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Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs.
Revision 1.249 by root, Wed Jul 8 04:29:31 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	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
…		…
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	113	for example).
86		114
87	=head2 CONVENTIONS	115	=head2 CONVENTIONS
88		116
89	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
95		124
96	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
97		126
98	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	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
101	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
102	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
103	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
104	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
105	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
106		156
107	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
108		158
109	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
110	library in any way.	160	library in any way.
…		…
119		169
120	=item ev_sleep (ev_tstamp interval)	170	=item ev_sleep (ev_tstamp interval)
121		171
122	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
123	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
124	this is a subsecond-resolution C<sleep ()>.	174	this is a sub-second-resolution C<sleep ()>.
125		175
126	=item int ev_version_major ()	176	=item int ev_version_major ()
127		177
128	=item int ev_version_minor ()	178	=item int ev_version_minor ()
129		179
…		…
142	not a problem.	192	not a problem.
143		193
144	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
145	version.	195	version.
146		196
147	assert (("libev version mismatch",	197	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
150		200
151	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
152		202
153	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_*>
154	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	206	a description of the set values.
157		207
158	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
159	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
160		210
161	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
163		213
164	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
165		215
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
172		222
173	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
174		224
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	229	recommended ones.
180		230
181	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
182		232
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		234
185	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
186	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
187	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
188	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
189	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
190	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.
191		244
192	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
195		248
196	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
197	retries).	250	retries (example requires a standards-compliant C<realloc>).
198		251
199	static void *	252	static void *
200	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
201	{	254	{
202	for (;;)	255	for (;;)
…		…
211	}	264	}
212		265
213	...	266	...
214	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
215		268
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		270
218	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
219	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
220	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	277	(such as abort).
225		278
226	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.
…		…
237		290
238	=back	291	=back
239		292
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		294
242	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>
243	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>
244	events, and dynamically created loops which do not.	297	I<function>).
245		298
246	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
247	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
248	create, you also create another event loop. Libev itself does no locking	301	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		302
253	=over 4	303	=over 4
254		304
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		306
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		311
262	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
263	function.	313	function.
264		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
265	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
266	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
267	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
268	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
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
270	C<ev_default_init>.	324	C<ev_default_init>.
271		325
272	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
…		…
281	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
282	thing, believe me).	336	thing, believe me).
283		337
284	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
285		339
286	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
287	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
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	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
290	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
291	around bugs.	345	around bugs.
…		…
297	enabling this flag.	351	enabling this flag.
298		352
299	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,
300	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
301	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
302	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
303	without a syscall and thus I<very> fast, but my Linux system also has	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
305		359
306	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
307	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
308	flag.	362	flag.
309		363
310	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>
311	environment variable.	365	environment variable.
312		366
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		368
315	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
…		…
317	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
318	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
319	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.
320		374
321	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
322	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
323	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
324	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
325	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
326	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).
327		385
328	=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)
329		387
330	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
331	than select, but handles sparse fds better and has no artificial	389	than select, but handles sparse fds better and has no artificial
332	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
333	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,
334	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
335	performance tips.	393	performance tips.
336		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		397
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
338		399
339	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,
340	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
341	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),
342	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).
343	of shortcomings, such as silently dropping events in some hard-to-detect	404
344	cases and rewiring a syscall per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
345	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.
346		421
347	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
348	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
349	(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
350	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
351	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
352		427	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		428
357	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
358	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,
359	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.
360		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
361	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
362	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>.
363		446
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		448
366	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
367	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
368	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
369	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
370	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
371	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)
372	system like NetBSD.	457	system like NetBSD.
373		458
374	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
375	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
376	the target platform). See C<ev_embed> watchers for more info.	461	the target platform). See C<ev_embed> watchers for more info.
377		462
378	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
379	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
380	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
381	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
382	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
383	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
384		470
385	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
386		472
387	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
388	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
389	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
390	(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
391	(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
392	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>.
393		483
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		485
396	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
397	implementation). According to reports, C</dev/poll> only supports sockets	487	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		492
403	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,
404	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)).
405		495
406	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
407	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
408	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
409		499
410	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
411	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
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	503	might perform better.
414		504
415	On the positive side, ignoring the spurious readyness notifications, this	505	On the positive side, with the exception of the spurious readiness
416	backend actually performed to specification in all tests and is fully	506	notifications, this backend actually performed fully to specification
417	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>.
418		512
419	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
420		514
421	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
422	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
…		…
424		518
425	It is definitely not recommended to use this flag.	519	It is definitely not recommended to use this flag.
426		520
427	=back	521	=back
428		522
429	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
430	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
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
432		526
433	The most typical usage is like this:	527	Example: This is the most typical usage.
434		528
435	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437		531
438	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
439	environment settings to be taken into account:	533	environment settings to be taken into account:
440		534
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442		536
443	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
444	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
445	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):
446		541
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448		543
449	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
450		545
451	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
452	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
453	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
454	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
455		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
456	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.
457		556
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	558	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
461		560
462	=item ev_default_destroy ()	561	=item ev_default_destroy ()
463		562
464	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
465	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
466	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
467	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
468	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
469	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
470	for example).	569	for example).
471		570
472	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
473	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
475		574
476	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
477	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
478	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
479	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
504		603
505	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
506		605
507	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
508	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
509	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.
		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
510		615
511	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
512		617
513	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
514	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
515	happily wraps around with enough iterations.	620	happily wraps around with enough iterations.
516		621
517	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
518	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
519	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
520		637
521	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
522		639
523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
524	use.	641	use.
…		…
529	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
530	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
531	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
532	event occurring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
533		650
		651	=item ev_now_update (loop)
		652
		653	Establishes the current time by querying the kernel, updating the time
		654	returned by C<ev_now ()> in the progress. This is a costly operation and
		655	is usually done automatically within C<ev_loop ()>.
		656
		657	This function is rarely useful, but when some event callback runs for a
		658	very long time without entering the event loop, updating libev's idea of
		659	the current time is a good idea.
		660
		661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
		688
534	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
535		690
536	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
537	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
538	events.	693	events.
…		…
540	If the flags argument is specified as C<0>, it will not return until	695	If the flags argument is specified as C<0>, it will not return until
541	either no event watchers are active anymore or C<ev_unloop> was called.	696	either no event watchers are active anymore or C<ev_unloop> was called.
542		697
543	Please note that an explicit C<ev_unloop> is usually better than	698	Please note that an explicit C<ev_unloop> is usually better than
544	relying on all watchers to be stopped when deciding when a program has	699	relying on all watchers to be stopped when deciding when a program has
545	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
546	automatically loops as long as it has to and no longer by virtue of	701	that automatically loops as long as it has to and no longer by virtue
547	relying on its watchers stopping correctly is a thing of beauty.	702	of relying on its watchers stopping correctly, that is truly a thing of
		703	beauty.
548		704
549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	705	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
550	those events and any outstanding ones, but will not block your process in	706	those events and any already outstanding ones, but will not block your
551	case there are no events and will return after one iteration of the loop.	707	process in case there are no events and will return after one iteration of
		708	the loop.
552		709
553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
554	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
555	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
556	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
557	external event in conjunction with something not expressible using other	714	user-registered callback will be called), and will return after one
		715	iteration of the loop.
		716
		717	This is useful if you are waiting for some external event in conjunction
		718	with something not expressible using other libev watchers (i.e. "roll your
558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	719	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
559	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
560		721
561	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
562		723
563	- Before the first iteration, call any pending watchers.	724	- Before the first iteration, call any pending watchers.
564	* If EVFLAG_FORKCHECK was used, check for a fork.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	726	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	727	- Queue and call all prepare watchers.
567	- If we have been forked, recreate the kernel state.	728	- If we have been forked, detach and recreate the kernel state
		729	as to not disturb the other process.
568	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	732	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	733	(active idle watchers, EVLOOP_NONBLOCK or not having
572	any active watchers at all will result in not sleeping).	734	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	735	- Sleep if the I/O and timer collect interval say so.
574	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	739	- Queue all expired timers.
578	- Queue all outstanding periodics.	740	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
580	- Queue all check watchers.	742	- Queue all check watchers.
581	- Call all queued watchers in reverse order (i.e. check watchers first).	743	- Call all queued watchers in reverse order (i.e. check watchers first).
582	Signals and child watchers are implemented as I/O watchers, and will	744	Signals and child watchers are implemented as I/O watchers, and will
583	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	746	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
589	anymore.	751	anymore.
590		752
591	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
592	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
593	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
594	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
595		757
596	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
597		759
598	Can be used to make a call to C<ev_loop> return early (but only after it	760	Can be used to make a call to C<ev_loop> return early (but only after it
599	has processed all outstanding events). The C<how> argument must be either	761	has processed all outstanding events). The C<how> argument must be either
600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	762	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	763	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
602		764
603	This "unloop state" will be cleared when entering C<ev_loop> again.	765	This "unloop state" will be cleared when entering C<ev_loop> again.
604		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
605	=item ev_ref (loop)	769	=item ev_ref (loop)
606		770
607	=item ev_unref (loop)	771	=item ev_unref (loop)
608		772
609	Ref/unref can be used to add or remove a reference count on the event	773	Ref/unref can be used to add or remove a reference count on the event
610	loop: Every watcher keeps one reference, and as long as the reference	774	loop: Every watcher keeps one reference, and as long as the reference
611	count is nonzero, C<ev_loop> will not return on its own. If you have	775	count is nonzero, C<ev_loop> will not return on its own.
		776
612	a watcher you never unregister that should not keep C<ev_loop> from	777	If you have a watcher you never unregister that should not keep C<ev_loop>
613	returning, ev_unref() after starting, and ev_ref() before stopping it. For	778	from returning, call ev_unref() after starting, and ev_ref() before
		779	stopping it.
		780
614	example, libev itself uses this for its internal signal pipe: It is not	781	As an example, libev itself uses this for its internal signal pipe: It
615	visible to the libev user and should not keep C<ev_loop> from exiting if	782	is not visible to the libev user and should not keep C<ev_loop> from
616	no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
617	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
618	libraries. Just remember to I<unref after start> and I<ref before stop>	785	third-party libraries. Just remember to I<unref after start> and I<ref
619	(but only if the watcher wasn't active before, or was active before,	786	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
621		790
622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
623	running when nothing else is active.	792	running when nothing else is active.
624		793
625	struct ev_signal exitsig;	794	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	796	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	797	evf_unref (loop);
629		798
630	Example: For some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
631		800
632	ev_ref (loop);	801	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
634		803
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		805
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		807
639	These advanced functions influence the time that libev will spend waiting	808	These advanced functions influence the time that libev will spend waiting
640	for events. Both are by default C<0>, meaning that libev will try to	809	for events. Both time intervals are by default C<0>, meaning that libev
641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
642		812
643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
644	allows libev to delay invocation of I/O and timer/periodic callbacks to	814	allows libev to delay invocation of I/O and timer/periodic callbacks
645	increase efficiency of loop iterations.	815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
646		817
647	The background is that sometimes your program runs just fast enough to	818	The idea is that sometimes your program runs just fast enough to handle
648	handle one (or very few) event(s) per loop iteration. While this makes	819	one (or very few) event(s) per loop iteration. While this makes the
649	the program responsive, it also wastes a lot of CPU time to poll for new	820	program responsive, it also wastes a lot of CPU time to poll for new
650	events, especially with backends like C<select ()> which have a high	821	events, especially with backends like C<select ()> which have a high
651	overhead for the actual polling but can deliver many events at once.	822	overhead for the actual polling but can deliver many events at once.
652		823
653	By setting a higher I<io collect interval> you allow libev to spend more	824	By setting a higher I<io collect interval> you allow libev to spend more
654	time collecting I/O events, so you can handle more events per iteration,	825	time collecting I/O events, so you can handle more events per iteration,
655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
656	C<ev_timer>) will be not affected. Setting this to a non-null value will	827	C<ev_timer>) will be not affected. Setting this to a non-null value will
657	introduce an additional C<ev_sleep ()> call into most loop iterations.	828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
658		831
659	Likewise, by setting a higher I<timeout collect interval> you allow libev	832	Likewise, by setting a higher I<timeout collect interval> you allow libev
660	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	834	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	836	value will not introduce any overhead in libev.
664		837
665	Many (busy) programs can usually benefit by setting the io collect	838	Many (busy) programs can usually benefit by setting the I/O collect
666	interval to a value near C<0.1> or so, which is often enough for	839	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	841	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches the timing granularity of most systems.	842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
		847
		848	Setting the I<timeout collect interval> can improve the opportunity for
		849	saving power, as the program will "bundle" timer callback invocations that
		850	are "near" in time together, by delaying some, thus reducing the number of
		851	times the process sleeps and wakes up again. Another useful technique to
		852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_loop_verify (loop)
		862
		863	This function only does something when C<EV_VERIFY> support has been
		864	compiled in, which is the default for non-minimal builds. It tries to go
		865	through all internal structures and checks them for validity. If anything
		866	is found to be inconsistent, it will print an error message to standard
		867	error and call C<abort ()>.
		868
		869	This can be used to catch bugs inside libev itself: under normal
		870	circumstances, this function will never abort as of course libev keeps its
		871	data structures consistent.
670		872
671	=back	873	=back
672		874
673		875
674	=head1 ANATOMY OF A WATCHER	876	=head1 ANATOMY OF A WATCHER
		877
		878	In the following description, uppercase C<TYPE> in names stands for the
		879	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		880	watchers and C<ev_io_start> for I/O watchers.
675		881
676	A watcher is a structure that you create and register to record your	882	A watcher is a structure that you create and register to record your
677	interest in some event. For instance, if you want to wait for STDIN to	883	interest in some event. For instance, if you want to wait for STDIN to
678	become readable, you would create an C<ev_io> watcher for that:	884	become readable, you would create an C<ev_io> watcher for that:
679		885
680	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	886	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
681	{	887	{
682	ev_io_stop (w);	888	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	889	ev_unloop (loop, EVUNLOOP_ALL);
684	}	890	}
685		891
686	struct ev_loop *loop = ev_default_loop (0);	892	struct ev_loop *loop = ev_default_loop (0);
		893
687	struct ev_io stdin_watcher;	894	ev_io stdin_watcher;
		895
688	ev_init (&stdin_watcher, my_cb);	896	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	897	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	898	ev_io_start (loop, &stdin_watcher);
		899
691	ev_loop (loop, 0);	900	ev_loop (loop, 0);
692		901
693	As you can see, you are responsible for allocating the memory for your	902	As you can see, you are responsible for allocating the memory for your
694	watcher structures (and it is usually a bad idea to do this on the stack,	903	watcher structures (and it is I<usually> a bad idea to do this on the
695	although this can sometimes be quite valid).	904	stack).
		905
		906	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		907	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
696		908
697	Each watcher structure must be initialised by a call to C<ev_init	909	Each watcher structure must be initialised by a call to C<ev_init
698	(watcher *, callback)>, which expects a callback to be provided. This	910	(watcher *, callback)>, which expects a callback to be provided. This
699	callback gets invoked each time the event occurs (or, in the case of io	911	callback gets invoked each time the event occurs (or, in the case of I/O
700	watchers, each time the event loop detects that the file descriptor given	912	watchers, each time the event loop detects that the file descriptor given
701	is readable and/or writable).	913	is readable and/or writable).
702		914
703	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	915	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
704	with arguments specific to this watcher type. There is also a macro	916	macro to configure it, with arguments specific to the watcher type. There
705	to combine initialisation and setting in one call: C<< ev_<type>_init	917	is also a macro to combine initialisation and setting in one call: C<<
706	(watcher *, callback, ...) >>.	918	ev_TYPE_init (watcher *, callback, ...) >>.
707		919
708	To make the watcher actually watch out for events, you have to start it	920	To make the watcher actually watch out for events, you have to start it
709	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	921	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
710	*) >>), and you can stop watching for events at any time by calling the	922	*) >>), and you can stop watching for events at any time by calling the
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	923	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		924
713	As long as your watcher is active (has been started but not stopped) you	925	As long as your watcher is active (has been started but not stopped) you
714	must not touch the values stored in it. Most specifically you must never	926	must not touch the values stored in it. Most specifically you must never
715	reinitialise it or call its C<set> macro.	927	reinitialise it or call its C<ev_TYPE_set> macro.
716		928
717	Each and every callback receives the event loop pointer as first, the	929	Each and every callback receives the event loop pointer as first, the
718	registered watcher structure as second, and a bitset of received events as	930	registered watcher structure as second, and a bitset of received events as
719	third argument.	931	third argument.
720		932
…		…
774	=item C<EV_FORK>	986	=item C<EV_FORK>
775		987
776	The event loop has been resumed in the child process after fork (see	988	The event loop has been resumed in the child process after fork (see
777	C<ev_fork>).	989	C<ev_fork>).
778		990
		991	=item C<EV_ASYNC>
		992
		993	The given async watcher has been asynchronously notified (see C<ev_async>).
		994
		995	=item C<EV_CUSTOM>
		996
		997	Not ever sent (or otherwise used) by libev itself, but can be freely used
		998	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		999
779	=item C<EV_ERROR>	1000	=item C<EV_ERROR>
780		1001
781	An unspecified error has occured, the watcher has been stopped. This might	1002	An unspecified error has occurred, the watcher has been stopped. This might
782	happen because the watcher could not be properly started because libev	1003	happen because the watcher could not be properly started because libev
783	ran out of memory, a file descriptor was found to be closed or any other	1004	ran out of memory, a file descriptor was found to be closed or any other
		1005	problem. Libev considers these application bugs.
		1006
784	problem. You best act on it by reporting the problem and somehow coping	1007	You best act on it by reporting the problem and somehow coping with the
785	with the watcher being stopped.	1008	watcher being stopped. Note that well-written programs should not receive
		1009	an error ever, so when your watcher receives it, this usually indicates a
		1010	bug in your program.
786		1011
787	Libev will usually signal a few "dummy" events together with an error,	1012	Libev will usually signal a few "dummy" events together with an error, for
788	for example it might indicate that a fd is readable or writable, and if	1013	example it might indicate that a fd is readable or writable, and if your
789	your callbacks is well-written it can just attempt the operation and cope	1014	callbacks is well-written it can just attempt the operation and cope with
790	with the error from read() or write(). This will not work in multithreaded	1015	the error from read() or write(). This will not work in multi-threaded
791	programs, though, so beware.	1016	programs, though, as the fd could already be closed and reused for another
		1017	thing, so beware.
