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Revision 1.265 by root, Wed Aug 26 17:11:42 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<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_NOSIGNALFD>
		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
312	For few fds, this backend is a bit little slower than poll and select,	416	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	417	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	418	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	419	epoll scales either O(1) or O(active_fds).
316		420
		421	The epoll mechanism deserves honorable mention as the most misdesigned
		422	of the more advanced event mechanisms: mere annoyances include silently
		423	dropping file descriptors, requiring a system call per change per file
		424	descriptor (and unnecessary guessing of parameters), problems with dup and
		425	so on. The biggest issue is fork races, however - if a program forks then
		426	I<both> parent and child process have to recreate the epoll set, which can
		427	take considerable time (one syscall per file descriptor) and is of course
		428	hard to detect.
		429
		430	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		431	of course I<doesn't>, and epoll just loves to report events for totally
		432	I<different> file descriptors (even already closed ones, so one cannot
		433	even remove them from the set) than registered in the set (especially
		434	on SMP systems). Libev tries to counter these spurious notifications by
		435	employing an additional generation counter and comparing that against the
		436	events to filter out spurious ones, recreating the set when required.
		437
317	While stopping and starting an I/O watcher in the same iteration will	438	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	439	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	440	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	441	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	442	file descriptors might not work very well if you register events for both
		443	file descriptors.
322		444
323	Please note that epoll sometimes generates spurious notifications, so you	445	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	446	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	447	i.e. keep at least one watcher active per fd at all times. Stopping and
		448	starting a watcher (without re-setting it) also usually doesn't cause
		449	extra overhead. A fork can both result in spurious notifications as well
		450	as in libev having to destroy and recreate the epoll object, which can
		451	take considerable time and thus should be avoided.
		452
		453	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		454	faster than epoll for maybe up to a hundred file descriptors, depending on
		455	the usage. So sad.
		456
		457	While nominally embeddable in other event loops, this feature is broken in
		458	all kernel versions tested so far.
		459
		460	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		461	C<EVBACKEND_POLL>.
326		462
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		464
329	Kqueue deserves special mention, as at the time of this writing, it	465	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	466	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	467	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	468	it's completely useless). Unlike epoll, however, whose brokenness
		469	is by design, these kqueue bugs can (and eventually will) be fixed
		470	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	471	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	472	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		473	system like NetBSD.
		474
		475	You still can embed kqueue into a normal poll or select backend and use it
		476	only for sockets (after having made sure that sockets work with kqueue on
		477	the target platform). See C<ev_embed> watchers for more info.
335		478
336	It scales in the same way as the epoll backend, but the interface to the	479	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	480	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	481	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	482	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	483	two event changes per incident. Support for C<fork ()> is very bad (but
		484	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		485	cases
		486
		487	This backend usually performs well under most conditions.
		488
		489	While nominally embeddable in other event loops, this doesn't work
		490	everywhere, so you might need to test for this. And since it is broken
		491	almost everywhere, you should only use it when you have a lot of sockets
		492	(for which it usually works), by embedding it into another event loop
		493	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		494	also broken on OS X)) and, did I mention it, using it only for sockets.
		495
		496	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		497	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		498	C<NOTE_EOF>.
341		499
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	500	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		501
344	This is not implemented yet (and might never be).	502	This is not implemented yet (and might never be, unless you send me an
		503	implementation). According to reports, C</dev/poll> only supports sockets
		504	and is not embeddable, which would limit the usefulness of this backend
		505	immensely.
345		506
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	507	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		508
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	509	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)).	510	it's really slow, but it still scales very well (O(active_fds)).
350		511
351	Please note that solaris ports can result in a lot of spurious	512	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	513	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	514	blocking when no data (or space) is available.
		515
		516	While this backend scales well, it requires one system call per active
		517	file descriptor per loop iteration. For small and medium numbers of file
		518	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		519	might perform better.
		520
		521	On the positive side, with the exception of the spurious readiness
		522	notifications, this backend actually performed fully to specification
		523	in all tests and is fully embeddable, which is a rare feat among the
		524	OS-specific backends (I vastly prefer correctness over speed hacks).
		525
		526	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		527	C<EVBACKEND_POLL>.
354		528
355	=item C<EVBACKEND_ALL>	529	=item C<EVBACKEND_ALL>
356		530
357	Try all backends (even potentially broken ones that wouldn't be tried	531	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	532	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	533	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		534
		535	It is definitely not recommended to use this flag.
		536
361	=back	537	=back
362		538
363	If one or more of these are ored into the flags value, then only these	539	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	540	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	541	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	542	()> will be tried.
367		543
368	The most typical usage is like this:	544	Example: This is the most typical usage.
369		545
370	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		548
373	Restrict libev to the select and poll backends, and do not allow	549	Example: Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:	550	environment settings to be taken into account:
375		551
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	552	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		553
378	Use whatever libev has to offer, but make sure that kqueue is used if	554	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	555	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):	556	private event loop and only if you know the OS supports your types of
		557	fds):
381		558
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	559	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		560
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	561	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		562
386	Similar to C<ev_default_loop>, but always creates a new event loop that is	563	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	564	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	565	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).	566	undefined behaviour (or a failed assertion if assertions are enabled).
390		567
		568	Note that this function I<is> thread-safe, and the recommended way to use
		569	libev with threads is indeed to create one loop per thread, and using the
		570	default loop in the "main" or "initial" thread.
		571
391	Example: Try to create a event loop that uses epoll and nothing else.	572	Example: Try to create a event loop that uses epoll and nothing else.
392		573
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	574	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	575	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	576	fatal ("no epoll found here, maybe it hides under your chair");
396		577
397	=item ev_default_destroy ()	578	=item ev_default_destroy ()
398		579
399	Destroys the default loop again (frees all memory and kernel state	580	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	581	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	582	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>	583	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	584	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	585	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	586	for example).
		587
		588	Note that certain global state, such as signal state (and installed signal
		589	handlers), will not be freed by this function, and related watchers (such
		590	as signal and child watchers) would need to be stopped manually.
		591
		592	In general it is not advisable to call this function except in the
		593	rare occasion where you really need to free e.g. the signal handling
		594	pipe fds. If you need dynamically allocated loops it is better to use
		595	C<ev_loop_new> and C<ev_loop_destroy>).
406		596
407	=item ev_loop_destroy (loop)	597	=item ev_loop_destroy (loop)
408		598
409	Like C<ev_default_destroy>, but destroys an event loop created by an	599	Like C<ev_default_destroy>, but destroys an event loop created by an
410	earlier call to C<ev_loop_new>.	600	earlier call to C<ev_loop_new>.
411		601
412	=item ev_default_fork ()	602	=item ev_default_fork ()
413		603
		604	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	605	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	606	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	607	the child process (or both child and parent, but that again makes little
417	again makes little sense).	608	sense). You I<must> call it in the child before using any of the libev
		609	functions, and it will only take effect at the next C<ev_loop> iteration.
418		610
419	You I<must> call this function in the child process after forking if and	611	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	612	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.	613	you just fork+exec, you don't have to call it at all.
422		614
423	The function itself is quite fast and it's usually not a problem to call	615	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	616	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>:	617	quite nicely into a call to C<pthread_atfork>:
426		618
427	pthread_atfork (0, 0, ev_default_fork);	619	pthread_atfork (0, 0, ev_default_fork);
428		620
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)	621	=item ev_loop_fork (loop)
434		622
435	Like C<ev_default_fork>, but acts on an event loop created by	623	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	624	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.	625	after fork that you want to re-use in the child, and how you do this is
		626	entirely your own problem.
		627
		628	=item int ev_is_default_loop (loop)
		629
		630	Returns true when the given loop is, in fact, the default loop, and false
		631	otherwise.
438		632
439	=item unsigned int ev_loop_count (loop)	633	=item unsigned int ev_loop_count (loop)
440		634
441	Returns the count of loop iterations for the loop, which is identical to	635	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	636	the number of times libev did poll for new events. It starts at C<0> and
443	happily wraps around with enough iterations.	637	happily wraps around with enough iterations.
444		638
445	This value can sometimes be useful as a generation counter of sorts (it	639	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	640	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
448		654
449	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
450		656
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	658	use.
…		…
455		661
456	Returns the current "event loop time", which is the time the event loop	662	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	663	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	664	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	665	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).	666	event occurring (or more correctly, libev finding out about it).
		667
		668	=item ev_now_update (loop)
		669
		670	Establishes the current time by querying the kernel, updating the time
		671	returned by C<ev_now ()> in the progress. This is a costly operation and
		672	is usually done automatically within C<ev_loop ()>.
		673
		674	This function is rarely useful, but when some event callback runs for a
		675	very long time without entering the event loop, updating libev's idea of
		676	the current time is a good idea.
		677
		678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
461		705
462	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
463		707
464	Finally, this is it, the event handler. This function usually is called	708	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	709	after you initialised all your watchers and you want to start handling
…		…
468	If the flags argument is specified as C<0>, it will not return until	712	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.	713	either no event watchers are active anymore or C<ev_unloop> was called.
470		714
471	Please note that an explicit C<ev_unloop> is usually better than	715	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	716	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	717	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	718	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.	719	of relying on its watchers stopping correctly, that is truly a thing of
		720	beauty.
476		721
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	722	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	723	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.	724	process in case there are no events and will return after one iteration of
		725	the loop.
480		726
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	727	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	728	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	729	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	730	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	731	user-registered callback will be called), and will return after one
		732	iteration of the loop.
		733
		734	This is useful if you are waiting for some external event in conjunction
		735	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	736	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.	737	usually a better approach for this kind of thing.
488		738
489	Here are the gory details of what C<ev_loop> does:	739	Here are the gory details of what C<ev_loop> does:
490		740
491	- Before the first iteration, call any pending watchers.	741	- Before the first iteration, call any pending watchers.
492	* If there are no active watchers (reference count is zero), return.	742	* If EVFLAG_FORKCHECK was used, check for a fork.
493	- Queue all prepare watchers and then call all outstanding watchers.	743	- If a fork was detected (by any means), queue and call all fork watchers.
		744	- Queue and call all prepare watchers.
494	- If we have been forked, recreate the kernel state.	745	- If we have been forked, detach and recreate the kernel state
		746	as to not disturb the other process.
495	- Update the kernel state with all outstanding changes.	747	- Update the kernel state with all outstanding changes.
496	- Update the "event loop time".	748	- Update the "event loop time" (ev_now ()).
497	- Calculate for how long to block.	749	- Calculate for how long to sleep or block, if at all
		750	(active idle watchers, EVLOOP_NONBLOCK or not having
		751	any active watchers at all will result in not sleeping).
		752	- Sleep if the I/O and timer collect interval say so.
498	- Block the process, waiting for any events.	753	- Block the process, waiting for any events.
499	- Queue all outstanding I/O (fd) events.	754	- Queue all outstanding I/O (fd) events.
500	- Update the "event loop time" and do time jump handling.	755	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
501	- Queue all outstanding timers.	756	- Queue all expired timers.
502	- Queue all outstanding periodics.	757	- Queue all expired periodics.
503	- If no events are pending now, queue all idle watchers.	758	- Unless any events are pending now, queue all idle watchers.
504	- Queue all check watchers.	759	- Queue all check watchers.
505	- Call all queued watchers in reverse order (i.e. check watchers first).	760	- Call all queued watchers in reverse order (i.e. check watchers first).
506	Signals and child watchers are implemented as I/O watchers, and will	761	Signals and child watchers are implemented as I/O watchers, and will
507	be handled here by queueing them when their watcher gets executed.	762	be handled here by queueing them when their watcher gets executed.
508	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	763	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
509	were used, return, otherwise continue with step *.	764	were used, or there are no active watchers, return, otherwise
		765	continue with step *.
510		766
511	Example: Queue some jobs and then loop until no events are outsanding	767	Example: Queue some jobs and then loop until no events are outstanding
512	anymore.	768	anymore.
513		769
514	... queue jobs here, make sure they register event watchers as long	770	... queue jobs here, make sure they register event watchers as long
515	... as they still have work to do (even an idle watcher will do..)	771	... as they still have work to do (even an idle watcher will do..)
516	ev_loop (my_loop, 0);	772	ev_loop (my_loop, 0);
517	... jobs done. yeah!	773	... jobs done or somebody called unloop. yeah!
518		774
519	=item ev_unloop (loop, how)	775	=item ev_unloop (loop, how)
520		776
521	Can be used to make a call to C<ev_loop> return early (but only after it	777	Can be used to make a call to C<ev_loop> return early (but only after it
522	has processed all outstanding events). The C<how> argument must be either	778	has processed all outstanding events). The C<how> argument must be either
523	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	779	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
524	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	780	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
525		781
		782	This "unloop state" will be cleared when entering C<ev_loop> again.
		783
		784	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		785
526	=item ev_ref (loop)	786	=item ev_ref (loop)
527		787
528	=item ev_unref (loop)	788	=item ev_unref (loop)
529		789
530	Ref/unref can be used to add or remove a reference count on the event	790	Ref/unref can be used to add or remove a reference count on the event
531	loop: Every watcher keeps one reference, and as long as the reference	791	loop: Every watcher keeps one reference, and as long as the reference
532	count is nonzero, C<ev_loop> will not return on its own. If you have	792	count is nonzero, C<ev_loop> will not return on its own.
		793
533	a watcher you never unregister that should not keep C<ev_loop> from	794	If you have a watcher you never unregister that should not keep C<ev_loop>
534	returning, ev_unref() after starting, and ev_ref() before stopping it. For	795	from returning, call ev_unref() after starting, and ev_ref() before
		796	stopping it.
		797
535	example, libev itself uses this for its internal signal pipe: It is not	798	As an example, libev itself uses this for its internal signal pipe: It
536	visible to the libev user and should not keep C<ev_loop> from exiting if	799	is not visible to the libev user and should not keep C<ev_loop> from
537	no event watchers registered by it are active. It is also an excellent	800	exiting if no event watchers registered by it are active. It is also an
538	way to do this for generic recurring timers or from within third-party	801	excellent way to do this for generic recurring timers or from within
539	libraries. Just remember to I<unref after start> and I<ref before stop>.	802	third-party libraries. Just remember to I<unref after start> and I<ref
		803	before stop> (but only if the watcher wasn't active before, or was active
		804	before, respectively. Note also that libev might stop watchers itself
		805	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		806	in the callback).
540		807
541	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	808	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
542	running when nothing else is active.	809	running when nothing else is active.
543		810
544	struct ev_signal exitsig;	811	ev_signal exitsig;
545	ev_signal_init (&exitsig, sig_cb, SIGINT);	812	ev_signal_init (&exitsig, sig_cb, SIGINT);
546	ev_signal_start (loop, &exitsig);	813	ev_signal_start (loop, &exitsig);
547	evf_unref (loop);	814	evf_unref (loop);
548		815
549	Example: For some weird reason, unregister the above signal handler again.	816	Example: For some weird reason, unregister the above signal handler again.
550		817
551	ev_ref (loop);	818	ev_ref (loop);
552	ev_signal_stop (loop, &exitsig);	819	ev_signal_stop (loop, &exitsig);
		820
		821	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		822
		823	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		824
		825	These advanced functions influence the time that libev will spend waiting
		826	for events. Both time intervals are by default C<0>, meaning that libev
		827	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		828	latency.
		829
		830	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		831	allows libev to delay invocation of I/O and timer/periodic callbacks
		832	to increase efficiency of loop iterations (or to increase power-saving
		833	opportunities).
		834
		835	The idea is that sometimes your program runs just fast enough to handle
		836	one (or very few) event(s) per loop iteration. While this makes the
		837	program responsive, it also wastes a lot of CPU time to poll for new
		838	events, especially with backends like C<select ()> which have a high
		839	overhead for the actual polling but can deliver many events at once.
		840
		841	By setting a higher I<io collect interval> you allow libev to spend more
		842	time collecting I/O events, so you can handle more events per iteration,
		843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		844	C<ev_timer>) will be not affected. Setting this to a non-null value will
		845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
		848
		849	Likewise, by setting a higher I<timeout collect interval> you allow libev
		850	to spend more time collecting timeouts, at the expense of increased
		851	latency/jitter/inexactness (the watcher callback will be called
		852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		853	value will not introduce any overhead in libev.
		854
		855	Many (busy) programs can usually benefit by setting the I/O collect
		856	interval to a value near C<0.1> or so, which is often enough for
		857	interactive servers (of course not for games), likewise for timeouts. It
		858	usually doesn't make much sense to set it to a lower value than C<0.01>,
		859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
		864
		865	Setting the I<timeout collect interval> can improve the opportunity for
		866	saving power, as the program will "bundle" timer callback invocations that
		867	are "near" in time together, by delaying some, thus reducing the number of
		868	times the process sleeps and wakes up again. Another useful technique to
		869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		870	they fire on, say, one-second boundaries only.
		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
		942
		943	=item ev_loop_verify (loop)
		944
		945	This function only does something when C<EV_VERIFY> support has been
		946	compiled in, which is the default for non-minimal builds. It tries to go
		947	through all internal structures and checks them for validity. If anything
		948	is found to be inconsistent, it will print an error message to standard
		949	error and call C<abort ()>.
		950
		951	This can be used to catch bugs inside libev itself: under normal
		952	circumstances, this function will never abort as of course libev keeps its
		953	data structures consistent.
553		954
554	=back	955	=back
555		956
556		957
557	=head1 ANATOMY OF A WATCHER	958	=head1 ANATOMY OF A WATCHER
		959
		960	In the following description, uppercase C<TYPE> in names stands for the
		961	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		962	watchers and C<ev_io_start> for I/O watchers.
558		963
559	A watcher is a structure that you create and register to record your	964	A watcher is a structure that you create and register to record your
560	interest in some event. For instance, if you want to wait for STDIN to	965	interest in some event. For instance, if you want to wait for STDIN to
561	become readable, you would create an C<ev_io> watcher for that:	966	become readable, you would create an C<ev_io> watcher for that:
562		967
563	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	968	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
564	{	969	{
565	ev_io_stop (w);	970	ev_io_stop (w);
566	ev_unloop (loop, EVUNLOOP_ALL);	971	ev_unloop (loop, EVUNLOOP_ALL);
567	}	972	}
568		973
569	struct ev_loop *loop = ev_default_loop (0);	974	struct ev_loop *loop = ev_default_loop (0);
		975
570	struct ev_io stdin_watcher;	976	ev_io stdin_watcher;
		977
571	ev_init (&stdin_watcher, my_cb);	978	ev_init (&stdin_watcher, my_cb);
572	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	979	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
573	ev_io_start (loop, &stdin_watcher);	980	ev_io_start (loop, &stdin_watcher);
		981
574	ev_loop (loop, 0);	982	ev_loop (loop, 0);
575		983
576	As you can see, you are responsible for allocating the memory for your	984	As you can see, you are responsible for allocating the memory for your
577	watcher structures (and it is usually a bad idea to do this on the stack,	985	watcher structures (and it is I<usually> a bad idea to do this on the
578	although this can sometimes be quite valid).	986	stack).
		987
		988	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		989	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
579		990
580	Each watcher structure must be initialised by a call to C<ev_init	991	Each watcher structure must be initialised by a call to C<ev_init
581	(watcher *, callback)>, which expects a callback to be provided. This	992	(watcher *, callback)>, which expects a callback to be provided. This
582	callback gets invoked each time the event occurs (or, in the case of io	993	callback gets invoked each time the event occurs (or, in the case of I/O
583	watchers, each time the event loop detects that the file descriptor given	994	watchers, each time the event loop detects that the file descriptor given
584	is readable and/or writable).	995	is readable and/or writable).
585		996
586	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	997	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
587	with arguments specific to this watcher type. There is also a macro	998	macro to configure it, with arguments specific to the watcher type. There
588	to combine initialisation and setting in one call: C<< ev_<type>_init	999	is also a macro to combine initialisation and setting in one call: C<<
589	(watcher *, callback, ...) >>.	1000	ev_TYPE_init (watcher *, callback, ...) >>.
590		1001
591	To make the watcher actually watch out for events, you have to start it	1002	To make the watcher actually watch out for events, you have to start it
592	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1003	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
593	*) >>), and you can stop watching for events at any time by calling the	1004	*) >>), and you can stop watching for events at any time by calling the
594	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1005	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
595		1006
596	As long as your watcher is active (has been started but not stopped) you	1007	As long as your watcher is active (has been started but not stopped) you
597	must not touch the values stored in it. Most specifically you must never	1008	must not touch the values stored in it. Most specifically you must never
598	reinitialise it or call its C<set> macro.	1009	reinitialise it or call its C<ev_TYPE_set> macro.
599		1010
600	Each and every callback receives the event loop pointer as first, the	1011	Each and every callback receives the event loop pointer as first, the
601	registered watcher structure as second, and a bitset of received events as	1012	registered watcher structure as second, and a bitset of received events as
602	third argument.	1013	third argument.
603		1014
…		…
657	=item C<EV_FORK>	1068	=item C<EV_FORK>
658		1069
659	The event loop has been resumed in the child process after fork (see	1070	The event loop has been resumed in the child process after fork (see
660	C<ev_fork>).	1071	C<ev_fork>).
661		1072
		1073	=item C<EV_ASYNC>
		1074
		1075	The given async watcher has been asynchronously notified (see C<ev_async>).
		1076
		1077	=item C<EV_CUSTOM>
		1078
		1079	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1080	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1081
662	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
663		1083
664	An unspecified error has occured, the watcher has been stopped. This might	1084	An unspecified error has occurred, the watcher has been stopped. This might
665	happen because the watcher could not be properly started because libev	1085	happen because the watcher could not be properly started because libev
666	ran out of memory, a file descriptor was found to be closed or any other	1086	ran out of memory, a file descriptor was found to be closed or any other
		1087	problem. Libev considers these application bugs.
