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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 AND OTHER GLOBAL FUNCTIONS	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
		168
		169	=head1 GLOBAL FUNCTIONS
		170
		171	These functions can be called anytime, even before initialising the
		172	library in any way.
51		173
52	=over 4	174	=over 4
53		175
54	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
55		177
56	Returns the current time as libev would use it.	178	Returns the current time as libev would use it. Please note that the
		179	C<ev_now> function is usually faster and also often returns the timestamp
		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 >>).
57		194
58	=item int ev_version_major ()	195	=item int ev_version_major ()
59		196
60	=item int ev_version_minor ()	197	=item int ev_version_minor ()
61		198
62	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
63	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
64	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
65	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
66	version of the library your program was compiled against.	203	version of the library your program was compiled against.
67		204
		205	These version numbers refer to the ABI version of the library, not the
		206	release version.
		207
68	Usually, its a good idea to terminate if the major versions mismatch,	208	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
70	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
71	not a problem.	211	not a problem.
72		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
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
74		255
75	Sets the allocation function to use (the prototype is similar to the	256	Sets the allocation function to use (the prototype is similar - the
76	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
77	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
78	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
79	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.
80		265
81	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
82	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,
83	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.
84		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
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
86		291
87	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
88	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
89	indicating the system call or subsystem causing the problem. If this	294	indicating the system call or subsystem causing the problem. If this
90	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
91	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
92	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
93	(such as abort).	298	(such as abort).
94		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
95	=back	325	=back
96		326
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
98		328
99	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
100	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
101	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
102		332
103	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
104	in your main thread (or in a separate thrad) and for each thread you	334	supports child process events, and dynamically created event loops which
105	create, you also create another event loop. Libev itself does no locking	335	do not.
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because its hideous and inefficient).
109		336
110	=over 4	337	=over 4
111		338
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		340
114	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
115	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
116	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
117	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".
118		351
119	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
120	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.
121		384
122	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
123	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>).
124		387
125	It supports the following flags:	388	The following flags are supported:
126		389
127	=over 4	390	=over 4
128		391
129	=item EVFLAG_AUTO	392	=item C<EVFLAG_AUTO>
130		393
131	The default flags value. Use this if you have no clue (its the right	394	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	395	thing, believe me).
133		396
134	=item EVFLAG_NOENV	397	=item C<EVFLAG_NOENV>
135		398
136	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
137	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
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	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
140	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
141	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).
142		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 sequence
		417	without a system call and thus I<very> fast, but my GNU/Linux system also has
		418	C<pthread_atfork> which is even faster).
		419
		420	The big advantage of this flag is that you can forget about fork (and
		421	forget about forgetting to tell libev about forking, although you still
		422	have to ignore C<SIGPIPE>) when you use this flag.
		423
		424	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		425	environment variable.
		426
		427	=item C<EVFLAG_NOINOTIFY>
		428
		429	When this flag is specified, then libev will not attempt to use the
		430	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		431	testing, this flag can be useful to conserve inotify file descriptors, as
		432	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		433
		434	=item C<EVFLAG_SIGNALFD>
		435
		436	When this flag is specified, then libev will attempt to use the
		437	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		438	delivers signals synchronously, which makes it both faster and might make
		439	it possible to get the queued signal data. It can also simplify signal
		440	handling with threads, as long as you properly block signals in your
		441	threads that are not interested in handling them.
		442
		443	Signalfd will not be used by default as this changes your signal mask, and
		444	there are a lot of shoddy libraries and programs (glib's threadpool for
		445	example) that can't properly initialise their signal masks.
		446
		447	=item C<EVFLAG_NOSIGMASK>
		448
		449	When this flag is specified, then libev will avoid to modify the signal
		450	mask. Specifically, this means you have to make sure signals are unblocked
		451	when you want to receive them.
		452
		453	This behaviour is useful when you want to do your own signal handling, or
		454	want to handle signals only in specific threads and want to avoid libev
		455	unblocking the signals.
		456
		457	It's also required by POSIX in a threaded program, as libev calls
		458	C<sigprocmask>, whose behaviour is officially unspecified.
		459
		460	This flag's behaviour will become the default in future versions of libev.
		461
143	=item EVMETHOD_SELECT portable select backend	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		463
145	=item EVMETHOD_POLL poll backend (everywhere except windows)	464	This is your standard select(2) backend. Not I<completely> standard, as
		465	libev tries to roll its own fd_set with no limits on the number of fds,
		466	but if that fails, expect a fairly low limit on the number of fds when
		467	using this backend. It doesn't scale too well (O(highest_fd)), but its
		468	usually the fastest backend for a low number of (low-numbered :) fds.
146		469
147	=item EVMETHOD_EPOLL linux only	470	To get good performance out of this backend you need a high amount of
		471	parallelism (most of the file descriptors should be busy). If you are
		472	writing a server, you should C<accept ()> in a loop to accept as many
		473	connections as possible during one iteration. You might also want to have
		474	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		475	readiness notifications you get per iteration.
148		476
149	=item EVMETHOD_KQUEUE some bsds only	477	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		478	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		479	C<exceptfds> set on that platform).
150		480
151	=item EVMETHOD_DEVPOLL solaris 8 only	481	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
152		482
153	=item EVMETHOD_PORT solaris 10 only	483	And this is your standard poll(2) backend. It's more complicated
		484	than select, but handles sparse fds better and has no artificial
		485	limit on the number of fds you can use (except it will slow down
		486	considerably with a lot of inactive fds). It scales similarly to select,
		487	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		488	performance tips.
154		489
155	If one or more of these are ored into the flags value, then only these	490	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
156	backends will be tried (in the reverse order as given here). If one are	491	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
157	specified, any backend will do.	492
		493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		494
		495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		496	kernels).
		497
		498	For few fds, this backend is a bit little slower than poll and select, but
		499	it scales phenomenally better. While poll and select usually scale like
		500	O(total_fds) where total_fds is the total number of fds (or the highest
		501	fd), epoll scales either O(1) or O(active_fds).
		502
		503	The epoll mechanism deserves honorable mention as the most misdesigned
		504	of the more advanced event mechanisms: mere annoyances include silently
		505	dropping file descriptors, requiring a system call per change per file
		506	descriptor (and unnecessary guessing of parameters), problems with dup,
		507	returning before the timeout value, resulting in additional iterations
		508	(and only giving 5ms accuracy while select on the same platform gives
		509	0.1ms) and so on. The biggest issue is fork races, however - if a program
		510	forks then I<both> parent and child process have to recreate the epoll
		511	set, which can take considerable time (one syscall per file descriptor)
		512	and is of course hard to detect.
		513
		514	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		515	but of course I<doesn't>, and epoll just loves to report events for
		516	totally I<different> file descriptors (even already closed ones, so
		517	one cannot even remove them from the set) than registered in the set
		518	(especially on SMP systems). Libev tries to counter these spurious
		519	notifications by employing an additional generation counter and comparing
		520	that against the events to filter out spurious ones, recreating the set
		521	when required. Epoll also erroneously rounds down timeouts, but gives you
		522	no way to know when and by how much, so sometimes you have to busy-wait
		523	because epoll returns immediately despite a nonzero timeout. And last
		524	not least, it also refuses to work with some file descriptors which work
		525	perfectly fine with C<select> (files, many character devices...).
		526
		527	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		528	cobbled together in a hurry, no thought to design or interaction with
		529	others. Oh, the pain, will it ever stop...
		530
		531	While stopping, setting and starting an I/O watcher in the same iteration
		532	will result in some caching, there is still a system call per such
		533	incident (because the same I<file descriptor> could point to a different
		534	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		535	file descriptors might not work very well if you register events for both
		536	file descriptors.
		537
		538	Best performance from this backend is achieved by not unregistering all
		539	watchers for a file descriptor until it has been closed, if possible,
		540	i.e. keep at least one watcher active per fd at all times. Stopping and
		541	starting a watcher (without re-setting it) also usually doesn't cause
		542	extra overhead. A fork can both result in spurious notifications as well
		543	as in libev having to destroy and recreate the epoll object, which can
		544	take considerable time and thus should be avoided.
		545
		546	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		547	faster than epoll for maybe up to a hundred file descriptors, depending on
		548	the usage. So sad.
		549
		550	While nominally embeddable in other event loops, this feature is broken in
		551	all kernel versions tested so far.
		552
		553	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		554	C<EVBACKEND_POLL>.
		555
		556	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		557
		558	Kqueue deserves special mention, as at the time of this writing, it
		559	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		560	with anything but sockets and pipes, except on Darwin, where of course
		561	it's completely useless). Unlike epoll, however, whose brokenness
		562	is by design, these kqueue bugs can (and eventually will) be fixed
		563	without API changes to existing programs. For this reason it's not being
		564	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		565	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		566	system like NetBSD.
		567
		568	You still can embed kqueue into a normal poll or select backend and use it
		569	only for sockets (after having made sure that sockets work with kqueue on
		570	the target platform). See C<ev_embed> watchers for more info.
		571
		572	It scales in the same way as the epoll backend, but the interface to the
		573	kernel is more efficient (which says nothing about its actual speed, of
		574	course). While stopping, setting and starting an I/O watcher does never
		575	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		576	two event changes per incident. Support for C<fork ()> is very bad (you
		577	might have to leak fd's on fork, but it's more sane than epoll) and it
		578	drops fds silently in similarly hard-to-detect cases.
		579
		580	This backend usually performs well under most conditions.
		581
		582	While nominally embeddable in other event loops, this doesn't work
		583	everywhere, so you might need to test for this. And since it is broken
		584	almost everywhere, you should only use it when you have a lot of sockets
		585	(for which it usually works), by embedding it into another event loop
		586	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		587	also broken on OS X)) and, did I mention it, using it only for sockets.
		588
		589	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		590	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		591	C<NOTE_EOF>.
		592
		593	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		594
		595	This is not implemented yet (and might never be, unless you send me an
		596	implementation). According to reports, C</dev/poll> only supports sockets
		597	and is not embeddable, which would limit the usefulness of this backend
		598	immensely.
		599
		600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		601
		602	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		603	it's really slow, but it still scales very well (O(active_fds)).
		604
		605	While this backend scales well, it requires one system call per active
		606	file descriptor per loop iteration. For small and medium numbers of file
		607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		608	might perform better.
		609
		610	On the positive side, this backend actually performed fully to
		611	specification in all tests and is fully embeddable, which is a rare feat
		612	among the OS-specific backends (I vastly prefer correctness over speed
		613	hacks).
		614
		615	On the negative side, the interface is I<bizarre> - so bizarre that
		616	even sun itself gets it wrong in their code examples: The event polling
		617	function sometimes returns events to the caller even though an error
		618	occurred, but with no indication whether it has done so or not (yes, it's
		619	even documented that way) - deadly for edge-triggered interfaces where you
		620	absolutely have to know whether an event occurred or not because you have
		621	to re-arm the watcher.
		622
		623	Fortunately libev seems to be able to work around these idiocies.
		624
		625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		626	C<EVBACKEND_POLL>.
		627
		628	=item C<EVBACKEND_ALL>
		629
		630	Try all backends (even potentially broken ones that wouldn't be tried
		631	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		633
		634	It is definitely not recommended to use this flag, use whatever
		635	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		636	at all.
		637
		638	=item C<EVBACKEND_MASK>
		639
		640	Not a backend at all, but a mask to select all backend bits from a
		641	C<flags> value, in case you want to mask out any backends from a flags
		642	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
158		643
159	=back	644	=back
160		645
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	646	If one or more of the backend flags are or'ed into the flags value,
		647	then only these backends will be tried (in the reverse order as listed
		648	here). If none are specified, all backends in C<ev_recommended_backends
		649	()> will be tried.
162		650
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	651	Example: Try to create a event loop that uses epoll and nothing else.
164	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).
167		652
168	=item ev_default_destroy ()	653	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		654	if (!epoller)
		655	fatal ("no epoll found here, maybe it hides under your chair");
169		656
170	Destroys the default loop again (frees all memory and kernel state	657	Example: Use whatever libev has to offer, but make sure that kqueue is
171	etc.). This stops all registered event watchers (by not touching them in	658	used if available.
172	any way whatsoever, although you cnanot rely on this :).	659
		660	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
173		661
174	=item ev_loop_destroy (loop)	662	=item ev_loop_destroy (loop)
175		663
176	Like C<ev_default_destroy>, but destroys an event loop created by an	664	Destroys an event loop object (frees all memory and kernel state
177	earlier call to C<ev_loop_new>.	665	etc.). None of the active event watchers will be stopped in the normal
		666	sense, so e.g. C<ev_is_active> might still return true. It is your
		667	responsibility to either stop all watchers cleanly yourself I<before>
		668	calling this function, or cope with the fact afterwards (which is usually
		669	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		670	for example).
178		671
179	=item ev_default_fork ()	672	Note that certain global state, such as signal state (and installed signal
		673	handlers), will not be freed by this function, and related watchers (such
		674	as signal and child watchers) would need to be stopped manually.
180		675
181	This function reinitialises the kernel state for backends that have	676	This function is normally used on loop objects allocated by
182	one. Despite the name, you can call it anytime, but it makes most sense	677	C<ev_loop_new>, but it can also be used on the default loop returned by
183	after forking, in either the parent or child process (or both, but that	678	C<ev_default_loop>, in which case it is not thread-safe.
184	again makes little sense).
185		679
186	You I<must> call this function after forking if and only if you want to	680	Note that it is not advisable to call this function on the default loop
187	use the event library in both processes. If you just fork+exec, you don't	681	except in the rare occasion where you really need to free its resources.
188	have to call it.	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
189		683	and C<ev_loop_destroy>.
190	The function itself is quite fast and its usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in
192	quite nicely into a call to C<pthread_atfork>:
193
194	pthread_atfork (0, 0, ev_default_fork);
195		684
196	=item ev_loop_fork (loop)	685	=item ev_loop_fork (loop)
197		686
198	Like C<ev_default_fork>, but acts on an event loop created by	687	This function sets a flag that causes subsequent C<ev_run> iterations
199	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	688	to reinitialise the kernel state for backends that have one. Despite
200	after fork, and how you do this is entirely your own problem.	689	the name, you can call it anytime you are allowed to start or stop
		690	watchers (except inside an C<ev_prepare> callback), but it makes most
		691	sense after forking, in the child process. You I<must> call it (or use
		692	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
201		693
		694	In addition, if you want to reuse a loop (via this function of
		695	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		696
		697	Again, you I<have> to call it on I<any> loop that you want to re-use after
		698	a fork, I<even if you do not plan to use the loop in the parent>. This is
		699	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		700	during fork.
		701
		702	On the other hand, you only need to call this function in the child
		703	process if and only if you want to use the event loop in the child. If
		704	you just fork+exec or create a new loop in the child, you don't have to
		705	call it at all (in fact, C<epoll> is so badly broken that it makes a
		706	difference, but libev will usually detect this case on its own and do a
		707	costly reset of the backend).
		708
		709	The function itself is quite fast and it's usually not a problem to call
		710	it just in case after a fork.
		711
		712	Example: Automate calling C<ev_loop_fork> on the default loop when
		713	using pthreads.
		714
		715	static void
		716	post_fork_child (void)
		717	{
		718	ev_loop_fork (EV_DEFAULT);
		719	}
		720
		721	...
		722	pthread_atfork (0, 0, post_fork_child);
		723
		724	=item int ev_is_default_loop (loop)
		725
		726	Returns true when the given loop is, in fact, the default loop, and false
		727	otherwise.
		728
		729	=item unsigned int ev_iteration (loop)
		730
		731	Returns the current iteration count for the event loop, which is identical
		732	to the number of times libev did poll for new events. It starts at C<0>
		733	and happily wraps around with enough iterations.
		734
		735	This value can sometimes be useful as a generation counter of sorts (it
		736	"ticks" the number of loop iterations), as it roughly corresponds with
		737	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		738	prepare and check phases.
		739
202	=item unsigned int ev_method (loop)	740	=item unsigned int ev_depth (loop)
203		741
		742	Returns the number of times C<ev_run> was entered minus the number of
		743	times C<ev_run> was exited normally, in other words, the recursion depth.
		744
		745	Outside C<ev_run>, this number is zero. In a callback, this number is
		746	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		747	in which case it is higher.
		748
		749	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		750	throwing an exception etc.), doesn't count as "exit" - consider this
		751	as a hint to avoid such ungentleman-like behaviour unless it's really
		752	convenient, in which case it is fully supported.
		753
		754	=item unsigned int ev_backend (loop)
		755
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	756	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	757	use.
206		758
207	=item ev_tstamp = ev_now (loop)	759	=item ev_tstamp ev_now (loop)
208		760
209	Returns the current "event loop time", which is the time the event loop	761	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	762	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	763	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	764	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	765	event occurring (or more correctly, libev finding out about it).
214		766
		767	=item ev_now_update (loop)
		768
		769	Establishes the current time by querying the kernel, updating the time
		770	returned by C<ev_now ()> in the progress. This is a costly operation and
		771	is usually done automatically within C<ev_run ()>.
		772
		773	This function is rarely useful, but when some event callback runs for a
		774	very long time without entering the event loop, updating libev's idea of
		775	the current time is a good idea.
		776
		777	See also L</The special problem of time updates> in the C<ev_timer> section.
		778
		779	=item ev_suspend (loop)
		780
		781	=item ev_resume (loop)
		782
		783	These two functions suspend and resume an event loop, for use when the
		784	loop is not used for a while and timeouts should not be processed.
		785
		786	A typical use case would be an interactive program such as a game: When
		787	the user presses C<^Z> to suspend the game and resumes it an hour later it
		788	would be best to handle timeouts as if no time had actually passed while
		789	the program was suspended. This can be achieved by calling C<ev_suspend>
		790	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		791	C<ev_resume> directly afterwards to resume timer processing.
		792
		793	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		794	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		795	will be rescheduled (that is, they will lose any events that would have
		796	occurred while suspended).
		797
		798	After calling C<ev_suspend> you B<must not> call I<any> function on the
		799	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		800	without a previous call to C<ev_suspend>.
		801
		802	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		803	event loop time (see C<ev_now_update>).
		804
215	=item ev_loop (loop, int flags)	805	=item bool ev_run (loop, int flags)
216		806
217	Finally, this is it, the event handler. This function usually is called	807	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	808	after you have initialised all your watchers and you want to start
219	events.	809	handling events. It will ask the operating system for any new events, call
		810	the watcher callbacks, and then repeat the whole process indefinitely: This
		811	is why event loops are called I<loops>.
220		812
221	If the flags argument is specified as 0, it will not return until either	813	If the flags argument is specified as C<0>, it will keep handling events
222	no event watchers are active anymore or C<ev_unloop> was called.	814	until either no event watchers are active anymore or C<ev_break> was
		815	called.
223		816
		817	The return value is false if there are no more active watchers (which
		818	usually means "all jobs done" or "deadlock"), and true in all other cases
		819	(which usually means " you should call C<ev_run> again").
		820
		821	Please note that an explicit C<ev_break> is usually better than
		822	relying on all watchers to be stopped when deciding when a program has
		823	finished (especially in interactive programs), but having a program
		824	that automatically loops as long as it has to and no longer by virtue
		825	of relying on its watchers stopping correctly, that is truly a thing of
		826	beauty.
		827
		828	This function is I<mostly> exception-safe - you can break out of a
		829	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		830	exception and so on. This does not decrement the C<ev_depth> value, nor
		831	will it clear any outstanding C<EVBREAK_ONE> breaks.
		832
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	833	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
225	those events and any outstanding ones, but will not block your process in	834	those events and any already outstanding ones, but will not wait and
226	case there are no events.	835	block your process in case there are no events and will return after one
		836	iteration of the loop. This is sometimes useful to poll and handle new
		837	events while doing lengthy calculations, to keep the program responsive.
227		838
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	839	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
229	neccessary) and will handle those and any outstanding ones. It will block	840	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives.	841	will block your process until at least one new event arrives (which could
		842	be an event internal to libev itself, so there is no guarantee that a
		843	user-registered callback will be called), and will return after one
		844	iteration of the loop.
231		845
232	This flags value could be used to implement alternative looping	846	This is useful if you are waiting for some external event in conjunction
233	constructs, but the C<prepare> and C<check> watchers provide a better and	847	with something not expressible using other libev watchers (i.e. "roll your
234	more generic mechanism.	848	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		849	usually a better approach for this kind of thing.
235		850
		851	Here are the gory details of what C<ev_run> does (this is for your
		852	understanding, not a guarantee that things will work exactly like this in
		853	future versions):
		854
		855	- Increment loop depth.
		856	- Reset the ev_break status.
		857	- Before the first iteration, call any pending watchers.
		858	LOOP:
		859	- If EVFLAG_FORKCHECK was used, check for a fork.
		860	- If a fork was detected (by any means), queue and call all fork watchers.
		861	- Queue and call all prepare watchers.
		862	- If ev_break was called, goto FINISH.
		863	- If we have been forked, detach and recreate the kernel state
		864	as to not disturb the other process.
		865	- Update the kernel state with all outstanding changes.
		866	- Update the "event loop time" (ev_now ()).
		867	- Calculate for how long to sleep or block, if at all
		868	(active idle watchers, EVRUN_NOWAIT or not having
		869	any active watchers at all will result in not sleeping).
		870	- Sleep if the I/O and timer collect interval say so.
		871	- Increment loop iteration counter.
		872	- Block the process, waiting for any events.
		873	- Queue all outstanding I/O (fd) events.
		874	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		875	- Queue all expired timers.
		876	- Queue all expired periodics.
		877	- Queue all idle watchers with priority higher than that of pending events.
		878	- Queue all check watchers.
		879	- Call all queued watchers in reverse order (i.e. check watchers first).
		880	Signals and child watchers are implemented as I/O watchers, and will
		881	be handled here by queueing them when their watcher gets executed.
		882	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		883	were used, or there are no active watchers, goto FINISH, otherwise
		884	continue with step LOOP.
		885	FINISH:
		886	- Reset the ev_break status iff it was EVBREAK_ONE.
		887	- Decrement the loop depth.
		888	- Return.
		889
		890	Example: Queue some jobs and then loop until no events are outstanding
		891	anymore.
		892
		893	... queue jobs here, make sure they register event watchers as long
		894	... as they still have work to do (even an idle watcher will do..)
		895	ev_run (my_loop, 0);
		896	... jobs done or somebody called break. yeah!
		897
236	=item ev_unloop (loop, how)	898	=item ev_break (loop, how)
237		899
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	900	Can be used to make a call to C<ev_run> return early (but only after it
239	must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>	901	has processed all outstanding events). The C<how> argument must be either
240	call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>	902	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
241	calls return.	903	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		904
		905	This "break state" will be cleared on the next call to C<ev_run>.
		906
		907	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		908	which case it will have no effect.
242		909
243	=item ev_ref (loop)	910	=item ev_ref (loop)
244		911
245	=item ev_unref (loop)	912	=item ev_unref (loop)
246		913
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	914	Ref/unref can be used to add or remove a reference count on the event
248	watcher keeps one reference. If you have a long-runing watcher you never	915	loop: Every watcher keeps one reference, and as long as the reference
249	unregister that should not keep ev_loop from running, ev_unref() after	916	count is nonzero, C<ev_run> will not return on its own.
250	starting, and ev_ref() before stopping it. Libev itself uses this for	917
251	example for its internal signal pipe: It is not visible to you as a user	918	This is useful when you have a watcher that you never intend to
252	and should not keep C<ev_loop> from exiting if the work is done. It is	919	unregister, but that nevertheless should not keep C<ev_run> from
		920	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		921	before stopping it.
		922
		923	As an example, libev itself uses this for its internal signal pipe: It
		924	is not visible to the libev user and should not keep C<ev_run> from
		925	exiting if no event watchers registered by it are active. It is also an
253	also an excellent way to do this for generic recurring timers or from	926	excellent way to do this for generic recurring timers or from within
254	within third-party libraries. Just remember to unref after start and ref	927	third-party libraries. Just remember to I<unref after start> and I<ref
255	before stop.	928	before stop> (but only if the watcher wasn't active before, or was active
		929	before, respectively. Note also that libev might stop watchers itself
		930	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		931	in the callback).
		932
		933	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		934	running when nothing else is active.
		935
		936	ev_signal exitsig;
		937	ev_signal_init (&exitsig, sig_cb, SIGINT);
		938	ev_signal_start (loop, &exitsig);
		939	ev_unref (loop);
		940
		941	Example: For some weird reason, unregister the above signal handler again.
		942
		943	ev_ref (loop);
		944	ev_signal_stop (loop, &exitsig);
		945
		946	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		947
		948	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		949
		950	These advanced functions influence the time that libev will spend waiting
		951	for events. Both time intervals are by default C<0>, meaning that libev
		952	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		953	latency.