792		1018
793	=back	1019	=back
794		1020
795	=head2 GENERIC WATCHER FUNCTIONS	1021	=head2 GENERIC WATCHER FUNCTIONS
796
797	In the following description, C<TYPE> stands for the watcher type,
798	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
799		1022
800	=over 4	1023	=over 4
801		1024
802	=item C<ev_init> (ev_TYPE *watcher, callback)	1025	=item C<ev_init> (ev_TYPE *watcher, callback)
803		1026
…		…
809	which rolls both calls into one.	1032	which rolls both calls into one.
810		1033
811	You can reinitialise a watcher at any time as long as it has been stopped	1034	You can reinitialise a watcher at any time as long as it has been stopped
812	(or never started) and there are no pending events outstanding.	1035	(or never started) and there are no pending events outstanding.
813		1036
814	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1037	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
815	int revents)>.	1038	int revents)>.
		1039
		1040	Example: Initialise an C<ev_io> watcher in two steps.
		1041
		1042	ev_io w;
		1043	ev_init (&w, my_cb);
		1044	ev_io_set (&w, STDIN_FILENO, EV_READ);
816		1045
817	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1046	=item C<ev_TYPE_set> (ev_TYPE *, [args])
818		1047
819	This macro initialises the type-specific parts of a watcher. You need to	1048	This macro initialises the type-specific parts of a watcher. You need to
820	call C<ev_init> at least once before you call this macro, but you can	1049	call C<ev_init> at least once before you call this macro, but you can
…		…
823	difference to the C<ev_init> macro).	1052	difference to the C<ev_init> macro).
824		1053
825	Although some watcher types do not have type-specific arguments	1054	Although some watcher types do not have type-specific arguments
826	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1055	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
827		1056
		1057	See C<ev_init>, above, for an example.
		1058
828	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1059	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
829		1060
830	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1061	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
831	calls into a single call. This is the most convinient method to initialise	1062	calls into a single call. This is the most convenient method to initialise
832	a watcher. The same limitations apply, of course.	1063	a watcher. The same limitations apply, of course.
		1064
		1065	Example: Initialise and set an C<ev_io> watcher in one step.
		1066
		1067	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
833		1068
834	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1069	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
835		1070
836	Starts (activates) the given watcher. Only active watchers will receive	1071	Starts (activates) the given watcher. Only active watchers will receive
837	events. If the watcher is already active nothing will happen.	1072	events. If the watcher is already active nothing will happen.
838		1073
		1074	Example: Start the C<ev_io> watcher that is being abused as example in this
		1075	whole section.
		1076
		1077	ev_io_start (EV_DEFAULT_UC, &w);
		1078
839	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1079	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
840		1080
841	Stops the given watcher again (if active) and clears the pending	1081	Stops the given watcher if active, and clears the pending status (whether
		1082	the watcher was active or not).
		1083
842	status. It is possible that stopped watchers are pending (for example,	1084	It is possible that stopped watchers are pending - for example,
843	non-repeating timers are being stopped when they become pending), but	1085	non-repeating timers are being stopped when they become pending - but
844	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1086	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
845	you want to free or reuse the memory used by the watcher it is therefore a	1087	pending. If you want to free or reuse the memory used by the watcher it is
846	good idea to always call its C<ev_TYPE_stop> function.	1088	therefore a good idea to always call its C<ev_TYPE_stop> function.
847		1089
848	=item bool ev_is_active (ev_TYPE *watcher)	1090	=item bool ev_is_active (ev_TYPE *watcher)
849		1091
850	Returns a true value iff the watcher is active (i.e. it has been started	1092	Returns a true value iff the watcher is active (i.e. it has been started
851	and not yet been stopped). As long as a watcher is active you must not modify	1093	and not yet been stopped). As long as a watcher is active you must not modify
…		…
877	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1119	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
878	(default: C<-2>). Pending watchers with higher priority will be invoked	1120	(default: C<-2>). Pending watchers with higher priority will be invoked
879	before watchers with lower priority, but priority will not keep watchers	1121	before watchers with lower priority, but priority will not keep watchers
880	from being executed (except for C<ev_idle> watchers).	1122	from being executed (except for C<ev_idle> watchers).
881		1123
882	This means that priorities are I<only> used for ordering callback
883	invocation after new events have been received. This is useful, for
884	example, to reduce latency after idling, or more often, to bind two
885	watchers on the same event and make sure one is called first.
886
887	If you need to suppress invocation when higher priority events are pending	1124	If you need to suppress invocation when higher priority events are pending
888	you need to look at C<ev_idle> watchers, which provide this functionality.	1125	you need to look at C<ev_idle> watchers, which provide this functionality.
889		1126
890	You I<must not> change the priority of a watcher as long as it is active or	1127	You I<must not> change the priority of a watcher as long as it is active or
891	pending.	1128	pending.
892		1129
		1130	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1131	fine, as long as you do not mind that the priority value you query might
		1132	or might not have been clamped to the valid range.
		1133
893	The default priority used by watchers when no priority has been set is	1134	The default priority used by watchers when no priority has been set is
894	always C<0>, which is supposed to not be too high and not be too low :).	1135	always C<0>, which is supposed to not be too high and not be too low :).
895		1136
896	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1137	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
897	fine, as long as you do not mind that the priority value you query might	1138	priorities.
898	or might not have been adjusted to be within valid range.
899		1139
900	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1140	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
901		1141
902	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1142	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
903	C<loop> nor C<revents> need to be valid as long as the watcher callback	1143	C<loop> nor C<revents> need to be valid as long as the watcher callback
904	can deal with that fact.	1144	can deal with that fact, as both are simply passed through to the
		1145	callback.
905		1146
906	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1147	=item int ev_clear_pending (loop, ev_TYPE *watcher)
907		1148
908	If the watcher is pending, this function returns clears its pending status	1149	If the watcher is pending, this function clears its pending status and
909	and returns its C<revents> bitset (as if its callback was invoked). If the	1150	returns its C<revents> bitset (as if its callback was invoked). If the
910	watcher isn't pending it does nothing and returns C<0>.	1151	watcher isn't pending it does nothing and returns C<0>.
911		1152
		1153	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1154	callback to be invoked, which can be accomplished with this function.
		1155
912	=back	1156	=back
913		1157
914		1158
915	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1159	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
916		1160
917	Each watcher has, by default, a member C<void *data> that you can change	1161	Each watcher has, by default, a member C<void *data> that you can change
918	and read at any time, libev will completely ignore it. This can be used	1162	and read at any time: libev will completely ignore it. This can be used
919	to associate arbitrary data with your watcher. If you need more data and	1163	to associate arbitrary data with your watcher. If you need more data and
920	don't want to allocate memory and store a pointer to it in that data	1164	don't want to allocate memory and store a pointer to it in that data
921	member, you can also "subclass" the watcher type and provide your own	1165	member, you can also "subclass" the watcher type and provide your own
922	data:	1166	data:
923		1167
924	struct my_io	1168	struct my_io
925	{	1169	{
926	struct ev_io io;	1170	ev_io io;
927	int otherfd;	1171	int otherfd;
928	void *somedata;	1172	void *somedata;
929	struct whatever *mostinteresting;	1173	struct whatever *mostinteresting;
930	}	1174	};
		1175
		1176	...
		1177	struct my_io w;
		1178	ev_io_init (&w.io, my_cb, fd, EV_READ);
931		1179
932	And since your callback will be called with a pointer to the watcher, you	1180	And since your callback will be called with a pointer to the watcher, you
933	can cast it back to your own type:	1181	can cast it back to your own type:
934		1182
935	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
936	{	1184	{
937	struct my_io *w = (struct my_io *)w_;	1185	struct my_io *w = (struct my_io *)w_;
938	...	1186	...
939	}	1187	}
940		1188
941	More interesting and less C-conformant ways of casting your callback type	1189	More interesting and less C-conformant ways of casting your callback type
942	instead have been omitted.	1190	instead have been omitted.
943		1191
944	Another common scenario is having some data structure with multiple	1192	Another common scenario is to use some data structure with multiple
945	watchers:	1193	embedded watchers:
946		1194
947	struct my_biggy	1195	struct my_biggy
948	{	1196	{
949	int some_data;	1197	int some_data;
950	ev_timer t1;	1198	ev_timer t1;
951	ev_timer t2;	1199	ev_timer t2;
952	}	1200	}
953		1201
954	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1202	In this case getting the pointer to C<my_biggy> is a bit more
955	you need to use C<offsetof>:	1203	complicated: Either you store the address of your C<my_biggy> struct
		1204	in the C<data> member of the watcher (for woozies), or you need to use
		1205	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1206	programmers):
956		1207
957	#include <stddef.h>	1208	#include <stddef.h>
958		1209
959	static void	1210	static void
960	t1_cb (EV_P_ struct ev_timer *w, int revents)	1211	t1_cb (EV_P_ ev_timer *w, int revents)
961	{	1212	{
962	struct my_biggy big = (struct my_biggy *	1213	struct my_biggy big = (struct my_biggy *)
963	(((char *)w) - offsetof (struct my_biggy, t1));	1214	(((char *)w) - offsetof (struct my_biggy, t1));
964	}	1215	}
965		1216
966	static void	1217	static void
967	t2_cb (EV_P_ struct ev_timer *w, int revents)	1218	t2_cb (EV_P_ ev_timer *w, int revents)
968	{	1219	{
969	struct my_biggy big = (struct my_biggy *	1220	struct my_biggy big = (struct my_biggy *)
970	(((char *)w) - offsetof (struct my_biggy, t2));	1221	(((char *)w) - offsetof (struct my_biggy, t2));
971	}	1222	}
		1223
		1224	=head2 WATCHER PRIORITY MODELS
		1225
		1226	Many event loops support I<watcher priorities>, which are usually small
		1227	integers that influence the ordering of event callback invocation
		1228	between watchers in some way, all else being equal.
		1229
		1230	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1231	description for the more technical details such as the actual priority
		1232	range.
		1233
		1234	There are two common ways how these these priorities are being interpreted
		1235	by event loops:
		1236
		1237	In the more common lock-out model, higher priorities "lock out" invocation
		1238	of lower priority watchers, which means as long as higher priority
		1239	watchers receive events, lower priority watchers are not being invoked.
		1240
		1241	The less common only-for-ordering model uses priorities solely to order
		1242	callback invocation within a single event loop iteration: Higher priority
		1243	watchers are invoked before lower priority ones, but they all get invoked
		1244	before polling for new events.
		1245
		1246	Libev uses the second (only-for-ordering) model for all its watchers
		1247	except for idle watchers (which use the lock-out model).
		1248
		1249	The rationale behind this is that implementing the lock-out model for
		1250	watchers is not well supported by most kernel interfaces, and most event
		1251	libraries will just poll for the same events again and again as long as
		1252	their callbacks have not been executed, which is very inefficient in the
		1253	common case of one high-priority watcher locking out a mass of lower
		1254	priority ones.
		1255
		1256	Static (ordering) priorities are most useful when you have two or more
		1257	watchers handling the same resource: a typical usage example is having an
		1258	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1259	timeouts. Under load, data might be received while the program handles
		1260	other jobs, but since timers normally get invoked first, the timeout
		1261	handler will be executed before checking for data. In that case, giving
		1262	the timer a lower priority than the I/O watcher ensures that I/O will be
		1263	handled first even under adverse conditions (which is usually, but not
		1264	always, what you want).
		1265
		1266	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1267	will only be executed when no same or higher priority watchers have
		1268	received events, they can be used to implement the "lock-out" model when
		1269	required.
		1270
		1271	For example, to emulate how many other event libraries handle priorities,
		1272	you can associate an C<ev_idle> watcher to each such watcher, and in
		1273	the normal watcher callback, you just start the idle watcher. The real
		1274	processing is done in the idle watcher callback. This causes libev to
		1275	continously poll and process kernel event data for the watcher, but when
		1276	the lock-out case is known to be rare (which in turn is rare :), this is
		1277	workable.
		1278
		1279	Usually, however, the lock-out model implemented that way will perform
		1280	miserably under the type of load it was designed to handle. In that case,
		1281	it might be preferable to stop the real watcher before starting the
		1282	idle watcher, so the kernel will not have to process the event in case
		1283	the actual processing will be delayed for considerable time.
		1284
		1285	Here is an example of an I/O watcher that should run at a strictly lower
		1286	priority than the default, and which should only process data when no
		1287	other events are pending:
		1288
		1289	ev_idle idle; // actual processing watcher
		1290	ev_io io; // actual event watcher
		1291
		1292	static void
		1293	io_cb (EV_P_ ev_io *w, int revents)
		1294	{
		1295	// stop the I/O watcher, we received the event, but
		1296	// are not yet ready to handle it.
		1297	ev_io_stop (EV_A_ w);
		1298
		1299	// start the idle watcher to ahndle the actual event.
		1300	// it will not be executed as long as other watchers
		1301	// with the default priority are receiving events.
		1302	ev_idle_start (EV_A_ &idle);
		1303	}
		1304
		1305	static void
		1306	idle_cb (EV_P_ ev_idle *w, int revents)
		1307	{
		1308	// actual processing
		1309	read (STDIN_FILENO, ...);
		1310
		1311	// have to start the I/O watcher again, as
		1312	// we have handled the event
		1313	ev_io_start (EV_P_ &io);
		1314	}
		1315
		1316	// initialisation
		1317	ev_idle_init (&idle, idle_cb);
		1318	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1319	ev_io_start (EV_DEFAULT_ &io);
		1320
		1321	In the "real" world, it might also be beneficial to start a timer, so that
		1322	low-priority connections can not be locked out forever under load. This
		1323	enables your program to keep a lower latency for important connections
		1324	during short periods of high load, while not completely locking out less
		1325	important ones.
972		1326
973		1327
974	=head1 WATCHER TYPES	1328	=head1 WATCHER TYPES
975		1329
976	This section describes each watcher in detail, but will not repeat	1330	This section describes each watcher in detail, but will not repeat
…		…
1000	In general you can register as many read and/or write event watchers per	1354	In general you can register as many read and/or write event watchers per
1001	fd as you want (as long as you don't confuse yourself). Setting all file	1355	fd as you want (as long as you don't confuse yourself). Setting all file
1002	descriptors to non-blocking mode is also usually a good idea (but not	1356	descriptors to non-blocking mode is also usually a good idea (but not
1003	required if you know what you are doing).	1357	required if you know what you are doing).
1004		1358
1005	If you must do this, then force the use of a known-to-be-good backend	1359	If you cannot use non-blocking mode, then force the use of a
1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1360	known-to-be-good backend (at the time of this writing, this includes only
1007	C<EVBACKEND_POLL>).	1361	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1362	descriptors for which non-blocking operation makes no sense (such as
		1363	files) - libev doesn't guarentee any specific behaviour in that case.
1008		1364
1009	Another thing you have to watch out for is that it is quite easy to	1365	Another thing you have to watch out for is that it is quite easy to
1010	receive "spurious" readyness notifications, that is your callback might	1366	receive "spurious" readiness notifications, that is your callback might
1011	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1367	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1012	because there is no data. Not only are some backends known to create a	1368	because there is no data. Not only are some backends known to create a
1013	lot of those (for example solaris ports), it is very easy to get into	1369	lot of those (for example Solaris ports), it is very easy to get into
1014	this situation even with a relatively standard program structure. Thus	1370	this situation even with a relatively standard program structure. Thus
1015	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1371	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1016	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1372	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1017		1373
1018	If you cannot run the fd in non-blocking mode (for example you should not	1374	If you cannot run the fd in non-blocking mode (for example you should
1019	play around with an Xlib connection), then you have to seperately re-test	1375	not play around with an Xlib connection), then you have to separately
1020	whether a file descriptor is really ready with a known-to-be good interface	1376	re-test whether a file descriptor is really ready with a known-to-be good
1021	such as poll (fortunately in our Xlib example, Xlib already does this on	1377	interface such as poll (fortunately in our Xlib example, Xlib already
1022	its own, so its quite safe to use).	1378	does this on its own, so its quite safe to use). Some people additionally
		1379	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1380	indefinitely.
		1381
		1382	But really, best use non-blocking mode.
1023		1383
1024	=head3 The special problem of disappearing file descriptors	1384	=head3 The special problem of disappearing file descriptors
1025		1385
1026	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1386	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1027	descriptor (either by calling C<close> explicitly or by any other means,	1387	descriptor (either due to calling C<close> explicitly or any other means,
1028	such as C<dup>). The reason is that you register interest in some file	1388	such as C<dup2>). The reason is that you register interest in some file
1029	descriptor, but when it goes away, the operating system will silently drop	1389	descriptor, but when it goes away, the operating system will silently drop
1030	this interest. If another file descriptor with the same number then is	1390	this interest. If another file descriptor with the same number then is
1031	registered with libev, there is no efficient way to see that this is, in	1391	registered with libev, there is no efficient way to see that this is, in
1032	fact, a different file descriptor.	1392	fact, a different file descriptor.
1033		1393
…		…
1062	To support fork in your programs, you either have to call	1422	To support fork in your programs, you either have to call
1063	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1423	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1424	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1065	C<EVBACKEND_POLL>.	1425	C<EVBACKEND_POLL>.
1066		1426
		1427	=head3 The special problem of SIGPIPE
		1428
		1429	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1430	when writing to a pipe whose other end has been closed, your program gets
		1431	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1432	this is sensible behaviour, for daemons, this is usually undesirable.
		1433
		1434	So when you encounter spurious, unexplained daemon exits, make sure you
		1435	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1436	somewhere, as that would have given you a big clue).
		1437
1067		1438
1068	=head3 Watcher-Specific Functions	1439	=head3 Watcher-Specific Functions
1069		1440
1070	=over 4	1441	=over 4
1071		1442
1072	=item ev_io_init (ev_io *, callback, int fd, int events)	1443	=item ev_io_init (ev_io *, callback, int fd, int events)
1073		1444
1074	=item ev_io_set (ev_io *, int fd, int events)	1445	=item ev_io_set (ev_io *, int fd, int events)
1075		1446
1076	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1447	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1077	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1448	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1078	C<EV_READ | EV_WRITE> to receive the given events.	1449	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1079		1450
1080	=item int fd [read-only]	1451	=item int fd [read-only]
1081		1452
1082	The file descriptor being watched.	1453	The file descriptor being watched.
1083		1454
…		…
1091		1462
1092	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1463	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1093	readable, but only once. Since it is likely line-buffered, you could	1464	readable, but only once. Since it is likely line-buffered, you could
1094	attempt to read a whole line in the callback.	1465	attempt to read a whole line in the callback.