		1088
667	problem. You best act on it by reporting the problem and somehow coping	1089	You best act on it by reporting the problem and somehow coping with the
668	with the watcher being stopped.	1090	watcher being stopped. Note that well-written programs should not receive
		1091	an error ever, so when your watcher receives it, this usually indicates a
		1092	bug in your program.
669		1093
670	Libev will usually signal a few "dummy" events together with an error,	1094	Libev will usually signal a few "dummy" events together with an error, for
671	for example it might indicate that a fd is readable or writable, and if	1095	example it might indicate that a fd is readable or writable, and if your
672	your callbacks is well-written it can just attempt the operation and cope	1096	callbacks is well-written it can just attempt the operation and cope with
673	with the error from read() or write(). This will not work in multithreaded	1097	the error from read() or write(). This will not work in multi-threaded
674	programs, though, so beware.	1098	programs, though, as the fd could already be closed and reused for another
		1099	thing, so beware.
675		1100
676	=back	1101	=back
677		1102
678	=head2 GENERIC WATCHER FUNCTIONS	1103	=head2 GENERIC WATCHER FUNCTIONS
679
680	In the following description, C<TYPE> stands for the watcher type,
681	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
682		1104
683	=over 4	1105	=over 4
684		1106
685	=item C<ev_init> (ev_TYPE *watcher, callback)	1107	=item C<ev_init> (ev_TYPE *watcher, callback)
686		1108
…		…
692	which rolls both calls into one.	1114	which rolls both calls into one.
693		1115
694	You can reinitialise a watcher at any time as long as it has been stopped	1116	You can reinitialise a watcher at any time as long as it has been stopped
695	(or never started) and there are no pending events outstanding.	1117	(or never started) and there are no pending events outstanding.
696		1118
697	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1119	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
698	int revents)>.	1120	int revents)>.
		1121
		1122	Example: Initialise an C<ev_io> watcher in two steps.
		1123
		1124	ev_io w;
		1125	ev_init (&w, my_cb);
		1126	ev_io_set (&w, STDIN_FILENO, EV_READ);
699		1127
700	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1128	=item C<ev_TYPE_set> (ev_TYPE *, [args])
701		1129
702	This macro initialises the type-specific parts of a watcher. You need to	1130	This macro initialises the type-specific parts of a watcher. You need to
703	call C<ev_init> at least once before you call this macro, but you can	1131	call C<ev_init> at least once before you call this macro, but you can
…		…
706	difference to the C<ev_init> macro).	1134	difference to the C<ev_init> macro).
707		1135
708	Although some watcher types do not have type-specific arguments	1136	Although some watcher types do not have type-specific arguments
709	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1137	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
710		1138
		1139	See C<ev_init>, above, for an example.
		1140
711	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1141	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
712		1142
713	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1143	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
714	calls into a single call. This is the most convinient method to initialise	1144	calls into a single call. This is the most convenient method to initialise
715	a watcher. The same limitations apply, of course.	1145	a watcher. The same limitations apply, of course.
		1146
		1147	Example: Initialise and set an C<ev_io> watcher in one step.
		1148
		1149	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
716		1150
717	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1151	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
718		1152
719	Starts (activates) the given watcher. Only active watchers will receive	1153	Starts (activates) the given watcher. Only active watchers will receive
720	events. If the watcher is already active nothing will happen.	1154	events. If the watcher is already active nothing will happen.
721		1155
		1156	Example: Start the C<ev_io> watcher that is being abused as example in this
		1157	whole section.
		1158
		1159	ev_io_start (EV_DEFAULT_UC, &w);
		1160
722	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1161	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
723		1162
724	Stops the given watcher again (if active) and clears the pending	1163	Stops the given watcher if active, and clears the pending status (whether
		1164	the watcher was active or not).
		1165
725	status. It is possible that stopped watchers are pending (for example,	1166	It is possible that stopped watchers are pending - for example,
726	non-repeating timers are being stopped when they become pending), but	1167	non-repeating timers are being stopped when they become pending - but
727	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1168	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
728	you want to free or reuse the memory used by the watcher it is therefore a	1169	pending. If you want to free or reuse the memory used by the watcher it is
729	good idea to always call its C<ev_TYPE_stop> function.	1170	therefore a good idea to always call its C<ev_TYPE_stop> function.
730		1171
731	=item bool ev_is_active (ev_TYPE *watcher)	1172	=item bool ev_is_active (ev_TYPE *watcher)
732		1173
733	Returns a true value iff the watcher is active (i.e. it has been started	1174	Returns a true value iff the watcher is active (i.e. it has been started
734	and not yet been stopped). As long as a watcher is active you must not modify	1175	and not yet been stopped). As long as a watcher is active you must not modify
…		…
760	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
761	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
762	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
763	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
764		1205
765	This means that priorities are I<only> used for ordering callback
766	invocation after new events have been received. This is useful, for
767	example, to reduce latency after idling, or more often, to bind two
768	watchers on the same event and make sure one is called first.
769
770	If you need to suppress invocation when higher priority events are pending	1206	If you need to suppress invocation when higher priority events are pending
771	you need to look at C<ev_idle> watchers, which provide this functionality.	1207	you need to look at C<ev_idle> watchers, which provide this functionality.
772		1208
773	You I<must not> change the priority of a watcher as long as it is active or	1209	You I<must not> change the priority of a watcher as long as it is active or
774	pending.	1210	pending.
775		1211
		1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1213	fine, as long as you do not mind that the priority value you query might
		1214	or might not have been clamped to the valid range.
		1215
776	The default priority used by watchers when no priority has been set is	1216	The default priority used by watchers when no priority has been set is
777	always C<0>, which is supposed to not be too high and not be too low :).	1217	always C<0>, which is supposed to not be too high and not be too low :).
778		1218
779	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
780	fine, as long as you do not mind that the priority value you query might	1220	priorities.
781	or might not have been adjusted to be within valid range.
782		1221
783	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
784		1223
785	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
786	C<loop> nor C<revents> need to be valid as long as the watcher callback	1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
787	can deal with that fact.	1226	can deal with that fact, as both are simply passed through to the
		1227	callback.
788		1228
789	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1229	=item int ev_clear_pending (loop, ev_TYPE *watcher)
790		1230
791	If the watcher is pending, this function returns clears its pending status	1231	If the watcher is pending, this function clears its pending status and
792	and returns its C<revents> bitset (as if its callback was invoked). If the	1232	returns its C<revents> bitset (as if its callback was invoked). If the
793	watcher isn't pending it does nothing and returns C<0>.	1233	watcher isn't pending it does nothing and returns C<0>.
794		1234
		1235	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1236	callback to be invoked, which can be accomplished with this function.
		1237
795	=back	1238	=back
796		1239
797		1240
798	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1241	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
799		1242
800	Each watcher has, by default, a member C<void *data> that you can change	1243	Each watcher has, by default, a member C<void *data> that you can change
801	and read at any time, libev will completely ignore it. This can be used	1244	and read at any time: libev will completely ignore it. This can be used
802	to associate arbitrary data with your watcher. If you need more data and	1245	to associate arbitrary data with your watcher. If you need more data and
803	don't want to allocate memory and store a pointer to it in that data	1246	don't want to allocate memory and store a pointer to it in that data
804	member, you can also "subclass" the watcher type and provide your own	1247	member, you can also "subclass" the watcher type and provide your own
805	data:	1248	data:
806		1249
807	struct my_io	1250	struct my_io
808	{	1251	{
809	struct ev_io io;	1252	ev_io io;
810	int otherfd;	1253	int otherfd;
811	void *somedata;	1254	void *somedata;
812	struct whatever *mostinteresting;	1255	struct whatever *mostinteresting;
813	}	1256	};
		1257
		1258	...
		1259	struct my_io w;
		1260	ev_io_init (&w.io, my_cb, fd, EV_READ);
814		1261
815	And since your callback will be called with a pointer to the watcher, you	1262	And since your callback will be called with a pointer to the watcher, you
816	can cast it back to your own type:	1263	can cast it back to your own type:
817		1264
818	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1265	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
819	{	1266	{
820	struct my_io *w = (struct my_io *)w_;	1267	struct my_io *w = (struct my_io *)w_;
821	...	1268	...
822	}	1269	}
823		1270
824	More interesting and less C-conformant ways of casting your callback type	1271	More interesting and less C-conformant ways of casting your callback type
825	instead have been omitted.	1272	instead have been omitted.
826		1273
827	Another common scenario is having some data structure with multiple	1274	Another common scenario is to use some data structure with multiple
828	watchers:	1275	embedded watchers:
829		1276
830	struct my_biggy	1277	struct my_biggy
831	{	1278	{
832	int some_data;	1279	int some_data;
833	ev_timer t1;	1280	ev_timer t1;
834	ev_timer t2;	1281	ev_timer t2;
835	}	1282	}
836		1283
837	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1284	In this case getting the pointer to C<my_biggy> is a bit more
838	you need to use C<offsetof>:	1285	complicated: Either you store the address of your C<my_biggy> struct
		1286	in the C<data> member of the watcher (for woozies), or you need to use
		1287	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1288	programmers):
839		1289
840	#include <stddef.h>	1290	#include <stddef.h>
841		1291
842	static void	1292	static void
843	t1_cb (EV_P_ struct ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
844	{	1294	{
845	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
846	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
847	}	1297	}
848		1298
849	static void	1299	static void
850	t2_cb (EV_P_ struct ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
851	{	1301	{
852	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
853	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
854	}	1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
855		1408
856		1409
857	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
858		1411
859	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
883	In general you can register as many read and/or write event watchers per	1436	In general you can register as many read and/or write event watchers per
884	fd as you want (as long as you don't confuse yourself). Setting all file	1437	fd as you want (as long as you don't confuse yourself). Setting all file
885	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
886	required if you know what you are doing).	1439	required if you know what you are doing).
887		1440
888	You have to be careful with dup'ed file descriptors, though. Some backends	1441	If you cannot use non-blocking mode, then force the use of a
889	(the linux epoll backend is a notable example) cannot handle dup'ed file	1442	known-to-be-good backend (at the time of this writing, this includes only
890	descriptors correctly if you register interest in two or more fds pointing	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
891	to the same underlying file/socket/etc. description (that is, they share	1444	descriptors for which non-blocking operation makes no sense (such as
892	the same underlying "file open").	1445	files) - libev doesn't guarentee any specific behaviour in that case.
893
894	If you must do this, then force the use of a known-to-be-good backend
895	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
896	C<EVBACKEND_POLL>).
897		1446
898	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
899	receive "spurious" readyness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
900	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
901	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
902	lot of those (for example solaris ports), it is very easy to get into	1451	lot of those (for example Solaris ports), it is very easy to get into
903	this situation even with a relatively standard program structure. Thus	1452	this situation even with a relatively standard program structure. Thus
904	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1453	it is best to always use non-blocking I/O: An extra C<read>(2) returning
905	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1454	C<EAGAIN> is far preferable to a program hanging until some data arrives.
906		1455
907	If you cannot run the fd in non-blocking mode (for example you should not	1456	If you cannot run the fd in non-blocking mode (for example you should
908	play around with an Xlib connection), then you have to seperately re-test	1457	not play around with an Xlib connection), then you have to separately
909	whether a file descriptor is really ready with a known-to-be good interface	1458	re-test whether a file descriptor is really ready with a known-to-be good
910	such as poll (fortunately in our Xlib example, Xlib already does this on	1459	interface such as poll (fortunately in our Xlib example, Xlib already
911	its own, so its quite safe to use).	1460	does this on its own, so its quite safe to use). Some people additionally
		1461	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1462	indefinitely.
		1463
		1464	But really, best use non-blocking mode.
		1465
		1466	=head3 The special problem of disappearing file descriptors
		1467
		1468	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1469	descriptor (either due to calling C<close> explicitly or any other means,
		1470	such as C<dup2>). The reason is that you register interest in some file
		1471	descriptor, but when it goes away, the operating system will silently drop
		1472	this interest. If another file descriptor with the same number then is
		1473	registered with libev, there is no efficient way to see that this is, in
		1474	fact, a different file descriptor.
		1475
		1476	To avoid having to explicitly tell libev about such cases, libev follows
		1477	the following policy: Each time C<ev_io_set> is being called, libev
		1478	will assume that this is potentially a new file descriptor, otherwise
		1479	it is assumed that the file descriptor stays the same. That means that
		1480	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1481	descriptor even if the file descriptor number itself did not change.
		1482
		1483	This is how one would do it normally anyway, the important point is that
		1484	the libev application should not optimise around libev but should leave
		1485	optimisations to libev.
		1486
		1487	=head3 The special problem of dup'ed file descriptors
		1488
		1489	Some backends (e.g. epoll), cannot register events for file descriptors,
		1490	but only events for the underlying file descriptions. That means when you
		1491	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1492	events for them, only one file descriptor might actually receive events.
		1493
		1494	There is no workaround possible except not registering events
		1495	for potentially C<dup ()>'ed file descriptors, or to resort to
		1496	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1497
		1498	=head3 The special problem of fork
		1499
		1500	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1501	useless behaviour. Libev fully supports fork, but needs to be told about
		1502	it in the child.
		1503
		1504	To support fork in your programs, you either have to call
		1505	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1506	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1507	C<EVBACKEND_POLL>.
		1508
		1509	=head3 The special problem of SIGPIPE
		1510
		1511	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1512	when writing to a pipe whose other end has been closed, your program gets
		1513	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1514	this is sensible behaviour, for daemons, this is usually undesirable.
		1515
		1516	So when you encounter spurious, unexplained daemon exits, make sure you
		1517	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1518	somewhere, as that would have given you a big clue).
		1519
		1520
		1521	=head3 Watcher-Specific Functions
912		1522
913	=over 4	1523	=over 4
914		1524
915	=item ev_io_init (ev_io *, callback, int fd, int events)	1525	=item ev_io_init (ev_io *, callback, int fd, int events)
916		1526
917	=item ev_io_set (ev_io *, int fd, int events)	1527	=item ev_io_set (ev_io *, int fd, int events)
918		1528
919	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1529	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
920	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1530	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
921	C<EV_READ | EV_WRITE> to receive the given events.	1531	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
922		1532
923	=item int fd [read-only]	1533	=item int fd [read-only]
924		1534
925	The file descriptor being watched.	1535	The file descriptor being watched.
926		1536
927	=item int events [read-only]	1537	=item int events [read-only]
928		1538
929	The events being watched.	1539	The events being watched.
930		1540
931	=back	1541	=back
		1542
		1543	=head3 Examples
932		1544
933	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1545	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
934	readable, but only once. Since it is likely line-buffered, you could	1546	readable, but only once. Since it is likely line-buffered, you could
935	attempt to read a whole line in the callback.	1547	attempt to read a whole line in the callback.
936		1548
937	static void	1549	static void
938	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1550	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
939	{	1551	{
940	ev_io_stop (loop, w);	1552	ev_io_stop (loop, w);
941	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1553	.. read from stdin here (or from w->fd) and handle any I/O errors
942	}	1554	}
943		1555
944	...	1556	...
945	struct ev_loop *loop = ev_default_init (0);	1557	struct ev_loop *loop = ev_default_init (0);
946	struct ev_io stdin_readable;	1558	ev_io stdin_readable;
947	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1559	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
948	ev_io_start (loop, &stdin_readable);	1560	ev_io_start (loop, &stdin_readable);
949	ev_loop (loop, 0);	1561	ev_loop (loop, 0);
950		1562
951		1563
952	=head2 C<ev_timer> - relative and optionally repeating timeouts	1564	=head2 C<ev_timer> - relative and optionally repeating timeouts
953		1565
954	Timer watchers are simple relative timers that generate an event after a	1566	Timer watchers are simple relative timers that generate an event after a
955	given time, and optionally repeating in regular intervals after that.	1567	given time, and optionally repeating in regular intervals after that.
956		1568
957	The timers are based on real time, that is, if you register an event that	1569	The timers are based on real time, that is, if you register an event that
958	times out after an hour and you reset your system clock to last years	1570	times out after an hour and you reset your system clock to January last
959	time, it will still time out after (roughly) and hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
960	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
961	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
		1574
		1575	The callback is guaranteed to be invoked only I<after> its timeout has
		1576	passed (not I<at>, so on systems with very low-resolution clocks this
		1577	might introduce a small delay). If multiple timers become ready during the
		1578	same loop iteration then the ones with earlier time-out values are invoked
		1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
		1581
		1582	=head3 Be smart about timeouts
		1583
		1584	Many real-world problems involve some kind of timeout, usually for error
		1585	recovery. A typical example is an HTTP request - if the other side hangs,
		1586	you want to raise some error after a while.
		1587
		1588	What follows are some ways to handle this problem, from obvious and
		1589	inefficient to smart and efficient.
		1590
		1591	In the following, a 60 second activity timeout is assumed - a timeout that
		1592	gets reset to 60 seconds each time there is activity (e.g. each time some
		1593	data or other life sign was received).
		1594
		1595	=over 4
		1596
		1597	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1598
		1599	This is the most obvious, but not the most simple way: In the beginning,
		1600	start the watcher:
		1601
		1602	ev_timer_init (timer, callback, 60., 0.);
		1603	ev_timer_start (loop, timer);
		1604
		1605	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1606	and start it again:
		1607
		1608	ev_timer_stop (loop, timer);
		1609	ev_timer_set (timer, 60., 0.);
		1610	ev_timer_start (loop, timer);
		1611
		1612	This is relatively simple to implement, but means that each time there is
		1613	some activity, libev will first have to remove the timer from its internal
		1614	data structure and then add it again. Libev tries to be fast, but it's
		1615	still not a constant-time operation.
		1616
		1617	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1618
		1619	This is the easiest way, and involves using C<ev_timer_again> instead of
		1620	C<ev_timer_start>.
		1621
		1622	To implement this, configure an C<ev_timer> with a C<repeat> value
		1623	of C<60> and then call C<ev_timer_again> at start and each time you
		1624	successfully read or write some data. If you go into an idle state where
		1625	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1626	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1627
		1628	That means you can ignore both the C<ev_timer_start> function and the
		1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1630	member and C<ev_timer_again>.
		1631
		1632	At start:
		1633
		1634	ev_init (timer, callback);
		1635	timer->repeat = 60.;
		1636	ev_timer_again (loop, timer);
		1637
		1638	Each time there is some activity:
		1639
		1640	ev_timer_again (loop, timer);
		1641
		1642	It is even possible to change the time-out on the fly, regardless of
		1643	whether the watcher is active or not:
		1644
		1645	timer->repeat = 30.;
		1646	ev_timer_again (loop, timer);
		1647
		1648	This is slightly more efficient then stopping/starting the timer each time
		1649	you want to modify its timeout value, as libev does not have to completely
		1650	remove and re-insert the timer from/into its internal data structure.
		1651
		1652	It is, however, even simpler than the "obvious" way to do it.
		1653
		1654	=item 3. Let the timer time out, but then re-arm it as required.
		1655
		1656	This method is more tricky, but usually most efficient: Most timeouts are
		1657	relatively long compared to the intervals between other activity - in
		1658	our example, within 60 seconds, there are usually many I/O events with
		1659	associated activity resets.
		1660
		1661	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1662	but remember the time of last activity, and check for a real timeout only
		1663	within the callback:
		1664
		1665	ev_tstamp last_activity; // time of last activity
		1666
		1667	static void
		1668	callback (EV_P_ ev_timer *w, int revents)
		1669	{
		1670	ev_tstamp now = ev_now (EV_A);
		1671	ev_tstamp timeout = last_activity + 60.;
		1672
		1673	// if last_activity + 60. is older than now, we did time out
		1674	if (timeout < now)
		1675	{
		1676	// timeout occured, take action
		1677	}
		1678	else
		1679	{
		1680	// callback was invoked, but there was some activity, re-arm
		1681	// the watcher to fire in last_activity + 60, which is
		1682	// guaranteed to be in the future, so "again" is positive:
		1683	w->repeat = timeout - now;
		1684	ev_timer_again (EV_A_ w);
		1685	}
		1686	}
		1687
		1688	To summarise the callback: first calculate the real timeout (defined
		1689	as "60 seconds after the last activity"), then check if that time has
		1690	been reached, which means something I<did>, in fact, time out. Otherwise
		1691	the callback was invoked too early (C<timeout> is in the future), so
		1692	re-schedule the timer to fire at that future time, to see if maybe we have
		1693	a timeout then.
		1694
		1695	Note how C<ev_timer_again> is used, taking advantage of the
		1696	C<ev_timer_again> optimisation when the timer is already running.
		1697
		1698	This scheme causes more callback invocations (about one every 60 seconds
		1699	minus half the average time between activity), but virtually no calls to
		1700	libev to change the timeout.
		1701
		1702	To start the timer, simply initialise the watcher and set C<last_activity>
		1703	to the current time (meaning we just have some activity :), then call the
		1704	callback, which will "do the right thing" and start the timer:
		1705
		1706	ev_init (timer, callback);
		1707	last_activity = ev_now (loop);
		1708	callback (loop, timer, EV_TIMEOUT);
		1709
		1710	And when there is some activity, simply store the current time in
		1711	C<last_activity>, no libev calls at all:
		1712
		1713	last_actiivty = ev_now (loop);
		1714
		1715	This technique is slightly more complex, but in most cases where the
		1716	time-out is unlikely to be triggered, much more efficient.
		1717
		1718	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1719	callback :) - just change the timeout and invoke the callback, which will
		1720	fix things for you.
		1721
		1722	=item 4. Wee, just use a double-linked list for your timeouts.
		1723
		1724	If there is not one request, but many thousands (millions...), all
		1725	employing some kind of timeout with the same timeout value, then one can
		1726	do even better:
		1727
		1728	When starting the timeout, calculate the timeout value and put the timeout
		1729	at the I<end> of the list.
