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Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.276 by root, Tue Dec 29 13:11:00 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
82		111
83	It also is quite fast (see this	112	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	114	for example).
86		115
87	=head1 CONVENTIONS	116	=head2 CONVENTIONS
88		117
89	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	122	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		124	this argument.
95		125
96	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
97		127
98	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as such.	133	on it, you should treat it as some floating point value. Unlike the name
		134	component C<stamp> might indicate, it is also used for time differences
		135	throughout libev.
		136
		137	=head1 ERROR HANDLING
		138
		139	Libev knows three classes of errors: operating system errors, usage errors
		140	and internal errors (bugs).
		141
		142	When libev catches an operating system error it cannot handle (for example
		143	a system call indicating a condition libev cannot fix), it calls the callback
		144	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		145	abort. The default is to print a diagnostic message and to call C<abort
		146	()>.
		147
		148	When libev detects a usage error such as a negative timer interval, then
		149	it will print a diagnostic message and abort (via the C<assert> mechanism,
		150	so C<NDEBUG> will disable this checking): these are programming errors in
		151	the libev caller and need to be fixed there.
		152
		153	Libev also has a few internal error-checking C<assert>ions, and also has
		154	extensive consistency checking code. These do not trigger under normal
		155	circumstances, as they indicate either a bug in libev or worse.
		156
104		157
105	=head1 GLOBAL FUNCTIONS	158	=head1 GLOBAL FUNCTIONS
106		159
107	These functions can be called anytime, even before initialising the	160	These functions can be called anytime, even before initialising the
108	library in any way.	161	library in any way.
…		…
113		166
114	Returns the current time as libev would use it. Please note that the	167	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	168	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	169	you actually want to know.
117		170
		171	=item ev_sleep (ev_tstamp interval)
		172
		173	Sleep for the given interval: The current thread will be blocked until
		174	either it is interrupted or the given time interval has passed. Basically
		175	this is a sub-second-resolution C<sleep ()>.
		176
118	=item int ev_version_major ()	177	=item int ev_version_major ()
119		178
120	=item int ev_version_minor ()	179	=item int ev_version_minor ()
121		180
122	You can find out the major and minor version numbers of the library	181	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	182	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	183	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	184	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	185	version of the library your program was compiled against.
127		186
		187	These version numbers refer to the ABI version of the library, not the
		188	release version.
		189
128	Usually, it's a good idea to terminate if the major versions mismatch,	190	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	191	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	192	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	193	not a problem.
132		194
133	Example: Make sure we haven't accidentally been linked against the wrong	195	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	196	version.
135		197
136	assert (("libev version mismatch",	198	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
139		201
140	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
141		203
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	204	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	207	a description of the set values.
146		208
147	Example: make sure we have the epoll method, because yeah this is cool and	209	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	210	a must have and can we have a torrent of it please!!!11
149		211
150	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
152		214
153	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
154		216
155	Return the set of all backends compiled into this binary of libev and also	217	Return the set of all backends compiled into this binary of libev and also
156	recommended for this platform. This set is often smaller than the one	218	recommended for this platform. This set is often smaller than the one
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	219	returned by C<ev_supported_backends>, as for example kqueue is broken on
158	most BSDs and will not be autodetected unless you explicitly request it	220	most BSDs and will not be auto-detected unless you explicitly request it
159	(assuming you know what you are doing). This is the set of backends that	221	(assuming you know what you are doing). This is the set of backends that
160	libev will probe for if you specify no backends explicitly.	222	libev will probe for if you specify no backends explicitly.
161		223
162	=item unsigned int ev_embeddable_backends ()	224	=item unsigned int ev_embeddable_backends ()
163		225
…		…
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
168	recommended ones.	230	recommended ones.
169		231
170	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
171		233
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		235
174	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	238	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	239	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	240	or take some potentially destructive action.
179	function.	241
		242	Since some systems (at least OpenBSD and Darwin) fail to implement
		243	correct C<realloc> semantics, libev will use a wrapper around the system
		244	C<realloc> and C<free> functions by default.
180		245
181	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	247	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	248	or even to sleep a while and retry until some memory is available.
184		249
185	Example: Replace the libev allocator with one that waits a bit and then	250	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	251	retries (example requires a standards-compliant C<realloc>).
187		252
188	static void *	253	static void *
189	persistent_realloc (void *ptr, size_t size)	254	persistent_realloc (void *ptr, size_t size)
190	{	255	{
191	for (;;)	256	for (;;)
…		…
200	}	265	}
201		266
202	...	267	...
203	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
204		269
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		271
207	Set the callback function to call on a retryable syscall error (such	272	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	273	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	275	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	276	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	277	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	278	(such as abort).
214		279
215	Example: This is basically the same thing that libev does internally, too.	280	Example: This is basically the same thing that libev does internally, too.
…		…
226		291
227	=back	292	=back
228		293
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		295
231	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
232	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
233	events, and dynamically created loops which do not.	298	I<function>).
234		299
235	If you use threads, a common model is to run the default event loop	300	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	301	supports signals and child events, and dynamically created loops which do
237	create, you also create another event loop. Libev itself does no locking	302	not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		303
242	=over 4	304	=over 4
243		305
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		307
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		312
251	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
252	function.	314	function.
253		315
		316	Note that this function is I<not> thread-safe, so if you want to use it
		317	from multiple threads, you have to lock (note also that this is unlikely,
		318	as loops cannot be shared easily between threads anyway).
		319
		320	The default loop is the only loop that can handle C<ev_signal> and
		321	C<ev_child> watchers, and to do this, it always registers a handler
		322	for C<SIGCHLD>. If this is a problem for your application you can either
		323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		324	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		325	C<ev_default_init>.
		326
254	The flags argument can be used to specify special behaviour or specific	327	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	328	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		329
257	The following flags are supported:	330	The following flags are supported:
258		331
…		…
263	The default flags value. Use this if you have no clue (it's the right	336	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	337	thing, believe me).
265		338
266	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
267		340
268	If this flag bit is ored into the flag value (or the program runs setuid	341	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	342	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	344	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	345	useful to try out specific backends to test their performance, or to work
273	around bugs.	346	around bugs.
…		…
279	enabling this flag.	352	enabling this flag.
280		353
281	This works by calling C<getpid ()> on every iteration of the loop,	354	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	355	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	356	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	358	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
287		360
288	The big advantage of this flag is that you can forget about fork (and	361	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	362	forget about forgetting to tell libev about forking) when you use this
290	flag.	363	flag.
291		364
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
294		382
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		384
297	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	388	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	389	usually the fastest backend for a low number of (low-numbered :) fds.
		390
		391	To get good performance out of this backend you need a high amount of
		392	parallelism (most of the file descriptors should be busy). If you are
		393	writing a server, you should C<accept ()> in a loop to accept as many
		394	connections as possible during one iteration. You might also want to have
		395	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		396	readiness notifications you get per iteration.
		397
		398	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		399	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		400	C<exceptfds> set on that platform).
302		401
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	402	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		403
305	And this is your standard poll(2) backend. It's more complicated than	404	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	405	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	406	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	407	considerably with a lot of inactive fds). It scales similarly to select,
		408	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		409	performance tips.
		410
		411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		413
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
		418
312	For few fds, this backend is a bit little slower than poll and select,	419	For few fds, this backend is a bit little slower than poll and select,
313	but it scales phenomenally better. While poll and select usually scale like	420	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	421	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	422	epoll scales either O(1) or O(active_fds).
316		423
		424	The epoll mechanism deserves honorable mention as the most misdesigned
		425	of the more advanced event mechanisms: mere annoyances include silently
		426	dropping file descriptors, requiring a system call per change per file
		427	descriptor (and unnecessary guessing of parameters), problems with dup and
		428	so on. The biggest issue is fork races, however - if a program forks then
		429	I<both> parent and child process have to recreate the epoll set, which can
		430	take considerable time (one syscall per file descriptor) and is of course
		431	hard to detect.
		432
		433	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		434	of course I<doesn't>, and epoll just loves to report events for totally
		435	I<different> file descriptors (even already closed ones, so one cannot
		436	even remove them from the set) than registered in the set (especially
		437	on SMP systems). Libev tries to counter these spurious notifications by
		438	employing an additional generation counter and comparing that against the
		439	events to filter out spurious ones, recreating the set when required.
		440
317	While stopping and starting an I/O watcher in the same iteration will	441	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	442	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	443	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	444	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	445	file descriptors might not work very well if you register events for both
		446	file descriptors.
322		447
323	Please note that epoll sometimes generates spurious notifications, so you	448	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	449	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	450	i.e. keep at least one watcher active per fd at all times. Stopping and
		451	starting a watcher (without re-setting it) also usually doesn't cause
		452	extra overhead. A fork can both result in spurious notifications as well
		453	as in libev having to destroy and recreate the epoll object, which can
		454	take considerable time and thus should be avoided.
		455
		456	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		457	faster than epoll for maybe up to a hundred file descriptors, depending on
		458	the usage. So sad.
		459
		460	While nominally embeddable in other event loops, this feature is broken in
		461	all kernel versions tested so far.
		462
		463	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		464	C<EVBACKEND_POLL>.
326		465
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	466	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		467
329	Kqueue deserves special mention, as at the time of this writing, it	468	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	469	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	470	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	471	it's completely useless). Unlike epoll, however, whose brokenness
		472	is by design, these kqueue bugs can (and eventually will) be fixed
		473	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	474	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	475	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		476	system like NetBSD.
		477
		478	You still can embed kqueue into a normal poll or select backend and use it
		479	only for sockets (after having made sure that sockets work with kqueue on
		480	the target platform). See C<ev_embed> watchers for more info.
335		481
336	It scales in the same way as the epoll backend, but the interface to the	482	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	483	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	484	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	485	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	486	two event changes per incident. Support for C<fork ()> is very bad (but
		487	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		488	cases
		489
		490	This backend usually performs well under most conditions.
		491
		492	While nominally embeddable in other event loops, this doesn't work
		493	everywhere, so you might need to test for this. And since it is broken
		494	almost everywhere, you should only use it when you have a lot of sockets
		495	(for which it usually works), by embedding it into another event loop
		496	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		497	also broken on OS X)) and, did I mention it, using it only for sockets.
		498
		499	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		500	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		501	C<NOTE_EOF>.
341		502
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	503	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		504
344	This is not implemented yet (and might never be).	505	This is not implemented yet (and might never be, unless you send me an
		506	implementation). According to reports, C</dev/poll> only supports sockets
		507	and is not embeddable, which would limit the usefulness of this backend
		508	immensely.
345		509
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	510	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		511
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	512	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	513	it's really slow, but it still scales very well (O(active_fds)).
350		514
351	Please note that solaris ports can result in a lot of spurious	515	Please note that Solaris event ports can deliver a lot of spurious
352	notifications, so you need to use non-blocking I/O or other means to avoid	516	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	517	blocking when no data (or space) is available.
		518
		519	While this backend scales well, it requires one system call per active
		520	file descriptor per loop iteration. For small and medium numbers of file
		521	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		522	might perform better.
		523
		524	On the positive side, with the exception of the spurious readiness
		525	notifications, this backend actually performed fully to specification
		526	in all tests and is fully embeddable, which is a rare feat among the
		527	OS-specific backends (I vastly prefer correctness over speed hacks).
		528
		529	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		530	C<EVBACKEND_POLL>.
354		531
355	=item C<EVBACKEND_ALL>	532	=item C<EVBACKEND_ALL>
356		533
357	Try all backends (even potentially broken ones that wouldn't be tried	534	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	535	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	536	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		537
		538	It is definitely not recommended to use this flag.
		539
361	=back	540	=back
362		541
363	If one or more of these are ored into the flags value, then only these	542	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	543	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	544	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	545	()> will be tried.
367		546
368	The most typical usage is like this:	547	Example: This is the most typical usage.
369		548
370	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		551
373	Restrict libev to the select and poll backends, and do not allow	552	Example: Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:	553	environment settings to be taken into account:
375		554
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	555	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		556
378	Use whatever libev has to offer, but make sure that kqueue is used if	557	Example: Use whatever libev has to offer, but make sure that kqueue is
379	available (warning, breaks stuff, best use only with your own private	558	used if available (warning, breaks stuff, best use only with your own
380	event loop and only if you know the OS supports your types of fds):	559	private event loop and only if you know the OS supports your types of
		560	fds):
381		561
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	562	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		563
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	564	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		565
386	Similar to C<ev_default_loop>, but always creates a new event loop that is	566	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot	567	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by	568	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).	569	undefined behaviour (or a failed assertion if assertions are enabled).
390		570
		571	Note that this function I<is> thread-safe, and the recommended way to use
		572	libev with threads is indeed to create one loop per thread, and using the
		573	default loop in the "main" or "initial" thread.
		574
391	Example: Try to create a event loop that uses epoll and nothing else.	575	Example: Try to create a event loop that uses epoll and nothing else.
392		576
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	577	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	578	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	579	fatal ("no epoll found here, maybe it hides under your chair");
396		580
397	=item ev_default_destroy ()	581	=item ev_default_destroy ()
398		582
399	Destroys the default loop again (frees all memory and kernel state	583	Destroys the default loop again (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	584	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	585	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	586	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	587	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	588	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	589	for example).
		590
		591	Note that certain global state, such as signal state (and installed signal
		592	handlers), will not be freed by this function, and related watchers (such
		593	as signal and child watchers) would need to be stopped manually.
		594
		595	In general it is not advisable to call this function except in the
		596	rare occasion where you really need to free e.g. the signal handling
		597	pipe fds. If you need dynamically allocated loops it is better to use
		598	C<ev_loop_new> and C<ev_loop_destroy>.
406		599
407	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
408		601
409	Like C<ev_default_destroy>, but destroys an event loop created by an	602	Like C<ev_default_destroy>, but destroys an event loop created by an
410	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
411		604
412	=item ev_default_fork ()	605	=item ev_default_fork ()
413		606
		607	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	608	to reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	609	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	610	the child process (or both child and parent, but that again makes little
417	again makes little sense).	611	sense). You I<must> call it in the child before using any of the libev
		612	functions, and it will only take effect at the next C<ev_loop> iteration.
418		613
419	You I<must> call this function in the child process after forking if and	614	On the other hand, you only need to call this function in the child
420	only if you want to use the event library in both processes. If you just	615	process if and only if you want to use the event library in the child. If
421	fork+exec, you don't have to call it.	616	you just fork+exec, you don't have to call it at all.
422		617
423	The function itself is quite fast and it's usually not a problem to call	618	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	619	it just in case after a fork. To make this easy, the function will fit in
425	quite nicely into a call to C<pthread_atfork>:	620	quite nicely into a call to C<pthread_atfork>:
426		621
427	pthread_atfork (0, 0, ev_default_fork);	622	pthread_atfork (0, 0, ev_default_fork);
428		623
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	624	=item ev_loop_fork (loop)
434		625
435	Like C<ev_default_fork>, but acts on an event loop created by	626	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	627	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.	628	after fork that you want to re-use in the child, and how you do this is
		629	entirely your own problem.
		630
		631	=item int ev_is_default_loop (loop)
		632
		633	Returns true when the given loop is, in fact, the default loop, and false
		634	otherwise.
438		635
439	=item unsigned int ev_loop_count (loop)	636	=item unsigned int ev_loop_count (loop)
440		637
441	Returns the count of loop iterations for the loop, which is identical to	638	Returns the count of loop iterations for the loop, which is identical to
442	the number of times libev did poll for new events. It starts at C<0> and	639	the number of times libev did poll for new events. It starts at C<0> and
443	happily wraps around with enough iterations.	640	happily wraps around with enough iterations.
444		641
445	This value can sometimes be useful as a generation counter of sorts (it	642	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	643	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	644	C<ev_prepare> and C<ev_check> calls.
		645
		646	=item unsigned int ev_loop_depth (loop)
		647
		648	Returns the number of times C<ev_loop> was entered minus the number of
		649	times C<ev_loop> was exited, in other words, the recursion depth.
		650
		651	Outside C<ev_loop>, this number is zero. In a callback, this number is
		652	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		653	in which case it is higher.
		654
		655	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		656	etc.), doesn't count as exit.
448		657
449	=item unsigned int ev_backend (loop)	658	=item unsigned int ev_backend (loop)
450		659
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	660	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	661	use.
…		…
455		664
456	Returns the current "event loop time", which is the time the event loop	665	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	666	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	667	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	668	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	669	event occurring (or more correctly, libev finding out about it).
		670
		671	=item ev_now_update (loop)
		672
		673	Establishes the current time by querying the kernel, updating the time
		674	returned by C<ev_now ()> in the progress. This is a costly operation and
		675	is usually done automatically within C<ev_loop ()>.
		676
		677	This function is rarely useful, but when some event callback runs for a
		678	very long time without entering the event loop, updating libev's idea of
		679	the current time is a good idea.
		680
		681	See also L<The special problem of time updates> in the C<ev_timer> section.
		682
		683	=item ev_suspend (loop)
		684
		685	=item ev_resume (loop)
		686
		687	These two functions suspend and resume a loop, for use when the loop is
		688	not used for a while and timeouts should not be processed.
		689
		690	A typical use case would be an interactive program such as a game: When
		691	the user presses C<^Z> to suspend the game and resumes it an hour later it
		692	would be best to handle timeouts as if no time had actually passed while
		693	the program was suspended. This can be achieved by calling C<ev_suspend>
		694	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		695	C<ev_resume> directly afterwards to resume timer processing.
		696
		697	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		698	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		699	will be rescheduled (that is, they will lose any events that would have
		700	occured while suspended).
		701
		702	After calling C<ev_suspend> you B<must not> call I<any> function on the
		703	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		704	without a previous call to C<ev_suspend>.
		705
		706	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		707	event loop time (see C<ev_now_update>).
461		708
462	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
463		710
464	Finally, this is it, the event handler. This function usually is called	711	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	712	after you have initialised all your watchers and you want to start
466	events.	713	handling events.
467		714
468	If the flags argument is specified as C<0>, it will not return until	715	If the flags argument is specified as C<0>, it will not return until
469	either no event watchers are active anymore or C<ev_unloop> was called.	716	either no event watchers are active anymore or C<ev_unloop> was called.
470		717
471	Please note that an explicit C<ev_unloop> is usually better than	718	Please note that an explicit C<ev_unloop> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	719	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	720	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	721	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	722	of relying on its watchers stopping correctly, that is truly a thing of
		723	beauty.
476		724
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	725	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	726	those events and any already outstanding ones, but will not block your
479	case there are no events and will return after one iteration of the loop.	727	process in case there are no events and will return after one iteration of
		728	the loop.
480		729
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	730	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	731	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	732	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	733	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	734	user-registered callback will be called), and will return after one
		735	iteration of the loop.
