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Revision 1.136 by root, Thu Mar 13 13:06:16 2008 UTC vs.
Revision 1.238 by root, Sat Apr 18 12:10:41 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	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
28		30
29	// this causes all nested ev_loop's to stop iterating	31	// this causes all nested ev_loop's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	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);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
52		54
53	// initialise a timer watcher, then start it	55	// initialise a timer watcher, then start it
54	// simple non-repeating 5.5 second timeout	56	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
57		59
58	// now wait for events to arrive	60	// now wait for events to arrive
59	ev_loop (loop, 0);	61	ev_loop (loop, 0);
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	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
69	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
70		84
71	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
72	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
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
103	Libev is very configurable. In this manual the default (and most common)	117	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	118	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	119	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	120	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	121	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	123	this argument.
110		124
111	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
112		126
113	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floatingpoint value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
121		156
122	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
123		158
124	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
125	library in any way.	160	library in any way.
…		…
134		169
135	=item ev_sleep (ev_tstamp interval)	170	=item ev_sleep (ev_tstamp interval)
136		171
137	Sleep for the given interval: The current thread will be blocked until	172	Sleep for the given interval: The current thread will be blocked until
138	either it is interrupted or the given time interval has passed. Basically	173	either it is interrupted or the given time interval has passed. Basically
139	this is a subsecond-resolution C<sleep ()>.	174	this is a sub-second-resolution C<sleep ()>.
140		175
141	=item int ev_version_major ()	176	=item int ev_version_major ()
142		177
143	=item int ev_version_minor ()	178	=item int ev_version_minor ()
144		179
…		…
157	not a problem.	192	not a problem.
158		193
159	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	195	version.
161		196
162	assert (("libev version mismatch",	197	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
165		200
166	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
167		202
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	206	a description of the set values.
172		207
173	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
174	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
175		210
176	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
178		213
179	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
180		215
181	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
182	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
183	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
184	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
185	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
186	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
187		222
188	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
189		224
…		…
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
194	recommended ones.	229	recommended ones.
195		230
196	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
197		232
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
199		234
200	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
201	semantics is identical - to the realloc C function). It is used to	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	allocate and free memory (no surprises here). If it returns zero when	237	used to allocate and free memory (no surprises here). If it returns zero
203	memory needs to be allocated, the library might abort or take some	238	when memory needs to be allocated (C<size != 0>), the library might abort
204	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
205	function.	240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
206		244
207	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
208	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
209	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
210		248
211	Example: Replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
212	retries).	250	retries (example requires a standards-compliant C<realloc>).
213		251
214	static void *	252	static void *
215	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
216	{	254	{
217	for (;;)	255	for (;;)
…		…
226	}	264	}
227		265
228	...	266	...
229	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
230		268
231	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
232		270
233	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
234	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
235	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
236	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
237	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
238	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
239	(such as abort).	277	(such as abort).
240		278
241	Example: This is basically the same thing that libev does internally, too.	279	Example: This is basically the same thing that libev does internally, too.
…		…
252		290
253	=back	291	=back
254		292
255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
256		294
257	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
258	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
259	events, and dynamically created loops which do not.	297	I<function>).
260		298
261	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
262	in your main thread (or in a separate thread) and for each thread you	300	supports signals and child events, and dynamically created loops which do
263	create, you also create another event loop. Libev itself does no locking	301	not.
264	whatsoever, so if you mix calls to the same event loop in different
265	threads, make sure you lock (this is usually a bad idea, though, even if
266	done correctly, because it's hideous and inefficient).
267		302
268	=over 4	303	=over 4
269		304
270	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
271		306
…		…
275	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
276		311
277	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
278	function.	313	function.
279		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
280	The default loop is the only loop that can handle C<ev_signal> and	319	The default loop is the only loop that can handle C<ev_signal> and
281	C<ev_child> watchers, and to do this, it always registers a handler	320	C<ev_child> watchers, and to do this, it always registers a handler
282	for C<SIGCHLD>. If this is a problem for your app you can either	321	for C<SIGCHLD>. If this is a problem for your application you can either
283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
285	C<ev_default_init>.	324	C<ev_default_init>.
286		325
287	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
…		…
296	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	336	thing, believe me).
298		337
299	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
300		339
301	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
302	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
305	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
306	around bugs.	345	around bugs.
…		…
313		352
314	This works by calling C<getpid ()> on every iteration of the loop,	353	This works by calling C<getpid ()> on every iteration of the loop,
315	and thus this might slow down your event loop if you do a lot of loop	354	and thus this might slow down your event loop if you do a lot of loop
316	iterations and little real work, but is usually not noticeable (on my	355	iterations and little real work, but is usually not noticeable (on my
317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
318	without a syscall and thus I<very> fast, but my GNU/Linux system also has	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
319	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
320		359
321	The big advantage of this flag is that you can forget about fork (and	360	The big advantage of this flag is that you can forget about fork (and
322	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
323	flag.	362	flag.
324		363
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	365	environment variable.
327		366
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		368
330	This is your standard select(2) backend. Not I<completely> standard, as	369	This is your standard select(2) backend. Not I<completely> standard, as
…		…
332	but if that fails, expect a fairly low limit on the number of fds when	371	but if that fails, expect a fairly low limit on the number of fds when
333	using this backend. It doesn't scale too well (O(highest_fd)), but its	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
334	usually the fastest backend for a low number of (low-numbered :) fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
335		374
336	To get good performance out of this backend you need a high amount of	375	To get good performance out of this backend you need a high amount of
337	parallelity (most of the file descriptors should be busy). If you are	376	parallelism (most of the file descriptors should be busy). If you are
338	writing a server, you should C<accept ()> in a loop to accept as many	377	writing a server, you should C<accept ()> in a loop to accept as many
339	connections as possible during one iteration. You might also want to have	378	connections as possible during one iteration. You might also want to have
340	a look at C<ev_set_io_collect_interval ()> to increase the amount of	379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readyness notifications you get per iteration.	380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
342		385
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		387
345	And this is your standard poll(2) backend. It's more complicated	388	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	389	than select, but handles sparse fds better and has no artificial
347	limit on the number of fds you can use (except it will slow down	390	limit on the number of fds you can use (except it will slow down
348	considerably with a lot of inactive fds). It scales similarly to select,	391	considerably with a lot of inactive fds). It scales similarly to select,
349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	393	performance tips.
351		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		397
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
353		399
354	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
355	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
356	like O(total_fds) where n is the total number of fds (or the highest fd),	402	like O(total_fds) where n is the total number of fds (or the highest fd),
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	403	epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	404
359	cases and rewiring a syscall per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
361		421
362	While stopping, setting and starting an I/O watcher in the same iteration	422	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
364	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
367		427	file descriptors.
368	Please note that epoll sometimes generates spurious notifications, so you
369	need to use non-blocking I/O or other means to avoid blocking when no data
370	(or space) is available.
371		428
372	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
373	watchers for a file descriptor until it has been closed, if possible, i.e.	430	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
375		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
376	While nominally embeddeble in other event loops, this feature is broken in	441	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
378		446
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		448
381	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
382	was broken on all BSDs except NetBSD (usually it doesn't work reliably	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
383	with anything but sockets and pipes, except on Darwin, where of course	451	with anything but sockets and pipes, except on Darwin, where of course
384	it's completely useless). For this reason it's not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
385	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
387	system like NetBSD.	457	system like NetBSD.
388		458
389	You still can embed kqueue into a normal poll or select backend and use it	459	You still can embed kqueue into a normal poll or select backend and use it
390	only for sockets (after having made sure that sockets work with kqueue on	460	only for sockets (after having made sure that sockets work with kqueue on
391	the target platform). See C<ev_embed> watchers for more info.	461	the target platform). See C<ev_embed> watchers for more info.
392		462
393	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
394	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
395	course). While stopping, setting and starting an I/O watcher does never	465	course). While stopping, setting and starting an I/O watcher does never
396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
397	two event changes per incident, support for C<fork ()> is very bad and it	467	two event changes per incident. Support for C<fork ()> is very bad (but
398	drops fds silently in similarly hard-to-detect cases.	468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
399		470
400	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
401		472
402	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
403	everywhere, so you might need to test for this. And since it is broken	474	everywhere, so you might need to test for this. And since it is broken
404	almost everywhere, you should only use it when you have a lot of sockets	475	almost everywhere, you should only use it when you have a lot of sockets
405	(for which it usually works), by embedding it into another event loop	476	(for which it usually works), by embedding it into another event loop
406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
408		483
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		485
411	This is not implemented yet (and might never be, unless you send me an	486	This is not implemented yet (and might never be, unless you send me an
412	implementation). According to reports, C</dev/poll> only supports sockets	487	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		492
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
419	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
420		495
421	Please note that solaris event ports can deliver a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
422	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
423	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
424		499
425	While this backend scales well, it requires one system call per active	500	While this backend scales well, it requires one system call per active
426	file descriptor per loop iteration. For small and medium numbers of file	501	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	503	might perform better.
429		504
430	On the positive side, ignoring the spurious readyness notifications, this	505	On the positive side, with the exception of the spurious readiness
431	backend actually performed to specification in all tests and is fully	506	notifications, this backend actually performed fully to specification
432	embeddable, which is a rare feat among the OS-specific backends.	507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
433		512
434	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
435		514
436	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
439		518
440	It is definitely not recommended to use this flag.	519	It is definitely not recommended to use this flag.
441		520
442	=back	521	=back
443		522
444	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
445	backends will be tried (in the reverse order as listed here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
446	specified, all backends in C<ev_recommended_backends ()> will be tried.	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
447		526
448	The most typical usage is like this:	527	Example: This is the most typical usage.
449		528
450	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
452		531
453	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
454	environment settings to be taken into account:	533	environment settings to be taken into account:
455		534
456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
457		536
458	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
459	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
460	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
461		541
462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
463		543
464	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
465		545
466	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
468	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
469	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
470		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
471	Example: Try to create a event loop that uses epoll and nothing else.	555	Example: Try to create a event loop that uses epoll and nothing else.
472		556
473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
474	if (!epoller)	558	if (!epoller)
475	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
476		560
477	=item ev_default_destroy ()	561	=item ev_default_destroy ()
478		562
479	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
480	etc.). None of the active event watchers will be stopped in the normal	564	etc.). None of the active event watchers will be stopped in the normal
481	sense, so e.g. C<ev_is_active> might still return true. It is your	565	sense, so e.g. C<ev_is_active> might still return true. It is your
482	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
483	calling this function, or cope with the fact afterwards (which is usually	567	calling this function, or cope with the fact afterwards (which is usually
484	the easiest thing, you can just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
485	for example).	569	for example).
486		570
487	Note that certain global state, such as signal state, will not be freed by	571	Note that certain global state, such as signal state (and installed signal
488	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
489	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
490		574
491	In general it is not advisable to call this function except in the	575	In general it is not advisable to call this function except in the
492	rare occasion where you really need to free e.g. the signal handling	576	rare occasion where you really need to free e.g. the signal handling
493	pipe fds. If you need dynamically allocated loops it is better to use	577	pipe fds. If you need dynamically allocated loops it is better to use
494	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
519		603
520	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
521		605
522	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
523	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
524	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
525		610
526	=item int ev_is_default_loop (loop)	611	=item int ev_is_default_loop (loop)
527		612
528	Returns true when the given loop actually is the default loop, false otherwise.	613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
529		615
530	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
531		617
532	Returns the count of loop iterations for the loop, which is identical to	618	Returns the count of loop iterations for the loop, which is identical to
533	the number of times libev did poll for new events. It starts at C<0> and	619	the number of times libev did poll for new events. It starts at C<0> and
…		…
548	received events and started processing them. This timestamp does not	634	received events and started processing them. This timestamp does not
549	change as long as callbacks are being processed, and this is also the base	635	change as long as callbacks are being processed, and this is also the base
550	time used for relative timers. You can treat it as the timestamp of the	636	time used for relative timers. You can treat it as the timestamp of the
551	event occurring (or more correctly, libev finding out about it).	637	event occurring (or more correctly, libev finding out about it).
552		638
		639	=item ev_now_update (loop)
		640
		641	Establishes the current time by querying the kernel, updating the time
		642	returned by C<ev_now ()> in the progress. This is a costly operation and
		643	is usually done automatically within C<ev_loop ()>.
		644
		645	This function is rarely useful, but when some event callback runs for a
		646	very long time without entering the event loop, updating libev's idea of
		647	the current time is a good idea.
		648
		649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
		676
553	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
554		678
555	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
556	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
557	events.	681	events.
…		…
559	If the flags argument is specified as C<0>, it will not return until	683	If the flags argument is specified as C<0>, it will not return until
560	either no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
561		685
562	Please note that an explicit C<ev_unloop> is usually better than	686	Please note that an explicit C<ev_unloop> is usually better than
563	relying on all watchers to be stopped when deciding when a program has	687	relying on all watchers to be stopped when deciding when a program has
564	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
565	automatically loops as long as it has to and no longer by virtue of	689	that automatically loops as long as it has to and no longer by virtue
566	relying on its watchers stopping correctly is a thing of beauty.	690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
567		692
568	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
569	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
570	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
571		697
572	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
573	neccessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
574	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
575	one iteration of the loop. This is useful if you are waiting for some	701	be an event internal to libev itself, so there is no guarantee that a
576	external event in conjunction with something not expressible using other	702	user-registered callback will be called), and will return after one
		703	iteration of the loop.
		704
		705	This is useful if you are waiting for some external event in conjunction
		706	with something not expressible using other libev watchers (i.e. "roll your
577	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
578	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
579		709
580	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
581		711
582	- Before the first iteration, call any pending watchers.	712	- Before the first iteration, call any pending watchers.
583	* If EVFLAG_FORKCHECK was used, check for a fork.	713	* If EVFLAG_FORKCHECK was used, check for a fork.
584	- If a fork was detected, queue and call all fork watchers.	714	- If a fork was detected (by any means), queue and call all fork watchers.
585	- Queue and call all prepare watchers.	715	- Queue and call all prepare watchers.
586	- If we have been forked, recreate the kernel state.	716	- If we have been forked, detach and recreate the kernel state
		717	as to not disturb the other process.
587	- Update the kernel state with all outstanding changes.	718	- Update the kernel state with all outstanding changes.
588	- Update the "event loop time".	719	- Update the "event loop time" (ev_now ()).
589	- Calculate for how long to sleep or block, if at all	720	- Calculate for how long to sleep or block, if at all
590	(active idle watchers, EVLOOP_NONBLOCK or not having	721	(active idle watchers, EVLOOP_NONBLOCK or not having
591	any active watchers at all will result in not sleeping).	722	any active watchers at all will result in not sleeping).
592	- Sleep if the I/O and timer collect interval say so.	723	- Sleep if the I/O and timer collect interval say so.
593	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
594	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
595	- Update the "event loop time" and do time jump handling.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
596	- Queue all outstanding timers.	727	- Queue all expired timers.
597	- Queue all outstanding periodics.	728	- Queue all expired periodics.
598	- If no events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
599	- Queue all check watchers.	730	- Queue all check watchers.
600	- Call all queued watchers in reverse order (i.e. check watchers first).	731	- Call all queued watchers in reverse order (i.e. check watchers first).
601	Signals and child watchers are implemented as I/O watchers, and will	732	Signals and child watchers are implemented as I/O watchers, and will
602	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
603	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	734	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
608	anymore.	739	anymore.
609		740
610	... queue jobs here, make sure they register event watchers as long	741	... queue jobs here, make sure they register event watchers as long
611	... as they still have work to do (even an idle watcher will do..)	742	... as they still have work to do (even an idle watcher will do..)
612	ev_loop (my_loop, 0);	743	ev_loop (my_loop, 0);
613	... jobs done. yeah!	744	... jobs done or somebody called unloop. yeah!
614		745
615	=item ev_unloop (loop, how)	746	=item ev_unloop (loop, how)
616		747
617	Can be used to make a call to C<ev_loop> return early (but only after it	748	Can be used to make a call to C<ev_loop> return early (but only after it
618	has processed all outstanding events). The C<how> argument must be either	749	has processed all outstanding events). The C<how> argument must be either
619	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
620	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
621		752
622	This "unloop state" will be cleared when entering C<ev_loop> again.	753	This "unloop state" will be cleared when entering C<ev_loop> again.
623		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
624	=item ev_ref (loop)	757	=item ev_ref (loop)
625		758
626	=item ev_unref (loop)	759	=item ev_unref (loop)
627		760
628	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
629	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
630	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
631	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
632	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
633	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
634	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
635	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
636	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
637	libraries. Just remember to I<unref after start> and I<ref before stop>	773	third-party libraries. Just remember to I<unref after start> and I<ref
638	(but only if the watcher wasn't active before, or was active before,	774	before stop> (but only if the watcher wasn't active before, or was active
639	respectively).	775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
640		778
641	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
642	running when nothing else is active.	780	running when nothing else is active.
643		781
644	struct ev_signal exitsig;	782	ev_signal exitsig;
645	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
646	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
647	evf_unref (loop);	785	evf_unref (loop);
648		786
649	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
650		788
651	ev_ref (loop);	789	ev_ref (loop);
652	ev_signal_stop (loop, &exitsig);	790	ev_signal_stop (loop, &exitsig);
653		791
654	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	792	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
655		793
656	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	794	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
657		795
658	These advanced functions influence the time that libev will spend waiting	796	These advanced functions influence the time that libev will spend waiting
659	for events. Both are by default C<0>, meaning that libev will try to	797	for events. Both time intervals are by default C<0>, meaning that libev
660	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	798	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		799	latency.
661		800
662	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
663	allows libev to delay invocation of I/O and timer/periodic callbacks to	802	allows libev to delay invocation of I/O and timer/periodic callbacks
664	increase efficiency of loop iterations.	803	to increase efficiency of loop iterations (or to increase power-saving
		804	opportunities).
665		805
666	The background is that sometimes your program runs just fast enough to	806	The idea is that sometimes your program runs just fast enough to handle
667	handle one (or very few) event(s) per loop iteration. While this makes	807	one (or very few) event(s) per loop iteration. While this makes the
668	the program responsive, it also wastes a lot of CPU time to poll for new	808	program responsive, it also wastes a lot of CPU time to poll for new
669	events, especially with backends like C<select ()> which have a high	809	events, especially with backends like C<select ()> which have a high
670	overhead for the actual polling but can deliver many events at once.	810	overhead for the actual polling but can deliver many events at once.
671		811
672	By setting a higher I<io collect interval> you allow libev to spend more	812	By setting a higher I<io collect interval> you allow libev to spend more
673	time collecting I/O events, so you can handle more events per iteration,	813	time collecting I/O events, so you can handle more events per iteration,
…		…
675	C<ev_timer>) will be not affected. Setting this to a non-null value will	815	C<ev_timer>) will be not affected. Setting this to a non-null value will
676	introduce an additional C<ev_sleep ()> call into most loop iterations.	816	introduce an additional C<ev_sleep ()> call into most loop iterations.
677		817
678	Likewise, by setting a higher I<timeout collect interval> you allow libev	818	Likewise, by setting a higher I<timeout collect interval> you allow libev
679	to spend more time collecting timeouts, at the expense of increased	819	to spend more time collecting timeouts, at the expense of increased
680	latency (the watcher callback will be called later). C<ev_io> watchers	820	latency/jitter/inexactness (the watcher callback will be called
681	will not be affected. Setting this to a non-null value will not introduce	821	later). C<ev_io> watchers will not be affected. Setting this to a non-null
682	any overhead in libev.	822	value will not introduce any overhead in libev.
683		823
684	Many (busy) programs can usually benefit by setting the io collect	824	Many (busy) programs can usually benefit by setting the I/O collect
685	interval to a value near C<0.1> or so, which is often enough for	825	interval to a value near C<0.1> or so, which is often enough for
686	interactive servers (of course not for games), likewise for timeouts. It	826	interactive servers (of course not for games), likewise for timeouts. It
687	usually doesn't make much sense to set it to a lower value than C<0.01>,	827	usually doesn't make much sense to set it to a lower value than C<0.01>,
688	as this approsaches the timing granularity of most systems.	828	as this approaches the timing granularity of most systems.
		829
		830	Setting the I<timeout collect interval> can improve the opportunity for
		831	saving power, as the program will "bundle" timer callback invocations that
		832	are "near" in time together, by delaying some, thus reducing the number of
		833	times the process sleeps and wakes up again. Another useful technique to
		834	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		835	they fire on, say, one-second boundaries only.
		836
		837	=item ev_loop_verify (loop)
		838
		839	This function only does something when C<EV_VERIFY> support has been
		840	compiled in, which is the default for non-minimal builds. It tries to go
		841	through all internal structures and checks them for validity. If anything
		842	is found to be inconsistent, it will print an error message to standard
		843	error and call C<abort ()>.
		844
		845	This can be used to catch bugs inside libev itself: under normal
		846	circumstances, this function will never abort as of course libev keeps its
		847	data structures consistent.
689		848
690	=back	849	=back
691		850
692		851
693	=head1 ANATOMY OF A WATCHER	852	=head1 ANATOMY OF A WATCHER
		853
		854	In the following description, uppercase C<TYPE> in names stands for the
		855	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		856	watchers and C<ev_io_start> for I/O watchers.
694		857
695	A watcher is a structure that you create and register to record your	858	A watcher is a structure that you create and register to record your
696	interest in some event. For instance, if you want to wait for STDIN to	859	interest in some event. For instance, if you want to wait for STDIN to
697	become readable, you would create an C<ev_io> watcher for that:	860	become readable, you would create an C<ev_io> watcher for that:
698		861
699	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	862	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
700	{	863	{
701	ev_io_stop (w);	864	ev_io_stop (w);
702	ev_unloop (loop, EVUNLOOP_ALL);	865	ev_unloop (loop, EVUNLOOP_ALL);
703	}	866	}
704		867
705	struct ev_loop *loop = ev_default_loop (0);	868	struct ev_loop *loop = ev_default_loop (0);
		869
706	struct ev_io stdin_watcher;	870	ev_io stdin_watcher;
		871
707	ev_init (&stdin_watcher, my_cb);	872	ev_init (&stdin_watcher, my_cb);
708	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	873	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
709	ev_io_start (loop, &stdin_watcher);	874	ev_io_start (loop, &stdin_watcher);
		875
710	ev_loop (loop, 0);	876	ev_loop (loop, 0);
711		877
712	As you can see, you are responsible for allocating the memory for your	878	As you can see, you are responsible for allocating the memory for your
713	watcher structures (and it is usually a bad idea to do this on the stack,	879	watcher structures (and it is I<usually> a bad idea to do this on the
714	although this can sometimes be quite valid).	880	stack).