1095		1466
1096	static void	1467	static void
1097	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1468	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1098	{	1469	{
1099	ev_io_stop (loop, w);	1470	ev_io_stop (loop, w);
1100	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1471	.. read from stdin here (or from w->fd) and handle any I/O errors
1101	}	1472	}
1102		1473
1103	...	1474	...
1104	struct ev_loop *loop = ev_default_init (0);	1475	struct ev_loop *loop = ev_default_init (0);
1105	struct ev_io stdin_readable;	1476	ev_io stdin_readable;
1106	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1477	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1107	ev_io_start (loop, &stdin_readable);	1478	ev_io_start (loop, &stdin_readable);
1108	ev_loop (loop, 0);	1479	ev_loop (loop, 0);
1109		1480
1110		1481
1111	=head2 C<ev_timer> - relative and optionally repeating timeouts	1482	=head2 C<ev_timer> - relative and optionally repeating timeouts
1112		1483
1113	Timer watchers are simple relative timers that generate an event after a	1484	Timer watchers are simple relative timers that generate an event after a
1114	given time, and optionally repeating in regular intervals after that.	1485	given time, and optionally repeating in regular intervals after that.
1115		1486
1116	The timers are based on real time, that is, if you register an event that	1487	The timers are based on real time, that is, if you register an event that
1117	times out after an hour and you reset your system clock to last years	1488	times out after an hour and you reset your system clock to January last
1118	time, it will still time out after (roughly) and hour. "Roughly" because	1489	year, it will still time out after (roughly) one hour. "Roughly" because
1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1490	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1120	monotonic clock option helps a lot here).	1491	monotonic clock option helps a lot here).
		1492
		1493	The callback is guaranteed to be invoked only I<after> its timeout has
		1494	passed (not I<at>, so on systems with very low-resolution clocks this
		1495	might introduce a small delay). If multiple timers become ready during the
		1496	same loop iteration then the ones with earlier time-out values are invoked
		1497	before ones of the same priority with later time-out values (but this is
		1498	no longer true when a callback calls C<ev_loop> recursively).
		1499
		1500	=head3 Be smart about timeouts
		1501
		1502	Many real-world problems involve some kind of timeout, usually for error
		1503	recovery. A typical example is an HTTP request - if the other side hangs,
		1504	you want to raise some error after a while.
		1505
		1506	What follows are some ways to handle this problem, from obvious and
		1507	inefficient to smart and efficient.
		1508
		1509	In the following, a 60 second activity timeout is assumed - a timeout that
		1510	gets reset to 60 seconds each time there is activity (e.g. each time some
		1511	data or other life sign was received).
		1512
		1513	=over 4
		1514
		1515	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1516
		1517	This is the most obvious, but not the most simple way: In the beginning,
		1518	start the watcher:
		1519
		1520	ev_timer_init (timer, callback, 60., 0.);
		1521	ev_timer_start (loop, timer);
		1522
		1523	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1524	and start it again:
		1525
		1526	ev_timer_stop (loop, timer);
		1527	ev_timer_set (timer, 60., 0.);
		1528	ev_timer_start (loop, timer);
		1529
		1530	This is relatively simple to implement, but means that each time there is
		1531	some activity, libev will first have to remove the timer from its internal
		1532	data structure and then add it again. Libev tries to be fast, but it's
		1533	still not a constant-time operation.
		1534
		1535	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1536
		1537	This is the easiest way, and involves using C<ev_timer_again> instead of
		1538	C<ev_timer_start>.
		1539
		1540	To implement this, configure an C<ev_timer> with a C<repeat> value
		1541	of C<60> and then call C<ev_timer_again> at start and each time you
		1542	successfully read or write some data. If you go into an idle state where
		1543	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1544	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1545
		1546	That means you can ignore both the C<ev_timer_start> function and the
		1547	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1548	member and C<ev_timer_again>.
		1549
		1550	At start:
		1551
		1552	ev_init (timer, callback);
		1553	timer->repeat = 60.;
		1554	ev_timer_again (loop, timer);
		1555
		1556	Each time there is some activity:
		1557
		1558	ev_timer_again (loop, timer);
		1559
		1560	It is even possible to change the time-out on the fly, regardless of
		1561	whether the watcher is active or not:
		1562
		1563	timer->repeat = 30.;
		1564	ev_timer_again (loop, timer);
		1565
		1566	This is slightly more efficient then stopping/starting the timer each time
		1567	you want to modify its timeout value, as libev does not have to completely
		1568	remove and re-insert the timer from/into its internal data structure.
		1569
		1570	It is, however, even simpler than the "obvious" way to do it.
		1571
		1572	=item 3. Let the timer time out, but then re-arm it as required.
		1573
		1574	This method is more tricky, but usually most efficient: Most timeouts are
		1575	relatively long compared to the intervals between other activity - in
		1576	our example, within 60 seconds, there are usually many I/O events with
		1577	associated activity resets.
		1578
		1579	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1580	but remember the time of last activity, and check for a real timeout only
		1581	within the callback:
		1582
		1583	ev_tstamp last_activity; // time of last activity
		1584
		1585	static void
		1586	callback (EV_P_ ev_timer *w, int revents)
		1587	{
		1588	ev_tstamp now = ev_now (EV_A);
		1589	ev_tstamp timeout = last_activity + 60.;
		1590
		1591	// if last_activity + 60. is older than now, we did time out
		1592	if (timeout < now)
		1593	{
		1594	// timeout occured, take action
		1595	}
		1596	else
		1597	{
		1598	// callback was invoked, but there was some activity, re-arm
		1599	// the watcher to fire in last_activity + 60, which is
		1600	// guaranteed to be in the future, so "again" is positive:
		1601	w->repeat = timeout - now;
		1602	ev_timer_again (EV_A_ w);
		1603	}
		1604	}
		1605
		1606	To summarise the callback: first calculate the real timeout (defined
		1607	as "60 seconds after the last activity"), then check if that time has
		1608	been reached, which means something I<did>, in fact, time out. Otherwise
		1609	the callback was invoked too early (C<timeout> is in the future), so
		1610	re-schedule the timer to fire at that future time, to see if maybe we have
		1611	a timeout then.
		1612
		1613	Note how C<ev_timer_again> is used, taking advantage of the
		1614	C<ev_timer_again> optimisation when the timer is already running.
		1615
		1616	This scheme causes more callback invocations (about one every 60 seconds
		1617	minus half the average time between activity), but virtually no calls to
		1618	libev to change the timeout.
		1619
		1620	To start the timer, simply initialise the watcher and set C<last_activity>
		1621	to the current time (meaning we just have some activity :), then call the
		1622	callback, which will "do the right thing" and start the timer:
		1623
		1624	ev_init (timer, callback);
		1625	last_activity = ev_now (loop);
		1626	callback (loop, timer, EV_TIMEOUT);
		1627
		1628	And when there is some activity, simply store the current time in
		1629	C<last_activity>, no libev calls at all:
		1630
		1631	last_actiivty = ev_now (loop);
		1632
		1633	This technique is slightly more complex, but in most cases where the
		1634	time-out is unlikely to be triggered, much more efficient.
		1635
		1636	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1637	callback :) - just change the timeout and invoke the callback, which will
		1638	fix things for you.
		1639
		1640	=item 4. Wee, just use a double-linked list for your timeouts.
		1641
		1642	If there is not one request, but many thousands (millions...), all
		1643	employing some kind of timeout with the same timeout value, then one can
		1644	do even better:
		1645
		1646	When starting the timeout, calculate the timeout value and put the timeout
		1647	at the I<end> of the list.
		1648
		1649	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1650	the list is expected to fire (for example, using the technique #3).
		1651
		1652	When there is some activity, remove the timer from the list, recalculate
		1653	the timeout, append it to the end of the list again, and make sure to
		1654	update the C<ev_timer> if it was taken from the beginning of the list.
		1655
		1656	This way, one can manage an unlimited number of timeouts in O(1) time for
		1657	starting, stopping and updating the timers, at the expense of a major
		1658	complication, and having to use a constant timeout. The constant timeout
		1659	ensures that the list stays sorted.
		1660
		1661	=back
		1662
		1663	So which method the best?
		1664
		1665	Method #2 is a simple no-brain-required solution that is adequate in most
		1666	situations. Method #3 requires a bit more thinking, but handles many cases
		1667	better, and isn't very complicated either. In most case, choosing either
		1668	one is fine, with #3 being better in typical situations.
		1669
		1670	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1671	rather complicated, but extremely efficient, something that really pays
		1672	off after the first million or so of active timers, i.e. it's usually
		1673	overkill :)
		1674
		1675	=head3 The special problem of time updates
		1676
		1677	Establishing the current time is a costly operation (it usually takes at
		1678	least two system calls): EV therefore updates its idea of the current
		1679	time only before and after C<ev_loop> collects new events, which causes a
		1680	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1681	lots of events in one iteration.
1121		1682
1122	The relative timeouts are calculated relative to the C<ev_now ()>	1683	The relative timeouts are calculated relative to the C<ev_now ()>
1123	time. This is usually the right thing as this timestamp refers to the time	1684	time. This is usually the right thing as this timestamp refers to the time
1124	of the event triggering whatever timeout you are modifying/starting. If	1685	of the event triggering whatever timeout you are modifying/starting. If
1125	you suspect event processing to be delayed and you I<need> to base the timeout	1686	you suspect event processing to be delayed and you I<need> to base the
1126	on the current time, use something like this to adjust for this:	1687	timeout on the current time, use something like this to adjust for this:
1127		1688
1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1689	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1129		1690
1130	The callback is guarenteed to be invoked only when its timeout has passed,	1691	If the event loop is suspended for a long time, you can also force an
1131	but if multiple timers become ready during the same loop iteration then	1692	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1132	order of execution is undefined.	1693	()>.
1133		1694
1134	=head3 Watcher-Specific Functions and Data Members	1695	=head3 Watcher-Specific Functions and Data Members
1135		1696
1136	=over 4	1697	=over 4
1137		1698
1138	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1699	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1139		1700
1140	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1701	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1141		1702
1142	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1703	Configure the timer to trigger after C<after> seconds. If C<repeat>
1143	C<0.>, then it will automatically be stopped. If it is positive, then the	1704	is C<0.>, then it will automatically be stopped once the timeout is
1144	timer will automatically be configured to trigger again C<repeat> seconds	1705	reached. If it is positive, then the timer will automatically be
1145	later, again, and again, until stopped manually.	1706	configured to trigger again C<repeat> seconds later, again, and again,
		1707	until stopped manually.
1146		1708
1147	The timer itself will do a best-effort at avoiding drift, that is, if you	1709	The timer itself will do a best-effort at avoiding drift, that is, if
1148	configure a timer to trigger every 10 seconds, then it will trigger at	1710	you configure a timer to trigger every 10 seconds, then it will normally
1149	exactly 10 second intervals. If, however, your program cannot keep up with	1711	trigger at exactly 10 second intervals. If, however, your program cannot
1150	the timer (because it takes longer than those 10 seconds to do stuff) the	1712	keep up with the timer (because it takes longer than those 10 seconds to
1151	timer will not fire more than once per event loop iteration.	1713	do stuff) the timer will not fire more than once per event loop iteration.
1152		1714
1153	=item ev_timer_again (loop)	1715	=item ev_timer_again (loop, ev_timer *)
1154		1716
1155	This will act as if the timer timed out and restart it again if it is	1717	This will act as if the timer timed out and restart it again if it is
1156	repeating. The exact semantics are:	1718	repeating. The exact semantics are:
1157		1719
1158	If the timer is pending, its pending status is cleared.	1720	If the timer is pending, its pending status is cleared.
1159		1721
1160	If the timer is started but nonrepeating, stop it (as if it timed out).	1722	If the timer is started but non-repeating, stop it (as if it timed out).
1161		1723
1162	If the timer is repeating, either start it if necessary (with the	1724	If the timer is repeating, either start it if necessary (with the
1163	C<repeat> value), or reset the running timer to the C<repeat> value.	1725	C<repeat> value), or reset the running timer to the C<repeat> value.
1164		1726
1165	This sounds a bit complicated, but here is a useful and typical	1727	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1166	example: Imagine you have a tcp connection and you want a so-called idle	1728	usage example.
1167	timeout, that is, you want to be called when there have been, say, 60
1168	seconds of inactivity on the socket. The easiest way to do this is to
1169	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1170	C<ev_timer_again> each time you successfully read or write some data. If
1171	you go into an idle state where you do not expect data to travel on the
1172	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1173	automatically restart it if need be.
1174
1175	That means you can ignore the C<after> value and C<ev_timer_start>
1176	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1177
1178	ev_timer_init (timer, callback, 0., 5.);
1179	ev_timer_again (loop, timer);
1180	...
1181	timer->again = 17.;
1182	ev_timer_again (loop, timer);
1183	...
1184	timer->again = 10.;
1185	ev_timer_again (loop, timer);
1186
1187	This is more slightly efficient then stopping/starting the timer each time
1188	you want to modify its timeout value.
1189		1729
1190	=item ev_tstamp repeat [read-write]	1730	=item ev_tstamp repeat [read-write]
1191		1731
1192	The current C<repeat> value. Will be used each time the watcher times out	1732	The current C<repeat> value. Will be used each time the watcher times out
1193	or C<ev_timer_again> is called and determines the next timeout (if any),	1733	or C<ev_timer_again> is called, and determines the next timeout (if any),
1194	which is also when any modifications are taken into account.	1734	which is also when any modifications are taken into account.
1195		1735
1196	=back	1736	=back
1197		1737
1198	=head3 Examples	1738	=head3 Examples
1199		1739
1200	Example: Create a timer that fires after 60 seconds.	1740	Example: Create a timer that fires after 60 seconds.
1201		1741
1202	static void	1742	static void
1203	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1743	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1204	{	1744	{
1205	.. one minute over, w is actually stopped right here	1745	.. one minute over, w is actually stopped right here
1206	}	1746	}
1207		1747
1208	struct ev_timer mytimer;	1748	ev_timer mytimer;
1209	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1749	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1210	ev_timer_start (loop, &mytimer);	1750	ev_timer_start (loop, &mytimer);
1211		1751
1212	Example: Create a timeout timer that times out after 10 seconds of	1752	Example: Create a timeout timer that times out after 10 seconds of
1213	inactivity.	1753	inactivity.
1214		1754
1215	static void	1755	static void
1216	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1756	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1217	{	1757	{
1218	.. ten seconds without any activity	1758	.. ten seconds without any activity
1219	}	1759	}
1220		1760
1221	struct ev_timer mytimer;	1761	ev_timer mytimer;
1222	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1762	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1223	ev_timer_again (&mytimer); /* start timer */	1763	ev_timer_again (&mytimer); /* start timer */
1224	ev_loop (loop, 0);	1764	ev_loop (loop, 0);
1225		1765
1226	// and in some piece of code that gets executed on any "activity":	1766	// and in some piece of code that gets executed on any "activity":
1227	// reset the timeout to start ticking again at 10 seconds	1767	// reset the timeout to start ticking again at 10 seconds
1228	ev_timer_again (&mytimer);	1768	ev_timer_again (&mytimer);
1229		1769
1230		1770
1231	=head2 C<ev_periodic> - to cron or not to cron?	1771	=head2 C<ev_periodic> - to cron or not to cron?
1232		1772
1233	Periodic watchers are also timers of a kind, but they are very versatile	1773	Periodic watchers are also timers of a kind, but they are very versatile
1234	(and unfortunately a bit complex).	1774	(and unfortunately a bit complex).
1235		1775
1236	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1776	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1237	but on wallclock time (absolute time). You can tell a periodic watcher	1777	relative time, the physical time that passes) but on wall clock time
1238	to trigger "at" some specific point in time. For example, if you tell a	1778	(absolute time, the thing you can read on your calender or clock). The
1239	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1779	difference is that wall clock time can run faster or slower than real
1240	+ 10.>) and then reset your system clock to the last year, then it will	1780	time, and time jumps are not uncommon (e.g. when you adjust your
1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1781	wrist-watch).
1242	roughly 10 seconds later).
1243		1782
1244	They can also be used to implement vastly more complex timers, such as	1783	You can tell a periodic watcher to trigger after some specific point
1245	triggering an event on each midnight, local time or other, complicated,	1784	in time: for example, if you tell a periodic watcher to trigger "in 10
1246	rules.	1785	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1786	not a delay) and then reset your system clock to January of the previous
		1787	year, then it will take a year or more to trigger the event (unlike an
		1788	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1789	it, as it uses a relative timeout).
1247		1790
		1791	C<ev_periodic> watchers can also be used to implement vastly more complex
		1792	timers, such as triggering an event on each "midnight, local time", or
		1793	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1794	those cannot react to time jumps.
		1795
1248	As with timers, the callback is guarenteed to be invoked only when the	1796	As with timers, the callback is guaranteed to be invoked only when the
1249	time (C<at>) has been passed, but if multiple periodic timers become ready	1797	point in time where it is supposed to trigger has passed. If multiple
1250	during the same loop iteration then order of execution is undefined.	1798	timers become ready during the same loop iteration then the ones with
		1799	earlier time-out values are invoked before ones with later time-out values
		1800	(but this is no longer true when a callback calls C<ev_loop> recursively).
1251		1801
1252	=head3 Watcher-Specific Functions and Data Members	1802	=head3 Watcher-Specific Functions and Data Members
1253		1803
1254	=over 4	1804	=over 4
1255		1805
1256	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1806	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1257		1807
1258	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1808	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1259		1809
1260	Lots of arguments, lets sort it out... There are basically three modes of	1810	Lots of arguments, let's sort it out... There are basically three modes of
1261	operation, and we will explain them from simplest to complex:	1811	operation, and we will explain them from simplest to most complex:
1262		1812
1263	=over 4	1813	=over 4
1264		1814
1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1815	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1266		1816
1267	In this configuration the watcher triggers an event at the wallclock time	1817	In this configuration the watcher triggers an event after the wall clock
1268	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1818	time C<offset> has passed. It will not repeat and will not adjust when a
1269	that is, if it is to be run at January 1st 2011 then it will run when the	1819	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1270	system time reaches or surpasses this time.	1820	will be stopped and invoked when the system clock reaches or surpasses
		1821	this point in time.