		1730
		1731	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1732	the list is expected to fire (for example, using the technique #3).
		1733
		1734	When there is some activity, remove the timer from the list, recalculate
		1735	the timeout, append it to the end of the list again, and make sure to
		1736	update the C<ev_timer> if it was taken from the beginning of the list.
		1737
		1738	This way, one can manage an unlimited number of timeouts in O(1) time for
		1739	starting, stopping and updating the timers, at the expense of a major
		1740	complication, and having to use a constant timeout. The constant timeout
		1741	ensures that the list stays sorted.
		1742
		1743	=back
		1744
		1745	So which method the best?
		1746
		1747	Method #2 is a simple no-brain-required solution that is adequate in most
		1748	situations. Method #3 requires a bit more thinking, but handles many cases
		1749	better, and isn't very complicated either. In most case, choosing either
		1750	one is fine, with #3 being better in typical situations.
		1751
		1752	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1753	rather complicated, but extremely efficient, something that really pays
		1754	off after the first million or so of active timers, i.e. it's usually
		1755	overkill :)
		1756
		1757	=head3 The special problem of time updates
		1758
		1759	Establishing the current time is a costly operation (it usually takes at
		1760	least two system calls): EV therefore updates its idea of the current
		1761	time only before and after C<ev_loop> collects new events, which causes a
		1762	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1763	lots of events in one iteration.
962		1764
963	The relative timeouts are calculated relative to the C<ev_now ()>	1765	The relative timeouts are calculated relative to the C<ev_now ()>
964	time. This is usually the right thing as this timestamp refers to the time	1766	time. This is usually the right thing as this timestamp refers to the time
965	of the event triggering whatever timeout you are modifying/starting. If	1767	of the event triggering whatever timeout you are modifying/starting. If
966	you suspect event processing to be delayed and you I<need> to base the timeout	1768	you suspect event processing to be delayed and you I<need> to base the
967	on the current time, use something like this to adjust for this:	1769	timeout on the current time, use something like this to adjust for this:
968		1770
969	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1771	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
970		1772
971	The callback is guarenteed to be invoked only when its timeout has passed,	1773	If the event loop is suspended for a long time, you can also force an
972	but if multiple timers become ready during the same loop iteration then	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
973	order of execution is undefined.	1775	()>.
		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
		1807	=head3 Watcher-Specific Functions and Data Members
974		1808
975	=over 4	1809	=over 4
976		1810
977	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
978		1812
979	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1813	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
980		1814
981	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1815	Configure the timer to trigger after C<after> seconds. If C<repeat>
982	C<0.>, then it will automatically be stopped. If it is positive, then the	1816	is C<0.>, then it will automatically be stopped once the timeout is
983	timer will automatically be configured to trigger again C<repeat> seconds	1817	reached. If it is positive, then the timer will automatically be
984	later, again, and again, until stopped manually.	1818	configured to trigger again C<repeat> seconds later, again, and again,
		1819	until stopped manually.
985		1820
986	The timer itself will do a best-effort at avoiding drift, that is, if you	1821	The timer itself will do a best-effort at avoiding drift, that is, if
987	configure a timer to trigger every 10 seconds, then it will trigger at	1822	you configure a timer to trigger every 10 seconds, then it will normally
988	exactly 10 second intervals. If, however, your program cannot keep up with	1823	trigger at exactly 10 second intervals. If, however, your program cannot
989	the timer (because it takes longer than those 10 seconds to do stuff) the	1824	keep up with the timer (because it takes longer than those 10 seconds to
990	timer will not fire more than once per event loop iteration.	1825	do stuff) the timer will not fire more than once per event loop iteration.
991		1826
992	=item ev_timer_again (loop)	1827	=item ev_timer_again (loop, ev_timer *)
993		1828
994	This will act as if the timer timed out and restart it again if it is	1829	This will act as if the timer timed out and restart it again if it is
995	repeating. The exact semantics are:	1830	repeating. The exact semantics are:
996		1831
997	If the timer is pending, its pending status is cleared.	1832	If the timer is pending, its pending status is cleared.
998		1833
999	If the timer is started but nonrepeating, stop it (as if it timed out).	1834	If the timer is started but non-repeating, stop it (as if it timed out).
1000		1835
1001	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
1002	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
1003		1838
1004	This sounds a bit complicated, but here is a useful and typical	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1005	example: Imagine you have a tcp connection and you want a so-called idle	1840	usage example.
1006	timeout, that is, you want to be called when there have been, say, 60
1007	seconds of inactivity on the socket. The easiest way to do this is to
1008	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1009	C<ev_timer_again> each time you successfully read or write some data. If
1010	you go into an idle state where you do not expect data to travel on the
1011	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1012	automatically restart it if need be.
1013		1841
1014	That means you can ignore the C<after> value and C<ev_timer_start>	1842	=item ev_timer_remaining (loop, ev_timer *)
1015	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1016		1843
1017	ev_timer_init (timer, callback, 0., 5.);	1844	Returns the remaining time until a timer fires. If the timer is active,
1018	ev_timer_again (loop, timer);	1845	then this time is relative to the current event loop time, otherwise it's
1019	...	1846	the timeout value currently configured.
1020	timer->again = 17.;
1021	ev_timer_again (loop, timer);
1022	...
1023	timer->again = 10.;
1024	ev_timer_again (loop, timer);
1025		1847
1026	This is more slightly efficient then stopping/starting the timer each time	1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1027	you want to modify its timeout value.	1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
1028		1853
1029	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1030		1855
1031	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1032	or C<ev_timer_again> is called and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
1033	which is also when any modifications are taken into account.	1858	which is also when any modifications are taken into account.
1034		1859
1035	=back	1860	=back
1036		1861
		1862	=head3 Examples
		1863
1037	Example: Create a timer that fires after 60 seconds.	1864	Example: Create a timer that fires after 60 seconds.
1038		1865
1039	static void	1866	static void
1040	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1867	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1041	{	1868	{
1042	.. one minute over, w is actually stopped right here	1869	.. one minute over, w is actually stopped right here
1043	}	1870	}
1044		1871
1045	struct ev_timer mytimer;	1872	ev_timer mytimer;
1046	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1873	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1047	ev_timer_start (loop, &mytimer);	1874	ev_timer_start (loop, &mytimer);
1048		1875
1049	Example: Create a timeout timer that times out after 10 seconds of	1876	Example: Create a timeout timer that times out after 10 seconds of
1050	inactivity.	1877	inactivity.
1051		1878
1052	static void	1879	static void
1053	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1880	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1054	{	1881	{
1055	.. ten seconds without any activity	1882	.. ten seconds without any activity
1056	}	1883	}
1057		1884
1058	struct ev_timer mytimer;	1885	ev_timer mytimer;
1059	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1886	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1060	ev_timer_again (&mytimer); /* start timer */	1887	ev_timer_again (&mytimer); /* start timer */
1061	ev_loop (loop, 0);	1888	ev_loop (loop, 0);
1062		1889
1063	// and in some piece of code that gets executed on any "activity":	1890	// and in some piece of code that gets executed on any "activity":
1064	// reset the timeout to start ticking again at 10 seconds	1891	// reset the timeout to start ticking again at 10 seconds
1065	ev_timer_again (&mytimer);	1892	ev_timer_again (&mytimer);
1066		1893
1067		1894
1068	=head2 C<ev_periodic> - to cron or not to cron?	1895	=head2 C<ev_periodic> - to cron or not to cron?
1069		1896
1070	Periodic watchers are also timers of a kind, but they are very versatile	1897	Periodic watchers are also timers of a kind, but they are very versatile
1071	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
1072		1899
1073	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1900	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1074	but on wallclock time (absolute time). You can tell a periodic watcher	1901	relative time, the physical time that passes) but on wall clock time
1075	to trigger "at" some specific point in time. For example, if you tell a	1902	(absolute time, the thing you can read on your calender or clock). The
1076	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1903	difference is that wall clock time can run faster or slower than real
1077	+ 10.>) and then reset your system clock to the last year, then it will	1904	time, and time jumps are not uncommon (e.g. when you adjust your
1078	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1905	wrist-watch).
1079	roughly 10 seconds later).
1080		1906
1081	They can also be used to implement vastly more complex timers, such as	1907	You can tell a periodic watcher to trigger after some specific point
1082	triggering an event on each midnight, local time or other, complicated,	1908	in time: for example, if you tell a periodic watcher to trigger "in 10
1083	rules.	1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
1084		1914
		1915	C<ev_periodic> watchers can also be used to implement vastly more complex
		1916	timers, such as triggering an event on each "midnight, local time", or
		1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
		1919
1085	As with timers, the callback is guarenteed to be invoked only when the	1920	As with timers, the callback is guaranteed to be invoked only when the
1086	time (C<at>) has been passed, but if multiple periodic timers become ready	1921	point in time where it is supposed to trigger has passed. If multiple
1087	during the same loop iteration then order of execution is undefined.	1922	timers become ready during the same loop iteration then the ones with
		1923	earlier time-out values are invoked before ones with later time-out values
		1924	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1925
		1926	=head3 Watcher-Specific Functions and Data Members
1088		1927
1089	=over 4	1928	=over 4
1090		1929
1091	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1930	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1092		1931
1093	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1932	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1094		1933
1095	Lots of arguments, lets sort it out... There are basically three modes of	1934	Lots of arguments, let's sort it out... There are basically three modes of
1096	operation, and we will explain them from simplest to complex:	1935	operation, and we will explain them from simplest to most complex:
1097		1936
1098	=over 4	1937	=over 4
1099		1938
1100	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1101		1940
1102	In this configuration the watcher triggers an event at the wallclock time	1941	In this configuration the watcher triggers an event after the wall clock
1103	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1942	time C<offset> has passed. It will not repeat and will not adjust when a
1104	that is, if it is to be run at January 1st 2011 then it will run when the	1943	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1105	system time reaches or surpasses this time.	1944	will be stopped and invoked when the system clock reaches or surpasses
		1945	this point in time.
1106		1946
1107	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1108		1948
1109	In this mode the watcher will always be scheduled to time out at the next	1949	In this mode the watcher will always be scheduled to time out at the next
1110	C<at + N * interval> time (for some integer N, which can also be negative)	1950	C<offset + N * interval> time (for some integer N, which can also be
1111	and then repeat, regardless of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
1112		1953
1113	This can be used to create timers that do not drift with respect to system	1954	This can be used to create timers that do not drift with respect to the
1114	time:	1955	system clock, for example, here is an C<ev_periodic> that triggers each
		1956	hour, on the hour (with respect to UTC):
1115		1957
1116	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
1117		1959
1118	This doesn't mean there will always be 3600 seconds in between triggers,	1960	This doesn't mean there will always be 3600 seconds in between triggers,
1119	but only that the the callback will be called when the system time shows a	1961	but only that the callback will be called when the system time shows a
1120	full hour (UTC), or more correctly, when the system time is evenly divisible	1962	full hour (UTC), or more correctly, when the system time is evenly divisible
1121	by 3600.	1963	by 3600.
1122		1964
1123	Another way to think about it (for the mathematically inclined) is that	1965	Another way to think about it (for the mathematically inclined) is that
1124	C<ev_periodic> will try to run the callback in this mode at the next possible	1966	C<ev_periodic> will try to run the callback in this mode at the next possible
1125	time where C<time = at (mod interval)>, regardless of any time jumps.	1967	time where C<time = offset (mod interval)>, regardless of any time jumps.
1126		1968
1127	For numerical stability it is preferable that the C<at> value is near	1969	For numerical stability it is preferable that the C<offset> value is near
1128	C<ev_now ()> (the current time), but there is no range requirement for	1970	C<ev_now ()> (the current time), but there is no range requirement for
1129	this value.	1971	this value, and in fact is often specified as zero.
1130		1972
		1973	Note also that there is an upper limit to how often a timer can fire (CPU
		1974	speed for example), so if C<interval> is very small then timing stability
		1975	will of course deteriorate. Libev itself tries to be exact to be about one
		1976	millisecond (if the OS supports it and the machine is fast enough).
		1977
1131	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1132		1979
1133	In this mode the values for C<interval> and C<at> are both being	1980	In this mode the values for C<interval> and C<offset> are both being
1134	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
1135	reschedule callback will be called with the watcher as first, and the	1982	reschedule callback will be called with the watcher as first, and the
1136	current time as second argument.	1983	current time as second argument.
1137		1984
1138	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1985	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1139	ever, or make any event loop modifications>. If you need to stop it,	1986	or make ANY other event loop modifications whatsoever, unless explicitly
1140	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1987	allowed by documentation here>.
1141	starting an C<ev_prepare> watcher, which is legal).
1142		1988
		1989	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1990	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1991	only event loop modification you are allowed to do).
		1992
1143	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1993	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1144	ev_tstamp now)>, e.g.:	1994	*w, ev_tstamp now)>, e.g.:
1145		1995
		1996	static ev_tstamp
1146	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1997	my_rescheduler (ev_periodic *w, ev_tstamp now)
1147	{	1998	{
1148	return now + 60.;	1999	return now + 60.;
1149	}	2000	}
1150		2001
1151	It must return the next time to trigger, based on the passed time value	2002	It must return the next time to trigger, based on the passed time value
1152	(that is, the lowest time value larger than to the second argument). It	2003	(that is, the lowest time value larger than to the second argument). It
1153	will usually be called just before the callback will be triggered, but	2004	will usually be called just before the callback will be triggered, but
1154	might be called at other times, too.	2005	might be called at other times, too.
1155		2006
1156	NOTE: I<< This callback must always return a time that is later than the	2007	NOTE: I<< This callback must always return a time that is higher than or
1157	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2008	equal to the passed C<now> value >>.
1158		2009
1159	This can be used to create very complex timers, such as a timer that	2010	This can be used to create very complex timers, such as a timer that
1160	triggers on each midnight, local time. To do this, you would calculate the	2011	triggers on "next midnight, local time". To do this, you would calculate the
1161	next midnight after C<now> and return the timestamp value for this. How	2012	next midnight after C<now> and return the timestamp value for this. How
1162	you do this is, again, up to you (but it is not trivial, which is the main	2013	you do this is, again, up to you (but it is not trivial, which is the main
1163	reason I omitted it as an example).	2014	reason I omitted it as an example).
1164		2015
1165	=back	2016	=back
…		…
1169	Simply stops and restarts the periodic watcher again. This is only useful	2020	Simply stops and restarts the periodic watcher again. This is only useful
1170	when you changed some parameters or the reschedule callback would return	2021	when you changed some parameters or the reschedule callback would return
1171	a different time than the last time it was called (e.g. in a crond like	2022	a different time than the last time it was called (e.g. in a crond like
1172	program when the crontabs have changed).	2023	program when the crontabs have changed).
1173		2024
		2025	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2026
		2027	When active, returns the absolute time that the watcher is supposed
		2028	to trigger next. This is not the same as the C<offset> argument to
		2029	C<ev_periodic_set>, but indeed works even in interval and manual
		2030	rescheduling modes.
		2031
1174	=item ev_tstamp offset [read-write]	2032	=item ev_tstamp offset [read-write]
1175		2033
1176	When repeating, this contains the offset value, otherwise this is the	2034	When repeating, this contains the offset value, otherwise this is the
1177	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
1178		2037
1179	Can be modified any time, but changes only take effect when the periodic	2038	Can be modified any time, but changes only take effect when the periodic
1180	timer fires or C<ev_periodic_again> is being called.	2039	timer fires or C<ev_periodic_again> is being called.
1181		2040
1182	=item ev_tstamp interval [read-write]	2041	=item ev_tstamp interval [read-write]
1183		2042
1184	The current interval value. Can be modified any time, but changes only	2043	The current interval value. Can be modified any time, but changes only
1185	take effect when the periodic timer fires or C<ev_periodic_again> is being	2044	take effect when the periodic timer fires or C<ev_periodic_again> is being
1186	called.	2045	called.
1187		2046
1188	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2047	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1189		2048
1190	The current reschedule callback, or C<0>, if this functionality is	2049	The current reschedule callback, or C<0>, if this functionality is
1191	switched off. Can be changed any time, but changes only take effect when	2050	switched off. Can be changed any time, but changes only take effect when
1192	the periodic timer fires or C<ev_periodic_again> is being called.	2051	the periodic timer fires or C<ev_periodic_again> is being called.
1193		2052
1194	=back	2053	=back
1195		2054
		2055	=head3 Examples
		2056
1196	Example: Call a callback every hour, or, more precisely, whenever the	2057	Example: Call a callback every hour, or, more precisely, whenever the
1197	system clock is divisible by 3600. The callback invocation times have	2058	system time is divisible by 3600. The callback invocation times have
1198	potentially a lot of jittering, but good long-term stability.	2059	potentially a lot of jitter, but good long-term stability.
1199		2060
1200	static void	2061	static void
1201	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2062	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1202	{	2063	{
1203	... its now a full hour (UTC, or TAI or whatever your clock follows)	2064	... its now a full hour (UTC, or TAI or whatever your clock follows)
1204	}	2065	}
1205		2066
1206	struct ev_periodic hourly_tick;	2067	ev_periodic hourly_tick;
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2068	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1208	ev_periodic_start (loop, &hourly_tick);	2069	ev_periodic_start (loop, &hourly_tick);
1209		2070
1210	Example: The same as above, but use a reschedule callback to do it:	2071	Example: The same as above, but use a reschedule callback to do it:
1211		2072
1212	#include <math.h>	2073	#include <math.h>
1213		2074
1214	static ev_tstamp	2075	static ev_tstamp
1215	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2076	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1216	{	2077	{
1217	return fmod (now, 3600.) + 3600.;	2078	return now + (3600. - fmod (now, 3600.));
1218	}	2079	}
1219		2080
1220	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2081	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1221		2082
1222	Example: Call a callback every hour, starting now:	2083	Example: Call a callback every hour, starting now:
1223		2084
1224	struct ev_periodic hourly_tick;	2085	ev_periodic hourly_tick;
1225	ev_periodic_init (&hourly_tick, clock_cb,	2086	ev_periodic_init (&hourly_tick, clock_cb,
1226	fmod (ev_now (loop), 3600.), 3600., 0);	2087	fmod (ev_now (loop), 3600.), 3600., 0);
1227	ev_periodic_start (loop, &hourly_tick);	2088	ev_periodic_start (loop, &hourly_tick);
1228		2089
1229		2090
1230	=head2 C<ev_signal> - signal me when a signal gets signalled!	2091	=head2 C<ev_signal> - signal me when a signal gets signalled!
1231		2092
1232	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1233	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1234	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1235	normal event processing, like any other event.	2096	normal event processing, like any other event.
1236		2097
		2098	If you want signals to be delivered truly asynchronously, just use
		2099	C<sigaction> as you would do without libev and forget about sharing
		2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
		2102
1237	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1238	first watcher gets started will libev actually register a signal watcher	2109	When the first watcher gets started will libev actually register something
1239	with the kernel (thus it coexists with your own signal handlers as long	2110	with the kernel (thus it coexists with your own signal handlers as long as
1240	as you don't register any with libev). Similarly, when the last signal	2111	you don't register any with libev for the same signal).
1241	watcher for a signal is stopped libev will reset the signal handler to	2112
1242	SIG_DFL (regardless of what it was set to before).	2113	If possible and supported, libev will install its handlers with
		2114	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2115	not be unduly interrupted. If you have a problem with system calls getting
		2116	interrupted by signals you can block all signals in an C<ev_check> watcher
		2117	and unblock them in an C<ev_prepare> watcher.
		2118
		2119	=head3 The special problem of inheritance over execve
		2120
		2121	Both the signal mask (C<sigprocmask>) and the signal disposition
		2122	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2123	stopping it again), that is, libev might or might not block the signal,
		2124	and might or might not set or restore the installed signal handler.
		2125
		2126	While this does not matter for the signal disposition (libev never
		2127	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2128	C<execve>), this matters for the signal mask: many programs do not expect
		2129	many signals to be blocked.
		2130
		2131	This means that before calling C<exec> (from the child) you should reset
		2132	the signal mask to whatever "default" you expect (all clear is a good
		2133	choice usually).
		2134
		2135	=head3 Watcher-Specific Functions and Data Members
1243		2136
1244	=over 4	2137	=over 4
1245		2138
1246	=item ev_signal_init (ev_signal *, callback, int signum)	2139	=item ev_signal_init (ev_signal *, callback, int signum)
1247		2140
…		…
1254		2147
1255	The signal the watcher watches out for.	2148	The signal the watcher watches out for.
1256		2149
1257	=back	2150	=back
1258		2151
		2152	=head3 Examples
		2153
		2154	Example: Try to exit cleanly on SIGINT.
		2155
		2156	static void
		2157	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2158	{
		2159	ev_unloop (loop, EVUNLOOP_ALL);
		2160	}
		2161
		2162	ev_signal signal_watcher;
		2163	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2164	ev_signal_start (loop, &signal_watcher);
		2165
1259		2166
1260	=head2 C<ev_child> - watch out for process status changes	2167	=head2 C<ev_child> - watch out for process status changes
1261		2168
1262	Child watchers trigger when your process receives a SIGCHLD in response to	2169	Child watchers trigger when your process receives a SIGCHLD in response to
1263	some child status changes (most typically when a child of yours dies).	2170	some child status changes (most typically when a child of yours dies or
		2171	exits). It is permissible to install a child watcher I<after> the child
		2172	has been forked (which implies it might have already exited), as long
		2173	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2174	forking and then immediately registering a watcher for the child is fine,
		2175	but forking and registering a watcher a few event loop iterations later or
		2176	in the next callback invocation is not.
		2177
		2178	Only the default event loop is capable of handling signals, and therefore
		2179	you can only register child watchers in the default event loop.
