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Revision 1.30 by root, Fri Nov 23 04:36:03 2007 UTC vs.
Revision 1.64 by root, Sat Dec 1 15:32:53 2007 UTC

…		…
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		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	}
8		50
9	=head1 DESCRIPTION	51	=head1 DESCRIPTION
10		52
11	Libev is an event loop: you register interest in certain events (such as a	53	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	54	file descriptor being readable or a timeout occuring), and it will manage
…		…
21	details of the event, and then hand it over to libev by I<starting> the	63	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	64	watcher.
23		65
24	=head1 FEATURES	66	=head1 FEATURES
25		67
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	68	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	70	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	72	with customised rescheduling (C<ev_periodic>), synchronous signals
		73	(C<ev_signal>), process status change events (C<ev_child>), and event
		74	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		75	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		76	file watchers (C<ev_stat>) and even limited support for fork events
		77	(C<ev_fork>).
		78
		79	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	80	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	81	for example).
33		82
34	=head1 CONVENTIONS	83	=head1 CONVENTIONS
35		84
36	Libev is very configurable. In this manual the default configuration	85	Libev is very configurable. In this manual the default configuration will
37	will be described, which supports multiple event loops. For more info	86	be described, which supports multiple event loops. For more info about
38	about various configuration options please have a look at the file	87	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	88	this manual. If libev was configured without support for multiple event
40	support for multiple event loops, then all functions taking an initial	89	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 *>)	90	(which is always of type C<struct ev_loop *>) will not have this argument.
42	will not have this argument.
43		91
44	=head1 TIME REPRESENTATION	92	=head1 TIME REPRESENTATION
45		93
46	Libev represents time as a single floating point number, representing the	94	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	95	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	96	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	97	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	98	to the C<double> type in C, and when you need to do any calculations on
		99	it, you should treat it as such.
51		100
52	=head1 GLOBAL FUNCTIONS	101	=head1 GLOBAL FUNCTIONS
53		102
54	These functions can be called anytime, even before initialising the	103	These functions can be called anytime, even before initialising the
55	library in any way.	104	library in any way.
…		…
75	Usually, it's a good idea to terminate if the major versions mismatch,	124	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	125	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	126	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	127	not a problem.
79		128
		129	Example: Make sure we haven't accidentally been linked against the wrong
		130	version.
		131
		132	assert (("libev version mismatch",
		133	ev_version_major () == EV_VERSION_MAJOR
		134	&& ev_version_minor () >= EV_VERSION_MINOR));
		135
		136	=item unsigned int ev_supported_backends ()
		137
		138	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		139	value) compiled into this binary of libev (independent of their
		140	availability on the system you are running on). See C<ev_default_loop> for
		141	a description of the set values.
		142
		143	Example: make sure we have the epoll method, because yeah this is cool and
		144	a must have and can we have a torrent of it please!!!11
		145
		146	assert (("sorry, no epoll, no sex",
		147	ev_supported_backends () & EVBACKEND_EPOLL));
		148
		149	=item unsigned int ev_recommended_backends ()
		150
		151	Return the set of all backends compiled into this binary of libev and also
		152	recommended for this platform. This set is often smaller than the one
		153	returned by C<ev_supported_backends>, as for example kqueue is broken on
		154	most BSDs and will not be autodetected unless you explicitly request it
		155	(assuming you know what you are doing). This is the set of backends that
		156	libev will probe for if you specify no backends explicitly.
		157
		158	=item unsigned int ev_embeddable_backends ()
		159
		160	Returns the set of backends that are embeddable in other event loops. This
		161	is the theoretical, all-platform, value. To find which backends
		162	might be supported on the current system, you would need to look at
		163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		164	recommended ones.
		165
		166	See the description of C<ev_embed> watchers for more info.
		167
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	168	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		169
82	Sets the allocation function to use (the prototype is similar to the	170	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	171	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	172	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	173	memory needs to be allocated, the library might abort or take some
86	destructive action. The default is your system realloc function.	174	potentially destructive action. The default is your system realloc
		175	function.
87		176
88	You could override this function in high-availability programs to, say,	177	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,	178	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.	179	or even to sleep a while and retry until some memory is available.
		180
		181	Example: Replace the libev allocator with one that waits a bit and then
		182	retries).
		183
		184	static void *
		185	persistent_realloc (void *ptr, size_t size)
		186	{
		187	for (;;)
		188	{
		189	void *newptr = realloc (ptr, size);
		190
		191	if (newptr)
		192	return newptr;
		193
		194	sleep (60);
		195	}
		196	}
		197
		198	...
		199	ev_set_allocator (persistent_realloc);
91		200
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	201	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		202
94	Set the callback function to call on a retryable syscall error (such	203	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	204	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	206	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	207	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	208	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	209	(such as abort).
101		210
		211	Example: This is basically the same thing that libev does internally, too.
		212
		213	static void
		214	fatal_error (const char *msg)
		215	{
		216	perror (msg);
		217	abort ();
		218	}
		219
		220	...
		221	ev_set_syserr_cb (fatal_error);
		222
102	=back	223	=back
103		224
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	225	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		226
106	An event loop is described by a C<struct ev_loop *>. The library knows two	227	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)	240	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		241
121	This will initialise the default event loop if it hasn't been initialised	242	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	243	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	244	false. If it already was initialised it simply returns it (and ignores the
124	flags).	245	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		246
126	If you don't know what event loop to use, use the one returned from this	247	If you don't know what event loop to use, use the one returned from this
127	function.	248	function.
128		249
129	The flags argument can be used to specify special behaviour or specific	250	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).	251	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		252
132	It supports the following flags:	253	The following flags are supported:
133		254
134	=over 4	255	=over 4
135		256
136	=item C<EVFLAG_AUTO>	257	=item C<EVFLAG_AUTO>
137		258
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	266	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	267	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	268	useful to try out specific backends to test their performance, or to work
148	around bugs.	269	around bugs.
149		270
		271	=item C<EVFLAG_FORKCHECK>
		272
		273	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		274	a fork, you can also make libev check for a fork in each iteration by
		275	enabling this flag.
		276
		277	This works by calling C<getpid ()> on every iteration of the loop,
		278	and thus this might slow down your event loop if you do a lot of loop
		279	iterations and little real work, but is usually not noticable (on my
		280	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		281	without a syscall and thus I<very> fast, but my Linux system also has
		282	C<pthread_atfork> which is even faster).
		283
		284	The big advantage of this flag is that you can forget about fork (and
		285	forget about forgetting to tell libev about forking) when you use this
		286	flag.
		287
		288	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		289	environment variable.
		290
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	291	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		292
152	This is your standard select(2) backend. Not I<completely> standard, as	293	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,	294	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	295	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	296	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.	297	the fastest backend for a low number of fds.
157		298
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	299	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		300
160	And this is your standard poll(2) backend. It's more complicated than	301	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	302	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	303	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).	304	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
164		305
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	306	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		307
167	For few fds, this backend is a bit little slower than poll and select,	308	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	309	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	310	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).	311	either O(1) or O(active_fds).
…		…
173	result in some caching, there is still a syscall per such incident	314	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	315	(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	316	best to avoid that. Also, dup()ed file descriptors might not work very
176	well if you register events for both fds.	317	well if you register events for both fds.
177		318
		319	Please note that epoll sometimes generates spurious notifications, so you
		320	need to use non-blocking I/O or other means to avoid blocking when no data
		321	(or space) is available.
		322
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	323	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		324
180	Kqueue deserves special mention, as at the time of this writing, it	325	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	326	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	327	anything but sockets and pipes, except on Darwin, where of course its
183	completely useless). For this reason its not being "autodetected" unless	328	completely useless). For this reason its not being "autodetected"
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	329	unless you explicitly specify it explicitly in the flags (i.e. using
		330	C<EVBACKEND_KQUEUE>).
185		331
186	It scales in the same way as the epoll backend, but the interface to the	332	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	333	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	334	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	335	extra syscall as with epoll, it still adds up to four event changes per
190	incident, so its best to avoid that.	336	incident, so its best to avoid that.