		736
		737	This is useful if you are waiting for some external event in conjunction
		738	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	739	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	740	usually a better approach for this kind of thing.
488		741
489	Here are the gory details of what C<ev_loop> does:	742	Here are the gory details of what C<ev_loop> does:
490		743
491	* If there are no active watchers (reference count is zero), return.	744	- Before the first iteration, call any pending watchers.
492	- Queue prepare watchers and then call all outstanding watchers.	745	* If EVFLAG_FORKCHECK was used, check for a fork.
		746	- If a fork was detected (by any means), queue and call all fork watchers.
		747	- Queue and call all prepare watchers.
493	- If we have been forked, recreate the kernel state.	748	- If we have been forked, detach and recreate the kernel state
		749	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	750	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	751	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	752	- Calculate for how long to sleep or block, if at all
		753	(active idle watchers, EVLOOP_NONBLOCK or not having
		754	any active watchers at all will result in not sleeping).
		755	- Sleep if the I/O and timer collect interval say so.
497	- Block the process, waiting for any events.	756	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	757	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	758	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	759	- Queue all expired timers.
501	- Queue all outstanding periodics.	760	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	761	- Unless any events are pending now, queue all idle watchers.
503	- Queue all check watchers.	762	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	763	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	764	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	765	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	766	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
508	were used, return, otherwise continue with step *.	767	were used, or there are no active watchers, return, otherwise
		768	continue with step *.
509		769
510	Example: Queue some jobs and then loop until no events are outsanding	770	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	771	anymore.
512		772
513	... queue jobs here, make sure they register event watchers as long	773	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	774	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	775	ev_loop (my_loop, 0);
516	... jobs done. yeah!	776	... jobs done or somebody called unloop. yeah!
517		777
518	=item ev_unloop (loop, how)	778	=item ev_unloop (loop, how)
519		779
520	Can be used to make a call to C<ev_loop> return early (but only after it	780	Can be used to make a call to C<ev_loop> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	781	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	782	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	783	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
524		784
		785	This "unloop state" will be cleared when entering C<ev_loop> again.
		786
		787	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		788
525	=item ev_ref (loop)	789	=item ev_ref (loop)
526		790
527	=item ev_unref (loop)	791	=item ev_unref (loop)
528		792
529	Ref/unref can be used to add or remove a reference count on the event	793	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	794	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	795	count is nonzero, C<ev_loop> will not return on its own.
532	a watcher you never unregister that should not keep C<ev_loop> from	796
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	797	This is useful when you have a watcher that you never intend to
		798	unregister, but that nevertheless should not keep C<ev_loop> from
		799	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		800	before stopping it.
		801
534	example, libev itself uses this for its internal signal pipe: It is not	802	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	803	is not visible to the libev user and should not keep C<ev_loop> from
536	no event watchers registered by it are active. It is also an excellent	804	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	805	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	806	third-party libraries. Just remember to I<unref after start> and I<ref
		807	before stop> (but only if the watcher wasn't active before, or was active
		808	before, respectively. Note also that libev might stop watchers itself
		809	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		810	in the callback).
539		811
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	812	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
541	running when nothing else is active.	813	running when nothing else is active.
542		814
543	struct ev_signal exitsig;	815	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	816	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	817	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	818	evf_unref (loop);
547		819
548	Example: For some weird reason, unregister the above signal handler again.	820	Example: For some weird reason, unregister the above signal handler again.
549		821
550	ev_ref (loop);	822	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	823	ev_signal_stop (loop, &exitsig);
		824
		825	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		826
		827	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		828
		829	These advanced functions influence the time that libev will spend waiting
		830	for events. Both time intervals are by default C<0>, meaning that libev
		831	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		832	latency.
		833
		834	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		835	allows libev to delay invocation of I/O and timer/periodic callbacks
		836	to increase efficiency of loop iterations (or to increase power-saving
		837	opportunities).
		838
		839	The idea is that sometimes your program runs just fast enough to handle
		840	one (or very few) event(s) per loop iteration. While this makes the
		841	program responsive, it also wastes a lot of CPU time to poll for new
		842	events, especially with backends like C<select ()> which have a high
		843	overhead for the actual polling but can deliver many events at once.
		844
		845	By setting a higher I<io collect interval> you allow libev to spend more
		846	time collecting I/O events, so you can handle more events per iteration,
		847	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		848	C<ev_timer>) will be not affected. Setting this to a non-null value will
		849	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		850	sleep time ensures that libev will not poll for I/O events more often then
		851	once per this interval, on average.
		852
		853	Likewise, by setting a higher I<timeout collect interval> you allow libev
		854	to spend more time collecting timeouts, at the expense of increased
		855	latency/jitter/inexactness (the watcher callback will be called
		856	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		857	value will not introduce any overhead in libev.
		858
		859	Many (busy) programs can usually benefit by setting the I/O collect
		860	interval to a value near C<0.1> or so, which is often enough for
		861	interactive servers (of course not for games), likewise for timeouts. It
		862	usually doesn't make much sense to set it to a lower value than C<0.01>,
		863	as this approaches the timing granularity of most systems. Note that if
		864	you do transactions with the outside world and you can't increase the
		865	parallelity, then this setting will limit your transaction rate (if you
		866	need to poll once per transaction and the I/O collect interval is 0.01,
		867	then you can't do more than 100 transations per second).
		868
		869	Setting the I<timeout collect interval> can improve the opportunity for
		870	saving power, as the program will "bundle" timer callback invocations that
		871	are "near" in time together, by delaying some, thus reducing the number of
		872	times the process sleeps and wakes up again. Another useful technique to
		873	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		874	they fire on, say, one-second boundaries only.
		875
		876	Example: we only need 0.1s timeout granularity, and we wish not to poll
		877	more often than 100 times per second:
		878
		879	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		880	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		881
		882	=item ev_invoke_pending (loop)
		883
		884	This call will simply invoke all pending watchers while resetting their
		885	pending state. Normally, C<ev_loop> does this automatically when required,
		886	but when overriding the invoke callback this call comes handy.
		887
		888	=item int ev_pending_count (loop)
		889
		890	Returns the number of pending watchers - zero indicates that no watchers
		891	are pending.
		892
		893	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		894
		895	This overrides the invoke pending functionality of the loop: Instead of
		896	invoking all pending watchers when there are any, C<ev_loop> will call
		897	this callback instead. This is useful, for example, when you want to
		898	invoke the actual watchers inside another context (another thread etc.).
		899
		900	If you want to reset the callback, use C<ev_invoke_pending> as new
		901	callback.
		902
		903	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		904
		905	Sometimes you want to share the same loop between multiple threads. This
		906	can be done relatively simply by putting mutex_lock/unlock calls around
		907	each call to a libev function.
		908
		909	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		910	wait for it to return. One way around this is to wake up the loop via
		911	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		912	and I<acquire> callbacks on the loop.
		913
		914	When set, then C<release> will be called just before the thread is
		915	suspended waiting for new events, and C<acquire> is called just
		916	afterwards.
		917
		918	Ideally, C<release> will just call your mutex_unlock function, and
		919	C<acquire> will just call the mutex_lock function again.
		920
		921	While event loop modifications are allowed between invocations of
		922	C<release> and C<acquire> (that's their only purpose after all), no
		923	modifications done will affect the event loop, i.e. adding watchers will
		924	have no effect on the set of file descriptors being watched, or the time
		925	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		926	to take note of any changes you made.
		927
		928	In theory, threads executing C<ev_loop> will be async-cancel safe between
		929	invocations of C<release> and C<acquire>.
		930
		931	See also the locking example in the C<THREADS> section later in this
		932	document.
		933
		934	=item ev_set_userdata (loop, void *data)
		935
		936	=item ev_userdata (loop)
		937
		938	Set and retrieve a single C<void *> associated with a loop. When
		939	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		940	C<0.>
		941
		942	These two functions can be used to associate arbitrary data with a loop,
		943	and are intended solely for the C<invoke_pending_cb>, C<release> and
		944	C<acquire> callbacks described above, but of course can be (ab-)used for
		945	any other purpose as well.
		946
		947	=item ev_loop_verify (loop)
		948
		949	This function only does something when C<EV_VERIFY> support has been
		950	compiled in, which is the default for non-minimal builds. It tries to go
		951	through all internal structures and checks them for validity. If anything
		952	is found to be inconsistent, it will print an error message to standard
		953	error and call C<abort ()>.
		954
		955	This can be used to catch bugs inside libev itself: under normal
		956	circumstances, this function will never abort as of course libev keeps its
		957	data structures consistent.
552		958
553	=back	959	=back
554		960
555		961
556	=head1 ANATOMY OF A WATCHER	962	=head1 ANATOMY OF A WATCHER
		963
		964	In the following description, uppercase C<TYPE> in names stands for the
		965	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		966	watchers and C<ev_io_start> for I/O watchers.
557		967
558	A watcher is a structure that you create and register to record your	968	A watcher is a structure that you create and register to record your
559	interest in some event. For instance, if you want to wait for STDIN to	969	interest in some event. For instance, if you want to wait for STDIN to
560	become readable, you would create an C<ev_io> watcher for that:	970	become readable, you would create an C<ev_io> watcher for that:
561		971
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	972	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	973	{
564	ev_io_stop (w);	974	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	975	ev_unloop (loop, EVUNLOOP_ALL);
566	}	976	}
567		977
568	struct ev_loop *loop = ev_default_loop (0);	978	struct ev_loop *loop = ev_default_loop (0);
		979
569	struct ev_io stdin_watcher;	980	ev_io stdin_watcher;
		981
570	ev_init (&stdin_watcher, my_cb);	982	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	983	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	984	ev_io_start (loop, &stdin_watcher);
		985
573	ev_loop (loop, 0);	986	ev_loop (loop, 0);
574		987
575	As you can see, you are responsible for allocating the memory for your	988	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	989	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	990	stack).
		991
		992	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		993	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
578		994
579	Each watcher structure must be initialised by a call to C<ev_init	995	Each watcher structure must be initialised by a call to C<ev_init
580	(watcher *, callback)>, which expects a callback to be provided. This	996	(watcher *, callback)>, which expects a callback to be provided. This
581	callback gets invoked each time the event occurs (or, in the case of io	997	callback gets invoked each time the event occurs (or, in the case of I/O
582	watchers, each time the event loop detects that the file descriptor given	998	watchers, each time the event loop detects that the file descriptor given
583	is readable and/or writable).	999	is readable and/or writable).
584		1000
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1001	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	1002	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	1003	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	1004	ev_TYPE_init (watcher *, callback, ...) >>.
589		1005
590	To make the watcher actually watch out for events, you have to start it	1006	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1007	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1008	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1009	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1010
595	As long as your watcher is active (has been started but not stopped) you	1011	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1012	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1013	reinitialise it or call its C<ev_TYPE_set> macro.
598		1014
599	Each and every callback receives the event loop pointer as first, the	1015	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1016	registered watcher structure as second, and a bitset of received events as
601	third argument.	1017	third argument.
602		1018
…		…
656	=item C<EV_FORK>	1072	=item C<EV_FORK>
657		1073
658	The event loop has been resumed in the child process after fork (see	1074	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1075	C<ev_fork>).
660		1076
		1077	=item C<EV_ASYNC>
		1078
		1079	The given async watcher has been asynchronously notified (see C<ev_async>).
		1080
		1081	=item C<EV_CUSTOM>
		1082
		1083	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1084	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1085
661	=item C<EV_ERROR>	1086	=item C<EV_ERROR>
662		1087
663	An unspecified error has occured, the watcher has been stopped. This might	1088	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1089	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1090	ran out of memory, a file descriptor was found to be closed or any other
		1091	problem. Libev considers these application bugs.
		1092
666	problem. You best act on it by reporting the problem and somehow coping	1093	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1094	watcher being stopped. Note that well-written programs should not receive
		1095	an error ever, so when your watcher receives it, this usually indicates a
		1096	bug in your program.
668		1097
669	Libev will usually signal a few "dummy" events together with an error,	1098	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1099	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1100	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1101	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1102	programs, though, as the fd could already be closed and reused for another
		1103	thing, so beware.
674		1104
675	=back	1105	=back
676		1106
677	=head2 GENERIC WATCHER FUNCTIONS	1107	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1108
682	=over 4	1109	=over 4
683		1110
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1111	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1112
…		…
691	which rolls both calls into one.	1118	which rolls both calls into one.
692		1119
693	You can reinitialise a watcher at any time as long as it has been stopped	1120	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1121	(or never started) and there are no pending events outstanding.
695		1122
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1123	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1124	int revents)>.
698		1125
		1126	Example: Initialise an C<ev_io> watcher in two steps.
		1127
		1128	ev_io w;
		1129	ev_init (&w, my_cb);
		1130	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1131
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1132	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
700		1133
701	This macro initialises the type-specific parts of a watcher. You need to	1134	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1135	call C<ev_init> at least once before you call this macro, but you can
703	call C<ev_TYPE_set> any number of times. You must not, however, call this	1136	call C<ev_TYPE_set> any number of times. You must not, however, call this
704	macro on a watcher that is active (it can be pending, however, which is a	1137	macro on a watcher that is active (it can be pending, however, which is a
705	difference to the C<ev_init> macro).	1138	difference to the C<ev_init> macro).
706		1139
707	Although some watcher types do not have type-specific arguments	1140	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1141	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1142
		1143	See C<ev_init>, above, for an example.
		1144
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1145	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1146
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1147	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1148	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1149	a watcher. The same limitations apply, of course.
715		1150
		1151	Example: Initialise and set an C<ev_io> watcher in one step.
		1152
		1153	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1154
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1155	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
717		1156
718	Starts (activates) the given watcher. Only active watchers will receive	1157	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1158	events. If the watcher is already active nothing will happen.
720		1159
		1160	Example: Start the C<ev_io> watcher that is being abused as example in this
		1161	whole section.
		1162
		1163	ev_io_start (EV_DEFAULT_UC, &w);
		1164
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1165	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
722		1166
723	Stops the given watcher again (if active) and clears the pending	1167	Stops the given watcher if active, and clears the pending status (whether
		1168	the watcher was active or not).
		1169
724	status. It is possible that stopped watchers are pending (for example,	1170	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1171	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1172	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1173	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1174	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1175
730	=item bool ev_is_active (ev_TYPE *watcher)	1176	=item bool ev_is_active (ev_TYPE *watcher)
731		1177
732	Returns a true value iff the watcher is active (i.e. it has been started	1178	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1179	and not yet been stopped). As long as a watcher is active you must not modify
…		…
749	=item ev_cb_set (ev_TYPE *watcher, callback)	1195	=item ev_cb_set (ev_TYPE *watcher, callback)
750		1196
751	Change the callback. You can change the callback at virtually any time	1197	Change the callback. You can change the callback at virtually any time
752	(modulo threads).	1198	(modulo threads).
753		1199
754	=item ev_set_priority (ev_TYPE *watcher, priority)	1200	=item ev_set_priority (ev_TYPE *watcher, int priority)
755		1201
756	=item int ev_priority (ev_TYPE *watcher)	1202	=item int ev_priority (ev_TYPE *watcher)
757		1203
758	Set and query the priority of the watcher. The priority is a small	1204	Set and query the priority of the watcher. The priority is a small
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1205	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1206	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1207	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1208	from being executed (except for C<ev_idle> watchers).
763		1209
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1210	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1211	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1212
772	You I<must not> change the priority of a watcher as long as it is active or	1213	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1214	pending.
774		1215
		1216	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1217	fine, as long as you do not mind that the priority value you query might
		1218	or might not have been clamped to the valid range.
		1219
775	The default priority used by watchers when no priority has been set is	1220	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1221	always C<0>, which is supposed to not be too high and not be too low :).
777		1222
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1223	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1224	priorities.
780	or might not have been adjusted to be within valid range.
781		1225
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1226	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1227
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1228	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1229	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1230	can deal with that fact, as both are simply passed through to the
		1231	callback.
787		1232
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1233	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1234
790	If the watcher is pending, this function returns clears its pending status	1235	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1236	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1237	watcher isn't pending it does nothing and returns C<0>.
793		1238
		1239	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1240	callback to be invoked, which can be accomplished with this function.
		1241
		1242	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1243
		1244	Feeds the given event set into the event loop, as if the specified event
		1245	had happened for the specified watcher (which must be a pointer to an
		1246	initialised but not necessarily started event watcher). Obviously you must
		1247	not free the watcher as long as it has pending events.
		1248
		1249	Stopping the watcher, letting libev invoke it, or calling
		1250	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1251	not started in the first place.
		1252
		1253	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1254	functions that do not need a watcher.
		1255
794	=back	1256	=back
795		1257
796		1258
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1259	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
798		1260
799	Each watcher has, by default, a member C<void *data> that you can change	1261	Each watcher has, by default, a member C<void *data> that you can change
800	and read at any time, libev will completely ignore it. This can be used	1262	and read at any time: libev will completely ignore it. This can be used
801	to associate arbitrary data with your watcher. If you need more data and	1263	to associate arbitrary data with your watcher. If you need more data and
802	don't want to allocate memory and store a pointer to it in that data	1264	don't want to allocate memory and store a pointer to it in that data
803	member, you can also "subclass" the watcher type and provide your own	1265	member, you can also "subclass" the watcher type and provide your own
804	data:	1266	data:
805		1267
806	struct my_io	1268	struct my_io
807	{	1269	{
808	struct ev_io io;	1270	ev_io io;
809	int otherfd;	1271	int otherfd;
810	void *somedata;	1272	void *somedata;
811	struct whatever *mostinteresting;	1273	struct whatever *mostinteresting;
812	}	1274	};
		1275
		1276	...
		1277	struct my_io w;
		1278	ev_io_init (&w.io, my_cb, fd, EV_READ);
813		1279
814	And since your callback will be called with a pointer to the watcher, you	1280	And since your callback will be called with a pointer to the watcher, you
815	can cast it back to your own type:	1281	can cast it back to your own type:
816		1282
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1283	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
818	{	1284	{
819	struct my_io *w = (struct my_io *)w_;	1285	struct my_io *w = (struct my_io *)w_;
820	...	1286	...
821	}	1287	}
822		1288
823	More interesting and less C-conformant ways of casting your callback type	1289	More interesting and less C-conformant ways of casting your callback type
824	instead have been omitted.	1290	instead have been omitted.
