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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	#include <ev.h>
		12
		13	ev_io stdin_watcher;
		14	ev_timer timeout_watcher;
		15
		16	/* called when data readable on stdin */
		17	static void
		18	stdin_cb (EV_P_ struct ev_io *w, int revents)
		19	{
		20	/* puts ("stdin ready"); */
		21	ev_io_stop (EV_A_ w); /* just a syntax example */
		22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
		23	}
		24
		25	static void
		26	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		27	{
		28	/* puts ("timeout"); */
		29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
		30	}
		31
		32	int
		33	main (void)
		34	{
		35	struct ev_loop *loop = ev_default_loop (0);
		36
		37	/* initialise an io watcher, then start it */
		38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		39	ev_io_start (loop, &stdin_watcher);
		40
		41	/* simple non-repeating 5.5 second timeout */
		42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		43	ev_timer_start (loop, &timeout_watcher);
		44
		45	/* loop till timeout or data ready */
		46	ev_loop (loop, 0);
		47
		48	return 0;
		49	}
		50
9	=head1 DESCRIPTION	51	=head1 DESCRIPTION
10		52
		53	The newest version of this document is also available as a html-formatted
		54	web page you might find easier to navigate when reading it for the first
		55	time: L<http://cvs.schmorp.de/libev/ev.html>.
		56
11	Libev is an event loop: you register interest in certain events (such as a	57	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	58	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	59	these event sources and provide your program with events.
14		60
15	To do this, it must take more or less complete control over your process	61	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	62	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	63	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	65	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	66	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	67	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	68	watcher.
23		69
24	=head1 FEATURES	70	=head2 FEATURES
25		71
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	76	with customised rescheduling (C<ev_periodic>), synchronous signals
		77	(C<ev_signal>), process status change events (C<ev_child>), and event
		78	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		80	file watchers (C<ev_stat>) and even limited support for fork events
		81	(C<ev_fork>).
		82
		83	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	85	for example).
33		86
34	=head1 CONVENTIONS	87	=head2 CONVENTIONS
35		88
36	Libev is very configurable. In this manual the default configuration	89	Libev is very configurable. In this manual the default configuration will
37	will be described, which supports multiple event loops. For more info	90	be described, which supports multiple event loops. For more info about
38	about various configuration options please have a look at the file	91	various configuration options please have a look at B<EMBED> section in
39	F<README.embed> in the libev distribution. If libev was configured without	92	this manual. If libev was configured without support for multiple event
40	support for multiple event loops, then all functions taking an initial	93	loops, then all functions taking an initial argument of name C<loop>
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	94	(which is always of type C<struct ev_loop *>) will not have this argument.
42	will not have this argument.
43		95
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	96	=head2 TIME REPRESENTATION
45		97
46	Libev represents time as a single floating point number, representing the	98	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	99	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	100	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	101	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	102	to the C<double> type in C, and when you need to do any calculations on
		103	it, you should treat it as some floatingpoint value. Unlike the name
		104	component C<stamp> might indicate, it is also used for time differences
		105	throughout libev.
		106
		107	=head1 GLOBAL FUNCTIONS
		108
		109	These functions can be called anytime, even before initialising the
		110	library in any way.
51		111
52	=over 4	112	=over 4
53		113
54	=item ev_tstamp ev_time ()	114	=item ev_tstamp ev_time ()
55		115
56	Returns the current time as libev would use it.	116	Returns the current time as libev would use it. Please note that the
		117	C<ev_now> function is usually faster and also often returns the timestamp
		118	you actually want to know.
		119
		120	=item ev_sleep (ev_tstamp interval)
		121
		122	Sleep for the given interval: The current thread will be blocked until
		123	either it is interrupted or the given time interval has passed. Basically
		124	this is a subsecond-resolution C<sleep ()>.
57		125
58	=item int ev_version_major ()	126	=item int ev_version_major ()
59		127
60	=item int ev_version_minor ()	128	=item int ev_version_minor ()
61		129
62	You can find out the major and minor version numbers of the library	130	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	131	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	132	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	133	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	134	version of the library your program was compiled against.
67		135
		136	These version numbers refer to the ABI version of the library, not the
		137	release version.
		138
68	Usually, it's a good idea to terminate if the major versions mismatch,	139	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	140	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	141	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	142	not a problem.
72		143
		144	Example: Make sure we haven't accidentally been linked against the wrong
		145	version.
		146
		147	assert (("libev version mismatch",
		148	ev_version_major () == EV_VERSION_MAJOR
		149	&& ev_version_minor () >= EV_VERSION_MINOR));
		150
		151	=item unsigned int ev_supported_backends ()
		152
		153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		154	value) compiled into this binary of libev (independent of their
		155	availability on the system you are running on). See C<ev_default_loop> for
		156	a description of the set values.
		157
		158	Example: make sure we have the epoll method, because yeah this is cool and
		159	a must have and can we have a torrent of it please!!!11
		160
		161	assert (("sorry, no epoll, no sex",
		162	ev_supported_backends () & EVBACKEND_EPOLL));
		163
		164	=item unsigned int ev_recommended_backends ()
		165
		166	Return the set of all backends compiled into this binary of libev and also
		167	recommended for this platform. This set is often smaller than the one
		168	returned by C<ev_supported_backends>, as for example kqueue is broken on
		169	most BSDs and will not be autodetected unless you explicitly request it
		170	(assuming you know what you are doing). This is the set of backends that
		171	libev will probe for if you specify no backends explicitly.
		172
		173	=item unsigned int ev_embeddable_backends ()
		174
		175	Returns the set of backends that are embeddable in other event loops. This
		176	is the theoretical, all-platform, value. To find which backends
		177	might be supported on the current system, you would need to look at
		178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		179	recommended ones.
		180
		181	See the description of C<ev_embed> watchers for more info.
		182
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		184
75	Sets the allocation function to use (the prototype is similar to the	185	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	186	semantics is identical - to the realloc C function). It is used to
77	and free memory (no surprises here). If it returns zero when memory	187	allocate and free memory (no surprises here). If it returns zero when
78	needs to be allocated, the library might abort or take some potentially	188	memory needs to be allocated, the library might abort or take some
79	destructive action. The default is your system realloc function.	189	potentially destructive action. The default is your system realloc
		190	function.
80		191
81	You could override this function in high-availability programs to, say,	192	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,	193	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.	194	or even to sleep a while and retry until some memory is available.
		195
		196	Example: Replace the libev allocator with one that waits a bit and then
		197	retries).
		198
		199	static void *
		200	persistent_realloc (void *ptr, size_t size)
		201	{
		202	for (;;)
		203	{
		204	void *newptr = realloc (ptr, size);
		205
		206	if (newptr)
		207	return newptr;
		208
		209	sleep (60);
		210	}
		211	}
		212
		213	...
		214	ev_set_allocator (persistent_realloc);
84		215
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	216	=item ev_set_syserr_cb (void (*cb)(const char *msg));
86		217
87	Set the callback function to call on a retryable syscall error (such	218	Set the callback function to call on a retryable syscall error (such
88	as failed select, poll, epoll_wait). The message is a printable string	219	as failed select, poll, epoll_wait). The message is a printable string
…		…
90	callback is set, then libev will expect it to remedy the sitution, no	221	callback is set, then libev will expect it to remedy the sitution, no
91	matter what, when it returns. That is, libev will generally retry the	222	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	223	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	224	(such as abort).
94		225
		226	Example: This is basically the same thing that libev does internally, too.
		227
		228	static void
		229	fatal_error (const char *msg)
		230	{
		231	perror (msg);
		232	abort ();
		233	}
		234
		235	...
		236	ev_set_syserr_cb (fatal_error);
		237
95	=back	238	=back
96		239
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		241
99	An event loop is described by a C<struct ev_loop *>. The library knows two	242	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	243	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	244	events, and dynamically created loops which do not.
102		245
103	If you use threads, a common model is to run the default event loop	246	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	247	in your main thread (or in a separate thread) and for each thread you
105	create, you also create another event loop. Libev itself does no locking	248	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	249	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	250	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).	251	done correctly, because it's hideous and inefficient).
109		252
…		…
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	255	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		256
114	This will initialise the default event loop if it hasn't been initialised	257	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	258	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	259	false. If it already was initialised it simply returns it (and ignores the
117	flags).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		261
119	If you don't know what event loop to use, use the one returned from this	262	If you don't know what event loop to use, use the one returned from this
120	function.	263	function.
121		264
122	The flags argument can be used to specify special behaviour or specific	265	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).	266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		267
125	It supports the following flags:	268	The following flags are supported:
126		269
127	=over 4	270	=over 4
128		271
129	=item C<EVFLAG_AUTO>	272	=item C<EVFLAG_AUTO>
130		273
…		…
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	282	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	283	useful to try out specific backends to test their performance, or to work
141	around bugs.	284	around bugs.
142		285
		286	=item C<EVFLAG_FORKCHECK>
		287
		288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		289	a fork, you can also make libev check for a fork in each iteration by
		290	enabling this flag.
		291
		292	This works by calling C<getpid ()> on every iteration of the loop,
		293	and thus this might slow down your event loop if you do a lot of loop
		294	iterations and little real work, but is usually not noticeable (on my
		295	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		296	without a syscall and thus I<very> fast, but my Linux system also has
		297	C<pthread_atfork> which is even faster).
		298
		299	The big advantage of this flag is that you can forget about fork (and
		300	forget about forgetting to tell libev about forking) when you use this
		301	flag.
		302
		303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		304	environment variable.
		305
143	=item C<EVMETHOD_SELECT> (portable select backend)	306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		307
		308	This is your standard select(2) backend. Not I<completely> standard, as
		309	libev tries to roll its own fd_set with no limits on the number of fds,
		310	but if that fails, expect a fairly low limit on the number of fds when
		311	using this backend. It doesn't scale too well (O(highest_fd)), but its
		312	usually the fastest backend for a low number of (low-numbered :) fds.
		313
		314	To get good performance out of this backend you need a high amount of
		315	parallelity (most of the file descriptors should be busy). If you are
		316	writing a server, you should C<accept ()> in a loop to accept as many
		317	connections as possible during one iteration. You might also want to have
		318	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		319	readyness notifications you get per iteration.
		320
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		322
147	=item C<EVMETHOD_EPOLL> (linux only)	323	And this is your standard poll(2) backend. It's more complicated
		324	than select, but handles sparse fds better and has no artificial
		325	limit on the number of fds you can use (except it will slow down
		326	considerably with a lot of inactive fds). It scales similarly to select,
		327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		328	performance tips.
148		329
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	330	=item C<EVBACKEND_EPOLL> (value 4, Linux)
150		331
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	332	For few fds, this backend is a bit little slower than poll and select,
		333	but it scales phenomenally better. While poll and select usually scale
		334	like O(total_fds) where n is the total number of fds (or the highest fd),
		335	epoll scales either O(1) or O(active_fds). The epoll design has a number
		336	of shortcomings, such as silently dropping events in some hard-to-detect
		337	cases and rewiring a syscall per fd change, no fork support and bad
		338	support for dup.
152		339
153	=item C<EVMETHOD_PORT> (solaris 10 only)	340	While stopping, setting and starting an I/O watcher in the same iteration
		341	will result in some caching, there is still a syscall per such incident
		342	(because the fd could point to a different file description now), so its
		343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		344	very well if you register events for both fds.
		345
		346	Please note that epoll sometimes generates spurious notifications, so you
		347	need to use non-blocking I/O or other means to avoid blocking when no data
		348	(or space) is available.
		349
		350	Best performance from this backend is achieved by not unregistering all
		351	watchers for a file descriptor until it has been closed, if possible, i.e.
		352	keep at least one watcher active per fd at all times.
		353
		354	While nominally embeddeble in other event loops, this feature is broken in
		355	all kernel versions tested so far.
		356
		357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		358
		359	Kqueue deserves special mention, as at the time of this writing, it
		360	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		361	with anything but sockets and pipes, except on Darwin, where of course
		362	it's completely useless). For this reason it's not being "autodetected"
		363	unless you explicitly specify it explicitly in the flags (i.e. using
		364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		365	system like NetBSD.
