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Revision 1.8 by root, Mon Nov 12 08:20:02 2007 UTC vs.
Revision 1.178 by root, Sat Sep 13 18:25:50 2008 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
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	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	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	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	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	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	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	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 *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
		142
		143	=head1 GLOBAL FUNCTIONS
		144
		145	These functions can be called anytime, even before initialising the
		146	library in any way.
51		147
52	=over 4	148	=over 4
53		149
54	=item ev_tstamp ev_time ()	150	=item ev_tstamp ev_time ()
55		151
56	Returns the current time as libev would use it.	152	Returns the current time as libev would use it. Please note that the
		153	C<ev_now> function is usually faster and also often returns the timestamp
		154	you actually want to know.
		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
57		161
58	=item int ev_version_major ()	162	=item int ev_version_major ()
59		163
60	=item int ev_version_minor ()	164	=item int ev_version_minor ()
61		165
62	You can find out the major and minor version numbers of the library	166	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	167	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	168	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	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	170	version of the library your program was compiled against.
67		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
68	Usually, its a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	178	not a problem.
72		179
		180	Example: Make sure we haven't accidentally been linked against the wrong
		181	version.
		182
		183	assert (("libev version mismatch",
		184	ev_version_major () == EV_VERSION_MAJOR
		185	&& ev_version_minor () >= EV_VERSION_MINOR));
		186
		187	=item unsigned int ev_supported_backends ()
		188
		189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		190	value) compiled into this binary of libev (independent of their
		191	availability on the system you are running on). See C<ev_default_loop> for
		192	a description of the set values.
		193
		194	Example: make sure we have the epoll method, because yeah this is cool and
		195	a must have and can we have a torrent of it please!!!11
		196
		197	assert (("sorry, no epoll, no sex",
		198	ev_supported_backends () & EVBACKEND_EPOLL));
		199
		200	=item unsigned int ev_recommended_backends ()
		201
		202	Return the set of all backends compiled into this binary of libev and also
		203	recommended for this platform. This set is often smaller than the one
		204	returned by C<ev_supported_backends>, as for example kqueue is broken on
		205	most BSDs and will not be auto-detected unless you explicitly request it
		206	(assuming you know what you are doing). This is the set of backends that
		207	libev will probe for if you specify no backends explicitly.
		208
		209	=item unsigned int ev_embeddable_backends ()
		210
		211	Returns the set of backends that are embeddable in other event loops. This
		212	is the theoretical, all-platform, value. To find which backends
		213	might be supported on the current system, you would need to look at
		214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		215	recommended ones.
		216
		217	See the description of C<ev_embed> watchers for more info.
		218
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		220
75	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	222	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	223	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	224	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
80		230
81	You could override this function in high-availability programs to, say,	231	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,	232	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.	233	or even to sleep a while and retry until some memory is available.
84		234
		235	Example: Replace the libev allocator with one that waits a bit and then
		236	retries (example requires a standards-compliant C<realloc>).
		237
		238	static void *
		239	persistent_realloc (void *ptr, size_t size)
		240	{
		241	for (;;)
		242	{
		243	void *newptr = realloc (ptr, size);
		244
		245	if (newptr)
		246	return newptr;
		247
		248	sleep (60);
		249	}
		250	}
		251
		252	...
		253	ev_set_allocator (persistent_realloc);
		254
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg));
86		256
87	Set the callback function to call on a retryable syscall error (such	257	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	258	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	259	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	260	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	261	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	262	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	263	(such as abort).
94		264
		265	Example: This is basically the same thing that libev does internally, too.
		266
		267	static void
		268	fatal_error (const char *msg)
		269	{
		270	perror (msg);
		271	abort ();
		272	}
		273
		274	...
		275	ev_set_syserr_cb (fatal_error);
		276
95	=back	277	=back
96		278
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		280
99	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *>. The library knows two
100	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
102		284
103	If you use threads, a common model is to run the default event loop
104	in your main thread (or in a separate thrad) and for each thread you
105	create, you also create another event loop. Libev itself does no locking
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because its hideous and inefficient).
109
110	=over 4	285	=over 4
111		286
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		288
114	This will initialise the default event loop if it hasn't been initialised	289	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	290	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	291	false. If it already was initialised it simply returns it (and ignores the
117	flags).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		293
119	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
120	function.	295	function.
121		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
122	The flags argument can be used to specify special behaviour or specific	308	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).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		310
125	It supports the following flags:	311	The following flags are supported:
126		312
127	=over 4	313	=over 4
128		314
129	=item EVFLAG_AUTO	315	=item C<EVFLAG_AUTO>
130		316
131	The default flags value. Use this if you have no clue (its the right	317	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	318	thing, believe me).
133		319
134	=item EVFLAG_NOENV	320	=item C<EVFLAG_NOENV>
135		321
136	If this flag bit is ored into the flag value (or the program runs setuid	322	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	323	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	325	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	326	useful to try out specific backends to test their performance, or to work
141	around bugs.	327	around bugs.
142		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
143	=item EVMETHOD_SELECT portable select backend	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		350
145	=item EVMETHOD_POLL poll backend (everywhere except windows)	351	This is your standard select(2) backend. Not I<completely> standard, as
		352	libev tries to roll its own fd_set with no limits on the number of fds,
		353	but if that fails, expect a fairly low limit on the number of fds when
		354	using this backend. It doesn't scale too well (O(highest_fd)), but its
		355	usually the fastest backend for a low number of (low-numbered :) fds.
146		356
147	=item EVMETHOD_EPOLL linux only	357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
148		363
149	=item EVMETHOD_KQUEUE some bsds only	364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
150		365
151	=item EVMETHOD_DEVPOLL solaris 8 only	366	And this is your standard poll(2) backend. It's more complicated
		367	than select, but handles sparse fds better and has no artificial
		368	limit on the number of fds you can use (except it will slow down
		369	considerably with a lot of inactive fds). It scales similarly to select,
		370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		371	performance tips.
152		372
153	=item EVMETHOD_PORT solaris 10 only	373	=item C<EVBACKEND_EPOLL> (value 4, Linux)
154		374
155	If one or more of these are ored into the flags value, then only these	375	For few fds, this backend is a bit little slower than poll and select,
156	backends will be tried (in the reverse order as given here). If one are	376	but it scales phenomenally better. While poll and select usually scale
157	specified, any backend will do.	377	like O(total_fds) where n is the total number of fds (or the highest fd),
		378	epoll scales either O(1) or O(active_fds). The epoll design has a number
		379	of shortcomings, such as silently dropping events in some hard-to-detect
		380	cases and requiring a system call per fd change, no fork support and bad
		381	support for dup.
		382
		383	While stopping, setting and starting an I/O watcher in the same iteration
		384	will result in some caching, there is still a system call per such incident
		385	(because the fd could point to a different file description now), so its
		386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		387	very well if you register events for both fds.
		388
		389	Please note that epoll sometimes generates spurious notifications, so you
		390	need to use non-blocking I/O or other means to avoid blocking when no data
		391	(or space) is available.
		392
		393	Best performance from this backend is achieved by not unregistering all
		394	watchers for a file descriptor until it has been closed, if possible, i.e.
		395	keep at least one watcher active per fd at all times.
		396
		397	While nominally embeddable in other event loops, this feature is broken in
		398	all kernel versions tested so far.
		399
		400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		401
		402	Kqueue deserves special mention, as at the time of this writing, it
		403	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		404	with anything but sockets and pipes, except on Darwin, where of course
		405	it's completely useless). For this reason it's not being "auto-detected"
		406	unless you explicitly specify it explicitly in the flags (i.e. using
		407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		408	system like NetBSD.
		409
		410	You still can embed kqueue into a normal poll or select backend and use it
		411	only for sockets (after having made sure that sockets work with kqueue on
		412	the target platform). See C<ev_embed> watchers for more info.
		413
		414	It scales in the same way as the epoll backend, but the interface to the
		415	kernel is more efficient (which says nothing about its actual speed, of
		416	course). While stopping, setting and starting an I/O watcher does never
		417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		418	two event changes per incident, support for C<fork ()> is very bad and it
		419	drops fds silently in similarly hard-to-detect cases.
		420
		421	This backend usually performs well under most conditions.
		422
		423	While nominally embeddable in other event loops, this doesn't work
		424	everywhere, so you might need to test for this. And since it is broken
		425	almost everywhere, you should only use it when you have a lot of sockets
		426	(for which it usually works), by embedding it into another event loop
		427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		428	sockets.
		429
		430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		431
		432	This is not implemented yet (and might never be, unless you send me an
		433	implementation). According to reports, C</dev/poll> only supports sockets
		434	and is not embeddable, which would limit the usefulness of this backend
		435	immensely.
		436
		437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		438
		439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		440	it's really slow, but it still scales very well (O(active_fds)).
		441
		442	Please note that Solaris event ports can deliver a lot of spurious
		443	notifications, so you need to use non-blocking I/O or other means to avoid
		444	blocking when no data (or space) is available.
		445
		446	While this backend scales well, it requires one system call per active
		447	file descriptor per loop iteration. For small and medium numbers of file
		448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		449	might perform better.
		450
		451	On the positive side, ignoring the spurious readiness notifications, this
		452	backend actually performed to specification in all tests and is fully
		453	embeddable, which is a rare feat among the OS-specific backends.
		454
		455	=item C<EVBACKEND_ALL>
		456
		457	Try all backends (even potentially broken ones that wouldn't be tried
		458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		460
		461	It is definitely not recommended to use this flag.
158		462
159	=back	463	=back
		464
		465	If one or more of these are or'ed into the flags value, then only these
		466	backends will be tried (in the reverse order as listed here). If none are
		467	specified, all backends in C<ev_recommended_backends ()> will be tried.
		468
		469	The most typical usage is like this:
		470
		471	if (!ev_default_loop (0))
		472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		473
		474	Restrict libev to the select and poll backends, and do not allow
		475	environment settings to be taken into account:
		476
		477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		478
		479	Use whatever libev has to offer, but make sure that kqueue is used if
		480	available (warning, breaks stuff, best use only with your own private
		481	event loop and only if you know the OS supports your types of fds):
		482
		483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		484
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	485	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		486
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	487	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	488	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	489	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).	490	undefined behaviour (or a failed assertion if assertions are enabled).
167		491
		492	Note that this function I<is> thread-safe, and the recommended way to use
		493	libev with threads is indeed to create one loop per thread, and using the
		494	default loop in the "main" or "initial" thread.
		495
		496	Example: Try to create a event loop that uses epoll and nothing else.
		497
		498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		499	if (!epoller)
		500	fatal ("no epoll found here, maybe it hides under your chair");
		501
168	=item ev_default_destroy ()	502	=item ev_default_destroy ()
169		503
170	Destroys the default loop again (frees all memory and kernel state	504	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	505	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cnanot rely on this :).	506	sense, so e.g. C<ev_is_active> might still return true. It is your
		507	responsibility to either stop all watchers cleanly yourself I<before>
		508	calling this function, or cope with the fact afterwards (which is usually
		509	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		510	for example).
		511
		512	Note that certain global state, such as signal state, will not be freed by
		513	this function, and related watchers (such as signal and child watchers)
		514	would need to be stopped manually.
		515
		516	In general it is not advisable to call this function except in the
		517	rare occasion where you really need to free e.g. the signal handling
		518	pipe fds. If you need dynamically allocated loops it is better to use
		519	C<ev_loop_new> and C<ev_loop_destroy>).
173		520
174	=item ev_loop_destroy (loop)	521	=item ev_loop_destroy (loop)
175		522
176	Like C<ev_default_destroy>, but destroys an event loop created by an	523	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	524	earlier call to C<ev_loop_new>.
178		525
179	=item ev_default_fork ()	526	=item ev_default_fork ()
180		527
		528	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	529	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	530	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	531	the child process (or both child and parent, but that again makes little
184	again makes little sense).	532	sense). You I<must> call it in the child before using any of the libev
		533	functions, and it will only take effect at the next C<ev_loop> iteration.
185		534
186	You I<must> call this function after forking if and only if you want to	535	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	536	process if and only if you want to use the event library in the child. If
188	have to call it.	537	you just fork+exec, you don't have to call it at all.
189		538
190	The function itself is quite fast and its usually not a problem to call	539	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	540	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>:	541	quite nicely into a call to C<pthread_atfork>:
193		542
194	pthread_atfork (0, 0, ev_default_fork);	543	pthread_atfork (0, 0, ev_default_fork);
195		544
…		…
197		546
198	Like C<ev_default_fork>, but acts on an event loop created by	547	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	548	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.	549	after fork, and how you do this is entirely your own problem.
201		550
		551	=item int ev_is_default_loop (loop)
		552
		553	Returns true when the given loop actually is the default loop, false otherwise.
		554
		555	=item unsigned int ev_loop_count (loop)
		556
		557	Returns the count of loop iterations for the loop, which is identical to
		558	the number of times libev did poll for new events. It starts at C<0> and
		559	happily wraps around with enough iterations.
		560
		561	This value can sometimes be useful as a generation counter of sorts (it
		562	"ticks" the number of loop iterations), as it roughly corresponds with
		563	C<ev_prepare> and C<ev_check> calls.
		564
202	=item unsigned int ev_method (loop)	565	=item unsigned int ev_backend (loop)
203		566
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	568	use.
206		569
207	=item ev_tstamp = ev_now (loop)	570	=item ev_tstamp ev_now (loop)
208		571
209	Returns the current "event loop time", which is the time the event loop	572	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	573	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	574	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	575	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).	576	event occurring (or more correctly, libev finding out about it).
		577
		578	=item ev_now_update (loop)
		579
		580	Establishes the current time by querying the kernel, updating the time
		581	returned by C<ev_now ()> in the progress. This is a costly operation and
		582	is usually done automatically within C<ev_loop ()>.
		583
		584	This function is rarely useful, but when some event callback runs for a
		585	very long time without entering the event loop, updating libev's idea of
		586	the current time is a good idea.
		587
		588	See also "The special problem of time updates" in the C<ev_timer> section.
214		589
215	=item ev_loop (loop, int flags)	590	=item ev_loop (loop, int flags)
216		591
217	Finally, this is it, the event handler. This function usually is called	592	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	593	after you initialised all your watchers and you want to start handling
219	events.	594	events.
220		595
221	If the flags argument is specified as 0, it will not return until either	596	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.	597	either no event watchers are active anymore or C<ev_unloop> was called.
		598
		599	Please note that an explicit C<ev_unloop> is usually better than
		600	relying on all watchers to be stopped when deciding when a program has
		601	finished (especially in interactive programs), but having a program that
		602	automatically loops as long as it has to and no longer by virtue of
		603	relying on its watchers stopping correctly is a thing of beauty.
223		604
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	605	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	606	those events and any outstanding ones, but will not block your process in
226	case there are no events.	607	case there are no events and will return after one iteration of the loop.
227		608
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	609	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	610	necessary) and will handle those and any outstanding ones. It will block
230	your process until at least one new event arrives.	611	your process until at least one new event arrives, and will return after
		612	one iteration of the loop. This is useful if you are waiting for some
		613	external event in conjunction with something not expressible using other
		614	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		615	usually a better approach for this kind of thing.
231		616
232	This flags value could be used to implement alternative looping	617	Here are the gory details of what C<ev_loop> does:
233	constructs, but the C<prepare> and C<check> watchers provide a better and	618
234	more generic mechanism.	619	- Before the first iteration, call any pending watchers.
		620	* If EVFLAG_FORKCHECK was used, check for a fork.
		621	- If a fork was detected (by any means), queue and call all fork watchers.
		622	- Queue and call all prepare watchers.
		623	- If we have been forked, detach and recreate the kernel state
		624	as to not disturb the other process.
		625	- Update the kernel state with all outstanding changes.
		626	- Update the "event loop time" (ev_now ()).
		627	- Calculate for how long to sleep or block, if at all
		628	(active idle watchers, EVLOOP_NONBLOCK or not having
		629	any active watchers at all will result in not sleeping).
		630	- Sleep if the I/O and timer collect interval say so.
		631	- Block the process, waiting for any events.
		632	- Queue all outstanding I/O (fd) events.
		633	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		634	- Queue all outstanding timers.
		635	- Queue all outstanding periodics.
