ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.14 by root, Mon Nov 12 08:45:49 2007 UTC vs.
Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC

…		…
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 AND OTHER GLOBAL FUNCTIONS	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.
		106
		107	=head1 GLOBAL FUNCTIONS
		108
		109	These functions can be called anytime, even before initialising the
		110	library in any way.
51		111
52	=over 4	112	=over 4
53		113
54	=item ev_tstamp ev_time ()	114	=item ev_tstamp ev_time ()
55		115
56	Returns the current time as libev would use it.	116	Returns the current time as libev would use it. Please note that the
		117	C<ev_now> function is usually faster and also often returns the timestamp
		118	you actually want to know.
		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 ()>.
57		125
58	=item int ev_version_major ()	126	=item int ev_version_major ()
59		127
60	=item int ev_version_minor ()	128	=item int ev_version_minor ()
61		129
62	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
63	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
64	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
65	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
66	version of the library your program was compiled against.	134	version of the library your program was compiled against.
67		135
		136	These version numbers refer to the ABI version of the library, not the
		137	release version.
		138
68	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,
69	as this indicates an incompatible change. Minor versions are usually	140	as this indicates an incompatible change. Minor versions are usually
70	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
71	not a problem.	142	not a problem.
72		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
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		184
75	Sets the allocation function to use (the prototype is similar to the	185	Sets the allocation function to use (the prototype is similar - the
76	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
77	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
78	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
79	destructive action. The default is your system realloc function.	189	potentially destructive action. The default is your system realloc
		190	function.
80		191
81	You could override this function in high-availability programs to, say,	192	You could override this function in high-availability programs to, say,
82	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,
83	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);
84		215
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	216	=item ev_set_syserr_cb (void (*cb)(const char *msg));
86		217
87	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
88	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
…		…
90	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
91	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
92	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
93	(such as abort).	224	(such as abort).
94		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
95	=back	238	=back
96		239
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		241
99	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
100	types of such loops, the I<default> loop, which supports signals and child	243	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	244	events, and dynamically created loops which do not.
102		245
103	If you use threads, a common model is to run the default event loop	246	If you use threads, a common model is to run the default event loop
104	in your main thread (or in a separate thrad) and for each thread you	247	in your main thread (or in a separate thread) and for each thread you
105	create, you also create another event loop. Libev itself does no locking	248	create, you also create another event loop. Libev itself does no locking
106	whatsoever, so if you mix calls to the same event loop in different	249	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if	250	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).	251	done correctly, because it's hideous and inefficient).
109		252
…		…
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	255	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		256
114	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
115	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
116	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
117	flags).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		261
119	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
120	function.	263	function.
121		264
		265	The default loop is the only loop that can handle C<ev_signal> and
		266	C<ev_child> watchers, and to do this, it always registers a handler
		267	for C<SIGCHLD>. If this is a problem for your app you can either
		268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		270	C<ev_default_init>.
		271
122	The flags argument can be used to specify special behaviour or specific	272	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	273	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		274
125	It supports the following flags:	275	The following flags are supported:
126		276
127	=over 4	277	=over 4
128		278
129	=item C<EVFLAG_AUTO>	279	=item C<EVFLAG_AUTO>
130		280
…		…
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	289	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	290	useful to try out specific backends to test their performance, or to work
141	around bugs.	291	around bugs.
142		292
		293	=item C<EVFLAG_FORKCHECK>
		294
		295	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		296	a fork, you can also make libev check for a fork in each iteration by
		297	enabling this flag.
		298
		299	This works by calling C<getpid ()> on every iteration of the loop,
		300	and thus this might slow down your event loop if you do a lot of loop
		301	iterations and little real work, but is usually not noticeable (on my
		302	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		303	without a syscall and thus I<very> fast, but my Linux system also has
		304	C<pthread_atfork> which is even faster).
		305
		306	The big advantage of this flag is that you can forget about fork (and
		307	forget about forgetting to tell libev about forking) when you use this
		308	flag.
		309
		310	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		311	environment variable.
		312
143	=item C<EVMETHOD_SELECT> (portable select backend)	313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		314
		315	This is your standard select(2) backend. Not I<completely> standard, as
		316	libev tries to roll its own fd_set with no limits on the number of fds,
		317	but if that fails, expect a fairly low limit on the number of fds when
		318	using this backend. It doesn't scale too well (O(highest_fd)), but its
		319	usually the fastest backend for a low number of (low-numbered :) fds.
		320
		321	To get good performance out of this backend you need a high amount of
		322	parallelity (most of the file descriptors should be busy). If you are
		323	writing a server, you should C<accept ()> in a loop to accept as many
		324	connections as possible during one iteration. You might also want to have
		325	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		326	readyness notifications you get per iteration.
		327
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		329
147	=item C<EVMETHOD_EPOLL> (linux only)	330	And this is your standard poll(2) backend. It's more complicated
		331	than select, but handles sparse fds better and has no artificial
		332	limit on the number of fds you can use (except it will slow down
		333	considerably with a lot of inactive fds). It scales similarly to select,
		334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		335	performance tips.
148		336
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	337	=item C<EVBACKEND_EPOLL> (value 4, Linux)
150		338
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	339	For few fds, this backend is a bit little slower than poll and select,
		340	but it scales phenomenally better. While poll and select usually scale
		341	like O(total_fds) where n is the total number of fds (or the highest fd),
		342	epoll scales either O(1) or O(active_fds). The epoll design has a number
		343	of shortcomings, such as silently dropping events in some hard-to-detect
		344	cases and rewiring a syscall per fd change, no fork support and bad
		345	support for dup.
152		346
153	=item C<EVMETHOD_PORT> (solaris 10 only)	347	While stopping, setting and starting an I/O watcher in the same iteration
		348	will result in some caching, there is still a syscall per such incident
		349	(because the fd could point to a different file description now), so its
		350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		351	very well if you register events for both fds.
		352
		353	Please note that epoll sometimes generates spurious notifications, so you
		354	need to use non-blocking I/O or other means to avoid blocking when no data
		355	(or space) is available.
		356
		357	Best performance from this backend is achieved by not unregistering all
		358	watchers for a file descriptor until it has been closed, if possible, i.e.
		359	keep at least one watcher active per fd at all times.
		360
		361	While nominally embeddeble in other event loops, this feature is broken in
		362	all kernel versions tested so far.
		363
		364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		365
		366	Kqueue deserves special mention, as at the time of this writing, it
		367	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		368	with anything but sockets and pipes, except on Darwin, where of course
		369	it's completely useless). For this reason it's not being "autodetected"
		370	unless you explicitly specify it explicitly in the flags (i.e. using
		371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		372	system like NetBSD.
		373
		374	You still can embed kqueue into a normal poll or select backend and use it
		375	only for sockets (after having made sure that sockets work with kqueue on
		376	the target platform). See C<ev_embed> watchers for more info.
		377
		378	It scales in the same way as the epoll backend, but the interface to the
		379	kernel is more efficient (which says nothing about its actual speed, of
		380	course). While stopping, setting and starting an I/O watcher does never
		381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		382	two event changes per incident, support for C<fork ()> is very bad and it
		383	drops fds silently in similarly hard-to-detect cases.
		384
		385	This backend usually performs well under most conditions.
		386
		387	While nominally embeddable in other event loops, this doesn't work
		388	everywhere, so you might need to test for this. And since it is broken
		389	almost everywhere, you should only use it when you have a lot of sockets
		390	(for which it usually works), by embedding it into another event loop
		391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		392	sockets.
		393
		394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		395
		396	This is not implemented yet (and might never be, unless you send me an
		397	implementation). According to reports, C</dev/poll> only supports sockets
		398	and is not embeddable, which would limit the usefulness of this backend
		399	immensely.
		400
		401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		402
		403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		404	it's really slow, but it still scales very well (O(active_fds)).
		405
		406	Please note that solaris event ports can deliver a lot of spurious
		407	notifications, so you need to use non-blocking I/O or other means to avoid
		408	blocking when no data (or space) is available.
		409
		410	While this backend scales well, it requires one system call per active
		411	file descriptor per loop iteration. For small and medium numbers of file
		412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		413	might perform better.
		414
		415	On the positive side, ignoring the spurious readyness notifications, this
		416	backend actually performed to specification in all tests and is fully
		417	embeddable, which is a rare feat among the OS-specific backends.
		418
		419	=item C<EVBACKEND_ALL>
		420
		421	Try all backends (even potentially broken ones that wouldn't be tried
		422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		424
		425	It is definitely not recommended to use this flag.
		426
		427	=back
154		428
155	If one or more of these are ored into the flags value, then only these	429	If one or more of these are ored into the flags value, then only these
156	backends will be tried (in the reverse order as given here). If one are	430	backends will be tried (in the reverse order as listed here). If none are
157	specified, any backend will do.	431	specified, all backends in C<ev_recommended_backends ()> will be tried.
158		432
159	=back	433	The most typical usage is like this:
		434
		435	if (!ev_default_loop (0))
		436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		437
		438	Restrict libev to the select and poll backends, and do not allow
		439	environment settings to be taken into account:
		440
		441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		442
		443	Use whatever libev has to offer, but make sure that kqueue is used if
		444	available (warning, breaks stuff, best use only with your own private
		445	event loop and only if you know the OS supports your types of fds):
		446
		447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		448
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	449	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		450
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	451	Similar to C<ev_default_loop>, but always creates a new event loop that is
164	always distinct from the default loop. Unlike the default loop, it cannot	452	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by	453	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).	454	undefined behaviour (or a failed assertion if assertions are enabled).
167		455
		456	Example: Try to create a event loop that uses epoll and nothing else.
		457
		458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		459	if (!epoller)
		460	fatal ("no epoll found here, maybe it hides under your chair");
		461
168	=item ev_default_destroy ()	462	=item ev_default_destroy ()
169		463
170	Destroys the default loop again (frees all memory and kernel state	464	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	465	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cannot rely on this :).	466	sense, so e.g. C<ev_is_active> might still return true. It is your
		467	responsibility to either stop all watchers cleanly yoursef I<before>
		468	calling this function, or cope with the fact afterwards (which is usually
		469	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		470	for example).
		471
		472	Note that certain global state, such as signal state, will not be freed by
		473	this function, and related watchers (such as signal and child watchers)
		474	would need to be stopped manually.
		475
		476	In general it is not advisable to call this function except in the
		477	rare occasion where you really need to free e.g. the signal handling
		478	pipe fds. If you need dynamically allocated loops it is better to use
		479	C<ev_loop_new> and C<ev_loop_destroy>).
173		480
174	=item ev_loop_destroy (loop)	481	=item ev_loop_destroy (loop)
175		482
176	Like C<ev_default_destroy>, but destroys an event loop created by an	483	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	484	earlier call to C<ev_loop_new>.
178		485
179	=item ev_default_fork ()	486	=item ev_default_fork ()
180		487
		488	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	489	to reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	490	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	491	the child process (or both child and parent, but that again makes little
184	again makes little sense).	492	sense). You I<must> call it in the child before using any of the libev
		493	functions, and it will only take effect at the next C<ev_loop> iteration.
185		494
186	You I<must> call this function after forking if and only if you want to	495	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	496	process if and only if you want to use the event library in the child. If
188	have to call it.	497	you just fork+exec, you don't have to call it at all.
189		498
190	The function itself is quite fast and it's usually not a problem to call	499	The function itself is quite fast and it's usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in	500	it just in case after a fork. To make this easy, the function will fit in
192	quite nicely into a call to C<pthread_atfork>:	501	quite nicely into a call to C<pthread_atfork>:
193		502
…		…
197		506
198	Like C<ev_default_fork>, but acts on an event loop created by	507	Like C<ev_default_fork>, but acts on an event loop created by
199	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
200	after fork, and how you do this is entirely your own problem.	509	after fork, and how you do this is entirely your own problem.
201		510
		511	=item unsigned int ev_loop_count (loop)
		512
		513	Returns the count of loop iterations for the loop, which is identical to
		514	the number of times libev did poll for new events. It starts at C<0> and
		515	happily wraps around with enough iterations.