		2180
		2181	Due to some design glitches inside libev, child watchers will always be
		2182	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2183	libev)
		2184
		2185	=head3 Process Interaction
		2186
		2187	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2188	initialised. This is necessary to guarantee proper behaviour even if the
		2189	first child watcher is started after the child exits. The occurrence
		2190	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2191	synchronously as part of the event loop processing. Libev always reaps all
		2192	children, even ones not watched.
		2193
		2194	=head3 Overriding the Built-In Processing
		2195
		2196	Libev offers no special support for overriding the built-in child
		2197	processing, but if your application collides with libev's default child
		2198	handler, you can override it easily by installing your own handler for
		2199	C<SIGCHLD> after initialising the default loop, and making sure the
		2200	default loop never gets destroyed. You are encouraged, however, to use an
		2201	event-based approach to child reaping and thus use libev's support for
		2202	that, so other libev users can use C<ev_child> watchers freely.
		2203
		2204	=head3 Stopping the Child Watcher
		2205
		2206	Currently, the child watcher never gets stopped, even when the
		2207	child terminates, so normally one needs to stop the watcher in the
		2208	callback. Future versions of libev might stop the watcher automatically
		2209	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2210	problem).
		2211
		2212	=head3 Watcher-Specific Functions and Data Members
1264		2213
1265	=over 4	2214	=over 4
1266		2215
1267	=item ev_child_init (ev_child *, callback, int pid)	2216	=item ev_child_init (ev_child *, callback, int pid, int trace)
1268		2217
1269	=item ev_child_set (ev_child *, int pid)	2218	=item ev_child_set (ev_child *, int pid, int trace)
1270		2219
1271	Configures the watcher to wait for status changes of process C<pid> (or	2220	Configures the watcher to wait for status changes of process C<pid> (or
1272	I<any> process if C<pid> is specified as C<0>). The callback can look	2221	I<any> process if C<pid> is specified as C<0>). The callback can look
1273	at the C<rstatus> member of the C<ev_child> watcher structure to see	2222	at the C<rstatus> member of the C<ev_child> watcher structure to see
1274	the status word (use the macros from C<sys/wait.h> and see your systems	2223	the status word (use the macros from C<sys/wait.h> and see your systems
1275	C<waitpid> documentation). The C<rpid> member contains the pid of the	2224	C<waitpid> documentation). The C<rpid> member contains the pid of the
1276	process causing the status change.	2225	process causing the status change. C<trace> must be either C<0> (only
		2226	activate the watcher when the process terminates) or C<1> (additionally
		2227	activate the watcher when the process is stopped or continued).
1277		2228
1278	=item int pid [read-only]	2229	=item int pid [read-only]
1279		2230
1280	The process id this watcher watches out for, or C<0>, meaning any process id.	2231	The process id this watcher watches out for, or C<0>, meaning any process id.
1281		2232
…		…
1288	The process exit/trace status caused by C<rpid> (see your systems	2239	The process exit/trace status caused by C<rpid> (see your systems
1289	C<waitpid> and C<sys/wait.h> documentation for details).	2240	C<waitpid> and C<sys/wait.h> documentation for details).
1290		2241
1291	=back	2242	=back
1292		2243
1293	Example: Try to exit cleanly on SIGINT and SIGTERM.	2244	=head3 Examples
1294		2245
		2246	Example: C<fork()> a new process and install a child handler to wait for
		2247	its completion.
		2248
		2249	ev_child cw;
		2250
1295	static void	2251	static void
1296	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2252	child_cb (EV_P_ ev_child *w, int revents)
1297	{	2253	{
1298	ev_unloop (loop, EVUNLOOP_ALL);	2254	ev_child_stop (EV_A_ w);
		2255	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1299	}	2256	}
1300		2257
1301	struct ev_signal signal_watcher;	2258	pid_t pid = fork ();
1302	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2259
1303	ev_signal_start (loop, &sigint_cb);	2260	if (pid < 0)
		2261	// error
		2262	else if (pid == 0)
		2263	{
		2264	// the forked child executes here
		2265	exit (1);
		2266	}
		2267	else
		2268	{
		2269	ev_child_init (&cw, child_cb, pid, 0);
		2270	ev_child_start (EV_DEFAULT_ &cw);
		2271	}
1304		2272
1305		2273
1306	=head2 C<ev_stat> - did the file attributes just change?	2274	=head2 C<ev_stat> - did the file attributes just change?
1307		2275
1308	This watches a filesystem path for attribute changes. That is, it calls	2276	This watches a file system path for attribute changes. That is, it calls
1309	C<stat> regularly (or when the OS says it changed) and sees if it changed	2277	C<stat> on that path in regular intervals (or when the OS says it changed)
1310	compared to the last time, invoking the callback if it did.	2278	and sees if it changed compared to the last time, invoking the callback if
		2279	it did.
1311		2280
1312	The path does not need to exist: changing from "path exists" to "path does	2281	The path does not need to exist: changing from "path exists" to "path does
1313	not exist" is a status change like any other. The condition "path does	2282	not exist" is a status change like any other. The condition "path does not
1314	not exist" is signified by the C<st_nlink> field being zero (which is	2283	exist" (or more correctly "path cannot be stat'ed") is signified by the
1315	otherwise always forced to be at least one) and all the other fields of	2284	C<st_nlink> field being zero (which is otherwise always forced to be at
1316	the stat buffer having unspecified contents.	2285	least one) and all the other fields of the stat buffer having unspecified
		2286	contents.
1317		2287
1318	The path I<should> be absolute and I<must not> end in a slash. If it is	2288	The path I<must not> end in a slash or contain special components such as
		2289	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1319	relative and your working directory changes, the behaviour is undefined.	2290	your working directory changes, then the behaviour is undefined.
1320		2291
1321	Since there is no standard to do this, the portable implementation simply	2292	Since there is no portable change notification interface available, the
1322	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2293	portable implementation simply calls C<stat(2)> regularly on the path
1323	can specify a recommended polling interval for this case. If you specify	2294	to see if it changed somehow. You can specify a recommended polling
1324	a polling interval of C<0> (highly recommended!) then a I<suitable,	2295	interval for this case. If you specify a polling interval of C<0> (highly
1325	unspecified default> value will be used (which you can expect to be around	2296	recommended!) then a I<suitable, unspecified default> value will be used
1326	five seconds, although this might change dynamically). Libev will also	2297	(which you can expect to be around five seconds, although this might
1327	impose a minimum interval which is currently around C<0.1>, but thats	2298	change dynamically). Libev will also impose a minimum interval which is
1328	usually overkill.	2299	currently around C<0.1>, but that's usually overkill.
1329		2300
1330	This watcher type is not meant for massive numbers of stat watchers,	2301	This watcher type is not meant for massive numbers of stat watchers,
1331	as even with OS-supported change notifications, this can be	2302	as even with OS-supported change notifications, this can be
1332	resource-intensive.	2303	resource-intensive.
1333		2304
1334	At the time of this writing, only the Linux inotify interface is	2305	At the time of this writing, the only OS-specific interface implemented
1335	implemented (implementing kqueue support is left as an exercise for the	2306	is the Linux inotify interface (implementing kqueue support is left as an
1336	reader). Inotify will be used to give hints only and should not change the	2307	exercise for the reader. Note, however, that the author sees no way of
1337	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2308	implementing C<ev_stat> semantics with kqueue, except as a hint).
1338	to fall back to regular polling again even with inotify, but changes are	2309
1339	usually detected immediately, and if the file exists there will be no	2310	=head3 ABI Issues (Largefile Support)
1340	polling.	2311
		2312	Libev by default (unless the user overrides this) uses the default
		2313	compilation environment, which means that on systems with large file
		2314	support disabled by default, you get the 32 bit version of the stat
		2315	structure. When using the library from programs that change the ABI to
		2316	use 64 bit file offsets the programs will fail. In that case you have to
		2317	compile libev with the same flags to get binary compatibility. This is
		2318	obviously the case with any flags that change the ABI, but the problem is
		2319	most noticeably displayed with ev_stat and large file support.
		2320
		2321	The solution for this is to lobby your distribution maker to make large
		2322	file interfaces available by default (as e.g. FreeBSD does) and not
		2323	optional. Libev cannot simply switch on large file support because it has
		2324	to exchange stat structures with application programs compiled using the
		2325	default compilation environment.
		2326
		2327	=head3 Inotify and Kqueue
		2328
		2329	When C<inotify (7)> support has been compiled into libev and present at
		2330	runtime, it will be used to speed up change detection where possible. The
		2331	inotify descriptor will be created lazily when the first C<ev_stat>
		2332	watcher is being started.
		2333
		2334	Inotify presence does not change the semantics of C<ev_stat> watchers
		2335	except that changes might be detected earlier, and in some cases, to avoid
		2336	making regular C<stat> calls. Even in the presence of inotify support
		2337	there are many cases where libev has to resort to regular C<stat> polling,
		2338	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2339	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2340	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2341	xfs are fully working) libev usually gets away without polling.
		2342
		2343	There is no support for kqueue, as apparently it cannot be used to
		2344	implement this functionality, due to the requirement of having a file
		2345	descriptor open on the object at all times, and detecting renames, unlinks
		2346	etc. is difficult.
		2347
		2348	=head3 C<stat ()> is a synchronous operation
		2349
		2350	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2351	the process. The exception are C<ev_stat> watchers - those call C<stat
		2352	()>, which is a synchronous operation.
		2353
		2354	For local paths, this usually doesn't matter: unless the system is very
		2355	busy or the intervals between stat's are large, a stat call will be fast,
		2356	as the path data is usually in memory already (except when starting the
		2357	watcher).
		2358
		2359	For networked file systems, calling C<stat ()> can block an indefinite
		2360	time due to network issues, and even under good conditions, a stat call
		2361	often takes multiple milliseconds.
		2362
		2363	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2364	paths, although this is fully supported by libev.
		2365
		2366	=head3 The special problem of stat time resolution
		2367
		2368	The C<stat ()> system call only supports full-second resolution portably,
		2369	and even on systems where the resolution is higher, most file systems
		2370	still only support whole seconds.
		2371
		2372	That means that, if the time is the only thing that changes, you can
		2373	easily miss updates: on the first update, C<ev_stat> detects a change and
		2374	calls your callback, which does something. When there is another update
		2375	within the same second, C<ev_stat> will be unable to detect unless the
		2376	stat data does change in other ways (e.g. file size).
		2377
		2378	The solution to this is to delay acting on a change for slightly more
		2379	than a second (or till slightly after the next full second boundary), using
		2380	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2381	ev_timer_again (loop, w)>).
		2382
		2383	The C<.02> offset is added to work around small timing inconsistencies
		2384	of some operating systems (where the second counter of the current time
		2385	might be be delayed. One such system is the Linux kernel, where a call to
		2386	C<gettimeofday> might return a timestamp with a full second later than
		2387	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2388	update file times then there will be a small window where the kernel uses
		2389	the previous second to update file times but libev might already execute
		2390	the timer callback).
		2391
		2392	=head3 Watcher-Specific Functions and Data Members
1341		2393
1342	=over 4	2394	=over 4
1343		2395
1344	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2396	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1345		2397
…		…
1349	C<path>. The C<interval> is a hint on how quickly a change is expected to	2401	C<path>. The C<interval> is a hint on how quickly a change is expected to
1350	be detected and should normally be specified as C<0> to let libev choose	2402	be detected and should normally be specified as C<0> to let libev choose
1351	a suitable value. The memory pointed to by C<path> must point to the same	2403	a suitable value. The memory pointed to by C<path> must point to the same
1352	path for as long as the watcher is active.	2404	path for as long as the watcher is active.
1353		2405
1354	The callback will be receive C<EV_STAT> when a change was detected,	2406	The callback will receive an C<EV_STAT> event when a change was detected,
1355	relative to the attributes at the time the watcher was started (or the	2407	relative to the attributes at the time the watcher was started (or the
1356	last change was detected).	2408	last change was detected).
1357		2409
1358	=item ev_stat_stat (ev_stat *)	2410	=item ev_stat_stat (loop, ev_stat *)
1359		2411
1360	Updates the stat buffer immediately with new values. If you change the	2412	Updates the stat buffer immediately with new values. If you change the
1361	watched path in your callback, you could call this fucntion to avoid	2413	watched path in your callback, you could call this function to avoid
1362	detecting this change (while introducing a race condition). Can also be	2414	detecting this change (while introducing a race condition if you are not
1363	useful simply to find out the new values.	2415	the only one changing the path). Can also be useful simply to find out the
		2416	new values.
1364		2417
1365	=item ev_statdata attr [read-only]	2418	=item ev_statdata attr [read-only]
1366		2419
1367	The most-recently detected attributes of the file. Although the type is of	2420	The most-recently detected attributes of the file. Although the type is
1368	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2421	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1369	suitable for your system. If the C<st_nlink> member is C<0>, then there	2422	suitable for your system, but you can only rely on the POSIX-standardised
		2423	members to be present. If the C<st_nlink> member is C<0>, then there was
1370	was some error while C<stat>ing the file.	2424	some error while C<stat>ing the file.
1371		2425
1372	=item ev_statdata prev [read-only]	2426	=item ev_statdata prev [read-only]
1373		2427
1374	The previous attributes of the file. The callback gets invoked whenever	2428	The previous attributes of the file. The callback gets invoked whenever
1375	C<prev> != C<attr>.	2429	C<prev> != C<attr>, or, more precisely, one or more of these members
		2430	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2431	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1376		2432
1377	=item ev_tstamp interval [read-only]	2433	=item ev_tstamp interval [read-only]
1378		2434
1379	The specified interval.	2435	The specified interval.
1380		2436
1381	=item const char *path [read-only]	2437	=item const char *path [read-only]
1382		2438
1383	The filesystem path that is being watched.	2439	The file system path that is being watched.
1384		2440
1385	=back	2441	=back
1386		2442
		2443	=head3 Examples
		2444
1387	Example: Watch C</etc/passwd> for attribute changes.	2445	Example: Watch C</etc/passwd> for attribute changes.
1388		2446
1389	static void	2447	static void
1390	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2448	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1391	{	2449	{
1392	/* /etc/passwd changed in some way */	2450	/* /etc/passwd changed in some way */
1393	if (w->attr.st_nlink)	2451	if (w->attr.st_nlink)
1394	{	2452	{
1395	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2453	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1396	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2454	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1397	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2455	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1398	}	2456	}
1399	else	2457	else
1400	/* you shalt not abuse printf for puts */	2458	/* you shalt not abuse printf for puts */
1401	puts ("wow, /etc/passwd is not there, expect problems. "	2459	puts ("wow, /etc/passwd is not there, expect problems. "
1402	"if this is windows, they already arrived\n");	2460	"if this is windows, they already arrived\n");
1403	}	2461	}
1404		2462
1405	...	2463	...
1406	ev_stat passwd;	2464	ev_stat passwd;
1407		2465
1408	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2466	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1409	ev_stat_start (loop, &passwd);	2467	ev_stat_start (loop, &passwd);
		2468
		2469	Example: Like above, but additionally use a one-second delay so we do not
		2470	miss updates (however, frequent updates will delay processing, too, so
		2471	one might do the work both on C<ev_stat> callback invocation I<and> on
		2472	C<ev_timer> callback invocation).
		2473
		2474	static ev_stat passwd;
		2475	static ev_timer timer;
		2476
		2477	static void
		2478	timer_cb (EV_P_ ev_timer *w, int revents)
		2479	{
		2480	ev_timer_stop (EV_A_ w);
		2481
		2482	/* now it's one second after the most recent passwd change */
		2483	}
		2484
		2485	static void
		2486	stat_cb (EV_P_ ev_stat *w, int revents)
		2487	{
		2488	/* reset the one-second timer */
		2489	ev_timer_again (EV_A_ &timer);
		2490	}
		2491
		2492	...
		2493	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2494	ev_stat_start (loop, &passwd);
		2495	ev_timer_init (&timer, timer_cb, 0., 1.02);
1410		2496
1411		2497
1412	=head2 C<ev_idle> - when you've got nothing better to do...	2498	=head2 C<ev_idle> - when you've got nothing better to do...
1413		2499
1414	Idle watchers trigger events when no other events of the same or higher	2500	Idle watchers trigger events when no other events of the same or higher
1415	priority are pending (prepare, check and other idle watchers do not	2501	priority are pending (prepare, check and other idle watchers do not count
1416	count).	2502	as receiving "events").
1417		2503
1418	That is, as long as your process is busy handling sockets or timeouts	2504	That is, as long as your process is busy handling sockets or timeouts
1419	(or even signals, imagine) of the same or higher priority it will not be	2505	(or even signals, imagine) of the same or higher priority it will not be
1420	triggered. But when your process is idle (or only lower-priority watchers	2506	triggered. But when your process is idle (or only lower-priority watchers
1421	are pending), the idle watchers are being called once per event loop	2507	are pending), the idle watchers are being called once per event loop
…		…
1428	Apart from keeping your process non-blocking (which is a useful	2514	Apart from keeping your process non-blocking (which is a useful
1429	effect on its own sometimes), idle watchers are a good place to do	2515	effect on its own sometimes), idle watchers are a good place to do
1430	"pseudo-background processing", or delay processing stuff to after the	2516	"pseudo-background processing", or delay processing stuff to after the
1431	event loop has handled all outstanding events.	2517	event loop has handled all outstanding events.
1432		2518
		2519	=head3 Watcher-Specific Functions and Data Members
		2520
1433	=over 4	2521	=over 4
1434		2522
1435	=item ev_idle_init (ev_signal *, callback)	2523	=item ev_idle_init (ev_idle *, callback)
1436		2524
1437	Initialises and configures the idle watcher - it has no parameters of any	2525	Initialises and configures the idle watcher - it has no parameters of any
1438	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2526	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1439	believe me.	2527	believe me.
1440		2528
1441	=back	2529	=back
1442		2530
		2531	=head3 Examples
		2532
1443	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2533	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1444	callback, free it. Also, use no error checking, as usual.	2534	callback, free it. Also, use no error checking, as usual.
1445		2535
1446	static void	2536	static void
1447	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2537	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1448	{	2538	{
1449	free (w);	2539	free (w);
1450	// now do something you wanted to do when the program has	2540	// now do something you wanted to do when the program has
1451	// no longer asnything immediate to do.	2541	// no longer anything immediate to do.
1452	}	2542	}
1453		2543
1454	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2544	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1455	ev_idle_init (idle_watcher, idle_cb);	2545	ev_idle_init (idle_watcher, idle_cb);
1456	ev_idle_start (loop, idle_cb);	2546	ev_idle_start (loop, idle_watcher);
1457		2547
1458		2548
1459	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2549	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1460		2550
1461	Prepare and check watchers are usually (but not always) used in tandem:	2551	Prepare and check watchers are usually (but not always) used in pairs:
1462	prepare watchers get invoked before the process blocks and check watchers	2552	prepare watchers get invoked before the process blocks and check watchers
1463	afterwards.	2553	afterwards.
1464		2554
1465	You I<must not> call C<ev_loop> or similar functions that enter	2555	You I<must not> call C<ev_loop> or similar functions that enter
1466	the current event loop from either C<ev_prepare> or C<ev_check>	2556	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1469	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2559	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1470	C<ev_check> so if you have one watcher of each kind they will always be	2560	C<ev_check> so if you have one watcher of each kind they will always be
1471	called in pairs bracketing the blocking call.	2561	called in pairs bracketing the blocking call.
1472		2562
1473	Their main purpose is to integrate other event mechanisms into libev and	2563	Their main purpose is to integrate other event mechanisms into libev and
1474	their use is somewhat advanced. This could be used, for example, to track	2564	their use is somewhat advanced. They could be used, for example, to track
1475	variable changes, implement your own watchers, integrate net-snmp or a	2565	variable changes, implement your own watchers, integrate net-snmp or a
1476	coroutine library and lots more. They are also occasionally useful if	2566	coroutine library and lots more. They are also occasionally useful if
1477	you cache some data and want to flush it before blocking (for example,	2567	you cache some data and want to flush it before blocking (for example,
1478	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2568	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1479	watcher).	2569	watcher).
1480		2570
1481	This is done by examining in each prepare call which file descriptors need	2571	This is done by examining in each prepare call which file descriptors
1482	to be watched by the other library, registering C<ev_io> watchers for	2572	need to be watched by the other library, registering C<ev_io> watchers
1483	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2573	for them and starting an C<ev_timer> watcher for any timeouts (many
1484	provide just this functionality). Then, in the check watcher you check for	2574	libraries provide exactly this functionality). Then, in the check watcher,
1485	any events that occured (by checking the pending status of all watchers	2575	you check for any events that occurred (by checking the pending status
1486	and stopping them) and call back into the library. The I/O and timer	2576	of all watchers and stopping them) and call back into the library. The
1487	callbacks will never actually be called (but must be valid nevertheless,	2577	I/O and timer callbacks will never actually be called (but must be valid
1488	because you never know, you know?).	2578	nevertheless, because you never know, you know?).
1489		2579
1490	As another example, the Perl Coro module uses these hooks to integrate	2580	As another example, the Perl Coro module uses these hooks to integrate
1491	coroutines into libev programs, by yielding to other active coroutines	2581	coroutines into libev programs, by yielding to other active coroutines
1492	during each prepare and only letting the process block if no coroutines	2582	during each prepare and only letting the process block if no coroutines
1493	are ready to run (it's actually more complicated: it only runs coroutines	2583	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1496	loop from blocking if lower-priority coroutines are active, thus mapping	2586	loop from blocking if lower-priority coroutines are active, thus mapping
1497	low-priority coroutines to idle/background tasks).	2587	low-priority coroutines to idle/background tasks).
