that do not drift with respect to system	2267	This can be used to create timers that do not drift with respect to the
569	time:	2268	system clock, for example, here is an C<ev_periodic> that triggers each
		2269	hour, on the hour (with respect to UTC):
570		2270
571	ev_periodic_set (&periodic, 0., 3600., 0);	2271	ev_periodic_set (&periodic, 0., 3600., 0);
572		2272
573	This doesn't mean there will always be 3600 seconds in between triggers,	2273	This doesn't mean there will always be 3600 seconds in between triggers,
574	but only that the the callback will be called when the system time shows a	2274	but only that the callback will be called when the system time shows a
575	full hour (UTC), or more correctly, when the system time is evenly divisible	2275	full hour (UTC), or more correctly, when the system time is evenly divisible
576	by 3600.	2276	by 3600.
577		2277
578	Another way to think about it (for the mathematically inclined) is that	2278	Another way to think about it (for the mathematically inclined) is that
579	C<ev_periodic> will try to run the callback in this mode at the next possible	2279	C<ev_periodic> will try to run the callback in this mode at the next possible
580	time where C<time = at (mod interval)>, regardless of any time jumps.	2280	time where C<time = offset (mod interval)>, regardless of any time jumps.
581		2281
		2282	The C<interval> I<MUST> be positive, and for numerical stability, the
		2283	interval value should be higher than C<1/8192> (which is around 100
		2284	microseconds) and C<offset> should be higher than C<0> and should have
		2285	at most a similar magnitude as the current time (say, within a factor of
		2286	ten). Typical values for offset are, in fact, C<0> or something between
		2287	C<0> and C<interval>, which is also the recommended range.
		2288
		2289	Note also that there is an upper limit to how often a timer can fire (CPU
		2290	speed for example), so if C<interval> is very small then timing stability
		2291	will of course deteriorate. Libev itself tries to be exact to be about one
		2292	millisecond (if the OS supports it and the machine is fast enough).
		2293
582	=item * manual reschedule mode (reschedule_cb = callback)	2294	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
583		2295
584	In this mode the values for C<interval> and C<at> are both being	2296	In this mode the values for C<interval> and C<offset> are both being
585	ignored. Instead, each time the periodic watcher gets scheduled, the	2297	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	2298	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	2299	current time as second argument.
588		2300
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2301	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
590	ever, or make any event loop modifications>. If you need to stop it,	2302	or make ANY other event loop modifications whatsoever, unless explicitly
591	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2303	allowed by documentation here>.
592	starting a prepare watcher).
593		2304
		2305	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2306	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2307	only event loop modification you are allowed to do).
		2308
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2309	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
595	ev_tstamp now)>, e.g.:	2310	*w, ev_tstamp now)>, e.g.:
596		2311
		2312	static ev_tstamp
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2313	my_rescheduler (ev_periodic *w, ev_tstamp now)
598	{	2314	{
599	return now + 60.;	2315	return now + 60.;
600	}	2316	}
601		2317
602	It must return the next time to trigger, based on the passed time value	2318	It must return the next time to trigger, based on the passed time value
603	(that is, the lowest time value larger than to the second argument). It	2319	(that is, the lowest time value larger than to the second argument). It
604	will usually be called just before the callback will be triggered, but	2320	will usually be called just before the callback will be triggered, but
605	might be called at other times, too.	2321	might be called at other times, too.
606		2322
607	NOTE: I<< This callback must always return a time that is later than the	2323	NOTE: I<< This callback must always return a time that is higher than or
608	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2324	equal to the passed C<now> value >>.
609		2325
610	This can be used to create very complex timers, such as a timer that	2326	This can be used to create very complex timers, such as a timer that
611	triggers on each midnight, local time. To do this, you would calculate the	2327	triggers on "next midnight, local time". To do this, you would calculate the
612	next midnight after C<now> and return the timestamp value for this. How	2328	next midnight after C<now> and return the timestamp value for this. How
613	you do this is, again, up to you (but it is not trivial, which is the main	2329	you do this is, again, up to you (but it is not trivial, which is the main
614	reason I omitted it as an example).	2330	reason I omitted it as an example).
615		2331
616	=back	2332	=back
…		…
620	Simply stops and restarts the periodic watcher again. This is only useful	2336	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	2337	when you changed some parameters or the reschedule callback would return
622	a different time than the last time it was called (e.g. in a crond like	2338	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	2339	program when the crontabs have changed).
624		2340
		2341	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2342
		2343	When active, returns the absolute time that the watcher is supposed
		2344	to trigger next. This is not the same as the C<offset> argument to
		2345	C<ev_periodic_set>, but indeed works even in interval and manual
		2346	rescheduling modes.
		2347
		2348	=item ev_tstamp offset [read-write]
		2349
		2350	When repeating, this contains the offset value, otherwise this is the
		2351	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2352	although libev might modify this value for better numerical stability).
		2353
		2354	Can be modified any time, but changes only take effect when the periodic
		2355	timer fires or C<ev_periodic_again> is being called.
		2356
		2357	=item ev_tstamp interval [read-write]
		2358
		2359	The current interval value. Can be modified any time, but changes only
		2360	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2361	called.
		2362
		2363	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2364
		2365	The current reschedule callback, or C<0>, if this functionality is
		2366	switched off. Can be changed any time, but changes only take effect when
		2367	the periodic timer fires or C<ev_periodic_again> is being called.
		2368
625	=back	2369	=back
626		2370
		2371	=head3 Examples
		2372
		2373	Example: Call a callback every hour, or, more precisely, whenever the
		2374	system time is divisible by 3600. The callback invocation times have
		2375	potentially a lot of jitter, but good long-term stability.
		2376
		2377	static void
		2378	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2379	{
		2380	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2381	}
		2382
		2383	ev_periodic hourly_tick;
		2384	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2385	ev_periodic_start (loop, &hourly_tick);
		2386
		2387	Example: The same as above, but use a reschedule callback to do it:
		2388
		2389	#include <math.h>
		2390
		2391	static ev_tstamp
		2392	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2393	{
		2394	return now + (3600. - fmod (now, 3600.));
		2395	}
		2396
		2397	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2398
		2399	Example: Call a callback every hour, starting now:
		2400
		2401	ev_periodic hourly_tick;
		2402	ev_periodic_init (&hourly_tick, clock_cb,
		2403	fmod (ev_now (loop), 3600.), 3600., 0);
		2404	ev_periodic_start (loop, &hourly_tick);
		2405
		2406
627	=head2 C<ev_signal> - signal me when a signal gets signalled	2407	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		2408
629	Signal watchers will trigger an event when the process receives a specific	2409	Signal watchers will trigger an event when the process receives a specific
630	signal one or more times. Even though signals are very asynchronous, libev	2410	signal one or more times. Even though signals are very asynchronous, libev
631	will try it's best to deliver signals synchronously, i.e. as part of the	2411	will try its best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	2412	normal event processing, like any other event.
633		2413
		2414	If you want signals to be delivered truly asynchronously, just use
		2415	C<sigaction> as you would do without libev and forget about sharing
		2416	the signal. You can even use C<ev_async> from a signal handler to
		2417	synchronously wake up an event loop.
		2418
634	You can configure as many watchers as you like per signal. Only when the	2419	You can configure as many watchers as you like for the same signal, but
635	first watcher gets started will libev actually register a signal watcher	2420	only within the same loop, i.e. you can watch for C<SIGINT> in your
636	with the kernel (thus it coexists with your own signal handlers as long	2421	default loop and for C<SIGIO> in another loop, but you cannot watch for
637	as you don't register any with libev). Similarly, when the last signal	2422	C<SIGINT> in both the default loop and another loop at the same time. At
638	watcher for a signal is stopped libev will reset the signal handler to	2423	the moment, C<SIGCHLD> is permanently tied to the default loop.
639	SIG_DFL (regardless of what it was set to before).	2424
		2425	Only after the first watcher for a signal is started will libev actually
		2426	register something with the kernel. It thus coexists with your own signal
		2427	handlers as long as you don't register any with libev for the same signal.
		2428
		2429	If possible and supported, libev will install its handlers with
		2430	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2431	not be unduly interrupted. If you have a problem with system calls getting
		2432	interrupted by signals you can block all signals in an C<ev_check> watcher
		2433	and unblock them in an C<ev_prepare> watcher.
		2434
		2435	=head3 The special problem of inheritance over fork/execve/pthread_create
		2436
		2437	Both the signal mask (C<sigprocmask>) and the signal disposition
		2438	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2439	stopping it again), that is, libev might or might not block the signal,
		2440	and might or might not set or restore the installed signal handler (but
		2441	see C<EVFLAG_NOSIGMASK>).
		2442
		2443	While this does not matter for the signal disposition (libev never
		2444	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2445	C<execve>), this matters for the signal mask: many programs do not expect
		2446	certain signals to be blocked.
		2447
		2448	This means that before calling C<exec> (from the child) you should reset
		2449	the signal mask to whatever "default" you expect (all clear is a good
		2450	choice usually).
		2451
		2452	The simplest way to ensure that the signal mask is reset in the child is
		2453	to install a fork handler with C<pthread_atfork> that resets it. That will
		2454	catch fork calls done by libraries (such as the libc) as well.
		2455
		2456	In current versions of libev, the signal will not be blocked indefinitely
		2457	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2458	the window of opportunity for problems, it will not go away, as libev
		2459	I<has> to modify the signal mask, at least temporarily.
		2460
		2461	So I can't stress this enough: I<If you do not reset your signal mask when
		2462	you expect it to be empty, you have a race condition in your code>. This
		2463	is not a libev-specific thing, this is true for most event libraries.
		2464
		2465	=head3 The special problem of threads signal handling
		2466
		2467	POSIX threads has problematic signal handling semantics, specifically,
		2468	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2469	threads in a process block signals, which is hard to achieve.
		2470
		2471	When you want to use sigwait (or mix libev signal handling with your own
		2472	for the same signals), you can tackle this problem by globally blocking
		2473	all signals before creating any threads (or creating them with a fully set
		2474	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2475	loops. Then designate one thread as "signal receiver thread" which handles
		2476	these signals. You can pass on any signals that libev might be interested
		2477	in by calling C<ev_feed_signal>.
		2478
		2479	=head3 Watcher-Specific Functions and Data Members
640		2480
641	=over 4	2481	=over 4
642		2482
643	=item ev_signal_init (ev_signal *, callback, int signum)	2483	=item ev_signal_init (ev_signal *, callback, int signum)
644		2484
645	=item ev_signal_set (ev_signal *, int signum)	2485	=item ev_signal_set (ev_signal *, int signum)
646		2486
647	Configures the watcher to trigger on the given signal number (usually one	2487	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	2488	of the C<SIGxxx> constants).
649		2489
		2490	=item int signum [read-only]
		2491
		2492	The signal the watcher watches out for.
		2493
650	=back	2494	=back
651		2495
		2496	=head3 Examples
		2497
		2498	Example: Try to exit cleanly on SIGINT.
		2499
		2500	static void
		2501	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2502	{
		2503	ev_break (loop, EVBREAK_ALL);
		2504	}
		2505
		2506	ev_signal signal_watcher;
		2507	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2508	ev_signal_start (loop, &signal_watcher);
		2509
		2510
652	=head2 C<ev_child> - wait for pid status changes	2511	=head2 C<ev_child> - watch out for process status changes
653		2512
654	Child watchers trigger when your process receives a SIGCHLD in response to	2513	Child watchers trigger when your process receives a SIGCHLD in response to
655	some child status changes (most typically when a child of yours dies).	2514	some child status changes (most typically when a child of yours dies or
		2515	exits). It is permissible to install a child watcher I<after> the child
		2516	has been forked (which implies it might have already exited), as long
		2517	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2518	forking and then immediately registering a watcher for the child is fine,
		2519	but forking and registering a watcher a few event loop iterations later or
		2520	in the next callback invocation is not.
		2521
		2522	Only the default event loop is capable of handling signals, and therefore
		2523	you can only register child watchers in the default event loop.
		2524
		2525	Due to some design glitches inside libev, child watchers will always be
		2526	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2527	libev)
		2528
		2529	=head3 Process Interaction
		2530
		2531	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2532	initialised. This is necessary to guarantee proper behaviour even if the
		2533	first child watcher is started after the child exits. The occurrence
		2534	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2535	synchronously as part of the event loop processing. Libev always reaps all
		2536	children, even ones not watched.
		2537
		2538	=head3 Overriding the Built-In Processing
		2539
		2540	Libev offers no special support for overriding the built-in child
		2541	processing, but if your application collides with libev's default child
		2542	handler, you can override it easily by installing your own handler for
		2543	C<SIGCHLD> after initialising the default loop, and making sure the
		2544	default loop never gets destroyed. You are encouraged, however, to use an
		2545	event-based approach to child reaping and thus use libev's support for
		2546	that, so other libev users can use C<ev_child> watchers freely.
		2547
		2548	=head3 Stopping the Child Watcher
		2549
		2550	Currently, the child watcher never gets stopped, even when the
		2551	child terminates, so normally one needs to stop the watcher in the
		2552	callback. Future versions of libev might stop the watcher automatically
		2553	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2554	problem).
		2555
		2556	=head3 Watcher-Specific Functions and Data Members
656		2557
657	=over 4	2558	=over 4
658		2559
659	=item ev_child_init (ev_child *, callback, int pid)	2560	=item ev_child_init (ev_child *, callback, int pid, int trace)
660		2561
661	=item ev_child_set (ev_child *, int pid)	2562	=item ev_child_set (ev_child *, int pid, int trace)
662		2563
663	Configures the watcher to wait for status changes of process C<pid> (or	2564	Configures the watcher to wait for status changes of process C<pid> (or
664	I<any> process if C<pid> is specified as C<0>). The callback can look	2565	I<any> process if C<pid> is specified as C<0>). The callback can look
665	at the C<rstatus> member of the C<ev_child> watcher structure to see	2566	at the C<rstatus> member of the C<ev_child> watcher structure to see
666	the status word (use the macros from C<sys/wait.h> and see your systems	2567	the status word (use the macros from C<sys/wait.h> and see your systems
667	C<waitpid> documentation). The C<rpid> member contains the pid of the	2568	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	2569	process causing the status change. C<trace> must be either C<0> (only
		2570	activate the watcher when the process terminates) or C<1> (additionally
		2571	activate the watcher when the process is stopped or continued).
		2572
		2573	=item int pid [read-only]
		2574
		2575	The process id this watcher watches out for, or C<0>, meaning any process id.
		2576
		2577	=item int rpid [read-write]
		2578
		2579	The process id that detected a status change.
		2580
		2581	=item int rstatus [read-write]
		2582
		2583	The process exit/trace status caused by C<rpid> (see your systems
		2584	C<waitpid> and C<sys/wait.h> documentation for details).
669		2585
670	=back	2586	=back
671		2587
		2588	=head3 Examples
		2589
		2590	Example: C<fork()> a new process and install a child handler to wait for
		2591	its completion.
