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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 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.
18		102
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).	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>).
31		121
		122	It also is quite fast (see this
		123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
		124	for example).
		125
32	=head1 CONVENTIONS	126	=head2 CONVENTIONS
33		127
34	Libev is very configurable. In this manual the default configuration	128	Libev is very configurable. In this manual the default (and most common)
35	will be described, which supports multiple event loops. For more info	129	configuration will be described, which supports multiple event loops. For
36	about various configuraiton options please have a look at the file	130	more info about various configuration options please have a look at
37	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
38	support for multiple event loops, then all functions taking an initial	132	for multiple event loops, then all functions taking an initial argument of
39	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
40	will not have this argument.	134	this argument.
41		135
42	=head1 TIME AND OTHER GLOBAL FUNCTIONS	136	=head2 TIME REPRESENTATION
43		137
44	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
45	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
46	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
47	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
48	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.
49		173
50	=over 4	174	=over 4
51		175
52	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
53		177
54	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 >>).
55		194
56	=item int ev_version_major ()	195	=item int ev_version_major ()
57		196
58	=item int ev_version_minor ()	197	=item int ev_version_minor ()
59		198
60	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
61	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
62	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
63	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
64	version of the library your program was compiled against.	203	version of the library your program was compiled against.
65		204
		205	These version numbers refer to the ABI version of the library, not the
		206	release version.
		207
66	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,
67	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
68	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
69	not a problem.	211	not a problem.
70		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
71	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
72		255
73	Sets the allocation function to use (the prototype is similar to the	256	Sets the allocation function to use (the prototype is similar - the
74	realloc function). It is used to allocate and free memory (no surprises	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
75	here). If it returns zero when memory needs to be allocated, the library	258	used to allocate and free memory (no surprises here). If it returns zero
		259	when memory needs to be allocated (C<size != 0>), the library might abort
76	might abort or take some potentially destructive action. The default is	260	or take some potentially destructive action.
77	your system realloc function.	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.
78		265
79	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
80	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,
81	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.
82		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
83	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
84		291
85	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
86	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
87	indicating the system call or subsystem causing the problem. If this	294	indicating the system call or subsystem causing the problem. If this
88	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
89	matter what, when it returns. That is, libev will geenrally retry the	296	matter what, when it returns. That is, libev will generally retry the
90	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
91	(such as abort).	298	(such as abort).
92		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
93	=back	325	=back
94		326
95	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
96		328
97	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
98	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
99	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
100		332
101	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
102	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
103	create, you also create another event loop. Libev itself does no lockign	335	do not.
104	whatsoever, so if you mix calls to different event loops, make sure you
105	lock (this is usually a bad idea, though, even if done right).
106		336
107	=over 4	337	=over 4
108		338
109	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
110		340
111	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
112	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
113	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
114	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".
115		351
116	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
117	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.
118		384
119	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
120	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>).
121		387
122	It supports the following flags:	388	The following flags are supported:
123		389
124	=over 4	390	=over 4
125		391
126	=item EVFLAG_AUTO	392	=item C<EVFLAG_AUTO>
127		393
128	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
129	thing, believe me).	395	thing, believe me).
130		396
131	=item EVFLAG_NOENV	397	=item C<EVFLAG_NOENV>
132		398
133	If this flag bit is ored into the flag value then libev will I<not> look	399	If this flag bit is or'ed into the flag value (or the program runs setuid
134	at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this	400	or setgid) then libev will I<not> look at the environment variable
135	environment variable will override the flags completely. This is useful	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
		402	override the flags completely if it is found in the environment. This is
136	to try out specific backends to tets their performance, or to work around	403	useful to try out specific backends to test their performance, to work
137	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).
138		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) when you use this
		422	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
139	=item EVMETHOD_SELECT portable select backend	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
140		463
141	=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.
142		469
143	=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.
144		476
145	=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).
146		480
147	=item EVMETHOD_DEVPOLL solaris 8 only	481	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
148		482
149	=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.
150		489
151	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
152	backends will be tried (in the reverse order as given here). If one are	491	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
153	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).
154		643
155	=back	644	=back
156		645
157	=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.
158		650
159	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.
160	always distinct from the default loop. Unlike the default loop, it cannot
161	handle signal and child watchers, and attempts to do so will be greeted by
162	undefined behaviour (or a failed assertion if assertions are enabled).
163		652
164	=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");
165		656
166	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
167	etc.). This stops all registered event watchers (by not touching them in	658	used if available.
168	any way whatsoever, although you cnanot rely on this :).	659
		660	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
169		661
170	=item ev_loop_destroy (loop)	662	=item ev_loop_destroy (loop)
171		663
172	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
173	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).
174		671
175	=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.
176		675
177	This function reinitialises the kernel state for backends that have	676	This function is normally used on loop objects allocated by
178	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
179	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.
180	again makes little sense).
181		679
182	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
183	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.
184	have to call it.	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
185		683	and C<ev_loop_destroy>.
186	The function itself is quite fast and its usually not a problem to call
187	it just in case after a fork. To make this easy, the function will fit in
188	quite nicely into a call to C<pthread_atfork>:
189
190	pthread_atfork (0, 0, ev_default_fork);
191		684
192	=item ev_loop_fork (loop)	685	=item ev_loop_fork (loop)
193		686
194	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 to
195	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	688	reinitialise the kernel state for backends that have one. Despite the
196	after fork, and how you do this is entirely your own problem.	689	name, you can call it anytime, but it makes most sense after forking, in
		690	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
		691	child before resuming or calling C<ev_run>.
197		692
		693	Again, you I<have> to call it on I<any> loop that you want to re-use after
		694	a fork, I<even if you do not plan to use the loop in the parent>. This is
		695	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		696	during fork.
		697
		698	On the other hand, you only need to call this function in the child
		699	process if and only if you want to use the event loop in the child. If
		700	you just fork+exec or create a new loop in the child, you don't have to
		701	call it at all (in fact, C<epoll> is so badly broken that it makes a
		702	difference, but libev will usually detect this case on its own and do a
		703	costly reset of the backend).
		704
		705	The function itself is quite fast and it's usually not a problem to call
		706	it just in case after a fork.
		707
		708	Example: Automate calling C<ev_loop_fork> on the default loop when
		709	using pthreads.
		710
		711	static void
		712	post_fork_child (void)
		713	{
		714	ev_loop_fork (EV_DEFAULT);
		715	}
		716
		717	...
		718	pthread_atfork (0, 0, post_fork_child);
		719
		720	=item int ev_is_default_loop (loop)
		721
		722	Returns true when the given loop is, in fact, the default loop, and false
		723	otherwise.
		724
		725	=item unsigned int ev_iteration (loop)
		726
		727	Returns the current iteration count for the event loop, which is identical
		728	to the number of times libev did poll for new events. It starts at C<0>
		729	and happily wraps around with enough iterations.
		730
		731	This value can sometimes be useful as a generation counter of sorts (it
		732	"ticks" the number of loop iterations), as it roughly corresponds with
		733	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		734	prepare and check phases.
		735
198	=item unsigned int ev_method (loop)	736	=item unsigned int ev_depth (loop)
199		737
		738	Returns the number of times C<ev_run> was entered minus the number of
		739	times C<ev_run> was exited normally, in other words, the recursion depth.
		740
		741	Outside C<ev_run>, this number is zero. In a callback, this number is
		742	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		743	in which case it is higher.
		744
		745	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		746	throwing an exception etc.), doesn't count as "exit" - consider this
		747	as a hint to avoid such ungentleman-like behaviour unless it's really
		748	convenient, in which case it is fully supported.
		749
		750	=item unsigned int ev_backend (loop)
		751
200	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	752	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
201	use.	753	use.
202		754
203	=item ev_tstamp = ev_now (loop)	755	=item ev_tstamp ev_now (loop)
204		756
205	Returns the current "event loop time", which is the time the event loop	757	Returns the current "event loop time", which is the time the event loop
206	got events and started processing them. This timestamp does not change	758	received events and started processing them. This timestamp does not
207	as long as callbacks are being processed, and this is also the base time	759	change as long as callbacks are being processed, and this is also the base
208	used for relative timers. You can treat it as the timestamp of the event	760	time used for relative timers. You can treat it as the timestamp of the
209	occuring (or more correctly, the mainloop finding out about it).	761	event occurring (or more correctly, libev finding out about it).
210		762
		763	=item ev_now_update (loop)
		764
		765	Establishes the current time by querying the kernel, updating the time
		766	returned by C<ev_now ()> in the progress. This is a costly operation and
		767	is usually done automatically within C<ev_run ()>.
		768
		769	This function is rarely useful, but when some event callback runs for a
		770	very long time without entering the event loop, updating libev's idea of
		771	the current time is a good idea.
		772
		773	See also L</The special problem of time updates> in the C<ev_timer> section.
		774
		775	=item ev_suspend (loop)
		776
		777	=item ev_resume (loop)
		778
		779	These two functions suspend and resume an event loop, for use when the
		780	loop is not used for a while and timeouts should not be processed.
		781
		782	A typical use case would be an interactive program such as a game: When
		783	the user presses C<^Z> to suspend the game and resumes it an hour later it
		784	would be best to handle timeouts as if no time had actually passed while
		785	the program was suspended. This can be achieved by calling C<ev_suspend>
		786	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		787	C<ev_resume> directly afterwards to resume timer processing.
		788
		789	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		790	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		791	will be rescheduled (that is, they will lose any events that would have
		792	occurred while suspended).
		793
		794	After calling C<ev_suspend> you B<must not> call I<any> function on the
		795	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		796	without a previous call to C<ev_suspend>.
		797
		798	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		799	event loop time (see C<ev_now_update>).
		800
211	=item ev_loop (loop, int flags)	801	=item bool ev_run (loop, int flags)
212		802
213	Finally, this is it, the event handler. This function usually is called	803	Finally, this is it, the event handler. This function usually is called
214	after you initialised all your watchers and you want to start handling	804	after you have initialised all your watchers and you want to start
215	events.	805	handling events. It will ask the operating system for any new events, call
		806	the watcher callbacks, and then repeat the whole process indefinitely: This
		807	is why event loops are called I<loops>.
216		808
217	If the flags argument is specified as 0, it will not return until either	809	If the flags argument is specified as C<0>, it will keep handling events
218	no event watchers are active anymore or C<ev_unloop> was called.	810	until either no event watchers are active anymore or C<ev_break> was
		811	called.
219		812
		813	The return value is false if there are no more active watchers (which
		814	usually means "all jobs done" or "deadlock"), and true in all other cases
		815	(which usually means " you should call C<ev_run> again").
		816
		817	Please note that an explicit C<ev_break> is usually better than
		818	relying on all watchers to be stopped when deciding when a program has
		819	finished (especially in interactive programs), but having a program
		820	that automatically loops as long as it has to and no longer by virtue
		821	of relying on its watchers stopping correctly, that is truly a thing of
		822	beauty.
		823
		824	This function is I<mostly> exception-safe - you can break out of a
		825	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		826	exception and so on. This does not decrement the C<ev_depth> value, nor
		827	will it clear any outstanding C<EVBREAK_ONE> breaks.
		828
220	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	829	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
221	those events and any outstanding ones, but will not block your process in	830	those events and any already outstanding ones, but will not wait and
222	case there are no events.	831	block your process in case there are no events and will return after one
		832	iteration of the loop. This is sometimes useful to poll and handle new
		833	events while doing lengthy calculations, to keep the program responsive.
223		834
224	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	835	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
225	neccessary) and will handle those and any outstanding ones. It will block	836	necessary) and will handle those and any already outstanding ones. It
226	your process until at least one new event arrives.	837	will block your process until at least one new event arrives (which could
		838	be an event internal to libev itself, so there is no guarantee that a
		839	user-registered callback will be called), and will return after one
		840	iteration of the loop.
227		841
228	This flags value could be used to implement alternative looping	842	This is useful if you are waiting for some external event in conjunction
229	constructs, but the C<prepare> and C<check> watchers provide a better and	843	with something not expressible using other libev watchers (i.e. "roll your
230	more generic mechanism.	844	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		845	usually a better approach for this kind of thing.
231		846
		847	Here are the gory details of what C<ev_run> does (this is for your
		848	understanding, not a guarantee that things will work exactly like this in
		849	future versions):
		850
		851	- Increment loop depth.
		852	- Reset the ev_break status.
		853	- Before the first iteration, call any pending watchers.
		854	LOOP:
		855	- If EVFLAG_FORKCHECK was used, check for a fork.
		856	- If a fork was detected (by any means), queue and call all fork watchers.
		857	- Queue and call all prepare watchers.
		858	- If ev_break was called, goto FINISH.
		859	- If we have been forked, detach and recreate the kernel state
		860	as to not disturb the other process.
		861	- Update the kernel state with all outstanding changes.
		862	- Update the "event loop time" (ev_now ()).
		863	- Calculate for how long to sleep or block, if at all
		864	(active idle watchers, EVRUN_NOWAIT or not having
		865	any active watchers at all will result in not sleeping).
		866	- Sleep if the I/O and timer collect interval say so.
		867	- Increment loop iteration counter.
		868	- Block the process, waiting for any events.
		869	- Queue all outstanding I/O (fd) events.
		870	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		871	- Queue all expired timers.
		872	- Queue all expired periodics.
		873	- Queue all idle watchers with priority higher than that of pending events.
		874	- Queue all check watchers.
		875	- Call all queued watchers in reverse order (i.e. check watchers first).
		876	Signals and child watchers are implemented as I/O watchers, and will
		877	be handled here by queueing them when their watcher gets executed.
		878	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		879	were used, or there are no active watchers, goto FINISH, otherwise
		880	continue with step LOOP.
		881	FINISH:
		882	- Reset the ev_break status iff it was EVBREAK_ONE.
		883	- Decrement the loop depth.
		884	- Return.
		885
		886	Example: Queue some jobs and then loop until no events are outstanding
		887	anymore.
		888
		889	... queue jobs here, make sure they register event watchers as long
		890	... as they still have work to do (even an idle watcher will do..)
		891	ev_run (my_loop, 0);
		892	... jobs done or somebody called break. yeah!
		893
232	=item ev_unloop (loop, how)	894	=item ev_break (loop, how)
233		895
234	Can be used to make a call to C<ev_loop> return early. The C<how> argument	896	Can be used to make a call to C<ev_run> return early (but only after it
235	must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>	897	has processed all outstanding events). The C<how> argument must be either
236	call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>	898	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
237	calls return.	899	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		900
		901	This "break state" will be cleared on the next call to C<ev_run>.
		902
		903	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		904	which case it will have no effect.
238		905
239	=item ev_ref (loop)	906	=item ev_ref (loop)
240		907
241	=item ev_unref (loop)	908	=item ev_unref (loop)
242		909
243	Ref/unref can be used to add or remove a refcount on the event loop: Every	910	Ref/unref can be used to add or remove a reference count on the event
244	watcher keeps one reference. If you have a long-runing watcher you never	911	loop: Every watcher keeps one reference, and as long as the reference
245	unregister that should not keep ev_loop from running, ev_unref() after	912	count is nonzero, C<ev_run> will not return on its own.
246	starting, and ev_ref() before stopping it. Libev itself uses this for	913
247	example for its internal signal pipe: It is not visible to you as a user	914	This is useful when you have a watcher that you never intend to
248	and should not keep C<ev_loop> from exiting if the work is done. It is	915	unregister, but that nevertheless should not keep C<ev_run> from
		916	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		917	before stopping it.
		918
		919	As an example, libev itself uses this for its internal signal pipe: It
		920	is not visible to the libev user and should not keep C<ev_run> from
		921	exiting if no event watchers registered by it are active. It is also an
249	also an excellent way to do this for generic recurring timers or from	922	excellent way to do this for generic recurring timers or from within
250	within third-party libraries. Just remember to unref after start and ref	923	third-party libraries. Just remember to I<unref after start> and I<ref
251	before stop.	924	before stop> (but only if the watcher wasn't active before, or was active
		925	before, respectively. Note also that libev might stop watchers itself
		926	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		927	in the callback).
		928
		929	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		930	running when nothing else is active.
		931
		932	ev_signal exitsig;
		933	ev_signal_init (&exitsig, sig_cb, SIGINT);
		934	ev_signal_start (loop, &exitsig);
		935	ev_unref (loop);
		936
		937	Example: For some weird reason, unregister the above signal handler again.
		938
		939	ev_ref (loop);
		940	ev_signal_stop (loop, &exitsig);
		941
		942	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		943
		944	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		945
		946	These advanced functions influence the time that libev will spend waiting
		947	for events. Both time intervals are by default C<0>, meaning that libev
		948	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		949	latency.
		950
		951	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		952	allows libev to delay invocation of I/O and timer/periodic callbacks
		953	to increase efficiency of loop iterations (or to increase power-saving
		954	opportunities).
		955
		956	The idea is that sometimes your program runs just fast enough to handle
		957	one (or very few) event(s) per loop iteration. While this makes the
		958	program responsive, it also wastes a lot of CPU time to poll for new
		959	events, especially with backends like C<select ()> which have a high
		960	overhead for the actual polling but can deliver many events at once.
		961
		962	By setting a higher I<io collect interval> you allow libev to spend more
		963	time collecting I/O events, so you can handle more events per iteration,
		964	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		965	C<ev_timer>) will not be affected. Setting this to a non-null value will
		966	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		967	sleep time ensures that libev will not poll for I/O events more often then
		968	once per this interval, on average (as long as the host time resolution is
		969	good enough).
		970
		971	Likewise, by setting a higher I<timeout collect interval> you allow libev
		972	to spend more time collecting timeouts, at the expense of increased
		973	latency/jitter/inexactness (the watcher callback will be called
		974	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		975	value will not introduce any overhead in libev.
		976
		977	Many (busy) programs can usually benefit by setting the I/O collect
		978	interval to a value near C<0.1> or so, which is often enough for
		979	interactive servers (of course not for games), likewise for timeouts. It
		980	usually doesn't make much sense to set it to a lower value than C<0.01>,
		981	as this approaches the timing granularity of most systems. Note that if
		982	you do transactions with the outside world and you can't increase the
		983	parallelity, then this setting will limit your transaction rate (if you
		984	need to poll once per transaction and the I/O collect interval is 0.01,
		985	then you can't do more than 100 transactions per second).
		986
		987	Setting the I<timeout collect interval> can improve the opportunity for
		988	saving power, as the program will "bundle" timer callback invocations that
		989	are "near" in time together, by delaying some, thus reducing the number of
		990	times the process sleeps and wakes up again. Another useful technique to
		991	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		992	they fire on, say, one-second boundaries only.
		993
		994	Example: we only need 0.1s timeout granularity, and we wish not to poll
		995	more often than 100 times per second:
		996
		997	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		998	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		999
		1000	=item ev_invoke_pending (loop)
		1001
		1002	This call will simply invoke all pending watchers while resetting their
		1003	pending state. Normally, C<ev_run> does this automatically when required,
		1004	but when overriding the invoke callback this call comes handy. This
		1005	function can be invoked from a watcher - this can be useful for example
		1006	when you want to do some lengthy calculation and want to pass further
		1007	event handling to another thread (you still have to make sure only one
		1008	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1009
		1010	=item int ev_pending_count (loop)
		1011
		1012	Returns the number of pending watchers - zero indicates that no watchers
		1013	are pending.
		1014
		1015	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1016
		1017	This overrides the invoke pending functionality of the loop: Instead of
		1018	invoking all pending watchers when there are any, C<ev_run> will call
		1019	this callback instead. This is useful, for example, when you want to
		1020	invoke the actual watchers inside another context (another thread etc.).
		1021
		1022	If you want to reset the callback, use C<ev_invoke_pending> as new
		1023	callback.
		1024
		1025	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1026
		1027	Sometimes you want to share the same loop between multiple threads. This
		1028	can be done relatively simply by putting mutex_lock/unlock calls around
		1029	each call to a libev function.
		1030
		1031	However, C<ev_run> can run an indefinite time, so it is not feasible
		1032	to wait for it to return. One way around this is to wake up the event
		1033	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1034	I<release> and I<acquire> callbacks on the loop.
		1035
		1036	When set, then C<release> will be called just before the thread is
		1037	suspended waiting for new events, and C<acquire> is called just
		1038	afterwards.
		1039
		1040	Ideally, C<release> will just call your mutex_unlock function, and
		1041	C<acquire> will just call the mutex_lock function again.
		1042
		1043	While event loop modifications are allowed between invocations of
		1044	C<release> and C<acquire> (that's their only purpose after all), no
		1045	modifications done will affect the event loop, i.e. adding watchers will
		1046	have no effect on the set of file descriptors being watched, or the time
		1047	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1048	to take note of any changes you made.
		1049
		1050	In theory, threads executing C<ev_run> will be async-cancel safe between
		1051	invocations of C<release> and C<acquire>.
		1052
		1053	See also the locking example in the C<THREADS> section later in this
		1054	document.
		1055
		1056	=item ev_set_userdata (loop, void *data)
		1057
		1058	=item void *ev_userdata (loop)
		1059
		1060	Set and retrieve a single C<void *> associated with a loop. When
		1061	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1062	C<0>.
		1063
		1064	These two functions can be used to associate arbitrary data with a loop,
		1065	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1066	C<acquire> callbacks described above, but of course can be (ab-)used for
		1067	any other purpose as well.
		1068
		1069	=item ev_verify (loop)
		1070
		1071	This function only does something when C<EV_VERIFY> support has been
		1072	compiled in, which is the default for non-minimal builds. It tries to go
		1073	through all internal structures and checks them for validity. If anything
		1074	is found to be inconsistent, it will print an error message to standard
		1075	error and call C<abort ()>.
		1076
		1077	This can be used to catch bugs inside libev itself: under normal
		1078	circumstances, this function will never abort as of course libev keeps its
		1079	data structures consistent.
252		1080
253	=back	1081	=back
254		1082
		1083
255	=head1 ANATOMY OF A WATCHER	1084	=head1 ANATOMY OF A WATCHER
256		1085
		1086	In the following description, uppercase C<TYPE> in names stands for the
		1087	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1088	watchers and C<ev_io_start> for I/O watchers.
		1089
257	A watcher is a structure that you create and register to record your	1090	A watcher is an opaque structure that you allocate and register to record
258	interest in some event. For instance, if you want to wait for STDIN to	1091	your interest in some event. To make a concrete example, imagine you want
259	become readable, you would create an ev_io watcher for that:	1092	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1093	for that:
260		1094
261	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1095	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
262	{	1096	{
263	ev_io_stop (w);	1097	ev_io_stop (w);
264	ev_unloop (loop, EVUNLOOP_ALL);	1098	ev_break (loop, EVBREAK_ALL);
265	}	1099	}
266		1100
267	struct ev_loop *loop = ev_default_loop (0);	1101	struct ev_loop *loop = ev_default_loop (0);
		1102
268	struct ev_io stdin_watcher;	1103	ev_io stdin_watcher;
		1104
269	ev_init (&stdin_watcher, my_cb);	1105	ev_init (&stdin_watcher, my_cb);
270	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1106	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
271	ev_io_start (loop, &stdin_watcher);	1107	ev_io_start (loop, &stdin_watcher);
		1108
272	ev_loop (loop, 0);	1109	ev_run (loop, 0);
273		1110
274	As you can see, you are responsible for allocating the memory for your	1111	As you can see, you are responsible for allocating the memory for your
275	watcher structures (and it is usually a bad idea to do this on the stack,	1112	watcher structures (and it is I<usually> a bad idea to do this on the
276	although this can sometimes be quite valid).	1113	stack).
277		1114
		1115	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1116	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1117
278	Each watcher structure must be initialised by a call to C<ev_init	1118	Each watcher structure must be initialised by a call to C<ev_init (watcher
279	(watcher *, callback)>, which expects a callback to be provided. This	1119	*, callback)>, which expects a callback to be provided. This callback is
280	callback gets invoked each time the event occurs (or, in the case of io	1120	invoked each time the event occurs (or, in the case of I/O watchers, each
281	watchers, each time the event loop detects that the file descriptor given	1121	time the event loop detects that the file descriptor given is readable
282	is readable and/or writable).	1122	and/or writable).