191		337
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	338	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		339
194	This is not implemented yet (and might never be).	340	This is not implemented yet (and might never be).
195		341
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	342	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		343
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	344	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)).	345	it's really slow, but it still scales very well (O(active_fds)).
200		346
		347	Please note that solaris ports can result in a lot of spurious
		348	notifications, so you need to use non-blocking I/O or other means to avoid
		349	blocking when no data (or space) is available.
		350
201	=item C<EVMETHOD_ALL>	351	=item C<EVBACKEND_ALL>
202		352
203	Try all backends (even potentially broken ones that wouldn't be tried	353	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	354	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	355	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
206		356
207	=back	357	=back
208		358
209	If one or more of these are ored into the flags value, then only these	359	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	360	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	361	specified, most compiled-in backend will be tried, usually in reverse
212	order of their flag values :)	362	order of their flag values :)
213		363
		364	The most typical usage is like this:
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	Use whatever libev has to offer, but make sure that kqueue is used if
		375	available (warning, breaks stuff, best use only with your own private
		376	event loop and only if you know the OS supports your types of fds):
		377
		378	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
		379
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	380	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		381
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	382	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	383	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	384	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).	385	undefined behaviour (or a failed assertion if assertions are enabled).
220		386
		387	Example: Try to create a event loop that uses epoll and nothing else.
		388
		389	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		390	if (!epoller)
		391	fatal ("no epoll found here, maybe it hides under your chair");
		392
221	=item ev_default_destroy ()	393	=item ev_default_destroy ()
222		394
223	Destroys the default loop again (frees all memory and kernel state	395	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	396	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	397	sense, so e.g. C<ev_is_active> might still return true. It is your
		398	responsibility to either stop all watchers cleanly yoursef I<before>
		399	calling this function, or cope with the fact afterwards (which is usually
		400	the easiest thing, youc na just ignore the watchers and/or C<free ()> them
		401	for example).
226		402
227	=item ev_loop_destroy (loop)	403	=item ev_loop_destroy (loop)
228		404
229	Like C<ev_default_destroy>, but destroys an event loop created by an	405	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	406	earlier call to C<ev_loop_new>.
…		…
244	it just in case after a fork. To make this easy, the function will fit in	420	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>:	421	quite nicely into a call to C<pthread_atfork>:
246		422
247	pthread_atfork (0, 0, ev_default_fork);	423	pthread_atfork (0, 0, ev_default_fork);
248		424
		425	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		426	without calling this function, so if you force one of those backends you
		427	do not need to care.
		428
249	=item ev_loop_fork (loop)	429	=item ev_loop_fork (loop)
250		430
251	Like C<ev_default_fork>, but acts on an event loop created by	431	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	432	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.	433	after fork, and how you do this is entirely your own problem.
254		434
255	=item unsigned int ev_method (loop)	435	=item unsigned int ev_backend (loop)
256		436
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	437	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	438	use.
259		439
260	=item ev_tstamp ev_now (loop)	440	=item ev_tstamp ev_now (loop)
261		441
262	Returns the current "event loop time", which is the time the event loop	442	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	443	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	444	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	445	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).	446	event occuring (or more correctly, libev finding out about it).
267		447
268	=item ev_loop (loop, int flags)	448	=item ev_loop (loop, int flags)
269		449
270	Finally, this is it, the event handler. This function usually is called	450	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	451	after you initialised all your watchers and you want to start handling
272	events.	452	events.
273		453
274	If the flags argument is specified as 0, it will not return until either	454	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.	455	either no event watchers are active anymore or C<ev_unloop> was called.
		456
		457	Please note that an explicit C<ev_unloop> is usually better than
		458	relying on all watchers to be stopped when deciding when a program has
		459	finished (especially in interactive programs), but having a program that
		460	automatically loops as long as it has to and no longer by virtue of
		461	relying on its watchers stopping correctly is a thing of beauty.
276		462
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	463	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	464	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.	465	case there are no events and will return after one iteration of the loop.
280		466
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	467	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	468	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	469	your process until at least one new event arrives, and will return after
284	one iteration of the loop.	470	one iteration of the loop. This is useful if you are waiting for some
		471	external event in conjunction with something not expressible using other
		472	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		473	usually a better approach for this kind of thing.
285		474
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:	475	Here are the gory details of what C<ev_loop> does:
291		476
292	1. If there are no active watchers (reference count is zero), return.	477	* If there are no active watchers (reference count is zero), return.
293	2. Queue and immediately call all prepare watchers.	478	- Queue prepare watchers and then call all outstanding watchers.
294	3. If we have been forked, recreate the kernel state.	479	- If we have been forked, recreate the kernel state.
295	4. Update the kernel state with all outstanding changes.	480	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	481	- Update the "event loop time".
297	6. Calculate for how long to block.	482	- Calculate for how long to block.
298	7. Block the process, waiting for events.	483	- Block the process, waiting for any events.
		484	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	485	- Update the "event loop time" and do time jump handling.
300	9. Queue all outstanding timers.	486	- Queue all outstanding timers.
301	10. Queue all outstanding periodics.	487	- Queue all outstanding periodics.
302	11. If no events are pending now, queue all idle watchers.	488	- If no events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	489	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	490	- Call all queued watchers in reverse order (i.e. check watchers first).
		491	Signals and child watchers are implemented as I/O watchers, and will
		492	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	493	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	494	were used, return, otherwise continue with step *.
		495
		496	Example: Queue some jobs and then loop until no events are outsanding
		497	anymore.
		498
		499	... queue jobs here, make sure they register event watchers as long
		500	... as they still have work to do (even an idle watcher will do..)
		501	ev_loop (my_loop, 0);
		502	... jobs done. yeah!
307		503
308	=item ev_unloop (loop, how)	504	=item ev_unloop (loop, how)
309		505
310	Can be used to make a call to C<ev_loop> return early (but only after it	506	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	507	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	521	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	522	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	523	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>.	524	libraries. Just remember to I<unref after start> and I<ref before stop>.
329		525
		526	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		527	running when nothing else is active.
		528
		529	struct ev_signal exitsig;
		530	ev_signal_init (&exitsig, sig_cb, SIGINT);
		531	ev_signal_start (loop, &exitsig);
		532	evf_unref (loop);
		533
		534	Example: For some weird reason, unregister the above signal handler again.
		535
		536	ev_ref (loop);
		537	ev_signal_stop (loop, &exitsig);
		538
330	=back	539	=back
		540
331		541
332	=head1 ANATOMY OF A WATCHER	542	=head1 ANATOMY OF A WATCHER
333		543
334	A watcher is a structure that you create and register to record your	544	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	545	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	578	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	579	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
370		580
371	As long as your watcher is active (has been started but not stopped) you	581	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	582	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	583	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		584
380	Each and every callback receives the event loop pointer as first, the	585	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	586	registered watcher structure as second, and a bitset of received events as
382	third argument.	587	third argument.
383		588
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	612	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		613
409	=item C<EV_CHILD>	614	=item C<EV_CHILD>
410		615
411	The pid specified in the C<ev_child> watcher has received a status change.	616	The pid specified in the C<ev_child> watcher has received a status change.
		617
		618	=item C<EV_STAT>
		619
		620	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		621
413	=item C<EV_IDLE>	622	=item C<EV_IDLE>
414		623
415	The C<ev_idle> watcher has determined that you have nothing better to do.	624	The C<ev_idle> watcher has determined that you have nothing better to do.
