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Revision 1.274 by root, Tue Nov 24 14:54:17 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
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		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
52		84
53	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
54	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
55	these event sources and provide your program with events.	87	these event sources and provide your program with events.
56		88
57	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
58	(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
59	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
61	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
62	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
63	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
64	watcher.	96	watcher.
65		97
66	=head1 FEATURES	98	=head2 FEATURES
67		99
68	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
69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	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
71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
72	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
73	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
74	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
75	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
76	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
77	(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>).
78		111
79	It also is quite fast (see this	112	It also is quite fast (see this
80	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
81	for example).	114	for example).
82		115
83	=head1 CONVENTIONS	116	=head2 CONVENTIONS
84		117
85	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
86	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
87	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
88	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
89	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
90	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		124	this argument.
91		125
92	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
93		127
94	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
95	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
96	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
97	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
98	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
99	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
100		157
101	=head1 GLOBAL FUNCTIONS	158	=head1 GLOBAL FUNCTIONS
102		159
103	These functions can be called anytime, even before initialising the	160	These functions can be called anytime, even before initialising the
104	library in any way.	161	library in any way.
…		…
109		166
110	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
111	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
112	you actually want to know.	169	you actually want to know.
113		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
114	=item int ev_version_major ()	177	=item int ev_version_major ()
115		178
116	=item int ev_version_minor ()	179	=item int ev_version_minor ()
117		180
118	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
119	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
120	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
121	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
122	version of the library your program was compiled against.	185	version of the library your program was compiled against.
123		186
		187	These version numbers refer to the ABI version of the library, not the
		188	release version.
		189
124	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,
125	as this indicates an incompatible change. Minor versions are usually	191	as this indicates an incompatible change. Minor versions are usually
126	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
127	not a problem.	193	not a problem.
128		194
129	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
130	version.	196	version.
131		197
132	assert (("libev version mismatch",	198	assert (("libev version mismatch",
133	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
134	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
135		201
136	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
137		203
138	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_*>
139	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
141	a description of the set values.	207	a description of the set values.
142		208
143	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
144	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
145		211
146	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
147	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
148		214
149	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
150		216
151	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
152	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
153	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
154	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
155	(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
156	libev will probe for if you specify no backends explicitly.	222	libev will probe for if you specify no backends explicitly.
157		223
158	=item unsigned int ev_embeddable_backends ()	224	=item unsigned int ev_embeddable_backends ()
159		225
…		…
163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
164	recommended ones.	230	recommended ones.
165		231
166	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
167		233
168	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
169		235
170	Sets the allocation function to use (the prototype and semantics are	236	Sets the allocation function to use (the prototype is similar - the
171	identical to the realloc C function). It is used to allocate and free	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
172	memory (no surprises here). If it returns zero when memory needs to be	238	used to allocate and free memory (no surprises here). If it returns zero
173	allocated, the library might abort or take some potentially destructive	239	when memory needs to be allocated (C<size != 0>), the library might abort
174	action. The default is your system realloc function.	240	or take some potentially destructive action.
		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.
175		245
176	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
177	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,
178	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.
179		249
180	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
181	retries).	251	retries (example requires a standards-compliant C<realloc>).
182		252
183	static void *	253	static void *
184	persistent_realloc (void *ptr, size_t size)	254	persistent_realloc (void *ptr, size_t size)
185	{	255	{
186	for (;;)	256	for (;;)
…		…
195	}	265	}
196		266
197	...	267	...
198	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
199		269
200	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
201		271
202	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
203	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
204	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
205	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
206	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
207	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
208	(such as abort).	278	(such as abort).
209		279
210	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.
…		…
221		291
222	=back	292	=back
223		293
224	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
225		295
226	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>
227	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>
228	events, and dynamically created loops which do not.	298	I<function>).
229		299
230	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
231	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
232	create, you also create another event loop. Libev itself does no locking	302	not.
233	whatsoever, so if you mix calls to the same event loop in different
234	threads, make sure you lock (this is usually a bad idea, though, even if
235	done correctly, because it's hideous and inefficient).
236		303
237	=over 4	304	=over 4
238		305
239	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
240		307
…		…
244	flags. If that is troubling you, check C<ev_backend ()> afterwards).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
245		312
246	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
247	function.	314	function.
248		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
249	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
250	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>).
251		329
252	The following flags are supported:	330	The following flags are supported:
253		331
…		…
258	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
259	thing, believe me).	337	thing, believe me).
260		338
261	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
262		340
263	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
264	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
265	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
266	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
267	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
268	around bugs.	346	around bugs.
269		347
		348	=item C<EVFLAG_FORKCHECK>
		349
		350	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		351	a fork, you can also make libev check for a fork in each iteration by
		352	enabling this flag.
		353
		354	This works by calling C<getpid ()> on every iteration of the loop,
		355	and thus this might slow down your event loop if you do a lot of loop
		356	iterations and little real work, but is usually not noticeable (on my
		357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		358	without a system call and thus I<very> fast, but my GNU/Linux system also has
		359	C<pthread_atfork> which is even faster).
		360
		361	The big advantage of this flag is that you can forget about fork (and
		362	forget about forgetting to tell libev about forking) when you use this
		363	flag.
		364
		365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
		382
270	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
271		384
272	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
273	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,
274	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
275	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
276	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).
277		401
278	=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)
279		403
280	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
281	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
282	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
283	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>.
284		413
285	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
286		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
		418
287	For few fds, this backend is a bit little slower than poll and select,	419	For few fds, this backend is a bit little slower than poll and select,
288	but it scales phenomenally better. While poll and select usually scale like	420	but it scales phenomenally better. While poll and select usually scale
289	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	421	like O(total_fds) where n is the total number of fds (or the highest fd),
290	either O(1) or O(active_fds).	422	epoll scales either O(1) or O(active_fds).
291		423
		424	The epoll mechanism deserves honorable mention as the most misdesigned
		425	of the more advanced event mechanisms: mere annoyances include silently
		426	dropping file descriptors, requiring a system call per change per file
		427	descriptor (and unnecessary guessing of parameters), problems with dup and
		428	so on. The biggest issue is fork races, however - if a program forks then
		429	I<both> parent and child process have to recreate the epoll set, which can
		430	take considerable time (one syscall per file descriptor) and is of course
		431	hard to detect.
		432
		433	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		434	of course I<doesn't>, and epoll just loves to report events for totally
		435	I<different> file descriptors (even already closed ones, so one cannot
		436	even remove them from the set) than registered in the set (especially
		437	on SMP systems). Libev tries to counter these spurious notifications by
		438	employing an additional generation counter and comparing that against the
		439	events to filter out spurious ones, recreating the set when required.
		440
292	While stopping and starting an I/O watcher in the same iteration will	441	While stopping, setting and starting an I/O watcher in the same iteration
293	result in some caching, there is still a syscall per such incident	442	will result in some caching, there is still a system call per such
294	(because the fd could point to a different file description now), so its	443	incident (because the same I<file descriptor> could point to a different
295	best to avoid that. Also, dup()ed file descriptors might not work very	444	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
296	well if you register events for both fds.	445	file descriptors might not work very well if you register events for both
		446	file descriptors.
297		447
298	Please note that epoll sometimes generates spurious notifications, so you	448	Best performance from this backend is achieved by not unregistering all
299	need to use non-blocking I/O or other means to avoid blocking when no data	449	watchers for a file descriptor until it has been closed, if possible,
300	(or space) is available.	450	i.e. keep at least one watcher active per fd at all times. Stopping and
		451	starting a watcher (without re-setting it) also usually doesn't cause
		452	extra overhead. A fork can both result in spurious notifications as well
		453	as in libev having to destroy and recreate the epoll object, which can
		454	take considerable time and thus should be avoided.
		455
		456	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		457	faster than epoll for maybe up to a hundred file descriptors, depending on
		458	the usage. So sad.
		459
		460	While nominally embeddable in other event loops, this feature is broken in
		461	all kernel versions tested so far.
		462
		463	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		464	C<EVBACKEND_POLL>.
301		465
302	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	466	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
303		467
304	Kqueue deserves special mention, as at the time of this writing, it	468	Kqueue deserves special mention, as at the time of this writing, it
305	was broken on all BSDs except NetBSD (usually it doesn't work with	469	was broken on all BSDs except NetBSD (usually it doesn't work reliably
306	anything but sockets and pipes, except on Darwin, where of course its	470	with anything but sockets and pipes, except on Darwin, where of course
307	completely useless). For this reason its not being "autodetected"	471	it's completely useless). Unlike epoll, however, whose brokenness
		472	is by design, these kqueue bugs can (and eventually will) be fixed
		473	without API changes to existing programs. For this reason it's not being
308	unless you explicitly specify it explicitly in the flags (i.e. using	474	"auto-detected" unless you explicitly specify it in the flags (i.e. using
309	C<EVBACKEND_KQUEUE>).	475	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		476	system like NetBSD.
		477
		478	You still can embed kqueue into a normal poll or select backend and use it
		479	only for sockets (after having made sure that sockets work with kqueue on
		480	the target platform). See C<ev_embed> watchers for more info.
310		481
311	It scales in the same way as the epoll backend, but the interface to the	482	It scales in the same way as the epoll backend, but the interface to the
312	kernel is more efficient (which says nothing about its actual speed, of	483	kernel is more efficient (which says nothing about its actual speed, of
313	course). While starting and stopping an I/O watcher does not cause an	484	course). While stopping, setting and starting an I/O watcher does never
314	extra syscall as with epoll, it still adds up to four event changes per	485	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
315	incident, so its best to avoid that.	486	two event changes per incident. Support for C<fork ()> is very bad (but
		487	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		488	cases
		489
		490	This backend usually performs well under most conditions.
		491
		492	While nominally embeddable in other event loops, this doesn't work
		493	everywhere, so you might need to test for this. And since it is broken
		494	almost everywhere, you should only use it when you have a lot of sockets
		495	(for which it usually works), by embedding it into another event loop
		496	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		497	also broken on OS X)) and, did I mention it, using it only for sockets.
		498
		499	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		500	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		501	C<NOTE_EOF>.
316		502
317	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	503	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
318		504
319	This is not implemented yet (and might never be).	505	This is not implemented yet (and might never be, unless you send me an
		506	implementation). According to reports, C</dev/poll> only supports sockets
		507	and is not embeddable, which would limit the usefulness of this backend
		508	immensely.
320		509
321	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	510	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
322		511
323	This uses the Solaris 10 port mechanism. As with everything on Solaris,	512	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
324	it's really slow, but it still scales very well (O(active_fds)).	513	it's really slow, but it still scales very well (O(active_fds)).
325		514
326	Please note that solaris ports can result in a lot of spurious	515	Please note that Solaris event ports can deliver a lot of spurious
327	notifications, so you need to use non-blocking I/O or other means to avoid	516	notifications, so you need to use non-blocking I/O or other means to avoid
328	blocking when no data (or space) is available.	517	blocking when no data (or space) is available.
		518
		519	While this backend scales well, it requires one system call per active
		520	file descriptor per loop iteration. For small and medium numbers of file
		521	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		522	might perform better.
		523
		524	On the positive side, with the exception of the spurious readiness
		525	notifications, this backend actually performed fully to specification
		526	in all tests and is fully embeddable, which is a rare feat among the
		527	OS-specific backends (I vastly prefer correctness over speed hacks).
		528
		529	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		530	C<EVBACKEND_POLL>.
329		531
330	=item C<EVBACKEND_ALL>	532	=item C<EVBACKEND_ALL>
331		533
332	Try all backends (even potentially broken ones that wouldn't be tried	534	Try all backends (even potentially broken ones that wouldn't be tried
333	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	535	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
334	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	536	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
335		537
		538	It is definitely not recommended to use this flag.
		539
336	=back	540	=back
337		541
338	If one or more of these are ored into the flags value, then only these	542	If one or more of the backend flags are or'ed into the flags value,
339	backends will be tried (in the reverse order as given here). If none are	543	then only these backends will be tried (in the reverse order as listed
340	specified, most compiled-in backend will be tried, usually in reverse	544	here). If none are specified, all backends in C<ev_recommended_backends
341	order of their flag values :)	545	()> will be tried.
342		546
343	The most typical usage is like this:	547	Example: This is the most typical usage.
344		548
345	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
346	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
347		551
348	Restrict libev to the select and poll backends, and do not allow	552	Example: Restrict libev to the select and poll backends, and do not allow
349	environment settings to be taken into account:	553	environment settings to be taken into account:
350		554
351	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	555	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
352		556
353	Use whatever libev has to offer, but make sure that kqueue is used if	557	Example: Use whatever libev has to offer, but make sure that kqueue is
354	available (warning, breaks stuff, best use only with your own private	558	used if available (warning, breaks stuff, best use only with your own
355	event loop and only if you know the OS supports your types of fds):	559	private event loop and only if you know the OS supports your types of
		560	fds):
356		561
357	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	562	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
358		563
359	=item struct ev_loop *ev_loop_new (unsigned int flags)	564	=item struct ev_loop *ev_loop_new (unsigned int flags)
360		565
361	Similar to C<ev_default_loop>, but always creates a new event loop that is	566	Similar to C<ev_default_loop>, but always creates a new event loop that is
362	always distinct from the default loop. Unlike the default loop, it cannot	567	always distinct from the default loop. Unlike the default loop, it cannot
363	handle signal and child watchers, and attempts to do so will be greeted by	568	handle signal and child watchers, and attempts to do so will be greeted by
364	undefined behaviour (or a failed assertion if assertions are enabled).	569	undefined behaviour (or a failed assertion if assertions are enabled).
365		570
		571	Note that this function I<is> thread-safe, and the recommended way to use
		572	libev with threads is indeed to create one loop per thread, and using the
		573	default loop in the "main" or "initial" thread.
		574
366	Example: Try to create a event loop that uses epoll and nothing else.	575	Example: Try to create a event loop that uses epoll and nothing else.
367		576
368	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	577	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
369	if (!epoller)	578	if (!epoller)
370	fatal ("no epoll found here, maybe it hides under your chair");	579	fatal ("no epoll found here, maybe it hides under your chair");
371		580
372	=item ev_default_destroy ()	581	=item ev_default_destroy ()
373		582
374	Destroys the default loop again (frees all memory and kernel state	583	Destroys the default loop again (frees all memory and kernel state
375	etc.). None of the active event watchers will be stopped in the normal	584	etc.). None of the active event watchers will be stopped in the normal
376	sense, so e.g. C<ev_is_active> might still return true. It is your	585	sense, so e.g. C<ev_is_active> might still return true. It is your
377	responsibility to either stop all watchers cleanly yoursef I<before>	586	responsibility to either stop all watchers cleanly yourself I<before>
378	calling this function, or cope with the fact afterwards (which is usually	587	calling this function, or cope with the fact afterwards (which is usually
379	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	588	the easiest thing, you can just ignore the watchers and/or C<free ()> them
380	for example).	589	for example).
		590
		591	Note that certain global state, such as signal state (and installed signal
		592	handlers), will not be freed by this function, and related watchers (such
		593	as signal and child watchers) would need to be stopped manually.
		594
		595	In general it is not advisable to call this function except in the
		596	rare occasion where you really need to free e.g. the signal handling
		597	pipe fds. If you need dynamically allocated loops it is better to use
		598	C<ev_loop_new> and C<ev_loop_destroy>.
381		599
382	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
383		601
384	Like C<ev_default_destroy>, but destroys an event loop created by an	602	Like C<ev_default_destroy>, but destroys an event loop created by an
385	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
386		604
387	=item ev_default_fork ()	605	=item ev_default_fork ()
388		606
		607	This function sets a flag that causes subsequent C<ev_loop> iterations
389	This function reinitialises the kernel state for backends that have	608	to reinitialise the kernel state for backends that have one. Despite the
390	one. Despite the name, you can call it anytime, but it makes most sense	609	name, you can call it anytime, but it makes most sense after forking, in
391	after forking, in either the parent or child process (or both, but that	610	the child process (or both child and parent, but that again makes little
392	again makes little sense).	611	sense). You I<must> call it in the child before using any of the libev
		612	functions, and it will only take effect at the next C<ev_loop> iteration.
393		613
394	You I<must> call this function in the child process after forking if and	614	On the other hand, you only need to call this function in the child
395	only if you want to use the event library in both processes. If you just	615	process if and only if you want to use the event library in the child. If
396	fork+exec, you don't have to call it.	616	you just fork+exec, you don't have to call it at all.
397		617
398	The function itself is quite fast and it's usually not a problem to call	618	The function itself is quite fast and it's usually not a problem to call
399	it just in case after a fork. To make this easy, the function will fit in	619	it just in case after a fork. To make this easy, the function will fit in
400	quite nicely into a call to C<pthread_atfork>:	620	quite nicely into a call to C<pthread_atfork>:
401		621
402	pthread_atfork (0, 0, ev_default_fork);	622	pthread_atfork (0, 0, ev_default_fork);
403		623
404	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
405	without calling this function, so if you force one of those backends you
406	do not need to care.
407
408	=item ev_loop_fork (loop)	624	=item ev_loop_fork (loop)
409		625
410	Like C<ev_default_fork>, but acts on an event loop created by	626	Like C<ev_default_fork>, but acts on an event loop created by
411	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	627	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
412	after fork, and how you do this is entirely your own problem.	628	after fork that you want to re-use in the child, and how you do this is
		629	entirely your own problem.
		630
		631	=item int ev_is_default_loop (loop)
		632
		633	Returns true when the given loop is, in fact, the default loop, and false
		634	otherwise.
		635
		636	=item unsigned int ev_loop_count (loop)
		637
		638	Returns the count of loop iterations for the loop, which is identical to
		639	the number of times libev did poll for new events. It starts at C<0> and
		640	happily wraps around with enough iterations.
		641
		642	This value can sometimes be useful as a generation counter of sorts (it
		643	"ticks" the number of loop iterations), as it roughly corresponds with
		644	C<ev_prepare> and C<ev_check> calls.
		645
		646	=item unsigned int ev_loop_depth (loop)
		647
		648	Returns the number of times C<ev_loop> was entered minus the number of
		649	times C<ev_loop> was exited, in other words, the recursion depth.
		650
		651	Outside C<ev_loop>, this number is zero. In a callback, this number is
		652	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		653	in which case it is higher.
		654
		655	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		656	etc.), doesn't count as exit.
413		657
414	=item unsigned int ev_backend (loop)	658	=item unsigned int ev_backend (loop)
415		659
416	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	660	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
417	use.	661	use.
…		…
420		664
421	Returns the current "event loop time", which is the time the event loop	665	Returns the current "event loop time", which is the time the event loop
422	received events and started processing them. This timestamp does not	666	received events and started processing them. This timestamp does not
423	change as long as callbacks are being processed, and this is also the base	667	change as long as callbacks are being processed, and this is also the base
424	time used for relative timers. You can treat it as the timestamp of the	668	time used for relative timers. You can treat it as the timestamp of the
425	event occuring (or more correctly, libev finding out about it).	669	event occurring (or more correctly, libev finding out about it).
		670
		671	=item ev_now_update (loop)
		672
		673	Establishes the current time by querying the kernel, updating the time
		674	returned by C<ev_now ()> in the progress. This is a costly operation and
		675	is usually done automatically within C<ev_loop ()>.
		676
		677	This function is rarely useful, but when some event callback runs for a
		678	very long time without entering the event loop, updating libev's idea of
		679	the current time is a good idea.
		680
		681	See also L<The special problem of time updates> in the C<ev_timer> section.
		682
		683	=item ev_suspend (loop)
		684
		685	=item ev_resume (loop)
		686
		687	These two functions suspend and resume a loop, for use when the loop is
		688	not used for a while and timeouts should not be processed.
		689
		690	A typical use case would be an interactive program such as a game: When
		691	the user presses C<^Z> to suspend the game and resumes it an hour later it
		692	would be best to handle timeouts as if no time had actually passed while
		693	the program was suspended. This can be achieved by calling C<ev_suspend>
		694	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		695	C<ev_resume> directly afterwards to resume timer processing.
		696
		697	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		698	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		699	will be rescheduled (that is, they will lose any events that would have
		700	occured while suspended).
		701
		702	After calling C<ev_suspend> you B<must not> call I<any> function on the
		703	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		704	without a previous call to C<ev_suspend>.
		705
		706	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		707	event loop time (see C<ev_now_update>).
426		708
427	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
428		710
429	Finally, this is it, the event handler. This function usually is called	711	Finally, this is it, the event handler. This function usually is called
430	after you initialised all your watchers and you want to start handling	712	after you have initialised all your watchers and you want to start
431	events.	713	handling events.
432		714
433	If the flags argument is specified as C<0>, it will not return until	715	If the flags argument is specified as C<0>, it will not return until
434	either no event watchers are active anymore or C<ev_unloop> was called.	716	either no event watchers are active anymore or C<ev_unloop> was called.
435		717
436	Please note that an explicit C<ev_unloop> is usually better than	718	Please note that an explicit C<ev_unloop> is usually better than
437	relying on all watchers to be stopped when deciding when a program has	719	relying on all watchers to be stopped when deciding when a program has
438	finished (especially in interactive programs), but having a program that	720	finished (especially in interactive programs), but having a program
439	automatically loops as long as it has to and no longer by virtue of	721	that automatically loops as long as it has to and no longer by virtue
440	relying on its watchers stopping correctly is a thing of beauty.	722	of relying on its watchers stopping correctly, that is truly a thing of
		723	beauty.
441		724
442	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	725	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
443	those events and any outstanding ones, but will not block your process in	726	those events and any already outstanding ones, but will not block your
444	case there are no events and will return after one iteration of the loop.	727	process in case there are no events and will return after one iteration of
		728	the loop.
445		729
446	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	730	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
447	neccessary) and will handle those and any outstanding ones. It will block	731	necessary) and will handle those and any already outstanding ones. It
448	your process until at least one new event arrives, and will return after	732	will block your process until at least one new event arrives (which could
449	one iteration of the loop. This is useful if you are waiting for some	733	be an event internal to libev itself, so there is no guarantee that a
450	external event in conjunction with something not expressible using other	734	user-registered callback will be called), and will return after one
		735	iteration of the loop.
		736
		737	This is useful if you are waiting for some external event in conjunction
		738	with something not expressible using other libev watchers (i.e. "roll your
451	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	739	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
452	usually a better approach for this kind of thing.	740	usually a better approach for this kind of thing.
453		741
454	Here are the gory details of what C<ev_loop> does:	742	Here are the gory details of what C<ev_loop> does:
455		743
456	* If there are no active watchers (reference count is zero), return.	744	- Before the first iteration, call any pending watchers.
457	- Queue prepare watchers and then call all outstanding watchers.	745	* If EVFLAG_FORKCHECK was used, check for a fork.
		746	- If a fork was detected (by any means), queue and call all fork watchers.
		747	- Queue and call all prepare watchers.
458	- If we have been forked, recreate the kernel state.	748	- If we have been forked, detach and recreate the kernel state
		749	as to not disturb the other process.
459	- Update the kernel state with all outstanding changes.	750	- Update the kernel state with all outstanding changes.
460	- Update the "event loop time".	751	- Update the "event loop time" (ev_now ()).
461	- Calculate for how long to block.	752	- Calculate for how long to sleep or block, if at all
		753	(active idle watchers, EVLOOP_NONBLOCK or not having
		754	any active watchers at all will result in not sleeping).
		755	- Sleep if the I/O and timer collect interval say so.
462	- Block the process, waiting for any events.	756	- Block the process, waiting for any events.
463	- Queue all outstanding I/O (fd) events.	757	- Queue all outstanding I/O (fd) events.
464	- Update the "event loop time" and do time jump handling.	758	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
465	- Queue all outstanding timers.	759	- Queue all expired timers.
466	- Queue all outstanding periodics.	760	- Queue all expired periodics.
467	- If no events are pending now, queue all idle watchers.	761	- Unless any events are pending now, queue all idle watchers.
468	- Queue all check watchers.	762	- Queue all check watchers.
469	- Call all queued watchers in reverse order (i.e. check watchers first).	763	- Call all queued watchers in reverse order (i.e. check watchers first).
470	Signals and child watchers are implemented as I/O watchers, and will	764	Signals and child watchers are implemented as I/O watchers, and will
471	be handled here by queueing them when their watcher gets executed.	765	be handled here by queueing them when their watcher gets executed.
472	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	766	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
473	were used, return, otherwise continue with step *.	767	were used, or there are no active watchers, return, otherwise
		768	continue with step *.
474		769
475	Example: Queue some jobs and then loop until no events are outsanding	770	Example: Queue some jobs and then loop until no events are outstanding
476	anymore.	771	anymore.
477		772
478	... queue jobs here, make sure they register event watchers as long	773	... queue jobs here, make sure they register event watchers as long
479	... as they still have work to do (even an idle watcher will do..)	774	... as they still have work to do (even an idle watcher will do..)
480	ev_loop (my_loop, 0);	775	ev_loop (my_loop, 0);
481	... jobs done. yeah!	776	... jobs done or somebody called unloop. yeah!