		2592
		2593	ev_child cw;
		2594
		2595	static void
		2596	child_cb (EV_P_ ev_child *w, int revents)
		2597	{
		2598	ev_child_stop (EV_A_ w);
		2599	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2600	}
		2601
		2602	pid_t pid = fork ();
		2603
		2604	if (pid < 0)
		2605	// error
		2606	else if (pid == 0)
		2607	{
		2608	// the forked child executes here
		2609	exit (1);
		2610	}
		2611	else
		2612	{
		2613	ev_child_init (&cw, child_cb, pid, 0);
		2614	ev_child_start (EV_DEFAULT_ &cw);
		2615	}
		2616
		2617
		2618	=head2 C<ev_stat> - did the file attributes just change?
		2619
		2620	This watches a file system path for attribute changes. That is, it calls
		2621	C<stat> on that path in regular intervals (or when the OS says it changed)
		2622	and sees if it changed compared to the last time, invoking the callback
		2623	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2624	happen after the watcher has been started will be reported.
		2625
		2626	The path does not need to exist: changing from "path exists" to "path does
		2627	not exist" is a status change like any other. The condition "path does not
		2628	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2629	C<st_nlink> field being zero (which is otherwise always forced to be at
		2630	least one) and all the other fields of the stat buffer having unspecified
		2631	contents.
		2632
		2633	The path I<must not> end in a slash or contain special components such as
		2634	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2635	your working directory changes, then the behaviour is undefined.
		2636
		2637	Since there is no portable change notification interface available, the
		2638	portable implementation simply calls C<stat(2)> regularly on the path
		2639	to see if it changed somehow. You can specify a recommended polling
		2640	interval for this case. If you specify a polling interval of C<0> (highly
		2641	recommended!) then a I<suitable, unspecified default> value will be used
		2642	(which you can expect to be around five seconds, although this might
		2643	change dynamically). Libev will also impose a minimum interval which is
		2644	currently around C<0.1>, but that's usually overkill.
		2645
		2646	This watcher type is not meant for massive numbers of stat watchers,
		2647	as even with OS-supported change notifications, this can be
		2648	resource-intensive.
		2649
		2650	At the time of this writing, the only OS-specific interface implemented
		2651	is the Linux inotify interface (implementing kqueue support is left as an
		2652	exercise for the reader. Note, however, that the author sees no way of
		2653	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2654
		2655	=head3 ABI Issues (Largefile Support)
		2656
		2657	Libev by default (unless the user overrides this) uses the default
		2658	compilation environment, which means that on systems with large file
		2659	support disabled by default, you get the 32 bit version of the stat
		2660	structure. When using the library from programs that change the ABI to
		2661	use 64 bit file offsets the programs will fail. In that case you have to
		2662	compile libev with the same flags to get binary compatibility. This is
		2663	obviously the case with any flags that change the ABI, but the problem is
		2664	most noticeably displayed with ev_stat and large file support.
		2665
		2666	The solution for this is to lobby your distribution maker to make large
		2667	file interfaces available by default (as e.g. FreeBSD does) and not
		2668	optional. Libev cannot simply switch on large file support because it has
		2669	to exchange stat structures with application programs compiled using the
		2670	default compilation environment.
		2671
		2672	=head3 Inotify and Kqueue
		2673
		2674	When C<inotify (7)> support has been compiled into libev and present at
		2675	runtime, it will be used to speed up change detection where possible. The
		2676	inotify descriptor will be created lazily when the first C<ev_stat>
		2677	watcher is being started.
		2678
		2679	Inotify presence does not change the semantics of C<ev_stat> watchers
		2680	except that changes might be detected earlier, and in some cases, to avoid
		2681	making regular C<stat> calls. Even in the presence of inotify support
		2682	there are many cases where libev has to resort to regular C<stat> polling,
		2683	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2684	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2685	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2686	xfs are fully working) libev usually gets away without polling.
		2687
		2688	There is no support for kqueue, as apparently it cannot be used to
		2689	implement this functionality, due to the requirement of having a file
		2690	descriptor open on the object at all times, and detecting renames, unlinks
		2691	etc. is difficult.
		2692
		2693	=head3 C<stat ()> is a synchronous operation
		2694
		2695	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2696	the process. The exception are C<ev_stat> watchers - those call C<stat
		2697	()>, which is a synchronous operation.
		2698
		2699	For local paths, this usually doesn't matter: unless the system is very
		2700	busy or the intervals between stat's are large, a stat call will be fast,
		2701	as the path data is usually in memory already (except when starting the
		2702	watcher).
		2703
		2704	For networked file systems, calling C<stat ()> can block an indefinite
		2705	time due to network issues, and even under good conditions, a stat call
		2706	often takes multiple milliseconds.
		2707
		2708	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2709	paths, although this is fully supported by libev.
		2710
		2711	=head3 The special problem of stat time resolution
		2712
		2713	The C<stat ()> system call only supports full-second resolution portably,
		2714	and even on systems where the resolution is higher, most file systems
		2715	still only support whole seconds.
		2716
		2717	That means that, if the time is the only thing that changes, you can
		2718	easily miss updates: on the first update, C<ev_stat> detects a change and
		2719	calls your callback, which does something. When there is another update
		2720	within the same second, C<ev_stat> will be unable to detect unless the
		2721	stat data does change in other ways (e.g. file size).
		2722
		2723	The solution to this is to delay acting on a change for slightly more
		2724	than a second (or till slightly after the next full second boundary), using
		2725	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2726	ev_timer_again (loop, w)>).
		2727
		2728	The C<.02> offset is added to work around small timing inconsistencies
		2729	of some operating systems (where the second counter of the current time
		2730	might be be delayed. One such system is the Linux kernel, where a call to
		2731	C<gettimeofday> might return a timestamp with a full second later than
		2732	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2733	update file times then there will be a small window where the kernel uses
		2734	the previous second to update file times but libev might already execute
		2735	the timer callback).
		2736
		2737	=head3 Watcher-Specific Functions and Data Members
		2738
		2739	=over 4
		2740
		2741	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2742
		2743	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2744
		2745	Configures the watcher to wait for status changes of the given
		2746	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2747	be detected and should normally be specified as C<0> to let libev choose
		2748	a suitable value. The memory pointed to by C<path> must point to the same
		2749	path for as long as the watcher is active.
		2750
		2751	The callback will receive an C<EV_STAT> event when a change was detected,
		2752	relative to the attributes at the time the watcher was started (or the
		2753	last change was detected).
		2754
		2755	=item ev_stat_stat (loop, ev_stat *)
		2756
		2757	Updates the stat buffer immediately with new values. If you change the
		2758	watched path in your callback, you could call this function to avoid
		2759	detecting this change (while introducing a race condition if you are not
		2760	the only one changing the path). Can also be useful simply to find out the
		2761	new values.
		2762
		2763	=item ev_statdata attr [read-only]
		2764
		2765	The most-recently detected attributes of the file. Although the type is
		2766	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2767	suitable for your system, but you can only rely on the POSIX-standardised
		2768	members to be present. If the C<st_nlink> member is C<0>, then there was
		2769	some error while C<stat>ing the file.
		2770
		2771	=item ev_statdata prev [read-only]
		2772
		2773	The previous attributes of the file. The callback gets invoked whenever
		2774	C<prev> != C<attr>, or, more precisely, one or more of these members
		2775	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2776	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2777
		2778	=item ev_tstamp interval [read-only]
		2779
		2780	The specified interval.
		2781
		2782	=item const char *path [read-only]
		2783
		2784	The file system path that is being watched.
		2785
		2786	=back
		2787
		2788	=head3 Examples
		2789
		2790	Example: Watch C</etc/passwd> for attribute changes.
		2791
		2792	static void
		2793	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2794	{
		2795	/* /etc/passwd changed in some way */
		2796	if (w->attr.st_nlink)
		2797	{
		2798	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2799	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2800	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2801	}
		2802	else
		2803	/* you shalt not abuse printf for puts */
		2804	puts ("wow, /etc/passwd is not there, expect problems. "
		2805	"if this is windows, they already arrived\n");
		2806	}
		2807
		2808	...
		2809	ev_stat passwd;
		2810
		2811	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2812	ev_stat_start (loop, &passwd);
		2813
		2814	Example: Like above, but additionally use a one-second delay so we do not
		2815	miss updates (however, frequent updates will delay processing, too, so
		2816	one might do the work both on C<ev_stat> callback invocation I<and> on
		2817	C<ev_timer> callback invocation).
		2818
		2819	static ev_stat passwd;
		2820	static ev_timer timer;
		2821
		2822	static void
		2823	timer_cb (EV_P_ ev_timer *w, int revents)
		2824	{
		2825	ev_timer_stop (EV_A_ w);
		2826
		2827	/* now it's one second after the most recent passwd change */
		2828	}
		2829
		2830	static void
		2831	stat_cb (EV_P_ ev_stat *w, int revents)
		2832	{
		2833	/* reset the one-second timer */
		2834	ev_timer_again (EV_A_ &timer);
		2835	}
		2836
		2837	...
		2838	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2839	ev_stat_start (loop, &passwd);
		2840	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2841
		2842
672	=head2 C<ev_idle> - when you've got nothing better to do	2843	=head2 C<ev_idle> - when you've got nothing better to do...
673		2844
674	Idle watchers trigger events when there are no other events are pending	2845	Idle watchers trigger events when no other events of the same or higher
675	(prepare, check and other idle watchers do not count). That is, as long	2846	priority are pending (prepare, check and other idle watchers do not count
676	as your process is busy handling sockets or timeouts (or even signals,	2847	as receiving "events").
677	imagine) it will not be triggered. But when your process is idle all idle	2848
678	watchers are being called again and again, once per event loop iteration -	2849	That is, as long as your process is busy handling sockets or timeouts
		2850	(or even signals, imagine) of the same or higher priority it will not be
		2851	triggered. But when your process is idle (or only lower-priority watchers
		2852	are pending), the idle watchers are being called once per event loop
679	until stopped, that is, or your process receives more events and becomes	2853	iteration - until stopped, that is, or your process receives more events
680	busy.	2854	and becomes busy again with higher priority stuff.
681		2855
682	The most noteworthy effect is that as long as any idle watchers are	2856	The most noteworthy effect is that as long as any idle watchers are
683	active, the process will not block when waiting for new events.	2857	active, the process will not block when waiting for new events.
684		2858
685	Apart from keeping your process non-blocking (which is a useful	2859	Apart from keeping your process non-blocking (which is a useful
686	effect on its own sometimes), idle watchers are a good place to do	2860	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	2861	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	2862	event loop has handled all outstanding events.
689		2863
		2864	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2865
		2866	As long as there is at least one active idle watcher, libev will never
		2867	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2868	For this to work, the idle watcher doesn't need to be invoked at all - the
		2869	lowest priority will do.
		2870
		2871	This mode of operation can be useful together with an C<ev_check> watcher,
		2872	to do something on each event loop iteration - for example to balance load
		2873	between different connections.
		2874
		2875	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2876	example.
		2877
		2878	=head3 Watcher-Specific Functions and Data Members
		2879
690	=over 4	2880	=over 4
691		2881
692	=item ev_idle_init (ev_signal *, callback)	2882	=item ev_idle_init (ev_idle *, callback)
693		2883
694	Initialises and configures the idle watcher - it has no parameters of any	2884	Initialises and configures the idle watcher - it has no parameters of any
695	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2885	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	2886	believe me.
697		2887
698	=back	2888	=back
699		2889
		2890	=head3 Examples
		2891
		2892	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2893	callback, free it. Also, use no error checking, as usual.
		2894
		2895	static void
		2896	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2897	{
		2898	// stop the watcher
		2899	ev_idle_stop (loop, w);
		2900
		2901	// now we can free it
		2902	free (w);
		2903
		2904	// now do something you wanted to do when the program has
		2905	// no longer anything immediate to do.
		2906	}
		2907
		2908	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2909	ev_idle_init (idle_watcher, idle_cb);
		2910	ev_idle_start (loop, idle_watcher);
		2911
		2912
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2913	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		2914
702	Prepare and check watchers are usually (but not always) used in tandem:	2915	Prepare and check watchers are often (but not always) used in pairs:
703	prepare watchers get invoked before the process blocks and check watchers	2916	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	2917	afterwards.
705		2918
		2919	You I<must not> call C<ev_run> (or similar functions that enter the
		2920	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
		2921	C<ev_check> watchers. Other loops than the current one are fine,
		2922	however. The rationale behind this is that you do not need to check
		2923	for recursion in those watchers, i.e. the sequence will always be
		2924	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
		2925	kind they will always be called in pairs bracketing the blocking call.
		2926
706	Their main purpose is to integrate other event mechanisms into libev. This	2927	Their main purpose is to integrate other event mechanisms into libev and
707	could be used, for example, to track variable changes, implement your own	2928	their use is somewhat advanced. They could be used, for example, to track
708	watchers, integrate net-snmp or a coroutine library and lots more.	2929	variable changes, implement your own watchers, integrate net-snmp or a
		2930	coroutine library and lots more. They are also occasionally useful if
		2931	you cache some data and want to flush it before blocking (for example,
		2932	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2933	watcher).
709		2934
710	This is done by examining in each prepare call which file descriptors need	2935	This is done by examining in each prepare call which file descriptors
711	to be watched by the other library, registering C<ev_io> watchers for	2936	need to be watched by the other library, registering C<ev_io> watchers
712	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2937	for them and starting an C<ev_timer> watcher for any timeouts (many
713	provide just this functionality). Then, in the check watcher you check for	2938	libraries provide exactly this functionality). Then, in the check watcher,
714	any events that occured (by checking the pending status of all watchers	2939	you check for any events that occurred (by checking the pending status
715	and stopping them) and call back into the library. The I/O and timer	2940	of all watchers and stopping them) and call back into the library. The
716	callbacks will never actually be called (but must be valid nevertheless,	2941	I/O and timer callbacks will never actually be called (but must be valid
717	because you never know, you know?).	2942	nevertheless, because you never know, you know?).
718		2943
719	As another example, the Perl Coro module uses these hooks to integrate	2944	As another example, the Perl Coro module uses these hooks to integrate
720	coroutines into libev programs, by yielding to other active coroutines	2945	coroutines into libev programs, by yielding to other active coroutines
721	during each prepare and only letting the process block if no coroutines	2946	during each prepare and only letting the process block if no coroutines
722	are ready to run (it's actually more complicated: it only runs coroutines	2947	are ready to run (it's actually more complicated: it only runs coroutines
723	with priority higher than or equal to the event loop and one coroutine	2948	with priority higher than or equal to the event loop and one coroutine
724	of lower priority, but only once, using idle watchers to keep the event	2949	of lower priority, but only once, using idle watchers to keep the event
725	loop from blocking if lower-priority coroutines are active, thus mapping	2950	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	2951	low-priority coroutines to idle/background tasks).
727		2952
		2953	When used for this purpose, it is recommended to give C<ev_check> watchers
		2954	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2955	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2956	watchers).
		2957
		2958	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2959	activate ("feed") events into libev. While libev fully supports this, they
		2960	might get executed before other C<ev_check> watchers did their job. As
		2961	C<ev_check> watchers are often used to embed other (non-libev) event
		2962	loops those other event loops might be in an unusable state until their
		2963	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2964	others).
