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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 REPRESENTATION	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.
51		106
52	=head1 GLOBAL FUNCTIONS	107	=head1 GLOBAL FUNCTIONS
53		108
54	These functions can be called anytime, even before initialising the	109	These functions can be called anytime, even before initialising the
55	library in any way.	110	library in any way.
…		…
60		115
61	Returns the current time as libev would use it. Please note that the	116	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	117	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	118	you actually want to know.
64		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 ()>.
		125
65	=item int ev_version_major ()	126	=item int ev_version_major ()
66		127
67	=item int ev_version_minor ()	128	=item int ev_version_minor ()
68		129
69	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
70	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
71	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
72	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
73	version of the library your program was compiled against.	134	version of the library your program was compiled against.
74		135
		136	These version numbers refer to the ABI version of the library, not the
		137	release version.
		138
75	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,
76	as this indicates an incompatible change. Minor versions are usually	140	as this indicates an incompatible change. Minor versions are usually
77	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
78	not a problem.	142	not a problem.
79		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
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		184
82	Sets the allocation function to use (the prototype is similar to the	185	Sets the allocation function to use (the prototype is similar - the
83	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
84	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
85	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
86	destructive action. The default is your system realloc function.	189	potentially destructive action. The default is your system realloc
		190	function.
87		191
88	You could override this function in high-availability programs to, say,	192	You could override this function in high-availability programs to, say,
89	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,
90	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);
91		215
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	216	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		217
94	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
95	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
…		…
97	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
98	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
99	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
100	(such as abort).	224	(such as abort).
101		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
102	=back	238	=back
103		239
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		241
106	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
…		…
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	255	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		256
121	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
122	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
123	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
124	flags).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		261
126	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
127	function.	263	function.
128		264
		265	The default loop is the only loop that can handle C<ev_signal> and
		266	C<ev_child> watchers, and to do this, it always registers a handler
		267	for C<SIGCHLD>. If this is a problem for your app you can either
		268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		270	C<ev_default_init>.
		271
129	The flags argument can be used to specify special behaviour or specific	272	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	273	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		274
132	It supports the following flags:	275	The following flags are supported:
133		276
134	=over 4	277	=over 4
135		278
136	=item C<EVFLAG_AUTO>	279	=item C<EVFLAG_AUTO>
137		280
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	289	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	290	useful to try out specific backends to test their performance, or to work
148	around bugs.	291	around bugs.
149		292
		293	=item C<EVFLAG_FORKCHECK>
		294
		295	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		296	a fork, you can also make libev check for a fork in each iteration by
		297	enabling this flag.
		298
		299	This works by calling C<getpid ()> on every iteration of the loop,
		300	and thus this might slow down your event loop if you do a lot of loop
		301	iterations and little real work, but is usually not noticeable (on my
		302	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		303	without a syscall and thus I<very> fast, but my Linux system also has
		304	C<pthread_atfork> which is even faster).
		305
		306	The big advantage of this flag is that you can forget about fork (and
		307	forget about forgetting to tell libev about forking) when you use this
		308	flag.
		309
		310	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		311	environment variable.
		312
150	=item C<EVMETHOD_SELECT> (portable select backend)	313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		314
		315	This is your standard select(2) backend. Not I<completely> standard, as
		316	libev tries to roll its own fd_set with no limits on the number of fds,
		317	but if that fails, expect a fairly low limit on the number of fds when
		318	using this backend. It doesn't scale too well (O(highest_fd)), but its
		319	usually the fastest backend for a low number of (low-numbered :) fds.
		320
		321	To get good performance out of this backend you need a high amount of
		322	parallelity (most of the file descriptors should be busy). If you are
		323	writing a server, you should C<accept ()> in a loop to accept as many
		324	connections as possible during one iteration. You might also want to have
		325	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		326	readyness notifications you get per iteration.
		327
152	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
153		329
154	=item C<EVMETHOD_EPOLL> (linux only)	330	And this is your standard poll(2) backend. It's more complicated
		331	than select, but handles sparse fds better and has no artificial
		332	limit on the number of fds you can use (except it will slow down
		333	considerably with a lot of inactive fds). It scales similarly to select,
		334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		335	performance tips.
155		336
156	=item C<EVMETHOD_KQUEUE> (some bsds only)	337	=item C<EVBACKEND_EPOLL> (value 4, Linux)
157		338
158	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	339	For few fds, this backend is a bit little slower than poll and select,
		340	but it scales phenomenally better. While poll and select usually scale
		341	like O(total_fds) where n is the total number of fds (or the highest fd),
		342	epoll scales either O(1) or O(active_fds). The epoll design has a number
		343	of shortcomings, such as silently dropping events in some hard-to-detect
		344	cases and rewiring a syscall per fd change, no fork support and bad
		345	support for dup.
159		346
160	=item C<EVMETHOD_PORT> (solaris 10 only)	347	While stopping, setting and starting an I/O watcher in the same iteration
		348	will result in some caching, there is still a syscall per such incident
		349	(because the fd could point to a different file description now), so its
		350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		351	very well if you register events for both fds.
		352
		353	Please note that epoll sometimes generates spurious notifications, so you
		354	need to use non-blocking I/O or other means to avoid blocking when no data
		355	(or space) is available.
		356
		357	Best performance from this backend is achieved by not unregistering all
		358	watchers for a file descriptor until it has been closed, if possible, i.e.
		359	keep at least one watcher active per fd at all times.
		360
		361	While nominally embeddeble in other event loops, this feature is broken in
		362	all kernel versions tested so far.
		363
		364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		365
		366	Kqueue deserves special mention, as at the time of this writing, it
		367	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		368	with anything but sockets and pipes, except on Darwin, where of course
		369	it's completely useless). For this reason it's not being "autodetected"
		370	unless you explicitly specify it explicitly in the flags (i.e. using
		371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		372	system like NetBSD.
		373
		374	You still can embed kqueue into a normal poll or select backend and use it
		375	only for sockets (after having made sure that sockets work with kqueue on
		376	the target platform). See C<ev_embed> watchers for more info.
		377
		378	It scales in the same way as the epoll backend, but the interface to the
		379	kernel is more efficient (which says nothing about its actual speed, of
		380	course). While stopping, setting and starting an I/O watcher does never
		381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		382	two event changes per incident, support for C<fork ()> is very bad and it
		383	drops fds silently in similarly hard-to-detect cases.
		384
		385	This backend usually performs well under most conditions.
		386
		387	While nominally embeddable in other event loops, this doesn't work
		388	everywhere, so you might need to test for this. And since it is broken
		389	almost everywhere, you should only use it when you have a lot of sockets
		390	(for which it usually works), by embedding it into another event loop
		391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		392	sockets.
		393
		394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		395
		396	This is not implemented yet (and might never be, unless you send me an
		397	implementation). According to reports, C</dev/poll> only supports sockets
		398	and is not embeddable, which would limit the usefulness of this backend
		399	immensely.
		400
		401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		402
		403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		404	it's really slow, but it still scales very well (O(active_fds)).
		405
		406	Please note that solaris event ports can deliver a lot of spurious
		407	notifications, so you need to use non-blocking I/O or other means to avoid
		408	blocking when no data (or space) is available.
		409
		410	While this backend scales well, it requires one system call per active
		411	file descriptor per loop iteration. For small and medium numbers of file
		412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		413	might perform better.
		414
		415	On the positive side, ignoring the spurious readyness notifications, this
		416	backend actually performed to specification in all tests and is fully
		417	embeddable, which is a rare feat among the OS-specific backends.
		418
		419	=item C<EVBACKEND_ALL>
		420
		421	Try all backends (even potentially broken ones that wouldn't be tried
		422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		424
		425	It is definitely not recommended to use this flag.
		426
		427	=back
161		428
162	If one or more of these are ored into the flags value, then only these	429	If one or more of these are ored into the flags value, then only these
163	backends will be tried (in the reverse order as given here). If one are	430	backends will be tried (in the reverse order as listed here). If none are
164	specified, any backend will do.	431	specified, all backends in C<ev_recommended_backends ()> will be tried.
165		432
166	=back	433	The most typical usage is like this:
		434
		435	if (!ev_default_loop (0))
		436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		437
		438	Restrict libev to the select and poll backends, and do not allow
		439	environment settings to be taken into account:
		440
		441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		442
		443	Use whatever libev has to offer, but make sure that kqueue is used if
		444	available (warning, breaks stuff, best use only with your own private
		445	event loop and only if you know the OS supports your types of fds):
		446
		447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
167		448
168	=item struct ev_loop *ev_loop_new (unsigned int flags)	449	=item struct ev_loop *ev_loop_new (unsigned int flags)
169		450
170	Similar to C<ev_default_loop>, but always creates a new event loop that is	451	Similar to C<ev_default_loop>, but always creates a new event loop that is
171	always distinct from the default loop. Unlike the default loop, it cannot	452	always distinct from the default loop. Unlike the default loop, it cannot
172	handle signal and child watchers, and attempts to do so will be greeted by	453	handle signal and child watchers, and attempts to do so will be greeted by
173	undefined behaviour (or a failed assertion if assertions are enabled).	454	undefined behaviour (or a failed assertion if assertions are enabled).
174		455
		456	Example: Try to create a event loop that uses epoll and nothing else.
		457
		458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		459	if (!epoller)
		460	fatal ("no epoll found here, maybe it hides under your chair");
		461
175	=item ev_default_destroy ()	462	=item ev_default_destroy ()
176		463
177	Destroys the default loop again (frees all memory and kernel state	464	Destroys the default loop again (frees all memory and kernel state
178	etc.). This stops all registered event watchers (by not touching them in	465	etc.). None of the active event watchers will be stopped in the normal
179	any way whatsoever, although you cannot rely on this :).	466	sense, so e.g. C<ev_is_active> might still return true. It is your
		467	responsibility to either stop all watchers cleanly yoursef I<before>
		468	calling this function, or cope with the fact afterwards (which is usually
		469	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		470	for example).
		471
		472	Note that certain global state, such as signal state, will not be freed by
		473	this function, and related watchers (such as signal and child watchers)
		474	would need to be stopped manually.
		475
		476	In general it is not advisable to call this function except in the
		477	rare occasion where you really need to free e.g. the signal handling
		478	pipe fds. If you need dynamically allocated loops it is better to use
		479	C<ev_loop_new> and C<ev_loop_destroy>).
180		480
181	=item ev_loop_destroy (loop)	481	=item ev_loop_destroy (loop)
182		482
183	Like C<ev_default_destroy>, but destroys an event loop created by an	483	Like C<ev_default_destroy>, but destroys an event loop created by an
184	earlier call to C<ev_loop_new>.	484	earlier call to C<ev_loop_new>.
185		485
186	=item ev_default_fork ()	486	=item ev_default_fork ()
187		487
		488	This function sets a flag that causes subsequent C<ev_loop> iterations
188	This function reinitialises the kernel state for backends that have	489	to reinitialise the kernel state for backends that have one. Despite the
189	one. Despite the name, you can call it anytime, but it makes most sense	490	name, you can call it anytime, but it makes most sense after forking, in
190	after forking, in either the parent or child process (or both, but that	491	the child process (or both child and parent, but that again makes little
191	again makes little sense).	492	sense). You I<must> call it in the child before using any of the libev
		493	functions, and it will only take effect at the next C<ev_loop> iteration.
192		494
193	You I<must> call this function after forking if and only if you want to	495	On the other hand, you only need to call this function in the child
194	use the event library in both processes. If you just fork+exec, you don't	496	process if and only if you want to use the event library in the child. If
195	have to call it.	497	you just fork+exec, you don't have to call it at all.
196		498
197	The function itself is quite fast and it's usually not a problem to call	499	The function itself is quite fast and it's usually not a problem to call
198	it just in case after a fork. To make this easy, the function will fit in	500	it just in case after a fork. To make this easy, the function will fit in
199	quite nicely into a call to C<pthread_atfork>:	501	quite nicely into a call to C<pthread_atfork>:
200		502
…		…
204		506
205	Like C<ev_default_fork>, but acts on an event loop created by	507	Like C<ev_default_fork>, but acts on an event loop created by
206	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
207	after fork, and how you do this is entirely your own problem.	509	after fork, and how you do this is entirely your own problem.
208		510
		511	=item unsigned int ev_loop_count (loop)
		512
		513	Returns the count of loop iterations for the loop, which is identical to
		514	the number of times libev did poll for new events. It starts at C<0> and
		515	happily wraps around with enough iterations.
		516
		517	This value can sometimes be useful as a generation counter of sorts (it
		518	"ticks" the number of loop iterations), as it roughly corresponds with
		519	C<ev_prepare> and C<ev_check> calls.
		520
209	=item unsigned int ev_method (loop)	521	=item unsigned int ev_backend (loop)
210		522
211	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
212	use.	524	use.
