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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
129	The flags argument can be used to specify special behaviour or specific	265	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		267
132	It supports the following flags:	268	The following flags are supported:
133		269
134	=over 4	270	=over 4
135		271
136	=item C<EVFLAG_AUTO>	272	=item C<EVFLAG_AUTO>
137		273
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	282	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	283	useful to try out specific backends to test their performance, or to work
148	around bugs.	284	around bugs.
149		285
		286	=item C<EVFLAG_FORKCHECK>
		287
		288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		289	a fork, you can also make libev check for a fork in each iteration by
		290	enabling this flag.
		291
		292	This works by calling C<getpid ()> on every iteration of the loop,
		293	and thus this might slow down your event loop if you do a lot of loop
		294	iterations and little real work, but is usually not noticeable (on my
		295	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		296	without a syscall and thus I<very> fast, but my Linux system also has
		297	C<pthread_atfork> which is even faster).
		298
		299	The big advantage of this flag is that you can forget about fork (and
		300	forget about forgetting to tell libev about forking) when you use this
		301	flag.
		302
		303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		304	environment variable.
		305
150	=item C<EVMETHOD_SELECT> (portable select backend)	306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		307
		308	This is your standard select(2) backend. Not I<completely> standard, as
		309	libev tries to roll its own fd_set with no limits on the number of fds,
		310	but if that fails, expect a fairly low limit on the number of fds when
		311	using this backend. It doesn't scale too well (O(highest_fd)), but its
		312	usually the fastest backend for a low number of (low-numbered :) fds.
		313
		314	To get good performance out of this backend you need a high amount of
		315	parallelity (most of the file descriptors should be busy). If you are
		316	writing a server, you should C<accept ()> in a loop to accept as many
		317	connections as possible during one iteration. You might also want to have
		318	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		319	readyness notifications you get per iteration.
		320
152	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
153		322
154	=item C<EVMETHOD_EPOLL> (linux only)	323	And this is your standard poll(2) backend. It's more complicated
		324	than select, but handles sparse fds better and has no artificial
		325	limit on the number of fds you can use (except it will slow down
		326	considerably with a lot of inactive fds). It scales similarly to select,
		327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		328	performance tips.
155		329
156	=item C<EVMETHOD_KQUEUE> (some bsds only)	330	=item C<EVBACKEND_EPOLL> (value 4, Linux)
157		331
158	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	332	For few fds, this backend is a bit little slower than poll and select,
		333	but it scales phenomenally better. While poll and select usually scale
		334	like O(total_fds) where n is the total number of fds (or the highest fd),
		335	epoll scales either O(1) or O(active_fds). The epoll design has a number
		336	of shortcomings, such as silently dropping events in some hard-to-detect
		337	cases and rewiring a syscall per fd change, no fork support and bad
		338	support for dup.
159		339
160	=item C<EVMETHOD_PORT> (solaris 10 only)	340	While stopping, setting and starting an I/O watcher in the same iteration
		341	will result in some caching, there is still a syscall per such incident
		342	(because the fd could point to a different file description now), so its
		343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		344	very well if you register events for both fds.
		345
		346	Please note that epoll sometimes generates spurious notifications, so you
		347	need to use non-blocking I/O or other means to avoid blocking when no data
		348	(or space) is available.
		349
		350	Best performance from this backend is achieved by not unregistering all
		351	watchers for a file descriptor until it has been closed, if possible, i.e.
		352	keep at least one watcher active per fd at all times.
		353
		354	While nominally embeddeble in other event loops, this feature is broken in
		355	all kernel versions tested so far.
		356
		357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		358
		359	Kqueue deserves special mention, as at the time of this writing, it
		360	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		361	with anything but sockets and pipes, except on Darwin, where of course
		362	it's completely useless). For this reason it's not being "autodetected"
		363	unless you explicitly specify it explicitly in the flags (i.e. using
		364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		365	system like NetBSD.
		366
		367	You still can embed kqueue into a normal poll or select backend and use it
		368	only for sockets (after having made sure that sockets work with kqueue on
		369	the target platform). See C<ev_embed> watchers for more info.
		370
		371	It scales in the same way as the epoll backend, but the interface to the
		372	kernel is more efficient (which says nothing about its actual speed, of
		373	course). While stopping, setting and starting an I/O watcher does never
		374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		375	two event changes per incident, support for C<fork ()> is very bad and it
		376	drops fds silently in similarly hard-to-detect cases.
		377
		378	This backend usually performs well under most conditions.
		379
		380	While nominally embeddable in other event loops, this doesn't work
		381	everywhere, so you might need to test for this. And since it is broken
		382	almost everywhere, you should only use it when you have a lot of sockets
		383	(for which it usually works), by embedding it into another event loop
		384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		385	sockets.
		386
		387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		388
		389	This is not implemented yet (and might never be, unless you send me an
		390	implementation). According to reports, C</dev/poll> only supports sockets
		391	and is not embeddable, which would limit the usefulness of this backend
		392	immensely.
		393
		394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		395
		396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		397	it's really slow, but it still scales very well (O(active_fds)).
		398
		399	Please note that solaris event ports can deliver a lot of spurious
		400	notifications, so you need to use non-blocking I/O or other means to avoid
		401	blocking when no data (or space) is available.
		402
		403	While this backend scales well, it requires one system call per active
		404	file descriptor per loop iteration. For small and medium numbers of file
		405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		406	might perform better.
		407
		408	=item C<EVBACKEND_ALL>
		409
		410	Try all backends (even potentially broken ones that wouldn't be tried
		411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		413
		414	It is definitely not recommended to use this flag.
		415
		416	=back
161		417
162	If one or more of these are ored into the flags value, then only these	418	If one or more of these are ored into the flags value, then only these
163	backends will be tried (in the reverse order as given here). If one are	419	backends will be tried (in the reverse order as given here). If none are
164	specified, any backend will do.	420	specified, most compiled-in backend will be tried, usually in reverse
		421	order of their flag values :)
165		422
166	=back	423	The most typical usage is like this:
		424
		425	if (!ev_default_loop (0))
		426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		427
		428	Restrict libev to the select and poll backends, and do not allow
		429	environment settings to be taken into account:
		430
		431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		432
		433	Use whatever libev has to offer, but make sure that kqueue is used if
		434	available (warning, breaks stuff, best use only with your own private
		435	event loop and only if you know the OS supports your types of fds):
		436
		437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
167		438
168	=item struct ev_loop *ev_loop_new (unsigned int flags)	439	=item struct ev_loop *ev_loop_new (unsigned int flags)
169		440
170	Similar to C<ev_default_loop>, but always creates a new event loop that is	441	Similar to C<ev_default_loop>, but always creates a new event loop that is
171	always distinct from the default loop. Unlike the default loop, it cannot	442	always distinct from the default loop. Unlike the default loop, it cannot
172	handle signal and child watchers, and attempts to do so will be greeted by	443	handle signal and child watchers, and attempts to do so will be greeted by
173	undefined behaviour (or a failed assertion if assertions are enabled).	444	undefined behaviour (or a failed assertion if assertions are enabled).
174		445
		446	Example: Try to create a event loop that uses epoll and nothing else.
		447
		448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		449	if (!epoller)
		450	fatal ("no epoll found here, maybe it hides under your chair");
		451
175	=item ev_default_destroy ()	452	=item ev_default_destroy ()
176		453
177	Destroys the default loop again (frees all memory and kernel state	454	Destroys the default loop again (frees all memory and kernel state
178	etc.). This stops all registered event watchers (by not touching them in	455	etc.). None of the active event watchers will be stopped in the normal
179	any way whatsoever, although you cannot rely on this :).	456	sense, so e.g. C<ev_is_active> might still return true. It is your
		457	responsibility to either stop all watchers cleanly yoursef I<before>
		458	calling this function, or cope with the fact afterwards (which is usually
		459	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		460	for example).
		461
		462	Note that certain global state, such as signal state, will not be freed by
		463	this function, and related watchers (such as signal and child watchers)
		464	would need to be stopped manually.
		465
		466	In general it is not advisable to call this function except in the
		467	rare occasion where you really need to free e.g. the signal handling
		468	pipe fds. If you need dynamically allocated loops it is better to use
		469	C<ev_loop_new> and C<ev_loop_destroy>).
180		470
181	=item ev_loop_destroy (loop)	471	=item ev_loop_destroy (loop)
182		472
183	Like C<ev_default_destroy>, but destroys an event loop created by an	473	Like C<ev_default_destroy>, but destroys an event loop created by an
184	earlier call to C<ev_loop_new>.	474	earlier call to C<ev_loop_new>.
…		…
188	This function reinitialises the kernel state for backends that have	478	This function reinitialises the kernel state for backends that have
189	one. Despite the name, you can call it anytime, but it makes most sense	479	one. Despite the name, you can call it anytime, but it makes most sense
190	after forking, in either the parent or child process (or both, but that	480	after forking, in either the parent or child process (or both, but that
191	again makes little sense).	481	again makes little sense).
192		482
193	You I<must> call this function after forking if and only if you want to	483	You I<must> call this function in the child process after forking if and
194	use the event library in both processes. If you just fork+exec, you don't	484	only if you want to use the event library in both processes. If you just
195	have to call it.	485	fork+exec, you don't have to call it.
196		486
197	The function itself is quite fast and it's usually not a problem to call	487	The function itself is quite fast and it's usually not a problem to call
198	it just in case after a fork. To make this easy, the function will fit in	488	it just in case after a fork. To make this easy, the function will fit in
199	quite nicely into a call to C<pthread_atfork>:	489	quite nicely into a call to C<pthread_atfork>:
200		490
201	pthread_atfork (0, 0, ev_default_fork);	491	pthread_atfork (0, 0, ev_default_fork);
202		492
		493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		494	without calling this function, so if you force one of those backends you
		495	do not need to care.
		496
203	=item ev_loop_fork (loop)	497	=item ev_loop_fork (loop)
204		498
205	Like C<ev_default_fork>, but acts on an event loop created by	499	Like C<ev_default_fork>, but acts on an event loop created by
206	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
207	after fork, and how you do this is entirely your own problem.	501	after fork, and how you do this is entirely your own problem.
208		502
		503	=item unsigned int ev_loop_count (loop)
		504
		505	Returns the count of loop iterations for the loop, which is identical to
		506	the number of times libev did poll for new events. It starts at C<0> and
		507	happily wraps around with enough iterations.
		508
		509	This value can sometimes be useful as a generation counter of sorts (it
		510	"ticks" the number of loop iterations), as it roughly corresponds with
		511	C<ev_prepare> and C<ev_check> calls.
		512
209	=item unsigned int ev_method (loop)	513	=item unsigned int ev_backend (loop)
210		514
211	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
212	use.	516	use.