1498		2588
1499	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2589	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1500	priority, to ensure that they are being run before any other watchers	2590	priority, to ensure that they are being run before any other watchers
		2591	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2592
1501	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2593	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1502	too) should not activate ("feed") events into libev. While libev fully	2594	activate ("feed") events into libev. While libev fully supports this, they
1503	supports this, they will be called before other C<ev_check> watchers did	2595	might get executed before other C<ev_check> watchers did their job. As
1504	their job. As C<ev_check> watchers are often used to embed other event	2596	C<ev_check> watchers are often used to embed other (non-libev) event
1505	loops those other event loops might be in an unusable state until their	2597	loops those other event loops might be in an unusable state until their
1506	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2598	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1507	others).	2599	others).
1508		2600
		2601	=head3 Watcher-Specific Functions and Data Members
		2602
1509	=over 4	2603	=over 4
1510		2604
1511	=item ev_prepare_init (ev_prepare *, callback)	2605	=item ev_prepare_init (ev_prepare *, callback)
1512		2606
1513	=item ev_check_init (ev_check *, callback)	2607	=item ev_check_init (ev_check *, callback)
1514		2608
1515	Initialises and configures the prepare or check watcher - they have no	2609	Initialises and configures the prepare or check watcher - they have no
1516	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2610	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1517	macros, but using them is utterly, utterly and completely pointless.	2611	macros, but using them is utterly, utterly, utterly and completely
		2612	pointless.
1518		2613
1519	=back	2614	=back
		2615
		2616	=head3 Examples
1520		2617
1521	There are a number of principal ways to embed other event loops or modules	2618	There are a number of principal ways to embed other event loops or modules
1522	into libev. Here are some ideas on how to include libadns into libev	2619	into libev. Here are some ideas on how to include libadns into libev
1523	(there is a Perl module named C<EV::ADNS> that does this, which you could	2620	(there is a Perl module named C<EV::ADNS> that does this, which you could
1524	use for an actually working example. Another Perl module named C<EV::Glib>	2621	use as a working example. Another Perl module named C<EV::Glib> embeds a
1525	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2622	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1526	into the Glib event loop).	2623	Glib event loop).
1527		2624
1528	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2625	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1529	and in a check watcher, destroy them and call into libadns. What follows	2626	and in a check watcher, destroy them and call into libadns. What follows
1530	is pseudo-code only of course. This requires you to either use a low	2627	is pseudo-code only of course. This requires you to either use a low
1531	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2628	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1532	the callbacks for the IO/timeout watchers might not have been called yet.	2629	the callbacks for the IO/timeout watchers might not have been called yet.
1533		2630
1534	static ev_io iow [nfd];	2631	static ev_io iow [nfd];
1535	static ev_timer tw;	2632	static ev_timer tw;
1536		2633
1537	static void	2634	static void
1538	io_cb (ev_loop *loop, ev_io *w, int revents)	2635	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1539	{	2636	{
1540	}	2637	}
1541		2638
1542	// create io watchers for each fd and a timer before blocking	2639	// create io watchers for each fd and a timer before blocking
1543	static void	2640	static void
1544	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2641	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1545	{	2642	{
1546	int timeout = 3600000;	2643	int timeout = 3600000;
1547	struct pollfd fds [nfd];	2644	struct pollfd fds [nfd];
1548	// actual code will need to loop here and realloc etc.	2645	// actual code will need to loop here and realloc etc.
1549	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2646	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1550		2647
1551	/* the callback is illegal, but won't be called as we stop during check */	2648	/* the callback is illegal, but won't be called as we stop during check */
1552	ev_timer_init (&tw, 0, timeout * 1e-3);	2649	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1553	ev_timer_start (loop, &tw);	2650	ev_timer_start (loop, &tw);
1554		2651
1555	// create one ev_io per pollfd	2652	// create one ev_io per pollfd
1556	for (int i = 0; i < nfd; ++i)	2653	for (int i = 0; i < nfd; ++i)
1557	{	2654	{
1558	ev_io_init (iow + i, io_cb, fds [i].fd,	2655	ev_io_init (iow + i, io_cb, fds [i].fd,
1559	((fds [i].events & POLLIN ? EV_READ : 0)	2656	((fds [i].events & POLLIN ? EV_READ : 0)
1560	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2657	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1561		2658
1562	fds [i].revents = 0;	2659	fds [i].revents = 0;
1563	ev_io_start (loop, iow + i);	2660	ev_io_start (loop, iow + i);
1564	}	2661	}
1565	}	2662	}
1566		2663
1567	// stop all watchers after blocking	2664	// stop all watchers after blocking
1568	static void	2665	static void
1569	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2666	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1570	{	2667	{
1571	ev_timer_stop (loop, &tw);	2668	ev_timer_stop (loop, &tw);
1572		2669
1573	for (int i = 0; i < nfd; ++i)	2670	for (int i = 0; i < nfd; ++i)
1574	{	2671	{
1575	// set the relevant poll flags	2672	// set the relevant poll flags
1576	// could also call adns_processreadable etc. here	2673	// could also call adns_processreadable etc. here
1577	struct pollfd *fd = fds + i;	2674	struct pollfd *fd = fds + i;
1578	int revents = ev_clear_pending (iow + i);	2675	int revents = ev_clear_pending (iow + i);
1579	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2676	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1580	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2677	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1581		2678
1582	// now stop the watcher	2679	// now stop the watcher
1583	ev_io_stop (loop, iow + i);	2680	ev_io_stop (loop, iow + i);
1584	}	2681	}
1585		2682
1586	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2683	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1587	}	2684	}
1588		2685
1589	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2686	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1590	in the prepare watcher and would dispose of the check watcher.	2687	in the prepare watcher and would dispose of the check watcher.
1591		2688
1592	Method 3: If the module to be embedded supports explicit event	2689	Method 3: If the module to be embedded supports explicit event
1593	notification (adns does), you can also make use of the actual watcher	2690	notification (libadns does), you can also make use of the actual watcher
1594	callbacks, and only destroy/create the watchers in the prepare watcher.	2691	callbacks, and only destroy/create the watchers in the prepare watcher.
1595		2692
1596	static void	2693	static void
1597	timer_cb (EV_P_ ev_timer *w, int revents)	2694	timer_cb (EV_P_ ev_timer *w, int revents)
1598	{	2695	{
1599	adns_state ads = (adns_state)w->data;	2696	adns_state ads = (adns_state)w->data;
1600	update_now (EV_A);	2697	update_now (EV_A);
1601		2698
1602	adns_processtimeouts (ads, &tv_now);	2699	adns_processtimeouts (ads, &tv_now);
1603	}	2700	}
1604		2701
1605	static void	2702	static void
1606	io_cb (EV_P_ ev_io *w, int revents)	2703	io_cb (EV_P_ ev_io *w, int revents)
1607	{	2704	{
1608	adns_state ads = (adns_state)w->data;	2705	adns_state ads = (adns_state)w->data;
1609	update_now (EV_A);	2706	update_now (EV_A);
1610		2707
1611	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2708	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1612	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2709	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1613	}	2710	}
1614		2711
1615	// do not ever call adns_afterpoll	2712	// do not ever call adns_afterpoll
1616		2713
1617	Method 4: Do not use a prepare or check watcher because the module you	2714	Method 4: Do not use a prepare or check watcher because the module you
1618	want to embed is too inflexible to support it. Instead, youc na override	2715	want to embed is not flexible enough to support it. Instead, you can
1619	their poll function. The drawback with this solution is that the main	2716	override their poll function. The drawback with this solution is that the
1620	loop is now no longer controllable by EV. The C<Glib::EV> module does	2717	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1621	this.	2718	this approach, effectively embedding EV as a client into the horrible
		2719	libglib event loop.
1622		2720
1623	static gint	2721	static gint
1624	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2722	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1625	{	2723	{
1626	int got_events = 0;	2724	int got_events = 0;
1627		2725
1628	for (n = 0; n < nfds; ++n)	2726	for (n = 0; n < nfds; ++n)
1629	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2727	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1630		2728
1631	if (timeout >= 0)	2729	if (timeout >= 0)
1632	// create/start timer	2730	// create/start timer
1633		2731
1634	// poll	2732	// poll
1635	ev_loop (EV_A_ 0);	2733	ev_loop (EV_A_ 0);
1636		2734
1637	// stop timer again	2735	// stop timer again
1638	if (timeout >= 0)	2736	if (timeout >= 0)
1639	ev_timer_stop (EV_A_ &to);	2737	ev_timer_stop (EV_A_ &to);
1640		2738
1641	// stop io watchers again - their callbacks should have set	2739	// stop io watchers again - their callbacks should have set
1642	for (n = 0; n < nfds; ++n)	2740	for (n = 0; n < nfds; ++n)
1643	ev_io_stop (EV_A_ iow [n]);	2741	ev_io_stop (EV_A_ iow [n]);
1644		2742
1645	return got_events;	2743	return got_events;
1646	}	2744	}
1647		2745
1648		2746
1649	=head2 C<ev_embed> - when one backend isn't enough...	2747	=head2 C<ev_embed> - when one backend isn't enough...
1650		2748
1651	This is a rather advanced watcher type that lets you embed one event loop	2749	This is a rather advanced watcher type that lets you embed one event loop
…		…
1657	prioritise I/O.	2755	prioritise I/O.
1658		2756
1659	As an example for a bug workaround, the kqueue backend might only support	2757	As an example for a bug workaround, the kqueue backend might only support
1660	sockets on some platform, so it is unusable as generic backend, but you	2758	sockets on some platform, so it is unusable as generic backend, but you
1661	still want to make use of it because you have many sockets and it scales	2759	still want to make use of it because you have many sockets and it scales
1662	so nicely. In this case, you would create a kqueue-based loop and embed it	2760	so nicely. In this case, you would create a kqueue-based loop and embed
1663	into your default loop (which might use e.g. poll). Overall operation will	2761	it into your default loop (which might use e.g. poll). Overall operation
1664	be a bit slower because first libev has to poll and then call kevent, but	2762	will be a bit slower because first libev has to call C<poll> and then
1665	at least you can use both at what they are best.	2763	C<kevent>, but at least you can use both mechanisms for what they are
		2764	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1666		2765
1667	As for prioritising I/O: rarely you have the case where some fds have	2766	As for prioritising I/O: under rare circumstances you have the case where
1668	to be watched and handled very quickly (with low latency), and even	2767	some fds have to be watched and handled very quickly (with low latency),
1669	priorities and idle watchers might have too much overhead. In this case	2768	and even priorities and idle watchers might have too much overhead. In
1670	you would put all the high priority stuff in one loop and all the rest in	2769	this case you would put all the high priority stuff in one loop and all
1671	a second one, and embed the second one in the first.	2770	the rest in a second one, and embed the second one in the first.
1672		2771
1673	As long as the watcher is active, the callback will be invoked every time	2772	As long as the watcher is active, the callback will be invoked every
1674	there might be events pending in the embedded loop. The callback must then	2773	time there might be events pending in the embedded loop. The callback
1675	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2774	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1676	their callbacks (you could also start an idle watcher to give the embedded	2775	sweep and invoke their callbacks (the callback doesn't need to invoke the
1677	loop strictly lower priority for example). You can also set the callback	2776	C<ev_embed_sweep> function directly, it could also start an idle watcher
1678	to C<0>, in which case the embed watcher will automatically execute the	2777	to give the embedded loop strictly lower priority for example).
1679	embedded loop sweep.
1680		2778
1681	As long as the watcher is started it will automatically handle events. The	2779	You can also set the callback to C<0>, in which case the embed watcher
1682	callback will be invoked whenever some events have been handled. You can	2780	will automatically execute the embedded loop sweep whenever necessary.
1683	set the callback to C<0> to avoid having to specify one if you are not
1684	interested in that.
1685		2781
1686	Also, there have not currently been made special provisions for forking:	2782	Fork detection will be handled transparently while the C<ev_embed> watcher
1687	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2783	is active, i.e., the embedded loop will automatically be forked when the
1688	but you will also have to stop and restart any C<ev_embed> watchers	2784	embedding loop forks. In other cases, the user is responsible for calling
1689	yourself.	2785	C<ev_loop_fork> on the embedded loop.
1690		2786
1691	Unfortunately, not all backends are embeddable, only the ones returned by	2787	Unfortunately, not all backends are embeddable: only the ones returned by
1692	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2788	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1693	portable one.	2789	portable one.
1694		2790
1695	So when you want to use this feature you will always have to be prepared	2791	So when you want to use this feature you will always have to be prepared
1696	that you cannot get an embeddable loop. The recommended way to get around	2792	that you cannot get an embeddable loop. The recommended way to get around
1697	this is to have a separate variables for your embeddable loop, try to	2793	this is to have a separate variables for your embeddable loop, try to
1698	create it, and if that fails, use the normal loop for everything:	2794	create it, and if that fails, use the normal loop for everything.
1699		2795
1700	struct ev_loop *loop_hi = ev_default_init (0);	2796	=head3 C<ev_embed> and fork
1701	struct ev_loop *loop_lo = 0;
1702	struct ev_embed embed;
1703
1704	// see if there is a chance of getting one that works
1705	// (remember that a flags value of 0 means autodetection)
1706	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1707	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1708	: 0;
1709		2797
1710	// if we got one, then embed it, otherwise default to loop_hi	2798	While the C<ev_embed> watcher is running, forks in the embedding loop will
1711	if (loop_lo)	2799	automatically be applied to the embedded loop as well, so no special
1712	{	2800	fork handling is required in that case. When the watcher is not running,
1713	ev_embed_init (&embed, 0, loop_lo);	2801	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1714	ev_embed_start (loop_hi, &embed);	2802	as applicable.
1715	}	2803
1716	else	2804	=head3 Watcher-Specific Functions and Data Members
1717	loop_lo = loop_hi;
1718		2805
1719	=over 4	2806	=over 4
1720		2807
1721	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2808	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1722		2809
…		…
1724		2811
1725	Configures the watcher to embed the given loop, which must be	2812	Configures the watcher to embed the given loop, which must be
1726	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2813	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1727	invoked automatically, otherwise it is the responsibility of the callback	2814	invoked automatically, otherwise it is the responsibility of the callback
1728	to invoke it (it will continue to be called until the sweep has been done,	2815	to invoke it (it will continue to be called until the sweep has been done,
1729	if you do not want thta, you need to temporarily stop the embed watcher).	2816	if you do not want that, you need to temporarily stop the embed watcher).
1730		2817
1731	=item ev_embed_sweep (loop, ev_embed *)	2818	=item ev_embed_sweep (loop, ev_embed *)
1732		2819
1733	Make a single, non-blocking sweep over the embedded loop. This works	2820	Make a single, non-blocking sweep over the embedded loop. This works
1734	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2821	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1735	apropriate way for embedded loops.	2822	appropriate way for embedded loops.
1736		2823
1737	=item struct ev_loop *loop [read-only]	2824	=item struct ev_loop *other [read-only]
1738		2825
1739	The embedded event loop.	2826	The embedded event loop.
1740		2827
1741	=back	2828	=back
		2829
		2830	=head3 Examples
		2831
		2832	Example: Try to get an embeddable event loop and embed it into the default
		2833	event loop. If that is not possible, use the default loop. The default
		2834	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2835	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2836	used).
		2837
		2838	struct ev_loop *loop_hi = ev_default_init (0);
		2839	struct ev_loop *loop_lo = 0;
		2840	ev_embed embed;
		2841
		2842	// see if there is a chance of getting one that works
		2843	// (remember that a flags value of 0 means autodetection)
		2844	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2845	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2846	: 0;
		2847
		2848	// if we got one, then embed it, otherwise default to loop_hi
		2849	if (loop_lo)
		2850	{
		2851	ev_embed_init (&embed, 0, loop_lo);
		2852	ev_embed_start (loop_hi, &embed);
		2853	}
		2854	else
		2855	loop_lo = loop_hi;
		2856
		2857	Example: Check if kqueue is available but not recommended and create
		2858	a kqueue backend for use with sockets (which usually work with any
		2859	kqueue implementation). Store the kqueue/socket-only event loop in
		2860	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2861
		2862	struct ev_loop *loop = ev_default_init (0);
		2863	struct ev_loop *loop_socket = 0;
		2864	ev_embed embed;
		2865
		2866	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2867	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2868	{
		2869	ev_embed_init (&embed, 0, loop_socket);
		2870	ev_embed_start (loop, &embed);
		2871	}
		2872
		2873	if (!loop_socket)
		2874	loop_socket = loop;
		2875
		2876	// now use loop_socket for all sockets, and loop for everything else
1742		2877
1743		2878
1744	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2879	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1745		2880
1746	Fork watchers are called when a C<fork ()> was detected (usually because	2881	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1749	event loop blocks next and before C<ev_check> watchers are being called,	2884	event loop blocks next and before C<ev_check> watchers are being called,
1750	and only in the child after the fork. If whoever good citizen calling	2885	and only in the child after the fork. If whoever good citizen calling
1751	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2886	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1752	handlers will be invoked, too, of course.	2887	handlers will be invoked, too, of course.
1753		2888
		2889	=head3 The special problem of life after fork - how is it possible?
		2890
		2891	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2892	up/change the process environment, followed by a call to C<exec()>. This
		2893	sequence should be handled by libev without any problems.
		2894
		2895	This changes when the application actually wants to do event handling
		2896	in the child, or both parent in child, in effect "continuing" after the
		2897	fork.
		2898
		2899	The default mode of operation (for libev, with application help to detect
		2900	forks) is to duplicate all the state in the child, as would be expected
		2901	when I<either> the parent I<or> the child process continues.
		2902
		2903	When both processes want to continue using libev, then this is usually the
		2904	wrong result. In that case, usually one process (typically the parent) is
		2905	supposed to continue with all watchers in place as before, while the other
		2906	process typically wants to start fresh, i.e. without any active watchers.
		2907
		2908	The cleanest and most efficient way to achieve that with libev is to
		2909	simply create a new event loop, which of course will be "empty", and
		2910	use that for new watchers. This has the advantage of not touching more
		2911	memory than necessary, and thus avoiding the copy-on-write, and the
		2912	disadvantage of having to use multiple event loops (which do not support
		2913	signal watchers).
		2914
		2915	When this is not possible, or you want to use the default loop for
		2916	other reasons, then in the process that wants to start "fresh", call
		2917	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2918	the default loop will "orphan" (not stop) all registered watchers, so you
		2919	have to be careful not to execute code that modifies those watchers. Note
		2920	also that in that case, you have to re-register any signal watchers.
		2921
		2922	=head3 Watcher-Specific Functions and Data Members
		2923
1754	=over 4	2924	=over 4
1755		2925
1756	=item ev_fork_init (ev_signal *, callback)	2926	=item ev_fork_init (ev_signal *, callback)
1757		2927
1758	Initialises and configures the fork watcher - it has no parameters of any	2928	Initialises and configures the fork watcher - it has no parameters of any
…		…
1760	believe me.	2930	believe me.
1761		2931
1762	=back	2932	=back
1763		2933
1764		2934
		2935	=head2 C<ev_async> - how to wake up another event loop
		2936
		2937	In general, you cannot use an C<ev_loop> from multiple threads or other
		2938	asynchronous sources such as signal handlers (as opposed to multiple event
		2939	loops - those are of course safe to use in different threads).
		2940
		2941	Sometimes, however, you need to wake up another event loop you do not
		2942	control, for example because it belongs to another thread. This is what
		2943	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2944	can signal it by calling C<ev_async_send>, which is thread- and signal
		2945	safe.
		2946
		2947	This functionality is very similar to C<ev_signal> watchers, as signals,
		2948	too, are asynchronous in nature, and signals, too, will be compressed
		2949	(i.e. the number of callback invocations may be less than the number of
		2950	C<ev_async_sent> calls).
		2951
		2952	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2953	just the default loop.
		2954
		2955	=head3 Queueing
		2956
		2957	C<ev_async> does not support queueing of data in any way. The reason
		2958	is that the author does not know of a simple (or any) algorithm for a
		2959	multiple-writer-single-reader queue that works in all cases and doesn't
		2960	need elaborate support such as pthreads.
		2961
		2962	That means that if you want to queue data, you have to provide your own
		2963	queue. But at least I can tell you how to implement locking around your
		2964	queue:
		2965
		2966	=over 4
		2967
		2968	=item queueing from a signal handler context
		2969
		2970	To implement race-free queueing, you simply add to the queue in the signal
		2971	handler but you block the signal handler in the watcher callback. Here is
		2972	an example that does that for some fictitious SIGUSR1 handler:
		2973
		2974	static ev_async mysig;
		2975
		2976	static void
		2977	sigusr1_handler (void)
		2978	{
		2979	sometype data;
		2980
		2981	// no locking etc.
		2982	queue_put (data);
		2983	ev_async_send (EV_DEFAULT_ &mysig);
		2984	}
		2985
		2986	static void
		2987	mysig_cb (EV_P_ ev_async *w, int revents)
		2988	{
		2989	sometype data;
		2990	sigset_t block, prev;
		2991
		2992	sigemptyset (&block);
		2993	sigaddset (&block, SIGUSR1);
		2994	sigprocmask (SIG_BLOCK, &block, &prev);
		2995
		2996	while (queue_get (&data))
		2997	process (data);
		2998
		2999	if (sigismember (&prev, SIGUSR1)
		3000	sigprocmask (SIG_UNBLOCK, &block, 0);
		3001	}
		3002
		3003	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3004	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3005	either...).
