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…		…
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.
…		…
112	=item ev_tstamp ev_time ()	165	=item ev_tstamp ev_time ()
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.
		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 ()>.
117		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
…		…
134	not a problem.	193	not a problem.
135		194
136	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
137	version.	196	version.
138		197
139	assert (("libev version mismatch",	198	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
142		201
143	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
144		203
145	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_*>
146	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	207	a description of the set values.
149		208
150	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
151	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
152		211
153	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
155		214
156	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
157		216
158	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
159	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
160	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
161	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
162	(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
163	libev will probe for if you specify no backends explicitly.	222	libev will probe for if you specify no backends explicitly.
164		223
165	=item unsigned int ev_embeddable_backends ()	224	=item unsigned int ev_embeddable_backends ()
166		225
…		…
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
171	recommended ones.	230	recommended ones.
172		231
173	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
174		233
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
176		235
177	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
178	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
179	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
180	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
181	potentially destructive action. The default is your system realloc	240	or take some potentially destructive action.
182	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.
183		245
184	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
185	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,
186	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.
187		249
188	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
189	retries).	251	retries (example requires a standards-compliant C<realloc>).
190		252
191	static void *	253	static void *
192	persistent_realloc (void *ptr, size_t size)	254	persistent_realloc (void *ptr, size_t size)
193	{	255	{
194	for (;;)	256	for (;;)
…		…
203	}	265	}
204		266
205	...	267	...
206	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
207		269
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
209		271
210	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
211	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
212	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
213	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
214	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
215	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
216	(such as abort).	278	(such as abort).
217		279
218	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.
…		…
229		291
230	=back	292	=back
231		293
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
233		295
234	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>
235	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>
236	events, and dynamically created loops which do not.	298	I<function>).
237		299
238	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
239	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
240	create, you also create another event loop. Libev itself does no locking	302	not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		303
245	=over 4	304	=over 4
246		305
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		307
…		…
252	flags. If that is troubling you, check C<ev_backend ()> afterwards).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
253		312
254	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
255	function.	314	function.
256		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
257	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
258	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>).
259		329
260	The following flags are supported:	330	The following flags are supported:
261		331
…		…
266	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
267	thing, believe me).	337	thing, believe me).
268		338
269	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
270		340
271	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
272	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
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	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
275	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
276	around bugs.	346	around bugs.
…		…
282	enabling this flag.	352	enabling this flag.
283		353
284	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,
285	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
286	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
287	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
288	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
289	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
290		360
291	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
292	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
293	flag.	363	flag.
294		364
295	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>
296	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
297		382
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		384
300	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
301	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,
302	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
303	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
304	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).
305		401
306	=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)
307		403
308	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
309	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
310	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
311	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>.
312		413
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		415
315	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,
316	but it scales phenomenally better. While poll and select usually scale like	417	but it scales phenomenally better. While poll and select usually scale
317	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),
318	either O(1) or O(active_fds).	419	epoll scales either O(1) or O(active_fds).
319		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
320	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
321	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
322	(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
323	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
324	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.
325		444
326	Please note that epoll sometimes generates spurious notifications, so you	445	Best performance from this backend is achieved by not unregistering all
327	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,
328	(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>.
329		462
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		464
332	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
333	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
334	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
335	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
336	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
337	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.
338		478
339	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
340	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
341	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
342	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
343	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>.
344		499
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	500	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		501
347	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.
348		506
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	507	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		508
351	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,
352	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)).
353		511
354	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
355	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
356	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>.
357		528
358	=item C<EVBACKEND_ALL>	529	=item C<EVBACKEND_ALL>
359		530
360	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
361	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
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	533	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		534
		535	It is definitely not recommended to use this flag.
		536
364	=back	537	=back
365		538
366	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,
367	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
368	specified, most compiled-in backend will be tried, usually in reverse	541	here). If none are specified, all backends in C<ev_recommended_backends
369	order of their flag values :)	542	()> will be tried.
370		543
371	The most typical usage is like this:	544	Example: This is the most typical usage.
372		545
373	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375		548
376	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
377	environment settings to be taken into account:	550	environment settings to be taken into account:
378		551
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	552	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380		553
381	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
382	available (warning, breaks stuff, best use only with your own private	555	used if available (warning, breaks stuff, best use only with your own
383	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):
384		558
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	559	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386		560
387	=item struct ev_loop *ev_loop_new (unsigned int flags)	561	=item struct ev_loop *ev_loop_new (unsigned int flags)
388		562
389	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
390	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
391	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
392	undefined behaviour (or a failed assertion if assertions are enabled).	566	undefined behaviour (or a failed assertion if assertions are enabled).
393		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
394	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.
395		573
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	574	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	575	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	576	fatal ("no epoll found here, maybe it hides under your chair");
399		577
400	=item ev_default_destroy ()	578	=item ev_default_destroy ()
401		579
402	Destroys the default loop again (frees all memory and kernel state	580	Destroys the default loop again (frees all memory and kernel state
403	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
404	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
405	responsibility to either stop all watchers cleanly yoursef I<before>	583	responsibility to either stop all watchers cleanly yourself I<before>
406	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
407	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
408	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>.
409		596
410	=item ev_loop_destroy (loop)	597	=item ev_loop_destroy (loop)
411		598
412	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
413	earlier call to C<ev_loop_new>.	600	earlier call to C<ev_loop_new>.
414		601
415	=item ev_default_fork ()	602	=item ev_default_fork ()
416		603
		604	This function sets a flag that causes subsequent C<ev_loop> iterations
417	This function reinitialises the kernel state for backends that have	605	to reinitialise the kernel state for backends that have one. Despite the
418	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
419	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
420	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.
421		610
422	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
423	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
424	fork+exec, you don't have to call it.	613	you just fork+exec, you don't have to call it at all.
425		614
426	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
427	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
428	quite nicely into a call to C<pthread_atfork>:	617	quite nicely into a call to C<pthread_atfork>:
429		618
430	pthread_atfork (0, 0, ev_default_fork);	619	pthread_atfork (0, 0, ev_default_fork);
431		620
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435
436	=item ev_loop_fork (loop)	621	=item ev_loop_fork (loop)
437		622
438	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
439	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
440	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.
441		632
442	=item unsigned int ev_loop_count (loop)	633	=item unsigned int ev_loop_count (loop)
443		634
444	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
445	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
446	happily wraps around with enough iterations.	637	happily wraps around with enough iterations.
447		638
448	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
449	"ticks" the number of loop iterations), as it roughly corresponds with	640	"ticks" the number of loop iterations), as it roughly corresponds with
450	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.
451		654
452	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
453		656
454	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
455	use.	658	use.
…		…
458		661
459	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
460	received events and started processing them. This timestamp does not	663	received events and started processing them. This timestamp does not
461	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
462	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
463	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>).
464		705
465	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
466		707
467	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
468	after you initialised all your watchers and you want to start handling	709	after you have initialised all your watchers and you want to start
469	events.	710	handling events.
470		711
471	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
472	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.
473		714
474	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
475	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
476	finished (especially in interactive programs), but having a program that	717	finished (especially in interactive programs), but having a program
477	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
478	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.
479		721
480	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
481	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
482	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.
483		726
484	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
485	neccessary) and will handle those and any outstanding ones. It will block	728	necessary) and will handle those and any already outstanding ones. It
486	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
487	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
488	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
489	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
490	usually a better approach for this kind of thing.	737	usually a better approach for this kind of thing.
491		738
492	Here are the gory details of what C<ev_loop> does:	739	Here are the gory details of what C<ev_loop> does:
493		740
494	- Before the first iteration, call any pending watchers.	741	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	742	* If EVFLAG_FORKCHECK was used, check for a fork.
496	- Queue all prepare watchers and then call all outstanding watchers.	743	- If a fork was detected (by any means), queue and call all fork watchers.
		744	- Queue and call all prepare watchers.
497	- 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.
498	- Update the kernel state with all outstanding changes.	747	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	748	- Update the "event loop time" (ev_now ()).
500	- 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.
501	- Block the process, waiting for any events.	753	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	754	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	755	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	756	- Queue all expired timers.
505	- Queue all outstanding periodics.	757	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	758	- Unless any events are pending now, queue all idle watchers.
507	- Queue all check watchers.	759	- Queue all check watchers.
508	- 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).
509	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
510	be handled here by queueing them when their watcher gets executed.	762	be handled here by queueing them when their watcher gets executed.
511	- 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
512	were used, return, otherwise continue with step *.	764	were used, or there are no active watchers, return, otherwise
		765	continue with step *.
513		766
514	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
515	anymore.	768	anymore.
516		769
517	... queue jobs here, make sure they register event watchers as long	770	... queue jobs here, make sure they register event watchers as long
518	... 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..)
519	ev_loop (my_loop, 0);	772	ev_loop (my_loop, 0);
520	... jobs done. yeah!	773	... jobs done or somebody called unloop. yeah!
521		774
522	=item ev_unloop (loop, how)	775	=item ev_unloop (loop, how)
523		776
524	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
525	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
526	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
527	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.
528		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
529	=item ev_ref (loop)	786	=item ev_ref (loop)
530		787
531	=item ev_unref (loop)	788	=item ev_unref (loop)
532		789
533	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
534	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
535	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
536	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>
537	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
538	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
539	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
540	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
541	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
542	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).
543		807
544	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>
545	running when nothing else is active.	809	running when nothing else is active.
546		810
547	struct ev_signal exitsig;	811	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	812	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	813	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	814	evf_unref (loop);
551		815
552	Example: For some weird reason, unregister the above signal handler again.	816	Example: For some weird reason, unregister the above signal handler again.
553		817
554	ev_ref (loop);	818	ev_ref (loop);
555	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.
556		954
557	=back	955	=back
558		956
559		957
560	=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.
561		963
562	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
563	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
564	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:
565		967
566	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)
567	{	969	{
568	ev_io_stop (w);	970	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	971	ev_unloop (loop, EVUNLOOP_ALL);
570	}	972	}
571		973
572	struct ev_loop *loop = ev_default_loop (0);	974	struct ev_loop *loop = ev_default_loop (0);
		975
573	struct ev_io stdin_watcher;	976	ev_io stdin_watcher;
		977
574	ev_init (&stdin_watcher, my_cb);	978	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	979	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	980	ev_io_start (loop, &stdin_watcher);
		981
577	ev_loop (loop, 0);	982	ev_loop (loop, 0);
578		983
579	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
580	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
581	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).
582		990
583	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
584	(watcher *, callback)>, which expects a callback to be provided. This	992	(watcher *, callback)>, which expects a callback to be provided. This
585	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
586	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
587	is readable and/or writable).	995	is readable and/or writable).
588		996
589	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 *, ...) >>
590	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
591	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<<
592	(watcher *, callback, ...) >>.	1000	ev_TYPE_init (watcher *, callback, ...) >>.
593		1001
594	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
595	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
596	*) >>), 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
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1005	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		1006
599	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
600	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
601	reinitialise it or call its C<set> macro.	1009	reinitialise it or call its C<ev_TYPE_set> macro.
602		1010
603	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
604	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
605	third argument.	1013	third argument.
606		1014
…		…
660	=item C<EV_FORK>	1068	=item C<EV_FORK>
661		1069
662	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
663	C<ev_fork>).	1071	C<ev_fork>).
664		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
665	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
666		1083
667	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
668	happen because the watcher could not be properly started because libev	1085	happen because the watcher could not be properly started because libev
669	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
670	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
671	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.
672		1093
673	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
674	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
675	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
676	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
677	programs, though, so beware.	1098	programs, though, as the fd could already be closed and reused for another
		1099	thing, so beware.
678		1100
679	=back	1101	=back
680		1102
681	=head2 GENERIC WATCHER FUNCTIONS	1103	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1104
686	=over 4	1105	=over 4
687		1106
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1107	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1108
…		…
695	which rolls both calls into one.	1114	which rolls both calls into one.
696		1115
697	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
698	(or never started) and there are no pending events outstanding.	1117	(or never started) and there are no pending events outstanding.
699		1118
700	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,
701	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);
702		1127
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1128	=item C<ev_TYPE_set> (ev_TYPE *, [args])
704		1129
705	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
706	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
…		…
709	difference to the C<ev_init> macro).	1134	difference to the C<ev_init> macro).
710		1135
711	Although some watcher types do not have type-specific arguments	1136	Although some watcher types do not have type-specific arguments
712	(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.
713		1138
		1139	See C<ev_init>, above, for an example.
		1140
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1141	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1142
716	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
717	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
718	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);
719		1150
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1151	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
721		1152
722	Starts (activates) the given watcher. Only active watchers will receive	1153	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1154	events. If the watcher is already active nothing will happen.
724		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
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1161	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
726		1162
727	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
728	status. It is possible that stopped watchers are pending (for example,	1166	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1167	non-repeating timers are being stopped when they become pending - but
730	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
731	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
732	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.
733		1171
734	=item bool ev_is_active (ev_TYPE *watcher)	1172	=item bool ev_is_active (ev_TYPE *watcher)
735		1173
736	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
737	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
…		…
763	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>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
767		1205
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	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
774	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.
775		1208
776	You I<must not> change the priority of a watcher as long as it is active or	1209	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1210	pending.
778		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
779	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
780	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 :).
781		1218
782	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
783	fine, as long as you do not mind that the priority value you query might	1220	priorities.
784	or might not have been adjusted to be within valid range.
785		1221
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1223
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1226	can deal with that fact, as both are simply passed through to the
		1227	callback.
791		1228
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1229	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1230
794	If the watcher is pending, this function returns clears its pending status	1231	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1232	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1233	watcher isn't pending it does nothing and returns C<0>.
797		1234
		1235	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1236	callback to be invoked, which can be accomplished with this function.
		1237
798	=back	1238	=back
799		1239
800		1240
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1241	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
802		1242
803	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
804	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
805	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
806	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
807	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
808	data:	1248	data:
809		1249
810	struct my_io	1250	struct my_io
811	{	1251	{
812	struct ev_io io;	1252	ev_io io;
813	int otherfd;	1253	int otherfd;
814	void *somedata;	1254	void *somedata;
815	struct whatever *mostinteresting;	1255	struct whatever *mostinteresting;
816	}	1256	};
		1257
		1258	...
		1259	struct my_io w;
		1260	ev_io_init (&w.io, my_cb, fd, EV_READ);
817		1261
818	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
819	can cast it back to your own type:	1263	can cast it back to your own type:
820		1264
821	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)
822	{	1266	{
823	struct my_io *w = (struct my_io *)w_;	1267	struct my_io *w = (struct my_io *)w_;
824	...	1268	...
825	}	1269	}
826		1270
827	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
828	instead have been omitted.	1272	instead have been omitted.
829		1273
830	Another common scenario is having some data structure with multiple	1274	Another common scenario is to use some data structure with multiple
831	watchers:	1275	embedded watchers:
832		1276
833	struct my_biggy	1277	struct my_biggy
834	{	1278	{
835	int some_data;	1279	int some_data;
836	ev_timer t1;	1280	ev_timer t1;
837	ev_timer t2;	1281	ev_timer t2;
838	}	1282	}
839		1283
840	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
841	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):
842		1289
843	#include <stddef.h>	1290	#include <stddef.h>
844		1291
845	static void	1292	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
847	{	1294	{
848	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
849	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
850	}	1297	}
851		1298
852	static void	1299	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
854	{	1301	{
855	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
856	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
857	}	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.
858		1408
859		1409
860	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
861		1411
862	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
886	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
887	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
888	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
889	required if you know what you are doing).	1439	required if you know what you are doing).
890		1440
891	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
892	(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
893	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
894	to the same underlying file/socket/etc. description (that is, they share	1444	descriptors for which non-blocking operation makes no sense (such as
895	the same underlying "file open").	1445	files) - libev doesn't guarentee any specific behaviour in that case.
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900		1446
901	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
902	receive "spurious" readyness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
903	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
904	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
905	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
906	this situation even with a relatively standard program structure. Thus	1452	this situation even with a relatively standard program structure. Thus
907	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
908	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.
909		1455
910	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
911	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
912	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
913	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
914	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.
915		1465
916	=head3 The special problem of disappearing file descriptors	1466	=head3 The special problem of disappearing file descriptors
917		1467
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1468	Some backends (e.g. kqueue, epoll) need to be told about closing a file
919	descriptor (either by calling C<close> explicitly or by any other means,	1469	descriptor (either due to calling C<close> explicitly or any other means,
920	such as C<dup>). The reason is that you register interest in some file	1470	such as C<dup2>). The reason is that you register interest in some file
921	descriptor, but when it goes away, the operating system will silently drop	1471	descriptor, but when it goes away, the operating system will silently drop
922	this interest. If another file descriptor with the same number then is	1472	this interest. If another file descriptor with the same number then is
923	registered with libev, there is no efficient way to see that this is, in	1473	registered with libev, there is no efficient way to see that this is, in
924	fact, a different file descriptor.	1474	fact, a different file descriptor.
925		1475
…		…
932		1482
933	This is how one would do it normally anyway, the important point is that	1483	This is how one would do it normally anyway, the important point is that
934	the libev application should not optimise around libev but should leave	1484	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1485	optimisations to libev.
936		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
937		1520
938	=head3 Watcher-Specific Functions	1521	=head3 Watcher-Specific Functions
939		1522
940	=over 4	1523	=over 4
941		1524
942	=item ev_io_init (ev_io *, callback, int fd, int events)	1525	=item ev_io_init (ev_io *, callback, int fd, int events)
943		1526
944	=item ev_io_set (ev_io *, int fd, int events)	1527	=item ev_io_set (ev_io *, int fd, int events)
945		1528
946	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
947	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
948	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.
