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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	=head1 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
		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>.
10		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 occuring), 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
…		…
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	=head1 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	=head1 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	=head1 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 such.
51		104
52	=head1 GLOBAL FUNCTIONS	105	=head1 GLOBAL FUNCTIONS
53		106
54	These functions can be called anytime, even before initialising the	107	These functions can be called anytime, even before initialising the
55	library in any way.	108	library in any way.
…		…
75	Usually, it's a good idea to terminate if the major versions mismatch,	128	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	129	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	130	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	131	not a problem.
79		132
		133	Example: Make sure we haven't accidentally been linked against the wrong
		134	version.
		135
		136	assert (("libev version mismatch",
		137	ev_version_major () == EV_VERSION_MAJOR
		138	&& ev_version_minor () >= EV_VERSION_MINOR));
		139
		140	=item unsigned int ev_supported_backends ()
		141
		142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		143	value) compiled into this binary of libev (independent of their
		144	availability on the system you are running on). See C<ev_default_loop> for
		145	a description of the set values.
		146
		147	Example: make sure we have the epoll method, because yeah this is cool and
		148	a must have and can we have a torrent of it please!!!11
		149
		150	assert (("sorry, no epoll, no sex",
		151	ev_supported_backends () & EVBACKEND_EPOLL));
		152
		153	=item unsigned int ev_recommended_backends ()
		154
		155	Return the set of all backends compiled into this binary of libev and also
		156	recommended for this platform. This set is often smaller than the one
		157	returned by C<ev_supported_backends>, as for example kqueue is broken on
		158	most BSDs and will not be autodetected unless you explicitly request it
		159	(assuming you know what you are doing). This is the set of backends that
		160	libev will probe for if you specify no backends explicitly.
		161
		162	=item unsigned int ev_embeddable_backends ()
		163
		164	Returns the set of backends that are embeddable in other event loops. This
		165	is the theoretical, all-platform, value. To find which backends
		166	might be supported on the current system, you would need to look at
		167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		168	recommended ones.
		169
		170	See the description of C<ev_embed> watchers for more info.
		171
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		173
82	Sets the allocation function to use (the prototype is similar to the	174	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	175	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	176	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	177	memory needs to be allocated, the library might abort or take some
86	destructive action. The default is your system realloc function.	178	potentially destructive action. The default is your system realloc
		179	function.
87		180
88	You could override this function in high-availability programs to, say,	181	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,	182	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.	183	or even to sleep a while and retry until some memory is available.
		184
		185	Example: Replace the libev allocator with one that waits a bit and then
		186	retries).
		187
		188	static void *
		189	persistent_realloc (void *ptr, size_t size)
		190	{
		191	for (;;)
		192	{
		193	void *newptr = realloc (ptr, size);
		194
		195	if (newptr)
		196	return newptr;
		197
		198	sleep (60);
		199	}
		200	}
		201
		202	...
		203	ev_set_allocator (persistent_realloc);
91		204
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	205	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		206
94	Set the callback function to call on a retryable syscall error (such	207	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	208	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	210	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	211	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	212	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	213	(such as abort).
101		214
		215	Example: This is basically the same thing that libev does internally, too.
		216
		217	static void
		218	fatal_error (const char *msg)
		219	{
		220	perror (msg);
		221	abort ();
		222	}
		223
		224	...
		225	ev_set_syserr_cb (fatal_error);
		226
102	=back	227	=back
103		228
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		230
106	An event loop is described by a C<struct ev_loop *>. The library knows two	231	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)	244	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		245
121	This will initialise the default event loop if it hasn't been initialised	246	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	247	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	248	false. If it already was initialised it simply returns it (and ignores the
124	flags).	249	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		250
126	If you don't know what event loop to use, use the one returned from this	251	If you don't know what event loop to use, use the one returned from this
127	function.	252	function.
128		253
129	The flags argument can be used to specify special behaviour or specific	254	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).	255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		256
132	It supports the following flags:	257	The following flags are supported:
133		258
134	=over 4	259	=over 4
135		260
136	=item C<EVFLAG_AUTO>	261	=item C<EVFLAG_AUTO>
137		262
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	271	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	272	useful to try out specific backends to test their performance, or to work
148	around bugs.	273	around bugs.
149		274
		275	=item C<EVFLAG_FORKCHECK>
		276
		277	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		278	a fork, you can also make libev check for a fork in each iteration by
		279	enabling this flag.
		280
		281	This works by calling C<getpid ()> on every iteration of the loop,
		282	and thus this might slow down your event loop if you do a lot of loop
		283	iterations and little real work, but is usually not noticeable (on my
		284	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		285	without a syscall and thus I<very> fast, but my Linux system also has
		286	C<pthread_atfork> which is even faster).
		287
		288	The big advantage of this flag is that you can forget about fork (and
		289	forget about forgetting to tell libev about forking) when you use this
		290	flag.
		291
		292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		293	environment variable.
		294
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		296
152	This is your standard select(2) backend. Not I<completely> standard, as	297	This is your standard select(2) backend. Not I<completely> standard, as
153	libev tries to roll its own fd_set with no limits on the number of fds,	298	libev tries to roll its own fd_set with no limits on the number of fds,
154	but if that fails, expect a fairly low limit on the number of fds when	299	but if that fails, expect a fairly low limit on the number of fds when
155	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually
156	the fastest backend for a low number of fds.	301	the fastest backend for a low number of fds.
157		302
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		304
160	And this is your standard poll(2) backend. It's more complicated than	305	And this is your standard poll(2) backend. It's more complicated than
161	select, but handles sparse fds better and has no artificial limit on the	306	select, but handles sparse fds better and has no artificial limit on the
162	number of fds you can use (except it will slow down considerably with a	307	number of fds you can use (except it will slow down considerably with a
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
164		309
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	310	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		311
167	For few fds, this backend is a bit little slower than poll and select,	312	For few fds, this backend is a bit little slower than poll and select,
168	but it scales phenomenally better. While poll and select usually scale like	313	but it scales phenomenally better. While poll and select usually scale like
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
170	either O(1) or O(active_fds).	315	either O(1) or O(active_fds).
…		…
173	result in some caching, there is still a syscall per such incident	318	result in some caching, there is still a syscall per such incident
174	(because the fd could point to a different file description now), so its	319	(because the fd could point to a different file description now), so its
175	best to avoid that. Also, dup()ed file descriptors might not work very	320	best to avoid that. Also, dup()ed file descriptors might not work very
176	well if you register events for both fds.	321	well if you register events for both fds.
177		322
		323	Please note that epoll sometimes generates spurious notifications, so you
		324	need to use non-blocking I/O or other means to avoid blocking when no data
		325	(or space) is available.
		326
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		328
180	Kqueue deserves special mention, as at the time of this writing, it	329	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	330	was broken on all BSDs except NetBSD (usually it doesn't work with
182	anything but sockets and pipes, except on Darwin, where of course its	331	anything but sockets and pipes, except on Darwin, where of course its
183	completely useless). For this reason its not being "autodetected" unless	332	completely useless). For this reason its not being "autodetected"
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	333	unless you explicitly specify it explicitly in the flags (i.e. using
		334	C<EVBACKEND_KQUEUE>).
185		335
186	It scales in the same way as the epoll backend, but the interface to the	336	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	337	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	338	course). While starting and stopping an I/O watcher does not cause an
189	extra syscall as with epoll, it still adds up to four event changes per	339	extra syscall as with epoll, it still adds up to four event changes per
190	incident, so its best to avoid that.	340	incident, so its best to avoid that.
191		341
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		343
194	This is not implemented yet (and might never be).	344	This is not implemented yet (and might never be).
195		345
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		347
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	348	This uses the Solaris 10 port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	349	it's really slow, but it still scales very well (O(active_fds)).
200		350
		351	Please note that solaris ports can result in a lot of spurious
		352	notifications, so you need to use non-blocking I/O or other means to avoid
		353	blocking when no data (or space) is available.
		354
201	=item C<EVMETHOD_ALL>	355	=item C<EVBACKEND_ALL>
202		356
203	Try all backends (even potentially broken ones that wouldn't be tried	357	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
206		360
207	=back	361	=back
208		362
209	If one or more of these are ored into the flags value, then only these	363	If one or more of these are ored into the flags value, then only these
210	backends will be tried (in the reverse order as given here). If none are	364	backends will be tried (in the reverse order as given here). If none are
211	specified, most compiled-in backend will be tried, usually in reverse	365	specified, most compiled-in backend will be tried, usually in reverse
212	order of their flag values :)	366	order of their flag values :)
213		367
		368	The most typical usage is like this:
		369
		370	if (!ev_default_loop (0))
		371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		372
		373	Restrict libev to the select and poll backends, and do not allow
		374	environment settings to be taken into account:
		375
		376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		377
		378	Use whatever libev has to offer, but make sure that kqueue is used if
		379	available (warning, breaks stuff, best use only with your own private
		380	event loop and only if you know the OS supports your types of fds):
		381
		382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
		383
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	384	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		385
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	386	Similar to C<ev_default_loop>, but always creates a new event loop that is
217	always distinct from the default loop. Unlike the default loop, it cannot	387	always distinct from the default loop. Unlike the default loop, it cannot
218	handle signal and child watchers, and attempts to do so will be greeted by	388	handle signal and child watchers, and attempts to do so will be greeted by
219	undefined behaviour (or a failed assertion if assertions are enabled).	389	undefined behaviour (or a failed assertion if assertions are enabled).