		3006
		3007	=item queueing from a thread context
		3008
		3009	The strategy for threads is different, as you cannot (easily) block
		3010	threads but you can easily preempt them, so to queue safely you need to
		3011	employ a traditional mutex lock, such as in this pthread example:
		3012
		3013	static ev_async mysig;
		3014	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3015
		3016	static void
		3017	otherthread (void)
		3018	{
		3019	// only need to lock the actual queueing operation
		3020	pthread_mutex_lock (&mymutex);
		3021	queue_put (data);
		3022	pthread_mutex_unlock (&mymutex);
		3023
		3024	ev_async_send (EV_DEFAULT_ &mysig);
		3025	}
		3026
		3027	static void
		3028	mysig_cb (EV_P_ ev_async *w, int revents)
		3029	{
		3030	pthread_mutex_lock (&mymutex);
		3031
		3032	while (queue_get (&data))
		3033	process (data);
		3034
		3035	pthread_mutex_unlock (&mymutex);
		3036	}
		3037
		3038	=back
		3039
		3040
		3041	=head3 Watcher-Specific Functions and Data Members
		3042
		3043	=over 4
		3044
		3045	=item ev_async_init (ev_async *, callback)
		3046
		3047	Initialises and configures the async watcher - it has no parameters of any
		3048	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3049	trust me.
		3050
		3051	=item ev_async_send (loop, ev_async *)
		3052
		3053	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3054	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3055	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3056	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3057	section below on what exactly this means).
		3058
		3059	Note that, as with other watchers in libev, multiple events might get
		3060	compressed into a single callback invocation (another way to look at this
		3061	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3062	reset when the event loop detects that).
		3063
		3064	This call incurs the overhead of a system call only once per event loop
		3065	iteration, so while the overhead might be noticeable, it doesn't apply to
		3066	repeated calls to C<ev_async_send> for the same event loop.
		3067
		3068	=item bool = ev_async_pending (ev_async *)
		3069
		3070	Returns a non-zero value when C<ev_async_send> has been called on the
		3071	watcher but the event has not yet been processed (or even noted) by the
		3072	event loop.
		3073
		3074	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3075	the loop iterates next and checks for the watcher to have become active,
		3076	it will reset the flag again. C<ev_async_pending> can be used to very
		3077	quickly check whether invoking the loop might be a good idea.
		3078
		3079	Not that this does I<not> check whether the watcher itself is pending,
		3080	only whether it has been requested to make this watcher pending: there
		3081	is a time window between the event loop checking and resetting the async
		3082	notification, and the callback being invoked.
		3083
		3084	=back
		3085
		3086
1765	=head1 OTHER FUNCTIONS	3087	=head1 OTHER FUNCTIONS
1766		3088
1767	There are some other functions of possible interest. Described. Here. Now.	3089	There are some other functions of possible interest. Described. Here. Now.
1768		3090
1769	=over 4	3091	=over 4
1770		3092
1771	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3093	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1772		3094
1773	This function combines a simple timer and an I/O watcher, calls your	3095	This function combines a simple timer and an I/O watcher, calls your
1774	callback on whichever event happens first and automatically stop both	3096	callback on whichever event happens first and automatically stops both
1775	watchers. This is useful if you want to wait for a single event on an fd	3097	watchers. This is useful if you want to wait for a single event on an fd
1776	or timeout without having to allocate/configure/start/stop/free one or	3098	or timeout without having to allocate/configure/start/stop/free one or
1777	more watchers yourself.	3099	more watchers yourself.
1778		3100
1779	If C<fd> is less than 0, then no I/O watcher will be started and events	3101	If C<fd> is less than 0, then no I/O watcher will be started and the
1780	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3102	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1781	C<events> set will be craeted and started.	3103	the given C<fd> and C<events> set will be created and started.
1782		3104
1783	If C<timeout> is less than 0, then no timeout watcher will be	3105	If C<timeout> is less than 0, then no timeout watcher will be
1784	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3106	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1785	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3107	repeat = 0) will be started. C<0> is a valid timeout.
1786	dubious value.
1787		3108
1788	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3109	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1789	passed an C<revents> set like normal event callbacks (a combination of	3110	passed an C<revents> set like normal event callbacks (a combination of
1790	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3111	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1791	value passed to C<ev_once>:	3112	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3113	a timeout and an io event at the same time - you probably should give io
		3114	events precedence.
1792		3115
		3116	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3117
1793	static void stdin_ready (int revents, void *arg)	3118	static void stdin_ready (int revents, void *arg)
1794	{	3119	{
1795	if (revents & EV_TIMEOUT)
1796	/* doh, nothing entered */;
1797	else if (revents & EV_READ)	3120	if (revents & EV_READ)
1798	/* stdin might have data for us, joy! */;	3121	/* stdin might have data for us, joy! */;
		3122	else if (revents & EV_TIMEOUT)
		3123	/* doh, nothing entered */;
1799	}	3124	}
1800		3125
1801	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3126	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1802		3127
1803	=item ev_feed_event (ev_loop *, watcher *, int revents)	3128	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1804		3129
1805	Feeds the given event set into the event loop, as if the specified event	3130	Feeds the given event set into the event loop, as if the specified event
1806	had happened for the specified watcher (which must be a pointer to an	3131	had happened for the specified watcher (which must be a pointer to an
1807	initialised but not necessarily started event watcher).	3132	initialised but not necessarily started event watcher).
1808		3133
1809	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3134	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1810		3135
1811	Feed an event on the given fd, as if a file descriptor backend detected	3136	Feed an event on the given fd, as if a file descriptor backend detected
1812	the given events it.	3137	the given events it.
1813		3138
1814	=item ev_feed_signal_event (ev_loop *loop, int signum)	3139	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1815		3140
1816	Feed an event as if the given signal occured (C<loop> must be the default	3141	Feed an event as if the given signal occurred (C<loop> must be the default
1817	loop!).	3142	loop!).
1818		3143
1819	=back	3144	=back
1820		3145
1821		3146
…		…
1837		3162
1838	=item * Priorities are not currently supported. Initialising priorities	3163	=item * Priorities are not currently supported. Initialising priorities
1839	will fail and all watchers will have the same priority, even though there	3164	will fail and all watchers will have the same priority, even though there
1840	is an ev_pri field.	3165	is an ev_pri field.
1841		3166
		3167	=item * In libevent, the last base created gets the signals, in libev, the
		3168	first base created (== the default loop) gets the signals.
		3169
1842	=item * Other members are not supported.	3170	=item * Other members are not supported.
1843		3171
1844	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3172	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1845	to use the libev header file and library.	3173	to use the libev header file and library.
1846		3174
1847	=back	3175	=back
1848		3176
1849	=head1 C++ SUPPORT	3177	=head1 C++ SUPPORT
1850		3178
1851	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3179	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1852	you to use some convinience methods to start/stop watchers and also change	3180	you to use some convenience methods to start/stop watchers and also change
1853	the callback model to a model using method callbacks on objects.	3181	the callback model to a model using method callbacks on objects.
1854		3182
1855	To use it,	3183	To use it,
1856		3184
1857	#include <ev++.h>	3185	#include <ev++.h>
1858		3186
1859	This automatically includes F<ev.h> and puts all of its definitions (many	3187	This automatically includes F<ev.h> and puts all of its definitions (many
1860	of them macros) into the global namespace. All C++ specific things are	3188	of them macros) into the global namespace. All C++ specific things are
1861	put into the C<ev> namespace. It should support all the same embedding	3189	put into the C<ev> namespace. It should support all the same embedding
1862	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3190	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1929	your compiler is good :), then the method will be fully inlined into the	3257	your compiler is good :), then the method will be fully inlined into the
1930	thunking function, making it as fast as a direct C callback.	3258	thunking function, making it as fast as a direct C callback.
1931		3259
1932	Example: simple class declaration and watcher initialisation	3260	Example: simple class declaration and watcher initialisation
1933		3261
1934	struct myclass	3262	struct myclass
1935	{	3263	{
1936	void io_cb (ev::io &w, int revents) { }	3264	void io_cb (ev::io &w, int revents) { }
1937	}	3265	}
1938		3266
1939	myclass obj;	3267	myclass obj;
1940	ev::io iow;	3268	ev::io iow;
1941	iow.set <myclass, &myclass::io_cb> (&obj);	3269	iow.set <myclass, &myclass::io_cb> (&obj);
		3270
		3271	=item w->set (object *)
		3272
		3273	This is an B<experimental> feature that might go away in a future version.
		3274
		3275	This is a variation of a method callback - leaving out the method to call
		3276	will default the method to C<operator ()>, which makes it possible to use
		3277	functor objects without having to manually specify the C<operator ()> all
		3278	the time. Incidentally, you can then also leave out the template argument
		3279	list.
		3280
		3281	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3282	int revents)>.
		3283
		3284	See the method-C<set> above for more details.
		3285
		3286	Example: use a functor object as callback.
		3287
		3288	struct myfunctor
		3289	{
		3290	void operator() (ev::io &w, int revents)
		3291	{
		3292	...
		3293	}
		3294	}
		3295
		3296	myfunctor f;
		3297
		3298	ev::io w;
		3299	w.set (&f);
1942		3300
1943	=item w->set<function> (void *data = 0)	3301	=item w->set<function> (void *data = 0)
1944		3302
1945	Also sets a callback, but uses a static method or plain function as	3303	Also sets a callback, but uses a static method or plain function as
1946	callback. The optional C<data> argument will be stored in the watcher's	3304	callback. The optional C<data> argument will be stored in the watcher's
…		…
1948		3306
1949	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3307	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1950		3308
1951	See the method-C<set> above for more details.	3309	See the method-C<set> above for more details.
1952		3310
1953	Example:	3311	Example: Use a plain function as callback.
1954		3312
1955	static void io_cb (ev::io &w, int revents) { }	3313	static void io_cb (ev::io &w, int revents) { }
1956	iow.set <io_cb> ();	3314	iow.set <io_cb> ();
1957		3315
1958	=item w->set (struct ev_loop *)	3316	=item w->set (struct ev_loop *)
1959		3317
1960	Associates a different C<struct ev_loop> with this watcher. You can only	3318	Associates a different C<struct ev_loop> with this watcher. You can only
1961	do this when the watcher is inactive (and not pending either).	3319	do this when the watcher is inactive (and not pending either).
1962		3320
1963	=item w->set ([args])	3321	=item w->set ([arguments])
1964		3322
1965	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3323	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1966	called at least once. Unlike the C counterpart, an active watcher gets	3324	called at least once. Unlike the C counterpart, an active watcher gets
1967	automatically stopped and restarted when reconfiguring it with this	3325	automatically stopped and restarted when reconfiguring it with this
1968	method.	3326	method.
1969		3327
1970	=item w->start ()	3328	=item w->start ()
…		…
1974		3332
1975	=item w->stop ()	3333	=item w->stop ()
1976		3334
1977	Stops the watcher if it is active. Again, no C<loop> argument.	3335	Stops the watcher if it is active. Again, no C<loop> argument.
1978		3336
1979	=item w->again () C<ev::timer>, C<ev::periodic> only	3337	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1980		3338
1981	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3339	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1982	C<ev_TYPE_again> function.	3340	C<ev_TYPE_again> function.
1983		3341
1984	=item w->sweep () C<ev::embed> only	3342	=item w->sweep () (C<ev::embed> only)
1985		3343
1986	Invokes C<ev_embed_sweep>.	3344	Invokes C<ev_embed_sweep>.
1987		3345
1988	=item w->update () C<ev::stat> only	3346	=item w->update () (C<ev::stat> only)
1989		3347
1990	Invokes C<ev_stat_stat>.	3348	Invokes C<ev_stat_stat>.
1991		3349
1992	=back	3350	=back
1993		3351
1994	=back	3352	=back
1995		3353
1996	Example: Define a class with an IO and idle watcher, start one of them in	3354	Example: Define a class with an IO and idle watcher, start one of them in
1997	the constructor.	3355	the constructor.
1998		3356
1999	class myclass	3357	class myclass
2000	{	3358	{
2001	ev_io io; void io_cb (ev::io &w, int revents);	3359	ev::io io ; void io_cb (ev::io &w, int revents);
2002	ev_idle idle void idle_cb (ev::idle &w, int revents);	3360	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2003		3361
2004	myclass ();	3362	myclass (int fd)
2005	}	3363	{
2006
2007	myclass::myclass (int fd)
2008	{
2009	io .set <myclass, &myclass::io_cb > (this);	3364	io .set <myclass, &myclass::io_cb > (this);
2010	idle.set <myclass, &myclass::idle_cb> (this);	3365	idle.set <myclass, &myclass::idle_cb> (this);
2011		3366
2012	io.start (fd, ev::READ);	3367	io.start (fd, ev::READ);
		3368	}
2013	}	3369	};
		3370
		3371
		3372	=head1 OTHER LANGUAGE BINDINGS
		3373
		3374	Libev does not offer other language bindings itself, but bindings for a
		3375	number of languages exist in the form of third-party packages. If you know
		3376	any interesting language binding in addition to the ones listed here, drop
		3377	me a note.
		3378
		3379	=over 4
		3380
		3381	=item Perl
		3382
		3383	The EV module implements the full libev API and is actually used to test
		3384	libev. EV is developed together with libev. Apart from the EV core module,
		3385	there are additional modules that implement libev-compatible interfaces
		3386	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3387	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3388	and C<EV::Glib>).
		3389
		3390	It can be found and installed via CPAN, its homepage is at
		3391	L<http://software.schmorp.de/pkg/EV>.
		3392
		3393	=item Python
		3394
		3395	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3396	seems to be quite complete and well-documented.
		3397
		3398	=item Ruby
		3399
		3400	Tony Arcieri has written a ruby extension that offers access to a subset
		3401	of the libev API and adds file handle abstractions, asynchronous DNS and
		3402	more on top of it. It can be found via gem servers. Its homepage is at
		3403	L<http://rev.rubyforge.org/>.
		3404
		3405	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3406	makes rev work even on mingw.
		3407
		3408	=item Haskell
		3409
		3410	A haskell binding to libev is available at
		3411	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3412
		3413	=item D
		3414
		3415	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3416	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3417
		3418	=item Ocaml
		3419
		3420	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3421	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3422
		3423	=item Lua
		3424
		3425	Brian Maher has written a partial interface to libev
		3426	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3427	L<http://github.com/brimworks/lua-ev>.
		3428
		3429	=back
2014		3430
2015		3431
2016	=head1 MACRO MAGIC	3432	=head1 MACRO MAGIC
2017		3433
2018	Libev can be compiled with a variety of options, the most fundemantal is	3434	Libev can be compiled with a variety of options, the most fundamental
2019	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3435	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2020	callbacks have an initial C<struct ev_loop *> argument.	3436	functions and callbacks have an initial C<struct ev_loop *> argument.
2021		3437
2022	To make it easier to write programs that cope with either variant, the	3438	To make it easier to write programs that cope with either variant, the
2023	following macros are defined:	3439	following macros are defined:
2024		3440
2025	=over 4	3441	=over 4
…		…
2028		3444
2029	This provides the loop I<argument> for functions, if one is required ("ev	3445	This provides the loop I<argument> for functions, if one is required ("ev
2030	loop argument"). The C<EV_A> form is used when this is the sole argument,	3446	loop argument"). The C<EV_A> form is used when this is the sole argument,
2031	C<EV_A_> is used when other arguments are following. Example:	3447	C<EV_A_> is used when other arguments are following. Example:
2032		3448
2033	ev_unref (EV_A);	3449	ev_unref (EV_A);
2034	ev_timer_add (EV_A_ watcher);	3450	ev_timer_add (EV_A_ watcher);
2035	ev_loop (EV_A_ 0);	3451	ev_loop (EV_A_ 0);
2036		3452
2037	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3453	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2038	which is often provided by the following macro.	3454	which is often provided by the following macro.
2039		3455
2040	=item C<EV_P>, C<EV_P_>	3456	=item C<EV_P>, C<EV_P_>
2041		3457
2042	This provides the loop I<parameter> for functions, if one is required ("ev	3458	This provides the loop I<parameter> for functions, if one is required ("ev
2043	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3459	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2044	C<EV_P_> is used when other parameters are following. Example:	3460	C<EV_P_> is used when other parameters are following. Example:
2045		3461
2046	// this is how ev_unref is being declared	3462	// this is how ev_unref is being declared
2047	static void ev_unref (EV_P);	3463	static void ev_unref (EV_P);
2048		3464
2049	// this is how you can declare your typical callback	3465	// this is how you can declare your typical callback
2050	static void cb (EV_P_ ev_timer *w, int revents)	3466	static void cb (EV_P_ ev_timer *w, int revents)
2051		3467
2052	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3468	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2053	suitable for use with C<EV_A>.	3469	suitable for use with C<EV_A>.
2054		3470
2055	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3471	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2056		3472
2057	Similar to the other two macros, this gives you the value of the default	3473	Similar to the other two macros, this gives you the value of the default
2058	loop, if multiple loops are supported ("ev loop default").	3474	loop, if multiple loops are supported ("ev loop default").
		3475
		3476	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3477
		3478	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3479	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3480	is undefined when the default loop has not been initialised by a previous
		3481	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3482
		3483	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3484	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2059		3485
2060	=back	3486	=back
2061		3487
2062	Example: Declare and initialise a check watcher, utilising the above	3488	Example: Declare and initialise a check watcher, utilising the above
2063	macros so it will work regardless of whether multiple loops are supported	3489	macros so it will work regardless of whether multiple loops are supported
2064	or not.	3490	or not.
2065		3491
2066	static void	3492	static void
2067	check_cb (EV_P_ ev_timer *w, int revents)	3493	check_cb (EV_P_ ev_timer *w, int revents)
2068	{	3494	{
2069	ev_check_stop (EV_A_ w);	3495	ev_check_stop (EV_A_ w);
2070	}	3496	}
2071		3497
2072	ev_check check;	3498	ev_check check;
2073	ev_check_init (&check, check_cb);	3499	ev_check_init (&check, check_cb);
2074	ev_check_start (EV_DEFAULT_ &check);	3500	ev_check_start (EV_DEFAULT_ &check);
2075	ev_loop (EV_DEFAULT_ 0);	3501	ev_loop (EV_DEFAULT_ 0);
2076		3502
2077	=head1 EMBEDDING	3503	=head1 EMBEDDING
2078		3504
2079	Libev can (and often is) directly embedded into host	3505	Libev can (and often is) directly embedded into host
2080	applications. Examples of applications that embed it include the Deliantra	3506	applications. Examples of applications that embed it include the Deliantra
2081	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3507	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2082	and rxvt-unicode.	3508	and rxvt-unicode.
2083		3509
2084	The goal is to enable you to just copy the neecssary files into your	3510	The goal is to enable you to just copy the necessary files into your
2085	source directory without having to change even a single line in them, so	3511	source directory without having to change even a single line in them, so
2086	you can easily upgrade by simply copying (or having a checked-out copy of	3512	you can easily upgrade by simply copying (or having a checked-out copy of
2087	libev somewhere in your source tree).	3513	libev somewhere in your source tree).
2088		3514
2089	=head2 FILESETS	3515	=head2 FILESETS
2090		3516
2091	Depending on what features you need you need to include one or more sets of files	3517	Depending on what features you need you need to include one or more sets of files
2092	in your app.	3518	in your application.
2093		3519
2094	=head3 CORE EVENT LOOP	3520	=head3 CORE EVENT LOOP
2095		3521
2096	To include only the libev core (all the C<ev_*> functions), with manual	3522	To include only the libev core (all the C<ev_*> functions), with manual
2097	configuration (no autoconf):	3523	configuration (no autoconf):
2098		3524
2099	#define EV_STANDALONE 1	3525	#define EV_STANDALONE 1
2100	#include "ev.c"	3526	#include "ev.c"
2101		3527
2102	This will automatically include F<ev.h>, too, and should be done in a	3528	This will automatically include F<ev.h>, too, and should be done in a
2103	single C source file only to provide the function implementations. To use	3529	single C source file only to provide the function implementations. To use
2104	it, do the same for F<ev.h> in all files wishing to use this API (best	3530	it, do the same for F<ev.h> in all files wishing to use this API (best
2105	done by writing a wrapper around F<ev.h> that you can include instead and	3531	done by writing a wrapper around F<ev.h> that you can include instead and
2106	where you can put other configuration options):	3532	where you can put other configuration options):
2107		3533
2108	#define EV_STANDALONE 1	3534	#define EV_STANDALONE 1
2109	#include "ev.h"	3535	#include "ev.h"
2110		3536
2111	Both header files and implementation files can be compiled with a C++	3537	Both header files and implementation files can be compiled with a C++
2112	compiler (at least, thats a stated goal, and breakage will be treated	3538	compiler (at least, that's a stated goal, and breakage will be treated
2113	as a bug).	3539	as a bug).
2114		3540
2115	You need the following files in your source tree, or in a directory	3541	You need the following files in your source tree, or in a directory
2116	in your include path (e.g. in libev/ when using -Ilibev):	3542	in your include path (e.g. in libev/ when using -Ilibev):
2117		3543
2118	ev.h	3544	ev.h
2119	ev.c	3545	ev.c
2120	ev_vars.h	3546	ev_vars.h
2121	ev_wrap.h	3547	ev_wrap.h
2122		3548
2123	ev_win32.c required on win32 platforms only	3549	ev_win32.c required on win32 platforms only
2124		3550
2125	ev_select.c only when select backend is enabled (which is enabled by default)	3551	ev_select.c only when select backend is enabled (which is enabled by default)
2126	ev_poll.c only when poll backend is enabled (disabled by default)	3552	ev_poll.c only when poll backend is enabled (disabled by default)
2127	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3553	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2128	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3554	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2129	ev_port.c only when the solaris port backend is enabled (disabled by default)	3555	ev_port.c only when the solaris port backend is enabled (disabled by default)
2130		3556
2131	F<ev.c> includes the backend files directly when enabled, so you only need	3557	F<ev.c> includes the backend files directly when enabled, so you only need
2132	to compile this single file.	3558	to compile this single file.
2133		3559
2134	=head3 LIBEVENT COMPATIBILITY API	3560	=head3 LIBEVENT COMPATIBILITY API
2135		3561
2136	To include the libevent compatibility API, also include:	3562	To include the libevent compatibility API, also include:
2137		3563
2138	#include "event.c"	3564	#include "event.c"
2139		3565
2140	in the file including F<ev.c>, and:	3566	in the file including F<ev.c>, and:
2141		3567
2142	#include "event.h"	3568	#include "event.h"
2143		3569
2144	in the files that want to use the libevent API. This also includes F<ev.h>.	3570	in the files that want to use the libevent API. This also includes F<ev.h>.