		954
		955	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		956	allows libev to delay invocation of I/O and timer/periodic callbacks
		957	to increase efficiency of loop iterations (or to increase power-saving
		958	opportunities).
		959
		960	The idea is that sometimes your program runs just fast enough to handle
		961	one (or very few) event(s) per loop iteration. While this makes the
		962	program responsive, it also wastes a lot of CPU time to poll for new
		963	events, especially with backends like C<select ()> which have a high
		964	overhead for the actual polling but can deliver many events at once.
		965
		966	By setting a higher I<io collect interval> you allow libev to spend more
		967	time collecting I/O events, so you can handle more events per iteration,
		968	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		969	C<ev_timer>) will not be affected. Setting this to a non-null value will
		970	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		971	sleep time ensures that libev will not poll for I/O events more often then
		972	once per this interval, on average (as long as the host time resolution is
		973	good enough).
		974
		975	Likewise, by setting a higher I<timeout collect interval> you allow libev
		976	to spend more time collecting timeouts, at the expense of increased
		977	latency/jitter/inexactness (the watcher callback will be called
		978	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		979	value will not introduce any overhead in libev.
		980
		981	Many (busy) programs can usually benefit by setting the I/O collect
		982	interval to a value near C<0.1> or so, which is often enough for
		983	interactive servers (of course not for games), likewise for timeouts. It
		984	usually doesn't make much sense to set it to a lower value than C<0.01>,
		985	as this approaches the timing granularity of most systems. Note that if
		986	you do transactions with the outside world and you can't increase the
		987	parallelity, then this setting will limit your transaction rate (if you
		988	need to poll once per transaction and the I/O collect interval is 0.01,
		989	then you can't do more than 100 transactions per second).
		990
		991	Setting the I<timeout collect interval> can improve the opportunity for
		992	saving power, as the program will "bundle" timer callback invocations that
		993	are "near" in time together, by delaying some, thus reducing the number of
		994	times the process sleeps and wakes up again. Another useful technique to
		995	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		996	they fire on, say, one-second boundaries only.
		997
		998	Example: we only need 0.1s timeout granularity, and we wish not to poll
		999	more often than 100 times per second:
		1000
		1001	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1002	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1003
		1004	=item ev_invoke_pending (loop)
		1005
		1006	This call will simply invoke all pending watchers while resetting their
		1007	pending state. Normally, C<ev_run> does this automatically when required,
		1008	but when overriding the invoke callback this call comes handy. This
		1009	function can be invoked from a watcher - this can be useful for example
		1010	when you want to do some lengthy calculation and want to pass further
		1011	event handling to another thread (you still have to make sure only one
		1012	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1013
		1014	=item int ev_pending_count (loop)
		1015
		1016	Returns the number of pending watchers - zero indicates that no watchers
		1017	are pending.
		1018
		1019	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1020
		1021	This overrides the invoke pending functionality of the loop: Instead of
		1022	invoking all pending watchers when there are any, C<ev_run> will call
		1023	this callback instead. This is useful, for example, when you want to
		1024	invoke the actual watchers inside another context (another thread etc.).
		1025
		1026	If you want to reset the callback, use C<ev_invoke_pending> as new
		1027	callback.
		1028
		1029	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1030
		1031	Sometimes you want to share the same loop between multiple threads. This
		1032	can be done relatively simply by putting mutex_lock/unlock calls around
		1033	each call to a libev function.
		1034
		1035	However, C<ev_run> can run an indefinite time, so it is not feasible
		1036	to wait for it to return. One way around this is to wake up the event
		1037	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1038	I<release> and I<acquire> callbacks on the loop.
		1039
		1040	When set, then C<release> will be called just before the thread is
		1041	suspended waiting for new events, and C<acquire> is called just
		1042	afterwards.
		1043
		1044	Ideally, C<release> will just call your mutex_unlock function, and
		1045	C<acquire> will just call the mutex_lock function again.
		1046
		1047	While event loop modifications are allowed between invocations of
		1048	C<release> and C<acquire> (that's their only purpose after all), no
		1049	modifications done will affect the event loop, i.e. adding watchers will
		1050	have no effect on the set of file descriptors being watched, or the time
		1051	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1052	to take note of any changes you made.
		1053
		1054	In theory, threads executing C<ev_run> will be async-cancel safe between
		1055	invocations of C<release> and C<acquire>.
		1056
		1057	See also the locking example in the C<THREADS> section later in this
		1058	document.
		1059
		1060	=item ev_set_userdata (loop, void *data)
		1061
		1062	=item void *ev_userdata (loop)
		1063
		1064	Set and retrieve a single C<void *> associated with a loop. When
		1065	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1066	C<0>.
		1067
		1068	These two functions can be used to associate arbitrary data with a loop,
		1069	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1070	C<acquire> callbacks described above, but of course can be (ab-)used for
		1071	any other purpose as well.
		1072
		1073	=item ev_verify (loop)
		1074
		1075	This function only does something when C<EV_VERIFY> support has been
		1076	compiled in, which is the default for non-minimal builds. It tries to go
		1077	through all internal structures and checks them for validity. If anything
		1078	is found to be inconsistent, it will print an error message to standard
		1079	error and call C<abort ()>.
		1080
		1081	This can be used to catch bugs inside libev itself: under normal
		1082	circumstances, this function will never abort as of course libev keeps its
		1083	data structures consistent.
256		1084
257	=back	1085	=back
258		1086
		1087
259	=head1 ANATOMY OF A WATCHER	1088	=head1 ANATOMY OF A WATCHER
260		1089
		1090	In the following description, uppercase C<TYPE> in names stands for the
		1091	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1092	watchers and C<ev_io_start> for I/O watchers.
		1093
261	A watcher is a structure that you create and register to record your	1094	A watcher is an opaque structure that you allocate and register to record
262	interest in some event. For instance, if you want to wait for STDIN to	1095	your interest in some event. To make a concrete example, imagine you want
263	become readable, you would create an ev_io watcher for that:	1096	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1097	for that:
264		1098
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1099	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
266	{	1100	{
267	ev_io_stop (w);	1101	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	1102	ev_break (loop, EVBREAK_ALL);
269	}	1103	}
270		1104
271	struct ev_loop *loop = ev_default_loop (0);	1105	struct ev_loop *loop = ev_default_loop (0);
		1106
272	struct ev_io stdin_watcher;	1107	ev_io stdin_watcher;
		1108
273	ev_init (&stdin_watcher, my_cb);	1109	ev_init (&stdin_watcher, my_cb);
274	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1110	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
275	ev_io_start (loop, &stdin_watcher);	1111	ev_io_start (loop, &stdin_watcher);
		1112
276	ev_loop (loop, 0);	1113	ev_run (loop, 0);
277		1114
278	As you can see, you are responsible for allocating the memory for your	1115	As you can see, you are responsible for allocating the memory for your
279	watcher structures (and it is usually a bad idea to do this on the stack,	1116	watcher structures (and it is I<usually> a bad idea to do this on the
280	although this can sometimes be quite valid).	1117	stack).
281		1118
		1119	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1120	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1121
282	Each watcher structure must be initialised by a call to C<ev_init	1122	Each watcher structure must be initialised by a call to C<ev_init (watcher
283	(watcher *, callback)>, which expects a callback to be provided. This	1123	*, callback)>, which expects a callback to be provided. This callback is
284	callback gets invoked each time the event occurs (or, in the case of io	1124	invoked each time the event occurs (or, in the case of I/O watchers, each
285	watchers, each time the event loop detects that the file descriptor given	1125	time the event loop detects that the file descriptor given is readable
286	is readable and/or writable).	1126	and/or writable).
287		1127
288	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1128	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
289	with arguments specific to this watcher type. There is also a macro	1129	macro to configure it, with arguments specific to the watcher type. There
290	to combine initialisation and setting in one call: C<< ev_<type>_init	1130	is also a macro to combine initialisation and setting in one call: C<<
291	(watcher *, callback, ...) >>.	1131	ev_TYPE_init (watcher *, callback, ...) >>.
292		1132
293	To make the watcher actually watch out for events, you have to start it	1133	To make the watcher actually watch out for events, you have to start it
294	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1134	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
295	*) >>), and you can stop watching for events at any time by calling the	1135	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1136	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
297		1137
298	As long as your watcher is active (has been started but not stopped) you	1138	As long as your watcher is active (has been started but not stopped) you
299	must not touch the values stored in it. Most specifically you must never	1139	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	1140	reinitialise it or call its C<ev_TYPE_set> macro.
301
302	You cna check whether an event is active by calling the C<ev_is_active
303	(watcher *)> macro. To see whether an event is outstanding (but the
304	callback for it has not been called yet) you cna use the C<ev_is_pending
305	(watcher *)> macro.
306		1141
307	Each and every callback receives the event loop pointer as first, the	1142	Each and every callback receives the event loop pointer as first, the
308	registered watcher structure as second, and a bitset of received events as	1143	registered watcher structure as second, and a bitset of received events as
309	third argument.	1144	third argument.
310		1145
311	The rceeived events usually include a single bit per event type received	1146	The received events usually include a single bit per event type received
312	(you can receive multiple events at the same time). The possible bit masks	1147	(you can receive multiple events at the same time). The possible bit masks
313	are:	1148	are:
314		1149
315	=over 4	1150	=over 4
316		1151
317	=item EV_READ	1152	=item C<EV_READ>
318		1153
319	=item EV_WRITE	1154	=item C<EV_WRITE>
320		1155
321	The file descriptor in the ev_io watcher has become readable and/or	1156	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	1157	writable.
323		1158
324	=item EV_TIMEOUT	1159	=item C<EV_TIMER>
325		1160
326	The ev_timer watcher has timed out.	1161	The C<ev_timer> watcher has timed out.
327		1162
328	=item EV_PERIODIC	1163	=item C<EV_PERIODIC>
329		1164
330	The ev_periodic watcher has timed out.	1165	The C<ev_periodic> watcher has timed out.
331		1166
332	=item EV_SIGNAL	1167	=item C<EV_SIGNAL>
333		1168
334	The signal specified in the ev_signal watcher has been received by a thread.	1169	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		1170
336	=item EV_CHILD	1171	=item C<EV_CHILD>
337		1172
338	The pid specified in the ev_child watcher has received a status change.	1173	The pid specified in the C<ev_child> watcher has received a status change.
339		1174
		1175	=item C<EV_STAT>
		1176
		1177	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1178
340	=item EV_IDLE	1179	=item C<EV_IDLE>
341		1180
342	The ev_idle watcher has determined that you have nothing better to do.	1181	The C<ev_idle> watcher has determined that you have nothing better to do.
343		1182
344	=item EV_PREPARE	1183	=item C<EV_PREPARE>
345		1184
346	=item EV_CHECK	1185	=item C<EV_CHECK>
347		1186
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	1187	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
349	to gather new events, and all ev_check watchers are invoked just after	1188	gather new events, and all C<ev_check> watchers are queued (not invoked)
350	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1189	just after C<ev_run> has gathered them, but before it queues any callbacks
		1190	for any received events. That means C<ev_prepare> watchers are the last
		1191	watchers invoked before the event loop sleeps or polls for new events, and
		1192	C<ev_check> watchers will be invoked before any other watchers of the same
		1193	or lower priority within an event loop iteration.
		1194
351	received events. Callbacks of both watcher types can start and stop as	1195	Callbacks of both watcher types can start and stop as many watchers as
352	many watchers as they want, and all of them will be taken into account	1196	they want, and all of them will be taken into account (for example, a
353	(for example, a ev_prepare watcher might start an idle watcher to keep	1197	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
354	C<ev_loop> from blocking).	1198	blocking).
355		1199
		1200	=item C<EV_EMBED>
		1201
		1202	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1203
		1204	=item C<EV_FORK>
		1205
		1206	The event loop has been resumed in the child process after fork (see
		1207	C<ev_fork>).
		1208
		1209	=item C<EV_CLEANUP>
		1210
		1211	The event loop is about to be destroyed (see C<ev_cleanup>).
		1212
		1213	=item C<EV_ASYNC>
		1214
		1215	The given async watcher has been asynchronously notified (see C<ev_async>).
		1216
		1217	=item C<EV_CUSTOM>
		1218
		1219	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1220	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1221
356	=item EV_ERROR	1222	=item C<EV_ERROR>
357		1223
358	An unspecified error has occured, the watcher has been stopped. This might	1224	An unspecified error has occurred, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	1225	happen because the watcher could not be properly started because libev
360	ran out of memory, a file descriptor was found to be closed or any other	1226	ran out of memory, a file descriptor was found to be closed or any other
		1227	problem. Libev considers these application bugs.
		1228
361	problem. You best act on it by reporting the problem and somehow coping	1229	You best act on it by reporting the problem and somehow coping with the
362	with the watcher being stopped.	1230	watcher being stopped. Note that well-written programs should not receive
		1231	an error ever, so when your watcher receives it, this usually indicates a
		1232	bug in your program.
363		1233
364	Libev will usually signal a few "dummy" events together with an error,	1234	Libev will usually signal a few "dummy" events together with an error, for
365	for example it might indicate that a fd is readable or writable, and if	1235	example it might indicate that a fd is readable or writable, and if your
366	your callbacks is well-written it can just attempt the operation and cope	1236	callbacks is well-written it can just attempt the operation and cope with
367	with the error from read() or write(). This will not work in multithreaded	1237	the error from read() or write(). This will not work in multi-threaded
368	programs, though, so beware.	1238	programs, though, as the fd could already be closed and reused for another
		1239	thing, so beware.
369		1240
370	=back	1241	=back
371		1242
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1243	=head2 GENERIC WATCHER FUNCTIONS
373		1244
374	Each watcher has, by default, a member C<void *data> that you can change	1245	=over 4
375	and read at any time, libev will completely ignore it. This cna be used
376	to associate arbitrary data with your watcher. If you need more data and
377	don't want to allocate memory and store a pointer to it in that data
378	member, you can also "subclass" the watcher type and provide your own
379	data:
380		1246
381	struct my_io	1247	=item C<ev_init> (ev_TYPE *watcher, callback)
		1248
		1249	This macro initialises the generic portion of a watcher. The contents
		1250	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1251	the generic parts of the watcher are initialised, you I<need> to call
		1252	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1253	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1254	which rolls both calls into one.
		1255
		1256	You can reinitialise a watcher at any time as long as it has been stopped
		1257	(or never started) and there are no pending events outstanding.
		1258
		1259	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1260	int revents)>.
		1261
		1262	Example: Initialise an C<ev_io> watcher in two steps.
		1263
		1264	ev_io w;
		1265	ev_init (&w, my_cb);
		1266	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1267
		1268	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1269
		1270	This macro initialises the type-specific parts of a watcher. You need to
		1271	call C<ev_init> at least once before you call this macro, but you can
		1272	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1273	macro on a watcher that is active (it can be pending, however, which is a
		1274	difference to the C<ev_init> macro).
		1275
		1276	Although some watcher types do not have type-specific arguments
		1277	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1278
		1279	See C<ev_init>, above, for an example.
		1280
		1281	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1282
		1283	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1284	calls into a single call. This is the most convenient method to initialise
		1285	a watcher. The same limitations apply, of course.
		1286
		1287	Example: Initialise and set an C<ev_io> watcher in one step.
		1288
		1289	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1290
		1291	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1292
		1293	Starts (activates) the given watcher. Only active watchers will receive
		1294	events. If the watcher is already active nothing will happen.
		1295
		1296	Example: Start the C<ev_io> watcher that is being abused as example in this
		1297	whole section.
		1298
		1299	ev_io_start (EV_DEFAULT_UC, &w);
		1300
		1301	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1302
		1303	Stops the given watcher if active, and clears the pending status (whether
		1304	the watcher was active or not).
		1305
		1306	It is possible that stopped watchers are pending - for example,
		1307	non-repeating timers are being stopped when they become pending - but
		1308	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1309	pending. If you want to free or reuse the memory used by the watcher it is
		1310	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1311
		1312	=item bool ev_is_active (ev_TYPE *watcher)
		1313
		1314	Returns a true value iff the watcher is active (i.e. it has been started
		1315	and not yet been stopped). As long as a watcher is active you must not modify
		1316	it.
		1317
		1318	=item bool ev_is_pending (ev_TYPE *watcher)
		1319
		1320	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1321	events but its callback has not yet been invoked). As long as a watcher
		1322	is pending (but not active) you must not call an init function on it (but
		1323	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1324	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1325	it).
		1326
		1327	=item callback ev_cb (ev_TYPE *watcher)
		1328
		1329	Returns the callback currently set on the watcher.
		1330
		1331	=item ev_set_cb (ev_TYPE *watcher, callback)
		1332
		1333	Change the callback. You can change the callback at virtually any time
		1334	(modulo threads).
		1335
		1336	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1337
		1338	=item int ev_priority (ev_TYPE *watcher)
		1339
		1340	Set and query the priority of the watcher. The priority is a small
		1341	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1342	(default: C<-2>). Pending watchers with higher priority will be invoked
		1343	before watchers with lower priority, but priority will not keep watchers
		1344	from being executed (except for C<ev_idle> watchers).
		1345
		1346	If you need to suppress invocation when higher priority events are pending
		1347	you need to look at C<ev_idle> watchers, which provide this functionality.
		1348
		1349	You I<must not> change the priority of a watcher as long as it is active or
		1350	pending.
		1351
		1352	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1353	fine, as long as you do not mind that the priority value you query might
		1354	or might not have been clamped to the valid range.
		1355
		1356	The default priority used by watchers when no priority has been set is
		1357	always C<0>, which is supposed to not be too high and not be too low :).
		1358
		1359	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1360	priorities.
		1361
		1362	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1363
		1364	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1365	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1366	can deal with that fact, as both are simply passed through to the
		1367	callback.
		1368
		1369	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1370
		1371	If the watcher is pending, this function clears its pending status and
		1372	returns its C<revents> bitset (as if its callback was invoked). If the
		1373	watcher isn't pending it does nothing and returns C<0>.
		1374
		1375	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1376	callback to be invoked, which can be accomplished with this function.
		1377
		1378	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1379
		1380	Feeds the given event set into the event loop, as if the specified event
		1381	had happened for the specified watcher (which must be a pointer to an
		1382	initialised but not necessarily started event watcher). Obviously you must
		1383	not free the watcher as long as it has pending events.
		1384
		1385	Stopping the watcher, letting libev invoke it, or calling
		1386	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1387	not started in the first place.
		1388
		1389	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1390	functions that do not need a watcher.
		1391
		1392	=back
		1393
		1394	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1395	OWN COMPOSITE WATCHERS> idioms.
		1396
		1397	=head2 WATCHER STATES
		1398
		1399	There are various watcher states mentioned throughout this manual -
		1400	active, pending and so on. In this section these states and the rules to
		1401	transition between them will be described in more detail - and while these
		1402	rules might look complicated, they usually do "the right thing".
		1403
		1404	=over 4
		1405
		1406	=item initialised
		1407
		1408	Before a watcher can be registered with the event loop it has to be
		1409	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1410	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1411
		1412	In this state it is simply some block of memory that is suitable for
		1413	use in an event loop. It can be moved around, freed, reused etc. at
		1414	will - as long as you either keep the memory contents intact, or call
		1415	C<ev_TYPE_init> again.
		1416
		1417	=item started/running/active
		1418
		1419	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1420	property of the event loop, and is actively waiting for events. While in
		1421	this state it cannot be accessed (except in a few documented ways), moved,
		1422	freed or anything else - the only legal thing is to keep a pointer to it,
		1423	and call libev functions on it that are documented to work on active watchers.
		1424
		1425	=item pending
		1426
		1427	If a watcher is active and libev determines that an event it is interested
		1428	in has occurred (such as a timer expiring), it will become pending. It will
		1429	stay in this pending state until either it is stopped or its callback is
		1430	about to be invoked, so it is not normally pending inside the watcher
		1431	callback.
		1432
		1433	The watcher might or might not be active while it is pending (for example,
		1434	an expired non-repeating timer can be pending but no longer active). If it
		1435	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1436	but it is still property of the event loop at this time, so cannot be
		1437	moved, freed or reused. And if it is active the rules described in the
		1438	previous item still apply.
		1439
		1440	It is also possible to feed an event on a watcher that is not active (e.g.
		1441	via C<ev_feed_event>), in which case it becomes pending without being
		1442	active.
		1443
		1444	=item stopped
		1445
		1446	A watcher can be stopped implicitly by libev (in which case it might still
		1447	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1448	latter will clear any pending state the watcher might be in, regardless
		1449	of whether it was active or not, so stopping a watcher explicitly before
		1450	freeing it is often a good idea.
		1451
		1452	While stopped (and not pending) the watcher is essentially in the
		1453	initialised state, that is, it can be reused, moved, modified in any way
		1454	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1455	it again).
		1456
		1457	=back
		1458
		1459	=head2 WATCHER PRIORITY MODELS
		1460
		1461	Many event loops support I<watcher priorities>, which are usually small
		1462	integers that influence the ordering of event callback invocation
		1463	between watchers in some way, all else being equal.
		1464
		1465	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1466	description for the more technical details such as the actual priority
		1467	range.
		1468
		1469	There are two common ways how these these priorities are being interpreted
		1470	by event loops:
		1471
		1472	In the more common lock-out model, higher priorities "lock out" invocation
		1473	of lower priority watchers, which means as long as higher priority
		1474	watchers receive events, lower priority watchers are not being invoked.
		1475
		1476	The less common only-for-ordering model uses priorities solely to order
		1477	callback invocation within a single event loop iteration: Higher priority
		1478	watchers are invoked before lower priority ones, but they all get invoked
		1479	before polling for new events.
		1480
		1481	Libev uses the second (only-for-ordering) model for all its watchers
		1482	except for idle watchers (which use the lock-out model).
		1483
		1484	The rationale behind this is that implementing the lock-out model for
		1485	watchers is not well supported by most kernel interfaces, and most event
		1486	libraries will just poll for the same events again and again as long as
		1487	their callbacks have not been executed, which is very inefficient in the
		1488	common case of one high-priority watcher locking out a mass of lower
		1489	priority ones.
		1490
		1491	Static (ordering) priorities are most useful when you have two or more
		1492	watchers handling the same resource: a typical usage example is having an
		1493	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1494	timeouts. Under load, data might be received while the program handles
		1495	other jobs, but since timers normally get invoked first, the timeout
		1496	handler will be executed before checking for data. In that case, giving
		1497	the timer a lower priority than the I/O watcher ensures that I/O will be
		1498	handled first even under adverse conditions (which is usually, but not
		1499	always, what you want).
		1500
		1501	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1502	will only be executed when no same or higher priority watchers have
		1503	received events, they can be used to implement the "lock-out" model when
		1504	required.
		1505
		1506	For example, to emulate how many other event libraries handle priorities,
		1507	you can associate an C<ev_idle> watcher to each such watcher, and in
		1508	the normal watcher callback, you just start the idle watcher. The real
		1509	processing is done in the idle watcher callback. This causes libev to
		1510	continuously poll and process kernel event data for the watcher, but when
		1511	the lock-out case is known to be rare (which in turn is rare :), this is
		1512	workable.
		1513
		1514	Usually, however, the lock-out model implemented that way will perform
		1515	miserably under the type of load it was designed to handle. In that case,
		1516	it might be preferable to stop the real watcher before starting the
		1517	idle watcher, so the kernel will not have to process the event in case
		1518	the actual processing will be delayed for considerable time.
		1519
		1520	Here is an example of an I/O watcher that should run at a strictly lower
		1521	priority than the default, and which should only process data when no
		1522	other events are pending:
		1523
		1524	ev_idle idle; // actual processing watcher
		1525	ev_io io; // actual event watcher
		1526
		1527	static void
		1528	io_cb (EV_P_ ev_io *w, int revents)
382	{	1529	{
383	struct ev_io io;	1530	// stop the I/O watcher, we received the event, but
384	int otherfd;	1531	// are not yet ready to handle it.
385	void *somedata;	1532	ev_io_stop (EV_A_ w);
386	struct whatever *mostinteresting;	1533
		1534	// start the idle watcher to handle the actual event.
		1535	// it will not be executed as long as other watchers
		1536	// with the default priority are receiving events.
		1537	ev_idle_start (EV_A_ &idle);
387	}	1538	}
388		1539
389	And since your callback will be called with a pointer to the watcher, you	1540	static void
390	can cast it back to your own type:	1541	idle_cb (EV_P_ ev_idle *w, int revents)
391
392	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
393	{	1542	{
394	struct my_io *w = (struct my_io *)w_;	1543	// actual processing
395	...	1544	read (STDIN_FILENO, ...);
		1545
		1546	// have to start the I/O watcher again, as
		1547	// we have handled the event
		1548	ev_io_start (EV_P_ &io);
396	}	1549	}
397		1550
398	More interesting and less C-conformant ways of catsing your callback type	1551	// initialisation
399	have been omitted....	1552	ev_idle_init (&idle, idle_cb);
		1553	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1554	ev_io_start (EV_DEFAULT_ &io);
		1555
		1556	In the "real" world, it might also be beneficial to start a timer, so that
		1557	low-priority connections can not be locked out forever under load. This
		1558	enables your program to keep a lower latency for important connections
		1559	during short periods of high load, while not completely locking out less
		1560	important ones.