		881
		882	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		883	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
715		884
716	Each watcher structure must be initialised by a call to C<ev_init	885	Each watcher structure must be initialised by a call to C<ev_init
717	(watcher *, callback)>, which expects a callback to be provided. This	886	(watcher *, callback)>, which expects a callback to be provided. This
718	callback gets invoked each time the event occurs (or, in the case of io	887	callback gets invoked each time the event occurs (or, in the case of I/O
719	watchers, each time the event loop detects that the file descriptor given	888	watchers, each time the event loop detects that the file descriptor given
720	is readable and/or writable).	889	is readable and/or writable).
721		890
722	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	891	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
723	with arguments specific to this watcher type. There is also a macro	892	macro to configure it, with arguments specific to the watcher type. There
724	to combine initialisation and setting in one call: C<< ev_<type>_init	893	is also a macro to combine initialisation and setting in one call: C<<
725	(watcher *, callback, ...) >>.	894	ev_TYPE_init (watcher *, callback, ...) >>.
726		895
727	To make the watcher actually watch out for events, you have to start it	896	To make the watcher actually watch out for events, you have to start it
728	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	897	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
729	*) >>), and you can stop watching for events at any time by calling the	898	*) >>), and you can stop watching for events at any time by calling the
730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	899	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
731		900
732	As long as your watcher is active (has been started but not stopped) you	901	As long as your watcher is active (has been started but not stopped) you
733	must not touch the values stored in it. Most specifically you must never	902	must not touch the values stored in it. Most specifically you must never
734	reinitialise it or call its C<set> macro.	903	reinitialise it or call its C<ev_TYPE_set> macro.
735		904
736	Each and every callback receives the event loop pointer as first, the	905	Each and every callback receives the event loop pointer as first, the
737	registered watcher structure as second, and a bitset of received events as	906	registered watcher structure as second, and a bitset of received events as
738	third argument.	907	third argument.
739		908
…		…
797		966
798	=item C<EV_ASYNC>	967	=item C<EV_ASYNC>
799		968
800	The given async watcher has been asynchronously notified (see C<ev_async>).	969	The given async watcher has been asynchronously notified (see C<ev_async>).
801		970
		971	=item C<EV_CUSTOM>
		972
		973	Not ever sent (or otherwise used) by libev itself, but can be freely used
		974	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		975
802	=item C<EV_ERROR>	976	=item C<EV_ERROR>
803		977
804	An unspecified error has occured, the watcher has been stopped. This might	978	An unspecified error has occurred, the watcher has been stopped. This might
805	happen because the watcher could not be properly started because libev	979	happen because the watcher could not be properly started because libev
806	ran out of memory, a file descriptor was found to be closed or any other	980	ran out of memory, a file descriptor was found to be closed or any other
		981	problem. Libev considers these application bugs.
		982
807	problem. You best act on it by reporting the problem and somehow coping	983	You best act on it by reporting the problem and somehow coping with the
808	with the watcher being stopped.	984	watcher being stopped. Note that well-written programs should not receive
		985	an error ever, so when your watcher receives it, this usually indicates a
		986	bug in your program.
809		987
810	Libev will usually signal a few "dummy" events together with an error,	988	Libev will usually signal a few "dummy" events together with an error, for
811	for example it might indicate that a fd is readable or writable, and if	989	example it might indicate that a fd is readable or writable, and if your
812	your callbacks is well-written it can just attempt the operation and cope	990	callbacks is well-written it can just attempt the operation and cope with
813	with the error from read() or write(). This will not work in multithreaded	991	the error from read() or write(). This will not work in multi-threaded
814	programs, though, so beware.	992	programs, though, as the fd could already be closed and reused for another
		993	thing, so beware.
815		994
816	=back	995	=back
817		996
818	=head2 GENERIC WATCHER FUNCTIONS	997	=head2 GENERIC WATCHER FUNCTIONS
819
820	In the following description, C<TYPE> stands for the watcher type,
821	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
822		998
823	=over 4	999	=over 4
824		1000
825	=item C<ev_init> (ev_TYPE *watcher, callback)	1001	=item C<ev_init> (ev_TYPE *watcher, callback)
826		1002
…		…
832	which rolls both calls into one.	1008	which rolls both calls into one.
833		1009
834	You can reinitialise a watcher at any time as long as it has been stopped	1010	You can reinitialise a watcher at any time as long as it has been stopped
835	(or never started) and there are no pending events outstanding.	1011	(or never started) and there are no pending events outstanding.
836		1012
837	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1013	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
838	int revents)>.	1014	int revents)>.
		1015
		1016	Example: Initialise an C<ev_io> watcher in two steps.
		1017
		1018	ev_io w;
		1019	ev_init (&w, my_cb);
		1020	ev_io_set (&w, STDIN_FILENO, EV_READ);
839		1021
840	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1022	=item C<ev_TYPE_set> (ev_TYPE *, [args])
841		1023
842	This macro initialises the type-specific parts of a watcher. You need to	1024	This macro initialises the type-specific parts of a watcher. You need to
843	call C<ev_init> at least once before you call this macro, but you can	1025	call C<ev_init> at least once before you call this macro, but you can
…		…
846	difference to the C<ev_init> macro).	1028	difference to the C<ev_init> macro).
847		1029
848	Although some watcher types do not have type-specific arguments	1030	Although some watcher types do not have type-specific arguments
849	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1031	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
850		1032
		1033	See C<ev_init>, above, for an example.
		1034
851	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1035	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
852		1036
853	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1037	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
854	calls into a single call. This is the most convinient method to initialise	1038	calls into a single call. This is the most convenient method to initialise
855	a watcher. The same limitations apply, of course.	1039	a watcher. The same limitations apply, of course.
		1040
		1041	Example: Initialise and set an C<ev_io> watcher in one step.
		1042
		1043	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
856		1044
857	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1045	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
858		1046
859	Starts (activates) the given watcher. Only active watchers will receive	1047	Starts (activates) the given watcher. Only active watchers will receive
860	events. If the watcher is already active nothing will happen.	1048	events. If the watcher is already active nothing will happen.
861		1049
		1050	Example: Start the C<ev_io> watcher that is being abused as example in this
		1051	whole section.
		1052
		1053	ev_io_start (EV_DEFAULT_UC, &w);
		1054
862	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1055	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
863		1056
864	Stops the given watcher again (if active) and clears the pending	1057	Stops the given watcher if active, and clears the pending status (whether
		1058	the watcher was active or not).
		1059
865	status. It is possible that stopped watchers are pending (for example,	1060	It is possible that stopped watchers are pending - for example,
866	non-repeating timers are being stopped when they become pending), but	1061	non-repeating timers are being stopped when they become pending - but
867	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1062	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
868	you want to free or reuse the memory used by the watcher it is therefore a	1063	pending. If you want to free or reuse the memory used by the watcher it is
869	good idea to always call its C<ev_TYPE_stop> function.	1064	therefore a good idea to always call its C<ev_TYPE_stop> function.
870		1065
871	=item bool ev_is_active (ev_TYPE *watcher)	1066	=item bool ev_is_active (ev_TYPE *watcher)
872		1067
873	Returns a true value iff the watcher is active (i.e. it has been started	1068	Returns a true value iff the watcher is active (i.e. it has been started
874	and not yet been stopped). As long as a watcher is active you must not modify	1069	and not yet been stopped). As long as a watcher is active you must not modify
…		…
900	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1095	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
901	(default: C<-2>). Pending watchers with higher priority will be invoked	1096	(default: C<-2>). Pending watchers with higher priority will be invoked
902	before watchers with lower priority, but priority will not keep watchers	1097	before watchers with lower priority, but priority will not keep watchers
903	from being executed (except for C<ev_idle> watchers).	1098	from being executed (except for C<ev_idle> watchers).
904		1099
905	This means that priorities are I<only> used for ordering callback
906	invocation after new events have been received. This is useful, for
907	example, to reduce latency after idling, or more often, to bind two
908	watchers on the same event and make sure one is called first.
909
910	If you need to suppress invocation when higher priority events are pending	1100	If you need to suppress invocation when higher priority events are pending
911	you need to look at C<ev_idle> watchers, which provide this functionality.	1101	you need to look at C<ev_idle> watchers, which provide this functionality.
912		1102
913	You I<must not> change the priority of a watcher as long as it is active or	1103	You I<must not> change the priority of a watcher as long as it is active or
914	pending.	1104	pending.
915		1105
		1106	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1107	fine, as long as you do not mind that the priority value you query might
		1108	or might not have been clamped to the valid range.
		1109
916	The default priority used by watchers when no priority has been set is	1110	The default priority used by watchers when no priority has been set is
917	always C<0>, which is supposed to not be too high and not be too low :).	1111	always C<0>, which is supposed to not be too high and not be too low :).
918		1112
919	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
920	fine, as long as you do not mind that the priority value you query might	1114	priorities.
921	or might not have been adjusted to be within valid range.
922		1115
923	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
924		1117
925	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1118	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
926	C<loop> nor C<revents> need to be valid as long as the watcher callback	1119	C<loop> nor C<revents> need to be valid as long as the watcher callback
927	can deal with that fact.	1120	can deal with that fact, as both are simply passed through to the
		1121	callback.
928		1122
929	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1123	=item int ev_clear_pending (loop, ev_TYPE *watcher)
930		1124
931	If the watcher is pending, this function returns clears its pending status	1125	If the watcher is pending, this function clears its pending status and
932	and returns its C<revents> bitset (as if its callback was invoked). If the	1126	returns its C<revents> bitset (as if its callback was invoked). If the
933	watcher isn't pending it does nothing and returns C<0>.	1127	watcher isn't pending it does nothing and returns C<0>.
934		1128
		1129	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1130	callback to be invoked, which can be accomplished with this function.
		1131
935	=back	1132	=back
936		1133
937		1134
938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1135	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
939		1136
940	Each watcher has, by default, a member C<void *data> that you can change	1137	Each watcher has, by default, a member C<void *data> that you can change
941	and read at any time, libev will completely ignore it. This can be used	1138	and read at any time: libev will completely ignore it. This can be used
942	to associate arbitrary data with your watcher. If you need more data and	1139	to associate arbitrary data with your watcher. If you need more data and
943	don't want to allocate memory and store a pointer to it in that data	1140	don't want to allocate memory and store a pointer to it in that data
944	member, you can also "subclass" the watcher type and provide your own	1141	member, you can also "subclass" the watcher type and provide your own
945	data:	1142	data:
946		1143
947	struct my_io	1144	struct my_io
948	{	1145	{
949	struct ev_io io;	1146	ev_io io;
950	int otherfd;	1147	int otherfd;
951	void *somedata;	1148	void *somedata;
952	struct whatever *mostinteresting;	1149	struct whatever *mostinteresting;
953	}	1150	};
		1151
		1152	...
		1153	struct my_io w;
		1154	ev_io_init (&w.io, my_cb, fd, EV_READ);
954		1155
955	And since your callback will be called with a pointer to the watcher, you	1156	And since your callback will be called with a pointer to the watcher, you
956	can cast it back to your own type:	1157	can cast it back to your own type:
957		1158
958	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
959	{	1160	{
960	struct my_io *w = (struct my_io *)w_;	1161	struct my_io *w = (struct my_io *)w_;
961	...	1162	...
962	}	1163	}
963		1164
964	More interesting and less C-conformant ways of casting your callback type	1165	More interesting and less C-conformant ways of casting your callback type
965	instead have been omitted.	1166	instead have been omitted.
966		1167
967	Another common scenario is having some data structure with multiple	1168	Another common scenario is to use some data structure with multiple
968	watchers:	1169	embedded watchers:
969		1170
970	struct my_biggy	1171	struct my_biggy
971	{	1172	{
972	int some_data;	1173	int some_data;
973	ev_timer t1;	1174	ev_timer t1;
974	ev_timer t2;	1175	ev_timer t2;
975	}	1176	}
976		1177
977	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1178	In this case getting the pointer to C<my_biggy> is a bit more
978	you need to use C<offsetof>:	1179	complicated: Either you store the address of your C<my_biggy> struct
		1180	in the C<data> member of the watcher (for woozies), or you need to use
		1181	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1182	programmers):
979		1183
980	#include <stddef.h>	1184	#include <stddef.h>
981		1185
982	static void	1186	static void
983	t1_cb (EV_P_ struct ev_timer *w, int revents)	1187	t1_cb (EV_P_ ev_timer *w, int revents)
984	{	1188	{
985	struct my_biggy big = (struct my_biggy *	1189	struct my_biggy big = (struct my_biggy *
986	(((char *)w) - offsetof (struct my_biggy, t1));	1190	(((char *)w) - offsetof (struct my_biggy, t1));
987	}	1191	}
988		1192
989	static void	1193	static void
990	t2_cb (EV_P_ struct ev_timer *w, int revents)	1194	t2_cb (EV_P_ ev_timer *w, int revents)
991	{	1195	{
992	struct my_biggy big = (struct my_biggy *	1196	struct my_biggy big = (struct my_biggy *
993	(((char *)w) - offsetof (struct my_biggy, t2));	1197	(((char *)w) - offsetof (struct my_biggy, t2));
994	}	1198	}
		1199
		1200	=head2 WATCHER PRIORITY MODELS
		1201
		1202	Many event loops support I<watcher priorities>, which are usually small
		1203	integers that influence the ordering of event callback invocation
		1204	between watchers in some way, all else being equal.
		1205
		1206	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1207	description for the more technical details such as the actual priority
		1208	range.
		1209
		1210	There are two common ways how these these priorities are being interpreted
		1211	by event loops:
		1212
		1213	In the more common lock-out model, higher priorities "lock out" invocation
		1214	of lower priority watchers, which means as long as higher priority
		1215	watchers receive events, lower priority watchers are not being invoked.
		1216
		1217	The less common only-for-ordering model uses priorities solely to order
		1218	callback invocation within a single event loop iteration: Higher priority
		1219	watchers are invoked before lower priority ones, but they all get invoked
		1220	before polling for new events.
		1221
		1222	Libev uses the second (only-for-ordering) model for all its watchers
		1223	except for idle watchers (which use the lock-out model).
		1224
		1225	The rationale behind this is that implementing the lock-out model for
		1226	watchers is not well supported by most kernel interfaces, and most event
		1227	libraries will just poll for the same events again and again as long as
		1228	their callbacks have not been executed, which is very inefficient in the
		1229	common case of one high-priority watcher locking out a mass of lower
		1230	priority ones.
		1231
		1232	Static (ordering) priorities are most useful when you have two or more
		1233	watchers handling the same resource: a typical usage example is having an
		1234	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1235	timeouts. Under load, data might be received while the program handles
		1236	other jobs, but since timers normally get invoked first, the timeout
		1237	handler will be executed before checking for data. In that case, giving
		1238	the timer a lower priority than the I/O watcher ensures that I/O will be
		1239	handled first even under adverse conditions (which is usually, but not
		1240	always, what you want).
		1241
		1242	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1243	will only be executed when no same or higher priority watchers have
		1244	received events, they can be used to implement the "lock-out" model when
		1245	required.
		1246
		1247	For example, to emulate how many other event libraries handle priorities,
		1248	you can associate an C<ev_idle> watcher to each such watcher, and in
		1249	the normal watcher callback, you just start the idle watcher. The real
		1250	processing is done in the idle watcher callback. This causes libev to
		1251	continously poll and process kernel event data for the watcher, but when
		1252	the lock-out case is known to be rare (which in turn is rare :), this is
		1253	workable.
		1254
		1255	Usually, however, the lock-out model implemented that way will perform
		1256	miserably under the type of load it was designed to handle. In that case,
		1257	it might be preferable to stop the real watcher before starting the
		1258	idle watcher, so the kernel will not have to process the event in case
		1259	the actual processing will be delayed for considerable time.
		1260
		1261	Here is an example of an I/O watcher that should run at a strictly lower
		1262	priority than the default, and which should only process data when no
		1263	other events are pending:
		1264
		1265	ev_idle idle; // actual processing watcher
		1266	ev_io io; // actual event watcher
		1267
		1268	static void
		1269	io_cb (EV_P_ ev_io *w, int revents)
		1270	{
		1271	// stop the I/O watcher, we received the event, but
		1272	// are not yet ready to handle it.
		1273	ev_io_stop (EV_A_ w);
		1274
		1275	// start the idle watcher to ahndle the actual event.
		1276	// it will not be executed as long as other watchers
		1277	// with the default priority are receiving events.
		1278	ev_idle_start (EV_A_ &idle);
		1279	}
		1280
		1281	static void
		1282	idle-cb (EV_P_ ev_idle *w, int revents)
		1283	{
		1284	// actual processing
		1285	read (STDIN_FILENO, ...);
		1286
		1287	// have to start the I/O watcher again, as
		1288	// we have handled the event
		1289	ev_io_start (EV_P_ &io);
		1290	}
		1291
		1292	// initialisation
		1293	ev_idle_init (&idle, idle_cb);
		1294	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1295	ev_io_start (EV_DEFAULT_ &io);
		1296
		1297	In the "real" world, it might also be beneficial to start a timer, so that
		1298	low-priority connections can not be locked out forever under load. This
		1299	enables your program to keep a lower latency for important connections
		1300	during short periods of high load, while not completely locking out less
		1301	important ones.
995		1302
996		1303
997	=head1 WATCHER TYPES	1304	=head1 WATCHER TYPES
998		1305
999	This section describes each watcher in detail, but will not repeat	1306	This section describes each watcher in detail, but will not repeat
…		…
1023	In general you can register as many read and/or write event watchers per	1330	In general you can register as many read and/or write event watchers per
1024	fd as you want (as long as you don't confuse yourself). Setting all file	1331	fd as you want (as long as you don't confuse yourself). Setting all file
1025	descriptors to non-blocking mode is also usually a good idea (but not	1332	descriptors to non-blocking mode is also usually a good idea (but not
1026	required if you know what you are doing).	1333	required if you know what you are doing).
1027		1334
1028	If you must do this, then force the use of a known-to-be-good backend	1335	If you cannot use non-blocking mode, then force the use of a
1029	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1336	known-to-be-good backend (at the time of this writing, this includes only
1030	C<EVBACKEND_POLL>).	1337	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1031		1338
1032	Another thing you have to watch out for is that it is quite easy to	1339	Another thing you have to watch out for is that it is quite easy to
1033	receive "spurious" readyness notifications, that is your callback might	1340	receive "spurious" readiness notifications, that is your callback might
1034	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1341	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1035	because there is no data. Not only are some backends known to create a	1342	because there is no data. Not only are some backends known to create a
1036	lot of those (for example solaris ports), it is very easy to get into	1343	lot of those (for example Solaris ports), it is very easy to get into
1037	this situation even with a relatively standard program structure. Thus	1344	this situation even with a relatively standard program structure. Thus
1038	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1345	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1039	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1346	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1040		1347
1041	If you cannot run the fd in non-blocking mode (for example you should not	1348	If you cannot run the fd in non-blocking mode (for example you should
1042	play around with an Xlib connection), then you have to seperately re-test	1349	not play around with an Xlib connection), then you have to separately
1043	whether a file descriptor is really ready with a known-to-be good interface	1350	re-test whether a file descriptor is really ready with a known-to-be good
1044	such as poll (fortunately in our Xlib example, Xlib already does this on	1351	interface such as poll (fortunately in our Xlib example, Xlib already
1045	its own, so its quite safe to use).	1352	does this on its own, so its quite safe to use). Some people additionally
		1353	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1354	indefinitely.
		1355
		1356	But really, best use non-blocking mode.
1046		1357
1047	=head3 The special problem of disappearing file descriptors	1358	=head3 The special problem of disappearing file descriptors
1048		1359
1049	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1360	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1050	descriptor (either by calling C<close> explicitly or by any other means,	1361	descriptor (either due to calling C<close> explicitly or any other means,
1051	such as C<dup>). The reason is that you register interest in some file	1362	such as C<dup2>). The reason is that you register interest in some file
1052	descriptor, but when it goes away, the operating system will silently drop	1363	descriptor, but when it goes away, the operating system will silently drop
1053	this interest. If another file descriptor with the same number then is	1364	this interest. If another file descriptor with the same number then is
1054	registered with libev, there is no efficient way to see that this is, in	1365	registered with libev, there is no efficient way to see that this is, in
1055	fact, a different file descriptor.	1366	fact, a different file descriptor.
1056		1367
…		…
1085	To support fork in your programs, you either have to call	1396	To support fork in your programs, you either have to call
1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1397	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1398	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1088	C<EVBACKEND_POLL>.	1399	C<EVBACKEND_POLL>.
1089		1400
		1401	=head3 The special problem of SIGPIPE
		1402
		1403	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1404	when writing to a pipe whose other end has been closed, your program gets
		1405	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1406	this is sensible behaviour, for daemons, this is usually undesirable.
		1407
		1408	So when you encounter spurious, unexplained daemon exits, make sure you
		1409	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1410	somewhere, as that would have given you a big clue).
		1411
1090		1412
1091	=head3 Watcher-Specific Functions	1413	=head3 Watcher-Specific Functions
1092		1414
1093	=over 4	1415	=over 4
1094		1416
1095	=item ev_io_init (ev_io *, callback, int fd, int events)	1417	=item ev_io_init (ev_io *, callback, int fd, int events)
1096		1418
1097	=item ev_io_set (ev_io *, int fd, int events)	1419	=item ev_io_set (ev_io *, int fd, int events)
1098		1420
1099	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1421	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1100	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1422	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1101	C<EV_READ | EV_WRITE> to receive the given events.	1423	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1102		1424
1103	=item int fd [read-only]	1425	=item int fd [read-only]
1104		1426
1105	The file descriptor being watched.	1427	The file descriptor being watched.
1106		1428
…		…
1114		1436
1115	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1437	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1116	readable, but only once. Since it is likely line-buffered, you could	1438	readable, but only once. Since it is likely line-buffered, you could
1117	attempt to read a whole line in the callback.	1439	attempt to read a whole line in the callback.
