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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 int ev_is_default_loop (loop)
		512
		513	Returns true when the given loop actually is the default loop, false otherwise.
		514
		515	=item unsigned int ev_loop_count (loop)
		516
		517	Returns the count of loop iterations for the loop, which is identical to
		518	the number of times libev did poll for new events. It starts at C<0> and
		519	happily wraps around with enough iterations.
		520
		521	This value can sometimes be useful as a generation counter of sorts (it
		522	"ticks" the number of loop iterations), as it roughly corresponds with
		523	C<ev_prepare> and C<ev_check> calls.
		524
209	=item unsigned int ev_method (loop)	525	=item unsigned int ev_backend (loop)
210		526
211	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	527	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
212	use.	528	use.
213		529
214	=item ev_tstamp ev_now (loop)	530	=item ev_tstamp ev_now (loop)
215		531
216	Returns the current "event loop time", which is the time the event loop	532	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	533	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	534	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	535	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).	536	event occurring (or more correctly, libev finding out about it).
221		537
222	=item ev_loop (loop, int flags)	538	=item ev_loop (loop, int flags)
223		539
224	Finally, this is it, the event handler. This function usually is called	540	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	541	after you initialised all your watchers and you want to start handling
226	events.	542	events.
227		543
228	If the flags argument is specified as 0, it will not return until either	544	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.	545	either no event watchers are active anymore or C<ev_unloop> was called.
		546
		547	Please note that an explicit C<ev_unloop> is usually better than
		548	relying on all watchers to be stopped when deciding when a program has
		549	finished (especially in interactive programs), but having a program that
		550	automatically loops as long as it has to and no longer by virtue of
		551	relying on its watchers stopping correctly is a thing of beauty.
230		552
231	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	553	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	554	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.	555	case there are no events and will return after one iteration of the loop.
234		556
235	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	557	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	558	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	559	your process until at least one new event arrives, and will return after
238	one iteration of the loop.	560	one iteration of the loop. This is useful if you are waiting for some
		561	external event in conjunction with something not expressible using other
		562	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		563	usually a better approach for this kind of thing.
239		564
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:	565	Here are the gory details of what C<ev_loop> does:
245		566
246	1. If there are no active watchers (reference count is zero), return.	567	- Before the first iteration, call any pending watchers.
		568	* If EVFLAG_FORKCHECK was used, check for a fork.
		569	- If a fork was detected, queue and call all fork watchers.
247	2. Queue and immediately call all prepare watchers.	570	- Queue and call all prepare watchers.
248	3. If we have been forked, recreate the kernel state.	571	- If we have been forked, recreate the kernel state.
249	4. Update the kernel state with all outstanding changes.	572	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	573	- Update the "event loop time".
251	6. Calculate for how long to block.	574	- Calculate for how long to sleep or block, if at all
		575	(active idle watchers, EVLOOP_NONBLOCK or not having
		576	any active watchers at all will result in not sleeping).
		577	- Sleep if the I/O and timer collect interval say so.
252	7. Block the process, waiting for events.	578	- Block the process, waiting for any events.
		579	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	580	- Update the "event loop time" and do time jump handling.
254	9. Queue all outstanding timers.	581	- Queue all outstanding timers.
255	10. Queue all outstanding periodics.	582	- Queue all outstanding periodics.
256	11. If no events are pending now, queue all idle watchers.	583	- If no events are pending now, queue all idle watchers.
257	12. Queue all check watchers.	584	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	585	- Call all queued watchers in reverse order (i.e. check watchers first).
		586	Signals and child watchers are implemented as I/O watchers, and will
		587	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	588	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260	was used, return, otherwise continue with step #1.	589	were used, or there are no active watchers, return, otherwise
		590	continue with step *.
		591
		592	Example: Queue some jobs and then loop until no events are outstanding
		593	anymore.
		594
		595	... queue jobs here, make sure they register event watchers as long
		596	... as they still have work to do (even an idle watcher will do..)
		597	ev_loop (my_loop, 0);
		598	... jobs done. yeah!
261		599
262	=item ev_unloop (loop, how)	600	=item ev_unloop (loop, how)
263		601
264	Can be used to make a call to C<ev_loop> return early (but only after it	602	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	603	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	604	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.	605	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		606
		607	This "unloop state" will be cleared when entering C<ev_loop> again.
268		608
269	=item ev_ref (loop)	609	=item ev_ref (loop)
270		610
271	=item ev_unref (loop)	611	=item ev_unref (loop)
272		612
…		…
277	returning, ev_unref() after starting, and ev_ref() before stopping it. For	617	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	618	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	619	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	620	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	621	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>.	622	libraries. Just remember to I<unref after start> and I<ref before stop>
		623	(but only if the watcher wasn't active before, or was active before,
		624	respectively).
		625
		626	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		627	running when nothing else is active.
		628
		629	struct ev_signal exitsig;
		630	ev_signal_init (&exitsig, sig_cb, SIGINT);
		631	ev_signal_start (loop, &exitsig);
		632	evf_unref (loop);
		633
		634	Example: For some weird reason, unregister the above signal handler again.
		635
		636	ev_ref (loop);
		637	ev_signal_stop (loop, &exitsig);
		638
		639	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		640
		641	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		642
		643	These advanced functions influence the time that libev will spend waiting
		644	for events. Both are by default C<0>, meaning that libev will try to
		645	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		646
		647	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		648	allows libev to delay invocation of I/O and timer/periodic callbacks to
		649	increase efficiency of loop iterations.
		650
		651	The background is that sometimes your program runs just fast enough to
		652	handle one (or very few) event(s) per loop iteration. While this makes
		653	the program responsive, it also wastes a lot of CPU time to poll for new
		654	events, especially with backends like C<select ()> which have a high
		655	overhead for the actual polling but can deliver many events at once.
		656
		657	By setting a higher I<io collect interval> you allow libev to spend more
		658	time collecting I/O events, so you can handle more events per iteration,
		659	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		660	C<ev_timer>) will be not affected. Setting this to a non-null value will
		661	introduce an additional C<ev_sleep ()> call into most loop iterations.
		662
		663	Likewise, by setting a higher I<timeout collect interval> you allow libev
		664	to spend more time collecting timeouts, at the expense of increased
		665	latency (the watcher callback will be called later). C<ev_io> watchers
		666	will not be affected. Setting this to a non-null value will not introduce
		667	any overhead in libev.
		668
		669	Many (busy) programs can usually benefit by setting the io collect
		670	interval to a value near C<0.1> or so, which is often enough for
		671	interactive servers (of course not for games), likewise for timeouts. It
		672	usually doesn't make much sense to set it to a lower value than C<0.01>,
		673	as this approsaches the timing granularity of most systems.
283		674
284	=back	675	=back
		676
285		677
286	=head1 ANATOMY OF A WATCHER	678	=head1 ANATOMY OF A WATCHER
287		679
288	A watcher is a structure that you create and register to record your	680	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	681	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	714	*) >>), and you can stop watching for events at any time by calling the
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	715	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
324		716
325	As long as your watcher is active (has been started but not stopped) you	717	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	718	must not touch the values stored in it. Most specifically you must never
327	reinitialise it or call its set method.	719	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		720
334	Each and every callback receives the event loop pointer as first, the	721	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	722	registered watcher structure as second, and a bitset of received events as
336	third argument.	723	third argument.
337		724
…		…
361	The signal specified in the C<ev_signal> watcher has been received by a thread.	748	The signal specified in the C<ev_signal> watcher has been received by a thread.
362		749
363	=item C<EV_CHILD>	750	=item C<EV_CHILD>
364		751
365	The pid specified in the C<ev_child> watcher has received a status change.	752	The pid specified in the C<ev_child> watcher has received a status change.
		753
		754	=item C<EV_STAT>
		755
		756	The path specified in the C<ev_stat> watcher changed its attributes somehow.
366		757
367	=item C<EV_IDLE>	758	=item C<EV_IDLE>
368		759
369	The C<ev_idle> watcher has determined that you have nothing better to do.	760	The C<ev_idle> watcher has determined that you have nothing better to do.
370		761
…		…
378	received events. Callbacks of both watcher types can start and stop as	769	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	770	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	771	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
381	C<ev_loop> from blocking).	772	C<ev_loop> from blocking).
382		773
		774	=item C<EV_EMBED>
		775
		776	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		777
		778	=item C<EV_FORK>
		779
		780	The event loop has been resumed in the child process after fork (see
		781	C<ev_fork>).
		782
		783	=item C<EV_ASYNC>
		784
		785	The given async watcher has been asynchronously notified (see C<ev_async>).
		786
383	=item C<EV_ERROR>	787	=item C<EV_ERROR>
384		788
385	An unspecified error has occured, the watcher has been stopped. This might	789	An unspecified error has occured, the watcher has been stopped. This might
386	happen because the watcher could not be properly started because libev	790	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	791	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	797	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	798	with the error from read() or write(). This will not work in multithreaded
395	programs, though, so beware.	799	programs, though, so beware.
396		800
397	=back	801	=back
		802
		803	=head2 GENERIC WATCHER FUNCTIONS
		804
		805	In the following description, C<TYPE> stands for the watcher type,
		806	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		807
		808	=over 4
		809
		810	=item C<ev_init> (ev_TYPE *watcher, callback)
		811
		812	This macro initialises the generic portion of a watcher. The contents
		813	of the watcher object can be arbitrary (so C<malloc> will do). Only
		814	the generic parts of the watcher are initialised, you I<need> to call
		815	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		816	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		817	which rolls both calls into one.
		818
		819	You can reinitialise a watcher at any time as long as it has been stopped
		820	(or never started) and there are no pending events outstanding.
		821
		822	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		823	int revents)>.
		824
		825	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		826
		827	This macro initialises the type-specific parts of a watcher. You need to
		828	call C<ev_init> at least once before you call this macro, but you can
		829	call C<ev_TYPE_set> any number of times. You must not, however, call this
		830	macro on a watcher that is active (it can be pending, however, which is a
		831	difference to the C<ev_init> macro).
		832
		833	Although some watcher types do not have type-specific arguments
		834	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		835
		836	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		837
		838	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		839	calls into a single call. This is the most convinient method to initialise
		840	a watcher. The same limitations apply, of course.
		841
		842	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		843
		844	Starts (activates) the given watcher. Only active watchers will receive
		845	events. If the watcher is already active nothing will happen.
