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Revision 1.71 by root, Fri Dec 7 20:13:09 2007 UTC vs.
Revision 1.263 by root, Mon Jul 27 01:10:17 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
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
82		111
83	It also is quite fast (see this	112	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	114	for example).
86		115
87	=head1 CONVENTIONS	116	=head2 CONVENTIONS
88		117
89	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	122	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<ev_loop *>) will not have
		124	this argument.
95		125
96	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
97		127
98	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as such.	133	on it, you should treat it as some floating point value. Unlike the name
		134	component C<stamp> might indicate, it is also used for time differences
		135	throughout libev.
		136
		137	=head1 ERROR HANDLING
		138
		139	Libev knows three classes of errors: operating system errors, usage errors
		140	and internal errors (bugs).
		141
		142	When libev catches an operating system error it cannot handle (for example
		143	a system call indicating a condition libev cannot fix), it calls the callback
		144	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		145	abort. The default is to print a diagnostic message and to call C<abort
		146	()>.
		147
		148	When libev detects a usage error such as a negative timer interval, then
		149	it will print a diagnostic message and abort (via the C<assert> mechanism,
		150	so C<NDEBUG> will disable this checking): these are programming errors in
		151	the libev caller and need to be fixed there.
		152
		153	Libev also has a few internal error-checking C<assert>ions, and also has
		154	extensive consistency checking code. These do not trigger under normal
		155	circumstances, as they indicate either a bug in libev or worse.
		156
104		157
105	=head1 GLOBAL FUNCTIONS	158	=head1 GLOBAL FUNCTIONS
106		159
107	These functions can be called anytime, even before initialising the	160	These functions can be called anytime, even before initialising the
108	library in any way.	161	library in any way.
…		…
113		166
114	Returns the current time as libev would use it. Please note that the	167	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	168	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	169	you actually want to know.
117		170
		171	=item ev_sleep (ev_tstamp interval)
		172
		173	Sleep for the given interval: The current thread will be blocked until
		174	either it is interrupted or the given time interval has passed. Basically
		175	this is a sub-second-resolution C<sleep ()>.
		176
118	=item int ev_version_major ()	177	=item int ev_version_major ()
119		178
120	=item int ev_version_minor ()	179	=item int ev_version_minor ()
121		180
122	You can find out the major and minor version numbers of the library	181	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	182	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	183	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	184	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	185	version of the library your program was compiled against.
127		186
		187	These version numbers refer to the ABI version of the library, not the
		188	release version.
		189
128	Usually, it's a good idea to terminate if the major versions mismatch,	190	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	191	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	192	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	193	not a problem.
132		194
133	Example: Make sure we haven't accidentally been linked against the wrong	195	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	196	version.
135		197
136	assert (("libev version mismatch",	198	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
139		201
140	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
141		203
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	204	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	207	a description of the set values.
146		208
147	Example: make sure we have the epoll method, because yeah this is cool and	209	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	210	a must have and can we have a torrent of it please!!!11
149		211
150	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
152		214
153	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
154		216
155	Return the set of all backends compiled into this binary of libev and also	217	Return the set of all backends compiled into this binary of libev and also
156	recommended for this platform. This set is often smaller than the one	218	recommended for this platform. This set is often smaller than the one
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	219	returned by C<ev_supported_backends>, as for example kqueue is broken on
158	most BSDs and will not be autodetected unless you explicitly request it	220	most BSDs and will not be auto-detected unless you explicitly request it
159	(assuming you know what you are doing). This is the set of backends that	221	(assuming you know what you are doing). This is the set of backends that
160	libev will probe for if you specify no backends explicitly.	222	libev will probe for if you specify no backends explicitly.
161		223
162	=item unsigned int ev_embeddable_backends ()	224	=item unsigned int ev_embeddable_backends ()
163		225
…		…
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
168	recommended ones.	230	recommended ones.
169		231
170	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
171		233
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		235
174	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	238	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	239	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	240	or take some potentially destructive action.
179	function.	241
		242	Since some systems (at least OpenBSD and Darwin) fail to implement
		243	correct C<realloc> semantics, libev will use a wrapper around the system
		244	C<realloc> and C<free> functions by default.
180		245
181	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	247	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	248	or even to sleep a while and retry until some memory is available.
184		249
185	Example: Replace the libev allocator with one that waits a bit and then	250	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	251	retries (example requires a standards-compliant C<realloc>).
187		252
188	static void *	253	static void *
189	persistent_realloc (void *ptr, size_t size)	254	persistent_realloc (void *ptr, size_t size)
190	{	255	{
191	for (;;)	256	for (;;)
…		…
200	}	265	}
201		266
202	...	267	...
203	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
204		269
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		271
207	Set the callback function to call on a retryable syscall error (such	272	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	273	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	275	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	276	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	277	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	278	(such as abort).
214		279
215	Example: This is basically the same thing that libev does internally, too.	280	Example: This is basically the same thing that libev does internally, too.
…		…
226		291
227	=back	292	=back
228		293
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		295
231	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
232	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
233	events, and dynamically created loops which do not.	298	I<function>).
234		299
235	If you use threads, a common model is to run the default event loop	300	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	301	supports signals and child events, and dynamically created loops which do
237	create, you also create another event loop. Libev itself does no locking	302	not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		303
242	=over 4	304	=over 4
243		305
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		307
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		312
251	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
252	function.	314	function.
253		315
		316	Note that this function is I<not> thread-safe, so if you want to use it
		317	from multiple threads, you have to lock (note also that this is unlikely,
		318	as loops cannot be shared easily between threads anyway).
		319
		320	The default loop is the only loop that can handle C<ev_signal> and
		321	C<ev_child> watchers, and to do this, it always registers a handler
		322	for C<SIGCHLD>. If this is a problem for your application you can either
		323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		324	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		325	C<ev_default_init>.
		326
254	The flags argument can be used to specify special behaviour or specific	327	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	328	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		329
257	The following flags are supported:	330	The following flags are supported:
258		331
…		…
263	The default flags value. Use this if you have no clue (it's the right	336	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	337	thing, believe me).
265		338
266	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
267		340
268	If this flag bit is ored into the flag value (or the program runs setuid	341	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	342	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	344	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	345	useful to try out specific backends to test their performance, or to work
273	around bugs.	346	around bugs.
…		…
279	enabling this flag.	352	enabling this flag.
280		353
281	This works by calling C<getpid ()> on every iteration of the loop,	354	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	355	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	356	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	358	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
287		360
288	The big advantage of this flag is that you can forget about fork (and	361	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	362	forget about forgetting to tell libev about forking) when you use this
290	flag.	363	flag.
291		364
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
294		382
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		384
297	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	388	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	389	usually the fastest backend for a low number of (low-numbered :) fds.
		390
		391	To get good performance out of this backend you need a high amount of
		392	parallelism (most of the file descriptors should be busy). If you are
		393	writing a server, you should C<accept ()> in a loop to accept as many
		394	connections as possible during one iteration. You might also want to have
		395	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		396	readiness notifications you get per iteration.
		397
		398	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		399	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		400	C<exceptfds> set on that platform).
302		401
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	402	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		403
305	And this is your standard poll(2) backend. It's more complicated than	404	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	405	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	406	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	407	considerably with a lot of inactive fds). It scales similarly to select,
		408	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		409	performance tips.
		410
		411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		413
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		415
312	For few fds, this backend is a bit little slower than poll and select,	416	For few fds, this backend is a bit little slower than poll and select,
313	but it scales phenomenally better. While poll and select usually scale like	417	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	418	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	419	epoll scales either O(1) or O(active_fds).
316		420
		421	The epoll mechanism deserves honorable mention as the most misdesigned
		422	of the more advanced event mechanisms: mere annoyances include silently
		423	dropping file descriptors, requiring a system call per change per file
		424	descriptor (and unnecessary guessing of parameters), problems with dup and
		425	so on. The biggest issue is fork races, however - if a program forks then
		426	I<both> parent and child process have to recreate the epoll set, which can
		427	take considerable time (one syscall per file descriptor) and is of course
		428	hard to detect.
		429
		430	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		431	of course I<doesn't>, and epoll just loves to report events for totally
		432	I<different> file descriptors (even already closed ones, so one cannot
		433	even remove them from the set) than registered in the set (especially
		434	on SMP systems). Libev tries to counter these spurious notifications by
		435	employing an additional generation counter and comparing that against the
		436	events to filter out spurious ones, recreating the set when required.
		437
317	While stopping and starting an I/O watcher in the same iteration will	438	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	439	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	440	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	441	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	442	file descriptors might not work very well if you register events for both
		443	file descriptors.
322		444
323	Please note that epoll sometimes generates spurious notifications, so you	445	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	446	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	447	i.e. keep at least one watcher active per fd at all times. Stopping and
		448	starting a watcher (without re-setting it) also usually doesn't cause
		449	extra overhead. A fork can both result in spurious notifications as well
		450	as in libev having to destroy and recreate the epoll object, which can
		451	take considerable time and thus should be avoided.
		452
		453	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		454	faster than epoll for maybe up to a hundred file descriptors, depending on
		455	the usage. So sad.
		456
		457	While nominally embeddable in other event loops, this feature is broken in
		458	all kernel versions tested so far.
		459
		460	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		461	C<EVBACKEND_POLL>.
326		462
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		464
329	Kqueue deserves special mention, as at the time of this writing, it	465	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	466	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	467	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	468	it's completely useless). Unlike epoll, however, whose brokenness
		469	is by design, these kqueue bugs can (and eventually will) be fixed
		470	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	471	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	472	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		473	system like NetBSD.
		474
		475	You still can embed kqueue into a normal poll or select backend and use it
		476	only for sockets (after having made sure that sockets work with kqueue on
		477	the target platform). See C<ev_embed> watchers for more info.
335		478
336	It scales in the same way as the epoll backend, but the interface to the	479	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	480	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	481	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	482	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	483	two event changes per incident. Support for C<fork ()> is very bad (but
		484	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		485	cases
		486
		487	This backend usually performs well under most conditions.
		488
		489	While nominally embeddable in other event loops, this doesn't work
		490	everywhere, so you might need to test for this. And since it is broken
		491	almost everywhere, you should only use it when you have a lot of sockets
		492	(for which it usually works), by embedding it into another event loop
		493	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		494	also broken on OS X)) and, did I mention it, using it only for sockets.
		495
		496	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		497	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		498	C<NOTE_EOF>.
341		499
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	500	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		501
344	This is not implemented yet (and might never be).	502	This is not implemented yet (and might never be, unless you send me an
		503	implementation). According to reports, C</dev/poll> only supports sockets
		504	and is not embeddable, which would limit the usefulness of this backend
		505	immensely.
345		506
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	507	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		508
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	509	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	510	it's really slow, but it still scales very well (O(active_fds)).
350		511
351	Please note that solaris ports can result in a lot of spurious	512	Please note that Solaris event ports can deliver a lot of spurious
352	notifications, so you need to use non-blocking I/O or other means to avoid	513	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	514	blocking when no data (or space) is available.
		515
		516	While this backend scales well, it requires one system call per active
		517	file descriptor per loop iteration. For small and medium numbers of file
		518	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		519	might perform better.
		520
		521	On the positive side, with the exception of the spurious readiness
		522	notifications, this backend actually performed fully to specification
		523	in all tests and is fully embeddable, which is a rare feat among the
		524	OS-specific backends (I vastly prefer correctness over speed hacks).
		525
		526	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		527	C<EVBACKEND_POLL>.
354		528
355	=item C<EVBACKEND_ALL>	529	=item C<EVBACKEND_ALL>
356		530
357	Try all backends (even potentially broken ones that wouldn't be tried	531	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	532	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	533	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		534
		535	It is definitely not recommended to use this flag.
		536
361	=back	537	=back
362		538
363	If one or more of these are ored into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	540	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	541	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	542	()> will be tried.
367		543
368	The most typical usage is like this:	544	Example: This is the most typical usage.
369		545
370	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		548
373	Restrict libev to the select and poll backends, and do not allow	549	Example: Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:	550	environment settings to be taken into account:
375		551
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	552	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		553
378	Use whatever libev has to offer, but make sure that kqueue is used if	554	Example: Use whatever libev has to offer, but make sure that kqueue is
379	available (warning, breaks stuff, best use only with your own private	555	used if available (warning, breaks stuff, best use only with your own
380	event loop and only if you know the OS supports your types of fds):	556	private event loop and only if you know the OS supports your types of
		557	fds):
381		558
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	559	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		560
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	561	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		562
386	Similar to C<ev_default_loop>, but always creates a new event loop that is	563	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot	564	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by	565	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).	566	undefined behaviour (or a failed assertion if assertions are enabled).
390		567
		568	Note that this function I<is> thread-safe, and the recommended way to use
		569	libev with threads is indeed to create one loop per thread, and using the
		570	default loop in the "main" or "initial" thread.
		571
391	Example: Try to create a event loop that uses epoll and nothing else.	572	Example: Try to create a event loop that uses epoll and nothing else.
392		573
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	574	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	575	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	576	fatal ("no epoll found here, maybe it hides under your chair");
396		577
397	=item ev_default_destroy ()	578	=item ev_default_destroy ()
398		579
399	Destroys the default loop again (frees all memory and kernel state	580	Destroys the default loop again (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	581	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	582	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	583	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	584	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	585	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	586	for example).
		587
		588	Note that certain global state, such as signal state (and installed signal
		589	handlers), will not be freed by this function, and related watchers (such
		590	as signal and child watchers) would need to be stopped manually.
		591
		592	In general it is not advisable to call this function except in the
		593	rare occasion where you really need to free e.g. the signal handling
		594	pipe fds. If you need dynamically allocated loops it is better to use
		595	C<ev_loop_new> and C<ev_loop_destroy>).
406		596
407	=item ev_loop_destroy (loop)	597	=item ev_loop_destroy (loop)
408		598
409	Like C<ev_default_destroy>, but destroys an event loop created by an	599	Like C<ev_default_destroy>, but destroys an event loop created by an
410	earlier call to C<ev_loop_new>.	600	earlier call to C<ev_loop_new>.
411		601
412	=item ev_default_fork ()	602	=item ev_default_fork ()
413		603
		604	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	605	to reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	606	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	607	the child process (or both child and parent, but that again makes little
417	again makes little sense).	608	sense). You I<must> call it in the child before using any of the libev
		609	functions, and it will only take effect at the next C<ev_loop> iteration.
418		610
419	You I<must> call this function in the child process after forking if and	611	On the other hand, you only need to call this function in the child
420	only if you want to use the event library in both processes. If you just	612	process if and only if you want to use the event library in the child. If
421	fork+exec, you don't have to call it.	613	you just fork+exec, you don't have to call it at all.
422		614
423	The function itself is quite fast and it's usually not a problem to call	615	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	616	it just in case after a fork. To make this easy, the function will fit in
425	quite nicely into a call to C<pthread_atfork>:	617	quite nicely into a call to C<pthread_atfork>:
426		618
427	pthread_atfork (0, 0, ev_default_fork);	619	pthread_atfork (0, 0, ev_default_fork);
428		620
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	621	=item ev_loop_fork (loop)
434		622
435	Like C<ev_default_fork>, but acts on an event loop created by	623	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	624	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.	625	after fork that you want to re-use in the child, and how you do this is
		626	entirely your own problem.
		627
		628	=item int ev_is_default_loop (loop)
		629
		630	Returns true when the given loop is, in fact, the default loop, and false
		631	otherwise.
438		632
439	=item unsigned int ev_loop_count (loop)	633	=item unsigned int ev_loop_count (loop)
440		634
441	Returns the count of loop iterations for the loop, which is identical to	635	Returns the count of loop iterations for the loop, which is identical to
442	the number of times libev did poll for new events. It starts at C<0> and	636	the number of times libev did poll for new events. It starts at C<0> and
443	happily wraps around with enough iterations.	637	happily wraps around with enough iterations.
444		638
445	This value can sometimes be useful as a generation counter of sorts (it	639	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	640	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
448		654
449	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
450		656
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	658	use.
…		…
455		661
456	Returns the current "event loop time", which is the time the event loop	662	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	663	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	664	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	665	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	666	event occurring (or more correctly, libev finding out about it).
		667
		668	=item ev_now_update (loop)
		669
		670	Establishes the current time by querying the kernel, updating the time
		671	returned by C<ev_now ()> in the progress. This is a costly operation and
		672	is usually done automatically within C<ev_loop ()>.
		673
		674	This function is rarely useful, but when some event callback runs for a
		675	very long time without entering the event loop, updating libev's idea of
		676	the current time is a good idea.
		677
		678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
461		705
462	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
463		707
464	Finally, this is it, the event handler. This function usually is called	708	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	709	after you initialised all your watchers and you want to start handling
…		…
468	If the flags argument is specified as C<0>, it will not return until	712	If the flags argument is specified as C<0>, it will not return until
469	either no event watchers are active anymore or C<ev_unloop> was called.	713	either no event watchers are active anymore or C<ev_unloop> was called.
470		714
471	Please note that an explicit C<ev_unloop> is usually better than	715	Please note that an explicit C<ev_unloop> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	716	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	717	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	718	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	719	of relying on its watchers stopping correctly, that is truly a thing of
		720	beauty.
476		721
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	722	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	723	those events and any already outstanding ones, but will not block your
479	case there are no events and will return after one iteration of the loop.	724	process in case there are no events and will return after one iteration of
		725	the loop.
480		726
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	727	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	728	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	729	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	730	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	731	user-registered callback will be called), and will return after one
		732	iteration of the loop.
		733
		734	This is useful if you are waiting for some external event in conjunction
		735	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	736	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	737	usually a better approach for this kind of thing.
488		738
489	Here are the gory details of what C<ev_loop> does:	739	Here are the gory details of what C<ev_loop> does:
490		740
491	* If there are no active watchers (reference count is zero), return.	741	- Before the first iteration, call any pending watchers.
492	- Queue prepare watchers and then call all outstanding watchers.	742	* If EVFLAG_FORKCHECK was used, check for a fork.
		743	- If a fork was detected (by any means), queue and call all fork watchers.
		744	- Queue and call all prepare watchers.
493	- If we have been forked, recreate the kernel state.	745	- If we have been forked, detach and recreate the kernel state
		746	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	747	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	748	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	749	- Calculate for how long to sleep or block, if at all
		750	(active idle watchers, EVLOOP_NONBLOCK or not having
		751	any active watchers at all will result in not sleeping).
		752	- Sleep if the I/O and timer collect interval say so.
497	- Block the process, waiting for any events.	753	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	754	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	755	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	756	- Queue all expired timers.
501	- Queue all outstanding periodics.	757	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	758	- Unless any events are pending now, queue all idle watchers.
503	- Queue all check watchers.	759	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	760	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	761	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	762	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	763	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
508	were used, return, otherwise continue with step *.	764	were used, or there are no active watchers, return, otherwise
		765	continue with step *.
509		766
510	Example: Queue some jobs and then loop until no events are outsanding	767	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	768	anymore.
512		769
513	... queue jobs here, make sure they register event watchers as long	770	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	771	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	772	ev_loop (my_loop, 0);
516	... jobs done. yeah!	773	... jobs done or somebody called unloop. yeah!
517		774
518	=item ev_unloop (loop, how)	775	=item ev_unloop (loop, how)
519		776
520	Can be used to make a call to C<ev_loop> return early (but only after it	777	Can be used to make a call to C<ev_loop> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	778	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	779	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	780	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
524		781
		782	This "unloop state" will be cleared when entering C<ev_loop> again.
		783
		784	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		785
525	=item ev_ref (loop)	786	=item ev_ref (loop)
526		787
527	=item ev_unref (loop)	788	=item ev_unref (loop)
528		789
529	Ref/unref can be used to add or remove a reference count on the event	790	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	791	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	792	count is nonzero, C<ev_loop> will not return on its own.
		793
532	a watcher you never unregister that should not keep C<ev_loop> from	794	If you have a watcher you never unregister that should not keep C<ev_loop>
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	795	from returning, call ev_unref() after starting, and ev_ref() before
		796	stopping it.
		797
534	example, libev itself uses this for its internal signal pipe: It is not	798	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	799	is not visible to the libev user and should not keep C<ev_loop> from
536	no event watchers registered by it are active. It is also an excellent	800	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	801	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	802	third-party libraries. Just remember to I<unref after start> and I<ref
		803	before stop> (but only if the watcher wasn't active before, or was active
		804	before, respectively. Note also that libev might stop watchers itself
		805	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		806	in the callback).
539		807
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	808	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
541	running when nothing else is active.	809	running when nothing else is active.
542		810
543	struct ev_signal exitsig;	811	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	812	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	813	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	814	evf_unref (loop);
547		815
548	Example: For some weird reason, unregister the above signal handler again.	816	Example: For some weird reason, unregister the above signal handler again.
549		817
550	ev_ref (loop);	818	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	819	ev_signal_stop (loop, &exitsig);
		820
		821	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		822
		823	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		824
		825	These advanced functions influence the time that libev will spend waiting
		826	for events. Both time intervals are by default C<0>, meaning that libev
		827	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		828	latency.
		829
		830	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		831	allows libev to delay invocation of I/O and timer/periodic callbacks
		832	to increase efficiency of loop iterations (or to increase power-saving
		833	opportunities).
		834
		835	The idea is that sometimes your program runs just fast enough to handle
		836	one (or very few) event(s) per loop iteration. While this makes the
		837	program responsive, it also wastes a lot of CPU time to poll for new
		838	events, especially with backends like C<select ()> which have a high
		839	overhead for the actual polling but can deliver many events at once.
		840
		841	By setting a higher I<io collect interval> you allow libev to spend more
		842	time collecting I/O events, so you can handle more events per iteration,
		843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		844	C<ev_timer>) will be not affected. Setting this to a non-null value will
		845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
		848
		849	Likewise, by setting a higher I<timeout collect interval> you allow libev
		850	to spend more time collecting timeouts, at the expense of increased
		851	latency/jitter/inexactness (the watcher callback will be called
		852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		853	value will not introduce any overhead in libev.