213		525
214	=item ev_tstamp ev_now (loop)	526	=item ev_tstamp ev_now (loop)
215		527
216	Returns the current "event loop time", which is the time the event loop	528	Returns the current "event loop time", which is the time the event loop
217	got events and started processing them. This timestamp does not change	529	received events and started processing them. This timestamp does not
218	as long as callbacks are being processed, and this is also the base time	530	change as long as callbacks are being processed, and this is also the base
219	used for relative timers. You can treat it as the timestamp of the event	531	time used for relative timers. You can treat it as the timestamp of the
220	occuring (or more correctly, the mainloop finding out about it).	532	event occurring (or more correctly, libev finding out about it).
221		533
222	=item ev_loop (loop, int flags)	534	=item ev_loop (loop, int flags)
223		535
224	Finally, this is it, the event handler. This function usually is called	536	Finally, this is it, the event handler. This function usually is called
225	after you initialised all your watchers and you want to start handling	537	after you initialised all your watchers and you want to start handling
226	events.	538	events.
227		539
228	If the flags argument is specified as 0, it will not return until either	540	If the flags argument is specified as C<0>, it will not return until
229	no event watchers are active anymore or C<ev_unloop> was called.	541	either no event watchers are active anymore or C<ev_unloop> was called.
		542
		543	Please note that an explicit C<ev_unloop> is usually better than
		544	relying on all watchers to be stopped when deciding when a program has
		545	finished (especially in interactive programs), but having a program that
		546	automatically loops as long as it has to and no longer by virtue of
		547	relying on its watchers stopping correctly is a thing of beauty.
230		548
231	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
232	those events and any outstanding ones, but will not block your process in	550	those events and any outstanding ones, but will not block your process in
233	case there are no events and will return after one iteration of the loop.	551	case there are no events and will return after one iteration of the loop.
234		552
235	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
236	neccessary) and will handle those and any outstanding ones. It will block	554	neccessary) and will handle those and any outstanding ones. It will block
237	your process until at least one new event arrives, and will return after	555	your process until at least one new event arrives, and will return after
238	one iteration of the loop.	556	one iteration of the loop. This is useful if you are waiting for some
		557	external event in conjunction with something not expressible using other
		558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		559	usually a better approach for this kind of thing.
239		560
240	This flags value could be used to implement alternative looping
241	constructs, but the C<prepare> and C<check> watchers provide a better and
242	more generic mechanism.
243
244	Here are the gory details of what ev_loop does:	561	Here are the gory details of what C<ev_loop> does:
245		562
246	1. If there are no active watchers (reference count is zero), return.	563	- Before the first iteration, call any pending watchers.
		564	* If EVFLAG_FORKCHECK was used, check for a fork.
		565	- If a fork was detected, queue and call all fork watchers.
247	2. Queue and immediately call all prepare watchers.	566	- Queue and call all prepare watchers.
248	3. If we have been forked, recreate the kernel state.	567	- If we have been forked, recreate the kernel state.
249	4. Update the kernel state with all outstanding changes.	568	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	569	- Update the "event loop time".
251	6. Calculate for how long to block.	570	- Calculate for how long to sleep or block, if at all
		571	(active idle watchers, EVLOOP_NONBLOCK or not having
		572	any active watchers at all will result in not sleeping).
		573	- Sleep if the I/O and timer collect interval say so.
252	7. Block the process, waiting for events.	574	- Block the process, waiting for any events.
		575	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	576	- Update the "event loop time" and do time jump handling.
254	9. Queue all outstanding timers.	577	- Queue all outstanding timers.
255	10. Queue all outstanding periodics.	578	- Queue all outstanding periodics.
256	11. If no events are pending now, queue all idle watchers.	579	- If no events are pending now, queue all idle watchers.
257	12. Queue all check watchers.	580	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	581	- Call all queued watchers in reverse order (i.e. check watchers first).
		582	Signals and child watchers are implemented as I/O watchers, and will
		583	be handled here by queueing them when their watcher gets executed.
259	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260	was used, return, otherwise continue with step #1.	585	were used, or there are no active watchers, return, otherwise
		586	continue with step *.
		587
		588	Example: Queue some jobs and then loop until no events are outstanding
		589	anymore.
		590
		591	... queue jobs here, make sure they register event watchers as long
		592	... as they still have work to do (even an idle watcher will do..)
		593	ev_loop (my_loop, 0);
		594	... jobs done. yeah!
261		595
262	=item ev_unloop (loop, how)	596	=item ev_unloop (loop, how)
263		597
264	Can be used to make a call to C<ev_loop> return early (but only after it	598	Can be used to make a call to C<ev_loop> return early (but only after it
265	has processed all outstanding events). The C<how> argument must be either	599	has processed all outstanding events). The C<how> argument must be either
266	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
267	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		602
		603	This "unloop state" will be cleared when entering C<ev_loop> again.
268		604
269	=item ev_ref (loop)	605	=item ev_ref (loop)
270		606
271	=item ev_unref (loop)	607	=item ev_unref (loop)
272		608
…		…
277	returning, ev_unref() after starting, and ev_ref() before stopping it. For	613	returning, ev_unref() after starting, and ev_ref() before stopping it. For
278	example, libev itself uses this for its internal signal pipe: It is not	614	example, libev itself uses this for its internal signal pipe: It is not
279	visible to the libev user and should not keep C<ev_loop> from exiting if	615	visible to the libev user and should not keep C<ev_loop> from exiting if
280	no event watchers registered by it are active. It is also an excellent	616	no event watchers registered by it are active. It is also an excellent
281	way to do this for generic recurring timers or from within third-party	617	way to do this for generic recurring timers or from within third-party
282	libraries. Just remember to I<unref after start> and I<ref before stop>.	618	libraries. Just remember to I<unref after start> and I<ref before stop>
		619	(but only if the watcher wasn't active before, or was active before,
		620	respectively).
		621
		622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		623	running when nothing else is active.
		624
		625	struct ev_signal exitsig;
		626	ev_signal_init (&exitsig, sig_cb, SIGINT);
		627	ev_signal_start (loop, &exitsig);
		628	evf_unref (loop);
		629
		630	Example: For some weird reason, unregister the above signal handler again.
		631
		632	ev_ref (loop);
		633	ev_signal_stop (loop, &exitsig);
		634
		635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		636
		637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		638
		639	These advanced functions influence the time that libev will spend waiting
		640	for events. Both are by default C<0>, meaning that libev will try to
		641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		642
		643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		644	allows libev to delay invocation of I/O and timer/periodic callbacks to
		645	increase efficiency of loop iterations.
		646
		647	The background is that sometimes your program runs just fast enough to
		648	handle one (or very few) event(s) per loop iteration. While this makes
		649	the program responsive, it also wastes a lot of CPU time to poll for new
		650	events, especially with backends like C<select ()> which have a high
		651	overhead for the actual polling but can deliver many events at once.
		652
		653	By setting a higher I<io collect interval> you allow libev to spend more
		654	time collecting I/O events, so you can handle more events per iteration,
		655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		656	C<ev_timer>) will be not affected. Setting this to a non-null value will
		657	introduce an additional C<ev_sleep ()> call into most loop iterations.
		658
		659	Likewise, by setting a higher I<timeout collect interval> you allow libev
		660	to spend more time collecting timeouts, at the expense of increased
		661	latency (the watcher callback will be called later). C<ev_io> watchers
		662	will not be affected. Setting this to a non-null value will not introduce
		663	any overhead in libev.
		664
		665	Many (busy) programs can usually benefit by setting the io collect
		666	interval to a value near C<0.1> or so, which is often enough for
		667	interactive servers (of course not for games), likewise for timeouts. It
		668	usually doesn't make much sense to set it to a lower value than C<0.01>,
		669	as this approsaches the timing granularity of most systems.
283		670
284	=back	671	=back
		672
285		673
286	=head1 ANATOMY OF A WATCHER	674	=head1 ANATOMY OF A WATCHER
287		675
288	A watcher is a structure that you create and register to record your	676	A watcher is a structure that you create and register to record your
289	interest in some event. For instance, if you want to wait for STDIN to	677	interest in some event. For instance, if you want to wait for STDIN to
…		…
322	*) >>), and you can stop watching for events at any time by calling the	710	*) >>), and you can stop watching for events at any time by calling the
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
324		712
325	As long as your watcher is active (has been started but not stopped) you	713	As long as your watcher is active (has been started but not stopped) you
326	must not touch the values stored in it. Most specifically you must never	714	must not touch the values stored in it. Most specifically you must never
327	reinitialise it or call its set method.	715	reinitialise it or call its C<set> macro.
328
329	You can check whether an event is active by calling the C<ev_is_active
330	(watcher *)> macro. To see whether an event is outstanding (but the
331	callback for it has not been called yet) you can use the C<ev_is_pending
332	(watcher *)> macro.
333		716
334	Each and every callback receives the event loop pointer as first, the	717	Each and every callback receives the event loop pointer as first, the
335	registered watcher structure as second, and a bitset of received events as	718	registered watcher structure as second, and a bitset of received events as
336	third argument.	719	third argument.
337		720
…		…
361	The signal specified in the C<ev_signal> watcher has been received by a thread.	744	The signal specified in the C<ev_signal> watcher has been received by a thread.
362		745
363	=item C<EV_CHILD>	746	=item C<EV_CHILD>
364		747
365	The pid specified in the C<ev_child> watcher has received a status change.	748	The pid specified in the C<ev_child> watcher has received a status change.
		749
		750	=item C<EV_STAT>
		751
		752	The path specified in the C<ev_stat> watcher changed its attributes somehow.
366		753
367	=item C<EV_IDLE>	754	=item C<EV_IDLE>
368		755
369	The C<ev_idle> watcher has determined that you have nothing better to do.	756	The C<ev_idle> watcher has determined that you have nothing better to do.
370		757
…		…
378	received events. Callbacks of both watcher types can start and stop as	765	received events. Callbacks of both watcher types can start and stop as
379	many watchers as they want, and all of them will be taken into account	766	many watchers as they want, and all of them will be taken into account
380	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	767	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
381	C<ev_loop> from blocking).	768	C<ev_loop> from blocking).
382		769
		770	=item C<EV_EMBED>
		771
		772	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		773
		774	=item C<EV_FORK>
		775
		776	The event loop has been resumed in the child process after fork (see
		777	C<ev_fork>).
		778
		779	=item C<EV_ASYNC>
		780
		781	The given async watcher has been asynchronously notified (see C<ev_async>).
		782
383	=item C<EV_ERROR>	783	=item C<EV_ERROR>
384		784
385	An unspecified error has occured, the watcher has been stopped. This might	785	An unspecified error has occured, the watcher has been stopped. This might
386	happen because the watcher could not be properly started because libev	786	happen because the watcher could not be properly started because libev
387	ran out of memory, a file descriptor was found to be closed or any other	787	ran out of memory, a file descriptor was found to be closed or any other
…		…
393	your callbacks is well-written it can just attempt the operation and cope	793	your callbacks is well-written it can just attempt the operation and cope
394	with the error from read() or write(). This will not work in multithreaded	794	with the error from read() or write(). This will not work in multithreaded
395	programs, though, so beware.	795	programs, though, so beware.
396		796
397	=back	797	=back
		798
		799	=head2 GENERIC WATCHER FUNCTIONS
		800
		801	In the following description, C<TYPE> stands for the watcher type,
		802	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		803
		804	=over 4
		805
		806	=item C<ev_init> (ev_TYPE *watcher, callback)
		807
		808	This macro initialises the generic portion of a watcher. The contents
		809	of the watcher object can be arbitrary (so C<malloc> will do). Only
		810	the generic parts of the watcher are initialised, you I<need> to call
		811	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		812	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		813	which rolls both calls into one.
		814
		815	You can reinitialise a watcher at any time as long as it has been stopped
		816	(or never started) and there are no pending events outstanding.
		817
		818	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		819	int revents)>.
		820
		821	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		822
		823	This macro initialises the type-specific parts of a watcher. You need to
		824	call C<ev_init> at least once before you call this macro, but you can
		825	call C<ev_TYPE_set> any number of times. You must not, however, call this
		826	macro on a watcher that is active (it can be pending, however, which is a
		827	difference to the C<ev_init> macro).
		828
		829	Although some watcher types do not have type-specific arguments
		830	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		831
		832	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		833
		834	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		835	calls into a single call. This is the most convinient method to initialise
		836	a watcher. The same limitations apply, of course.
		837
		838	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		839
		840	Starts (activates) the given watcher. Only active watchers will receive
		841	events. If the watcher is already active nothing will happen.
		842
		843	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		844
		845	Stops the given watcher again (if active) and clears the pending
		846	status. It is possible that stopped watchers are pending (for example,
		847	non-repeating timers are being stopped when they become pending), but
		848	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		849	you want to free or reuse the memory used by the watcher it is therefore a
		850	good idea to always call its C<ev_TYPE_stop> function.
		851
		852	=item bool ev_is_active (ev_TYPE *watcher)
		853
		854	Returns a true value iff the watcher is active (i.e. it has been started
		855	and not yet been stopped). As long as a watcher is active you must not modify
		856	it.