220		390
		391	Example: Try to create a event loop that uses epoll and nothing else.
		392
		393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		394	if (!epoller)
		395	fatal ("no epoll found here, maybe it hides under your chair");
		396
221	=item ev_default_destroy ()	397	=item ev_default_destroy ()
222		398
223	Destroys the default loop again (frees all memory and kernel state	399	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	400	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	401	sense, so e.g. C<ev_is_active> might still return true. It is your
		402	responsibility to either stop all watchers cleanly yoursef I<before>
		403	calling this function, or cope with the fact afterwards (which is usually
		404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them
		405	for example).
226		406
227	=item ev_loop_destroy (loop)	407	=item ev_loop_destroy (loop)
228		408
229	Like C<ev_default_destroy>, but destroys an event loop created by an	409	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	410	earlier call to C<ev_loop_new>.
…		…
244	it just in case after a fork. To make this easy, the function will fit in	424	it just in case after a fork. To make this easy, the function will fit in
245	quite nicely into a call to C<pthread_atfork>:	425	quite nicely into a call to C<pthread_atfork>:
246		426
247	pthread_atfork (0, 0, ev_default_fork);	427	pthread_atfork (0, 0, ev_default_fork);
248		428
		429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		430	without calling this function, so if you force one of those backends you
		431	do not need to care.
		432
249	=item ev_loop_fork (loop)	433	=item ev_loop_fork (loop)
250		434
251	Like C<ev_default_fork>, but acts on an event loop created by	435	Like C<ev_default_fork>, but acts on an event loop created by
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
253	after fork, and how you do this is entirely your own problem.	437	after fork, and how you do this is entirely your own problem.
254		438
		439	=item unsigned int ev_loop_count (loop)
		440
		441	Returns the count of loop iterations for the loop, which is identical to
		442	the number of times libev did poll for new events. It starts at C<0> and
		443	happily wraps around with enough iterations.
		444
		445	This value can sometimes be useful as a generation counter of sorts (it
		446	"ticks" the number of loop iterations), as it roughly corresponds with
		447	C<ev_prepare> and C<ev_check> calls.
		448
255	=item unsigned int ev_method (loop)	449	=item unsigned int ev_backend (loop)
256		450
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	452	use.
259		453
260	=item ev_tstamp ev_now (loop)	454	=item ev_tstamp ev_now (loop)
261		455
262	Returns the current "event loop time", which is the time the event loop	456	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	457	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	458	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	459	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	460	event occuring (or more correctly, libev finding out about it).
267		461
268	=item ev_loop (loop, int flags)	462	=item ev_loop (loop, int flags)
269		463
270	Finally, this is it, the event handler. This function usually is called	464	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	465	after you initialised all your watchers and you want to start handling
272	events.	466	events.
273		467
274	If the flags argument is specified as 0, it will not return until either	468	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	469	either no event watchers are active anymore or C<ev_unloop> was called.
		470
		471	Please note that an explicit C<ev_unloop> is usually better than
		472	relying on all watchers to be stopped when deciding when a program has
		473	finished (especially in interactive programs), but having a program that
		474	automatically loops as long as it has to and no longer by virtue of
		475	relying on its watchers stopping correctly is a thing of beauty.
276		476
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	478	those events and any outstanding ones, but will not block your process in
279	case there are no events and will return after one iteration of the loop.	479	case there are no events and will return after one iteration of the loop.
280		480
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	482	neccessary) and will handle those and any outstanding ones. It will block
283	your process until at least one new event arrives, and will return after	483	your process until at least one new event arrives, and will return after
284	one iteration of the loop.	484	one iteration of the loop. This is useful if you are waiting for some
		485	external event in conjunction with something not expressible using other
		486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		487	usually a better approach for this kind of thing.
285		488
286	This flags value could be used to implement alternative looping
287	constructs, but the C<prepare> and C<check> watchers provide a better and
288	more generic mechanism.
289
290	Here are the gory details of what ev_loop does:	489	Here are the gory details of what C<ev_loop> does:
291		490
292	1. If there are no active watchers (reference count is zero), return.	491	* If there are no active watchers (reference count is zero), return.
293	2. Queue and immediately call all prepare watchers.	492	- Queue prepare watchers and then call all outstanding watchers.
294	3. If we have been forked, recreate the kernel state.	493	- If we have been forked, recreate the kernel state.
295	4. Update the kernel state with all outstanding changes.	494	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	495	- Update the "event loop time".
297	6. Calculate for how long to block.	496	- Calculate for how long to block.
298	7. Block the process, waiting for events.	497	- Block the process, waiting for any events.
		498	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	499	- Update the "event loop time" and do time jump handling.
300	9. Queue all outstanding timers.	500	- Queue all outstanding timers.
301	10. Queue all outstanding periodics.	501	- Queue all outstanding periodics.
302	11. If no events are pending now, queue all idle watchers.	502	- If no events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	503	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	504	- Call all queued watchers in reverse order (i.e. check watchers first).
		505	Signals and child watchers are implemented as I/O watchers, and will
		506	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	508	were used, return, otherwise continue with step *.
		509
		510	Example: Queue some jobs and then loop until no events are outsanding
		511	anymore.
		512
		513	... queue jobs here, make sure they register event watchers as long
		514	... as they still have work to do (even an idle watcher will do..)
		515	ev_loop (my_loop, 0);
		516	... jobs done. yeah!
307		517
308	=item ev_unloop (loop, how)	518	=item ev_unloop (loop, how)
309		519
310	Can be used to make a call to C<ev_loop> return early (but only after it	520	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	521	has processed all outstanding events). The C<how> argument must be either
…		…
325	visible to the libev user and should not keep C<ev_loop> from exiting if	535	visible to the libev user and should not keep C<ev_loop> from exiting if
326	no event watchers registered by it are active. It is also an excellent	536	no event watchers registered by it are active. It is also an excellent
327	way to do this for generic recurring timers or from within third-party	537	way to do this for generic recurring timers or from within third-party
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	538	libraries. Just remember to I<unref after start> and I<ref before stop>.
329		539
		540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		541	running when nothing else is active.
		542
		543	struct ev_signal exitsig;
		544	ev_signal_init (&exitsig, sig_cb, SIGINT);
		545	ev_signal_start (loop, &exitsig);
		546	evf_unref (loop);
		547
		548	Example: For some weird reason, unregister the above signal handler again.
		549
		550	ev_ref (loop);
		551	ev_signal_stop (loop, &exitsig);
		552
330	=back	553	=back
		554
331		555
332	=head1 ANATOMY OF A WATCHER	556	=head1 ANATOMY OF A WATCHER
333		557
334	A watcher is a structure that you create and register to record your	558	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	559	interest in some event. For instance, if you want to wait for STDIN to
…		…
368	*) >>), and you can stop watching for events at any time by calling the	592	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
370		594
371	As long as your watcher is active (has been started but not stopped) you	595	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	596	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	597	reinitialise it or call its C<set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		598
380	Each and every callback receives the event loop pointer as first, the	599	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	600	registered watcher structure as second, and a bitset of received events as
382	third argument.	601	third argument.
383		602
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	626	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		627
409	=item C<EV_CHILD>	628	=item C<EV_CHILD>
410		629
411	The pid specified in the C<ev_child> watcher has received a status change.	630	The pid specified in the C<ev_child> watcher has received a status change.
		631
		632	=item C<EV_STAT>
		633
		634	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		635
413	=item C<EV_IDLE>	636	=item C<EV_IDLE>
414		637
415	The C<ev_idle> watcher has determined that you have nothing better to do.	638	The C<ev_idle> watcher has determined that you have nothing better to do.
416		639
…		…
424	received events. Callbacks of both watcher types can start and stop as	647	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	648	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	649	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	650	C<ev_loop> from blocking).
428		651
		652	=item C<EV_EMBED>
		653
		654	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		655
		656	=item C<EV_FORK>
		657
		658	The event loop has been resumed in the child process after fork (see
		659	C<ev_fork>).
		660
429	=item C<EV_ERROR>	661	=item C<EV_ERROR>
430		662
431	An unspecified error has occured, the watcher has been stopped. This might	663	An unspecified error has occured, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	664	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	665	ran out of memory, a file descriptor was found to be closed or any other
…		…
439	your callbacks is well-written it can just attempt the operation and cope	671	your callbacks is well-written it can just attempt the operation and cope
440	with the error from read() or write(). This will not work in multithreaded	672	with the error from read() or write(). This will not work in multithreaded
441	programs, though, so beware.	673	programs, though, so beware.