		854
		855	Many (busy) programs can usually benefit by setting the I/O collect
		856	interval to a value near C<0.1> or so, which is often enough for
		857	interactive servers (of course not for games), likewise for timeouts. It
		858	usually doesn't make much sense to set it to a lower value than C<0.01>,
		859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
		864
		865	Setting the I<timeout collect interval> can improve the opportunity for
		866	saving power, as the program will "bundle" timer callback invocations that
		867	are "near" in time together, by delaying some, thus reducing the number of
		868	times the process sleeps and wakes up again. Another useful technique to
		869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		870	they fire on, say, one-second boundaries only.
		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
		942
		943	=item ev_loop_verify (loop)
		944
		945	This function only does something when C<EV_VERIFY> support has been
		946	compiled in, which is the default for non-minimal builds. It tries to go
		947	through all internal structures and checks them for validity. If anything
		948	is found to be inconsistent, it will print an error message to standard
		949	error and call C<abort ()>.
		950
		951	This can be used to catch bugs inside libev itself: under normal
		952	circumstances, this function will never abort as of course libev keeps its
		953	data structures consistent.
552		954
553	=back	955	=back
554		956
555		957
556	=head1 ANATOMY OF A WATCHER	958	=head1 ANATOMY OF A WATCHER
		959
		960	In the following description, uppercase C<TYPE> in names stands for the
		961	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		962	watchers and C<ev_io_start> for I/O watchers.
557		963
558	A watcher is a structure that you create and register to record your	964	A watcher is a structure that you create and register to record your
559	interest in some event. For instance, if you want to wait for STDIN to	965	interest in some event. For instance, if you want to wait for STDIN to
560	become readable, you would create an C<ev_io> watcher for that:	966	become readable, you would create an C<ev_io> watcher for that:
561		967
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	968	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	969	{
564	ev_io_stop (w);	970	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	971	ev_unloop (loop, EVUNLOOP_ALL);
566	}	972	}
567		973
568	struct ev_loop *loop = ev_default_loop (0);	974	struct ev_loop *loop = ev_default_loop (0);
		975
569	struct ev_io stdin_watcher;	976	ev_io stdin_watcher;
		977
570	ev_init (&stdin_watcher, my_cb);	978	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	979	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	980	ev_io_start (loop, &stdin_watcher);
		981
573	ev_loop (loop, 0);	982	ev_loop (loop, 0);
574		983
575	As you can see, you are responsible for allocating the memory for your	984	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	985	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	986	stack).
		987
		988	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		989	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
578		990
579	Each watcher structure must be initialised by a call to C<ev_init	991	Each watcher structure must be initialised by a call to C<ev_init
580	(watcher *, callback)>, which expects a callback to be provided. This	992	(watcher *, callback)>, which expects a callback to be provided. This
581	callback gets invoked each time the event occurs (or, in the case of io	993	callback gets invoked each time the event occurs (or, in the case of I/O
582	watchers, each time the event loop detects that the file descriptor given	994	watchers, each time the event loop detects that the file descriptor given
583	is readable and/or writable).	995	is readable and/or writable).
584		996
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	997	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	998	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	999	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	1000	ev_TYPE_init (watcher *, callback, ...) >>.
589		1001
590	To make the watcher actually watch out for events, you have to start it	1002	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1003	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1004	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1005	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1006
595	As long as your watcher is active (has been started but not stopped) you	1007	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1008	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1009	reinitialise it or call its C<ev_TYPE_set> macro.
598		1010
599	Each and every callback receives the event loop pointer as first, the	1011	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1012	registered watcher structure as second, and a bitset of received events as
601	third argument.	1013	third argument.
602		1014
…		…
656	=item C<EV_FORK>	1068	=item C<EV_FORK>
657		1069
658	The event loop has been resumed in the child process after fork (see	1070	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1071	C<ev_fork>).
660		1072
		1073	=item C<EV_ASYNC>
		1074
		1075	The given async watcher has been asynchronously notified (see C<ev_async>).
		1076
		1077	=item C<EV_CUSTOM>
		1078
		1079	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1080	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1081
661	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
662		1083
663	An unspecified error has occured, the watcher has been stopped. This might	1084	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1085	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1086	ran out of memory, a file descriptor was found to be closed or any other
		1087	problem. Libev considers these application bugs.
		1088
666	problem. You best act on it by reporting the problem and somehow coping	1089	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1090	watcher being stopped. Note that well-written programs should not receive
		1091	an error ever, so when your watcher receives it, this usually indicates a
		1092	bug in your program.
668		1093
669	Libev will usually signal a few "dummy" events together with an error,	1094	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1095	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1096	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1097	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1098	programs, though, as the fd could already be closed and reused for another
		1099	thing, so beware.
674		1100
675	=back	1101	=back
676		1102
677	=head2 GENERIC WATCHER FUNCTIONS	1103	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1104
682	=over 4	1105	=over 4
683		1106
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1107	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1108
…		…
691	which rolls both calls into one.	1114	which rolls both calls into one.
692		1115
693	You can reinitialise a watcher at any time as long as it has been stopped	1116	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1117	(or never started) and there are no pending events outstanding.
695		1118
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1119	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1120	int revents)>.
		1121
		1122	Example: Initialise an C<ev_io> watcher in two steps.
		1123
		1124	ev_io w;
		1125	ev_init (&w, my_cb);
		1126	ev_io_set (&w, STDIN_FILENO, EV_READ);
698		1127
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1128	=item C<ev_TYPE_set> (ev_TYPE *, [args])
700		1129
701	This macro initialises the type-specific parts of a watcher. You need to	1130	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1131	call C<ev_init> at least once before you call this macro, but you can
…		…
705	difference to the C<ev_init> macro).	1134	difference to the C<ev_init> macro).
706		1135
707	Although some watcher types do not have type-specific arguments	1136	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1137	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1138
		1139	See C<ev_init>, above, for an example.
		1140
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1141	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1142
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1143	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1144	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1145	a watcher. The same limitations apply, of course.
		1146
		1147	Example: Initialise and set an C<ev_io> watcher in one step.
		1148
		1149	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
715		1150
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1151	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
717		1152
718	Starts (activates) the given watcher. Only active watchers will receive	1153	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1154	events. If the watcher is already active nothing will happen.
720		1155
		1156	Example: Start the C<ev_io> watcher that is being abused as example in this
		1157	whole section.
		1158
		1159	ev_io_start (EV_DEFAULT_UC, &w);
		1160
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1161	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
722		1162
723	Stops the given watcher again (if active) and clears the pending	1163	Stops the given watcher if active, and clears the pending status (whether
		1164	the watcher was active or not).
		1165
724	status. It is possible that stopped watchers are pending (for example,	1166	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1167	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1168	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1169	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1170	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1171
730	=item bool ev_is_active (ev_TYPE *watcher)	1172	=item bool ev_is_active (ev_TYPE *watcher)
731		1173
732	Returns a true value iff the watcher is active (i.e. it has been started	1174	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1175	and not yet been stopped). As long as a watcher is active you must not modify
…		…
736	=item bool ev_is_pending (ev_TYPE *watcher)	1178	=item bool ev_is_pending (ev_TYPE *watcher)
737		1179
738	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1180	Returns a true value iff the watcher is pending, (i.e. it has outstanding
739	events but its callback has not yet been invoked). As long as a watcher	1181	events but its callback has not yet been invoked). As long as a watcher
740	is pending (but not active) you must not call an init function on it (but	1182	is pending (but not active) you must not call an init function on it (but
741	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1183	C<ev_TYPE_set> is safe), you must not change its priority, and you must
742	libev (e.g. you cnanot C<free ()> it).	1184	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1185	it).
743		1186
744	=item callback ev_cb (ev_TYPE *watcher)	1187	=item callback ev_cb (ev_TYPE *watcher)
745		1188
746	Returns the callback currently set on the watcher.	1189	Returns the callback currently set on the watcher.
747		1190
…		…
758	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
759	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
760	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
761	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
762		1205
763	This means that priorities are I<only> used for ordering callback
764	invocation after new events have been received. This is useful, for
765	example, to reduce latency after idling, or more often, to bind two
766	watchers on the same event and make sure one is called first.
767
768	If you need to suppress invocation when higher priority events are pending	1206	If you need to suppress invocation when higher priority events are pending
769	you need to look at C<ev_idle> watchers, which provide this functionality.	1207	you need to look at C<ev_idle> watchers, which provide this functionality.
770		1208
		1209	You I<must not> change the priority of a watcher as long as it is active or
		1210	pending.
		1211
		1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1213	fine, as long as you do not mind that the priority value you query might
		1214	or might not have been clamped to the valid range.
		1215
771	The default priority used by watchers when no priority has been set is	1216	The default priority used by watchers when no priority has been set is
772	always C<0>, which is supposed to not be too high and not be too low :).	1217	always C<0>, which is supposed to not be too high and not be too low :).
773		1218
774	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
775	fine, as long as you do not mind that the priority value you query might	1220	priorities.
776	or might not have been adjusted to be within valid range.	1221
		1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1223
		1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1226	can deal with that fact, as both are simply passed through to the
		1227	callback.
		1228
		1229	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1230
		1231	If the watcher is pending, this function clears its pending status and
		1232	returns its C<revents> bitset (as if its callback was invoked). If the
		1233	watcher isn't pending it does nothing and returns C<0>.
		1234
		1235	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1236	callback to be invoked, which can be accomplished with this function.
777		1237
778	=back	1238	=back
779		1239
780		1240
781	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1241	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
782		1242
783	Each watcher has, by default, a member C<void *data> that you can change	1243	Each watcher has, by default, a member C<void *data> that you can change
784	and read at any time, libev will completely ignore it. This can be used	1244	and read at any time: libev will completely ignore it. This can be used
785	to associate arbitrary data with your watcher. If you need more data and	1245	to associate arbitrary data with your watcher. If you need more data and
786	don't want to allocate memory and store a pointer to it in that data	1246	don't want to allocate memory and store a pointer to it in that data
787	member, you can also "subclass" the watcher type and provide your own	1247	member, you can also "subclass" the watcher type and provide your own
788	data:	1248	data:
789		1249
790	struct my_io	1250	struct my_io
791	{	1251	{
792	struct ev_io io;	1252	ev_io io;
793	int otherfd;	1253	int otherfd;
794	void *somedata;	1254	void *somedata;
795	struct whatever *mostinteresting;	1255	struct whatever *mostinteresting;
796	}	1256	};
		1257
		1258	...
		1259	struct my_io w;
		1260	ev_io_init (&w.io, my_cb, fd, EV_READ);
797		1261
798	And since your callback will be called with a pointer to the watcher, you	1262	And since your callback will be called with a pointer to the watcher, you
799	can cast it back to your own type:	1263	can cast it back to your own type:
800		1264
801	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1265	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
802	{	1266	{
803	struct my_io *w = (struct my_io *)w_;	1267	struct my_io *w = (struct my_io *)w_;
804	...	1268	...
805	}	1269	}
806		1270
807	More interesting and less C-conformant ways of casting your callback type	1271	More interesting and less C-conformant ways of casting your callback type
808	instead have been omitted.	1272	instead have been omitted.
809		1273
810	Another common scenario is having some data structure with multiple	1274	Another common scenario is to use some data structure with multiple
811	watchers:	1275	embedded watchers:
812		1276
813	struct my_biggy	1277	struct my_biggy
814	{	1278	{
815	int some_data;	1279	int some_data;
816	ev_timer t1;	1280	ev_timer t1;
817	ev_timer t2;	1281	ev_timer t2;
818	}	1282	}
819		1283
820	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1284	In this case getting the pointer to C<my_biggy> is a bit more
821	you need to use C<offsetof>:	1285	complicated: Either you store the address of your C<my_biggy> struct
		1286	in the C<data> member of the watcher (for woozies), or you need to use
		1287	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1288	programmers):
822		1289
823	#include <stddef.h>	1290	#include <stddef.h>
824		1291
825	static void	1292	static void
826	t1_cb (EV_P_ struct ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
827	{	1294	{
828	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
829	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
830	}	1297	}
831		1298
832	static void	1299	static void
833	t2_cb (EV_P_ struct ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
834	{	1301	{
835	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
836	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
837	}	1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
838		1408
839		1409
840	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
841		1411
842	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
866	In general you can register as many read and/or write event watchers per	1436	In general you can register as many read and/or write event watchers per
867	fd as you want (as long as you don't confuse yourself). Setting all file	1437	fd as you want (as long as you don't confuse yourself). Setting all file
868	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
869	required if you know what you are doing).	1439	required if you know what you are doing).
870		1440
871	You have to be careful with dup'ed file descriptors, though. Some backends	1441	If you cannot use non-blocking mode, then force the use of a
872	(the linux epoll backend is a notable example) cannot handle dup'ed file	1442	known-to-be-good backend (at the time of this writing, this includes only
873	descriptors correctly if you register interest in two or more fds pointing	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
874	to the same underlying file/socket/etc. description (that is, they share	1444	descriptors for which non-blocking operation makes no sense (such as
875	the same underlying "file open").	1445	files) - libev doesn't guarentee any specific behaviour in that case.
876
877	If you must do this, then force the use of a known-to-be-good backend
878	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
879	C<EVBACKEND_POLL>).
880		1446
881	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
882	receive "spurious" readyness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
883	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
884	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
885	lot of those (for example solaris ports), it is very easy to get into	1451	lot of those (for example Solaris ports), it is very easy to get into
886	this situation even with a relatively standard program structure. Thus	1452	this situation even with a relatively standard program structure. Thus
887	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1453	it is best to always use non-blocking I/O: An extra C<read>(2) returning
888	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1454	C<EAGAIN> is far preferable to a program hanging until some data arrives.
889		1455
890	If you cannot run the fd in non-blocking mode (for example you should not	1456	If you cannot run the fd in non-blocking mode (for example you should
891	play around with an Xlib connection), then you have to seperately re-test	1457	not play around with an Xlib connection), then you have to separately
892	whether a file descriptor is really ready with a known-to-be good interface	1458	re-test whether a file descriptor is really ready with a known-to-be good
893	such as poll (fortunately in our Xlib example, Xlib already does this on	1459	interface such as poll (fortunately in our Xlib example, Xlib already
894	its own, so its quite safe to use).	1460	does this on its own, so its quite safe to use). Some people additionally
		1461	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1462	indefinitely.
		1463
		1464	But really, best use non-blocking mode.
		1465
		1466	=head3 The special problem of disappearing file descriptors
		1467
		1468	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1469	descriptor (either due to calling C<close> explicitly or any other means,
		1470	such as C<dup2>). The reason is that you register interest in some file
		1471	descriptor, but when it goes away, the operating system will silently drop
		1472	this interest. If another file descriptor with the same number then is
		1473	registered with libev, there is no efficient way to see that this is, in
		1474	fact, a different file descriptor.
		1475
		1476	To avoid having to explicitly tell libev about such cases, libev follows
		1477	the following policy: Each time C<ev_io_set> is being called, libev
		1478	will assume that this is potentially a new file descriptor, otherwise
		1479	it is assumed that the file descriptor stays the same. That means that
		1480	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1481	descriptor even if the file descriptor number itself did not change.
		1482
		1483	This is how one would do it normally anyway, the important point is that
		1484	the libev application should not optimise around libev but should leave
		1485	optimisations to libev.
		1486
		1487	=head3 The special problem of dup'ed file descriptors
		1488
		1489	Some backends (e.g. epoll), cannot register events for file descriptors,
		1490	but only events for the underlying file descriptions. That means when you
		1491	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1492	events for them, only one file descriptor might actually receive events.
		1493
		1494	There is no workaround possible except not registering events
		1495	for potentially C<dup ()>'ed file descriptors, or to resort to
		1496	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1497
		1498	=head3 The special problem of fork
		1499
		1500	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1501	useless behaviour. Libev fully supports fork, but needs to be told about
		1502	it in the child.
		1503
		1504	To support fork in your programs, you either have to call
		1505	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1506	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1507	C<EVBACKEND_POLL>.
		1508
		1509	=head3 The special problem of SIGPIPE
		1510
		1511	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1512	when writing to a pipe whose other end has been closed, your program gets
		1513	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1514	this is sensible behaviour, for daemons, this is usually undesirable.
		1515
		1516	So when you encounter spurious, unexplained daemon exits, make sure you
		1517	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1518	somewhere, as that would have given you a big clue).
		1519
		1520
		1521	=head3 Watcher-Specific Functions
895		1522
896	=over 4	1523	=over 4
897		1524
898	=item ev_io_init (ev_io *, callback, int fd, int events)	1525	=item ev_io_init (ev_io *, callback, int fd, int events)
899		1526
900	=item ev_io_set (ev_io *, int fd, int events)	1527	=item ev_io_set (ev_io *, int fd, int events)
901		1528
902	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1529	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
903	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1530	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
904	C<EV_READ | EV_WRITE> to receive the given events.	1531	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
905		1532
906	=item int fd [read-only]	1533	=item int fd [read-only]
907		1534
908	The file descriptor being watched.	1535	The file descriptor being watched.
909		1536
910	=item int events [read-only]	1537	=item int events [read-only]
911		1538
912	The events being watched.	1539	The events being watched.
913		1540
914	=back	1541	=back
		1542
		1543	=head3 Examples
915		1544
916	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1545	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
917	readable, but only once. Since it is likely line-buffered, you could	1546	readable, but only once. Since it is likely line-buffered, you could
918	attempt to read a whole line in the callback.	1547	attempt to read a whole line in the callback.
919		1548
920	static void	1549	static void
921	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1550	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
922	{	1551	{
923	ev_io_stop (loop, w);	1552	ev_io_stop (loop, w);
924	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1553	.. read from stdin here (or from w->fd) and handle any I/O errors
925	}	1554	}
926		1555
927	...	1556	...
928	struct ev_loop *loop = ev_default_init (0);	1557	struct ev_loop *loop = ev_default_init (0);
929	struct ev_io stdin_readable;	1558	ev_io stdin_readable;
930	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1559	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
931	ev_io_start (loop, &stdin_readable);	1560	ev_io_start (loop, &stdin_readable);
932	ev_loop (loop, 0);	1561	ev_loop (loop, 0);
933		1562
934		1563
935	=head2 C<ev_timer> - relative and optionally repeating timeouts	1564	=head2 C<ev_timer> - relative and optionally repeating timeouts
936		1565
937	Timer watchers are simple relative timers that generate an event after a	1566	Timer watchers are simple relative timers that generate an event after a
938	given time, and optionally repeating in regular intervals after that.	1567	given time, and optionally repeating in regular intervals after that.
939		1568
940	The timers are based on real time, that is, if you register an event that	1569	The timers are based on real time, that is, if you register an event that
941	times out after an hour and you reset your system clock to last years	1570	times out after an hour and you reset your system clock to January last
942	time, it will still time out after (roughly) and hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
943	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
944	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
		1574
		1575	The callback is guaranteed to be invoked only I<after> its timeout has
		1576	passed (not I<at>, so on systems with very low-resolution clocks this
		1577	might introduce a small delay). If multiple timers become ready during the
		1578	same loop iteration then the ones with earlier time-out values are invoked
		1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
		1581
		1582	=head3 Be smart about timeouts
		1583
		1584	Many real-world problems involve some kind of timeout, usually for error
		1585	recovery. A typical example is an HTTP request - if the other side hangs,
		1586	you want to raise some error after a while.
		1587
		1588	What follows are some ways to handle this problem, from obvious and
		1589	inefficient to smart and efficient.
		1590
		1591	In the following, a 60 second activity timeout is assumed - a timeout that
		1592	gets reset to 60 seconds each time there is activity (e.g. each time some
		1593	data or other life sign was received).
		1594
		1595	=over 4
		1596
		1597	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1598
		1599	This is the most obvious, but not the most simple way: In the beginning,
		1600	start the watcher:
		1601
		1602	ev_timer_init (timer, callback, 60., 0.);
		1603	ev_timer_start (loop, timer);
		1604
		1605	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1606	and start it again:
		1607
		1608	ev_timer_stop (loop, timer);
		1609	ev_timer_set (timer, 60., 0.);
		1610	ev_timer_start (loop, timer);
		1611
		1612	This is relatively simple to implement, but means that each time there is
		1613	some activity, libev will first have to remove the timer from its internal
		1614	data structure and then add it again. Libev tries to be fast, but it's
		1615	still not a constant-time operation.
		1616
		1617	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1618
		1619	This is the easiest way, and involves using C<ev_timer_again> instead of
		1620	C<ev_timer_start>.
		1621
		1622	To implement this, configure an C<ev_timer> with a C<repeat> value
		1623	of C<60> and then call C<ev_timer_again> at start and each time you
		1624	successfully read or write some data. If you go into an idle state where
		1625	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1626	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1627
		1628	That means you can ignore both the C<ev_timer_start> function and the
		1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1630	member and C<ev_timer_again>.
		1631
		1632	At start:
		1633
		1634	ev_init (timer, callback);
		1635	timer->repeat = 60.;
		1636	ev_timer_again (loop, timer);
		1637
		1638	Each time there is some activity:
		1639
		1640	ev_timer_again (loop, timer);
		1641
		1642	It is even possible to change the time-out on the fly, regardless of
		1643	whether the watcher is active or not:
		1644
		1645	timer->repeat = 30.;
		1646	ev_timer_again (loop, timer);
		1647
		1648	This is slightly more efficient then stopping/starting the timer each time
		1649	you want to modify its timeout value, as libev does not have to completely
		1650	remove and re-insert the timer from/into its internal data structure.
		1651
		1652	It is, however, even simpler than the "obvious" way to do it.
		1653
		1654	=item 3. Let the timer time out, but then re-arm it as required.