283		1123
284	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1124	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
285	with arguments specific to this watcher type. There is also a macro	1125	macro to configure it, with arguments specific to the watcher type. There
286	to combine initialisation and setting in one call: C<< ev_<type>_init	1126	is also a macro to combine initialisation and setting in one call: C<<
287	(watcher *, callback, ...) >>.	1127	ev_TYPE_init (watcher *, callback, ...) >>.
288		1128
289	To make the watcher actually watch out for events, you have to start it	1129	To make the watcher actually watch out for events, you have to start it
290	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1130	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
291	*) >>), and you can stop watching for events at any time by calling the	1131	*) >>), and you can stop watching for events at any time by calling the
292	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1132	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
293		1133
294	As long as your watcher is active (has been started but not stopped) you	1134	As long as your watcher is active (has been started but not stopped) you
295	must not touch the values stored in it. Most specifically you must never	1135	must not touch the values stored in it. Most specifically you must never
296	reinitialise it or call its set method.	1136	reinitialise it or call its C<ev_TYPE_set> macro.
297
298	You cna check wether an event is active by calling the C<ev_is_active
299	(watcher *)> macro. To see wether an event is outstanding (but the
300	callback for it has not been called yet) you cna use the C<ev_is_pending
301	(watcher *)> macro.
302		1137
303	Each and every callback receives the event loop pointer as first, the	1138	Each and every callback receives the event loop pointer as first, the
304	registered watcher structure as second, and a bitset of received events as	1139	registered watcher structure as second, and a bitset of received events as
305	third argument.	1140	third argument.
306		1141
307	The rceeived events usually include a single bit per event type received	1142	The received events usually include a single bit per event type received
308	(you can receive multiple events at the same time). The possible bit masks	1143	(you can receive multiple events at the same time). The possible bit masks
309	are:	1144	are:
310		1145
311	=over 4	1146	=over 4
312		1147
313	=item EV_READ	1148	=item C<EV_READ>
314		1149
315	=item EV_WRITE	1150	=item C<EV_WRITE>
316		1151
317	The file descriptor in the ev_io watcher has become readable and/or	1152	The file descriptor in the C<ev_io> watcher has become readable and/or
318	writable.	1153	writable.
319		1154
320	=item EV_TIMEOUT	1155	=item C<EV_TIMER>
321		1156
322	The ev_timer watcher has timed out.	1157	The C<ev_timer> watcher has timed out.
323		1158
324	=item EV_PERIODIC	1159	=item C<EV_PERIODIC>
325		1160
326	The ev_periodic watcher has timed out.	1161	The C<ev_periodic> watcher has timed out.
327		1162
328	=item EV_SIGNAL	1163	=item C<EV_SIGNAL>
329		1164
330	The signal specified in the ev_signal watcher has been received by a thread.	1165	The signal specified in the C<ev_signal> watcher has been received by a thread.
331		1166
332	=item EV_CHILD	1167	=item C<EV_CHILD>
333		1168
334	The pid specified in the ev_child watcher has received a status change.	1169	The pid specified in the C<ev_child> watcher has received a status change.
335		1170
		1171	=item C<EV_STAT>
		1172
		1173	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1174
336	=item EV_IDLE	1175	=item C<EV_IDLE>
337		1176
338	The ev_idle watcher has determined that you have nothing better to do.	1177	The C<ev_idle> watcher has determined that you have nothing better to do.
339		1178
340	=item EV_PREPARE	1179	=item C<EV_PREPARE>
341		1180
342	=item EV_CHECK	1181	=item C<EV_CHECK>
343		1182
344	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	1183	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
345	to gather new events, and all ev_check watchers are invoked just after	1184	gather new events, and all C<ev_check> watchers are queued (not invoked)
346	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1185	just after C<ev_run> has gathered them, but before it queues any callbacks
		1186	for any received events. That means C<ev_prepare> watchers are the last
		1187	watchers invoked before the event loop sleeps or polls for new events, and
		1188	C<ev_check> watchers will be invoked before any other watchers of the same
		1189	or lower priority within an event loop iteration.
		1190
347	received events. Callbacks of both watcher types can start and stop as	1191	Callbacks of both watcher types can start and stop as many watchers as
348	many watchers as they want, and all of them will be taken into account	1192	they want, and all of them will be taken into account (for example, a
349	(for example, a ev_prepare watcher might start an idle watcher to keep	1193	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
350	C<ev_loop> from blocking).	1194	blocking).
351		1195
		1196	=item C<EV_EMBED>
		1197
		1198	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1199
		1200	=item C<EV_FORK>
		1201
		1202	The event loop has been resumed in the child process after fork (see
		1203	C<ev_fork>).
		1204
		1205	=item C<EV_CLEANUP>
		1206
		1207	The event loop is about to be destroyed (see C<ev_cleanup>).
		1208
		1209	=item C<EV_ASYNC>
		1210
		1211	The given async watcher has been asynchronously notified (see C<ev_async>).
		1212
		1213	=item C<EV_CUSTOM>
		1214
		1215	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1216	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1217
352	=item EV_ERROR	1218	=item C<EV_ERROR>
353		1219
354	An unspecified error has occured, the watcher has been stopped. This might	1220	An unspecified error has occurred, the watcher has been stopped. This might
355	happen because the watcher could not be properly started because libev	1221	happen because the watcher could not be properly started because libev
356	ran out of memory, a file descriptor was found to be closed or any other	1222	ran out of memory, a file descriptor was found to be closed or any other
		1223	problem. Libev considers these application bugs.
		1224
357	problem. You best act on it by reporting the problem and somehow coping	1225	You best act on it by reporting the problem and somehow coping with the
358	with the watcher being stopped.	1226	watcher being stopped. Note that well-written programs should not receive
		1227	an error ever, so when your watcher receives it, this usually indicates a
		1228	bug in your program.
359		1229
360	Libev will usually signal a few "dummy" events together with an error,	1230	Libev will usually signal a few "dummy" events together with an error, for
361	for example it might indicate that a fd is readable or writable, and if	1231	example it might indicate that a fd is readable or writable, and if your
362	your callbacks is well-written it can just attempt the operation and cope	1232	callbacks is well-written it can just attempt the operation and cope with
363	with the error from read() or write(). This will not work in multithreaded	1233	the error from read() or write(). This will not work in multi-threaded
364	programs, though, so beware.	1234	programs, though, as the fd could already be closed and reused for another
		1235	thing, so beware.
365		1236
366	=back	1237	=back
367		1238
368	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1239	=head2 GENERIC WATCHER FUNCTIONS
369		1240
370	Each watcher has, by default, a member C<void *data> that you can change	1241	=over 4
371	and read at any time, libev will completely ignore it. This cna be used
372	to associate arbitrary data with your watcher. If you need more data and
373	don't want to allocate memory and store a pointer to it in that data
374	member, you can also "subclass" the watcher type and provide your own
375	data:
376		1242
377	struct my_io	1243	=item C<ev_init> (ev_TYPE *watcher, callback)
		1244
		1245	This macro initialises the generic portion of a watcher. The contents
		1246	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1247	the generic parts of the watcher are initialised, you I<need> to call
		1248	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1249	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1250	which rolls both calls into one.
		1251
		1252	You can reinitialise a watcher at any time as long as it has been stopped
		1253	(or never started) and there are no pending events outstanding.
		1254
		1255	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1256	int revents)>.
		1257
		1258	Example: Initialise an C<ev_io> watcher in two steps.
		1259
		1260	ev_io w;
		1261	ev_init (&w, my_cb);
		1262	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1263
		1264	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1265
		1266	This macro initialises the type-specific parts of a watcher. You need to
		1267	call C<ev_init> at least once before you call this macro, but you can
		1268	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1269	macro on a watcher that is active (it can be pending, however, which is a
		1270	difference to the C<ev_init> macro).
		1271
		1272	Although some watcher types do not have type-specific arguments
		1273	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1274
		1275	See C<ev_init>, above, for an example.
		1276
		1277	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1278
		1279	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1280	calls into a single call. This is the most convenient method to initialise
		1281	a watcher. The same limitations apply, of course.
		1282
		1283	Example: Initialise and set an C<ev_io> watcher in one step.
		1284
		1285	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1286
		1287	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1288
		1289	Starts (activates) the given watcher. Only active watchers will receive
		1290	events. If the watcher is already active nothing will happen.
		1291
		1292	Example: Start the C<ev_io> watcher that is being abused as example in this
		1293	whole section.
		1294
		1295	ev_io_start (EV_DEFAULT_UC, &w);
		1296
		1297	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1298
		1299	Stops the given watcher if active, and clears the pending status (whether
		1300	the watcher was active or not).
		1301
		1302	It is possible that stopped watchers are pending - for example,
		1303	non-repeating timers are being stopped when they become pending - but
		1304	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1305	pending. If you want to free or reuse the memory used by the watcher it is
		1306	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1307
		1308	=item bool ev_is_active (ev_TYPE *watcher)
		1309
		1310	Returns a true value iff the watcher is active (i.e. it has been started
		1311	and not yet been stopped). As long as a watcher is active you must not modify
		1312	it.
		1313
		1314	=item bool ev_is_pending (ev_TYPE *watcher)
		1315
		1316	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1317	events but its callback has not yet been invoked). As long as a watcher
		1318	is pending (but not active) you must not call an init function on it (but
		1319	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1320	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1321	it).
		1322
		1323	=item callback ev_cb (ev_TYPE *watcher)
		1324
		1325	Returns the callback currently set on the watcher.
		1326
		1327	=item ev_set_cb (ev_TYPE *watcher, callback)
		1328
		1329	Change the callback. You can change the callback at virtually any time
		1330	(modulo threads).
		1331
		1332	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1333
		1334	=item int ev_priority (ev_TYPE *watcher)
		1335
		1336	Set and query the priority of the watcher. The priority is a small
		1337	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1338	(default: C<-2>). Pending watchers with higher priority will be invoked
		1339	before watchers with lower priority, but priority will not keep watchers
		1340	from being executed (except for C<ev_idle> watchers).
		1341
		1342	If you need to suppress invocation when higher priority events are pending
		1343	you need to look at C<ev_idle> watchers, which provide this functionality.
		1344
		1345	You I<must not> change the priority of a watcher as long as it is active or
		1346	pending.
		1347
		1348	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1349	fine, as long as you do not mind that the priority value you query might
		1350	or might not have been clamped to the valid range.
		1351
		1352	The default priority used by watchers when no priority has been set is
		1353	always C<0>, which is supposed to not be too high and not be too low :).
		1354
		1355	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1356	priorities.
		1357
		1358	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1359
		1360	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1361	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1362	can deal with that fact, as both are simply passed through to the
		1363	callback.
		1364
		1365	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1366
		1367	If the watcher is pending, this function clears its pending status and
		1368	returns its C<revents> bitset (as if its callback was invoked). If the
		1369	watcher isn't pending it does nothing and returns C<0>.
		1370
		1371	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1372	callback to be invoked, which can be accomplished with this function.
		1373
		1374	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1375
		1376	Feeds the given event set into the event loop, as if the specified event
		1377	had happened for the specified watcher (which must be a pointer to an
		1378	initialised but not necessarily started event watcher). Obviously you must
		1379	not free the watcher as long as it has pending events.
		1380
		1381	Stopping the watcher, letting libev invoke it, or calling
		1382	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1383	not started in the first place.
		1384
		1385	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1386	functions that do not need a watcher.
		1387
		1388	=back
		1389
		1390	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1391	OWN COMPOSITE WATCHERS> idioms.
		1392
		1393	=head2 WATCHER STATES
		1394
		1395	There are various watcher states mentioned throughout this manual -
		1396	active, pending and so on. In this section these states and the rules to
		1397	transition between them will be described in more detail - and while these
		1398	rules might look complicated, they usually do "the right thing".
		1399
		1400	=over 4
		1401
		1402	=item initialised
		1403
		1404	Before a watcher can be registered with the event loop it has to be
		1405	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1406	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1407
		1408	In this state it is simply some block of memory that is suitable for
		1409	use in an event loop. It can be moved around, freed, reused etc. at
		1410	will - as long as you either keep the memory contents intact, or call
		1411	C<ev_TYPE_init> again.
		1412
		1413	=item started/running/active
		1414
		1415	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1416	property of the event loop, and is actively waiting for events. While in
		1417	this state it cannot be accessed (except in a few documented ways), moved,
		1418	freed or anything else - the only legal thing is to keep a pointer to it,
		1419	and call libev functions on it that are documented to work on active watchers.
		1420
		1421	=item pending
		1422
		1423	If a watcher is active and libev determines that an event it is interested
		1424	in has occurred (such as a timer expiring), it will become pending. It will
		1425	stay in this pending state until either it is stopped or its callback is
		1426	about to be invoked, so it is not normally pending inside the watcher
		1427	callback.
		1428
		1429	The watcher might or might not be active while it is pending (for example,
		1430	an expired non-repeating timer can be pending but no longer active). If it
		1431	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1432	but it is still property of the event loop at this time, so cannot be
		1433	moved, freed or reused. And if it is active the rules described in the
		1434	previous item still apply.
		1435
		1436	It is also possible to feed an event on a watcher that is not active (e.g.
		1437	via C<ev_feed_event>), in which case it becomes pending without being
		1438	active.
		1439
		1440	=item stopped
		1441
		1442	A watcher can be stopped implicitly by libev (in which case it might still
		1443	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1444	latter will clear any pending state the watcher might be in, regardless
		1445	of whether it was active or not, so stopping a watcher explicitly before
		1446	freeing it is often a good idea.
		1447
		1448	While stopped (and not pending) the watcher is essentially in the
		1449	initialised state, that is, it can be reused, moved, modified in any way
		1450	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1451	it again).
		1452
		1453	=back
		1454
		1455	=head2 WATCHER PRIORITY MODELS
		1456
		1457	Many event loops support I<watcher priorities>, which are usually small
		1458	integers that influence the ordering of event callback invocation
		1459	between watchers in some way, all else being equal.
		1460
		1461	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1462	description for the more technical details such as the actual priority
		1463	range.
		1464
		1465	There are two common ways how these these priorities are being interpreted
		1466	by event loops:
		1467
		1468	In the more common lock-out model, higher priorities "lock out" invocation
		1469	of lower priority watchers, which means as long as higher priority
		1470	watchers receive events, lower priority watchers are not being invoked.
		1471
		1472	The less common only-for-ordering model uses priorities solely to order
		1473	callback invocation within a single event loop iteration: Higher priority
		1474	watchers are invoked before lower priority ones, but they all get invoked
		1475	before polling for new events.
		1476
		1477	Libev uses the second (only-for-ordering) model for all its watchers
		1478	except for idle watchers (which use the lock-out model).
		1479
		1480	The rationale behind this is that implementing the lock-out model for
		1481	watchers is not well supported by most kernel interfaces, and most event
		1482	libraries will just poll for the same events again and again as long as
		1483	their callbacks have not been executed, which is very inefficient in the
		1484	common case of one high-priority watcher locking out a mass of lower
		1485	priority ones.
		1486
		1487	Static (ordering) priorities are most useful when you have two or more
		1488	watchers handling the same resource: a typical usage example is having an
		1489	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1490	timeouts. Under load, data might be received while the program handles
		1491	other jobs, but since timers normally get invoked first, the timeout
		1492	handler will be executed before checking for data. In that case, giving
		1493	the timer a lower priority than the I/O watcher ensures that I/O will be
		1494	handled first even under adverse conditions (which is usually, but not
		1495	always, what you want).
		1496
		1497	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1498	will only be executed when no same or higher priority watchers have
		1499	received events, they can be used to implement the "lock-out" model when
		1500	required.
		1501
		1502	For example, to emulate how many other event libraries handle priorities,
		1503	you can associate an C<ev_idle> watcher to each such watcher, and in
		1504	the normal watcher callback, you just start the idle watcher. The real
		1505	processing is done in the idle watcher callback. This causes libev to
		1506	continuously poll and process kernel event data for the watcher, but when
		1507	the lock-out case is known to be rare (which in turn is rare :), this is
		1508	workable.
		1509
		1510	Usually, however, the lock-out model implemented that way will perform
		1511	miserably under the type of load it was designed to handle. In that case,
		1512	it might be preferable to stop the real watcher before starting the
		1513	idle watcher, so the kernel will not have to process the event in case
		1514	the actual processing will be delayed for considerable time.
		1515
		1516	Here is an example of an I/O watcher that should run at a strictly lower
		1517	priority than the default, and which should only process data when no
		1518	other events are pending:
		1519
		1520	ev_idle idle; // actual processing watcher
		1521	ev_io io; // actual event watcher
		1522
		1523	static void
		1524	io_cb (EV_P_ ev_io *w, int revents)
378	{	1525	{
379	struct ev_io io;	1526	// stop the I/O watcher, we received the event, but
380	int otherfd;	1527	// are not yet ready to handle it.
381	void *somedata;	1528	ev_io_stop (EV_A_ w);
382	struct whatever *mostinteresting;	1529
		1530	// start the idle watcher to handle the actual event.
		1531	// it will not be executed as long as other watchers
		1532	// with the default priority are receiving events.
		1533	ev_idle_start (EV_A_ &idle);
383	}	1534	}
384		1535
385	And since your callback will be called with a pointer to the watcher, you	1536	static void
386	can cast it back to your own type:	1537	idle_cb (EV_P_ ev_idle *w, int revents)
387
388	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
389	{	1538	{
390	struct my_io *w = (struct my_io *)w_;	1539	// actual processing
391	...	1540	read (STDIN_FILENO, ...);
		1541
		1542	// have to start the I/O watcher again, as
		1543	// we have handled the event
		1544	ev_io_start (EV_P_ &io);
392	}	1545	}
393		1546
394	More interesting and less C-conformant ways of catsing your callback type	1547	// initialisation
395	have been omitted....	1548	ev_idle_init (&idle, idle_cb);
		1549	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1550	ev_io_start (EV_DEFAULT_ &io);
		1551
		1552	In the "real" world, it might also be beneficial to start a timer, so that
		1553	low-priority connections can not be locked out forever under load. This
		1554	enables your program to keep a lower latency for important connections
		1555	during short periods of high load, while not completely locking out less
		1556	important ones.
396		1557
397		1558
398	=head1 WATCHER TYPES	1559	=head1 WATCHER TYPES
399		1560
400	This section describes each watcher in detail, but will not repeat	1561	This section describes each watcher in detail, but will not repeat
401	information given in the last section.	1562	information given in the last section. Any initialisation/set macros,
		1563	functions and members specific to the watcher type are explained.
402		1564
		1565	Members are additionally marked with either I<[read-only]>, meaning that,
		1566	while the watcher is active, you can look at the member and expect some
		1567	sensible content, but you must not modify it (you can modify it while the
		1568	watcher is stopped to your hearts content), or I<[read-write]>, which
		1569	means you can expect it to have some sensible content while the watcher
		1570	is active, but you can also modify it. Modifying it may not do something
		1571	sensible or take immediate effect (or do anything at all), but libev will
		1572	not crash or malfunction in any way.
		1573
		1574
403	=head2 struct ev_io - is my file descriptor readable or writable	1575	=head2 C<ev_io> - is this file descriptor readable or writable?
404		1576
405	I/O watchers check wether a file descriptor is readable or writable	1577	I/O watchers check whether a file descriptor is readable or writable
406	in each iteration of the event loop (This behaviour is called	1578	in each iteration of the event loop, or, more precisely, when reading
407	level-triggering because you keep receiving events as long as the	1579	would not block the process and writing would at least be able to write
408	condition persists. Remember you cna stop the watcher if you don't want to	1580	some data. This behaviour is called level-triggering because you keep
409	act on the event and neither want to receive future events).	1581	receiving events as long as the condition persists. Remember you can stop
		1582	the watcher if you don't want to act on the event and neither want to
		1583	receive future events.
		1584
		1585	In general you can register as many read and/or write event watchers per
		1586	fd as you want (as long as you don't confuse yourself). Setting all file
		1587	descriptors to non-blocking mode is also usually a good idea (but not
		1588	required if you know what you are doing).
		1589
		1590	Another thing you have to watch out for is that it is quite easy to
		1591	receive "spurious" readiness notifications, that is, your callback might
		1592	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1593	because there is no data. It is very easy to get into this situation even
		1594	with a relatively standard program structure. Thus it is best to always
		1595	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
		1596	preferable to a program hanging until some data arrives.
		1597
		1598	If you cannot run the fd in non-blocking mode (for example you should
		1599	not play around with an Xlib connection), then you have to separately
		1600	re-test whether a file descriptor is really ready with a known-to-be good
		1601	interface such as poll (fortunately in the case of Xlib, it already does
		1602	this on its own, so its quite safe to use). Some people additionally
		1603	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1604	indefinitely.
		1605
		1606	But really, best use non-blocking mode.
		1607
		1608	=head3 The special problem of disappearing file descriptors
		1609
		1610	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1611	descriptor (either due to calling C<close> explicitly or any other means,
		1612	such as C<dup2>). The reason is that you register interest in some file
		1613	descriptor, but when it goes away, the operating system will silently drop
		1614	this interest. If another file descriptor with the same number then is
		1615	registered with libev, there is no efficient way to see that this is, in
		1616	fact, a different file descriptor.
		1617
		1618	To avoid having to explicitly tell libev about such cases, libev follows
		1619	the following policy: Each time C<ev_io_set> is being called, libev
		1620	will assume that this is potentially a new file descriptor, otherwise
		1621	it is assumed that the file descriptor stays the same. That means that
		1622	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1623	descriptor even if the file descriptor number itself did not change.
		1624
		1625	This is how one would do it normally anyway, the important point is that
		1626	the libev application should not optimise around libev but should leave
		1627	optimisations to libev.
		1628
		1629	=head3 The special problem of dup'ed file descriptors
		1630
		1631	Some backends (e.g. epoll), cannot register events for file descriptors,
		1632	but only events for the underlying file descriptions. That means when you
		1633	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1634	events for them, only one file descriptor might actually receive events.
		1635
		1636	There is no workaround possible except not registering events
		1637	for potentially C<dup ()>'ed file descriptors, or to resort to
		1638	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1639
		1640	=head3 The special problem of files
		1641
		1642	Many people try to use C<select> (or libev) on file descriptors
		1643	representing files, and expect it to become ready when their program
		1644	doesn't block on disk accesses (which can take a long time on their own).
		1645
		1646	However, this cannot ever work in the "expected" way - you get a readiness
		1647	notification as soon as the kernel knows whether and how much data is
		1648	there, and in the case of open files, that's always the case, so you
		1649	always get a readiness notification instantly, and your read (or possibly
		1650	write) will still block on the disk I/O.
		1651
		1652	Another way to view it is that in the case of sockets, pipes, character
		1653	devices and so on, there is another party (the sender) that delivers data
		1654	on its own, but in the case of files, there is no such thing: the disk
		1655	will not send data on its own, simply because it doesn't know what you
		1656	wish to read - you would first have to request some data.
		1657
		1658	Since files are typically not-so-well supported by advanced notification
		1659	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1660	to files, even though you should not use it. The reason for this is
		1661	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1662	usually a tty, often a pipe, but also sometimes files or special devices
		1663	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1664	F</dev/urandom>), and even though the file might better be served with
		1665	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1666	it "just works" instead of freezing.
		1667
		1668	So avoid file descriptors pointing to files when you know it (e.g. use
		1669	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1670	when you rarely read from a file instead of from a socket, and want to
		1671	reuse the same code path.
		1672
		1673	=head3 The special problem of fork
		1674
		1675	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1676	useless behaviour. Libev fully supports fork, but needs to be told about
		1677	it in the child if you want to continue to use it in the child.
		1678
		1679	To support fork in your child processes, you have to call C<ev_loop_fork
		1680	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1681	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1682
		1683	=head3 The special problem of SIGPIPE
		1684
		1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1686	when writing to a pipe whose other end has been closed, your program gets
		1687	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1688	this is sensible behaviour, for daemons, this is usually undesirable.
		1689
		1690	So when you encounter spurious, unexplained daemon exits, make sure you
		1691	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1692	somewhere, as that would have given you a big clue).