213		517
214	=item ev_tstamp ev_now (loop)	518	=item ev_tstamp ev_now (loop)
215		519
216	Returns the current "event loop time", which is the time the event loop	520	Returns the current "event loop time", which is the time the event loop
217	got events and started processing them. This timestamp does not change	521	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	522	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	523	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).	524	event occurring (or more correctly, libev finding out about it).
221		525
222	=item ev_loop (loop, int flags)	526	=item ev_loop (loop, int flags)
223		527
224	Finally, this is it, the event handler. This function usually is called	528	Finally, this is it, the event handler. This function usually is called
225	after you initialised all your watchers and you want to start handling	529	after you initialised all your watchers and you want to start handling
226	events.	530	events.
227		531
228	If the flags argument is specified as 0, it will not return until either	532	If the flags argument is specified as C<0>, it will not return until
229	no event watchers are active anymore or C<ev_unloop> was called.	533	either no event watchers are active anymore or C<ev_unloop> was called.
		534
		535	Please note that an explicit C<ev_unloop> is usually better than
		536	relying on all watchers to be stopped when deciding when a program has
		537	finished (especially in interactive programs), but having a program that
		538	automatically loops as long as it has to and no longer by virtue of
		539	relying on its watchers stopping correctly is a thing of beauty.
230		540
231	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
232	those events and any outstanding ones, but will not block your process in	542	those events and any outstanding ones, but will not block your process in
233	case there are no events and will return after one iteration of the loop.	543	case there are no events and will return after one iteration of the loop.
234		544
235	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
236	neccessary) and will handle those and any outstanding ones. It will block	546	neccessary) and will handle those and any outstanding ones. It will block
237	your process until at least one new event arrives, and will return after	547	your process until at least one new event arrives, and will return after
238	one iteration of the loop.	548	one iteration of the loop. This is useful if you are waiting for some
		549	external event in conjunction with something not expressible using other
		550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		551	usually a better approach for this kind of thing.
239		552
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:	553	Here are the gory details of what C<ev_loop> does:
245		554
		555	- Before the first iteration, call any pending watchers.
246	1. If there are no active watchers (reference count is zero), return.	556	* If there are no active watchers (reference count is zero), return.
247	2. Queue and immediately call all prepare watchers.	557	- Queue all prepare watchers and then call all outstanding watchers.
248	3. If we have been forked, recreate the kernel state.	558	- If we have been forked, recreate the kernel state.
249	4. Update the kernel state with all outstanding changes.	559	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	560	- Update the "event loop time".
251	6. Calculate for how long to block.	561	- Calculate for how long to block.
252	7. Block the process, waiting for events.	562	- Block the process, waiting for any events.
		563	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	564	- Update the "event loop time" and do time jump handling.
254	9. Queue all outstanding timers.	565	- Queue all outstanding timers.
255	10. Queue all outstanding periodics.	566	- Queue all outstanding periodics.
256	11. If no events are pending now, queue all idle watchers.	567	- If no events are pending now, queue all idle watchers.
257	12. Queue all check watchers.	568	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	569	- Call all queued watchers in reverse order (i.e. check watchers first).
		570	Signals and child watchers are implemented as I/O watchers, and will
		571	be handled here by queueing them when their watcher gets executed.
259	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	572	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260	was used, return, otherwise continue with step #1.	573	were used, return, otherwise continue with step *.
		574
		575	Example: Queue some jobs and then loop until no events are outsanding
		576	anymore.
		577
		578	... queue jobs here, make sure they register event watchers as long
		579	... as they still have work to do (even an idle watcher will do..)
		580	ev_loop (my_loop, 0);
		581	... jobs done. yeah!
261		582
262	=item ev_unloop (loop, how)	583	=item ev_unloop (loop, how)
263		584
264	Can be used to make a call to C<ev_loop> return early (but only after it	585	Can be used to make a call to C<ev_loop> return early (but only after it
265	has processed all outstanding events). The C<how> argument must be either	586	has processed all outstanding events). The C<how> argument must be either
…		…
279	visible to the libev user and should not keep C<ev_loop> from exiting if	600	visible to the libev user and should not keep C<ev_loop> from exiting if
280	no event watchers registered by it are active. It is also an excellent	601	no event watchers registered by it are active. It is also an excellent
281	way to do this for generic recurring timers or from within third-party	602	way to do this for generic recurring timers or from within third-party
282	libraries. Just remember to I<unref after start> and I<ref before stop>.	603	libraries. Just remember to I<unref after start> and I<ref before stop>.
283		604
		605	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		606	running when nothing else is active.
		607
		608	struct ev_signal exitsig;
		609	ev_signal_init (&exitsig, sig_cb, SIGINT);
		610	ev_signal_start (loop, &exitsig);
		611	evf_unref (loop);
		612
		613	Example: For some weird reason, unregister the above signal handler again.
		614
		615	ev_ref (loop);
		616	ev_signal_stop (loop, &exitsig);
		617
		618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		619
		620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		621
		622	These advanced functions influence the time that libev will spend waiting
		623	for events. Both are by default C<0>, meaning that libev will try to
		624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		625
		626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		627	allows libev to delay invocation of I/O and timer/periodic callbacks to
		628	increase efficiency of loop iterations.
		629
		630	The background is that sometimes your program runs just fast enough to
		631	handle one (or very few) event(s) per loop iteration. While this makes
		632	the program responsive, it also wastes a lot of CPU time to poll for new
		633	events, especially with backends like C<select ()> which have a high
		634	overhead for the actual polling but can deliver many events at once.
		635
		636	By setting a higher I<io collect interval> you allow libev to spend more
		637	time collecting I/O events, so you can handle more events per iteration,
		638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		639	C<ev_timer>) will be not affected. Setting this to a non-null value will
		640	introduce an additional C<ev_sleep ()> call into most loop iterations.
		641
		642	Likewise, by setting a higher I<timeout collect interval> you allow libev
		643	to spend more time collecting timeouts, at the expense of increased
		644	latency (the watcher callback will be called later). C<ev_io> watchers
		645	will not be affected. Setting this to a non-null value will not introduce
		646	any overhead in libev.
		647
		648	Many (busy) programs can usually benefit by setting the io collect
		649	interval to a value near C<0.1> or so, which is often enough for
		650	interactive servers (of course not for games), likewise for timeouts. It
		651	usually doesn't make much sense to set it to a lower value than C<0.01>,
		652	as this approsaches the timing granularity of most systems.
		653
284	=back	654	=back
		655
285		656
286	=head1 ANATOMY OF A WATCHER	657	=head1 ANATOMY OF A WATCHER
287		658
288	A watcher is a structure that you create and register to record your	659	A watcher is a structure that you create and register to record your
289	interest in some event. For instance, if you want to wait for STDIN to	660	interest in some event. For instance, if you want to wait for STDIN to
…		…
322	*) >>), and you can stop watching for events at any time by calling the	693	*) >>), and you can stop watching for events at any time by calling the
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
324		695
325	As long as your watcher is active (has been started but not stopped) you	696	As long as your watcher is active (has been started but not stopped) you
326	must not touch the values stored in it. Most specifically you must never	697	must not touch the values stored in it. Most specifically you must never
327	reinitialise it or call its set method.	698	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		699
334	Each and every callback receives the event loop pointer as first, the	700	Each and every callback receives the event loop pointer as first, the
335	registered watcher structure as second, and a bitset of received events as	701	registered watcher structure as second, and a bitset of received events as
336	third argument.	702	third argument.
337		703
…		…
361	The signal specified in the C<ev_signal> watcher has been received by a thread.	727	The signal specified in the C<ev_signal> watcher has been received by a thread.
362		728
363	=item C<EV_CHILD>	729	=item C<EV_CHILD>
364		730
365	The pid specified in the C<ev_child> watcher has received a status change.	731	The pid specified in the C<ev_child> watcher has received a status change.
		732
		733	=item C<EV_STAT>
		734
		735	The path specified in the C<ev_stat> watcher changed its attributes somehow.
366		736
367	=item C<EV_IDLE>	737	=item C<EV_IDLE>
368		738
369	The C<ev_idle> watcher has determined that you have nothing better to do.	739	The C<ev_idle> watcher has determined that you have nothing better to do.
370		740
…		…
378	received events. Callbacks of both watcher types can start and stop as	748	received events. Callbacks of both watcher types can start and stop as
379	many watchers as they want, and all of them will be taken into account	749	many watchers as they want, and all of them will be taken into account
380	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	750	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
381	C<ev_loop> from blocking).	751	C<ev_loop> from blocking).
382		752
		753	=item C<EV_EMBED>
		754
		755	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		756
		757	=item C<EV_FORK>
		758
		759	The event loop has been resumed in the child process after fork (see
		760	C<ev_fork>).
		761
383	=item C<EV_ERROR>	762	=item C<EV_ERROR>
384		763
385	An unspecified error has occured, the watcher has been stopped. This might	764	An unspecified error has occured, the watcher has been stopped. This might
386	happen because the watcher could not be properly started because libev	765	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	766	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	772	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	773	with the error from read() or write(). This will not work in multithreaded
395	programs, though, so beware.	774	programs, though, so beware.
396		775
397	=back	776	=back
		777
		778	=head2 GENERIC WATCHER FUNCTIONS
		779
		780	In the following description, C<TYPE> stands for the watcher type,
		781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		782
		783	=over 4
		784
		785	=item C<ev_init> (ev_TYPE *watcher, callback)
		786
		787	This macro initialises the generic portion of a watcher. The contents
		788	of the watcher object can be arbitrary (so C<malloc> will do). Only
		789	the generic parts of the watcher are initialised, you I<need> to call
		790	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		791	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		792	which rolls both calls into one.
		793
		794	You can reinitialise a watcher at any time as long as it has been stopped
		795	(or never started) and there are no pending events outstanding.
		796
		797	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		798	int revents)>.
		799
		800	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		801
		802	This macro initialises the type-specific parts of a watcher. You need to
		803	call C<ev_init> at least once before you call this macro, but you can
		804	call C<ev_TYPE_set> any number of times. You must not, however, call this
		805	macro on a watcher that is active (it can be pending, however, which is a
		806	difference to the C<ev_init> macro).
		807
		808	Although some watcher types do not have type-specific arguments
		809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		810
		811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		812
		813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		814	calls into a single call. This is the most convinient method to initialise
		815	a watcher. The same limitations apply, of course.
		816
		817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		818
		819	Starts (activates) the given watcher. Only active watchers will receive
		820	events. If the watcher is already active nothing will happen.
		821
		822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		823
		824	Stops the given watcher again (if active) and clears the pending
		825	status. It is possible that stopped watchers are pending (for example,
		826	non-repeating timers are being stopped when they become pending), but
		827	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		828	you want to free or reuse the memory used by the watcher it is therefore a
		829	good idea to always call its C<ev_TYPE_stop> function.