482		777
483	=item ev_unloop (loop, how)	778	=item ev_unloop (loop, how)
484		779
485	Can be used to make a call to C<ev_loop> return early (but only after it	780	Can be used to make a call to C<ev_loop> return early (but only after it
486	has processed all outstanding events). The C<how> argument must be either	781	has processed all outstanding events). The C<how> argument must be either
487	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	782	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
488	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	783	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
489		784
		785	This "unloop state" will be cleared when entering C<ev_loop> again.
		786
		787	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		788
490	=item ev_ref (loop)	789	=item ev_ref (loop)
491		790
492	=item ev_unref (loop)	791	=item ev_unref (loop)
493		792
494	Ref/unref can be used to add or remove a reference count on the event	793	Ref/unref can be used to add or remove a reference count on the event
495	loop: Every watcher keeps one reference, and as long as the reference	794	loop: Every watcher keeps one reference, and as long as the reference
496	count is nonzero, C<ev_loop> will not return on its own. If you have	795	count is nonzero, C<ev_loop> will not return on its own.
		796
497	a watcher you never unregister that should not keep C<ev_loop> from	797	If you have a watcher you never unregister that should not keep C<ev_loop>
498	returning, ev_unref() after starting, and ev_ref() before stopping it. For	798	from returning, call ev_unref() after starting, and ev_ref() before
		799	stopping it.
		800
499	example, libev itself uses this for its internal signal pipe: It is not	801	As an example, libev itself uses this for its internal signal pipe: It
500	visible to the libev user and should not keep C<ev_loop> from exiting if	802	is not visible to the libev user and should not keep C<ev_loop> from
501	no event watchers registered by it are active. It is also an excellent	803	exiting if no event watchers registered by it are active. It is also an
502	way to do this for generic recurring timers or from within third-party	804	excellent way to do this for generic recurring timers or from within
503	libraries. Just remember to I<unref after start> and I<ref before stop>.	805	third-party libraries. Just remember to I<unref after start> and I<ref
		806	before stop> (but only if the watcher wasn't active before, or was active
		807	before, respectively. Note also that libev might stop watchers itself
		808	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		809	in the callback).
504		810
505	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	811	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
506	running when nothing else is active.	812	running when nothing else is active.
507		813
508	struct ev_signal exitsig;	814	ev_signal exitsig;
509	ev_signal_init (&exitsig, sig_cb, SIGINT);	815	ev_signal_init (&exitsig, sig_cb, SIGINT);
510	ev_signal_start (loop, &exitsig);	816	ev_signal_start (loop, &exitsig);
511	evf_unref (loop);	817	evf_unref (loop);
512		818
513	Example: For some weird reason, unregister the above signal handler again.	819	Example: For some weird reason, unregister the above signal handler again.
514		820
515	ev_ref (loop);	821	ev_ref (loop);
516	ev_signal_stop (loop, &exitsig);	822	ev_signal_stop (loop, &exitsig);
		823
		824	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		825
		826	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		827
		828	These advanced functions influence the time that libev will spend waiting
		829	for events. Both time intervals are by default C<0>, meaning that libev
		830	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		831	latency.
		832
		833	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		834	allows libev to delay invocation of I/O and timer/periodic callbacks
		835	to increase efficiency of loop iterations (or to increase power-saving
		836	opportunities).
		837
		838	The idea is that sometimes your program runs just fast enough to handle
		839	one (or very few) event(s) per loop iteration. While this makes the
		840	program responsive, it also wastes a lot of CPU time to poll for new
		841	events, especially with backends like C<select ()> which have a high
		842	overhead for the actual polling but can deliver many events at once.
		843
		844	By setting a higher I<io collect interval> you allow libev to spend more
		845	time collecting I/O events, so you can handle more events per iteration,
		846	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		847	C<ev_timer>) will be not affected. Setting this to a non-null value will
		848	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		849	sleep time ensures that libev will not poll for I/O events more often then
		850	once per this interval, on average.
		851
		852	Likewise, by setting a higher I<timeout collect interval> you allow libev
		853	to spend more time collecting timeouts, at the expense of increased
		854	latency/jitter/inexactness (the watcher callback will be called
		855	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		856	value will not introduce any overhead in libev.
		857
		858	Many (busy) programs can usually benefit by setting the I/O collect
		859	interval to a value near C<0.1> or so, which is often enough for
		860	interactive servers (of course not for games), likewise for timeouts. It
		861	usually doesn't make much sense to set it to a lower value than C<0.01>,
		862	as this approaches the timing granularity of most systems. Note that if
		863	you do transactions with the outside world and you can't increase the
		864	parallelity, then this setting will limit your transaction rate (if you
		865	need to poll once per transaction and the I/O collect interval is 0.01,
		866	then you can't do more than 100 transations per second).
		867
		868	Setting the I<timeout collect interval> can improve the opportunity for
		869	saving power, as the program will "bundle" timer callback invocations that
		870	are "near" in time together, by delaying some, thus reducing the number of
		871	times the process sleeps and wakes up again. Another useful technique to
		872	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		873	they fire on, say, one-second boundaries only.
		874
		875	Example: we only need 0.1s timeout granularity, and we wish not to poll
		876	more often than 100 times per second:
		877
		878	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		879	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		880
		881	=item ev_invoke_pending (loop)
		882
		883	This call will simply invoke all pending watchers while resetting their
		884	pending state. Normally, C<ev_loop> does this automatically when required,
		885	but when overriding the invoke callback this call comes handy.
		886
		887	=item int ev_pending_count (loop)
		888
		889	Returns the number of pending watchers - zero indicates that no watchers
		890	are pending.
		891
		892	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		893
		894	This overrides the invoke pending functionality of the loop: Instead of
		895	invoking all pending watchers when there are any, C<ev_loop> will call
		896	this callback instead. This is useful, for example, when you want to
		897	invoke the actual watchers inside another context (another thread etc.).
		898
		899	If you want to reset the callback, use C<ev_invoke_pending> as new
		900	callback.
		901
		902	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		903
		904	Sometimes you want to share the same loop between multiple threads. This
		905	can be done relatively simply by putting mutex_lock/unlock calls around
		906	each call to a libev function.
		907
		908	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		909	wait for it to return. One way around this is to wake up the loop via
		910	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		911	and I<acquire> callbacks on the loop.
		912
		913	When set, then C<release> will be called just before the thread is
		914	suspended waiting for new events, and C<acquire> is called just
		915	afterwards.
		916
		917	Ideally, C<release> will just call your mutex_unlock function, and
		918	C<acquire> will just call the mutex_lock function again.
		919
		920	While event loop modifications are allowed between invocations of
		921	C<release> and C<acquire> (that's their only purpose after all), no
		922	modifications done will affect the event loop, i.e. adding watchers will
		923	have no effect on the set of file descriptors being watched, or the time
		924	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		925	to take note of any changes you made.
		926
		927	In theory, threads executing C<ev_loop> will be async-cancel safe between
		928	invocations of C<release> and C<acquire>.
		929
		930	See also the locking example in the C<THREADS> section later in this
		931	document.
		932
		933	=item ev_set_userdata (loop, void *data)
		934
		935	=item ev_userdata (loop)
		936
		937	Set and retrieve a single C<void *> associated with a loop. When
		938	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		939	C<0.>
		940
		941	These two functions can be used to associate arbitrary data with a loop,
		942	and are intended solely for the C<invoke_pending_cb>, C<release> and
		943	C<acquire> callbacks described above, but of course can be (ab-)used for
		944	any other purpose as well.
		945
		946	=item ev_loop_verify (loop)
		947
		948	This function only does something when C<EV_VERIFY> support has been
		949	compiled in, which is the default for non-minimal builds. It tries to go
		950	through all internal structures and checks them for validity. If anything
		951	is found to be inconsistent, it will print an error message to standard
		952	error and call C<abort ()>.
		953
		954	This can be used to catch bugs inside libev itself: under normal
		955	circumstances, this function will never abort as of course libev keeps its
		956	data structures consistent.
517		957
518	=back	958	=back
519		959
520		960
521	=head1 ANATOMY OF A WATCHER	961	=head1 ANATOMY OF A WATCHER
		962
		963	In the following description, uppercase C<TYPE> in names stands for the
		964	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		965	watchers and C<ev_io_start> for I/O watchers.
522		966
523	A watcher is a structure that you create and register to record your	967	A watcher is a structure that you create and register to record your
524	interest in some event. For instance, if you want to wait for STDIN to	968	interest in some event. For instance, if you want to wait for STDIN to
525	become readable, you would create an C<ev_io> watcher for that:	969	become readable, you would create an C<ev_io> watcher for that:
526		970
527	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	971	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
528	{	972	{
529	ev_io_stop (w);	973	ev_io_stop (w);
530	ev_unloop (loop, EVUNLOOP_ALL);	974	ev_unloop (loop, EVUNLOOP_ALL);
531	}	975	}
532		976
533	struct ev_loop *loop = ev_default_loop (0);	977	struct ev_loop *loop = ev_default_loop (0);
		978
534	struct ev_io stdin_watcher;	979	ev_io stdin_watcher;
		980
535	ev_init (&stdin_watcher, my_cb);	981	ev_init (&stdin_watcher, my_cb);
536	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	982	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
537	ev_io_start (loop, &stdin_watcher);	983	ev_io_start (loop, &stdin_watcher);
		984
538	ev_loop (loop, 0);	985	ev_loop (loop, 0);
539		986
540	As you can see, you are responsible for allocating the memory for your	987	As you can see, you are responsible for allocating the memory for your
541	watcher structures (and it is usually a bad idea to do this on the stack,	988	watcher structures (and it is I<usually> a bad idea to do this on the
542	although this can sometimes be quite valid).	989	stack).
		990
		991	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		992	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
543		993
544	Each watcher structure must be initialised by a call to C<ev_init	994	Each watcher structure must be initialised by a call to C<ev_init
545	(watcher *, callback)>, which expects a callback to be provided. This	995	(watcher *, callback)>, which expects a callback to be provided. This
546	callback gets invoked each time the event occurs (or, in the case of io	996	callback gets invoked each time the event occurs (or, in the case of I/O
547	watchers, each time the event loop detects that the file descriptor given	997	watchers, each time the event loop detects that the file descriptor given
548	is readable and/or writable).	998	is readable and/or writable).
549		999
550	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1000	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
551	with arguments specific to this watcher type. There is also a macro	1001	macro to configure it, with arguments specific to the watcher type. There
552	to combine initialisation and setting in one call: C<< ev_<type>_init	1002	is also a macro to combine initialisation and setting in one call: C<<
553	(watcher *, callback, ...) >>.	1003	ev_TYPE_init (watcher *, callback, ...) >>.
554		1004
555	To make the watcher actually watch out for events, you have to start it	1005	To make the watcher actually watch out for events, you have to start it
556	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1006	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
557	*) >>), and you can stop watching for events at any time by calling the	1007	*) >>), and you can stop watching for events at any time by calling the
558	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1008	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
559		1009
560	As long as your watcher is active (has been started but not stopped) you	1010	As long as your watcher is active (has been started but not stopped) you
561	must not touch the values stored in it. Most specifically you must never	1011	must not touch the values stored in it. Most specifically you must never
562	reinitialise it or call its C<set> macro.	1012	reinitialise it or call its C<ev_TYPE_set> macro.
563		1013
564	Each and every callback receives the event loop pointer as first, the	1014	Each and every callback receives the event loop pointer as first, the
565	registered watcher structure as second, and a bitset of received events as	1015	registered watcher structure as second, and a bitset of received events as
566	third argument.	1016	third argument.
567		1017
…		…
621	=item C<EV_FORK>	1071	=item C<EV_FORK>
622		1072
623	The event loop has been resumed in the child process after fork (see	1073	The event loop has been resumed in the child process after fork (see
624	C<ev_fork>).	1074	C<ev_fork>).
625		1075
		1076	=item C<EV_ASYNC>
		1077
		1078	The given async watcher has been asynchronously notified (see C<ev_async>).
		1079
		1080	=item C<EV_CUSTOM>
		1081
		1082	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1083	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1084
626	=item C<EV_ERROR>	1085	=item C<EV_ERROR>
627		1086
628	An unspecified error has occured, the watcher has been stopped. This might	1087	An unspecified error has occurred, the watcher has been stopped. This might
629	happen because the watcher could not be properly started because libev	1088	happen because the watcher could not be properly started because libev
630	ran out of memory, a file descriptor was found to be closed or any other	1089	ran out of memory, a file descriptor was found to be closed or any other
		1090	problem. Libev considers these application bugs.
		1091
631	problem. You best act on it by reporting the problem and somehow coping	1092	You best act on it by reporting the problem and somehow coping with the
632	with the watcher being stopped.	1093	watcher being stopped. Note that well-written programs should not receive
		1094	an error ever, so when your watcher receives it, this usually indicates a
		1095	bug in your program.
633		1096
634	Libev will usually signal a few "dummy" events together with an error,	1097	Libev will usually signal a few "dummy" events together with an error, for
635	for example it might indicate that a fd is readable or writable, and if	1098	example it might indicate that a fd is readable or writable, and if your
636	your callbacks is well-written it can just attempt the operation and cope	1099	callbacks is well-written it can just attempt the operation and cope with
637	with the error from read() or write(). This will not work in multithreaded	1100	the error from read() or write(). This will not work in multi-threaded
638	programs, though, so beware.	1101	programs, though, as the fd could already be closed and reused for another
		1102	thing, so beware.
639		1103
640	=back	1104	=back
641		1105
642	=head2 GENERIC WATCHER FUNCTIONS	1106	=head2 GENERIC WATCHER FUNCTIONS
643
644	In the following description, C<TYPE> stands for the watcher type,
645	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
646		1107
647	=over 4	1108	=over 4
648		1109
649	=item C<ev_init> (ev_TYPE *watcher, callback)	1110	=item C<ev_init> (ev_TYPE *watcher, callback)
650		1111
…		…
656	which rolls both calls into one.	1117	which rolls both calls into one.
657		1118
658	You can reinitialise a watcher at any time as long as it has been stopped	1119	You can reinitialise a watcher at any time as long as it has been stopped
659	(or never started) and there are no pending events outstanding.	1120	(or never started) and there are no pending events outstanding.
660		1121
661	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1122	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
662	int revents)>.	1123	int revents)>.
663		1124
		1125	Example: Initialise an C<ev_io> watcher in two steps.
		1126
		1127	ev_io w;
		1128	ev_init (&w, my_cb);
		1129	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1130
664	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1131	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
665		1132
666	This macro initialises the type-specific parts of a watcher. You need to	1133	This macro initialises the type-specific parts of a watcher. You need to
667	call C<ev_init> at least once before you call this macro, but you can	1134	call C<ev_init> at least once before you call this macro, but you can
668	call C<ev_TYPE_set> any number of times. You must not, however, call this	1135	call C<ev_TYPE_set> any number of times. You must not, however, call this
669	macro on a watcher that is active (it can be pending, however, which is a	1136	macro on a watcher that is active (it can be pending, however, which is a
670	difference to the C<ev_init> macro).	1137	difference to the C<ev_init> macro).
671		1138
672	Although some watcher types do not have type-specific arguments	1139	Although some watcher types do not have type-specific arguments
673	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1140	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
674		1141
		1142	See C<ev_init>, above, for an example.
		1143
675	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1144	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
676		1145
677	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1146	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
678	calls into a single call. This is the most convinient method to initialise	1147	calls into a single call. This is the most convenient method to initialise
679	a watcher. The same limitations apply, of course.	1148	a watcher. The same limitations apply, of course.
680		1149
		1150	Example: Initialise and set an C<ev_io> watcher in one step.
		1151
		1152	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1153
681	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1154	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
682		1155
683	Starts (activates) the given watcher. Only active watchers will receive	1156	Starts (activates) the given watcher. Only active watchers will receive
684	events. If the watcher is already active nothing will happen.	1157	events. If the watcher is already active nothing will happen.
685		1158
		1159	Example: Start the C<ev_io> watcher that is being abused as example in this
		1160	whole section.
		1161
		1162	ev_io_start (EV_DEFAULT_UC, &w);
		1163
686	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1164	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
687		1165
688	Stops the given watcher again (if active) and clears the pending	1166	Stops the given watcher if active, and clears the pending status (whether
		1167	the watcher was active or not).
		1168
689	status. It is possible that stopped watchers are pending (for example,	1169	It is possible that stopped watchers are pending - for example,
690	non-repeating timers are being stopped when they become pending), but	1170	non-repeating timers are being stopped when they become pending - but
691	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1171	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
692	you want to free or reuse the memory used by the watcher it is therefore a	1172	pending. If you want to free or reuse the memory used by the watcher it is
693	good idea to always call its C<ev_TYPE_stop> function.	1173	therefore a good idea to always call its C<ev_TYPE_stop> function.
694		1174
695	=item bool ev_is_active (ev_TYPE *watcher)	1175	=item bool ev_is_active (ev_TYPE *watcher)
696		1176
697	Returns a true value iff the watcher is active (i.e. it has been started	1177	Returns a true value iff the watcher is active (i.e. it has been started
698	and not yet been stopped). As long as a watcher is active you must not modify	1178	and not yet been stopped). As long as a watcher is active you must not modify
…		…
701	=item bool ev_is_pending (ev_TYPE *watcher)	1181	=item bool ev_is_pending (ev_TYPE *watcher)
702		1182
703	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1183	Returns a true value iff the watcher is pending, (i.e. it has outstanding
704	events but its callback has not yet been invoked). As long as a watcher	1184	events but its callback has not yet been invoked). As long as a watcher
705	is pending (but not active) you must not call an init function on it (but	1185	is pending (but not active) you must not call an init function on it (but
706	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1186	C<ev_TYPE_set> is safe), you must not change its priority, and you must
707	libev (e.g. you cnanot C<free ()> it).	1187	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1188	it).
708		1189
709	=item callback ev_cb (ev_TYPE *watcher)	1190	=item callback ev_cb (ev_TYPE *watcher)
710		1191
711	Returns the callback currently set on the watcher.	1192	Returns the callback currently set on the watcher.
712		1193
713	=item ev_cb_set (ev_TYPE *watcher, callback)	1194	=item ev_cb_set (ev_TYPE *watcher, callback)
714		1195
715	Change the callback. You can change the callback at virtually any time	1196	Change the callback. You can change the callback at virtually any time
716	(modulo threads).	1197	(modulo threads).
717		1198
		1199	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1200
		1201	=item int ev_priority (ev_TYPE *watcher)
		1202
		1203	Set and query the priority of the watcher. The priority is a small
		1204	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1205	(default: C<-2>). Pending watchers with higher priority will be invoked
		1206	before watchers with lower priority, but priority will not keep watchers
		1207	from being executed (except for C<ev_idle> watchers).
		1208
		1209	If you need to suppress invocation when higher priority events are pending
		1210	you need to look at C<ev_idle> watchers, which provide this functionality.
		1211
		1212	You I<must not> change the priority of a watcher as long as it is active or
		1213	pending.
		1214
		1215	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1216	fine, as long as you do not mind that the priority value you query might
		1217	or might not have been clamped to the valid range.
		1218
		1219	The default priority used by watchers when no priority has been set is
		1220	always C<0>, which is supposed to not be too high and not be too low :).
		1221
		1222	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1223	priorities.
		1224
		1225	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1226
		1227	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1228	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1229	can deal with that fact, as both are simply passed through to the
		1230	callback.
		1231
		1232	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1233
		1234	If the watcher is pending, this function clears its pending status and
		1235	returns its C<revents> bitset (as if its callback was invoked). If the
		1236	watcher isn't pending it does nothing and returns C<0>.
		1237
		1238	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1239	callback to be invoked, which can be accomplished with this function.
		1240
		1241	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1242
		1243	Feeds the given event set into the event loop, as if the specified event
		1244	had happened for the specified watcher (which must be a pointer to an
		1245	initialised but not necessarily started event watcher). Obviously you must
		1246	not free the watcher as long as it has pending events.
		1247
		1248	Stopping the watcher, letting libev invoke it, or calling
		1249	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1250	not started in the first place.
		1251
		1252	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1253	functions that do not need a watcher.
		1254
718	=back	1255	=back
719		1256
720		1257
721	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1258	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
722		1259
723	Each watcher has, by default, a member C<void *data> that you can change	1260	Each watcher has, by default, a member C<void *data> that you can change
724	and read at any time, libev will completely ignore it. This can be used	1261	and read at any time: libev will completely ignore it. This can be used
725	to associate arbitrary data with your watcher. If you need more data and	1262	to associate arbitrary data with your watcher. If you need more data and
726	don't want to allocate memory and store a pointer to it in that data	1263	don't want to allocate memory and store a pointer to it in that data
727	member, you can also "subclass" the watcher type and provide your own	1264	member, you can also "subclass" the watcher type and provide your own
728	data:	1265	data:
729		1266
730	struct my_io	1267	struct my_io
731	{	1268	{
732	struct ev_io io;	1269	ev_io io;
733	int otherfd;	1270	int otherfd;
734	void *somedata;	1271	void *somedata;
735	struct whatever *mostinteresting;	1272	struct whatever *mostinteresting;
736	}	1273	};
		1274
		1275	...
		1276	struct my_io w;
		1277	ev_io_init (&w.io, my_cb, fd, EV_READ);
737		1278
738	And since your callback will be called with a pointer to the watcher, you	1279	And since your callback will be called with a pointer to the watcher, you
739	can cast it back to your own type:	1280	can cast it back to your own type:
740		1281
741	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1282	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
742	{	1283	{
743	struct my_io *w = (struct my_io *)w_;	1284	struct my_io *w = (struct my_io *)w_;
744	...	1285	...
745	}	1286	}
746		1287
747	More interesting and less C-conformant ways of casting your callback type	1288	More interesting and less C-conformant ways of casting your callback type
748	instead have been omitted.	1289	instead have been omitted.
749		1290
750	Another common scenario is having some data structure with multiple	1291	Another common scenario is to use some data structure with multiple
751	watchers:	1292	embedded watchers:
752		1293
753	struct my_biggy	1294	struct my_biggy
754	{	1295	{
755	int some_data;	1296	int some_data;
756	ev_timer t1;	1297	ev_timer t1;
757	ev_timer t2;	1298	ev_timer t2;
758	}	1299	}
759		1300
760	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1301	In this case getting the pointer to C<my_biggy> is a bit more
761	you need to use C<offsetof>:	1302	complicated: Either you store the address of your C<my_biggy> struct
		1303	in the C<data> member of the watcher (for woozies), or you need to use
		1304	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1305	programmers):
762		1306
763	#include <stddef.h>	1307	#include <stddef.h>
764		1308
765	static void	1309	static void
766	t1_cb (EV_P_ struct ev_timer *w, int revents)	1310	t1_cb (EV_P_ ev_timer *w, int revents)
767	{	1311	{
768	struct my_biggy big = (struct my_biggy *	1312	struct my_biggy big = (struct my_biggy *)
769	(((char *)w) - offsetof (struct my_biggy, t1));	1313	(((char *)w) - offsetof (struct my_biggy, t1));
770	}	1314	}
771		1315
772	static void	1316	static void
773	t2_cb (EV_P_ struct ev_timer *w, int revents)	1317	t2_cb (EV_P_ ev_timer *w, int revents)
774	{	1318	{
775	struct my_biggy big = (struct my_biggy *	1319	struct my_biggy big = (struct my_biggy *)
776	(((char *)w) - offsetof (struct my_biggy, t2));	1320	(((char *)w) - offsetof (struct my_biggy, t2));
777	}	1321	}
		1322
		1323	=head2 WATCHER PRIORITY MODELS
		1324
		1325	Many event loops support I<watcher priorities>, which are usually small
		1326	integers that influence the ordering of event callback invocation
		1327	between watchers in some way, all else being equal.
		1328
		1329	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1330	description for the more technical details such as the actual priority
		1331	range.
		1332
		1333	There are two common ways how these these priorities are being interpreted
		1334	by event loops:
		1335
		1336	In the more common lock-out model, higher priorities "lock out" invocation
		1337	of lower priority watchers, which means as long as higher priority
		1338	watchers receive events, lower priority watchers are not being invoked.
		1339
		1340	The less common only-for-ordering model uses priorities solely to order
		1341	callback invocation within a single event loop iteration: Higher priority
		1342	watchers are invoked before lower priority ones, but they all get invoked
		1343	before polling for new events.
		1344
		1345	Libev uses the second (only-for-ordering) model for all its watchers
		1346	except for idle watchers (which use the lock-out model).
		1347
		1348	The rationale behind this is that implementing the lock-out model for
		1349	watchers is not well supported by most kernel interfaces, and most event
		1350	libraries will just poll for the same events again and again as long as
		1351	their callbacks have not been executed, which is very inefficient in the
		1352	common case of one high-priority watcher locking out a mass of lower
		1353	priority ones.