416		625
…		…
424	received events. Callbacks of both watcher types can start and stop as	633	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	634	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	635	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	636	C<ev_loop> from blocking).
428		637
		638	=item C<EV_EMBED>
		639
		640	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		641
		642	=item C<EV_FORK>
		643
		644	The event loop has been resumed in the child process after fork (see
		645	C<ev_fork>).
		646
429	=item C<EV_ERROR>	647	=item C<EV_ERROR>
430		648
431	An unspecified error has occured, the watcher has been stopped. This might	649	An unspecified error has occured, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	650	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	651	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	657	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	658	with the error from read() or write(). This will not work in multithreaded
441	programs, though, so beware.	659	programs, though, so beware.
442		660
443	=back	661	=back
		662
		663	=head2 GENERIC WATCHER FUNCTIONS
		664
		665	In the following description, C<TYPE> stands for the watcher type,
		666	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		667
		668	=over 4
		669
		670	=item C<ev_init> (ev_TYPE *watcher, callback)
		671
		672	This macro initialises the generic portion of a watcher. The contents
		673	of the watcher object can be arbitrary (so C<malloc> will do). Only
		674	the generic parts of the watcher are initialised, you I<need> to call
		675	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		676	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		677	which rolls both calls into one.
		678
		679	You can reinitialise a watcher at any time as long as it has been stopped
		680	(or never started) and there are no pending events outstanding.
		681
		682	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		683	int revents)>.
		684
		685	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		686
		687	This macro initialises the type-specific parts of a watcher. You need to
		688	call C<ev_init> at least once before you call this macro, but you can
		689	call C<ev_TYPE_set> any number of times. You must not, however, call this
		690	macro on a watcher that is active (it can be pending, however, which is a
		691	difference to the C<ev_init> macro).
		692
		693	Although some watcher types do not have type-specific arguments
		694	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		695
		696	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		697
		698	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		699	calls into a single call. This is the most convinient method to initialise
		700	a watcher. The same limitations apply, of course.
		701
		702	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		703
		704	Starts (activates) the given watcher. Only active watchers will receive
		705	events. If the watcher is already active nothing will happen.
		706
		707	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		708
		709	Stops the given watcher again (if active) and clears the pending
		710	status. It is possible that stopped watchers are pending (for example,
		711	non-repeating timers are being stopped when they become pending), but
		712	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		713	you want to free or reuse the memory used by the watcher it is therefore a
		714	good idea to always call its C<ev_TYPE_stop> function.
		715
		716	=item bool ev_is_active (ev_TYPE *watcher)
		717
		718	Returns a true value iff the watcher is active (i.e. it has been started
		719	and not yet been stopped). As long as a watcher is active you must not modify
		720	it.
		721
		722	=item bool ev_is_pending (ev_TYPE *watcher)
		723
		724	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		725	events but its callback has not yet been invoked). As long as a watcher
		726	is pending (but not active) you must not call an init function on it (but
		727	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
		728	libev (e.g. you cnanot C<free ()> it).
		729
		730	=item callback ev_cb (ev_TYPE *watcher)
		731
		732	Returns the callback currently set on the watcher.
		733
		734	=item ev_cb_set (ev_TYPE *watcher, callback)
		735
		736	Change the callback. You can change the callback at virtually any time
		737	(modulo threads).
		738
		739	=back
		740
444		741
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	742	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		743
447	Each watcher has, by default, a member C<void *data> that you can change	744	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	745	and read at any time, libev will completely ignore it. This can be used
…		…
466	{	763	{
467	struct my_io *w = (struct my_io *)w_;	764	struct my_io *w = (struct my_io *)w_;
468	...	765	...
469	}	766	}
470		767
471	More interesting and less C-conformant ways of catsing your callback type	768	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	769	instead have been omitted.
		770
		771	Another common scenario is having some data structure with multiple
		772	watchers:
		773
		774	struct my_biggy
		775	{
		776	int some_data;
		777	ev_timer t1;
		778	ev_timer t2;
		779	}
		780
		781	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		782	you need to use C<offsetof>:
		783
		784	#include <stddef.h>
		785
		786	static void
		787	t1_cb (EV_P_ struct ev_timer *w, int revents)
		788	{
		789	struct my_biggy big = (struct my_biggy *
		790	(((char *)w) - offsetof (struct my_biggy, t1));
		791	}
		792
		793	static void
		794	t2_cb (EV_P_ struct ev_timer *w, int revents)
		795	{
		796	struct my_biggy big = (struct my_biggy *
		797	(((char *)w) - offsetof (struct my_biggy, t2));
		798	}
473		799
474		800
475	=head1 WATCHER TYPES	801	=head1 WATCHER TYPES
476		802
477	This section describes each watcher in detail, but will not repeat	803	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	804	information given in the last section. Any initialisation/set macros,
		805	functions and members specific to the watcher type are explained.
479		806
		807	Members are additionally marked with either I<[read-only]>, meaning that,
		808	while the watcher is active, you can look at the member and expect some
		809	sensible content, but you must not modify it (you can modify it while the
		810	watcher is stopped to your hearts content), or I<[read-write]>, which
		811	means you can expect it to have some sensible content while the watcher
		812	is active, but you can also modify it. Modifying it may not do something
		813	sensible or take immediate effect (or do anything at all), but libev will
		814	not crash or malfunction in any way.
		815
		816
480	=head2 C<ev_io> - is this file descriptor readable or writable	817	=head2 C<ev_io> - is this file descriptor readable or writable?
481		818
482	I/O watchers check whether a file descriptor is readable or writable	819	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	820	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	821	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	822	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	823	receiving events as long as the condition persists. Remember you can stop
		824	the watcher if you don't want to act on the event and neither want to
		825	receive future events.
487		826
488	In general you can register as many read and/or write event watchers per	827	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	828	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	829	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	830	required if you know what you are doing).
492		831
493	You have to be careful with dup'ed file descriptors, though. Some backends	832	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	833	(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	834	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	835	to the same underlying file/socket/etc. description (that is, they share
497	the same underlying "file open").	836	the same underlying "file open").
498		837
499	If you must do this, then force the use of a known-to-be-good backend	838	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	839	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
501	EVMETHOD_POLL).	840	C<EVBACKEND_POLL>).
		841
		842	Another thing you have to watch out for is that it is quite easy to
		843	receive "spurious" readyness notifications, that is your callback might
		844	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		845	because there is no data. Not only are some backends known to create a
		846	lot of those (for example solaris ports), it is very easy to get into
		847	this situation even with a relatively standard program structure. Thus
		848	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		849	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		850
		851	If you cannot run the fd in non-blocking mode (for example you should not
		852	play around with an Xlib connection), then you have to seperately re-test
		853	wether a file descriptor is really ready with a known-to-be good interface
		854	such as poll (fortunately in our Xlib example, Xlib already does this on
		855	its own, so its quite safe to use).
502		856
503	=over 4	857	=over 4
504		858
505	=item ev_io_init (ev_io *, callback, int fd, int events)	859	=item ev_io_init (ev_io *, callback, int fd, int events)
506		860
507	=item ev_io_set (ev_io *, int fd, int events)	861	=item ev_io_set (ev_io *, int fd, int events)
508		862
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	863	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 |	864	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	865	C<EV_READ | EV_WRITE> to receive the given events.
		866
		867	=item int fd [read-only]
		868
		869	The file descriptor being watched.
		870
		871	=item int events [read-only]
		872
		873	The events being watched.
512		874
513	=back	875	=back
514		876
		877	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		878	readable, but only once. Since it is likely line-buffered, you could
		879	attempt to read a whole line in the callback.
		880
		881	static void
		882	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		883	{
		884	ev_io_stop (loop, w);
		885	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		886	}
		887
		888	...