		857
		858	=item bool ev_is_pending (ev_TYPE *watcher)
		859
		860	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		861	events but its callback has not yet been invoked). As long as a watcher
		862	is pending (but not active) you must not call an init function on it (but
		863	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		864	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		865	it).
		866
		867	=item callback ev_cb (ev_TYPE *watcher)
		868
		869	Returns the callback currently set on the watcher.
		870
		871	=item ev_cb_set (ev_TYPE *watcher, callback)
		872
		873	Change the callback. You can change the callback at virtually any time
		874	(modulo threads).
		875
		876	=item ev_set_priority (ev_TYPE *watcher, priority)
		877
		878	=item int ev_priority (ev_TYPE *watcher)
		879
		880	Set and query the priority of the watcher. The priority is a small
		881	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		882	(default: C<-2>). Pending watchers with higher priority will be invoked
		883	before watchers with lower priority, but priority will not keep watchers
		884	from being executed (except for C<ev_idle> watchers).
		885
		886	This means that priorities are I<only> used for ordering callback
		887	invocation after new events have been received. This is useful, for
		888	example, to reduce latency after idling, or more often, to bind two
		889	watchers on the same event and make sure one is called first.
		890
		891	If you need to suppress invocation when higher priority events are pending
		892	you need to look at C<ev_idle> watchers, which provide this functionality.
		893
		894	You I<must not> change the priority of a watcher as long as it is active or
		895	pending.
		896
		897	The default priority used by watchers when no priority has been set is
		898	always C<0>, which is supposed to not be too high and not be too low :).
		899
		900	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		901	fine, as long as you do not mind that the priority value you query might
		902	or might not have been adjusted to be within valid range.
		903
		904	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		905
		906	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		907	C<loop> nor C<revents> need to be valid as long as the watcher callback
		908	can deal with that fact.
		909
		910	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		911
		912	If the watcher is pending, this function returns clears its pending status
		913	and returns its C<revents> bitset (as if its callback was invoked). If the
		914	watcher isn't pending it does nothing and returns C<0>.
		915
		916	=back
		917
398		918
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	919	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
400		920
401	Each watcher has, by default, a member C<void *data> that you can change	921	Each watcher has, by default, a member C<void *data> that you can change
402	and read at any time, libev will completely ignore it. This can be used	922	and read at any time, libev will completely ignore it. This can be used
…		…
420	{	940	{
421	struct my_io *w = (struct my_io *)w_;	941	struct my_io *w = (struct my_io *)w_;
422	...	942	...
423	}	943	}
424		944
425	More interesting and less C-conformant ways of catsing your callback type	945	More interesting and less C-conformant ways of casting your callback type
426	have been omitted....	946	instead have been omitted.
		947
		948	Another common scenario is having some data structure with multiple
		949	watchers:
		950
		951	struct my_biggy
		952	{
		953	int some_data;
		954	ev_timer t1;
		955	ev_timer t2;
		956	}
		957
		958	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		959	you need to use C<offsetof>:
		960
		961	#include <stddef.h>
		962
		963	static void
		964	t1_cb (EV_P_ struct ev_timer *w, int revents)
		965	{
		966	struct my_biggy big = (struct my_biggy *
		967	(((char *)w) - offsetof (struct my_biggy, t1));
		968	}
		969
		970	static void
		971	t2_cb (EV_P_ struct ev_timer *w, int revents)
		972	{
		973	struct my_biggy big = (struct my_biggy *
		974	(((char *)w) - offsetof (struct my_biggy, t2));
		975	}
427		976
428		977
429	=head1 WATCHER TYPES	978	=head1 WATCHER TYPES
430		979
431	This section describes each watcher in detail, but will not repeat	980	This section describes each watcher in detail, but will not repeat
432	information given in the last section.	981	information given in the last section. Any initialisation/set macros,
		982	functions and members specific to the watcher type are explained.
433		983
		984	Members are additionally marked with either I<[read-only]>, meaning that,
		985	while the watcher is active, you can look at the member and expect some
		986	sensible content, but you must not modify it (you can modify it while the
		987	watcher is stopped to your hearts content), or I<[read-write]>, which
		988	means you can expect it to have some sensible content while the watcher
		989	is active, but you can also modify it. Modifying it may not do something
		990	sensible or take immediate effect (or do anything at all), but libev will
		991	not crash or malfunction in any way.
		992
		993
434	=head2 C<ev_io> - is this file descriptor readable or writable	994	=head2 C<ev_io> - is this file descriptor readable or writable?
435		995
436	I/O watchers check whether a file descriptor is readable or writable	996	I/O watchers check whether a file descriptor is readable or writable
437	in each iteration of the event loop (This behaviour is called	997	in each iteration of the event loop, or, more precisely, when reading
438	level-triggering because you keep receiving events as long as the	998	would not block the process and writing would at least be able to write
439	condition persists. Remember you can stop the watcher if you don't want to	999	some data. This behaviour is called level-triggering because you keep
440	act on the event and neither want to receive future events).	1000	receiving events as long as the condition persists. Remember you can stop
		1001	the watcher if you don't want to act on the event and neither want to
		1002	receive future events.
441		1003
442	In general you can register as many read and/or write event watchers per	1004	In general you can register as many read and/or write event watchers per
443	fd as you want (as long as you don't confuse yourself). Setting all file	1005	fd as you want (as long as you don't confuse yourself). Setting all file
444	descriptors to non-blocking mode is also usually a good idea (but not	1006	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	1007	required if you know what you are doing).
446		1008
447	You have to be careful with dup'ed file descriptors, though. Some backends
448	(the linux epoll backend is a notable example) cannot handle dup'ed file
449	descriptors correctly if you register interest in two or more fds pointing
450	to the same underlying file/socket etc. description (that is, they share
451	the same underlying "file open").
452
453	If you must do this, then force the use of a known-to-be-good backend	1009	If you must do this, then force the use of a known-to-be-good backend
454	(at the time of this writing, this includes only EVMETHOD_SELECT and	1010	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
455	EVMETHOD_POLL).	1011	C<EVBACKEND_POLL>).
		1012
		1013	Another thing you have to watch out for is that it is quite easy to
		1014	receive "spurious" readyness notifications, that is your callback might
		1015	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1016	because there is no data. Not only are some backends known to create a
		1017	lot of those (for example solaris ports), it is very easy to get into
		1018	this situation even with a relatively standard program structure. Thus
		1019	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1020	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1021
		1022	If you cannot run the fd in non-blocking mode (for example you should not
		1023	play around with an Xlib connection), then you have to seperately re-test
		1024	whether a file descriptor is really ready with a known-to-be good interface
		1025	such as poll (fortunately in our Xlib example, Xlib already does this on
		1026	its own, so its quite safe to use).
		1027
		1028	=head3 The special problem of disappearing file descriptors
		1029
		1030	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1031	descriptor (either by calling C<close> explicitly or by any other means,
		1032	such as C<dup>). The reason is that you register interest in some file
		1033	descriptor, but when it goes away, the operating system will silently drop
		1034	this interest. If another file descriptor with the same number then is
		1035	registered with libev, there is no efficient way to see that this is, in
		1036	fact, a different file descriptor.
		1037
		1038	To avoid having to explicitly tell libev about such cases, libev follows
		1039	the following policy: Each time C<ev_io_set> is being called, libev
		1040	will assume that this is potentially a new file descriptor, otherwise
		1041	it is assumed that the file descriptor stays the same. That means that
		1042	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1043	descriptor even if the file descriptor number itself did not change.
		1044
		1045	This is how one would do it normally anyway, the important point is that
		1046	the libev application should not optimise around libev but should leave
		1047	optimisations to libev.
		1048
		1049	=head3 The special problem of dup'ed file descriptors
		1050
		1051	Some backends (e.g. epoll), cannot register events for file descriptors,
		1052	but only events for the underlying file descriptions. That means when you
		1053	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1054	events for them, only one file descriptor might actually receive events.
		1055
		1056	There is no workaround possible except not registering events
		1057	for potentially C<dup ()>'ed file descriptors, or to resort to
		1058	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1059
		1060	=head3 The special problem of fork
		1061
		1062	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1063	useless behaviour. Libev fully supports fork, but needs to be told about
		1064	it in the child.
		1065
		1066	To support fork in your programs, you either have to call
		1067	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1068	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1069	C<EVBACKEND_POLL>.
		1070
		1071
		1072	=head3 Watcher-Specific Functions
456		1073
457	=over 4	1074	=over 4
458		1075
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1076	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1077
461	=item ev_io_set (ev_io *, int fd, int events)	1078	=item ev_io_set (ev_io *, int fd, int events)
462		1079
463	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1080	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
464	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1081	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
465	EV_WRITE> to receive the given events.	1082	C<EV_READ | EV_WRITE> to receive the given events.
		1083
		1084	=item int fd [read-only]
		1085
		1086	The file descriptor being watched.
		1087
		1088	=item int events [read-only]
		1089
		1090	The events being watched.
466		1091
467	=back	1092	=back
468		1093
		1094	=head3 Examples
		1095
		1096	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1097	readable, but only once. Since it is likely line-buffered, you could
		1098	attempt to read a whole line in the callback.
		1099
		1100	static void
		1101	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1102	{
		1103	ev_io_stop (loop, w);
		1104	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1105	}
		1106
		1107	...
		1108	struct ev_loop *loop = ev_default_init (0);
		1109	struct ev_io stdin_readable;
		1110	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1111	ev_io_start (loop, &stdin_readable);
		1112	ev_loop (loop, 0);
		1113
		1114
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1115	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1116
471	Timer watchers are simple relative timers that generate an event after a	1117	Timer watchers are simple relative timers that generate an event after a
472	given time, and optionally repeating in regular intervals after that.	1118	given time, and optionally repeating in regular intervals after that.
473		1119
474	The timers are based on real time, that is, if you register an event that	1120	The timers are based on real time, that is, if you register an event that
475	times out after an hour and you reset your system clock to last years	1121	times out after an hour and you reset your system clock to last years
476	time, it will still time out after (roughly) and hour. "Roughly" because	1122	time, it will still time out after (roughly) and hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1123	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1124	monotonic clock option helps a lot here).
479		1125
480	The relative timeouts are calculated relative to the C<ev_now ()>	1126	The relative timeouts are calculated relative to the C<ev_now ()>
481	time. This is usually the right thing as this timestamp refers to the time	1127	time. This is usually the right thing as this timestamp refers to the time
482	of the event triggering whatever timeout you are modifying/starting. If	1128	of the event triggering whatever timeout you are modifying/starting. If
483	you suspect event processing to be delayed and you *need* to base the timeout	1129	you suspect event processing to be delayed and you I<need> to base the timeout
484	on the current time, use something like this to adjust for this:	1130	on the current time, use something like this to adjust for this:
485		1131
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1132	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1133
		1134	The callback is guarenteed to be invoked only when its timeout has passed,
		1135	but if multiple timers become ready during the same loop iteration then
		1136	order of execution is undefined.
		1137
		1138	=head3 Watcher-Specific Functions and Data Members
487		1139
488	=over 4	1140	=over 4
489		1141
490	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1142	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
491		1143
…		…
505	=item ev_timer_again (loop)	1157	=item ev_timer_again (loop)
506		1158
507	This will act as if the timer timed out and restart it again if it is	1159	This will act as if the timer timed out and restart it again if it is
508	repeating. The exact semantics are:	1160	repeating. The exact semantics are:
509		1161
		1162	If the timer is pending, its pending status is cleared.
		1163
510	If the timer is started but nonrepeating, stop it.	1164	If the timer is started but nonrepeating, stop it (as if it timed out).
511		1165
512	If the timer is repeating, either start it if necessary (with the repeat	1166	If the timer is repeating, either start it if necessary (with the
513	value), or reset the running timer to the repeat value.	1167	C<repeat> value), or reset the running timer to the C<repeat> value.
514		1168
515	This sounds a bit complicated, but here is a useful and typical	1169	This sounds a bit complicated, but here is a useful and typical
516	example: Imagine you have a tcp connection and you want a so-called idle	1170	example: Imagine you have a tcp connection and you want a so-called idle
517	timeout, that is, you want to be called when there have been, say, 60	1171	timeout, that is, you want to be called when there have been, say, 60
518	seconds of inactivity on the socket. The easiest way to do this is to	1172	seconds of inactivity on the socket. The easiest way to do this is to
519	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1173	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
520	time you successfully read or write some data. If you go into an idle	1174	C<ev_timer_again> each time you successfully read or write some data. If
521	state where you do not expect data to travel on the socket, you can stop	1175	you go into an idle state where you do not expect data to travel on the
522	the timer, and again will automatically restart it if need be.	1176	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1177	automatically restart it if need be.
		1178
		1179	That means you can ignore the C<after> value and C<ev_timer_start>
		1180	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1181
		1182	ev_timer_init (timer, callback, 0., 5.);
		1183	ev_timer_again (loop, timer);
		1184	...
		1185	timer->again = 17.;
		1186	ev_timer_again (loop, timer);
		1187	...