		2965
		2966	=head3 Abusing an C<ev_check> watcher for its side-effect
		2967
		2968	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2969	useful because they are called once per event loop iteration. For
		2970	example, if you want to handle a large number of connections fairly, you
		2971	normally only do a bit of work for each active connection, and if there
		2972	is more work to do, you wait for the next event loop iteration, so other
		2973	connections have a chance of making progress.
		2974
		2975	Using an C<ev_check> watcher is almost enough: it will be called on the
		2976	next event loop iteration. However, that isn't as soon as possible -
		2977	without external events, your C<ev_check> watcher will not be invoked.
		2978
		2979	This is where C<ev_idle> watchers come in handy - all you need is a
		2980	single global idle watcher that is active as long as you have one active
		2981	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2982	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2983	invoked. Neither watcher alone can do that.
		2984
		2985	=head3 Watcher-Specific Functions and Data Members
		2986
728	=over 4	2987	=over 4
729		2988
730	=item ev_prepare_init (ev_prepare *, callback)	2989	=item ev_prepare_init (ev_prepare *, callback)
731		2990
732	=item ev_check_init (ev_check *, callback)	2991	=item ev_check_init (ev_check *, callback)
733		2992
734	Initialises and configures the prepare or check watcher - they have no	2993	Initialises and configures the prepare or check watcher - they have no
735	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2994	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
736	macros, but using them is utterly, utterly and completely pointless.	2995	macros, but using them is utterly, utterly, utterly and completely
		2996	pointless.
737		2997
738	=back	2998	=back
739		2999
		3000	=head3 Examples
		3001
		3002	There are a number of principal ways to embed other event loops or modules
		3003	into libev. Here are some ideas on how to include libadns into libev
		3004	(there is a Perl module named C<EV::ADNS> that does this, which you could
		3005	use as a working example. Another Perl module named C<EV::Glib> embeds a
		3006	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		3007	Glib event loop).
		3008
		3009	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		3010	and in a check watcher, destroy them and call into libadns. What follows
		3011	is pseudo-code only of course. This requires you to either use a low
		3012	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		3013	the callbacks for the IO/timeout watchers might not have been called yet.
		3014
		3015	static ev_io iow [nfd];
		3016	static ev_timer tw;
		3017
		3018	static void
		3019	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		3020	{
		3021	}
		3022
		3023	// create io watchers for each fd and a timer before blocking
		3024	static void
		3025	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		3026	{
		3027	int timeout = 3600000;
		3028	struct pollfd fds [nfd];
		3029	// actual code will need to loop here and realloc etc.
		3030	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		3031
		3032	/* the callback is illegal, but won't be called as we stop during check */
		3033	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		3034	ev_timer_start (loop, &tw);
		3035
		3036	// create one ev_io per pollfd
		3037	for (int i = 0; i < nfd; ++i)
		3038	{
		3039	ev_io_init (iow + i, io_cb, fds [i].fd,
		3040	((fds [i].events & POLLIN ? EV_READ : 0)
		3041	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		3042
		3043	fds [i].revents = 0;
		3044	ev_io_start (loop, iow + i);
		3045	}
		3046	}
		3047
		3048	// stop all watchers after blocking
		3049	static void
		3050	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		3051	{
		3052	ev_timer_stop (loop, &tw);
		3053
		3054	for (int i = 0; i < nfd; ++i)
		3055	{
		3056	// set the relevant poll flags
		3057	// could also call adns_processreadable etc. here
		3058	struct pollfd *fd = fds + i;
		3059	int revents = ev_clear_pending (iow + i);
		3060	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3061	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3062
		3063	// now stop the watcher
		3064	ev_io_stop (loop, iow + i);
		3065	}
		3066
		3067	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		3068	}
		3069
		3070	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3071	in the prepare watcher and would dispose of the check watcher.
		3072
		3073	Method 3: If the module to be embedded supports explicit event
		3074	notification (libadns does), you can also make use of the actual watcher
		3075	callbacks, and only destroy/create the watchers in the prepare watcher.
		3076
		3077	static void
		3078	timer_cb (EV_P_ ev_timer *w, int revents)
		3079	{
		3080	adns_state ads = (adns_state)w->data;
		3081	update_now (EV_A);
		3082
		3083	adns_processtimeouts (ads, &tv_now);
		3084	}
		3085
		3086	static void
		3087	io_cb (EV_P_ ev_io *w, int revents)
		3088	{
		3089	adns_state ads = (adns_state)w->data;
		3090	update_now (EV_A);
		3091
		3092	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3093	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3094	}
		3095
		3096	// do not ever call adns_afterpoll
		3097
		3098	Method 4: Do not use a prepare or check watcher because the module you
		3099	want to embed is not flexible enough to support it. Instead, you can
		3100	override their poll function. The drawback with this solution is that the
		3101	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3102	this approach, effectively embedding EV as a client into the horrible
		3103	libglib event loop.
		3104
		3105	static gint
		3106	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3107	{
		3108	int got_events = 0;
		3109
		3110	for (n = 0; n < nfds; ++n)
		3111	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3112
		3113	if (timeout >= 0)
		3114	// create/start timer
		3115
		3116	// poll
		3117	ev_run (EV_A_ 0);
		3118
		3119	// stop timer again
		3120	if (timeout >= 0)
		3121	ev_timer_stop (EV_A_ &to);
		3122
		3123	// stop io watchers again - their callbacks should have set
		3124	for (n = 0; n < nfds; ++n)
		3125	ev_io_stop (EV_A_ iow [n]);
		3126
		3127	return got_events;
		3128	}
		3129
		3130
		3131	=head2 C<ev_embed> - when one backend isn't enough...
		3132
		3133	This is a rather advanced watcher type that lets you embed one event loop
		3134	into another (currently only C<ev_io> events are supported in the embedded
		3135	loop, other types of watchers might be handled in a delayed or incorrect
		3136	fashion and must not be used).
		3137
		3138	There are primarily two reasons you would want that: work around bugs and
		3139	prioritise I/O.
		3140
		3141	As an example for a bug workaround, the kqueue backend might only support
		3142	sockets on some platform, so it is unusable as generic backend, but you
		3143	still want to make use of it because you have many sockets and it scales
		3144	so nicely. In this case, you would create a kqueue-based loop and embed
		3145	it into your default loop (which might use e.g. poll). Overall operation
		3146	will be a bit slower because first libev has to call C<poll> and then
		3147	C<kevent>, but at least you can use both mechanisms for what they are
		3148	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3149
		3150	As for prioritising I/O: under rare circumstances you have the case where
		3151	some fds have to be watched and handled very quickly (with low latency),
		3152	and even priorities and idle watchers might have too much overhead. In
		3153	this case you would put all the high priority stuff in one loop and all
		3154	the rest in a second one, and embed the second one in the first.
		3155
		3156	As long as the watcher is active, the callback will be invoked every
		3157	time there might be events pending in the embedded loop. The callback
		3158	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3159	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3160	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3161	to give the embedded loop strictly lower priority for example).
		3162
		3163	You can also set the callback to C<0>, in which case the embed watcher
		3164	will automatically execute the embedded loop sweep whenever necessary.
		3165
		3166	Fork detection will be handled transparently while the C<ev_embed> watcher
		3167	is active, i.e., the embedded loop will automatically be forked when the
		3168	embedding loop forks. In other cases, the user is responsible for calling
		3169	C<ev_loop_fork> on the embedded loop.
		3170
		3171	Unfortunately, not all backends are embeddable: only the ones returned by
		3172	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3173	portable one.
		3174
		3175	So when you want to use this feature you will always have to be prepared
		3176	that you cannot get an embeddable loop. The recommended way to get around
		3177	this is to have a separate variables for your embeddable loop, try to
		3178	create it, and if that fails, use the normal loop for everything.
		3179
		3180	=head3 C<ev_embed> and fork
		3181
		3182	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3183	automatically be applied to the embedded loop as well, so no special
		3184	fork handling is required in that case. When the watcher is not running,
		3185	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3186	as applicable.
		3187
		3188	=head3 Watcher-Specific Functions and Data Members
		3189
		3190	=over 4
		3191
		3192	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3193
		3194	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
		3195
		3196	Configures the watcher to embed the given loop, which must be
		3197	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3198	invoked automatically, otherwise it is the responsibility of the callback
		3199	to invoke it (it will continue to be called until the sweep has been done,
		3200	if you do not want that, you need to temporarily stop the embed watcher).
		3201
		3202	=item ev_embed_sweep (loop, ev_embed *)
		3203
		3204	Make a single, non-blocking sweep over the embedded loop. This works
		3205	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3206	appropriate way for embedded loops.
		3207
		3208	=item struct ev_loop *other [read-only]
		3209
		3210	The embedded event loop.
		3211
		3212	=back
		3213
		3214	=head3 Examples
		3215
		3216	Example: Try to get an embeddable event loop and embed it into the default
		3217	event loop. If that is not possible, use the default loop. The default
		3218	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3220	used).
		3221
		3222	struct ev_loop *loop_hi = ev_default_init (0);
		3223	struct ev_loop *loop_lo = 0;
		3224	ev_embed embed;
		3225
		3226	// see if there is a chance of getting one that works
		3227	// (remember that a flags value of 0 means autodetection)
		3228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3230	: 0;
		3231
		3232	// if we got one, then embed it, otherwise default to loop_hi
		3233	if (loop_lo)
		3234	{
		3235	ev_embed_init (&embed, 0, loop_lo);
		3236	ev_embed_start (loop_hi, &embed);
		3237	}
		3238	else
		3239	loop_lo = loop_hi;
		3240
		3241	Example: Check if kqueue is available but not recommended and create
		3242	a kqueue backend for use with sockets (which usually work with any
		3243	kqueue implementation). Store the kqueue/socket-only event loop in
		3244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3245
		3246	struct ev_loop *loop = ev_default_init (0);
		3247	struct ev_loop *loop_socket = 0;
		3248	ev_embed embed;
		3249
		3250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3252	{
		3253	ev_embed_init (&embed, 0, loop_socket);
		3254	ev_embed_start (loop, &embed);
		3255	}
		3256
		3257	if (!loop_socket)
		3258	loop_socket = loop;
		3259
		3260	// now use loop_socket for all sockets, and loop for everything else
		3261
		3262
		3263	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3264
		3265	Fork watchers are called when a C<fork ()> was detected (usually because
		3266	whoever is a good citizen cared to tell libev about it by calling
		3267	C<ev_loop_fork>). The invocation is done before the event loop blocks next
		3268	and before C<ev_check> watchers are being called, and only in the child
		3269	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
		3270	and calls it in the wrong process, the fork handlers will be invoked, too,
		3271	of course.
		3272
		3273	=head3 The special problem of life after fork - how is it possible?
		3274
		3275	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3276	up/change the process environment, followed by a call to C<exec()>. This
		3277	sequence should be handled by libev without any problems.
		3278
		3279	This changes when the application actually wants to do event handling
		3280	in the child, or both parent in child, in effect "continuing" after the
		3281	fork.
		3282
		3283	The default mode of operation (for libev, with application help to detect
		3284	forks) is to duplicate all the state in the child, as would be expected
		3285	when I<either> the parent I<or> the child process continues.
		3286
		3287	When both processes want to continue using libev, then this is usually the
		3288	wrong result. In that case, usually one process (typically the parent) is
		3289	supposed to continue with all watchers in place as before, while the other
		3290	process typically wants to start fresh, i.e. without any active watchers.
		3291
		3292	The cleanest and most efficient way to achieve that with libev is to
		3293	simply create a new event loop, which of course will be "empty", and
		3294	use that for new watchers. This has the advantage of not touching more
		3295	memory than necessary, and thus avoiding the copy-on-write, and the
		3296	disadvantage of having to use multiple event loops (which do not support
		3297	signal watchers).
		3298
		3299	When this is not possible, or you want to use the default loop for
		3300	other reasons, then in the process that wants to start "fresh", call
		3301	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3302	Destroying the default loop will "orphan" (not stop) all registered
		3303	watchers, so you have to be careful not to execute code that modifies
		3304	those watchers. Note also that in that case, you have to re-register any
		3305	signal watchers.
		3306
		3307	=head3 Watcher-Specific Functions and Data Members
		3308
		3309	=over 4
		3310
		3311	=item ev_fork_init (ev_fork *, callback)
		3312
		3313	Initialises and configures the fork watcher - it has no parameters of any
		3314	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3315	really.
		3316
		3317	=back
		3318
		3319
		3320	=head2 C<ev_cleanup> - even the best things end
		3321
		3322	Cleanup watchers are called just before the event loop is being destroyed
		3323	by a call to C<ev_loop_destroy>.
		3324
		3325	While there is no guarantee that the event loop gets destroyed, cleanup
		3326	watchers provide a convenient method to install cleanup hooks for your
		3327	program, worker threads and so on - you just to make sure to destroy the
		3328	loop when you want them to be invoked.
		3329
		3330	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3331	all other watchers, they do not keep a reference to the event loop (which
		3332	makes a lot of sense if you think about it). Like all other watchers, you
		3333	can call libev functions in the callback, except C<ev_cleanup_start>.
		3334
		3335	=head3 Watcher-Specific Functions and Data Members
		3336
		3337	=over 4
		3338
		3339	=item ev_cleanup_init (ev_cleanup *, callback)
		3340
		3341	Initialises and configures the cleanup watcher - it has no parameters of
		3342	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3343	pointless, I assure you.
		3344
		3345	=back
		3346
		3347	Example: Register an atexit handler to destroy the default loop, so any
		3348	cleanup functions are called.
		3349
		3350	static void
		3351	program_exits (void)
		3352	{
		3353	ev_loop_destroy (EV_DEFAULT_UC);
		3354	}
		3355
		3356	...
		3357	atexit (program_exits);
		3358
		3359
		3360	=head2 C<ev_async> - how to wake up an event loop
		3361
		3362	In general, you cannot use an C<ev_loop> from multiple threads or other
		3363	asynchronous sources such as signal handlers (as opposed to multiple event
		3364	loops - those are of course safe to use in different threads).
		3365
		3366	Sometimes, however, you need to wake up an event loop you do not control,
		3367	for example because it belongs to another thread. This is what C<ev_async>
		3368	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3369	it by calling C<ev_async_send>, which is thread- and signal safe.
		3370
		3371	This functionality is very similar to C<ev_signal> watchers, as signals,
		3372	too, are asynchronous in nature, and signals, too, will be compressed
		3373	(i.e. the number of callback invocations may be less than the number of
		3374	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3375	of "global async watchers" by using a watcher on an otherwise unused
		3376	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3377	even without knowing which loop owns the signal.
		3378
		3379	=head3 Queueing
		3380
		3381	C<ev_async> does not support queueing of data in any way. The reason
		3382	is that the author does not know of a simple (or any) algorithm for a
		3383	multiple-writer-single-reader queue that works in all cases and doesn't
		3384	need elaborate support such as pthreads or unportable memory access
		3385	semantics.
		3386
		3387	That means that if you want to queue data, you have to provide your own
		3388	queue. But at least I can tell you how to implement locking around your
		3389	queue:
		3390
		3391	=over 4
		3392
		3393	=item queueing from a signal handler context
		3394
		3395	To implement race-free queueing, you simply add to the queue in the signal
		3396	handler but you block the signal handler in the watcher callback. Here is
		3397	an example that does that for some fictitious SIGUSR1 handler:
		3398
		3399	static ev_async mysig;
		3400
		3401	static void
		3402	sigusr1_handler (void)
		3403	{
		3404	sometype data;
		3405
		3406	// no locking etc.