400		1561
401		1562
402	=head1 WATCHER TYPES	1563	=head1 WATCHER TYPES
403		1564
404	This section describes each watcher in detail, but will not repeat	1565	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	1566	information given in the last section. Any initialisation/set macros,
		1567	functions and members specific to the watcher type are explained.
406		1568
		1569	Members are additionally marked with either I<[read-only]>, meaning that,
		1570	while the watcher is active, you can look at the member and expect some
		1571	sensible content, but you must not modify it (you can modify it while the
		1572	watcher is stopped to your hearts content), or I<[read-write]>, which
		1573	means you can expect it to have some sensible content while the watcher
		1574	is active, but you can also modify it. Modifying it may not do something
		1575	sensible or take immediate effect (or do anything at all), but libev will
		1576	not crash or malfunction in any way.
		1577
		1578
407	=head2 struct ev_io - is my file descriptor readable or writable	1579	=head2 C<ev_io> - is this file descriptor readable or writable?
408		1580
409	I/O watchers check whether a file descriptor is readable or writable	1581	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	1582	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	1583	would not block the process and writing would at least be able to write
412	condition persists. Remember you cna stop the watcher if you don't want to	1584	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	1585	receiving events as long as the condition persists. Remember you can stop
		1586	the watcher if you don't want to act on the event and neither want to
		1587	receive future events.
414		1588
415	In general you can register as many read and/or write event watchers oer	1589	In general you can register as many read and/or write event watchers per
416	fd as you want (as long as you don't confuse yourself). Setting all file	1590	fd as you want (as long as you don't confuse yourself). Setting all file
417	descriptors to non-blocking mode is also usually a good idea (but not	1591	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	1592	required if you know what you are doing).
419		1593
420	You have to be careful with dup'ed file descriptors, though. Some backends	1594	Another thing you have to watch out for is that it is quite easy to
421	(the linux epoll backend is a notable example) cannot handle dup'ed file	1595	receive "spurious" readiness notifications, that is, your callback might
422	descriptors correctly if you register interest in two or more fds pointing	1596	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
423	to the same file/socket etc. description.	1597	because there is no data. It is very easy to get into this situation even
		1598	with a relatively standard program structure. Thus it is best to always
		1599	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
		1600	preferable to a program hanging until some data arrives.
424		1601
425	If you must do this, then force the use of a known-to-be-good backend	1602	If you cannot run the fd in non-blocking mode (for example you should
426	(at the time of this writing, this includes only EVMETHOD_SELECT and	1603	not play around with an Xlib connection), then you have to separately
427	EVMETHOD_POLL).	1604	re-test whether a file descriptor is really ready with a known-to-be good
		1605	interface such as poll (fortunately in the case of Xlib, it already does
		1606	this on its own, so its quite safe to use). Some people additionally
		1607	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1608	indefinitely.
		1609
		1610	But really, best use non-blocking mode.
		1611
		1612	=head3 The special problem of disappearing file descriptors
		1613
		1614	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1615	descriptor (either due to calling C<close> explicitly or any other means,
		1616	such as C<dup2>). The reason is that you register interest in some file
		1617	descriptor, but when it goes away, the operating system will silently drop
		1618	this interest. If another file descriptor with the same number then is
		1619	registered with libev, there is no efficient way to see that this is, in
		1620	fact, a different file descriptor.
		1621
		1622	To avoid having to explicitly tell libev about such cases, libev follows
		1623	the following policy: Each time C<ev_io_set> is being called, libev
		1624	will assume that this is potentially a new file descriptor, otherwise
		1625	it is assumed that the file descriptor stays the same. That means that
		1626	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1627	descriptor even if the file descriptor number itself did not change.
		1628
		1629	This is how one would do it normally anyway, the important point is that
		1630	the libev application should not optimise around libev but should leave
		1631	optimisations to libev.
		1632
		1633	=head3 The special problem of dup'ed file descriptors
		1634
		1635	Some backends (e.g. epoll), cannot register events for file descriptors,
		1636	but only events for the underlying file descriptions. That means when you
		1637	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1638	events for them, only one file descriptor might actually receive events.
		1639
		1640	There is no workaround possible except not registering events
		1641	for potentially C<dup ()>'ed file descriptors, or to resort to
		1642	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1643
		1644	=head3 The special problem of files
		1645
		1646	Many people try to use C<select> (or libev) on file descriptors
		1647	representing files, and expect it to become ready when their program
		1648	doesn't block on disk accesses (which can take a long time on their own).
		1649
		1650	However, this cannot ever work in the "expected" way - you get a readiness
		1651	notification as soon as the kernel knows whether and how much data is
		1652	there, and in the case of open files, that's always the case, so you
		1653	always get a readiness notification instantly, and your read (or possibly
		1654	write) will still block on the disk I/O.
		1655
		1656	Another way to view it is that in the case of sockets, pipes, character
		1657	devices and so on, there is another party (the sender) that delivers data
		1658	on its own, but in the case of files, there is no such thing: the disk
		1659	will not send data on its own, simply because it doesn't know what you
		1660	wish to read - you would first have to request some data.
		1661
		1662	Since files are typically not-so-well supported by advanced notification
		1663	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1664	to files, even though you should not use it. The reason for this is
		1665	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1666	usually a tty, often a pipe, but also sometimes files or special devices
		1667	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1668	F</dev/urandom>), and even though the file might better be served with
		1669	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1670	it "just works" instead of freezing.
		1671
		1672	So avoid file descriptors pointing to files when you know it (e.g. use
		1673	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1674	when you rarely read from a file instead of from a socket, and want to
		1675	reuse the same code path.
		1676
		1677	=head3 The special problem of fork
		1678
		1679	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1680	useless behaviour. Libev fully supports fork, but needs to be told about
		1681	it in the child if you want to continue to use it in the child.
		1682
		1683	To support fork in your child processes, you have to call C<ev_loop_fork
		1684	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1685	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1686
		1687	=head3 The special problem of SIGPIPE
		1688
		1689	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1690	when writing to a pipe whose other end has been closed, your program gets
		1691	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1692	this is sensible behaviour, for daemons, this is usually undesirable.
		1693
		1694	So when you encounter spurious, unexplained daemon exits, make sure you
		1695	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1696	somewhere, as that would have given you a big clue).
		1697
		1698	=head3 The special problem of accept()ing when you can't
		1699
		1700	Many implementations of the POSIX C<accept> function (for example,
		1701	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1702	connection from the pending queue in all error cases.
		1703
		1704	For example, larger servers often run out of file descriptors (because
		1705	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1706	rejecting the connection, leading to libev signalling readiness on
		1707	the next iteration again (the connection still exists after all), and
		1708	typically causing the program to loop at 100% CPU usage.
		1709
		1710	Unfortunately, the set of errors that cause this issue differs between
		1711	operating systems, there is usually little the app can do to remedy the
		1712	situation, and no known thread-safe method of removing the connection to
		1713	cope with overload is known (to me).
		1714
		1715	One of the easiest ways to handle this situation is to just ignore it
		1716	- when the program encounters an overload, it will just loop until the
		1717	situation is over. While this is a form of busy waiting, no OS offers an
		1718	event-based way to handle this situation, so it's the best one can do.
		1719
		1720	A better way to handle the situation is to log any errors other than
		1721	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1722	messages, and continue as usual, which at least gives the user an idea of
		1723	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1724	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1725	usage.
		1726
		1727	If your program is single-threaded, then you could also keep a dummy file
		1728	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1729	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1730	close that fd, and create a new dummy fd. This will gracefully refuse
		1731	clients under typical overload conditions.
		1732
		1733	The last way to handle it is to simply log the error and C<exit>, as
		1734	is often done with C<malloc> failures, but this results in an easy
		1735	opportunity for a DoS attack.
		1736
		1737	=head3 Watcher-Specific Functions
428		1738
429	=over 4	1739	=over 4
430		1740
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1741	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1742
433	=item ev_io_set (ev_io *, int fd, int events)	1743	=item ev_io_set (ev_io *, int fd, int events)
434		1744
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1745	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
436	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1746	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1747	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1748
		1749	=item int fd [read-only]
		1750
		1751	The file descriptor being watched.
		1752
		1753	=item int events [read-only]
		1754
		1755	The events being watched.
438		1756
439	=back	1757	=back
440		1758
		1759	=head3 Examples
		1760
		1761	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1762	readable, but only once. Since it is likely line-buffered, you could
		1763	attempt to read a whole line in the callback.
		1764
		1765	static void
		1766	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1767	{
		1768	ev_io_stop (loop, w);
		1769	.. read from stdin here (or from w->fd) and handle any I/O errors
		1770	}
		1771
		1772	...
		1773	struct ev_loop *loop = ev_default_init (0);
		1774	ev_io stdin_readable;
		1775	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1776	ev_io_start (loop, &stdin_readable);
		1777	ev_run (loop, 0);
		1778
		1779
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1780	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1781
443	Timer watchers are simple relative timers that generate an event after a	1782	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1783	given time, and optionally repeating in regular intervals after that.
445		1784
446	The timers are based on real time, that is, if you register an event that	1785	The timers are based on real time, that is, if you register an event that
447	times out after an hour and youreset your system clock to last years	1786	times out after an hour and you reset your system clock to January last
448	time, it will still time out after (roughly) and hour. "Roughly" because	1787	year, it will still time out after (roughly) one hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1789	monotonic clock option helps a lot here).
451		1790
		1791	The callback is guaranteed to be invoked only I<after> its timeout has
		1792	passed (not I<at>, so on systems with very low-resolution clocks this
		1793	might introduce a small delay, see "the special problem of being too
		1794	early", below). If multiple timers become ready during the same loop
		1795	iteration then the ones with earlier time-out values are invoked before
		1796	ones of the same priority with later time-out values (but this is no
		1797	longer true when a callback calls C<ev_run> recursively).
		1798
		1799	=head3 Be smart about timeouts
		1800
		1801	Many real-world problems involve some kind of timeout, usually for error
		1802	recovery. A typical example is an HTTP request - if the other side hangs,
		1803	you want to raise some error after a while.
		1804
		1805	What follows are some ways to handle this problem, from obvious and
		1806	inefficient to smart and efficient.
		1807
		1808	In the following, a 60 second activity timeout is assumed - a timeout that
		1809	gets reset to 60 seconds each time there is activity (e.g. each time some
		1810	data or other life sign was received).
		1811
452	=over 4	1812	=over 4
453		1813
		1814	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1815
		1816	This is the most obvious, but not the most simple way: In the beginning,
		1817	start the watcher:
		1818
		1819	ev_timer_init (timer, callback, 60., 0.);
		1820	ev_timer_start (loop, timer);
		1821
		1822	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1823	and start it again:
		1824
		1825	ev_timer_stop (loop, timer);
		1826	ev_timer_set (timer, 60., 0.);
		1827	ev_timer_start (loop, timer);
		1828
		1829	This is relatively simple to implement, but means that each time there is
		1830	some activity, libev will first have to remove the timer from its internal
		1831	data structure and then add it again. Libev tries to be fast, but it's
		1832	still not a constant-time operation.
		1833
		1834	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1835
		1836	This is the easiest way, and involves using C<ev_timer_again> instead of
		1837	C<ev_timer_start>.
		1838
		1839	To implement this, configure an C<ev_timer> with a C<repeat> value
		1840	of C<60> and then call C<ev_timer_again> at start and each time you
		1841	successfully read or write some data. If you go into an idle state where
		1842	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1843	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1844
		1845	That means you can ignore both the C<ev_timer_start> function and the
		1846	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1847	member and C<ev_timer_again>.
		1848
		1849	At start:
		1850
		1851	ev_init (timer, callback);
		1852	timer->repeat = 60.;
		1853	ev_timer_again (loop, timer);
		1854
		1855	Each time there is some activity:
		1856
		1857	ev_timer_again (loop, timer);
		1858
		1859	It is even possible to change the time-out on the fly, regardless of
		1860	whether the watcher is active or not:
		1861
		1862	timer->repeat = 30.;
		1863	ev_timer_again (loop, timer);
		1864
		1865	This is slightly more efficient then stopping/starting the timer each time
		1866	you want to modify its timeout value, as libev does not have to completely
		1867	remove and re-insert the timer from/into its internal data structure.
		1868
		1869	It is, however, even simpler than the "obvious" way to do it.
		1870
		1871	=item 3. Let the timer time out, but then re-arm it as required.
		1872
		1873	This method is more tricky, but usually most efficient: Most timeouts are
		1874	relatively long compared to the intervals between other activity - in
		1875	our example, within 60 seconds, there are usually many I/O events with
		1876	associated activity resets.
		1877
		1878	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1879	but remember the time of last activity, and check for a real timeout only
		1880	within the callback:
		1881
		1882	ev_tstamp timeout = 60.;
		1883	ev_tstamp last_activity; // time of last activity
		1884	ev_timer timer;
		1885
		1886	static void
		1887	callback (EV_P_ ev_timer *w, int revents)
		1888	{
		1889	// calculate when the timeout would happen
		1890	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1891
		1892	// if negative, it means we the timeout already occurred
		1893	if (after < 0.)
		1894	{
		1895	// timeout occurred, take action
		1896	}
		1897	else
		1898	{
		1899	// callback was invoked, but there was some recent
		1900	// activity. simply restart the timer to time out
		1901	// after "after" seconds, which is the earliest time
		1902	// the timeout can occur.
		1903	ev_timer_set (w, after, 0.);
		1904	ev_timer_start (EV_A_ w);
		1905	}
		1906	}
		1907
		1908	To summarise the callback: first calculate in how many seconds the
		1909	timeout will occur (by calculating the absolute time when it would occur,
		1910	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1911	(EV_A)> from that).
		1912
		1913	If this value is negative, then we are already past the timeout, i.e. we
		1914	timed out, and need to do whatever is needed in this case.
		1915
		1916	Otherwise, we now the earliest time at which the timeout would trigger,
		1917	and simply start the timer with this timeout value.
		1918
		1919	In other words, each time the callback is invoked it will check whether
		1920	the timeout occurred. If not, it will simply reschedule itself to check
		1921	again at the earliest time it could time out. Rinse. Repeat.
		1922
		1923	This scheme causes more callback invocations (about one every 60 seconds
		1924	minus half the average time between activity), but virtually no calls to
		1925	libev to change the timeout.
		1926
		1927	To start the machinery, simply initialise the watcher and set
		1928	C<last_activity> to the current time (meaning there was some activity just
		1929	now), then call the callback, which will "do the right thing" and start
		1930	the timer:
		1931
		1932	last_activity = ev_now (EV_A);
		1933	ev_init (&timer, callback);
		1934	callback (EV_A_ &timer, 0);
		1935
		1936	When there is some activity, simply store the current time in
		1937	C<last_activity>, no libev calls at all:
		1938
		1939	if (activity detected)
		1940	last_activity = ev_now (EV_A);
		1941
		1942	When your timeout value changes, then the timeout can be changed by simply
		1943	providing a new value, stopping the timer and calling the callback, which
		1944	will again do the right thing (for example, time out immediately :).
		1945
		1946	timeout = new_value;
		1947	ev_timer_stop (EV_A_ &timer);
		1948	callback (EV_A_ &timer, 0);
		1949
		1950	This technique is slightly more complex, but in most cases where the
		1951	time-out is unlikely to be triggered, much more efficient.
		1952
		1953	=item 4. Wee, just use a double-linked list for your timeouts.
		1954
		1955	If there is not one request, but many thousands (millions...), all
		1956	employing some kind of timeout with the same timeout value, then one can
		1957	do even better:
		1958
		1959	When starting the timeout, calculate the timeout value and put the timeout
		1960	at the I<end> of the list.
		1961
		1962	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1963	the list is expected to fire (for example, using the technique #3).
		1964
		1965	When there is some activity, remove the timer from the list, recalculate
		1966	the timeout, append it to the end of the list again, and make sure to
		1967	update the C<ev_timer> if it was taken from the beginning of the list.
		1968
		1969	This way, one can manage an unlimited number of timeouts in O(1) time for
		1970	starting, stopping and updating the timers, at the expense of a major
		1971	complication, and having to use a constant timeout. The constant timeout
		1972	ensures that the list stays sorted.
		1973
		1974	=back
		1975
		1976	So which method the best?
		1977
		1978	Method #2 is a simple no-brain-required solution that is adequate in most
		1979	situations. Method #3 requires a bit more thinking, but handles many cases
		1980	better, and isn't very complicated either. In most case, choosing either
		1981	one is fine, with #3 being better in typical situations.
		1982
		1983	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1984	rather complicated, but extremely efficient, something that really pays
		1985	off after the first million or so of active timers, i.e. it's usually
		1986	overkill :)
		1987
		1988	=head3 The special problem of being too early
		1989
		1990	If you ask a timer to call your callback after three seconds, then
		1991	you expect it to be invoked after three seconds - but of course, this
		1992	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1993	guaranteed to any precision by libev - imagine somebody suspending the
		1994	process with a STOP signal for a few hours for example.
		1995
		1996	So, libev tries to invoke your callback as soon as possible I<after> the
		1997	delay has occurred, but cannot guarantee this.
		1998
		1999	A less obvious failure mode is calling your callback too early: many event
		2000	loops compare timestamps with a "elapsed delay >= requested delay", but
		2001	this can cause your callback to be invoked much earlier than you would
		2002	expect.
		2003
		2004	To see why, imagine a system with a clock that only offers full second
		2005	resolution (think windows if you can't come up with a broken enough OS
		2006	yourself). If you schedule a one-second timer at the time 500.9, then the
		2007	event loop will schedule your timeout to elapse at a system time of 500
		2008	(500.9 truncated to the resolution) + 1, or 501.
		2009
		2010	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2011	501" and invoke the callback 0.1s after it was started, even though a
		2012	one-second delay was requested - this is being "too early", despite best
		2013	intentions.
		2014
		2015	This is the reason why libev will never invoke the callback if the elapsed
		2016	delay equals the requested delay, but only when the elapsed delay is
		2017	larger than the requested delay. In the example above, libev would only invoke
		2018	the callback at system time 502, or 1.1s after the timer was started.
		2019
		2020	So, while libev cannot guarantee that your callback will be invoked
		2021	exactly when requested, it I<can> and I<does> guarantee that the requested
		2022	delay has actually elapsed, or in other words, it always errs on the "too
		2023	late" side of things.
		2024
		2025	=head3 The special problem of time updates
		2026
		2027	Establishing the current time is a costly operation (it usually takes
		2028	at least one system call): EV therefore updates its idea of the current
		2029	time only before and after C<ev_run> collects new events, which causes a
		2030	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2031	lots of events in one iteration.
		2032
		2033	The relative timeouts are calculated relative to the C<ev_now ()>
		2034	time. This is usually the right thing as this timestamp refers to the time
		2035	of the event triggering whatever timeout you are modifying/starting. If
		2036	you suspect event processing to be delayed and you I<need> to base the
		2037	timeout on the current time, use something like the following to adjust
		2038	for it:
		2039
		2040	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
		2041
		2042	If the event loop is suspended for a long time, you can also force an
		2043	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		2044	()>, although that will push the event time of all outstanding events
		2045	further into the future.
		2046
		2047	=head3 The special problem of unsynchronised clocks
		2048
		2049	Modern systems have a variety of clocks - libev itself uses the normal
		2050	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2051	jumps).
		2052
		2053	Neither of these clocks is synchronised with each other or any other clock
		2054	on the system, so C<ev_time ()> might return a considerably different time
		2055	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2056	a call to C<gettimeofday> might return a second count that is one higher
		2057	than a directly following call to C<time>.
		2058
		2059	The moral of this is to only compare libev-related timestamps with
		2060	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2061	a second or so.
		2062
		2063	One more problem arises due to this lack of synchronisation: if libev uses
		2064	the system monotonic clock and you compare timestamps from C<ev_time>
		2065	or C<ev_now> from when you started your timer and when your callback is
		2066	invoked, you will find that sometimes the callback is a bit "early".
		2067
		2068	This is because C<ev_timer>s work in real time, not wall clock time, so
		2069	libev makes sure your callback is not invoked before the delay happened,
		2070	I<measured according to the real time>, not the system clock.
		2071
		2072	If your timeouts are based on a physical timescale (e.g. "time out this
		2073	connection after 100 seconds") then this shouldn't bother you as it is
		2074	exactly the right behaviour.
		2075
		2076	If you want to compare wall clock/system timestamps to your timers, then
		2077	you need to use C<ev_periodic>s, as these are based on the wall clock
		2078	time, where your comparisons will always generate correct results.
		2079
		2080	=head3 The special problems of suspended animation
		2081
		2082	When you leave the server world it is quite customary to hit machines that
		2083	can suspend/hibernate - what happens to the clocks during such a suspend?
		2084
		2085	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2086	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2087	to run until the system is suspended, but they will not advance while the
		2088	system is suspended. That means, on resume, it will be as if the program
		2089	was frozen for a few seconds, but the suspend time will not be counted
		2090	towards C<ev_timer> when a monotonic clock source is used. The real time
		2091	clock advanced as expected, but if it is used as sole clocksource, then a
		2092	long suspend would be detected as a time jump by libev, and timers would
		2093	be adjusted accordingly.
		2094
		2095	I would not be surprised to see different behaviour in different between
		2096	operating systems, OS versions or even different hardware.
		2097
		2098	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2099	time jump in the monotonic clocks and the realtime clock. If the program
		2100	is suspended for a very long time, and monotonic clock sources are in use,
		2101	then you can expect C<ev_timer>s to expire as the full suspension time
		2102	will be counted towards the timers. When no monotonic clock source is in
		2103	use, then libev will again assume a timejump and adjust accordingly.
		2104
		2105	It might be beneficial for this latter case to call C<ev_suspend>
		2106	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2107	deterministic behaviour in this case (you can do nothing against
		2108	C<SIGSTOP>).
		2109
		2110	=head3 Watcher-Specific Functions and Data Members
		2111
		2112	=over 4
		2113
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2114	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		2115
456	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2116	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
457		2117
458	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2118	Configure the timer to trigger after C<after> seconds. If C<repeat>
459	C<0.>, then it will automatically be stopped. If it is positive, then the	2119	is C<0.>, then it will automatically be stopped once the timeout is
460	timer will automatically be configured to trigger again C<repeat> seconds	2120	reached. If it is positive, then the timer will automatically be
461	later, again, and again, until stopped manually.	2121	configured to trigger again C<repeat> seconds later, again, and again,
		2122	until stopped manually.
462		2123
463	The timer itself will do a best-effort at avoiding drift, that is, if you	2124	The timer itself will do a best-effort at avoiding drift, that is, if
464	configure a timer to trigger every 10 seconds, then it will trigger at	2125	you configure a timer to trigger every 10 seconds, then it will normally
465	exactly 10 second intervals. If, however, your program cannot keep up with	2126	trigger at exactly 10 second intervals. If, however, your program cannot
466	the timer (ecause it takes longer than those 10 seconds to do stuff) the	2127	keep up with the timer (because it takes longer than those 10 seconds to
467	timer will not fire more than once per event loop iteration.	2128	do stuff) the timer will not fire more than once per event loop iteration.
468		2129
469	=item ev_timer_again (loop)	2130	=item ev_timer_again (loop, ev_timer *)
470		2131
471	This will act as if the timer timed out and restart it again if it is	2132	This will act as if the timer timed out, and restarts it again if it is
472	repeating. The exact semantics are:	2133	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2134	timeout to the C<repeat> value and calling C<ev_timer_start>.
473		2135
		2136	The exact semantics are as in the following rules, all of which will be
		2137	applied to the watcher:
		2138
		2139	=over 4
		2140
		2141	=item If the timer is pending, the pending status is always cleared.
		2142
474	If the timer is started but nonrepeating, stop it.	2143	=item If the timer is started but non-repeating, stop it (as if it timed
		2144	out, without invoking it).
475		2145
476	If the timer is repeating, either start it if necessary (with the repeat	2146	=item If the timer is repeating, make the C<repeat> value the new timeout
477	value), or reset the running timer to the repeat value.	2147	and start the timer, if necessary.
478
479	This sounds a bit complicated, but here is a useful and typical
480	example: Imagine you have a tcp connection and you want a so-called idle
481	timeout, that is, you want to be called when there have been, say, 60
482	seconds of inactivity on the socket. The easiest way to do this is to
483	configure an ev_timer with after=repeat=60 and calling ev_timer_again each
484	time you successfully read or write some data. If you go into an idle
485	state where you do not expect data to travel on the socket, you can stop
486	the timer, and again will automatically restart it if need be.