		516
		517	This value can sometimes be useful as a generation counter of sorts (it
		518	"ticks" the number of loop iterations), as it roughly corresponds with
		519	C<ev_prepare> and C<ev_check> calls.
		520
202	=item unsigned int ev_method (loop)	521	=item unsigned int ev_backend (loop)
203		522
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	524	use.
206		525
207	=item ev_tstamp ev_now (loop)	526	=item ev_tstamp ev_now (loop)
208		527
209	Returns the current "event loop time", which is the time the event loop	528	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	529	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	530	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	531	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	532	event occurring (or more correctly, libev finding out about it).
214		533
215	=item ev_loop (loop, int flags)	534	=item ev_loop (loop, int flags)
216		535
217	Finally, this is it, the event handler. This function usually is called	536	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	537	after you initialised all your watchers and you want to start handling
219	events.	538	events.
220		539
221	If the flags argument is specified as 0, it will not return until either	540	If the flags argument is specified as C<0>, it will not return until
222	no event watchers are active anymore or C<ev_unloop> was called.	541	either no event watchers are active anymore or C<ev_unloop> was called.
		542
		543	Please note that an explicit C<ev_unloop> is usually better than
		544	relying on all watchers to be stopped when deciding when a program has
		545	finished (especially in interactive programs), but having a program that
		546	automatically loops as long as it has to and no longer by virtue of
		547	relying on its watchers stopping correctly is a thing of beauty.
223		548
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
225	those events and any outstanding ones, but will not block your process in	550	those events and any outstanding ones, but will not block your process in
226	case there are no events and will return after one iteration of the loop.	551	case there are no events and will return after one iteration of the loop.
227		552
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
229	neccessary) and will handle those and any outstanding ones. It will block	554	neccessary) and will handle those and any outstanding ones. It will block
230	your process until at least one new event arrives, and will return after	555	your process until at least one new event arrives, and will return after
231	one iteration of the loop.	556	one iteration of the loop. This is useful if you are waiting for some
		557	external event in conjunction with something not expressible using other
		558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		559	usually a better approach for this kind of thing.
232		560
233	This flags value could be used to implement alternative looping	561	Here are the gory details of what C<ev_loop> does:
234	constructs, but the C<prepare> and C<check> watchers provide a better and	562
235	more generic mechanism.	563	- Before the first iteration, call any pending watchers.
		564	* If EVFLAG_FORKCHECK was used, check for a fork.
		565	- If a fork was detected, queue and call all fork watchers.
		566	- Queue and call all prepare watchers.
		567	- If we have been forked, recreate the kernel state.
		568	- Update the kernel state with all outstanding changes.
		569	- Update the "event loop time".
		570	- Calculate for how long to sleep or block, if at all
		571	(active idle watchers, EVLOOP_NONBLOCK or not having
		572	any active watchers at all will result in not sleeping).
		573	- Sleep if the I/O and timer collect interval say so.
		574	- Block the process, waiting for any events.
		575	- Queue all outstanding I/O (fd) events.
		576	- Update the "event loop time" and do time jump handling.
		577	- Queue all outstanding timers.
		578	- Queue all outstanding periodics.
		579	- If no events are pending now, queue all idle watchers.
		580	- Queue all check watchers.
		581	- Call all queued watchers in reverse order (i.e. check watchers first).
		582	Signals and child watchers are implemented as I/O watchers, and will
		583	be handled here by queueing them when their watcher gets executed.
		584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		585	were used, or there are no active watchers, return, otherwise
		586	continue with step *.
		587
		588	Example: Queue some jobs and then loop until no events are outstanding
		589	anymore.
		590
		591	... queue jobs here, make sure they register event watchers as long
		592	... as they still have work to do (even an idle watcher will do..)
		593	ev_loop (my_loop, 0);
		594	... jobs done. yeah!
236		595
237	=item ev_unloop (loop, how)	596	=item ev_unloop (loop, how)
238		597
239	Can be used to make a call to C<ev_loop> return early (but only after it	598	Can be used to make a call to C<ev_loop> return early (but only after it
240	has processed all outstanding events). The C<how> argument must be either	599	has processed all outstanding events). The C<how> argument must be either
241	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
242	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		602
		603	This "unloop state" will be cleared when entering C<ev_loop> again.
243		604
244	=item ev_ref (loop)	605	=item ev_ref (loop)
245		606
246	=item ev_unref (loop)	607	=item ev_unref (loop)
247		608
…		…
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	613	returning, ev_unref() after starting, and ev_ref() before stopping it. For
253	example, libev itself uses this for its internal signal pipe: It is not	614	example, libev itself uses this for its internal signal pipe: It is not
254	visible to the libev user and should not keep C<ev_loop> from exiting if	615	visible to the libev user and should not keep C<ev_loop> from exiting if
255	no event watchers registered by it are active. It is also an excellent	616	no event watchers registered by it are active. It is also an excellent
256	way to do this for generic recurring timers or from within third-party	617	way to do this for generic recurring timers or from within third-party
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	618	libraries. Just remember to I<unref after start> and I<ref before stop>
		619	(but only if the watcher wasn't active before, or was active before,
		620	respectively).
		621
		622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		623	running when nothing else is active.
		624
		625	struct ev_signal exitsig;
		626	ev_signal_init (&exitsig, sig_cb, SIGINT);
		627	ev_signal_start (loop, &exitsig);
		628	evf_unref (loop);
		629
		630	Example: For some weird reason, unregister the above signal handler again.
		631
		632	ev_ref (loop);
		633	ev_signal_stop (loop, &exitsig);
		634
		635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		636
		637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		638
		639	These advanced functions influence the time that libev will spend waiting
		640	for events. Both are by default C<0>, meaning that libev will try to
		641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		642
		643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		644	allows libev to delay invocation of I/O and timer/periodic callbacks to
		645	increase efficiency of loop iterations.
		646
		647	The background is that sometimes your program runs just fast enough to
		648	handle one (or very few) event(s) per loop iteration. While this makes
		649	the program responsive, it also wastes a lot of CPU time to poll for new
		650	events, especially with backends like C<select ()> which have a high
		651	overhead for the actual polling but can deliver many events at once.
		652
		653	By setting a higher I<io collect interval> you allow libev to spend more
		654	time collecting I/O events, so you can handle more events per iteration,
		655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		656	C<ev_timer>) will be not affected. Setting this to a non-null value will
		657	introduce an additional C<ev_sleep ()> call into most loop iterations.
		658
		659	Likewise, by setting a higher I<timeout collect interval> you allow libev
		660	to spend more time collecting timeouts, at the expense of increased
		661	latency (the watcher callback will be called later). C<ev_io> watchers
		662	will not be affected. Setting this to a non-null value will not introduce
		663	any overhead in libev.
		664
		665	Many (busy) programs can usually benefit by setting the io collect
		666	interval to a value near C<0.1> or so, which is often enough for
		667	interactive servers (of course not for games), likewise for timeouts. It
		668	usually doesn't make much sense to set it to a lower value than C<0.01>,
		669	as this approsaches the timing granularity of most systems.
258		670
259	=back	671	=back
		672
260		673
261	=head1 ANATOMY OF A WATCHER	674	=head1 ANATOMY OF A WATCHER
262		675
263	A watcher is a structure that you create and register to record your	676	A watcher is a structure that you create and register to record your
264	interest in some event. For instance, if you want to wait for STDIN to	677	interest in some event. For instance, if you want to wait for STDIN to
…		…
297	*) >>), and you can stop watching for events at any time by calling the	710	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
299		712
300	As long as your watcher is active (has been started but not stopped) you	713	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	714	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	715	reinitialise it or call its C<set> macro.
303
304	You can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		716
309	Each and every callback receives the event loop pointer as first, the	717	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	718	registered watcher structure as second, and a bitset of received events as
311	third argument.	719	third argument.
312		720
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	744	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		745
338	=item C<EV_CHILD>	746	=item C<EV_CHILD>
339		747
340	The pid specified in the C<ev_child> watcher has received a status change.	748	The pid specified in the C<ev_child> watcher has received a status change.
		749
		750	=item C<EV_STAT>
		751
		752	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		753
342	=item C<EV_IDLE>	754	=item C<EV_IDLE>
343		755
344	The C<ev_idle> watcher has determined that you have nothing better to do.	756	The C<ev_idle> watcher has determined that you have nothing better to do.
345		757
…		…
353	received events. Callbacks of both watcher types can start and stop as	765	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	766	many watchers as they want, and all of them will be taken into account
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	767	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	768	C<ev_loop> from blocking).
357		769
		770	=item C<EV_EMBED>
		771
		772	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		773
		774	=item C<EV_FORK>
		775
		776	The event loop has been resumed in the child process after fork (see
		777	C<ev_fork>).
		778
358	=item C<EV_ERROR>	779	=item C<EV_ERROR>
359		780
360	An unspecified error has occured, the watcher has been stopped. This might	781	An unspecified error has occured, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	782	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	783	ran out of memory, a file descriptor was found to be closed or any other
…		…
368	your callbacks is well-written it can just attempt the operation and cope	789	your callbacks is well-written it can just attempt the operation and cope
369	with the error from read() or write(). This will not work in multithreaded	790	with the error from read() or write(). This will not work in multithreaded
370	programs, though, so beware.	791	programs, though, so beware.
371		792
372	=back	793	=back
		794
		795	=head2 GENERIC WATCHER FUNCTIONS
		796
		797	In the following description, C<TYPE> stands for the watcher type,
		798	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		799
		800	=over 4
		801
		802	=item C<ev_init> (ev_TYPE *watcher, callback)
		803
		804	This macro initialises the generic portion of a watcher. The contents
		805	of the watcher object can be arbitrary (so C<malloc> will do). Only
		806	the generic parts of the watcher are initialised, you I<need> to call
		807	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		808	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		809	which rolls both calls into one.
		810
		811	You can reinitialise a watcher at any time as long as it has been stopped
		812	(or never started) and there are no pending events outstanding.
		813
		814	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		815	int revents)>.
		816
		817	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		818
		819	This macro initialises the type-specific parts of a watcher. You need to
		820	call C<ev_init> at least once before you call this macro, but you can
		821	call C<ev_TYPE_set> any number of times. You must not, however, call this
		822	macro on a watcher that is active (it can be pending, however, which is a
		823	difference to the C<ev_init> macro).
		824
		825	Although some watcher types do not have type-specific arguments
		826	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		827
		828	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		829
		830	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		831	calls into a single call. This is the most convinient method to initialise
		832	a watcher. The same limitations apply, of course.
		833
		834	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		835
		836	Starts (activates) the given watcher. Only active watchers will receive
		837	events. If the watcher is already active nothing will happen.
		838
		839	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		840
		841	Stops the given watcher again (if active) and clears the pending
		842	status. It is possible that stopped watchers are pending (for example,
		843	non-repeating timers are being stopped when they become pending), but
		844	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		845	you want to free or reuse the memory used by the watcher it is therefore a
		846	good idea to always call its C<ev_TYPE_stop> function.
		847
		848	=item bool ev_is_active (ev_TYPE *watcher)
		849
		850	Returns a true value iff the watcher is active (i.e. it has been started
		851	and not yet been stopped). As long as a watcher is active you must not modify
		852	it.
		853
		854	=item bool ev_is_pending (ev_TYPE *watcher)
		855
		856	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		857	events but its callback has not yet been invoked). As long as a watcher
		858	is pending (but not active) you must not call an init function on it (but
		859	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		860	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		861	it).
		862
		863	=item callback ev_cb (ev_TYPE *watcher)
		864
		865	Returns the callback currently set on the watcher.
		866
		867	=item ev_cb_set (ev_TYPE *watcher, callback)
		868
		869	Change the callback. You can change the callback at virtually any time
		870	(modulo threads).