		1354
		1355	Static (ordering) priorities are most useful when you have two or more
		1356	watchers handling the same resource: a typical usage example is having an
		1357	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1358	timeouts. Under load, data might be received while the program handles
		1359	other jobs, but since timers normally get invoked first, the timeout
		1360	handler will be executed before checking for data. In that case, giving
		1361	the timer a lower priority than the I/O watcher ensures that I/O will be
		1362	handled first even under adverse conditions (which is usually, but not
		1363	always, what you want).
		1364
		1365	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1366	will only be executed when no same or higher priority watchers have
		1367	received events, they can be used to implement the "lock-out" model when
		1368	required.
		1369
		1370	For example, to emulate how many other event libraries handle priorities,
		1371	you can associate an C<ev_idle> watcher to each such watcher, and in
		1372	the normal watcher callback, you just start the idle watcher. The real
		1373	processing is done in the idle watcher callback. This causes libev to
		1374	continously poll and process kernel event data for the watcher, but when
		1375	the lock-out case is known to be rare (which in turn is rare :), this is
		1376	workable.
		1377
		1378	Usually, however, the lock-out model implemented that way will perform
		1379	miserably under the type of load it was designed to handle. In that case,
		1380	it might be preferable to stop the real watcher before starting the
		1381	idle watcher, so the kernel will not have to process the event in case
		1382	the actual processing will be delayed for considerable time.
		1383
		1384	Here is an example of an I/O watcher that should run at a strictly lower
		1385	priority than the default, and which should only process data when no
		1386	other events are pending:
		1387
		1388	ev_idle idle; // actual processing watcher
		1389	ev_io io; // actual event watcher
		1390
		1391	static void
		1392	io_cb (EV_P_ ev_io *w, int revents)
		1393	{
		1394	// stop the I/O watcher, we received the event, but
		1395	// are not yet ready to handle it.
		1396	ev_io_stop (EV_A_ w);
		1397
		1398	// start the idle watcher to ahndle the actual event.
		1399	// it will not be executed as long as other watchers
		1400	// with the default priority are receiving events.
		1401	ev_idle_start (EV_A_ &idle);
		1402	}
		1403
		1404	static void
		1405	idle_cb (EV_P_ ev_idle *w, int revents)
		1406	{
		1407	// actual processing
		1408	read (STDIN_FILENO, ...);
		1409
		1410	// have to start the I/O watcher again, as
		1411	// we have handled the event
		1412	ev_io_start (EV_P_ &io);
		1413	}
		1414
		1415	// initialisation
		1416	ev_idle_init (&idle, idle_cb);
		1417	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1418	ev_io_start (EV_DEFAULT_ &io);
		1419
		1420	In the "real" world, it might also be beneficial to start a timer, so that
		1421	low-priority connections can not be locked out forever under load. This
		1422	enables your program to keep a lower latency for important connections
		1423	during short periods of high load, while not completely locking out less
		1424	important ones.
778		1425
779		1426
780	=head1 WATCHER TYPES	1427	=head1 WATCHER TYPES
781		1428
782	This section describes each watcher in detail, but will not repeat	1429	This section describes each watcher in detail, but will not repeat
…		…
806	In general you can register as many read and/or write event watchers per	1453	In general you can register as many read and/or write event watchers per
807	fd as you want (as long as you don't confuse yourself). Setting all file	1454	fd as you want (as long as you don't confuse yourself). Setting all file
808	descriptors to non-blocking mode is also usually a good idea (but not	1455	descriptors to non-blocking mode is also usually a good idea (but not
809	required if you know what you are doing).	1456	required if you know what you are doing).
810		1457
811	You have to be careful with dup'ed file descriptors, though. Some backends	1458	If you cannot use non-blocking mode, then force the use of a
812	(the linux epoll backend is a notable example) cannot handle dup'ed file	1459	known-to-be-good backend (at the time of this writing, this includes only
813	descriptors correctly if you register interest in two or more fds pointing	1460	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
814	to the same underlying file/socket/etc. description (that is, they share	1461	descriptors for which non-blocking operation makes no sense (such as
815	the same underlying "file open").	1462	files) - libev doesn't guarentee any specific behaviour in that case.
816
817	If you must do this, then force the use of a known-to-be-good backend
818	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
819	C<EVBACKEND_POLL>).
820		1463
821	Another thing you have to watch out for is that it is quite easy to	1464	Another thing you have to watch out for is that it is quite easy to
822	receive "spurious" readyness notifications, that is your callback might	1465	receive "spurious" readiness notifications, that is your callback might
823	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1466	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
824	because there is no data. Not only are some backends known to create a	1467	because there is no data. Not only are some backends known to create a
825	lot of those (for example solaris ports), it is very easy to get into	1468	lot of those (for example Solaris ports), it is very easy to get into
826	this situation even with a relatively standard program structure. Thus	1469	this situation even with a relatively standard program structure. Thus
827	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1470	it is best to always use non-blocking I/O: An extra C<read>(2) returning
828	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1471	C<EAGAIN> is far preferable to a program hanging until some data arrives.
829		1472
830	If you cannot run the fd in non-blocking mode (for example you should not	1473	If you cannot run the fd in non-blocking mode (for example you should
831	play around with an Xlib connection), then you have to seperately re-test	1474	not play around with an Xlib connection), then you have to separately
832	wether a file descriptor is really ready with a known-to-be good interface	1475	re-test whether a file descriptor is really ready with a known-to-be good
833	such as poll (fortunately in our Xlib example, Xlib already does this on	1476	interface such as poll (fortunately in our Xlib example, Xlib already
834	its own, so its quite safe to use).	1477	does this on its own, so its quite safe to use). Some people additionally
		1478	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1479	indefinitely.
		1480
		1481	But really, best use non-blocking mode.
		1482
		1483	=head3 The special problem of disappearing file descriptors
		1484
		1485	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1486	descriptor (either due to calling C<close> explicitly or any other means,
		1487	such as C<dup2>). The reason is that you register interest in some file
		1488	descriptor, but when it goes away, the operating system will silently drop
		1489	this interest. If another file descriptor with the same number then is
		1490	registered with libev, there is no efficient way to see that this is, in
		1491	fact, a different file descriptor.
		1492
		1493	To avoid having to explicitly tell libev about such cases, libev follows
		1494	the following policy: Each time C<ev_io_set> is being called, libev
		1495	will assume that this is potentially a new file descriptor, otherwise
		1496	it is assumed that the file descriptor stays the same. That means that
		1497	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1498	descriptor even if the file descriptor number itself did not change.
		1499
		1500	This is how one would do it normally anyway, the important point is that
		1501	the libev application should not optimise around libev but should leave
		1502	optimisations to libev.
		1503
		1504	=head3 The special problem of dup'ed file descriptors
		1505
		1506	Some backends (e.g. epoll), cannot register events for file descriptors,
		1507	but only events for the underlying file descriptions. That means when you
		1508	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1509	events for them, only one file descriptor might actually receive events.
		1510
		1511	There is no workaround possible except not registering events
		1512	for potentially C<dup ()>'ed file descriptors, or to resort to
		1513	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1514
		1515	=head3 The special problem of fork
		1516
		1517	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1518	useless behaviour. Libev fully supports fork, but needs to be told about
		1519	it in the child.
		1520
		1521	To support fork in your programs, you either have to call
		1522	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1523	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1524	C<EVBACKEND_POLL>.
		1525
		1526	=head3 The special problem of SIGPIPE
		1527
		1528	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1529	when writing to a pipe whose other end has been closed, your program gets
		1530	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1531	this is sensible behaviour, for daemons, this is usually undesirable.
		1532
		1533	So when you encounter spurious, unexplained daemon exits, make sure you
		1534	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1535	somewhere, as that would have given you a big clue).
		1536
		1537
		1538	=head3 Watcher-Specific Functions
835		1539
836	=over 4	1540	=over 4
837		1541
838	=item ev_io_init (ev_io *, callback, int fd, int events)	1542	=item ev_io_init (ev_io *, callback, int fd, int events)
839		1543
840	=item ev_io_set (ev_io *, int fd, int events)	1544	=item ev_io_set (ev_io *, int fd, int events)
841		1545
842	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1546	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
843	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1547	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
844	C<EV_READ | EV_WRITE> to receive the given events.	1548	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
845		1549
846	=item int fd [read-only]	1550	=item int fd [read-only]
847		1551
848	The file descriptor being watched.	1552	The file descriptor being watched.
849		1553
850	=item int events [read-only]	1554	=item int events [read-only]
851		1555
852	The events being watched.	1556	The events being watched.
853		1557
854	=back	1558	=back
		1559
		1560	=head3 Examples
855		1561
856	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1562	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
857	readable, but only once. Since it is likely line-buffered, you could	1563	readable, but only once. Since it is likely line-buffered, you could
858	attempt to read a whole line in the callback.	1564	attempt to read a whole line in the callback.
859		1565
860	static void	1566	static void
861	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1567	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
862	{	1568	{
863	ev_io_stop (loop, w);	1569	ev_io_stop (loop, w);
864	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1570	.. read from stdin here (or from w->fd) and handle any I/O errors
865	}	1571	}
866		1572
867	...	1573	...
868	struct ev_loop *loop = ev_default_init (0);	1574	struct ev_loop *loop = ev_default_init (0);
869	struct ev_io stdin_readable;	1575	ev_io stdin_readable;
870	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1576	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
871	ev_io_start (loop, &stdin_readable);	1577	ev_io_start (loop, &stdin_readable);
872	ev_loop (loop, 0);	1578	ev_loop (loop, 0);
873		1579
874		1580
875	=head2 C<ev_timer> - relative and optionally repeating timeouts	1581	=head2 C<ev_timer> - relative and optionally repeating timeouts
876		1582
877	Timer watchers are simple relative timers that generate an event after a	1583	Timer watchers are simple relative timers that generate an event after a
878	given time, and optionally repeating in regular intervals after that.	1584	given time, and optionally repeating in regular intervals after that.
879		1585
880	The timers are based on real time, that is, if you register an event that	1586	The timers are based on real time, that is, if you register an event that
881	times out after an hour and you reset your system clock to last years	1587	times out after an hour and you reset your system clock to January last
882	time, it will still time out after (roughly) and hour. "Roughly" because	1588	year, it will still time out after (roughly) one hour. "Roughly" because
883	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1589	detecting time jumps is hard, and some inaccuracies are unavoidable (the
884	monotonic clock option helps a lot here).	1590	monotonic clock option helps a lot here).
		1591
		1592	The callback is guaranteed to be invoked only I<after> its timeout has
		1593	passed (not I<at>, so on systems with very low-resolution clocks this
		1594	might introduce a small delay). If multiple timers become ready during the
		1595	same loop iteration then the ones with earlier time-out values are invoked
		1596	before ones of the same priority with later time-out values (but this is
		1597	no longer true when a callback calls C<ev_loop> recursively).
		1598
		1599	=head3 Be smart about timeouts
		1600
		1601	Many real-world problems involve some kind of timeout, usually for error
		1602	recovery. A typical example is an HTTP request - if the other side hangs,
		1603	you want to raise some error after a while.
		1604
		1605	What follows are some ways to handle this problem, from obvious and
		1606	inefficient to smart and efficient.
		1607
		1608	In the following, a 60 second activity timeout is assumed - a timeout that
		1609	gets reset to 60 seconds each time there is activity (e.g. each time some
		1610	data or other life sign was received).
		1611
		1612	=over 4
		1613
		1614	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1615
		1616	This is the most obvious, but not the most simple way: In the beginning,
		1617	start the watcher:
		1618
		1619	ev_timer_init (timer, callback, 60., 0.);
		1620	ev_timer_start (loop, timer);
		1621
		1622	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1623	and start it again:
		1624
		1625	ev_timer_stop (loop, timer);
		1626	ev_timer_set (timer, 60., 0.);
		1627	ev_timer_start (loop, timer);
		1628
		1629	This is relatively simple to implement, but means that each time there is
		1630	some activity, libev will first have to remove the timer from its internal
		1631	data structure and then add it again. Libev tries to be fast, but it's
		1632	still not a constant-time operation.
		1633
		1634	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1635
		1636	This is the easiest way, and involves using C<ev_timer_again> instead of
		1637	C<ev_timer_start>.
		1638
		1639	To implement this, configure an C<ev_timer> with a C<repeat> value
		1640	of C<60> and then call C<ev_timer_again> at start and each time you
		1641	successfully read or write some data. If you go into an idle state where
		1642	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1643	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1644
		1645	That means you can ignore both the C<ev_timer_start> function and the
		1646	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1647	member and C<ev_timer_again>.
		1648
		1649	At start:
		1650
		1651	ev_init (timer, callback);
		1652	timer->repeat = 60.;
		1653	ev_timer_again (loop, timer);
		1654
		1655	Each time there is some activity:
		1656
		1657	ev_timer_again (loop, timer);
		1658
		1659	It is even possible to change the time-out on the fly, regardless of
		1660	whether the watcher is active or not:
		1661
		1662	timer->repeat = 30.;
		1663	ev_timer_again (loop, timer);
		1664
		1665	This is slightly more efficient then stopping/starting the timer each time
		1666	you want to modify its timeout value, as libev does not have to completely
		1667	remove and re-insert the timer from/into its internal data structure.
		1668
		1669	It is, however, even simpler than the "obvious" way to do it.
		1670
		1671	=item 3. Let the timer time out, but then re-arm it as required.
		1672
		1673	This method is more tricky, but usually most efficient: Most timeouts are
		1674	relatively long compared to the intervals between other activity - in
		1675	our example, within 60 seconds, there are usually many I/O events with
		1676	associated activity resets.
		1677
		1678	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1679	but remember the time of last activity, and check for a real timeout only
		1680	within the callback:
		1681
		1682	ev_tstamp last_activity; // time of last activity
		1683
		1684	static void
		1685	callback (EV_P_ ev_timer *w, int revents)
		1686	{
		1687	ev_tstamp now = ev_now (EV_A);
		1688	ev_tstamp timeout = last_activity + 60.;
		1689
		1690	// if last_activity + 60. is older than now, we did time out
		1691	if (timeout < now)
		1692	{
		1693	// timeout occured, take action
		1694	}
		1695	else
		1696	{
		1697	// callback was invoked, but there was some activity, re-arm
		1698	// the watcher to fire in last_activity + 60, which is
		1699	// guaranteed to be in the future, so "again" is positive:
		1700	w->repeat = timeout - now;
		1701	ev_timer_again (EV_A_ w);
		1702	}
		1703	}
		1704
		1705	To summarise the callback: first calculate the real timeout (defined
		1706	as "60 seconds after the last activity"), then check if that time has
		1707	been reached, which means something I<did>, in fact, time out. Otherwise
		1708	the callback was invoked too early (C<timeout> is in the future), so
		1709	re-schedule the timer to fire at that future time, to see if maybe we have
		1710	a timeout then.
		1711
		1712	Note how C<ev_timer_again> is used, taking advantage of the
		1713	C<ev_timer_again> optimisation when the timer is already running.
		1714
		1715	This scheme causes more callback invocations (about one every 60 seconds
		1716	minus half the average time between activity), but virtually no calls to
		1717	libev to change the timeout.
		1718
		1719	To start the timer, simply initialise the watcher and set C<last_activity>
		1720	to the current time (meaning we just have some activity :), then call the
		1721	callback, which will "do the right thing" and start the timer:
		1722
		1723	ev_init (timer, callback);
		1724	last_activity = ev_now (loop);
		1725	callback (loop, timer, EV_TIMEOUT);
		1726
		1727	And when there is some activity, simply store the current time in
		1728	C<last_activity>, no libev calls at all:
		1729
		1730	last_actiivty = ev_now (loop);
		1731
		1732	This technique is slightly more complex, but in most cases where the
		1733	time-out is unlikely to be triggered, much more efficient.
		1734
		1735	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1736	callback :) - just change the timeout and invoke the callback, which will
		1737	fix things for you.
		1738
		1739	=item 4. Wee, just use a double-linked list for your timeouts.
		1740
		1741	If there is not one request, but many thousands (millions...), all
		1742	employing some kind of timeout with the same timeout value, then one can
		1743	do even better:
		1744
		1745	When starting the timeout, calculate the timeout value and put the timeout
		1746	at the I<end> of the list.
		1747
		1748	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1749	the list is expected to fire (for example, using the technique #3).
		1750
		1751	When there is some activity, remove the timer from the list, recalculate
		1752	the timeout, append it to the end of the list again, and make sure to
		1753	update the C<ev_timer> if it was taken from the beginning of the list.
		1754
		1755	This way, one can manage an unlimited number of timeouts in O(1) time for
		1756	starting, stopping and updating the timers, at the expense of a major
		1757	complication, and having to use a constant timeout. The constant timeout
		1758	ensures that the list stays sorted.
		1759
		1760	=back
		1761
		1762	So which method the best?
		1763
		1764	Method #2 is a simple no-brain-required solution that is adequate in most
		1765	situations. Method #3 requires a bit more thinking, but handles many cases
		1766	better, and isn't very complicated either. In most case, choosing either
		1767	one is fine, with #3 being better in typical situations.
		1768
		1769	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1770	rather complicated, but extremely efficient, something that really pays
		1771	off after the first million or so of active timers, i.e. it's usually
		1772	overkill :)
		1773
		1774	=head3 The special problem of time updates
		1775
		1776	Establishing the current time is a costly operation (it usually takes at
		1777	least two system calls): EV therefore updates its idea of the current
		1778	time only before and after C<ev_loop> collects new events, which causes a
		1779	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1780	lots of events in one iteration.
885		1781
886	The relative timeouts are calculated relative to the C<ev_now ()>	1782	The relative timeouts are calculated relative to the C<ev_now ()>
887	time. This is usually the right thing as this timestamp refers to the time	1783	time. This is usually the right thing as this timestamp refers to the time
888	of the event triggering whatever timeout you are modifying/starting. If	1784	of the event triggering whatever timeout you are modifying/starting. If
889	you suspect event processing to be delayed and you I<need> to base the timeout	1785	you suspect event processing to be delayed and you I<need> to base the
890	on the current time, use something like this to adjust for this:	1786	timeout on the current time, use something like this to adjust for this:
891		1787
892	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1788	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
893		1789
894	The callback is guarenteed to be invoked only when its timeout has passed,	1790	If the event loop is suspended for a long time, you can also force an
895	but if multiple timers become ready during the same loop iteration then	1791	update of the time returned by C<ev_now ()> by calling C<ev_now_update
896	order of execution is undefined.	1792	()>.
		1793
		1794	=head3 The special problems of suspended animation
		1795
		1796	When you leave the server world it is quite customary to hit machines that
		1797	can suspend/hibernate - what happens to the clocks during such a suspend?
		1798
		1799	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1800	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1801	to run until the system is suspended, but they will not advance while the
		1802	system is suspended. That means, on resume, it will be as if the program
		1803	was frozen for a few seconds, but the suspend time will not be counted
		1804	towards C<ev_timer> when a monotonic clock source is used. The real time
		1805	clock advanced as expected, but if it is used as sole clocksource, then a
		1806	long suspend would be detected as a time jump by libev, and timers would
		1807	be adjusted accordingly.
		1808
		1809	I would not be surprised to see different behaviour in different between
		1810	operating systems, OS versions or even different hardware.
		1811
		1812	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1813	time jump in the monotonic clocks and the realtime clock. If the program
		1814	is suspended for a very long time, and monotonic clock sources are in use,
		1815	then you can expect C<ev_timer>s to expire as the full suspension time
		1816	will be counted towards the timers. When no monotonic clock source is in
		1817	use, then libev will again assume a timejump and adjust accordingly.
		1818
		1819	It might be beneficial for this latter case to call C<ev_suspend>
		1820	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1821	deterministic behaviour in this case (you can do nothing against
		1822	C<SIGSTOP>).
		1823
		1824	=head3 Watcher-Specific Functions and Data Members
897		1825
898	=over 4	1826	=over 4
899		1827
900	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1828	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
901		1829
902	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1830	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
903		1831
904	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1832	Configure the timer to trigger after C<after> seconds. If C<repeat>
905	C<0.>, then it will automatically be stopped. If it is positive, then the	1833	is C<0.>, then it will automatically be stopped once the timeout is
906	timer will automatically be configured to trigger again C<repeat> seconds	1834	reached. If it is positive, then the timer will automatically be
907	later, again, and again, until stopped manually.	1835	configured to trigger again C<repeat> seconds later, again, and again,
		1836	until stopped manually.
908		1837
909	The timer itself will do a best-effort at avoiding drift, that is, if you	1838	The timer itself will do a best-effort at avoiding drift, that is, if
910	configure a timer to trigger every 10 seconds, then it will trigger at	1839	you configure a timer to trigger every 10 seconds, then it will normally
911	exactly 10 second intervals. If, however, your program cannot keep up with	1840	trigger at exactly 10 second intervals. If, however, your program cannot
912	the timer (because it takes longer than those 10 seconds to do stuff) the	1841	keep up with the timer (because it takes longer than those 10 seconds to
913	timer will not fire more than once per event loop iteration.	1842	do stuff) the timer will not fire more than once per event loop iteration.
914		1843
915	=item ev_timer_again (loop)	1844	=item ev_timer_again (loop, ev_timer *)
916		1845
917	This will act as if the timer timed out and restart it again if it is	1846	This will act as if the timer timed out and restart it again if it is
918	repeating. The exact semantics are:	1847	repeating. The exact semantics are:
919		1848
		1849	If the timer is pending, its pending status is cleared.
		1850
920	If the timer is started but nonrepeating, stop it.	1851	If the timer is started but non-repeating, stop it (as if it timed out).
921		1852
922	If the timer is repeating, either start it if necessary (with the repeat	1853	If the timer is repeating, either start it if necessary (with the
923	value), or reset the running timer to the repeat value.	1854	C<repeat> value), or reset the running timer to the C<repeat> value.
924		1855
925	This sounds a bit complicated, but here is a useful and typical	1856	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
926	example: Imagine you have a tcp connection and you want a so-called	1857	usage example.
927	idle timeout, that is, you want to be called when there have been,
928	say, 60 seconds of inactivity on the socket. The easiest way to do
929	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
930	C<ev_timer_again> each time you successfully read or write some data. If
931	you go into an idle state where you do not expect data to travel on the
932	socket, you can stop the timer, and again will automatically restart it if
933	need be.
934		1858
935	You can also ignore the C<after> value and C<ev_timer_start> altogether	1859	=item ev_timer_remaining (loop, ev_timer *)
936	and only ever use the C<repeat> value:
937		1860
938	ev_timer_init (timer, callback, 0., 5.);	1861	Returns the remaining time until a timer fires. If the timer is active,
939	ev_timer_again (loop, timer);	1862	then this time is relative to the current event loop time, otherwise it's
940	...	1863	the timeout value currently configured.
941	timer->again = 17.;
942	ev_timer_again (loop, timer);
943	...
944	timer->again = 10.;
945	ev_timer_again (loop, timer);
946		1864
947	This is more efficient then stopping/starting the timer eahc time you want	1865	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
948	to modify its timeout value.	1866	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1867	will return C<4>. When the timer expires and is restarted, it will return
		1868	roughly C<7> (likely slightly less as callback invocation takes some time,
		1869	too), and so on.
949		1870
950	=item ev_tstamp repeat [read-write]	1871	=item ev_tstamp repeat [read-write]
951		1872
952	The current C<repeat> value. Will be used each time the watcher times out	1873	The current C<repeat> value. Will be used each time the watcher times out
953	or C<ev_timer_again> is called and determines the next timeout (if any),	1874	or C<ev_timer_again> is called, and determines the next timeout (if any),
954	which is also when any modifications are taken into account.	1875	which is also when any modifications are taken into account.
955		1876
956	=back	1877	=back
957		1878
		1879	=head3 Examples
		1880
958	Example: Create a timer that fires after 60 seconds.	1881	Example: Create a timer that fires after 60 seconds.
959		1882
960	static void	1883	static void
961	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1884	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
962	{	1885	{
963	.. one minute over, w is actually stopped right here	1886	.. one minute over, w is actually stopped right here
964	}	1887	}
965		1888
966	struct ev_timer mytimer;	1889	ev_timer mytimer;
967	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1890	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
968	ev_timer_start (loop, &mytimer);	1891	ev_timer_start (loop, &mytimer);
969		1892
970	Example: Create a timeout timer that times out after 10 seconds of	1893	Example: Create a timeout timer that times out after 10 seconds of
971	inactivity.	1894	inactivity.
972		1895
973	static void	1896	static void
974	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1897	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
975	{	1898	{
976	.. ten seconds without any activity	1899	.. ten seconds without any activity
977	}	1900	}
978		1901
979	struct ev_timer mytimer;	1902	ev_timer mytimer;
980	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1903	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
981	ev_timer_again (&mytimer); /* start timer */	1904	ev_timer_again (&mytimer); /* start timer */
982	ev_loop (loop, 0);	1905	ev_loop (loop, 0);
983		1906
984	// and in some piece of code that gets executed on any "activity":	1907	// and in some piece of code that gets executed on any "activity":
985	// reset the timeout to start ticking again at 10 seconds	1908	// reset the timeout to start ticking again at 10 seconds
986	ev_timer_again (&mytimer);	1909	ev_timer_again (&mytimer);
987		1910
988		1911
989	=head2 C<ev_periodic> - to cron or not to cron?	1912	=head2 C<ev_periodic> - to cron or not to cron?