825		1291
826	Another common scenario is having some data structure with multiple	1292	Another common scenario is to use some data structure with multiple
827	watchers:	1293	embedded watchers:
828		1294
829	struct my_biggy	1295	struct my_biggy
830	{	1296	{
831	int some_data;	1297	int some_data;
832	ev_timer t1;	1298	ev_timer t1;
833	ev_timer t2;	1299	ev_timer t2;
834	}	1300	}
835		1301
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1302	In this case getting the pointer to C<my_biggy> is a bit more
837	you need to use C<offsetof>:	1303	complicated: Either you store the address of your C<my_biggy> struct
		1304	in the C<data> member of the watcher (for woozies), or you need to use
		1305	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1306	programmers):
838		1307
839	#include <stddef.h>	1308	#include <stddef.h>
840		1309
841	static void	1310	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1311	t1_cb (EV_P_ ev_timer *w, int revents)
843	{	1312	{
844	struct my_biggy big = (struct my_biggy *	1313	struct my_biggy big = (struct my_biggy *)
845	(((char *)w) - offsetof (struct my_biggy, t1));	1314	(((char *)w) - offsetof (struct my_biggy, t1));
846	}	1315	}
847		1316
848	static void	1317	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1318	t2_cb (EV_P_ ev_timer *w, int revents)
850	{	1319	{
851	struct my_biggy big = (struct my_biggy *	1320	struct my_biggy big = (struct my_biggy *)
852	(((char *)w) - offsetof (struct my_biggy, t2));	1321	(((char *)w) - offsetof (struct my_biggy, t2));
853	}	1322	}
		1323
		1324	=head2 WATCHER PRIORITY MODELS
		1325
		1326	Many event loops support I<watcher priorities>, which are usually small
		1327	integers that influence the ordering of event callback invocation
		1328	between watchers in some way, all else being equal.
		1329
		1330	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1331	description for the more technical details such as the actual priority
		1332	range.
		1333
		1334	There are two common ways how these these priorities are being interpreted
		1335	by event loops:
		1336
		1337	In the more common lock-out model, higher priorities "lock out" invocation
		1338	of lower priority watchers, which means as long as higher priority
		1339	watchers receive events, lower priority watchers are not being invoked.
		1340
		1341	The less common only-for-ordering model uses priorities solely to order
		1342	callback invocation within a single event loop iteration: Higher priority
		1343	watchers are invoked before lower priority ones, but they all get invoked
		1344	before polling for new events.
		1345
		1346	Libev uses the second (only-for-ordering) model for all its watchers
		1347	except for idle watchers (which use the lock-out model).
		1348
		1349	The rationale behind this is that implementing the lock-out model for
		1350	watchers is not well supported by most kernel interfaces, and most event
		1351	libraries will just poll for the same events again and again as long as
		1352	their callbacks have not been executed, which is very inefficient in the
		1353	common case of one high-priority watcher locking out a mass of lower
		1354	priority ones.
		1355
		1356	Static (ordering) priorities are most useful when you have two or more
		1357	watchers handling the same resource: a typical usage example is having an
		1358	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1359	timeouts. Under load, data might be received while the program handles
		1360	other jobs, but since timers normally get invoked first, the timeout
		1361	handler will be executed before checking for data. In that case, giving
		1362	the timer a lower priority than the I/O watcher ensures that I/O will be
		1363	handled first even under adverse conditions (which is usually, but not
		1364	always, what you want).
		1365
		1366	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1367	will only be executed when no same or higher priority watchers have
		1368	received events, they can be used to implement the "lock-out" model when
		1369	required.
		1370
		1371	For example, to emulate how many other event libraries handle priorities,
		1372	you can associate an C<ev_idle> watcher to each such watcher, and in
		1373	the normal watcher callback, you just start the idle watcher. The real
		1374	processing is done in the idle watcher callback. This causes libev to
		1375	continously poll and process kernel event data for the watcher, but when
		1376	the lock-out case is known to be rare (which in turn is rare :), this is
		1377	workable.
		1378
		1379	Usually, however, the lock-out model implemented that way will perform
		1380	miserably under the type of load it was designed to handle. In that case,
		1381	it might be preferable to stop the real watcher before starting the
		1382	idle watcher, so the kernel will not have to process the event in case
		1383	the actual processing will be delayed for considerable time.
		1384
		1385	Here is an example of an I/O watcher that should run at a strictly lower
		1386	priority than the default, and which should only process data when no
		1387	other events are pending:
		1388
		1389	ev_idle idle; // actual processing watcher
		1390	ev_io io; // actual event watcher
		1391
		1392	static void
		1393	io_cb (EV_P_ ev_io *w, int revents)
		1394	{
		1395	// stop the I/O watcher, we received the event, but
		1396	// are not yet ready to handle it.
		1397	ev_io_stop (EV_A_ w);
		1398
		1399	// start the idle watcher to ahndle the actual event.
		1400	// it will not be executed as long as other watchers
		1401	// with the default priority are receiving events.
		1402	ev_idle_start (EV_A_ &idle);
		1403	}
		1404
		1405	static void
		1406	idle_cb (EV_P_ ev_idle *w, int revents)
		1407	{
		1408	// actual processing
		1409	read (STDIN_FILENO, ...);
		1410
		1411	// have to start the I/O watcher again, as
		1412	// we have handled the event
		1413	ev_io_start (EV_P_ &io);
		1414	}
		1415
		1416	// initialisation
		1417	ev_idle_init (&idle, idle_cb);
		1418	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1419	ev_io_start (EV_DEFAULT_ &io);
		1420
		1421	In the "real" world, it might also be beneficial to start a timer, so that
		1422	low-priority connections can not be locked out forever under load. This
		1423	enables your program to keep a lower latency for important connections
		1424	during short periods of high load, while not completely locking out less
		1425	important ones.
854		1426
855		1427
856	=head1 WATCHER TYPES	1428	=head1 WATCHER TYPES
857		1429
858	This section describes each watcher in detail, but will not repeat	1430	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1454	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1455	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1456	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1457	required if you know what you are doing).
886		1458
887	You have to be careful with dup'ed file descriptors, though. Some backends	1459	If you cannot use non-blocking mode, then force the use of a
888	(the linux epoll backend is a notable example) cannot handle dup'ed file	1460	known-to-be-good backend (at the time of this writing, this includes only
889	descriptors correctly if you register interest in two or more fds pointing	1461	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
890	to the same underlying file/socket/etc. description (that is, they share	1462	descriptors for which non-blocking operation makes no sense (such as
891	the same underlying "file open").	1463	files) - libev doesn't guarentee any specific behaviour in that case.
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896		1464
897	Another thing you have to watch out for is that it is quite easy to	1465	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1466	receive "spurious" readiness notifications, that is your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1467	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1468	because there is no data. Not only are some backends known to create a
901	lot of those (for example solaris ports), it is very easy to get into	1469	lot of those (for example Solaris ports), it is very easy to get into
902	this situation even with a relatively standard program structure. Thus	1470	this situation even with a relatively standard program structure. Thus
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1471	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1472	C<EAGAIN> is far preferable to a program hanging until some data arrives.
905		1473
906	If you cannot run the fd in non-blocking mode (for example you should not	1474	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1475	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1476	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1477	interface such as poll (fortunately in our Xlib example, Xlib already
910	its own, so its quite safe to use).	1478	does this on its own, so its quite safe to use). Some people additionally
		1479	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1480	indefinitely.
		1481
		1482	But really, best use non-blocking mode.
		1483
		1484	=head3 The special problem of disappearing file descriptors
		1485
		1486	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1487	descriptor (either due to calling C<close> explicitly or any other means,
		1488	such as C<dup2>). The reason is that you register interest in some file
		1489	descriptor, but when it goes away, the operating system will silently drop
		1490	this interest. If another file descriptor with the same number then is
		1491	registered with libev, there is no efficient way to see that this is, in
		1492	fact, a different file descriptor.
		1493
		1494	To avoid having to explicitly tell libev about such cases, libev follows
		1495	the following policy: Each time C<ev_io_set> is being called, libev
		1496	will assume that this is potentially a new file descriptor, otherwise
		1497	it is assumed that the file descriptor stays the same. That means that
		1498	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1499	descriptor even if the file descriptor number itself did not change.
		1500
		1501	This is how one would do it normally anyway, the important point is that
		1502	the libev application should not optimise around libev but should leave
		1503	optimisations to libev.
		1504
		1505	=head3 The special problem of dup'ed file descriptors
		1506
		1507	Some backends (e.g. epoll), cannot register events for file descriptors,
		1508	but only events for the underlying file descriptions. That means when you
		1509	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1510	events for them, only one file descriptor might actually receive events.
		1511
		1512	There is no workaround possible except not registering events
		1513	for potentially C<dup ()>'ed file descriptors, or to resort to
		1514	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1515
		1516	=head3 The special problem of fork
		1517
		1518	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1519	useless behaviour. Libev fully supports fork, but needs to be told about
		1520	it in the child.
		1521
		1522	To support fork in your programs, you either have to call
		1523	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1524	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1525	C<EVBACKEND_POLL>.
		1526
		1527	=head3 The special problem of SIGPIPE
		1528
		1529	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1530	when writing to a pipe whose other end has been closed, your program gets
		1531	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1532	this is sensible behaviour, for daemons, this is usually undesirable.
		1533
		1534	So when you encounter spurious, unexplained daemon exits, make sure you
		1535	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1536	somewhere, as that would have given you a big clue).
		1537
		1538
		1539	=head3 Watcher-Specific Functions
911		1540
912	=over 4	1541	=over 4
913		1542
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1543	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1544
916	=item ev_io_set (ev_io *, int fd, int events)	1545	=item ev_io_set (ev_io *, int fd, int events)
917		1546
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1547	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1548	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1549	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1550
922	=item int fd [read-only]	1551	=item int fd [read-only]
923		1552
924	The file descriptor being watched.	1553	The file descriptor being watched.
925		1554
926	=item int events [read-only]	1555	=item int events [read-only]
927		1556
928	The events being watched.	1557	The events being watched.
929		1558
930	=back	1559	=back
		1560
		1561	=head3 Examples
931		1562
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1563	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1564	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1565	attempt to read a whole line in the callback.
935		1566
936	static void	1567	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1568	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1569	{
939	ev_io_stop (loop, w);	1570	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1571	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1572	}
942		1573
943	...	1574	...
944	struct ev_loop *loop = ev_default_init (0);	1575	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1576	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1577	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1578	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1579	ev_loop (loop, 0);
949		1580
950		1581
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1582	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1583
953	Timer watchers are simple relative timers that generate an event after a	1584	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1585	given time, and optionally repeating in regular intervals after that.
955		1586
956	The timers are based on real time, that is, if you register an event that	1587	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1588	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1589	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1590	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1591	monotonic clock option helps a lot here).
		1592
		1593	The callback is guaranteed to be invoked only I<after> its timeout has
		1594	passed (not I<at>, so on systems with very low-resolution clocks this
		1595	might introduce a small delay). If multiple timers become ready during the
		1596	same loop iteration then the ones with earlier time-out values are invoked
		1597	before ones of the same priority with later time-out values (but this is
		1598	no longer true when a callback calls C<ev_loop> recursively).
		1599
		1600	=head3 Be smart about timeouts
		1601
		1602	Many real-world problems involve some kind of timeout, usually for error
		1603	recovery. A typical example is an HTTP request - if the other side hangs,
		1604	you want to raise some error after a while.
		1605
		1606	What follows are some ways to handle this problem, from obvious and
		1607	inefficient to smart and efficient.
		1608
		1609	In the following, a 60 second activity timeout is assumed - a timeout that
		1610	gets reset to 60 seconds each time there is activity (e.g. each time some
		1611	data or other life sign was received).
		1612
		1613	=over 4
		1614
		1615	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1616
		1617	This is the most obvious, but not the most simple way: In the beginning,
		1618	start the watcher:
		1619
		1620	ev_timer_init (timer, callback, 60., 0.);
		1621	ev_timer_start (loop, timer);
		1622
		1623	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1624	and start it again:
		1625
		1626	ev_timer_stop (loop, timer);
		1627	ev_timer_set (timer, 60., 0.);
		1628	ev_timer_start (loop, timer);
		1629
		1630	This is relatively simple to implement, but means that each time there is
		1631	some activity, libev will first have to remove the timer from its internal
		1632	data structure and then add it again. Libev tries to be fast, but it's
		1633	still not a constant-time operation.
		1634
		1635	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1636
		1637	This is the easiest way, and involves using C<ev_timer_again> instead of
		1638	C<ev_timer_start>.
		1639
		1640	To implement this, configure an C<ev_timer> with a C<repeat> value
		1641	of C<60> and then call C<ev_timer_again> at start and each time you
		1642	successfully read or write some data. If you go into an idle state where
		1643	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1644	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1645
		1646	That means you can ignore both the C<ev_timer_start> function and the
		1647	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1648	member and C<ev_timer_again>.
		1649
		1650	At start:
		1651
		1652	ev_init (timer, callback);
		1653	timer->repeat = 60.;
		1654	ev_timer_again (loop, timer);
		1655
		1656	Each time there is some activity:
		1657
		1658	ev_timer_again (loop, timer);
		1659
		1660	It is even possible to change the time-out on the fly, regardless of
		1661	whether the watcher is active or not:
		1662
		1663	timer->repeat = 30.;
		1664	ev_timer_again (loop, timer);
		1665
		1666	This is slightly more efficient then stopping/starting the timer each time
		1667	you want to modify its timeout value, as libev does not have to completely
		1668	remove and re-insert the timer from/into its internal data structure.
		1669
		1670	It is, however, even simpler than the "obvious" way to do it.
		1671
		1672	=item 3. Let the timer time out, but then re-arm it as required.
		1673
		1674	This method is more tricky, but usually most efficient: Most timeouts are
		1675	relatively long compared to the intervals between other activity - in
		1676	our example, within 60 seconds, there are usually many I/O events with
		1677	associated activity resets.
		1678
		1679	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1680	but remember the time of last activity, and check for a real timeout only
		1681	within the callback:
		1682
		1683	ev_tstamp last_activity; // time of last activity
		1684
		1685	static void
		1686	callback (EV_P_ ev_timer *w, int revents)
		1687	{
		1688	ev_tstamp now = ev_now (EV_A);
		1689	ev_tstamp timeout = last_activity + 60.;
		1690
		1691	// if last_activity + 60. is older than now, we did time out
		1692	if (timeout < now)
		1693	{
		1694	// timeout occured, take action
		1695	}
		1696	else
		1697	{
		1698	// callback was invoked, but there was some activity, re-arm
		1699	// the watcher to fire in last_activity + 60, which is
		1700	// guaranteed to be in the future, so "again" is positive:
		1701	w->repeat = timeout - now;
		1702	ev_timer_again (EV_A_ w);
		1703	}
		1704	}
		1705
		1706	To summarise the callback: first calculate the real timeout (defined
		1707	as "60 seconds after the last activity"), then check if that time has
		1708	been reached, which means something I<did>, in fact, time out. Otherwise
		1709	the callback was invoked too early (C<timeout> is in the future), so
		1710	re-schedule the timer to fire at that future time, to see if maybe we have
		1711	a timeout then.
		1712
		1713	Note how C<ev_timer_again> is used, taking advantage of the
		1714	C<ev_timer_again> optimisation when the timer is already running.
		1715
		1716	This scheme causes more callback invocations (about one every 60 seconds
		1717	minus half the average time between activity), but virtually no calls to
		1718	libev to change the timeout.
		1719
		1720	To start the timer, simply initialise the watcher and set C<last_activity>
		1721	to the current time (meaning we just have some activity :), then call the
		1722	callback, which will "do the right thing" and start the timer:
		1723
		1724	ev_init (timer, callback);
		1725	last_activity = ev_now (loop);
		1726	callback (loop, timer, EV_TIMEOUT);
		1727
		1728	And when there is some activity, simply store the current time in
		1729	C<last_activity>, no libev calls at all:
		1730
		1731	last_actiivty = ev_now (loop);
		1732
		1733	This technique is slightly more complex, but in most cases where the
		1734	time-out is unlikely to be triggered, much more efficient.
		1735
		1736	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1737	callback :) - just change the timeout and invoke the callback, which will
		1738	fix things for you.
		1739
		1740	=item 4. Wee, just use a double-linked list for your timeouts.
		1741
		1742	If there is not one request, but many thousands (millions...), all
		1743	employing some kind of timeout with the same timeout value, then one can
		1744	do even better:
		1745
		1746	When starting the timeout, calculate the timeout value and put the timeout
		1747	at the I<end> of the list.
		1748
		1749	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1750	the list is expected to fire (for example, using the technique #3).
		1751
		1752	When there is some activity, remove the timer from the list, recalculate
		1753	the timeout, append it to the end of the list again, and make sure to
		1754	update the C<ev_timer> if it was taken from the beginning of the list.
		1755
		1756	This way, one can manage an unlimited number of timeouts in O(1) time for
		1757	starting, stopping and updating the timers, at the expense of a major
		1758	complication, and having to use a constant timeout. The constant timeout
		1759	ensures that the list stays sorted.
		1760
		1761	=back
		1762
		1763	So which method the best?
		1764
		1765	Method #2 is a simple no-brain-required solution that is adequate in most
		1766	situations. Method #3 requires a bit more thinking, but handles many cases
		1767	better, and isn't very complicated either. In most case, choosing either
		1768	one is fine, with #3 being better in typical situations.
		1769
		1770	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1771	rather complicated, but extremely efficient, something that really pays
		1772	off after the first million or so of active timers, i.e. it's usually
		1773	overkill :)
		1774
		1775	=head3 The special problem of time updates
		1776
		1777	Establishing the current time is a costly operation (it usually takes at
		1778	least two system calls): EV therefore updates its idea of the current
		1779	time only before and after C<ev_loop> collects new events, which causes a
		1780	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1781	lots of events in one iteration.
961		1782
962	The relative timeouts are calculated relative to the C<ev_now ()>	1783	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	1784	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	1785	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	1786	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	1787	timeout on the current time, use something like this to adjust for this:
967		1788
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1789	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		1790
970	The callback is guarenteed to be invoked only when its timeout has passed,	1791	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	1792	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	1793	()>.
		1794
		1795	=head3 The special problems of suspended animation
		1796
		1797	When you leave the server world it is quite customary to hit machines that
		1798	can suspend/hibernate - what happens to the clocks during such a suspend?
		1799
		1800	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1801	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1802	to run until the system is suspended, but they will not advance while the
		1803	system is suspended. That means, on resume, it will be as if the program
		1804	was frozen for a few seconds, but the suspend time will not be counted
		1805	towards C<ev_timer> when a monotonic clock source is used. The real time
		1806	clock advanced as expected, but if it is used as sole clocksource, then a
		1807	long suspend would be detected as a time jump by libev, and timers would
		1808	be adjusted accordingly.
		1809
		1810	I would not be surprised to see different behaviour in different between
		1811	operating systems, OS versions or even different hardware.