442		674
443	=back	675	=back
		676
		677	=head2 GENERIC WATCHER FUNCTIONS
		678
		679	In the following description, C<TYPE> stands for the watcher type,
		680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		681
		682	=over 4
		683
		684	=item C<ev_init> (ev_TYPE *watcher, callback)
		685
		686	This macro initialises the generic portion of a watcher. The contents
		687	of the watcher object can be arbitrary (so C<malloc> will do). Only
		688	the generic parts of the watcher are initialised, you I<need> to call
		689	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		690	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		691	which rolls both calls into one.
		692
		693	You can reinitialise a watcher at any time as long as it has been stopped
		694	(or never started) and there are no pending events outstanding.
		695
		696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		697	int revents)>.
		698
		699	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		700
		701	This macro initialises the type-specific parts of a watcher. You need to
		702	call C<ev_init> at least once before you call this macro, but you can
		703	call C<ev_TYPE_set> any number of times. You must not, however, call this
		704	macro on a watcher that is active (it can be pending, however, which is a
		705	difference to the C<ev_init> macro).
		706
		707	Although some watcher types do not have type-specific arguments
		708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		709
		710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		711
		712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		713	calls into a single call. This is the most convinient method to initialise
		714	a watcher. The same limitations apply, of course.
		715
		716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		717
		718	Starts (activates) the given watcher. Only active watchers will receive
		719	events. If the watcher is already active nothing will happen.
		720
		721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		722
		723	Stops the given watcher again (if active) and clears the pending
		724	status. It is possible that stopped watchers are pending (for example,
		725	non-repeating timers are being stopped when they become pending), but
		726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		727	you want to free or reuse the memory used by the watcher it is therefore a
		728	good idea to always call its C<ev_TYPE_stop> function.
		729
		730	=item bool ev_is_active (ev_TYPE *watcher)
		731
		732	Returns a true value iff the watcher is active (i.e. it has been started
		733	and not yet been stopped). As long as a watcher is active you must not modify
		734	it.
		735
		736	=item bool ev_is_pending (ev_TYPE *watcher)
		737
		738	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		739	events but its callback has not yet been invoked). As long as a watcher
		740	is pending (but not active) you must not call an init function on it (but
		741	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		742	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		743	it).
		744
		745	=item callback ev_cb (ev_TYPE *watcher)
		746
		747	Returns the callback currently set on the watcher.
		748
		749	=item ev_cb_set (ev_TYPE *watcher, callback)
		750
		751	Change the callback. You can change the callback at virtually any time
		752	(modulo threads).
		753
		754	=item ev_set_priority (ev_TYPE *watcher, priority)
		755
		756	=item int ev_priority (ev_TYPE *watcher)
		757
		758	Set and query the priority of the watcher. The priority is a small
		759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		760	(default: C<-2>). Pending watchers with higher priority will be invoked
		761	before watchers with lower priority, but priority will not keep watchers
		762	from being executed (except for C<ev_idle> watchers).
		763
		764	This means that priorities are I<only> used for ordering callback
		765	invocation after new events have been received. This is useful, for
		766	example, to reduce latency after idling, or more often, to bind two
		767	watchers on the same event and make sure one is called first.
		768
		769	If you need to suppress invocation when higher priority events are pending
		770	you need to look at C<ev_idle> watchers, which provide this functionality.
		771
		772	You I<must not> change the priority of a watcher as long as it is active or
		773	pending.
		774
		775	The default priority used by watchers when no priority has been set is
		776	always C<0>, which is supposed to not be too high and not be too low :).
		777
		778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		779	fine, as long as you do not mind that the priority value you query might
		780	or might not have been adjusted to be within valid range.
		781
		782	=back
		783
444		784
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	785	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		786
447	Each watcher has, by default, a member C<void *data> that you can change	787	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	788	and read at any time, libev will completely ignore it. This can be used
…		…
466	{	806	{
467	struct my_io *w = (struct my_io *)w_;	807	struct my_io *w = (struct my_io *)w_;
468	...	808	...
469	}	809	}
470		810
471	More interesting and less C-conformant ways of catsing your callback type	811	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	812	instead have been omitted.
		813
		814	Another common scenario is having some data structure with multiple
		815	watchers:
		816
		817	struct my_biggy
		818	{
		819	int some_data;
		820	ev_timer t1;
		821	ev_timer t2;
		822	}
		823
		824	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		825	you need to use C<offsetof>:
		826
		827	#include <stddef.h>
		828
		829	static void
		830	t1_cb (EV_P_ struct ev_timer *w, int revents)
		831	{
		832	struct my_biggy big = (struct my_biggy *
		833	(((char *)w) - offsetof (struct my_biggy, t1));
		834	}
		835
		836	static void
		837	t2_cb (EV_P_ struct ev_timer *w, int revents)
		838	{
		839	struct my_biggy big = (struct my_biggy *
		840	(((char *)w) - offsetof (struct my_biggy, t2));
		841	}
473		842
474		843
475	=head1 WATCHER TYPES	844	=head1 WATCHER TYPES
476		845
477	This section describes each watcher in detail, but will not repeat	846	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	847	information given in the last section. Any initialisation/set macros,
		848	functions and members specific to the watcher type are explained.
479		849
		850	Members are additionally marked with either I<[read-only]>, meaning that,
		851	while the watcher is active, you can look at the member and expect some
		852	sensible content, but you must not modify it (you can modify it while the
		853	watcher is stopped to your hearts content), or I<[read-write]>, which
		854	means you can expect it to have some sensible content while the watcher
		855	is active, but you can also modify it. Modifying it may not do something
		856	sensible or take immediate effect (or do anything at all), but libev will
		857	not crash or malfunction in any way.
		858
		859
480	=head2 C<ev_io> - is this file descriptor readable or writable	860	=head2 C<ev_io> - is this file descriptor readable or writable?
481		861
482	I/O watchers check whether a file descriptor is readable or writable	862	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	863	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	864	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	865	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	866	receiving events as long as the condition persists. Remember you can stop
		867	the watcher if you don't want to act on the event and neither want to
		868	receive future events.
487		869
488	In general you can register as many read and/or write event watchers per	870	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	871	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	872	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	873	required if you know what you are doing).
492		874
493	You have to be careful with dup'ed file descriptors, though. Some backends	875	You have to be careful with dup'ed file descriptors, though. Some backends
494	(the linux epoll backend is a notable example) cannot handle dup'ed file	876	(the linux epoll backend is a notable example) cannot handle dup'ed file
495	descriptors correctly if you register interest in two or more fds pointing	877	descriptors correctly if you register interest in two or more fds pointing
496	to the same underlying file/socket etc. description (that is, they share	878	to the same underlying file/socket/etc. description (that is, they share
497	the same underlying "file open").	879	the same underlying "file open").
498		880
499	If you must do this, then force the use of a known-to-be-good backend	881	If you must do this, then force the use of a known-to-be-good backend
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	882	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
501	EVMETHOD_POLL).	883	C<EVBACKEND_POLL>).
		884
		885	Another thing you have to watch out for is that it is quite easy to
		886	receive "spurious" readyness notifications, that is your callback might
		887	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		888	because there is no data. Not only are some backends known to create a
		889	lot of those (for example solaris ports), it is very easy to get into
		890	this situation even with a relatively standard program structure. Thus
		891	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		892	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		893
		894	If you cannot run the fd in non-blocking mode (for example you should not
		895	play around with an Xlib connection), then you have to seperately re-test
		896	whether a file descriptor is really ready with a known-to-be good interface
		897	such as poll (fortunately in our Xlib example, Xlib already does this on
		898	its own, so its quite safe to use).
502		899
503	=over 4	900	=over 4
504		901
505	=item ev_io_init (ev_io *, callback, int fd, int events)	902	=item ev_io_init (ev_io *, callback, int fd, int events)
506		903
507	=item ev_io_set (ev_io *, int fd, int events)	904	=item ev_io_set (ev_io *, int fd, int events)
508		905
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	906	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	907	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	908	C<EV_READ | EV_WRITE> to receive the given events.
		909
		910	=item int fd [read-only]
		911
		912	The file descriptor being watched.
		913
		914	=item int events [read-only]
		915
		916	The events being watched.
512		917
513	=back	918	=back
514		919
		920	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		921	readable, but only once. Since it is likely line-buffered, you could
		922	attempt to read a whole line in the callback.
		923
		924	static void
		925	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		926	{
		927	ev_io_stop (loop, w);
		928	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		929	}
		930
		931	...