		636	- Unless any events are pending now, queue all idle watchers.
		637	- Queue all check watchers.
		638	- Call all queued watchers in reverse order (i.e. check watchers first).
		639	Signals and child watchers are implemented as I/O watchers, and will
		640	be handled here by queueing them when their watcher gets executed.
		641	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		642	were used, or there are no active watchers, return, otherwise
		643	continue with step *.
		644
		645	Example: Queue some jobs and then loop until no events are outstanding
		646	anymore.
		647
		648	... queue jobs here, make sure they register event watchers as long
		649	... as they still have work to do (even an idle watcher will do..)
		650	ev_loop (my_loop, 0);
		651	... jobs done or somebody called unloop. yeah!
235		652
236	=item ev_unloop (loop, how)	653	=item ev_unloop (loop, how)
237		654
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	655	Can be used to make a call to C<ev_loop> return early (but only after it
		656	has processed all outstanding events). The C<how> argument must be either
239	must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>	657	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
240	call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>	658	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
241	calls return.	659
		660	This "unloop state" will be cleared when entering C<ev_loop> again.
242		661
243	=item ev_ref (loop)	662	=item ev_ref (loop)
244		663
245	=item ev_unref (loop)	664	=item ev_unref (loop)
246		665
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	666	Ref/unref can be used to add or remove a reference count on the event
248	watcher keeps one reference. If you have a long-runing watcher you never	667	loop: Every watcher keeps one reference, and as long as the reference
249	unregister that should not keep ev_loop from running, ev_unref() after	668	count is nonzero, C<ev_loop> will not return on its own. If you have
250	starting, and ev_ref() before stopping it. Libev itself uses this for	669	a watcher you never unregister that should not keep C<ev_loop> from
251	example for its internal signal pipe: It is not visible to you as a user	670	returning, ev_unref() after starting, and ev_ref() before stopping it. For
252	and should not keep C<ev_loop> from exiting if the work is done. It is	671	example, libev itself uses this for its internal signal pipe: It is not
253	also an excellent way to do this for generic recurring timers or from	672	visible to the libev user and should not keep C<ev_loop> from exiting if
254	within third-party libraries. Just remember to unref after start and ref	673	no event watchers registered by it are active. It is also an excellent
255	before stop.	674	way to do this for generic recurring timers or from within third-party
		675	libraries. Just remember to I<unref after start> and I<ref before stop>
		676	(but only if the watcher wasn't active before, or was active before,
		677	respectively).
		678
		679	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		680	running when nothing else is active.
		681
		682	struct ev_signal exitsig;
		683	ev_signal_init (&exitsig, sig_cb, SIGINT);
		684	ev_signal_start (loop, &exitsig);
		685	evf_unref (loop);
		686
		687	Example: For some weird reason, unregister the above signal handler again.
		688
		689	ev_ref (loop);
		690	ev_signal_stop (loop, &exitsig);
		691
		692	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		693
		694	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		695
		696	These advanced functions influence the time that libev will spend waiting
		697	for events. Both time intervals are by default C<0>, meaning that libev
		698	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		699	latency.
		700
		701	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		702	allows libev to delay invocation of I/O and timer/periodic callbacks
		703	to increase efficiency of loop iterations (or to increase power-saving
		704	opportunities).
		705
		706	The background is that sometimes your program runs just fast enough to
		707	handle one (or very few) event(s) per loop iteration. While this makes
		708	the program responsive, it also wastes a lot of CPU time to poll for new
		709	events, especially with backends like C<select ()> which have a high
		710	overhead for the actual polling but can deliver many events at once.
		711
		712	By setting a higher I<io collect interval> you allow libev to spend more
		713	time collecting I/O events, so you can handle more events per iteration,
		714	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		715	C<ev_timer>) will be not affected. Setting this to a non-null value will
		716	introduce an additional C<ev_sleep ()> call into most loop iterations.
		717
		718	Likewise, by setting a higher I<timeout collect interval> you allow libev
		719	to spend more time collecting timeouts, at the expense of increased
		720	latency (the watcher callback will be called later). C<ev_io> watchers
		721	will not be affected. Setting this to a non-null value will not introduce
		722	any overhead in libev.
		723
		724	Many (busy) programs can usually benefit by setting the I/O collect
		725	interval to a value near C<0.1> or so, which is often enough for
		726	interactive servers (of course not for games), likewise for timeouts. It
		727	usually doesn't make much sense to set it to a lower value than C<0.01>,
		728	as this approaches the timing granularity of most systems.
		729
		730	Setting the I<timeout collect interval> can improve the opportunity for
		731	saving power, as the program will "bundle" timer callback invocations that
		732	are "near" in time together, by delaying some, thus reducing the number of
		733	times the process sleeps and wakes up again. Another useful technique to
		734	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		735	they fire on, say, one-second boundaries only.
		736
		737	=item ev_loop_verify (loop)
		738
		739	This function only does something when C<EV_VERIFY> support has been
		740	compiled in. It tries to go through all internal structures and checks
		741	them for validity. If anything is found to be inconsistent, it will print
		742	an error message to standard error and call C<abort ()>.
		743
		744	This can be used to catch bugs inside libev itself: under normal
		745	circumstances, this function will never abort as of course libev keeps its
		746	data structures consistent.
256		747
257	=back	748	=back
		749
258		750
259	=head1 ANATOMY OF A WATCHER	751	=head1 ANATOMY OF A WATCHER
260		752
261	A watcher is a structure that you create and register to record your	753	A watcher is a structure that you create and register to record your
262	interest in some event. For instance, if you want to wait for STDIN to	754	interest in some event. For instance, if you want to wait for STDIN to
263	become readable, you would create an ev_io watcher for that:	755	become readable, you would create an C<ev_io> watcher for that:
264		756
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	757	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
266	{	758	{
267	ev_io_stop (w);	759	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	760	ev_unloop (loop, EVUNLOOP_ALL);
269	}	761	}
270		762
271	struct ev_loop *loop = ev_default_loop (0);	763	struct ev_loop *loop = ev_default_loop (0);
272	struct ev_io stdin_watcher;	764	struct ev_io stdin_watcher;
273	ev_init (&stdin_watcher, my_cb);	765	ev_init (&stdin_watcher, my_cb);
274	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	766	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
275	ev_io_start (loop, &stdin_watcher);	767	ev_io_start (loop, &stdin_watcher);
276	ev_loop (loop, 0);	768	ev_loop (loop, 0);
277		769
278	As you can see, you are responsible for allocating the memory for your	770	As you can see, you are responsible for allocating the memory for your
279	watcher structures (and it is usually a bad idea to do this on the stack,	771	watcher structures (and it is usually a bad idea to do this on the stack,
280	although this can sometimes be quite valid).	772	although this can sometimes be quite valid).
281		773
282	Each watcher structure must be initialised by a call to C<ev_init	774	Each watcher structure must be initialised by a call to C<ev_init
283	(watcher *, callback)>, which expects a callback to be provided. This	775	(watcher *, callback)>, which expects a callback to be provided. This
284	callback gets invoked each time the event occurs (or, in the case of io	776	callback gets invoked each time the event occurs (or, in the case of I/O
285	watchers, each time the event loop detects that the file descriptor given	777	watchers, each time the event loop detects that the file descriptor given
286	is readable and/or writable).	778	is readable and/or writable).
287		779
288	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	780	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
289	with arguments specific to this watcher type. There is also a macro	781	with arguments specific to this watcher type. There is also a macro
…		…
295	*) >>), and you can stop watching for events at any time by calling the	787	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	788	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
297		789
298	As long as your watcher is active (has been started but not stopped) you	790	As long as your watcher is active (has been started but not stopped) you
299	must not touch the values stored in it. Most specifically you must never	791	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	792	reinitialise it or call its C<set> macro.
301
302	You cna check whether an event is active by calling the C<ev_is_active
303	(watcher *)> macro. To see whether an event is outstanding (but the
304	callback for it has not been called yet) you cna use the C<ev_is_pending
305	(watcher *)> macro.
306		793
307	Each and every callback receives the event loop pointer as first, the	794	Each and every callback receives the event loop pointer as first, the
308	registered watcher structure as second, and a bitset of received events as	795	registered watcher structure as second, and a bitset of received events as
309	third argument.	796	third argument.
310		797
311	The rceeived events usually include a single bit per event type received	798	The received events usually include a single bit per event type received
312	(you can receive multiple events at the same time). The possible bit masks	799	(you can receive multiple events at the same time). The possible bit masks
313	are:	800	are:
314		801
315	=over 4	802	=over 4
316		803
317	=item EV_READ	804	=item C<EV_READ>
318		805
319	=item EV_WRITE	806	=item C<EV_WRITE>
320		807
321	The file descriptor in the ev_io watcher has become readable and/or	808	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	809	writable.
323		810
324	=item EV_TIMEOUT	811	=item C<EV_TIMEOUT>
325		812
326	The ev_timer watcher has timed out.	813	The C<ev_timer> watcher has timed out.
327		814
328	=item EV_PERIODIC	815	=item C<EV_PERIODIC>
329		816
330	The ev_periodic watcher has timed out.	817	The C<ev_periodic> watcher has timed out.
331		818
332	=item EV_SIGNAL	819	=item C<EV_SIGNAL>
333		820
334	The signal specified in the ev_signal watcher has been received by a thread.	821	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		822
336	=item EV_CHILD	823	=item C<EV_CHILD>
337		824
338	The pid specified in the ev_child watcher has received a status change.	825	The pid specified in the C<ev_child> watcher has received a status change.
339		826
		827	=item C<EV_STAT>
		828
		829	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		830
340	=item EV_IDLE	831	=item C<EV_IDLE>
341		832
342	The ev_idle watcher has determined that you have nothing better to do.	833	The C<ev_idle> watcher has determined that you have nothing better to do.
343		834
344	=item EV_PREPARE	835	=item C<EV_PREPARE>
345		836
346	=item EV_CHECK	837	=item C<EV_CHECK>
347		838
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	839	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
349	to gather new events, and all ev_check watchers are invoked just after	840	to gather new events, and all C<ev_check> watchers are invoked just after
350	C<ev_loop> has gathered them, but before it invokes any callbacks for any	841	C<ev_loop> has gathered them, but before it invokes any callbacks for any
351	received events. Callbacks of both watcher types can start and stop as	842	received events. Callbacks of both watcher types can start and stop as
352	many watchers as they want, and all of them will be taken into account	843	many watchers as they want, and all of them will be taken into account
353	(for example, a ev_prepare watcher might start an idle watcher to keep	844	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
354	C<ev_loop> from blocking).	845	C<ev_loop> from blocking).
355		846
		847	=item C<EV_EMBED>
		848
		849	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		850
		851	=item C<EV_FORK>
		852
		853	The event loop has been resumed in the child process after fork (see
		854	C<ev_fork>).
		855
		856	=item C<EV_ASYNC>
		857
		858	The given async watcher has been asynchronously notified (see C<ev_async>).
		859
356	=item EV_ERROR	860	=item C<EV_ERROR>
357		861
358	An unspecified error has occured, the watcher has been stopped. This might	862	An unspecified error has occurred, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	863	happen because the watcher could not be properly started because libev
360	ran out of memory, a file descriptor was found to be closed or any other	864	ran out of memory, a file descriptor was found to be closed or any other
361	problem. You best act on it by reporting the problem and somehow coping	865	problem. You best act on it by reporting the problem and somehow coping
362	with the watcher being stopped.	866	with the watcher being stopped.
363		867
364	Libev will usually signal a few "dummy" events together with an error,	868	Libev will usually signal a few "dummy" events together with an error,
365	for example it might indicate that a fd is readable or writable, and if	869	for example it might indicate that a fd is readable or writable, and if
366	your callbacks is well-written it can just attempt the operation and cope	870	your callbacks is well-written it can just attempt the operation and cope
367	with the error from read() or write(). This will not work in multithreaded	871	with the error from read() or write(). This will not work in multi-threaded
368	programs, though, so beware.	872	programs, though, so beware.
369		873
370	=back	874	=back
371		875
		876	=head2 GENERIC WATCHER FUNCTIONS
		877
		878	In the following description, C<TYPE> stands for the watcher type,
		879	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		880
		881	=over 4
		882
		883	=item C<ev_init> (ev_TYPE *watcher, callback)
		884
		885	This macro initialises the generic portion of a watcher. The contents
		886	of the watcher object can be arbitrary (so C<malloc> will do). Only
		887	the generic parts of the watcher are initialised, you I<need> to call
		888	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		889	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		890	which rolls both calls into one.
		891
		892	You can reinitialise a watcher at any time as long as it has been stopped
		893	(or never started) and there are no pending events outstanding.
		894
		895	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		896	int revents)>.
		897
		898	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		899
		900	This macro initialises the type-specific parts of a watcher. You need to
		901	call C<ev_init> at least once before you call this macro, but you can
		902	call C<ev_TYPE_set> any number of times. You must not, however, call this
		903	macro on a watcher that is active (it can be pending, however, which is a
		904	difference to the C<ev_init> macro).
		905
		906	Although some watcher types do not have type-specific arguments
		907	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		908
		909	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		910
		911	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		912	calls into a single call. This is the most convenient method to initialise
		913	a watcher. The same limitations apply, of course.
		914
		915	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		916
		917	Starts (activates) the given watcher. Only active watchers will receive
		918	events. If the watcher is already active nothing will happen.
		919
		920	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		921
		922	Stops the given watcher again (if active) and clears the pending
		923	status. It is possible that stopped watchers are pending (for example,
		924	non-repeating timers are being stopped when they become pending), but
		925	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		926	you want to free or reuse the memory used by the watcher it is therefore a
		927	good idea to always call its C<ev_TYPE_stop> function.
		928
		929	=item bool ev_is_active (ev_TYPE *watcher)
		930
		931	Returns a true value iff the watcher is active (i.e. it has been started
		932	and not yet been stopped). As long as a watcher is active you must not modify
		933	it.
		934
		935	=item bool ev_is_pending (ev_TYPE *watcher)
		936
		937	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		938	events but its callback has not yet been invoked). As long as a watcher
		939	is pending (but not active) you must not call an init function on it (but
		940	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		941	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		942	it).
		943
		944	=item callback ev_cb (ev_TYPE *watcher)
		945
		946	Returns the callback currently set on the watcher.
		947
		948	=item ev_cb_set (ev_TYPE *watcher, callback)
		949
		950	Change the callback. You can change the callback at virtually any time
		951	(modulo threads).
		952
		953	=item ev_set_priority (ev_TYPE *watcher, priority)
		954
		955	=item int ev_priority (ev_TYPE *watcher)
		956
		957	Set and query the priority of the watcher. The priority is a small
		958	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		959	(default: C<-2>). Pending watchers with higher priority will be invoked
		960	before watchers with lower priority, but priority will not keep watchers
		961	from being executed (except for C<ev_idle> watchers).
		962
		963	This means that priorities are I<only> used for ordering callback
		964	invocation after new events have been received. This is useful, for
		965	example, to reduce latency after idling, or more often, to bind two
		966	watchers on the same event and make sure one is called first.
		967
		968	If you need to suppress invocation when higher priority events are pending
		969	you need to look at C<ev_idle> watchers, which provide this functionality.
		970
		971	You I<must not> change the priority of a watcher as long as it is active or
		972	pending.
		973
		974	The default priority used by watchers when no priority has been set is
		975	always C<0>, which is supposed to not be too high and not be too low :).
		976
		977	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		978	fine, as long as you do not mind that the priority value you query might
		979	or might not have been adjusted to be within valid range.
		980
		981	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		982
		983	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		984	C<loop> nor C<revents> need to be valid as long as the watcher callback
		985	can deal with that fact.
		986
		987	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		988
		989	If the watcher is pending, this function returns clears its pending status
		990	and returns its C<revents> bitset (as if its callback was invoked). If the
		991	watcher isn't pending it does nothing and returns C<0>.