		1693
		1694	=head3 The special problem of accept()ing when you can't
		1695
		1696	Many implementations of the POSIX C<accept> function (for example,
		1697	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1698	connection from the pending queue in all error cases.
		1699
		1700	For example, larger servers often run out of file descriptors (because
		1701	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1702	rejecting the connection, leading to libev signalling readiness on
		1703	the next iteration again (the connection still exists after all), and
		1704	typically causing the program to loop at 100% CPU usage.
		1705
		1706	Unfortunately, the set of errors that cause this issue differs between
		1707	operating systems, there is usually little the app can do to remedy the
		1708	situation, and no known thread-safe method of removing the connection to
		1709	cope with overload is known (to me).
		1710
		1711	One of the easiest ways to handle this situation is to just ignore it
		1712	- when the program encounters an overload, it will just loop until the
		1713	situation is over. While this is a form of busy waiting, no OS offers an
		1714	event-based way to handle this situation, so it's the best one can do.
		1715
		1716	A better way to handle the situation is to log any errors other than
		1717	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1718	messages, and continue as usual, which at least gives the user an idea of
		1719	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1720	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1721	usage.
		1722
		1723	If your program is single-threaded, then you could also keep a dummy file
		1724	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1725	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1726	close that fd, and create a new dummy fd. This will gracefully refuse
		1727	clients under typical overload conditions.
		1728
		1729	The last way to handle it is to simply log the error and C<exit>, as
		1730	is often done with C<malloc> failures, but this results in an easy
		1731	opportunity for a DoS attack.
		1732
		1733	=head3 Watcher-Specific Functions
410		1734
411	=over 4	1735	=over 4
412		1736
413	=item ev_io_init (ev_io *, callback, int fd, int events)	1737	=item ev_io_init (ev_io *, callback, int fd, int events)
414		1738
415	=item ev_io_set (ev_io *, int fd, int events)	1739	=item ev_io_set (ev_io *, int fd, int events)
416		1740
417	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1741	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
418	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1742	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
419	EV_WRITE> to receive the given events.	1743	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1744
		1745	=item int fd [read-only]
		1746
		1747	The file descriptor being watched.
		1748
		1749	=item int events [read-only]
		1750
		1751	The events being watched.
420		1752
421	=back	1753	=back
422		1754
		1755	=head3 Examples
		1756
		1757	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1758	readable, but only once. Since it is likely line-buffered, you could
		1759	attempt to read a whole line in the callback.
		1760
		1761	static void
		1762	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1763	{
		1764	ev_io_stop (loop, w);
		1765	.. read from stdin here (or from w->fd) and handle any I/O errors
		1766	}
		1767
		1768	...
		1769	struct ev_loop *loop = ev_default_init (0);
		1770	ev_io stdin_readable;
		1771	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1772	ev_io_start (loop, &stdin_readable);
		1773	ev_run (loop, 0);
		1774
		1775
423	=head2 struct ev_timer - relative and optionally recurring timeouts	1776	=head2 C<ev_timer> - relative and optionally repeating timeouts
424		1777
425	Timer watchers are simple relative timers that generate an event after a	1778	Timer watchers are simple relative timers that generate an event after a
426	given time, and optionally repeating in regular intervals after that.	1779	given time, and optionally repeating in regular intervals after that.
427		1780
428	The timers are based on real time, that is, if you register an event that	1781	The timers are based on real time, that is, if you register an event that
429	times out after an hour and youreset your system clock to last years	1782	times out after an hour and you reset your system clock to January last
430	time, it will still time out after (roughly) and hour. "Roughly" because	1783	year, it will still time out after (roughly) one hour. "Roughly" because
431	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1784	detecting time jumps is hard, and some inaccuracies are unavoidable (the
432	monotonic clock option helps a lot here).	1785	monotonic clock option helps a lot here).
433		1786
		1787	The callback is guaranteed to be invoked only I<after> its timeout has
		1788	passed (not I<at>, so on systems with very low-resolution clocks this
		1789	might introduce a small delay, see "the special problem of being too
		1790	early", below). If multiple timers become ready during the same loop
		1791	iteration then the ones with earlier time-out values are invoked before
		1792	ones of the same priority with later time-out values (but this is no
		1793	longer true when a callback calls C<ev_run> recursively).
		1794
		1795	=head3 Be smart about timeouts
		1796
		1797	Many real-world problems involve some kind of timeout, usually for error
		1798	recovery. A typical example is an HTTP request - if the other side hangs,
		1799	you want to raise some error after a while.
		1800
		1801	What follows are some ways to handle this problem, from obvious and
		1802	inefficient to smart and efficient.
		1803
		1804	In the following, a 60 second activity timeout is assumed - a timeout that
		1805	gets reset to 60 seconds each time there is activity (e.g. each time some
		1806	data or other life sign was received).
		1807
434	=over 4	1808	=over 4
435		1809
		1810	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1811
		1812	This is the most obvious, but not the most simple way: In the beginning,
		1813	start the watcher:
		1814
		1815	ev_timer_init (timer, callback, 60., 0.);
		1816	ev_timer_start (loop, timer);
		1817
		1818	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1819	and start it again:
		1820
		1821	ev_timer_stop (loop, timer);
		1822	ev_timer_set (timer, 60., 0.);
		1823	ev_timer_start (loop, timer);
		1824
		1825	This is relatively simple to implement, but means that each time there is
		1826	some activity, libev will first have to remove the timer from its internal
		1827	data structure and then add it again. Libev tries to be fast, but it's
		1828	still not a constant-time operation.
		1829
		1830	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1831
		1832	This is the easiest way, and involves using C<ev_timer_again> instead of
		1833	C<ev_timer_start>.
		1834
		1835	To implement this, configure an C<ev_timer> with a C<repeat> value
		1836	of C<60> and then call C<ev_timer_again> at start and each time you
		1837	successfully read or write some data. If you go into an idle state where
		1838	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1839	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1840
		1841	That means you can ignore both the C<ev_timer_start> function and the
		1842	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1843	member and C<ev_timer_again>.
		1844
		1845	At start:
		1846
		1847	ev_init (timer, callback);
		1848	timer->repeat = 60.;
		1849	ev_timer_again (loop, timer);
		1850
		1851	Each time there is some activity:
		1852
		1853	ev_timer_again (loop, timer);
		1854
		1855	It is even possible to change the time-out on the fly, regardless of
		1856	whether the watcher is active or not:
		1857
		1858	timer->repeat = 30.;
		1859	ev_timer_again (loop, timer);
		1860
		1861	This is slightly more efficient then stopping/starting the timer each time
		1862	you want to modify its timeout value, as libev does not have to completely
		1863	remove and re-insert the timer from/into its internal data structure.
		1864
		1865	It is, however, even simpler than the "obvious" way to do it.
		1866
		1867	=item 3. Let the timer time out, but then re-arm it as required.
		1868
		1869	This method is more tricky, but usually most efficient: Most timeouts are
		1870	relatively long compared to the intervals between other activity - in
		1871	our example, within 60 seconds, there are usually many I/O events with
		1872	associated activity resets.
		1873
		1874	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1875	but remember the time of last activity, and check for a real timeout only
		1876	within the callback:
		1877
		1878	ev_tstamp timeout = 60.;
		1879	ev_tstamp last_activity; // time of last activity
		1880	ev_timer timer;
		1881
		1882	static void
		1883	callback (EV_P_ ev_timer *w, int revents)
		1884	{
		1885	// calculate when the timeout would happen
		1886	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1887
		1888	// if negative, it means we the timeout already occurred
		1889	if (after < 0.)
		1890	{
		1891	// timeout occurred, take action
		1892	}
		1893	else
		1894	{
		1895	// callback was invoked, but there was some recent
		1896	// activity. simply restart the timer to time out
		1897	// after "after" seconds, which is the earliest time
		1898	// the timeout can occur.
		1899	ev_timer_set (w, after, 0.);
		1900	ev_timer_start (EV_A_ w);
		1901	}
		1902	}
		1903
		1904	To summarise the callback: first calculate in how many seconds the
		1905	timeout will occur (by calculating the absolute time when it would occur,
		1906	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1907	(EV_A)> from that).
		1908
		1909	If this value is negative, then we are already past the timeout, i.e. we
		1910	timed out, and need to do whatever is needed in this case.
		1911
		1912	Otherwise, we now the earliest time at which the timeout would trigger,
		1913	and simply start the timer with this timeout value.
		1914
		1915	In other words, each time the callback is invoked it will check whether
		1916	the timeout occurred. If not, it will simply reschedule itself to check
		1917	again at the earliest time it could time out. Rinse. Repeat.
		1918
		1919	This scheme causes more callback invocations (about one every 60 seconds
		1920	minus half the average time between activity), but virtually no calls to
		1921	libev to change the timeout.
		1922
		1923	To start the machinery, simply initialise the watcher and set
		1924	C<last_activity> to the current time (meaning there was some activity just
		1925	now), then call the callback, which will "do the right thing" and start
		1926	the timer:
		1927
		1928	last_activity = ev_now (EV_A);
		1929	ev_init (&timer, callback);
		1930	callback (EV_A_ &timer, 0);
		1931
		1932	When there is some activity, simply store the current time in
		1933	C<last_activity>, no libev calls at all:
		1934
		1935	if (activity detected)
		1936	last_activity = ev_now (EV_A);
		1937
		1938	When your timeout value changes, then the timeout can be changed by simply
		1939	providing a new value, stopping the timer and calling the callback, which
		1940	will again do the right thing (for example, time out immediately :).
		1941
		1942	timeout = new_value;
		1943	ev_timer_stop (EV_A_ &timer);
		1944	callback (EV_A_ &timer, 0);
		1945
		1946	This technique is slightly more complex, but in most cases where the
		1947	time-out is unlikely to be triggered, much more efficient.
		1948
		1949	=item 4. Wee, just use a double-linked list for your timeouts.
		1950
		1951	If there is not one request, but many thousands (millions...), all
		1952	employing some kind of timeout with the same timeout value, then one can
		1953	do even better:
		1954
		1955	When starting the timeout, calculate the timeout value and put the timeout
		1956	at the I<end> of the list.
		1957
		1958	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1959	the list is expected to fire (for example, using the technique #3).
		1960
		1961	When there is some activity, remove the timer from the list, recalculate
		1962	the timeout, append it to the end of the list again, and make sure to
		1963	update the C<ev_timer> if it was taken from the beginning of the list.
		1964
		1965	This way, one can manage an unlimited number of timeouts in O(1) time for
		1966	starting, stopping and updating the timers, at the expense of a major
		1967	complication, and having to use a constant timeout. The constant timeout
		1968	ensures that the list stays sorted.
		1969
		1970	=back
		1971
		1972	So which method the best?
		1973
		1974	Method #2 is a simple no-brain-required solution that is adequate in most
		1975	situations. Method #3 requires a bit more thinking, but handles many cases
		1976	better, and isn't very complicated either. In most case, choosing either
		1977	one is fine, with #3 being better in typical situations.
		1978
		1979	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1980	rather complicated, but extremely efficient, something that really pays
		1981	off after the first million or so of active timers, i.e. it's usually
		1982	overkill :)
		1983
		1984	=head3 The special problem of being too early
		1985
		1986	If you ask a timer to call your callback after three seconds, then
		1987	you expect it to be invoked after three seconds - but of course, this
		1988	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1989	guaranteed to any precision by libev - imagine somebody suspending the
		1990	process with a STOP signal for a few hours for example.
		1991
		1992	So, libev tries to invoke your callback as soon as possible I<after> the
		1993	delay has occurred, but cannot guarantee this.
		1994
		1995	A less obvious failure mode is calling your callback too early: many event
		1996	loops compare timestamps with a "elapsed delay >= requested delay", but
		1997	this can cause your callback to be invoked much earlier than you would
		1998	expect.
		1999
		2000	To see why, imagine a system with a clock that only offers full second
		2001	resolution (think windows if you can't come up with a broken enough OS
		2002	yourself). If you schedule a one-second timer at the time 500.9, then the
		2003	event loop will schedule your timeout to elapse at a system time of 500
		2004	(500.9 truncated to the resolution) + 1, or 501.
		2005
		2006	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2007	501" and invoke the callback 0.1s after it was started, even though a
		2008	one-second delay was requested - this is being "too early", despite best
		2009	intentions.
		2010
		2011	This is the reason why libev will never invoke the callback if the elapsed
		2012	delay equals the requested delay, but only when the elapsed delay is
		2013	larger than the requested delay. In the example above, libev would only invoke
		2014	the callback at system time 502, or 1.1s after the timer was started.
		2015
		2016	So, while libev cannot guarantee that your callback will be invoked
		2017	exactly when requested, it I<can> and I<does> guarantee that the requested
		2018	delay has actually elapsed, or in other words, it always errs on the "too
		2019	late" side of things.
		2020
		2021	=head3 The special problem of time updates
		2022
		2023	Establishing the current time is a costly operation (it usually takes
		2024	at least one system call): EV therefore updates its idea of the current
		2025	time only before and after C<ev_run> collects new events, which causes a
		2026	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2027	lots of events in one iteration.
		2028
		2029	The relative timeouts are calculated relative to the C<ev_now ()>
		2030	time. This is usually the right thing as this timestamp refers to the time
		2031	of the event triggering whatever timeout you are modifying/starting. If
		2032	you suspect event processing to be delayed and you I<need> to base the
		2033	timeout on the current time, use something like this to adjust for this:
		2034
		2035	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		2036
		2037	If the event loop is suspended for a long time, you can also force an
		2038	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		2039	()>.
		2040
		2041	=head3 The special problem of unsynchronised clocks
		2042
		2043	Modern systems have a variety of clocks - libev itself uses the normal
		2044	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2045	jumps).
		2046
		2047	Neither of these clocks is synchronised with each other or any other clock
		2048	on the system, so C<ev_time ()> might return a considerably different time
		2049	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2050	a call to C<gettimeofday> might return a second count that is one higher
		2051	than a directly following call to C<time>.
		2052
		2053	The moral of this is to only compare libev-related timestamps with
		2054	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2055	a second or so.
		2056
		2057	One more problem arises due to this lack of synchronisation: if libev uses
		2058	the system monotonic clock and you compare timestamps from C<ev_time>
		2059	or C<ev_now> from when you started your timer and when your callback is
		2060	invoked, you will find that sometimes the callback is a bit "early".
		2061
		2062	This is because C<ev_timer>s work in real time, not wall clock time, so
		2063	libev makes sure your callback is not invoked before the delay happened,
		2064	I<measured according to the real time>, not the system clock.
		2065
		2066	If your timeouts are based on a physical timescale (e.g. "time out this
		2067	connection after 100 seconds") then this shouldn't bother you as it is
		2068	exactly the right behaviour.
		2069
		2070	If you want to compare wall clock/system timestamps to your timers, then
		2071	you need to use C<ev_periodic>s, as these are based on the wall clock
		2072	time, where your comparisons will always generate correct results.
		2073
		2074	=head3 The special problems of suspended animation
		2075
		2076	When you leave the server world it is quite customary to hit machines that
		2077	can suspend/hibernate - what happens to the clocks during such a suspend?
		2078
		2079	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2080	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2081	to run until the system is suspended, but they will not advance while the
		2082	system is suspended. That means, on resume, it will be as if the program
		2083	was frozen for a few seconds, but the suspend time will not be counted
		2084	towards C<ev_timer> when a monotonic clock source is used. The real time
		2085	clock advanced as expected, but if it is used as sole clocksource, then a
		2086	long suspend would be detected as a time jump by libev, and timers would
		2087	be adjusted accordingly.
		2088
		2089	I would not be surprised to see different behaviour in different between
		2090	operating systems, OS versions or even different hardware.
		2091
		2092	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2093	time jump in the monotonic clocks and the realtime clock. If the program
		2094	is suspended for a very long time, and monotonic clock sources are in use,
		2095	then you can expect C<ev_timer>s to expire as the full suspension time
		2096	will be counted towards the timers. When no monotonic clock source is in
		2097	use, then libev will again assume a timejump and adjust accordingly.
		2098
		2099	It might be beneficial for this latter case to call C<ev_suspend>
		2100	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2101	deterministic behaviour in this case (you can do nothing against
		2102	C<SIGSTOP>).
		2103
		2104	=head3 Watcher-Specific Functions and Data Members
		2105
		2106	=over 4
		2107
436	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2108	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
437		2109
438	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2110	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
439		2111
440	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2112	Configure the timer to trigger after C<after> seconds. If C<repeat>
441	C<0.>, then it will automatically be stopped. If it is positive, then the	2113	is C<0.>, then it will automatically be stopped once the timeout is
442	timer will automatically be configured to trigger again C<repeat> seconds	2114	reached. If it is positive, then the timer will automatically be
443	later, again, and again, until stopped manually.	2115	configured to trigger again C<repeat> seconds later, again, and again,
		2116	until stopped manually.
444		2117
445	The timer itself will do a best-effort at avoiding drift, that is, if you	2118	The timer itself will do a best-effort at avoiding drift, that is, if
446	configure a timer to trigger every 10 seconds, then it will trigger at	2119	you configure a timer to trigger every 10 seconds, then it will normally
447	exactly 10 second intervals. If, however, your program cannot keep up with	2120	trigger at exactly 10 second intervals. If, however, your program cannot
448	the timer (ecause it takes longer than those 10 seconds to do stuff) the	2121	keep up with the timer (because it takes longer than those 10 seconds to
449	timer will not fire more than once per event loop iteration.	2122	do stuff) the timer will not fire more than once per event loop iteration.
450		2123
451	=item ev_timer_again (loop)	2124	=item ev_timer_again (loop, ev_timer *)
452		2125
453	This will act as if the timer timed out and restart it again if it is	2126	This will act as if the timer timed out, and restarts it again if it is
454	repeating. The exact semantics are:	2127	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2128	timeout to the C<repeat> value and calling C<ev_timer_start>.
455		2129
		2130	The exact semantics are as in the following rules, all of which will be
		2131	applied to the watcher:
		2132
		2133	=over 4
		2134
		2135	=item If the timer is pending, the pending status is always cleared.
		2136
456	If the timer is started but nonrepeating, stop it.	2137	=item If the timer is started but non-repeating, stop it (as if it timed
		2138	out, without invoking it).
457		2139
458	If the timer is repeating, either start it if necessary (with the repeat	2140	=item If the timer is repeating, make the C<repeat> value the new timeout
459	value), or reset the running timer to the repeat value.	2141	and start the timer, if necessary.
460
461	This sounds a bit complicated, but here is a useful and typical
462	example: Imagine you have a tcp connection and you want a so-called idle
463	timeout, that is, you want to be called when there have been, say, 60
464	seconds of inactivity on the socket. The easiest way to do this is to
465	configure an ev_timer with after=repeat=60 and calling ev_timer_again each
466	time you successfully read or write some data. If you go into an idle
467	state where you do not expect data to travel on the socket, you can stop
468	the timer, and again will automatically restart it if need be.
469		2142
470	=back	2143	=back
471		2144
472	=head2 ev_periodic	2145	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
		2146	usage example.
		2147
		2148	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2149
		2150	Returns the remaining time until a timer fires. If the timer is active,
		2151	then this time is relative to the current event loop time, otherwise it's
		2152	the timeout value currently configured.
		2153
		2154	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2155	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2156	will return C<4>. When the timer expires and is restarted, it will return
		2157	roughly C<7> (likely slightly less as callback invocation takes some time,
		2158	too), and so on.
		2159
		2160	=item ev_tstamp repeat [read-write]
		2161
		2162	The current C<repeat> value. Will be used each time the watcher times out
		2163	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2164	which is also when any modifications are taken into account.
		2165
		2166	=back
		2167
		2168	=head3 Examples
		2169
		2170	Example: Create a timer that fires after 60 seconds.
		2171
		2172	static void
		2173	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2174	{
		2175	.. one minute over, w is actually stopped right here
		2176	}
		2177
		2178	ev_timer mytimer;
		2179	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2180	ev_timer_start (loop, &mytimer);
		2181
		2182	Example: Create a timeout timer that times out after 10 seconds of
		2183	inactivity.
		2184
		2185	static void
		2186	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2187	{
		2188	.. ten seconds without any activity
		2189	}
		2190
		2191	ev_timer mytimer;
		2192	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2193	ev_timer_again (&mytimer); /* start timer */
		2194	ev_run (loop, 0);
		2195
		2196	// and in some piece of code that gets executed on any "activity":
		2197	// reset the timeout to start ticking again at 10 seconds
		2198	ev_timer_again (&mytimer);
		2199
		2200
		2201	=head2 C<ev_periodic> - to cron or not to cron?
473		2202
474	Periodic watchers are also timers of a kind, but they are very versatile	2203	Periodic watchers are also timers of a kind, but they are very versatile
475	(and unfortunately a bit complex).	2204	(and unfortunately a bit complex).
476		2205
477	Unlike ev_timer's, they are not based on real time (or relative time)	2206	Unlike C<ev_timer>, periodic watchers are not based on real time (or
478	but on wallclock time (absolute time). You can tell a periodic watcher	2207	relative time, the physical time that passes) but on wall clock time
479	to trigger "at" some specific point in time. For example, if you tell a	2208	(absolute time, the thing you can read on your calender or clock). The
480	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2209	difference is that wall clock time can run faster or slower than real
481	+ 10.>) and then reset your system clock to the last year, then it will	2210	time, and time jumps are not uncommon (e.g. when you adjust your
482	take a year to trigger the event (unlike an ev_timer, which would trigger	2211	wrist-watch).
483	roughly 10 seconds later and of course not if you reset your system time
484	again).
485		2212
486	They can also be used to implement vastly more complex timers, such as	2213	You can tell a periodic watcher to trigger after some specific point
		2214	in time: for example, if you tell a periodic watcher to trigger "in 10
		2215	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2216	not a delay) and then reset your system clock to January of the previous
		2217	year, then it will take a year or more to trigger the event (unlike an
		2218	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2219	it, as it uses a relative timeout).
		2220
		2221	C<ev_periodic> watchers can also be used to implement vastly more complex
487	triggering an event on eahc midnight, local time.	2222	timers, such as triggering an event on each "midnight, local time", or
		2223	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2224	those cannot react to time jumps.
		2225
		2226	As with timers, the callback is guaranteed to be invoked only when the
		2227	point in time where it is supposed to trigger has passed. If multiple
		2228	timers become ready during the same loop iteration then the ones with
		2229	earlier time-out values are invoked before ones with later time-out values
		2230	(but this is no longer true when a callback calls C<ev_run> recursively).
		2231
		2232	=head3 Watcher-Specific Functions and Data Members
488		2233
489	=over 4	2234	=over 4
490		2235
491	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2236	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
492		2237
493	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2238	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
494		2239
495	Lots of arguments, lets sort it out... There are basically three modes of	2240	Lots of arguments, let's sort it out... There are basically three modes of
496	operation, and we will explain them from simplest to complex:	2241	operation, and we will explain them from simplest to most complex:
497
498		2242
499	=over 4	2243	=over 4
500		2244
501	=item * absolute timer (interval = reschedule_cb = 0)	2245	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
502		2246
503	In this configuration the watcher triggers an event at the wallclock time	2247	In this configuration the watcher triggers an event after the wall clock
504	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2248	time C<offset> has passed. It will not repeat and will not adjust when a
505	that is, if it is to be run at January 1st 2011 then it will run when the	2249	time jump occurs, that is, if it is to be run at January 1st 2011 then it
506	system time reaches or surpasses this time.	2250	will be stopped and invoked when the system clock reaches or surpasses
		2251	this point in time.
507		2252
508	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2253	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
509		2254
510	In this mode the watcher will always be scheduled to time out at the next	2255	In this mode the watcher will always be scheduled to time out at the next
511	C<at + N * interval> time (for some integer N) and then repeat, regardless	2256	C<offset + N * interval> time (for some integer N, which can also be
512	of any time jumps.	2257	negative) and then repeat, regardless of any time jumps. The C<offset>
		2258	argument is merely an offset into the C<interval> periods.