1271		1822
1272	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1823	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1273		1824
1274	In this mode the watcher will always be scheduled to time out at the next	1825	In this mode the watcher will always be scheduled to time out at the next
1275	C<at + N * interval> time (for some integer N, which can also be negative)	1826	C<offset + N * interval> time (for some integer N, which can also be
1276	and then repeat, regardless of any time jumps.	1827	negative) and then repeat, regardless of any time jumps. The C<offset>
		1828	argument is merely an offset into the C<interval> periods.
1277		1829
1278	This can be used to create timers that do not drift with respect to system	1830	This can be used to create timers that do not drift with respect to the
1279	time:	1831	system clock, for example, here is an C<ev_periodic> that triggers each
		1832	hour, on the hour (with respect to UTC):
1280		1833
1281	ev_periodic_set (&periodic, 0., 3600., 0);	1834	ev_periodic_set (&periodic, 0., 3600., 0);
1282		1835
1283	This doesn't mean there will always be 3600 seconds in between triggers,	1836	This doesn't mean there will always be 3600 seconds in between triggers,
1284	but only that the the callback will be called when the system time shows a	1837	but only that the callback will be called when the system time shows a
1285	full hour (UTC), or more correctly, when the system time is evenly divisible	1838	full hour (UTC), or more correctly, when the system time is evenly divisible
1286	by 3600.	1839	by 3600.
1287		1840
1288	Another way to think about it (for the mathematically inclined) is that	1841	Another way to think about it (for the mathematically inclined) is that
1289	C<ev_periodic> will try to run the callback in this mode at the next possible	1842	C<ev_periodic> will try to run the callback in this mode at the next possible
1290	time where C<time = at (mod interval)>, regardless of any time jumps.	1843	time where C<time = offset (mod interval)>, regardless of any time jumps.
1291		1844
1292	For numerical stability it is preferable that the C<at> value is near	1845	For numerical stability it is preferable that the C<offset> value is near
1293	C<ev_now ()> (the current time), but there is no range requirement for	1846	C<ev_now ()> (the current time), but there is no range requirement for
1294	this value.	1847	this value, and in fact is often specified as zero.
1295		1848
		1849	Note also that there is an upper limit to how often a timer can fire (CPU
		1850	speed for example), so if C<interval> is very small then timing stability
		1851	will of course deteriorate. Libev itself tries to be exact to be about one
		1852	millisecond (if the OS supports it and the machine is fast enough).
		1853
1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1854	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1297		1855
1298	In this mode the values for C<interval> and C<at> are both being	1856	In this mode the values for C<interval> and C<offset> are both being
1299	ignored. Instead, each time the periodic watcher gets scheduled, the	1857	ignored. Instead, each time the periodic watcher gets scheduled, the
1300	reschedule callback will be called with the watcher as first, and the	1858	reschedule callback will be called with the watcher as first, and the
1301	current time as second argument.	1859	current time as second argument.
1302		1860
1303	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1861	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1304	ever, or make any event loop modifications>. If you need to stop it,	1862	or make ANY other event loop modifications whatsoever, unless explicitly
1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1863	allowed by documentation here>.
1306	starting an C<ev_prepare> watcher, which is legal).
1307		1864
		1865	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1866	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1867	only event loop modification you are allowed to do).
		1868
1308	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1869	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1309	ev_tstamp now)>, e.g.:	1870	*w, ev_tstamp now)>, e.g.:
1310		1871
		1872	static ev_tstamp
1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1873	my_rescheduler (ev_periodic *w, ev_tstamp now)
1312	{	1874	{
1313	return now + 60.;	1875	return now + 60.;
1314	}	1876	}
1315		1877
1316	It must return the next time to trigger, based on the passed time value	1878	It must return the next time to trigger, based on the passed time value
1317	(that is, the lowest time value larger than to the second argument). It	1879	(that is, the lowest time value larger than to the second argument). It
1318	will usually be called just before the callback will be triggered, but	1880	will usually be called just before the callback will be triggered, but
1319	might be called at other times, too.	1881	might be called at other times, too.
1320		1882
1321	NOTE: I<< This callback must always return a time that is later than the	1883	NOTE: I<< This callback must always return a time that is higher than or
1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1884	equal to the passed C<now> value >>.
1323		1885
1324	This can be used to create very complex timers, such as a timer that	1886	This can be used to create very complex timers, such as a timer that
1325	triggers on each midnight, local time. To do this, you would calculate the	1887	triggers on "next midnight, local time". To do this, you would calculate the
1326	next midnight after C<now> and return the timestamp value for this. How	1888	next midnight after C<now> and return the timestamp value for this. How
1327	you do this is, again, up to you (but it is not trivial, which is the main	1889	you do this is, again, up to you (but it is not trivial, which is the main
1328	reason I omitted it as an example).	1890	reason I omitted it as an example).
1329		1891
1330	=back	1892	=back
…		…
1334	Simply stops and restarts the periodic watcher again. This is only useful	1896	Simply stops and restarts the periodic watcher again. This is only useful
1335	when you changed some parameters or the reschedule callback would return	1897	when you changed some parameters or the reschedule callback would return
1336	a different time than the last time it was called (e.g. in a crond like	1898	a different time than the last time it was called (e.g. in a crond like
1337	program when the crontabs have changed).	1899	program when the crontabs have changed).
1338		1900
		1901	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1902
		1903	When active, returns the absolute time that the watcher is supposed
		1904	to trigger next. This is not the same as the C<offset> argument to
		1905	C<ev_periodic_set>, but indeed works even in interval and manual
		1906	rescheduling modes.
		1907
1339	=item ev_tstamp offset [read-write]	1908	=item ev_tstamp offset [read-write]
1340		1909
1341	When repeating, this contains the offset value, otherwise this is the	1910	When repeating, this contains the offset value, otherwise this is the
1342	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1911	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1912	although libev might modify this value for better numerical stability).
1343		1913
1344	Can be modified any time, but changes only take effect when the periodic	1914	Can be modified any time, but changes only take effect when the periodic
1345	timer fires or C<ev_periodic_again> is being called.	1915	timer fires or C<ev_periodic_again> is being called.
1346		1916
1347	=item ev_tstamp interval [read-write]	1917	=item ev_tstamp interval [read-write]
1348		1918
1349	The current interval value. Can be modified any time, but changes only	1919	The current interval value. Can be modified any time, but changes only
1350	take effect when the periodic timer fires or C<ev_periodic_again> is being	1920	take effect when the periodic timer fires or C<ev_periodic_again> is being
1351	called.	1921	called.
1352		1922
1353	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1923	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1354		1924
1355	The current reschedule callback, or C<0>, if this functionality is	1925	The current reschedule callback, or C<0>, if this functionality is
1356	switched off. Can be changed any time, but changes only take effect when	1926	switched off. Can be changed any time, but changes only take effect when
1357	the periodic timer fires or C<ev_periodic_again> is being called.	1927	the periodic timer fires or C<ev_periodic_again> is being called.
1358		1928
1359	=item ev_tstamp at [read-only]
1360
1361	When active, contains the absolute time that the watcher is supposed to
1362	trigger next.
1363
1364	=back	1929	=back
1365		1930
1366	=head3 Examples	1931	=head3 Examples
1367		1932
1368	Example: Call a callback every hour, or, more precisely, whenever the	1933	Example: Call a callback every hour, or, more precisely, whenever the
1369	system clock is divisible by 3600. The callback invocation times have	1934	system time is divisible by 3600. The callback invocation times have
1370	potentially a lot of jittering, but good long-term stability.	1935	potentially a lot of jitter, but good long-term stability.
1371		1936
1372	static void	1937	static void
1373	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1938	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1374	{	1939	{
1375	... its now a full hour (UTC, or TAI or whatever your clock follows)	1940	... its now a full hour (UTC, or TAI or whatever your clock follows)
1376	}	1941	}
1377		1942
1378	struct ev_periodic hourly_tick;	1943	ev_periodic hourly_tick;
1379	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1944	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1380	ev_periodic_start (loop, &hourly_tick);	1945	ev_periodic_start (loop, &hourly_tick);
1381		1946
1382	Example: The same as above, but use a reschedule callback to do it:	1947	Example: The same as above, but use a reschedule callback to do it:
1383		1948
1384	#include <math.h>	1949	#include <math.h>
1385		1950
1386	static ev_tstamp	1951	static ev_tstamp
1387	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1952	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1388	{	1953	{
1389	return fmod (now, 3600.) + 3600.;	1954	return now + (3600. - fmod (now, 3600.));
1390	}	1955	}
1391		1956
1392	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1957	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1393		1958
1394	Example: Call a callback every hour, starting now:	1959	Example: Call a callback every hour, starting now:
1395		1960
1396	struct ev_periodic hourly_tick;	1961	ev_periodic hourly_tick;
1397	ev_periodic_init (&hourly_tick, clock_cb,	1962	ev_periodic_init (&hourly_tick, clock_cb,
1398	fmod (ev_now (loop), 3600.), 3600., 0);	1963	fmod (ev_now (loop), 3600.), 3600., 0);
1399	ev_periodic_start (loop, &hourly_tick);	1964	ev_periodic_start (loop, &hourly_tick);
1400		1965
1401		1966
1402	=head2 C<ev_signal> - signal me when a signal gets signalled!	1967	=head2 C<ev_signal> - signal me when a signal gets signalled!
1403		1968
1404	Signal watchers will trigger an event when the process receives a specific	1969	Signal watchers will trigger an event when the process receives a specific
1405	signal one or more times. Even though signals are very asynchronous, libev	1970	signal one or more times. Even though signals are very asynchronous, libev
1406	will try it's best to deliver signals synchronously, i.e. as part of the	1971	will try it's best to deliver signals synchronously, i.e. as part of the
1407	normal event processing, like any other event.	1972	normal event processing, like any other event.
1408		1973
		1974	If you want signals asynchronously, just use C<sigaction> as you would
		1975	do without libev and forget about sharing the signal. You can even use
		1976	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1977
1409	You can configure as many watchers as you like per signal. Only when the	1978	You can configure as many watchers as you like per signal. Only when the
1410	first watcher gets started will libev actually register a signal watcher	1979	first watcher gets started will libev actually register a signal handler
1411	with the kernel (thus it coexists with your own signal handlers as long	1980	with the kernel (thus it coexists with your own signal handlers as long as
1412	as you don't register any with libev). Similarly, when the last signal	1981	you don't register any with libev for the same signal). Similarly, when
1413	watcher for a signal is stopped libev will reset the signal handler to	1982	the last signal watcher for a signal is stopped, libev will reset the
1414	SIG_DFL (regardless of what it was set to before).	1983	signal handler to SIG_DFL (regardless of what it was set to before).
		1984
		1985	If possible and supported, libev will install its handlers with
		1986	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1987	interrupted. If you have a problem with system calls getting interrupted by
		1988	signals you can block all signals in an C<ev_check> watcher and unblock
		1989	them in an C<ev_prepare> watcher.
1415		1990
1416	=head3 Watcher-Specific Functions and Data Members	1991	=head3 Watcher-Specific Functions and Data Members
1417		1992
1418	=over 4	1993	=over 4
1419		1994
…		…
1428		2003
1429	The signal the watcher watches out for.	2004	The signal the watcher watches out for.
1430		2005
1431	=back	2006	=back
1432		2007
		2008	=head3 Examples
		2009
		2010	Example: Try to exit cleanly on SIGINT.
		2011
		2012	static void
		2013	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2014	{
		2015	ev_unloop (loop, EVUNLOOP_ALL);
		2016	}
		2017
		2018	ev_signal signal_watcher;
		2019	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2020	ev_signal_start (loop, &signal_watcher);
		2021
1433		2022
1434	=head2 C<ev_child> - watch out for process status changes	2023	=head2 C<ev_child> - watch out for process status changes
1435		2024
1436	Child watchers trigger when your process receives a SIGCHLD in response to	2025	Child watchers trigger when your process receives a SIGCHLD in response to
1437	some child status changes (most typically when a child of yours dies).	2026	some child status changes (most typically when a child of yours dies or
		2027	exits). It is permissible to install a child watcher I<after> the child
		2028	has been forked (which implies it might have already exited), as long
		2029	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2030	forking and then immediately registering a watcher for the child is fine,
		2031	but forking and registering a watcher a few event loop iterations later or
		2032	in the next callback invocation is not.
		2033
		2034	Only the default event loop is capable of handling signals, and therefore
		2035	you can only register child watchers in the default event loop.
		2036
		2037	Due to some design glitches inside libev, child watchers will always be
		2038	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2039	libev)
		2040
		2041	=head3 Process Interaction
		2042
		2043	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2044	initialised. This is necessary to guarantee proper behaviour even if
		2045	the first child watcher is started after the child exits. The occurrence
		2046	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2047	synchronously as part of the event loop processing. Libev always reaps all
		2048	children, even ones not watched.
		2049
		2050	=head3 Overriding the Built-In Processing
		2051
		2052	Libev offers no special support for overriding the built-in child
		2053	processing, but if your application collides with libev's default child
		2054	handler, you can override it easily by installing your own handler for
		2055	C<SIGCHLD> after initialising the default loop, and making sure the
		2056	default loop never gets destroyed. You are encouraged, however, to use an
		2057	event-based approach to child reaping and thus use libev's support for
		2058	that, so other libev users can use C<ev_child> watchers freely.
		2059
		2060	=head3 Stopping the Child Watcher
		2061
		2062	Currently, the child watcher never gets stopped, even when the
		2063	child terminates, so normally one needs to stop the watcher in the
		2064	callback. Future versions of libev might stop the watcher automatically
		2065	when a child exit is detected.
1438		2066
1439	=head3 Watcher-Specific Functions and Data Members	2067	=head3 Watcher-Specific Functions and Data Members
1440		2068
1441	=over 4	2069	=over 4
1442		2070
…		…
1468		2096
1469	=back	2097	=back
1470		2098
1471	=head3 Examples	2099	=head3 Examples
1472		2100
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	2101	Example: C<fork()> a new process and install a child handler to wait for
		2102	its completion.
1474		2103
		2104	ev_child cw;
		2105
1475	static void	2106	static void
1476	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2107	child_cb (EV_P_ ev_child *w, int revents)
1477	{	2108	{
1478	ev_unloop (loop, EVUNLOOP_ALL);	2109	ev_child_stop (EV_A_ w);
		2110	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1479	}	2111	}
1480		2112
1481	struct ev_signal signal_watcher;	2113	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2114
1483	ev_signal_start (loop, &sigint_cb);	2115	if (pid < 0)
		2116	// error
		2117	else if (pid == 0)
		2118	{
		2119	// the forked child executes here
		2120	exit (1);
		2121	}
		2122	else
		2123	{
		2124	ev_child_init (&cw, child_cb, pid, 0);
		2125	ev_child_start (EV_DEFAULT_ &cw);
		2126	}
1484		2127
1485		2128
1486	=head2 C<ev_stat> - did the file attributes just change?	2129	=head2 C<ev_stat> - did the file attributes just change?
1487		2130
1488	This watches a filesystem path for attribute changes. That is, it calls	2131	This watches a file system path for attribute changes. That is, it calls
1489	C<stat> regularly (or when the OS says it changed) and sees if it changed	2132	C<stat> on that path in regular intervals (or when the OS says it changed)
1490	compared to the last time, invoking the callback if it did.	2133	and sees if it changed compared to the last time, invoking the callback if
		2134	it did.
1491		2135
1492	The path does not need to exist: changing from "path exists" to "path does	2136	The path does not need to exist: changing from "path exists" to "path does
1493	not exist" is a status change like any other. The condition "path does	2137	not exist" is a status change like any other. The condition "path does not
1494	not exist" is signified by the C<st_nlink> field being zero (which is	2138	exist" (or more correctly "path cannot be stat'ed") is signified by the
1495	otherwise always forced to be at least one) and all the other fields of	2139	C<st_nlink> field being zero (which is otherwise always forced to be at
1496	the stat buffer having unspecified contents.	2140	least one) and all the other fields of the stat buffer having unspecified
		2141	contents.
1497		2142
1498	The path I<should> be absolute and I<must not> end in a slash. If it is	2143	The path I<must not> end in a slash or contain special components such as
		2144	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1499	relative and your working directory changes, the behaviour is undefined.	2145	your working directory changes, then the behaviour is undefined.
1500		2146
1501	Since there is no standard to do this, the portable implementation simply	2147	Since there is no portable change notification interface available, the
1502	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2148	portable implementation simply calls C<stat(2)> regularly on the path
1503	can specify a recommended polling interval for this case. If you specify	2149	to see if it changed somehow. You can specify a recommended polling
1504	a polling interval of C<0> (highly recommended!) then a I<suitable,	2150	interval for this case. If you specify a polling interval of C<0> (highly
1505	unspecified default> value will be used (which you can expect to be around	2151	recommended!) then a I<suitable, unspecified default> value will be used
1506	five seconds, although this might change dynamically). Libev will also	2152	(which you can expect to be around five seconds, although this might
1507	impose a minimum interval which is currently around C<0.1>, but thats	2153	change dynamically). Libev will also impose a minimum interval which is
1508	usually overkill.	2154	currently around C<0.1>, but that's usually overkill.
1509		2155
1510	This watcher type is not meant for massive numbers of stat watchers,	2156	This watcher type is not meant for massive numbers of stat watchers,
1511	as even with OS-supported change notifications, this can be	2157	as even with OS-supported change notifications, this can be
1512	resource-intensive.	2158	resource-intensive.
1513		2159
1514	At the time of this writing, only the Linux inotify interface is	2160	At the time of this writing, the only OS-specific interface implemented
1515	implemented (implementing kqueue support is left as an exercise for the	2161	is the Linux inotify interface (implementing kqueue support is left as an
1516	reader). Inotify will be used to give hints only and should not change the	2162	exercise for the reader. Note, however, that the author sees no way of
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2163	implementing C<ev_stat> semantics with kqueue, except as a hint).
1518	to fall back to regular polling again even with inotify, but changes are
1519	usually detected immediately, and if the file exists there will be no
1520	polling.
1521		2164
1522	=head3 Inotify	2165	=head3 ABI Issues (Largefile Support)
1523		2166
		2167	Libev by default (unless the user overrides this) uses the default
		2168	compilation environment, which means that on systems with large file
		2169	support disabled by default, you get the 32 bit version of the stat
		2170	structure. When using the library from programs that change the ABI to
		2171	use 64 bit file offsets the programs will fail. In that case you have to
		2172	compile libev with the same flags to get binary compatibility. This is
		2173	obviously the case with any flags that change the ABI, but the problem is
		2174	most noticeably displayed with ev_stat and large file support.