		366
		367	You still can embed kqueue into a normal poll or select backend and use it
		368	only for sockets (after having made sure that sockets work with kqueue on
		369	the target platform). See C<ev_embed> watchers for more info.
		370
		371	It scales in the same way as the epoll backend, but the interface to the
		372	kernel is more efficient (which says nothing about its actual speed, of
		373	course). While stopping, setting and starting an I/O watcher does never
		374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		375	two event changes per incident, support for C<fork ()> is very bad and it
		376	drops fds silently in similarly hard-to-detect cases.
		377
		378	This backend usually performs well under most conditions.
		379
		380	While nominally embeddable in other event loops, this doesn't work
		381	everywhere, so you might need to test for this. And since it is broken
		382	almost everywhere, you should only use it when you have a lot of sockets
		383	(for which it usually works), by embedding it into another event loop
		384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		385	sockets.
		386
		387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		388
		389	This is not implemented yet (and might never be, unless you send me an
		390	implementation). According to reports, C</dev/poll> only supports sockets
		391	and is not embeddable, which would limit the usefulness of this backend
		392	immensely.
		393
		394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		395
		396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		397	it's really slow, but it still scales very well (O(active_fds)).
		398
		399	Please note that solaris event ports can deliver a lot of spurious
		400	notifications, so you need to use non-blocking I/O or other means to avoid
		401	blocking when no data (or space) is available.
		402
		403	While this backend scales well, it requires one system call per active
		404	file descriptor per loop iteration. For small and medium numbers of file
		405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		406	might perform better.
		407
		408	=item C<EVBACKEND_ALL>
		409
		410	Try all backends (even potentially broken ones that wouldn't be tried
		411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		413
		414	It is definitely not recommended to use this flag.
		415
		416	=back
154		417
155	If one or more of these are ored into the flags value, then only these	418	If one or more of these are ored into the flags value, then only these
156	backends will be tried (in the reverse order as given here). If one are	419	backends will be tried (in the reverse order as given here). If none are
157	specified, any backend will do.	420	specified, most compiled-in backend will be tried, usually in reverse
		421	order of their flag values :)
158		422
159	=back	423	The most typical usage is like this:
		424
		425	if (!ev_default_loop (0))
		426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		427
		428	Restrict libev to the select and poll backends, and do not allow
		429	environment settings to be taken into account:
		430
		431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		432
		433	Use whatever libev has to offer, but make sure that kqueue is used if
		434	available (warning, breaks stuff, best use only with your own private
		435	event loop and only if you know the OS supports your types of fds):
		436
		437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		438
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	439	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		440
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	441	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	442	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	443	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).	444	undefined behaviour (or a failed assertion if assertions are enabled).
167		445
		446	Example: Try to create a event loop that uses epoll and nothing else.
		447
		448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		449	if (!epoller)
		450	fatal ("no epoll found here, maybe it hides under your chair");
		451
168	=item ev_default_destroy ()	452	=item ev_default_destroy ()
169		453
170	Destroys the default loop again (frees all memory and kernel state	454	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	455	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cannot rely on this :).	456	sense, so e.g. C<ev_is_active> might still return true. It is your
		457	responsibility to either stop all watchers cleanly yoursef I<before>
		458	calling this function, or cope with the fact afterwards (which is usually
		459	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		460	for example).
		461
		462	Note that certain global state, such as signal state, will not be freed by
		463	this function, and related watchers (such as signal and child watchers)
		464	would need to be stopped manually.
		465
		466	In general it is not advisable to call this function except in the
		467	rare occasion where you really need to free e.g. the signal handling
		468	pipe fds. If you need dynamically allocated loops it is better to use
		469	C<ev_loop_new> and C<ev_loop_destroy>).
173		470
174	=item ev_loop_destroy (loop)	471	=item ev_loop_destroy (loop)
175		472
176	Like C<ev_default_destroy>, but destroys an event loop created by an	473	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	474	earlier call to C<ev_loop_new>.
…		…
181	This function reinitialises the kernel state for backends that have	478	This function reinitialises the kernel state for backends that have
182	one. Despite the name, you can call it anytime, but it makes most sense	479	one. Despite the name, you can call it anytime, but it makes most sense
183	after forking, in either the parent or child process (or both, but that	480	after forking, in either the parent or child process (or both, but that
184	again makes little sense).	481	again makes little sense).
185		482
186	You I<must> call this function after forking if and only if you want to	483	You I<must> call this function in the child process after forking if and
187	use the event library in both processes. If you just fork+exec, you don't	484	only if you want to use the event library in both processes. If you just
188	have to call it.	485	fork+exec, you don't have to call it.
189		486
190	The function itself is quite fast and it's usually not a problem to call	487	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	488	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>:	489	quite nicely into a call to C<pthread_atfork>:
193		490
194	pthread_atfork (0, 0, ev_default_fork);	491	pthread_atfork (0, 0, ev_default_fork);
195		492
		493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		494	without calling this function, so if you force one of those backends you
		495	do not need to care.
		496
196	=item ev_loop_fork (loop)	497	=item ev_loop_fork (loop)
197		498
198	Like C<ev_default_fork>, but acts on an event loop created by	499	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	500	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.	501	after fork, and how you do this is entirely your own problem.
201		502
		503	=item unsigned int ev_loop_count (loop)
		504
		505	Returns the count of loop iterations for the loop, which is identical to
		506	the number of times libev did poll for new events. It starts at C<0> and
		507	happily wraps around with enough iterations.
		508
		509	This value can sometimes be useful as a generation counter of sorts (it
		510	"ticks" the number of loop iterations), as it roughly corresponds with
		511	C<ev_prepare> and C<ev_check> calls.
		512
202	=item unsigned int ev_method (loop)	513	=item unsigned int ev_backend (loop)
203		514
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	516	use.
206		517
207	=item ev_tstamp ev_now (loop)	518	=item ev_tstamp ev_now (loop)
208		519
209	Returns the current "event loop time", which is the time the event loop	520	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	521	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	522	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	523	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).	524	event occurring (or more correctly, libev finding out about it).
214		525
215	=item ev_loop (loop, int flags)	526	=item ev_loop (loop, int flags)
216		527
217	Finally, this is it, the event handler. This function usually is called	528	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	529	after you initialised all your watchers and you want to start handling
219	events.	530	events.
220		531
221	If the flags argument is specified as 0, it will not return until either	532	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.	533	either no event watchers are active anymore or C<ev_unloop> was called.
		534
		535	Please note that an explicit C<ev_unloop> is usually better than
		536	relying on all watchers to be stopped when deciding when a program has
		537	finished (especially in interactive programs), but having a program that
		538	automatically loops as long as it has to and no longer by virtue of
		539	relying on its watchers stopping correctly is a thing of beauty.
223		540
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	541	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	542	those events and any outstanding ones, but will not block your process in
226	case there are no events and will return after one iteration of the loop.	543	case there are no events and will return after one iteration of the loop.
227		544
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	545	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	546	neccessary) and will handle those and any outstanding ones. It will block
230	your process until at least one new event arrives, and will return after	547	your process until at least one new event arrives, and will return after
231	one iteration of the loop.	548	one iteration of the loop. This is useful if you are waiting for some
		549	external event in conjunction with something not expressible using other
		550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		551	usually a better approach for this kind of thing.
232		552
233	This flags value could be used to implement alternative looping	553	Here are the gory details of what C<ev_loop> does:
234	constructs, but the C<prepare> and C<check> watchers provide a better and	554
235	more generic mechanism.	555	- Before the first iteration, call any pending watchers.
		556	* If there are no active watchers (reference count is zero), return.
		557	- Queue all prepare watchers and then call all outstanding watchers.
		558	- If we have been forked, recreate the kernel state.
		559	- Update the kernel state with all outstanding changes.
		560	- Update the "event loop time".
		561	- Calculate for how long to block.
		562	- Block the process, waiting for any events.
		563	- Queue all outstanding I/O (fd) events.
		564	- Update the "event loop time" and do time jump handling.
		565	- Queue all outstanding timers.
		566	- Queue all outstanding periodics.
		567	- If no events are pending now, queue all idle watchers.
		568	- Queue all check watchers.
		569	- Call all queued watchers in reverse order (i.e. check watchers first).
		570	Signals and child watchers are implemented as I/O watchers, and will
		571	be handled here by queueing them when their watcher gets executed.
		572	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		573	were used, return, otherwise continue with step *.
		574
		575	Example: Queue some jobs and then loop until no events are outsanding
		576	anymore.
		577
		578	... queue jobs here, make sure they register event watchers as long
		579	... as they still have work to do (even an idle watcher will do..)
		580	ev_loop (my_loop, 0);
		581	... jobs done. yeah!
236		582
237	=item ev_unloop (loop, how)	583	=item ev_unloop (loop, how)
238		584
239	Can be used to make a call to C<ev_loop> return early (but only after it	585	Can be used to make a call to C<ev_loop> return early (but only after it
240	has processed all outstanding events). The C<how> argument must be either	586	has processed all outstanding events). The C<how> argument must be either
241	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	587	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
242	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	588	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
243		589
244	=item ev_ref (loop)	590	=item ev_ref (loop)
245		591
246	=item ev_unref (loop)	592	=item ev_unref (loop)
…		…
254	visible to the libev user and should not keep C<ev_loop> from exiting if	600	visible to the libev user and should not keep C<ev_loop> from exiting if
255	no event watchers registered by it are active. It is also an excellent	601	no event watchers registered by it are active. It is also an excellent
256	way to do this for generic recurring timers or from within third-party	602	way to do this for generic recurring timers or from within third-party
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	603	libraries. Just remember to I<unref after start> and I<ref before stop>.
258		604
		605	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		606	running when nothing else is active.
		607
		608	struct ev_signal exitsig;
		609	ev_signal_init (&exitsig, sig_cb, SIGINT);
		610	ev_signal_start (loop, &exitsig);
		611	evf_unref (loop);
		612
		613	Example: For some weird reason, unregister the above signal handler again.
		614
		615	ev_ref (loop);
		616	ev_signal_stop (loop, &exitsig);
		617
		618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		619
		620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		621
		622	These advanced functions influence the time that libev will spend waiting
		623	for events. Both are by default C<0>, meaning that libev will try to
		624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		625
		626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		627	allows libev to delay invocation of I/O and timer/periodic callbacks to
		628	increase efficiency of loop iterations.
		629
		630	The background is that sometimes your program runs just fast enough to
		631	handle one (or very few) event(s) per loop iteration. While this makes
		632	the program responsive, it also wastes a lot of CPU time to poll for new
		633	events, especially with backends like C<select ()> which have a high
		634	overhead for the actual polling but can deliver many events at once.
		635
		636	By setting a higher I<io collect interval> you allow libev to spend more
		637	time collecting I/O events, so you can handle more events per iteration,
		638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		639	C<ev_timer>) will be not affected. Setting this to a non-null value will
		640	introduce an additional C<ev_sleep ()> call into most loop iterations.
		641
		642	Likewise, by setting a higher I<timeout collect interval> you allow libev
		643	to spend more time collecting timeouts, at the expense of increased
		644	latency (the watcher callback will be called later). C<ev_io> watchers
		645	will not be affected. Setting this to a non-null value will not introduce
		646	any overhead in libev.
		647
		648	Many (busy) programs can usually benefit by setting the io collect
		649	interval to a value near C<0.1> or so, which is often enough for
		650	interactive servers (of course not for games), likewise for timeouts. It
		651	usually doesn't make much sense to set it to a lower value than C<0.01>,
		652	as this approsaches the timing granularity of most systems.
		653
259	=back	654	=back
		655
260		656
261	=head1 ANATOMY OF A WATCHER	657	=head1 ANATOMY OF A WATCHER
262		658
263	A watcher is a structure that you create and register to record your	659	A watcher is a structure that you create and register to record your
264	interest in some event. For instance, if you want to wait for STDIN to	660	interest in some event. For instance, if you want to wait for STDIN to
…		…
297	*) >>), and you can stop watching for events at any time by calling the	693	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
299		695
300	As long as your watcher is active (has been started but not stopped) you	696	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	697	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	698	reinitialise it or call its C<set> macro.