487		2148
488	=back	2149	=back
489		2150
		2151	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
		2152	usage example.
		2153
		2154	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2155
		2156	Returns the remaining time until a timer fires. If the timer is active,
		2157	then this time is relative to the current event loop time, otherwise it's
		2158	the timeout value currently configured.
		2159
		2160	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2161	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2162	will return C<4>. When the timer expires and is restarted, it will return
		2163	roughly C<7> (likely slightly less as callback invocation takes some time,
		2164	too), and so on.
		2165
		2166	=item ev_tstamp repeat [read-write]
		2167
		2168	The current C<repeat> value. Will be used each time the watcher times out
		2169	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2170	which is also when any modifications are taken into account.
		2171
		2172	=back
		2173
		2174	=head3 Examples
		2175
		2176	Example: Create a timer that fires after 60 seconds.
		2177
		2178	static void
		2179	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2180	{
		2181	.. one minute over, w is actually stopped right here
		2182	}
		2183
		2184	ev_timer mytimer;
		2185	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2186	ev_timer_start (loop, &mytimer);
		2187
		2188	Example: Create a timeout timer that times out after 10 seconds of
		2189	inactivity.
		2190
		2191	static void
		2192	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2193	{
		2194	.. ten seconds without any activity
		2195	}
		2196
		2197	ev_timer mytimer;
		2198	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2199	ev_timer_again (&mytimer); /* start timer */
		2200	ev_run (loop, 0);
		2201
		2202	// and in some piece of code that gets executed on any "activity":
		2203	// reset the timeout to start ticking again at 10 seconds
		2204	ev_timer_again (&mytimer);
		2205
		2206
490	=head2 ev_periodic - to cron or not to cron it	2207	=head2 C<ev_periodic> - to cron or not to cron?
491		2208
492	Periodic watchers are also timers of a kind, but they are very versatile	2209	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	2210	(and unfortunately a bit complex).
494		2211
495	Unlike ev_timer's, they are not based on real time (or relative time)	2212	Unlike C<ev_timer>, periodic watchers are not based on real time (or
496	but on wallclock time (absolute time). You can tell a periodic watcher	2213	relative time, the physical time that passes) but on wall clock time
497	to trigger "at" some specific point in time. For example, if you tell a	2214	(absolute time, the thing you can read on your calender or clock). The
498	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2215	difference is that wall clock time can run faster or slower than real
499	+ 10.>) and then reset your system clock to the last year, then it will	2216	time, and time jumps are not uncommon (e.g. when you adjust your
500	take a year to trigger the event (unlike an ev_timer, which would trigger	2217	wrist-watch).
501	roughly 10 seconds later and of course not if you reset your system time
502	again).
503		2218
504	They can also be used to implement vastly more complex timers, such as	2219	You can tell a periodic watcher to trigger after some specific point
		2220	in time: for example, if you tell a periodic watcher to trigger "in 10
		2221	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2222	not a delay) and then reset your system clock to January of the previous
		2223	year, then it will take a year or more to trigger the event (unlike an
		2224	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2225	it, as it uses a relative timeout).
		2226
		2227	C<ev_periodic> watchers can also be used to implement vastly more complex
505	triggering an event on eahc midnight, local time.	2228	timers, such as triggering an event on each "midnight, local time", or
		2229	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2230	those cannot react to time jumps.
		2231
		2232	As with timers, the callback is guaranteed to be invoked only when the
		2233	point in time where it is supposed to trigger has passed. If multiple
		2234	timers become ready during the same loop iteration then the ones with
		2235	earlier time-out values are invoked before ones with later time-out values
		2236	(but this is no longer true when a callback calls C<ev_run> recursively).
		2237
		2238	=head3 Watcher-Specific Functions and Data Members
506		2239
507	=over 4	2240	=over 4
508		2241
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2242	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
510		2243
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2244	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
512		2245
513	Lots of arguments, lets sort it out... There are basically three modes of	2246	Lots of arguments, let's sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	2247	operation, and we will explain them from simplest to most complex:
515
516		2248
517	=over 4	2249	=over 4
518		2250
519	=item * absolute timer (interval = reschedule_cb = 0)	2251	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
520		2252
521	In this configuration the watcher triggers an event at the wallclock time	2253	In this configuration the watcher triggers an event after the wall clock
522	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2254	time C<offset> has passed. It will not repeat and will not adjust when a
523	that is, if it is to be run at January 1st 2011 then it will run when the	2255	time jump occurs, that is, if it is to be run at January 1st 2011 then it
524	system time reaches or surpasses this time.	2256	will be stopped and invoked when the system clock reaches or surpasses
		2257	this point in time.
525		2258
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2259	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
527		2260
528	In this mode the watcher will always be scheduled to time out at the next	2261	In this mode the watcher will always be scheduled to time out at the next
529	C<at + N * interval> time (for some integer N) and then repeat, regardless	2262	C<offset + N * interval> time (for some integer N, which can also be
530	of any time jumps.	2263	negative) and then repeat, regardless of any time jumps. The C<offset>
		2264	argument is merely an offset into the C<interval> periods.
531		2265
532	This can be used to create timers that do not drift with respect to system	2266	This can be used to create timers that do not drift with respect to the
533	time:	2267	system clock, for example, here is an C<ev_periodic> that triggers each
		2268	hour, on the hour (with respect to UTC):
534		2269
535	ev_periodic_set (&periodic, 0., 3600., 0);	2270	ev_periodic_set (&periodic, 0., 3600., 0);
536		2271
537	This doesn't mean there will always be 3600 seconds in between triggers,	2272	This doesn't mean there will always be 3600 seconds in between triggers,
538	but only that the the callback will be called when the system time shows a	2273	but only that the callback will be called when the system time shows a
539	full hour (UTC), or more correct, when the system time is evenly divisible	2274	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	2275	by 3600.
541		2276
542	Another way to think about it (for the mathematically inclined) is that	2277	Another way to think about it (for the mathematically inclined) is that
543	ev_periodic will try to run the callback in this mode at the next possible	2278	C<ev_periodic> will try to run the callback in this mode at the next possible
544	time where C<time = at (mod interval)>, regardless of any time jumps.	2279	time where C<time = offset (mod interval)>, regardless of any time jumps.
545		2280
		2281	The C<interval> I<MUST> be positive, and for numerical stability, the
		2282	interval value should be higher than C<1/8192> (which is around 100
		2283	microseconds) and C<offset> should be higher than C<0> and should have
		2284	at most a similar magnitude as the current time (say, within a factor of
		2285	ten). Typical values for offset are, in fact, C<0> or something between
		2286	C<0> and C<interval>, which is also the recommended range.
		2287
		2288	Note also that there is an upper limit to how often a timer can fire (CPU
		2289	speed for example), so if C<interval> is very small then timing stability
		2290	will of course deteriorate. Libev itself tries to be exact to be about one
		2291	millisecond (if the OS supports it and the machine is fast enough).
		2292
546	=item * manual reschedule mode (reschedule_cb = callback)	2293	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
547		2294
548	In this mode the values for C<interval> and C<at> are both being	2295	In this mode the values for C<interval> and C<offset> are both being
549	ignored. Instead, each time the periodic watcher gets scheduled, the	2296	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	2297	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	2298	current time as second argument.
552		2299
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2300	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
554	periodic watcher, ever, or make any event loop modificstions>. If you need	2301	or make ANY other event loop modifications whatsoever, unless explicitly
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.	2302	allowed by documentation here>.
556		2303
		2304	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2305	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2306	only event loop modification you are allowed to do).
		2307
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2308	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
558	ev_tstamp now)>, e.g.:	2309	*w, ev_tstamp now)>, e.g.:
559		2310
		2311	static ev_tstamp
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2312	my_rescheduler (ev_periodic *w, ev_tstamp now)
561	{	2313	{
562	return now + 60.;	2314	return now + 60.;
563	}	2315	}
564		2316
565	It must return the next time to trigger, based on the passed time value	2317	It must return the next time to trigger, based on the passed time value
566	(that is, the lowest time value larger than to the second argument). It	2318	(that is, the lowest time value larger than to the second argument). It
567	will usually be called just before the callback will be triggered, but	2319	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	2320	might be called at other times, too.
569		2321
		2322	NOTE: I<< This callback must always return a time that is higher than or
		2323	equal to the passed C<now> value >>.
		2324
570	This can be used to create very complex timers, such as a timer that	2325	This can be used to create very complex timers, such as a timer that
571	triggers on each midnight, local time. To do this, you would calculate the	2326	triggers on "next midnight, local time". To do this, you would calculate the
572	next midnight after C<now> and return the timestamp value for this. How you do this	2327	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	2328	you do this is, again, up to you (but it is not trivial, which is the main
		2329	reason I omitted it as an example).
574		2330
575	=back	2331	=back
576		2332
577	=item ev_periodic_again (loop, ev_periodic *)	2333	=item ev_periodic_again (loop, ev_periodic *)
578		2334
579	Simply stops and restarts the periodic watcher again. This is only useful	2335	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	2336	when you changed some parameters or the reschedule callback would return
581	a different time than the last time it was called (e.g. in a crond like	2337	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	2338	program when the crontabs have changed).
583		2339
		2340	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2341
		2342	When active, returns the absolute time that the watcher is supposed
		2343	to trigger next. This is not the same as the C<offset> argument to
		2344	C<ev_periodic_set>, but indeed works even in interval and manual
		2345	rescheduling modes.
		2346
		2347	=item ev_tstamp offset [read-write]
		2348
		2349	When repeating, this contains the offset value, otherwise this is the
		2350	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2351	although libev might modify this value for better numerical stability).
		2352
		2353	Can be modified any time, but changes only take effect when the periodic
		2354	timer fires or C<ev_periodic_again> is being called.
		2355
		2356	=item ev_tstamp interval [read-write]
		2357
		2358	The current interval value. Can be modified any time, but changes only
		2359	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2360	called.
		2361
		2362	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2363
		2364	The current reschedule callback, or C<0>, if this functionality is
		2365	switched off. Can be changed any time, but changes only take effect when
		2366	the periodic timer fires or C<ev_periodic_again> is being called.
		2367
584	=back	2368	=back
585		2369
		2370	=head3 Examples
		2371
		2372	Example: Call a callback every hour, or, more precisely, whenever the
		2373	system time is divisible by 3600. The callback invocation times have
		2374	potentially a lot of jitter, but good long-term stability.
		2375
		2376	static void
		2377	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2378	{
		2379	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2380	}
		2381
		2382	ev_periodic hourly_tick;
		2383	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2384	ev_periodic_start (loop, &hourly_tick);
		2385
		2386	Example: The same as above, but use a reschedule callback to do it:
		2387
		2388	#include <math.h>
		2389
		2390	static ev_tstamp
		2391	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2392	{
		2393	return now + (3600. - fmod (now, 3600.));
		2394	}
		2395
		2396	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2397
		2398	Example: Call a callback every hour, starting now:
		2399
		2400	ev_periodic hourly_tick;
		2401	ev_periodic_init (&hourly_tick, clock_cb,
		2402	fmod (ev_now (loop), 3600.), 3600., 0);
		2403	ev_periodic_start (loop, &hourly_tick);
		2404
		2405
586	=head2 ev_signal - signal me when a signal gets signalled	2406	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		2407
588	Signal watchers will trigger an event when the process receives a specific	2408	Signal watchers will trigger an event when the process receives a specific
589	signal one or more times. Even though signals are very asynchronous, libev	2409	signal one or more times. Even though signals are very asynchronous, libev
590	will try its best to deliver signals synchronously, i.e. as part of the	2410	will try its best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	2411	normal event processing, like any other event.
592		2412
		2413	If you want signals to be delivered truly asynchronously, just use
		2414	C<sigaction> as you would do without libev and forget about sharing
		2415	the signal. You can even use C<ev_async> from a signal handler to
		2416	synchronously wake up an event loop.
		2417
593	You cna configure as many watchers as you like per signal. Only when the	2418	You can configure as many watchers as you like for the same signal, but
594	first watcher gets started will libev actually register a signal watcher	2419	only within the same loop, i.e. you can watch for C<SIGINT> in your
595	with the kernel (thus it coexists with your own signal handlers as long	2420	default loop and for C<SIGIO> in another loop, but you cannot watch for
596	as you don't register any with libev). Similarly, when the last signal	2421	C<SIGINT> in both the default loop and another loop at the same time. At
597	watcher for a signal is stopped libev will reset the signal handler to	2422	the moment, C<SIGCHLD> is permanently tied to the default loop.
598	SIG_DFL (regardless of what it was set to before).	2423
		2424	Only after the first watcher for a signal is started will libev actually
		2425	register something with the kernel. It thus coexists with your own signal
		2426	handlers as long as you don't register any with libev for the same signal.
		2427
		2428	If possible and supported, libev will install its handlers with
		2429	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2430	not be unduly interrupted. If you have a problem with system calls getting
		2431	interrupted by signals you can block all signals in an C<ev_check> watcher
		2432	and unblock them in an C<ev_prepare> watcher.
		2433
		2434	=head3 The special problem of inheritance over fork/execve/pthread_create
		2435
		2436	Both the signal mask (C<sigprocmask>) and the signal disposition
		2437	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2438	stopping it again), that is, libev might or might not block the signal,
		2439	and might or might not set or restore the installed signal handler (but
		2440	see C<EVFLAG_NOSIGMASK>).
		2441
		2442	While this does not matter for the signal disposition (libev never
		2443	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2444	C<execve>), this matters for the signal mask: many programs do not expect
		2445	certain signals to be blocked.
		2446
		2447	This means that before calling C<exec> (from the child) you should reset
		2448	the signal mask to whatever "default" you expect (all clear is a good
		2449	choice usually).
		2450
		2451	The simplest way to ensure that the signal mask is reset in the child is
		2452	to install a fork handler with C<pthread_atfork> that resets it. That will
		2453	catch fork calls done by libraries (such as the libc) as well.
		2454
		2455	In current versions of libev, the signal will not be blocked indefinitely
		2456	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2457	the window of opportunity for problems, it will not go away, as libev
		2458	I<has> to modify the signal mask, at least temporarily.
		2459
		2460	So I can't stress this enough: I<If you do not reset your signal mask when
		2461	you expect it to be empty, you have a race condition in your code>. This
		2462	is not a libev-specific thing, this is true for most event libraries.
		2463
		2464	=head3 The special problem of threads signal handling
		2465
		2466	POSIX threads has problematic signal handling semantics, specifically,
		2467	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2468	threads in a process block signals, which is hard to achieve.
		2469
		2470	When you want to use sigwait (or mix libev signal handling with your own
		2471	for the same signals), you can tackle this problem by globally blocking
		2472	all signals before creating any threads (or creating them with a fully set
		2473	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2474	loops. Then designate one thread as "signal receiver thread" which handles
		2475	these signals. You can pass on any signals that libev might be interested
		2476	in by calling C<ev_feed_signal>.
		2477
		2478	=head3 Watcher-Specific Functions and Data Members
599		2479
600	=over 4	2480	=over 4
601		2481
602	=item ev_signal_init (ev_signal *, callback, int signum)	2482	=item ev_signal_init (ev_signal *, callback, int signum)
603		2483
604	=item ev_signal_set (ev_signal *, int signum)	2484	=item ev_signal_set (ev_signal *, int signum)
605		2485
606	Configures the watcher to trigger on the given signal number (usually one	2486	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	2487	of the C<SIGxxx> constants).
608		2488
		2489	=item int signum [read-only]
		2490
		2491	The signal the watcher watches out for.
		2492
609	=back	2493	=back
610		2494
		2495	=head3 Examples
		2496
		2497	Example: Try to exit cleanly on SIGINT.
		2498
		2499	static void
		2500	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2501	{
		2502	ev_break (loop, EVBREAK_ALL);
		2503	}
		2504
		2505	ev_signal signal_watcher;
		2506	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2507	ev_signal_start (loop, &signal_watcher);
		2508
		2509
611	=head2 ev_child - wait for pid status changes	2510	=head2 C<ev_child> - watch out for process status changes
612		2511
613	Child watchers trigger when your process receives a SIGCHLD in response to	2512	Child watchers trigger when your process receives a SIGCHLD in response to
614	some child status changes (most typically when a child of yours dies).	2513	some child status changes (most typically when a child of yours dies or
		2514	exits). It is permissible to install a child watcher I<after> the child
		2515	has been forked (which implies it might have already exited), as long
		2516	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2517	forking and then immediately registering a watcher for the child is fine,
		2518	but forking and registering a watcher a few event loop iterations later or
		2519	in the next callback invocation is not.
		2520
		2521	Only the default event loop is capable of handling signals, and therefore
		2522	you can only register child watchers in the default event loop.
		2523
		2524	Due to some design glitches inside libev, child watchers will always be
		2525	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2526	libev)
		2527
		2528	=head3 Process Interaction
		2529
		2530	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2531	initialised. This is necessary to guarantee proper behaviour even if the
		2532	first child watcher is started after the child exits. The occurrence
		2533	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2534	synchronously as part of the event loop processing. Libev always reaps all
		2535	children, even ones not watched.
		2536
		2537	=head3 Overriding the Built-In Processing
		2538
		2539	Libev offers no special support for overriding the built-in child
		2540	processing, but if your application collides with libev's default child
		2541	handler, you can override it easily by installing your own handler for
		2542	C<SIGCHLD> after initialising the default loop, and making sure the
		2543	default loop never gets destroyed. You are encouraged, however, to use an
		2544	event-based approach to child reaping and thus use libev's support for
		2545	that, so other libev users can use C<ev_child> watchers freely.
		2546
		2547	=head3 Stopping the Child Watcher
		2548
		2549	Currently, the child watcher never gets stopped, even when the
		2550	child terminates, so normally one needs to stop the watcher in the
		2551	callback. Future versions of libev might stop the watcher automatically
		2552	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2553	problem).
		2554
		2555	=head3 Watcher-Specific Functions and Data Members
615		2556
616	=over 4	2557	=over 4
617		2558
618	=item ev_child_init (ev_child *, callback, int pid)	2559	=item ev_child_init (ev_child *, callback, int pid, int trace)
619		2560
620	=item ev_child_set (ev_child *, int pid)	2561	=item ev_child_set (ev_child *, int pid, int trace)
621		2562
622	Configures the watcher to wait for status changes of process C<pid> (or	2563	Configures the watcher to wait for status changes of process C<pid> (or
623	I<any> process if C<pid> is specified as C<0>). The callback can look	2564	I<any> process if C<pid> is specified as C<0>). The callback can look
624	at the C<rstatus> member of the C<ev_child> watcher structure to see	2565	at the C<rstatus> member of the C<ev_child> watcher structure to see
625	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	2566	the status word (use the macros from C<sys/wait.h> and see your systems
626	contains the pid of the process causing the status change.	2567	C<waitpid> documentation). The C<rpid> member contains the pid of the
		2568	process causing the status change. C<trace> must be either C<0> (only
		2569	activate the watcher when the process terminates) or C<1> (additionally
		2570	activate the watcher when the process is stopped or continued).
		2571
		2572	=item int pid [read-only]
		2573
		2574	The process id this watcher watches out for, or C<0>, meaning any process id.
		2575
		2576	=item int rpid [read-write]
		2577
		2578	The process id that detected a status change.
		2579
		2580	=item int rstatus [read-write]
		2581
		2582	The process exit/trace status caused by C<rpid> (see your systems
		2583	C<waitpid> and C<sys/wait.h> documentation for details).
627		2584
628	=back	2585	=back
629		2586
		2587	=head3 Examples
		2588
		2589	Example: C<fork()> a new process and install a child handler to wait for
		2590	its completion.
		2591
		2592	ev_child cw;
		2593
		2594	static void
		2595	child_cb (EV_P_ ev_child *w, int revents)
		2596	{
		2597	ev_child_stop (EV_A_ w);
		2598	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2599	}
		2600
		2601	pid_t pid = fork ();
		2602
		2603	if (pid < 0)
		2604	// error
		2605	else if (pid == 0)
		2606	{
		2607	// the forked child executes here
		2608	exit (1);
		2609	}
		2610	else
		2611	{
		2612	ev_child_init (&cw, child_cb, pid, 0);
		2613	ev_child_start (EV_DEFAULT_ &cw);
		2614	}
		2615
		2616
		2617	=head2 C<ev_stat> - did the file attributes just change?
		2618
		2619	This watches a file system path for attribute changes. That is, it calls
		2620	C<stat> on that path in regular intervals (or when the OS says it changed)
		2621	and sees if it changed compared to the last time, invoking the callback
		2622	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2623	happen after the watcher has been started will be reported.
		2624
		2625	The path does not need to exist: changing from "path exists" to "path does
		2626	not exist" is a status change like any other. The condition "path does not
		2627	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2628	C<st_nlink> field being zero (which is otherwise always forced to be at
		2629	least one) and all the other fields of the stat buffer having unspecified
		2630	contents.
		2631
		2632	The path I<must not> end in a slash or contain special components such as
		2633	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2634	your working directory changes, then the behaviour is undefined.
		2635
		2636	Since there is no portable change notification interface available, the
		2637	portable implementation simply calls C<stat(2)> regularly on the path
		2638	to see if it changed somehow. You can specify a recommended polling
		2639	interval for this case. If you specify a polling interval of C<0> (highly
		2640	recommended!) then a I<suitable, unspecified default> value will be used
		2641	(which you can expect to be around five seconds, although this might
		2642	change dynamically). Libev will also impose a minimum interval which is
		2643	currently around C<0.1>, but that's usually overkill.
		2644
		2645	This watcher type is not meant for massive numbers of stat watchers,
		2646	as even with OS-supported change notifications, this can be
		2647	resource-intensive.
		2648
		2649	At the time of this writing, the only OS-specific interface implemented
		2650	is the Linux inotify interface (implementing kqueue support is left as an
		2651	exercise for the reader. Note, however, that the author sees no way of
		2652	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2653
		2654	=head3 ABI Issues (Largefile Support)
		2655
		2656	Libev by default (unless the user overrides this) uses the default
		2657	compilation environment, which means that on systems with large file
		2658	support disabled by default, you get the 32 bit version of the stat
		2659	structure. When using the library from programs that change the ABI to
		2660	use 64 bit file offsets the programs will fail. In that case you have to
		2661	compile libev with the same flags to get binary compatibility. This is
		2662	obviously the case with any flags that change the ABI, but the problem is
		2663	most noticeably displayed with ev_stat and large file support.
		2664
		2665	The solution for this is to lobby your distribution maker to make large
		2666	file interfaces available by default (as e.g. FreeBSD does) and not
		2667	optional. Libev cannot simply switch on large file support because it has
		2668	to exchange stat structures with application programs compiled using the
		2669	default compilation environment.
		2670
		2671	=head3 Inotify and Kqueue
		2672
		2673	When C<inotify (7)> support has been compiled into libev and present at
		2674	runtime, it will be used to speed up change detection where possible. The
		2675	inotify descriptor will be created lazily when the first C<ev_stat>
		2676	watcher is being started.
		2677
		2678	Inotify presence does not change the semantics of C<ev_stat> watchers
		2679	except that changes might be detected earlier, and in some cases, to avoid
		2680	making regular C<stat> calls. Even in the presence of inotify support
		2681	there are many cases where libev has to resort to regular C<stat> polling,
		2682	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2683	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2684	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2685	xfs are fully working) libev usually gets away without polling.
		2686
		2687	There is no support for kqueue, as apparently it cannot be used to
		2688	implement this functionality, due to the requirement of having a file
		2689	descriptor open on the object at all times, and detecting renames, unlinks
		2690	etc. is difficult.
		2691
		2692	=head3 C<stat ()> is a synchronous operation
		2693
		2694	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2695	the process. The exception are C<ev_stat> watchers - those call C<stat
		2696	()>, which is a synchronous operation.
		2697
		2698	For local paths, this usually doesn't matter: unless the system is very
		2699	busy or the intervals between stat's are large, a stat call will be fast,
		2700	as the path data is usually in memory already (except when starting the
		2701	watcher).
		2702
		2703	For networked file systems, calling C<stat ()> can block an indefinite
		2704	time due to network issues, and even under good conditions, a stat call
		2705	often takes multiple milliseconds.
		2706
		2707	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2708	paths, although this is fully supported by libev.
		2709
		2710	=head3 The special problem of stat time resolution
		2711
		2712	The C<stat ()> system call only supports full-second resolution portably,
		2713	and even on systems where the resolution is higher, most file systems
		2714	still only support whole seconds.