949		1532
950	=item int fd [read-only]	1533	=item int fd [read-only]
951		1534
952	The file descriptor being watched.	1535	The file descriptor being watched.
953		1536
954	=item int events [read-only]	1537	=item int events [read-only]
955		1538
956	The events being watched.	1539	The events being watched.
957		1540
958	=back	1541	=back
		1542
		1543	=head3 Examples
959		1544
960	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
961	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
962	attempt to read a whole line in the callback.	1547	attempt to read a whole line in the callback.
963		1548
964	static void	1549	static void
965	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)
966	{	1551	{
967	ev_io_stop (loop, w);	1552	ev_io_stop (loop, w);
968	.. 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
969	}	1554	}
970		1555
971	...	1556	...
972	struct ev_loop *loop = ev_default_init (0);	1557	struct ev_loop *loop = ev_default_init (0);
973	struct ev_io stdin_readable;	1558	ev_io stdin_readable;
974	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);
975	ev_io_start (loop, &stdin_readable);	1560	ev_io_start (loop, &stdin_readable);
976	ev_loop (loop, 0);	1561	ev_loop (loop, 0);
977		1562
978		1563
979	=head2 C<ev_timer> - relative and optionally repeating timeouts	1564	=head2 C<ev_timer> - relative and optionally repeating timeouts
980		1565
981	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
982	given time, and optionally repeating in regular intervals after that.	1567	given time, and optionally repeating in regular intervals after that.
983		1568
984	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
985	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
986	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
987	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
988	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.
989		1764
990	The relative timeouts are calculated relative to the C<ev_now ()>	1765	The relative timeouts are calculated relative to the C<ev_now ()>
991	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
992	of the event triggering whatever timeout you are modifying/starting. If	1767	of the event triggering whatever timeout you are modifying/starting. If
993	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
994	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:
995		1770
996	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1771	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
997		1772
998	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
999	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
1000	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>).
1001		1806
1002	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1003		1808
1004	=over 4	1809	=over 4
1005		1810
1006	=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)
1007		1812
1008	=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)
1009		1814
1010	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>
1011	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
1012	timer will automatically be configured to trigger again C<repeat> seconds	1817	reached. If it is positive, then the timer will automatically be
1013	later, again, and again, until stopped manually.	1818	configured to trigger again C<repeat> seconds later, again, and again,
		1819	until stopped manually.
1014		1820
1015	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
1016	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
1017	exactly 10 second intervals. If, however, your program cannot keep up with	1823	trigger at exactly 10 second intervals. If, however, your program cannot
1018	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
1019	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.
1020		1826
1021	=item ev_timer_again (loop)	1827	=item ev_timer_again (loop, ev_timer *)
1022		1828
1023	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
1024	repeating. The exact semantics are:	1830	repeating. The exact semantics are:
1025		1831
1026	If the timer is pending, its pending status is cleared.	1832	If the timer is pending, its pending status is cleared.
1027		1833
1028	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).
1029		1835
1030	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
1031	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.
1032		1838
1033	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
1034	example: Imagine you have a tcp connection and you want a so-called idle	1840	usage example.
1035	timeout, that is, you want to be called when there have been, say, 60
1036	seconds of inactivity on the socket. The easiest way to do this is to
1037	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1038	C<ev_timer_again> each time you successfully read or write some data. If
1039	you go into an idle state where you do not expect data to travel on the
1040	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1041	automatically restart it if need be.
1042		1841
1043	That means you can ignore the C<after> value and C<ev_timer_start>	1842	=item ev_timer_remaining (loop, ev_timer *)
1044	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1045		1843
1046	ev_timer_init (timer, callback, 0., 5.);	1844	Returns the remaining time until a timer fires. If the timer is active,
1047	ev_timer_again (loop, timer);	1845	then this time is relative to the current event loop time, otherwise it's
1048	...	1846	the timeout value currently configured.
1049	timer->again = 17.;
1050	ev_timer_again (loop, timer);
1051	...
1052	timer->again = 10.;
1053	ev_timer_again (loop, timer);
1054		1847
1055	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
1056	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.
1057		1853
1058	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1059		1855
1060	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
1061	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),
1062	which is also when any modifications are taken into account.	1858	which is also when any modifications are taken into account.
1063		1859
1064	=back	1860	=back
1065		1861
		1862	=head3 Examples
		1863
1066	Example: Create a timer that fires after 60 seconds.	1864	Example: Create a timer that fires after 60 seconds.
1067		1865
1068	static void	1866	static void
1069	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)
1070	{	1868	{
1071	.. one minute over, w is actually stopped right here	1869	.. one minute over, w is actually stopped right here
1072	}	1870	}
1073		1871
1074	struct ev_timer mytimer;	1872	ev_timer mytimer;
1075	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1873	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1076	ev_timer_start (loop, &mytimer);	1874	ev_timer_start (loop, &mytimer);
1077		1875
1078	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
1079	inactivity.	1877	inactivity.
1080		1878
1081	static void	1879	static void
1082	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1880	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1083	{	1881	{
1084	.. ten seconds without any activity	1882	.. ten seconds without any activity
1085	}	1883	}
1086		1884
1087	struct ev_timer mytimer;	1885	ev_timer mytimer;
1088	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 */
1089	ev_timer_again (&mytimer); /* start timer */	1887	ev_timer_again (&mytimer); /* start timer */
1090	ev_loop (loop, 0);	1888	ev_loop (loop, 0);
1091		1889
1092	// 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":
1093	// reset the timeout to start ticking again at 10 seconds	1891	// reset the timeout to start ticking again at 10 seconds
1094	ev_timer_again (&mytimer);	1892	ev_timer_again (&mytimer);
1095		1893
1096		1894
1097	=head2 C<ev_periodic> - to cron or not to cron?	1895	=head2 C<ev_periodic> - to cron or not to cron?
1098		1896
1099	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
1100	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
1101		1899
1102	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
1103	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
1104	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
1105	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
1106	+ 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
1107	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1905	wrist-watch).
1108	roughly 10 seconds later).
1109		1906
1110	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
1111	triggering an event on each midnight, local time or other, complicated,	1908	in time: for example, if you tell a periodic watcher to trigger "in 10
1112	rules.	1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
1113		1914
		1915	C<ev_periodic> watchers can also be used to implement vastly more complex
		1916	timers, such as triggering an event on each "midnight, local time", or
		1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
		1919
1114	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
1115	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
1116	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).
1117		1925
1118	=head3 Watcher-Specific Functions and Data Members	1926	=head3 Watcher-Specific Functions and Data Members
1119		1927
1120	=over 4	1928	=over 4
1121		1929
1122	=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)
1123		1931
1124	=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)
1125		1933
1126	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
1127	operation, and we will explain them from simplest to complex:	1935	operation, and we will explain them from simplest to most complex:
1128		1936
1129	=over 4	1937	=over 4
1130		1938
1131	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1132		1940
1133	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
1134	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
1135	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
1136	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.
1137		1946
1138	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1139		1948
1140	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
1141	C<at + N * interval> time (for some integer N, which can also be negative)	1950	C<offset + N * interval> time (for some integer N, which can also be
1142	and then repeat, regardless of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
1143		1953
1144	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
1145	time:	1955	system clock, for example, here is an C<ev_periodic> that triggers each
		1956	hour, on the hour (with respect to UTC):
1146		1957
1147	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
1148		1959
1149	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,
1150	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
1151	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
1152	by 3600.	1963	by 3600.
1153		1964
1154	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
1155	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
1156	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.
1157		1968
1158	For numerical stability it is preferable that the C<at> value is near	1969	For numerical stability it is preferable that the C<offset> value is near
1159	C<ev_now ()> (the current time), but there is no range requirement for	1970	C<ev_now ()> (the current time), but there is no range requirement for
1160	this value.	1971	this value, and in fact is often specified as zero.
1161		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
1162	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1163		1979
1164	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
1165	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
1166	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
1167	current time as second argument.	1983	current time as second argument.
1168		1984
1169	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,
1170	ever, or make any event loop modifications>. If you need to stop it,	1986	or make ANY other event loop modifications whatsoever, unless explicitly
1171	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1987	allowed by documentation here>.
1172	starting an C<ev_prepare> watcher, which is legal).
1173		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
1174	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1993	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1175	ev_tstamp now)>, e.g.:	1994	*w, ev_tstamp now)>, e.g.:
1176		1995
		1996	static ev_tstamp
1177	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1997	my_rescheduler (ev_periodic *w, ev_tstamp now)
1178	{	1998	{
1179	return now + 60.;	1999	return now + 60.;
1180	}	2000	}
1181		2001
1182	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
1183	(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
1184	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
1185	might be called at other times, too.	2005	might be called at other times, too.
1186		2006
1187	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
1188	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2008	equal to the passed C<now> value >>.
1189		2009
1190	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
1191	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
1192	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
1193	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
1194	reason I omitted it as an example).	2014	reason I omitted it as an example).
1195		2015
1196	=back	2016	=back
…		…
1200	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
1201	when you changed some parameters or the reschedule callback would return	2021	when you changed some parameters or the reschedule callback would return
1202	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
1203	program when the crontabs have changed).	2023	program when the crontabs have changed).
1204		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
1205	=item ev_tstamp offset [read-write]	2032	=item ev_tstamp offset [read-write]
1206		2033
1207	When repeating, this contains the offset value, otherwise this is the	2034	When repeating, this contains the offset value, otherwise this is the
1208	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
1209		2037
1210	Can be modified any time, but changes only take effect when the periodic	2038	Can be modified any time, but changes only take effect when the periodic
1211	timer fires or C<ev_periodic_again> is being called.	2039	timer fires or C<ev_periodic_again> is being called.
1212		2040
1213	=item ev_tstamp interval [read-write]	2041	=item ev_tstamp interval [read-write]
1214		2042
1215	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
1216	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
1217	called.	2045	called.
1218		2046
1219	=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]
1220		2048
1221	The current reschedule callback, or C<0>, if this functionality is	2049	The current reschedule callback, or C<0>, if this functionality is
1222	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
1223	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.
1224		2052
1225	=back	2053	=back
1226		2054
		2055	=head3 Examples
		2056
1227	Example: Call a callback every hour, or, more precisely, whenever the	2057	Example: Call a callback every hour, or, more precisely, whenever the
1228	system clock is divisible by 3600. The callback invocation times have	2058	system time is divisible by 3600. The callback invocation times have
1229	potentially a lot of jittering, but good long-term stability.	2059	potentially a lot of jitter, but good long-term stability.
1230		2060
1231	static void	2061	static void
1232	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2062	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1233	{	2063	{
1234	... 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)
1235	}	2065	}
1236		2066
1237	struct ev_periodic hourly_tick;	2067	ev_periodic hourly_tick;
1238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2068	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1239	ev_periodic_start (loop, &hourly_tick);	2069	ev_periodic_start (loop, &hourly_tick);
1240		2070
1241	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:
1242		2072
1243	#include <math.h>	2073	#include <math.h>
1244		2074
1245	static ev_tstamp	2075	static ev_tstamp
1246	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2076	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1247	{	2077	{
1248	return fmod (now, 3600.) + 3600.;	2078	return now + (3600. - fmod (now, 3600.));
1249	}	2079	}
1250		2080
1251	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);
1252		2082
1253	Example: Call a callback every hour, starting now:	2083	Example: Call a callback every hour, starting now:
1254		2084
1255	struct ev_periodic hourly_tick;	2085	ev_periodic hourly_tick;
1256	ev_periodic_init (&hourly_tick, clock_cb,	2086	ev_periodic_init (&hourly_tick, clock_cb,
1257	fmod (ev_now (loop), 3600.), 3600., 0);	2087	fmod (ev_now (loop), 3600.), 3600., 0);
1258	ev_periodic_start (loop, &hourly_tick);	2088	ev_periodic_start (loop, &hourly_tick);
1259		2089
1260		2090
1261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2091	=head2 C<ev_signal> - signal me when a signal gets signalled!
1262		2092
1263	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
1264	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
1265	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
1266	normal event processing, like any other event.	2096	normal event processing, like any other event.
1267		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
1268	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
1269	first watcher gets started will libev actually register a signal watcher	2109	When the first watcher gets started will libev actually register something
1270	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
1271	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).
1272	watcher for a signal is stopped libev will reset the signal handler to	2112
1273	SIG_DFL (regardless of what it was set to before).	2113	If possible and supported, libev will install its handlers with
		2114	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2115	not be unduly interrupted. If you have a problem with system calls getting
		2116	interrupted by signals you can block all signals in an C<ev_check> watcher
		2117	and unblock them in an C<ev_prepare> watcher.
		2118
		2119	=head3 The special problem of inheritance over execve
		2120
		2121	Both the signal mask (C<sigprocmask>) and the signal disposition
		2122	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2123	stopping it again), that is, libev might or might not block the signal,
		2124	and might or might not set or restore the installed signal handler.
		2125
		2126	While this does not matter for the signal disposition (libev never
		2127	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2128	C<execve>), this matters for the signal mask: many programs do not expect
		2129	certain signals to be blocked.
		2130
		2131	This means that before calling C<exec> (from the child) you should reset
		2132	the signal mask to whatever "default" you expect (all clear is a good
		2133	choice usually).
		2134
		2135	The simplest way to ensure that the signal mask is reset in the child is
		2136	to install a fork handler with C<pthread_atfork> that resets it. That will
		2137	catch fork calls done by libraries (such as the libc) as well.
		2138
		2139	In current versions of libev, you can also ensure that the signal mask is
		2140	not blocking any signals (except temporarily, so thread users watch out)
		2141	by specifying the C<EVFLAG_NOSIGNALFD> when creating the event loop. This
		2142	is not guaranteed for future versions, however.
1274		2143
1275	=head3 Watcher-Specific Functions and Data Members	2144	=head3 Watcher-Specific Functions and Data Members
1276		2145
1277	=over 4	2146	=over 4
1278		2147
…		…
1287		2156
1288	The signal the watcher watches out for.	2157	The signal the watcher watches out for.
1289		2158
1290	=back	2159	=back
1291		2160
		2161	=head3 Examples
		2162
		2163	Example: Try to exit cleanly on SIGINT.
		2164
		2165	static void
		2166	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2167	{
		2168	ev_unloop (loop, EVUNLOOP_ALL);
		2169	}
		2170
		2171	ev_signal signal_watcher;
		2172	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2173	ev_signal_start (loop, &signal_watcher);
		2174
1292		2175
1293	=head2 C<ev_child> - watch out for process status changes	2176	=head2 C<ev_child> - watch out for process status changes
1294		2177
1295	Child watchers trigger when your process receives a SIGCHLD in response to	2178	Child watchers trigger when your process receives a SIGCHLD in response to
1296	some child status changes (most typically when a child of yours dies).	2179	some child status changes (most typically when a child of yours dies or
		2180	exits). It is permissible to install a child watcher I<after> the child
		2181	has been forked (which implies it might have already exited), as long
		2182	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2183	forking and then immediately registering a watcher for the child is fine,
		2184	but forking and registering a watcher a few event loop iterations later or
		2185	in the next callback invocation is not.
		2186
		2187	Only the default event loop is capable of handling signals, and therefore
		2188	you can only register child watchers in the default event loop.
		2189
		2190	Due to some design glitches inside libev, child watchers will always be
		2191	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2192	libev)
		2193
		2194	=head3 Process Interaction
		2195
		2196	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2197	initialised. This is necessary to guarantee proper behaviour even if the
		2198	first child watcher is started after the child exits. The occurrence
		2199	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2200	synchronously as part of the event loop processing. Libev always reaps all
		2201	children, even ones not watched.
		2202
		2203	=head3 Overriding the Built-In Processing
		2204
		2205	Libev offers no special support for overriding the built-in child
		2206	processing, but if your application collides with libev's default child
		2207	handler, you can override it easily by installing your own handler for
		2208	C<SIGCHLD> after initialising the default loop, and making sure the
		2209	default loop never gets destroyed. You are encouraged, however, to use an
		2210	event-based approach to child reaping and thus use libev's support for
		2211	that, so other libev users can use C<ev_child> watchers freely.
		2212
		2213	=head3 Stopping the Child Watcher
		2214
		2215	Currently, the child watcher never gets stopped, even when the
		2216	child terminates, so normally one needs to stop the watcher in the
		2217	callback. Future versions of libev might stop the watcher automatically
		2218	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2219	problem).
1297		2220
1298	=head3 Watcher-Specific Functions and Data Members	2221	=head3 Watcher-Specific Functions and Data Members
1299		2222
1300	=over 4	2223	=over 4
1301		2224
1302	=item ev_child_init (ev_child *, callback, int pid)	2225	=item ev_child_init (ev_child *, callback, int pid, int trace)
1303		2226
1304	=item ev_child_set (ev_child *, int pid)	2227	=item ev_child_set (ev_child *, int pid, int trace)
1305		2228
1306	Configures the watcher to wait for status changes of process C<pid> (or	2229	Configures the watcher to wait for status changes of process C<pid> (or
1307	I<any> process if C<pid> is specified as C<0>). The callback can look	2230	I<any> process if C<pid> is specified as C<0>). The callback can look
1308	at the C<rstatus> member of the C<ev_child> watcher structure to see	2231	at the C<rstatus> member of the C<ev_child> watcher structure to see
1309	the status word (use the macros from C<sys/wait.h> and see your systems	2232	the status word (use the macros from C<sys/wait.h> and see your systems
1310	C<waitpid> documentation). The C<rpid> member contains the pid of the	2233	C<waitpid> documentation). The C<rpid> member contains the pid of the
1311	process causing the status change.	2234	process causing the status change. C<trace> must be either C<0> (only
		2235	activate the watcher when the process terminates) or C<1> (additionally
		2236	activate the watcher when the process is stopped or continued).
1312		2237
1313	=item int pid [read-only]	2238	=item int pid [read-only]
1314		2239
1315	The process id this watcher watches out for, or C<0>, meaning any process id.	2240	The process id this watcher watches out for, or C<0>, meaning any process id.
1316		2241
…		…
1323	The process exit/trace status caused by C<rpid> (see your systems	2248	The process exit/trace status caused by C<rpid> (see your systems
1324	C<waitpid> and C<sys/wait.h> documentation for details).	2249	C<waitpid> and C<sys/wait.h> documentation for details).
1325		2250
1326	=back	2251	=back
1327		2252
1328	Example: Try to exit cleanly on SIGINT and SIGTERM.	2253	=head3 Examples
1329		2254
		2255	Example: C<fork()> a new process and install a child handler to wait for
		2256	its completion.
		2257
		2258	ev_child cw;
		2259
1330	static void	2260	static void
1331	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2261	child_cb (EV_P_ ev_child *w, int revents)
1332	{	2262	{
1333	ev_unloop (loop, EVUNLOOP_ALL);	2263	ev_child_stop (EV_A_ w);
		2264	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1334	}	2265	}
1335		2266
1336	struct ev_signal signal_watcher;	2267	pid_t pid = fork ();
1337	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2268
1338	ev_signal_start (loop, &sigint_cb);	2269	if (pid < 0)
		2270	// error
		2271	else if (pid == 0)
		2272	{
		2273	// the forked child executes here
		2274	exit (1);
		2275	}
		2276	else
		2277	{
		2278	ev_child_init (&cw, child_cb, pid, 0);
		2279	ev_child_start (EV_DEFAULT_ &cw);
		2280	}
1339		2281
1340		2282
1341	=head2 C<ev_stat> - did the file attributes just change?	2283	=head2 C<ev_stat> - did the file attributes just change?
1342		2284
1343	This watches a filesystem path for attribute changes. That is, it calls	2285	This watches a file system path for attribute changes. That is, it calls
1344	C<stat> regularly (or when the OS says it changed) and sees if it changed	2286	C<stat> on that path in regular intervals (or when the OS says it changed)
1345	compared to the last time, invoking the callback if it did.	2287	and sees if it changed compared to the last time, invoking the callback if
		2288	it did.
1346		2289
1347	The path does not need to exist: changing from "path exists" to "path does	2290	The path does not need to exist: changing from "path exists" to "path does
1348	not exist" is a status change like any other. The condition "path does	2291	not exist" is a status change like any other. The condition "path does not
1349	not exist" is signified by the C<st_nlink> field being zero (which is	2292	exist" (or more correctly "path cannot be stat'ed") is signified by the
1350	otherwise always forced to be at least one) and all the other fields of	2293	C<st_nlink> field being zero (which is otherwise always forced to be at
1351	the stat buffer having unspecified contents.	2294	least one) and all the other fields of the stat buffer having unspecified
		2295	contents.
1352		2296
1353	The path I<should> be absolute and I<must not> end in a slash. If it is	2297	The path I<must not> end in a slash or contain special components such as
		2298	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1354	relative and your working directory changes, the behaviour is undefined.	2299	your working directory changes, then the behaviour is undefined.
1355		2300
1356	Since there is no standard to do this, the portable implementation simply	2301	Since there is no portable change notification interface available, the
1357	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2302	portable implementation simply calls C<stat(2)> regularly on the path
1358	can specify a recommended polling interval for this case. If you specify	2303	to see if it changed somehow. You can specify a recommended polling
1359	a polling interval of C<0> (highly recommended!) then a I<suitable,	2304	interval for this case. If you specify a polling interval of C<0> (highly
1360	unspecified default> value will be used (which you can expect to be around	2305	recommended!) then a I<suitable, unspecified default> value will be used
1361	five seconds, although this might change dynamically). Libev will also	2306	(which you can expect to be around five seconds, although this might
1362	impose a minimum interval which is currently around C<0.1>, but thats	2307	change dynamically). Libev will also impose a minimum interval which is
1363	usually overkill.	2308	currently around C<0.1>, but that's usually overkill.
1364		2309
1365	This watcher type is not meant for massive numbers of stat watchers,	2310	This watcher type is not meant for massive numbers of stat watchers,
1366	as even with OS-supported change notifications, this can be	2311	as even with OS-supported change notifications, this can be
1367	resource-intensive.	2312	resource-intensive.
1368		2313
1369	At the time of this writing, only the Linux inotify interface is	2314	At the time of this writing, the only OS-specific interface implemented
1370	implemented (implementing kqueue support is left as an exercise for the	2315	is the Linux inotify interface (implementing kqueue support is left as an
1371	reader). Inotify will be used to give hints only and should not change the	2316	exercise for the reader. Note, however, that the author sees no way of
1372	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2317	implementing C<ev_stat> semantics with kqueue, except as a hint).
1373	to fall back to regular polling again even with inotify, but changes are	2318
1374	usually detected immediately, and if the file exists there will be no	2319	=head3 ABI Issues (Largefile Support)
1375	polling.	2320
		2321	Libev by default (unless the user overrides this) uses the default
		2322	compilation environment, which means that on systems with large file
		2323	support disabled by default, you get the 32 bit version of the stat
		2324	structure. When using the library from programs that change the ABI to
		2325	use 64 bit file offsets the programs will fail. In that case you have to
		2326	compile libev with the same flags to get binary compatibility. This is
		2327	obviously the case with any flags that change the ABI, but the problem is
		2328	most noticeably displayed with ev_stat and large file support.
		2329
		2330	The solution for this is to lobby your distribution maker to make large
		2331	file interfaces available by default (as e.g. FreeBSD does) and not
		2332	optional. Libev cannot simply switch on large file support because it has
		2333	to exchange stat structures with application programs compiled using the
		2334	default compilation environment.
		2335
		2336	=head3 Inotify and Kqueue
		2337
		2338	When C<inotify (7)> support has been compiled into libev and present at
		2339	runtime, it will be used to speed up change detection where possible. The
		2340	inotify descriptor will be created lazily when the first C<ev_stat>
		2341	watcher is being started.
		2342
		2343	Inotify presence does not change the semantics of C<ev_stat> watchers
		2344	except that changes might be detected earlier, and in some cases, to avoid
		2345	making regular C<stat> calls. Even in the presence of inotify support
		2346	there are many cases where libev has to resort to regular C<stat> polling,
		2347	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2348	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2349	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2350	xfs are fully working) libev usually gets away without polling.
		2351
		2352	There is no support for kqueue, as apparently it cannot be used to
		2353	implement this functionality, due to the requirement of having a file
		2354	descriptor open on the object at all times, and detecting renames, unlinks
		2355	etc. is difficult.
		2356
		2357	=head3 C<stat ()> is a synchronous operation
		2358
		2359	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2360	the process. The exception are C<ev_stat> watchers - those call C<stat
		2361	()>, which is a synchronous operation.
		2362
		2363	For local paths, this usually doesn't matter: unless the system is very
		2364	busy or the intervals between stat's are large, a stat call will be fast,
		2365	as the path data is usually in memory already (except when starting the
		2366	watcher).
		2367
		2368	For networked file systems, calling C<stat ()> can block an indefinite
		2369	time due to network issues, and even under good conditions, a stat call
		2370	often takes multiple milliseconds.
		2371
		2372	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2373	paths, although this is fully supported by libev.
		2374
		2375	=head3 The special problem of stat time resolution
		2376
		2377	The C<stat ()> system call only supports full-second resolution portably,
		2378	and even on systems where the resolution is higher, most file systems
		2379	still only support whole seconds.
		2380
		2381	That means that, if the time is the only thing that changes, you can
		2382	easily miss updates: on the first update, C<ev_stat> detects a change and
		2383	calls your callback, which does something. When there is another update
		2384	within the same second, C<ev_stat> will be unable to detect unless the
		2385	stat data does change in other ways (e.g. file size).
		2386
		2387	The solution to this is to delay acting on a change for slightly more
		2388	than a second (or till slightly after the next full second boundary), using
		2389	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2390	ev_timer_again (loop, w)>).
		2391
		2392	The C<.02> offset is added to work around small timing inconsistencies
		2393	of some operating systems (where the second counter of the current time
		2394	might be be delayed. One such system is the Linux kernel, where a call to
		2395	C<gettimeofday> might return a timestamp with a full second later than
		2396	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2397	update file times then there will be a small window where the kernel uses
		2398	the previous second to update file times but libev might already execute
		2399	the timer callback).
1376		2400
1377	=head3 Watcher-Specific Functions and Data Members	2401	=head3 Watcher-Specific Functions and Data Members
1378		2402
1379	=over 4	2403	=over 4
1380		2404
…		…
1386	C<path>. The C<interval> is a hint on how quickly a change is expected to	2410	C<path>. The C<interval> is a hint on how quickly a change is expected to
1387	be detected and should normally be specified as C<0> to let libev choose	2411	be detected and should normally be specified as C<0> to let libev choose
1388	a suitable value. The memory pointed to by C<path> must point to the same	2412	a suitable value. The memory pointed to by C<path> must point to the same
1389	path for as long as the watcher is active.	2413	path for as long as the watcher is active.
1390		2414
1391	The callback will be receive C<EV_STAT> when a change was detected,	2415	The callback will receive an C<EV_STAT> event when a change was detected,
1392	relative to the attributes at the time the watcher was started (or the	2416	relative to the attributes at the time the watcher was started (or the
1393	last change was detected).	2417	last change was detected).
1394		2418
1395	=item ev_stat_stat (ev_stat *)	2419	=item ev_stat_stat (loop, ev_stat *)
1396		2420
1397	Updates the stat buffer immediately with new values. If you change the	2421	Updates the stat buffer immediately with new values. If you change the
1398	watched path in your callback, you could call this fucntion to avoid	2422	watched path in your callback, you could call this function to avoid
1399	detecting this change (while introducing a race condition). Can also be	2423	detecting this change (while introducing a race condition if you are not
1400	useful simply to find out the new values.	2424	the only one changing the path). Can also be useful simply to find out the
		2425	new values.
1401		2426
1402	=item ev_statdata attr [read-only]	2427	=item ev_statdata attr [read-only]
1403		2428
1404	The most-recently detected attributes of the file. Although the type is of	2429	The most-recently detected attributes of the file. Although the type is
1405	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2430	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1406	suitable for your system. If the C<st_nlink> member is C<0>, then there	2431	suitable for your system, but you can only rely on the POSIX-standardised
		2432	members to be present. If the C<st_nlink> member is C<0>, then there was
1407	was some error while C<stat>ing the file.	2433	some error while C<stat>ing the file.
1408		2434
1409	=item ev_statdata prev [read-only]	2435	=item ev_statdata prev [read-only]
1410		2436
1411	The previous attributes of the file. The callback gets invoked whenever	2437	The previous attributes of the file. The callback gets invoked whenever
1412	C<prev> != C<attr>.	2438	C<prev> != C<attr>, or, more precisely, one or more of these members
		2439	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2440	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1413		2441
1414	=item ev_tstamp interval [read-only]	2442	=item ev_tstamp interval [read-only]
1415		2443
1416	The specified interval.	2444	The specified interval.
1417		2445
1418	=item const char *path [read-only]	2446	=item const char *path [read-only]
1419		2447
1420	The filesystem path that is being watched.	2448	The file system path that is being watched.
1421		2449
1422	=back	2450	=back
1423		2451
		2452	=head3 Examples
		2453
1424	Example: Watch C</etc/passwd> for attribute changes.	2454	Example: Watch C</etc/passwd> for attribute changes.
1425		2455
1426	static void	2456	static void
1427	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2457	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1428	{	2458	{
1429	/* /etc/passwd changed in some way */	2459	/* /etc/passwd changed in some way */
1430	if (w->attr.st_nlink)	2460	if (w->attr.st_nlink)
1431	{	2461	{
1432	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2462	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1433	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2463	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1434	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2464	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1435	}	2465	}
1436	else	2466	else
1437	/* you shalt not abuse printf for puts */	2467	/* you shalt not abuse printf for puts */
1438	puts ("wow, /etc/passwd is not there, expect problems. "	2468	puts ("wow, /etc/passwd is not there, expect problems. "
1439	"if this is windows, they already arrived\n");	2469	"if this is windows, they already arrived\n");
1440	}	2470	}
1441		2471
1442	...	2472	...
1443	ev_stat passwd;	2473	ev_stat passwd;
1444		2474
1445	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2475	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1446	ev_stat_start (loop, &passwd);	2476	ev_stat_start (loop, &passwd);
		2477
		2478	Example: Like above, but additionally use a one-second delay so we do not
		2479	miss updates (however, frequent updates will delay processing, too, so
		2480	one might do the work both on C<ev_stat> callback invocation I<and> on
		2481	C<ev_timer> callback invocation).
		2482
		2483	static ev_stat passwd;
		2484	static ev_timer timer;
		2485
		2486	static void
		2487	timer_cb (EV_P_ ev_timer *w, int revents)
		2488	{
		2489	ev_timer_stop (EV_A_ w);
		2490
		2491	/* now it's one second after the most recent passwd change */
		2492	}
		2493
		2494	static void
		2495	stat_cb (EV_P_ ev_stat *w, int revents)
		2496	{
		2497	/* reset the one-second timer */
		2498	ev_timer_again (EV_A_ &timer);
		2499	}
		2500
		2501	...
		2502	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2503	ev_stat_start (loop, &passwd);
		2504	ev_timer_init (&timer, timer_cb, 0., 1.02);
1447		2505
1448		2506
1449	=head2 C<ev_idle> - when you've got nothing better to do...	2507	=head2 C<ev_idle> - when you've got nothing better to do...
1450		2508
1451	Idle watchers trigger events when no other events of the same or higher	2509	Idle watchers trigger events when no other events of the same or higher
1452	priority are pending (prepare, check and other idle watchers do not	2510	priority are pending (prepare, check and other idle watchers do not count
1453	count).	2511	as receiving "events").
1454		2512
1455	That is, as long as your process is busy handling sockets or timeouts	2513	That is, as long as your process is busy handling sockets or timeouts
1456	(or even signals, imagine) of the same or higher priority it will not be	2514	(or even signals, imagine) of the same or higher priority it will not be
1457	triggered. But when your process is idle (or only lower-priority watchers	2515	triggered. But when your process is idle (or only lower-priority watchers
1458	are pending), the idle watchers are being called once per event loop	2516	are pending), the idle watchers are being called once per event loop
…		…
1469		2527
1470	=head3 Watcher-Specific Functions and Data Members	2528	=head3 Watcher-Specific Functions and Data Members
1471		2529
1472	=over 4	2530	=over 4
1473		2531
1474	=item ev_idle_init (ev_signal *, callback)	2532	=item ev_idle_init (ev_idle *, callback)
1475		2533
1476	Initialises and configures the idle watcher - it has no parameters of any	2534	Initialises and configures the idle watcher - it has no parameters of any
1477	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2535	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1478	believe me.	2536	believe me.
1479		2537
1480	=back	2538	=back
1481		2539
		2540	=head3 Examples
		2541
1482	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2542	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1483	callback, free it. Also, use no error checking, as usual.	2543	callback, free it. Also, use no error checking, as usual.
1484		2544
1485	static void	2545	static void
1486	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2546	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1487	{	2547	{
1488	free (w);	2548	free (w);
1489	// now do something you wanted to do when the program has	2549	// now do something you wanted to do when the program has
1490	// no longer asnything immediate to do.	2550	// no longer anything immediate to do.
1491	}	2551	}
1492		2552
1493	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2553	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1494	ev_idle_init (idle_watcher, idle_cb);	2554	ev_idle_init (idle_watcher, idle_cb);
1495	ev_idle_start (loop, idle_cb);	2555	ev_idle_start (loop, idle_watcher);
1496		2556
1497		2557
1498	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2558	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1499		2559
1500	Prepare and check watchers are usually (but not always) used in tandem:	2560	Prepare and check watchers are usually (but not always) used in pairs:
1501	prepare watchers get invoked before the process blocks and check watchers	2561	prepare watchers get invoked before the process blocks and check watchers
1502	afterwards.	2562	afterwards.
1503		2563
1504	You I<must not> call C<ev_loop> or similar functions that enter	2564	You I<must not> call C<ev_loop> or similar functions that enter
1505	the current event loop from either C<ev_prepare> or C<ev_check>	2565	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1508	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2568	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1509	C<ev_check> so if you have one watcher of each kind they will always be	2569	C<ev_check> so if you have one watcher of each kind they will always be
1510	called in pairs bracketing the blocking call.	2570	called in pairs bracketing the blocking call.
1511		2571
1512	Their main purpose is to integrate other event mechanisms into libev and	2572	Their main purpose is to integrate other event mechanisms into libev and
1513	their use is somewhat advanced. This could be used, for example, to track	2573	their use is somewhat advanced. They could be used, for example, to track
1514	variable changes, implement your own watchers, integrate net-snmp or a	2574	variable changes, implement your own watchers, integrate net-snmp or a
1515	coroutine library and lots more. They are also occasionally useful if	2575	coroutine library and lots more. They are also occasionally useful if
1516	you cache some data and want to flush it before blocking (for example,	2576	you cache some data and want to flush it before blocking (for example,
1517	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2577	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1518	watcher).	2578	watcher).
1519		2579
1520	This is done by examining in each prepare call which file descriptors need	2580	This is done by examining in each prepare call which file descriptors
1521	to be watched by the other library, registering C<ev_io> watchers for	2581	need to be watched by the other library, registering C<ev_io> watchers
1522	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2582	for them and starting an C<ev_timer> watcher for any timeouts (many
1523	provide just this functionality). Then, in the check watcher you check for	2583	libraries provide exactly this functionality). Then, in the check watcher,
1524	any events that occured (by checking the pending status of all watchers	2584	you check for any events that occurred (by checking the pending status
1525	and stopping them) and call back into the library. The I/O and timer	2585	of all watchers and stopping them) and call back into the library. The
1526	callbacks will never actually be called (but must be valid nevertheless,	2586	I/O and timer callbacks will never actually be called (but must be valid
1527	because you never know, you know?).	2587	nevertheless, because you never know, you know?).
1528		2588
1529	As another example, the Perl Coro module uses these hooks to integrate	2589	As another example, the Perl Coro module uses these hooks to integrate
1530	coroutines into libev programs, by yielding to other active coroutines	2590	coroutines into libev programs, by yielding to other active coroutines
1531	during each prepare and only letting the process block if no coroutines	2591	during each prepare and only letting the process block if no coroutines
1532	are ready to run (it's actually more complicated: it only runs coroutines	2592	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1535	loop from blocking if lower-priority coroutines are active, thus mapping	2595	loop from blocking if lower-priority coroutines are active, thus mapping
1536	low-priority coroutines to idle/background tasks).	2596	low-priority coroutines to idle/background tasks).
1537		2597
1538	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2598	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1539	priority, to ensure that they are being run before any other watchers	2599	priority, to ensure that they are being run before any other watchers
		2600	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2601
1540	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2602	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1541	too) should not activate ("feed") events into libev. While libev fully	2603	activate ("feed") events into libev. While libev fully supports this, they
1542	supports this, they will be called before other C<ev_check> watchers did	2604	might get executed before other C<ev_check> watchers did their job. As
1543	their job. As C<ev_check> watchers are often used to embed other event	2605	C<ev_check> watchers are often used to embed other (non-libev) event
1544	loops those other event loops might be in an unusable state until their	2606	loops those other event loops might be in an unusable state until their
1545	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2607	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1546	others).	2608	others).
1547		2609
1548	=head3 Watcher-Specific Functions and Data Members	2610	=head3 Watcher-Specific Functions and Data Members
…		…
1553		2615
1554	=item ev_check_init (ev_check *, callback)	2616	=item ev_check_init (ev_check *, callback)
1555		2617
1556	Initialises and configures the prepare or check watcher - they have no	2618	Initialises and configures the prepare or check watcher - they have no
1557	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2619	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1558	macros, but using them is utterly, utterly and completely pointless.	2620	macros, but using them is utterly, utterly, utterly and completely
		2621	pointless.
1559		2622
1560	=back	2623	=back
		2624
		2625	=head3 Examples
1561		2626
1562	There are a number of principal ways to embed other event loops or modules	2627	There are a number of principal ways to embed other event loops or modules
1563	into libev. Here are some ideas on how to include libadns into libev	2628	into libev. Here are some ideas on how to include libadns into libev
1564	(there is a Perl module named C<EV::ADNS> that does this, which you could	2629	(there is a Perl module named C<EV::ADNS> that does this, which you could
1565	use for an actually working example. Another Perl module named C<EV::Glib>	2630	use as a working example. Another Perl module named C<EV::Glib> embeds a
1566	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2631	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1567	into the Glib event loop).	2632	Glib event loop).
1568		2633
1569	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2634	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1570	and in a check watcher, destroy them and call into libadns. What follows	2635	and in a check watcher, destroy them and call into libadns. What follows
1571	is pseudo-code only of course. This requires you to either use a low	2636	is pseudo-code only of course. This requires you to either use a low
1572	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2637	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1573	the callbacks for the IO/timeout watchers might not have been called yet.	2638	the callbacks for the IO/timeout watchers might not have been called yet.
1574		2639
1575	static ev_io iow [nfd];	2640	static ev_io iow [nfd];
1576	static ev_timer tw;	2641	static ev_timer tw;
1577		2642
1578	static void	2643	static void
1579	io_cb (ev_loop *loop, ev_io *w, int revents)	2644	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1580	{	2645	{
1581	}	2646	}
1582		2647
1583	// create io watchers for each fd and a timer before blocking	2648	// create io watchers for each fd and a timer before blocking
1584	static void	2649	static void
1585	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2650	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1586	{	2651	{
1587	int timeout = 3600000;	2652	int timeout = 3600000;
1588	struct pollfd fds [nfd];	2653	struct pollfd fds [nfd];
1589	// actual code will need to loop here and realloc etc.	2654	// actual code will need to loop here and realloc etc.
1590	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2655	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1591		2656
1592	/* the callback is illegal, but won't be called as we stop during check */	2657	/* the callback is illegal, but won't be called as we stop during check */
1593	ev_timer_init (&tw, 0, timeout * 1e-3);	2658	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1594	ev_timer_start (loop, &tw);	2659	ev_timer_start (loop, &tw);
1595		2660
1596	// create one ev_io per pollfd	2661	// create one ev_io per pollfd
1597	for (int i = 0; i < nfd; ++i)	2662	for (int i = 0; i < nfd; ++i)
1598	{	2663	{
1599	ev_io_init (iow + i, io_cb, fds [i].fd,	2664	ev_io_init (iow + i, io_cb, fds [i].fd,
1600	((fds [i].events & POLLIN ? EV_READ : 0)	2665	((fds [i].events & POLLIN ? EV_READ : 0)
1601	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2666	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1602		2667
1603	fds [i].revents = 0;	2668	fds [i].revents = 0;
1604	ev_io_start (loop, iow + i);	2669	ev_io_start (loop, iow + i);
1605	}	2670	}
1606	}	2671	}
1607		2672
1608	// stop all watchers after blocking	2673	// stop all watchers after blocking
1609	static void	2674	static void
1610	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2675	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1611	{	2676	{
1612	ev_timer_stop (loop, &tw);	2677	ev_timer_stop (loop, &tw);
1613		2678
1614	for (int i = 0; i < nfd; ++i)	2679	for (int i = 0; i < nfd; ++i)
1615	{	2680	{
1616	// set the relevant poll flags	2681	// set the relevant poll flags
1617	// could also call adns_processreadable etc. here	2682	// could also call adns_processreadable etc. here
1618	struct pollfd *fd = fds + i;	2683	struct pollfd *fd = fds + i;
1619	int revents = ev_clear_pending (iow + i);	2684	int revents = ev_clear_pending (iow + i);
1620	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2685	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1621	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2686	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1622		2687
1623	// now stop the watcher	2688	// now stop the watcher
1624	ev_io_stop (loop, iow + i);	2689	ev_io_stop (loop, iow + i);
1625	}	2690	}
1626		2691
1627	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2692	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1628	}	2693	}
1629		2694
1630	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2695	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1631	in the prepare watcher and would dispose of the check watcher.	2696	in the prepare watcher and would dispose of the check watcher.
1632		2697
1633	Method 3: If the module to be embedded supports explicit event	2698	Method 3: If the module to be embedded supports explicit event
1634	notification (adns does), you can also make use of the actual watcher	2699	notification (libadns does), you can also make use of the actual watcher
1635	callbacks, and only destroy/create the watchers in the prepare watcher.	2700	callbacks, and only destroy/create the watchers in the prepare watcher.
1636		2701
1637	static void	2702	static void
1638	timer_cb (EV_P_ ev_timer *w, int revents)	2703	timer_cb (EV_P_ ev_timer *w, int revents)
1639	{	2704	{
1640	adns_state ads = (adns_state)w->data;	2705	adns_state ads = (adns_state)w->data;
1641	update_now (EV_A);	2706	update_now (EV_A);
1642		2707
1643	adns_processtimeouts (ads, &tv_now);	2708	adns_processtimeouts (ads, &tv_now);
1644	}	2709	}
1645		2710
1646	static void	2711	static void
1647	io_cb (EV_P_ ev_io *w, int revents)	2712	io_cb (EV_P_ ev_io *w, int revents)
1648	{	2713	{
1649	adns_state ads = (adns_state)w->data;	2714	adns_state ads = (adns_state)w->data;
1650	update_now (EV_A);	2715	update_now (EV_A);
1651		2716
1652	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2717	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1653	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2718	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1654	}	2719	}
1655		2720
1656	// do not ever call adns_afterpoll	2721	// do not ever call adns_afterpoll
1657		2722
1658	Method 4: Do not use a prepare or check watcher because the module you	2723	Method 4: Do not use a prepare or check watcher because the module you
1659	want to embed is too inflexible to support it. Instead, youc na override	2724	want to embed is not flexible enough to support it. Instead, you can
1660	their poll function. The drawback with this solution is that the main	2725	override their poll function. The drawback with this solution is that the
1661	loop is now no longer controllable by EV. The C<Glib::EV> module does	2726	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1662	this.	2727	this approach, effectively embedding EV as a client into the horrible
		2728	libglib event loop.
1663		2729
1664	static gint	2730	static gint
1665	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2731	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1666	{	2732	{
1667	int got_events = 0;	2733	int got_events = 0;
1668		2734
1669	for (n = 0; n < nfds; ++n)	2735	for (n = 0; n < nfds; ++n)
1670	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2736	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1671		2737
1672	if (timeout >= 0)	2738	if (timeout >= 0)
1673	// create/start timer	2739	// create/start timer
1674		2740
1675	// poll	2741	// poll
1676	ev_loop (EV_A_ 0);	2742	ev_loop (EV_A_ 0);
1677		2743
1678	// stop timer again	2744	// stop timer again
1679	if (timeout >= 0)	2745	if (timeout >= 0)
1680	ev_timer_stop (EV_A_ &to);	2746	ev_timer_stop (EV_A_ &to);
1681		2747
1682	// stop io watchers again - their callbacks should have set	2748	// stop io watchers again - their callbacks should have set
1683	for (n = 0; n < nfds; ++n)	2749	for (n = 0; n < nfds; ++n)
1684	ev_io_stop (EV_A_ iow [n]);	2750	ev_io_stop (EV_A_ iow [n]);
1685		2751
1686	return got_events;	2752	return got_events;
1687	}	2753	}
1688		2754
1689		2755
1690	=head2 C<ev_embed> - when one backend isn't enough...	2756	=head2 C<ev_embed> - when one backend isn't enough...
1691		2757
1692	This is a rather advanced watcher type that lets you embed one event loop	2758	This is a rather advanced watcher type that lets you embed one event loop
…		…
1698	prioritise I/O.	2764	prioritise I/O.
1699		2765
1700	As an example for a bug workaround, the kqueue backend might only support	2766	As an example for a bug workaround, the kqueue backend might only support
1701	sockets on some platform, so it is unusable as generic backend, but you	2767	sockets on some platform, so it is unusable as generic backend, but you
1702	still want to make use of it because you have many sockets and it scales	2768	still want to make use of it because you have many sockets and it scales
1703	so nicely. In this case, you would create a kqueue-based loop and embed it	2769	so nicely. In this case, you would create a kqueue-based loop and embed
1704	into your default loop (which might use e.g. poll). Overall operation will	2770	it into your default loop (which might use e.g. poll). Overall operation
1705	be a bit slower because first libev has to poll and then call kevent, but	2771	will be a bit slower because first libev has to call C<poll> and then
1706	at least you can use both at what they are best.	2772	C<kevent>, but at least you can use both mechanisms for what they are
		2773	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1707		2774
1708	As for prioritising I/O: rarely you have the case where some fds have	2775	As for prioritising I/O: under rare circumstances you have the case where
1709	to be watched and handled very quickly (with low latency), and even	2776	some fds have to be watched and handled very quickly (with low latency),
1710	priorities and idle watchers might have too much overhead. In this case	2777	and even priorities and idle watchers might have too much overhead. In
1711	you would put all the high priority stuff in one loop and all the rest in	2778	this case you would put all the high priority stuff in one loop and all
1712	a second one, and embed the second one in the first.	2779	the rest in a second one, and embed the second one in the first.
1713		2780
1714	As long as the watcher is active, the callback will be invoked every time	2781	As long as the watcher is active, the callback will be invoked every
1715	there might be events pending in the embedded loop. The callback must then	2782	time there might be events pending in the embedded loop. The callback
1716	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2783	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1717	their callbacks (you could also start an idle watcher to give the embedded	2784	sweep and invoke their callbacks (the callback doesn't need to invoke the
1718	loop strictly lower priority for example). You can also set the callback	2785	C<ev_embed_sweep> function directly, it could also start an idle watcher
1719	to C<0>, in which case the embed watcher will automatically execute the	2786	to give the embedded loop strictly lower priority for example).
1720	embedded loop sweep.
1721		2787
1722	As long as the watcher is started it will automatically handle events. The	2788	You can also set the callback to C<0>, in which case the embed watcher
1723	callback will be invoked whenever some events have been handled. You can	2789	will automatically execute the embedded loop sweep whenever necessary.
1724	set the callback to C<0> to avoid having to specify one if you are not
1725	interested in that.
1726		2790
1727	Also, there have not currently been made special provisions for forking:	2791	Fork detection will be handled transparently while the C<ev_embed> watcher
1728	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2792	is active, i.e., the embedded loop will automatically be forked when the
1729	but you will also have to stop and restart any C<ev_embed> watchers	2793	embedding loop forks. In other cases, the user is responsible for calling
1730	yourself.	2794	C<ev_loop_fork> on the embedded loop.
1731		2795
1732	Unfortunately, not all backends are embeddable, only the ones returned by	2796	Unfortunately, not all backends are embeddable: only the ones returned by
1733	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2797	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1734	portable one.	2798	portable one.
1735		2799
1736	So when you want to use this feature you will always have to be prepared	2800	So when you want to use this feature you will always have to be prepared
1737	that you cannot get an embeddable loop. The recommended way to get around	2801	that you cannot get an embeddable loop. The recommended way to get around
1738	this is to have a separate variables for your embeddable loop, try to	2802	this is to have a separate variables for your embeddable loop, try to
1739	create it, and if that fails, use the normal loop for everything:	2803	create it, and if that fails, use the normal loop for everything.
1740		2804
1741	struct ev_loop *loop_hi = ev_default_init (0);	2805	=head3 C<ev_embed> and fork
1742	struct ev_loop *loop_lo = 0;
1743	struct ev_embed embed;
1744
1745	// see if there is a chance of getting one that works
1746	// (remember that a flags value of 0 means autodetection)
1747	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1748	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1749	: 0;
1750		2806
1751	// if we got one, then embed it, otherwise default to loop_hi	2807	While the C<ev_embed> watcher is running, forks in the embedding loop will
1752	if (loop_lo)	2808	automatically be applied to the embedded loop as well, so no special
1753	{	2809	fork handling is required in that case. When the watcher is not running,
1754	ev_embed_init (&embed, 0, loop_lo);	2810	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1755	ev_embed_start (loop_hi, &embed);	2811	as applicable.
1756	}
1757	else
1758	loop_lo = loop_hi;
1759		2812
1760	=head3 Watcher-Specific Functions and Data Members	2813	=head3 Watcher-Specific Functions and Data Members
1761		2814
1762	=over 4	2815	=over 4
1763		2816
…		…
1767		2820
1768	Configures the watcher to embed the given loop, which must be	2821	Configures the watcher to embed the given loop, which must be
1769	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2822	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1770	invoked automatically, otherwise it is the responsibility of the callback	2823	invoked automatically, otherwise it is the responsibility of the callback
1771	to invoke it (it will continue to be called until the sweep has been done,	2824	to invoke it (it will continue to be called until the sweep has been done,
1772	if you do not want thta, you need to temporarily stop the embed watcher).	2825	if you do not want that, you need to temporarily stop the embed watcher).
1773		2826
1774	=item ev_embed_sweep (loop, ev_embed *)	2827	=item ev_embed_sweep (loop, ev_embed *)
1775		2828
1776	Make a single, non-blocking sweep over the embedded loop. This works	2829	Make a single, non-blocking sweep over the embedded loop. This works
1777	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2830	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1778	apropriate way for embedded loops.	2831	appropriate way for embedded loops.
1779		2832
1780	=item struct ev_loop *loop [read-only]	2833	=item struct ev_loop *other [read-only]
1781		2834
1782	The embedded event loop.	2835	The embedded event loop.
1783		2836
1784	=back	2837	=back
		2838
		2839	=head3 Examples
		2840
		2841	Example: Try to get an embeddable event loop and embed it into the default
		2842	event loop. If that is not possible, use the default loop. The default
		2843	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2844	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2845	used).
		2846
		2847	struct ev_loop *loop_hi = ev_default_init (0);
		2848	struct ev_loop *loop_lo = 0;
		2849	ev_embed embed;
		2850
		2851	// see if there is a chance of getting one that works
		2852	// (remember that a flags value of 0 means autodetection)
		2853	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2854	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2855	: 0;
		2856
		2857	// if we got one, then embed it, otherwise default to loop_hi
		2858	if (loop_lo)
		2859	{
		2860	ev_embed_init (&embed, 0, loop_lo);
		2861	ev_embed_start (loop_hi, &embed);
		2862	}
		2863	else
		2864	loop_lo = loop_hi;
		2865
		2866	Example: Check if kqueue is available but not recommended and create
		2867	a kqueue backend for use with sockets (which usually work with any
		2868	kqueue implementation). Store the kqueue/socket-only event loop in
		2869	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2870
		2871	struct ev_loop *loop = ev_default_init (0);
		2872	struct ev_loop *loop_socket = 0;
		2873	ev_embed embed;
		2874
		2875	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2876	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2877	{
		2878	ev_embed_init (&embed, 0, loop_socket);
		2879	ev_embed_start (loop, &embed);
		2880	}
		2881
		2882	if (!loop_socket)
		2883	loop_socket = loop;
		2884
		2885	// now use loop_socket for all sockets, and loop for everything else
1785		2886
1786		2887
1787	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2888	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1788		2889
1789	Fork watchers are called when a C<fork ()> was detected (usually because	2890	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1792	event loop blocks next and before C<ev_check> watchers are being called,	2893	event loop blocks next and before C<ev_check> watchers are being called,
1793	and only in the child after the fork. If whoever good citizen calling	2894	and only in the child after the fork. If whoever good citizen calling
1794	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2895	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1795	handlers will be invoked, too, of course.	2896	handlers will be invoked, too, of course.
1796		2897
		2898	=head3 The special problem of life after fork - how is it possible?
		2899
		2900	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2901	up/change the process environment, followed by a call to C<exec()>. This
		2902	sequence should be handled by libev without any problems.
		2903
		2904	This changes when the application actually wants to do event handling
		2905	in the child, or both parent in child, in effect "continuing" after the
		2906	fork.
		2907
		2908	The default mode of operation (for libev, with application help to detect
		2909	forks) is to duplicate all the state in the child, as would be expected
		2910	when I<either> the parent I<or> the child process continues.
		2911
		2912	When both processes want to continue using libev, then this is usually the
		2913	wrong result. In that case, usually one process (typically the parent) is
		2914	supposed to continue with all watchers in place as before, while the other
		2915	process typically wants to start fresh, i.e. without any active watchers.
		2916
		2917	The cleanest and most efficient way to achieve that with libev is to
		2918	simply create a new event loop, which of course will be "empty", and
		2919	use that for new watchers. This has the advantage of not touching more
		2920	memory than necessary, and thus avoiding the copy-on-write, and the
		2921	disadvantage of having to use multiple event loops (which do not support
		2922	signal watchers).
		2923
		2924	When this is not possible, or you want to use the default loop for
		2925	other reasons, then in the process that wants to start "fresh", call
		2926	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2927	the default loop will "orphan" (not stop) all registered watchers, so you
		2928	have to be careful not to execute code that modifies those watchers. Note
		2929	also that in that case, you have to re-register any signal watchers.
		2930
1797	=head3 Watcher-Specific Functions and Data Members	2931	=head3 Watcher-Specific Functions and Data Members
1798		2932
1799	=over 4	2933	=over 4
1800		2934
1801	=item ev_fork_init (ev_signal *, callback)	2935	=item ev_fork_init (ev_signal *, callback)
…		…
1805	believe me.	2939	believe me.
1806		2940
1807	=back	2941	=back
1808		2942
1809		2943
		2944	=head2 C<ev_async> - how to wake up another event loop
		2945
		2946	In general, you cannot use an C<ev_loop> from multiple threads or other
		2947	asynchronous sources such as signal handlers (as opposed to multiple event
		2948	loops - those are of course safe to use in different threads).
		2949
		2950	Sometimes, however, you need to wake up another event loop you do not
		2951	control, for example because it belongs to another thread. This is what
		2952	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2953	can signal it by calling C<ev_async_send>, which is thread- and signal
		2954	safe.
		2955
		2956	This functionality is very similar to C<ev_signal> watchers, as signals,
		2957	too, are asynchronous in nature, and signals, too, will be compressed
		2958	(i.e. the number of callback invocations may be less than the number of
		2959	C<ev_async_sent> calls).
		2960
		2961	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2962	just the default loop.
		2963
		2964	=head3 Queueing
		2965
		2966	C<ev_async> does not support queueing of data in any way. The reason
		2967	is that the author does not know of a simple (or any) algorithm for a
		2968	multiple-writer-single-reader queue that works in all cases and doesn't
		2969	need elaborate support such as pthreads.
		2970
		2971	That means that if you want to queue data, you have to provide your own
		2972	queue. But at least I can tell you how to implement locking around your
		2973	queue:
		2974
		2975	=over 4
		2976
		2977	=item queueing from a signal handler context
		2978
		2979	To implement race-free queueing, you simply add to the queue in the signal
		2980	handler but you block the signal handler in the watcher callback. Here is
		2981	an example that does that for some fictitious SIGUSR1 handler:
		2982
		2983	static ev_async mysig;
		2984
		2985	static void
		2986	sigusr1_handler (void)
		2987	{
		2988	sometype data;
		2989
		2990	// no locking etc.
		2991	queue_put (data);
		2992	ev_async_send (EV_DEFAULT_ &mysig);
		2993	}
		2994
		2995	static void
		2996	mysig_cb (EV_P_ ev_async *w, int revents)
		2997	{
		2998	sometype data;
		2999	sigset_t block, prev;
		3000
		3001	sigemptyset (&block);
		3002	sigaddset (&block, SIGUSR1);
		3003	sigprocmask (SIG_BLOCK, &block, &prev);
		3004
		3005	while (queue_get (&data))
		3006	process (data);
		3007
		3008	if (sigismember (&prev, SIGUSR1)
		3009	sigprocmask (SIG_UNBLOCK, &block, 0);
		3010	}
		3011
		3012	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3013	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3014	either...).
		3015
		3016	=item queueing from a thread context
		3017
		3018	The strategy for threads is different, as you cannot (easily) block
		3019	threads but you can easily preempt them, so to queue safely you need to
		3020	employ a traditional mutex lock, such as in this pthread example:
		3021
		3022	static ev_async mysig;
		3023	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3024
		3025	static void
		3026	otherthread (void)
		3027	{
		3028	// only need to lock the actual queueing operation
		3029	pthread_mutex_lock (&mymutex);
		3030	queue_put (data);
		3031	pthread_mutex_unlock (&mymutex);
		3032
		3033	ev_async_send (EV_DEFAULT_ &mysig);
		3034	}
		3035
		3036	static void
		3037	mysig_cb (EV_P_ ev_async *w, int revents)
		3038	{
		3039	pthread_mutex_lock (&mymutex);
		3040
		3041	while (queue_get (&data))
		3042	process (data);
		3043
		3044	pthread_mutex_unlock (&mymutex);
		3045	}
		3046
		3047	=back
		3048
		3049
		3050	=head3 Watcher-Specific Functions and Data Members
		3051
		3052	=over 4
		3053
		3054	=item ev_async_init (ev_async *, callback)
		3055
		3056	Initialises and configures the async watcher - it has no parameters of any
		3057	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3058	trust me.
		3059
		3060	=item ev_async_send (loop, ev_async *)
		3061
		3062	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3063	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3064	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3065	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3066	section below on what exactly this means).
		3067
		3068	Note that, as with other watchers in libev, multiple events might get
		3069	compressed into a single callback invocation (another way to look at this
		3070	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3071	reset when the event loop detects that).
		3072
		3073	This call incurs the overhead of a system call only once per event loop
		3074	iteration, so while the overhead might be noticeable, it doesn't apply to
		3075	repeated calls to C<ev_async_send> for the same event loop.
		3076
		3077	=item bool = ev_async_pending (ev_async *)
		3078
		3079	Returns a non-zero value when C<ev_async_send> has been called on the
		3080	watcher but the event has not yet been processed (or even noted) by the
		3081	event loop.
		3082
		3083	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3084	the loop iterates next and checks for the watcher to have become active,
		3085	it will reset the flag again. C<ev_async_pending> can be used to very
		3086	quickly check whether invoking the loop might be a good idea.
		3087
		3088	Not that this does I<not> check whether the watcher itself is pending,
		3089	only whether it has been requested to make this watcher pending: there
		3090	is a time window between the event loop checking and resetting the async
		3091	notification, and the callback being invoked.
		3092
		3093	=back
		3094
		3095
1810	=head1 OTHER FUNCTIONS	3096	=head1 OTHER FUNCTIONS
1811		3097
1812	There are some other functions of possible interest. Described. Here. Now.	3098	There are some other functions of possible interest. Described. Here. Now.
1813		3099
1814	=over 4	3100	=over 4
1815		3101
1816	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3102	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1817		3103
1818	This function combines a simple timer and an I/O watcher, calls your	3104	This function combines a simple timer and an I/O watcher, calls your
1819	callback on whichever event happens first and automatically stop both	3105	callback on whichever event happens first and automatically stops both
1820	watchers. This is useful if you want to wait for a single event on an fd	3106	watchers. This is useful if you want to wait for a single event on an fd
1821	or timeout without having to allocate/configure/start/stop/free one or	3107	or timeout without having to allocate/configure/start/stop/free one or
1822	more watchers yourself.	3108	more watchers yourself.
1823		3109
1824	If C<fd> is less than 0, then no I/O watcher will be started and events	3110	If C<fd> is less than 0, then no I/O watcher will be started and the
1825	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3111	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1826	C<events> set will be craeted and started.	3112	the given C<fd> and C<events> set will be created and started.
1827		3113
1828	If C<timeout> is less than 0, then no timeout watcher will be	3114	If C<timeout> is less than 0, then no timeout watcher will be
1829	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3115	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1830	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3116	repeat = 0) will be started. C<0> is a valid timeout.
1831	dubious value.
1832		3117
1833	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3118	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1834	passed an C<revents> set like normal event callbacks (a combination of	3119	passed an C<revents> set like normal event callbacks (a combination of
1835	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3120	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1836	value passed to C<ev_once>:	3121	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3122	a timeout and an io event at the same time - you probably should give io
		3123	events precedence.
1837		3124
		3125	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3126
1838	static void stdin_ready (int revents, void *arg)	3127	static void stdin_ready (int revents, void *arg)
1839	{	3128	{
1840	if (revents & EV_TIMEOUT)
1841	/* doh, nothing entered */;
1842	else if (revents & EV_READ)	3129	if (revents & EV_READ)
1843	/* stdin might have data for us, joy! */;	3130	/* stdin might have data for us, joy! */;
		3131	else if (revents & EV_TIMEOUT)
		3132	/* doh, nothing entered */;
1844	}	3133	}
1845		3134
1846	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3135	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1847		3136
1848	=item ev_feed_event (ev_loop *, watcher *, int revents)	3137	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1849		3138
1850	Feeds the given event set into the event loop, as if the specified event	3139	Feeds the given event set into the event loop, as if the specified event
1851	had happened for the specified watcher (which must be a pointer to an	3140	had happened for the specified watcher (which must be a pointer to an
1852	initialised but not necessarily started event watcher).	3141	initialised but not necessarily started event watcher).
1853		3142
1854	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3143	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1855		3144
1856	Feed an event on the given fd, as if a file descriptor backend detected	3145	Feed an event on the given fd, as if a file descriptor backend detected
1857	the given events it.	3146	the given events it.
1858		3147
1859	=item ev_feed_signal_event (ev_loop *loop, int signum)	3148	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1860		3149
1861	Feed an event as if the given signal occured (C<loop> must be the default	3150	Feed an event as if the given signal occurred (C<loop> must be the default
1862	loop!).	3151	loop!).
1863		3152
1864	=back	3153	=back
1865		3154
1866		3155
…		…
1882		3171
1883	=item * Priorities are not currently supported. Initialising priorities	3172	=item * Priorities are not currently supported. Initialising priorities
1884	will fail and all watchers will have the same priority, even though there	3173	will fail and all watchers will have the same priority, even though there
1885	is an ev_pri field.	3174	is an ev_pri field.
1886		3175
		3176	=item * In libevent, the last base created gets the signals, in libev, the
		3177	first base created (== the default loop) gets the signals.
		3178
1887	=item * Other members are not supported.	3179	=item * Other members are not supported.
1888		3180
1889	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3181	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1890	to use the libev header file and library.	3182	to use the libev header file and library.
1891		3183
1892	=back	3184	=back
1893		3185
1894	=head1 C++ SUPPORT	3186	=head1 C++ SUPPORT
1895		3187
1896	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3188	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1897	you to use some convinience methods to start/stop watchers and also change	3189	you to use some convenience methods to start/stop watchers and also change
1898	the callback model to a model using method callbacks on objects.	3190	the callback model to a model using method callbacks on objects.
1899		3191
1900	To use it,	3192	To use it,
1901		3193
1902	#include <ev++.h>	3194	#include <ev++.h>
1903		3195
1904	This automatically includes F<ev.h> and puts all of its definitions (many	3196	This automatically includes F<ev.h> and puts all of its definitions (many
1905	of them macros) into the global namespace. All C++ specific things are	3197	of them macros) into the global namespace. All C++ specific things are
1906	put into the C<ev> namespace. It should support all the same embedding	3198	put into the C<ev> namespace. It should support all the same embedding
1907	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3199	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1974	your compiler is good :), then the method will be fully inlined into the	3266	your compiler is good :), then the method will be fully inlined into the
1975	thunking function, making it as fast as a direct C callback.	3267	thunking function, making it as fast as a direct C callback.
1976		3268
1977	Example: simple class declaration and watcher initialisation	3269	Example: simple class declaration and watcher initialisation
1978		3270
1979	struct myclass	3271	struct myclass
1980	{	3272	{
1981	void io_cb (ev::io &w, int revents) { }	3273	void io_cb (ev::io &w, int revents) { }
1982	}	3274	}
1983		3275
1984	myclass obj;	3276	myclass obj;
1985	ev::io iow;	3277	ev::io iow;
1986	iow.set <myclass, &myclass::io_cb> (&obj);	3278	iow.set <myclass, &myclass::io_cb> (&obj);
		3279
		3280	=item w->set (object *)
		3281
		3282	This is an B<experimental> feature that might go away in a future version.
		3283
		3284	This is a variation of a method callback - leaving out the method to call
		3285	will default the method to C<operator ()>, which makes it possible to use
		3286	functor objects without having to manually specify the C<operator ()> all
		3287	the time. Incidentally, you can then also leave out the template argument
		3288	list.
		3289
		3290	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3291	int revents)>.
		3292
		3293	See the method-C<set> above for more details.
		3294
		3295	Example: use a functor object as callback.
		3296
		3297	struct myfunctor
		3298	{
		3299	void operator() (ev::io &w, int revents)
		3300	{
		3301	...
		3302	}
		3303	}
		3304
		3305	myfunctor f;
		3306
		3307	ev::io w;
		3308	w.set (&f);
1987		3309
1988	=item w->set<function> (void *data = 0)	3310	=item w->set<function> (void *data = 0)
1989		3311
1990	Also sets a callback, but uses a static method or plain function as	3312	Also sets a callback, but uses a static method or plain function as
1991	callback. The optional C<data> argument will be stored in the watcher's	3313	callback. The optional C<data> argument will be stored in the watcher's
…		…
1993		3315
1994	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3316	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1995		3317
1996	See the method-C<set> above for more details.	3318	See the method-C<set> above for more details.
1997		3319
1998	Example:	3320	Example: Use a plain function as callback.
1999		3321
2000	static void io_cb (ev::io &w, int revents) { }	3322	static void io_cb (ev::io &w, int revents) { }
2001	iow.set <io_cb> ();	3323	iow.set <io_cb> ();
2002		3324
2003	=item w->set (struct ev_loop *)	3325	=item w->set (struct ev_loop *)
2004		3326
2005	Associates a different C<struct ev_loop> with this watcher. You can only	3327	Associates a different C<struct ev_loop> with this watcher. You can only
2006	do this when the watcher is inactive (and not pending either).	3328	do this when the watcher is inactive (and not pending either).
2007		3329
2008	=item w->set ([args])	3330	=item w->set ([arguments])
2009		3331
2010	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3332	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2011	called at least once. Unlike the C counterpart, an active watcher gets	3333	called at least once. Unlike the C counterpart, an active watcher gets
2012	automatically stopped and restarted when reconfiguring it with this	3334	automatically stopped and restarted when reconfiguring it with this
2013	method.	3335	method.
2014		3336
2015	=item w->start ()	3337	=item w->start ()
…		…
2039	=back	3361	=back
2040		3362
2041	Example: Define a class with an IO and idle watcher, start one of them in	3363	Example: Define a class with an IO and idle watcher, start one of them in
2042	the constructor.	3364	the constructor.
2043		3365
2044	class myclass	3366	class myclass
2045	{	3367	{
2046	ev_io io; void io_cb (ev::io &w, int revents);	3368	ev::io io ; void io_cb (ev::io &w, int revents);
2047	ev_idle idle void idle_cb (ev::idle &w, int revents);	3369	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2048		3370
2049	myclass ();	3371	myclass (int fd)
2050	}	3372	{
2051
2052	myclass::myclass (int fd)
2053	{
2054	io .set <myclass, &myclass::io_cb > (this);	3373	io .set <myclass, &myclass::io_cb > (this);
2055	idle.set <myclass, &myclass::idle_cb> (this);	3374	idle.set <myclass, &myclass::idle_cb> (this);
2056		3375
2057	io.start (fd, ev::READ);	3376	io.start (fd, ev::READ);
		3377	}
2058	}	3378	};
		3379
		3380
		3381	=head1 OTHER LANGUAGE BINDINGS
		3382
		3383	Libev does not offer other language bindings itself, but bindings for a
		3384	number of languages exist in the form of third-party packages. If you know
		3385	any interesting language binding in addition to the ones listed here, drop
		3386	me a note.
		3387
		3388	=over 4
		3389
		3390	=item Perl
		3391
		3392	The EV module implements the full libev API and is actually used to test
		3393	libev. EV is developed together with libev. Apart from the EV core module,
		3394	there are additional modules that implement libev-compatible interfaces
		3395	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3396	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3397	and C<EV::Glib>).
		3398
		3399	It can be found and installed via CPAN, its homepage is at
		3400	L<http://software.schmorp.de/pkg/EV>.
		3401
		3402	=item Python
		3403
		3404	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3405	seems to be quite complete and well-documented.
		3406
		3407	=item Ruby
		3408
		3409	Tony Arcieri has written a ruby extension that offers access to a subset
		3410	of the libev API and adds file handle abstractions, asynchronous DNS and
		3411	more on top of it. It can be found via gem servers. Its homepage is at
		3412	L<http://rev.rubyforge.org/>.
		3413
		3414	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3415	makes rev work even on mingw.
		3416
		3417	=item Haskell
		3418
		3419	A haskell binding to libev is available at
		3420	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3421
		3422	=item D
		3423
		3424	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3425	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3426
		3427	=item Ocaml
		3428
		3429	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3430	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3431
		3432	=item Lua
		3433
		3434	Brian Maher has written a partial interface to libev
		3435	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3436	L<http://github.com/brimworks/lua-ev>.
		3437
		3438	=back
2059		3439
2060		3440
2061	=head1 MACRO MAGIC	3441	=head1 MACRO MAGIC
2062		3442
2063	Libev can be compiled with a variety of options, the most fundamantal	3443	Libev can be compiled with a variety of options, the most fundamental
2064	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3444	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2065	functions and callbacks have an initial C<struct ev_loop *> argument.	3445	functions and callbacks have an initial C<struct ev_loop *> argument.
2066		3446
2067	To make it easier to write programs that cope with either variant, the	3447	To make it easier to write programs that cope with either variant, the
2068	following macros are defined:	3448	following macros are defined:
…		…
2073		3453
2074	This provides the loop I<argument> for functions, if one is required ("ev	3454	This provides the loop I<argument> for functions, if one is required ("ev
2075	loop argument"). The C<EV_A> form is used when this is the sole argument,	3455	loop argument"). The C<EV_A> form is used when this is the sole argument,
2076	C<EV_A_> is used when other arguments are following. Example:	3456	C<EV_A_> is used when other arguments are following. Example:
2077		3457
2078	ev_unref (EV_A);	3458	ev_unref (EV_A);
2079	ev_timer_add (EV_A_ watcher);	3459	ev_timer_add (EV_A_ watcher);
2080	ev_loop (EV_A_ 0);	3460	ev_loop (EV_A_ 0);
2081		3461
2082	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3462	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2083	which is often provided by the following macro.	3463	which is often provided by the following macro.
2084		3464
2085	=item C<EV_P>, C<EV_P_>	3465	=item C<EV_P>, C<EV_P_>
2086		3466
2087	This provides the loop I<parameter> for functions, if one is required ("ev	3467	This provides the loop I<parameter> for functions, if one is required ("ev
2088	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3468	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2089	C<EV_P_> is used when other parameters are following. Example:	3469	C<EV_P_> is used when other parameters are following. Example:
2090		3470
2091	// this is how ev_unref is being declared	3471	// this is how ev_unref is being declared
2092	static void ev_unref (EV_P);	3472	static void ev_unref (EV_P);
2093		3473
2094	// this is how you can declare your typical callback	3474	// this is how you can declare your typical callback
2095	static void cb (EV_P_ ev_timer *w, int revents)	3475	static void cb (EV_P_ ev_timer *w, int revents)
2096		3476
2097	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3477	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2098	suitable for use with C<EV_A>.	3478	suitable for use with C<EV_A>.
2099		3479
2100	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3480	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2101		3481
2102	Similar to the other two macros, this gives you the value of the default	3482	Similar to the other two macros, this gives you the value of the default
2103	loop, if multiple loops are supported ("ev loop default").	3483	loop, if multiple loops are supported ("ev loop default").
		3484
		3485	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3486
		3487	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3488	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3489	is undefined when the default loop has not been initialised by a previous
		3490	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3491
		3492	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3493	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2104		3494
2105	=back	3495	=back
2106		3496
2107	Example: Declare and initialise a check watcher, utilising the above	3497	Example: Declare and initialise a check watcher, utilising the above
2108	macros so it will work regardless of whether multiple loops are supported	3498	macros so it will work regardless of whether multiple loops are supported
2109	or not.	3499	or not.
2110		3500
2111	static void	3501	static void
2112	check_cb (EV_P_ ev_timer *w, int revents)	3502	check_cb (EV_P_ ev_timer *w, int revents)
2113	{	3503	{
2114	ev_check_stop (EV_A_ w);	3504	ev_check_stop (EV_A_ w);
2115	}	3505	}
2116		3506
2117	ev_check check;	3507	ev_check check;
2118	ev_check_init (&check, check_cb);	3508	ev_check_init (&check, check_cb);
2119	ev_check_start (EV_DEFAULT_ &check);	3509	ev_check_start (EV_DEFAULT_ &check);
2120	ev_loop (EV_DEFAULT_ 0);	3510	ev_loop (EV_DEFAULT_ 0);
2121		3511
2122	=head1 EMBEDDING	3512	=head1 EMBEDDING
2123		3513
2124	Libev can (and often is) directly embedded into host	3514	Libev can (and often is) directly embedded into host
2125	applications. Examples of applications that embed it include the Deliantra	3515	applications. Examples of applications that embed it include the Deliantra
2126	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3516	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2127	and rxvt-unicode.	3517	and rxvt-unicode.
2128		3518
2129	The goal is to enable you to just copy the neecssary files into your	3519	The goal is to enable you to just copy the necessary files into your
2130	source directory without having to change even a single line in them, so	3520	source directory without having to change even a single line in them, so
2131	you can easily upgrade by simply copying (or having a checked-out copy of	3521	you can easily upgrade by simply copying (or having a checked-out copy of
2132	libev somewhere in your source tree).	3522	libev somewhere in your source tree).
2133		3523
2134	=head2 FILESETS	3524	=head2 FILESETS
2135		3525
2136	Depending on what features you need you need to include one or more sets of files	3526	Depending on what features you need you need to include one or more sets of files
2137	in your app.	3527	in your application.
2138		3528
2139	=head3 CORE EVENT LOOP	3529	=head3 CORE EVENT LOOP
2140		3530
2141	To include only the libev core (all the C<ev_*> functions), with manual	3531	To include only the libev core (all the C<ev_*> functions), with manual
2142	configuration (no autoconf):	3532	configuration (no autoconf):
2143		3533
2144	#define EV_STANDALONE 1	3534	#define EV_STANDALONE 1
2145	#include "ev.c"	3535	#include "ev.c"
2146		3536
2147	This will automatically include F<ev.h>, too, and should be done in a	3537	This will automatically include F<ev.h>, too, and should be done in a
2148	single C source file only to provide the function implementations. To use	3538	single C source file only to provide the function implementations. To use
2149	it, do the same for F<ev.h> in all files wishing to use this API (best	3539	it, do the same for F<ev.h> in all files wishing to use this API (best
2150	done by writing a wrapper around F<ev.h> that you can include instead and	3540	done by writing a wrapper around F<ev.h> that you can include instead and
2151	where you can put other configuration options):	3541	where you can put other configuration options):
2152		3542
2153	#define EV_STANDALONE 1	3543	#define EV_STANDALONE 1
2154	#include "ev.h"	3544	#include "ev.h"
2155		3545
2156	Both header files and implementation files can be compiled with a C++	3546	Both header files and implementation files can be compiled with a C++
2157	compiler (at least, thats a stated goal, and breakage will be treated	3547	compiler (at least, that's a stated goal, and breakage will be treated
2158	as a bug).	3548	as a bug).
2159		3549
2160	You need the following files in your source tree, or in a directory	3550	You need the following files in your source tree, or in a directory
2161	in your include path (e.g. in libev/ when using -Ilibev):	3551	in your include path (e.g. in libev/ when using -Ilibev):
2162		3552
2163	ev.h	3553	ev.h
2164	ev.c	3554	ev.c
2165	ev_vars.h	3555	ev_vars.h
2166	ev_wrap.h	3556	ev_wrap.h
2167		3557
2168	ev_win32.c required on win32 platforms only	3558	ev_win32.c required on win32 platforms only
2169		3559
2170	ev_select.c only when select backend is enabled (which is enabled by default)	3560	ev_select.c only when select backend is enabled (which is enabled by default)
2171	ev_poll.c only when poll backend is enabled (disabled by default)	3561	ev_poll.c only when poll backend is enabled (disabled by default)
2172	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3562	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2173	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3563	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2174	ev_port.c only when the solaris port backend is enabled (disabled by default)	3564	ev_port.c only when the solaris port backend is enabled (disabled by default)
2175		3565
2176	F<ev.c> includes the backend files directly when enabled, so you only need	3566	F<ev.c> includes the backend files directly when enabled, so you only need
2177	to compile this single file.	3567	to compile this single file.
2178		3568
2179	=head3 LIBEVENT COMPATIBILITY API	3569	=head3 LIBEVENT COMPATIBILITY API
2180		3570
2181	To include the libevent compatibility API, also include:	3571	To include the libevent compatibility API, also include:
2182		3572
2183	#include "event.c"	3573	#include "event.c"
2184		3574
2185	in the file including F<ev.c>, and:	3575	in the file including F<ev.c>, and:
2186		3576
2187	#include "event.h"	3577	#include "event.h"
2188		3578
2189	in the files that want to use the libevent API. This also includes F<ev.h>.	3579	in the files that want to use the libevent API. This also includes F<ev.h>.
2190		3580
2191	You need the following additional files for this:	3581	You need the following additional files for this:
2192		3582
2193	event.h	3583	event.h
2194	event.c	3584	event.c
2195		3585
2196	=head3 AUTOCONF SUPPORT	3586	=head3 AUTOCONF SUPPORT
2197		3587
2198	Instead of using C<EV_STANDALONE=1> and providing your config in	3588	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2199	whatever way you want, you can also C<m4_include([libev.m4])> in your	3589	whatever way you want, you can also C<m4_include([libev.m4])> in your
2200	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3590	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2201	include F<config.h> and configure itself accordingly.	3591	include F<config.h> and configure itself accordingly.
2202		3592
2203	For this of course you need the m4 file:	3593	For this of course you need the m4 file:
2204		3594
2205	libev.m4	3595	libev.m4
2206		3596
2207	=head2 PREPROCESSOR SYMBOLS/MACROS	3597	=head2 PREPROCESSOR SYMBOLS/MACROS
2208		3598
2209	Libev can be configured via a variety of preprocessor symbols you have to define	3599	Libev can be configured via a variety of preprocessor symbols you have to
2210	before including any of its files. The default is not to build for multiplicity	3600	define before including any of its files. The default in the absence of
2211	and only include the select backend.	3601	autoconf is documented for every option.
2212		3602
2213	=over 4	3603	=over 4
2214		3604
2215	=item EV_STANDALONE	3605	=item EV_STANDALONE
2216		3606
…		…
2218	keeps libev from including F<config.h>, and it also defines dummy	3608	keeps libev from including F<config.h>, and it also defines dummy
2219	implementations for some libevent functions (such as logging, which is not	3609	implementations for some libevent functions (such as logging, which is not
2220	supported). It will also not define any of the structs usually found in	3610	supported). It will also not define any of the structs usually found in
2221	F<event.h> that are not directly supported by the libev core alone.	3611	F<event.h> that are not directly supported by the libev core alone.
2222		3612
		3613	In standalone mode, libev will still try to automatically deduce the
		3614	configuration, but has to be more conservative.
		3615
2223	=item EV_USE_MONOTONIC	3616	=item EV_USE_MONOTONIC
2224		3617
2225	If defined to be C<1>, libev will try to detect the availability of the	3618	If defined to be C<1>, libev will try to detect the availability of the
2226	monotonic clock option at both compiletime and runtime. Otherwise no use	3619	monotonic clock option at both compile time and runtime. Otherwise no
2227	of the monotonic clock option will be attempted. If you enable this, you	3620	use of the monotonic clock option will be attempted. If you enable this,
2228	usually have to link against librt or something similar. Enabling it when	3621	you usually have to link against librt or something similar. Enabling it
2229	the functionality isn't available is safe, though, althoguh you have	3622	when the functionality isn't available is safe, though, although you have
2230	to make sure you link against any libraries where the C<clock_gettime>	3623	to make sure you link against any libraries where the C<clock_gettime>
2231	function is hiding in (often F<-lrt>).	3624	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2232		3625
2233	=item EV_USE_REALTIME	3626	=item EV_USE_REALTIME
2234		3627
2235	If defined to be C<1>, libev will try to detect the availability of the	3628	If defined to be C<1>, libev will try to detect the availability of the
2236	realtime clock option at compiletime (and assume its availability at	3629	real-time clock option at compile time (and assume its availability
2237	runtime if successful). Otherwise no use of the realtime clock option will	3630	at runtime if successful). Otherwise no use of the real-time clock
2238	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3631	option will be attempted. This effectively replaces C<gettimeofday>
2239	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3632	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2240	in the description of C<EV_USE_MONOTONIC>, though.	3633	correctness. See the note about libraries in the description of
		3634	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3635	C<EV_USE_CLOCK_SYSCALL>.
		3636
		3637	=item EV_USE_CLOCK_SYSCALL
		3638
		3639	If defined to be C<1>, libev will try to use a direct syscall instead
		3640	of calling the system-provided C<clock_gettime> function. This option
		3641	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3642	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3643	programs needlessly. Using a direct syscall is slightly slower (in
		3644	theory), because no optimised vdso implementation can be used, but avoids
		3645	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3646	higher, as it simplifies linking (no need for C<-lrt>).
		3647
		3648	=item EV_USE_NANOSLEEP
		3649
		3650	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3651	and will use it for delays. Otherwise it will use C<select ()>.
		3652
		3653	=item EV_USE_EVENTFD
		3654
		3655	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3656	available and will probe for kernel support at runtime. This will improve
		3657	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3658	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3659	2.7 or newer, otherwise disabled.
2241		3660
2242	=item EV_USE_SELECT	3661	=item EV_USE_SELECT
2243		3662
2244	If undefined or defined to be C<1>, libev will compile in support for the	3663	If undefined or defined to be C<1>, libev will compile in support for the
2245	C<select>(2) backend. No attempt at autodetection will be done: if no	3664	C<select>(2) backend. No attempt at auto-detection will be done: if no
2246	other method takes over, select will be it. Otherwise the select backend	3665	other method takes over, select will be it. Otherwise the select backend
2247	will not be compiled in.	3666	will not be compiled in.
2248		3667
2249	=item EV_SELECT_USE_FD_SET	3668	=item EV_SELECT_USE_FD_SET
2250		3669
2251	If defined to C<1>, then the select backend will use the system C<fd_set>	3670	If defined to C<1>, then the select backend will use the system C<fd_set>
2252	structure. This is useful if libev doesn't compile due to a missing	3671	structure. This is useful if libev doesn't compile due to a missing
2253	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3672	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2254	exotic systems. This usually limits the range of file descriptors to some	3673	on exotic systems. This usually limits the range of file descriptors to
2255	low limit such as 1024 or might have other limitations (winsocket only	3674	some low limit such as 1024 or might have other limitations (winsocket
2256	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3675	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2257	influence the size of the C<fd_set> used.	3676	configures the maximum size of the C<fd_set>.
2258		3677
2259	=item EV_SELECT_IS_WINSOCKET	3678	=item EV_SELECT_IS_WINSOCKET
2260		3679
2261	When defined to C<1>, the select backend will assume that	3680	When defined to C<1>, the select backend will assume that
2262	select/socket/connect etc. don't understand file descriptors but	3681	select/socket/connect etc. don't understand file descriptors but
…		…
2264	be used is the winsock select). This means that it will call	3683	be used is the winsock select). This means that it will call
2265	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3684	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2266	it is assumed that all these functions actually work on fds, even	3685	it is assumed that all these functions actually work on fds, even
2267	on win32. Should not be defined on non-win32 platforms.	3686	on win32. Should not be defined on non-win32 platforms.
2268		3687
		3688	=item EV_FD_TO_WIN32_HANDLE(fd)
		3689
		3690	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3691	file descriptors to socket handles. When not defining this symbol (the
		3692	default), then libev will call C<_get_osfhandle>, which is usually
		3693	correct. In some cases, programs use their own file descriptor management,
		3694	in which case they can provide this function to map fds to socket handles.
		3695
		3696	=item EV_WIN32_HANDLE_TO_FD(handle)
		3697
		3698	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3699	using the standard C<_open_osfhandle> function. For programs implementing
		3700	their own fd to handle mapping, overwriting this function makes it easier
		3701	to do so. This can be done by defining this macro to an appropriate value.
		3702
		3703	=item EV_WIN32_CLOSE_FD(fd)
		3704
		3705	If programs implement their own fd to handle mapping on win32, then this
		3706	macro can be used to override the C<close> function, useful to unregister
		3707	file descriptors again. Note that the replacement function has to close
		3708	the underlying OS handle.
		3709
2269	=item EV_USE_POLL	3710	=item EV_USE_POLL
2270		3711
2271	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3712	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2272	backend. Otherwise it will be enabled on non-win32 platforms. It	3713	backend. Otherwise it will be enabled on non-win32 platforms. It
2273	takes precedence over select.	3714	takes precedence over select.
2274		3715
2275	=item EV_USE_EPOLL	3716	=item EV_USE_EPOLL
2276		3717
2277	If defined to be C<1>, libev will compile in support for the Linux	3718	If defined to be C<1>, libev will compile in support for the Linux
2278	C<epoll>(7) backend. Its availability will be detected at runtime,	3719	C<epoll>(7) backend. Its availability will be detected at runtime,
2279	otherwise another method will be used as fallback. This is the	3720	otherwise another method will be used as fallback. This is the preferred
2280	preferred backend for GNU/Linux systems.	3721	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3722	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2281		3723
2282	=item EV_USE_KQUEUE	3724	=item EV_USE_KQUEUE
2283		3725
2284	If defined to be C<1>, libev will compile in support for the BSD style	3726	If defined to be C<1>, libev will compile in support for the BSD style
2285	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3727	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2298	otherwise another method will be used as fallback. This is the preferred	3740	otherwise another method will be used as fallback. This is the preferred
2299	backend for Solaris 10 systems.	3741	backend for Solaris 10 systems.
2300		3742
2301	=item EV_USE_DEVPOLL	3743	=item EV_USE_DEVPOLL
2302		3744
2303	reserved for future expansion, works like the USE symbols above.	3745	Reserved for future expansion, works like the USE symbols above.
2304		3746
2305	=item EV_USE_INOTIFY	3747	=item EV_USE_INOTIFY
2306		3748
2307	If defined to be C<1>, libev will compile in support for the Linux inotify	3749	If defined to be C<1>, libev will compile in support for the Linux inotify
2308	interface to speed up C<ev_stat> watchers. Its actual availability will	3750	interface to speed up C<ev_stat> watchers. Its actual availability will
2309	be detected at runtime.	3751	be detected at runtime. If undefined, it will be enabled if the headers
		3752	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3753
		3754	=item EV_ATOMIC_T
		3755
		3756	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3757	access is atomic with respect to other threads or signal contexts. No such
		3758	type is easily found in the C language, so you can provide your own type
		3759	that you know is safe for your purposes. It is used both for signal handler "locking"
		3760	as well as for signal and thread safety in C<ev_async> watchers.
		3761
		3762	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3763	(from F<signal.h>), which is usually good enough on most platforms.
2310		3764
2311	=item EV_H	3765	=item EV_H
2312		3766
2313	The name of the F<ev.h> header file used to include it. The default if	3767	The name of the F<ev.h> header file used to include it. The default if
2314	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3768	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2315	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3769	used to virtually rename the F<ev.h> header file in case of conflicts.
2316		3770
2317	=item EV_CONFIG_H	3771	=item EV_CONFIG_H
2318		3772
2319	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3773	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2320	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3774	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2321	C<EV_H>, above.	3775	C<EV_H>, above.
2322		3776
2323	=item EV_EVENT_H	3777	=item EV_EVENT_H
2324		3778
2325	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3779	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2326	of how the F<event.h> header can be found.	3780	of how the F<event.h> header can be found, the default is C<"event.h">.
2327		3781
2328	=item EV_PROTOTYPES	3782	=item EV_PROTOTYPES
2329		3783
2330	If defined to be C<0>, then F<ev.h> will not define any function	3784	If defined to be C<0>, then F<ev.h> will not define any function
2331	prototypes, but still define all the structs and other symbols. This is	3785	prototypes, but still define all the structs and other symbols. This is
…		…
2352	When doing priority-based operations, libev usually has to linearly search	3806	When doing priority-based operations, libev usually has to linearly search
2353	all the priorities, so having many of them (hundreds) uses a lot of space	3807	all the priorities, so having many of them (hundreds) uses a lot of space
2354	and time, so using the defaults of five priorities (-2 .. +2) is usually	3808	and time, so using the defaults of five priorities (-2 .. +2) is usually
2355	fine.	3809	fine.
2356		3810
2357	If your embedding app does not need any priorities, defining these both to	3811	If your embedding application does not need any priorities, defining these
2358	C<0> will save some memory and cpu.	3812	both to C<0> will save some memory and CPU.
2359		3813
2360	=item EV_PERIODIC_ENABLE	3814	=item EV_PERIODIC_ENABLE
2361		3815
2362	If undefined or defined to be C<1>, then periodic timers are supported. If	3816	If undefined or defined to be C<1>, then periodic timers are supported. If
2363	defined to be C<0>, then they are not. Disabling them saves a few kB of	3817	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2370	code.	3824	code.
2371		3825
2372	=item EV_EMBED_ENABLE	3826	=item EV_EMBED_ENABLE
2373		3827
2374	If undefined or defined to be C<1>, then embed watchers are supported. If	3828	If undefined or defined to be C<1>, then embed watchers are supported. If
2375	defined to be C<0>, then they are not.	3829	defined to be C<0>, then they are not. Embed watchers rely on most other
		3830	watcher types, which therefore must not be disabled.
2376		3831
2377	=item EV_STAT_ENABLE	3832	=item EV_STAT_ENABLE
2378		3833
2379	If undefined or defined to be C<1>, then stat watchers are supported. If	3834	If undefined or defined to be C<1>, then stat watchers are supported. If
2380	defined to be C<0>, then they are not.	3835	defined to be C<0>, then they are not.
…		…
2382	=item EV_FORK_ENABLE	3837	=item EV_FORK_ENABLE
2383		3838
2384	If undefined or defined to be C<1>, then fork watchers are supported. If	3839	If undefined or defined to be C<1>, then fork watchers are supported. If
2385	defined to be C<0>, then they are not.	3840	defined to be C<0>, then they are not.
2386		3841
		3842	=item EV_ASYNC_ENABLE
		3843
		3844	If undefined or defined to be C<1>, then async watchers are supported. If
		3845	defined to be C<0>, then they are not.
		3846
2387	=item EV_MINIMAL	3847	=item EV_MINIMAL
2388		3848
2389	If you need to shave off some kilobytes of code at the expense of some	3849	If you need to shave off some kilobytes of code at the expense of some
2390	speed, define this symbol to C<1>. Currently only used for gcc to override	3850	speed (but with the full API), define this symbol to C<1>. Currently this
2391	some inlining decisions, saves roughly 30% codesize of amd64.	3851	is used to override some inlining decisions, saves roughly 30% code size
		3852	on amd64. It also selects a much smaller 2-heap for timer management over
		3853	the default 4-heap.
		3854
		3855	You can save even more by disabling watcher types you do not need
		3856	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3857	(C<-DNDEBUG>) will usually reduce code size a lot.
		3858
		3859	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3860	provide a bare-bones event library. See C<ev.h> for details on what parts
		3861	of the API are still available, and do not complain if this subset changes
		3862	over time.
		3863
		3864	=item EV_NSIG
		3865
		3866	The highest supported signal number, +1 (or, the number of
		3867	signals): Normally, libev tries to deduce the maximum number of signals
		3868	automatically, but sometimes this fails, in which case it can be
		3869	specified. Also, using a lower number than detected (C<32> should be
		3870	good for about any system in existance) can save some memory, as libev
		3871	statically allocates some 12-24 bytes per signal number.
2392		3872
2393	=item EV_PID_HASHSIZE	3873	=item EV_PID_HASHSIZE
2394		3874
2395	C<ev_child> watchers use a small hash table to distribute workload by	3875	C<ev_child> watchers use a small hash table to distribute workload by
2396	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3876	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2397	than enough. If you need to manage thousands of children you might want to	3877	than enough. If you need to manage thousands of children you might want to
2398	increase this value (I<must> be a power of two).	3878	increase this value (I<must> be a power of two).
2399		3879
2400	=item EV_INOTIFY_HASHSIZE	3880	=item EV_INOTIFY_HASHSIZE
2401		3881
2402	C<ev_staz> watchers use a small hash table to distribute workload by	3882	C<ev_stat> watchers use a small hash table to distribute workload by
2403	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3883	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2404	usually more than enough. If you need to manage thousands of C<ev_stat>	3884	usually more than enough. If you need to manage thousands of C<ev_stat>
2405	watchers you might want to increase this value (I<must> be a power of	3885	watchers you might want to increase this value (I<must> be a power of
2406	two).	3886	two).
2407		3887
		3888	=item EV_USE_4HEAP
		3889
		3890	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3891	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3892	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3893	faster performance with many (thousands) of watchers.
		3894
		3895	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3896	(disabled).
		3897
		3898	=item EV_HEAP_CACHE_AT
		3899
		3900	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3901	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3902	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3903	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3904	but avoids random read accesses on heap changes. This improves performance
		3905	noticeably with many (hundreds) of watchers.
		3906
		3907	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3908	(disabled).
		3909
		3910	=item EV_VERIFY
		3911
		3912	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3913	be done: If set to C<0>, no internal verification code will be compiled
		3914	in. If set to C<1>, then verification code will be compiled in, but not
		3915	called. If set to C<2>, then the internal verification code will be
		3916	called once per loop, which can slow down libev. If set to C<3>, then the
		3917	verification code will be called very frequently, which will slow down
		3918	libev considerably.
		3919
		3920	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3921	C<0>.
		3922
2408	=item EV_COMMON	3923	=item EV_COMMON
2409		3924
2410	By default, all watchers have a C<void *data> member. By redefining	3925	By default, all watchers have a C<void *data> member. By redefining
2411	this macro to a something else you can include more and other types of	3926	this macro to a something else you can include more and other types of
2412	members. You have to define it each time you include one of the files,	3927	members. You have to define it each time you include one of the files,
2413	though, and it must be identical each time.	3928	though, and it must be identical each time.
2414		3929
2415	For example, the perl EV module uses something like this:	3930	For example, the perl EV module uses something like this:
2416		3931
2417	#define EV_COMMON \	3932	#define EV_COMMON \
2418	SV *self; /* contains this struct */ \	3933	SV *self; /* contains this struct */ \
2419	SV *cb_sv, *fh /* note no trailing ";" */	3934	SV *cb_sv, *fh /* note no trailing ";" */
2420		3935
2421	=item EV_CB_DECLARE (type)	3936	=item EV_CB_DECLARE (type)
2422		3937
2423	=item EV_CB_INVOKE (watcher, revents)	3938	=item EV_CB_INVOKE (watcher, revents)
2424		3939
2425	=item ev_set_cb (ev, cb)	3940	=item ev_set_cb (ev, cb)
2426		3941
2427	Can be used to change the callback member declaration in each watcher,	3942	Can be used to change the callback member declaration in each watcher,
2428	and the way callbacks are invoked and set. Must expand to a struct member	3943	and the way callbacks are invoked and set. Must expand to a struct member
2429	definition and a statement, respectively. See the F<ev.v> header file for	3944	definition and a statement, respectively. See the F<ev.h> header file for
2430	their default definitions. One possible use for overriding these is to	3945	their default definitions. One possible use for overriding these is to
2431	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3946	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2432	method calls instead of plain function calls in C++.	3947	method calls instead of plain function calls in C++.
		3948
		3949	=back
		3950
		3951	=head2 EXPORTED API SYMBOLS
		3952
		3953	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3954	exported symbols, you can use the provided F<Symbol.*> files which list
		3955	all public symbols, one per line:
		3956
		3957	Symbols.ev for libev proper
		3958	Symbols.event for the libevent emulation
		3959
		3960	This can also be used to rename all public symbols to avoid clashes with
		3961	multiple versions of libev linked together (which is obviously bad in
		3962	itself, but sometimes it is inconvenient to avoid this).
		3963
		3964	A sed command like this will create wrapper C<#define>'s that you need to
		3965	include before including F<ev.h>:
		3966
		3967	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3968
		3969	This would create a file F<wrap.h> which essentially looks like this:
		3970
		3971	#define ev_backend myprefix_ev_backend
		3972	#define ev_check_start myprefix_ev_check_start
		3973	#define ev_check_stop myprefix_ev_check_stop
		3974	...
2433		3975
2434	=head2 EXAMPLES	3976	=head2 EXAMPLES
2435		3977
2436	For a real-world example of a program the includes libev	3978	For a real-world example of a program the includes libev
2437	verbatim, you can have a look at the EV perl module	3979	verbatim, you can have a look at the EV perl module
…		…
2442	file.	3984	file.
2443		3985
2444	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3986	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2445	that everybody includes and which overrides some configure choices:	3987	that everybody includes and which overrides some configure choices:
2446		3988
2447	#define EV_MINIMAL 1	3989	#define EV_MINIMAL 1
2448	#define EV_USE_POLL 0	3990	#define EV_USE_POLL 0
2449	#define EV_MULTIPLICITY 0	3991	#define EV_MULTIPLICITY 0
2450	#define EV_PERIODIC_ENABLE 0	3992	#define EV_PERIODIC_ENABLE 0
2451	#define EV_STAT_ENABLE 0	3993	#define EV_STAT_ENABLE 0
2452	#define EV_FORK_ENABLE 0	3994	#define EV_FORK_ENABLE 0
2453	#define EV_CONFIG_H <config.h>	3995	#define EV_CONFIG_H <config.h>
2454	#define EV_MINPRI 0	3996	#define EV_MINPRI 0
2455	#define EV_MAXPRI 0	3997	#define EV_MAXPRI 0
2456		3998
2457	#include "ev++.h"	3999	#include "ev++.h"
2458		4000
2459	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4001	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2460		4002
2461	#include "ev_cpp.h"	4003	#include "ev_cpp.h"
2462	#include "ev.c"	4004	#include "ev.c"
2463		4005
		4006	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2464		4007
		4008	=head2 THREADS AND COROUTINES
		4009
		4010	=head3 THREADS
		4011
		4012	All libev functions are reentrant and thread-safe unless explicitly
		4013	documented otherwise, but libev implements no locking itself. This means
		4014	that you can use as many loops as you want in parallel, as long as there
		4015	are no concurrent calls into any libev function with the same loop
		4016	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4017	of course): libev guarantees that different event loops share no data
		4018	structures that need any locking.
		4019
		4020	Or to put it differently: calls with different loop parameters can be done
		4021	concurrently from multiple threads, calls with the same loop parameter
		4022	must be done serially (but can be done from different threads, as long as
		4023	only one thread ever is inside a call at any point in time, e.g. by using
		4024	a mutex per loop).
		4025
		4026	Specifically to support threads (and signal handlers), libev implements
		4027	so-called C<ev_async> watchers, which allow some limited form of
		4028	concurrency on the same event loop, namely waking it up "from the
		4029	outside".
		4030
		4031	If you want to know which design (one loop, locking, or multiple loops
		4032	without or something else still) is best for your problem, then I cannot
		4033	help you, but here is some generic advice:
		4034
		4035	=over 4
		4036
		4037	=item * most applications have a main thread: use the default libev loop
		4038	in that thread, or create a separate thread running only the default loop.
		4039
		4040	This helps integrating other libraries or software modules that use libev
		4041	themselves and don't care/know about threading.
		4042
		4043	=item * one loop per thread is usually a good model.
		4044
		4045	Doing this is almost never wrong, sometimes a better-performance model
		4046	exists, but it is always a good start.
		4047
		4048	=item * other models exist, such as the leader/follower pattern, where one
		4049	loop is handed through multiple threads in a kind of round-robin fashion.
		4050
		4051	Choosing a model is hard - look around, learn, know that usually you can do
		4052	better than you currently do :-)
		4053
		4054	=item * often you need to talk to some other thread which blocks in the
		4055	event loop.
		4056
		4057	C<ev_async> watchers can be used to wake them up from other threads safely
		4058	(or from signal contexts...).
		4059
		4060	An example use would be to communicate signals or other events that only
		4061	work in the default loop by registering the signal watcher with the
		4062	default loop and triggering an C<ev_async> watcher from the default loop
		4063	watcher callback into the event loop interested in the signal.
		4064
		4065	=back
		4066
		4067	=head4 THREAD LOCKING EXAMPLE
		4068
		4069	Here is a fictitious example of how to run an event loop in a different
		4070	thread than where callbacks are being invoked and watchers are
		4071	created/added/removed.
		4072
		4073	For a real-world example, see the C<EV::Loop::Async> perl module,
		4074	which uses exactly this technique (which is suited for many high-level
		4075	languages).
		4076
		4077	The example uses a pthread mutex to protect the loop data, a condition
		4078	variable to wait for callback invocations, an async watcher to notify the
		4079	event loop thread and an unspecified mechanism to wake up the main thread.
		4080
		4081	First, you need to associate some data with the event loop:
		4082
		4083	typedef struct {
		4084	mutex_t lock; /* global loop lock */
		4085	ev_async async_w;
		4086	thread_t tid;
		4087	cond_t invoke_cv;
		4088	} userdata;
		4089
		4090	void prepare_loop (EV_P)
		4091	{
		4092	// for simplicity, we use a static userdata struct.
		4093	static userdata u;
		4094
		4095	ev_async_init (&u->async_w, async_cb);
		4096	ev_async_start (EV_A_ &u->async_w);
		4097
		4098	pthread_mutex_init (&u->lock, 0);
		4099	pthread_cond_init (&u->invoke_cv, 0);
		4100
		4101	// now associate this with the loop
		4102	ev_set_userdata (EV_A_ u);
		4103	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4104	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4105
		4106	// then create the thread running ev_loop
		4107	pthread_create (&u->tid, 0, l_run, EV_A);
		4108	}
		4109
		4110	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4111	solely to wake up the event loop so it takes notice of any new watchers
		4112	that might have been added:
		4113
		4114	static void
		4115	async_cb (EV_P_ ev_async *w, int revents)
		4116	{
		4117	// just used for the side effects
		4118	}
		4119
		4120	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4121	protecting the loop data, respectively.
		4122
		4123	static void
		4124	l_release (EV_P)
		4125	{
		4126	userdata *u = ev_userdata (EV_A);
		4127	pthread_mutex_unlock (&u->lock);
		4128	}
		4129
		4130	static void
		4131	l_acquire (EV_P)
		4132	{
		4133	userdata *u = ev_userdata (EV_A);
		4134	pthread_mutex_lock (&u->lock);
		4135	}
		4136
		4137	The event loop thread first acquires the mutex, and then jumps straight
		4138	into C<ev_loop>:
		4139
		4140	void *
		4141	l_run (void *thr_arg)
		4142	{
		4143	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4144
		4145	l_acquire (EV_A);
		4146	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4147	ev_loop (EV_A_ 0);
		4148	l_release (EV_A);
		4149
		4150	return 0;
		4151	}
		4152
		4153	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4154	signal the main thread via some unspecified mechanism (signals? pipe
		4155	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4156	have been called (in a while loop because a) spurious wakeups are possible
		4157	and b) skipping inter-thread-communication when there are no pending
		4158	watchers is very beneficial):
		4159
		4160	static void
		4161	l_invoke (EV_P)
		4162	{
		4163	userdata *u = ev_userdata (EV_A);
		4164
		4165	while (ev_pending_count (EV_A))
		4166	{
		4167	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4168	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4169	}
		4170	}
		4171
		4172	Now, whenever the main thread gets told to invoke pending watchers, it
		4173	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4174	thread to continue:
		4175
		4176	static void
		4177	real_invoke_pending (EV_P)
		4178	{
		4179	userdata *u = ev_userdata (EV_A);
		4180
		4181	pthread_mutex_lock (&u->lock);
		4182	ev_invoke_pending (EV_A);
		4183	pthread_cond_signal (&u->invoke_cv);
		4184	pthread_mutex_unlock (&u->lock);
		4185	}
		4186
		4187	Whenever you want to start/stop a watcher or do other modifications to an
		4188	event loop, you will now have to lock:
		4189
		4190	ev_timer timeout_watcher;
		4191	userdata *u = ev_userdata (EV_A);
		4192
		4193	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4194
		4195	pthread_mutex_lock (&u->lock);
		4196	ev_timer_start (EV_A_ &timeout_watcher);
		4197	ev_async_send (EV_A_ &u->async_w);
		4198	pthread_mutex_unlock (&u->lock);
		4199
		4200	Note that sending the C<ev_async> watcher is required because otherwise
		4201	an event loop currently blocking in the kernel will have no knowledge
		4202	about the newly added timer. By waking up the loop it will pick up any new
		4203	watchers in the next event loop iteration.
		4204
		4205	=head3 COROUTINES
		4206
		4207	Libev is very accommodating to coroutines ("cooperative threads"):
		4208	libev fully supports nesting calls to its functions from different
		4209	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4210	different coroutines, and switch freely between both coroutines running
		4211	the loop, as long as you don't confuse yourself). The only exception is
		4212	that you must not do this from C<ev_periodic> reschedule callbacks.
		4213
		4214	Care has been taken to ensure that libev does not keep local state inside
		4215	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4216	they do not call any callbacks.
		4217
		4218	=head2 COMPILER WARNINGS
		4219
		4220	Depending on your compiler and compiler settings, you might get no or a
		4221	lot of warnings when compiling libev code. Some people are apparently
		4222	scared by this.
		4223
		4224	However, these are unavoidable for many reasons. For one, each compiler
		4225	has different warnings, and each user has different tastes regarding
		4226	warning options. "Warn-free" code therefore cannot be a goal except when
		4227	targeting a specific compiler and compiler-version.
		4228
		4229	Another reason is that some compiler warnings require elaborate
		4230	workarounds, or other changes to the code that make it less clear and less
		4231	maintainable.
		4232
		4233	And of course, some compiler warnings are just plain stupid, or simply
		4234	wrong (because they don't actually warn about the condition their message
		4235	seems to warn about). For example, certain older gcc versions had some
		4236	warnings that resulted an extreme number of false positives. These have
		4237	been fixed, but some people still insist on making code warn-free with
		4238	such buggy versions.
		4239
		4240	While libev is written to generate as few warnings as possible,
		4241	"warn-free" code is not a goal, and it is recommended not to build libev
		4242	with any compiler warnings enabled unless you are prepared to cope with
		4243	them (e.g. by ignoring them). Remember that warnings are just that:
		4244	warnings, not errors, or proof of bugs.
		4245
		4246
		4247	=head2 VALGRIND
		4248
		4249	Valgrind has a special section here because it is a popular tool that is
		4250	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4251
		4252	If you think you found a bug (memory leak, uninitialised data access etc.)
		4253	in libev, then check twice: If valgrind reports something like:
		4254
		4255	==2274== definitely lost: 0 bytes in 0 blocks.
		4256	==2274== possibly lost: 0 bytes in 0 blocks.
		4257	==2274== still reachable: 256 bytes in 1 blocks.
		4258
		4259	Then there is no memory leak, just as memory accounted to global variables
		4260	is not a memleak - the memory is still being referenced, and didn't leak.
		4261
		4262	Similarly, under some circumstances, valgrind might report kernel bugs
		4263	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4264	although an acceptable workaround has been found here), or it might be
		4265	confused.
		4266
		4267	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4268	make it into some kind of religion.
		4269
		4270	If you are unsure about something, feel free to contact the mailing list
		4271	with the full valgrind report and an explanation on why you think this
		4272	is a bug in libev (best check the archives, too :). However, don't be
		4273	annoyed when you get a brisk "this is no bug" answer and take the chance
		4274	of learning how to interpret valgrind properly.
		4275
		4276	If you need, for some reason, empty reports from valgrind for your project
		4277	I suggest using suppression lists.
		4278
		4279
		4280	=head1 PORTABILITY NOTES
		4281
		4282	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4283
		4284	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4285	requires, and its I/O model is fundamentally incompatible with the POSIX
		4286	model. Libev still offers limited functionality on this platform in
		4287	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4288	descriptors. This only applies when using Win32 natively, not when using
		4289	e.g. cygwin.
		4290
		4291	Lifting these limitations would basically require the full
		4292	re-implementation of the I/O system. If you are into these kinds of
		4293	things, then note that glib does exactly that for you in a very portable
		4294	way (note also that glib is the slowest event library known to man).
		4295
		4296	There is no supported compilation method available on windows except
		4297	embedding it into other applications.
		4298
		4299	Sensible signal handling is officially unsupported by Microsoft - libev
		4300	tries its best, but under most conditions, signals will simply not work.
		4301
		4302	Not a libev limitation but worth mentioning: windows apparently doesn't
		4303	accept large writes: instead of resulting in a partial write, windows will
		4304	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4305	so make sure you only write small amounts into your sockets (less than a
		4306	megabyte seems safe, but this apparently depends on the amount of memory
		4307	available).
		4308
		4309	Due to the many, low, and arbitrary limits on the win32 platform and
		4310	the abysmal performance of winsockets, using a large number of sockets
		4311	is not recommended (and not reasonable). If your program needs to use
		4312	more than a hundred or so sockets, then likely it needs to use a totally
		4313	different implementation for windows, as libev offers the POSIX readiness
		4314	notification model, which cannot be implemented efficiently on windows
		4315	(due to Microsoft monopoly games).
		4316
		4317	A typical way to use libev under windows is to embed it (see the embedding
		4318	section for details) and use the following F<evwrap.h> header file instead
		4319	of F<ev.h>:
		4320
		4321	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4322	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4323
		4324	#include "ev.h"
		4325
		4326	And compile the following F<evwrap.c> file into your project (make sure
		4327	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4328
		4329	#include "evwrap.h"
		4330	#include "ev.c"
		4331
		4332	=over 4
		4333
		4334	=item The winsocket select function
		4335
		4336	The winsocket C<select> function doesn't follow POSIX in that it
		4337	requires socket I<handles> and not socket I<file descriptors> (it is
		4338	also extremely buggy). This makes select very inefficient, and also
		4339	requires a mapping from file descriptors to socket handles (the Microsoft
		4340	C runtime provides the function C<_open_osfhandle> for this). See the
		4341	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4342	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4343
		4344	The configuration for a "naked" win32 using the Microsoft runtime
		4345	libraries and raw winsocket select is:
		4346
		4347	#define EV_USE_SELECT 1
		4348	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4349
		4350	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4351	complexity in the O(n²) range when using win32.
		4352
		4353	=item Limited number of file descriptors
		4354
		4355	Windows has numerous arbitrary (and low) limits on things.
		4356
		4357	Early versions of winsocket's select only supported waiting for a maximum
		4358	of C<64> handles (probably owning to the fact that all windows kernels
		4359	can only wait for C<64> things at the same time internally; Microsoft
		4360	recommends spawning a chain of threads and wait for 63 handles and the
		4361	previous thread in each. Sounds great!).
		4362
		4363	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4364	to some high number (e.g. C<2048>) before compiling the winsocket select
		4365	call (which might be in libev or elsewhere, for example, perl and many
		4366	other interpreters do their own select emulation on windows).
		4367
		4368	Another limit is the number of file descriptors in the Microsoft runtime
		4369	libraries, which by default is C<64> (there must be a hidden I<64>
		4370	fetish or something like this inside Microsoft). You can increase this
		4371	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4372	(another arbitrary limit), but is broken in many versions of the Microsoft
		4373	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4374	(depending on windows version and/or the phase of the moon). To get more,
		4375	you need to wrap all I/O functions and provide your own fd management, but
		4376	the cost of calling select (O(n²)) will likely make this unworkable.
		4377
		4378	=back
		4379
		4380	=head2 PORTABILITY REQUIREMENTS
		4381
		4382	In addition to a working ISO-C implementation and of course the
		4383	backend-specific APIs, libev relies on a few additional extensions:
		4384
		4385	=over 4
		4386
		4387	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4388	calling conventions regardless of C<ev_watcher_type *>.
		4389
		4390	Libev assumes not only that all watcher pointers have the same internal
		4391	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4392	assumes that the same (machine) code can be used to call any watcher
		4393	callback: The watcher callbacks have different type signatures, but libev
		4394	calls them using an C<ev_watcher *> internally.
		4395
		4396	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4397
		4398	The type C<sig_atomic_t volatile> (or whatever is defined as
		4399	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4400	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4401	believed to be sufficiently portable.
		4402
		4403	=item C<sigprocmask> must work in a threaded environment
		4404
		4405	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4406	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4407	pthread implementations will either allow C<sigprocmask> in the "main
		4408	thread" or will block signals process-wide, both behaviours would
		4409	be compatible with libev. Interaction between C<sigprocmask> and
		4410	C<pthread_sigmask> could complicate things, however.
		4411
		4412	The most portable way to handle signals is to block signals in all threads
		4413	except the initial one, and run the default loop in the initial thread as
		4414	well.
		4415
		4416	=item C<long> must be large enough for common memory allocation sizes
		4417
		4418	To improve portability and simplify its API, libev uses C<long> internally
		4419	instead of C<size_t> when allocating its data structures. On non-POSIX
		4420	systems (Microsoft...) this might be unexpectedly low, but is still at
		4421	least 31 bits everywhere, which is enough for hundreds of millions of
		4422	watchers.
		4423
		4424	=item C<double> must hold a time value in seconds with enough accuracy
		4425
		4426	The type C<double> is used to represent timestamps. It is required to
		4427	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4428	enough for at least into the year 4000. This requirement is fulfilled by
		4429	implementations implementing IEEE 754, which is basically all existing
		4430	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4431	2200.
		4432
		4433	=back
		4434
		4435	If you know of other additional requirements drop me a note.
		4436
		4437
2465	=head1 COMPLEXITIES	4438	=head1 ALGORITHMIC COMPLEXITIES
2466		4439
2467	In this section the complexities of (many of) the algorithms used inside	4440	In this section the complexities of (many of) the algorithms used inside
2468	libev will be explained. For complexity discussions about backends see the	4441	libev will be documented. For complexity discussions about backends see
2469	documentation for C<ev_default_init>.	4442	the documentation for C<ev_default_init>.
2470		4443
2471	All of the following are about amortised time: If an array needs to be	4444	All of the following are about amortised time: If an array needs to be
2472	extended, libev needs to realloc and move the whole array, but this	4445	extended, libev needs to realloc and move the whole array, but this
2473	happens asymptotically never with higher number of elements, so O(1) might	4446	happens asymptotically rarer with higher number of elements, so O(1) might
2474	mean it might do a lengthy realloc operation in rare cases, but on average	4447	mean that libev does a lengthy realloc operation in rare cases, but on
2475	it is much faster and asymptotically approaches constant time.	4448	average it is much faster and asymptotically approaches constant time.
2476		4449
2477	=over 4	4450	=over 4
2478		4451
2479	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4452	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2480		4453
2481	This means that, when you have a watcher that triggers in one hour and	4454	This means that, when you have a watcher that triggers in one hour and
2482	there are 100 watchers that would trigger before that then inserting will	4455	there are 100 watchers that would trigger before that, then inserting will
2483	have to skip those 100 watchers.	4456	have to skip roughly seven (C<ld 100>) of these watchers.
2484		4457
2485	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4458	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2486		4459
2487	That means that for changing a timer costs less than removing/adding them	4460	That means that changing a timer costs less than removing/adding them,
2488	as only the relative motion in the event queue has to be paid for.	4461	as only the relative motion in the event queue has to be paid for.
2489		4462
2490	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4463	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2491		4464
2492	These just add the watcher into an array or at the head of a list.	4465	These just add the watcher into an array or at the head of a list.
		4466
2493	=item Stopping check/prepare/idle watchers: O(1)	4467	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2494		4468
2495	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4469	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2496		4470
2497	These watchers are stored in lists then need to be walked to find the	4471	These watchers are stored in lists, so they need to be walked to find the
2498	correct watcher to remove. The lists are usually short (you don't usually	4472	correct watcher to remove. The lists are usually short (you don't usually
2499	have many watchers waiting for the same fd or signal).	4473	have many watchers waiting for the same fd or signal: one is typical, two
		4474	is rare).
2500		4475
2501	=item Finding the next timer per loop iteration: O(1)	4476	=item Finding the next timer in each loop iteration: O(1)
		4477
		4478	By virtue of using a binary or 4-heap, the next timer is always found at a
		4479	fixed position in the storage array.
2502		4480
2503	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4481	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2504		4482
2505	A change means an I/O watcher gets started or stopped, which requires	4483	A change means an I/O watcher gets started or stopped, which requires
2506	libev to recalculate its status (and possibly tell the kernel).	4484	libev to recalculate its status (and possibly tell the kernel, depending
		4485	on backend and whether C<ev_io_set> was used).
2507		4486
2508	=item Activating one watcher: O(1)	4487	=item Activating one watcher (putting it into the pending state): O(1)
2509		4488
2510	=item Priority handling: O(number_of_priorities)	4489	=item Priority handling: O(number_of_priorities)
2511		4490
2512	Priorities are implemented by allocating some space for each	4491	Priorities are implemented by allocating some space for each
2513	priority. When doing priority-based operations, libev usually has to	4492	priority. When doing priority-based operations, libev usually has to
2514	linearly search all the priorities.	4493	linearly search all the priorities, but starting/stopping and activating
		4494	watchers becomes O(1) with respect to priority handling.
		4495
		4496	=item Sending an ev_async: O(1)
		4497
		4498	=item Processing ev_async_send: O(number_of_async_watchers)
		4499
		4500	=item Processing signals: O(max_signal_number)
		4501
		4502	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4503	calls in the current loop iteration. Checking for async and signal events
		4504	involves iterating over all running async watchers or all signal numbers.
2515		4505
2516	=back	4506	=back
2517		4507
2518		4508
		4509	=head1 GLOSSARY
		4510
		4511	=over 4
		4512
		4513	=item active
		4514
		4515	A watcher is active as long as it has been started (has been attached to
		4516	an event loop) but not yet stopped (disassociated from the event loop).
		4517
		4518	=item application
		4519
		4520	In this document, an application is whatever is using libev.
		4521
		4522	=item callback
		4523
		4524	The address of a function that is called when some event has been
		4525	detected. Callbacks are being passed the event loop, the watcher that
		4526	received the event, and the actual event bitset.
		4527
		4528	=item callback invocation
		4529
		4530	The act of calling the callback associated with a watcher.
		4531
		4532	=item event
		4533
		4534	A change of state of some external event, such as data now being available
		4535	for reading on a file descriptor, time having passed or simply not having
		4536	any other events happening anymore.
		4537
		4538	In libev, events are represented as single bits (such as C<EV_READ> or
		4539	C<EV_TIMEOUT>).
		4540
		4541	=item event library
		4542
		4543	A software package implementing an event model and loop.
		4544
		4545	=item event loop
		4546
		4547	An entity that handles and processes external events and converts them
		4548	into callback invocations.
		4549
		4550	=item event model
		4551
		4552	The model used to describe how an event loop handles and processes
		4553	watchers and events.
		4554
		4555	=item pending
		4556
		4557	A watcher is pending as soon as the corresponding event has been detected,
		4558	and stops being pending as soon as the watcher will be invoked or its
		4559	pending status is explicitly cleared by the application.
		4560
		4561	A watcher can be pending, but not active. Stopping a watcher also clears
		4562	its pending status.
		4563
		4564	=item real time
		4565
		4566	The physical time that is observed. It is apparently strictly monotonic :)
		4567
		4568	=item wall-clock time
		4569
		4570	The time and date as shown on clocks. Unlike real time, it can actually
		4571	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4572	clock.
		4573
		4574	=item watcher
		4575
		4576	A data structure that describes interest in certain events. Watchers need
		4577	to be started (attached to an event loop) before they can receive events.
		4578
		4579	=item watcher invocation
		4580
		4581	The act of calling the callback associated with a watcher.
		4582
		4583	=back
		4584
2519	=head1 AUTHOR	4585	=head1 AUTHOR
2520		4586
2521	Marc Lehmann <libev@schmorp.de>.	4587	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2522		4588

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