		871
		872	=item ev_set_priority (ev_TYPE *watcher, priority)
		873
		874	=item int ev_priority (ev_TYPE *watcher)
		875
		876	Set and query the priority of the watcher. The priority is a small
		877	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		878	(default: C<-2>). Pending watchers with higher priority will be invoked
		879	before watchers with lower priority, but priority will not keep watchers
		880	from being executed (except for C<ev_idle> watchers).
		881
		882	This means that priorities are I<only> used for ordering callback
		883	invocation after new events have been received. This is useful, for
		884	example, to reduce latency after idling, or more often, to bind two
		885	watchers on the same event and make sure one is called first.
		886
		887	If you need to suppress invocation when higher priority events are pending
		888	you need to look at C<ev_idle> watchers, which provide this functionality.
		889
		890	You I<must not> change the priority of a watcher as long as it is active or
		891	pending.
		892
		893	The default priority used by watchers when no priority has been set is
		894	always C<0>, which is supposed to not be too high and not be too low :).
		895
		896	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		897	fine, as long as you do not mind that the priority value you query might
		898	or might not have been adjusted to be within valid range.
		899
		900	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		901
		902	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		903	C<loop> nor C<revents> need to be valid as long as the watcher callback
		904	can deal with that fact.
		905
		906	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		907
		908	If the watcher is pending, this function returns clears its pending status
		909	and returns its C<revents> bitset (as if its callback was invoked). If the
		910	watcher isn't pending it does nothing and returns C<0>.
		911
		912	=back
		913
373		914
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	915	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		916
376	Each watcher has, by default, a member C<void *data> that you can change	917	Each watcher has, by default, a member C<void *data> that you can change
377	and read at any time, libev will completely ignore it. This can be used	918	and read at any time, libev will completely ignore it. This can be used
…		…
395	{	936	{
396	struct my_io *w = (struct my_io *)w_;	937	struct my_io *w = (struct my_io *)w_;
397	...	938	...
398	}	939	}
399		940
400	More interesting and less C-conformant ways of catsing your callback type	941	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	942	instead have been omitted.
		943
		944	Another common scenario is having some data structure with multiple
		945	watchers:
		946
		947	struct my_biggy
		948	{
		949	int some_data;
		950	ev_timer t1;
		951	ev_timer t2;
		952	}
		953
		954	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		955	you need to use C<offsetof>:
		956
		957	#include <stddef.h>
		958
		959	static void
		960	t1_cb (EV_P_ struct ev_timer *w, int revents)
		961	{
		962	struct my_biggy big = (struct my_biggy *
		963	(((char *)w) - offsetof (struct my_biggy, t1));
		964	}
		965
		966	static void
		967	t2_cb (EV_P_ struct ev_timer *w, int revents)
		968	{
		969	struct my_biggy big = (struct my_biggy *
		970	(((char *)w) - offsetof (struct my_biggy, t2));
		971	}
402		972
403		973
404	=head1 WATCHER TYPES	974	=head1 WATCHER TYPES
405		975
406	This section describes each watcher in detail, but will not repeat	976	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	977	information given in the last section. Any initialisation/set macros,
		978	functions and members specific to the watcher type are explained.
408		979
		980	Members are additionally marked with either I<[read-only]>, meaning that,
		981	while the watcher is active, you can look at the member and expect some
		982	sensible content, but you must not modify it (you can modify it while the
		983	watcher is stopped to your hearts content), or I<[read-write]>, which
		984	means you can expect it to have some sensible content while the watcher
		985	is active, but you can also modify it. Modifying it may not do something
		986	sensible or take immediate effect (or do anything at all), but libev will
		987	not crash or malfunction in any way.
		988
		989
409	=head2 C<ev_io> - is this file descriptor readable or writable	990	=head2 C<ev_io> - is this file descriptor readable or writable?
410		991
411	I/O watchers check whether a file descriptor is readable or writable	992	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	993	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	994	would not block the process and writing would at least be able to write
414	condition persists. Remember you can stop the watcher if you don't want to	995	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	996	receiving events as long as the condition persists. Remember you can stop
		997	the watcher if you don't want to act on the event and neither want to
		998	receive future events.
416		999
417	In general you can register as many read and/or write event watchers oer	1000	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	1001	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	1002	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1003	required if you know what you are doing).
421		1004
422	You have to be careful with dup'ed file descriptors, though. Some backends
423	(the linux epoll backend is a notable example) cannot handle dup'ed file
424	descriptors correctly if you register interest in two or more fds pointing
425	to the same file/socket etc. description.
426
427	If you must do this, then force the use of a known-to-be-good backend	1005	If you must do this, then force the use of a known-to-be-good backend
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
429	EVMETHOD_POLL).	1007	C<EVBACKEND_POLL>).
		1008
		1009	Another thing you have to watch out for is that it is quite easy to
		1010	receive "spurious" readyness notifications, that is your callback might
		1011	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1012	because there is no data. Not only are some backends known to create a
		1013	lot of those (for example solaris ports), it is very easy to get into
		1014	this situation even with a relatively standard program structure. Thus
		1015	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1016	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1017
		1018	If you cannot run the fd in non-blocking mode (for example you should not
		1019	play around with an Xlib connection), then you have to seperately re-test
		1020	whether a file descriptor is really ready with a known-to-be good interface
		1021	such as poll (fortunately in our Xlib example, Xlib already does this on
		1022	its own, so its quite safe to use).
		1023
		1024	=head3 The special problem of disappearing file descriptors
		1025
		1026	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1027	descriptor (either by calling C<close> explicitly or by any other means,
		1028	such as C<dup>). The reason is that you register interest in some file
		1029	descriptor, but when it goes away, the operating system will silently drop
		1030	this interest. If another file descriptor with the same number then is
		1031	registered with libev, there is no efficient way to see that this is, in
		1032	fact, a different file descriptor.
		1033
		1034	To avoid having to explicitly tell libev about such cases, libev follows
		1035	the following policy: Each time C<ev_io_set> is being called, libev
		1036	will assume that this is potentially a new file descriptor, otherwise
		1037	it is assumed that the file descriptor stays the same. That means that
		1038	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1039	descriptor even if the file descriptor number itself did not change.
		1040
		1041	This is how one would do it normally anyway, the important point is that
		1042	the libev application should not optimise around libev but should leave
		1043	optimisations to libev.
		1044
		1045	=head3 The special problem of dup'ed file descriptors
		1046
		1047	Some backends (e.g. epoll), cannot register events for file descriptors,
		1048	but only events for the underlying file descriptions. That means when you
		1049	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1050	events for them, only one file descriptor might actually receive events.
		1051
		1052	There is no workaround possible except not registering events
		1053	for potentially C<dup ()>'ed file descriptors, or to resort to
		1054	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1055
		1056	=head3 The special problem of fork
		1057
		1058	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1059	useless behaviour. Libev fully supports fork, but needs to be told about
		1060	it in the child.
		1061
		1062	To support fork in your programs, you either have to call
		1063	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1065	C<EVBACKEND_POLL>.
		1066
		1067
		1068	=head3 Watcher-Specific Functions
430		1069
431	=over 4	1070	=over 4
432		1071
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1072	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1073
435	=item ev_io_set (ev_io *, int fd, int events)	1074	=item ev_io_set (ev_io *, int fd, int events)
436		1075
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1076	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1077	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1078	C<EV_READ | EV_WRITE> to receive the given events.
		1079
		1080	=item int fd [read-only]
		1081
		1082	The file descriptor being watched.
		1083
		1084	=item int events [read-only]
		1085
		1086	The events being watched.
440		1087
441	=back	1088	=back
442		1089
		1090	=head3 Examples
		1091
		1092	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1093	readable, but only once. Since it is likely line-buffered, you could
		1094	attempt to read a whole line in the callback.
		1095
		1096	static void
		1097	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1098	{
		1099	ev_io_stop (loop, w);
		1100	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1101	}
		1102
		1103	...
		1104	struct ev_loop *loop = ev_default_init (0);
		1105	struct ev_io stdin_readable;
		1106	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1107	ev_io_start (loop, &stdin_readable);
		1108	ev_loop (loop, 0);
		1109
		1110
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1111	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1112
445	Timer watchers are simple relative timers that generate an event after a	1113	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1114	given time, and optionally repeating in regular intervals after that.
447		1115
448	The timers are based on real time, that is, if you register an event that	1116	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1117	times out after an hour and you reset your system clock to last years
450	time, it will still time out after (roughly) and hour. "Roughly" because	1118	time, it will still time out after (roughly) and hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1120	monotonic clock option helps a lot here).
453		1121
454	The relative timeouts are calculated relative to the C<ev_now ()>	1122	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	1123	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	1124	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	1125	you suspect event processing to be delayed and you I<need> to base the timeout
458	ion the current time, use something like this to adjust for this:	1126	on the current time, use something like this to adjust for this:
459		1127
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1129
		1130	The callback is guarenteed to be invoked only when its timeout has passed,
		1131	but if multiple timers become ready during the same loop iteration then
		1132	order of execution is undefined.
		1133
		1134	=head3 Watcher-Specific Functions and Data Members
461		1135
462	=over 4	1136	=over 4
463		1137
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1138	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1139
…		…
471	later, again, and again, until stopped manually.	1145	later, again, and again, until stopped manually.
472		1146
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1147	The timer itself will do a best-effort at avoiding drift, that is, if you
474	configure a timer to trigger every 10 seconds, then it will trigger at	1148	configure a timer to trigger every 10 seconds, then it will trigger at
475	exactly 10 second intervals. If, however, your program cannot keep up with	1149	exactly 10 second intervals. If, however, your program cannot keep up with
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1150	the timer (because it takes longer than those 10 seconds to do stuff) the
477	timer will not fire more than once per event loop iteration.	1151	timer will not fire more than once per event loop iteration.
478		1152
479	=item ev_timer_again (loop)	1153	=item ev_timer_again (loop)
480		1154
481	This will act as if the timer timed out and restart it again if it is	1155	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1156	repeating. The exact semantics are:
483		1157
		1158	If the timer is pending, its pending status is cleared.
		1159
484	If the timer is started but nonrepeating, stop it.	1160	If the timer is started but nonrepeating, stop it (as if it timed out).
485		1161
486	If the timer is repeating, either start it if necessary (with the repeat	1162	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1163	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1164
489	This sounds a bit complicated, but here is a useful and typical	1165	This sounds a bit complicated, but here is a useful and typical
490	example: Imagine you have a tcp connection and you want a so-called idle	1166	example: Imagine you have a tcp connection and you want a so-called idle
491	timeout, that is, you want to be called when there have been, say, 60	1167	timeout, that is, you want to be called when there have been, say, 60
492	seconds of inactivity on the socket. The easiest way to do this is to	1168	seconds of inactivity on the socket. The easiest way to do this is to
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1169	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
494	time you successfully read or write some data. If you go into an idle	1170	C<ev_timer_again> each time you successfully read or write some data. If
495	state where you do not expect data to travel on the socket, you can stop	1171	you go into an idle state where you do not expect data to travel on the
496	the timer, and again will automatically restart it if need be.	1172	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1173	automatically restart it if need be.
		1174
		1175	That means you can ignore the C<after> value and C<ev_timer_start>
		1176	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1177
		1178	ev_timer_init (timer, callback, 0., 5.);
		1179	ev_timer_again (loop, timer);
		1180	...
		1181	timer->again = 17.;
		1182	ev_timer_again (loop, timer);
		1183	...
		1184	timer->again = 10.;
		1185	ev_timer_again (loop, timer);
		1186
		1187	This is more slightly efficient then stopping/starting the timer each time
		1188	you want to modify its timeout value.
		1189
		1190	=item ev_tstamp repeat [read-write]
		1191
		1192	The current C<repeat> value. Will be used each time the watcher times out
		1193	or C<ev_timer_again> is called and determines the next timeout (if any),
		1194	which is also when any modifications are taken into account.