990		1913
991	Periodic watchers are also timers of a kind, but they are very versatile	1914	Periodic watchers are also timers of a kind, but they are very versatile
992	(and unfortunately a bit complex).	1915	(and unfortunately a bit complex).
993		1916
994	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1917	Unlike C<ev_timer>, periodic watchers are not based on real time (or
995	but on wallclock time (absolute time). You can tell a periodic watcher	1918	relative time, the physical time that passes) but on wall clock time
996	to trigger "at" some specific point in time. For example, if you tell a	1919	(absolute time, the thing you can read on your calender or clock). The
997	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1920	difference is that wall clock time can run faster or slower than real
998	+ 10.>) and then reset your system clock to the last year, then it will	1921	time, and time jumps are not uncommon (e.g. when you adjust your
999	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1922	wrist-watch).
1000	roughly 10 seconds later and of course not if you reset your system time
1001	again).
1002		1923
1003	They can also be used to implement vastly more complex timers, such as	1924	You can tell a periodic watcher to trigger after some specific point
		1925	in time: for example, if you tell a periodic watcher to trigger "in 10
		1926	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1927	not a delay) and then reset your system clock to January of the previous
		1928	year, then it will take a year or more to trigger the event (unlike an
		1929	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1930	it, as it uses a relative timeout).
		1931
		1932	C<ev_periodic> watchers can also be used to implement vastly more complex
1004	triggering an event on eahc midnight, local time.	1933	timers, such as triggering an event on each "midnight, local time", or
		1934	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1935	those cannot react to time jumps.
1005		1936
1006	As with timers, the callback is guarenteed to be invoked only when the	1937	As with timers, the callback is guaranteed to be invoked only when the
1007	time (C<at>) has been passed, but if multiple periodic timers become ready	1938	point in time where it is supposed to trigger has passed. If multiple
1008	during the same loop iteration then order of execution is undefined.	1939	timers become ready during the same loop iteration then the ones with
		1940	earlier time-out values are invoked before ones with later time-out values
		1941	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1942
		1943	=head3 Watcher-Specific Functions and Data Members
1009		1944
1010	=over 4	1945	=over 4
1011		1946
1012	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1947	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1013		1948
1014	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1949	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1015		1950
1016	Lots of arguments, lets sort it out... There are basically three modes of	1951	Lots of arguments, let's sort it out... There are basically three modes of
1017	operation, and we will explain them from simplest to complex:	1952	operation, and we will explain them from simplest to most complex:
1018		1953
1019	=over 4	1954	=over 4
1020		1955
1021	=item * absolute timer (interval = reschedule_cb = 0)	1956	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1022		1957
1023	In this configuration the watcher triggers an event at the wallclock time	1958	In this configuration the watcher triggers an event after the wall clock
1024	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1959	time C<offset> has passed. It will not repeat and will not adjust when a
1025	that is, if it is to be run at January 1st 2011 then it will run when the	1960	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1026	system time reaches or surpasses this time.	1961	will be stopped and invoked when the system clock reaches or surpasses
		1962	this point in time.
1027		1963
1028	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1964	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1029		1965
1030	In this mode the watcher will always be scheduled to time out at the next	1966	In this mode the watcher will always be scheduled to time out at the next
1031	C<at + N * interval> time (for some integer N) and then repeat, regardless	1967	C<offset + N * interval> time (for some integer N, which can also be
1032	of any time jumps.	1968	negative) and then repeat, regardless of any time jumps. The C<offset>
		1969	argument is merely an offset into the C<interval> periods.
1033		1970
1034	This can be used to create timers that do not drift with respect to system	1971	This can be used to create timers that do not drift with respect to the
1035	time:	1972	system clock, for example, here is an C<ev_periodic> that triggers each
		1973	hour, on the hour (with respect to UTC):
1036		1974
1037	ev_periodic_set (&periodic, 0., 3600., 0);	1975	ev_periodic_set (&periodic, 0., 3600., 0);
1038		1976
1039	This doesn't mean there will always be 3600 seconds in between triggers,	1977	This doesn't mean there will always be 3600 seconds in between triggers,
1040	but only that the the callback will be called when the system time shows a	1978	but only that the callback will be called when the system time shows a
1041	full hour (UTC), or more correctly, when the system time is evenly divisible	1979	full hour (UTC), or more correctly, when the system time is evenly divisible
1042	by 3600.	1980	by 3600.
1043		1981
1044	Another way to think about it (for the mathematically inclined) is that	1982	Another way to think about it (for the mathematically inclined) is that
1045	C<ev_periodic> will try to run the callback in this mode at the next possible	1983	C<ev_periodic> will try to run the callback in this mode at the next possible
1046	time where C<time = at (mod interval)>, regardless of any time jumps.	1984	time where C<time = offset (mod interval)>, regardless of any time jumps.
1047		1985
		1986	For numerical stability it is preferable that the C<offset> value is near
		1987	C<ev_now ()> (the current time), but there is no range requirement for
		1988	this value, and in fact is often specified as zero.
		1989
		1990	Note also that there is an upper limit to how often a timer can fire (CPU
		1991	speed for example), so if C<interval> is very small then timing stability
		1992	will of course deteriorate. Libev itself tries to be exact to be about one
		1993	millisecond (if the OS supports it and the machine is fast enough).
		1994
1048	=item * manual reschedule mode (reschedule_cb = callback)	1995	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1049		1996
1050	In this mode the values for C<interval> and C<at> are both being	1997	In this mode the values for C<interval> and C<offset> are both being
1051	ignored. Instead, each time the periodic watcher gets scheduled, the	1998	ignored. Instead, each time the periodic watcher gets scheduled, the
1052	reschedule callback will be called with the watcher as first, and the	1999	reschedule callback will be called with the watcher as first, and the
1053	current time as second argument.	2000	current time as second argument.
1054		2001
1055	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2002	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1056	ever, or make any event loop modifications>. If you need to stop it,	2003	or make ANY other event loop modifications whatsoever, unless explicitly
1057	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2004	allowed by documentation here>.
1058	starting a prepare watcher).
1059		2005
		2006	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2007	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2008	only event loop modification you are allowed to do).
		2009
1060	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2010	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1061	ev_tstamp now)>, e.g.:	2011	*w, ev_tstamp now)>, e.g.:
1062		2012
		2013	static ev_tstamp
1063	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2014	my_rescheduler (ev_periodic *w, ev_tstamp now)
1064	{	2015	{
1065	return now + 60.;	2016	return now + 60.;
1066	}	2017	}
1067		2018
1068	It must return the next time to trigger, based on the passed time value	2019	It must return the next time to trigger, based on the passed time value
1069	(that is, the lowest time value larger than to the second argument). It	2020	(that is, the lowest time value larger than to the second argument). It
1070	will usually be called just before the callback will be triggered, but	2021	will usually be called just before the callback will be triggered, but
1071	might be called at other times, too.	2022	might be called at other times, too.
1072		2023
1073	NOTE: I<< This callback must always return a time that is later than the	2024	NOTE: I<< This callback must always return a time that is higher than or
1074	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2025	equal to the passed C<now> value >>.
1075		2026
1076	This can be used to create very complex timers, such as a timer that	2027	This can be used to create very complex timers, such as a timer that
1077	triggers on each midnight, local time. To do this, you would calculate the	2028	triggers on "next midnight, local time". To do this, you would calculate the
1078	next midnight after C<now> and return the timestamp value for this. How	2029	next midnight after C<now> and return the timestamp value for this. How
1079	you do this is, again, up to you (but it is not trivial, which is the main	2030	you do this is, again, up to you (but it is not trivial, which is the main
1080	reason I omitted it as an example).	2031	reason I omitted it as an example).
1081		2032
1082	=back	2033	=back
…		…
1086	Simply stops and restarts the periodic watcher again. This is only useful	2037	Simply stops and restarts the periodic watcher again. This is only useful
1087	when you changed some parameters or the reschedule callback would return	2038	when you changed some parameters or the reschedule callback would return
1088	a different time than the last time it was called (e.g. in a crond like	2039	a different time than the last time it was called (e.g. in a crond like
1089	program when the crontabs have changed).	2040	program when the crontabs have changed).
1090		2041
		2042	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2043
		2044	When active, returns the absolute time that the watcher is supposed
		2045	to trigger next. This is not the same as the C<offset> argument to
		2046	C<ev_periodic_set>, but indeed works even in interval and manual
		2047	rescheduling modes.
		2048
		2049	=item ev_tstamp offset [read-write]
		2050
		2051	When repeating, this contains the offset value, otherwise this is the
		2052	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2053	although libev might modify this value for better numerical stability).
		2054
		2055	Can be modified any time, but changes only take effect when the periodic
		2056	timer fires or C<ev_periodic_again> is being called.
		2057
1091	=item ev_tstamp interval [read-write]	2058	=item ev_tstamp interval [read-write]
1092		2059
1093	The current interval value. Can be modified any time, but changes only	2060	The current interval value. Can be modified any time, but changes only
1094	take effect when the periodic timer fires or C<ev_periodic_again> is being	2061	take effect when the periodic timer fires or C<ev_periodic_again> is being
1095	called.	2062	called.
1096		2063
1097	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2064	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1098		2065
1099	The current reschedule callback, or C<0>, if this functionality is	2066	The current reschedule callback, or C<0>, if this functionality is
1100	switched off. Can be changed any time, but changes only take effect when	2067	switched off. Can be changed any time, but changes only take effect when
1101	the periodic timer fires or C<ev_periodic_again> is being called.	2068	the periodic timer fires or C<ev_periodic_again> is being called.
1102		2069
1103	=back	2070	=back
1104		2071
		2072	=head3 Examples
		2073
1105	Example: Call a callback every hour, or, more precisely, whenever the	2074	Example: Call a callback every hour, or, more precisely, whenever the
1106	system clock is divisible by 3600. The callback invocation times have	2075	system time is divisible by 3600. The callback invocation times have
1107	potentially a lot of jittering, but good long-term stability.	2076	potentially a lot of jitter, but good long-term stability.
1108		2077
1109	static void	2078	static void
1110	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2079	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1111	{	2080	{
1112	... its now a full hour (UTC, or TAI or whatever your clock follows)	2081	... its now a full hour (UTC, or TAI or whatever your clock follows)
1113	}	2082	}
1114		2083
1115	struct ev_periodic hourly_tick;	2084	ev_periodic hourly_tick;
1116	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2085	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1117	ev_periodic_start (loop, &hourly_tick);	2086	ev_periodic_start (loop, &hourly_tick);
1118		2087
1119	Example: The same as above, but use a reschedule callback to do it:	2088	Example: The same as above, but use a reschedule callback to do it:
1120		2089
1121	#include <math.h>	2090	#include <math.h>
1122		2091
1123	static ev_tstamp	2092	static ev_tstamp
1124	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2093	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1125	{	2094	{
1126	return fmod (now, 3600.) + 3600.;	2095	return now + (3600. - fmod (now, 3600.));
1127	}	2096	}
1128		2097
1129	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2098	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1130		2099
1131	Example: Call a callback every hour, starting now:	2100	Example: Call a callback every hour, starting now:
1132		2101
1133	struct ev_periodic hourly_tick;	2102	ev_periodic hourly_tick;
1134	ev_periodic_init (&hourly_tick, clock_cb,	2103	ev_periodic_init (&hourly_tick, clock_cb,
1135	fmod (ev_now (loop), 3600.), 3600., 0);	2104	fmod (ev_now (loop), 3600.), 3600., 0);
1136	ev_periodic_start (loop, &hourly_tick);	2105	ev_periodic_start (loop, &hourly_tick);
1137		2106
1138		2107
1139	=head2 C<ev_signal> - signal me when a signal gets signalled!	2108	=head2 C<ev_signal> - signal me when a signal gets signalled!
1140		2109
1141	Signal watchers will trigger an event when the process receives a specific	2110	Signal watchers will trigger an event when the process receives a specific
1142	signal one or more times. Even though signals are very asynchronous, libev	2111	signal one or more times. Even though signals are very asynchronous, libev
1143	will try it's best to deliver signals synchronously, i.e. as part of the	2112	will try it's best to deliver signals synchronously, i.e. as part of the
1144	normal event processing, like any other event.	2113	normal event processing, like any other event.
1145		2114
		2115	If you want signals to be delivered truly asynchronously, just use
		2116	C<sigaction> as you would do without libev and forget about sharing
		2117	the signal. You can even use C<ev_async> from a signal handler to
		2118	synchronously wake up an event loop.
		2119
1146	You can configure as many watchers as you like per signal. Only when the	2120	You can configure as many watchers as you like for the same signal, but
		2121	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2122	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2123	C<SIGINT> in both the default loop and another loop at the same time. At
		2124	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2125
1147	first watcher gets started will libev actually register a signal watcher	2126	When the first watcher gets started will libev actually register something
1148	with the kernel (thus it coexists with your own signal handlers as long	2127	with the kernel (thus it coexists with your own signal handlers as long as
1149	as you don't register any with libev). Similarly, when the last signal	2128	you don't register any with libev for the same signal).
1150	watcher for a signal is stopped libev will reset the signal handler to	2129
1151	SIG_DFL (regardless of what it was set to before).	2130	If possible and supported, libev will install its handlers with
		2131	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2132	not be unduly interrupted. If you have a problem with system calls getting
		2133	interrupted by signals you can block all signals in an C<ev_check> watcher
		2134	and unblock them in an C<ev_prepare> watcher.
		2135
		2136	=head3 The special problem of inheritance over execve
		2137
		2138	Both the signal mask (C<sigprocmask>) and the signal disposition
		2139	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2140	stopping it again), that is, libev might or might not block the signal,
		2141	and might or might not set or restore the installed signal handler.
		2142
		2143	While this does not matter for the signal disposition (libev never
		2144	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2145	C<execve>), this matters for the signal mask: many programs do not expect
		2146	certain signals to be blocked.
		2147
		2148	This means that before calling C<exec> (from the child) you should reset
		2149	the signal mask to whatever "default" you expect (all clear is a good
		2150	choice usually).
		2151
		2152	The simplest way to ensure that the signal mask is reset in the child is
		2153	to install a fork handler with C<pthread_atfork> that resets it. That will
		2154	catch fork calls done by libraries (such as the libc) as well.
		2155
		2156	In current versions of libev, you can also ensure that the signal mask is
		2157	not blocking any signals (except temporarily, so thread users watch out)
		2158	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2159	is not guaranteed for future versions, however.
		2160
		2161	=head3 Watcher-Specific Functions and Data Members
1152		2162
1153	=over 4	2163	=over 4
1154		2164
1155	=item ev_signal_init (ev_signal *, callback, int signum)	2165	=item ev_signal_init (ev_signal *, callback, int signum)
1156		2166
…		…
1163		2173
1164	The signal the watcher watches out for.	2174	The signal the watcher watches out for.
1165		2175
1166	=back	2176	=back
1167		2177
		2178	=head3 Examples
		2179
		2180	Example: Try to exit cleanly on SIGINT.
		2181
		2182	static void
		2183	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2184	{
		2185	ev_unloop (loop, EVUNLOOP_ALL);
		2186	}
		2187
		2188	ev_signal signal_watcher;
		2189	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2190	ev_signal_start (loop, &signal_watcher);
		2191
1168		2192
1169	=head2 C<ev_child> - watch out for process status changes	2193	=head2 C<ev_child> - watch out for process status changes
1170		2194
1171	Child watchers trigger when your process receives a SIGCHLD in response to	2195	Child watchers trigger when your process receives a SIGCHLD in response to
1172	some child status changes (most typically when a child of yours dies).	2196	some child status changes (most typically when a child of yours dies or
		2197	exits). It is permissible to install a child watcher I<after> the child
		2198	has been forked (which implies it might have already exited), as long
		2199	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2200	forking and then immediately registering a watcher for the child is fine,
		2201	but forking and registering a watcher a few event loop iterations later or
		2202	in the next callback invocation is not.
		2203
		2204	Only the default event loop is capable of handling signals, and therefore
		2205	you can only register child watchers in the default event loop.
		2206
		2207	Due to some design glitches inside libev, child watchers will always be
		2208	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2209	libev)
		2210
		2211	=head3 Process Interaction
		2212
		2213	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2214	initialised. This is necessary to guarantee proper behaviour even if the
		2215	first child watcher is started after the child exits. The occurrence
		2216	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2217	synchronously as part of the event loop processing. Libev always reaps all
		2218	children, even ones not watched.
		2219
		2220	=head3 Overriding the Built-In Processing
		2221
		2222	Libev offers no special support for overriding the built-in child
		2223	processing, but if your application collides with libev's default child
		2224	handler, you can override it easily by installing your own handler for
		2225	C<SIGCHLD> after initialising the default loop, and making sure the
		2226	default loop never gets destroyed. You are encouraged, however, to use an
		2227	event-based approach to child reaping and thus use libev's support for
		2228	that, so other libev users can use C<ev_child> watchers freely.
		2229
		2230	=head3 Stopping the Child Watcher
		2231
		2232	Currently, the child watcher never gets stopped, even when the
		2233	child terminates, so normally one needs to stop the watcher in the
		2234	callback. Future versions of libev might stop the watcher automatically
		2235	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2236	problem).
		2237
		2238	=head3 Watcher-Specific Functions and Data Members
1173		2239
1174	=over 4	2240	=over 4
1175		2241
1176	=item ev_child_init (ev_child *, callback, int pid)	2242	=item ev_child_init (ev_child *, callback, int pid, int trace)
1177		2243
1178	=item ev_child_set (ev_child *, int pid)	2244	=item ev_child_set (ev_child *, int pid, int trace)
1179		2245
1180	Configures the watcher to wait for status changes of process C<pid> (or	2246	Configures the watcher to wait for status changes of process C<pid> (or
1181	I<any> process if C<pid> is specified as C<0>). The callback can look	2247	I<any> process if C<pid> is specified as C<0>). The callback can look
1182	at the C<rstatus> member of the C<ev_child> watcher structure to see	2248	at the C<rstatus> member of the C<ev_child> watcher structure to see
1183	the status word (use the macros from C<sys/wait.h> and see your systems	2249	the status word (use the macros from C<sys/wait.h> and see your systems
1184	C<waitpid> documentation). The C<rpid> member contains the pid of the	2250	C<waitpid> documentation). The C<rpid> member contains the pid of the
1185	process causing the status change.	2251	process causing the status change. C<trace> must be either C<0> (only
		2252	activate the watcher when the process terminates) or C<1> (additionally
		2253	activate the watcher when the process is stopped or continued).
1186		2254
1187	=item int pid [read-only]	2255	=item int pid [read-only]
1188		2256
1189	The process id this watcher watches out for, or C<0>, meaning any process id.	2257	The process id this watcher watches out for, or C<0>, meaning any process id.
1190		2258
…		…
1197	The process exit/trace status caused by C<rpid> (see your systems	2265	The process exit/trace status caused by C<rpid> (see your systems
1198	C<waitpid> and C<sys/wait.h> documentation for details).	2266	C<waitpid> and C<sys/wait.h> documentation for details).
1199		2267
1200	=back	2268	=back
1201		2269
1202	Example: Try to exit cleanly on SIGINT and SIGTERM.	2270	=head3 Examples
1203		2271
		2272	Example: C<fork()> a new process and install a child handler to wait for
		2273	its completion.
		2274
		2275	ev_child cw;
		2276
1204	static void	2277	static void
1205	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2278	child_cb (EV_P_ ev_child *w, int revents)
1206	{	2279	{
1207	ev_unloop (loop, EVUNLOOP_ALL);	2280	ev_child_stop (EV_A_ w);
		2281	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1208	}	2282	}
1209		2283
1210	struct ev_signal signal_watcher;	2284	pid_t pid = fork ();
1211	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2285
1212	ev_signal_start (loop, &sigint_cb);	2286	if (pid < 0)
		2287	// error
		2288	else if (pid == 0)
		2289	{
		2290	// the forked child executes here
		2291	exit (1);
		2292	}
		2293	else
		2294	{
		2295	ev_child_init (&cw, child_cb, pid, 0);
		2296	ev_child_start (EV_DEFAULT_ &cw);
		2297	}
1213		2298
1214		2299
1215	=head2 C<ev_stat> - did the file attributes just change?	2300	=head2 C<ev_stat> - did the file attributes just change?
1216		2301
1217	This watches a filesystem path for attribute changes. That is, it calls	2302	This watches a file system path for attribute changes. That is, it calls
1218	C<stat> regularly (or when the OS says it changed) and sees if it changed	2303	C<stat> on that path in regular intervals (or when the OS says it changed)
1219	compared to the last time, invoking the callback if it did.	2304	and sees if it changed compared to the last time, invoking the callback if
		2305	it did.
1220		2306
1221	The path does not need to exist: changing from "path exists" to "path does	2307	The path does not need to exist: changing from "path exists" to "path does
1222	not exist" is a status change like any other. The condition "path does	2308	not exist" is a status change like any other. The condition "path does not
1223	not exist" is signified by the C<st_nlink> field being zero (which is	2309	exist" (or more correctly "path cannot be stat'ed") is signified by the
1224	otherwise always forced to be at least one) and all the other fields of	2310	C<st_nlink> field being zero (which is otherwise always forced to be at
1225	the stat buffer having unspecified contents.	2311	least one) and all the other fields of the stat buffer having unspecified
		2312	contents.
1226		2313
1227	Since there is no standard to do this, the portable implementation simply	2314	The path I<must not> end in a slash or contain special components such as
1228	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2315	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1229	can specify a recommended polling interval for this case. If you specify	2316	your working directory changes, then the behaviour is undefined.
1230	a polling interval of C<0> (highly recommended!) then a I<suitable,	2317
1231	unspecified default> value will be used (which you can expect to be around	2318	Since there is no portable change notification interface available, the
1232	five seconds, although this might change dynamically). Libev will also	2319	portable implementation simply calls C<stat(2)> regularly on the path
1233	impose a minimum interval which is currently around C<0.1>, but thats	2320	to see if it changed somehow. You can specify a recommended polling
1234	usually overkill.	2321	interval for this case. If you specify a polling interval of C<0> (highly
		2322	recommended!) then a I<suitable, unspecified default> value will be used
		2323	(which you can expect to be around five seconds, although this might
		2324	change dynamically). Libev will also impose a minimum interval which is
		2325	currently around C<0.1>, but that's usually overkill.
1235		2326
1236	This watcher type is not meant for massive numbers of stat watchers,	2327	This watcher type is not meant for massive numbers of stat watchers,
1237	as even with OS-supported change notifications, this can be	2328	as even with OS-supported change notifications, this can be
1238	resource-intensive.	2329	resource-intensive.
1239		2330
1240	At the time of this writing, only the Linux inotify interface is	2331	At the time of this writing, the only OS-specific interface implemented
1241	implemented (implementing kqueue support is left as an exercise for the	2332	is the Linux inotify interface (implementing kqueue support is left as an
1242	reader). Inotify will be used to give hints only and should not change the	2333	exercise for the reader. Note, however, that the author sees no way of
1243	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2334	implementing C<ev_stat> semantics with kqueue, except as a hint).
1244	to fall back to regular polling again even with inotify, but changes are	2335
1245	usually detected immediately, and if the file exists there will be no	2336	=head3 ABI Issues (Largefile Support)
1246	polling.	2337
		2338	Libev by default (unless the user overrides this) uses the default
		2339	compilation environment, which means that on systems with large file
		2340	support disabled by default, you get the 32 bit version of the stat
		2341	structure. When using the library from programs that change the ABI to
		2342	use 64 bit file offsets the programs will fail. In that case you have to
		2343	compile libev with the same flags to get binary compatibility. This is
		2344	obviously the case with any flags that change the ABI, but the problem is
		2345	most noticeably displayed with ev_stat and large file support.
		2346
		2347	The solution for this is to lobby your distribution maker to make large
		2348	file interfaces available by default (as e.g. FreeBSD does) and not
		2349	optional. Libev cannot simply switch on large file support because it has
		2350	to exchange stat structures with application programs compiled using the
		2351	default compilation environment.
		2352
		2353	=head3 Inotify and Kqueue
		2354
		2355	When C<inotify (7)> support has been compiled into libev and present at
		2356	runtime, it will be used to speed up change detection where possible. The
		2357	inotify descriptor will be created lazily when the first C<ev_stat>
		2358	watcher is being started.
		2359
		2360	Inotify presence does not change the semantics of C<ev_stat> watchers
		2361	except that changes might be detected earlier, and in some cases, to avoid
		2362	making regular C<stat> calls. Even in the presence of inotify support
		2363	there are many cases where libev has to resort to regular C<stat> polling,
		2364	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2365	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2366	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2367	xfs are fully working) libev usually gets away without polling.