513		2259
514	This can be used to create timers that do not drift with respect to system	2260	This can be used to create timers that do not drift with respect to the
515	time:	2261	system clock, for example, here is an C<ev_periodic> that triggers each
		2262	hour, on the hour (with respect to UTC):
516		2263
517	ev_periodic_set (&periodic, 0., 3600., 0);	2264	ev_periodic_set (&periodic, 0., 3600., 0);
518		2265
519	This doesn't mean there will always be 3600 seconds in between triggers,	2266	This doesn't mean there will always be 3600 seconds in between triggers,
520	but only that the the callback will be called when the system time shows a	2267	but only that the callback will be called when the system time shows a
521	full hour (UTC), or more correct, when the system time is evenly divisible	2268	full hour (UTC), or more correctly, when the system time is evenly divisible
522	by 3600.	2269	by 3600.
523		2270
524	Another way to think about it (for the mathematically inclined) is that	2271	Another way to think about it (for the mathematically inclined) is that
525	ev_periodic will try to run the callback in this mode at the next possible	2272	C<ev_periodic> will try to run the callback in this mode at the next possible
526	time where C<time = at (mod interval)>, regardless of any time jumps.	2273	time where C<time = offset (mod interval)>, regardless of any time jumps.
527		2274
		2275	The C<interval> I<MUST> be positive, and for numerical stability, the
		2276	interval value should be higher than C<1/8192> (which is around 100
		2277	microseconds) and C<offset> should be higher than C<0> and should have
		2278	at most a similar magnitude as the current time (say, within a factor of
		2279	ten). Typical values for offset are, in fact, C<0> or something between
		2280	C<0> and C<interval>, which is also the recommended range.
		2281
		2282	Note also that there is an upper limit to how often a timer can fire (CPU
		2283	speed for example), so if C<interval> is very small then timing stability
		2284	will of course deteriorate. Libev itself tries to be exact to be about one
		2285	millisecond (if the OS supports it and the machine is fast enough).
		2286
528	=item * manual reschedule mode (reschedule_cb = callback)	2287	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
529		2288
530	In this mode the values for C<interval> and C<at> are both being	2289	In this mode the values for C<interval> and C<offset> are both being
531	ignored. Instead, each time the periodic watcher gets scheduled, the	2290	ignored. Instead, each time the periodic watcher gets scheduled, the
532	reschedule callback will be called with the watcher as first, and the	2291	reschedule callback will be called with the watcher as first, and the
533	current time as second argument.	2292	current time as second argument.
534		2293
535	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2294	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
536	periodic watcher, ever, or make any event loop modificstions>. If you need	2295	or make ANY other event loop modifications whatsoever, unless explicitly
537	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.	2296	allowed by documentation here>.
538		2297
		2298	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2299	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2300	only event loop modification you are allowed to do).
		2301
539	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2302	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
540	ev_tstamp now)>, e.g.:	2303	*w, ev_tstamp now)>, e.g.:
541		2304
		2305	static ev_tstamp
542	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2306	my_rescheduler (ev_periodic *w, ev_tstamp now)
543	{	2307	{
544	return now + 60.;	2308	return now + 60.;
545	}	2309	}
546		2310
547	It must return the next time to trigger, based on the passed time value	2311	It must return the next time to trigger, based on the passed time value
548	(that is, the lowest time value larger than to the second argument). It	2312	(that is, the lowest time value larger than to the second argument). It
549	will usually be called just before the callback will be triggered, but	2313	will usually be called just before the callback will be triggered, but
550	might be called at other times, too.	2314	might be called at other times, too.
551		2315
		2316	NOTE: I<< This callback must always return a time that is higher than or
		2317	equal to the passed C<now> value >>.
		2318
552	This can be used to create very complex timers, such as a timer that	2319	This can be used to create very complex timers, such as a timer that
553	triggers on each midnight, local time. To do this, you would calculate the	2320	triggers on "next midnight, local time". To do this, you would calculate the
554	next midnight after C<now> and return the timestamp value for this. How you do this	2321	next midnight after C<now> and return the timestamp value for this. How
555	is, again, up to you (but it is not trivial).	2322	you do this is, again, up to you (but it is not trivial, which is the main
		2323	reason I omitted it as an example).
556		2324
557	=back	2325	=back
558		2326
559	=item ev_periodic_again (loop, ev_periodic *)	2327	=item ev_periodic_again (loop, ev_periodic *)
560		2328
561	Simply stops and restarts the periodic watcher again. This is only useful	2329	Simply stops and restarts the periodic watcher again. This is only useful
562	when you changed some parameters or the reschedule callback would return	2330	when you changed some parameters or the reschedule callback would return
563	a different time than the last time it was called (e.g. in a crond like	2331	a different time than the last time it was called (e.g. in a crond like
564	program when the crontabs have changed).	2332	program when the crontabs have changed).
565		2333
		2334	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2335
		2336	When active, returns the absolute time that the watcher is supposed
		2337	to trigger next. This is not the same as the C<offset> argument to
		2338	C<ev_periodic_set>, but indeed works even in interval and manual
		2339	rescheduling modes.
		2340
		2341	=item ev_tstamp offset [read-write]
		2342
		2343	When repeating, this contains the offset value, otherwise this is the
		2344	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2345	although libev might modify this value for better numerical stability).
		2346
		2347	Can be modified any time, but changes only take effect when the periodic
		2348	timer fires or C<ev_periodic_again> is being called.
		2349
		2350	=item ev_tstamp interval [read-write]
		2351
		2352	The current interval value. Can be modified any time, but changes only
		2353	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2354	called.
		2355
		2356	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2357
		2358	The current reschedule callback, or C<0>, if this functionality is
		2359	switched off. Can be changed any time, but changes only take effect when
		2360	the periodic timer fires or C<ev_periodic_again> is being called.
		2361
566	=back	2362	=back
567		2363
		2364	=head3 Examples
		2365
		2366	Example: Call a callback every hour, or, more precisely, whenever the
		2367	system time is divisible by 3600. The callback invocation times have
		2368	potentially a lot of jitter, but good long-term stability.
		2369
		2370	static void
		2371	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2372	{
		2373	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2374	}
		2375
		2376	ev_periodic hourly_tick;
		2377	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2378	ev_periodic_start (loop, &hourly_tick);
		2379
		2380	Example: The same as above, but use a reschedule callback to do it:
		2381
		2382	#include <math.h>
		2383
		2384	static ev_tstamp
		2385	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2386	{
		2387	return now + (3600. - fmod (now, 3600.));
		2388	}
		2389
		2390	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2391
		2392	Example: Call a callback every hour, starting now:
		2393
		2394	ev_periodic hourly_tick;
		2395	ev_periodic_init (&hourly_tick, clock_cb,
		2396	fmod (ev_now (loop), 3600.), 3600., 0);
		2397	ev_periodic_start (loop, &hourly_tick);
		2398
		2399
568	=head2 ev_signal - signal me when a signal gets signalled	2400	=head2 C<ev_signal> - signal me when a signal gets signalled!
569		2401
570	Signal watchers will trigger an event when the process receives a specific	2402	Signal watchers will trigger an event when the process receives a specific
571	signal one or more times. Even though signals are very asynchronous, libev	2403	signal one or more times. Even though signals are very asynchronous, libev
572	will try its best to deliver signals synchronously, i.e. as part of the	2404	will try its best to deliver signals synchronously, i.e. as part of the
573	normal event processing, like any other event.	2405	normal event processing, like any other event.
574		2406
		2407	If you want signals to be delivered truly asynchronously, just use
		2408	C<sigaction> as you would do without libev and forget about sharing
		2409	the signal. You can even use C<ev_async> from a signal handler to
		2410	synchronously wake up an event loop.
		2411
575	You cna configure as many watchers as you like per signal. Only when the	2412	You can configure as many watchers as you like for the same signal, but
576	first watcher gets started will libev actually register a signal watcher	2413	only within the same loop, i.e. you can watch for C<SIGINT> in your
577	with the kernel (thus it coexists with your own signal handlers as long	2414	default loop and for C<SIGIO> in another loop, but you cannot watch for
578	as you don't register any with libev). Similarly, when the last signal	2415	C<SIGINT> in both the default loop and another loop at the same time. At
579	watcher for a signal is stopped libev will reset the signal handler to	2416	the moment, C<SIGCHLD> is permanently tied to the default loop.
580	SIG_DFL (regardless of what it was set to before).	2417
		2418	Only after the first watcher for a signal is started will libev actually
		2419	register something with the kernel. It thus coexists with your own signal
		2420	handlers as long as you don't register any with libev for the same signal.
		2421
		2422	If possible and supported, libev will install its handlers with
		2423	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2424	not be unduly interrupted. If you have a problem with system calls getting
		2425	interrupted by signals you can block all signals in an C<ev_check> watcher
		2426	and unblock them in an C<ev_prepare> watcher.
		2427
		2428	=head3 The special problem of inheritance over fork/execve/pthread_create
		2429
		2430	Both the signal mask (C<sigprocmask>) and the signal disposition
		2431	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2432	stopping it again), that is, libev might or might not block the signal,
		2433	and might or might not set or restore the installed signal handler (but
		2434	see C<EVFLAG_NOSIGMASK>).
		2435
		2436	While this does not matter for the signal disposition (libev never
		2437	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2438	C<execve>), this matters for the signal mask: many programs do not expect
		2439	certain signals to be blocked.
		2440
		2441	This means that before calling C<exec> (from the child) you should reset
		2442	the signal mask to whatever "default" you expect (all clear is a good
		2443	choice usually).
		2444
		2445	The simplest way to ensure that the signal mask is reset in the child is
		2446	to install a fork handler with C<pthread_atfork> that resets it. That will
		2447	catch fork calls done by libraries (such as the libc) as well.
		2448
		2449	In current versions of libev, the signal will not be blocked indefinitely
		2450	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2451	the window of opportunity for problems, it will not go away, as libev
		2452	I<has> to modify the signal mask, at least temporarily.
		2453
		2454	So I can't stress this enough: I<If you do not reset your signal mask when
		2455	you expect it to be empty, you have a race condition in your code>. This
		2456	is not a libev-specific thing, this is true for most event libraries.
		2457
		2458	=head3 The special problem of threads signal handling
		2459
		2460	POSIX threads has problematic signal handling semantics, specifically,
		2461	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2462	threads in a process block signals, which is hard to achieve.
		2463
		2464	When you want to use sigwait (or mix libev signal handling with your own
		2465	for the same signals), you can tackle this problem by globally blocking
		2466	all signals before creating any threads (or creating them with a fully set
		2467	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2468	loops. Then designate one thread as "signal receiver thread" which handles
		2469	these signals. You can pass on any signals that libev might be interested
		2470	in by calling C<ev_feed_signal>.
		2471
		2472	=head3 Watcher-Specific Functions and Data Members
581		2473
582	=over 4	2474	=over 4
583		2475
584	=item ev_signal_init (ev_signal *, callback, int signum)	2476	=item ev_signal_init (ev_signal *, callback, int signum)
585		2477
586	=item ev_signal_set (ev_signal *, int signum)	2478	=item ev_signal_set (ev_signal *, int signum)
587		2479
588	Configures the watcher to trigger on the given signal number (usually one	2480	Configures the watcher to trigger on the given signal number (usually one
589	of the C<SIGxxx> constants).	2481	of the C<SIGxxx> constants).
590		2482
		2483	=item int signum [read-only]
		2484
		2485	The signal the watcher watches out for.
		2486
591	=back	2487	=back
592		2488
		2489	=head3 Examples
		2490
		2491	Example: Try to exit cleanly on SIGINT.
		2492
		2493	static void
		2494	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2495	{
		2496	ev_break (loop, EVBREAK_ALL);
		2497	}
		2498
		2499	ev_signal signal_watcher;
		2500	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2501	ev_signal_start (loop, &signal_watcher);
		2502
		2503
593	=head2 ev_child - wait for pid status changes	2504	=head2 C<ev_child> - watch out for process status changes
594		2505
595	Child watchers trigger when your process receives a SIGCHLD in response to	2506	Child watchers trigger when your process receives a SIGCHLD in response to
596	some child status changes (most typically when a child of yours dies).	2507	some child status changes (most typically when a child of yours dies or
		2508	exits). It is permissible to install a child watcher I<after> the child
		2509	has been forked (which implies it might have already exited), as long
		2510	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2511	forking and then immediately registering a watcher for the child is fine,
		2512	but forking and registering a watcher a few event loop iterations later or
		2513	in the next callback invocation is not.
		2514
		2515	Only the default event loop is capable of handling signals, and therefore
		2516	you can only register child watchers in the default event loop.
		2517
		2518	Due to some design glitches inside libev, child watchers will always be
		2519	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2520	libev)
		2521
		2522	=head3 Process Interaction
		2523
		2524	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2525	initialised. This is necessary to guarantee proper behaviour even if the
		2526	first child watcher is started after the child exits. The occurrence
		2527	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2528	synchronously as part of the event loop processing. Libev always reaps all
		2529	children, even ones not watched.
		2530
		2531	=head3 Overriding the Built-In Processing
		2532
		2533	Libev offers no special support for overriding the built-in child
		2534	processing, but if your application collides with libev's default child
		2535	handler, you can override it easily by installing your own handler for
		2536	C<SIGCHLD> after initialising the default loop, and making sure the
		2537	default loop never gets destroyed. You are encouraged, however, to use an
		2538	event-based approach to child reaping and thus use libev's support for
		2539	that, so other libev users can use C<ev_child> watchers freely.
		2540
		2541	=head3 Stopping the Child Watcher
		2542
		2543	Currently, the child watcher never gets stopped, even when the
		2544	child terminates, so normally one needs to stop the watcher in the
		2545	callback. Future versions of libev might stop the watcher automatically
		2546	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2547	problem).
		2548
		2549	=head3 Watcher-Specific Functions and Data Members
597		2550
598	=over 4	2551	=over 4
599		2552
600	=item ev_child_init (ev_child *, callback, int pid)	2553	=item ev_child_init (ev_child *, callback, int pid, int trace)
601		2554
602	=item ev_child_set (ev_child *, int pid)	2555	=item ev_child_set (ev_child *, int pid, int trace)
603		2556
604	Configures the watcher to wait for status changes of process C<pid> (or	2557	Configures the watcher to wait for status changes of process C<pid> (or
605	I<any> process if C<pid> is specified as C<0>). The callback can look	2558	I<any> process if C<pid> is specified as C<0>). The callback can look
606	at the C<rstatus> member of the C<ev_child> watcher structure to see	2559	at the C<rstatus> member of the C<ev_child> watcher structure to see
607	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	2560	the status word (use the macros from C<sys/wait.h> and see your systems
608	contains the pid of the process causing the status change.	2561	C<waitpid> documentation). The C<rpid> member contains the pid of the
		2562	process causing the status change. C<trace> must be either C<0> (only
		2563	activate the watcher when the process terminates) or C<1> (additionally
		2564	activate the watcher when the process is stopped or continued).
		2565
		2566	=item int pid [read-only]
		2567
		2568	The process id this watcher watches out for, or C<0>, meaning any process id.
		2569
		2570	=item int rpid [read-write]
		2571
		2572	The process id that detected a status change.
		2573
		2574	=item int rstatus [read-write]
		2575
		2576	The process exit/trace status caused by C<rpid> (see your systems
		2577	C<waitpid> and C<sys/wait.h> documentation for details).
609		2578
610	=back	2579	=back
611		2580
		2581	=head3 Examples
		2582
		2583	Example: C<fork()> a new process and install a child handler to wait for
		2584	its completion.
		2585
		2586	ev_child cw;
		2587
		2588	static void
		2589	child_cb (EV_P_ ev_child *w, int revents)
		2590	{
		2591	ev_child_stop (EV_A_ w);
		2592	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2593	}
		2594
		2595	pid_t pid = fork ();
		2596
		2597	if (pid < 0)
		2598	// error
		2599	else if (pid == 0)
		2600	{
		2601	// the forked child executes here
		2602	exit (1);
		2603	}
		2604	else
		2605	{
		2606	ev_child_init (&cw, child_cb, pid, 0);
		2607	ev_child_start (EV_DEFAULT_ &cw);
		2608	}
		2609
		2610
		2611	=head2 C<ev_stat> - did the file attributes just change?
		2612
		2613	This watches a file system path for attribute changes. That is, it calls
		2614	C<stat> on that path in regular intervals (or when the OS says it changed)
		2615	and sees if it changed compared to the last time, invoking the callback
		2616	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2617	happen after the watcher has been started will be reported.
		2618
		2619	The path does not need to exist: changing from "path exists" to "path does
		2620	not exist" is a status change like any other. The condition "path does not
		2621	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2622	C<st_nlink> field being zero (which is otherwise always forced to be at
		2623	least one) and all the other fields of the stat buffer having unspecified
		2624	contents.
		2625
		2626	The path I<must not> end in a slash or contain special components such as
		2627	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2628	your working directory changes, then the behaviour is undefined.
		2629
		2630	Since there is no portable change notification interface available, the
		2631	portable implementation simply calls C<stat(2)> regularly on the path
		2632	to see if it changed somehow. You can specify a recommended polling
		2633	interval for this case. If you specify a polling interval of C<0> (highly
		2634	recommended!) then a I<suitable, unspecified default> value will be used
		2635	(which you can expect to be around five seconds, although this might
		2636	change dynamically). Libev will also impose a minimum interval which is
		2637	currently around C<0.1>, but that's usually overkill.
		2638
		2639	This watcher type is not meant for massive numbers of stat watchers,
		2640	as even with OS-supported change notifications, this can be
		2641	resource-intensive.
		2642
		2643	At the time of this writing, the only OS-specific interface implemented
		2644	is the Linux inotify interface (implementing kqueue support is left as an
		2645	exercise for the reader. Note, however, that the author sees no way of
		2646	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2647
		2648	=head3 ABI Issues (Largefile Support)
		2649
		2650	Libev by default (unless the user overrides this) uses the default
		2651	compilation environment, which means that on systems with large file
		2652	support disabled by default, you get the 32 bit version of the stat
		2653	structure. When using the library from programs that change the ABI to
		2654	use 64 bit file offsets the programs will fail. In that case you have to
		2655	compile libev with the same flags to get binary compatibility. This is
		2656	obviously the case with any flags that change the ABI, but the problem is
		2657	most noticeably displayed with ev_stat and large file support.
		2658
		2659	The solution for this is to lobby your distribution maker to make large
		2660	file interfaces available by default (as e.g. FreeBSD does) and not
		2661	optional. Libev cannot simply switch on large file support because it has
		2662	to exchange stat structures with application programs compiled using the
		2663	default compilation environment.
		2664
		2665	=head3 Inotify and Kqueue
		2666
		2667	When C<inotify (7)> support has been compiled into libev and present at
		2668	runtime, it will be used to speed up change detection where possible. The
		2669	inotify descriptor will be created lazily when the first C<ev_stat>
		2670	watcher is being started.
		2671
		2672	Inotify presence does not change the semantics of C<ev_stat> watchers
		2673	except that changes might be detected earlier, and in some cases, to avoid
		2674	making regular C<stat> calls. Even in the presence of inotify support
		2675	there are many cases where libev has to resort to regular C<stat> polling,
		2676	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2677	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2678	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2679	xfs are fully working) libev usually gets away without polling.
		2680
		2681	There is no support for kqueue, as apparently it cannot be used to
		2682	implement this functionality, due to the requirement of having a file
		2683	descriptor open on the object at all times, and detecting renames, unlinks
		2684	etc. is difficult.
		2685
		2686	=head3 C<stat ()> is a synchronous operation
		2687
		2688	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2689	the process. The exception are C<ev_stat> watchers - those call C<stat
		2690	()>, which is a synchronous operation.
		2691
		2692	For local paths, this usually doesn't matter: unless the system is very
		2693	busy or the intervals between stat's are large, a stat call will be fast,
		2694	as the path data is usually in memory already (except when starting the
		2695	watcher).
		2696
		2697	For networked file systems, calling C<stat ()> can block an indefinite
		2698	time due to network issues, and even under good conditions, a stat call
		2699	often takes multiple milliseconds.
		2700
		2701	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2702	paths, although this is fully supported by libev.
		2703
		2704	=head3 The special problem of stat time resolution
		2705
		2706	The C<stat ()> system call only supports full-second resolution portably,
		2707	and even on systems where the resolution is higher, most file systems
		2708	still only support whole seconds.
		2709
		2710	That means that, if the time is the only thing that changes, you can
		2711	easily miss updates: on the first update, C<ev_stat> detects a change and
		2712	calls your callback, which does something. When there is another update
		2713	within the same second, C<ev_stat> will be unable to detect unless the
		2714	stat data does change in other ways (e.g. file size).
		2715
		2716	The solution to this is to delay acting on a change for slightly more
		2717	than a second (or till slightly after the next full second boundary), using
		2718	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2719	ev_timer_again (loop, w)>).
		2720
		2721	The C<.02> offset is added to work around small timing inconsistencies
		2722	of some operating systems (where the second counter of the current time
		2723	might be be delayed. One such system is the Linux kernel, where a call to
		2724	C<gettimeofday> might return a timestamp with a full second later than
		2725	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2726	update file times then there will be a small window where the kernel uses
		2727	the previous second to update file times but libev might already execute
		2728	the timer callback).
		2729
		2730	=head3 Watcher-Specific Functions and Data Members
		2731
		2732	=over 4
		2733
		2734	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2735
		2736	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2737
		2738	Configures the watcher to wait for status changes of the given
		2739	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2740	be detected and should normally be specified as C<0> to let libev choose
		2741	a suitable value. The memory pointed to by C<path> must point to the same
		2742	path for as long as the watcher is active.
		2743
		2744	The callback will receive an C<EV_STAT> event when a change was detected,
		2745	relative to the attributes at the time the watcher was started (or the
		2746	last change was detected).
		2747
		2748	=item ev_stat_stat (loop, ev_stat *)
		2749
		2750	Updates the stat buffer immediately with new values. If you change the
		2751	watched path in your callback, you could call this function to avoid
		2752	detecting this change (while introducing a race condition if you are not
		2753	the only one changing the path). Can also be useful simply to find out the
		2754	new values.
		2755
		2756	=item ev_statdata attr [read-only]
		2757
		2758	The most-recently detected attributes of the file. Although the type is
		2759	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2760	suitable for your system, but you can only rely on the POSIX-standardised
		2761	members to be present. If the C<st_nlink> member is C<0>, then there was
		2762	some error while C<stat>ing the file.
		2763
		2764	=item ev_statdata prev [read-only]
		2765
		2766	The previous attributes of the file. The callback gets invoked whenever
		2767	C<prev> != C<attr>, or, more precisely, one or more of these members
		2768	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2769	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2770
		2771	=item ev_tstamp interval [read-only]
		2772
		2773	The specified interval.
		2774
		2775	=item const char *path [read-only]
		2776
		2777	The file system path that is being watched.
		2778
		2779	=back
		2780
		2781	=head3 Examples
		2782
		2783	Example: Watch C</etc/passwd> for attribute changes.
		2784
		2785	static void
		2786	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2787	{
		2788	/* /etc/passwd changed in some way */
		2789	if (w->attr.st_nlink)
		2790	{
		2791	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2792	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2793	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2794	}
		2795	else
		2796	/* you shalt not abuse printf for puts */
		2797	puts ("wow, /etc/passwd is not there, expect problems. "
		2798	"if this is windows, they already arrived\n");
		2799	}
		2800
		2801	...
		2802	ev_stat passwd;
		2803
		2804	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2805	ev_stat_start (loop, &passwd);
		2806
		2807	Example: Like above, but additionally use a one-second delay so we do not
		2808	miss updates (however, frequent updates will delay processing, too, so
		2809	one might do the work both on C<ev_stat> callback invocation I<and> on
		2810	C<ev_timer> callback invocation).
		2811
		2812	static ev_stat passwd;
		2813	static ev_timer timer;
		2814
		2815	static void
		2816	timer_cb (EV_P_ ev_timer *w, int revents)
		2817	{
		2818	ev_timer_stop (EV_A_ w);
		2819
		2820	/* now it's one second after the most recent passwd change */
		2821	}
		2822
		2823	static void
		2824	stat_cb (EV_P_ ev_stat *w, int revents)
		2825	{
		2826	/* reset the one-second timer */
		2827	ev_timer_again (EV_A_ &timer);
		2828	}
		2829
		2830	...