		3407	queue_put (data);
		3408	ev_async_send (EV_DEFAULT_ &mysig);
		3409	}
		3410
		3411	static void
		3412	mysig_cb (EV_P_ ev_async *w, int revents)
		3413	{
		3414	sometype data;
		3415	sigset_t block, prev;
		3416
		3417	sigemptyset (&block);
		3418	sigaddset (&block, SIGUSR1);
		3419	sigprocmask (SIG_BLOCK, &block, &prev);
		3420
		3421	while (queue_get (&data))
		3422	process (data);
		3423
		3424	if (sigismember (&prev, SIGUSR1)
		3425	sigprocmask (SIG_UNBLOCK, &block, 0);
		3426	}
		3427
		3428	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3429	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3430	either...).
		3431
		3432	=item queueing from a thread context
		3433
		3434	The strategy for threads is different, as you cannot (easily) block
		3435	threads but you can easily preempt them, so to queue safely you need to
		3436	employ a traditional mutex lock, such as in this pthread example:
		3437
		3438	static ev_async mysig;
		3439	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3440
		3441	static void
		3442	otherthread (void)
		3443	{
		3444	// only need to lock the actual queueing operation
		3445	pthread_mutex_lock (&mymutex);
		3446	queue_put (data);
		3447	pthread_mutex_unlock (&mymutex);
		3448
		3449	ev_async_send (EV_DEFAULT_ &mysig);
		3450	}
		3451
		3452	static void
		3453	mysig_cb (EV_P_ ev_async *w, int revents)
		3454	{
		3455	pthread_mutex_lock (&mymutex);
		3456
		3457	while (queue_get (&data))
		3458	process (data);
		3459
		3460	pthread_mutex_unlock (&mymutex);
		3461	}
		3462
		3463	=back
		3464
		3465
		3466	=head3 Watcher-Specific Functions and Data Members
		3467
		3468	=over 4
		3469
		3470	=item ev_async_init (ev_async *, callback)
		3471
		3472	Initialises and configures the async watcher - it has no parameters of any
		3473	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3474	trust me.
		3475
		3476	=item ev_async_send (loop, ev_async *)
		3477
		3478	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3479	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3480	returns.
		3481
		3482	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3483	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3484	embedding section below on what exactly this means).
		3485
		3486	Note that, as with other watchers in libev, multiple events might get
		3487	compressed into a single callback invocation (another way to look at
		3488	this is that C<ev_async> watchers are level-triggered: they are set on
		3489	C<ev_async_send>, reset when the event loop detects that).
		3490
		3491	This call incurs the overhead of at most one extra system call per event
		3492	loop iteration, if the event loop is blocked, and no syscall at all if
		3493	the event loop (or your program) is processing events. That means that
		3494	repeated calls are basically free (there is no need to avoid calls for
		3495	performance reasons) and that the overhead becomes smaller (typically
		3496	zero) under load.
		3497
		3498	=item bool = ev_async_pending (ev_async *)
		3499
		3500	Returns a non-zero value when C<ev_async_send> has been called on the
		3501	watcher but the event has not yet been processed (or even noted) by the
		3502	event loop.
		3503
		3504	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3505	the loop iterates next and checks for the watcher to have become active,
		3506	it will reset the flag again. C<ev_async_pending> can be used to very
		3507	quickly check whether invoking the loop might be a good idea.
		3508
		3509	Not that this does I<not> check whether the watcher itself is pending,
		3510	only whether it has been requested to make this watcher pending: there
		3511	is a time window between the event loop checking and resetting the async
		3512	notification, and the callback being invoked.
		3513
		3514	=back
		3515
		3516
740	=head1 OTHER FUNCTIONS	3517	=head1 OTHER FUNCTIONS
741		3518
742	There are some other functions of possible interest. Described. Here. Now.	3519	There are some other functions of possible interest. Described. Here. Now.
743		3520
744	=over 4	3521	=over 4
745		3522
746	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3523	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
747		3524
748	This function combines a simple timer and an I/O watcher, calls your	3525	This function combines a simple timer and an I/O watcher, calls your
749	callback on whichever event happens first and automatically stop both	3526	callback on whichever event happens first and automatically stops both
750	watchers. This is useful if you want to wait for a single event on an fd	3527	watchers. This is useful if you want to wait for a single event on an fd
751	or timeout without having to allocate/configure/start/stop/free one or	3528	or timeout without having to allocate/configure/start/stop/free one or
752	more watchers yourself.	3529	more watchers yourself.
753		3530
754	If C<fd> is less than 0, then no I/O watcher will be started and events	3531	If C<fd> is less than 0, then no I/O watcher will be started and the
755	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3532	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
756	C<events> set will be craeted and started.	3533	the given C<fd> and C<events> set will be created and started.
757		3534
758	If C<timeout> is less than 0, then no timeout watcher will be	3535	If C<timeout> is less than 0, then no timeout watcher will be
759	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3536	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
760	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3537	repeat = 0) will be started. C<0> is a valid timeout.
761	dubious value.
762		3538
763	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3539	The callback has the type C<void (*cb)(int revents, void *arg)> and is
764	passed an C<revents> set like normal event callbacks (a combination of	3540	passed an C<revents> set like normal event callbacks (a combination of
765	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3541	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
766	value passed to C<ev_once>:	3542	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3543	a timeout and an io event at the same time - you probably should give io
		3544	events precedence.
767		3545
		3546	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3547
768	static void stdin_ready (int revents, void *arg)	3548	static void stdin_ready (int revents, void *arg)
		3549	{
		3550	if (revents & EV_READ)
		3551	/* stdin might have data for us, joy! */;
		3552	else if (revents & EV_TIMER)
		3553	/* doh, nothing entered */;
		3554	}
		3555
		3556	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3557
		3558	=item ev_feed_fd_event (loop, int fd, int revents)
		3559
		3560	Feed an event on the given fd, as if a file descriptor backend detected
		3561	the given events.
		3562
		3563	=item ev_feed_signal_event (loop, int signum)
		3564
		3565	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3566	which is async-safe.
		3567
		3568	=back
		3569
		3570
		3571	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3572
		3573	This section explains some common idioms that are not immediately
		3574	obvious. Note that examples are sprinkled over the whole manual, and this
		3575	section only contains stuff that wouldn't fit anywhere else.
		3576
		3577	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3578
		3579	Each watcher has, by default, a C<void *data> member that you can read
		3580	or modify at any time: libev will completely ignore it. This can be used
		3581	to associate arbitrary data with your watcher. If you need more data and
		3582	don't want to allocate memory separately and store a pointer to it in that
		3583	data member, you can also "subclass" the watcher type and provide your own
		3584	data:
		3585
		3586	struct my_io
		3587	{
		3588	ev_io io;
		3589	int otherfd;
		3590	void *somedata;
		3591	struct whatever *mostinteresting;
		3592	};
		3593
		3594	...
		3595	struct my_io w;
		3596	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3597
		3598	And since your callback will be called with a pointer to the watcher, you
		3599	can cast it back to your own type:
		3600
		3601	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3602	{
		3603	struct my_io *w = (struct my_io *)w_;
		3604	...
		3605	}
		3606
		3607	More interesting and less C-conformant ways of casting your callback
		3608	function type instead have been omitted.
		3609
		3610	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3611
		3612	Another common scenario is to use some data structure with multiple
		3613	embedded watchers, in effect creating your own watcher that combines
		3614	multiple libev event sources into one "super-watcher":
		3615
		3616	struct my_biggy
		3617	{
		3618	int some_data;
		3619	ev_timer t1;
		3620	ev_timer t2;
		3621	}
		3622
		3623	In this case getting the pointer to C<my_biggy> is a bit more
		3624	complicated: Either you store the address of your C<my_biggy> struct in
		3625	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3626	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3627	real programmers):
		3628
		3629	#include <stddef.h>
		3630
		3631	static void
		3632	t1_cb (EV_P_ ev_timer *w, int revents)
		3633	{
		3634	struct my_biggy big = (struct my_biggy *)
		3635	(((char *)w) - offsetof (struct my_biggy, t1));
		3636	}
		3637
		3638	static void
		3639	t2_cb (EV_P_ ev_timer *w, int revents)
		3640	{
		3641	struct my_biggy big = (struct my_biggy *)
		3642	(((char *)w) - offsetof (struct my_biggy, t2));
		3643	}
		3644
		3645	=head2 AVOIDING FINISHING BEFORE RETURNING
		3646
		3647	Often you have structures like this in event-based programs:
		3648
		3649	callback ()
769	{	3650	{
770	if (revents & EV_TIMEOUT)	3651	free (request);
771	/* doh, nothing entered */;
772	else if (revents & EV_READ)
773	/* stdin might have data for us, joy! */;
774	}	3652	}
775		3653
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3654	request = start_new_request (..., callback);
777		3655
778	=item ev_feed_event (loop, watcher, int events)	3656	The intent is to start some "lengthy" operation. The C<request> could be
		3657	used to cancel the operation, or do other things with it.
779		3658
780	Feeds the given event set into the event loop, as if the specified event	3659	It's not uncommon to have code paths in C<start_new_request> that
781	had happened for the specified watcher (which must be a pointer to an	3660	immediately invoke the callback, for example, to report errors. Or you add
782	initialised but not necessarily started event watcher).	3661	some caching layer that finds that it can skip the lengthy aspects of the
		3662	operation and simply invoke the callback with the result.
783		3663
784	=item ev_feed_fd_event (loop, int fd, int revents)	3664	The problem here is that this will happen I<before> C<start_new_request>
		3665	has returned, so C<request> is not set.
785		3666
786	Feed an event on the given fd, as if a file descriptor backend detected	3667	Even if you pass the request by some safer means to the callback, you
787	the given events it.	3668	might want to do something to the request after starting it, such as
		3669	canceling it, which probably isn't working so well when the callback has
		3670	already been invoked.
788		3671
789	=item ev_feed_signal_event (loop, int signum)	3672	A common way around all these issues is to make sure that
		3673	C<start_new_request> I<always> returns before the callback is invoked. If
		3674	C<start_new_request> immediately knows the result, it can artificially
		3675	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3676	example, or more sneakily, by reusing an existing (stopped) watcher and
		3677	pushing it into the pending queue:
790		3678
791	Feed an event as if the given signal occured (loop must be the default loop!).	3679	ev_set_cb (watcher, callback);
		3680	ev_feed_event (EV_A_ watcher, 0);
792		3681
793	=back	3682	This way, C<start_new_request> can safely return before the callback is
		3683	invoked, while not delaying callback invocation too much.
		3684
		3685	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3686
		3687	Often (especially in GUI toolkits) there are places where you have
		3688	I<modal> interaction, which is most easily implemented by recursively
		3689	invoking C<ev_run>.
		3690
		3691	This brings the problem of exiting - a callback might want to finish the
		3692	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3693	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3694	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3695	other combination: In these cases, a simple C<ev_break> will not work.
		3696
		3697	The solution is to maintain "break this loop" variable for each C<ev_run>
		3698	invocation, and use a loop around C<ev_run> until the condition is
		3699	triggered, using C<EVRUN_ONCE>:
		3700
		3701	// main loop
		3702	int exit_main_loop = 0;
		3703
		3704	while (!exit_main_loop)
		3705	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3706
		3707	// in a modal watcher
		3708	int exit_nested_loop = 0;
		3709
		3710	while (!exit_nested_loop)
		3711	ev_run (EV_A_ EVRUN_ONCE);
		3712
		3713	To exit from any of these loops, just set the corresponding exit variable:
		3714
		3715	// exit modal loop
		3716	exit_nested_loop = 1;
		3717
		3718	// exit main program, after modal loop is finished
		3719	exit_main_loop = 1;
		3720
		3721	// exit both
		3722	exit_main_loop = exit_nested_loop = 1;
		3723
		3724	=head2 THREAD LOCKING EXAMPLE
		3725
		3726	Here is a fictitious example of how to run an event loop in a different
		3727	thread from where callbacks are being invoked and watchers are
		3728	created/added/removed.
		3729
		3730	For a real-world example, see the C<EV::Loop::Async> perl module,
		3731	which uses exactly this technique (which is suited for many high-level
		3732	languages).
		3733
		3734	The example uses a pthread mutex to protect the loop data, a condition
		3735	variable to wait for callback invocations, an async watcher to notify the
		3736	event loop thread and an unspecified mechanism to wake up the main thread.
		3737
		3738	First, you need to associate some data with the event loop:
		3739
		3740	typedef struct {
		3741	mutex_t lock; /* global loop lock */
		3742	ev_async async_w;
		3743	thread_t tid;
		3744	cond_t invoke_cv;
		3745	} userdata;
		3746
		3747	void prepare_loop (EV_P)
		3748	{
		3749	// for simplicity, we use a static userdata struct.
		3750	static userdata u;
		3751
		3752	ev_async_init (&u->async_w, async_cb);
		3753	ev_async_start (EV_A_ &u->async_w);
		3754
		3755	pthread_mutex_init (&u->lock, 0);
		3756	pthread_cond_init (&u->invoke_cv, 0);
		3757
		3758	// now associate this with the loop
		3759	ev_set_userdata (EV_A_ u);
		3760	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3761	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3762
		3763	// then create the thread running ev_run
		3764	pthread_create (&u->tid, 0, l_run, EV_A);
		3765	}
		3766
		3767	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3768	solely to wake up the event loop so it takes notice of any new watchers
		3769	that might have been added:
		3770
		3771	static void
		3772	async_cb (EV_P_ ev_async *w, int revents)
		3773	{
		3774	// just used for the side effects
		3775	}
		3776
		3777	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3778	protecting the loop data, respectively.