		2368
		2369	There is no support for kqueue, as apparently it cannot be used to
		2370	implement this functionality, due to the requirement of having a file
		2371	descriptor open on the object at all times, and detecting renames, unlinks
		2372	etc. is difficult.
		2373
		2374	=head3 C<stat ()> is a synchronous operation
		2375
		2376	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2377	the process. The exception are C<ev_stat> watchers - those call C<stat
		2378	()>, which is a synchronous operation.
		2379
		2380	For local paths, this usually doesn't matter: unless the system is very
		2381	busy or the intervals between stat's are large, a stat call will be fast,
		2382	as the path data is usually in memory already (except when starting the
		2383	watcher).
		2384
		2385	For networked file systems, calling C<stat ()> can block an indefinite
		2386	time due to network issues, and even under good conditions, a stat call
		2387	often takes multiple milliseconds.
		2388
		2389	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2390	paths, although this is fully supported by libev.
		2391
		2392	=head3 The special problem of stat time resolution
		2393
		2394	The C<stat ()> system call only supports full-second resolution portably,
		2395	and even on systems where the resolution is higher, most file systems
		2396	still only support whole seconds.
		2397
		2398	That means that, if the time is the only thing that changes, you can
		2399	easily miss updates: on the first update, C<ev_stat> detects a change and
		2400	calls your callback, which does something. When there is another update
		2401	within the same second, C<ev_stat> will be unable to detect unless the
		2402	stat data does change in other ways (e.g. file size).
		2403
		2404	The solution to this is to delay acting on a change for slightly more
		2405	than a second (or till slightly after the next full second boundary), using
		2406	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2407	ev_timer_again (loop, w)>).
		2408
		2409	The C<.02> offset is added to work around small timing inconsistencies
		2410	of some operating systems (where the second counter of the current time
		2411	might be be delayed. One such system is the Linux kernel, where a call to
		2412	C<gettimeofday> might return a timestamp with a full second later than
		2413	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2414	update file times then there will be a small window where the kernel uses
		2415	the previous second to update file times but libev might already execute
		2416	the timer callback).
		2417
		2418	=head3 Watcher-Specific Functions and Data Members
1247		2419
1248	=over 4	2420	=over 4
1249		2421
1250	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2422	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1251		2423
…		…
1255	C<path>. The C<interval> is a hint on how quickly a change is expected to	2427	C<path>. The C<interval> is a hint on how quickly a change is expected to
1256	be detected and should normally be specified as C<0> to let libev choose	2428	be detected and should normally be specified as C<0> to let libev choose
1257	a suitable value. The memory pointed to by C<path> must point to the same	2429	a suitable value. The memory pointed to by C<path> must point to the same
1258	path for as long as the watcher is active.	2430	path for as long as the watcher is active.
1259		2431
1260	The callback will be receive C<EV_STAT> when a change was detected,	2432	The callback will receive an C<EV_STAT> event when a change was detected,
1261	relative to the attributes at the time the watcher was started (or the	2433	relative to the attributes at the time the watcher was started (or the
1262	last change was detected).	2434	last change was detected).
1263		2435
1264	=item ev_stat_stat (ev_stat *)	2436	=item ev_stat_stat (loop, ev_stat *)
1265		2437
1266	Updates the stat buffer immediately with new values. If you change the	2438	Updates the stat buffer immediately with new values. If you change the
1267	watched path in your callback, you could call this fucntion to avoid	2439	watched path in your callback, you could call this function to avoid
1268	detecting this change (while introducing a race condition). Can also be	2440	detecting this change (while introducing a race condition if you are not
1269	useful simply to find out the new values.	2441	the only one changing the path). Can also be useful simply to find out the
		2442	new values.
1270		2443
1271	=item ev_statdata attr [read-only]	2444	=item ev_statdata attr [read-only]
1272		2445
1273	The most-recently detected attributes of the file. Although the type is of	2446	The most-recently detected attributes of the file. Although the type is
1274	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2447	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1275	suitable for your system. If the C<st_nlink> member is C<0>, then there	2448	suitable for your system, but you can only rely on the POSIX-standardised
		2449	members to be present. If the C<st_nlink> member is C<0>, then there was
1276	was some error while C<stat>ing the file.	2450	some error while C<stat>ing the file.
1277		2451
1278	=item ev_statdata prev [read-only]	2452	=item ev_statdata prev [read-only]
1279		2453
1280	The previous attributes of the file. The callback gets invoked whenever	2454	The previous attributes of the file. The callback gets invoked whenever
1281	C<prev> != C<attr>.	2455	C<prev> != C<attr>, or, more precisely, one or more of these members
		2456	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2457	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1282		2458
1283	=item ev_tstamp interval [read-only]	2459	=item ev_tstamp interval [read-only]
1284		2460
1285	The specified interval.	2461	The specified interval.
1286		2462
1287	=item const char *path [read-only]	2463	=item const char *path [read-only]
1288		2464
1289	The filesystem path that is being watched.	2465	The file system path that is being watched.
1290		2466
1291	=back	2467	=back
1292		2468
		2469	=head3 Examples
		2470
1293	Example: Watch C</etc/passwd> for attribute changes.	2471	Example: Watch C</etc/passwd> for attribute changes.
1294		2472
1295	static void	2473	static void
1296	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2474	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1297	{	2475	{
1298	/* /etc/passwd changed in some way */	2476	/* /etc/passwd changed in some way */
1299	if (w->attr.st_nlink)	2477	if (w->attr.st_nlink)
1300	{	2478	{
1301	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2479	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1302	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2480	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1303	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2481	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1304	}	2482	}
1305	else	2483	else
1306	/* you shalt not abuse printf for puts */	2484	/* you shalt not abuse printf for puts */
1307	puts ("wow, /etc/passwd is not there, expect problems. "	2485	puts ("wow, /etc/passwd is not there, expect problems. "
1308	"if this is windows, they already arrived\n");	2486	"if this is windows, they already arrived\n");
1309	}	2487	}
1310		2488
1311	...	2489	...
1312	ev_stat passwd;	2490	ev_stat passwd;
1313		2491
1314	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2492	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1315	ev_stat_start (loop, &passwd);	2493	ev_stat_start (loop, &passwd);
		2494
		2495	Example: Like above, but additionally use a one-second delay so we do not
		2496	miss updates (however, frequent updates will delay processing, too, so
		2497	one might do the work both on C<ev_stat> callback invocation I<and> on
		2498	C<ev_timer> callback invocation).
		2499
		2500	static ev_stat passwd;
		2501	static ev_timer timer;
		2502
		2503	static void
		2504	timer_cb (EV_P_ ev_timer *w, int revents)
		2505	{
		2506	ev_timer_stop (EV_A_ w);
		2507
		2508	/* now it's one second after the most recent passwd change */
		2509	}
		2510
		2511	static void
		2512	stat_cb (EV_P_ ev_stat *w, int revents)
		2513	{
		2514	/* reset the one-second timer */
		2515	ev_timer_again (EV_A_ &timer);
		2516	}
		2517
		2518	...
		2519	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2520	ev_stat_start (loop, &passwd);
		2521	ev_timer_init (&timer, timer_cb, 0., 1.02);
1316		2522
1317		2523
1318	=head2 C<ev_idle> - when you've got nothing better to do...	2524	=head2 C<ev_idle> - when you've got nothing better to do...
1319		2525
1320	Idle watchers trigger events when there are no other events are pending	2526	Idle watchers trigger events when no other events of the same or higher
1321	(prepare, check and other idle watchers do not count). That is, as long	2527	priority are pending (prepare, check and other idle watchers do not count
1322	as your process is busy handling sockets or timeouts (or even signals,	2528	as receiving "events").
1323	imagine) it will not be triggered. But when your process is idle all idle	2529
1324	watchers are being called again and again, once per event loop iteration -	2530	That is, as long as your process is busy handling sockets or timeouts
		2531	(or even signals, imagine) of the same or higher priority it will not be
		2532	triggered. But when your process is idle (or only lower-priority watchers
		2533	are pending), the idle watchers are being called once per event loop
1325	until stopped, that is, or your process receives more events and becomes	2534	iteration - until stopped, that is, or your process receives more events
1326	busy.	2535	and becomes busy again with higher priority stuff.
1327		2536
1328	The most noteworthy effect is that as long as any idle watchers are	2537	The most noteworthy effect is that as long as any idle watchers are
1329	active, the process will not block when waiting for new events.	2538	active, the process will not block when waiting for new events.
1330		2539
1331	Apart from keeping your process non-blocking (which is a useful	2540	Apart from keeping your process non-blocking (which is a useful
1332	effect on its own sometimes), idle watchers are a good place to do	2541	effect on its own sometimes), idle watchers are a good place to do
1333	"pseudo-background processing", or delay processing stuff to after the	2542	"pseudo-background processing", or delay processing stuff to after the
1334	event loop has handled all outstanding events.	2543	event loop has handled all outstanding events.
1335		2544
		2545	=head3 Watcher-Specific Functions and Data Members
		2546
1336	=over 4	2547	=over 4
1337		2548
1338	=item ev_idle_init (ev_signal *, callback)	2549	=item ev_idle_init (ev_idle *, callback)
1339		2550
1340	Initialises and configures the idle watcher - it has no parameters of any	2551	Initialises and configures the idle watcher - it has no parameters of any
1341	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2552	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1342	believe me.	2553	believe me.
1343		2554
1344	=back	2555	=back
1345		2556
		2557	=head3 Examples
		2558
1346	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2559	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1347	callback, free it. Also, use no error checking, as usual.	2560	callback, free it. Also, use no error checking, as usual.
1348		2561
1349	static void	2562	static void
1350	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2563	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1351	{	2564	{
1352	free (w);	2565	free (w);
1353	// now do something you wanted to do when the program has	2566	// now do something you wanted to do when the program has
1354	// no longer asnything immediate to do.	2567	// no longer anything immediate to do.
1355	}	2568	}
1356		2569
1357	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2570	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1358	ev_idle_init (idle_watcher, idle_cb);	2571	ev_idle_init (idle_watcher, idle_cb);
1359	ev_idle_start (loop, idle_cb);	2572	ev_idle_start (loop, idle_watcher);
1360		2573
1361		2574
1362	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2575	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1363		2576
1364	Prepare and check watchers are usually (but not always) used in tandem:	2577	Prepare and check watchers are usually (but not always) used in pairs:
1365	prepare watchers get invoked before the process blocks and check watchers	2578	prepare watchers get invoked before the process blocks and check watchers
1366	afterwards.	2579	afterwards.
1367		2580
1368	You I<must not> call C<ev_loop> or similar functions that enter	2581	You I<must not> call C<ev_loop> or similar functions that enter
1369	the current event loop from either C<ev_prepare> or C<ev_check>	2582	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1372	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2585	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1373	C<ev_check> so if you have one watcher of each kind they will always be	2586	C<ev_check> so if you have one watcher of each kind they will always be
1374	called in pairs bracketing the blocking call.	2587	called in pairs bracketing the blocking call.
1375		2588
1376	Their main purpose is to integrate other event mechanisms into libev and	2589	Their main purpose is to integrate other event mechanisms into libev and
1377	their use is somewhat advanced. This could be used, for example, to track	2590	their use is somewhat advanced. They could be used, for example, to track
1378	variable changes, implement your own watchers, integrate net-snmp or a	2591	variable changes, implement your own watchers, integrate net-snmp or a
1379	coroutine library and lots more. They are also occasionally useful if	2592	coroutine library and lots more. They are also occasionally useful if
1380	you cache some data and want to flush it before blocking (for example,	2593	you cache some data and want to flush it before blocking (for example,
1381	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2594	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1382	watcher).	2595	watcher).
1383		2596
1384	This is done by examining in each prepare call which file descriptors need	2597	This is done by examining in each prepare call which file descriptors
1385	to be watched by the other library, registering C<ev_io> watchers for	2598	need to be watched by the other library, registering C<ev_io> watchers
1386	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2599	for them and starting an C<ev_timer> watcher for any timeouts (many
1387	provide just this functionality). Then, in the check watcher you check for	2600	libraries provide exactly this functionality). Then, in the check watcher,
1388	any events that occured (by checking the pending status of all watchers	2601	you check for any events that occurred (by checking the pending status
1389	and stopping them) and call back into the library. The I/O and timer	2602	of all watchers and stopping them) and call back into the library. The
1390	callbacks will never actually be called (but must be valid nevertheless,	2603	I/O and timer callbacks will never actually be called (but must be valid
1391	because you never know, you know?).	2604	nevertheless, because you never know, you know?).
1392		2605
1393	As another example, the Perl Coro module uses these hooks to integrate	2606	As another example, the Perl Coro module uses these hooks to integrate
1394	coroutines into libev programs, by yielding to other active coroutines	2607	coroutines into libev programs, by yielding to other active coroutines
1395	during each prepare and only letting the process block if no coroutines	2608	during each prepare and only letting the process block if no coroutines
1396	are ready to run (it's actually more complicated: it only runs coroutines	2609	are ready to run (it's actually more complicated: it only runs coroutines
1397	with priority higher than or equal to the event loop and one coroutine	2610	with priority higher than or equal to the event loop and one coroutine
1398	of lower priority, but only once, using idle watchers to keep the event	2611	of lower priority, but only once, using idle watchers to keep the event
1399	loop from blocking if lower-priority coroutines are active, thus mapping	2612	loop from blocking if lower-priority coroutines are active, thus mapping
1400	low-priority coroutines to idle/background tasks).	2613	low-priority coroutines to idle/background tasks).
1401		2614
		2615	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2616	priority, to ensure that they are being run before any other watchers
		2617	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2618
		2619	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2620	activate ("feed") events into libev. While libev fully supports this, they
		2621	might get executed before other C<ev_check> watchers did their job. As
		2622	C<ev_check> watchers are often used to embed other (non-libev) event
		2623	loops those other event loops might be in an unusable state until their
		2624	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2625	others).
		2626
		2627	=head3 Watcher-Specific Functions and Data Members
		2628
1402	=over 4	2629	=over 4
1403		2630
1404	=item ev_prepare_init (ev_prepare *, callback)	2631	=item ev_prepare_init (ev_prepare *, callback)
1405		2632
1406	=item ev_check_init (ev_check *, callback)	2633	=item ev_check_init (ev_check *, callback)
1407		2634
1408	Initialises and configures the prepare or check watcher - they have no	2635	Initialises and configures the prepare or check watcher - they have no
1409	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2636	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1410	macros, but using them is utterly, utterly and completely pointless.	2637	macros, but using them is utterly, utterly, utterly and completely
		2638	pointless.
1411		2639
1412	=back	2640	=back
1413		2641
1414	Example: To include a library such as adns, you would add IO watchers	2642	=head3 Examples
1415	and a timeout watcher in a prepare handler, as required by libadns, and	2643
		2644	There are a number of principal ways to embed other event loops or modules
		2645	into libev. Here are some ideas on how to include libadns into libev
		2646	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2647	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2648	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2649	Glib event loop).
		2650
		2651	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1416	in a check watcher, destroy them and call into libadns. What follows is	2652	and in a check watcher, destroy them and call into libadns. What follows
1417	pseudo-code only of course:	2653	is pseudo-code only of course. This requires you to either use a low
		2654	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2655	the callbacks for the IO/timeout watchers might not have been called yet.
1418		2656
1419	static ev_io iow [nfd];	2657	static ev_io iow [nfd];
1420	static ev_timer tw;	2658	static ev_timer tw;
1421		2659
1422	static void	2660	static void
1423	io_cb (ev_loop *loop, ev_io *w, int revents)	2661	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1424	{	2662	{
1425	// set the relevant poll flags
1426	// could also call adns_processreadable etc. here
1427	struct pollfd *fd = (struct pollfd *)w->data;
1428	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1429	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1430	}	2663	}
1431		2664
1432	// create io watchers for each fd and a timer before blocking	2665	// create io watchers for each fd and a timer before blocking
1433	static void	2666	static void
1434	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2667	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1435	{	2668	{
1436	int timeout = 3600000;truct pollfd fds [nfd];	2669	int timeout = 3600000;
		2670	struct pollfd fds [nfd];
1437	// actual code will need to loop here and realloc etc.	2671	// actual code will need to loop here and realloc etc.
1438	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2672	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1439		2673
1440	/* the callback is illegal, but won't be called as we stop during check */	2674	/* the callback is illegal, but won't be called as we stop during check */
1441	ev_timer_init (&tw, 0, timeout * 1e-3);	2675	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1442	ev_timer_start (loop, &tw);	2676	ev_timer_start (loop, &tw);
1443		2677
1444	// create on ev_io per pollfd	2678	// create one ev_io per pollfd
1445	for (int i = 0; i < nfd; ++i)	2679	for (int i = 0; i < nfd; ++i)
1446	{	2680	{
1447	ev_io_init (iow + i, io_cb, fds [i].fd,	2681	ev_io_init (iow + i, io_cb, fds [i].fd,
1448	((fds [i].events & POLLIN ? EV_READ : 0)	2682	((fds [i].events & POLLIN ? EV_READ : 0)
1449	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2683	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1450		2684
1451	fds [i].revents = 0;	2685	fds [i].revents = 0;
1452	iow [i].data = fds + i;
1453	ev_io_start (loop, iow + i);	2686	ev_io_start (loop, iow + i);
1454	}	2687	}
1455	}	2688	}
1456		2689
1457	// stop all watchers after blocking	2690	// stop all watchers after blocking
1458	static void	2691	static void
1459	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2692	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1460	{	2693	{
1461	ev_timer_stop (loop, &tw);	2694	ev_timer_stop (loop, &tw);
1462		2695
1463	for (int i = 0; i < nfd; ++i)	2696	for (int i = 0; i < nfd; ++i)
		2697	{
		2698	// set the relevant poll flags
		2699	// could also call adns_processreadable etc. here
		2700	struct pollfd *fd = fds + i;
		2701	int revents = ev_clear_pending (iow + i);
		2702	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2703	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2704
		2705	// now stop the watcher
1464	ev_io_stop (loop, iow + i);	2706	ev_io_stop (loop, iow + i);
		2707	}
1465		2708
1466	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2709	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1467	}	2710	}
		2711
		2712	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2713	in the prepare watcher and would dispose of the check watcher.
		2714
		2715	Method 3: If the module to be embedded supports explicit event
		2716	notification (libadns does), you can also make use of the actual watcher
		2717	callbacks, and only destroy/create the watchers in the prepare watcher.
		2718
		2719	static void
		2720	timer_cb (EV_P_ ev_timer *w, int revents)
		2721	{
		2722	adns_state ads = (adns_state)w->data;
		2723	update_now (EV_A);
		2724
		2725	adns_processtimeouts (ads, &tv_now);
		2726	}
		2727
		2728	static void
		2729	io_cb (EV_P_ ev_io *w, int revents)
		2730	{
		2731	adns_state ads = (adns_state)w->data;
		2732	update_now (EV_A);
		2733
		2734	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2735	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2736	}
		2737
		2738	// do not ever call adns_afterpoll
		2739
		2740	Method 4: Do not use a prepare or check watcher because the module you
		2741	want to embed is not flexible enough to support it. Instead, you can
		2742	override their poll function. The drawback with this solution is that the
		2743	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2744	this approach, effectively embedding EV as a client into the horrible
		2745	libglib event loop.
		2746
		2747	static gint
		2748	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2749	{
		2750	int got_events = 0;
		2751
		2752	for (n = 0; n < nfds; ++n)
		2753	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2754
		2755	if (timeout >= 0)
		2756	// create/start timer
		2757
		2758	// poll
		2759	ev_loop (EV_A_ 0);
		2760
		2761	// stop timer again
		2762	if (timeout >= 0)
		2763	ev_timer_stop (EV_A_ &to);
		2764
		2765	// stop io watchers again - their callbacks should have set
		2766	for (n = 0; n < nfds; ++n)
		2767	ev_io_stop (EV_A_ iow [n]);
		2768
		2769	return got_events;
		2770	}
1468		2771
1469		2772
1470	=head2 C<ev_embed> - when one backend isn't enough...	2773	=head2 C<ev_embed> - when one backend isn't enough...
1471		2774
1472	This is a rather advanced watcher type that lets you embed one event loop	2775	This is a rather advanced watcher type that lets you embed one event loop
…		…
1478	prioritise I/O.	2781	prioritise I/O.
1479		2782
1480	As an example for a bug workaround, the kqueue backend might only support	2783	As an example for a bug workaround, the kqueue backend might only support
1481	sockets on some platform, so it is unusable as generic backend, but you	2784	sockets on some platform, so it is unusable as generic backend, but you
1482	still want to make use of it because you have many sockets and it scales	2785	still want to make use of it because you have many sockets and it scales
1483	so nicely. In this case, you would create a kqueue-based loop and embed it	2786	so nicely. In this case, you would create a kqueue-based loop and embed
1484	into your default loop (which might use e.g. poll). Overall operation will	2787	it into your default loop (which might use e.g. poll). Overall operation
1485	be a bit slower because first libev has to poll and then call kevent, but	2788	will be a bit slower because first libev has to call C<poll> and then
1486	at least you can use both at what they are best.	2789	C<kevent>, but at least you can use both mechanisms for what they are
		2790	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1487		2791
1488	As for prioritising I/O: rarely you have the case where some fds have	2792	As for prioritising I/O: under rare circumstances you have the case where
1489	to be watched and handled very quickly (with low latency), and even	2793	some fds have to be watched and handled very quickly (with low latency),
1490	priorities and idle watchers might have too much overhead. In this case	2794	and even priorities and idle watchers might have too much overhead. In
1491	you would put all the high priority stuff in one loop and all the rest in	2795	this case you would put all the high priority stuff in one loop and all
1492	a second one, and embed the second one in the first.	2796	the rest in a second one, and embed the second one in the first.
1493		2797
1494	As long as the watcher is active, the callback will be invoked every time	2798	As long as the watcher is active, the callback will be invoked every
1495	there might be events pending in the embedded loop. The callback must then	2799	time there might be events pending in the embedded loop. The callback
1496	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2800	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1497	their callbacks (you could also start an idle watcher to give the embedded	2801	sweep and invoke their callbacks (the callback doesn't need to invoke the
1498	loop strictly lower priority for example). You can also set the callback	2802	C<ev_embed_sweep> function directly, it could also start an idle watcher
1499	to C<0>, in which case the embed watcher will automatically execute the	2803	to give the embedded loop strictly lower priority for example).
1500	embedded loop sweep.
1501		2804
1502	As long as the watcher is started it will automatically handle events. The	2805	You can also set the callback to C<0>, in which case the embed watcher
1503	callback will be invoked whenever some events have been handled. You can	2806	will automatically execute the embedded loop sweep whenever necessary.
1504	set the callback to C<0> to avoid having to specify one if you are not
1505	interested in that.
1506		2807
1507	Also, there have not currently been made special provisions for forking:	2808	Fork detection will be handled transparently while the C<ev_embed> watcher
1508	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2809	is active, i.e., the embedded loop will automatically be forked when the
1509	but you will also have to stop and restart any C<ev_embed> watchers	2810	embedding loop forks. In other cases, the user is responsible for calling
1510	yourself.	2811	C<ev_loop_fork> on the embedded loop.
1511		2812
1512	Unfortunately, not all backends are embeddable, only the ones returned by	2813	Unfortunately, not all backends are embeddable: only the ones returned by
1513	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2814	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1514	portable one.	2815	portable one.
1515		2816
1516	So when you want to use this feature you will always have to be prepared	2817	So when you want to use this feature you will always have to be prepared
1517	that you cannot get an embeddable loop. The recommended way to get around	2818	that you cannot get an embeddable loop. The recommended way to get around
1518	this is to have a separate variables for your embeddable loop, try to	2819	this is to have a separate variables for your embeddable loop, try to
1519	create it, and if that fails, use the normal loop for everything:	2820	create it, and if that fails, use the normal loop for everything.
1520		2821
1521	struct ev_loop *loop_hi = ev_default_init (0);	2822	=head3 C<ev_embed> and fork
1522	struct ev_loop *loop_lo = 0;
1523	struct ev_embed embed;
1524
1525	// see if there is a chance of getting one that works
1526	// (remember that a flags value of 0 means autodetection)
1527	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1528	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1529	: 0;
1530		2823
1531	// if we got one, then embed it, otherwise default to loop_hi	2824	While the C<ev_embed> watcher is running, forks in the embedding loop will
1532	if (loop_lo)	2825	automatically be applied to the embedded loop as well, so no special
1533	{	2826	fork handling is required in that case. When the watcher is not running,
1534	ev_embed_init (&embed, 0, loop_lo);	2827	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1535	ev_embed_start (loop_hi, &embed);	2828	as applicable.