		2831	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2832	ev_stat_start (loop, &passwd);
		2833	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2834
		2835
612	=head2 ev_idle - when you've got nothing better to do	2836	=head2 C<ev_idle> - when you've got nothing better to do...
613		2837
614	Idle watchers trigger events when there are no other I/O or timer (or	2838	Idle watchers trigger events when no other events of the same or higher
615	periodic) events pending. That is, as long as your process is busy	2839	priority are pending (prepare, check and other idle watchers do not count
616	handling sockets or timeouts it will not be called. But when your process	2840	as receiving "events").
617	is idle all idle watchers are being called again and again - until	2841
		2842	That is, as long as your process is busy handling sockets or timeouts
		2843	(or even signals, imagine) of the same or higher priority it will not be
		2844	triggered. But when your process is idle (or only lower-priority watchers
		2845	are pending), the idle watchers are being called once per event loop
618	stopped, that is, or your process receives more events.	2846	iteration - until stopped, that is, or your process receives more events
		2847	and becomes busy again with higher priority stuff.
619		2848
620	The most noteworthy effect is that as long as any idle watchers are	2849	The most noteworthy effect is that as long as any idle watchers are
621	active, the process will not block when waiting for new events.	2850	active, the process will not block when waiting for new events.
622		2851
623	Apart from keeping your process non-blocking (which is a useful	2852	Apart from keeping your process non-blocking (which is a useful
624	effect on its own sometimes), idle watchers are a good place to do	2853	effect on its own sometimes), idle watchers are a good place to do
625	"pseudo-background processing", or delay processing stuff to after the	2854	"pseudo-background processing", or delay processing stuff to after the
626	event loop has handled all outstanding events.	2855	event loop has handled all outstanding events.
627		2856
		2857	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2858
		2859	As long as there is at least one active idle watcher, libev will never
		2860	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2861	For this to work, the idle watcher doesn't need to be invoked at all - the
		2862	lowest priority will do.
		2863
		2864	This mode of operation can be useful together with an C<ev_check> watcher,
		2865	to do something on each event loop iteration - for example to balance load
		2866	between different connections.
		2867
		2868	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2869	example.
		2870
		2871	=head3 Watcher-Specific Functions and Data Members
		2872
628	=over 4	2873	=over 4
629		2874
630	=item ev_idle_init (ev_signal *, callback)	2875	=item ev_idle_init (ev_idle *, callback)
631		2876
632	Initialises and configures the idle watcher - it has no parameters of any	2877	Initialises and configures the idle watcher - it has no parameters of any
633	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2878	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
634	believe me.	2879	believe me.
635		2880
636	=back	2881	=back
637		2882
638	=head2 prepare and check - your hooks into the event loop	2883	=head3 Examples
639		2884
		2885	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2886	callback, free it. Also, use no error checking, as usual.
		2887
		2888	static void
		2889	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2890	{
		2891	// stop the watcher
		2892	ev_idle_stop (loop, w);
		2893
		2894	// now we can free it
		2895	free (w);
		2896
		2897	// now do something you wanted to do when the program has
		2898	// no longer anything immediate to do.
		2899	}
		2900
		2901	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2902	ev_idle_init (idle_watcher, idle_cb);
		2903	ev_idle_start (loop, idle_watcher);
		2904
		2905
		2906	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2907
640	Prepare and check watchers usually (but not always) are used in	2908	Prepare and check watchers are often (but not always) used in pairs:
641	tandom. Prepare watchers get invoked before the process blocks and check	2909	prepare watchers get invoked before the process blocks and check watchers
642	watchers afterwards.	2910	afterwards.
643		2911
		2912	You I<must not> call C<ev_run> or similar functions that enter
		2913	the current event loop from either C<ev_prepare> or C<ev_check>
		2914	watchers. Other loops than the current one are fine, however. The
		2915	rationale behind this is that you do not need to check for recursion in
		2916	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2917	C<ev_check> so if you have one watcher of each kind they will always be
		2918	called in pairs bracketing the blocking call.
		2919
644	Their main purpose is to integrate other event mechanisms into libev. This	2920	Their main purpose is to integrate other event mechanisms into libev and
645	could be used, for example, to track variable changes, implement your own	2921	their use is somewhat advanced. They could be used, for example, to track
646	watchers, integrate net-snmp or a coroutine library and lots more.	2922	variable changes, implement your own watchers, integrate net-snmp or a
		2923	coroutine library and lots more. They are also occasionally useful if
		2924	you cache some data and want to flush it before blocking (for example,
		2925	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2926	watcher).
647		2927
648	This is done by examining in each prepare call which file descriptors need	2928	This is done by examining in each prepare call which file descriptors
649	to be watched by the other library, registering ev_io watchers for them	2929	need to be watched by the other library, registering C<ev_io> watchers
650	and starting an ev_timer watcher for any timeouts (many libraries provide	2930	for them and starting an C<ev_timer> watcher for any timeouts (many
651	just this functionality). Then, in the check watcher you check for any	2931	libraries provide exactly this functionality). Then, in the check watcher,
652	events that occured (by making your callbacks set soem flags for example)	2932	you check for any events that occurred (by checking the pending status
653	and call back into the library.	2933	of all watchers and stopping them) and call back into the library. The
		2934	I/O and timer callbacks will never actually be called (but must be valid
		2935	nevertheless, because you never know, you know?).
654		2936
655	As another example, the perl Coro module uses these hooks to integrate	2937	As another example, the Perl Coro module uses these hooks to integrate
656	coroutines into libev programs, by yielding to other active coroutines	2938	coroutines into libev programs, by yielding to other active coroutines
657	during each prepare and only letting the process block if no coroutines	2939	during each prepare and only letting the process block if no coroutines
658	are ready to run.	2940	are ready to run (it's actually more complicated: it only runs coroutines
		2941	with priority higher than or equal to the event loop and one coroutine
		2942	of lower priority, but only once, using idle watchers to keep the event
		2943	loop from blocking if lower-priority coroutines are active, thus mapping
		2944	low-priority coroutines to idle/background tasks).
		2945
		2946	When used for this purpose, it is recommended to give C<ev_check> watchers
		2947	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2948	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2949	watchers).
		2950
		2951	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2952	activate ("feed") events into libev. While libev fully supports this, they
		2953	might get executed before other C<ev_check> watchers did their job. As
		2954	C<ev_check> watchers are often used to embed other (non-libev) event
		2955	loops those other event loops might be in an unusable state until their
		2956	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2957	others).
		2958
		2959	=head3 Abusing an C<ev_check> watcher for its side-effect
		2960
		2961	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2962	useful because they are called once per event loop iteration. For
		2963	example, if you want to handle a large number of connections fairly, you
		2964	normally only do a bit of work for each active connection, and if there
		2965	is more work to do, you wait for the next event loop iteration, so other
		2966	connections have a chance of making progress.
		2967
		2968	Using an C<ev_check> watcher is almost enough: it will be called on the
		2969	next event loop iteration. However, that isn't as soon as possible -
		2970	without external events, your C<ev_check> watcher will not be invoked.
		2971
		2972	This is where C<ev_idle> watchers come in handy - all you need is a
		2973	single global idle watcher that is active as long as you have one active
		2974	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2975	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2976	invoked. Neither watcher alone can do that.
		2977
		2978	=head3 Watcher-Specific Functions and Data Members
659		2979
660	=over 4	2980	=over 4
661		2981
662	=item ev_prepare_init (ev_prepare *, callback)	2982	=item ev_prepare_init (ev_prepare *, callback)
663		2983
664	=item ev_check_init (ev_check *, callback)	2984	=item ev_check_init (ev_check *, callback)
665		2985
666	Initialises and configures the prepare or check watcher - they have no	2986	Initialises and configures the prepare or check watcher - they have no
667	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2987	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
668	macros, but using them is utterly, utterly pointless.	2988	macros, but using them is utterly, utterly, utterly and completely
		2989	pointless.
669		2990
670	=back	2991	=back
671		2992
		2993	=head3 Examples
		2994
		2995	There are a number of principal ways to embed other event loops or modules
		2996	into libev. Here are some ideas on how to include libadns into libev
		2997	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2998	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2999	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		3000	Glib event loop).
		3001
		3002	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		3003	and in a check watcher, destroy them and call into libadns. What follows
		3004	is pseudo-code only of course. This requires you to either use a low
		3005	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		3006	the callbacks for the IO/timeout watchers might not have been called yet.
		3007
		3008	static ev_io iow [nfd];
		3009	static ev_timer tw;
		3010
		3011	static void
		3012	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		3013	{
		3014	}
		3015
		3016	// create io watchers for each fd and a timer before blocking
		3017	static void
		3018	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		3019	{
		3020	int timeout = 3600000;
		3021	struct pollfd fds [nfd];
		3022	// actual code will need to loop here and realloc etc.
		3023	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		3024
		3025	/* the callback is illegal, but won't be called as we stop during check */
		3026	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		3027	ev_timer_start (loop, &tw);
		3028
		3029	// create one ev_io per pollfd
		3030	for (int i = 0; i < nfd; ++i)
		3031	{
		3032	ev_io_init (iow + i, io_cb, fds [i].fd,
		3033	((fds [i].events & POLLIN ? EV_READ : 0)
		3034	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		3035
		3036	fds [i].revents = 0;
		3037	ev_io_start (loop, iow + i);
		3038	}
		3039	}
		3040
		3041	// stop all watchers after blocking
		3042	static void
		3043	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		3044	{
		3045	ev_timer_stop (loop, &tw);
		3046
		3047	for (int i = 0; i < nfd; ++i)
		3048	{
		3049	// set the relevant poll flags
		3050	// could also call adns_processreadable etc. here
		3051	struct pollfd *fd = fds + i;
		3052	int revents = ev_clear_pending (iow + i);
		3053	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3054	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3055
		3056	// now stop the watcher
		3057	ev_io_stop (loop, iow + i);
		3058	}
		3059
		3060	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		3061	}
		3062
		3063	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3064	in the prepare watcher and would dispose of the check watcher.
		3065
		3066	Method 3: If the module to be embedded supports explicit event
		3067	notification (libadns does), you can also make use of the actual watcher
		3068	callbacks, and only destroy/create the watchers in the prepare watcher.
		3069
		3070	static void
		3071	timer_cb (EV_P_ ev_timer *w, int revents)
		3072	{
		3073	adns_state ads = (adns_state)w->data;
		3074	update_now (EV_A);
		3075
		3076	adns_processtimeouts (ads, &tv_now);
		3077	}
		3078
		3079	static void
		3080	io_cb (EV_P_ ev_io *w, int revents)
		3081	{
		3082	adns_state ads = (adns_state)w->data;
		3083	update_now (EV_A);
		3084
		3085	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3086	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3087	}
		3088
		3089	// do not ever call adns_afterpoll
		3090
		3091	Method 4: Do not use a prepare or check watcher because the module you
		3092	want to embed is not flexible enough to support it. Instead, you can
		3093	override their poll function. The drawback with this solution is that the
		3094	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3095	this approach, effectively embedding EV as a client into the horrible
		3096	libglib event loop.
		3097
		3098	static gint
		3099	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3100	{
		3101	int got_events = 0;
		3102
		3103	for (n = 0; n < nfds; ++n)
		3104	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3105
		3106	if (timeout >= 0)
		3107	// create/start timer
		3108
		3109	// poll
		3110	ev_run (EV_A_ 0);
		3111
		3112	// stop timer again
		3113	if (timeout >= 0)
		3114	ev_timer_stop (EV_A_ &to);
		3115
		3116	// stop io watchers again - their callbacks should have set
		3117	for (n = 0; n < nfds; ++n)
		3118	ev_io_stop (EV_A_ iow [n]);
		3119
		3120	return got_events;
		3121	}
		3122
		3123
		3124	=head2 C<ev_embed> - when one backend isn't enough...
		3125
		3126	This is a rather advanced watcher type that lets you embed one event loop
		3127	into another (currently only C<ev_io> events are supported in the embedded
		3128	loop, other types of watchers might be handled in a delayed or incorrect
		3129	fashion and must not be used).
		3130
		3131	There are primarily two reasons you would want that: work around bugs and
		3132	prioritise I/O.
		3133
		3134	As an example for a bug workaround, the kqueue backend might only support
		3135	sockets on some platform, so it is unusable as generic backend, but you
		3136	still want to make use of it because you have many sockets and it scales
		3137	so nicely. In this case, you would create a kqueue-based loop and embed
		3138	it into your default loop (which might use e.g. poll). Overall operation
		3139	will be a bit slower because first libev has to call C<poll> and then
		3140	C<kevent>, but at least you can use both mechanisms for what they are
		3141	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3142
		3143	As for prioritising I/O: under rare circumstances you have the case where
		3144	some fds have to be watched and handled very quickly (with low latency),
		3145	and even priorities and idle watchers might have too much overhead. In
		3146	this case you would put all the high priority stuff in one loop and all
		3147	the rest in a second one, and embed the second one in the first.
		3148
		3149	As long as the watcher is active, the callback will be invoked every
		3150	time there might be events pending in the embedded loop. The callback
		3151	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3152	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3153	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3154	to give the embedded loop strictly lower priority for example).
		3155
		3156	You can also set the callback to C<0>, in which case the embed watcher
		3157	will automatically execute the embedded loop sweep whenever necessary.
		3158
		3159	Fork detection will be handled transparently while the C<ev_embed> watcher
		3160	is active, i.e., the embedded loop will automatically be forked when the
		3161	embedding loop forks. In other cases, the user is responsible for calling
		3162	C<ev_loop_fork> on the embedded loop.
		3163
		3164	Unfortunately, not all backends are embeddable: only the ones returned by
		3165	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3166	portable one.
		3167
		3168	So when you want to use this feature you will always have to be prepared
		3169	that you cannot get an embeddable loop. The recommended way to get around
		3170	this is to have a separate variables for your embeddable loop, try to
		3171	create it, and if that fails, use the normal loop for everything.
		3172
		3173	=head3 C<ev_embed> and fork
		3174
		3175	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3176	automatically be applied to the embedded loop as well, so no special
		3177	fork handling is required in that case. When the watcher is not running,
		3178	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3179	as applicable.
		3180
		3181	=head3 Watcher-Specific Functions and Data Members
		3182
		3183	=over 4
		3184
		3185	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3186
		3187	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
		3188
		3189	Configures the watcher to embed the given loop, which must be
		3190	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3191	invoked automatically, otherwise it is the responsibility of the callback
		3192	to invoke it (it will continue to be called until the sweep has been done,
		3193	if you do not want that, you need to temporarily stop the embed watcher).
		3194
		3195	=item ev_embed_sweep (loop, ev_embed *)
		3196
		3197	Make a single, non-blocking sweep over the embedded loop. This works
		3198	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3199	appropriate way for embedded loops.
		3200
		3201	=item struct ev_loop *other [read-only]
		3202
		3203	The embedded event loop.
		3204
		3205	=back
		3206
		3207	=head3 Examples
		3208
		3209	Example: Try to get an embeddable event loop and embed it into the default
		3210	event loop. If that is not possible, use the default loop. The default
		3211	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3212	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3213	used).
		3214
		3215	struct ev_loop *loop_hi = ev_default_init (0);
		3216	struct ev_loop *loop_lo = 0;
		3217	ev_embed embed;
		3218
		3219	// see if there is a chance of getting one that works
		3220	// (remember that a flags value of 0 means autodetection)
		3221	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3222	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3223	: 0;
		3224
		3225	// if we got one, then embed it, otherwise default to loop_hi
		3226	if (loop_lo)
		3227	{
		3228	ev_embed_init (&embed, 0, loop_lo);
		3229	ev_embed_start (loop_hi, &embed);
		3230	}
		3231	else
		3232	loop_lo = loop_hi;
		3233
		3234	Example: Check if kqueue is available but not recommended and create
		3235	a kqueue backend for use with sockets (which usually work with any
		3236	kqueue implementation). Store the kqueue/socket-only event loop in
		3237	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3238
		3239	struct ev_loop *loop = ev_default_init (0);
		3240	struct ev_loop *loop_socket = 0;
		3241	ev_embed embed;
		3242
		3243	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3244	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3245	{
		3246	ev_embed_init (&embed, 0, loop_socket);
		3247	ev_embed_start (loop, &embed);
		3248	}
		3249
		3250	if (!loop_socket)
		3251	loop_socket = loop;
		3252
		3253	// now use loop_socket for all sockets, and loop for everything else
		3254
		3255
		3256	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3257
		3258	Fork watchers are called when a C<fork ()> was detected (usually because
		3259	whoever is a good citizen cared to tell libev about it by calling
		3260	C<ev_loop_fork>). The invocation is done before the event loop blocks next
		3261	and before C<ev_check> watchers are being called, and only in the child
		3262	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
		3263	and calls it in the wrong process, the fork handlers will be invoked, too,
		3264	of course.
		3265
		3266	=head3 The special problem of life after fork - how is it possible?
		3267
		3268	Most uses of C<fork()> consist of forking, then some simple calls to set
		3269	up/change the process environment, followed by a call to C<exec()>. This
		3270	sequence should be handled by libev without any problems.
		3271
		3272	This changes when the application actually wants to do event handling
		3273	in the child, or both parent in child, in effect "continuing" after the
		3274	fork.
		3275
		3276	The default mode of operation (for libev, with application help to detect
		3277	forks) is to duplicate all the state in the child, as would be expected
		3278	when I<either> the parent I<or> the child process continues.
		3279
		3280	When both processes want to continue using libev, then this is usually the
		3281	wrong result. In that case, usually one process (typically the parent) is
		3282	supposed to continue with all watchers in place as before, while the other
		3283	process typically wants to start fresh, i.e. without any active watchers.
		3284
		3285	The cleanest and most efficient way to achieve that with libev is to
		3286	simply create a new event loop, which of course will be "empty", and
		3287	use that for new watchers. This has the advantage of not touching more
		3288	memory than necessary, and thus avoiding the copy-on-write, and the
		3289	disadvantage of having to use multiple event loops (which do not support
		3290	signal watchers).
		3291
		3292	When this is not possible, or you want to use the default loop for
		3293	other reasons, then in the process that wants to start "fresh", call
		3294	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3295	Destroying the default loop will "orphan" (not stop) all registered
		3296	watchers, so you have to be careful not to execute code that modifies
		3297	those watchers. Note also that in that case, you have to re-register any
		3298	signal watchers.
		3299
		3300	=head3 Watcher-Specific Functions and Data Members
		3301
		3302	=over 4
		3303
		3304	=item ev_fork_init (ev_fork *, callback)
		3305
		3306	Initialises and configures the fork watcher - it has no parameters of any
		3307	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3308	really.
		3309
		3310	=back
		3311
		3312
		3313	=head2 C<ev_cleanup> - even the best things end
		3314
		3315	Cleanup watchers are called just before the event loop is being destroyed
		3316	by a call to C<ev_loop_destroy>.
		3317
		3318	While there is no guarantee that the event loop gets destroyed, cleanup
		3319	watchers provide a convenient method to install cleanup hooks for your
		3320	program, worker threads and so on - you just to make sure to destroy the
		3321	loop when you want them to be invoked.
		3322
		3323	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3324	all other watchers, they do not keep a reference to the event loop (which
		3325	makes a lot of sense if you think about it). Like all other watchers, you
		3326	can call libev functions in the callback, except C<ev_cleanup_start>.
		3327
		3328	=head3 Watcher-Specific Functions and Data Members
		3329
		3330	=over 4
		3331
		3332	=item ev_cleanup_init (ev_cleanup *, callback)
		3333
		3334	Initialises and configures the cleanup watcher - it has no parameters of
		3335	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3336	pointless, I assure you.
		3337
		3338	=back
		3339
		3340	Example: Register an atexit handler to destroy the default loop, so any
		3341	cleanup functions are called.
		3342
		3343	static void
		3344	program_exits (void)
		3345	{
		3346	ev_loop_destroy (EV_DEFAULT_UC);
		3347	}
		3348
		3349	...
		3350	atexit (program_exits);
		3351
		3352
		3353	=head2 C<ev_async> - how to wake up an event loop
		3354
		3355	In general, you cannot use an C<ev_loop> from multiple threads or other
		3356	asynchronous sources such as signal handlers (as opposed to multiple event
		3357	loops - those are of course safe to use in different threads).
		3358
		3359	Sometimes, however, you need to wake up an event loop you do not control,
		3360	for example because it belongs to another thread. This is what C<ev_async>
		3361	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3362	it by calling C<ev_async_send>, which is thread- and signal safe.
		3363
		3364	This functionality is very similar to C<ev_signal> watchers, as signals,
		3365	too, are asynchronous in nature, and signals, too, will be compressed
		3366	(i.e. the number of callback invocations may be less than the number of
		3367	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3368	of "global async watchers" by using a watcher on an otherwise unused
		3369	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3370	even without knowing which loop owns the signal.
		3371
		3372	=head3 Queueing
		3373
		3374	C<ev_async> does not support queueing of data in any way. The reason
		3375	is that the author does not know of a simple (or any) algorithm for a
		3376	multiple-writer-single-reader queue that works in all cases and doesn't
		3377	need elaborate support such as pthreads or unportable memory access
		3378	semantics.
		3379
		3380	That means that if you want to queue data, you have to provide your own
		3381	queue. But at least I can tell you how to implement locking around your
		3382	queue:
		3383
		3384	=over 4
		3385
		3386	=item queueing from a signal handler context
		3387
		3388	To implement race-free queueing, you simply add to the queue in the signal
		3389	handler but you block the signal handler in the watcher callback. Here is
		3390	an example that does that for some fictitious SIGUSR1 handler:
		3391
		3392	static ev_async mysig;
		3393
		3394	static void
		3395	sigusr1_handler (void)
		3396	{
		3397	sometype data;
		3398
		3399	// no locking etc.
		3400	queue_put (data);
		3401	ev_async_send (EV_DEFAULT_ &mysig);
		3402	}
		3403
		3404	static void
		3405	mysig_cb (EV_P_ ev_async *w, int revents)
		3406	{
		3407	sometype data;
		3408	sigset_t block, prev;
		3409
		3410	sigemptyset (&block);
		3411	sigaddset (&block, SIGUSR1);
		3412	sigprocmask (SIG_BLOCK, &block, &prev);
		3413
		3414	while (queue_get (&data))
		3415	process (data);
		3416
		3417	if (sigismember (&prev, SIGUSR1)
		3418	sigprocmask (SIG_UNBLOCK, &block, 0);
		3419	}
		3420
		3421	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3422	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3423	either...).
		3424
		3425	=item queueing from a thread context
		3426
		3427	The strategy for threads is different, as you cannot (easily) block
		3428	threads but you can easily preempt them, so to queue safely you need to
		3429	employ a traditional mutex lock, such as in this pthread example:
		3430
		3431	static ev_async mysig;
		3432	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3433
		3434	static void
		3435	otherthread (void)
		3436	{
		3437	// only need to lock the actual queueing operation
		3438	pthread_mutex_lock (&mymutex);
		3439	queue_put (data);
		3440	pthread_mutex_unlock (&mymutex);
		3441
		3442	ev_async_send (EV_DEFAULT_ &mysig);
		3443	}
		3444
		3445	static void
		3446	mysig_cb (EV_P_ ev_async *w, int revents)
		3447	{
		3448	pthread_mutex_lock (&mymutex);
		3449
		3450	while (queue_get (&data))
		3451	process (data);
		3452
		3453	pthread_mutex_unlock (&mymutex);
		3454	}
		3455
		3456	=back
		3457
		3458
		3459	=head3 Watcher-Specific Functions and Data Members
		3460
		3461	=over 4
		3462
		3463	=item ev_async_init (ev_async *, callback)
		3464
		3465	Initialises and configures the async watcher - it has no parameters of any
		3466	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3467	trust me.
		3468
		3469	=item ev_async_send (loop, ev_async *)
		3470
		3471	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3472	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3473	returns.