		2715
		2716	That means that, if the time is the only thing that changes, you can
		2717	easily miss updates: on the first update, C<ev_stat> detects a change and
		2718	calls your callback, which does something. When there is another update
		2719	within the same second, C<ev_stat> will be unable to detect unless the
		2720	stat data does change in other ways (e.g. file size).
		2721
		2722	The solution to this is to delay acting on a change for slightly more
		2723	than a second (or till slightly after the next full second boundary), using
		2724	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2725	ev_timer_again (loop, w)>).
		2726
		2727	The C<.02> offset is added to work around small timing inconsistencies
		2728	of some operating systems (where the second counter of the current time
		2729	might be be delayed. One such system is the Linux kernel, where a call to
		2730	C<gettimeofday> might return a timestamp with a full second later than
		2731	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2732	update file times then there will be a small window where the kernel uses
		2733	the previous second to update file times but libev might already execute
		2734	the timer callback).
		2735
		2736	=head3 Watcher-Specific Functions and Data Members
		2737
		2738	=over 4
		2739
		2740	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2741
		2742	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2743
		2744	Configures the watcher to wait for status changes of the given
		2745	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2746	be detected and should normally be specified as C<0> to let libev choose
		2747	a suitable value. The memory pointed to by C<path> must point to the same
		2748	path for as long as the watcher is active.
		2749
		2750	The callback will receive an C<EV_STAT> event when a change was detected,
		2751	relative to the attributes at the time the watcher was started (or the
		2752	last change was detected).
		2753
		2754	=item ev_stat_stat (loop, ev_stat *)
		2755
		2756	Updates the stat buffer immediately with new values. If you change the
		2757	watched path in your callback, you could call this function to avoid
		2758	detecting this change (while introducing a race condition if you are not
		2759	the only one changing the path). Can also be useful simply to find out the
		2760	new values.
		2761
		2762	=item ev_statdata attr [read-only]
		2763
		2764	The most-recently detected attributes of the file. Although the type is
		2765	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2766	suitable for your system, but you can only rely on the POSIX-standardised
		2767	members to be present. If the C<st_nlink> member is C<0>, then there was
		2768	some error while C<stat>ing the file.
		2769
		2770	=item ev_statdata prev [read-only]
		2771
		2772	The previous attributes of the file. The callback gets invoked whenever
		2773	C<prev> != C<attr>, or, more precisely, one or more of these members
		2774	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2775	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2776
		2777	=item ev_tstamp interval [read-only]
		2778
		2779	The specified interval.
		2780
		2781	=item const char *path [read-only]
		2782
		2783	The file system path that is being watched.
		2784
		2785	=back
		2786
		2787	=head3 Examples
		2788
		2789	Example: Watch C</etc/passwd> for attribute changes.
		2790
		2791	static void
		2792	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2793	{
		2794	/* /etc/passwd changed in some way */
		2795	if (w->attr.st_nlink)
		2796	{
		2797	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2798	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2799	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2800	}
		2801	else
		2802	/* you shalt not abuse printf for puts */
		2803	puts ("wow, /etc/passwd is not there, expect problems. "
		2804	"if this is windows, they already arrived\n");
		2805	}
		2806
		2807	...
		2808	ev_stat passwd;
		2809
		2810	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2811	ev_stat_start (loop, &passwd);
		2812
		2813	Example: Like above, but additionally use a one-second delay so we do not
		2814	miss updates (however, frequent updates will delay processing, too, so
		2815	one might do the work both on C<ev_stat> callback invocation I<and> on
		2816	C<ev_timer> callback invocation).
		2817
		2818	static ev_stat passwd;
		2819	static ev_timer timer;
		2820
		2821	static void
		2822	timer_cb (EV_P_ ev_timer *w, int revents)
		2823	{
		2824	ev_timer_stop (EV_A_ w);
		2825
		2826	/* now it's one second after the most recent passwd change */
		2827	}
		2828
		2829	static void
		2830	stat_cb (EV_P_ ev_stat *w, int revents)
		2831	{
		2832	/* reset the one-second timer */
		2833	ev_timer_again (EV_A_ &timer);
		2834	}
		2835
		2836	...
		2837	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2838	ev_stat_start (loop, &passwd);
		2839	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2840
		2841
630	=head2 ev_idle - when you've got nothing better to do	2842	=head2 C<ev_idle> - when you've got nothing better to do...
631		2843
632	Idle watchers trigger events when there are no other I/O or timer (or	2844	Idle watchers trigger events when no other events of the same or higher
633	periodic) events pending. That is, as long as your process is busy	2845	priority are pending (prepare, check and other idle watchers do not count
634	handling sockets or timeouts it will not be called. But when your process	2846	as receiving "events").
635	is idle all idle watchers are being called again and again - until	2847
		2848	That is, as long as your process is busy handling sockets or timeouts
		2849	(or even signals, imagine) of the same or higher priority it will not be
		2850	triggered. But when your process is idle (or only lower-priority watchers
		2851	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	2852	iteration - until stopped, that is, or your process receives more events
		2853	and becomes busy again with higher priority stuff.
637		2854
638	The most noteworthy effect is that as long as any idle watchers are	2855	The most noteworthy effect is that as long as any idle watchers are
639	active, the process will not block when waiting for new events.	2856	active, the process will not block when waiting for new events.
640		2857
641	Apart from keeping your process non-blocking (which is a useful	2858	Apart from keeping your process non-blocking (which is a useful
642	effect on its own sometimes), idle watchers are a good place to do	2859	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	2860	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	2861	event loop has handled all outstanding events.
645		2862
		2863	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2864
		2865	As long as there is at least one active idle watcher, libev will never
		2866	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2867	For this to work, the idle watcher doesn't need to be invoked at all - the
		2868	lowest priority will do.
		2869
		2870	This mode of operation can be useful together with an C<ev_check> watcher,
		2871	to do something on each event loop iteration - for example to balance load
		2872	between different connections.
		2873
		2874	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2875	example.
		2876
		2877	=head3 Watcher-Specific Functions and Data Members
		2878
646	=over 4	2879	=over 4
647		2880
648	=item ev_idle_init (ev_signal *, callback)	2881	=item ev_idle_init (ev_idle *, callback)
649		2882
650	Initialises and configures the idle watcher - it has no parameters of any	2883	Initialises and configures the idle watcher - it has no parameters of any
651	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2884	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	2885	believe me.
653		2886
654	=back	2887	=back
655		2888
656	=head2 prepare and check - your hooks into the event loop	2889	=head3 Examples
657		2890
		2891	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2892	callback, free it. Also, use no error checking, as usual.
		2893
		2894	static void
		2895	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2896	{
		2897	// stop the watcher
		2898	ev_idle_stop (loop, w);
		2899
		2900	// now we can free it
		2901	free (w);
		2902
		2903	// now do something you wanted to do when the program has
		2904	// no longer anything immediate to do.
		2905	}
		2906
		2907	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2908	ev_idle_init (idle_watcher, idle_cb);
		2909	ev_idle_start (loop, idle_watcher);
		2910
		2911
		2912	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2913
658	Prepare and check watchers usually (but not always) are used in	2914	Prepare and check watchers are often (but not always) used in pairs:
659	tandom. Prepare watchers get invoked before the process blocks and check	2915	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	2916	afterwards.
661		2917
		2918	You I<must not> call C<ev_run> (or similar functions that enter the
		2919	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
		2920	C<ev_check> watchers. Other loops than the current one are fine,
		2921	however. The rationale behind this is that you do not need to check
		2922	for recursion in those watchers, i.e. the sequence will always be
		2923	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
		2924	kind they will always be called in pairs bracketing the blocking call.
		2925
662	Their main purpose is to integrate other event mechanisms into libev. This	2926	Their main purpose is to integrate other event mechanisms into libev and
663	could be used, for example, to track variable changes, implement your own	2927	their use is somewhat advanced. They could be used, for example, to track
664	watchers, integrate net-snmp or a coroutine library and lots more.	2928	variable changes, implement your own watchers, integrate net-snmp or a
		2929	coroutine library and lots more. They are also occasionally useful if
		2930	you cache some data and want to flush it before blocking (for example,
		2931	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2932	watcher).
665		2933
666	This is done by examining in each prepare call which file descriptors need	2934	This is done by examining in each prepare call which file descriptors
667	to be watched by the other library, registering ev_io watchers for them	2935	need to be watched by the other library, registering C<ev_io> watchers
668	and starting an ev_timer watcher for any timeouts (many libraries provide	2936	for them and starting an C<ev_timer> watcher for any timeouts (many
669	just this functionality). Then, in the check watcher you check for any	2937	libraries provide exactly this functionality). Then, in the check watcher,
670	events that occured (by making your callbacks set soem flags for example)	2938	you check for any events that occurred (by checking the pending status
671	and call back into the library.	2939	of all watchers and stopping them) and call back into the library. The
		2940	I/O and timer callbacks will never actually be called (but must be valid
		2941	nevertheless, because you never know, you know?).
672		2942
673	As another example, the perl Coro module uses these hooks to integrate	2943	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	2944	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	2945	during each prepare and only letting the process block if no coroutines
676	are ready to run.	2946	are ready to run (it's actually more complicated: it only runs coroutines
		2947	with priority higher than or equal to the event loop and one coroutine
		2948	of lower priority, but only once, using idle watchers to keep the event
		2949	loop from blocking if lower-priority coroutines are active, thus mapping
		2950	low-priority coroutines to idle/background tasks).
		2951
		2952	When used for this purpose, it is recommended to give C<ev_check> watchers
		2953	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2954	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2955	watchers).
		2956
		2957	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2958	activate ("feed") events into libev. While libev fully supports this, they
		2959	might get executed before other C<ev_check> watchers did their job. As
		2960	C<ev_check> watchers are often used to embed other (non-libev) event
		2961	loops those other event loops might be in an unusable state until their
		2962	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2963	others).
		2964
		2965	=head3 Abusing an C<ev_check> watcher for its side-effect
		2966
		2967	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2968	useful because they are called once per event loop iteration. For
		2969	example, if you want to handle a large number of connections fairly, you
		2970	normally only do a bit of work for each active connection, and if there
		2971	is more work to do, you wait for the next event loop iteration, so other
		2972	connections have a chance of making progress.
		2973
		2974	Using an C<ev_check> watcher is almost enough: it will be called on the
		2975	next event loop iteration. However, that isn't as soon as possible -
		2976	without external events, your C<ev_check> watcher will not be invoked.
		2977
		2978	This is where C<ev_idle> watchers come in handy - all you need is a
		2979	single global idle watcher that is active as long as you have one active
		2980	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2981	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2982	invoked. Neither watcher alone can do that.
		2983
		2984	=head3 Watcher-Specific Functions and Data Members
677		2985
678	=over 4	2986	=over 4
679		2987
680	=item ev_prepare_init (ev_prepare *, callback)	2988	=item ev_prepare_init (ev_prepare *, callback)
681		2989
682	=item ev_check_init (ev_check *, callback)	2990	=item ev_check_init (ev_check *, callback)
683		2991
684	Initialises and configures the prepare or check watcher - they have no	2992	Initialises and configures the prepare or check watcher - they have no
685	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2993	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	2994	macros, but using them is utterly, utterly, utterly and completely
		2995	pointless.
687		2996
688	=back	2997	=back
689		2998
		2999	=head3 Examples
		3000
		3001	There are a number of principal ways to embed other event loops or modules
		3002	into libev. Here are some ideas on how to include libadns into libev
		3003	(there is a Perl module named C<EV::ADNS> that does this, which you could
		3004	use as a working example. Another Perl module named C<EV::Glib> embeds a
		3005	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		3006	Glib event loop).
		3007
		3008	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		3009	and in a check watcher, destroy them and call into libadns. What follows
		3010	is pseudo-code only of course. This requires you to either use a low
		3011	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		3012	the callbacks for the IO/timeout watchers might not have been called yet.
		3013
		3014	static ev_io iow [nfd];
		3015	static ev_timer tw;
		3016
		3017	static void
		3018	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		3019	{
		3020	}
		3021
		3022	// create io watchers for each fd and a timer before blocking
		3023	static void
		3024	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		3025	{
		3026	int timeout = 3600000;
		3027	struct pollfd fds [nfd];
		3028	// actual code will need to loop here and realloc etc.
		3029	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		3030
		3031	/* the callback is illegal, but won't be called as we stop during check */
		3032	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		3033	ev_timer_start (loop, &tw);
		3034
		3035	// create one ev_io per pollfd
		3036	for (int i = 0; i < nfd; ++i)
		3037	{
		3038	ev_io_init (iow + i, io_cb, fds [i].fd,
		3039	((fds [i].events & POLLIN ? EV_READ : 0)
		3040	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		3041
		3042	fds [i].revents = 0;
		3043	ev_io_start (loop, iow + i);
		3044	}
		3045	}
		3046
		3047	// stop all watchers after blocking
		3048	static void
		3049	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		3050	{
		3051	ev_timer_stop (loop, &tw);
		3052
		3053	for (int i = 0; i < nfd; ++i)
		3054	{
		3055	// set the relevant poll flags
		3056	// could also call adns_processreadable etc. here
		3057	struct pollfd *fd = fds + i;
		3058	int revents = ev_clear_pending (iow + i);
		3059	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3060	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3061
		3062	// now stop the watcher
		3063	ev_io_stop (loop, iow + i);
		3064	}
		3065
		3066	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		3067	}
		3068
		3069	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3070	in the prepare watcher and would dispose of the check watcher.
		3071
		3072	Method 3: If the module to be embedded supports explicit event
		3073	notification (libadns does), you can also make use of the actual watcher
		3074	callbacks, and only destroy/create the watchers in the prepare watcher.
		3075
		3076	static void
		3077	timer_cb (EV_P_ ev_timer *w, int revents)
		3078	{
		3079	adns_state ads = (adns_state)w->data;
		3080	update_now (EV_A);
		3081
		3082	adns_processtimeouts (ads, &tv_now);
		3083	}
		3084
		3085	static void
		3086	io_cb (EV_P_ ev_io *w, int revents)
		3087	{
		3088	adns_state ads = (adns_state)w->data;
		3089	update_now (EV_A);
		3090
		3091	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3092	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3093	}
		3094
		3095	// do not ever call adns_afterpoll
		3096
		3097	Method 4: Do not use a prepare or check watcher because the module you
		3098	want to embed is not flexible enough to support it. Instead, you can
		3099	override their poll function. The drawback with this solution is that the
		3100	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3101	this approach, effectively embedding EV as a client into the horrible
		3102	libglib event loop.
		3103
		3104	static gint
		3105	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3106	{
		3107	int got_events = 0;
		3108
		3109	for (n = 0; n < nfds; ++n)
		3110	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3111
		3112	if (timeout >= 0)
		3113	// create/start timer
		3114
		3115	// poll
		3116	ev_run (EV_A_ 0);
		3117
		3118	// stop timer again
		3119	if (timeout >= 0)
		3120	ev_timer_stop (EV_A_ &to);
		3121
		3122	// stop io watchers again - their callbacks should have set
		3123	for (n = 0; n < nfds; ++n)
		3124	ev_io_stop (EV_A_ iow [n]);
		3125
		3126	return got_events;
		3127	}
		3128
		3129
		3130	=head2 C<ev_embed> - when one backend isn't enough...
		3131
		3132	This is a rather advanced watcher type that lets you embed one event loop
		3133	into another (currently only C<ev_io> events are supported in the embedded
		3134	loop, other types of watchers might be handled in a delayed or incorrect
		3135	fashion and must not be used).
		3136
		3137	There are primarily two reasons you would want that: work around bugs and
		3138	prioritise I/O.
		3139
		3140	As an example for a bug workaround, the kqueue backend might only support
		3141	sockets on some platform, so it is unusable as generic backend, but you
		3142	still want to make use of it because you have many sockets and it scales
		3143	so nicely. In this case, you would create a kqueue-based loop and embed
		3144	it into your default loop (which might use e.g. poll). Overall operation
		3145	will be a bit slower because first libev has to call C<poll> and then
		3146	C<kevent>, but at least you can use both mechanisms for what they are
		3147	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3148
		3149	As for prioritising I/O: under rare circumstances you have the case where
		3150	some fds have to be watched and handled very quickly (with low latency),
		3151	and even priorities and idle watchers might have too much overhead. In
		3152	this case you would put all the high priority stuff in one loop and all
		3153	the rest in a second one, and embed the second one in the first.
		3154
		3155	As long as the watcher is active, the callback will be invoked every
		3156	time there might be events pending in the embedded loop. The callback
		3157	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3158	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3159	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3160	to give the embedded loop strictly lower priority for example).
		3161
		3162	You can also set the callback to C<0>, in which case the embed watcher
		3163	will automatically execute the embedded loop sweep whenever necessary.
		3164
		3165	Fork detection will be handled transparently while the C<ev_embed> watcher
		3166	is active, i.e., the embedded loop will automatically be forked when the
		3167	embedding loop forks. In other cases, the user is responsible for calling
		3168	C<ev_loop_fork> on the embedded loop.
		3169
		3170	Unfortunately, not all backends are embeddable: only the ones returned by
		3171	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3172	portable one.
		3173
		3174	So when you want to use this feature you will always have to be prepared
		3175	that you cannot get an embeddable loop. The recommended way to get around
		3176	this is to have a separate variables for your embeddable loop, try to
		3177	create it, and if that fails, use the normal loop for everything.
		3178
		3179	=head3 C<ev_embed> and fork
		3180
		3181	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3182	automatically be applied to the embedded loop as well, so no special
		3183	fork handling is required in that case. When the watcher is not running,
		3184	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3185	as applicable.
		3186
		3187	=head3 Watcher-Specific Functions and Data Members
		3188
		3189	=over 4
		3190
		3191	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3192
		3193	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
		3194
		3195	Configures the watcher to embed the given loop, which must be
		3196	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3197	invoked automatically, otherwise it is the responsibility of the callback
		3198	to invoke it (it will continue to be called until the sweep has been done,
		3199	if you do not want that, you need to temporarily stop the embed watcher).
		3200
		3201	=item ev_embed_sweep (loop, ev_embed *)
		3202
		3203	Make a single, non-blocking sweep over the embedded loop. This works
		3204	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3205	appropriate way for embedded loops.
		3206
		3207	=item struct ev_loop *other [read-only]
		3208
		3209	The embedded event loop.
		3210
		3211	=back
		3212
		3213	=head3 Examples
		3214
		3215	Example: Try to get an embeddable event loop and embed it into the default
		3216	event loop. If that is not possible, use the default loop. The default
		3217	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3218	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3219	used).
		3220
		3221	struct ev_loop *loop_hi = ev_default_init (0);
		3222	struct ev_loop *loop_lo = 0;
		3223	ev_embed embed;
		3224
		3225	// see if there is a chance of getting one that works
		3226	// (remember that a flags value of 0 means autodetection)
		3227	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3228	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3229	: 0;
		3230
		3231	// if we got one, then embed it, otherwise default to loop_hi
		3232	if (loop_lo)
		3233	{
		3234	ev_embed_init (&embed, 0, loop_lo);
		3235	ev_embed_start (loop_hi, &embed);
		3236	}
		3237	else
		3238	loop_lo = loop_hi;
		3239
		3240	Example: Check if kqueue is available but not recommended and create
		3241	a kqueue backend for use with sockets (which usually work with any
		3242	kqueue implementation). Store the kqueue/socket-only event loop in
		3243	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3244
		3245	struct ev_loop *loop = ev_default_init (0);
		3246	struct ev_loop *loop_socket = 0;
		3247	ev_embed embed;
		3248
		3249	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3250	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3251	{
		3252	ev_embed_init (&embed, 0, loop_socket);
		3253	ev_embed_start (loop, &embed);
		3254	}
		3255
		3256	if (!loop_socket)
		3257	loop_socket = loop;
		3258
		3259	// now use loop_socket for all sockets, and loop for everything else
		3260
		3261
		3262	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3263
		3264	Fork watchers are called when a C<fork ()> was detected (usually because
		3265	whoever is a good citizen cared to tell libev about it by calling
		3266	C<ev_loop_fork>). The invocation is done before the event loop blocks next
		3267	and before C<ev_check> watchers are being called, and only in the child
		3268	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
		3269	and calls it in the wrong process, the fork handlers will be invoked, too,
		3270	of course.
		3271
		3272	=head3 The special problem of life after fork - how is it possible?
		3273
		3274	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3275	up/change the process environment, followed by a call to C<exec()>. This
		3276	sequence should be handled by libev without any problems.
		3277
		3278	This changes when the application actually wants to do event handling
		3279	in the child, or both parent in child, in effect "continuing" after the
		3280	fork.
		3281
		3282	The default mode of operation (for libev, with application help to detect
		3283	forks) is to duplicate all the state in the child, as would be expected
		3284	when I<either> the parent I<or> the child process continues.
		3285
		3286	When both processes want to continue using libev, then this is usually the
		3287	wrong result. In that case, usually one process (typically the parent) is
		3288	supposed to continue with all watchers in place as before, while the other
		3289	process typically wants to start fresh, i.e. without any active watchers.
		3290
		3291	The cleanest and most efficient way to achieve that with libev is to
		3292	simply create a new event loop, which of course will be "empty", and
		3293	use that for new watchers. This has the advantage of not touching more
		3294	memory than necessary, and thus avoiding the copy-on-write, and the
		3295	disadvantage of having to use multiple event loops (which do not support
		3296	signal watchers).
		3297
		3298	When this is not possible, or you want to use the default loop for
		3299	other reasons, then in the process that wants to start "fresh", call
		3300	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3301	Destroying the default loop will "orphan" (not stop) all registered
		3302	watchers, so you have to be careful not to execute code that modifies
		3303	those watchers. Note also that in that case, you have to re-register any
		3304	signal watchers.
		3305
		3306	=head3 Watcher-Specific Functions and Data Members
		3307
		3308	=over 4
		3309
		3310	=item ev_fork_init (ev_fork *, callback)
		3311
		3312	Initialises and configures the fork watcher - it has no parameters of any
		3313	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3314	really.
		3315
		3316	=back
		3317
		3318
		3319	=head2 C<ev_cleanup> - even the best things end
		3320
		3321	Cleanup watchers are called just before the event loop is being destroyed
		3322	by a call to C<ev_loop_destroy>.
		3323
		3324	While there is no guarantee that the event loop gets destroyed, cleanup
		3325	watchers provide a convenient method to install cleanup hooks for your
		3326	program, worker threads and so on - you just to make sure to destroy the
		3327	loop when you want them to be invoked.
		3328
		3329	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3330	all other watchers, they do not keep a reference to the event loop (which
		3331	makes a lot of sense if you think about it). Like all other watchers, you
		3332	can call libev functions in the callback, except C<ev_cleanup_start>.
		3333
		3334	=head3 Watcher-Specific Functions and Data Members
		3335
		3336	=over 4
		3337
		3338	=item ev_cleanup_init (ev_cleanup *, callback)
		3339
		3340	Initialises and configures the cleanup watcher - it has no parameters of
		3341	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3342	pointless, I assure you.
		3343
		3344	=back
		3345
		3346	Example: Register an atexit handler to destroy the default loop, so any
		3347	cleanup functions are called.
		3348
		3349	static void
		3350	program_exits (void)
		3351	{
		3352	ev_loop_destroy (EV_DEFAULT_UC);
		3353	}
		3354
		3355	...
		3356	atexit (program_exits);
		3357
		3358
		3359	=head2 C<ev_async> - how to wake up an event loop
		3360
		3361	In general, you cannot use an C<ev_loop> from multiple threads or other
		3362	asynchronous sources such as signal handlers (as opposed to multiple event
		3363	loops - those are of course safe to use in different threads).
		3364
		3365	Sometimes, however, you need to wake up an event loop you do not control,
		3366	for example because it belongs to another thread. This is what C<ev_async>
		3367	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3368	it by calling C<ev_async_send>, which is thread- and signal safe.
		3369
		3370	This functionality is very similar to C<ev_signal> watchers, as signals,
		3371	too, are asynchronous in nature, and signals, too, will be compressed
		3372	(i.e. the number of callback invocations may be less than the number of
		3373	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3374	of "global async watchers" by using a watcher on an otherwise unused
		3375	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3376	even without knowing which loop owns the signal.
		3377
		3378	=head3 Queueing
		3379
		3380	C<ev_async> does not support queueing of data in any way. The reason
		3381	is that the author does not know of a simple (or any) algorithm for a
		3382	multiple-writer-single-reader queue that works in all cases and doesn't
		3383	need elaborate support such as pthreads or unportable memory access
		3384	semantics.
		3385
		3386	That means that if you want to queue data, you have to provide your own
		3387	queue. But at least I can tell you how to implement locking around your
		3388	queue:
		3389
		3390	=over 4
		3391
		3392	=item queueing from a signal handler context
		3393
		3394	To implement race-free queueing, you simply add to the queue in the signal
		3395	handler but you block the signal handler in the watcher callback. Here is
		3396	an example that does that for some fictitious SIGUSR1 handler:
		3397
		3398	static ev_async mysig;
		3399
		3400	static void
		3401	sigusr1_handler (void)
		3402	{
		3403	sometype data;
		3404
		3405	// no locking etc.