		889	struct ev_loop *loop = ev_default_init (0);
		890	struct ev_io stdin_readable;
		891	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		892	ev_io_start (loop, &stdin_readable);
		893	ev_loop (loop, 0);
		894
		895
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	896	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		897
517	Timer watchers are simple relative timers that generate an event after a	898	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	899	given time, and optionally repeating in regular intervals after that.
519		900
520	The timers are based on real time, that is, if you register an event that	901	The timers are based on real time, that is, if you register an event that
…		…
555	=item ev_timer_again (loop)	936	=item ev_timer_again (loop)
556		937
557	This will act as if the timer timed out and restart it again if it is	938	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	939	repeating. The exact semantics are:
559		940
		941	If the timer is pending, its pending status is cleared.
		942
560	If the timer is started but nonrepeating, stop it.	943	If the timer is started but nonrepeating, stop it (as if it timed out).
561		944
562	If the timer is repeating, either start it if necessary (with the repeat	945	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	946	C<repeat> value), or reset the running timer to the C<repeat> value.
564		947
565	This sounds a bit complicated, but here is a useful and typical	948	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	949	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	950	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	951	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	952	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	953	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	954	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.	955	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		956	automatically restart it if need be.
		957
		958	That means you can ignore the C<after> value and C<ev_timer_start>
		959	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		960
		961	ev_timer_init (timer, callback, 0., 5.);
		962	ev_timer_again (loop, timer);
		963	...
		964	timer->again = 17.;
		965	ev_timer_again (loop, timer);
		966	...
		967	timer->again = 10.;
		968	ev_timer_again (loop, timer);
		969
		970	This is more slightly efficient then stopping/starting the timer each time
		971	you want to modify its timeout value.
		972
		973	=item ev_tstamp repeat [read-write]
		974
		975	The current C<repeat> value. Will be used each time the watcher times out
		976	or C<ev_timer_again> is called and determines the next timeout (if any),
		977	which is also when any modifications are taken into account.
573		978
574	=back	979	=back
575		980
		981	Example: Create a timer that fires after 60 seconds.
		982
		983	static void
		984	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		985	{
		986	.. one minute over, w is actually stopped right here
		987	}
		988
		989	struct ev_timer mytimer;
		990	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		991	ev_timer_start (loop, &mytimer);
		992
		993	Example: Create a timeout timer that times out after 10 seconds of
		994	inactivity.
		995
		996	static void
		997	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		998	{
		999	.. ten seconds without any activity
		1000	}
		1001
		1002	struct ev_timer mytimer;
		1003	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1004	ev_timer_again (&mytimer); /* start timer */
		1005	ev_loop (loop, 0);
		1006
		1007	// and in some piece of code that gets executed on any "activity":
		1008	// reset the timeout to start ticking again at 10 seconds
		1009	ev_timer_again (&mytimer);
		1010
		1011
576	=head2 C<ev_periodic> - to cron or not to cron	1012	=head2 C<ev_periodic> - to cron or not to cron?
577		1013
578	Periodic watchers are also timers of a kind, but they are very versatile	1014	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1015	(and unfortunately a bit complex).
580		1016
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1017	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	1018	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	1019	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 ()	1020	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	1021	+ 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	1022	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	1023	roughly 10 seconds later and of course not if you reset your system time
588	again).	1024	again).
589		1025
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1109	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1110	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	1111	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1112	program when the crontabs have changed).
677		1113
		1114	=item ev_tstamp interval [read-write]
		1115
		1116	The current interval value. Can be modified any time, but changes only
		1117	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1118	called.
		1119
		1120	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1121
		1122	The current reschedule callback, or C<0>, if this functionality is
		1123	switched off. Can be changed any time, but changes only take effect when
		1124	the periodic timer fires or C<ev_periodic_again> is being called.
		1125
678	=back	1126	=back
679		1127
		1128	Example: Call a callback every hour, or, more precisely, whenever the
		1129	system clock is divisible by 3600. The callback invocation times have
		1130	potentially a lot of jittering, but good long-term stability.
		1131
		1132	static void
		1133	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1134	{
		1135	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1136	}
		1137
		1138	struct ev_periodic hourly_tick;
		1139	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1140	ev_periodic_start (loop, &hourly_tick);
		1141
		1142	Example: The same as above, but use a reschedule callback to do it:
		1143
		1144	#include <math.h>
		1145
		1146	static ev_tstamp
		1147	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1148	{
		1149	return fmod (now, 3600.) + 3600.;
		1150	}
		1151
		1152	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1153
		1154	Example: Call a callback every hour, starting now:
		1155
		1156	struct ev_periodic hourly_tick;
		1157	ev_periodic_init (&hourly_tick, clock_cb,
		1158	fmod (ev_now (loop), 3600.), 3600., 0);
		1159	ev_periodic_start (loop, &hourly_tick);
		1160
		1161
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1162	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1163
682	Signal watchers will trigger an event when the process receives a specific	1164	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	1165	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	1166	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1167	normal event processing, like any other event.
…		…
698	=item ev_signal_set (ev_signal *, int signum)	1180	=item ev_signal_set (ev_signal *, int signum)
699		1181
700	Configures the watcher to trigger on the given signal number (usually one	1182	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1183	of the C<SIGxxx> constants).
702		1184
		1185	=item int signum [read-only]
		1186
		1187	The signal the watcher watches out for.
		1188
703	=back	1189	=back
704		1190
		1191
705	=head2 C<ev_child> - wait for pid status changes	1192	=head2 C<ev_child> - watch out for process status changes
706		1193
707	Child watchers trigger when your process receives a SIGCHLD in response to	1194	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).	1195	some child status changes (most typically when a child of yours dies).
709		1196
710	=over 4	1197	=over 4
…		…
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	1205	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	1206	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	1207	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	1208	process causing the status change.
722		1209
		1210	=item int pid [read-only]
		1211
		1212	The process id this watcher watches out for, or C<0>, meaning any process id.
		1213
		1214	=item int rpid [read-write]
		1215
		1216	The process id that detected a status change.
		1217
		1218	=item int rstatus [read-write]
		1219
		1220	The process exit/trace status caused by C<rpid> (see your systems
		1221	C<waitpid> and C<sys/wait.h> documentation for details).
		1222
723	=back	1223	=back
724		1224
		1225	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1226
		1227	static void
		1228	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1229	{
		1230	ev_unloop (loop, EVUNLOOP_ALL);
		1231	}
		1232
		1233	struct ev_signal signal_watcher;
		1234	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1235	ev_signal_start (loop, &sigint_cb);
		1236
		1237
		1238	=head2 C<ev_stat> - did the file attributes just change?
		1239
		1240	This watches a filesystem path for attribute changes. That is, it calls
		1241	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1242	compared to the last time, invoking the callback if it did.
		1243
		1244	The path does not need to exist: changing from "path exists" to "path does
		1245	not exist" is a status change like any other. The condition "path does
		1246	not exist" is signified by the C<st_nlink> field being zero (which is
		1247	otherwise always forced to be at least one) and all the other fields of
		1248	the stat buffer having unspecified contents.
		1249
		1250	The path I<should> be absolute and I<must not> end in a slash. If it is
		1251	relative and your working directory changes, the behaviour is undefined.
		1252
		1253	Since there is no standard to do this, the portable implementation simply
		1254	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1255	can specify a recommended polling interval for this case. If you specify
		1256	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1257	unspecified default> value will be used (which you can expect to be around
		1258	five seconds, although this might change dynamically). Libev will also
		1259	impose a minimum interval which is currently around C<0.1>, but thats
		1260	usually overkill.
		1261
		1262	This watcher type is not meant for massive numbers of stat watchers,
		1263	as even with OS-supported change notifications, this can be
		1264	resource-intensive.