		1812
		1813	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1814	time jump in the monotonic clocks and the realtime clock. If the program
		1815	is suspended for a very long time, and monotonic clock sources are in use,
		1816	then you can expect C<ev_timer>s to expire as the full suspension time
		1817	will be counted towards the timers. When no monotonic clock source is in
		1818	use, then libev will again assume a timejump and adjust accordingly.
		1819
		1820	It might be beneficial for this latter case to call C<ev_suspend>
		1821	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1822	deterministic behaviour in this case (you can do nothing against
		1823	C<SIGSTOP>).
		1824
		1825	=head3 Watcher-Specific Functions and Data Members
973		1826
974	=over 4	1827	=over 4
975		1828
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1829	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		1830
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1831	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		1832
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1833	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	1834	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	1835	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	1836	configured to trigger again C<repeat> seconds later, again, and again,
		1837	until stopped manually.
984		1838
985	The timer itself will do a best-effort at avoiding drift, that is, if you	1839	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	1840	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	1841	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	1842	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	1843	do stuff) the timer will not fire more than once per event loop iteration.
990		1844
991	=item ev_timer_again (loop)	1845	=item ev_timer_again (loop, ev_timer *)
992		1846
993	This will act as if the timer timed out and restart it again if it is	1847	This will act as if the timer timed out and restart it again if it is
994	repeating. The exact semantics are:	1848	repeating. The exact semantics are:
995		1849
996	If the timer is pending, its pending status is cleared.	1850	If the timer is pending, its pending status is cleared.
997		1851
998	If the timer is started but nonrepeating, stop it (as if it timed out).	1852	If the timer is started but non-repeating, stop it (as if it timed out).
999		1853
1000	If the timer is repeating, either start it if necessary (with the	1854	If the timer is repeating, either start it if necessary (with the
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	1855	C<repeat> value), or reset the running timer to the C<repeat> value.
1002		1856
1003	This sounds a bit complicated, but here is a useful and typical	1857	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1004	example: Imagine you have a tcp connection and you want a so-called idle	1858	usage example.
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012		1859
1013	That means you can ignore the C<after> value and C<ev_timer_start>	1860	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1015		1861
1016	ev_timer_init (timer, callback, 0., 5.);	1862	Returns the remaining time until a timer fires. If the timer is active,
1017	ev_timer_again (loop, timer);	1863	then this time is relative to the current event loop time, otherwise it's
1018	...	1864	the timeout value currently configured.
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024		1865
1025	This is more slightly efficient then stopping/starting the timer each time	1866	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1026	you want to modify its timeout value.	1867	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1868	will return C<4>. When the timer expires and is restarted, it will return
		1869	roughly C<7> (likely slightly less as callback invocation takes some time,
		1870	too), and so on.
1027		1871
1028	=item ev_tstamp repeat [read-write]	1872	=item ev_tstamp repeat [read-write]
1029		1873
1030	The current C<repeat> value. Will be used each time the watcher times out	1874	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	1875	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	1876	which is also when any modifications are taken into account.
1033		1877
1034	=back	1878	=back
1035		1879
		1880	=head3 Examples
		1881
1036	Example: Create a timer that fires after 60 seconds.	1882	Example: Create a timer that fires after 60 seconds.
1037		1883
1038	static void	1884	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1885	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	1886	{
1041	.. one minute over, w is actually stopped right here	1887	.. one minute over, w is actually stopped right here
1042	}	1888	}
1043		1889
1044	struct ev_timer mytimer;	1890	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1891	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	1892	ev_timer_start (loop, &mytimer);
1047		1893
1048	Example: Create a timeout timer that times out after 10 seconds of	1894	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	1895	inactivity.
1050		1896
1051	static void	1897	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1898	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	1899	{
1054	.. ten seconds without any activity	1900	.. ten seconds without any activity
1055	}	1901	}
1056		1902
1057	struct ev_timer mytimer;	1903	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1904	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	1905	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	1906	ev_loop (loop, 0);
1061		1907
1062	// and in some piece of code that gets executed on any "activity":	1908	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	1909	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	1910	ev_timer_again (&mytimer);
1065		1911
1066		1912
1067	=head2 C<ev_periodic> - to cron or not to cron?	1913	=head2 C<ev_periodic> - to cron or not to cron?
1068		1914
1069	Periodic watchers are also timers of a kind, but they are very versatile	1915	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	1916	(and unfortunately a bit complex).
1071		1917
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1918	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	1919	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	1920	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1921	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	1922	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1923	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		1924
1081	They can also be used to implement vastly more complex timers, such as	1925	You can tell a periodic watcher to trigger after some specific point
		1926	in time: for example, if you tell a periodic watcher to trigger "in 10
		1927	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1928	not a delay) and then reset your system clock to January of the previous
		1929	year, then it will take a year or more to trigger the event (unlike an
		1930	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1931	it, as it uses a relative timeout).
		1932
		1933	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	1934	timers, such as triggering an event on each "midnight, local time", or
		1935	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1936	those cannot react to time jumps.
1083		1937
1084	As with timers, the callback is guarenteed to be invoked only when the	1938	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	1939	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	1940	timers become ready during the same loop iteration then the ones with
		1941	earlier time-out values are invoked before ones with later time-out values
		1942	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1943
		1944	=head3 Watcher-Specific Functions and Data Members
1087		1945
1088	=over 4	1946	=over 4
1089		1947
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1948	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		1949
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1950	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		1951
1094	Lots of arguments, lets sort it out... There are basically three modes of	1952	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	1953	operation, and we will explain them from simplest to most complex:
1096		1954
1097	=over 4	1955	=over 4
1098		1956
1099	=item * absolute timer (interval = reschedule_cb = 0)	1957	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		1958
1101	In this configuration the watcher triggers an event at the wallclock time	1959	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1960	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	1961	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	1962	will be stopped and invoked when the system clock reaches or surpasses
		1963	this point in time.
1105		1964
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1965	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		1966
1108	In this mode the watcher will always be scheduled to time out at the next	1967	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	1968	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	1969	negative) and then repeat, regardless of any time jumps. The C<offset>
		1970	argument is merely an offset into the C<interval> periods.
1111		1971
1112	This can be used to create timers that do not drift with respect to system	1972	This can be used to create timers that do not drift with respect to the
1113	time:	1973	system clock, for example, here is an C<ev_periodic> that triggers each
		1974	hour, on the hour (with respect to UTC):
1114		1975
1115	ev_periodic_set (&periodic, 0., 3600., 0);	1976	ev_periodic_set (&periodic, 0., 3600., 0);
1116		1977
1117	This doesn't mean there will always be 3600 seconds in between triggers,	1978	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	1979	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	1980	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	1981	by 3600.
1121		1982
1122	Another way to think about it (for the mathematically inclined) is that	1983	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	1984	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	1985	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		1986
		1987	For numerical stability it is preferable that the C<offset> value is near
		1988	C<ev_now ()> (the current time), but there is no range requirement for
		1989	this value, and in fact is often specified as zero.
		1990
		1991	Note also that there is an upper limit to how often a timer can fire (CPU
		1992	speed for example), so if C<interval> is very small then timing stability
		1993	will of course deteriorate. Libev itself tries to be exact to be about one
		1994	millisecond (if the OS supports it and the machine is fast enough).
		1995
1126	=item * manual reschedule mode (reschedule_cb = callback)	1996	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		1997
1128	In this mode the values for C<interval> and C<at> are both being	1998	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	1999	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	2000	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	2001	current time as second argument.
1132		2002
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2003	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	2004	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2005	allowed by documentation here>.
1136	starting a prepare watcher).
1137		2006
		2007	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2008	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2009	only event loop modification you are allowed to do).
		2010
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2011	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	2012	*w, ev_tstamp now)>, e.g.:
1140		2013
		2014	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2015	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	2016	{
1143	return now + 60.;	2017	return now + 60.;
1144	}	2018	}
1145		2019
1146	It must return the next time to trigger, based on the passed time value	2020	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	2021	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	2022	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	2023	might be called at other times, too.
1150		2024
1151	NOTE: I<< This callback must always return a time that is later than the	2025	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2026	equal to the passed C<now> value >>.
1153		2027
1154	This can be used to create very complex timers, such as a timer that	2028	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	2029	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	2030	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	2031	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	2032	reason I omitted it as an example).
1159		2033
1160	=back	2034	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	2038	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	2039	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	2040	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	2041	program when the crontabs have changed).
1168		2042
		2043	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2044
		2045	When active, returns the absolute time that the watcher is supposed
		2046	to trigger next. This is not the same as the C<offset> argument to
		2047	C<ev_periodic_set>, but indeed works even in interval and manual
		2048	rescheduling modes.
		2049
		2050	=item ev_tstamp offset [read-write]
		2051
		2052	When repeating, this contains the offset value, otherwise this is the
		2053	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2054	although libev might modify this value for better numerical stability).
		2055
		2056	Can be modified any time, but changes only take effect when the periodic
		2057	timer fires or C<ev_periodic_again> is being called.
		2058
1169	=item ev_tstamp interval [read-write]	2059	=item ev_tstamp interval [read-write]
1170		2060
1171	The current interval value. Can be modified any time, but changes only	2061	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	2062	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	2063	called.
1174		2064
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2065	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		2066
1177	The current reschedule callback, or C<0>, if this functionality is	2067	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	2068	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	2069	the periodic timer fires or C<ev_periodic_again> is being called.
1180		2070
1181	=back	2071	=back
1182		2072
		2073	=head3 Examples
		2074
1183	Example: Call a callback every hour, or, more precisely, whenever the	2075	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	2076	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	2077	potentially a lot of jitter, but good long-term stability.
1186		2078
1187	static void	2079	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2080	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1189	{	2081	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	2082	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	2083	}
1192		2084
1193	struct ev_periodic hourly_tick;	2085	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2086	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	2087	ev_periodic_start (loop, &hourly_tick);
1196		2088
1197	Example: The same as above, but use a reschedule callback to do it:	2089	Example: The same as above, but use a reschedule callback to do it:
1198		2090
1199	#include <math.h>	2091	#include <math.h>
1200		2092
1201	static ev_tstamp	2093	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2094	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	2095	{
1204	return fmod (now, 3600.) + 3600.;	2096	return now + (3600. - fmod (now, 3600.));
1205	}	2097	}
1206		2098
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2099	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		2100
1209	Example: Call a callback every hour, starting now:	2101	Example: Call a callback every hour, starting now:
1210		2102
1211	struct ev_periodic hourly_tick;	2103	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	2104	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	2105	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	2106	ev_periodic_start (loop, &hourly_tick);
1215		2107
1216		2108
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	2109	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		2110
1219	Signal watchers will trigger an event when the process receives a specific	2111	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	2112	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	2113	will try it's best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	2114	normal event processing, like any other event.
1223		2115
		2116	If you want signals to be delivered truly asynchronously, just use
		2117	C<sigaction> as you would do without libev and forget about sharing
		2118	the signal. You can even use C<ev_async> from a signal handler to
		2119	synchronously wake up an event loop.
		2120
1224	You can configure as many watchers as you like per signal. Only when the	2121	You can configure as many watchers as you like for the same signal, but
		2122	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2123	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2124	C<SIGINT> in both the default loop and another loop at the same time. At
		2125	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2126
1225	first watcher gets started will libev actually register a signal watcher	2127	When the first watcher gets started will libev actually register something
1226	with the kernel (thus it coexists with your own signal handlers as long	2128	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	2129	you don't register any with libev for the same signal).
1228	watcher for a signal is stopped libev will reset the signal handler to	2130
1229	SIG_DFL (regardless of what it was set to before).	2131	If possible and supported, libev will install its handlers with
		2132	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2133	not be unduly interrupted. If you have a problem with system calls getting
		2134	interrupted by signals you can block all signals in an C<ev_check> watcher
		2135	and unblock them in an C<ev_prepare> watcher.
		2136
		2137	=head3 The special problem of inheritance over execve
		2138
		2139	Both the signal mask (C<sigprocmask>) and the signal disposition
		2140	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2141	stopping it again), that is, libev might or might not block the signal,
		2142	and might or might not set or restore the installed signal handler.
		2143
		2144	While this does not matter for the signal disposition (libev never
		2145	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2146	C<execve>), this matters for the signal mask: many programs do not expect
		2147	certain signals to be blocked.
		2148
		2149	This means that before calling C<exec> (from the child) you should reset
		2150	the signal mask to whatever "default" you expect (all clear is a good
		2151	choice usually).
		2152
		2153	The simplest way to ensure that the signal mask is reset in the child is
		2154	to install a fork handler with C<pthread_atfork> that resets it. That will
		2155	catch fork calls done by libraries (such as the libc) as well.
		2156
		2157	In current versions of libev, you can also ensure that the signal mask is
		2158	not blocking any signals (except temporarily, so thread users watch out)
		2159	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2160	is not guaranteed for future versions, however.
		2161
		2162	=head3 Watcher-Specific Functions and Data Members
1230		2163
1231	=over 4	2164	=over 4
1232		2165
1233	=item ev_signal_init (ev_signal *, callback, int signum)	2166	=item ev_signal_init (ev_signal *, callback, int signum)
1234		2167
…		…
1241		2174
1242	The signal the watcher watches out for.	2175	The signal the watcher watches out for.
1243		2176
1244	=back	2177	=back
1245		2178
		2179	=head3 Examples
		2180
		2181	Example: Try to exit cleanly on SIGINT.
		2182
		2183	static void
		2184	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2185	{
		2186	ev_unloop (loop, EVUNLOOP_ALL);
		2187	}
		2188
		2189	ev_signal signal_watcher;
		2190	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2191	ev_signal_start (loop, &signal_watcher);
		2192
1246		2193
1247	=head2 C<ev_child> - watch out for process status changes	2194	=head2 C<ev_child> - watch out for process status changes
1248		2195
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2196	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2197	some child status changes (most typically when a child of yours dies or
		2198	exits). It is permissible to install a child watcher I<after> the child
		2199	has been forked (which implies it might have already exited), as long
		2200	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2201	forking and then immediately registering a watcher for the child is fine,
		2202	but forking and registering a watcher a few event loop iterations later or
		2203	in the next callback invocation is not.
		2204
		2205	Only the default event loop is capable of handling signals, and therefore
		2206	you can only register child watchers in the default event loop.
		2207
		2208	Due to some design glitches inside libev, child watchers will always be
		2209	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2210	libev)
		2211
		2212	=head3 Process Interaction
		2213
		2214	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2215	initialised. This is necessary to guarantee proper behaviour even if the
		2216	first child watcher is started after the child exits. The occurrence
		2217	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2218	synchronously as part of the event loop processing. Libev always reaps all
		2219	children, even ones not watched.
		2220
		2221	=head3 Overriding the Built-In Processing
		2222
		2223	Libev offers no special support for overriding the built-in child
		2224	processing, but if your application collides with libev's default child
		2225	handler, you can override it easily by installing your own handler for
		2226	C<SIGCHLD> after initialising the default loop, and making sure the
		2227	default loop never gets destroyed. You are encouraged, however, to use an
		2228	event-based approach to child reaping and thus use libev's support for
		2229	that, so other libev users can use C<ev_child> watchers freely.
		2230
		2231	=head3 Stopping the Child Watcher
		2232
		2233	Currently, the child watcher never gets stopped, even when the
		2234	child terminates, so normally one needs to stop the watcher in the
		2235	callback. Future versions of libev might stop the watcher automatically
		2236	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2237	problem).
		2238
		2239	=head3 Watcher-Specific Functions and Data Members
1251		2240
1252	=over 4	2241	=over 4
1253		2242
1254	=item ev_child_init (ev_child *, callback, int pid)	2243	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2244
1256	=item ev_child_set (ev_child *, int pid)	2245	=item ev_child_set (ev_child *, int pid, int trace)
1257		2246
1258	Configures the watcher to wait for status changes of process C<pid> (or	2247	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2248	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2249	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2250	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2251	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2252	process causing the status change. C<trace> must be either C<0> (only
		2253	activate the watcher when the process terminates) or C<1> (additionally
		2254	activate the watcher when the process is stopped or continued).
1264		2255
1265	=item int pid [read-only]	2256	=item int pid [read-only]
1266		2257
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2258	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2259
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2266	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2267	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2268
1278	=back	2269	=back
1279		2270
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2271	=head3 Examples
1281		2272
		2273	Example: C<fork()> a new process and install a child handler to wait for
		2274	its completion.
		2275
		2276	ev_child cw;
		2277
1282	static void	2278	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2279	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2280	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2281	ev_child_stop (EV_A_ w);
		2282	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2283	}
1287		2284
1288	struct ev_signal signal_watcher;	2285	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2286
1290	ev_signal_start (loop, &sigint_cb);	2287	if (pid < 0)
		2288	// error
		2289	else if (pid == 0)
		2290	{
		2291	// the forked child executes here
		2292	exit (1);
		2293	}
		2294	else
		2295	{
		2296	ev_child_init (&cw, child_cb, pid, 0);
		2297	ev_child_start (EV_DEFAULT_ &cw);
		2298	}
1291		2299
1292		2300
1293	=head2 C<ev_stat> - did the file attributes just change?	2301	=head2 C<ev_stat> - did the file attributes just change?
1294		2302
1295	This watches a filesystem path for attribute changes. That is, it calls	2303	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2304	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2305	and sees if it changed compared to the last time, invoking the callback if
		2306	it did.
1298		2307
1299	The path does not need to exist: changing from "path exists" to "path does	2308	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2309	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2310	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2311	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2312	least one) and all the other fields of the stat buffer having unspecified
		2313	contents.
1304		2314
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2315	The path I<must not> end in a slash or contain special components such as
		2316	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2317	your working directory changes, then the behaviour is undefined.
1307		2318
1308	Since there is no standard to do this, the portable implementation simply	2319	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2320	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2321	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2322	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2323	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2324	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2325	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2326	currently around C<0.1>, but that's usually overkill.
1316		2327
1317	This watcher type is not meant for massive numbers of stat watchers,	2328	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2329	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2330	resource-intensive.
1320		2331
1321	At the time of this writing, only the Linux inotify interface is	2332	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2333	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2334	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2335	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2336
1326	usually detected immediately, and if the file exists there will be no	2337	=head3 ABI Issues (Largefile Support)
1327	polling.	2338
		2339	Libev by default (unless the user overrides this) uses the default
		2340	compilation environment, which means that on systems with large file
		2341	support disabled by default, you get the 32 bit version of the stat
		2342	structure. When using the library from programs that change the ABI to
		2343	use 64 bit file offsets the programs will fail. In that case you have to
		2344	compile libev with the same flags to get binary compatibility. This is
		2345	obviously the case with any flags that change the ABI, but the problem is
		2346	most noticeably displayed with ev_stat and large file support.