1118		1440
1119	static void	1441	static void
1120	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1442	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1121	{	1443	{
1122	ev_io_stop (loop, w);	1444	ev_io_stop (loop, w);
1123	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1445	.. read from stdin here (or from w->fd) and handle any I/O errors
1124	}	1446	}
1125		1447
1126	...	1448	...
1127	struct ev_loop *loop = ev_default_init (0);	1449	struct ev_loop *loop = ev_default_init (0);
1128	struct ev_io stdin_readable;	1450	ev_io stdin_readable;
1129	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1451	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1130	ev_io_start (loop, &stdin_readable);	1452	ev_io_start (loop, &stdin_readable);
1131	ev_loop (loop, 0);	1453	ev_loop (loop, 0);
1132		1454
1133		1455
1134	=head2 C<ev_timer> - relative and optionally repeating timeouts	1456	=head2 C<ev_timer> - relative and optionally repeating timeouts
1135		1457
1136	Timer watchers are simple relative timers that generate an event after a	1458	Timer watchers are simple relative timers that generate an event after a
1137	given time, and optionally repeating in regular intervals after that.	1459	given time, and optionally repeating in regular intervals after that.
1138		1460
1139	The timers are based on real time, that is, if you register an event that	1461	The timers are based on real time, that is, if you register an event that
1140	times out after an hour and you reset your system clock to last years	1462	times out after an hour and you reset your system clock to January last
1141	time, it will still time out after (roughly) and hour. "Roughly" because	1463	year, it will still time out after (roughly) one hour. "Roughly" because
1142	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1464	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1143	monotonic clock option helps a lot here).	1465	monotonic clock option helps a lot here).
		1466
		1467	The callback is guaranteed to be invoked only I<after> its timeout has
		1468	passed. If multiple timers become ready during the same loop iteration
		1469	then the ones with earlier time-out values are invoked before ones with
		1470	later time-out values (but this is no longer true when a callback calls
		1471	C<ev_loop> recursively).
		1472
		1473	=head3 Be smart about timeouts
		1474
		1475	Many real-world problems involve some kind of timeout, usually for error
		1476	recovery. A typical example is an HTTP request - if the other side hangs,
		1477	you want to raise some error after a while.
		1478
		1479	What follows are some ways to handle this problem, from obvious and
		1480	inefficient to smart and efficient.
		1481
		1482	In the following, a 60 second activity timeout is assumed - a timeout that
		1483	gets reset to 60 seconds each time there is activity (e.g. each time some
		1484	data or other life sign was received).
		1485
		1486	=over 4
		1487
		1488	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1489
		1490	This is the most obvious, but not the most simple way: In the beginning,
		1491	start the watcher:
		1492
		1493	ev_timer_init (timer, callback, 60., 0.);
		1494	ev_timer_start (loop, timer);
		1495
		1496	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1497	and start it again:
		1498
		1499	ev_timer_stop (loop, timer);
		1500	ev_timer_set (timer, 60., 0.);
		1501	ev_timer_start (loop, timer);
		1502
		1503	This is relatively simple to implement, but means that each time there is
		1504	some activity, libev will first have to remove the timer from its internal
		1505	data structure and then add it again. Libev tries to be fast, but it's
		1506	still not a constant-time operation.
		1507
		1508	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1509
		1510	This is the easiest way, and involves using C<ev_timer_again> instead of
		1511	C<ev_timer_start>.
		1512
		1513	To implement this, configure an C<ev_timer> with a C<repeat> value
		1514	of C<60> and then call C<ev_timer_again> at start and each time you
		1515	successfully read or write some data. If you go into an idle state where
		1516	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1517	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1518
		1519	That means you can ignore both the C<ev_timer_start> function and the
		1520	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1521	member and C<ev_timer_again>.
		1522
		1523	At start:
		1524
		1525	ev_timer_init (timer, callback);
		1526	timer->repeat = 60.;
		1527	ev_timer_again (loop, timer);
		1528
		1529	Each time there is some activity:
		1530
		1531	ev_timer_again (loop, timer);
		1532
		1533	It is even possible to change the time-out on the fly, regardless of
		1534	whether the watcher is active or not:
		1535
		1536	timer->repeat = 30.;
		1537	ev_timer_again (loop, timer);
		1538
		1539	This is slightly more efficient then stopping/starting the timer each time
		1540	you want to modify its timeout value, as libev does not have to completely
		1541	remove and re-insert the timer from/into its internal data structure.
		1542
		1543	It is, however, even simpler than the "obvious" way to do it.
		1544
		1545	=item 3. Let the timer time out, but then re-arm it as required.
		1546
		1547	This method is more tricky, but usually most efficient: Most timeouts are
		1548	relatively long compared to the intervals between other activity - in
		1549	our example, within 60 seconds, there are usually many I/O events with
		1550	associated activity resets.
		1551
		1552	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1553	but remember the time of last activity, and check for a real timeout only
		1554	within the callback:
		1555
		1556	ev_tstamp last_activity; // time of last activity
		1557
		1558	static void
		1559	callback (EV_P_ ev_timer *w, int revents)
		1560	{
		1561	ev_tstamp now = ev_now (EV_A);
		1562	ev_tstamp timeout = last_activity + 60.;
		1563
		1564	// if last_activity + 60. is older than now, we did time out
		1565	if (timeout < now)
		1566	{
		1567	// timeout occured, take action
		1568	}
		1569	else
		1570	{
		1571	// callback was invoked, but there was some activity, re-arm
		1572	// the watcher to fire in last_activity + 60, which is
		1573	// guaranteed to be in the future, so "again" is positive:
		1574	w->repeat = timeout - now;
		1575	ev_timer_again (EV_A_ w);
		1576	}
		1577	}
		1578
		1579	To summarise the callback: first calculate the real timeout (defined
		1580	as "60 seconds after the last activity"), then check if that time has
		1581	been reached, which means something I<did>, in fact, time out. Otherwise
		1582	the callback was invoked too early (C<timeout> is in the future), so
		1583	re-schedule the timer to fire at that future time, to see if maybe we have
		1584	a timeout then.
		1585
		1586	Note how C<ev_timer_again> is used, taking advantage of the
		1587	C<ev_timer_again> optimisation when the timer is already running.
		1588
		1589	This scheme causes more callback invocations (about one every 60 seconds
		1590	minus half the average time between activity), but virtually no calls to
		1591	libev to change the timeout.
		1592
		1593	To start the timer, simply initialise the watcher and set C<last_activity>
		1594	to the current time (meaning we just have some activity :), then call the
		1595	callback, which will "do the right thing" and start the timer:
		1596
		1597	ev_timer_init (timer, callback);
		1598	last_activity = ev_now (loop);
		1599	callback (loop, timer, EV_TIMEOUT);
		1600
		1601	And when there is some activity, simply store the current time in
		1602	C<last_activity>, no libev calls at all:
		1603
		1604	last_actiivty = ev_now (loop);
		1605
		1606	This technique is slightly more complex, but in most cases where the
		1607	time-out is unlikely to be triggered, much more efficient.
		1608
		1609	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1610	callback :) - just change the timeout and invoke the callback, which will
		1611	fix things for you.
		1612
		1613	=item 4. Wee, just use a double-linked list for your timeouts.
		1614
		1615	If there is not one request, but many thousands (millions...), all
		1616	employing some kind of timeout with the same timeout value, then one can
		1617	do even better:
		1618
		1619	When starting the timeout, calculate the timeout value and put the timeout
		1620	at the I<end> of the list.
		1621
		1622	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1623	the list is expected to fire (for example, using the technique #3).
		1624
		1625	When there is some activity, remove the timer from the list, recalculate
		1626	the timeout, append it to the end of the list again, and make sure to
		1627	update the C<ev_timer> if it was taken from the beginning of the list.
		1628
		1629	This way, one can manage an unlimited number of timeouts in O(1) time for
		1630	starting, stopping and updating the timers, at the expense of a major
		1631	complication, and having to use a constant timeout. The constant timeout
		1632	ensures that the list stays sorted.
		1633
		1634	=back
		1635
		1636	So which method the best?
		1637
		1638	Method #2 is a simple no-brain-required solution that is adequate in most
		1639	situations. Method #3 requires a bit more thinking, but handles many cases
		1640	better, and isn't very complicated either. In most case, choosing either
		1641	one is fine, with #3 being better in typical situations.
		1642
		1643	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1644	rather complicated, but extremely efficient, something that really pays
		1645	off after the first million or so of active timers, i.e. it's usually
		1646	overkill :)
		1647
		1648	=head3 The special problem of time updates
		1649
		1650	Establishing the current time is a costly operation (it usually takes at
		1651	least two system calls): EV therefore updates its idea of the current
		1652	time only before and after C<ev_loop> collects new events, which causes a
		1653	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1654	lots of events in one iteration.
1144		1655
1145	The relative timeouts are calculated relative to the C<ev_now ()>	1656	The relative timeouts are calculated relative to the C<ev_now ()>
1146	time. This is usually the right thing as this timestamp refers to the time	1657	time. This is usually the right thing as this timestamp refers to the time
1147	of the event triggering whatever timeout you are modifying/starting. If	1658	of the event triggering whatever timeout you are modifying/starting. If
1148	you suspect event processing to be delayed and you I<need> to base the timeout	1659	you suspect event processing to be delayed and you I<need> to base the
1149	on the current time, use something like this to adjust for this:	1660	timeout on the current time, use something like this to adjust for this:
1150		1661
1151	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1662	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1152		1663
1153	The callback is guarenteed to be invoked only when its timeout has passed,	1664	If the event loop is suspended for a long time, you can also force an
1154	but if multiple timers become ready during the same loop iteration then	1665	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1155	order of execution is undefined.	1666	()>.
1156		1667
1157	=head3 Watcher-Specific Functions and Data Members	1668	=head3 Watcher-Specific Functions and Data Members
1158		1669
1159	=over 4	1670	=over 4
1160		1671
1161	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1672	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1162		1673
1163	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1674	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1164		1675
1165	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1676	Configure the timer to trigger after C<after> seconds. If C<repeat>
1166	C<0.>, then it will automatically be stopped. If it is positive, then the	1677	is C<0.>, then it will automatically be stopped once the timeout is
1167	timer will automatically be configured to trigger again C<repeat> seconds	1678	reached. If it is positive, then the timer will automatically be
1168	later, again, and again, until stopped manually.	1679	configured to trigger again C<repeat> seconds later, again, and again,
		1680	until stopped manually.
1169		1681
1170	The timer itself will do a best-effort at avoiding drift, that is, if you	1682	The timer itself will do a best-effort at avoiding drift, that is, if
1171	configure a timer to trigger every 10 seconds, then it will trigger at	1683	you configure a timer to trigger every 10 seconds, then it will normally
1172	exactly 10 second intervals. If, however, your program cannot keep up with	1684	trigger at exactly 10 second intervals. If, however, your program cannot
1173	the timer (because it takes longer than those 10 seconds to do stuff) the	1685	keep up with the timer (because it takes longer than those 10 seconds to
1174	timer will not fire more than once per event loop iteration.	1686	do stuff) the timer will not fire more than once per event loop iteration.
1175		1687
1176	=item ev_timer_again (loop, ev_timer *)	1688	=item ev_timer_again (loop, ev_timer *)
1177		1689
1178	This will act as if the timer timed out and restart it again if it is	1690	This will act as if the timer timed out and restart it again if it is
1179	repeating. The exact semantics are:	1691	repeating. The exact semantics are:
1180		1692
1181	If the timer is pending, its pending status is cleared.	1693	If the timer is pending, its pending status is cleared.
1182		1694
1183	If the timer is started but nonrepeating, stop it (as if it timed out).	1695	If the timer is started but non-repeating, stop it (as if it timed out).
1184		1696
1185	If the timer is repeating, either start it if necessary (with the	1697	If the timer is repeating, either start it if necessary (with the
1186	C<repeat> value), or reset the running timer to the C<repeat> value.	1698	C<repeat> value), or reset the running timer to the C<repeat> value.
1187		1699
1188	This sounds a bit complicated, but here is a useful and typical	1700	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1189	example: Imagine you have a tcp connection and you want a so-called idle	1701	usage example.
1190	timeout, that is, you want to be called when there have been, say, 60
1191	seconds of inactivity on the socket. The easiest way to do this is to
1192	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1193	C<ev_timer_again> each time you successfully read or write some data. If
1194	you go into an idle state where you do not expect data to travel on the
1195	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1196	automatically restart it if need be.
1197
1198	That means you can ignore the C<after> value and C<ev_timer_start>
1199	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1200
1201	ev_timer_init (timer, callback, 0., 5.);
1202	ev_timer_again (loop, timer);
1203	...
1204	timer->again = 17.;
1205	ev_timer_again (loop, timer);
1206	...
1207	timer->again = 10.;
1208	ev_timer_again (loop, timer);
1209
1210	This is more slightly efficient then stopping/starting the timer each time
1211	you want to modify its timeout value.
1212		1702
1213	=item ev_tstamp repeat [read-write]	1703	=item ev_tstamp repeat [read-write]
1214		1704
1215	The current C<repeat> value. Will be used each time the watcher times out	1705	The current C<repeat> value. Will be used each time the watcher times out
1216	or C<ev_timer_again> is called and determines the next timeout (if any),	1706	or C<ev_timer_again> is called, and determines the next timeout (if any),
1217	which is also when any modifications are taken into account.	1707	which is also when any modifications are taken into account.
1218		1708
1219	=back	1709	=back
1220		1710
1221	=head3 Examples	1711	=head3 Examples
1222		1712
1223	Example: Create a timer that fires after 60 seconds.	1713	Example: Create a timer that fires after 60 seconds.
1224		1714
1225	static void	1715	static void
1226	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1716	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1227	{	1717	{
1228	.. one minute over, w is actually stopped right here	1718	.. one minute over, w is actually stopped right here
1229	}	1719	}
1230		1720
1231	struct ev_timer mytimer;	1721	ev_timer mytimer;
1232	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1722	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1233	ev_timer_start (loop, &mytimer);	1723	ev_timer_start (loop, &mytimer);
1234		1724
1235	Example: Create a timeout timer that times out after 10 seconds of	1725	Example: Create a timeout timer that times out after 10 seconds of
1236	inactivity.	1726	inactivity.
1237		1727
1238	static void	1728	static void
1239	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1729	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1240	{	1730	{
1241	.. ten seconds without any activity	1731	.. ten seconds without any activity
1242	}	1732	}
1243		1733
1244	struct ev_timer mytimer;	1734	ev_timer mytimer;
1245	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1735	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1246	ev_timer_again (&mytimer); /* start timer */	1736	ev_timer_again (&mytimer); /* start timer */
1247	ev_loop (loop, 0);	1737	ev_loop (loop, 0);
1248		1738
1249	// and in some piece of code that gets executed on any "activity":	1739	// and in some piece of code that gets executed on any "activity":
1250	// reset the timeout to start ticking again at 10 seconds	1740	// reset the timeout to start ticking again at 10 seconds
1251	ev_timer_again (&mytimer);	1741	ev_timer_again (&mytimer);
1252		1742
1253		1743
1254	=head2 C<ev_periodic> - to cron or not to cron?	1744	=head2 C<ev_periodic> - to cron or not to cron?
1255		1745
1256	Periodic watchers are also timers of a kind, but they are very versatile	1746	Periodic watchers are also timers of a kind, but they are very versatile
1257	(and unfortunately a bit complex).	1747	(and unfortunately a bit complex).
1258		1748
1259	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1749	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1260	but on wallclock time (absolute time). You can tell a periodic watcher	1750	relative time, the physical time that passes) but on wall clock time
1261	to trigger "at" some specific point in time. For example, if you tell a	1751	(absolute time, the thing you can read on your calender or clock). The
1262	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1752	difference is that wall clock time can run faster or slower than real
1263	+ 10.>) and then reset your system clock to the last year, then it will	1753	time, and time jumps are not uncommon (e.g. when you adjust your
1264	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1754	wrist-watch).
1265	roughly 10 seconds later).
1266		1755
1267	They can also be used to implement vastly more complex timers, such as	1756	You can tell a periodic watcher to trigger after some specific point
1268	triggering an event on each midnight, local time or other, complicated,	1757	in time: for example, if you tell a periodic watcher to trigger "in 10
1269	rules.	1758	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1759	not a delay) and then reset your system clock to January of the previous
		1760	year, then it will take a year or more to trigger the event (unlike an
		1761	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1762	it, as it uses a relative timeout).
1270		1763
		1764	C<ev_periodic> watchers can also be used to implement vastly more complex
		1765	timers, such as triggering an event on each "midnight, local time", or
		1766	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1767	those cannot react to time jumps.
		1768
1271	As with timers, the callback is guarenteed to be invoked only when the	1769	As with timers, the callback is guaranteed to be invoked only when the
1272	time (C<at>) has been passed, but if multiple periodic timers become ready	1770	point in time where it is supposed to trigger has passed. If multiple
1273	during the same loop iteration then order of execution is undefined.	1771	timers become ready during the same loop iteration then the ones with
		1772	earlier time-out values are invoked before ones with later time-out values
		1773	(but this is no longer true when a callback calls C<ev_loop> recursively).
1274		1774
1275	=head3 Watcher-Specific Functions and Data Members	1775	=head3 Watcher-Specific Functions and Data Members
1276		1776
1277	=over 4	1777	=over 4
1278		1778
1279	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1779	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1280		1780
1281	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1781	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1282		1782
1283	Lots of arguments, lets sort it out... There are basically three modes of	1783	Lots of arguments, let's sort it out... There are basically three modes of
1284	operation, and we will explain them from simplest to complex:	1784	operation, and we will explain them from simplest to most complex:
1285		1785
1286	=over 4	1786	=over 4
1287		1787
1288	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1788	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1289		1789
1290	In this configuration the watcher triggers an event at the wallclock time	1790	In this configuration the watcher triggers an event after the wall clock
1291	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1791	time C<offset> has passed. It will not repeat and will not adjust when a
1292	that is, if it is to be run at January 1st 2011 then it will run when the	1792	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1293	system time reaches or surpasses this time.	1793	will be stopped and invoked when the system clock reaches or surpasses
		1794	this point in time.
1294		1795
1295	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1796	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1296		1797
1297	In this mode the watcher will always be scheduled to time out at the next	1798	In this mode the watcher will always be scheduled to time out at the next
1298	C<at + N * interval> time (for some integer N, which can also be negative)	1799	C<offset + N * interval> time (for some integer N, which can also be
1299	and then repeat, regardless of any time jumps.	1800	negative) and then repeat, regardless of any time jumps. The C<offset>
		1801	argument is merely an offset into the C<interval> periods.
1300		1802
1301	This can be used to create timers that do not drift with respect to system	1803	This can be used to create timers that do not drift with respect to the
1302	time:	1804	system clock, for example, here is an C<ev_periodic> that triggers each
		1805	hour, on the hour (with respect to UTC):
1303		1806
1304	ev_periodic_set (&periodic, 0., 3600., 0);	1807	ev_periodic_set (&periodic, 0., 3600., 0);
1305		1808
1306	This doesn't mean there will always be 3600 seconds in between triggers,	1809	This doesn't mean there will always be 3600 seconds in between triggers,
1307	but only that the the callback will be called when the system time shows a	1810	but only that the callback will be called when the system time shows a
1308	full hour (UTC), or more correctly, when the system time is evenly divisible	1811	full hour (UTC), or more correctly, when the system time is evenly divisible
1309	by 3600.	1812	by 3600.
1310		1813
1311	Another way to think about it (for the mathematically inclined) is that	1814	Another way to think about it (for the mathematically inclined) is that
1312	C<ev_periodic> will try to run the callback in this mode at the next possible	1815	C<ev_periodic> will try to run the callback in this mode at the next possible
1313	time where C<time = at (mod interval)>, regardless of any time jumps.	1816	time where C<time = offset (mod interval)>, regardless of any time jumps.
1314		1817
1315	For numerical stability it is preferable that the C<at> value is near	1818	For numerical stability it is preferable that the C<offset> value is near
1316	C<ev_now ()> (the current time), but there is no range requirement for	1819	C<ev_now ()> (the current time), but there is no range requirement for
1317	this value.	1820	this value, and in fact is often specified as zero.
1318		1821
		1822	Note also that there is an upper limit to how often a timer can fire (CPU
		1823	speed for example), so if C<interval> is very small then timing stability
		1824	will of course deteriorate. Libev itself tries to be exact to be about one
		1825	millisecond (if the OS supports it and the machine is fast enough).
		1826
1319	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1827	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1320		1828
1321	In this mode the values for C<interval> and C<at> are both being	1829	In this mode the values for C<interval> and C<offset> are both being
1322	ignored. Instead, each time the periodic watcher gets scheduled, the	1830	ignored. Instead, each time the periodic watcher gets scheduled, the
1323	reschedule callback will be called with the watcher as first, and the	1831	reschedule callback will be called with the watcher as first, and the
1324	current time as second argument.	1832	current time as second argument.
1325		1833
1326	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1834	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1327	ever, or make any event loop modifications>. If you need to stop it,	1835	or make ANY other event loop modifications whatsoever, unless explicitly
1328	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1836	allowed by documentation here>.
1329	starting an C<ev_prepare> watcher, which is legal).
1330		1837
		1838	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1839	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1840	only event loop modification you are allowed to do).
		1841
1331	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1842	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1332	ev_tstamp now)>, e.g.:	1843	*w, ev_tstamp now)>, e.g.:
1333		1844
		1845	static ev_tstamp
1334	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1846	my_rescheduler (ev_periodic *w, ev_tstamp now)
1335	{	1847	{
1336	return now + 60.;	1848	return now + 60.;
1337	}	1849	}
1338		1850
1339	It must return the next time to trigger, based on the passed time value	1851	It must return the next time to trigger, based on the passed time value
1340	(that is, the lowest time value larger than to the second argument). It	1852	(that is, the lowest time value larger than to the second argument). It
1341	will usually be called just before the callback will be triggered, but	1853	will usually be called just before the callback will be triggered, but
1342	might be called at other times, too.	1854	might be called at other times, too.
1343		1855
1344	NOTE: I<< This callback must always return a time that is later than the	1856	NOTE: I<< This callback must always return a time that is higher than or
1345	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1857	equal to the passed C<now> value >>.