		1265
		1266	At the time of this writing, only the Linux inotify interface is
		1267	implemented (implementing kqueue support is left as an exercise for the
		1268	reader). Inotify will be used to give hints only and should not change the
		1269	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1270	to fall back to regular polling again even with inotify, but changes are
		1271	usually detected immediately, and if the file exists there will be no
		1272	polling.
		1273
		1274	=over 4
		1275
		1276	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1277
		1278	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1279
		1280	Configures the watcher to wait for status changes of the given
		1281	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1282	be detected and should normally be specified as C<0> to let libev choose
		1283	a suitable value. The memory pointed to by C<path> must point to the same
		1284	path for as long as the watcher is active.
		1285
		1286	The callback will be receive C<EV_STAT> when a change was detected,
		1287	relative to the attributes at the time the watcher was started (or the
		1288	last change was detected).
		1289
		1290	=item ev_stat_stat (ev_stat *)
		1291
		1292	Updates the stat buffer immediately with new values. If you change the
		1293	watched path in your callback, you could call this fucntion to avoid
		1294	detecting this change (while introducing a race condition). Can also be
		1295	useful simply to find out the new values.
		1296
		1297	=item ev_statdata attr [read-only]
		1298
		1299	The most-recently detected attributes of the file. Although the type is of
		1300	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1301	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1302	was some error while C<stat>ing the file.
		1303
		1304	=item ev_statdata prev [read-only]
		1305
		1306	The previous attributes of the file. The callback gets invoked whenever
		1307	C<prev> != C<attr>.
		1308
		1309	=item ev_tstamp interval [read-only]
		1310
		1311	The specified interval.
		1312
		1313	=item const char *path [read-only]
		1314
		1315	The filesystem path that is being watched.
		1316
		1317	=back
		1318
		1319	Example: Watch C</etc/passwd> for attribute changes.
		1320
		1321	static void
		1322	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1323	{
		1324	/* /etc/passwd changed in some way */
		1325	if (w->attr.st_nlink)
		1326	{
		1327	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1328	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1329	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1330	}
		1331	else
		1332	/* you shalt not abuse printf for puts */
		1333	puts ("wow, /etc/passwd is not there, expect problems. "
		1334	"if this is windows, they already arrived\n");
		1335	}
		1336
		1337	...
		1338	ev_stat passwd;
		1339
		1340	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
		1341	ev_stat_start (loop, &passwd);
		1342
		1343
725	=head2 C<ev_idle> - when you've got nothing better to do	1344	=head2 C<ev_idle> - when you've got nothing better to do...
726		1345
727	Idle watchers trigger events when there are no other events are pending	1346	Idle watchers trigger events when there are no other events are pending
728	(prepare, check and other idle watchers do not count). That is, as long	1347	(prepare, check and other idle watchers do not count). That is, as long
729	as your process is busy handling sockets or timeouts (or even signals,	1348	as your process is busy handling sockets or timeouts (or even signals,
730	imagine) it will not be triggered. But when your process is idle all idle	1349	imagine) it will not be triggered. But when your process is idle all idle
…		…
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1367	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	1368	believe me.
750		1369
751	=back	1370	=back
752		1371
		1372	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1373	callback, free it. Also, use no error checking, as usual.
		1374
		1375	static void
		1376	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1377	{
		1378	free (w);
		1379	// now do something you wanted to do when the program has
		1380	// no longer asnything immediate to do.
		1381	}
		1382
		1383	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1384	ev_idle_init (idle_watcher, idle_cb);
		1385	ev_idle_start (loop, idle_cb);
		1386
		1387
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1388	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		1389
755	Prepare and check watchers are usually (but not always) used in tandem:	1390	Prepare and check watchers are usually (but not always) used in tandem:
756	prepare watchers get invoked before the process blocks and check watchers	1391	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	1392	afterwards.
758		1393
		1394	You I<must not> call C<ev_loop> or similar functions that enter
		1395	the current event loop from either C<ev_prepare> or C<ev_check>
		1396	watchers. Other loops than the current one are fine, however. The
		1397	rationale behind this is that you do not need to check for recursion in
		1398	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1399	C<ev_check> so if you have one watcher of each kind they will always be
		1400	called in pairs bracketing the blocking call.
		1401
759	Their main purpose is to integrate other event mechanisms into libev. This	1402	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	1403	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.	1404	variable changes, implement your own watchers, integrate net-snmp or a
		1405	coroutine library and lots more. They are also occasionally useful if
		1406	you cache some data and want to flush it before blocking (for example,
		1407	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1408	watcher).
762		1409
763	This is done by examining in each prepare call which file descriptors need	1410	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	1411	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	1412	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	1413	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>	1435	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.	1436	macros, but using them is utterly, utterly and completely pointless.
790		1437
791	=back	1438	=back
792		1439
		1440	Example: To include a library such as adns, you would add IO watchers
		1441	and a timeout watcher in a prepare handler, as required by libadns, and
		1442	in a check watcher, destroy them and call into libadns. What follows is
		1443	pseudo-code only of course:
		1444
		1445	static ev_io iow [nfd];
		1446	static ev_timer tw;
		1447
		1448	static void
		1449	io_cb (ev_loop *loop, ev_io *w, int revents)
		1450	{
		1451	// set the relevant poll flags
		1452	// could also call adns_processreadable etc. here
		1453	struct pollfd *fd = (struct pollfd *)w->data;
		1454	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1455	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1456	}
		1457
		1458	// create io watchers for each fd and a timer before blocking
		1459	static void
		1460	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1461	{
		1462	int timeout = 3600000;
		1463	struct pollfd fds [nfd];
		1464	// actual code will need to loop here and realloc etc.
		1465	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1466
		1467	/* the callback is illegal, but won't be called as we stop during check */
		1468	ev_timer_init (&tw, 0, timeout * 1e-3);
		1469	ev_timer_start (loop, &tw);
		1470
		1471	// create on ev_io per pollfd
		1472	for (int i = 0; i < nfd; ++i)
		1473	{
		1474	ev_io_init (iow + i, io_cb, fds [i].fd,
		1475	((fds [i].events & POLLIN ? EV_READ : 0)
		1476	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1477
		1478	fds [i].revents = 0;
		1479	iow [i].data = fds + i;
		1480	ev_io_start (loop, iow + i);
		1481	}
		1482	}
		1483
		1484	// stop all watchers after blocking
		1485	static void
		1486	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1487	{
		1488	ev_timer_stop (loop, &tw);
		1489
		1490	for (int i = 0; i < nfd; ++i)
		1491	ev_io_stop (loop, iow + i);
		1492
		1493	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1494	}
		1495
		1496
		1497	=head2 C<ev_embed> - when one backend isn't enough...
		1498
		1499	This is a rather advanced watcher type that lets you embed one event loop
		1500	into another (currently only C<ev_io> events are supported in the embedded
		1501	loop, other types of watchers might be handled in a delayed or incorrect
		1502	fashion and must not be used).
		1503
		1504	There are primarily two reasons you would want that: work around bugs and
		1505	prioritise I/O.
		1506
		1507	As an example for a bug workaround, the kqueue backend might only support
		1508	sockets on some platform, so it is unusable as generic backend, but you
		1509	still want to make use of it because you have many sockets and it scales
		1510	so nicely. In this case, you would create a kqueue-based loop and embed it
		1511	into your default loop (which might use e.g. poll). Overall operation will
		1512	be a bit slower because first libev has to poll and then call kevent, but
		1513	at least you can use both at what they are best.
		1514
		1515	As for prioritising I/O: rarely you have the case where some fds have
		1516	to be watched and handled very quickly (with low latency), and even
		1517	priorities and idle watchers might have too much overhead. In this case
		1518	you would put all the high priority stuff in one loop and all the rest in
		1519	a second one, and embed the second one in the first.