		1655
		1656	This method is more tricky, but usually most efficient: Most timeouts are
		1657	relatively long compared to the intervals between other activity - in
		1658	our example, within 60 seconds, there are usually many I/O events with
		1659	associated activity resets.
		1660
		1661	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1662	but remember the time of last activity, and check for a real timeout only
		1663	within the callback:
		1664
		1665	ev_tstamp last_activity; // time of last activity
		1666
		1667	static void
		1668	callback (EV_P_ ev_timer *w, int revents)
		1669	{
		1670	ev_tstamp now = ev_now (EV_A);
		1671	ev_tstamp timeout = last_activity + 60.;
		1672
		1673	// if last_activity + 60. is older than now, we did time out
		1674	if (timeout < now)
		1675	{
		1676	// timeout occured, take action
		1677	}
		1678	else
		1679	{
		1680	// callback was invoked, but there was some activity, re-arm
		1681	// the watcher to fire in last_activity + 60, which is
		1682	// guaranteed to be in the future, so "again" is positive:
		1683	w->repeat = timeout - now;
		1684	ev_timer_again (EV_A_ w);
		1685	}
		1686	}
		1687
		1688	To summarise the callback: first calculate the real timeout (defined
		1689	as "60 seconds after the last activity"), then check if that time has
		1690	been reached, which means something I<did>, in fact, time out. Otherwise
		1691	the callback was invoked too early (C<timeout> is in the future), so
		1692	re-schedule the timer to fire at that future time, to see if maybe we have
		1693	a timeout then.
		1694
		1695	Note how C<ev_timer_again> is used, taking advantage of the
		1696	C<ev_timer_again> optimisation when the timer is already running.
		1697
		1698	This scheme causes more callback invocations (about one every 60 seconds
		1699	minus half the average time between activity), but virtually no calls to
		1700	libev to change the timeout.
		1701
		1702	To start the timer, simply initialise the watcher and set C<last_activity>
		1703	to the current time (meaning we just have some activity :), then call the
		1704	callback, which will "do the right thing" and start the timer:
		1705
		1706	ev_init (timer, callback);
		1707	last_activity = ev_now (loop);
		1708	callback (loop, timer, EV_TIMEOUT);
		1709
		1710	And when there is some activity, simply store the current time in
		1711	C<last_activity>, no libev calls at all:
		1712
		1713	last_actiivty = ev_now (loop);
		1714
		1715	This technique is slightly more complex, but in most cases where the
		1716	time-out is unlikely to be triggered, much more efficient.
		1717
		1718	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1719	callback :) - just change the timeout and invoke the callback, which will
		1720	fix things for you.
		1721
		1722	=item 4. Wee, just use a double-linked list for your timeouts.
		1723
		1724	If there is not one request, but many thousands (millions...), all
		1725	employing some kind of timeout with the same timeout value, then one can
		1726	do even better:
		1727
		1728	When starting the timeout, calculate the timeout value and put the timeout
		1729	at the I<end> of the list.
		1730
		1731	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1732	the list is expected to fire (for example, using the technique #3).
		1733
		1734	When there is some activity, remove the timer from the list, recalculate
		1735	the timeout, append it to the end of the list again, and make sure to
		1736	update the C<ev_timer> if it was taken from the beginning of the list.
		1737
		1738	This way, one can manage an unlimited number of timeouts in O(1) time for
		1739	starting, stopping and updating the timers, at the expense of a major
		1740	complication, and having to use a constant timeout. The constant timeout
		1741	ensures that the list stays sorted.
		1742
		1743	=back
		1744
		1745	So which method the best?
		1746
		1747	Method #2 is a simple no-brain-required solution that is adequate in most
		1748	situations. Method #3 requires a bit more thinking, but handles many cases
		1749	better, and isn't very complicated either. In most case, choosing either
		1750	one is fine, with #3 being better in typical situations.
		1751
		1752	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1753	rather complicated, but extremely efficient, something that really pays
		1754	off after the first million or so of active timers, i.e. it's usually
		1755	overkill :)
		1756
		1757	=head3 The special problem of time updates
		1758
		1759	Establishing the current time is a costly operation (it usually takes at
		1760	least two system calls): EV therefore updates its idea of the current
		1761	time only before and after C<ev_loop> collects new events, which causes a
		1762	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1763	lots of events in one iteration.
945		1764
946	The relative timeouts are calculated relative to the C<ev_now ()>	1765	The relative timeouts are calculated relative to the C<ev_now ()>
947	time. This is usually the right thing as this timestamp refers to the time	1766	time. This is usually the right thing as this timestamp refers to the time
948	of the event triggering whatever timeout you are modifying/starting. If	1767	of the event triggering whatever timeout you are modifying/starting. If
949	you suspect event processing to be delayed and you I<need> to base the timeout	1768	you suspect event processing to be delayed and you I<need> to base the
950	on the current time, use something like this to adjust for this:	1769	timeout on the current time, use something like this to adjust for this:
951		1770
952	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1771	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
953		1772
954	The callback is guarenteed to be invoked only when its timeout has passed,	1773	If the event loop is suspended for a long time, you can also force an
955	but if multiple timers become ready during the same loop iteration then	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
956	order of execution is undefined.	1775	()>.
		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
		1807	=head3 Watcher-Specific Functions and Data Members
957		1808
958	=over 4	1809	=over 4
959		1810
960	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
961		1812
962	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1813	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
963		1814
964	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1815	Configure the timer to trigger after C<after> seconds. If C<repeat>
965	C<0.>, then it will automatically be stopped. If it is positive, then the	1816	is C<0.>, then it will automatically be stopped once the timeout is
966	timer will automatically be configured to trigger again C<repeat> seconds	1817	reached. If it is positive, then the timer will automatically be
967	later, again, and again, until stopped manually.	1818	configured to trigger again C<repeat> seconds later, again, and again,
		1819	until stopped manually.
968		1820
969	The timer itself will do a best-effort at avoiding drift, that is, if you	1821	The timer itself will do a best-effort at avoiding drift, that is, if
970	configure a timer to trigger every 10 seconds, then it will trigger at	1822	you configure a timer to trigger every 10 seconds, then it will normally
971	exactly 10 second intervals. If, however, your program cannot keep up with	1823	trigger at exactly 10 second intervals. If, however, your program cannot
972	the timer (because it takes longer than those 10 seconds to do stuff) the	1824	keep up with the timer (because it takes longer than those 10 seconds to
973	timer will not fire more than once per event loop iteration.	1825	do stuff) the timer will not fire more than once per event loop iteration.
974		1826
975	=item ev_timer_again (loop)	1827	=item ev_timer_again (loop, ev_timer *)
976		1828
977	This will act as if the timer timed out and restart it again if it is	1829	This will act as if the timer timed out and restart it again if it is
978	repeating. The exact semantics are:	1830	repeating. The exact semantics are:
979		1831
980	If the timer is pending, its pending status is cleared.	1832	If the timer is pending, its pending status is cleared.
981		1833
982	If the timer is started but nonrepeating, stop it (as if it timed out).	1834	If the timer is started but non-repeating, stop it (as if it timed out).
983		1835
984	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
985	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
986		1838
987	This sounds a bit complicated, but here is a useful and typical	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
988	example: Imagine you have a tcp connection and you want a so-called idle	1840	usage example.
989	timeout, that is, you want to be called when there have been, say, 60
990	seconds of inactivity on the socket. The easiest way to do this is to
991	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
992	C<ev_timer_again> each time you successfully read or write some data. If
993	you go into an idle state where you do not expect data to travel on the
994	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
995	automatically restart it if need be.
996		1841
997	That means you can ignore the C<after> value and C<ev_timer_start>	1842	=item ev_timer_remaining (loop, ev_timer *)
998	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
999		1843
1000	ev_timer_init (timer, callback, 0., 5.);	1844	Returns the remaining time until a timer fires. If the timer is active,
1001	ev_timer_again (loop, timer);	1845	then this time is relative to the current event loop time, otherwise it's
1002	...	1846	the timeout value currently configured.
1003	timer->again = 17.;
1004	ev_timer_again (loop, timer);
1005	...
1006	timer->again = 10.;
1007	ev_timer_again (loop, timer);
1008		1847
1009	This is more slightly efficient then stopping/starting the timer each time	1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1010	you want to modify its timeout value.	1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
1011		1853
1012	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1013		1855
1014	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1015	or C<ev_timer_again> is called and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
1016	which is also when any modifications are taken into account.	1858	which is also when any modifications are taken into account.
1017		1859
1018	=back	1860	=back
1019		1861
		1862	=head3 Examples
		1863
1020	Example: Create a timer that fires after 60 seconds.	1864	Example: Create a timer that fires after 60 seconds.
1021		1865
1022	static void	1866	static void
1023	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1867	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1024	{	1868	{
1025	.. one minute over, w is actually stopped right here	1869	.. one minute over, w is actually stopped right here
1026	}	1870	}
1027		1871
1028	struct ev_timer mytimer;	1872	ev_timer mytimer;
1029	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1873	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1030	ev_timer_start (loop, &mytimer);	1874	ev_timer_start (loop, &mytimer);
1031		1875
1032	Example: Create a timeout timer that times out after 10 seconds of	1876	Example: Create a timeout timer that times out after 10 seconds of
1033	inactivity.	1877	inactivity.
1034		1878
1035	static void	1879	static void
1036	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1880	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1037	{	1881	{
1038	.. ten seconds without any activity	1882	.. ten seconds without any activity
1039	}	1883	}
1040		1884
1041	struct ev_timer mytimer;	1885	ev_timer mytimer;
1042	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1886	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1043	ev_timer_again (&mytimer); /* start timer */	1887	ev_timer_again (&mytimer); /* start timer */
1044	ev_loop (loop, 0);	1888	ev_loop (loop, 0);
1045		1889
1046	// and in some piece of code that gets executed on any "activity":	1890	// and in some piece of code that gets executed on any "activity":
1047	// reset the timeout to start ticking again at 10 seconds	1891	// reset the timeout to start ticking again at 10 seconds
1048	ev_timer_again (&mytimer);	1892	ev_timer_again (&mytimer);
1049		1893
1050		1894
1051	=head2 C<ev_periodic> - to cron or not to cron?	1895	=head2 C<ev_periodic> - to cron or not to cron?
1052		1896
1053	Periodic watchers are also timers of a kind, but they are very versatile	1897	Periodic watchers are also timers of a kind, but they are very versatile
1054	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
1055		1899
1056	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1900	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1057	but on wallclock time (absolute time). You can tell a periodic watcher	1901	relative time, the physical time that passes) but on wall clock time
1058	to trigger "at" some specific point in time. For example, if you tell a	1902	(absolute time, the thing you can read on your calender or clock). The
1059	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1903	difference is that wall clock time can run faster or slower than real
1060	+ 10.>) and then reset your system clock to the last year, then it will	1904	time, and time jumps are not uncommon (e.g. when you adjust your
1061	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1905	wrist-watch).
1062	roughly 10 seconds later and of course not if you reset your system time
1063	again).
1064		1906
1065	They can also be used to implement vastly more complex timers, such as	1907	You can tell a periodic watcher to trigger after some specific point
		1908	in time: for example, if you tell a periodic watcher to trigger "in 10
		1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
		1914
		1915	C<ev_periodic> watchers can also be used to implement vastly more complex
1066	triggering an event on eahc midnight, local time.	1916	timers, such as triggering an event on each "midnight, local time", or
		1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
1067		1919
1068	As with timers, the callback is guarenteed to be invoked only when the	1920	As with timers, the callback is guaranteed to be invoked only when the
1069	time (C<at>) has been passed, but if multiple periodic timers become ready	1921	point in time where it is supposed to trigger has passed. If multiple
1070	during the same loop iteration then order of execution is undefined.	1922	timers become ready during the same loop iteration then the ones with
		1923	earlier time-out values are invoked before ones with later time-out values
		1924	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1925
		1926	=head3 Watcher-Specific Functions and Data Members
1071		1927
1072	=over 4	1928	=over 4
1073		1929
1074	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1930	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1075		1931
1076	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1932	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1077		1933
1078	Lots of arguments, lets sort it out... There are basically three modes of	1934	Lots of arguments, let's sort it out... There are basically three modes of
1079	operation, and we will explain them from simplest to complex:	1935	operation, and we will explain them from simplest to most complex:
1080		1936
1081	=over 4	1937	=over 4
1082		1938
1083	=item * absolute timer (interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1084		1940
1085	In this configuration the watcher triggers an event at the wallclock time	1941	In this configuration the watcher triggers an event after the wall clock
1086	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1942	time C<offset> has passed. It will not repeat and will not adjust when a
1087	that is, if it is to be run at January 1st 2011 then it will run when the	1943	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1088	system time reaches or surpasses this time.	1944	will be stopped and invoked when the system clock reaches or surpasses
		1945	this point in time.
1089		1946
1090	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1091		1948
1092	In this mode the watcher will always be scheduled to time out at the next	1949	In this mode the watcher will always be scheduled to time out at the next
1093	C<at + N * interval> time (for some integer N) and then repeat, regardless	1950	C<offset + N * interval> time (for some integer N, which can also be
1094	of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
1095		1953
1096	This can be used to create timers that do not drift with respect to system	1954	This can be used to create timers that do not drift with respect to the
1097	time:	1955	system clock, for example, here is an C<ev_periodic> that triggers each
		1956	hour, on the hour (with respect to UTC):
1098		1957
1099	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
1100		1959
1101	This doesn't mean there will always be 3600 seconds in between triggers,	1960	This doesn't mean there will always be 3600 seconds in between triggers,
1102	but only that the the callback will be called when the system time shows a	1961	but only that the callback will be called when the system time shows a
1103	full hour (UTC), or more correctly, when the system time is evenly divisible	1962	full hour (UTC), or more correctly, when the system time is evenly divisible
1104	by 3600.	1963	by 3600.
1105		1964
1106	Another way to think about it (for the mathematically inclined) is that	1965	Another way to think about it (for the mathematically inclined) is that
1107	C<ev_periodic> will try to run the callback in this mode at the next possible	1966	C<ev_periodic> will try to run the callback in this mode at the next possible
1108	time where C<time = at (mod interval)>, regardless of any time jumps.	1967	time where C<time = offset (mod interval)>, regardless of any time jumps.
1109		1968
		1969	For numerical stability it is preferable that the C<offset> value is near
		1970	C<ev_now ()> (the current time), but there is no range requirement for
		1971	this value, and in fact is often specified as zero.
		1972
		1973	Note also that there is an upper limit to how often a timer can fire (CPU
		1974	speed for example), so if C<interval> is very small then timing stability
		1975	will of course deteriorate. Libev itself tries to be exact to be about one
		1976	millisecond (if the OS supports it and the machine is fast enough).
		1977
1110	=item * manual reschedule mode (reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1111		1979
1112	In this mode the values for C<interval> and C<at> are both being	1980	In this mode the values for C<interval> and C<offset> are both being
1113	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
1114	reschedule callback will be called with the watcher as first, and the	1982	reschedule callback will be called with the watcher as first, and the
1115	current time as second argument.	1983	current time as second argument.
1116		1984
1117	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1985	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1118	ever, or make any event loop modifications>. If you need to stop it,	1986	or make ANY other event loop modifications whatsoever, unless explicitly
1119	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1987	allowed by documentation here>.
1120	starting a prepare watcher).
1121		1988
		1989	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1990	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1991	only event loop modification you are allowed to do).
		1992
1122	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1993	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1123	ev_tstamp now)>, e.g.:	1994	*w, ev_tstamp now)>, e.g.:
1124		1995
		1996	static ev_tstamp
1125	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1997	my_rescheduler (ev_periodic *w, ev_tstamp now)
1126	{	1998	{
1127	return now + 60.;	1999	return now + 60.;
1128	}	2000	}
1129		2001
1130	It must return the next time to trigger, based on the passed time value	2002	It must return the next time to trigger, based on the passed time value
1131	(that is, the lowest time value larger than to the second argument). It	2003	(that is, the lowest time value larger than to the second argument). It
1132	will usually be called just before the callback will be triggered, but	2004	will usually be called just before the callback will be triggered, but
1133	might be called at other times, too.	2005	might be called at other times, too.
1134		2006
1135	NOTE: I<< This callback must always return a time that is later than the	2007	NOTE: I<< This callback must always return a time that is higher than or
1136	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2008	equal to the passed C<now> value >>.
1137		2009
1138	This can be used to create very complex timers, such as a timer that	2010	This can be used to create very complex timers, such as a timer that
1139	triggers on each midnight, local time. To do this, you would calculate the	2011	triggers on "next midnight, local time". To do this, you would calculate the
1140	next midnight after C<now> and return the timestamp value for this. How	2012	next midnight after C<now> and return the timestamp value for this. How
1141	you do this is, again, up to you (but it is not trivial, which is the main	2013	you do this is, again, up to you (but it is not trivial, which is the main
1142	reason I omitted it as an example).	2014	reason I omitted it as an example).
1143		2015
1144	=back	2016	=back
…		…
1148	Simply stops and restarts the periodic watcher again. This is only useful	2020	Simply stops and restarts the periodic watcher again. This is only useful
1149	when you changed some parameters or the reschedule callback would return	2021	when you changed some parameters or the reschedule callback would return
1150	a different time than the last time it was called (e.g. in a crond like	2022	a different time than the last time it was called (e.g. in a crond like
1151	program when the crontabs have changed).	2023	program when the crontabs have changed).
1152		2024
		2025	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2026
		2027	When active, returns the absolute time that the watcher is supposed
		2028	to trigger next. This is not the same as the C<offset> argument to
		2029	C<ev_periodic_set>, but indeed works even in interval and manual
		2030	rescheduling modes.
		2031
		2032	=item ev_tstamp offset [read-write]
		2033
		2034	When repeating, this contains the offset value, otherwise this is the
		2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
		2037
		2038	Can be modified any time, but changes only take effect when the periodic
		2039	timer fires or C<ev_periodic_again> is being called.
		2040
1153	=item ev_tstamp interval [read-write]	2041	=item ev_tstamp interval [read-write]
1154		2042
1155	The current interval value. Can be modified any time, but changes only	2043	The current interval value. Can be modified any time, but changes only
1156	take effect when the periodic timer fires or C<ev_periodic_again> is being	2044	take effect when the periodic timer fires or C<ev_periodic_again> is being
1157	called.	2045	called.
1158		2046
1159	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2047	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1160		2048
1161	The current reschedule callback, or C<0>, if this functionality is	2049	The current reschedule callback, or C<0>, if this functionality is
1162	switched off. Can be changed any time, but changes only take effect when	2050	switched off. Can be changed any time, but changes only take effect when
1163	the periodic timer fires or C<ev_periodic_again> is being called.	2051	the periodic timer fires or C<ev_periodic_again> is being called.
1164		2052
1165	=back	2053	=back
1166		2054
		2055	=head3 Examples
		2056
1167	Example: Call a callback every hour, or, more precisely, whenever the	2057	Example: Call a callback every hour, or, more precisely, whenever the
1168	system clock is divisible by 3600. The callback invocation times have	2058	system time is divisible by 3600. The callback invocation times have
1169	potentially a lot of jittering, but good long-term stability.	2059	potentially a lot of jitter, but good long-term stability.
1170		2060
1171	static void	2061	static void
1172	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2062	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1173	{	2063	{
1174	... its now a full hour (UTC, or TAI or whatever your clock follows)	2064	... its now a full hour (UTC, or TAI or whatever your clock follows)
1175	}	2065	}
1176		2066
1177	struct ev_periodic hourly_tick;	2067	ev_periodic hourly_tick;
1178	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2068	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1179	ev_periodic_start (loop, &hourly_tick);	2069	ev_periodic_start (loop, &hourly_tick);
1180		2070
1181	Example: The same as above, but use a reschedule callback to do it:	2071	Example: The same as above, but use a reschedule callback to do it:
1182		2072
1183	#include <math.h>	2073	#include <math.h>
1184		2074
1185	static ev_tstamp	2075	static ev_tstamp
1186	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2076	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1187	{	2077	{
1188	return fmod (now, 3600.) + 3600.;	2078	return now + (3600. - fmod (now, 3600.));
1189	}	2079	}
1190		2080
1191	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2081	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1192		2082
1193	Example: Call a callback every hour, starting now:	2083	Example: Call a callback every hour, starting now:
1194		2084
1195	struct ev_periodic hourly_tick;	2085	ev_periodic hourly_tick;
1196	ev_periodic_init (&hourly_tick, clock_cb,	2086	ev_periodic_init (&hourly_tick, clock_cb,
1197	fmod (ev_now (loop), 3600.), 3600., 0);	2087	fmod (ev_now (loop), 3600.), 3600., 0);
1198	ev_periodic_start (loop, &hourly_tick);	2088	ev_periodic_start (loop, &hourly_tick);
1199		2089
1200		2090
1201	=head2 C<ev_signal> - signal me when a signal gets signalled!	2091	=head2 C<ev_signal> - signal me when a signal gets signalled!
1202		2092
1203	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1204	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1205	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1206	normal event processing, like any other event.	2096	normal event processing, like any other event.
1207		2097
		2098	If you want signals to be delivered truly asynchronously, just use
		2099	C<sigaction> as you would do without libev and forget about sharing
		2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
		2102
1208	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1209	first watcher gets started will libev actually register a signal watcher	2109	When the first watcher gets started will libev actually register something
1210	with the kernel (thus it coexists with your own signal handlers as long	2110	with the kernel (thus it coexists with your own signal handlers as long as
1211	as you don't register any with libev). Similarly, when the last signal	2111	you don't register any with libev for the same signal).
1212	watcher for a signal is stopped libev will reset the signal handler to	2112
1213	SIG_DFL (regardless of what it was set to before).	2113	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2114	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2115	sotpping it again), that is, libev might or might not block the signal,
		2116	and might or might not set or restore the installed signal handler.