303
304	You can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		699
309	Each and every callback receives the event loop pointer as first, the	700	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	701	registered watcher structure as second, and a bitset of received events as
311	third argument.	702	third argument.
312		703
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	727	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		728
338	=item C<EV_CHILD>	729	=item C<EV_CHILD>
339		730
340	The pid specified in the C<ev_child> watcher has received a status change.	731	The pid specified in the C<ev_child> watcher has received a status change.
		732
		733	=item C<EV_STAT>
		734
		735	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		736
342	=item C<EV_IDLE>	737	=item C<EV_IDLE>
343		738
344	The C<ev_idle> watcher has determined that you have nothing better to do.	739	The C<ev_idle> watcher has determined that you have nothing better to do.
345		740
…		…
353	received events. Callbacks of both watcher types can start and stop as	748	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	749	many watchers as they want, and all of them will be taken into account
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	750	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	751	C<ev_loop> from blocking).
357		752
		753	=item C<EV_EMBED>
		754
		755	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		756
		757	=item C<EV_FORK>
		758
		759	The event loop has been resumed in the child process after fork (see
		760	C<ev_fork>).
		761
358	=item C<EV_ERROR>	762	=item C<EV_ERROR>
359		763
360	An unspecified error has occured, the watcher has been stopped. This might	764	An unspecified error has occured, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	765	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	766	ran out of memory, a file descriptor was found to be closed or any other
…		…
368	your callbacks is well-written it can just attempt the operation and cope	772	your callbacks is well-written it can just attempt the operation and cope
369	with the error from read() or write(). This will not work in multithreaded	773	with the error from read() or write(). This will not work in multithreaded
370	programs, though, so beware.	774	programs, though, so beware.
371		775
372	=back	776	=back
		777
		778	=head2 GENERIC WATCHER FUNCTIONS
		779
		780	In the following description, C<TYPE> stands for the watcher type,
		781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		782
		783	=over 4
		784
		785	=item C<ev_init> (ev_TYPE *watcher, callback)
		786
		787	This macro initialises the generic portion of a watcher. The contents
		788	of the watcher object can be arbitrary (so C<malloc> will do). Only
		789	the generic parts of the watcher are initialised, you I<need> to call
		790	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		791	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		792	which rolls both calls into one.
		793
		794	You can reinitialise a watcher at any time as long as it has been stopped
		795	(or never started) and there are no pending events outstanding.
		796
		797	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		798	int revents)>.
		799
		800	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		801
		802	This macro initialises the type-specific parts of a watcher. You need to
		803	call C<ev_init> at least once before you call this macro, but you can
		804	call C<ev_TYPE_set> any number of times. You must not, however, call this
		805	macro on a watcher that is active (it can be pending, however, which is a
		806	difference to the C<ev_init> macro).
		807
		808	Although some watcher types do not have type-specific arguments
		809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		810
		811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		812
		813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		814	calls into a single call. This is the most convinient method to initialise
		815	a watcher. The same limitations apply, of course.
		816
		817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		818
		819	Starts (activates) the given watcher. Only active watchers will receive
		820	events. If the watcher is already active nothing will happen.
		821
		822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		823
		824	Stops the given watcher again (if active) and clears the pending
		825	status. It is possible that stopped watchers are pending (for example,
		826	non-repeating timers are being stopped when they become pending), but
		827	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		828	you want to free or reuse the memory used by the watcher it is therefore a
		829	good idea to always call its C<ev_TYPE_stop> function.
		830
		831	=item bool ev_is_active (ev_TYPE *watcher)
		832
		833	Returns a true value iff the watcher is active (i.e. it has been started
		834	and not yet been stopped). As long as a watcher is active you must not modify
		835	it.
		836
		837	=item bool ev_is_pending (ev_TYPE *watcher)
		838
		839	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		840	events but its callback has not yet been invoked). As long as a watcher
		841	is pending (but not active) you must not call an init function on it (but
		842	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		843	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		844	it).
		845
		846	=item callback ev_cb (ev_TYPE *watcher)
		847
		848	Returns the callback currently set on the watcher.
		849
		850	=item ev_cb_set (ev_TYPE *watcher, callback)
		851
		852	Change the callback. You can change the callback at virtually any time
		853	(modulo threads).
		854
		855	=item ev_set_priority (ev_TYPE *watcher, priority)
		856
		857	=item int ev_priority (ev_TYPE *watcher)
		858
		859	Set and query the priority of the watcher. The priority is a small
		860	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		861	(default: C<-2>). Pending watchers with higher priority will be invoked
		862	before watchers with lower priority, but priority will not keep watchers
		863	from being executed (except for C<ev_idle> watchers).
		864
		865	This means that priorities are I<only> used for ordering callback
		866	invocation after new events have been received. This is useful, for
		867	example, to reduce latency after idling, or more often, to bind two
		868	watchers on the same event and make sure one is called first.
		869
		870	If you need to suppress invocation when higher priority events are pending
		871	you need to look at C<ev_idle> watchers, which provide this functionality.
		872
		873	You I<must not> change the priority of a watcher as long as it is active or
		874	pending.
		875
		876	The default priority used by watchers when no priority has been set is
		877	always C<0>, which is supposed to not be too high and not be too low :).
		878
		879	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		880	fine, as long as you do not mind that the priority value you query might
		881	or might not have been adjusted to be within valid range.
		882
		883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		884
		885	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		886	C<loop> nor C<revents> need to be valid as long as the watcher callback
		887	can deal with that fact.
		888
		889	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		890
		891	If the watcher is pending, this function returns clears its pending status
		892	and returns its C<revents> bitset (as if its callback was invoked). If the
		893	watcher isn't pending it does nothing and returns C<0>.
		894
		895	=back
		896
373		897
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		899
376	Each watcher has, by default, a member C<void *data> that you can change	900	Each watcher has, by default, a member C<void *data> that you can change
377	and read at any time, libev will completely ignore it. This can be used	901	and read at any time, libev will completely ignore it. This can be used
…		…
395	{	919	{
396	struct my_io *w = (struct my_io *)w_;	920	struct my_io *w = (struct my_io *)w_;
397	...	921	...
398	}	922	}
399		923
400	More interesting and less C-conformant ways of catsing your callback type	924	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	925	instead have been omitted.
		926
		927	Another common scenario is having some data structure with multiple
		928	watchers:
		929
		930	struct my_biggy
		931	{
		932	int some_data;
		933	ev_timer t1;
		934	ev_timer t2;
		935	}
		936
		937	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		938	you need to use C<offsetof>:
		939
		940	#include <stddef.h>
		941
		942	static void
		943	t1_cb (EV_P_ struct ev_timer *w, int revents)
		944	{
		945	struct my_biggy big = (struct my_biggy *
		946	(((char *)w) - offsetof (struct my_biggy, t1));
		947	}
		948
		949	static void
		950	t2_cb (EV_P_ struct ev_timer *w, int revents)
		951	{
		952	struct my_biggy big = (struct my_biggy *
		953	(((char *)w) - offsetof (struct my_biggy, t2));
		954	}
402		955
403		956
404	=head1 WATCHER TYPES	957	=head1 WATCHER TYPES
405		958
406	This section describes each watcher in detail, but will not repeat	959	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	960	information given in the last section. Any initialisation/set macros,
		961	functions and members specific to the watcher type are explained.
408		962
		963	Members are additionally marked with either I<[read-only]>, meaning that,
		964	while the watcher is active, you can look at the member and expect some
		965	sensible content, but you must not modify it (you can modify it while the
		966	watcher is stopped to your hearts content), or I<[read-write]>, which
		967	means you can expect it to have some sensible content while the watcher
		968	is active, but you can also modify it. Modifying it may not do something
		969	sensible or take immediate effect (or do anything at all), but libev will
		970	not crash or malfunction in any way.
		971
		972
409	=head2 C<ev_io> - is this file descriptor readable or writable	973	=head2 C<ev_io> - is this file descriptor readable or writable?
410		974
411	I/O watchers check whether a file descriptor is readable or writable	975	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	976	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	977	would not block the process and writing would at least be able to write
414	condition persists. Remember you can stop the watcher if you don't want to	978	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	979	receiving events as long as the condition persists. Remember you can stop
		980	the watcher if you don't want to act on the event and neither want to
		981	receive future events.
416		982
417	In general you can register as many read and/or write event watchers oer	983	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	984	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	985	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	986	required if you know what you are doing).
421		987
422	You have to be careful with dup'ed file descriptors, though. Some backends
423	(the linux epoll backend is a notable example) cannot handle dup'ed file
424	descriptors correctly if you register interest in two or more fds pointing
425	to the same file/socket etc. description.
426
427	If you must do this, then force the use of a known-to-be-good backend	988	If you must do this, then force the use of a known-to-be-good backend
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	989	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
429	EVMETHOD_POLL).	990	C<EVBACKEND_POLL>).
		991
		992	Another thing you have to watch out for is that it is quite easy to
		993	receive "spurious" readyness notifications, that is your callback might
		994	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		995	because there is no data. Not only are some backends known to create a
		996	lot of those (for example solaris ports), it is very easy to get into
		997	this situation even with a relatively standard program structure. Thus
		998	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		999	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1000
		1001	If you cannot run the fd in non-blocking mode (for example you should not
		1002	play around with an Xlib connection), then you have to seperately re-test
		1003	whether a file descriptor is really ready with a known-to-be good interface
		1004	such as poll (fortunately in our Xlib example, Xlib already does this on
		1005	its own, so its quite safe to use).
		1006
		1007	=head3 The special problem of disappearing file descriptors
		1008
		1009	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1010	descriptor (either by calling C<close> explicitly or by any other means,
		1011	such as C<dup>). The reason is that you register interest in some file
		1012	descriptor, but when it goes away, the operating system will silently drop
		1013	this interest. If another file descriptor with the same number then is
		1014	registered with libev, there is no efficient way to see that this is, in
		1015	fact, a different file descriptor.
		1016
		1017	To avoid having to explicitly tell libev about such cases, libev follows
		1018	the following policy: Each time C<ev_io_set> is being called, libev
		1019	will assume that this is potentially a new file descriptor, otherwise
		1020	it is assumed that the file descriptor stays the same. That means that
		1021	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1022	descriptor even if the file descriptor number itself did not change.
		1023
		1024	This is how one would do it normally anyway, the important point is that
		1025	the libev application should not optimise around libev but should leave
		1026	optimisations to libev.
		1027
		1028	=head3 The special problem of dup'ed file descriptors
		1029
		1030	Some backends (e.g. epoll), cannot register events for file descriptors,
		1031	but only events for the underlying file descriptions. That means when you
		1032	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1033	events for them, only one file descriptor might actually receive events.
		1034
		1035	There is no workaround possible except not registering events
		1036	for potentially C<dup ()>'ed file descriptors, or to resort to
		1037	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1038
		1039	=head3 The special problem of fork
		1040
		1041	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1042	useless behaviour. Libev fully supports fork, but needs to be told about
		1043	it in the child.
		1044
		1045	To support fork in your programs, you either have to call
		1046	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1047	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1048	C<EVBACKEND_POLL>.
		1049
		1050
		1051	=head3 Watcher-Specific Functions
430		1052
431	=over 4	1053	=over 4
432		1054
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1055	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1056
435	=item ev_io_set (ev_io *, int fd, int events)	1057	=item ev_io_set (ev_io *, int fd, int events)
436		1058
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1059	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1060	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1061	C<EV_READ | EV_WRITE> to receive the given events.
		1062
		1063	=item int fd [read-only]
		1064
		1065	The file descriptor being watched.
		1066
		1067	=item int events [read-only]
		1068
		1069	The events being watched.
440		1070
441	=back	1071	=back
442		1072
		1073	=head3 Examples
		1074
		1075	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1076	readable, but only once. Since it is likely line-buffered, you could
		1077	attempt to read a whole line in the callback.
		1078
		1079	static void
		1080	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1081	{
		1082	ev_io_stop (loop, w);
		1083	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1084	}
		1085
		1086	...