		846
		847	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		848
		849	Stops the given watcher again (if active) and clears the pending
		850	status. It is possible that stopped watchers are pending (for example,
		851	non-repeating timers are being stopped when they become pending), but
		852	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		853	you want to free or reuse the memory used by the watcher it is therefore a
		854	good idea to always call its C<ev_TYPE_stop> function.
		855
		856	=item bool ev_is_active (ev_TYPE *watcher)
		857
		858	Returns a true value iff the watcher is active (i.e. it has been started
		859	and not yet been stopped). As long as a watcher is active you must not modify
		860	it.
		861
		862	=item bool ev_is_pending (ev_TYPE *watcher)
		863
		864	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		865	events but its callback has not yet been invoked). As long as a watcher
		866	is pending (but not active) you must not call an init function on it (but
		867	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		868	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		869	it).
		870
		871	=item callback ev_cb (ev_TYPE *watcher)
		872
		873	Returns the callback currently set on the watcher.
		874
		875	=item ev_cb_set (ev_TYPE *watcher, callback)
		876
		877	Change the callback. You can change the callback at virtually any time
		878	(modulo threads).
		879
		880	=item ev_set_priority (ev_TYPE *watcher, priority)
		881
		882	=item int ev_priority (ev_TYPE *watcher)
		883
		884	Set and query the priority of the watcher. The priority is a small
		885	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		886	(default: C<-2>). Pending watchers with higher priority will be invoked
		887	before watchers with lower priority, but priority will not keep watchers
		888	from being executed (except for C<ev_idle> watchers).
		889
		890	This means that priorities are I<only> used for ordering callback
		891	invocation after new events have been received. This is useful, for
		892	example, to reduce latency after idling, or more often, to bind two
		893	watchers on the same event and make sure one is called first.
		894
		895	If you need to suppress invocation when higher priority events are pending
		896	you need to look at C<ev_idle> watchers, which provide this functionality.
		897
		898	You I<must not> change the priority of a watcher as long as it is active or
		899	pending.
		900
		901	The default priority used by watchers when no priority has been set is
		902	always C<0>, which is supposed to not be too high and not be too low :).
		903
		904	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		905	fine, as long as you do not mind that the priority value you query might
		906	or might not have been adjusted to be within valid range.
		907
		908	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		909
		910	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		911	C<loop> nor C<revents> need to be valid as long as the watcher callback
		912	can deal with that fact.
		913
		914	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		915
		916	If the watcher is pending, this function returns clears its pending status
		917	and returns its C<revents> bitset (as if its callback was invoked). If the
		918	watcher isn't pending it does nothing and returns C<0>.
		919
		920	=back
		921
398		922
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	923	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
400		924
401	Each watcher has, by default, a member C<void *data> that you can change	925	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	926	and read at any time, libev will completely ignore it. This can be used
…		…
420	{	944	{
421	struct my_io *w = (struct my_io *)w_;	945	struct my_io *w = (struct my_io *)w_;
422	...	946	...
423	}	947	}
424		948
425	More interesting and less C-conformant ways of catsing your callback type	949	More interesting and less C-conformant ways of casting your callback type
426	have been omitted....	950	instead have been omitted.
		951
		952	Another common scenario is having some data structure with multiple
		953	watchers:
		954
		955	struct my_biggy
		956	{
		957	int some_data;
		958	ev_timer t1;
		959	ev_timer t2;
		960	}
		961
		962	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		963	you need to use C<offsetof>:
		964
		965	#include <stddef.h>
		966
		967	static void
		968	t1_cb (EV_P_ struct ev_timer *w, int revents)
		969	{
		970	struct my_biggy big = (struct my_biggy *
		971	(((char *)w) - offsetof (struct my_biggy, t1));
		972	}
		973
		974	static void
		975	t2_cb (EV_P_ struct ev_timer *w, int revents)
		976	{
		977	struct my_biggy big = (struct my_biggy *
		978	(((char *)w) - offsetof (struct my_biggy, t2));
		979	}
427		980
428		981
429	=head1 WATCHER TYPES	982	=head1 WATCHER TYPES
430		983
431	This section describes each watcher in detail, but will not repeat	984	This section describes each watcher in detail, but will not repeat
432	information given in the last section.	985	information given in the last section. Any initialisation/set macros,
		986	functions and members specific to the watcher type are explained.
433		987
		988	Members are additionally marked with either I<[read-only]>, meaning that,
		989	while the watcher is active, you can look at the member and expect some
		990	sensible content, but you must not modify it (you can modify it while the
		991	watcher is stopped to your hearts content), or I<[read-write]>, which
		992	means you can expect it to have some sensible content while the watcher
		993	is active, but you can also modify it. Modifying it may not do something
		994	sensible or take immediate effect (or do anything at all), but libev will
		995	not crash or malfunction in any way.
		996
		997
434	=head2 C<ev_io> - is this file descriptor readable or writable	998	=head2 C<ev_io> - is this file descriptor readable or writable?
435		999
436	I/O watchers check whether a file descriptor is readable or writable	1000	I/O watchers check whether a file descriptor is readable or writable
437	in each iteration of the event loop (This behaviour is called	1001	in each iteration of the event loop, or, more precisely, when reading
438	level-triggering because you keep receiving events as long as the	1002	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	1003	some data. This behaviour is called level-triggering because you keep
440	act on the event and neither want to receive future events).	1004	receiving events as long as the condition persists. Remember you can stop
		1005	the watcher if you don't want to act on the event and neither want to
		1006	receive future events.
441		1007
442	In general you can register as many read and/or write event watchers per	1008	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	1009	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	1010	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	1011	required if you know what you are doing).
446		1012
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	1013	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	1014	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
455	EVMETHOD_POLL).	1015	C<EVBACKEND_POLL>).
		1016
		1017	Another thing you have to watch out for is that it is quite easy to
		1018	receive "spurious" readyness notifications, that is your callback might
		1019	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1020	because there is no data. Not only are some backends known to create a
		1021	lot of those (for example solaris ports), it is very easy to get into
		1022	this situation even with a relatively standard program structure. Thus
		1023	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1024	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1025
		1026	If you cannot run the fd in non-blocking mode (for example you should not
		1027	play around with an Xlib connection), then you have to seperately re-test
		1028	whether a file descriptor is really ready with a known-to-be good interface
		1029	such as poll (fortunately in our Xlib example, Xlib already does this on
		1030	its own, so its quite safe to use).
		1031
		1032	=head3 The special problem of disappearing file descriptors
		1033
		1034	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1035	descriptor (either by calling C<close> explicitly or by any other means,
		1036	such as C<dup>). The reason is that you register interest in some file
		1037	descriptor, but when it goes away, the operating system will silently drop
		1038	this interest. If another file descriptor with the same number then is
		1039	registered with libev, there is no efficient way to see that this is, in
		1040	fact, a different file descriptor.
		1041
		1042	To avoid having to explicitly tell libev about such cases, libev follows
		1043	the following policy: Each time C<ev_io_set> is being called, libev
		1044	will assume that this is potentially a new file descriptor, otherwise
		1045	it is assumed that the file descriptor stays the same. That means that
		1046	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1047	descriptor even if the file descriptor number itself did not change.
		1048
		1049	This is how one would do it normally anyway, the important point is that
		1050	the libev application should not optimise around libev but should leave
		1051	optimisations to libev.
		1052
		1053	=head3 The special problem of dup'ed file descriptors
		1054
		1055	Some backends (e.g. epoll), cannot register events for file descriptors,
		1056	but only events for the underlying file descriptions. That means when you
		1057	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1058	events for them, only one file descriptor might actually receive events.
		1059
		1060	There is no workaround possible except not registering events
		1061	for potentially C<dup ()>'ed file descriptors, or to resort to
		1062	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1063
		1064	=head3 The special problem of fork
		1065
		1066	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1067	useless behaviour. Libev fully supports fork, but needs to be told about
		1068	it in the child.
		1069
		1070	To support fork in your programs, you either have to call
		1071	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1072	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1073	C<EVBACKEND_POLL>.
		1074
		1075
		1076	=head3 Watcher-Specific Functions
456		1077
457	=over 4	1078	=over 4
458		1079
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1080	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1081
461	=item ev_io_set (ev_io *, int fd, int events)	1082	=item ev_io_set (ev_io *, int fd, int events)
462		1083
463	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1084	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 |	1085	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
465	EV_WRITE> to receive the given events.	1086	C<EV_READ | EV_WRITE> to receive the given events.
		1087
		1088	=item int fd [read-only]
		1089
		1090	The file descriptor being watched.
		1091
		1092	=item int events [read-only]
		1093
		1094	The events being watched.
466		1095
467	=back	1096	=back
468		1097
		1098	=head3 Examples
		1099
		1100	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1101	readable, but only once. Since it is likely line-buffered, you could
		1102	attempt to read a whole line in the callback.
		1103
		1104	static void
		1105	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1106	{
		1107	ev_io_stop (loop, w);
		1108	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1109	}
		1110
		1111	...
		1112	struct ev_loop *loop = ev_default_init (0);
		1113	struct ev_io stdin_readable;
		1114	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1115	ev_io_start (loop, &stdin_readable);
		1116	ev_loop (loop, 0);
		1117
		1118
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1119	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1120
471	Timer watchers are simple relative timers that generate an event after a	1121	Timer watchers are simple relative timers that generate an event after a
472	given time, and optionally repeating in regular intervals after that.	1122	given time, and optionally repeating in regular intervals after that.
473		1123
474	The timers are based on real time, that is, if you register an event that	1124	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	1125	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	1126	time, it will still time out after (roughly) and hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1127	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1128	monotonic clock option helps a lot here).
479		1129
480	The relative timeouts are calculated relative to the C<ev_now ()>	1130	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	1131	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	1132	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	1133	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:	1134	on the current time, use something like this to adjust for this:
485		1135
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1136	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1137
		1138	The callback is guarenteed to be invoked only when its timeout has passed,
		1139	but if multiple timers become ready during the same loop iteration then
		1140	order of execution is undefined.
		1141
		1142	=head3 Watcher-Specific Functions and Data Members
487		1143
488	=over 4	1144	=over 4
489		1145
490	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1146	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
491		1147
…		…
500	configure a timer to trigger every 10 seconds, then it will trigger at	1156	configure a timer to trigger every 10 seconds, then it will trigger at
501	exactly 10 second intervals. If, however, your program cannot keep up with	1157	exactly 10 second intervals. If, however, your program cannot keep up with
502	the timer (because it takes longer than those 10 seconds to do stuff) the	1158	the timer (because it takes longer than those 10 seconds to do stuff) the
503	timer will not fire more than once per event loop iteration.	1159	timer will not fire more than once per event loop iteration.