2145		3571
2146	You need the following additional files for this:	3572	You need the following additional files for this:
2147		3573
2148	event.h	3574	event.h
2149	event.c	3575	event.c
2150		3576
2151	=head3 AUTOCONF SUPPORT	3577	=head3 AUTOCONF SUPPORT
2152		3578
2153	Instead of using C<EV_STANDALONE=1> and providing your config in	3579	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2154	whatever way you want, you can also C<m4_include([libev.m4])> in your	3580	whatever way you want, you can also C<m4_include([libev.m4])> in your
2155	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3581	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2156	include F<config.h> and configure itself accordingly.	3582	include F<config.h> and configure itself accordingly.
2157		3583
2158	For this of course you need the m4 file:	3584	For this of course you need the m4 file:
2159		3585
2160	libev.m4	3586	libev.m4
2161		3587
2162	=head2 PREPROCESSOR SYMBOLS/MACROS	3588	=head2 PREPROCESSOR SYMBOLS/MACROS
2163		3589
2164	Libev can be configured via a variety of preprocessor symbols you have to define	3590	Libev can be configured via a variety of preprocessor symbols you have to
2165	before including any of its files. The default is not to build for multiplicity	3591	define before including any of its files. The default in the absence of
2166	and only include the select backend.	3592	autoconf is documented for every option.
2167		3593
2168	=over 4	3594	=over 4
2169		3595
2170	=item EV_STANDALONE	3596	=item EV_STANDALONE
2171		3597
…		…
2173	keeps libev from including F<config.h>, and it also defines dummy	3599	keeps libev from including F<config.h>, and it also defines dummy
2174	implementations for some libevent functions (such as logging, which is not	3600	implementations for some libevent functions (such as logging, which is not
2175	supported). It will also not define any of the structs usually found in	3601	supported). It will also not define any of the structs usually found in
2176	F<event.h> that are not directly supported by the libev core alone.	3602	F<event.h> that are not directly supported by the libev core alone.
2177		3603
		3604	In standalone mode, libev will still try to automatically deduce the
		3605	configuration, but has to be more conservative.
		3606
2178	=item EV_USE_MONOTONIC	3607	=item EV_USE_MONOTONIC
2179		3608
2180	If defined to be C<1>, libev will try to detect the availability of the	3609	If defined to be C<1>, libev will try to detect the availability of the
2181	monotonic clock option at both compiletime and runtime. Otherwise no use	3610	monotonic clock option at both compile time and runtime. Otherwise no
2182	of the monotonic clock option will be attempted. If you enable this, you	3611	use of the monotonic clock option will be attempted. If you enable this,
2183	usually have to link against librt or something similar. Enabling it when	3612	you usually have to link against librt or something similar. Enabling it
2184	the functionality isn't available is safe, though, althoguh you have	3613	when the functionality isn't available is safe, though, although you have
2185	to make sure you link against any libraries where the C<clock_gettime>	3614	to make sure you link against any libraries where the C<clock_gettime>
2186	function is hiding in (often F<-lrt>).	3615	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2187		3616
2188	=item EV_USE_REALTIME	3617	=item EV_USE_REALTIME
2189		3618
2190	If defined to be C<1>, libev will try to detect the availability of the	3619	If defined to be C<1>, libev will try to detect the availability of the
2191	realtime clock option at compiletime (and assume its availability at	3620	real-time clock option at compile time (and assume its availability
2192	runtime if successful). Otherwise no use of the realtime clock option will	3621	at runtime if successful). Otherwise no use of the real-time clock
2193	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3622	option will be attempted. This effectively replaces C<gettimeofday>
2194	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3623	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2195	in the description of C<EV_USE_MONOTONIC>, though.	3624	correctness. See the note about libraries in the description of
		3625	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3626	C<EV_USE_CLOCK_SYSCALL>.
		3627
		3628	=item EV_USE_CLOCK_SYSCALL
		3629
		3630	If defined to be C<1>, libev will try to use a direct syscall instead
		3631	of calling the system-provided C<clock_gettime> function. This option
		3632	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3633	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3634	programs needlessly. Using a direct syscall is slightly slower (in
		3635	theory), because no optimised vdso implementation can be used, but avoids
		3636	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3637	higher, as it simplifies linking (no need for C<-lrt>).
		3638
		3639	=item EV_USE_NANOSLEEP
		3640
		3641	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3642	and will use it for delays. Otherwise it will use C<select ()>.
		3643
		3644	=item EV_USE_EVENTFD
		3645
		3646	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3647	available and will probe for kernel support at runtime. This will improve
		3648	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3649	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3650	2.7 or newer, otherwise disabled.
2196		3651
2197	=item EV_USE_SELECT	3652	=item EV_USE_SELECT
2198		3653
2199	If undefined or defined to be C<1>, libev will compile in support for the	3654	If undefined or defined to be C<1>, libev will compile in support for the
2200	C<select>(2) backend. No attempt at autodetection will be done: if no	3655	C<select>(2) backend. No attempt at auto-detection will be done: if no
2201	other method takes over, select will be it. Otherwise the select backend	3656	other method takes over, select will be it. Otherwise the select backend
2202	will not be compiled in.	3657	will not be compiled in.
2203		3658
2204	=item EV_SELECT_USE_FD_SET	3659	=item EV_SELECT_USE_FD_SET
2205		3660
2206	If defined to C<1>, then the select backend will use the system C<fd_set>	3661	If defined to C<1>, then the select backend will use the system C<fd_set>
2207	structure. This is useful if libev doesn't compile due to a missing	3662	structure. This is useful if libev doesn't compile due to a missing
2208	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3663	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2209	exotic systems. This usually limits the range of file descriptors to some	3664	on exotic systems. This usually limits the range of file descriptors to
2210	low limit such as 1024 or might have other limitations (winsocket only	3665	some low limit such as 1024 or might have other limitations (winsocket
2211	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3666	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2212	influence the size of the C<fd_set> used.	3667	configures the maximum size of the C<fd_set>.
2213		3668
2214	=item EV_SELECT_IS_WINSOCKET	3669	=item EV_SELECT_IS_WINSOCKET
2215		3670
2216	When defined to C<1>, the select backend will assume that	3671	When defined to C<1>, the select backend will assume that
2217	select/socket/connect etc. don't understand file descriptors but	3672	select/socket/connect etc. don't understand file descriptors but
…		…
2219	be used is the winsock select). This means that it will call	3674	be used is the winsock select). This means that it will call
2220	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3675	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2221	it is assumed that all these functions actually work on fds, even	3676	it is assumed that all these functions actually work on fds, even
2222	on win32. Should not be defined on non-win32 platforms.	3677	on win32. Should not be defined on non-win32 platforms.
2223		3678
		3679	=item EV_FD_TO_WIN32_HANDLE(fd)
		3680
		3681	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3682	file descriptors to socket handles. When not defining this symbol (the
		3683	default), then libev will call C<_get_osfhandle>, which is usually
		3684	correct. In some cases, programs use their own file descriptor management,
		3685	in which case they can provide this function to map fds to socket handles.
		3686
		3687	=item EV_WIN32_HANDLE_TO_FD(handle)
		3688
		3689	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3690	using the standard C<_open_osfhandle> function. For programs implementing
		3691	their own fd to handle mapping, overwriting this function makes it easier
		3692	to do so. This can be done by defining this macro to an appropriate value.
		3693
		3694	=item EV_WIN32_CLOSE_FD(fd)
		3695
		3696	If programs implement their own fd to handle mapping on win32, then this
		3697	macro can be used to override the C<close> function, useful to unregister
		3698	file descriptors again. Note that the replacement function has to close
		3699	the underlying OS handle.
		3700
2224	=item EV_USE_POLL	3701	=item EV_USE_POLL
2225		3702
2226	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3703	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2227	backend. Otherwise it will be enabled on non-win32 platforms. It	3704	backend. Otherwise it will be enabled on non-win32 platforms. It
2228	takes precedence over select.	3705	takes precedence over select.
2229		3706
2230	=item EV_USE_EPOLL	3707	=item EV_USE_EPOLL
2231		3708
2232	If defined to be C<1>, libev will compile in support for the Linux	3709	If defined to be C<1>, libev will compile in support for the Linux
2233	C<epoll>(7) backend. Its availability will be detected at runtime,	3710	C<epoll>(7) backend. Its availability will be detected at runtime,
2234	otherwise another method will be used as fallback. This is the	3711	otherwise another method will be used as fallback. This is the preferred
2235	preferred backend for GNU/Linux systems.	3712	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3713	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2236		3714
2237	=item EV_USE_KQUEUE	3715	=item EV_USE_KQUEUE
2238		3716
2239	If defined to be C<1>, libev will compile in support for the BSD style	3717	If defined to be C<1>, libev will compile in support for the BSD style
2240	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3718	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2253	otherwise another method will be used as fallback. This is the preferred	3731	otherwise another method will be used as fallback. This is the preferred
2254	backend for Solaris 10 systems.	3732	backend for Solaris 10 systems.
2255		3733
2256	=item EV_USE_DEVPOLL	3734	=item EV_USE_DEVPOLL
2257		3735
2258	reserved for future expansion, works like the USE symbols above.	3736	Reserved for future expansion, works like the USE symbols above.
2259		3737
2260	=item EV_USE_INOTIFY	3738	=item EV_USE_INOTIFY
2261		3739
2262	If defined to be C<1>, libev will compile in support for the Linux inotify	3740	If defined to be C<1>, libev will compile in support for the Linux inotify
2263	interface to speed up C<ev_stat> watchers. Its actual availability will	3741	interface to speed up C<ev_stat> watchers. Its actual availability will
2264	be detected at runtime.	3742	be detected at runtime. If undefined, it will be enabled if the headers
		3743	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3744
		3745	=item EV_ATOMIC_T
		3746
		3747	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3748	access is atomic with respect to other threads or signal contexts. No such
		3749	type is easily found in the C language, so you can provide your own type
		3750	that you know is safe for your purposes. It is used both for signal handler "locking"
		3751	as well as for signal and thread safety in C<ev_async> watchers.
		3752
		3753	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3754	(from F<signal.h>), which is usually good enough on most platforms.
2265		3755
2266	=item EV_H	3756	=item EV_H
2267		3757
2268	The name of the F<ev.h> header file used to include it. The default if	3758	The name of the F<ev.h> header file used to include it. The default if
2269	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3759	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2270	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3760	used to virtually rename the F<ev.h> header file in case of conflicts.
2271		3761
2272	=item EV_CONFIG_H	3762	=item EV_CONFIG_H
2273		3763
2274	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3764	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2275	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3765	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2276	C<EV_H>, above.	3766	C<EV_H>, above.
2277		3767
2278	=item EV_EVENT_H	3768	=item EV_EVENT_H
2279		3769
2280	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3770	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2281	of how the F<event.h> header can be found.	3771	of how the F<event.h> header can be found, the default is C<"event.h">.
2282		3772
2283	=item EV_PROTOTYPES	3773	=item EV_PROTOTYPES
2284		3774
2285	If defined to be C<0>, then F<ev.h> will not define any function	3775	If defined to be C<0>, then F<ev.h> will not define any function
2286	prototypes, but still define all the structs and other symbols. This is	3776	prototypes, but still define all the structs and other symbols. This is
…		…
2307	When doing priority-based operations, libev usually has to linearly search	3797	When doing priority-based operations, libev usually has to linearly search
2308	all the priorities, so having many of them (hundreds) uses a lot of space	3798	all the priorities, so having many of them (hundreds) uses a lot of space
2309	and time, so using the defaults of five priorities (-2 .. +2) is usually	3799	and time, so using the defaults of five priorities (-2 .. +2) is usually
2310	fine.	3800	fine.
2311		3801
2312	If your embedding app does not need any priorities, defining these both to	3802	If your embedding application does not need any priorities, defining these
2313	C<0> will save some memory and cpu.	3803	both to C<0> will save some memory and CPU.
2314		3804
2315	=item EV_PERIODIC_ENABLE	3805	=item EV_PERIODIC_ENABLE
2316		3806
2317	If undefined or defined to be C<1>, then periodic timers are supported. If	3807	If undefined or defined to be C<1>, then periodic timers are supported. If
2318	defined to be C<0>, then they are not. Disabling them saves a few kB of	3808	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2325	code.	3815	code.
2326		3816
2327	=item EV_EMBED_ENABLE	3817	=item EV_EMBED_ENABLE
2328		3818
2329	If undefined or defined to be C<1>, then embed watchers are supported. If	3819	If undefined or defined to be C<1>, then embed watchers are supported. If
2330	defined to be C<0>, then they are not.	3820	defined to be C<0>, then they are not. Embed watchers rely on most other
		3821	watcher types, which therefore must not be disabled.
2331		3822
2332	=item EV_STAT_ENABLE	3823	=item EV_STAT_ENABLE
2333		3824
2334	If undefined or defined to be C<1>, then stat watchers are supported. If	3825	If undefined or defined to be C<1>, then stat watchers are supported. If
2335	defined to be C<0>, then they are not.	3826	defined to be C<0>, then they are not.
…		…
2337	=item EV_FORK_ENABLE	3828	=item EV_FORK_ENABLE
2338		3829
2339	If undefined or defined to be C<1>, then fork watchers are supported. If	3830	If undefined or defined to be C<1>, then fork watchers are supported. If
2340	defined to be C<0>, then they are not.	3831	defined to be C<0>, then they are not.
2341		3832
		3833	=item EV_ASYNC_ENABLE
		3834
		3835	If undefined or defined to be C<1>, then async watchers are supported. If
		3836	defined to be C<0>, then they are not.
		3837
2342	=item EV_MINIMAL	3838	=item EV_MINIMAL
2343		3839
2344	If you need to shave off some kilobytes of code at the expense of some	3840	If you need to shave off some kilobytes of code at the expense of some
2345	speed, define this symbol to C<1>. Currently only used for gcc to override	3841	speed (but with the full API), define this symbol to C<1>. Currently this
2346	some inlining decisions, saves roughly 30% codesize of amd64.	3842	is used to override some inlining decisions, saves roughly 30% code size
		3843	on amd64. It also selects a much smaller 2-heap for timer management over
		3844	the default 4-heap.
		3845
		3846	You can save even more by disabling watcher types you do not need
		3847	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3848	(C<-DNDEBUG>) will usually reduce code size a lot.
		3849
		3850	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3851	provide a bare-bones event library. See C<ev.h> for details on what parts
		3852	of the API are still available, and do not complain if this subset changes
		3853	over time.
		3854
		3855	=item EV_NSIG
		3856
		3857	The highest supported signal number, +1 (or, the number of
		3858	signals): Normally, libev tries to deduce the maximum number of signals
		3859	automatically, but sometimes this fails, in which case it can be
		3860	specified. Also, using a lower number than detected (C<32> should be
		3861	good for about any system in existance) can save some memory, as libev
		3862	statically allocates some 12-24 bytes per signal number.
2347		3863
2348	=item EV_PID_HASHSIZE	3864	=item EV_PID_HASHSIZE
2349		3865
2350	C<ev_child> watchers use a small hash table to distribute workload by	3866	C<ev_child> watchers use a small hash table to distribute workload by
2351	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3867	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2352	than enough. If you need to manage thousands of children you might want to	3868	than enough. If you need to manage thousands of children you might want to
2353	increase this value (I<must> be a power of two).	3869	increase this value (I<must> be a power of two).
2354		3870
2355	=item EV_INOTIFY_HASHSIZE	3871	=item EV_INOTIFY_HASHSIZE
2356		3872
2357	C<ev_staz> watchers use a small hash table to distribute workload by	3873	C<ev_stat> watchers use a small hash table to distribute workload by
2358	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3874	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2359	usually more than enough. If you need to manage thousands of C<ev_stat>	3875	usually more than enough. If you need to manage thousands of C<ev_stat>
2360	watchers you might want to increase this value (I<must> be a power of	3876	watchers you might want to increase this value (I<must> be a power of
2361	two).	3877	two).
2362		3878
		3879	=item EV_USE_4HEAP
		3880
		3881	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3882	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3883	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3884	faster performance with many (thousands) of watchers.
		3885
		3886	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3887	(disabled).
		3888
		3889	=item EV_HEAP_CACHE_AT
		3890
		3891	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3892	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3893	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3894	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3895	but avoids random read accesses on heap changes. This improves performance
		3896	noticeably with many (hundreds) of watchers.
		3897
		3898	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3899	(disabled).
		3900
		3901	=item EV_VERIFY
		3902
		3903	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3904	be done: If set to C<0>, no internal verification code will be compiled
		3905	in. If set to C<1>, then verification code will be compiled in, but not
		3906	called. If set to C<2>, then the internal verification code will be
		3907	called once per loop, which can slow down libev. If set to C<3>, then the
		3908	verification code will be called very frequently, which will slow down
		3909	libev considerably.
		3910
		3911	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3912	C<0>.
		3913
2363	=item EV_COMMON	3914	=item EV_COMMON
2364		3915
2365	By default, all watchers have a C<void *data> member. By redefining	3916	By default, all watchers have a C<void *data> member. By redefining
2366	this macro to a something else you can include more and other types of	3917	this macro to a something else you can include more and other types of
2367	members. You have to define it each time you include one of the files,	3918	members. You have to define it each time you include one of the files,
2368	though, and it must be identical each time.	3919	though, and it must be identical each time.
2369		3920
2370	For example, the perl EV module uses something like this:	3921	For example, the perl EV module uses something like this:
2371		3922
2372	#define EV_COMMON \	3923	#define EV_COMMON \
2373	SV *self; /* contains this struct */ \	3924	SV *self; /* contains this struct */ \
2374	SV *cb_sv, *fh /* note no trailing ";" */	3925	SV *cb_sv, *fh /* note no trailing ";" */
2375		3926
2376	=item EV_CB_DECLARE (type)	3927	=item EV_CB_DECLARE (type)
2377		3928
2378	=item EV_CB_INVOKE (watcher, revents)	3929	=item EV_CB_INVOKE (watcher, revents)
2379		3930
2380	=item ev_set_cb (ev, cb)	3931	=item ev_set_cb (ev, cb)
2381		3932
2382	Can be used to change the callback member declaration in each watcher,	3933	Can be used to change the callback member declaration in each watcher,
2383	and the way callbacks are invoked and set. Must expand to a struct member	3934	and the way callbacks are invoked and set. Must expand to a struct member
2384	definition and a statement, respectively. See the F<ev.v> header file for	3935	definition and a statement, respectively. See the F<ev.h> header file for
2385	their default definitions. One possible use for overriding these is to	3936	their default definitions. One possible use for overriding these is to
2386	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3937	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2387	method calls instead of plain function calls in C++.	3938	method calls instead of plain function calls in C++.
		3939
		3940	=back
		3941
		3942	=head2 EXPORTED API SYMBOLS
		3943
		3944	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3945	exported symbols, you can use the provided F<Symbol.*> files which list
		3946	all public symbols, one per line:
		3947
		3948	Symbols.ev for libev proper
		3949	Symbols.event for the libevent emulation
		3950
		3951	This can also be used to rename all public symbols to avoid clashes with
		3952	multiple versions of libev linked together (which is obviously bad in
		3953	itself, but sometimes it is inconvenient to avoid this).
		3954
		3955	A sed command like this will create wrapper C<#define>'s that you need to
		3956	include before including F<ev.h>:
		3957
		3958	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3959
		3960	This would create a file F<wrap.h> which essentially looks like this:
		3961
		3962	#define ev_backend myprefix_ev_backend
		3963	#define ev_check_start myprefix_ev_check_start
		3964	#define ev_check_stop myprefix_ev_check_stop
		3965	...
2388		3966
2389	=head2 EXAMPLES	3967	=head2 EXAMPLES
2390		3968
2391	For a real-world example of a program the includes libev	3969	For a real-world example of a program the includes libev
2392	verbatim, you can have a look at the EV perl module	3970	verbatim, you can have a look at the EV perl module
…		…
2397	file.	3975	file.
2398		3976
2399	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3977	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2400	that everybody includes and which overrides some configure choices:	3978	that everybody includes and which overrides some configure choices:
2401		3979
2402	#define EV_MINIMAL 1	3980	#define EV_MINIMAL 1
2403	#define EV_USE_POLL 0	3981	#define EV_USE_POLL 0
2404	#define EV_MULTIPLICITY 0	3982	#define EV_MULTIPLICITY 0
2405	#define EV_PERIODIC_ENABLE 0	3983	#define EV_PERIODIC_ENABLE 0
2406	#define EV_STAT_ENABLE 0	3984	#define EV_STAT_ENABLE 0
2407	#define EV_FORK_ENABLE 0	3985	#define EV_FORK_ENABLE 0
2408	#define EV_CONFIG_H <config.h>	3986	#define EV_CONFIG_H <config.h>
2409	#define EV_MINPRI 0	3987	#define EV_MINPRI 0
2410	#define EV_MAXPRI 0	3988	#define EV_MAXPRI 0
2411		3989
2412	#include "ev++.h"	3990	#include "ev++.h"
2413		3991
2414	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3992	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2415		3993
2416	#include "ev_cpp.h"	3994	#include "ev_cpp.h"
2417	#include "ev.c"	3995	#include "ev.c"
2418		3996
		3997	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2419		3998
		3999	=head2 THREADS AND COROUTINES
		4000
		4001	=head3 THREADS
		4002
		4003	All libev functions are reentrant and thread-safe unless explicitly
		4004	documented otherwise, but libev implements no locking itself. This means
		4005	that you can use as many loops as you want in parallel, as long as there
		4006	are no concurrent calls into any libev function with the same loop
		4007	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4008	of course): libev guarantees that different event loops share no data
		4009	structures that need any locking.