		992
		993	=back
		994
		995
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	996	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
373		997
374	Each watcher has, by default, a member C<void *data> that you can change	998	Each watcher has, by default, a member C<void *data> that you can change
375	and read at any time, libev will completely ignore it. This cna be used	999	and read at any time, libev will completely ignore it. This can be used
376	to associate arbitrary data with your watcher. If you need more data and	1000	to associate arbitrary data with your watcher. If you need more data and
377	don't want to allocate memory and store a pointer to it in that data	1001	don't want to allocate memory and store a pointer to it in that data
378	member, you can also "subclass" the watcher type and provide your own	1002	member, you can also "subclass" the watcher type and provide your own
379	data:	1003	data:
380		1004
381	struct my_io	1005	struct my_io
382	{	1006	{
383	struct ev_io io;	1007	struct ev_io io;
384	int otherfd;	1008	int otherfd;
385	void *somedata;	1009	void *somedata;
386	struct whatever *mostinteresting;	1010	struct whatever *mostinteresting;
387	}	1011	};
		1012
		1013	...
		1014	struct my_io w;
		1015	ev_io_init (&w.io, my_cb, fd, EV_READ);
388		1016
389	And since your callback will be called with a pointer to the watcher, you	1017	And since your callback will be called with a pointer to the watcher, you
390	can cast it back to your own type:	1018	can cast it back to your own type:
391		1019
392	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1020	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
393	{	1021	{
394	struct my_io *w = (struct my_io *)w_;	1022	struct my_io *w = (struct my_io *)w_;
395	...	1023	...
396	}	1024	}
397		1025
398	More interesting and less C-conformant ways of catsing your callback type	1026	More interesting and less C-conformant ways of casting your callback type
399	have been omitted....	1027	instead have been omitted.
		1028
		1029	Another common scenario is to use some data structure with multiple
		1030	embedded watchers:
		1031
		1032	struct my_biggy
		1033	{
		1034	int some_data;
		1035	ev_timer t1;
		1036	ev_timer t2;
		1037	}
		1038
		1039	In this case getting the pointer to C<my_biggy> is a bit more
		1040	complicated: Either you store the address of your C<my_biggy> struct
		1041	in the C<data> member of the watcher, or you need to use some pointer
		1042	arithmetic using C<offsetof> inside your watchers:
		1043
		1044	#include <stddef.h>
		1045
		1046	static void
		1047	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1048	{
		1049	struct my_biggy big = (struct my_biggy *
		1050	(((char *)w) - offsetof (struct my_biggy, t1));
		1051	}
		1052
		1053	static void
		1054	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1055	{
		1056	struct my_biggy big = (struct my_biggy *
		1057	(((char *)w) - offsetof (struct my_biggy, t2));
		1058	}
400		1059
401		1060
402	=head1 WATCHER TYPES	1061	=head1 WATCHER TYPES
403		1062
404	This section describes each watcher in detail, but will not repeat	1063	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	1064	information given in the last section. Any initialisation/set macros,
		1065	functions and members specific to the watcher type are explained.
406		1066
		1067	Members are additionally marked with either I<[read-only]>, meaning that,
		1068	while the watcher is active, you can look at the member and expect some
		1069	sensible content, but you must not modify it (you can modify it while the
		1070	watcher is stopped to your hearts content), or I<[read-write]>, which
		1071	means you can expect it to have some sensible content while the watcher
		1072	is active, but you can also modify it. Modifying it may not do something
		1073	sensible or take immediate effect (or do anything at all), but libev will
		1074	not crash or malfunction in any way.
		1075
		1076
407	=head2 struct ev_io - is my file descriptor readable or writable	1077	=head2 C<ev_io> - is this file descriptor readable or writable?
408		1078
409	I/O watchers check whether a file descriptor is readable or writable	1079	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	1080	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	1081	would not block the process and writing would at least be able to write
412	condition persists. Remember you cna stop the watcher if you don't want to	1082	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	1083	receiving events as long as the condition persists. Remember you can stop
		1084	the watcher if you don't want to act on the event and neither want to
		1085	receive future events.
414		1086
415	In general you can register as many read and/or write event watchers oer	1087	In general you can register as many read and/or write event watchers per
416	fd as you want (as long as you don't confuse yourself). Setting all file	1088	fd as you want (as long as you don't confuse yourself). Setting all file
417	descriptors to non-blocking mode is also usually a good idea (but not	1089	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	1090	required if you know what you are doing).
419		1091
420	You have to be careful with dup'ed file descriptors, though. Some backends
421	(the linux epoll backend is a notable example) cannot handle dup'ed file
422	descriptors correctly if you register interest in two or more fds pointing
423	to the same file/socket etc. description.
424
425	If you must do this, then force the use of a known-to-be-good backend	1092	If you must do this, then force the use of a known-to-be-good backend
426	(at the time of this writing, this includes only EVMETHOD_SELECT and	1093	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
427	EVMETHOD_POLL).	1094	C<EVBACKEND_POLL>).
		1095
		1096	Another thing you have to watch out for is that it is quite easy to
		1097	receive "spurious" readiness notifications, that is your callback might
		1098	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1099	because there is no data. Not only are some backends known to create a
		1100	lot of those (for example Solaris ports), it is very easy to get into
		1101	this situation even with a relatively standard program structure. Thus
		1102	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1103	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1104
		1105	If you cannot run the fd in non-blocking mode (for example you should not
		1106	play around with an Xlib connection), then you have to separately re-test
		1107	whether a file descriptor is really ready with a known-to-be good interface
		1108	such as poll (fortunately in our Xlib example, Xlib already does this on
		1109	its own, so its quite safe to use).
		1110
		1111	=head3 The special problem of disappearing file descriptors
		1112
		1113	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1114	descriptor (either by calling C<close> explicitly or by any other means,
		1115	such as C<dup>). The reason is that you register interest in some file
		1116	descriptor, but when it goes away, the operating system will silently drop
		1117	this interest. If another file descriptor with the same number then is
		1118	registered with libev, there is no efficient way to see that this is, in
		1119	fact, a different file descriptor.
		1120
		1121	To avoid having to explicitly tell libev about such cases, libev follows
		1122	the following policy: Each time C<ev_io_set> is being called, libev
		1123	will assume that this is potentially a new file descriptor, otherwise
		1124	it is assumed that the file descriptor stays the same. That means that
		1125	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1126	descriptor even if the file descriptor number itself did not change.
		1127
		1128	This is how one would do it normally anyway, the important point is that
		1129	the libev application should not optimise around libev but should leave
		1130	optimisations to libev.
		1131
		1132	=head3 The special problem of dup'ed file descriptors
		1133
		1134	Some backends (e.g. epoll), cannot register events for file descriptors,
		1135	but only events for the underlying file descriptions. That means when you
		1136	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1137	events for them, only one file descriptor might actually receive events.
		1138
		1139	There is no workaround possible except not registering events
		1140	for potentially C<dup ()>'ed file descriptors, or to resort to
		1141	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1142
		1143	=head3 The special problem of fork
		1144
		1145	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1146	useless behaviour. Libev fully supports fork, but needs to be told about
		1147	it in the child.
		1148
		1149	To support fork in your programs, you either have to call
		1150	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1151	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1152	C<EVBACKEND_POLL>.
		1153
		1154	=head3 The special problem of SIGPIPE
		1155
		1156	While not really specific to libev, it is easy to forget about SIGPIPE:
		1157	when writing to a pipe whose other end has been closed, your program gets
		1158	send a SIGPIPE, which, by default, aborts your program. For most programs
		1159	this is sensible behaviour, for daemons, this is usually undesirable.
		1160
		1161	So when you encounter spurious, unexplained daemon exits, make sure you
		1162	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1163	somewhere, as that would have given you a big clue).
		1164
		1165
		1166	=head3 Watcher-Specific Functions
428		1167
429	=over 4	1168	=over 4
430		1169
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1170	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1171
433	=item ev_io_set (ev_io *, int fd, int events)	1172	=item ev_io_set (ev_io *, int fd, int events)
434		1173
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1174	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
436	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1175	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1176	C<EV_READ | EV_WRITE> to receive the given events.
		1177
		1178	=item int fd [read-only]
		1179
		1180	The file descriptor being watched.
		1181
		1182	=item int events [read-only]
		1183
		1184	The events being watched.
438		1185
439	=back	1186	=back
440		1187
		1188	=head3 Examples
		1189
		1190	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1191	readable, but only once. Since it is likely line-buffered, you could
		1192	attempt to read a whole line in the callback.
		1193
		1194	static void
		1195	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1196	{
		1197	ev_io_stop (loop, w);
		1198	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1199	}
		1200
		1201	...
		1202	struct ev_loop *loop = ev_default_init (0);
		1203	struct ev_io stdin_readable;
		1204	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1205	ev_io_start (loop, &stdin_readable);
		1206	ev_loop (loop, 0);
		1207
		1208
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1209	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1210
443	Timer watchers are simple relative timers that generate an event after a	1211	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1212	given time, and optionally repeating in regular intervals after that.
445		1213
446	The timers are based on real time, that is, if you register an event that	1214	The timers are based on real time, that is, if you register an event that
447	times out after an hour and youreset your system clock to last years	1215	times out after an hour and you reset your system clock to January last
448	time, it will still time out after (roughly) and hour. "Roughly" because	1216	year, it will still time out after (roughly) and hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1217	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1218	monotonic clock option helps a lot here).
451		1219
		1220	The callback is guaranteed to be invoked only after its timeout has passed,
		1221	but if multiple timers become ready during the same loop iteration then
		1222	order of execution is undefined.
		1223
		1224	=head3 The special problem of time updates
		1225
		1226	Establishing the current time is a costly operation (it usually takes at
		1227	least two system calls): EV therefore updates its idea of the current
		1228	time only before and after C<ev_loop> polls for new events, which causes
		1229	a growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1230	lots of events.
		1231
		1232	The relative timeouts are calculated relative to the C<ev_now ()>
		1233	time. This is usually the right thing as this timestamp refers to the time
		1234	of the event triggering whatever timeout you are modifying/starting. If
		1235	you suspect event processing to be delayed and you I<need> to base the
		1236	timeout on the current time, use something like this to adjust for this:
		1237
		1238	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1239
		1240	If the event loop is suspended for a long time, you can also force an
		1241	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1242	()>.
		1243
		1244	=head3 Watcher-Specific Functions and Data Members
		1245
452	=over 4	1246	=over 4
453		1247
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1248	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		1249
456	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1250	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
457		1251
458	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1252	Configure the timer to trigger after C<after> seconds. If C<repeat>
459	C<0.>, then it will automatically be stopped. If it is positive, then the	1253	is C<0.>, then it will automatically be stopped once the timeout is
460	timer will automatically be configured to trigger again C<repeat> seconds	1254	reached. If it is positive, then the timer will automatically be
461	later, again, and again, until stopped manually.	1255	configured to trigger again C<repeat> seconds later, again, and again,
		1256	until stopped manually.
462		1257
463	The timer itself will do a best-effort at avoiding drift, that is, if you	1258	The timer itself will do a best-effort at avoiding drift, that is, if
464	configure a timer to trigger every 10 seconds, then it will trigger at	1259	you configure a timer to trigger every 10 seconds, then it will normally
465	exactly 10 second intervals. If, however, your program cannot keep up with	1260	trigger at exactly 10 second intervals. If, however, your program cannot
466	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1261	keep up with the timer (because it takes longer than those 10 seconds to
467	timer will not fire more than once per event loop iteration.	1262	do stuff) the timer will not fire more than once per event loop iteration.
468		1263
469	=item ev_timer_again (loop)	1264	=item ev_timer_again (loop, ev_timer *)
470		1265
471	This will act as if the timer timed out and restart it again if it is	1266	This will act as if the timer timed out and restart it again if it is
472	repeating. The exact semantics are:	1267	repeating. The exact semantics are:
473		1268
		1269	If the timer is pending, its pending status is cleared.
		1270
474	If the timer is started but nonrepeating, stop it.	1271	If the timer is started but non-repeating, stop it (as if it timed out).
475		1272
476	If the timer is repeating, either start it if necessary (with the repeat	1273	If the timer is repeating, either start it if necessary (with the
477	value), or reset the running timer to the repeat value.	1274	C<repeat> value), or reset the running timer to the C<repeat> value.
478		1275
479	This sounds a bit complicated, but here is a useful and typical	1276	This sounds a bit complicated, but here is a useful and typical
480	example: Imagine you have a tcp connection and you want a so-called idle	1277	example: Imagine you have a TCP connection and you want a so-called idle
481	timeout, that is, you want to be called when there have been, say, 60	1278	timeout, that is, you want to be called when there have been, say, 60
482	seconds of inactivity on the socket. The easiest way to do this is to	1279	seconds of inactivity on the socket. The easiest way to do this is to
483	configure an ev_timer with after=repeat=60 and calling ev_timer_again each	1280	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
484	time you successfully read or write some data. If you go into an idle	1281	C<ev_timer_again> each time you successfully read or write some data. If
485	state where you do not expect data to travel on the socket, you can stop	1282	you go into an idle state where you do not expect data to travel on the
486	the timer, and again will automatically restart it if need be.	1283	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1284	automatically restart it if need be.
		1285
		1286	That means you can ignore the C<after> value and C<ev_timer_start>
		1287	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1288
		1289	ev_timer_init (timer, callback, 0., 5.);
		1290	ev_timer_again (loop, timer);
		1291	...
		1292	timer->again = 17.;
		1293	ev_timer_again (loop, timer);
		1294	...
		1295	timer->again = 10.;
		1296	ev_timer_again (loop, timer);
		1297
		1298	This is more slightly efficient then stopping/starting the timer each time
		1299	you want to modify its timeout value.
		1300
		1301	=item ev_tstamp repeat [read-write]
		1302
		1303	The current C<repeat> value. Will be used each time the watcher times out
		1304	or C<ev_timer_again> is called and determines the next timeout (if any),
		1305	which is also when any modifications are taken into account.
487		1306
488	=back	1307	=back
489		1308
		1309	=head3 Examples
		1310
		1311	Example: Create a timer that fires after 60 seconds.
		1312
		1313	static void
		1314	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1315	{
		1316	.. one minute over, w is actually stopped right here
		1317	}
		1318
		1319	struct ev_timer mytimer;
		1320	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1321	ev_timer_start (loop, &mytimer);
		1322
		1323	Example: Create a timeout timer that times out after 10 seconds of
		1324	inactivity.
		1325
		1326	static void
		1327	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1328	{
		1329	.. ten seconds without any activity
		1330	}
		1331
		1332	struct ev_timer mytimer;
		1333	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1334	ev_timer_again (&mytimer); /* start timer */
		1335	ev_loop (loop, 0);
		1336
		1337	// and in some piece of code that gets executed on any "activity":
		1338	// reset the timeout to start ticking again at 10 seconds
		1339	ev_timer_again (&mytimer);
		1340
		1341
490	=head2 ev_periodic - to cron or not to cron it	1342	=head2 C<ev_periodic> - to cron or not to cron?
491		1343
492	Periodic watchers are also timers of a kind, but they are very versatile	1344	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	1345	(and unfortunately a bit complex).
494		1346
495	Unlike ev_timer's, they are not based on real time (or relative time)	1347	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
496	but on wallclock time (absolute time). You can tell a periodic watcher	1348	but on wall clock time (absolute time). You can tell a periodic watcher
497	to trigger "at" some specific point in time. For example, if you tell a	1349	to trigger after some specific point in time. For example, if you tell a
498	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1350	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
499	+ 10.>) and then reset your system clock to the last year, then it will	1351	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1352	clock to January of the previous year, then it will take more than year
500	take a year to trigger the event (unlike an ev_timer, which would trigger	1353	to trigger the event (unlike an C<ev_timer>, which would still trigger
501	roughly 10 seconds later and of course not if you reset your system time	1354	roughly 10 seconds later as it uses a relative timeout).
502	again).
503		1355
504	They can also be used to implement vastly more complex timers, such as	1356	C<ev_periodic>s can also be used to implement vastly more complex timers,
505	triggering an event on eahc midnight, local time.	1357	such as triggering an event on each "midnight, local time", or other
		1358	complicated, rules.
		1359
		1360	As with timers, the callback is guaranteed to be invoked only when the
		1361	time (C<at>) has passed, but if multiple periodic timers become ready
		1362	during the same loop iteration then order of execution is undefined.