		3474
		3475	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3476	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3477	embedding section below on what exactly this means).
		3478
		3479	Note that, as with other watchers in libev, multiple events might get
		3480	compressed into a single callback invocation (another way to look at
		3481	this is that C<ev_async> watchers are level-triggered: they are set on
		3482	C<ev_async_send>, reset when the event loop detects that).
		3483
		3484	This call incurs the overhead of at most one extra system call per event
		3485	loop iteration, if the event loop is blocked, and no syscall at all if
		3486	the event loop (or your program) is processing events. That means that
		3487	repeated calls are basically free (there is no need to avoid calls for
		3488	performance reasons) and that the overhead becomes smaller (typically
		3489	zero) under load.
		3490
		3491	=item bool = ev_async_pending (ev_async *)
		3492
		3493	Returns a non-zero value when C<ev_async_send> has been called on the
		3494	watcher but the event has not yet been processed (or even noted) by the
		3495	event loop.
		3496
		3497	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3498	the loop iterates next and checks for the watcher to have become active,
		3499	it will reset the flag again. C<ev_async_pending> can be used to very
		3500	quickly check whether invoking the loop might be a good idea.
		3501
		3502	Not that this does I<not> check whether the watcher itself is pending,
		3503	only whether it has been requested to make this watcher pending: there
		3504	is a time window between the event loop checking and resetting the async
		3505	notification, and the callback being invoked.
		3506
		3507	=back
		3508
		3509
672	=head1 OTHER FUNCTIONS	3510	=head1 OTHER FUNCTIONS
673		3511
674	There are some other fucntions of possible interest. Described. Here. Now.	3512	There are some other functions of possible interest. Described. Here. Now.
675		3513
676	=over 4	3514	=over 4
677		3515
678	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3516	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
679		3517
680	This function combines a simple timer and an I/O watcher, calls your	3518	This function combines a simple timer and an I/O watcher, calls your
681	callback on whichever event happens first and automatically stop both	3519	callback on whichever event happens first and automatically stops both
682	watchers. This is useful if you want to wait for a single event on an fd	3520	watchers. This is useful if you want to wait for a single event on an fd
683	or timeout without havign to allocate/configure/start/stop/free one or	3521	or timeout without having to allocate/configure/start/stop/free one or
684	more watchers yourself.	3522	more watchers yourself.
685		3523
686	If C<fd> is less than 0, then no I/O watcher will be started and events is	3524	If C<fd> is less than 0, then no I/O watcher will be started and the
687	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	3525	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
688	will be craeted and started.	3526	the given C<fd> and C<events> set will be created and started.
689		3527
690	If C<timeout> is less than 0, then no timeout watcher will be	3528	If C<timeout> is less than 0, then no timeout watcher will be
691	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	3529	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
692	= 0) will be started.	3530	repeat = 0) will be started. C<0> is a valid timeout.
693		3531
694	The callback has the type C<void (*cb)(int revents, void *arg)> and	3532	The callback has the type C<void (*cb)(int revents, void *arg)> and is
695	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	3533	passed an C<revents> set like normal event callbacks (a combination of
696	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	3534	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
		3535	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3536	a timeout and an io event at the same time - you probably should give io
		3537	events precedence.
697		3538
		3539	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3540
698	static void stdin_ready (int revents, void *arg)	3541	static void stdin_ready (int revents, void *arg)
		3542	{
		3543	if (revents & EV_READ)
		3544	/* stdin might have data for us, joy! */;
		3545	else if (revents & EV_TIMER)
		3546	/* doh, nothing entered */;
		3547	}
		3548
		3549	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3550
		3551	=item ev_feed_fd_event (loop, int fd, int revents)
		3552
		3553	Feed an event on the given fd, as if a file descriptor backend detected
		3554	the given events.
		3555
		3556	=item ev_feed_signal_event (loop, int signum)
		3557
		3558	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3559	which is async-safe.
		3560
		3561	=back
		3562
		3563
		3564	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3565
		3566	This section explains some common idioms that are not immediately
		3567	obvious. Note that examples are sprinkled over the whole manual, and this
		3568	section only contains stuff that wouldn't fit anywhere else.
		3569
		3570	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3571
		3572	Each watcher has, by default, a C<void *data> member that you can read
		3573	or modify at any time: libev will completely ignore it. This can be used
		3574	to associate arbitrary data with your watcher. If you need more data and
		3575	don't want to allocate memory separately and store a pointer to it in that
		3576	data member, you can also "subclass" the watcher type and provide your own
		3577	data:
		3578
		3579	struct my_io
		3580	{
		3581	ev_io io;
		3582	int otherfd;
		3583	void *somedata;
		3584	struct whatever *mostinteresting;
		3585	};
		3586
		3587	...
		3588	struct my_io w;
		3589	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3590
		3591	And since your callback will be called with a pointer to the watcher, you
		3592	can cast it back to your own type:
		3593
		3594	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3595	{
		3596	struct my_io *w = (struct my_io *)w_;
		3597	...
		3598	}
		3599
		3600	More interesting and less C-conformant ways of casting your callback
		3601	function type instead have been omitted.
		3602
		3603	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3604
		3605	Another common scenario is to use some data structure with multiple
		3606	embedded watchers, in effect creating your own watcher that combines
		3607	multiple libev event sources into one "super-watcher":
		3608
		3609	struct my_biggy
		3610	{
		3611	int some_data;
		3612	ev_timer t1;
		3613	ev_timer t2;
		3614	}
		3615
		3616	In this case getting the pointer to C<my_biggy> is a bit more
		3617	complicated: Either you store the address of your C<my_biggy> struct in
		3618	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3619	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3620	real programmers):
		3621
		3622	#include <stddef.h>
		3623
		3624	static void
		3625	t1_cb (EV_P_ ev_timer *w, int revents)
		3626	{
		3627	struct my_biggy big = (struct my_biggy *)
		3628	(((char *)w) - offsetof (struct my_biggy, t1));
		3629	}
		3630
		3631	static void
		3632	t2_cb (EV_P_ ev_timer *w, int revents)
		3633	{
		3634	struct my_biggy big = (struct my_biggy *)
		3635	(((char *)w) - offsetof (struct my_biggy, t2));
		3636	}
		3637
		3638	=head2 AVOIDING FINISHING BEFORE RETURNING
		3639
		3640	Often you have structures like this in event-based programs:
		3641
		3642	callback ()
699	{	3643	{
700	if (revents & EV_TIMEOUT)	3644	free (request);
701	/* doh, nothing entered */
702	else if (revents & EV_READ)
703	/* stdin might have data for us, joy! */
704	}	3645	}
705		3646
706	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	3647	request = start_new_request (..., callback);
707		3648
708	=item ev_feed_event (loop, watcher, int events)	3649	The intent is to start some "lengthy" operation. The C<request> could be
		3650	used to cancel the operation, or do other things with it.
709		3651
710	Feeds the given event set into the event loop, as if the specified event	3652	It's not uncommon to have code paths in C<start_new_request> that
711	has happened for the specified watcher (which must be a pointer to an	3653	immediately invoke the callback, for example, to report errors. Or you add
712	initialised but not necessarily active event watcher).	3654	some caching layer that finds that it can skip the lengthy aspects of the
		3655	operation and simply invoke the callback with the result.
713		3656
714	=item ev_feed_fd_event (loop, int fd, int revents)	3657	The problem here is that this will happen I<before> C<start_new_request>
		3658	has returned, so C<request> is not set.
715		3659
716	Feed an event on the given fd, as if a file descriptor backend detected it.	3660	Even if you pass the request by some safer means to the callback, you
		3661	might want to do something to the request after starting it, such as
		3662	canceling it, which probably isn't working so well when the callback has
		3663	already been invoked.
717		3664
718	=item ev_feed_signal_event (loop, int signum)	3665	A common way around all these issues is to make sure that
		3666	C<start_new_request> I<always> returns before the callback is invoked. If
		3667	C<start_new_request> immediately knows the result, it can artificially
		3668	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3669	example, or more sneakily, by reusing an existing (stopped) watcher and
		3670	pushing it into the pending queue:
719		3671
720	Feed an event as if the given signal occured (loop must be the default loop!).	3672	ev_set_cb (watcher, callback);
		3673	ev_feed_event (EV_A_ watcher, 0);
		3674
		3675	This way, C<start_new_request> can safely return before the callback is
		3676	invoked, while not delaying callback invocation too much.
		3677
		3678	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3679
		3680	Often (especially in GUI toolkits) there are places where you have
		3681	I<modal> interaction, which is most easily implemented by recursively
		3682	invoking C<ev_run>.
		3683
		3684	This brings the problem of exiting - a callback might want to finish the
		3685	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3686	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3687	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3688	other combination: In these cases, a simple C<ev_break> will not work.
		3689
		3690	The solution is to maintain "break this loop" variable for each C<ev_run>
		3691	invocation, and use a loop around C<ev_run> until the condition is
		3692	triggered, using C<EVRUN_ONCE>:
		3693
		3694	// main loop
		3695	int exit_main_loop = 0;
		3696
		3697	while (!exit_main_loop)
		3698	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3699
		3700	// in a modal watcher
		3701	int exit_nested_loop = 0;
		3702
		3703	while (!exit_nested_loop)
		3704	ev_run (EV_A_ EVRUN_ONCE);
		3705
		3706	To exit from any of these loops, just set the corresponding exit variable:
		3707
		3708	// exit modal loop
		3709	exit_nested_loop = 1;
		3710
		3711	// exit main program, after modal loop is finished
		3712	exit_main_loop = 1;
		3713
		3714	// exit both
		3715	exit_main_loop = exit_nested_loop = 1;
		3716
		3717	=head2 THREAD LOCKING EXAMPLE
		3718
		3719	Here is a fictitious example of how to run an event loop in a different
		3720	thread from where callbacks are being invoked and watchers are
		3721	created/added/removed.
		3722
		3723	For a real-world example, see the C<EV::Loop::Async> perl module,
		3724	which uses exactly this technique (which is suited for many high-level
		3725	languages).
		3726
		3727	The example uses a pthread mutex to protect the loop data, a condition
		3728	variable to wait for callback invocations, an async watcher to notify the
		3729	event loop thread and an unspecified mechanism to wake up the main thread.
		3730
		3731	First, you need to associate some data with the event loop:
		3732
		3733	typedef struct {
		3734	mutex_t lock; /* global loop lock */
		3735	ev_async async_w;
		3736	thread_t tid;
		3737	cond_t invoke_cv;
		3738	} userdata;
		3739
		3740	void prepare_loop (EV_P)
		3741	{
		3742	// for simplicity, we use a static userdata struct.
		3743	static userdata u;
		3744
		3745	ev_async_init (&u->async_w, async_cb);
		3746	ev_async_start (EV_A_ &u->async_w);
		3747
		3748	pthread_mutex_init (&u->lock, 0);
		3749	pthread_cond_init (&u->invoke_cv, 0);
		3750
		3751	// now associate this with the loop
		3752	ev_set_userdata (EV_A_ u);
		3753	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3754	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3755
		3756	// then create the thread running ev_run
		3757	pthread_create (&u->tid, 0, l_run, EV_A);
		3758	}
		3759
		3760	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3761	solely to wake up the event loop so it takes notice of any new watchers
		3762	that might have been added:
		3763
		3764	static void
		3765	async_cb (EV_P_ ev_async *w, int revents)
		3766	{
		3767	// just used for the side effects
		3768	}
		3769
		3770	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3771	protecting the loop data, respectively.
		3772
		3773	static void
		3774	l_release (EV_P)
		3775	{
		3776	userdata *u = ev_userdata (EV_A);
		3777	pthread_mutex_unlock (&u->lock);
		3778	}
		3779
		3780	static void
		3781	l_acquire (EV_P)
		3782	{
		3783	userdata *u = ev_userdata (EV_A);
		3784	pthread_mutex_lock (&u->lock);
		3785	}
		3786
		3787	The event loop thread first acquires the mutex, and then jumps straight
		3788	into C<ev_run>:
		3789
		3790	void *
		3791	l_run (void *thr_arg)
		3792	{
		3793	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3794
		3795	l_acquire (EV_A);
		3796	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3797	ev_run (EV_A_ 0);
		3798	l_release (EV_A);
		3799
		3800	return 0;
		3801	}
		3802
		3803	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3804	signal the main thread via some unspecified mechanism (signals? pipe
		3805	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3806	have been called (in a while loop because a) spurious wakeups are possible
		3807	and b) skipping inter-thread-communication when there are no pending
		3808	watchers is very beneficial):
		3809
		3810	static void
		3811	l_invoke (EV_P)
		3812	{
		3813	userdata *u = ev_userdata (EV_A);
		3814
		3815	while (ev_pending_count (EV_A))
		3816	{
		3817	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3818	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3819	}
		3820	}
		3821
		3822	Now, whenever the main thread gets told to invoke pending watchers, it
		3823	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3824	thread to continue:
		3825
		3826	static void
		3827	real_invoke_pending (EV_P)
		3828	{
		3829	userdata *u = ev_userdata (EV_A);
		3830
		3831	pthread_mutex_lock (&u->lock);
		3832	ev_invoke_pending (EV_A);
		3833	pthread_cond_signal (&u->invoke_cv);
		3834	pthread_mutex_unlock (&u->lock);
		3835	}
		3836
		3837	Whenever you want to start/stop a watcher or do other modifications to an
		3838	event loop, you will now have to lock:
		3839
		3840	ev_timer timeout_watcher;
		3841	userdata *u = ev_userdata (EV_A);
		3842
		3843	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3844
		3845	pthread_mutex_lock (&u->lock);
		3846	ev_timer_start (EV_A_ &timeout_watcher);
		3847	ev_async_send (EV_A_ &u->async_w);
		3848	pthread_mutex_unlock (&u->lock);
		3849
		3850	Note that sending the C<ev_async> watcher is required because otherwise
		3851	an event loop currently blocking in the kernel will have no knowledge
		3852	about the newly added timer. By waking up the loop it will pick up any new
		3853	watchers in the next event loop iteration.
		3854
		3855	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3856
		3857	While the overhead of a callback that e.g. schedules a thread is small, it
		3858	is still an overhead. If you embed libev, and your main usage is with some
		3859	kind of threads or coroutines, you might want to customise libev so that
		3860	doesn't need callbacks anymore.
		3861
		3862	Imagine you have coroutines that you can switch to using a function
		3863	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3864	and that due to some magic, the currently active coroutine is stored in a
		3865	global called C<current_coro>. Then you can build your own "wait for libev
		3866	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3867	the differing C<;> conventions):
		3868
		3869	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3870	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3871
		3872	That means instead of having a C callback function, you store the
		3873	coroutine to switch to in each watcher, and instead of having libev call
		3874	your callback, you instead have it switch to that coroutine.
		3875
		3876	A coroutine might now wait for an event with a function called
		3877	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3878	matter when, or whether the watcher is active or not when this function is
		3879	called):
		3880
		3881	void
		3882	wait_for_event (ev_watcher *w)
		3883	{
		3884	ev_set_cb (w, current_coro);
		3885	switch_to (libev_coro);
		3886	}
		3887
		3888	That basically suspends the coroutine inside C<wait_for_event> and
		3889	continues the libev coroutine, which, when appropriate, switches back to
		3890	this or any other coroutine.
		3891
		3892	You can do similar tricks if you have, say, threads with an event queue -
		3893	instead of storing a coroutine, you store the queue object and instead of
		3894	switching to a coroutine, you push the watcher onto the queue and notify
		3895	any waiters.
		3896
		3897	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3898	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3899
		3900	// my_ev.h
		3901	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3902	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3903	#include "../libev/ev.h"
		3904
		3905	// my_ev.c
		3906	#define EV_H "my_ev.h"
		3907	#include "../libev/ev.c"
		3908
		3909	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3910	F<my_ev.c> into your project. When properly specifying include paths, you
		3911	can even use F<ev.h> as header file name directly.
		3912
		3913
		3914	=head1 LIBEVENT EMULATION
		3915
		3916	Libev offers a compatibility emulation layer for libevent. It cannot
		3917	emulate the internals of libevent, so here are some usage hints:
		3918
		3919	=over 4
		3920
		3921	=item * Only the libevent-1.4.1-beta API is being emulated.
		3922
		3923	This was the newest libevent version available when libev was implemented,
		3924	and is still mostly unchanged in 2010.
		3925
		3926	=item * Use it by including <event.h>, as usual.
		3927
		3928	=item * The following members are fully supported: ev_base, ev_callback,
		3929	ev_arg, ev_fd, ev_res, ev_events.
		3930
		3931	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		3932	maintained by libev, it does not work exactly the same way as in libevent (consider
		3933	it a private API).
		3934
		3935	=item * Priorities are not currently supported. Initialising priorities
		3936	will fail and all watchers will have the same priority, even though there
		3937	is an ev_pri field.
		3938
		3939	=item * In libevent, the last base created gets the signals, in libev, the
		3940	base that registered the signal gets the signals.
		3941
		3942	=item * Other members are not supported.
		3943
		3944	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3945	to use the libev header file and library.
721		3946
722	=back	3947	=back
723		3948
		3949	=head1 C++ SUPPORT
		3950
		3951	=head2 C API
		3952
		3953	The normal C API should work fine when used from C++: both ev.h and the
		3954	libev sources can be compiled as C++. Therefore, code that uses the C API
		3955	will work fine.
		3956
		3957	Proper exception specifications might have to be added to callbacks passed
		3958	to libev: exceptions may be thrown only from watcher callbacks, all
		3959	other callbacks (allocator, syserr, loop acquire/release and periodic
		3960	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3961	()> specification. If you have code that needs to be compiled as both C
		3962	and C++ you can use the C<EV_THROW> macro for this:
		3963
		3964	static void
		3965	fatal_error (const char *msg) EV_THROW
		3966	{
		3967	perror (msg);
		3968	abort ();
		3969	}
		3970
		3971	...
		3972	ev_set_syserr_cb (fatal_error);
		3973
		3974	The only API functions that can currently throw exceptions are C<ev_run>,
		3975	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3976	because it runs cleanup watchers).
		3977
		3978	Throwing exceptions in watcher callbacks is only supported if libev itself
		3979	is compiled with a C++ compiler or your C and C++ environments allow
		3980	throwing exceptions through C libraries (most do).
		3981
		3982	=head2 C++ API
		3983
		3984	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3985	you to use some convenience methods to start/stop watchers and also change
		3986	the callback model to a model using method callbacks on objects.
		3987
		3988	To use it,
		3989
		3990	#include <ev++.h>
		3991
		3992	This automatically includes F<ev.h> and puts all of its definitions (many
		3993	of them macros) into the global namespace. All C++ specific things are
		3994	put into the C<ev> namespace. It should support all the same embedding
		3995	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3996
		3997	Care has been taken to keep the overhead low. The only data member the C++
		3998	classes add (compared to plain C-style watchers) is the event loop pointer
		3999	that the watcher is associated with (or no additional members at all if
		4000	you disable C<EV_MULTIPLICITY> when embedding libev).
		4001
		4002	Currently, functions, static and non-static member functions and classes
		4003	with C<operator ()> can be used as callbacks. Other types should be easy
		4004	to add as long as they only need one additional pointer for context. If
		4005	you need support for other types of functors please contact the author
		4006	(preferably after implementing it).
		4007
		4008	For all this to work, your C++ compiler either has to use the same calling
		4009	conventions as your C compiler (for static member functions), or you have
		4010	to embed libev and compile libev itself as C++.
		4011
		4012	Here is a list of things available in the C<ev> namespace:
		4013
		4014	=over 4
		4015
		4016	=item C<ev::READ>, C<ev::WRITE> etc.
		4017
		4018	These are just enum values with the same values as the C<EV_READ> etc.
		4019	macros from F<ev.h>.
		4020
		4021	=item C<ev::tstamp>, C<ev::now>
		4022
		4023	Aliases to the same types/functions as with the C<ev_> prefix.
		4024
		4025	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		4026
		4027	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		4028	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		4029	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		4030	defined by many implementations.
		4031
		4032	All of those classes have these methods:
		4033
		4034	=over 4
		4035
		4036	=item ev::TYPE::TYPE ()
		4037
		4038	=item ev::TYPE::TYPE (loop)
		4039
		4040	=item ev::TYPE::~TYPE
		4041
		4042	The constructor (optionally) takes an event loop to associate the watcher
		4043	with. If it is omitted, it will use C<EV_DEFAULT>.
		4044
		4045	The constructor calls C<ev_init> for you, which means you have to call the
		4046	C<set> method before starting it.
		4047
		4048	It will not set a callback, however: You have to call the templated C<set>
		4049	method to set a callback before you can start the watcher.
		4050
		4051	(The reason why you have to use a method is a limitation in C++ which does
		4052	not allow explicit template arguments for constructors).
		4053
		4054	The destructor automatically stops the watcher if it is active.
		4055
		4056	=item w->set<class, &class::method> (object *)
		4057
		4058	This method sets the callback method to call. The method has to have a
		4059	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		4060	first argument and the C<revents> as second. The object must be given as
		4061	parameter and is stored in the C<data> member of the watcher.
		4062
		4063	This method synthesizes efficient thunking code to call your method from
		4064	the C callback that libev requires. If your compiler can inline your
		4065	callback (i.e. it is visible to it at the place of the C<set> call and
		4066	your compiler is good :), then the method will be fully inlined into the
		4067	thunking function, making it as fast as a direct C callback.
		4068
		4069	Example: simple class declaration and watcher initialisation
		4070
		4071	struct myclass
		4072	{
		4073	void io_cb (ev::io &w, int revents) { }
		4074	}
		4075
		4076	myclass obj;
		4077	ev::io iow;
		4078	iow.set <myclass, &myclass::io_cb> (&obj);
		4079
		4080	=item w->set (object *)
		4081
		4082	This is a variation of a method callback - leaving out the method to call
		4083	will default the method to C<operator ()>, which makes it possible to use
		4084	functor objects without having to manually specify the C<operator ()> all
		4085	the time. Incidentally, you can then also leave out the template argument
		4086	list.
		4087
		4088	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4089	int revents)>.
		4090
		4091	See the method-C<set> above for more details.
		4092
		4093	Example: use a functor object as callback.
		4094
		4095	struct myfunctor
		4096	{
		4097	void operator() (ev::io &w, int revents)
		4098	{
		4099	...
		4100	}
		4101	}
		4102
		4103	myfunctor f;
		4104
		4105	ev::io w;
		4106	w.set (&f);
		4107
		4108	=item w->set<function> (void *data = 0)
		4109
		4110	Also sets a callback, but uses a static method or plain function as
		4111	callback. The optional C<data> argument will be stored in the watcher's
		4112	C<data> member and is free for you to use.
		4113
		4114	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4115
		4116	See the method-C<set> above for more details.
		4117
		4118	Example: Use a plain function as callback.
		4119
		4120	static void io_cb (ev::io &w, int revents) { }
		4121	iow.set <io_cb> ();
		4122
		4123	=item w->set (loop)
		4124
		4125	Associates a different C<struct ev_loop> with this watcher. You can only
		4126	do this when the watcher is inactive (and not pending either).
		4127
		4128	=item w->set ([arguments])
		4129
		4130	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4131	with the same arguments. Either this method or a suitable start method
		4132	must be called at least once. Unlike the C counterpart, an active watcher
		4133	gets automatically stopped and restarted when reconfiguring it with this
		4134	method.
		4135
		4136	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4137	clashing with the C<set (loop)> method.
		4138
		4139	=item w->start ()
		4140
		4141	Starts the watcher. Note that there is no C<loop> argument, as the
		4142	constructor already stores the event loop.
		4143
		4144	=item w->start ([arguments])
		4145
		4146	Instead of calling C<set> and C<start> methods separately, it is often
		4147	convenient to wrap them in one call. Uses the same type of arguments as
		4148	the configure C<set> method of the watcher.
		4149
		4150	=item w->stop ()
		4151
		4152	Stops the watcher if it is active. Again, no C<loop> argument.
		4153
		4154	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		4155
		4156	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		4157	C<ev_TYPE_again> function.