		1087	struct ev_loop *loop = ev_default_init (0);
		1088	struct ev_io stdin_readable;
		1089	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1090	ev_io_start (loop, &stdin_readable);
		1091	ev_loop (loop, 0);
		1092
		1093
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1094	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1095
445	Timer watchers are simple relative timers that generate an event after a	1096	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1097	given time, and optionally repeating in regular intervals after that.
447		1098
448	The timers are based on real time, that is, if you register an event that	1099	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1100	times out after an hour and you reset your system clock to last years
450	time, it will still time out after (roughly) and hour. "Roughly" because	1101	time, it will still time out after (roughly) and hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1102	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1103	monotonic clock option helps a lot here).
453		1104
454	The relative timeouts are calculated relative to the C<ev_now ()>	1105	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	1106	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	1107	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	1108	you suspect event processing to be delayed and you I<need> to base the timeout
458	ion the current time, use something like this to adjust for this:	1109	on the current time, use something like this to adjust for this:
459		1110
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1111	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1112
		1113	The callback is guarenteed to be invoked only when its timeout has passed,
		1114	but if multiple timers become ready during the same loop iteration then
		1115	order of execution is undefined.
		1116
		1117	=head3 Watcher-Specific Functions and Data Members
461		1118
462	=over 4	1119	=over 4
463		1120
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1121	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1122
…		…
471	later, again, and again, until stopped manually.	1128	later, again, and again, until stopped manually.
472		1129
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1130	The timer itself will do a best-effort at avoiding drift, that is, if you
474	configure a timer to trigger every 10 seconds, then it will trigger at	1131	configure a timer to trigger every 10 seconds, then it will trigger at
475	exactly 10 second intervals. If, however, your program cannot keep up with	1132	exactly 10 second intervals. If, however, your program cannot keep up with
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1133	the timer (because it takes longer than those 10 seconds to do stuff) the
477	timer will not fire more than once per event loop iteration.	1134	timer will not fire more than once per event loop iteration.
478		1135
479	=item ev_timer_again (loop)	1136	=item ev_timer_again (loop)
480		1137
481	This will act as if the timer timed out and restart it again if it is	1138	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1139	repeating. The exact semantics are:
483		1140
		1141	If the timer is pending, its pending status is cleared.
		1142
484	If the timer is started but nonrepeating, stop it.	1143	If the timer is started but nonrepeating, stop it (as if it timed out).
485		1144
486	If the timer is repeating, either start it if necessary (with the repeat	1145	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1146	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1147
489	This sounds a bit complicated, but here is a useful and typical	1148	This sounds a bit complicated, but here is a useful and typical
490	example: Imagine you have a tcp connection and you want a so-called idle	1149	example: Imagine you have a tcp connection and you want a so-called idle
491	timeout, that is, you want to be called when there have been, say, 60	1150	timeout, that is, you want to be called when there have been, say, 60
492	seconds of inactivity on the socket. The easiest way to do this is to	1151	seconds of inactivity on the socket. The easiest way to do this is to
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1152	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
494	time you successfully read or write some data. If you go into an idle	1153	C<ev_timer_again> each time you successfully read or write some data. If
495	state where you do not expect data to travel on the socket, you can stop	1154	you go into an idle state where you do not expect data to travel on the
496	the timer, and again will automatically restart it if need be.	1155	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1156	automatically restart it if need be.
		1157
		1158	That means you can ignore the C<after> value and C<ev_timer_start>
		1159	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1160
		1161	ev_timer_init (timer, callback, 0., 5.);
		1162	ev_timer_again (loop, timer);
		1163	...
		1164	timer->again = 17.;
		1165	ev_timer_again (loop, timer);
		1166	...
		1167	timer->again = 10.;
		1168	ev_timer_again (loop, timer);
		1169
		1170	This is more slightly efficient then stopping/starting the timer each time
		1171	you want to modify its timeout value.
		1172
		1173	=item ev_tstamp repeat [read-write]
		1174
		1175	The current C<repeat> value. Will be used each time the watcher times out
		1176	or C<ev_timer_again> is called and determines the next timeout (if any),
		1177	which is also when any modifications are taken into account.
497		1178
498	=back	1179	=back
499		1180
		1181	=head3 Examples
		1182
		1183	Example: Create a timer that fires after 60 seconds.
		1184
		1185	static void
		1186	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1187	{
		1188	.. one minute over, w is actually stopped right here
		1189	}
		1190
		1191	struct ev_timer mytimer;
		1192	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1193	ev_timer_start (loop, &mytimer);
		1194
		1195	Example: Create a timeout timer that times out after 10 seconds of
		1196	inactivity.
		1197
		1198	static void
		1199	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1200	{
		1201	.. ten seconds without any activity
		1202	}
		1203
		1204	struct ev_timer mytimer;
		1205	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1206	ev_timer_again (&mytimer); /* start timer */
		1207	ev_loop (loop, 0);
		1208
		1209	// and in some piece of code that gets executed on any "activity":
		1210	// reset the timeout to start ticking again at 10 seconds
		1211	ev_timer_again (&mytimer);
		1212
		1213
500	=head2 C<ev_periodic> - to cron or not to cron	1214	=head2 C<ev_periodic> - to cron or not to cron?
501		1215
502	Periodic watchers are also timers of a kind, but they are very versatile	1216	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1217	(and unfortunately a bit complex).
504		1218
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1219	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506	but on wallclock time (absolute time). You can tell a periodic watcher	1220	but on wallclock time (absolute time). You can tell a periodic watcher
507	to trigger "at" some specific point in time. For example, if you tell a	1221	to trigger "at" some specific point in time. For example, if you tell a
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1222	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
509	+ 10.>) and then reset your system clock to the last year, then it will	1223	+ 10.>) and then reset your system clock to the last year, then it will
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1224	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
511	roughly 10 seconds later and of course not if you reset your system time	1225	roughly 10 seconds later).
512	again).
513		1226
514	They can also be used to implement vastly more complex timers, such as	1227	They can also be used to implement vastly more complex timers, such as
515	triggering an event on eahc midnight, local time.	1228	triggering an event on each midnight, local time or other, complicated,
		1229	rules.
		1230
		1231	As with timers, the callback is guarenteed to be invoked only when the
		1232	time (C<at>) has been passed, but if multiple periodic timers become ready
		1233	during the same loop iteration then order of execution is undefined.
		1234
		1235	=head3 Watcher-Specific Functions and Data Members
516		1236
517	=over 4	1237	=over 4
518		1238
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1239	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520		1240
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1241	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522		1242
523	Lots of arguments, lets sort it out... There are basically three modes of	1243	Lots of arguments, lets sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	1244	operation, and we will explain them from simplest to complex:
525		1245
526
527	=over 4	1246	=over 4
528		1247
529	=item * absolute timer (interval = reschedule_cb = 0)	1248	=item * absolute timer (at = time, interval = reschedule_cb = 0)
530		1249
531	In this configuration the watcher triggers an event at the wallclock time	1250	In this configuration the watcher triggers an event at the wallclock time
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1251	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
533	that is, if it is to be run at January 1st 2011 then it will run when the	1252	that is, if it is to be run at January 1st 2011 then it will run when the
534	system time reaches or surpasses this time.	1253	system time reaches or surpasses this time.
535		1254
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1255	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
537		1256
538	In this mode the watcher will always be scheduled to time out at the next	1257	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	1258	C<at + N * interval> time (for some integer N, which can also be negative)
540	of any time jumps.	1259	and then repeat, regardless of any time jumps.
541		1260
542	This can be used to create timers that do not drift with respect to system	1261	This can be used to create timers that do not drift with respect to system
543	time:	1262	time:
544		1263
545	ev_periodic_set (&periodic, 0., 3600., 0);	1264	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
551		1270
552	Another way to think about it (for the mathematically inclined) is that	1271	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	1272	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	1273	time where C<time = at (mod interval)>, regardless of any time jumps.
555		1274
		1275	For numerical stability it is preferable that the C<at> value is near
		1276	C<ev_now ()> (the current time), but there is no range requirement for
		1277	this value.
		1278
556	=item * manual reschedule mode (reschedule_cb = callback)	1279	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
557		1280
558	In this mode the values for C<interval> and C<at> are both being	1281	In this mode the values for C<interval> and C<at> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	1282	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	1283	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	1284	current time as second argument.
562		1285
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1286	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
564	periodic watcher, ever, or make any event loop modifications>. If you need	1287	ever, or make any event loop modifications>. If you need to stop it,
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	1288	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
566		1289	starting an C<ev_prepare> watcher, which is legal).
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569		1290
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1291	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
571	ev_tstamp now)>, e.g.:	1292	ev_tstamp now)>, e.g.:
572		1293
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1294	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
578	It must return the next time to trigger, based on the passed time value	1299	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	1300	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	1301	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	1302	might be called at other times, too.
582		1303
		1304	NOTE: I<< This callback must always return a time that is later than the
		1305	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
		1306
583	This can be used to create very complex timers, such as a timer that	1307	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	1308	triggers on each midnight, local time. To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	1309	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	1310	you do this is, again, up to you (but it is not trivial, which is the main
		1311	reason I omitted it as an example).
587		1312
588	=back	1313	=back
589		1314
590	=item ev_periodic_again (loop, ev_periodic *)	1315	=item ev_periodic_again (loop, ev_periodic *)
591		1316
592	Simply stops and restarts the periodic watcher again. This is only useful	1317	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	1318	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	1319	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	1320	program when the crontabs have changed).
596		1321
		1322	=item ev_tstamp offset [read-write]
		1323
		1324	When repeating, this contains the offset value, otherwise this is the
		1325	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1326
		1327	Can be modified any time, but changes only take effect when the periodic
		1328	timer fires or C<ev_periodic_again> is being called.
		1329
		1330	=item ev_tstamp interval [read-write]
		1331
		1332	The current interval value. Can be modified any time, but changes only
		1333	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1334	called.
		1335
		1336	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1337
		1338	The current reschedule callback, or C<0>, if this functionality is
		1339	switched off. Can be changed any time, but changes only take effect when
		1340	the periodic timer fires or C<ev_periodic_again> is being called.
		1341
		1342	=item ev_tstamp at [read-only]
		1343
		1344	When active, contains the absolute time that the watcher is supposed to
		1345	trigger next.
		1346
597	=back	1347	=back
598		1348
		1349	=head3 Examples
		1350
		1351	Example: Call a callback every hour, or, more precisely, whenever the
		1352	system clock is divisible by 3600. The callback invocation times have
		1353	potentially a lot of jittering, but good long-term stability.
		1354
		1355	static void
		1356	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1357	{
		1358	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1359	}
		1360
		1361	struct ev_periodic hourly_tick;
		1362	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1363	ev_periodic_start (loop, &hourly_tick);
		1364
		1365	Example: The same as above, but use a reschedule callback to do it:
		1366
		1367	#include <math.h>
		1368
		1369	static ev_tstamp
		1370	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1371	{
		1372	return fmod (now, 3600.) + 3600.;
		1373	}
		1374
		1375	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1376
		1377	Example: Call a callback every hour, starting now:
		1378
		1379	struct ev_periodic hourly_tick;
		1380	ev_periodic_init (&hourly_tick, clock_cb,
		1381	fmod (ev_now (loop), 3600.), 3600., 0);
		1382	ev_periodic_start (loop, &hourly_tick);
		1383
		1384
599	=head2 C<ev_signal> - signal me when a signal gets signalled	1385	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		1386
601	Signal watchers will trigger an event when the process receives a specific	1387	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	1388	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	1389	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	1390	normal event processing, like any other event.
…		…
608	with the kernel (thus it coexists with your own signal handlers as long	1394	with the kernel (thus it coexists with your own signal handlers as long
609	as you don't register any with libev). Similarly, when the last signal	1395	as you don't register any with libev). Similarly, when the last signal
610	watcher for a signal is stopped libev will reset the signal handler to	1396	watcher for a signal is stopped libev will reset the signal handler to
611	SIG_DFL (regardless of what it was set to before).	1397	SIG_DFL (regardless of what it was set to before).
612		1398
		1399	=head3 Watcher-Specific Functions and Data Members
		1400
613	=over 4	1401	=over 4
614		1402
615	=item ev_signal_init (ev_signal *, callback, int signum)	1403	=item ev_signal_init (ev_signal *, callback, int signum)
616		1404
617	=item ev_signal_set (ev_signal *, int signum)	1405	=item ev_signal_set (ev_signal *, int signum)
618		1406
619	Configures the watcher to trigger on the given signal number (usually one	1407	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	1408	of the C<SIGxxx> constants).