504		1160
505	=item ev_timer_again (loop)	1161	=item ev_timer_again (loop, ev_timer *)
506		1162
507	This will act as if the timer timed out and restart it again if it is	1163	This will act as if the timer timed out and restart it again if it is
508	repeating. The exact semantics are:	1164	repeating. The exact semantics are:
509		1165
		1166	If the timer is pending, its pending status is cleared.
		1167
510	If the timer is started but nonrepeating, stop it.	1168	If the timer is started but nonrepeating, stop it (as if it timed out).
511		1169
512	If the timer is repeating, either start it if necessary (with the repeat	1170	If the timer is repeating, either start it if necessary (with the
513	value), or reset the running timer to the repeat value.	1171	C<repeat> value), or reset the running timer to the C<repeat> value.
514		1172
515	This sounds a bit complicated, but here is a useful and typical	1173	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	1174	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	1175	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	1176	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	1177	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	1178	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	1179	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.	1180	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1181	automatically restart it if need be.
		1182
		1183	That means you can ignore the C<after> value and C<ev_timer_start>
		1184	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1185
		1186	ev_timer_init (timer, callback, 0., 5.);
		1187	ev_timer_again (loop, timer);
		1188	...
		1189	timer->again = 17.;
		1190	ev_timer_again (loop, timer);
		1191	...
		1192	timer->again = 10.;
		1193	ev_timer_again (loop, timer);
		1194
		1195	This is more slightly efficient then stopping/starting the timer each time
		1196	you want to modify its timeout value.
		1197
		1198	=item ev_tstamp repeat [read-write]
		1199
		1200	The current C<repeat> value. Will be used each time the watcher times out
		1201	or C<ev_timer_again> is called and determines the next timeout (if any),
		1202	which is also when any modifications are taken into account.
523		1203
524	=back	1204	=back
525		1205
		1206	=head3 Examples
		1207
		1208	Example: Create a timer that fires after 60 seconds.
		1209
		1210	static void
		1211	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1212	{
		1213	.. one minute over, w is actually stopped right here
		1214	}
		1215
		1216	struct ev_timer mytimer;
		1217	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1218	ev_timer_start (loop, &mytimer);
		1219
		1220	Example: Create a timeout timer that times out after 10 seconds of
		1221	inactivity.
		1222
		1223	static void
		1224	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1225	{
		1226	.. ten seconds without any activity
		1227	}
		1228
		1229	struct ev_timer mytimer;
		1230	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1231	ev_timer_again (&mytimer); /* start timer */
		1232	ev_loop (loop, 0);
		1233
		1234	// and in some piece of code that gets executed on any "activity":
		1235	// reset the timeout to start ticking again at 10 seconds
		1236	ev_timer_again (&mytimer);
		1237
		1238
526	=head2 C<ev_periodic> - to cron or not to cron	1239	=head2 C<ev_periodic> - to cron or not to cron?
527		1240
528	Periodic watchers are also timers of a kind, but they are very versatile	1241	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	1242	(and unfortunately a bit complex).
530		1243
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1244	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	1245	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	1246	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 ()	1247	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	1248	+ 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	1249	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	1250	roughly 10 seconds later).
538	again).
539		1251
540	They can also be used to implement vastly more complex timers, such as	1252	They can also be used to implement vastly more complex timers, such as
541	triggering an event on eahc midnight, local time.	1253	triggering an event on each midnight, local time or other, complicated,
		1254	rules.
		1255
		1256	As with timers, the callback is guarenteed to be invoked only when the
		1257	time (C<at>) has been passed, but if multiple periodic timers become ready
		1258	during the same loop iteration then order of execution is undefined.
		1259
		1260	=head3 Watcher-Specific Functions and Data Members
542		1261
543	=over 4	1262	=over 4
544		1263
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1264	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
546		1265
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1266	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
548		1267
549	Lots of arguments, lets sort it out... There are basically three modes of	1268	Lots of arguments, lets sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	1269	operation, and we will explain them from simplest to complex:
551		1270
552
553	=over 4	1271	=over 4
554		1272
555	=item * absolute timer (interval = reschedule_cb = 0)	1273	=item * absolute timer (at = time, interval = reschedule_cb = 0)
556		1274
557	In this configuration the watcher triggers an event at the wallclock time	1275	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,	1276	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	1277	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.	1278	system time reaches or surpasses this time.
561		1279
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1280	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
563		1281
564	In this mode the watcher will always be scheduled to time out at the next	1282	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	1283	C<at + N * interval> time (for some integer N, which can also be negative)
566	of any time jumps.	1284	and then repeat, regardless of any time jumps.
567		1285
568	This can be used to create timers that do not drift with respect to system	1286	This can be used to create timers that do not drift with respect to system
569	time:	1287	time:
570		1288
571	ev_periodic_set (&periodic, 0., 3600., 0);	1289	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
577		1295
578	Another way to think about it (for the mathematically inclined) is that	1296	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	1297	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.	1298	time where C<time = at (mod interval)>, regardless of any time jumps.
581		1299
		1300	For numerical stability it is preferable that the C<at> value is near
		1301	C<ev_now ()> (the current time), but there is no range requirement for
		1302	this value.
		1303
582	=item * manual reschedule mode (reschedule_cb = callback)	1304	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
583		1305
584	In this mode the values for C<interval> and C<at> are both being	1306	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	1307	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	1308	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	1309	current time as second argument.
588		1310
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1311	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,	1312	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	1313	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592	starting a prepare watcher).	1314	starting an C<ev_prepare> watcher, which is legal).
593		1315
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1316	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
595	ev_tstamp now)>, e.g.:	1317	ev_tstamp now)>, e.g.:
596		1318
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1319	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	1342	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	1343	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	1344	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	1345	program when the crontabs have changed).
624		1346
		1347	=item ev_tstamp offset [read-write]
		1348
		1349	When repeating, this contains the offset value, otherwise this is the
		1350	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1351
		1352	Can be modified any time, but changes only take effect when the periodic
		1353	timer fires or C<ev_periodic_again> is being called.
		1354
		1355	=item ev_tstamp interval [read-write]
		1356
		1357	The current interval value. Can be modified any time, but changes only
		1358	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1359	called.
		1360
		1361	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1362
		1363	The current reschedule callback, or C<0>, if this functionality is
		1364	switched off. Can be changed any time, but changes only take effect when
		1365	the periodic timer fires or C<ev_periodic_again> is being called.
		1366
		1367	=item ev_tstamp at [read-only]
		1368
		1369	When active, contains the absolute time that the watcher is supposed to
		1370	trigger next.
		1371
625	=back	1372	=back
626		1373
		1374	=head3 Examples
		1375
		1376	Example: Call a callback every hour, or, more precisely, whenever the
		1377	system clock is divisible by 3600. The callback invocation times have
		1378	potentially a lot of jittering, but good long-term stability.
		1379
		1380	static void
		1381	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1382	{
		1383	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1384	}
		1385
		1386	struct ev_periodic hourly_tick;
		1387	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1388	ev_periodic_start (loop, &hourly_tick);
		1389
		1390	Example: The same as above, but use a reschedule callback to do it:
		1391
		1392	#include <math.h>
		1393
		1394	static ev_tstamp
		1395	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1396	{
		1397	return fmod (now, 3600.) + 3600.;
		1398	}
		1399
		1400	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1401
		1402	Example: Call a callback every hour, starting now:
		1403
		1404	struct ev_periodic hourly_tick;
		1405	ev_periodic_init (&hourly_tick, clock_cb,
		1406	fmod (ev_now (loop), 3600.), 3600., 0);
		1407	ev_periodic_start (loop, &hourly_tick);
		1408
		1409
627	=head2 C<ev_signal> - signal me when a signal gets signalled	1410	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		1411
629	Signal watchers will trigger an event when the process receives a specific	1412	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	1413	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	1414	will try it's best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	1415	normal event processing, like any other event.
…		…
636	with the kernel (thus it coexists with your own signal handlers as long	1419	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	1420	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	1421	watcher for a signal is stopped libev will reset the signal handler to
639	SIG_DFL (regardless of what it was set to before).	1422	SIG_DFL (regardless of what it was set to before).
640		1423
		1424	=head3 Watcher-Specific Functions and Data Members
		1425
641	=over 4	1426	=over 4
642		1427
643	=item ev_signal_init (ev_signal *, callback, int signum)	1428	=item ev_signal_init (ev_signal *, callback, int signum)
644		1429
645	=item ev_signal_set (ev_signal *, int signum)	1430	=item ev_signal_set (ev_signal *, int signum)
646		1431
647	Configures the watcher to trigger on the given signal number (usually one	1432	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	1433	of the C<SIGxxx> constants).
649		1434
		1435	=item int signum [read-only]
		1436
		1437	The signal the watcher watches out for.
		1438
650	=back	1439	=back
651		1440
		1441	=head3 Examples
		1442
		1443	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1444
		1445	static void
		1446	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1447	{
		1448	ev_unloop (loop, EVUNLOOP_ALL);
		1449	}
		1450
		1451	struct ev_signal signal_watcher;
		1452	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1453	ev_signal_start (loop, &sigint_cb);
		1454
		1455
652	=head2 C<ev_child> - wait for pid status changes	1456	=head2 C<ev_child> - watch out for process status changes
653		1457
654	Child watchers trigger when your process receives a SIGCHLD in response to	1458	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).	1459	some child status changes (most typically when a child of yours dies).
656		1460
		1461	=head3 Watcher-Specific Functions and Data Members
		1462
657	=over 4	1463	=over 4
658		1464
659	=item ev_child_init (ev_child *, callback, int pid)	1465	=item ev_child_init (ev_child *, callback, int pid, int trace)
660		1466
661	=item ev_child_set (ev_child *, int pid)	1467	=item ev_child_set (ev_child *, int pid, int trace)
662		1468
663	Configures the watcher to wait for status changes of process C<pid> (or	1469	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	1470	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	1471	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	1472	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	1473	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	1474	process causing the status change. C<trace> must be either C<0> (only
		1475	activate the watcher when the process terminates) or C<1> (additionally
		1476	activate the watcher when the process is stopped or continued).
		1477
		1478	=item int pid [read-only]
		1479
		1480	The process id this watcher watches out for, or C<0>, meaning any process id.
		1481
		1482	=item int rpid [read-write]
		1483
		1484	The process id that detected a status change.
		1485
		1486	=item int rstatus [read-write]
		1487
		1488	The process exit/trace status caused by C<rpid> (see your systems
		1489	C<waitpid> and C<sys/wait.h> documentation for details).
669		1490
670	=back	1491	=back
671		1492
		1493
		1494	=head2 C<ev_stat> - did the file attributes just change?