		830
		831	=item bool ev_is_active (ev_TYPE *watcher)
		832
		833	Returns a true value iff the watcher is active (i.e. it has been started
		834	and not yet been stopped). As long as a watcher is active you must not modify
		835	it.
		836
		837	=item bool ev_is_pending (ev_TYPE *watcher)
		838
		839	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		840	events but its callback has not yet been invoked). As long as a watcher
		841	is pending (but not active) you must not call an init function on it (but
		842	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		843	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		844	it).
		845
		846	=item callback ev_cb (ev_TYPE *watcher)
		847
		848	Returns the callback currently set on the watcher.
		849
		850	=item ev_cb_set (ev_TYPE *watcher, callback)
		851
		852	Change the callback. You can change the callback at virtually any time
		853	(modulo threads).
		854
		855	=item ev_set_priority (ev_TYPE *watcher, priority)
		856
		857	=item int ev_priority (ev_TYPE *watcher)
		858
		859	Set and query the priority of the watcher. The priority is a small
		860	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		861	(default: C<-2>). Pending watchers with higher priority will be invoked
		862	before watchers with lower priority, but priority will not keep watchers
		863	from being executed (except for C<ev_idle> watchers).
		864
		865	This means that priorities are I<only> used for ordering callback
		866	invocation after new events have been received. This is useful, for
		867	example, to reduce latency after idling, or more often, to bind two
		868	watchers on the same event and make sure one is called first.
		869
		870	If you need to suppress invocation when higher priority events are pending
		871	you need to look at C<ev_idle> watchers, which provide this functionality.
		872
		873	You I<must not> change the priority of a watcher as long as it is active or
		874	pending.
		875
		876	The default priority used by watchers when no priority has been set is
		877	always C<0>, which is supposed to not be too high and not be too low :).
		878
		879	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		880	fine, as long as you do not mind that the priority value you query might
		881	or might not have been adjusted to be within valid range.
		882
		883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		884
		885	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		886	C<loop> nor C<revents> need to be valid as long as the watcher callback
		887	can deal with that fact.
		888
		889	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		890
		891	If the watcher is pending, this function returns clears its pending status
		892	and returns its C<revents> bitset (as if its callback was invoked). If the
		893	watcher isn't pending it does nothing and returns C<0>.
		894
		895	=back
		896
398		897
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
400		899
401	Each watcher has, by default, a member C<void *data> that you can change	900	Each watcher has, by default, a member C<void *data> that you can change
402	and read at any time, libev will completely ignore it. This can be used	901	and read at any time, libev will completely ignore it. This can be used
…		…
420	{	919	{
421	struct my_io *w = (struct my_io *)w_;	920	struct my_io *w = (struct my_io *)w_;
422	...	921	...
423	}	922	}
424		923
425	More interesting and less C-conformant ways of catsing your callback type	924	More interesting and less C-conformant ways of casting your callback type
426	have been omitted....	925	instead have been omitted.
		926
		927	Another common scenario is having some data structure with multiple
		928	watchers:
		929
		930	struct my_biggy
		931	{
		932	int some_data;
		933	ev_timer t1;
		934	ev_timer t2;
		935	}
		936
		937	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		938	you need to use C<offsetof>:
		939
		940	#include <stddef.h>
		941
		942	static void
		943	t1_cb (EV_P_ struct ev_timer *w, int revents)
		944	{
		945	struct my_biggy big = (struct my_biggy *
		946	(((char *)w) - offsetof (struct my_biggy, t1));
		947	}
		948
		949	static void
		950	t2_cb (EV_P_ struct ev_timer *w, int revents)
		951	{
		952	struct my_biggy big = (struct my_biggy *
		953	(((char *)w) - offsetof (struct my_biggy, t2));
		954	}
427		955
428		956
429	=head1 WATCHER TYPES	957	=head1 WATCHER TYPES
430		958
431	This section describes each watcher in detail, but will not repeat	959	This section describes each watcher in detail, but will not repeat
432	information given in the last section.	960	information given in the last section. Any initialisation/set macros,
		961	functions and members specific to the watcher type are explained.
433		962
		963	Members are additionally marked with either I<[read-only]>, meaning that,
		964	while the watcher is active, you can look at the member and expect some
		965	sensible content, but you must not modify it (you can modify it while the
		966	watcher is stopped to your hearts content), or I<[read-write]>, which
		967	means you can expect it to have some sensible content while the watcher
		968	is active, but you can also modify it. Modifying it may not do something
		969	sensible or take immediate effect (or do anything at all), but libev will
		970	not crash or malfunction in any way.
		971
		972
434	=head2 C<ev_io> - is this file descriptor readable or writable	973	=head2 C<ev_io> - is this file descriptor readable or writable?
435		974
436	I/O watchers check whether a file descriptor is readable or writable	975	I/O watchers check whether a file descriptor is readable or writable
437	in each iteration of the event loop (This behaviour is called	976	in each iteration of the event loop, or, more precisely, when reading
438	level-triggering because you keep receiving events as long as the	977	would not block the process and writing would at least be able to write
439	condition persists. Remember you can stop the watcher if you don't want to	978	some data. This behaviour is called level-triggering because you keep
440	act on the event and neither want to receive future events).	979	receiving events as long as the condition persists. Remember you can stop
		980	the watcher if you don't want to act on the event and neither want to
		981	receive future events.
441		982
442	In general you can register as many read and/or write event watchers per	983	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	984	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	985	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	986	required if you know what you are doing).
446		987
447	You have to be careful with dup'ed file descriptors, though. Some backends	988	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	989	(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	990	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	991	to the same underlying file/socket/etc. description (that is, they share
451	the same underlying "file open").	992	the same underlying "file open").
452		993
453	If you must do this, then force the use of a known-to-be-good backend	994	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	995	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
455	EVMETHOD_POLL).	996	C<EVBACKEND_POLL>).
		997
		998	Another thing you have to watch out for is that it is quite easy to
		999	receive "spurious" readyness notifications, that is your callback might
		1000	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1001	because there is no data. Not only are some backends known to create a
		1002	lot of those (for example solaris ports), it is very easy to get into
		1003	this situation even with a relatively standard program structure. Thus
		1004	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1005	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1006
		1007	If you cannot run the fd in non-blocking mode (for example you should not
		1008	play around with an Xlib connection), then you have to seperately re-test
		1009	whether a file descriptor is really ready with a known-to-be good interface
		1010	such as poll (fortunately in our Xlib example, Xlib already does this on
		1011	its own, so its quite safe to use).
		1012
		1013	=head3 The special problem of disappearing file descriptors
		1014
		1015	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1016	descriptor (either by calling C<close> explicitly or by any other means,
		1017	such as C<dup>). The reason is that you register interest in some file
		1018	descriptor, but when it goes away, the operating system will silently drop
		1019	this interest. If another file descriptor with the same number then is
		1020	registered with libev, there is no efficient way to see that this is, in
		1021	fact, a different file descriptor.
		1022
		1023	To avoid having to explicitly tell libev about such cases, libev follows
		1024	the following policy: Each time C<ev_io_set> is being called, libev
		1025	will assume that this is potentially a new file descriptor, otherwise
		1026	it is assumed that the file descriptor stays the same. That means that
		1027	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1028	descriptor even if the file descriptor number itself did not change.
		1029
		1030	This is how one would do it normally anyway, the important point is that
		1031	the libev application should not optimise around libev but should leave
		1032	optimisations to libev.
		1033
		1034	=head3 The special problem of dup'ed file descriptors
		1035
		1036	Some backends (e.g. epoll), cannot register events for file descriptors,
		1037	but only events for the underlying file descriptions. That means when you
		1038	have C<dup ()>'ed file descriptors and register events for them, only one
		1039	file descriptor might actually receive events.
		1040
		1041	There is no workaround possible except not registering events
		1042	for potentially C<dup ()>'ed file descriptors, or to resort to
		1043	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1044
		1045	=head3 The special problem of fork
		1046
		1047	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1048	useless behaviour. Libev fully supports fork, but needs to be told about
		1049	it in the child.
		1050
		1051	To support fork in your programs, you either have to call
		1052	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1053	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1054	C<EVBACKEND_POLL>.
		1055
		1056
		1057	=head3 Watcher-Specific Functions
456		1058
457	=over 4	1059	=over 4
458		1060
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1061	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1062
461	=item ev_io_set (ev_io *, int fd, int events)	1063	=item ev_io_set (ev_io *, int fd, int events)
462		1064
463	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1065	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 |	1066	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
465	EV_WRITE> to receive the given events.	1067	C<EV_READ | EV_WRITE> to receive the given events.
		1068
		1069	=item int fd [read-only]
		1070
		1071	The file descriptor being watched.
		1072
		1073	=item int events [read-only]
		1074
		1075	The events being watched.
466		1076
467	=back	1077	=back
468		1078
		1079	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1080	readable, but only once. Since it is likely line-buffered, you could
		1081	attempt to read a whole line in the callback.
		1082
		1083	static void
		1084	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1085	{
		1086	ev_io_stop (loop, w);
		1087	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1088	}
		1089
		1090	...
		1091	struct ev_loop *loop = ev_default_init (0);
		1092	struct ev_io stdin_readable;
		1093	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1094	ev_io_start (loop, &stdin_readable);
		1095	ev_loop (loop, 0);
		1096
		1097
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1098	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1099
471	Timer watchers are simple relative timers that generate an event after a	1100	Timer watchers are simple relative timers that generate an event after a
472	given time, and optionally repeating in regular intervals after that.	1101	given time, and optionally repeating in regular intervals after that.
473		1102
474	The timers are based on real time, that is, if you register an event that	1103	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	1104	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	1105	time, it will still time out after (roughly) and hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1106	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1107	monotonic clock option helps a lot here).
479		1108
480	The relative timeouts are calculated relative to the C<ev_now ()>	1109	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	1110	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	1111	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	1112	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:	1113	on the current time, use something like this to adjust for this:
485		1114
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1115	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1116
		1117	The callback is guarenteed to be invoked only when its timeout has passed,
		1118	but if multiple timers become ready during the same loop iteration then
		1119	order of execution is undefined.
		1120
		1121	=head3 Watcher-Specific Functions and Data Members
487		1122
488	=over 4	1123	=over 4
489		1124
490	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1125	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
491		1126
…		…
505	=item ev_timer_again (loop)	1140	=item ev_timer_again (loop)
506		1141
507	This will act as if the timer timed out and restart it again if it is	1142	This will act as if the timer timed out and restart it again if it is
508	repeating. The exact semantics are:	1143	repeating. The exact semantics are:
509		1144
		1145	If the timer is pending, its pending status is cleared.
		1146
510	If the timer is started but nonrepeating, stop it.	1147	If the timer is started but nonrepeating, stop it (as if it timed out).
