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Revision 1.246 by root, Thu Jul 2 12:08:55 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = ev_default_loop (0);
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_loop (loop, 0);
		62
		63	// unloop was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
10		84
11	Libev is an event loop: you register interest in certain events (such as a	85	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	86	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	To do this, it must take more or less complete control over your process	89	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	90	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	94	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	95	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	104	with customised rescheduling (C<ev_periodic>), synchronous signals
		105	(C<ev_signal>), process status change events (C<ev_child>), and event
		106	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		108	file watchers (C<ev_stat>) and even limited support for fork events
		109	(C<ev_fork>).
		110
		111	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	113	for example).
33		114
34	=head1 CONVENTIONS	115	=head2 CONVENTIONS
35		116
36	Libev is very configurable. In this manual the default configuration	117	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	118	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	119	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	120	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	121	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	122	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	123	this argument.
43		124
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	125	=head2 TIME REPRESENTATION
45		126
46	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
48	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
50	to the double type in C.	131	aliases to the C<double> type in C. When you need to do any calculations
		132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
		156
		157	=head1 GLOBAL FUNCTIONS
		158
		159	These functions can be called anytime, even before initialising the
		160	library in any way.
51		161
52	=over 4	162	=over 4
53		163
54	=item ev_tstamp ev_time ()	164	=item ev_tstamp ev_time ()
55		165
56	Returns the current time as libev would use it.	166	Returns the current time as libev would use it. Please note that the
		167	C<ev_now> function is usually faster and also often returns the timestamp
		168	you actually want to know.
		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
57		175
58	=item int ev_version_major ()	176	=item int ev_version_major ()
59		177
60	=item int ev_version_minor ()	178	=item int ev_version_minor ()
61		179
62	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
63	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
64	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
65	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	184	version of the library your program was compiled against.
67		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
68	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	192	not a problem.
72		193
		194	Example: Make sure we haven't accidentally been linked against the wrong
		195	version.
		196
		197	assert (("libev version mismatch",
		198	ev_version_major () == EV_VERSION_MAJOR
		199	&& ev_version_minor () >= EV_VERSION_MINOR));
		200
		201	=item unsigned int ev_supported_backends ()
		202
		203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		204	value) compiled into this binary of libev (independent of their
		205	availability on the system you are running on). See C<ev_default_loop> for
		206	a description of the set values.
		207
		208	Example: make sure we have the epoll method, because yeah this is cool and
		209	a must have and can we have a torrent of it please!!!11
		210
		211	assert (("sorry, no epoll, no sex",
		212	ev_supported_backends () & EVBACKEND_EPOLL));
		213
		214	=item unsigned int ev_recommended_backends ()
		215
		216	Return the set of all backends compiled into this binary of libev and also
		217	recommended for this platform. This set is often smaller than the one
		218	returned by C<ev_supported_backends>, as for example kqueue is broken on
		219	most BSDs and will not be auto-detected unless you explicitly request it
		220	(assuming you know what you are doing). This is the set of backends that
		221	libev will probe for if you specify no backends explicitly.
		222
		223	=item unsigned int ev_embeddable_backends ()
		224
		225	Returns the set of backends that are embeddable in other event loops. This
		226	is the theoretical, all-platform, value. To find which backends
		227	might be supported on the current system, you would need to look at
		228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		229	recommended ones.
		230
		231	See the description of C<ev_embed> watchers for more info.
		232
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
74		234
75	Sets the allocation function to use (the prototype is similar to the	235	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
77	and free memory (no surprises here). If it returns zero when memory	237	used to allocate and free memory (no surprises here). If it returns zero
78	needs to be allocated, the library might abort or take some potentially	238	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	239	or take some potentially destructive action.
		240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
80		244
81	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
82	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
83	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
84		248
		249	Example: Replace the libev allocator with one that waits a bit and then
		250	retries (example requires a standards-compliant C<realloc>).
		251
		252	static void *
		253	persistent_realloc (void *ptr, size_t size)
		254	{
		255	for (;;)
		256	{
		257	void *newptr = realloc (ptr, size);
		258
		259	if (newptr)
		260	return newptr;
		261
		262	sleep (60);
		263	}
		264	}
		265
		266	...
		267	ev_set_allocator (persistent_realloc);
		268
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
86		270
87	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
88	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
90	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
91	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
92	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	277	(such as abort).
94		278
		279	Example: This is basically the same thing that libev does internally, too.
		280
		281	static void
		282	fatal_error (const char *msg)
		283	{
		284	perror (msg);
		285	abort ();
		286	}
		287
		288	...
		289	ev_set_syserr_cb (fatal_error);
		290
95	=back	291	=back
96		292
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		294
99	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
100	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
101	events, and dynamically created loops which do not.	297	I<function>).
102		298
103	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
104	in your main thread (or in a separate thrad) and for each thread you	300	supports signals and child events, and dynamically created loops which do
105	create, you also create another event loop. Libev itself does no locking	301	not.
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).
109		302
110	=over 4	303	=over 4
111		304
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		306
114	This will initialise the default event loop if it hasn't been initialised	307	This will initialise the default event loop if it hasn't been initialised
115	yet and return it. If the default loop could not be initialised, returns	308	yet and return it. If the default loop could not be initialised, returns
116	false. If it already was initialised it simply returns it (and ignores the	309	false. If it already was initialised it simply returns it (and ignores the
117	flags).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		311
119	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
120	function.	313	function.
121		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
122	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		328
125	It supports the following flags:	329	The following flags are supported:
126		330
127	=over 4	331	=over 4
128		332
129	=item C<EVFLAG_AUTO>	333	=item C<EVFLAG_AUTO>
130		334
131	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	336	thing, believe me).
133		337
134	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
135		339
136	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
137	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
141	around bugs.	345	around bugs.
142		346
		347	=item C<EVFLAG_FORKCHECK>
		348
		349	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		350	a fork, you can also make libev check for a fork in each iteration by
		351	enabling this flag.
		352
		353	This works by calling C<getpid ()> on every iteration of the loop,
		354	and thus this might slow down your event loop if you do a lot of loop
		355	iterations and little real work, but is usually not noticeable (on my
		356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		357	without a system call and thus I<very> fast, but my GNU/Linux system also has
		358	C<pthread_atfork> which is even faster).
		359
		360	The big advantage of this flag is that you can forget about fork (and
		361	forget about forgetting to tell libev about forking) when you use this
		362	flag.
		363
		364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		365	environment variable.
		366
143	=item C<EVMETHOD_SELECT> (portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		368
		369	This is your standard select(2) backend. Not I<completely> standard, as
		370	libev tries to roll its own fd_set with no limits on the number of fds,
		371	but if that fails, expect a fairly low limit on the number of fds when
		372	using this backend. It doesn't scale too well (O(highest_fd)), but its
		373	usually the fastest backend for a low number of (low-numbered :) fds.
		374
		375	To get good performance out of this backend you need a high amount of
		376	parallelism (most of the file descriptors should be busy). If you are
		377	writing a server, you should C<accept ()> in a loop to accept as many
		378	connections as possible during one iteration. You might also want to have
		379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
		385
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		387
147	=item C<EVMETHOD_EPOLL> (linux only)	388	And this is your standard poll(2) backend. It's more complicated
		389	than select, but handles sparse fds better and has no artificial
		390	limit on the number of fds you can use (except it will slow down
		391	considerably with a lot of inactive fds). It scales similarly to select,
		392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		393	performance tips.
148		394
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
150		397
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
152		399
153	=item C<EVMETHOD_PORT> (solaris 10 only)	400	For few fds, this backend is a bit little slower than poll and select,
		401	but it scales phenomenally better. While poll and select usually scale
		402	like O(total_fds) where n is the total number of fds (or the highest fd),
		403	epoll scales either O(1) or O(active_fds).
154		404
155	If one or more of these are ored into the flags value, then only these	405	The epoll mechanism deserves honorable mention as the most misdesigned
156	backends will be tried (in the reverse order as given here). If one are	406	of the more advanced event mechanisms: mere annoyances include silently
157	specified, any backend will do.	407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
		421
		422	While stopping, setting and starting an I/O watcher in the same iteration
		423	will result in some caching, there is still a system call per such
		424	incident (because the same I<file descriptor> could point to a different
		425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		426	file descriptors might not work very well if you register events for both
		427	file descriptors.
		428
		429	Best performance from this backend is achieved by not unregistering all
		430	watchers for a file descriptor until it has been closed, if possible,
		431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
		441	While nominally embeddable in other event loops, this feature is broken in
		442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
		446
		447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		448
		449	Kqueue deserves special mention, as at the time of this writing, it
		450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		451	with anything but sockets and pipes, except on Darwin, where of course
		452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
		455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
		462
		463	It scales in the same way as the epoll backend, but the interface to the
		464	kernel is more efficient (which says nothing about its actual speed, of
		465	course). While stopping, setting and starting an I/O watcher does never
		466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		467	two event changes per incident. Support for C<fork ()> is very bad (but
		468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
		483
		484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		485
		486	This is not implemented yet (and might never be, unless you send me an
		487	implementation). According to reports, C</dev/poll> only supports sockets
		488	and is not embeddable, which would limit the usefulness of this backend
		489	immensely.
		490
		491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		492
		493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		494	it's really slow, but it still scales very well (O(active_fds)).
		495
		496	Please note that Solaris event ports can deliver a lot of spurious
		497	notifications, so you need to use non-blocking I/O or other means to avoid
		498	blocking when no data (or space) is available.
		499
		500	While this backend scales well, it requires one system call per active
		501	file descriptor per loop iteration. For small and medium numbers of file
		502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		503	might perform better.
		504
		505	On the positive side, with the exception of the spurious readiness
		506	notifications, this backend actually performed fully to specification
		507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
		512
		513	=item C<EVBACKEND_ALL>
		514
		515	Try all backends (even potentially broken ones that wouldn't be tried
		516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		518
		519	It is definitely not recommended to use this flag.
158		520
159	=back	521	=back
		522
		523	If one or more of these are or'ed into the flags value, then only these
		524	backends will be tried (in the reverse order as listed here). If none are
		525	specified, all backends in C<ev_recommended_backends ()> will be tried.
		526
		527	Example: This is the most typical usage.
		528
		529	if (!ev_default_loop (0))
		530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		531
		532	Example: Restrict libev to the select and poll backends, and do not allow
		533	environment settings to be taken into account:
		534
		535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		536
		537	Example: Use whatever libev has to offer, but make sure that kqueue is
		538	used if available (warning, breaks stuff, best use only with your own
		539	private event loop and only if you know the OS supports your types of
		540	fds):
		541
		542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		543
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		545
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
164	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
167		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
		555	Example: Try to create a event loop that uses epoll and nothing else.
		556
		557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		558	if (!epoller)
		559	fatal ("no epoll found here, maybe it hides under your chair");
		560
168	=item ev_default_destroy ()	561	=item ev_default_destroy ()
169		562
170	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	564	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cannot rely on this :).	565	sense, so e.g. C<ev_is_active> might still return true. It is your
		566	responsibility to either stop all watchers cleanly yourself I<before>
		567	calling this function, or cope with the fact afterwards (which is usually
		568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
173		579
174	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
175		581
176	Like C<ev_default_destroy>, but destroys an event loop created by an	582	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
178		584
179	=item ev_default_fork ()	585	=item ev_default_fork ()
180		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
184	again makes little sense).	591	sense). You I<must> call it in the child before using any of the libev
		592	functions, and it will only take effect at the next C<ev_loop> iteration.
185		593
186	You I<must> call this function after forking if and only if you want to	594	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	595	process if and only if you want to use the event library in the child. If
188	have to call it.	596	you just fork+exec, you don't have to call it at all.
189		597
190	The function itself is quite fast and it's usually not a problem to call	598	The function itself is quite fast and it's usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in	599	it just in case after a fork. To make this easy, the function will fit in
192	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
193		601
…		…
195		603
196	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
197		605
198	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
199	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
200	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
201		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
		615
		616	=item unsigned int ev_loop_count (loop)
		617
		618	Returns the count of loop iterations for the loop, which is identical to
		619	the number of times libev did poll for new events. It starts at C<0> and
		620	happily wraps around with enough iterations.
		621
		622	This value can sometimes be useful as a generation counter of sorts (it
		623	"ticks" the number of loop iterations), as it roughly corresponds with
		624	C<ev_prepare> and C<ev_check> calls.
		625
202	=item unsigned int ev_method (loop)	626	=item unsigned int ev_backend (loop)
203		627
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	628	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	629	use.
206		630
207	=item ev_tstamp ev_now (loop)	631	=item ev_tstamp ev_now (loop)
208		632
209	Returns the current "event loop time", which is the time the event loop	633	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	634	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	635	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	636	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	637	event occurring (or more correctly, libev finding out about it).
		638
		639	=item ev_now_update (loop)
		640
		641	Establishes the current time by querying the kernel, updating the time
		642	returned by C<ev_now ()> in the progress. This is a costly operation and
		643	is usually done automatically within C<ev_loop ()>.
		644
		645	This function is rarely useful, but when some event callback runs for a
		646	very long time without entering the event loop, updating libev's idea of
		647	the current time is a good idea.
		648
		649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
214		676
215	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
216		678
217	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
219	events.	681	events.
220		682
221	If the flags argument is specified as 0, it will not return until either	683	If the flags argument is specified as C<0>, it will not return until
222	no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
		685
		686	Please note that an explicit C<ev_unloop> is usually better than
		687	relying on all watchers to be stopped when deciding when a program has
		688	finished (especially in interactive programs), but having a program
		689	that automatically loops as long as it has to and no longer by virtue
		690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
223		692
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
225	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
226	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
227		697
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
229	neccessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
		701	be an event internal to libev itself, so there is no guarantee that a
		702	user-registered callback will be called), and will return after one
231	one iteration of the loop.	703	iteration of the loop.
232		704
233	This flags value could be used to implement alternative looping	705	This is useful if you are waiting for some external event in conjunction
234	constructs, but the C<prepare> and C<check> watchers provide a better and	706	with something not expressible using other libev watchers (i.e. "roll your
235	more generic mechanism.	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		708	usually a better approach for this kind of thing.
		709
		710	Here are the gory details of what C<ev_loop> does:
		711
		712	- Before the first iteration, call any pending watchers.
		713	* If EVFLAG_FORKCHECK was used, check for a fork.
		714	- If a fork was detected (by any means), queue and call all fork watchers.
		715	- Queue and call all prepare watchers.
		716	- If we have been forked, detach and recreate the kernel state
		717	as to not disturb the other process.
		718	- Update the kernel state with all outstanding changes.
		719	- Update the "event loop time" (ev_now ()).
		720	- Calculate for how long to sleep or block, if at all
		721	(active idle watchers, EVLOOP_NONBLOCK or not having
		722	any active watchers at all will result in not sleeping).
		723	- Sleep if the I/O and timer collect interval say so.
		724	- Block the process, waiting for any events.
		725	- Queue all outstanding I/O (fd) events.
		726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		727	- Queue all expired timers.
		728	- Queue all expired periodics.
		729	- Unless any events are pending now, queue all idle watchers.
		730	- Queue all check watchers.
		731	- Call all queued watchers in reverse order (i.e. check watchers first).
		732	Signals and child watchers are implemented as I/O watchers, and will
		733	be handled here by queueing them when their watcher gets executed.
		734	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		735	were used, or there are no active watchers, return, otherwise
		736	continue with step *.
		737
		738	Example: Queue some jobs and then loop until no events are outstanding
		739	anymore.
		740
		741	... queue jobs here, make sure they register event watchers as long
		742	... as they still have work to do (even an idle watcher will do..)
		743	ev_loop (my_loop, 0);
		744	... jobs done or somebody called unloop. yeah!
236		745
237	=item ev_unloop (loop, how)	746	=item ev_unloop (loop, how)
238		747
239	Can be used to make a call to C<ev_loop> return early (but only after it	748	Can be used to make a call to C<ev_loop> return early (but only after it
240	has processed all outstanding events). The C<how> argument must be either	749	has processed all outstanding events). The C<how> argument must be either
241	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
242	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		752
		753	This "unloop state" will be cleared when entering C<ev_loop> again.
		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
243		756
244	=item ev_ref (loop)	757	=item ev_ref (loop)
245		758
246	=item ev_unref (loop)	759	=item ev_unref (loop)
247		760
248	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
249	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
250	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
251	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
253	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
254	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
255	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
256	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	773	third-party libraries. Just remember to I<unref after start> and I<ref
		774	before stop> (but only if the watcher wasn't active before, or was active
		775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
		778
		779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		780	running when nothing else is active.
		781
		782	ev_signal exitsig;
		783	ev_signal_init (&exitsig, sig_cb, SIGINT);
		784	ev_signal_start (loop, &exitsig);
		785	evf_unref (loop);
		786
		787	Example: For some weird reason, unregister the above signal handler again.
		788
		789	ev_ref (loop);
		790	ev_signal_stop (loop, &exitsig);
		791
		792	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		793
		794	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		795
		796	These advanced functions influence the time that libev will spend waiting
		797	for events. Both time intervals are by default C<0>, meaning that libev
		798	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		799	latency.
		800
		801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		802	allows libev to delay invocation of I/O and timer/periodic callbacks
		803	to increase efficiency of loop iterations (or to increase power-saving
		804	opportunities).
		805
		806	The idea is that sometimes your program runs just fast enough to handle
		807	one (or very few) event(s) per loop iteration. While this makes the
		808	program responsive, it also wastes a lot of CPU time to poll for new
		809	events, especially with backends like C<select ()> which have a high
		810	overhead for the actual polling but can deliver many events at once.
		811
		812	By setting a higher I<io collect interval> you allow libev to spend more
		813	time collecting I/O events, so you can handle more events per iteration,
		814	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		815	C<ev_timer>) will be not affected. Setting this to a non-null value will
		816	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		817	sleep time ensures that libev will not poll for I/O events more often then
		818	once per this interval, on average.