		932	struct ev_loop *loop = ev_default_init (0);
		933	struct ev_io stdin_readable;
		934	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		935	ev_io_start (loop, &stdin_readable);
		936	ev_loop (loop, 0);
		937
		938
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	939	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		940
517	Timer watchers are simple relative timers that generate an event after a	941	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	942	given time, and optionally repeating in regular intervals after that.
519		943
520	The timers are based on real time, that is, if you register an event that	944	The timers are based on real time, that is, if you register an event that
…		…
555	=item ev_timer_again (loop)	979	=item ev_timer_again (loop)
556		980
557	This will act as if the timer timed out and restart it again if it is	981	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	982	repeating. The exact semantics are:
559		983
		984	If the timer is pending, its pending status is cleared.
		985
560	If the timer is started but nonrepeating, stop it.	986	If the timer is started but nonrepeating, stop it (as if it timed out).
561		987
562	If the timer is repeating, either start it if necessary (with the repeat	988	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	989	C<repeat> value), or reset the running timer to the C<repeat> value.
564		990
565	This sounds a bit complicated, but here is a useful and typical	991	This sounds a bit complicated, but here is a useful and typical
566	example: Imagine you have a tcp connection and you want a so-called idle	992	example: Imagine you have a tcp connection and you want a so-called idle
567	timeout, that is, you want to be called when there have been, say, 60	993	timeout, that is, you want to be called when there have been, say, 60
568	seconds of inactivity on the socket. The easiest way to do this is to	994	seconds of inactivity on the socket. The easiest way to do this is to
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	995	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
570	time you successfully read or write some data. If you go into an idle	996	C<ev_timer_again> each time you successfully read or write some data. If
571	state where you do not expect data to travel on the socket, you can stop	997	you go into an idle state where you do not expect data to travel on the
572	the timer, and again will automatically restart it if need be.	998	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		999	automatically restart it if need be.
		1000
		1001	That means you can ignore the C<after> value and C<ev_timer_start>
		1002	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1003
		1004	ev_timer_init (timer, callback, 0., 5.);
		1005	ev_timer_again (loop, timer);
		1006	...
		1007	timer->again = 17.;
		1008	ev_timer_again (loop, timer);
		1009	...
		1010	timer->again = 10.;
		1011	ev_timer_again (loop, timer);
		1012
		1013	This is more slightly efficient then stopping/starting the timer each time
		1014	you want to modify its timeout value.
		1015
		1016	=item ev_tstamp repeat [read-write]
		1017
		1018	The current C<repeat> value. Will be used each time the watcher times out
		1019	or C<ev_timer_again> is called and determines the next timeout (if any),
		1020	which is also when any modifications are taken into account.
573		1021
574	=back	1022	=back
575		1023
		1024	Example: Create a timer that fires after 60 seconds.
		1025
		1026	static void
		1027	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1028	{
		1029	.. one minute over, w is actually stopped right here
		1030	}
		1031
		1032	struct ev_timer mytimer;
		1033	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1034	ev_timer_start (loop, &mytimer);
		1035
		1036	Example: Create a timeout timer that times out after 10 seconds of
		1037	inactivity.
		1038
		1039	static void
		1040	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1041	{
		1042	.. ten seconds without any activity
		1043	}
		1044
		1045	struct ev_timer mytimer;
		1046	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1047	ev_timer_again (&mytimer); /* start timer */
		1048	ev_loop (loop, 0);
		1049
		1050	// and in some piece of code that gets executed on any "activity":
		1051	// reset the timeout to start ticking again at 10 seconds
		1052	ev_timer_again (&mytimer);
		1053
		1054
576	=head2 C<ev_periodic> - to cron or not to cron	1055	=head2 C<ev_periodic> - to cron or not to cron?
577		1056
578	Periodic watchers are also timers of a kind, but they are very versatile	1057	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1058	(and unfortunately a bit complex).
580		1059
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1060	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
582	but on wallclock time (absolute time). You can tell a periodic watcher	1061	but on wallclock time (absolute time). You can tell a periodic watcher
583	to trigger "at" some specific point in time. For example, if you tell a	1062	to trigger "at" some specific point in time. For example, if you tell a
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1063	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
585	+ 10.>) and then reset your system clock to the last year, then it will	1064	+ 10.>) and then reset your system clock to the last year, then it will
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1065	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
587	roughly 10 seconds later and of course not if you reset your system time	1066	roughly 10 seconds later and of course not if you reset your system time
588	again).	1067	again).
589		1068
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1152	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1153	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	1154	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1155	program when the crontabs have changed).
677		1156
		1157	=item ev_tstamp interval [read-write]
		1158
		1159	The current interval value. Can be modified any time, but changes only
		1160	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1161	called.
		1162
		1163	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1164
		1165	The current reschedule callback, or C<0>, if this functionality is
		1166	switched off. Can be changed any time, but changes only take effect when
		1167	the periodic timer fires or C<ev_periodic_again> is being called.
		1168
678	=back	1169	=back
679		1170
		1171	Example: Call a callback every hour, or, more precisely, whenever the
		1172	system clock is divisible by 3600. The callback invocation times have
		1173	potentially a lot of jittering, but good long-term stability.
		1174
		1175	static void
		1176	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1177	{
		1178	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1179	}
		1180
		1181	struct ev_periodic hourly_tick;
		1182	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1183	ev_periodic_start (loop, &hourly_tick);
		1184
		1185	Example: The same as above, but use a reschedule callback to do it:
		1186
		1187	#include <math.h>
		1188
		1189	static ev_tstamp
		1190	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1191	{
		1192	return fmod (now, 3600.) + 3600.;
		1193	}
		1194
		1195	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1196
		1197	Example: Call a callback every hour, starting now:
		1198
		1199	struct ev_periodic hourly_tick;
		1200	ev_periodic_init (&hourly_tick, clock_cb,
		1201	fmod (ev_now (loop), 3600.), 3600., 0);
		1202	ev_periodic_start (loop, &hourly_tick);
		1203
		1204
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1205	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1206
682	Signal watchers will trigger an event when the process receives a specific	1207	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	1208	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	1209	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1210	normal event processing, like any other event.
…		…
698	=item ev_signal_set (ev_signal *, int signum)	1223	=item ev_signal_set (ev_signal *, int signum)
699		1224
700	Configures the watcher to trigger on the given signal number (usually one	1225	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1226	of the C<SIGxxx> constants).
702		1227
		1228	=item int signum [read-only]
		1229
		1230	The signal the watcher watches out for.
		1231
703	=back	1232	=back
704		1233
		1234
705	=head2 C<ev_child> - wait for pid status changes	1235	=head2 C<ev_child> - watch out for process status changes
706		1236
707	Child watchers trigger when your process receives a SIGCHLD in response to	1237	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	1238	some child status changes (most typically when a child of yours dies).
709		1239
710	=over 4	1240	=over 4
…		…
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	1248	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	1249	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	1250	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	1251	process causing the status change.
722		1252
		1253	=item int pid [read-only]
		1254
		1255	The process id this watcher watches out for, or C<0>, meaning any process id.
		1256
		1257	=item int rpid [read-write]
		1258
		1259	The process id that detected a status change.
		1260
		1261	=item int rstatus [read-write]
		1262
		1263	The process exit/trace status caused by C<rpid> (see your systems
		1264	C<waitpid> and C<sys/wait.h> documentation for details).
		1265
723	=back	1266	=back
724		1267
		1268	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1269
		1270	static void
		1271	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1272	{
		1273	ev_unloop (loop, EVUNLOOP_ALL);
		1274	}
		1275
		1276	struct ev_signal signal_watcher;
		1277	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1278	ev_signal_start (loop, &sigint_cb);
		1279
		1280
		1281	=head2 C<ev_stat> - did the file attributes just change?
		1282
		1283	This watches a filesystem path for attribute changes. That is, it calls
		1284	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1285	compared to the last time, invoking the callback if it did.
		1286
		1287	The path does not need to exist: changing from "path exists" to "path does
		1288	not exist" is a status change like any other. The condition "path does
		1289	not exist" is signified by the C<st_nlink> field being zero (which is
		1290	otherwise always forced to be at least one) and all the other fields of
		1291	the stat buffer having unspecified contents.
		1292
		1293	The path I<should> be absolute and I<must not> end in a slash. If it is
		1294	relative and your working directory changes, the behaviour is undefined.
		1295
		1296	Since there is no standard to do this, the portable implementation simply
		1297	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1298	can specify a recommended polling interval for this case. If you specify
		1299	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1300	unspecified default> value will be used (which you can expect to be around
		1301	five seconds, although this might change dynamically). Libev will also
		1302	impose a minimum interval which is currently around C<0.1>, but thats
		1303	usually overkill.
		1304
		1305	This watcher type is not meant for massive numbers of stat watchers,
		1306	as even with OS-supported change notifications, this can be
		1307	resource-intensive.