		1520
		1521	As long as the watcher is active, the callback will be invoked every time
		1522	there might be events pending in the embedded loop. The callback must then
		1523	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1524	their callbacks (you could also start an idle watcher to give the embedded
		1525	loop strictly lower priority for example). You can also set the callback
		1526	to C<0>, in which case the embed watcher will automatically execute the
		1527	embedded loop sweep.
		1528
		1529	As long as the watcher is started it will automatically handle events. The
		1530	callback will be invoked whenever some events have been handled. You can
		1531	set the callback to C<0> to avoid having to specify one if you are not
		1532	interested in that.
		1533
		1534	Also, there have not currently been made special provisions for forking:
		1535	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1536	but you will also have to stop and restart any C<ev_embed> watchers
		1537	yourself.
		1538
		1539	Unfortunately, not all backends are embeddable, only the ones returned by
		1540	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1541	portable one.
		1542
		1543	So when you want to use this feature you will always have to be prepared
		1544	that you cannot get an embeddable loop. The recommended way to get around
		1545	this is to have a separate variables for your embeddable loop, try to
		1546	create it, and if that fails, use the normal loop for everything:
		1547
		1548	struct ev_loop *loop_hi = ev_default_init (0);
		1549	struct ev_loop *loop_lo = 0;
		1550	struct ev_embed embed;
		1551
		1552	// see if there is a chance of getting one that works
		1553	// (remember that a flags value of 0 means autodetection)
		1554	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1555	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1556	: 0;
		1557
		1558	// if we got one, then embed it, otherwise default to loop_hi
		1559	if (loop_lo)
		1560	{
		1561	ev_embed_init (&embed, 0, loop_lo);
		1562	ev_embed_start (loop_hi, &embed);
		1563	}
		1564	else
		1565	loop_lo = loop_hi;
		1566
		1567	=over 4
		1568
		1569	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1570
		1571	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1572
		1573	Configures the watcher to embed the given loop, which must be
		1574	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1575	invoked automatically, otherwise it is the responsibility of the callback
		1576	to invoke it (it will continue to be called until the sweep has been done,
		1577	if you do not want thta, you need to temporarily stop the embed watcher).
		1578
		1579	=item ev_embed_sweep (loop, ev_embed *)
		1580
		1581	Make a single, non-blocking sweep over the embedded loop. This works
		1582	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1583	apropriate way for embedded loops.
		1584
		1585	=item struct ev_loop *loop [read-only]
		1586
		1587	The embedded event loop.
		1588
		1589	=back
		1590
		1591
		1592	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		1593
		1594	Fork watchers are called when a C<fork ()> was detected (usually because
		1595	whoever is a good citizen cared to tell libev about it by calling
		1596	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		1597	event loop blocks next and before C<ev_check> watchers are being called,
		1598	and only in the child after the fork. If whoever good citizen calling
		1599	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		1600	handlers will be invoked, too, of course.
		1601
		1602	=over 4
		1603
		1604	=item ev_fork_init (ev_signal *, callback)
		1605
		1606	Initialises and configures the fork watcher - it has no parameters of any
		1607	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		1608	believe me.
		1609
		1610	=back
		1611
		1612
793	=head1 OTHER FUNCTIONS	1613	=head1 OTHER FUNCTIONS
794		1614
795	There are some other functions of possible interest. Described. Here. Now.	1615	There are some other functions of possible interest. Described. Here. Now.
796		1616
797	=over 4	1617	=over 4
…		…
826	/* stdin might have data for us, joy! */;	1646	/* stdin might have data for us, joy! */;
827	}	1647	}
828		1648
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	1649	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		1650
831	=item ev_feed_event (loop, watcher, int events)	1651	=item ev_feed_event (ev_loop *, watcher *, int revents)
832		1652
833	Feeds the given event set into the event loop, as if the specified event	1653	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	1654	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	1655	initialised but not necessarily started event watcher).
836		1656
837	=item ev_feed_fd_event (loop, int fd, int revents)	1657	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
838		1658
839	Feed an event on the given fd, as if a file descriptor backend detected	1659	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	1660	the given events it.
841		1661
842	=item ev_feed_signal_event (loop, int signum)	1662	=item ev_feed_signal_event (ev_loop *loop, int signum)
843		1663
844	Feed an event as if the given signal occured (loop must be the default loop!).	1664	Feed an event as if the given signal occured (C<loop> must be the default
		1665	loop!).
845		1666
846	=back	1667	=back
		1668
847		1669
848	=head1 LIBEVENT EMULATION	1670	=head1 LIBEVENT EMULATION
849		1671
850	Libev offers a compatibility emulation layer for libevent. It cannot	1672	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	1673	emulate the internals of libevent, so here are some usage hints:
…		…
872		1694
873	=back	1695	=back
874		1696
875	=head1 C++ SUPPORT	1697	=head1 C++ SUPPORT
876		1698
877	TBD.	1699	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		1700	you to use some convinience methods to start/stop watchers and also change
		1701	the callback model to a model using method callbacks on objects.
		1702
		1703	To use it,
		1704
		1705	#include <ev++.h>
		1706
		1707	(it is not installed by default). This automatically includes F<ev.h>
		1708	and puts all of its definitions (many of them macros) into the global
		1709	namespace. All C++ specific things are put into the C<ev> namespace.
		1710
		1711	It should support all the same embedding options as F<ev.h>, most notably
		1712	C<EV_MULTIPLICITY>.
		1713
		1714	Here is a list of things available in the C<ev> namespace:
		1715
		1716	=over 4
		1717
		1718	=item C<ev::READ>, C<ev::WRITE> etc.
		1719
		1720	These are just enum values with the same values as the C<EV_READ> etc.
		1721	macros from F<ev.h>.
		1722
		1723	=item C<ev::tstamp>, C<ev::now>
		1724
		1725	Aliases to the same types/functions as with the C<ev_> prefix.
		1726
		1727	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		1728
		1729	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		1730	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		1731	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		1732	defines by many implementations.
		1733
		1734	All of those classes have these methods:
		1735
		1736	=over 4
		1737
		1738	=item ev::TYPE::TYPE (object *, object::method *)
		1739
		1740	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)
		1741
		1742	=item ev::TYPE::~TYPE
		1743
		1744	The constructor takes a pointer to an object and a method pointer to
		1745	the event handler callback to call in this class. The constructor calls
		1746	C<ev_init> for you, which means you have to call the C<set> method
		1747	before starting it. If you do not specify a loop then the constructor
		1748	automatically associates the default loop with this watcher.
		1749
		1750	The destructor automatically stops the watcher if it is active.
		1751
		1752	=item w->set (struct ev_loop *)
		1753
		1754	Associates a different C<struct ev_loop> with this watcher. You can only
		1755	do this when the watcher is inactive (and not pending either).
		1756
		1757	=item w->set ([args])
		1758
		1759	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		1760	called at least once. Unlike the C counterpart, an active watcher gets
		1761	automatically stopped and restarted.
		1762
		1763	=item w->start ()
		1764
		1765	Starts the watcher. Note that there is no C<loop> argument as the
		1766	constructor already takes the loop.
		1767
		1768	=item w->stop ()
		1769
		1770	Stops the watcher if it is active. Again, no C<loop> argument.
		1771
		1772	=item w->again () C<ev::timer>, C<ev::periodic> only
		1773
		1774	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		1775	C<ev_TYPE_again> function.
		1776
		1777	=item w->sweep () C<ev::embed> only
		1778
		1779	Invokes C<ev_embed_sweep>.
		1780
		1781	=item w->update () C<ev::stat> only
		1782
		1783	Invokes C<ev_stat_stat>.
		1784
		1785	=back
		1786
		1787	=back
		1788
		1789	Example: Define a class with an IO and idle watcher, start one of them in
		1790	the constructor.