		3779
		3780	static void
		3781	l_release (EV_P)
		3782	{
		3783	userdata *u = ev_userdata (EV_A);
		3784	pthread_mutex_unlock (&u->lock);
		3785	}
		3786
		3787	static void
		3788	l_acquire (EV_P)
		3789	{
		3790	userdata *u = ev_userdata (EV_A);
		3791	pthread_mutex_lock (&u->lock);
		3792	}
		3793
		3794	The event loop thread first acquires the mutex, and then jumps straight
		3795	into C<ev_run>:
		3796
		3797	void *
		3798	l_run (void *thr_arg)
		3799	{
		3800	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3801
		3802	l_acquire (EV_A);
		3803	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3804	ev_run (EV_A_ 0);
		3805	l_release (EV_A);
		3806
		3807	return 0;
		3808	}
		3809
		3810	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3811	signal the main thread via some unspecified mechanism (signals? pipe
		3812	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3813	have been called (in a while loop because a) spurious wakeups are possible
		3814	and b) skipping inter-thread-communication when there are no pending
		3815	watchers is very beneficial):
		3816
		3817	static void
		3818	l_invoke (EV_P)
		3819	{
		3820	userdata *u = ev_userdata (EV_A);
		3821
		3822	while (ev_pending_count (EV_A))
		3823	{
		3824	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3825	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3826	}
		3827	}
		3828
		3829	Now, whenever the main thread gets told to invoke pending watchers, it
		3830	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3831	thread to continue:
		3832
		3833	static void
		3834	real_invoke_pending (EV_P)
		3835	{
		3836	userdata *u = ev_userdata (EV_A);
		3837
		3838	pthread_mutex_lock (&u->lock);
		3839	ev_invoke_pending (EV_A);
		3840	pthread_cond_signal (&u->invoke_cv);
		3841	pthread_mutex_unlock (&u->lock);
		3842	}
		3843
		3844	Whenever you want to start/stop a watcher or do other modifications to an
		3845	event loop, you will now have to lock:
		3846
		3847	ev_timer timeout_watcher;
		3848	userdata *u = ev_userdata (EV_A);
		3849
		3850	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3851
		3852	pthread_mutex_lock (&u->lock);
		3853	ev_timer_start (EV_A_ &timeout_watcher);
		3854	ev_async_send (EV_A_ &u->async_w);
		3855	pthread_mutex_unlock (&u->lock);
		3856
		3857	Note that sending the C<ev_async> watcher is required because otherwise
		3858	an event loop currently blocking in the kernel will have no knowledge
		3859	about the newly added timer. By waking up the loop it will pick up any new
		3860	watchers in the next event loop iteration.
		3861
		3862	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3863
		3864	While the overhead of a callback that e.g. schedules a thread is small, it
		3865	is still an overhead. If you embed libev, and your main usage is with some
		3866	kind of threads or coroutines, you might want to customise libev so that
		3867	doesn't need callbacks anymore.
		3868
		3869	Imagine you have coroutines that you can switch to using a function
		3870	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3871	and that due to some magic, the currently active coroutine is stored in a
		3872	global called C<current_coro>. Then you can build your own "wait for libev
		3873	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3874	the differing C<;> conventions):
		3875
		3876	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3877	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3878
		3879	That means instead of having a C callback function, you store the
		3880	coroutine to switch to in each watcher, and instead of having libev call
		3881	your callback, you instead have it switch to that coroutine.
		3882
		3883	A coroutine might now wait for an event with a function called
		3884	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3885	matter when, or whether the watcher is active or not when this function is
		3886	called):
		3887
		3888	void
		3889	wait_for_event (ev_watcher *w)
		3890	{
		3891	ev_set_cb (w, current_coro);
		3892	switch_to (libev_coro);
		3893	}
		3894
		3895	That basically suspends the coroutine inside C<wait_for_event> and
		3896	continues the libev coroutine, which, when appropriate, switches back to
		3897	this or any other coroutine.
		3898
		3899	You can do similar tricks if you have, say, threads with an event queue -
		3900	instead of storing a coroutine, you store the queue object and instead of
		3901	switching to a coroutine, you push the watcher onto the queue and notify
		3902	any waiters.
		3903
		3904	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3905	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3906
		3907	// my_ev.h
		3908	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3909	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3910	#include "../libev/ev.h"
		3911
		3912	// my_ev.c
		3913	#define EV_H "my_ev.h"
		3914	#include "../libev/ev.c"
		3915
		3916	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3917	F<my_ev.c> into your project. When properly specifying include paths, you
		3918	can even use F<ev.h> as header file name directly.
		3919
794		3920
795	=head1 LIBEVENT EMULATION	3921	=head1 LIBEVENT EMULATION
796		3922
797	Libev offers a compatibility emulation layer for libevent. It cannot	3923	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	3924	emulate the internals of libevent, so here are some usage hints:
799		3925
800	=over 4	3926	=over 4
		3927
		3928	=item * Only the libevent-1.4.1-beta API is being emulated.
		3929
		3930	This was the newest libevent version available when libev was implemented,
		3931	and is still mostly unchanged in 2010.
801		3932
802	=item * Use it by including <event.h>, as usual.	3933	=item * Use it by including <event.h>, as usual.
803		3934
804	=item * The following members are fully supported: ev_base, ev_callback,	3935	=item * The following members are fully supported: ev_base, ev_callback,
805	ev_arg, ev_fd, ev_res, ev_events.	3936	ev_arg, ev_fd, ev_res, ev_events.
…		…
810		3941
811	=item * Priorities are not currently supported. Initialising priorities	3942	=item * Priorities are not currently supported. Initialising priorities
812	will fail and all watchers will have the same priority, even though there	3943	will fail and all watchers will have the same priority, even though there
813	is an ev_pri field.	3944	is an ev_pri field.
814		3945
		3946	=item * In libevent, the last base created gets the signals, in libev, the
		3947	base that registered the signal gets the signals.
		3948
815	=item * Other members are not supported.	3949	=item * Other members are not supported.
816		3950
817	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3951	=item * The libev emulation is I<not> ABI compatible to libevent, you need
818	to use the libev header file and library.	3952	to use the libev header file and library.
819		3953
820	=back	3954	=back
821		3955
822	=head1 C++ SUPPORT	3956	=head1 C++ SUPPORT
823		3957
824	TBD.	3958	=head2 C API
		3959
		3960	The normal C API should work fine when used from C++: both ev.h and the
		3961	libev sources can be compiled as C++. Therefore, code that uses the C API
		3962	will work fine.
		3963
		3964	Proper exception specifications might have to be added to callbacks passed
		3965	to libev: exceptions may be thrown only from watcher callbacks, all
		3966	other callbacks (allocator, syserr, loop acquire/release and periodic
		3967	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3968	()> specification. If you have code that needs to be compiled as both C
		3969	and C++ you can use the C<EV_THROW> macro for this:
		3970
		3971	static void
		3972	fatal_error (const char *msg) EV_THROW
		3973	{
		3974	perror (msg);
		3975	abort ();
		3976	}
		3977
		3978	...
		3979	ev_set_syserr_cb (fatal_error);
		3980
		3981	The only API functions that can currently throw exceptions are C<ev_run>,
		3982	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3983	because it runs cleanup watchers).
		3984
		3985	Throwing exceptions in watcher callbacks is only supported if libev itself
		3986	is compiled with a C++ compiler or your C and C++ environments allow
		3987	throwing exceptions through C libraries (most do).
		3988
		3989	=head2 C++ API
		3990
		3991	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3992	you to use some convenience methods to start/stop watchers and also change
		3993	the callback model to a model using method callbacks on objects.
		3994
		3995	To use it,
		3996
		3997	#include <ev++.h>
		3998
		3999	This automatically includes F<ev.h> and puts all of its definitions (many
		4000	of them macros) into the global namespace. All C++ specific things are
		4001	put into the C<ev> namespace. It should support all the same embedding
		4002	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		4003
		4004	Care has been taken to keep the overhead low. The only data member the C++
		4005	classes add (compared to plain C-style watchers) is the event loop pointer
		4006	that the watcher is associated with (or no additional members at all if
		4007	you disable C<EV_MULTIPLICITY> when embedding libev).
		4008
		4009	Currently, functions, static and non-static member functions and classes
		4010	with C<operator ()> can be used as callbacks. Other types should be easy
		4011	to add as long as they only need one additional pointer for context. If
		4012	you need support for other types of functors please contact the author
		4013	(preferably after implementing it).
		4014
		4015	For all this to work, your C++ compiler either has to use the same calling
		4016	conventions as your C compiler (for static member functions), or you have
		4017	to embed libev and compile libev itself as C++.
		4018
		4019	Here is a list of things available in the C<ev> namespace:
		4020
		4021	=over 4
		4022
		4023	=item C<ev::READ>, C<ev::WRITE> etc.
		4024
		4025	These are just enum values with the same values as the C<EV_READ> etc.
		4026	macros from F<ev.h>.
		4027
		4028	=item C<ev::tstamp>, C<ev::now>
		4029
		4030	Aliases to the same types/functions as with the C<ev_> prefix.
		4031
		4032	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		4033
		4034	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		4035	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		4036	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		4037	defined by many implementations.
		4038
		4039	All of those classes have these methods:
		4040
		4041	=over 4
		4042
		4043	=item ev::TYPE::TYPE ()
		4044
		4045	=item ev::TYPE::TYPE (loop)
		4046
		4047	=item ev::TYPE::~TYPE
		4048
		4049	The constructor (optionally) takes an event loop to associate the watcher
		4050	with. If it is omitted, it will use C<EV_DEFAULT>.
		4051
		4052	The constructor calls C<ev_init> for you, which means you have to call the
		4053	C<set> method before starting it.
		4054
		4055	It will not set a callback, however: You have to call the templated C<set>
		4056	method to set a callback before you can start the watcher.
		4057
		4058	(The reason why you have to use a method is a limitation in C++ which does
		4059	not allow explicit template arguments for constructors).
		4060
		4061	The destructor automatically stops the watcher if it is active.
		4062
		4063	=item w->set<class, &class::method> (object *)
		4064
		4065	This method sets the callback method to call. The method has to have a
		4066	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		4067	first argument and the C<revents> as second. The object must be given as
		4068	parameter and is stored in the C<data> member of the watcher.
		4069
		4070	This method synthesizes efficient thunking code to call your method from
		4071	the C callback that libev requires. If your compiler can inline your
		4072	callback (i.e. it is visible to it at the place of the C<set> call and
		4073	your compiler is good :), then the method will be fully inlined into the
		4074	thunking function, making it as fast as a direct C callback.
		4075
		4076	Example: simple class declaration and watcher initialisation
		4077
		4078	struct myclass
		4079	{
		4080	void io_cb (ev::io &w, int revents) { }
		4081	}
		4082
		4083	myclass obj;
		4084	ev::io iow;
		4085	iow.set <myclass, &myclass::io_cb> (&obj);
		4086
		4087	=item w->set (object *)
		4088
		4089	This is a variation of a method callback - leaving out the method to call
		4090	will default the method to C<operator ()>, which makes it possible to use
		4091	functor objects without having to manually specify the C<operator ()> all
		4092	the time. Incidentally, you can then also leave out the template argument
		4093	list.
		4094
		4095	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4096	int revents)>.
		4097
		4098	See the method-C<set> above for more details.
		4099
		4100	Example: use a functor object as callback.
		4101
		4102	struct myfunctor
		4103	{
		4104	void operator() (ev::io &w, int revents)
		4105	{
		4106	...
		4107	}
		4108	}
		4109
		4110	myfunctor f;
		4111
		4112	ev::io w;
		4113	w.set (&f);
		4114
		4115	=item w->set<function> (void *data = 0)
		4116
		4117	Also sets a callback, but uses a static method or plain function as
		4118	callback. The optional C<data> argument will be stored in the watcher's
		4119	C<data> member and is free for you to use.
		4120
		4121	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4122
		4123	See the method-C<set> above for more details.
		4124
		4125	Example: Use a plain function as callback.
		4126
		4127	static void io_cb (ev::io &w, int revents) { }
		4128	iow.set <io_cb> ();
		4129
		4130	=item w->set (loop)
		4131
		4132	Associates a different C<struct ev_loop> with this watcher. You can only
		4133	do this when the watcher is inactive (and not pending either).
		4134
		4135	=item w->set ([arguments])
		4136
		4137	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4138	with the same arguments. Either this method or a suitable start method
		4139	must be called at least once. Unlike the C counterpart, an active watcher
		4140	gets automatically stopped and restarted when reconfiguring it with this
		4141	method.
		4142
		4143	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4144	clashing with the C<set (loop)> method.
		4145
		4146	=item w->start ()
		4147
		4148	Starts the watcher. Note that there is no C<loop> argument, as the
		4149	constructor already stores the event loop.
		4150
		4151	=item w->start ([arguments])
		4152
		4153	Instead of calling C<set> and C<start> methods separately, it is often
		4154	convenient to wrap them in one call. Uses the same type of arguments as
		4155	the configure C<set> method of the watcher.
		4156
		4157	=item w->stop ()
		4158
		4159	Stops the watcher if it is active. Again, no C<loop> argument.
		4160
		4161	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		4162
		4163	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		4164	C<ev_TYPE_again> function.
		4165
		4166	=item w->sweep () (C<ev::embed> only)
		4167
		4168	Invokes C<ev_embed_sweep>.
		4169
		4170	=item w->update () (C<ev::stat> only)
		4171
		4172	Invokes C<ev_stat_stat>.
		4173
		4174	=back
		4175
		4176	=back
		4177
		4178	Example: Define a class with two I/O and idle watchers, start the I/O
		4179	watchers in the constructor.
		4180
		4181	class myclass
		4182	{
		4183	ev::io io ; void io_cb (ev::io &w, int revents);
		4184	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		4185	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		4186
		4187	myclass (int fd)
		4188	{
		4189	io .set <myclass, &myclass::io_cb > (this);
		4190	io2 .set <myclass, &myclass::io2_cb > (this);
		4191	idle.set <myclass, &myclass::idle_cb> (this);
		4192
		4193	io.set (fd, ev::WRITE); // configure the watcher
		4194	io.start (); // start it whenever convenient
		4195
		4196	io2.start (fd, ev::READ); // set + start in one call
		4197	}
		4198	};
		4199
		4200
		4201	=head1 OTHER LANGUAGE BINDINGS
		4202
		4203	Libev does not offer other language bindings itself, but bindings for a
		4204	number of languages exist in the form of third-party packages. If you know
		4205	any interesting language binding in addition to the ones listed here, drop
		4206	me a note.
		4207
		4208	=over 4
		4209
		4210	=item Perl
		4211
		4212	The EV module implements the full libev API and is actually used to test
		4213	libev. EV is developed together with libev. Apart from the EV core module,
		4214	there are additional modules that implement libev-compatible interfaces
		4215	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4216	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4217	and C<EV::Glib>).
		4218
		4219	It can be found and installed via CPAN, its homepage is at
		4220	L<http://software.schmorp.de/pkg/EV>.
		4221
		4222	=item Python
		4223
		4224	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4225	seems to be quite complete and well-documented.
		4226
		4227	=item Ruby
		4228
		4229	Tony Arcieri has written a ruby extension that offers access to a subset
		4230	of the libev API and adds file handle abstractions, asynchronous DNS and
		4231	more on top of it. It can be found via gem servers. Its homepage is at
		4232	L<http://rev.rubyforge.org/>.
		4233
		4234	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4235	makes rev work even on mingw.
		4236
		4237	=item Haskell
		4238
		4239	A haskell binding to libev is available at
		4240	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4241
		4242	=item D
		4243
		4244	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4245	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4246
		4247	=item Ocaml
		4248
		4249	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4250	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4251
		4252	=item Lua
		4253
		4254	Brian Maher has written a partial interface to libev for lua (at the
		4255	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4256	L<http://github.com/brimworks/lua-ev>.
		4257
		4258	=item Javascript
		4259
		4260	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4261
		4262	=item Others
		4263
		4264	There are others, and I stopped counting.
		4265
		4266	=back
		4267
		4268
		4269	=head1 MACRO MAGIC
		4270
		4271	Libev can be compiled with a variety of options, the most fundamental
		4272	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4273	functions and callbacks have an initial C<struct ev_loop *> argument.