		1188	timer->again = 10.;
		1189	ev_timer_again (loop, timer);
		1190
		1191	This is more slightly efficient then stopping/starting the timer each time
		1192	you want to modify its timeout value.
		1193
		1194	=item ev_tstamp repeat [read-write]
		1195
		1196	The current C<repeat> value. Will be used each time the watcher times out
		1197	or C<ev_timer_again> is called and determines the next timeout (if any),
		1198	which is also when any modifications are taken into account.
523		1199
524	=back	1200	=back
525		1201
		1202	=head3 Examples
		1203
		1204	Example: Create a timer that fires after 60 seconds.
		1205
		1206	static void
		1207	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1208	{
		1209	.. one minute over, w is actually stopped right here
		1210	}
		1211
		1212	struct ev_timer mytimer;
		1213	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1214	ev_timer_start (loop, &mytimer);
		1215
		1216	Example: Create a timeout timer that times out after 10 seconds of
		1217	inactivity.
		1218
		1219	static void
		1220	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1221	{
		1222	.. ten seconds without any activity
		1223	}
		1224
		1225	struct ev_timer mytimer;
		1226	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1227	ev_timer_again (&mytimer); /* start timer */
		1228	ev_loop (loop, 0);
		1229
		1230	// and in some piece of code that gets executed on any "activity":
		1231	// reset the timeout to start ticking again at 10 seconds
		1232	ev_timer_again (&mytimer);
		1233
		1234
526	=head2 C<ev_periodic> - to cron or not to cron	1235	=head2 C<ev_periodic> - to cron or not to cron?
527		1236
528	Periodic watchers are also timers of a kind, but they are very versatile	1237	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	1238	(and unfortunately a bit complex).
530		1239
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1240	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
532	but on wallclock time (absolute time). You can tell a periodic watcher	1241	but on wallclock time (absolute time). You can tell a periodic watcher
533	to trigger "at" some specific point in time. For example, if you tell a	1242	to trigger "at" some specific point in time. For example, if you tell a
534	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1243	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
535	+ 10.>) and then reset your system clock to the last year, then it will	1244	+ 10.>) and then reset your system clock to the last year, then it will
536	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1245	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
537	roughly 10 seconds later and of course not if you reset your system time	1246	roughly 10 seconds later).
538	again).
539		1247
540	They can also be used to implement vastly more complex timers, such as	1248	They can also be used to implement vastly more complex timers, such as
541	triggering an event on eahc midnight, local time.	1249	triggering an event on each midnight, local time or other, complicated,
		1250	rules.
		1251
		1252	As with timers, the callback is guarenteed to be invoked only when the
		1253	time (C<at>) has been passed, but if multiple periodic timers become ready
		1254	during the same loop iteration then order of execution is undefined.
		1255
		1256	=head3 Watcher-Specific Functions and Data Members
542		1257
543	=over 4	1258	=over 4
544		1259
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1260	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
546		1261
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1262	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
548		1263
549	Lots of arguments, lets sort it out... There are basically three modes of	1264	Lots of arguments, lets sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	1265	operation, and we will explain them from simplest to complex:
551		1266
552
553	=over 4	1267	=over 4
554		1268
555	=item * absolute timer (interval = reschedule_cb = 0)	1269	=item * absolute timer (at = time, interval = reschedule_cb = 0)
556		1270
557	In this configuration the watcher triggers an event at the wallclock time	1271	In this configuration the watcher triggers an event at the wallclock time
558	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1272	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
559	that is, if it is to be run at January 1st 2011 then it will run when the	1273	that is, if it is to be run at January 1st 2011 then it will run when the
560	system time reaches or surpasses this time.	1274	system time reaches or surpasses this time.
561		1275
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1276	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
563		1277
564	In this mode the watcher will always be scheduled to time out at the next	1278	In this mode the watcher will always be scheduled to time out at the next
565	C<at + N * interval> time (for some integer N) and then repeat, regardless	1279	C<at + N * interval> time (for some integer N, which can also be negative)
566	of any time jumps.	1280	and then repeat, regardless of any time jumps.
567		1281
568	This can be used to create timers that do not drift with respect to system	1282	This can be used to create timers that do not drift with respect to system
569	time:	1283	time:
570		1284
571	ev_periodic_set (&periodic, 0., 3600., 0);	1285	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
577		1291
578	Another way to think about it (for the mathematically inclined) is that	1292	Another way to think about it (for the mathematically inclined) is that
579	C<ev_periodic> will try to run the callback in this mode at the next possible	1293	C<ev_periodic> will try to run the callback in this mode at the next possible
580	time where C<time = at (mod interval)>, regardless of any time jumps.	1294	time where C<time = at (mod interval)>, regardless of any time jumps.
581		1295
		1296	For numerical stability it is preferable that the C<at> value is near
		1297	C<ev_now ()> (the current time), but there is no range requirement for
		1298	this value.
		1299
582	=item * manual reschedule mode (reschedule_cb = callback)	1300	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
583		1301
584	In this mode the values for C<interval> and C<at> are both being	1302	In this mode the values for C<interval> and C<at> are both being
585	ignored. Instead, each time the periodic watcher gets scheduled, the	1303	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	1304	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	1305	current time as second argument.
588		1306
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1307	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
590	ever, or make any event loop modifications>. If you need to stop it,	1308	ever, or make any event loop modifications>. If you need to stop it,
591	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1309	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592	starting a prepare watcher).	1310	starting an C<ev_prepare> watcher, which is legal).
593		1311
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1312	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
595	ev_tstamp now)>, e.g.:	1313	ev_tstamp now)>, e.g.:
596		1314
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1315	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
620	Simply stops and restarts the periodic watcher again. This is only useful	1338	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	1339	when you changed some parameters or the reschedule callback would return
622	a different time than the last time it was called (e.g. in a crond like	1340	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	1341	program when the crontabs have changed).
624		1342
		1343	=item ev_tstamp offset [read-write]
		1344
		1345	When repeating, this contains the offset value, otherwise this is the
		1346	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1347
		1348	Can be modified any time, but changes only take effect when the periodic
		1349	timer fires or C<ev_periodic_again> is being called.
		1350
		1351	=item ev_tstamp interval [read-write]
		1352
		1353	The current interval value. Can be modified any time, but changes only
		1354	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1355	called.
		1356
		1357	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1358
		1359	The current reschedule callback, or C<0>, if this functionality is
		1360	switched off. Can be changed any time, but changes only take effect when
		1361	the periodic timer fires or C<ev_periodic_again> is being called.
		1362
		1363	=item ev_tstamp at [read-only]
		1364
		1365	When active, contains the absolute time that the watcher is supposed to
		1366	trigger next.
		1367
625	=back	1368	=back
626		1369
		1370	=head3 Examples
		1371
		1372	Example: Call a callback every hour, or, more precisely, whenever the
		1373	system clock is divisible by 3600. The callback invocation times have
		1374	potentially a lot of jittering, but good long-term stability.
		1375
		1376	static void
		1377	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1378	{
		1379	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1380	}
		1381
		1382	struct ev_periodic hourly_tick;
		1383	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1384	ev_periodic_start (loop, &hourly_tick);
		1385
		1386	Example: The same as above, but use a reschedule callback to do it:
		1387
		1388	#include <math.h>
		1389
		1390	static ev_tstamp
		1391	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1392	{
		1393	return fmod (now, 3600.) + 3600.;
		1394	}
		1395
		1396	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1397
		1398	Example: Call a callback every hour, starting now:
		1399
		1400	struct ev_periodic hourly_tick;
		1401	ev_periodic_init (&hourly_tick, clock_cb,
		1402	fmod (ev_now (loop), 3600.), 3600., 0);
		1403	ev_periodic_start (loop, &hourly_tick);
		1404
		1405
627	=head2 C<ev_signal> - signal me when a signal gets signalled	1406	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		1407
629	Signal watchers will trigger an event when the process receives a specific	1408	Signal watchers will trigger an event when the process receives a specific
630	signal one or more times. Even though signals are very asynchronous, libev	1409	signal one or more times. Even though signals are very asynchronous, libev
631	will try it's best to deliver signals synchronously, i.e. as part of the	1410	will try it's best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	1411	normal event processing, like any other event.
…		…
636	with the kernel (thus it coexists with your own signal handlers as long	1415	with the kernel (thus it coexists with your own signal handlers as long
637	as you don't register any with libev). Similarly, when the last signal	1416	as you don't register any with libev). Similarly, when the last signal
638	watcher for a signal is stopped libev will reset the signal handler to	1417	watcher for a signal is stopped libev will reset the signal handler to
639	SIG_DFL (regardless of what it was set to before).	1418	SIG_DFL (regardless of what it was set to before).
640		1419
		1420	=head3 Watcher-Specific Functions and Data Members
		1421
641	=over 4	1422	=over 4
642		1423
643	=item ev_signal_init (ev_signal *, callback, int signum)	1424	=item ev_signal_init (ev_signal *, callback, int signum)
644		1425
645	=item ev_signal_set (ev_signal *, int signum)	1426	=item ev_signal_set (ev_signal *, int signum)
646		1427
647	Configures the watcher to trigger on the given signal number (usually one	1428	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	1429	of the C<SIGxxx> constants).
649		1430
		1431	=item int signum [read-only]
		1432
		1433	The signal the watcher watches out for.
		1434
650	=back	1435	=back
651		1436
		1437
652	=head2 C<ev_child> - wait for pid status changes	1438	=head2 C<ev_child> - watch out for process status changes
653		1439
654	Child watchers trigger when your process receives a SIGCHLD in response to	1440	Child watchers trigger when your process receives a SIGCHLD in response to
655	some child status changes (most typically when a child of yours dies).	1441	some child status changes (most typically when a child of yours dies).
656		1442
		1443	=head3 Watcher-Specific Functions and Data Members
		1444
657	=over 4	1445	=over 4
658		1446
659	=item ev_child_init (ev_child *, callback, int pid)	1447	=item ev_child_init (ev_child *, callback, int pid, int trace)
660		1448
661	=item ev_child_set (ev_child *, int pid)	1449	=item ev_child_set (ev_child *, int pid, int trace)
662		1450
663	Configures the watcher to wait for status changes of process C<pid> (or	1451	Configures the watcher to wait for status changes of process C<pid> (or
664	I<any> process if C<pid> is specified as C<0>). The callback can look	1452	I<any> process if C<pid> is specified as C<0>). The callback can look
665	at the C<rstatus> member of the C<ev_child> watcher structure to see	1453	at the C<rstatus> member of the C<ev_child> watcher structure to see
666	the status word (use the macros from C<sys/wait.h> and see your systems	1454	the status word (use the macros from C<sys/wait.h> and see your systems
667	C<waitpid> documentation). The C<rpid> member contains the pid of the	1455	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	1456	process causing the status change. C<trace> must be either C<0> (only
		1457	activate the watcher when the process terminates) or C<1> (additionally
		1458	activate the watcher when the process is stopped or continued).
		1459
		1460	=item int pid [read-only]
		1461
		1462	The process id this watcher watches out for, or C<0>, meaning any process id.
		1463
		1464	=item int rpid [read-write]
		1465
		1466	The process id that detected a status change.
		1467
		1468	=item int rstatus [read-write]
		1469
		1470	The process exit/trace status caused by C<rpid> (see your systems
		1471	C<waitpid> and C<sys/wait.h> documentation for details).
669		1472
670	=back	1473	=back
671		1474
		1475	=head3 Examples
		1476
		1477	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1478
		1479	static void
		1480	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1481	{
		1482	ev_unloop (loop, EVUNLOOP_ALL);
		1483	}
		1484
		1485	struct ev_signal signal_watcher;
		1486	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1487	ev_signal_start (loop, &sigint_cb);
		1488
		1489
		1490	=head2 C<ev_stat> - did the file attributes just change?
		1491
		1492	This watches a filesystem path for attribute changes. That is, it calls
		1493	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1494	compared to the last time, invoking the callback if it did.
		1495
		1496	The path does not need to exist: changing from "path exists" to "path does
		1497	not exist" is a status change like any other. The condition "path does
		1498	not exist" is signified by the C<st_nlink> field being zero (which is
		1499	otherwise always forced to be at least one) and all the other fields of
		1500	the stat buffer having unspecified contents.
		1501
		1502	The path I<should> be absolute and I<must not> end in a slash. If it is
		1503	relative and your working directory changes, the behaviour is undefined.
		1504
		1505	Since there is no standard to do this, the portable implementation simply
		1506	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1507	can specify a recommended polling interval for this case. If you specify
		1508	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1509	unspecified default> value will be used (which you can expect to be around
		1510	five seconds, although this might change dynamically). Libev will also
		1511	impose a minimum interval which is currently around C<0.1>, but thats
		1512	usually overkill.
		1513
		1514	This watcher type is not meant for massive numbers of stat watchers,
		1515	as even with OS-supported change notifications, this can be
		1516	resource-intensive.
		1517
		1518	At the time of this writing, only the Linux inotify interface is
		1519	implemented (implementing kqueue support is left as an exercise for the
		1520	reader). Inotify will be used to give hints only and should not change the
		1521	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1522	to fall back to regular polling again even with inotify, but changes are
		1523	usually detected immediately, and if the file exists there will be no
		1524	polling.