		1791
		1792	class myclass
		1793	{
		1794	ev_io io; void io_cb (ev::io &w, int revents);
		1795	ev_idle idle void idle_cb (ev::idle &w, int revents);
		1796
		1797	myclass ();
		1798	}
		1799
		1800	myclass::myclass (int fd)
		1801	: io (this, &myclass::io_cb),
		1802	idle (this, &myclass::idle_cb)
		1803	{
		1804	io.start (fd, ev::READ);
		1805	}
		1806
		1807
		1808	=head1 MACRO MAGIC
		1809
		1810	Libev can be compiled with a variety of options, the most fundemantal is
		1811	C<EV_MULTIPLICITY>. This option determines wether (most) functions and
		1812	callbacks have an initial C<struct ev_loop *> argument.
		1813
		1814	To make it easier to write programs that cope with either variant, the
		1815	following macros are defined:
		1816
		1817	=over 4
		1818
		1819	=item C<EV_A>, C<EV_A_>
		1820
		1821	This provides the loop I<argument> for functions, if one is required ("ev
		1822	loop argument"). The C<EV_A> form is used when this is the sole argument,
		1823	C<EV_A_> is used when other arguments are following. Example:
		1824
		1825	ev_unref (EV_A);
		1826	ev_timer_add (EV_A_ watcher);
		1827	ev_loop (EV_A_ 0);
		1828
		1829	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		1830	which is often provided by the following macro.
		1831
		1832	=item C<EV_P>, C<EV_P_>
		1833
		1834	This provides the loop I<parameter> for functions, if one is required ("ev
		1835	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		1836	C<EV_P_> is used when other parameters are following. Example:
		1837
		1838	// this is how ev_unref is being declared
		1839	static void ev_unref (EV_P);
		1840
		1841	// this is how you can declare your typical callback
		1842	static void cb (EV_P_ ev_timer *w, int revents)
		1843
		1844	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		1845	suitable for use with C<EV_A>.
		1846
		1847	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		1848
		1849	Similar to the other two macros, this gives you the value of the default
		1850	loop, if multiple loops are supported ("ev loop default").
		1851
		1852	=back
		1853
		1854	Example: Declare and initialise a check watcher, utilising the above
		1855	macros so it will work regardless of wether multiple loops are supported
		1856	or not.
		1857
		1858	static void
		1859	check_cb (EV_P_ ev_timer *w, int revents)
		1860	{
		1861	ev_check_stop (EV_A_ w);
		1862	}
		1863
		1864	ev_check check;
		1865	ev_check_init (&check, check_cb);
		1866	ev_check_start (EV_DEFAULT_ &check);
		1867	ev_loop (EV_DEFAULT_ 0);
		1868
		1869	=head1 EMBEDDING
		1870
		1871	Libev can (and often is) directly embedded into host
		1872	applications. Examples of applications that embed it include the Deliantra
		1873	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		1874	and rxvt-unicode.
		1875
		1876	The goal is to enable you to just copy the neecssary files into your
		1877	source directory without having to change even a single line in them, so
		1878	you can easily upgrade by simply copying (or having a checked-out copy of
		1879	libev somewhere in your source tree).
		1880
		1881	=head2 FILESETS
		1882
		1883	Depending on what features you need you need to include one or more sets of files
		1884	in your app.
		1885
		1886	=head3 CORE EVENT LOOP
		1887
		1888	To include only the libev core (all the C<ev_*> functions), with manual
		1889	configuration (no autoconf):
		1890
		1891	#define EV_STANDALONE 1
		1892	#include "ev.c"
		1893
		1894	This will automatically include F<ev.h>, too, and should be done in a
		1895	single C source file only to provide the function implementations. To use
		1896	it, do the same for F<ev.h> in all files wishing to use this API (best
		1897	done by writing a wrapper around F<ev.h> that you can include instead and
		1898	where you can put other configuration options):
		1899
		1900	#define EV_STANDALONE 1
		1901	#include "ev.h"
		1902
		1903	Both header files and implementation files can be compiled with a C++
		1904	compiler (at least, thats a stated goal, and breakage will be treated
		1905	as a bug).
		1906
		1907	You need the following files in your source tree, or in a directory
		1908	in your include path (e.g. in libev/ when using -Ilibev):
		1909
		1910	ev.h
		1911	ev.c
		1912	ev_vars.h
		1913	ev_wrap.h
		1914
		1915	ev_win32.c required on win32 platforms only
		1916
		1917	ev_select.c only when select backend is enabled (which is enabled by default)
		1918	ev_poll.c only when poll backend is enabled (disabled by default)
		1919	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		1920	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		1921	ev_port.c only when the solaris port backend is enabled (disabled by default)
		1922
		1923	F<ev.c> includes the backend files directly when enabled, so you only need
		1924	to compile this single file.
		1925
		1926	=head3 LIBEVENT COMPATIBILITY API
		1927
		1928	To include the libevent compatibility API, also include:
		1929
		1930	#include "event.c"
		1931
		1932	in the file including F<ev.c>, and:
		1933
		1934	#include "event.h"
		1935
		1936	in the files that want to use the libevent API. This also includes F<ev.h>.
		1937
		1938	You need the following additional files for this:
		1939
		1940	event.h
		1941	event.c
		1942
		1943	=head3 AUTOCONF SUPPORT
		1944
		1945	Instead of using C<EV_STANDALONE=1> and providing your config in
		1946	whatever way you want, you can also C<m4_include([libev.m4])> in your
		1947	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		1948	include F<config.h> and configure itself accordingly.
		1949
		1950	For this of course you need the m4 file:
		1951
		1952	libev.m4
		1953
		1954	=head2 PREPROCESSOR SYMBOLS/MACROS
		1955
		1956	Libev can be configured via a variety of preprocessor symbols you have to define
		1957	before including any of its files. The default is not to build for multiplicity
		1958	and only include the select backend.
		1959
		1960	=over 4
		1961
		1962	=item EV_STANDALONE
		1963
		1964	Must always be C<1> if you do not use autoconf configuration, which
		1965	keeps libev from including F<config.h>, and it also defines dummy
		1966	implementations for some libevent functions (such as logging, which is not
		1967	supported). It will also not define any of the structs usually found in
		1968	F<event.h> that are not directly supported by the libev core alone.
		1969
		1970	=item EV_USE_MONOTONIC
		1971
		1972	If defined to be C<1>, libev will try to detect the availability of the
		1973	monotonic clock option at both compiletime and runtime. Otherwise no use
		1974	of the monotonic clock option will be attempted. If you enable this, you
		1975	usually have to link against librt or something similar. Enabling it when
		1976	the functionality isn't available is safe, though, althoguh you have
		1977	to make sure you link against any libraries where the C<clock_gettime>
		1978	function is hiding in (often F<-lrt>).
		1979
		1980	=item EV_USE_REALTIME
		1981
		1982	If defined to be C<1>, libev will try to detect the availability of the
		1983	realtime clock option at compiletime (and assume its availability at
		1984	runtime if successful). Otherwise no use of the realtime clock option will
		1985	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		1986	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
		1987	in the description of C<EV_USE_MONOTONIC>, though.
		1988
		1989	=item EV_USE_SELECT
		1990
		1991	If undefined or defined to be C<1>, libev will compile in support for the
		1992	C<select>(2) backend. No attempt at autodetection will be done: if no
		1993	other method takes over, select will be it. Otherwise the select backend
		1994	will not be compiled in.
		1995
		1996	=item EV_SELECT_USE_FD_SET
		1997
		1998	If defined to C<1>, then the select backend will use the system C<fd_set>
		1999	structure. This is useful if libev doesn't compile due to a missing
		2000	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2001	exotic systems. This usually limits the range of file descriptors to some
		2002	low limit such as 1024 or might have other limitations (winsocket only
		2003	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2004	influence the size of the C<fd_set> used.