		3406	queue_put (data);
		3407	ev_async_send (EV_DEFAULT_ &mysig);
		3408	}
		3409
		3410	static void
		3411	mysig_cb (EV_P_ ev_async *w, int revents)
		3412	{
		3413	sometype data;
		3414	sigset_t block, prev;
		3415
		3416	sigemptyset (&block);
		3417	sigaddset (&block, SIGUSR1);
		3418	sigprocmask (SIG_BLOCK, &block, &prev);
		3419
		3420	while (queue_get (&data))
		3421	process (data);
		3422
		3423	if (sigismember (&prev, SIGUSR1)
		3424	sigprocmask (SIG_UNBLOCK, &block, 0);
		3425	}
		3426
		3427	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3428	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3429	either...).
		3430
		3431	=item queueing from a thread context
		3432
		3433	The strategy for threads is different, as you cannot (easily) block
		3434	threads but you can easily preempt them, so to queue safely you need to
		3435	employ a traditional mutex lock, such as in this pthread example:
		3436
		3437	static ev_async mysig;
		3438	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3439
		3440	static void
		3441	otherthread (void)
		3442	{
		3443	// only need to lock the actual queueing operation
		3444	pthread_mutex_lock (&mymutex);
		3445	queue_put (data);
		3446	pthread_mutex_unlock (&mymutex);
		3447
		3448	ev_async_send (EV_DEFAULT_ &mysig);
		3449	}
		3450
		3451	static void
		3452	mysig_cb (EV_P_ ev_async *w, int revents)
		3453	{
		3454	pthread_mutex_lock (&mymutex);
		3455
		3456	while (queue_get (&data))
		3457	process (data);
		3458
		3459	pthread_mutex_unlock (&mymutex);
		3460	}
		3461
		3462	=back
		3463
		3464
		3465	=head3 Watcher-Specific Functions and Data Members
		3466
		3467	=over 4
		3468
		3469	=item ev_async_init (ev_async *, callback)
		3470
		3471	Initialises and configures the async watcher - it has no parameters of any
		3472	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3473	trust me.
		3474
		3475	=item ev_async_send (loop, ev_async *)
		3476
		3477	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3478	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3479	returns.
		3480
		3481	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3482	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3483	embedding section below on what exactly this means).
		3484
		3485	Note that, as with other watchers in libev, multiple events might get
		3486	compressed into a single callback invocation (another way to look at
		3487	this is that C<ev_async> watchers are level-triggered: they are set on
		3488	C<ev_async_send>, reset when the event loop detects that).
		3489
		3490	This call incurs the overhead of at most one extra system call per event
		3491	loop iteration, if the event loop is blocked, and no syscall at all if
		3492	the event loop (or your program) is processing events. That means that
		3493	repeated calls are basically free (there is no need to avoid calls for
		3494	performance reasons) and that the overhead becomes smaller (typically
		3495	zero) under load.
		3496
		3497	=item bool = ev_async_pending (ev_async *)
		3498
		3499	Returns a non-zero value when C<ev_async_send> has been called on the
		3500	watcher but the event has not yet been processed (or even noted) by the
		3501	event loop.
		3502
		3503	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3504	the loop iterates next and checks for the watcher to have become active,
		3505	it will reset the flag again. C<ev_async_pending> can be used to very
		3506	quickly check whether invoking the loop might be a good idea.
		3507
		3508	Not that this does I<not> check whether the watcher itself is pending,
		3509	only whether it has been requested to make this watcher pending: there
		3510	is a time window between the event loop checking and resetting the async
		3511	notification, and the callback being invoked.
		3512
		3513	=back
		3514
		3515
690	=head1 OTHER FUNCTIONS	3516	=head1 OTHER FUNCTIONS
691		3517
692	There are some other fucntions of possible interest. Described. Here. Now.	3518	There are some other functions of possible interest. Described. Here. Now.
693		3519
694	=over 4	3520	=over 4
695		3521
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3522	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		3523
698	This function combines a simple timer and an I/O watcher, calls your	3524	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	3525	callback on whichever event happens first and automatically stops both
700	watchers. This is useful if you want to wait for a single event on an fd	3526	watchers. This is useful if you want to wait for a single event on an fd
701	or timeout without havign to allocate/configure/start/stop/free one or	3527	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	3528	more watchers yourself.
703		3529
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	3530	If C<fd> is less than 0, then no I/O watcher will be started and the
705	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	3531	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
706	will be craeted and started.	3532	the given C<fd> and C<events> set will be created and started.
707		3533
708	If C<timeout> is less than 0, then no timeout watcher will be	3534	If C<timeout> is less than 0, then no timeout watcher will be
709	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	3535	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	3536	repeat = 0) will be started. C<0> is a valid timeout.
711		3537
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	3538	The callback has the type C<void (*cb)(int revents, void *arg)> and is
713	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	3539	passed an C<revents> set like normal event callbacks (a combination of
714	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	3540	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
		3541	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3542	a timeout and an io event at the same time - you probably should give io
		3543	events precedence.
715		3544
		3545	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3546
716	static void stdin_ready (int revents, void *arg)	3547	static void stdin_ready (int revents, void *arg)
		3548	{
		3549	if (revents & EV_READ)
		3550	/* stdin might have data for us, joy! */;
		3551	else if (revents & EV_TIMER)
		3552	/* doh, nothing entered */;
		3553	}
		3554
		3555	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3556
		3557	=item ev_feed_fd_event (loop, int fd, int revents)
		3558
		3559	Feed an event on the given fd, as if a file descriptor backend detected
		3560	the given events.
		3561
		3562	=item ev_feed_signal_event (loop, int signum)
		3563
		3564	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3565	which is async-safe.
		3566
		3567	=back
		3568
		3569
		3570	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3571
		3572	This section explains some common idioms that are not immediately
		3573	obvious. Note that examples are sprinkled over the whole manual, and this
		3574	section only contains stuff that wouldn't fit anywhere else.
		3575
		3576	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3577
		3578	Each watcher has, by default, a C<void *data> member that you can read
		3579	or modify at any time: libev will completely ignore it. This can be used
		3580	to associate arbitrary data with your watcher. If you need more data and
		3581	don't want to allocate memory separately and store a pointer to it in that
		3582	data member, you can also "subclass" the watcher type and provide your own
		3583	data:
		3584
		3585	struct my_io
		3586	{
		3587	ev_io io;
		3588	int otherfd;
		3589	void *somedata;
		3590	struct whatever *mostinteresting;
		3591	};
		3592
		3593	...
		3594	struct my_io w;
		3595	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3596
		3597	And since your callback will be called with a pointer to the watcher, you
		3598	can cast it back to your own type:
		3599
		3600	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3601	{
		3602	struct my_io *w = (struct my_io *)w_;
		3603	...
		3604	}
		3605
		3606	More interesting and less C-conformant ways of casting your callback
		3607	function type instead have been omitted.
		3608
		3609	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3610
		3611	Another common scenario is to use some data structure with multiple
		3612	embedded watchers, in effect creating your own watcher that combines
		3613	multiple libev event sources into one "super-watcher":
		3614
		3615	struct my_biggy
		3616	{
		3617	int some_data;
		3618	ev_timer t1;
		3619	ev_timer t2;
		3620	}
		3621
		3622	In this case getting the pointer to C<my_biggy> is a bit more
		3623	complicated: Either you store the address of your C<my_biggy> struct in
		3624	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3625	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3626	real programmers):
		3627
		3628	#include <stddef.h>
		3629
		3630	static void
		3631	t1_cb (EV_P_ ev_timer *w, int revents)
		3632	{
		3633	struct my_biggy big = (struct my_biggy *)
		3634	(((char *)w) - offsetof (struct my_biggy, t1));
		3635	}
		3636
		3637	static void
		3638	t2_cb (EV_P_ ev_timer *w, int revents)
		3639	{
		3640	struct my_biggy big = (struct my_biggy *)
		3641	(((char *)w) - offsetof (struct my_biggy, t2));
		3642	}
		3643
		3644	=head2 AVOIDING FINISHING BEFORE RETURNING
		3645
		3646	Often you have structures like this in event-based programs:
		3647
		3648	callback ()
717	{	3649	{
718	if (revents & EV_TIMEOUT)	3650	free (request);
719	/* doh, nothing entered */
720	else if (revents & EV_READ)
721	/* stdin might have data for us, joy! */
722	}	3651	}
723		3652
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	3653	request = start_new_request (..., callback);
725		3654
726	=item ev_feed_event (loop, watcher, int events)	3655	The intent is to start some "lengthy" operation. The C<request> could be
		3656	used to cancel the operation, or do other things with it.
727		3657
728	Feeds the given event set into the event loop, as if the specified event	3658	It's not uncommon to have code paths in C<start_new_request> that
729	has happened for the specified watcher (which must be a pointer to an	3659	immediately invoke the callback, for example, to report errors. Or you add
730	initialised but not necessarily active event watcher).	3660	some caching layer that finds that it can skip the lengthy aspects of the
		3661	operation and simply invoke the callback with the result.
731		3662
732	=item ev_feed_fd_event (loop, int fd, int revents)	3663	The problem here is that this will happen I<before> C<start_new_request>
		3664	has returned, so C<request> is not set.
733		3665
734	Feed an event on the given fd, as if a file descriptor backend detected it.	3666	Even if you pass the request by some safer means to the callback, you
		3667	might want to do something to the request after starting it, such as
		3668	canceling it, which probably isn't working so well when the callback has
		3669	already been invoked.
735		3670
736	=item ev_feed_signal_event (loop, int signum)	3671	A common way around all these issues is to make sure that
		3672	C<start_new_request> I<always> returns before the callback is invoked. If
		3673	C<start_new_request> immediately knows the result, it can artificially
		3674	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3675	example, or more sneakily, by reusing an existing (stopped) watcher and
		3676	pushing it into the pending queue:
737		3677
738	Feed an event as if the given signal occured (loop must be the default loop!).	3678	ev_set_cb (watcher, callback);
		3679	ev_feed_event (EV_A_ watcher, 0);
		3680
		3681	This way, C<start_new_request> can safely return before the callback is
		3682	invoked, while not delaying callback invocation too much.
		3683
		3684	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3685
		3686	Often (especially in GUI toolkits) there are places where you have
		3687	I<modal> interaction, which is most easily implemented by recursively
		3688	invoking C<ev_run>.
		3689
		3690	This brings the problem of exiting - a callback might want to finish the
		3691	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3692	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3693	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3694	other combination: In these cases, a simple C<ev_break> will not work.
		3695
		3696	The solution is to maintain "break this loop" variable for each C<ev_run>
		3697	invocation, and use a loop around C<ev_run> until the condition is
		3698	triggered, using C<EVRUN_ONCE>:
		3699
		3700	// main loop
		3701	int exit_main_loop = 0;
		3702
		3703	while (!exit_main_loop)
		3704	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3705
		3706	// in a modal watcher
		3707	int exit_nested_loop = 0;
		3708
		3709	while (!exit_nested_loop)
		3710	ev_run (EV_A_ EVRUN_ONCE);
		3711
		3712	To exit from any of these loops, just set the corresponding exit variable:
		3713
		3714	// exit modal loop
		3715	exit_nested_loop = 1;
		3716
		3717	// exit main program, after modal loop is finished
		3718	exit_main_loop = 1;
		3719
		3720	// exit both
		3721	exit_main_loop = exit_nested_loop = 1;
		3722
		3723	=head2 THREAD LOCKING EXAMPLE
		3724
		3725	Here is a fictitious example of how to run an event loop in a different
		3726	thread from where callbacks are being invoked and watchers are
		3727	created/added/removed.
		3728
		3729	For a real-world example, see the C<EV::Loop::Async> perl module,
		3730	which uses exactly this technique (which is suited for many high-level
		3731	languages).
		3732
		3733	The example uses a pthread mutex to protect the loop data, a condition
		3734	variable to wait for callback invocations, an async watcher to notify the
		3735	event loop thread and an unspecified mechanism to wake up the main thread.
		3736
		3737	First, you need to associate some data with the event loop:
		3738
		3739	typedef struct {
		3740	mutex_t lock; /* global loop lock */
		3741	ev_async async_w;
		3742	thread_t tid;
		3743	cond_t invoke_cv;
		3744	} userdata;
		3745
		3746	void prepare_loop (EV_P)
		3747	{
		3748	// for simplicity, we use a static userdata struct.
		3749	static userdata u;
		3750
		3751	ev_async_init (&u->async_w, async_cb);
		3752	ev_async_start (EV_A_ &u->async_w);
		3753
		3754	pthread_mutex_init (&u->lock, 0);
		3755	pthread_cond_init (&u->invoke_cv, 0);
		3756
		3757	// now associate this with the loop
		3758	ev_set_userdata (EV_A_ u);
		3759	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3760	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3761
		3762	// then create the thread running ev_run
		3763	pthread_create (&u->tid, 0, l_run, EV_A);
		3764	}
		3765
		3766	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3767	solely to wake up the event loop so it takes notice of any new watchers
		3768	that might have been added:
		3769
		3770	static void
		3771	async_cb (EV_P_ ev_async *w, int revents)
		3772	{
		3773	// just used for the side effects
		3774	}
		3775
		3776	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3777	protecting the loop data, respectively.
		3778
		3779	static void
		3780	l_release (EV_P)
		3781	{
		3782	userdata *u = ev_userdata (EV_A);
		3783	pthread_mutex_unlock (&u->lock);
		3784	}
		3785
		3786	static void
		3787	l_acquire (EV_P)
		3788	{
		3789	userdata *u = ev_userdata (EV_A);
		3790	pthread_mutex_lock (&u->lock);
		3791	}
		3792
		3793	The event loop thread first acquires the mutex, and then jumps straight
		3794	into C<ev_run>:
		3795
		3796	void *
		3797	l_run (void *thr_arg)
		3798	{
		3799	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3800
		3801	l_acquire (EV_A);
		3802	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3803	ev_run (EV_A_ 0);
		3804	l_release (EV_A);
		3805
		3806	return 0;
		3807	}
		3808
		3809	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3810	signal the main thread via some unspecified mechanism (signals? pipe
		3811	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3812	have been called (in a while loop because a) spurious wakeups are possible
		3813	and b) skipping inter-thread-communication when there are no pending
		3814	watchers is very beneficial):
		3815
		3816	static void
		3817	l_invoke (EV_P)
		3818	{
		3819	userdata *u = ev_userdata (EV_A);
		3820
		3821	while (ev_pending_count (EV_A))
		3822	{
		3823	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3824	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3825	}
		3826	}
		3827
		3828	Now, whenever the main thread gets told to invoke pending watchers, it
		3829	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3830	thread to continue:
		3831
		3832	static void
		3833	real_invoke_pending (EV_P)
		3834	{
		3835	userdata *u = ev_userdata (EV_A);
		3836
		3837	pthread_mutex_lock (&u->lock);
		3838	ev_invoke_pending (EV_A);
		3839	pthread_cond_signal (&u->invoke_cv);
		3840	pthread_mutex_unlock (&u->lock);
		3841	}
		3842
		3843	Whenever you want to start/stop a watcher or do other modifications to an
		3844	event loop, you will now have to lock:
		3845
		3846	ev_timer timeout_watcher;
		3847	userdata *u = ev_userdata (EV_A);
		3848
		3849	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3850
		3851	pthread_mutex_lock (&u->lock);
		3852	ev_timer_start (EV_A_ &timeout_watcher);
		3853	ev_async_send (EV_A_ &u->async_w);
		3854	pthread_mutex_unlock (&u->lock);
		3855
		3856	Note that sending the C<ev_async> watcher is required because otherwise
		3857	an event loop currently blocking in the kernel will have no knowledge
		3858	about the newly added timer. By waking up the loop it will pick up any new
		3859	watchers in the next event loop iteration.
		3860
		3861	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3862
		3863	While the overhead of a callback that e.g. schedules a thread is small, it
		3864	is still an overhead. If you embed libev, and your main usage is with some
		3865	kind of threads or coroutines, you might want to customise libev so that
		3866	doesn't need callbacks anymore.
		3867
		3868	Imagine you have coroutines that you can switch to using a function
		3869	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3870	and that due to some magic, the currently active coroutine is stored in a
		3871	global called C<current_coro>. Then you can build your own "wait for libev
		3872	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3873	the differing C<;> conventions):
		3874
		3875	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3876	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3877
		3878	That means instead of having a C callback function, you store the
		3879	coroutine to switch to in each watcher, and instead of having libev call
		3880	your callback, you instead have it switch to that coroutine.
		3881
		3882	A coroutine might now wait for an event with a function called
		3883	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3884	matter when, or whether the watcher is active or not when this function is
		3885	called):
		3886
		3887	void
		3888	wait_for_event (ev_watcher *w)
		3889	{
		3890	ev_set_cb (w, current_coro);
		3891	switch_to (libev_coro);
		3892	}
		3893
		3894	That basically suspends the coroutine inside C<wait_for_event> and
		3895	continues the libev coroutine, which, when appropriate, switches back to
		3896	this or any other coroutine.
		3897
		3898	You can do similar tricks if you have, say, threads with an event queue -
		3899	instead of storing a coroutine, you store the queue object and instead of
		3900	switching to a coroutine, you push the watcher onto the queue and notify
		3901	any waiters.
		3902
		3903	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3904	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3905
		3906	// my_ev.h
		3907	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3908	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3909	#include "../libev/ev.h"
		3910
		3911	// my_ev.c
		3912	#define EV_H "my_ev.h"
		3913	#include "../libev/ev.c"
		3914
		3915	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3916	F<my_ev.c> into your project. When properly specifying include paths, you
		3917	can even use F<ev.h> as header file name directly.
		3918
		3919
		3920	=head1 LIBEVENT EMULATION
		3921
		3922	Libev offers a compatibility emulation layer for libevent. It cannot
		3923	emulate the internals of libevent, so here are some usage hints:
		3924
		3925	=over 4
		3926
		3927	=item * Only the libevent-1.4.1-beta API is being emulated.
		3928
		3929	This was the newest libevent version available when libev was implemented,
		3930	and is still mostly unchanged in 2010.
		3931
		3932	=item * Use it by including <event.h>, as usual.
		3933
		3934	=item * The following members are fully supported: ev_base, ev_callback,
		3935	ev_arg, ev_fd, ev_res, ev_events.
		3936
		3937	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		3938	maintained by libev, it does not work exactly the same way as in libevent (consider
		3939	it a private API).
		3940
		3941	=item * Priorities are not currently supported. Initialising priorities
		3942	will fail and all watchers will have the same priority, even though there
		3943	is an ev_pri field.
		3944
		3945	=item * In libevent, the last base created gets the signals, in libev, the
		3946	base that registered the signal gets the signals.
		3947
		3948	=item * Other members are not supported.
		3949
		3950	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3951	to use the libev header file and library.
739		3952
740	=back	3953	=back
741		3954
		3955	=head1 C++ SUPPORT
		3956
		3957	=head2 C API
		3958
		3959	The normal C API should work fine when used from C++: both ev.h and the
		3960	libev sources can be compiled as C++. Therefore, code that uses the C API
		3961	will work fine.
		3962
		3963	Proper exception specifications might have to be added to callbacks passed
		3964	to libev: exceptions may be thrown only from watcher callbacks, all
		3965	other callbacks (allocator, syserr, loop acquire/release and periodic
		3966	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3967	()> specification. If you have code that needs to be compiled as both C
		3968	and C++ you can use the C<EV_THROW> macro for this:
		3969
		3970	static void
		3971	fatal_error (const char *msg) EV_THROW
		3972	{
		3973	perror (msg);
		3974	abort ();
		3975	}
		3976
		3977	...
		3978	ev_set_syserr_cb (fatal_error);
		3979
		3980	The only API functions that can currently throw exceptions are C<ev_run>,
		3981	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3982	because it runs cleanup watchers).
		3983
		3984	Throwing exceptions in watcher callbacks is only supported if libev itself
		3985	is compiled with a C++ compiler or your C and C++ environments allow
		3986	throwing exceptions through C libraries (most do).
		3987
		3988	=head2 C++ API
		3989
		3990	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3991	you to use some convenience methods to start/stop watchers and also change
		3992	the callback model to a model using method callbacks on objects.
		3993
		3994	To use it,
		3995
		3996	#include <ev++.h>
		3997
		3998	This automatically includes F<ev.h> and puts all of its definitions (many
		3999	of them macros) into the global namespace. All C++ specific things are
		4000	put into the C<ev> namespace. It should support all the same embedding
		4001	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		4002
		4003	Care has been taken to keep the overhead low. The only data member the C++
		4004	classes add (compared to plain C-style watchers) is the event loop pointer
		4005	that the watcher is associated with (or no additional members at all if
		4006	you disable C<EV_MULTIPLICITY> when embedding libev).
		4007
		4008	Currently, functions, static and non-static member functions and classes
		4009	with C<operator ()> can be used as callbacks. Other types should be easy
		4010	to add as long as they only need one additional pointer for context. If
		4011	you need support for other types of functors please contact the author
		4012	(preferably after implementing it).
		4013
		4014	For all this to work, your C++ compiler either has to use the same calling
		4015	conventions as your C compiler (for static member functions), or you have
		4016	to embed libev and compile libev itself as C++.
		4017
		4018	Here is a list of things available in the C<ev> namespace:
		4019
		4020	=over 4
		4021
		4022	=item C<ev::READ>, C<ev::WRITE> etc.
		4023
		4024	These are just enum values with the same values as the C<EV_READ> etc.
		4025	macros from F<ev.h>.
		4026
		4027	=item C<ev::tstamp>, C<ev::now>
		4028
		4029	Aliases to the same types/functions as with the C<ev_> prefix.
		4030
		4031	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		4032
		4033	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		4034	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		4035	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		4036	defined by many implementations.
		4037
		4038	All of those classes have these methods:
		4039
		4040	=over 4
		4041
		4042	=item ev::TYPE::TYPE ()
		4043
		4044	=item ev::TYPE::TYPE (loop)
		4045
		4046	=item ev::TYPE::~TYPE
		4047
		4048	The constructor (optionally) takes an event loop to associate the watcher
		4049	with. If it is omitted, it will use C<EV_DEFAULT>.
		4050
		4051	The constructor calls C<ev_init> for you, which means you have to call the
		4052	C<set> method before starting it.
		4053
		4054	It will not set a callback, however: You have to call the templated C<set>
		4055	method to set a callback before you can start the watcher.
		4056
		4057	(The reason why you have to use a method is a limitation in C++ which does
		4058	not allow explicit template arguments for constructors).
		4059
		4060	The destructor automatically stops the watcher if it is active.
		4061
		4062	=item w->set<class, &class::method> (object *)
		4063
		4064	This method sets the callback method to call. The method has to have a
		4065	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		4066	first argument and the C<revents> as second. The object must be given as
		4067	parameter and is stored in the C<data> member of the watcher.
		4068
		4069	This method synthesizes efficient thunking code to call your method from
		4070	the C callback that libev requires. If your compiler can inline your
		4071	callback (i.e. it is visible to it at the place of the C<set> call and
		4072	your compiler is good :), then the method will be fully inlined into the
		4073	thunking function, making it as fast as a direct C callback.
		4074
		4075	Example: simple class declaration and watcher initialisation
		4076
		4077	struct myclass
		4078	{
		4079	void io_cb (ev::io &w, int revents) { }
		4080	}
		4081
		4082	myclass obj;
		4083	ev::io iow;
		4084	iow.set <myclass, &myclass::io_cb> (&obj);
		4085
		4086	=item w->set (object *)
		4087
		4088	This is a variation of a method callback - leaving out the method to call
		4089	will default the method to C<operator ()>, which makes it possible to use
		4090	functor objects without having to manually specify the C<operator ()> all
		4091	the time. Incidentally, you can then also leave out the template argument
		4092	list.
		4093
		4094	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4095	int revents)>.
		4096
		4097	See the method-C<set> above for more details.
		4098
		4099	Example: use a functor object as callback.
		4100
		4101	struct myfunctor
		4102	{
		4103	void operator() (ev::io &w, int revents)
		4104	{
		4105	...
		4106	}
		4107	}
		4108
		4109	myfunctor f;
		4110
		4111	ev::io w;
		4112	w.set (&f);
		4113
		4114	=item w->set<function> (void *data = 0)
		4115
		4116	Also sets a callback, but uses a static method or plain function as
		4117	callback. The optional C<data> argument will be stored in the watcher's
		4118	C<data> member and is free for you to use.
		4119
		4120	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4121
		4122	See the method-C<set> above for more details.
		4123
		4124	Example: Use a plain function as callback.
		4125
		4126	static void io_cb (ev::io &w, int revents) { }
		4127	iow.set <io_cb> ();
		4128
		4129	=item w->set (loop)
		4130
		4131	Associates a different C<struct ev_loop> with this watcher. You can only
		4132	do this when the watcher is inactive (and not pending either).