1346		1858
1347	This can be used to create very complex timers, such as a timer that	1859	This can be used to create very complex timers, such as a timer that
1348	triggers on each midnight, local time. To do this, you would calculate the	1860	triggers on "next midnight, local time". To do this, you would calculate the
1349	next midnight after C<now> and return the timestamp value for this. How	1861	next midnight after C<now> and return the timestamp value for this. How
1350	you do this is, again, up to you (but it is not trivial, which is the main	1862	you do this is, again, up to you (but it is not trivial, which is the main
1351	reason I omitted it as an example).	1863	reason I omitted it as an example).
1352		1864
1353	=back	1865	=back
…		…
1357	Simply stops and restarts the periodic watcher again. This is only useful	1869	Simply stops and restarts the periodic watcher again. This is only useful
1358	when you changed some parameters or the reschedule callback would return	1870	when you changed some parameters or the reschedule callback would return
1359	a different time than the last time it was called (e.g. in a crond like	1871	a different time than the last time it was called (e.g. in a crond like
1360	program when the crontabs have changed).	1872	program when the crontabs have changed).
1361		1873
		1874	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1875
		1876	When active, returns the absolute time that the watcher is supposed
		1877	to trigger next. This is not the same as the C<offset> argument to
		1878	C<ev_periodic_set>, but indeed works even in interval and manual
		1879	rescheduling modes.
		1880
1362	=item ev_tstamp offset [read-write]	1881	=item ev_tstamp offset [read-write]
1363		1882
1364	When repeating, this contains the offset value, otherwise this is the	1883	When repeating, this contains the offset value, otherwise this is the
1365	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1884	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1885	although libev might modify this value for better numerical stability).
1366		1886
1367	Can be modified any time, but changes only take effect when the periodic	1887	Can be modified any time, but changes only take effect when the periodic
1368	timer fires or C<ev_periodic_again> is being called.	1888	timer fires or C<ev_periodic_again> is being called.
1369		1889
1370	=item ev_tstamp interval [read-write]	1890	=item ev_tstamp interval [read-write]
1371		1891
1372	The current interval value. Can be modified any time, but changes only	1892	The current interval value. Can be modified any time, but changes only
1373	take effect when the periodic timer fires or C<ev_periodic_again> is being	1893	take effect when the periodic timer fires or C<ev_periodic_again> is being
1374	called.	1894	called.
1375		1895
1376	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1896	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1377		1897
1378	The current reschedule callback, or C<0>, if this functionality is	1898	The current reschedule callback, or C<0>, if this functionality is
1379	switched off. Can be changed any time, but changes only take effect when	1899	switched off. Can be changed any time, but changes only take effect when
1380	the periodic timer fires or C<ev_periodic_again> is being called.	1900	the periodic timer fires or C<ev_periodic_again> is being called.
1381		1901
1382	=item ev_tstamp at [read-only]
1383
1384	When active, contains the absolute time that the watcher is supposed to
1385	trigger next.
1386
1387	=back	1902	=back
1388		1903
1389	=head3 Examples	1904	=head3 Examples
1390		1905
1391	Example: Call a callback every hour, or, more precisely, whenever the	1906	Example: Call a callback every hour, or, more precisely, whenever the
1392	system clock is divisible by 3600. The callback invocation times have	1907	system time is divisible by 3600. The callback invocation times have
1393	potentially a lot of jittering, but good long-term stability.	1908	potentially a lot of jitter, but good long-term stability.
1394		1909
1395	static void	1910	static void
1396	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1911	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1397	{	1912	{
1398	... its now a full hour (UTC, or TAI or whatever your clock follows)	1913	... its now a full hour (UTC, or TAI or whatever your clock follows)
1399	}	1914	}
1400		1915
1401	struct ev_periodic hourly_tick;	1916	ev_periodic hourly_tick;
1402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1917	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1403	ev_periodic_start (loop, &hourly_tick);	1918	ev_periodic_start (loop, &hourly_tick);
1404		1919
1405	Example: The same as above, but use a reschedule callback to do it:	1920	Example: The same as above, but use a reschedule callback to do it:
1406		1921
1407	#include <math.h>	1922	#include <math.h>
1408		1923
1409	static ev_tstamp	1924	static ev_tstamp
1410	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1925	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1411	{	1926	{
1412	return fmod (now, 3600.) + 3600.;	1927	return now + (3600. - fmod (now, 3600.));
1413	}	1928	}
1414		1929
1415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1930	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1416		1931
1417	Example: Call a callback every hour, starting now:	1932	Example: Call a callback every hour, starting now:
1418		1933
1419	struct ev_periodic hourly_tick;	1934	ev_periodic hourly_tick;
1420	ev_periodic_init (&hourly_tick, clock_cb,	1935	ev_periodic_init (&hourly_tick, clock_cb,
1421	fmod (ev_now (loop), 3600.), 3600., 0);	1936	fmod (ev_now (loop), 3600.), 3600., 0);
1422	ev_periodic_start (loop, &hourly_tick);	1937	ev_periodic_start (loop, &hourly_tick);
1423		1938
1424		1939
1425	=head2 C<ev_signal> - signal me when a signal gets signalled!	1940	=head2 C<ev_signal> - signal me when a signal gets signalled!
1426		1941
1427	Signal watchers will trigger an event when the process receives a specific	1942	Signal watchers will trigger an event when the process receives a specific
1428	signal one or more times. Even though signals are very asynchronous, libev	1943	signal one or more times. Even though signals are very asynchronous, libev
1429	will try it's best to deliver signals synchronously, i.e. as part of the	1944	will try it's best to deliver signals synchronously, i.e. as part of the
1430	normal event processing, like any other event.	1945	normal event processing, like any other event.
1431		1946
		1947	If you want signals asynchronously, just use C<sigaction> as you would
		1948	do without libev and forget about sharing the signal. You can even use
		1949	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1950
1432	You can configure as many watchers as you like per signal. Only when the	1951	You can configure as many watchers as you like per signal. Only when the
1433	first watcher gets started will libev actually register a signal watcher	1952	first watcher gets started will libev actually register a signal handler
1434	with the kernel (thus it coexists with your own signal handlers as long	1953	with the kernel (thus it coexists with your own signal handlers as long as
1435	as you don't register any with libev). Similarly, when the last signal	1954	you don't register any with libev for the same signal). Similarly, when
1436	watcher for a signal is stopped libev will reset the signal handler to	1955	the last signal watcher for a signal is stopped, libev will reset the
1437	SIG_DFL (regardless of what it was set to before).	1956	signal handler to SIG_DFL (regardless of what it was set to before).
1438		1957
1439	If possible and supported, libev will install its handlers with	1958	If possible and supported, libev will install its handlers with
1440	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	1959	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
1441	interrupted. If you have a problem with syscalls getting interrupted by	1960	interrupted. If you have a problem with system calls getting interrupted by
1442	signals you can block all signals in an C<ev_check> watcher and unblock	1961	signals you can block all signals in an C<ev_check> watcher and unblock
1443	them in an C<ev_prepare> watcher.	1962	them in an C<ev_prepare> watcher.
1444		1963
1445	=head3 Watcher-Specific Functions and Data Members	1964	=head3 Watcher-Specific Functions and Data Members
1446		1965
…		…
1459		1978
1460	=back	1979	=back
1461		1980
1462	=head3 Examples	1981	=head3 Examples
1463		1982
1464	Example: Try to exit cleanly on SIGINT and SIGTERM.	1983	Example: Try to exit cleanly on SIGINT.
1465		1984
1466	static void	1985	static void
1467	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1986	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1468	{	1987	{
1469	ev_unloop (loop, EVUNLOOP_ALL);	1988	ev_unloop (loop, EVUNLOOP_ALL);
1470	}	1989	}
1471		1990
1472	struct ev_signal signal_watcher;	1991	ev_signal signal_watcher;
1473	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1992	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1474	ev_signal_start (loop, &sigint_cb);	1993	ev_signal_start (loop, &signal_watcher);
1475		1994
1476		1995
1477	=head2 C<ev_child> - watch out for process status changes	1996	=head2 C<ev_child> - watch out for process status changes
1478		1997
1479	Child watchers trigger when your process receives a SIGCHLD in response to	1998	Child watchers trigger when your process receives a SIGCHLD in response to
1480	some child status changes (most typically when a child of yours dies). It	1999	some child status changes (most typically when a child of yours dies or
1481	is permissible to install a child watcher I<after> the child has been	2000	exits). It is permissible to install a child watcher I<after> the child
1482	forked (which implies it might have already exited), as long as the event	2001	has been forked (which implies it might have already exited), as long
1483	loop isn't entered (or is continued from a watcher).	2002	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2003	forking and then immediately registering a watcher for the child is fine,
		2004	but forking and registering a watcher a few event loop iterations later is
		2005	not.
1484		2006
1485	Only the default event loop is capable of handling signals, and therefore	2007	Only the default event loop is capable of handling signals, and therefore
1486	you can only rgeister child watchers in the default event loop.	2008	you can only register child watchers in the default event loop.
1487		2009
1488	=head3 Process Interaction	2010	=head3 Process Interaction
1489		2011
1490	Libev grabs C<SIGCHLD> as soon as the default event loop is	2012	Libev grabs C<SIGCHLD> as soon as the default event loop is
1491	initialised. This is necessary to guarantee proper behaviour even if	2013	initialised. This is necessary to guarantee proper behaviour even if
1492	the first child watcher is started after the child exits. The occurance	2014	the first child watcher is started after the child exits. The occurrence
1493	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2015	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1494	synchronously as part of the event loop processing. Libev always reaps all	2016	synchronously as part of the event loop processing. Libev always reaps all
1495	children, even ones not watched.	2017	children, even ones not watched.
1496		2018
1497	=head3 Overriding the Built-In Processing	2019	=head3 Overriding the Built-In Processing
…		…
1501	handler, you can override it easily by installing your own handler for	2023	handler, you can override it easily by installing your own handler for
1502	C<SIGCHLD> after initialising the default loop, and making sure the	2024	C<SIGCHLD> after initialising the default loop, and making sure the
1503	default loop never gets destroyed. You are encouraged, however, to use an	2025	default loop never gets destroyed. You are encouraged, however, to use an
1504	event-based approach to child reaping and thus use libev's support for	2026	event-based approach to child reaping and thus use libev's support for
1505	that, so other libev users can use C<ev_child> watchers freely.	2027	that, so other libev users can use C<ev_child> watchers freely.
		2028
		2029	=head3 Stopping the Child Watcher
		2030
		2031	Currently, the child watcher never gets stopped, even when the
		2032	child terminates, so normally one needs to stop the watcher in the
		2033	callback. Future versions of libev might stop the watcher automatically
		2034	when a child exit is detected.
1506		2035
1507	=head3 Watcher-Specific Functions and Data Members	2036	=head3 Watcher-Specific Functions and Data Members
1508		2037
1509	=over 4	2038	=over 4
1510		2039
…		…
1539	=head3 Examples	2068	=head3 Examples
1540		2069
1541	Example: C<fork()> a new process and install a child handler to wait for	2070	Example: C<fork()> a new process and install a child handler to wait for
1542	its completion.	2071	its completion.
1543		2072
1544	ev_child cw;	2073	ev_child cw;
1545		2074
1546	static void	2075	static void
1547	child_cb (EV_P_ struct ev_child *w, int revents)	2076	child_cb (EV_P_ ev_child *w, int revents)
1548	{	2077	{
1549	ev_child_stop (EV_A_ w);	2078	ev_child_stop (EV_A_ w);
1550	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2079	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1551	}	2080	}
1552		2081
1553	pid_t pid = fork ();	2082	pid_t pid = fork ();
1554		2083
1555	if (pid < 0)	2084	if (pid < 0)
1556	// error	2085	// error
1557	else if (pid == 0)	2086	else if (pid == 0)
1558	{	2087	{
1559	// the forked child executes here	2088	// the forked child executes here
1560	exit (1);	2089	exit (1);
1561	}	2090	}
1562	else	2091	else
1563	{	2092	{
1564	ev_child_init (&cw, child_cb, pid, 0);	2093	ev_child_init (&cw, child_cb, pid, 0);
1565	ev_child_start (EV_DEFAULT_ &cw);	2094	ev_child_start (EV_DEFAULT_ &cw);
1566	}	2095	}
1567		2096
1568		2097
1569	=head2 C<ev_stat> - did the file attributes just change?	2098	=head2 C<ev_stat> - did the file attributes just change?
1570		2099
1571	This watches a filesystem path for attribute changes. That is, it calls	2100	This watches a file system path for attribute changes. That is, it calls
1572	C<stat> regularly (or when the OS says it changed) and sees if it changed	2101	C<stat> on that path in regular intervals (or when the OS says it changed)
1573	compared to the last time, invoking the callback if it did.	2102	and sees if it changed compared to the last time, invoking the callback if
		2103	it did.
1574		2104
1575	The path does not need to exist: changing from "path exists" to "path does	2105	The path does not need to exist: changing from "path exists" to "path does
1576	not exist" is a status change like any other. The condition "path does	2106	not exist" is a status change like any other. The condition "path does not
1577	not exist" is signified by the C<st_nlink> field being zero (which is	2107	exist" (or more correctly "path cannot be stat'ed") is signified by the
1578	otherwise always forced to be at least one) and all the other fields of	2108	C<st_nlink> field being zero (which is otherwise always forced to be at
1579	the stat buffer having unspecified contents.	2109	least one) and all the other fields of the stat buffer having unspecified
		2110	contents.
1580		2111
1581	The path I<should> be absolute and I<must not> end in a slash. If it is	2112	The path I<must not> end in a slash or contain special components such as
		2113	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1582	relative and your working directory changes, the behaviour is undefined.	2114	your working directory changes, then the behaviour is undefined.
1583		2115
1584	Since there is no standard to do this, the portable implementation simply	2116	Since there is no portable change notification interface available, the
1585	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2117	portable implementation simply calls C<stat(2)> regularly on the path
1586	can specify a recommended polling interval for this case. If you specify	2118	to see if it changed somehow. You can specify a recommended polling
1587	a polling interval of C<0> (highly recommended!) then a I<suitable,	2119	interval for this case. If you specify a polling interval of C<0> (highly
1588	unspecified default> value will be used (which you can expect to be around	2120	recommended!) then a I<suitable, unspecified default> value will be used
1589	five seconds, although this might change dynamically). Libev will also	2121	(which you can expect to be around five seconds, although this might
1590	impose a minimum interval which is currently around C<0.1>, but thats	2122	change dynamically). Libev will also impose a minimum interval which is
1591	usually overkill.	2123	currently around C<0.1>, but that's usually overkill.
1592		2124
1593	This watcher type is not meant for massive numbers of stat watchers,	2125	This watcher type is not meant for massive numbers of stat watchers,
1594	as even with OS-supported change notifications, this can be	2126	as even with OS-supported change notifications, this can be
1595	resource-intensive.	2127	resource-intensive.
1596		2128
1597	At the time of this writing, only the Linux inotify interface is	2129	At the time of this writing, the only OS-specific interface implemented
1598	implemented (implementing kqueue support is left as an exercise for the	2130	is the Linux inotify interface (implementing kqueue support is left as an
1599	reader). Inotify will be used to give hints only and should not change the	2131	exercise for the reader. Note, however, that the author sees no way of
1600	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2132	implementing C<ev_stat> semantics with kqueue, except as a hint).
1601	to fall back to regular polling again even with inotify, but changes are
1602	usually detected immediately, and if the file exists there will be no
1603	polling.
1604		2133
1605	=head3 Inotify	2134	=head3 ABI Issues (Largefile Support)
1606		2135
		2136	Libev by default (unless the user overrides this) uses the default
		2137	compilation environment, which means that on systems with large file
		2138	support disabled by default, you get the 32 bit version of the stat
		2139	structure. When using the library from programs that change the ABI to
		2140	use 64 bit file offsets the programs will fail. In that case you have to
		2141	compile libev with the same flags to get binary compatibility. This is
		2142	obviously the case with any flags that change the ABI, but the problem is
		2143	most noticeably displayed with ev_stat and large file support.
		2144
		2145	The solution for this is to lobby your distribution maker to make large
		2146	file interfaces available by default (as e.g. FreeBSD does) and not
		2147	optional. Libev cannot simply switch on large file support because it has
		2148	to exchange stat structures with application programs compiled using the
		2149	default compilation environment.
		2150
		2151	=head3 Inotify and Kqueue
		2152
1607	When C<inotify (7)> support has been compiled into libev (generally only	2153	When C<inotify (7)> support has been compiled into libev and present at
1608	available on Linux) and present at runtime, it will be used to speed up	2154	runtime, it will be used to speed up change detection where possible. The
1609	change detection where possible. The inotify descriptor will be created lazily	2155	inotify descriptor will be created lazily when the first C<ev_stat>
1610	when the first C<ev_stat> watcher is being started.	2156	watcher is being started.
1611		2157
1612	Inotify presense does not change the semantics of C<ev_stat> watchers	2158	Inotify presence does not change the semantics of C<ev_stat> watchers
1613	except that changes might be detected earlier, and in some cases, to avoid	2159	except that changes might be detected earlier, and in some cases, to avoid
1614	making regular C<stat> calls. Even in the presense of inotify support	2160	making regular C<stat> calls. Even in the presence of inotify support
1615	there are many cases where libev has to resort to regular C<stat> polling.	2161	there are many cases where libev has to resort to regular C<stat> polling,
		2162	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2163	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2164	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2165	xfs are fully working) libev usually gets away without polling.
1616		2166
1617	(There is no support for kqueue, as apparently it cannot be used to	2167	There is no support for kqueue, as apparently it cannot be used to
1618	implement this functionality, due to the requirement of having a file	2168	implement this functionality, due to the requirement of having a file
1619	descriptor open on the object at all times).	2169	descriptor open on the object at all times, and detecting renames, unlinks
		2170	etc. is difficult.
		2171
		2172	=head3 C<stat ()> is a synchronous operation
		2173
		2174	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2175	the process. The exception are C<ev_stat> watchers - those call C<stat
		2176	()>, which is a synchronous operation.
		2177
		2178	For local paths, this usually doesn't matter: unless the system is very
		2179	busy or the intervals between stat's are large, a stat call will be fast,
		2180	as the path data is usually in memory already (except when starting the
		2181	watcher).
		2182
		2183	For networked file systems, calling C<stat ()> can block an indefinite
		2184	time due to network issues, and even under good conditions, a stat call
		2185	often takes multiple milliseconds.
		2186
		2187	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2188	paths, although this is fully supported by libev.
1620		2189
1621	=head3 The special problem of stat time resolution	2190	=head3 The special problem of stat time resolution
1622		2191
1623	The C<stat ()> syscall only supports full-second resolution portably, and	2192	The C<stat ()> system call only supports full-second resolution portably,
1624	even on systems where the resolution is higher, many filesystems still	2193	and even on systems where the resolution is higher, most file systems
1625	only support whole seconds.	2194	still only support whole seconds.
1626		2195
1627	That means that, if the time is the only thing that changes, you might	2196	That means that, if the time is the only thing that changes, you can
1628	miss updates: on the first update, C<ev_stat> detects a change and calls	2197	easily miss updates: on the first update, C<ev_stat> detects a change and
1629	your callback, which does something. When there is another update within	2198	calls your callback, which does something. When there is another update
1630	the same second, C<ev_stat> will be unable to detect it.	2199	within the same second, C<ev_stat> will be unable to detect unless the
		2200	stat data does change in other ways (e.g. file size).
1631		2201
1632	The solution to this is to delay acting on a change for a second (or till	2202	The solution to this is to delay acting on a change for slightly more
1633	the next second boundary), using a roughly one-second delay C<ev_timer>	2203	than a second (or till slightly after the next full second boundary), using
1634	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2204	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1635	is added to work around small timing inconsistencies of some operating	2205	ev_timer_again (loop, w)>).
1636	systems.	2206
		2207	The C<.02> offset is added to work around small timing inconsistencies
		2208	of some operating systems (where the second counter of the current time
		2209	might be be delayed. One such system is the Linux kernel, where a call to
		2210	C<gettimeofday> might return a timestamp with a full second later than
		2211	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2212	update file times then there will be a small window where the kernel uses
		2213	the previous second to update file times but libev might already execute
		2214	the timer callback).
1637		2215
1638	=head3 Watcher-Specific Functions and Data Members	2216	=head3 Watcher-Specific Functions and Data Members
1639		2217
1640	=over 4	2218	=over 4
1641		2219
…		…
1647	C<path>. The C<interval> is a hint on how quickly a change is expected to	2225	C<path>. The C<interval> is a hint on how quickly a change is expected to
1648	be detected and should normally be specified as C<0> to let libev choose	2226	be detected and should normally be specified as C<0> to let libev choose
1649	a suitable value. The memory pointed to by C<path> must point to the same	2227	a suitable value. The memory pointed to by C<path> must point to the same
1650	path for as long as the watcher is active.	2228	path for as long as the watcher is active.
1651		2229
1652	The callback will be receive C<EV_STAT> when a change was detected,	2230	The callback will receive an C<EV_STAT> event when a change was detected,
1653	relative to the attributes at the time the watcher was started (or the	2231	relative to the attributes at the time the watcher was started (or the
1654	last change was detected).	2232	last change was detected).
1655		2233
1656	=item ev_stat_stat (loop, ev_stat *)	2234	=item ev_stat_stat (loop, ev_stat *)
1657		2235
1658	Updates the stat buffer immediately with new values. If you change the	2236	Updates the stat buffer immediately with new values. If you change the
1659	watched path in your callback, you could call this fucntion to avoid	2237	watched path in your callback, you could call this function to avoid
1660	detecting this change (while introducing a race condition). Can also be	2238	detecting this change (while introducing a race condition if you are not
1661	useful simply to find out the new values.	2239	the only one changing the path). Can also be useful simply to find out the
		2240	new values.
1662		2241
1663	=item ev_statdata attr [read-only]	2242	=item ev_statdata attr [read-only]
1664		2243
1665	The most-recently detected attributes of the file. Although the type is of	2244	The most-recently detected attributes of the file. Although the type is
1666	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2245	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1667	suitable for your system. If the C<st_nlink> member is C<0>, then there	2246	suitable for your system, but you can only rely on the POSIX-standardised
		2247	members to be present. If the C<st_nlink> member is C<0>, then there was
1668	was some error while C<stat>ing the file.	2248	some error while C<stat>ing the file.