		819
		820	Likewise, by setting a higher I<timeout collect interval> you allow libev
		821	to spend more time collecting timeouts, at the expense of increased
		822	latency/jitter/inexactness (the watcher callback will be called
		823	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		824	value will not introduce any overhead in libev.
		825
		826	Many (busy) programs can usually benefit by setting the I/O collect
		827	interval to a value near C<0.1> or so, which is often enough for
		828	interactive servers (of course not for games), likewise for timeouts. It
		829	usually doesn't make much sense to set it to a lower value than C<0.01>,
		830	as this approaches the timing granularity of most systems. Note that if
		831	you do transactions with the outside world and you can't increase the
		832	parallelity, then this setting will limit your transaction rate (if you
		833	need to poll once per transaction and the I/O collect interval is 0.01,
		834	then you can't do more than 100 transations per second).
		835
		836	Setting the I<timeout collect interval> can improve the opportunity for
		837	saving power, as the program will "bundle" timer callback invocations that
		838	are "near" in time together, by delaying some, thus reducing the number of
		839	times the process sleeps and wakes up again. Another useful technique to
		840	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		841	they fire on, say, one-second boundaries only.
		842
		843	Example: we only need 0.1s timeout granularity, and we wish not to poll
		844	more often than 100 times per second:
		845
		846	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		847	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		848
		849	=item ev_loop_verify (loop)
		850
		851	This function only does something when C<EV_VERIFY> support has been
		852	compiled in, which is the default for non-minimal builds. It tries to go
		853	through all internal structures and checks them for validity. If anything
		854	is found to be inconsistent, it will print an error message to standard
		855	error and call C<abort ()>.
		856
		857	This can be used to catch bugs inside libev itself: under normal
		858	circumstances, this function will never abort as of course libev keeps its
		859	data structures consistent.
258		860
259	=back	861	=back
260		862
		863
261	=head1 ANATOMY OF A WATCHER	864	=head1 ANATOMY OF A WATCHER
		865
		866	In the following description, uppercase C<TYPE> in names stands for the
		867	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		868	watchers and C<ev_io_start> for I/O watchers.
262		869
263	A watcher is a structure that you create and register to record your	870	A watcher is a structure that you create and register to record your
264	interest in some event. For instance, if you want to wait for STDIN to	871	interest in some event. For instance, if you want to wait for STDIN to
265	become readable, you would create an C<ev_io> watcher for that:	872	become readable, you would create an C<ev_io> watcher for that:
266		873
267	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	874	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
268	{	875	{
269	ev_io_stop (w);	876	ev_io_stop (w);
270	ev_unloop (loop, EVUNLOOP_ALL);	877	ev_unloop (loop, EVUNLOOP_ALL);
271	}	878	}
272		879
273	struct ev_loop *loop = ev_default_loop (0);	880	struct ev_loop *loop = ev_default_loop (0);
		881
274	struct ev_io stdin_watcher;	882	ev_io stdin_watcher;
		883
275	ev_init (&stdin_watcher, my_cb);	884	ev_init (&stdin_watcher, my_cb);
276	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	885	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
277	ev_io_start (loop, &stdin_watcher);	886	ev_io_start (loop, &stdin_watcher);
		887
278	ev_loop (loop, 0);	888	ev_loop (loop, 0);
279		889
280	As you can see, you are responsible for allocating the memory for your	890	As you can see, you are responsible for allocating the memory for your
281	watcher structures (and it is usually a bad idea to do this on the stack,	891	watcher structures (and it is I<usually> a bad idea to do this on the
282	although this can sometimes be quite valid).	892	stack).
		893
		894	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		895	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
283		896
284	Each watcher structure must be initialised by a call to C<ev_init	897	Each watcher structure must be initialised by a call to C<ev_init
285	(watcher *, callback)>, which expects a callback to be provided. This	898	(watcher *, callback)>, which expects a callback to be provided. This
286	callback gets invoked each time the event occurs (or, in the case of io	899	callback gets invoked each time the event occurs (or, in the case of I/O
287	watchers, each time the event loop detects that the file descriptor given	900	watchers, each time the event loop detects that the file descriptor given
288	is readable and/or writable).	901	is readable and/or writable).
289		902
290	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	903	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
291	with arguments specific to this watcher type. There is also a macro	904	macro to configure it, with arguments specific to the watcher type. There
292	to combine initialisation and setting in one call: C<< ev_<type>_init	905	is also a macro to combine initialisation and setting in one call: C<<
293	(watcher *, callback, ...) >>.	906	ev_TYPE_init (watcher *, callback, ...) >>.
294		907
295	To make the watcher actually watch out for events, you have to start it	908	To make the watcher actually watch out for events, you have to start it
296	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	909	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
297	*) >>), and you can stop watching for events at any time by calling the	910	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	911	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
299		912
300	As long as your watcher is active (has been started but not stopped) you	913	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	914	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	915	reinitialise it or call its C<ev_TYPE_set> macro.
303
304	You can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		916
309	Each and every callback receives the event loop pointer as first, the	917	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	918	registered watcher structure as second, and a bitset of received events as
311	third argument.	919	third argument.
312		920
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	944	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		945
338	=item C<EV_CHILD>	946	=item C<EV_CHILD>
339		947
340	The pid specified in the C<ev_child> watcher has received a status change.	948	The pid specified in the C<ev_child> watcher has received a status change.
		949
		950	=item C<EV_STAT>
		951
		952	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		953
342	=item C<EV_IDLE>	954	=item C<EV_IDLE>
343		955
344	The C<ev_idle> watcher has determined that you have nothing better to do.	956	The C<ev_idle> watcher has determined that you have nothing better to do.
345		957
…		…
353	received events. Callbacks of both watcher types can start and stop as	965	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	966	many watchers as they want, and all of them will be taken into account
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	967	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	968	C<ev_loop> from blocking).
357		969
		970	=item C<EV_EMBED>
		971
		972	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		973
		974	=item C<EV_FORK>
		975
		976	The event loop has been resumed in the child process after fork (see
		977	C<ev_fork>).
		978
		979	=item C<EV_ASYNC>
		980
		981	The given async watcher has been asynchronously notified (see C<ev_async>).
		982
		983	=item C<EV_CUSTOM>
		984
		985	Not ever sent (or otherwise used) by libev itself, but can be freely used
		986	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		987
358	=item C<EV_ERROR>	988	=item C<EV_ERROR>
359		989
360	An unspecified error has occured, the watcher has been stopped. This might	990	An unspecified error has occurred, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	991	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	992	ran out of memory, a file descriptor was found to be closed or any other
		993	problem. Libev considers these application bugs.
		994
363	problem. You best act on it by reporting the problem and somehow coping	995	You best act on it by reporting the problem and somehow coping with the
364	with the watcher being stopped.	996	watcher being stopped. Note that well-written programs should not receive
		997	an error ever, so when your watcher receives it, this usually indicates a
		998	bug in your program.
365		999
366	Libev will usually signal a few "dummy" events together with an error,	1000	Libev will usually signal a few "dummy" events together with an error, for
367	for example it might indicate that a fd is readable or writable, and if	1001	example it might indicate that a fd is readable or writable, and if your
368	your callbacks is well-written it can just attempt the operation and cope	1002	callbacks is well-written it can just attempt the operation and cope with
369	with the error from read() or write(). This will not work in multithreaded	1003	the error from read() or write(). This will not work in multi-threaded
370	programs, though, so beware.	1004	programs, though, as the fd could already be closed and reused for another
		1005	thing, so beware.
371		1006
372	=back	1007	=back
373		1008
		1009	=head2 GENERIC WATCHER FUNCTIONS
		1010
		1011	=over 4
		1012
		1013	=item C<ev_init> (ev_TYPE *watcher, callback)
		1014
		1015	This macro initialises the generic portion of a watcher. The contents
		1016	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1017	the generic parts of the watcher are initialised, you I<need> to call
		1018	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1019	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1020	which rolls both calls into one.
		1021
		1022	You can reinitialise a watcher at any time as long as it has been stopped
		1023	(or never started) and there are no pending events outstanding.
		1024
		1025	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1026	int revents)>.
		1027
		1028	Example: Initialise an C<ev_io> watcher in two steps.
		1029
		1030	ev_io w;
		1031	ev_init (&w, my_cb);
		1032	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1033
		1034	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		1035
		1036	This macro initialises the type-specific parts of a watcher. You need to
		1037	call C<ev_init> at least once before you call this macro, but you can
		1038	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1039	macro on a watcher that is active (it can be pending, however, which is a
		1040	difference to the C<ev_init> macro).
		1041
		1042	Although some watcher types do not have type-specific arguments
		1043	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1044
		1045	See C<ev_init>, above, for an example.
		1046
		1047	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1048
		1049	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1050	calls into a single call. This is the most convenient method to initialise
		1051	a watcher. The same limitations apply, of course.
		1052
		1053	Example: Initialise and set an C<ev_io> watcher in one step.
		1054
		1055	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1056
		1057	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		1058
		1059	Starts (activates) the given watcher. Only active watchers will receive
		1060	events. If the watcher is already active nothing will happen.
		1061
		1062	Example: Start the C<ev_io> watcher that is being abused as example in this
		1063	whole section.
		1064
		1065	ev_io_start (EV_DEFAULT_UC, &w);
		1066
		1067	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1068
		1069	Stops the given watcher if active, and clears the pending status (whether
		1070	the watcher was active or not).
		1071
		1072	It is possible that stopped watchers are pending - for example,
		1073	non-repeating timers are being stopped when they become pending - but
		1074	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1075	pending. If you want to free or reuse the memory used by the watcher it is
		1076	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1077
		1078	=item bool ev_is_active (ev_TYPE *watcher)
		1079
		1080	Returns a true value iff the watcher is active (i.e. it has been started
		1081	and not yet been stopped). As long as a watcher is active you must not modify
		1082	it.
		1083
		1084	=item bool ev_is_pending (ev_TYPE *watcher)
		1085
		1086	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1087	events but its callback has not yet been invoked). As long as a watcher
		1088	is pending (but not active) you must not call an init function on it (but
		1089	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1090	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1091	it).
		1092
		1093	=item callback ev_cb (ev_TYPE *watcher)
		1094
		1095	Returns the callback currently set on the watcher.
		1096
		1097	=item ev_cb_set (ev_TYPE *watcher, callback)
		1098
		1099	Change the callback. You can change the callback at virtually any time
		1100	(modulo threads).
		1101
		1102	=item ev_set_priority (ev_TYPE *watcher, priority)
		1103
		1104	=item int ev_priority (ev_TYPE *watcher)
		1105
		1106	Set and query the priority of the watcher. The priority is a small
		1107	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1108	(default: C<-2>). Pending watchers with higher priority will be invoked
		1109	before watchers with lower priority, but priority will not keep watchers
		1110	from being executed (except for C<ev_idle> watchers).
		1111
		1112	If you need to suppress invocation when higher priority events are pending
		1113	you need to look at C<ev_idle> watchers, which provide this functionality.
		1114
		1115	You I<must not> change the priority of a watcher as long as it is active or
		1116	pending.
		1117
		1118	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1119	fine, as long as you do not mind that the priority value you query might
		1120	or might not have been clamped to the valid range.
		1121
		1122	The default priority used by watchers when no priority has been set is
		1123	always C<0>, which is supposed to not be too high and not be too low :).
		1124
		1125	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1126	priorities.
		1127
		1128	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1129
		1130	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1131	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1132	can deal with that fact, as both are simply passed through to the
		1133	callback.
		1134
		1135	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1136
		1137	If the watcher is pending, this function clears its pending status and
		1138	returns its C<revents> bitset (as if its callback was invoked). If the
		1139	watcher isn't pending it does nothing and returns C<0>.
		1140
		1141	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1142	callback to be invoked, which can be accomplished with this function.
		1143
		1144	=back
		1145
		1146
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1147	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		1148
376	Each watcher has, by default, a member C<void *data> that you can change	1149	Each watcher has, by default, a member C<void *data> that you can change
377	and read at any time, libev will completely ignore it. This can be used	1150	and read at any time: libev will completely ignore it. This can be used
378	to associate arbitrary data with your watcher. If you need more data and	1151	to associate arbitrary data with your watcher. If you need more data and
379	don't want to allocate memory and store a pointer to it in that data	1152	don't want to allocate memory and store a pointer to it in that data
380	member, you can also "subclass" the watcher type and provide your own	1153	member, you can also "subclass" the watcher type and provide your own
381	data:	1154	data:
382		1155
383	struct my_io	1156	struct my_io
384	{	1157	{
385	struct ev_io io;	1158	ev_io io;
386	int otherfd;	1159	int otherfd;
387	void *somedata;	1160	void *somedata;
388	struct whatever *mostinteresting;	1161	struct whatever *mostinteresting;
389	}	1162	};
		1163
		1164	...
		1165	struct my_io w;
		1166	ev_io_init (&w.io, my_cb, fd, EV_READ);
390		1167
391	And since your callback will be called with a pointer to the watcher, you	1168	And since your callback will be called with a pointer to the watcher, you
392	can cast it back to your own type:	1169	can cast it back to your own type:
393		1170
394	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1171	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
395	{	1172	{
396	struct my_io *w = (struct my_io *)w_;	1173	struct my_io *w = (struct my_io *)w_;
397	...	1174	...
398	}	1175	}
399		1176
400	More interesting and less C-conformant ways of catsing your callback type	1177	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	1178	instead have been omitted.
		1179
		1180	Another common scenario is to use some data structure with multiple
		1181	embedded watchers:
		1182
		1183	struct my_biggy
		1184	{
		1185	int some_data;
		1186	ev_timer t1;
		1187	ev_timer t2;
		1188	}
		1189
		1190	In this case getting the pointer to C<my_biggy> is a bit more
		1191	complicated: Either you store the address of your C<my_biggy> struct
		1192	in the C<data> member of the watcher (for woozies), or you need to use
		1193	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1194	programmers):
		1195
		1196	#include <stddef.h>
		1197
		1198	static void
		1199	t1_cb (EV_P_ ev_timer *w, int revents)
		1200	{
		1201	struct my_biggy big = (struct my_biggy *)
		1202	(((char *)w) - offsetof (struct my_biggy, t1));
		1203	}
		1204
		1205	static void
		1206	t2_cb (EV_P_ ev_timer *w, int revents)
		1207	{
		1208	struct my_biggy big = (struct my_biggy *)
		1209	(((char *)w) - offsetof (struct my_biggy, t2));
		1210	}
		1211
		1212	=head2 WATCHER PRIORITY MODELS
		1213
		1214	Many event loops support I<watcher priorities>, which are usually small
		1215	integers that influence the ordering of event callback invocation
		1216	between watchers in some way, all else being equal.
		1217
		1218	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1219	description for the more technical details such as the actual priority
		1220	range.
		1221
		1222	There are two common ways how these these priorities are being interpreted
		1223	by event loops:
		1224
		1225	In the more common lock-out model, higher priorities "lock out" invocation
		1226	of lower priority watchers, which means as long as higher priority
		1227	watchers receive events, lower priority watchers are not being invoked.
		1228
		1229	The less common only-for-ordering model uses priorities solely to order
		1230	callback invocation within a single event loop iteration: Higher priority
		1231	watchers are invoked before lower priority ones, but they all get invoked
		1232	before polling for new events.
		1233
		1234	Libev uses the second (only-for-ordering) model for all its watchers
		1235	except for idle watchers (which use the lock-out model).
		1236
		1237	The rationale behind this is that implementing the lock-out model for
		1238	watchers is not well supported by most kernel interfaces, and most event
		1239	libraries will just poll for the same events again and again as long as
		1240	their callbacks have not been executed, which is very inefficient in the
		1241	common case of one high-priority watcher locking out a mass of lower
		1242	priority ones.
		1243
		1244	Static (ordering) priorities are most useful when you have two or more
		1245	watchers handling the same resource: a typical usage example is having an
		1246	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1247	timeouts. Under load, data might be received while the program handles
		1248	other jobs, but since timers normally get invoked first, the timeout
		1249	handler will be executed before checking for data. In that case, giving
		1250	the timer a lower priority than the I/O watcher ensures that I/O will be
		1251	handled first even under adverse conditions (which is usually, but not
		1252	always, what you want).
		1253
		1254	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1255	will only be executed when no same or higher priority watchers have
		1256	received events, they can be used to implement the "lock-out" model when
		1257	required.
		1258
		1259	For example, to emulate how many other event libraries handle priorities,
		1260	you can associate an C<ev_idle> watcher to each such watcher, and in
		1261	the normal watcher callback, you just start the idle watcher. The real
		1262	processing is done in the idle watcher callback. This causes libev to
		1263	continously poll and process kernel event data for the watcher, but when
		1264	the lock-out case is known to be rare (which in turn is rare :), this is
		1265	workable.
		1266
		1267	Usually, however, the lock-out model implemented that way will perform
		1268	miserably under the type of load it was designed to handle. In that case,
		1269	it might be preferable to stop the real watcher before starting the
		1270	idle watcher, so the kernel will not have to process the event in case
		1271	the actual processing will be delayed for considerable time.
		1272
		1273	Here is an example of an I/O watcher that should run at a strictly lower
		1274	priority than the default, and which should only process data when no
		1275	other events are pending:
		1276
		1277	ev_idle idle; // actual processing watcher
		1278	ev_io io; // actual event watcher
		1279
		1280	static void
		1281	io_cb (EV_P_ ev_io *w, int revents)
		1282	{
		1283	// stop the I/O watcher, we received the event, but
		1284	// are not yet ready to handle it.
		1285	ev_io_stop (EV_A_ w);
		1286
		1287	// start the idle watcher to ahndle the actual event.
		1288	// it will not be executed as long as other watchers
		1289	// with the default priority are receiving events.