497		1195
498	=back	1196	=back
499		1197
		1198	=head3 Examples
		1199
		1200	Example: Create a timer that fires after 60 seconds.
		1201
		1202	static void
		1203	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1204	{
		1205	.. one minute over, w is actually stopped right here
		1206	}
		1207
		1208	struct ev_timer mytimer;
		1209	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1210	ev_timer_start (loop, &mytimer);
		1211
		1212	Example: Create a timeout timer that times out after 10 seconds of
		1213	inactivity.
		1214
		1215	static void
		1216	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1217	{
		1218	.. ten seconds without any activity
		1219	}
		1220
		1221	struct ev_timer mytimer;
		1222	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1223	ev_timer_again (&mytimer); /* start timer */
		1224	ev_loop (loop, 0);
		1225
		1226	// and in some piece of code that gets executed on any "activity":
		1227	// reset the timeout to start ticking again at 10 seconds
		1228	ev_timer_again (&mytimer);
		1229
		1230
500	=head2 C<ev_periodic> - to cron or not to cron	1231	=head2 C<ev_periodic> - to cron or not to cron?
501		1232
502	Periodic watchers are also timers of a kind, but they are very versatile	1233	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1234	(and unfortunately a bit complex).
504		1235
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1236	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506	but on wallclock time (absolute time). You can tell a periodic watcher	1237	but on wallclock time (absolute time). You can tell a periodic watcher
507	to trigger "at" some specific point in time. For example, if you tell a	1238	to trigger "at" some specific point in time. For example, if you tell a
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1239	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
509	+ 10.>) and then reset your system clock to the last year, then it will	1240	+ 10.>) and then reset your system clock to the last year, then it will
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
511	roughly 10 seconds later and of course not if you reset your system time	1242	roughly 10 seconds later).
512	again).
513		1243
514	They can also be used to implement vastly more complex timers, such as	1244	They can also be used to implement vastly more complex timers, such as
515	triggering an event on eahc midnight, local time.	1245	triggering an event on each midnight, local time or other, complicated,
		1246	rules.
		1247
		1248	As with timers, the callback is guarenteed to be invoked only when the
		1249	time (C<at>) has been passed, but if multiple periodic timers become ready
		1250	during the same loop iteration then order of execution is undefined.
		1251
		1252	=head3 Watcher-Specific Functions and Data Members
516		1253
517	=over 4	1254	=over 4
518		1255
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1256	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520		1257
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1258	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522		1259
523	Lots of arguments, lets sort it out... There are basically three modes of	1260	Lots of arguments, lets sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	1261	operation, and we will explain them from simplest to complex:
525		1262
526
527	=over 4	1263	=over 4
528		1264
529	=item * absolute timer (interval = reschedule_cb = 0)	1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)
530		1266
531	In this configuration the watcher triggers an event at the wallclock time	1267	In this configuration the watcher triggers an event at the wallclock time
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1268	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
533	that is, if it is to be run at January 1st 2011 then it will run when the	1269	that is, if it is to be run at January 1st 2011 then it will run when the
534	system time reaches or surpasses this time.	1270	system time reaches or surpasses this time.
535		1271
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1272	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
537		1273
538	In this mode the watcher will always be scheduled to time out at the next	1274	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	1275	C<at + N * interval> time (for some integer N, which can also be negative)
540	of any time jumps.	1276	and then repeat, regardless of any time jumps.
541		1277
542	This can be used to create timers that do not drift with respect to system	1278	This can be used to create timers that do not drift with respect to system
543	time:	1279	time:
544		1280
545	ev_periodic_set (&periodic, 0., 3600., 0);	1281	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
551		1287
552	Another way to think about it (for the mathematically inclined) is that	1288	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	1289	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	1290	time where C<time = at (mod interval)>, regardless of any time jumps.
555		1291
		1292	For numerical stability it is preferable that the C<at> value is near
		1293	C<ev_now ()> (the current time), but there is no range requirement for
		1294	this value.
		1295
556	=item * manual reschedule mode (reschedule_cb = callback)	1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
557		1297
558	In this mode the values for C<interval> and C<at> are both being	1298	In this mode the values for C<interval> and C<at> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	1299	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	1300	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	1301	current time as second argument.
562		1302
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1303	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
564	periodic watcher, ever, or make any event loop modifications>. If you need	1304	ever, or make any event loop modifications>. If you need to stop it,
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
566		1306	starting an C<ev_prepare> watcher, which is legal).
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569		1307
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1308	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
571	ev_tstamp now)>, e.g.:	1309	ev_tstamp now)>, e.g.:
572		1310
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
578	It must return the next time to trigger, based on the passed time value	1316	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	1317	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	1318	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	1319	might be called at other times, too.
582		1320
		1321	NOTE: I<< This callback must always return a time that is later than the
		1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
		1323
583	This can be used to create very complex timers, such as a timer that	1324	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	1325	triggers on each midnight, local time. To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	1326	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	1327	you do this is, again, up to you (but it is not trivial, which is the main
		1328	reason I omitted it as an example).
587		1329
588	=back	1330	=back
589		1331
590	=item ev_periodic_again (loop, ev_periodic *)	1332	=item ev_periodic_again (loop, ev_periodic *)
591		1333
592	Simply stops and restarts the periodic watcher again. This is only useful	1334	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	1335	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	1336	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	1337	program when the crontabs have changed).
596		1338
		1339	=item ev_tstamp offset [read-write]
		1340
		1341	When repeating, this contains the offset value, otherwise this is the
		1342	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1343
		1344	Can be modified any time, but changes only take effect when the periodic
		1345	timer fires or C<ev_periodic_again> is being called.
		1346
		1347	=item ev_tstamp interval [read-write]
		1348
		1349	The current interval value. Can be modified any time, but changes only
		1350	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1351	called.
		1352
		1353	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1354
		1355	The current reschedule callback, or C<0>, if this functionality is
		1356	switched off. Can be changed any time, but changes only take effect when
		1357	the periodic timer fires or C<ev_periodic_again> is being called.
		1358
		1359	=item ev_tstamp at [read-only]
		1360
		1361	When active, contains the absolute time that the watcher is supposed to
		1362	trigger next.
		1363
597	=back	1364	=back
598		1365
		1366	=head3 Examples
		1367
		1368	Example: Call a callback every hour, or, more precisely, whenever the
		1369	system clock is divisible by 3600. The callback invocation times have
		1370	potentially a lot of jittering, but good long-term stability.
		1371
		1372	static void
		1373	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1374	{
		1375	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1376	}
		1377
		1378	struct ev_periodic hourly_tick;
		1379	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1380	ev_periodic_start (loop, &hourly_tick);
		1381
		1382	Example: The same as above, but use a reschedule callback to do it:
		1383
		1384	#include <math.h>
		1385
		1386	static ev_tstamp
		1387	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1388	{
		1389	return fmod (now, 3600.) + 3600.;
		1390	}
		1391
		1392	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1393
		1394	Example: Call a callback every hour, starting now:
		1395
		1396	struct ev_periodic hourly_tick;
		1397	ev_periodic_init (&hourly_tick, clock_cb,
		1398	fmod (ev_now (loop), 3600.), 3600., 0);
		1399	ev_periodic_start (loop, &hourly_tick);
		1400
		1401
599	=head2 C<ev_signal> - signal me when a signal gets signalled	1402	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		1403
601	Signal watchers will trigger an event when the process receives a specific	1404	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	1405	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	1406	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	1407	normal event processing, like any other event.
…		…
608	with the kernel (thus it coexists with your own signal handlers as long	1411	with the kernel (thus it coexists with your own signal handlers as long
609	as you don't register any with libev). Similarly, when the last signal	1412	as you don't register any with libev). Similarly, when the last signal
610	watcher for a signal is stopped libev will reset the signal handler to	1413	watcher for a signal is stopped libev will reset the signal handler to
611	SIG_DFL (regardless of what it was set to before).	1414	SIG_DFL (regardless of what it was set to before).
612		1415
		1416	=head3 Watcher-Specific Functions and Data Members
		1417
613	=over 4	1418	=over 4
614		1419
615	=item ev_signal_init (ev_signal *, callback, int signum)	1420	=item ev_signal_init (ev_signal *, callback, int signum)
616		1421
617	=item ev_signal_set (ev_signal *, int signum)	1422	=item ev_signal_set (ev_signal *, int signum)
618		1423
619	Configures the watcher to trigger on the given signal number (usually one	1424	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	1425	of the C<SIGxxx> constants).
621		1426
		1427	=item int signum [read-only]
		1428
		1429	The signal the watcher watches out for.
		1430
622	=back	1431	=back
623		1432
		1433
624	=head2 C<ev_child> - wait for pid status changes	1434	=head2 C<ev_child> - watch out for process status changes
625		1435
626	Child watchers trigger when your process receives a SIGCHLD in response to	1436	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	1437	some child status changes (most typically when a child of yours dies).
628		1438
		1439	=head3 Watcher-Specific Functions and Data Members
		1440
629	=over 4	1441	=over 4
630		1442
631	=item ev_child_init (ev_child *, callback, int pid)	1443	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		1444
633	=item ev_child_set (ev_child *, int pid)	1445	=item ev_child_set (ev_child *, int pid, int trace)
634		1446
635	Configures the watcher to wait for status changes of process C<pid> (or	1447	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	1448	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	1449	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	1450	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	1451	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	1452	process causing the status change. C<trace> must be either C<0> (only
		1453	activate the watcher when the process terminates) or C<1> (additionally
		1454	activate the watcher when the process is stopped or continued).
		1455
		1456	=item int pid [read-only]
		1457
		1458	The process id this watcher watches out for, or C<0>, meaning any process id.
		1459
		1460	=item int rpid [read-write]
		1461
		1462	The process id that detected a status change.
		1463
		1464	=item int rstatus [read-write]
		1465
		1466	The process exit/trace status caused by C<rpid> (see your systems
		1467	C<waitpid> and C<sys/wait.h> documentation for details).
641		1468
642	=back	1469	=back
643		1470
		1471	=head3 Examples
		1472
		1473	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1474
		1475	static void
		1476	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1477	{
		1478	ev_unloop (loop, EVUNLOOP_ALL);
		1479	}
		1480
		1481	struct ev_signal signal_watcher;
		1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1483	ev_signal_start (loop, &sigint_cb);
		1484
		1485
		1486	=head2 C<ev_stat> - did the file attributes just change?
		1487
		1488	This watches a filesystem path for attribute changes. That is, it calls
		1489	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1490	compared to the last time, invoking the callback if it did.
		1491
		1492	The path does not need to exist: changing from "path exists" to "path does
		1493	not exist" is a status change like any other. The condition "path does
		1494	not exist" is signified by the C<st_nlink> field being zero (which is
		1495	otherwise always forced to be at least one) and all the other fields of
		1496	the stat buffer having unspecified contents.
		1497
		1498	The path I<should> be absolute and I<must not> end in a slash. If it is
		1499	relative and your working directory changes, the behaviour is undefined.
		1500
		1501	Since there is no standard to do this, the portable implementation simply
		1502	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1503	can specify a recommended polling interval for this case. If you specify
		1504	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1505	unspecified default> value will be used (which you can expect to be around
		1506	five seconds, although this might change dynamically). Libev will also
		1507	impose a minimum interval which is currently around C<0.1>, but thats
		1508	usually overkill.
		1509
		1510	This watcher type is not meant for massive numbers of stat watchers,
		1511	as even with OS-supported change notifications, this can be
		1512	resource-intensive.
		1513
		1514	At the time of this writing, only the Linux inotify interface is
		1515	implemented (implementing kqueue support is left as an exercise for the
		1516	reader). Inotify will be used to give hints only and should not change the
		1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1518	to fall back to regular polling again even with inotify, but changes are
		1519	usually detected immediately, and if the file exists there will be no
		1520	polling.
		1521
		1522	=head3 Inotify
		1523
		1524	When C<inotify (7)> support has been compiled into libev (generally only
		1525	available on Linux) and present at runtime, it will be used to speed up
		1526	change detection where possible. The inotify descriptor will be created lazily
		1527	when the first C<ev_stat> watcher is being started.