		4158
		4159	=item w->sweep () (C<ev::embed> only)
		4160
		4161	Invokes C<ev_embed_sweep>.
		4162
		4163	=item w->update () (C<ev::stat> only)
		4164
		4165	Invokes C<ev_stat_stat>.
		4166
		4167	=back
		4168
		4169	=back
		4170
		4171	Example: Define a class with two I/O and idle watchers, start the I/O
		4172	watchers in the constructor.
		4173
		4174	class myclass
		4175	{
		4176	ev::io io ; void io_cb (ev::io &w, int revents);
		4177	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		4178	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		4179
		4180	myclass (int fd)
		4181	{
		4182	io .set <myclass, &myclass::io_cb > (this);
		4183	io2 .set <myclass, &myclass::io2_cb > (this);
		4184	idle.set <myclass, &myclass::idle_cb> (this);
		4185
		4186	io.set (fd, ev::WRITE); // configure the watcher
		4187	io.start (); // start it whenever convenient
		4188
		4189	io2.start (fd, ev::READ); // set + start in one call
		4190	}
		4191	};
		4192
		4193
		4194	=head1 OTHER LANGUAGE BINDINGS
		4195
		4196	Libev does not offer other language bindings itself, but bindings for a
		4197	number of languages exist in the form of third-party packages. If you know
		4198	any interesting language binding in addition to the ones listed here, drop
		4199	me a note.
		4200
		4201	=over 4
		4202
		4203	=item Perl
		4204
		4205	The EV module implements the full libev API and is actually used to test
		4206	libev. EV is developed together with libev. Apart from the EV core module,
		4207	there are additional modules that implement libev-compatible interfaces
		4208	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4209	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4210	and C<EV::Glib>).
		4211
		4212	It can be found and installed via CPAN, its homepage is at
		4213	L<http://software.schmorp.de/pkg/EV>.
		4214
		4215	=item Python
		4216
		4217	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4218	seems to be quite complete and well-documented.
		4219
		4220	=item Ruby
		4221
		4222	Tony Arcieri has written a ruby extension that offers access to a subset
		4223	of the libev API and adds file handle abstractions, asynchronous DNS and
		4224	more on top of it. It can be found via gem servers. Its homepage is at
		4225	L<http://rev.rubyforge.org/>.
		4226
		4227	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4228	makes rev work even on mingw.
		4229
		4230	=item Haskell
		4231
		4232	A haskell binding to libev is available at
		4233	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4234
		4235	=item D
		4236
		4237	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4238	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4239
		4240	=item Ocaml
		4241
		4242	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4243	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4244
		4245	=item Lua
		4246
		4247	Brian Maher has written a partial interface to libev for lua (at the
		4248	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4249	L<http://github.com/brimworks/lua-ev>.
		4250
		4251	=item Javascript
		4252
		4253	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4254
		4255	=item Others
		4256
		4257	There are others, and I stopped counting.
		4258
		4259	=back
		4260
		4261
		4262	=head1 MACRO MAGIC
		4263
		4264	Libev can be compiled with a variety of options, the most fundamental
		4265	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4266	functions and callbacks have an initial C<struct ev_loop *> argument.
		4267
		4268	To make it easier to write programs that cope with either variant, the
		4269	following macros are defined:
		4270
		4271	=over 4
		4272
		4273	=item C<EV_A>, C<EV_A_>
		4274
		4275	This provides the loop I<argument> for functions, if one is required ("ev
		4276	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4277	C<EV_A_> is used when other arguments are following. Example:
		4278
		4279	ev_unref (EV_A);
		4280	ev_timer_add (EV_A_ watcher);
		4281	ev_run (EV_A_ 0);
		4282
		4283	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4284	which is often provided by the following macro.
		4285
		4286	=item C<EV_P>, C<EV_P_>
		4287
		4288	This provides the loop I<parameter> for functions, if one is required ("ev
		4289	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4290	C<EV_P_> is used when other parameters are following. Example:
		4291
		4292	// this is how ev_unref is being declared
		4293	static void ev_unref (EV_P);
		4294
		4295	// this is how you can declare your typical callback
		4296	static void cb (EV_P_ ev_timer *w, int revents)
		4297
		4298	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4299	suitable for use with C<EV_A>.
		4300
		4301	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4302
		4303	Similar to the other two macros, this gives you the value of the default
		4304	loop, if multiple loops are supported ("ev loop default"). The default loop
		4305	will be initialised if it isn't already initialised.
		4306
		4307	For non-multiplicity builds, these macros do nothing, so you always have
		4308	to initialise the loop somewhere.
		4309
		4310	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4311
		4312	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4313	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4314	is undefined when the default loop has not been initialised by a previous
		4315	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4316
		4317	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4318	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4319
		4320	=back
		4321
		4322	Example: Declare and initialise a check watcher, utilising the above
		4323	macros so it will work regardless of whether multiple loops are supported
		4324	or not.
		4325
		4326	static void
		4327	check_cb (EV_P_ ev_timer *w, int revents)
		4328	{
		4329	ev_check_stop (EV_A_ w);
		4330	}
		4331
		4332	ev_check check;
		4333	ev_check_init (&check, check_cb);
		4334	ev_check_start (EV_DEFAULT_ &check);
		4335	ev_run (EV_DEFAULT_ 0);
		4336
		4337	=head1 EMBEDDING
		4338
		4339	Libev can (and often is) directly embedded into host
		4340	applications. Examples of applications that embed it include the Deliantra
		4341	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4342	and rxvt-unicode.
		4343
		4344	The goal is to enable you to just copy the necessary files into your
		4345	source directory without having to change even a single line in them, so
		4346	you can easily upgrade by simply copying (or having a checked-out copy of
		4347	libev somewhere in your source tree).
		4348
		4349	=head2 FILESETS
		4350
		4351	Depending on what features you need you need to include one or more sets of files
		4352	in your application.
		4353
		4354	=head3 CORE EVENT LOOP
		4355
		4356	To include only the libev core (all the C<ev_*> functions), with manual
		4357	configuration (no autoconf):
		4358
		4359	#define EV_STANDALONE 1
		4360	#include "ev.c"
		4361
		4362	This will automatically include F<ev.h>, too, and should be done in a
		4363	single C source file only to provide the function implementations. To use
		4364	it, do the same for F<ev.h> in all files wishing to use this API (best
		4365	done by writing a wrapper around F<ev.h> that you can include instead and
		4366	where you can put other configuration options):
		4367
		4368	#define EV_STANDALONE 1
		4369	#include "ev.h"
		4370
		4371	Both header files and implementation files can be compiled with a C++
		4372	compiler (at least, that's a stated goal, and breakage will be treated
		4373	as a bug).
		4374
		4375	You need the following files in your source tree, or in a directory
		4376	in your include path (e.g. in libev/ when using -Ilibev):
		4377
		4378	ev.h
		4379	ev.c
		4380	ev_vars.h
		4381	ev_wrap.h
		4382
		4383	ev_win32.c required on win32 platforms only
		4384
		4385	ev_select.c only when select backend is enabled (which is enabled by default)
		4386	ev_poll.c only when poll backend is enabled (disabled by default)
		4387	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		4388	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		4389	ev_port.c only when the solaris port backend is enabled (disabled by default)
		4390
		4391	F<ev.c> includes the backend files directly when enabled, so you only need
		4392	to compile this single file.
		4393
		4394	=head3 LIBEVENT COMPATIBILITY API
		4395
		4396	To include the libevent compatibility API, also include:
		4397
		4398	#include "event.c"
		4399
		4400	in the file including F<ev.c>, and:
		4401
		4402	#include "event.h"
		4403
		4404	in the files that want to use the libevent API. This also includes F<ev.h>.
		4405
		4406	You need the following additional files for this:
		4407
		4408	event.h
		4409	event.c
		4410
		4411	=head3 AUTOCONF SUPPORT
		4412
		4413	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4414	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4415	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4416	include F<config.h> and configure itself accordingly.
		4417
		4418	For this of course you need the m4 file:
		4419
		4420	libev.m4
		4421
		4422	=head2 PREPROCESSOR SYMBOLS/MACROS
		4423
		4424	Libev can be configured via a variety of preprocessor symbols you have to
		4425	define before including (or compiling) any of its files. The default in
		4426	the absence of autoconf is documented for every option.
		4427
		4428	Symbols marked with "(h)" do not change the ABI, and can have different
		4429	values when compiling libev vs. including F<ev.h>, so it is permissible
		4430	to redefine them before including F<ev.h> without breaking compatibility
		4431	to a compiled library. All other symbols change the ABI, which means all
		4432	users of libev and the libev code itself must be compiled with compatible
		4433	settings.
		4434
		4435	=over 4
		4436
		4437	=item EV_COMPAT3 (h)
		4438
		4439	Backwards compatibility is a major concern for libev. This is why this
		4440	release of libev comes with wrappers for the functions and symbols that
		4441	have been renamed between libev version 3 and 4.
		4442
		4443	You can disable these wrappers (to test compatibility with future
		4444	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4445	sources. This has the additional advantage that you can drop the C<struct>
		4446	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4447	typedef in that case.
		4448
		4449	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4450	and in some even more future version the compatibility code will be
		4451	removed completely.
		4452
		4453	=item EV_STANDALONE (h)
		4454
		4455	Must always be C<1> if you do not use autoconf configuration, which
		4456	keeps libev from including F<config.h>, and it also defines dummy
		4457	implementations for some libevent functions (such as logging, which is not
		4458	supported). It will also not define any of the structs usually found in
		4459	F<event.h> that are not directly supported by the libev core alone.
		4460
		4461	In standalone mode, libev will still try to automatically deduce the
		4462	configuration, but has to be more conservative.
		4463
		4464	=item EV_USE_FLOOR
		4465
		4466	If defined to be C<1>, libev will use the C<floor ()> function for its
		4467	periodic reschedule calculations, otherwise libev will fall back on a
		4468	portable (slower) implementation. If you enable this, you usually have to
		4469	link against libm or something equivalent. Enabling this when the C<floor>
		4470	function is not available will fail, so the safe default is to not enable
		4471	this.
		4472
		4473	=item EV_USE_MONOTONIC
		4474
		4475	If defined to be C<1>, libev will try to detect the availability of the
		4476	monotonic clock option at both compile time and runtime. Otherwise no
		4477	use of the monotonic clock option will be attempted. If you enable this,
		4478	you usually have to link against librt or something similar. Enabling it
		4479	when the functionality isn't available is safe, though, although you have
		4480	to make sure you link against any libraries where the C<clock_gettime>
		4481	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4482
		4483	=item EV_USE_REALTIME
		4484
		4485	If defined to be C<1>, libev will try to detect the availability of the
		4486	real-time clock option at compile time (and assume its availability
		4487	at runtime if successful). Otherwise no use of the real-time clock
		4488	option will be attempted. This effectively replaces C<gettimeofday>
		4489	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4490	correctness. See the note about libraries in the description of
		4491	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4492	C<EV_USE_CLOCK_SYSCALL>.
		4493
		4494	=item EV_USE_CLOCK_SYSCALL
		4495
		4496	If defined to be C<1>, libev will try to use a direct syscall instead
		4497	of calling the system-provided C<clock_gettime> function. This option
		4498	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4499	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4500	programs needlessly. Using a direct syscall is slightly slower (in
		4501	theory), because no optimised vdso implementation can be used, but avoids
		4502	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4503	higher, as it simplifies linking (no need for C<-lrt>).
		4504
		4505	=item EV_USE_NANOSLEEP
		4506
		4507	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4508	and will use it for delays. Otherwise it will use C<select ()>.
		4509
		4510	=item EV_USE_EVENTFD
		4511
		4512	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4513	available and will probe for kernel support at runtime. This will improve
		4514	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4515	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4516	2.7 or newer, otherwise disabled.
		4517
		4518	=item EV_USE_SELECT
		4519
		4520	If undefined or defined to be C<1>, libev will compile in support for the
		4521	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4522	other method takes over, select will be it. Otherwise the select backend
		4523	will not be compiled in.
		4524
		4525	=item EV_SELECT_USE_FD_SET
		4526
		4527	If defined to C<1>, then the select backend will use the system C<fd_set>
		4528	structure. This is useful if libev doesn't compile due to a missing
		4529	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4530	on exotic systems. This usually limits the range of file descriptors to
		4531	some low limit such as 1024 or might have other limitations (winsocket
		4532	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4533	configures the maximum size of the C<fd_set>.
		4534
		4535	=item EV_SELECT_IS_WINSOCKET
		4536
		4537	When defined to C<1>, the select backend will assume that
		4538	select/socket/connect etc. don't understand file descriptors but
		4539	wants osf handles on win32 (this is the case when the select to
		4540	be used is the winsock select). This means that it will call
		4541	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4542	it is assumed that all these functions actually work on fds, even
		4543	on win32. Should not be defined on non-win32 platforms.
		4544
		4545	=item EV_FD_TO_WIN32_HANDLE(fd)
		4546
		4547	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4548	file descriptors to socket handles. When not defining this symbol (the
		4549	default), then libev will call C<_get_osfhandle>, which is usually
		4550	correct. In some cases, programs use their own file descriptor management,
		4551	in which case they can provide this function to map fds to socket handles.
		4552
		4553	=item EV_WIN32_HANDLE_TO_FD(handle)
		4554
		4555	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4556	using the standard C<_open_osfhandle> function. For programs implementing
		4557	their own fd to handle mapping, overwriting this function makes it easier
		4558	to do so. This can be done by defining this macro to an appropriate value.
		4559
		4560	=item EV_WIN32_CLOSE_FD(fd)
		4561
		4562	If programs implement their own fd to handle mapping on win32, then this
		4563	macro can be used to override the C<close> function, useful to unregister
		4564	file descriptors again. Note that the replacement function has to close
		4565	the underlying OS handle.
		4566
		4567	=item EV_USE_WSASOCKET
		4568
		4569	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4570	communication socket, which works better in some environments. Otherwise,
		4571	the normal C<socket> function will be used, which works better in other
		4572	environments.
		4573
		4574	=item EV_USE_POLL
		4575
		4576	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4577	backend. Otherwise it will be enabled on non-win32 platforms. It
		4578	takes precedence over select.
		4579
		4580	=item EV_USE_EPOLL
		4581
		4582	If defined to be C<1>, libev will compile in support for the Linux
		4583	C<epoll>(7) backend. Its availability will be detected at runtime,
		4584	otherwise another method will be used as fallback. This is the preferred
		4585	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4586	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4587
		4588	=item EV_USE_KQUEUE
		4589
		4590	If defined to be C<1>, libev will compile in support for the BSD style
		4591	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4592	otherwise another method will be used as fallback. This is the preferred
		4593	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4594	supports some types of fds correctly (the only platform we found that
		4595	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4596	not be used unless explicitly requested. The best way to use it is to find
		4597	out whether kqueue supports your type of fd properly and use an embedded
		4598	kqueue loop.
		4599
		4600	=item EV_USE_PORT
		4601
		4602	If defined to be C<1>, libev will compile in support for the Solaris
		4603	10 port style backend. Its availability will be detected at runtime,
		4604	otherwise another method will be used as fallback. This is the preferred
		4605	backend for Solaris 10 systems.
		4606
		4607	=item EV_USE_DEVPOLL
		4608
		4609	Reserved for future expansion, works like the USE symbols above.
		4610
		4611	=item EV_USE_INOTIFY
		4612
		4613	If defined to be C<1>, libev will compile in support for the Linux inotify
		4614	interface to speed up C<ev_stat> watchers. Its actual availability will
		4615	be detected at runtime. If undefined, it will be enabled if the headers
		4616	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4617
		4618	=item EV_NO_SMP
		4619
		4620	If defined to be C<1>, libev will assume that memory is always coherent
		4621	between threads, that is, threads can be used, but threads never run on
		4622	different cpus (or different cpu cores). This reduces dependencies
		4623	and makes libev faster.
		4624
		4625	=item EV_NO_THREADS
		4626
		4627	If defined to be C<1>, libev will assume that it will never be called from
		4628	different threads (that includes signal handlers), which is a stronger
		4629	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4630	libev faster.
		4631
		4632	=item EV_ATOMIC_T
		4633
		4634	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4635	access is atomic with respect to other threads or signal contexts. No
		4636	such type is easily found in the C language, so you can provide your own
		4637	type that you know is safe for your purposes. It is used both for signal
		4638	handler "locking" as well as for signal and thread safety in C<ev_async>
		4639	watchers.
		4640
		4641	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4642	(from F<signal.h>), which is usually good enough on most platforms.
		4643
		4644	=item EV_H (h)
		4645
		4646	The name of the F<ev.h> header file used to include it. The default if
		4647	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4648	used to virtually rename the F<ev.h> header file in case of conflicts.
		4649
		4650	=item EV_CONFIG_H (h)
		4651
		4652	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4653	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4654	C<EV_H>, above.
		4655
		4656	=item EV_EVENT_H (h)
		4657
		4658	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4659	of how the F<event.h> header can be found, the default is C<"event.h">.
		4660
		4661	=item EV_PROTOTYPES (h)
		4662
		4663	If defined to be C<0>, then F<ev.h> will not define any function
		4664	prototypes, but still define all the structs and other symbols. This is
		4665	occasionally useful if you want to provide your own wrapper functions
		4666	around libev functions.
		4667
		4668	=item EV_MULTIPLICITY
		4669
		4670	If undefined or defined to C<1>, then all event-loop-specific functions
		4671	will have the C<struct ev_loop *> as first argument, and you can create
		4672	additional independent event loops. Otherwise there will be no support
		4673	for multiple event loops and there is no first event loop pointer
		4674	argument. Instead, all functions act on the single default loop.
		4675
		4676	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4677	default loop when multiplicity is switched off - you always have to
		4678	initialise the loop manually in this case.
		4679
		4680	=item EV_MINPRI
		4681
		4682	=item EV_MAXPRI
		4683
		4684	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4685	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4686	provide for more priorities by overriding those symbols (usually defined
		4687	to be C<-2> and C<2>, respectively).
		4688
		4689	When doing priority-based operations, libev usually has to linearly search
		4690	all the priorities, so having many of them (hundreds) uses a lot of space
		4691	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4692	fine.
		4693
		4694	If your embedding application does not need any priorities, defining these
		4695	both to C<0> will save some memory and CPU.
		4696
		4697	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4698	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4699	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4700
		4701	If undefined or defined to be C<1> (and the platform supports it), then
		4702	the respective watcher type is supported. If defined to be C<0>, then it
		4703	is not. Disabling watcher types mainly saves code size.
		4704
		4705	=item EV_FEATURES
		4706
		4707	If you need to shave off some kilobytes of code at the expense of some
		4708	speed (but with the full API), you can define this symbol to request
		4709	certain subsets of functionality. The default is to enable all features
		4710	that can be enabled on the platform.
		4711
		4712	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4713	with some broad features you want) and then selectively re-enable
		4714	additional parts you want, for example if you want everything minimal,
		4715	but multiple event loop support, async and child watchers and the poll
		4716	backend, use this:
		4717
		4718	#define EV_FEATURES 0
		4719	#define EV_MULTIPLICITY 1
		4720	#define EV_USE_POLL 1
		4721	#define EV_CHILD_ENABLE 1
		4722	#define EV_ASYNC_ENABLE 1
		4723
		4724	The actual value is a bitset, it can be a combination of the following
		4725	values (by default, all of these are enabled):
		4726
		4727	=over 4
		4728
		4729	=item C<1> - faster/larger code
		4730
		4731	Use larger code to speed up some operations.
		4732
		4733	Currently this is used to override some inlining decisions (enlarging the
		4734	code size by roughly 30% on amd64).
		4735
		4736	When optimising for size, use of compiler flags such as C<-Os> with
		4737	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4738	assertions.
		4739
		4740	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4741	(e.g. gcc with C<-Os>).
		4742
		4743	=item C<2> - faster/larger data structures
		4744
		4745	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4746	hash table sizes and so on. This will usually further increase code size
		4747	and can additionally have an effect on the size of data structures at
		4748	runtime.
		4749
		4750	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4751	(e.g. gcc with C<-Os>).
		4752
		4753	=item C<4> - full API configuration
		4754
		4755	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4756	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4757
		4758	=item C<8> - full API
		4759
		4760	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4761	details on which parts of the API are still available without this
		4762	feature, and do not complain if this subset changes over time.
		4763
		4764	=item C<16> - enable all optional watcher types
		4765
		4766	Enables all optional watcher types. If you want to selectively enable
		4767	only some watcher types other than I/O and timers (e.g. prepare,
		4768	embed, async, child...) you can enable them manually by defining
		4769	C<EV_watchertype_ENABLE> to C<1> instead.
		4770
		4771	=item C<32> - enable all backends
		4772
		4773	This enables all backends - without this feature, you need to enable at
		4774	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4775
		4776	=item C<64> - enable OS-specific "helper" APIs
		4777
		4778	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4779	default.
		4780
		4781	=back
		4782
		4783	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4784	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4785	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4786	watchers, timers and monotonic clock support.
		4787
		4788	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4789	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4790	your program might be left out as well - a binary starting a timer and an
		4791	I/O watcher then might come out at only 5Kb.
		4792
		4793	=item EV_API_STATIC
		4794
		4795	If this symbol is defined (by default it is not), then all identifiers
		4796	will have static linkage. This means that libev will not export any
		4797	identifiers, and you cannot link against libev anymore. This can be useful
		4798	when you embed libev, only want to use libev functions in a single file,
		4799	and do not want its identifiers to be visible.
		4800
		4801	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4802	wants to use libev.
		4803
		4804	This option only works when libev is compiled with a C compiler, as C++
		4805	doesn't support the required declaration syntax.
		4806
		4807	=item EV_AVOID_STDIO
		4808
		4809	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4810	functions (printf, scanf, perror etc.). This will increase the code size
		4811	somewhat, but if your program doesn't otherwise depend on stdio and your
		4812	libc allows it, this avoids linking in the stdio library which is quite
		4813	big.
		4814
		4815	Note that error messages might become less precise when this option is
		4816	enabled.
		4817
		4818	=item EV_NSIG
		4819
		4820	The highest supported signal number, +1 (or, the number of
		4821	signals): Normally, libev tries to deduce the maximum number of signals
		4822	automatically, but sometimes this fails, in which case it can be
		4823	specified. Also, using a lower number than detected (C<32> should be
		4824	good for about any system in existence) can save some memory, as libev
		4825	statically allocates some 12-24 bytes per signal number.
		4826
		4827	=item EV_PID_HASHSIZE
		4828
		4829	C<ev_child> watchers use a small hash table to distribute workload by
		4830	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4831	usually more than enough. If you need to manage thousands of children you
		4832	might want to increase this value (I<must> be a power of two).
		4833
		4834	=item EV_INOTIFY_HASHSIZE
		4835
		4836	C<ev_stat> watchers use a small hash table to distribute workload by
		4837	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4838	disabled), usually more than enough. If you need to manage thousands of
		4839	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4840	power of two).
		4841
		4842	=item EV_USE_4HEAP
		4843
		4844	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4845	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4846	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4847	faster performance with many (thousands) of watchers.
		4848
		4849	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4850	will be C<0>.
		4851
		4852	=item EV_HEAP_CACHE_AT
		4853
		4854	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4855	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4856	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4857	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4858	but avoids random read accesses on heap changes. This improves performance
		4859	noticeably with many (hundreds) of watchers.
		4860
		4861	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4862	will be C<0>.
		4863
		4864	=item EV_VERIFY
		4865
		4866	Controls how much internal verification (see C<ev_verify ()>) will
		4867	be done: If set to C<0>, no internal verification code will be compiled
		4868	in. If set to C<1>, then verification code will be compiled in, but not
		4869	called. If set to C<2>, then the internal verification code will be
		4870	called once per loop, which can slow down libev. If set to C<3>, then the
		4871	verification code will be called very frequently, which will slow down
		4872	libev considerably.
		4873
		4874	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4875	will be C<0>.
		4876
		4877	=item EV_COMMON
		4878
		4879	By default, all watchers have a C<void *data> member. By redefining
		4880	this macro to something else you can include more and other types of
		4881	members. You have to define it each time you include one of the files,
		4882	though, and it must be identical each time.