		2117
		2118	If possible and supported, libev will install its handlers with
		2119	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2120	not be unduly interrupted. If you have a problem with system calls getting
		2121	interrupted by signals you can block all signals in an C<ev_check> watcher
		2122	and unblock them in an C<ev_prepare> watcher.
		2123
		2124	=head3 Watcher-Specific Functions and Data Members
1214		2125
1215	=over 4	2126	=over 4
1216		2127
1217	=item ev_signal_init (ev_signal *, callback, int signum)	2128	=item ev_signal_init (ev_signal *, callback, int signum)
1218		2129
…		…
1225		2136
1226	The signal the watcher watches out for.	2137	The signal the watcher watches out for.
1227		2138
1228	=back	2139	=back
1229		2140
		2141	=head3 Examples
		2142
		2143	Example: Try to exit cleanly on SIGINT.
		2144
		2145	static void
		2146	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2147	{
		2148	ev_unloop (loop, EVUNLOOP_ALL);
		2149	}
		2150
		2151	ev_signal signal_watcher;
		2152	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2153	ev_signal_start (loop, &signal_watcher);
		2154
1230		2155
1231	=head2 C<ev_child> - watch out for process status changes	2156	=head2 C<ev_child> - watch out for process status changes
1232		2157
1233	Child watchers trigger when your process receives a SIGCHLD in response to	2158	Child watchers trigger when your process receives a SIGCHLD in response to
1234	some child status changes (most typically when a child of yours dies).	2159	some child status changes (most typically when a child of yours dies or
		2160	exits). It is permissible to install a child watcher I<after> the child
		2161	has been forked (which implies it might have already exited), as long
		2162	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2163	forking and then immediately registering a watcher for the child is fine,
		2164	but forking and registering a watcher a few event loop iterations later or
		2165	in the next callback invocation is not.
		2166
		2167	Only the default event loop is capable of handling signals, and therefore
		2168	you can only register child watchers in the default event loop.
		2169
		2170	Due to some design glitches inside libev, child watchers will always be
		2171	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2172	libev)
		2173
		2174	=head3 Process Interaction
		2175
		2176	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2177	initialised. This is necessary to guarantee proper behaviour even if the
		2178	first child watcher is started after the child exits. The occurrence
		2179	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2180	synchronously as part of the event loop processing. Libev always reaps all
		2181	children, even ones not watched.
		2182
		2183	=head3 Overriding the Built-In Processing
		2184
		2185	Libev offers no special support for overriding the built-in child
		2186	processing, but if your application collides with libev's default child
		2187	handler, you can override it easily by installing your own handler for
		2188	C<SIGCHLD> after initialising the default loop, and making sure the
		2189	default loop never gets destroyed. You are encouraged, however, to use an
		2190	event-based approach to child reaping and thus use libev's support for
		2191	that, so other libev users can use C<ev_child> watchers freely.
		2192
		2193	=head3 Stopping the Child Watcher
		2194
		2195	Currently, the child watcher never gets stopped, even when the
		2196	child terminates, so normally one needs to stop the watcher in the
		2197	callback. Future versions of libev might stop the watcher automatically
		2198	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2199	problem).
		2200
		2201	=head3 Watcher-Specific Functions and Data Members
1235		2202
1236	=over 4	2203	=over 4
1237		2204
1238	=item ev_child_init (ev_child *, callback, int pid)	2205	=item ev_child_init (ev_child *, callback, int pid, int trace)
1239		2206
1240	=item ev_child_set (ev_child *, int pid)	2207	=item ev_child_set (ev_child *, int pid, int trace)
1241		2208
1242	Configures the watcher to wait for status changes of process C<pid> (or	2209	Configures the watcher to wait for status changes of process C<pid> (or
1243	I<any> process if C<pid> is specified as C<0>). The callback can look	2210	I<any> process if C<pid> is specified as C<0>). The callback can look
1244	at the C<rstatus> member of the C<ev_child> watcher structure to see	2211	at the C<rstatus> member of the C<ev_child> watcher structure to see
1245	the status word (use the macros from C<sys/wait.h> and see your systems	2212	the status word (use the macros from C<sys/wait.h> and see your systems
1246	C<waitpid> documentation). The C<rpid> member contains the pid of the	2213	C<waitpid> documentation). The C<rpid> member contains the pid of the
1247	process causing the status change.	2214	process causing the status change. C<trace> must be either C<0> (only
		2215	activate the watcher when the process terminates) or C<1> (additionally
		2216	activate the watcher when the process is stopped or continued).
1248		2217
1249	=item int pid [read-only]	2218	=item int pid [read-only]
1250		2219
1251	The process id this watcher watches out for, or C<0>, meaning any process id.	2220	The process id this watcher watches out for, or C<0>, meaning any process id.
1252		2221
…		…
1259	The process exit/trace status caused by C<rpid> (see your systems	2228	The process exit/trace status caused by C<rpid> (see your systems
1260	C<waitpid> and C<sys/wait.h> documentation for details).	2229	C<waitpid> and C<sys/wait.h> documentation for details).
1261		2230
1262	=back	2231	=back
1263		2232
1264	Example: Try to exit cleanly on SIGINT and SIGTERM.	2233	=head3 Examples
1265		2234
		2235	Example: C<fork()> a new process and install a child handler to wait for
		2236	its completion.
		2237
		2238	ev_child cw;
		2239
1266	static void	2240	static void
1267	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2241	child_cb (EV_P_ ev_child *w, int revents)
1268	{	2242	{
1269	ev_unloop (loop, EVUNLOOP_ALL);	2243	ev_child_stop (EV_A_ w);
		2244	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1270	}	2245	}
1271		2246
1272	struct ev_signal signal_watcher;	2247	pid_t pid = fork ();
1273	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2248
1274	ev_signal_start (loop, &sigint_cb);	2249	if (pid < 0)
		2250	// error
		2251	else if (pid == 0)
		2252	{
		2253	// the forked child executes here
		2254	exit (1);
		2255	}
		2256	else
		2257	{
		2258	ev_child_init (&cw, child_cb, pid, 0);
		2259	ev_child_start (EV_DEFAULT_ &cw);
		2260	}
1275		2261
1276		2262
1277	=head2 C<ev_stat> - did the file attributes just change?	2263	=head2 C<ev_stat> - did the file attributes just change?
1278		2264
1279	This watches a filesystem path for attribute changes. That is, it calls	2265	This watches a file system path for attribute changes. That is, it calls
1280	C<stat> regularly (or when the OS says it changed) and sees if it changed	2266	C<stat> on that path in regular intervals (or when the OS says it changed)
1281	compared to the last time, invoking the callback if it did.	2267	and sees if it changed compared to the last time, invoking the callback if
		2268	it did.
1282		2269
1283	The path does not need to exist: changing from "path exists" to "path does	2270	The path does not need to exist: changing from "path exists" to "path does
1284	not exist" is a status change like any other. The condition "path does	2271	not exist" is a status change like any other. The condition "path does not
1285	not exist" is signified by the C<st_nlink> field being zero (which is	2272	exist" (or more correctly "path cannot be stat'ed") is signified by the
1286	otherwise always forced to be at least one) and all the other fields of	2273	C<st_nlink> field being zero (which is otherwise always forced to be at
1287	the stat buffer having unspecified contents.	2274	least one) and all the other fields of the stat buffer having unspecified
		2275	contents.
1288		2276
1289	The path I<should> be absolute and I<must not> end in a slash. If it is	2277	The path I<must not> end in a slash or contain special components such as
		2278	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1290	relative and your working directory changes, the behaviour is undefined.	2279	your working directory changes, then the behaviour is undefined.
1291		2280
1292	Since there is no standard to do this, the portable implementation simply	2281	Since there is no portable change notification interface available, the
1293	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2282	portable implementation simply calls C<stat(2)> regularly on the path
1294	can specify a recommended polling interval for this case. If you specify	2283	to see if it changed somehow. You can specify a recommended polling
1295	a polling interval of C<0> (highly recommended!) then a I<suitable,	2284	interval for this case. If you specify a polling interval of C<0> (highly
1296	unspecified default> value will be used (which you can expect to be around	2285	recommended!) then a I<suitable, unspecified default> value will be used
1297	five seconds, although this might change dynamically). Libev will also	2286	(which you can expect to be around five seconds, although this might
1298	impose a minimum interval which is currently around C<0.1>, but thats	2287	change dynamically). Libev will also impose a minimum interval which is
1299	usually overkill.	2288	currently around C<0.1>, but that's usually overkill.
1300		2289
1301	This watcher type is not meant for massive numbers of stat watchers,	2290	This watcher type is not meant for massive numbers of stat watchers,
1302	as even with OS-supported change notifications, this can be	2291	as even with OS-supported change notifications, this can be
1303	resource-intensive.	2292	resource-intensive.
1304		2293
1305	At the time of this writing, only the Linux inotify interface is	2294	At the time of this writing, the only OS-specific interface implemented
1306	implemented (implementing kqueue support is left as an exercise for the	2295	is the Linux inotify interface (implementing kqueue support is left as an
1307	reader). Inotify will be used to give hints only and should not change the	2296	exercise for the reader. Note, however, that the author sees no way of
1308	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2297	implementing C<ev_stat> semantics with kqueue, except as a hint).
1309	to fall back to regular polling again even with inotify, but changes are	2298
1310	usually detected immediately, and if the file exists there will be no	2299	=head3 ABI Issues (Largefile Support)
1311	polling.	2300
		2301	Libev by default (unless the user overrides this) uses the default
		2302	compilation environment, which means that on systems with large file
		2303	support disabled by default, you get the 32 bit version of the stat
		2304	structure. When using the library from programs that change the ABI to
		2305	use 64 bit file offsets the programs will fail. In that case you have to
		2306	compile libev with the same flags to get binary compatibility. This is
		2307	obviously the case with any flags that change the ABI, but the problem is
		2308	most noticeably displayed with ev_stat and large file support.
		2309
		2310	The solution for this is to lobby your distribution maker to make large
		2311	file interfaces available by default (as e.g. FreeBSD does) and not
		2312	optional. Libev cannot simply switch on large file support because it has
		2313	to exchange stat structures with application programs compiled using the
		2314	default compilation environment.
		2315
		2316	=head3 Inotify and Kqueue
		2317
		2318	When C<inotify (7)> support has been compiled into libev and present at
		2319	runtime, it will be used to speed up change detection where possible. The
		2320	inotify descriptor will be created lazily when the first C<ev_stat>
		2321	watcher is being started.
		2322
		2323	Inotify presence does not change the semantics of C<ev_stat> watchers
		2324	except that changes might be detected earlier, and in some cases, to avoid
		2325	making regular C<stat> calls. Even in the presence of inotify support
		2326	there are many cases where libev has to resort to regular C<stat> polling,
		2327	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2328	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2329	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2330	xfs are fully working) libev usually gets away without polling.
		2331
		2332	There is no support for kqueue, as apparently it cannot be used to
		2333	implement this functionality, due to the requirement of having a file
		2334	descriptor open on the object at all times, and detecting renames, unlinks
		2335	etc. is difficult.
		2336
		2337	=head3 C<stat ()> is a synchronous operation
		2338
		2339	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2340	the process. The exception are C<ev_stat> watchers - those call C<stat
		2341	()>, which is a synchronous operation.
		2342
		2343	For local paths, this usually doesn't matter: unless the system is very
		2344	busy or the intervals between stat's are large, a stat call will be fast,
		2345	as the path data is usually in memory already (except when starting the
		2346	watcher).
		2347
		2348	For networked file systems, calling C<stat ()> can block an indefinite
		2349	time due to network issues, and even under good conditions, a stat call
		2350	often takes multiple milliseconds.
		2351
		2352	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2353	paths, although this is fully supported by libev.
		2354
		2355	=head3 The special problem of stat time resolution
		2356
		2357	The C<stat ()> system call only supports full-second resolution portably,
		2358	and even on systems where the resolution is higher, most file systems
		2359	still only support whole seconds.
		2360
		2361	That means that, if the time is the only thing that changes, you can
		2362	easily miss updates: on the first update, C<ev_stat> detects a change and
		2363	calls your callback, which does something. When there is another update
		2364	within the same second, C<ev_stat> will be unable to detect unless the
		2365	stat data does change in other ways (e.g. file size).
		2366
		2367	The solution to this is to delay acting on a change for slightly more
		2368	than a second (or till slightly after the next full second boundary), using
		2369	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2370	ev_timer_again (loop, w)>).
		2371
		2372	The C<.02> offset is added to work around small timing inconsistencies
		2373	of some operating systems (where the second counter of the current time
		2374	might be be delayed. One such system is the Linux kernel, where a call to
		2375	C<gettimeofday> might return a timestamp with a full second later than
		2376	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2377	update file times then there will be a small window where the kernel uses
		2378	the previous second to update file times but libev might already execute
		2379	the timer callback).
		2380
		2381	=head3 Watcher-Specific Functions and Data Members
1312		2382
1313	=over 4	2383	=over 4
1314		2384
1315	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2385	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1316		2386
…		…
1320	C<path>. The C<interval> is a hint on how quickly a change is expected to	2390	C<path>. The C<interval> is a hint on how quickly a change is expected to
1321	be detected and should normally be specified as C<0> to let libev choose	2391	be detected and should normally be specified as C<0> to let libev choose
1322	a suitable value. The memory pointed to by C<path> must point to the same	2392	a suitable value. The memory pointed to by C<path> must point to the same
1323	path for as long as the watcher is active.	2393	path for as long as the watcher is active.
1324		2394
1325	The callback will be receive C<EV_STAT> when a change was detected,	2395	The callback will receive an C<EV_STAT> event when a change was detected,
1326	relative to the attributes at the time the watcher was started (or the	2396	relative to the attributes at the time the watcher was started (or the
1327	last change was detected).	2397	last change was detected).
1328		2398
1329	=item ev_stat_stat (ev_stat *)	2399	=item ev_stat_stat (loop, ev_stat *)
1330		2400
1331	Updates the stat buffer immediately with new values. If you change the	2401	Updates the stat buffer immediately with new values. If you change the
1332	watched path in your callback, you could call this fucntion to avoid	2402	watched path in your callback, you could call this function to avoid
1333	detecting this change (while introducing a race condition). Can also be	2403	detecting this change (while introducing a race condition if you are not
1334	useful simply to find out the new values.	2404	the only one changing the path). Can also be useful simply to find out the
		2405	new values.
1335		2406
1336	=item ev_statdata attr [read-only]	2407	=item ev_statdata attr [read-only]
1337		2408
1338	The most-recently detected attributes of the file. Although the type is of	2409	The most-recently detected attributes of the file. Although the type is
1339	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2410	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1340	suitable for your system. If the C<st_nlink> member is C<0>, then there	2411	suitable for your system, but you can only rely on the POSIX-standardised
		2412	members to be present. If the C<st_nlink> member is C<0>, then there was
1341	was some error while C<stat>ing the file.	2413	some error while C<stat>ing the file.
1342		2414
1343	=item ev_statdata prev [read-only]	2415	=item ev_statdata prev [read-only]
1344		2416
1345	The previous attributes of the file. The callback gets invoked whenever	2417	The previous attributes of the file. The callback gets invoked whenever
1346	C<prev> != C<attr>.	2418	C<prev> != C<attr>, or, more precisely, one or more of these members
		2419	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2420	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1347		2421
1348	=item ev_tstamp interval [read-only]	2422	=item ev_tstamp interval [read-only]
1349		2423
1350	The specified interval.	2424	The specified interval.
1351		2425
1352	=item const char *path [read-only]	2426	=item const char *path [read-only]
1353		2427
1354	The filesystem path that is being watched.	2428	The file system path that is being watched.
1355		2429
1356	=back	2430	=back
1357		2431
		2432	=head3 Examples
		2433
1358	Example: Watch C</etc/passwd> for attribute changes.	2434	Example: Watch C</etc/passwd> for attribute changes.
1359		2435
1360	static void	2436	static void
1361	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2437	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1362	{	2438	{
1363	/* /etc/passwd changed in some way */	2439	/* /etc/passwd changed in some way */
1364	if (w->attr.st_nlink)	2440	if (w->attr.st_nlink)
1365	{	2441	{
1366	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2442	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1367	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2443	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1368	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2444	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1369	}	2445	}
1370	else	2446	else
1371	/* you shalt not abuse printf for puts */	2447	/* you shalt not abuse printf for puts */
1372	puts ("wow, /etc/passwd is not there, expect problems. "	2448	puts ("wow, /etc/passwd is not there, expect problems. "
1373	"if this is windows, they already arrived\n");	2449	"if this is windows, they already arrived\n");
1374	}	2450	}
1375		2451
1376	...	2452	...
1377	ev_stat passwd;	2453	ev_stat passwd;
1378		2454
1379	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2455	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1380	ev_stat_start (loop, &passwd);	2456	ev_stat_start (loop, &passwd);
		2457
		2458	Example: Like above, but additionally use a one-second delay so we do not
		2459	miss updates (however, frequent updates will delay processing, too, so
		2460	one might do the work both on C<ev_stat> callback invocation I<and> on
		2461	C<ev_timer> callback invocation).
		2462
		2463	static ev_stat passwd;
		2464	static ev_timer timer;
		2465
		2466	static void
		2467	timer_cb (EV_P_ ev_timer *w, int revents)
		2468	{
		2469	ev_timer_stop (EV_A_ w);
		2470
		2471	/* now it's one second after the most recent passwd change */
		2472	}
		2473
		2474	static void
		2475	stat_cb (EV_P_ ev_stat *w, int revents)
		2476	{
		2477	/* reset the one-second timer */
		2478	ev_timer_again (EV_A_ &timer);
		2479	}
		2480
		2481	...
		2482	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2483	ev_stat_start (loop, &passwd);
		2484	ev_timer_init (&timer, timer_cb, 0., 1.02);
1381		2485
1382		2486
1383	=head2 C<ev_idle> - when you've got nothing better to do...	2487	=head2 C<ev_idle> - when you've got nothing better to do...
1384		2488
1385	Idle watchers trigger events when no other events of the same or higher	2489	Idle watchers trigger events when no other events of the same or higher
1386	priority are pending (prepare, check and other idle watchers do not	2490	priority are pending (prepare, check and other idle watchers do not count
1387	count).	2491	as receiving "events").
1388		2492
1389	That is, as long as your process is busy handling sockets or timeouts	2493	That is, as long as your process is busy handling sockets or timeouts
1390	(or even signals, imagine) of the same or higher priority it will not be	2494	(or even signals, imagine) of the same or higher priority it will not be
1391	triggered. But when your process is idle (or only lower-priority watchers	2495	triggered. But when your process is idle (or only lower-priority watchers
1392	are pending), the idle watchers are being called once per event loop	2496	are pending), the idle watchers are being called once per event loop
…		…
1399	Apart from keeping your process non-blocking (which is a useful	2503	Apart from keeping your process non-blocking (which is a useful
1400	effect on its own sometimes), idle watchers are a good place to do	2504	effect on its own sometimes), idle watchers are a good place to do
1401	"pseudo-background processing", or delay processing stuff to after the	2505	"pseudo-background processing", or delay processing stuff to after the
1402	event loop has handled all outstanding events.	2506	event loop has handled all outstanding events.
1403		2507
		2508	=head3 Watcher-Specific Functions and Data Members
		2509
1404	=over 4	2510	=over 4
1405		2511
1406	=item ev_idle_init (ev_signal *, callback)	2512	=item ev_idle_init (ev_idle *, callback)
1407		2513
1408	Initialises and configures the idle watcher - it has no parameters of any	2514	Initialises and configures the idle watcher - it has no parameters of any
1409	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2515	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1410	believe me.	2516	believe me.
1411		2517
1412	=back	2518	=back
1413		2519
		2520	=head3 Examples
		2521
1414	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2522	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1415	callback, free it. Also, use no error checking, as usual.	2523	callback, free it. Also, use no error checking, as usual.
1416		2524
1417	static void	2525	static void
1418	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2526	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1419	{	2527	{
1420	free (w);	2528	free (w);
1421	// now do something you wanted to do when the program has	2529	// now do something you wanted to do when the program has
1422	// no longer asnything immediate to do.	2530	// no longer anything immediate to do.
1423	}	2531	}
1424		2532
1425	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2533	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1426	ev_idle_init (idle_watcher, idle_cb);	2534	ev_idle_init (idle_watcher, idle_cb);
1427	ev_idle_start (loop, idle_cb);	2535	ev_idle_start (loop, idle_watcher);
1428		2536
1429		2537
1430	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2538	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1431		2539
1432	Prepare and check watchers are usually (but not always) used in tandem:	2540	Prepare and check watchers are usually (but not always) used in pairs:
1433	prepare watchers get invoked before the process blocks and check watchers	2541	prepare watchers get invoked before the process blocks and check watchers
1434	afterwards.	2542	afterwards.
1435		2543
1436	You I<must not> call C<ev_loop> or similar functions that enter	2544	You I<must not> call C<ev_loop> or similar functions that enter
1437	the current event loop from either C<ev_prepare> or C<ev_check>	2545	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1440	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2548	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1441	C<ev_check> so if you have one watcher of each kind they will always be	2549	C<ev_check> so if you have one watcher of each kind they will always be
1442	called in pairs bracketing the blocking call.	2550	called in pairs bracketing the blocking call.
1443		2551
1444	Their main purpose is to integrate other event mechanisms into libev and	2552	Their main purpose is to integrate other event mechanisms into libev and
1445	their use is somewhat advanced. This could be used, for example, to track	2553	their use is somewhat advanced. They could be used, for example, to track
1446	variable changes, implement your own watchers, integrate net-snmp or a	2554	variable changes, implement your own watchers, integrate net-snmp or a
1447	coroutine library and lots more. They are also occasionally useful if	2555	coroutine library and lots more. They are also occasionally useful if
1448	you cache some data and want to flush it before blocking (for example,	2556	you cache some data and want to flush it before blocking (for example,
1449	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2557	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1450	watcher).	2558	watcher).