		1525
		1526	=head3 Inotify
		1527
		1528	When C<inotify (7)> support has been compiled into libev (generally only
		1529	available on Linux) and present at runtime, it will be used to speed up
		1530	change detection where possible. The inotify descriptor will be created lazily
		1531	when the first C<ev_stat> watcher is being started.
		1532
		1533	Inotify presense does not change the semantics of C<ev_stat> watchers
		1534	except that changes might be detected earlier, and in some cases, to avoid
		1535	making regular C<stat> calls. Even in the presense of inotify support
		1536	there are many cases where libev has to resort to regular C<stat> polling.
		1537
		1538	(There is no support for kqueue, as apparently it cannot be used to
		1539	implement this functionality, due to the requirement of having a file
		1540	descriptor open on the object at all times).
		1541
		1542	=head3 The special problem of stat time resolution
		1543
		1544	The C<stat ()> syscall only supports full-second resolution portably, and
		1545	even on systems where the resolution is higher, many filesystems still
		1546	only support whole seconds.
		1547
		1548	That means that, if the time is the only thing that changes, you might
		1549	miss updates: on the first update, C<ev_stat> detects a change and calls
		1550	your callback, which does something. When there is another update within
		1551	the same second, C<ev_stat> will be unable to detect it.
		1552
		1553	The solution to this is to delay acting on a change for a second (or till
		1554	the next second boundary), using a roughly one-second delay C<ev_timer>
		1555	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1556	is added to work around small timing inconsistencies of some operating
		1557	systems.
		1558
		1559	=head3 Watcher-Specific Functions and Data Members
		1560
		1561	=over 4
		1562
		1563	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1564
		1565	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1566
		1567	Configures the watcher to wait for status changes of the given
		1568	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1569	be detected and should normally be specified as C<0> to let libev choose
		1570	a suitable value. The memory pointed to by C<path> must point to the same
		1571	path for as long as the watcher is active.
		1572
		1573	The callback will be receive C<EV_STAT> when a change was detected,
		1574	relative to the attributes at the time the watcher was started (or the
		1575	last change was detected).
		1576
		1577	=item ev_stat_stat (ev_stat *)
		1578
		1579	Updates the stat buffer immediately with new values. If you change the
		1580	watched path in your callback, you could call this fucntion to avoid
		1581	detecting this change (while introducing a race condition). Can also be
		1582	useful simply to find out the new values.
		1583
		1584	=item ev_statdata attr [read-only]
		1585
		1586	The most-recently detected attributes of the file. Although the type is of
		1587	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1588	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1589	was some error while C<stat>ing the file.
		1590
		1591	=item ev_statdata prev [read-only]
		1592
		1593	The previous attributes of the file. The callback gets invoked whenever
		1594	C<prev> != C<attr>.
		1595
		1596	=item ev_tstamp interval [read-only]
		1597
		1598	The specified interval.
		1599
		1600	=item const char *path [read-only]
		1601
		1602	The filesystem path that is being watched.
		1603
		1604	=back
		1605
		1606	=head3 Examples
		1607
		1608	Example: Watch C</etc/passwd> for attribute changes.
		1609
		1610	static void
		1611	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1612	{
		1613	/* /etc/passwd changed in some way */
		1614	if (w->attr.st_nlink)
		1615	{
		1616	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1617	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1618	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1619	}
		1620	else
		1621	/* you shalt not abuse printf for puts */
		1622	puts ("wow, /etc/passwd is not there, expect problems. "
		1623	"if this is windows, they already arrived\n");
		1624	}
		1625
		1626	...
		1627	ev_stat passwd;
		1628
		1629	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1630	ev_stat_start (loop, &passwd);
		1631
		1632	Example: Like above, but additionally use a one-second delay so we do not
		1633	miss updates (however, frequent updates will delay processing, too, so
		1634	one might do the work both on C<ev_stat> callback invocation I<and> on
		1635	C<ev_timer> callback invocation).
		1636
		1637	static ev_stat passwd;
		1638	static ev_timer timer;
		1639
		1640	static void
		1641	timer_cb (EV_P_ ev_timer *w, int revents)
		1642	{
		1643	ev_timer_stop (EV_A_ w);
		1644
		1645	/* now it's one second after the most recent passwd change */
		1646	}
		1647
		1648	static void
		1649	stat_cb (EV_P_ ev_stat *w, int revents)
		1650	{
		1651	/* reset the one-second timer */
		1652	ev_timer_again (EV_A_ &timer);
		1653	}
		1654
		1655	...
		1656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1657	ev_stat_start (loop, &passwd);
		1658	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1659
		1660
672	=head2 C<ev_idle> - when you've got nothing better to do	1661	=head2 C<ev_idle> - when you've got nothing better to do...
673		1662
674	Idle watchers trigger events when there are no other events are pending	1663	Idle watchers trigger events when no other events of the same or higher
675	(prepare, check and other idle watchers do not count). That is, as long	1664	priority are pending (prepare, check and other idle watchers do not
676	as your process is busy handling sockets or timeouts (or even signals,	1665	count).
677	imagine) it will not be triggered. But when your process is idle all idle	1666
678	watchers are being called again and again, once per event loop iteration -	1667	That is, as long as your process is busy handling sockets or timeouts
		1668	(or even signals, imagine) of the same or higher priority it will not be
		1669	triggered. But when your process is idle (or only lower-priority watchers
		1670	are pending), the idle watchers are being called once per event loop
679	until stopped, that is, or your process receives more events and becomes	1671	iteration - until stopped, that is, or your process receives more events
680	busy.	1672	and becomes busy again with higher priority stuff.
681		1673
682	The most noteworthy effect is that as long as any idle watchers are	1674	The most noteworthy effect is that as long as any idle watchers are
683	active, the process will not block when waiting for new events.	1675	active, the process will not block when waiting for new events.
684		1676
685	Apart from keeping your process non-blocking (which is a useful	1677	Apart from keeping your process non-blocking (which is a useful
686	effect on its own sometimes), idle watchers are a good place to do	1678	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	1679	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	1680	event loop has handled all outstanding events.
689		1681
		1682	=head3 Watcher-Specific Functions and Data Members
		1683
690	=over 4	1684	=over 4
691		1685
692	=item ev_idle_init (ev_signal *, callback)	1686	=item ev_idle_init (ev_signal *, callback)
693		1687
694	Initialises and configures the idle watcher - it has no parameters of any	1688	Initialises and configures the idle watcher - it has no parameters of any
695	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1689	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	1690	believe me.
697		1691
698	=back	1692	=back
699		1693
		1694	=head3 Examples
		1695
		1696	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1697	callback, free it. Also, use no error checking, as usual.
		1698
		1699	static void
		1700	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1701	{
		1702	free (w);
		1703	// now do something you wanted to do when the program has
		1704	// no longer anything immediate to do.
		1705	}
		1706
		1707	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1708	ev_idle_init (idle_watcher, idle_cb);
		1709	ev_idle_start (loop, idle_cb);
		1710
		1711
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		1713
702	Prepare and check watchers are usually (but not always) used in tandem:	1714	Prepare and check watchers are usually (but not always) used in tandem:
703	prepare watchers get invoked before the process blocks and check watchers	1715	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	1716	afterwards.
705		1717
		1718	You I<must not> call C<ev_loop> or similar functions that enter
		1719	the current event loop from either C<ev_prepare> or C<ev_check>
		1720	watchers. Other loops than the current one are fine, however. The
		1721	rationale behind this is that you do not need to check for recursion in
		1722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1723	C<ev_check> so if you have one watcher of each kind they will always be
		1724	called in pairs bracketing the blocking call.
		1725
706	Their main purpose is to integrate other event mechanisms into libev. This	1726	Their main purpose is to integrate other event mechanisms into libev and
707	could be used, for example, to track variable changes, implement your own	1727	their use is somewhat advanced. This could be used, for example, to track
708	watchers, integrate net-snmp or a coroutine library and lots more.	1728	variable changes, implement your own watchers, integrate net-snmp or a
		1729	coroutine library and lots more. They are also occasionally useful if
		1730	you cache some data and want to flush it before blocking (for example,
		1731	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1732	watcher).
709		1733
710	This is done by examining in each prepare call which file descriptors need	1734	This is done by examining in each prepare call which file descriptors need
711	to be watched by the other library, registering C<ev_io> watchers for	1735	to be watched by the other library, registering C<ev_io> watchers for
712	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1736	them and starting an C<ev_timer> watcher for any timeouts (many libraries
713	provide just this functionality). Then, in the check watcher you check for	1737	provide just this functionality). Then, in the check watcher you check for
…		…
723	with priority higher than or equal to the event loop and one coroutine	1747	with priority higher than or equal to the event loop and one coroutine
724	of lower priority, but only once, using idle watchers to keep the event	1748	of lower priority, but only once, using idle watchers to keep the event
725	loop from blocking if lower-priority coroutines are active, thus mapping	1749	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	1750	low-priority coroutines to idle/background tasks).
727		1751
		1752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1753	priority, to ensure that they are being run before any other watchers
		1754	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1755	too) should not activate ("feed") events into libev. While libev fully
		1756	supports this, they will be called before other C<ev_check> watchers
		1757	did their job. As C<ev_check> watchers are often used to embed other
		1758	(non-libev) event loops those other event loops might be in an unusable
		1759	state until their C<ev_check> watcher ran (always remind yourself to
		1760	coexist peacefully with others).
		1761
		1762	=head3 Watcher-Specific Functions and Data Members
		1763
728	=over 4	1764	=over 4
729		1765
730	=item ev_prepare_init (ev_prepare *, callback)	1766	=item ev_prepare_init (ev_prepare *, callback)
731		1767
732	=item ev_check_init (ev_check *, callback)	1768	=item ev_check_init (ev_check *, callback)
…		…
734	Initialises and configures the prepare or check watcher - they have no	1770	Initialises and configures the prepare or check watcher - they have no
735	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1771	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
736	macros, but using them is utterly, utterly and completely pointless.	1772	macros, but using them is utterly, utterly and completely pointless.
737		1773
738	=back	1774	=back
		1775
		1776	=head3 Examples
		1777
		1778	There are a number of principal ways to embed other event loops or modules
		1779	into libev. Here are some ideas on how to include libadns into libev
		1780	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1781	use for an actually working example. Another Perl module named C<EV::Glib>
		1782	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1783	into the Glib event loop).
		1784
		1785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1786	and in a check watcher, destroy them and call into libadns. What follows
		1787	is pseudo-code only of course. This requires you to either use a low
		1788	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1789	the callbacks for the IO/timeout watchers might not have been called yet.
		1790
		1791	static ev_io iow [nfd];
		1792	static ev_timer tw;
		1793
		1794	static void
		1795	io_cb (ev_loop *loop, ev_io *w, int revents)
		1796	{
		1797	}
		1798
		1799	// create io watchers for each fd and a timer before blocking
		1800	static void
		1801	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1802	{
		1803	int timeout = 3600000;
		1804	struct pollfd fds [nfd];
		1805	// actual code will need to loop here and realloc etc.
		1806	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1807
		1808	/* the callback is illegal, but won't be called as we stop during check */
		1809	ev_timer_init (&tw, 0, timeout * 1e-3);
		1810	ev_timer_start (loop, &tw);
		1811
		1812	// create one ev_io per pollfd
		1813	for (int i = 0; i < nfd; ++i)
		1814	{
		1815	ev_io_init (iow + i, io_cb, fds [i].fd,
		1816	((fds [i].events & POLLIN ? EV_READ : 0)
		1817	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1818
		1819	fds [i].revents = 0;
		1820	ev_io_start (loop, iow + i);
		1821	}
		1822	}
		1823
		1824	// stop all watchers after blocking
		1825	static void
		1826	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1827	{
		1828	ev_timer_stop (loop, &tw);
		1829
		1830	for (int i = 0; i < nfd; ++i)
		1831	{
		1832	// set the relevant poll flags
		1833	// could also call adns_processreadable etc. here
		1834	struct pollfd *fd = fds + i;
		1835	int revents = ev_clear_pending (iow + i);
		1836	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1837	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1838
		1839	// now stop the watcher
		1840	ev_io_stop (loop, iow + i);
		1841	}
		1842
		1843	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1844	}
		1845
		1846	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1847	in the prepare watcher and would dispose of the check watcher.
		1848
		1849	Method 3: If the module to be embedded supports explicit event
		1850	notification (adns does), you can also make use of the actual watcher
		1851	callbacks, and only destroy/create the watchers in the prepare watcher.