		1290	ev_idle_start (EV_A_ &idle);
		1291	}
		1292
		1293	static void
		1294	idle_cb (EV_P_ ev_idle *w, int revents)
		1295	{
		1296	// actual processing
		1297	read (STDIN_FILENO, ...);
		1298
		1299	// have to start the I/O watcher again, as
		1300	// we have handled the event
		1301	ev_io_start (EV_P_ &io);
		1302	}
		1303
		1304	// initialisation
		1305	ev_idle_init (&idle, idle_cb);
		1306	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1307	ev_io_start (EV_DEFAULT_ &io);
		1308
		1309	In the "real" world, it might also be beneficial to start a timer, so that
		1310	low-priority connections can not be locked out forever under load. This
		1311	enables your program to keep a lower latency for important connections
		1312	during short periods of high load, while not completely locking out less
		1313	important ones.
402		1314
403		1315
404	=head1 WATCHER TYPES	1316	=head1 WATCHER TYPES
405		1317
406	This section describes each watcher in detail, but will not repeat	1318	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1319	information given in the last section. Any initialisation/set macros,
		1320	functions and members specific to the watcher type are explained.
408		1321
		1322	Members are additionally marked with either I<[read-only]>, meaning that,
		1323	while the watcher is active, you can look at the member and expect some
		1324	sensible content, but you must not modify it (you can modify it while the
		1325	watcher is stopped to your hearts content), or I<[read-write]>, which
		1326	means you can expect it to have some sensible content while the watcher
		1327	is active, but you can also modify it. Modifying it may not do something
		1328	sensible or take immediate effect (or do anything at all), but libev will
		1329	not crash or malfunction in any way.
		1330
		1331
409	=head2 C<ev_io> - is this file descriptor readable or writable	1332	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1333
411	I/O watchers check whether a file descriptor is readable or writable	1334	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1335	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1336	would not block the process and writing would at least be able to write
414	condition persists. Remember you can stop the watcher if you don't want to	1337	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1338	receiving events as long as the condition persists. Remember you can stop
		1339	the watcher if you don't want to act on the event and neither want to
		1340	receive future events.
416		1341
417	In general you can register as many read and/or write event watchers oer	1342	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	1343	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	1344	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1345	required if you know what you are doing).
421		1346
422	You have to be careful with dup'ed file descriptors, though. Some backends	1347	If you cannot use non-blocking mode, then force the use of a
423	(the linux epoll backend is a notable example) cannot handle dup'ed file	1348	known-to-be-good backend (at the time of this writing, this includes only
424	descriptors correctly if you register interest in two or more fds pointing	1349	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
425	to the same file/socket etc. description.	1350	descriptors for which non-blocking operation makes no sense (such as
		1351	files) - libev doesn't guarentee any specific behaviour in that case.
426		1352
427	If you must do this, then force the use of a known-to-be-good backend	1353	Another thing you have to watch out for is that it is quite easy to
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	1354	receive "spurious" readiness notifications, that is your callback might
429	EVMETHOD_POLL).	1355	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1356	because there is no data. Not only are some backends known to create a
		1357	lot of those (for example Solaris ports), it is very easy to get into
		1358	this situation even with a relatively standard program structure. Thus
		1359	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1360	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1361
		1362	If you cannot run the fd in non-blocking mode (for example you should
		1363	not play around with an Xlib connection), then you have to separately
		1364	re-test whether a file descriptor is really ready with a known-to-be good
		1365	interface such as poll (fortunately in our Xlib example, Xlib already
		1366	does this on its own, so its quite safe to use). Some people additionally
		1367	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1368	indefinitely.
		1369
		1370	But really, best use non-blocking mode.
		1371
		1372	=head3 The special problem of disappearing file descriptors
		1373
		1374	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1375	descriptor (either due to calling C<close> explicitly or any other means,
		1376	such as C<dup2>). The reason is that you register interest in some file
		1377	descriptor, but when it goes away, the operating system will silently drop
		1378	this interest. If another file descriptor with the same number then is
		1379	registered with libev, there is no efficient way to see that this is, in
		1380	fact, a different file descriptor.
		1381
		1382	To avoid having to explicitly tell libev about such cases, libev follows
		1383	the following policy: Each time C<ev_io_set> is being called, libev
		1384	will assume that this is potentially a new file descriptor, otherwise
		1385	it is assumed that the file descriptor stays the same. That means that
		1386	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1387	descriptor even if the file descriptor number itself did not change.
		1388
		1389	This is how one would do it normally anyway, the important point is that
		1390	the libev application should not optimise around libev but should leave
		1391	optimisations to libev.
		1392
		1393	=head3 The special problem of dup'ed file descriptors
		1394
		1395	Some backends (e.g. epoll), cannot register events for file descriptors,
		1396	but only events for the underlying file descriptions. That means when you
		1397	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1398	events for them, only one file descriptor might actually receive events.
		1399
		1400	There is no workaround possible except not registering events
		1401	for potentially C<dup ()>'ed file descriptors, or to resort to
		1402	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1403
		1404	=head3 The special problem of fork
		1405
		1406	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1407	useless behaviour. Libev fully supports fork, but needs to be told about
		1408	it in the child.
		1409
		1410	To support fork in your programs, you either have to call
		1411	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1412	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1413	C<EVBACKEND_POLL>.
		1414
		1415	=head3 The special problem of SIGPIPE
		1416
		1417	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1418	when writing to a pipe whose other end has been closed, your program gets
		1419	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1420	this is sensible behaviour, for daemons, this is usually undesirable.
		1421
		1422	So when you encounter spurious, unexplained daemon exits, make sure you
		1423	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1424	somewhere, as that would have given you a big clue).
		1425
		1426
		1427	=head3 Watcher-Specific Functions
430		1428
431	=over 4	1429	=over 4
432		1430
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1431	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1432
435	=item ev_io_set (ev_io *, int fd, int events)	1433	=item ev_io_set (ev_io *, int fd, int events)
436		1434
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1435	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1436	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1437	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1438
		1439	=item int fd [read-only]
		1440
		1441	The file descriptor being watched.
		1442
		1443	=item int events [read-only]
		1444
		1445	The events being watched.
440		1446
441	=back	1447	=back
442		1448
		1449	=head3 Examples
		1450
		1451	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1452	readable, but only once. Since it is likely line-buffered, you could
		1453	attempt to read a whole line in the callback.
		1454
		1455	static void
		1456	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1457	{
		1458	ev_io_stop (loop, w);
		1459	.. read from stdin here (or from w->fd) and handle any I/O errors
		1460	}
		1461
		1462	...
		1463	struct ev_loop *loop = ev_default_init (0);
		1464	ev_io stdin_readable;
		1465	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1466	ev_io_start (loop, &stdin_readable);
		1467	ev_loop (loop, 0);
		1468
		1469
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1470	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1471
445	Timer watchers are simple relative timers that generate an event after a	1472	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1473	given time, and optionally repeating in regular intervals after that.
447		1474
448	The timers are based on real time, that is, if you register an event that	1475	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1476	times out after an hour and you reset your system clock to January last
450	time, it will still time out after (roughly) and hour. "Roughly" because	1477	year, it will still time out after (roughly) one hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1478	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1479	monotonic clock option helps a lot here).
		1480
		1481	The callback is guaranteed to be invoked only I<after> its timeout has
		1482	passed (not I<at>, so on systems with very low-resolution clocks this
		1483	might introduce a small delay). If multiple timers become ready during the
		1484	same loop iteration then the ones with earlier time-out values are invoked
		1485	before ones with later time-out values (but this is no longer true when a
		1486	callback calls C<ev_loop> recursively).
		1487
		1488	=head3 Be smart about timeouts
		1489
		1490	Many real-world problems involve some kind of timeout, usually for error
		1491	recovery. A typical example is an HTTP request - if the other side hangs,
		1492	you want to raise some error after a while.
		1493
		1494	What follows are some ways to handle this problem, from obvious and
		1495	inefficient to smart and efficient.
		1496
		1497	In the following, a 60 second activity timeout is assumed - a timeout that
		1498	gets reset to 60 seconds each time there is activity (e.g. each time some
		1499	data or other life sign was received).
		1500
		1501	=over 4
		1502
		1503	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1504
		1505	This is the most obvious, but not the most simple way: In the beginning,
		1506	start the watcher:
		1507
		1508	ev_timer_init (timer, callback, 60., 0.);
		1509	ev_timer_start (loop, timer);
		1510
		1511	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1512	and start it again:
		1513
		1514	ev_timer_stop (loop, timer);
		1515	ev_timer_set (timer, 60., 0.);
		1516	ev_timer_start (loop, timer);
		1517
		1518	This is relatively simple to implement, but means that each time there is
		1519	some activity, libev will first have to remove the timer from its internal
		1520	data structure and then add it again. Libev tries to be fast, but it's
		1521	still not a constant-time operation.
		1522
		1523	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1524
		1525	This is the easiest way, and involves using C<ev_timer_again> instead of
		1526	C<ev_timer_start>.
		1527
		1528	To implement this, configure an C<ev_timer> with a C<repeat> value
		1529	of C<60> and then call C<ev_timer_again> at start and each time you
		1530	successfully read or write some data. If you go into an idle state where
		1531	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1532	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1533
		1534	That means you can ignore both the C<ev_timer_start> function and the
		1535	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1536	member and C<ev_timer_again>.
		1537
		1538	At start:
		1539
		1540	ev_init (timer, callback);
		1541	timer->repeat = 60.;
		1542	ev_timer_again (loop, timer);
		1543
		1544	Each time there is some activity:
		1545
		1546	ev_timer_again (loop, timer);
		1547
		1548	It is even possible to change the time-out on the fly, regardless of
		1549	whether the watcher is active or not:
		1550
		1551	timer->repeat = 30.;
		1552	ev_timer_again (loop, timer);
		1553
		1554	This is slightly more efficient then stopping/starting the timer each time
		1555	you want to modify its timeout value, as libev does not have to completely
		1556	remove and re-insert the timer from/into its internal data structure.
		1557
		1558	It is, however, even simpler than the "obvious" way to do it.
		1559
		1560	=item 3. Let the timer time out, but then re-arm it as required.
		1561
		1562	This method is more tricky, but usually most efficient: Most timeouts are
		1563	relatively long compared to the intervals between other activity - in
		1564	our example, within 60 seconds, there are usually many I/O events with
		1565	associated activity resets.
		1566
		1567	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1568	but remember the time of last activity, and check for a real timeout only
		1569	within the callback:
		1570
		1571	ev_tstamp last_activity; // time of last activity
		1572
		1573	static void
		1574	callback (EV_P_ ev_timer *w, int revents)
		1575	{
		1576	ev_tstamp now = ev_now (EV_A);
		1577	ev_tstamp timeout = last_activity + 60.;
		1578
		1579	// if last_activity + 60. is older than now, we did time out
		1580	if (timeout < now)
		1581	{
		1582	// timeout occured, take action
		1583	}
		1584	else
		1585	{
		1586	// callback was invoked, but there was some activity, re-arm
		1587	// the watcher to fire in last_activity + 60, which is
		1588	// guaranteed to be in the future, so "again" is positive:
		1589	w->repeat = timeout - now;
		1590	ev_timer_again (EV_A_ w);
		1591	}
		1592	}
		1593
		1594	To summarise the callback: first calculate the real timeout (defined
		1595	as "60 seconds after the last activity"), then check if that time has
		1596	been reached, which means something I<did>, in fact, time out. Otherwise
		1597	the callback was invoked too early (C<timeout> is in the future), so
		1598	re-schedule the timer to fire at that future time, to see if maybe we have
		1599	a timeout then.
		1600
		1601	Note how C<ev_timer_again> is used, taking advantage of the
		1602	C<ev_timer_again> optimisation when the timer is already running.
		1603
		1604	This scheme causes more callback invocations (about one every 60 seconds
		1605	minus half the average time between activity), but virtually no calls to
		1606	libev to change the timeout.
		1607
		1608	To start the timer, simply initialise the watcher and set C<last_activity>
		1609	to the current time (meaning we just have some activity :), then call the
		1610	callback, which will "do the right thing" and start the timer:
		1611
		1612	ev_init (timer, callback);
		1613	last_activity = ev_now (loop);
		1614	callback (loop, timer, EV_TIMEOUT);
		1615
		1616	And when there is some activity, simply store the current time in
		1617	C<last_activity>, no libev calls at all:
		1618
		1619	last_actiivty = ev_now (loop);
		1620
		1621	This technique is slightly more complex, but in most cases where the
		1622	time-out is unlikely to be triggered, much more efficient.
		1623
		1624	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1625	callback :) - just change the timeout and invoke the callback, which will
		1626	fix things for you.
		1627
		1628	=item 4. Wee, just use a double-linked list for your timeouts.
		1629
		1630	If there is not one request, but many thousands (millions...), all
		1631	employing some kind of timeout with the same timeout value, then one can
		1632	do even better:
		1633
		1634	When starting the timeout, calculate the timeout value and put the timeout
		1635	at the I<end> of the list.
		1636
		1637	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1638	the list is expected to fire (for example, using the technique #3).
		1639
		1640	When there is some activity, remove the timer from the list, recalculate
		1641	the timeout, append it to the end of the list again, and make sure to
		1642	update the C<ev_timer> if it was taken from the beginning of the list.
		1643
		1644	This way, one can manage an unlimited number of timeouts in O(1) time for
		1645	starting, stopping and updating the timers, at the expense of a major
		1646	complication, and having to use a constant timeout. The constant timeout
		1647	ensures that the list stays sorted.
		1648
		1649	=back
		1650
		1651	So which method the best?
		1652
		1653	Method #2 is a simple no-brain-required solution that is adequate in most
		1654	situations. Method #3 requires a bit more thinking, but handles many cases
		1655	better, and isn't very complicated either. In most case, choosing either
		1656	one is fine, with #3 being better in typical situations.
		1657
		1658	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1659	rather complicated, but extremely efficient, something that really pays
		1660	off after the first million or so of active timers, i.e. it's usually
		1661	overkill :)
		1662
		1663	=head3 The special problem of time updates
		1664
		1665	Establishing the current time is a costly operation (it usually takes at
		1666	least two system calls): EV therefore updates its idea of the current
		1667	time only before and after C<ev_loop> collects new events, which causes a
		1668	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1669	lots of events in one iteration.
453		1670
454	The relative timeouts are calculated relative to the C<ev_now ()>	1671	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	1672	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	1673	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	1674	you suspect event processing to be delayed and you I<need> to base the
458	ion the current time, use something like this to adjust for this:	1675	timeout on the current time, use something like this to adjust for this:
459		1676
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1677	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461		1678
		1679	If the event loop is suspended for a long time, you can also force an
		1680	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1681	()>.
		1682
		1683	=head3 Watcher-Specific Functions and Data Members
		1684
462	=over 4	1685	=over 4
463		1686
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1687	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1688
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1689	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		1690
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1691	Configure the timer to trigger after C<after> seconds. If C<repeat>
469	C<0.>, then it will automatically be stopped. If it is positive, then the	1692	is C<0.>, then it will automatically be stopped once the timeout is
470	timer will automatically be configured to trigger again C<repeat> seconds	1693	reached. If it is positive, then the timer will automatically be
471	later, again, and again, until stopped manually.	1694	configured to trigger again C<repeat> seconds later, again, and again,
		1695	until stopped manually.
472		1696
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1697	The timer itself will do a best-effort at avoiding drift, that is, if
474	configure a timer to trigger every 10 seconds, then it will trigger at	1698	you configure a timer to trigger every 10 seconds, then it will normally
475	exactly 10 second intervals. If, however, your program cannot keep up with	1699	trigger at exactly 10 second intervals. If, however, your program cannot
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1700	keep up with the timer (because it takes longer than those 10 seconds to
477	timer will not fire more than once per event loop iteration.	1701	do stuff) the timer will not fire more than once per event loop iteration.
478		1702
479	=item ev_timer_again (loop)	1703	=item ev_timer_again (loop, ev_timer *)
480		1704
481	This will act as if the timer timed out and restart it again if it is	1705	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1706	repeating. The exact semantics are:
483		1707
		1708	If the timer is pending, its pending status is cleared.
		1709
484	If the timer is started but nonrepeating, stop it.	1710	If the timer is started but non-repeating, stop it (as if it timed out).
485		1711
486	If the timer is repeating, either start it if necessary (with the repeat	1712	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1713	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1714
489	This sounds a bit complicated, but here is a useful and typical	1715	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
490	example: Imagine you have a tcp connection and you want a so-called idle	1716	usage example.
491	timeout, that is, you want to be called when there have been, say, 60	1717
492	seconds of inactivity on the socket. The easiest way to do this is to	1718	=item ev_tstamp repeat [read-write]
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1719
494	time you successfully read or write some data. If you go into an idle	1720	The current C<repeat> value. Will be used each time the watcher times out
495	state where you do not expect data to travel on the socket, you can stop	1721	or C<ev_timer_again> is called, and determines the next timeout (if any),
496	the timer, and again will automatically restart it if need be.	1722	which is also when any modifications are taken into account.
497		1723
498	=back	1724	=back
499		1725
		1726	=head3 Examples
		1727
		1728	Example: Create a timer that fires after 60 seconds.
		1729
		1730	static void
		1731	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1732	{
		1733	.. one minute over, w is actually stopped right here
		1734	}
		1735
		1736	ev_timer mytimer;
		1737	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1738	ev_timer_start (loop, &mytimer);
		1739
		1740	Example: Create a timeout timer that times out after 10 seconds of
		1741	inactivity.
		1742
		1743	static void
		1744	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1745	{
		1746	.. ten seconds without any activity
		1747	}
		1748
		1749	ev_timer mytimer;
		1750	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1751	ev_timer_again (&mytimer); /* start timer */
		1752	ev_loop (loop, 0);
		1753
		1754	// and in some piece of code that gets executed on any "activity":
		1755	// reset the timeout to start ticking again at 10 seconds
		1756	ev_timer_again (&mytimer);
		1757
		1758
500	=head2 C<ev_periodic> - to cron or not to cron	1759	=head2 C<ev_periodic> - to cron or not to cron?