		1363
		1364	=head3 Watcher-Specific Functions and Data Members
506		1365
507	=over 4	1366	=over 4
508		1367
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1368	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
510		1369
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1370	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
512		1371
513	Lots of arguments, lets sort it out... There are basically three modes of	1372	Lots of arguments, lets sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	1373	operation, and we will explain them from simplest to complex:
515		1374
516
517	=over 4	1375	=over 4
518		1376
519	=item * absolute timer (interval = reschedule_cb = 0)	1377	=item * absolute timer (at = time, interval = reschedule_cb = 0)
520		1378
521	In this configuration the watcher triggers an event at the wallclock time	1379	In this configuration the watcher triggers an event after the wall clock
522	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1380	time C<at> has passed and doesn't repeat. It will not adjust when a time
523	that is, if it is to be run at January 1st 2011 then it will run when the	1381	jump occurs, that is, if it is to be run at January 1st 2011 then it will
524	system time reaches or surpasses this time.	1382	run when the system time reaches or surpasses this time.
525		1383
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1384	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
527		1385
528	In this mode the watcher will always be scheduled to time out at the next	1386	In this mode the watcher will always be scheduled to time out at the next
529	C<at + N * interval> time (for some integer N) and then repeat, regardless	1387	C<at + N * interval> time (for some integer N, which can also be negative)
530	of any time jumps.	1388	and then repeat, regardless of any time jumps.
531		1389
532	This can be used to create timers that do not drift with respect to system	1390	This can be used to create timers that do not drift with respect to system
533	time:	1391	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1392	the hour:
534		1393
535	ev_periodic_set (&periodic, 0., 3600., 0);	1394	ev_periodic_set (&periodic, 0., 3600., 0);
536		1395
537	This doesn't mean there will always be 3600 seconds in between triggers,	1396	This doesn't mean there will always be 3600 seconds in between triggers,
538	but only that the the callback will be called when the system time shows a	1397	but only that the callback will be called when the system time shows a
539	full hour (UTC), or more correct, when the system time is evenly divisible	1398	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	1399	by 3600.
541		1400
542	Another way to think about it (for the mathematically inclined) is that	1401	Another way to think about it (for the mathematically inclined) is that
543	ev_periodic will try to run the callback in this mode at the next possible	1402	C<ev_periodic> will try to run the callback in this mode at the next possible
544	time where C<time = at (mod interval)>, regardless of any time jumps.	1403	time where C<time = at (mod interval)>, regardless of any time jumps.
545		1404
		1405	For numerical stability it is preferable that the C<at> value is near
		1406	C<ev_now ()> (the current time), but there is no range requirement for
		1407	this value, and in fact is often specified as zero.
		1408
		1409	Note also that there is an upper limit to how often a timer can fire (CPU
		1410	speed for example), so if C<interval> is very small then timing stability
		1411	will of course deteriorate. Libev itself tries to be exact to be about one
		1412	millisecond (if the OS supports it and the machine is fast enough).
		1413
546	=item * manual reschedule mode (reschedule_cb = callback)	1414	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
547		1415
548	In this mode the values for C<interval> and C<at> are both being	1416	In this mode the values for C<interval> and C<at> are both being
549	ignored. Instead, each time the periodic watcher gets scheduled, the	1417	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	1418	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	1419	current time as second argument.
552		1420
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1421	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
554	periodic watcher, ever, or make any event loop modificstions>. If you need	1422	ever, or make ANY event loop modifications whatsoever>.
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
556		1423
		1424	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1425	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1426	only event loop modification you are allowed to do).
		1427
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1428	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
558	ev_tstamp now)>, e.g.:	1429	*w, ev_tstamp now)>, e.g.:
559		1430
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1431	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
561	{	1432	{
562	return now + 60.;	1433	return now + 60.;
563	}	1434	}
…		…
565	It must return the next time to trigger, based on the passed time value	1436	It must return the next time to trigger, based on the passed time value
566	(that is, the lowest time value larger than to the second argument). It	1437	(that is, the lowest time value larger than to the second argument). It
567	will usually be called just before the callback will be triggered, but	1438	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	1439	might be called at other times, too.
569		1440
		1441	NOTE: I<< This callback must always return a time that is higher than or
		1442	equal to the passed C<now> value >>.
		1443
570	This can be used to create very complex timers, such as a timer that	1444	This can be used to create very complex timers, such as a timer that
571	triggers on each midnight, local time. To do this, you would calculate the	1445	triggers on "next midnight, local time". To do this, you would calculate the
572	next midnight after C<now> and return the timestamp value for this. How you do this	1446	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	1447	you do this is, again, up to you (but it is not trivial, which is the main
		1448	reason I omitted it as an example).
574		1449
575	=back	1450	=back
576		1451
577	=item ev_periodic_again (loop, ev_periodic *)	1452	=item ev_periodic_again (loop, ev_periodic *)
578		1453
579	Simply stops and restarts the periodic watcher again. This is only useful	1454	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	1455	when you changed some parameters or the reschedule callback would return
581	a different time than the last time it was called (e.g. in a crond like	1456	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	1457	program when the crontabs have changed).
583		1458
		1459	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1460
		1461	When active, returns the absolute time that the watcher is supposed to
		1462	trigger next.
		1463
		1464	=item ev_tstamp offset [read-write]
		1465
		1466	When repeating, this contains the offset value, otherwise this is the
		1467	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1468
		1469	Can be modified any time, but changes only take effect when the periodic
		1470	timer fires or C<ev_periodic_again> is being called.
		1471
		1472	=item ev_tstamp interval [read-write]
		1473
		1474	The current interval value. Can be modified any time, but changes only
		1475	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1476	called.
		1477
		1478	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1479
		1480	The current reschedule callback, or C<0>, if this functionality is
		1481	switched off. Can be changed any time, but changes only take effect when
		1482	the periodic timer fires or C<ev_periodic_again> is being called.
		1483
584	=back	1484	=back
585		1485
		1486	=head3 Examples
		1487
		1488	Example: Call a callback every hour, or, more precisely, whenever the
		1489	system clock is divisible by 3600. The callback invocation times have
		1490	potentially a lot of jitter, but good long-term stability.
		1491
		1492	static void
		1493	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1494	{
		1495	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1496	}
		1497
		1498	struct ev_periodic hourly_tick;
		1499	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1500	ev_periodic_start (loop, &hourly_tick);
		1501
		1502	Example: The same as above, but use a reschedule callback to do it:
		1503
		1504	#include <math.h>
		1505
		1506	static ev_tstamp
		1507	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1508	{
		1509	return fmod (now, 3600.) + 3600.;
		1510	}
		1511
		1512	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1513
		1514	Example: Call a callback every hour, starting now:
		1515
		1516	struct ev_periodic hourly_tick;
		1517	ev_periodic_init (&hourly_tick, clock_cb,
		1518	fmod (ev_now (loop), 3600.), 3600., 0);
		1519	ev_periodic_start (loop, &hourly_tick);
		1520
		1521
586	=head2 ev_signal - signal me when a signal gets signalled	1522	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		1523
588	Signal watchers will trigger an event when the process receives a specific	1524	Signal watchers will trigger an event when the process receives a specific
589	signal one or more times. Even though signals are very asynchronous, libev	1525	signal one or more times. Even though signals are very asynchronous, libev
590	will try its best to deliver signals synchronously, i.e. as part of the	1526	will try it's best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	1527	normal event processing, like any other event.
592		1528
593	You cna configure as many watchers as you like per signal. Only when the	1529	You can configure as many watchers as you like per signal. Only when the
594	first watcher gets started will libev actually register a signal watcher	1530	first watcher gets started will libev actually register a signal watcher
595	with the kernel (thus it coexists with your own signal handlers as long	1531	with the kernel (thus it coexists with your own signal handlers as long
596	as you don't register any with libev). Similarly, when the last signal	1532	as you don't register any with libev). Similarly, when the last signal
597	watcher for a signal is stopped libev will reset the signal handler to	1533	watcher for a signal is stopped libev will reset the signal handler to
598	SIG_DFL (regardless of what it was set to before).	1534	SIG_DFL (regardless of what it was set to before).
599		1535
		1536	If possible and supported, libev will install its handlers with
		1537	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1538	interrupted. If you have a problem with system calls getting interrupted by
		1539	signals you can block all signals in an C<ev_check> watcher and unblock
		1540	them in an C<ev_prepare> watcher.
		1541
		1542	=head3 Watcher-Specific Functions and Data Members
		1543
600	=over 4	1544	=over 4
601		1545
602	=item ev_signal_init (ev_signal *, callback, int signum)	1546	=item ev_signal_init (ev_signal *, callback, int signum)
603		1547
604	=item ev_signal_set (ev_signal *, int signum)	1548	=item ev_signal_set (ev_signal *, int signum)
605		1549
606	Configures the watcher to trigger on the given signal number (usually one	1550	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	1551	of the C<SIGxxx> constants).
608		1552
		1553	=item int signum [read-only]
		1554
		1555	The signal the watcher watches out for.
		1556
609	=back	1557	=back
610		1558
		1559	=head3 Examples
		1560
		1561	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1562
		1563	static void
		1564	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1565	{
		1566	ev_unloop (loop, EVUNLOOP_ALL);
		1567	}
		1568
		1569	struct ev_signal signal_watcher;
		1570	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1571	ev_signal_start (loop, &sigint_cb);
		1572
		1573
611	=head2 ev_child - wait for pid status changes	1574	=head2 C<ev_child> - watch out for process status changes
612		1575
613	Child watchers trigger when your process receives a SIGCHLD in response to	1576	Child watchers trigger when your process receives a SIGCHLD in response to
614	some child status changes (most typically when a child of yours dies).	1577	some child status changes (most typically when a child of yours dies). It
		1578	is permissible to install a child watcher I<after> the child has been
		1579	forked (which implies it might have already exited), as long as the event
		1580	loop isn't entered (or is continued from a watcher).
		1581
		1582	Only the default event loop is capable of handling signals, and therefore
		1583	you can only register child watchers in the default event loop.
		1584
		1585	=head3 Process Interaction
		1586
		1587	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1588	initialised. This is necessary to guarantee proper behaviour even if
		1589	the first child watcher is started after the child exits. The occurrence
		1590	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1591	synchronously as part of the event loop processing. Libev always reaps all
		1592	children, even ones not watched.
		1593
		1594	=head3 Overriding the Built-In Processing
		1595
		1596	Libev offers no special support for overriding the built-in child
		1597	processing, but if your application collides with libev's default child
		1598	handler, you can override it easily by installing your own handler for
		1599	C<SIGCHLD> after initialising the default loop, and making sure the
		1600	default loop never gets destroyed. You are encouraged, however, to use an
		1601	event-based approach to child reaping and thus use libev's support for
		1602	that, so other libev users can use C<ev_child> watchers freely.
		1603
		1604	=head3 Stopping the Child Watcher
		1605
		1606	Currently, the child watcher never gets stopped, even when the
		1607	child terminates, so normally one needs to stop the watcher in the
		1608	callback. Future versions of libev might stop the watcher automatically
		1609	when a child exit is detected.
		1610
		1611	=head3 Watcher-Specific Functions and Data Members
615		1612
616	=over 4	1613	=over 4
617		1614
618	=item ev_child_init (ev_child *, callback, int pid)	1615	=item ev_child_init (ev_child *, callback, int pid, int trace)
619		1616
620	=item ev_child_set (ev_child *, int pid)	1617	=item ev_child_set (ev_child *, int pid, int trace)
621		1618
622	Configures the watcher to wait for status changes of process C<pid> (or	1619	Configures the watcher to wait for status changes of process C<pid> (or
623	I<any> process if C<pid> is specified as C<0>). The callback can look	1620	I<any> process if C<pid> is specified as C<0>). The callback can look
624	at the C<rstatus> member of the C<ev_child> watcher structure to see	1621	at the C<rstatus> member of the C<ev_child> watcher structure to see
625	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	1622	the status word (use the macros from C<sys/wait.h> and see your systems
626	contains the pid of the process causing the status change.	1623	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1624	process causing the status change. C<trace> must be either C<0> (only
		1625	activate the watcher when the process terminates) or C<1> (additionally
		1626	activate the watcher when the process is stopped or continued).
		1627
		1628	=item int pid [read-only]
		1629
		1630	The process id this watcher watches out for, or C<0>, meaning any process id.
		1631
		1632	=item int rpid [read-write]
		1633
		1634	The process id that detected a status change.
		1635
		1636	=item int rstatus [read-write]
		1637
		1638	The process exit/trace status caused by C<rpid> (see your systems
		1639	C<waitpid> and C<sys/wait.h> documentation for details).
627		1640
628	=back	1641	=back
629		1642
		1643	=head3 Examples
		1644
		1645	Example: C<fork()> a new process and install a child handler to wait for
		1646	its completion.
		1647
		1648	ev_child cw;
		1649
		1650	static void
		1651	child_cb (EV_P_ struct ev_child *w, int revents)
		1652	{
		1653	ev_child_stop (EV_A_ w);
		1654	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1655	}
		1656
		1657	pid_t pid = fork ();
		1658
		1659	if (pid < 0)
		1660	// error
		1661	else if (pid == 0)
		1662	{
		1663	// the forked child executes here
		1664	exit (1);
		1665	}
		1666	else
		1667	{
		1668	ev_child_init (&cw, child_cb, pid, 0);
		1669	ev_child_start (EV_DEFAULT_ &cw);
		1670	}
		1671
		1672
		1673	=head2 C<ev_stat> - did the file attributes just change?
		1674
		1675	This watches a file system path for attribute changes. That is, it calls
		1676	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1677	compared to the last time, invoking the callback if it did.
		1678
		1679	The path does not need to exist: changing from "path exists" to "path does
		1680	not exist" is a status change like any other. The condition "path does
		1681	not exist" is signified by the C<st_nlink> field being zero (which is
		1682	otherwise always forced to be at least one) and all the other fields of
		1683	the stat buffer having unspecified contents.
		1684
		1685	The path I<should> be absolute and I<must not> end in a slash. If it is
		1686	relative and your working directory changes, the behaviour is undefined.
		1687
		1688	Since there is no standard to do this, the portable implementation simply
		1689	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1690	can specify a recommended polling interval for this case. If you specify
		1691	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1692	unspecified default> value will be used (which you can expect to be around
		1693	five seconds, although this might change dynamically). Libev will also
		1694	impose a minimum interval which is currently around C<0.1>, but thats
		1695	usually overkill.
		1696
		1697	This watcher type is not meant for massive numbers of stat watchers,
		1698	as even with OS-supported change notifications, this can be
		1699	resource-intensive.
		1700
		1701	At the time of this writing, only the Linux inotify interface is
		1702	implemented (implementing kqueue support is left as an exercise for the
		1703	reader, note, however, that the author sees no way of implementing ev_stat
		1704	semantics with kqueue). Inotify will be used to give hints only and should
		1705	not change the semantics of C<ev_stat> watchers, which means that libev
		1706	sometimes needs to fall back to regular polling again even with inotify,
		1707	but changes are usually detected immediately, and if the file exists there
		1708	will be no polling.
		1709
		1710	=head3 ABI Issues (Largefile Support)
		1711
		1712	Libev by default (unless the user overrides this) uses the default
		1713	compilation environment, which means that on systems with large file
		1714	support disabled by default, you get the 32 bit version of the stat
		1715	structure. When using the library from programs that change the ABI to
		1716	use 64 bit file offsets the programs will fail. In that case you have to
		1717	compile libev with the same flags to get binary compatibility. This is
		1718	obviously the case with any flags that change the ABI, but the problem is
		1719	most noticeably disabled with ev_stat and large file support.
		1720
		1721	The solution for this is to lobby your distribution maker to make large
		1722	file interfaces available by default (as e.g. FreeBSD does) and not
		1723	optional. Libev cannot simply switch on large file support because it has
		1724	to exchange stat structures with application programs compiled using the
		1725	default compilation environment.
		1726
		1727	=head3 Inotify
		1728
		1729	When C<inotify (7)> support has been compiled into libev (generally only
		1730	available on Linux) and present at runtime, it will be used to speed up
		1731	change detection where possible. The inotify descriptor will be created lazily
		1732	when the first C<ev_stat> watcher is being started.
		1733
		1734	Inotify presence does not change the semantics of C<ev_stat> watchers
		1735	except that changes might be detected earlier, and in some cases, to avoid
		1736	making regular C<stat> calls. Even in the presence of inotify support
		1737	there are many cases where libev has to resort to regular C<stat> polling.