1669		2249
1670	=item ev_statdata prev [read-only]	2250	=item ev_statdata prev [read-only]
1671		2251
1672	The previous attributes of the file. The callback gets invoked whenever	2252	The previous attributes of the file. The callback gets invoked whenever
1673	C<prev> != C<attr>.	2253	C<prev> != C<attr>, or, more precisely, one or more of these members
		2254	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2255	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1674		2256
1675	=item ev_tstamp interval [read-only]	2257	=item ev_tstamp interval [read-only]
1676		2258
1677	The specified interval.	2259	The specified interval.
1678		2260
1679	=item const char *path [read-only]	2261	=item const char *path [read-only]
1680		2262
1681	The filesystem path that is being watched.	2263	The file system path that is being watched.
1682		2264
1683	=back	2265	=back
1684		2266
1685	=head3 Examples	2267	=head3 Examples
1686		2268
1687	Example: Watch C</etc/passwd> for attribute changes.	2269	Example: Watch C</etc/passwd> for attribute changes.
1688		2270
1689	static void	2271	static void
1690	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2272	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1691	{	2273	{
1692	/* /etc/passwd changed in some way */	2274	/* /etc/passwd changed in some way */
1693	if (w->attr.st_nlink)	2275	if (w->attr.st_nlink)
1694	{	2276	{
1695	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2277	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1696	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2278	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1697	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2279	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1698	}	2280	}
1699	else	2281	else
1700	/* you shalt not abuse printf for puts */	2282	/* you shalt not abuse printf for puts */
1701	puts ("wow, /etc/passwd is not there, expect problems. "	2283	puts ("wow, /etc/passwd is not there, expect problems. "
1702	"if this is windows, they already arrived\n");	2284	"if this is windows, they already arrived\n");
1703	}	2285	}
1704		2286
1705	...	2287	...
1706	ev_stat passwd;	2288	ev_stat passwd;
1707		2289
1708	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2290	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1709	ev_stat_start (loop, &passwd);	2291	ev_stat_start (loop, &passwd);
1710		2292
1711	Example: Like above, but additionally use a one-second delay so we do not	2293	Example: Like above, but additionally use a one-second delay so we do not
1712	miss updates (however, frequent updates will delay processing, too, so	2294	miss updates (however, frequent updates will delay processing, too, so
1713	one might do the work both on C<ev_stat> callback invocation I<and> on	2295	one might do the work both on C<ev_stat> callback invocation I<and> on
1714	C<ev_timer> callback invocation).	2296	C<ev_timer> callback invocation).
1715		2297
1716	static ev_stat passwd;	2298	static ev_stat passwd;
1717	static ev_timer timer;	2299	static ev_timer timer;
1718		2300
1719	static void	2301	static void
1720	timer_cb (EV_P_ ev_timer *w, int revents)	2302	timer_cb (EV_P_ ev_timer *w, int revents)
1721	{	2303	{
1722	ev_timer_stop (EV_A_ w);	2304	ev_timer_stop (EV_A_ w);
1723		2305
1724	/* now it's one second after the most recent passwd change */	2306	/* now it's one second after the most recent passwd change */
1725	}	2307	}
1726		2308
1727	static void	2309	static void
1728	stat_cb (EV_P_ ev_stat *w, int revents)	2310	stat_cb (EV_P_ ev_stat *w, int revents)
1729	{	2311	{
1730	/* reset the one-second timer */	2312	/* reset the one-second timer */
1731	ev_timer_again (EV_A_ &timer);	2313	ev_timer_again (EV_A_ &timer);
1732	}	2314	}
1733		2315
1734	...	2316	...
1735	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2317	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1736	ev_stat_start (loop, &passwd);	2318	ev_stat_start (loop, &passwd);
1737	ev_timer_init (&timer, timer_cb, 0., 1.01);	2319	ev_timer_init (&timer, timer_cb, 0., 1.02);
1738		2320
1739		2321
1740	=head2 C<ev_idle> - when you've got nothing better to do...	2322	=head2 C<ev_idle> - when you've got nothing better to do...
1741		2323
1742	Idle watchers trigger events when no other events of the same or higher	2324	Idle watchers trigger events when no other events of the same or higher
1743	priority are pending (prepare, check and other idle watchers do not	2325	priority are pending (prepare, check and other idle watchers do not count
1744	count).	2326	as receiving "events").
1745		2327
1746	That is, as long as your process is busy handling sockets or timeouts	2328	That is, as long as your process is busy handling sockets or timeouts
1747	(or even signals, imagine) of the same or higher priority it will not be	2329	(or even signals, imagine) of the same or higher priority it will not be
1748	triggered. But when your process is idle (or only lower-priority watchers	2330	triggered. But when your process is idle (or only lower-priority watchers
1749	are pending), the idle watchers are being called once per event loop	2331	are pending), the idle watchers are being called once per event loop
…		…
1760		2342
1761	=head3 Watcher-Specific Functions and Data Members	2343	=head3 Watcher-Specific Functions and Data Members
1762		2344
1763	=over 4	2345	=over 4
1764		2346
1765	=item ev_idle_init (ev_signal *, callback)	2347	=item ev_idle_init (ev_idle *, callback)
1766		2348
1767	Initialises and configures the idle watcher - it has no parameters of any	2349	Initialises and configures the idle watcher - it has no parameters of any
1768	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2350	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1769	believe me.	2351	believe me.
1770		2352
…		…
1773	=head3 Examples	2355	=head3 Examples
1774		2356
1775	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2357	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1776	callback, free it. Also, use no error checking, as usual.	2358	callback, free it. Also, use no error checking, as usual.
1777		2359
1778	static void	2360	static void
1779	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2361	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1780	{	2362	{
1781	free (w);	2363	free (w);
1782	// now do something you wanted to do when the program has	2364	// now do something you wanted to do when the program has
1783	// no longer anything immediate to do.	2365	// no longer anything immediate to do.
1784	}	2366	}
1785		2367
1786	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2368	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1787	ev_idle_init (idle_watcher, idle_cb);	2369	ev_idle_init (idle_watcher, idle_cb);
1788	ev_idle_start (loop, idle_cb);	2370	ev_idle_start (loop, idle_cb);
1789		2371
1790		2372
1791	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2373	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1792		2374
1793	Prepare and check watchers are usually (but not always) used in tandem:	2375	Prepare and check watchers are usually (but not always) used in pairs:
1794	prepare watchers get invoked before the process blocks and check watchers	2376	prepare watchers get invoked before the process blocks and check watchers
1795	afterwards.	2377	afterwards.
1796		2378
1797	You I<must not> call C<ev_loop> or similar functions that enter	2379	You I<must not> call C<ev_loop> or similar functions that enter
1798	the current event loop from either C<ev_prepare> or C<ev_check>	2380	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1801	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2383	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1802	C<ev_check> so if you have one watcher of each kind they will always be	2384	C<ev_check> so if you have one watcher of each kind they will always be
1803	called in pairs bracketing the blocking call.	2385	called in pairs bracketing the blocking call.
1804		2386
1805	Their main purpose is to integrate other event mechanisms into libev and	2387	Their main purpose is to integrate other event mechanisms into libev and
1806	their use is somewhat advanced. This could be used, for example, to track	2388	their use is somewhat advanced. They could be used, for example, to track
1807	variable changes, implement your own watchers, integrate net-snmp or a	2389	variable changes, implement your own watchers, integrate net-snmp or a
1808	coroutine library and lots more. They are also occasionally useful if	2390	coroutine library and lots more. They are also occasionally useful if
1809	you cache some data and want to flush it before blocking (for example,	2391	you cache some data and want to flush it before blocking (for example,
1810	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2392	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1811	watcher).	2393	watcher).
1812		2394
1813	This is done by examining in each prepare call which file descriptors need	2395	This is done by examining in each prepare call which file descriptors
1814	to be watched by the other library, registering C<ev_io> watchers for	2396	need to be watched by the other library, registering C<ev_io> watchers
1815	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2397	for them and starting an C<ev_timer> watcher for any timeouts (many
1816	provide just this functionality). Then, in the check watcher you check for	2398	libraries provide exactly this functionality). Then, in the check watcher,
1817	any events that occured (by checking the pending status of all watchers	2399	you check for any events that occurred (by checking the pending status
1818	and stopping them) and call back into the library. The I/O and timer	2400	of all watchers and stopping them) and call back into the library. The
1819	callbacks will never actually be called (but must be valid nevertheless,	2401	I/O and timer callbacks will never actually be called (but must be valid
1820	because you never know, you know?).	2402	nevertheless, because you never know, you know?).
1821		2403
1822	As another example, the Perl Coro module uses these hooks to integrate	2404	As another example, the Perl Coro module uses these hooks to integrate
1823	coroutines into libev programs, by yielding to other active coroutines	2405	coroutines into libev programs, by yielding to other active coroutines
1824	during each prepare and only letting the process block if no coroutines	2406	during each prepare and only letting the process block if no coroutines
1825	are ready to run (it's actually more complicated: it only runs coroutines	2407	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1828	loop from blocking if lower-priority coroutines are active, thus mapping	2410	loop from blocking if lower-priority coroutines are active, thus mapping
1829	low-priority coroutines to idle/background tasks).	2411	low-priority coroutines to idle/background tasks).
1830		2412
1831	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2413	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1832	priority, to ensure that they are being run before any other watchers	2414	priority, to ensure that they are being run before any other watchers
		2415	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2416
1833	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2417	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1834	too) should not activate ("feed") events into libev. While libev fully	2418	activate ("feed") events into libev. While libev fully supports this, they
1835	supports this, they will be called before other C<ev_check> watchers	2419	might get executed before other C<ev_check> watchers did their job. As
1836	did their job. As C<ev_check> watchers are often used to embed other	2420	C<ev_check> watchers are often used to embed other (non-libev) event
1837	(non-libev) event loops those other event loops might be in an unusable	2421	loops those other event loops might be in an unusable state until their
1838	state until their C<ev_check> watcher ran (always remind yourself to	2422	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1839	coexist peacefully with others).	2423	others).
1840		2424
1841	=head3 Watcher-Specific Functions and Data Members	2425	=head3 Watcher-Specific Functions and Data Members
1842		2426
1843	=over 4	2427	=over 4
1844		2428
…		…
1846		2430
1847	=item ev_check_init (ev_check *, callback)	2431	=item ev_check_init (ev_check *, callback)
1848		2432
1849	Initialises and configures the prepare or check watcher - they have no	2433	Initialises and configures the prepare or check watcher - they have no
1850	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2434	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1851	macros, but using them is utterly, utterly and completely pointless.	2435	macros, but using them is utterly, utterly, utterly and completely
		2436	pointless.
1852		2437
1853	=back	2438	=back
1854		2439
1855	=head3 Examples	2440	=head3 Examples
1856		2441
1857	There are a number of principal ways to embed other event loops or modules	2442	There are a number of principal ways to embed other event loops or modules
1858	into libev. Here are some ideas on how to include libadns into libev	2443	into libev. Here are some ideas on how to include libadns into libev
1859	(there is a Perl module named C<EV::ADNS> that does this, which you could	2444	(there is a Perl module named C<EV::ADNS> that does this, which you could
1860	use for an actually working example. Another Perl module named C<EV::Glib>	2445	use as a working example. Another Perl module named C<EV::Glib> embeds a
1861	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2446	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1862	into the Glib event loop).	2447	Glib event loop).
1863		2448
1864	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2449	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1865	and in a check watcher, destroy them and call into libadns. What follows	2450	and in a check watcher, destroy them and call into libadns. What follows
1866	is pseudo-code only of course. This requires you to either use a low	2451	is pseudo-code only of course. This requires you to either use a low
1867	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2452	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1868	the callbacks for the IO/timeout watchers might not have been called yet.	2453	the callbacks for the IO/timeout watchers might not have been called yet.
1869		2454
1870	static ev_io iow [nfd];	2455	static ev_io iow [nfd];
1871	static ev_timer tw;	2456	static ev_timer tw;
1872		2457
1873	static void	2458	static void
1874	io_cb (ev_loop *loop, ev_io *w, int revents)	2459	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1875	{	2460	{
1876	}	2461	}
1877		2462
1878	// create io watchers for each fd and a timer before blocking	2463	// create io watchers for each fd and a timer before blocking
1879	static void	2464	static void
1880	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2465	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1881	{	2466	{
1882	int timeout = 3600000;	2467	int timeout = 3600000;
1883	struct pollfd fds [nfd];	2468	struct pollfd fds [nfd];
1884	// actual code will need to loop here and realloc etc.	2469	// actual code will need to loop here and realloc etc.
1885	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2470	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1886		2471
1887	/* the callback is illegal, but won't be called as we stop during check */	2472	/* the callback is illegal, but won't be called as we stop during check */
1888	ev_timer_init (&tw, 0, timeout * 1e-3);	2473	ev_timer_init (&tw, 0, timeout * 1e-3);
1889	ev_timer_start (loop, &tw);	2474	ev_timer_start (loop, &tw);
1890		2475
1891	// create one ev_io per pollfd	2476	// create one ev_io per pollfd
1892	for (int i = 0; i < nfd; ++i)	2477	for (int i = 0; i < nfd; ++i)
1893	{	2478	{
1894	ev_io_init (iow + i, io_cb, fds [i].fd,	2479	ev_io_init (iow + i, io_cb, fds [i].fd,
1895	((fds [i].events & POLLIN ? EV_READ : 0)	2480	((fds [i].events & POLLIN ? EV_READ : 0)
1896	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2481	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1897		2482
1898	fds [i].revents = 0;	2483	fds [i].revents = 0;
1899	ev_io_start (loop, iow + i);	2484	ev_io_start (loop, iow + i);
1900	}	2485	}
1901	}	2486	}
1902		2487
1903	// stop all watchers after blocking	2488	// stop all watchers after blocking
1904	static void	2489	static void
1905	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2490	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1906	{	2491	{
1907	ev_timer_stop (loop, &tw);	2492	ev_timer_stop (loop, &tw);
1908		2493
1909	for (int i = 0; i < nfd; ++i)	2494	for (int i = 0; i < nfd; ++i)
1910	{	2495	{
1911	// set the relevant poll flags	2496	// set the relevant poll flags
1912	// could also call adns_processreadable etc. here	2497	// could also call adns_processreadable etc. here
1913	struct pollfd *fd = fds + i;	2498	struct pollfd *fd = fds + i;
1914	int revents = ev_clear_pending (iow + i);	2499	int revents = ev_clear_pending (iow + i);
1915	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2500	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1916	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2501	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1917		2502
1918	// now stop the watcher	2503	// now stop the watcher
1919	ev_io_stop (loop, iow + i);	2504	ev_io_stop (loop, iow + i);
1920	}	2505	}
1921		2506
1922	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2507	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1923	}	2508	}
1924		2509
1925	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2510	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1926	in the prepare watcher and would dispose of the check watcher.	2511	in the prepare watcher and would dispose of the check watcher.
1927		2512
1928	Method 3: If the module to be embedded supports explicit event	2513	Method 3: If the module to be embedded supports explicit event
1929	notification (adns does), you can also make use of the actual watcher	2514	notification (libadns does), you can also make use of the actual watcher
1930	callbacks, and only destroy/create the watchers in the prepare watcher.	2515	callbacks, and only destroy/create the watchers in the prepare watcher.
1931		2516
1932	static void	2517	static void
1933	timer_cb (EV_P_ ev_timer *w, int revents)	2518	timer_cb (EV_P_ ev_timer *w, int revents)
1934	{	2519	{
1935	adns_state ads = (adns_state)w->data;	2520	adns_state ads = (adns_state)w->data;
1936	update_now (EV_A);	2521	update_now (EV_A);
1937		2522
1938	adns_processtimeouts (ads, &tv_now);	2523	adns_processtimeouts (ads, &tv_now);
1939	}	2524	}
1940		2525
1941	static void	2526	static void
1942	io_cb (EV_P_ ev_io *w, int revents)	2527	io_cb (EV_P_ ev_io *w, int revents)
1943	{	2528	{
1944	adns_state ads = (adns_state)w->data;	2529	adns_state ads = (adns_state)w->data;
1945	update_now (EV_A);	2530	update_now (EV_A);
1946		2531
1947	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2532	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1948	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2533	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1949	}	2534	}
1950		2535
1951	// do not ever call adns_afterpoll	2536	// do not ever call adns_afterpoll
1952		2537
1953	Method 4: Do not use a prepare or check watcher because the module you	2538	Method 4: Do not use a prepare or check watcher because the module you
1954	want to embed is too inflexible to support it. Instead, youc na override	2539	want to embed is not flexible enough to support it. Instead, you can
1955	their poll function. The drawback with this solution is that the main	2540	override their poll function. The drawback with this solution is that the
1956	loop is now no longer controllable by EV. The C<Glib::EV> module does	2541	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1957	this.	2542	this approach, effectively embedding EV as a client into the horrible
		2543	libglib event loop.
1958		2544
1959	static gint	2545	static gint
1960	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2546	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1961	{	2547	{
1962	int got_events = 0;	2548	int got_events = 0;
1963		2549
1964	for (n = 0; n < nfds; ++n)	2550	for (n = 0; n < nfds; ++n)
1965	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2551	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1966		2552
1967	if (timeout >= 0)	2553	if (timeout >= 0)
1968	// create/start timer	2554	// create/start timer
1969		2555
1970	// poll	2556	// poll
1971	ev_loop (EV_A_ 0);	2557	ev_loop (EV_A_ 0);
1972		2558
1973	// stop timer again	2559	// stop timer again
1974	if (timeout >= 0)	2560	if (timeout >= 0)
1975	ev_timer_stop (EV_A_ &to);	2561	ev_timer_stop (EV_A_ &to);
1976		2562
1977	// stop io watchers again - their callbacks should have set	2563	// stop io watchers again - their callbacks should have set
1978	for (n = 0; n < nfds; ++n)	2564	for (n = 0; n < nfds; ++n)
1979	ev_io_stop (EV_A_ iow [n]);	2565	ev_io_stop (EV_A_ iow [n]);
1980		2566
1981	return got_events;	2567	return got_events;
1982	}	2568	}
1983		2569
1984		2570
1985	=head2 C<ev_embed> - when one backend isn't enough...	2571	=head2 C<ev_embed> - when one backend isn't enough...
1986		2572
1987	This is a rather advanced watcher type that lets you embed one event loop	2573	This is a rather advanced watcher type that lets you embed one event loop
…		…
1993	prioritise I/O.	2579	prioritise I/O.
1994		2580
1995	As an example for a bug workaround, the kqueue backend might only support	2581	As an example for a bug workaround, the kqueue backend might only support
1996	sockets on some platform, so it is unusable as generic backend, but you	2582	sockets on some platform, so it is unusable as generic backend, but you
1997	still want to make use of it because you have many sockets and it scales	2583	still want to make use of it because you have many sockets and it scales
1998	so nicely. In this case, you would create a kqueue-based loop and embed it	2584	so nicely. In this case, you would create a kqueue-based loop and embed
1999	into your default loop (which might use e.g. poll). Overall operation will	2585	it into your default loop (which might use e.g. poll). Overall operation
2000	be a bit slower because first libev has to poll and then call kevent, but	2586	will be a bit slower because first libev has to call C<poll> and then
2001	at least you can use both at what they are best.	2587	C<kevent>, but at least you can use both mechanisms for what they are
		2588	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2002		2589
2003	As for prioritising I/O: rarely you have the case where some fds have	2590	As for prioritising I/O: under rare circumstances you have the case where
2004	to be watched and handled very quickly (with low latency), and even	2591	some fds have to be watched and handled very quickly (with low latency),
2005	priorities and idle watchers might have too much overhead. In this case	2592	and even priorities and idle watchers might have too much overhead. In
2006	you would put all the high priority stuff in one loop and all the rest in	2593	this case you would put all the high priority stuff in one loop and all
2007	a second one, and embed the second one in the first.	2594	the rest in a second one, and embed the second one in the first.
2008		2595
2009	As long as the watcher is active, the callback will be invoked every time	2596	As long as the watcher is active, the callback will be invoked every
2010	there might be events pending in the embedded loop. The callback must then	2597	time there might be events pending in the embedded loop. The callback
2011	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2598	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2012	their callbacks (you could also start an idle watcher to give the embedded	2599	sweep and invoke their callbacks (the callback doesn't need to invoke the
2013	loop strictly lower priority for example). You can also set the callback	2600	C<ev_embed_sweep> function directly, it could also start an idle watcher
2014	to C<0>, in which case the embed watcher will automatically execute the	2601	to give the embedded loop strictly lower priority for example).
2015	embedded loop sweep.
2016		2602
2017	As long as the watcher is started it will automatically handle events. The	2603	You can also set the callback to C<0>, in which case the embed watcher
2018	callback will be invoked whenever some events have been handled. You can	2604	will automatically execute the embedded loop sweep whenever necessary.
2019	set the callback to C<0> to avoid having to specify one if you are not
2020	interested in that.
2021		2605
2022	Also, there have not currently been made special provisions for forking:	2606	Fork detection will be handled transparently while the C<ev_embed> watcher
2023	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2607	is active, i.e., the embedded loop will automatically be forked when the
2024	but you will also have to stop and restart any C<ev_embed> watchers	2608	embedding loop forks. In other cases, the user is responsible for calling
2025	yourself.	2609	C<ev_loop_fork> on the embedded loop.
2026		2610
2027	Unfortunately, not all backends are embeddable, only the ones returned by	2611	Unfortunately, not all backends are embeddable: only the ones returned by
2028	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2612	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2029	portable one.	2613	portable one.
2030		2614
2031	So when you want to use this feature you will always have to be prepared	2615	So when you want to use this feature you will always have to be prepared
2032	that you cannot get an embeddable loop. The recommended way to get around	2616	that you cannot get an embeddable loop. The recommended way to get around
2033	this is to have a separate variables for your embeddable loop, try to	2617	this is to have a separate variables for your embeddable loop, try to
2034	create it, and if that fails, use the normal loop for everything.	2618	create it, and if that fails, use the normal loop for everything.
2035		2619
		2620	=head3 C<ev_embed> and fork
		2621
		2622	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2623	automatically be applied to the embedded loop as well, so no special
		2624	fork handling is required in that case. When the watcher is not running,
		2625	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2626	as applicable.