		1528
		1529	Inotify presense does not change the semantics of C<ev_stat> watchers
		1530	except that changes might be detected earlier, and in some cases, to avoid
		1531	making regular C<stat> calls. Even in the presense of inotify support
		1532	there are many cases where libev has to resort to regular C<stat> polling.
		1533
		1534	(There is no support for kqueue, as apparently it cannot be used to
		1535	implement this functionality, due to the requirement of having a file
		1536	descriptor open on the object at all times).
		1537
		1538	=head3 The special problem of stat time resolution
		1539
		1540	The C<stat ()> syscall only supports full-second resolution portably, and
		1541	even on systems where the resolution is higher, many filesystems still
		1542	only support whole seconds.
		1543
		1544	That means that, if the time is the only thing that changes, you might
		1545	miss updates: on the first update, C<ev_stat> detects a change and calls
		1546	your callback, which does something. When there is another update within
		1547	the same second, C<ev_stat> will be unable to detect it.
		1548
		1549	The solution to this is to delay acting on a change for a second (or till
		1550	the next second boundary), using a roughly one-second delay C<ev_timer>
		1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1552	is added to work around small timing inconsistencies of some operating
		1553	systems.
		1554
		1555	=head3 Watcher-Specific Functions and Data Members
		1556
		1557	=over 4
		1558
		1559	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1560
		1561	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1562
		1563	Configures the watcher to wait for status changes of the given
		1564	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1565	be detected and should normally be specified as C<0> to let libev choose
		1566	a suitable value. The memory pointed to by C<path> must point to the same
		1567	path for as long as the watcher is active.
		1568
		1569	The callback will be receive C<EV_STAT> when a change was detected,
		1570	relative to the attributes at the time the watcher was started (or the
		1571	last change was detected).
		1572
		1573	=item ev_stat_stat (ev_stat *)
		1574
		1575	Updates the stat buffer immediately with new values. If you change the
		1576	watched path in your callback, you could call this fucntion to avoid
		1577	detecting this change (while introducing a race condition). Can also be
		1578	useful simply to find out the new values.
		1579
		1580	=item ev_statdata attr [read-only]
		1581
		1582	The most-recently detected attributes of the file. Although the type is of
		1583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1584	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1585	was some error while C<stat>ing the file.
		1586
		1587	=item ev_statdata prev [read-only]
		1588
		1589	The previous attributes of the file. The callback gets invoked whenever
		1590	C<prev> != C<attr>.
		1591
		1592	=item ev_tstamp interval [read-only]
		1593
		1594	The specified interval.
		1595
		1596	=item const char *path [read-only]
		1597
		1598	The filesystem path that is being watched.
		1599
		1600	=back
		1601
		1602	=head3 Examples
		1603
		1604	Example: Watch C</etc/passwd> for attribute changes.
		1605
		1606	static void
		1607	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1608	{
		1609	/* /etc/passwd changed in some way */
		1610	if (w->attr.st_nlink)
		1611	{
		1612	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1613	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1614	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1615	}
		1616	else
		1617	/* you shalt not abuse printf for puts */
		1618	puts ("wow, /etc/passwd is not there, expect problems. "
		1619	"if this is windows, they already arrived\n");
		1620	}
		1621
		1622	...
		1623	ev_stat passwd;
		1624
		1625	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1626	ev_stat_start (loop, &passwd);
		1627
		1628	Example: Like above, but additionally use a one-second delay so we do not
		1629	miss updates (however, frequent updates will delay processing, too, so
		1630	one might do the work both on C<ev_stat> callback invocation I<and> on
		1631	C<ev_timer> callback invocation).
		1632
		1633	static ev_stat passwd;
		1634	static ev_timer timer;
		1635
		1636	static void
		1637	timer_cb (EV_P_ ev_timer *w, int revents)
		1638	{
		1639	ev_timer_stop (EV_A_ w);
		1640
		1641	/* now it's one second after the most recent passwd change */
		1642	}
		1643
		1644	static void
		1645	stat_cb (EV_P_ ev_stat *w, int revents)
		1646	{
		1647	/* reset the one-second timer */
		1648	ev_timer_again (EV_A_ &timer);
		1649	}
		1650
		1651	...
		1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1653	ev_stat_start (loop, &passwd);
		1654	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1655
		1656
644	=head2 C<ev_idle> - when you've got nothing better to do	1657	=head2 C<ev_idle> - when you've got nothing better to do...
645		1658
646	Idle watchers trigger events when there are no other events are pending	1659	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	1660	priority are pending (prepare, check and other idle watchers do not
648	as your process is busy handling sockets or timeouts (or even signals,	1661	count).
649	imagine) it will not be triggered. But when your process is idle all idle	1662
650	watchers are being called again and again, once per event loop iteration -	1663	That is, as long as your process is busy handling sockets or timeouts
		1664	(or even signals, imagine) of the same or higher priority it will not be
		1665	triggered. But when your process is idle (or only lower-priority watchers
		1666	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	1667	iteration - until stopped, that is, or your process receives more events
652	busy.	1668	and becomes busy again with higher priority stuff.
653		1669
654	The most noteworthy effect is that as long as any idle watchers are	1670	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	1671	active, the process will not block when waiting for new events.
656		1672
657	Apart from keeping your process non-blocking (which is a useful	1673	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	1674	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	1675	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	1676	event loop has handled all outstanding events.
661		1677
		1678	=head3 Watcher-Specific Functions and Data Members
		1679
662	=over 4	1680	=over 4
663		1681
664	=item ev_idle_init (ev_signal *, callback)	1682	=item ev_idle_init (ev_signal *, callback)
665		1683
666	Initialises and configures the idle watcher - it has no parameters of any	1684	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1685	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	1686	believe me.
669		1687
670	=back	1688	=back
671		1689
672	=head2 prepare and check - your hooks into the event loop	1690	=head3 Examples
		1691
		1692	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1693	callback, free it. Also, use no error checking, as usual.
		1694
		1695	static void
		1696	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1697	{
		1698	free (w);
		1699	// now do something you wanted to do when the program has
		1700	// no longer anything immediate to do.
		1701	}
		1702
		1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1704	ev_idle_init (idle_watcher, idle_cb);
		1705	ev_idle_start (loop, idle_cb);
		1706
		1707
		1708	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		1709
674	Prepare and check watchers are usually (but not always) used in tandem:	1710	Prepare and check watchers are usually (but not always) used in tandem:
675	Prepare watchers get invoked before the process blocks and check watchers	1711	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	1712	afterwards.
677		1713
		1714	You I<must not> call C<ev_loop> or similar functions that enter
		1715	the current event loop from either C<ev_prepare> or C<ev_check>
		1716	watchers. Other loops than the current one are fine, however. The
		1717	rationale behind this is that you do not need to check for recursion in
		1718	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1719	C<ev_check> so if you have one watcher of each kind they will always be
		1720	called in pairs bracketing the blocking call.
		1721
678	Their main purpose is to integrate other event mechanisms into libev. This	1722	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	1723	their use is somewhat advanced. This could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	1724	variable changes, implement your own watchers, integrate net-snmp or a
		1725	coroutine library and lots more. They are also occasionally useful if
		1726	you cache some data and want to flush it before blocking (for example,
		1727	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1728	watcher).
681		1729
682	This is done by examining in each prepare call which file descriptors need	1730	This is done by examining in each prepare call which file descriptors need
683	to be watched by the other library, registering C<ev_io> watchers for	1731	to be watched by the other library, registering C<ev_io> watchers for
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1732	them and starting an C<ev_timer> watcher for any timeouts (many libraries
685	provide just this functionality). Then, in the check watcher you check for	1733	provide just this functionality). Then, in the check watcher you check for
686	any events that occured (by checking the pending status of all watchers	1734	any events that occured (by checking the pending status of all watchers
687	and stopping them) and call back into the library. The I/O and timer	1735	and stopping them) and call back into the library. The I/O and timer
688	callbacks will never actually be called (but must be valid neverthelles,	1736	callbacks will never actually be called (but must be valid nevertheless,
689	because you never know, you know?).	1737	because you never know, you know?).
690		1738
691	As another example, the Perl Coro module uses these hooks to integrate	1739	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	1740	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	1741	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	1742	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	1743	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	1744	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	1745	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	1746	low-priority coroutines to idle/background tasks).
		1747
		1748	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1749	priority, to ensure that they are being run before any other watchers
		1750	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1751	too) should not activate ("feed") events into libev. While libev fully
		1752	supports this, they will be called before other C<ev_check> watchers
		1753	did their job. As C<ev_check> watchers are often used to embed other
		1754	(non-libev) event loops those other event loops might be in an unusable
		1755	state until their C<ev_check> watcher ran (always remind yourself to
		1756	coexist peacefully with others).
		1757
		1758	=head3 Watcher-Specific Functions and Data Members
699		1759
700	=over 4	1760	=over 4
701		1761
702	=item ev_prepare_init (ev_prepare *, callback)	1762	=item ev_prepare_init (ev_prepare *, callback)
703		1763
…		…
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1767	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	1768	macros, but using them is utterly, utterly and completely pointless.
709		1769
710	=back	1770	=back
711		1771
		1772	=head3 Examples
		1773
		1774	There are a number of principal ways to embed other event loops or modules
		1775	into libev. Here are some ideas on how to include libadns into libev
		1776	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1777	use for an actually working example. Another Perl module named C<EV::Glib>
		1778	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1779	into the Glib event loop).
		1780
		1781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1782	and in a check watcher, destroy them and call into libadns. What follows
		1783	is pseudo-code only of course. This requires you to either use a low
		1784	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1785	the callbacks for the IO/timeout watchers might not have been called yet.
		1786
		1787	static ev_io iow [nfd];
		1788	static ev_timer tw;
		1789
		1790	static void
		1791	io_cb (ev_loop *loop, ev_io *w, int revents)
		1792	{
		1793	}
		1794
		1795	// create io watchers for each fd and a timer before blocking
		1796	static void
		1797	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1798	{
		1799	int timeout = 3600000;
		1800	struct pollfd fds [nfd];
		1801	// actual code will need to loop here and realloc etc.
		1802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1803
		1804	/* the callback is illegal, but won't be called as we stop during check */
		1805	ev_timer_init (&tw, 0, timeout * 1e-3);
		1806	ev_timer_start (loop, &tw);
		1807
		1808	// create one ev_io per pollfd
		1809	for (int i = 0; i < nfd; ++i)
		1810	{
		1811	ev_io_init (iow + i, io_cb, fds [i].fd,
		1812	((fds [i].events & POLLIN ? EV_READ : 0)
		1813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1814
		1815	fds [i].revents = 0;
		1816	ev_io_start (loop, iow + i);
		1817	}
		1818	}
		1819
		1820	// stop all watchers after blocking
		1821	static void
		1822	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1823	{
		1824	ev_timer_stop (loop, &tw);
		1825
		1826	for (int i = 0; i < nfd; ++i)
		1827	{
		1828	// set the relevant poll flags
		1829	// could also call adns_processreadable etc. here
		1830	struct pollfd *fd = fds + i;
		1831	int revents = ev_clear_pending (iow + i);
		1832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1834
		1835	// now stop the watcher
		1836	ev_io_stop (loop, iow + i);
		1837	}
		1838
		1839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1840	}
		1841
		1842	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1843	in the prepare watcher and would dispose of the check watcher.
		1844
		1845	Method 3: If the module to be embedded supports explicit event
		1846	notification (adns does), you can also make use of the actual watcher
		1847	callbacks, and only destroy/create the watchers in the prepare watcher.
