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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	#include <ev.h>
		12
		13	ev_io stdin_watcher;
		14	ev_timer timeout_watcher;
		15
		16	/* called when data readable on stdin */
		17	static void
		18	stdin_cb (EV_P_ struct ev_io *w, int revents)
		19	{
		20	/* puts ("stdin ready"); */
		21	ev_io_stop (EV_A_ w); /* just a syntax example */
		22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
		23	}
		24
		25	static void
		26	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		27	{
		28	/* puts ("timeout"); */
		29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
		30	}
		31
		32	int
		33	main (void)
		34	{
		35	struct ev_loop *loop = ev_default_loop (0);
		36
		37	/* initialise an io watcher, then start it */
		38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		39	ev_io_start (loop, &stdin_watcher);
		40
		41	/* simple non-repeating 5.5 second timeout */
		42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		43	ev_timer_start (loop, &timeout_watcher);
		44
		45	/* loop till timeout or data ready */
		46	ev_loop (loop, 0);
		47
		48	return 0;
		49	}
		50
9	=head1 DESCRIPTION	51	=head1 DESCRIPTION
10		52
		53	The newest version of this document is also available as a html-formatted
		54	web page you might find easier to navigate when reading it for the first
		55	time: L<http://cvs.schmorp.de/libev/ev.html>.
		56
11	Libev is an event loop: you register interest in certain events (such as a	57	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	58	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	59	these event sources and provide your program with events.
14		60
15	To do this, it must take more or less complete control over your process	61	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	62	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	63	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	65	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	66	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	67	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	68	watcher.
23		69
24	=head1 FEATURES	70	=head2 FEATURES
25		71
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	76	with customised rescheduling (C<ev_periodic>), synchronous signals
		77	(C<ev_signal>), process status change events (C<ev_child>), and event
		78	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		80	file watchers (C<ev_stat>) and even limited support for fork events
		81	(C<ev_fork>).
		82
		83	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	85	for example).
33		86
34	=head1 CONVENTIONS	87	=head2 CONVENTIONS
35		88
36	Libev is very configurable. In this manual the default configuration	89	Libev is very configurable. In this manual the default configuration will
37	will be described, which supports multiple event loops. For more info	90	be described, which supports multiple event loops. For more info about
38	about various configuration options please have a look at the file	91	various configuration options please have a look at B<EMBED> section in
39	F<README.embed> in the libev distribution. If libev was configured without	92	this manual. If libev was configured without support for multiple event
40	support for multiple event loops, then all functions taking an initial	93	loops, then all functions taking an initial argument of name C<loop>
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	94	(which is always of type C<struct ev_loop *>) will not have this argument.
42	will not have this argument.
43		95
44	=head1 TIME REPRESENTATION	96	=head2 TIME REPRESENTATION
45		97
46	Libev represents time as a single floating point number, representing the	98	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	99	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	100	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	101	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	102	to the C<double> type in C, and when you need to do any calculations on
		103	it, you should treat it as some floatingpoint value. Unlike the name
		104	component C<stamp> might indicate, it is also used for time differences
		105	throughout libev.
51		106
52	=head1 GLOBAL FUNCTIONS	107	=head1 GLOBAL FUNCTIONS
53		108
54	These functions can be called anytime, even before initialising the	109	These functions can be called anytime, even before initialising the
55	library in any way.	110	library in any way.
…		…
60		115
61	Returns the current time as libev would use it. Please note that the	116	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	117	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	118	you actually want to know.
64		119
		120	=item ev_sleep (ev_tstamp interval)
		121
		122	Sleep for the given interval: The current thread will be blocked until
		123	either it is interrupted or the given time interval has passed. Basically
		124	this is a subsecond-resolution C<sleep ()>.
		125
65	=item int ev_version_major ()	126	=item int ev_version_major ()
66		127
67	=item int ev_version_minor ()	128	=item int ev_version_minor ()
68		129
69	You can find out the major and minor version numbers of the library	130	You can find out the major and minor ABI version numbers of the library
70	you linked against by calling the functions C<ev_version_major> and	131	you linked against by calling the functions C<ev_version_major> and
71	C<ev_version_minor>. If you want, you can compare against the global	132	C<ev_version_minor>. If you want, you can compare against the global
72	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	133	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	134	version of the library your program was compiled against.
74		135
		136	These version numbers refer to the ABI version of the library, not the
		137	release version.
		138
75	Usually, it's a good idea to terminate if the major versions mismatch,	139	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	140	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	141	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	142	not a problem.
79		143
		144	Example: Make sure we haven't accidentally been linked against the wrong
		145	version.
		146
		147	assert (("libev version mismatch",
		148	ev_version_major () == EV_VERSION_MAJOR
		149	&& ev_version_minor () >= EV_VERSION_MINOR));
		150
		151	=item unsigned int ev_supported_backends ()
		152
		153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		154	value) compiled into this binary of libev (independent of their
		155	availability on the system you are running on). See C<ev_default_loop> for
		156	a description of the set values.
		157
		158	Example: make sure we have the epoll method, because yeah this is cool and
		159	a must have and can we have a torrent of it please!!!11
		160
		161	assert (("sorry, no epoll, no sex",
		162	ev_supported_backends () & EVBACKEND_EPOLL));
		163
		164	=item unsigned int ev_recommended_backends ()
		165
		166	Return the set of all backends compiled into this binary of libev and also
		167	recommended for this platform. This set is often smaller than the one
		168	returned by C<ev_supported_backends>, as for example kqueue is broken on
		169	most BSDs and will not be autodetected unless you explicitly request it
		170	(assuming you know what you are doing). This is the set of backends that
		171	libev will probe for if you specify no backends explicitly.
		172
		173	=item unsigned int ev_embeddable_backends ()
		174
		175	Returns the set of backends that are embeddable in other event loops. This
		176	is the theoretical, all-platform, value. To find which backends
		177	might be supported on the current system, you would need to look at
		178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		179	recommended ones.
		180
		181	See the description of C<ev_embed> watchers for more info.
		182
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		184
82	Sets the allocation function to use (the prototype is similar to the	185	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	186	semantics is identical - to the realloc C function). It is used to
84	and free memory (no surprises here). If it returns zero when memory	187	allocate and free memory (no surprises here). If it returns zero when
85	needs to be allocated, the library might abort or take some potentially	188	memory needs to be allocated, the library might abort or take some
86	destructive action. The default is your system realloc function.	189	potentially destructive action. The default is your system realloc
		190	function.
87		191
88	You could override this function in high-availability programs to, say,	192	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	193	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	194	or even to sleep a while and retry until some memory is available.
		195
		196	Example: Replace the libev allocator with one that waits a bit and then
		197	retries).
		198
		199	static void *
		200	persistent_realloc (void *ptr, size_t size)
		201	{
		202	for (;;)
		203	{
		204	void *newptr = realloc (ptr, size);
		205
		206	if (newptr)
		207	return newptr;
		208
		209	sleep (60);
		210	}
		211	}
		212
		213	...
		214	ev_set_allocator (persistent_realloc);
91		215
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	216	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		217
94	Set the callback function to call on a retryable syscall error (such	218	Set the callback function to call on a retryable syscall error (such
95	as failed select, poll, epoll_wait). The message is a printable string	219	as failed select, poll, epoll_wait). The message is a printable string
…		…
97	callback is set, then libev will expect it to remedy the sitution, no	221	callback is set, then libev will expect it to remedy the sitution, no
98	matter what, when it returns. That is, libev will generally retry the	222	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	223	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	224	(such as abort).
101		225
		226	Example: This is basically the same thing that libev does internally, too.
		227
		228	static void
		229	fatal_error (const char *msg)
		230	{
		231	perror (msg);
		232	abort ();
		233	}
		234
		235	...
		236	ev_set_syserr_cb (fatal_error);
		237
102	=back	238	=back
103		239
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		241
106	An event loop is described by a C<struct ev_loop *>. The library knows two	242	An event loop is described by a C<struct ev_loop *>. The library knows two
…		…
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	255	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		256
121	This will initialise the default event loop if it hasn't been initialised	257	This will initialise the default event loop if it hasn't been initialised
122	yet and return it. If the default loop could not be initialised, returns	258	yet and return it. If the default loop could not be initialised, returns
123	false. If it already was initialised it simply returns it (and ignores the	259	false. If it already was initialised it simply returns it (and ignores the
124	flags).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		261
126	If you don't know what event loop to use, use the one returned from this	262	If you don't know what event loop to use, use the one returned from this
127	function.	263	function.
128		264
129	The flags argument can be used to specify special behaviour or specific	265	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		267
132	It supports the following flags:	268	The following flags are supported:
133		269
134	=over 4	270	=over 4
135		271
136	=item C<EVFLAG_AUTO>	272	=item C<EVFLAG_AUTO>
137		273
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	282	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	283	useful to try out specific backends to test their performance, or to work
148	around bugs.	284	around bugs.
149		285
		286	=item C<EVFLAG_FORKCHECK>
		287
		288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		289	a fork, you can also make libev check for a fork in each iteration by
		290	enabling this flag.
		291
		292	This works by calling C<getpid ()> on every iteration of the loop,
		293	and thus this might slow down your event loop if you do a lot of loop
		294	iterations and little real work, but is usually not noticeable (on my
		295	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		296	without a syscall and thus I<very> fast, but my Linux system also has
		297	C<pthread_atfork> which is even faster).
		298
		299	The big advantage of this flag is that you can forget about fork (and
		300	forget about forgetting to tell libev about forking) when you use this
		301	flag.
		302
		303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		304	environment variable.
		305
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		307
152	This is your standard select(2) backend. Not I<completely> standard, as	308	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,	309	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	310	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	311	using this backend. It doesn't scale too well (O(highest_fd)), but its
156	the fastest backend for a low number of fds.	312	usually the fastest backend for a low number of (low-numbered :) fds.
157		313
		314	To get good performance out of this backend you need a high amount of
		315	parallelity (most of the file descriptors should be busy). If you are
		316	writing a server, you should C<accept ()> in a loop to accept as many
		317	connections as possible during one iteration. You might also want to have
		318	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		319	readyness notifications you get per iteration.
		320
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		322
160	And this is your standard poll(2) backend. It's more complicated than	323	And this is your standard poll(2) backend. It's more complicated
161	select, but handles sparse fds better and has no artificial limit on the	324	than select, but handles sparse fds better and has no artificial
162	number of fds you can use (except it will slow down considerably with a	325	limit on the number of fds you can use (except it will slow down
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	326	considerably with a lot of inactive fds). It scales similarly to select,
		327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		328	performance tips.
164		329
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	330	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		331
167	For few fds, this backend is a bit little slower than poll and select,	332	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	333	but it scales phenomenally better. While poll and select usually scale
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	334	like O(total_fds) where n is the total number of fds (or the highest fd),
170	either O(1) or O(active_fds).	335	epoll scales either O(1) or O(active_fds). The epoll design has a number
		336	of shortcomings, such as silently dropping events in some hard-to-detect
		337	cases and rewiring a syscall per fd change, no fork support and bad
		338	support for dup.
171		339
172	While stopping and starting an I/O watcher in the same iteration will	340	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	341	will 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	342	(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	343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
176	well if you register events for both fds.	344	very well if you register events for both fds.