		4274
		4275	To make it easier to write programs that cope with either variant, the
		4276	following macros are defined:
		4277
		4278	=over 4
		4279
		4280	=item C<EV_A>, C<EV_A_>
		4281
		4282	This provides the loop I<argument> for functions, if one is required ("ev
		4283	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4284	C<EV_A_> is used when other arguments are following. Example:
		4285
		4286	ev_unref (EV_A);
		4287	ev_timer_add (EV_A_ watcher);
		4288	ev_run (EV_A_ 0);
		4289
		4290	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4291	which is often provided by the following macro.
		4292
		4293	=item C<EV_P>, C<EV_P_>
		4294
		4295	This provides the loop I<parameter> for functions, if one is required ("ev
		4296	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4297	C<EV_P_> is used when other parameters are following. Example:
		4298
		4299	// this is how ev_unref is being declared
		4300	static void ev_unref (EV_P);
		4301
		4302	// this is how you can declare your typical callback
		4303	static void cb (EV_P_ ev_timer *w, int revents)
		4304
		4305	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4306	suitable for use with C<EV_A>.
		4307
		4308	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4309
		4310	Similar to the other two macros, this gives you the value of the default
		4311	loop, if multiple loops are supported ("ev loop default"). The default loop
		4312	will be initialised if it isn't already initialised.
		4313
		4314	For non-multiplicity builds, these macros do nothing, so you always have
		4315	to initialise the loop somewhere.
		4316
		4317	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4318
		4319	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4320	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4321	is undefined when the default loop has not been initialised by a previous
		4322	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4323
		4324	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4325	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4326
		4327	=back
		4328
		4329	Example: Declare and initialise a check watcher, utilising the above
		4330	macros so it will work regardless of whether multiple loops are supported
		4331	or not.
		4332
		4333	static void
		4334	check_cb (EV_P_ ev_timer *w, int revents)
		4335	{
		4336	ev_check_stop (EV_A_ w);
		4337	}
		4338
		4339	ev_check check;
		4340	ev_check_init (&check, check_cb);
		4341	ev_check_start (EV_DEFAULT_ &check);
		4342	ev_run (EV_DEFAULT_ 0);
		4343
		4344	=head1 EMBEDDING
		4345
		4346	Libev can (and often is) directly embedded into host
		4347	applications. Examples of applications that embed it include the Deliantra
		4348	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4349	and rxvt-unicode.
		4350
		4351	The goal is to enable you to just copy the necessary files into your
		4352	source directory without having to change even a single line in them, so
		4353	you can easily upgrade by simply copying (or having a checked-out copy of
		4354	libev somewhere in your source tree).
		4355
		4356	=head2 FILESETS
		4357
		4358	Depending on what features you need you need to include one or more sets of files
		4359	in your application.
		4360
		4361	=head3 CORE EVENT LOOP
		4362
		4363	To include only the libev core (all the C<ev_*> functions), with manual
		4364	configuration (no autoconf):
		4365
		4366	#define EV_STANDALONE 1
		4367	#include "ev.c"
		4368
		4369	This will automatically include F<ev.h>, too, and should be done in a
		4370	single C source file only to provide the function implementations. To use
		4371	it, do the same for F<ev.h> in all files wishing to use this API (best
		4372	done by writing a wrapper around F<ev.h> that you can include instead and
		4373	where you can put other configuration options):
		4374
		4375	#define EV_STANDALONE 1
		4376	#include "ev.h"
		4377
		4378	Both header files and implementation files can be compiled with a C++
		4379	compiler (at least, that's a stated goal, and breakage will be treated
		4380	as a bug).
		4381
		4382	You need the following files in your source tree, or in a directory
		4383	in your include path (e.g. in libev/ when using -Ilibev):
		4384
		4385	ev.h
		4386	ev.c
		4387	ev_vars.h
		4388	ev_wrap.h
		4389
		4390	ev_win32.c required on win32 platforms only
		4391
		4392	ev_select.c only when select backend is enabled
		4393	ev_poll.c only when poll backend is enabled
		4394	ev_epoll.c only when the epoll backend is enabled
		4395	ev_kqueue.c only when the kqueue backend is enabled
		4396	ev_port.c only when the solaris port backend is enabled
		4397
		4398	F<ev.c> includes the backend files directly when enabled, so you only need
		4399	to compile this single file.
		4400
		4401	=head3 LIBEVENT COMPATIBILITY API
		4402
		4403	To include the libevent compatibility API, also include:
		4404
		4405	#include "event.c"
		4406
		4407	in the file including F<ev.c>, and:
		4408
		4409	#include "event.h"
		4410
		4411	in the files that want to use the libevent API. This also includes F<ev.h>.
		4412
		4413	You need the following additional files for this:
		4414
		4415	event.h
		4416	event.c
		4417
		4418	=head3 AUTOCONF SUPPORT
		4419
		4420	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4421	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4422	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4423	include F<config.h> and configure itself accordingly.
		4424
		4425	For this of course you need the m4 file:
		4426
		4427	libev.m4
		4428
		4429	=head2 PREPROCESSOR SYMBOLS/MACROS
		4430
		4431	Libev can be configured via a variety of preprocessor symbols you have to
		4432	define before including (or compiling) any of its files. The default in
		4433	the absence of autoconf is documented for every option.
		4434
		4435	Symbols marked with "(h)" do not change the ABI, and can have different
		4436	values when compiling libev vs. including F<ev.h>, so it is permissible
		4437	to redefine them before including F<ev.h> without breaking compatibility
		4438	to a compiled library. All other symbols change the ABI, which means all
		4439	users of libev and the libev code itself must be compiled with compatible
		4440	settings.
		4441
		4442	=over 4
		4443
		4444	=item EV_COMPAT3 (h)
		4445
		4446	Backwards compatibility is a major concern for libev. This is why this
		4447	release of libev comes with wrappers for the functions and symbols that
		4448	have been renamed between libev version 3 and 4.
		4449
		4450	You can disable these wrappers (to test compatibility with future
		4451	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4452	sources. This has the additional advantage that you can drop the C<struct>
		4453	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4454	typedef in that case.
		4455
		4456	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4457	and in some even more future version the compatibility code will be
		4458	removed completely.
		4459
		4460	=item EV_STANDALONE (h)
		4461
		4462	Must always be C<1> if you do not use autoconf configuration, which
		4463	keeps libev from including F<config.h>, and it also defines dummy
		4464	implementations for some libevent functions (such as logging, which is not
		4465	supported). It will also not define any of the structs usually found in
		4466	F<event.h> that are not directly supported by the libev core alone.
		4467
		4468	In standalone mode, libev will still try to automatically deduce the
		4469	configuration, but has to be more conservative.
		4470
		4471	=item EV_USE_FLOOR
		4472
		4473	If defined to be C<1>, libev will use the C<floor ()> function for its
		4474	periodic reschedule calculations, otherwise libev will fall back on a
		4475	portable (slower) implementation. If you enable this, you usually have to
		4476	link against libm or something equivalent. Enabling this when the C<floor>
		4477	function is not available will fail, so the safe default is to not enable
		4478	this.
		4479
		4480	=item EV_USE_MONOTONIC
		4481
		4482	If defined to be C<1>, libev will try to detect the availability of the
		4483	monotonic clock option at both compile time and runtime. Otherwise no
		4484	use of the monotonic clock option will be attempted. If you enable this,
		4485	you usually have to link against librt or something similar. Enabling it
		4486	when the functionality isn't available is safe, though, although you have
		4487	to make sure you link against any libraries where the C<clock_gettime>
		4488	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4489
		4490	=item EV_USE_REALTIME
		4491
		4492	If defined to be C<1>, libev will try to detect the availability of the
		4493	real-time clock option at compile time (and assume its availability
		4494	at runtime if successful). Otherwise no use of the real-time clock
		4495	option will be attempted. This effectively replaces C<gettimeofday>
		4496	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4497	correctness. See the note about libraries in the description of
		4498	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4499	C<EV_USE_CLOCK_SYSCALL>.
		4500
		4501	=item EV_USE_CLOCK_SYSCALL
		4502
		4503	If defined to be C<1>, libev will try to use a direct syscall instead
		4504	of calling the system-provided C<clock_gettime> function. This option
		4505	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4506	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4507	programs needlessly. Using a direct syscall is slightly slower (in
		4508	theory), because no optimised vdso implementation can be used, but avoids
		4509	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4510	higher, as it simplifies linking (no need for C<-lrt>).
		4511
		4512	=item EV_USE_NANOSLEEP
		4513
		4514	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4515	and will use it for delays. Otherwise it will use C<select ()>.
		4516
		4517	=item EV_USE_EVENTFD
		4518
		4519	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4520	available and will probe for kernel support at runtime. This will improve
		4521	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4522	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4523	2.7 or newer, otherwise disabled.
		4524
		4525	=item EV_USE_SELECT
		4526
		4527	If undefined or defined to be C<1>, libev will compile in support for the
		4528	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4529	other method takes over, select will be it. Otherwise the select backend
		4530	will not be compiled in.
		4531
		4532	=item EV_SELECT_USE_FD_SET
		4533
		4534	If defined to C<1>, then the select backend will use the system C<fd_set>
		4535	structure. This is useful if libev doesn't compile due to a missing
		4536	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4537	on exotic systems. This usually limits the range of file descriptors to
		4538	some low limit such as 1024 or might have other limitations (winsocket
		4539	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4540	configures the maximum size of the C<fd_set>.
		4541
		4542	=item EV_SELECT_IS_WINSOCKET
		4543
		4544	When defined to C<1>, the select backend will assume that
		4545	select/socket/connect etc. don't understand file descriptors but
		4546	wants osf handles on win32 (this is the case when the select to
		4547	be used is the winsock select). This means that it will call
		4548	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4549	it is assumed that all these functions actually work on fds, even
		4550	on win32. Should not be defined on non-win32 platforms.
		4551
		4552	=item EV_FD_TO_WIN32_HANDLE(fd)
		4553
		4554	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4555	file descriptors to socket handles. When not defining this symbol (the
		4556	default), then libev will call C<_get_osfhandle>, which is usually
		4557	correct. In some cases, programs use their own file descriptor management,
		4558	in which case they can provide this function to map fds to socket handles.
		4559
		4560	=item EV_WIN32_HANDLE_TO_FD(handle)
		4561
		4562	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4563	using the standard C<_open_osfhandle> function. For programs implementing
		4564	their own fd to handle mapping, overwriting this function makes it easier
		4565	to do so. This can be done by defining this macro to an appropriate value.
		4566
		4567	=item EV_WIN32_CLOSE_FD(fd)
		4568
		4569	If programs implement their own fd to handle mapping on win32, then this
		4570	macro can be used to override the C<close> function, useful to unregister
		4571	file descriptors again. Note that the replacement function has to close
		4572	the underlying OS handle.
		4573
		4574	=item EV_USE_WSASOCKET
		4575
		4576	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4577	communication socket, which works better in some environments. Otherwise,
		4578	the normal C<socket> function will be used, which works better in other
		4579	environments.
		4580
		4581	=item EV_USE_POLL
		4582
		4583	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4584	backend. Otherwise it will be enabled on non-win32 platforms. It
		4585	takes precedence over select.
		4586
		4587	=item EV_USE_EPOLL
		4588
		4589	If defined to be C<1>, libev will compile in support for the Linux
		4590	C<epoll>(7) backend. Its availability will be detected at runtime,
		4591	otherwise another method will be used as fallback. This is the preferred
		4592	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4593	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4594
		4595	=item EV_USE_KQUEUE
		4596
		4597	If defined to be C<1>, libev will compile in support for the BSD style
		4598	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4599	otherwise another method will be used as fallback. This is the preferred
		4600	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4601	supports some types of fds correctly (the only platform we found that
		4602	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4603	not be used unless explicitly requested. The best way to use it is to find
		4604	out whether kqueue supports your type of fd properly and use an embedded
		4605	kqueue loop.
		4606
		4607	=item EV_USE_PORT
		4608
		4609	If defined to be C<1>, libev will compile in support for the Solaris
		4610	10 port style backend. Its availability will be detected at runtime,
		4611	otherwise another method will be used as fallback. This is the preferred
		4612	backend for Solaris 10 systems.
		4613
		4614	=item EV_USE_DEVPOLL
		4615
		4616	Reserved for future expansion, works like the USE symbols above.
		4617
		4618	=item EV_USE_INOTIFY
		4619
		4620	If defined to be C<1>, libev will compile in support for the Linux inotify
		4621	interface to speed up C<ev_stat> watchers. Its actual availability will
		4622	be detected at runtime. If undefined, it will be enabled if the headers
		4623	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4624
		4625	=item EV_NO_SMP
		4626
		4627	If defined to be C<1>, libev will assume that memory is always coherent
		4628	between threads, that is, threads can be used, but threads never run on
		4629	different cpus (or different cpu cores). This reduces dependencies
		4630	and makes libev faster.
		4631
		4632	=item EV_NO_THREADS
		4633
		4634	If defined to be C<1>, libev will assume that it will never be called from
		4635	different threads (that includes signal handlers), which is a stronger
		4636	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4637	libev faster.
		4638
		4639	=item EV_ATOMIC_T
		4640
		4641	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4642	access is atomic with respect to other threads or signal contexts. No
		4643	such type is easily found in the C language, so you can provide your own
		4644	type that you know is safe for your purposes. It is used both for signal
		4645	handler "locking" as well as for signal and thread safety in C<ev_async>
		4646	watchers.
		4647
		4648	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4649	(from F<signal.h>), which is usually good enough on most platforms.
		4650
		4651	=item EV_H (h)
		4652
		4653	The name of the F<ev.h> header file used to include it. The default if
		4654	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4655	used to virtually rename the F<ev.h> header file in case of conflicts.
		4656
		4657	=item EV_CONFIG_H (h)
		4658
		4659	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4660	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4661	C<EV_H>, above.
		4662
		4663	=item EV_EVENT_H (h)
		4664
		4665	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4666	of how the F<event.h> header can be found, the default is C<"event.h">.
		4667
		4668	=item EV_PROTOTYPES (h)
		4669
		4670	If defined to be C<0>, then F<ev.h> will not define any function
		4671	prototypes, but still define all the structs and other symbols. This is
		4672	occasionally useful if you want to provide your own wrapper functions
		4673	around libev functions.
		4674
		4675	=item EV_MULTIPLICITY
		4676
		4677	If undefined or defined to C<1>, then all event-loop-specific functions
		4678	will have the C<struct ev_loop *> as first argument, and you can create
		4679	additional independent event loops. Otherwise there will be no support
		4680	for multiple event loops and there is no first event loop pointer
		4681	argument. Instead, all functions act on the single default loop.
		4682
		4683	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4684	default loop when multiplicity is switched off - you always have to
		4685	initialise the loop manually in this case.
		4686
		4687	=item EV_MINPRI
		4688
		4689	=item EV_MAXPRI
		4690
		4691	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4692	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4693	provide for more priorities by overriding those symbols (usually defined
		4694	to be C<-2> and C<2>, respectively).
		4695
		4696	When doing priority-based operations, libev usually has to linearly search
		4697	all the priorities, so having many of them (hundreds) uses a lot of space
		4698	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4699	fine.
		4700
		4701	If your embedding application does not need any priorities, defining these
		4702	both to C<0> will save some memory and CPU.