		1848
		1849	static void
		1850	timer_cb (EV_P_ ev_timer *w, int revents)
		1851	{
		1852	adns_state ads = (adns_state)w->data;
		1853	update_now (EV_A);
		1854
		1855	adns_processtimeouts (ads, &tv_now);
		1856	}
		1857
		1858	static void
		1859	io_cb (EV_P_ ev_io *w, int revents)
		1860	{
		1861	adns_state ads = (adns_state)w->data;
		1862	update_now (EV_A);
		1863
		1864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1866	}
		1867
		1868	// do not ever call adns_afterpoll
		1869
		1870	Method 4: Do not use a prepare or check watcher because the module you
		1871	want to embed is too inflexible to support it. Instead, youc na override
		1872	their poll function. The drawback with this solution is that the main
		1873	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1874	this.
		1875
		1876	static gint
		1877	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1878	{
		1879	int got_events = 0;
		1880
		1881	for (n = 0; n < nfds; ++n)
		1882	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1883
		1884	if (timeout >= 0)
		1885	// create/start timer
		1886
		1887	// poll
		1888	ev_loop (EV_A_ 0);
		1889
		1890	// stop timer again
		1891	if (timeout >= 0)
		1892	ev_timer_stop (EV_A_ &to);
		1893
		1894	// stop io watchers again - their callbacks should have set
		1895	for (n = 0; n < nfds; ++n)
		1896	ev_io_stop (EV_A_ iow [n]);
		1897
		1898	return got_events;
		1899	}
		1900
		1901
		1902	=head2 C<ev_embed> - when one backend isn't enough...
		1903
		1904	This is a rather advanced watcher type that lets you embed one event loop
		1905	into another (currently only C<ev_io> events are supported in the embedded
		1906	loop, other types of watchers might be handled in a delayed or incorrect
		1907	fashion and must not be used).
		1908
		1909	There are primarily two reasons you would want that: work around bugs and
		1910	prioritise I/O.
		1911
		1912	As an example for a bug workaround, the kqueue backend might only support
		1913	sockets on some platform, so it is unusable as generic backend, but you
		1914	still want to make use of it because you have many sockets and it scales
		1915	so nicely. In this case, you would create a kqueue-based loop and embed it
		1916	into your default loop (which might use e.g. poll). Overall operation will
		1917	be a bit slower because first libev has to poll and then call kevent, but
		1918	at least you can use both at what they are best.
		1919
		1920	As for prioritising I/O: rarely you have the case where some fds have
		1921	to be watched and handled very quickly (with low latency), and even
		1922	priorities and idle watchers might have too much overhead. In this case
		1923	you would put all the high priority stuff in one loop and all the rest in
		1924	a second one, and embed the second one in the first.
		1925
		1926	As long as the watcher is active, the callback will be invoked every time
		1927	there might be events pending in the embedded loop. The callback must then
		1928	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1929	their callbacks (you could also start an idle watcher to give the embedded
		1930	loop strictly lower priority for example). You can also set the callback
		1931	to C<0>, in which case the embed watcher will automatically execute the
		1932	embedded loop sweep.
		1933
		1934	As long as the watcher is started it will automatically handle events. The
		1935	callback will be invoked whenever some events have been handled. You can
		1936	set the callback to C<0> to avoid having to specify one if you are not
		1937	interested in that.
		1938
		1939	Also, there have not currently been made special provisions for forking:
		1940	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1941	but you will also have to stop and restart any C<ev_embed> watchers
		1942	yourself.
		1943
		1944	Unfortunately, not all backends are embeddable, only the ones returned by
		1945	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1946	portable one.
		1947
		1948	So when you want to use this feature you will always have to be prepared
		1949	that you cannot get an embeddable loop. The recommended way to get around
		1950	this is to have a separate variables for your embeddable loop, try to
		1951	create it, and if that fails, use the normal loop for everything.
		1952
		1953	=head3 Watcher-Specific Functions and Data Members
		1954
		1955	=over 4
		1956
		1957	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1958
		1959	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1960
		1961	Configures the watcher to embed the given loop, which must be
		1962	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1963	invoked automatically, otherwise it is the responsibility of the callback
		1964	to invoke it (it will continue to be called until the sweep has been done,
		1965	if you do not want thta, you need to temporarily stop the embed watcher).
		1966
		1967	=item ev_embed_sweep (loop, ev_embed *)
		1968
		1969	Make a single, non-blocking sweep over the embedded loop. This works
		1970	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1971	apropriate way for embedded loops.
		1972
		1973	=item struct ev_loop *other [read-only]
		1974
		1975	The embedded event loop.
		1976
		1977	=back
		1978
		1979	=head3 Examples
		1980
		1981	Example: Try to get an embeddable event loop and embed it into the default
		1982	event loop. If that is not possible, use the default loop. The default
		1983	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1984	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1985	used).
		1986
		1987	struct ev_loop *loop_hi = ev_default_init (0);
		1988	struct ev_loop *loop_lo = 0;
		1989	struct ev_embed embed;
		1990
		1991	// see if there is a chance of getting one that works
		1992	// (remember that a flags value of 0 means autodetection)
		1993	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1994	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1995	: 0;
		1996
		1997	// if we got one, then embed it, otherwise default to loop_hi
		1998	if (loop_lo)
		1999	{
		2000	ev_embed_init (&embed, 0, loop_lo);
		2001	ev_embed_start (loop_hi, &embed);
		2002	}
		2003	else
		2004	loop_lo = loop_hi;
		2005
		2006	Example: Check if kqueue is available but not recommended and create
		2007	a kqueue backend for use with sockets (which usually work with any
		2008	kqueue implementation). Store the kqueue/socket-only event loop in
		2009	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2010
		2011	struct ev_loop *loop = ev_default_init (0);
		2012	struct ev_loop *loop_socket = 0;
		2013	struct ev_embed embed;
		2014
		2015	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2016	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2017	{
		2018	ev_embed_init (&embed, 0, loop_socket);
		2019	ev_embed_start (loop, &embed);
		2020	}
		2021
		2022	if (!loop_socket)
		2023	loop_socket = loop;
		2024
		2025	// now use loop_socket for all sockets, and loop for everything else
		2026
		2027
		2028	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2029
		2030	Fork watchers are called when a C<fork ()> was detected (usually because
		2031	whoever is a good citizen cared to tell libev about it by calling
		2032	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2033	event loop blocks next and before C<ev_check> watchers are being called,
		2034	and only in the child after the fork. If whoever good citizen calling
		2035	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2036	handlers will be invoked, too, of course.
		2037
		2038	=head3 Watcher-Specific Functions and Data Members
		2039
		2040	=over 4
		2041
		2042	=item ev_fork_init (ev_signal *, callback)
		2043
		2044	Initialises and configures the fork watcher - it has no parameters of any
		2045	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2046	believe me.
		2047
		2048	=back
		2049
		2050
712	=head1 OTHER FUNCTIONS	2051	=head1 OTHER FUNCTIONS
713		2052
714	There are some other functions of possible interest. Described. Here. Now.	2053	There are some other functions of possible interest. Described. Here. Now.
715		2054
716	=over 4	2055	=over 4
…		…
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2057	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		2058
720	This function combines a simple timer and an I/O watcher, calls your	2059	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	2060	callback on whichever event happens first and automatically stop both
722	watchers. This is useful if you want to wait for a single event on an fd	2061	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	2062	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	2063	more watchers yourself.
725		2064
726	If C<fd> is less than 0, then no I/O watcher will be started and events	2065	If C<fd> is less than 0, then no I/O watcher will be started and events
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2066	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
728	C<events> set will be craeted and started.	2067	C<events> set will be craeted and started.
…		…
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2070	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2071	repeat = 0) will be started. While C<0> is a valid timeout, it is of
733	dubious value.	2072	dubious value.
734		2073
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2074	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
736	passed an events set like normal event callbacks (with a combination of	2075	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2076	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738	value passed to C<ev_once>:	2077	value passed to C<ev_once>:
739		2078
740	static void stdin_ready (int revents, void *arg)	2079	static void stdin_ready (int revents, void *arg)
741	{	2080	{
…		…
745	/* stdin might have data for us, joy! */;	2084	/* stdin might have data for us, joy! */;
746	}	2085	}
747		2086
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2087	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749		2088
750	=item ev_feed_event (loop, watcher, int events)	2089	=item ev_feed_event (ev_loop *, watcher *, int revents)
751		2090
752	Feeds the given event set into the event loop, as if the specified event	2091	Feeds the given event set into the event loop, as if the specified event
753	had happened for the specified watcher (which must be a pointer to an	2092	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).	2093	initialised but not necessarily started event watcher).
755		2094
756	=item ev_feed_fd_event (loop, int fd, int revents)	2095	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
757		2096
758	Feed an event on the given fd, as if a file descriptor backend detected	2097	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	2098	the given events it.
760		2099
761	=item ev_feed_signal_event (loop, int signum)	2100	=item ev_feed_signal_event (ev_loop *loop, int signum)
762		2101
763	Feed an event as if the given signal occured (loop must be the default loop!).	2102	Feed an event as if the given signal occured (C<loop> must be the default
		2103	loop!).
764		2104
765	=back	2105	=back
766		2106
		2107
		2108	=head1 LIBEVENT EMULATION
		2109
		2110	Libev offers a compatibility emulation layer for libevent. It cannot
		2111	emulate the internals of libevent, so here are some usage hints:
		2112
		2113	=over 4
		2114
		2115	=item * Use it by including <event.h>, as usual.
		2116
		2117	=item * The following members are fully supported: ev_base, ev_callback,
		2118	ev_arg, ev_fd, ev_res, ev_events.
		2119
		2120	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2121	maintained by libev, it does not work exactly the same way as in libevent (consider
		2122	it a private API).
		2123
		2124	=item * Priorities are not currently supported. Initialising priorities
		2125	will fail and all watchers will have the same priority, even though there
		2126	is an ev_pri field.
		2127
		2128	=item * Other members are not supported.
		2129
		2130	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2131	to use the libev header file and library.
		2132
		2133	=back
		2134
		2135	=head1 C++ SUPPORT
		2136
		2137	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2138	you to use some convinience methods to start/stop watchers and also change
		2139	the callback model to a model using method callbacks on objects.
		2140
		2141	To use it,
		2142
		2143	#include <ev++.h>
		2144
		2145	This automatically includes F<ev.h> and puts all of its definitions (many
		2146	of them macros) into the global namespace. All C++ specific things are
		2147	put into the C<ev> namespace. It should support all the same embedding
		2148	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2149
		2150	Care has been taken to keep the overhead low. The only data member the C++
		2151	classes add (compared to plain C-style watchers) is the event loop pointer
		2152	that the watcher is associated with (or no additional members at all if
		2153	you disable C<EV_MULTIPLICITY> when embedding libev).
		2154
		2155	Currently, functions, and static and non-static member functions can be
		2156	used as callbacks. Other types should be easy to add as long as they only
		2157	need one additional pointer for context. If you need support for other
		2158	types of functors please contact the author (preferably after implementing
		2159	it).
		2160
		2161	Here is a list of things available in the C<ev> namespace:
		2162
		2163	=over 4
		2164
		2165	=item C<ev::READ>, C<ev::WRITE> etc.
		2166
		2167	These are just enum values with the same values as the C<EV_READ> etc.
		2168	macros from F<ev.h>.
		2169
		2170	=item C<ev::tstamp>, C<ev::now>
		2171
		2172	Aliases to the same types/functions as with the C<ev_> prefix.
		2173
		2174	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2175
		2176	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2177	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2178	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2179	defines by many implementations.
		2180
		2181	All of those classes have these methods:
		2182
		2183	=over 4
		2184
		2185	=item ev::TYPE::TYPE ()
		2186
		2187	=item ev::TYPE::TYPE (struct ev_loop *)
		2188
		2189	=item ev::TYPE::~TYPE
		2190
		2191	The constructor (optionally) takes an event loop to associate the watcher
		2192	with. If it is omitted, it will use C<EV_DEFAULT>.
		2193
		2194	The constructor calls C<ev_init> for you, which means you have to call the
		2195	C<set> method before starting it.
		2196
		2197	It will not set a callback, however: You have to call the templated C<set>
		2198	method to set a callback before you can start the watcher.
		2199
		2200	(The reason why you have to use a method is a limitation in C++ which does
		2201	not allow explicit template arguments for constructors).