		1308
		1309	At the time of this writing, only the Linux inotify interface is
		1310	implemented (implementing kqueue support is left as an exercise for the
		1311	reader). Inotify will be used to give hints only and should not change the
		1312	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1313	to fall back to regular polling again even with inotify, but changes are
		1314	usually detected immediately, and if the file exists there will be no
		1315	polling.
		1316
		1317	=over 4
		1318
		1319	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1320
		1321	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1322
		1323	Configures the watcher to wait for status changes of the given
		1324	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1325	be detected and should normally be specified as C<0> to let libev choose
		1326	a suitable value. The memory pointed to by C<path> must point to the same
		1327	path for as long as the watcher is active.
		1328
		1329	The callback will be receive C<EV_STAT> when a change was detected,
		1330	relative to the attributes at the time the watcher was started (or the
		1331	last change was detected).
		1332
		1333	=item ev_stat_stat (ev_stat *)
		1334
		1335	Updates the stat buffer immediately with new values. If you change the
		1336	watched path in your callback, you could call this fucntion to avoid
		1337	detecting this change (while introducing a race condition). Can also be
		1338	useful simply to find out the new values.
		1339
		1340	=item ev_statdata attr [read-only]
		1341
		1342	The most-recently detected attributes of the file. Although the type is of
		1343	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1344	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1345	was some error while C<stat>ing the file.
		1346
		1347	=item ev_statdata prev [read-only]
		1348
		1349	The previous attributes of the file. The callback gets invoked whenever
		1350	C<prev> != C<attr>.
		1351
		1352	=item ev_tstamp interval [read-only]
		1353
		1354	The specified interval.
		1355
		1356	=item const char *path [read-only]
		1357
		1358	The filesystem path that is being watched.
		1359
		1360	=back
		1361
		1362	Example: Watch C</etc/passwd> for attribute changes.
		1363
		1364	static void
		1365	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1366	{
		1367	/* /etc/passwd changed in some way */
		1368	if (w->attr.st_nlink)
		1369	{
		1370	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1371	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1372	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1373	}
		1374	else
		1375	/* you shalt not abuse printf for puts */
		1376	puts ("wow, /etc/passwd is not there, expect problems. "
		1377	"if this is windows, they already arrived\n");
		1378	}
		1379
		1380	...
		1381	ev_stat passwd;
		1382
		1383	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
		1384	ev_stat_start (loop, &passwd);
		1385
		1386
725	=head2 C<ev_idle> - when you've got nothing better to do	1387	=head2 C<ev_idle> - when you've got nothing better to do...
726		1388
727	Idle watchers trigger events when there are no other events are pending	1389	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	1390	priority are pending (prepare, check and other idle watchers do not
729	as your process is busy handling sockets or timeouts (or even signals,	1391	count).
730	imagine) it will not be triggered. But when your process is idle all idle	1392
731	watchers are being called again and again, once per event loop iteration -	1393	That is, as long as your process is busy handling sockets or timeouts
		1394	(or even signals, imagine) of the same or higher priority it will not be
		1395	triggered. But when your process is idle (or only lower-priority watchers
		1396	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	1397	iteration - until stopped, that is, or your process receives more events
733	busy.	1398	and becomes busy again with higher priority stuff.
734		1399
735	The most noteworthy effect is that as long as any idle watchers are	1400	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	1401	active, the process will not block when waiting for new events.
737		1402
738	Apart from keeping your process non-blocking (which is a useful	1403	Apart from keeping your process non-blocking (which is a useful
…		…
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1413	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	1414	believe me.
750		1415
751	=back	1416	=back
752		1417
		1418	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1419	callback, free it. Also, use no error checking, as usual.
		1420
		1421	static void
		1422	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1423	{
		1424	free (w);
		1425	// now do something you wanted to do when the program has
		1426	// no longer asnything immediate to do.
		1427	}
		1428
		1429	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1430	ev_idle_init (idle_watcher, idle_cb);
		1431	ev_idle_start (loop, idle_cb);
		1432
		1433
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1434	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		1435
755	Prepare and check watchers are usually (but not always) used in tandem:	1436	Prepare and check watchers are usually (but not always) used in tandem:
756	prepare watchers get invoked before the process blocks and check watchers	1437	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	1438	afterwards.
758		1439
		1440	You I<must not> call C<ev_loop> or similar functions that enter
		1441	the current event loop from either C<ev_prepare> or C<ev_check>
		1442	watchers. Other loops than the current one are fine, however. The
		1443	rationale behind this is that you do not need to check for recursion in
		1444	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1445	C<ev_check> so if you have one watcher of each kind they will always be
		1446	called in pairs bracketing the blocking call.
		1447
759	Their main purpose is to integrate other event mechanisms into libev. This	1448	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	1449	their use is somewhat advanced. This could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	1450	variable changes, implement your own watchers, integrate net-snmp or a
		1451	coroutine library and lots more. They are also occasionally useful if
		1452	you cache some data and want to flush it before blocking (for example,
		1453	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1454	watcher).
762		1455
763	This is done by examining in each prepare call which file descriptors need	1456	This is done by examining in each prepare call which file descriptors need
764	to be watched by the other library, registering C<ev_io> watchers for	1457	to be watched by the other library, registering C<ev_io> watchers for
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1458	them and starting an C<ev_timer> watcher for any timeouts (many libraries
766	provide just this functionality). Then, in the check watcher you check for	1459	provide just this functionality). Then, in the check watcher you check for
…		…
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1481	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	1482	macros, but using them is utterly, utterly and completely pointless.
790		1483
791	=back	1484	=back
792		1485
		1486	Example: To include a library such as adns, you would add IO watchers
		1487	and a timeout watcher in a prepare handler, as required by libadns, and
		1488	in a check watcher, destroy them and call into libadns. What follows is
		1489	pseudo-code only of course:
		1490
		1491	static ev_io iow [nfd];
		1492	static ev_timer tw;
		1493
		1494	static void
		1495	io_cb (ev_loop *loop, ev_io *w, int revents)
		1496	{
		1497	// set the relevant poll flags
		1498	// could also call adns_processreadable etc. here
		1499	struct pollfd *fd = (struct pollfd *)w->data;
		1500	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1501	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1502	}
		1503
		1504	// create io watchers for each fd and a timer before blocking
		1505	static void
		1506	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1507	{
		1508	int timeout = 3600000;
		1509	struct pollfd fds [nfd];
		1510	// actual code will need to loop here and realloc etc.
		1511	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1512
		1513	/* the callback is illegal, but won't be called as we stop during check */
		1514	ev_timer_init (&tw, 0, timeout * 1e-3);
		1515	ev_timer_start (loop, &tw);
		1516
		1517	// create on ev_io per pollfd
		1518	for (int i = 0; i < nfd; ++i)
		1519	{
		1520	ev_io_init (iow + i, io_cb, fds [i].fd,
		1521	((fds [i].events & POLLIN ? EV_READ : 0)
		1522	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1523
		1524	fds [i].revents = 0;
		1525	iow [i].data = fds + i;
		1526	ev_io_start (loop, iow + i);
		1527	}
		1528	}
		1529
		1530	// stop all watchers after blocking
		1531	static void
		1532	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1533	{
		1534	ev_timer_stop (loop, &tw);
		1535
		1536	for (int i = 0; i < nfd; ++i)
		1537	ev_io_stop (loop, iow + i);
		1538
		1539	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1540	}
		1541
		1542
		1543	=head2 C<ev_embed> - when one backend isn't enough...
		1544
		1545	This is a rather advanced watcher type that lets you embed one event loop
		1546	into another (currently only C<ev_io> events are supported in the embedded
		1547	loop, other types of watchers might be handled in a delayed or incorrect
		1548	fashion and must not be used).
		1549
		1550	There are primarily two reasons you would want that: work around bugs and
		1551	prioritise I/O.
		1552
		1553	As an example for a bug workaround, the kqueue backend might only support
		1554	sockets on some platform, so it is unusable as generic backend, but you
		1555	still want to make use of it because you have many sockets and it scales
		1556	so nicely. In this case, you would create a kqueue-based loop and embed it
		1557	into your default loop (which might use e.g. poll). Overall operation will
		1558	be a bit slower because first libev has to poll and then call kevent, but
		1559	at least you can use both at what they are best.
		1560
		1561	As for prioritising I/O: rarely you have the case where some fds have
		1562	to be watched and handled very quickly (with low latency), and even
		1563	priorities and idle watchers might have too much overhead. In this case
		1564	you would put all the high priority stuff in one loop and all the rest in
		1565	a second one, and embed the second one in the first.
		1566
		1567	As long as the watcher is active, the callback will be invoked every time
		1568	there might be events pending in the embedded loop. The callback must then
		1569	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1570	their callbacks (you could also start an idle watcher to give the embedded
		1571	loop strictly lower priority for example). You can also set the callback
		1572	to C<0>, in which case the embed watcher will automatically execute the
		1573	embedded loop sweep.