621		1409
		1410	=item int signum [read-only]
		1411
		1412	The signal the watcher watches out for.
		1413
622	=back	1414	=back
623		1415
		1416
624	=head2 C<ev_child> - wait for pid status changes	1417	=head2 C<ev_child> - watch out for process status changes
625		1418
626	Child watchers trigger when your process receives a SIGCHLD in response to	1419	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	1420	some child status changes (most typically when a child of yours dies).
		1421
		1422	=head3 Watcher-Specific Functions and Data Members
628		1423
629	=over 4	1424	=over 4
630		1425
631	=item ev_child_init (ev_child *, callback, int pid)	1426	=item ev_child_init (ev_child *, callback, int pid)
632		1427
…		…
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	1432	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	1433	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	1434	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	1435	process causing the status change.
641		1436
		1437	=item int pid [read-only]
		1438
		1439	The process id this watcher watches out for, or C<0>, meaning any process id.
		1440
		1441	=item int rpid [read-write]
		1442
		1443	The process id that detected a status change.
		1444
		1445	=item int rstatus [read-write]
		1446
		1447	The process exit/trace status caused by C<rpid> (see your systems
		1448	C<waitpid> and C<sys/wait.h> documentation for details).
		1449
642	=back	1450	=back
643		1451
		1452	=head3 Examples
		1453
		1454	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1455
		1456	static void
		1457	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1458	{
		1459	ev_unloop (loop, EVUNLOOP_ALL);
		1460	}
		1461
		1462	struct ev_signal signal_watcher;
		1463	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1464	ev_signal_start (loop, &sigint_cb);
		1465
		1466
		1467	=head2 C<ev_stat> - did the file attributes just change?
		1468
		1469	This watches a filesystem path for attribute changes. That is, it calls
		1470	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1471	compared to the last time, invoking the callback if it did.
		1472
		1473	The path does not need to exist: changing from "path exists" to "path does
		1474	not exist" is a status change like any other. The condition "path does
		1475	not exist" is signified by the C<st_nlink> field being zero (which is
		1476	otherwise always forced to be at least one) and all the other fields of
		1477	the stat buffer having unspecified contents.
		1478
		1479	The path I<should> be absolute and I<must not> end in a slash. If it is
		1480	relative and your working directory changes, the behaviour is undefined.
		1481
		1482	Since there is no standard to do this, the portable implementation simply
		1483	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1484	can specify a recommended polling interval for this case. If you specify
		1485	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1486	unspecified default> value will be used (which you can expect to be around
		1487	five seconds, although this might change dynamically). Libev will also
		1488	impose a minimum interval which is currently around C<0.1>, but thats
		1489	usually overkill.
		1490
		1491	This watcher type is not meant for massive numbers of stat watchers,
		1492	as even with OS-supported change notifications, this can be
		1493	resource-intensive.
		1494
		1495	At the time of this writing, only the Linux inotify interface is
		1496	implemented (implementing kqueue support is left as an exercise for the
		1497	reader). Inotify will be used to give hints only and should not change the
		1498	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1499	to fall back to regular polling again even with inotify, but changes are
		1500	usually detected immediately, and if the file exists there will be no
		1501	polling.
		1502
		1503	=head3 Inotify
		1504
		1505	When C<inotify (7)> support has been compiled into libev (generally only
		1506	available on Linux) and present at runtime, it will be used to speed up
		1507	change detection where possible. The inotify descriptor will be created lazily
		1508	when the first C<ev_stat> watcher is being started.
		1509
		1510	Inotify presense does not change the semantics of C<ev_stat> watchers
		1511	except that changes might be detected earlier, and in some cases, to avoid
		1512	making regular C<stat> calls. Even in the presense of inotify support
		1513	there are many cases where libev has to resort to regular C<stat> polling.
		1514
		1515	(There is no support for kqueue, as apparently it cannot be used to
		1516	implement this functionality, due to the requirement of having a file
		1517	descriptor open on the object at all times).
		1518
		1519	=head3 The special problem of stat time resolution
		1520
		1521	The C<stat ()> syscall only supports full-second resolution portably, and
		1522	even on systems where the resolution is higher, many filesystems still
		1523	only support whole seconds.
		1524
		1525	That means that, if the time is the only thing that changes, you might
		1526	miss updates: on the first update, C<ev_stat> detects a change and calls
		1527	your callback, which does something. When there is another update within
		1528	the same second, C<ev_stat> will be unable to detect it.
		1529
		1530	The solution to this is to delay acting on a change for a second (or till
		1531	the next second boundary), using a roughly one-second delay C<ev_timer>
		1532	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1533	is added to work around small timing inconsistencies of some operating
		1534	systems.
		1535
		1536	=head3 Watcher-Specific Functions and Data Members
		1537
		1538	=over 4
		1539
		1540	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1541
		1542	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1543
		1544	Configures the watcher to wait for status changes of the given
		1545	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1546	be detected and should normally be specified as C<0> to let libev choose
		1547	a suitable value. The memory pointed to by C<path> must point to the same
		1548	path for as long as the watcher is active.
		1549
		1550	The callback will be receive C<EV_STAT> when a change was detected,
		1551	relative to the attributes at the time the watcher was started (or the
		1552	last change was detected).
		1553
		1554	=item ev_stat_stat (ev_stat *)
		1555
		1556	Updates the stat buffer immediately with new values. If you change the
		1557	watched path in your callback, you could call this fucntion to avoid
		1558	detecting this change (while introducing a race condition). Can also be
		1559	useful simply to find out the new values.
		1560
		1561	=item ev_statdata attr [read-only]
		1562
		1563	The most-recently detected attributes of the file. Although the type is of
		1564	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1565	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1566	was some error while C<stat>ing the file.
		1567
		1568	=item ev_statdata prev [read-only]
		1569
		1570	The previous attributes of the file. The callback gets invoked whenever
		1571	C<prev> != C<attr>.
		1572
		1573	=item ev_tstamp interval [read-only]
		1574
		1575	The specified interval.
		1576
		1577	=item const char *path [read-only]
		1578
		1579	The filesystem path that is being watched.
		1580
		1581	=back
		1582
		1583	=head3 Examples
		1584
		1585	Example: Watch C</etc/passwd> for attribute changes.
		1586
		1587	static void
		1588	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1589	{
		1590	/* /etc/passwd changed in some way */
		1591	if (w->attr.st_nlink)
		1592	{
		1593	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1594	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1595	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1596	}
		1597	else
		1598	/* you shalt not abuse printf for puts */
		1599	puts ("wow, /etc/passwd is not there, expect problems. "
		1600	"if this is windows, they already arrived\n");
		1601	}
		1602
		1603	...
		1604	ev_stat passwd;
		1605
		1606	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1607	ev_stat_start (loop, &passwd);
		1608
		1609	Example: Like above, but additionally use a one-second delay so we do not
		1610	miss updates (however, frequent updates will delay processing, too, so
		1611	one might do the work both on C<ev_stat> callback invocation I<and> on
		1612	C<ev_timer> callback invocation).
		1613
		1614	static ev_stat passwd;
		1615	static ev_timer timer;
		1616
		1617	static void
		1618	timer_cb (EV_P_ ev_timer *w, int revents)
		1619	{
		1620	ev_timer_stop (EV_A_ w);
		1621
		1622	/* now it's one second after the most recent passwd change */
		1623	}
		1624
		1625	static void
		1626	stat_cb (EV_P_ ev_stat *w, int revents)
		1627	{
		1628	/* reset the one-second timer */
		1629	ev_timer_again (EV_A_ &timer);
		1630	}
		1631
		1632	...
		1633	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1634	ev_stat_start (loop, &passwd);
		1635	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1636
		1637
644	=head2 C<ev_idle> - when you've got nothing better to do	1638	=head2 C<ev_idle> - when you've got nothing better to do...
645		1639
646	Idle watchers trigger events when there are no other events are pending	1640	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	1641	priority are pending (prepare, check and other idle watchers do not
648	as your process is busy handling sockets or timeouts (or even signals,	1642	count).
649	imagine) it will not be triggered. But when your process is idle all idle	1643
650	watchers are being called again and again, once per event loop iteration -	1644	That is, as long as your process is busy handling sockets or timeouts
		1645	(or even signals, imagine) of the same or higher priority it will not be
		1646	triggered. But when your process is idle (or only lower-priority watchers
		1647	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	1648	iteration - until stopped, that is, or your process receives more events
652	busy.	1649	and becomes busy again with higher priority stuff.
653		1650
654	The most noteworthy effect is that as long as any idle watchers are	1651	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	1652	active, the process will not block when waiting for new events.
656		1653
657	Apart from keeping your process non-blocking (which is a useful	1654	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	1655	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	1656	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	1657	event loop has handled all outstanding events.
661		1658
		1659	=head3 Watcher-Specific Functions and Data Members
		1660
662	=over 4	1661	=over 4
663		1662
664	=item ev_idle_init (ev_signal *, callback)	1663	=item ev_idle_init (ev_signal *, callback)
665		1664
666	Initialises and configures the idle watcher - it has no parameters of any	1665	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1666	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	1667	believe me.
669		1668
670	=back	1669	=back
671		1670
		1671	=head3 Examples
		1672
		1673	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1674	callback, free it. Also, use no error checking, as usual.
		1675
		1676	static void
		1677	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1678	{
		1679	free (w);
		1680	// now do something you wanted to do when the program has
		1681	// no longer asnything immediate to do.
		1682	}
		1683
		1684	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1685	ev_idle_init (idle_watcher, idle_cb);
		1686	ev_idle_start (loop, idle_cb);
		1687
		1688
672	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1689	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		1690
674	Prepare and check watchers are usually (but not always) used in tandem:	1691	Prepare and check watchers are usually (but not always) used in tandem:
675	Prepare watchers get invoked before the process blocks and check watchers	1692	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	1693	afterwards.
677		1694
		1695	You I<must not> call C<ev_loop> or similar functions that enter
		1696	the current event loop from either C<ev_prepare> or C<ev_check>
		1697	watchers. Other loops than the current one are fine, however. The
		1698	rationale behind this is that you do not need to check for recursion in
		1699	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1700	C<ev_check> so if you have one watcher of each kind they will always be
		1701	called in pairs bracketing the blocking call.
		1702
678	Their main purpose is to integrate other event mechanisms into libev. This	1703	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	1704	their use is somewhat advanced. This could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	1705	variable changes, implement your own watchers, integrate net-snmp or a
		1706	coroutine library and lots more. They are also occasionally useful if
		1707	you cache some data and want to flush it before blocking (for example,
		1708	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1709	watcher).
681		1710
682	This is done by examining in each prepare call which file descriptors need	1711	This is done by examining in each prepare call which file descriptors need
683	to be watched by the other library, registering C<ev_io> watchers for	1712	to be watched by the other library, registering C<ev_io> watchers for
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1713	them and starting an C<ev_timer> watcher for any timeouts (many libraries
685	provide just this functionality). Then, in the check watcher you check for	1714	provide just this functionality). Then, in the check watcher you check for
686	any events that occured (by checking the pending status of all watchers	1715	any events that occured (by checking the pending status of all watchers
687	and stopping them) and call back into the library. The I/O and timer	1716	and stopping them) and call back into the library. The I/O and timer
688	callbacks will never actually be called (but must be valid neverthelles,	1717	callbacks will never actually be called (but must be valid nevertheless,
689	because you never know, you know?).	1718	because you never know, you know?).
690		1719
691	As another example, the Perl Coro module uses these hooks to integrate	1720	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	1721	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	1722	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	1723	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	1724	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	1725	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	1726	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	1727	low-priority coroutines to idle/background tasks).
		1728
		1729	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1730	priority, to ensure that they are being run before any other watchers
		1731	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1732	too) should not activate ("feed") events into libev. While libev fully
		1733	supports this, they will be called before other C<ev_check> watchers
		1734	did their job. As C<ev_check> watchers are often used to embed other
		1735	(non-libev) event loops those other event loops might be in an unusable
		1736	state until their C<ev_check> watcher ran (always remind yourself to
		1737	coexist peacefully with others).