		4133
		4134	=item w->set ([arguments])
		4135
		4136	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4137	with the same arguments. Either this method or a suitable start method
		4138	must be called at least once. Unlike the C counterpart, an active watcher
		4139	gets automatically stopped and restarted when reconfiguring it with this
		4140	method.
		4141
		4142	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4143	clashing with the C<set (loop)> method.
		4144
		4145	=item w->start ()
		4146
		4147	Starts the watcher. Note that there is no C<loop> argument, as the
		4148	constructor already stores the event loop.
		4149
		4150	=item w->start ([arguments])
		4151
		4152	Instead of calling C<set> and C<start> methods separately, it is often
		4153	convenient to wrap them in one call. Uses the same type of arguments as
		4154	the configure C<set> method of the watcher.
		4155
		4156	=item w->stop ()
		4157
		4158	Stops the watcher if it is active. Again, no C<loop> argument.
		4159
		4160	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		4161
		4162	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		4163	C<ev_TYPE_again> function.
		4164
		4165	=item w->sweep () (C<ev::embed> only)
		4166
		4167	Invokes C<ev_embed_sweep>.
		4168
		4169	=item w->update () (C<ev::stat> only)
		4170
		4171	Invokes C<ev_stat_stat>.
		4172
		4173	=back
		4174
		4175	=back
		4176
		4177	Example: Define a class with two I/O and idle watchers, start the I/O
		4178	watchers in the constructor.
		4179
		4180	class myclass
		4181	{
		4182	ev::io io ; void io_cb (ev::io &w, int revents);
		4183	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		4184	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		4185
		4186	myclass (int fd)
		4187	{
		4188	io .set <myclass, &myclass::io_cb > (this);
		4189	io2 .set <myclass, &myclass::io2_cb > (this);
		4190	idle.set <myclass, &myclass::idle_cb> (this);
		4191
		4192	io.set (fd, ev::WRITE); // configure the watcher
		4193	io.start (); // start it whenever convenient
		4194
		4195	io2.start (fd, ev::READ); // set + start in one call
		4196	}
		4197	};
		4198
		4199
		4200	=head1 OTHER LANGUAGE BINDINGS
		4201
		4202	Libev does not offer other language bindings itself, but bindings for a
		4203	number of languages exist in the form of third-party packages. If you know
		4204	any interesting language binding in addition to the ones listed here, drop
		4205	me a note.
		4206
		4207	=over 4
		4208
		4209	=item Perl
		4210
		4211	The EV module implements the full libev API and is actually used to test
		4212	libev. EV is developed together with libev. Apart from the EV core module,
		4213	there are additional modules that implement libev-compatible interfaces
		4214	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4215	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4216	and C<EV::Glib>).
		4217
		4218	It can be found and installed via CPAN, its homepage is at
		4219	L<http://software.schmorp.de/pkg/EV>.
		4220
		4221	=item Python
		4222
		4223	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4224	seems to be quite complete and well-documented.
		4225
		4226	=item Ruby
		4227
		4228	Tony Arcieri has written a ruby extension that offers access to a subset
		4229	of the libev API and adds file handle abstractions, asynchronous DNS and
		4230	more on top of it. It can be found via gem servers. Its homepage is at
		4231	L<http://rev.rubyforge.org/>.
		4232
		4233	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4234	makes rev work even on mingw.
		4235
		4236	=item Haskell
		4237
		4238	A haskell binding to libev is available at
		4239	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4240
		4241	=item D
		4242
		4243	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4244	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4245
		4246	=item Ocaml
		4247
		4248	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4249	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4250
		4251	=item Lua
		4252
		4253	Brian Maher has written a partial interface to libev for lua (at the
		4254	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4255	L<http://github.com/brimworks/lua-ev>.
		4256
		4257	=item Javascript
		4258
		4259	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4260
		4261	=item Others
		4262
		4263	There are others, and I stopped counting.
		4264
		4265	=back
		4266
		4267
		4268	=head1 MACRO MAGIC
		4269
		4270	Libev can be compiled with a variety of options, the most fundamental
		4271	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4272	functions and callbacks have an initial C<struct ev_loop *> argument.
		4273
		4274	To make it easier to write programs that cope with either variant, the
		4275	following macros are defined:
		4276
		4277	=over 4
		4278
		4279	=item C<EV_A>, C<EV_A_>
		4280
		4281	This provides the loop I<argument> for functions, if one is required ("ev
		4282	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4283	C<EV_A_> is used when other arguments are following. Example:
		4284
		4285	ev_unref (EV_A);
		4286	ev_timer_add (EV_A_ watcher);
		4287	ev_run (EV_A_ 0);
		4288
		4289	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4290	which is often provided by the following macro.
		4291
		4292	=item C<EV_P>, C<EV_P_>
		4293
		4294	This provides the loop I<parameter> for functions, if one is required ("ev
		4295	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4296	C<EV_P_> is used when other parameters are following. Example:
		4297
		4298	// this is how ev_unref is being declared
		4299	static void ev_unref (EV_P);
		4300
		4301	// this is how you can declare your typical callback
		4302	static void cb (EV_P_ ev_timer *w, int revents)
		4303
		4304	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4305	suitable for use with C<EV_A>.
		4306
		4307	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4308
		4309	Similar to the other two macros, this gives you the value of the default
		4310	loop, if multiple loops are supported ("ev loop default"). The default loop
		4311	will be initialised if it isn't already initialised.
		4312
		4313	For non-multiplicity builds, these macros do nothing, so you always have
		4314	to initialise the loop somewhere.
		4315
		4316	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4317
		4318	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4319	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4320	is undefined when the default loop has not been initialised by a previous
		4321	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4322
		4323	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4324	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4325
		4326	=back
		4327
		4328	Example: Declare and initialise a check watcher, utilising the above
		4329	macros so it will work regardless of whether multiple loops are supported
		4330	or not.
		4331
		4332	static void
		4333	check_cb (EV_P_ ev_timer *w, int revents)
		4334	{
		4335	ev_check_stop (EV_A_ w);
		4336	}
		4337
		4338	ev_check check;
		4339	ev_check_init (&check, check_cb);
		4340	ev_check_start (EV_DEFAULT_ &check);
		4341	ev_run (EV_DEFAULT_ 0);
		4342
		4343	=head1 EMBEDDING
		4344
		4345	Libev can (and often is) directly embedded into host
		4346	applications. Examples of applications that embed it include the Deliantra
		4347	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4348	and rxvt-unicode.
		4349
		4350	The goal is to enable you to just copy the necessary files into your
		4351	source directory without having to change even a single line in them, so
		4352	you can easily upgrade by simply copying (or having a checked-out copy of
		4353	libev somewhere in your source tree).
		4354
		4355	=head2 FILESETS
		4356
		4357	Depending on what features you need you need to include one or more sets of files
		4358	in your application.
		4359
		4360	=head3 CORE EVENT LOOP
		4361
		4362	To include only the libev core (all the C<ev_*> functions), with manual
		4363	configuration (no autoconf):
		4364
		4365	#define EV_STANDALONE 1
		4366	#include "ev.c"
		4367
		4368	This will automatically include F<ev.h>, too, and should be done in a
		4369	single C source file only to provide the function implementations. To use
		4370	it, do the same for F<ev.h> in all files wishing to use this API (best
		4371	done by writing a wrapper around F<ev.h> that you can include instead and
		4372	where you can put other configuration options):
		4373
		4374	#define EV_STANDALONE 1
		4375	#include "ev.h"
		4376
		4377	Both header files and implementation files can be compiled with a C++
		4378	compiler (at least, that's a stated goal, and breakage will be treated
		4379	as a bug).
		4380
		4381	You need the following files in your source tree, or in a directory
		4382	in your include path (e.g. in libev/ when using -Ilibev):
		4383
		4384	ev.h
		4385	ev.c
		4386	ev_vars.h
		4387	ev_wrap.h
		4388
		4389	ev_win32.c required on win32 platforms only
		4390
		4391	ev_select.c only when select backend is enabled (which is enabled by default)
		4392	ev_poll.c only when poll backend is enabled (disabled by default)
		4393	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		4394	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		4395	ev_port.c only when the solaris port backend is enabled (disabled by default)
		4396
		4397	F<ev.c> includes the backend files directly when enabled, so you only need
		4398	to compile this single file.
		4399
		4400	=head3 LIBEVENT COMPATIBILITY API
		4401
		4402	To include the libevent compatibility API, also include:
		4403
		4404	#include "event.c"
		4405
		4406	in the file including F<ev.c>, and:
		4407
		4408	#include "event.h"
		4409
		4410	in the files that want to use the libevent API. This also includes F<ev.h>.
		4411
		4412	You need the following additional files for this:
		4413
		4414	event.h
		4415	event.c
		4416
		4417	=head3 AUTOCONF SUPPORT
		4418
		4419	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4420	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4421	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4422	include F<config.h> and configure itself accordingly.
		4423
		4424	For this of course you need the m4 file:
		4425
		4426	libev.m4
		4427
		4428	=head2 PREPROCESSOR SYMBOLS/MACROS
		4429
		4430	Libev can be configured via a variety of preprocessor symbols you have to
		4431	define before including (or compiling) any of its files. The default in
		4432	the absence of autoconf is documented for every option.
		4433
		4434	Symbols marked with "(h)" do not change the ABI, and can have different
		4435	values when compiling libev vs. including F<ev.h>, so it is permissible
		4436	to redefine them before including F<ev.h> without breaking compatibility
		4437	to a compiled library. All other symbols change the ABI, which means all
		4438	users of libev and the libev code itself must be compiled with compatible
		4439	settings.
		4440
		4441	=over 4
		4442
		4443	=item EV_COMPAT3 (h)
		4444
		4445	Backwards compatibility is a major concern for libev. This is why this
		4446	release of libev comes with wrappers for the functions and symbols that
		4447	have been renamed between libev version 3 and 4.
		4448
		4449	You can disable these wrappers (to test compatibility with future
		4450	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4451	sources. This has the additional advantage that you can drop the C<struct>
		4452	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4453	typedef in that case.
		4454
		4455	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4456	and in some even more future version the compatibility code will be
		4457	removed completely.
		4458
		4459	=item EV_STANDALONE (h)
		4460
		4461	Must always be C<1> if you do not use autoconf configuration, which
		4462	keeps libev from including F<config.h>, and it also defines dummy
		4463	implementations for some libevent functions (such as logging, which is not
		4464	supported). It will also not define any of the structs usually found in
		4465	F<event.h> that are not directly supported by the libev core alone.
		4466
		4467	In standalone mode, libev will still try to automatically deduce the
		4468	configuration, but has to be more conservative.
		4469
		4470	=item EV_USE_FLOOR
		4471
		4472	If defined to be C<1>, libev will use the C<floor ()> function for its
		4473	periodic reschedule calculations, otherwise libev will fall back on a
		4474	portable (slower) implementation. If you enable this, you usually have to
		4475	link against libm or something equivalent. Enabling this when the C<floor>
		4476	function is not available will fail, so the safe default is to not enable
		4477	this.
		4478
		4479	=item EV_USE_MONOTONIC
		4480
		4481	If defined to be C<1>, libev will try to detect the availability of the
		4482	monotonic clock option at both compile time and runtime. Otherwise no
		4483	use of the monotonic clock option will be attempted. If you enable this,
		4484	you usually have to link against librt or something similar. Enabling it
		4485	when the functionality isn't available is safe, though, although you have
		4486	to make sure you link against any libraries where the C<clock_gettime>
		4487	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4488
		4489	=item EV_USE_REALTIME
		4490
		4491	If defined to be C<1>, libev will try to detect the availability of the
		4492	real-time clock option at compile time (and assume its availability
		4493	at runtime if successful). Otherwise no use of the real-time clock
		4494	option will be attempted. This effectively replaces C<gettimeofday>
		4495	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4496	correctness. See the note about libraries in the description of
		4497	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4498	C<EV_USE_CLOCK_SYSCALL>.
		4499
		4500	=item EV_USE_CLOCK_SYSCALL
		4501
		4502	If defined to be C<1>, libev will try to use a direct syscall instead
		4503	of calling the system-provided C<clock_gettime> function. This option
		4504	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4505	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4506	programs needlessly. Using a direct syscall is slightly slower (in
		4507	theory), because no optimised vdso implementation can be used, but avoids
		4508	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4509	higher, as it simplifies linking (no need for C<-lrt>).
		4510
		4511	=item EV_USE_NANOSLEEP
		4512
		4513	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4514	and will use it for delays. Otherwise it will use C<select ()>.
		4515
		4516	=item EV_USE_EVENTFD
		4517
		4518	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4519	available and will probe for kernel support at runtime. This will improve
		4520	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4521	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4522	2.7 or newer, otherwise disabled.
		4523
		4524	=item EV_USE_SELECT
		4525
		4526	If undefined or defined to be C<1>, libev will compile in support for the
		4527	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4528	other method takes over, select will be it. Otherwise the select backend
		4529	will not be compiled in.
		4530
		4531	=item EV_SELECT_USE_FD_SET
		4532
		4533	If defined to C<1>, then the select backend will use the system C<fd_set>
		4534	structure. This is useful if libev doesn't compile due to a missing
		4535	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4536	on exotic systems. This usually limits the range of file descriptors to
		4537	some low limit such as 1024 or might have other limitations (winsocket
		4538	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4539	configures the maximum size of the C<fd_set>.
		4540
		4541	=item EV_SELECT_IS_WINSOCKET
		4542
		4543	When defined to C<1>, the select backend will assume that
		4544	select/socket/connect etc. don't understand file descriptors but
		4545	wants osf handles on win32 (this is the case when the select to
		4546	be used is the winsock select). This means that it will call
		4547	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4548	it is assumed that all these functions actually work on fds, even
		4549	on win32. Should not be defined on non-win32 platforms.
		4550
		4551	=item EV_FD_TO_WIN32_HANDLE(fd)
		4552
		4553	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4554	file descriptors to socket handles. When not defining this symbol (the
		4555	default), then libev will call C<_get_osfhandle>, which is usually
		4556	correct. In some cases, programs use their own file descriptor management,
		4557	in which case they can provide this function to map fds to socket handles.
		4558
		4559	=item EV_WIN32_HANDLE_TO_FD(handle)
		4560
		4561	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4562	using the standard C<_open_osfhandle> function. For programs implementing
		4563	their own fd to handle mapping, overwriting this function makes it easier
		4564	to do so. This can be done by defining this macro to an appropriate value.
		4565
		4566	=item EV_WIN32_CLOSE_FD(fd)
		4567
		4568	If programs implement their own fd to handle mapping on win32, then this
		4569	macro can be used to override the C<close> function, useful to unregister
		4570	file descriptors again. Note that the replacement function has to close
		4571	the underlying OS handle.
		4572
		4573	=item EV_USE_WSASOCKET
		4574
		4575	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4576	communication socket, which works better in some environments. Otherwise,
		4577	the normal C<socket> function will be used, which works better in other
		4578	environments.
		4579
		4580	=item EV_USE_POLL
		4581
		4582	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4583	backend. Otherwise it will be enabled on non-win32 platforms. It
		4584	takes precedence over select.
		4585
		4586	=item EV_USE_EPOLL
		4587
		4588	If defined to be C<1>, libev will compile in support for the Linux
		4589	C<epoll>(7) backend. Its availability will be detected at runtime,
		4590	otherwise another method will be used as fallback. This is the preferred
		4591	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4592	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4593
		4594	=item EV_USE_KQUEUE
		4595
		4596	If defined to be C<1>, libev will compile in support for the BSD style
		4597	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4598	otherwise another method will be used as fallback. This is the preferred
		4599	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4600	supports some types of fds correctly (the only platform we found that
		4601	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4602	not be used unless explicitly requested. The best way to use it is to find
		4603	out whether kqueue supports your type of fd properly and use an embedded
		4604	kqueue loop.
		4605
		4606	=item EV_USE_PORT
		4607
		4608	If defined to be C<1>, libev will compile in support for the Solaris
		4609	10 port style backend. Its availability will be detected at runtime,
		4610	otherwise another method will be used as fallback. This is the preferred
		4611	backend for Solaris 10 systems.
		4612
		4613	=item EV_USE_DEVPOLL
		4614
		4615	Reserved for future expansion, works like the USE symbols above.
		4616
		4617	=item EV_USE_INOTIFY
		4618
		4619	If defined to be C<1>, libev will compile in support for the Linux inotify
		4620	interface to speed up C<ev_stat> watchers. Its actual availability will
		4621	be detected at runtime. If undefined, it will be enabled if the headers
		4622	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4623
		4624	=item EV_NO_SMP
		4625
		4626	If defined to be C<1>, libev will assume that memory is always coherent
		4627	between threads, that is, threads can be used, but threads never run on
		4628	different cpus (or different cpu cores). This reduces dependencies
		4629	and makes libev faster.
		4630
		4631	=item EV_NO_THREADS
		4632
		4633	If defined to be C<1>, libev will assume that it will never be called from
		4634	different threads (that includes signal handlers), which is a stronger
		4635	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4636	libev faster.
		4637
		4638	=item EV_ATOMIC_T
		4639
		4640	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4641	access is atomic with respect to other threads or signal contexts. No
		4642	such type is easily found in the C language, so you can provide your own
		4643	type that you know is safe for your purposes. It is used both for signal
		4644	handler "locking" as well as for signal and thread safety in C<ev_async>
		4645	watchers.
		4646
		4647	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4648	(from F<signal.h>), which is usually good enough on most platforms.
		4649
		4650	=item EV_H (h)
		4651
		4652	The name of the F<ev.h> header file used to include it. The default if
		4653	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4654	used to virtually rename the F<ev.h> header file in case of conflicts.
		4655
		4656	=item EV_CONFIG_H (h)
		4657
		4658	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4659	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4660	C<EV_H>, above.
		4661
		4662	=item EV_EVENT_H (h)
		4663
		4664	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4665	of how the F<event.h> header can be found, the default is C<"event.h">.
		4666
		4667	=item EV_PROTOTYPES (h)
		4668
		4669	If defined to be C<0>, then F<ev.h> will not define any function
		4670	prototypes, but still define all the structs and other symbols. This is
		4671	occasionally useful if you want to provide your own wrapper functions
		4672	around libev functions.
		4673
		4674	=item EV_MULTIPLICITY
		4675
		4676	If undefined or defined to C<1>, then all event-loop-specific functions
		4677	will have the C<struct ev_loop *> as first argument, and you can create
		4678	additional independent event loops. Otherwise there will be no support
		4679	for multiple event loops and there is no first event loop pointer
		4680	argument. Instead, all functions act on the single default loop.
		4681
		4682	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4683	default loop when multiplicity is switched off - you always have to
		4684	initialise the loop manually in this case.
		4685
		4686	=item EV_MINPRI
		4687
		4688	=item EV_MAXPRI
		4689
		4690	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4691	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4692	provide for more priorities by overriding those symbols (usually defined
		4693	to be C<-2> and C<2>, respectively).
		4694
		4695	When doing priority-based operations, libev usually has to linearly search
		4696	all the priorities, so having many of them (hundreds) uses a lot of space
		4697	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4698	fine.
		4699
		4700	If your embedding application does not need any priorities, defining these
		4701	both to C<0> will save some memory and CPU.
		4702
		4703	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4704	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4705	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4706
		4707	If undefined or defined to be C<1> (and the platform supports it), then
		4708	the respective watcher type is supported. If defined to be C<0>, then it
		4709	is not. Disabling watcher types mainly saves code size.
		4710
		4711	=item EV_FEATURES
		4712
		4713	If you need to shave off some kilobytes of code at the expense of some
		4714	speed (but with the full API), you can define this symbol to request
		4715	certain subsets of functionality. The default is to enable all features
		4716	that can be enabled on the platform.
		4717
		4718	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4719	with some broad features you want) and then selectively re-enable
		4720	additional parts you want, for example if you want everything minimal,
		4721	but multiple event loop support, async and child watchers and the poll
		4722	backend, use this:
		4723
		4724	#define EV_FEATURES 0
		4725	#define EV_MULTIPLICITY 1
		4726	#define EV_USE_POLL 1
		4727	#define EV_CHILD_ENABLE 1
		4728	#define EV_ASYNC_ENABLE 1
		4729
		4730	The actual value is a bitset, it can be a combination of the following
		4731	values (by default, all of these are enabled):
		4732
		4733	=over 4
		4734
		4735	=item C<1> - faster/larger code
		4736
		4737	Use larger code to speed up some operations.
		4738
		4739	Currently this is used to override some inlining decisions (enlarging the
		4740	code size by roughly 30% on amd64).
		4741
		4742	When optimising for size, use of compiler flags such as C<-Os> with
		4743	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4744	assertions.
		4745
		4746	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4747	(e.g. gcc with C<-Os>).
		4748
		4749	=item C<2> - faster/larger data structures
		4750
		4751	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4752	hash table sizes and so on. This will usually further increase code size
		4753	and can additionally have an effect on the size of data structures at
		4754	runtime.
		4755
		4756	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4757	(e.g. gcc with C<-Os>).
		4758
		4759	=item C<4> - full API configuration
		4760
		4761	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4762	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4763
		4764	=item C<8> - full API
		4765
		4766	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4767	details on which parts of the API are still available without this
		4768	feature, and do not complain if this subset changes over time.
		4769
		4770	=item C<16> - enable all optional watcher types
		4771
		4772	Enables all optional watcher types. If you want to selectively enable
		4773	only some watcher types other than I/O and timers (e.g. prepare,
		4774	embed, async, child...) you can enable them manually by defining
		4775	C<EV_watchertype_ENABLE> to C<1> instead.
		4776
		4777	=item C<32> - enable all backends
		4778
		4779	This enables all backends - without this feature, you need to enable at
		4780	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4781
		4782	=item C<64> - enable OS-specific "helper" APIs
		4783
		4784	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4785	default.
		4786
		4787	=back
		4788
		4789	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4790	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4791	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4792	watchers, timers and monotonic clock support.
		4793
		4794	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4795	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4796	your program might be left out as well - a binary starting a timer and an
		4797	I/O watcher then might come out at only 5Kb.
		4798
		4799	=item EV_API_STATIC
		4800
		4801	If this symbol is defined (by default it is not), then all identifiers
		4802	will have static linkage. This means that libev will not export any
		4803	identifiers, and you cannot link against libev anymore. This can be useful
		4804	when you embed libev, only want to use libev functions in a single file,
		4805	and do not want its identifiers to be visible.
		4806
		4807	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4808	wants to use libev.
		4809
		4810	This option only works when libev is compiled with a C compiler, as C++
		4811	doesn't support the required declaration syntax.
		4812
		4813	=item EV_AVOID_STDIO
		4814
		4815	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4816	functions (printf, scanf, perror etc.). This will increase the code size
		4817	somewhat, but if your program doesn't otherwise depend on stdio and your
		4818	libc allows it, this avoids linking in the stdio library which is quite
		4819	big.
		4820
		4821	Note that error messages might become less precise when this option is
		4822	enabled.
		4823
		4824	=item EV_NSIG
		4825
		4826	The highest supported signal number, +1 (or, the number of
		4827	signals): Normally, libev tries to deduce the maximum number of signals
		4828	automatically, but sometimes this fails, in which case it can be
		4829	specified. Also, using a lower number than detected (C<32> should be
		4830	good for about any system in existence) can save some memory, as libev
		4831	statically allocates some 12-24 bytes per signal number.
		4832
		4833	=item EV_PID_HASHSIZE
		4834
		4835	C<ev_child> watchers use a small hash table to distribute workload by
		4836	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4837	usually more than enough. If you need to manage thousands of children you
		4838	might want to increase this value (I<must> be a power of two).
		4839
		4840	=item EV_INOTIFY_HASHSIZE
		4841
		4842	C<ev_stat> watchers use a small hash table to distribute workload by
		4843	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4844	disabled), usually more than enough. If you need to manage thousands of
		4845	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4846	power of two).
		4847
		4848	=item EV_USE_4HEAP
		4849
		4850	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4851	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4852	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4853	faster performance with many (thousands) of watchers.
		4854
		4855	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4856	will be C<0>.
		4857
		4858	=item EV_HEAP_CACHE_AT
		4859
		4860	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4861	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4862	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4863	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4864	but avoids random read accesses on heap changes. This improves performance
		4865	noticeably with many (hundreds) of watchers.
		4866
		4867	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4868	will be C<0>.