		2627
2036	=head3 Watcher-Specific Functions and Data Members	2628	=head3 Watcher-Specific Functions and Data Members
2037		2629
2038	=over 4	2630	=over 4
2039		2631
2040	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2632	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2043		2635
2044	Configures the watcher to embed the given loop, which must be	2636	Configures the watcher to embed the given loop, which must be
2045	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2637	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2046	invoked automatically, otherwise it is the responsibility of the callback	2638	invoked automatically, otherwise it is the responsibility of the callback
2047	to invoke it (it will continue to be called until the sweep has been done,	2639	to invoke it (it will continue to be called until the sweep has been done,
2048	if you do not want thta, you need to temporarily stop the embed watcher).	2640	if you do not want that, you need to temporarily stop the embed watcher).
2049		2641
2050	=item ev_embed_sweep (loop, ev_embed *)	2642	=item ev_embed_sweep (loop, ev_embed *)
2051		2643
2052	Make a single, non-blocking sweep over the embedded loop. This works	2644	Make a single, non-blocking sweep over the embedded loop. This works
2053	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2645	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
2054	apropriate way for embedded loops.	2646	appropriate way for embedded loops.
2055		2647
2056	=item struct ev_loop *other [read-only]	2648	=item struct ev_loop *other [read-only]
2057		2649
2058	The embedded event loop.	2650	The embedded event loop.
2059		2651
…		…
2061		2653
2062	=head3 Examples	2654	=head3 Examples
2063		2655
2064	Example: Try to get an embeddable event loop and embed it into the default	2656	Example: Try to get an embeddable event loop and embed it into the default
2065	event loop. If that is not possible, use the default loop. The default	2657	event loop. If that is not possible, use the default loop. The default
2066	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2658	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2067	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2659	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2068	used).	2660	used).
2069		2661
2070	struct ev_loop *loop_hi = ev_default_init (0);	2662	struct ev_loop *loop_hi = ev_default_init (0);
2071	struct ev_loop *loop_lo = 0;	2663	struct ev_loop *loop_lo = 0;
2072	struct ev_embed embed;	2664	ev_embed embed;
2073		2665
2074	// see if there is a chance of getting one that works	2666	// see if there is a chance of getting one that works
2075	// (remember that a flags value of 0 means autodetection)	2667	// (remember that a flags value of 0 means autodetection)
2076	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2668	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2077	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2669	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2078	: 0;	2670	: 0;
2079		2671
2080	// if we got one, then embed it, otherwise default to loop_hi	2672	// if we got one, then embed it, otherwise default to loop_hi
2081	if (loop_lo)	2673	if (loop_lo)
2082	{	2674	{
2083	ev_embed_init (&embed, 0, loop_lo);	2675	ev_embed_init (&embed, 0, loop_lo);
2084	ev_embed_start (loop_hi, &embed);	2676	ev_embed_start (loop_hi, &embed);
2085	}	2677	}
2086	else	2678	else
2087	loop_lo = loop_hi;	2679	loop_lo = loop_hi;
2088		2680
2089	Example: Check if kqueue is available but not recommended and create	2681	Example: Check if kqueue is available but not recommended and create
2090	a kqueue backend for use with sockets (which usually work with any	2682	a kqueue backend for use with sockets (which usually work with any
2091	kqueue implementation). Store the kqueue/socket-only event loop in	2683	kqueue implementation). Store the kqueue/socket-only event loop in
2092	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2684	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2093		2685
2094	struct ev_loop *loop = ev_default_init (0);	2686	struct ev_loop *loop = ev_default_init (0);
2095	struct ev_loop *loop_socket = 0;	2687	struct ev_loop *loop_socket = 0;
2096	struct ev_embed embed;	2688	ev_embed embed;
2097		2689
2098	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2690	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2099	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2691	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2100	{	2692	{
2101	ev_embed_init (&embed, 0, loop_socket);	2693	ev_embed_init (&embed, 0, loop_socket);
2102	ev_embed_start (loop, &embed);	2694	ev_embed_start (loop, &embed);
2103	}	2695	}
2104		2696
2105	if (!loop_socket)	2697	if (!loop_socket)
2106	loop_socket = loop;	2698	loop_socket = loop;
2107		2699
2108	// now use loop_socket for all sockets, and loop for everything else	2700	// now use loop_socket for all sockets, and loop for everything else
2109		2701
2110		2702
2111	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2703	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2112		2704
2113	Fork watchers are called when a C<fork ()> was detected (usually because	2705	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2116	event loop blocks next and before C<ev_check> watchers are being called,	2708	event loop blocks next and before C<ev_check> watchers are being called,
2117	and only in the child after the fork. If whoever good citizen calling	2709	and only in the child after the fork. If whoever good citizen calling
2118	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2710	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2119	handlers will be invoked, too, of course.	2711	handlers will be invoked, too, of course.
2120		2712
		2713	=head3 The special problem of life after fork - how is it possible?
		2714
		2715	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2716	up/change the process environment, followed by a call to C<exec()>. This
		2717	sequence should be handled by libev without any problems.
		2718
		2719	This changes when the application actually wants to do event handling
		2720	in the child, or both parent in child, in effect "continuing" after the
		2721	fork.
		2722
		2723	The default mode of operation (for libev, with application help to detect
		2724	forks) is to duplicate all the state in the child, as would be expected
		2725	when I<either> the parent I<or> the child process continues.
		2726
		2727	When both processes want to continue using libev, then this is usually the
		2728	wrong result. In that case, usually one process (typically the parent) is
		2729	supposed to continue with all watchers in place as before, while the other
		2730	process typically wants to start fresh, i.e. without any active watchers.
		2731
		2732	The cleanest and most efficient way to achieve that with libev is to
		2733	simply create a new event loop, which of course will be "empty", and
		2734	use that for new watchers. This has the advantage of not touching more
		2735	memory than necessary, and thus avoiding the copy-on-write, and the
		2736	disadvantage of having to use multiple event loops (which do not support
		2737	signal watchers).
		2738
		2739	When this is not possible, or you want to use the default loop for
		2740	other reasons, then in the process that wants to start "fresh", call
		2741	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2742	the default loop will "orphan" (not stop) all registered watchers, so you
		2743	have to be careful not to execute code that modifies those watchers. Note
		2744	also that in that case, you have to re-register any signal watchers.
		2745
2121	=head3 Watcher-Specific Functions and Data Members	2746	=head3 Watcher-Specific Functions and Data Members
2122		2747
2123	=over 4	2748	=over 4
2124		2749
2125	=item ev_fork_init (ev_signal *, callback)	2750	=item ev_fork_init (ev_signal *, callback)
…		…
2157	is that the author does not know of a simple (or any) algorithm for a	2782	is that the author does not know of a simple (or any) algorithm for a
2158	multiple-writer-single-reader queue that works in all cases and doesn't	2783	multiple-writer-single-reader queue that works in all cases and doesn't
2159	need elaborate support such as pthreads.	2784	need elaborate support such as pthreads.
2160		2785
2161	That means that if you want to queue data, you have to provide your own	2786	That means that if you want to queue data, you have to provide your own
2162	queue. But at least I can tell you would implement locking around your	2787	queue. But at least I can tell you how to implement locking around your
2163	queue:	2788	queue:
2164		2789
2165	=over 4	2790	=over 4
2166		2791
2167	=item queueing from a signal handler context	2792	=item queueing from a signal handler context
2168		2793
2169	To implement race-free queueing, you simply add to the queue in the signal	2794	To implement race-free queueing, you simply add to the queue in the signal
2170	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2795	handler but you block the signal handler in the watcher callback. Here is
2171	some fictitiuous SIGUSR1 handler:	2796	an example that does that for some fictitious SIGUSR1 handler:
2172		2797
2173	static ev_async mysig;	2798	static ev_async mysig;
2174		2799
2175	static void	2800	static void
2176	sigusr1_handler (void)	2801	sigusr1_handler (void)
…		…
2242	=over 4	2867	=over 4
2243		2868
2244	=item ev_async_init (ev_async *, callback)	2869	=item ev_async_init (ev_async *, callback)
2245		2870
2246	Initialises and configures the async watcher - it has no parameters of any	2871	Initialises and configures the async watcher - it has no parameters of any
2247	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2872	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2248	believe me.	2873	trust me.
2249		2874
2250	=item ev_async_send (loop, ev_async *)	2875	=item ev_async_send (loop, ev_async *)
2251		2876
2252	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2877	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2253	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2878	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2254	C<ev_feed_event>, this call is safe to do in other threads, signal or	2879	C<ev_feed_event>, this call is safe to do from other threads, signal or
2255	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	2880	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2256	section below on what exactly this means).	2881	section below on what exactly this means).
2257		2882
		2883	Note that, as with other watchers in libev, multiple events might get
		2884	compressed into a single callback invocation (another way to look at this
		2885	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2886	reset when the event loop detects that).
		2887
2258	This call incurs the overhead of a syscall only once per loop iteration,	2888	This call incurs the overhead of a system call only once per event loop
2259	so while the overhead might be noticable, it doesn't apply to repeated	2889	iteration, so while the overhead might be noticeable, it doesn't apply to
2260	calls to C<ev_async_send>.	2890	repeated calls to C<ev_async_send> for the same event loop.
		2891
		2892	=item bool = ev_async_pending (ev_async *)
		2893
		2894	Returns a non-zero value when C<ev_async_send> has been called on the
		2895	watcher but the event has not yet been processed (or even noted) by the
		2896	event loop.
		2897
		2898	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2899	the loop iterates next and checks for the watcher to have become active,
		2900	it will reset the flag again. C<ev_async_pending> can be used to very
		2901	quickly check whether invoking the loop might be a good idea.
		2902
		2903	Not that this does I<not> check whether the watcher itself is pending,
		2904	only whether it has been requested to make this watcher pending: there
		2905	is a time window between the event loop checking and resetting the async
		2906	notification, and the callback being invoked.
2261		2907
2262	=back	2908	=back
2263		2909
2264		2910
2265	=head1 OTHER FUNCTIONS	2911	=head1 OTHER FUNCTIONS
…		…
2269	=over 4	2915	=over 4
2270		2916
2271	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2917	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2272		2918
2273	This function combines a simple timer and an I/O watcher, calls your	2919	This function combines a simple timer and an I/O watcher, calls your
2274	callback on whichever event happens first and automatically stop both	2920	callback on whichever event happens first and automatically stops both
2275	watchers. This is useful if you want to wait for a single event on an fd	2921	watchers. This is useful if you want to wait for a single event on an fd
2276	or timeout without having to allocate/configure/start/stop/free one or	2922	or timeout without having to allocate/configure/start/stop/free one or
2277	more watchers yourself.	2923	more watchers yourself.
2278		2924
2279	If C<fd> is less than 0, then no I/O watcher will be started and events	2925	If C<fd> is less than 0, then no I/O watcher will be started and the
2280	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2926	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2281	C<events> set will be craeted and started.	2927	the given C<fd> and C<events> set will be created and started.
2282		2928
2283	If C<timeout> is less than 0, then no timeout watcher will be	2929	If C<timeout> is less than 0, then no timeout watcher will be
2284	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2930	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2285	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2931	repeat = 0) will be started. C<0> is a valid timeout.
2286	dubious value.
2287		2932
2288	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2933	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2289	passed an C<revents> set like normal event callbacks (a combination of	2934	passed an C<revents> set like normal event callbacks (a combination of
2290	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2935	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2291	value passed to C<ev_once>:	2936	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2937	a timeout and an io event at the same time - you probably should give io
		2938	events precedence.
2292		2939
		2940	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2941
2293	static void stdin_ready (int revents, void *arg)	2942	static void stdin_ready (int revents, void *arg)
2294	{	2943	{
2295	if (revents & EV_TIMEOUT)
2296	/* doh, nothing entered */;
2297	else if (revents & EV_READ)	2944	if (revents & EV_READ)
2298	/* stdin might have data for us, joy! */;	2945	/* stdin might have data for us, joy! */;
		2946	else if (revents & EV_TIMEOUT)
		2947	/* doh, nothing entered */;
2299	}	2948	}
2300		2949
2301	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2950	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2302		2951
2303	=item ev_feed_event (ev_loop *, watcher *, int revents)	2952	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2304		2953
2305	Feeds the given event set into the event loop, as if the specified event	2954	Feeds the given event set into the event loop, as if the specified event
2306	had happened for the specified watcher (which must be a pointer to an	2955	had happened for the specified watcher (which must be a pointer to an
2307	initialised but not necessarily started event watcher).	2956	initialised but not necessarily started event watcher).
2308		2957
2309	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2958	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2310		2959
2311	Feed an event on the given fd, as if a file descriptor backend detected	2960	Feed an event on the given fd, as if a file descriptor backend detected
2312	the given events it.	2961	the given events it.
2313		2962
2314	=item ev_feed_signal_event (ev_loop *loop, int signum)	2963	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2315		2964
2316	Feed an event as if the given signal occured (C<loop> must be the default	2965	Feed an event as if the given signal occurred (C<loop> must be the default
2317	loop!).	2966	loop!).
2318		2967
2319	=back	2968	=back
2320		2969
2321		2970
…		…
2337		2986
2338	=item * Priorities are not currently supported. Initialising priorities	2987	=item * Priorities are not currently supported. Initialising priorities
2339	will fail and all watchers will have the same priority, even though there	2988	will fail and all watchers will have the same priority, even though there
2340	is an ev_pri field.	2989	is an ev_pri field.
2341		2990
		2991	=item * In libevent, the last base created gets the signals, in libev, the
		2992	first base created (== the default loop) gets the signals.
		2993
2342	=item * Other members are not supported.	2994	=item * Other members are not supported.
2343		2995
2344	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2996	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2345	to use the libev header file and library.	2997	to use the libev header file and library.
2346		2998
2347	=back	2999	=back
2348		3000
2349	=head1 C++ SUPPORT	3001	=head1 C++ SUPPORT
2350		3002
2351	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3003	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2352	you to use some convinience methods to start/stop watchers and also change	3004	you to use some convenience methods to start/stop watchers and also change
2353	the callback model to a model using method callbacks on objects.	3005	the callback model to a model using method callbacks on objects.
2354		3006
2355	To use it,	3007	To use it,
2356		3008
2357	#include <ev++.h>	3009	#include <ev++.h>
2358		3010
2359	This automatically includes F<ev.h> and puts all of its definitions (many	3011	This automatically includes F<ev.h> and puts all of its definitions (many
2360	of them macros) into the global namespace. All C++ specific things are	3012	of them macros) into the global namespace. All C++ specific things are
2361	put into the C<ev> namespace. It should support all the same embedding	3013	put into the C<ev> namespace. It should support all the same embedding
2362	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3014	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2429	your compiler is good :), then the method will be fully inlined into the	3081	your compiler is good :), then the method will be fully inlined into the
2430	thunking function, making it as fast as a direct C callback.	3082	thunking function, making it as fast as a direct C callback.
2431		3083
2432	Example: simple class declaration and watcher initialisation	3084	Example: simple class declaration and watcher initialisation
2433		3085
2434	struct myclass	3086	struct myclass
2435	{	3087	{
2436	void io_cb (ev::io &w, int revents) { }	3088	void io_cb (ev::io &w, int revents) { }
2437	}	3089	}
2438		3090
2439	myclass obj;	3091	myclass obj;
2440	ev::io iow;	3092	ev::io iow;
2441	iow.set <myclass, &myclass::io_cb> (&obj);	3093	iow.set <myclass, &myclass::io_cb> (&obj);
		3094
		3095	=item w->set (object *)
		3096
		3097	This is an B<experimental> feature that might go away in a future version.
		3098
		3099	This is a variation of a method callback - leaving out the method to call
		3100	will default the method to C<operator ()>, which makes it possible to use
		3101	functor objects without having to manually specify the C<operator ()> all
		3102	the time. Incidentally, you can then also leave out the template argument
		3103	list.
		3104
		3105	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3106	int revents)>.
		3107
		3108	See the method-C<set> above for more details.
		3109
		3110	Example: use a functor object as callback.
		3111
		3112	struct myfunctor
		3113	{
		3114	void operator() (ev::io &w, int revents)
		3115	{
		3116	...
		3117	}
		3118	}
		3119
		3120	myfunctor f;
		3121
		3122	ev::io w;
		3123	w.set (&f);
2442		3124
2443	=item w->set<function> (void *data = 0)	3125	=item w->set<function> (void *data = 0)
2444		3126
2445	Also sets a callback, but uses a static method or plain function as	3127	Also sets a callback, but uses a static method or plain function as
2446	callback. The optional C<data> argument will be stored in the watcher's	3128	callback. The optional C<data> argument will be stored in the watcher's
…		…
2448		3130
2449	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3131	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2450		3132
2451	See the method-C<set> above for more details.	3133	See the method-C<set> above for more details.
2452		3134
2453	Example:	3135	Example: Use a plain function as callback.
2454		3136
2455	static void io_cb (ev::io &w, int revents) { }	3137	static void io_cb (ev::io &w, int revents) { }
2456	iow.set <io_cb> ();	3138	iow.set <io_cb> ();
2457		3139
2458	=item w->set (struct ev_loop *)	3140	=item w->set (struct ev_loop *)
2459		3141
2460	Associates a different C<struct ev_loop> with this watcher. You can only	3142	Associates a different C<struct ev_loop> with this watcher. You can only
2461	do this when the watcher is inactive (and not pending either).	3143	do this when the watcher is inactive (and not pending either).
2462		3144
2463	=item w->set ([args])	3145	=item w->set ([arguments])
2464		3146
2465	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3147	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2466	called at least once. Unlike the C counterpart, an active watcher gets	3148	called at least once. Unlike the C counterpart, an active watcher gets
2467	automatically stopped and restarted when reconfiguring it with this	3149	automatically stopped and restarted when reconfiguring it with this
2468	method.	3150	method.
2469		3151
2470	=item w->start ()	3152	=item w->start ()
…		…
2494	=back	3176	=back
2495		3177
2496	Example: Define a class with an IO and idle watcher, start one of them in	3178	Example: Define a class with an IO and idle watcher, start one of them in
2497	the constructor.	3179	the constructor.
2498		3180
2499	class myclass	3181	class myclass
2500	{	3182	{
2501	ev::io io; void io_cb (ev::io &w, int revents);	3183	ev::io io ; void io_cb (ev::io &w, int revents);
2502	ev:idle idle void idle_cb (ev::idle &w, int revents);	3184	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2503		3185
2504	myclass (int fd)	3186	myclass (int fd)
2505	{	3187	{
2506	io .set <myclass, &myclass::io_cb > (this);	3188	io .set <myclass, &myclass::io_cb > (this);
2507	idle.set <myclass, &myclass::idle_cb> (this);	3189	idle.set <myclass, &myclass::idle_cb> (this);
2508		3190
2509	io.start (fd, ev::READ);	3191	io.start (fd, ev::READ);
2510	}	3192	}
2511	};	3193	};
2512		3194
2513		3195
2514	=head1 OTHER LANGUAGE BINDINGS	3196	=head1 OTHER LANGUAGE BINDINGS
2515		3197
2516	Libev does not offer other language bindings itself, but bindings for a	3198	Libev does not offer other language bindings itself, but bindings for a
2517	numbe rof languages exist in the form of third-party packages. If you know	3199	number of languages exist in the form of third-party packages. If you know
2518	any interesting language binding in addition to the ones listed here, drop	3200	any interesting language binding in addition to the ones listed here, drop
2519	me a note.	3201	me a note.
2520		3202
2521	=over 4	3203	=over 4
2522		3204
2523	=item Perl	3205	=item Perl
2524		3206
2525	The EV module implements the full libev API and is actually used to test	3207	The EV module implements the full libev API and is actually used to test
2526	libev. EV is developed together with libev. Apart from the EV core module,	3208	libev. EV is developed together with libev. Apart from the EV core module,
2527	there are additional modules that implement libev-compatible interfaces	3209	there are additional modules that implement libev-compatible interfaces
2528	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3210	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2529	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3211	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3212	and C<EV::Glib>).
2530		3213
2531	It can be found and installed via CPAN, its homepage is found at	3214	It can be found and installed via CPAN, its homepage is at
2532	L<http://software.schmorp.de/pkg/EV>.	3215	L<http://software.schmorp.de/pkg/EV>.
2533		3216
		3217	=item Python
		3218
		3219	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3220	seems to be quite complete and well-documented.
		3221
2534	=item Ruby	3222	=item Ruby
2535		3223
2536	Tony Arcieri has written a ruby extension that offers access to a subset	3224	Tony Arcieri has written a ruby extension that offers access to a subset
2537	of the libev API and adds filehandle abstractions, asynchronous DNS and	3225	of the libev API and adds file handle abstractions, asynchronous DNS and
2538	more on top of it. It can be found via gem servers. Its homepage is at	3226	more on top of it. It can be found via gem servers. Its homepage is at
2539	L<http://rev.rubyforge.org/>.	3227	L<http://rev.rubyforge.org/>.
2540		3228
		3229	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3230	makes rev work even on mingw.
		3231
		3232	=item Haskell
		3233
		3234	A haskell binding to libev is available at
		3235	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3236
2541	=item D	3237	=item D
2542		3238
2543	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3239	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2544	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3240	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3241
		3242	=item Ocaml
		3243
		3244	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3245	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2545		3246
2546	=back	3247	=back
2547		3248
2548		3249
2549	=head1 MACRO MAGIC	3250	=head1 MACRO MAGIC
2550		3251
2551	Libev can be compiled with a variety of options, the most fundamantal	3252	Libev can be compiled with a variety of options, the most fundamental
2552	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3253	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2553	functions and callbacks have an initial C<struct ev_loop *> argument.	3254	functions and callbacks have an initial C<struct ev_loop *> argument.
2554		3255
2555	To make it easier to write programs that cope with either variant, the	3256	To make it easier to write programs that cope with either variant, the
2556	following macros are defined:	3257	following macros are defined:
…		…
2561		3262
2562	This provides the loop I<argument> for functions, if one is required ("ev	3263	This provides the loop I<argument> for functions, if one is required ("ev
2563	loop argument"). The C<EV_A> form is used when this is the sole argument,	3264	loop argument"). The C<EV_A> form is used when this is the sole argument,
2564	C<EV_A_> is used when other arguments are following. Example:	3265	C<EV_A_> is used when other arguments are following. Example:
2565		3266
2566	ev_unref (EV_A);	3267	ev_unref (EV_A);
2567	ev_timer_add (EV_A_ watcher);	3268	ev_timer_add (EV_A_ watcher);
2568	ev_loop (EV_A_ 0);	3269	ev_loop (EV_A_ 0);
2569		3270
2570	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3271	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2571	which is often provided by the following macro.	3272	which is often provided by the following macro.