		1738
		1739	=head3 Watcher-Specific Functions and Data Members
699		1740
700	=over 4	1741	=over 4
701		1742
702	=item ev_prepare_init (ev_prepare *, callback)	1743	=item ev_prepare_init (ev_prepare *, callback)
703		1744
…		…
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1748	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	1749	macros, but using them is utterly, utterly and completely pointless.
709		1750
710	=back	1751	=back
711		1752
		1753	=head3 Examples
		1754
		1755	There are a number of principal ways to embed other event loops or modules
		1756	into libev. Here are some ideas on how to include libadns into libev
		1757	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1758	use for an actually working example. Another Perl module named C<EV::Glib>
		1759	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1760	into the Glib event loop).
		1761
		1762	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1763	and in a check watcher, destroy them and call into libadns. What follows
		1764	is pseudo-code only of course. This requires you to either use a low
		1765	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1766	the callbacks for the IO/timeout watchers might not have been called yet.
		1767
		1768	static ev_io iow [nfd];
		1769	static ev_timer tw;
		1770
		1771	static void
		1772	io_cb (ev_loop *loop, ev_io *w, int revents)
		1773	{
		1774	}
		1775
		1776	// create io watchers for each fd and a timer before blocking
		1777	static void
		1778	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1779	{
		1780	int timeout = 3600000;
		1781	struct pollfd fds [nfd];
		1782	// actual code will need to loop here and realloc etc.
		1783	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1784
		1785	/* the callback is illegal, but won't be called as we stop during check */
		1786	ev_timer_init (&tw, 0, timeout * 1e-3);
		1787	ev_timer_start (loop, &tw);
		1788
		1789	// create one ev_io per pollfd
		1790	for (int i = 0; i < nfd; ++i)
		1791	{
		1792	ev_io_init (iow + i, io_cb, fds [i].fd,
		1793	((fds [i].events & POLLIN ? EV_READ : 0)
		1794	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1795
		1796	fds [i].revents = 0;
		1797	ev_io_start (loop, iow + i);
		1798	}
		1799	}
		1800
		1801	// stop all watchers after blocking
		1802	static void
		1803	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1804	{
		1805	ev_timer_stop (loop, &tw);
		1806
		1807	for (int i = 0; i < nfd; ++i)
		1808	{
		1809	// set the relevant poll flags
		1810	// could also call adns_processreadable etc. here
		1811	struct pollfd *fd = fds + i;
		1812	int revents = ev_clear_pending (iow + i);
		1813	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1814	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1815
		1816	// now stop the watcher
		1817	ev_io_stop (loop, iow + i);
		1818	}
		1819
		1820	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1821	}
		1822
		1823	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1824	in the prepare watcher and would dispose of the check watcher.
		1825
		1826	Method 3: If the module to be embedded supports explicit event
		1827	notification (adns does), you can also make use of the actual watcher
		1828	callbacks, and only destroy/create the watchers in the prepare watcher.
		1829
		1830	static void
		1831	timer_cb (EV_P_ ev_timer *w, int revents)
		1832	{
		1833	adns_state ads = (adns_state)w->data;
		1834	update_now (EV_A);
		1835
		1836	adns_processtimeouts (ads, &tv_now);
		1837	}
		1838
		1839	static void
		1840	io_cb (EV_P_ ev_io *w, int revents)
		1841	{
		1842	adns_state ads = (adns_state)w->data;
		1843	update_now (EV_A);
		1844
		1845	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1846	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1847	}
		1848
		1849	// do not ever call adns_afterpoll
		1850
		1851	Method 4: Do not use a prepare or check watcher because the module you
		1852	want to embed is too inflexible to support it. Instead, youc na override
		1853	their poll function. The drawback with this solution is that the main
		1854	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1855	this.
		1856
		1857	static gint
		1858	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1859	{
		1860	int got_events = 0;
		1861
		1862	for (n = 0; n < nfds; ++n)
		1863	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1864
		1865	if (timeout >= 0)
		1866	// create/start timer
		1867
		1868	// poll
		1869	ev_loop (EV_A_ 0);
		1870
		1871	// stop timer again
		1872	if (timeout >= 0)
		1873	ev_timer_stop (EV_A_ &to);
		1874
		1875	// stop io watchers again - their callbacks should have set
		1876	for (n = 0; n < nfds; ++n)
		1877	ev_io_stop (EV_A_ iow [n]);
		1878
		1879	return got_events;
		1880	}
		1881
		1882
		1883	=head2 C<ev_embed> - when one backend isn't enough...
		1884
		1885	This is a rather advanced watcher type that lets you embed one event loop
		1886	into another (currently only C<ev_io> events are supported in the embedded
		1887	loop, other types of watchers might be handled in a delayed or incorrect
		1888	fashion and must not be used).
		1889
		1890	There are primarily two reasons you would want that: work around bugs and
		1891	prioritise I/O.
		1892
		1893	As an example for a bug workaround, the kqueue backend might only support
		1894	sockets on some platform, so it is unusable as generic backend, but you
		1895	still want to make use of it because you have many sockets and it scales
		1896	so nicely. In this case, you would create a kqueue-based loop and embed it
		1897	into your default loop (which might use e.g. poll). Overall operation will
		1898	be a bit slower because first libev has to poll and then call kevent, but
		1899	at least you can use both at what they are best.
		1900
		1901	As for prioritising I/O: rarely you have the case where some fds have
		1902	to be watched and handled very quickly (with low latency), and even
		1903	priorities and idle watchers might have too much overhead. In this case
		1904	you would put all the high priority stuff in one loop and all the rest in
		1905	a second one, and embed the second one in the first.
		1906
		1907	As long as the watcher is active, the callback will be invoked every time
		1908	there might be events pending in the embedded loop. The callback must then
		1909	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1910	their callbacks (you could also start an idle watcher to give the embedded
		1911	loop strictly lower priority for example). You can also set the callback
		1912	to C<0>, in which case the embed watcher will automatically execute the
		1913	embedded loop sweep.
		1914
		1915	As long as the watcher is started it will automatically handle events. The
		1916	callback will be invoked whenever some events have been handled. You can
		1917	set the callback to C<0> to avoid having to specify one if you are not
		1918	interested in that.
		1919
		1920	Also, there have not currently been made special provisions for forking:
		1921	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1922	but you will also have to stop and restart any C<ev_embed> watchers
		1923	yourself.
		1924
		1925	Unfortunately, not all backends are embeddable, only the ones returned by
		1926	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1927	portable one.
		1928
		1929	So when you want to use this feature you will always have to be prepared
		1930	that you cannot get an embeddable loop. The recommended way to get around
		1931	this is to have a separate variables for your embeddable loop, try to
		1932	create it, and if that fails, use the normal loop for everything.
		1933
		1934	=head3 Watcher-Specific Functions and Data Members
		1935
		1936	=over 4
		1937
		1938	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1939
		1940	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1941
		1942	Configures the watcher to embed the given loop, which must be
		1943	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1944	invoked automatically, otherwise it is the responsibility of the callback
		1945	to invoke it (it will continue to be called until the sweep has been done,
		1946	if you do not want thta, you need to temporarily stop the embed watcher).
		1947
		1948	=item ev_embed_sweep (loop, ev_embed *)
		1949
		1950	Make a single, non-blocking sweep over the embedded loop. This works
		1951	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1952	apropriate way for embedded loops.
		1953
		1954	=item struct ev_loop *other [read-only]
		1955
		1956	The embedded event loop.
		1957
		1958	=back
		1959
		1960	=head3 Examples
		1961
		1962	Example: Try to get an embeddable event loop and embed it into the default
		1963	event loop. If that is not possible, use the default loop. The default
		1964	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1965	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1966	used).
		1967
		1968	struct ev_loop *loop_hi = ev_default_init (0);
		1969	struct ev_loop *loop_lo = 0;
		1970	struct ev_embed embed;
		1971
		1972	// see if there is a chance of getting one that works
		1973	// (remember that a flags value of 0 means autodetection)
		1974	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1975	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1976	: 0;
		1977
		1978	// if we got one, then embed it, otherwise default to loop_hi
		1979	if (loop_lo)
		1980	{
		1981	ev_embed_init (&embed, 0, loop_lo);
		1982	ev_embed_start (loop_hi, &embed);
		1983	}
		1984	else
		1985	loop_lo = loop_hi;
		1986
		1987	Example: Check if kqueue is available but not recommended and create
		1988	a kqueue backend for use with sockets (which usually work with any
		1989	kqueue implementation). Store the kqueue/socket-only event loop in
		1990	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		1991
		1992	struct ev_loop *loop = ev_default_init (0);
		1993	struct ev_loop *loop_socket = 0;
		1994	struct ev_embed embed;
		1995
		1996	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		1997	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		1998	{
		1999	ev_embed_init (&embed, 0, loop_socket);
		2000	ev_embed_start (loop, &embed);
		2001	}
		2002
		2003	if (!loop_socket)
		2004	loop_socket = loop;
		2005
		2006	// now use loop_socket for all sockets, and loop for everything else
		2007
		2008
		2009	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2010
		2011	Fork watchers are called when a C<fork ()> was detected (usually because
		2012	whoever is a good citizen cared to tell libev about it by calling
		2013	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2014	event loop blocks next and before C<ev_check> watchers are being called,
		2015	and only in the child after the fork. If whoever good citizen calling
		2016	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2017	handlers will be invoked, too, of course.
		2018
		2019	=head3 Watcher-Specific Functions and Data Members
		2020
		2021	=over 4
		2022
		2023	=item ev_fork_init (ev_signal *, callback)
		2024
		2025	Initialises and configures the fork watcher - it has no parameters of any
		2026	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2027	believe me.
		2028
		2029	=back
		2030
		2031
712	=head1 OTHER FUNCTIONS	2032	=head1 OTHER FUNCTIONS
713		2033
714	There are some other functions of possible interest. Described. Here. Now.	2034	There are some other functions of possible interest. Described. Here. Now.
715		2035
716	=over 4	2036	=over 4
…		…
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2038	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		2039
720	This function combines a simple timer and an I/O watcher, calls your	2040	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	2041	callback on whichever event happens first and automatically stop both
722	watchers. This is useful if you want to wait for a single event on an fd	2042	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	2043	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	2044	more watchers yourself.
725		2045
726	If C<fd> is less than 0, then no I/O watcher will be started and events	2046	If C<fd> is less than 0, then no I/O watcher will be started and events
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2047	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
728	C<events> set will be craeted and started.	2048	C<events> set will be craeted and started.
…		…
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2051	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2052	repeat = 0) will be started. While C<0> is a valid timeout, it is of
733	dubious value.	2053	dubious value.
734		2054
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2055	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
736	passed an events set like normal event callbacks (with a combination of	2056	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2057	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738	value passed to C<ev_once>:	2058	value passed to C<ev_once>:
739		2059
740	static void stdin_ready (int revents, void *arg)	2060	static void stdin_ready (int revents, void *arg)
741	{	2061	{
…		…
745	/* stdin might have data for us, joy! */;	2065	/* stdin might have data for us, joy! */;
746	}	2066	}
747		2067
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2068	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749		2069
750	=item ev_feed_event (loop, watcher, int events)	2070	=item ev_feed_event (ev_loop *, watcher *, int revents)
751		2071
752	Feeds the given event set into the event loop, as if the specified event	2072	Feeds the given event set into the event loop, as if the specified event
753	had happened for the specified watcher (which must be a pointer to an	2073	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).	2074	initialised but not necessarily started event watcher).
755		2075
756	=item ev_feed_fd_event (loop, int fd, int revents)	2076	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
757		2077
758	Feed an event on the given fd, as if a file descriptor backend detected	2078	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	2079	the given events it.
760		2080
761	=item ev_feed_signal_event (loop, int signum)	2081	=item ev_feed_signal_event (ev_loop *loop, int signum)
762		2082
763	Feed an event as if the given signal occured (loop must be the default loop!).	2083	Feed an event as if the given signal occured (C<loop> must be the default
		2084	loop!).