		1852
		1853	static void
		1854	timer_cb (EV_P_ ev_timer *w, int revents)
		1855	{
		1856	adns_state ads = (adns_state)w->data;
		1857	update_now (EV_A);
		1858
		1859	adns_processtimeouts (ads, &tv_now);
		1860	}
		1861
		1862	static void
		1863	io_cb (EV_P_ ev_io *w, int revents)
		1864	{
		1865	adns_state ads = (adns_state)w->data;
		1866	update_now (EV_A);
		1867
		1868	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1869	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1870	}
		1871
		1872	// do not ever call adns_afterpoll
		1873
		1874	Method 4: Do not use a prepare or check watcher because the module you
		1875	want to embed is too inflexible to support it. Instead, youc na override
		1876	their poll function. The drawback with this solution is that the main
		1877	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1878	this.
		1879
		1880	static gint
		1881	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1882	{
		1883	int got_events = 0;
		1884
		1885	for (n = 0; n < nfds; ++n)
		1886	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1887
		1888	if (timeout >= 0)
		1889	// create/start timer
		1890
		1891	// poll
		1892	ev_loop (EV_A_ 0);
		1893
		1894	// stop timer again
		1895	if (timeout >= 0)
		1896	ev_timer_stop (EV_A_ &to);
		1897
		1898	// stop io watchers again - their callbacks should have set
		1899	for (n = 0; n < nfds; ++n)
		1900	ev_io_stop (EV_A_ iow [n]);
		1901
		1902	return got_events;
		1903	}
		1904
		1905
		1906	=head2 C<ev_embed> - when one backend isn't enough...
		1907
		1908	This is a rather advanced watcher type that lets you embed one event loop
		1909	into another (currently only C<ev_io> events are supported in the embedded
		1910	loop, other types of watchers might be handled in a delayed or incorrect
		1911	fashion and must not be used).
		1912
		1913	There are primarily two reasons you would want that: work around bugs and
		1914	prioritise I/O.
		1915
		1916	As an example for a bug workaround, the kqueue backend might only support
		1917	sockets on some platform, so it is unusable as generic backend, but you
		1918	still want to make use of it because you have many sockets and it scales
		1919	so nicely. In this case, you would create a kqueue-based loop and embed it
		1920	into your default loop (which might use e.g. poll). Overall operation will
		1921	be a bit slower because first libev has to poll and then call kevent, but
		1922	at least you can use both at what they are best.
		1923
		1924	As for prioritising I/O: rarely you have the case where some fds have
		1925	to be watched and handled very quickly (with low latency), and even
		1926	priorities and idle watchers might have too much overhead. In this case
		1927	you would put all the high priority stuff in one loop and all the rest in
		1928	a second one, and embed the second one in the first.
		1929
		1930	As long as the watcher is active, the callback will be invoked every time
		1931	there might be events pending in the embedded loop. The callback must then
		1932	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1933	their callbacks (you could also start an idle watcher to give the embedded
		1934	loop strictly lower priority for example). You can also set the callback
		1935	to C<0>, in which case the embed watcher will automatically execute the
		1936	embedded loop sweep.
		1937
		1938	As long as the watcher is started it will automatically handle events. The
		1939	callback will be invoked whenever some events have been handled. You can
		1940	set the callback to C<0> to avoid having to specify one if you are not
		1941	interested in that.
		1942
		1943	Also, there have not currently been made special provisions for forking:
		1944	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1945	but you will also have to stop and restart any C<ev_embed> watchers
		1946	yourself.
		1947
		1948	Unfortunately, not all backends are embeddable, only the ones returned by
		1949	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1950	portable one.
		1951
		1952	So when you want to use this feature you will always have to be prepared
		1953	that you cannot get an embeddable loop. The recommended way to get around
		1954	this is to have a separate variables for your embeddable loop, try to
		1955	create it, and if that fails, use the normal loop for everything.
		1956
		1957	=head3 Watcher-Specific Functions and Data Members
		1958
		1959	=over 4
		1960
		1961	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1962
		1963	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1964
		1965	Configures the watcher to embed the given loop, which must be
		1966	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1967	invoked automatically, otherwise it is the responsibility of the callback
		1968	to invoke it (it will continue to be called until the sweep has been done,
		1969	if you do not want thta, you need to temporarily stop the embed watcher).
		1970
		1971	=item ev_embed_sweep (loop, ev_embed *)
		1972
		1973	Make a single, non-blocking sweep over the embedded loop. This works
		1974	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1975	apropriate way for embedded loops.
		1976
		1977	=item struct ev_loop *other [read-only]
		1978
		1979	The embedded event loop.
		1980
		1981	=back
		1982
		1983	=head3 Examples
		1984
		1985	Example: Try to get an embeddable event loop and embed it into the default
		1986	event loop. If that is not possible, use the default loop. The default
		1987	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1988	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1989	used).
		1990
		1991	struct ev_loop *loop_hi = ev_default_init (0);
		1992	struct ev_loop *loop_lo = 0;
		1993	struct ev_embed embed;
		1994
		1995	// see if there is a chance of getting one that works
		1996	// (remember that a flags value of 0 means autodetection)
		1997	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1998	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1999	: 0;
		2000
		2001	// if we got one, then embed it, otherwise default to loop_hi
		2002	if (loop_lo)
		2003	{
		2004	ev_embed_init (&embed, 0, loop_lo);
		2005	ev_embed_start (loop_hi, &embed);
		2006	}
		2007	else
		2008	loop_lo = loop_hi;
		2009
		2010	Example: Check if kqueue is available but not recommended and create
		2011	a kqueue backend for use with sockets (which usually work with any
		2012	kqueue implementation). Store the kqueue/socket-only event loop in
		2013	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2014
		2015	struct ev_loop *loop = ev_default_init (0);
		2016	struct ev_loop *loop_socket = 0;
		2017	struct ev_embed embed;
		2018
		2019	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2020	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2021	{
		2022	ev_embed_init (&embed, 0, loop_socket);
		2023	ev_embed_start (loop, &embed);
		2024	}
		2025
		2026	if (!loop_socket)
		2027	loop_socket = loop;
		2028
		2029	// now use loop_socket for all sockets, and loop for everything else
		2030
		2031
		2032	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2033
		2034	Fork watchers are called when a C<fork ()> was detected (usually because
		2035	whoever is a good citizen cared to tell libev about it by calling
		2036	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2037	event loop blocks next and before C<ev_check> watchers are being called,
		2038	and only in the child after the fork. If whoever good citizen calling
		2039	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2040	handlers will be invoked, too, of course.
		2041
		2042	=head3 Watcher-Specific Functions and Data Members
		2043
		2044	=over 4
		2045
		2046	=item ev_fork_init (ev_signal *, callback)
		2047
		2048	Initialises and configures the fork watcher - it has no parameters of any
		2049	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2050	believe me.
		2051
		2052	=back
		2053
		2054
		2055	=head2 C<ev_async> - how to wake up another event loop
		2056
		2057	In general, you cannot use an C<ev_loop> from multiple threads or other
		2058	asynchronous sources such as signal handlers (as opposed to multiple event
		2059	loops - those are of course safe to use in different threads).
		2060
		2061	Sometimes, however, you need to wake up another event loop you do not
		2062	control, for example because it belongs to another thread. This is what
		2063	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2064	can signal it by calling C<ev_async_send>, which is thread- and signal
		2065	safe.
		2066
		2067	This functionality is very similar to C<ev_signal> watchers, as signals,
		2068	too, are asynchronous in nature, and signals, too, will be compressed
		2069	(i.e. the number of callback invocations may be less than the number of
		2070	C<ev_async_sent> calls).
		2071
		2072	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2073	just the default loop.
		2074
		2075	=head3 Queueing
		2076
		2077	C<ev_async> does not support queueing of data in any way. The reason
		2078	is that the author does not know of a simple (or any) algorithm for a
		2079	multiple-writer-single-reader queue that works in all cases and doesn't
		2080	need elaborate support such as pthreads.
		2081
		2082	That means that if you want to queue data, you have to provide your own
		2083	queue. And here is how you would implement locking:
		2084
		2085	=over 4
		2086
		2087	=item queueing from a signal handler context
		2088
		2089	To implement race-free queueing, you simply add to the queue in the signal
		2090	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2091	some fictitiuous SIGUSR1 handler:
		2092
		2093	static ev_async mysig;
		2094
		2095	static void
		2096	sigusr1_handler (void)
		2097	{
		2098	sometype data;
		2099
		2100	// no locking etc.
		2101	queue_put (data);
		2102	ev_async_send (DEFAULT_LOOP, &mysig);
		2103	}
		2104
		2105	static void
		2106	mysig_cb (EV_P_ ev_async *w, int revents)
		2107	{
		2108	sometype data;
		2109	sigset_t block, prev;
		2110
		2111	sigemptyset (&block);
		2112	sigaddset (&block, SIGUSR1);
		2113	sigprocmask (SIG_BLOCK, &block, &prev);
		2114
		2115	while (queue_get (&data))
		2116	process (data);
		2117
		2118	if (sigismember (&prev, SIGUSR1)
		2119	sigprocmask (SIG_UNBLOCK, &block, 0);
		2120	}
		2121
		2122	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2123	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2124	either...).
		2125
		2126	=item queueing from a thread context
		2127
		2128	The strategy for threads is different, as you cannot (easily) block
		2129	threads but you can easily preempt them, so to queue safely you need to
		2130	emply a traditional mutex lock, such as in this pthread example:
		2131
		2132	static ev_async mysig;
		2133	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2134
		2135	static void
		2136	otherthread (void)
		2137	{
		2138	// only need to lock the actual queueing operation
		2139	pthread_mutex_lock (&mymutex);
		2140	queue_put (data);
		2141	pthread_mutex_unlock (&mymutex);
		2142
		2143	ev_async_send (DEFAULT_LOOP, &mysig);
		2144	}
		2145
		2146	static void
		2147	mysig_cb (EV_P_ ev_async *w, int revents)
		2148	{
		2149	pthread_mutex_lock (&mymutex);
		2150
		2151	while (queue_get (&data))
		2152	process (data);
		2153
		2154	pthread_mutex_unlock (&mymutex);
		2155	}
		2156
		2157	=back
		2158
		2159
		2160	=head3 Watcher-Specific Functions and Data Members
		2161
		2162	=over 4
		2163
		2164	=item ev_async_init (ev_async *, callback)
		2165
		2166	Initialises and configures the async watcher - it has no parameters of any
		2167	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2168	believe me.
		2169
		2170	=item ev_async_send (loop, ev_async *)
		2171
		2172	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2173	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2174	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2175	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2176	section below on what exactly this means).
		2177
		2178	This call incurs the overhead of a syscall only once per loop iteration,
		2179	so while the overhead might be noticable, it doesn't apply to repeated
		2180	calls to C<ev_async_send>.
		2181
		2182	=back
		2183
739		2184
740	=head1 OTHER FUNCTIONS	2185	=head1 OTHER FUNCTIONS
741		2186
742	There are some other functions of possible interest. Described. Here. Now.	2187	There are some other functions of possible interest. Described. Here. Now.
743		2188
…		…
773	/* stdin might have data for us, joy! */;	2218	/* stdin might have data for us, joy! */;
774	}	2219	}
775		2220
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2221	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
777		2222
778	=item ev_feed_event (loop, watcher, int events)	2223	=item ev_feed_event (ev_loop *, watcher *, int revents)
779		2224
780	Feeds the given event set into the event loop, as if the specified event	2225	Feeds the given event set into the event loop, as if the specified event
781	had happened for the specified watcher (which must be a pointer to an	2226	had happened for the specified watcher (which must be a pointer to an
782	initialised but not necessarily started event watcher).	2227	initialised but not necessarily started event watcher).
783		2228
784	=item ev_feed_fd_event (loop, int fd, int revents)	2229	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
785		2230
786	Feed an event on the given fd, as if a file descriptor backend detected	2231	Feed an event on the given fd, as if a file descriptor backend detected
787	the given events it.	2232	the given events it.
788		2233
789	=item ev_feed_signal_event (loop, int signum)	2234	=item ev_feed_signal_event (ev_loop *loop, int signum)
790		2235
791	Feed an event as if the given signal occured (loop must be the default loop!).	2236	Feed an event as if the given signal occured (C<loop> must be the default
		2237	loop!).
792		2238
793	=back	2239	=back
		2240
794		2241
795	=head1 LIBEVENT EMULATION	2242	=head1 LIBEVENT EMULATION
796		2243
797	Libev offers a compatibility emulation layer for libevent. It cannot	2244	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	2245	emulate the internals of libevent, so here are some usage hints:
…		…
819		2266
820	=back	2267	=back
821		2268
822	=head1 C++ SUPPORT	2269	=head1 C++ SUPPORT
823		2270
824	TBD.	2271	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2272	you to use some convinience methods to start/stop watchers and also change
		2273	the callback model to a model using method callbacks on objects.
		2274
		2275	To use it,
		2276
		2277	#include <ev++.h>
		2278
		2279	This automatically includes F<ev.h> and puts all of its definitions (many
		2280	of them macros) into the global namespace. All C++ specific things are
		2281	put into the C<ev> namespace. It should support all the same embedding
		2282	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2283
		2284	Care has been taken to keep the overhead low. The only data member the C++
		2285	classes add (compared to plain C-style watchers) is the event loop pointer
		2286	that the watcher is associated with (or no additional members at all if
		2287	you disable C<EV_MULTIPLICITY> when embedding libev).