		2202
		2203	The destructor automatically stops the watcher if it is active.
		2204
		2205	=item w->set<class, &class::method> (object *)
		2206
		2207	This method sets the callback method to call. The method has to have a
		2208	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2209	first argument and the C<revents> as second. The object must be given as
		2210	parameter and is stored in the C<data> member of the watcher.
		2211
		2212	This method synthesizes efficient thunking code to call your method from
		2213	the C callback that libev requires. If your compiler can inline your
		2214	callback (i.e. it is visible to it at the place of the C<set> call and
		2215	your compiler is good :), then the method will be fully inlined into the
		2216	thunking function, making it as fast as a direct C callback.
		2217
		2218	Example: simple class declaration and watcher initialisation
		2219
		2220	struct myclass
		2221	{
		2222	void io_cb (ev::io &w, int revents) { }
		2223	}
		2224
		2225	myclass obj;
		2226	ev::io iow;
		2227	iow.set <myclass, &myclass::io_cb> (&obj);
		2228
		2229	=item w->set<function> (void *data = 0)
		2230
		2231	Also sets a callback, but uses a static method or plain function as
		2232	callback. The optional C<data> argument will be stored in the watcher's
		2233	C<data> member and is free for you to use.
		2234
		2235	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2236
		2237	See the method-C<set> above for more details.
		2238
		2239	Example:
		2240
		2241	static void io_cb (ev::io &w, int revents) { }
		2242	iow.set <io_cb> ();
		2243
		2244	=item w->set (struct ev_loop *)
		2245
		2246	Associates a different C<struct ev_loop> with this watcher. You can only
		2247	do this when the watcher is inactive (and not pending either).
		2248
		2249	=item w->set ([args])
		2250
		2251	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2252	called at least once. Unlike the C counterpart, an active watcher gets
		2253	automatically stopped and restarted when reconfiguring it with this
		2254	method.
		2255
		2256	=item w->start ()
		2257
		2258	Starts the watcher. Note that there is no C<loop> argument, as the
		2259	constructor already stores the event loop.
		2260
		2261	=item w->stop ()
		2262
		2263	Stops the watcher if it is active. Again, no C<loop> argument.
		2264
		2265	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2266
		2267	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2268	C<ev_TYPE_again> function.
		2269
		2270	=item w->sweep () (C<ev::embed> only)
		2271
		2272	Invokes C<ev_embed_sweep>.
		2273
		2274	=item w->update () (C<ev::stat> only)
		2275
		2276	Invokes C<ev_stat_stat>.
		2277
		2278	=back
		2279
		2280	=back
		2281
		2282	Example: Define a class with an IO and idle watcher, start one of them in
		2283	the constructor.
		2284
		2285	class myclass
		2286	{
		2287	ev::io io; void io_cb (ev::io &w, int revents);
		2288	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2289
		2290	myclass (int fd)
		2291	{
		2292	io .set <myclass, &myclass::io_cb > (this);
		2293	idle.set <myclass, &myclass::idle_cb> (this);
		2294
		2295	io.start (fd, ev::READ);
		2296	}
		2297	};
		2298
		2299
		2300	=head1 MACRO MAGIC
		2301
		2302	Libev can be compiled with a variety of options, the most fundamantal
		2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2304	functions and callbacks have an initial C<struct ev_loop *> argument.
		2305
		2306	To make it easier to write programs that cope with either variant, the
		2307	following macros are defined:
		2308
		2309	=over 4
		2310
		2311	=item C<EV_A>, C<EV_A_>
		2312
		2313	This provides the loop I<argument> for functions, if one is required ("ev
		2314	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2315	C<EV_A_> is used when other arguments are following. Example:
		2316
		2317	ev_unref (EV_A);
		2318	ev_timer_add (EV_A_ watcher);
		2319	ev_loop (EV_A_ 0);
		2320
		2321	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2322	which is often provided by the following macro.
		2323
		2324	=item C<EV_P>, C<EV_P_>
		2325
		2326	This provides the loop I<parameter> for functions, if one is required ("ev
		2327	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2328	C<EV_P_> is used when other parameters are following. Example:
		2329
		2330	// this is how ev_unref is being declared
		2331	static void ev_unref (EV_P);
		2332
		2333	// this is how you can declare your typical callback
		2334	static void cb (EV_P_ ev_timer *w, int revents)
		2335
		2336	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2337	suitable for use with C<EV_A>.
		2338
		2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2340
		2341	Similar to the other two macros, this gives you the value of the default
		2342	loop, if multiple loops are supported ("ev loop default").
		2343
		2344	=back
		2345
		2346	Example: Declare and initialise a check watcher, utilising the above
		2347	macros so it will work regardless of whether multiple loops are supported
		2348	or not.
		2349
		2350	static void
		2351	check_cb (EV_P_ ev_timer *w, int revents)
		2352	{
		2353	ev_check_stop (EV_A_ w);
		2354	}
		2355
		2356	ev_check check;
		2357	ev_check_init (&check, check_cb);
		2358	ev_check_start (EV_DEFAULT_ &check);
		2359	ev_loop (EV_DEFAULT_ 0);
		2360
		2361	=head1 EMBEDDING
		2362
		2363	Libev can (and often is) directly embedded into host
		2364	applications. Examples of applications that embed it include the Deliantra
		2365	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2366	and rxvt-unicode.
		2367
		2368	The goal is to enable you to just copy the necessary files into your
		2369	source directory without having to change even a single line in them, so
		2370	you can easily upgrade by simply copying (or having a checked-out copy of
		2371	libev somewhere in your source tree).
		2372
		2373	=head2 FILESETS
		2374
		2375	Depending on what features you need you need to include one or more sets of files
		2376	in your app.
		2377
		2378	=head3 CORE EVENT LOOP
		2379
		2380	To include only the libev core (all the C<ev_*> functions), with manual
		2381	configuration (no autoconf):
		2382
		2383	#define EV_STANDALONE 1
		2384	#include "ev.c"
		2385
		2386	This will automatically include F<ev.h>, too, and should be done in a
		2387	single C source file only to provide the function implementations. To use
		2388	it, do the same for F<ev.h> in all files wishing to use this API (best
		2389	done by writing a wrapper around F<ev.h> that you can include instead and
		2390	where you can put other configuration options):
		2391
		2392	#define EV_STANDALONE 1
		2393	#include "ev.h"
		2394
		2395	Both header files and implementation files can be compiled with a C++
		2396	compiler (at least, thats a stated goal, and breakage will be treated
		2397	as a bug).
		2398
		2399	You need the following files in your source tree, or in a directory
		2400	in your include path (e.g. in libev/ when using -Ilibev):
		2401
		2402	ev.h
		2403	ev.c
		2404	ev_vars.h
		2405	ev_wrap.h
		2406
		2407	ev_win32.c required on win32 platforms only
		2408
		2409	ev_select.c only when select backend is enabled (which is enabled by default)
		2410	ev_poll.c only when poll backend is enabled (disabled by default)
		2411	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2412	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2413	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2414
		2415	F<ev.c> includes the backend files directly when enabled, so you only need
		2416	to compile this single file.
		2417
		2418	=head3 LIBEVENT COMPATIBILITY API
		2419
		2420	To include the libevent compatibility API, also include:
		2421
		2422	#include "event.c"
		2423
		2424	in the file including F<ev.c>, and:
		2425
		2426	#include "event.h"
		2427
		2428	in the files that want to use the libevent API. This also includes F<ev.h>.
		2429
		2430	You need the following additional files for this:
		2431
		2432	event.h
		2433	event.c
		2434
		2435	=head3 AUTOCONF SUPPORT
		2436
		2437	Instead of using C<EV_STANDALONE=1> and providing your config in
		2438	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2439	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2440	include F<config.h> and configure itself accordingly.
		2441
		2442	For this of course you need the m4 file:
		2443
		2444	libev.m4
		2445
		2446	=head2 PREPROCESSOR SYMBOLS/MACROS
		2447
		2448	Libev can be configured via a variety of preprocessor symbols you have to define
		2449	before including any of its files. The default is not to build for multiplicity
		2450	and only include the select backend.
		2451
		2452	=over 4
		2453
		2454	=item EV_STANDALONE
		2455
		2456	Must always be C<1> if you do not use autoconf configuration, which
		2457	keeps libev from including F<config.h>, and it also defines dummy
		2458	implementations for some libevent functions (such as logging, which is not
		2459	supported). It will also not define any of the structs usually found in
		2460	F<event.h> that are not directly supported by the libev core alone.
		2461
		2462	=item EV_USE_MONOTONIC
		2463
		2464	If defined to be C<1>, libev will try to detect the availability of the
		2465	monotonic clock option at both compiletime and runtime. Otherwise no use
		2466	of the monotonic clock option will be attempted. If you enable this, you
		2467	usually have to link against librt or something similar. Enabling it when
		2468	the functionality isn't available is safe, though, although you have
		2469	to make sure you link against any libraries where the C<clock_gettime>
		2470	function is hiding in (often F<-lrt>).
		2471
		2472	=item EV_USE_REALTIME
		2473
		2474	If defined to be C<1>, libev will try to detect the availability of the
		2475	realtime clock option at compiletime (and assume its availability at
		2476	runtime if successful). Otherwise no use of the realtime clock option will
		2477	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2478	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2479	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2480
		2481	=item EV_USE_NANOSLEEP
		2482
		2483	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2484	and will use it for delays. Otherwise it will use C<select ()>.
		2485
		2486	=item EV_USE_SELECT
		2487
		2488	If undefined or defined to be C<1>, libev will compile in support for the
		2489	C<select>(2) backend. No attempt at autodetection will be done: if no
		2490	other method takes over, select will be it. Otherwise the select backend
		2491	will not be compiled in.
		2492
		2493	=item EV_SELECT_USE_FD_SET
		2494
		2495	If defined to C<1>, then the select backend will use the system C<fd_set>
		2496	structure. This is useful if libev doesn't compile due to a missing
		2497	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2498	exotic systems. This usually limits the range of file descriptors to some
		2499	low limit such as 1024 or might have other limitations (winsocket only
		2500	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2501	influence the size of the C<fd_set> used.
		2502
		2503	=item EV_SELECT_IS_WINSOCKET
		2504
		2505	When defined to C<1>, the select backend will assume that
		2506	select/socket/connect etc. don't understand file descriptors but
		2507	wants osf handles on win32 (this is the case when the select to
		2508	be used is the winsock select). This means that it will call
		2509	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2510	it is assumed that all these functions actually work on fds, even
		2511	on win32. Should not be defined on non-win32 platforms.
		2512
		2513	=item EV_FD_TO_WIN32_HANDLE
		2514
		2515	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2516	file descriptors to socket handles. When not defining this symbol (the
		2517	default), then libev will call C<_get_osfhandle>, which is usually
		2518	correct. In some cases, programs use their own file descriptor management,
		2519	in which case they can provide this function to map fds to socket handles.
		2520
		2521	=item EV_USE_POLL
		2522
		2523	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2524	backend. Otherwise it will be enabled on non-win32 platforms. It
		2525	takes precedence over select.
		2526
		2527	=item EV_USE_EPOLL
		2528
		2529	If defined to be C<1>, libev will compile in support for the Linux
		2530	C<epoll>(7) backend. Its availability will be detected at runtime,
		2531	otherwise another method will be used as fallback. This is the
		2532	preferred backend for GNU/Linux systems.
		2533
		2534	=item EV_USE_KQUEUE
		2535
		2536	If defined to be C<1>, libev will compile in support for the BSD style
		2537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2538	otherwise another method will be used as fallback. This is the preferred
		2539	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2540	supports some types of fds correctly (the only platform we found that
		2541	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2542	not be used unless explicitly requested. The best way to use it is to find
		2543	out whether kqueue supports your type of fd properly and use an embedded
		2544	kqueue loop.