		2347
		2348	The solution for this is to lobby your distribution maker to make large
		2349	file interfaces available by default (as e.g. FreeBSD does) and not
		2350	optional. Libev cannot simply switch on large file support because it has
		2351	to exchange stat structures with application programs compiled using the
		2352	default compilation environment.
		2353
		2354	=head3 Inotify and Kqueue
		2355
		2356	When C<inotify (7)> support has been compiled into libev and present at
		2357	runtime, it will be used to speed up change detection where possible. The
		2358	inotify descriptor will be created lazily when the first C<ev_stat>
		2359	watcher is being started.
		2360
		2361	Inotify presence does not change the semantics of C<ev_stat> watchers
		2362	except that changes might be detected earlier, and in some cases, to avoid
		2363	making regular C<stat> calls. Even in the presence of inotify support
		2364	there are many cases where libev has to resort to regular C<stat> polling,
		2365	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2366	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2367	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2368	xfs are fully working) libev usually gets away without polling.
		2369
		2370	There is no support for kqueue, as apparently it cannot be used to
		2371	implement this functionality, due to the requirement of having a file
		2372	descriptor open on the object at all times, and detecting renames, unlinks
		2373	etc. is difficult.
		2374
		2375	=head3 C<stat ()> is a synchronous operation
		2376
		2377	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2378	the process. The exception are C<ev_stat> watchers - those call C<stat
		2379	()>, which is a synchronous operation.
		2380
		2381	For local paths, this usually doesn't matter: unless the system is very
		2382	busy or the intervals between stat's are large, a stat call will be fast,
		2383	as the path data is usually in memory already (except when starting the
		2384	watcher).
		2385
		2386	For networked file systems, calling C<stat ()> can block an indefinite
		2387	time due to network issues, and even under good conditions, a stat call
		2388	often takes multiple milliseconds.
		2389
		2390	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2391	paths, although this is fully supported by libev.
		2392
		2393	=head3 The special problem of stat time resolution
		2394
		2395	The C<stat ()> system call only supports full-second resolution portably,
		2396	and even on systems where the resolution is higher, most file systems
		2397	still only support whole seconds.
		2398
		2399	That means that, if the time is the only thing that changes, you can
		2400	easily miss updates: on the first update, C<ev_stat> detects a change and
		2401	calls your callback, which does something. When there is another update
		2402	within the same second, C<ev_stat> will be unable to detect unless the
		2403	stat data does change in other ways (e.g. file size).
		2404
		2405	The solution to this is to delay acting on a change for slightly more
		2406	than a second (or till slightly after the next full second boundary), using
		2407	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2408	ev_timer_again (loop, w)>).
		2409
		2410	The C<.02> offset is added to work around small timing inconsistencies
		2411	of some operating systems (where the second counter of the current time
		2412	might be be delayed. One such system is the Linux kernel, where a call to
		2413	C<gettimeofday> might return a timestamp with a full second later than
		2414	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2415	update file times then there will be a small window where the kernel uses
		2416	the previous second to update file times but libev might already execute
		2417	the timer callback).
		2418
		2419	=head3 Watcher-Specific Functions and Data Members
1328		2420
1329	=over 4	2421	=over 4
1330		2422
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2423	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2424
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2428	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2429	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2430	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2431	path for as long as the watcher is active.
1340		2432
1341	The callback will be receive C<EV_STAT> when a change was detected,	2433	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2434	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2435	last change was detected).
1344		2436
1345	=item ev_stat_stat (ev_stat *)	2437	=item ev_stat_stat (loop, ev_stat *)
1346		2438
1347	Updates the stat buffer immediately with new values. If you change the	2439	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2440	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2441	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2442	the only one changing the path). Can also be useful simply to find out the
		2443	new values.
1351		2444
1352	=item ev_statdata attr [read-only]	2445	=item ev_statdata attr [read-only]
1353		2446
1354	The most-recently detected attributes of the file. Although the type is of	2447	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2448	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2449	suitable for your system, but you can only rely on the POSIX-standardised
		2450	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2451	some error while C<stat>ing the file.
1358		2452
1359	=item ev_statdata prev [read-only]	2453	=item ev_statdata prev [read-only]
1360		2454
1361	The previous attributes of the file. The callback gets invoked whenever	2455	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2456	C<prev> != C<attr>, or, more precisely, one or more of these members
		2457	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2458	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2459
1364	=item ev_tstamp interval [read-only]	2460	=item ev_tstamp interval [read-only]
1365		2461
1366	The specified interval.	2462	The specified interval.
1367		2463
1368	=item const char *path [read-only]	2464	=item const char *path [read-only]
1369		2465
1370	The filesystem path that is being watched.	2466	The file system path that is being watched.
1371		2467
1372	=back	2468	=back
1373		2469
		2470	=head3 Examples
		2471
1374	Example: Watch C</etc/passwd> for attribute changes.	2472	Example: Watch C</etc/passwd> for attribute changes.
1375		2473
1376	static void	2474	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2475	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2476	{
1379	/* /etc/passwd changed in some way */	2477	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2478	if (w->attr.st_nlink)
1381	{	2479	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2480	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2481	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2482	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2483	}
1386	else	2484	else
1387	/* you shalt not abuse printf for puts */	2485	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2486	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2487	"if this is windows, they already arrived\n");
1390	}	2488	}
1391		2489
1392	...	2490	...
1393	ev_stat passwd;	2491	ev_stat passwd;
1394		2492
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2493	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2494	ev_stat_start (loop, &passwd);
		2495
		2496	Example: Like above, but additionally use a one-second delay so we do not
		2497	miss updates (however, frequent updates will delay processing, too, so
		2498	one might do the work both on C<ev_stat> callback invocation I<and> on
		2499	C<ev_timer> callback invocation).
		2500
		2501	static ev_stat passwd;
		2502	static ev_timer timer;
		2503
		2504	static void
		2505	timer_cb (EV_P_ ev_timer *w, int revents)
		2506	{
		2507	ev_timer_stop (EV_A_ w);
		2508
		2509	/* now it's one second after the most recent passwd change */
		2510	}
		2511
		2512	static void
		2513	stat_cb (EV_P_ ev_stat *w, int revents)
		2514	{
		2515	/* reset the one-second timer */
		2516	ev_timer_again (EV_A_ &timer);
		2517	}
		2518
		2519	...
		2520	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2521	ev_stat_start (loop, &passwd);
		2522	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2523
1398		2524
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2525	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2526
1401	Idle watchers trigger events when no other events of the same or higher	2527	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2528	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2529	as receiving "events").
1404		2530
1405	That is, as long as your process is busy handling sockets or timeouts	2531	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2532	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2533	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2534	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2541	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2542	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2543	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2544	event loop has handled all outstanding events.
1419		2545
		2546	=head3 Watcher-Specific Functions and Data Members
		2547
1420	=over 4	2548	=over 4
1421		2549
1422	=item ev_idle_init (ev_signal *, callback)	2550	=item ev_idle_init (ev_idle *, callback)
1423		2551
1424	Initialises and configures the idle watcher - it has no parameters of any	2552	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2553	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2554	believe me.
1427		2555
1428	=back	2556	=back
1429		2557
		2558	=head3 Examples
		2559
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2560	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2561	callback, free it. Also, use no error checking, as usual.
1432		2562
1433	static void	2563	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2564	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2565	{
1436	free (w);	2566	free (w);
1437	// now do something you wanted to do when the program has	2567	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2568	// no longer anything immediate to do.
1439	}	2569	}
1440		2570
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2571	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2572	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2573	ev_idle_start (loop, idle_watcher);
1444		2574
1445		2575
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2576	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2577
1448	Prepare and check watchers are usually (but not always) used in tandem:	2578	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2579	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2580	afterwards.
1451		2581
1452	You I<must not> call C<ev_loop> or similar functions that enter	2582	You I<must not> call C<ev_loop> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2583	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2586	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2587	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2588	called in pairs bracketing the blocking call.
1459		2589
1460	Their main purpose is to integrate other event mechanisms into libev and	2590	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2591	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2592	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2593	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2594	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2595	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2596	watcher).
1467		2597
1468	This is done by examining in each prepare call which file descriptors need	2598	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2599	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2600	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2601	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2602	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2603	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2604	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2605	nevertheless, because you never know, you know?).
1476		2606
1477	As another example, the Perl Coro module uses these hooks to integrate	2607	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2608	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2609	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2610	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2611	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2612	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2613	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2614	low-priority coroutines to idle/background tasks).
1485		2615
		2616	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2617	priority, to ensure that they are being run before any other watchers
		2618	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2619
		2620	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2621	activate ("feed") events into libev. While libev fully supports this, they
		2622	might get executed before other C<ev_check> watchers did their job. As
		2623	C<ev_check> watchers are often used to embed other (non-libev) event
		2624	loops those other event loops might be in an unusable state until their
		2625	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2626	others).
		2627
		2628	=head3 Watcher-Specific Functions and Data Members
		2629
1486	=over 4	2630	=over 4
1487		2631
1488	=item ev_prepare_init (ev_prepare *, callback)	2632	=item ev_prepare_init (ev_prepare *, callback)
1489		2633
1490	=item ev_check_init (ev_check *, callback)	2634	=item ev_check_init (ev_check *, callback)
1491		2635
1492	Initialises and configures the prepare or check watcher - they have no	2636	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2637	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2638	macros, but using them is utterly, utterly, utterly and completely
		2639	pointless.
1495		2640
1496	=back	2641	=back
1497		2642
1498	Example: To include a library such as adns, you would add IO watchers	2643	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	2644
		2645	There are a number of principal ways to embed other event loops or modules
		2646	into libev. Here are some ideas on how to include libadns into libev
		2647	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2648	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2649	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2650	Glib event loop).
		2651
		2652	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	2653	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	2654	is pseudo-code only of course. This requires you to either use a low
		2655	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2656	the callbacks for the IO/timeout watchers might not have been called yet.
1502		2657
1503	static ev_io iow [nfd];	2658	static ev_io iow [nfd];
1504	static ev_timer tw;	2659	static ev_timer tw;
1505		2660
1506	static void	2661	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	2662	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	2663	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	2664	}
1515		2665
1516	// create io watchers for each fd and a timer before blocking	2666	// create io watchers for each fd and a timer before blocking
1517	static void	2667	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2668	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	2669	{
1520	int timeout = 3600000;	2670	int timeout = 3600000;
1521	struct pollfd fds [nfd];	2671	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	2672	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2673	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		2674
1525	/* the callback is illegal, but won't be called as we stop during check */	2675	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	2676	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1527	ev_timer_start (loop, &tw);	2677	ev_timer_start (loop, &tw);
1528		2678
1529	// create on ev_io per pollfd	2679	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	2680	for (int i = 0; i < nfd; ++i)
1531	{	2681	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	2682	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	2683	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2684	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		2685
1536	fds [i].revents = 0;	2686	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	2687	ev_io_start (loop, iow + i);
1539	}	2688	}
1540	}	2689	}
1541		2690
1542	// stop all watchers after blocking	2691	// stop all watchers after blocking
1543	static void	2692	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2693	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	2694	{
1546	ev_timer_stop (loop, &tw);	2695	ev_timer_stop (loop, &tw);
1547		2696
1548	for (int i = 0; i < nfd; ++i)	2697	for (int i = 0; i < nfd; ++i)
		2698	{
		2699	// set the relevant poll flags
		2700	// could also call adns_processreadable etc. here
		2701	struct pollfd *fd = fds + i;
		2702	int revents = ev_clear_pending (iow + i);
		2703	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2704	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2705
		2706	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	2707	ev_io_stop (loop, iow + i);
		2708	}
1550		2709
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2710	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	2711	}
		2712
		2713	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2714	in the prepare watcher and would dispose of the check watcher.
		2715
		2716	Method 3: If the module to be embedded supports explicit event
		2717	notification (libadns does), you can also make use of the actual watcher
		2718	callbacks, and only destroy/create the watchers in the prepare watcher.
		2719
		2720	static void
		2721	timer_cb (EV_P_ ev_timer *w, int revents)
		2722	{
		2723	adns_state ads = (adns_state)w->data;
		2724	update_now (EV_A);
		2725
		2726	adns_processtimeouts (ads, &tv_now);
		2727	}
		2728
		2729	static void
		2730	io_cb (EV_P_ ev_io *w, int revents)
		2731	{
		2732	adns_state ads = (adns_state)w->data;
		2733	update_now (EV_A);
		2734
		2735	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2736	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2737	}
		2738
		2739	// do not ever call adns_afterpoll
		2740
		2741	Method 4: Do not use a prepare or check watcher because the module you
		2742	want to embed is not flexible enough to support it. Instead, you can
		2743	override their poll function. The drawback with this solution is that the
		2744	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2745	this approach, effectively embedding EV as a client into the horrible
		2746	libglib event loop.
		2747
		2748	static gint
		2749	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2750	{
		2751	int got_events = 0;
		2752
		2753	for (n = 0; n < nfds; ++n)
		2754	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2755
		2756	if (timeout >= 0)
		2757	// create/start timer
		2758
		2759	// poll
		2760	ev_loop (EV_A_ 0);
		2761
		2762	// stop timer again
		2763	if (timeout >= 0)
		2764	ev_timer_stop (EV_A_ &to);
		2765
		2766	// stop io watchers again - their callbacks should have set
		2767	for (n = 0; n < nfds; ++n)
		2768	ev_io_stop (EV_A_ iow [n]);
		2769
		2770	return got_events;
		2771	}
1553		2772
1554		2773
1555	=head2 C<ev_embed> - when one backend isn't enough...	2774	=head2 C<ev_embed> - when one backend isn't enough...
1556		2775
1557	This is a rather advanced watcher type that lets you embed one event loop	2776	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	2782	prioritise I/O.
1564		2783
1565	As an example for a bug workaround, the kqueue backend might only support	2784	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	2785	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	2786	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	2787	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	2788	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	2789	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	2790	C<kevent>, but at least you can use both mechanisms for what they are
		2791	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		2792
1573	As for prioritising I/O: rarely you have the case where some fds have	2793	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	2794	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	2795	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	2796	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	2797	the rest in a second one, and embed the second one in the first.
1578		2798
1579	As long as the watcher is active, the callback will be invoked every time	2799	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	2800	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2801	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	2802	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	2803	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	2804	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		2805
1587	As long as the watcher is started it will automatically handle events. The	2806	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	2807	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		2808
1592	Also, there have not currently been made special provisions for forking:	2809	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2810	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	2811	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	2812	C<ev_loop_fork> on the embedded loop.
1596		2813
1597	Unfortunately, not all backends are embeddable, only the ones returned by	2814	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2815	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	2816	portable one.
1600		2817
1601	So when you want to use this feature you will always have to be prepared	2818	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	2819	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	2820	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	2821	create it, and if that fails, use the normal loop for everything.
1605		2822
1606	struct ev_loop *loop_hi = ev_default_init (0);	2823	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		2824
1616	// if we got one, then embed it, otherwise default to loop_hi	2825	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	2826	automatically be applied to the embedded loop as well, so no special
1618	{	2827	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	2828	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	2829	as applicable.
1621	}	2830
1622	else	2831	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		2832
1625	=over 4	2833	=over 4
1626		2834
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2835	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		2836
…		…
1630		2838
1631	Configures the watcher to embed the given loop, which must be	2839	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2840	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	2841	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	2842	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	2843	if you do not want that, you need to temporarily stop the embed watcher).
1636		2844
1637	=item ev_embed_sweep (loop, ev_embed *)	2845	=item ev_embed_sweep (loop, ev_embed *)
1638		2846
1639	Make a single, non-blocking sweep over the embedded loop. This works	2847	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2848	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1641	apropriate way for embedded loops.	2849	appropriate way for embedded loops.
1642		2850
1643	=item struct ev_loop *loop [read-only]	2851	=item struct ev_loop *other [read-only]
1644		2852
1645	The embedded event loop.	2853	The embedded event loop.
1646		2854
1647	=back	2855	=back
		2856
		2857	=head3 Examples
		2858
		2859	Example: Try to get an embeddable event loop and embed it into the default
		2860	event loop. If that is not possible, use the default loop. The default
		2861	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2862	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2863	used).
		2864
		2865	struct ev_loop *loop_hi = ev_default_init (0);
		2866	struct ev_loop *loop_lo = 0;
		2867	ev_embed embed;
		2868
		2869	// see if there is a chance of getting one that works
		2870	// (remember that a flags value of 0 means autodetection)
		2871	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2872	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2873	: 0;
		2874
		2875	// if we got one, then embed it, otherwise default to loop_hi
		2876	if (loop_lo)
		2877	{
		2878	ev_embed_init (&embed, 0, loop_lo);
		2879	ev_embed_start (loop_hi, &embed);
		2880	}
		2881	else
		2882	loop_lo = loop_hi;
		2883
		2884	Example: Check if kqueue is available but not recommended and create
		2885	a kqueue backend for use with sockets (which usually work with any
		2886	kqueue implementation). Store the kqueue/socket-only event loop in
		2887	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2888
		2889	struct ev_loop *loop = ev_default_init (0);
		2890	struct ev_loop *loop_socket = 0;
		2891	ev_embed embed;
		2892
		2893	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2894	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2895	{
		2896	ev_embed_init (&embed, 0, loop_socket);
		2897	ev_embed_start (loop, &embed);
		2898	}
		2899
		2900	if (!loop_socket)
		2901	loop_socket = loop;
		2902
		2903	// now use loop_socket for all sockets, and loop for everything else
1648		2904
1649		2905
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2906	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		2907
1652	Fork watchers are called when a C<fork ()> was detected (usually because	2908	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1655	event loop blocks next and before C<ev_check> watchers are being called,	2911	event loop blocks next and before C<ev_check> watchers are being called,
1656	and only in the child after the fork. If whoever good citizen calling	2912	and only in the child after the fork. If whoever good citizen calling
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2913	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1658	handlers will be invoked, too, of course.	2914	handlers will be invoked, too, of course.
1659		2915
		2916	=head3 The special problem of life after fork - how is it possible?
		2917
		2918	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2919	up/change the process environment, followed by a call to C<exec()>. This
		2920	sequence should be handled by libev without any problems.
		2921
		2922	This changes when the application actually wants to do event handling
		2923	in the child, or both parent in child, in effect "continuing" after the
		2924	fork.
		2925
		2926	The default mode of operation (for libev, with application help to detect
		2927	forks) is to duplicate all the state in the child, as would be expected
		2928	when I<either> the parent I<or> the child process continues.