		2175
		2176	The solution for this is to lobby your distribution maker to make large
		2177	file interfaces available by default (as e.g. FreeBSD does) and not
		2178	optional. Libev cannot simply switch on large file support because it has
		2179	to exchange stat structures with application programs compiled using the
		2180	default compilation environment.
		2181
		2182	=head3 Inotify and Kqueue
		2183
1524	When C<inotify (7)> support has been compiled into libev (generally only	2184	When C<inotify (7)> support has been compiled into libev and present at
1525	available on Linux) and present at runtime, it will be used to speed up	2185	runtime, it will be used to speed up change detection where possible. The
1526	change detection where possible. The inotify descriptor will be created lazily	2186	inotify descriptor will be created lazily when the first C<ev_stat>
1527	when the first C<ev_stat> watcher is being started.	2187	watcher is being started.
1528		2188
1529	Inotify presense does not change the semantics of C<ev_stat> watchers	2189	Inotify presence does not change the semantics of C<ev_stat> watchers
1530	except that changes might be detected earlier, and in some cases, to avoid	2190	except that changes might be detected earlier, and in some cases, to avoid
1531	making regular C<stat> calls. Even in the presense of inotify support	2191	making regular C<stat> calls. Even in the presence of inotify support
1532	there are many cases where libev has to resort to regular C<stat> polling.	2192	there are many cases where libev has to resort to regular C<stat> polling,
		2193	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2194	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2195	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2196	xfs are fully working) libev usually gets away without polling.
1533		2197
1534	(There is no support for kqueue, as apparently it cannot be used to	2198	There is no support for kqueue, as apparently it cannot be used to
1535	implement this functionality, due to the requirement of having a file	2199	implement this functionality, due to the requirement of having a file
1536	descriptor open on the object at all times).	2200	descriptor open on the object at all times, and detecting renames, unlinks
		2201	etc. is difficult.
		2202
		2203	=head3 C<stat ()> is a synchronous operation
		2204
		2205	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2206	the process. The exception are C<ev_stat> watchers - those call C<stat
		2207	()>, which is a synchronous operation.
		2208
		2209	For local paths, this usually doesn't matter: unless the system is very
		2210	busy or the intervals between stat's are large, a stat call will be fast,
		2211	as the path data is usually in memory already (except when starting the
		2212	watcher).
		2213
		2214	For networked file systems, calling C<stat ()> can block an indefinite
		2215	time due to network issues, and even under good conditions, a stat call
		2216	often takes multiple milliseconds.
		2217
		2218	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2219	paths, although this is fully supported by libev.
1537		2220
1538	=head3 The special problem of stat time resolution	2221	=head3 The special problem of stat time resolution
1539		2222
1540	The C<stat ()> syscall only supports full-second resolution portably, and	2223	The C<stat ()> system call only supports full-second resolution portably,
1541	even on systems where the resolution is higher, many filesystems still	2224	and even on systems where the resolution is higher, most file systems
1542	only support whole seconds.	2225	still only support whole seconds.
1543		2226
1544	That means that, if the time is the only thing that changes, you might	2227	That means that, if the time is the only thing that changes, you can
1545	miss updates: on the first update, C<ev_stat> detects a change and calls	2228	easily miss updates: on the first update, C<ev_stat> detects a change and
1546	your callback, which does something. When there is another update within	2229	calls your callback, which does something. When there is another update
1547	the same second, C<ev_stat> will be unable to detect it.	2230	within the same second, C<ev_stat> will be unable to detect unless the
		2231	stat data does change in other ways (e.g. file size).
1548		2232
1549	The solution to this is to delay acting on a change for a second (or till	2233	The solution to this is to delay acting on a change for slightly more
1550	the next second boundary), using a roughly one-second delay C<ev_timer>	2234	than a second (or till slightly after the next full second boundary), using
1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2235	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1552	is added to work around small timing inconsistencies of some operating	2236	ev_timer_again (loop, w)>).
1553	systems.	2237
		2238	The C<.02> offset is added to work around small timing inconsistencies
		2239	of some operating systems (where the second counter of the current time
		2240	might be be delayed. One such system is the Linux kernel, where a call to
		2241	C<gettimeofday> might return a timestamp with a full second later than
		2242	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2243	update file times then there will be a small window where the kernel uses
		2244	the previous second to update file times but libev might already execute
		2245	the timer callback).
1554		2246
1555	=head3 Watcher-Specific Functions and Data Members	2247	=head3 Watcher-Specific Functions and Data Members
1556		2248
1557	=over 4	2249	=over 4
1558		2250
…		…
1564	C<path>. The C<interval> is a hint on how quickly a change is expected to	2256	C<path>. The C<interval> is a hint on how quickly a change is expected to
1565	be detected and should normally be specified as C<0> to let libev choose	2257	be detected and should normally be specified as C<0> to let libev choose
1566	a suitable value. The memory pointed to by C<path> must point to the same	2258	a suitable value. The memory pointed to by C<path> must point to the same
1567	path for as long as the watcher is active.	2259	path for as long as the watcher is active.
1568		2260
1569	The callback will be receive C<EV_STAT> when a change was detected,	2261	The callback will receive an C<EV_STAT> event when a change was detected,
1570	relative to the attributes at the time the watcher was started (or the	2262	relative to the attributes at the time the watcher was started (or the
1571	last change was detected).	2263	last change was detected).
1572		2264
1573	=item ev_stat_stat (ev_stat *)	2265	=item ev_stat_stat (loop, ev_stat *)
1574		2266
1575	Updates the stat buffer immediately with new values. If you change the	2267	Updates the stat buffer immediately with new values. If you change the
1576	watched path in your callback, you could call this fucntion to avoid	2268	watched path in your callback, you could call this function to avoid
1577	detecting this change (while introducing a race condition). Can also be	2269	detecting this change (while introducing a race condition if you are not
1578	useful simply to find out the new values.	2270	the only one changing the path). Can also be useful simply to find out the
		2271	new values.
1579		2272
1580	=item ev_statdata attr [read-only]	2273	=item ev_statdata attr [read-only]
1581		2274
1582	The most-recently detected attributes of the file. Although the type is of	2275	The most-recently detected attributes of the file. Although the type is
1583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2276	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1584	suitable for your system. If the C<st_nlink> member is C<0>, then there	2277	suitable for your system, but you can only rely on the POSIX-standardised
		2278	members to be present. If the C<st_nlink> member is C<0>, then there was
1585	was some error while C<stat>ing the file.	2279	some error while C<stat>ing the file.
1586		2280
1587	=item ev_statdata prev [read-only]	2281	=item ev_statdata prev [read-only]
1588		2282
1589	The previous attributes of the file. The callback gets invoked whenever	2283	The previous attributes of the file. The callback gets invoked whenever
1590	C<prev> != C<attr>.	2284	C<prev> != C<attr>, or, more precisely, one or more of these members
		2285	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2286	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1591		2287
1592	=item ev_tstamp interval [read-only]	2288	=item ev_tstamp interval [read-only]
1593		2289
1594	The specified interval.	2290	The specified interval.
1595		2291
1596	=item const char *path [read-only]	2292	=item const char *path [read-only]
1597		2293
1598	The filesystem path that is being watched.	2294	The file system path that is being watched.
1599		2295
1600	=back	2296	=back
1601		2297
1602	=head3 Examples	2298	=head3 Examples
1603		2299
1604	Example: Watch C</etc/passwd> for attribute changes.	2300	Example: Watch C</etc/passwd> for attribute changes.
1605		2301
1606	static void	2302	static void
1607	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2303	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1608	{	2304	{
1609	/* /etc/passwd changed in some way */	2305	/* /etc/passwd changed in some way */
1610	if (w->attr.st_nlink)	2306	if (w->attr.st_nlink)
1611	{	2307	{
1612	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2308	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1613	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2309	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1614	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2310	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1615	}	2311	}
1616	else	2312	else
1617	/* you shalt not abuse printf for puts */	2313	/* you shalt not abuse printf for puts */
1618	puts ("wow, /etc/passwd is not there, expect problems. "	2314	puts ("wow, /etc/passwd is not there, expect problems. "
1619	"if this is windows, they already arrived\n");	2315	"if this is windows, they already arrived\n");
1620	}	2316	}
1621		2317
1622	...	2318	...
1623	ev_stat passwd;	2319	ev_stat passwd;
1624		2320
1625	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2321	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1626	ev_stat_start (loop, &passwd);	2322	ev_stat_start (loop, &passwd);
1627		2323
1628	Example: Like above, but additionally use a one-second delay so we do not	2324	Example: Like above, but additionally use a one-second delay so we do not
1629	miss updates (however, frequent updates will delay processing, too, so	2325	miss updates (however, frequent updates will delay processing, too, so
1630	one might do the work both on C<ev_stat> callback invocation I<and> on	2326	one might do the work both on C<ev_stat> callback invocation I<and> on
1631	C<ev_timer> callback invocation).	2327	C<ev_timer> callback invocation).
1632		2328
1633	static ev_stat passwd;	2329	static ev_stat passwd;
1634	static ev_timer timer;	2330	static ev_timer timer;
1635		2331
1636	static void	2332	static void
1637	timer_cb (EV_P_ ev_timer *w, int revents)	2333	timer_cb (EV_P_ ev_timer *w, int revents)
1638	{	2334	{
1639	ev_timer_stop (EV_A_ w);	2335	ev_timer_stop (EV_A_ w);
1640		2336
1641	/* now it's one second after the most recent passwd change */	2337	/* now it's one second after the most recent passwd change */
1642	}	2338	}
1643		2339
1644	static void	2340	static void
1645	stat_cb (EV_P_ ev_stat *w, int revents)	2341	stat_cb (EV_P_ ev_stat *w, int revents)
1646	{	2342	{
1647	/* reset the one-second timer */	2343	/* reset the one-second timer */
1648	ev_timer_again (EV_A_ &timer);	2344	ev_timer_again (EV_A_ &timer);
1649	}	2345	}
1650		2346
1651	...	2347	...
1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2348	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1653	ev_stat_start (loop, &passwd);	2349	ev_stat_start (loop, &passwd);
1654	ev_timer_init (&timer, timer_cb, 0., 1.01);	2350	ev_timer_init (&timer, timer_cb, 0., 1.02);
1655		2351
1656		2352
1657	=head2 C<ev_idle> - when you've got nothing better to do...	2353	=head2 C<ev_idle> - when you've got nothing better to do...
1658		2354
1659	Idle watchers trigger events when no other events of the same or higher	2355	Idle watchers trigger events when no other events of the same or higher
1660	priority are pending (prepare, check and other idle watchers do not	2356	priority are pending (prepare, check and other idle watchers do not count
1661	count).	2357	as receiving "events").
1662		2358
1663	That is, as long as your process is busy handling sockets or timeouts	2359	That is, as long as your process is busy handling sockets or timeouts
1664	(or even signals, imagine) of the same or higher priority it will not be	2360	(or even signals, imagine) of the same or higher priority it will not be
1665	triggered. But when your process is idle (or only lower-priority watchers	2361	triggered. But when your process is idle (or only lower-priority watchers
1666	are pending), the idle watchers are being called once per event loop	2362	are pending), the idle watchers are being called once per event loop
…		…
1677		2373
1678	=head3 Watcher-Specific Functions and Data Members	2374	=head3 Watcher-Specific Functions and Data Members
1679		2375
1680	=over 4	2376	=over 4
1681		2377
1682	=item ev_idle_init (ev_signal *, callback)	2378	=item ev_idle_init (ev_idle *, callback)
1683		2379
1684	Initialises and configures the idle watcher - it has no parameters of any	2380	Initialises and configures the idle watcher - it has no parameters of any
1685	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2381	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1686	believe me.	2382	believe me.
1687		2383
…		…
1690	=head3 Examples	2386	=head3 Examples
1691		2387
1692	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2388	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1693	callback, free it. Also, use no error checking, as usual.	2389	callback, free it. Also, use no error checking, as usual.
1694		2390
1695	static void	2391	static void
1696	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2392	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1697	{	2393	{
1698	free (w);	2394	free (w);
1699	// now do something you wanted to do when the program has	2395	// now do something you wanted to do when the program has
1700	// no longer anything immediate to do.	2396	// no longer anything immediate to do.
1701	}	2397	}
1702		2398
1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2399	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1704	ev_idle_init (idle_watcher, idle_cb);	2400	ev_idle_init (idle_watcher, idle_cb);
1705	ev_idle_start (loop, idle_cb);	2401	ev_idle_start (loop, idle_watcher);
1706		2402
1707		2403
1708	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2404	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1709		2405
1710	Prepare and check watchers are usually (but not always) used in tandem:	2406	Prepare and check watchers are usually (but not always) used in pairs:
1711	prepare watchers get invoked before the process blocks and check watchers	2407	prepare watchers get invoked before the process blocks and check watchers
1712	afterwards.	2408	afterwards.
1713		2409
1714	You I<must not> call C<ev_loop> or similar functions that enter	2410	You I<must not> call C<ev_loop> or similar functions that enter
1715	the current event loop from either C<ev_prepare> or C<ev_check>	2411	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1718	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2414	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1719	C<ev_check> so if you have one watcher of each kind they will always be	2415	C<ev_check> so if you have one watcher of each kind they will always be
1720	called in pairs bracketing the blocking call.	2416	called in pairs bracketing the blocking call.
1721		2417
1722	Their main purpose is to integrate other event mechanisms into libev and	2418	Their main purpose is to integrate other event mechanisms into libev and
1723	their use is somewhat advanced. This could be used, for example, to track	2419	their use is somewhat advanced. They could be used, for example, to track
1724	variable changes, implement your own watchers, integrate net-snmp or a	2420	variable changes, implement your own watchers, integrate net-snmp or a
1725	coroutine library and lots more. They are also occasionally useful if	2421	coroutine library and lots more. They are also occasionally useful if
1726	you cache some data and want to flush it before blocking (for example,	2422	you cache some data and want to flush it before blocking (for example,
1727	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2423	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1728	watcher).	2424	watcher).
1729		2425
1730	This is done by examining in each prepare call which file descriptors need	2426	This is done by examining in each prepare call which file descriptors
1731	to be watched by the other library, registering C<ev_io> watchers for	2427	need to be watched by the other library, registering C<ev_io> watchers
1732	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2428	for them and starting an C<ev_timer> watcher for any timeouts (many
1733	provide just this functionality). Then, in the check watcher you check for	2429	libraries provide exactly this functionality). Then, in the check watcher,
1734	any events that occured (by checking the pending status of all watchers	2430	you check for any events that occurred (by checking the pending status
1735	and stopping them) and call back into the library. The I/O and timer	2431	of all watchers and stopping them) and call back into the library. The
1736	callbacks will never actually be called (but must be valid nevertheless,	2432	I/O and timer callbacks will never actually be called (but must be valid
1737	because you never know, you know?).	2433	nevertheless, because you never know, you know?).
1738		2434
1739	As another example, the Perl Coro module uses these hooks to integrate	2435	As another example, the Perl Coro module uses these hooks to integrate
1740	coroutines into libev programs, by yielding to other active coroutines	2436	coroutines into libev programs, by yielding to other active coroutines
1741	during each prepare and only letting the process block if no coroutines	2437	during each prepare and only letting the process block if no coroutines
1742	are ready to run (it's actually more complicated: it only runs coroutines	2438	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1745	loop from blocking if lower-priority coroutines are active, thus mapping	2441	loop from blocking if lower-priority coroutines are active, thus mapping
1746	low-priority coroutines to idle/background tasks).	2442	low-priority coroutines to idle/background tasks).
1747		2443
1748	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2444	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1749	priority, to ensure that they are being run before any other watchers	2445	priority, to ensure that they are being run before any other watchers
		2446	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2447
1750	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2448	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1751	too) should not activate ("feed") events into libev. While libev fully	2449	activate ("feed") events into libev. While libev fully supports this, they
1752	supports this, they will be called before other C<ev_check> watchers	2450	might get executed before other C<ev_check> watchers did their job. As
1753	did their job. As C<ev_check> watchers are often used to embed other	2451	C<ev_check> watchers are often used to embed other (non-libev) event
1754	(non-libev) event loops those other event loops might be in an unusable	2452	loops those other event loops might be in an unusable state until their
1755	state until their C<ev_check> watcher ran (always remind yourself to	2453	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1756	coexist peacefully with others).	2454	others).
1757		2455
1758	=head3 Watcher-Specific Functions and Data Members	2456	=head3 Watcher-Specific Functions and Data Members
1759		2457
1760	=over 4	2458	=over 4
1761		2459
…		…
1763		2461
1764	=item ev_check_init (ev_check *, callback)	2462	=item ev_check_init (ev_check *, callback)
1765		2463
1766	Initialises and configures the prepare or check watcher - they have no	2464	Initialises and configures the prepare or check watcher - they have no
1767	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2465	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1768	macros, but using them is utterly, utterly and completely pointless.	2466	macros, but using them is utterly, utterly, utterly and completely
		2467	pointless.
1769		2468
1770	=back	2469	=back
1771		2470
1772	=head3 Examples	2471	=head3 Examples
1773		2472
1774	There are a number of principal ways to embed other event loops or modules	2473	There are a number of principal ways to embed other event loops or modules
1775	into libev. Here are some ideas on how to include libadns into libev	2474	into libev. Here are some ideas on how to include libadns into libev
1776	(there is a Perl module named C<EV::ADNS> that does this, which you could	2475	(there is a Perl module named C<EV::ADNS> that does this, which you could
1777	use for an actually working example. Another Perl module named C<EV::Glib>	2476	use as a working example. Another Perl module named C<EV::Glib> embeds a
1778	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2477	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1779	into the Glib event loop).	2478	Glib event loop).
1780		2479
1781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2480	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1782	and in a check watcher, destroy them and call into libadns. What follows	2481	and in a check watcher, destroy them and call into libadns. What follows
1783	is pseudo-code only of course. This requires you to either use a low	2482	is pseudo-code only of course. This requires you to either use a low
1784	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2483	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1785	the callbacks for the IO/timeout watchers might not have been called yet.	2484	the callbacks for the IO/timeout watchers might not have been called yet.