1451		2559
1452	This is done by examining in each prepare call which file descriptors need	2560	This is done by examining in each prepare call which file descriptors
1453	to be watched by the other library, registering C<ev_io> watchers for	2561	need to be watched by the other library, registering C<ev_io> watchers
1454	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2562	for them and starting an C<ev_timer> watcher for any timeouts (many
1455	provide just this functionality). Then, in the check watcher you check for	2563	libraries provide exactly this functionality). Then, in the check watcher,
1456	any events that occured (by checking the pending status of all watchers	2564	you check for any events that occurred (by checking the pending status
1457	and stopping them) and call back into the library. The I/O and timer	2565	of all watchers and stopping them) and call back into the library. The
1458	callbacks will never actually be called (but must be valid nevertheless,	2566	I/O and timer callbacks will never actually be called (but must be valid
1459	because you never know, you know?).	2567	nevertheless, because you never know, you know?).
1460		2568
1461	As another example, the Perl Coro module uses these hooks to integrate	2569	As another example, the Perl Coro module uses these hooks to integrate
1462	coroutines into libev programs, by yielding to other active coroutines	2570	coroutines into libev programs, by yielding to other active coroutines
1463	during each prepare and only letting the process block if no coroutines	2571	during each prepare and only letting the process block if no coroutines
1464	are ready to run (it's actually more complicated: it only runs coroutines	2572	are ready to run (it's actually more complicated: it only runs coroutines
1465	with priority higher than or equal to the event loop and one coroutine	2573	with priority higher than or equal to the event loop and one coroutine
1466	of lower priority, but only once, using idle watchers to keep the event	2574	of lower priority, but only once, using idle watchers to keep the event
1467	loop from blocking if lower-priority coroutines are active, thus mapping	2575	loop from blocking if lower-priority coroutines are active, thus mapping
1468	low-priority coroutines to idle/background tasks).	2576	low-priority coroutines to idle/background tasks).
1469		2577
		2578	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2579	priority, to ensure that they are being run before any other watchers
		2580	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2581
		2582	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2583	activate ("feed") events into libev. While libev fully supports this, they
		2584	might get executed before other C<ev_check> watchers did their job. As
		2585	C<ev_check> watchers are often used to embed other (non-libev) event
		2586	loops those other event loops might be in an unusable state until their
		2587	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2588	others).
		2589
		2590	=head3 Watcher-Specific Functions and Data Members
		2591
1470	=over 4	2592	=over 4
1471		2593
1472	=item ev_prepare_init (ev_prepare *, callback)	2594	=item ev_prepare_init (ev_prepare *, callback)
1473		2595
1474	=item ev_check_init (ev_check *, callback)	2596	=item ev_check_init (ev_check *, callback)
1475		2597
1476	Initialises and configures the prepare or check watcher - they have no	2598	Initialises and configures the prepare or check watcher - they have no
1477	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2599	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1478	macros, but using them is utterly, utterly and completely pointless.	2600	macros, but using them is utterly, utterly, utterly and completely
		2601	pointless.
1479		2602
1480	=back	2603	=back
1481		2604
1482	Example: To include a library such as adns, you would add IO watchers	2605	=head3 Examples
1483	and a timeout watcher in a prepare handler, as required by libadns, and	2606
		2607	There are a number of principal ways to embed other event loops or modules
		2608	into libev. Here are some ideas on how to include libadns into libev
		2609	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2610	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2611	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2612	Glib event loop).
		2613
		2614	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1484	in a check watcher, destroy them and call into libadns. What follows is	2615	and in a check watcher, destroy them and call into libadns. What follows
1485	pseudo-code only of course:	2616	is pseudo-code only of course. This requires you to either use a low
		2617	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2618	the callbacks for the IO/timeout watchers might not have been called yet.
1486		2619
1487	static ev_io iow [nfd];	2620	static ev_io iow [nfd];
1488	static ev_timer tw;	2621	static ev_timer tw;
1489		2622
1490	static void	2623	static void
1491	io_cb (ev_loop *loop, ev_io *w, int revents)	2624	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1492	{	2625	{
1493	// set the relevant poll flags
1494	// could also call adns_processreadable etc. here
1495	struct pollfd *fd = (struct pollfd *)w->data;
1496	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1497	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1498	}	2626	}
1499		2627
1500	// create io watchers for each fd and a timer before blocking	2628	// create io watchers for each fd and a timer before blocking
1501	static void	2629	static void
1502	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2630	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1503	{	2631	{
1504	int timeout = 3600000;	2632	int timeout = 3600000;
1505	struct pollfd fds [nfd];	2633	struct pollfd fds [nfd];
1506	// actual code will need to loop here and realloc etc.	2634	// actual code will need to loop here and realloc etc.
1507	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2635	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1508		2636
1509	/* the callback is illegal, but won't be called as we stop during check */	2637	/* the callback is illegal, but won't be called as we stop during check */
1510	ev_timer_init (&tw, 0, timeout * 1e-3);	2638	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1511	ev_timer_start (loop, &tw);	2639	ev_timer_start (loop, &tw);
1512		2640
1513	// create on ev_io per pollfd	2641	// create one ev_io per pollfd
1514	for (int i = 0; i < nfd; ++i)	2642	for (int i = 0; i < nfd; ++i)
1515	{	2643	{
1516	ev_io_init (iow + i, io_cb, fds [i].fd,	2644	ev_io_init (iow + i, io_cb, fds [i].fd,
1517	((fds [i].events & POLLIN ? EV_READ : 0)	2645	((fds [i].events & POLLIN ? EV_READ : 0)
1518	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2646	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1519		2647
1520	fds [i].revents = 0;	2648	fds [i].revents = 0;
1521	iow [i].data = fds + i;
1522	ev_io_start (loop, iow + i);	2649	ev_io_start (loop, iow + i);
1523	}	2650	}
1524	}	2651	}
1525		2652
1526	// stop all watchers after blocking	2653	// stop all watchers after blocking
1527	static void	2654	static void
1528	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2655	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1529	{	2656	{
1530	ev_timer_stop (loop, &tw);	2657	ev_timer_stop (loop, &tw);
1531		2658
1532	for (int i = 0; i < nfd; ++i)	2659	for (int i = 0; i < nfd; ++i)
		2660	{
		2661	// set the relevant poll flags
		2662	// could also call adns_processreadable etc. here
		2663	struct pollfd *fd = fds + i;
		2664	int revents = ev_clear_pending (iow + i);
		2665	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2666	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2667
		2668	// now stop the watcher
1533	ev_io_stop (loop, iow + i);	2669	ev_io_stop (loop, iow + i);
		2670	}
1534		2671
1535	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2672	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1536	}	2673	}
		2674
		2675	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2676	in the prepare watcher and would dispose of the check watcher.
		2677
		2678	Method 3: If the module to be embedded supports explicit event
		2679	notification (libadns does), you can also make use of the actual watcher
		2680	callbacks, and only destroy/create the watchers in the prepare watcher.
		2681
		2682	static void
		2683	timer_cb (EV_P_ ev_timer *w, int revents)
		2684	{
		2685	adns_state ads = (adns_state)w->data;
		2686	update_now (EV_A);
		2687
		2688	adns_processtimeouts (ads, &tv_now);
		2689	}
		2690
		2691	static void
		2692	io_cb (EV_P_ ev_io *w, int revents)
		2693	{
		2694	adns_state ads = (adns_state)w->data;
		2695	update_now (EV_A);
		2696
		2697	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2698	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2699	}
		2700
		2701	// do not ever call adns_afterpoll
		2702
		2703	Method 4: Do not use a prepare or check watcher because the module you
		2704	want to embed is not flexible enough to support it. Instead, you can
		2705	override their poll function. The drawback with this solution is that the
		2706	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2707	this approach, effectively embedding EV as a client into the horrible
		2708	libglib event loop.
		2709
		2710	static gint
		2711	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2712	{
		2713	int got_events = 0;
		2714
		2715	for (n = 0; n < nfds; ++n)
		2716	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2717
		2718	if (timeout >= 0)
		2719	// create/start timer
		2720
		2721	// poll
		2722	ev_loop (EV_A_ 0);
		2723
		2724	// stop timer again
		2725	if (timeout >= 0)
		2726	ev_timer_stop (EV_A_ &to);
		2727
		2728	// stop io watchers again - their callbacks should have set
		2729	for (n = 0; n < nfds; ++n)
		2730	ev_io_stop (EV_A_ iow [n]);
		2731
		2732	return got_events;
		2733	}
1537		2734
1538		2735
1539	=head2 C<ev_embed> - when one backend isn't enough...	2736	=head2 C<ev_embed> - when one backend isn't enough...
1540		2737
1541	This is a rather advanced watcher type that lets you embed one event loop	2738	This is a rather advanced watcher type that lets you embed one event loop
…		…
1547	prioritise I/O.	2744	prioritise I/O.
1548		2745
1549	As an example for a bug workaround, the kqueue backend might only support	2746	As an example for a bug workaround, the kqueue backend might only support
1550	sockets on some platform, so it is unusable as generic backend, but you	2747	sockets on some platform, so it is unusable as generic backend, but you
1551	still want to make use of it because you have many sockets and it scales	2748	still want to make use of it because you have many sockets and it scales
1552	so nicely. In this case, you would create a kqueue-based loop and embed it	2749	so nicely. In this case, you would create a kqueue-based loop and embed
1553	into your default loop (which might use e.g. poll). Overall operation will	2750	it into your default loop (which might use e.g. poll). Overall operation
1554	be a bit slower because first libev has to poll and then call kevent, but	2751	will be a bit slower because first libev has to call C<poll> and then
1555	at least you can use both at what they are best.	2752	C<kevent>, but at least you can use both mechanisms for what they are
		2753	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1556		2754
1557	As for prioritising I/O: rarely you have the case where some fds have	2755	As for prioritising I/O: under rare circumstances you have the case where
1558	to be watched and handled very quickly (with low latency), and even	2756	some fds have to be watched and handled very quickly (with low latency),
1559	priorities and idle watchers might have too much overhead. In this case	2757	and even priorities and idle watchers might have too much overhead. In
1560	you would put all the high priority stuff in one loop and all the rest in	2758	this case you would put all the high priority stuff in one loop and all
1561	a second one, and embed the second one in the first.	2759	the rest in a second one, and embed the second one in the first.
1562		2760
1563	As long as the watcher is active, the callback will be invoked every time	2761	As long as the watcher is active, the callback will be invoked every
1564	there might be events pending in the embedded loop. The callback must then	2762	time there might be events pending in the embedded loop. The callback
1565	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2763	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1566	their callbacks (you could also start an idle watcher to give the embedded	2764	sweep and invoke their callbacks (the callback doesn't need to invoke the
1567	loop strictly lower priority for example). You can also set the callback	2765	C<ev_embed_sweep> function directly, it could also start an idle watcher
1568	to C<0>, in which case the embed watcher will automatically execute the	2766	to give the embedded loop strictly lower priority for example).
1569	embedded loop sweep.
1570		2767
1571	As long as the watcher is started it will automatically handle events. The	2768	You can also set the callback to C<0>, in which case the embed watcher
1572	callback will be invoked whenever some events have been handled. You can	2769	will automatically execute the embedded loop sweep whenever necessary.
1573	set the callback to C<0> to avoid having to specify one if you are not
1574	interested in that.
1575		2770
1576	Also, there have not currently been made special provisions for forking:	2771	Fork detection will be handled transparently while the C<ev_embed> watcher
1577	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2772	is active, i.e., the embedded loop will automatically be forked when the
1578	but you will also have to stop and restart any C<ev_embed> watchers	2773	embedding loop forks. In other cases, the user is responsible for calling
1579	yourself.	2774	C<ev_loop_fork> on the embedded loop.
1580		2775
1581	Unfortunately, not all backends are embeddable, only the ones returned by	2776	Unfortunately, not all backends are embeddable: only the ones returned by
1582	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2777	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1583	portable one.	2778	portable one.
1584		2779
1585	So when you want to use this feature you will always have to be prepared	2780	So when you want to use this feature you will always have to be prepared
1586	that you cannot get an embeddable loop. The recommended way to get around	2781	that you cannot get an embeddable loop. The recommended way to get around
1587	this is to have a separate variables for your embeddable loop, try to	2782	this is to have a separate variables for your embeddable loop, try to
1588	create it, and if that fails, use the normal loop for everything:	2783	create it, and if that fails, use the normal loop for everything.
1589		2784
1590	struct ev_loop *loop_hi = ev_default_init (0);	2785	=head3 C<ev_embed> and fork
1591	struct ev_loop *loop_lo = 0;
1592	struct ev_embed embed;
1593
1594	// see if there is a chance of getting one that works
1595	// (remember that a flags value of 0 means autodetection)
1596	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1597	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1598	: 0;
1599		2786
1600	// if we got one, then embed it, otherwise default to loop_hi	2787	While the C<ev_embed> watcher is running, forks in the embedding loop will
1601	if (loop_lo)	2788	automatically be applied to the embedded loop as well, so no special
1602	{	2789	fork handling is required in that case. When the watcher is not running,
1603	ev_embed_init (&embed, 0, loop_lo);	2790	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1604	ev_embed_start (loop_hi, &embed);	2791	as applicable.
1605	}	2792
1606	else	2793	=head3 Watcher-Specific Functions and Data Members
1607	loop_lo = loop_hi;
1608		2794
1609	=over 4	2795	=over 4
1610		2796
1611	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2797	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1612		2798
…		…
1614		2800
1615	Configures the watcher to embed the given loop, which must be	2801	Configures the watcher to embed the given loop, which must be
1616	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2802	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1617	invoked automatically, otherwise it is the responsibility of the callback	2803	invoked automatically, otherwise it is the responsibility of the callback
1618	to invoke it (it will continue to be called until the sweep has been done,	2804	to invoke it (it will continue to be called until the sweep has been done,
1619	if you do not want thta, you need to temporarily stop the embed watcher).	2805	if you do not want that, you need to temporarily stop the embed watcher).
1620		2806
1621	=item ev_embed_sweep (loop, ev_embed *)	2807	=item ev_embed_sweep (loop, ev_embed *)
1622		2808
1623	Make a single, non-blocking sweep over the embedded loop. This works	2809	Make a single, non-blocking sweep over the embedded loop. This works
1624	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2810	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1625	apropriate way for embedded loops.	2811	appropriate way for embedded loops.
1626		2812
1627	=item struct ev_loop *loop [read-only]	2813	=item struct ev_loop *other [read-only]
1628		2814
1629	The embedded event loop.	2815	The embedded event loop.
1630		2816
1631	=back	2817	=back
		2818
		2819	=head3 Examples
		2820
		2821	Example: Try to get an embeddable event loop and embed it into the default
		2822	event loop. If that is not possible, use the default loop. The default
		2823	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2824	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2825	used).
		2826
		2827	struct ev_loop *loop_hi = ev_default_init (0);
		2828	struct ev_loop *loop_lo = 0;
		2829	ev_embed embed;
		2830
		2831	// see if there is a chance of getting one that works
		2832	// (remember that a flags value of 0 means autodetection)
		2833	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2834	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2835	: 0;
		2836
		2837	// if we got one, then embed it, otherwise default to loop_hi
		2838	if (loop_lo)
		2839	{
		2840	ev_embed_init (&embed, 0, loop_lo);
		2841	ev_embed_start (loop_hi, &embed);
		2842	}
		2843	else
		2844	loop_lo = loop_hi;
		2845
		2846	Example: Check if kqueue is available but not recommended and create
		2847	a kqueue backend for use with sockets (which usually work with any
		2848	kqueue implementation). Store the kqueue/socket-only event loop in
		2849	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2850
		2851	struct ev_loop *loop = ev_default_init (0);
		2852	struct ev_loop *loop_socket = 0;
		2853	ev_embed embed;
		2854
		2855	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2856	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2857	{
		2858	ev_embed_init (&embed, 0, loop_socket);
		2859	ev_embed_start (loop, &embed);
		2860	}
		2861
		2862	if (!loop_socket)
		2863	loop_socket = loop;
		2864
		2865	// now use loop_socket for all sockets, and loop for everything else
1632		2866
1633		2867
1634	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2868	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1635		2869
1636	Fork watchers are called when a C<fork ()> was detected (usually because	2870	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1639	event loop blocks next and before C<ev_check> watchers are being called,	2873	event loop blocks next and before C<ev_check> watchers are being called,
1640	and only in the child after the fork. If whoever good citizen calling	2874	and only in the child after the fork. If whoever good citizen calling
1641	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2875	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1642	handlers will be invoked, too, of course.	2876	handlers will be invoked, too, of course.
1643		2877
		2878	=head3 The special problem of life after fork - how is it possible?
		2879
		2880	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2881	up/change the process environment, followed by a call to C<exec()>. This
		2882	sequence should be handled by libev without any problems.
		2883
		2884	This changes when the application actually wants to do event handling
		2885	in the child, or both parent in child, in effect "continuing" after the
		2886	fork.
		2887
		2888	The default mode of operation (for libev, with application help to detect
		2889	forks) is to duplicate all the state in the child, as would be expected
		2890	when I<either> the parent I<or> the child process continues.
		2891
		2892	When both processes want to continue using libev, then this is usually the
		2893	wrong result. In that case, usually one process (typically the parent) is
		2894	supposed to continue with all watchers in place as before, while the other
		2895	process typically wants to start fresh, i.e. without any active watchers.
		2896
		2897	The cleanest and most efficient way to achieve that with libev is to
		2898	simply create a new event loop, which of course will be "empty", and
		2899	use that for new watchers. This has the advantage of not touching more
		2900	memory than necessary, and thus avoiding the copy-on-write, and the
		2901	disadvantage of having to use multiple event loops (which do not support
		2902	signal watchers).
		2903
		2904	When this is not possible, or you want to use the default loop for
		2905	other reasons, then in the process that wants to start "fresh", call
		2906	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2907	the default loop will "orphan" (not stop) all registered watchers, so you
		2908	have to be careful not to execute code that modifies those watchers. Note
		2909	also that in that case, you have to re-register any signal watchers.
		2910
		2911	=head3 Watcher-Specific Functions and Data Members
		2912
1644	=over 4	2913	=over 4
1645		2914
1646	=item ev_fork_init (ev_signal *, callback)	2915	=item ev_fork_init (ev_signal *, callback)
1647		2916
1648	Initialises and configures the fork watcher - it has no parameters of any	2917	Initialises and configures the fork watcher - it has no parameters of any
…		…
1650	believe me.	2919	believe me.
1651		2920
1652	=back	2921	=back
1653		2922
1654		2923
		2924	=head2 C<ev_async> - how to wake up another event loop
		2925
		2926	In general, you cannot use an C<ev_loop> from multiple threads or other
		2927	asynchronous sources such as signal handlers (as opposed to multiple event
		2928	loops - those are of course safe to use in different threads).
		2929
		2930	Sometimes, however, you need to wake up another event loop you do not
		2931	control, for example because it belongs to another thread. This is what
		2932	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2933	can signal it by calling C<ev_async_send>, which is thread- and signal
		2934	safe.
		2935
		2936	This functionality is very similar to C<ev_signal> watchers, as signals,
		2937	too, are asynchronous in nature, and signals, too, will be compressed
		2938	(i.e. the number of callback invocations may be less than the number of
		2939	C<ev_async_sent> calls).
		2940
		2941	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2942	just the default loop.
		2943
		2944	=head3 Queueing
		2945
		2946	C<ev_async> does not support queueing of data in any way. The reason
		2947	is that the author does not know of a simple (or any) algorithm for a
		2948	multiple-writer-single-reader queue that works in all cases and doesn't
		2949	need elaborate support such as pthreads.
		2950
		2951	That means that if you want to queue data, you have to provide your own
		2952	queue. But at least I can tell you how to implement locking around your
		2953	queue:
		2954
		2955	=over 4
		2956
		2957	=item queueing from a signal handler context
		2958
		2959	To implement race-free queueing, you simply add to the queue in the signal
		2960	handler but you block the signal handler in the watcher callback. Here is
		2961	an example that does that for some fictitious SIGUSR1 handler:
		2962
		2963	static ev_async mysig;
		2964
		2965	static void
		2966	sigusr1_handler (void)
		2967	{
		2968	sometype data;
		2969
		2970	// no locking etc.
		2971	queue_put (data);
		2972	ev_async_send (EV_DEFAULT_ &mysig);
		2973	}
		2974
		2975	static void
		2976	mysig_cb (EV_P_ ev_async *w, int revents)
		2977	{
		2978	sometype data;
		2979	sigset_t block, prev;
		2980
		2981	sigemptyset (&block);
		2982	sigaddset (&block, SIGUSR1);
		2983	sigprocmask (SIG_BLOCK, &block, &prev);
		2984
		2985	while (queue_get (&data))
		2986	process (data);
		2987
		2988	if (sigismember (&prev, SIGUSR1)
		2989	sigprocmask (SIG_UNBLOCK, &block, 0);
		2990	}
		2991
		2992	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2993	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2994	either...).
		2995
		2996	=item queueing from a thread context
		2997
		2998	The strategy for threads is different, as you cannot (easily) block
		2999	threads but you can easily preempt them, so to queue safely you need to
		3000	employ a traditional mutex lock, such as in this pthread example:
		3001
		3002	static ev_async mysig;
		3003	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3004
		3005	static void
		3006	otherthread (void)
		3007	{
		3008	// only need to lock the actual queueing operation
		3009	pthread_mutex_lock (&mymutex);
		3010	queue_put (data);
		3011	pthread_mutex_unlock (&mymutex);
		3012
		3013	ev_async_send (EV_DEFAULT_ &mysig);
		3014	}
		3015
		3016	static void
		3017	mysig_cb (EV_P_ ev_async *w, int revents)
		3018	{
		3019	pthread_mutex_lock (&mymutex);
		3020
		3021	while (queue_get (&data))
		3022	process (data);
		3023
		3024	pthread_mutex_unlock (&mymutex);
		3025	}
		3026
		3027	=back
		3028
		3029
		3030	=head3 Watcher-Specific Functions and Data Members
		3031
		3032	=over 4
		3033
		3034	=item ev_async_init (ev_async *, callback)
		3035
		3036	Initialises and configures the async watcher - it has no parameters of any
		3037	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3038	trust me.