2572		3273
2573	=item C<EV_P>, C<EV_P_>	3274	=item C<EV_P>, C<EV_P_>
2574		3275
2575	This provides the loop I<parameter> for functions, if one is required ("ev	3276	This provides the loop I<parameter> for functions, if one is required ("ev
2576	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3277	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2577	C<EV_P_> is used when other parameters are following. Example:	3278	C<EV_P_> is used when other parameters are following. Example:
2578		3279
2579	// this is how ev_unref is being declared	3280	// this is how ev_unref is being declared
2580	static void ev_unref (EV_P);	3281	static void ev_unref (EV_P);
2581		3282
2582	// this is how you can declare your typical callback	3283	// this is how you can declare your typical callback
2583	static void cb (EV_P_ ev_timer *w, int revents)	3284	static void cb (EV_P_ ev_timer *w, int revents)
2584		3285
2585	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3286	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2586	suitable for use with C<EV_A>.	3287	suitable for use with C<EV_A>.
2587		3288
2588	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3289	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2589		3290
2590	Similar to the other two macros, this gives you the value of the default	3291	Similar to the other two macros, this gives you the value of the default
2591	loop, if multiple loops are supported ("ev loop default").	3292	loop, if multiple loops are supported ("ev loop default").
		3293
		3294	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3295
		3296	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3297	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3298	is undefined when the default loop has not been initialised by a previous
		3299	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3300
		3301	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3302	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2592		3303
2593	=back	3304	=back
2594		3305
2595	Example: Declare and initialise a check watcher, utilising the above	3306	Example: Declare and initialise a check watcher, utilising the above
2596	macros so it will work regardless of whether multiple loops are supported	3307	macros so it will work regardless of whether multiple loops are supported
2597	or not.	3308	or not.
2598		3309
2599	static void	3310	static void
2600	check_cb (EV_P_ ev_timer *w, int revents)	3311	check_cb (EV_P_ ev_timer *w, int revents)
2601	{	3312	{
2602	ev_check_stop (EV_A_ w);	3313	ev_check_stop (EV_A_ w);
2603	}	3314	}
2604		3315
2605	ev_check check;	3316	ev_check check;
2606	ev_check_init (&check, check_cb);	3317	ev_check_init (&check, check_cb);
2607	ev_check_start (EV_DEFAULT_ &check);	3318	ev_check_start (EV_DEFAULT_ &check);
2608	ev_loop (EV_DEFAULT_ 0);	3319	ev_loop (EV_DEFAULT_ 0);
2609		3320
2610	=head1 EMBEDDING	3321	=head1 EMBEDDING
2611		3322
2612	Libev can (and often is) directly embedded into host	3323	Libev can (and often is) directly embedded into host
2613	applications. Examples of applications that embed it include the Deliantra	3324	applications. Examples of applications that embed it include the Deliantra
…		…
2620	libev somewhere in your source tree).	3331	libev somewhere in your source tree).
2621		3332
2622	=head2 FILESETS	3333	=head2 FILESETS
2623		3334
2624	Depending on what features you need you need to include one or more sets of files	3335	Depending on what features you need you need to include one or more sets of files
2625	in your app.	3336	in your application.
2626		3337
2627	=head3 CORE EVENT LOOP	3338	=head3 CORE EVENT LOOP
2628		3339
2629	To include only the libev core (all the C<ev_*> functions), with manual	3340	To include only the libev core (all the C<ev_*> functions), with manual
2630	configuration (no autoconf):	3341	configuration (no autoconf):
2631		3342
2632	#define EV_STANDALONE 1	3343	#define EV_STANDALONE 1
2633	#include "ev.c"	3344	#include "ev.c"
2634		3345
2635	This will automatically include F<ev.h>, too, and should be done in a	3346	This will automatically include F<ev.h>, too, and should be done in a
2636	single C source file only to provide the function implementations. To use	3347	single C source file only to provide the function implementations. To use
2637	it, do the same for F<ev.h> in all files wishing to use this API (best	3348	it, do the same for F<ev.h> in all files wishing to use this API (best
2638	done by writing a wrapper around F<ev.h> that you can include instead and	3349	done by writing a wrapper around F<ev.h> that you can include instead and
2639	where you can put other configuration options):	3350	where you can put other configuration options):
2640		3351
2641	#define EV_STANDALONE 1	3352	#define EV_STANDALONE 1
2642	#include "ev.h"	3353	#include "ev.h"
2643		3354
2644	Both header files and implementation files can be compiled with a C++	3355	Both header files and implementation files can be compiled with a C++
2645	compiler (at least, thats a stated goal, and breakage will be treated	3356	compiler (at least, that's a stated goal, and breakage will be treated
2646	as a bug).	3357	as a bug).
2647		3358
2648	You need the following files in your source tree, or in a directory	3359	You need the following files in your source tree, or in a directory
2649	in your include path (e.g. in libev/ when using -Ilibev):	3360	in your include path (e.g. in libev/ when using -Ilibev):
2650		3361
2651	ev.h	3362	ev.h
2652	ev.c	3363	ev.c
2653	ev_vars.h	3364	ev_vars.h
2654	ev_wrap.h	3365	ev_wrap.h
2655		3366
2656	ev_win32.c required on win32 platforms only	3367	ev_win32.c required on win32 platforms only
2657		3368
2658	ev_select.c only when select backend is enabled (which is enabled by default)	3369	ev_select.c only when select backend is enabled (which is enabled by default)
2659	ev_poll.c only when poll backend is enabled (disabled by default)	3370	ev_poll.c only when poll backend is enabled (disabled by default)
2660	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3371	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2661	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3372	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2662	ev_port.c only when the solaris port backend is enabled (disabled by default)	3373	ev_port.c only when the solaris port backend is enabled (disabled by default)
2663		3374
2664	F<ev.c> includes the backend files directly when enabled, so you only need	3375	F<ev.c> includes the backend files directly when enabled, so you only need
2665	to compile this single file.	3376	to compile this single file.
2666		3377
2667	=head3 LIBEVENT COMPATIBILITY API	3378	=head3 LIBEVENT COMPATIBILITY API
2668		3379
2669	To include the libevent compatibility API, also include:	3380	To include the libevent compatibility API, also include:
2670		3381
2671	#include "event.c"	3382	#include "event.c"
2672		3383
2673	in the file including F<ev.c>, and:	3384	in the file including F<ev.c>, and:
2674		3385
2675	#include "event.h"	3386	#include "event.h"
2676		3387
2677	in the files that want to use the libevent API. This also includes F<ev.h>.	3388	in the files that want to use the libevent API. This also includes F<ev.h>.
2678		3389
2679	You need the following additional files for this:	3390	You need the following additional files for this:
2680		3391
2681	event.h	3392	event.h
2682	event.c	3393	event.c
2683		3394
2684	=head3 AUTOCONF SUPPORT	3395	=head3 AUTOCONF SUPPORT
2685		3396
2686	Instead of using C<EV_STANDALONE=1> and providing your config in	3397	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2687	whatever way you want, you can also C<m4_include([libev.m4])> in your	3398	whatever way you want, you can also C<m4_include([libev.m4])> in your
2688	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3399	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2689	include F<config.h> and configure itself accordingly.	3400	include F<config.h> and configure itself accordingly.
2690		3401
2691	For this of course you need the m4 file:	3402	For this of course you need the m4 file:
2692		3403
2693	libev.m4	3404	libev.m4
2694		3405
2695	=head2 PREPROCESSOR SYMBOLS/MACROS	3406	=head2 PREPROCESSOR SYMBOLS/MACROS
2696		3407
2697	Libev can be configured via a variety of preprocessor symbols you have to define	3408	Libev can be configured via a variety of preprocessor symbols you have to
2698	before including any of its files. The default is not to build for multiplicity	3409	define before including any of its files. The default in the absence of
2699	and only include the select backend.	3410	autoconf is documented for every option.
2700		3411
2701	=over 4	3412	=over 4
2702		3413
2703	=item EV_STANDALONE	3414	=item EV_STANDALONE
2704		3415
…		…
2706	keeps libev from including F<config.h>, and it also defines dummy	3417	keeps libev from including F<config.h>, and it also defines dummy
2707	implementations for some libevent functions (such as logging, which is not	3418	implementations for some libevent functions (such as logging, which is not
2708	supported). It will also not define any of the structs usually found in	3419	supported). It will also not define any of the structs usually found in
2709	F<event.h> that are not directly supported by the libev core alone.	3420	F<event.h> that are not directly supported by the libev core alone.
2710		3421
		3422	In stanbdalone mode, libev will still try to automatically deduce the
		3423	configuration, but has to be more conservative.
		3424
2711	=item EV_USE_MONOTONIC	3425	=item EV_USE_MONOTONIC
2712		3426
2713	If defined to be C<1>, libev will try to detect the availability of the	3427	If defined to be C<1>, libev will try to detect the availability of the
2714	monotonic clock option at both compiletime and runtime. Otherwise no use	3428	monotonic clock option at both compile time and runtime. Otherwise no
2715	of the monotonic clock option will be attempted. If you enable this, you	3429	use of the monotonic clock option will be attempted. If you enable this,
2716	usually have to link against librt or something similar. Enabling it when	3430	you usually have to link against librt or something similar. Enabling it
2717	the functionality isn't available is safe, though, although you have	3431	when the functionality isn't available is safe, though, although you have
2718	to make sure you link against any libraries where the C<clock_gettime>	3432	to make sure you link against any libraries where the C<clock_gettime>
2719	function is hiding in (often F<-lrt>).	3433	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2720		3434
2721	=item EV_USE_REALTIME	3435	=item EV_USE_REALTIME
2722		3436
2723	If defined to be C<1>, libev will try to detect the availability of the	3437	If defined to be C<1>, libev will try to detect the availability of the
2724	realtime clock option at compiletime (and assume its availability at	3438	real-time clock option at compile time (and assume its availability
2725	runtime if successful). Otherwise no use of the realtime clock option will	3439	at runtime if successful). Otherwise no use of the real-time clock
2726	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3440	option will be attempted. This effectively replaces C<gettimeofday>
2727	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3441	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2728	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3442	correctness. See the note about libraries in the description of
		3443	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3444	C<EV_USE_CLOCK_SYSCALL>.
		3445
		3446	=item EV_USE_CLOCK_SYSCALL
		3447
		3448	If defined to be C<1>, libev will try to use a direct syscall instead
		3449	of calling the system-provided C<clock_gettime> function. This option
		3450	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3451	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3452	programs needlessly. Using a direct syscall is slightly slower (in
		3453	theory), because no optimised vdso implementation can be used, but avoids
		3454	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3455	higher, as it simplifies linking (no need for C<-lrt>).
2729		3456
2730	=item EV_USE_NANOSLEEP	3457	=item EV_USE_NANOSLEEP
2731		3458
2732	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3459	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2733	and will use it for delays. Otherwise it will use C<select ()>.	3460	and will use it for delays. Otherwise it will use C<select ()>.
2734		3461
		3462	=item EV_USE_EVENTFD
		3463
		3464	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3465	available and will probe for kernel support at runtime. This will improve
		3466	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3467	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3468	2.7 or newer, otherwise disabled.
		3469
2735	=item EV_USE_SELECT	3470	=item EV_USE_SELECT
2736		3471
2737	If undefined or defined to be C<1>, libev will compile in support for the	3472	If undefined or defined to be C<1>, libev will compile in support for the
2738	C<select>(2) backend. No attempt at autodetection will be done: if no	3473	C<select>(2) backend. No attempt at auto-detection will be done: if no
2739	other method takes over, select will be it. Otherwise the select backend	3474	other method takes over, select will be it. Otherwise the select backend
2740	will not be compiled in.	3475	will not be compiled in.
2741		3476
2742	=item EV_SELECT_USE_FD_SET	3477	=item EV_SELECT_USE_FD_SET
2743		3478
2744	If defined to C<1>, then the select backend will use the system C<fd_set>	3479	If defined to C<1>, then the select backend will use the system C<fd_set>
2745	structure. This is useful if libev doesn't compile due to a missing	3480	structure. This is useful if libev doesn't compile due to a missing
2746	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3481	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2747	exotic systems. This usually limits the range of file descriptors to some	3482	on exotic systems. This usually limits the range of file descriptors to
2748	low limit such as 1024 or might have other limitations (winsocket only	3483	some low limit such as 1024 or might have other limitations (winsocket
2749	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3484	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2750	influence the size of the C<fd_set> used.	3485	configures the maximum size of the C<fd_set>.
2751		3486
2752	=item EV_SELECT_IS_WINSOCKET	3487	=item EV_SELECT_IS_WINSOCKET
2753		3488
2754	When defined to C<1>, the select backend will assume that	3489	When defined to C<1>, the select backend will assume that
2755	select/socket/connect etc. don't understand file descriptors but	3490	select/socket/connect etc. don't understand file descriptors but
…		…
2775		3510
2776	=item EV_USE_EPOLL	3511	=item EV_USE_EPOLL
2777		3512
2778	If defined to be C<1>, libev will compile in support for the Linux	3513	If defined to be C<1>, libev will compile in support for the Linux
2779	C<epoll>(7) backend. Its availability will be detected at runtime,	3514	C<epoll>(7) backend. Its availability will be detected at runtime,
2780	otherwise another method will be used as fallback. This is the	3515	otherwise another method will be used as fallback. This is the preferred
2781	preferred backend for GNU/Linux systems.	3516	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3517	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2782		3518
2783	=item EV_USE_KQUEUE	3519	=item EV_USE_KQUEUE
2784		3520
2785	If defined to be C<1>, libev will compile in support for the BSD style	3521	If defined to be C<1>, libev will compile in support for the BSD style
2786	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3522	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2799	otherwise another method will be used as fallback. This is the preferred	3535	otherwise another method will be used as fallback. This is the preferred
2800	backend for Solaris 10 systems.	3536	backend for Solaris 10 systems.
2801		3537
2802	=item EV_USE_DEVPOLL	3538	=item EV_USE_DEVPOLL
2803		3539
2804	reserved for future expansion, works like the USE symbols above.	3540	Reserved for future expansion, works like the USE symbols above.
2805		3541
2806	=item EV_USE_INOTIFY	3542	=item EV_USE_INOTIFY
2807		3543
2808	If defined to be C<1>, libev will compile in support for the Linux inotify	3544	If defined to be C<1>, libev will compile in support for the Linux inotify
2809	interface to speed up C<ev_stat> watchers. Its actual availability will	3545	interface to speed up C<ev_stat> watchers. Its actual availability will
2810	be detected at runtime.	3546	be detected at runtime. If undefined, it will be enabled if the headers
		3547	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2811		3548
2812	=item EV_ATOMIC_T	3549	=item EV_ATOMIC_T
2813		3550
2814	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	3551	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2815	access is atomic with respect to other threads or signal contexts. No such	3552	access is atomic with respect to other threads or signal contexts. No such
2816	type is easily found in the C language, so you can provide your own type	3553	type is easily found in the C language, so you can provide your own type
2817	that you know is safe for your purposes. It is used both for signal handler "locking"	3554	that you know is safe for your purposes. It is used both for signal handler "locking"
2818	as well as for signal and thread safety in C<ev_async> watchers.	3555	as well as for signal and thread safety in C<ev_async> watchers.
2819		3556
2820	In the absense of this define, libev will use C<sig_atomic_t volatile>	3557	In the absence of this define, libev will use C<sig_atomic_t volatile>
2821	(from F<signal.h>), which is usually good enough on most platforms.	3558	(from F<signal.h>), which is usually good enough on most platforms.
2822		3559
2823	=item EV_H	3560	=item EV_H
2824		3561
2825	The name of the F<ev.h> header file used to include it. The default if	3562	The name of the F<ev.h> header file used to include it. The default if
…		…
2864	When doing priority-based operations, libev usually has to linearly search	3601	When doing priority-based operations, libev usually has to linearly search
2865	all the priorities, so having many of them (hundreds) uses a lot of space	3602	all the priorities, so having many of them (hundreds) uses a lot of space
2866	and time, so using the defaults of five priorities (-2 .. +2) is usually	3603	and time, so using the defaults of five priorities (-2 .. +2) is usually
2867	fine.	3604	fine.
2868		3605
2869	If your embedding app does not need any priorities, defining these both to	3606	If your embedding application does not need any priorities, defining these
2870	C<0> will save some memory and cpu.	3607	both to C<0> will save some memory and CPU.
2871		3608
2872	=item EV_PERIODIC_ENABLE	3609	=item EV_PERIODIC_ENABLE
2873		3610
2874	If undefined or defined to be C<1>, then periodic timers are supported. If	3611	If undefined or defined to be C<1>, then periodic timers are supported. If
2875	defined to be C<0>, then they are not. Disabling them saves a few kB of	3612	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2882	code.	3619	code.
2883		3620
2884	=item EV_EMBED_ENABLE	3621	=item EV_EMBED_ENABLE
2885		3622
2886	If undefined or defined to be C<1>, then embed watchers are supported. If	3623	If undefined or defined to be C<1>, then embed watchers are supported. If
2887	defined to be C<0>, then they are not.	3624	defined to be C<0>, then they are not. Embed watchers rely on most other
		3625	watcher types, which therefore must not be disabled.
2888		3626
2889	=item EV_STAT_ENABLE	3627	=item EV_STAT_ENABLE
2890		3628
2891	If undefined or defined to be C<1>, then stat watchers are supported. If	3629	If undefined or defined to be C<1>, then stat watchers are supported. If
2892	defined to be C<0>, then they are not.	3630	defined to be C<0>, then they are not.
…		…
2902	defined to be C<0>, then they are not.	3640	defined to be C<0>, then they are not.
2903		3641
2904	=item EV_MINIMAL	3642	=item EV_MINIMAL
2905		3643
2906	If you need to shave off some kilobytes of code at the expense of some	3644	If you need to shave off some kilobytes of code at the expense of some
2907	speed, define this symbol to C<1>. Currently only used for gcc to override	3645	speed, define this symbol to C<1>. Currently this is used to override some
2908	some inlining decisions, saves roughly 30% codesize of amd64.	3646	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3647	much smaller 2-heap for timer management over the default 4-heap.
2909		3648
2910	=item EV_PID_HASHSIZE	3649	=item EV_PID_HASHSIZE
2911		3650
2912	C<ev_child> watchers use a small hash table to distribute workload by	3651	C<ev_child> watchers use a small hash table to distribute workload by
2913	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3652	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2920	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3659	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2921	usually more than enough. If you need to manage thousands of C<ev_stat>	3660	usually more than enough. If you need to manage thousands of C<ev_stat>
2922	watchers you might want to increase this value (I<must> be a power of	3661	watchers you might want to increase this value (I<must> be a power of
2923	two).	3662	two).
2924		3663
		3664	=item EV_USE_4HEAP
		3665
		3666	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3667	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3668	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3669	faster performance with many (thousands) of watchers.
		3670
		3671	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3672	(disabled).
		3673
		3674	=item EV_HEAP_CACHE_AT
		3675
		3676	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3677	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3678	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3679	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3680	but avoids random read accesses on heap changes. This improves performance
		3681	noticeably with many (hundreds) of watchers.
		3682
		3683	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3684	(disabled).
		3685
		3686	=item EV_VERIFY
		3687
		3688	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3689	be done: If set to C<0>, no internal verification code will be compiled
		3690	in. If set to C<1>, then verification code will be compiled in, but not
		3691	called. If set to C<2>, then the internal verification code will be
		3692	called once per loop, which can slow down libev. If set to C<3>, then the
		3693	verification code will be called very frequently, which will slow down
		3694	libev considerably.
		3695
		3696	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3697	C<0>.
		3698
2925	=item EV_COMMON	3699	=item EV_COMMON
2926		3700
2927	By default, all watchers have a C<void *data> member. By redefining	3701	By default, all watchers have a C<void *data> member. By redefining
2928	this macro to a something else you can include more and other types of	3702	this macro to a something else you can include more and other types of
2929	members. You have to define it each time you include one of the files,	3703	members. You have to define it each time you include one of the files,
2930	though, and it must be identical each time.	3704	though, and it must be identical each time.
2931		3705
2932	For example, the perl EV module uses something like this:	3706	For example, the perl EV module uses something like this:
2933		3707
2934	#define EV_COMMON \	3708	#define EV_COMMON \
2935	SV *self; /* contains this struct */ \	3709	SV *self; /* contains this struct */ \
2936	SV *cb_sv, *fh /* note no trailing ";" */	3710	SV *cb_sv, *fh /* note no trailing ";" */
2937		3711
2938	=item EV_CB_DECLARE (type)	3712	=item EV_CB_DECLARE (type)
2939		3713
2940	=item EV_CB_INVOKE (watcher, revents)	3714	=item EV_CB_INVOKE (watcher, revents)
2941		3715
…		…
2946	definition and a statement, respectively. See the F<ev.h> header file for	3720	definition and a statement, respectively. See the F<ev.h> header file for
2947	their default definitions. One possible use for overriding these is to	3721	their default definitions. One possible use for overriding these is to
2948	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3722	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2949	method calls instead of plain function calls in C++.	3723	method calls instead of plain function calls in C++.
2950		3724
		3725	=back
		3726
2951	=head2 EXPORTED API SYMBOLS	3727	=head2 EXPORTED API SYMBOLS
2952		3728
2953	If you need to re-export the API (e.g. via a dll) and you need a list of	3729	If you need to re-export the API (e.g. via a DLL) and you need a list of
2954	exported symbols, you can use the provided F<Symbol.*> files which list	3730	exported symbols, you can use the provided F<Symbol.*> files which list
2955	all public symbols, one per line:	3731	all public symbols, one per line:
2956		3732
2957	Symbols.ev for libev proper	3733	Symbols.ev for libev proper
2958	Symbols.event for the libevent emulation	3734	Symbols.event for the libevent emulation
2959		3735
2960	This can also be used to rename all public symbols to avoid clashes with	3736	This can also be used to rename all public symbols to avoid clashes with
2961	multiple versions of libev linked together (which is obviously bad in	3737	multiple versions of libev linked together (which is obviously bad in
2962	itself, but sometimes it is inconvinient to avoid this).	3738	itself, but sometimes it is inconvenient to avoid this).