764		2085
765	=back	2086	=back
766		2087
		2088
		2089	=head1 LIBEVENT EMULATION
		2090
		2091	Libev offers a compatibility emulation layer for libevent. It cannot
		2092	emulate the internals of libevent, so here are some usage hints:
		2093
		2094	=over 4
		2095
		2096	=item * Use it by including <event.h>, as usual.
		2097
		2098	=item * The following members are fully supported: ev_base, ev_callback,
		2099	ev_arg, ev_fd, ev_res, ev_events.
		2100
		2101	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2102	maintained by libev, it does not work exactly the same way as in libevent (consider
		2103	it a private API).
		2104
		2105	=item * Priorities are not currently supported. Initialising priorities
		2106	will fail and all watchers will have the same priority, even though there
		2107	is an ev_pri field.
		2108
		2109	=item * Other members are not supported.
		2110
		2111	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2112	to use the libev header file and library.
		2113
		2114	=back
		2115
		2116	=head1 C++ SUPPORT
		2117
		2118	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2119	you to use some convinience methods to start/stop watchers and also change
		2120	the callback model to a model using method callbacks on objects.
		2121
		2122	To use it,
		2123
		2124	#include <ev++.h>
		2125
		2126	This automatically includes F<ev.h> and puts all of its definitions (many
		2127	of them macros) into the global namespace. All C++ specific things are
		2128	put into the C<ev> namespace. It should support all the same embedding
		2129	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2130
		2131	Care has been taken to keep the overhead low. The only data member the C++
		2132	classes add (compared to plain C-style watchers) is the event loop pointer
		2133	that the watcher is associated with (or no additional members at all if
		2134	you disable C<EV_MULTIPLICITY> when embedding libev).
		2135
		2136	Currently, functions, and static and non-static member functions can be
		2137	used as callbacks. Other types should be easy to add as long as they only
		2138	need one additional pointer for context. If you need support for other
		2139	types of functors please contact the author (preferably after implementing
		2140	it).
		2141
		2142	Here is a list of things available in the C<ev> namespace:
		2143
		2144	=over 4
		2145
		2146	=item C<ev::READ>, C<ev::WRITE> etc.
		2147
		2148	These are just enum values with the same values as the C<EV_READ> etc.
		2149	macros from F<ev.h>.
		2150
		2151	=item C<ev::tstamp>, C<ev::now>
		2152
		2153	Aliases to the same types/functions as with the C<ev_> prefix.
		2154
		2155	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2156
		2157	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2158	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2159	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2160	defines by many implementations.
		2161
		2162	All of those classes have these methods:
		2163
		2164	=over 4
		2165
		2166	=item ev::TYPE::TYPE ()
		2167
		2168	=item ev::TYPE::TYPE (struct ev_loop *)
		2169
		2170	=item ev::TYPE::~TYPE
		2171
		2172	The constructor (optionally) takes an event loop to associate the watcher
		2173	with. If it is omitted, it will use C<EV_DEFAULT>.
		2174
		2175	The constructor calls C<ev_init> for you, which means you have to call the
		2176	C<set> method before starting it.
		2177
		2178	It will not set a callback, however: You have to call the templated C<set>
		2179	method to set a callback before you can start the watcher.
		2180
		2181	(The reason why you have to use a method is a limitation in C++ which does
		2182	not allow explicit template arguments for constructors).
		2183
		2184	The destructor automatically stops the watcher if it is active.
		2185
		2186	=item w->set<class, &class::method> (object *)
		2187
		2188	This method sets the callback method to call. The method has to have a
		2189	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2190	first argument and the C<revents> as second. The object must be given as
		2191	parameter and is stored in the C<data> member of the watcher.
		2192
		2193	This method synthesizes efficient thunking code to call your method from
		2194	the C callback that libev requires. If your compiler can inline your
		2195	callback (i.e. it is visible to it at the place of the C<set> call and
		2196	your compiler is good :), then the method will be fully inlined into the
		2197	thunking function, making it as fast as a direct C callback.
		2198
		2199	Example: simple class declaration and watcher initialisation
		2200
		2201	struct myclass
		2202	{
		2203	void io_cb (ev::io &w, int revents) { }
		2204	}
		2205
		2206	myclass obj;
		2207	ev::io iow;
		2208	iow.set <myclass, &myclass::io_cb> (&obj);
		2209
		2210	=item w->set<function> (void *data = 0)
		2211
		2212	Also sets a callback, but uses a static method or plain function as
		2213	callback. The optional C<data> argument will be stored in the watcher's
		2214	C<data> member and is free for you to use.
		2215
		2216	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2217
		2218	See the method-C<set> above for more details.
		2219
		2220	Example:
		2221
		2222	static void io_cb (ev::io &w, int revents) { }
		2223	iow.set <io_cb> ();
		2224
		2225	=item w->set (struct ev_loop *)
		2226
		2227	Associates a different C<struct ev_loop> with this watcher. You can only
		2228	do this when the watcher is inactive (and not pending either).
		2229
		2230	=item w->set ([args])
		2231
		2232	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2233	called at least once. Unlike the C counterpart, an active watcher gets
		2234	automatically stopped and restarted when reconfiguring it with this
		2235	method.
		2236
		2237	=item w->start ()
		2238
		2239	Starts the watcher. Note that there is no C<loop> argument, as the
		2240	constructor already stores the event loop.
		2241
		2242	=item w->stop ()
		2243
		2244	Stops the watcher if it is active. Again, no C<loop> argument.
		2245
		2246	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2247
		2248	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2249	C<ev_TYPE_again> function.
		2250
		2251	=item w->sweep () (C<ev::embed> only)
		2252
		2253	Invokes C<ev_embed_sweep>.
		2254
		2255	=item w->update () (C<ev::stat> only)
		2256
		2257	Invokes C<ev_stat_stat>.
		2258
		2259	=back
		2260
		2261	=back
		2262
		2263	Example: Define a class with an IO and idle watcher, start one of them in
		2264	the constructor.
		2265
		2266	class myclass
		2267	{
		2268	ev_io io; void io_cb (ev::io &w, int revents);
		2269	ev_idle idle void idle_cb (ev::idle &w, int revents);
		2270
		2271	myclass ();
		2272	}
		2273
		2274	myclass::myclass (int fd)
		2275	{
		2276	io .set <myclass, &myclass::io_cb > (this);
		2277	idle.set <myclass, &myclass::idle_cb> (this);
		2278
		2279	io.start (fd, ev::READ);
		2280	}
		2281
		2282
		2283	=head1 MACRO MAGIC
		2284
		2285	Libev can be compiled with a variety of options, the most fundamantal
		2286	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2287	functions and callbacks have an initial C<struct ev_loop *> argument.
		2288
		2289	To make it easier to write programs that cope with either variant, the
		2290	following macros are defined:
		2291
		2292	=over 4
		2293
		2294	=item C<EV_A>, C<EV_A_>
		2295
		2296	This provides the loop I<argument> for functions, if one is required ("ev
		2297	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2298	C<EV_A_> is used when other arguments are following. Example:
		2299
		2300	ev_unref (EV_A);
		2301	ev_timer_add (EV_A_ watcher);
		2302	ev_loop (EV_A_ 0);
		2303
		2304	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2305	which is often provided by the following macro.
		2306
		2307	=item C<EV_P>, C<EV_P_>
		2308
		2309	This provides the loop I<parameter> for functions, if one is required ("ev
		2310	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2311	C<EV_P_> is used when other parameters are following. Example:
		2312
		2313	// this is how ev_unref is being declared
		2314	static void ev_unref (EV_P);
		2315
		2316	// this is how you can declare your typical callback
		2317	static void cb (EV_P_ ev_timer *w, int revents)
		2318
		2319	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2320	suitable for use with C<EV_A>.
		2321
		2322	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2323
		2324	Similar to the other two macros, this gives you the value of the default
		2325	loop, if multiple loops are supported ("ev loop default").
		2326
		2327	=back
		2328
		2329	Example: Declare and initialise a check watcher, utilising the above
		2330	macros so it will work regardless of whether multiple loops are supported
		2331	or not.
		2332
		2333	static void
		2334	check_cb (EV_P_ ev_timer *w, int revents)
		2335	{
		2336	ev_check_stop (EV_A_ w);
		2337	}
		2338
		2339	ev_check check;
		2340	ev_check_init (&check, check_cb);
		2341	ev_check_start (EV_DEFAULT_ &check);
		2342	ev_loop (EV_DEFAULT_ 0);
		2343
		2344	=head1 EMBEDDING
		2345
		2346	Libev can (and often is) directly embedded into host
		2347	applications. Examples of applications that embed it include the Deliantra
		2348	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2349	and rxvt-unicode.
		2350
		2351	The goal is to enable you to just copy the necessary files into your
		2352	source directory without having to change even a single line in them, so
		2353	you can easily upgrade by simply copying (or having a checked-out copy of
		2354	libev somewhere in your source tree).
		2355
		2356	=head2 FILESETS
		2357
		2358	Depending on what features you need you need to include one or more sets of files
		2359	in your app.
		2360
		2361	=head3 CORE EVENT LOOP
		2362
		2363	To include only the libev core (all the C<ev_*> functions), with manual
		2364	configuration (no autoconf):
		2365
		2366	#define EV_STANDALONE 1
		2367	#include "ev.c"
		2368
		2369	This will automatically include F<ev.h>, too, and should be done in a
		2370	single C source file only to provide the function implementations. To use
		2371	it, do the same for F<ev.h> in all files wishing to use this API (best
		2372	done by writing a wrapper around F<ev.h> that you can include instead and
		2373	where you can put other configuration options):
		2374
		2375	#define EV_STANDALONE 1
		2376	#include "ev.h"
		2377
		2378	Both header files and implementation files can be compiled with a C++
		2379	compiler (at least, thats a stated goal, and breakage will be treated
		2380	as a bug).
		2381
		2382	You need the following files in your source tree, or in a directory
		2383	in your include path (e.g. in libev/ when using -Ilibev):
		2384
		2385	ev.h
		2386	ev.c
		2387	ev_vars.h
		2388	ev_wrap.h
		2389
		2390	ev_win32.c required on win32 platforms only
		2391
		2392	ev_select.c only when select backend is enabled (which is enabled by default)
		2393	ev_poll.c only when poll backend is enabled (disabled by default)
		2394	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2395	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2396	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2397
		2398	F<ev.c> includes the backend files directly when enabled, so you only need
		2399	to compile this single file.
		2400
		2401	=head3 LIBEVENT COMPATIBILITY API
		2402
		2403	To include the libevent compatibility API, also include:
		2404
		2405	#include "event.c"
		2406
		2407	in the file including F<ev.c>, and:
		2408
		2409	#include "event.h"
		2410
		2411	in the files that want to use the libevent API. This also includes F<ev.h>.
		2412
		2413	You need the following additional files for this:
		2414
		2415	event.h
		2416	event.c
		2417
		2418	=head3 AUTOCONF SUPPORT
		2419
		2420	Instead of using C<EV_STANDALONE=1> and providing your config in
		2421	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2422	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2423	include F<config.h> and configure itself accordingly.
		2424
		2425	For this of course you need the m4 file:
		2426
		2427	libev.m4
		2428
		2429	=head2 PREPROCESSOR SYMBOLS/MACROS
		2430
		2431	Libev can be configured via a variety of preprocessor symbols you have to define
		2432	before including any of its files. The default is not to build for multiplicity
		2433	and only include the select backend.
		2434
		2435	=over 4
		2436
		2437	=item EV_STANDALONE
		2438
		2439	Must always be C<1> if you do not use autoconf configuration, which
		2440	keeps libev from including F<config.h>, and it also defines dummy
		2441	implementations for some libevent functions (such as logging, which is not
		2442	supported). It will also not define any of the structs usually found in
		2443	F<event.h> that are not directly supported by the libev core alone.
		2444
		2445	=item EV_USE_MONOTONIC
		2446
		2447	If defined to be C<1>, libev will try to detect the availability of the
		2448	monotonic clock option at both compiletime and runtime. Otherwise no use
		2449	of the monotonic clock option will be attempted. If you enable this, you
		2450	usually have to link against librt or something similar. Enabling it when
		2451	the functionality isn't available is safe, though, although you have
		2452	to make sure you link against any libraries where the C<clock_gettime>
		2453	function is hiding in (often F<-lrt>).