		1574
		1575	As long as the watcher is started it will automatically handle events. The
		1576	callback will be invoked whenever some events have been handled. You can
		1577	set the callback to C<0> to avoid having to specify one if you are not
		1578	interested in that.
		1579
		1580	Also, there have not currently been made special provisions for forking:
		1581	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1582	but you will also have to stop and restart any C<ev_embed> watchers
		1583	yourself.
		1584
		1585	Unfortunately, not all backends are embeddable, only the ones returned by
		1586	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1587	portable one.
		1588
		1589	So when you want to use this feature you will always have to be prepared
		1590	that you cannot get an embeddable loop. The recommended way to get around
		1591	this is to have a separate variables for your embeddable loop, try to
		1592	create it, and if that fails, use the normal loop for everything:
		1593
		1594	struct ev_loop *loop_hi = ev_default_init (0);
		1595	struct ev_loop *loop_lo = 0;
		1596	struct ev_embed embed;
		1597
		1598	// see if there is a chance of getting one that works
		1599	// (remember that a flags value of 0 means autodetection)
		1600	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1601	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1602	: 0;
		1603
		1604	// if we got one, then embed it, otherwise default to loop_hi
		1605	if (loop_lo)
		1606	{
		1607	ev_embed_init (&embed, 0, loop_lo);
		1608	ev_embed_start (loop_hi, &embed);
		1609	}
		1610	else
		1611	loop_lo = loop_hi;
		1612
		1613	=over 4
		1614
		1615	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1616
		1617	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1618
		1619	Configures the watcher to embed the given loop, which must be
		1620	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1621	invoked automatically, otherwise it is the responsibility of the callback
		1622	to invoke it (it will continue to be called until the sweep has been done,
		1623	if you do not want thta, you need to temporarily stop the embed watcher).
		1624
		1625	=item ev_embed_sweep (loop, ev_embed *)
		1626
		1627	Make a single, non-blocking sweep over the embedded loop. This works
		1628	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1629	apropriate way for embedded loops.
		1630
		1631	=item struct ev_loop *loop [read-only]
		1632
		1633	The embedded event loop.
		1634
		1635	=back
		1636
		1637
		1638	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		1639
		1640	Fork watchers are called when a C<fork ()> was detected (usually because
		1641	whoever is a good citizen cared to tell libev about it by calling
		1642	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		1643	event loop blocks next and before C<ev_check> watchers are being called,
		1644	and only in the child after the fork. If whoever good citizen calling
		1645	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		1646	handlers will be invoked, too, of course.
		1647
		1648	=over 4
		1649
		1650	=item ev_fork_init (ev_signal *, callback)
		1651
		1652	Initialises and configures the fork watcher - it has no parameters of any
		1653	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		1654	believe me.
		1655
		1656	=back
		1657
		1658
793	=head1 OTHER FUNCTIONS	1659	=head1 OTHER FUNCTIONS
794		1660
795	There are some other functions of possible interest. Described. Here. Now.	1661	There are some other functions of possible interest. Described. Here. Now.
796		1662
797	=over 4	1663	=over 4
…		…
826	/* stdin might have data for us, joy! */;	1692	/* stdin might have data for us, joy! */;
827	}	1693	}
828		1694
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	1695	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		1696
831	=item ev_feed_event (loop, watcher, int events)	1697	=item ev_feed_event (ev_loop *, watcher *, int revents)
832		1698
833	Feeds the given event set into the event loop, as if the specified event	1699	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an	1700	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	1701	initialised but not necessarily started event watcher).
836		1702
837	=item ev_feed_fd_event (loop, int fd, int revents)	1703	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
838		1704
839	Feed an event on the given fd, as if a file descriptor backend detected	1705	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	1706	the given events it.
841		1707
842	=item ev_feed_signal_event (loop, int signum)	1708	=item ev_feed_signal_event (ev_loop *loop, int signum)
843		1709
844	Feed an event as if the given signal occured (loop must be the default loop!).	1710	Feed an event as if the given signal occured (C<loop> must be the default
		1711	loop!).
845		1712
846	=back	1713	=back
		1714
847		1715
848	=head1 LIBEVENT EMULATION	1716	=head1 LIBEVENT EMULATION
849		1717
850	Libev offers a compatibility emulation layer for libevent. It cannot	1718	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	1719	emulate the internals of libevent, so here are some usage hints:
…		…
872		1740
873	=back	1741	=back
874		1742
875	=head1 C++ SUPPORT	1743	=head1 C++ SUPPORT
876		1744
877	TBD.	1745	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		1746	you to use some convinience methods to start/stop watchers and also change
		1747	the callback model to a model using method callbacks on objects.
		1748
		1749	To use it,
		1750
		1751	#include <ev++.h>
		1752
		1753	This automatically includes F<ev.h> and puts all of its definitions (many
		1754	of them macros) into the global namespace. All C++ specific things are
		1755	put into the C<ev> namespace. It should support all the same embedding
		1756	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		1757
		1758	Care has been taken to keep the overhead low. The only data member the C++
		1759	classes add (compared to plain C-style watchers) is the event loop pointer
		1760	that the watcher is associated with (or no additional members at all if
		1761	you disable C<EV_MULTIPLICITY> when embedding libev).
		1762
		1763	Currently, functions, and static and non-static member functions can be
		1764	used as callbacks. Other types should be easy to add as long as they only
		1765	need one additional pointer for context. If you need support for other
		1766	types of functors please contact the author (preferably after implementing
		1767	it).
		1768
		1769	Here is a list of things available in the C<ev> namespace:
		1770
		1771	=over 4
		1772
		1773	=item C<ev::READ>, C<ev::WRITE> etc.
		1774
		1775	These are just enum values with the same values as the C<EV_READ> etc.
		1776	macros from F<ev.h>.
		1777
		1778	=item C<ev::tstamp>, C<ev::now>
		1779
		1780	Aliases to the same types/functions as with the C<ev_> prefix.
		1781
		1782	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		1783
		1784	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		1785	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		1786	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		1787	defines by many implementations.
		1788
		1789	All of those classes have these methods:
		1790
		1791	=over 4
		1792
		1793	=item ev::TYPE::TYPE ()
		1794
		1795	=item ev::TYPE::TYPE (struct ev_loop *)
		1796
		1797	=item ev::TYPE::~TYPE
		1798
		1799	The constructor (optionally) takes an event loop to associate the watcher
		1800	with. If it is omitted, it will use C<EV_DEFAULT>.
		1801
		1802	The constructor calls C<ev_init> for you, which means you have to call the
		1803	C<set> method before starting it.
		1804
		1805	It will not set a callback, however: You have to call the templated C<set>
		1806	method to set a callback before you can start the watcher.
		1807
		1808	(The reason why you have to use a method is a limitation in C++ which does
		1809	not allow explicit template arguments for constructors).
		1810
		1811	The destructor automatically stops the watcher if it is active.
		1812
		1813	=item w->set<class, &class::method> (object *)
		1814
		1815	This method sets the callback method to call. The method has to have a
		1816	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		1817	first argument and the C<revents> as second. The object must be given as
		1818	parameter and is stored in the C<data> member of the watcher.
		1819
		1820	This method synthesizes efficient thunking code to call your method from
		1821	the C callback that libev requires. If your compiler can inline your
		1822	callback (i.e. it is visible to it at the place of the C<set> call and
		1823	your compiler is good :), then the method will be fully inlined into the
		1824	thunking function, making it as fast as a direct C callback.
		1825
		1826	Example: simple class declaration and watcher initialisation
		1827
		1828	struct myclass
		1829	{
		1830	void io_cb (ev::io &w, int revents) { }
		1831	}
		1832
		1833	myclass obj;
		1834	ev::io iow;
		1835	iow.set <myclass, &myclass::io_cb> (&obj);
		1836
		1837	=item w->set (void (*function)(watcher &w, int), void *data = 0)
		1838
		1839	Also sets a callback, but uses a static method or plain function as
		1840	callback. The optional C<data> argument will be stored in the watcher's
		1841	C<data> member and is free for you to use.
		1842
		1843	See the method-C<set> above for more details.
		1844
		1845	=item w->set (struct ev_loop *)
		1846
		1847	Associates a different C<struct ev_loop> with this watcher. You can only
		1848	do this when the watcher is inactive (and not pending either).
		1849
		1850	=item w->set ([args])
		1851
		1852	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		1853	called at least once. Unlike the C counterpart, an active watcher gets
		1854	automatically stopped and restarted when reconfiguring it with this
		1855	method.
		1856
		1857	=item w->start ()
		1858
		1859	Starts the watcher. Note that there is no C<loop> argument, as the
		1860	constructor already stores the event loop.
		1861
		1862	=item w->stop ()
		1863
		1864	Stops the watcher if it is active. Again, no C<loop> argument.
		1865
		1866	=item w->again () C<ev::timer>, C<ev::periodic> only
		1867
		1868	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		1869	C<ev_TYPE_again> function.