		4703
		4704	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4705	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4706	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4707
		4708	If undefined or defined to be C<1> (and the platform supports it), then
		4709	the respective watcher type is supported. If defined to be C<0>, then it
		4710	is not. Disabling watcher types mainly saves code size.
		4711
		4712	=item EV_FEATURES
		4713
		4714	If you need to shave off some kilobytes of code at the expense of some
		4715	speed (but with the full API), you can define this symbol to request
		4716	certain subsets of functionality. The default is to enable all features
		4717	that can be enabled on the platform.
		4718
		4719	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4720	with some broad features you want) and then selectively re-enable
		4721	additional parts you want, for example if you want everything minimal,
		4722	but multiple event loop support, async and child watchers and the poll
		4723	backend, use this:
		4724
		4725	#define EV_FEATURES 0
		4726	#define EV_MULTIPLICITY 1
		4727	#define EV_USE_POLL 1
		4728	#define EV_CHILD_ENABLE 1
		4729	#define EV_ASYNC_ENABLE 1
		4730
		4731	The actual value is a bitset, it can be a combination of the following
		4732	values (by default, all of these are enabled):
		4733
		4734	=over 4
		4735
		4736	=item C<1> - faster/larger code
		4737
		4738	Use larger code to speed up some operations.
		4739
		4740	Currently this is used to override some inlining decisions (enlarging the
		4741	code size by roughly 30% on amd64).
		4742
		4743	When optimising for size, use of compiler flags such as C<-Os> with
		4744	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4745	assertions.
		4746
		4747	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4748	(e.g. gcc with C<-Os>).
		4749
		4750	=item C<2> - faster/larger data structures
		4751
		4752	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4753	hash table sizes and so on. This will usually further increase code size
		4754	and can additionally have an effect on the size of data structures at
		4755	runtime.
		4756
		4757	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4758	(e.g. gcc with C<-Os>).
		4759
		4760	=item C<4> - full API configuration
		4761
		4762	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4763	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4764
		4765	=item C<8> - full API
		4766
		4767	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4768	details on which parts of the API are still available without this
		4769	feature, and do not complain if this subset changes over time.
		4770
		4771	=item C<16> - enable all optional watcher types
		4772
		4773	Enables all optional watcher types. If you want to selectively enable
		4774	only some watcher types other than I/O and timers (e.g. prepare,
		4775	embed, async, child...) you can enable them manually by defining
		4776	C<EV_watchertype_ENABLE> to C<1> instead.
		4777
		4778	=item C<32> - enable all backends
		4779
		4780	This enables all backends - without this feature, you need to enable at
		4781	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4782
		4783	=item C<64> - enable OS-specific "helper" APIs
		4784
		4785	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4786	default.
		4787
		4788	=back
		4789
		4790	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4791	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4792	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4793	watchers, timers and monotonic clock support.
		4794
		4795	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4796	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4797	your program might be left out as well - a binary starting a timer and an
		4798	I/O watcher then might come out at only 5Kb.
		4799
		4800	=item EV_API_STATIC
		4801
		4802	If this symbol is defined (by default it is not), then all identifiers
		4803	will have static linkage. This means that libev will not export any
		4804	identifiers, and you cannot link against libev anymore. This can be useful
		4805	when you embed libev, only want to use libev functions in a single file,
		4806	and do not want its identifiers to be visible.
		4807
		4808	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4809	wants to use libev.
		4810
		4811	This option only works when libev is compiled with a C compiler, as C++
		4812	doesn't support the required declaration syntax.
		4813
		4814	=item EV_AVOID_STDIO
		4815
		4816	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4817	functions (printf, scanf, perror etc.). This will increase the code size
		4818	somewhat, but if your program doesn't otherwise depend on stdio and your
		4819	libc allows it, this avoids linking in the stdio library which is quite
		4820	big.
		4821
		4822	Note that error messages might become less precise when this option is
		4823	enabled.
		4824
		4825	=item EV_NSIG
		4826
		4827	The highest supported signal number, +1 (or, the number of
		4828	signals): Normally, libev tries to deduce the maximum number of signals
		4829	automatically, but sometimes this fails, in which case it can be
		4830	specified. Also, using a lower number than detected (C<32> should be
		4831	good for about any system in existence) can save some memory, as libev
		4832	statically allocates some 12-24 bytes per signal number.
		4833
		4834	=item EV_PID_HASHSIZE
		4835
		4836	C<ev_child> watchers use a small hash table to distribute workload by
		4837	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4838	usually more than enough. If you need to manage thousands of children you
		4839	might want to increase this value (I<must> be a power of two).
		4840
		4841	=item EV_INOTIFY_HASHSIZE
		4842
		4843	C<ev_stat> watchers use a small hash table to distribute workload by
		4844	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4845	disabled), usually more than enough. If you need to manage thousands of
		4846	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4847	power of two).
		4848
		4849	=item EV_USE_4HEAP
		4850
		4851	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4852	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4853	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4854	faster performance with many (thousands) of watchers.
		4855
		4856	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4857	will be C<0>.
		4858
		4859	=item EV_HEAP_CACHE_AT
		4860
		4861	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4862	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4863	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4864	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4865	but avoids random read accesses on heap changes. This improves performance
		4866	noticeably with many (hundreds) of watchers.
		4867
		4868	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4869	will be C<0>.
		4870
		4871	=item EV_VERIFY
		4872
		4873	Controls how much internal verification (see C<ev_verify ()>) will
		4874	be done: If set to C<0>, no internal verification code will be compiled
		4875	in. If set to C<1>, then verification code will be compiled in, but not
		4876	called. If set to C<2>, then the internal verification code will be
		4877	called once per loop, which can slow down libev. If set to C<3>, then the
		4878	verification code will be called very frequently, which will slow down
		4879	libev considerably.
		4880
		4881	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4882	will be C<0>.
		4883
		4884	=item EV_COMMON
		4885
		4886	By default, all watchers have a C<void *data> member. By redefining
		4887	this macro to something else you can include more and other types of
		4888	members. You have to define it each time you include one of the files,
		4889	though, and it must be identical each time.
		4890
		4891	For example, the perl EV module uses something like this:
		4892
		4893	#define EV_COMMON \
		4894	SV *self; /* contains this struct */ \
		4895	SV *cb_sv, *fh /* note no trailing ";" */
		4896
		4897	=item EV_CB_DECLARE (type)
		4898
		4899	=item EV_CB_INVOKE (watcher, revents)
		4900
		4901	=item ev_set_cb (ev, cb)
		4902
		4903	Can be used to change the callback member declaration in each watcher,
		4904	and the way callbacks are invoked and set. Must expand to a struct member
		4905	definition and a statement, respectively. See the F<ev.h> header file for
		4906	their default definitions. One possible use for overriding these is to
		4907	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4908	method calls instead of plain function calls in C++.
		4909
		4910	=back
		4911
		4912	=head2 EXPORTED API SYMBOLS
		4913
		4914	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4915	exported symbols, you can use the provided F<Symbol.*> files which list
		4916	all public symbols, one per line:
		4917
		4918	Symbols.ev for libev proper
		4919	Symbols.event for the libevent emulation
		4920
		4921	This can also be used to rename all public symbols to avoid clashes with
		4922	multiple versions of libev linked together (which is obviously bad in
		4923	itself, but sometimes it is inconvenient to avoid this).
		4924
		4925	A sed command like this will create wrapper C<#define>'s that you need to
		4926	include before including F<ev.h>:
		4927
		4928	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4929
		4930	This would create a file F<wrap.h> which essentially looks like this:
		4931
		4932	#define ev_backend myprefix_ev_backend
		4933	#define ev_check_start myprefix_ev_check_start
		4934	#define ev_check_stop myprefix_ev_check_stop
		4935	...
		4936
		4937	=head2 EXAMPLES
		4938
		4939	For a real-world example of a program the includes libev
		4940	verbatim, you can have a look at the EV perl module
		4941	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4942	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4943	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4944	will be compiled. It is pretty complex because it provides its own header
		4945	file.
		4946
		4947	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4948	that everybody includes and which overrides some configure choices:
		4949
		4950	#define EV_FEATURES 8
		4951	#define EV_USE_SELECT 1
		4952	#define EV_PREPARE_ENABLE 1
		4953	#define EV_IDLE_ENABLE 1
		4954	#define EV_SIGNAL_ENABLE 1
		4955	#define EV_CHILD_ENABLE 1
		4956	#define EV_USE_STDEXCEPT 0
		4957	#define EV_CONFIG_H <config.h>
		4958
		4959	#include "ev++.h"
		4960
		4961	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4962
		4963	#include "ev_cpp.h"
		4964	#include "ev.c"
		4965
		4966	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		4967
		4968	=head2 THREADS AND COROUTINES
		4969
		4970	=head3 THREADS
		4971
		4972	All libev functions are reentrant and thread-safe unless explicitly
		4973	documented otherwise, but libev implements no locking itself. This means
		4974	that you can use as many loops as you want in parallel, as long as there
		4975	are no concurrent calls into any libev function with the same loop
		4976	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4977	of course): libev guarantees that different event loops share no data
		4978	structures that need any locking.
		4979
		4980	Or to put it differently: calls with different loop parameters can be done
		4981	concurrently from multiple threads, calls with the same loop parameter
		4982	must be done serially (but can be done from different threads, as long as
		4983	only one thread ever is inside a call at any point in time, e.g. by using
		4984	a mutex per loop).
		4985
		4986	Specifically to support threads (and signal handlers), libev implements
		4987	so-called C<ev_async> watchers, which allow some limited form of
		4988	concurrency on the same event loop, namely waking it up "from the
		4989	outside".
		4990
		4991	If you want to know which design (one loop, locking, or multiple loops
		4992	without or something else still) is best for your problem, then I cannot
		4993	help you, but here is some generic advice:
		4994
		4995	=over 4
		4996
		4997	=item * most applications have a main thread: use the default libev loop
		4998	in that thread, or create a separate thread running only the default loop.
		4999
		5000	This helps integrating other libraries or software modules that use libev
		5001	themselves and don't care/know about threading.
		5002
		5003	=item * one loop per thread is usually a good model.
		5004
		5005	Doing this is almost never wrong, sometimes a better-performance model
		5006	exists, but it is always a good start.
		5007
		5008	=item * other models exist, such as the leader/follower pattern, where one
		5009	loop is handed through multiple threads in a kind of round-robin fashion.
		5010
		5011	Choosing a model is hard - look around, learn, know that usually you can do
		5012	better than you currently do :-)
		5013
		5014	=item * often you need to talk to some other thread which blocks in the
		5015	event loop.
		5016
		5017	C<ev_async> watchers can be used to wake them up from other threads safely
		5018	(or from signal contexts...).
		5019
		5020	An example use would be to communicate signals or other events that only
		5021	work in the default loop by registering the signal watcher with the
		5022	default loop and triggering an C<ev_async> watcher from the default loop
		5023	watcher callback into the event loop interested in the signal.
		5024
		5025	=back
		5026
		5027	See also L</THREAD LOCKING EXAMPLE>.
		5028
		5029	=head3 COROUTINES
		5030
		5031	Libev is very accommodating to coroutines ("cooperative threads"):
		5032	libev fully supports nesting calls to its functions from different
		5033	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5034	different coroutines, and switch freely between both coroutines running
		5035	the loop, as long as you don't confuse yourself). The only exception is
		5036	that you must not do this from C<ev_periodic> reschedule callbacks.
		5037
		5038	Care has been taken to ensure that libev does not keep local state inside
		5039	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5040	they do not call any callbacks.
		5041
		5042	=head2 COMPILER WARNINGS
		5043
		5044	Depending on your compiler and compiler settings, you might get no or a
		5045	lot of warnings when compiling libev code. Some people are apparently
		5046	scared by this.
		5047
		5048	However, these are unavoidable for many reasons. For one, each compiler
		5049	has different warnings, and each user has different tastes regarding
		5050	warning options. "Warn-free" code therefore cannot be a goal except when
		5051	targeting a specific compiler and compiler-version.
		5052
		5053	Another reason is that some compiler warnings require elaborate
		5054	workarounds, or other changes to the code that make it less clear and less
		5055	maintainable.
		5056
		5057	And of course, some compiler warnings are just plain stupid, or simply
		5058	wrong (because they don't actually warn about the condition their message
		5059	seems to warn about). For example, certain older gcc versions had some
		5060	warnings that resulted in an extreme number of false positives. These have
		5061	been fixed, but some people still insist on making code warn-free with
		5062	such buggy versions.
		5063
		5064	While libev is written to generate as few warnings as possible,
		5065	"warn-free" code is not a goal, and it is recommended not to build libev
		5066	with any compiler warnings enabled unless you are prepared to cope with
		5067	them (e.g. by ignoring them). Remember that warnings are just that:
		5068	warnings, not errors, or proof of bugs.
		5069
		5070
		5071	=head2 VALGRIND
		5072
		5073	Valgrind has a special section here because it is a popular tool that is
		5074	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5075
		5076	If you think you found a bug (memory leak, uninitialised data access etc.)
		5077	in libev, then check twice: If valgrind reports something like:
		5078
		5079	==2274== definitely lost: 0 bytes in 0 blocks.
		5080	==2274== possibly lost: 0 bytes in 0 blocks.
		5081	==2274== still reachable: 256 bytes in 1 blocks.
		5082
		5083	Then there is no memory leak, just as memory accounted to global variables
		5084	is not a memleak - the memory is still being referenced, and didn't leak.
		5085
		5086	Similarly, under some circumstances, valgrind might report kernel bugs
		5087	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5088	although an acceptable workaround has been found here), or it might be
		5089	confused.
		5090
		5091	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5092	make it into some kind of religion.
		5093
		5094	If you are unsure about something, feel free to contact the mailing list
		5095	with the full valgrind report and an explanation on why you think this
		5096	is a bug in libev (best check the archives, too :). However, don't be
		5097	annoyed when you get a brisk "this is no bug" answer and take the chance
		5098	of learning how to interpret valgrind properly.
		5099
		5100	If you need, for some reason, empty reports from valgrind for your project
		5101	I suggest using suppression lists.
		5102
		5103
		5104	=head1 PORTABILITY NOTES
		5105
		5106	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5107
		5108	GNU/Linux is the only common platform that supports 64 bit file/large file
		5109	interfaces but I<disables> them by default.
		5110
		5111	That means that libev compiled in the default environment doesn't support
		5112	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5113
		5114	Unfortunately, many programs try to work around this GNU/Linux issue
		5115	by enabling the large file API, which makes them incompatible with the
		5116	standard libev compiled for their system.
		5117
		5118	Likewise, libev cannot enable the large file API itself as this would
		5119	suddenly make it incompatible to the default compile time environment,
		5120	i.e. all programs not using special compile switches.
		5121
		5122	=head2 OS/X AND DARWIN BUGS
		5123
		5124	The whole thing is a bug if you ask me - basically any system interface
		5125	you touch is broken, whether it is locales, poll, kqueue or even the
		5126	OpenGL drivers.
		5127
		5128	=head3 C<kqueue> is buggy
		5129
		5130	The kqueue syscall is broken in all known versions - most versions support
		5131	only sockets, many support pipes.