		1738
		1739	(There is no support for kqueue, as apparently it cannot be used to
		1740	implement this functionality, due to the requirement of having a file
		1741	descriptor open on the object at all times).
		1742
		1743	=head3 The special problem of stat time resolution
		1744
		1745	The C<stat ()> system call only supports full-second resolution portably, and
		1746	even on systems where the resolution is higher, many file systems still
		1747	only support whole seconds.
		1748
		1749	That means that, if the time is the only thing that changes, you can
		1750	easily miss updates: on the first update, C<ev_stat> detects a change and
		1751	calls your callback, which does something. When there is another update
		1752	within the same second, C<ev_stat> will be unable to detect it as the stat
		1753	data does not change.
		1754
		1755	The solution to this is to delay acting on a change for slightly more
		1756	than a second (or till slightly after the next full second boundary), using
		1757	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1758	ev_timer_again (loop, w)>).
		1759
		1760	The C<.02> offset is added to work around small timing inconsistencies
		1761	of some operating systems (where the second counter of the current time
		1762	might be be delayed. One such system is the Linux kernel, where a call to
		1763	C<gettimeofday> might return a timestamp with a full second later than
		1764	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1765	update file times then there will be a small window where the kernel uses
		1766	the previous second to update file times but libev might already execute
		1767	the timer callback).
		1768
		1769	=head3 Watcher-Specific Functions and Data Members
		1770
		1771	=over 4
		1772
		1773	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1774
		1775	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1776
		1777	Configures the watcher to wait for status changes of the given
		1778	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1779	be detected and should normally be specified as C<0> to let libev choose
		1780	a suitable value. The memory pointed to by C<path> must point to the same
		1781	path for as long as the watcher is active.
		1782
		1783	The callback will receive C<EV_STAT> when a change was detected, relative
		1784	to the attributes at the time the watcher was started (or the last change
		1785	was detected).
		1786
		1787	=item ev_stat_stat (loop, ev_stat *)
		1788
		1789	Updates the stat buffer immediately with new values. If you change the
		1790	watched path in your callback, you could call this function to avoid
		1791	detecting this change (while introducing a race condition if you are not
		1792	the only one changing the path). Can also be useful simply to find out the
		1793	new values.
		1794
		1795	=item ev_statdata attr [read-only]
		1796
		1797	The most-recently detected attributes of the file. Although the type is
		1798	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1799	suitable for your system, but you can only rely on the POSIX-standardised
		1800	members to be present. If the C<st_nlink> member is C<0>, then there was
		1801	some error while C<stat>ing the file.
		1802
		1803	=item ev_statdata prev [read-only]
		1804
		1805	The previous attributes of the file. The callback gets invoked whenever
		1806	C<prev> != C<attr>, or, more precisely, one or more of these members
		1807	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1808	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1809
		1810	=item ev_tstamp interval [read-only]
		1811
		1812	The specified interval.
		1813
		1814	=item const char *path [read-only]
		1815
		1816	The file system path that is being watched.
		1817
		1818	=back
		1819
		1820	=head3 Examples
		1821
		1822	Example: Watch C</etc/passwd> for attribute changes.
		1823
		1824	static void
		1825	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1826	{
		1827	/* /etc/passwd changed in some way */
		1828	if (w->attr.st_nlink)
		1829	{
		1830	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1831	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1832	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1833	}
		1834	else
		1835	/* you shalt not abuse printf for puts */
		1836	puts ("wow, /etc/passwd is not there, expect problems. "
		1837	"if this is windows, they already arrived\n");
		1838	}
		1839
		1840	...
		1841	ev_stat passwd;
		1842
		1843	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1844	ev_stat_start (loop, &passwd);
		1845
		1846	Example: Like above, but additionally use a one-second delay so we do not
		1847	miss updates (however, frequent updates will delay processing, too, so
		1848	one might do the work both on C<ev_stat> callback invocation I<and> on
		1849	C<ev_timer> callback invocation).
		1850
		1851	static ev_stat passwd;
		1852	static ev_timer timer;
		1853
		1854	static void
		1855	timer_cb (EV_P_ ev_timer *w, int revents)
		1856	{
		1857	ev_timer_stop (EV_A_ w);
		1858
		1859	/* now it's one second after the most recent passwd change */
		1860	}
		1861
		1862	static void
		1863	stat_cb (EV_P_ ev_stat *w, int revents)
		1864	{
		1865	/* reset the one-second timer */
		1866	ev_timer_again (EV_A_ &timer);
		1867	}
		1868
		1869	...
		1870	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1871	ev_stat_start (loop, &passwd);
		1872	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1873
		1874
630	=head2 ev_idle - when you've got nothing better to do	1875	=head2 C<ev_idle> - when you've got nothing better to do...
631		1876
632	Idle watchers trigger events when there are no other I/O or timer (or	1877	Idle watchers trigger events when no other events of the same or higher
633	periodic) events pending. That is, as long as your process is busy	1878	priority are pending (prepare, check and other idle watchers do not
634	handling sockets or timeouts it will not be called. But when your process	1879	count).
635	is idle all idle watchers are being called again and again - until	1880
		1881	That is, as long as your process is busy handling sockets or timeouts
		1882	(or even signals, imagine) of the same or higher priority it will not be
		1883	triggered. But when your process is idle (or only lower-priority watchers
		1884	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	1885	iteration - until stopped, that is, or your process receives more events
		1886	and becomes busy again with higher priority stuff.
637		1887
638	The most noteworthy effect is that as long as any idle watchers are	1888	The most noteworthy effect is that as long as any idle watchers are
639	active, the process will not block when waiting for new events.	1889	active, the process will not block when waiting for new events.
640		1890
641	Apart from keeping your process non-blocking (which is a useful	1891	Apart from keeping your process non-blocking (which is a useful
642	effect on its own sometimes), idle watchers are a good place to do	1892	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	1893	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	1894	event loop has handled all outstanding events.
645		1895
		1896	=head3 Watcher-Specific Functions and Data Members
		1897
646	=over 4	1898	=over 4
647		1899
648	=item ev_idle_init (ev_signal *, callback)	1900	=item ev_idle_init (ev_signal *, callback)
649		1901
650	Initialises and configures the idle watcher - it has no parameters of any	1902	Initialises and configures the idle watcher - it has no parameters of any
651	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1903	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	1904	believe me.
653		1905
654	=back	1906	=back
655		1907
656	=head2 prepare and check - your hooks into the event loop	1908	=head3 Examples
657		1909
		1910	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1911	callback, free it. Also, use no error checking, as usual.
		1912
		1913	static void
		1914	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1915	{
		1916	free (w);
		1917	// now do something you wanted to do when the program has
		1918	// no longer anything immediate to do.
		1919	}
		1920
		1921	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1922	ev_idle_init (idle_watcher, idle_cb);
		1923	ev_idle_start (loop, idle_cb);
		1924
		1925
		1926	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		1927
658	Prepare and check watchers usually (but not always) are used in	1928	Prepare and check watchers are usually (but not always) used in tandem:
659	tandom. Prepare watchers get invoked before the process blocks and check	1929	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	1930	afterwards.
661		1931
		1932	You I<must not> call C<ev_loop> or similar functions that enter
		1933	the current event loop from either C<ev_prepare> or C<ev_check>
		1934	watchers. Other loops than the current one are fine, however. The
		1935	rationale behind this is that you do not need to check for recursion in
		1936	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1937	C<ev_check> so if you have one watcher of each kind they will always be
		1938	called in pairs bracketing the blocking call.
		1939
662	Their main purpose is to integrate other event mechanisms into libev. This	1940	Their main purpose is to integrate other event mechanisms into libev and
663	could be used, for example, to track variable changes, implement your own	1941	their use is somewhat advanced. This could be used, for example, to track
664	watchers, integrate net-snmp or a coroutine library and lots more.	1942	variable changes, implement your own watchers, integrate net-snmp or a
		1943	coroutine library and lots more. They are also occasionally useful if
		1944	you cache some data and want to flush it before blocking (for example,
		1945	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1946	watcher).
665		1947
666	This is done by examining in each prepare call which file descriptors need	1948	This is done by examining in each prepare call which file descriptors need
667	to be watched by the other library, registering ev_io watchers for them	1949	to be watched by the other library, registering C<ev_io> watchers for
668	and starting an ev_timer watcher for any timeouts (many libraries provide	1950	them and starting an C<ev_timer> watcher for any timeouts (many libraries
669	just this functionality). Then, in the check watcher you check for any	1951	provide just this functionality). Then, in the check watcher you check for
670	events that occured (by making your callbacks set soem flags for example)	1952	any events that occurred (by checking the pending status of all watchers
671	and call back into the library.	1953	and stopping them) and call back into the library. The I/O and timer
		1954	callbacks will never actually be called (but must be valid nevertheless,
		1955	because you never know, you know?).
672		1956
673	As another example, the perl Coro module uses these hooks to integrate	1957	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	1958	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	1959	during each prepare and only letting the process block if no coroutines
676	are ready to run.	1960	are ready to run (it's actually more complicated: it only runs coroutines
		1961	with priority higher than or equal to the event loop and one coroutine
		1962	of lower priority, but only once, using idle watchers to keep the event
		1963	loop from blocking if lower-priority coroutines are active, thus mapping
		1964	low-priority coroutines to idle/background tasks).
		1965
		1966	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1967	priority, to ensure that they are being run before any other watchers
		1968	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1969	too) should not activate ("feed") events into libev. While libev fully
		1970	supports this, they might get executed before other C<ev_check> watchers
		1971	did their job. As C<ev_check> watchers are often used to embed other
		1972	(non-libev) event loops those other event loops might be in an unusable
		1973	state until their C<ev_check> watcher ran (always remind yourself to
		1974	coexist peacefully with others).
		1975
		1976	=head3 Watcher-Specific Functions and Data Members
677		1977
678	=over 4	1978	=over 4
679		1979
680	=item ev_prepare_init (ev_prepare *, callback)	1980	=item ev_prepare_init (ev_prepare *, callback)
681		1981
682	=item ev_check_init (ev_check *, callback)	1982	=item ev_check_init (ev_check *, callback)
683		1983
684	Initialises and configures the prepare or check watcher - they have no	1984	Initialises and configures the prepare or check watcher - they have no
685	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1985	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	1986	macros, but using them is utterly, utterly and completely pointless.
687		1987
688	=back	1988	=back
689		1989
		1990	=head3 Examples
		1991
		1992	There are a number of principal ways to embed other event loops or modules
		1993	into libev. Here are some ideas on how to include libadns into libev
		1994	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1995	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1996	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1997	Glib event loop).
		1998
		1999	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2000	and in a check watcher, destroy them and call into libadns. What follows
		2001	is pseudo-code only of course. This requires you to either use a low
		2002	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2003	the callbacks for the IO/timeout watchers might not have been called yet.
		2004
		2005	static ev_io iow [nfd];
		2006	static ev_timer tw;
		2007
		2008	static void
		2009	io_cb (ev_loop *loop, ev_io *w, int revents)
		2010	{
		2011	}
		2012
		2013	// create io watchers for each fd and a timer before blocking
		2014	static void
		2015	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		2016	{
		2017	int timeout = 3600000;
		2018	struct pollfd fds [nfd];
		2019	// actual code will need to loop here and realloc etc.
		2020	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2021
		2022	/* the callback is illegal, but won't be called as we stop during check */
		2023	ev_timer_init (&tw, 0, timeout * 1e-3);
		2024	ev_timer_start (loop, &tw);
		2025
		2026	// create one ev_io per pollfd
		2027	for (int i = 0; i < nfd; ++i)
		2028	{
		2029	ev_io_init (iow + i, io_cb, fds [i].fd,
		2030	((fds [i].events & POLLIN ? EV_READ : 0)
		2031	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2032
		2033	fds [i].revents = 0;
		2034	ev_io_start (loop, iow + i);
		2035	}
		2036	}
		2037
		2038	// stop all watchers after blocking
		2039	static void
		2040	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2041	{
		2042	ev_timer_stop (loop, &tw);
		2043
		2044	for (int i = 0; i < nfd; ++i)
		2045	{
		2046	// set the relevant poll flags
		2047	// could also call adns_processreadable etc. here
		2048	struct pollfd *fd = fds + i;
		2049	int revents = ev_clear_pending (iow + i);
		2050	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2051	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2052
		2053	// now stop the watcher
		2054	ev_io_stop (loop, iow + i);
		2055	}
		2056
		2057	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2058	}
		2059
		2060	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2061	in the prepare watcher and would dispose of the check watcher.
		2062
		2063	Method 3: If the module to be embedded supports explicit event
		2064	notification (libadns does), you can also make use of the actual watcher
		2065	callbacks, and only destroy/create the watchers in the prepare watcher.
		2066
		2067	static void
		2068	timer_cb (EV_P_ ev_timer *w, int revents)
		2069	{
		2070	adns_state ads = (adns_state)w->data;
		2071	update_now (EV_A);
		2072
		2073	adns_processtimeouts (ads, &tv_now);
		2074	}
		2075
		2076	static void
		2077	io_cb (EV_P_ ev_io *w, int revents)
		2078	{
		2079	adns_state ads = (adns_state)w->data;
		2080	update_now (EV_A);
		2081
		2082	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2083	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2084	}
		2085
		2086	// do not ever call adns_afterpoll
		2087
		2088	Method 4: Do not use a prepare or check watcher because the module you
		2089	want to embed is too inflexible to support it. Instead, you can override
		2090	their poll function. The drawback with this solution is that the main
		2091	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2092	this.
		2093
		2094	static gint
		2095	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2096	{
		2097	int got_events = 0;
		2098
		2099	for (n = 0; n < nfds; ++n)
		2100	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2101
		2102	if (timeout >= 0)
		2103	// create/start timer
		2104
		2105	// poll
		2106	ev_loop (EV_A_ 0);
		2107
		2108	// stop timer again
		2109	if (timeout >= 0)
		2110	ev_timer_stop (EV_A_ &to);
		2111
		2112	// stop io watchers again - their callbacks should have set
		2113	for (n = 0; n < nfds; ++n)
		2114	ev_io_stop (EV_A_ iow [n]);
		2115
		2116	return got_events;
		2117	}
		2118
		2119
		2120	=head2 C<ev_embed> - when one backend isn't enough...
		2121
		2122	This is a rather advanced watcher type that lets you embed one event loop
		2123	into another (currently only C<ev_io> events are supported in the embedded
		2124	loop, other types of watchers might be handled in a delayed or incorrect
		2125	fashion and must not be used).
		2126
		2127	There are primarily two reasons you would want that: work around bugs and
		2128	prioritise I/O.
		2129
		2130	As an example for a bug workaround, the kqueue backend might only support
		2131	sockets on some platform, so it is unusable as generic backend, but you
		2132	still want to make use of it because you have many sockets and it scales
		2133	so nicely. In this case, you would create a kqueue-based loop and embed it
		2134	into your default loop (which might use e.g. poll). Overall operation will
		2135	be a bit slower because first libev has to poll and then call kevent, but
		2136	at least you can use both at what they are best.
		2137
		2138	As for prioritising I/O: rarely you have the case where some fds have
		2139	to be watched and handled very quickly (with low latency), and even
		2140	priorities and idle watchers might have too much overhead. In this case
		2141	you would put all the high priority stuff in one loop and all the rest in
		2142	a second one, and embed the second one in the first.
		2143
		2144	As long as the watcher is active, the callback will be invoked every time
		2145	there might be events pending in the embedded loop. The callback must then
		2146	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2147	their callbacks (you could also start an idle watcher to give the embedded
		2148	loop strictly lower priority for example). You can also set the callback
		2149	to C<0>, in which case the embed watcher will automatically execute the
		2150	embedded loop sweep.
		2151
		2152	As long as the watcher is started it will automatically handle events. The
		2153	callback will be invoked whenever some events have been handled. You can
		2154	set the callback to C<0> to avoid having to specify one if you are not
		2155	interested in that.
		2156
		2157	Also, there have not currently been made special provisions for forking:
		2158	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2159	but you will also have to stop and restart any C<ev_embed> watchers
		2160	yourself.
		2161
		2162	Unfortunately, not all backends are embeddable, only the ones returned by
		2163	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2164	portable one.