1786		2485
1787	static ev_io iow [nfd];	2486	static ev_io iow [nfd];
1788	static ev_timer tw;	2487	static ev_timer tw;
1789		2488
1790	static void	2489	static void
1791	io_cb (ev_loop *loop, ev_io *w, int revents)	2490	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1792	{	2491	{
1793	}	2492	}
1794		2493
1795	// create io watchers for each fd and a timer before blocking	2494	// create io watchers for each fd and a timer before blocking
1796	static void	2495	static void
1797	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2496	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1798	{	2497	{
1799	int timeout = 3600000;	2498	int timeout = 3600000;
1800	struct pollfd fds [nfd];	2499	struct pollfd fds [nfd];
1801	// actual code will need to loop here and realloc etc.	2500	// actual code will need to loop here and realloc etc.
1802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2501	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1803		2502
1804	/* the callback is illegal, but won't be called as we stop during check */	2503	/* the callback is illegal, but won't be called as we stop during check */
1805	ev_timer_init (&tw, 0, timeout * 1e-3);	2504	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1806	ev_timer_start (loop, &tw);	2505	ev_timer_start (loop, &tw);
1807		2506
1808	// create one ev_io per pollfd	2507	// create one ev_io per pollfd
1809	for (int i = 0; i < nfd; ++i)	2508	for (int i = 0; i < nfd; ++i)
1810	{	2509	{
1811	ev_io_init (iow + i, io_cb, fds [i].fd,	2510	ev_io_init (iow + i, io_cb, fds [i].fd,
1812	((fds [i].events & POLLIN ? EV_READ : 0)	2511	((fds [i].events & POLLIN ? EV_READ : 0)
1813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2512	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1814		2513
1815	fds [i].revents = 0;	2514	fds [i].revents = 0;
1816	ev_io_start (loop, iow + i);	2515	ev_io_start (loop, iow + i);
1817	}	2516	}
1818	}	2517	}
1819		2518
1820	// stop all watchers after blocking	2519	// stop all watchers after blocking
1821	static void	2520	static void
1822	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2521	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1823	{	2522	{
1824	ev_timer_stop (loop, &tw);	2523	ev_timer_stop (loop, &tw);
1825		2524
1826	for (int i = 0; i < nfd; ++i)	2525	for (int i = 0; i < nfd; ++i)
1827	{	2526	{
1828	// set the relevant poll flags	2527	// set the relevant poll flags
1829	// could also call adns_processreadable etc. here	2528	// could also call adns_processreadable etc. here
1830	struct pollfd *fd = fds + i;	2529	struct pollfd *fd = fds + i;
1831	int revents = ev_clear_pending (iow + i);	2530	int revents = ev_clear_pending (iow + i);
1832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2531	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2532	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1834		2533
1835	// now stop the watcher	2534	// now stop the watcher
1836	ev_io_stop (loop, iow + i);	2535	ev_io_stop (loop, iow + i);
1837	}	2536	}
1838		2537
1839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2538	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1840	}	2539	}
1841		2540
1842	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2541	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1843	in the prepare watcher and would dispose of the check watcher.	2542	in the prepare watcher and would dispose of the check watcher.
1844		2543
1845	Method 3: If the module to be embedded supports explicit event	2544	Method 3: If the module to be embedded supports explicit event
1846	notification (adns does), you can also make use of the actual watcher	2545	notification (libadns does), you can also make use of the actual watcher
1847	callbacks, and only destroy/create the watchers in the prepare watcher.	2546	callbacks, and only destroy/create the watchers in the prepare watcher.
1848		2547
1849	static void	2548	static void
1850	timer_cb (EV_P_ ev_timer *w, int revents)	2549	timer_cb (EV_P_ ev_timer *w, int revents)
1851	{	2550	{
1852	adns_state ads = (adns_state)w->data;	2551	adns_state ads = (adns_state)w->data;
1853	update_now (EV_A);	2552	update_now (EV_A);
1854		2553
1855	adns_processtimeouts (ads, &tv_now);	2554	adns_processtimeouts (ads, &tv_now);
1856	}	2555	}
1857		2556
1858	static void	2557	static void
1859	io_cb (EV_P_ ev_io *w, int revents)	2558	io_cb (EV_P_ ev_io *w, int revents)
1860	{	2559	{
1861	adns_state ads = (adns_state)w->data;	2560	adns_state ads = (adns_state)w->data;
1862	update_now (EV_A);	2561	update_now (EV_A);
1863		2562
1864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2563	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2564	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1866	}	2565	}
1867		2566
1868	// do not ever call adns_afterpoll	2567	// do not ever call adns_afterpoll
1869		2568
1870	Method 4: Do not use a prepare or check watcher because the module you	2569	Method 4: Do not use a prepare or check watcher because the module you
1871	want to embed is too inflexible to support it. Instead, youc na override	2570	want to embed is not flexible enough to support it. Instead, you can
1872	their poll function. The drawback with this solution is that the main	2571	override their poll function. The drawback with this solution is that the
1873	loop is now no longer controllable by EV. The C<Glib::EV> module does	2572	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1874	this.	2573	this approach, effectively embedding EV as a client into the horrible
		2574	libglib event loop.
1875		2575
1876	static gint	2576	static gint
1877	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2577	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1878	{	2578	{
1879	int got_events = 0;	2579	int got_events = 0;
1880		2580
1881	for (n = 0; n < nfds; ++n)	2581	for (n = 0; n < nfds; ++n)
1882	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2582	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1883		2583
1884	if (timeout >= 0)	2584	if (timeout >= 0)
1885	// create/start timer	2585	// create/start timer
1886		2586
1887	// poll	2587	// poll
1888	ev_loop (EV_A_ 0);	2588	ev_loop (EV_A_ 0);
1889		2589
1890	// stop timer again	2590	// stop timer again
1891	if (timeout >= 0)	2591	if (timeout >= 0)
1892	ev_timer_stop (EV_A_ &to);	2592	ev_timer_stop (EV_A_ &to);
1893		2593
1894	// stop io watchers again - their callbacks should have set	2594	// stop io watchers again - their callbacks should have set
1895	for (n = 0; n < nfds; ++n)	2595	for (n = 0; n < nfds; ++n)
1896	ev_io_stop (EV_A_ iow [n]);	2596	ev_io_stop (EV_A_ iow [n]);
1897		2597
1898	return got_events;	2598	return got_events;
1899	}	2599	}
1900		2600
1901		2601
1902	=head2 C<ev_embed> - when one backend isn't enough...	2602	=head2 C<ev_embed> - when one backend isn't enough...
1903		2603
1904	This is a rather advanced watcher type that lets you embed one event loop	2604	This is a rather advanced watcher type that lets you embed one event loop
…		…
1910	prioritise I/O.	2610	prioritise I/O.
1911		2611
1912	As an example for a bug workaround, the kqueue backend might only support	2612	As an example for a bug workaround, the kqueue backend might only support
1913	sockets on some platform, so it is unusable as generic backend, but you	2613	sockets on some platform, so it is unusable as generic backend, but you
1914	still want to make use of it because you have many sockets and it scales	2614	still want to make use of it because you have many sockets and it scales
1915	so nicely. In this case, you would create a kqueue-based loop and embed it	2615	so nicely. In this case, you would create a kqueue-based loop and embed
1916	into your default loop (which might use e.g. poll). Overall operation will	2616	it into your default loop (which might use e.g. poll). Overall operation
1917	be a bit slower because first libev has to poll and then call kevent, but	2617	will be a bit slower because first libev has to call C<poll> and then
1918	at least you can use both at what they are best.	2618	C<kevent>, but at least you can use both mechanisms for what they are
		2619	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1919		2620
1920	As for prioritising I/O: rarely you have the case where some fds have	2621	As for prioritising I/O: under rare circumstances you have the case where
1921	to be watched and handled very quickly (with low latency), and even	2622	some fds have to be watched and handled very quickly (with low latency),
1922	priorities and idle watchers might have too much overhead. In this case	2623	and even priorities and idle watchers might have too much overhead. In
1923	you would put all the high priority stuff in one loop and all the rest in	2624	this case you would put all the high priority stuff in one loop and all
1924	a second one, and embed the second one in the first.	2625	the rest in a second one, and embed the second one in the first.
1925		2626
1926	As long as the watcher is active, the callback will be invoked every time	2627	As long as the watcher is active, the callback will be invoked every
1927	there might be events pending in the embedded loop. The callback must then	2628	time there might be events pending in the embedded loop. The callback
1928	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2629	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1929	their callbacks (you could also start an idle watcher to give the embedded	2630	sweep and invoke their callbacks (the callback doesn't need to invoke the
1930	loop strictly lower priority for example). You can also set the callback	2631	C<ev_embed_sweep> function directly, it could also start an idle watcher
1931	to C<0>, in which case the embed watcher will automatically execute the	2632	to give the embedded loop strictly lower priority for example).
1932	embedded loop sweep.
1933		2633
1934	As long as the watcher is started it will automatically handle events. The	2634	You can also set the callback to C<0>, in which case the embed watcher
1935	callback will be invoked whenever some events have been handled. You can	2635	will automatically execute the embedded loop sweep whenever necessary.
1936	set the callback to C<0> to avoid having to specify one if you are not
1937	interested in that.
1938		2636
1939	Also, there have not currently been made special provisions for forking:	2637	Fork detection will be handled transparently while the C<ev_embed> watcher
1940	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2638	is active, i.e., the embedded loop will automatically be forked when the
1941	but you will also have to stop and restart any C<ev_embed> watchers	2639	embedding loop forks. In other cases, the user is responsible for calling
1942	yourself.	2640	C<ev_loop_fork> on the embedded loop.
1943		2641
1944	Unfortunately, not all backends are embeddable, only the ones returned by	2642	Unfortunately, not all backends are embeddable: only the ones returned by
1945	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2643	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1946	portable one.	2644	portable one.
1947		2645
1948	So when you want to use this feature you will always have to be prepared	2646	So when you want to use this feature you will always have to be prepared
1949	that you cannot get an embeddable loop. The recommended way to get around	2647	that you cannot get an embeddable loop. The recommended way to get around
1950	this is to have a separate variables for your embeddable loop, try to	2648	this is to have a separate variables for your embeddable loop, try to
1951	create it, and if that fails, use the normal loop for everything.	2649	create it, and if that fails, use the normal loop for everything.
1952		2650
		2651	=head3 C<ev_embed> and fork
		2652
		2653	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2654	automatically be applied to the embedded loop as well, so no special
		2655	fork handling is required in that case. When the watcher is not running,
		2656	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2657	as applicable.
		2658
1953	=head3 Watcher-Specific Functions and Data Members	2659	=head3 Watcher-Specific Functions and Data Members
1954		2660
1955	=over 4	2661	=over 4
1956		2662
1957	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2663	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1960		2666
1961	Configures the watcher to embed the given loop, which must be	2667	Configures the watcher to embed the given loop, which must be
1962	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2668	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1963	invoked automatically, otherwise it is the responsibility of the callback	2669	invoked automatically, otherwise it is the responsibility of the callback
1964	to invoke it (it will continue to be called until the sweep has been done,	2670	to invoke it (it will continue to be called until the sweep has been done,
1965	if you do not want thta, you need to temporarily stop the embed watcher).	2671	if you do not want that, you need to temporarily stop the embed watcher).
1966		2672
1967	=item ev_embed_sweep (loop, ev_embed *)	2673	=item ev_embed_sweep (loop, ev_embed *)
1968		2674
1969	Make a single, non-blocking sweep over the embedded loop. This works	2675	Make a single, non-blocking sweep over the embedded loop. This works
1970	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2676	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1971	apropriate way for embedded loops.	2677	appropriate way for embedded loops.
1972		2678
1973	=item struct ev_loop *other [read-only]	2679	=item struct ev_loop *other [read-only]
1974		2680
1975	The embedded event loop.	2681	The embedded event loop.
1976		2682
…		…
1978		2684
1979	=head3 Examples	2685	=head3 Examples
1980		2686
1981	Example: Try to get an embeddable event loop and embed it into the default	2687	Example: Try to get an embeddable event loop and embed it into the default
1982	event loop. If that is not possible, use the default loop. The default	2688	event loop. If that is not possible, use the default loop. The default
1983	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2689	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1984	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2690	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1985	used).	2691	used).
1986		2692
1987	struct ev_loop *loop_hi = ev_default_init (0);	2693	struct ev_loop *loop_hi = ev_default_init (0);
1988	struct ev_loop *loop_lo = 0;	2694	struct ev_loop *loop_lo = 0;
1989	struct ev_embed embed;	2695	ev_embed embed;
1990		2696
1991	// see if there is a chance of getting one that works	2697	// see if there is a chance of getting one that works
1992	// (remember that a flags value of 0 means autodetection)	2698	// (remember that a flags value of 0 means autodetection)
1993	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2699	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1994	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2700	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1995	: 0;	2701	: 0;
1996		2702
1997	// if we got one, then embed it, otherwise default to loop_hi	2703	// if we got one, then embed it, otherwise default to loop_hi
1998	if (loop_lo)	2704	if (loop_lo)
1999	{	2705	{
2000	ev_embed_init (&embed, 0, loop_lo);	2706	ev_embed_init (&embed, 0, loop_lo);
2001	ev_embed_start (loop_hi, &embed);	2707	ev_embed_start (loop_hi, &embed);
2002	}	2708	}
2003	else	2709	else
2004	loop_lo = loop_hi;	2710	loop_lo = loop_hi;
2005		2711
2006	Example: Check if kqueue is available but not recommended and create	2712	Example: Check if kqueue is available but not recommended and create
2007	a kqueue backend for use with sockets (which usually work with any	2713	a kqueue backend for use with sockets (which usually work with any
2008	kqueue implementation). Store the kqueue/socket-only event loop in	2714	kqueue implementation). Store the kqueue/socket-only event loop in
2009	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2715	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2010		2716
2011	struct ev_loop *loop = ev_default_init (0);	2717	struct ev_loop *loop = ev_default_init (0);
2012	struct ev_loop *loop_socket = 0;	2718	struct ev_loop *loop_socket = 0;
2013	struct ev_embed embed;	2719	ev_embed embed;
2014		2720
2015	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2721	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2016	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2722	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2017	{	2723	{
2018	ev_embed_init (&embed, 0, loop_socket);	2724	ev_embed_init (&embed, 0, loop_socket);
2019	ev_embed_start (loop, &embed);	2725	ev_embed_start (loop, &embed);
2020	}	2726	}
2021		2727
2022	if (!loop_socket)	2728	if (!loop_socket)
2023	loop_socket = loop;	2729	loop_socket = loop;
2024		2730
2025	// now use loop_socket for all sockets, and loop for everything else	2731	// now use loop_socket for all sockets, and loop for everything else
2026		2732
2027		2733
2028	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2734	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2029		2735
2030	Fork watchers are called when a C<fork ()> was detected (usually because	2736	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2033	event loop blocks next and before C<ev_check> watchers are being called,	2739	event loop blocks next and before C<ev_check> watchers are being called,
2034	and only in the child after the fork. If whoever good citizen calling	2740	and only in the child after the fork. If whoever good citizen calling
2035	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2741	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2036	handlers will be invoked, too, of course.	2742	handlers will be invoked, too, of course.
2037		2743
		2744	=head3 The special problem of life after fork - how is it possible?
		2745
		2746	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2747	up/change the process environment, followed by a call to C<exec()>. This
		2748	sequence should be handled by libev without any problems.
		2749
		2750	This changes when the application actually wants to do event handling
		2751	in the child, or both parent in child, in effect "continuing" after the
		2752	fork.
		2753
		2754	The default mode of operation (for libev, with application help to detect
		2755	forks) is to duplicate all the state in the child, as would be expected
		2756	when I<either> the parent I<or> the child process continues.
		2757
		2758	When both processes want to continue using libev, then this is usually the
		2759	wrong result. In that case, usually one process (typically the parent) is
		2760	supposed to continue with all watchers in place as before, while the other
		2761	process typically wants to start fresh, i.e. without any active watchers.
		2762
		2763	The cleanest and most efficient way to achieve that with libev is to
		2764	simply create a new event loop, which of course will be "empty", and
		2765	use that for new watchers. This has the advantage of not touching more
		2766	memory than necessary, and thus avoiding the copy-on-write, and the
		2767	disadvantage of having to use multiple event loops (which do not support
		2768	signal watchers).
		2769
		2770	When this is not possible, or you want to use the default loop for
		2771	other reasons, then in the process that wants to start "fresh", call
		2772	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2773	the default loop will "orphan" (not stop) all registered watchers, so you
		2774	have to be careful not to execute code that modifies those watchers. Note
		2775	also that in that case, you have to re-register any signal watchers.
		2776
2038	=head3 Watcher-Specific Functions and Data Members	2777	=head3 Watcher-Specific Functions and Data Members
2039		2778
2040	=over 4	2779	=over 4
2041		2780
2042	=item ev_fork_init (ev_signal *, callback)	2781	=item ev_fork_init (ev_signal *, callback)
…		…
2046	believe me.	2785	believe me.
2047		2786
2048	=back	2787	=back
2049		2788
2050		2789
		2790	=head2 C<ev_async> - how to wake up another event loop
		2791
		2792	In general, you cannot use an C<ev_loop> from multiple threads or other
		2793	asynchronous sources such as signal handlers (as opposed to multiple event
		2794	loops - those are of course safe to use in different threads).
		2795
		2796	Sometimes, however, you need to wake up another event loop you do not
		2797	control, for example because it belongs to another thread. This is what
		2798	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2799	can signal it by calling C<ev_async_send>, which is thread- and signal
		2800	safe.
		2801
		2802	This functionality is very similar to C<ev_signal> watchers, as signals,
		2803	too, are asynchronous in nature, and signals, too, will be compressed
		2804	(i.e. the number of callback invocations may be less than the number of
		2805	C<ev_async_sent> calls).
		2806
		2807	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2808	just the default loop.
		2809
		2810	=head3 Queueing
		2811
		2812	C<ev_async> does not support queueing of data in any way. The reason
		2813	is that the author does not know of a simple (or any) algorithm for a
		2814	multiple-writer-single-reader queue that works in all cases and doesn't
		2815	need elaborate support such as pthreads.
		2816
		2817	That means that if you want to queue data, you have to provide your own
		2818	queue. But at least I can tell you how to implement locking around your
		2819	queue:
		2820
		2821	=over 4
		2822
		2823	=item queueing from a signal handler context
		2824
		2825	To implement race-free queueing, you simply add to the queue in the signal
		2826	handler but you block the signal handler in the watcher callback. Here is
		2827	an example that does that for some fictitious SIGUSR1 handler:
		2828
		2829	static ev_async mysig;
		2830
		2831	static void
		2832	sigusr1_handler (void)
		2833	{
		2834	sometype data;
		2835
		2836	// no locking etc.