		2454
		2455	=item EV_USE_REALTIME
		2456
		2457	If defined to be C<1>, libev will try to detect the availability of the
		2458	realtime clock option at compiletime (and assume its availability at
		2459	runtime if successful). Otherwise no use of the realtime clock option will
		2460	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2461	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2462	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2463
		2464	=item EV_USE_NANOSLEEP
		2465
		2466	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2467	and will use it for delays. Otherwise it will use C<select ()>.
		2468
		2469	=item EV_USE_SELECT
		2470
		2471	If undefined or defined to be C<1>, libev will compile in support for the
		2472	C<select>(2) backend. No attempt at autodetection will be done: if no
		2473	other method takes over, select will be it. Otherwise the select backend
		2474	will not be compiled in.
		2475
		2476	=item EV_SELECT_USE_FD_SET
		2477
		2478	If defined to C<1>, then the select backend will use the system C<fd_set>
		2479	structure. This is useful if libev doesn't compile due to a missing
		2480	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2481	exotic systems. This usually limits the range of file descriptors to some
		2482	low limit such as 1024 or might have other limitations (winsocket only
		2483	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2484	influence the size of the C<fd_set> used.
		2485
		2486	=item EV_SELECT_IS_WINSOCKET
		2487
		2488	When defined to C<1>, the select backend will assume that
		2489	select/socket/connect etc. don't understand file descriptors but
		2490	wants osf handles on win32 (this is the case when the select to
		2491	be used is the winsock select). This means that it will call
		2492	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2493	it is assumed that all these functions actually work on fds, even
		2494	on win32. Should not be defined on non-win32 platforms.
		2495
		2496	=item EV_USE_POLL
		2497
		2498	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2499	backend. Otherwise it will be enabled on non-win32 platforms. It
		2500	takes precedence over select.
		2501
		2502	=item EV_USE_EPOLL
		2503
		2504	If defined to be C<1>, libev will compile in support for the Linux
		2505	C<epoll>(7) backend. Its availability will be detected at runtime,
		2506	otherwise another method will be used as fallback. This is the
		2507	preferred backend for GNU/Linux systems.
		2508
		2509	=item EV_USE_KQUEUE
		2510
		2511	If defined to be C<1>, libev will compile in support for the BSD style
		2512	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2513	otherwise another method will be used as fallback. This is the preferred
		2514	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2515	supports some types of fds correctly (the only platform we found that
		2516	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2517	not be used unless explicitly requested. The best way to use it is to find
		2518	out whether kqueue supports your type of fd properly and use an embedded
		2519	kqueue loop.
		2520
		2521	=item EV_USE_PORT
		2522
		2523	If defined to be C<1>, libev will compile in support for the Solaris
		2524	10 port style backend. Its availability will be detected at runtime,
		2525	otherwise another method will be used as fallback. This is the preferred
		2526	backend for Solaris 10 systems.
		2527
		2528	=item EV_USE_DEVPOLL
		2529
		2530	reserved for future expansion, works like the USE symbols above.
		2531
		2532	=item EV_USE_INOTIFY
		2533
		2534	If defined to be C<1>, libev will compile in support for the Linux inotify
		2535	interface to speed up C<ev_stat> watchers. Its actual availability will
		2536	be detected at runtime.
		2537
		2538	=item EV_H
		2539
		2540	The name of the F<ev.h> header file used to include it. The default if
		2541	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to
		2542	virtually rename the F<ev.h> header file in case of conflicts.
		2543
		2544	=item EV_CONFIG_H
		2545
		2546	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2547	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2548	C<EV_H>, above.
		2549
		2550	=item EV_EVENT_H
		2551
		2552	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2553	of how the F<event.h> header can be found, the dfeault is C<"event.h">.
		2554
		2555	=item EV_PROTOTYPES
		2556
		2557	If defined to be C<0>, then F<ev.h> will not define any function
		2558	prototypes, but still define all the structs and other symbols. This is
		2559	occasionally useful if you want to provide your own wrapper functions
		2560	around libev functions.
		2561
		2562	=item EV_MULTIPLICITY
		2563
		2564	If undefined or defined to C<1>, then all event-loop-specific functions
		2565	will have the C<struct ev_loop *> as first argument, and you can create
		2566	additional independent event loops. Otherwise there will be no support
		2567	for multiple event loops and there is no first event loop pointer
		2568	argument. Instead, all functions act on the single default loop.
		2569
		2570	=item EV_MINPRI
		2571
		2572	=item EV_MAXPRI
		2573
		2574	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2575	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2576	provide for more priorities by overriding those symbols (usually defined
		2577	to be C<-2> and C<2>, respectively).
		2578
		2579	When doing priority-based operations, libev usually has to linearly search
		2580	all the priorities, so having many of them (hundreds) uses a lot of space
		2581	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2582	fine.
		2583
		2584	If your embedding app does not need any priorities, defining these both to
		2585	C<0> will save some memory and cpu.
		2586
		2587	=item EV_PERIODIC_ENABLE
		2588
		2589	If undefined or defined to be C<1>, then periodic timers are supported. If
		2590	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2591	code.
		2592
		2593	=item EV_IDLE_ENABLE
		2594
		2595	If undefined or defined to be C<1>, then idle watchers are supported. If
		2596	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2597	code.
		2598
		2599	=item EV_EMBED_ENABLE
		2600
		2601	If undefined or defined to be C<1>, then embed watchers are supported. If
		2602	defined to be C<0>, then they are not.
		2603
		2604	=item EV_STAT_ENABLE
		2605
		2606	If undefined or defined to be C<1>, then stat watchers are supported. If
		2607	defined to be C<0>, then they are not.
		2608
		2609	=item EV_FORK_ENABLE
		2610
		2611	If undefined or defined to be C<1>, then fork watchers are supported. If
		2612	defined to be C<0>, then they are not.
		2613
		2614	=item EV_MINIMAL
		2615
		2616	If you need to shave off some kilobytes of code at the expense of some
		2617	speed, define this symbol to C<1>. Currently only used for gcc to override
		2618	some inlining decisions, saves roughly 30% codesize of amd64.
		2619
		2620	=item EV_PID_HASHSIZE
		2621
		2622	C<ev_child> watchers use a small hash table to distribute workload by
		2623	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2624	than enough. If you need to manage thousands of children you might want to
		2625	increase this value (I<must> be a power of two).
		2626
		2627	=item EV_INOTIFY_HASHSIZE
		2628
		2629	C<ev_stat> watchers use a small hash table to distribute workload by
		2630	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2631	usually more than enough. If you need to manage thousands of C<ev_stat>
		2632	watchers you might want to increase this value (I<must> be a power of
		2633	two).
		2634
		2635	=item EV_COMMON
		2636
		2637	By default, all watchers have a C<void *data> member. By redefining
		2638	this macro to a something else you can include more and other types of
		2639	members. You have to define it each time you include one of the files,
		2640	though, and it must be identical each time.
		2641
		2642	For example, the perl EV module uses something like this:
		2643
		2644	#define EV_COMMON \
		2645	SV *self; /* contains this struct */ \
		2646	SV *cb_sv, *fh /* note no trailing ";" */
		2647
		2648	=item EV_CB_DECLARE (type)
		2649
		2650	=item EV_CB_INVOKE (watcher, revents)
		2651
		2652	=item ev_set_cb (ev, cb)
		2653
		2654	Can be used to change the callback member declaration in each watcher,
		2655	and the way callbacks are invoked and set. Must expand to a struct member
		2656	definition and a statement, respectively. See the F<ev.h> header file for
		2657	their default definitions. One possible use for overriding these is to
		2658	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2659	method calls instead of plain function calls in C++.
		2660
		2661	=head2 EXPORTED API SYMBOLS
		2662
		2663	If you need to re-export the API (e.g. via a dll) and you need a list of
		2664	exported symbols, you can use the provided F<Symbol.*> files which list
		2665	all public symbols, one per line:
		2666
		2667	Symbols.ev for libev proper
		2668	Symbols.event for the libevent emulation
		2669
		2670	This can also be used to rename all public symbols to avoid clashes with
		2671	multiple versions of libev linked together (which is obviously bad in
		2672	itself, but sometimes it is inconvinient to avoid this).
		2673
		2674	A sed command like this will create wrapper C<#define>'s that you need to
		2675	include before including F<ev.h>:
		2676
		2677	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2678
		2679	This would create a file F<wrap.h> which essentially looks like this:
		2680
		2681	#define ev_backend myprefix_ev_backend
		2682	#define ev_check_start myprefix_ev_check_start
		2683	#define ev_check_stop myprefix_ev_check_stop
		2684	...
		2685
		2686	=head2 EXAMPLES
		2687
		2688	For a real-world example of a program the includes libev
		2689	verbatim, you can have a look at the EV perl module
		2690	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2691	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2692	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2693	will be compiled. It is pretty complex because it provides its own header
		2694	file.
		2695
		2696	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2697	that everybody includes and which overrides some configure choices:
		2698
		2699	#define EV_MINIMAL 1
		2700	#define EV_USE_POLL 0
		2701	#define EV_MULTIPLICITY 0
		2702	#define EV_PERIODIC_ENABLE 0
		2703	#define EV_STAT_ENABLE 0
		2704	#define EV_FORK_ENABLE 0
		2705	#define EV_CONFIG_H <config.h>
		2706	#define EV_MINPRI 0
		2707	#define EV_MAXPRI 0
		2708
		2709	#include "ev++.h"
		2710
		2711	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2712
		2713	#include "ev_cpp.h"
		2714	#include "ev.c"
		2715
		2716
		2717	=head1 COMPLEXITIES
		2718
		2719	In this section the complexities of (many of) the algorithms used inside
		2720	libev will be explained. For complexity discussions about backends see the
		2721	documentation for C<ev_default_init>.
		2722
		2723	All of the following are about amortised time: If an array needs to be
		2724	extended, libev needs to realloc and move the whole array, but this
		2725	happens asymptotically never with higher number of elements, so O(1) might
		2726	mean it might do a lengthy realloc operation in rare cases, but on average
		2727	it is much faster and asymptotically approaches constant time.
		2728
		2729	=over 4
		2730
		2731	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2732
		2733	This means that, when you have a watcher that triggers in one hour and
		2734	there are 100 watchers that would trigger before that then inserting will
		2735	have to skip roughly seven (C<ld 100>) of these watchers.
		2736
		2737	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2738
		2739	That means that changing a timer costs less than removing/adding them
		2740	as only the relative motion in the event queue has to be paid for.
		2741
		2742	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2743
		2744	These just add the watcher into an array or at the head of a list.
		2745
		2746	=item Stopping check/prepare/idle watchers: O(1)
		2747
		2748	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2749
		2750	These watchers are stored in lists then need to be walked to find the
		2751	correct watcher to remove. The lists are usually short (you don't usually
		2752	have many watchers waiting for the same fd or signal).
		2753
		2754	=item Finding the next timer in each loop iteration: O(1)
		2755
		2756	By virtue of using a binary heap, the next timer is always found at the
		2757	beginning of the storage array.
		2758
		2759	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2760
		2761	A change means an I/O watcher gets started or stopped, which requires
		2762	libev to recalculate its status (and possibly tell the kernel, depending
		2763	on backend and wether C<ev_io_set> was used).
		2764
		2765	=item Activating one watcher (putting it into the pending state): O(1)
		2766
		2767	=item Priority handling: O(number_of_priorities)
		2768
		2769	Priorities are implemented by allocating some space for each
		2770	priority. When doing priority-based operations, libev usually has to
		2771	linearly search all the priorities, but starting/stopping and activating
		2772	watchers becomes O(1) w.r.t. prioritiy handling.
		2773
		2774	=back
		2775
		2776
767	=head1 AUTHOR	2777	=head1 AUTHOR
768		2778
769	Marc Lehmann <libev@schmorp.de>.	2779	Marc Lehmann <libev@schmorp.de>.
770		2780

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