501		1760
502	Periodic watchers are also timers of a kind, but they are very versatile	1761	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1762	(and unfortunately a bit complex).
504		1763
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1764	Unlike C<ev_timer>, periodic watchers are not based on real time (or
506	but on wallclock time (absolute time). You can tell a periodic watcher	1765	relative time, the physical time that passes) but on wall clock time
507	to trigger "at" some specific point in time. For example, if you tell a	1766	(absolute time, the thing you can read on your calender or clock). The
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1767	difference is that wall clock time can run faster or slower than real
509	+ 10.>) and then reset your system clock to the last year, then it will	1768	time, and time jumps are not uncommon (e.g. when you adjust your
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1769	wrist-watch).
511	roughly 10 seconds later and of course not if you reset your system time
512	again).
513		1770
514	They can also be used to implement vastly more complex timers, such as	1771	You can tell a periodic watcher to trigger after some specific point
		1772	in time: for example, if you tell a periodic watcher to trigger "in 10
		1773	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1774	not a delay) and then reset your system clock to January of the previous
		1775	year, then it will take a year or more to trigger the event (unlike an
		1776	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1777	it, as it uses a relative timeout).
		1778
		1779	C<ev_periodic> watchers can also be used to implement vastly more complex
515	triggering an event on eahc midnight, local time.	1780	timers, such as triggering an event on each "midnight, local time", or
		1781	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1782	those cannot react to time jumps.
		1783
		1784	As with timers, the callback is guaranteed to be invoked only when the
		1785	point in time where it is supposed to trigger has passed. If multiple
		1786	timers become ready during the same loop iteration then the ones with
		1787	earlier time-out values are invoked before ones with later time-out values
		1788	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1789
		1790	=head3 Watcher-Specific Functions and Data Members
516		1791
517	=over 4	1792	=over 4
518		1793
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1794	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
520		1795
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1796	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
522		1797
523	Lots of arguments, lets sort it out... There are basically three modes of	1798	Lots of arguments, let's sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	1799	operation, and we will explain them from simplest to most complex:
525
526		1800
527	=over 4	1801	=over 4
528		1802
529	=item * absolute timer (interval = reschedule_cb = 0)	1803	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
530		1804
531	In this configuration the watcher triggers an event at the wallclock time	1805	In this configuration the watcher triggers an event after the wall clock
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1806	time C<offset> has passed. It will not repeat and will not adjust when a
533	that is, if it is to be run at January 1st 2011 then it will run when the	1807	time jump occurs, that is, if it is to be run at January 1st 2011 then it
534	system time reaches or surpasses this time.	1808	will be stopped and invoked when the system clock reaches or surpasses
		1809	this point in time.
535		1810
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1811	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
537		1812
538	In this mode the watcher will always be scheduled to time out at the next	1813	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	1814	C<offset + N * interval> time (for some integer N, which can also be
540	of any time jumps.	1815	negative) and then repeat, regardless of any time jumps. The C<offset>
		1816	argument is merely an offset into the C<interval> periods.
541		1817
542	This can be used to create timers that do not drift with respect to system	1818	This can be used to create timers that do not drift with respect to the
543	time:	1819	system clock, for example, here is an C<ev_periodic> that triggers each
		1820	hour, on the hour (with respect to UTC):
544		1821
545	ev_periodic_set (&periodic, 0., 3600., 0);	1822	ev_periodic_set (&periodic, 0., 3600., 0);
546		1823
547	This doesn't mean there will always be 3600 seconds in between triggers,	1824	This doesn't mean there will always be 3600 seconds in between triggers,
548	but only that the the callback will be called when the system time shows a	1825	but only that the callback will be called when the system time shows a
549	full hour (UTC), or more correctly, when the system time is evenly divisible	1826	full hour (UTC), or more correctly, when the system time is evenly divisible
550	by 3600.	1827	by 3600.
551		1828
552	Another way to think about it (for the mathematically inclined) is that	1829	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	1830	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	1831	time where C<time = offset (mod interval)>, regardless of any time jumps.
555		1832
		1833	For numerical stability it is preferable that the C<offset> value is near
		1834	C<ev_now ()> (the current time), but there is no range requirement for
		1835	this value, and in fact is often specified as zero.
		1836
		1837	Note also that there is an upper limit to how often a timer can fire (CPU
		1838	speed for example), so if C<interval> is very small then timing stability
		1839	will of course deteriorate. Libev itself tries to be exact to be about one
		1840	millisecond (if the OS supports it and the machine is fast enough).
		1841
556	=item * manual reschedule mode (reschedule_cb = callback)	1842	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
557		1843
558	In this mode the values for C<interval> and C<at> are both being	1844	In this mode the values for C<interval> and C<offset> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	1845	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	1846	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	1847	current time as second argument.
562		1848
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1849	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
564	periodic watcher, ever, or make any event loop modifications>. If you need	1850	or make ANY other event loop modifications whatsoever, unless explicitly
		1851	allowed by documentation here>.
		1852
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	1853	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1854	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1855	only event loop modification you are allowed to do).
566		1856
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1857	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
571	ev_tstamp now)>, e.g.:	1858	*w, ev_tstamp now)>, e.g.:
572		1859
		1860	static ev_tstamp
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1861	my_rescheduler (ev_periodic *w, ev_tstamp now)
574	{	1862	{
575	return now + 60.;	1863	return now + 60.;
576	}	1864	}
577		1865
578	It must return the next time to trigger, based on the passed time value	1866	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	1867	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	1868	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	1869	might be called at other times, too.
582		1870
		1871	NOTE: I<< This callback must always return a time that is higher than or
		1872	equal to the passed C<now> value >>.
		1873
583	This can be used to create very complex timers, such as a timer that	1874	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	1875	triggers on "next midnight, local time". To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	1876	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	1877	you do this is, again, up to you (but it is not trivial, which is the main
		1878	reason I omitted it as an example).
587		1879
588	=back	1880	=back
589		1881
590	=item ev_periodic_again (loop, ev_periodic *)	1882	=item ev_periodic_again (loop, ev_periodic *)
591		1883
592	Simply stops and restarts the periodic watcher again. This is only useful	1884	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	1885	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	1886	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	1887	program when the crontabs have changed).
596		1888
		1889	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1890
		1891	When active, returns the absolute time that the watcher is supposed
		1892	to trigger next. This is not the same as the C<offset> argument to
		1893	C<ev_periodic_set>, but indeed works even in interval and manual
		1894	rescheduling modes.
		1895
		1896	=item ev_tstamp offset [read-write]
		1897
		1898	When repeating, this contains the offset value, otherwise this is the
		1899	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1900	although libev might modify this value for better numerical stability).
		1901
		1902	Can be modified any time, but changes only take effect when the periodic
		1903	timer fires or C<ev_periodic_again> is being called.
		1904
		1905	=item ev_tstamp interval [read-write]
		1906
		1907	The current interval value. Can be modified any time, but changes only
		1908	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1909	called.
		1910
		1911	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1912
		1913	The current reschedule callback, or C<0>, if this functionality is
		1914	switched off. Can be changed any time, but changes only take effect when
		1915	the periodic timer fires or C<ev_periodic_again> is being called.
		1916
597	=back	1917	=back
598		1918
		1919	=head3 Examples
		1920
		1921	Example: Call a callback every hour, or, more precisely, whenever the
		1922	system time is divisible by 3600. The callback invocation times have
		1923	potentially a lot of jitter, but good long-term stability.
		1924
		1925	static void
		1926	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		1927	{
		1928	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1929	}
		1930
		1931	ev_periodic hourly_tick;
		1932	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1933	ev_periodic_start (loop, &hourly_tick);
		1934
		1935	Example: The same as above, but use a reschedule callback to do it:
		1936
		1937	#include <math.h>
		1938
		1939	static ev_tstamp
		1940	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		1941	{
		1942	return now + (3600. - fmod (now, 3600.));
		1943	}
		1944
		1945	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1946
		1947	Example: Call a callback every hour, starting now:
		1948
		1949	ev_periodic hourly_tick;
		1950	ev_periodic_init (&hourly_tick, clock_cb,
		1951	fmod (ev_now (loop), 3600.), 3600., 0);
		1952	ev_periodic_start (loop, &hourly_tick);
		1953
		1954
599	=head2 C<ev_signal> - signal me when a signal gets signalled	1955	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		1956
601	Signal watchers will trigger an event when the process receives a specific	1957	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	1958	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	1959	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	1960	normal event processing, like any other event.
605		1961
		1962	If you want signals asynchronously, just use C<sigaction> as you would
		1963	do without libev and forget about sharing the signal. You can even use
		1964	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1965
606	You can configure as many watchers as you like per signal. Only when the	1966	You can configure as many watchers as you like per signal. Only when the
607	first watcher gets started will libev actually register a signal watcher	1967	first watcher gets started will libev actually register a signal handler
608	with the kernel (thus it coexists with your own signal handlers as long	1968	with the kernel (thus it coexists with your own signal handlers as long as
609	as you don't register any with libev). Similarly, when the last signal	1969	you don't register any with libev for the same signal). Similarly, when
610	watcher for a signal is stopped libev will reset the signal handler to	1970	the last signal watcher for a signal is stopped, libev will reset the
611	SIG_DFL (regardless of what it was set to before).	1971	signal handler to SIG_DFL (regardless of what it was set to before).
		1972
		1973	If possible and supported, libev will install its handlers with
		1974	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1975	interrupted. If you have a problem with system calls getting interrupted by
		1976	signals you can block all signals in an C<ev_check> watcher and unblock
		1977	them in an C<ev_prepare> watcher.
		1978
		1979	=head3 Watcher-Specific Functions and Data Members
612		1980
613	=over 4	1981	=over 4
614		1982
615	=item ev_signal_init (ev_signal *, callback, int signum)	1983	=item ev_signal_init (ev_signal *, callback, int signum)
616		1984
617	=item ev_signal_set (ev_signal *, int signum)	1985	=item ev_signal_set (ev_signal *, int signum)
618		1986
619	Configures the watcher to trigger on the given signal number (usually one	1987	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	1988	of the C<SIGxxx> constants).
621		1989
		1990	=item int signum [read-only]
		1991
		1992	The signal the watcher watches out for.
		1993
622	=back	1994	=back
623		1995
		1996	=head3 Examples
		1997
		1998	Example: Try to exit cleanly on SIGINT.
		1999
		2000	static void
		2001	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2002	{
		2003	ev_unloop (loop, EVUNLOOP_ALL);
		2004	}
		2005
		2006	ev_signal signal_watcher;
		2007	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2008	ev_signal_start (loop, &signal_watcher);
		2009
		2010
624	=head2 C<ev_child> - wait for pid status changes	2011	=head2 C<ev_child> - watch out for process status changes
625		2012
626	Child watchers trigger when your process receives a SIGCHLD in response to	2013	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	2014	some child status changes (most typically when a child of yours dies or
		2015	exits). It is permissible to install a child watcher I<after> the child
		2016	has been forked (which implies it might have already exited), as long
		2017	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2018	forking and then immediately registering a watcher for the child is fine,
		2019	but forking and registering a watcher a few event loop iterations later or
		2020	in the next callback invocation is not.
		2021
		2022	Only the default event loop is capable of handling signals, and therefore
		2023	you can only register child watchers in the default event loop.
		2024
		2025	=head3 Process Interaction
		2026
		2027	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2028	initialised. This is necessary to guarantee proper behaviour even if
		2029	the first child watcher is started after the child exits. The occurrence
		2030	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2031	synchronously as part of the event loop processing. Libev always reaps all
		2032	children, even ones not watched.
		2033
		2034	=head3 Overriding the Built-In Processing
		2035
		2036	Libev offers no special support for overriding the built-in child
		2037	processing, but if your application collides with libev's default child
		2038	handler, you can override it easily by installing your own handler for
		2039	C<SIGCHLD> after initialising the default loop, and making sure the
		2040	default loop never gets destroyed. You are encouraged, however, to use an
		2041	event-based approach to child reaping and thus use libev's support for
		2042	that, so other libev users can use C<ev_child> watchers freely.
		2043
		2044	=head3 Stopping the Child Watcher
		2045
		2046	Currently, the child watcher never gets stopped, even when the
		2047	child terminates, so normally one needs to stop the watcher in the
		2048	callback. Future versions of libev might stop the watcher automatically
		2049	when a child exit is detected.
		2050
		2051	=head3 Watcher-Specific Functions and Data Members
628		2052
629	=over 4	2053	=over 4
630		2054
631	=item ev_child_init (ev_child *, callback, int pid)	2055	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		2056
633	=item ev_child_set (ev_child *, int pid)	2057	=item ev_child_set (ev_child *, int pid, int trace)
634		2058
635	Configures the watcher to wait for status changes of process C<pid> (or	2059	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	2060	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	2061	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	2062	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	2063	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	2064	process causing the status change. C<trace> must be either C<0> (only
		2065	activate the watcher when the process terminates) or C<1> (additionally
		2066	activate the watcher when the process is stopped or continued).
		2067
		2068	=item int pid [read-only]
		2069
		2070	The process id this watcher watches out for, or C<0>, meaning any process id.
		2071
		2072	=item int rpid [read-write]
		2073
		2074	The process id that detected a status change.
		2075
		2076	=item int rstatus [read-write]
		2077
		2078	The process exit/trace status caused by C<rpid> (see your systems
		2079	C<waitpid> and C<sys/wait.h> documentation for details).
641		2080
642	=back	2081	=back
643		2082
		2083	=head3 Examples
		2084
		2085	Example: C<fork()> a new process and install a child handler to wait for
		2086	its completion.
		2087
		2088	ev_child cw;
		2089
		2090	static void
		2091	child_cb (EV_P_ ev_child *w, int revents)
		2092	{
		2093	ev_child_stop (EV_A_ w);
		2094	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2095	}
		2096
		2097	pid_t pid = fork ();
		2098
		2099	if (pid < 0)
		2100	// error
		2101	else if (pid == 0)
		2102	{
		2103	// the forked child executes here
		2104	exit (1);
		2105	}
		2106	else
		2107	{
		2108	ev_child_init (&cw, child_cb, pid, 0);
		2109	ev_child_start (EV_DEFAULT_ &cw);
		2110	}
		2111
		2112
		2113	=head2 C<ev_stat> - did the file attributes just change?
		2114
		2115	This watches a file system path for attribute changes. That is, it calls
		2116	C<stat> on that path in regular intervals (or when the OS says it changed)
		2117	and sees if it changed compared to the last time, invoking the callback if
		2118	it did.
		2119
		2120	The path does not need to exist: changing from "path exists" to "path does
		2121	not exist" is a status change like any other. The condition "path does not
		2122	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2123	C<st_nlink> field being zero (which is otherwise always forced to be at
		2124	least one) and all the other fields of the stat buffer having unspecified
		2125	contents.
		2126
		2127	The path I<must not> end in a slash or contain special components such as
		2128	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2129	your working directory changes, then the behaviour is undefined.
		2130
		2131	Since there is no portable change notification interface available, the
		2132	portable implementation simply calls C<stat(2)> regularly on the path
		2133	to see if it changed somehow. You can specify a recommended polling
		2134	interval for this case. If you specify a polling interval of C<0> (highly
		2135	recommended!) then a I<suitable, unspecified default> value will be used
		2136	(which you can expect to be around five seconds, although this might
		2137	change dynamically). Libev will also impose a minimum interval which is
		2138	currently around C<0.1>, but that's usually overkill.
		2139
		2140	This watcher type is not meant for massive numbers of stat watchers,
		2141	as even with OS-supported change notifications, this can be
		2142	resource-intensive.
		2143
		2144	At the time of this writing, the only OS-specific interface implemented
		2145	is the Linux inotify interface (implementing kqueue support is left as an
		2146	exercise for the reader. Note, however, that the author sees no way of
		2147	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2148
		2149	=head3 ABI Issues (Largefile Support)
		2150
		2151	Libev by default (unless the user overrides this) uses the default
		2152	compilation environment, which means that on systems with large file
		2153	support disabled by default, you get the 32 bit version of the stat
		2154	structure. When using the library from programs that change the ABI to
		2155	use 64 bit file offsets the programs will fail. In that case you have to
		2156	compile libev with the same flags to get binary compatibility. This is
		2157	obviously the case with any flags that change the ABI, but the problem is
		2158	most noticeably displayed with ev_stat and large file support.
		2159
		2160	The solution for this is to lobby your distribution maker to make large
		2161	file interfaces available by default (as e.g. FreeBSD does) and not
		2162	optional. Libev cannot simply switch on large file support because it has
		2163	to exchange stat structures with application programs compiled using the
		2164	default compilation environment.
		2165
		2166	=head3 Inotify and Kqueue
		2167
		2168	When C<inotify (7)> support has been compiled into libev and present at
		2169	runtime, it will be used to speed up change detection where possible. The
		2170	inotify descriptor will be created lazily when the first C<ev_stat>
		2171	watcher is being started.
		2172
		2173	Inotify presence does not change the semantics of C<ev_stat> watchers
		2174	except that changes might be detected earlier, and in some cases, to avoid
		2175	making regular C<stat> calls. Even in the presence of inotify support
		2176	there are many cases where libev has to resort to regular C<stat> polling,
		2177	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2178	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2179	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2180	xfs are fully working) libev usually gets away without polling.
		2181
		2182	There is no support for kqueue, as apparently it cannot be used to
		2183	implement this functionality, due to the requirement of having a file
		2184	descriptor open on the object at all times, and detecting renames, unlinks
		2185	etc. is difficult.