511		1148
512	If the timer is repeating, either start it if necessary (with the repeat	1149	If the timer is repeating, either start it if necessary (with the
513	value), or reset the running timer to the repeat value.	1150	C<repeat> value), or reset the running timer to the C<repeat> value.
514		1151
515	This sounds a bit complicated, but here is a useful and typical	1152	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	1153	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	1154	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	1155	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	1156	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	1157	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	1158	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.	1159	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1160	automatically restart it if need be.
		1161
		1162	That means you can ignore the C<after> value and C<ev_timer_start>
		1163	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1164
		1165	ev_timer_init (timer, callback, 0., 5.);
		1166	ev_timer_again (loop, timer);
		1167	...
		1168	timer->again = 17.;
		1169	ev_timer_again (loop, timer);
		1170	...
		1171	timer->again = 10.;
		1172	ev_timer_again (loop, timer);
		1173
		1174	This is more slightly efficient then stopping/starting the timer each time
		1175	you want to modify its timeout value.
		1176
		1177	=item ev_tstamp repeat [read-write]
		1178
		1179	The current C<repeat> value. Will be used each time the watcher times out
		1180	or C<ev_timer_again> is called and determines the next timeout (if any),
		1181	which is also when any modifications are taken into account.
523		1182
524	=back	1183	=back
525		1184
		1185	Example: Create a timer that fires after 60 seconds.
		1186
		1187	static void
		1188	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1189	{
		1190	.. one minute over, w is actually stopped right here
		1191	}
		1192
		1193	struct ev_timer mytimer;
		1194	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1195	ev_timer_start (loop, &mytimer);
		1196
		1197	Example: Create a timeout timer that times out after 10 seconds of
		1198	inactivity.
		1199
		1200	static void
		1201	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1202	{
		1203	.. ten seconds without any activity
		1204	}
		1205
		1206	struct ev_timer mytimer;
		1207	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1208	ev_timer_again (&mytimer); /* start timer */
		1209	ev_loop (loop, 0);
		1210
		1211	// and in some piece of code that gets executed on any "activity":
		1212	// reset the timeout to start ticking again at 10 seconds
		1213	ev_timer_again (&mytimer);
		1214
		1215
526	=head2 C<ev_periodic> - to cron or not to cron	1216	=head2 C<ev_periodic> - to cron or not to cron?
527		1217
528	Periodic watchers are also timers of a kind, but they are very versatile	1218	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	1219	(and unfortunately a bit complex).
530		1220
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1221	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	1222	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	1223	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 ()	1224	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	1225	+ 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	1226	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	1227	roughly 10 seconds later).
538	again).
539		1228
540	They can also be used to implement vastly more complex timers, such as	1229	They can also be used to implement vastly more complex timers, such as
541	triggering an event on eahc midnight, local time.	1230	triggering an event on each midnight, local time or other, complicated,
		1231	rules.
		1232
		1233	As with timers, the callback is guarenteed to be invoked only when the
		1234	time (C<at>) has been passed, but if multiple periodic timers become ready
		1235	during the same loop iteration then order of execution is undefined.
		1236
		1237	=head3 Watcher-Specific Functions and Data Members
542		1238
543	=over 4	1239	=over 4
544		1240
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1241	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
546		1242
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1243	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
548		1244
549	Lots of arguments, lets sort it out... There are basically three modes of	1245	Lots of arguments, lets sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	1246	operation, and we will explain them from simplest to complex:
551		1247
552
553	=over 4	1248	=over 4
554		1249
555	=item * absolute timer (interval = reschedule_cb = 0)	1250	=item * absolute timer (at = time, interval = reschedule_cb = 0)
556		1251
557	In this configuration the watcher triggers an event at the wallclock time	1252	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,	1253	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	1254	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.	1255	system time reaches or surpasses this time.
561		1256
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1257	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
563		1258
564	In this mode the watcher will always be scheduled to time out at the next	1259	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	1260	C<at + N * interval> time (for some integer N, which can also be negative)
566	of any time jumps.	1261	and then repeat, regardless of any time jumps.
567		1262
568	This can be used to create timers that do not drift with respect to system	1263	This can be used to create timers that do not drift with respect to system
569	time:	1264	time:
570		1265
571	ev_periodic_set (&periodic, 0., 3600., 0);	1266	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
577		1272
578	Another way to think about it (for the mathematically inclined) is that	1273	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	1274	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.	1275	time where C<time = at (mod interval)>, regardless of any time jumps.
581		1276
		1277	For numerical stability it is preferable that the C<at> value is near
		1278	C<ev_now ()> (the current time), but there is no range requirement for
		1279	this value.
		1280
582	=item * manual reschedule mode (reschedule_cb = callback)	1281	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
583		1282
584	In this mode the values for C<interval> and C<at> are both being	1283	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	1284	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	1285	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	1286	current time as second argument.
588		1287
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1288	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,	1289	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	1290	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592	starting a prepare watcher).	1291	starting an C<ev_prepare> watcher, which is legal).
593		1292
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1293	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
595	ev_tstamp now)>, e.g.:	1294	ev_tstamp now)>, e.g.:
596		1295
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1296	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	1319	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	1320	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	1321	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	1322	program when the crontabs have changed).
624		1323
		1324	=item ev_tstamp offset [read-write]
		1325
		1326	When repeating, this contains the offset value, otherwise this is the
		1327	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1328
		1329	Can be modified any time, but changes only take effect when the periodic
		1330	timer fires or C<ev_periodic_again> is being called.
		1331
		1332	=item ev_tstamp interval [read-write]
		1333
		1334	The current interval value. Can be modified any time, but changes only
		1335	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1336	called.
		1337
		1338	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1339
		1340	The current reschedule callback, or C<0>, if this functionality is
		1341	switched off. Can be changed any time, but changes only take effect when
		1342	the periodic timer fires or C<ev_periodic_again> is being called.
		1343
		1344	=item ev_tstamp at [read-only]
		1345
		1346	When active, contains the absolute time that the watcher is supposed to
		1347	trigger next.
		1348
625	=back	1349	=back
626		1350
		1351	Example: Call a callback every hour, or, more precisely, whenever the
		1352	system clock is divisible by 3600. The callback invocation times have
		1353	potentially a lot of jittering, but good long-term stability.
		1354
		1355	static void
		1356	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1357	{
		1358	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1359	}
		1360
		1361	struct ev_periodic hourly_tick;
		1362	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1363	ev_periodic_start (loop, &hourly_tick);
		1364
		1365	Example: The same as above, but use a reschedule callback to do it:
		1366
		1367	#include <math.h>
		1368
		1369	static ev_tstamp
		1370	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1371	{
		1372	return fmod (now, 3600.) + 3600.;
		1373	}
		1374
		1375	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1376
		1377	Example: Call a callback every hour, starting now:
		1378
		1379	struct ev_periodic hourly_tick;
		1380	ev_periodic_init (&hourly_tick, clock_cb,
		1381	fmod (ev_now (loop), 3600.), 3600., 0);
		1382	ev_periodic_start (loop, &hourly_tick);
		1383
		1384
627	=head2 C<ev_signal> - signal me when a signal gets signalled	1385	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		1386
629	Signal watchers will trigger an event when the process receives a specific	1387	Signal watchers will trigger an event when the process receives a specific
630	signal one or more times. Even though signals are very asynchronous, libev	1388	signal one or more times. Even though signals are very asynchronous, libev
631	will try it's best to deliver signals synchronously, i.e. as part of the	1389	will try it's best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	1390	normal event processing, like any other event.
…		…
636	with the kernel (thus it coexists with your own signal handlers as long	1394	with the kernel (thus it coexists with your own signal handlers as long
637	as you don't register any with libev). Similarly, when the last signal	1395	as you don't register any with libev). Similarly, when the last signal
638	watcher for a signal is stopped libev will reset the signal handler to	1396	watcher for a signal is stopped libev will reset the signal handler to
639	SIG_DFL (regardless of what it was set to before).	1397	SIG_DFL (regardless of what it was set to before).
640		1398
		1399	=head3 Watcher-Specific Functions and Data Members
		1400
641	=over 4	1401	=over 4
642		1402
643	=item ev_signal_init (ev_signal *, callback, int signum)	1403	=item ev_signal_init (ev_signal *, callback, int signum)
644		1404
645	=item ev_signal_set (ev_signal *, int signum)	1405	=item ev_signal_set (ev_signal *, int signum)
646		1406
647	Configures the watcher to trigger on the given signal number (usually one	1407	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	1408	of the C<SIGxxx> constants).
649		1409
		1410	=item int signum [read-only]
		1411
		1412	The signal the watcher watches out for.
		1413
650	=back	1414	=back
651		1415
		1416
652	=head2 C<ev_child> - wait for pid status changes	1417	=head2 C<ev_child> - watch out for process status changes
653		1418
654	Child watchers trigger when your process receives a SIGCHLD in response to	1419	Child watchers trigger when your process receives a SIGCHLD in response to
655	some child status changes (most typically when a child of yours dies).	1420	some child status changes (most typically when a child of yours dies).
		1421
		1422	=head3 Watcher-Specific Functions and Data Members
656		1423
657	=over 4	1424	=over 4
658		1425
659	=item ev_child_init (ev_child *, callback, int pid)	1426	=item ev_child_init (ev_child *, callback, int pid)
660		1427
…		…
665	at the C<rstatus> member of the C<ev_child> watcher structure to see	1432	at the C<rstatus> member of the C<ev_child> watcher structure to see
666	the status word (use the macros from C<sys/wait.h> and see your systems	1433	the status word (use the macros from C<sys/wait.h> and see your systems
667	C<waitpid> documentation). The C<rpid> member contains the pid of the	1434	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	1435	process causing the status change.
669		1436
		1437	=item int pid [read-only]
		1438
		1439	The process id this watcher watches out for, or C<0>, meaning any process id.
		1440
		1441	=item int rpid [read-write]
		1442
		1443	The process id that detected a status change.
		1444
		1445	=item int rstatus [read-write]
		1446
		1447	The process exit/trace status caused by C<rpid> (see your systems
		1448	C<waitpid> and C<sys/wait.h> documentation for details).
		1449
670	=back	1450	=back
671		1451
		1452	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1453
		1454	static void
		1455	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1456	{
		1457	ev_unloop (loop, EVUNLOOP_ALL);
		1458	}
		1459
		1460	struct ev_signal signal_watcher;
		1461	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1462	ev_signal_start (loop, &sigint_cb);
		1463
		1464
		1465	=head2 C<ev_stat> - did the file attributes just change?
		1466
		1467	This watches a filesystem path for attribute changes. That is, it calls
		1468	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1469	compared to the last time, invoking the callback if it did.
		1470
		1471	The path does not need to exist: changing from "path exists" to "path does
		1472	not exist" is a status change like any other. The condition "path does
		1473	not exist" is signified by the C<st_nlink> field being zero (which is
		1474	otherwise always forced to be at least one) and all the other fields of
		1475	the stat buffer having unspecified contents.