		2165
		2166	So when you want to use this feature you will always have to be prepared
		2167	that you cannot get an embeddable loop. The recommended way to get around
		2168	this is to have a separate variables for your embeddable loop, try to
		2169	create it, and if that fails, use the normal loop for everything.
		2170
		2171	=head3 Watcher-Specific Functions and Data Members
		2172
		2173	=over 4
		2174
		2175	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2176
		2177	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2178
		2179	Configures the watcher to embed the given loop, which must be
		2180	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2181	invoked automatically, otherwise it is the responsibility of the callback
		2182	to invoke it (it will continue to be called until the sweep has been done,
		2183	if you do not want that, you need to temporarily stop the embed watcher).
		2184
		2185	=item ev_embed_sweep (loop, ev_embed *)
		2186
		2187	Make a single, non-blocking sweep over the embedded loop. This works
		2188	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2189	appropriate way for embedded loops.
		2190
		2191	=item struct ev_loop *other [read-only]
		2192
		2193	The embedded event loop.
		2194
		2195	=back
		2196
		2197	=head3 Examples
		2198
		2199	Example: Try to get an embeddable event loop and embed it into the default
		2200	event loop. If that is not possible, use the default loop. The default
		2201	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2202	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2203	used).
		2204
		2205	struct ev_loop *loop_hi = ev_default_init (0);
		2206	struct ev_loop *loop_lo = 0;
		2207	struct ev_embed embed;
		2208
		2209	// see if there is a chance of getting one that works
		2210	// (remember that a flags value of 0 means autodetection)
		2211	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2212	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2213	: 0;
		2214
		2215	// if we got one, then embed it, otherwise default to loop_hi
		2216	if (loop_lo)
		2217	{
		2218	ev_embed_init (&embed, 0, loop_lo);
		2219	ev_embed_start (loop_hi, &embed);
		2220	}
		2221	else
		2222	loop_lo = loop_hi;
		2223
		2224	Example: Check if kqueue is available but not recommended and create
		2225	a kqueue backend for use with sockets (which usually work with any
		2226	kqueue implementation). Store the kqueue/socket-only event loop in
		2227	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2228
		2229	struct ev_loop *loop = ev_default_init (0);
		2230	struct ev_loop *loop_socket = 0;
		2231	struct ev_embed embed;
		2232
		2233	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2234	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2235	{
		2236	ev_embed_init (&embed, 0, loop_socket);
		2237	ev_embed_start (loop, &embed);
		2238	}
		2239
		2240	if (!loop_socket)
		2241	loop_socket = loop;
		2242
		2243	// now use loop_socket for all sockets, and loop for everything else
		2244
		2245
		2246	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2247
		2248	Fork watchers are called when a C<fork ()> was detected (usually because
		2249	whoever is a good citizen cared to tell libev about it by calling
		2250	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2251	event loop blocks next and before C<ev_check> watchers are being called,
		2252	and only in the child after the fork. If whoever good citizen calling
		2253	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2254	handlers will be invoked, too, of course.
		2255
		2256	=head3 Watcher-Specific Functions and Data Members
		2257
		2258	=over 4
		2259
		2260	=item ev_fork_init (ev_signal *, callback)
		2261
		2262	Initialises and configures the fork watcher - it has no parameters of any
		2263	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2264	believe me.
		2265
		2266	=back
		2267
		2268
		2269	=head2 C<ev_async> - how to wake up another event loop
		2270
		2271	In general, you cannot use an C<ev_loop> from multiple threads or other
		2272	asynchronous sources such as signal handlers (as opposed to multiple event
		2273	loops - those are of course safe to use in different threads).
		2274
		2275	Sometimes, however, you need to wake up another event loop you do not
		2276	control, for example because it belongs to another thread. This is what
		2277	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2278	can signal it by calling C<ev_async_send>, which is thread- and signal
		2279	safe.
		2280
		2281	This functionality is very similar to C<ev_signal> watchers, as signals,
		2282	too, are asynchronous in nature, and signals, too, will be compressed
		2283	(i.e. the number of callback invocations may be less than the number of
		2284	C<ev_async_sent> calls).
		2285
		2286	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2287	just the default loop.
		2288
		2289	=head3 Queueing
		2290
		2291	C<ev_async> does not support queueing of data in any way. The reason
		2292	is that the author does not know of a simple (or any) algorithm for a
		2293	multiple-writer-single-reader queue that works in all cases and doesn't
		2294	need elaborate support such as pthreads.
		2295
		2296	That means that if you want to queue data, you have to provide your own
		2297	queue. But at least I can tell you would implement locking around your
		2298	queue:
		2299
		2300	=over 4
		2301
		2302	=item queueing from a signal handler context
		2303
		2304	To implement race-free queueing, you simply add to the queue in the signal
		2305	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2306	some fictitious SIGUSR1 handler:
		2307
		2308	static ev_async mysig;
		2309
		2310	static void
		2311	sigusr1_handler (void)
		2312	{
		2313	sometype data;
		2314
		2315	// no locking etc.
		2316	queue_put (data);
		2317	ev_async_send (EV_DEFAULT_ &mysig);
		2318	}
		2319
		2320	static void
		2321	mysig_cb (EV_P_ ev_async *w, int revents)
		2322	{
		2323	sometype data;
		2324	sigset_t block, prev;
		2325
		2326	sigemptyset (&block);
		2327	sigaddset (&block, SIGUSR1);
		2328	sigprocmask (SIG_BLOCK, &block, &prev);
		2329
		2330	while (queue_get (&data))
		2331	process (data);
		2332
		2333	if (sigismember (&prev, SIGUSR1)
		2334	sigprocmask (SIG_UNBLOCK, &block, 0);
		2335	}
		2336
		2337	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2338	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2339	either...).
		2340
		2341	=item queueing from a thread context
		2342
		2343	The strategy for threads is different, as you cannot (easily) block
		2344	threads but you can easily preempt them, so to queue safely you need to
		2345	employ a traditional mutex lock, such as in this pthread example:
		2346
		2347	static ev_async mysig;
		2348	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2349
		2350	static void
		2351	otherthread (void)
		2352	{
		2353	// only need to lock the actual queueing operation
		2354	pthread_mutex_lock (&mymutex);
		2355	queue_put (data);
		2356	pthread_mutex_unlock (&mymutex);
		2357
		2358	ev_async_send (EV_DEFAULT_ &mysig);
		2359	}
		2360
		2361	static void
		2362	mysig_cb (EV_P_ ev_async *w, int revents)
		2363	{
		2364	pthread_mutex_lock (&mymutex);
		2365
		2366	while (queue_get (&data))
		2367	process (data);
		2368
		2369	pthread_mutex_unlock (&mymutex);
		2370	}
		2371
		2372	=back
		2373
		2374
		2375	=head3 Watcher-Specific Functions and Data Members
		2376
		2377	=over 4
		2378
		2379	=item ev_async_init (ev_async *, callback)
		2380
		2381	Initialises and configures the async watcher - it has no parameters of any
		2382	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2383	believe me.
		2384
		2385	=item ev_async_send (loop, ev_async *)
		2386
		2387	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2388	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2389	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2390	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2391	section below on what exactly this means).
		2392
		2393	This call incurs the overhead of a system call only once per loop iteration,
		2394	so while the overhead might be noticeable, it doesn't apply to repeated
		2395	calls to C<ev_async_send>.
		2396
		2397	=item bool = ev_async_pending (ev_async *)
		2398
		2399	Returns a non-zero value when C<ev_async_send> has been called on the
		2400	watcher but the event has not yet been processed (or even noted) by the
		2401	event loop.
		2402
		2403	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2404	the loop iterates next and checks for the watcher to have become active,
		2405	it will reset the flag again. C<ev_async_pending> can be used to very
		2406	quickly check whether invoking the loop might be a good idea.
		2407
		2408	Not that this does I<not> check whether the watcher itself is pending, only
		2409	whether it has been requested to make this watcher pending.
		2410
		2411	=back
		2412
		2413
690	=head1 OTHER FUNCTIONS	2414	=head1 OTHER FUNCTIONS
691		2415
692	There are some other fucntions of possible interest. Described. Here. Now.	2416	There are some other functions of possible interest. Described. Here. Now.
693		2417
694	=over 4	2418	=over 4
695		2419
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2420	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		2421
698	This function combines a simple timer and an I/O watcher, calls your	2422	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	2423	callback on whichever event happens first and automatically stop both
700	watchers. This is useful if you want to wait for a single event on an fd	2424	watchers. This is useful if you want to wait for a single event on an fd
701	or timeout without havign to allocate/configure/start/stop/free one or	2425	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	2426	more watchers yourself.
703		2427
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	2428	If C<fd> is less than 0, then no I/O watcher will be started and events
705	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	2429	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
706	will be craeted and started.	2430	C<events> set will be created and started.
707		2431
708	If C<timeout> is less than 0, then no timeout watcher will be	2432	If C<timeout> is less than 0, then no timeout watcher will be
709	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	2433	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	2434	repeat = 0) will be started. While C<0> is a valid timeout, it is of
		2435	dubious value.
711		2436
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	2437	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
713	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	2438	passed an C<revents> set like normal event callbacks (a combination of
714	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	2439	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2440	value passed to C<ev_once>:
715		2441
716	static void stdin_ready (int revents, void *arg)	2442	static void stdin_ready (int revents, void *arg)
717	{	2443	{
718	if (revents & EV_TIMEOUT)	2444	if (revents & EV_TIMEOUT)
719	/* doh, nothing entered */	2445	/* doh, nothing entered */;
720	else if (revents & EV_READ)	2446	else if (revents & EV_READ)
721	/* stdin might have data for us, joy! */	2447	/* stdin might have data for us, joy! */;
722	}	2448	}
723		2449
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2450	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
725		2451
726	=item ev_feed_event (loop, watcher, int events)	2452	=item ev_feed_event (ev_loop *, watcher *, int revents)
727		2453
728	Feeds the given event set into the event loop, as if the specified event	2454	Feeds the given event set into the event loop, as if the specified event
729	has happened for the specified watcher (which must be a pointer to an	2455	had happened for the specified watcher (which must be a pointer to an
730	initialised but not necessarily active event watcher).	2456	initialised but not necessarily started event watcher).
731		2457
732	=item ev_feed_fd_event (loop, int fd, int revents)	2458	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
733		2459
734	Feed an event on the given fd, as if a file descriptor backend detected it.	2460	Feed an event on the given fd, as if a file descriptor backend detected
		2461	the given events it.
735		2462
736	=item ev_feed_signal_event (loop, int signum)	2463	=item ev_feed_signal_event (ev_loop *loop, int signum)
737		2464
738	Feed an event as if the given signal occured (loop must be the default loop!).	2465	Feed an event as if the given signal occurred (C<loop> must be the default
		2466	loop!).
739		2467
740	=back	2468	=back
741		2469
		2470
		2471	=head1 LIBEVENT EMULATION
		2472
		2473	Libev offers a compatibility emulation layer for libevent. It cannot
		2474	emulate the internals of libevent, so here are some usage hints:
		2475
		2476	=over 4
		2477
		2478	=item * Use it by including <event.h>, as usual.
		2479
		2480	=item * The following members are fully supported: ev_base, ev_callback,
		2481	ev_arg, ev_fd, ev_res, ev_events.
		2482
		2483	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2484	maintained by libev, it does not work exactly the same way as in libevent (consider
		2485	it a private API).
		2486
		2487	=item * Priorities are not currently supported. Initialising priorities
		2488	will fail and all watchers will have the same priority, even though there
		2489	is an ev_pri field.
		2490
		2491	=item * In libevent, the last base created gets the signals, in libev, the
		2492	first base created (== the default loop) gets the signals.
		2493
		2494	=item * Other members are not supported.
		2495
		2496	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2497	to use the libev header file and library.
		2498
		2499	=back
		2500
		2501	=head1 C++ SUPPORT
		2502
		2503	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2504	you to use some convenience methods to start/stop watchers and also change
		2505	the callback model to a model using method callbacks on objects.
		2506
		2507	To use it,
		2508
		2509	#include <ev++.h>
		2510
		2511	This automatically includes F<ev.h> and puts all of its definitions (many
		2512	of them macros) into the global namespace. All C++ specific things are
		2513	put into the C<ev> namespace. It should support all the same embedding
		2514	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2515
		2516	Care has been taken to keep the overhead low. The only data member the C++
		2517	classes add (compared to plain C-style watchers) is the event loop pointer
		2518	that the watcher is associated with (or no additional members at all if
		2519	you disable C<EV_MULTIPLICITY> when embedding libev).
		2520
		2521	Currently, functions, and static and non-static member functions can be
		2522	used as callbacks. Other types should be easy to add as long as they only
		2523	need one additional pointer for context. If you need support for other
		2524	types of functors please contact the author (preferably after implementing
		2525	it).
		2526
		2527	Here is a list of things available in the C<ev> namespace:
		2528
		2529	=over 4
		2530
		2531	=item C<ev::READ>, C<ev::WRITE> etc.
		2532
		2533	These are just enum values with the same values as the C<EV_READ> etc.
		2534	macros from F<ev.h>.
		2535
		2536	=item C<ev::tstamp>, C<ev::now>
		2537
		2538	Aliases to the same types/functions as with the C<ev_> prefix.
		2539
		2540	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2541
		2542	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2543	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2544	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2545	defines by many implementations.
		2546
		2547	All of those classes have these methods:
		2548
		2549	=over 4
		2550
		2551	=item ev::TYPE::TYPE ()
		2552
		2553	=item ev::TYPE::TYPE (struct ev_loop *)
		2554
		2555	=item ev::TYPE::~TYPE
		2556
		2557	The constructor (optionally) takes an event loop to associate the watcher
		2558	with. If it is omitted, it will use C<EV_DEFAULT>.
		2559
		2560	The constructor calls C<ev_init> for you, which means you have to call the
		2561	C<set> method before starting it.
		2562
		2563	It will not set a callback, however: You have to call the templated C<set>
		2564	method to set a callback before you can start the watcher.
		2565
		2566	(The reason why you have to use a method is a limitation in C++ which does
		2567	not allow explicit template arguments for constructors).
		2568
		2569	The destructor automatically stops the watcher if it is active.
		2570
		2571	=item w->set<class, &class::method> (object *)
		2572
		2573	This method sets the callback method to call. The method has to have a
		2574	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2575	first argument and the C<revents> as second. The object must be given as
		2576	parameter and is stored in the C<data> member of the watcher.
		2577
		2578	This method synthesizes efficient thunking code to call your method from
		2579	the C callback that libev requires. If your compiler can inline your
		2580	callback (i.e. it is visible to it at the place of the C<set> call and
		2581	your compiler is good :), then the method will be fully inlined into the
		2582	thunking function, making it as fast as a direct C callback.
		2583
		2584	Example: simple class declaration and watcher initialisation
		2585
		2586	struct myclass
		2587	{
		2588	void io_cb (ev::io &w, int revents) { }
		2589	}
		2590
		2591	myclass obj;
		2592	ev::io iow;
		2593	iow.set <myclass, &myclass::io_cb> (&obj);
		2594
		2595	=item w->set<function> (void *data = 0)
		2596
		2597	Also sets a callback, but uses a static method or plain function as
		2598	callback. The optional C<data> argument will be stored in the watcher's
		2599	C<data> member and is free for you to use.
		2600
		2601	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2602
		2603	See the method-C<set> above for more details.
		2604
		2605	Example:
		2606
		2607	static void io_cb (ev::io &w, int revents) { }
		2608	iow.set <io_cb> ();
		2609
		2610	=item w->set (struct ev_loop *)
		2611
		2612	Associates a different C<struct ev_loop> with this watcher. You can only
		2613	do this when the watcher is inactive (and not pending either).
		2614
		2615	=item w->set ([arguments])
		2616
		2617	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2618	called at least once. Unlike the C counterpart, an active watcher gets
		2619	automatically stopped and restarted when reconfiguring it with this
		2620	method.
		2621
		2622	=item w->start ()
		2623
		2624	Starts the watcher. Note that there is no C<loop> argument, as the
		2625	constructor already stores the event loop.
		2626
		2627	=item w->stop ()
		2628
		2629	Stops the watcher if it is active. Again, no C<loop> argument.
		2630
		2631	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2632
		2633	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2634	C<ev_TYPE_again> function.