		3039
		3040	=item ev_async_send (loop, ev_async *)
		3041
		3042	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3043	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3044	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3045	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3046	section below on what exactly this means).
		3047
		3048	Note that, as with other watchers in libev, multiple events might get
		3049	compressed into a single callback invocation (another way to look at this
		3050	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3051	reset when the event loop detects that).
		3052
		3053	This call incurs the overhead of a system call only once per event loop
		3054	iteration, so while the overhead might be noticeable, it doesn't apply to
		3055	repeated calls to C<ev_async_send> for the same event loop.
		3056
		3057	=item bool = ev_async_pending (ev_async *)
		3058
		3059	Returns a non-zero value when C<ev_async_send> has been called on the
		3060	watcher but the event has not yet been processed (or even noted) by the
		3061	event loop.
		3062
		3063	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3064	the loop iterates next and checks for the watcher to have become active,
		3065	it will reset the flag again. C<ev_async_pending> can be used to very
		3066	quickly check whether invoking the loop might be a good idea.
		3067
		3068	Not that this does I<not> check whether the watcher itself is pending,
		3069	only whether it has been requested to make this watcher pending: there
		3070	is a time window between the event loop checking and resetting the async
		3071	notification, and the callback being invoked.
		3072
		3073	=back
		3074
		3075
1655	=head1 OTHER FUNCTIONS	3076	=head1 OTHER FUNCTIONS
1656		3077
1657	There are some other functions of possible interest. Described. Here. Now.	3078	There are some other functions of possible interest. Described. Here. Now.
1658		3079
1659	=over 4	3080	=over 4
1660		3081
1661	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3082	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1662		3083
1663	This function combines a simple timer and an I/O watcher, calls your	3084	This function combines a simple timer and an I/O watcher, calls your
1664	callback on whichever event happens first and automatically stop both	3085	callback on whichever event happens first and automatically stops both
1665	watchers. This is useful if you want to wait for a single event on an fd	3086	watchers. This is useful if you want to wait for a single event on an fd
1666	or timeout without having to allocate/configure/start/stop/free one or	3087	or timeout without having to allocate/configure/start/stop/free one or
1667	more watchers yourself.	3088	more watchers yourself.
1668		3089
1669	If C<fd> is less than 0, then no I/O watcher will be started and events	3090	If C<fd> is less than 0, then no I/O watcher will be started and the
1670	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3091	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1671	C<events> set will be craeted and started.	3092	the given C<fd> and C<events> set will be created and started.
1672		3093
1673	If C<timeout> is less than 0, then no timeout watcher will be	3094	If C<timeout> is less than 0, then no timeout watcher will be
1674	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3095	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1675	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3096	repeat = 0) will be started. C<0> is a valid timeout.
1676	dubious value.
1677		3097
1678	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3098	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1679	passed an C<revents> set like normal event callbacks (a combination of	3099	passed an C<revents> set like normal event callbacks (a combination of
1680	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3100	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1681	value passed to C<ev_once>:	3101	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3102	a timeout and an io event at the same time - you probably should give io
		3103	events precedence.
1682		3104
		3105	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3106
1683	static void stdin_ready (int revents, void *arg)	3107	static void stdin_ready (int revents, void *arg)
1684	{	3108	{
1685	if (revents & EV_TIMEOUT)
1686	/* doh, nothing entered */;
1687	else if (revents & EV_READ)	3109	if (revents & EV_READ)
1688	/* stdin might have data for us, joy! */;	3110	/* stdin might have data for us, joy! */;
		3111	else if (revents & EV_TIMEOUT)
		3112	/* doh, nothing entered */;
1689	}	3113	}
1690		3114
1691	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3115	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1692		3116
1693	=item ev_feed_event (ev_loop *, watcher *, int revents)	3117	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1694		3118
1695	Feeds the given event set into the event loop, as if the specified event	3119	Feeds the given event set into the event loop, as if the specified event
1696	had happened for the specified watcher (which must be a pointer to an	3120	had happened for the specified watcher (which must be a pointer to an
1697	initialised but not necessarily started event watcher).	3121	initialised but not necessarily started event watcher).
1698		3122
1699	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3123	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1700		3124
1701	Feed an event on the given fd, as if a file descriptor backend detected	3125	Feed an event on the given fd, as if a file descriptor backend detected
1702	the given events it.	3126	the given events it.
1703		3127
1704	=item ev_feed_signal_event (ev_loop *loop, int signum)	3128	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1705		3129
1706	Feed an event as if the given signal occured (C<loop> must be the default	3130	Feed an event as if the given signal occurred (C<loop> must be the default
1707	loop!).	3131	loop!).
1708		3132
1709	=back	3133	=back
1710		3134
1711		3135
…		…
1727		3151
1728	=item * Priorities are not currently supported. Initialising priorities	3152	=item * Priorities are not currently supported. Initialising priorities
1729	will fail and all watchers will have the same priority, even though there	3153	will fail and all watchers will have the same priority, even though there
1730	is an ev_pri field.	3154	is an ev_pri field.
1731		3155
		3156	=item * In libevent, the last base created gets the signals, in libev, the
		3157	first base created (== the default loop) gets the signals.
		3158
1732	=item * Other members are not supported.	3159	=item * Other members are not supported.
1733		3160
1734	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3161	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1735	to use the libev header file and library.	3162	to use the libev header file and library.
1736		3163
1737	=back	3164	=back
1738		3165
1739	=head1 C++ SUPPORT	3166	=head1 C++ SUPPORT
1740		3167
1741	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3168	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1742	you to use some convinience methods to start/stop watchers and also change	3169	you to use some convenience methods to start/stop watchers and also change
1743	the callback model to a model using method callbacks on objects.	3170	the callback model to a model using method callbacks on objects.
1744		3171
1745	To use it,	3172	To use it,
1746		3173
1747	#include <ev++.h>	3174	#include <ev++.h>
1748		3175
1749	This automatically includes F<ev.h> and puts all of its definitions (many	3176	This automatically includes F<ev.h> and puts all of its definitions (many
1750	of them macros) into the global namespace. All C++ specific things are	3177	of them macros) into the global namespace. All C++ specific things are
1751	put into the C<ev> namespace. It should support all the same embedding	3178	put into the C<ev> namespace. It should support all the same embedding
1752	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3179	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1753		3180
1754	Care has been taken to keep the overhead low. The only data member added	3181	Care has been taken to keep the overhead low. The only data member the C++
1755	to the C-style watchers is the event loop the watcher is associated with	3182	classes add (compared to plain C-style watchers) is the event loop pointer
1756	(or no additional members at all if you disable C<EV_MULTIPLICITY> when	3183	that the watcher is associated with (or no additional members at all if
1757	embedding libev).	3184	you disable C<EV_MULTIPLICITY> when embedding libev).
1758		3185
1759	Currently, functions and static and non-static member functions can be	3186	Currently, functions, and static and non-static member functions can be
1760	used as callbacks. Other types should be easy to add as long as they only	3187	used as callbacks. Other types should be easy to add as long as they only
1761	need one additional pointer for context. If you need support for other	3188	need one additional pointer for context. If you need support for other
1762	types of functors please contact the author (preferably after implementing	3189	types of functors please contact the author (preferably after implementing
1763	it).	3190	it).
1764		3191
…		…
1819	your compiler is good :), then the method will be fully inlined into the	3246	your compiler is good :), then the method will be fully inlined into the
1820	thunking function, making it as fast as a direct C callback.	3247	thunking function, making it as fast as a direct C callback.
1821		3248
1822	Example: simple class declaration and watcher initialisation	3249	Example: simple class declaration and watcher initialisation
1823		3250
1824	struct myclass	3251	struct myclass
1825	{	3252	{
1826	void io_cb (ev::io &w, int revents) { }	3253	void io_cb (ev::io &w, int revents) { }
1827	}	3254	}
1828		3255
1829	myclass obj;	3256	myclass obj;
1830	ev::io iow;	3257	ev::io iow;
1831	iow.set <myclass, &myclass::io_cb> (&obj);	3258	iow.set <myclass, &myclass::io_cb> (&obj);
1832		3259
1833	=item w->set (void (*function)(watcher &w, int), void *data = 0)	3260	=item w->set (object *)
		3261
		3262	This is an B<experimental> feature that might go away in a future version.
		3263
		3264	This is a variation of a method callback - leaving out the method to call
		3265	will default the method to C<operator ()>, which makes it possible to use
		3266	functor objects without having to manually specify the C<operator ()> all
		3267	the time. Incidentally, you can then also leave out the template argument
		3268	list.
		3269
		3270	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3271	int revents)>.
		3272
		3273	See the method-C<set> above for more details.
		3274
		3275	Example: use a functor object as callback.
		3276
		3277	struct myfunctor
		3278	{
		3279	void operator() (ev::io &w, int revents)
		3280	{
		3281	...
		3282	}
		3283	}
		3284
		3285	myfunctor f;
		3286
		3287	ev::io w;
		3288	w.set (&f);
		3289
		3290	=item w->set<function> (void *data = 0)
1834		3291
1835	Also sets a callback, but uses a static method or plain function as	3292	Also sets a callback, but uses a static method or plain function as
1836	callback. The optional C<data> argument will be stored in the watcher's	3293	callback. The optional C<data> argument will be stored in the watcher's
1837	C<data> member and is free for you to use.	3294	C<data> member and is free for you to use.
1838		3295
		3296	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3297
1839	See the method-C<set> above for more details.	3298	See the method-C<set> above for more details.
		3299
		3300	Example: Use a plain function as callback.
		3301
		3302	static void io_cb (ev::io &w, int revents) { }
		3303	iow.set <io_cb> ();
1840		3304
1841	=item w->set (struct ev_loop *)	3305	=item w->set (struct ev_loop *)
1842		3306
1843	Associates a different C<struct ev_loop> with this watcher. You can only	3307	Associates a different C<struct ev_loop> with this watcher. You can only
1844	do this when the watcher is inactive (and not pending either).	3308	do this when the watcher is inactive (and not pending either).
1845		3309
1846	=item w->set ([args])	3310	=item w->set ([arguments])
1847		3311
1848	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3312	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1849	called at least once. Unlike the C counterpart, an active watcher gets	3313	called at least once. Unlike the C counterpart, an active watcher gets
1850	automatically stopped and restarted when reconfiguring it with this	3314	automatically stopped and restarted when reconfiguring it with this
1851	method.	3315	method.
1852		3316
1853	=item w->start ()	3317	=item w->start ()
…		…
1857		3321
1858	=item w->stop ()	3322	=item w->stop ()
1859		3323
1860	Stops the watcher if it is active. Again, no C<loop> argument.	3324	Stops the watcher if it is active. Again, no C<loop> argument.
1861		3325
1862	=item w->again () C<ev::timer>, C<ev::periodic> only	3326	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1863		3327
1864	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3328	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1865	C<ev_TYPE_again> function.	3329	C<ev_TYPE_again> function.
1866		3330
1867	=item w->sweep () C<ev::embed> only	3331	=item w->sweep () (C<ev::embed> only)
1868		3332
1869	Invokes C<ev_embed_sweep>.	3333	Invokes C<ev_embed_sweep>.
1870		3334
1871	=item w->update () C<ev::stat> only	3335	=item w->update () (C<ev::stat> only)
1872		3336
1873	Invokes C<ev_stat_stat>.	3337	Invokes C<ev_stat_stat>.
1874		3338
1875	=back	3339	=back
1876		3340
1877	=back	3341	=back
1878		3342
1879	Example: Define a class with an IO and idle watcher, start one of them in	3343	Example: Define a class with an IO and idle watcher, start one of them in
1880	the constructor.	3344	the constructor.
1881		3345
1882	class myclass	3346	class myclass
1883	{	3347	{
1884	ev_io io; void io_cb (ev::io &w, int revents);	3348	ev::io io ; void io_cb (ev::io &w, int revents);
1885	ev_idle idle void idle_cb (ev::idle &w, int revents);	3349	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1886		3350
1887	myclass ();	3351	myclass (int fd)
1888	}	3352	{
1889
1890	myclass::myclass (int fd)
1891	{
1892	io .set <myclass, &myclass::io_cb > (this);	3353	io .set <myclass, &myclass::io_cb > (this);
1893	idle.set <myclass, &myclass::idle_cb> (this);	3354	idle.set <myclass, &myclass::idle_cb> (this);
1894		3355
1895	io.start (fd, ev::READ);	3356	io.start (fd, ev::READ);
		3357	}
1896	}	3358	};
		3359
		3360
		3361	=head1 OTHER LANGUAGE BINDINGS
		3362
		3363	Libev does not offer other language bindings itself, but bindings for a
		3364	number of languages exist in the form of third-party packages. If you know
		3365	any interesting language binding in addition to the ones listed here, drop
		3366	me a note.
		3367
		3368	=over 4
		3369
		3370	=item Perl
		3371
		3372	The EV module implements the full libev API and is actually used to test
		3373	libev. EV is developed together with libev. Apart from the EV core module,
		3374	there are additional modules that implement libev-compatible interfaces
		3375	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3376	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3377	and C<EV::Glib>).
		3378
		3379	It can be found and installed via CPAN, its homepage is at
		3380	L<http://software.schmorp.de/pkg/EV>.
		3381
		3382	=item Python
		3383
		3384	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3385	seems to be quite complete and well-documented.
		3386
		3387	=item Ruby
		3388
		3389	Tony Arcieri has written a ruby extension that offers access to a subset
		3390	of the libev API and adds file handle abstractions, asynchronous DNS and
		3391	more on top of it. It can be found via gem servers. Its homepage is at
		3392	L<http://rev.rubyforge.org/>.
		3393
		3394	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3395	makes rev work even on mingw.
		3396
		3397	=item Haskell
		3398
		3399	A haskell binding to libev is available at
		3400	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3401
		3402	=item D
		3403
		3404	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3405	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3406
		3407	=item Ocaml
		3408
		3409	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3410	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3411
		3412	=item Lua
		3413
		3414	Brian Maher has written a partial interface to libev
		3415	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3416	L<http://github.com/brimworks/lua-ev>.
		3417
		3418	=back
1897		3419
1898		3420
1899	=head1 MACRO MAGIC	3421	=head1 MACRO MAGIC
1900		3422
1901	Libev can be compiled with a variety of options, the most fundemantal is	3423	Libev can be compiled with a variety of options, the most fundamental
1902	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3424	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1903	callbacks have an initial C<struct ev_loop *> argument.	3425	functions and callbacks have an initial C<struct ev_loop *> argument.
1904		3426
1905	To make it easier to write programs that cope with either variant, the	3427	To make it easier to write programs that cope with either variant, the
1906	following macros are defined:	3428	following macros are defined:
1907		3429
1908	=over 4	3430	=over 4
…		…
1911		3433
1912	This provides the loop I<argument> for functions, if one is required ("ev	3434	This provides the loop I<argument> for functions, if one is required ("ev
1913	loop argument"). The C<EV_A> form is used when this is the sole argument,	3435	loop argument"). The C<EV_A> form is used when this is the sole argument,
1914	C<EV_A_> is used when other arguments are following. Example:	3436	C<EV_A_> is used when other arguments are following. Example:
1915		3437
1916	ev_unref (EV_A);	3438	ev_unref (EV_A);
1917	ev_timer_add (EV_A_ watcher);	3439	ev_timer_add (EV_A_ watcher);
1918	ev_loop (EV_A_ 0);	3440	ev_loop (EV_A_ 0);
1919		3441
1920	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3442	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1921	which is often provided by the following macro.	3443	which is often provided by the following macro.
1922		3444
1923	=item C<EV_P>, C<EV_P_>	3445	=item C<EV_P>, C<EV_P_>
1924		3446
1925	This provides the loop I<parameter> for functions, if one is required ("ev	3447	This provides the loop I<parameter> for functions, if one is required ("ev
1926	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3448	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1927	C<EV_P_> is used when other parameters are following. Example:	3449	C<EV_P_> is used when other parameters are following. Example:
1928		3450
1929	// this is how ev_unref is being declared	3451	// this is how ev_unref is being declared
1930	static void ev_unref (EV_P);	3452	static void ev_unref (EV_P);
1931		3453
1932	// this is how you can declare your typical callback	3454	// this is how you can declare your typical callback
1933	static void cb (EV_P_ ev_timer *w, int revents)	3455	static void cb (EV_P_ ev_timer *w, int revents)
1934		3456
1935	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3457	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1936	suitable for use with C<EV_A>.	3458	suitable for use with C<EV_A>.
1937		3459
1938	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3460	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1939		3461
1940	Similar to the other two macros, this gives you the value of the default	3462	Similar to the other two macros, this gives you the value of the default
1941	loop, if multiple loops are supported ("ev loop default").	3463	loop, if multiple loops are supported ("ev loop default").
		3464
		3465	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3466
		3467	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3468	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3469	is undefined when the default loop has not been initialised by a previous
		3470	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3471
		3472	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3473	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1942		3474
1943	=back	3475	=back
1944		3476
1945	Example: Declare and initialise a check watcher, utilising the above	3477	Example: Declare and initialise a check watcher, utilising the above
1946	macros so it will work regardless of whether multiple loops are supported	3478	macros so it will work regardless of whether multiple loops are supported
1947	or not.	3479	or not.
1948		3480
1949	static void	3481	static void
1950	check_cb (EV_P_ ev_timer *w, int revents)	3482	check_cb (EV_P_ ev_timer *w, int revents)
1951	{	3483	{
1952	ev_check_stop (EV_A_ w);	3484	ev_check_stop (EV_A_ w);
1953	}	3485	}
1954		3486
1955	ev_check check;	3487	ev_check check;
1956	ev_check_init (&check, check_cb);	3488	ev_check_init (&check, check_cb);
1957	ev_check_start (EV_DEFAULT_ &check);	3489	ev_check_start (EV_DEFAULT_ &check);
1958	ev_loop (EV_DEFAULT_ 0);	3490	ev_loop (EV_DEFAULT_ 0);
1959		3491
1960	=head1 EMBEDDING	3492	=head1 EMBEDDING
1961		3493
1962	Libev can (and often is) directly embedded into host	3494	Libev can (and often is) directly embedded into host
1963	applications. Examples of applications that embed it include the Deliantra	3495	applications. Examples of applications that embed it include the Deliantra
1964	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3496	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1965	and rxvt-unicode.	3497	and rxvt-unicode.
1966		3498
1967	The goal is to enable you to just copy the neecssary files into your	3499	The goal is to enable you to just copy the necessary files into your
1968	source directory without having to change even a single line in them, so	3500	source directory without having to change even a single line in them, so
1969	you can easily upgrade by simply copying (or having a checked-out copy of	3501	you can easily upgrade by simply copying (or having a checked-out copy of
1970	libev somewhere in your source tree).	3502	libev somewhere in your source tree).
1971		3503
1972	=head2 FILESETS	3504	=head2 FILESETS
1973		3505
1974	Depending on what features you need you need to include one or more sets of files	3506	Depending on what features you need you need to include one or more sets of files
1975	in your app.	3507	in your application.
1976		3508
1977	=head3 CORE EVENT LOOP	3509	=head3 CORE EVENT LOOP
1978		3510
1979	To include only the libev core (all the C<ev_*> functions), with manual	3511	To include only the libev core (all the C<ev_*> functions), with manual
1980	configuration (no autoconf):	3512	configuration (no autoconf):
1981		3513
1982	#define EV_STANDALONE 1	3514	#define EV_STANDALONE 1
1983	#include "ev.c"	3515	#include "ev.c"
1984		3516
1985	This will automatically include F<ev.h>, too, and should be done in a	3517	This will automatically include F<ev.h>, too, and should be done in a
1986	single C source file only to provide the function implementations. To use	3518	single C source file only to provide the function implementations. To use
1987	it, do the same for F<ev.h> in all files wishing to use this API (best	3519	it, do the same for F<ev.h> in all files wishing to use this API (best
1988	done by writing a wrapper around F<ev.h> that you can include instead and	3520	done by writing a wrapper around F<ev.h> that you can include instead and
1989	where you can put other configuration options):	3521	where you can put other configuration options):
1990		3522
1991	#define EV_STANDALONE 1	3523	#define EV_STANDALONE 1
1992	#include "ev.h"	3524	#include "ev.h"
1993		3525
1994	Both header files and implementation files can be compiled with a C++	3526	Both header files and implementation files can be compiled with a C++
1995	compiler (at least, thats a stated goal, and breakage will be treated	3527	compiler (at least, that's a stated goal, and breakage will be treated
1996	as a bug).	3528	as a bug).
1997		3529
1998	You need the following files in your source tree, or in a directory	3530	You need the following files in your source tree, or in a directory
1999	in your include path (e.g. in libev/ when using -Ilibev):	3531	in your include path (e.g. in libev/ when using -Ilibev):
2000		3532
2001	ev.h	3533	ev.h
2002	ev.c	3534	ev.c
2003	ev_vars.h	3535	ev_vars.h
2004	ev_wrap.h	3536	ev_wrap.h
2005		3537
2006	ev_win32.c required on win32 platforms only	3538	ev_win32.c required on win32 platforms only
2007		3539
2008	ev_select.c only when select backend is enabled (which is enabled by default)	3540	ev_select.c only when select backend is enabled (which is enabled by default)
2009	ev_poll.c only when poll backend is enabled (disabled by default)	3541	ev_poll.c only when poll backend is enabled (disabled by default)
2010	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3542	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2011	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3543	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2012	ev_port.c only when the solaris port backend is enabled (disabled by default)	3544	ev_port.c only when the solaris port backend is enabled (disabled by default)
2013		3545
2014	F<ev.c> includes the backend files directly when enabled, so you only need	3546	F<ev.c> includes the backend files directly when enabled, so you only need
2015	to compile this single file.	3547	to compile this single file.