		2837	queue_put (data);
		2838	ev_async_send (EV_DEFAULT_ &mysig);
		2839	}
		2840
		2841	static void
		2842	mysig_cb (EV_P_ ev_async *w, int revents)
		2843	{
		2844	sometype data;
		2845	sigset_t block, prev;
		2846
		2847	sigemptyset (&block);
		2848	sigaddset (&block, SIGUSR1);
		2849	sigprocmask (SIG_BLOCK, &block, &prev);
		2850
		2851	while (queue_get (&data))
		2852	process (data);
		2853
		2854	if (sigismember (&prev, SIGUSR1)
		2855	sigprocmask (SIG_UNBLOCK, &block, 0);
		2856	}
		2857
		2858	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2859	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2860	either...).
		2861
		2862	=item queueing from a thread context
		2863
		2864	The strategy for threads is different, as you cannot (easily) block
		2865	threads but you can easily preempt them, so to queue safely you need to
		2866	employ a traditional mutex lock, such as in this pthread example:
		2867
		2868	static ev_async mysig;
		2869	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2870
		2871	static void
		2872	otherthread (void)
		2873	{
		2874	// only need to lock the actual queueing operation
		2875	pthread_mutex_lock (&mymutex);
		2876	queue_put (data);
		2877	pthread_mutex_unlock (&mymutex);
		2878
		2879	ev_async_send (EV_DEFAULT_ &mysig);
		2880	}
		2881
		2882	static void
		2883	mysig_cb (EV_P_ ev_async *w, int revents)
		2884	{
		2885	pthread_mutex_lock (&mymutex);
		2886
		2887	while (queue_get (&data))
		2888	process (data);
		2889
		2890	pthread_mutex_unlock (&mymutex);
		2891	}
		2892
		2893	=back
		2894
		2895
		2896	=head3 Watcher-Specific Functions and Data Members
		2897
		2898	=over 4
		2899
		2900	=item ev_async_init (ev_async *, callback)
		2901
		2902	Initialises and configures the async watcher - it has no parameters of any
		2903	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2904	trust me.
		2905
		2906	=item ev_async_send (loop, ev_async *)
		2907
		2908	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2909	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2910	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2911	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2912	section below on what exactly this means).
		2913
		2914	Note that, as with other watchers in libev, multiple events might get
		2915	compressed into a single callback invocation (another way to look at this
		2916	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2917	reset when the event loop detects that).
		2918
		2919	This call incurs the overhead of a system call only once per event loop
		2920	iteration, so while the overhead might be noticeable, it doesn't apply to
		2921	repeated calls to C<ev_async_send> for the same event loop.
		2922
		2923	=item bool = ev_async_pending (ev_async *)
		2924
		2925	Returns a non-zero value when C<ev_async_send> has been called on the
		2926	watcher but the event has not yet been processed (or even noted) by the
		2927	event loop.
		2928
		2929	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2930	the loop iterates next and checks for the watcher to have become active,
		2931	it will reset the flag again. C<ev_async_pending> can be used to very
		2932	quickly check whether invoking the loop might be a good idea.
		2933
		2934	Not that this does I<not> check whether the watcher itself is pending,
		2935	only whether it has been requested to make this watcher pending: there
		2936	is a time window between the event loop checking and resetting the async
		2937	notification, and the callback being invoked.
		2938
		2939	=back
		2940
		2941
2051	=head1 OTHER FUNCTIONS	2942	=head1 OTHER FUNCTIONS
2052		2943
2053	There are some other functions of possible interest. Described. Here. Now.	2944	There are some other functions of possible interest. Described. Here. Now.
2054		2945
2055	=over 4	2946	=over 4
2056		2947
2057	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2948	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2058		2949
2059	This function combines a simple timer and an I/O watcher, calls your	2950	This function combines a simple timer and an I/O watcher, calls your
2060	callback on whichever event happens first and automatically stop both	2951	callback on whichever event happens first and automatically stops both
2061	watchers. This is useful if you want to wait for a single event on an fd	2952	watchers. This is useful if you want to wait for a single event on an fd
2062	or timeout without having to allocate/configure/start/stop/free one or	2953	or timeout without having to allocate/configure/start/stop/free one or
2063	more watchers yourself.	2954	more watchers yourself.
2064		2955
2065	If C<fd> is less than 0, then no I/O watcher will be started and events	2956	If C<fd> is less than 0, then no I/O watcher will be started and the
2066	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2957	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2067	C<events> set will be craeted and started.	2958	the given C<fd> and C<events> set will be created and started.
2068		2959
2069	If C<timeout> is less than 0, then no timeout watcher will be	2960	If C<timeout> is less than 0, then no timeout watcher will be
2070	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2961	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2071	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2962	repeat = 0) will be started. C<0> is a valid timeout.
2072	dubious value.
2073		2963
2074	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2964	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2075	passed an C<revents> set like normal event callbacks (a combination of	2965	passed an C<revents> set like normal event callbacks (a combination of
2076	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2966	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2077	value passed to C<ev_once>:	2967	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2968	a timeout and an io event at the same time - you probably should give io
		2969	events precedence.
2078		2970
		2971	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2972
2079	static void stdin_ready (int revents, void *arg)	2973	static void stdin_ready (int revents, void *arg)
2080	{	2974	{
2081	if (revents & EV_TIMEOUT)
2082	/* doh, nothing entered */;
2083	else if (revents & EV_READ)	2975	if (revents & EV_READ)
2084	/* stdin might have data for us, joy! */;	2976	/* stdin might have data for us, joy! */;
		2977	else if (revents & EV_TIMEOUT)
		2978	/* doh, nothing entered */;
2085	}	2979	}
2086		2980
2087	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2981	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2088		2982
2089	=item ev_feed_event (ev_loop *, watcher *, int revents)	2983	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2090		2984
2091	Feeds the given event set into the event loop, as if the specified event	2985	Feeds the given event set into the event loop, as if the specified event
2092	had happened for the specified watcher (which must be a pointer to an	2986	had happened for the specified watcher (which must be a pointer to an
2093	initialised but not necessarily started event watcher).	2987	initialised but not necessarily started event watcher).
2094		2988
2095	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2989	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2096		2990
2097	Feed an event on the given fd, as if a file descriptor backend detected	2991	Feed an event on the given fd, as if a file descriptor backend detected
2098	the given events it.	2992	the given events it.
2099		2993
2100	=item ev_feed_signal_event (ev_loop *loop, int signum)	2994	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2101		2995
2102	Feed an event as if the given signal occured (C<loop> must be the default	2996	Feed an event as if the given signal occurred (C<loop> must be the default
2103	loop!).	2997	loop!).
2104		2998
2105	=back	2999	=back
2106		3000
2107		3001
…		…
2123		3017
2124	=item * Priorities are not currently supported. Initialising priorities	3018	=item * Priorities are not currently supported. Initialising priorities
2125	will fail and all watchers will have the same priority, even though there	3019	will fail and all watchers will have the same priority, even though there
2126	is an ev_pri field.	3020	is an ev_pri field.
2127		3021
		3022	=item * In libevent, the last base created gets the signals, in libev, the
		3023	first base created (== the default loop) gets the signals.
		3024
2128	=item * Other members are not supported.	3025	=item * Other members are not supported.
2129		3026
2130	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3027	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2131	to use the libev header file and library.	3028	to use the libev header file and library.
2132		3029
2133	=back	3030	=back
2134		3031
2135	=head1 C++ SUPPORT	3032	=head1 C++ SUPPORT
2136		3033
2137	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3034	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2138	you to use some convinience methods to start/stop watchers and also change	3035	you to use some convenience methods to start/stop watchers and also change
2139	the callback model to a model using method callbacks on objects.	3036	the callback model to a model using method callbacks on objects.
2140		3037
2141	To use it,	3038	To use it,
2142		3039
2143	#include <ev++.h>	3040	#include <ev++.h>
2144		3041
2145	This automatically includes F<ev.h> and puts all of its definitions (many	3042	This automatically includes F<ev.h> and puts all of its definitions (many
2146	of them macros) into the global namespace. All C++ specific things are	3043	of them macros) into the global namespace. All C++ specific things are
2147	put into the C<ev> namespace. It should support all the same embedding	3044	put into the C<ev> namespace. It should support all the same embedding
2148	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3045	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2215	your compiler is good :), then the method will be fully inlined into the	3112	your compiler is good :), then the method will be fully inlined into the
2216	thunking function, making it as fast as a direct C callback.	3113	thunking function, making it as fast as a direct C callback.
2217		3114
2218	Example: simple class declaration and watcher initialisation	3115	Example: simple class declaration and watcher initialisation
2219		3116
2220	struct myclass	3117	struct myclass
2221	{	3118	{
2222	void io_cb (ev::io &w, int revents) { }	3119	void io_cb (ev::io &w, int revents) { }
2223	}	3120	}
2224		3121
2225	myclass obj;	3122	myclass obj;
2226	ev::io iow;	3123	ev::io iow;
2227	iow.set <myclass, &myclass::io_cb> (&obj);	3124	iow.set <myclass, &myclass::io_cb> (&obj);
		3125
		3126	=item w->set (object *)
		3127
		3128	This is an B<experimental> feature that might go away in a future version.
		3129
		3130	This is a variation of a method callback - leaving out the method to call
		3131	will default the method to C<operator ()>, which makes it possible to use
		3132	functor objects without having to manually specify the C<operator ()> all
		3133	the time. Incidentally, you can then also leave out the template argument
		3134	list.
		3135
		3136	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3137	int revents)>.
		3138
		3139	See the method-C<set> above for more details.
		3140
		3141	Example: use a functor object as callback.
		3142
		3143	struct myfunctor
		3144	{
		3145	void operator() (ev::io &w, int revents)
		3146	{
		3147	...
		3148	}
		3149	}
		3150
		3151	myfunctor f;
		3152
		3153	ev::io w;
		3154	w.set (&f);
2228		3155
2229	=item w->set<function> (void *data = 0)	3156	=item w->set<function> (void *data = 0)
2230		3157
2231	Also sets a callback, but uses a static method or plain function as	3158	Also sets a callback, but uses a static method or plain function as
2232	callback. The optional C<data> argument will be stored in the watcher's	3159	callback. The optional C<data> argument will be stored in the watcher's
…		…
2234		3161
2235	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3162	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2236		3163
2237	See the method-C<set> above for more details.	3164	See the method-C<set> above for more details.
2238		3165
2239	Example:	3166	Example: Use a plain function as callback.
2240		3167
2241	static void io_cb (ev::io &w, int revents) { }	3168	static void io_cb (ev::io &w, int revents) { }
2242	iow.set <io_cb> ();	3169	iow.set <io_cb> ();
2243		3170
2244	=item w->set (struct ev_loop *)	3171	=item w->set (struct ev_loop *)
2245		3172
2246	Associates a different C<struct ev_loop> with this watcher. You can only	3173	Associates a different C<struct ev_loop> with this watcher. You can only
2247	do this when the watcher is inactive (and not pending either).	3174	do this when the watcher is inactive (and not pending either).
2248		3175
2249	=item w->set ([args])	3176	=item w->set ([arguments])
2250		3177
2251	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3178	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2252	called at least once. Unlike the C counterpart, an active watcher gets	3179	called at least once. Unlike the C counterpart, an active watcher gets
2253	automatically stopped and restarted when reconfiguring it with this	3180	automatically stopped and restarted when reconfiguring it with this
2254	method.	3181	method.
2255		3182
2256	=item w->start ()	3183	=item w->start ()
…		…
2280	=back	3207	=back
2281		3208
2282	Example: Define a class with an IO and idle watcher, start one of them in	3209	Example: Define a class with an IO and idle watcher, start one of them in
2283	the constructor.	3210	the constructor.
2284		3211
2285	class myclass	3212	class myclass
2286	{	3213	{
2287	ev::io io; void io_cb (ev::io &w, int revents);	3214	ev::io io ; void io_cb (ev::io &w, int revents);
2288	ev:idle idle void idle_cb (ev::idle &w, int revents);	3215	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2289		3216
2290	myclass (int fd)	3217	myclass (int fd)
2291	{	3218	{
2292	io .set <myclass, &myclass::io_cb > (this);	3219	io .set <myclass, &myclass::io_cb > (this);
2293	idle.set <myclass, &myclass::idle_cb> (this);	3220	idle.set <myclass, &myclass::idle_cb> (this);
2294		3221
2295	io.start (fd, ev::READ);	3222	io.start (fd, ev::READ);
2296	}	3223	}
2297	};	3224	};
		3225
		3226
		3227	=head1 OTHER LANGUAGE BINDINGS
		3228
		3229	Libev does not offer other language bindings itself, but bindings for a
		3230	number of languages exist in the form of third-party packages. If you know
		3231	any interesting language binding in addition to the ones listed here, drop
		3232	me a note.
		3233
		3234	=over 4
		3235
		3236	=item Perl
		3237
		3238	The EV module implements the full libev API and is actually used to test
		3239	libev. EV is developed together with libev. Apart from the EV core module,
		3240	there are additional modules that implement libev-compatible interfaces
		3241	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3242	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3243	and C<EV::Glib>).
		3244
		3245	It can be found and installed via CPAN, its homepage is at
		3246	L<http://software.schmorp.de/pkg/EV>.
		3247
		3248	=item Python
		3249
		3250	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3251	seems to be quite complete and well-documented.
		3252
		3253	=item Ruby
		3254
		3255	Tony Arcieri has written a ruby extension that offers access to a subset
		3256	of the libev API and adds file handle abstractions, asynchronous DNS and
		3257	more on top of it. It can be found via gem servers. Its homepage is at
		3258	L<http://rev.rubyforge.org/>.
		3259
		3260	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3261	makes rev work even on mingw.
		3262
		3263	=item Haskell
		3264
		3265	A haskell binding to libev is available at
		3266	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3267
		3268	=item D
		3269
		3270	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3271	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3272
		3273	=item Ocaml
		3274
		3275	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3276	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3277
		3278	=back
2298		3279
2299		3280
2300	=head1 MACRO MAGIC	3281	=head1 MACRO MAGIC
2301		3282
2302	Libev can be compiled with a variety of options, the most fundamantal	3283	Libev can be compiled with a variety of options, the most fundamental
2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3284	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2304	functions and callbacks have an initial C<struct ev_loop *> argument.	3285	functions and callbacks have an initial C<struct ev_loop *> argument.
2305		3286
2306	To make it easier to write programs that cope with either variant, the	3287	To make it easier to write programs that cope with either variant, the
2307	following macros are defined:	3288	following macros are defined:
…		…
2312		3293
2313	This provides the loop I<argument> for functions, if one is required ("ev	3294	This provides the loop I<argument> for functions, if one is required ("ev
2314	loop argument"). The C<EV_A> form is used when this is the sole argument,	3295	loop argument"). The C<EV_A> form is used when this is the sole argument,
2315	C<EV_A_> is used when other arguments are following. Example:	3296	C<EV_A_> is used when other arguments are following. Example:
2316		3297
2317	ev_unref (EV_A);	3298	ev_unref (EV_A);
2318	ev_timer_add (EV_A_ watcher);	3299	ev_timer_add (EV_A_ watcher);
2319	ev_loop (EV_A_ 0);	3300	ev_loop (EV_A_ 0);
2320		3301
2321	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3302	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2322	which is often provided by the following macro.	3303	which is often provided by the following macro.
2323		3304
2324	=item C<EV_P>, C<EV_P_>	3305	=item C<EV_P>, C<EV_P_>
2325		3306
2326	This provides the loop I<parameter> for functions, if one is required ("ev	3307	This provides the loop I<parameter> for functions, if one is required ("ev
2327	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3308	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2328	C<EV_P_> is used when other parameters are following. Example:	3309	C<EV_P_> is used when other parameters are following. Example:
2329		3310
2330	// this is how ev_unref is being declared	3311	// this is how ev_unref is being declared
2331	static void ev_unref (EV_P);	3312	static void ev_unref (EV_P);
2332		3313
2333	// this is how you can declare your typical callback	3314	// this is how you can declare your typical callback
2334	static void cb (EV_P_ ev_timer *w, int revents)	3315	static void cb (EV_P_ ev_timer *w, int revents)
2335		3316
2336	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3317	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2337	suitable for use with C<EV_A>.	3318	suitable for use with C<EV_A>.
2338		3319
2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3320	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2340		3321
2341	Similar to the other two macros, this gives you the value of the default	3322	Similar to the other two macros, this gives you the value of the default
2342	loop, if multiple loops are supported ("ev loop default").	3323	loop, if multiple loops are supported ("ev loop default").
		3324
		3325	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3326
		3327	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3328	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3329	is undefined when the default loop has not been initialised by a previous
		3330	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3331
		3332	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3333	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2343		3334
2344	=back	3335	=back
2345		3336
2346	Example: Declare and initialise a check watcher, utilising the above	3337	Example: Declare and initialise a check watcher, utilising the above
2347	macros so it will work regardless of whether multiple loops are supported	3338	macros so it will work regardless of whether multiple loops are supported
2348	or not.	3339	or not.
2349		3340
2350	static void	3341	static void
2351	check_cb (EV_P_ ev_timer *w, int revents)	3342	check_cb (EV_P_ ev_timer *w, int revents)
2352	{	3343	{
2353	ev_check_stop (EV_A_ w);	3344	ev_check_stop (EV_A_ w);
2354	}	3345	}
2355		3346
2356	ev_check check;	3347	ev_check check;
2357	ev_check_init (&check, check_cb);	3348	ev_check_init (&check, check_cb);
2358	ev_check_start (EV_DEFAULT_ &check);	3349	ev_check_start (EV_DEFAULT_ &check);
2359	ev_loop (EV_DEFAULT_ 0);	3350	ev_loop (EV_DEFAULT_ 0);
2360		3351
2361	=head1 EMBEDDING	3352	=head1 EMBEDDING
2362		3353
2363	Libev can (and often is) directly embedded into host	3354	Libev can (and often is) directly embedded into host
2364	applications. Examples of applications that embed it include the Deliantra	3355	applications. Examples of applications that embed it include the Deliantra
…		…
2371	libev somewhere in your source tree).	3362	libev somewhere in your source tree).