		1495
		1496	This watches a filesystem path for attribute changes. That is, it calls
		1497	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1498	compared to the last time, invoking the callback if it did.
		1499
		1500	The path does not need to exist: changing from "path exists" to "path does
		1501	not exist" is a status change like any other. The condition "path does
		1502	not exist" is signified by the C<st_nlink> field being zero (which is
		1503	otherwise always forced to be at least one) and all the other fields of
		1504	the stat buffer having unspecified contents.
		1505
		1506	The path I<should> be absolute and I<must not> end in a slash. If it is
		1507	relative and your working directory changes, the behaviour is undefined.
		1508
		1509	Since there is no standard to do this, the portable implementation simply
		1510	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1511	can specify a recommended polling interval for this case. If you specify
		1512	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1513	unspecified default> value will be used (which you can expect to be around
		1514	five seconds, although this might change dynamically). Libev will also
		1515	impose a minimum interval which is currently around C<0.1>, but thats
		1516	usually overkill.
		1517
		1518	This watcher type is not meant for massive numbers of stat watchers,
		1519	as even with OS-supported change notifications, this can be
		1520	resource-intensive.
		1521
		1522	At the time of this writing, only the Linux inotify interface is
		1523	implemented (implementing kqueue support is left as an exercise for the
		1524	reader). Inotify will be used to give hints only and should not change the
		1525	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1526	to fall back to regular polling again even with inotify, but changes are
		1527	usually detected immediately, and if the file exists there will be no
		1528	polling.
		1529
		1530	=head3 Inotify
		1531
		1532	When C<inotify (7)> support has been compiled into libev (generally only
		1533	available on Linux) and present at runtime, it will be used to speed up
		1534	change detection where possible. The inotify descriptor will be created lazily
		1535	when the first C<ev_stat> watcher is being started.
		1536
		1537	Inotify presense does not change the semantics of C<ev_stat> watchers
		1538	except that changes might be detected earlier, and in some cases, to avoid
		1539	making regular C<stat> calls. Even in the presense of inotify support
		1540	there are many cases where libev has to resort to regular C<stat> polling.
		1541
		1542	(There is no support for kqueue, as apparently it cannot be used to
		1543	implement this functionality, due to the requirement of having a file
		1544	descriptor open on the object at all times).
		1545
		1546	=head3 The special problem of stat time resolution
		1547
		1548	The C<stat ()> syscall only supports full-second resolution portably, and
		1549	even on systems where the resolution is higher, many filesystems still
		1550	only support whole seconds.
		1551
		1552	That means that, if the time is the only thing that changes, you might
		1553	miss updates: on the first update, C<ev_stat> detects a change and calls
		1554	your callback, which does something. When there is another update within
		1555	the same second, C<ev_stat> will be unable to detect it.
		1556
		1557	The solution to this is to delay acting on a change for a second (or till
		1558	the next second boundary), using a roughly one-second delay C<ev_timer>
		1559	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1560	is added to work around small timing inconsistencies of some operating
		1561	systems.
		1562
		1563	=head3 Watcher-Specific Functions and Data Members
		1564
		1565	=over 4
		1566
		1567	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1568
		1569	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1570
		1571	Configures the watcher to wait for status changes of the given
		1572	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1573	be detected and should normally be specified as C<0> to let libev choose
		1574	a suitable value. The memory pointed to by C<path> must point to the same
		1575	path for as long as the watcher is active.
		1576
		1577	The callback will be receive C<EV_STAT> when a change was detected,
		1578	relative to the attributes at the time the watcher was started (or the
		1579	last change was detected).
		1580
		1581	=item ev_stat_stat (loop, ev_stat *)
		1582
		1583	Updates the stat buffer immediately with new values. If you change the
		1584	watched path in your callback, you could call this fucntion to avoid
		1585	detecting this change (while introducing a race condition). Can also be
		1586	useful simply to find out the new values.
		1587
		1588	=item ev_statdata attr [read-only]
		1589
		1590	The most-recently detected attributes of the file. Although the type is of
		1591	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1592	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1593	was some error while C<stat>ing the file.
		1594
		1595	=item ev_statdata prev [read-only]
		1596
		1597	The previous attributes of the file. The callback gets invoked whenever
		1598	C<prev> != C<attr>.
		1599
		1600	=item ev_tstamp interval [read-only]
		1601
		1602	The specified interval.
		1603
		1604	=item const char *path [read-only]
		1605
		1606	The filesystem path that is being watched.
		1607
		1608	=back
		1609
		1610	=head3 Examples
		1611
		1612	Example: Watch C</etc/passwd> for attribute changes.
		1613
		1614	static void
		1615	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1616	{
		1617	/* /etc/passwd changed in some way */
		1618	if (w->attr.st_nlink)
		1619	{
		1620	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1621	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1622	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1623	}
		1624	else
		1625	/* you shalt not abuse printf for puts */
		1626	puts ("wow, /etc/passwd is not there, expect problems. "
		1627	"if this is windows, they already arrived\n");
		1628	}
		1629
		1630	...
		1631	ev_stat passwd;
		1632
		1633	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1634	ev_stat_start (loop, &passwd);
		1635
		1636	Example: Like above, but additionally use a one-second delay so we do not
		1637	miss updates (however, frequent updates will delay processing, too, so
		1638	one might do the work both on C<ev_stat> callback invocation I<and> on
		1639	C<ev_timer> callback invocation).
		1640
		1641	static ev_stat passwd;
		1642	static ev_timer timer;
		1643
		1644	static void
		1645	timer_cb (EV_P_ ev_timer *w, int revents)
		1646	{
		1647	ev_timer_stop (EV_A_ w);
		1648
		1649	/* now it's one second after the most recent passwd change */
		1650	}
		1651
		1652	static void
		1653	stat_cb (EV_P_ ev_stat *w, int revents)
		1654	{
		1655	/* reset the one-second timer */
		1656	ev_timer_again (EV_A_ &timer);
		1657	}
		1658
		1659	...
		1660	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1661	ev_stat_start (loop, &passwd);
		1662	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1663
		1664
672	=head2 C<ev_idle> - when you've got nothing better to do	1665	=head2 C<ev_idle> - when you've got nothing better to do...
673		1666
674	Idle watchers trigger events when there are no other events are pending	1667	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	1668	priority are pending (prepare, check and other idle watchers do not
676	as your process is busy handling sockets or timeouts (or even signals,	1669	count).
677	imagine) it will not be triggered. But when your process is idle all idle	1670
678	watchers are being called again and again, once per event loop iteration -	1671	That is, as long as your process is busy handling sockets or timeouts
		1672	(or even signals, imagine) of the same or higher priority it will not be
		1673	triggered. But when your process is idle (or only lower-priority watchers
		1674	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	1675	iteration - until stopped, that is, or your process receives more events
680	busy.	1676	and becomes busy again with higher priority stuff.
681		1677
682	The most noteworthy effect is that as long as any idle watchers are	1678	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.	1679	active, the process will not block when waiting for new events.
684		1680
685	Apart from keeping your process non-blocking (which is a useful	1681	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	1682	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	1683	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	1684	event loop has handled all outstanding events.
689		1685
		1686	=head3 Watcher-Specific Functions and Data Members
		1687
690	=over 4	1688	=over 4
691		1689
692	=item ev_idle_init (ev_signal *, callback)	1690	=item ev_idle_init (ev_signal *, callback)
693		1691
694	Initialises and configures the idle watcher - it has no parameters of any	1692	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,	1693	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	1694	believe me.
697		1695
698	=back	1696	=back
699		1697
		1698	=head3 Examples
		1699
		1700	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1701	callback, free it. Also, use no error checking, as usual.
		1702
		1703	static void
		1704	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1705	{
		1706	free (w);
		1707	// now do something you wanted to do when the program has
		1708	// no longer anything immediate to do.
		1709	}
		1710
		1711	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1712	ev_idle_init (idle_watcher, idle_cb);
		1713	ev_idle_start (loop, idle_cb);
		1714
		1715
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1716	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		1717
702	Prepare and check watchers are usually (but not always) used in tandem:	1718	Prepare and check watchers are usually (but not always) used in tandem:
703	prepare watchers get invoked before the process blocks and check watchers	1719	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	1720	afterwards.
705		1721
		1722	You I<must not> call C<ev_loop> or similar functions that enter
		1723	the current event loop from either C<ev_prepare> or C<ev_check>
		1724	watchers. Other loops than the current one are fine, however. The
		1725	rationale behind this is that you do not need to check for recursion in
		1726	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1727	C<ev_check> so if you have one watcher of each kind they will always be
		1728	called in pairs bracketing the blocking call.
		1729
706	Their main purpose is to integrate other event mechanisms into libev. This	1730	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	1731	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.	1732	variable changes, implement your own watchers, integrate net-snmp or a
		1733	coroutine library and lots more. They are also occasionally useful if
		1734	you cache some data and want to flush it before blocking (for example,
		1735	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1736	watcher).
709		1737
710	This is done by examining in each prepare call which file descriptors need	1738	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	1739	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	1740	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	1741	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	1751	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	1752	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	1753	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	1754	low-priority coroutines to idle/background tasks).
727		1755
		1756	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1757	priority, to ensure that they are being run before any other watchers
		1758	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1759	too) should not activate ("feed") events into libev. While libev fully
		1760	supports this, they will be called before other C<ev_check> watchers
		1761	did their job. As C<ev_check> watchers are often used to embed other
		1762	(non-libev) event loops those other event loops might be in an unusable
		1763	state until their C<ev_check> watcher ran (always remind yourself to
		1764	coexist peacefully with others).
		1765
		1766	=head3 Watcher-Specific Functions and Data Members
		1767
728	=over 4	1768	=over 4
729		1769
730	=item ev_prepare_init (ev_prepare *, callback)	1770	=item ev_prepare_init (ev_prepare *, callback)
731		1771
732	=item ev_check_init (ev_check *, callback)	1772	=item ev_check_init (ev_check *, callback)
…		…
734	Initialises and configures the prepare or check watcher - they have no	1774	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>	1775	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.	1776	macros, but using them is utterly, utterly and completely pointless.
737		1777
738	=back	1778	=back
		1779
		1780	=head3 Examples
		1781
		1782	There are a number of principal ways to embed other event loops or modules
		1783	into libev. Here are some ideas on how to include libadns into libev
		1784	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1785	use for an actually working example. Another Perl module named C<EV::Glib>
		1786	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1787	into the Glib event loop).