1536	}	2829
1537	else	2830	=head3 Watcher-Specific Functions and Data Members
1538	loop_lo = loop_hi;
1539		2831
1540	=over 4	2832	=over 4
1541		2833
1542	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2834	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1543		2835
…		…
1545		2837
1546	Configures the watcher to embed the given loop, which must be	2838	Configures the watcher to embed the given loop, which must be
1547	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2839	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1548	invoked automatically, otherwise it is the responsibility of the callback	2840	invoked automatically, otherwise it is the responsibility of the callback
1549	to invoke it (it will continue to be called until the sweep has been done,	2841	to invoke it (it will continue to be called until the sweep has been done,
1550	if you do not want thta, you need to temporarily stop the embed watcher).	2842	if you do not want that, you need to temporarily stop the embed watcher).
1551		2843
1552	=item ev_embed_sweep (loop, ev_embed *)	2844	=item ev_embed_sweep (loop, ev_embed *)
1553		2845
1554	Make a single, non-blocking sweep over the embedded loop. This works	2846	Make a single, non-blocking sweep over the embedded loop. This works
1555	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2847	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1556	apropriate way for embedded loops.	2848	appropriate way for embedded loops.
1557		2849
1558	=item struct ev_loop *loop [read-only]	2850	=item struct ev_loop *other [read-only]
1559		2851
1560	The embedded event loop.	2852	The embedded event loop.
1561		2853
1562	=back	2854	=back
		2855
		2856	=head3 Examples
		2857
		2858	Example: Try to get an embeddable event loop and embed it into the default
		2859	event loop. If that is not possible, use the default loop. The default
		2860	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2861	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2862	used).
		2863
		2864	struct ev_loop *loop_hi = ev_default_init (0);
		2865	struct ev_loop *loop_lo = 0;
		2866	ev_embed embed;
		2867
		2868	// see if there is a chance of getting one that works
		2869	// (remember that a flags value of 0 means autodetection)
		2870	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2871	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2872	: 0;
		2873
		2874	// if we got one, then embed it, otherwise default to loop_hi
		2875	if (loop_lo)
		2876	{
		2877	ev_embed_init (&embed, 0, loop_lo);
		2878	ev_embed_start (loop_hi, &embed);
		2879	}
		2880	else
		2881	loop_lo = loop_hi;
		2882
		2883	Example: Check if kqueue is available but not recommended and create
		2884	a kqueue backend for use with sockets (which usually work with any
		2885	kqueue implementation). Store the kqueue/socket-only event loop in
		2886	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2887
		2888	struct ev_loop *loop = ev_default_init (0);
		2889	struct ev_loop *loop_socket = 0;
		2890	ev_embed embed;
		2891
		2892	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2893	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2894	{
		2895	ev_embed_init (&embed, 0, loop_socket);
		2896	ev_embed_start (loop, &embed);
		2897	}
		2898
		2899	if (!loop_socket)
		2900	loop_socket = loop;
		2901
		2902	// now use loop_socket for all sockets, and loop for everything else
1563		2903
1564		2904
1565	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2905	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1566		2906
1567	Fork watchers are called when a C<fork ()> was detected (usually because	2907	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1570	event loop blocks next and before C<ev_check> watchers are being called,	2910	event loop blocks next and before C<ev_check> watchers are being called,
1571	and only in the child after the fork. If whoever good citizen calling	2911	and only in the child after the fork. If whoever good citizen calling
1572	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2912	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1573	handlers will be invoked, too, of course.	2913	handlers will be invoked, too, of course.
1574		2914
		2915	=head3 The special problem of life after fork - how is it possible?
		2916
		2917	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2918	up/change the process environment, followed by a call to C<exec()>. This
		2919	sequence should be handled by libev without any problems.
		2920
		2921	This changes when the application actually wants to do event handling
		2922	in the child, or both parent in child, in effect "continuing" after the
		2923	fork.
		2924
		2925	The default mode of operation (for libev, with application help to detect
		2926	forks) is to duplicate all the state in the child, as would be expected
		2927	when I<either> the parent I<or> the child process continues.
		2928
		2929	When both processes want to continue using libev, then this is usually the
		2930	wrong result. In that case, usually one process (typically the parent) is
		2931	supposed to continue with all watchers in place as before, while the other
		2932	process typically wants to start fresh, i.e. without any active watchers.
		2933
		2934	The cleanest and most efficient way to achieve that with libev is to
		2935	simply create a new event loop, which of course will be "empty", and
		2936	use that for new watchers. This has the advantage of not touching more
		2937	memory than necessary, and thus avoiding the copy-on-write, and the
		2938	disadvantage of having to use multiple event loops (which do not support
		2939	signal watchers).
		2940
		2941	When this is not possible, or you want to use the default loop for
		2942	other reasons, then in the process that wants to start "fresh", call
		2943	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2944	the default loop will "orphan" (not stop) all registered watchers, so you
		2945	have to be careful not to execute code that modifies those watchers. Note
		2946	also that in that case, you have to re-register any signal watchers.
		2947
		2948	=head3 Watcher-Specific Functions and Data Members
		2949
1575	=over 4	2950	=over 4
1576		2951
1577	=item ev_fork_init (ev_signal *, callback)	2952	=item ev_fork_init (ev_signal *, callback)
1578		2953
1579	Initialises and configures the fork watcher - it has no parameters of any	2954	Initialises and configures the fork watcher - it has no parameters of any
…		…
1581	believe me.	2956	believe me.
1582		2957
1583	=back	2958	=back
1584		2959
1585		2960
		2961	=head2 C<ev_async> - how to wake up another event loop
		2962
		2963	In general, you cannot use an C<ev_loop> from multiple threads or other
		2964	asynchronous sources such as signal handlers (as opposed to multiple event
		2965	loops - those are of course safe to use in different threads).
		2966
		2967	Sometimes, however, you need to wake up another event loop you do not
		2968	control, for example because it belongs to another thread. This is what
		2969	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2970	can signal it by calling C<ev_async_send>, which is thread- and signal
		2971	safe.
		2972
		2973	This functionality is very similar to C<ev_signal> watchers, as signals,
		2974	too, are asynchronous in nature, and signals, too, will be compressed
		2975	(i.e. the number of callback invocations may be less than the number of
		2976	C<ev_async_sent> calls).
		2977
		2978	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2979	just the default loop.
		2980
		2981	=head3 Queueing
		2982
		2983	C<ev_async> does not support queueing of data in any way. The reason
		2984	is that the author does not know of a simple (or any) algorithm for a
		2985	multiple-writer-single-reader queue that works in all cases and doesn't
		2986	need elaborate support such as pthreads or unportable memory access
		2987	semantics.
		2988
		2989	That means that if you want to queue data, you have to provide your own
		2990	queue. But at least I can tell you how to implement locking around your
		2991	queue:
		2992
		2993	=over 4
		2994
		2995	=item queueing from a signal handler context
		2996
		2997	To implement race-free queueing, you simply add to the queue in the signal
		2998	handler but you block the signal handler in the watcher callback. Here is
		2999	an example that does that for some fictitious SIGUSR1 handler:
		3000
		3001	static ev_async mysig;
		3002
		3003	static void
		3004	sigusr1_handler (void)
		3005	{
		3006	sometype data;
		3007
		3008	// no locking etc.
		3009	queue_put (data);
		3010	ev_async_send (EV_DEFAULT_ &mysig);
		3011	}
		3012
		3013	static void
		3014	mysig_cb (EV_P_ ev_async *w, int revents)
		3015	{
		3016	sometype data;
		3017	sigset_t block, prev;
		3018
		3019	sigemptyset (&block);
		3020	sigaddset (&block, SIGUSR1);
		3021	sigprocmask (SIG_BLOCK, &block, &prev);
		3022
		3023	while (queue_get (&data))
		3024	process (data);
		3025
		3026	if (sigismember (&prev, SIGUSR1)
		3027	sigprocmask (SIG_UNBLOCK, &block, 0);
		3028	}
		3029
		3030	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3031	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3032	either...).
		3033
		3034	=item queueing from a thread context
		3035
		3036	The strategy for threads is different, as you cannot (easily) block
		3037	threads but you can easily preempt them, so to queue safely you need to
		3038	employ a traditional mutex lock, such as in this pthread example:
		3039
		3040	static ev_async mysig;
		3041	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3042
		3043	static void
		3044	otherthread (void)
		3045	{
		3046	// only need to lock the actual queueing operation
		3047	pthread_mutex_lock (&mymutex);
		3048	queue_put (data);
		3049	pthread_mutex_unlock (&mymutex);
		3050
		3051	ev_async_send (EV_DEFAULT_ &mysig);
		3052	}
		3053
		3054	static void
		3055	mysig_cb (EV_P_ ev_async *w, int revents)
		3056	{
		3057	pthread_mutex_lock (&mymutex);
		3058
		3059	while (queue_get (&data))
		3060	process (data);
		3061
		3062	pthread_mutex_unlock (&mymutex);
		3063	}
		3064
		3065	=back
		3066
		3067
		3068	=head3 Watcher-Specific Functions and Data Members
		3069
		3070	=over 4
		3071
		3072	=item ev_async_init (ev_async *, callback)
		3073
		3074	Initialises and configures the async watcher - it has no parameters of any
		3075	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3076	trust me.
		3077
		3078	=item ev_async_send (loop, ev_async *)
		3079
		3080	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3081	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3082	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3083	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3084	section below on what exactly this means).
		3085
		3086	Note that, as with other watchers in libev, multiple events might get
		3087	compressed into a single callback invocation (another way to look at this
		3088	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3089	reset when the event loop detects that).
		3090
		3091	This call incurs the overhead of a system call only once per event loop
		3092	iteration, so while the overhead might be noticeable, it doesn't apply to
		3093	repeated calls to C<ev_async_send> for the same event loop.
		3094
		3095	=item bool = ev_async_pending (ev_async *)
		3096
		3097	Returns a non-zero value when C<ev_async_send> has been called on the
		3098	watcher but the event has not yet been processed (or even noted) by the
		3099	event loop.
		3100
		3101	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3102	the loop iterates next and checks for the watcher to have become active,
		3103	it will reset the flag again. C<ev_async_pending> can be used to very
		3104	quickly check whether invoking the loop might be a good idea.
		3105
		3106	Not that this does I<not> check whether the watcher itself is pending,
		3107	only whether it has been requested to make this watcher pending: there
		3108	is a time window between the event loop checking and resetting the async
		3109	notification, and the callback being invoked.
		3110
		3111	=back
		3112
		3113
1586	=head1 OTHER FUNCTIONS	3114	=head1 OTHER FUNCTIONS
1587		3115
1588	There are some other functions of possible interest. Described. Here. Now.	3116	There are some other functions of possible interest. Described. Here. Now.
1589		3117
1590	=over 4	3118	=over 4
1591		3119
1592	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3120	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1593		3121
1594	This function combines a simple timer and an I/O watcher, calls your	3122	This function combines a simple timer and an I/O watcher, calls your
1595	callback on whichever event happens first and automatically stop both	3123	callback on whichever event happens first and automatically stops both
1596	watchers. This is useful if you want to wait for a single event on an fd	3124	watchers. This is useful if you want to wait for a single event on an fd
1597	or timeout without having to allocate/configure/start/stop/free one or	3125	or timeout without having to allocate/configure/start/stop/free one or
1598	more watchers yourself.	3126	more watchers yourself.
1599		3127
1600	If C<fd> is less than 0, then no I/O watcher will be started and events	3128	If C<fd> is less than 0, then no I/O watcher will be started and the
1601	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3129	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1602	C<events> set will be craeted and started.	3130	the given C<fd> and C<events> set will be created and started.
1603		3131
1604	If C<timeout> is less than 0, then no timeout watcher will be	3132	If C<timeout> is less than 0, then no timeout watcher will be
1605	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3133	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1606	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3134	repeat = 0) will be started. C<0> is a valid timeout.
1607	dubious value.
1608		3135
1609	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3136	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1610	passed an C<revents> set like normal event callbacks (a combination of	3137	passed an C<revents> set like normal event callbacks (a combination of
1611	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3138	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1612	value passed to C<ev_once>:	3139	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3140	a timeout and an io event at the same time - you probably should give io
		3141	events precedence.
1613		3142
		3143	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3144
1614	static void stdin_ready (int revents, void *arg)	3145	static void stdin_ready (int revents, void *arg)
1615	{	3146	{
1616	if (revents & EV_TIMEOUT)
1617	/* doh, nothing entered */;
1618	else if (revents & EV_READ)	3147	if (revents & EV_READ)
1619	/* stdin might have data for us, joy! */;	3148	/* stdin might have data for us, joy! */;
		3149	else if (revents & EV_TIMEOUT)
		3150	/* doh, nothing entered */;
1620	}	3151	}
1621		3152
1622	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3153	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1623		3154
1624	=item ev_feed_event (ev_loop *, watcher *, int revents)
1625
1626	Feeds the given event set into the event loop, as if the specified event
1627	had happened for the specified watcher (which must be a pointer to an
1628	initialised but not necessarily started event watcher).
1629
1630	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3155	=item ev_feed_fd_event (loop, int fd, int revents)
1631		3156
1632	Feed an event on the given fd, as if a file descriptor backend detected	3157	Feed an event on the given fd, as if a file descriptor backend detected
1633	the given events it.	3158	the given events it.
1634		3159
1635	=item ev_feed_signal_event (ev_loop *loop, int signum)	3160	=item ev_feed_signal_event (loop, int signum)
1636		3161
1637	Feed an event as if the given signal occured (C<loop> must be the default	3162	Feed an event as if the given signal occurred (C<loop> must be the default
1638	loop!).	3163	loop!).
1639		3164
1640	=back	3165	=back
1641		3166
1642		3167
…		…
1658		3183
1659	=item * Priorities are not currently supported. Initialising priorities	3184	=item * Priorities are not currently supported. Initialising priorities
1660	will fail and all watchers will have the same priority, even though there	3185	will fail and all watchers will have the same priority, even though there
1661	is an ev_pri field.	3186	is an ev_pri field.
1662		3187
		3188	=item * In libevent, the last base created gets the signals, in libev, the
		3189	first base created (== the default loop) gets the signals.
		3190
1663	=item * Other members are not supported.	3191	=item * Other members are not supported.
1664		3192
1665	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3193	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1666	to use the libev header file and library.	3194	to use the libev header file and library.
1667		3195
1668	=back	3196	=back
1669		3197
1670	=head1 C++ SUPPORT	3198	=head1 C++ SUPPORT
1671		3199
1672	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3200	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1673	you to use some convinience methods to start/stop watchers and also change	3201	you to use some convenience methods to start/stop watchers and also change
1674	the callback model to a model using method callbacks on objects.	3202	the callback model to a model using method callbacks on objects.
1675		3203
1676	To use it,	3204	To use it,
1677		3205
1678	#include <ev++.h>	3206	#include <ev++.h>
1679		3207
1680	(it is not installed by default). This automatically includes F<ev.h>	3208	This automatically includes F<ev.h> and puts all of its definitions (many
1681	and puts all of its definitions (many of them macros) into the global	3209	of them macros) into the global namespace. All C++ specific things are
1682	namespace. All C++ specific things are put into the C<ev> namespace.	3210	put into the C<ev> namespace. It should support all the same embedding
		3211	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1683		3212
1684	It should support all the same embedding options as F<ev.h>, most notably	3213	Care has been taken to keep the overhead low. The only data member the C++
1685	C<EV_MULTIPLICITY>.	3214	classes add (compared to plain C-style watchers) is the event loop pointer
		3215	that the watcher is associated with (or no additional members at all if
		3216	you disable C<EV_MULTIPLICITY> when embedding libev).
		3217
		3218	Currently, functions, and static and non-static member functions can be
		3219	used as callbacks. Other types should be easy to add as long as they only
		3220	need one additional pointer for context. If you need support for other
		3221	types of functors please contact the author (preferably after implementing
		3222	it).
1686		3223
1687	Here is a list of things available in the C<ev> namespace:	3224	Here is a list of things available in the C<ev> namespace:
1688		3225
1689	=over 4	3226	=over 4
1690		3227
…		…
1706		3243
1707	All of those classes have these methods:	3244	All of those classes have these methods:
1708		3245
1709	=over 4	3246	=over 4
1710		3247
1711	=item ev::TYPE::TYPE (object *, object::method *)	3248	=item ev::TYPE::TYPE ()
1712		3249
1713	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3250	=item ev::TYPE::TYPE (loop)
1714		3251
1715	=item ev::TYPE::~TYPE	3252	=item ev::TYPE::~TYPE
1716		3253
1717	The constructor takes a pointer to an object and a method pointer to	3254	The constructor (optionally) takes an event loop to associate the watcher
1718	the event handler callback to call in this class. The constructor calls	3255	with. If it is omitted, it will use C<EV_DEFAULT>.
1719	C<ev_init> for you, which means you have to call the C<set> method	3256
1720	before starting it. If you do not specify a loop then the constructor	3257	The constructor calls C<ev_init> for you, which means you have to call the
1721	automatically associates the default loop with this watcher.	3258	C<set> method before starting it.
		3259
		3260	It will not set a callback, however: You have to call the templated C<set>
		3261	method to set a callback before you can start the watcher.
		3262
		3263	(The reason why you have to use a method is a limitation in C++ which does
		3264	not allow explicit template arguments for constructors).
1722		3265
1723	The destructor automatically stops the watcher if it is active.	3266	The destructor automatically stops the watcher if it is active.
1724		3267
		3268	=item w->set<class, &class::method> (object *)
		3269
		3270	This method sets the callback method to call. The method has to have a
		3271	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3272	first argument and the C<revents> as second. The object must be given as
		3273	parameter and is stored in the C<data> member of the watcher.
		3274
		3275	This method synthesizes efficient thunking code to call your method from
		3276	the C callback that libev requires. If your compiler can inline your
		3277	callback (i.e. it is visible to it at the place of the C<set> call and
		3278	your compiler is good :), then the method will be fully inlined into the
		3279	thunking function, making it as fast as a direct C callback.
		3280
		3281	Example: simple class declaration and watcher initialisation
		3282
		3283	struct myclass
		3284	{
		3285	void io_cb (ev::io &w, int revents) { }
		3286	}
		3287
		3288	myclass obj;
		3289	ev::io iow;
		3290	iow.set <myclass, &myclass::io_cb> (&obj);
		3291
		3292	=item w->set (object *)
		3293
		3294	This is an B<experimental> feature that might go away in a future version.
		3295
		3296	This is a variation of a method callback - leaving out the method to call
		3297	will default the method to C<operator ()>, which makes it possible to use
		3298	functor objects without having to manually specify the C<operator ()> all
		3299	the time. Incidentally, you can then also leave out the template argument
		3300	list.
		3301
		3302	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3303	int revents)>.
		3304
		3305	See the method-C<set> above for more details.
		3306
		3307	Example: use a functor object as callback.
		3308
		3309	struct myfunctor
		3310	{
		3311	void operator() (ev::io &w, int revents)
		3312	{
		3313	...
		3314	}
		3315	}
		3316
		3317	myfunctor f;
		3318
		3319	ev::io w;
		3320	w.set (&f);
		3321
		3322	=item w->set<function> (void *data = 0)
		3323
		3324	Also sets a callback, but uses a static method or plain function as
		3325	callback. The optional C<data> argument will be stored in the watcher's
		3326	C<data> member and is free for you to use.
		3327
		3328	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3329
		3330	See the method-C<set> above for more details.
		3331
		3332	Example: Use a plain function as callback.
		3333
		3334	static void io_cb (ev::io &w, int revents) { }
		3335	iow.set <io_cb> ();
		3336
1725	=item w->set (struct ev_loop *)	3337	=item w->set (loop)
1726		3338
1727	Associates a different C<struct ev_loop> with this watcher. You can only	3339	Associates a different C<struct ev_loop> with this watcher. You can only
1728	do this when the watcher is inactive (and not pending either).	3340	do this when the watcher is inactive (and not pending either).
1729		3341
1730	=item w->set ([args])	3342	=item w->set ([arguments])
1731		3343
1732	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3344	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1733	called at least once. Unlike the C counterpart, an active watcher gets	3345	called at least once. Unlike the C counterpart, an active watcher gets
1734	automatically stopped and restarted.	3346	automatically stopped and restarted when reconfiguring it with this
		3347	method.
1735		3348
1736	=item w->start ()	3349	=item w->start ()
1737		3350
1738	Starts the watcher. Note that there is no C<loop> argument as the	3351	Starts the watcher. Note that there is no C<loop> argument, as the
1739	constructor already takes the loop.	3352	constructor already stores the event loop.
1740		3353
1741	=item w->stop ()	3354	=item w->stop ()
1742		3355
1743	Stops the watcher if it is active. Again, no C<loop> argument.	3356	Stops the watcher if it is active. Again, no C<loop> argument.
1744		3357
1745	=item w->again () C<ev::timer>, C<ev::periodic> only	3358	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1746		3359
1747	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3360	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1748	C<ev_TYPE_again> function.	3361	C<ev_TYPE_again> function.
1749		3362
1750	=item w->sweep () C<ev::embed> only	3363	=item w->sweep () (C<ev::embed> only)
1751		3364
1752	Invokes C<ev_embed_sweep>.	3365	Invokes C<ev_embed_sweep>.
1753		3366
1754	=item w->update () C<ev::stat> only	3367	=item w->update () (C<ev::stat> only)
1755		3368
1756	Invokes C<ev_stat_stat>.	3369	Invokes C<ev_stat_stat>.
1757		3370
1758	=back	3371	=back
1759		3372
1760	=back	3373	=back
1761		3374
1762	Example: Define a class with an IO and idle watcher, start one of them in	3375	Example: Define a class with an IO and idle watcher, start one of them in
1763	the constructor.	3376	the constructor.
1764		3377
1765	class myclass	3378	class myclass
1766	{	3379	{
1767	ev_io io; void io_cb (ev::io &w, int revents);	3380	ev::io io ; void io_cb (ev::io &w, int revents);
1768	ev_idle idle void idle_cb (ev::idle &w, int revents);	3381	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1769		3382
1770	myclass ();	3383	myclass (int fd)
1771	}	3384	{
		3385	io .set <myclass, &myclass::io_cb > (this);
		3386	idle.set <myclass, &myclass::idle_cb> (this);
1772		3387
1773	myclass::myclass (int fd)
1774	: io (this, &myclass::io_cb),
1775	idle (this, &myclass::idle_cb)
1776	{
1777	io.start (fd, ev::READ);	3388	io.start (fd, ev::READ);
		3389	}
1778	}	3390	};
		3391
		3392
		3393	=head1 OTHER LANGUAGE BINDINGS
		3394
		3395	Libev does not offer other language bindings itself, but bindings for a
		3396	number of languages exist in the form of third-party packages. If you know
		3397	any interesting language binding in addition to the ones listed here, drop
		3398	me a note.
		3399
		3400	=over 4
		3401
		3402	=item Perl
		3403
		3404	The EV module implements the full libev API and is actually used to test
		3405	libev. EV is developed together with libev. Apart from the EV core module,
		3406	there are additional modules that implement libev-compatible interfaces
		3407	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3408	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3409	and C<EV::Glib>).
		3410
		3411	It can be found and installed via CPAN, its homepage is at
		3412	L<http://software.schmorp.de/pkg/EV>.
		3413
		3414	=item Python
		3415
		3416	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3417	seems to be quite complete and well-documented.
		3418
		3419	=item Ruby
		3420
		3421	Tony Arcieri has written a ruby extension that offers access to a subset
		3422	of the libev API and adds file handle abstractions, asynchronous DNS and
		3423	more on top of it. It can be found via gem servers. Its homepage is at
		3424	L<http://rev.rubyforge.org/>.
		3425
		3426	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3427	makes rev work even on mingw.
		3428
		3429	=item Haskell
		3430
		3431	A haskell binding to libev is available at
		3432	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3433
		3434	=item D
		3435
		3436	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3437	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3438
		3439	=item Ocaml
		3440
		3441	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3442	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3443
		3444	=item Lua
		3445
		3446	Brian Maher has written a partial interface to libev
		3447	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3448	L<http://github.com/brimworks/lua-ev>.
		3449
		3450	=back
1779		3451
1780		3452
1781	=head1 MACRO MAGIC	3453	=head1 MACRO MAGIC
1782		3454
1783	Libev can be compiled with a variety of options, the most fundemantal is	3455	Libev can be compiled with a variety of options, the most fundamental
1784	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3456	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1785	callbacks have an initial C<struct ev_loop *> argument.	3457	functions and callbacks have an initial C<struct ev_loop *> argument.
1786		3458
1787	To make it easier to write programs that cope with either variant, the	3459	To make it easier to write programs that cope with either variant, the
1788	following macros are defined:	3460	following macros are defined:
1789		3461
1790	=over 4	3462	=over 4
…		…
1793		3465
1794	This provides the loop I<argument> for functions, if one is required ("ev	3466	This provides the loop I<argument> for functions, if one is required ("ev
1795	loop argument"). The C<EV_A> form is used when this is the sole argument,	3467	loop argument"). The C<EV_A> form is used when this is the sole argument,
1796	C<EV_A_> is used when other arguments are following. Example:	3468	C<EV_A_> is used when other arguments are following. Example:
1797		3469
1798	ev_unref (EV_A);	3470	ev_unref (EV_A);
1799	ev_timer_add (EV_A_ watcher);	3471	ev_timer_add (EV_A_ watcher);
1800	ev_loop (EV_A_ 0);	3472	ev_loop (EV_A_ 0);
1801		3473
1802	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3474	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1803	which is often provided by the following macro.	3475	which is often provided by the following macro.