2016		3548
2017	=head3 LIBEVENT COMPATIBILITY API	3549	=head3 LIBEVENT COMPATIBILITY API
2018		3550
2019	To include the libevent compatibility API, also include:	3551	To include the libevent compatibility API, also include:
2020		3552
2021	#include "event.c"	3553	#include "event.c"
2022		3554
2023	in the file including F<ev.c>, and:	3555	in the file including F<ev.c>, and:
2024		3556
2025	#include "event.h"	3557	#include "event.h"
2026		3558
2027	in the files that want to use the libevent API. This also includes F<ev.h>.	3559	in the files that want to use the libevent API. This also includes F<ev.h>.
2028		3560
2029	You need the following additional files for this:	3561	You need the following additional files for this:
2030		3562
2031	event.h	3563	event.h
2032	event.c	3564	event.c
2033		3565
2034	=head3 AUTOCONF SUPPORT	3566	=head3 AUTOCONF SUPPORT
2035		3567
2036	Instead of using C<EV_STANDALONE=1> and providing your config in	3568	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2037	whatever way you want, you can also C<m4_include([libev.m4])> in your	3569	whatever way you want, you can also C<m4_include([libev.m4])> in your
2038	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3570	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2039	include F<config.h> and configure itself accordingly.	3571	include F<config.h> and configure itself accordingly.
2040		3572
2041	For this of course you need the m4 file:	3573	For this of course you need the m4 file:
2042		3574
2043	libev.m4	3575	libev.m4
2044		3576
2045	=head2 PREPROCESSOR SYMBOLS/MACROS	3577	=head2 PREPROCESSOR SYMBOLS/MACROS
2046		3578
2047	Libev can be configured via a variety of preprocessor symbols you have to define	3579	Libev can be configured via a variety of preprocessor symbols you have to
2048	before including any of its files. The default is not to build for multiplicity	3580	define before including any of its files. The default in the absence of
2049	and only include the select backend.	3581	autoconf is documented for every option.
2050		3582
2051	=over 4	3583	=over 4
2052		3584
2053	=item EV_STANDALONE	3585	=item EV_STANDALONE
2054		3586
…		…
2056	keeps libev from including F<config.h>, and it also defines dummy	3588	keeps libev from including F<config.h>, and it also defines dummy
2057	implementations for some libevent functions (such as logging, which is not	3589	implementations for some libevent functions (such as logging, which is not
2058	supported). It will also not define any of the structs usually found in	3590	supported). It will also not define any of the structs usually found in
2059	F<event.h> that are not directly supported by the libev core alone.	3591	F<event.h> that are not directly supported by the libev core alone.
2060		3592
		3593	In standalone mode, libev will still try to automatically deduce the
		3594	configuration, but has to be more conservative.
		3595
2061	=item EV_USE_MONOTONIC	3596	=item EV_USE_MONOTONIC
2062		3597
2063	If defined to be C<1>, libev will try to detect the availability of the	3598	If defined to be C<1>, libev will try to detect the availability of the
2064	monotonic clock option at both compiletime and runtime. Otherwise no use	3599	monotonic clock option at both compile time and runtime. Otherwise no
2065	of the monotonic clock option will be attempted. If you enable this, you	3600	use of the monotonic clock option will be attempted. If you enable this,
2066	usually have to link against librt or something similar. Enabling it when	3601	you usually have to link against librt or something similar. Enabling it
2067	the functionality isn't available is safe, though, althoguh you have	3602	when the functionality isn't available is safe, though, although you have
2068	to make sure you link against any libraries where the C<clock_gettime>	3603	to make sure you link against any libraries where the C<clock_gettime>
2069	function is hiding in (often F<-lrt>).	3604	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2070		3605
2071	=item EV_USE_REALTIME	3606	=item EV_USE_REALTIME
2072		3607
2073	If defined to be C<1>, libev will try to detect the availability of the	3608	If defined to be C<1>, libev will try to detect the availability of the
2074	realtime clock option at compiletime (and assume its availability at	3609	real-time clock option at compile time (and assume its availability
2075	runtime if successful). Otherwise no use of the realtime clock option will	3610	at runtime if successful). Otherwise no use of the real-time clock
2076	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3611	option will be attempted. This effectively replaces C<gettimeofday>
2077	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3612	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2078	in the description of C<EV_USE_MONOTONIC>, though.	3613	correctness. See the note about libraries in the description of
		3614	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3615	C<EV_USE_CLOCK_SYSCALL>.
		3616
		3617	=item EV_USE_CLOCK_SYSCALL
		3618
		3619	If defined to be C<1>, libev will try to use a direct syscall instead
		3620	of calling the system-provided C<clock_gettime> function. This option
		3621	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3622	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3623	programs needlessly. Using a direct syscall is slightly slower (in
		3624	theory), because no optimised vdso implementation can be used, but avoids
		3625	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3626	higher, as it simplifies linking (no need for C<-lrt>).
		3627
		3628	=item EV_USE_NANOSLEEP
		3629
		3630	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3631	and will use it for delays. Otherwise it will use C<select ()>.
		3632
		3633	=item EV_USE_EVENTFD
		3634
		3635	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3636	available and will probe for kernel support at runtime. This will improve
		3637	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3638	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3639	2.7 or newer, otherwise disabled.
2079		3640
2080	=item EV_USE_SELECT	3641	=item EV_USE_SELECT
2081		3642
2082	If undefined or defined to be C<1>, libev will compile in support for the	3643	If undefined or defined to be C<1>, libev will compile in support for the
2083	C<select>(2) backend. No attempt at autodetection will be done: if no	3644	C<select>(2) backend. No attempt at auto-detection will be done: if no
2084	other method takes over, select will be it. Otherwise the select backend	3645	other method takes over, select will be it. Otherwise the select backend
2085	will not be compiled in.	3646	will not be compiled in.
2086		3647
2087	=item EV_SELECT_USE_FD_SET	3648	=item EV_SELECT_USE_FD_SET
2088		3649
2089	If defined to C<1>, then the select backend will use the system C<fd_set>	3650	If defined to C<1>, then the select backend will use the system C<fd_set>
2090	structure. This is useful if libev doesn't compile due to a missing	3651	structure. This is useful if libev doesn't compile due to a missing
2091	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3652	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2092	exotic systems. This usually limits the range of file descriptors to some	3653	on exotic systems. This usually limits the range of file descriptors to
2093	low limit such as 1024 or might have other limitations (winsocket only	3654	some low limit such as 1024 or might have other limitations (winsocket
2094	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3655	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2095	influence the size of the C<fd_set> used.	3656	configures the maximum size of the C<fd_set>.
2096		3657
2097	=item EV_SELECT_IS_WINSOCKET	3658	=item EV_SELECT_IS_WINSOCKET
2098		3659
2099	When defined to C<1>, the select backend will assume that	3660	When defined to C<1>, the select backend will assume that
2100	select/socket/connect etc. don't understand file descriptors but	3661	select/socket/connect etc. don't understand file descriptors but
…		…
2102	be used is the winsock select). This means that it will call	3663	be used is the winsock select). This means that it will call
2103	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3664	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2104	it is assumed that all these functions actually work on fds, even	3665	it is assumed that all these functions actually work on fds, even
2105	on win32. Should not be defined on non-win32 platforms.	3666	on win32. Should not be defined on non-win32 platforms.
2106		3667
		3668	=item EV_FD_TO_WIN32_HANDLE
		3669
		3670	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3671	file descriptors to socket handles. When not defining this symbol (the
		3672	default), then libev will call C<_get_osfhandle>, which is usually
		3673	correct. In some cases, programs use their own file descriptor management,
		3674	in which case they can provide this function to map fds to socket handles.
		3675
2107	=item EV_USE_POLL	3676	=item EV_USE_POLL
2108		3677
2109	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3678	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2110	backend. Otherwise it will be enabled on non-win32 platforms. It	3679	backend. Otherwise it will be enabled on non-win32 platforms. It
2111	takes precedence over select.	3680	takes precedence over select.
2112		3681
2113	=item EV_USE_EPOLL	3682	=item EV_USE_EPOLL
2114		3683
2115	If defined to be C<1>, libev will compile in support for the Linux	3684	If defined to be C<1>, libev will compile in support for the Linux
2116	C<epoll>(7) backend. Its availability will be detected at runtime,	3685	C<epoll>(7) backend. Its availability will be detected at runtime,
2117	otherwise another method will be used as fallback. This is the	3686	otherwise another method will be used as fallback. This is the preferred
2118	preferred backend for GNU/Linux systems.	3687	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3688	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2119		3689
2120	=item EV_USE_KQUEUE	3690	=item EV_USE_KQUEUE
2121		3691
2122	If defined to be C<1>, libev will compile in support for the BSD style	3692	If defined to be C<1>, libev will compile in support for the BSD style
2123	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3693	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2136	otherwise another method will be used as fallback. This is the preferred	3706	otherwise another method will be used as fallback. This is the preferred
2137	backend for Solaris 10 systems.	3707	backend for Solaris 10 systems.
2138		3708
2139	=item EV_USE_DEVPOLL	3709	=item EV_USE_DEVPOLL
2140		3710
2141	reserved for future expansion, works like the USE symbols above.	3711	Reserved for future expansion, works like the USE symbols above.
2142		3712
2143	=item EV_USE_INOTIFY	3713	=item EV_USE_INOTIFY
2144		3714
2145	If defined to be C<1>, libev will compile in support for the Linux inotify	3715	If defined to be C<1>, libev will compile in support for the Linux inotify
2146	interface to speed up C<ev_stat> watchers. Its actual availability will	3716	interface to speed up C<ev_stat> watchers. Its actual availability will
2147	be detected at runtime.	3717	be detected at runtime. If undefined, it will be enabled if the headers
		3718	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3719
		3720	=item EV_ATOMIC_T
		3721
		3722	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3723	access is atomic with respect to other threads or signal contexts. No such
		3724	type is easily found in the C language, so you can provide your own type
		3725	that you know is safe for your purposes. It is used both for signal handler "locking"
		3726	as well as for signal and thread safety in C<ev_async> watchers.
		3727
		3728	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3729	(from F<signal.h>), which is usually good enough on most platforms.
2148		3730
2149	=item EV_H	3731	=item EV_H
2150		3732
2151	The name of the F<ev.h> header file used to include it. The default if	3733	The name of the F<ev.h> header file used to include it. The default if
2152	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3734	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2153	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3735	used to virtually rename the F<ev.h> header file in case of conflicts.
2154		3736
2155	=item EV_CONFIG_H	3737	=item EV_CONFIG_H
2156		3738
2157	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3739	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2158	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3740	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2159	C<EV_H>, above.	3741	C<EV_H>, above.
2160		3742
2161	=item EV_EVENT_H	3743	=item EV_EVENT_H
2162		3744
2163	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3745	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2164	of how the F<event.h> header can be found.	3746	of how the F<event.h> header can be found, the default is C<"event.h">.
2165		3747
2166	=item EV_PROTOTYPES	3748	=item EV_PROTOTYPES
2167		3749
2168	If defined to be C<0>, then F<ev.h> will not define any function	3750	If defined to be C<0>, then F<ev.h> will not define any function
2169	prototypes, but still define all the structs and other symbols. This is	3751	prototypes, but still define all the structs and other symbols. This is
…		…
2190	When doing priority-based operations, libev usually has to linearly search	3772	When doing priority-based operations, libev usually has to linearly search
2191	all the priorities, so having many of them (hundreds) uses a lot of space	3773	all the priorities, so having many of them (hundreds) uses a lot of space
2192	and time, so using the defaults of five priorities (-2 .. +2) is usually	3774	and time, so using the defaults of five priorities (-2 .. +2) is usually
2193	fine.	3775	fine.
2194		3776
2195	If your embedding app does not need any priorities, defining these both to	3777	If your embedding application does not need any priorities, defining these
2196	C<0> will save some memory and cpu.	3778	both to C<0> will save some memory and CPU.
2197		3779
2198	=item EV_PERIODIC_ENABLE	3780	=item EV_PERIODIC_ENABLE
2199		3781
2200	If undefined or defined to be C<1>, then periodic timers are supported. If	3782	If undefined or defined to be C<1>, then periodic timers are supported. If
2201	defined to be C<0>, then they are not. Disabling them saves a few kB of	3783	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2208	code.	3790	code.
2209		3791
2210	=item EV_EMBED_ENABLE	3792	=item EV_EMBED_ENABLE
2211		3793
2212	If undefined or defined to be C<1>, then embed watchers are supported. If	3794	If undefined or defined to be C<1>, then embed watchers are supported. If
2213	defined to be C<0>, then they are not.	3795	defined to be C<0>, then they are not. Embed watchers rely on most other
		3796	watcher types, which therefore must not be disabled.
2214		3797
2215	=item EV_STAT_ENABLE	3798	=item EV_STAT_ENABLE
2216		3799
2217	If undefined or defined to be C<1>, then stat watchers are supported. If	3800	If undefined or defined to be C<1>, then stat watchers are supported. If
2218	defined to be C<0>, then they are not.	3801	defined to be C<0>, then they are not.
…		…
2220	=item EV_FORK_ENABLE	3803	=item EV_FORK_ENABLE
2221		3804
2222	If undefined or defined to be C<1>, then fork watchers are supported. If	3805	If undefined or defined to be C<1>, then fork watchers are supported. If
2223	defined to be C<0>, then they are not.	3806	defined to be C<0>, then they are not.
2224		3807
		3808	=item EV_ASYNC_ENABLE
		3809
		3810	If undefined or defined to be C<1>, then async watchers are supported. If
		3811	defined to be C<0>, then they are not.
		3812
2225	=item EV_MINIMAL	3813	=item EV_MINIMAL
2226		3814
2227	If you need to shave off some kilobytes of code at the expense of some	3815	If you need to shave off some kilobytes of code at the expense of some
2228	speed, define this symbol to C<1>. Currently only used for gcc to override	3816	speed (but with the full API), define this symbol to C<1>. Currently this
2229	some inlining decisions, saves roughly 30% codesize of amd64.	3817	is used to override some inlining decisions, saves roughly 30% code size
		3818	on amd64. It also selects a much smaller 2-heap for timer management over
		3819	the default 4-heap.
		3820
		3821	You can save even more by disabling watcher types you do not need
		3822	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3823	(C<-DNDEBUG>) will usually reduce code size a lot.
		3824
		3825	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3826	provide a bare-bones event library. See C<ev.h> for details on what parts
		3827	of the API are still available, and do not complain if this subset changes
		3828	over time.
		3829
		3830	=item EV_NSIG
		3831
		3832	The highest supported signal number, +1 (or, the number of
		3833	signals): Normally, libev tries to deduce the maximum number of signals
		3834	automatically, but sometimes this fails, in which case it can be
		3835	specified. Also, using a lower number than detected (C<32> should be
		3836	good for about any system in existance) can save some memory, as libev
		3837	statically allocates some 12-24 bytes per signal number.
2230		3838
2231	=item EV_PID_HASHSIZE	3839	=item EV_PID_HASHSIZE
2232		3840
2233	C<ev_child> watchers use a small hash table to distribute workload by	3841	C<ev_child> watchers use a small hash table to distribute workload by
2234	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3842	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2235	than enough. If you need to manage thousands of children you might want to	3843	than enough. If you need to manage thousands of children you might want to
2236	increase this value (I<must> be a power of two).	3844	increase this value (I<must> be a power of two).
2237		3845
2238	=item EV_INOTIFY_HASHSIZE	3846	=item EV_INOTIFY_HASHSIZE
2239		3847
2240	C<ev_staz> watchers use a small hash table to distribute workload by	3848	C<ev_stat> watchers use a small hash table to distribute workload by
2241	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3849	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2242	usually more than enough. If you need to manage thousands of C<ev_stat>	3850	usually more than enough. If you need to manage thousands of C<ev_stat>
2243	watchers you might want to increase this value (I<must> be a power of	3851	watchers you might want to increase this value (I<must> be a power of
2244	two).	3852	two).
2245		3853
		3854	=item EV_USE_4HEAP
		3855
		3856	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3857	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3858	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3859	faster performance with many (thousands) of watchers.
		3860
		3861	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3862	(disabled).
		3863
		3864	=item EV_HEAP_CACHE_AT
		3865
		3866	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3867	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3868	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3869	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3870	but avoids random read accesses on heap changes. This improves performance
		3871	noticeably with many (hundreds) of watchers.
		3872
		3873	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3874	(disabled).
		3875
		3876	=item EV_VERIFY
		3877
		3878	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3879	be done: If set to C<0>, no internal verification code will be compiled
		3880	in. If set to C<1>, then verification code will be compiled in, but not
		3881	called. If set to C<2>, then the internal verification code will be
		3882	called once per loop, which can slow down libev. If set to C<3>, then the
		3883	verification code will be called very frequently, which will slow down
		3884	libev considerably.
		3885
		3886	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3887	C<0>.
		3888
2246	=item EV_COMMON	3889	=item EV_COMMON
2247		3890
2248	By default, all watchers have a C<void *data> member. By redefining	3891	By default, all watchers have a C<void *data> member. By redefining
2249	this macro to a something else you can include more and other types of	3892	this macro to a something else you can include more and other types of
2250	members. You have to define it each time you include one of the files,	3893	members. You have to define it each time you include one of the files,
2251	though, and it must be identical each time.	3894	though, and it must be identical each time.
2252		3895
2253	For example, the perl EV module uses something like this:	3896	For example, the perl EV module uses something like this:
2254		3897
2255	#define EV_COMMON \	3898	#define EV_COMMON \
2256	SV *self; /* contains this struct */ \	3899	SV *self; /* contains this struct */ \
2257	SV *cb_sv, *fh /* note no trailing ";" */	3900	SV *cb_sv, *fh /* note no trailing ";" */
2258		3901
2259	=item EV_CB_DECLARE (type)	3902	=item EV_CB_DECLARE (type)
2260		3903
2261	=item EV_CB_INVOKE (watcher, revents)	3904	=item EV_CB_INVOKE (watcher, revents)
2262		3905
2263	=item ev_set_cb (ev, cb)	3906	=item ev_set_cb (ev, cb)
2264		3907
2265	Can be used to change the callback member declaration in each watcher,	3908	Can be used to change the callback member declaration in each watcher,
2266	and the way callbacks are invoked and set. Must expand to a struct member	3909	and the way callbacks are invoked and set. Must expand to a struct member
2267	definition and a statement, respectively. See the F<ev.v> header file for	3910	definition and a statement, respectively. See the F<ev.h> header file for
2268	their default definitions. One possible use for overriding these is to	3911	their default definitions. One possible use for overriding these is to
2269	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3912	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2270	method calls instead of plain function calls in C++.	3913	method calls instead of plain function calls in C++.
		3914
		3915	=back
		3916
		3917	=head2 EXPORTED API SYMBOLS
		3918
		3919	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3920	exported symbols, you can use the provided F<Symbol.*> files which list
		3921	all public symbols, one per line:
		3922
		3923	Symbols.ev for libev proper
		3924	Symbols.event for the libevent emulation
		3925
		3926	This can also be used to rename all public symbols to avoid clashes with
		3927	multiple versions of libev linked together (which is obviously bad in
		3928	itself, but sometimes it is inconvenient to avoid this).
		3929
		3930	A sed command like this will create wrapper C<#define>'s that you need to
		3931	include before including F<ev.h>:
		3932
		3933	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3934
		3935	This would create a file F<wrap.h> which essentially looks like this:
		3936
		3937	#define ev_backend myprefix_ev_backend
		3938	#define ev_check_start myprefix_ev_check_start
		3939	#define ev_check_stop myprefix_ev_check_stop
		3940	...
2271		3941
2272	=head2 EXAMPLES	3942	=head2 EXAMPLES
2273		3943
2274	For a real-world example of a program the includes libev	3944	For a real-world example of a program the includes libev
2275	verbatim, you can have a look at the EV perl module	3945	verbatim, you can have a look at the EV perl module
…		…
2280	file.	3950	file.
2281		3951
2282	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3952	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2283	that everybody includes and which overrides some configure choices:	3953	that everybody includes and which overrides some configure choices:
2284		3954
2285	#define EV_MINIMAL 1	3955	#define EV_MINIMAL 1
2286	#define EV_USE_POLL 0	3956	#define EV_USE_POLL 0
2287	#define EV_MULTIPLICITY 0	3957	#define EV_MULTIPLICITY 0
2288	#define EV_PERIODIC_ENABLE 0	3958	#define EV_PERIODIC_ENABLE 0
2289	#define EV_STAT_ENABLE 0	3959	#define EV_STAT_ENABLE 0
2290	#define EV_FORK_ENABLE 0	3960	#define EV_FORK_ENABLE 0
2291	#define EV_CONFIG_H <config.h>	3961	#define EV_CONFIG_H <config.h>
2292	#define EV_MINPRI 0	3962	#define EV_MINPRI 0
2293	#define EV_MAXPRI 0	3963	#define EV_MAXPRI 0
2294		3964
2295	#include "ev++.h"	3965	#include "ev++.h"
2296		3966
2297	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3967	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2298		3968
2299	#include "ev_cpp.h"	3969	#include "ev_cpp.h"
2300	#include "ev.c"	3970	#include "ev.c"
2301		3971
		3972	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2302		3973
		3974	=head2 THREADS AND COROUTINES
		3975
		3976	=head3 THREADS
		3977
		3978	All libev functions are reentrant and thread-safe unless explicitly
		3979	documented otherwise, but libev implements no locking itself. This means
		3980	that you can use as many loops as you want in parallel, as long as there
		3981	are no concurrent calls into any libev function with the same loop
		3982	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3983	of course): libev guarantees that different event loops share no data
		3984	structures that need any locking.