		2186
		2187	=head3 C<stat ()> is a synchronous operation
		2188
		2189	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2190	the process. The exception are C<ev_stat> watchers - those call C<stat
		2191	()>, which is a synchronous operation.
		2192
		2193	For local paths, this usually doesn't matter: unless the system is very
		2194	busy or the intervals between stat's are large, a stat call will be fast,
		2195	as the path data is usually in memory already (except when starting the
		2196	watcher).
		2197
		2198	For networked file systems, calling C<stat ()> can block an indefinite
		2199	time due to network issues, and even under good conditions, a stat call
		2200	often takes multiple milliseconds.
		2201
		2202	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2203	paths, although this is fully supported by libev.
		2204
		2205	=head3 The special problem of stat time resolution
		2206
		2207	The C<stat ()> system call only supports full-second resolution portably,
		2208	and even on systems where the resolution is higher, most file systems
		2209	still only support whole seconds.
		2210
		2211	That means that, if the time is the only thing that changes, you can
		2212	easily miss updates: on the first update, C<ev_stat> detects a change and
		2213	calls your callback, which does something. When there is another update
		2214	within the same second, C<ev_stat> will be unable to detect unless the
		2215	stat data does change in other ways (e.g. file size).
		2216
		2217	The solution to this is to delay acting on a change for slightly more
		2218	than a second (or till slightly after the next full second boundary), using
		2219	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2220	ev_timer_again (loop, w)>).
		2221
		2222	The C<.02> offset is added to work around small timing inconsistencies
		2223	of some operating systems (where the second counter of the current time
		2224	might be be delayed. One such system is the Linux kernel, where a call to
		2225	C<gettimeofday> might return a timestamp with a full second later than
		2226	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2227	update file times then there will be a small window where the kernel uses
		2228	the previous second to update file times but libev might already execute
		2229	the timer callback).
		2230
		2231	=head3 Watcher-Specific Functions and Data Members
		2232
		2233	=over 4
		2234
		2235	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2236
		2237	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2238
		2239	Configures the watcher to wait for status changes of the given
		2240	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2241	be detected and should normally be specified as C<0> to let libev choose
		2242	a suitable value. The memory pointed to by C<path> must point to the same
		2243	path for as long as the watcher is active.
		2244
		2245	The callback will receive an C<EV_STAT> event when a change was detected,
		2246	relative to the attributes at the time the watcher was started (or the
		2247	last change was detected).
		2248
		2249	=item ev_stat_stat (loop, ev_stat *)
		2250
		2251	Updates the stat buffer immediately with new values. If you change the
		2252	watched path in your callback, you could call this function to avoid
		2253	detecting this change (while introducing a race condition if you are not
		2254	the only one changing the path). Can also be useful simply to find out the
		2255	new values.
		2256
		2257	=item ev_statdata attr [read-only]
		2258
		2259	The most-recently detected attributes of the file. Although the type is
		2260	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2261	suitable for your system, but you can only rely on the POSIX-standardised
		2262	members to be present. If the C<st_nlink> member is C<0>, then there was
		2263	some error while C<stat>ing the file.
		2264
		2265	=item ev_statdata prev [read-only]
		2266
		2267	The previous attributes of the file. The callback gets invoked whenever
		2268	C<prev> != C<attr>, or, more precisely, one or more of these members
		2269	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2270	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2271
		2272	=item ev_tstamp interval [read-only]
		2273
		2274	The specified interval.
		2275
		2276	=item const char *path [read-only]
		2277
		2278	The file system path that is being watched.
		2279
		2280	=back
		2281
		2282	=head3 Examples
		2283
		2284	Example: Watch C</etc/passwd> for attribute changes.
		2285
		2286	static void
		2287	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2288	{
		2289	/* /etc/passwd changed in some way */
		2290	if (w->attr.st_nlink)
		2291	{
		2292	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2293	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2294	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2295	}
		2296	else
		2297	/* you shalt not abuse printf for puts */
		2298	puts ("wow, /etc/passwd is not there, expect problems. "
		2299	"if this is windows, they already arrived\n");
		2300	}
		2301
		2302	...
		2303	ev_stat passwd;
		2304
		2305	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2306	ev_stat_start (loop, &passwd);
		2307
		2308	Example: Like above, but additionally use a one-second delay so we do not
		2309	miss updates (however, frequent updates will delay processing, too, so
		2310	one might do the work both on C<ev_stat> callback invocation I<and> on
		2311	C<ev_timer> callback invocation).
		2312
		2313	static ev_stat passwd;
		2314	static ev_timer timer;
		2315
		2316	static void
		2317	timer_cb (EV_P_ ev_timer *w, int revents)
		2318	{
		2319	ev_timer_stop (EV_A_ w);
		2320
		2321	/* now it's one second after the most recent passwd change */
		2322	}
		2323
		2324	static void
		2325	stat_cb (EV_P_ ev_stat *w, int revents)
		2326	{
		2327	/* reset the one-second timer */
		2328	ev_timer_again (EV_A_ &timer);
		2329	}
		2330
		2331	...
		2332	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2333	ev_stat_start (loop, &passwd);
		2334	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2335
		2336
644	=head2 C<ev_idle> - when you've got nothing better to do	2337	=head2 C<ev_idle> - when you've got nothing better to do...
645		2338
646	Idle watchers trigger events when there are no other events are pending	2339	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	2340	priority are pending (prepare, check and other idle watchers do not count
648	as your process is busy handling sockets or timeouts (or even signals,	2341	as receiving "events").
649	imagine) it will not be triggered. But when your process is idle all idle	2342
650	watchers are being called again and again, once per event loop iteration -	2343	That is, as long as your process is busy handling sockets or timeouts
		2344	(or even signals, imagine) of the same or higher priority it will not be
		2345	triggered. But when your process is idle (or only lower-priority watchers
		2346	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	2347	iteration - until stopped, that is, or your process receives more events
652	busy.	2348	and becomes busy again with higher priority stuff.
653		2349
654	The most noteworthy effect is that as long as any idle watchers are	2350	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	2351	active, the process will not block when waiting for new events.
656		2352
657	Apart from keeping your process non-blocking (which is a useful	2353	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	2354	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	2355	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	2356	event loop has handled all outstanding events.
661		2357
		2358	=head3 Watcher-Specific Functions and Data Members
		2359
662	=over 4	2360	=over 4
663		2361
664	=item ev_idle_init (ev_signal *, callback)	2362	=item ev_idle_init (ev_idle *, callback)
665		2363
666	Initialises and configures the idle watcher - it has no parameters of any	2364	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2365	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	2366	believe me.
669		2367
670	=back	2368	=back
671		2369
		2370	=head3 Examples
		2371
		2372	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2373	callback, free it. Also, use no error checking, as usual.
		2374
		2375	static void
		2376	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2377	{
		2378	free (w);
		2379	// now do something you wanted to do when the program has
		2380	// no longer anything immediate to do.
		2381	}
		2382
		2383	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2384	ev_idle_init (idle_watcher, idle_cb);
		2385	ev_idle_start (loop, idle_watcher);
		2386
		2387
672	=head2 C<ev_prepare> and C<ev_check> - your hooks into the event loop	2388	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		2389
674	Prepare and check watchers are usually (but not always) used in tandem:	2390	Prepare and check watchers are usually (but not always) used in pairs:
675	Prepare watchers get invoked before the process blocks and check watchers	2391	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	2392	afterwards.
677		2393
		2394	You I<must not> call C<ev_loop> or similar functions that enter
		2395	the current event loop from either C<ev_prepare> or C<ev_check>
		2396	watchers. Other loops than the current one are fine, however. The
		2397	rationale behind this is that you do not need to check for recursion in
		2398	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2399	C<ev_check> so if you have one watcher of each kind they will always be
		2400	called in pairs bracketing the blocking call.
		2401
678	Their main purpose is to integrate other event mechanisms into libev. This	2402	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	2403	their use is somewhat advanced. They could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	2404	variable changes, implement your own watchers, integrate net-snmp or a
		2405	coroutine library and lots more. They are also occasionally useful if
		2406	you cache some data and want to flush it before blocking (for example,
		2407	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2408	watcher).
681		2409
682	This is done by examining in each prepare call which file descriptors need	2410	This is done by examining in each prepare call which file descriptors
683	to be watched by the other library, registering C<ev_io> watchers for	2411	need to be watched by the other library, registering C<ev_io> watchers
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2412	for them and starting an C<ev_timer> watcher for any timeouts (many
685	provide just this functionality). Then, in the check watcher you check for	2413	libraries provide exactly this functionality). Then, in the check watcher,
686	any events that occured (by checking the pending status of all watchers	2414	you check for any events that occurred (by checking the pending status
687	and stopping them) and call back into the library. The I/O and timer	2415	of all watchers and stopping them) and call back into the library. The
688	callbacks will never actually be called (but must be valid neverthelles,	2416	I/O and timer callbacks will never actually be called (but must be valid
689	because you never know, you know?).	2417	nevertheless, because you never know, you know?).
690		2418
691	As another example, the Perl Coro module uses these hooks to integrate	2419	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	2420	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	2421	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	2422	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	2423	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	2424	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	2425	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	2426	low-priority coroutines to idle/background tasks).
		2427
		2428	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2429	priority, to ensure that they are being run before any other watchers
		2430	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2431
		2432	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2433	activate ("feed") events into libev. While libev fully supports this, they
		2434	might get executed before other C<ev_check> watchers did their job. As
		2435	C<ev_check> watchers are often used to embed other (non-libev) event
		2436	loops those other event loops might be in an unusable state until their
		2437	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2438	others).
		2439
		2440	=head3 Watcher-Specific Functions and Data Members
699		2441
700	=over 4	2442	=over 4
701		2443
702	=item ev_prepare_init (ev_prepare *, callback)	2444	=item ev_prepare_init (ev_prepare *, callback)
703		2445
704	=item ev_check_init (ev_check *, callback)	2446	=item ev_check_init (ev_check *, callback)
705		2447
706	Initialises and configures the prepare or check watcher - they have no	2448	Initialises and configures the prepare or check watcher - they have no
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2449	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	2450	macros, but using them is utterly, utterly, utterly and completely
		2451	pointless.
709		2452
710	=back	2453	=back
711		2454
		2455	=head3 Examples
		2456
		2457	There are a number of principal ways to embed other event loops or modules
		2458	into libev. Here are some ideas on how to include libadns into libev
		2459	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2460	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2461	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2462	Glib event loop).
		2463
		2464	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2465	and in a check watcher, destroy them and call into libadns. What follows
		2466	is pseudo-code only of course. This requires you to either use a low
		2467	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2468	the callbacks for the IO/timeout watchers might not have been called yet.
		2469
		2470	static ev_io iow [nfd];
		2471	static ev_timer tw;
		2472
		2473	static void
		2474	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2475	{
		2476	}
		2477
		2478	// create io watchers for each fd and a timer before blocking
		2479	static void
		2480	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2481	{
		2482	int timeout = 3600000;
		2483	struct pollfd fds [nfd];
		2484	// actual code will need to loop here and realloc etc.
		2485	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2486
		2487	/* the callback is illegal, but won't be called as we stop during check */
		2488	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2489	ev_timer_start (loop, &tw);
		2490
		2491	// create one ev_io per pollfd
		2492	for (int i = 0; i < nfd; ++i)
		2493	{
		2494	ev_io_init (iow + i, io_cb, fds [i].fd,
		2495	((fds [i].events & POLLIN ? EV_READ : 0)
		2496	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2497
		2498	fds [i].revents = 0;
		2499	ev_io_start (loop, iow + i);
		2500	}
		2501	}
		2502
		2503	// stop all watchers after blocking
		2504	static void
		2505	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2506	{
		2507	ev_timer_stop (loop, &tw);
		2508
		2509	for (int i = 0; i < nfd; ++i)
		2510	{
		2511	// set the relevant poll flags
		2512	// could also call adns_processreadable etc. here
		2513	struct pollfd *fd = fds + i;
		2514	int revents = ev_clear_pending (iow + i);
		2515	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2516	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2517
		2518	// now stop the watcher
		2519	ev_io_stop (loop, iow + i);
		2520	}
		2521
		2522	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2523	}
		2524
		2525	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2526	in the prepare watcher and would dispose of the check watcher.
		2527
		2528	Method 3: If the module to be embedded supports explicit event
		2529	notification (libadns does), you can also make use of the actual watcher
		2530	callbacks, and only destroy/create the watchers in the prepare watcher.
		2531
		2532	static void
		2533	timer_cb (EV_P_ ev_timer *w, int revents)
		2534	{
		2535	adns_state ads = (adns_state)w->data;
		2536	update_now (EV_A);
		2537
		2538	adns_processtimeouts (ads, &tv_now);
		2539	}
		2540
		2541	static void
		2542	io_cb (EV_P_ ev_io *w, int revents)
		2543	{
		2544	adns_state ads = (adns_state)w->data;
		2545	update_now (EV_A);
		2546
		2547	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2548	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2549	}
		2550
		2551	// do not ever call adns_afterpoll
		2552
		2553	Method 4: Do not use a prepare or check watcher because the module you
		2554	want to embed is not flexible enough to support it. Instead, you can
		2555	override their poll function. The drawback with this solution is that the
		2556	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2557	this approach, effectively embedding EV as a client into the horrible
		2558	libglib event loop.
		2559
		2560	static gint
		2561	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2562	{
		2563	int got_events = 0;
		2564
		2565	for (n = 0; n < nfds; ++n)
		2566	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2567
		2568	if (timeout >= 0)
		2569	// create/start timer
		2570
		2571	// poll
		2572	ev_loop (EV_A_ 0);
		2573
		2574	// stop timer again
		2575	if (timeout >= 0)
		2576	ev_timer_stop (EV_A_ &to);
		2577
		2578	// stop io watchers again - their callbacks should have set
		2579	for (n = 0; n < nfds; ++n)
		2580	ev_io_stop (EV_A_ iow [n]);
		2581
		2582	return got_events;
		2583	}
		2584
		2585
		2586	=head2 C<ev_embed> - when one backend isn't enough...
		2587
		2588	This is a rather advanced watcher type that lets you embed one event loop
		2589	into another (currently only C<ev_io> events are supported in the embedded
		2590	loop, other types of watchers might be handled in a delayed or incorrect
		2591	fashion and must not be used).
		2592
		2593	There are primarily two reasons you would want that: work around bugs and
		2594	prioritise I/O.
		2595
		2596	As an example for a bug workaround, the kqueue backend might only support
		2597	sockets on some platform, so it is unusable as generic backend, but you
		2598	still want to make use of it because you have many sockets and it scales
		2599	so nicely. In this case, you would create a kqueue-based loop and embed
		2600	it into your default loop (which might use e.g. poll). Overall operation
		2601	will be a bit slower because first libev has to call C<poll> and then
		2602	C<kevent>, but at least you can use both mechanisms for what they are
		2603	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2604
		2605	As for prioritising I/O: under rare circumstances you have the case where
		2606	some fds have to be watched and handled very quickly (with low latency),
		2607	and even priorities and idle watchers might have too much overhead. In
		2608	this case you would put all the high priority stuff in one loop and all
		2609	the rest in a second one, and embed the second one in the first.
		2610
		2611	As long as the watcher is active, the callback will be invoked every
		2612	time there might be events pending in the embedded loop. The callback
		2613	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2614	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2615	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2616	to give the embedded loop strictly lower priority for example).
		2617
		2618	You can also set the callback to C<0>, in which case the embed watcher
		2619	will automatically execute the embedded loop sweep whenever necessary.
		2620
		2621	Fork detection will be handled transparently while the C<ev_embed> watcher
		2622	is active, i.e., the embedded loop will automatically be forked when the
		2623	embedding loop forks. In other cases, the user is responsible for calling
		2624	C<ev_loop_fork> on the embedded loop.
		2625
		2626	Unfortunately, not all backends are embeddable: only the ones returned by
		2627	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2628	portable one.
		2629
		2630	So when you want to use this feature you will always have to be prepared
		2631	that you cannot get an embeddable loop. The recommended way to get around
		2632	this is to have a separate variables for your embeddable loop, try to
		2633	create it, and if that fails, use the normal loop for everything.
		2634
		2635	=head3 C<ev_embed> and fork
		2636
		2637	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2638	automatically be applied to the embedded loop as well, so no special
		2639	fork handling is required in that case. When the watcher is not running,
		2640	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2641	as applicable.
		2642
		2643	=head3 Watcher-Specific Functions and Data Members
		2644
		2645	=over 4
		2646
		2647	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2648
		2649	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2650
		2651	Configures the watcher to embed the given loop, which must be
		2652	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2653	invoked automatically, otherwise it is the responsibility of the callback
		2654	to invoke it (it will continue to be called until the sweep has been done,
		2655	if you do not want that, you need to temporarily stop the embed watcher).
		2656
		2657	=item ev_embed_sweep (loop, ev_embed *)
		2658
		2659	Make a single, non-blocking sweep over the embedded loop. This works
		2660	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2661	appropriate way for embedded loops.
		2662
		2663	=item struct ev_loop *other [read-only]
		2664
		2665	The embedded event loop.
		2666
		2667	=back
		2668
		2669	=head3 Examples
		2670
		2671	Example: Try to get an embeddable event loop and embed it into the default
		2672	event loop. If that is not possible, use the default loop. The default
		2673	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2674	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2675	used).