1804		3476
1805	=item C<EV_P>, C<EV_P_>	3477	=item C<EV_P>, C<EV_P_>
1806		3478
1807	This provides the loop I<parameter> for functions, if one is required ("ev	3479	This provides the loop I<parameter> for functions, if one is required ("ev
1808	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3480	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1809	C<EV_P_> is used when other parameters are following. Example:	3481	C<EV_P_> is used when other parameters are following. Example:
1810		3482
1811	// this is how ev_unref is being declared	3483	// this is how ev_unref is being declared
1812	static void ev_unref (EV_P);	3484	static void ev_unref (EV_P);
1813		3485
1814	// this is how you can declare your typical callback	3486	// this is how you can declare your typical callback
1815	static void cb (EV_P_ ev_timer *w, int revents)	3487	static void cb (EV_P_ ev_timer *w, int revents)
1816		3488
1817	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3489	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1818	suitable for use with C<EV_A>.	3490	suitable for use with C<EV_A>.
1819		3491
1820	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3492	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1821		3493
1822	Similar to the other two macros, this gives you the value of the default	3494	Similar to the other two macros, this gives you the value of the default
1823	loop, if multiple loops are supported ("ev loop default").	3495	loop, if multiple loops are supported ("ev loop default").
1824		3496
		3497	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3498
		3499	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3500	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3501	is undefined when the default loop has not been initialised by a previous
		3502	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3503
		3504	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3505	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3506
1825	=back	3507	=back
1826		3508
1827	Example: Declare and initialise a check watcher, working regardless of	3509	Example: Declare and initialise a check watcher, utilising the above
1828	wether multiple loops are supported or not.	3510	macros so it will work regardless of whether multiple loops are supported
		3511	or not.
1829		3512
1830	static void	3513	static void
1831	check_cb (EV_P_ ev_timer *w, int revents)	3514	check_cb (EV_P_ ev_timer *w, int revents)
1832	{	3515	{
1833	ev_check_stop (EV_A_ w);	3516	ev_check_stop (EV_A_ w);
1834	}	3517	}
1835		3518
1836	ev_check check;	3519	ev_check check;
1837	ev_check_init (&check, check_cb);	3520	ev_check_init (&check, check_cb);
1838	ev_check_start (EV_DEFAULT_ &check);	3521	ev_check_start (EV_DEFAULT_ &check);
1839	ev_loop (EV_DEFAULT_ 0);	3522	ev_loop (EV_DEFAULT_ 0);
1840
1841		3523
1842	=head1 EMBEDDING	3524	=head1 EMBEDDING
1843		3525
1844	Libev can (and often is) directly embedded into host	3526	Libev can (and often is) directly embedded into host
1845	applications. Examples of applications that embed it include the Deliantra	3527	applications. Examples of applications that embed it include the Deliantra
1846	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3528	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1847	and rxvt-unicode.	3529	and rxvt-unicode.
1848		3530
1849	The goal is to enable you to just copy the neecssary files into your	3531	The goal is to enable you to just copy the necessary files into your
1850	source directory without having to change even a single line in them, so	3532	source directory without having to change even a single line in them, so
1851	you can easily upgrade by simply copying (or having a checked-out copy of	3533	you can easily upgrade by simply copying (or having a checked-out copy of
1852	libev somewhere in your source tree).	3534	libev somewhere in your source tree).
1853		3535
1854	=head2 FILESETS	3536	=head2 FILESETS
1855		3537
1856	Depending on what features you need you need to include one or more sets of files	3538	Depending on what features you need you need to include one or more sets of files
1857	in your app.	3539	in your application.
1858		3540
1859	=head3 CORE EVENT LOOP	3541	=head3 CORE EVENT LOOP
1860		3542
1861	To include only the libev core (all the C<ev_*> functions), with manual	3543	To include only the libev core (all the C<ev_*> functions), with manual
1862	configuration (no autoconf):	3544	configuration (no autoconf):
1863		3545
1864	#define EV_STANDALONE 1	3546	#define EV_STANDALONE 1
1865	#include "ev.c"	3547	#include "ev.c"
1866		3548
1867	This will automatically include F<ev.h>, too, and should be done in a	3549	This will automatically include F<ev.h>, too, and should be done in a
1868	single C source file only to provide the function implementations. To use	3550	single C source file only to provide the function implementations. To use
1869	it, do the same for F<ev.h> in all files wishing to use this API (best	3551	it, do the same for F<ev.h> in all files wishing to use this API (best
1870	done by writing a wrapper around F<ev.h> that you can include instead and	3552	done by writing a wrapper around F<ev.h> that you can include instead and
1871	where you can put other configuration options):	3553	where you can put other configuration options):
1872		3554
1873	#define EV_STANDALONE 1	3555	#define EV_STANDALONE 1
1874	#include "ev.h"	3556	#include "ev.h"
1875		3557
1876	Both header files and implementation files can be compiled with a C++	3558	Both header files and implementation files can be compiled with a C++
1877	compiler (at least, thats a stated goal, and breakage will be treated	3559	compiler (at least, that's a stated goal, and breakage will be treated
1878	as a bug).	3560	as a bug).
1879		3561
1880	You need the following files in your source tree, or in a directory	3562	You need the following files in your source tree, or in a directory
1881	in your include path (e.g. in libev/ when using -Ilibev):	3563	in your include path (e.g. in libev/ when using -Ilibev):
1882		3564
1883	ev.h	3565	ev.h
1884	ev.c	3566	ev.c
1885	ev_vars.h	3567	ev_vars.h
1886	ev_wrap.h	3568	ev_wrap.h
1887		3569
1888	ev_win32.c required on win32 platforms only	3570	ev_win32.c required on win32 platforms only
1889		3571
1890	ev_select.c only when select backend is enabled (which is by default)	3572	ev_select.c only when select backend is enabled (which is enabled by default)
1891	ev_poll.c only when poll backend is enabled (disabled by default)	3573	ev_poll.c only when poll backend is enabled (disabled by default)
1892	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3574	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1893	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3575	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1894	ev_port.c only when the solaris port backend is enabled (disabled by default)	3576	ev_port.c only when the solaris port backend is enabled (disabled by default)
1895		3577
1896	F<ev.c> includes the backend files directly when enabled, so you only need	3578	F<ev.c> includes the backend files directly when enabled, so you only need
1897	to compile this single file.	3579	to compile this single file.
1898		3580
1899	=head3 LIBEVENT COMPATIBILITY API	3581	=head3 LIBEVENT COMPATIBILITY API
1900		3582
1901	To include the libevent compatibility API, also include:	3583	To include the libevent compatibility API, also include:
1902		3584
1903	#include "event.c"	3585	#include "event.c"
1904		3586
1905	in the file including F<ev.c>, and:	3587	in the file including F<ev.c>, and:
1906		3588
1907	#include "event.h"	3589	#include "event.h"
1908		3590
1909	in the files that want to use the libevent API. This also includes F<ev.h>.	3591	in the files that want to use the libevent API. This also includes F<ev.h>.
1910		3592
1911	You need the following additional files for this:	3593	You need the following additional files for this:
1912		3594
1913	event.h	3595	event.h
1914	event.c	3596	event.c
1915		3597
1916	=head3 AUTOCONF SUPPORT	3598	=head3 AUTOCONF SUPPORT
1917		3599
1918	Instead of using C<EV_STANDALONE=1> and providing your config in	3600	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1919	whatever way you want, you can also C<m4_include([libev.m4])> in your	3601	whatever way you want, you can also C<m4_include([libev.m4])> in your
1920	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3602	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1921	include F<config.h> and configure itself accordingly.	3603	include F<config.h> and configure itself accordingly.
1922		3604
1923	For this of course you need the m4 file:	3605	For this of course you need the m4 file:
1924		3606
1925	libev.m4	3607	libev.m4
1926		3608
1927	=head2 PREPROCESSOR SYMBOLS/MACROS	3609	=head2 PREPROCESSOR SYMBOLS/MACROS
1928		3610
1929	Libev can be configured via a variety of preprocessor symbols you have to define	3611	Libev can be configured via a variety of preprocessor symbols you have to
1930	before including any of its files. The default is not to build for multiplicity	3612	define before including any of its files. The default in the absence of
1931	and only include the select backend.	3613	autoconf is documented for every option.
1932		3614
1933	=over 4	3615	=over 4
1934		3616
1935	=item EV_STANDALONE	3617	=item EV_STANDALONE
1936		3618
…		…
1938	keeps libev from including F<config.h>, and it also defines dummy	3620	keeps libev from including F<config.h>, and it also defines dummy
1939	implementations for some libevent functions (such as logging, which is not	3621	implementations for some libevent functions (such as logging, which is not
1940	supported). It will also not define any of the structs usually found in	3622	supported). It will also not define any of the structs usually found in
1941	F<event.h> that are not directly supported by the libev core alone.	3623	F<event.h> that are not directly supported by the libev core alone.
1942		3624
		3625	In standalone mode, libev will still try to automatically deduce the
		3626	configuration, but has to be more conservative.
		3627
1943	=item EV_USE_MONOTONIC	3628	=item EV_USE_MONOTONIC
1944		3629
1945	If defined to be C<1>, libev will try to detect the availability of the	3630	If defined to be C<1>, libev will try to detect the availability of the
1946	monotonic clock option at both compiletime and runtime. Otherwise no use	3631	monotonic clock option at both compile time and runtime. Otherwise no
1947	of the monotonic clock option will be attempted. If you enable this, you	3632	use of the monotonic clock option will be attempted. If you enable this,
1948	usually have to link against librt or something similar. Enabling it when	3633	you usually have to link against librt or something similar. Enabling it
1949	the functionality isn't available is safe, though, althoguh you have	3634	when the functionality isn't available is safe, though, although you have
1950	to make sure you link against any libraries where the C<clock_gettime>	3635	to make sure you link against any libraries where the C<clock_gettime>
1951	function is hiding in (often F<-lrt>).	3636	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1952		3637
1953	=item EV_USE_REALTIME	3638	=item EV_USE_REALTIME
1954		3639
1955	If defined to be C<1>, libev will try to detect the availability of the	3640	If defined to be C<1>, libev will try to detect the availability of the
1956	realtime clock option at compiletime (and assume its availability at	3641	real-time clock option at compile time (and assume its availability
1957	runtime if successful). Otherwise no use of the realtime clock option will	3642	at runtime if successful). Otherwise no use of the real-time clock
1958	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3643	option will be attempted. This effectively replaces C<gettimeofday>
1959	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3644	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1960	in the description of C<EV_USE_MONOTONIC>, though.	3645	correctness. See the note about libraries in the description of
		3646	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3647	C<EV_USE_CLOCK_SYSCALL>.
		3648
		3649	=item EV_USE_CLOCK_SYSCALL
		3650
		3651	If defined to be C<1>, libev will try to use a direct syscall instead
		3652	of calling the system-provided C<clock_gettime> function. This option
		3653	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3654	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3655	programs needlessly. Using a direct syscall is slightly slower (in
		3656	theory), because no optimised vdso implementation can be used, but avoids
		3657	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3658	higher, as it simplifies linking (no need for C<-lrt>).
		3659
		3660	=item EV_USE_NANOSLEEP
		3661
		3662	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3663	and will use it for delays. Otherwise it will use C<select ()>.
		3664
		3665	=item EV_USE_EVENTFD
		3666
		3667	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3668	available and will probe for kernel support at runtime. This will improve
		3669	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3670	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3671	2.7 or newer, otherwise disabled.
1961		3672
1962	=item EV_USE_SELECT	3673	=item EV_USE_SELECT
1963		3674
1964	If undefined or defined to be C<1>, libev will compile in support for the	3675	If undefined or defined to be C<1>, libev will compile in support for the
1965	C<select>(2) backend. No attempt at autodetection will be done: if no	3676	C<select>(2) backend. No attempt at auto-detection will be done: if no
1966	other method takes over, select will be it. Otherwise the select backend	3677	other method takes over, select will be it. Otherwise the select backend
1967	will not be compiled in.	3678	will not be compiled in.
1968		3679
1969	=item EV_SELECT_USE_FD_SET	3680	=item EV_SELECT_USE_FD_SET
1970		3681
1971	If defined to C<1>, then the select backend will use the system C<fd_set>	3682	If defined to C<1>, then the select backend will use the system C<fd_set>
1972	structure. This is useful if libev doesn't compile due to a missing	3683	structure. This is useful if libev doesn't compile due to a missing
1973	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3684	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1974	exotic systems. This usually limits the range of file descriptors to some	3685	on exotic systems. This usually limits the range of file descriptors to
1975	low limit such as 1024 or might have other limitations (winsocket only	3686	some low limit such as 1024 or might have other limitations (winsocket
1976	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3687	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1977	influence the size of the C<fd_set> used.	3688	configures the maximum size of the C<fd_set>.
1978		3689
1979	=item EV_SELECT_IS_WINSOCKET	3690	=item EV_SELECT_IS_WINSOCKET
1980		3691
1981	When defined to C<1>, the select backend will assume that	3692	When defined to C<1>, the select backend will assume that
1982	select/socket/connect etc. don't understand file descriptors but	3693	select/socket/connect etc. don't understand file descriptors but
…		…
1984	be used is the winsock select). This means that it will call	3695	be used is the winsock select). This means that it will call
1985	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3696	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1986	it is assumed that all these functions actually work on fds, even	3697	it is assumed that all these functions actually work on fds, even
1987	on win32. Should not be defined on non-win32 platforms.	3698	on win32. Should not be defined on non-win32 platforms.
1988		3699
		3700	=item EV_FD_TO_WIN32_HANDLE(fd)
		3701
		3702	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3703	file descriptors to socket handles. When not defining this symbol (the
		3704	default), then libev will call C<_get_osfhandle>, which is usually
		3705	correct. In some cases, programs use their own file descriptor management,
		3706	in which case they can provide this function to map fds to socket handles.
		3707
		3708	=item EV_WIN32_HANDLE_TO_FD(handle)
		3709
		3710	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3711	using the standard C<_open_osfhandle> function. For programs implementing
		3712	their own fd to handle mapping, overwriting this function makes it easier
		3713	to do so. This can be done by defining this macro to an appropriate value.
		3714
		3715	=item EV_WIN32_CLOSE_FD(fd)
		3716
		3717	If programs implement their own fd to handle mapping on win32, then this
		3718	macro can be used to override the C<close> function, useful to unregister
		3719	file descriptors again. Note that the replacement function has to close
		3720	the underlying OS handle.
		3721
1989	=item EV_USE_POLL	3722	=item EV_USE_POLL
1990		3723
1991	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3724	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1992	backend. Otherwise it will be enabled on non-win32 platforms. It	3725	backend. Otherwise it will be enabled on non-win32 platforms. It
1993	takes precedence over select.	3726	takes precedence over select.
1994		3727
1995	=item EV_USE_EPOLL	3728	=item EV_USE_EPOLL
1996		3729
1997	If defined to be C<1>, libev will compile in support for the Linux	3730	If defined to be C<1>, libev will compile in support for the Linux
1998	C<epoll>(7) backend. Its availability will be detected at runtime,	3731	C<epoll>(7) backend. Its availability will be detected at runtime,
1999	otherwise another method will be used as fallback. This is the	3732	otherwise another method will be used as fallback. This is the preferred
2000	preferred backend for GNU/Linux systems.	3733	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3734	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2001		3735
2002	=item EV_USE_KQUEUE	3736	=item EV_USE_KQUEUE
2003		3737
2004	If defined to be C<1>, libev will compile in support for the BSD style	3738	If defined to be C<1>, libev will compile in support for the BSD style
2005	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3739	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2018	otherwise another method will be used as fallback. This is the preferred	3752	otherwise another method will be used as fallback. This is the preferred
2019	backend for Solaris 10 systems.	3753	backend for Solaris 10 systems.
2020		3754
2021	=item EV_USE_DEVPOLL	3755	=item EV_USE_DEVPOLL
2022		3756
2023	reserved for future expansion, works like the USE symbols above.	3757	Reserved for future expansion, works like the USE symbols above.
2024		3758
2025	=item EV_USE_INOTIFY	3759	=item EV_USE_INOTIFY
2026		3760
2027	If defined to be C<1>, libev will compile in support for the Linux inotify	3761	If defined to be C<1>, libev will compile in support for the Linux inotify
2028	interface to speed up C<ev_stat> watchers. Its actual availability will	3762	interface to speed up C<ev_stat> watchers. Its actual availability will
2029	be detected at runtime.	3763	be detected at runtime. If undefined, it will be enabled if the headers
		3764	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3765
		3766	=item EV_ATOMIC_T
		3767
		3768	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3769	access is atomic with respect to other threads or signal contexts. No such
		3770	type is easily found in the C language, so you can provide your own type
		3771	that you know is safe for your purposes. It is used both for signal handler "locking"
		3772	as well as for signal and thread safety in C<ev_async> watchers.
		3773
		3774	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3775	(from F<signal.h>), which is usually good enough on most platforms.
2030		3776
2031	=item EV_H	3777	=item EV_H
2032		3778
2033	The name of the F<ev.h> header file used to include it. The default if	3779	The name of the F<ev.h> header file used to include it. The default if
2034	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3780	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2035	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3781	used to virtually rename the F<ev.h> header file in case of conflicts.
2036		3782
2037	=item EV_CONFIG_H	3783	=item EV_CONFIG_H
2038		3784
2039	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3785	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2040	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3786	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2041	C<EV_H>, above.	3787	C<EV_H>, above.
2042		3788
2043	=item EV_EVENT_H	3789	=item EV_EVENT_H
2044		3790
2045	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3791	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2046	of how the F<event.h> header can be found.	3792	of how the F<event.h> header can be found, the default is C<"event.h">.
2047		3793
2048	=item EV_PROTOTYPES	3794	=item EV_PROTOTYPES
2049		3795
2050	If defined to be C<0>, then F<ev.h> will not define any function	3796	If defined to be C<0>, then F<ev.h> will not define any function
2051	prototypes, but still define all the structs and other symbols. This is	3797	prototypes, but still define all the structs and other symbols. This is
…		…
2058	will have the C<struct ev_loop *> as first argument, and you can create	3804	will have the C<struct ev_loop *> as first argument, and you can create
2059	additional independent event loops. Otherwise there will be no support	3805	additional independent event loops. Otherwise there will be no support
2060	for multiple event loops and there is no first event loop pointer	3806	for multiple event loops and there is no first event loop pointer
2061	argument. Instead, all functions act on the single default loop.	3807	argument. Instead, all functions act on the single default loop.
2062		3808
		3809	=item EV_MINPRI
		3810
		3811	=item EV_MAXPRI
		3812
		3813	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3814	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3815	provide for more priorities by overriding those symbols (usually defined
		3816	to be C<-2> and C<2>, respectively).
		3817
		3818	When doing priority-based operations, libev usually has to linearly search
		3819	all the priorities, so having many of them (hundreds) uses a lot of space
		3820	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3821	fine.
		3822
		3823	If your embedding application does not need any priorities, defining these
		3824	both to C<0> will save some memory and CPU.
		3825
2063	=item EV_PERIODIC_ENABLE	3826	=item EV_PERIODIC_ENABLE
2064		3827
2065	If undefined or defined to be C<1>, then periodic timers are supported. If	3828	If undefined or defined to be C<1>, then periodic timers are supported. If
2066	defined to be C<0>, then they are not. Disabling them saves a few kB of	3829	defined to be C<0>, then they are not. Disabling them saves a few kB of
2067	code.	3830	code.
2068		3831
		3832	=item EV_IDLE_ENABLE
		3833
		3834	If undefined or defined to be C<1>, then idle watchers are supported. If
		3835	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3836	code.
		3837
2069	=item EV_EMBED_ENABLE	3838	=item EV_EMBED_ENABLE
2070		3839
2071	If undefined or defined to be C<1>, then embed watchers are supported. If	3840	If undefined or defined to be C<1>, then embed watchers are supported. If
2072	defined to be C<0>, then they are not.	3841	defined to be C<0>, then they are not. Embed watchers rely on most other
		3842	watcher types, which therefore must not be disabled.
2073		3843
2074	=item EV_STAT_ENABLE	3844	=item EV_STAT_ENABLE
2075		3845
2076	If undefined or defined to be C<1>, then stat watchers are supported. If	3846	If undefined or defined to be C<1>, then stat watchers are supported. If
2077	defined to be C<0>, then they are not.	3847	defined to be C<0>, then they are not.
…		…
2079	=item EV_FORK_ENABLE	3849	=item EV_FORK_ENABLE
2080		3850
2081	If undefined or defined to be C<1>, then fork watchers are supported. If	3851	If undefined or defined to be C<1>, then fork watchers are supported. If
2082	defined to be C<0>, then they are not.	3852	defined to be C<0>, then they are not.
2083		3853
		3854	=item EV_ASYNC_ENABLE
		3855
		3856	If undefined or defined to be C<1>, then async watchers are supported. If
		3857	defined to be C<0>, then they are not.
		3858
2084	=item EV_MINIMAL	3859	=item EV_MINIMAL
2085		3860
2086	If you need to shave off some kilobytes of code at the expense of some	3861	If you need to shave off some kilobytes of code at the expense of some
2087	speed, define this symbol to C<1>. Currently only used for gcc to override	3862	speed (but with the full API), define this symbol to C<1>. Currently this
2088	some inlining decisions, saves roughly 30% codesize of amd64.	3863	is used to override some inlining decisions, saves roughly 30% code size
		3864	on amd64. It also selects a much smaller 2-heap for timer management over
		3865	the default 4-heap.
		3866
		3867	You can save even more by disabling watcher types you do not need
		3868	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3869	(C<-DNDEBUG>) will usually reduce code size a lot.
		3870
		3871	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3872	provide a bare-bones event library. See C<ev.h> for details on what parts
		3873	of the API are still available, and do not complain if this subset changes
		3874	over time.
		3875
		3876	=item EV_NSIG
		3877
		3878	The highest supported signal number, +1 (or, the number of
		3879	signals): Normally, libev tries to deduce the maximum number of signals
		3880	automatically, but sometimes this fails, in which case it can be
		3881	specified. Also, using a lower number than detected (C<32> should be
		3882	good for about any system in existance) can save some memory, as libev
		3883	statically allocates some 12-24 bytes per signal number.
2089		3884
2090	=item EV_PID_HASHSIZE	3885	=item EV_PID_HASHSIZE
2091		3886
2092	C<ev_child> watchers use a small hash table to distribute workload by	3887	C<ev_child> watchers use a small hash table to distribute workload by
2093	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3888	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2094	than enough. If you need to manage thousands of children you might want to	3889	than enough. If you need to manage thousands of children you might want to
2095	increase this value (I<must> be a power of two).	3890	increase this value (I<must> be a power of two).
2096		3891
2097	=item EV_INOTIFY_HASHSIZE	3892	=item EV_INOTIFY_HASHSIZE
2098		3893
2099	C<ev_staz> watchers use a small hash table to distribute workload by	3894	C<ev_stat> watchers use a small hash table to distribute workload by
2100	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3895	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2101	usually more than enough. If you need to manage thousands of C<ev_stat>	3896	usually more than enough. If you need to manage thousands of C<ev_stat>
2102	watchers you might want to increase this value (I<must> be a power of	3897	watchers you might want to increase this value (I<must> be a power of
2103	two).	3898	two).
2104		3899
		3900	=item EV_USE_4HEAP
		3901
		3902	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3903	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3904	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3905	faster performance with many (thousands) of watchers.
		3906
		3907	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3908	(disabled).
		3909
		3910	=item EV_HEAP_CACHE_AT
		3911
		3912	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3913	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3914	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3915	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3916	but avoids random read accesses on heap changes. This improves performance
		3917	noticeably with many (hundreds) of watchers.
		3918
		3919	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3920	(disabled).
		3921
		3922	=item EV_VERIFY
		3923
		3924	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3925	be done: If set to C<0>, no internal verification code will be compiled
		3926	in. If set to C<1>, then verification code will be compiled in, but not
		3927	called. If set to C<2>, then the internal verification code will be
		3928	called once per loop, which can slow down libev. If set to C<3>, then the
		3929	verification code will be called very frequently, which will slow down
		3930	libev considerably.
		3931
		3932	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3933	C<0>.
		3934
2105	=item EV_COMMON	3935	=item EV_COMMON
2106		3936
2107	By default, all watchers have a C<void *data> member. By redefining	3937	By default, all watchers have a C<void *data> member. By redefining
2108	this macro to a something else you can include more and other types of	3938	this macro to a something else you can include more and other types of
2109	members. You have to define it each time you include one of the files,	3939	members. You have to define it each time you include one of the files,
2110	though, and it must be identical each time.	3940	though, and it must be identical each time.