		4869
		4870	=item EV_VERIFY
		4871
		4872	Controls how much internal verification (see C<ev_verify ()>) will
		4873	be done: If set to C<0>, no internal verification code will be compiled
		4874	in. If set to C<1>, then verification code will be compiled in, but not
		4875	called. If set to C<2>, then the internal verification code will be
		4876	called once per loop, which can slow down libev. If set to C<3>, then the
		4877	verification code will be called very frequently, which will slow down
		4878	libev considerably.
		4879
		4880	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4881	will be C<0>.
		4882
		4883	=item EV_COMMON
		4884
		4885	By default, all watchers have a C<void *data> member. By redefining
		4886	this macro to something else you can include more and other types of
		4887	members. You have to define it each time you include one of the files,
		4888	though, and it must be identical each time.
		4889
		4890	For example, the perl EV module uses something like this:
		4891
		4892	#define EV_COMMON \
		4893	SV *self; /* contains this struct */ \
		4894	SV *cb_sv, *fh /* note no trailing ";" */
		4895
		4896	=item EV_CB_DECLARE (type)
		4897
		4898	=item EV_CB_INVOKE (watcher, revents)
		4899
		4900	=item ev_set_cb (ev, cb)
		4901
		4902	Can be used to change the callback member declaration in each watcher,
		4903	and the way callbacks are invoked and set. Must expand to a struct member
		4904	definition and a statement, respectively. See the F<ev.h> header file for
		4905	their default definitions. One possible use for overriding these is to
		4906	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4907	method calls instead of plain function calls in C++.
		4908
		4909	=back
		4910
		4911	=head2 EXPORTED API SYMBOLS
		4912
		4913	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4914	exported symbols, you can use the provided F<Symbol.*> files which list
		4915	all public symbols, one per line:
		4916
		4917	Symbols.ev for libev proper
		4918	Symbols.event for the libevent emulation
		4919
		4920	This can also be used to rename all public symbols to avoid clashes with
		4921	multiple versions of libev linked together (which is obviously bad in
		4922	itself, but sometimes it is inconvenient to avoid this).
		4923
		4924	A sed command like this will create wrapper C<#define>'s that you need to
		4925	include before including F<ev.h>:
		4926
		4927	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4928
		4929	This would create a file F<wrap.h> which essentially looks like this:
		4930
		4931	#define ev_backend myprefix_ev_backend
		4932	#define ev_check_start myprefix_ev_check_start
		4933	#define ev_check_stop myprefix_ev_check_stop
		4934	...
		4935
		4936	=head2 EXAMPLES
		4937
		4938	For a real-world example of a program the includes libev
		4939	verbatim, you can have a look at the EV perl module
		4940	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4941	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4942	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4943	will be compiled. It is pretty complex because it provides its own header
		4944	file.
		4945
		4946	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4947	that everybody includes and which overrides some configure choices:
		4948
		4949	#define EV_FEATURES 8
		4950	#define EV_USE_SELECT 1
		4951	#define EV_PREPARE_ENABLE 1
		4952	#define EV_IDLE_ENABLE 1
		4953	#define EV_SIGNAL_ENABLE 1
		4954	#define EV_CHILD_ENABLE 1
		4955	#define EV_USE_STDEXCEPT 0
		4956	#define EV_CONFIG_H <config.h>
		4957
		4958	#include "ev++.h"
		4959
		4960	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4961
		4962	#include "ev_cpp.h"
		4963	#include "ev.c"
		4964
		4965	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		4966
		4967	=head2 THREADS AND COROUTINES
		4968
		4969	=head3 THREADS
		4970
		4971	All libev functions are reentrant and thread-safe unless explicitly
		4972	documented otherwise, but libev implements no locking itself. This means
		4973	that you can use as many loops as you want in parallel, as long as there
		4974	are no concurrent calls into any libev function with the same loop
		4975	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4976	of course): libev guarantees that different event loops share no data
		4977	structures that need any locking.
		4978
		4979	Or to put it differently: calls with different loop parameters can be done
		4980	concurrently from multiple threads, calls with the same loop parameter
		4981	must be done serially (but can be done from different threads, as long as
		4982	only one thread ever is inside a call at any point in time, e.g. by using
		4983	a mutex per loop).
		4984
		4985	Specifically to support threads (and signal handlers), libev implements
		4986	so-called C<ev_async> watchers, which allow some limited form of
		4987	concurrency on the same event loop, namely waking it up "from the
		4988	outside".
		4989
		4990	If you want to know which design (one loop, locking, or multiple loops
		4991	without or something else still) is best for your problem, then I cannot
		4992	help you, but here is some generic advice:
		4993
		4994	=over 4
		4995
		4996	=item * most applications have a main thread: use the default libev loop
		4997	in that thread, or create a separate thread running only the default loop.
		4998
		4999	This helps integrating other libraries or software modules that use libev
		5000	themselves and don't care/know about threading.
		5001
		5002	=item * one loop per thread is usually a good model.
		5003
		5004	Doing this is almost never wrong, sometimes a better-performance model
		5005	exists, but it is always a good start.
		5006
		5007	=item * other models exist, such as the leader/follower pattern, where one
		5008	loop is handed through multiple threads in a kind of round-robin fashion.
		5009
		5010	Choosing a model is hard - look around, learn, know that usually you can do
		5011	better than you currently do :-)
		5012
		5013	=item * often you need to talk to some other thread which blocks in the
		5014	event loop.
		5015
		5016	C<ev_async> watchers can be used to wake them up from other threads safely
		5017	(or from signal contexts...).
		5018
		5019	An example use would be to communicate signals or other events that only
		5020	work in the default loop by registering the signal watcher with the
		5021	default loop and triggering an C<ev_async> watcher from the default loop
		5022	watcher callback into the event loop interested in the signal.
		5023
		5024	=back
		5025
		5026	See also L</THREAD LOCKING EXAMPLE>.
		5027
		5028	=head3 COROUTINES
		5029
		5030	Libev is very accommodating to coroutines ("cooperative threads"):
		5031	libev fully supports nesting calls to its functions from different
		5032	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5033	different coroutines, and switch freely between both coroutines running
		5034	the loop, as long as you don't confuse yourself). The only exception is
		5035	that you must not do this from C<ev_periodic> reschedule callbacks.
		5036
		5037	Care has been taken to ensure that libev does not keep local state inside
		5038	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5039	they do not call any callbacks.
		5040
		5041	=head2 COMPILER WARNINGS
		5042
		5043	Depending on your compiler and compiler settings, you might get no or a
		5044	lot of warnings when compiling libev code. Some people are apparently
		5045	scared by this.
		5046
		5047	However, these are unavoidable for many reasons. For one, each compiler
		5048	has different warnings, and each user has different tastes regarding
		5049	warning options. "Warn-free" code therefore cannot be a goal except when
		5050	targeting a specific compiler and compiler-version.
		5051
		5052	Another reason is that some compiler warnings require elaborate
		5053	workarounds, or other changes to the code that make it less clear and less
		5054	maintainable.
		5055
		5056	And of course, some compiler warnings are just plain stupid, or simply
		5057	wrong (because they don't actually warn about the condition their message
		5058	seems to warn about). For example, certain older gcc versions had some
		5059	warnings that resulted in an extreme number of false positives. These have
		5060	been fixed, but some people still insist on making code warn-free with
		5061	such buggy versions.
		5062
		5063	While libev is written to generate as few warnings as possible,
		5064	"warn-free" code is not a goal, and it is recommended not to build libev
		5065	with any compiler warnings enabled unless you are prepared to cope with
		5066	them (e.g. by ignoring them). Remember that warnings are just that:
		5067	warnings, not errors, or proof of bugs.
		5068
		5069
		5070	=head2 VALGRIND
		5071
		5072	Valgrind has a special section here because it is a popular tool that is
		5073	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5074
		5075	If you think you found a bug (memory leak, uninitialised data access etc.)
		5076	in libev, then check twice: If valgrind reports something like:
		5077
		5078	==2274== definitely lost: 0 bytes in 0 blocks.
		5079	==2274== possibly lost: 0 bytes in 0 blocks.
		5080	==2274== still reachable: 256 bytes in 1 blocks.
		5081
		5082	Then there is no memory leak, just as memory accounted to global variables
		5083	is not a memleak - the memory is still being referenced, and didn't leak.
		5084
		5085	Similarly, under some circumstances, valgrind might report kernel bugs
		5086	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5087	although an acceptable workaround has been found here), or it might be
		5088	confused.
		5089
		5090	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5091	make it into some kind of religion.
		5092
		5093	If you are unsure about something, feel free to contact the mailing list
		5094	with the full valgrind report and an explanation on why you think this
		5095	is a bug in libev (best check the archives, too :). However, don't be
		5096	annoyed when you get a brisk "this is no bug" answer and take the chance
		5097	of learning how to interpret valgrind properly.
		5098
		5099	If you need, for some reason, empty reports from valgrind for your project
		5100	I suggest using suppression lists.
		5101
		5102
		5103	=head1 PORTABILITY NOTES
		5104
		5105	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5106
		5107	GNU/Linux is the only common platform that supports 64 bit file/large file
		5108	interfaces but I<disables> them by default.
		5109
		5110	That means that libev compiled in the default environment doesn't support
		5111	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5112
		5113	Unfortunately, many programs try to work around this GNU/Linux issue
		5114	by enabling the large file API, which makes them incompatible with the
		5115	standard libev compiled for their system.
		5116
		5117	Likewise, libev cannot enable the large file API itself as this would
		5118	suddenly make it incompatible to the default compile time environment,
		5119	i.e. all programs not using special compile switches.
		5120
		5121	=head2 OS/X AND DARWIN BUGS
		5122
		5123	The whole thing is a bug if you ask me - basically any system interface
		5124	you touch is broken, whether it is locales, poll, kqueue or even the
		5125	OpenGL drivers.
		5126
		5127	=head3 C<kqueue> is buggy
		5128
		5129	The kqueue syscall is broken in all known versions - most versions support
		5130	only sockets, many support pipes.
		5131
		5132	Libev tries to work around this by not using C<kqueue> by default on this
		5133	rotten platform, but of course you can still ask for it when creating a
		5134	loop - embedding a socket-only kqueue loop into a select-based one is
		5135	probably going to work well.
		5136
		5137	=head3 C<poll> is buggy
		5138
		5139	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5140	implementation by something calling C<kqueue> internally around the 10.5.6
		5141	release, so now C<kqueue> I<and> C<poll> are broken.
		5142
		5143	Libev tries to work around this by not using C<poll> by default on
		5144	this rotten platform, but of course you can still ask for it when creating
		5145	a loop.
		5146
		5147	=head3 C<select> is buggy
		5148
		5149	All that's left is C<select>, and of course Apple found a way to fuck this
		5150	one up as well: On OS/X, C<select> actively limits the number of file
		5151	descriptors you can pass in to 1024 - your program suddenly crashes when
		5152	you use more.
		5153
		5154	There is an undocumented "workaround" for this - defining
		5155	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5156	work on OS/X.
		5157
		5158	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5159
		5160	=head3 C<errno> reentrancy
		5161
		5162	The default compile environment on Solaris is unfortunately so
		5163	thread-unsafe that you can't even use components/libraries compiled
		5164	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5165	defined by default. A valid, if stupid, implementation choice.
		5166
		5167	If you want to use libev in threaded environments you have to make sure
		5168	it's compiled with C<_REENTRANT> defined.
		5169
		5170	=head3 Event port backend
		5171
		5172	The scalable event interface for Solaris is called "event
		5173	ports". Unfortunately, this mechanism is very buggy in all major
		5174	releases. If you run into high CPU usage, your program freezes or you get
		5175	a large number of spurious wakeups, make sure you have all the relevant
		5176	and latest kernel patches applied. No, I don't know which ones, but there
		5177	are multiple ones to apply, and afterwards, event ports actually work
		5178	great.
		5179
		5180	If you can't get it to work, you can try running the program by setting
		5181	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5182	C<select> backends.
		5183
		5184	=head2 AIX POLL BUG
		5185
		5186	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5187	this by trying to avoid the poll backend altogether (i.e. it's not even
		5188	compiled in), which normally isn't a big problem as C<select> works fine
		5189	with large bitsets on AIX, and AIX is dead anyway.
		5190
		5191	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5192
		5193	=head3 General issues
		5194
		5195	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5196	requires, and its I/O model is fundamentally incompatible with the POSIX
		5197	model. Libev still offers limited functionality on this platform in
		5198	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5199	descriptors. This only applies when using Win32 natively, not when using
		5200	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5201	as every compiler comes with a slightly differently broken/incompatible
		5202	environment.
		5203
		5204	Lifting these limitations would basically require the full
		5205	re-implementation of the I/O system. If you are into this kind of thing,
		5206	then note that glib does exactly that for you in a very portable way (note
		5207	also that glib is the slowest event library known to man).
		5208
		5209	There is no supported compilation method available on windows except
		5210	embedding it into other applications.
		5211
		5212	Sensible signal handling is officially unsupported by Microsoft - libev
		5213	tries its best, but under most conditions, signals will simply not work.
		5214
		5215	Not a libev limitation but worth mentioning: windows apparently doesn't
		5216	accept large writes: instead of resulting in a partial write, windows will
		5217	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5218	so make sure you only write small amounts into your sockets (less than a
		5219	megabyte seems safe, but this apparently depends on the amount of memory
		5220	available).
		5221
		5222	Due to the many, low, and arbitrary limits on the win32 platform and
		5223	the abysmal performance of winsockets, using a large number of sockets
		5224	is not recommended (and not reasonable). If your program needs to use
		5225	more than a hundred or so sockets, then likely it needs to use a totally
		5226	different implementation for windows, as libev offers the POSIX readiness
		5227	notification model, which cannot be implemented efficiently on windows
		5228	(due to Microsoft monopoly games).
		5229
		5230	A typical way to use libev under windows is to embed it (see the embedding
		5231	section for details) and use the following F<evwrap.h> header file instead
		5232	of F<ev.h>:
		5233
		5234	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5235	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5236
		5237	#include "ev.h"
		5238
		5239	And compile the following F<evwrap.c> file into your project (make sure
		5240	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5241
		5242	#include "evwrap.h"
		5243	#include "ev.c"
		5244
		5245	=head3 The winsocket C<select> function
		5246
		5247	The winsocket C<select> function doesn't follow POSIX in that it
		5248	requires socket I<handles> and not socket I<file descriptors> (it is
		5249	also extremely buggy). This makes select very inefficient, and also
		5250	requires a mapping from file descriptors to socket handles (the Microsoft
		5251	C runtime provides the function C<_open_osfhandle> for this). See the
		5252	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5253	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5254
		5255	The configuration for a "naked" win32 using the Microsoft runtime
		5256	libraries and raw winsocket select is:
		5257
		5258	#define EV_USE_SELECT 1
		5259	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5260
		5261	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5262	complexity in the O(n²) range when using win32.
		5263
		5264	=head3 Limited number of file descriptors
		5265
		5266	Windows has numerous arbitrary (and low) limits on things.
		5267
		5268	Early versions of winsocket's select only supported waiting for a maximum
		5269	of C<64> handles (probably owning to the fact that all windows kernels
		5270	can only wait for C<64> things at the same time internally; Microsoft
		5271	recommends spawning a chain of threads and wait for 63 handles and the
		5272	previous thread in each. Sounds great!).
		5273
		5274	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5275	to some high number (e.g. C<2048>) before compiling the winsocket select
		5276	call (which might be in libev or elsewhere, for example, perl and many
		5277	other interpreters do their own select emulation on windows).
		5278
		5279	Another limit is the number of file descriptors in the Microsoft runtime
		5280	libraries, which by default is C<64> (there must be a hidden I<64>
		5281	fetish or something like this inside Microsoft). You can increase this
		5282	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5283	(another arbitrary limit), but is broken in many versions of the Microsoft
		5284	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5285	(depending on windows version and/or the phase of the moon). To get more,
		5286	you need to wrap all I/O functions and provide your own fd management, but
		5287	the cost of calling select (O(n²)) will likely make this unworkable.
		5288
		5289	=head2 PORTABILITY REQUIREMENTS
		5290
		5291	In addition to a working ISO-C implementation and of course the
		5292	backend-specific APIs, libev relies on a few additional extensions:
		5293
		5294	=over 4
		5295
		5296	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5297	calling conventions regardless of C<ev_watcher_type *>.
		5298
		5299	Libev assumes not only that all watcher pointers have the same internal
		5300	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5301	assumes that the same (machine) code can be used to call any watcher
		5302	callback: The watcher callbacks have different type signatures, but libev
		5303	calls them using an C<ev_watcher *> internally.
		5304
		5305	=item pointer accesses must be thread-atomic
		5306
		5307	Accessing a pointer value must be atomic, it must both be readable and
		5308	writable in one piece - this is the case on all current architectures.
		5309
		5310	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5311
		5312	The type C<sig_atomic_t volatile> (or whatever is defined as
		5313	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5314	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5315	believed to be sufficiently portable.
		5316
		5317	=item C<sigprocmask> must work in a threaded environment
		5318
		5319	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5320	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5321	pthread implementations will either allow C<sigprocmask> in the "main
		5322	thread" or will block signals process-wide, both behaviours would
		5323	be compatible with libev. Interaction between C<sigprocmask> and
		5324	C<pthread_sigmask> could complicate things, however.
		5325
		5326	The most portable way to handle signals is to block signals in all threads
		5327	except the initial one, and run the signal handling loop in the initial
		5328	thread as well.
		5329
		5330	=item C<long> must be large enough for common memory allocation sizes
		5331
		5332	To improve portability and simplify its API, libev uses C<long> internally
		5333	instead of C<size_t> when allocating its data structures. On non-POSIX
		5334	systems (Microsoft...) this might be unexpectedly low, but is still at
		5335	least 31 bits everywhere, which is enough for hundreds of millions of
		5336	watchers.
		5337
		5338	=item C<double> must hold a time value in seconds with enough accuracy
		5339
		5340	The type C<double> is used to represent timestamps. It is required to
		5341	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5342	good enough for at least into the year 4000 with millisecond accuracy
		5343	(the design goal for libev). This requirement is overfulfilled by
		5344	implementations using IEEE 754, which is basically all existing ones.
		5345
		5346	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5347	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5348	is either obsolete or somebody patched it to use C<long double> or
		5349	something like that, just kidding).
		5350
		5351	=back
		5352
		5353	If you know of other additional requirements drop me a note.
		5354
		5355
		5356	=head1 ALGORITHMIC COMPLEXITIES
		5357
		5358	In this section the complexities of (many of) the algorithms used inside
		5359	libev will be documented. For complexity discussions about backends see
		5360	the documentation for C<ev_default_init>.
		5361
		5362	All of the following are about amortised time: If an array needs to be
		5363	extended, libev needs to realloc and move the whole array, but this
		5364	happens asymptotically rarer with higher number of elements, so O(1) might
		5365	mean that libev does a lengthy realloc operation in rare cases, but on
		5366	average it is much faster and asymptotically approaches constant time.
		5367
		5368	=over 4
		5369
		5370	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5371
		5372	This means that, when you have a watcher that triggers in one hour and
		5373	there are 100 watchers that would trigger before that, then inserting will
		5374	have to skip roughly seven (C<ld 100>) of these watchers.
		5375
		5376	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5377
		5378	That means that changing a timer costs less than removing/adding them,
		5379	as only the relative motion in the event queue has to be paid for.
		5380
		5381	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5382
		5383	These just add the watcher into an array or at the head of a list.
		5384
		5385	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5386
		5387	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5388
		5389	These watchers are stored in lists, so they need to be walked to find the
		5390	correct watcher to remove. The lists are usually short (you don't usually
		5391	have many watchers waiting for the same fd or signal: one is typical, two
		5392	is rare).
		5393
		5394	=item Finding the next timer in each loop iteration: O(1)
		5395
		5396	By virtue of using a binary or 4-heap, the next timer is always found at a
		5397	fixed position in the storage array.
		5398
		5399	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5400
		5401	A change means an I/O watcher gets started or stopped, which requires
		5402	libev to recalculate its status (and possibly tell the kernel, depending
		5403	on backend and whether C<ev_io_set> was used).
		5404
		5405	=item Activating one watcher (putting it into the pending state): O(1)
		5406
		5407	=item Priority handling: O(number_of_priorities)
		5408
		5409	Priorities are implemented by allocating some space for each
		5410	priority. When doing priority-based operations, libev usually has to
		5411	linearly search all the priorities, but starting/stopping and activating
		5412	watchers becomes O(1) with respect to priority handling.
		5413
		5414	=item Sending an ev_async: O(1)
		5415
		5416	=item Processing ev_async_send: O(number_of_async_watchers)
		5417
		5418	=item Processing signals: O(max_signal_number)
		5419
		5420	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5421	calls in the current loop iteration and the loop is currently
		5422	blocked. Checking for async and signal events involves iterating over all
		5423	running async watchers or all signal numbers.
		5424
		5425	=back
		5426
		5427
		5428	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5429
		5430	The major version 4 introduced some incompatible changes to the API.
		5431
		5432	At the moment, the C<ev.h> header file provides compatibility definitions
		5433	for all changes, so most programs should still compile. The compatibility
		5434	layer might be removed in later versions of libev, so better update to the
		5435	new API early than late.
		5436
		5437	=over 4
		5438
		5439	=item C<EV_COMPAT3> backwards compatibility mechanism
		5440
		5441	The backward compatibility mechanism can be controlled by
		5442	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5443	section.
		5444
		5445	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5446
		5447	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5448
		5449	ev_loop_destroy (EV_DEFAULT_UC);
		5450	ev_loop_fork (EV_DEFAULT);
		5451
		5452	=item function/symbol renames
		5453
		5454	A number of functions and symbols have been renamed:
		5455
		5456	ev_loop => ev_run
		5457	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5458	EVLOOP_ONESHOT => EVRUN_ONCE
		5459
		5460	ev_unloop => ev_break
		5461	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5462	EVUNLOOP_ONE => EVBREAK_ONE
		5463	EVUNLOOP_ALL => EVBREAK_ALL
		5464
		5465	EV_TIMEOUT => EV_TIMER
		5466
		5467	ev_loop_count => ev_iteration
		5468	ev_loop_depth => ev_depth
		5469	ev_loop_verify => ev_verify
		5470
		5471	Most functions working on C<struct ev_loop> objects don't have an
		5472	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5473	associated constants have been renamed to not collide with the C<struct
		5474	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5475	as all other watcher types. Note that C<ev_loop_fork> is still called
		5476	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5477	typedef.
		5478
		5479	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5480
		5481	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5482	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5483	and work, but the library code will of course be larger.
		5484
		5485	=back
		5486
		5487
		5488	=head1 GLOSSARY
		5489
		5490	=over 4
		5491
		5492	=item active
		5493
		5494	A watcher is active as long as it has been started and not yet stopped.
		5495	See L</WATCHER STATES> for details.
		5496
		5497	=item application
		5498
		5499	In this document, an application is whatever is using libev.
		5500
		5501	=item backend
		5502
		5503	The part of the code dealing with the operating system interfaces.
		5504
		5505	=item callback
		5506
		5507	The address of a function that is called when some event has been
		5508	detected. Callbacks are being passed the event loop, the watcher that
		5509	received the event, and the actual event bitset.
		5510
		5511	=item callback/watcher invocation
		5512
		5513	The act of calling the callback associated with a watcher.
		5514
		5515	=item event
		5516
		5517	A change of state of some external event, such as data now being available
		5518	for reading on a file descriptor, time having passed or simply not having
		5519	any other events happening anymore.
		5520
		5521	In libev, events are represented as single bits (such as C<EV_READ> or
		5522	C<EV_TIMER>).
		5523
		5524	=item event library
		5525
		5526	A software package implementing an event model and loop.
		5527
		5528	=item event loop
		5529
		5530	An entity that handles and processes external events and converts them
		5531	into callback invocations.
		5532
		5533	=item event model
		5534
		5535	The model used to describe how an event loop handles and processes
		5536	watchers and events.
		5537
		5538	=item pending
		5539
		5540	A watcher is pending as soon as the corresponding event has been
		5541	detected. See L</WATCHER STATES> for details.
		5542
		5543	=item real time
		5544
		5545	The physical time that is observed. It is apparently strictly monotonic :)
		5546
		5547	=item wall-clock time
		5548
		5549	The time and date as shown on clocks. Unlike real time, it can actually
		5550	be wrong and jump forwards and backwards, e.g. when you adjust your
		5551	clock.
		5552
		5553	=item watcher
		5554
		5555	A data structure that describes interest in certain events. Watchers need
		5556	to be started (attached to an event loop) before they can receive events.
		5557
		5558	=back
		5559
742	=head1 AUTHOR	5560	=head1 AUTHOR
743		5561
744	Marc Lehmann <libev@schmorp.de>.	5562	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5563	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
745		5564

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