		2676
		2677	struct ev_loop *loop_hi = ev_default_init (0);
		2678	struct ev_loop *loop_lo = 0;
		2679	ev_embed embed;
		2680
		2681	// see if there is a chance of getting one that works
		2682	// (remember that a flags value of 0 means autodetection)
		2683	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2684	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2685	: 0;
		2686
		2687	// if we got one, then embed it, otherwise default to loop_hi
		2688	if (loop_lo)
		2689	{
		2690	ev_embed_init (&embed, 0, loop_lo);
		2691	ev_embed_start (loop_hi, &embed);
		2692	}
		2693	else
		2694	loop_lo = loop_hi;
		2695
		2696	Example: Check if kqueue is available but not recommended and create
		2697	a kqueue backend for use with sockets (which usually work with any
		2698	kqueue implementation). Store the kqueue/socket-only event loop in
		2699	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2700
		2701	struct ev_loop *loop = ev_default_init (0);
		2702	struct ev_loop *loop_socket = 0;
		2703	ev_embed embed;
		2704
		2705	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2706	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2707	{
		2708	ev_embed_init (&embed, 0, loop_socket);
		2709	ev_embed_start (loop, &embed);
		2710	}
		2711
		2712	if (!loop_socket)
		2713	loop_socket = loop;
		2714
		2715	// now use loop_socket for all sockets, and loop for everything else
		2716
		2717
		2718	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2719
		2720	Fork watchers are called when a C<fork ()> was detected (usually because
		2721	whoever is a good citizen cared to tell libev about it by calling
		2722	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2723	event loop blocks next and before C<ev_check> watchers are being called,
		2724	and only in the child after the fork. If whoever good citizen calling
		2725	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2726	handlers will be invoked, too, of course.
		2727
		2728	=head3 The special problem of life after fork - how is it possible?
		2729
		2730	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2731	up/change the process environment, followed by a call to C<exec()>. This
		2732	sequence should be handled by libev without any problems.
		2733
		2734	This changes when the application actually wants to do event handling
		2735	in the child, or both parent in child, in effect "continuing" after the
		2736	fork.
		2737
		2738	The default mode of operation (for libev, with application help to detect
		2739	forks) is to duplicate all the state in the child, as would be expected
		2740	when I<either> the parent I<or> the child process continues.
		2741
		2742	When both processes want to continue using libev, then this is usually the
		2743	wrong result. In that case, usually one process (typically the parent) is
		2744	supposed to continue with all watchers in place as before, while the other
		2745	process typically wants to start fresh, i.e. without any active watchers.
		2746
		2747	The cleanest and most efficient way to achieve that with libev is to
		2748	simply create a new event loop, which of course will be "empty", and
		2749	use that for new watchers. This has the advantage of not touching more
		2750	memory than necessary, and thus avoiding the copy-on-write, and the
		2751	disadvantage of having to use multiple event loops (which do not support
		2752	signal watchers).
		2753
		2754	When this is not possible, or you want to use the default loop for
		2755	other reasons, then in the process that wants to start "fresh", call
		2756	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2757	the default loop will "orphan" (not stop) all registered watchers, so you
		2758	have to be careful not to execute code that modifies those watchers. Note
		2759	also that in that case, you have to re-register any signal watchers.
		2760
		2761	=head3 Watcher-Specific Functions and Data Members
		2762
		2763	=over 4
		2764
		2765	=item ev_fork_init (ev_signal *, callback)
		2766
		2767	Initialises and configures the fork watcher - it has no parameters of any
		2768	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2769	believe me.
		2770
		2771	=back
		2772
		2773
		2774	=head2 C<ev_async> - how to wake up another event loop
		2775
		2776	In general, you cannot use an C<ev_loop> from multiple threads or other
		2777	asynchronous sources such as signal handlers (as opposed to multiple event
		2778	loops - those are of course safe to use in different threads).
		2779
		2780	Sometimes, however, you need to wake up another event loop you do not
		2781	control, for example because it belongs to another thread. This is what
		2782	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2783	can signal it by calling C<ev_async_send>, which is thread- and signal
		2784	safe.
		2785
		2786	This functionality is very similar to C<ev_signal> watchers, as signals,
		2787	too, are asynchronous in nature, and signals, too, will be compressed
		2788	(i.e. the number of callback invocations may be less than the number of
		2789	C<ev_async_sent> calls).
		2790
		2791	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2792	just the default loop.
		2793
		2794	=head3 Queueing
		2795
		2796	C<ev_async> does not support queueing of data in any way. The reason
		2797	is that the author does not know of a simple (or any) algorithm for a
		2798	multiple-writer-single-reader queue that works in all cases and doesn't
		2799	need elaborate support such as pthreads.
		2800
		2801	That means that if you want to queue data, you have to provide your own
		2802	queue. But at least I can tell you how to implement locking around your
		2803	queue:
		2804
		2805	=over 4
		2806
		2807	=item queueing from a signal handler context
		2808
		2809	To implement race-free queueing, you simply add to the queue in the signal
		2810	handler but you block the signal handler in the watcher callback. Here is
		2811	an example that does that for some fictitious SIGUSR1 handler:
		2812
		2813	static ev_async mysig;
		2814
		2815	static void
		2816	sigusr1_handler (void)
		2817	{
		2818	sometype data;
		2819
		2820	// no locking etc.
		2821	queue_put (data);
		2822	ev_async_send (EV_DEFAULT_ &mysig);
		2823	}
		2824
		2825	static void
		2826	mysig_cb (EV_P_ ev_async *w, int revents)
		2827	{
		2828	sometype data;
		2829	sigset_t block, prev;
		2830
		2831	sigemptyset (&block);
		2832	sigaddset (&block, SIGUSR1);
		2833	sigprocmask (SIG_BLOCK, &block, &prev);
		2834
		2835	while (queue_get (&data))
		2836	process (data);
		2837
		2838	if (sigismember (&prev, SIGUSR1)
		2839	sigprocmask (SIG_UNBLOCK, &block, 0);
		2840	}
		2841
		2842	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2843	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2844	either...).
		2845
		2846	=item queueing from a thread context
		2847
		2848	The strategy for threads is different, as you cannot (easily) block
		2849	threads but you can easily preempt them, so to queue safely you need to
		2850	employ a traditional mutex lock, such as in this pthread example:
		2851
		2852	static ev_async mysig;
		2853	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2854
		2855	static void
		2856	otherthread (void)
		2857	{
		2858	// only need to lock the actual queueing operation
		2859	pthread_mutex_lock (&mymutex);
		2860	queue_put (data);
		2861	pthread_mutex_unlock (&mymutex);
		2862
		2863	ev_async_send (EV_DEFAULT_ &mysig);
		2864	}
		2865
		2866	static void
		2867	mysig_cb (EV_P_ ev_async *w, int revents)
		2868	{
		2869	pthread_mutex_lock (&mymutex);
		2870
		2871	while (queue_get (&data))
		2872	process (data);
		2873
		2874	pthread_mutex_unlock (&mymutex);
		2875	}
		2876
		2877	=back
		2878
		2879
		2880	=head3 Watcher-Specific Functions and Data Members
		2881
		2882	=over 4
		2883
		2884	=item ev_async_init (ev_async *, callback)
		2885
		2886	Initialises and configures the async watcher - it has no parameters of any
		2887	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2888	trust me.
		2889
		2890	=item ev_async_send (loop, ev_async *)
		2891
		2892	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2893	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2894	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2895	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2896	section below on what exactly this means).
		2897
		2898	Note that, as with other watchers in libev, multiple events might get
		2899	compressed into a single callback invocation (another way to look at this
		2900	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2901	reset when the event loop detects that).
		2902
		2903	This call incurs the overhead of a system call only once per event loop
		2904	iteration, so while the overhead might be noticeable, it doesn't apply to
		2905	repeated calls to C<ev_async_send> for the same event loop.
		2906
		2907	=item bool = ev_async_pending (ev_async *)
		2908
		2909	Returns a non-zero value when C<ev_async_send> has been called on the
		2910	watcher but the event has not yet been processed (or even noted) by the
		2911	event loop.
		2912
		2913	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2914	the loop iterates next and checks for the watcher to have become active,
		2915	it will reset the flag again. C<ev_async_pending> can be used to very
		2916	quickly check whether invoking the loop might be a good idea.
		2917
		2918	Not that this does I<not> check whether the watcher itself is pending,
		2919	only whether it has been requested to make this watcher pending: there
		2920	is a time window between the event loop checking and resetting the async
		2921	notification, and the callback being invoked.
		2922
		2923	=back
		2924
		2925
712	=head1 OTHER FUNCTIONS	2926	=head1 OTHER FUNCTIONS
713		2927
714	There are some other functions of possible interest. Described. Here. Now.	2928	There are some other functions of possible interest. Described. Here. Now.
715		2929
716	=over 4	2930	=over 4
717		2931
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2932	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		2933
720	This function combines a simple timer and an I/O watcher, calls your	2934	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	2935	callback on whichever event happens first and automatically stops both
722	watchers. This is useful if you want to wait for a single event on an fd	2936	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	2937	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	2938	more watchers yourself.
725		2939
726	If C<fd> is less than 0, then no I/O watcher will be started and events	2940	If C<fd> is less than 0, then no I/O watcher will be started and the
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2941	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
728	C<events> set will be craeted and started.	2942	the given C<fd> and C<events> set will be created and started.
729		2943
730	If C<timeout> is less than 0, then no timeout watcher will be	2944	If C<timeout> is less than 0, then no timeout watcher will be
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2945	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2946	repeat = 0) will be started. C<0> is a valid timeout.
733	dubious value.
734		2947
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2948	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
736	passed an events set like normal event callbacks (with a combination of	2949	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2950	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738	value passed to C<ev_once>:	2951	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2952	a timeout and an io event at the same time - you probably should give io
		2953	events precedence.
739		2954
		2955	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2956
740	static void stdin_ready (int revents, void *arg)	2957	static void stdin_ready (int revents, void *arg)
741	{	2958	{
742	if (revents & EV_TIMEOUT)
743	/* doh, nothing entered */;
744	else if (revents & EV_READ)	2959	if (revents & EV_READ)
745	/* stdin might have data for us, joy! */;	2960	/* stdin might have data for us, joy! */;
		2961	else if (revents & EV_TIMEOUT)
		2962	/* doh, nothing entered */;
746	}	2963	}
747		2964
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2965	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749		2966
750	=item ev_feed_event (loop, watcher, int events)	2967	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
751		2968
752	Feeds the given event set into the event loop, as if the specified event	2969	Feeds the given event set into the event loop, as if the specified event
753	had happened for the specified watcher (which must be a pointer to an	2970	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).	2971	initialised but not necessarily started event watcher).
755		2972
756	=item ev_feed_fd_event (loop, int fd, int revents)	2973	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
757		2974
758	Feed an event on the given fd, as if a file descriptor backend detected	2975	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	2976	the given events it.
760		2977
761	=item ev_feed_signal_event (loop, int signum)	2978	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
762		2979
763	Feed an event as if the given signal occured (loop must be the default loop!).	2980	Feed an event as if the given signal occurred (C<loop> must be the default
		2981	loop!).
764		2982
765	=back	2983	=back
766		2984
		2985
		2986	=head1 LIBEVENT EMULATION
		2987
		2988	Libev offers a compatibility emulation layer for libevent. It cannot
		2989	emulate the internals of libevent, so here are some usage hints:
		2990
		2991	=over 4
		2992
		2993	=item * Use it by including <event.h>, as usual.
		2994
		2995	=item * The following members are fully supported: ev_base, ev_callback,
		2996	ev_arg, ev_fd, ev_res, ev_events.
		2997
		2998	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2999	maintained by libev, it does not work exactly the same way as in libevent (consider
		3000	it a private API).
		3001
		3002	=item * Priorities are not currently supported. Initialising priorities
		3003	will fail and all watchers will have the same priority, even though there
		3004	is an ev_pri field.
		3005
		3006	=item * In libevent, the last base created gets the signals, in libev, the
		3007	first base created (== the default loop) gets the signals.
		3008
		3009	=item * Other members are not supported.
		3010
		3011	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3012	to use the libev header file and library.
		3013
		3014	=back
		3015
		3016	=head1 C++ SUPPORT
		3017
		3018	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3019	you to use some convenience methods to start/stop watchers and also change
		3020	the callback model to a model using method callbacks on objects.
		3021
		3022	To use it,
		3023
		3024	#include <ev++.h>
		3025
		3026	This automatically includes F<ev.h> and puts all of its definitions (many
		3027	of them macros) into the global namespace. All C++ specific things are
		3028	put into the C<ev> namespace. It should support all the same embedding
		3029	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3030
		3031	Care has been taken to keep the overhead low. The only data member the C++
		3032	classes add (compared to plain C-style watchers) is the event loop pointer
		3033	that the watcher is associated with (or no additional members at all if
		3034	you disable C<EV_MULTIPLICITY> when embedding libev).
		3035
		3036	Currently, functions, and static and non-static member functions can be
		3037	used as callbacks. Other types should be easy to add as long as they only
		3038	need one additional pointer for context. If you need support for other
		3039	types of functors please contact the author (preferably after implementing
		3040	it).
		3041
		3042	Here is a list of things available in the C<ev> namespace:
		3043
		3044	=over 4
		3045
		3046	=item C<ev::READ>, C<ev::WRITE> etc.
		3047
		3048	These are just enum values with the same values as the C<EV_READ> etc.
		3049	macros from F<ev.h>.
		3050
		3051	=item C<ev::tstamp>, C<ev::now>
		3052
		3053	Aliases to the same types/functions as with the C<ev_> prefix.
		3054
		3055	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3056
		3057	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3058	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3059	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3060	defines by many implementations.
		3061
		3062	All of those classes have these methods:
		3063
		3064	=over 4
		3065
		3066	=item ev::TYPE::TYPE ()
		3067
		3068	=item ev::TYPE::TYPE (struct ev_loop *)
		3069
		3070	=item ev::TYPE::~TYPE
		3071
		3072	The constructor (optionally) takes an event loop to associate the watcher
		3073	with. If it is omitted, it will use C<EV_DEFAULT>.
		3074
		3075	The constructor calls C<ev_init> for you, which means you have to call the
		3076	C<set> method before starting it.
		3077
		3078	It will not set a callback, however: You have to call the templated C<set>
		3079	method to set a callback before you can start the watcher.
		3080
		3081	(The reason why you have to use a method is a limitation in C++ which does
		3082	not allow explicit template arguments for constructors).
		3083
		3084	The destructor automatically stops the watcher if it is active.
		3085
		3086	=item w->set<class, &class::method> (object *)
		3087
		3088	This method sets the callback method to call. The method has to have a
		3089	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3090	first argument and the C<revents> as second. The object must be given as
		3091	parameter and is stored in the C<data> member of the watcher.
		3092
		3093	This method synthesizes efficient thunking code to call your method from
		3094	the C callback that libev requires. If your compiler can inline your
		3095	callback (i.e. it is visible to it at the place of the C<set> call and
		3096	your compiler is good :), then the method will be fully inlined into the
		3097	thunking function, making it as fast as a direct C callback.
		3098
		3099	Example: simple class declaration and watcher initialisation
		3100
		3101	struct myclass
		3102	{
		3103	void io_cb (ev::io &w, int revents) { }
		3104	}
		3105
		3106	myclass obj;
		3107	ev::io iow;
		3108	iow.set <myclass, &myclass::io_cb> (&obj);
		3109
		3110	=item w->set (object *)
		3111
		3112	This is an B<experimental> feature that might go away in a future version.
		3113
		3114	This is a variation of a method callback - leaving out the method to call
		3115	will default the method to C<operator ()>, which makes it possible to use
		3116	functor objects without having to manually specify the C<operator ()> all
		3117	the time. Incidentally, you can then also leave out the template argument
		3118	list.
		3119
		3120	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3121	int revents)>.
		3122
		3123	See the method-C<set> above for more details.
		3124
		3125	Example: use a functor object as callback.
		3126
		3127	struct myfunctor
		3128	{
		3129	void operator() (ev::io &w, int revents)
		3130	{
		3131	...
		3132	}
		3133	}
		3134
		3135	myfunctor f;
		3136
		3137	ev::io w;
		3138	w.set (&f);
		3139
		3140	=item w->set<function> (void *data = 0)
		3141
		3142	Also sets a callback, but uses a static method or plain function as
		3143	callback. The optional C<data> argument will be stored in the watcher's
		3144	C<data> member and is free for you to use.
		3145
		3146	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3147
		3148	See the method-C<set> above for more details.
		3149
		3150	Example: Use a plain function as callback.
		3151
		3152	static void io_cb (ev::io &w, int revents) { }
		3153	iow.set <io_cb> ();
		3154
		3155	=item w->set (struct ev_loop *)
		3156
		3157	Associates a different C<struct ev_loop> with this watcher. You can only
		3158	do this when the watcher is inactive (and not pending either).
		3159
		3160	=item w->set ([arguments])
		3161
		3162	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3163	called at least once. Unlike the C counterpart, an active watcher gets
		3164	automatically stopped and restarted when reconfiguring it with this
		3165	method.
		3166
		3167	=item w->start ()
		3168
		3169	Starts the watcher. Note that there is no C<loop> argument, as the
		3170	constructor already stores the event loop.
		3171
		3172	=item w->stop ()
		3173
		3174	Stops the watcher if it is active. Again, no C<loop> argument.
		3175
		3176	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3177
		3178	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3179	C<ev_TYPE_again> function.
		3180
		3181	=item w->sweep () (C<ev::embed> only)
		3182
		3183	Invokes C<ev_embed_sweep>.
		3184
		3185	=item w->update () (C<ev::stat> only)
		3186
		3187	Invokes C<ev_stat_stat>.
		3188
		3189	=back
		3190
		3191	=back
		3192
		3193	Example: Define a class with an IO and idle watcher, start one of them in
		3194	the constructor.
		3195
		3196	class myclass
		3197	{
		3198	ev::io io ; void io_cb (ev::io &w, int revents);
		3199	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3200
		3201	myclass (int fd)
		3202	{
		3203	io .set <myclass, &myclass::io_cb > (this);
		3204	idle.set <myclass, &myclass::idle_cb> (this);
		3205
		3206	io.start (fd, ev::READ);
		3207	}
		3208	};
		3209
		3210
		3211	=head1 OTHER LANGUAGE BINDINGS
		3212
		3213	Libev does not offer other language bindings itself, but bindings for a
		3214	number of languages exist in the form of third-party packages. If you know
		3215	any interesting language binding in addition to the ones listed here, drop
		3216	me a note.