		2005
		2006	=item EV_SELECT_IS_WINSOCKET
		2007
		2008	When defined to C<1>, the select backend will assume that
		2009	select/socket/connect etc. don't understand file descriptors but
		2010	wants osf handles on win32 (this is the case when the select to
		2011	be used is the winsock select). This means that it will call
		2012	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2013	it is assumed that all these functions actually work on fds, even
		2014	on win32. Should not be defined on non-win32 platforms.
		2015
		2016	=item EV_USE_POLL
		2017
		2018	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2019	backend. Otherwise it will be enabled on non-win32 platforms. It
		2020	takes precedence over select.
		2021
		2022	=item EV_USE_EPOLL
		2023
		2024	If defined to be C<1>, libev will compile in support for the Linux
		2025	C<epoll>(7) backend. Its availability will be detected at runtime,
		2026	otherwise another method will be used as fallback. This is the
		2027	preferred backend for GNU/Linux systems.
		2028
		2029	=item EV_USE_KQUEUE
		2030
		2031	If defined to be C<1>, libev will compile in support for the BSD style
		2032	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2033	otherwise another method will be used as fallback. This is the preferred
		2034	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2035	supports some types of fds correctly (the only platform we found that
		2036	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2037	not be used unless explicitly requested. The best way to use it is to find
		2038	out whether kqueue supports your type of fd properly and use an embedded
		2039	kqueue loop.
		2040
		2041	=item EV_USE_PORT
		2042
		2043	If defined to be C<1>, libev will compile in support for the Solaris
		2044	10 port style backend. Its availability will be detected at runtime,
		2045	otherwise another method will be used as fallback. This is the preferred
		2046	backend for Solaris 10 systems.
		2047
		2048	=item EV_USE_DEVPOLL
		2049
		2050	reserved for future expansion, works like the USE symbols above.
		2051
		2052	=item EV_USE_INOTIFY
		2053
		2054	If defined to be C<1>, libev will compile in support for the Linux inotify
		2055	interface to speed up C<ev_stat> watchers. Its actual availability will
		2056	be detected at runtime.
		2057
		2058	=item EV_H
		2059
		2060	The name of the F<ev.h> header file used to include it. The default if
		2061	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
		2062	can be used to virtually rename the F<ev.h> header file in case of conflicts.
		2063
		2064	=item EV_CONFIG_H
		2065
		2066	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2067	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2068	C<EV_H>, above.
		2069
		2070	=item EV_EVENT_H
		2071
		2072	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2073	of how the F<event.h> header can be found.
		2074
		2075	=item EV_PROTOTYPES
		2076
		2077	If defined to be C<0>, then F<ev.h> will not define any function
		2078	prototypes, but still define all the structs and other symbols. This is
		2079	occasionally useful if you want to provide your own wrapper functions
		2080	around libev functions.
		2081
		2082	=item EV_MULTIPLICITY
		2083
		2084	If undefined or defined to C<1>, then all event-loop-specific functions
		2085	will have the C<struct ev_loop *> as first argument, and you can create
		2086	additional independent event loops. Otherwise there will be no support
		2087	for multiple event loops and there is no first event loop pointer
		2088	argument. Instead, all functions act on the single default loop.
		2089
		2090	=item EV_PERIODIC_ENABLE
		2091
		2092	If undefined or defined to be C<1>, then periodic timers are supported. If
		2093	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2094	code.
		2095
		2096	=item EV_EMBED_ENABLE
		2097
		2098	If undefined or defined to be C<1>, then embed watchers are supported. If
		2099	defined to be C<0>, then they are not.
		2100
		2101	=item EV_STAT_ENABLE
		2102
		2103	If undefined or defined to be C<1>, then stat watchers are supported. If
		2104	defined to be C<0>, then they are not.
		2105
		2106	=item EV_FORK_ENABLE
		2107
		2108	If undefined or defined to be C<1>, then fork watchers are supported. If
		2109	defined to be C<0>, then they are not.
		2110
		2111	=item EV_MINIMAL
		2112
		2113	If you need to shave off some kilobytes of code at the expense of some
		2114	speed, define this symbol to C<1>. Currently only used for gcc to override
		2115	some inlining decisions, saves roughly 30% codesize of amd64.
		2116
		2117	=item EV_PID_HASHSIZE
		2118
		2119	C<ev_child> watchers use a small hash table to distribute workload by
		2120	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2121	than enough. If you need to manage thousands of children you might want to
		2122	increase this value (I<must> be a power of two).
		2123
		2124	=item EV_INOTIFY_HASHSIZE
		2125
		2126	C<ev_staz> watchers use a small hash table to distribute workload by
		2127	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2128	usually more than enough. If you need to manage thousands of C<ev_stat>
		2129	watchers you might want to increase this value (I<must> be a power of
		2130	two).
		2131
		2132	=item EV_COMMON
		2133
		2134	By default, all watchers have a C<void *data> member. By redefining
		2135	this macro to a something else you can include more and other types of
		2136	members. You have to define it each time you include one of the files,
		2137	though, and it must be identical each time.
		2138
		2139	For example, the perl EV module uses something like this:
		2140
		2141	#define EV_COMMON \
		2142	SV *self; /* contains this struct */ \
		2143	SV *cb_sv, *fh /* note no trailing ";" */
		2144
		2145	=item EV_CB_DECLARE (type)
		2146
		2147	=item EV_CB_INVOKE (watcher, revents)
		2148
		2149	=item ev_set_cb (ev, cb)
		2150
		2151	Can be used to change the callback member declaration in each watcher,
		2152	and the way callbacks are invoked and set. Must expand to a struct member
		2153	definition and a statement, respectively. See the F<ev.v> header file for
		2154	their default definitions. One possible use for overriding these is to
		2155	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2156	method calls instead of plain function calls in C++.
		2157
		2158	=head2 EXAMPLES
		2159
		2160	For a real-world example of a program the includes libev
		2161	verbatim, you can have a look at the EV perl module
		2162	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2163	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2164	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2165	will be compiled. It is pretty complex because it provides its own header
		2166	file.
		2167
		2168	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2169	that everybody includes and which overrides some configure choices:
		2170
		2171	#define EV_MINIMAL 1
		2172	#define EV_USE_POLL 0
		2173	#define EV_MULTIPLICITY 0
		2174	#define EV_PERIODIC_ENABLE 0
		2175	#define EV_STAT_ENABLE 0
		2176	#define EV_FORK_ENABLE 0
		2177	#define EV_CONFIG_H <config.h>
		2178	#define EV_MINPRI 0
		2179	#define EV_MAXPRI 0
		2180
		2181	#include "ev++.h"
		2182
		2183	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2184
		2185	#include "ev_cpp.h"
		2186	#include "ev.c"
		2187
		2188
		2189	=head1 COMPLEXITIES
		2190
		2191	In this section the complexities of (many of) the algorithms used inside
		2192	libev will be explained. For complexity discussions about backends see the
		2193	documentation for C<ev_default_init>.
		2194
		2195	=over 4
		2196
		2197	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2198
		2199	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
		2200
		2201	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2202
		2203	=item Stopping check/prepare/idle watchers: O(1)
		2204
		2205	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2206
		2207	=item Finding the next timer per loop iteration: O(1)
		2208
		2209	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2210
		2211	=item Activating one watcher: O(1)
		2212
		2213	=back
		2214
878		2215
879	=head1 AUTHOR	2216	=head1 AUTHOR
880		2217
881	Marc Lehmann <libev@schmorp.de>.	2218	Marc Lehmann <libev@schmorp.de>.
882		2219

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