		1476
		1477	The path I<should> be absolute and I<must not> end in a slash. If it is
		1478	relative and your working directory changes, the behaviour is undefined.
		1479
		1480	Since there is no standard to do this, the portable implementation simply
		1481	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1482	can specify a recommended polling interval for this case. If you specify
		1483	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1484	unspecified default> value will be used (which you can expect to be around
		1485	five seconds, although this might change dynamically). Libev will also
		1486	impose a minimum interval which is currently around C<0.1>, but thats
		1487	usually overkill.
		1488
		1489	This watcher type is not meant for massive numbers of stat watchers,
		1490	as even with OS-supported change notifications, this can be
		1491	resource-intensive.
		1492
		1493	At the time of this writing, only the Linux inotify interface is
		1494	implemented (implementing kqueue support is left as an exercise for the
		1495	reader). Inotify will be used to give hints only and should not change the
		1496	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1497	to fall back to regular polling again even with inotify, but changes are
		1498	usually detected immediately, and if the file exists there will be no
		1499	polling.
		1500
		1501	=head3 Inotify
		1502
		1503	When C<inotify (7)> support has been compiled into libev (generally only
		1504	available on Linux) and present at runtime, it will be used to speed up
		1505	change detection where possible. The inotify descriptor will be created lazily
		1506	when the first C<ev_stat> watcher is being started.
		1507
		1508	Inotify presense does not change the semantics of C<ev_stat> watchers
		1509	except that changes might be detected earlier, and in some cases, to avoid
		1510	making regular C<stat> calls. Even in the presense of inotify support
		1511	there are many cases where libev has to resort to regular C<stat> polling.
		1512
		1513	(There is no support for kqueue, as apparently it cannot be used to
		1514	implement this functionality, due to the requirement of having a file
		1515	descriptor open on the object at all times).
		1516
		1517	=head3 The special problem of stat time resolution
		1518
		1519	The C<stat ()> syscall only supports full-second resolution portably, and
		1520	even on systems where the resolution is higher, many filesystems still
		1521	only support whole seconds.
		1522
		1523	That means that, if the time is the only thing that changes, you might
		1524	miss updates: on the first update, C<ev_stat> detects a change and calls
		1525	your callback, which does something. When there is another update within
		1526	the same second, C<ev_stat> will be unable to detect it.
		1527
		1528	The solution to this is to delay acting on a change for a second (or till
		1529	the next second boundary), using a roughly one-second delay C<ev_timer>
		1530	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1531	is added to work around small timing inconsistencies of some operating
		1532	systems.
		1533
		1534	=head3 Watcher-Specific Functions and Data Members
		1535
		1536	=over 4
		1537
		1538	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1539
		1540	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1541
		1542	Configures the watcher to wait for status changes of the given
		1543	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1544	be detected and should normally be specified as C<0> to let libev choose
		1545	a suitable value. The memory pointed to by C<path> must point to the same
		1546	path for as long as the watcher is active.
		1547
		1548	The callback will be receive C<EV_STAT> when a change was detected,
		1549	relative to the attributes at the time the watcher was started (or the
		1550	last change was detected).
		1551
		1552	=item ev_stat_stat (ev_stat *)
		1553
		1554	Updates the stat buffer immediately with new values. If you change the
		1555	watched path in your callback, you could call this fucntion to avoid
		1556	detecting this change (while introducing a race condition). Can also be
		1557	useful simply to find out the new values.
		1558
		1559	=item ev_statdata attr [read-only]
		1560
		1561	The most-recently detected attributes of the file. Although the type is of
		1562	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1563	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1564	was some error while C<stat>ing the file.
		1565
		1566	=item ev_statdata prev [read-only]
		1567
		1568	The previous attributes of the file. The callback gets invoked whenever
		1569	C<prev> != C<attr>.
		1570
		1571	=item ev_tstamp interval [read-only]
		1572
		1573	The specified interval.
		1574
		1575	=item const char *path [read-only]
		1576
		1577	The filesystem path that is being watched.
		1578
		1579	=back
		1580
		1581	=head3 Examples
		1582
		1583	Example: Watch C</etc/passwd> for attribute changes.
		1584
		1585	static void
		1586	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1587	{
		1588	/* /etc/passwd changed in some way */
		1589	if (w->attr.st_nlink)
		1590	{
		1591	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1592	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1593	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1594	}
		1595	else
		1596	/* you shalt not abuse printf for puts */
		1597	puts ("wow, /etc/passwd is not there, expect problems. "
		1598	"if this is windows, they already arrived\n");
		1599	}
		1600
		1601	...
		1602	ev_stat passwd;
		1603
		1604	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1605	ev_stat_start (loop, &passwd);
		1606
		1607	Example: Like above, but additionally use a one-second delay so we do not
		1608	miss updates (however, frequent updates will delay processing, too, so
		1609	one might do the work both on C<ev_stat> callback invocation I<and> on
		1610	C<ev_timer> callback invocation).
		1611
		1612	static ev_stat passwd;
		1613	static ev_timer timer;
		1614
		1615	static void
		1616	timer_cb (EV_P_ ev_timer *w, int revents)
		1617	{
		1618	ev_timer_stop (EV_A_ w);
		1619
		1620	/* now it's one second after the most recent passwd change */
		1621	}
		1622
		1623	static void
		1624	stat_cb (EV_P_ ev_stat *w, int revents)
		1625	{
		1626	/* reset the one-second timer */
		1627	ev_timer_again (EV_A_ &timer);
		1628	}
		1629
		1630	...
		1631	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1632	ev_stat_start (loop, &passwd);
		1633	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1634
		1635
672	=head2 C<ev_idle> - when you've got nothing better to do	1636	=head2 C<ev_idle> - when you've got nothing better to do...
673		1637
674	Idle watchers trigger events when there are no other events are pending	1638	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	1639	priority are pending (prepare, check and other idle watchers do not
676	as your process is busy handling sockets or timeouts (or even signals,	1640	count).
677	imagine) it will not be triggered. But when your process is idle all idle	1641
678	watchers are being called again and again, once per event loop iteration -	1642	That is, as long as your process is busy handling sockets or timeouts
		1643	(or even signals, imagine) of the same or higher priority it will not be
		1644	triggered. But when your process is idle (or only lower-priority watchers
		1645	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	1646	iteration - until stopped, that is, or your process receives more events
680	busy.	1647	and becomes busy again with higher priority stuff.
681		1648
682	The most noteworthy effect is that as long as any idle watchers are	1649	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.	1650	active, the process will not block when waiting for new events.
684		1651
685	Apart from keeping your process non-blocking (which is a useful	1652	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	1653	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	1654	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	1655	event loop has handled all outstanding events.
689		1656
		1657	=head3 Watcher-Specific Functions and Data Members
		1658
690	=over 4	1659	=over 4
691		1660
692	=item ev_idle_init (ev_signal *, callback)	1661	=item ev_idle_init (ev_signal *, callback)
693		1662
694	Initialises and configures the idle watcher - it has no parameters of any	1663	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,	1664	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	1665	believe me.
697		1666
698	=back	1667	=back
699		1668
		1669	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1670	callback, free it. Also, use no error checking, as usual.
		1671
		1672	static void
		1673	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1674	{
		1675	free (w);
		1676	// now do something you wanted to do when the program has
		1677	// no longer asnything immediate to do.
		1678	}
		1679
		1680	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1681	ev_idle_init (idle_watcher, idle_cb);
		1682	ev_idle_start (loop, idle_cb);
		1683
		1684
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1685	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		1686
702	Prepare and check watchers are usually (but not always) used in tandem:	1687	Prepare and check watchers are usually (but not always) used in tandem:
703	prepare watchers get invoked before the process blocks and check watchers	1688	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	1689	afterwards.
705		1690
		1691	You I<must not> call C<ev_loop> or similar functions that enter
		1692	the current event loop from either C<ev_prepare> or C<ev_check>
		1693	watchers. Other loops than the current one are fine, however. The
		1694	rationale behind this is that you do not need to check for recursion in
		1695	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1696	C<ev_check> so if you have one watcher of each kind they will always be
		1697	called in pairs bracketing the blocking call.
		1698
706	Their main purpose is to integrate other event mechanisms into libev. This	1699	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	1700	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.	1701	variable changes, implement your own watchers, integrate net-snmp or a
		1702	coroutine library and lots more. They are also occasionally useful if
		1703	you cache some data and want to flush it before blocking (for example,
		1704	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1705	watcher).
709		1706
710	This is done by examining in each prepare call which file descriptors need	1707	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	1708	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	1709	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	1710	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	1720	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	1721	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	1722	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	1723	low-priority coroutines to idle/background tasks).
727		1724
		1725	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1726	priority, to ensure that they are being run before any other watchers
		1727	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1728	too) should not activate ("feed") events into libev. While libev fully
		1729	supports this, they will be called before other C<ev_check> watchers
		1730	did their job. As C<ev_check> watchers are often used to embed other
		1731	(non-libev) event loops those other event loops might be in an unusable
		1732	state until their C<ev_check> watcher ran (always remind yourself to
		1733	coexist peacefully with others).
		1734
		1735	=head3 Watcher-Specific Functions and Data Members
		1736
728	=over 4	1737	=over 4
729		1738
730	=item ev_prepare_init (ev_prepare *, callback)	1739	=item ev_prepare_init (ev_prepare *, callback)
731		1740
732	=item ev_check_init (ev_check *, callback)	1741	=item ev_check_init (ev_check *, callback)
…		…
734	Initialises and configures the prepare or check watcher - they have no	1743	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>	1744	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.	1745	macros, but using them is utterly, utterly and completely pointless.
737		1746
738	=back	1747	=back
		1748
		1749	There are a number of principal ways to embed other event loops or modules
		1750	into libev. Here are some ideas on how to include libadns into libev
		1751	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1752	use for an actually working example. Another Perl module named C<EV::Glib>
		1753	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1754	into the Glib event loop).
		1755
		1756	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1757	and in a check watcher, destroy them and call into libadns. What follows
		1758	is pseudo-code only of course. This requires you to either use a low
		1759	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1760	the callbacks for the IO/timeout watchers might not have been called yet.
		1761
		1762	static ev_io iow [nfd];
		1763	static ev_timer tw;
		1764
		1765	static void
		1766	io_cb (ev_loop *loop, ev_io *w, int revents)
		1767	{
		1768	}
		1769
		1770	// create io watchers for each fd and a timer before blocking
		1771	static void
		1772	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1773	{
		1774	int timeout = 3600000;
		1775	struct pollfd fds [nfd];
		1776	// actual code will need to loop here and realloc etc.