		3217
		3218	=over 4
		3219
		3220	=item Perl
		3221
		3222	The EV module implements the full libev API and is actually used to test
		3223	libev. EV is developed together with libev. Apart from the EV core module,
		3224	there are additional modules that implement libev-compatible interfaces
		3225	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3226	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3227	and C<EV::Glib>).
		3228
		3229	It can be found and installed via CPAN, its homepage is at
		3230	L<http://software.schmorp.de/pkg/EV>.
		3231
		3232	=item Python
		3233
		3234	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3235	seems to be quite complete and well-documented.
		3236
		3237	=item Ruby
		3238
		3239	Tony Arcieri has written a ruby extension that offers access to a subset
		3240	of the libev API and adds file handle abstractions, asynchronous DNS and
		3241	more on top of it. It can be found via gem servers. Its homepage is at
		3242	L<http://rev.rubyforge.org/>.
		3243
		3244	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3245	makes rev work even on mingw.
		3246
		3247	=item Haskell
		3248
		3249	A haskell binding to libev is available at
		3250	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3251
		3252	=item D
		3253
		3254	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3255	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3256
		3257	=item Ocaml
		3258
		3259	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3260	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3261
		3262	=back
		3263
		3264
		3265	=head1 MACRO MAGIC
		3266
		3267	Libev can be compiled with a variety of options, the most fundamental
		3268	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3269	functions and callbacks have an initial C<struct ev_loop *> argument.
		3270
		3271	To make it easier to write programs that cope with either variant, the
		3272	following macros are defined:
		3273
		3274	=over 4
		3275
		3276	=item C<EV_A>, C<EV_A_>
		3277
		3278	This provides the loop I<argument> for functions, if one is required ("ev
		3279	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3280	C<EV_A_> is used when other arguments are following. Example:
		3281
		3282	ev_unref (EV_A);
		3283	ev_timer_add (EV_A_ watcher);
		3284	ev_loop (EV_A_ 0);
		3285
		3286	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3287	which is often provided by the following macro.
		3288
		3289	=item C<EV_P>, C<EV_P_>
		3290
		3291	This provides the loop I<parameter> for functions, if one is required ("ev
		3292	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3293	C<EV_P_> is used when other parameters are following. Example:
		3294
		3295	// this is how ev_unref is being declared
		3296	static void ev_unref (EV_P);
		3297
		3298	// this is how you can declare your typical callback
		3299	static void cb (EV_P_ ev_timer *w, int revents)
		3300
		3301	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3302	suitable for use with C<EV_A>.
		3303
		3304	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3305
		3306	Similar to the other two macros, this gives you the value of the default
		3307	loop, if multiple loops are supported ("ev loop default").
		3308
		3309	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3310
		3311	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3312	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3313	is undefined when the default loop has not been initialised by a previous
		3314	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3315
		3316	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3317	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3318
		3319	=back
		3320
		3321	Example: Declare and initialise a check watcher, utilising the above
		3322	macros so it will work regardless of whether multiple loops are supported
		3323	or not.
		3324
		3325	static void
		3326	check_cb (EV_P_ ev_timer *w, int revents)
		3327	{
		3328	ev_check_stop (EV_A_ w);
		3329	}
		3330
		3331	ev_check check;
		3332	ev_check_init (&check, check_cb);
		3333	ev_check_start (EV_DEFAULT_ &check);
		3334	ev_loop (EV_DEFAULT_ 0);
		3335
		3336	=head1 EMBEDDING
		3337
		3338	Libev can (and often is) directly embedded into host
		3339	applications. Examples of applications that embed it include the Deliantra
		3340	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3341	and rxvt-unicode.
		3342
		3343	The goal is to enable you to just copy the necessary files into your
		3344	source directory without having to change even a single line in them, so
		3345	you can easily upgrade by simply copying (or having a checked-out copy of
		3346	libev somewhere in your source tree).
		3347
		3348	=head2 FILESETS
		3349
		3350	Depending on what features you need you need to include one or more sets of files
		3351	in your application.
		3352
		3353	=head3 CORE EVENT LOOP
		3354
		3355	To include only the libev core (all the C<ev_*> functions), with manual
		3356	configuration (no autoconf):
		3357
		3358	#define EV_STANDALONE 1
		3359	#include "ev.c"
		3360
		3361	This will automatically include F<ev.h>, too, and should be done in a
		3362	single C source file only to provide the function implementations. To use
		3363	it, do the same for F<ev.h> in all files wishing to use this API (best
		3364	done by writing a wrapper around F<ev.h> that you can include instead and
		3365	where you can put other configuration options):
		3366
		3367	#define EV_STANDALONE 1
		3368	#include "ev.h"
		3369
		3370	Both header files and implementation files can be compiled with a C++
		3371	compiler (at least, that's a stated goal, and breakage will be treated
		3372	as a bug).
		3373
		3374	You need the following files in your source tree, or in a directory
		3375	in your include path (e.g. in libev/ when using -Ilibev):
		3376
		3377	ev.h
		3378	ev.c
		3379	ev_vars.h
		3380	ev_wrap.h
		3381
		3382	ev_win32.c required on win32 platforms only
		3383
		3384	ev_select.c only when select backend is enabled (which is enabled by default)
		3385	ev_poll.c only when poll backend is enabled (disabled by default)
		3386	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3387	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3388	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3389
		3390	F<ev.c> includes the backend files directly when enabled, so you only need
		3391	to compile this single file.
		3392
		3393	=head3 LIBEVENT COMPATIBILITY API
		3394
		3395	To include the libevent compatibility API, also include:
		3396
		3397	#include "event.c"
		3398
		3399	in the file including F<ev.c>, and:
		3400
		3401	#include "event.h"
		3402
		3403	in the files that want to use the libevent API. This also includes F<ev.h>.
		3404
		3405	You need the following additional files for this:
		3406
		3407	event.h
		3408	event.c
		3409
		3410	=head3 AUTOCONF SUPPORT
		3411
		3412	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3413	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3414	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3415	include F<config.h> and configure itself accordingly.
		3416
		3417	For this of course you need the m4 file:
		3418
		3419	libev.m4
		3420
		3421	=head2 PREPROCESSOR SYMBOLS/MACROS
		3422
		3423	Libev can be configured via a variety of preprocessor symbols you have to
		3424	define before including any of its files. The default in the absence of
		3425	autoconf is documented for every option.
		3426
		3427	=over 4
		3428
		3429	=item EV_STANDALONE
		3430
		3431	Must always be C<1> if you do not use autoconf configuration, which
		3432	keeps libev from including F<config.h>, and it also defines dummy
		3433	implementations for some libevent functions (such as logging, which is not
		3434	supported). It will also not define any of the structs usually found in
		3435	F<event.h> that are not directly supported by the libev core alone.
		3436
		3437	In stanbdalone mode, libev will still try to automatically deduce the
		3438	configuration, but has to be more conservative.
		3439
		3440	=item EV_USE_MONOTONIC
		3441
		3442	If defined to be C<1>, libev will try to detect the availability of the
		3443	monotonic clock option at both compile time and runtime. Otherwise no
		3444	use of the monotonic clock option will be attempted. If you enable this,
		3445	you usually have to link against librt or something similar. Enabling it
		3446	when the functionality isn't available is safe, though, although you have
		3447	to make sure you link against any libraries where the C<clock_gettime>
		3448	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3449
		3450	=item EV_USE_REALTIME
		3451
		3452	If defined to be C<1>, libev will try to detect the availability of the
		3453	real-time clock option at compile time (and assume its availability
		3454	at runtime if successful). Otherwise no use of the real-time clock
		3455	option will be attempted. This effectively replaces C<gettimeofday>
		3456	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3457	correctness. See the note about libraries in the description of
		3458	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3459	C<EV_USE_CLOCK_SYSCALL>.
		3460
		3461	=item EV_USE_CLOCK_SYSCALL
		3462
		3463	If defined to be C<1>, libev will try to use a direct syscall instead
		3464	of calling the system-provided C<clock_gettime> function. This option
		3465	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3466	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3467	programs needlessly. Using a direct syscall is slightly slower (in
		3468	theory), because no optimised vdso implementation can be used, but avoids
		3469	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3470	higher, as it simplifies linking (no need for C<-lrt>).
		3471
		3472	=item EV_USE_NANOSLEEP
		3473
		3474	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3475	and will use it for delays. Otherwise it will use C<select ()>.
		3476
		3477	=item EV_USE_EVENTFD
		3478
		3479	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3480	available and will probe for kernel support at runtime. This will improve
		3481	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3482	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3483	2.7 or newer, otherwise disabled.
		3484
		3485	=item EV_USE_SELECT
		3486
		3487	If undefined or defined to be C<1>, libev will compile in support for the
		3488	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3489	other method takes over, select will be it. Otherwise the select backend
		3490	will not be compiled in.
		3491
		3492	=item EV_SELECT_USE_FD_SET
		3493
		3494	If defined to C<1>, then the select backend will use the system C<fd_set>
		3495	structure. This is useful if libev doesn't compile due to a missing
		3496	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3497	on exotic systems. This usually limits the range of file descriptors to
		3498	some low limit such as 1024 or might have other limitations (winsocket
		3499	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3500	configures the maximum size of the C<fd_set>.
		3501
		3502	=item EV_SELECT_IS_WINSOCKET
		3503
		3504	When defined to C<1>, the select backend will assume that
		3505	select/socket/connect etc. don't understand file descriptors but
		3506	wants osf handles on win32 (this is the case when the select to
		3507	be used is the winsock select). This means that it will call
		3508	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3509	it is assumed that all these functions actually work on fds, even
		3510	on win32. Should not be defined on non-win32 platforms.
		3511
		3512	=item EV_FD_TO_WIN32_HANDLE
		3513
		3514	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3515	file descriptors to socket handles. When not defining this symbol (the
		3516	default), then libev will call C<_get_osfhandle>, which is usually
		3517	correct. In some cases, programs use their own file descriptor management,
		3518	in which case they can provide this function to map fds to socket handles.
		3519
		3520	=item EV_USE_POLL
		3521
		3522	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3523	backend. Otherwise it will be enabled on non-win32 platforms. It
		3524	takes precedence over select.
		3525
		3526	=item EV_USE_EPOLL
		3527
		3528	If defined to be C<1>, libev will compile in support for the Linux
		3529	C<epoll>(7) backend. Its availability will be detected at runtime,
		3530	otherwise another method will be used as fallback. This is the preferred
		3531	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3532	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3533
		3534	=item EV_USE_KQUEUE
		3535
		3536	If defined to be C<1>, libev will compile in support for the BSD style
		3537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3538	otherwise another method will be used as fallback. This is the preferred
		3539	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3540	supports some types of fds correctly (the only platform we found that
		3541	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3542	not be used unless explicitly requested. The best way to use it is to find
		3543	out whether kqueue supports your type of fd properly and use an embedded
		3544	kqueue loop.
		3545
		3546	=item EV_USE_PORT
		3547
		3548	If defined to be C<1>, libev will compile in support for the Solaris
		3549	10 port style backend. Its availability will be detected at runtime,
		3550	otherwise another method will be used as fallback. This is the preferred
		3551	backend for Solaris 10 systems.
		3552
		3553	=item EV_USE_DEVPOLL
		3554
		3555	Reserved for future expansion, works like the USE symbols above.
		3556
		3557	=item EV_USE_INOTIFY
		3558
		3559	If defined to be C<1>, libev will compile in support for the Linux inotify
		3560	interface to speed up C<ev_stat> watchers. Its actual availability will
		3561	be detected at runtime. If undefined, it will be enabled if the headers
		3562	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3563
		3564	=item EV_ATOMIC_T
		3565
		3566	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3567	access is atomic with respect to other threads or signal contexts. No such
		3568	type is easily found in the C language, so you can provide your own type
		3569	that you know is safe for your purposes. It is used both for signal handler "locking"
		3570	as well as for signal and thread safety in C<ev_async> watchers.
		3571
		3572	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3573	(from F<signal.h>), which is usually good enough on most platforms.
		3574
		3575	=item EV_H
		3576
		3577	The name of the F<ev.h> header file used to include it. The default if
		3578	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3579	used to virtually rename the F<ev.h> header file in case of conflicts.
		3580
		3581	=item EV_CONFIG_H
		3582
		3583	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3584	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3585	C<EV_H>, above.
		3586
		3587	=item EV_EVENT_H
		3588
		3589	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3590	of how the F<event.h> header can be found, the default is C<"event.h">.
		3591
		3592	=item EV_PROTOTYPES
		3593
		3594	If defined to be C<0>, then F<ev.h> will not define any function
		3595	prototypes, but still define all the structs and other symbols. This is
		3596	occasionally useful if you want to provide your own wrapper functions
		3597	around libev functions.
		3598
		3599	=item EV_MULTIPLICITY
		3600
		3601	If undefined or defined to C<1>, then all event-loop-specific functions
		3602	will have the C<struct ev_loop *> as first argument, and you can create
		3603	additional independent event loops. Otherwise there will be no support
		3604	for multiple event loops and there is no first event loop pointer
		3605	argument. Instead, all functions act on the single default loop.
		3606
		3607	=item EV_MINPRI
		3608
		3609	=item EV_MAXPRI
		3610
		3611	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3612	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3613	provide for more priorities by overriding those symbols (usually defined
		3614	to be C<-2> and C<2>, respectively).
		3615
		3616	When doing priority-based operations, libev usually has to linearly search
		3617	all the priorities, so having many of them (hundreds) uses a lot of space
		3618	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3619	fine.
		3620
		3621	If your embedding application does not need any priorities, defining these
		3622	both to C<0> will save some memory and CPU.
		3623
		3624	=item EV_PERIODIC_ENABLE
		3625
		3626	If undefined or defined to be C<1>, then periodic timers are supported. If
		3627	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3628	code.
		3629
		3630	=item EV_IDLE_ENABLE
		3631
		3632	If undefined or defined to be C<1>, then idle watchers are supported. If
		3633	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3634	code.
		3635
		3636	=item EV_EMBED_ENABLE
		3637
		3638	If undefined or defined to be C<1>, then embed watchers are supported. If
		3639	defined to be C<0>, then they are not. Embed watchers rely on most other
		3640	watcher types, which therefore must not be disabled.
		3641
		3642	=item EV_STAT_ENABLE
		3643
		3644	If undefined or defined to be C<1>, then stat watchers are supported. If
		3645	defined to be C<0>, then they are not.
		3646
		3647	=item EV_FORK_ENABLE
		3648
		3649	If undefined or defined to be C<1>, then fork watchers are supported. If
		3650	defined to be C<0>, then they are not.
		3651
		3652	=item EV_ASYNC_ENABLE
		3653
		3654	If undefined or defined to be C<1>, then async watchers are supported. If
		3655	defined to be C<0>, then they are not.
		3656
		3657	=item EV_MINIMAL
		3658
		3659	If you need to shave off some kilobytes of code at the expense of some
		3660	speed, define this symbol to C<1>. Currently this is used to override some
		3661	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3662	much smaller 2-heap for timer management over the default 4-heap.
		3663
		3664	=item EV_PID_HASHSIZE
		3665
		3666	C<ev_child> watchers use a small hash table to distribute workload by
		3667	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3668	than enough. If you need to manage thousands of children you might want to
		3669	increase this value (I<must> be a power of two).
		3670
		3671	=item EV_INOTIFY_HASHSIZE
		3672
		3673	C<ev_stat> watchers use a small hash table to distribute workload by
		3674	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3675	usually more than enough. If you need to manage thousands of C<ev_stat>
		3676	watchers you might want to increase this value (I<must> be a power of
		3677	two).
		3678
		3679	=item EV_USE_4HEAP
		3680
		3681	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3682	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3683	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3684	faster performance with many (thousands) of watchers.
		3685
		3686	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3687	(disabled).
		3688
		3689	=item EV_HEAP_CACHE_AT
		3690
		3691	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3692	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3693	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3694	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3695	but avoids random read accesses on heap changes. This improves performance
		3696	noticeably with many (hundreds) of watchers.
		3697
		3698	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3699	(disabled).
		3700
		3701	=item EV_VERIFY
		3702
		3703	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3704	be done: If set to C<0>, no internal verification code will be compiled
		3705	in. If set to C<1>, then verification code will be compiled in, but not
		3706	called. If set to C<2>, then the internal verification code will be
		3707	called once per loop, which can slow down libev. If set to C<3>, then the
		3708	verification code will be called very frequently, which will slow down
		3709	libev considerably.
		3710
		3711	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3712	C<0>.
		3713
		3714	=item EV_COMMON
		3715
		3716	By default, all watchers have a C<void *data> member. By redefining
		3717	this macro to a something else you can include more and other types of
		3718	members. You have to define it each time you include one of the files,
		3719	though, and it must be identical each time.
		3720
		3721	For example, the perl EV module uses something like this:
		3722
		3723	#define EV_COMMON \
		3724	SV *self; /* contains this struct */ \
		3725	SV *cb_sv, *fh /* note no trailing ";" */
		3726
		3727	=item EV_CB_DECLARE (type)
		3728
		3729	=item EV_CB_INVOKE (watcher, revents)
		3730
		3731	=item ev_set_cb (ev, cb)
		3732
		3733	Can be used to change the callback member declaration in each watcher,
		3734	and the way callbacks are invoked and set. Must expand to a struct member
		3735	definition and a statement, respectively. See the F<ev.h> header file for
		3736	their default definitions. One possible use for overriding these is to
		3737	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3738	method calls instead of plain function calls in C++.