		5132
		5133	Libev tries to work around this by not using C<kqueue> by default on this
		5134	rotten platform, but of course you can still ask for it when creating a
		5135	loop - embedding a socket-only kqueue loop into a select-based one is
		5136	probably going to work well.
		5137
		5138	=head3 C<poll> is buggy
		5139
		5140	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5141	implementation by something calling C<kqueue> internally around the 10.5.6
		5142	release, so now C<kqueue> I<and> C<poll> are broken.
		5143
		5144	Libev tries to work around this by not using C<poll> by default on
		5145	this rotten platform, but of course you can still ask for it when creating
		5146	a loop.
		5147
		5148	=head3 C<select> is buggy
		5149
		5150	All that's left is C<select>, and of course Apple found a way to fuck this
		5151	one up as well: On OS/X, C<select> actively limits the number of file
		5152	descriptors you can pass in to 1024 - your program suddenly crashes when
		5153	you use more.
		5154
		5155	There is an undocumented "workaround" for this - defining
		5156	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5157	work on OS/X.
		5158
		5159	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5160
		5161	=head3 C<errno> reentrancy
		5162
		5163	The default compile environment on Solaris is unfortunately so
		5164	thread-unsafe that you can't even use components/libraries compiled
		5165	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5166	defined by default. A valid, if stupid, implementation choice.
		5167
		5168	If you want to use libev in threaded environments you have to make sure
		5169	it's compiled with C<_REENTRANT> defined.
		5170
		5171	=head3 Event port backend
		5172
		5173	The scalable event interface for Solaris is called "event
		5174	ports". Unfortunately, this mechanism is very buggy in all major
		5175	releases. If you run into high CPU usage, your program freezes or you get
		5176	a large number of spurious wakeups, make sure you have all the relevant
		5177	and latest kernel patches applied. No, I don't know which ones, but there
		5178	are multiple ones to apply, and afterwards, event ports actually work
		5179	great.
		5180
		5181	If you can't get it to work, you can try running the program by setting
		5182	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5183	C<select> backends.
		5184
		5185	=head2 AIX POLL BUG
		5186
		5187	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5188	this by trying to avoid the poll backend altogether (i.e. it's not even
		5189	compiled in), which normally isn't a big problem as C<select> works fine
		5190	with large bitsets on AIX, and AIX is dead anyway.
		5191
		5192	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5193
		5194	=head3 General issues
		5195
		5196	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5197	requires, and its I/O model is fundamentally incompatible with the POSIX
		5198	model. Libev still offers limited functionality on this platform in
		5199	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5200	descriptors. This only applies when using Win32 natively, not when using
		5201	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5202	as every compiler comes with a slightly differently broken/incompatible
		5203	environment.
		5204
		5205	Lifting these limitations would basically require the full
		5206	re-implementation of the I/O system. If you are into this kind of thing,
		5207	then note that glib does exactly that for you in a very portable way (note
		5208	also that glib is the slowest event library known to man).
		5209
		5210	There is no supported compilation method available on windows except
		5211	embedding it into other applications.
		5212
		5213	Sensible signal handling is officially unsupported by Microsoft - libev
		5214	tries its best, but under most conditions, signals will simply not work.
		5215
		5216	Not a libev limitation but worth mentioning: windows apparently doesn't
		5217	accept large writes: instead of resulting in a partial write, windows will
		5218	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5219	so make sure you only write small amounts into your sockets (less than a
		5220	megabyte seems safe, but this apparently depends on the amount of memory
		5221	available).
		5222
		5223	Due to the many, low, and arbitrary limits on the win32 platform and
		5224	the abysmal performance of winsockets, using a large number of sockets
		5225	is not recommended (and not reasonable). If your program needs to use
		5226	more than a hundred or so sockets, then likely it needs to use a totally
		5227	different implementation for windows, as libev offers the POSIX readiness
		5228	notification model, which cannot be implemented efficiently on windows
		5229	(due to Microsoft monopoly games).
		5230
		5231	A typical way to use libev under windows is to embed it (see the embedding
		5232	section for details) and use the following F<evwrap.h> header file instead
		5233	of F<ev.h>:
		5234
		5235	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5236	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5237
		5238	#include "ev.h"
		5239
		5240	And compile the following F<evwrap.c> file into your project (make sure
		5241	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5242
		5243	#include "evwrap.h"
		5244	#include "ev.c"
		5245
		5246	=head3 The winsocket C<select> function
		5247
		5248	The winsocket C<select> function doesn't follow POSIX in that it
		5249	requires socket I<handles> and not socket I<file descriptors> (it is
		5250	also extremely buggy). This makes select very inefficient, and also
		5251	requires a mapping from file descriptors to socket handles (the Microsoft
		5252	C runtime provides the function C<_open_osfhandle> for this). See the
		5253	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5254	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5255
		5256	The configuration for a "naked" win32 using the Microsoft runtime
		5257	libraries and raw winsocket select is:
		5258
		5259	#define EV_USE_SELECT 1
		5260	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5261
		5262	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5263	complexity in the O(n²) range when using win32.
		5264
		5265	=head3 Limited number of file descriptors
		5266
		5267	Windows has numerous arbitrary (and low) limits on things.
		5268
		5269	Early versions of winsocket's select only supported waiting for a maximum
		5270	of C<64> handles (probably owning to the fact that all windows kernels
		5271	can only wait for C<64> things at the same time internally; Microsoft
		5272	recommends spawning a chain of threads and wait for 63 handles and the
		5273	previous thread in each. Sounds great!).
		5274
		5275	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5276	to some high number (e.g. C<2048>) before compiling the winsocket select
		5277	call (which might be in libev or elsewhere, for example, perl and many
		5278	other interpreters do their own select emulation on windows).
		5279
		5280	Another limit is the number of file descriptors in the Microsoft runtime
		5281	libraries, which by default is C<64> (there must be a hidden I<64>
		5282	fetish or something like this inside Microsoft). You can increase this
		5283	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5284	(another arbitrary limit), but is broken in many versions of the Microsoft
		5285	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5286	(depending on windows version and/or the phase of the moon). To get more,
		5287	you need to wrap all I/O functions and provide your own fd management, but
		5288	the cost of calling select (O(n²)) will likely make this unworkable.
		5289
		5290	=head2 PORTABILITY REQUIREMENTS
		5291
		5292	In addition to a working ISO-C implementation and of course the
		5293	backend-specific APIs, libev relies on a few additional extensions:
		5294
		5295	=over 4
		5296
		5297	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5298	calling conventions regardless of C<ev_watcher_type *>.
		5299
		5300	Libev assumes not only that all watcher pointers have the same internal
		5301	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5302	assumes that the same (machine) code can be used to call any watcher
		5303	callback: The watcher callbacks have different type signatures, but libev
		5304	calls them using an C<ev_watcher *> internally.
		5305
		5306	=item null pointers and integer zero are represented by 0 bytes
		5307
		5308	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5309	relies on this setting pointers and integers to null.
		5310
		5311	=item pointer accesses must be thread-atomic
		5312
		5313	Accessing a pointer value must be atomic, it must both be readable and
		5314	writable in one piece - this is the case on all current architectures.
		5315
		5316	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5317
		5318	The type C<sig_atomic_t volatile> (or whatever is defined as
		5319	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5320	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5321	believed to be sufficiently portable.
		5322
		5323	=item C<sigprocmask> must work in a threaded environment
		5324
		5325	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5326	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5327	pthread implementations will either allow C<sigprocmask> in the "main
		5328	thread" or will block signals process-wide, both behaviours would
		5329	be compatible with libev. Interaction between C<sigprocmask> and
		5330	C<pthread_sigmask> could complicate things, however.
		5331
		5332	The most portable way to handle signals is to block signals in all threads
		5333	except the initial one, and run the signal handling loop in the initial
		5334	thread as well.
		5335
		5336	=item C<long> must be large enough for common memory allocation sizes
		5337
		5338	To improve portability and simplify its API, libev uses C<long> internally
		5339	instead of C<size_t> when allocating its data structures. On non-POSIX
		5340	systems (Microsoft...) this might be unexpectedly low, but is still at
		5341	least 31 bits everywhere, which is enough for hundreds of millions of
		5342	watchers.
		5343
		5344	=item C<double> must hold a time value in seconds with enough accuracy
		5345
		5346	The type C<double> is used to represent timestamps. It is required to
		5347	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5348	good enough for at least into the year 4000 with millisecond accuracy
		5349	(the design goal for libev). This requirement is overfulfilled by
		5350	implementations using IEEE 754, which is basically all existing ones.
		5351
		5352	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5353	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5354	is either obsolete or somebody patched it to use C<long double> or
		5355	something like that, just kidding).
		5356
		5357	=back
		5358
		5359	If you know of other additional requirements drop me a note.
		5360
		5361
		5362	=head1 ALGORITHMIC COMPLEXITIES
		5363
		5364	In this section the complexities of (many of) the algorithms used inside
		5365	libev will be documented. For complexity discussions about backends see
		5366	the documentation for C<ev_default_init>.
		5367
		5368	All of the following are about amortised time: If an array needs to be
		5369	extended, libev needs to realloc and move the whole array, but this
		5370	happens asymptotically rarer with higher number of elements, so O(1) might
		5371	mean that libev does a lengthy realloc operation in rare cases, but on
		5372	average it is much faster and asymptotically approaches constant time.
		5373
		5374	=over 4
		5375
		5376	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5377
		5378	This means that, when you have a watcher that triggers in one hour and
		5379	there are 100 watchers that would trigger before that, then inserting will
		5380	have to skip roughly seven (C<ld 100>) of these watchers.
		5381
		5382	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5383
		5384	That means that changing a timer costs less than removing/adding them,
		5385	as only the relative motion in the event queue has to be paid for.
		5386
		5387	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5388
		5389	These just add the watcher into an array or at the head of a list.
		5390
		5391	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5392
		5393	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5394
		5395	These watchers are stored in lists, so they need to be walked to find the
		5396	correct watcher to remove. The lists are usually short (you don't usually
		5397	have many watchers waiting for the same fd or signal: one is typical, two
		5398	is rare).
		5399
		5400	=item Finding the next timer in each loop iteration: O(1)
		5401
		5402	By virtue of using a binary or 4-heap, the next timer is always found at a
		5403	fixed position in the storage array.
		5404
		5405	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5406
		5407	A change means an I/O watcher gets started or stopped, which requires
		5408	libev to recalculate its status (and possibly tell the kernel, depending
		5409	on backend and whether C<ev_io_set> was used).
		5410
		5411	=item Activating one watcher (putting it into the pending state): O(1)
		5412
		5413	=item Priority handling: O(number_of_priorities)
		5414
		5415	Priorities are implemented by allocating some space for each
		5416	priority. When doing priority-based operations, libev usually has to
		5417	linearly search all the priorities, but starting/stopping and activating
		5418	watchers becomes O(1) with respect to priority handling.
		5419
		5420	=item Sending an ev_async: O(1)
		5421
		5422	=item Processing ev_async_send: O(number_of_async_watchers)
		5423
		5424	=item Processing signals: O(max_signal_number)
		5425
		5426	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5427	calls in the current loop iteration and the loop is currently
		5428	blocked. Checking for async and signal events involves iterating over all
		5429	running async watchers or all signal numbers.
		5430
		5431	=back
		5432
		5433
		5434	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5435
		5436	The major version 4 introduced some incompatible changes to the API.
		5437
		5438	At the moment, the C<ev.h> header file provides compatibility definitions
		5439	for all changes, so most programs should still compile. The compatibility
		5440	layer might be removed in later versions of libev, so better update to the
		5441	new API early than late.
		5442
		5443	=over 4
		5444
		5445	=item C<EV_COMPAT3> backwards compatibility mechanism
		5446
		5447	The backward compatibility mechanism can be controlled by
		5448	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5449	section.
		5450
		5451	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5452
		5453	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5454
		5455	ev_loop_destroy (EV_DEFAULT_UC);
		5456	ev_loop_fork (EV_DEFAULT);
		5457
		5458	=item function/symbol renames
		5459
		5460	A number of functions and symbols have been renamed:
		5461
		5462	ev_loop => ev_run
		5463	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5464	EVLOOP_ONESHOT => EVRUN_ONCE
		5465
		5466	ev_unloop => ev_break
		5467	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5468	EVUNLOOP_ONE => EVBREAK_ONE
		5469	EVUNLOOP_ALL => EVBREAK_ALL
		5470
		5471	EV_TIMEOUT => EV_TIMER
		5472
		5473	ev_loop_count => ev_iteration
		5474	ev_loop_depth => ev_depth
		5475	ev_loop_verify => ev_verify
		5476
		5477	Most functions working on C<struct ev_loop> objects don't have an
		5478	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5479	associated constants have been renamed to not collide with the C<struct
		5480	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5481	as all other watcher types. Note that C<ev_loop_fork> is still called
		5482	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5483	typedef.
		5484
		5485	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5486
		5487	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5488	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5489	and work, but the library code will of course be larger.
		5490
		5491	=back
		5492
		5493
		5494	=head1 GLOSSARY
		5495
		5496	=over 4
		5497
		5498	=item active
		5499
		5500	A watcher is active as long as it has been started and not yet stopped.
		5501	See L</WATCHER STATES> for details.
		5502
		5503	=item application
		5504
		5505	In this document, an application is whatever is using libev.
		5506
		5507	=item backend
		5508
		5509	The part of the code dealing with the operating system interfaces.
		5510
		5511	=item callback
		5512
		5513	The address of a function that is called when some event has been
		5514	detected. Callbacks are being passed the event loop, the watcher that
		5515	received the event, and the actual event bitset.
		5516
		5517	=item callback/watcher invocation
		5518
		5519	The act of calling the callback associated with a watcher.
		5520
		5521	=item event
		5522
		5523	A change of state of some external event, such as data now being available
		5524	for reading on a file descriptor, time having passed or simply not having
		5525	any other events happening anymore.
		5526
		5527	In libev, events are represented as single bits (such as C<EV_READ> or
		5528	C<EV_TIMER>).
		5529
		5530	=item event library
		5531
		5532	A software package implementing an event model and loop.
		5533
		5534	=item event loop
		5535
		5536	An entity that handles and processes external events and converts them
		5537	into callback invocations.
		5538
		5539	=item event model
		5540
		5541	The model used to describe how an event loop handles and processes
		5542	watchers and events.
		5543
		5544	=item pending
		5545
		5546	A watcher is pending as soon as the corresponding event has been
		5547	detected. See L</WATCHER STATES> for details.
		5548
		5549	=item real time
		5550
		5551	The physical time that is observed. It is apparently strictly monotonic :)
		5552
		5553	=item wall-clock time
		5554
		5555	The time and date as shown on clocks. Unlike real time, it can actually
		5556	be wrong and jump forwards and backwards, e.g. when you adjust your
		5557	clock.
		5558
		5559	=item watcher
		5560
		5561	A data structure that describes interest in certain events. Watchers need
		5562	to be started (attached to an event loop) before they can receive events.
		5563
		5564	=back
825		5565
826	=head1 AUTHOR	5566	=head1 AUTHOR
827		5567
828	Marc Lehmann <libev@schmorp.de>.	5568	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5569	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
829		5570

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