		4010
		4011	Or to put it differently: calls with different loop parameters can be done
		4012	concurrently from multiple threads, calls with the same loop parameter
		4013	must be done serially (but can be done from different threads, as long as
		4014	only one thread ever is inside a call at any point in time, e.g. by using
		4015	a mutex per loop).
		4016
		4017	Specifically to support threads (and signal handlers), libev implements
		4018	so-called C<ev_async> watchers, which allow some limited form of
		4019	concurrency on the same event loop, namely waking it up "from the
		4020	outside".
		4021
		4022	If you want to know which design (one loop, locking, or multiple loops
		4023	without or something else still) is best for your problem, then I cannot
		4024	help you, but here is some generic advice:
		4025
		4026	=over 4
		4027
		4028	=item * most applications have a main thread: use the default libev loop
		4029	in that thread, or create a separate thread running only the default loop.
		4030
		4031	This helps integrating other libraries or software modules that use libev
		4032	themselves and don't care/know about threading.
		4033
		4034	=item * one loop per thread is usually a good model.
		4035
		4036	Doing this is almost never wrong, sometimes a better-performance model
		4037	exists, but it is always a good start.
		4038
		4039	=item * other models exist, such as the leader/follower pattern, where one
		4040	loop is handed through multiple threads in a kind of round-robin fashion.
		4041
		4042	Choosing a model is hard - look around, learn, know that usually you can do
		4043	better than you currently do :-)
		4044
		4045	=item * often you need to talk to some other thread which blocks in the
		4046	event loop.
		4047
		4048	C<ev_async> watchers can be used to wake them up from other threads safely
		4049	(or from signal contexts...).
		4050
		4051	An example use would be to communicate signals or other events that only
		4052	work in the default loop by registering the signal watcher with the
		4053	default loop and triggering an C<ev_async> watcher from the default loop
		4054	watcher callback into the event loop interested in the signal.
		4055
		4056	=back
		4057
		4058	=head4 THREAD LOCKING EXAMPLE
		4059
		4060	Here is a fictitious example of how to run an event loop in a different
		4061	thread than where callbacks are being invoked and watchers are
		4062	created/added/removed.
		4063
		4064	For a real-world example, see the C<EV::Loop::Async> perl module,
		4065	which uses exactly this technique (which is suited for many high-level
		4066	languages).
		4067
		4068	The example uses a pthread mutex to protect the loop data, a condition
		4069	variable to wait for callback invocations, an async watcher to notify the
		4070	event loop thread and an unspecified mechanism to wake up the main thread.
		4071
		4072	First, you need to associate some data with the event loop:
		4073
		4074	typedef struct {
		4075	mutex_t lock; /* global loop lock */
		4076	ev_async async_w;
		4077	thread_t tid;
		4078	cond_t invoke_cv;
		4079	} userdata;
		4080
		4081	void prepare_loop (EV_P)
		4082	{
		4083	// for simplicity, we use a static userdata struct.
		4084	static userdata u;
		4085
		4086	ev_async_init (&u->async_w, async_cb);
		4087	ev_async_start (EV_A_ &u->async_w);
		4088
		4089	pthread_mutex_init (&u->lock, 0);
		4090	pthread_cond_init (&u->invoke_cv, 0);
		4091
		4092	// now associate this with the loop
		4093	ev_set_userdata (EV_A_ u);
		4094	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4095	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4096
		4097	// then create the thread running ev_loop
		4098	pthread_create (&u->tid, 0, l_run, EV_A);
		4099	}
		4100
		4101	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4102	solely to wake up the event loop so it takes notice of any new watchers
		4103	that might have been added:
		4104
		4105	static void
		4106	async_cb (EV_P_ ev_async *w, int revents)
		4107	{
		4108	// just used for the side effects
		4109	}
		4110
		4111	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4112	protecting the loop data, respectively.
		4113
		4114	static void
		4115	l_release (EV_P)
		4116	{
		4117	userdata *u = ev_userdata (EV_A);
		4118	pthread_mutex_unlock (&u->lock);
		4119	}
		4120
		4121	static void
		4122	l_acquire (EV_P)
		4123	{
		4124	userdata *u = ev_userdata (EV_A);
		4125	pthread_mutex_lock (&u->lock);
		4126	}
		4127
		4128	The event loop thread first acquires the mutex, and then jumps straight
		4129	into C<ev_loop>:
		4130
		4131	void *
		4132	l_run (void *thr_arg)
		4133	{
		4134	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4135
		4136	l_acquire (EV_A);
		4137	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4138	ev_loop (EV_A_ 0);
		4139	l_release (EV_A);
		4140
		4141	return 0;
		4142	}
		4143
		4144	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4145	signal the main thread via some unspecified mechanism (signals? pipe
		4146	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4147	have been called (in a while loop because a) spurious wakeups are possible
		4148	and b) skipping inter-thread-communication when there are no pending
		4149	watchers is very beneficial):
		4150
		4151	static void
		4152	l_invoke (EV_P)
		4153	{
		4154	userdata *u = ev_userdata (EV_A);
		4155
		4156	while (ev_pending_count (EV_A))
		4157	{
		4158	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4159	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4160	}
		4161	}
		4162
		4163	Now, whenever the main thread gets told to invoke pending watchers, it
		4164	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4165	thread to continue:
		4166
		4167	static void
		4168	real_invoke_pending (EV_P)
		4169	{
		4170	userdata *u = ev_userdata (EV_A);
		4171
		4172	pthread_mutex_lock (&u->lock);
		4173	ev_invoke_pending (EV_A);
		4174	pthread_cond_signal (&u->invoke_cv);
		4175	pthread_mutex_unlock (&u->lock);
		4176	}
		4177
		4178	Whenever you want to start/stop a watcher or do other modifications to an
		4179	event loop, you will now have to lock:
		4180
		4181	ev_timer timeout_watcher;
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4185
		4186	pthread_mutex_lock (&u->lock);
		4187	ev_timer_start (EV_A_ &timeout_watcher);
		4188	ev_async_send (EV_A_ &u->async_w);
		4189	pthread_mutex_unlock (&u->lock);
		4190
		4191	Note that sending the C<ev_async> watcher is required because otherwise
		4192	an event loop currently blocking in the kernel will have no knowledge
		4193	about the newly added timer. By waking up the loop it will pick up any new
		4194	watchers in the next event loop iteration.
		4195
		4196	=head3 COROUTINES
		4197
		4198	Libev is very accommodating to coroutines ("cooperative threads"):
		4199	libev fully supports nesting calls to its functions from different
		4200	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4201	different coroutines, and switch freely between both coroutines running
		4202	the loop, as long as you don't confuse yourself). The only exception is
		4203	that you must not do this from C<ev_periodic> reschedule callbacks.
		4204
		4205	Care has been taken to ensure that libev does not keep local state inside
		4206	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4207	they do not call any callbacks.
		4208
		4209	=head2 COMPILER WARNINGS
		4210
		4211	Depending on your compiler and compiler settings, you might get no or a
		4212	lot of warnings when compiling libev code. Some people are apparently
		4213	scared by this.
		4214
		4215	However, these are unavoidable for many reasons. For one, each compiler
		4216	has different warnings, and each user has different tastes regarding
		4217	warning options. "Warn-free" code therefore cannot be a goal except when
		4218	targeting a specific compiler and compiler-version.
		4219
		4220	Another reason is that some compiler warnings require elaborate
		4221	workarounds, or other changes to the code that make it less clear and less
		4222	maintainable.
		4223
		4224	And of course, some compiler warnings are just plain stupid, or simply
		4225	wrong (because they don't actually warn about the condition their message
		4226	seems to warn about). For example, certain older gcc versions had some
		4227	warnings that resulted an extreme number of false positives. These have
		4228	been fixed, but some people still insist on making code warn-free with
		4229	such buggy versions.
		4230
		4231	While libev is written to generate as few warnings as possible,
		4232	"warn-free" code is not a goal, and it is recommended not to build libev
		4233	with any compiler warnings enabled unless you are prepared to cope with
		4234	them (e.g. by ignoring them). Remember that warnings are just that:
		4235	warnings, not errors, or proof of bugs.
		4236
		4237
		4238	=head2 VALGRIND
		4239
		4240	Valgrind has a special section here because it is a popular tool that is
		4241	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4242
		4243	If you think you found a bug (memory leak, uninitialised data access etc.)
		4244	in libev, then check twice: If valgrind reports something like:
		4245
		4246	==2274== definitely lost: 0 bytes in 0 blocks.
		4247	==2274== possibly lost: 0 bytes in 0 blocks.
		4248	==2274== still reachable: 256 bytes in 1 blocks.
		4249
		4250	Then there is no memory leak, just as memory accounted to global variables
		4251	is not a memleak - the memory is still being referenced, and didn't leak.
		4252
		4253	Similarly, under some circumstances, valgrind might report kernel bugs
		4254	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4255	although an acceptable workaround has been found here), or it might be
		4256	confused.
		4257
		4258	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4259	make it into some kind of religion.
		4260
		4261	If you are unsure about something, feel free to contact the mailing list
		4262	with the full valgrind report and an explanation on why you think this
		4263	is a bug in libev (best check the archives, too :). However, don't be
		4264	annoyed when you get a brisk "this is no bug" answer and take the chance
		4265	of learning how to interpret valgrind properly.
		4266
		4267	If you need, for some reason, empty reports from valgrind for your project
		4268	I suggest using suppression lists.
		4269
		4270
		4271	=head1 PORTABILITY NOTES
		4272
		4273	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4274
		4275	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4276	requires, and its I/O model is fundamentally incompatible with the POSIX
		4277	model. Libev still offers limited functionality on this platform in
		4278	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4279	descriptors. This only applies when using Win32 natively, not when using
		4280	e.g. cygwin.
		4281
		4282	Lifting these limitations would basically require the full
		4283	re-implementation of the I/O system. If you are into these kinds of
		4284	things, then note that glib does exactly that for you in a very portable
		4285	way (note also that glib is the slowest event library known to man).
		4286
		4287	There is no supported compilation method available on windows except
		4288	embedding it into other applications.
		4289
		4290	Sensible signal handling is officially unsupported by Microsoft - libev
		4291	tries its best, but under most conditions, signals will simply not work.
		4292
		4293	Not a libev limitation but worth mentioning: windows apparently doesn't
		4294	accept large writes: instead of resulting in a partial write, windows will
		4295	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4296	so make sure you only write small amounts into your sockets (less than a
		4297	megabyte seems safe, but this apparently depends on the amount of memory
		4298	available).
		4299
		4300	Due to the many, low, and arbitrary limits on the win32 platform and
		4301	the abysmal performance of winsockets, using a large number of sockets
		4302	is not recommended (and not reasonable). If your program needs to use
		4303	more than a hundred or so sockets, then likely it needs to use a totally
		4304	different implementation for windows, as libev offers the POSIX readiness
		4305	notification model, which cannot be implemented efficiently on windows
		4306	(due to Microsoft monopoly games).
		4307
		4308	A typical way to use libev under windows is to embed it (see the embedding
		4309	section for details) and use the following F<evwrap.h> header file instead
		4310	of F<ev.h>:
		4311
		4312	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4313	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4314
		4315	#include "ev.h"
		4316
		4317	And compile the following F<evwrap.c> file into your project (make sure
		4318	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4319
		4320	#include "evwrap.h"
		4321	#include "ev.c"
		4322
		4323	=over 4
		4324
		4325	=item The winsocket select function
		4326
		4327	The winsocket C<select> function doesn't follow POSIX in that it
		4328	requires socket I<handles> and not socket I<file descriptors> (it is
		4329	also extremely buggy). This makes select very inefficient, and also
		4330	requires a mapping from file descriptors to socket handles (the Microsoft
		4331	C runtime provides the function C<_open_osfhandle> for this). See the
		4332	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4333	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4334
		4335	The configuration for a "naked" win32 using the Microsoft runtime
		4336	libraries and raw winsocket select is:
		4337
		4338	#define EV_USE_SELECT 1
		4339	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4340
		4341	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4342	complexity in the O(n²) range when using win32.
		4343
		4344	=item Limited number of file descriptors
		4345
		4346	Windows has numerous arbitrary (and low) limits on things.
		4347
		4348	Early versions of winsocket's select only supported waiting for a maximum
		4349	of C<64> handles (probably owning to the fact that all windows kernels
		4350	can only wait for C<64> things at the same time internally; Microsoft
		4351	recommends spawning a chain of threads and wait for 63 handles and the
		4352	previous thread in each. Sounds great!).
		4353
		4354	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4355	to some high number (e.g. C<2048>) before compiling the winsocket select
		4356	call (which might be in libev or elsewhere, for example, perl and many
		4357	other interpreters do their own select emulation on windows).
		4358
		4359	Another limit is the number of file descriptors in the Microsoft runtime
		4360	libraries, which by default is C<64> (there must be a hidden I<64>
		4361	fetish or something like this inside Microsoft). You can increase this
		4362	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4363	(another arbitrary limit), but is broken in many versions of the Microsoft
		4364	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4365	(depending on windows version and/or the phase of the moon). To get more,
		4366	you need to wrap all I/O functions and provide your own fd management, but
		4367	the cost of calling select (O(n²)) will likely make this unworkable.
		4368
		4369	=back
		4370
		4371	=head2 PORTABILITY REQUIREMENTS
		4372
		4373	In addition to a working ISO-C implementation and of course the
		4374	backend-specific APIs, libev relies on a few additional extensions:
		4375
		4376	=over 4
		4377
		4378	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4379	calling conventions regardless of C<ev_watcher_type *>.
		4380
		4381	Libev assumes not only that all watcher pointers have the same internal
		4382	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4383	assumes that the same (machine) code can be used to call any watcher
		4384	callback: The watcher callbacks have different type signatures, but libev
		4385	calls them using an C<ev_watcher *> internally.
		4386
		4387	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4388
		4389	The type C<sig_atomic_t volatile> (or whatever is defined as
		4390	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4391	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4392	believed to be sufficiently portable.
		4393
		4394	=item C<sigprocmask> must work in a threaded environment
		4395
		4396	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4397	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4398	pthread implementations will either allow C<sigprocmask> in the "main
		4399	thread" or will block signals process-wide, both behaviours would
		4400	be compatible with libev. Interaction between C<sigprocmask> and
		4401	C<pthread_sigmask> could complicate things, however.
		4402
		4403	The most portable way to handle signals is to block signals in all threads
		4404	except the initial one, and run the default loop in the initial thread as
		4405	well.
		4406
		4407	=item C<long> must be large enough for common memory allocation sizes
		4408
		4409	To improve portability and simplify its API, libev uses C<long> internally
		4410	instead of C<size_t> when allocating its data structures. On non-POSIX
		4411	systems (Microsoft...) this might be unexpectedly low, but is still at
		4412	least 31 bits everywhere, which is enough for hundreds of millions of
		4413	watchers.
		4414
		4415	=item C<double> must hold a time value in seconds with enough accuracy
		4416
		4417	The type C<double> is used to represent timestamps. It is required to
		4418	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4419	enough for at least into the year 4000. This requirement is fulfilled by
		4420	implementations implementing IEEE 754, which is basically all existing
		4421	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4422	2200.
		4423
		4424	=back
		4425
		4426	If you know of other additional requirements drop me a note.
		4427
		4428
2420	=head1 COMPLEXITIES	4429	=head1 ALGORITHMIC COMPLEXITIES
2421		4430
2422	In this section the complexities of (many of) the algorithms used inside	4431	In this section the complexities of (many of) the algorithms used inside
2423	libev will be explained. For complexity discussions about backends see the	4432	libev will be documented. For complexity discussions about backends see
2424	documentation for C<ev_default_init>.	4433	the documentation for C<ev_default_init>.
2425		4434
2426	All of the following are about amortised time: If an array needs to be	4435	All of the following are about amortised time: If an array needs to be
2427	extended, libev needs to realloc and move the whole array, but this	4436	extended, libev needs to realloc and move the whole array, but this
2428	happens asymptotically never with higher number of elements, so O(1) might	4437	happens asymptotically rarer with higher number of elements, so O(1) might
2429	mean it might do a lengthy realloc operation in rare cases, but on average	4438	mean that libev does a lengthy realloc operation in rare cases, but on
2430	it is much faster and asymptotically approaches constant time.	4439	average it is much faster and asymptotically approaches constant time.
2431		4440
2432	=over 4	4441	=over 4
2433		4442
2434	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4443	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2435		4444
2436	This means that, when you have a watcher that triggers in one hour and	4445	This means that, when you have a watcher that triggers in one hour and
2437	there are 100 watchers that would trigger before that then inserting will	4446	there are 100 watchers that would trigger before that, then inserting will
2438	have to skip those 100 watchers.	4447	have to skip roughly seven (C<ld 100>) of these watchers.
2439		4448
2440	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4449	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2441		4450
2442	That means that for changing a timer costs less than removing/adding them	4451	That means that changing a timer costs less than removing/adding them,
2443	as only the relative motion in the event queue has to be paid for.	4452	as only the relative motion in the event queue has to be paid for.
2444		4453
2445	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4454	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2446		4455
2447	These just add the watcher into an array or at the head of a list.	4456	These just add the watcher into an array or at the head of a list.
		4457
2448	=item Stopping check/prepare/idle watchers: O(1)	4458	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2449		4459
2450	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4460	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2451		4461
2452	These watchers are stored in lists then need to be walked to find the	4462	These watchers are stored in lists, so they need to be walked to find the
2453	correct watcher to remove. The lists are usually short (you don't usually	4463	correct watcher to remove. The lists are usually short (you don't usually
2454	have many watchers waiting for the same fd or signal).	4464	have many watchers waiting for the same fd or signal: one is typical, two
		4465	is rare).
2455		4466
2456	=item Finding the next timer per loop iteration: O(1)	4467	=item Finding the next timer in each loop iteration: O(1)
		4468
		4469	By virtue of using a binary or 4-heap, the next timer is always found at a
		4470	fixed position in the storage array.
2457		4471
2458	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4472	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2459		4473
2460	A change means an I/O watcher gets started or stopped, which requires	4474	A change means an I/O watcher gets started or stopped, which requires
2461	libev to recalculate its status (and possibly tell the kernel).	4475	libev to recalculate its status (and possibly tell the kernel, depending
		4476	on backend and whether C<ev_io_set> was used).
2462		4477
2463	=item Activating one watcher: O(1)	4478	=item Activating one watcher (putting it into the pending state): O(1)
2464		4479
2465	=item Priority handling: O(number_of_priorities)	4480	=item Priority handling: O(number_of_priorities)
2466		4481
2467	Priorities are implemented by allocating some space for each	4482	Priorities are implemented by allocating some space for each
2468	priority. When doing priority-based operations, libev usually has to	4483	priority. When doing priority-based operations, libev usually has to
2469	linearly search all the priorities.	4484	linearly search all the priorities, but starting/stopping and activating
		4485	watchers becomes O(1) with respect to priority handling.
		4486
		4487	=item Sending an ev_async: O(1)
		4488
		4489	=item Processing ev_async_send: O(number_of_async_watchers)
		4490
		4491	=item Processing signals: O(max_signal_number)
		4492
		4493	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4494	calls in the current loop iteration. Checking for async and signal events
		4495	involves iterating over all running async watchers or all signal numbers.
2470		4496
2471	=back	4497	=back
2472		4498
2473		4499
		4500	=head1 GLOSSARY
		4501
		4502	=over 4
		4503
		4504	=item active
		4505
		4506	A watcher is active as long as it has been started (has been attached to
		4507	an event loop) but not yet stopped (disassociated from the event loop).
		4508
		4509	=item application
		4510
		4511	In this document, an application is whatever is using libev.
		4512
		4513	=item callback
		4514
		4515	The address of a function that is called when some event has been
		4516	detected. Callbacks are being passed the event loop, the watcher that
		4517	received the event, and the actual event bitset.
		4518
		4519	=item callback invocation
		4520
		4521	The act of calling the callback associated with a watcher.
		4522
		4523	=item event
		4524
		4525	A change of state of some external event, such as data now being available
		4526	for reading on a file descriptor, time having passed or simply not having
		4527	any other events happening anymore.
		4528
		4529	In libev, events are represented as single bits (such as C<EV_READ> or
		4530	C<EV_TIMEOUT>).
		4531
		4532	=item event library
		4533
		4534	A software package implementing an event model and loop.
		4535
		4536	=item event loop
		4537
		4538	An entity that handles and processes external events and converts them
		4539	into callback invocations.
		4540
		4541	=item event model
		4542
		4543	The model used to describe how an event loop handles and processes
		4544	watchers and events.
		4545
		4546	=item pending
		4547
		4548	A watcher is pending as soon as the corresponding event has been detected,
		4549	and stops being pending as soon as the watcher will be invoked or its
		4550	pending status is explicitly cleared by the application.
		4551
		4552	A watcher can be pending, but not active. Stopping a watcher also clears
		4553	its pending status.
		4554
		4555	=item real time
		4556
		4557	The physical time that is observed. It is apparently strictly monotonic :)
		4558
		4559	=item wall-clock time
		4560
		4561	The time and date as shown on clocks. Unlike real time, it can actually
		4562	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4563	clock.
		4564
		4565	=item watcher
		4566
		4567	A data structure that describes interest in certain events. Watchers need
		4568	to be started (attached to an event loop) before they can receive events.
		4569
		4570	=item watcher invocation
		4571
		4572	The act of calling the callback associated with a watcher.
		4573
		4574	=back
		4575
2474	=head1 AUTHOR	4576	=head1 AUTHOR
2475		4577
2476	Marc Lehmann <libev@schmorp.de>.	4578	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2477		4579

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