		2635
		2636	=item w->sweep () (C<ev::embed> only)
		2637
		2638	Invokes C<ev_embed_sweep>.
		2639
		2640	=item w->update () (C<ev::stat> only)
		2641
		2642	Invokes C<ev_stat_stat>.
		2643
		2644	=back
		2645
		2646	=back
		2647
		2648	Example: Define a class with an IO and idle watcher, start one of them in
		2649	the constructor.
		2650
		2651	class myclass
		2652	{
		2653	ev::io io; void io_cb (ev::io &w, int revents);
		2654	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2655
		2656	myclass (int fd)
		2657	{
		2658	io .set <myclass, &myclass::io_cb > (this);
		2659	idle.set <myclass, &myclass::idle_cb> (this);
		2660
		2661	io.start (fd, ev::READ);
		2662	}
		2663	};
		2664
		2665
		2666	=head1 OTHER LANGUAGE BINDINGS
		2667
		2668	Libev does not offer other language bindings itself, but bindings for a
		2669	number of languages exist in the form of third-party packages. If you know
		2670	any interesting language binding in addition to the ones listed here, drop
		2671	me a note.
		2672
		2673	=over 4
		2674
		2675	=item Perl
		2676
		2677	The EV module implements the full libev API and is actually used to test
		2678	libev. EV is developed together with libev. Apart from the EV core module,
		2679	there are additional modules that implement libev-compatible interfaces
		2680	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2681	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2682
		2683	It can be found and installed via CPAN, its homepage is at
		2684	L<http://software.schmorp.de/pkg/EV>.
		2685
		2686	=item Python
		2687
		2688	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2689	seems to be quite complete and well-documented. Note, however, that the
		2690	patch they require for libev is outright dangerous as it breaks the ABI
		2691	for everybody else, and therefore, should never be applied in an installed
		2692	libev (if python requires an incompatible ABI then it needs to embed
		2693	libev).
		2694
		2695	=item Ruby
		2696
		2697	Tony Arcieri has written a ruby extension that offers access to a subset
		2698	of the libev API and adds file handle abstractions, asynchronous DNS and
		2699	more on top of it. It can be found via gem servers. Its homepage is at
		2700	L<http://rev.rubyforge.org/>.
		2701
		2702	=item D
		2703
		2704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2705	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2706
		2707	=back
		2708
		2709
		2710	=head1 MACRO MAGIC
		2711
		2712	Libev can be compiled with a variety of options, the most fundamental
		2713	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2714	functions and callbacks have an initial C<struct ev_loop *> argument.
		2715
		2716	To make it easier to write programs that cope with either variant, the
		2717	following macros are defined:
		2718
		2719	=over 4
		2720
		2721	=item C<EV_A>, C<EV_A_>
		2722
		2723	This provides the loop I<argument> for functions, if one is required ("ev
		2724	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2725	C<EV_A_> is used when other arguments are following. Example:
		2726
		2727	ev_unref (EV_A);
		2728	ev_timer_add (EV_A_ watcher);
		2729	ev_loop (EV_A_ 0);
		2730
		2731	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2732	which is often provided by the following macro.
		2733
		2734	=item C<EV_P>, C<EV_P_>
		2735
		2736	This provides the loop I<parameter> for functions, if one is required ("ev
		2737	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2738	C<EV_P_> is used when other parameters are following. Example:
		2739
		2740	// this is how ev_unref is being declared
		2741	static void ev_unref (EV_P);
		2742
		2743	// this is how you can declare your typical callback
		2744	static void cb (EV_P_ ev_timer *w, int revents)
		2745
		2746	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2747	suitable for use with C<EV_A>.
		2748
		2749	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2750
		2751	Similar to the other two macros, this gives you the value of the default
		2752	loop, if multiple loops are supported ("ev loop default").
		2753
		2754	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2755
		2756	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2757	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2758	is undefined when the default loop has not been initialised by a previous
		2759	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2760
		2761	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2762	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2763
		2764	=back
		2765
		2766	Example: Declare and initialise a check watcher, utilising the above
		2767	macros so it will work regardless of whether multiple loops are supported
		2768	or not.
		2769
		2770	static void
		2771	check_cb (EV_P_ ev_timer *w, int revents)
		2772	{
		2773	ev_check_stop (EV_A_ w);
		2774	}
		2775
		2776	ev_check check;
		2777	ev_check_init (&check, check_cb);
		2778	ev_check_start (EV_DEFAULT_ &check);
		2779	ev_loop (EV_DEFAULT_ 0);
		2780
		2781	=head1 EMBEDDING
		2782
		2783	Libev can (and often is) directly embedded into host
		2784	applications. Examples of applications that embed it include the Deliantra
		2785	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2786	and rxvt-unicode.
		2787
		2788	The goal is to enable you to just copy the necessary files into your
		2789	source directory without having to change even a single line in them, so
		2790	you can easily upgrade by simply copying (or having a checked-out copy of
		2791	libev somewhere in your source tree).
		2792
		2793	=head2 FILESETS
		2794
		2795	Depending on what features you need you need to include one or more sets of files
		2796	in your application.
		2797
		2798	=head3 CORE EVENT LOOP
		2799
		2800	To include only the libev core (all the C<ev_*> functions), with manual
		2801	configuration (no autoconf):
		2802
		2803	#define EV_STANDALONE 1
		2804	#include "ev.c"
		2805
		2806	This will automatically include F<ev.h>, too, and should be done in a
		2807	single C source file only to provide the function implementations. To use
		2808	it, do the same for F<ev.h> in all files wishing to use this API (best
		2809	done by writing a wrapper around F<ev.h> that you can include instead and
		2810	where you can put other configuration options):
		2811
		2812	#define EV_STANDALONE 1
		2813	#include "ev.h"
		2814
		2815	Both header files and implementation files can be compiled with a C++
		2816	compiler (at least, thats a stated goal, and breakage will be treated
		2817	as a bug).
		2818
		2819	You need the following files in your source tree, or in a directory
		2820	in your include path (e.g. in libev/ when using -Ilibev):
		2821
		2822	ev.h
		2823	ev.c
		2824	ev_vars.h
		2825	ev_wrap.h
		2826
		2827	ev_win32.c required on win32 platforms only
		2828
		2829	ev_select.c only when select backend is enabled (which is enabled by default)
		2830	ev_poll.c only when poll backend is enabled (disabled by default)
		2831	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2832	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2833	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2834
		2835	F<ev.c> includes the backend files directly when enabled, so you only need
		2836	to compile this single file.
		2837
		2838	=head3 LIBEVENT COMPATIBILITY API
		2839
		2840	To include the libevent compatibility API, also include:
		2841
		2842	#include "event.c"
		2843
		2844	in the file including F<ev.c>, and:
		2845
		2846	#include "event.h"
		2847
		2848	in the files that want to use the libevent API. This also includes F<ev.h>.
		2849
		2850	You need the following additional files for this:
		2851
		2852	event.h
		2853	event.c
		2854
		2855	=head3 AUTOCONF SUPPORT
		2856
		2857	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2858	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2859	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2860	include F<config.h> and configure itself accordingly.
		2861
		2862	For this of course you need the m4 file:
		2863
		2864	libev.m4
		2865
		2866	=head2 PREPROCESSOR SYMBOLS/MACROS
		2867
		2868	Libev can be configured via a variety of preprocessor symbols you have to
		2869	define before including any of its files. The default in the absence of
		2870	autoconf is noted for every option.
		2871
		2872	=over 4
		2873
		2874	=item EV_STANDALONE
		2875
		2876	Must always be C<1> if you do not use autoconf configuration, which
		2877	keeps libev from including F<config.h>, and it also defines dummy
		2878	implementations for some libevent functions (such as logging, which is not
		2879	supported). It will also not define any of the structs usually found in
		2880	F<event.h> that are not directly supported by the libev core alone.
		2881
		2882	=item EV_USE_MONOTONIC
		2883
		2884	If defined to be C<1>, libev will try to detect the availability of the
		2885	monotonic clock option at both compile time and runtime. Otherwise no use
		2886	of the monotonic clock option will be attempted. If you enable this, you
		2887	usually have to link against librt or something similar. Enabling it when
		2888	the functionality isn't available is safe, though, although you have
		2889	to make sure you link against any libraries where the C<clock_gettime>
		2890	function is hiding in (often F<-lrt>).
		2891
		2892	=item EV_USE_REALTIME
		2893
		2894	If defined to be C<1>, libev will try to detect the availability of the
		2895	real-time clock option at compile time (and assume its availability at
		2896	runtime if successful). Otherwise no use of the real-time clock option will
		2897	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2898	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2899	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2900
		2901	=item EV_USE_NANOSLEEP
		2902
		2903	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2904	and will use it for delays. Otherwise it will use C<select ()>.
		2905
		2906	=item EV_USE_EVENTFD
		2907
		2908	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2909	available and will probe for kernel support at runtime. This will improve
		2910	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2911	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2912	2.7 or newer, otherwise disabled.
		2913
		2914	=item EV_USE_SELECT
		2915
		2916	If undefined or defined to be C<1>, libev will compile in support for the
		2917	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2918	other method takes over, select will be it. Otherwise the select backend
		2919	will not be compiled in.
		2920
		2921	=item EV_SELECT_USE_FD_SET
		2922
		2923	If defined to C<1>, then the select backend will use the system C<fd_set>
		2924	structure. This is useful if libev doesn't compile due to a missing
		2925	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		2926	exotic systems. This usually limits the range of file descriptors to some
		2927	low limit such as 1024 or might have other limitations (winsocket only
		2928	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2929	influence the size of the C<fd_set> used.
		2930
		2931	=item EV_SELECT_IS_WINSOCKET
		2932
		2933	When defined to C<1>, the select backend will assume that
		2934	select/socket/connect etc. don't understand file descriptors but
		2935	wants osf handles on win32 (this is the case when the select to
		2936	be used is the winsock select). This means that it will call
		2937	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2938	it is assumed that all these functions actually work on fds, even
		2939	on win32. Should not be defined on non-win32 platforms.
		2940
		2941	=item EV_FD_TO_WIN32_HANDLE
		2942
		2943	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2944	file descriptors to socket handles. When not defining this symbol (the
		2945	default), then libev will call C<_get_osfhandle>, which is usually
		2946	correct. In some cases, programs use their own file descriptor management,
		2947	in which case they can provide this function to map fds to socket handles.
		2948
		2949	=item EV_USE_POLL
		2950
		2951	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2952	backend. Otherwise it will be enabled on non-win32 platforms. It
		2953	takes precedence over select.
		2954
		2955	=item EV_USE_EPOLL
		2956
		2957	If defined to be C<1>, libev will compile in support for the Linux
		2958	C<epoll>(7) backend. Its availability will be detected at runtime,
		2959	otherwise another method will be used as fallback. This is the preferred
		2960	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2961	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2962
		2963	=item EV_USE_KQUEUE
		2964
		2965	If defined to be C<1>, libev will compile in support for the BSD style
		2966	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2967	otherwise another method will be used as fallback. This is the preferred
		2968	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2969	supports some types of fds correctly (the only platform we found that
		2970	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2971	not be used unless explicitly requested. The best way to use it is to find
		2972	out whether kqueue supports your type of fd properly and use an embedded
		2973	kqueue loop.
		2974
		2975	=item EV_USE_PORT
		2976
		2977	If defined to be C<1>, libev will compile in support for the Solaris
		2978	10 port style backend. Its availability will be detected at runtime,
		2979	otherwise another method will be used as fallback. This is the preferred
		2980	backend for Solaris 10 systems.
		2981
		2982	=item EV_USE_DEVPOLL
		2983
		2984	Reserved for future expansion, works like the USE symbols above.
		2985
		2986	=item EV_USE_INOTIFY
		2987
		2988	If defined to be C<1>, libev will compile in support for the Linux inotify
		2989	interface to speed up C<ev_stat> watchers. Its actual availability will
		2990	be detected at runtime. If undefined, it will be enabled if the headers
		2991	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2992
		2993	=item EV_ATOMIC_T
		2994
		2995	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2996	access is atomic with respect to other threads or signal contexts. No such
		2997	type is easily found in the C language, so you can provide your own type
		2998	that you know is safe for your purposes. It is used both for signal handler "locking"
		2999	as well as for signal and thread safety in C<ev_async> watchers.
		3000
		3001	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3002	(from F<signal.h>), which is usually good enough on most platforms.
		3003
		3004	=item EV_H
		3005
		3006	The name of the F<ev.h> header file used to include it. The default if
		3007	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3008	used to virtually rename the F<ev.h> header file in case of conflicts.
		3009
		3010	=item EV_CONFIG_H
		3011
		3012	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3013	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3014	C<EV_H>, above.
		3015
		3016	=item EV_EVENT_H
		3017
		3018	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3019	of how the F<event.h> header can be found, the default is C<"event.h">.
		3020
		3021	=item EV_PROTOTYPES
		3022
		3023	If defined to be C<0>, then F<ev.h> will not define any function
		3024	prototypes, but still define all the structs and other symbols. This is
		3025	occasionally useful if you want to provide your own wrapper functions
		3026	around libev functions.
		3027
		3028	=item EV_MULTIPLICITY
		3029
		3030	If undefined or defined to C<1>, then all event-loop-specific functions
		3031	will have the C<struct ev_loop *> as first argument, and you can create
		3032	additional independent event loops. Otherwise there will be no support
		3033	for multiple event loops and there is no first event loop pointer
		3034	argument. Instead, all functions act on the single default loop.
		3035
		3036	=item EV_MINPRI
		3037
		3038	=item EV_MAXPRI
		3039
		3040	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3041	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3042	provide for more priorities by overriding those symbols (usually defined
		3043	to be C<-2> and C<2>, respectively).
		3044
		3045	When doing priority-based operations, libev usually has to linearly search
		3046	all the priorities, so having many of them (hundreds) uses a lot of space
		3047	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3048	fine.
		3049
		3050	If your embedding application does not need any priorities, defining these both to
		3051	C<0> will save some memory and CPU.
		3052
		3053	=item EV_PERIODIC_ENABLE
		3054
		3055	If undefined or defined to be C<1>, then periodic timers are supported. If
		3056	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3057	code.
		3058
		3059	=item EV_IDLE_ENABLE
		3060
		3061	If undefined or defined to be C<1>, then idle watchers are supported. If
		3062	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3063	code.
		3064
		3065	=item EV_EMBED_ENABLE
		3066
		3067	If undefined or defined to be C<1>, then embed watchers are supported. If
		3068	defined to be C<0>, then they are not.
		3069
		3070	=item EV_STAT_ENABLE
		3071
		3072	If undefined or defined to be C<1>, then stat watchers are supported. If
		3073	defined to be C<0>, then they are not.
		3074
		3075	=item EV_FORK_ENABLE
		3076
		3077	If undefined or defined to be C<1>, then fork watchers are supported. If
		3078	defined to be C<0>, then they are not.
		3079
		3080	=item EV_ASYNC_ENABLE
		3081
		3082	If undefined or defined to be C<1>, then async watchers are supported. If
		3083	defined to be C<0>, then they are not.
		3084
		3085	=item EV_MINIMAL
		3086
		3087	If you need to shave off some kilobytes of code at the expense of some
		3088	speed, define this symbol to C<1>. Currently this is used to override some
		3089	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3090	much smaller 2-heap for timer management over the default 4-heap.
		3091
		3092	=item EV_PID_HASHSIZE
		3093
		3094	C<ev_child> watchers use a small hash table to distribute workload by
		3095	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3096	than enough. If you need to manage thousands of children you might want to
		3097	increase this value (I<must> be a power of two).
		3098
		3099	=item EV_INOTIFY_HASHSIZE
		3100
		3101	C<ev_stat> watchers use a small hash table to distribute workload by
		3102	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3103	usually more than enough. If you need to manage thousands of C<ev_stat>
		3104	watchers you might want to increase this value (I<must> be a power of
		3105	two).
		3106
		3107	=item EV_USE_4HEAP
		3108
		3109	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3110	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3111	to C<1>. The 4-heap uses more complicated (longer) code but has
		3112	noticeably faster performance with many (thousands) of watchers.