		2288
		2289	Currently, functions, and static and non-static member functions can be
		2290	used as callbacks. Other types should be easy to add as long as they only
		2291	need one additional pointer for context. If you need support for other
		2292	types of functors please contact the author (preferably after implementing
		2293	it).
		2294
		2295	Here is a list of things available in the C<ev> namespace:
		2296
		2297	=over 4
		2298
		2299	=item C<ev::READ>, C<ev::WRITE> etc.
		2300
		2301	These are just enum values with the same values as the C<EV_READ> etc.
		2302	macros from F<ev.h>.
		2303
		2304	=item C<ev::tstamp>, C<ev::now>
		2305
		2306	Aliases to the same types/functions as with the C<ev_> prefix.
		2307
		2308	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2309
		2310	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2311	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2312	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2313	defines by many implementations.
		2314
		2315	All of those classes have these methods:
		2316
		2317	=over 4
		2318
		2319	=item ev::TYPE::TYPE ()
		2320
		2321	=item ev::TYPE::TYPE (struct ev_loop *)
		2322
		2323	=item ev::TYPE::~TYPE
		2324
		2325	The constructor (optionally) takes an event loop to associate the watcher
		2326	with. If it is omitted, it will use C<EV_DEFAULT>.
		2327
		2328	The constructor calls C<ev_init> for you, which means you have to call the
		2329	C<set> method before starting it.
		2330
		2331	It will not set a callback, however: You have to call the templated C<set>
		2332	method to set a callback before you can start the watcher.
		2333
		2334	(The reason why you have to use a method is a limitation in C++ which does
		2335	not allow explicit template arguments for constructors).
		2336
		2337	The destructor automatically stops the watcher if it is active.
		2338
		2339	=item w->set<class, &class::method> (object *)
		2340
		2341	This method sets the callback method to call. The method has to have a
		2342	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2343	first argument and the C<revents> as second. The object must be given as
		2344	parameter and is stored in the C<data> member of the watcher.
		2345
		2346	This method synthesizes efficient thunking code to call your method from
		2347	the C callback that libev requires. If your compiler can inline your
		2348	callback (i.e. it is visible to it at the place of the C<set> call and
		2349	your compiler is good :), then the method will be fully inlined into the
		2350	thunking function, making it as fast as a direct C callback.
		2351
		2352	Example: simple class declaration and watcher initialisation
		2353
		2354	struct myclass
		2355	{
		2356	void io_cb (ev::io &w, int revents) { }
		2357	}
		2358
		2359	myclass obj;
		2360	ev::io iow;
		2361	iow.set <myclass, &myclass::io_cb> (&obj);
		2362
		2363	=item w->set<function> (void *data = 0)
		2364
		2365	Also sets a callback, but uses a static method or plain function as
		2366	callback. The optional C<data> argument will be stored in the watcher's
		2367	C<data> member and is free for you to use.
		2368
		2369	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2370
		2371	See the method-C<set> above for more details.
		2372
		2373	Example:
		2374
		2375	static void io_cb (ev::io &w, int revents) { }
		2376	iow.set <io_cb> ();
		2377
		2378	=item w->set (struct ev_loop *)
		2379
		2380	Associates a different C<struct ev_loop> with this watcher. You can only
		2381	do this when the watcher is inactive (and not pending either).
		2382
		2383	=item w->set ([args])
		2384
		2385	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2386	called at least once. Unlike the C counterpart, an active watcher gets
		2387	automatically stopped and restarted when reconfiguring it with this
		2388	method.
		2389
		2390	=item w->start ()
		2391
		2392	Starts the watcher. Note that there is no C<loop> argument, as the
		2393	constructor already stores the event loop.
		2394
		2395	=item w->stop ()
		2396
		2397	Stops the watcher if it is active. Again, no C<loop> argument.
		2398
		2399	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2400
		2401	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2402	C<ev_TYPE_again> function.
		2403
		2404	=item w->sweep () (C<ev::embed> only)
		2405
		2406	Invokes C<ev_embed_sweep>.
		2407
		2408	=item w->update () (C<ev::stat> only)
		2409
		2410	Invokes C<ev_stat_stat>.
		2411
		2412	=back
		2413
		2414	=back
		2415
		2416	Example: Define a class with an IO and idle watcher, start one of them in
		2417	the constructor.
		2418
		2419	class myclass
		2420	{
		2421	ev::io io; void io_cb (ev::io &w, int revents);
		2422	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2423
		2424	myclass (int fd)
		2425	{
		2426	io .set <myclass, &myclass::io_cb > (this);
		2427	idle.set <myclass, &myclass::idle_cb> (this);
		2428
		2429	io.start (fd, ev::READ);
		2430	}
		2431	};
		2432
		2433
		2434	=head1 MACRO MAGIC
		2435
		2436	Libev can be compiled with a variety of options, the most fundamantal
		2437	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2438	functions and callbacks have an initial C<struct ev_loop *> argument.
		2439
		2440	To make it easier to write programs that cope with either variant, the
		2441	following macros are defined:
		2442
		2443	=over 4
		2444
		2445	=item C<EV_A>, C<EV_A_>
		2446
		2447	This provides the loop I<argument> for functions, if one is required ("ev
		2448	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2449	C<EV_A_> is used when other arguments are following. Example:
		2450
		2451	ev_unref (EV_A);
		2452	ev_timer_add (EV_A_ watcher);
		2453	ev_loop (EV_A_ 0);
		2454
		2455	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2456	which is often provided by the following macro.
		2457
		2458	=item C<EV_P>, C<EV_P_>
		2459
		2460	This provides the loop I<parameter> for functions, if one is required ("ev
		2461	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2462	C<EV_P_> is used when other parameters are following. Example:
		2463
		2464	// this is how ev_unref is being declared
		2465	static void ev_unref (EV_P);
		2466
		2467	// this is how you can declare your typical callback
		2468	static void cb (EV_P_ ev_timer *w, int revents)
		2469
		2470	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2471	suitable for use with C<EV_A>.
		2472
		2473	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2474
		2475	Similar to the other two macros, this gives you the value of the default
		2476	loop, if multiple loops are supported ("ev loop default").
		2477
		2478	=back
		2479
		2480	Example: Declare and initialise a check watcher, utilising the above
		2481	macros so it will work regardless of whether multiple loops are supported
		2482	or not.
		2483
		2484	static void
		2485	check_cb (EV_P_ ev_timer *w, int revents)
		2486	{
		2487	ev_check_stop (EV_A_ w);
		2488	}
		2489
		2490	ev_check check;
		2491	ev_check_init (&check, check_cb);
		2492	ev_check_start (EV_DEFAULT_ &check);
		2493	ev_loop (EV_DEFAULT_ 0);
		2494
		2495	=head1 EMBEDDING
		2496
		2497	Libev can (and often is) directly embedded into host
		2498	applications. Examples of applications that embed it include the Deliantra
		2499	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2500	and rxvt-unicode.
		2501
		2502	The goal is to enable you to just copy the necessary files into your
		2503	source directory without having to change even a single line in them, so
		2504	you can easily upgrade by simply copying (or having a checked-out copy of
		2505	libev somewhere in your source tree).
		2506
		2507	=head2 FILESETS
		2508
		2509	Depending on what features you need you need to include one or more sets of files
		2510	in your app.
		2511
		2512	=head3 CORE EVENT LOOP
		2513
		2514	To include only the libev core (all the C<ev_*> functions), with manual
		2515	configuration (no autoconf):
		2516
		2517	#define EV_STANDALONE 1
		2518	#include "ev.c"
		2519
		2520	This will automatically include F<ev.h>, too, and should be done in a
		2521	single C source file only to provide the function implementations. To use
		2522	it, do the same for F<ev.h> in all files wishing to use this API (best
		2523	done by writing a wrapper around F<ev.h> that you can include instead and
		2524	where you can put other configuration options):
		2525
		2526	#define EV_STANDALONE 1
		2527	#include "ev.h"
		2528
		2529	Both header files and implementation files can be compiled with a C++
		2530	compiler (at least, thats a stated goal, and breakage will be treated
		2531	as a bug).
		2532
		2533	You need the following files in your source tree, or in a directory
		2534	in your include path (e.g. in libev/ when using -Ilibev):
		2535
		2536	ev.h
		2537	ev.c
		2538	ev_vars.h
		2539	ev_wrap.h
		2540
		2541	ev_win32.c required on win32 platforms only
		2542
		2543	ev_select.c only when select backend is enabled (which is enabled by default)
		2544	ev_poll.c only when poll backend is enabled (disabled by default)
		2545	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2546	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2547	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2548
		2549	F<ev.c> includes the backend files directly when enabled, so you only need
		2550	to compile this single file.
		2551
		2552	=head3 LIBEVENT COMPATIBILITY API
		2553
		2554	To include the libevent compatibility API, also include:
		2555
		2556	#include "event.c"
		2557
		2558	in the file including F<ev.c>, and:
		2559
		2560	#include "event.h"
		2561
		2562	in the files that want to use the libevent API. This also includes F<ev.h>.
		2563
		2564	You need the following additional files for this:
		2565
		2566	event.h
		2567	event.c
		2568
		2569	=head3 AUTOCONF SUPPORT
		2570
		2571	Instead of using C<EV_STANDALONE=1> and providing your config in
		2572	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2573	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2574	include F<config.h> and configure itself accordingly.
		2575
		2576	For this of course you need the m4 file:
		2577
		2578	libev.m4
		2579
		2580	=head2 PREPROCESSOR SYMBOLS/MACROS
		2581
		2582	Libev can be configured via a variety of preprocessor symbols you have to define
		2583	before including any of its files. The default is not to build for multiplicity
		2584	and only include the select backend.
		2585
		2586	=over 4
		2587
		2588	=item EV_STANDALONE
		2589
		2590	Must always be C<1> if you do not use autoconf configuration, which
		2591	keeps libev from including F<config.h>, and it also defines dummy
		2592	implementations for some libevent functions (such as logging, which is not
		2593	supported). It will also not define any of the structs usually found in
		2594	F<event.h> that are not directly supported by the libev core alone.
		2595
		2596	=item EV_USE_MONOTONIC
		2597
		2598	If defined to be C<1>, libev will try to detect the availability of the
		2599	monotonic clock option at both compiletime and runtime. Otherwise no use
		2600	of the monotonic clock option will be attempted. If you enable this, you
		2601	usually have to link against librt or something similar. Enabling it when
		2602	the functionality isn't available is safe, though, although you have
		2603	to make sure you link against any libraries where the C<clock_gettime>
		2604	function is hiding in (often F<-lrt>).
		2605
		2606	=item EV_USE_REALTIME
		2607
		2608	If defined to be C<1>, libev will try to detect the availability of the
		2609	realtime clock option at compiletime (and assume its availability at
		2610	runtime if successful). Otherwise no use of the realtime clock option will
		2611	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2612	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2613	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2614
		2615	=item EV_USE_NANOSLEEP
		2616
		2617	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2618	and will use it for delays. Otherwise it will use C<select ()>.
		2619
		2620	=item EV_USE_SELECT
		2621
		2622	If undefined or defined to be C<1>, libev will compile in support for the
		2623	C<select>(2) backend. No attempt at autodetection will be done: if no
		2624	other method takes over, select will be it. Otherwise the select backend
		2625	will not be compiled in.
		2626
		2627	=item EV_SELECT_USE_FD_SET
		2628
		2629	If defined to C<1>, then the select backend will use the system C<fd_set>
		2630	structure. This is useful if libev doesn't compile due to a missing
		2631	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2632	exotic systems. This usually limits the range of file descriptors to some
		2633	low limit such as 1024 or might have other limitations (winsocket only
		2634	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2635	influence the size of the C<fd_set> used.
		2636
		2637	=item EV_SELECT_IS_WINSOCKET
		2638
		2639	When defined to C<1>, the select backend will assume that
		2640	select/socket/connect etc. don't understand file descriptors but
		2641	wants osf handles on win32 (this is the case when the select to
		2642	be used is the winsock select). This means that it will call
		2643	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2644	it is assumed that all these functions actually work on fds, even
		2645	on win32. Should not be defined on non-win32 platforms.
		2646
		2647	=item EV_FD_TO_WIN32_HANDLE
		2648
		2649	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2650	file descriptors to socket handles. When not defining this symbol (the
		2651	default), then libev will call C<_get_osfhandle>, which is usually
		2652	correct. In some cases, programs use their own file descriptor management,
		2653	in which case they can provide this function to map fds to socket handles.
		2654
		2655	=item EV_USE_POLL
		2656
		2657	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2658	backend. Otherwise it will be enabled on non-win32 platforms. It
		2659	takes precedence over select.
		2660
		2661	=item EV_USE_EPOLL
		2662
		2663	If defined to be C<1>, libev will compile in support for the Linux
		2664	C<epoll>(7) backend. Its availability will be detected at runtime,
		2665	otherwise another method will be used as fallback. This is the
		2666	preferred backend for GNU/Linux systems.