		1788
		1789	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1790	and in a check watcher, destroy them and call into libadns. What follows
		1791	is pseudo-code only of course. This requires you to either use a low
		1792	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1793	the callbacks for the IO/timeout watchers might not have been called yet.
		1794
		1795	static ev_io iow [nfd];
		1796	static ev_timer tw;
		1797
		1798	static void
		1799	io_cb (ev_loop *loop, ev_io *w, int revents)
		1800	{
		1801	}
		1802
		1803	// create io watchers for each fd and a timer before blocking
		1804	static void
		1805	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1806	{
		1807	int timeout = 3600000;
		1808	struct pollfd fds [nfd];
		1809	// actual code will need to loop here and realloc etc.
		1810	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1811
		1812	/* the callback is illegal, but won't be called as we stop during check */
		1813	ev_timer_init (&tw, 0, timeout * 1e-3);
		1814	ev_timer_start (loop, &tw);
		1815
		1816	// create one ev_io per pollfd
		1817	for (int i = 0; i < nfd; ++i)
		1818	{
		1819	ev_io_init (iow + i, io_cb, fds [i].fd,
		1820	((fds [i].events & POLLIN ? EV_READ : 0)
		1821	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1822
		1823	fds [i].revents = 0;
		1824	ev_io_start (loop, iow + i);
		1825	}
		1826	}
		1827
		1828	// stop all watchers after blocking
		1829	static void
		1830	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1831	{
		1832	ev_timer_stop (loop, &tw);
		1833
		1834	for (int i = 0; i < nfd; ++i)
		1835	{
		1836	// set the relevant poll flags
		1837	// could also call adns_processreadable etc. here
		1838	struct pollfd *fd = fds + i;
		1839	int revents = ev_clear_pending (iow + i);
		1840	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1841	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1842
		1843	// now stop the watcher
		1844	ev_io_stop (loop, iow + i);
		1845	}
		1846
		1847	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1848	}
		1849
		1850	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1851	in the prepare watcher and would dispose of the check watcher.
		1852
		1853	Method 3: If the module to be embedded supports explicit event
		1854	notification (adns does), you can also make use of the actual watcher
		1855	callbacks, and only destroy/create the watchers in the prepare watcher.
		1856
		1857	static void
		1858	timer_cb (EV_P_ ev_timer *w, int revents)
		1859	{
		1860	adns_state ads = (adns_state)w->data;
		1861	update_now (EV_A);
		1862
		1863	adns_processtimeouts (ads, &tv_now);
		1864	}
		1865
		1866	static void
		1867	io_cb (EV_P_ ev_io *w, int revents)
		1868	{
		1869	adns_state ads = (adns_state)w->data;
		1870	update_now (EV_A);
		1871
		1872	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1873	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1874	}
		1875
		1876	// do not ever call adns_afterpoll
		1877
		1878	Method 4: Do not use a prepare or check watcher because the module you
		1879	want to embed is too inflexible to support it. Instead, youc na override
		1880	their poll function. The drawback with this solution is that the main
		1881	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1882	this.
		1883
		1884	static gint
		1885	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1886	{
		1887	int got_events = 0;
		1888
		1889	for (n = 0; n < nfds; ++n)
		1890	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1891
		1892	if (timeout >= 0)
		1893	// create/start timer
		1894
		1895	// poll
		1896	ev_loop (EV_A_ 0);
		1897
		1898	// stop timer again
		1899	if (timeout >= 0)
		1900	ev_timer_stop (EV_A_ &to);
		1901
		1902	// stop io watchers again - their callbacks should have set
		1903	for (n = 0; n < nfds; ++n)
		1904	ev_io_stop (EV_A_ iow [n]);
		1905
		1906	return got_events;
		1907	}
		1908
		1909
		1910	=head2 C<ev_embed> - when one backend isn't enough...
		1911
		1912	This is a rather advanced watcher type that lets you embed one event loop
		1913	into another (currently only C<ev_io> events are supported in the embedded
		1914	loop, other types of watchers might be handled in a delayed or incorrect
		1915	fashion and must not be used).
		1916
		1917	There are primarily two reasons you would want that: work around bugs and
		1918	prioritise I/O.
		1919
		1920	As an example for a bug workaround, the kqueue backend might only support
		1921	sockets on some platform, so it is unusable as generic backend, but you
		1922	still want to make use of it because you have many sockets and it scales
		1923	so nicely. In this case, you would create a kqueue-based loop and embed it
		1924	into your default loop (which might use e.g. poll). Overall operation will
		1925	be a bit slower because first libev has to poll and then call kevent, but
		1926	at least you can use both at what they are best.
		1927
		1928	As for prioritising I/O: rarely you have the case where some fds have
		1929	to be watched and handled very quickly (with low latency), and even
		1930	priorities and idle watchers might have too much overhead. In this case
		1931	you would put all the high priority stuff in one loop and all the rest in
		1932	a second one, and embed the second one in the first.
		1933
		1934	As long as the watcher is active, the callback will be invoked every time
		1935	there might be events pending in the embedded loop. The callback must then
		1936	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1937	their callbacks (you could also start an idle watcher to give the embedded
		1938	loop strictly lower priority for example). You can also set the callback
		1939	to C<0>, in which case the embed watcher will automatically execute the
		1940	embedded loop sweep.
		1941
		1942	As long as the watcher is started it will automatically handle events. The
		1943	callback will be invoked whenever some events have been handled. You can
		1944	set the callback to C<0> to avoid having to specify one if you are not
		1945	interested in that.
		1946
		1947	Also, there have not currently been made special provisions for forking:
		1948	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1949	but you will also have to stop and restart any C<ev_embed> watchers
		1950	yourself.
		1951
		1952	Unfortunately, not all backends are embeddable, only the ones returned by
		1953	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1954	portable one.
		1955
		1956	So when you want to use this feature you will always have to be prepared
		1957	that you cannot get an embeddable loop. The recommended way to get around
		1958	this is to have a separate variables for your embeddable loop, try to
		1959	create it, and if that fails, use the normal loop for everything.
		1960
		1961	=head3 Watcher-Specific Functions and Data Members
		1962
		1963	=over 4
		1964
		1965	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1966
		1967	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1968
		1969	Configures the watcher to embed the given loop, which must be
		1970	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1971	invoked automatically, otherwise it is the responsibility of the callback
		1972	to invoke it (it will continue to be called until the sweep has been done,
		1973	if you do not want thta, you need to temporarily stop the embed watcher).
		1974
		1975	=item ev_embed_sweep (loop, ev_embed *)
		1976
		1977	Make a single, non-blocking sweep over the embedded loop. This works
		1978	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1979	apropriate way for embedded loops.
		1980
		1981	=item struct ev_loop *other [read-only]
		1982
		1983	The embedded event loop.
		1984
		1985	=back
		1986
		1987	=head3 Examples
		1988
		1989	Example: Try to get an embeddable event loop and embed it into the default
		1990	event loop. If that is not possible, use the default loop. The default
		1991	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1992	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1993	used).
		1994
		1995	struct ev_loop *loop_hi = ev_default_init (0);
		1996	struct ev_loop *loop_lo = 0;
		1997	struct ev_embed embed;
		1998
		1999	// see if there is a chance of getting one that works
		2000	// (remember that a flags value of 0 means autodetection)
		2001	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2002	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2003	: 0;
		2004
		2005	// if we got one, then embed it, otherwise default to loop_hi
		2006	if (loop_lo)
		2007	{
		2008	ev_embed_init (&embed, 0, loop_lo);
		2009	ev_embed_start (loop_hi, &embed);
		2010	}
		2011	else
		2012	loop_lo = loop_hi;
		2013
		2014	Example: Check if kqueue is available but not recommended and create
		2015	a kqueue backend for use with sockets (which usually work with any
		2016	kqueue implementation). Store the kqueue/socket-only event loop in
		2017	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2018
		2019	struct ev_loop *loop = ev_default_init (0);
		2020	struct ev_loop *loop_socket = 0;
		2021	struct ev_embed embed;
		2022
		2023	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2024	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2025	{
		2026	ev_embed_init (&embed, 0, loop_socket);
		2027	ev_embed_start (loop, &embed);
		2028	}
		2029
		2030	if (!loop_socket)
		2031	loop_socket = loop;
		2032
		2033	// now use loop_socket for all sockets, and loop for everything else
		2034
		2035
		2036	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2037
		2038	Fork watchers are called when a C<fork ()> was detected (usually because
		2039	whoever is a good citizen cared to tell libev about it by calling
		2040	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2041	event loop blocks next and before C<ev_check> watchers are being called,
		2042	and only in the child after the fork. If whoever good citizen calling
		2043	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2044	handlers will be invoked, too, of course.
		2045
		2046	=head3 Watcher-Specific Functions and Data Members
		2047
		2048	=over 4
		2049
		2050	=item ev_fork_init (ev_signal *, callback)
		2051
		2052	Initialises and configures the fork watcher - it has no parameters of any
		2053	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2054	believe me.
		2055
		2056	=back
		2057
		2058
		2059	=head2 C<ev_async> - how to wake up another event loop
		2060
		2061	In general, you cannot use an C<ev_loop> from multiple threads or other
		2062	asynchronous sources such as signal handlers (as opposed to multiple event
		2063	loops - those are of course safe to use in different threads).
		2064
		2065	Sometimes, however, you need to wake up another event loop you do not
		2066	control, for example because it belongs to another thread. This is what
		2067	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2068	can signal it by calling C<ev_async_send>, which is thread- and signal
		2069	safe.
		2070
		2071	This functionality is very similar to C<ev_signal> watchers, as signals,
		2072	too, are asynchronous in nature, and signals, too, will be compressed
		2073	(i.e. the number of callback invocations may be less than the number of
		2074	C<ev_async_sent> calls).
		2075
		2076	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2077	just the default loop.
		2078
		2079	=head3 Queueing
		2080
		2081	C<ev_async> does not support queueing of data in any way. The reason
		2082	is that the author does not know of a simple (or any) algorithm for a
		2083	multiple-writer-single-reader queue that works in all cases and doesn't
		2084	need elaborate support such as pthreads.
		2085
		2086	That means that if you want to queue data, you have to provide your own
		2087	queue. But at least I can tell you would implement locking around your
		2088	queue:
		2089
		2090	=over 4
		2091
		2092	=item queueing from a signal handler context
		2093
		2094	To implement race-free queueing, you simply add to the queue in the signal
		2095	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2096	some fictitiuous SIGUSR1 handler:
		2097
		2098	static ev_async mysig;
		2099
		2100	static void
		2101	sigusr1_handler (void)
		2102	{
		2103	sometype data;
		2104
		2105	// no locking etc.