		1777	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1778
		1779	/* the callback is illegal, but won't be called as we stop during check */
		1780	ev_timer_init (&tw, 0, timeout * 1e-3);
		1781	ev_timer_start (loop, &tw);
		1782
		1783	// create one ev_io per pollfd
		1784	for (int i = 0; i < nfd; ++i)
		1785	{
		1786	ev_io_init (iow + i, io_cb, fds [i].fd,
		1787	((fds [i].events & POLLIN ? EV_READ : 0)
		1788	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1789
		1790	fds [i].revents = 0;
		1791	ev_io_start (loop, iow + i);
		1792	}
		1793	}
		1794
		1795	// stop all watchers after blocking
		1796	static void
		1797	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1798	{
		1799	ev_timer_stop (loop, &tw);
		1800
		1801	for (int i = 0; i < nfd; ++i)
		1802	{
		1803	// set the relevant poll flags
		1804	// could also call adns_processreadable etc. here
		1805	struct pollfd *fd = fds + i;
		1806	int revents = ev_clear_pending (iow + i);
		1807	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1808	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1809
		1810	// now stop the watcher
		1811	ev_io_stop (loop, iow + i);
		1812	}
		1813
		1814	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1815	}
		1816
		1817	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1818	in the prepare watcher and would dispose of the check watcher.
		1819
		1820	Method 3: If the module to be embedded supports explicit event
		1821	notification (adns does), you can also make use of the actual watcher
		1822	callbacks, and only destroy/create the watchers in the prepare watcher.
		1823
		1824	static void
		1825	timer_cb (EV_P_ ev_timer *w, int revents)
		1826	{
		1827	adns_state ads = (adns_state)w->data;
		1828	update_now (EV_A);
		1829
		1830	adns_processtimeouts (ads, &tv_now);
		1831	}
		1832
		1833	static void
		1834	io_cb (EV_P_ ev_io *w, int revents)
		1835	{
		1836	adns_state ads = (adns_state)w->data;
		1837	update_now (EV_A);
		1838
		1839	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1840	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1841	}
		1842
		1843	// do not ever call adns_afterpoll
		1844
		1845	Method 4: Do not use a prepare or check watcher because the module you
		1846	want to embed is too inflexible to support it. Instead, youc na override
		1847	their poll function. The drawback with this solution is that the main
		1848	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1849	this.
		1850
		1851	static gint
		1852	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1853	{
		1854	int got_events = 0;
		1855
		1856	for (n = 0; n < nfds; ++n)
		1857	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1858
		1859	if (timeout >= 0)
		1860	// create/start timer
		1861
		1862	// poll
		1863	ev_loop (EV_A_ 0);
		1864
		1865	// stop timer again
		1866	if (timeout >= 0)
		1867	ev_timer_stop (EV_A_ &to);
		1868
		1869	// stop io watchers again - their callbacks should have set
		1870	for (n = 0; n < nfds; ++n)
		1871	ev_io_stop (EV_A_ iow [n]);
		1872
		1873	return got_events;
		1874	}
		1875
		1876
		1877	=head2 C<ev_embed> - when one backend isn't enough...
		1878
		1879	This is a rather advanced watcher type that lets you embed one event loop
		1880	into another (currently only C<ev_io> events are supported in the embedded
		1881	loop, other types of watchers might be handled in a delayed or incorrect
		1882	fashion and must not be used).
		1883
		1884	There are primarily two reasons you would want that: work around bugs and
		1885	prioritise I/O.
		1886
		1887	As an example for a bug workaround, the kqueue backend might only support
		1888	sockets on some platform, so it is unusable as generic backend, but you
		1889	still want to make use of it because you have many sockets and it scales
		1890	so nicely. In this case, you would create a kqueue-based loop and embed it
		1891	into your default loop (which might use e.g. poll). Overall operation will
		1892	be a bit slower because first libev has to poll and then call kevent, but
		1893	at least you can use both at what they are best.
		1894
		1895	As for prioritising I/O: rarely you have the case where some fds have
		1896	to be watched and handled very quickly (with low latency), and even
		1897	priorities and idle watchers might have too much overhead. In this case
		1898	you would put all the high priority stuff in one loop and all the rest in
		1899	a second one, and embed the second one in the first.
		1900
		1901	As long as the watcher is active, the callback will be invoked every time
		1902	there might be events pending in the embedded loop. The callback must then
		1903	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1904	their callbacks (you could also start an idle watcher to give the embedded
		1905	loop strictly lower priority for example). You can also set the callback
		1906	to C<0>, in which case the embed watcher will automatically execute the
		1907	embedded loop sweep.
		1908
		1909	As long as the watcher is started it will automatically handle events. The
		1910	callback will be invoked whenever some events have been handled. You can
		1911	set the callback to C<0> to avoid having to specify one if you are not
		1912	interested in that.
		1913
		1914	Also, there have not currently been made special provisions for forking:
		1915	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1916	but you will also have to stop and restart any C<ev_embed> watchers
		1917	yourself.
		1918
		1919	Unfortunately, not all backends are embeddable, only the ones returned by
		1920	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1921	portable one.
		1922
		1923	So when you want to use this feature you will always have to be prepared
		1924	that you cannot get an embeddable loop. The recommended way to get around
		1925	this is to have a separate variables for your embeddable loop, try to
		1926	create it, and if that fails, use the normal loop for everything:
		1927
		1928	struct ev_loop *loop_hi = ev_default_init (0);
		1929	struct ev_loop *loop_lo = 0;
		1930	struct ev_embed embed;
		1931
		1932	// see if there is a chance of getting one that works
		1933	// (remember that a flags value of 0 means autodetection)
		1934	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1935	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1936	: 0;
		1937
		1938	// if we got one, then embed it, otherwise default to loop_hi
		1939	if (loop_lo)
		1940	{
		1941	ev_embed_init (&embed, 0, loop_lo);
		1942	ev_embed_start (loop_hi, &embed);
		1943	}
		1944	else
		1945	loop_lo = loop_hi;
		1946
		1947	=head3 Watcher-Specific Functions and Data Members
		1948
		1949	=over 4
		1950
		1951	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1952
		1953	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1954
		1955	Configures the watcher to embed the given loop, which must be
		1956	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1957	invoked automatically, otherwise it is the responsibility of the callback
		1958	to invoke it (it will continue to be called until the sweep has been done,
		1959	if you do not want thta, you need to temporarily stop the embed watcher).
		1960
		1961	=item ev_embed_sweep (loop, ev_embed *)
		1962
		1963	Make a single, non-blocking sweep over the embedded loop. This works
		1964	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1965	apropriate way for embedded loops.
		1966
		1967	=item struct ev_loop *other [read-only]
		1968
		1969	The embedded event loop.
		1970
		1971	=back
		1972
		1973
		1974	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		1975
		1976	Fork watchers are called when a C<fork ()> was detected (usually because
		1977	whoever is a good citizen cared to tell libev about it by calling
		1978	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		1979	event loop blocks next and before C<ev_check> watchers are being called,
		1980	and only in the child after the fork. If whoever good citizen calling
		1981	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		1982	handlers will be invoked, too, of course.
		1983
		1984	=head3 Watcher-Specific Functions and Data Members
		1985
		1986	=over 4
		1987
		1988	=item ev_fork_init (ev_signal *, callback)
		1989
		1990	Initialises and configures the fork watcher - it has no parameters of any
		1991	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		1992	believe me.
		1993
		1994	=back
		1995
739		1996
740	=head1 OTHER FUNCTIONS	1997	=head1 OTHER FUNCTIONS
741		1998
742	There are some other functions of possible interest. Described. Here. Now.	1999	There are some other functions of possible interest. Described. Here. Now.
743		2000
…		…
773	/* stdin might have data for us, joy! */;	2030	/* stdin might have data for us, joy! */;
774	}	2031	}
775		2032
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2033	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
777		2034
778	=item ev_feed_event (loop, watcher, int events)	2035	=item ev_feed_event (ev_loop *, watcher *, int revents)
779		2036
780	Feeds the given event set into the event loop, as if the specified event	2037	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	2038	had happened for the specified watcher (which must be a pointer to an
782	initialised but not necessarily started event watcher).	2039	initialised but not necessarily started event watcher).
783		2040
784	=item ev_feed_fd_event (loop, int fd, int revents)	2041	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
785		2042
786	Feed an event on the given fd, as if a file descriptor backend detected	2043	Feed an event on the given fd, as if a file descriptor backend detected
787	the given events it.	2044	the given events it.
788		2045
789	=item ev_feed_signal_event (loop, int signum)	2046	=item ev_feed_signal_event (ev_loop *loop, int signum)
790		2047
791	Feed an event as if the given signal occured (loop must be the default loop!).	2048	Feed an event as if the given signal occured (C<loop> must be the default
		2049	loop!).
792		2050
793	=back	2051	=back
		2052
794		2053
795	=head1 LIBEVENT EMULATION	2054	=head1 LIBEVENT EMULATION
796		2055
797	Libev offers a compatibility emulation layer for libevent. It cannot	2056	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	2057	emulate the internals of libevent, so here are some usage hints:
…		…
819		2078
820	=back	2079	=back
821		2080
822	=head1 C++ SUPPORT	2081	=head1 C++ SUPPORT
823		2082
824	TBD.	2083	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2084	you to use some convinience methods to start/stop watchers and also change
		2085	the callback model to a model using method callbacks on objects.
		2086
		2087	To use it,
		2088
		2089	#include <ev++.h>
		2090
		2091	This automatically includes F<ev.h> and puts all of its definitions (many
		2092	of them macros) into the global namespace. All C++ specific things are
		2093	put into the C<ev> namespace. It should support all the same embedding
		2094	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2095
		2096	Care has been taken to keep the overhead low. The only data member the C++
		2097	classes add (compared to plain C-style watchers) is the event loop pointer
		2098	that the watcher is associated with (or no additional members at all if
		2099	you disable C<EV_MULTIPLICITY> when embedding libev).
		2100
		2101	Currently, functions, and static and non-static member functions can be
		2102	used as callbacks. Other types should be easy to add as long as they only
		2103	need one additional pointer for context. If you need support for other
		2104	types of functors please contact the author (preferably after implementing
		2105	it).
		2106
		2107	Here is a list of things available in the C<ev> namespace:
		2108
		2109	=over 4
		2110
		2111	=item C<ev::READ>, C<ev::WRITE> etc.
		2112
		2113	These are just enum values with the same values as the C<EV_READ> etc.
		2114	macros from F<ev.h>.
		2115
		2116	=item C<ev::tstamp>, C<ev::now>
		2117
		2118	Aliases to the same types/functions as with the C<ev_> prefix.
		2119
		2120	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2121
		2122	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2123	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2124	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2125	defines by many implementations.