2111		3941
2112	For example, the perl EV module uses something like this:	3942	For example, the perl EV module uses something like this:
2113		3943
2114	#define EV_COMMON \	3944	#define EV_COMMON \
2115	SV *self; /* contains this struct */ \	3945	SV *self; /* contains this struct */ \
2116	SV *cb_sv, *fh /* note no trailing ";" */	3946	SV *cb_sv, *fh /* note no trailing ";" */
2117		3947
2118	=item EV_CB_DECLARE (type)	3948	=item EV_CB_DECLARE (type)
2119		3949
2120	=item EV_CB_INVOKE (watcher, revents)	3950	=item EV_CB_INVOKE (watcher, revents)
2121		3951
2122	=item ev_set_cb (ev, cb)	3952	=item ev_set_cb (ev, cb)
2123		3953
2124	Can be used to change the callback member declaration in each watcher,	3954	Can be used to change the callback member declaration in each watcher,
2125	and the way callbacks are invoked and set. Must expand to a struct member	3955	and the way callbacks are invoked and set. Must expand to a struct member
2126	definition and a statement, respectively. See the F<ev.v> header file for	3956	definition and a statement, respectively. See the F<ev.h> header file for
2127	their default definitions. One possible use for overriding these is to	3957	their default definitions. One possible use for overriding these is to
2128	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3958	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2129	method calls instead of plain function calls in C++.	3959	method calls instead of plain function calls in C++.
		3960
		3961	=back
		3962
		3963	=head2 EXPORTED API SYMBOLS
		3964
		3965	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3966	exported symbols, you can use the provided F<Symbol.*> files which list
		3967	all public symbols, one per line:
		3968
		3969	Symbols.ev for libev proper
		3970	Symbols.event for the libevent emulation
		3971
		3972	This can also be used to rename all public symbols to avoid clashes with
		3973	multiple versions of libev linked together (which is obviously bad in
		3974	itself, but sometimes it is inconvenient to avoid this).
		3975
		3976	A sed command like this will create wrapper C<#define>'s that you need to
		3977	include before including F<ev.h>:
		3978
		3979	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3980
		3981	This would create a file F<wrap.h> which essentially looks like this:
		3982
		3983	#define ev_backend myprefix_ev_backend
		3984	#define ev_check_start myprefix_ev_check_start
		3985	#define ev_check_stop myprefix_ev_check_stop
		3986	...
2130		3987
2131	=head2 EXAMPLES	3988	=head2 EXAMPLES
2132		3989
2133	For a real-world example of a program the includes libev	3990	For a real-world example of a program the includes libev
2134	verbatim, you can have a look at the EV perl module	3991	verbatim, you can have a look at the EV perl module
…		…
2137	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3994	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2138	will be compiled. It is pretty complex because it provides its own header	3995	will be compiled. It is pretty complex because it provides its own header
2139	file.	3996	file.
2140		3997
2141	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3998	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2142	that everybody includes and which overrides some autoconf choices:	3999	that everybody includes and which overrides some configure choices:
2143		4000
		4001	#define EV_MINIMAL 1
2144	#define EV_USE_POLL 0	4002	#define EV_USE_POLL 0
2145	#define EV_MULTIPLICITY 0	4003	#define EV_MULTIPLICITY 0
2146	#define EV_PERIODICS 0	4004	#define EV_PERIODIC_ENABLE 0
		4005	#define EV_STAT_ENABLE 0
		4006	#define EV_FORK_ENABLE 0
2147	#define EV_CONFIG_H <config.h>	4007	#define EV_CONFIG_H <config.h>
		4008	#define EV_MINPRI 0
		4009	#define EV_MAXPRI 0
2148		4010
2149	#include "ev++.h"	4011	#include "ev++.h"
2150		4012
2151	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4013	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2152		4014
2153	#include "ev_cpp.h"	4015	#include "ev_cpp.h"
2154	#include "ev.c"	4016	#include "ev.c"
2155		4017
		4018	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2156		4019
		4020	=head2 THREADS AND COROUTINES
		4021
		4022	=head3 THREADS
		4023
		4024	All libev functions are reentrant and thread-safe unless explicitly
		4025	documented otherwise, but libev implements no locking itself. This means
		4026	that you can use as many loops as you want in parallel, as long as there
		4027	are no concurrent calls into any libev function with the same loop
		4028	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4029	of course): libev guarantees that different event loops share no data
		4030	structures that need any locking.
		4031
		4032	Or to put it differently: calls with different loop parameters can be done
		4033	concurrently from multiple threads, calls with the same loop parameter
		4034	must be done serially (but can be done from different threads, as long as
		4035	only one thread ever is inside a call at any point in time, e.g. by using
		4036	a mutex per loop).
		4037
		4038	Specifically to support threads (and signal handlers), libev implements
		4039	so-called C<ev_async> watchers, which allow some limited form of
		4040	concurrency on the same event loop, namely waking it up "from the
		4041	outside".
		4042
		4043	If you want to know which design (one loop, locking, or multiple loops
		4044	without or something else still) is best for your problem, then I cannot
		4045	help you, but here is some generic advice:
		4046
		4047	=over 4
		4048
		4049	=item * most applications have a main thread: use the default libev loop
		4050	in that thread, or create a separate thread running only the default loop.
		4051
		4052	This helps integrating other libraries or software modules that use libev
		4053	themselves and don't care/know about threading.
		4054
		4055	=item * one loop per thread is usually a good model.
		4056
		4057	Doing this is almost never wrong, sometimes a better-performance model
		4058	exists, but it is always a good start.
		4059
		4060	=item * other models exist, such as the leader/follower pattern, where one
		4061	loop is handed through multiple threads in a kind of round-robin fashion.
		4062
		4063	Choosing a model is hard - look around, learn, know that usually you can do
		4064	better than you currently do :-)
		4065
		4066	=item * often you need to talk to some other thread which blocks in the
		4067	event loop.
		4068
		4069	C<ev_async> watchers can be used to wake them up from other threads safely
		4070	(or from signal contexts...).
		4071
		4072	An example use would be to communicate signals or other events that only
		4073	work in the default loop by registering the signal watcher with the
		4074	default loop and triggering an C<ev_async> watcher from the default loop
		4075	watcher callback into the event loop interested in the signal.
		4076
		4077	=back
		4078
		4079	=head4 THREAD LOCKING EXAMPLE
		4080
		4081	Here is a fictitious example of how to run an event loop in a different
		4082	thread than where callbacks are being invoked and watchers are
		4083	created/added/removed.
		4084
		4085	For a real-world example, see the C<EV::Loop::Async> perl module,
		4086	which uses exactly this technique (which is suited for many high-level
		4087	languages).
		4088
		4089	The example uses a pthread mutex to protect the loop data, a condition
		4090	variable to wait for callback invocations, an async watcher to notify the
		4091	event loop thread and an unspecified mechanism to wake up the main thread.
		4092
		4093	First, you need to associate some data with the event loop:
		4094
		4095	typedef struct {
		4096	mutex_t lock; /* global loop lock */
		4097	ev_async async_w;
		4098	thread_t tid;
		4099	cond_t invoke_cv;
		4100	} userdata;
		4101
		4102	void prepare_loop (EV_P)
		4103	{
		4104	// for simplicity, we use a static userdata struct.
		4105	static userdata u;
		4106
		4107	ev_async_init (&u->async_w, async_cb);
		4108	ev_async_start (EV_A_ &u->async_w);
		4109
		4110	pthread_mutex_init (&u->lock, 0);
		4111	pthread_cond_init (&u->invoke_cv, 0);
		4112
		4113	// now associate this with the loop
		4114	ev_set_userdata (EV_A_ u);
		4115	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4116	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4117
		4118	// then create the thread running ev_loop
		4119	pthread_create (&u->tid, 0, l_run, EV_A);
		4120	}
		4121
		4122	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4123	solely to wake up the event loop so it takes notice of any new watchers
		4124	that might have been added:
		4125
		4126	static void
		4127	async_cb (EV_P_ ev_async *w, int revents)
		4128	{
		4129	// just used for the side effects
		4130	}
		4131
		4132	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4133	protecting the loop data, respectively.
		4134
		4135	static void
		4136	l_release (EV_P)
		4137	{
		4138	userdata *u = ev_userdata (EV_A);
		4139	pthread_mutex_unlock (&u->lock);
		4140	}
		4141
		4142	static void
		4143	l_acquire (EV_P)
		4144	{
		4145	userdata *u = ev_userdata (EV_A);
		4146	pthread_mutex_lock (&u->lock);
		4147	}
		4148
		4149	The event loop thread first acquires the mutex, and then jumps straight
		4150	into C<ev_loop>:
		4151
		4152	void *
		4153	l_run (void *thr_arg)
		4154	{
		4155	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4156
		4157	l_acquire (EV_A);
		4158	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4159	ev_loop (EV_A_ 0);
		4160	l_release (EV_A);
		4161
		4162	return 0;
		4163	}
		4164
		4165	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4166	signal the main thread via some unspecified mechanism (signals? pipe
		4167	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4168	have been called (in a while loop because a) spurious wakeups are possible
		4169	and b) skipping inter-thread-communication when there are no pending
		4170	watchers is very beneficial):
		4171
		4172	static void
		4173	l_invoke (EV_P)
		4174	{
		4175	userdata *u = ev_userdata (EV_A);
		4176
		4177	while (ev_pending_count (EV_A))
		4178	{
		4179	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4180	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4181	}
		4182	}
		4183
		4184	Now, whenever the main thread gets told to invoke pending watchers, it
		4185	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4186	thread to continue:
		4187
		4188	static void
		4189	real_invoke_pending (EV_P)
		4190	{
		4191	userdata *u = ev_userdata (EV_A);
		4192
		4193	pthread_mutex_lock (&u->lock);
		4194	ev_invoke_pending (EV_A);
		4195	pthread_cond_signal (&u->invoke_cv);
		4196	pthread_mutex_unlock (&u->lock);
		4197	}
		4198
		4199	Whenever you want to start/stop a watcher or do other modifications to an
		4200	event loop, you will now have to lock:
		4201
		4202	ev_timer timeout_watcher;
		4203	userdata *u = ev_userdata (EV_A);
		4204
		4205	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4206
		4207	pthread_mutex_lock (&u->lock);
		4208	ev_timer_start (EV_A_ &timeout_watcher);
		4209	ev_async_send (EV_A_ &u->async_w);
		4210	pthread_mutex_unlock (&u->lock);
		4211
		4212	Note that sending the C<ev_async> watcher is required because otherwise
		4213	an event loop currently blocking in the kernel will have no knowledge
		4214	about the newly added timer. By waking up the loop it will pick up any new
		4215	watchers in the next event loop iteration.
		4216
		4217	=head3 COROUTINES
		4218
		4219	Libev is very accommodating to coroutines ("cooperative threads"):
		4220	libev fully supports nesting calls to its functions from different
		4221	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4222	different coroutines, and switch freely between both coroutines running
		4223	the loop, as long as you don't confuse yourself). The only exception is
		4224	that you must not do this from C<ev_periodic> reschedule callbacks.
		4225
		4226	Care has been taken to ensure that libev does not keep local state inside
		4227	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4228	they do not call any callbacks.
		4229
		4230	=head2 COMPILER WARNINGS
		4231
		4232	Depending on your compiler and compiler settings, you might get no or a
		4233	lot of warnings when compiling libev code. Some people are apparently
		4234	scared by this.
		4235
		4236	However, these are unavoidable for many reasons. For one, each compiler
		4237	has different warnings, and each user has different tastes regarding
		4238	warning options. "Warn-free" code therefore cannot be a goal except when
		4239	targeting a specific compiler and compiler-version.
		4240
		4241	Another reason is that some compiler warnings require elaborate
		4242	workarounds, or other changes to the code that make it less clear and less
		4243	maintainable.
		4244
		4245	And of course, some compiler warnings are just plain stupid, or simply
		4246	wrong (because they don't actually warn about the condition their message
		4247	seems to warn about). For example, certain older gcc versions had some
		4248	warnings that resulted an extreme number of false positives. These have
		4249	been fixed, but some people still insist on making code warn-free with
		4250	such buggy versions.
		4251
		4252	While libev is written to generate as few warnings as possible,
		4253	"warn-free" code is not a goal, and it is recommended not to build libev
		4254	with any compiler warnings enabled unless you are prepared to cope with
		4255	them (e.g. by ignoring them). Remember that warnings are just that:
		4256	warnings, not errors, or proof of bugs.
		4257
		4258
		4259	=head2 VALGRIND
		4260
		4261	Valgrind has a special section here because it is a popular tool that is
		4262	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4263
		4264	If you think you found a bug (memory leak, uninitialised data access etc.)
		4265	in libev, then check twice: If valgrind reports something like:
		4266
		4267	==2274== definitely lost: 0 bytes in 0 blocks.
		4268	==2274== possibly lost: 0 bytes in 0 blocks.
		4269	==2274== still reachable: 256 bytes in 1 blocks.
		4270
		4271	Then there is no memory leak, just as memory accounted to global variables
		4272	is not a memleak - the memory is still being referenced, and didn't leak.
		4273
		4274	Similarly, under some circumstances, valgrind might report kernel bugs
		4275	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4276	although an acceptable workaround has been found here), or it might be
		4277	confused.
		4278
		4279	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4280	make it into some kind of religion.
		4281
		4282	If you are unsure about something, feel free to contact the mailing list
		4283	with the full valgrind report and an explanation on why you think this
		4284	is a bug in libev (best check the archives, too :). However, don't be
		4285	annoyed when you get a brisk "this is no bug" answer and take the chance
		4286	of learning how to interpret valgrind properly.
		4287
		4288	If you need, for some reason, empty reports from valgrind for your project
		4289	I suggest using suppression lists.
		4290
		4291
		4292	=head1 PORTABILITY NOTES
		4293
		4294	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4295
		4296	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4297	requires, and its I/O model is fundamentally incompatible with the POSIX
		4298	model. Libev still offers limited functionality on this platform in
		4299	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4300	descriptors. This only applies when using Win32 natively, not when using
		4301	e.g. cygwin.
		4302
		4303	Lifting these limitations would basically require the full
		4304	re-implementation of the I/O system. If you are into these kinds of
		4305	things, then note that glib does exactly that for you in a very portable
		4306	way (note also that glib is the slowest event library known to man).
		4307
		4308	There is no supported compilation method available on windows except
		4309	embedding it into other applications.
		4310
		4311	Sensible signal handling is officially unsupported by Microsoft - libev
		4312	tries its best, but under most conditions, signals will simply not work.
		4313
		4314	Not a libev limitation but worth mentioning: windows apparently doesn't
		4315	accept large writes: instead of resulting in a partial write, windows will
		4316	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4317	so make sure you only write small amounts into your sockets (less than a
		4318	megabyte seems safe, but this apparently depends on the amount of memory
		4319	available).
		4320
		4321	Due to the many, low, and arbitrary limits on the win32 platform and
		4322	the abysmal performance of winsockets, using a large number of sockets
		4323	is not recommended (and not reasonable). If your program needs to use
		4324	more than a hundred or so sockets, then likely it needs to use a totally
		4325	different implementation for windows, as libev offers the POSIX readiness
		4326	notification model, which cannot be implemented efficiently on windows
		4327	(due to Microsoft monopoly games).
		4328
		4329	A typical way to use libev under windows is to embed it (see the embedding
		4330	section for details) and use the following F<evwrap.h> header file instead
		4331	of F<ev.h>:
		4332
		4333	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4334	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4335
		4336	#include "ev.h"
		4337
		4338	And compile the following F<evwrap.c> file into your project (make sure
		4339	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4340
		4341	#include "evwrap.h"
		4342	#include "ev.c"
		4343
		4344	=over 4
		4345
		4346	=item The winsocket select function
		4347
		4348	The winsocket C<select> function doesn't follow POSIX in that it
		4349	requires socket I<handles> and not socket I<file descriptors> (it is
		4350	also extremely buggy). This makes select very inefficient, and also
		4351	requires a mapping from file descriptors to socket handles (the Microsoft
		4352	C runtime provides the function C<_open_osfhandle> for this). See the
		4353	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4354	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4355
		4356	The configuration for a "naked" win32 using the Microsoft runtime
		4357	libraries and raw winsocket select is:
		4358
		4359	#define EV_USE_SELECT 1
		4360	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4361
		4362	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4363	complexity in the O(n²) range when using win32.
		4364
		4365	=item Limited number of file descriptors
		4366
		4367	Windows has numerous arbitrary (and low) limits on things.
		4368
		4369	Early versions of winsocket's select only supported waiting for a maximum
		4370	of C<64> handles (probably owning to the fact that all windows kernels
		4371	can only wait for C<64> things at the same time internally; Microsoft
		4372	recommends spawning a chain of threads and wait for 63 handles and the
		4373	previous thread in each. Sounds great!).
		4374
		4375	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4376	to some high number (e.g. C<2048>) before compiling the winsocket select
		4377	call (which might be in libev or elsewhere, for example, perl and many
		4378	other interpreters do their own select emulation on windows).
		4379
		4380	Another limit is the number of file descriptors in the Microsoft runtime
		4381	libraries, which by default is C<64> (there must be a hidden I<64>
		4382	fetish or something like this inside Microsoft). You can increase this
		4383	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4384	(another arbitrary limit), but is broken in many versions of the Microsoft
		4385	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4386	(depending on windows version and/or the phase of the moon). To get more,
		4387	you need to wrap all I/O functions and provide your own fd management, but
		4388	the cost of calling select (O(n²)) will likely make this unworkable.
		4389
		4390	=back
		4391
		4392	=head2 PORTABILITY REQUIREMENTS
		4393
		4394	In addition to a working ISO-C implementation and of course the
		4395	backend-specific APIs, libev relies on a few additional extensions:
		4396
		4397	=over 4
		4398
		4399	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4400	calling conventions regardless of C<ev_watcher_type *>.
		4401
		4402	Libev assumes not only that all watcher pointers have the same internal
		4403	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4404	assumes that the same (machine) code can be used to call any watcher
		4405	callback: The watcher callbacks have different type signatures, but libev
		4406	calls them using an C<ev_watcher *> internally.
		4407
		4408	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4409
		4410	The type C<sig_atomic_t volatile> (or whatever is defined as
		4411	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4412	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4413	believed to be sufficiently portable.
		4414
		4415	=item C<sigprocmask> must work in a threaded environment
		4416
		4417	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4418	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4419	pthread implementations will either allow C<sigprocmask> in the "main
		4420	thread" or will block signals process-wide, both behaviours would
		4421	be compatible with libev. Interaction between C<sigprocmask> and
		4422	C<pthread_sigmask> could complicate things, however.
		4423
		4424	The most portable way to handle signals is to block signals in all threads
		4425	except the initial one, and run the default loop in the initial thread as
		4426	well.
		4427
		4428	=item C<long> must be large enough for common memory allocation sizes
		4429
		4430	To improve portability and simplify its API, libev uses C<long> internally
		4431	instead of C<size_t> when allocating its data structures. On non-POSIX
		4432	systems (Microsoft...) this might be unexpectedly low, but is still at
		4433	least 31 bits everywhere, which is enough for hundreds of millions of
		4434	watchers.
		4435
		4436	=item C<double> must hold a time value in seconds with enough accuracy
		4437
		4438	The type C<double> is used to represent timestamps. It is required to
		4439	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4440	enough for at least into the year 4000. This requirement is fulfilled by
		4441	implementations implementing IEEE 754, which is basically all existing
		4442	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4443	2200.
		4444
		4445	=back
		4446
		4447	If you know of other additional requirements drop me a note.
		4448
		4449
2157	=head1 COMPLEXITIES	4450	=head1 ALGORITHMIC COMPLEXITIES
2158		4451
2159	In this section the complexities of (many of) the algorithms used inside	4452	In this section the complexities of (many of) the algorithms used inside
2160	libev will be explained. For complexity discussions about backends see the	4453	libev will be documented. For complexity discussions about backends see
2161	documentation for C<ev_default_init>.	4454	the documentation for C<ev_default_init>.
		4455
		4456	All of the following are about amortised time: If an array needs to be
		4457	extended, libev needs to realloc and move the whole array, but this
		4458	happens asymptotically rarer with higher number of elements, so O(1) might
		4459	mean that libev does a lengthy realloc operation in rare cases, but on
		4460	average it is much faster and asymptotically approaches constant time.
2162		4461
2163	=over 4	4462	=over 4
2164		4463
2165	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4464	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2166		4465
		4466	This means that, when you have a watcher that triggers in one hour and
		4467	there are 100 watchers that would trigger before that, then inserting will
		4468	have to skip roughly seven (C<ld 100>) of these watchers.
		4469
2167	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4470	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2168		4471
		4472	That means that changing a timer costs less than removing/adding them,
		4473	as only the relative motion in the event queue has to be paid for.
		4474
2169	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4475	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2170		4476
		4477	These just add the watcher into an array or at the head of a list.
		4478
2171	=item Stopping check/prepare/idle watchers: O(1)	4479	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2172		4480
2173	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4481	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2174		4482
		4483	These watchers are stored in lists, so they need to be walked to find the
		4484	correct watcher to remove. The lists are usually short (you don't usually
		4485	have many watchers waiting for the same fd or signal: one is typical, two
		4486	is rare).
		4487
2175	=item Finding the next timer per loop iteration: O(1)	4488	=item Finding the next timer in each loop iteration: O(1)
		4489
		4490	By virtue of using a binary or 4-heap, the next timer is always found at a
		4491	fixed position in the storage array.
2176		4492
2177	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4493	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2178		4494
2179	=item Activating one watcher: O(1)	4495	A change means an I/O watcher gets started or stopped, which requires
		4496	libev to recalculate its status (and possibly tell the kernel, depending
		4497	on backend and whether C<ev_io_set> was used).
		4498
		4499	=item Activating one watcher (putting it into the pending state): O(1)
		4500
		4501	=item Priority handling: O(number_of_priorities)
		4502
		4503	Priorities are implemented by allocating some space for each
		4504	priority. When doing priority-based operations, libev usually has to
		4505	linearly search all the priorities, but starting/stopping and activating
		4506	watchers becomes O(1) with respect to priority handling.
		4507
		4508	=item Sending an ev_async: O(1)
		4509
		4510	=item Processing ev_async_send: O(number_of_async_watchers)
		4511
		4512	=item Processing signals: O(max_signal_number)
		4513
		4514	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4515	calls in the current loop iteration. Checking for async and signal events
		4516	involves iterating over all running async watchers or all signal numbers.
2180		4517
2181	=back	4518	=back
2182		4519
2183		4520
		4521	=head1 GLOSSARY
		4522
		4523	=over 4
		4524
		4525	=item active
		4526
		4527	A watcher is active as long as it has been started (has been attached to
		4528	an event loop) but not yet stopped (disassociated from the event loop).
		4529
		4530	=item application
		4531
		4532	In this document, an application is whatever is using libev.
		4533
		4534	=item callback
		4535
		4536	The address of a function that is called when some event has been
		4537	detected. Callbacks are being passed the event loop, the watcher that
		4538	received the event, and the actual event bitset.
		4539
		4540	=item callback invocation
		4541
		4542	The act of calling the callback associated with a watcher.
		4543
		4544	=item event
		4545
		4546	A change of state of some external event, such as data now being available
		4547	for reading on a file descriptor, time having passed or simply not having
		4548	any other events happening anymore.
		4549
		4550	In libev, events are represented as single bits (such as C<EV_READ> or
		4551	C<EV_TIMEOUT>).
		4552
		4553	=item event library
		4554
		4555	A software package implementing an event model and loop.
		4556
		4557	=item event loop
		4558
		4559	An entity that handles and processes external events and converts them
		4560	into callback invocations.
		4561
		4562	=item event model
		4563
		4564	The model used to describe how an event loop handles and processes
		4565	watchers and events.
		4566
		4567	=item pending
		4568
		4569	A watcher is pending as soon as the corresponding event has been detected,
		4570	and stops being pending as soon as the watcher will be invoked or its
		4571	pending status is explicitly cleared by the application.
		4572
		4573	A watcher can be pending, but not active. Stopping a watcher also clears
		4574	its pending status.
		4575
		4576	=item real time
		4577
		4578	The physical time that is observed. It is apparently strictly monotonic :)
		4579
		4580	=item wall-clock time
		4581
		4582	The time and date as shown on clocks. Unlike real time, it can actually
		4583	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4584	clock.
		4585
		4586	=item watcher
		4587
		4588	A data structure that describes interest in certain events. Watchers need
		4589	to be started (attached to an event loop) before they can receive events.
		4590
		4591	=item watcher invocation
		4592
		4593	The act of calling the callback associated with a watcher.
		4594
		4595	=back
		4596
2184	=head1 AUTHOR	4597	=head1 AUTHOR
2185		4598
2186	Marc Lehmann <libev@schmorp.de>.	4599	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2187		4600

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