2963		3739
2964	A sed command like this will create wrapper C<#define>'s that you need to	3740	A sed command like this will create wrapper C<#define>'s that you need to
2965	include before including F<ev.h>:	3741	include before including F<ev.h>:
2966		3742
2967	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3743	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2984	file.	3760	file.
2985		3761
2986	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3762	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2987	that everybody includes and which overrides some configure choices:	3763	that everybody includes and which overrides some configure choices:
2988		3764
2989	#define EV_MINIMAL 1	3765	#define EV_MINIMAL 1
2990	#define EV_USE_POLL 0	3766	#define EV_USE_POLL 0
2991	#define EV_MULTIPLICITY 0	3767	#define EV_MULTIPLICITY 0
2992	#define EV_PERIODIC_ENABLE 0	3768	#define EV_PERIODIC_ENABLE 0
2993	#define EV_STAT_ENABLE 0	3769	#define EV_STAT_ENABLE 0
2994	#define EV_FORK_ENABLE 0	3770	#define EV_FORK_ENABLE 0
2995	#define EV_CONFIG_H <config.h>	3771	#define EV_CONFIG_H <config.h>
2996	#define EV_MINPRI 0	3772	#define EV_MINPRI 0
2997	#define EV_MAXPRI 0	3773	#define EV_MAXPRI 0
2998		3774
2999	#include "ev++.h"	3775	#include "ev++.h"
3000		3776
3001	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3777	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3002		3778
3003	#include "ev_cpp.h"	3779	#include "ev_cpp.h"
3004	#include "ev.c"	3780	#include "ev.c"
3005		3781
		3782	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3006		3783
3007	=head1 COMPLEXITIES	3784	=head2 THREADS AND COROUTINES
3008		3785
3009	In this section the complexities of (many of) the algorithms used inside	3786	=head3 THREADS
3010	libev will be explained. For complexity discussions about backends see the
3011	documentation for C<ev_default_init>.
3012		3787
3013	All of the following are about amortised time: If an array needs to be	3788	All libev functions are reentrant and thread-safe unless explicitly
3014	extended, libev needs to realloc and move the whole array, but this	3789	documented otherwise, but libev implements no locking itself. This means
3015	happens asymptotically never with higher number of elements, so O(1) might	3790	that you can use as many loops as you want in parallel, as long as there
3016	mean it might do a lengthy realloc operation in rare cases, but on average	3791	are no concurrent calls into any libev function with the same loop
3017	it is much faster and asymptotically approaches constant time.	3792	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3793	of course): libev guarantees that different event loops share no data
		3794	structures that need any locking.
		3795
		3796	Or to put it differently: calls with different loop parameters can be done
		3797	concurrently from multiple threads, calls with the same loop parameter
		3798	must be done serially (but can be done from different threads, as long as
		3799	only one thread ever is inside a call at any point in time, e.g. by using
		3800	a mutex per loop).
		3801
		3802	Specifically to support threads (and signal handlers), libev implements
		3803	so-called C<ev_async> watchers, which allow some limited form of
		3804	concurrency on the same event loop, namely waking it up "from the
		3805	outside".
		3806
		3807	If you want to know which design (one loop, locking, or multiple loops
		3808	without or something else still) is best for your problem, then I cannot
		3809	help you, but here is some generic advice:
3018		3810
3019	=over 4	3811	=over 4
3020		3812
3021	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3813	=item * most applications have a main thread: use the default libev loop
		3814	in that thread, or create a separate thread running only the default loop.
3022		3815
3023	This means that, when you have a watcher that triggers in one hour and	3816	This helps integrating other libraries or software modules that use libev
3024	there are 100 watchers that would trigger before that then inserting will	3817	themselves and don't care/know about threading.
3025	have to skip roughly seven (C<ld 100>) of these watchers.
3026		3818
3027	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3819	=item * one loop per thread is usually a good model.
3028		3820
3029	That means that changing a timer costs less than removing/adding them	3821	Doing this is almost never wrong, sometimes a better-performance model
3030	as only the relative motion in the event queue has to be paid for.	3822	exists, but it is always a good start.
3031		3823
3032	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3824	=item * other models exist, such as the leader/follower pattern, where one
		3825	loop is handed through multiple threads in a kind of round-robin fashion.
3033		3826
3034	These just add the watcher into an array or at the head of a list.	3827	Choosing a model is hard - look around, learn, know that usually you can do
		3828	better than you currently do :-)
3035		3829
3036	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3830	=item * often you need to talk to some other thread which blocks in the
		3831	event loop.
3037		3832
3038	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3833	C<ev_async> watchers can be used to wake them up from other threads safely
		3834	(or from signal contexts...).
3039		3835
3040	These watchers are stored in lists then need to be walked to find the	3836	An example use would be to communicate signals or other events that only
3041	correct watcher to remove. The lists are usually short (you don't usually	3837	work in the default loop by registering the signal watcher with the
3042	have many watchers waiting for the same fd or signal).	3838	default loop and triggering an C<ev_async> watcher from the default loop
3043		3839	watcher callback into the event loop interested in the signal.
3044	=item Finding the next timer in each loop iteration: O(1)
3045
3046	By virtue of using a binary heap, the next timer is always found at the
3047	beginning of the storage array.
3048
3049	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3050
3051	A change means an I/O watcher gets started or stopped, which requires
3052	libev to recalculate its status (and possibly tell the kernel, depending
3053	on backend and wether C<ev_io_set> was used).
3054
3055	=item Activating one watcher (putting it into the pending state): O(1)
3056
3057	=item Priority handling: O(number_of_priorities)
3058
3059	Priorities are implemented by allocating some space for each
3060	priority. When doing priority-based operations, libev usually has to
3061	linearly search all the priorities, but starting/stopping and activating
3062	watchers becomes O(1) w.r.t. priority handling.
3063
3064	=item Sending an ev_async: O(1)
3065
3066	=item Processing ev_async_send: O(number_of_async_watchers)
3067
3068	=item Processing signals: O(max_signal_number)
3069
3070	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3071	calls in the current loop iteration. Checking for async and signal events
3072	involves iterating over all running async watchers or all signal numbers.
3073		3840
3074	=back	3841	=back
3075		3842
		3843	=head3 COROUTINES
3076		3844
3077	=head1 Win32 platform limitations and workarounds	3845	Libev is very accommodating to coroutines ("cooperative threads"):
		3846	libev fully supports nesting calls to its functions from different
		3847	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3848	different coroutines, and switch freely between both coroutines running the
		3849	loop, as long as you don't confuse yourself). The only exception is that
		3850	you must not do this from C<ev_periodic> reschedule callbacks.
		3851
		3852	Care has been taken to ensure that libev does not keep local state inside
		3853	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3854	they do not call any callbacks.
		3855
		3856	=head2 COMPILER WARNINGS
		3857
		3858	Depending on your compiler and compiler settings, you might get no or a
		3859	lot of warnings when compiling libev code. Some people are apparently
		3860	scared by this.
		3861
		3862	However, these are unavoidable for many reasons. For one, each compiler
		3863	has different warnings, and each user has different tastes regarding
		3864	warning options. "Warn-free" code therefore cannot be a goal except when
		3865	targeting a specific compiler and compiler-version.
		3866
		3867	Another reason is that some compiler warnings require elaborate
		3868	workarounds, or other changes to the code that make it less clear and less
		3869	maintainable.
		3870
		3871	And of course, some compiler warnings are just plain stupid, or simply
		3872	wrong (because they don't actually warn about the condition their message
		3873	seems to warn about). For example, certain older gcc versions had some
		3874	warnings that resulted an extreme number of false positives. These have
		3875	been fixed, but some people still insist on making code warn-free with
		3876	such buggy versions.
		3877
		3878	While libev is written to generate as few warnings as possible,
		3879	"warn-free" code is not a goal, and it is recommended not to build libev
		3880	with any compiler warnings enabled unless you are prepared to cope with
		3881	them (e.g. by ignoring them). Remember that warnings are just that:
		3882	warnings, not errors, or proof of bugs.
		3883
		3884
		3885	=head2 VALGRIND
		3886
		3887	Valgrind has a special section here because it is a popular tool that is
		3888	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3889
		3890	If you think you found a bug (memory leak, uninitialised data access etc.)
		3891	in libev, then check twice: If valgrind reports something like:
		3892
		3893	==2274== definitely lost: 0 bytes in 0 blocks.
		3894	==2274== possibly lost: 0 bytes in 0 blocks.
		3895	==2274== still reachable: 256 bytes in 1 blocks.
		3896
		3897	Then there is no memory leak, just as memory accounted to global variables
		3898	is not a memleak - the memory is still being referenced, and didn't leak.
		3899
		3900	Similarly, under some circumstances, valgrind might report kernel bugs
		3901	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3902	although an acceptable workaround has been found here), or it might be
		3903	confused.
		3904
		3905	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3906	make it into some kind of religion.
		3907
		3908	If you are unsure about something, feel free to contact the mailing list
		3909	with the full valgrind report and an explanation on why you think this
		3910	is a bug in libev (best check the archives, too :). However, don't be
		3911	annoyed when you get a brisk "this is no bug" answer and take the chance
		3912	of learning how to interpret valgrind properly.
		3913
		3914	If you need, for some reason, empty reports from valgrind for your project
		3915	I suggest using suppression lists.
		3916
		3917
		3918	=head1 PORTABILITY NOTES
		3919
		3920	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3078		3921
3079	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3922	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3080	requires, and its I/O model is fundamentally incompatible with the POSIX	3923	requires, and its I/O model is fundamentally incompatible with the POSIX
3081	model. Libev still offers limited functionality on this platform in	3924	model. Libev still offers limited functionality on this platform in
3082	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3925	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3083	descriptors. This only applies when using Win32 natively, not when using	3926	descriptors. This only applies when using Win32 natively, not when using
3084	e.g. cygwin.	3927	e.g. cygwin.
3085		3928
		3929	Lifting these limitations would basically require the full
		3930	re-implementation of the I/O system. If you are into these kinds of
		3931	things, then note that glib does exactly that for you in a very portable
		3932	way (note also that glib is the slowest event library known to man).
		3933
3086	There is no supported compilation method available on windows except	3934	There is no supported compilation method available on windows except
3087	embedding it into other applications.	3935	embedding it into other applications.
3088		3936
		3937	Not a libev limitation but worth mentioning: windows apparently doesn't
		3938	accept large writes: instead of resulting in a partial write, windows will
		3939	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3940	so make sure you only write small amounts into your sockets (less than a
		3941	megabyte seems safe, but this apparently depends on the amount of memory
		3942	available).
		3943
3089	Due to the many, low, and arbitrary limits on the win32 platform and the	3944	Due to the many, low, and arbitrary limits on the win32 platform and
3090	abysmal performance of winsockets, using a large number of sockets is not	3945	the abysmal performance of winsockets, using a large number of sockets
3091	recommended (and not reasonable). If your program needs to use more than	3946	is not recommended (and not reasonable). If your program needs to use
3092	a hundred or so sockets, then likely it needs to use a totally different	3947	more than a hundred or so sockets, then likely it needs to use a totally
3093	implementation for windows, as libev offers the POSIX model, which cannot	3948	different implementation for windows, as libev offers the POSIX readiness
3094	be implemented efficiently on windows (microsoft monopoly games).	3949	notification model, which cannot be implemented efficiently on windows
		3950	(Microsoft monopoly games).
		3951
		3952	A typical way to use libev under windows is to embed it (see the embedding
		3953	section for details) and use the following F<evwrap.h> header file instead
		3954	of F<ev.h>:
		3955
		3956	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3957	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3958
		3959	#include "ev.h"
		3960
		3961	And compile the following F<evwrap.c> file into your project (make sure
		3962	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3963
		3964	#include "evwrap.h"
		3965	#include "ev.c"
3095		3966
3096	=over 4	3967	=over 4
3097		3968
3098	=item The winsocket select function	3969	=item The winsocket select function
3099		3970
3100	The winsocket C<select> function doesn't follow POSIX in that it requires	3971	The winsocket C<select> function doesn't follow POSIX in that it
3101	socket I<handles> and not socket I<file descriptors>. This makes select	3972	requires socket I<handles> and not socket I<file descriptors> (it is
3102	very inefficient, and also requires a mapping from file descriptors	3973	also extremely buggy). This makes select very inefficient, and also
3103	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	3974	requires a mapping from file descriptors to socket handles (the Microsoft
3104	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	3975	C runtime provides the function C<_open_osfhandle> for this). See the
3105	symbols for more info.	3976	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3977	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3106		3978
3107	The configuration for a "naked" win32 using the microsoft runtime	3979	The configuration for a "naked" win32 using the Microsoft runtime
3108	libraries and raw winsocket select is:	3980	libraries and raw winsocket select is:
3109		3981
3110	#define EV_USE_SELECT 1	3982	#define EV_USE_SELECT 1
3111	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	3983	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3112		3984
3113	Note that winsockets handling of fd sets is O(n), so you can easily get a	3985	Note that winsockets handling of fd sets is O(n), so you can easily get a
3114	complexity in the O(n²) range when using win32.	3986	complexity in the O(n²) range when using win32.
3115		3987
3116	=item Limited number of file descriptors	3988	=item Limited number of file descriptors
3117		3989
3118	Windows has numerous arbitrary (and low) limits on things. Early versions	3990	Windows has numerous arbitrary (and low) limits on things.
3119	of winsocket's select only supported waiting for a max. of C<64> handles	3991
		3992	Early versions of winsocket's select only supported waiting for a maximum
3120	(probably owning to the fact that all windows kernels can only wait for	3993	of C<64> handles (probably owning to the fact that all windows kernels
3121	C<64> things at the same time internally; microsoft recommends spawning a	3994	can only wait for C<64> things at the same time internally; Microsoft
3122	chain of threads and wait for 63 handles and the previous thread in each).	3995	recommends spawning a chain of threads and wait for 63 handles and the
		3996	previous thread in each. Great).
3123		3997
3124	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3998	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3125	to some high number (e.g. C<2048>) before compiling the winsocket select	3999	to some high number (e.g. C<2048>) before compiling the winsocket select
3126	call (which might be in libev or elsewhere, for example, perl does its own	4000	call (which might be in libev or elsewhere, for example, perl does its own
3127	select emulation on windows).	4001	select emulation on windows).
3128		4002
3129	Another limit is the number of file descriptors in the microsoft runtime	4003	Another limit is the number of file descriptors in the Microsoft runtime
3130	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4004	libraries, which by default is C<64> (there must be a hidden I<64> fetish
3131	or something like this inside microsoft). You can increase this by calling	4005	or something like this inside Microsoft). You can increase this by calling
3132	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4006	C<_setmaxstdio>, which can increase this limit to C<2048> (another
3133	arbitrary limit), but is broken in many versions of the microsoft runtime	4007	arbitrary limit), but is broken in many versions of the Microsoft runtime
3134	libraries.	4008	libraries.
3135		4009
3136	This might get you to about C<512> or C<2048> sockets (depending on	4010	This might get you to about C<512> or C<2048> sockets (depending on
3137	windows version and/or the phase of the moon). To get more, you need to	4011	windows version and/or the phase of the moon). To get more, you need to
3138	wrap all I/O functions and provide your own fd management, but the cost of	4012	wrap all I/O functions and provide your own fd management, but the cost of
3139	calling select (O(n²)) will likely make this unworkable.	4013	calling select (O(n²)) will likely make this unworkable.
3140		4014
3141	=back	4015	=back
3142		4016
		4017	=head2 PORTABILITY REQUIREMENTS
		4018
		4019	In addition to a working ISO-C implementation and of course the
		4020	backend-specific APIs, libev relies on a few additional extensions:
		4021
		4022	=over 4
		4023
		4024	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4025	calling conventions regardless of C<ev_watcher_type *>.
		4026
		4027	Libev assumes not only that all watcher pointers have the same internal
		4028	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4029	assumes that the same (machine) code can be used to call any watcher
		4030	callback: The watcher callbacks have different type signatures, but libev
		4031	calls them using an C<ev_watcher *> internally.
		4032
		4033	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4034
		4035	The type C<sig_atomic_t volatile> (or whatever is defined as
		4036	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4037	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4038	believed to be sufficiently portable.
		4039
		4040	=item C<sigprocmask> must work in a threaded environment
		4041
		4042	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4043	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4044	pthread implementations will either allow C<sigprocmask> in the "main
		4045	thread" or will block signals process-wide, both behaviours would
		4046	be compatible with libev. Interaction between C<sigprocmask> and
		4047	C<pthread_sigmask> could complicate things, however.
		4048
		4049	The most portable way to handle signals is to block signals in all threads
		4050	except the initial one, and run the default loop in the initial thread as
		4051	well.
		4052
		4053	=item C<long> must be large enough for common memory allocation sizes
		4054
		4055	To improve portability and simplify its API, libev uses C<long> internally
		4056	instead of C<size_t> when allocating its data structures. On non-POSIX
		4057	systems (Microsoft...) this might be unexpectedly low, but is still at
		4058	least 31 bits everywhere, which is enough for hundreds of millions of
		4059	watchers.
		4060
		4061	=item C<double> must hold a time value in seconds with enough accuracy
		4062
		4063	The type C<double> is used to represent timestamps. It is required to
		4064	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4065	enough for at least into the year 4000. This requirement is fulfilled by
		4066	implementations implementing IEEE 754 (basically all existing ones).
		4067
		4068	=back
		4069
		4070	If you know of other additional requirements drop me a note.
		4071
		4072
		4073	=head1 ALGORITHMIC COMPLEXITIES
		4074
		4075	In this section the complexities of (many of) the algorithms used inside
		4076	libev will be documented. For complexity discussions about backends see
		4077	the documentation for C<ev_default_init>.
		4078
		4079	All of the following are about amortised time: If an array needs to be
		4080	extended, libev needs to realloc and move the whole array, but this
		4081	happens asymptotically rarer with higher number of elements, so O(1) might
		4082	mean that libev does a lengthy realloc operation in rare cases, but on
		4083	average it is much faster and asymptotically approaches constant time.
		4084
		4085	=over 4
		4086
		4087	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4088
		4089	This means that, when you have a watcher that triggers in one hour and
		4090	there are 100 watchers that would trigger before that, then inserting will
		4091	have to skip roughly seven (C<ld 100>) of these watchers.
		4092
		4093	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4094
		4095	That means that changing a timer costs less than removing/adding them,
		4096	as only the relative motion in the event queue has to be paid for.
		4097
		4098	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4099
		4100	These just add the watcher into an array or at the head of a list.
		4101
		4102	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4103
		4104	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4105
		4106	These watchers are stored in lists, so they need to be walked to find the
		4107	correct watcher to remove. The lists are usually short (you don't usually
		4108	have many watchers waiting for the same fd or signal: one is typical, two
		4109	is rare).
		4110
		4111	=item Finding the next timer in each loop iteration: O(1)
		4112
		4113	By virtue of using a binary or 4-heap, the next timer is always found at a
		4114	fixed position in the storage array.
		4115
		4116	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4117
		4118	A change means an I/O watcher gets started or stopped, which requires
		4119	libev to recalculate its status (and possibly tell the kernel, depending
		4120	on backend and whether C<ev_io_set> was used).
		4121
		4122	=item Activating one watcher (putting it into the pending state): O(1)
		4123
		4124	=item Priority handling: O(number_of_priorities)
		4125
		4126	Priorities are implemented by allocating some space for each
		4127	priority. When doing priority-based operations, libev usually has to
		4128	linearly search all the priorities, but starting/stopping and activating
		4129	watchers becomes O(1) with respect to priority handling.
		4130
		4131	=item Sending an ev_async: O(1)
		4132
		4133	=item Processing ev_async_send: O(number_of_async_watchers)
		4134
		4135	=item Processing signals: O(max_signal_number)
		4136
		4137	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4138	calls in the current loop iteration. Checking for async and signal events
		4139	involves iterating over all running async watchers or all signal numbers.
		4140
		4141	=back
		4142
		4143
		4144	=head1 GLOSSARY
		4145
		4146	=over 4
		4147
		4148	=item active
		4149
		4150	A watcher is active as long as it has been started (has been attached to
		4151	an event loop) but not yet stopped (disassociated from the event loop).
		4152
		4153	=item application
		4154
		4155	In this document, an application is whatever is using libev.
		4156
		4157	=item callback
		4158
		4159	The address of a function that is called when some event has been
		4160	detected. Callbacks are being passed the event loop, the watcher that
		4161	received the event, and the actual event bitset.
		4162
		4163	=item callback invocation
		4164
		4165	The act of calling the callback associated with a watcher.
		4166
		4167	=item event
		4168
		4169	A change of state of some external event, such as data now being available
		4170	for reading on a file descriptor, time having passed or simply not having
		4171	any other events happening anymore.
		4172
		4173	In libev, events are represented as single bits (such as C<EV_READ> or
		4174	C<EV_TIMEOUT>).
		4175
		4176	=item event library
		4177
		4178	A software package implementing an event model and loop.
		4179
		4180	=item event loop
		4181
		4182	An entity that handles and processes external events and converts them
		4183	into callback invocations.
		4184
		4185	=item event model
		4186
		4187	The model used to describe how an event loop handles and processes
		4188	watchers and events.
		4189
		4190	=item pending
		4191
		4192	A watcher is pending as soon as the corresponding event has been detected,
		4193	and stops being pending as soon as the watcher will be invoked or its
		4194	pending status is explicitly cleared by the application.
		4195
		4196	A watcher can be pending, but not active. Stopping a watcher also clears
		4197	its pending status.
		4198
		4199	=item real time
		4200
		4201	The physical time that is observed. It is apparently strictly monotonic :)
		4202
		4203	=item wall-clock time
		4204
		4205	The time and date as shown on clocks. Unlike real time, it can actually
		4206	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4207	clock.
		4208
		4209	=item watcher
		4210
		4211	A data structure that describes interest in certain events. Watchers need
		4212	to be started (attached to an event loop) before they can receive events.
		4213
		4214	=item watcher invocation
		4215
		4216	The act of calling the callback associated with a watcher.
		4217
		4218	=back
3143		4219
3144	=head1 AUTHOR	4220	=head1 AUTHOR
3145		4221
3146	Marc Lehmann <libev@schmorp.de>.	4222	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3147		4223

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