		2126
		2127	All of those classes have these methods:
		2128
		2129	=over 4
		2130
		2131	=item ev::TYPE::TYPE ()
		2132
		2133	=item ev::TYPE::TYPE (struct ev_loop *)
		2134
		2135	=item ev::TYPE::~TYPE
		2136
		2137	The constructor (optionally) takes an event loop to associate the watcher
		2138	with. If it is omitted, it will use C<EV_DEFAULT>.
		2139
		2140	The constructor calls C<ev_init> for you, which means you have to call the
		2141	C<set> method before starting it.
		2142
		2143	It will not set a callback, however: You have to call the templated C<set>
		2144	method to set a callback before you can start the watcher.
		2145
		2146	(The reason why you have to use a method is a limitation in C++ which does
		2147	not allow explicit template arguments for constructors).
		2148
		2149	The destructor automatically stops the watcher if it is active.
		2150
		2151	=item w->set<class, &class::method> (object *)
		2152
		2153	This method sets the callback method to call. The method has to have a
		2154	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2155	first argument and the C<revents> as second. The object must be given as
		2156	parameter and is stored in the C<data> member of the watcher.
		2157
		2158	This method synthesizes efficient thunking code to call your method from
		2159	the C callback that libev requires. If your compiler can inline your
		2160	callback (i.e. it is visible to it at the place of the C<set> call and
		2161	your compiler is good :), then the method will be fully inlined into the
		2162	thunking function, making it as fast as a direct C callback.
		2163
		2164	Example: simple class declaration and watcher initialisation
		2165
		2166	struct myclass
		2167	{
		2168	void io_cb (ev::io &w, int revents) { }
		2169	}
		2170
		2171	myclass obj;
		2172	ev::io iow;
		2173	iow.set <myclass, &myclass::io_cb> (&obj);
		2174
		2175	=item w->set<function> (void *data = 0)
		2176
		2177	Also sets a callback, but uses a static method or plain function as
		2178	callback. The optional C<data> argument will be stored in the watcher's
		2179	C<data> member and is free for you to use.
		2180
		2181	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2182
		2183	See the method-C<set> above for more details.
		2184
		2185	Example:
		2186
		2187	static void io_cb (ev::io &w, int revents) { }
		2188	iow.set <io_cb> ();
		2189
		2190	=item w->set (struct ev_loop *)
		2191
		2192	Associates a different C<struct ev_loop> with this watcher. You can only
		2193	do this when the watcher is inactive (and not pending either).
		2194
		2195	=item w->set ([args])
		2196
		2197	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2198	called at least once. Unlike the C counterpart, an active watcher gets
		2199	automatically stopped and restarted when reconfiguring it with this
		2200	method.
		2201
		2202	=item w->start ()
		2203
		2204	Starts the watcher. Note that there is no C<loop> argument, as the
		2205	constructor already stores the event loop.
		2206
		2207	=item w->stop ()
		2208
		2209	Stops the watcher if it is active. Again, no C<loop> argument.
		2210
		2211	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2212
		2213	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2214	C<ev_TYPE_again> function.
		2215
		2216	=item w->sweep () (C<ev::embed> only)
		2217
		2218	Invokes C<ev_embed_sweep>.
		2219
		2220	=item w->update () (C<ev::stat> only)
		2221
		2222	Invokes C<ev_stat_stat>.
		2223
		2224	=back
		2225
		2226	=back
		2227
		2228	Example: Define a class with an IO and idle watcher, start one of them in
		2229	the constructor.
		2230
		2231	class myclass
		2232	{
		2233	ev_io io; void io_cb (ev::io &w, int revents);
		2234	ev_idle idle void idle_cb (ev::idle &w, int revents);
		2235
		2236	myclass ();
		2237	}
		2238
		2239	myclass::myclass (int fd)
		2240	{
		2241	io .set <myclass, &myclass::io_cb > (this);
		2242	idle.set <myclass, &myclass::idle_cb> (this);
		2243
		2244	io.start (fd, ev::READ);
		2245	}
		2246
		2247
		2248	=head1 MACRO MAGIC
		2249
		2250	Libev can be compiled with a variety of options, the most fundamantal
		2251	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2252	functions and callbacks have an initial C<struct ev_loop *> argument.
		2253
		2254	To make it easier to write programs that cope with either variant, the
		2255	following macros are defined:
		2256
		2257	=over 4
		2258
		2259	=item C<EV_A>, C<EV_A_>
		2260
		2261	This provides the loop I<argument> for functions, if one is required ("ev
		2262	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2263	C<EV_A_> is used when other arguments are following. Example:
		2264
		2265	ev_unref (EV_A);
		2266	ev_timer_add (EV_A_ watcher);
		2267	ev_loop (EV_A_ 0);
		2268
		2269	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2270	which is often provided by the following macro.
		2271
		2272	=item C<EV_P>, C<EV_P_>
		2273
		2274	This provides the loop I<parameter> for functions, if one is required ("ev
		2275	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2276	C<EV_P_> is used when other parameters are following. Example:
		2277
		2278	// this is how ev_unref is being declared
		2279	static void ev_unref (EV_P);
		2280
		2281	// this is how you can declare your typical callback
		2282	static void cb (EV_P_ ev_timer *w, int revents)
		2283
		2284	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2285	suitable for use with C<EV_A>.
		2286
		2287	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2288
		2289	Similar to the other two macros, this gives you the value of the default
		2290	loop, if multiple loops are supported ("ev loop default").
		2291
		2292	=back
		2293
		2294	Example: Declare and initialise a check watcher, utilising the above
		2295	macros so it will work regardless of whether multiple loops are supported
		2296	or not.
		2297
		2298	static void
		2299	check_cb (EV_P_ ev_timer *w, int revents)
		2300	{
		2301	ev_check_stop (EV_A_ w);
		2302	}
		2303
		2304	ev_check check;
		2305	ev_check_init (&check, check_cb);
		2306	ev_check_start (EV_DEFAULT_ &check);
		2307	ev_loop (EV_DEFAULT_ 0);
		2308
		2309	=head1 EMBEDDING
		2310
		2311	Libev can (and often is) directly embedded into host
		2312	applications. Examples of applications that embed it include the Deliantra
		2313	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2314	and rxvt-unicode.
		2315
		2316	The goal is to enable you to just copy the necessary files into your
		2317	source directory without having to change even a single line in them, so
		2318	you can easily upgrade by simply copying (or having a checked-out copy of
		2319	libev somewhere in your source tree).
		2320
		2321	=head2 FILESETS
		2322
		2323	Depending on what features you need you need to include one or more sets of files
		2324	in your app.
		2325
		2326	=head3 CORE EVENT LOOP
		2327
		2328	To include only the libev core (all the C<ev_*> functions), with manual
		2329	configuration (no autoconf):
		2330
		2331	#define EV_STANDALONE 1
		2332	#include "ev.c"
		2333
		2334	This will automatically include F<ev.h>, too, and should be done in a
		2335	single C source file only to provide the function implementations. To use
		2336	it, do the same for F<ev.h> in all files wishing to use this API (best
		2337	done by writing a wrapper around F<ev.h> that you can include instead and
		2338	where you can put other configuration options):
		2339
		2340	#define EV_STANDALONE 1
		2341	#include "ev.h"
		2342
		2343	Both header files and implementation files can be compiled with a C++
		2344	compiler (at least, thats a stated goal, and breakage will be treated
		2345	as a bug).
		2346
		2347	You need the following files in your source tree, or in a directory
		2348	in your include path (e.g. in libev/ when using -Ilibev):
		2349
		2350	ev.h
		2351	ev.c
		2352	ev_vars.h
		2353	ev_wrap.h
		2354
		2355	ev_win32.c required on win32 platforms only
		2356
		2357	ev_select.c only when select backend is enabled (which is enabled by default)
		2358	ev_poll.c only when poll backend is enabled (disabled by default)
		2359	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2360	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2361	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2362
		2363	F<ev.c> includes the backend files directly when enabled, so you only need
		2364	to compile this single file.
		2365
		2366	=head3 LIBEVENT COMPATIBILITY API
		2367
		2368	To include the libevent compatibility API, also include:
		2369
		2370	#include "event.c"
		2371
		2372	in the file including F<ev.c>, and:
		2373
		2374	#include "event.h"
		2375
		2376	in the files that want to use the libevent API. This also includes F<ev.h>.
		2377
		2378	You need the following additional files for this:
		2379
		2380	event.h
		2381	event.c
		2382
		2383	=head3 AUTOCONF SUPPORT
		2384
		2385	Instead of using C<EV_STANDALONE=1> and providing your config in
		2386	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2387	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2388	include F<config.h> and configure itself accordingly.
		2389
		2390	For this of course you need the m4 file:
		2391
		2392	libev.m4
		2393
		2394	=head2 PREPROCESSOR SYMBOLS/MACROS
		2395
		2396	Libev can be configured via a variety of preprocessor symbols you have to define
		2397	before including any of its files. The default is not to build for multiplicity
		2398	and only include the select backend.
		2399
		2400	=over 4
		2401
		2402	=item EV_STANDALONE
		2403
		2404	Must always be C<1> if you do not use autoconf configuration, which
		2405	keeps libev from including F<config.h>, and it also defines dummy
		2406	implementations for some libevent functions (such as logging, which is not
		2407	supported). It will also not define any of the structs usually found in
		2408	F<event.h> that are not directly supported by the libev core alone.
		2409
		2410	=item EV_USE_MONOTONIC
		2411
		2412	If defined to be C<1>, libev will try to detect the availability of the
		2413	monotonic clock option at both compiletime and runtime. Otherwise no use
		2414	of the monotonic clock option will be attempted. If you enable this, you
		2415	usually have to link against librt or something similar. Enabling it when
		2416	the functionality isn't available is safe, though, although you have
		2417	to make sure you link against any libraries where the C<clock_gettime>
		2418	function is hiding in (often F<-lrt>).
		2419
		2420	=item EV_USE_REALTIME
		2421
		2422	If defined to be C<1>, libev will try to detect the availability of the
		2423	realtime clock option at compiletime (and assume its availability at
		2424	runtime if successful). Otherwise no use of the realtime clock option will
		2425	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2426	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2427	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2428
		2429	=item EV_USE_NANOSLEEP
		2430
		2431	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2432	and will use it for delays. Otherwise it will use C<select ()>.
		2433
		2434	=item EV_USE_SELECT
		2435
		2436	If undefined or defined to be C<1>, libev will compile in support for the
		2437	C<select>(2) backend. No attempt at autodetection will be done: if no
		2438	other method takes over, select will be it. Otherwise the select backend
		2439	will not be compiled in.
		2440
		2441	=item EV_SELECT_USE_FD_SET
		2442
		2443	If defined to C<1>, then the select backend will use the system C<fd_set>
		2444	structure. This is useful if libev doesn't compile due to a missing
		2445	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2446	exotic systems. This usually limits the range of file descriptors to some
		2447	low limit such as 1024 or might have other limitations (winsocket only
		2448	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2449	influence the size of the C<fd_set> used.