		2106	queue_put (data);
		2107	ev_async_send (DEFAULT_ &mysig);
		2108	}
		2109
		2110	static void
		2111	mysig_cb (EV_P_ ev_async *w, int revents)
		2112	{
		2113	sometype data;
		2114	sigset_t block, prev;
		2115
		2116	sigemptyset (&block);
		2117	sigaddset (&block, SIGUSR1);
		2118	sigprocmask (SIG_BLOCK, &block, &prev);
		2119
		2120	while (queue_get (&data))
		2121	process (data);
		2122
		2123	if (sigismember (&prev, SIGUSR1)
		2124	sigprocmask (SIG_UNBLOCK, &block, 0);
		2125	}
		2126
		2127	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2128	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2129	either...).
		2130
		2131	=item queueing from a thread context
		2132
		2133	The strategy for threads is different, as you cannot (easily) block
		2134	threads but you can easily preempt them, so to queue safely you need to
		2135	employ a traditional mutex lock, such as in this pthread example:
		2136
		2137	static ev_async mysig;
		2138	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2139
		2140	static void
		2141	otherthread (void)
		2142	{
		2143	// only need to lock the actual queueing operation
		2144	pthread_mutex_lock (&mymutex);
		2145	queue_put (data);
		2146	pthread_mutex_unlock (&mymutex);
		2147
		2148	ev_async_send (DEFAULT_ &mysig);
		2149	}
		2150
		2151	static void
		2152	mysig_cb (EV_P_ ev_async *w, int revents)
		2153	{
		2154	pthread_mutex_lock (&mymutex);
		2155
		2156	while (queue_get (&data))
		2157	process (data);
		2158
		2159	pthread_mutex_unlock (&mymutex);
		2160	}
		2161
		2162	=back
		2163
		2164
		2165	=head3 Watcher-Specific Functions and Data Members
		2166
		2167	=over 4
		2168
		2169	=item ev_async_init (ev_async *, callback)
		2170
		2171	Initialises and configures the async watcher - it has no parameters of any
		2172	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2173	believe me.
		2174
		2175	=item ev_async_send (loop, ev_async *)
		2176
		2177	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2178	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2179	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2180	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2181	section below on what exactly this means).
		2182
		2183	This call incurs the overhead of a syscall only once per loop iteration,
		2184	so while the overhead might be noticable, it doesn't apply to repeated
		2185	calls to C<ev_async_send>.
		2186
		2187	=back
		2188
739		2189
740	=head1 OTHER FUNCTIONS	2190	=head1 OTHER FUNCTIONS
741		2191
742	There are some other functions of possible interest. Described. Here. Now.	2192	There are some other functions of possible interest. Described. Here. Now.
743		2193
…		…
773	/* stdin might have data for us, joy! */;	2223	/* stdin might have data for us, joy! */;
774	}	2224	}
775		2225
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2226	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
777		2227
778	=item ev_feed_event (loop, watcher, int events)	2228	=item ev_feed_event (ev_loop *, watcher *, int revents)
779		2229
780	Feeds the given event set into the event loop, as if the specified event	2230	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	2231	had happened for the specified watcher (which must be a pointer to an
782	initialised but not necessarily started event watcher).	2232	initialised but not necessarily started event watcher).
783		2233
784	=item ev_feed_fd_event (loop, int fd, int revents)	2234	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
785		2235
786	Feed an event on the given fd, as if a file descriptor backend detected	2236	Feed an event on the given fd, as if a file descriptor backend detected
787	the given events it.	2237	the given events it.
788		2238
789	=item ev_feed_signal_event (loop, int signum)	2239	=item ev_feed_signal_event (ev_loop *loop, int signum)
790		2240
791	Feed an event as if the given signal occured (loop must be the default loop!).	2241	Feed an event as if the given signal occured (C<loop> must be the default
		2242	loop!).
792		2243
793	=back	2244	=back
		2245
794		2246
795	=head1 LIBEVENT EMULATION	2247	=head1 LIBEVENT EMULATION
796		2248
797	Libev offers a compatibility emulation layer for libevent. It cannot	2249	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	2250	emulate the internals of libevent, so here are some usage hints:
…		…
819		2271
820	=back	2272	=back
821		2273
822	=head1 C++ SUPPORT	2274	=head1 C++ SUPPORT
823		2275
824	TBD.	2276	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2277	you to use some convinience methods to start/stop watchers and also change
		2278	the callback model to a model using method callbacks on objects.
		2279
		2280	To use it,
		2281
		2282	#include <ev++.h>
		2283
		2284	This automatically includes F<ev.h> and puts all of its definitions (many
		2285	of them macros) into the global namespace. All C++ specific things are
		2286	put into the C<ev> namespace. It should support all the same embedding
		2287	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2288
		2289	Care has been taken to keep the overhead low. The only data member the C++
		2290	classes add (compared to plain C-style watchers) is the event loop pointer
		2291	that the watcher is associated with (or no additional members at all if
		2292	you disable C<EV_MULTIPLICITY> when embedding libev).
		2293
		2294	Currently, functions, and static and non-static member functions can be
		2295	used as callbacks. Other types should be easy to add as long as they only
		2296	need one additional pointer for context. If you need support for other
		2297	types of functors please contact the author (preferably after implementing
		2298	it).
		2299
		2300	Here is a list of things available in the C<ev> namespace:
		2301
		2302	=over 4
		2303
		2304	=item C<ev::READ>, C<ev::WRITE> etc.
		2305
		2306	These are just enum values with the same values as the C<EV_READ> etc.
		2307	macros from F<ev.h>.
		2308
		2309	=item C<ev::tstamp>, C<ev::now>
		2310
		2311	Aliases to the same types/functions as with the C<ev_> prefix.
		2312
		2313	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2314
		2315	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2316	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2317	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2318	defines by many implementations.
		2319
		2320	All of those classes have these methods:
		2321
		2322	=over 4
		2323
		2324	=item ev::TYPE::TYPE ()
		2325
		2326	=item ev::TYPE::TYPE (struct ev_loop *)
		2327
		2328	=item ev::TYPE::~TYPE
		2329
		2330	The constructor (optionally) takes an event loop to associate the watcher
		2331	with. If it is omitted, it will use C<EV_DEFAULT>.
		2332
		2333	The constructor calls C<ev_init> for you, which means you have to call the
		2334	C<set> method before starting it.
		2335
		2336	It will not set a callback, however: You have to call the templated C<set>
		2337	method to set a callback before you can start the watcher.
		2338
		2339	(The reason why you have to use a method is a limitation in C++ which does
		2340	not allow explicit template arguments for constructors).
		2341
		2342	The destructor automatically stops the watcher if it is active.
		2343
		2344	=item w->set<class, &class::method> (object *)
		2345
		2346	This method sets the callback method to call. The method has to have a
		2347	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2348	first argument and the C<revents> as second. The object must be given as
		2349	parameter and is stored in the C<data> member of the watcher.
		2350
		2351	This method synthesizes efficient thunking code to call your method from
		2352	the C callback that libev requires. If your compiler can inline your
		2353	callback (i.e. it is visible to it at the place of the C<set> call and
		2354	your compiler is good :), then the method will be fully inlined into the
		2355	thunking function, making it as fast as a direct C callback.
		2356
		2357	Example: simple class declaration and watcher initialisation
		2358
		2359	struct myclass
		2360	{
		2361	void io_cb (ev::io &w, int revents) { }
		2362	}
		2363
		2364	myclass obj;
		2365	ev::io iow;
		2366	iow.set <myclass, &myclass::io_cb> (&obj);
		2367
		2368	=item w->set<function> (void *data = 0)
		2369
		2370	Also sets a callback, but uses a static method or plain function as
		2371	callback. The optional C<data> argument will be stored in the watcher's
		2372	C<data> member and is free for you to use.
		2373
		2374	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2375
		2376	See the method-C<set> above for more details.
		2377
		2378	Example:
		2379
		2380	static void io_cb (ev::io &w, int revents) { }
		2381	iow.set <io_cb> ();
		2382
		2383	=item w->set (struct ev_loop *)
		2384
		2385	Associates a different C<struct ev_loop> with this watcher. You can only
		2386	do this when the watcher is inactive (and not pending either).
		2387
		2388	=item w->set ([args])
		2389
		2390	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2391	called at least once. Unlike the C counterpart, an active watcher gets
		2392	automatically stopped and restarted when reconfiguring it with this
		2393	method.
		2394
		2395	=item w->start ()
		2396
		2397	Starts the watcher. Note that there is no C<loop> argument, as the
		2398	constructor already stores the event loop.
		2399
		2400	=item w->stop ()
		2401
		2402	Stops the watcher if it is active. Again, no C<loop> argument.
		2403
		2404	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2405
		2406	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2407	C<ev_TYPE_again> function.
		2408
		2409	=item w->sweep () (C<ev::embed> only)
		2410
		2411	Invokes C<ev_embed_sweep>.
		2412
		2413	=item w->update () (C<ev::stat> only)
		2414
		2415	Invokes C<ev_stat_stat>.
		2416
		2417	=back
		2418
		2419	=back
		2420
		2421	Example: Define a class with an IO and idle watcher, start one of them in
		2422	the constructor.
		2423
		2424	class myclass
		2425	{
		2426	ev::io io; void io_cb (ev::io &w, int revents);
		2427	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2428
		2429	myclass (int fd)
		2430	{
		2431	io .set <myclass, &myclass::io_cb > (this);
		2432	idle.set <myclass, &myclass::idle_cb> (this);
		2433
		2434	io.start (fd, ev::READ);
		2435	}
		2436	};
		2437
		2438
		2439	=head1 MACRO MAGIC
		2440
		2441	Libev can be compiled with a variety of options, the most fundamantal
		2442	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2443	functions and callbacks have an initial C<struct ev_loop *> argument.
		2444
		2445	To make it easier to write programs that cope with either variant, the
		2446	following macros are defined:
		2447
		2448	=over 4
		2449
		2450	=item C<EV_A>, C<EV_A_>
		2451
		2452	This provides the loop I<argument> for functions, if one is required ("ev
		2453	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2454	C<EV_A_> is used when other arguments are following. Example:
		2455
		2456	ev_unref (EV_A);
		2457	ev_timer_add (EV_A_ watcher);
		2458	ev_loop (EV_A_ 0);
		2459
		2460	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2461	which is often provided by the following macro.