		1870
		1871	=item w->sweep () C<ev::embed> only
		1872
		1873	Invokes C<ev_embed_sweep>.
		1874
		1875	=item w->update () C<ev::stat> only
		1876
		1877	Invokes C<ev_stat_stat>.
		1878
		1879	=back
		1880
		1881	=back
		1882
		1883	Example: Define a class with an IO and idle watcher, start one of them in
		1884	the constructor.
		1885
		1886	class myclass
		1887	{
		1888	ev_io io; void io_cb (ev::io &w, int revents);
		1889	ev_idle idle void idle_cb (ev::idle &w, int revents);
		1890
		1891	myclass ();
		1892	}
		1893
		1894	myclass::myclass (int fd)
		1895	{
		1896	io .set <myclass, &myclass::io_cb > (this);
		1897	idle.set <myclass, &myclass::idle_cb> (this);
		1898
		1899	io.start (fd, ev::READ);
		1900	}
		1901
		1902
		1903	=head1 MACRO MAGIC
		1904
		1905	Libev can be compiled with a variety of options, the most fundemantal is
		1906	C<EV_MULTIPLICITY>. This option determines whether (most) functions and
		1907	callbacks have an initial C<struct ev_loop *> argument.
		1908
		1909	To make it easier to write programs that cope with either variant, the
		1910	following macros are defined:
		1911
		1912	=over 4
		1913
		1914	=item C<EV_A>, C<EV_A_>
		1915
		1916	This provides the loop I<argument> for functions, if one is required ("ev
		1917	loop argument"). The C<EV_A> form is used when this is the sole argument,
		1918	C<EV_A_> is used when other arguments are following. Example:
		1919
		1920	ev_unref (EV_A);
		1921	ev_timer_add (EV_A_ watcher);
		1922	ev_loop (EV_A_ 0);
		1923
		1924	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		1925	which is often provided by the following macro.
		1926
		1927	=item C<EV_P>, C<EV_P_>
		1928
		1929	This provides the loop I<parameter> for functions, if one is required ("ev
		1930	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		1931	C<EV_P_> is used when other parameters are following. Example:
		1932
		1933	// this is how ev_unref is being declared
		1934	static void ev_unref (EV_P);
		1935
		1936	// this is how you can declare your typical callback
		1937	static void cb (EV_P_ ev_timer *w, int revents)
		1938
		1939	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		1940	suitable for use with C<EV_A>.
		1941
		1942	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		1943
		1944	Similar to the other two macros, this gives you the value of the default
		1945	loop, if multiple loops are supported ("ev loop default").
		1946
		1947	=back
		1948
		1949	Example: Declare and initialise a check watcher, utilising the above
		1950	macros so it will work regardless of whether multiple loops are supported
		1951	or not.
		1952
		1953	static void
		1954	check_cb (EV_P_ ev_timer *w, int revents)
		1955	{
		1956	ev_check_stop (EV_A_ w);
		1957	}
		1958
		1959	ev_check check;
		1960	ev_check_init (&check, check_cb);
		1961	ev_check_start (EV_DEFAULT_ &check);
		1962	ev_loop (EV_DEFAULT_ 0);
		1963
		1964	=head1 EMBEDDING
		1965
		1966	Libev can (and often is) directly embedded into host
		1967	applications. Examples of applications that embed it include the Deliantra
		1968	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		1969	and rxvt-unicode.
		1970
		1971	The goal is to enable you to just copy the neecssary files into your
		1972	source directory without having to change even a single line in them, so
		1973	you can easily upgrade by simply copying (or having a checked-out copy of
		1974	libev somewhere in your source tree).
		1975
		1976	=head2 FILESETS
		1977
		1978	Depending on what features you need you need to include one or more sets of files
		1979	in your app.
		1980
		1981	=head3 CORE EVENT LOOP
		1982
		1983	To include only the libev core (all the C<ev_*> functions), with manual
		1984	configuration (no autoconf):
		1985
		1986	#define EV_STANDALONE 1
		1987	#include "ev.c"
		1988
		1989	This will automatically include F<ev.h>, too, and should be done in a
		1990	single C source file only to provide the function implementations. To use
		1991	it, do the same for F<ev.h> in all files wishing to use this API (best
		1992	done by writing a wrapper around F<ev.h> that you can include instead and
		1993	where you can put other configuration options):
		1994
		1995	#define EV_STANDALONE 1
		1996	#include "ev.h"
		1997
		1998	Both header files and implementation files can be compiled with a C++
		1999	compiler (at least, thats a stated goal, and breakage will be treated
		2000	as a bug).
		2001
		2002	You need the following files in your source tree, or in a directory
		2003	in your include path (e.g. in libev/ when using -Ilibev):
		2004
		2005	ev.h
		2006	ev.c
		2007	ev_vars.h
		2008	ev_wrap.h
		2009
		2010	ev_win32.c required on win32 platforms only
		2011
		2012	ev_select.c only when select backend is enabled (which is enabled by default)
		2013	ev_poll.c only when poll backend is enabled (disabled by default)
		2014	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2015	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2016	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2017
		2018	F<ev.c> includes the backend files directly when enabled, so you only need
		2019	to compile this single file.
		2020
		2021	=head3 LIBEVENT COMPATIBILITY API
		2022
		2023	To include the libevent compatibility API, also include:
		2024
		2025	#include "event.c"
		2026
		2027	in the file including F<ev.c>, and:
		2028
		2029	#include "event.h"
		2030
		2031	in the files that want to use the libevent API. This also includes F<ev.h>.
		2032
		2033	You need the following additional files for this:
		2034
		2035	event.h
		2036	event.c
		2037
		2038	=head3 AUTOCONF SUPPORT
		2039
		2040	Instead of using C<EV_STANDALONE=1> and providing your config in
		2041	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2042	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2043	include F<config.h> and configure itself accordingly.
		2044
		2045	For this of course you need the m4 file:
		2046
		2047	libev.m4
		2048
		2049	=head2 PREPROCESSOR SYMBOLS/MACROS
		2050
		2051	Libev can be configured via a variety of preprocessor symbols you have to define
		2052	before including any of its files. The default is not to build for multiplicity
		2053	and only include the select backend.
		2054
		2055	=over 4
		2056
		2057	=item EV_STANDALONE
		2058
		2059	Must always be C<1> if you do not use autoconf configuration, which
		2060	keeps libev from including F<config.h>, and it also defines dummy
		2061	implementations for some libevent functions (such as logging, which is not
		2062	supported). It will also not define any of the structs usually found in
		2063	F<event.h> that are not directly supported by the libev core alone.
		2064
		2065	=item EV_USE_MONOTONIC
		2066
		2067	If defined to be C<1>, libev will try to detect the availability of the
		2068	monotonic clock option at both compiletime and runtime. Otherwise no use
		2069	of the monotonic clock option will be attempted. If you enable this, you
		2070	usually have to link against librt or something similar. Enabling it when
		2071	the functionality isn't available is safe, though, althoguh you have
		2072	to make sure you link against any libraries where the C<clock_gettime>
		2073	function is hiding in (often F<-lrt>).
		2074
		2075	=item EV_USE_REALTIME
		2076
		2077	If defined to be C<1>, libev will try to detect the availability of the
		2078	realtime clock option at compiletime (and assume its availability at
		2079	runtime if successful). Otherwise no use of the realtime clock option will
		2080	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2081	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
		2082	in the description of C<EV_USE_MONOTONIC>, though.
		2083
		2084	=item EV_USE_SELECT
		2085
		2086	If undefined or defined to be C<1>, libev will compile in support for the
		2087	C<select>(2) backend. No attempt at autodetection will be done: if no
		2088	other method takes over, select will be it. Otherwise the select backend
		2089	will not be compiled in.
		2090
		2091	=item EV_SELECT_USE_FD_SET
		2092
		2093	If defined to C<1>, then the select backend will use the system C<fd_set>
		2094	structure. This is useful if libev doesn't compile due to a missing
		2095	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2096	exotic systems. This usually limits the range of file descriptors to some
		2097	low limit such as 1024 or might have other limitations (winsocket only
		2098	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2099	influence the size of the C<fd_set> used.
		2100
		2101	=item EV_SELECT_IS_WINSOCKET
		2102
		2103	When defined to C<1>, the select backend will assume that
		2104	select/socket/connect etc. don't understand file descriptors but
		2105	wants osf handles on win32 (this is the case when the select to
		2106	be used is the winsock select). This means that it will call
		2107	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2108	it is assumed that all these functions actually work on fds, even
		2109	on win32. Should not be defined on non-win32 platforms.
		2110
		2111	=item EV_USE_POLL
		2112
		2113	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2114	backend. Otherwise it will be enabled on non-win32 platforms. It
		2115	takes precedence over select.