		2667
		2668	=item EV_USE_KQUEUE
		2669
		2670	If defined to be C<1>, libev will compile in support for the BSD style
		2671	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2672	otherwise another method will be used as fallback. This is the preferred
		2673	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2674	supports some types of fds correctly (the only platform we found that
		2675	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2676	not be used unless explicitly requested. The best way to use it is to find
		2677	out whether kqueue supports your type of fd properly and use an embedded
		2678	kqueue loop.
		2679
		2680	=item EV_USE_PORT
		2681
		2682	If defined to be C<1>, libev will compile in support for the Solaris
		2683	10 port style backend. Its availability will be detected at runtime,
		2684	otherwise another method will be used as fallback. This is the preferred
		2685	backend for Solaris 10 systems.
		2686
		2687	=item EV_USE_DEVPOLL
		2688
		2689	reserved for future expansion, works like the USE symbols above.
		2690
		2691	=item EV_USE_INOTIFY
		2692
		2693	If defined to be C<1>, libev will compile in support for the Linux inotify
		2694	interface to speed up C<ev_stat> watchers. Its actual availability will
		2695	be detected at runtime.
		2696
		2697	=item EV_ATOMIC_T
		2698
		2699	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2700	access is atomic with respect to other threads or signal contexts. No such type
		2701	is easily found using, so you cna provide your own type that you know is safe.
		2702
		2703	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2704	from F<signal.h>, which is usually good enough on most platforms.
		2705
		2706	=item EV_H
		2707
		2708	The name of the F<ev.h> header file used to include it. The default if
		2709	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2710	used to virtually rename the F<ev.h> header file in case of conflicts.
		2711
		2712	=item EV_CONFIG_H
		2713
		2714	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2715	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2716	C<EV_H>, above.
		2717
		2718	=item EV_EVENT_H
		2719
		2720	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2721	of how the F<event.h> header can be found, the default is C<"event.h">.
		2722
		2723	=item EV_PROTOTYPES
		2724
		2725	If defined to be C<0>, then F<ev.h> will not define any function
		2726	prototypes, but still define all the structs and other symbols. This is
		2727	occasionally useful if you want to provide your own wrapper functions
		2728	around libev functions.
		2729
		2730	=item EV_MULTIPLICITY
		2731
		2732	If undefined or defined to C<1>, then all event-loop-specific functions
		2733	will have the C<struct ev_loop *> as first argument, and you can create
		2734	additional independent event loops. Otherwise there will be no support
		2735	for multiple event loops and there is no first event loop pointer
		2736	argument. Instead, all functions act on the single default loop.
		2737
		2738	=item EV_MINPRI
		2739
		2740	=item EV_MAXPRI
		2741
		2742	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2743	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2744	provide for more priorities by overriding those symbols (usually defined
		2745	to be C<-2> and C<2>, respectively).
		2746
		2747	When doing priority-based operations, libev usually has to linearly search
		2748	all the priorities, so having many of them (hundreds) uses a lot of space
		2749	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2750	fine.
		2751
		2752	If your embedding app does not need any priorities, defining these both to
		2753	C<0> will save some memory and cpu.
		2754
		2755	=item EV_PERIODIC_ENABLE
		2756
		2757	If undefined or defined to be C<1>, then periodic timers are supported. If
		2758	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2759	code.
		2760
		2761	=item EV_IDLE_ENABLE
		2762
		2763	If undefined or defined to be C<1>, then idle watchers are supported. If
		2764	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2765	code.
		2766
		2767	=item EV_EMBED_ENABLE
		2768
		2769	If undefined or defined to be C<1>, then embed watchers are supported. If
		2770	defined to be C<0>, then they are not.
		2771
		2772	=item EV_STAT_ENABLE
		2773
		2774	If undefined or defined to be C<1>, then stat watchers are supported. If
		2775	defined to be C<0>, then they are not.
		2776
		2777	=item EV_FORK_ENABLE
		2778
		2779	If undefined or defined to be C<1>, then fork watchers are supported. If
		2780	defined to be C<0>, then they are not.
		2781
		2782	=item EV_ASYNC_ENABLE
		2783
		2784	If undefined or defined to be C<1>, then async watchers are supported. If
		2785	defined to be C<0>, then they are not.
		2786
		2787	=item EV_MINIMAL
		2788
		2789	If you need to shave off some kilobytes of code at the expense of some
		2790	speed, define this symbol to C<1>. Currently only used for gcc to override
		2791	some inlining decisions, saves roughly 30% codesize of amd64.
		2792
		2793	=item EV_PID_HASHSIZE
		2794
		2795	C<ev_child> watchers use a small hash table to distribute workload by
		2796	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2797	than enough. If you need to manage thousands of children you might want to
		2798	increase this value (I<must> be a power of two).
		2799
		2800	=item EV_INOTIFY_HASHSIZE
		2801
		2802	C<ev_stat> watchers use a small hash table to distribute workload by
		2803	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2804	usually more than enough. If you need to manage thousands of C<ev_stat>
		2805	watchers you might want to increase this value (I<must> be a power of
		2806	two).
		2807
		2808	=item EV_COMMON
		2809
		2810	By default, all watchers have a C<void *data> member. By redefining
		2811	this macro to a something else you can include more and other types of
		2812	members. You have to define it each time you include one of the files,
		2813	though, and it must be identical each time.
		2814
		2815	For example, the perl EV module uses something like this:
		2816
		2817	#define EV_COMMON \
		2818	SV *self; /* contains this struct */ \
		2819	SV *cb_sv, *fh /* note no trailing ";" */
		2820
		2821	=item EV_CB_DECLARE (type)
		2822
		2823	=item EV_CB_INVOKE (watcher, revents)
		2824
		2825	=item ev_set_cb (ev, cb)
		2826
		2827	Can be used to change the callback member declaration in each watcher,
		2828	and the way callbacks are invoked and set. Must expand to a struct member
		2829	definition and a statement, respectively. See the F<ev.h> header file for
		2830	their default definitions. One possible use for overriding these is to
		2831	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2832	method calls instead of plain function calls in C++.
		2833
		2834	=head2 EXPORTED API SYMBOLS
		2835
		2836	If you need to re-export the API (e.g. via a dll) and you need a list of
		2837	exported symbols, you can use the provided F<Symbol.*> files which list
		2838	all public symbols, one per line:
		2839
		2840	Symbols.ev for libev proper
		2841	Symbols.event for the libevent emulation
		2842
		2843	This can also be used to rename all public symbols to avoid clashes with
		2844	multiple versions of libev linked together (which is obviously bad in
		2845	itself, but sometimes it is inconvinient to avoid this).
		2846
		2847	A sed command like this will create wrapper C<#define>'s that you need to
		2848	include before including F<ev.h>:
		2849
		2850	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2851
		2852	This would create a file F<wrap.h> which essentially looks like this:
		2853
		2854	#define ev_backend myprefix_ev_backend
		2855	#define ev_check_start myprefix_ev_check_start
		2856	#define ev_check_stop myprefix_ev_check_stop
		2857	...
		2858
		2859	=head2 EXAMPLES
		2860
		2861	For a real-world example of a program the includes libev
		2862	verbatim, you can have a look at the EV perl module
		2863	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2864	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2865	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2866	will be compiled. It is pretty complex because it provides its own header
		2867	file.
		2868
		2869	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2870	that everybody includes and which overrides some configure choices:
		2871
		2872	#define EV_MINIMAL 1
		2873	#define EV_USE_POLL 0
		2874	#define EV_MULTIPLICITY 0
		2875	#define EV_PERIODIC_ENABLE 0
		2876	#define EV_STAT_ENABLE 0
		2877	#define EV_FORK_ENABLE 0
		2878	#define EV_CONFIG_H <config.h>
		2879	#define EV_MINPRI 0
		2880	#define EV_MAXPRI 0
		2881
		2882	#include "ev++.h"
		2883
		2884	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2885
		2886	#include "ev_cpp.h"
		2887	#include "ev.c"
		2888
		2889
		2890	=head1 COMPLEXITIES
		2891
		2892	In this section the complexities of (many of) the algorithms used inside
		2893	libev will be explained. For complexity discussions about backends see the
		2894	documentation for C<ev_default_init>.
		2895
		2896	All of the following are about amortised time: If an array needs to be
		2897	extended, libev needs to realloc and move the whole array, but this
		2898	happens asymptotically never with higher number of elements, so O(1) might
		2899	mean it might do a lengthy realloc operation in rare cases, but on average
		2900	it is much faster and asymptotically approaches constant time.
		2901
		2902	=over 4
		2903
		2904	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2905
		2906	This means that, when you have a watcher that triggers in one hour and
		2907	there are 100 watchers that would trigger before that then inserting will
		2908	have to skip roughly seven (C<ld 100>) of these watchers.
		2909
		2910	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2911
		2912	That means that changing a timer costs less than removing/adding them
		2913	as only the relative motion in the event queue has to be paid for.
		2914
		2915	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2916
		2917	These just add the watcher into an array or at the head of a list.
		2918
		2919	=item Stopping check/prepare/idle watchers: O(1)
		2920
		2921	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2922
		2923	These watchers are stored in lists then need to be walked to find the
		2924	correct watcher to remove. The lists are usually short (you don't usually
		2925	have many watchers waiting for the same fd or signal).
		2926
		2927	=item Finding the next timer in each loop iteration: O(1)
		2928
		2929	By virtue of using a binary heap, the next timer is always found at the
		2930	beginning of the storage array.
		2931
		2932	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2933
		2934	A change means an I/O watcher gets started or stopped, which requires
		2935	libev to recalculate its status (and possibly tell the kernel, depending
		2936	on backend and wether C<ev_io_set> was used).
		2937
		2938	=item Activating one watcher (putting it into the pending state): O(1)
		2939
		2940	=item Priority handling: O(number_of_priorities)
		2941
		2942	Priorities are implemented by allocating some space for each
		2943	priority. When doing priority-based operations, libev usually has to
		2944	linearly search all the priorities, but starting/stopping and activating
		2945	watchers becomes O(1) w.r.t. prioritiy handling.
		2946
		2947	=back
		2948
		2949
		2950	=head1 Win32 platform limitations and workarounds
		2951
		2952	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2953	requires, and its I/O model is fundamentally incompatible with the POSIX
		2954	model. Libev still offers limited functionality on this platform in
		2955	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2956	descriptors. This only applies when using Win32 natively, not when using
		2957	e.g. cygwin.
		2958
		2959	There is no supported compilation method available on windows except
		2960	embedding it into other applications.
		2961
		2962	Due to the many, low, and arbitrary limits on the win32 platform and the
		2963	abysmal performance of winsockets, using a large number of sockets is not
		2964	recommended (and not reasonable). If your program needs to use more than
		2965	a hundred or so sockets, then likely it needs to use a totally different
		2966	implementation for windows, as libev offers the POSIX model, which cannot
		2967	be implemented efficiently on windows (microsoft monopoly games).
		2968
		2969	=over 4
		2970
		2971	=item The winsocket select function
		2972
		2973	The winsocket C<select> function doesn't follow POSIX in that it requires
		2974	socket I<handles> and not socket I<file descriptors>. This makes select
		2975	very inefficient, and also requires a mapping from file descriptors
		2976	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2977	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2978	symbols for more info.
		2979
		2980	The configuration for a "naked" win32 using the microsoft runtime
		2981	libraries and raw winsocket select is:
		2982
		2983	#define EV_USE_SELECT 1
		2984	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		2985
		2986	Note that winsockets handling of fd sets is O(n), so you can easily get a
		2987	complexity in the O(n²) range when using win32.
		2988
		2989	=item Limited number of file descriptors
		2990
		2991	Windows has numerous arbitrary (and low) limits on things. Early versions
		2992	of winsocket's select only supported waiting for a max. of C<64> handles
		2993	(probably owning to the fact that all windows kernels can only wait for
		2994	C<64> things at the same time internally; microsoft recommends spawning a
		2995	chain of threads and wait for 63 handles and the previous thread in each).
		2996
		2997	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		2998	to some high number (e.g. C<2048>) before compiling the winsocket select
		2999	call (which might be in libev or elsewhere, for example, perl does its own
		3000	select emulation on windows).
		3001
		3002	Another limit is the number of file descriptors in the microsoft runtime
		3003	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3004	or something like this inside microsoft). You can increase this by calling
		3005	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3006	arbitrary limit), but is broken in many versions of the microsoft runtime
		3007	libraries.
		3008
		3009	This might get you to about C<512> or C<2048> sockets (depending on
		3010	windows version and/or the phase of the moon). To get more, you need to
		3011	wrap all I/O functions and provide your own fd management, but the cost of
		3012	calling select (O(n²)) will likely make this unworkable.
		3013
		3014	=back
		3015
825		3016
826	=head1 AUTHOR	3017	=head1 AUTHOR
827		3018
828	Marc Lehmann <libev@schmorp.de>.	3019	Marc Lehmann <libev@schmorp.de>.
829		3020

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