		3985
		3986	Or to put it differently: calls with different loop parameters can be done
		3987	concurrently from multiple threads, calls with the same loop parameter
		3988	must be done serially (but can be done from different threads, as long as
		3989	only one thread ever is inside a call at any point in time, e.g. by using
		3990	a mutex per loop).
		3991
		3992	Specifically to support threads (and signal handlers), libev implements
		3993	so-called C<ev_async> watchers, which allow some limited form of
		3994	concurrency on the same event loop, namely waking it up "from the
		3995	outside".
		3996
		3997	If you want to know which design (one loop, locking, or multiple loops
		3998	without or something else still) is best for your problem, then I cannot
		3999	help you, but here is some generic advice:
		4000
		4001	=over 4
		4002
		4003	=item * most applications have a main thread: use the default libev loop
		4004	in that thread, or create a separate thread running only the default loop.
		4005
		4006	This helps integrating other libraries or software modules that use libev
		4007	themselves and don't care/know about threading.
		4008
		4009	=item * one loop per thread is usually a good model.
		4010
		4011	Doing this is almost never wrong, sometimes a better-performance model
		4012	exists, but it is always a good start.
		4013
		4014	=item * other models exist, such as the leader/follower pattern, where one
		4015	loop is handed through multiple threads in a kind of round-robin fashion.
		4016
		4017	Choosing a model is hard - look around, learn, know that usually you can do
		4018	better than you currently do :-)
		4019
		4020	=item * often you need to talk to some other thread which blocks in the
		4021	event loop.
		4022
		4023	C<ev_async> watchers can be used to wake them up from other threads safely
		4024	(or from signal contexts...).
		4025
		4026	An example use would be to communicate signals or other events that only
		4027	work in the default loop by registering the signal watcher with the
		4028	default loop and triggering an C<ev_async> watcher from the default loop
		4029	watcher callback into the event loop interested in the signal.
		4030
		4031	=back
		4032
		4033	=head4 THREAD LOCKING EXAMPLE
		4034
		4035	Here is a fictitious example of how to run an event loop in a different
		4036	thread than where callbacks are being invoked and watchers are
		4037	created/added/removed.
		4038
		4039	For a real-world example, see the C<EV::Loop::Async> perl module,
		4040	which uses exactly this technique (which is suited for many high-level
		4041	languages).
		4042
		4043	The example uses a pthread mutex to protect the loop data, a condition
		4044	variable to wait for callback invocations, an async watcher to notify the
		4045	event loop thread and an unspecified mechanism to wake up the main thread.
		4046
		4047	First, you need to associate some data with the event loop:
		4048
		4049	typedef struct {
		4050	mutex_t lock; /* global loop lock */
		4051	ev_async async_w;
		4052	thread_t tid;
		4053	cond_t invoke_cv;
		4054	} userdata;
		4055
		4056	void prepare_loop (EV_P)
		4057	{
		4058	// for simplicity, we use a static userdata struct.
		4059	static userdata u;
		4060
		4061	ev_async_init (&u->async_w, async_cb);
		4062	ev_async_start (EV_A_ &u->async_w);
		4063
		4064	pthread_mutex_init (&u->lock, 0);
		4065	pthread_cond_init (&u->invoke_cv, 0);
		4066
		4067	// now associate this with the loop
		4068	ev_set_userdata (EV_A_ u);
		4069	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4070	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4071
		4072	// then create the thread running ev_loop
		4073	pthread_create (&u->tid, 0, l_run, EV_A);
		4074	}
		4075
		4076	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4077	solely to wake up the event loop so it takes notice of any new watchers
		4078	that might have been added:
		4079
		4080	static void
		4081	async_cb (EV_P_ ev_async *w, int revents)
		4082	{
		4083	// just used for the side effects
		4084	}
		4085
		4086	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4087	protecting the loop data, respectively.
		4088
		4089	static void
		4090	l_release (EV_P)
		4091	{
		4092	userdata *u = ev_userdata (EV_A);
		4093	pthread_mutex_unlock (&u->lock);
		4094	}
		4095
		4096	static void
		4097	l_acquire (EV_P)
		4098	{
		4099	userdata *u = ev_userdata (EV_A);
		4100	pthread_mutex_lock (&u->lock);
		4101	}
		4102
		4103	The event loop thread first acquires the mutex, and then jumps straight
		4104	into C<ev_loop>:
		4105
		4106	void *
		4107	l_run (void *thr_arg)
		4108	{
		4109	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4110
		4111	l_acquire (EV_A);
		4112	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4113	ev_loop (EV_A_ 0);
		4114	l_release (EV_A);
		4115
		4116	return 0;
		4117	}
		4118
		4119	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4120	signal the main thread via some unspecified mechanism (signals? pipe
		4121	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4122	have been called (in a while loop because a) spurious wakeups are possible
		4123	and b) skipping inter-thread-communication when there are no pending
		4124	watchers is very beneficial):
		4125
		4126	static void
		4127	l_invoke (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130
		4131	while (ev_pending_count (EV_A))
		4132	{
		4133	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4134	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4135	}
		4136	}
		4137
		4138	Now, whenever the main thread gets told to invoke pending watchers, it
		4139	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4140	thread to continue:
		4141
		4142	static void
		4143	real_invoke_pending (EV_P)
		4144	{
		4145	userdata *u = ev_userdata (EV_A);
		4146
		4147	pthread_mutex_lock (&u->lock);
		4148	ev_invoke_pending (EV_A);
		4149	pthread_cond_signal (&u->invoke_cv);
		4150	pthread_mutex_unlock (&u->lock);
		4151	}
		4152
		4153	Whenever you want to start/stop a watcher or do other modifications to an
		4154	event loop, you will now have to lock:
		4155
		4156	ev_timer timeout_watcher;
		4157	userdata *u = ev_userdata (EV_A);
		4158
		4159	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4160
		4161	pthread_mutex_lock (&u->lock);
		4162	ev_timer_start (EV_A_ &timeout_watcher);
		4163	ev_async_send (EV_A_ &u->async_w);
		4164	pthread_mutex_unlock (&u->lock);
		4165
		4166	Note that sending the C<ev_async> watcher is required because otherwise
		4167	an event loop currently blocking in the kernel will have no knowledge
		4168	about the newly added timer. By waking up the loop it will pick up any new
		4169	watchers in the next event loop iteration.
		4170
		4171	=head3 COROUTINES
		4172
		4173	Libev is very accommodating to coroutines ("cooperative threads"):
		4174	libev fully supports nesting calls to its functions from different
		4175	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4176	different coroutines, and switch freely between both coroutines running
		4177	the loop, as long as you don't confuse yourself). The only exception is
		4178	that you must not do this from C<ev_periodic> reschedule callbacks.
		4179
		4180	Care has been taken to ensure that libev does not keep local state inside
		4181	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4182	they do not call any callbacks.
		4183
		4184	=head2 COMPILER WARNINGS
		4185
		4186	Depending on your compiler and compiler settings, you might get no or a
		4187	lot of warnings when compiling libev code. Some people are apparently
		4188	scared by this.
		4189
		4190	However, these are unavoidable for many reasons. For one, each compiler
		4191	has different warnings, and each user has different tastes regarding
		4192	warning options. "Warn-free" code therefore cannot be a goal except when
		4193	targeting a specific compiler and compiler-version.
		4194
		4195	Another reason is that some compiler warnings require elaborate
		4196	workarounds, or other changes to the code that make it less clear and less
		4197	maintainable.
		4198
		4199	And of course, some compiler warnings are just plain stupid, or simply
		4200	wrong (because they don't actually warn about the condition their message
		4201	seems to warn about). For example, certain older gcc versions had some
		4202	warnings that resulted an extreme number of false positives. These have
		4203	been fixed, but some people still insist on making code warn-free with
		4204	such buggy versions.
		4205
		4206	While libev is written to generate as few warnings as possible,
		4207	"warn-free" code is not a goal, and it is recommended not to build libev
		4208	with any compiler warnings enabled unless you are prepared to cope with
		4209	them (e.g. by ignoring them). Remember that warnings are just that:
		4210	warnings, not errors, or proof of bugs.
		4211
		4212
		4213	=head2 VALGRIND
		4214
		4215	Valgrind has a special section here because it is a popular tool that is
		4216	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4217
		4218	If you think you found a bug (memory leak, uninitialised data access etc.)
		4219	in libev, then check twice: If valgrind reports something like:
		4220
		4221	==2274== definitely lost: 0 bytes in 0 blocks.
		4222	==2274== possibly lost: 0 bytes in 0 blocks.
		4223	==2274== still reachable: 256 bytes in 1 blocks.
		4224
		4225	Then there is no memory leak, just as memory accounted to global variables
		4226	is not a memleak - the memory is still being referenced, and didn't leak.
		4227
		4228	Similarly, under some circumstances, valgrind might report kernel bugs
		4229	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4230	although an acceptable workaround has been found here), or it might be
		4231	confused.
		4232
		4233	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4234	make it into some kind of religion.
		4235
		4236	If you are unsure about something, feel free to contact the mailing list
		4237	with the full valgrind report and an explanation on why you think this
		4238	is a bug in libev (best check the archives, too :). However, don't be
		4239	annoyed when you get a brisk "this is no bug" answer and take the chance
		4240	of learning how to interpret valgrind properly.
		4241
		4242	If you need, for some reason, empty reports from valgrind for your project
		4243	I suggest using suppression lists.
		4244
		4245
		4246	=head1 PORTABILITY NOTES
		4247
		4248	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4249
		4250	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4251	requires, and its I/O model is fundamentally incompatible with the POSIX
		4252	model. Libev still offers limited functionality on this platform in
		4253	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4254	descriptors. This only applies when using Win32 natively, not when using
		4255	e.g. cygwin.
		4256
		4257	Lifting these limitations would basically require the full
		4258	re-implementation of the I/O system. If you are into these kinds of
		4259	things, then note that glib does exactly that for you in a very portable
		4260	way (note also that glib is the slowest event library known to man).
		4261
		4262	There is no supported compilation method available on windows except
		4263	embedding it into other applications.
		4264
		4265	Sensible signal handling is officially unsupported by Microsoft - libev
		4266	tries its best, but under most conditions, signals will simply not work.
		4267
		4268	Not a libev limitation but worth mentioning: windows apparently doesn't
		4269	accept large writes: instead of resulting in a partial write, windows will
		4270	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4271	so make sure you only write small amounts into your sockets (less than a
		4272	megabyte seems safe, but this apparently depends on the amount of memory
		4273	available).
		4274
		4275	Due to the many, low, and arbitrary limits on the win32 platform and
		4276	the abysmal performance of winsockets, using a large number of sockets
		4277	is not recommended (and not reasonable). If your program needs to use
		4278	more than a hundred or so sockets, then likely it needs to use a totally
		4279	different implementation for windows, as libev offers the POSIX readiness
		4280	notification model, which cannot be implemented efficiently on windows
		4281	(due to Microsoft monopoly games).
		4282
		4283	A typical way to use libev under windows is to embed it (see the embedding
		4284	section for details) and use the following F<evwrap.h> header file instead
		4285	of F<ev.h>:
		4286
		4287	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4288	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4289
		4290	#include "ev.h"
		4291
		4292	And compile the following F<evwrap.c> file into your project (make sure
		4293	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4294
		4295	#include "evwrap.h"
		4296	#include "ev.c"
		4297
		4298	=over 4
		4299
		4300	=item The winsocket select function
		4301
		4302	The winsocket C<select> function doesn't follow POSIX in that it
		4303	requires socket I<handles> and not socket I<file descriptors> (it is
		4304	also extremely buggy). This makes select very inefficient, and also
		4305	requires a mapping from file descriptors to socket handles (the Microsoft
		4306	C runtime provides the function C<_open_osfhandle> for this). See the
		4307	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4308	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4309
		4310	The configuration for a "naked" win32 using the Microsoft runtime
		4311	libraries and raw winsocket select is:
		4312
		4313	#define EV_USE_SELECT 1
		4314	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4315
		4316	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4317	complexity in the O(n²) range when using win32.
		4318
		4319	=item Limited number of file descriptors
		4320
		4321	Windows has numerous arbitrary (and low) limits on things.
		4322
		4323	Early versions of winsocket's select only supported waiting for a maximum
		4324	of C<64> handles (probably owning to the fact that all windows kernels
		4325	can only wait for C<64> things at the same time internally; Microsoft
		4326	recommends spawning a chain of threads and wait for 63 handles and the
		4327	previous thread in each. Sounds great!).
		4328
		4329	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4330	to some high number (e.g. C<2048>) before compiling the winsocket select
		4331	call (which might be in libev or elsewhere, for example, perl and many
		4332	other interpreters do their own select emulation on windows).
		4333
		4334	Another limit is the number of file descriptors in the Microsoft runtime
		4335	libraries, which by default is C<64> (there must be a hidden I<64>
		4336	fetish or something like this inside Microsoft). You can increase this
		4337	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4338	(another arbitrary limit), but is broken in many versions of the Microsoft
		4339	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4340	(depending on windows version and/or the phase of the moon). To get more,
		4341	you need to wrap all I/O functions and provide your own fd management, but
		4342	the cost of calling select (O(n²)) will likely make this unworkable.
		4343
		4344	=back
		4345
		4346	=head2 PORTABILITY REQUIREMENTS
		4347
		4348	In addition to a working ISO-C implementation and of course the
		4349	backend-specific APIs, libev relies on a few additional extensions:
		4350
		4351	=over 4
		4352
		4353	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4354	calling conventions regardless of C<ev_watcher_type *>.
		4355
		4356	Libev assumes not only that all watcher pointers have the same internal
		4357	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4358	assumes that the same (machine) code can be used to call any watcher
		4359	callback: The watcher callbacks have different type signatures, but libev
		4360	calls them using an C<ev_watcher *> internally.
		4361
		4362	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4363
		4364	The type C<sig_atomic_t volatile> (or whatever is defined as
		4365	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4366	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4367	believed to be sufficiently portable.
		4368
		4369	=item C<sigprocmask> must work in a threaded environment
		4370
		4371	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4372	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4373	pthread implementations will either allow C<sigprocmask> in the "main
		4374	thread" or will block signals process-wide, both behaviours would
		4375	be compatible with libev. Interaction between C<sigprocmask> and
		4376	C<pthread_sigmask> could complicate things, however.
		4377
		4378	The most portable way to handle signals is to block signals in all threads
		4379	except the initial one, and run the default loop in the initial thread as
		4380	well.
		4381
		4382	=item C<long> must be large enough for common memory allocation sizes
		4383
		4384	To improve portability and simplify its API, libev uses C<long> internally
		4385	instead of C<size_t> when allocating its data structures. On non-POSIX
		4386	systems (Microsoft...) this might be unexpectedly low, but is still at
		4387	least 31 bits everywhere, which is enough for hundreds of millions of
		4388	watchers.
		4389
		4390	=item C<double> must hold a time value in seconds with enough accuracy
		4391
		4392	The type C<double> is used to represent timestamps. It is required to
		4393	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4394	enough for at least into the year 4000. This requirement is fulfilled by
		4395	implementations implementing IEEE 754, which is basically all existing
		4396	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4397	2200.
		4398
		4399	=back
		4400
		4401	If you know of other additional requirements drop me a note.
		4402
		4403
2303	=head1 COMPLEXITIES	4404	=head1 ALGORITHMIC COMPLEXITIES
2304		4405
2305	In this section the complexities of (many of) the algorithms used inside	4406	In this section the complexities of (many of) the algorithms used inside
2306	libev will be explained. For complexity discussions about backends see the	4407	libev will be documented. For complexity discussions about backends see
2307	documentation for C<ev_default_init>.	4408	the documentation for C<ev_default_init>.
2308		4409
2309	All of the following are about amortised time: If an array needs to be	4410	All of the following are about amortised time: If an array needs to be
2310	extended, libev needs to realloc and move the whole array, but this	4411	extended, libev needs to realloc and move the whole array, but this
2311	happens asymptotically never with higher number of elements, so O(1) might	4412	happens asymptotically rarer with higher number of elements, so O(1) might
2312	mean it might do a lengthy realloc operation in rare cases, but on average	4413	mean that libev does a lengthy realloc operation in rare cases, but on
2313	it is much faster and asymptotically approaches constant time.	4414	average it is much faster and asymptotically approaches constant time.
2314		4415
2315	=over 4	4416	=over 4
2316		4417
2317	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4418	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2318		4419
2319	This means that, when you have a watcher that triggers in one hour and	4420	This means that, when you have a watcher that triggers in one hour and
2320	there are 100 watchers that would trigger before that then inserting will	4421	there are 100 watchers that would trigger before that, then inserting will
2321	have to skip those 100 watchers.	4422	have to skip roughly seven (C<ld 100>) of these watchers.
2322		4423
2323	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4424	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2324		4425
2325	That means that for changing a timer costs less than removing/adding them	4426	That means that changing a timer costs less than removing/adding them,
2326	as only the relative motion in the event queue has to be paid for.	4427	as only the relative motion in the event queue has to be paid for.
2327		4428
2328	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4429	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2329		4430
2330	These just add the watcher into an array or at the head of a list.	4431	These just add the watcher into an array or at the head of a list.
		4432
2331	=item Stopping check/prepare/idle watchers: O(1)	4433	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2332		4434
2333	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4435	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2334		4436
2335	These watchers are stored in lists then need to be walked to find the	4437	These watchers are stored in lists, so they need to be walked to find the
2336	correct watcher to remove. The lists are usually short (you don't usually	4438	correct watcher to remove. The lists are usually short (you don't usually
2337	have many watchers waiting for the same fd or signal).	4439	have many watchers waiting for the same fd or signal: one is typical, two
		4440	is rare).
2338		4441
2339	=item Finding the next timer per loop iteration: O(1)	4442	=item Finding the next timer in each loop iteration: O(1)
		4443
		4444	By virtue of using a binary or 4-heap, the next timer is always found at a
		4445	fixed position in the storage array.
2340		4446
2341	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4447	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2342		4448
2343	A change means an I/O watcher gets started or stopped, which requires	4449	A change means an I/O watcher gets started or stopped, which requires
2344	libev to recalculate its status (and possibly tell the kernel).	4450	libev to recalculate its status (and possibly tell the kernel, depending
		4451	on backend and whether C<ev_io_set> was used).
2345		4452
2346	=item Activating one watcher: O(1)	4453	=item Activating one watcher (putting it into the pending state): O(1)
2347		4454
2348	=item Priority handling: O(number_of_priorities)	4455	=item Priority handling: O(number_of_priorities)
2349		4456
2350	Priorities are implemented by allocating some space for each	4457	Priorities are implemented by allocating some space for each
2351	priority. When doing priority-based operations, libev usually has to	4458	priority. When doing priority-based operations, libev usually has to
2352	linearly search all the priorities.	4459	linearly search all the priorities, but starting/stopping and activating
		4460	watchers becomes O(1) with respect to priority handling.
		4461
		4462	=item Sending an ev_async: O(1)
		4463
		4464	=item Processing ev_async_send: O(number_of_async_watchers)
		4465
		4466	=item Processing signals: O(max_signal_number)
		4467
		4468	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4469	calls in the current loop iteration. Checking for async and signal events
		4470	involves iterating over all running async watchers or all signal numbers.
2353		4471
2354	=back	4472	=back
2355		4473
2356		4474
		4475	=head1 GLOSSARY
		4476
		4477	=over 4
		4478
		4479	=item active
		4480
		4481	A watcher is active as long as it has been started (has been attached to
		4482	an event loop) but not yet stopped (disassociated from the event loop).
		4483
		4484	=item application
		4485
		4486	In this document, an application is whatever is using libev.
		4487
		4488	=item callback
		4489
		4490	The address of a function that is called when some event has been
		4491	detected. Callbacks are being passed the event loop, the watcher that
		4492	received the event, and the actual event bitset.
		4493
		4494	=item callback invocation
		4495
		4496	The act of calling the callback associated with a watcher.
		4497
		4498	=item event
		4499
		4500	A change of state of some external event, such as data now being available
		4501	for reading on a file descriptor, time having passed or simply not having
		4502	any other events happening anymore.
		4503
		4504	In libev, events are represented as single bits (such as C<EV_READ> or
		4505	C<EV_TIMEOUT>).
		4506
		4507	=item event library
		4508
		4509	A software package implementing an event model and loop.
		4510
		4511	=item event loop
		4512
		4513	An entity that handles and processes external events and converts them
		4514	into callback invocations.
		4515
		4516	=item event model
		4517
		4518	The model used to describe how an event loop handles and processes
		4519	watchers and events.
		4520
		4521	=item pending
		4522
		4523	A watcher is pending as soon as the corresponding event has been detected,
		4524	and stops being pending as soon as the watcher will be invoked or its
		4525	pending status is explicitly cleared by the application.
		4526
		4527	A watcher can be pending, but not active. Stopping a watcher also clears
		4528	its pending status.
		4529
		4530	=item real time
		4531
		4532	The physical time that is observed. It is apparently strictly monotonic :)
		4533
		4534	=item wall-clock time
		4535
		4536	The time and date as shown on clocks. Unlike real time, it can actually
		4537	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4538	clock.
		4539
		4540	=item watcher
		4541
		4542	A data structure that describes interest in certain events. Watchers need
		4543	to be started (attached to an event loop) before they can receive events.
		4544
		4545	=item watcher invocation
		4546
		4547	The act of calling the callback associated with a watcher.
		4548
		4549	=back
		4550
2357	=head1 AUTHOR	4551	=head1 AUTHOR
2358		4552
2359	Marc Lehmann <libev@schmorp.de>.	4553	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2360		4554

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