		2116
		2117	=item EV_USE_EPOLL
		2118
		2119	If defined to be C<1>, libev will compile in support for the Linux
		2120	C<epoll>(7) backend. Its availability will be detected at runtime,
		2121	otherwise another method will be used as fallback. This is the
		2122	preferred backend for GNU/Linux systems.
		2123
		2124	=item EV_USE_KQUEUE
		2125
		2126	If defined to be C<1>, libev will compile in support for the BSD style
		2127	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2128	otherwise another method will be used as fallback. This is the preferred
		2129	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2130	supports some types of fds correctly (the only platform we found that
		2131	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2132	not be used unless explicitly requested. The best way to use it is to find
		2133	out whether kqueue supports your type of fd properly and use an embedded
		2134	kqueue loop.
		2135
		2136	=item EV_USE_PORT
		2137
		2138	If defined to be C<1>, libev will compile in support for the Solaris
		2139	10 port style backend. Its availability will be detected at runtime,
		2140	otherwise another method will be used as fallback. This is the preferred
		2141	backend for Solaris 10 systems.
		2142
		2143	=item EV_USE_DEVPOLL
		2144
		2145	reserved for future expansion, works like the USE symbols above.
		2146
		2147	=item EV_USE_INOTIFY
		2148
		2149	If defined to be C<1>, libev will compile in support for the Linux inotify
		2150	interface to speed up C<ev_stat> watchers. Its actual availability will
		2151	be detected at runtime.
		2152
		2153	=item EV_H
		2154
		2155	The name of the F<ev.h> header file used to include it. The default if
		2156	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
		2157	can be used to virtually rename the F<ev.h> header file in case of conflicts.
		2158
		2159	=item EV_CONFIG_H
		2160
		2161	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2162	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2163	C<EV_H>, above.
		2164
		2165	=item EV_EVENT_H
		2166
		2167	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2168	of how the F<event.h> header can be found.
		2169
		2170	=item EV_PROTOTYPES
		2171
		2172	If defined to be C<0>, then F<ev.h> will not define any function
		2173	prototypes, but still define all the structs and other symbols. This is
		2174	occasionally useful if you want to provide your own wrapper functions
		2175	around libev functions.
		2176
		2177	=item EV_MULTIPLICITY
		2178
		2179	If undefined or defined to C<1>, then all event-loop-specific functions
		2180	will have the C<struct ev_loop *> as first argument, and you can create
		2181	additional independent event loops. Otherwise there will be no support
		2182	for multiple event loops and there is no first event loop pointer
		2183	argument. Instead, all functions act on the single default loop.
		2184
		2185	=item EV_MINPRI
		2186
		2187	=item EV_MAXPRI
		2188
		2189	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2190	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2191	provide for more priorities by overriding those symbols (usually defined
		2192	to be C<-2> and C<2>, respectively).
		2193
		2194	When doing priority-based operations, libev usually has to linearly search
		2195	all the priorities, so having many of them (hundreds) uses a lot of space
		2196	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2197	fine.
		2198
		2199	If your embedding app does not need any priorities, defining these both to
		2200	C<0> will save some memory and cpu.
		2201
		2202	=item EV_PERIODIC_ENABLE
		2203
		2204	If undefined or defined to be C<1>, then periodic timers are supported. If
		2205	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2206	code.
		2207
		2208	=item EV_IDLE_ENABLE
		2209
		2210	If undefined or defined to be C<1>, then idle watchers are supported. If
		2211	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2212	code.
		2213
		2214	=item EV_EMBED_ENABLE
		2215
		2216	If undefined or defined to be C<1>, then embed watchers are supported. If
		2217	defined to be C<0>, then they are not.
		2218
		2219	=item EV_STAT_ENABLE
		2220
		2221	If undefined or defined to be C<1>, then stat watchers are supported. If
		2222	defined to be C<0>, then they are not.
		2223
		2224	=item EV_FORK_ENABLE
		2225
		2226	If undefined or defined to be C<1>, then fork watchers are supported. If
		2227	defined to be C<0>, then they are not.
		2228
		2229	=item EV_MINIMAL
		2230
		2231	If you need to shave off some kilobytes of code at the expense of some
		2232	speed, define this symbol to C<1>. Currently only used for gcc to override
		2233	some inlining decisions, saves roughly 30% codesize of amd64.
		2234
		2235	=item EV_PID_HASHSIZE
		2236
		2237	C<ev_child> watchers use a small hash table to distribute workload by
		2238	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2239	than enough. If you need to manage thousands of children you might want to
		2240	increase this value (I<must> be a power of two).
		2241
		2242	=item EV_INOTIFY_HASHSIZE
		2243
		2244	C<ev_staz> watchers use a small hash table to distribute workload by
		2245	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2246	usually more than enough. If you need to manage thousands of C<ev_stat>
		2247	watchers you might want to increase this value (I<must> be a power of
		2248	two).
		2249
		2250	=item EV_COMMON
		2251
		2252	By default, all watchers have a C<void *data> member. By redefining
		2253	this macro to a something else you can include more and other types of
		2254	members. You have to define it each time you include one of the files,
		2255	though, and it must be identical each time.
		2256
		2257	For example, the perl EV module uses something like this:
		2258
		2259	#define EV_COMMON \
		2260	SV *self; /* contains this struct */ \
		2261	SV *cb_sv, *fh /* note no trailing ";" */
		2262
		2263	=item EV_CB_DECLARE (type)
		2264
		2265	=item EV_CB_INVOKE (watcher, revents)
		2266
		2267	=item ev_set_cb (ev, cb)
		2268
		2269	Can be used to change the callback member declaration in each watcher,
		2270	and the way callbacks are invoked and set. Must expand to a struct member
		2271	definition and a statement, respectively. See the F<ev.v> header file for
		2272	their default definitions. One possible use for overriding these is to
		2273	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2274	method calls instead of plain function calls in C++.
		2275
		2276	=head2 EXAMPLES
		2277
		2278	For a real-world example of a program the includes libev
		2279	verbatim, you can have a look at the EV perl module
		2280	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2281	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2282	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2283	will be compiled. It is pretty complex because it provides its own header
		2284	file.
		2285
		2286	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2287	that everybody includes and which overrides some configure choices:
		2288
		2289	#define EV_MINIMAL 1
		2290	#define EV_USE_POLL 0
		2291	#define EV_MULTIPLICITY 0
		2292	#define EV_PERIODIC_ENABLE 0
		2293	#define EV_STAT_ENABLE 0
		2294	#define EV_FORK_ENABLE 0
		2295	#define EV_CONFIG_H <config.h>
		2296	#define EV_MINPRI 0
		2297	#define EV_MAXPRI 0
		2298
		2299	#include "ev++.h"
		2300
		2301	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2302
		2303	#include "ev_cpp.h"
		2304	#include "ev.c"
		2305
		2306
		2307	=head1 COMPLEXITIES
		2308
		2309	In this section the complexities of (many of) the algorithms used inside
		2310	libev will be explained. For complexity discussions about backends see the
		2311	documentation for C<ev_default_init>.
		2312
		2313	All of the following are about amortised time: If an array needs to be
		2314	extended, libev needs to realloc and move the whole array, but this
		2315	happens asymptotically never with higher number of elements, so O(1) might
		2316	mean it might do a lengthy realloc operation in rare cases, but on average
		2317	it is much faster and asymptotically approaches constant time.
		2318
		2319	=over 4
		2320
		2321	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2322
		2323	This means that, when you have a watcher that triggers in one hour and
		2324	there are 100 watchers that would trigger before that then inserting will
		2325	have to skip those 100 watchers.
		2326
		2327	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
		2328
		2329	That means that for changing a timer costs less than removing/adding them
		2330	as only the relative motion in the event queue has to be paid for.
		2331
		2332	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2333
		2334	These just add the watcher into an array or at the head of a list.
		2335	=item Stopping check/prepare/idle watchers: O(1)
		2336
		2337	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2338
		2339	These watchers are stored in lists then need to be walked to find the
		2340	correct watcher to remove. The lists are usually short (you don't usually
		2341	have many watchers waiting for the same fd or signal).
		2342
		2343	=item Finding the next timer per loop iteration: O(1)
		2344
		2345	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2346
		2347	A change means an I/O watcher gets started or stopped, which requires
		2348	libev to recalculate its status (and possibly tell the kernel).
		2349
		2350	=item Activating one watcher: O(1)
		2351
		2352	=item Priority handling: O(number_of_priorities)
		2353
		2354	Priorities are implemented by allocating some space for each
		2355	priority. When doing priority-based operations, libev usually has to
		2356	linearly search all the priorities.
		2357
		2358	=back
		2359
878		2360
879	=head1 AUTHOR	2361	=head1 AUTHOR
880		2362
881	Marc Lehmann <libev@schmorp.de>.	2363	Marc Lehmann <libev@schmorp.de>.
882		2364

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