		2929
		2930	When both processes want to continue using libev, then this is usually the
		2931	wrong result. In that case, usually one process (typically the parent) is
		2932	supposed to continue with all watchers in place as before, while the other
		2933	process typically wants to start fresh, i.e. without any active watchers.
		2934
		2935	The cleanest and most efficient way to achieve that with libev is to
		2936	simply create a new event loop, which of course will be "empty", and
		2937	use that for new watchers. This has the advantage of not touching more
		2938	memory than necessary, and thus avoiding the copy-on-write, and the
		2939	disadvantage of having to use multiple event loops (which do not support
		2940	signal watchers).
		2941
		2942	When this is not possible, or you want to use the default loop for
		2943	other reasons, then in the process that wants to start "fresh", call
		2944	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2945	the default loop will "orphan" (not stop) all registered watchers, so you
		2946	have to be careful not to execute code that modifies those watchers. Note
		2947	also that in that case, you have to re-register any signal watchers.
		2948
		2949	=head3 Watcher-Specific Functions and Data Members
		2950
1660	=over 4	2951	=over 4
1661		2952
1662	=item ev_fork_init (ev_signal *, callback)	2953	=item ev_fork_init (ev_signal *, callback)
1663		2954
1664	Initialises and configures the fork watcher - it has no parameters of any	2955	Initialises and configures the fork watcher - it has no parameters of any
…		…
1666	believe me.	2957	believe me.
1667		2958
1668	=back	2959	=back
1669		2960
1670		2961
		2962	=head2 C<ev_async> - how to wake up another event loop
		2963
		2964	In general, you cannot use an C<ev_loop> from multiple threads or other
		2965	asynchronous sources such as signal handlers (as opposed to multiple event
		2966	loops - those are of course safe to use in different threads).
		2967
		2968	Sometimes, however, you need to wake up another event loop you do not
		2969	control, for example because it belongs to another thread. This is what
		2970	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2971	can signal it by calling C<ev_async_send>, which is thread- and signal
		2972	safe.
		2973
		2974	This functionality is very similar to C<ev_signal> watchers, as signals,
		2975	too, are asynchronous in nature, and signals, too, will be compressed
		2976	(i.e. the number of callback invocations may be less than the number of
		2977	C<ev_async_sent> calls).
		2978
		2979	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2980	just the default loop.
		2981
		2982	=head3 Queueing
		2983
		2984	C<ev_async> does not support queueing of data in any way. The reason
		2985	is that the author does not know of a simple (or any) algorithm for a
		2986	multiple-writer-single-reader queue that works in all cases and doesn't
		2987	need elaborate support such as pthreads or unportable memory access
		2988	semantics.
		2989
		2990	That means that if you want to queue data, you have to provide your own
		2991	queue. But at least I can tell you how to implement locking around your
		2992	queue:
		2993
		2994	=over 4
		2995
		2996	=item queueing from a signal handler context
		2997
		2998	To implement race-free queueing, you simply add to the queue in the signal
		2999	handler but you block the signal handler in the watcher callback. Here is
		3000	an example that does that for some fictitious SIGUSR1 handler:
		3001
		3002	static ev_async mysig;
		3003
		3004	static void
		3005	sigusr1_handler (void)
		3006	{
		3007	sometype data;
		3008
		3009	// no locking etc.
		3010	queue_put (data);
		3011	ev_async_send (EV_DEFAULT_ &mysig);
		3012	}
		3013
		3014	static void
		3015	mysig_cb (EV_P_ ev_async *w, int revents)
		3016	{
		3017	sometype data;
		3018	sigset_t block, prev;
		3019
		3020	sigemptyset (&block);
		3021	sigaddset (&block, SIGUSR1);
		3022	sigprocmask (SIG_BLOCK, &block, &prev);
		3023
		3024	while (queue_get (&data))
		3025	process (data);
		3026
		3027	if (sigismember (&prev, SIGUSR1)
		3028	sigprocmask (SIG_UNBLOCK, &block, 0);
		3029	}
		3030
		3031	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3032	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3033	either...).
		3034
		3035	=item queueing from a thread context
		3036
		3037	The strategy for threads is different, as you cannot (easily) block
		3038	threads but you can easily preempt them, so to queue safely you need to
		3039	employ a traditional mutex lock, such as in this pthread example:
		3040
		3041	static ev_async mysig;
		3042	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3043
		3044	static void
		3045	otherthread (void)
		3046	{
		3047	// only need to lock the actual queueing operation
		3048	pthread_mutex_lock (&mymutex);
		3049	queue_put (data);
		3050	pthread_mutex_unlock (&mymutex);
		3051
		3052	ev_async_send (EV_DEFAULT_ &mysig);
		3053	}
		3054
		3055	static void
		3056	mysig_cb (EV_P_ ev_async *w, int revents)
		3057	{
		3058	pthread_mutex_lock (&mymutex);
		3059
		3060	while (queue_get (&data))
		3061	process (data);
		3062
		3063	pthread_mutex_unlock (&mymutex);
		3064	}
		3065
		3066	=back
		3067
		3068
		3069	=head3 Watcher-Specific Functions and Data Members
		3070
		3071	=over 4
		3072
		3073	=item ev_async_init (ev_async *, callback)
		3074
		3075	Initialises and configures the async watcher - it has no parameters of any
		3076	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3077	trust me.
		3078
		3079	=item ev_async_send (loop, ev_async *)
		3080
		3081	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3082	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3083	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3084	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3085	section below on what exactly this means).
		3086
		3087	Note that, as with other watchers in libev, multiple events might get
		3088	compressed into a single callback invocation (another way to look at this
		3089	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3090	reset when the event loop detects that).
		3091
		3092	This call incurs the overhead of a system call only once per event loop
		3093	iteration, so while the overhead might be noticeable, it doesn't apply to
		3094	repeated calls to C<ev_async_send> for the same event loop.
		3095
		3096	=item bool = ev_async_pending (ev_async *)
		3097
		3098	Returns a non-zero value when C<ev_async_send> has been called on the
		3099	watcher but the event has not yet been processed (or even noted) by the
		3100	event loop.
		3101
		3102	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3103	the loop iterates next and checks for the watcher to have become active,
		3104	it will reset the flag again. C<ev_async_pending> can be used to very
		3105	quickly check whether invoking the loop might be a good idea.
		3106
		3107	Not that this does I<not> check whether the watcher itself is pending,
		3108	only whether it has been requested to make this watcher pending: there
		3109	is a time window between the event loop checking and resetting the async
		3110	notification, and the callback being invoked.
		3111
		3112	=back
		3113
		3114
1671	=head1 OTHER FUNCTIONS	3115	=head1 OTHER FUNCTIONS
1672		3116
1673	There are some other functions of possible interest. Described. Here. Now.	3117	There are some other functions of possible interest. Described. Here. Now.
1674		3118
1675	=over 4	3119	=over 4
1676		3120
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3121	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1678		3122
1679	This function combines a simple timer and an I/O watcher, calls your	3123	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	3124	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	3125	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	3126	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	3127	more watchers yourself.
1684		3128
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	3129	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3130	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	3131	the given C<fd> and C<events> set will be created and started.
1688		3132
1689	If C<timeout> is less than 0, then no timeout watcher will be	3133	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3134	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3135	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		3136
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3137	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1695	passed an C<revents> set like normal event callbacks (a combination of	3138	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3139	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1697	value passed to C<ev_once>:	3140	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3141	a timeout and an io event at the same time - you probably should give io
		3142	events precedence.
1698		3143
		3144	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3145
1699	static void stdin_ready (int revents, void *arg)	3146	static void stdin_ready (int revents, void *arg)
1700	{	3147	{
1701	if (revents & EV_TIMEOUT)
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)	3148	if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;	3149	/* stdin might have data for us, joy! */;
		3150	else if (revents & EV_TIMEOUT)
		3151	/* doh, nothing entered */;
1705	}	3152	}
1706		3153
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3154	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1708		3155
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)
1710
1711	Feeds the given event set into the event loop, as if the specified event
1712	had happened for the specified watcher (which must be a pointer to an
1713	initialised but not necessarily started event watcher).
1714
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3156	=item ev_feed_fd_event (loop, int fd, int revents)
1716		3157
1717	Feed an event on the given fd, as if a file descriptor backend detected	3158	Feed an event on the given fd, as if a file descriptor backend detected
1718	the given events it.	3159	the given events it.
1719		3160
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	3161	=item ev_feed_signal_event (loop, int signum)
1721		3162
1722	Feed an event as if the given signal occured (C<loop> must be the default	3163	Feed an event as if the given signal occurred (C<loop> must be the default
1723	loop!).	3164	loop!).
1724		3165
1725	=back	3166	=back
1726		3167
1727		3168
…		…
1743		3184
1744	=item * Priorities are not currently supported. Initialising priorities	3185	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	3186	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	3187	is an ev_pri field.
1747		3188
		3189	=item * In libevent, the last base created gets the signals, in libev, the
		3190	first base created (== the default loop) gets the signals.
		3191
1748	=item * Other members are not supported.	3192	=item * Other members are not supported.
1749		3193
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3194	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	3195	to use the libev header file and library.
1752		3196
1753	=back	3197	=back
1754		3198
1755	=head1 C++ SUPPORT	3199	=head1 C++ SUPPORT
1756		3200
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3201	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	3202	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	3203	the callback model to a model using method callbacks on objects.
1760		3204
1761	To use it,	3205	To use it,
1762		3206
1763	#include <ev++.h>	3207	#include <ev++.h>
1764		3208
1765	This automatically includes F<ev.h> and puts all of its definitions (many	3209	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	3210	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	3211	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3212	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1802		3246
1803	=over 4	3247	=over 4
1804		3248
1805	=item ev::TYPE::TYPE ()	3249	=item ev::TYPE::TYPE ()
1806		3250
1807	=item ev::TYPE::TYPE (struct ev_loop *)	3251	=item ev::TYPE::TYPE (loop)
1808		3252
1809	=item ev::TYPE::~TYPE	3253	=item ev::TYPE::~TYPE
1810		3254
1811	The constructor (optionally) takes an event loop to associate the watcher	3255	The constructor (optionally) takes an event loop to associate the watcher
1812	with. If it is omitted, it will use C<EV_DEFAULT>.	3256	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	3279	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	3280	thunking function, making it as fast as a direct C callback.
1837		3281
1838	Example: simple class declaration and watcher initialisation	3282	Example: simple class declaration and watcher initialisation
1839		3283
1840	struct myclass	3284	struct myclass
1841	{	3285	{
1842	void io_cb (ev::io &w, int revents) { }	3286	void io_cb (ev::io &w, int revents) { }
1843	}	3287	}
1844		3288
1845	myclass obj;	3289	myclass obj;
1846	ev::io iow;	3290	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	3291	iow.set <myclass, &myclass::io_cb> (&obj);
1848		3292
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	3293	=item w->set (object *)
		3294
		3295	This is an B<experimental> feature that might go away in a future version.
		3296
		3297	This is a variation of a method callback - leaving out the method to call
		3298	will default the method to C<operator ()>, which makes it possible to use
		3299	functor objects without having to manually specify the C<operator ()> all
		3300	the time. Incidentally, you can then also leave out the template argument
		3301	list.
		3302
		3303	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3304	int revents)>.
		3305
		3306	See the method-C<set> above for more details.
		3307
		3308	Example: use a functor object as callback.
		3309
		3310	struct myfunctor
		3311	{
		3312	void operator() (ev::io &w, int revents)
		3313	{
		3314	...
		3315	}
		3316	}
		3317
		3318	myfunctor f;
		3319
		3320	ev::io w;
		3321	w.set (&f);
		3322
		3323	=item w->set<function> (void *data = 0)
1850		3324
1851	Also sets a callback, but uses a static method or plain function as	3325	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	3326	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	3327	C<data> member and is free for you to use.
1854		3328
		3329	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3330
1855	See the method-C<set> above for more details.	3331	See the method-C<set> above for more details.
1856		3332
		3333	Example: Use a plain function as callback.
		3334
		3335	static void io_cb (ev::io &w, int revents) { }
		3336	iow.set <io_cb> ();
		3337
1857	=item w->set (struct ev_loop *)	3338	=item w->set (loop)
1858		3339
1859	Associates a different C<struct ev_loop> with this watcher. You can only	3340	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	3341	do this when the watcher is inactive (and not pending either).
1861		3342
1862	=item w->set ([args])	3343	=item w->set ([arguments])
1863		3344
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3345	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1865	called at least once. Unlike the C counterpart, an active watcher gets	3346	called at least once. Unlike the C counterpart, an active watcher gets
1866	automatically stopped and restarted when reconfiguring it with this	3347	automatically stopped and restarted when reconfiguring it with this
1867	method.	3348	method.
1868		3349
1869	=item w->start ()	3350	=item w->start ()
…		…
1873		3354
1874	=item w->stop ()	3355	=item w->stop ()
1875		3356
1876	Stops the watcher if it is active. Again, no C<loop> argument.	3357	Stops the watcher if it is active. Again, no C<loop> argument.
1877		3358
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	3359	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		3360
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3361	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	3362	C<ev_TYPE_again> function.
1882		3363
1883	=item w->sweep () C<ev::embed> only	3364	=item w->sweep () (C<ev::embed> only)
1884		3365
1885	Invokes C<ev_embed_sweep>.	3366	Invokes C<ev_embed_sweep>.
1886		3367
1887	=item w->update () C<ev::stat> only	3368	=item w->update () (C<ev::stat> only)
1888		3369
1889	Invokes C<ev_stat_stat>.	3370	Invokes C<ev_stat_stat>.
1890		3371
1891	=back	3372	=back
1892		3373
1893	=back	3374	=back
1894		3375
1895	Example: Define a class with an IO and idle watcher, start one of them in	3376	Example: Define a class with an IO and idle watcher, start one of them in
1896	the constructor.	3377	the constructor.
1897		3378
1898	class myclass	3379	class myclass
1899	{	3380	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	3381	ev::io io ; void io_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	3382	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		3383
1903	myclass ();	3384	myclass (int fd)
1904	}	3385	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	3386	io .set <myclass, &myclass::io_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	3387	idle.set <myclass, &myclass::idle_cb> (this);
1910		3388
1911	io.start (fd, ev::READ);	3389	io.start (fd, ev::READ);
		3390	}
1912	}	3391	};
		3392
		3393
		3394	=head1 OTHER LANGUAGE BINDINGS
		3395
		3396	Libev does not offer other language bindings itself, but bindings for a
		3397	number of languages exist in the form of third-party packages. If you know
		3398	any interesting language binding in addition to the ones listed here, drop
		3399	me a note.
		3400
		3401	=over 4
		3402
		3403	=item Perl
		3404
		3405	The EV module implements the full libev API and is actually used to test
		3406	libev. EV is developed together with libev. Apart from the EV core module,
		3407	there are additional modules that implement libev-compatible interfaces
		3408	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3409	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3410	and C<EV::Glib>).
		3411
		3412	It can be found and installed via CPAN, its homepage is at
		3413	L<http://software.schmorp.de/pkg/EV>.
		3414
		3415	=item Python
		3416
		3417	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3418	seems to be quite complete and well-documented.
		3419
		3420	=item Ruby
		3421
		3422	Tony Arcieri has written a ruby extension that offers access to a subset
		3423	of the libev API and adds file handle abstractions, asynchronous DNS and
		3424	more on top of it. It can be found via gem servers. Its homepage is at
		3425	L<http://rev.rubyforge.org/>.
		3426
		3427	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3428	makes rev work even on mingw.
		3429
		3430	=item Haskell
		3431
		3432	A haskell binding to libev is available at
		3433	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3434
		3435	=item D
		3436
		3437	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3438	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3439
		3440	=item Ocaml
		3441
		3442	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3443	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3444
		3445	=item Lua
		3446
		3447	Brian Maher has written a partial interface to libev
		3448	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3449	L<http://github.com/brimworks/lua-ev>.
		3450
		3451	=back
1913		3452
1914		3453
1915	=head1 MACRO MAGIC	3454	=head1 MACRO MAGIC
1916		3455
1917	Libev can be compiled with a variety of options, the most fundemantal is	3456	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3457	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	3458	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		3459
1921	To make it easier to write programs that cope with either variant, the	3460	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	3461	following macros are defined:
1923		3462
1924	=over 4	3463	=over 4
…		…
1927		3466
1928	This provides the loop I<argument> for functions, if one is required ("ev	3467	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	3468	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	3469	C<EV_A_> is used when other arguments are following. Example:
1931		3470
1932	ev_unref (EV_A);	3471	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	3472	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	3473	ev_loop (EV_A_ 0);
1935		3474
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3475	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	3476	which is often provided by the following macro.
1938		3477
1939	=item C<EV_P>, C<EV_P_>	3478	=item C<EV_P>, C<EV_P_>
1940		3479
1941	This provides the loop I<parameter> for functions, if one is required ("ev	3480	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3481	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	3482	C<EV_P_> is used when other parameters are following. Example:
1944		3483
1945	// this is how ev_unref is being declared	3484	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	3485	static void ev_unref (EV_P);
1947		3486
1948	// this is how you can declare your typical callback	3487	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	3488	static void cb (EV_P_ ev_timer *w, int revents)
1950		3489
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3490	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	3491	suitable for use with C<EV_A>.
1953		3492
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3493	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		3494
1956	Similar to the other two macros, this gives you the value of the default	3495	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	3496	loop, if multiple loops are supported ("ev loop default").
		3497
		3498	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3499
		3500	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3501	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3502	is undefined when the default loop has not been initialised by a previous
		3503	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3504
		3505	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3506	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		3507
1959	=back	3508	=back
1960		3509
1961	Example: Declare and initialise a check watcher, utilising the above	3510	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	3511	macros so it will work regardless of whether multiple loops are supported
1963	or not.	3512	or not.
1964		3513
1965	static void	3514	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	3515	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	3516	{
1968	ev_check_stop (EV_A_ w);	3517	ev_check_stop (EV_A_ w);
1969	}	3518	}
1970		3519
1971	ev_check check;	3520	ev_check check;
1972	ev_check_init (&check, check_cb);	3521	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	3522	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	3523	ev_loop (EV_DEFAULT_ 0);
1975		3524
1976	=head1 EMBEDDING	3525	=head1 EMBEDDING
1977		3526
1978	Libev can (and often is) directly embedded into host	3527	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	3528	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3529	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	3530	and rxvt-unicode.
1982		3531
1983	The goal is to enable you to just copy the neecssary files into your	3532	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	3533	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	3534	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	3535	libev somewhere in your source tree).
1987		3536
1988	=head2 FILESETS	3537	=head2 FILESETS
1989		3538
1990	Depending on what features you need you need to include one or more sets of files	3539	Depending on what features you need you need to include one or more sets of files
1991	in your app.	3540	in your application.