		2545
		2546	=item EV_USE_PORT
		2547
		2548	If defined to be C<1>, libev will compile in support for the Solaris
		2549	10 port style backend. Its availability will be detected at runtime,
		2550	otherwise another method will be used as fallback. This is the preferred
		2551	backend for Solaris 10 systems.
		2552
		2553	=item EV_USE_DEVPOLL
		2554
		2555	reserved for future expansion, works like the USE symbols above.
		2556
		2557	=item EV_USE_INOTIFY
		2558
		2559	If defined to be C<1>, libev will compile in support for the Linux inotify
		2560	interface to speed up C<ev_stat> watchers. Its actual availability will
		2561	be detected at runtime.
		2562
		2563	=item EV_H
		2564
		2565	The name of the F<ev.h> header file used to include it. The default if
		2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2567	used to virtually rename the F<ev.h> header file in case of conflicts.
		2568
		2569	=item EV_CONFIG_H
		2570
		2571	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2572	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2573	C<EV_H>, above.
		2574
		2575	=item EV_EVENT_H
		2576
		2577	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2578	of how the F<event.h> header can be found, the default is C<"event.h">.
		2579
		2580	=item EV_PROTOTYPES
		2581
		2582	If defined to be C<0>, then F<ev.h> will not define any function
		2583	prototypes, but still define all the structs and other symbols. This is
		2584	occasionally useful if you want to provide your own wrapper functions
		2585	around libev functions.
		2586
		2587	=item EV_MULTIPLICITY
		2588
		2589	If undefined or defined to C<1>, then all event-loop-specific functions
		2590	will have the C<struct ev_loop *> as first argument, and you can create
		2591	additional independent event loops. Otherwise there will be no support
		2592	for multiple event loops and there is no first event loop pointer
		2593	argument. Instead, all functions act on the single default loop.
		2594
		2595	=item EV_MINPRI
		2596
		2597	=item EV_MAXPRI
		2598
		2599	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2600	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2601	provide for more priorities by overriding those symbols (usually defined
		2602	to be C<-2> and C<2>, respectively).
		2603
		2604	When doing priority-based operations, libev usually has to linearly search
		2605	all the priorities, so having many of them (hundreds) uses a lot of space
		2606	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2607	fine.
		2608
		2609	If your embedding app does not need any priorities, defining these both to
		2610	C<0> will save some memory and cpu.
		2611
		2612	=item EV_PERIODIC_ENABLE
		2613
		2614	If undefined or defined to be C<1>, then periodic timers are supported. If
		2615	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2616	code.
		2617
		2618	=item EV_IDLE_ENABLE
		2619
		2620	If undefined or defined to be C<1>, then idle watchers are supported. If
		2621	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2622	code.
		2623
		2624	=item EV_EMBED_ENABLE
		2625
		2626	If undefined or defined to be C<1>, then embed watchers are supported. If
		2627	defined to be C<0>, then they are not.
		2628
		2629	=item EV_STAT_ENABLE
		2630
		2631	If undefined or defined to be C<1>, then stat watchers are supported. If
		2632	defined to be C<0>, then they are not.
		2633
		2634	=item EV_FORK_ENABLE
		2635
		2636	If undefined or defined to be C<1>, then fork watchers are supported. If
		2637	defined to be C<0>, then they are not.
		2638
		2639	=item EV_MINIMAL
		2640
		2641	If you need to shave off some kilobytes of code at the expense of some
		2642	speed, define this symbol to C<1>. Currently only used for gcc to override
		2643	some inlining decisions, saves roughly 30% codesize of amd64.
		2644
		2645	=item EV_PID_HASHSIZE
		2646
		2647	C<ev_child> watchers use a small hash table to distribute workload by
		2648	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2649	than enough. If you need to manage thousands of children you might want to
		2650	increase this value (I<must> be a power of two).
		2651
		2652	=item EV_INOTIFY_HASHSIZE
		2653
		2654	C<ev_stat> watchers use a small hash table to distribute workload by
		2655	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2656	usually more than enough. If you need to manage thousands of C<ev_stat>
		2657	watchers you might want to increase this value (I<must> be a power of
		2658	two).
		2659
		2660	=item EV_COMMON
		2661
		2662	By default, all watchers have a C<void *data> member. By redefining
		2663	this macro to a something else you can include more and other types of
		2664	members. You have to define it each time you include one of the files,
		2665	though, and it must be identical each time.
		2666
		2667	For example, the perl EV module uses something like this:
		2668
		2669	#define EV_COMMON \
		2670	SV *self; /* contains this struct */ \
		2671	SV *cb_sv, *fh /* note no trailing ";" */
		2672
		2673	=item EV_CB_DECLARE (type)
		2674
		2675	=item EV_CB_INVOKE (watcher, revents)
		2676
		2677	=item ev_set_cb (ev, cb)
		2678
		2679	Can be used to change the callback member declaration in each watcher,
		2680	and the way callbacks are invoked and set. Must expand to a struct member
		2681	definition and a statement, respectively. See the F<ev.h> header file for
		2682	their default definitions. One possible use for overriding these is to
		2683	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2684	method calls instead of plain function calls in C++.
		2685
		2686	=head2 EXPORTED API SYMBOLS
		2687
		2688	If you need to re-export the API (e.g. via a dll) and you need a list of
		2689	exported symbols, you can use the provided F<Symbol.*> files which list
		2690	all public symbols, one per line:
		2691
		2692	Symbols.ev for libev proper
		2693	Symbols.event for the libevent emulation
		2694
		2695	This can also be used to rename all public symbols to avoid clashes with
		2696	multiple versions of libev linked together (which is obviously bad in
		2697	itself, but sometimes it is inconvinient to avoid this).
		2698
		2699	A sed command like this will create wrapper C<#define>'s that you need to
		2700	include before including F<ev.h>:
		2701
		2702	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2703
		2704	This would create a file F<wrap.h> which essentially looks like this:
		2705
		2706	#define ev_backend myprefix_ev_backend
		2707	#define ev_check_start myprefix_ev_check_start
		2708	#define ev_check_stop myprefix_ev_check_stop
		2709	...
		2710
		2711	=head2 EXAMPLES
		2712
		2713	For a real-world example of a program the includes libev
		2714	verbatim, you can have a look at the EV perl module
		2715	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2716	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2717	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2718	will be compiled. It is pretty complex because it provides its own header
		2719	file.
		2720
		2721	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2722	that everybody includes and which overrides some configure choices:
		2723
		2724	#define EV_MINIMAL 1
		2725	#define EV_USE_POLL 0
		2726	#define EV_MULTIPLICITY 0
		2727	#define EV_PERIODIC_ENABLE 0
		2728	#define EV_STAT_ENABLE 0
		2729	#define EV_FORK_ENABLE 0
		2730	#define EV_CONFIG_H <config.h>
		2731	#define EV_MINPRI 0
		2732	#define EV_MAXPRI 0
		2733
		2734	#include "ev++.h"
		2735
		2736	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2737
		2738	#include "ev_cpp.h"
		2739	#include "ev.c"
		2740
		2741
		2742	=head1 COMPLEXITIES
		2743
		2744	In this section the complexities of (many of) the algorithms used inside
		2745	libev will be explained. For complexity discussions about backends see the
		2746	documentation for C<ev_default_init>.
		2747
		2748	All of the following are about amortised time: If an array needs to be
		2749	extended, libev needs to realloc and move the whole array, but this
		2750	happens asymptotically never with higher number of elements, so O(1) might
		2751	mean it might do a lengthy realloc operation in rare cases, but on average
		2752	it is much faster and asymptotically approaches constant time.
		2753
		2754	=over 4
		2755
		2756	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2757
		2758	This means that, when you have a watcher that triggers in one hour and
		2759	there are 100 watchers that would trigger before that then inserting will
		2760	have to skip roughly seven (C<ld 100>) of these watchers.
		2761
		2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2763
		2764	That means that changing a timer costs less than removing/adding them
		2765	as only the relative motion in the event queue has to be paid for.
		2766
		2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2768
		2769	These just add the watcher into an array or at the head of a list.
		2770
		2771	=item Stopping check/prepare/idle watchers: O(1)
		2772
		2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2774
		2775	These watchers are stored in lists then need to be walked to find the
		2776	correct watcher to remove. The lists are usually short (you don't usually
		2777	have many watchers waiting for the same fd or signal).
		2778
		2779	=item Finding the next timer in each loop iteration: O(1)
		2780
		2781	By virtue of using a binary heap, the next timer is always found at the
		2782	beginning of the storage array.
		2783
		2784	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2785
		2786	A change means an I/O watcher gets started or stopped, which requires
		2787	libev to recalculate its status (and possibly tell the kernel, depending
		2788	on backend and wether C<ev_io_set> was used).
		2789
		2790	=item Activating one watcher (putting it into the pending state): O(1)
		2791
		2792	=item Priority handling: O(number_of_priorities)
		2793
		2794	Priorities are implemented by allocating some space for each
		2795	priority. When doing priority-based operations, libev usually has to
		2796	linearly search all the priorities, but starting/stopping and activating
		2797	watchers becomes O(1) w.r.t. prioritiy handling.
		2798
		2799	=back
		2800
		2801
		2802	=head1 Win32 platform limitations and workarounds
		2803
		2804	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2805	requires, and its I/O model is fundamentally incompatible with the POSIX
		2806	model. Libev still offers limited functionality on this platform in
		2807	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2808	descriptors. This only applies when using Win32 natively, not when using
		2809	e.g. cygwin.
		2810
		2811	There is no supported compilation method available on windows except
		2812	embedding it into other applications.
		2813
		2814	Due to the many, low, and arbitrary limits on the win32 platform and the
		2815	abysmal performance of winsockets, using a large number of sockets is not
		2816	recommended (and not reasonable). If your program needs to use more than
		2817	a hundred or so sockets, then likely it needs to use a totally different
		2818	implementation for windows, as libev offers the POSIX model, which cannot
		2819	be implemented efficiently on windows (microsoft monopoly games).
		2820
		2821	=over 4
		2822
		2823	=item The winsocket select function
		2824
		2825	The winsocket C<select> function doesn't follow POSIX in that it requires
		2826	socket I<handles> and not socket I<file descriptors>. This makes select
		2827	very inefficient, and also requires a mapping from file descriptors
		2828	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2829	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2830	symbols for more info.
		2831
		2832	The configuration for a "naked" win32 using the microsoft runtime
		2833	libraries and raw winsocket select is:
		2834
		2835	#define EV_USE_SELECT 1
		2836	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		2837
		2838	Note that winsockets handling of fd sets is O(n), so you can easily get a
		2839	complexity in the O(n²) range when using win32.
		2840
		2841	=item Limited number of file descriptors
		2842
		2843	Windows has numerous arbitrary (and low) limits on things. Early versions
		2844	of winsocket's select only supported waiting for a max. of C<64> handles
		2845	(probably owning to the fact that all windows kernels can only wait for
		2846	C<64> things at the same time internally; microsoft recommends spawning a
		2847	chain of threads and wait for 63 handles and the previous thread in each).
		2848
		2849	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		2850	to some high number (e.g. C<2048>) before compiling the winsocket select
		2851	call (which might be in libev or elsewhere, for example, perl does its own
		2852	select emulation on windows).
		2853
		2854	Another limit is the number of file descriptors in the microsoft runtime
		2855	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		2856	or something like this inside microsoft). You can increase this by calling
		2857	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		2858	arbitrary limit), but is broken in many versions of the microsoft runtime
		2859	libraries.
		2860
		2861	This might get you to about C<512> or C<2048> sockets (depending on
		2862	windows version and/or the phase of the moon). To get more, you need to
		2863	wrap all I/O functions and provide your own fd management, but the cost of
		2864	calling select (O(n²)) will likely make this unworkable.
		2865
		2866	=back
		2867
		2868
767	=head1 AUTHOR	2869	=head1 AUTHOR
768		2870
769	Marc Lehmann <libev@schmorp.de>.	2871	Marc Lehmann <libev@schmorp.de>.
770		2872

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines