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Revision 1.100 by root, Sat Dec 22 11:49:17 2007 UTC vs.
Revision 1.277 by root, Thu Dec 31 06:50:17 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), 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
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
82		111
83	It also is quite fast (see this	112	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	114	for example).
86		115
87	=head1 CONVENTIONS	116	=head2 CONVENTIONS
88		117
89	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	122	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		124	this argument.
95		125
96	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
97		127
98	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as some floatingpoint value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	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
106		157
107	=head1 GLOBAL FUNCTIONS	158	=head1 GLOBAL FUNCTIONS
108		159
109	These functions can be called anytime, even before initialising the	160	These functions can be called anytime, even before initialising the
110	library in any way.	161	library in any way.
…		…
119		170
120	=item ev_sleep (ev_tstamp interval)	171	=item ev_sleep (ev_tstamp interval)
121		172
122	Sleep for the given interval: The current thread will be blocked until	173	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	174	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	175	this is a sub-second-resolution C<sleep ()>.
125		176
126	=item int ev_version_major ()	177	=item int ev_version_major ()
127		178
128	=item int ev_version_minor ()	179	=item int ev_version_minor ()
129		180
…		…
142	not a problem.	193	not a problem.
143		194
144	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
145	version.	196	version.
146		197
147	assert (("libev version mismatch",	198	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
150		201
151	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
152		203
153	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_*>
154	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	207	a description of the set values.
157		208
158	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
159	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
160		211
161	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
163		214
164	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
165		216
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	222	libev will probe for if you specify no backends explicitly.
172		223
173	=item unsigned int ev_embeddable_backends ()	224	=item unsigned int ev_embeddable_backends ()
174		225
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	230	recommended ones.
180		231
181	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
182		233
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		235
185	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
186	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
187	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
188	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
189	potentially destructive action. The default is your system realloc	240	or take some potentially destructive action.
190	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.
191		245
192	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
193	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,
194	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.
195		249
196	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
197	retries).	251	retries (example requires a standards-compliant C<realloc>).
198		252
199	static void *	253	static void *
200	persistent_realloc (void *ptr, size_t size)	254	persistent_realloc (void *ptr, size_t size)
201	{	255	{
202	for (;;)	256	for (;;)
…		…
211	}	265	}
212		266
213	...	267	...
214	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
215		269
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		271
218	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
219	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
220	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
221	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
222	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
223	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
224	(such as abort).	278	(such as abort).
225		279
226	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.
…		…
237		291
238	=back	292	=back
239		293
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		295
242	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>
243	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>
244	events, and dynamically created loops which do not.	298	I<function>).
245		299
246	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
247	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
248	create, you also create another event loop. Libev itself does no locking	302	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		303
253	=over 4	304	=over 4
254		305
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		307
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		312
262	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
263	function.	314	function.
264		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
265	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
266	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>).
267		329
268	The following flags are supported:	330	The following flags are supported:
269		331
…		…
274	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
275	thing, believe me).	337	thing, believe me).
276		338
277	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
278		340
279	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
280	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
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	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
283	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
284	around bugs.	346	around bugs.
…		…
290	enabling this flag.	352	enabling this flag.
291		353
292	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,
293	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
294	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
295	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
296	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
297	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
298		360
299	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
300	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
301	flag.	363	flag.
302		364
303	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>
304	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_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes is both faster and might make
		380	it possible to get the queued signal data.
		381
		382	Signalfd will not be used by default as this changes your signal mask, and
		383	there are a lot of shoddy libraries and programs (glib's threadpool for
		384	example) that can't properly initialise their signal masks.
305		385
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	386	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		387
308	This is your standard select(2) backend. Not I<completely> standard, as	388	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	389	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	390	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	391	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	392	usually the fastest backend for a low number of (low-numbered :) fds.
		393
		394	To get good performance out of this backend you need a high amount of
		395	parallelism (most of the file descriptors should be busy). If you are
		396	writing a server, you should C<accept ()> in a loop to accept as many
		397	connections as possible during one iteration. You might also want to have
		398	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		399	readiness notifications you get per iteration.
		400
		401	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		402	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		403	C<exceptfds> set on that platform).
313		404
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	405	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		406
316	And this is your standard poll(2) backend. It's more complicated than	407	And this is your standard poll(2) backend. It's more complicated
317	select, but handles sparse fds better and has no artificial limit on the	408	than select, but handles sparse fds better and has no artificial
318	number of fds you can use (except it will slow down considerably with a	409	limit on the number of fds you can use (except it will slow down
319	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	410	considerably with a lot of inactive fds). It scales similarly to select,
		411	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		412	performance tips.
		413
		414	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		415	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
320		416
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	417	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		418
		419	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		420	kernels).
322		421
323	For few fds, this backend is a bit little slower than poll and select,	422	For few fds, this backend is a bit little slower than poll and select,
324	but it scales phenomenally better. While poll and select usually scale	423	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	424	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	425	epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	426
328	cases and rewiring a syscall per fd change, no fork support and bad	427	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	428	of the more advanced event mechanisms: mere annoyances include silently
		429	dropping file descriptors, requiring a system call per change per file
		430	descriptor (and unnecessary guessing of parameters), problems with dup and
		431	so on. The biggest issue is fork races, however - if a program forks then
		432	I<both> parent and child process have to recreate the epoll set, which can
		433	take considerable time (one syscall per file descriptor) and is of course
		434	hard to detect.
		435
		436	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		437	of course I<doesn't>, and epoll just loves to report events for totally
		438	I<different> file descriptors (even already closed ones, so one cannot
		439	even remove them from the set) than registered in the set (especially
		440	on SMP systems). Libev tries to counter these spurious notifications by
		441	employing an additional generation counter and comparing that against the
		442	events to filter out spurious ones, recreating the set when required.
330		443
331	While stopping, setting and starting an I/O watcher in the same iteration	444	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	445	will result in some caching, there is still a system call per such
333	(because the fd could point to a different file description now), so its	446	incident (because the same I<file descriptor> could point to a different
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	447	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very well if you register events for both fds.	448	file descriptors might not work very well if you register events for both
		449	file descriptors.
336		450
337	Please note that epoll sometimes generates spurious notifications, so you	451	Best performance from this backend is achieved by not unregistering all
338	need to use non-blocking I/O or other means to avoid blocking when no data	452	watchers for a file descriptor until it has been closed, if possible,
339	(or space) is available.	453	i.e. keep at least one watcher active per fd at all times. Stopping and
		454	starting a watcher (without re-setting it) also usually doesn't cause
		455	extra overhead. A fork can both result in spurious notifications as well
		456	as in libev having to destroy and recreate the epoll object, which can
		457	take considerable time and thus should be avoided.
		458
		459	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		460	faster than epoll for maybe up to a hundred file descriptors, depending on
		461	the usage. So sad.
		462
		463	While nominally embeddable in other event loops, this feature is broken in
		464	all kernel versions tested so far.
		465
		466	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		467	C<EVBACKEND_POLL>.
340		468
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	469	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		470
343	Kqueue deserves special mention, as at the time of this writing, it	471	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on all BSDs except NetBSD (usually it doesn't work reliably	472	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	with anything but sockets and pipes, except on Darwin, where of course	473	with anything but sockets and pipes, except on Darwin, where of course
346	it's completely useless). For this reason it's not being "autodetected"	474	it's completely useless). Unlike epoll, however, whose brokenness
		475	is by design, these kqueue bugs can (and eventually will) be fixed
		476	without API changes to existing programs. For this reason it's not being
347	unless you explicitly specify it explicitly in the flags (i.e. using	477	"auto-detected" unless you explicitly specify it in the flags (i.e. using
348	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	478	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
349	system like NetBSD.	479	system like NetBSD.
350		480
351	You still can embed kqueue into a normal poll or select backend and use it	481	You still can embed kqueue into a normal poll or select backend and use it
352	only for sockets (after having made sure that sockets work with kqueue on	482	only for sockets (after having made sure that sockets work with kqueue on
353	the target platform). See C<ev_embed> watchers for more info.	483	the target platform). See C<ev_embed> watchers for more info.
354		484
355	It scales in the same way as the epoll backend, but the interface to the	485	It scales in the same way as the epoll backend, but the interface to the
356	kernel is more efficient (which says nothing about its actual speed, of	486	kernel is more efficient (which says nothing about its actual speed, of
357	course). While stopping, setting and starting an I/O watcher does never	487	course). While stopping, setting and starting an I/O watcher does never
358	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	488	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
359	two event changes per incident, support for C<fork ()> is very bad and it	489	two event changes per incident. Support for C<fork ()> is very bad (but
360	drops fds silently in similarly hard-to-detect cases.	490	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		491	cases
		492
		493	This backend usually performs well under most conditions.
		494
		495	While nominally embeddable in other event loops, this doesn't work
		496	everywhere, so you might need to test for this. And since it is broken
		497	almost everywhere, you should only use it when you have a lot of sockets
		498	(for which it usually works), by embedding it into another event loop
		499	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		500	also broken on OS X)) and, did I mention it, using it only for sockets.
		501
		502	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		503	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		504	C<NOTE_EOF>.
361		505
362	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	506	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
363		507
364	This is not implemented yet (and might never be).	508	This is not implemented yet (and might never be, unless you send me an
		509	implementation). According to reports, C</dev/poll> only supports sockets
		510	and is not embeddable, which would limit the usefulness of this backend
		511	immensely.
365		512
366	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	513	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
367		514
368	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	515	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
369	it's really slow, but it still scales very well (O(active_fds)).	516	it's really slow, but it still scales very well (O(active_fds)).
370		517
371	Please note that solaris event ports can deliver a lot of spurious	518	Please note that Solaris event ports can deliver a lot of spurious
372	notifications, so you need to use non-blocking I/O or other means to avoid	519	notifications, so you need to use non-blocking I/O or other means to avoid
373	blocking when no data (or space) is available.	520	blocking when no data (or space) is available.
		521
		522	While this backend scales well, it requires one system call per active
		523	file descriptor per loop iteration. For small and medium numbers of file
		524	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		525	might perform better.
		526
		527	On the positive side, with the exception of the spurious readiness
		528	notifications, this backend actually performed fully to specification
		529	in all tests and is fully embeddable, which is a rare feat among the
		530	OS-specific backends (I vastly prefer correctness over speed hacks).
		531
		532	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		533	C<EVBACKEND_POLL>.
374		534
375	=item C<EVBACKEND_ALL>	535	=item C<EVBACKEND_ALL>
376		536
377	Try all backends (even potentially broken ones that wouldn't be tried	537	Try all backends (even potentially broken ones that wouldn't be tried
378	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	538	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
379	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	539	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
380		540
		541	It is definitely not recommended to use this flag.
		542
381	=back	543	=back
382		544
383	If one or more of these are ored into the flags value, then only these	545	If one or more of the backend flags are or'ed into the flags value,
384	backends will be tried (in the reverse order as given here). If none are	546	then only these backends will be tried (in the reverse order as listed
385	specified, most compiled-in backend will be tried, usually in reverse	547	here). If none are specified, all backends in C<ev_recommended_backends
386	order of their flag values :)	548	()> will be tried.
387		549
388	The most typical usage is like this:	550	Example: This is the most typical usage.
389		551
390	if (!ev_default_loop (0))	552	if (!ev_default_loop (0))
391	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	553	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
392		554
393	Restrict libev to the select and poll backends, and do not allow	555	Example: Restrict libev to the select and poll backends, and do not allow
394	environment settings to be taken into account:	556	environment settings to be taken into account:
395		557
396	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	558	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
397		559
398	Use whatever libev has to offer, but make sure that kqueue is used if	560	Example: Use whatever libev has to offer, but make sure that kqueue is
399	available (warning, breaks stuff, best use only with your own private	561	used if available (warning, breaks stuff, best use only with your own
400	event loop and only if you know the OS supports your types of fds):	562	private event loop and only if you know the OS supports your types of
		563	fds):
401		564
402	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	565	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
403		566
404	=item struct ev_loop *ev_loop_new (unsigned int flags)	567	=item struct ev_loop *ev_loop_new (unsigned int flags)
405		568
406	Similar to C<ev_default_loop>, but always creates a new event loop that is	569	Similar to C<ev_default_loop>, but always creates a new event loop that is
407	always distinct from the default loop. Unlike the default loop, it cannot	570	always distinct from the default loop. Unlike the default loop, it cannot
408	handle signal and child watchers, and attempts to do so will be greeted by	571	handle signal and child watchers, and attempts to do so will be greeted by
409	undefined behaviour (or a failed assertion if assertions are enabled).	572	undefined behaviour (or a failed assertion if assertions are enabled).
410		573
		574	Note that this function I<is> thread-safe, and the recommended way to use
		575	libev with threads is indeed to create one loop per thread, and using the
		576	default loop in the "main" or "initial" thread.
		577
411	Example: Try to create a event loop that uses epoll and nothing else.	578	Example: Try to create a event loop that uses epoll and nothing else.
412		579
413	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	580	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
414	if (!epoller)	581	if (!epoller)
415	fatal ("no epoll found here, maybe it hides under your chair");	582	fatal ("no epoll found here, maybe it hides under your chair");
416		583
417	=item ev_default_destroy ()	584	=item ev_default_destroy ()
418		585
419	Destroys the default loop again (frees all memory and kernel state	586	Destroys the default loop again (frees all memory and kernel state
420	etc.). None of the active event watchers will be stopped in the normal	587	etc.). None of the active event watchers will be stopped in the normal
421	sense, so e.g. C<ev_is_active> might still return true. It is your	588	sense, so e.g. C<ev_is_active> might still return true. It is your
422	responsibility to either stop all watchers cleanly yoursef I<before>	589	responsibility to either stop all watchers cleanly yourself I<before>
423	calling this function, or cope with the fact afterwards (which is usually	590	calling this function, or cope with the fact afterwards (which is usually
424	the easiest thing, you can just ignore the watchers and/or C<free ()> them	591	the easiest thing, you can just ignore the watchers and/or C<free ()> them
425	for example).	592	for example).
426		593
427	Note that certain global state, such as signal state, will not be freed by	594	Note that certain global state, such as signal state (and installed signal
428	this function, and related watchers (such as signal and child watchers)	595	handlers), will not be freed by this function, and related watchers (such
429	would need to be stopped manually.	596	as signal and child watchers) would need to be stopped manually.
430		597
431	In general it is not advisable to call this function except in the	598	In general it is not advisable to call this function except in the
432	rare occasion where you really need to free e.g. the signal handling	599	rare occasion where you really need to free e.g. the signal handling
433	pipe fds. If you need dynamically allocated loops it is better to use	600	pipe fds. If you need dynamically allocated loops it is better to use
434	C<ev_loop_new> and C<ev_loop_destroy>).	601	C<ev_loop_new> and C<ev_loop_destroy>.
435		602
436	=item ev_loop_destroy (loop)	603	=item ev_loop_destroy (loop)
437		604
438	Like C<ev_default_destroy>, but destroys an event loop created by an	605	Like C<ev_default_destroy>, but destroys an event loop created by an
439	earlier call to C<ev_loop_new>.	606	earlier call to C<ev_loop_new>.
440		607
441	=item ev_default_fork ()	608	=item ev_default_fork ()
442		609
		610	This function sets a flag that causes subsequent C<ev_loop> iterations
443	This function reinitialises the kernel state for backends that have	611	to reinitialise the kernel state for backends that have one. Despite the
444	one. Despite the name, you can call it anytime, but it makes most sense	612	name, you can call it anytime, but it makes most sense after forking, in
445	after forking, in either the parent or child process (or both, but that	613	the child process (or both child and parent, but that again makes little
446	again makes little sense).	614	sense). You I<must> call it in the child before using any of the libev
		615	functions, and it will only take effect at the next C<ev_loop> iteration.
447		616
448	You I<must> call this function in the child process after forking if and	617	On the other hand, you only need to call this function in the child
449	only if you want to use the event library in both processes. If you just	618	process if and only if you want to use the event library in the child. If
450	fork+exec, you don't have to call it.	619	you just fork+exec, you don't have to call it at all.
451		620
452	The function itself is quite fast and it's usually not a problem to call	621	The function itself is quite fast and it's usually not a problem to call
453	it just in case after a fork. To make this easy, the function will fit in	622	it just in case after a fork. To make this easy, the function will fit in
454	quite nicely into a call to C<pthread_atfork>:	623	quite nicely into a call to C<pthread_atfork>:
455		624
456	pthread_atfork (0, 0, ev_default_fork);	625	pthread_atfork (0, 0, ev_default_fork);
457		626
458	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
459	without calling this function, so if you force one of those backends you
460	do not need to care.
461
462	=item ev_loop_fork (loop)	627	=item ev_loop_fork (loop)
463		628
464	Like C<ev_default_fork>, but acts on an event loop created by	629	Like C<ev_default_fork>, but acts on an event loop created by
465	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	630	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
466	after fork, and how you do this is entirely your own problem.	631	after fork that you want to re-use in the child, and how you do this is
		632	entirely your own problem.
		633
		634	=item int ev_is_default_loop (loop)
		635
		636	Returns true when the given loop is, in fact, the default loop, and false
		637	otherwise.
467		638
468	=item unsigned int ev_loop_count (loop)	639	=item unsigned int ev_loop_count (loop)
469		640
470	Returns the count of loop iterations for the loop, which is identical to	641	Returns the count of loop iterations for the loop, which is identical to
471	the number of times libev did poll for new events. It starts at C<0> and	642	the number of times libev did poll for new events. It starts at C<0> and
472	happily wraps around with enough iterations.	643	happily wraps around with enough iterations.
473		644
474	This value can sometimes be useful as a generation counter of sorts (it	645	This value can sometimes be useful as a generation counter of sorts (it
475	"ticks" the number of loop iterations), as it roughly corresponds with	646	"ticks" the number of loop iterations), as it roughly corresponds with
476	C<ev_prepare> and C<ev_check> calls.	647	C<ev_prepare> and C<ev_check> calls.
		648
		649	=item unsigned int ev_loop_depth (loop)
		650
		651	Returns the number of times C<ev_loop> was entered minus the number of
		652	times C<ev_loop> was exited, in other words, the recursion depth.
		653
		654	Outside C<ev_loop>, this number is zero. In a callback, this number is
		655	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		656	in which case it is higher.
		657
		658	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		659	etc.), doesn't count as exit.
477		660
478	=item unsigned int ev_backend (loop)	661	=item unsigned int ev_backend (loop)
479		662
480	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	663	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
481	use.	664	use.
…		…
486	received events and started processing them. This timestamp does not	669	received events and started processing them. This timestamp does not
487	change as long as callbacks are being processed, and this is also the base	670	change as long as callbacks are being processed, and this is also the base
488	time used for relative timers. You can treat it as the timestamp of the	671	time used for relative timers. You can treat it as the timestamp of the
489	event occurring (or more correctly, libev finding out about it).	672	event occurring (or more correctly, libev finding out about it).
490		673
		674	=item ev_now_update (loop)
		675
		676	Establishes the current time by querying the kernel, updating the time
		677	returned by C<ev_now ()> in the progress. This is a costly operation and
		678	is usually done automatically within C<ev_loop ()>.
		679
		680	This function is rarely useful, but when some event callback runs for a
		681	very long time without entering the event loop, updating libev's idea of
		682	the current time is a good idea.
		683
		684	See also L<The special problem of time updates> in the C<ev_timer> section.
		685
		686	=item ev_suspend (loop)
		687
		688	=item ev_resume (loop)
		689
		690	These two functions suspend and resume a loop, for use when the loop is
		691	not used for a while and timeouts should not be processed.
		692
		693	A typical use case would be an interactive program such as a game: When
		694	the user presses C<^Z> to suspend the game and resumes it an hour later it
		695	would be best to handle timeouts as if no time had actually passed while
		696	the program was suspended. This can be achieved by calling C<ev_suspend>
		697	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		698	C<ev_resume> directly afterwards to resume timer processing.
		699
		700	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		701	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		702	will be rescheduled (that is, they will lose any events that would have
		703	occured while suspended).
		704
		705	After calling C<ev_suspend> you B<must not> call I<any> function on the
		706	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		707	without a previous call to C<ev_suspend>.
		708
		709	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		710	event loop time (see C<ev_now_update>).
		711
491	=item ev_loop (loop, int flags)	712	=item ev_loop (loop, int flags)
492		713
493	Finally, this is it, the event handler. This function usually is called	714	Finally, this is it, the event handler. This function usually is called
494	after you initialised all your watchers and you want to start handling	715	after you have initialised all your watchers and you want to start
495	events.	716	handling events.
496		717
497	If the flags argument is specified as C<0>, it will not return until	718	If the flags argument is specified as C<0>, it will not return until
498	either no event watchers are active anymore or C<ev_unloop> was called.	719	either no event watchers are active anymore or C<ev_unloop> was called.
499		720
500	Please note that an explicit C<ev_unloop> is usually better than	721	Please note that an explicit C<ev_unloop> is usually better than
501	relying on all watchers to be stopped when deciding when a program has	722	relying on all watchers to be stopped when deciding when a program has
502	finished (especially in interactive programs), but having a program that	723	finished (especially in interactive programs), but having a program
503	automatically loops as long as it has to and no longer by virtue of	724	that automatically loops as long as it has to and no longer by virtue
504	relying on its watchers stopping correctly is a thing of beauty.	725	of relying on its watchers stopping correctly, that is truly a thing of
		726	beauty.
505		727
506	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	728	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
507	those events and any outstanding ones, but will not block your process in	729	those events and any already outstanding ones, but will not block your
508	case there are no events and will return after one iteration of the loop.	730	process in case there are no events and will return after one iteration of
		731	the loop.
509		732
510	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	733	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
511	neccessary) and will handle those and any outstanding ones. It will block	734	necessary) and will handle those and any already outstanding ones. It
512	your process until at least one new event arrives, and will return after	735	will block your process until at least one new event arrives (which could
513	one iteration of the loop. This is useful if you are waiting for some	736	be an event internal to libev itself, so there is no guarantee that a
514	external event in conjunction with something not expressible using other	737	user-registered callback will be called), and will return after one
		738	iteration of the loop.
		739
		740	This is useful if you are waiting for some external event in conjunction
		741	with something not expressible using other libev watchers (i.e. "roll your
515	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	742	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
516	usually a better approach for this kind of thing.	743	usually a better approach for this kind of thing.
517		744
518	Here are the gory details of what C<ev_loop> does:	745	Here are the gory details of what C<ev_loop> does:
519		746
520	- Before the first iteration, call any pending watchers.	747	- Before the first iteration, call any pending watchers.
521	* If there are no active watchers (reference count is zero), return.	748	* If EVFLAG_FORKCHECK was used, check for a fork.
522	- Queue all prepare watchers and then call all outstanding watchers.	749	- If a fork was detected (by any means), queue and call all fork watchers.
		750	- Queue and call all prepare watchers.
523	- If we have been forked, recreate the kernel state.	751	- If we have been forked, detach and recreate the kernel state
		752	as to not disturb the other process.
524	- Update the kernel state with all outstanding changes.	753	- Update the kernel state with all outstanding changes.
525	- Update the "event loop time".	754	- Update the "event loop time" (ev_now ()).
526	- Calculate for how long to block.	755	- Calculate for how long to sleep or block, if at all
		756	(active idle watchers, EVLOOP_NONBLOCK or not having
		757	any active watchers at all will result in not sleeping).
		758	- Sleep if the I/O and timer collect interval say so.
527	- Block the process, waiting for any events.	759	- Block the process, waiting for any events.
528	- Queue all outstanding I/O (fd) events.	760	- Queue all outstanding I/O (fd) events.
529	- Update the "event loop time" and do time jump handling.	761	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
530	- Queue all outstanding timers.	762	- Queue all expired timers.
531	- Queue all outstanding periodics.	763	- Queue all expired periodics.
532	- If no events are pending now, queue all idle watchers.	764	- Unless any events are pending now, queue all idle watchers.
533	- Queue all check watchers.	765	- Queue all check watchers.
534	- Call all queued watchers in reverse order (i.e. check watchers first).	766	- Call all queued watchers in reverse order (i.e. check watchers first).
535	Signals and child watchers are implemented as I/O watchers, and will	767	Signals and child watchers are implemented as I/O watchers, and will
536	be handled here by queueing them when their watcher gets executed.	768	be handled here by queueing them when their watcher gets executed.
537	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	769	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
538	were used, return, otherwise continue with step *.	770	were used, or there are no active watchers, return, otherwise
		771	continue with step *.
539		772
540	Example: Queue some jobs and then loop until no events are outsanding	773	Example: Queue some jobs and then loop until no events are outstanding
541	anymore.	774	anymore.
542		775
543	... queue jobs here, make sure they register event watchers as long	776	... queue jobs here, make sure they register event watchers as long
544	... as they still have work to do (even an idle watcher will do..)	777	... as they still have work to do (even an idle watcher will do..)
545	ev_loop (my_loop, 0);	778	ev_loop (my_loop, 0);
546	... jobs done. yeah!	779	... jobs done or somebody called unloop. yeah!
547		780
548	=item ev_unloop (loop, how)	781	=item ev_unloop (loop, how)
549		782
550	Can be used to make a call to C<ev_loop> return early (but only after it	783	Can be used to make a call to C<ev_loop> return early (but only after it
551	has processed all outstanding events). The C<how> argument must be either	784	has processed all outstanding events). The C<how> argument must be either
552	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	785	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
553	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	786	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
554		787
		788	This "unloop state" will be cleared when entering C<ev_loop> again.
		789
		790	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		791
555	=item ev_ref (loop)	792	=item ev_ref (loop)
556		793
557	=item ev_unref (loop)	794	=item ev_unref (loop)
558		795
559	Ref/unref can be used to add or remove a reference count on the event	796	Ref/unref can be used to add or remove a reference count on the event
560	loop: Every watcher keeps one reference, and as long as the reference	797	loop: Every watcher keeps one reference, and as long as the reference
561	count is nonzero, C<ev_loop> will not return on its own. If you have	798	count is nonzero, C<ev_loop> will not return on its own.
562	a watcher you never unregister that should not keep C<ev_loop> from	799
563	returning, ev_unref() after starting, and ev_ref() before stopping it. For	800	This is useful when you have a watcher that you never intend to
		801	unregister, but that nevertheless should not keep C<ev_loop> from
		802	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		803	before stopping it.
		804
564	example, libev itself uses this for its internal signal pipe: It is not	805	As an example, libev itself uses this for its internal signal pipe: It
565	visible to the libev user and should not keep C<ev_loop> from exiting if	806	is not visible to the libev user and should not keep C<ev_loop> from
566	no event watchers registered by it are active. It is also an excellent	807	exiting if no event watchers registered by it are active. It is also an
567	way to do this for generic recurring timers or from within third-party	808	excellent way to do this for generic recurring timers or from within
568	libraries. Just remember to I<unref after start> and I<ref before stop>.	809	third-party libraries. Just remember to I<unref after start> and I<ref
		810	before stop> (but only if the watcher wasn't active before, or was active
		811	before, respectively. Note also that libev might stop watchers itself
		812	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		813	in the callback).
569		814
570	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	815	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
571	running when nothing else is active.	816	running when nothing else is active.
572		817
573	struct ev_signal exitsig;	818	ev_signal exitsig;
574	ev_signal_init (&exitsig, sig_cb, SIGINT);	819	ev_signal_init (&exitsig, sig_cb, SIGINT);
575	ev_signal_start (loop, &exitsig);	820	ev_signal_start (loop, &exitsig);
576	evf_unref (loop);	821	evf_unref (loop);
577		822
578	Example: For some weird reason, unregister the above signal handler again.	823	Example: For some weird reason, unregister the above signal handler again.
579		824
580	ev_ref (loop);	825	ev_ref (loop);
581	ev_signal_stop (loop, &exitsig);	826	ev_signal_stop (loop, &exitsig);
582		827
583	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	828	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
584		829
585	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	830	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
586		831
587	These advanced functions influence the time that libev will spend waiting	832	These advanced functions influence the time that libev will spend waiting
588	for events. Both are by default C<0>, meaning that libev will try to	833	for events. Both time intervals are by default C<0>, meaning that libev
589	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	834	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		835	latency.
590		836
591	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	837	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
592	allows libev to delay invocation of I/O and timer/periodic callbacks to	838	allows libev to delay invocation of I/O and timer/periodic callbacks
593	increase efficiency of loop iterations.	839	to increase efficiency of loop iterations (or to increase power-saving
		840	opportunities).
594		841
595	The background is that sometimes your program runs just fast enough to	842	The idea is that sometimes your program runs just fast enough to handle
596	handle one (or very few) event(s) per loop iteration. While this makes	843	one (or very few) event(s) per loop iteration. While this makes the
597	the program responsive, it also wastes a lot of CPU time to poll for new	844	program responsive, it also wastes a lot of CPU time to poll for new
598	events, especially with backends like C<select ()> which have a high	845	events, especially with backends like C<select ()> which have a high
599	overhead for the actual polling but can deliver many events at once.	846	overhead for the actual polling but can deliver many events at once.
600		847
601	By setting a higher I<io collect interval> you allow libev to spend more	848	By setting a higher I<io collect interval> you allow libev to spend more
602	time collecting I/O events, so you can handle more events per iteration,	849	time collecting I/O events, so you can handle more events per iteration,
603	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	850	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
604	C<ev_timer>) will be not affected. Setting this to a non-null bvalue will	851	C<ev_timer>) will be not affected. Setting this to a non-null value will
605	introduce an additional C<ev_sleep ()> call into most loop iterations.	852	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		853	sleep time ensures that libev will not poll for I/O events more often then
		854	once per this interval, on average.
606		855
607	Likewise, by setting a higher I<timeout collect interval> you allow libev	856	Likewise, by setting a higher I<timeout collect interval> you allow libev
608	to spend more time collecting timeouts, at the expense of increased	857	to spend more time collecting timeouts, at the expense of increased
609	latency (the watcher callback will be called later). C<ev_io> watchers	858	latency/jitter/inexactness (the watcher callback will be called
610	will not be affected. Setting this to a non-null value will not introduce	859	later). C<ev_io> watchers will not be affected. Setting this to a non-null
611	any overhead in libev.	860	value will not introduce any overhead in libev.
612		861
613	Many (busy) programs can usually benefit by setting the io collect	862	Many (busy) programs can usually benefit by setting the I/O collect
614	interval to a value near C<0.1> or so, which is often enough for	863	interval to a value near C<0.1> or so, which is often enough for
615	interactive servers (of course not for games), likewise for timeouts. It	864	interactive servers (of course not for games), likewise for timeouts. It
616	usually doesn't make much sense to set it to a lower value than C<0.01>,	865	usually doesn't make much sense to set it to a lower value than C<0.01>,
617	as this approsaches the timing granularity of most systems.	866	as this approaches the timing granularity of most systems. Note that if
		867	you do transactions with the outside world and you can't increase the
		868	parallelity, then this setting will limit your transaction rate (if you
		869	need to poll once per transaction and the I/O collect interval is 0.01,
		870	then you can't do more than 100 transations per second).
		871
		872	Setting the I<timeout collect interval> can improve the opportunity for
		873	saving power, as the program will "bundle" timer callback invocations that
		874	are "near" in time together, by delaying some, thus reducing the number of
		875	times the process sleeps and wakes up again. Another useful technique to
		876	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		877	they fire on, say, one-second boundaries only.
		878
		879	Example: we only need 0.1s timeout granularity, and we wish not to poll
		880	more often than 100 times per second:
		881
		882	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		883	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		884
		885	=item ev_invoke_pending (loop)
		886
		887	This call will simply invoke all pending watchers while resetting their
		888	pending state. Normally, C<ev_loop> does this automatically when required,
		889	but when overriding the invoke callback this call comes handy.
		890
		891	=item int ev_pending_count (loop)
		892
		893	Returns the number of pending watchers - zero indicates that no watchers
		894	are pending.
		895
		896	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		897
		898	This overrides the invoke pending functionality of the loop: Instead of
		899	invoking all pending watchers when there are any, C<ev_loop> will call
		900	this callback instead. This is useful, for example, when you want to
		901	invoke the actual watchers inside another context (another thread etc.).
		902
		903	If you want to reset the callback, use C<ev_invoke_pending> as new
		904	callback.
		905
		906	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		907
		908	Sometimes you want to share the same loop between multiple threads. This
		909	can be done relatively simply by putting mutex_lock/unlock calls around
		910	each call to a libev function.
		911
		912	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		913	wait for it to return. One way around this is to wake up the loop via
		914	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		915	and I<acquire> callbacks on the loop.
		916
		917	When set, then C<release> will be called just before the thread is
		918	suspended waiting for new events, and C<acquire> is called just
		919	afterwards.
		920
		921	Ideally, C<release> will just call your mutex_unlock function, and
		922	C<acquire> will just call the mutex_lock function again.
		923
		924	While event loop modifications are allowed between invocations of
		925	C<release> and C<acquire> (that's their only purpose after all), no
		926	modifications done will affect the event loop, i.e. adding watchers will
		927	have no effect on the set of file descriptors being watched, or the time
		928	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		929	to take note of any changes you made.
		930
		931	In theory, threads executing C<ev_loop> will be async-cancel safe between
		932	invocations of C<release> and C<acquire>.
		933
		934	See also the locking example in the C<THREADS> section later in this
		935	document.
		936
		937	=item ev_set_userdata (loop, void *data)
		938
		939	=item ev_userdata (loop)
		940
		941	Set and retrieve a single C<void *> associated with a loop. When
		942	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		943	C<0.>
		944
		945	These two functions can be used to associate arbitrary data with a loop,
		946	and are intended solely for the C<invoke_pending_cb>, C<release> and
		947	C<acquire> callbacks described above, but of course can be (ab-)used for
		948	any other purpose as well.
		949
		950	=item ev_loop_verify (loop)
		951
		952	This function only does something when C<EV_VERIFY> support has been
		953	compiled in, which is the default for non-minimal builds. It tries to go
		954	through all internal structures and checks them for validity. If anything
		955	is found to be inconsistent, it will print an error message to standard
		956	error and call C<abort ()>.
		957
		958	This can be used to catch bugs inside libev itself: under normal
		959	circumstances, this function will never abort as of course libev keeps its
		960	data structures consistent.
618		961
619	=back	962	=back
620		963
621		964
622	=head1 ANATOMY OF A WATCHER	965	=head1 ANATOMY OF A WATCHER
		966
		967	In the following description, uppercase C<TYPE> in names stands for the
		968	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		969	watchers and C<ev_io_start> for I/O watchers.
623		970
624	A watcher is a structure that you create and register to record your	971	A watcher is a structure that you create and register to record your
625	interest in some event. For instance, if you want to wait for STDIN to	972	interest in some event. For instance, if you want to wait for STDIN to
626	become readable, you would create an C<ev_io> watcher for that:	973	become readable, you would create an C<ev_io> watcher for that:
627		974
628	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	975	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
629	{	976	{
630	ev_io_stop (w);	977	ev_io_stop (w);
631	ev_unloop (loop, EVUNLOOP_ALL);	978	ev_unloop (loop, EVUNLOOP_ALL);
632	}	979	}
633		980
634	struct ev_loop *loop = ev_default_loop (0);	981	struct ev_loop *loop = ev_default_loop (0);
		982
635	struct ev_io stdin_watcher;	983	ev_io stdin_watcher;
		984
636	ev_init (&stdin_watcher, my_cb);	985	ev_init (&stdin_watcher, my_cb);
637	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	986	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
638	ev_io_start (loop, &stdin_watcher);	987	ev_io_start (loop, &stdin_watcher);
		988
639	ev_loop (loop, 0);	989	ev_loop (loop, 0);
640		990
641	As you can see, you are responsible for allocating the memory for your	991	As you can see, you are responsible for allocating the memory for your
642	watcher structures (and it is usually a bad idea to do this on the stack,	992	watcher structures (and it is I<usually> a bad idea to do this on the
643	although this can sometimes be quite valid).	993	stack).
		994
		995	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		996	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
644		997
645	Each watcher structure must be initialised by a call to C<ev_init	998	Each watcher structure must be initialised by a call to C<ev_init
646	(watcher *, callback)>, which expects a callback to be provided. This	999	(watcher *, callback)>, which expects a callback to be provided. This
647	callback gets invoked each time the event occurs (or, in the case of io	1000	callback gets invoked each time the event occurs (or, in the case of I/O
648	watchers, each time the event loop detects that the file descriptor given	1001	watchers, each time the event loop detects that the file descriptor given
649	is readable and/or writable).	1002	is readable and/or writable).
650		1003
651	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1004	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
652	with arguments specific to this watcher type. There is also a macro	1005	macro to configure it, with arguments specific to the watcher type. There
653	to combine initialisation and setting in one call: C<< ev_<type>_init	1006	is also a macro to combine initialisation and setting in one call: C<<
654	(watcher *, callback, ...) >>.	1007	ev_TYPE_init (watcher *, callback, ...) >>.
655		1008
656	To make the watcher actually watch out for events, you have to start it	1009	To make the watcher actually watch out for events, you have to start it
657	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1010	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
658	*) >>), and you can stop watching for events at any time by calling the	1011	*) >>), and you can stop watching for events at any time by calling the
659	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1012	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
660		1013
661	As long as your watcher is active (has been started but not stopped) you	1014	As long as your watcher is active (has been started but not stopped) you
662	must not touch the values stored in it. Most specifically you must never	1015	must not touch the values stored in it. Most specifically you must never
663	reinitialise it or call its C<set> macro.	1016	reinitialise it or call its C<ev_TYPE_set> macro.
664		1017
665	Each and every callback receives the event loop pointer as first, the	1018	Each and every callback receives the event loop pointer as first, the
666	registered watcher structure as second, and a bitset of received events as	1019	registered watcher structure as second, and a bitset of received events as
667	third argument.	1020	third argument.
668		1021
…		…
722	=item C<EV_FORK>	1075	=item C<EV_FORK>
723		1076
724	The event loop has been resumed in the child process after fork (see	1077	The event loop has been resumed in the child process after fork (see
725	C<ev_fork>).	1078	C<ev_fork>).
726		1079
		1080	=item C<EV_ASYNC>
		1081
		1082	The given async watcher has been asynchronously notified (see C<ev_async>).
		1083
		1084	=item C<EV_CUSTOM>
		1085
		1086	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1087	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1088
727	=item C<EV_ERROR>	1089	=item C<EV_ERROR>
728		1090
729	An unspecified error has occured, the watcher has been stopped. This might	1091	An unspecified error has occurred, the watcher has been stopped. This might
730	happen because the watcher could not be properly started because libev	1092	happen because the watcher could not be properly started because libev
731	ran out of memory, a file descriptor was found to be closed or any other	1093	ran out of memory, a file descriptor was found to be closed or any other
		1094	problem. Libev considers these application bugs.
		1095
732	problem. You best act on it by reporting the problem and somehow coping	1096	You best act on it by reporting the problem and somehow coping with the
733	with the watcher being stopped.	1097	watcher being stopped. Note that well-written programs should not receive
		1098	an error ever, so when your watcher receives it, this usually indicates a
		1099	bug in your program.
734		1100
735	Libev will usually signal a few "dummy" events together with an error,	1101	Libev will usually signal a few "dummy" events together with an error, for
736	for example it might indicate that a fd is readable or writable, and if	1102	example it might indicate that a fd is readable or writable, and if your
737	your callbacks is well-written it can just attempt the operation and cope	1103	callbacks is well-written it can just attempt the operation and cope with
738	with the error from read() or write(). This will not work in multithreaded	1104	the error from read() or write(). This will not work in multi-threaded
739	programs, though, so beware.	1105	programs, though, as the fd could already be closed and reused for another
		1106	thing, so beware.
740		1107
741	=back	1108	=back
742		1109
743	=head2 GENERIC WATCHER FUNCTIONS	1110	=head2 GENERIC WATCHER FUNCTIONS
744
745	In the following description, C<TYPE> stands for the watcher type,
746	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
747		1111
748	=over 4	1112	=over 4
749		1113
750	=item C<ev_init> (ev_TYPE *watcher, callback)	1114	=item C<ev_init> (ev_TYPE *watcher, callback)
751		1115
…		…
757	which rolls both calls into one.	1121	which rolls both calls into one.
758		1122
759	You can reinitialise a watcher at any time as long as it has been stopped	1123	You can reinitialise a watcher at any time as long as it has been stopped
760	(or never started) and there are no pending events outstanding.	1124	(or never started) and there are no pending events outstanding.
761		1125
762	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1126	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
763	int revents)>.	1127	int revents)>.
764		1128
		1129	Example: Initialise an C<ev_io> watcher in two steps.
		1130
		1131	ev_io w;
		1132	ev_init (&w, my_cb);
		1133	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1134
765	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1135	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
766		1136
767	This macro initialises the type-specific parts of a watcher. You need to	1137	This macro initialises the type-specific parts of a watcher. You need to
768	call C<ev_init> at least once before you call this macro, but you can	1138	call C<ev_init> at least once before you call this macro, but you can
769	call C<ev_TYPE_set> any number of times. You must not, however, call this	1139	call C<ev_TYPE_set> any number of times. You must not, however, call this
770	macro on a watcher that is active (it can be pending, however, which is a	1140	macro on a watcher that is active (it can be pending, however, which is a
771	difference to the C<ev_init> macro).	1141	difference to the C<ev_init> macro).
772		1142
773	Although some watcher types do not have type-specific arguments	1143	Although some watcher types do not have type-specific arguments
774	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1144	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
775		1145
		1146	See C<ev_init>, above, for an example.
		1147
776	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1148	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
777		1149
778	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1150	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
779	calls into a single call. This is the most convinient method to initialise	1151	calls into a single call. This is the most convenient method to initialise
780	a watcher. The same limitations apply, of course.	1152	a watcher. The same limitations apply, of course.
781		1153
		1154	Example: Initialise and set an C<ev_io> watcher in one step.
		1155
		1156	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1157
782	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1158	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
783		1159
784	Starts (activates) the given watcher. Only active watchers will receive	1160	Starts (activates) the given watcher. Only active watchers will receive
785	events. If the watcher is already active nothing will happen.	1161	events. If the watcher is already active nothing will happen.
786		1162
		1163	Example: Start the C<ev_io> watcher that is being abused as example in this
		1164	whole section.
		1165
		1166	ev_io_start (EV_DEFAULT_UC, &w);
		1167
787	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1168	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
788		1169
789	Stops the given watcher again (if active) and clears the pending	1170	Stops the given watcher if active, and clears the pending status (whether
		1171	the watcher was active or not).
		1172
790	status. It is possible that stopped watchers are pending (for example,	1173	It is possible that stopped watchers are pending - for example,
791	non-repeating timers are being stopped when they become pending), but	1174	non-repeating timers are being stopped when they become pending - but
792	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1175	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
793	you want to free or reuse the memory used by the watcher it is therefore a	1176	pending. If you want to free or reuse the memory used by the watcher it is
794	good idea to always call its C<ev_TYPE_stop> function.	1177	therefore a good idea to always call its C<ev_TYPE_stop> function.
795		1178
796	=item bool ev_is_active (ev_TYPE *watcher)	1179	=item bool ev_is_active (ev_TYPE *watcher)
797		1180
798	Returns a true value iff the watcher is active (i.e. it has been started	1181	Returns a true value iff the watcher is active (i.e. it has been started
799	and not yet been stopped). As long as a watcher is active you must not modify	1182	and not yet been stopped). As long as a watcher is active you must not modify
…		…
815	=item ev_cb_set (ev_TYPE *watcher, callback)	1198	=item ev_cb_set (ev_TYPE *watcher, callback)
816		1199
817	Change the callback. You can change the callback at virtually any time	1200	Change the callback. You can change the callback at virtually any time
818	(modulo threads).	1201	(modulo threads).
819		1202
820	=item ev_set_priority (ev_TYPE *watcher, priority)	1203	=item ev_set_priority (ev_TYPE *watcher, int priority)
821		1204
822	=item int ev_priority (ev_TYPE *watcher)	1205	=item int ev_priority (ev_TYPE *watcher)
823		1206
824	Set and query the priority of the watcher. The priority is a small	1207	Set and query the priority of the watcher. The priority is a small
825	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1208	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
826	(default: C<-2>). Pending watchers with higher priority will be invoked	1209	(default: C<-2>). Pending watchers with higher priority will be invoked
827	before watchers with lower priority, but priority will not keep watchers	1210	before watchers with lower priority, but priority will not keep watchers
828	from being executed (except for C<ev_idle> watchers).	1211	from being executed (except for C<ev_idle> watchers).
829		1212
830	This means that priorities are I<only> used for ordering callback
831	invocation after new events have been received. This is useful, for
832	example, to reduce latency after idling, or more often, to bind two
833	watchers on the same event and make sure one is called first.
834
835	If you need to suppress invocation when higher priority events are pending	1213	If you need to suppress invocation when higher priority events are pending
836	you need to look at C<ev_idle> watchers, which provide this functionality.	1214	you need to look at C<ev_idle> watchers, which provide this functionality.
837		1215
838	You I<must not> change the priority of a watcher as long as it is active or	1216	You I<must not> change the priority of a watcher as long as it is active or
839	pending.	1217	pending.
840		1218
		1219	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1220	fine, as long as you do not mind that the priority value you query might
		1221	or might not have been clamped to the valid range.
		1222
841	The default priority used by watchers when no priority has been set is	1223	The default priority used by watchers when no priority has been set is
842	always C<0>, which is supposed to not be too high and not be too low :).	1224	always C<0>, which is supposed to not be too high and not be too low :).
843		1225
844	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1226	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
845	fine, as long as you do not mind that the priority value you query might	1227	priorities.
846	or might not have been adjusted to be within valid range.
847		1228
848	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1229	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
849		1230
850	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1231	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
851	C<loop> nor C<revents> need to be valid as long as the watcher callback	1232	C<loop> nor C<revents> need to be valid as long as the watcher callback
852	can deal with that fact.	1233	can deal with that fact, as both are simply passed through to the
		1234	callback.
853		1235
854	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1236	=item int ev_clear_pending (loop, ev_TYPE *watcher)
855		1237
856	If the watcher is pending, this function returns clears its pending status	1238	If the watcher is pending, this function clears its pending status and
857	and returns its C<revents> bitset (as if its callback was invoked). If the	1239	returns its C<revents> bitset (as if its callback was invoked). If the
858	watcher isn't pending it does nothing and returns C<0>.	1240	watcher isn't pending it does nothing and returns C<0>.
859		1241
		1242	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1243	callback to be invoked, which can be accomplished with this function.
		1244
		1245	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1246
		1247	Feeds the given event set into the event loop, as if the specified event
		1248	had happened for the specified watcher (which must be a pointer to an
		1249	initialised but not necessarily started event watcher). Obviously you must
		1250	not free the watcher as long as it has pending events.
		1251
		1252	Stopping the watcher, letting libev invoke it, or calling
		1253	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1254	not started in the first place.
		1255
		1256	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1257	functions that do not need a watcher.
		1258
860	=back	1259	=back
861		1260
862		1261
863	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1262	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
864		1263
865	Each watcher has, by default, a member C<void *data> that you can change	1264	Each watcher has, by default, a member C<void *data> that you can change
866	and read at any time, libev will completely ignore it. This can be used	1265	and read at any time: libev will completely ignore it. This can be used
867	to associate arbitrary data with your watcher. If you need more data and	1266	to associate arbitrary data with your watcher. If you need more data and
868	don't want to allocate memory and store a pointer to it in that data	1267	don't want to allocate memory and store a pointer to it in that data
869	member, you can also "subclass" the watcher type and provide your own	1268	member, you can also "subclass" the watcher type and provide your own
870	data:	1269	data:
871		1270
872	struct my_io	1271	struct my_io
873	{	1272	{
874	struct ev_io io;	1273	ev_io io;
875	int otherfd;	1274	int otherfd;
876	void *somedata;	1275	void *somedata;
877	struct whatever *mostinteresting;	1276	struct whatever *mostinteresting;
878	}	1277	};
		1278
		1279	...
		1280	struct my_io w;
		1281	ev_io_init (&w.io, my_cb, fd, EV_READ);
879		1282
880	And since your callback will be called with a pointer to the watcher, you	1283	And since your callback will be called with a pointer to the watcher, you
881	can cast it back to your own type:	1284	can cast it back to your own type:
882		1285
883	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1286	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
884	{	1287	{
885	struct my_io *w = (struct my_io *)w_;	1288	struct my_io *w = (struct my_io *)w_;
886	...	1289	...
887	}	1290	}
888		1291
889	More interesting and less C-conformant ways of casting your callback type	1292	More interesting and less C-conformant ways of casting your callback type
890	instead have been omitted.	1293	instead have been omitted.
891		1294
892	Another common scenario is having some data structure with multiple	1295	Another common scenario is to use some data structure with multiple
893	watchers:	1296	embedded watchers:
894		1297
895	struct my_biggy	1298	struct my_biggy
896	{	1299	{
897	int some_data;	1300	int some_data;
898	ev_timer t1;	1301	ev_timer t1;
899	ev_timer t2;	1302	ev_timer t2;
900	}	1303	}
901		1304
902	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1305	In this case getting the pointer to C<my_biggy> is a bit more
903	you need to use C<offsetof>:	1306	complicated: Either you store the address of your C<my_biggy> struct
		1307	in the C<data> member of the watcher (for woozies), or you need to use
		1308	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1309	programmers):
904		1310
905	#include <stddef.h>	1311	#include <stddef.h>
906		1312
907	static void	1313	static void
908	t1_cb (EV_P_ struct ev_timer *w, int revents)	1314	t1_cb (EV_P_ ev_timer *w, int revents)
909	{	1315	{
910	struct my_biggy big = (struct my_biggy *	1316	struct my_biggy big = (struct my_biggy *)
911	(((char *)w) - offsetof (struct my_biggy, t1));	1317	(((char *)w) - offsetof (struct my_biggy, t1));
912	}	1318	}
913		1319
914	static void	1320	static void
915	t2_cb (EV_P_ struct ev_timer *w, int revents)	1321	t2_cb (EV_P_ ev_timer *w, int revents)
916	{	1322	{
917	struct my_biggy big = (struct my_biggy *	1323	struct my_biggy big = (struct my_biggy *)
918	(((char *)w) - offsetof (struct my_biggy, t2));	1324	(((char *)w) - offsetof (struct my_biggy, t2));
919	}	1325	}
		1326
		1327	=head2 WATCHER PRIORITY MODELS
		1328
		1329	Many event loops support I<watcher priorities>, which are usually small
		1330	integers that influence the ordering of event callback invocation
		1331	between watchers in some way, all else being equal.
		1332
		1333	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1334	description for the more technical details such as the actual priority
		1335	range.
		1336
		1337	There are two common ways how these these priorities are being interpreted
		1338	by event loops:
		1339
		1340	In the more common lock-out model, higher priorities "lock out" invocation
		1341	of lower priority watchers, which means as long as higher priority
		1342	watchers receive events, lower priority watchers are not being invoked.
		1343
		1344	The less common only-for-ordering model uses priorities solely to order
		1345	callback invocation within a single event loop iteration: Higher priority
		1346	watchers are invoked before lower priority ones, but they all get invoked
		1347	before polling for new events.
		1348
		1349	Libev uses the second (only-for-ordering) model for all its watchers
		1350	except for idle watchers (which use the lock-out model).
		1351
		1352	The rationale behind this is that implementing the lock-out model for
		1353	watchers is not well supported by most kernel interfaces, and most event
		1354	libraries will just poll for the same events again and again as long as
		1355	their callbacks have not been executed, which is very inefficient in the
		1356	common case of one high-priority watcher locking out a mass of lower
		1357	priority ones.
		1358
		1359	Static (ordering) priorities are most useful when you have two or more
		1360	watchers handling the same resource: a typical usage example is having an
		1361	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1362	timeouts. Under load, data might be received while the program handles
		1363	other jobs, but since timers normally get invoked first, the timeout
		1364	handler will be executed before checking for data. In that case, giving
		1365	the timer a lower priority than the I/O watcher ensures that I/O will be
		1366	handled first even under adverse conditions (which is usually, but not
		1367	always, what you want).
		1368
		1369	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1370	will only be executed when no same or higher priority watchers have
		1371	received events, they can be used to implement the "lock-out" model when
		1372	required.
		1373
		1374	For example, to emulate how many other event libraries handle priorities,
		1375	you can associate an C<ev_idle> watcher to each such watcher, and in
		1376	the normal watcher callback, you just start the idle watcher. The real
		1377	processing is done in the idle watcher callback. This causes libev to
		1378	continously poll and process kernel event data for the watcher, but when
		1379	the lock-out case is known to be rare (which in turn is rare :), this is
		1380	workable.
		1381
		1382	Usually, however, the lock-out model implemented that way will perform
		1383	miserably under the type of load it was designed to handle. In that case,
		1384	it might be preferable to stop the real watcher before starting the
		1385	idle watcher, so the kernel will not have to process the event in case
		1386	the actual processing will be delayed for considerable time.
		1387
		1388	Here is an example of an I/O watcher that should run at a strictly lower
		1389	priority than the default, and which should only process data when no
		1390	other events are pending:
		1391
		1392	ev_idle idle; // actual processing watcher
		1393	ev_io io; // actual event watcher
		1394
		1395	static void
		1396	io_cb (EV_P_ ev_io *w, int revents)
		1397	{
		1398	// stop the I/O watcher, we received the event, but
		1399	// are not yet ready to handle it.
		1400	ev_io_stop (EV_A_ w);
		1401
		1402	// start the idle watcher to ahndle the actual event.
		1403	// it will not be executed as long as other watchers
		1404	// with the default priority are receiving events.
		1405	ev_idle_start (EV_A_ &idle);
		1406	}
		1407
		1408	static void
		1409	idle_cb (EV_P_ ev_idle *w, int revents)
		1410	{
		1411	// actual processing
		1412	read (STDIN_FILENO, ...);
		1413
		1414	// have to start the I/O watcher again, as
		1415	// we have handled the event
		1416	ev_io_start (EV_P_ &io);
		1417	}
		1418
		1419	// initialisation
		1420	ev_idle_init (&idle, idle_cb);
		1421	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1422	ev_io_start (EV_DEFAULT_ &io);
		1423
		1424	In the "real" world, it might also be beneficial to start a timer, so that
		1425	low-priority connections can not be locked out forever under load. This
		1426	enables your program to keep a lower latency for important connections
		1427	during short periods of high load, while not completely locking out less
		1428	important ones.
920		1429
921		1430
922	=head1 WATCHER TYPES	1431	=head1 WATCHER TYPES
923		1432
924	This section describes each watcher in detail, but will not repeat	1433	This section describes each watcher in detail, but will not repeat
…		…
948	In general you can register as many read and/or write event watchers per	1457	In general you can register as many read and/or write event watchers per
949	fd as you want (as long as you don't confuse yourself). Setting all file	1458	fd as you want (as long as you don't confuse yourself). Setting all file
950	descriptors to non-blocking mode is also usually a good idea (but not	1459	descriptors to non-blocking mode is also usually a good idea (but not
951	required if you know what you are doing).	1460	required if you know what you are doing).
952		1461
953	You have to be careful with dup'ed file descriptors, though. Some backends	1462	If you cannot use non-blocking mode, then force the use of a
954	(the linux epoll backend is a notable example) cannot handle dup'ed file	1463	known-to-be-good backend (at the time of this writing, this includes only
955	descriptors correctly if you register interest in two or more fds pointing	1464	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
956	to the same underlying file/socket/etc. description (that is, they share	1465	descriptors for which non-blocking operation makes no sense (such as
957	the same underlying "file open").	1466	files) - libev doesn't guarentee any specific behaviour in that case.
958
959	If you must do this, then force the use of a known-to-be-good backend
960	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
961	C<EVBACKEND_POLL>).
962		1467
963	Another thing you have to watch out for is that it is quite easy to	1468	Another thing you have to watch out for is that it is quite easy to
964	receive "spurious" readyness notifications, that is your callback might	1469	receive "spurious" readiness notifications, that is your callback might
965	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1470	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
966	because there is no data. Not only are some backends known to create a	1471	because there is no data. Not only are some backends known to create a
967	lot of those (for example solaris ports), it is very easy to get into	1472	lot of those (for example Solaris ports), it is very easy to get into
968	this situation even with a relatively standard program structure. Thus	1473	this situation even with a relatively standard program structure. Thus
969	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1474	it is best to always use non-blocking I/O: An extra C<read>(2) returning
970	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1475	C<EAGAIN> is far preferable to a program hanging until some data arrives.
971		1476
972	If you cannot run the fd in non-blocking mode (for example you should not	1477	If you cannot run the fd in non-blocking mode (for example you should
973	play around with an Xlib connection), then you have to seperately re-test	1478	not play around with an Xlib connection), then you have to separately
974	whether a file descriptor is really ready with a known-to-be good interface	1479	re-test whether a file descriptor is really ready with a known-to-be good
975	such as poll (fortunately in our Xlib example, Xlib already does this on	1480	interface such as poll (fortunately in our Xlib example, Xlib already
976	its own, so its quite safe to use).	1481	does this on its own, so its quite safe to use). Some people additionally
		1482	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1483	indefinitely.
		1484
		1485	But really, best use non-blocking mode.
977		1486
978	=head3 The special problem of disappearing file descriptors	1487	=head3 The special problem of disappearing file descriptors
979		1488
980	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1489	Some backends (e.g. kqueue, epoll) need to be told about closing a file
981	descriptor (either by calling C<close> explicitly or by any other means,	1490	descriptor (either due to calling C<close> explicitly or any other means,
982	such as C<dup>). The reason is that you register interest in some file	1491	such as C<dup2>). The reason is that you register interest in some file
983	descriptor, but when it goes away, the operating system will silently drop	1492	descriptor, but when it goes away, the operating system will silently drop
984	this interest. If another file descriptor with the same number then is	1493	this interest. If another file descriptor with the same number then is
985	registered with libev, there is no efficient way to see that this is, in	1494	registered with libev, there is no efficient way to see that this is, in
986	fact, a different file descriptor.	1495	fact, a different file descriptor.
987		1496
…		…
997	optimisations to libev.	1506	optimisations to libev.
998		1507
999	=head3 The special problem of dup'ed file descriptors	1508	=head3 The special problem of dup'ed file descriptors
1000		1509
1001	Some backends (e.g. epoll), cannot register events for file descriptors,	1510	Some backends (e.g. epoll), cannot register events for file descriptors,
1002	but only events for the underlying file descriptions. That menas when you	1511	but only events for the underlying file descriptions. That means when you
1003	have C<dup ()>'ed file descriptors and register events for them, only one	1512	have C<dup ()>'ed file descriptors or weirder constellations, and register
1004	file descriptor might actually receive events.	1513	events for them, only one file descriptor might actually receive events.
1005		1514
1006	There is no workaorund possible except not registering events	1515	There is no workaround possible except not registering events
1007	for potentially C<dup ()>'ed file descriptors or to resort to	1516	for potentially C<dup ()>'ed file descriptors, or to resort to
1008	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1517	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1009		1518
1010	=head3 The special problem of fork	1519	=head3 The special problem of fork
1011		1520
1012	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1521	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1016	To support fork in your programs, you either have to call	1525	To support fork in your programs, you either have to call
1017	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1526	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1018	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1527	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1019	C<EVBACKEND_POLL>.	1528	C<EVBACKEND_POLL>.
1020		1529
		1530	=head3 The special problem of SIGPIPE
		1531
		1532	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1533	when writing to a pipe whose other end has been closed, your program gets
		1534	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1535	this is sensible behaviour, for daemons, this is usually undesirable.
		1536
		1537	So when you encounter spurious, unexplained daemon exits, make sure you
		1538	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1539	somewhere, as that would have given you a big clue).
		1540
1021		1541
1022	=head3 Watcher-Specific Functions	1542	=head3 Watcher-Specific Functions
1023		1543
1024	=over 4	1544	=over 4
1025		1545
1026	=item ev_io_init (ev_io *, callback, int fd, int events)	1546	=item ev_io_init (ev_io *, callback, int fd, int events)
1027		1547
1028	=item ev_io_set (ev_io *, int fd, int events)	1548	=item ev_io_set (ev_io *, int fd, int events)
1029		1549
1030	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1550	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1031	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1551	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1032	C<EV_READ | EV_WRITE> to receive the given events.	1552	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1033		1553
1034	=item int fd [read-only]	1554	=item int fd [read-only]
1035		1555
1036	The file descriptor being watched.	1556	The file descriptor being watched.
1037		1557
1038	=item int events [read-only]	1558	=item int events [read-only]
1039		1559
1040	The events being watched.	1560	The events being watched.
1041		1561
1042	=back	1562	=back
		1563
		1564	=head3 Examples
1043		1565
1044	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1566	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1045	readable, but only once. Since it is likely line-buffered, you could	1567	readable, but only once. Since it is likely line-buffered, you could
1046	attempt to read a whole line in the callback.	1568	attempt to read a whole line in the callback.
1047		1569
1048	static void	1570	static void
1049	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1571	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1050	{	1572	{
1051	ev_io_stop (loop, w);	1573	ev_io_stop (loop, w);
1052	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1574	.. read from stdin here (or from w->fd) and handle any I/O errors
1053	}	1575	}
1054		1576
1055	...	1577	...
1056	struct ev_loop *loop = ev_default_init (0);	1578	struct ev_loop *loop = ev_default_init (0);
1057	struct ev_io stdin_readable;	1579	ev_io stdin_readable;
1058	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1580	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1059	ev_io_start (loop, &stdin_readable);	1581	ev_io_start (loop, &stdin_readable);
1060	ev_loop (loop, 0);	1582	ev_loop (loop, 0);
1061		1583
1062		1584
1063	=head2 C<ev_timer> - relative and optionally repeating timeouts	1585	=head2 C<ev_timer> - relative and optionally repeating timeouts
1064		1586
1065	Timer watchers are simple relative timers that generate an event after a	1587	Timer watchers are simple relative timers that generate an event after a
1066	given time, and optionally repeating in regular intervals after that.	1588	given time, and optionally repeating in regular intervals after that.
1067		1589
1068	The timers are based on real time, that is, if you register an event that	1590	The timers are based on real time, that is, if you register an event that
1069	times out after an hour and you reset your system clock to last years	1591	times out after an hour and you reset your system clock to January last
1070	time, it will still time out after (roughly) and hour. "Roughly" because	1592	year, it will still time out after (roughly) one hour. "Roughly" because
1071	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1593	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1072	monotonic clock option helps a lot here).	1594	monotonic clock option helps a lot here).
		1595
		1596	The callback is guaranteed to be invoked only I<after> its timeout has
		1597	passed (not I<at>, so on systems with very low-resolution clocks this
		1598	might introduce a small delay). If multiple timers become ready during the
		1599	same loop iteration then the ones with earlier time-out values are invoked
		1600	before ones of the same priority with later time-out values (but this is
		1601	no longer true when a callback calls C<ev_loop> recursively).
		1602
		1603	=head3 Be smart about timeouts
		1604
		1605	Many real-world problems involve some kind of timeout, usually for error
		1606	recovery. A typical example is an HTTP request - if the other side hangs,
		1607	you want to raise some error after a while.
		1608
		1609	What follows are some ways to handle this problem, from obvious and
		1610	inefficient to smart and efficient.
		1611
		1612	In the following, a 60 second activity timeout is assumed - a timeout that
		1613	gets reset to 60 seconds each time there is activity (e.g. each time some
		1614	data or other life sign was received).
		1615
		1616	=over 4
		1617
		1618	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1619
		1620	This is the most obvious, but not the most simple way: In the beginning,
		1621	start the watcher:
		1622
		1623	ev_timer_init (timer, callback, 60., 0.);
		1624	ev_timer_start (loop, timer);
		1625
		1626	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1627	and start it again:
		1628
		1629	ev_timer_stop (loop, timer);
		1630	ev_timer_set (timer, 60., 0.);
		1631	ev_timer_start (loop, timer);
		1632
		1633	This is relatively simple to implement, but means that each time there is
		1634	some activity, libev will first have to remove the timer from its internal
		1635	data structure and then add it again. Libev tries to be fast, but it's
		1636	still not a constant-time operation.
		1637
		1638	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1639
		1640	This is the easiest way, and involves using C<ev_timer_again> instead of
		1641	C<ev_timer_start>.
		1642
		1643	To implement this, configure an C<ev_timer> with a C<repeat> value
		1644	of C<60> and then call C<ev_timer_again> at start and each time you
		1645	successfully read or write some data. If you go into an idle state where
		1646	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1647	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1648
		1649	That means you can ignore both the C<ev_timer_start> function and the
		1650	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1651	member and C<ev_timer_again>.
		1652
		1653	At start:
		1654
		1655	ev_init (timer, callback);
		1656	timer->repeat = 60.;
		1657	ev_timer_again (loop, timer);
		1658
		1659	Each time there is some activity:
		1660
		1661	ev_timer_again (loop, timer);
		1662
		1663	It is even possible to change the time-out on the fly, regardless of
		1664	whether the watcher is active or not:
		1665
		1666	timer->repeat = 30.;
		1667	ev_timer_again (loop, timer);
		1668
		1669	This is slightly more efficient then stopping/starting the timer each time
		1670	you want to modify its timeout value, as libev does not have to completely
		1671	remove and re-insert the timer from/into its internal data structure.
		1672
		1673	It is, however, even simpler than the "obvious" way to do it.
		1674
		1675	=item 3. Let the timer time out, but then re-arm it as required.
		1676
		1677	This method is more tricky, but usually most efficient: Most timeouts are
		1678	relatively long compared to the intervals between other activity - in
		1679	our example, within 60 seconds, there are usually many I/O events with
		1680	associated activity resets.
		1681
		1682	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1683	but remember the time of last activity, and check for a real timeout only
		1684	within the callback:
		1685
		1686	ev_tstamp last_activity; // time of last activity
		1687
		1688	static void
		1689	callback (EV_P_ ev_timer *w, int revents)
		1690	{
		1691	ev_tstamp now = ev_now (EV_A);
		1692	ev_tstamp timeout = last_activity + 60.;
		1693
		1694	// if last_activity + 60. is older than now, we did time out
		1695	if (timeout < now)
		1696	{
		1697	// timeout occured, take action
		1698	}
		1699	else
		1700	{
		1701	// callback was invoked, but there was some activity, re-arm
		1702	// the watcher to fire in last_activity + 60, which is
		1703	// guaranteed to be in the future, so "again" is positive:
		1704	w->repeat = timeout - now;
		1705	ev_timer_again (EV_A_ w);
		1706	}
		1707	}
		1708
		1709	To summarise the callback: first calculate the real timeout (defined
		1710	as "60 seconds after the last activity"), then check if that time has
		1711	been reached, which means something I<did>, in fact, time out. Otherwise
		1712	the callback was invoked too early (C<timeout> is in the future), so
		1713	re-schedule the timer to fire at that future time, to see if maybe we have
		1714	a timeout then.
		1715
		1716	Note how C<ev_timer_again> is used, taking advantage of the
		1717	C<ev_timer_again> optimisation when the timer is already running.
		1718
		1719	This scheme causes more callback invocations (about one every 60 seconds
		1720	minus half the average time between activity), but virtually no calls to
		1721	libev to change the timeout.
		1722
		1723	To start the timer, simply initialise the watcher and set C<last_activity>
		1724	to the current time (meaning we just have some activity :), then call the
		1725	callback, which will "do the right thing" and start the timer:
		1726
		1727	ev_init (timer, callback);
		1728	last_activity = ev_now (loop);
		1729	callback (loop, timer, EV_TIMEOUT);
		1730
		1731	And when there is some activity, simply store the current time in
		1732	C<last_activity>, no libev calls at all:
		1733
		1734	last_actiivty = ev_now (loop);
		1735
		1736	This technique is slightly more complex, but in most cases where the
		1737	time-out is unlikely to be triggered, much more efficient.
		1738
		1739	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1740	callback :) - just change the timeout and invoke the callback, which will
		1741	fix things for you.
		1742
		1743	=item 4. Wee, just use a double-linked list for your timeouts.
		1744
		1745	If there is not one request, but many thousands (millions...), all
		1746	employing some kind of timeout with the same timeout value, then one can
		1747	do even better:
		1748
		1749	When starting the timeout, calculate the timeout value and put the timeout
		1750	at the I<end> of the list.
		1751
		1752	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1753	the list is expected to fire (for example, using the technique #3).
		1754
		1755	When there is some activity, remove the timer from the list, recalculate
		1756	the timeout, append it to the end of the list again, and make sure to
		1757	update the C<ev_timer> if it was taken from the beginning of the list.
		1758
		1759	This way, one can manage an unlimited number of timeouts in O(1) time for
		1760	starting, stopping and updating the timers, at the expense of a major
		1761	complication, and having to use a constant timeout. The constant timeout
		1762	ensures that the list stays sorted.
		1763
		1764	=back
		1765
		1766	So which method the best?
		1767
		1768	Method #2 is a simple no-brain-required solution that is adequate in most
		1769	situations. Method #3 requires a bit more thinking, but handles many cases
		1770	better, and isn't very complicated either. In most case, choosing either
		1771	one is fine, with #3 being better in typical situations.
		1772
		1773	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1774	rather complicated, but extremely efficient, something that really pays
		1775	off after the first million or so of active timers, i.e. it's usually
		1776	overkill :)
		1777
		1778	=head3 The special problem of time updates
		1779
		1780	Establishing the current time is a costly operation (it usually takes at
		1781	least two system calls): EV therefore updates its idea of the current
		1782	time only before and after C<ev_loop> collects new events, which causes a
		1783	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1784	lots of events in one iteration.
1073		1785
1074	The relative timeouts are calculated relative to the C<ev_now ()>	1786	The relative timeouts are calculated relative to the C<ev_now ()>
1075	time. This is usually the right thing as this timestamp refers to the time	1787	time. This is usually the right thing as this timestamp refers to the time
1076	of the event triggering whatever timeout you are modifying/starting. If	1788	of the event triggering whatever timeout you are modifying/starting. If
1077	you suspect event processing to be delayed and you I<need> to base the timeout	1789	you suspect event processing to be delayed and you I<need> to base the
1078	on the current time, use something like this to adjust for this:	1790	timeout on the current time, use something like this to adjust for this:
1079		1791
1080	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1792	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1081		1793
1082	The callback is guarenteed to be invoked only when its timeout has passed,	1794	If the event loop is suspended for a long time, you can also force an
1083	but if multiple timers become ready during the same loop iteration then	1795	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1084	order of execution is undefined.	1796	()>.
		1797
		1798	=head3 The special problems of suspended animation
		1799
		1800	When you leave the server world it is quite customary to hit machines that
		1801	can suspend/hibernate - what happens to the clocks during such a suspend?
		1802
		1803	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1804	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1805	to run until the system is suspended, but they will not advance while the
		1806	system is suspended. That means, on resume, it will be as if the program
		1807	was frozen for a few seconds, but the suspend time will not be counted
		1808	towards C<ev_timer> when a monotonic clock source is used. The real time
		1809	clock advanced as expected, but if it is used as sole clocksource, then a
		1810	long suspend would be detected as a time jump by libev, and timers would
		1811	be adjusted accordingly.
		1812
		1813	I would not be surprised to see different behaviour in different between
		1814	operating systems, OS versions or even different hardware.
		1815
		1816	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1817	time jump in the monotonic clocks and the realtime clock. If the program
		1818	is suspended for a very long time, and monotonic clock sources are in use,
		1819	then you can expect C<ev_timer>s to expire as the full suspension time
		1820	will be counted towards the timers. When no monotonic clock source is in
		1821	use, then libev will again assume a timejump and adjust accordingly.
		1822
		1823	It might be beneficial for this latter case to call C<ev_suspend>
		1824	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1825	deterministic behaviour in this case (you can do nothing against
		1826	C<SIGSTOP>).
1085		1827
1086	=head3 Watcher-Specific Functions and Data Members	1828	=head3 Watcher-Specific Functions and Data Members
1087		1829
1088	=over 4	1830	=over 4
1089		1831
1090	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1832	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1091		1833
1092	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1834	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1093		1835
1094	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1836	Configure the timer to trigger after C<after> seconds. If C<repeat>
1095	C<0.>, then it will automatically be stopped. If it is positive, then the	1837	is C<0.>, then it will automatically be stopped once the timeout is
1096	timer will automatically be configured to trigger again C<repeat> seconds	1838	reached. If it is positive, then the timer will automatically be
1097	later, again, and again, until stopped manually.	1839	configured to trigger again C<repeat> seconds later, again, and again,
		1840	until stopped manually.
1098		1841
1099	The timer itself will do a best-effort at avoiding drift, that is, if you	1842	The timer itself will do a best-effort at avoiding drift, that is, if
1100	configure a timer to trigger every 10 seconds, then it will trigger at	1843	you configure a timer to trigger every 10 seconds, then it will normally
1101	exactly 10 second intervals. If, however, your program cannot keep up with	1844	trigger at exactly 10 second intervals. If, however, your program cannot
1102	the timer (because it takes longer than those 10 seconds to do stuff) the	1845	keep up with the timer (because it takes longer than those 10 seconds to
1103	timer will not fire more than once per event loop iteration.	1846	do stuff) the timer will not fire more than once per event loop iteration.
1104		1847
1105	=item ev_timer_again (loop)	1848	=item ev_timer_again (loop, ev_timer *)
1106		1849
1107	This will act as if the timer timed out and restart it again if it is	1850	This will act as if the timer timed out and restart it again if it is
1108	repeating. The exact semantics are:	1851	repeating. The exact semantics are:
1109		1852
1110	If the timer is pending, its pending status is cleared.	1853	If the timer is pending, its pending status is cleared.
1111		1854
1112	If the timer is started but nonrepeating, stop it (as if it timed out).	1855	If the timer is started but non-repeating, stop it (as if it timed out).
1113		1856
1114	If the timer is repeating, either start it if necessary (with the	1857	If the timer is repeating, either start it if necessary (with the
1115	C<repeat> value), or reset the running timer to the C<repeat> value.	1858	C<repeat> value), or reset the running timer to the C<repeat> value.
1116		1859
1117	This sounds a bit complicated, but here is a useful and typical	1860	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1118	example: Imagine you have a tcp connection and you want a so-called idle	1861	usage example.
1119	timeout, that is, you want to be called when there have been, say, 60
1120	seconds of inactivity on the socket. The easiest way to do this is to
1121	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1122	C<ev_timer_again> each time you successfully read or write some data. If
1123	you go into an idle state where you do not expect data to travel on the
1124	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1125	automatically restart it if need be.
1126		1862
1127	That means you can ignore the C<after> value and C<ev_timer_start>	1863	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1128	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1129		1864
1130	ev_timer_init (timer, callback, 0., 5.);	1865	Returns the remaining time until a timer fires. If the timer is active,
1131	ev_timer_again (loop, timer);	1866	then this time is relative to the current event loop time, otherwise it's
1132	...	1867	the timeout value currently configured.
1133	timer->again = 17.;
1134	ev_timer_again (loop, timer);
1135	...
1136	timer->again = 10.;
1137	ev_timer_again (loop, timer);
1138		1868
1139	This is more slightly efficient then stopping/starting the timer each time	1869	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1140	you want to modify its timeout value.	1870	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1871	will return C<4>. When the timer expires and is restarted, it will return
		1872	roughly C<7> (likely slightly less as callback invocation takes some time,
		1873	too), and so on.
1141		1874
1142	=item ev_tstamp repeat [read-write]	1875	=item ev_tstamp repeat [read-write]
1143		1876
1144	The current C<repeat> value. Will be used each time the watcher times out	1877	The current C<repeat> value. Will be used each time the watcher times out
1145	or C<ev_timer_again> is called and determines the next timeout (if any),	1878	or C<ev_timer_again> is called, and determines the next timeout (if any),
1146	which is also when any modifications are taken into account.	1879	which is also when any modifications are taken into account.
1147		1880
1148	=back	1881	=back
1149		1882
		1883	=head3 Examples
		1884
1150	Example: Create a timer that fires after 60 seconds.	1885	Example: Create a timer that fires after 60 seconds.
1151		1886
1152	static void	1887	static void
1153	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1888	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1154	{	1889	{
1155	.. one minute over, w is actually stopped right here	1890	.. one minute over, w is actually stopped right here
1156	}	1891	}
1157		1892
1158	struct ev_timer mytimer;	1893	ev_timer mytimer;
1159	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1894	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1160	ev_timer_start (loop, &mytimer);	1895	ev_timer_start (loop, &mytimer);
1161		1896
1162	Example: Create a timeout timer that times out after 10 seconds of	1897	Example: Create a timeout timer that times out after 10 seconds of
1163	inactivity.	1898	inactivity.
1164		1899
1165	static void	1900	static void
1166	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1901	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1167	{	1902	{
1168	.. ten seconds without any activity	1903	.. ten seconds without any activity
1169	}	1904	}
1170		1905
1171	struct ev_timer mytimer;	1906	ev_timer mytimer;
1172	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1907	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1173	ev_timer_again (&mytimer); /* start timer */	1908	ev_timer_again (&mytimer); /* start timer */
1174	ev_loop (loop, 0);	1909	ev_loop (loop, 0);
1175		1910
1176	// and in some piece of code that gets executed on any "activity":	1911	// and in some piece of code that gets executed on any "activity":
1177	// reset the timeout to start ticking again at 10 seconds	1912	// reset the timeout to start ticking again at 10 seconds
1178	ev_timer_again (&mytimer);	1913	ev_timer_again (&mytimer);
1179		1914
1180		1915
1181	=head2 C<ev_periodic> - to cron or not to cron?	1916	=head2 C<ev_periodic> - to cron or not to cron?
1182		1917
1183	Periodic watchers are also timers of a kind, but they are very versatile	1918	Periodic watchers are also timers of a kind, but they are very versatile
1184	(and unfortunately a bit complex).	1919	(and unfortunately a bit complex).
1185		1920
1186	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1921	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1187	but on wallclock time (absolute time). You can tell a periodic watcher	1922	relative time, the physical time that passes) but on wall clock time
1188	to trigger "at" some specific point in time. For example, if you tell a	1923	(absolute time, the thing you can read on your calender or clock). The
1189	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1924	difference is that wall clock time can run faster or slower than real
1190	+ 10.>) and then reset your system clock to the last year, then it will	1925	time, and time jumps are not uncommon (e.g. when you adjust your
1191	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1926	wrist-watch).
1192	roughly 10 seconds later).
1193		1927
1194	They can also be used to implement vastly more complex timers, such as	1928	You can tell a periodic watcher to trigger after some specific point
1195	triggering an event on each midnight, local time or other, complicated,	1929	in time: for example, if you tell a periodic watcher to trigger "in 10
1196	rules.	1930	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1931	not a delay) and then reset your system clock to January of the previous
		1932	year, then it will take a year or more to trigger the event (unlike an
		1933	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1934	it, as it uses a relative timeout).
1197		1935
		1936	C<ev_periodic> watchers can also be used to implement vastly more complex
		1937	timers, such as triggering an event on each "midnight, local time", or
		1938	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1939	those cannot react to time jumps.
		1940
1198	As with timers, the callback is guarenteed to be invoked only when the	1941	As with timers, the callback is guaranteed to be invoked only when the
1199	time (C<at>) has been passed, but if multiple periodic timers become ready	1942	point in time where it is supposed to trigger has passed. If multiple
1200	during the same loop iteration then order of execution is undefined.	1943	timers become ready during the same loop iteration then the ones with
		1944	earlier time-out values are invoked before ones with later time-out values
		1945	(but this is no longer true when a callback calls C<ev_loop> recursively).
1201		1946
1202	=head3 Watcher-Specific Functions and Data Members	1947	=head3 Watcher-Specific Functions and Data Members
1203		1948
1204	=over 4	1949	=over 4
1205		1950
1206	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1951	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1207		1952
1208	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1953	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1209		1954
1210	Lots of arguments, lets sort it out... There are basically three modes of	1955	Lots of arguments, let's sort it out... There are basically three modes of
1211	operation, and we will explain them from simplest to complex:	1956	operation, and we will explain them from simplest to most complex:
1212		1957
1213	=over 4	1958	=over 4
1214		1959
1215	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1960	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1216		1961
1217	In this configuration the watcher triggers an event at the wallclock time	1962	In this configuration the watcher triggers an event after the wall clock
1218	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1963	time C<offset> has passed. It will not repeat and will not adjust when a
1219	that is, if it is to be run at January 1st 2011 then it will run when the	1964	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1220	system time reaches or surpasses this time.	1965	will be stopped and invoked when the system clock reaches or surpasses
		1966	this point in time.
1221		1967
1222	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1968	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1223		1969
1224	In this mode the watcher will always be scheduled to time out at the next	1970	In this mode the watcher will always be scheduled to time out at the next
1225	C<at + N * interval> time (for some integer N, which can also be negative)	1971	C<offset + N * interval> time (for some integer N, which can also be
1226	and then repeat, regardless of any time jumps.	1972	negative) and then repeat, regardless of any time jumps. The C<offset>
		1973	argument is merely an offset into the C<interval> periods.
1227		1974
1228	This can be used to create timers that do not drift with respect to system	1975	This can be used to create timers that do not drift with respect to the
1229	time:	1976	system clock, for example, here is an C<ev_periodic> that triggers each
		1977	hour, on the hour (with respect to UTC):
1230		1978
1231	ev_periodic_set (&periodic, 0., 3600., 0);	1979	ev_periodic_set (&periodic, 0., 3600., 0);
1232		1980
1233	This doesn't mean there will always be 3600 seconds in between triggers,	1981	This doesn't mean there will always be 3600 seconds in between triggers,
1234	but only that the the callback will be called when the system time shows a	1982	but only that the callback will be called when the system time shows a
1235	full hour (UTC), or more correctly, when the system time is evenly divisible	1983	full hour (UTC), or more correctly, when the system time is evenly divisible
1236	by 3600.	1984	by 3600.
1237		1985
1238	Another way to think about it (for the mathematically inclined) is that	1986	Another way to think about it (for the mathematically inclined) is that
1239	C<ev_periodic> will try to run the callback in this mode at the next possible	1987	C<ev_periodic> will try to run the callback in this mode at the next possible
1240	time where C<time = at (mod interval)>, regardless of any time jumps.	1988	time where C<time = offset (mod interval)>, regardless of any time jumps.
1241		1989
1242	For numerical stability it is preferable that the C<at> value is near	1990	For numerical stability it is preferable that the C<offset> value is near
1243	C<ev_now ()> (the current time), but there is no range requirement for	1991	C<ev_now ()> (the current time), but there is no range requirement for
1244	this value.	1992	this value, and in fact is often specified as zero.
1245		1993
		1994	Note also that there is an upper limit to how often a timer can fire (CPU
		1995	speed for example), so if C<interval> is very small then timing stability
		1996	will of course deteriorate. Libev itself tries to be exact to be about one
		1997	millisecond (if the OS supports it and the machine is fast enough).
		1998
1246	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1999	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1247		2000
1248	In this mode the values for C<interval> and C<at> are both being	2001	In this mode the values for C<interval> and C<offset> are both being
1249	ignored. Instead, each time the periodic watcher gets scheduled, the	2002	ignored. Instead, each time the periodic watcher gets scheduled, the
1250	reschedule callback will be called with the watcher as first, and the	2003	reschedule callback will be called with the watcher as first, and the
1251	current time as second argument.	2004	current time as second argument.
1252		2005
1253	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2006	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1254	ever, or make any event loop modifications>. If you need to stop it,	2007	or make ANY other event loop modifications whatsoever, unless explicitly
1255	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2008	allowed by documentation here>.
1256	starting an C<ev_prepare> watcher, which is legal).
1257		2009
		2010	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2011	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2012	only event loop modification you are allowed to do).
		2013
1258	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2014	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1259	ev_tstamp now)>, e.g.:	2015	*w, ev_tstamp now)>, e.g.:
1260		2016
		2017	static ev_tstamp
1261	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2018	my_rescheduler (ev_periodic *w, ev_tstamp now)
1262	{	2019	{
1263	return now + 60.;	2020	return now + 60.;
1264	}	2021	}
1265		2022
1266	It must return the next time to trigger, based on the passed time value	2023	It must return the next time to trigger, based on the passed time value
1267	(that is, the lowest time value larger than to the second argument). It	2024	(that is, the lowest time value larger than to the second argument). It
1268	will usually be called just before the callback will be triggered, but	2025	will usually be called just before the callback will be triggered, but
1269	might be called at other times, too.	2026	might be called at other times, too.
1270		2027
1271	NOTE: I<< This callback must always return a time that is later than the	2028	NOTE: I<< This callback must always return a time that is higher than or
1272	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2029	equal to the passed C<now> value >>.
1273		2030
1274	This can be used to create very complex timers, such as a timer that	2031	This can be used to create very complex timers, such as a timer that
1275	triggers on each midnight, local time. To do this, you would calculate the	2032	triggers on "next midnight, local time". To do this, you would calculate the
1276	next midnight after C<now> and return the timestamp value for this. How	2033	next midnight after C<now> and return the timestamp value for this. How
1277	you do this is, again, up to you (but it is not trivial, which is the main	2034	you do this is, again, up to you (but it is not trivial, which is the main
1278	reason I omitted it as an example).	2035	reason I omitted it as an example).
1279		2036
1280	=back	2037	=back
…		…
1284	Simply stops and restarts the periodic watcher again. This is only useful	2041	Simply stops and restarts the periodic watcher again. This is only useful
1285	when you changed some parameters or the reschedule callback would return	2042	when you changed some parameters or the reschedule callback would return
1286	a different time than the last time it was called (e.g. in a crond like	2043	a different time than the last time it was called (e.g. in a crond like
1287	program when the crontabs have changed).	2044	program when the crontabs have changed).
1288		2045
		2046	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2047
		2048	When active, returns the absolute time that the watcher is supposed
		2049	to trigger next. This is not the same as the C<offset> argument to
		2050	C<ev_periodic_set>, but indeed works even in interval and manual
		2051	rescheduling modes.
		2052
1289	=item ev_tstamp offset [read-write]	2053	=item ev_tstamp offset [read-write]
1290		2054
1291	When repeating, this contains the offset value, otherwise this is the	2055	When repeating, this contains the offset value, otherwise this is the
1292	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2056	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2057	although libev might modify this value for better numerical stability).
1293		2058
1294	Can be modified any time, but changes only take effect when the periodic	2059	Can be modified any time, but changes only take effect when the periodic
1295	timer fires or C<ev_periodic_again> is being called.	2060	timer fires or C<ev_periodic_again> is being called.
1296		2061
1297	=item ev_tstamp interval [read-write]	2062	=item ev_tstamp interval [read-write]
1298		2063
1299	The current interval value. Can be modified any time, but changes only	2064	The current interval value. Can be modified any time, but changes only
1300	take effect when the periodic timer fires or C<ev_periodic_again> is being	2065	take effect when the periodic timer fires or C<ev_periodic_again> is being
1301	called.	2066	called.
1302		2067
1303	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2068	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1304		2069
1305	The current reschedule callback, or C<0>, if this functionality is	2070	The current reschedule callback, or C<0>, if this functionality is
1306	switched off. Can be changed any time, but changes only take effect when	2071	switched off. Can be changed any time, but changes only take effect when
1307	the periodic timer fires or C<ev_periodic_again> is being called.	2072	the periodic timer fires or C<ev_periodic_again> is being called.
1308		2073
1309	=item ev_tstamp at [read-only]
1310
1311	When active, contains the absolute time that the watcher is supposed to
1312	trigger next.
1313
1314	=back	2074	=back
1315		2075
		2076	=head3 Examples
		2077
1316	Example: Call a callback every hour, or, more precisely, whenever the	2078	Example: Call a callback every hour, or, more precisely, whenever the
1317	system clock is divisible by 3600. The callback invocation times have	2079	system time is divisible by 3600. The callback invocation times have
1318	potentially a lot of jittering, but good long-term stability.	2080	potentially a lot of jitter, but good long-term stability.
1319		2081
1320	static void	2082	static void
1321	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2083	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1322	{	2084	{
1323	... its now a full hour (UTC, or TAI or whatever your clock follows)	2085	... its now a full hour (UTC, or TAI or whatever your clock follows)
1324	}	2086	}
1325		2087
1326	struct ev_periodic hourly_tick;	2088	ev_periodic hourly_tick;
1327	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2089	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1328	ev_periodic_start (loop, &hourly_tick);	2090	ev_periodic_start (loop, &hourly_tick);
1329		2091
1330	Example: The same as above, but use a reschedule callback to do it:	2092	Example: The same as above, but use a reschedule callback to do it:
1331		2093
1332	#include <math.h>	2094	#include <math.h>
1333		2095
1334	static ev_tstamp	2096	static ev_tstamp
1335	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2097	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1336	{	2098	{
1337	return fmod (now, 3600.) + 3600.;	2099	return now + (3600. - fmod (now, 3600.));
1338	}	2100	}
1339		2101
1340	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2102	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1341		2103
1342	Example: Call a callback every hour, starting now:	2104	Example: Call a callback every hour, starting now:
1343		2105
1344	struct ev_periodic hourly_tick;	2106	ev_periodic hourly_tick;
1345	ev_periodic_init (&hourly_tick, clock_cb,	2107	ev_periodic_init (&hourly_tick, clock_cb,
1346	fmod (ev_now (loop), 3600.), 3600., 0);	2108	fmod (ev_now (loop), 3600.), 3600., 0);
1347	ev_periodic_start (loop, &hourly_tick);	2109	ev_periodic_start (loop, &hourly_tick);
1348		2110
1349		2111
1350	=head2 C<ev_signal> - signal me when a signal gets signalled!	2112	=head2 C<ev_signal> - signal me when a signal gets signalled!
1351		2113
1352	Signal watchers will trigger an event when the process receives a specific	2114	Signal watchers will trigger an event when the process receives a specific
1353	signal one or more times. Even though signals are very asynchronous, libev	2115	signal one or more times. Even though signals are very asynchronous, libev
1354	will try it's best to deliver signals synchronously, i.e. as part of the	2116	will try it's best to deliver signals synchronously, i.e. as part of the
1355	normal event processing, like any other event.	2117	normal event processing, like any other event.
1356		2118
		2119	If you want signals to be delivered truly asynchronously, just use
		2120	C<sigaction> as you would do without libev and forget about sharing
		2121	the signal. You can even use C<ev_async> from a signal handler to
		2122	synchronously wake up an event loop.
		2123
1357	You can configure as many watchers as you like per signal. Only when the	2124	You can configure as many watchers as you like for the same signal, but
		2125	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2126	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2127	C<SIGINT> in both the default loop and another loop at the same time. At
		2128	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2129
1358	first watcher gets started will libev actually register a signal watcher	2130	When the first watcher gets started will libev actually register something
1359	with the kernel (thus it coexists with your own signal handlers as long	2131	with the kernel (thus it coexists with your own signal handlers as long as
1360	as you don't register any with libev). Similarly, when the last signal	2132	you don't register any with libev for the same signal).
1361	watcher for a signal is stopped libev will reset the signal handler to	2133
1362	SIG_DFL (regardless of what it was set to before).	2134	If possible and supported, libev will install its handlers with
		2135	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2136	not be unduly interrupted. If you have a problem with system calls getting
		2137	interrupted by signals you can block all signals in an C<ev_check> watcher
		2138	and unblock them in an C<ev_prepare> watcher.
		2139
		2140	=head3 The special problem of inheritance over fork/execve/pthread_create
		2141
		2142	Both the signal mask (C<sigprocmask>) and the signal disposition
		2143	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2144	stopping it again), that is, libev might or might not block the signal,
		2145	and might or might not set or restore the installed signal handler.
		2146
		2147	While this does not matter for the signal disposition (libev never
		2148	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2149	C<execve>), this matters for the signal mask: many programs do not expect
		2150	certain signals to be blocked.
		2151
		2152	This means that before calling C<exec> (from the child) you should reset
		2153	the signal mask to whatever "default" you expect (all clear is a good
		2154	choice usually).
		2155
		2156	The simplest way to ensure that the signal mask is reset in the child is
		2157	to install a fork handler with C<pthread_atfork> that resets it. That will
		2158	catch fork calls done by libraries (such as the libc) as well.
		2159
		2160	In current versions of libev, the signal will not be blocked indefinitely
		2161	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2162	the window of opportunity for problems, it will not go away, as libev
		2163	I<has> to modify the signal mask, at least temporarily.
		2164
		2165	So I can't stress this enough I<if you do not reset your signal mask
		2166	when you expect it to be empty, you have a race condition in your
		2167	program>. This is not a libev-specific thing, this is true for most event
		2168	libraries.
1363		2169
1364	=head3 Watcher-Specific Functions and Data Members	2170	=head3 Watcher-Specific Functions and Data Members
1365		2171
1366	=over 4	2172	=over 4
1367		2173
…		…
1376		2182
1377	The signal the watcher watches out for.	2183	The signal the watcher watches out for.
1378		2184
1379	=back	2185	=back
1380		2186
		2187	=head3 Examples
		2188
		2189	Example: Try to exit cleanly on SIGINT.
		2190
		2191	static void
		2192	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2193	{
		2194	ev_unloop (loop, EVUNLOOP_ALL);
		2195	}
		2196
		2197	ev_signal signal_watcher;
		2198	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2199	ev_signal_start (loop, &signal_watcher);
		2200
1381		2201
1382	=head2 C<ev_child> - watch out for process status changes	2202	=head2 C<ev_child> - watch out for process status changes
1383		2203
1384	Child watchers trigger when your process receives a SIGCHLD in response to	2204	Child watchers trigger when your process receives a SIGCHLD in response to
1385	some child status changes (most typically when a child of yours dies).	2205	some child status changes (most typically when a child of yours dies or
		2206	exits). It is permissible to install a child watcher I<after> the child
		2207	has been forked (which implies it might have already exited), as long
		2208	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2209	forking and then immediately registering a watcher for the child is fine,
		2210	but forking and registering a watcher a few event loop iterations later or
		2211	in the next callback invocation is not.
		2212
		2213	Only the default event loop is capable of handling signals, and therefore
		2214	you can only register child watchers in the default event loop.
		2215
		2216	Due to some design glitches inside libev, child watchers will always be
		2217	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2218	libev)
		2219
		2220	=head3 Process Interaction
		2221
		2222	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2223	initialised. This is necessary to guarantee proper behaviour even if the
		2224	first child watcher is started after the child exits. The occurrence
		2225	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2226	synchronously as part of the event loop processing. Libev always reaps all
		2227	children, even ones not watched.
		2228
		2229	=head3 Overriding the Built-In Processing
		2230
		2231	Libev offers no special support for overriding the built-in child
		2232	processing, but if your application collides with libev's default child
		2233	handler, you can override it easily by installing your own handler for
		2234	C<SIGCHLD> after initialising the default loop, and making sure the
		2235	default loop never gets destroyed. You are encouraged, however, to use an
		2236	event-based approach to child reaping and thus use libev's support for
		2237	that, so other libev users can use C<ev_child> watchers freely.
		2238
		2239	=head3 Stopping the Child Watcher
		2240
		2241	Currently, the child watcher never gets stopped, even when the
		2242	child terminates, so normally one needs to stop the watcher in the
		2243	callback. Future versions of libev might stop the watcher automatically
		2244	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2245	problem).
1386		2246
1387	=head3 Watcher-Specific Functions and Data Members	2247	=head3 Watcher-Specific Functions and Data Members
1388		2248
1389	=over 4	2249	=over 4
1390		2250
1391	=item ev_child_init (ev_child *, callback, int pid)	2251	=item ev_child_init (ev_child *, callback, int pid, int trace)
1392		2252
1393	=item ev_child_set (ev_child *, int pid)	2253	=item ev_child_set (ev_child *, int pid, int trace)
1394		2254
1395	Configures the watcher to wait for status changes of process C<pid> (or	2255	Configures the watcher to wait for status changes of process C<pid> (or
1396	I<any> process if C<pid> is specified as C<0>). The callback can look	2256	I<any> process if C<pid> is specified as C<0>). The callback can look
1397	at the C<rstatus> member of the C<ev_child> watcher structure to see	2257	at the C<rstatus> member of the C<ev_child> watcher structure to see
1398	the status word (use the macros from C<sys/wait.h> and see your systems	2258	the status word (use the macros from C<sys/wait.h> and see your systems
1399	C<waitpid> documentation). The C<rpid> member contains the pid of the	2259	C<waitpid> documentation). The C<rpid> member contains the pid of the
1400	process causing the status change.	2260	process causing the status change. C<trace> must be either C<0> (only
		2261	activate the watcher when the process terminates) or C<1> (additionally
		2262	activate the watcher when the process is stopped or continued).
1401		2263
1402	=item int pid [read-only]	2264	=item int pid [read-only]
1403		2265
1404	The process id this watcher watches out for, or C<0>, meaning any process id.	2266	The process id this watcher watches out for, or C<0>, meaning any process id.
1405		2267
…		…
1412	The process exit/trace status caused by C<rpid> (see your systems	2274	The process exit/trace status caused by C<rpid> (see your systems
1413	C<waitpid> and C<sys/wait.h> documentation for details).	2275	C<waitpid> and C<sys/wait.h> documentation for details).
1414		2276
1415	=back	2277	=back
1416		2278
1417	Example: Try to exit cleanly on SIGINT and SIGTERM.	2279	=head3 Examples
1418		2280
		2281	Example: C<fork()> a new process and install a child handler to wait for
		2282	its completion.
		2283
		2284	ev_child cw;
		2285
1419	static void	2286	static void
1420	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2287	child_cb (EV_P_ ev_child *w, int revents)
1421	{	2288	{
1422	ev_unloop (loop, EVUNLOOP_ALL);	2289	ev_child_stop (EV_A_ w);
		2290	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1423	}	2291	}
1424		2292
1425	struct ev_signal signal_watcher;	2293	pid_t pid = fork ();
1426	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2294
1427	ev_signal_start (loop, &sigint_cb);	2295	if (pid < 0)
		2296	// error
		2297	else if (pid == 0)
		2298	{
		2299	// the forked child executes here
		2300	exit (1);
		2301	}
		2302	else
		2303	{
		2304	ev_child_init (&cw, child_cb, pid, 0);
		2305	ev_child_start (EV_DEFAULT_ &cw);
		2306	}
1428		2307
1429		2308
1430	=head2 C<ev_stat> - did the file attributes just change?	2309	=head2 C<ev_stat> - did the file attributes just change?
1431		2310
1432	This watches a filesystem path for attribute changes. That is, it calls	2311	This watches a file system path for attribute changes. That is, it calls
1433	C<stat> regularly (or when the OS says it changed) and sees if it changed	2312	C<stat> on that path in regular intervals (or when the OS says it changed)
1434	compared to the last time, invoking the callback if it did.	2313	and sees if it changed compared to the last time, invoking the callback if
		2314	it did.
1435		2315
1436	The path does not need to exist: changing from "path exists" to "path does	2316	The path does not need to exist: changing from "path exists" to "path does
1437	not exist" is a status change like any other. The condition "path does	2317	not exist" is a status change like any other. The condition "path does not
1438	not exist" is signified by the C<st_nlink> field being zero (which is	2318	exist" (or more correctly "path cannot be stat'ed") is signified by the
1439	otherwise always forced to be at least one) and all the other fields of	2319	C<st_nlink> field being zero (which is otherwise always forced to be at
1440	the stat buffer having unspecified contents.	2320	least one) and all the other fields of the stat buffer having unspecified
		2321	contents.
1441		2322
1442	The path I<should> be absolute and I<must not> end in a slash. If it is	2323	The path I<must not> end in a slash or contain special components such as
		2324	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1443	relative and your working directory changes, the behaviour is undefined.	2325	your working directory changes, then the behaviour is undefined.
1444		2326
1445	Since there is no standard to do this, the portable implementation simply	2327	Since there is no portable change notification interface available, the
1446	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2328	portable implementation simply calls C<stat(2)> regularly on the path
1447	can specify a recommended polling interval for this case. If you specify	2329	to see if it changed somehow. You can specify a recommended polling
1448	a polling interval of C<0> (highly recommended!) then a I<suitable,	2330	interval for this case. If you specify a polling interval of C<0> (highly
1449	unspecified default> value will be used (which you can expect to be around	2331	recommended!) then a I<suitable, unspecified default> value will be used
1450	five seconds, although this might change dynamically). Libev will also	2332	(which you can expect to be around five seconds, although this might
1451	impose a minimum interval which is currently around C<0.1>, but thats	2333	change dynamically). Libev will also impose a minimum interval which is
1452	usually overkill.	2334	currently around C<0.1>, but that's usually overkill.
1453		2335
1454	This watcher type is not meant for massive numbers of stat watchers,	2336	This watcher type is not meant for massive numbers of stat watchers,
1455	as even with OS-supported change notifications, this can be	2337	as even with OS-supported change notifications, this can be
1456	resource-intensive.	2338	resource-intensive.
1457		2339
1458	At the time of this writing, only the Linux inotify interface is	2340	At the time of this writing, the only OS-specific interface implemented
1459	implemented (implementing kqueue support is left as an exercise for the	2341	is the Linux inotify interface (implementing kqueue support is left as an
1460	reader). Inotify will be used to give hints only and should not change the	2342	exercise for the reader. Note, however, that the author sees no way of
1461	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2343	implementing C<ev_stat> semantics with kqueue, except as a hint).
1462	to fall back to regular polling again even with inotify, but changes are	2344
1463	usually detected immediately, and if the file exists there will be no	2345	=head3 ABI Issues (Largefile Support)
1464	polling.	2346
		2347	Libev by default (unless the user overrides this) uses the default
		2348	compilation environment, which means that on systems with large file
		2349	support disabled by default, you get the 32 bit version of the stat
		2350	structure. When using the library from programs that change the ABI to
		2351	use 64 bit file offsets the programs will fail. In that case you have to
		2352	compile libev with the same flags to get binary compatibility. This is
		2353	obviously the case with any flags that change the ABI, but the problem is
		2354	most noticeably displayed with ev_stat and large file support.
		2355
		2356	The solution for this is to lobby your distribution maker to make large
		2357	file interfaces available by default (as e.g. FreeBSD does) and not
		2358	optional. Libev cannot simply switch on large file support because it has
		2359	to exchange stat structures with application programs compiled using the
		2360	default compilation environment.
		2361
		2362	=head3 Inotify and Kqueue
		2363
		2364	When C<inotify (7)> support has been compiled into libev and present at
		2365	runtime, it will be used to speed up change detection where possible. The
		2366	inotify descriptor will be created lazily when the first C<ev_stat>
		2367	watcher is being started.
		2368
		2369	Inotify presence does not change the semantics of C<ev_stat> watchers
		2370	except that changes might be detected earlier, and in some cases, to avoid
		2371	making regular C<stat> calls. Even in the presence of inotify support
		2372	there are many cases where libev has to resort to regular C<stat> polling,
		2373	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2374	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2375	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2376	xfs are fully working) libev usually gets away without polling.
		2377
		2378	There is no support for kqueue, as apparently it cannot be used to
		2379	implement this functionality, due to the requirement of having a file
		2380	descriptor open on the object at all times, and detecting renames, unlinks
		2381	etc. is difficult.
		2382
		2383	=head3 C<stat ()> is a synchronous operation
		2384
		2385	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2386	the process. The exception are C<ev_stat> watchers - those call C<stat
		2387	()>, which is a synchronous operation.
		2388
		2389	For local paths, this usually doesn't matter: unless the system is very
		2390	busy or the intervals between stat's are large, a stat call will be fast,
		2391	as the path data is usually in memory already (except when starting the
		2392	watcher).
		2393
		2394	For networked file systems, calling C<stat ()> can block an indefinite
		2395	time due to network issues, and even under good conditions, a stat call
		2396	often takes multiple milliseconds.
		2397
		2398	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2399	paths, although this is fully supported by libev.
		2400
		2401	=head3 The special problem of stat time resolution
		2402
		2403	The C<stat ()> system call only supports full-second resolution portably,
		2404	and even on systems where the resolution is higher, most file systems
		2405	still only support whole seconds.
		2406
		2407	That means that, if the time is the only thing that changes, you can
		2408	easily miss updates: on the first update, C<ev_stat> detects a change and
		2409	calls your callback, which does something. When there is another update
		2410	within the same second, C<ev_stat> will be unable to detect unless the
		2411	stat data does change in other ways (e.g. file size).
		2412
		2413	The solution to this is to delay acting on a change for slightly more
		2414	than a second (or till slightly after the next full second boundary), using
		2415	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2416	ev_timer_again (loop, w)>).
		2417
		2418	The C<.02> offset is added to work around small timing inconsistencies
		2419	of some operating systems (where the second counter of the current time
		2420	might be be delayed. One such system is the Linux kernel, where a call to
		2421	C<gettimeofday> might return a timestamp with a full second later than
		2422	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2423	update file times then there will be a small window where the kernel uses
		2424	the previous second to update file times but libev might already execute
		2425	the timer callback).
1465		2426
1466	=head3 Watcher-Specific Functions and Data Members	2427	=head3 Watcher-Specific Functions and Data Members
1467		2428
1468	=over 4	2429	=over 4
1469		2430
…		…
1475	C<path>. The C<interval> is a hint on how quickly a change is expected to	2436	C<path>. The C<interval> is a hint on how quickly a change is expected to
1476	be detected and should normally be specified as C<0> to let libev choose	2437	be detected and should normally be specified as C<0> to let libev choose
1477	a suitable value. The memory pointed to by C<path> must point to the same	2438	a suitable value. The memory pointed to by C<path> must point to the same
1478	path for as long as the watcher is active.	2439	path for as long as the watcher is active.
1479		2440
1480	The callback will be receive C<EV_STAT> when a change was detected,	2441	The callback will receive an C<EV_STAT> event when a change was detected,
1481	relative to the attributes at the time the watcher was started (or the	2442	relative to the attributes at the time the watcher was started (or the
1482	last change was detected).	2443	last change was detected).
1483		2444
1484	=item ev_stat_stat (ev_stat *)	2445	=item ev_stat_stat (loop, ev_stat *)
1485		2446
1486	Updates the stat buffer immediately with new values. If you change the	2447	Updates the stat buffer immediately with new values. If you change the
1487	watched path in your callback, you could call this fucntion to avoid	2448	watched path in your callback, you could call this function to avoid
1488	detecting this change (while introducing a race condition). Can also be	2449	detecting this change (while introducing a race condition if you are not
1489	useful simply to find out the new values.	2450	the only one changing the path). Can also be useful simply to find out the
		2451	new values.
1490		2452
1491	=item ev_statdata attr [read-only]	2453	=item ev_statdata attr [read-only]
1492		2454
1493	The most-recently detected attributes of the file. Although the type is of	2455	The most-recently detected attributes of the file. Although the type is
1494	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2456	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1495	suitable for your system. If the C<st_nlink> member is C<0>, then there	2457	suitable for your system, but you can only rely on the POSIX-standardised
		2458	members to be present. If the C<st_nlink> member is C<0>, then there was
1496	was some error while C<stat>ing the file.	2459	some error while C<stat>ing the file.
1497		2460
1498	=item ev_statdata prev [read-only]	2461	=item ev_statdata prev [read-only]
1499		2462
1500	The previous attributes of the file. The callback gets invoked whenever	2463	The previous attributes of the file. The callback gets invoked whenever
1501	C<prev> != C<attr>.	2464	C<prev> != C<attr>, or, more precisely, one or more of these members
		2465	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2466	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1502		2467
1503	=item ev_tstamp interval [read-only]	2468	=item ev_tstamp interval [read-only]
1504		2469
1505	The specified interval.	2470	The specified interval.
1506		2471
1507	=item const char *path [read-only]	2472	=item const char *path [read-only]
1508		2473
1509	The filesystem path that is being watched.	2474	The file system path that is being watched.
1510		2475
1511	=back	2476	=back
1512		2477
		2478	=head3 Examples
		2479
1513	Example: Watch C</etc/passwd> for attribute changes.	2480	Example: Watch C</etc/passwd> for attribute changes.
1514		2481
1515	static void	2482	static void
1516	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2483	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1517	{	2484	{
1518	/* /etc/passwd changed in some way */	2485	/* /etc/passwd changed in some way */
1519	if (w->attr.st_nlink)	2486	if (w->attr.st_nlink)
1520	{	2487	{
1521	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2488	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1522	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2489	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1523	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2490	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1524	}	2491	}
1525	else	2492	else
1526	/* you shalt not abuse printf for puts */	2493	/* you shalt not abuse printf for puts */
1527	puts ("wow, /etc/passwd is not there, expect problems. "	2494	puts ("wow, /etc/passwd is not there, expect problems. "
1528	"if this is windows, they already arrived\n");	2495	"if this is windows, they already arrived\n");
1529	}	2496	}
1530		2497
1531	...	2498	...
1532	ev_stat passwd;	2499	ev_stat passwd;
1533		2500
1534	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2501	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1535	ev_stat_start (loop, &passwd);	2502	ev_stat_start (loop, &passwd);
		2503
		2504	Example: Like above, but additionally use a one-second delay so we do not
		2505	miss updates (however, frequent updates will delay processing, too, so
		2506	one might do the work both on C<ev_stat> callback invocation I<and> on
		2507	C<ev_timer> callback invocation).
		2508
		2509	static ev_stat passwd;
		2510	static ev_timer timer;
		2511
		2512	static void
		2513	timer_cb (EV_P_ ev_timer *w, int revents)
		2514	{
		2515	ev_timer_stop (EV_A_ w);
		2516
		2517	/* now it's one second after the most recent passwd change */
		2518	}
		2519
		2520	static void
		2521	stat_cb (EV_P_ ev_stat *w, int revents)
		2522	{
		2523	/* reset the one-second timer */
		2524	ev_timer_again (EV_A_ &timer);
		2525	}
		2526
		2527	...
		2528	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2529	ev_stat_start (loop, &passwd);
		2530	ev_timer_init (&timer, timer_cb, 0., 1.02);
1536		2531
1537		2532
1538	=head2 C<ev_idle> - when you've got nothing better to do...	2533	=head2 C<ev_idle> - when you've got nothing better to do...
1539		2534
1540	Idle watchers trigger events when no other events of the same or higher	2535	Idle watchers trigger events when no other events of the same or higher
1541	priority are pending (prepare, check and other idle watchers do not	2536	priority are pending (prepare, check and other idle watchers do not count
1542	count).	2537	as receiving "events").
1543		2538
1544	That is, as long as your process is busy handling sockets or timeouts	2539	That is, as long as your process is busy handling sockets or timeouts
1545	(or even signals, imagine) of the same or higher priority it will not be	2540	(or even signals, imagine) of the same or higher priority it will not be
1546	triggered. But when your process is idle (or only lower-priority watchers	2541	triggered. But when your process is idle (or only lower-priority watchers
1547	are pending), the idle watchers are being called once per event loop	2542	are pending), the idle watchers are being called once per event loop
…		…
1558		2553
1559	=head3 Watcher-Specific Functions and Data Members	2554	=head3 Watcher-Specific Functions and Data Members
1560		2555
1561	=over 4	2556	=over 4
1562		2557
1563	=item ev_idle_init (ev_signal *, callback)	2558	=item ev_idle_init (ev_idle *, callback)
1564		2559
1565	Initialises and configures the idle watcher - it has no parameters of any	2560	Initialises and configures the idle watcher - it has no parameters of any
1566	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2561	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1567	believe me.	2562	believe me.
1568		2563
1569	=back	2564	=back
1570		2565
		2566	=head3 Examples
		2567
1571	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2568	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1572	callback, free it. Also, use no error checking, as usual.	2569	callback, free it. Also, use no error checking, as usual.
1573		2570
1574	static void	2571	static void
1575	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2572	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1576	{	2573	{
1577	free (w);	2574	free (w);
1578	// now do something you wanted to do when the program has	2575	// now do something you wanted to do when the program has
1579	// no longer asnything immediate to do.	2576	// no longer anything immediate to do.
1580	}	2577	}
1581		2578
1582	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2579	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1583	ev_idle_init (idle_watcher, idle_cb);	2580	ev_idle_init (idle_watcher, idle_cb);
1584	ev_idle_start (loop, idle_cb);	2581	ev_idle_start (loop, idle_watcher);
1585		2582
1586		2583
1587	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2584	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1588		2585
1589	Prepare and check watchers are usually (but not always) used in tandem:	2586	Prepare and check watchers are usually (but not always) used in pairs:
1590	prepare watchers get invoked before the process blocks and check watchers	2587	prepare watchers get invoked before the process blocks and check watchers
1591	afterwards.	2588	afterwards.
1592		2589
1593	You I<must not> call C<ev_loop> or similar functions that enter	2590	You I<must not> call C<ev_loop> or similar functions that enter
1594	the current event loop from either C<ev_prepare> or C<ev_check>	2591	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1597	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2594	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1598	C<ev_check> so if you have one watcher of each kind they will always be	2595	C<ev_check> so if you have one watcher of each kind they will always be
1599	called in pairs bracketing the blocking call.	2596	called in pairs bracketing the blocking call.
1600		2597
1601	Their main purpose is to integrate other event mechanisms into libev and	2598	Their main purpose is to integrate other event mechanisms into libev and
1602	their use is somewhat advanced. This could be used, for example, to track	2599	their use is somewhat advanced. They could be used, for example, to track
1603	variable changes, implement your own watchers, integrate net-snmp or a	2600	variable changes, implement your own watchers, integrate net-snmp or a
1604	coroutine library and lots more. They are also occasionally useful if	2601	coroutine library and lots more. They are also occasionally useful if
1605	you cache some data and want to flush it before blocking (for example,	2602	you cache some data and want to flush it before blocking (for example,
1606	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2603	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1607	watcher).	2604	watcher).
1608		2605
1609	This is done by examining in each prepare call which file descriptors need	2606	This is done by examining in each prepare call which file descriptors
1610	to be watched by the other library, registering C<ev_io> watchers for	2607	need to be watched by the other library, registering C<ev_io> watchers
1611	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2608	for them and starting an C<ev_timer> watcher for any timeouts (many
1612	provide just this functionality). Then, in the check watcher you check for	2609	libraries provide exactly this functionality). Then, in the check watcher,
1613	any events that occured (by checking the pending status of all watchers	2610	you check for any events that occurred (by checking the pending status
1614	and stopping them) and call back into the library. The I/O and timer	2611	of all watchers and stopping them) and call back into the library. The
1615	callbacks will never actually be called (but must be valid nevertheless,	2612	I/O and timer callbacks will never actually be called (but must be valid
1616	because you never know, you know?).	2613	nevertheless, because you never know, you know?).
1617		2614
1618	As another example, the Perl Coro module uses these hooks to integrate	2615	As another example, the Perl Coro module uses these hooks to integrate
1619	coroutines into libev programs, by yielding to other active coroutines	2616	coroutines into libev programs, by yielding to other active coroutines
1620	during each prepare and only letting the process block if no coroutines	2617	during each prepare and only letting the process block if no coroutines
1621	are ready to run (it's actually more complicated: it only runs coroutines	2618	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1624	loop from blocking if lower-priority coroutines are active, thus mapping	2621	loop from blocking if lower-priority coroutines are active, thus mapping
1625	low-priority coroutines to idle/background tasks).	2622	low-priority coroutines to idle/background tasks).
1626		2623
1627	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2624	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1628	priority, to ensure that they are being run before any other watchers	2625	priority, to ensure that they are being run before any other watchers
		2626	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2627
1629	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2628	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1630	too) should not activate ("feed") events into libev. While libev fully	2629	activate ("feed") events into libev. While libev fully supports this, they
1631	supports this, they will be called before other C<ev_check> watchers	2630	might get executed before other C<ev_check> watchers did their job. As
1632	did their job. As C<ev_check> watchers are often used to embed other	2631	C<ev_check> watchers are often used to embed other (non-libev) event
1633	(non-libev) event loops those other event loops might be in an unusable	2632	loops those other event loops might be in an unusable state until their
1634	state until their C<ev_check> watcher ran (always remind yourself to	2633	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1635	coexist peacefully with others).	2634	others).
1636		2635
1637	=head3 Watcher-Specific Functions and Data Members	2636	=head3 Watcher-Specific Functions and Data Members
1638		2637
1639	=over 4	2638	=over 4
1640		2639
…		…
1642		2641
1643	=item ev_check_init (ev_check *, callback)	2642	=item ev_check_init (ev_check *, callback)
1644		2643
1645	Initialises and configures the prepare or check watcher - they have no	2644	Initialises and configures the prepare or check watcher - they have no
1646	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2645	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1647	macros, but using them is utterly, utterly and completely pointless.	2646	macros, but using them is utterly, utterly, utterly and completely
		2647	pointless.
1648		2648
1649	=back	2649	=back
		2650
		2651	=head3 Examples
1650		2652
1651	There are a number of principal ways to embed other event loops or modules	2653	There are a number of principal ways to embed other event loops or modules
1652	into libev. Here are some ideas on how to include libadns into libev	2654	into libev. Here are some ideas on how to include libadns into libev
1653	(there is a Perl module named C<EV::ADNS> that does this, which you could	2655	(there is a Perl module named C<EV::ADNS> that does this, which you could
1654	use for an actually working example. Another Perl module named C<EV::Glib>	2656	use as a working example. Another Perl module named C<EV::Glib> embeds a
1655	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2657	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1656	into the Glib event loop).	2658	Glib event loop).
1657		2659
1658	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2660	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1659	and in a check watcher, destroy them and call into libadns. What follows	2661	and in a check watcher, destroy them and call into libadns. What follows
1660	is pseudo-code only of course. This requires you to either use a low	2662	is pseudo-code only of course. This requires you to either use a low
1661	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2663	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1662	the callbacks for the IO/timeout watchers might not have been called yet.	2664	the callbacks for the IO/timeout watchers might not have been called yet.
1663		2665
1664	static ev_io iow [nfd];	2666	static ev_io iow [nfd];
1665	static ev_timer tw;	2667	static ev_timer tw;
1666		2668
1667	static void	2669	static void
1668	io_cb (ev_loop *loop, ev_io *w, int revents)	2670	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1669	{	2671	{
1670	}	2672	}
1671		2673
1672	// create io watchers for each fd and a timer before blocking	2674	// create io watchers for each fd and a timer before blocking
1673	static void	2675	static void
1674	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2676	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1675	{	2677	{
1676	int timeout = 3600000;	2678	int timeout = 3600000;
1677	struct pollfd fds [nfd];	2679	struct pollfd fds [nfd];
1678	// actual code will need to loop here and realloc etc.	2680	// actual code will need to loop here and realloc etc.
1679	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2681	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1680		2682
1681	/* the callback is illegal, but won't be called as we stop during check */	2683	/* the callback is illegal, but won't be called as we stop during check */
1682	ev_timer_init (&tw, 0, timeout * 1e-3);	2684	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1683	ev_timer_start (loop, &tw);	2685	ev_timer_start (loop, &tw);
1684		2686
1685	// create one ev_io per pollfd	2687	// create one ev_io per pollfd
1686	for (int i = 0; i < nfd; ++i)	2688	for (int i = 0; i < nfd; ++i)
1687	{	2689	{
1688	ev_io_init (iow + i, io_cb, fds [i].fd,	2690	ev_io_init (iow + i, io_cb, fds [i].fd,
1689	((fds [i].events & POLLIN ? EV_READ : 0)	2691	((fds [i].events & POLLIN ? EV_READ : 0)
1690	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2692	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1691		2693
1692	fds [i].revents = 0;	2694	fds [i].revents = 0;
1693	ev_io_start (loop, iow + i);	2695	ev_io_start (loop, iow + i);
1694	}	2696	}
1695	}	2697	}
1696		2698
1697	// stop all watchers after blocking	2699	// stop all watchers after blocking
1698	static void	2700	static void
1699	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2701	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1700	{	2702	{
1701	ev_timer_stop (loop, &tw);	2703	ev_timer_stop (loop, &tw);
1702		2704
1703	for (int i = 0; i < nfd; ++i)	2705	for (int i = 0; i < nfd; ++i)
1704	{	2706	{
1705	// set the relevant poll flags	2707	// set the relevant poll flags
1706	// could also call adns_processreadable etc. here	2708	// could also call adns_processreadable etc. here
1707	struct pollfd *fd = fds + i;	2709	struct pollfd *fd = fds + i;
1708	int revents = ev_clear_pending (iow + i);	2710	int revents = ev_clear_pending (iow + i);
1709	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2711	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1710	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2712	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1711		2713
1712	// now stop the watcher	2714	// now stop the watcher
1713	ev_io_stop (loop, iow + i);	2715	ev_io_stop (loop, iow + i);
1714	}	2716	}
1715		2717
1716	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2718	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1717	}	2719	}
1718		2720
1719	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2721	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1720	in the prepare watcher and would dispose of the check watcher.	2722	in the prepare watcher and would dispose of the check watcher.
1721		2723
1722	Method 3: If the module to be embedded supports explicit event	2724	Method 3: If the module to be embedded supports explicit event
1723	notification (adns does), you can also make use of the actual watcher	2725	notification (libadns does), you can also make use of the actual watcher
1724	callbacks, and only destroy/create the watchers in the prepare watcher.	2726	callbacks, and only destroy/create the watchers in the prepare watcher.
1725		2727
1726	static void	2728	static void
1727	timer_cb (EV_P_ ev_timer *w, int revents)	2729	timer_cb (EV_P_ ev_timer *w, int revents)
1728	{	2730	{
1729	adns_state ads = (adns_state)w->data;	2731	adns_state ads = (adns_state)w->data;
1730	update_now (EV_A);	2732	update_now (EV_A);
1731		2733
1732	adns_processtimeouts (ads, &tv_now);	2734	adns_processtimeouts (ads, &tv_now);
1733	}	2735	}
1734		2736
1735	static void	2737	static void
1736	io_cb (EV_P_ ev_io *w, int revents)	2738	io_cb (EV_P_ ev_io *w, int revents)
1737	{	2739	{
1738	adns_state ads = (adns_state)w->data;	2740	adns_state ads = (adns_state)w->data;
1739	update_now (EV_A);	2741	update_now (EV_A);
1740		2742
1741	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2743	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1742	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2744	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1743	}	2745	}
1744		2746
1745	// do not ever call adns_afterpoll	2747	// do not ever call adns_afterpoll
1746		2748
1747	Method 4: Do not use a prepare or check watcher because the module you	2749	Method 4: Do not use a prepare or check watcher because the module you
1748	want to embed is too inflexible to support it. Instead, youc na override	2750	want to embed is not flexible enough to support it. Instead, you can
1749	their poll function. The drawback with this solution is that the main	2751	override their poll function. The drawback with this solution is that the
1750	loop is now no longer controllable by EV. The C<Glib::EV> module does	2752	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1751	this.	2753	this approach, effectively embedding EV as a client into the horrible
		2754	libglib event loop.
1752		2755
1753	static gint	2756	static gint
1754	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2757	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1755	{	2758	{
1756	int got_events = 0;	2759	int got_events = 0;
1757		2760
1758	for (n = 0; n < nfds; ++n)	2761	for (n = 0; n < nfds; ++n)
1759	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2762	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1760		2763
1761	if (timeout >= 0)	2764	if (timeout >= 0)
1762	// create/start timer	2765	// create/start timer
1763		2766
1764	// poll	2767	// poll
1765	ev_loop (EV_A_ 0);	2768	ev_loop (EV_A_ 0);
1766		2769
1767	// stop timer again	2770	// stop timer again
1768	if (timeout >= 0)	2771	if (timeout >= 0)
1769	ev_timer_stop (EV_A_ &to);	2772	ev_timer_stop (EV_A_ &to);
1770		2773
1771	// stop io watchers again - their callbacks should have set	2774	// stop io watchers again - their callbacks should have set
1772	for (n = 0; n < nfds; ++n)	2775	for (n = 0; n < nfds; ++n)
1773	ev_io_stop (EV_A_ iow [n]);	2776	ev_io_stop (EV_A_ iow [n]);
1774		2777
1775	return got_events;	2778	return got_events;
1776	}	2779	}
1777		2780
1778		2781
1779	=head2 C<ev_embed> - when one backend isn't enough...	2782	=head2 C<ev_embed> - when one backend isn't enough...
1780		2783
1781	This is a rather advanced watcher type that lets you embed one event loop	2784	This is a rather advanced watcher type that lets you embed one event loop
…		…
1787	prioritise I/O.	2790	prioritise I/O.
1788		2791
1789	As an example for a bug workaround, the kqueue backend might only support	2792	As an example for a bug workaround, the kqueue backend might only support
1790	sockets on some platform, so it is unusable as generic backend, but you	2793	sockets on some platform, so it is unusable as generic backend, but you
1791	still want to make use of it because you have many sockets and it scales	2794	still want to make use of it because you have many sockets and it scales
1792	so nicely. In this case, you would create a kqueue-based loop and embed it	2795	so nicely. In this case, you would create a kqueue-based loop and embed
1793	into your default loop (which might use e.g. poll). Overall operation will	2796	it into your default loop (which might use e.g. poll). Overall operation
1794	be a bit slower because first libev has to poll and then call kevent, but	2797	will be a bit slower because first libev has to call C<poll> and then
1795	at least you can use both at what they are best.	2798	C<kevent>, but at least you can use both mechanisms for what they are
		2799	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1796		2800
1797	As for prioritising I/O: rarely you have the case where some fds have	2801	As for prioritising I/O: under rare circumstances you have the case where
1798	to be watched and handled very quickly (with low latency), and even	2802	some fds have to be watched and handled very quickly (with low latency),
1799	priorities and idle watchers might have too much overhead. In this case	2803	and even priorities and idle watchers might have too much overhead. In
1800	you would put all the high priority stuff in one loop and all the rest in	2804	this case you would put all the high priority stuff in one loop and all
1801	a second one, and embed the second one in the first.	2805	the rest in a second one, and embed the second one in the first.
1802		2806
1803	As long as the watcher is active, the callback will be invoked every time	2807	As long as the watcher is active, the callback will be invoked every
1804	there might be events pending in the embedded loop. The callback must then	2808	time there might be events pending in the embedded loop. The callback
1805	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2809	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1806	their callbacks (you could also start an idle watcher to give the embedded	2810	sweep and invoke their callbacks (the callback doesn't need to invoke the
1807	loop strictly lower priority for example). You can also set the callback	2811	C<ev_embed_sweep> function directly, it could also start an idle watcher
1808	to C<0>, in which case the embed watcher will automatically execute the	2812	to give the embedded loop strictly lower priority for example).
1809	embedded loop sweep.
1810		2813
1811	As long as the watcher is started it will automatically handle events. The	2814	You can also set the callback to C<0>, in which case the embed watcher
1812	callback will be invoked whenever some events have been handled. You can	2815	will automatically execute the embedded loop sweep whenever necessary.
1813	set the callback to C<0> to avoid having to specify one if you are not
1814	interested in that.
1815		2816
1816	Also, there have not currently been made special provisions for forking:	2817	Fork detection will be handled transparently while the C<ev_embed> watcher
1817	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2818	is active, i.e., the embedded loop will automatically be forked when the
1818	but you will also have to stop and restart any C<ev_embed> watchers	2819	embedding loop forks. In other cases, the user is responsible for calling
1819	yourself.	2820	C<ev_loop_fork> on the embedded loop.
1820		2821
1821	Unfortunately, not all backends are embeddable, only the ones returned by	2822	Unfortunately, not all backends are embeddable: only the ones returned by
1822	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2823	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1823	portable one.	2824	portable one.
1824		2825
1825	So when you want to use this feature you will always have to be prepared	2826	So when you want to use this feature you will always have to be prepared
1826	that you cannot get an embeddable loop. The recommended way to get around	2827	that you cannot get an embeddable loop. The recommended way to get around
1827	this is to have a separate variables for your embeddable loop, try to	2828	this is to have a separate variables for your embeddable loop, try to
1828	create it, and if that fails, use the normal loop for everything:	2829	create it, and if that fails, use the normal loop for everything.
1829		2830
1830	struct ev_loop *loop_hi = ev_default_init (0);	2831	=head3 C<ev_embed> and fork
1831	struct ev_loop *loop_lo = 0;
1832	struct ev_embed embed;
1833
1834	// see if there is a chance of getting one that works
1835	// (remember that a flags value of 0 means autodetection)
1836	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1837	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1838	: 0;
1839		2832
1840	// if we got one, then embed it, otherwise default to loop_hi	2833	While the C<ev_embed> watcher is running, forks in the embedding loop will
1841	if (loop_lo)	2834	automatically be applied to the embedded loop as well, so no special
1842	{	2835	fork handling is required in that case. When the watcher is not running,
1843	ev_embed_init (&embed, 0, loop_lo);	2836	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1844	ev_embed_start (loop_hi, &embed);	2837	as applicable.
1845	}
1846	else
1847	loop_lo = loop_hi;
1848		2838
1849	=head3 Watcher-Specific Functions and Data Members	2839	=head3 Watcher-Specific Functions and Data Members
1850		2840
1851	=over 4	2841	=over 4
1852		2842
…		…
1856		2846
1857	Configures the watcher to embed the given loop, which must be	2847	Configures the watcher to embed the given loop, which must be
1858	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2848	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1859	invoked automatically, otherwise it is the responsibility of the callback	2849	invoked automatically, otherwise it is the responsibility of the callback
1860	to invoke it (it will continue to be called until the sweep has been done,	2850	to invoke it (it will continue to be called until the sweep has been done,
1861	if you do not want thta, you need to temporarily stop the embed watcher).	2851	if you do not want that, you need to temporarily stop the embed watcher).
1862		2852
1863	=item ev_embed_sweep (loop, ev_embed *)	2853	=item ev_embed_sweep (loop, ev_embed *)
1864		2854
1865	Make a single, non-blocking sweep over the embedded loop. This works	2855	Make a single, non-blocking sweep over the embedded loop. This works
1866	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2856	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1867	apropriate way for embedded loops.	2857	appropriate way for embedded loops.
1868		2858
1869	=item struct ev_loop *other [read-only]	2859	=item struct ev_loop *other [read-only]
1870		2860
1871	The embedded event loop.	2861	The embedded event loop.
1872		2862
1873	=back	2863	=back
		2864
		2865	=head3 Examples
		2866
		2867	Example: Try to get an embeddable event loop and embed it into the default
		2868	event loop. If that is not possible, use the default loop. The default
		2869	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2870	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2871	used).
		2872
		2873	struct ev_loop *loop_hi = ev_default_init (0);
		2874	struct ev_loop *loop_lo = 0;
		2875	ev_embed embed;
		2876
		2877	// see if there is a chance of getting one that works
		2878	// (remember that a flags value of 0 means autodetection)
		2879	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2880	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2881	: 0;
		2882
		2883	// if we got one, then embed it, otherwise default to loop_hi
		2884	if (loop_lo)
		2885	{
		2886	ev_embed_init (&embed, 0, loop_lo);
		2887	ev_embed_start (loop_hi, &embed);
		2888	}
		2889	else
		2890	loop_lo = loop_hi;
		2891
		2892	Example: Check if kqueue is available but not recommended and create
		2893	a kqueue backend for use with sockets (which usually work with any
		2894	kqueue implementation). Store the kqueue/socket-only event loop in
		2895	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2896
		2897	struct ev_loop *loop = ev_default_init (0);
		2898	struct ev_loop *loop_socket = 0;
		2899	ev_embed embed;
		2900
		2901	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2902	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2903	{
		2904	ev_embed_init (&embed, 0, loop_socket);
		2905	ev_embed_start (loop, &embed);
		2906	}
		2907
		2908	if (!loop_socket)
		2909	loop_socket = loop;
		2910
		2911	// now use loop_socket for all sockets, and loop for everything else
1874		2912
1875		2913
1876	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2914	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1877		2915
1878	Fork watchers are called when a C<fork ()> was detected (usually because	2916	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1881	event loop blocks next and before C<ev_check> watchers are being called,	2919	event loop blocks next and before C<ev_check> watchers are being called,
1882	and only in the child after the fork. If whoever good citizen calling	2920	and only in the child after the fork. If whoever good citizen calling
1883	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2921	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1884	handlers will be invoked, too, of course.	2922	handlers will be invoked, too, of course.
1885		2923
		2924	=head3 The special problem of life after fork - how is it possible?
		2925
		2926	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2927	up/change the process environment, followed by a call to C<exec()>. This
		2928	sequence should be handled by libev without any problems.
		2929
		2930	This changes when the application actually wants to do event handling
		2931	in the child, or both parent in child, in effect "continuing" after the
		2932	fork.
		2933
		2934	The default mode of operation (for libev, with application help to detect
		2935	forks) is to duplicate all the state in the child, as would be expected
		2936	when I<either> the parent I<or> the child process continues.
		2937
		2938	When both processes want to continue using libev, then this is usually the
		2939	wrong result. In that case, usually one process (typically the parent) is
		2940	supposed to continue with all watchers in place as before, while the other
		2941	process typically wants to start fresh, i.e. without any active watchers.
		2942
		2943	The cleanest and most efficient way to achieve that with libev is to
		2944	simply create a new event loop, which of course will be "empty", and
		2945	use that for new watchers. This has the advantage of not touching more
		2946	memory than necessary, and thus avoiding the copy-on-write, and the
		2947	disadvantage of having to use multiple event loops (which do not support
		2948	signal watchers).
		2949
		2950	When this is not possible, or you want to use the default loop for
		2951	other reasons, then in the process that wants to start "fresh", call
		2952	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2953	the default loop will "orphan" (not stop) all registered watchers, so you
		2954	have to be careful not to execute code that modifies those watchers. Note
		2955	also that in that case, you have to re-register any signal watchers.
		2956
1886	=head3 Watcher-Specific Functions and Data Members	2957	=head3 Watcher-Specific Functions and Data Members
1887		2958
1888	=over 4	2959	=over 4
1889		2960
1890	=item ev_fork_init (ev_signal *, callback)	2961	=item ev_fork_init (ev_signal *, callback)
…		…
1894	believe me.	2965	believe me.
1895		2966
1896	=back	2967	=back
1897		2968
1898		2969
		2970	=head2 C<ev_async> - how to wake up another event loop
		2971
		2972	In general, you cannot use an C<ev_loop> from multiple threads or other
		2973	asynchronous sources such as signal handlers (as opposed to multiple event
		2974	loops - those are of course safe to use in different threads).
		2975
		2976	Sometimes, however, you need to wake up another event loop you do not
		2977	control, for example because it belongs to another thread. This is what
		2978	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2979	can signal it by calling C<ev_async_send>, which is thread- and signal
		2980	safe.
		2981
		2982	This functionality is very similar to C<ev_signal> watchers, as signals,
		2983	too, are asynchronous in nature, and signals, too, will be compressed
		2984	(i.e. the number of callback invocations may be less than the number of
		2985	C<ev_async_sent> calls).
		2986
		2987	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2988	just the default loop.
		2989
		2990	=head3 Queueing
		2991
		2992	C<ev_async> does not support queueing of data in any way. The reason
		2993	is that the author does not know of a simple (or any) algorithm for a
		2994	multiple-writer-single-reader queue that works in all cases and doesn't
		2995	need elaborate support such as pthreads or unportable memory access
		2996	semantics.
		2997
		2998	That means that if you want to queue data, you have to provide your own
		2999	queue. But at least I can tell you how to implement locking around your
		3000	queue:
		3001
		3002	=over 4
		3003
		3004	=item queueing from a signal handler context
		3005
		3006	To implement race-free queueing, you simply add to the queue in the signal
		3007	handler but you block the signal handler in the watcher callback. Here is
		3008	an example that does that for some fictitious SIGUSR1 handler:
		3009
		3010	static ev_async mysig;
		3011
		3012	static void
		3013	sigusr1_handler (void)
		3014	{
		3015	sometype data;
		3016
		3017	// no locking etc.
		3018	queue_put (data);
		3019	ev_async_send (EV_DEFAULT_ &mysig);
		3020	}
		3021
		3022	static void
		3023	mysig_cb (EV_P_ ev_async *w, int revents)
		3024	{
		3025	sometype data;
		3026	sigset_t block, prev;
		3027
		3028	sigemptyset (&block);
		3029	sigaddset (&block, SIGUSR1);
		3030	sigprocmask (SIG_BLOCK, &block, &prev);
		3031
		3032	while (queue_get (&data))
		3033	process (data);
		3034
		3035	if (sigismember (&prev, SIGUSR1)
		3036	sigprocmask (SIG_UNBLOCK, &block, 0);
		3037	}
		3038
		3039	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3040	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3041	either...).
		3042
		3043	=item queueing from a thread context
		3044
		3045	The strategy for threads is different, as you cannot (easily) block
		3046	threads but you can easily preempt them, so to queue safely you need to
		3047	employ a traditional mutex lock, such as in this pthread example:
		3048
		3049	static ev_async mysig;
		3050	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3051
		3052	static void
		3053	otherthread (void)
		3054	{
		3055	// only need to lock the actual queueing operation
		3056	pthread_mutex_lock (&mymutex);
		3057	queue_put (data);
		3058	pthread_mutex_unlock (&mymutex);
		3059
		3060	ev_async_send (EV_DEFAULT_ &mysig);
		3061	}
		3062
		3063	static void
		3064	mysig_cb (EV_P_ ev_async *w, int revents)
		3065	{
		3066	pthread_mutex_lock (&mymutex);
		3067
		3068	while (queue_get (&data))
		3069	process (data);
		3070
		3071	pthread_mutex_unlock (&mymutex);
		3072	}
		3073
		3074	=back
		3075
		3076
		3077	=head3 Watcher-Specific Functions and Data Members
		3078
		3079	=over 4
		3080
		3081	=item ev_async_init (ev_async *, callback)
		3082
		3083	Initialises and configures the async watcher - it has no parameters of any
		3084	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3085	trust me.
		3086
		3087	=item ev_async_send (loop, ev_async *)
		3088
		3089	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3090	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3091	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3092	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3093	section below on what exactly this means).
		3094
		3095	Note that, as with other watchers in libev, multiple events might get
		3096	compressed into a single callback invocation (another way to look at this
		3097	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3098	reset when the event loop detects that).
		3099
		3100	This call incurs the overhead of a system call only once per event loop
		3101	iteration, so while the overhead might be noticeable, it doesn't apply to
		3102	repeated calls to C<ev_async_send> for the same event loop.
		3103
		3104	=item bool = ev_async_pending (ev_async *)
		3105
		3106	Returns a non-zero value when C<ev_async_send> has been called on the
		3107	watcher but the event has not yet been processed (or even noted) by the
		3108	event loop.
		3109
		3110	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3111	the loop iterates next and checks for the watcher to have become active,
		3112	it will reset the flag again. C<ev_async_pending> can be used to very
		3113	quickly check whether invoking the loop might be a good idea.
		3114
		3115	Not that this does I<not> check whether the watcher itself is pending,
		3116	only whether it has been requested to make this watcher pending: there
		3117	is a time window between the event loop checking and resetting the async
		3118	notification, and the callback being invoked.
		3119
		3120	=back
		3121
		3122
1899	=head1 OTHER FUNCTIONS	3123	=head1 OTHER FUNCTIONS
1900		3124
1901	There are some other functions of possible interest. Described. Here. Now.	3125	There are some other functions of possible interest. Described. Here. Now.
1902		3126
1903	=over 4	3127	=over 4
1904		3128
1905	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3129	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1906		3130
1907	This function combines a simple timer and an I/O watcher, calls your	3131	This function combines a simple timer and an I/O watcher, calls your
1908	callback on whichever event happens first and automatically stop both	3132	callback on whichever event happens first and automatically stops both
1909	watchers. This is useful if you want to wait for a single event on an fd	3133	watchers. This is useful if you want to wait for a single event on an fd
1910	or timeout without having to allocate/configure/start/stop/free one or	3134	or timeout without having to allocate/configure/start/stop/free one or
1911	more watchers yourself.	3135	more watchers yourself.
1912		3136
1913	If C<fd> is less than 0, then no I/O watcher will be started and events	3137	If C<fd> is less than 0, then no I/O watcher will be started and the
1914	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3138	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1915	C<events> set will be craeted and started.	3139	the given C<fd> and C<events> set will be created and started.
1916		3140
1917	If C<timeout> is less than 0, then no timeout watcher will be	3141	If C<timeout> is less than 0, then no timeout watcher will be
1918	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3142	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1919	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3143	repeat = 0) will be started. C<0> is a valid timeout.
1920	dubious value.
1921		3144
1922	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3145	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1923	passed an C<revents> set like normal event callbacks (a combination of	3146	passed an C<revents> set like normal event callbacks (a combination of
1924	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3147	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1925	value passed to C<ev_once>:	3148	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3149	a timeout and an io event at the same time - you probably should give io
		3150	events precedence.
1926		3151
		3152	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3153
1927	static void stdin_ready (int revents, void *arg)	3154	static void stdin_ready (int revents, void *arg)
1928	{	3155	{
1929	if (revents & EV_TIMEOUT)
1930	/* doh, nothing entered */;
1931	else if (revents & EV_READ)	3156	if (revents & EV_READ)
1932	/* stdin might have data for us, joy! */;	3157	/* stdin might have data for us, joy! */;
		3158	else if (revents & EV_TIMEOUT)
		3159	/* doh, nothing entered */;
1933	}	3160	}
1934		3161
1935	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3162	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1936		3163
1937	=item ev_feed_event (ev_loop *, watcher *, int revents)
1938
1939	Feeds the given event set into the event loop, as if the specified event
1940	had happened for the specified watcher (which must be a pointer to an
1941	initialised but not necessarily started event watcher).
1942
1943	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3164	=item ev_feed_fd_event (loop, int fd, int revents)
1944		3165
1945	Feed an event on the given fd, as if a file descriptor backend detected	3166	Feed an event on the given fd, as if a file descriptor backend detected
1946	the given events it.	3167	the given events it.
1947		3168
1948	=item ev_feed_signal_event (ev_loop *loop, int signum)	3169	=item ev_feed_signal_event (loop, int signum)
1949		3170
1950	Feed an event as if the given signal occured (C<loop> must be the default	3171	Feed an event as if the given signal occurred (C<loop> must be the default
1951	loop!).	3172	loop!).
1952		3173
1953	=back	3174	=back
1954		3175
1955		3176
…		…
1971		3192
1972	=item * Priorities are not currently supported. Initialising priorities	3193	=item * Priorities are not currently supported. Initialising priorities
1973	will fail and all watchers will have the same priority, even though there	3194	will fail and all watchers will have the same priority, even though there
1974	is an ev_pri field.	3195	is an ev_pri field.
1975		3196
		3197	=item * In libevent, the last base created gets the signals, in libev, the
		3198	first base created (== the default loop) gets the signals.
		3199
1976	=item * Other members are not supported.	3200	=item * Other members are not supported.
1977		3201
1978	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3202	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1979	to use the libev header file and library.	3203	to use the libev header file and library.
1980		3204
1981	=back	3205	=back
1982		3206
1983	=head1 C++ SUPPORT	3207	=head1 C++ SUPPORT
1984		3208
1985	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3209	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1986	you to use some convinience methods to start/stop watchers and also change	3210	you to use some convenience methods to start/stop watchers and also change
1987	the callback model to a model using method callbacks on objects.	3211	the callback model to a model using method callbacks on objects.
1988		3212
1989	To use it,	3213	To use it,
1990		3214
1991	#include <ev++.h>	3215	#include <ev++.h>
1992		3216
1993	This automatically includes F<ev.h> and puts all of its definitions (many	3217	This automatically includes F<ev.h> and puts all of its definitions (many
1994	of them macros) into the global namespace. All C++ specific things are	3218	of them macros) into the global namespace. All C++ specific things are
1995	put into the C<ev> namespace. It should support all the same embedding	3219	put into the C<ev> namespace. It should support all the same embedding
1996	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3220	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2030		3254
2031	=over 4	3255	=over 4
2032		3256
2033	=item ev::TYPE::TYPE ()	3257	=item ev::TYPE::TYPE ()
2034		3258
2035	=item ev::TYPE::TYPE (struct ev_loop *)	3259	=item ev::TYPE::TYPE (loop)
2036		3260
2037	=item ev::TYPE::~TYPE	3261	=item ev::TYPE::~TYPE
2038		3262
2039	The constructor (optionally) takes an event loop to associate the watcher	3263	The constructor (optionally) takes an event loop to associate the watcher
2040	with. If it is omitted, it will use C<EV_DEFAULT>.	3264	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2063	your compiler is good :), then the method will be fully inlined into the	3287	your compiler is good :), then the method will be fully inlined into the
2064	thunking function, making it as fast as a direct C callback.	3288	thunking function, making it as fast as a direct C callback.
2065		3289
2066	Example: simple class declaration and watcher initialisation	3290	Example: simple class declaration and watcher initialisation
2067		3291
2068	struct myclass	3292	struct myclass
2069	{	3293	{
2070	void io_cb (ev::io &w, int revents) { }	3294	void io_cb (ev::io &w, int revents) { }
2071	}	3295	}
2072		3296
2073	myclass obj;	3297	myclass obj;
2074	ev::io iow;	3298	ev::io iow;
2075	iow.set <myclass, &myclass::io_cb> (&obj);	3299	iow.set <myclass, &myclass::io_cb> (&obj);
		3300
		3301	=item w->set (object *)
		3302
		3303	This is an B<experimental> feature that might go away in a future version.
		3304
		3305	This is a variation of a method callback - leaving out the method to call
		3306	will default the method to C<operator ()>, which makes it possible to use
		3307	functor objects without having to manually specify the C<operator ()> all
		3308	the time. Incidentally, you can then also leave out the template argument
		3309	list.
		3310
		3311	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3312	int revents)>.
		3313
		3314	See the method-C<set> above for more details.
		3315
		3316	Example: use a functor object as callback.
		3317
		3318	struct myfunctor
		3319	{
		3320	void operator() (ev::io &w, int revents)
		3321	{
		3322	...
		3323	}
		3324	}
		3325
		3326	myfunctor f;
		3327
		3328	ev::io w;
		3329	w.set (&f);
2076		3330
2077	=item w->set<function> (void *data = 0)	3331	=item w->set<function> (void *data = 0)
2078		3332
2079	Also sets a callback, but uses a static method or plain function as	3333	Also sets a callback, but uses a static method or plain function as
2080	callback. The optional C<data> argument will be stored in the watcher's	3334	callback. The optional C<data> argument will be stored in the watcher's
…		…
2082		3336
2083	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3337	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2084		3338
2085	See the method-C<set> above for more details.	3339	See the method-C<set> above for more details.
2086		3340
2087	Example:	3341	Example: Use a plain function as callback.
2088		3342
2089	static void io_cb (ev::io &w, int revents) { }	3343	static void io_cb (ev::io &w, int revents) { }
2090	iow.set <io_cb> ();	3344	iow.set <io_cb> ();
2091		3345
2092	=item w->set (struct ev_loop *)	3346	=item w->set (loop)
2093		3347
2094	Associates a different C<struct ev_loop> with this watcher. You can only	3348	Associates a different C<struct ev_loop> with this watcher. You can only
2095	do this when the watcher is inactive (and not pending either).	3349	do this when the watcher is inactive (and not pending either).
2096		3350
2097	=item w->set ([args])	3351	=item w->set ([arguments])
2098		3352
2099	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3353	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2100	called at least once. Unlike the C counterpart, an active watcher gets	3354	called at least once. Unlike the C counterpart, an active watcher gets
2101	automatically stopped and restarted when reconfiguring it with this	3355	automatically stopped and restarted when reconfiguring it with this
2102	method.	3356	method.
2103		3357
2104	=item w->start ()	3358	=item w->start ()
…		…
2128	=back	3382	=back
2129		3383
2130	Example: Define a class with an IO and idle watcher, start one of them in	3384	Example: Define a class with an IO and idle watcher, start one of them in
2131	the constructor.	3385	the constructor.
2132		3386
2133	class myclass	3387	class myclass
2134	{	3388	{
2135	ev_io io; void io_cb (ev::io &w, int revents);	3389	ev::io io ; void io_cb (ev::io &w, int revents);
2136	ev_idle idle void idle_cb (ev::idle &w, int revents);	3390	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2137		3391
2138	myclass ();	3392	myclass (int fd)
2139	}	3393	{
2140
2141	myclass::myclass (int fd)
2142	{
2143	io .set <myclass, &myclass::io_cb > (this);	3394	io .set <myclass, &myclass::io_cb > (this);
2144	idle.set <myclass, &myclass::idle_cb> (this);	3395	idle.set <myclass, &myclass::idle_cb> (this);
2145		3396
2146	io.start (fd, ev::READ);	3397	io.start (fd, ev::READ);
		3398	}
2147	}	3399	};
		3400
		3401
		3402	=head1 OTHER LANGUAGE BINDINGS
		3403
		3404	Libev does not offer other language bindings itself, but bindings for a
		3405	number of languages exist in the form of third-party packages. If you know
		3406	any interesting language binding in addition to the ones listed here, drop
		3407	me a note.
		3408
		3409	=over 4
		3410
		3411	=item Perl
		3412
		3413	The EV module implements the full libev API and is actually used to test
		3414	libev. EV is developed together with libev. Apart from the EV core module,
		3415	there are additional modules that implement libev-compatible interfaces
		3416	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3417	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3418	and C<EV::Glib>).
		3419
		3420	It can be found and installed via CPAN, its homepage is at
		3421	L<http://software.schmorp.de/pkg/EV>.
		3422
		3423	=item Python
		3424
		3425	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3426	seems to be quite complete and well-documented.
		3427
		3428	=item Ruby
		3429
		3430	Tony Arcieri has written a ruby extension that offers access to a subset
		3431	of the libev API and adds file handle abstractions, asynchronous DNS and
		3432	more on top of it. It can be found via gem servers. Its homepage is at
		3433	L<http://rev.rubyforge.org/>.
		3434
		3435	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3436	makes rev work even on mingw.
		3437
		3438	=item Haskell
		3439
		3440	A haskell binding to libev is available at
		3441	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3442
		3443	=item D
		3444
		3445	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3446	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3447
		3448	=item Ocaml
		3449
		3450	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3451	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3452
		3453	=item Lua
		3454
		3455	Brian Maher has written a partial interface to libev
		3456	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3457	L<http://github.com/brimworks/lua-ev>.
		3458
		3459	=back
2148		3460
2149		3461
2150	=head1 MACRO MAGIC	3462	=head1 MACRO MAGIC
2151		3463
2152	Libev can be compiled with a variety of options, the most fundamantal	3464	Libev can be compiled with a variety of options, the most fundamental
2153	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3465	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2154	functions and callbacks have an initial C<struct ev_loop *> argument.	3466	functions and callbacks have an initial C<struct ev_loop *> argument.
2155		3467
2156	To make it easier to write programs that cope with either variant, the	3468	To make it easier to write programs that cope with either variant, the
2157	following macros are defined:	3469	following macros are defined:
…		…
2162		3474
2163	This provides the loop I<argument> for functions, if one is required ("ev	3475	This provides the loop I<argument> for functions, if one is required ("ev
2164	loop argument"). The C<EV_A> form is used when this is the sole argument,	3476	loop argument"). The C<EV_A> form is used when this is the sole argument,
2165	C<EV_A_> is used when other arguments are following. Example:	3477	C<EV_A_> is used when other arguments are following. Example:
2166		3478
2167	ev_unref (EV_A);	3479	ev_unref (EV_A);
2168	ev_timer_add (EV_A_ watcher);	3480	ev_timer_add (EV_A_ watcher);
2169	ev_loop (EV_A_ 0);	3481	ev_loop (EV_A_ 0);
2170		3482
2171	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3483	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2172	which is often provided by the following macro.	3484	which is often provided by the following macro.
2173		3485
2174	=item C<EV_P>, C<EV_P_>	3486	=item C<EV_P>, C<EV_P_>
2175		3487
2176	This provides the loop I<parameter> for functions, if one is required ("ev	3488	This provides the loop I<parameter> for functions, if one is required ("ev
2177	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3489	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2178	C<EV_P_> is used when other parameters are following. Example:	3490	C<EV_P_> is used when other parameters are following. Example:
2179		3491
2180	// this is how ev_unref is being declared	3492	// this is how ev_unref is being declared
2181	static void ev_unref (EV_P);	3493	static void ev_unref (EV_P);
2182		3494
2183	// this is how you can declare your typical callback	3495	// this is how you can declare your typical callback
2184	static void cb (EV_P_ ev_timer *w, int revents)	3496	static void cb (EV_P_ ev_timer *w, int revents)
2185		3497
2186	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3498	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2187	suitable for use with C<EV_A>.	3499	suitable for use with C<EV_A>.
2188		3500
2189	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3501	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2190		3502
2191	Similar to the other two macros, this gives you the value of the default	3503	Similar to the other two macros, this gives you the value of the default
2192	loop, if multiple loops are supported ("ev loop default").	3504	loop, if multiple loops are supported ("ev loop default").
		3505
		3506	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3507
		3508	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3509	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3510	is undefined when the default loop has not been initialised by a previous
		3511	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3512
		3513	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3514	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2193		3515
2194	=back	3516	=back
2195		3517
2196	Example: Declare and initialise a check watcher, utilising the above	3518	Example: Declare and initialise a check watcher, utilising the above
2197	macros so it will work regardless of whether multiple loops are supported	3519	macros so it will work regardless of whether multiple loops are supported
2198	or not.	3520	or not.
2199		3521
2200	static void	3522	static void
2201	check_cb (EV_P_ ev_timer *w, int revents)	3523	check_cb (EV_P_ ev_timer *w, int revents)
2202	{	3524	{
2203	ev_check_stop (EV_A_ w);	3525	ev_check_stop (EV_A_ w);
2204	}	3526	}
2205		3527
2206	ev_check check;	3528	ev_check check;
2207	ev_check_init (&check, check_cb);	3529	ev_check_init (&check, check_cb);
2208	ev_check_start (EV_DEFAULT_ &check);	3530	ev_check_start (EV_DEFAULT_ &check);
2209	ev_loop (EV_DEFAULT_ 0);	3531	ev_loop (EV_DEFAULT_ 0);
2210		3532
2211	=head1 EMBEDDING	3533	=head1 EMBEDDING
2212		3534
2213	Libev can (and often is) directly embedded into host	3535	Libev can (and often is) directly embedded into host
2214	applications. Examples of applications that embed it include the Deliantra	3536	applications. Examples of applications that embed it include the Deliantra
…		…
2221	libev somewhere in your source tree).	3543	libev somewhere in your source tree).
2222		3544
2223	=head2 FILESETS	3545	=head2 FILESETS
2224		3546
2225	Depending on what features you need you need to include one or more sets of files	3547	Depending on what features you need you need to include one or more sets of files
2226	in your app.	3548	in your application.
2227		3549
2228	=head3 CORE EVENT LOOP	3550	=head3 CORE EVENT LOOP
2229		3551
2230	To include only the libev core (all the C<ev_*> functions), with manual	3552	To include only the libev core (all the C<ev_*> functions), with manual
2231	configuration (no autoconf):	3553	configuration (no autoconf):
2232		3554
2233	#define EV_STANDALONE 1	3555	#define EV_STANDALONE 1
2234	#include "ev.c"	3556	#include "ev.c"
2235		3557
2236	This will automatically include F<ev.h>, too, and should be done in a	3558	This will automatically include F<ev.h>, too, and should be done in a
2237	single C source file only to provide the function implementations. To use	3559	single C source file only to provide the function implementations. To use
2238	it, do the same for F<ev.h> in all files wishing to use this API (best	3560	it, do the same for F<ev.h> in all files wishing to use this API (best
2239	done by writing a wrapper around F<ev.h> that you can include instead and	3561	done by writing a wrapper around F<ev.h> that you can include instead and
2240	where you can put other configuration options):	3562	where you can put other configuration options):
2241		3563
2242	#define EV_STANDALONE 1	3564	#define EV_STANDALONE 1
2243	#include "ev.h"	3565	#include "ev.h"
2244		3566
2245	Both header files and implementation files can be compiled with a C++	3567	Both header files and implementation files can be compiled with a C++
2246	compiler (at least, thats a stated goal, and breakage will be treated	3568	compiler (at least, that's a stated goal, and breakage will be treated
2247	as a bug).	3569	as a bug).
2248		3570
2249	You need the following files in your source tree, or in a directory	3571	You need the following files in your source tree, or in a directory
2250	in your include path (e.g. in libev/ when using -Ilibev):	3572	in your include path (e.g. in libev/ when using -Ilibev):
2251		3573
2252	ev.h	3574	ev.h
2253	ev.c	3575	ev.c
2254	ev_vars.h	3576	ev_vars.h
2255	ev_wrap.h	3577	ev_wrap.h
2256		3578
2257	ev_win32.c required on win32 platforms only	3579	ev_win32.c required on win32 platforms only
2258		3580
2259	ev_select.c only when select backend is enabled (which is enabled by default)	3581	ev_select.c only when select backend is enabled (which is enabled by default)
2260	ev_poll.c only when poll backend is enabled (disabled by default)	3582	ev_poll.c only when poll backend is enabled (disabled by default)
2261	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3583	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2262	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3584	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2263	ev_port.c only when the solaris port backend is enabled (disabled by default)	3585	ev_port.c only when the solaris port backend is enabled (disabled by default)
2264		3586
2265	F<ev.c> includes the backend files directly when enabled, so you only need	3587	F<ev.c> includes the backend files directly when enabled, so you only need
2266	to compile this single file.	3588	to compile this single file.
2267		3589
2268	=head3 LIBEVENT COMPATIBILITY API	3590	=head3 LIBEVENT COMPATIBILITY API
2269		3591
2270	To include the libevent compatibility API, also include:	3592	To include the libevent compatibility API, also include:
2271		3593
2272	#include "event.c"	3594	#include "event.c"
2273		3595
2274	in the file including F<ev.c>, and:	3596	in the file including F<ev.c>, and:
2275		3597
2276	#include "event.h"	3598	#include "event.h"
2277		3599
2278	in the files that want to use the libevent API. This also includes F<ev.h>.	3600	in the files that want to use the libevent API. This also includes F<ev.h>.
2279		3601
2280	You need the following additional files for this:	3602	You need the following additional files for this:
2281		3603
2282	event.h	3604	event.h
2283	event.c	3605	event.c
2284		3606
2285	=head3 AUTOCONF SUPPORT	3607	=head3 AUTOCONF SUPPORT
2286		3608
2287	Instead of using C<EV_STANDALONE=1> and providing your config in	3609	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2288	whatever way you want, you can also C<m4_include([libev.m4])> in your	3610	whatever way you want, you can also C<m4_include([libev.m4])> in your
2289	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3611	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2290	include F<config.h> and configure itself accordingly.	3612	include F<config.h> and configure itself accordingly.
2291		3613
2292	For this of course you need the m4 file:	3614	For this of course you need the m4 file:
2293		3615
2294	libev.m4	3616	libev.m4
2295		3617
2296	=head2 PREPROCESSOR SYMBOLS/MACROS	3618	=head2 PREPROCESSOR SYMBOLS/MACROS
2297		3619
2298	Libev can be configured via a variety of preprocessor symbols you have to define	3620	Libev can be configured via a variety of preprocessor symbols you have to
2299	before including any of its files. The default is not to build for multiplicity	3621	define before including any of its files. The default in the absence of
2300	and only include the select backend.	3622	autoconf is documented for every option.
2301		3623
2302	=over 4	3624	=over 4
2303		3625
2304	=item EV_STANDALONE	3626	=item EV_STANDALONE
2305		3627
…		…
2307	keeps libev from including F<config.h>, and it also defines dummy	3629	keeps libev from including F<config.h>, and it also defines dummy
2308	implementations for some libevent functions (such as logging, which is not	3630	implementations for some libevent functions (such as logging, which is not
2309	supported). It will also not define any of the structs usually found in	3631	supported). It will also not define any of the structs usually found in
2310	F<event.h> that are not directly supported by the libev core alone.	3632	F<event.h> that are not directly supported by the libev core alone.
2311		3633
		3634	In standalone mode, libev will still try to automatically deduce the
		3635	configuration, but has to be more conservative.
		3636
2312	=item EV_USE_MONOTONIC	3637	=item EV_USE_MONOTONIC
2313		3638
2314	If defined to be C<1>, libev will try to detect the availability of the	3639	If defined to be C<1>, libev will try to detect the availability of the
2315	monotonic clock option at both compiletime and runtime. Otherwise no use	3640	monotonic clock option at both compile time and runtime. Otherwise no
2316	of the monotonic clock option will be attempted. If you enable this, you	3641	use of the monotonic clock option will be attempted. If you enable this,
2317	usually have to link against librt or something similar. Enabling it when	3642	you usually have to link against librt or something similar. Enabling it
2318	the functionality isn't available is safe, though, although you have	3643	when the functionality isn't available is safe, though, although you have
2319	to make sure you link against any libraries where the C<clock_gettime>	3644	to make sure you link against any libraries where the C<clock_gettime>
2320	function is hiding in (often F<-lrt>).	3645	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2321		3646
2322	=item EV_USE_REALTIME	3647	=item EV_USE_REALTIME
2323		3648
2324	If defined to be C<1>, libev will try to detect the availability of the	3649	If defined to be C<1>, libev will try to detect the availability of the
2325	realtime clock option at compiletime (and assume its availability at	3650	real-time clock option at compile time (and assume its availability
2326	runtime if successful). Otherwise no use of the realtime clock option will	3651	at runtime if successful). Otherwise no use of the real-time clock
2327	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3652	option will be attempted. This effectively replaces C<gettimeofday>
2328	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3653	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2329	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3654	correctness. See the note about libraries in the description of
		3655	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3656	C<EV_USE_CLOCK_SYSCALL>.
		3657
		3658	=item EV_USE_CLOCK_SYSCALL
		3659
		3660	If defined to be C<1>, libev will try to use a direct syscall instead
		3661	of calling the system-provided C<clock_gettime> function. This option
		3662	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3663	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3664	programs needlessly. Using a direct syscall is slightly slower (in
		3665	theory), because no optimised vdso implementation can be used, but avoids
		3666	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3667	higher, as it simplifies linking (no need for C<-lrt>).
2330		3668
2331	=item EV_USE_NANOSLEEP	3669	=item EV_USE_NANOSLEEP
2332		3670
2333	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3671	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2334	and will use it for delays. Otherwise it will use C<select ()>.	3672	and will use it for delays. Otherwise it will use C<select ()>.
2335		3673
		3674	=item EV_USE_EVENTFD
		3675
		3676	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3677	available and will probe for kernel support at runtime. This will improve
		3678	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3679	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3680	2.7 or newer, otherwise disabled.
		3681
2336	=item EV_USE_SELECT	3682	=item EV_USE_SELECT
2337		3683
2338	If undefined or defined to be C<1>, libev will compile in support for the	3684	If undefined or defined to be C<1>, libev will compile in support for the
2339	C<select>(2) backend. No attempt at autodetection will be done: if no	3685	C<select>(2) backend. No attempt at auto-detection will be done: if no
2340	other method takes over, select will be it. Otherwise the select backend	3686	other method takes over, select will be it. Otherwise the select backend
2341	will not be compiled in.	3687	will not be compiled in.
2342		3688
2343	=item EV_SELECT_USE_FD_SET	3689	=item EV_SELECT_USE_FD_SET
2344		3690
2345	If defined to C<1>, then the select backend will use the system C<fd_set>	3691	If defined to C<1>, then the select backend will use the system C<fd_set>
2346	structure. This is useful if libev doesn't compile due to a missing	3692	structure. This is useful if libev doesn't compile due to a missing
2347	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3693	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2348	exotic systems. This usually limits the range of file descriptors to some	3694	on exotic systems. This usually limits the range of file descriptors to
2349	low limit such as 1024 or might have other limitations (winsocket only	3695	some low limit such as 1024 or might have other limitations (winsocket
2350	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3696	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2351	influence the size of the C<fd_set> used.	3697	configures the maximum size of the C<fd_set>.
2352		3698
2353	=item EV_SELECT_IS_WINSOCKET	3699	=item EV_SELECT_IS_WINSOCKET
2354		3700
2355	When defined to C<1>, the select backend will assume that	3701	When defined to C<1>, the select backend will assume that
2356	select/socket/connect etc. don't understand file descriptors but	3702	select/socket/connect etc. don't understand file descriptors but
…		…
2358	be used is the winsock select). This means that it will call	3704	be used is the winsock select). This means that it will call
2359	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3705	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2360	it is assumed that all these functions actually work on fds, even	3706	it is assumed that all these functions actually work on fds, even
2361	on win32. Should not be defined on non-win32 platforms.	3707	on win32. Should not be defined on non-win32 platforms.
2362		3708
		3709	=item EV_FD_TO_WIN32_HANDLE(fd)
		3710
		3711	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3712	file descriptors to socket handles. When not defining this symbol (the
		3713	default), then libev will call C<_get_osfhandle>, which is usually
		3714	correct. In some cases, programs use their own file descriptor management,
		3715	in which case they can provide this function to map fds to socket handles.
		3716
		3717	=item EV_WIN32_HANDLE_TO_FD(handle)
		3718
		3719	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3720	using the standard C<_open_osfhandle> function. For programs implementing
		3721	their own fd to handle mapping, overwriting this function makes it easier
		3722	to do so. This can be done by defining this macro to an appropriate value.
		3723
		3724	=item EV_WIN32_CLOSE_FD(fd)
		3725
		3726	If programs implement their own fd to handle mapping on win32, then this
		3727	macro can be used to override the C<close> function, useful to unregister
		3728	file descriptors again. Note that the replacement function has to close
		3729	the underlying OS handle.
		3730
2363	=item EV_USE_POLL	3731	=item EV_USE_POLL
2364		3732
2365	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3733	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2366	backend. Otherwise it will be enabled on non-win32 platforms. It	3734	backend. Otherwise it will be enabled on non-win32 platforms. It
2367	takes precedence over select.	3735	takes precedence over select.
2368		3736
2369	=item EV_USE_EPOLL	3737	=item EV_USE_EPOLL
2370		3738
2371	If defined to be C<1>, libev will compile in support for the Linux	3739	If defined to be C<1>, libev will compile in support for the Linux
2372	C<epoll>(7) backend. Its availability will be detected at runtime,	3740	C<epoll>(7) backend. Its availability will be detected at runtime,
2373	otherwise another method will be used as fallback. This is the	3741	otherwise another method will be used as fallback. This is the preferred
2374	preferred backend for GNU/Linux systems.	3742	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3743	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2375		3744
2376	=item EV_USE_KQUEUE	3745	=item EV_USE_KQUEUE
2377		3746
2378	If defined to be C<1>, libev will compile in support for the BSD style	3747	If defined to be C<1>, libev will compile in support for the BSD style
2379	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3748	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2392	otherwise another method will be used as fallback. This is the preferred	3761	otherwise another method will be used as fallback. This is the preferred
2393	backend for Solaris 10 systems.	3762	backend for Solaris 10 systems.
2394		3763
2395	=item EV_USE_DEVPOLL	3764	=item EV_USE_DEVPOLL
2396		3765
2397	reserved for future expansion, works like the USE symbols above.	3766	Reserved for future expansion, works like the USE symbols above.
2398		3767
2399	=item EV_USE_INOTIFY	3768	=item EV_USE_INOTIFY
2400		3769
2401	If defined to be C<1>, libev will compile in support for the Linux inotify	3770	If defined to be C<1>, libev will compile in support for the Linux inotify
2402	interface to speed up C<ev_stat> watchers. Its actual availability will	3771	interface to speed up C<ev_stat> watchers. Its actual availability will
2403	be detected at runtime.	3772	be detected at runtime. If undefined, it will be enabled if the headers
		3773	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3774
		3775	=item EV_ATOMIC_T
		3776
		3777	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3778	access is atomic with respect to other threads or signal contexts. No such
		3779	type is easily found in the C language, so you can provide your own type
		3780	that you know is safe for your purposes. It is used both for signal handler "locking"
		3781	as well as for signal and thread safety in C<ev_async> watchers.
		3782
		3783	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3784	(from F<signal.h>), which is usually good enough on most platforms.
2404		3785
2405	=item EV_H	3786	=item EV_H
2406		3787
2407	The name of the F<ev.h> header file used to include it. The default if	3788	The name of the F<ev.h> header file used to include it. The default if
2408	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3789	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2409	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3790	used to virtually rename the F<ev.h> header file in case of conflicts.
2410		3791
2411	=item EV_CONFIG_H	3792	=item EV_CONFIG_H
2412		3793
2413	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3794	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2414	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3795	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2415	C<EV_H>, above.	3796	C<EV_H>, above.
2416		3797
2417	=item EV_EVENT_H	3798	=item EV_EVENT_H
2418		3799
2419	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3800	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2420	of how the F<event.h> header can be found.	3801	of how the F<event.h> header can be found, the default is C<"event.h">.
2421		3802
2422	=item EV_PROTOTYPES	3803	=item EV_PROTOTYPES
2423		3804
2424	If defined to be C<0>, then F<ev.h> will not define any function	3805	If defined to be C<0>, then F<ev.h> will not define any function
2425	prototypes, but still define all the structs and other symbols. This is	3806	prototypes, but still define all the structs and other symbols. This is
…		…
2446	When doing priority-based operations, libev usually has to linearly search	3827	When doing priority-based operations, libev usually has to linearly search
2447	all the priorities, so having many of them (hundreds) uses a lot of space	3828	all the priorities, so having many of them (hundreds) uses a lot of space
2448	and time, so using the defaults of five priorities (-2 .. +2) is usually	3829	and time, so using the defaults of five priorities (-2 .. +2) is usually
2449	fine.	3830	fine.
2450		3831
2451	If your embedding app does not need any priorities, defining these both to	3832	If your embedding application does not need any priorities, defining these
2452	C<0> will save some memory and cpu.	3833	both to C<0> will save some memory and CPU.
2453		3834
2454	=item EV_PERIODIC_ENABLE	3835	=item EV_PERIODIC_ENABLE
2455		3836
2456	If undefined or defined to be C<1>, then periodic timers are supported. If	3837	If undefined or defined to be C<1>, then periodic timers are supported. If
2457	defined to be C<0>, then they are not. Disabling them saves a few kB of	3838	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2464	code.	3845	code.
2465		3846
2466	=item EV_EMBED_ENABLE	3847	=item EV_EMBED_ENABLE
2467		3848
2468	If undefined or defined to be C<1>, then embed watchers are supported. If	3849	If undefined or defined to be C<1>, then embed watchers are supported. If
2469	defined to be C<0>, then they are not.	3850	defined to be C<0>, then they are not. Embed watchers rely on most other
		3851	watcher types, which therefore must not be disabled.
2470		3852
2471	=item EV_STAT_ENABLE	3853	=item EV_STAT_ENABLE
2472		3854
2473	If undefined or defined to be C<1>, then stat watchers are supported. If	3855	If undefined or defined to be C<1>, then stat watchers are supported. If
2474	defined to be C<0>, then they are not.	3856	defined to be C<0>, then they are not.
…		…
2476	=item EV_FORK_ENABLE	3858	=item EV_FORK_ENABLE
2477		3859
2478	If undefined or defined to be C<1>, then fork watchers are supported. If	3860	If undefined or defined to be C<1>, then fork watchers are supported. If
2479	defined to be C<0>, then they are not.	3861	defined to be C<0>, then they are not.
2480		3862
		3863	=item EV_ASYNC_ENABLE
		3864
		3865	If undefined or defined to be C<1>, then async watchers are supported. If
		3866	defined to be C<0>, then they are not.
		3867
2481	=item EV_MINIMAL	3868	=item EV_MINIMAL
2482		3869
2483	If you need to shave off some kilobytes of code at the expense of some	3870	If you need to shave off some kilobytes of code at the expense of some
2484	speed, define this symbol to C<1>. Currently only used for gcc to override	3871	speed (but with the full API), define this symbol to C<1>. Currently this
2485	some inlining decisions, saves roughly 30% codesize of amd64.	3872	is used to override some inlining decisions, saves roughly 30% code size
		3873	on amd64. It also selects a much smaller 2-heap for timer management over
		3874	the default 4-heap.
		3875
		3876	You can save even more by disabling watcher types you do not need
		3877	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3878	(C<-DNDEBUG>) will usually reduce code size a lot.
		3879
		3880	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3881	provide a bare-bones event library. See C<ev.h> for details on what parts
		3882	of the API are still available, and do not complain if this subset changes
		3883	over time.
		3884
		3885	=item EV_NSIG
		3886
		3887	The highest supported signal number, +1 (or, the number of
		3888	signals): Normally, libev tries to deduce the maximum number of signals
		3889	automatically, but sometimes this fails, in which case it can be
		3890	specified. Also, using a lower number than detected (C<32> should be
		3891	good for about any system in existance) can save some memory, as libev
		3892	statically allocates some 12-24 bytes per signal number.
2486		3893
2487	=item EV_PID_HASHSIZE	3894	=item EV_PID_HASHSIZE
2488		3895
2489	C<ev_child> watchers use a small hash table to distribute workload by	3896	C<ev_child> watchers use a small hash table to distribute workload by
2490	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3897	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2491	than enough. If you need to manage thousands of children you might want to	3898	than enough. If you need to manage thousands of children you might want to
2492	increase this value (I<must> be a power of two).	3899	increase this value (I<must> be a power of two).
2493		3900
2494	=item EV_INOTIFY_HASHSIZE	3901	=item EV_INOTIFY_HASHSIZE
2495		3902
2496	C<ev_staz> watchers use a small hash table to distribute workload by	3903	C<ev_stat> watchers use a small hash table to distribute workload by
2497	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3904	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2498	usually more than enough. If you need to manage thousands of C<ev_stat>	3905	usually more than enough. If you need to manage thousands of C<ev_stat>
2499	watchers you might want to increase this value (I<must> be a power of	3906	watchers you might want to increase this value (I<must> be a power of
2500	two).	3907	two).
2501		3908
		3909	=item EV_USE_4HEAP
		3910
		3911	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3912	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3913	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3914	faster performance with many (thousands) of watchers.
		3915
		3916	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3917	(disabled).
		3918
		3919	=item EV_HEAP_CACHE_AT
		3920
		3921	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3922	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3923	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3924	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3925	but avoids random read accesses on heap changes. This improves performance
		3926	noticeably with many (hundreds) of watchers.
		3927
		3928	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3929	(disabled).
		3930
		3931	=item EV_VERIFY
		3932
		3933	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3934	be done: If set to C<0>, no internal verification code will be compiled
		3935	in. If set to C<1>, then verification code will be compiled in, but not
		3936	called. If set to C<2>, then the internal verification code will be
		3937	called once per loop, which can slow down libev. If set to C<3>, then the
		3938	verification code will be called very frequently, which will slow down
		3939	libev considerably.
		3940
		3941	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3942	C<0>.
		3943
2502	=item EV_COMMON	3944	=item EV_COMMON
2503		3945
2504	By default, all watchers have a C<void *data> member. By redefining	3946	By default, all watchers have a C<void *data> member. By redefining
2505	this macro to a something else you can include more and other types of	3947	this macro to a something else you can include more and other types of
2506	members. You have to define it each time you include one of the files,	3948	members. You have to define it each time you include one of the files,
2507	though, and it must be identical each time.	3949	though, and it must be identical each time.
2508		3950
2509	For example, the perl EV module uses something like this:	3951	For example, the perl EV module uses something like this:
2510		3952
2511	#define EV_COMMON \	3953	#define EV_COMMON \
2512	SV *self; /* contains this struct */ \	3954	SV *self; /* contains this struct */ \
2513	SV *cb_sv, *fh /* note no trailing ";" */	3955	SV *cb_sv, *fh /* note no trailing ";" */
2514		3956
2515	=item EV_CB_DECLARE (type)	3957	=item EV_CB_DECLARE (type)
2516		3958
2517	=item EV_CB_INVOKE (watcher, revents)	3959	=item EV_CB_INVOKE (watcher, revents)
2518		3960
…		…
2523	definition and a statement, respectively. See the F<ev.h> header file for	3965	definition and a statement, respectively. See the F<ev.h> header file for
2524	their default definitions. One possible use for overriding these is to	3966	their default definitions. One possible use for overriding these is to
2525	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3967	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2526	method calls instead of plain function calls in C++.	3968	method calls instead of plain function calls in C++.
2527		3969
		3970	=back
		3971
2528	=head2 EXPORTED API SYMBOLS	3972	=head2 EXPORTED API SYMBOLS
2529		3973
2530	If you need to re-export the API (e.g. via a dll) and you need a list of	3974	If you need to re-export the API (e.g. via a DLL) and you need a list of
2531	exported symbols, you can use the provided F<Symbol.*> files which list	3975	exported symbols, you can use the provided F<Symbol.*> files which list
2532	all public symbols, one per line:	3976	all public symbols, one per line:
2533		3977
2534	Symbols.ev for libev proper	3978	Symbols.ev for libev proper
2535	Symbols.event for the libevent emulation	3979	Symbols.event for the libevent emulation
2536		3980
2537	This can also be used to rename all public symbols to avoid clashes with	3981	This can also be used to rename all public symbols to avoid clashes with
2538	multiple versions of libev linked together (which is obviously bad in	3982	multiple versions of libev linked together (which is obviously bad in
2539	itself, but sometimes it is inconvinient to avoid this).	3983	itself, but sometimes it is inconvenient to avoid this).
2540		3984
2541	A sed command like this will create wrapper C<#define>'s that you need to	3985	A sed command like this will create wrapper C<#define>'s that you need to
2542	include before including F<ev.h>:	3986	include before including F<ev.h>:
2543		3987
2544	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3988	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2561	file.	4005	file.
2562		4006
2563	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4007	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2564	that everybody includes and which overrides some configure choices:	4008	that everybody includes and which overrides some configure choices:
2565		4009
2566	#define EV_MINIMAL 1	4010	#define EV_MINIMAL 1
2567	#define EV_USE_POLL 0	4011	#define EV_USE_POLL 0
2568	#define EV_MULTIPLICITY 0	4012	#define EV_MULTIPLICITY 0
2569	#define EV_PERIODIC_ENABLE 0	4013	#define EV_PERIODIC_ENABLE 0
2570	#define EV_STAT_ENABLE 0	4014	#define EV_STAT_ENABLE 0
2571	#define EV_FORK_ENABLE 0	4015	#define EV_FORK_ENABLE 0
2572	#define EV_CONFIG_H <config.h>	4016	#define EV_CONFIG_H <config.h>
2573	#define EV_MINPRI 0	4017	#define EV_MINPRI 0
2574	#define EV_MAXPRI 0	4018	#define EV_MAXPRI 0
2575		4019
2576	#include "ev++.h"	4020	#include "ev++.h"
2577		4021
2578	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4022	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2579		4023
2580	#include "ev_cpp.h"	4024	#include "ev_cpp.h"
2581	#include "ev.c"	4025	#include "ev.c"
2582		4026
		4027	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2583		4028
		4029	=head2 THREADS AND COROUTINES
		4030
		4031	=head3 THREADS
		4032
		4033	All libev functions are reentrant and thread-safe unless explicitly
		4034	documented otherwise, but libev implements no locking itself. This means
		4035	that you can use as many loops as you want in parallel, as long as there
		4036	are no concurrent calls into any libev function with the same loop
		4037	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4038	of course): libev guarantees that different event loops share no data
		4039	structures that need any locking.
		4040
		4041	Or to put it differently: calls with different loop parameters can be done
		4042	concurrently from multiple threads, calls with the same loop parameter
		4043	must be done serially (but can be done from different threads, as long as
		4044	only one thread ever is inside a call at any point in time, e.g. by using
		4045	a mutex per loop).
		4046
		4047	Specifically to support threads (and signal handlers), libev implements
		4048	so-called C<ev_async> watchers, which allow some limited form of
		4049	concurrency on the same event loop, namely waking it up "from the
		4050	outside".
		4051
		4052	If you want to know which design (one loop, locking, or multiple loops
		4053	without or something else still) is best for your problem, then I cannot
		4054	help you, but here is some generic advice:
		4055
		4056	=over 4
		4057
		4058	=item * most applications have a main thread: use the default libev loop
		4059	in that thread, or create a separate thread running only the default loop.
		4060
		4061	This helps integrating other libraries or software modules that use libev
		4062	themselves and don't care/know about threading.
		4063
		4064	=item * one loop per thread is usually a good model.
		4065
		4066	Doing this is almost never wrong, sometimes a better-performance model
		4067	exists, but it is always a good start.
		4068
		4069	=item * other models exist, such as the leader/follower pattern, where one
		4070	loop is handed through multiple threads in a kind of round-robin fashion.
		4071
		4072	Choosing a model is hard - look around, learn, know that usually you can do
		4073	better than you currently do :-)
		4074
		4075	=item * often you need to talk to some other thread which blocks in the
		4076	event loop.
		4077
		4078	C<ev_async> watchers can be used to wake them up from other threads safely
		4079	(or from signal contexts...).
		4080
		4081	An example use would be to communicate signals or other events that only
		4082	work in the default loop by registering the signal watcher with the
		4083	default loop and triggering an C<ev_async> watcher from the default loop
		4084	watcher callback into the event loop interested in the signal.
		4085
		4086	=back
		4087
		4088	=head4 THREAD LOCKING EXAMPLE
		4089
		4090	Here is a fictitious example of how to run an event loop in a different
		4091	thread than where callbacks are being invoked and watchers are
		4092	created/added/removed.
		4093
		4094	For a real-world example, see the C<EV::Loop::Async> perl module,
		4095	which uses exactly this technique (which is suited for many high-level
		4096	languages).
		4097
		4098	The example uses a pthread mutex to protect the loop data, a condition
		4099	variable to wait for callback invocations, an async watcher to notify the
		4100	event loop thread and an unspecified mechanism to wake up the main thread.
		4101
		4102	First, you need to associate some data with the event loop:
		4103
		4104	typedef struct {
		4105	mutex_t lock; /* global loop lock */
		4106	ev_async async_w;
		4107	thread_t tid;
		4108	cond_t invoke_cv;
		4109	} userdata;
		4110
		4111	void prepare_loop (EV_P)
		4112	{
		4113	// for simplicity, we use a static userdata struct.
		4114	static userdata u;
		4115
		4116	ev_async_init (&u->async_w, async_cb);
		4117	ev_async_start (EV_A_ &u->async_w);
		4118
		4119	pthread_mutex_init (&u->lock, 0);
		4120	pthread_cond_init (&u->invoke_cv, 0);
		4121
		4122	// now associate this with the loop
		4123	ev_set_userdata (EV_A_ u);
		4124	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4125	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4126
		4127	// then create the thread running ev_loop
		4128	pthread_create (&u->tid, 0, l_run, EV_A);
		4129	}
		4130
		4131	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4132	solely to wake up the event loop so it takes notice of any new watchers
		4133	that might have been added:
		4134
		4135	static void
		4136	async_cb (EV_P_ ev_async *w, int revents)
		4137	{
		4138	// just used for the side effects
		4139	}
		4140
		4141	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4142	protecting the loop data, respectively.
		4143
		4144	static void
		4145	l_release (EV_P)
		4146	{
		4147	userdata *u = ev_userdata (EV_A);
		4148	pthread_mutex_unlock (&u->lock);
		4149	}
		4150
		4151	static void
		4152	l_acquire (EV_P)
		4153	{
		4154	userdata *u = ev_userdata (EV_A);
		4155	pthread_mutex_lock (&u->lock);
		4156	}
		4157
		4158	The event loop thread first acquires the mutex, and then jumps straight
		4159	into C<ev_loop>:
		4160
		4161	void *
		4162	l_run (void *thr_arg)
		4163	{
		4164	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4165
		4166	l_acquire (EV_A);
		4167	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4168	ev_loop (EV_A_ 0);
		4169	l_release (EV_A);
		4170
		4171	return 0;
		4172	}
		4173
		4174	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4175	signal the main thread via some unspecified mechanism (signals? pipe
		4176	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4177	have been called (in a while loop because a) spurious wakeups are possible
		4178	and b) skipping inter-thread-communication when there are no pending
		4179	watchers is very beneficial):
		4180
		4181	static void
		4182	l_invoke (EV_P)
		4183	{
		4184	userdata *u = ev_userdata (EV_A);
		4185
		4186	while (ev_pending_count (EV_A))
		4187	{
		4188	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4189	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4190	}
		4191	}
		4192
		4193	Now, whenever the main thread gets told to invoke pending watchers, it
		4194	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4195	thread to continue:
		4196
		4197	static void
		4198	real_invoke_pending (EV_P)
		4199	{
		4200	userdata *u = ev_userdata (EV_A);
		4201
		4202	pthread_mutex_lock (&u->lock);
		4203	ev_invoke_pending (EV_A);
		4204	pthread_cond_signal (&u->invoke_cv);
		4205	pthread_mutex_unlock (&u->lock);
		4206	}
		4207
		4208	Whenever you want to start/stop a watcher or do other modifications to an
		4209	event loop, you will now have to lock:
		4210
		4211	ev_timer timeout_watcher;
		4212	userdata *u = ev_userdata (EV_A);
		4213
		4214	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4215
		4216	pthread_mutex_lock (&u->lock);
		4217	ev_timer_start (EV_A_ &timeout_watcher);
		4218	ev_async_send (EV_A_ &u->async_w);
		4219	pthread_mutex_unlock (&u->lock);
		4220
		4221	Note that sending the C<ev_async> watcher is required because otherwise
		4222	an event loop currently blocking in the kernel will have no knowledge
		4223	about the newly added timer. By waking up the loop it will pick up any new
		4224	watchers in the next event loop iteration.
		4225
		4226	=head3 COROUTINES
		4227
		4228	Libev is very accommodating to coroutines ("cooperative threads"):
		4229	libev fully supports nesting calls to its functions from different
		4230	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4231	different coroutines, and switch freely between both coroutines running
		4232	the loop, as long as you don't confuse yourself). The only exception is
		4233	that you must not do this from C<ev_periodic> reschedule callbacks.
		4234
		4235	Care has been taken to ensure that libev does not keep local state inside
		4236	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4237	they do not call any callbacks.
		4238
		4239	=head2 COMPILER WARNINGS
		4240
		4241	Depending on your compiler and compiler settings, you might get no or a
		4242	lot of warnings when compiling libev code. Some people are apparently
		4243	scared by this.
		4244
		4245	However, these are unavoidable for many reasons. For one, each compiler
		4246	has different warnings, and each user has different tastes regarding
		4247	warning options. "Warn-free" code therefore cannot be a goal except when
		4248	targeting a specific compiler and compiler-version.
		4249
		4250	Another reason is that some compiler warnings require elaborate
		4251	workarounds, or other changes to the code that make it less clear and less
		4252	maintainable.
		4253
		4254	And of course, some compiler warnings are just plain stupid, or simply
		4255	wrong (because they don't actually warn about the condition their message
		4256	seems to warn about). For example, certain older gcc versions had some
		4257	warnings that resulted an extreme number of false positives. These have
		4258	been fixed, but some people still insist on making code warn-free with
		4259	such buggy versions.
		4260
		4261	While libev is written to generate as few warnings as possible,
		4262	"warn-free" code is not a goal, and it is recommended not to build libev
		4263	with any compiler warnings enabled unless you are prepared to cope with
		4264	them (e.g. by ignoring them). Remember that warnings are just that:
		4265	warnings, not errors, or proof of bugs.
		4266
		4267
		4268	=head2 VALGRIND
		4269
		4270	Valgrind has a special section here because it is a popular tool that is
		4271	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4272
		4273	If you think you found a bug (memory leak, uninitialised data access etc.)
		4274	in libev, then check twice: If valgrind reports something like:
		4275
		4276	==2274== definitely lost: 0 bytes in 0 blocks.
		4277	==2274== possibly lost: 0 bytes in 0 blocks.
		4278	==2274== still reachable: 256 bytes in 1 blocks.
		4279
		4280	Then there is no memory leak, just as memory accounted to global variables
		4281	is not a memleak - the memory is still being referenced, and didn't leak.
		4282
		4283	Similarly, under some circumstances, valgrind might report kernel bugs
		4284	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4285	although an acceptable workaround has been found here), or it might be
		4286	confused.
		4287
		4288	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4289	make it into some kind of religion.
		4290
		4291	If you are unsure about something, feel free to contact the mailing list
		4292	with the full valgrind report and an explanation on why you think this
		4293	is a bug in libev (best check the archives, too :). However, don't be
		4294	annoyed when you get a brisk "this is no bug" answer and take the chance
		4295	of learning how to interpret valgrind properly.
		4296
		4297	If you need, for some reason, empty reports from valgrind for your project
		4298	I suggest using suppression lists.
		4299
		4300
		4301	=head1 PORTABILITY NOTES
		4302
		4303	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4304
		4305	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4306	requires, and its I/O model is fundamentally incompatible with the POSIX
		4307	model. Libev still offers limited functionality on this platform in
		4308	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4309	descriptors. This only applies when using Win32 natively, not when using
		4310	e.g. cygwin.
		4311
		4312	Lifting these limitations would basically require the full
		4313	re-implementation of the I/O system. If you are into these kinds of
		4314	things, then note that glib does exactly that for you in a very portable
		4315	way (note also that glib is the slowest event library known to man).
		4316
		4317	There is no supported compilation method available on windows except
		4318	embedding it into other applications.
		4319
		4320	Sensible signal handling is officially unsupported by Microsoft - libev
		4321	tries its best, but under most conditions, signals will simply not work.
		4322
		4323	Not a libev limitation but worth mentioning: windows apparently doesn't
		4324	accept large writes: instead of resulting in a partial write, windows will
		4325	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4326	so make sure you only write small amounts into your sockets (less than a
		4327	megabyte seems safe, but this apparently depends on the amount of memory
		4328	available).
		4329
		4330	Due to the many, low, and arbitrary limits on the win32 platform and
		4331	the abysmal performance of winsockets, using a large number of sockets
		4332	is not recommended (and not reasonable). If your program needs to use
		4333	more than a hundred or so sockets, then likely it needs to use a totally
		4334	different implementation for windows, as libev offers the POSIX readiness
		4335	notification model, which cannot be implemented efficiently on windows
		4336	(due to Microsoft monopoly games).
		4337
		4338	A typical way to use libev under windows is to embed it (see the embedding
		4339	section for details) and use the following F<evwrap.h> header file instead
		4340	of F<ev.h>:
		4341
		4342	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4343	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4344
		4345	#include "ev.h"
		4346
		4347	And compile the following F<evwrap.c> file into your project (make sure
		4348	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4349
		4350	#include "evwrap.h"
		4351	#include "ev.c"
		4352
		4353	=over 4
		4354
		4355	=item The winsocket select function
		4356
		4357	The winsocket C<select> function doesn't follow POSIX in that it
		4358	requires socket I<handles> and not socket I<file descriptors> (it is
		4359	also extremely buggy). This makes select very inefficient, and also
		4360	requires a mapping from file descriptors to socket handles (the Microsoft
		4361	C runtime provides the function C<_open_osfhandle> for this). See the
		4362	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4363	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4364
		4365	The configuration for a "naked" win32 using the Microsoft runtime
		4366	libraries and raw winsocket select is:
		4367
		4368	#define EV_USE_SELECT 1
		4369	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4370
		4371	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4372	complexity in the O(n²) range when using win32.
		4373
		4374	=item Limited number of file descriptors
		4375
		4376	Windows has numerous arbitrary (and low) limits on things.
		4377
		4378	Early versions of winsocket's select only supported waiting for a maximum
		4379	of C<64> handles (probably owning to the fact that all windows kernels
		4380	can only wait for C<64> things at the same time internally; Microsoft
		4381	recommends spawning a chain of threads and wait for 63 handles and the
		4382	previous thread in each. Sounds great!).
		4383
		4384	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4385	to some high number (e.g. C<2048>) before compiling the winsocket select
		4386	call (which might be in libev or elsewhere, for example, perl and many
		4387	other interpreters do their own select emulation on windows).
		4388
		4389	Another limit is the number of file descriptors in the Microsoft runtime
		4390	libraries, which by default is C<64> (there must be a hidden I<64>
		4391	fetish or something like this inside Microsoft). You can increase this
		4392	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4393	(another arbitrary limit), but is broken in many versions of the Microsoft
		4394	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4395	(depending on windows version and/or the phase of the moon). To get more,
		4396	you need to wrap all I/O functions and provide your own fd management, but
		4397	the cost of calling select (O(n²)) will likely make this unworkable.
		4398
		4399	=back
		4400
		4401	=head2 PORTABILITY REQUIREMENTS
		4402
		4403	In addition to a working ISO-C implementation and of course the
		4404	backend-specific APIs, libev relies on a few additional extensions:
		4405
		4406	=over 4
		4407
		4408	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4409	calling conventions regardless of C<ev_watcher_type *>.
		4410
		4411	Libev assumes not only that all watcher pointers have the same internal
		4412	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4413	assumes that the same (machine) code can be used to call any watcher
		4414	callback: The watcher callbacks have different type signatures, but libev
		4415	calls them using an C<ev_watcher *> internally.
		4416
		4417	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4418
		4419	The type C<sig_atomic_t volatile> (or whatever is defined as
		4420	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4421	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4422	believed to be sufficiently portable.
		4423
		4424	=item C<sigprocmask> must work in a threaded environment
		4425
		4426	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4427	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4428	pthread implementations will either allow C<sigprocmask> in the "main
		4429	thread" or will block signals process-wide, both behaviours would
		4430	be compatible with libev. Interaction between C<sigprocmask> and
		4431	C<pthread_sigmask> could complicate things, however.
		4432
		4433	The most portable way to handle signals is to block signals in all threads
		4434	except the initial one, and run the default loop in the initial thread as
		4435	well.
		4436
		4437	=item C<long> must be large enough for common memory allocation sizes
		4438
		4439	To improve portability and simplify its API, libev uses C<long> internally
		4440	instead of C<size_t> when allocating its data structures. On non-POSIX
		4441	systems (Microsoft...) this might be unexpectedly low, but is still at
		4442	least 31 bits everywhere, which is enough for hundreds of millions of
		4443	watchers.
		4444
		4445	=item C<double> must hold a time value in seconds with enough accuracy
		4446
		4447	The type C<double> is used to represent timestamps. It is required to
		4448	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4449	enough for at least into the year 4000. This requirement is fulfilled by
		4450	implementations implementing IEEE 754, which is basically all existing
		4451	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4452	2200.
		4453
		4454	=back
		4455
		4456	If you know of other additional requirements drop me a note.
		4457
		4458
2584	=head1 COMPLEXITIES	4459	=head1 ALGORITHMIC COMPLEXITIES
2585		4460
2586	In this section the complexities of (many of) the algorithms used inside	4461	In this section the complexities of (many of) the algorithms used inside
2587	libev will be explained. For complexity discussions about backends see the	4462	libev will be documented. For complexity discussions about backends see
2588	documentation for C<ev_default_init>.	4463	the documentation for C<ev_default_init>.
2589		4464
2590	All of the following are about amortised time: If an array needs to be	4465	All of the following are about amortised time: If an array needs to be
2591	extended, libev needs to realloc and move the whole array, but this	4466	extended, libev needs to realloc and move the whole array, but this
2592	happens asymptotically never with higher number of elements, so O(1) might	4467	happens asymptotically rarer with higher number of elements, so O(1) might
2593	mean it might do a lengthy realloc operation in rare cases, but on average	4468	mean that libev does a lengthy realloc operation in rare cases, but on
2594	it is much faster and asymptotically approaches constant time.	4469	average it is much faster and asymptotically approaches constant time.
2595		4470
2596	=over 4	4471	=over 4
2597		4472
2598	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4473	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2599		4474
2600	This means that, when you have a watcher that triggers in one hour and	4475	This means that, when you have a watcher that triggers in one hour and
2601	there are 100 watchers that would trigger before that then inserting will	4476	there are 100 watchers that would trigger before that, then inserting will
2602	have to skip those 100 watchers.	4477	have to skip roughly seven (C<ld 100>) of these watchers.
2603		4478
2604	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4479	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2605		4480
2606	That means that for changing a timer costs less than removing/adding them	4481	That means that changing a timer costs less than removing/adding them,
2607	as only the relative motion in the event queue has to be paid for.	4482	as only the relative motion in the event queue has to be paid for.
2608		4483
2609	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4484	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2610		4485
2611	These just add the watcher into an array or at the head of a list.	4486	These just add the watcher into an array or at the head of a list.
		4487
2612	=item Stopping check/prepare/idle watchers: O(1)	4488	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2613		4489
2614	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4490	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2615		4491
2616	These watchers are stored in lists then need to be walked to find the	4492	These watchers are stored in lists, so they need to be walked to find the
2617	correct watcher to remove. The lists are usually short (you don't usually	4493	correct watcher to remove. The lists are usually short (you don't usually
2618	have many watchers waiting for the same fd or signal).	4494	have many watchers waiting for the same fd or signal: one is typical, two
		4495	is rare).
2619		4496
2620	=item Finding the next timer per loop iteration: O(1)	4497	=item Finding the next timer in each loop iteration: O(1)
		4498
		4499	By virtue of using a binary or 4-heap, the next timer is always found at a
		4500	fixed position in the storage array.
2621		4501
2622	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4502	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2623		4503
2624	A change means an I/O watcher gets started or stopped, which requires	4504	A change means an I/O watcher gets started or stopped, which requires
2625	libev to recalculate its status (and possibly tell the kernel).	4505	libev to recalculate its status (and possibly tell the kernel, depending
		4506	on backend and whether C<ev_io_set> was used).
2626		4507
2627	=item Activating one watcher: O(1)	4508	=item Activating one watcher (putting it into the pending state): O(1)
2628		4509
2629	=item Priority handling: O(number_of_priorities)	4510	=item Priority handling: O(number_of_priorities)
2630		4511
2631	Priorities are implemented by allocating some space for each	4512	Priorities are implemented by allocating some space for each
2632	priority. When doing priority-based operations, libev usually has to	4513	priority. When doing priority-based operations, libev usually has to
2633	linearly search all the priorities.	4514	linearly search all the priorities, but starting/stopping and activating
		4515	watchers becomes O(1) with respect to priority handling.
		4516
		4517	=item Sending an ev_async: O(1)
		4518
		4519	=item Processing ev_async_send: O(number_of_async_watchers)
		4520
		4521	=item Processing signals: O(max_signal_number)
		4522
		4523	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4524	calls in the current loop iteration. Checking for async and signal events
		4525	involves iterating over all running async watchers or all signal numbers.
2634		4526
2635	=back	4527	=back
2636		4528
2637		4529
		4530	=head1 GLOSSARY
		4531
		4532	=over 4
		4533
		4534	=item active
		4535
		4536	A watcher is active as long as it has been started (has been attached to
		4537	an event loop) but not yet stopped (disassociated from the event loop).
		4538
		4539	=item application
		4540
		4541	In this document, an application is whatever is using libev.
		4542
		4543	=item callback
		4544
		4545	The address of a function that is called when some event has been
		4546	detected. Callbacks are being passed the event loop, the watcher that
		4547	received the event, and the actual event bitset.
		4548
		4549	=item callback invocation
		4550
		4551	The act of calling the callback associated with a watcher.
		4552
		4553	=item event
		4554
		4555	A change of state of some external event, such as data now being available
		4556	for reading on a file descriptor, time having passed or simply not having
		4557	any other events happening anymore.
		4558
		4559	In libev, events are represented as single bits (such as C<EV_READ> or
		4560	C<EV_TIMEOUT>).
		4561
		4562	=item event library
		4563
		4564	A software package implementing an event model and loop.
		4565
		4566	=item event loop
		4567
		4568	An entity that handles and processes external events and converts them
		4569	into callback invocations.
		4570
		4571	=item event model
		4572
		4573	The model used to describe how an event loop handles and processes
		4574	watchers and events.
		4575
		4576	=item pending
		4577
		4578	A watcher is pending as soon as the corresponding event has been detected,
		4579	and stops being pending as soon as the watcher will be invoked or its
		4580	pending status is explicitly cleared by the application.
		4581
		4582	A watcher can be pending, but not active. Stopping a watcher also clears
		4583	its pending status.
		4584
		4585	=item real time
		4586
		4587	The physical time that is observed. It is apparently strictly monotonic :)
		4588
		4589	=item wall-clock time
		4590
		4591	The time and date as shown on clocks. Unlike real time, it can actually
		4592	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4593	clock.
		4594
		4595	=item watcher
		4596
		4597	A data structure that describes interest in certain events. Watchers need
		4598	to be started (attached to an event loop) before they can receive events.
		4599
		4600	=item watcher invocation
		4601
		4602	The act of calling the callback associated with a watcher.
		4603
		4604	=back
		4605
2638	=head1 AUTHOR	4606	=head1 AUTHOR
2639		4607
2640	Marc Lehmann <libev@schmorp.de>.	4608	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2641		4609

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