		3739
		3740	=back
		3741
		3742	=head2 EXPORTED API SYMBOLS
		3743
		3744	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3745	exported symbols, you can use the provided F<Symbol.*> files which list
		3746	all public symbols, one per line:
		3747
		3748	Symbols.ev for libev proper
		3749	Symbols.event for the libevent emulation
		3750
		3751	This can also be used to rename all public symbols to avoid clashes with
		3752	multiple versions of libev linked together (which is obviously bad in
		3753	itself, but sometimes it is inconvenient to avoid this).
		3754
		3755	A sed command like this will create wrapper C<#define>'s that you need to
		3756	include before including F<ev.h>:
		3757
		3758	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3759
		3760	This would create a file F<wrap.h> which essentially looks like this:
		3761
		3762	#define ev_backend myprefix_ev_backend
		3763	#define ev_check_start myprefix_ev_check_start
		3764	#define ev_check_stop myprefix_ev_check_stop
		3765	...
		3766
		3767	=head2 EXAMPLES
		3768
		3769	For a real-world example of a program the includes libev
		3770	verbatim, you can have a look at the EV perl module
		3771	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3772	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3773	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3774	will be compiled. It is pretty complex because it provides its own header
		3775	file.
		3776
		3777	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3778	that everybody includes and which overrides some configure choices:
		3779
		3780	#define EV_MINIMAL 1
		3781	#define EV_USE_POLL 0
		3782	#define EV_MULTIPLICITY 0
		3783	#define EV_PERIODIC_ENABLE 0
		3784	#define EV_STAT_ENABLE 0
		3785	#define EV_FORK_ENABLE 0
		3786	#define EV_CONFIG_H <config.h>
		3787	#define EV_MINPRI 0
		3788	#define EV_MAXPRI 0
		3789
		3790	#include "ev++.h"
		3791
		3792	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3793
		3794	#include "ev_cpp.h"
		3795	#include "ev.c"
		3796
		3797	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3798
		3799	=head2 THREADS AND COROUTINES
		3800
		3801	=head3 THREADS
		3802
		3803	All libev functions are reentrant and thread-safe unless explicitly
		3804	documented otherwise, but libev implements no locking itself. This means
		3805	that you can use as many loops as you want in parallel, as long as there
		3806	are no concurrent calls into any libev function with the same loop
		3807	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3808	of course): libev guarantees that different event loops share no data
		3809	structures that need any locking.
		3810
		3811	Or to put it differently: calls with different loop parameters can be done
		3812	concurrently from multiple threads, calls with the same loop parameter
		3813	must be done serially (but can be done from different threads, as long as
		3814	only one thread ever is inside a call at any point in time, e.g. by using
		3815	a mutex per loop).
		3816
		3817	Specifically to support threads (and signal handlers), libev implements
		3818	so-called C<ev_async> watchers, which allow some limited form of
		3819	concurrency on the same event loop, namely waking it up "from the
		3820	outside".
		3821
		3822	If you want to know which design (one loop, locking, or multiple loops
		3823	without or something else still) is best for your problem, then I cannot
		3824	help you, but here is some generic advice:
		3825
		3826	=over 4
		3827
		3828	=item * most applications have a main thread: use the default libev loop
		3829	in that thread, or create a separate thread running only the default loop.
		3830
		3831	This helps integrating other libraries or software modules that use libev
		3832	themselves and don't care/know about threading.
		3833
		3834	=item * one loop per thread is usually a good model.
		3835
		3836	Doing this is almost never wrong, sometimes a better-performance model
		3837	exists, but it is always a good start.
		3838
		3839	=item * other models exist, such as the leader/follower pattern, where one
		3840	loop is handed through multiple threads in a kind of round-robin fashion.
		3841
		3842	Choosing a model is hard - look around, learn, know that usually you can do
		3843	better than you currently do :-)
		3844
		3845	=item * often you need to talk to some other thread which blocks in the
		3846	event loop.
		3847
		3848	C<ev_async> watchers can be used to wake them up from other threads safely
		3849	(or from signal contexts...).
		3850
		3851	An example use would be to communicate signals or other events that only
		3852	work in the default loop by registering the signal watcher with the
		3853	default loop and triggering an C<ev_async> watcher from the default loop
		3854	watcher callback into the event loop interested in the signal.
		3855
		3856	=back
		3857
		3858	=head3 COROUTINES
		3859
		3860	Libev is very accommodating to coroutines ("cooperative threads"):
		3861	libev fully supports nesting calls to its functions from different
		3862	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3863	different coroutines, and switch freely between both coroutines running the
		3864	loop, as long as you don't confuse yourself). The only exception is that
		3865	you must not do this from C<ev_periodic> reschedule callbacks.
		3866
		3867	Care has been taken to ensure that libev does not keep local state inside
		3868	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3869	they do not call any callbacks.
		3870
		3871	=head2 COMPILER WARNINGS
		3872
		3873	Depending on your compiler and compiler settings, you might get no or a
		3874	lot of warnings when compiling libev code. Some people are apparently
		3875	scared by this.
		3876
		3877	However, these are unavoidable for many reasons. For one, each compiler
		3878	has different warnings, and each user has different tastes regarding
		3879	warning options. "Warn-free" code therefore cannot be a goal except when
		3880	targeting a specific compiler and compiler-version.
		3881
		3882	Another reason is that some compiler warnings require elaborate
		3883	workarounds, or other changes to the code that make it less clear and less
		3884	maintainable.
		3885
		3886	And of course, some compiler warnings are just plain stupid, or simply
		3887	wrong (because they don't actually warn about the condition their message
		3888	seems to warn about). For example, certain older gcc versions had some
		3889	warnings that resulted an extreme number of false positives. These have
		3890	been fixed, but some people still insist on making code warn-free with
		3891	such buggy versions.
		3892
		3893	While libev is written to generate as few warnings as possible,
		3894	"warn-free" code is not a goal, and it is recommended not to build libev
		3895	with any compiler warnings enabled unless you are prepared to cope with
		3896	them (e.g. by ignoring them). Remember that warnings are just that:
		3897	warnings, not errors, or proof of bugs.
		3898
		3899
		3900	=head2 VALGRIND
		3901
		3902	Valgrind has a special section here because it is a popular tool that is
		3903	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3904
		3905	If you think you found a bug (memory leak, uninitialised data access etc.)
		3906	in libev, then check twice: If valgrind reports something like:
		3907
		3908	==2274== definitely lost: 0 bytes in 0 blocks.
		3909	==2274== possibly lost: 0 bytes in 0 blocks.
		3910	==2274== still reachable: 256 bytes in 1 blocks.
		3911
		3912	Then there is no memory leak, just as memory accounted to global variables
		3913	is not a memleak - the memory is still being referenced, and didn't leak.
		3914
		3915	Similarly, under some circumstances, valgrind might report kernel bugs
		3916	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3917	although an acceptable workaround has been found here), or it might be
		3918	confused.
		3919
		3920	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3921	make it into some kind of religion.
		3922
		3923	If you are unsure about something, feel free to contact the mailing list
		3924	with the full valgrind report and an explanation on why you think this
		3925	is a bug in libev (best check the archives, too :). However, don't be
		3926	annoyed when you get a brisk "this is no bug" answer and take the chance
		3927	of learning how to interpret valgrind properly.
		3928
		3929	If you need, for some reason, empty reports from valgrind for your project
		3930	I suggest using suppression lists.
		3931
		3932
		3933	=head1 PORTABILITY NOTES
		3934
		3935	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3936
		3937	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3938	requires, and its I/O model is fundamentally incompatible with the POSIX
		3939	model. Libev still offers limited functionality on this platform in
		3940	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3941	descriptors. This only applies when using Win32 natively, not when using
		3942	e.g. cygwin.
		3943
		3944	Lifting these limitations would basically require the full
		3945	re-implementation of the I/O system. If you are into these kinds of
		3946	things, then note that glib does exactly that for you in a very portable
		3947	way (note also that glib is the slowest event library known to man).
		3948
		3949	There is no supported compilation method available on windows except
		3950	embedding it into other applications.
		3951
		3952	Sensible signal handling is officially unsupported by Microsoft - libev
		3953	tries its best, but under most conditions, signals will simply not work.
		3954
		3955	Not a libev limitation but worth mentioning: windows apparently doesn't
		3956	accept large writes: instead of resulting in a partial write, windows will
		3957	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3958	so make sure you only write small amounts into your sockets (less than a
		3959	megabyte seems safe, but this apparently depends on the amount of memory
		3960	available).
		3961
		3962	Due to the many, low, and arbitrary limits on the win32 platform and
		3963	the abysmal performance of winsockets, using a large number of sockets
		3964	is not recommended (and not reasonable). If your program needs to use
		3965	more than a hundred or so sockets, then likely it needs to use a totally
		3966	different implementation for windows, as libev offers the POSIX readiness
		3967	notification model, which cannot be implemented efficiently on windows
		3968	(due to Microsoft monopoly games).
		3969
		3970	A typical way to use libev under windows is to embed it (see the embedding
		3971	section for details) and use the following F<evwrap.h> header file instead
		3972	of F<ev.h>:
		3973
		3974	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3975	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3976
		3977	#include "ev.h"
		3978
		3979	And compile the following F<evwrap.c> file into your project (make sure
		3980	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3981
		3982	#include "evwrap.h"
		3983	#include "ev.c"
		3984
		3985	=over 4
		3986
		3987	=item The winsocket select function
		3988
		3989	The winsocket C<select> function doesn't follow POSIX in that it
		3990	requires socket I<handles> and not socket I<file descriptors> (it is
		3991	also extremely buggy). This makes select very inefficient, and also
		3992	requires a mapping from file descriptors to socket handles (the Microsoft
		3993	C runtime provides the function C<_open_osfhandle> for this). See the
		3994	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3995	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3996
		3997	The configuration for a "naked" win32 using the Microsoft runtime
		3998	libraries and raw winsocket select is:
		3999
		4000	#define EV_USE_SELECT 1
		4001	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4002
		4003	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4004	complexity in the O(n²) range when using win32.
		4005
		4006	=item Limited number of file descriptors
		4007
		4008	Windows has numerous arbitrary (and low) limits on things.
		4009
		4010	Early versions of winsocket's select only supported waiting for a maximum
		4011	of C<64> handles (probably owning to the fact that all windows kernels
		4012	can only wait for C<64> things at the same time internally; Microsoft
		4013	recommends spawning a chain of threads and wait for 63 handles and the
		4014	previous thread in each. Sounds great!).
		4015
		4016	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4017	to some high number (e.g. C<2048>) before compiling the winsocket select
		4018	call (which might be in libev or elsewhere, for example, perl and many
		4019	other interpreters do their own select emulation on windows).
		4020
		4021	Another limit is the number of file descriptors in the Microsoft runtime
		4022	libraries, which by default is C<64> (there must be a hidden I<64>
		4023	fetish or something like this inside Microsoft). You can increase this
		4024	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4025	(another arbitrary limit), but is broken in many versions of the Microsoft
		4026	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4027	(depending on windows version and/or the phase of the moon). To get more,
		4028	you need to wrap all I/O functions and provide your own fd management, but
		4029	the cost of calling select (O(n²)) will likely make this unworkable.
		4030
		4031	=back
		4032
		4033	=head2 PORTABILITY REQUIREMENTS
		4034
		4035	In addition to a working ISO-C implementation and of course the
		4036	backend-specific APIs, libev relies on a few additional extensions:
		4037
		4038	=over 4
		4039
		4040	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4041	calling conventions regardless of C<ev_watcher_type *>.
		4042
		4043	Libev assumes not only that all watcher pointers have the same internal
		4044	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4045	assumes that the same (machine) code can be used to call any watcher
		4046	callback: The watcher callbacks have different type signatures, but libev
		4047	calls them using an C<ev_watcher *> internally.
		4048
		4049	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4050
		4051	The type C<sig_atomic_t volatile> (or whatever is defined as
		4052	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4053	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4054	believed to be sufficiently portable.
		4055
		4056	=item C<sigprocmask> must work in a threaded environment
		4057
		4058	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4059	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4060	pthread implementations will either allow C<sigprocmask> in the "main
		4061	thread" or will block signals process-wide, both behaviours would
		4062	be compatible with libev. Interaction between C<sigprocmask> and
		4063	C<pthread_sigmask> could complicate things, however.
		4064
		4065	The most portable way to handle signals is to block signals in all threads
		4066	except the initial one, and run the default loop in the initial thread as
		4067	well.
		4068
		4069	=item C<long> must be large enough for common memory allocation sizes
		4070
		4071	To improve portability and simplify its API, libev uses C<long> internally
		4072	instead of C<size_t> when allocating its data structures. On non-POSIX
		4073	systems (Microsoft...) this might be unexpectedly low, but is still at
		4074	least 31 bits everywhere, which is enough for hundreds of millions of
		4075	watchers.
		4076
		4077	=item C<double> must hold a time value in seconds with enough accuracy
		4078
		4079	The type C<double> is used to represent timestamps. It is required to
		4080	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4081	enough for at least into the year 4000. This requirement is fulfilled by
		4082	implementations implementing IEEE 754, which is basically all existing
		4083	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4084	2200.
		4085
		4086	=back
		4087
		4088	If you know of other additional requirements drop me a note.
		4089
		4090
		4091	=head1 ALGORITHMIC COMPLEXITIES
		4092
		4093	In this section the complexities of (many of) the algorithms used inside
		4094	libev will be documented. For complexity discussions about backends see
		4095	the documentation for C<ev_default_init>.
		4096
		4097	All of the following are about amortised time: If an array needs to be
		4098	extended, libev needs to realloc and move the whole array, but this
		4099	happens asymptotically rarer with higher number of elements, so O(1) might
		4100	mean that libev does a lengthy realloc operation in rare cases, but on
		4101	average it is much faster and asymptotically approaches constant time.
		4102
		4103	=over 4
		4104
		4105	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4106
		4107	This means that, when you have a watcher that triggers in one hour and
		4108	there are 100 watchers that would trigger before that, then inserting will
		4109	have to skip roughly seven (C<ld 100>) of these watchers.
		4110
		4111	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4112
		4113	That means that changing a timer costs less than removing/adding them,
		4114	as only the relative motion in the event queue has to be paid for.
		4115
		4116	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4117
		4118	These just add the watcher into an array or at the head of a list.
		4119
		4120	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4121
		4122	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4123
		4124	These watchers are stored in lists, so they need to be walked to find the
		4125	correct watcher to remove. The lists are usually short (you don't usually
		4126	have many watchers waiting for the same fd or signal: one is typical, two
		4127	is rare).
		4128
		4129	=item Finding the next timer in each loop iteration: O(1)
		4130
		4131	By virtue of using a binary or 4-heap, the next timer is always found at a
		4132	fixed position in the storage array.
		4133
		4134	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4135
		4136	A change means an I/O watcher gets started or stopped, which requires
		4137	libev to recalculate its status (and possibly tell the kernel, depending
		4138	on backend and whether C<ev_io_set> was used).
		4139
		4140	=item Activating one watcher (putting it into the pending state): O(1)
		4141
		4142	=item Priority handling: O(number_of_priorities)
		4143
		4144	Priorities are implemented by allocating some space for each
		4145	priority. When doing priority-based operations, libev usually has to
		4146	linearly search all the priorities, but starting/stopping and activating
		4147	watchers becomes O(1) with respect to priority handling.
		4148
		4149	=item Sending an ev_async: O(1)
		4150
		4151	=item Processing ev_async_send: O(number_of_async_watchers)
		4152
		4153	=item Processing signals: O(max_signal_number)
		4154
		4155	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4156	calls in the current loop iteration. Checking for async and signal events
		4157	involves iterating over all running async watchers or all signal numbers.
		4158
		4159	=back
		4160
		4161
		4162	=head1 GLOSSARY
		4163
		4164	=over 4
		4165
		4166	=item active
		4167
		4168	A watcher is active as long as it has been started (has been attached to
		4169	an event loop) but not yet stopped (disassociated from the event loop).
		4170
		4171	=item application
		4172
		4173	In this document, an application is whatever is using libev.
		4174
		4175	=item callback
		4176
		4177	The address of a function that is called when some event has been
		4178	detected. Callbacks are being passed the event loop, the watcher that
		4179	received the event, and the actual event bitset.
		4180
		4181	=item callback invocation
		4182
		4183	The act of calling the callback associated with a watcher.
		4184
		4185	=item event
		4186
		4187	A change of state of some external event, such as data now being available
		4188	for reading on a file descriptor, time having passed or simply not having
		4189	any other events happening anymore.
		4190
		4191	In libev, events are represented as single bits (such as C<EV_READ> or
		4192	C<EV_TIMEOUT>).
		4193
		4194	=item event library
		4195
		4196	A software package implementing an event model and loop.
		4197
		4198	=item event loop
		4199
		4200	An entity that handles and processes external events and converts them
		4201	into callback invocations.
		4202
		4203	=item event model
		4204
		4205	The model used to describe how an event loop handles and processes
		4206	watchers and events.
		4207
		4208	=item pending
		4209
		4210	A watcher is pending as soon as the corresponding event has been detected,
		4211	and stops being pending as soon as the watcher will be invoked or its
		4212	pending status is explicitly cleared by the application.
		4213
		4214	A watcher can be pending, but not active. Stopping a watcher also clears
		4215	its pending status.
		4216
		4217	=item real time
		4218
		4219	The physical time that is observed. It is apparently strictly monotonic :)
		4220
		4221	=item wall-clock time
		4222
		4223	The time and date as shown on clocks. Unlike real time, it can actually
		4224	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4225	clock.
		4226
		4227	=item watcher
		4228
		4229	A data structure that describes interest in certain events. Watchers need
		4230	to be started (attached to an event loop) before they can receive events.
		4231
		4232	=item watcher invocation
		4233
		4234	The act of calling the callback associated with a watcher.
		4235
		4236	=back
		4237
767	=head1 AUTHOR	4238	=head1 AUTHOR
768		4239
769	Marc Lehmann <libev@schmorp.de>.	4240	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
770		4241

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