1992		3541
1993	=head3 CORE EVENT LOOP	3542	=head3 CORE EVENT LOOP
1994		3543
1995	To include only the libev core (all the C<ev_*> functions), with manual	3544	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	3545	configuration (no autoconf):
1997		3546
1998	#define EV_STANDALONE 1	3547	#define EV_STANDALONE 1
1999	#include "ev.c"	3548	#include "ev.c"
2000		3549
2001	This will automatically include F<ev.h>, too, and should be done in a	3550	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	3551	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	3552	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	3553	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	3554	where you can put other configuration options):
2006		3555
2007	#define EV_STANDALONE 1	3556	#define EV_STANDALONE 1
2008	#include "ev.h"	3557	#include "ev.h"
2009		3558
2010	Both header files and implementation files can be compiled with a C++	3559	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	3560	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	3561	as a bug).
2013		3562
2014	You need the following files in your source tree, or in a directory	3563	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	3564	in your include path (e.g. in libev/ when using -Ilibev):
2016		3565
2017	ev.h	3566	ev.h
2018	ev.c	3567	ev.c
2019	ev_vars.h	3568	ev_vars.h
2020	ev_wrap.h	3569	ev_wrap.h
2021		3570
2022	ev_win32.c required on win32 platforms only	3571	ev_win32.c required on win32 platforms only
2023		3572
2024	ev_select.c only when select backend is enabled (which is enabled by default)	3573	ev_select.c only when select backend is enabled (which is enabled by default)
2025	ev_poll.c only when poll backend is enabled (disabled by default)	3574	ev_poll.c only when poll backend is enabled (disabled by default)
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3575	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3576	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	3577	ev_port.c only when the solaris port backend is enabled (disabled by default)
2029		3578
2030	F<ev.c> includes the backend files directly when enabled, so you only need	3579	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	3580	to compile this single file.
2032		3581
2033	=head3 LIBEVENT COMPATIBILITY API	3582	=head3 LIBEVENT COMPATIBILITY API
2034		3583
2035	To include the libevent compatibility API, also include:	3584	To include the libevent compatibility API, also include:
2036		3585
2037	#include "event.c"	3586	#include "event.c"
2038		3587
2039	in the file including F<ev.c>, and:	3588	in the file including F<ev.c>, and:
2040		3589
2041	#include "event.h"	3590	#include "event.h"
2042		3591
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	3592	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		3593
2045	You need the following additional files for this:	3594	You need the following additional files for this:
2046		3595
2047	event.h	3596	event.h
2048	event.c	3597	event.c
2049		3598
2050	=head3 AUTOCONF SUPPORT	3599	=head3 AUTOCONF SUPPORT
2051		3600
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	3601	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	3602	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3603	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	3604	include F<config.h> and configure itself accordingly.
2056		3605
2057	For this of course you need the m4 file:	3606	For this of course you need the m4 file:
2058		3607
2059	libev.m4	3608	libev.m4
2060		3609
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	3610	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		3611
2063	Libev can be configured via a variety of preprocessor symbols you have to define	3612	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	3613	define before including any of its files. The default in the absence of
2065	and only include the select backend.	3614	autoconf is documented for every option.
2066		3615
2067	=over 4	3616	=over 4
2068		3617
2069	=item EV_STANDALONE	3618	=item EV_STANDALONE
2070		3619
…		…
2072	keeps libev from including F<config.h>, and it also defines dummy	3621	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	3622	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	3623	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	3624	F<event.h> that are not directly supported by the libev core alone.
2076		3625
		3626	In standalone mode, libev will still try to automatically deduce the
		3627	configuration, but has to be more conservative.
		3628
2077	=item EV_USE_MONOTONIC	3629	=item EV_USE_MONOTONIC
2078		3630
2079	If defined to be C<1>, libev will try to detect the availability of the	3631	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	3632	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	3633	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	3634	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	3635	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	3636	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	3637	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		3638
2087	=item EV_USE_REALTIME	3639	=item EV_USE_REALTIME
2088		3640
2089	If defined to be C<1>, libev will try to detect the availability of the	3641	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	3642	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	3643	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3644	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3645	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	3646	correctness. See the note about libraries in the description of
		3647	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3648	C<EV_USE_CLOCK_SYSCALL>.
		3649
		3650	=item EV_USE_CLOCK_SYSCALL
		3651
		3652	If defined to be C<1>, libev will try to use a direct syscall instead
		3653	of calling the system-provided C<clock_gettime> function. This option
		3654	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3655	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3656	programs needlessly. Using a direct syscall is slightly slower (in
		3657	theory), because no optimised vdso implementation can be used, but avoids
		3658	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3659	higher, as it simplifies linking (no need for C<-lrt>).
		3660
		3661	=item EV_USE_NANOSLEEP
		3662
		3663	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3664	and will use it for delays. Otherwise it will use C<select ()>.
		3665
		3666	=item EV_USE_EVENTFD
		3667
		3668	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3669	available and will probe for kernel support at runtime. This will improve
		3670	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3671	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3672	2.7 or newer, otherwise disabled.
2095		3673
2096	=item EV_USE_SELECT	3674	=item EV_USE_SELECT
2097		3675
2098	If undefined or defined to be C<1>, libev will compile in support for the	3676	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	3677	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	3678	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	3679	will not be compiled in.
2102		3680
2103	=item EV_SELECT_USE_FD_SET	3681	=item EV_SELECT_USE_FD_SET
2104		3682
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	3683	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	3684	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3685	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	3686	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	3687	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3688	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	3689	configures the maximum size of the C<fd_set>.
2112		3690
2113	=item EV_SELECT_IS_WINSOCKET	3691	=item EV_SELECT_IS_WINSOCKET
2114		3692
2115	When defined to C<1>, the select backend will assume that	3693	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	3694	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	3696	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3697	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	3698	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	3699	on win32. Should not be defined on non-win32 platforms.
2122		3700
		3701	=item EV_FD_TO_WIN32_HANDLE(fd)
		3702
		3703	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3704	file descriptors to socket handles. When not defining this symbol (the
		3705	default), then libev will call C<_get_osfhandle>, which is usually
		3706	correct. In some cases, programs use their own file descriptor management,
		3707	in which case they can provide this function to map fds to socket handles.
		3708
		3709	=item EV_WIN32_HANDLE_TO_FD(handle)
		3710
		3711	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3712	using the standard C<_open_osfhandle> function. For programs implementing
		3713	their own fd to handle mapping, overwriting this function makes it easier
		3714	to do so. This can be done by defining this macro to an appropriate value.
		3715
		3716	=item EV_WIN32_CLOSE_FD(fd)
		3717
		3718	If programs implement their own fd to handle mapping on win32, then this
		3719	macro can be used to override the C<close> function, useful to unregister
		3720	file descriptors again. Note that the replacement function has to close
		3721	the underlying OS handle.
		3722
2123	=item EV_USE_POLL	3723	=item EV_USE_POLL
2124		3724
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3725	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	3726	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	3727	takes precedence over select.
2128		3728
2129	=item EV_USE_EPOLL	3729	=item EV_USE_EPOLL
2130		3730
2131	If defined to be C<1>, libev will compile in support for the Linux	3731	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	3732	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	3733	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	3734	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3735	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2135		3736
2136	=item EV_USE_KQUEUE	3737	=item EV_USE_KQUEUE
2137		3738
2138	If defined to be C<1>, libev will compile in support for the BSD style	3739	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3740	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	3753	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	3754	backend for Solaris 10 systems.
2154		3755
2155	=item EV_USE_DEVPOLL	3756	=item EV_USE_DEVPOLL
2156		3757
2157	reserved for future expansion, works like the USE symbols above.	3758	Reserved for future expansion, works like the USE symbols above.
2158		3759
2159	=item EV_USE_INOTIFY	3760	=item EV_USE_INOTIFY
2160		3761
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	3762	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	3763	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	3764	be detected at runtime. If undefined, it will be enabled if the headers
		3765	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3766
		3767	=item EV_ATOMIC_T
		3768
		3769	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3770	access is atomic with respect to other threads or signal contexts. No such
		3771	type is easily found in the C language, so you can provide your own type
		3772	that you know is safe for your purposes. It is used both for signal handler "locking"
		3773	as well as for signal and thread safety in C<ev_async> watchers.
		3774
		3775	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3776	(from F<signal.h>), which is usually good enough on most platforms.
2164		3777
2165	=item EV_H	3778	=item EV_H
2166		3779
2167	The name of the F<ev.h> header file used to include it. The default if	3780	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3781	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3782	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		3783
2171	=item EV_CONFIG_H	3784	=item EV_CONFIG_H
2172		3785
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3786	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3787	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	3788	C<EV_H>, above.
2176		3789
2177	=item EV_EVENT_H	3790	=item EV_EVENT_H
2178		3791
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3792	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	3793	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		3794
2182	=item EV_PROTOTYPES	3795	=item EV_PROTOTYPES
2183		3796
2184	If defined to be C<0>, then F<ev.h> will not define any function	3797	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	3798	prototypes, but still define all the structs and other symbols. This is
…		…
2206	When doing priority-based operations, libev usually has to linearly search	3819	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	3820	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	3821	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	3822	fine.
2210		3823
2211	If your embedding app does not need any priorities, defining these both to	3824	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	3825	both to C<0> will save some memory and CPU.
2213		3826
2214	=item EV_PERIODIC_ENABLE	3827	=item EV_PERIODIC_ENABLE
2215		3828
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	3829	If undefined or defined to be C<1>, then periodic timers are supported. If
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	3830	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2224	code.	3837	code.
2225		3838
2226	=item EV_EMBED_ENABLE	3839	=item EV_EMBED_ENABLE
2227		3840
2228	If undefined or defined to be C<1>, then embed watchers are supported. If	3841	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.	3842	defined to be C<0>, then they are not. Embed watchers rely on most other
		3843	watcher types, which therefore must not be disabled.
2230		3844
2231	=item EV_STAT_ENABLE	3845	=item EV_STAT_ENABLE
2232		3846
2233	If undefined or defined to be C<1>, then stat watchers are supported. If	3847	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.	3848	defined to be C<0>, then they are not.
…		…
2236	=item EV_FORK_ENABLE	3850	=item EV_FORK_ENABLE
2237		3851
2238	If undefined or defined to be C<1>, then fork watchers are supported. If	3852	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.	3853	defined to be C<0>, then they are not.
2240		3854
		3855	=item EV_ASYNC_ENABLE
		3856
		3857	If undefined or defined to be C<1>, then async watchers are supported. If
		3858	defined to be C<0>, then they are not.
		3859
2241	=item EV_MINIMAL	3860	=item EV_MINIMAL
2242		3861
2243	If you need to shave off some kilobytes of code at the expense of some	3862	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	3863	speed (but with the full API), define this symbol to C<1>. Currently this
2245	some inlining decisions, saves roughly 30% codesize of amd64.	3864	is used to override some inlining decisions, saves roughly 30% code size
		3865	on amd64. It also selects a much smaller 2-heap for timer management over
		3866	the default 4-heap.
		3867
		3868	You can save even more by disabling watcher types you do not need
		3869	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3870	(C<-DNDEBUG>) will usually reduce code size a lot.
		3871
		3872	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3873	provide a bare-bones event library. See C<ev.h> for details on what parts
		3874	of the API are still available, and do not complain if this subset changes
		3875	over time.
		3876
		3877	=item EV_NSIG
		3878
		3879	The highest supported signal number, +1 (or, the number of
		3880	signals): Normally, libev tries to deduce the maximum number of signals
		3881	automatically, but sometimes this fails, in which case it can be
		3882	specified. Also, using a lower number than detected (C<32> should be
		3883	good for about any system in existance) can save some memory, as libev
		3884	statically allocates some 12-24 bytes per signal number.
2246		3885
2247	=item EV_PID_HASHSIZE	3886	=item EV_PID_HASHSIZE
2248		3887
2249	C<ev_child> watchers use a small hash table to distribute workload by	3888	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3889	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2251	than enough. If you need to manage thousands of children you might want to	3890	than enough. If you need to manage thousands of children you might want to
2252	increase this value (I<must> be a power of two).	3891	increase this value (I<must> be a power of two).
2253		3892
2254	=item EV_INOTIFY_HASHSIZE	3893	=item EV_INOTIFY_HASHSIZE
2255		3894
2256	C<ev_staz> watchers use a small hash table to distribute workload by	3895	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3896	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	3897	usually more than enough. If you need to manage thousands of C<ev_stat>
2259	watchers you might want to increase this value (I<must> be a power of	3898	watchers you might want to increase this value (I<must> be a power of
2260	two).	3899	two).
2261		3900
		3901	=item EV_USE_4HEAP
		3902
		3903	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3904	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3905	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3906	faster performance with many (thousands) of watchers.
		3907
		3908	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3909	(disabled).
		3910
		3911	=item EV_HEAP_CACHE_AT
		3912
		3913	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3914	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3915	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3916	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3917	but avoids random read accesses on heap changes. This improves performance
		3918	noticeably with many (hundreds) of watchers.
		3919
		3920	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3921	(disabled).
		3922
		3923	=item EV_VERIFY
		3924
		3925	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3926	be done: If set to C<0>, no internal verification code will be compiled
		3927	in. If set to C<1>, then verification code will be compiled in, but not
		3928	called. If set to C<2>, then the internal verification code will be
		3929	called once per loop, which can slow down libev. If set to C<3>, then the
		3930	verification code will be called very frequently, which will slow down
		3931	libev considerably.
		3932
		3933	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3934	C<0>.
		3935
2262	=item EV_COMMON	3936	=item EV_COMMON
2263		3937
2264	By default, all watchers have a C<void *data> member. By redefining	3938	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	3939	this macro to a something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	3940	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	3941	though, and it must be identical each time.
2268		3942
2269	For example, the perl EV module uses something like this:	3943	For example, the perl EV module uses something like this:
2270		3944
2271	#define EV_COMMON \	3945	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	3946	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	3947	SV *cb_sv, *fh /* note no trailing ";" */
2274		3948
2275	=item EV_CB_DECLARE (type)	3949	=item EV_CB_DECLARE (type)
2276		3950
2277	=item EV_CB_INVOKE (watcher, revents)	3951	=item EV_CB_INVOKE (watcher, revents)
2278		3952
2279	=item ev_set_cb (ev, cb)	3953	=item ev_set_cb (ev, cb)
2280		3954
2281	Can be used to change the callback member declaration in each watcher,	3955	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	3956	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	3957	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	3958	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3959	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	3960	method calls instead of plain function calls in C++.
		3961
		3962	=back
		3963
		3964	=head2 EXPORTED API SYMBOLS
		3965
		3966	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3967	exported symbols, you can use the provided F<Symbol.*> files which list
		3968	all public symbols, one per line:
		3969
		3970	Symbols.ev for libev proper
		3971	Symbols.event for the libevent emulation
		3972
		3973	This can also be used to rename all public symbols to avoid clashes with
		3974	multiple versions of libev linked together (which is obviously bad in
		3975	itself, but sometimes it is inconvenient to avoid this).
		3976
		3977	A sed command like this will create wrapper C<#define>'s that you need to
		3978	include before including F<ev.h>:
		3979
		3980	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3981
		3982	This would create a file F<wrap.h> which essentially looks like this:
		3983
		3984	#define ev_backend myprefix_ev_backend
		3985	#define ev_check_start myprefix_ev_check_start
		3986	#define ev_check_stop myprefix_ev_check_stop
		3987	...
2287		3988
2288	=head2 EXAMPLES	3989	=head2 EXAMPLES
2289		3990
2290	For a real-world example of a program the includes libev	3991	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	3992	verbatim, you can have a look at the EV perl module
…		…
2296	file.	3997	file.
2297		3998
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3999	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	4000	that everybody includes and which overrides some configure choices:
2300		4001
2301	#define EV_MINIMAL 1	4002	#define EV_MINIMAL 1
2302	#define EV_USE_POLL 0	4003	#define EV_USE_POLL 0
2303	#define EV_MULTIPLICITY 0	4004	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	4005	#define EV_PERIODIC_ENABLE 0
2305	#define EV_STAT_ENABLE 0	4006	#define EV_STAT_ENABLE 0
2306	#define EV_FORK_ENABLE 0	4007	#define EV_FORK_ENABLE 0
2307	#define EV_CONFIG_H <config.h>	4008	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0	4009	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0	4010	#define EV_MAXPRI 0
2310		4011
2311	#include "ev++.h"	4012	#include "ev++.h"
2312		4013
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4014	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		4015
2315	#include "ev_cpp.h"	4016	#include "ev_cpp.h"
2316	#include "ev.c"	4017	#include "ev.c"
2317		4018
		4019	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2318		4020
		4021	=head2 THREADS AND COROUTINES
		4022
		4023	=head3 THREADS
		4024
		4025	All libev functions are reentrant and thread-safe unless explicitly
		4026	documented otherwise, but libev implements no locking itself. This means
		4027	that you can use as many loops as you want in parallel, as long as there
		4028	are no concurrent calls into any libev function with the same loop
		4029	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4030	of course): libev guarantees that different event loops share no data
		4031	structures that need any locking.
		4032
		4033	Or to put it differently: calls with different loop parameters can be done
		4034	concurrently from multiple threads, calls with the same loop parameter
		4035	must be done serially (but can be done from different threads, as long as
		4036	only one thread ever is inside a call at any point in time, e.g. by using
		4037	a mutex per loop).
		4038
		4039	Specifically to support threads (and signal handlers), libev implements
		4040	so-called C<ev_async> watchers, which allow some limited form of
		4041	concurrency on the same event loop, namely waking it up "from the
		4042	outside".
		4043
		4044	If you want to know which design (one loop, locking, or multiple loops
		4045	without or something else still) is best for your problem, then I cannot
		4046	help you, but here is some generic advice:
		4047
		4048	=over 4
		4049
		4050	=item * most applications have a main thread: use the default libev loop
		4051	in that thread, or create a separate thread running only the default loop.
		4052
		4053	This helps integrating other libraries or software modules that use libev
		4054	themselves and don't care/know about threading.
		4055
		4056	=item * one loop per thread is usually a good model.
		4057
		4058	Doing this is almost never wrong, sometimes a better-performance model
		4059	exists, but it is always a good start.
		4060
		4061	=item * other models exist, such as the leader/follower pattern, where one
		4062	loop is handed through multiple threads in a kind of round-robin fashion.
		4063
		4064	Choosing a model is hard - look around, learn, know that usually you can do
		4065	better than you currently do :-)
		4066
		4067	=item * often you need to talk to some other thread which blocks in the
		4068	event loop.
		4069
		4070	C<ev_async> watchers can be used to wake them up from other threads safely
		4071	(or from signal contexts...).