		3113
		3114	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3115	(disabled).
		3116
		3117	=item EV_HEAP_CACHE_AT
		3118
		3119	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3120	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3121	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3122	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3123	but avoids random read accesses on heap changes. This improves performance
		3124	noticeably with with many (hundreds) of watchers.
		3125
		3126	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3127	(disabled).
		3128
		3129	=item EV_VERIFY
		3130
		3131	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3132	be done: If set to C<0>, no internal verification code will be compiled
		3133	in. If set to C<1>, then verification code will be compiled in, but not
		3134	called. If set to C<2>, then the internal verification code will be
		3135	called once per loop, which can slow down libev. If set to C<3>, then the
		3136	verification code will be called very frequently, which will slow down
		3137	libev considerably.
		3138
		3139	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3140	C<0.>
		3141
		3142	=item EV_COMMON
		3143
		3144	By default, all watchers have a C<void *data> member. By redefining
		3145	this macro to a something else you can include more and other types of
		3146	members. You have to define it each time you include one of the files,
		3147	though, and it must be identical each time.
		3148
		3149	For example, the perl EV module uses something like this:
		3150
		3151	#define EV_COMMON \
		3152	SV *self; /* contains this struct */ \
		3153	SV *cb_sv, *fh /* note no trailing ";" */
		3154
		3155	=item EV_CB_DECLARE (type)
		3156
		3157	=item EV_CB_INVOKE (watcher, revents)
		3158
		3159	=item ev_set_cb (ev, cb)
		3160
		3161	Can be used to change the callback member declaration in each watcher,
		3162	and the way callbacks are invoked and set. Must expand to a struct member
		3163	definition and a statement, respectively. See the F<ev.h> header file for
		3164	their default definitions. One possible use for overriding these is to
		3165	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3166	method calls instead of plain function calls in C++.
		3167
		3168	=head2 EXPORTED API SYMBOLS
		3169
		3170	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3171	exported symbols, you can use the provided F<Symbol.*> files which list
		3172	all public symbols, one per line:
		3173
		3174	Symbols.ev for libev proper
		3175	Symbols.event for the libevent emulation
		3176
		3177	This can also be used to rename all public symbols to avoid clashes with
		3178	multiple versions of libev linked together (which is obviously bad in
		3179	itself, but sometimes it is inconvenient to avoid this).
		3180
		3181	A sed command like this will create wrapper C<#define>'s that you need to
		3182	include before including F<ev.h>:
		3183
		3184	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3185
		3186	This would create a file F<wrap.h> which essentially looks like this:
		3187
		3188	#define ev_backend myprefix_ev_backend
		3189	#define ev_check_start myprefix_ev_check_start
		3190	#define ev_check_stop myprefix_ev_check_stop
		3191	...
		3192
		3193	=head2 EXAMPLES
		3194
		3195	For a real-world example of a program the includes libev
		3196	verbatim, you can have a look at the EV perl module
		3197	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3198	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3199	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3200	will be compiled. It is pretty complex because it provides its own header
		3201	file.
		3202
		3203	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3204	that everybody includes and which overrides some configure choices:
		3205
		3206	#define EV_MINIMAL 1
		3207	#define EV_USE_POLL 0
		3208	#define EV_MULTIPLICITY 0
		3209	#define EV_PERIODIC_ENABLE 0
		3210	#define EV_STAT_ENABLE 0
		3211	#define EV_FORK_ENABLE 0
		3212	#define EV_CONFIG_H <config.h>
		3213	#define EV_MINPRI 0
		3214	#define EV_MAXPRI 0
		3215
		3216	#include "ev++.h"
		3217
		3218	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3219
		3220	#include "ev_cpp.h"
		3221	#include "ev.c"
		3222
		3223
		3224	=head1 THREADS AND COROUTINES
		3225
		3226	=head2 THREADS
		3227
		3228	Libev itself is completely thread-safe, but it uses no locking. This
		3229	means that you can use as many loops as you want in parallel, as long as
		3230	only one thread ever calls into one libev function with the same loop
		3231	parameter.
		3232
		3233	Or put differently: calls with different loop parameters can be done in
		3234	parallel from multiple threads, calls with the same loop parameter must be
		3235	done serially (but can be done from different threads, as long as only one
		3236	thread ever is inside a call at any point in time, e.g. by using a mutex
		3237	per loop).
		3238
		3239	If you want to know which design (one loop, locking, or multiple loops
		3240	without or something else still) is best for your problem, then I cannot
		3241	help you. I can give some generic advice however:
		3242
		3243	=over 4
		3244
		3245	=item * most applications have a main thread: use the default libev loop
		3246	in that thread, or create a separate thread running only the default loop.
		3247
		3248	This helps integrating other libraries or software modules that use libev
		3249	themselves and don't care/know about threading.
		3250
		3251	=item * one loop per thread is usually a good model.
		3252
		3253	Doing this is almost never wrong, sometimes a better-performance model
		3254	exists, but it is always a good start.
		3255
		3256	=item * other models exist, such as the leader/follower pattern, where one
		3257	loop is handed through multiple threads in a kind of round-robin fashion.
		3258
		3259	Choosing a model is hard - look around, learn, know that usually you can do
		3260	better than you currently do :-)
		3261
		3262	=item * often you need to talk to some other thread which blocks in the
		3263	event loop - C<ev_async> watchers can be used to wake them up from other
		3264	threads safely (or from signal contexts...).
		3265
		3266	=back
		3267
		3268	=head2 COROUTINES
		3269
		3270	Libev is much more accommodating to coroutines ("cooperative threads"):
		3271	libev fully supports nesting calls to it's functions from different
		3272	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3273	different coroutines and switch freely between both coroutines running the
		3274	loop, as long as you don't confuse yourself). The only exception is that
		3275	you must not do this from C<ev_periodic> reschedule callbacks.
		3276
		3277	Care has been invested into making sure that libev does not keep local
		3278	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3279	switches.
		3280
		3281
		3282	=head1 COMPLEXITIES
		3283
		3284	In this section the complexities of (many of) the algorithms used inside
		3285	libev will be explained. For complexity discussions about backends see the
		3286	documentation for C<ev_default_init>.
		3287
		3288	All of the following are about amortised time: If an array needs to be
		3289	extended, libev needs to realloc and move the whole array, but this
		3290	happens asymptotically never with higher number of elements, so O(1) might
		3291	mean it might do a lengthy realloc operation in rare cases, but on average
		3292	it is much faster and asymptotically approaches constant time.
		3293
		3294	=over 4
		3295
		3296	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3297
		3298	This means that, when you have a watcher that triggers in one hour and
		3299	there are 100 watchers that would trigger before that then inserting will
		3300	have to skip roughly seven (C<ld 100>) of these watchers.
		3301
		3302	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3303
		3304	That means that changing a timer costs less than removing/adding them
		3305	as only the relative motion in the event queue has to be paid for.
		3306
		3307	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3308
		3309	These just add the watcher into an array or at the head of a list.
		3310
		3311	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3312
		3313	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3314
		3315	These watchers are stored in lists then need to be walked to find the
		3316	correct watcher to remove. The lists are usually short (you don't usually
		3317	have many watchers waiting for the same fd or signal).
		3318
		3319	=item Finding the next timer in each loop iteration: O(1)
		3320
		3321	By virtue of using a binary or 4-heap, the next timer is always found at a
		3322	fixed position in the storage array.
		3323
		3324	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3325
		3326	A change means an I/O watcher gets started or stopped, which requires
		3327	libev to recalculate its status (and possibly tell the kernel, depending
		3328	on backend and whether C<ev_io_set> was used).
		3329
		3330	=item Activating one watcher (putting it into the pending state): O(1)
		3331
		3332	=item Priority handling: O(number_of_priorities)
		3333
		3334	Priorities are implemented by allocating some space for each
		3335	priority. When doing priority-based operations, libev usually has to
		3336	linearly search all the priorities, but starting/stopping and activating
		3337	watchers becomes O(1) w.r.t. priority handling.
		3338
		3339	=item Sending an ev_async: O(1)
		3340
		3341	=item Processing ev_async_send: O(number_of_async_watchers)
		3342
		3343	=item Processing signals: O(max_signal_number)
		3344
		3345	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3346	calls in the current loop iteration. Checking for async and signal events
		3347	involves iterating over all running async watchers or all signal numbers.
		3348
		3349	=back
		3350
		3351
		3352	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3353
		3354	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3355	requires, and its I/O model is fundamentally incompatible with the POSIX
		3356	model. Libev still offers limited functionality on this platform in
		3357	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3358	descriptors. This only applies when using Win32 natively, not when using
		3359	e.g. cygwin.
		3360
		3361	Lifting these limitations would basically require the full
		3362	re-implementation of the I/O system. If you are into these kinds of
		3363	things, then note that glib does exactly that for you in a very portable
		3364	way (note also that glib is the slowest event library known to man).
		3365
		3366	There is no supported compilation method available on windows except
		3367	embedding it into other applications.
		3368
		3369	Not a libev limitation but worth mentioning: windows apparently doesn't
		3370	accept large writes: instead of resulting in a partial write, windows will
		3371	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3372	so make sure you only write small amounts into your sockets (less than a
		3373	megabyte seems safe, but thsi apparently depends on the amount of memory
		3374	available).
		3375
		3376	Due to the many, low, and arbitrary limits on the win32 platform and
		3377	the abysmal performance of winsockets, using a large number of sockets
		3378	is not recommended (and not reasonable). If your program needs to use
		3379	more than a hundred or so sockets, then likely it needs to use a totally
		3380	different implementation for windows, as libev offers the POSIX readiness
		3381	notification model, which cannot be implemented efficiently on windows
		3382	(Microsoft monopoly games).
		3383
		3384	A typical way to use libev under windows is to embed it (see the embedding
		3385	section for details) and use the following F<evwrap.h> header file instead
		3386	of F<ev.h>:
		3387
		3388	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3389	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3390
		3391	#include "ev.h"
		3392
		3393	And compile the following F<evwrap.c> file into your project (make sure
		3394	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3395
		3396	#include "evwrap.h"
		3397	#include "ev.c"
		3398
		3399	=over 4
		3400
		3401	=item The winsocket select function
		3402
		3403	The winsocket C<select> function doesn't follow POSIX in that it
		3404	requires socket I<handles> and not socket I<file descriptors> (it is
		3405	also extremely buggy). This makes select very inefficient, and also
		3406	requires a mapping from file descriptors to socket handles (the Microsoft
		3407	C runtime provides the function C<_open_osfhandle> for this). See the
		3408	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3409	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3410
		3411	The configuration for a "naked" win32 using the Microsoft runtime
		3412	libraries and raw winsocket select is:
		3413
		3414	#define EV_USE_SELECT 1
		3415	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3416
		3417	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3418	complexity in the O(n²) range when using win32.
		3419
		3420	=item Limited number of file descriptors
		3421
		3422	Windows has numerous arbitrary (and low) limits on things.
		3423
		3424	Early versions of winsocket's select only supported waiting for a maximum
		3425	of C<64> handles (probably owning to the fact that all windows kernels
		3426	can only wait for C<64> things at the same time internally; Microsoft
		3427	recommends spawning a chain of threads and wait for 63 handles and the
		3428	previous thread in each. Great).
		3429
		3430	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3431	to some high number (e.g. C<2048>) before compiling the winsocket select
		3432	call (which might be in libev or elsewhere, for example, perl does its own
		3433	select emulation on windows).
		3434
		3435	Another limit is the number of file descriptors in the Microsoft runtime
		3436	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3437	or something like this inside Microsoft). You can increase this by calling
		3438	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3439	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3440	libraries.
		3441
		3442	This might get you to about C<512> or C<2048> sockets (depending on
		3443	windows version and/or the phase of the moon). To get more, you need to
		3444	wrap all I/O functions and provide your own fd management, but the cost of
		3445	calling select (O(n²)) will likely make this unworkable.
		3446
		3447	=back
		3448
		3449
		3450	=head1 PORTABILITY REQUIREMENTS
		3451
		3452	In addition to a working ISO-C implementation, libev relies on a few
		3453	additional extensions:
		3454
		3455	=over 4
		3456
		3457	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3458	calling conventions regardless of C<ev_watcher_type *>.
		3459
		3460	Libev assumes not only that all watcher pointers have the same internal
		3461	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3462	assumes that the same (machine) code can be used to call any watcher
		3463	callback: The watcher callbacks have different type signatures, but libev
		3464	calls them using an C<ev_watcher *> internally.
		3465
		3466	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3467
		3468	The type C<sig_atomic_t volatile> (or whatever is defined as
		3469	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3470	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3471	believed to be sufficiently portable.
		3472
		3473	=item C<sigprocmask> must work in a threaded environment
		3474
		3475	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3476	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3477	pthread implementations will either allow C<sigprocmask> in the "main
		3478	thread" or will block signals process-wide, both behaviours would
		3479	be compatible with libev. Interaction between C<sigprocmask> and
		3480	C<pthread_sigmask> could complicate things, however.
		3481
		3482	The most portable way to handle signals is to block signals in all threads
		3483	except the initial one, and run the default loop in the initial thread as
		3484	well.
		3485
		3486	=item C<long> must be large enough for common memory allocation sizes
		3487
		3488	To improve portability and simplify using libev, libev uses C<long>
		3489	internally instead of C<size_t> when allocating its data structures. On
		3490	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3491	is still at least 31 bits everywhere, which is enough for hundreds of
		3492	millions of watchers.
		3493
		3494	=item C<double> must hold a time value in seconds with enough accuracy
		3495
		3496	The type C<double> is used to represent timestamps. It is required to
		3497	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3498	enough for at least into the year 4000. This requirement is fulfilled by
		3499	implementations implementing IEEE 754 (basically all existing ones).
		3500
		3501	=back
		3502
		3503	If you know of other additional requirements drop me a note.
		3504
		3505
		3506	=head1 COMPILER WARNINGS
		3507
		3508	Depending on your compiler and compiler settings, you might get no or a
		3509	lot of warnings when compiling libev code. Some people are apparently
		3510	scared by this.
		3511
		3512	However, these are unavoidable for many reasons. For one, each compiler
		3513	has different warnings, and each user has different tastes regarding
		3514	warning options. "Warn-free" code therefore cannot be a goal except when
		3515	targeting a specific compiler and compiler-version.
		3516
		3517	Another reason is that some compiler warnings require elaborate
		3518	workarounds, or other changes to the code that make it less clear and less
		3519	maintainable.
		3520
		3521	And of course, some compiler warnings are just plain stupid, or simply
		3522	wrong (because they don't actually warn about the condition their message
		3523	seems to warn about).
		3524
		3525	While libev is written to generate as few warnings as possible,
		3526	"warn-free" code is not a goal, and it is recommended not to build libev
		3527	with any compiler warnings enabled unless you are prepared to cope with
		3528	them (e.g. by ignoring them). Remember that warnings are just that:
		3529	warnings, not errors, or proof of bugs.
		3530
		3531
		3532	=head1 VALGRIND
		3533
		3534	Valgrind has a special section here because it is a popular tool that is
		3535	highly useful, but valgrind reports are very hard to interpret.
		3536
		3537	If you think you found a bug (memory leak, uninitialised data access etc.)
		3538	in libev, then check twice: If valgrind reports something like:
		3539
		3540	==2274== definitely lost: 0 bytes in 0 blocks.
		3541	==2274== possibly lost: 0 bytes in 0 blocks.
		3542	==2274== still reachable: 256 bytes in 1 blocks.
		3543
		3544	Then there is no memory leak. Similarly, under some circumstances,
		3545	valgrind might report kernel bugs as if it were a bug in libev, or it
		3546	might be confused (it is a very good tool, but only a tool).
		3547
		3548	If you are unsure about something, feel free to contact the mailing list
		3549	with the full valgrind report and an explanation on why you think this is
		3550	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3551	no bug" answer and take the chance of learning how to interpret valgrind
		3552	properly.
		3553
		3554	If you need, for some reason, empty reports from valgrind for your project
		3555	I suggest using suppression lists.
		3556
		3557
742	=head1 AUTHOR	3558	=head1 AUTHOR
743		3559
744	Marc Lehmann <libev@schmorp.de>.	3560	Marc Lehmann <libev@schmorp.de>.
745		3561

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