177		345
		346	Please note that epoll sometimes generates spurious notifications, so you
		347	need to use non-blocking I/O or other means to avoid blocking when no data
		348	(or space) is available.
		349
		350	Best performance from this backend is achieved by not unregistering all
		351	watchers for a file descriptor until it has been closed, if possible, i.e.
		352	keep at least one watcher active per fd at all times.
		353
		354	While nominally embeddeble in other event loops, this feature is broken in
		355	all kernel versions tested so far.
		356
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		358
180	Kqueue deserves special mention, as at the time of this writing, it	359	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	360	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	361	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	362	it's completely useless). For this reason it's not being "autodetected"
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	363	unless you explicitly specify it explicitly in the flags (i.e. using
		364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		365	system like NetBSD.
		366
		367	You still can embed kqueue into a normal poll or select backend and use it
		368	only for sockets (after having made sure that sockets work with kqueue on
		369	the target platform). See C<ev_embed> watchers for more info.
185		370
186	It scales in the same way as the epoll backend, but the interface to the	371	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	372	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	373	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	375	two event changes per incident, support for C<fork ()> is very bad and it
		376	drops fds silently in similarly hard-to-detect cases.
191		377
		378	This backend usually performs well under most conditions.
		379
		380	While nominally embeddable in other event loops, this doesn't work
		381	everywhere, so you might need to test for this. And since it is broken
		382	almost everywhere, you should only use it when you have a lot of sockets
		383	(for which it usually works), by embedding it into another event loop
		384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		385	sockets.
		386
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		388
194	This is not implemented yet (and might never be).	389	This is not implemented yet (and might never be, unless you send me an
		390	implementation). According to reports, C</dev/poll> only supports sockets
		391	and is not embeddable, which would limit the usefulness of this backend
		392	immensely.
195		393
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		395
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	397	it's really slow, but it still scales very well (O(active_fds)).
200		398
		399	Please note that solaris event ports can deliver a lot of spurious
		400	notifications, so you need to use non-blocking I/O or other means to avoid
		401	blocking when no data (or space) is available.
		402
		403	While this backend scales well, it requires one system call per active
		404	file descriptor per loop iteration. For small and medium numbers of file
		405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		406	might perform better.
		407
201	=item C<EVMETHOD_ALL>	408	=item C<EVBACKEND_ALL>
202		409
203	Try all backends (even potentially broken ones that wouldn't be tried	410	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	411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		413
		414	It is definitely not recommended to use this flag.
206		415
207	=back	416	=back
208		417
209	If one or more of these are ored into the flags value, then only these	418	If one or more of these are ored into the flags value, then only these
210	backends will be tried (in the reverse order as given here). If none are	419	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	420	specified, most compiled-in backend will be tried, usually in reverse
212	order of their flag values :)	421	order of their flag values :)
213		422
		423	The most typical usage is like this:
		424
		425	if (!ev_default_loop (0))
		426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		427
		428	Restrict libev to the select and poll backends, and do not allow
		429	environment settings to be taken into account:
		430
		431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		432
		433	Use whatever libev has to offer, but make sure that kqueue is used if
		434	available (warning, breaks stuff, best use only with your own private
		435	event loop and only if you know the OS supports your types of fds):
		436
		437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
		438
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	439	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		440
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	441	Similar to C<ev_default_loop>, but always creates a new event loop that is
217	always distinct from the default loop. Unlike the default loop, it cannot	442	always distinct from the default loop. Unlike the default loop, it cannot
218	handle signal and child watchers, and attempts to do so will be greeted by	443	handle signal and child watchers, and attempts to do so will be greeted by
219	undefined behaviour (or a failed assertion if assertions are enabled).	444	undefined behaviour (or a failed assertion if assertions are enabled).
220		445
		446	Example: Try to create a event loop that uses epoll and nothing else.
		447
		448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		449	if (!epoller)
		450	fatal ("no epoll found here, maybe it hides under your chair");
		451
221	=item ev_default_destroy ()	452	=item ev_default_destroy ()
222		453
223	Destroys the default loop again (frees all memory and kernel state	454	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	455	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	456	sense, so e.g. C<ev_is_active> might still return true. It is your
		457	responsibility to either stop all watchers cleanly yoursef I<before>
		458	calling this function, or cope with the fact afterwards (which is usually
		459	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		460	for example).
		461
		462	Note that certain global state, such as signal state, will not be freed by
		463	this function, and related watchers (such as signal and child watchers)
		464	would need to be stopped manually.
		465
		466	In general it is not advisable to call this function except in the
		467	rare occasion where you really need to free e.g. the signal handling
		468	pipe fds. If you need dynamically allocated loops it is better to use
		469	C<ev_loop_new> and C<ev_loop_destroy>).
226		470
227	=item ev_loop_destroy (loop)	471	=item ev_loop_destroy (loop)
228		472
229	Like C<ev_default_destroy>, but destroys an event loop created by an	473	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	474	earlier call to C<ev_loop_new>.
…		…
244	it just in case after a fork. To make this easy, the function will fit in	488	it just in case after a fork. To make this easy, the function will fit in
245	quite nicely into a call to C<pthread_atfork>:	489	quite nicely into a call to C<pthread_atfork>:
246		490
247	pthread_atfork (0, 0, ev_default_fork);	491	pthread_atfork (0, 0, ev_default_fork);
248		492
		493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		494	without calling this function, so if you force one of those backends you
		495	do not need to care.
		496
249	=item ev_loop_fork (loop)	497	=item ev_loop_fork (loop)
250		498
251	Like C<ev_default_fork>, but acts on an event loop created by	499	Like C<ev_default_fork>, but acts on an event loop created by
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
253	after fork, and how you do this is entirely your own problem.	501	after fork, and how you do this is entirely your own problem.
254		502
		503	=item unsigned int ev_loop_count (loop)
		504
		505	Returns the count of loop iterations for the loop, which is identical to
		506	the number of times libev did poll for new events. It starts at C<0> and
		507	happily wraps around with enough iterations.
		508
		509	This value can sometimes be useful as a generation counter of sorts (it
		510	"ticks" the number of loop iterations), as it roughly corresponds with
		511	C<ev_prepare> and C<ev_check> calls.
		512
255	=item unsigned int ev_method (loop)	513	=item unsigned int ev_backend (loop)
256		514
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	516	use.
259		517
260	=item ev_tstamp ev_now (loop)	518	=item ev_tstamp ev_now (loop)
261		519
262	Returns the current "event loop time", which is the time the event loop	520	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	521	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	522	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	523	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).	524	event occurring (or more correctly, libev finding out about it).
267		525
268	=item ev_loop (loop, int flags)	526	=item ev_loop (loop, int flags)
269		527
270	Finally, this is it, the event handler. This function usually is called	528	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	529	after you initialised all your watchers and you want to start handling
272	events.	530	events.
273		531
274	If the flags argument is specified as 0, it will not return until either	532	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	533	either no event watchers are active anymore or C<ev_unloop> was called.
		534
		535	Please note that an explicit C<ev_unloop> is usually better than
		536	relying on all watchers to be stopped when deciding when a program has
		537	finished (especially in interactive programs), but having a program that
		538	automatically loops as long as it has to and no longer by virtue of
		539	relying on its watchers stopping correctly is a thing of beauty.
276		540
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	542	those events and any outstanding ones, but will not block your process in
279	case there are no events and will return after one iteration of the loop.	543	case there are no events and will return after one iteration of the loop.
280		544
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	546	neccessary) and will handle those and any outstanding ones. It will block
283	your process until at least one new event arrives, and will return after	547	your process until at least one new event arrives, and will return after
284	one iteration of the loop.	548	one iteration of the loop. This is useful if you are waiting for some
		549	external event in conjunction with something not expressible using other
		550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		551	usually a better approach for this kind of thing.
285		552
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:	553	Here are the gory details of what C<ev_loop> does:
291		554
		555	- Before the first iteration, call any pending watchers.
292	1. If there are no active watchers (reference count is zero), return.	556	* If there are no active watchers (reference count is zero), return.
293	2. Queue and immediately call all prepare watchers.	557	- Queue all prepare watchers and then call all outstanding watchers.
294	3. If we have been forked, recreate the kernel state.	558	- If we have been forked, recreate the kernel state.
295	4. Update the kernel state with all outstanding changes.	559	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	560	- Update the "event loop time".
297	6. Calculate for how long to block.	561	- Calculate for how long to block.
298	7. Block the process, waiting for events.	562	- Block the process, waiting for any events.
		563	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	564	- Update the "event loop time" and do time jump handling.
300	9. Queue all outstanding timers.	565	- Queue all outstanding timers.
301	10. Queue all outstanding periodics.	566	- Queue all outstanding periodics.
302	11. If no events are pending now, queue all idle watchers.	567	- If no events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	568	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	569	- Call all queued watchers in reverse order (i.e. check watchers first).
		570	Signals and child watchers are implemented as I/O watchers, and will
		571	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	572	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	573	were used, return, otherwise continue with step *.
		574
		575	Example: Queue some jobs and then loop until no events are outsanding
		576	anymore.
		577
		578	... queue jobs here, make sure they register event watchers as long
		579	... as they still have work to do (even an idle watcher will do..)
		580	ev_loop (my_loop, 0);
		581	... jobs done. yeah!
307		582
308	=item ev_unloop (loop, how)	583	=item ev_unloop (loop, how)
309		584
310	Can be used to make a call to C<ev_loop> return early (but only after it	585	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	586	has processed all outstanding events). The C<how> argument must be either
…		…
325	visible to the libev user and should not keep C<ev_loop> from exiting if	600	visible to the libev user and should not keep C<ev_loop> from exiting if
326	no event watchers registered by it are active. It is also an excellent	601	no event watchers registered by it are active. It is also an excellent
327	way to do this for generic recurring timers or from within third-party	602	way to do this for generic recurring timers or from within third-party
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	603	libraries. Just remember to I<unref after start> and I<ref before stop>.
329		604
		605	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		606	running when nothing else is active.
		607
		608	struct ev_signal exitsig;
		609	ev_signal_init (&exitsig, sig_cb, SIGINT);
		610	ev_signal_start (loop, &exitsig);
		611	evf_unref (loop);
		612
		613	Example: For some weird reason, unregister the above signal handler again.
		614
		615	ev_ref (loop);
		616	ev_signal_stop (loop, &exitsig);
		617
		618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		619
		620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		621
		622	These advanced functions influence the time that libev will spend waiting
		623	for events. Both are by default C<0>, meaning that libev will try to
		624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		625
		626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		627	allows libev to delay invocation of I/O and timer/periodic callbacks to
		628	increase efficiency of loop iterations.
		629
		630	The background is that sometimes your program runs just fast enough to
		631	handle one (or very few) event(s) per loop iteration. While this makes
		632	the program responsive, it also wastes a lot of CPU time to poll for new
		633	events, especially with backends like C<select ()> which have a high
		634	overhead for the actual polling but can deliver many events at once.
		635
		636	By setting a higher I<io collect interval> you allow libev to spend more
		637	time collecting I/O events, so you can handle more events per iteration,
		638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		639	C<ev_timer>) will be not affected. Setting this to a non-null value will
		640	introduce an additional C<ev_sleep ()> call into most loop iterations.
		641
		642	Likewise, by setting a higher I<timeout collect interval> you allow libev
		643	to spend more time collecting timeouts, at the expense of increased
		644	latency (the watcher callback will be called later). C<ev_io> watchers
		645	will not be affected. Setting this to a non-null value will not introduce
		646	any overhead in libev.
		647
		648	Many (busy) programs can usually benefit by setting the io collect
		649	interval to a value near C<0.1> or so, which is often enough for
		650	interactive servers (of course not for games), likewise for timeouts. It
		651	usually doesn't make much sense to set it to a lower value than C<0.01>,
		652	as this approsaches the timing granularity of most systems.
		653
330	=back	654	=back
		655
331		656
332	=head1 ANATOMY OF A WATCHER	657	=head1 ANATOMY OF A WATCHER
333		658
334	A watcher is a structure that you create and register to record your	659	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	660	interest in some event. For instance, if you want to wait for STDIN to
…		…
368	*) >>), and you can stop watching for events at any time by calling the	693	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
370		695
371	As long as your watcher is active (has been started but not stopped) you	696	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	697	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	698	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		699
380	Each and every callback receives the event loop pointer as first, the	700	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	701	registered watcher structure as second, and a bitset of received events as
382	third argument.	702	third argument.
383		703
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	727	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		728
409	=item C<EV_CHILD>	729	=item C<EV_CHILD>
410		730
411	The pid specified in the C<ev_child> watcher has received a status change.	731	The pid specified in the C<ev_child> watcher has received a status change.
		732
		733	=item C<EV_STAT>
		734
		735	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		736
413	=item C<EV_IDLE>	737	=item C<EV_IDLE>
414		738
415	The C<ev_idle> watcher has determined that you have nothing better to do.	739	The C<ev_idle> watcher has determined that you have nothing better to do.
416		740
…		…
424	received events. Callbacks of both watcher types can start and stop as	748	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	749	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	750	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	751	C<ev_loop> from blocking).
428		752
		753	=item C<EV_EMBED>
		754
		755	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		756
		757	=item C<EV_FORK>
		758
		759	The event loop has been resumed in the child process after fork (see
		760	C<ev_fork>).
		761
429	=item C<EV_ERROR>	762	=item C<EV_ERROR>
430		763
431	An unspecified error has occured, the watcher has been stopped. This might	764	An unspecified error has occured, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	765	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	766	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	772	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	773	with the error from read() or write(). This will not work in multithreaded
441	programs, though, so beware.	774	programs, though, so beware.
442		775
443	=back	776	=back
		777
		778	=head2 GENERIC WATCHER FUNCTIONS
		779
		780	In the following description, C<TYPE> stands for the watcher type,
		781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		782
		783	=over 4
		784
		785	=item C<ev_init> (ev_TYPE *watcher, callback)
		786
		787	This macro initialises the generic portion of a watcher. The contents
		788	of the watcher object can be arbitrary (so C<malloc> will do). Only
		789	the generic parts of the watcher are initialised, you I<need> to call
		790	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		791	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		792	which rolls both calls into one.
		793
		794	You can reinitialise a watcher at any time as long as it has been stopped
		795	(or never started) and there are no pending events outstanding.
		796
		797	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		798	int revents)>.
		799
		800	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		801
		802	This macro initialises the type-specific parts of a watcher. You need to
		803	call C<ev_init> at least once before you call this macro, but you can
		804	call C<ev_TYPE_set> any number of times. You must not, however, call this
		805	macro on a watcher that is active (it can be pending, however, which is a
		806	difference to the C<ev_init> macro).
		807
		808	Although some watcher types do not have type-specific arguments
		809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		810
		811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		812
		813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		814	calls into a single call. This is the most convinient method to initialise
		815	a watcher. The same limitations apply, of course.
		816
		817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		818
		819	Starts (activates) the given watcher. Only active watchers will receive
		820	events. If the watcher is already active nothing will happen.
		821
		822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		823
		824	Stops the given watcher again (if active) and clears the pending
		825	status. It is possible that stopped watchers are pending (for example,
		826	non-repeating timers are being stopped when they become pending), but
		827	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		828	you want to free or reuse the memory used by the watcher it is therefore a
		829	good idea to always call its C<ev_TYPE_stop> function.
		830
		831	=item bool ev_is_active (ev_TYPE *watcher)
		832
		833	Returns a true value iff the watcher is active (i.e. it has been started
		834	and not yet been stopped). As long as a watcher is active you must not modify
		835	it.
		836
		837	=item bool ev_is_pending (ev_TYPE *watcher)
		838
		839	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		840	events but its callback has not yet been invoked). As long as a watcher
		841	is pending (but not active) you must not call an init function on it (but
		842	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		843	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		844	it).
		845
		846	=item callback ev_cb (ev_TYPE *watcher)
		847
		848	Returns the callback currently set on the watcher.
		849
		850	=item ev_cb_set (ev_TYPE *watcher, callback)
		851
		852	Change the callback. You can change the callback at virtually any time
		853	(modulo threads).
		854
		855	=item ev_set_priority (ev_TYPE *watcher, priority)
		856
		857	=item int ev_priority (ev_TYPE *watcher)
		858
		859	Set and query the priority of the watcher. The priority is a small
		860	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		861	(default: C<-2>). Pending watchers with higher priority will be invoked
		862	before watchers with lower priority, but priority will not keep watchers
		863	from being executed (except for C<ev_idle> watchers).
		864
		865	This means that priorities are I<only> used for ordering callback
		866	invocation after new events have been received. This is useful, for
		867	example, to reduce latency after idling, or more often, to bind two
		868	watchers on the same event and make sure one is called first.
		869
		870	If you need to suppress invocation when higher priority events are pending
		871	you need to look at C<ev_idle> watchers, which provide this functionality.
		872
		873	You I<must not> change the priority of a watcher as long as it is active or
		874	pending.
		875
		876	The default priority used by watchers when no priority has been set is
		877	always C<0>, which is supposed to not be too high and not be too low :).
		878
		879	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		880	fine, as long as you do not mind that the priority value you query might
		881	or might not have been adjusted to be within valid range.
		882
		883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		884
		885	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		886	C<loop> nor C<revents> need to be valid as long as the watcher callback
		887	can deal with that fact.
		888
		889	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		890
		891	If the watcher is pending, this function returns clears its pending status
		892	and returns its C<revents> bitset (as if its callback was invoked). If the
		893	watcher isn't pending it does nothing and returns C<0>.
		894
		895	=back
		896
444		897
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		899
447	Each watcher has, by default, a member C<void *data> that you can change	900	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	901	and read at any time, libev will completely ignore it. This can be used
…		…
466	{	919	{
467	struct my_io *w = (struct my_io *)w_;	920	struct my_io *w = (struct my_io *)w_;
468	...	921	...
469	}	922	}
470		923
471	More interesting and less C-conformant ways of catsing your callback type	924	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	925	instead have been omitted.
		926
		927	Another common scenario is having some data structure with multiple
		928	watchers:
		929
		930	struct my_biggy
		931	{
		932	int some_data;
		933	ev_timer t1;
		934	ev_timer t2;
		935	}
		936
		937	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		938	you need to use C<offsetof>:
		939
		940	#include <stddef.h>
		941
		942	static void
		943	t1_cb (EV_P_ struct ev_timer *w, int revents)
		944	{
		945	struct my_biggy big = (struct my_biggy *
		946	(((char *)w) - offsetof (struct my_biggy, t1));
		947	}
		948
		949	static void
		950	t2_cb (EV_P_ struct ev_timer *w, int revents)
		951	{
		952	struct my_biggy big = (struct my_biggy *
		953	(((char *)w) - offsetof (struct my_biggy, t2));
		954	}
473		955
474		956
475	=head1 WATCHER TYPES	957	=head1 WATCHER TYPES
476		958
477	This section describes each watcher in detail, but will not repeat	959	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	960	information given in the last section. Any initialisation/set macros,
		961	functions and members specific to the watcher type are explained.
479		962
		963	Members are additionally marked with either I<[read-only]>, meaning that,
		964	while the watcher is active, you can look at the member and expect some
		965	sensible content, but you must not modify it (you can modify it while the
		966	watcher is stopped to your hearts content), or I<[read-write]>, which
		967	means you can expect it to have some sensible content while the watcher
		968	is active, but you can also modify it. Modifying it may not do something
		969	sensible or take immediate effect (or do anything at all), but libev will
		970	not crash or malfunction in any way.
		971
		972
480	=head2 C<ev_io> - is this file descriptor readable or writable	973	=head2 C<ev_io> - is this file descriptor readable or writable?
481		974
482	I/O watchers check whether a file descriptor is readable or writable	975	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	976	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	977	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	978	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	979	receiving events as long as the condition persists. Remember you can stop
		980	the watcher if you don't want to act on the event and neither want to
		981	receive future events.
487		982
488	In general you can register as many read and/or write event watchers per	983	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	984	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	985	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	986	required if you know what you are doing).
492		987
493	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
495	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
497	the same underlying "file open").
498
499	If you must do this, then force the use of a known-to-be-good backend	988	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	989	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
501	EVMETHOD_POLL).	990	C<EVBACKEND_POLL>).
		991
		992	Another thing you have to watch out for is that it is quite easy to
		993	receive "spurious" readyness notifications, that is your callback might
		994	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		995	because there is no data. Not only are some backends known to create a
		996	lot of those (for example solaris ports), it is very easy to get into
		997	this situation even with a relatively standard program structure. Thus
		998	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		999	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1000
		1001	If you cannot run the fd in non-blocking mode (for example you should not
		1002	play around with an Xlib connection), then you have to seperately re-test
		1003	whether a file descriptor is really ready with a known-to-be good interface
		1004	such as poll (fortunately in our Xlib example, Xlib already does this on
		1005	its own, so its quite safe to use).
		1006
		1007	=head3 The special problem of disappearing file descriptors
		1008
		1009	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1010	descriptor (either by calling C<close> explicitly or by any other means,
		1011	such as C<dup>). The reason is that you register interest in some file
		1012	descriptor, but when it goes away, the operating system will silently drop
		1013	this interest. If another file descriptor with the same number then is
		1014	registered with libev, there is no efficient way to see that this is, in
		1015	fact, a different file descriptor.
		1016
		1017	To avoid having to explicitly tell libev about such cases, libev follows
		1018	the following policy: Each time C<ev_io_set> is being called, libev
		1019	will assume that this is potentially a new file descriptor, otherwise
		1020	it is assumed that the file descriptor stays the same. That means that
		1021	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1022	descriptor even if the file descriptor number itself did not change.
		1023
		1024	This is how one would do it normally anyway, the important point is that
		1025	the libev application should not optimise around libev but should leave
		1026	optimisations to libev.
		1027
		1028	=head3 The special problem of dup'ed file descriptors
		1029
		1030	Some backends (e.g. epoll), cannot register events for file descriptors,
		1031	but only events for the underlying file descriptions. That means when you
		1032	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1033	events for them, only one file descriptor might actually receive events.
		1034
		1035	There is no workaround possible except not registering events
		1036	for potentially C<dup ()>'ed file descriptors, or to resort to
		1037	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1038
		1039	=head3 The special problem of fork
		1040
		1041	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1042	useless behaviour. Libev fully supports fork, but needs to be told about
		1043	it in the child.
		1044
		1045	To support fork in your programs, you either have to call
		1046	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1047	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1048	C<EVBACKEND_POLL>.
		1049
		1050
		1051	=head3 Watcher-Specific Functions
502		1052
503	=over 4	1053	=over 4
504		1054
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1055	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1056
507	=item ev_io_set (ev_io *, int fd, int events)	1057	=item ev_io_set (ev_io *, int fd, int events)
508		1058
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1059	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 |	1060	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1061	C<EV_READ | EV_WRITE> to receive the given events.
		1062
		1063	=item int fd [read-only]
		1064
		1065	The file descriptor being watched.
		1066
		1067	=item int events [read-only]
		1068
		1069	The events being watched.
512		1070
513	=back	1071	=back
514		1072
		1073	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1074	readable, but only once. Since it is likely line-buffered, you could
		1075	attempt to read a whole line in the callback.
		1076
		1077	static void
		1078	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1079	{
		1080	ev_io_stop (loop, w);
		1081	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1082	}
		1083
		1084	...
		1085	struct ev_loop *loop = ev_default_init (0);
		1086	struct ev_io stdin_readable;
		1087	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1088	ev_io_start (loop, &stdin_readable);
		1089	ev_loop (loop, 0);
		1090
		1091
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1092	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1093
517	Timer watchers are simple relative timers that generate an event after a	1094	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1095	given time, and optionally repeating in regular intervals after that.
519		1096
520	The timers are based on real time, that is, if you register an event that	1097	The timers are based on real time, that is, if you register an event that
…		…
533		1110
534	The callback is guarenteed to be invoked only when its timeout has passed,	1111	The callback is guarenteed to be invoked only when its timeout has passed,
535	but if multiple timers become ready during the same loop iteration then	1112	but if multiple timers become ready during the same loop iteration then
536	order of execution is undefined.	1113	order of execution is undefined.
537		1114
		1115	=head3 Watcher-Specific Functions and Data Members
		1116
538	=over 4	1117	=over 4
539		1118
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1119	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1120
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1121	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
…		…
555	=item ev_timer_again (loop)	1134	=item ev_timer_again (loop)
556		1135
557	This will act as if the timer timed out and restart it again if it is	1136	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1137	repeating. The exact semantics are:
559		1138
		1139	If the timer is pending, its pending status is cleared.
		1140
560	If the timer is started but nonrepeating, stop it.	1141	If the timer is started but nonrepeating, stop it (as if it timed out).
561		1142
562	If the timer is repeating, either start it if necessary (with the repeat	1143	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1144	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1145
565	This sounds a bit complicated, but here is a useful and typical	1146	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	1147	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	1148	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	1149	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	1150	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	1151	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	1152	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.	1153	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1154	automatically restart it if need be.
		1155
		1156	That means you can ignore the C<after> value and C<ev_timer_start>
		1157	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1158
		1159	ev_timer_init (timer, callback, 0., 5.);
		1160	ev_timer_again (loop, timer);
		1161	...
		1162	timer->again = 17.;
		1163	ev_timer_again (loop, timer);
		1164	...
		1165	timer->again = 10.;
		1166	ev_timer_again (loop, timer);
		1167
		1168	This is more slightly efficient then stopping/starting the timer each time
		1169	you want to modify its timeout value.
		1170
		1171	=item ev_tstamp repeat [read-write]
		1172
		1173	The current C<repeat> value. Will be used each time the watcher times out
		1174	or C<ev_timer_again> is called and determines the next timeout (if any),
		1175	which is also when any modifications are taken into account.
573		1176
574	=back	1177	=back
575		1178
		1179	Example: Create a timer that fires after 60 seconds.
		1180
		1181	static void
		1182	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1183	{
		1184	.. one minute over, w is actually stopped right here
		1185	}
		1186
		1187	struct ev_timer mytimer;
		1188	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1189	ev_timer_start (loop, &mytimer);
		1190
		1191	Example: Create a timeout timer that times out after 10 seconds of
		1192	inactivity.
		1193
		1194	static void
		1195	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1196	{
		1197	.. ten seconds without any activity
		1198	}
		1199
		1200	struct ev_timer mytimer;
		1201	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1202	ev_timer_again (&mytimer); /* start timer */
		1203	ev_loop (loop, 0);
		1204
		1205	// and in some piece of code that gets executed on any "activity":
		1206	// reset the timeout to start ticking again at 10 seconds
		1207	ev_timer_again (&mytimer);
		1208
		1209
576	=head2 C<ev_periodic> - to cron or not to cron	1210	=head2 C<ev_periodic> - to cron or not to cron?
577		1211
578	Periodic watchers are also timers of a kind, but they are very versatile	1212	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1213	(and unfortunately a bit complex).
580		1214
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1215	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	1216	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	1217	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 ()	1218	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	1219	+ 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	1220	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	1221	roughly 10 seconds later).
588	again).
589		1222
590	They can also be used to implement vastly more complex timers, such as	1223	They can also be used to implement vastly more complex timers, such as
591	triggering an event on eahc midnight, local time.	1224	triggering an event on each midnight, local time or other, complicated,
		1225	rules.
592		1226
593	As with timers, the callback is guarenteed to be invoked only when the	1227	As with timers, the callback is guarenteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	1228	time (C<at>) has been passed, but if multiple periodic timers become ready
595	during the same loop iteration then order of execution is undefined.	1229	during the same loop iteration then order of execution is undefined.
596		1230
		1231	=head3 Watcher-Specific Functions and Data Members
		1232
597	=over 4	1233	=over 4
598		1234
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1235	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
600		1236
601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1237	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
…		…
603	Lots of arguments, lets sort it out... There are basically three modes of	1239	Lots of arguments, lets sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1240	operation, and we will explain them from simplest to complex:
605		1241
606	=over 4	1242	=over 4
607		1243
608	=item * absolute timer (interval = reschedule_cb = 0)	1244	=item * absolute timer (at = time, interval = reschedule_cb = 0)
609		1245
610	In this configuration the watcher triggers an event at the wallclock time	1246	In this configuration the watcher triggers an event at the wallclock time
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1247	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
612	that is, if it is to be run at January 1st 2011 then it will run when the	1248	that is, if it is to be run at January 1st 2011 then it will run when the
613	system time reaches or surpasses this time.	1249	system time reaches or surpasses this time.
614		1250
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1251	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
616		1252
617	In this mode the watcher will always be scheduled to time out at the next	1253	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	1254	C<at + N * interval> time (for some integer N, which can also be negative)
619	of any time jumps.	1255	and then repeat, regardless of any time jumps.
620		1256
621	This can be used to create timers that do not drift with respect to system	1257	This can be used to create timers that do not drift with respect to system
622	time:	1258	time:
623		1259
624	ev_periodic_set (&periodic, 0., 3600., 0);	1260	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
630		1266
631	Another way to think about it (for the mathematically inclined) is that	1267	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	1268	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	1269	time where C<time = at (mod interval)>, regardless of any time jumps.
634		1270
		1271	For numerical stability it is preferable that the C<at> value is near
		1272	C<ev_now ()> (the current time), but there is no range requirement for
		1273	this value.
		1274
635	=item * manual reschedule mode (reschedule_cb = callback)	1275	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
636		1276
637	In this mode the values for C<interval> and C<at> are both being	1277	In this mode the values for C<interval> and C<at> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	1278	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1279	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1280	current time as second argument.
641		1281
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1282	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
643	ever, or make any event loop modifications>. If you need to stop it,	1283	ever, or make any event loop modifications>. If you need to stop it,
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1284	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
645	starting a prepare watcher).	1285	starting an C<ev_prepare> watcher, which is legal).
646		1286
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1287	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
648	ev_tstamp now)>, e.g.:	1288	ev_tstamp now)>, e.g.:
649		1289
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1290	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1313	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1314	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	1315	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1316	program when the crontabs have changed).
677		1317
		1318	=item ev_tstamp offset [read-write]
		1319
		1320	When repeating, this contains the offset value, otherwise this is the
		1321	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1322
		1323	Can be modified any time, but changes only take effect when the periodic
		1324	timer fires or C<ev_periodic_again> is being called.
		1325
		1326	=item ev_tstamp interval [read-write]
		1327
		1328	The current interval value. Can be modified any time, but changes only
		1329	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1330	called.
		1331
		1332	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1333
		1334	The current reschedule callback, or C<0>, if this functionality is
		1335	switched off. Can be changed any time, but changes only take effect when
		1336	the periodic timer fires or C<ev_periodic_again> is being called.
		1337
		1338	=item ev_tstamp at [read-only]
		1339
		1340	When active, contains the absolute time that the watcher is supposed to
		1341	trigger next.
		1342
678	=back	1343	=back
679		1344
		1345	Example: Call a callback every hour, or, more precisely, whenever the
		1346	system clock is divisible by 3600. The callback invocation times have
		1347	potentially a lot of jittering, but good long-term stability.
		1348
		1349	static void
		1350	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1351	{
		1352	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1353	}
		1354
		1355	struct ev_periodic hourly_tick;
		1356	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1357	ev_periodic_start (loop, &hourly_tick);
		1358
		1359	Example: The same as above, but use a reschedule callback to do it:
		1360
		1361	#include <math.h>
		1362
		1363	static ev_tstamp
		1364	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1365	{
		1366	return fmod (now, 3600.) + 3600.;
		1367	}
		1368
		1369	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1370
		1371	Example: Call a callback every hour, starting now:
		1372
		1373	struct ev_periodic hourly_tick;
		1374	ev_periodic_init (&hourly_tick, clock_cb,
		1375	fmod (ev_now (loop), 3600.), 3600., 0);
		1376	ev_periodic_start (loop, &hourly_tick);
		1377
		1378
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1379	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1380
682	Signal watchers will trigger an event when the process receives a specific	1381	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	1382	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	1383	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1384	normal event processing, like any other event.
…		…
689	with the kernel (thus it coexists with your own signal handlers as long	1388	with the kernel (thus it coexists with your own signal handlers as long
690	as you don't register any with libev). Similarly, when the last signal	1389	as you don't register any with libev). Similarly, when the last signal
691	watcher for a signal is stopped libev will reset the signal handler to	1390	watcher for a signal is stopped libev will reset the signal handler to
692	SIG_DFL (regardless of what it was set to before).	1391	SIG_DFL (regardless of what it was set to before).
693		1392
		1393	=head3 Watcher-Specific Functions and Data Members
		1394
694	=over 4	1395	=over 4
695		1396
696	=item ev_signal_init (ev_signal *, callback, int signum)	1397	=item ev_signal_init (ev_signal *, callback, int signum)
697		1398
698	=item ev_signal_set (ev_signal *, int signum)	1399	=item ev_signal_set (ev_signal *, int signum)
699		1400
700	Configures the watcher to trigger on the given signal number (usually one	1401	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1402	of the C<SIGxxx> constants).
702		1403
		1404	=item int signum [read-only]
		1405
		1406	The signal the watcher watches out for.
		1407
703	=back	1408	=back
704		1409
		1410
705	=head2 C<ev_child> - wait for pid status changes	1411	=head2 C<ev_child> - watch out for process status changes
706		1412
707	Child watchers trigger when your process receives a SIGCHLD in response to	1413	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).	1414	some child status changes (most typically when a child of yours dies).
		1415
		1416	=head3 Watcher-Specific Functions and Data Members
709		1417
710	=over 4	1418	=over 4
711		1419
712	=item ev_child_init (ev_child *, callback, int pid)	1420	=item ev_child_init (ev_child *, callback, int pid)
713		1421
…		…
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	1426	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	1427	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	1428	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	1429	process causing the status change.
722		1430
		1431	=item int pid [read-only]
		1432
		1433	The process id this watcher watches out for, or C<0>, meaning any process id.
		1434
		1435	=item int rpid [read-write]
		1436
		1437	The process id that detected a status change.
		1438
		1439	=item int rstatus [read-write]
		1440
		1441	The process exit/trace status caused by C<rpid> (see your systems
		1442	C<waitpid> and C<sys/wait.h> documentation for details).
		1443
723	=back	1444	=back
724		1445
		1446	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1447
		1448	static void
		1449	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1450	{
		1451	ev_unloop (loop, EVUNLOOP_ALL);
		1452	}
		1453
		1454	struct ev_signal signal_watcher;
		1455	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1456	ev_signal_start (loop, &sigint_cb);
		1457
		1458
		1459	=head2 C<ev_stat> - did the file attributes just change?
		1460
		1461	This watches a filesystem path for attribute changes. That is, it calls
		1462	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1463	compared to the last time, invoking the callback if it did.
		1464
		1465	The path does not need to exist: changing from "path exists" to "path does
		1466	not exist" is a status change like any other. The condition "path does
		1467	not exist" is signified by the C<st_nlink> field being zero (which is
		1468	otherwise always forced to be at least one) and all the other fields of
		1469	the stat buffer having unspecified contents.
		1470
		1471	The path I<should> be absolute and I<must not> end in a slash. If it is
		1472	relative and your working directory changes, the behaviour is undefined.
		1473
		1474	Since there is no standard to do this, the portable implementation simply
		1475	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1476	can specify a recommended polling interval for this case. If you specify
		1477	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1478	unspecified default> value will be used (which you can expect to be around
		1479	five seconds, although this might change dynamically). Libev will also
		1480	impose a minimum interval which is currently around C<0.1>, but thats
		1481	usually overkill.
		1482
		1483	This watcher type is not meant for massive numbers of stat watchers,
		1484	as even with OS-supported change notifications, this can be
		1485	resource-intensive.
		1486
		1487	At the time of this writing, only the Linux inotify interface is
		1488	implemented (implementing kqueue support is left as an exercise for the
		1489	reader). Inotify will be used to give hints only and should not change the
		1490	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1491	to fall back to regular polling again even with inotify, but changes are
		1492	usually detected immediately, and if the file exists there will be no
		1493	polling.
		1494
		1495	=head3 Inotify
		1496
		1497	When C<inotify (7)> support has been compiled into libev (generally only
		1498	available on Linux) and present at runtime, it will be used to speed up
		1499	change detection where possible. The inotify descriptor will be created lazily
		1500	when the first C<ev_stat> watcher is being started.
		1501
		1502	Inotify presense does not change the semantics of C<ev_stat> watchers
		1503	except that changes might be detected earlier, and in some cases, to avoid
		1504	making regular C<stat> calls. Even in the presense of inotify support
		1505	there are many cases where libev has to resort to regular C<stat> polling.
		1506
		1507	(There is no support for kqueue, as apparently it cannot be used to
		1508	implement this functionality, due to the requirement of having a file
		1509	descriptor open on the object at all times).
		1510
		1511	=head3 The special problem of stat time resolution
		1512
		1513	The C<stat ()> syscall only supports full-second resolution portably, and
		1514	even on systems where the resolution is higher, many filesystems still
		1515	only support whole seconds.
		1516
		1517	That means that, if the time is the only thing that changes, you might
		1518	miss updates: on the first update, C<ev_stat> detects a change and calls
		1519	your callback, which does something. When there is another update within
		1520	the same second, C<ev_stat> will be unable to detect it.
		1521
		1522	The solution to this is to delay acting on a change for a second (or till
		1523	the next second boundary), using a roughly one-second delay C<ev_timer>
		1524	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1525	is added to work around small timing inconsistencies of some operating
		1526	systems.
		1527
		1528	=head3 Watcher-Specific Functions and Data Members
		1529
		1530	=over 4
		1531
		1532	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1533
		1534	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1535
		1536	Configures the watcher to wait for status changes of the given
		1537	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1538	be detected and should normally be specified as C<0> to let libev choose
		1539	a suitable value. The memory pointed to by C<path> must point to the same
		1540	path for as long as the watcher is active.
		1541
		1542	The callback will be receive C<EV_STAT> when a change was detected,
		1543	relative to the attributes at the time the watcher was started (or the
		1544	last change was detected).
		1545
		1546	=item ev_stat_stat (ev_stat *)
		1547
		1548	Updates the stat buffer immediately with new values. If you change the
		1549	watched path in your callback, you could call this fucntion to avoid
		1550	detecting this change (while introducing a race condition). Can also be
		1551	useful simply to find out the new values.
		1552
		1553	=item ev_statdata attr [read-only]
		1554
		1555	The most-recently detected attributes of the file. Although the type is of
		1556	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1557	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1558	was some error while C<stat>ing the file.
		1559
		1560	=item ev_statdata prev [read-only]
		1561
		1562	The previous attributes of the file. The callback gets invoked whenever
		1563	C<prev> != C<attr>.
		1564
		1565	=item ev_tstamp interval [read-only]
		1566
		1567	The specified interval.
		1568
		1569	=item const char *path [read-only]
		1570
		1571	The filesystem path that is being watched.
		1572
		1573	=back
		1574
		1575	=head3 Examples
		1576
		1577	Example: Watch C</etc/passwd> for attribute changes.
		1578
		1579	static void
		1580	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1581	{
		1582	/* /etc/passwd changed in some way */
		1583	if (w->attr.st_nlink)
		1584	{
		1585	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1586	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1587	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1588	}
		1589	else
		1590	/* you shalt not abuse printf for puts */
		1591	puts ("wow, /etc/passwd is not there, expect problems. "
		1592	"if this is windows, they already arrived\n");
		1593	}
		1594
		1595	...
		1596	ev_stat passwd;
		1597
		1598	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1599	ev_stat_start (loop, &passwd);
		1600
		1601	Example: Like above, but additionally use a one-second delay so we do not
		1602	miss updates (however, frequent updates will delay processing, too, so
		1603	one might do the work both on C<ev_stat> callback invocation I<and> on
		1604	C<ev_timer> callback invocation).
		1605
		1606	static ev_stat passwd;
		1607	static ev_timer timer;
		1608
		1609	static void
		1610	timer_cb (EV_P_ ev_timer *w, int revents)
		1611	{
		1612	ev_timer_stop (EV_A_ w);
		1613
		1614	/* now it's one second after the most recent passwd change */
		1615	}
		1616
		1617	static void
		1618	stat_cb (EV_P_ ev_stat *w, int revents)
		1619	{
		1620	/* reset the one-second timer */
		1621	ev_timer_again (EV_A_ &timer);
		1622	}
		1623
		1624	...
		1625	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1626	ev_stat_start (loop, &passwd);
		1627	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1628
		1629
725	=head2 C<ev_idle> - when you've got nothing better to do	1630	=head2 C<ev_idle> - when you've got nothing better to do...
726		1631
727	Idle watchers trigger events when there are no other events are pending	1632	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	1633	priority are pending (prepare, check and other idle watchers do not
729	as your process is busy handling sockets or timeouts (or even signals,	1634	count).
730	imagine) it will not be triggered. But when your process is idle all idle	1635
731	watchers are being called again and again, once per event loop iteration -	1636	That is, as long as your process is busy handling sockets or timeouts
		1637	(or even signals, imagine) of the same or higher priority it will not be
		1638	triggered. But when your process is idle (or only lower-priority watchers
		1639	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	1640	iteration - until stopped, that is, or your process receives more events
733	busy.	1641	and becomes busy again with higher priority stuff.
734		1642
735	The most noteworthy effect is that as long as any idle watchers are	1643	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	1644	active, the process will not block when waiting for new events.
737		1645
738	Apart from keeping your process non-blocking (which is a useful	1646	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	1647	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	1648	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	1649	event loop has handled all outstanding events.
742		1650
		1651	=head3 Watcher-Specific Functions and Data Members
		1652
743	=over 4	1653	=over 4
744		1654
745	=item ev_idle_init (ev_signal *, callback)	1655	=item ev_idle_init (ev_signal *, callback)
746		1656
747	Initialises and configures the idle watcher - it has no parameters of any	1657	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1658	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	1659	believe me.
750		1660
751	=back	1661	=back
752		1662
		1663	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1664	callback, free it. Also, use no error checking, as usual.
		1665
		1666	static void
		1667	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1668	{
		1669	free (w);
		1670	// now do something you wanted to do when the program has
		1671	// no longer asnything immediate to do.
		1672	}
		1673
		1674	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1675	ev_idle_init (idle_watcher, idle_cb);
		1676	ev_idle_start (loop, idle_cb);
		1677
		1678
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1679	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		1680
755	Prepare and check watchers are usually (but not always) used in tandem:	1681	Prepare and check watchers are usually (but not always) used in tandem:
756	prepare watchers get invoked before the process blocks and check watchers	1682	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	1683	afterwards.
758		1684
		1685	You I<must not> call C<ev_loop> or similar functions that enter
		1686	the current event loop from either C<ev_prepare> or C<ev_check>
		1687	watchers. Other loops than the current one are fine, however. The
		1688	rationale behind this is that you do not need to check for recursion in
		1689	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1690	C<ev_check> so if you have one watcher of each kind they will always be
		1691	called in pairs bracketing the blocking call.
		1692
759	Their main purpose is to integrate other event mechanisms into libev. This	1693	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	1694	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.	1695	variable changes, implement your own watchers, integrate net-snmp or a
		1696	coroutine library and lots more. They are also occasionally useful if
		1697	you cache some data and want to flush it before blocking (for example,
		1698	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1699	watcher).
762		1700
763	This is done by examining in each prepare call which file descriptors need	1701	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	1702	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	1703	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	1704	provide just this functionality). Then, in the check watcher you check for
…		…
776	with priority higher than or equal to the event loop and one coroutine	1714	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	1715	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	1716	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	1717	low-priority coroutines to idle/background tasks).
780		1718
		1719	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1720	priority, to ensure that they are being run before any other watchers
		1721	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1722	too) should not activate ("feed") events into libev. While libev fully
		1723	supports this, they will be called before other C<ev_check> watchers
		1724	did their job. As C<ev_check> watchers are often used to embed other
		1725	(non-libev) event loops those other event loops might be in an unusable
		1726	state until their C<ev_check> watcher ran (always remind yourself to
		1727	coexist peacefully with others).
		1728
		1729	=head3 Watcher-Specific Functions and Data Members
		1730
781	=over 4	1731	=over 4
782		1732
783	=item ev_prepare_init (ev_prepare *, callback)	1733	=item ev_prepare_init (ev_prepare *, callback)
784		1734
785	=item ev_check_init (ev_check *, callback)	1735	=item ev_check_init (ev_check *, callback)
…		…
787	Initialises and configures the prepare or check watcher - they have no	1737	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1738	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.	1739	macros, but using them is utterly, utterly and completely pointless.
790		1740
791	=back	1741	=back
		1742
		1743	There are a number of principal ways to embed other event loops or modules
		1744	into libev. Here are some ideas on how to include libadns into libev
		1745	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1746	use for an actually working example. Another Perl module named C<EV::Glib>
		1747	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1748	into the Glib event loop).
		1749
		1750	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1751	and in a check watcher, destroy them and call into libadns. What follows
		1752	is pseudo-code only of course. This requires you to either use a low
		1753	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1754	the callbacks for the IO/timeout watchers might not have been called yet.
		1755
		1756	static ev_io iow [nfd];
		1757	static ev_timer tw;
		1758
		1759	static void
		1760	io_cb (ev_loop *loop, ev_io *w, int revents)
		1761	{
		1762	}
		1763
		1764	// create io watchers for each fd and a timer before blocking
		1765	static void
		1766	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1767	{
		1768	int timeout = 3600000;
		1769	struct pollfd fds [nfd];
		1770	// actual code will need to loop here and realloc etc.
		1771	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1772
		1773	/* the callback is illegal, but won't be called as we stop during check */
		1774	ev_timer_init (&tw, 0, timeout * 1e-3);
		1775	ev_timer_start (loop, &tw);
		1776
		1777	// create one ev_io per pollfd
		1778	for (int i = 0; i < nfd; ++i)
		1779	{
		1780	ev_io_init (iow + i, io_cb, fds [i].fd,
		1781	((fds [i].events & POLLIN ? EV_READ : 0)
		1782	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1783
		1784	fds [i].revents = 0;
		1785	ev_io_start (loop, iow + i);
		1786	}
		1787	}
		1788
		1789	// stop all watchers after blocking
		1790	static void
		1791	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1792	{
		1793	ev_timer_stop (loop, &tw);
		1794
		1795	for (int i = 0; i < nfd; ++i)
		1796	{
		1797	// set the relevant poll flags
		1798	// could also call adns_processreadable etc. here
		1799	struct pollfd *fd = fds + i;
		1800	int revents = ev_clear_pending (iow + i);
		1801	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1802	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1803
		1804	// now stop the watcher
		1805	ev_io_stop (loop, iow + i);
		1806	}
		1807
		1808	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1809	}
		1810
		1811	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1812	in the prepare watcher and would dispose of the check watcher.
		1813
		1814	Method 3: If the module to be embedded supports explicit event
		1815	notification (adns does), you can also make use of the actual watcher
		1816	callbacks, and only destroy/create the watchers in the prepare watcher.
		1817
		1818	static void
		1819	timer_cb (EV_P_ ev_timer *w, int revents)
		1820	{
		1821	adns_state ads = (adns_state)w->data;
		1822	update_now (EV_A);
		1823
		1824	adns_processtimeouts (ads, &tv_now);
		1825	}
		1826
		1827	static void
		1828	io_cb (EV_P_ ev_io *w, int revents)
		1829	{
		1830	adns_state ads = (adns_state)w->data;
		1831	update_now (EV_A);
		1832
		1833	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1834	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1835	}
		1836
		1837	// do not ever call adns_afterpoll
		1838
		1839	Method 4: Do not use a prepare or check watcher because the module you
		1840	want to embed is too inflexible to support it. Instead, youc na override
		1841	their poll function. The drawback with this solution is that the main
		1842	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1843	this.
		1844
		1845	static gint
		1846	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1847	{
		1848	int got_events = 0;
		1849
		1850	for (n = 0; n < nfds; ++n)
		1851	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1852
		1853	if (timeout >= 0)
		1854	// create/start timer
		1855
		1856	// poll
		1857	ev_loop (EV_A_ 0);
		1858
		1859	// stop timer again
		1860	if (timeout >= 0)
		1861	ev_timer_stop (EV_A_ &to);
		1862
		1863	// stop io watchers again - their callbacks should have set
		1864	for (n = 0; n < nfds; ++n)
		1865	ev_io_stop (EV_A_ iow [n]);
		1866
		1867	return got_events;
		1868	}
		1869
		1870
		1871	=head2 C<ev_embed> - when one backend isn't enough...
		1872
		1873	This is a rather advanced watcher type that lets you embed one event loop
		1874	into another (currently only C<ev_io> events are supported in the embedded
		1875	loop, other types of watchers might be handled in a delayed or incorrect
		1876	fashion and must not be used).
		1877
		1878	There are primarily two reasons you would want that: work around bugs and
		1879	prioritise I/O.
		1880
		1881	As an example for a bug workaround, the kqueue backend might only support
		1882	sockets on some platform, so it is unusable as generic backend, but you
		1883	still want to make use of it because you have many sockets and it scales
		1884	so nicely. In this case, you would create a kqueue-based loop and embed it
		1885	into your default loop (which might use e.g. poll). Overall operation will
		1886	be a bit slower because first libev has to poll and then call kevent, but
		1887	at least you can use both at what they are best.
		1888
		1889	As for prioritising I/O: rarely you have the case where some fds have
		1890	to be watched and handled very quickly (with low latency), and even
		1891	priorities and idle watchers might have too much overhead. In this case
		1892	you would put all the high priority stuff in one loop and all the rest in
		1893	a second one, and embed the second one in the first.
		1894
		1895	As long as the watcher is active, the callback will be invoked every time
		1896	there might be events pending in the embedded loop. The callback must then
		1897	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1898	their callbacks (you could also start an idle watcher to give the embedded
		1899	loop strictly lower priority for example). You can also set the callback
		1900	to C<0>, in which case the embed watcher will automatically execute the
		1901	embedded loop sweep.
		1902
		1903	As long as the watcher is started it will automatically handle events. The
		1904	callback will be invoked whenever some events have been handled. You can
		1905	set the callback to C<0> to avoid having to specify one if you are not
		1906	interested in that.
		1907
		1908	Also, there have not currently been made special provisions for forking:
		1909	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1910	but you will also have to stop and restart any C<ev_embed> watchers
		1911	yourself.
		1912
		1913	Unfortunately, not all backends are embeddable, only the ones returned by
		1914	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1915	portable one.
		1916
		1917	So when you want to use this feature you will always have to be prepared
		1918	that you cannot get an embeddable loop. The recommended way to get around
		1919	this is to have a separate variables for your embeddable loop, try to
		1920	create it, and if that fails, use the normal loop for everything:
		1921
		1922	struct ev_loop *loop_hi = ev_default_init (0);
		1923	struct ev_loop *loop_lo = 0;
		1924	struct ev_embed embed;
		1925
		1926	// see if there is a chance of getting one that works
		1927	// (remember that a flags value of 0 means autodetection)
		1928	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1929	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1930	: 0;
		1931
		1932	// if we got one, then embed it, otherwise default to loop_hi
		1933	if (loop_lo)
		1934	{
		1935	ev_embed_init (&embed, 0, loop_lo);
		1936	ev_embed_start (loop_hi, &embed);
		1937	}
		1938	else
		1939	loop_lo = loop_hi;
		1940
		1941	=head3 Watcher-Specific Functions and Data Members
		1942
		1943	=over 4
		1944
		1945	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1946
		1947	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1948
		1949	Configures the watcher to embed the given loop, which must be
		1950	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1951	invoked automatically, otherwise it is the responsibility of the callback
		1952	to invoke it (it will continue to be called until the sweep has been done,
		1953	if you do not want thta, you need to temporarily stop the embed watcher).
		1954
		1955	=item ev_embed_sweep (loop, ev_embed *)
		1956
		1957	Make a single, non-blocking sweep over the embedded loop. This works
		1958	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1959	apropriate way for embedded loops.
		1960
		1961	=item struct ev_loop *other [read-only]
		1962
		1963	The embedded event loop.
		1964
		1965	=back
		1966
		1967
		1968	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		1969
		1970	Fork watchers are called when a C<fork ()> was detected (usually because
		1971	whoever is a good citizen cared to tell libev about it by calling
		1972	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		1973	event loop blocks next and before C<ev_check> watchers are being called,
		1974	and only in the child after the fork. If whoever good citizen calling
		1975	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		1976	handlers will be invoked, too, of course.
		1977
		1978	=head3 Watcher-Specific Functions and Data Members
		1979
		1980	=over 4
		1981
		1982	=item ev_fork_init (ev_signal *, callback)
		1983
		1984	Initialises and configures the fork watcher - it has no parameters of any
		1985	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		1986	believe me.
		1987
		1988	=back
		1989
792		1990
793	=head1 OTHER FUNCTIONS	1991	=head1 OTHER FUNCTIONS
794		1992
795	There are some other functions of possible interest. Described. Here. Now.	1993	There are some other functions of possible interest. Described. Here. Now.
796		1994
…		…
826	/* stdin might have data for us, joy! */;	2024	/* stdin might have data for us, joy! */;
827	}	2025	}
828		2026
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2027	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		2028
831	=item ev_feed_event (loop, watcher, int events)	2029	=item ev_feed_event (ev_loop *, watcher *, int revents)
832		2030
833	Feeds the given event set into the event loop, as if the specified event	2031	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	2032	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	2033	initialised but not necessarily started event watcher).
836		2034
837	=item ev_feed_fd_event (loop, int fd, int revents)	2035	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
838		2036
839	Feed an event on the given fd, as if a file descriptor backend detected	2037	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	2038	the given events it.
841		2039
842	=item ev_feed_signal_event (loop, int signum)	2040	=item ev_feed_signal_event (ev_loop *loop, int signum)
843		2041
844	Feed an event as if the given signal occured (loop must be the default loop!).	2042	Feed an event as if the given signal occured (C<loop> must be the default
		2043	loop!).
845		2044
846	=back	2045	=back
		2046
847		2047
848	=head1 LIBEVENT EMULATION	2048	=head1 LIBEVENT EMULATION
849		2049
850	Libev offers a compatibility emulation layer for libevent. It cannot	2050	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	2051	emulate the internals of libevent, so here are some usage hints:
…		…
872		2072
873	=back	2073	=back
874		2074
875	=head1 C++ SUPPORT	2075	=head1 C++ SUPPORT
876		2076
877	TBD.	2077	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2078	you to use some convinience methods to start/stop watchers and also change
		2079	the callback model to a model using method callbacks on objects.
		2080
		2081	To use it,
		2082
		2083	#include <ev++.h>
		2084
		2085	This automatically includes F<ev.h> and puts all of its definitions (many
		2086	of them macros) into the global namespace. All C++ specific things are
		2087	put into the C<ev> namespace. It should support all the same embedding
		2088	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2089
		2090	Care has been taken to keep the overhead low. The only data member the C++
		2091	classes add (compared to plain C-style watchers) is the event loop pointer
		2092	that the watcher is associated with (or no additional members at all if
		2093	you disable C<EV_MULTIPLICITY> when embedding libev).
		2094
		2095	Currently, functions, and static and non-static member functions can be
		2096	used as callbacks. Other types should be easy to add as long as they only
		2097	need one additional pointer for context. If you need support for other
		2098	types of functors please contact the author (preferably after implementing
		2099	it).
		2100
		2101	Here is a list of things available in the C<ev> namespace:
		2102
		2103	=over 4
		2104
		2105	=item C<ev::READ>, C<ev::WRITE> etc.
		2106
		2107	These are just enum values with the same values as the C<EV_READ> etc.
		2108	macros from F<ev.h>.
		2109
		2110	=item C<ev::tstamp>, C<ev::now>
		2111
		2112	Aliases to the same types/functions as with the C<ev_> prefix.
		2113
		2114	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2115
		2116	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2117	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2118	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2119	defines by many implementations.
		2120
		2121	All of those classes have these methods:
		2122
		2123	=over 4
		2124
		2125	=item ev::TYPE::TYPE ()
		2126
		2127	=item ev::TYPE::TYPE (struct ev_loop *)
		2128
		2129	=item ev::TYPE::~TYPE
		2130
		2131	The constructor (optionally) takes an event loop to associate the watcher
		2132	with. If it is omitted, it will use C<EV_DEFAULT>.
		2133
		2134	The constructor calls C<ev_init> for you, which means you have to call the
		2135	C<set> method before starting it.
		2136
		2137	It will not set a callback, however: You have to call the templated C<set>
		2138	method to set a callback before you can start the watcher.
		2139
		2140	(The reason why you have to use a method is a limitation in C++ which does
		2141	not allow explicit template arguments for constructors).
		2142
		2143	The destructor automatically stops the watcher if it is active.
		2144
		2145	=item w->set<class, &class::method> (object *)
		2146
		2147	This method sets the callback method to call. The method has to have a
		2148	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2149	first argument and the C<revents> as second. The object must be given as
		2150	parameter and is stored in the C<data> member of the watcher.
		2151
		2152	This method synthesizes efficient thunking code to call your method from
		2153	the C callback that libev requires. If your compiler can inline your
		2154	callback (i.e. it is visible to it at the place of the C<set> call and
		2155	your compiler is good :), then the method will be fully inlined into the
		2156	thunking function, making it as fast as a direct C callback.
		2157
		2158	Example: simple class declaration and watcher initialisation
		2159
		2160	struct myclass
		2161	{
		2162	void io_cb (ev::io &w, int revents) { }
		2163	}
		2164
		2165	myclass obj;
		2166	ev::io iow;
		2167	iow.set <myclass, &myclass::io_cb> (&obj);
		2168
		2169	=item w->set<function> (void *data = 0)
		2170
		2171	Also sets a callback, but uses a static method or plain function as
		2172	callback. The optional C<data> argument will be stored in the watcher's
		2173	C<data> member and is free for you to use.
		2174
		2175	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2176
		2177	See the method-C<set> above for more details.
		2178
		2179	Example:
		2180
		2181	static void io_cb (ev::io &w, int revents) { }
		2182	iow.set <io_cb> ();
		2183
		2184	=item w->set (struct ev_loop *)
		2185
		2186	Associates a different C<struct ev_loop> with this watcher. You can only
		2187	do this when the watcher is inactive (and not pending either).
		2188
		2189	=item w->set ([args])
		2190
		2191	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2192	called at least once. Unlike the C counterpart, an active watcher gets
		2193	automatically stopped and restarted when reconfiguring it with this
		2194	method.
		2195
		2196	=item w->start ()
		2197
		2198	Starts the watcher. Note that there is no C<loop> argument, as the
		2199	constructor already stores the event loop.
		2200
		2201	=item w->stop ()
		2202
		2203	Stops the watcher if it is active. Again, no C<loop> argument.
		2204
		2205	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2206
		2207	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2208	C<ev_TYPE_again> function.
		2209
		2210	=item w->sweep () (C<ev::embed> only)
		2211
		2212	Invokes C<ev_embed_sweep>.
		2213
		2214	=item w->update () (C<ev::stat> only)
		2215
		2216	Invokes C<ev_stat_stat>.
		2217
		2218	=back
		2219
		2220	=back
		2221
		2222	Example: Define a class with an IO and idle watcher, start one of them in
		2223	the constructor.
		2224
		2225	class myclass
		2226	{
		2227	ev_io io; void io_cb (ev::io &w, int revents);
		2228	ev_idle idle void idle_cb (ev::idle &w, int revents);
		2229
		2230	myclass ();
		2231	}
		2232
		2233	myclass::myclass (int fd)
		2234	{
		2235	io .set <myclass, &myclass::io_cb > (this);
		2236	idle.set <myclass, &myclass::idle_cb> (this);
		2237
		2238	io.start (fd, ev::READ);
		2239	}
		2240
		2241
		2242	=head1 MACRO MAGIC
		2243
		2244	Libev can be compiled with a variety of options, the most fundamantal
		2245	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2246	functions and callbacks have an initial C<struct ev_loop *> argument.
		2247
		2248	To make it easier to write programs that cope with either variant, the
		2249	following macros are defined:
		2250
		2251	=over 4
		2252
		2253	=item C<EV_A>, C<EV_A_>
		2254
		2255	This provides the loop I<argument> for functions, if one is required ("ev
		2256	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2257	C<EV_A_> is used when other arguments are following. Example:
		2258
		2259	ev_unref (EV_A);
		2260	ev_timer_add (EV_A_ watcher);
		2261	ev_loop (EV_A_ 0);
		2262
		2263	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2264	which is often provided by the following macro.
		2265
		2266	=item C<EV_P>, C<EV_P_>
		2267
		2268	This provides the loop I<parameter> for functions, if one is required ("ev
		2269	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2270	C<EV_P_> is used when other parameters are following. Example:
		2271
		2272	// this is how ev_unref is being declared
		2273	static void ev_unref (EV_P);
		2274
		2275	// this is how you can declare your typical callback
		2276	static void cb (EV_P_ ev_timer *w, int revents)
		2277
		2278	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2279	suitable for use with C<EV_A>.
		2280
		2281	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2282
		2283	Similar to the other two macros, this gives you the value of the default
		2284	loop, if multiple loops are supported ("ev loop default").
		2285
		2286	=back
		2287
		2288	Example: Declare and initialise a check watcher, utilising the above
		2289	macros so it will work regardless of whether multiple loops are supported
		2290	or not.
		2291
		2292	static void
		2293	check_cb (EV_P_ ev_timer *w, int revents)
		2294	{
		2295	ev_check_stop (EV_A_ w);
		2296	}
		2297
		2298	ev_check check;
		2299	ev_check_init (&check, check_cb);
		2300	ev_check_start (EV_DEFAULT_ &check);
		2301	ev_loop (EV_DEFAULT_ 0);
		2302
		2303	=head1 EMBEDDING
		2304
		2305	Libev can (and often is) directly embedded into host
		2306	applications. Examples of applications that embed it include the Deliantra
		2307	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2308	and rxvt-unicode.
		2309
		2310	The goal is to enable you to just copy the necessary files into your
		2311	source directory without having to change even a single line in them, so
		2312	you can easily upgrade by simply copying (or having a checked-out copy of
		2313	libev somewhere in your source tree).
		2314
		2315	=head2 FILESETS
		2316
		2317	Depending on what features you need you need to include one or more sets of files
		2318	in your app.
		2319
		2320	=head3 CORE EVENT LOOP
		2321
		2322	To include only the libev core (all the C<ev_*> functions), with manual
		2323	configuration (no autoconf):
		2324
		2325	#define EV_STANDALONE 1
		2326	#include "ev.c"
		2327
		2328	This will automatically include F<ev.h>, too, and should be done in a
		2329	single C source file only to provide the function implementations. To use
		2330	it, do the same for F<ev.h> in all files wishing to use this API (best
		2331	done by writing a wrapper around F<ev.h> that you can include instead and
		2332	where you can put other configuration options):
		2333
		2334	#define EV_STANDALONE 1
		2335	#include "ev.h"
		2336
		2337	Both header files and implementation files can be compiled with a C++
		2338	compiler (at least, thats a stated goal, and breakage will be treated
		2339	as a bug).
		2340
		2341	You need the following files in your source tree, or in a directory
		2342	in your include path (e.g. in libev/ when using -Ilibev):
		2343
		2344	ev.h
		2345	ev.c
		2346	ev_vars.h
		2347	ev_wrap.h
		2348
		2349	ev_win32.c required on win32 platforms only
		2350
		2351	ev_select.c only when select backend is enabled (which is enabled by default)
		2352	ev_poll.c only when poll backend is enabled (disabled by default)
		2353	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2354	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2355	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2356
		2357	F<ev.c> includes the backend files directly when enabled, so you only need
		2358	to compile this single file.
		2359
		2360	=head3 LIBEVENT COMPATIBILITY API
		2361
		2362	To include the libevent compatibility API, also include:
		2363
		2364	#include "event.c"
		2365
		2366	in the file including F<ev.c>, and:
		2367
		2368	#include "event.h"
		2369
		2370	in the files that want to use the libevent API. This also includes F<ev.h>.
		2371
		2372	You need the following additional files for this:
		2373
		2374	event.h
		2375	event.c
		2376
		2377	=head3 AUTOCONF SUPPORT
		2378
		2379	Instead of using C<EV_STANDALONE=1> and providing your config in
		2380	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2381	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2382	include F<config.h> and configure itself accordingly.
		2383
		2384	For this of course you need the m4 file:
		2385
		2386	libev.m4
		2387
		2388	=head2 PREPROCESSOR SYMBOLS/MACROS
		2389
		2390	Libev can be configured via a variety of preprocessor symbols you have to define
		2391	before including any of its files. The default is not to build for multiplicity
		2392	and only include the select backend.
		2393
		2394	=over 4
		2395
		2396	=item EV_STANDALONE
		2397
		2398	Must always be C<1> if you do not use autoconf configuration, which
		2399	keeps libev from including F<config.h>, and it also defines dummy
		2400	implementations for some libevent functions (such as logging, which is not
		2401	supported). It will also not define any of the structs usually found in
		2402	F<event.h> that are not directly supported by the libev core alone.
		2403
		2404	=item EV_USE_MONOTONIC
		2405
		2406	If defined to be C<1>, libev will try to detect the availability of the
		2407	monotonic clock option at both compiletime and runtime. Otherwise no use
		2408	of the monotonic clock option will be attempted. If you enable this, you
		2409	usually have to link against librt or something similar. Enabling it when
		2410	the functionality isn't available is safe, though, although you have
		2411	to make sure you link against any libraries where the C<clock_gettime>
		2412	function is hiding in (often F<-lrt>).
		2413
		2414	=item EV_USE_REALTIME
		2415
		2416	If defined to be C<1>, libev will try to detect the availability of the
		2417	realtime clock option at compiletime (and assume its availability at
		2418	runtime if successful). Otherwise no use of the realtime clock option will
		2419	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2420	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2421	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2422
		2423	=item EV_USE_NANOSLEEP
		2424
		2425	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2426	and will use it for delays. Otherwise it will use C<select ()>.
		2427
		2428	=item EV_USE_SELECT
		2429
		2430	If undefined or defined to be C<1>, libev will compile in support for the
		2431	C<select>(2) backend. No attempt at autodetection will be done: if no
		2432	other method takes over, select will be it. Otherwise the select backend
		2433	will not be compiled in.
		2434
		2435	=item EV_SELECT_USE_FD_SET
		2436
		2437	If defined to C<1>, then the select backend will use the system C<fd_set>
		2438	structure. This is useful if libev doesn't compile due to a missing
		2439	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2440	exotic systems. This usually limits the range of file descriptors to some
		2441	low limit such as 1024 or might have other limitations (winsocket only
		2442	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2443	influence the size of the C<fd_set> used.
		2444
		2445	=item EV_SELECT_IS_WINSOCKET
		2446
		2447	When defined to C<1>, the select backend will assume that
		2448	select/socket/connect etc. don't understand file descriptors but
		2449	wants osf handles on win32 (this is the case when the select to
		2450	be used is the winsock select). This means that it will call
		2451	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2452	it is assumed that all these functions actually work on fds, even
		2453	on win32. Should not be defined on non-win32 platforms.
		2454
		2455	=item EV_USE_POLL
		2456
		2457	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2458	backend. Otherwise it will be enabled on non-win32 platforms. It
		2459	takes precedence over select.
		2460
		2461	=item EV_USE_EPOLL
		2462
		2463	If defined to be C<1>, libev will compile in support for the Linux
		2464	C<epoll>(7) backend. Its availability will be detected at runtime,
		2465	otherwise another method will be used as fallback. This is the
		2466	preferred backend for GNU/Linux systems.
		2467
		2468	=item EV_USE_KQUEUE
		2469
		2470	If defined to be C<1>, libev will compile in support for the BSD style
		2471	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2472	otherwise another method will be used as fallback. This is the preferred
		2473	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2474	supports some types of fds correctly (the only platform we found that
		2475	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2476	not be used unless explicitly requested. The best way to use it is to find
		2477	out whether kqueue supports your type of fd properly and use an embedded
		2478	kqueue loop.
		2479
		2480	=item EV_USE_PORT
		2481
		2482	If defined to be C<1>, libev will compile in support for the Solaris
		2483	10 port style backend. Its availability will be detected at runtime,
		2484	otherwise another method will be used as fallback. This is the preferred
		2485	backend for Solaris 10 systems.
		2486
		2487	=item EV_USE_DEVPOLL
		2488
		2489	reserved for future expansion, works like the USE symbols above.
		2490
		2491	=item EV_USE_INOTIFY
		2492
		2493	If defined to be C<1>, libev will compile in support for the Linux inotify
		2494	interface to speed up C<ev_stat> watchers. Its actual availability will
		2495	be detected at runtime.
		2496
		2497	=item EV_H
		2498
		2499	The name of the F<ev.h> header file used to include it. The default if
		2500	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
		2501	can be used to virtually rename the F<ev.h> header file in case of conflicts.
		2502
		2503	=item EV_CONFIG_H
		2504
		2505	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2506	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2507	C<EV_H>, above.
		2508
		2509	=item EV_EVENT_H
		2510
		2511	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2512	of how the F<event.h> header can be found.
		2513
		2514	=item EV_PROTOTYPES
		2515
		2516	If defined to be C<0>, then F<ev.h> will not define any function
		2517	prototypes, but still define all the structs and other symbols. This is
		2518	occasionally useful if you want to provide your own wrapper functions
		2519	around libev functions.
		2520
		2521	=item EV_MULTIPLICITY
		2522
		2523	If undefined or defined to C<1>, then all event-loop-specific functions
		2524	will have the C<struct ev_loop *> as first argument, and you can create
		2525	additional independent event loops. Otherwise there will be no support
		2526	for multiple event loops and there is no first event loop pointer
		2527	argument. Instead, all functions act on the single default loop.
		2528
		2529	=item EV_MINPRI
		2530
		2531	=item EV_MAXPRI
		2532
		2533	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2534	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2535	provide for more priorities by overriding those symbols (usually defined
		2536	to be C<-2> and C<2>, respectively).
		2537
		2538	When doing priority-based operations, libev usually has to linearly search
		2539	all the priorities, so having many of them (hundreds) uses a lot of space
		2540	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2541	fine.
		2542
		2543	If your embedding app does not need any priorities, defining these both to
		2544	C<0> will save some memory and cpu.
		2545
		2546	=item EV_PERIODIC_ENABLE
		2547
		2548	If undefined or defined to be C<1>, then periodic timers are supported. If
		2549	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2550	code.
		2551
		2552	=item EV_IDLE_ENABLE
		2553
		2554	If undefined or defined to be C<1>, then idle watchers are supported. If
		2555	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2556	code.
		2557
		2558	=item EV_EMBED_ENABLE
		2559
		2560	If undefined or defined to be C<1>, then embed watchers are supported. If
		2561	defined to be C<0>, then they are not.
		2562
		2563	=item EV_STAT_ENABLE
		2564
		2565	If undefined or defined to be C<1>, then stat watchers are supported. If
		2566	defined to be C<0>, then they are not.
		2567
		2568	=item EV_FORK_ENABLE
		2569
		2570	If undefined or defined to be C<1>, then fork watchers are supported. If
		2571	defined to be C<0>, then they are not.
		2572
		2573	=item EV_MINIMAL
		2574
		2575	If you need to shave off some kilobytes of code at the expense of some
		2576	speed, define this symbol to C<1>. Currently only used for gcc to override
		2577	some inlining decisions, saves roughly 30% codesize of amd64.
		2578
		2579	=item EV_PID_HASHSIZE
		2580
		2581	C<ev_child> watchers use a small hash table to distribute workload by
		2582	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2583	than enough. If you need to manage thousands of children you might want to
		2584	increase this value (I<must> be a power of two).
		2585
		2586	=item EV_INOTIFY_HASHSIZE
		2587
		2588	C<ev_stat> watchers use a small hash table to distribute workload by
		2589	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2590	usually more than enough. If you need to manage thousands of C<ev_stat>
		2591	watchers you might want to increase this value (I<must> be a power of
		2592	two).
		2593
		2594	=item EV_COMMON
		2595
		2596	By default, all watchers have a C<void *data> member. By redefining
		2597	this macro to a something else you can include more and other types of
		2598	members. You have to define it each time you include one of the files,
		2599	though, and it must be identical each time.
		2600
		2601	For example, the perl EV module uses something like this:
		2602
		2603	#define EV_COMMON \
		2604	SV *self; /* contains this struct */ \
		2605	SV *cb_sv, *fh /* note no trailing ";" */
		2606
		2607	=item EV_CB_DECLARE (type)
		2608
		2609	=item EV_CB_INVOKE (watcher, revents)
		2610
		2611	=item ev_set_cb (ev, cb)
		2612
		2613	Can be used to change the callback member declaration in each watcher,
		2614	and the way callbacks are invoked and set. Must expand to a struct member
		2615	definition and a statement, respectively. See the F<ev.h> header file for
		2616	their default definitions. One possible use for overriding these is to
		2617	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2618	method calls instead of plain function calls in C++.
		2619
		2620	=head2 EXPORTED API SYMBOLS
		2621
		2622	If you need to re-export the API (e.g. via a dll) and you need a list of
		2623	exported symbols, you can use the provided F<Symbol.*> files which list
		2624	all public symbols, one per line:
		2625
		2626	Symbols.ev for libev proper
		2627	Symbols.event for the libevent emulation
		2628
		2629	This can also be used to rename all public symbols to avoid clashes with
		2630	multiple versions of libev linked together (which is obviously bad in
		2631	itself, but sometimes it is inconvinient to avoid this).
		2632
		2633	A sed command like this will create wrapper C<#define>'s that you need to
		2634	include before including F<ev.h>:
		2635
		2636	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2637
		2638	This would create a file F<wrap.h> which essentially looks like this:
		2639
		2640	#define ev_backend myprefix_ev_backend
		2641	#define ev_check_start myprefix_ev_check_start
		2642	#define ev_check_stop myprefix_ev_check_stop
		2643	...
		2644
		2645	=head2 EXAMPLES
		2646
		2647	For a real-world example of a program the includes libev
		2648	verbatim, you can have a look at the EV perl module
		2649	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2650	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2651	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2652	will be compiled. It is pretty complex because it provides its own header
		2653	file.
		2654
		2655	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2656	that everybody includes and which overrides some configure choices:
		2657
		2658	#define EV_MINIMAL 1
		2659	#define EV_USE_POLL 0
		2660	#define EV_MULTIPLICITY 0
		2661	#define EV_PERIODIC_ENABLE 0
		2662	#define EV_STAT_ENABLE 0
		2663	#define EV_FORK_ENABLE 0
		2664	#define EV_CONFIG_H <config.h>
		2665	#define EV_MINPRI 0
		2666	#define EV_MAXPRI 0
		2667
		2668	#include "ev++.h"
		2669
		2670	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2671
		2672	#include "ev_cpp.h"
		2673	#include "ev.c"
		2674
		2675
		2676	=head1 COMPLEXITIES
		2677
		2678	In this section the complexities of (many of) the algorithms used inside
		2679	libev will be explained. For complexity discussions about backends see the
		2680	documentation for C<ev_default_init>.
		2681
		2682	All of the following are about amortised time: If an array needs to be
		2683	extended, libev needs to realloc and move the whole array, but this
		2684	happens asymptotically never with higher number of elements, so O(1) might
		2685	mean it might do a lengthy realloc operation in rare cases, but on average
		2686	it is much faster and asymptotically approaches constant time.
		2687
		2688	=over 4
		2689
		2690	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2691
		2692	This means that, when you have a watcher that triggers in one hour and
		2693	there are 100 watchers that would trigger before that then inserting will
		2694	have to skip roughly seven (C<ld 100>) of these watchers.
		2695
		2696	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2697
		2698	That means that changing a timer costs less than removing/adding them
		2699	as only the relative motion in the event queue has to be paid for.
		2700
		2701	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2702
		2703	These just add the watcher into an array or at the head of a list.
		2704
		2705	=item Stopping check/prepare/idle watchers: O(1)
		2706
		2707	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2708
		2709	These watchers are stored in lists then need to be walked to find the
		2710	correct watcher to remove. The lists are usually short (you don't usually
		2711	have many watchers waiting for the same fd or signal).
		2712
		2713	=item Finding the next timer in each loop iteration: O(1)
		2714
		2715	By virtue of using a binary heap, the next timer is always found at the
		2716	beginning of the storage array.
		2717
		2718	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2719
		2720	A change means an I/O watcher gets started or stopped, which requires
		2721	libev to recalculate its status (and possibly tell the kernel, depending
		2722	on backend and wether C<ev_io_set> was used).
		2723
		2724	=item Activating one watcher (putting it into the pending state): O(1)
		2725
		2726	=item Priority handling: O(number_of_priorities)
		2727
		2728	Priorities are implemented by allocating some space for each
		2729	priority. When doing priority-based operations, libev usually has to
		2730	linearly search all the priorities, but starting/stopping and activating
		2731	watchers becomes O(1) w.r.t. prioritiy handling.
		2732
		2733	=back
		2734
878		2735
879	=head1 AUTHOR	2736	=head1 AUTHOR
880		2737
881	Marc Lehmann <libev@schmorp.de>.	2738	Marc Lehmann <libev@schmorp.de>.
882		2739

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