		4072
		4073	An example use would be to communicate signals or other events that only
		4074	work in the default loop by registering the signal watcher with the
		4075	default loop and triggering an C<ev_async> watcher from the default loop
		4076	watcher callback into the event loop interested in the signal.
		4077
		4078	=back
		4079
		4080	=head4 THREAD LOCKING EXAMPLE
		4081
		4082	Here is a fictitious example of how to run an event loop in a different
		4083	thread than where callbacks are being invoked and watchers are
		4084	created/added/removed.
		4085
		4086	For a real-world example, see the C<EV::Loop::Async> perl module,
		4087	which uses exactly this technique (which is suited for many high-level
		4088	languages).
		4089
		4090	The example uses a pthread mutex to protect the loop data, a condition
		4091	variable to wait for callback invocations, an async watcher to notify the
		4092	event loop thread and an unspecified mechanism to wake up the main thread.
		4093
		4094	First, you need to associate some data with the event loop:
		4095
		4096	typedef struct {
		4097	mutex_t lock; /* global loop lock */
		4098	ev_async async_w;
		4099	thread_t tid;
		4100	cond_t invoke_cv;
		4101	} userdata;
		4102
		4103	void prepare_loop (EV_P)
		4104	{
		4105	// for simplicity, we use a static userdata struct.
		4106	static userdata u;
		4107
		4108	ev_async_init (&u->async_w, async_cb);
		4109	ev_async_start (EV_A_ &u->async_w);
		4110
		4111	pthread_mutex_init (&u->lock, 0);
		4112	pthread_cond_init (&u->invoke_cv, 0);
		4113
		4114	// now associate this with the loop
		4115	ev_set_userdata (EV_A_ u);
		4116	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4117	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4118
		4119	// then create the thread running ev_loop
		4120	pthread_create (&u->tid, 0, l_run, EV_A);
		4121	}
		4122
		4123	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4124	solely to wake up the event loop so it takes notice of any new watchers
		4125	that might have been added:
		4126
		4127	static void
		4128	async_cb (EV_P_ ev_async *w, int revents)
		4129	{
		4130	// just used for the side effects
		4131	}
		4132
		4133	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4134	protecting the loop data, respectively.
		4135
		4136	static void
		4137	l_release (EV_P)
		4138	{
		4139	userdata *u = ev_userdata (EV_A);
		4140	pthread_mutex_unlock (&u->lock);
		4141	}
		4142
		4143	static void
		4144	l_acquire (EV_P)
		4145	{
		4146	userdata *u = ev_userdata (EV_A);
		4147	pthread_mutex_lock (&u->lock);
		4148	}
		4149
		4150	The event loop thread first acquires the mutex, and then jumps straight
		4151	into C<ev_loop>:
		4152
		4153	void *
		4154	l_run (void *thr_arg)
		4155	{
		4156	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4157
		4158	l_acquire (EV_A);
		4159	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4160	ev_loop (EV_A_ 0);
		4161	l_release (EV_A);
		4162
		4163	return 0;
		4164	}
		4165
		4166	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4167	signal the main thread via some unspecified mechanism (signals? pipe
		4168	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4169	have been called (in a while loop because a) spurious wakeups are possible
		4170	and b) skipping inter-thread-communication when there are no pending
		4171	watchers is very beneficial):
		4172
		4173	static void
		4174	l_invoke (EV_P)
		4175	{
		4176	userdata *u = ev_userdata (EV_A);
		4177
		4178	while (ev_pending_count (EV_A))
		4179	{
		4180	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4181	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4182	}
		4183	}
		4184
		4185	Now, whenever the main thread gets told to invoke pending watchers, it
		4186	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4187	thread to continue:
		4188
		4189	static void
		4190	real_invoke_pending (EV_P)
		4191	{
		4192	userdata *u = ev_userdata (EV_A);
		4193
		4194	pthread_mutex_lock (&u->lock);
		4195	ev_invoke_pending (EV_A);
		4196	pthread_cond_signal (&u->invoke_cv);
		4197	pthread_mutex_unlock (&u->lock);
		4198	}
		4199
		4200	Whenever you want to start/stop a watcher or do other modifications to an
		4201	event loop, you will now have to lock:
		4202
		4203	ev_timer timeout_watcher;
		4204	userdata *u = ev_userdata (EV_A);
		4205
		4206	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4207
		4208	pthread_mutex_lock (&u->lock);
		4209	ev_timer_start (EV_A_ &timeout_watcher);
		4210	ev_async_send (EV_A_ &u->async_w);
		4211	pthread_mutex_unlock (&u->lock);
		4212
		4213	Note that sending the C<ev_async> watcher is required because otherwise
		4214	an event loop currently blocking in the kernel will have no knowledge
		4215	about the newly added timer. By waking up the loop it will pick up any new
		4216	watchers in the next event loop iteration.
		4217
		4218	=head3 COROUTINES
		4219
		4220	Libev is very accommodating to coroutines ("cooperative threads"):
		4221	libev fully supports nesting calls to its functions from different
		4222	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4223	different coroutines, and switch freely between both coroutines running
		4224	the loop, as long as you don't confuse yourself). The only exception is
		4225	that you must not do this from C<ev_periodic> reschedule callbacks.
		4226
		4227	Care has been taken to ensure that libev does not keep local state inside
		4228	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4229	they do not call any callbacks.
		4230
		4231	=head2 COMPILER WARNINGS
		4232
		4233	Depending on your compiler and compiler settings, you might get no or a
		4234	lot of warnings when compiling libev code. Some people are apparently
		4235	scared by this.
		4236
		4237	However, these are unavoidable for many reasons. For one, each compiler
		4238	has different warnings, and each user has different tastes regarding
		4239	warning options. "Warn-free" code therefore cannot be a goal except when
		4240	targeting a specific compiler and compiler-version.
		4241
		4242	Another reason is that some compiler warnings require elaborate
		4243	workarounds, or other changes to the code that make it less clear and less
		4244	maintainable.
		4245
		4246	And of course, some compiler warnings are just plain stupid, or simply
		4247	wrong (because they don't actually warn about the condition their message
		4248	seems to warn about). For example, certain older gcc versions had some
		4249	warnings that resulted an extreme number of false positives. These have
		4250	been fixed, but some people still insist on making code warn-free with
		4251	such buggy versions.
		4252
		4253	While libev is written to generate as few warnings as possible,
		4254	"warn-free" code is not a goal, and it is recommended not to build libev
		4255	with any compiler warnings enabled unless you are prepared to cope with
		4256	them (e.g. by ignoring them). Remember that warnings are just that:
		4257	warnings, not errors, or proof of bugs.
		4258
		4259
		4260	=head2 VALGRIND
		4261
		4262	Valgrind has a special section here because it is a popular tool that is
		4263	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4264
		4265	If you think you found a bug (memory leak, uninitialised data access etc.)
		4266	in libev, then check twice: If valgrind reports something like:
		4267
		4268	==2274== definitely lost: 0 bytes in 0 blocks.
		4269	==2274== possibly lost: 0 bytes in 0 blocks.
		4270	==2274== still reachable: 256 bytes in 1 blocks.
		4271
		4272	Then there is no memory leak, just as memory accounted to global variables
		4273	is not a memleak - the memory is still being referenced, and didn't leak.
		4274
		4275	Similarly, under some circumstances, valgrind might report kernel bugs
		4276	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4277	although an acceptable workaround has been found here), or it might be
		4278	confused.
		4279
		4280	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4281	make it into some kind of religion.
		4282
		4283	If you are unsure about something, feel free to contact the mailing list
		4284	with the full valgrind report and an explanation on why you think this
		4285	is a bug in libev (best check the archives, too :). However, don't be
		4286	annoyed when you get a brisk "this is no bug" answer and take the chance
		4287	of learning how to interpret valgrind properly.
		4288
		4289	If you need, for some reason, empty reports from valgrind for your project
		4290	I suggest using suppression lists.
		4291
		4292
		4293	=head1 PORTABILITY NOTES
		4294
		4295	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4296
		4297	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4298	requires, and its I/O model is fundamentally incompatible with the POSIX
		4299	model. Libev still offers limited functionality on this platform in
		4300	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4301	descriptors. This only applies when using Win32 natively, not when using
		4302	e.g. cygwin.
		4303
		4304	Lifting these limitations would basically require the full
		4305	re-implementation of the I/O system. If you are into these kinds of
		4306	things, then note that glib does exactly that for you in a very portable
		4307	way (note also that glib is the slowest event library known to man).
		4308
		4309	There is no supported compilation method available on windows except
		4310	embedding it into other applications.
		4311
		4312	Sensible signal handling is officially unsupported by Microsoft - libev
		4313	tries its best, but under most conditions, signals will simply not work.
		4314
		4315	Not a libev limitation but worth mentioning: windows apparently doesn't
		4316	accept large writes: instead of resulting in a partial write, windows will
		4317	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4318	so make sure you only write small amounts into your sockets (less than a
		4319	megabyte seems safe, but this apparently depends on the amount of memory
		4320	available).
		4321
		4322	Due to the many, low, and arbitrary limits on the win32 platform and
		4323	the abysmal performance of winsockets, using a large number of sockets
		4324	is not recommended (and not reasonable). If your program needs to use
		4325	more than a hundred or so sockets, then likely it needs to use a totally
		4326	different implementation for windows, as libev offers the POSIX readiness
		4327	notification model, which cannot be implemented efficiently on windows
		4328	(due to Microsoft monopoly games).
		4329
		4330	A typical way to use libev under windows is to embed it (see the embedding
		4331	section for details) and use the following F<evwrap.h> header file instead
		4332	of F<ev.h>:
		4333
		4334	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4335	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4336
		4337	#include "ev.h"
		4338
		4339	And compile the following F<evwrap.c> file into your project (make sure
		4340	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4341
		4342	#include "evwrap.h"
		4343	#include "ev.c"
		4344
		4345	=over 4
		4346
		4347	=item The winsocket select function
		4348
		4349	The winsocket C<select> function doesn't follow POSIX in that it
		4350	requires socket I<handles> and not socket I<file descriptors> (it is
		4351	also extremely buggy). This makes select very inefficient, and also
		4352	requires a mapping from file descriptors to socket handles (the Microsoft
		4353	C runtime provides the function C<_open_osfhandle> for this). See the
		4354	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4355	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4356
		4357	The configuration for a "naked" win32 using the Microsoft runtime
		4358	libraries and raw winsocket select is:
		4359
		4360	#define EV_USE_SELECT 1
		4361	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4362
		4363	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4364	complexity in the O(n²) range when using win32.
		4365
		4366	=item Limited number of file descriptors
		4367
		4368	Windows has numerous arbitrary (and low) limits on things.
		4369
		4370	Early versions of winsocket's select only supported waiting for a maximum
		4371	of C<64> handles (probably owning to the fact that all windows kernels
		4372	can only wait for C<64> things at the same time internally; Microsoft
		4373	recommends spawning a chain of threads and wait for 63 handles and the
		4374	previous thread in each. Sounds great!).
		4375
		4376	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4377	to some high number (e.g. C<2048>) before compiling the winsocket select
		4378	call (which might be in libev or elsewhere, for example, perl and many
		4379	other interpreters do their own select emulation on windows).
		4380
		4381	Another limit is the number of file descriptors in the Microsoft runtime
		4382	libraries, which by default is C<64> (there must be a hidden I<64>
		4383	fetish or something like this inside Microsoft). You can increase this
		4384	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4385	(another arbitrary limit), but is broken in many versions of the Microsoft
		4386	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4387	(depending on windows version and/or the phase of the moon). To get more,
		4388	you need to wrap all I/O functions and provide your own fd management, but
		4389	the cost of calling select (O(n²)) will likely make this unworkable.
		4390
		4391	=back
		4392
		4393	=head2 PORTABILITY REQUIREMENTS
		4394
		4395	In addition to a working ISO-C implementation and of course the
		4396	backend-specific APIs, libev relies on a few additional extensions:
		4397
		4398	=over 4
		4399
		4400	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4401	calling conventions regardless of C<ev_watcher_type *>.
		4402
		4403	Libev assumes not only that all watcher pointers have the same internal
		4404	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4405	assumes that the same (machine) code can be used to call any watcher
		4406	callback: The watcher callbacks have different type signatures, but libev
		4407	calls them using an C<ev_watcher *> internally.
		4408
		4409	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4410
		4411	The type C<sig_atomic_t volatile> (or whatever is defined as
		4412	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4413	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4414	believed to be sufficiently portable.
		4415
		4416	=item C<sigprocmask> must work in a threaded environment
		4417
		4418	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4419	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4420	pthread implementations will either allow C<sigprocmask> in the "main
		4421	thread" or will block signals process-wide, both behaviours would
		4422	be compatible with libev. Interaction between C<sigprocmask> and
		4423	C<pthread_sigmask> could complicate things, however.
		4424
		4425	The most portable way to handle signals is to block signals in all threads
		4426	except the initial one, and run the default loop in the initial thread as
		4427	well.
		4428
		4429	=item C<long> must be large enough for common memory allocation sizes
		4430
		4431	To improve portability and simplify its API, libev uses C<long> internally
		4432	instead of C<size_t> when allocating its data structures. On non-POSIX
		4433	systems (Microsoft...) this might be unexpectedly low, but is still at
		4434	least 31 bits everywhere, which is enough for hundreds of millions of
		4435	watchers.
		4436
		4437	=item C<double> must hold a time value in seconds with enough accuracy
		4438
		4439	The type C<double> is used to represent timestamps. It is required to
		4440	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4441	enough for at least into the year 4000. This requirement is fulfilled by
		4442	implementations implementing IEEE 754, which is basically all existing
		4443	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4444	2200.
		4445
		4446	=back
		4447
		4448	If you know of other additional requirements drop me a note.
		4449
		4450
2319	=head1 COMPLEXITIES	4451	=head1 ALGORITHMIC COMPLEXITIES
2320		4452
2321	In this section the complexities of (many of) the algorithms used inside	4453	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	4454	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	4455	the documentation for C<ev_default_init>.
2324		4456
2325	All of the following are about amortised time: If an array needs to be	4457	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	4458	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	4459	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	4460	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	4461	average it is much faster and asymptotically approaches constant time.
2330		4462
2331	=over 4	4463	=over 4
2332		4464
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4465	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		4466
2335	This means that, when you have a watcher that triggers in one hour and	4467	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	4468	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	4469	have to skip roughly seven (C<ld 100>) of these watchers.
2338		4470
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4471	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		4472
2341	That means that for changing a timer costs less than removing/adding them	4473	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	4474	as only the relative motion in the event queue has to be paid for.
2343		4475
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4476	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		4477
2346	These just add the watcher into an array or at the head of a list.	4478	These just add the watcher into an array or at the head of a list.
		4479
2347	=item Stopping check/prepare/idle watchers: O(1)	4480	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		4481
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4482	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		4483
2351	These watchers are stored in lists then need to be walked to find the	4484	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	4485	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	4486	have many watchers waiting for the same fd or signal: one is typical, two
		4487	is rare).
2354		4488
2355	=item Finding the next timer per loop iteration: O(1)	4489	=item Finding the next timer in each loop iteration: O(1)
		4490
		4491	By virtue of using a binary or 4-heap, the next timer is always found at a
		4492	fixed position in the storage array.
2356		4493
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4494	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		4495
2359	A change means an I/O watcher gets started or stopped, which requires	4496	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	4497	libev to recalculate its status (and possibly tell the kernel, depending
		4498	on backend and whether C<ev_io_set> was used).
2361		4499
2362	=item Activating one watcher: O(1)	4500	=item Activating one watcher (putting it into the pending state): O(1)
2363		4501
2364	=item Priority handling: O(number_of_priorities)	4502	=item Priority handling: O(number_of_priorities)
2365		4503
2366	Priorities are implemented by allocating some space for each	4504	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	4505	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	4506	linearly search all the priorities, but starting/stopping and activating
		4507	watchers becomes O(1) with respect to priority handling.
		4508
		4509	=item Sending an ev_async: O(1)
		4510
		4511	=item Processing ev_async_send: O(number_of_async_watchers)
		4512
		4513	=item Processing signals: O(max_signal_number)
		4514
		4515	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4516	calls in the current loop iteration. Checking for async and signal events
		4517	involves iterating over all running async watchers or all signal numbers.
2369		4518
2370	=back	4519	=back
2371		4520
2372		4521
		4522	=head1 GLOSSARY
		4523
		4524	=over 4
		4525
		4526	=item active
		4527
		4528	A watcher is active as long as it has been started (has been attached to
		4529	an event loop) but not yet stopped (disassociated from the event loop).
		4530
		4531	=item application
		4532
		4533	In this document, an application is whatever is using libev.
		4534
		4535	=item callback
		4536
		4537	The address of a function that is called when some event has been
		4538	detected. Callbacks are being passed the event loop, the watcher that
		4539	received the event, and the actual event bitset.
		4540
		4541	=item callback invocation
		4542
		4543	The act of calling the callback associated with a watcher.
		4544
		4545	=item event
		4546
		4547	A change of state of some external event, such as data now being available
		4548	for reading on a file descriptor, time having passed or simply not having
		4549	any other events happening anymore.
		4550
		4551	In libev, events are represented as single bits (such as C<EV_READ> or
		4552	C<EV_TIMEOUT>).
		4553
		4554	=item event library
		4555
		4556	A software package implementing an event model and loop.
		4557
		4558	=item event loop
		4559
		4560	An entity that handles and processes external events and converts them
		4561	into callback invocations.
		4562
		4563	=item event model
		4564
		4565	The model used to describe how an event loop handles and processes
		4566	watchers and events.
		4567
		4568	=item pending
		4569
		4570	A watcher is pending as soon as the corresponding event has been detected,
		4571	and stops being pending as soon as the watcher will be invoked or its
		4572	pending status is explicitly cleared by the application.
		4573
		4574	A watcher can be pending, but not active. Stopping a watcher also clears
		4575	its pending status.
		4576
		4577	=item real time
		4578
		4579	The physical time that is observed. It is apparently strictly monotonic :)
		4580
		4581	=item wall-clock time
		4582
		4583	The time and date as shown on clocks. Unlike real time, it can actually
		4584	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4585	clock.
		4586
		4587	=item watcher
		4588
		4589	A data structure that describes interest in certain events. Watchers need
		4590	to be started (attached to an event loop) before they can receive events.
		4591
		4592	=item watcher invocation
		4593
		4594	The act of calling the callback associated with a watcher.
		4595
		4596	=back
		4597
2373	=head1 AUTHOR	4598	=head1 AUTHOR
2374		4599
2375	Marc Lehmann <libev@schmorp.de>.	4600	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2376		4601

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