		2462
		2463	=item C<EV_P>, C<EV_P_>
		2464
		2465	This provides the loop I<parameter> for functions, if one is required ("ev
		2466	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2467	C<EV_P_> is used when other parameters are following. Example:
		2468
		2469	// this is how ev_unref is being declared
		2470	static void ev_unref (EV_P);
		2471
		2472	// this is how you can declare your typical callback
		2473	static void cb (EV_P_ ev_timer *w, int revents)
		2474
		2475	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2476	suitable for use with C<EV_A>.
		2477
		2478	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2479
		2480	Similar to the other two macros, this gives you the value of the default
		2481	loop, if multiple loops are supported ("ev loop default").
		2482
		2483	=back
		2484
		2485	Example: Declare and initialise a check watcher, utilising the above
		2486	macros so it will work regardless of whether multiple loops are supported
		2487	or not.
		2488
		2489	static void
		2490	check_cb (EV_P_ ev_timer *w, int revents)
		2491	{
		2492	ev_check_stop (EV_A_ w);
		2493	}
		2494
		2495	ev_check check;
		2496	ev_check_init (&check, check_cb);
		2497	ev_check_start (EV_DEFAULT_ &check);
		2498	ev_loop (EV_DEFAULT_ 0);
		2499
		2500	=head1 EMBEDDING
		2501
		2502	Libev can (and often is) directly embedded into host
		2503	applications. Examples of applications that embed it include the Deliantra
		2504	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2505	and rxvt-unicode.
		2506
		2507	The goal is to enable you to just copy the necessary files into your
		2508	source directory without having to change even a single line in them, so
		2509	you can easily upgrade by simply copying (or having a checked-out copy of
		2510	libev somewhere in your source tree).
		2511
		2512	=head2 FILESETS
		2513
		2514	Depending on what features you need you need to include one or more sets of files
		2515	in your app.
		2516
		2517	=head3 CORE EVENT LOOP
		2518
		2519	To include only the libev core (all the C<ev_*> functions), with manual
		2520	configuration (no autoconf):
		2521
		2522	#define EV_STANDALONE 1
		2523	#include "ev.c"
		2524
		2525	This will automatically include F<ev.h>, too, and should be done in a
		2526	single C source file only to provide the function implementations. To use
		2527	it, do the same for F<ev.h> in all files wishing to use this API (best
		2528	done by writing a wrapper around F<ev.h> that you can include instead and
		2529	where you can put other configuration options):
		2530
		2531	#define EV_STANDALONE 1
		2532	#include "ev.h"
		2533
		2534	Both header files and implementation files can be compiled with a C++
		2535	compiler (at least, thats a stated goal, and breakage will be treated
		2536	as a bug).
		2537
		2538	You need the following files in your source tree, or in a directory
		2539	in your include path (e.g. in libev/ when using -Ilibev):
		2540
		2541	ev.h
		2542	ev.c
		2543	ev_vars.h
		2544	ev_wrap.h
		2545
		2546	ev_win32.c required on win32 platforms only
		2547
		2548	ev_select.c only when select backend is enabled (which is enabled by default)
		2549	ev_poll.c only when poll backend is enabled (disabled by default)
		2550	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2551	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2552	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2553
		2554	F<ev.c> includes the backend files directly when enabled, so you only need
		2555	to compile this single file.
		2556
		2557	=head3 LIBEVENT COMPATIBILITY API
		2558
		2559	To include the libevent compatibility API, also include:
		2560
		2561	#include "event.c"
		2562
		2563	in the file including F<ev.c>, and:
		2564
		2565	#include "event.h"
		2566
		2567	in the files that want to use the libevent API. This also includes F<ev.h>.
		2568
		2569	You need the following additional files for this:
		2570
		2571	event.h
		2572	event.c
		2573
		2574	=head3 AUTOCONF SUPPORT
		2575
		2576	Instead of using C<EV_STANDALONE=1> and providing your config in
		2577	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2578	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2579	include F<config.h> and configure itself accordingly.
		2580
		2581	For this of course you need the m4 file:
		2582
		2583	libev.m4
		2584
		2585	=head2 PREPROCESSOR SYMBOLS/MACROS
		2586
		2587	Libev can be configured via a variety of preprocessor symbols you have to define
		2588	before including any of its files. The default is not to build for multiplicity
		2589	and only include the select backend.
		2590
		2591	=over 4
		2592
		2593	=item EV_STANDALONE
		2594
		2595	Must always be C<1> if you do not use autoconf configuration, which
		2596	keeps libev from including F<config.h>, and it also defines dummy
		2597	implementations for some libevent functions (such as logging, which is not
		2598	supported). It will also not define any of the structs usually found in
		2599	F<event.h> that are not directly supported by the libev core alone.
		2600
		2601	=item EV_USE_MONOTONIC
		2602
		2603	If defined to be C<1>, libev will try to detect the availability of the
		2604	monotonic clock option at both compiletime and runtime. Otherwise no use
		2605	of the monotonic clock option will be attempted. If you enable this, you
		2606	usually have to link against librt or something similar. Enabling it when
		2607	the functionality isn't available is safe, though, although you have
		2608	to make sure you link against any libraries where the C<clock_gettime>
		2609	function is hiding in (often F<-lrt>).
		2610
		2611	=item EV_USE_REALTIME
		2612
		2613	If defined to be C<1>, libev will try to detect the availability of the
		2614	realtime clock option at compiletime (and assume its availability at
		2615	runtime if successful). Otherwise no use of the realtime clock option will
		2616	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2617	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2618	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2619
		2620	=item EV_USE_NANOSLEEP
		2621
		2622	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2623	and will use it for delays. Otherwise it will use C<select ()>.
		2624
		2625	=item EV_USE_SELECT
		2626
		2627	If undefined or defined to be C<1>, libev will compile in support for the
		2628	C<select>(2) backend. No attempt at autodetection will be done: if no
		2629	other method takes over, select will be it. Otherwise the select backend
		2630	will not be compiled in.
		2631
		2632	=item EV_SELECT_USE_FD_SET
		2633
		2634	If defined to C<1>, then the select backend will use the system C<fd_set>
		2635	structure. This is useful if libev doesn't compile due to a missing
		2636	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2637	exotic systems. This usually limits the range of file descriptors to some
		2638	low limit such as 1024 or might have other limitations (winsocket only
		2639	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2640	influence the size of the C<fd_set> used.
		2641
		2642	=item EV_SELECT_IS_WINSOCKET
		2643
		2644	When defined to C<1>, the select backend will assume that
		2645	select/socket/connect etc. don't understand file descriptors but
		2646	wants osf handles on win32 (this is the case when the select to
		2647	be used is the winsock select). This means that it will call
		2648	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2649	it is assumed that all these functions actually work on fds, even
		2650	on win32. Should not be defined on non-win32 platforms.
		2651
		2652	=item EV_FD_TO_WIN32_HANDLE
		2653
		2654	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2655	file descriptors to socket handles. When not defining this symbol (the
		2656	default), then libev will call C<_get_osfhandle>, which is usually
		2657	correct. In some cases, programs use their own file descriptor management,
		2658	in which case they can provide this function to map fds to socket handles.
		2659
		2660	=item EV_USE_POLL
		2661
		2662	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2663	backend. Otherwise it will be enabled on non-win32 platforms. It
		2664	takes precedence over select.
		2665
		2666	=item EV_USE_EPOLL
		2667
		2668	If defined to be C<1>, libev will compile in support for the Linux
		2669	C<epoll>(7) backend. Its availability will be detected at runtime,
		2670	otherwise another method will be used as fallback. This is the
		2671	preferred backend for GNU/Linux systems.
		2672
		2673	=item EV_USE_KQUEUE
		2674
		2675	If defined to be C<1>, libev will compile in support for the BSD style
		2676	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2677	otherwise another method will be used as fallback. This is the preferred
		2678	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2679	supports some types of fds correctly (the only platform we found that
		2680	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2681	not be used unless explicitly requested. The best way to use it is to find
		2682	out whether kqueue supports your type of fd properly and use an embedded
		2683	kqueue loop.
		2684
		2685	=item EV_USE_PORT
		2686
		2687	If defined to be C<1>, libev will compile in support for the Solaris
		2688	10 port style backend. Its availability will be detected at runtime,
		2689	otherwise another method will be used as fallback. This is the preferred
		2690	backend for Solaris 10 systems.
		2691
		2692	=item EV_USE_DEVPOLL
		2693
		2694	reserved for future expansion, works like the USE symbols above.
		2695
		2696	=item EV_USE_INOTIFY
		2697
		2698	If defined to be C<1>, libev will compile in support for the Linux inotify
		2699	interface to speed up C<ev_stat> watchers. Its actual availability will
		2700	be detected at runtime.
		2701
		2702	=item EV_ATOMIC_T
		2703
		2704	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2705	access is atomic with respect to other threads or signal contexts. No such
		2706	type is easily found in the C language, so you can provide your own type
		2707	that you know is safe for your purposes. It is used both for signal handler "locking"
		2708	as well as for signal and thread safety in C<ev_async> watchers.
		2709
		2710	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2711	(from F<signal.h>), which is usually good enough on most platforms.
		2712
		2713	=item EV_H
		2714
		2715	The name of the F<ev.h> header file used to include it. The default if
		2716	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2717	used to virtually rename the F<ev.h> header file in case of conflicts.
		2718
		2719	=item EV_CONFIG_H
		2720
		2721	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2722	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2723	C<EV_H>, above.
		2724
		2725	=item EV_EVENT_H
		2726
		2727	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2728	of how the F<event.h> header can be found, the default is C<"event.h">.
		2729
		2730	=item EV_PROTOTYPES
		2731
		2732	If defined to be C<0>, then F<ev.h> will not define any function
		2733	prototypes, but still define all the structs and other symbols. This is
		2734	occasionally useful if you want to provide your own wrapper functions
		2735	around libev functions.
		2736
		2737	=item EV_MULTIPLICITY
		2738
		2739	If undefined or defined to C<1>, then all event-loop-specific functions
		2740	will have the C<struct ev_loop *> as first argument, and you can create
		2741	additional independent event loops. Otherwise there will be no support
		2742	for multiple event loops and there is no first event loop pointer
		2743	argument. Instead, all functions act on the single default loop.
		2744
		2745	=item EV_MINPRI
		2746
		2747	=item EV_MAXPRI
		2748
		2749	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2750	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2751	provide for more priorities by overriding those symbols (usually defined
		2752	to be C<-2> and C<2>, respectively).