		4883
		4884	For example, the perl EV module uses something like this:
		4885
		4886	#define EV_COMMON \
		4887	SV *self; /* contains this struct */ \
		4888	SV *cb_sv, *fh /* note no trailing ";" */
		4889
		4890	=item EV_CB_DECLARE (type)
		4891
		4892	=item EV_CB_INVOKE (watcher, revents)
		4893
		4894	=item ev_set_cb (ev, cb)
		4895
		4896	Can be used to change the callback member declaration in each watcher,
		4897	and the way callbacks are invoked and set. Must expand to a struct member
		4898	definition and a statement, respectively. See the F<ev.h> header file for
		4899	their default definitions. One possible use for overriding these is to
		4900	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4901	method calls instead of plain function calls in C++.
		4902
		4903	=back
		4904
		4905	=head2 EXPORTED API SYMBOLS
		4906
		4907	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4908	exported symbols, you can use the provided F<Symbol.*> files which list
		4909	all public symbols, one per line:
		4910
		4911	Symbols.ev for libev proper
		4912	Symbols.event for the libevent emulation
		4913
		4914	This can also be used to rename all public symbols to avoid clashes with
		4915	multiple versions of libev linked together (which is obviously bad in
		4916	itself, but sometimes it is inconvenient to avoid this).
		4917
		4918	A sed command like this will create wrapper C<#define>'s that you need to
		4919	include before including F<ev.h>:
		4920
		4921	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4922
		4923	This would create a file F<wrap.h> which essentially looks like this:
		4924
		4925	#define ev_backend myprefix_ev_backend
		4926	#define ev_check_start myprefix_ev_check_start
		4927	#define ev_check_stop myprefix_ev_check_stop
		4928	...
		4929
		4930	=head2 EXAMPLES
		4931
		4932	For a real-world example of a program the includes libev
		4933	verbatim, you can have a look at the EV perl module
		4934	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4935	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4936	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4937	will be compiled. It is pretty complex because it provides its own header
		4938	file.
		4939
		4940	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4941	that everybody includes and which overrides some configure choices:
		4942
		4943	#define EV_FEATURES 8
		4944	#define EV_USE_SELECT 1
		4945	#define EV_PREPARE_ENABLE 1
		4946	#define EV_IDLE_ENABLE 1
		4947	#define EV_SIGNAL_ENABLE 1
		4948	#define EV_CHILD_ENABLE 1
		4949	#define EV_USE_STDEXCEPT 0
		4950	#define EV_CONFIG_H <config.h>
		4951
		4952	#include "ev++.h"
		4953
		4954	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4955
		4956	#include "ev_cpp.h"
		4957	#include "ev.c"
		4958
		4959	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		4960
		4961	=head2 THREADS AND COROUTINES
		4962
		4963	=head3 THREADS
		4964
		4965	All libev functions are reentrant and thread-safe unless explicitly
		4966	documented otherwise, but libev implements no locking itself. This means
		4967	that you can use as many loops as you want in parallel, as long as there
		4968	are no concurrent calls into any libev function with the same loop
		4969	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4970	of course): libev guarantees that different event loops share no data
		4971	structures that need any locking.
		4972
		4973	Or to put it differently: calls with different loop parameters can be done
		4974	concurrently from multiple threads, calls with the same loop parameter
		4975	must be done serially (but can be done from different threads, as long as
		4976	only one thread ever is inside a call at any point in time, e.g. by using
		4977	a mutex per loop).
		4978
		4979	Specifically to support threads (and signal handlers), libev implements
		4980	so-called C<ev_async> watchers, which allow some limited form of
		4981	concurrency on the same event loop, namely waking it up "from the
		4982	outside".
		4983
		4984	If you want to know which design (one loop, locking, or multiple loops
		4985	without or something else still) is best for your problem, then I cannot
		4986	help you, but here is some generic advice:
		4987
		4988	=over 4
		4989
		4990	=item * most applications have a main thread: use the default libev loop
		4991	in that thread, or create a separate thread running only the default loop.
		4992
		4993	This helps integrating other libraries or software modules that use libev
		4994	themselves and don't care/know about threading.
		4995
		4996	=item * one loop per thread is usually a good model.
		4997
		4998	Doing this is almost never wrong, sometimes a better-performance model
		4999	exists, but it is always a good start.
		5000
		5001	=item * other models exist, such as the leader/follower pattern, where one
		5002	loop is handed through multiple threads in a kind of round-robin fashion.
		5003
		5004	Choosing a model is hard - look around, learn, know that usually you can do
		5005	better than you currently do :-)
		5006
		5007	=item * often you need to talk to some other thread which blocks in the
		5008	event loop.
		5009
		5010	C<ev_async> watchers can be used to wake them up from other threads safely
		5011	(or from signal contexts...).
		5012
		5013	An example use would be to communicate signals or other events that only
		5014	work in the default loop by registering the signal watcher with the
		5015	default loop and triggering an C<ev_async> watcher from the default loop
		5016	watcher callback into the event loop interested in the signal.
		5017
		5018	=back
		5019
		5020	See also L</THREAD LOCKING EXAMPLE>.
		5021
		5022	=head3 COROUTINES
		5023
		5024	Libev is very accommodating to coroutines ("cooperative threads"):
		5025	libev fully supports nesting calls to its functions from different
		5026	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5027	different coroutines, and switch freely between both coroutines running
		5028	the loop, as long as you don't confuse yourself). The only exception is
		5029	that you must not do this from C<ev_periodic> reschedule callbacks.
		5030
		5031	Care has been taken to ensure that libev does not keep local state inside
		5032	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5033	they do not call any callbacks.
		5034
		5035	=head2 COMPILER WARNINGS
		5036
		5037	Depending on your compiler and compiler settings, you might get no or a
		5038	lot of warnings when compiling libev code. Some people are apparently
		5039	scared by this.
		5040
		5041	However, these are unavoidable for many reasons. For one, each compiler
		5042	has different warnings, and each user has different tastes regarding
		5043	warning options. "Warn-free" code therefore cannot be a goal except when
		5044	targeting a specific compiler and compiler-version.
		5045
		5046	Another reason is that some compiler warnings require elaborate
		5047	workarounds, or other changes to the code that make it less clear and less
		5048	maintainable.
		5049
		5050	And of course, some compiler warnings are just plain stupid, or simply
		5051	wrong (because they don't actually warn about the condition their message
		5052	seems to warn about). For example, certain older gcc versions had some
		5053	warnings that resulted in an extreme number of false positives. These have
		5054	been fixed, but some people still insist on making code warn-free with
		5055	such buggy versions.
		5056
		5057	While libev is written to generate as few warnings as possible,
		5058	"warn-free" code is not a goal, and it is recommended not to build libev
		5059	with any compiler warnings enabled unless you are prepared to cope with
		5060	them (e.g. by ignoring them). Remember that warnings are just that:
		5061	warnings, not errors, or proof of bugs.
		5062
		5063
		5064	=head2 VALGRIND
		5065
		5066	Valgrind has a special section here because it is a popular tool that is
		5067	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5068
		5069	If you think you found a bug (memory leak, uninitialised data access etc.)
		5070	in libev, then check twice: If valgrind reports something like:
		5071
		5072	==2274== definitely lost: 0 bytes in 0 blocks.
		5073	==2274== possibly lost: 0 bytes in 0 blocks.
		5074	==2274== still reachable: 256 bytes in 1 blocks.
		5075
		5076	Then there is no memory leak, just as memory accounted to global variables
		5077	is not a memleak - the memory is still being referenced, and didn't leak.
		5078
		5079	Similarly, under some circumstances, valgrind might report kernel bugs
		5080	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5081	although an acceptable workaround has been found here), or it might be
		5082	confused.
		5083
		5084	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5085	make it into some kind of religion.
		5086
		5087	If you are unsure about something, feel free to contact the mailing list
		5088	with the full valgrind report and an explanation on why you think this
		5089	is a bug in libev (best check the archives, too :). However, don't be
		5090	annoyed when you get a brisk "this is no bug" answer and take the chance
		5091	of learning how to interpret valgrind properly.
		5092
		5093	If you need, for some reason, empty reports from valgrind for your project
		5094	I suggest using suppression lists.
		5095
		5096
		5097	=head1 PORTABILITY NOTES
		5098
		5099	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5100
		5101	GNU/Linux is the only common platform that supports 64 bit file/large file
		5102	interfaces but I<disables> them by default.
		5103
		5104	That means that libev compiled in the default environment doesn't support
		5105	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5106
		5107	Unfortunately, many programs try to work around this GNU/Linux issue
		5108	by enabling the large file API, which makes them incompatible with the
		5109	standard libev compiled for their system.
		5110
		5111	Likewise, libev cannot enable the large file API itself as this would
		5112	suddenly make it incompatible to the default compile time environment,
		5113	i.e. all programs not using special compile switches.
		5114
		5115	=head2 OS/X AND DARWIN BUGS
		5116
		5117	The whole thing is a bug if you ask me - basically any system interface
		5118	you touch is broken, whether it is locales, poll, kqueue or even the
		5119	OpenGL drivers.
		5120
		5121	=head3 C<kqueue> is buggy
		5122
		5123	The kqueue syscall is broken in all known versions - most versions support
		5124	only sockets, many support pipes.
		5125
		5126	Libev tries to work around this by not using C<kqueue> by default on this
		5127	rotten platform, but of course you can still ask for it when creating a
		5128	loop - embedding a socket-only kqueue loop into a select-based one is
		5129	probably going to work well.
		5130
		5131	=head3 C<poll> is buggy
		5132
		5133	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5134	implementation by something calling C<kqueue> internally around the 10.5.6
		5135	release, so now C<kqueue> I<and> C<poll> are broken.
		5136
		5137	Libev tries to work around this by not using C<poll> by default on
		5138	this rotten platform, but of course you can still ask for it when creating
		5139	a loop.
		5140
		5141	=head3 C<select> is buggy
		5142
		5143	All that's left is C<select>, and of course Apple found a way to fuck this
		5144	one up as well: On OS/X, C<select> actively limits the number of file
		5145	descriptors you can pass in to 1024 - your program suddenly crashes when
		5146	you use more.
		5147
		5148	There is an undocumented "workaround" for this - defining
		5149	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5150	work on OS/X.
		5151
		5152	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5153
		5154	=head3 C<errno> reentrancy
		5155
		5156	The default compile environment on Solaris is unfortunately so
		5157	thread-unsafe that you can't even use components/libraries compiled
		5158	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5159	defined by default. A valid, if stupid, implementation choice.
		5160
		5161	If you want to use libev in threaded environments you have to make sure
		5162	it's compiled with C<_REENTRANT> defined.
		5163
		5164	=head3 Event port backend
		5165
		5166	The scalable event interface for Solaris is called "event
		5167	ports". Unfortunately, this mechanism is very buggy in all major
		5168	releases. If you run into high CPU usage, your program freezes or you get
		5169	a large number of spurious wakeups, make sure you have all the relevant
		5170	and latest kernel patches applied. No, I don't know which ones, but there
		5171	are multiple ones to apply, and afterwards, event ports actually work
		5172	great.
		5173
		5174	If you can't get it to work, you can try running the program by setting
		5175	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5176	C<select> backends.
		5177
		5178	=head2 AIX POLL BUG
		5179
		5180	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5181	this by trying to avoid the poll backend altogether (i.e. it's not even
		5182	compiled in), which normally isn't a big problem as C<select> works fine
		5183	with large bitsets on AIX, and AIX is dead anyway.
		5184
		5185	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5186
		5187	=head3 General issues
		5188
		5189	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5190	requires, and its I/O model is fundamentally incompatible with the POSIX
		5191	model. Libev still offers limited functionality on this platform in
		5192	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5193	descriptors. This only applies when using Win32 natively, not when using
		5194	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5195	as every compiler comes with a slightly differently broken/incompatible
		5196	environment.
		5197
		5198	Lifting these limitations would basically require the full
		5199	re-implementation of the I/O system. If you are into this kind of thing,
		5200	then note that glib does exactly that for you in a very portable way (note
		5201	also that glib is the slowest event library known to man).
		5202
		5203	There is no supported compilation method available on windows except
		5204	embedding it into other applications.
		5205
		5206	Sensible signal handling is officially unsupported by Microsoft - libev
		5207	tries its best, but under most conditions, signals will simply not work.
		5208
		5209	Not a libev limitation but worth mentioning: windows apparently doesn't
		5210	accept large writes: instead of resulting in a partial write, windows will
		5211	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5212	so make sure you only write small amounts into your sockets (less than a
		5213	megabyte seems safe, but this apparently depends on the amount of memory
		5214	available).
		5215
		5216	Due to the many, low, and arbitrary limits on the win32 platform and
		5217	the abysmal performance of winsockets, using a large number of sockets
		5218	is not recommended (and not reasonable). If your program needs to use
		5219	more than a hundred or so sockets, then likely it needs to use a totally
		5220	different implementation for windows, as libev offers the POSIX readiness
		5221	notification model, which cannot be implemented efficiently on windows
		5222	(due to Microsoft monopoly games).
		5223
		5224	A typical way to use libev under windows is to embed it (see the embedding
		5225	section for details) and use the following F<evwrap.h> header file instead
		5226	of F<ev.h>:
		5227
		5228	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5229	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5230
		5231	#include "ev.h"
		5232
		5233	And compile the following F<evwrap.c> file into your project (make sure
		5234	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5235
		5236	#include "evwrap.h"
		5237	#include "ev.c"
		5238
		5239	=head3 The winsocket C<select> function
		5240
		5241	The winsocket C<select> function doesn't follow POSIX in that it
		5242	requires socket I<handles> and not socket I<file descriptors> (it is
		5243	also extremely buggy). This makes select very inefficient, and also
		5244	requires a mapping from file descriptors to socket handles (the Microsoft
		5245	C runtime provides the function C<_open_osfhandle> for this). See the
		5246	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5247	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5248
		5249	The configuration for a "naked" win32 using the Microsoft runtime
		5250	libraries and raw winsocket select is:
		5251
		5252	#define EV_USE_SELECT 1
		5253	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5254
		5255	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5256	complexity in the O(n²) range when using win32.
		5257
		5258	=head3 Limited number of file descriptors
		5259
		5260	Windows has numerous arbitrary (and low) limits on things.
		5261
		5262	Early versions of winsocket's select only supported waiting for a maximum
		5263	of C<64> handles (probably owning to the fact that all windows kernels
		5264	can only wait for C<64> things at the same time internally; Microsoft
		5265	recommends spawning a chain of threads and wait for 63 handles and the
		5266	previous thread in each. Sounds great!).
		5267
		5268	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5269	to some high number (e.g. C<2048>) before compiling the winsocket select
		5270	call (which might be in libev or elsewhere, for example, perl and many
		5271	other interpreters do their own select emulation on windows).
		5272
		5273	Another limit is the number of file descriptors in the Microsoft runtime
		5274	libraries, which by default is C<64> (there must be a hidden I<64>
		5275	fetish or something like this inside Microsoft). You can increase this
		5276	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5277	(another arbitrary limit), but is broken in many versions of the Microsoft
		5278	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5279	(depending on windows version and/or the phase of the moon). To get more,
		5280	you need to wrap all I/O functions and provide your own fd management, but
		5281	the cost of calling select (O(n²)) will likely make this unworkable.
		5282
		5283	=head2 PORTABILITY REQUIREMENTS
		5284
		5285	In addition to a working ISO-C implementation and of course the
		5286	backend-specific APIs, libev relies on a few additional extensions:
		5287
		5288	=over 4
		5289
		5290	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5291	calling conventions regardless of C<ev_watcher_type *>.
		5292
		5293	Libev assumes not only that all watcher pointers have the same internal
		5294	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5295	assumes that the same (machine) code can be used to call any watcher
		5296	callback: The watcher callbacks have different type signatures, but libev
		5297	calls them using an C<ev_watcher *> internally.
		5298
		5299	=item pointer accesses must be thread-atomic
		5300
		5301	Accessing a pointer value must be atomic, it must both be readable and
		5302	writable in one piece - this is the case on all current architectures.
		5303
		5304	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5305
		5306	The type C<sig_atomic_t volatile> (or whatever is defined as
		5307	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5308	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5309	believed to be sufficiently portable.
		5310
		5311	=item C<sigprocmask> must work in a threaded environment
		5312
		5313	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5314	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5315	pthread implementations will either allow C<sigprocmask> in the "main
		5316	thread" or will block signals process-wide, both behaviours would
		5317	be compatible with libev. Interaction between C<sigprocmask> and
		5318	C<pthread_sigmask> could complicate things, however.
		5319
		5320	The most portable way to handle signals is to block signals in all threads
		5321	except the initial one, and run the signal handling loop in the initial
		5322	thread as well.
		5323
		5324	=item C<long> must be large enough for common memory allocation sizes
		5325
		5326	To improve portability and simplify its API, libev uses C<long> internally
		5327	instead of C<size_t> when allocating its data structures. On non-POSIX
		5328	systems (Microsoft...) this might be unexpectedly low, but is still at
		5329	least 31 bits everywhere, which is enough for hundreds of millions of
		5330	watchers.
		5331
		5332	=item C<double> must hold a time value in seconds with enough accuracy
		5333
		5334	The type C<double> is used to represent timestamps. It is required to
		5335	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5336	good enough for at least into the year 4000 with millisecond accuracy
		5337	(the design goal for libev). This requirement is overfulfilled by
		5338	implementations using IEEE 754, which is basically all existing ones.
		5339
		5340	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5341	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5342	is either obsolete or somebody patched it to use C<long double> or
		5343	something like that, just kidding).
		5344
		5345	=back
		5346
		5347	If you know of other additional requirements drop me a note.
		5348
		5349
		5350	=head1 ALGORITHMIC COMPLEXITIES
		5351
		5352	In this section the complexities of (many of) the algorithms used inside
		5353	libev will be documented. For complexity discussions about backends see
		5354	the documentation for C<ev_default_init>.
		5355
		5356	All of the following are about amortised time: If an array needs to be
		5357	extended, libev needs to realloc and move the whole array, but this
		5358	happens asymptotically rarer with higher number of elements, so O(1) might
		5359	mean that libev does a lengthy realloc operation in rare cases, but on
		5360	average it is much faster and asymptotically approaches constant time.
		5361
		5362	=over 4
		5363
		5364	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5365
		5366	This means that, when you have a watcher that triggers in one hour and
		5367	there are 100 watchers that would trigger before that, then inserting will
		5368	have to skip roughly seven (C<ld 100>) of these watchers.
		5369
		5370	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5371
		5372	That means that changing a timer costs less than removing/adding them,
		5373	as only the relative motion in the event queue has to be paid for.
		5374
		5375	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5376
		5377	These just add the watcher into an array or at the head of a list.
		5378
		5379	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5380
		5381	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5382
		5383	These watchers are stored in lists, so they need to be walked to find the
		5384	correct watcher to remove. The lists are usually short (you don't usually
		5385	have many watchers waiting for the same fd or signal: one is typical, two
		5386	is rare).
		5387
		5388	=item Finding the next timer in each loop iteration: O(1)
		5389
		5390	By virtue of using a binary or 4-heap, the next timer is always found at a
		5391	fixed position in the storage array.
		5392
		5393	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5394
		5395	A change means an I/O watcher gets started or stopped, which requires
		5396	libev to recalculate its status (and possibly tell the kernel, depending
		5397	on backend and whether C<ev_io_set> was used).
		5398
		5399	=item Activating one watcher (putting it into the pending state): O(1)
		5400
		5401	=item Priority handling: O(number_of_priorities)
		5402
		5403	Priorities are implemented by allocating some space for each
		5404	priority. When doing priority-based operations, libev usually has to
		5405	linearly search all the priorities, but starting/stopping and activating
		5406	watchers becomes O(1) with respect to priority handling.
		5407
		5408	=item Sending an ev_async: O(1)
		5409
		5410	=item Processing ev_async_send: O(number_of_async_watchers)
		5411
		5412	=item Processing signals: O(max_signal_number)
		5413
		5414	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5415	calls in the current loop iteration and the loop is currently
		5416	blocked. Checking for async and signal events involves iterating over all
		5417	running async watchers or all signal numbers.
		5418
		5419	=back
		5420
		5421
		5422	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5423
		5424	The major version 4 introduced some incompatible changes to the API.
		5425
		5426	At the moment, the C<ev.h> header file provides compatibility definitions
		5427	for all changes, so most programs should still compile. The compatibility
		5428	layer might be removed in later versions of libev, so better update to the
		5429	new API early than late.
		5430
		5431	=over 4
		5432
		5433	=item C<EV_COMPAT3> backwards compatibility mechanism
		5434
		5435	The backward compatibility mechanism can be controlled by
		5436	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5437	section.
		5438
		5439	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5440
		5441	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5442
		5443	ev_loop_destroy (EV_DEFAULT_UC);
		5444	ev_loop_fork (EV_DEFAULT);
		5445
		5446	=item function/symbol renames
		5447
		5448	A number of functions and symbols have been renamed:
		5449
		5450	ev_loop => ev_run
		5451	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5452	EVLOOP_ONESHOT => EVRUN_ONCE
		5453
		5454	ev_unloop => ev_break
		5455	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5456	EVUNLOOP_ONE => EVBREAK_ONE
		5457	EVUNLOOP_ALL => EVBREAK_ALL
		5458
		5459	EV_TIMEOUT => EV_TIMER
		5460
		5461	ev_loop_count => ev_iteration
		5462	ev_loop_depth => ev_depth
		5463	ev_loop_verify => ev_verify
		5464
		5465	Most functions working on C<struct ev_loop> objects don't have an
		5466	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5467	associated constants have been renamed to not collide with the C<struct
		5468	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5469	as all other watcher types. Note that C<ev_loop_fork> is still called
		5470	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5471	typedef.
		5472
		5473	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5474
		5475	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5476	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5477	and work, but the library code will of course be larger.
		5478
		5479	=back
		5480
		5481
		5482	=head1 GLOSSARY
		5483
		5484	=over 4
		5485
		5486	=item active
		5487
		5488	A watcher is active as long as it has been started and not yet stopped.
		5489	See L</WATCHER STATES> for details.
		5490
		5491	=item application
		5492
		5493	In this document, an application is whatever is using libev.
		5494
		5495	=item backend
		5496
		5497	The part of the code dealing with the operating system interfaces.
		5498
		5499	=item callback
		5500
		5501	The address of a function that is called when some event has been
		5502	detected. Callbacks are being passed the event loop, the watcher that
		5503	received the event, and the actual event bitset.
		5504
		5505	=item callback/watcher invocation
		5506
		5507	The act of calling the callback associated with a watcher.
		5508
		5509	=item event
		5510
		5511	A change of state of some external event, such as data now being available
		5512	for reading on a file descriptor, time having passed or simply not having
		5513	any other events happening anymore.
		5514
		5515	In libev, events are represented as single bits (such as C<EV_READ> or
		5516	C<EV_TIMER>).
		5517
		5518	=item event library
		5519
		5520	A software package implementing an event model and loop.
		5521
		5522	=item event loop
		5523
		5524	An entity that handles and processes external events and converts them
		5525	into callback invocations.
		5526
		5527	=item event model
		5528
		5529	The model used to describe how an event loop handles and processes
		5530	watchers and events.
		5531
		5532	=item pending
		5533
		5534	A watcher is pending as soon as the corresponding event has been
		5535	detected. See L</WATCHER STATES> for details.
		5536
		5537	=item real time
		5538
		5539	The physical time that is observed. It is apparently strictly monotonic :)
		5540
		5541	=item wall-clock time
		5542
		5543	The time and date as shown on clocks. Unlike real time, it can actually
		5544	be wrong and jump forwards and backwards, e.g. when you adjust your
		5545	clock.
		5546
		5547	=item watcher
		5548
		5549	A data structure that describes interest in certain events. Watchers need
		5550	to be started (attached to an event loop) before they can receive events.
		5551
		5552	=back
		5553
724	=head1 AUTHOR	5554	=head1 AUTHOR
725		5555
726	Marc Lehmann <libev@schmorp.de>.	5556	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5557	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
727		5558

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