		2450
		2451	=item EV_SELECT_IS_WINSOCKET
		2452
		2453	When defined to C<1>, the select backend will assume that
		2454	select/socket/connect etc. don't understand file descriptors but
		2455	wants osf handles on win32 (this is the case when the select to
		2456	be used is the winsock select). This means that it will call
		2457	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2458	it is assumed that all these functions actually work on fds, even
		2459	on win32. Should not be defined on non-win32 platforms.
		2460
		2461	=item EV_USE_POLL
		2462
		2463	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2464	backend. Otherwise it will be enabled on non-win32 platforms. It
		2465	takes precedence over select.
		2466
		2467	=item EV_USE_EPOLL
		2468
		2469	If defined to be C<1>, libev will compile in support for the Linux
		2470	C<epoll>(7) backend. Its availability will be detected at runtime,
		2471	otherwise another method will be used as fallback. This is the
		2472	preferred backend for GNU/Linux systems.
		2473
		2474	=item EV_USE_KQUEUE
		2475
		2476	If defined to be C<1>, libev will compile in support for the BSD style
		2477	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2478	otherwise another method will be used as fallback. This is the preferred
		2479	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2480	supports some types of fds correctly (the only platform we found that
		2481	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2482	not be used unless explicitly requested. The best way to use it is to find
		2483	out whether kqueue supports your type of fd properly and use an embedded
		2484	kqueue loop.
		2485
		2486	=item EV_USE_PORT
		2487
		2488	If defined to be C<1>, libev will compile in support for the Solaris
		2489	10 port style backend. Its availability will be detected at runtime,
		2490	otherwise another method will be used as fallback. This is the preferred
		2491	backend for Solaris 10 systems.
		2492
		2493	=item EV_USE_DEVPOLL
		2494
		2495	reserved for future expansion, works like the USE symbols above.
		2496
		2497	=item EV_USE_INOTIFY
		2498
		2499	If defined to be C<1>, libev will compile in support for the Linux inotify
		2500	interface to speed up C<ev_stat> watchers. Its actual availability will
		2501	be detected at runtime.
		2502
		2503	=item EV_H
		2504
		2505	The name of the F<ev.h> header file used to include it. The default if
		2506	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
		2507	can be used to virtually rename the F<ev.h> header file in case of conflicts.
		2508
		2509	=item EV_CONFIG_H
		2510
		2511	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2512	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2513	C<EV_H>, above.
		2514
		2515	=item EV_EVENT_H
		2516
		2517	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2518	of how the F<event.h> header can be found.
		2519
		2520	=item EV_PROTOTYPES
		2521
		2522	If defined to be C<0>, then F<ev.h> will not define any function
		2523	prototypes, but still define all the structs and other symbols. This is
		2524	occasionally useful if you want to provide your own wrapper functions
		2525	around libev functions.
		2526
		2527	=item EV_MULTIPLICITY
		2528
		2529	If undefined or defined to C<1>, then all event-loop-specific functions
		2530	will have the C<struct ev_loop *> as first argument, and you can create
		2531	additional independent event loops. Otherwise there will be no support
		2532	for multiple event loops and there is no first event loop pointer
		2533	argument. Instead, all functions act on the single default loop.
		2534
		2535	=item EV_MINPRI
		2536
		2537	=item EV_MAXPRI
		2538
		2539	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2540	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2541	provide for more priorities by overriding those symbols (usually defined
		2542	to be C<-2> and C<2>, respectively).
		2543
		2544	When doing priority-based operations, libev usually has to linearly search
		2545	all the priorities, so having many of them (hundreds) uses a lot of space
		2546	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2547	fine.
		2548
		2549	If your embedding app does not need any priorities, defining these both to
		2550	C<0> will save some memory and cpu.
		2551
		2552	=item EV_PERIODIC_ENABLE
		2553
		2554	If undefined or defined to be C<1>, then periodic timers are supported. If
		2555	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2556	code.
		2557
		2558	=item EV_IDLE_ENABLE
		2559
		2560	If undefined or defined to be C<1>, then idle watchers are supported. If
		2561	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2562	code.
		2563
		2564	=item EV_EMBED_ENABLE
		2565
		2566	If undefined or defined to be C<1>, then embed watchers are supported. If
		2567	defined to be C<0>, then they are not.
		2568
		2569	=item EV_STAT_ENABLE
		2570
		2571	If undefined or defined to be C<1>, then stat watchers are supported. If
		2572	defined to be C<0>, then they are not.
		2573
		2574	=item EV_FORK_ENABLE
		2575
		2576	If undefined or defined to be C<1>, then fork watchers are supported. If
		2577	defined to be C<0>, then they are not.
		2578
		2579	=item EV_MINIMAL
		2580
		2581	If you need to shave off some kilobytes of code at the expense of some
		2582	speed, define this symbol to C<1>. Currently only used for gcc to override
		2583	some inlining decisions, saves roughly 30% codesize of amd64.
		2584
		2585	=item EV_PID_HASHSIZE
		2586
		2587	C<ev_child> watchers use a small hash table to distribute workload by
		2588	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2589	than enough. If you need to manage thousands of children you might want to
		2590	increase this value (I<must> be a power of two).
		2591
		2592	=item EV_INOTIFY_HASHSIZE
		2593
		2594	C<ev_stat> watchers use a small hash table to distribute workload by
		2595	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2596	usually more than enough. If you need to manage thousands of C<ev_stat>
		2597	watchers you might want to increase this value (I<must> be a power of
		2598	two).
		2599
		2600	=item EV_COMMON
		2601
		2602	By default, all watchers have a C<void *data> member. By redefining
		2603	this macro to a something else you can include more and other types of
		2604	members. You have to define it each time you include one of the files,
		2605	though, and it must be identical each time.
		2606
		2607	For example, the perl EV module uses something like this:
		2608
		2609	#define EV_COMMON \
		2610	SV *self; /* contains this struct */ \
		2611	SV *cb_sv, *fh /* note no trailing ";" */
		2612
		2613	=item EV_CB_DECLARE (type)
		2614
		2615	=item EV_CB_INVOKE (watcher, revents)
		2616
		2617	=item ev_set_cb (ev, cb)
		2618
		2619	Can be used to change the callback member declaration in each watcher,
		2620	and the way callbacks are invoked and set. Must expand to a struct member
		2621	definition and a statement, respectively. See the F<ev.h> header file for
		2622	their default definitions. One possible use for overriding these is to
		2623	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2624	method calls instead of plain function calls in C++.
		2625
		2626	=head2 EXPORTED API SYMBOLS
		2627
		2628	If you need to re-export the API (e.g. via a dll) and you need a list of
		2629	exported symbols, you can use the provided F<Symbol.*> files which list
		2630	all public symbols, one per line:
		2631
		2632	Symbols.ev for libev proper
		2633	Symbols.event for the libevent emulation
		2634
		2635	This can also be used to rename all public symbols to avoid clashes with
		2636	multiple versions of libev linked together (which is obviously bad in
		2637	itself, but sometimes it is inconvinient to avoid this).
		2638
		2639	A sed command like this will create wrapper C<#define>'s that you need to
		2640	include before including F<ev.h>:
		2641
		2642	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2643
		2644	This would create a file F<wrap.h> which essentially looks like this:
		2645
		2646	#define ev_backend myprefix_ev_backend
		2647	#define ev_check_start myprefix_ev_check_start
		2648	#define ev_check_stop myprefix_ev_check_stop
		2649	...
		2650
		2651	=head2 EXAMPLES
		2652
		2653	For a real-world example of a program the includes libev
		2654	verbatim, you can have a look at the EV perl module
		2655	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2656	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2657	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2658	will be compiled. It is pretty complex because it provides its own header
		2659	file.
		2660
		2661	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2662	that everybody includes and which overrides some configure choices:
		2663
		2664	#define EV_MINIMAL 1
		2665	#define EV_USE_POLL 0
		2666	#define EV_MULTIPLICITY 0
		2667	#define EV_PERIODIC_ENABLE 0
		2668	#define EV_STAT_ENABLE 0
		2669	#define EV_FORK_ENABLE 0
		2670	#define EV_CONFIG_H <config.h>
		2671	#define EV_MINPRI 0
		2672	#define EV_MAXPRI 0
		2673
		2674	#include "ev++.h"
		2675
		2676	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2677
		2678	#include "ev_cpp.h"
		2679	#include "ev.c"
		2680
		2681
		2682	=head1 COMPLEXITIES
		2683
		2684	In this section the complexities of (many of) the algorithms used inside
		2685	libev will be explained. For complexity discussions about backends see the
		2686	documentation for C<ev_default_init>.
		2687
		2688	All of the following are about amortised time: If an array needs to be
		2689	extended, libev needs to realloc and move the whole array, but this
		2690	happens asymptotically never with higher number of elements, so O(1) might
		2691	mean it might do a lengthy realloc operation in rare cases, but on average
		2692	it is much faster and asymptotically approaches constant time.
		2693
		2694	=over 4
		2695
		2696	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2697
		2698	This means that, when you have a watcher that triggers in one hour and
		2699	there are 100 watchers that would trigger before that then inserting will
		2700	have to skip roughly seven (C<ld 100>) of these watchers.
		2701
		2702	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2703
		2704	That means that changing a timer costs less than removing/adding them
		2705	as only the relative motion in the event queue has to be paid for.
		2706
		2707	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2708
		2709	These just add the watcher into an array or at the head of a list.
		2710
		2711	=item Stopping check/prepare/idle watchers: O(1)
		2712
		2713	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2714
		2715	These watchers are stored in lists then need to be walked to find the
		2716	correct watcher to remove. The lists are usually short (you don't usually
		2717	have many watchers waiting for the same fd or signal).
		2718
		2719	=item Finding the next timer in each loop iteration: O(1)
		2720
		2721	By virtue of using a binary heap, the next timer is always found at the
		2722	beginning of the storage array.
		2723
		2724	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2725
		2726	A change means an I/O watcher gets started or stopped, which requires
		2727	libev to recalculate its status (and possibly tell the kernel, depending
		2728	on backend and wether C<ev_io_set> was used).
		2729
		2730	=item Activating one watcher (putting it into the pending state): O(1)
		2731
		2732	=item Priority handling: O(number_of_priorities)
		2733
		2734	Priorities are implemented by allocating some space for each
		2735	priority. When doing priority-based operations, libev usually has to
		2736	linearly search all the priorities, but starting/stopping and activating
		2737	watchers becomes O(1) w.r.t. prioritiy handling.
		2738
		2739	=back
		2740
825		2741
826	=head1 AUTHOR	2742	=head1 AUTHOR
827		2743
828	Marc Lehmann <libev@schmorp.de>.	2744	Marc Lehmann <libev@schmorp.de>.
829		2745

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