		2753
		2754	When doing priority-based operations, libev usually has to linearly search
		2755	all the priorities, so having many of them (hundreds) uses a lot of space
		2756	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2757	fine.
		2758
		2759	If your embedding app does not need any priorities, defining these both to
		2760	C<0> will save some memory and cpu.
		2761
		2762	=item EV_PERIODIC_ENABLE
		2763
		2764	If undefined or defined to be C<1>, then periodic timers are supported. If
		2765	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2766	code.
		2767
		2768	=item EV_IDLE_ENABLE
		2769
		2770	If undefined or defined to be C<1>, then idle watchers are supported. If
		2771	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2772	code.
		2773
		2774	=item EV_EMBED_ENABLE
		2775
		2776	If undefined or defined to be C<1>, then embed watchers are supported. If
		2777	defined to be C<0>, then they are not.
		2778
		2779	=item EV_STAT_ENABLE
		2780
		2781	If undefined or defined to be C<1>, then stat watchers are supported. If
		2782	defined to be C<0>, then they are not.
		2783
		2784	=item EV_FORK_ENABLE
		2785
		2786	If undefined or defined to be C<1>, then fork watchers are supported. If
		2787	defined to be C<0>, then they are not.
		2788
		2789	=item EV_ASYNC_ENABLE
		2790
		2791	If undefined or defined to be C<1>, then async watchers are supported. If
		2792	defined to be C<0>, then they are not.
		2793
		2794	=item EV_MINIMAL
		2795
		2796	If you need to shave off some kilobytes of code at the expense of some
		2797	speed, define this symbol to C<1>. Currently only used for gcc to override
		2798	some inlining decisions, saves roughly 30% codesize of amd64.
		2799
		2800	=item EV_PID_HASHSIZE
		2801
		2802	C<ev_child> watchers use a small hash table to distribute workload by
		2803	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2804	than enough. If you need to manage thousands of children you might want to
		2805	increase this value (I<must> be a power of two).
		2806
		2807	=item EV_INOTIFY_HASHSIZE
		2808
		2809	C<ev_stat> watchers use a small hash table to distribute workload by
		2810	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2811	usually more than enough. If you need to manage thousands of C<ev_stat>
		2812	watchers you might want to increase this value (I<must> be a power of
		2813	two).
		2814
		2815	=item EV_COMMON
		2816
		2817	By default, all watchers have a C<void *data> member. By redefining
		2818	this macro to a something else you can include more and other types of
		2819	members. You have to define it each time you include one of the files,
		2820	though, and it must be identical each time.
		2821
		2822	For example, the perl EV module uses something like this:
		2823
		2824	#define EV_COMMON \
		2825	SV *self; /* contains this struct */ \
		2826	SV *cb_sv, *fh /* note no trailing ";" */
		2827
		2828	=item EV_CB_DECLARE (type)
		2829
		2830	=item EV_CB_INVOKE (watcher, revents)
		2831
		2832	=item ev_set_cb (ev, cb)
		2833
		2834	Can be used to change the callback member declaration in each watcher,
		2835	and the way callbacks are invoked and set. Must expand to a struct member
		2836	definition and a statement, respectively. See the F<ev.h> header file for
		2837	their default definitions. One possible use for overriding these is to
		2838	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2839	method calls instead of plain function calls in C++.
		2840
		2841	=head2 EXPORTED API SYMBOLS
		2842
		2843	If you need to re-export the API (e.g. via a dll) and you need a list of
		2844	exported symbols, you can use the provided F<Symbol.*> files which list
		2845	all public symbols, one per line:
		2846
		2847	Symbols.ev for libev proper
		2848	Symbols.event for the libevent emulation
		2849
		2850	This can also be used to rename all public symbols to avoid clashes with
		2851	multiple versions of libev linked together (which is obviously bad in
		2852	itself, but sometimes it is inconvinient to avoid this).
		2853
		2854	A sed command like this will create wrapper C<#define>'s that you need to
		2855	include before including F<ev.h>:
		2856
		2857	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2858
		2859	This would create a file F<wrap.h> which essentially looks like this:
		2860
		2861	#define ev_backend myprefix_ev_backend
		2862	#define ev_check_start myprefix_ev_check_start
		2863	#define ev_check_stop myprefix_ev_check_stop
		2864	...
		2865
		2866	=head2 EXAMPLES
		2867
		2868	For a real-world example of a program the includes libev
		2869	verbatim, you can have a look at the EV perl module
		2870	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2871	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2872	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2873	will be compiled. It is pretty complex because it provides its own header
		2874	file.
		2875
		2876	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2877	that everybody includes and which overrides some configure choices:
		2878
		2879	#define EV_MINIMAL 1
		2880	#define EV_USE_POLL 0
		2881	#define EV_MULTIPLICITY 0
		2882	#define EV_PERIODIC_ENABLE 0
		2883	#define EV_STAT_ENABLE 0
		2884	#define EV_FORK_ENABLE 0
		2885	#define EV_CONFIG_H <config.h>
		2886	#define EV_MINPRI 0
		2887	#define EV_MAXPRI 0
		2888
		2889	#include "ev++.h"
		2890
		2891	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2892
		2893	#include "ev_cpp.h"
		2894	#include "ev.c"
		2895
		2896
		2897	=head1 COMPLEXITIES
		2898
		2899	In this section the complexities of (many of) the algorithms used inside
		2900	libev will be explained. For complexity discussions about backends see the
		2901	documentation for C<ev_default_init>.
		2902
		2903	All of the following are about amortised time: If an array needs to be
		2904	extended, libev needs to realloc and move the whole array, but this
		2905	happens asymptotically never with higher number of elements, so O(1) might
		2906	mean it might do a lengthy realloc operation in rare cases, but on average
		2907	it is much faster and asymptotically approaches constant time.
		2908
		2909	=over 4
		2910
		2911	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2912
		2913	This means that, when you have a watcher that triggers in one hour and
		2914	there are 100 watchers that would trigger before that then inserting will
		2915	have to skip roughly seven (C<ld 100>) of these watchers.
		2916
		2917	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2918
		2919	That means that changing a timer costs less than removing/adding them
		2920	as only the relative motion in the event queue has to be paid for.
		2921
		2922	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		2923
		2924	These just add the watcher into an array or at the head of a list.
		2925
		2926	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		2927
		2928	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2929
		2930	These watchers are stored in lists then need to be walked to find the
		2931	correct watcher to remove. The lists are usually short (you don't usually
		2932	have many watchers waiting for the same fd or signal).
		2933
		2934	=item Finding the next timer in each loop iteration: O(1)
		2935
		2936	By virtue of using a binary heap, the next timer is always found at the
		2937	beginning of the storage array.
		2938
		2939	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2940
		2941	A change means an I/O watcher gets started or stopped, which requires
		2942	libev to recalculate its status (and possibly tell the kernel, depending
		2943	on backend and wether C<ev_io_set> was used).
		2944
		2945	=item Activating one watcher (putting it into the pending state): O(1)
		2946
		2947	=item Priority handling: O(number_of_priorities)
		2948
		2949	Priorities are implemented by allocating some space for each
		2950	priority. When doing priority-based operations, libev usually has to
		2951	linearly search all the priorities, but starting/stopping and activating
		2952	watchers becomes O(1) w.r.t. priority handling.
		2953
		2954	=item Sending an ev_async: O(1)
		2955
		2956	=item Processing ev_async_send: O(number_of_async_watchers)
		2957
		2958	=item Processing signals: O(max_signal_number)
		2959
		2960	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		2961	calls in the current loop iteration. Checking for async and signal events
		2962	involves iterating over all running async watchers or all signal numbers.
		2963
		2964	=back
		2965
		2966
		2967	=head1 Win32 platform limitations and workarounds
		2968
		2969	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2970	requires, and its I/O model is fundamentally incompatible with the POSIX
		2971	model. Libev still offers limited functionality on this platform in
		2972	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2973	descriptors. This only applies when using Win32 natively, not when using
		2974	e.g. cygwin.
		2975
		2976	There is no supported compilation method available on windows except
		2977	embedding it into other applications.
		2978
		2979	Due to the many, low, and arbitrary limits on the win32 platform and the
		2980	abysmal performance of winsockets, using a large number of sockets is not
		2981	recommended (and not reasonable). If your program needs to use more than
		2982	a hundred or so sockets, then likely it needs to use a totally different
		2983	implementation for windows, as libev offers the POSIX model, which cannot
		2984	be implemented efficiently on windows (microsoft monopoly games).
		2985
		2986	=over 4
		2987
		2988	=item The winsocket select function
		2989
		2990	The winsocket C<select> function doesn't follow POSIX in that it requires
		2991	socket I<handles> and not socket I<file descriptors>. This makes select
		2992	very inefficient, and also requires a mapping from file descriptors
		2993	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2994	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2995	symbols for more info.
		2996
		2997	The configuration for a "naked" win32 using the microsoft runtime
		2998	libraries and raw winsocket select is:
		2999
		3000	#define EV_USE_SELECT 1
		3001	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3002
		3003	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3004	complexity in the O(n²) range when using win32.
		3005
		3006	=item Limited number of file descriptors
		3007
		3008	Windows has numerous arbitrary (and low) limits on things. Early versions
		3009	of winsocket's select only supported waiting for a max. of C<64> handles
		3010	(probably owning to the fact that all windows kernels can only wait for
		3011	C<64> things at the same time internally; microsoft recommends spawning a
		3012	chain of threads and wait for 63 handles and the previous thread in each).
		3013
		3014	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3015	to some high number (e.g. C<2048>) before compiling the winsocket select
		3016	call (which might be in libev or elsewhere, for example, perl does its own
		3017	select emulation on windows).
		3018
		3019	Another limit is the number of file descriptors in the microsoft runtime
		3020	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3021	or something like this inside microsoft). You can increase this by calling
		3022	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3023	arbitrary limit), but is broken in many versions of the microsoft runtime
		3024	libraries.
		3025
		3026	This might get you to about C<512> or C<2048> sockets (depending on
		3027	windows version and/or the phase of the moon). To get more, you need to
		3028	wrap all I/O functions and provide your own fd management, but the cost of
		3029	calling select (O(n²)) will likely make this unworkable.
		3030
		3031	=back
		3032
825		3033
826	=head1 AUTHOR	3034	=head1 AUTHOR
827		3035
828	Marc Lehmann <libev@schmorp.de>.	3036	Marc Lehmann <libev@schmorp.de>.
829		3037

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