2372		3363
2373	=head2 FILESETS	3364	=head2 FILESETS
2374		3365
2375	Depending on what features you need you need to include one or more sets of files	3366	Depending on what features you need you need to include one or more sets of files
2376	in your app.	3367	in your application.
2377		3368
2378	=head3 CORE EVENT LOOP	3369	=head3 CORE EVENT LOOP
2379		3370
2380	To include only the libev core (all the C<ev_*> functions), with manual	3371	To include only the libev core (all the C<ev_*> functions), with manual
2381	configuration (no autoconf):	3372	configuration (no autoconf):
2382		3373
2383	#define EV_STANDALONE 1	3374	#define EV_STANDALONE 1
2384	#include "ev.c"	3375	#include "ev.c"
2385		3376
2386	This will automatically include F<ev.h>, too, and should be done in a	3377	This will automatically include F<ev.h>, too, and should be done in a
2387	single C source file only to provide the function implementations. To use	3378	single C source file only to provide the function implementations. To use
2388	it, do the same for F<ev.h> in all files wishing to use this API (best	3379	it, do the same for F<ev.h> in all files wishing to use this API (best
2389	done by writing a wrapper around F<ev.h> that you can include instead and	3380	done by writing a wrapper around F<ev.h> that you can include instead and
2390	where you can put other configuration options):	3381	where you can put other configuration options):
2391		3382
2392	#define EV_STANDALONE 1	3383	#define EV_STANDALONE 1
2393	#include "ev.h"	3384	#include "ev.h"
2394		3385
2395	Both header files and implementation files can be compiled with a C++	3386	Both header files and implementation files can be compiled with a C++
2396	compiler (at least, thats a stated goal, and breakage will be treated	3387	compiler (at least, that's a stated goal, and breakage will be treated
2397	as a bug).	3388	as a bug).
2398		3389
2399	You need the following files in your source tree, or in a directory	3390	You need the following files in your source tree, or in a directory
2400	in your include path (e.g. in libev/ when using -Ilibev):	3391	in your include path (e.g. in libev/ when using -Ilibev):
2401		3392
2402	ev.h	3393	ev.h
2403	ev.c	3394	ev.c
2404	ev_vars.h	3395	ev_vars.h
2405	ev_wrap.h	3396	ev_wrap.h
2406		3397
2407	ev_win32.c required on win32 platforms only	3398	ev_win32.c required on win32 platforms only
2408		3399
2409	ev_select.c only when select backend is enabled (which is enabled by default)	3400	ev_select.c only when select backend is enabled (which is enabled by default)
2410	ev_poll.c only when poll backend is enabled (disabled by default)	3401	ev_poll.c only when poll backend is enabled (disabled by default)
2411	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3402	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2412	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3403	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2413	ev_port.c only when the solaris port backend is enabled (disabled by default)	3404	ev_port.c only when the solaris port backend is enabled (disabled by default)
2414		3405
2415	F<ev.c> includes the backend files directly when enabled, so you only need	3406	F<ev.c> includes the backend files directly when enabled, so you only need
2416	to compile this single file.	3407	to compile this single file.
2417		3408
2418	=head3 LIBEVENT COMPATIBILITY API	3409	=head3 LIBEVENT COMPATIBILITY API
2419		3410
2420	To include the libevent compatibility API, also include:	3411	To include the libevent compatibility API, also include:
2421		3412
2422	#include "event.c"	3413	#include "event.c"
2423		3414
2424	in the file including F<ev.c>, and:	3415	in the file including F<ev.c>, and:
2425		3416
2426	#include "event.h"	3417	#include "event.h"
2427		3418
2428	in the files that want to use the libevent API. This also includes F<ev.h>.	3419	in the files that want to use the libevent API. This also includes F<ev.h>.
2429		3420
2430	You need the following additional files for this:	3421	You need the following additional files for this:
2431		3422
2432	event.h	3423	event.h
2433	event.c	3424	event.c
2434		3425
2435	=head3 AUTOCONF SUPPORT	3426	=head3 AUTOCONF SUPPORT
2436		3427
2437	Instead of using C<EV_STANDALONE=1> and providing your config in	3428	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2438	whatever way you want, you can also C<m4_include([libev.m4])> in your	3429	whatever way you want, you can also C<m4_include([libev.m4])> in your
2439	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3430	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2440	include F<config.h> and configure itself accordingly.	3431	include F<config.h> and configure itself accordingly.
2441		3432
2442	For this of course you need the m4 file:	3433	For this of course you need the m4 file:
2443		3434
2444	libev.m4	3435	libev.m4
2445		3436
2446	=head2 PREPROCESSOR SYMBOLS/MACROS	3437	=head2 PREPROCESSOR SYMBOLS/MACROS
2447		3438
2448	Libev can be configured via a variety of preprocessor symbols you have to define	3439	Libev can be configured via a variety of preprocessor symbols you have to
2449	before including any of its files. The default is not to build for multiplicity	3440	define before including any of its files. The default in the absence of
2450	and only include the select backend.	3441	autoconf is documented for every option.
2451		3442
2452	=over 4	3443	=over 4
2453		3444
2454	=item EV_STANDALONE	3445	=item EV_STANDALONE
2455		3446
…		…
2457	keeps libev from including F<config.h>, and it also defines dummy	3448	keeps libev from including F<config.h>, and it also defines dummy
2458	implementations for some libevent functions (such as logging, which is not	3449	implementations for some libevent functions (such as logging, which is not
2459	supported). It will also not define any of the structs usually found in	3450	supported). It will also not define any of the structs usually found in
2460	F<event.h> that are not directly supported by the libev core alone.	3451	F<event.h> that are not directly supported by the libev core alone.
2461		3452
		3453	In stanbdalone mode, libev will still try to automatically deduce the
		3454	configuration, but has to be more conservative.
		3455
2462	=item EV_USE_MONOTONIC	3456	=item EV_USE_MONOTONIC
2463		3457
2464	If defined to be C<1>, libev will try to detect the availability of the	3458	If defined to be C<1>, libev will try to detect the availability of the
2465	monotonic clock option at both compiletime and runtime. Otherwise no use	3459	monotonic clock option at both compile time and runtime. Otherwise no
2466	of the monotonic clock option will be attempted. If you enable this, you	3460	use of the monotonic clock option will be attempted. If you enable this,
2467	usually have to link against librt or something similar. Enabling it when	3461	you usually have to link against librt or something similar. Enabling it
2468	the functionality isn't available is safe, though, although you have	3462	when the functionality isn't available is safe, though, although you have
2469	to make sure you link against any libraries where the C<clock_gettime>	3463	to make sure you link against any libraries where the C<clock_gettime>
2470	function is hiding in (often F<-lrt>).	3464	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2471		3465
2472	=item EV_USE_REALTIME	3466	=item EV_USE_REALTIME
2473		3467
2474	If defined to be C<1>, libev will try to detect the availability of the	3468	If defined to be C<1>, libev will try to detect the availability of the
2475	realtime clock option at compiletime (and assume its availability at	3469	real-time clock option at compile time (and assume its availability
2476	runtime if successful). Otherwise no use of the realtime clock option will	3470	at runtime if successful). Otherwise no use of the real-time clock
2477	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3471	option will be attempted. This effectively replaces C<gettimeofday>
2478	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3472	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2479	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3473	correctness. See the note about libraries in the description of
		3474	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3475	C<EV_USE_CLOCK_SYSCALL>.
		3476
		3477	=item EV_USE_CLOCK_SYSCALL
		3478
		3479	If defined to be C<1>, libev will try to use a direct syscall instead
		3480	of calling the system-provided C<clock_gettime> function. This option
		3481	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3482	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3483	programs needlessly. Using a direct syscall is slightly slower (in
		3484	theory), because no optimised vdso implementation can be used, but avoids
		3485	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3486	higher, as it simplifies linking (no need for C<-lrt>).
2480		3487
2481	=item EV_USE_NANOSLEEP	3488	=item EV_USE_NANOSLEEP
2482		3489
2483	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3490	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2484	and will use it for delays. Otherwise it will use C<select ()>.	3491	and will use it for delays. Otherwise it will use C<select ()>.
2485		3492
		3493	=item EV_USE_EVENTFD
		3494
		3495	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3496	available and will probe for kernel support at runtime. This will improve
		3497	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3498	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3499	2.7 or newer, otherwise disabled.
		3500
2486	=item EV_USE_SELECT	3501	=item EV_USE_SELECT
2487		3502
2488	If undefined or defined to be C<1>, libev will compile in support for the	3503	If undefined or defined to be C<1>, libev will compile in support for the
2489	C<select>(2) backend. No attempt at autodetection will be done: if no	3504	C<select>(2) backend. No attempt at auto-detection will be done: if no
2490	other method takes over, select will be it. Otherwise the select backend	3505	other method takes over, select will be it. Otherwise the select backend
2491	will not be compiled in.	3506	will not be compiled in.
2492		3507
2493	=item EV_SELECT_USE_FD_SET	3508	=item EV_SELECT_USE_FD_SET
2494		3509
2495	If defined to C<1>, then the select backend will use the system C<fd_set>	3510	If defined to C<1>, then the select backend will use the system C<fd_set>
2496	structure. This is useful if libev doesn't compile due to a missing	3511	structure. This is useful if libev doesn't compile due to a missing
2497	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3512	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2498	exotic systems. This usually limits the range of file descriptors to some	3513	on exotic systems. This usually limits the range of file descriptors to
2499	low limit such as 1024 or might have other limitations (winsocket only	3514	some low limit such as 1024 or might have other limitations (winsocket
2500	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3515	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2501	influence the size of the C<fd_set> used.	3516	configures the maximum size of the C<fd_set>.
2502		3517
2503	=item EV_SELECT_IS_WINSOCKET	3518	=item EV_SELECT_IS_WINSOCKET
2504		3519
2505	When defined to C<1>, the select backend will assume that	3520	When defined to C<1>, the select backend will assume that
2506	select/socket/connect etc. don't understand file descriptors but	3521	select/socket/connect etc. don't understand file descriptors but
…		…
2526		3541
2527	=item EV_USE_EPOLL	3542	=item EV_USE_EPOLL
2528		3543
2529	If defined to be C<1>, libev will compile in support for the Linux	3544	If defined to be C<1>, libev will compile in support for the Linux
2530	C<epoll>(7) backend. Its availability will be detected at runtime,	3545	C<epoll>(7) backend. Its availability will be detected at runtime,
2531	otherwise another method will be used as fallback. This is the	3546	otherwise another method will be used as fallback. This is the preferred
2532	preferred backend for GNU/Linux systems.	3547	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3548	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2533		3549
2534	=item EV_USE_KQUEUE	3550	=item EV_USE_KQUEUE
2535		3551
2536	If defined to be C<1>, libev will compile in support for the BSD style	3552	If defined to be C<1>, libev will compile in support for the BSD style
2537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3553	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2550	otherwise another method will be used as fallback. This is the preferred	3566	otherwise another method will be used as fallback. This is the preferred
2551	backend for Solaris 10 systems.	3567	backend for Solaris 10 systems.
2552		3568
2553	=item EV_USE_DEVPOLL	3569	=item EV_USE_DEVPOLL
2554		3570
2555	reserved for future expansion, works like the USE symbols above.	3571	Reserved for future expansion, works like the USE symbols above.
2556		3572
2557	=item EV_USE_INOTIFY	3573	=item EV_USE_INOTIFY
2558		3574
2559	If defined to be C<1>, libev will compile in support for the Linux inotify	3575	If defined to be C<1>, libev will compile in support for the Linux inotify
2560	interface to speed up C<ev_stat> watchers. Its actual availability will	3576	interface to speed up C<ev_stat> watchers. Its actual availability will
2561	be detected at runtime.	3577	be detected at runtime. If undefined, it will be enabled if the headers
		3578	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3579
		3580	=item EV_ATOMIC_T
		3581
		3582	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3583	access is atomic with respect to other threads or signal contexts. No such
		3584	type is easily found in the C language, so you can provide your own type
		3585	that you know is safe for your purposes. It is used both for signal handler "locking"
		3586	as well as for signal and thread safety in C<ev_async> watchers.
		3587
		3588	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3589	(from F<signal.h>), which is usually good enough on most platforms.
2562		3590
2563	=item EV_H	3591	=item EV_H
2564		3592
2565	The name of the F<ev.h> header file used to include it. The default if	3593	The name of the F<ev.h> header file used to include it. The default if
2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3594	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
2604	When doing priority-based operations, libev usually has to linearly search	3632	When doing priority-based operations, libev usually has to linearly search
2605	all the priorities, so having many of them (hundreds) uses a lot of space	3633	all the priorities, so having many of them (hundreds) uses a lot of space
2606	and time, so using the defaults of five priorities (-2 .. +2) is usually	3634	and time, so using the defaults of five priorities (-2 .. +2) is usually
2607	fine.	3635	fine.
2608		3636
2609	If your embedding app does not need any priorities, defining these both to	3637	If your embedding application does not need any priorities, defining these
2610	C<0> will save some memory and cpu.	3638	both to C<0> will save some memory and CPU.
2611		3639
2612	=item EV_PERIODIC_ENABLE	3640	=item EV_PERIODIC_ENABLE
2613		3641
2614	If undefined or defined to be C<1>, then periodic timers are supported. If	3642	If undefined or defined to be C<1>, then periodic timers are supported. If
2615	defined to be C<0>, then they are not. Disabling them saves a few kB of	3643	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2622	code.	3650	code.
2623		3651
2624	=item EV_EMBED_ENABLE	3652	=item EV_EMBED_ENABLE
2625		3653
2626	If undefined or defined to be C<1>, then embed watchers are supported. If	3654	If undefined or defined to be C<1>, then embed watchers are supported. If
2627	defined to be C<0>, then they are not.	3655	defined to be C<0>, then they are not. Embed watchers rely on most other
		3656	watcher types, which therefore must not be disabled.
2628		3657
2629	=item EV_STAT_ENABLE	3658	=item EV_STAT_ENABLE
2630		3659
2631	If undefined or defined to be C<1>, then stat watchers are supported. If	3660	If undefined or defined to be C<1>, then stat watchers are supported. If
2632	defined to be C<0>, then they are not.	3661	defined to be C<0>, then they are not.
…		…
2634	=item EV_FORK_ENABLE	3663	=item EV_FORK_ENABLE
2635		3664
2636	If undefined or defined to be C<1>, then fork watchers are supported. If	3665	If undefined or defined to be C<1>, then fork watchers are supported. If
2637	defined to be C<0>, then they are not.	3666	defined to be C<0>, then they are not.
2638		3667
		3668	=item EV_ASYNC_ENABLE
		3669
		3670	If undefined or defined to be C<1>, then async watchers are supported. If
		3671	defined to be C<0>, then they are not.
		3672
2639	=item EV_MINIMAL	3673	=item EV_MINIMAL
2640		3674
2641	If you need to shave off some kilobytes of code at the expense of some	3675	If you need to shave off some kilobytes of code at the expense of some
2642	speed, define this symbol to C<1>. Currently only used for gcc to override	3676	speed, define this symbol to C<1>. Currently this is used to override some
2643	some inlining decisions, saves roughly 30% codesize of amd64.	3677	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3678	much smaller 2-heap for timer management over the default 4-heap.
2644		3679
2645	=item EV_PID_HASHSIZE	3680	=item EV_PID_HASHSIZE
2646		3681
2647	C<ev_child> watchers use a small hash table to distribute workload by	3682	C<ev_child> watchers use a small hash table to distribute workload by
2648	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3683	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2655	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3690	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2656	usually more than enough. If you need to manage thousands of C<ev_stat>	3691	usually more than enough. If you need to manage thousands of C<ev_stat>
2657	watchers you might want to increase this value (I<must> be a power of	3692	watchers you might want to increase this value (I<must> be a power of
2658	two).	3693	two).
2659		3694
		3695	=item EV_USE_4HEAP
		3696
		3697	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3698	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3699	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3700	faster performance with many (thousands) of watchers.
		3701
		3702	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3703	(disabled).
		3704
		3705	=item EV_HEAP_CACHE_AT
		3706
		3707	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3708	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3709	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3710	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3711	but avoids random read accesses on heap changes. This improves performance
		3712	noticeably with many (hundreds) of watchers.
		3713
		3714	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3715	(disabled).
		3716
		3717	=item EV_VERIFY
		3718
		3719	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3720	be done: If set to C<0>, no internal verification code will be compiled
		3721	in. If set to C<1>, then verification code will be compiled in, but not
		3722	called. If set to C<2>, then the internal verification code will be
		3723	called once per loop, which can slow down libev. If set to C<3>, then the
		3724	verification code will be called very frequently, which will slow down
		3725	libev considerably.
		3726
		3727	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3728	C<0>.
		3729
2660	=item EV_COMMON	3730	=item EV_COMMON
2661		3731
2662	By default, all watchers have a C<void *data> member. By redefining	3732	By default, all watchers have a C<void *data> member. By redefining
2663	this macro to a something else you can include more and other types of	3733	this macro to a something else you can include more and other types of
2664	members. You have to define it each time you include one of the files,	3734	members. You have to define it each time you include one of the files,
2665	though, and it must be identical each time.	3735	though, and it must be identical each time.
2666		3736
2667	For example, the perl EV module uses something like this:	3737	For example, the perl EV module uses something like this:
2668		3738
2669	#define EV_COMMON \	3739	#define EV_COMMON \
2670	SV *self; /* contains this struct */ \	3740	SV *self; /* contains this struct */ \
2671	SV *cb_sv, *fh /* note no trailing ";" */	3741	SV *cb_sv, *fh /* note no trailing ";" */
2672		3742
2673	=item EV_CB_DECLARE (type)	3743	=item EV_CB_DECLARE (type)
2674		3744
2675	=item EV_CB_INVOKE (watcher, revents)	3745	=item EV_CB_INVOKE (watcher, revents)
2676		3746
…		…
2681	definition and a statement, respectively. See the F<ev.h> header file for	3751	definition and a statement, respectively. See the F<ev.h> header file for
2682	their default definitions. One possible use for overriding these is to	3752	their default definitions. One possible use for overriding these is to
2683	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3753	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2684	method calls instead of plain function calls in C++.	3754	method calls instead of plain function calls in C++.
2685		3755
		3756	=back
		3757
2686	=head2 EXPORTED API SYMBOLS	3758	=head2 EXPORTED API SYMBOLS
2687		3759
2688	If you need to re-export the API (e.g. via a dll) and you need a list of	3760	If you need to re-export the API (e.g. via a DLL) and you need a list of
2689	exported symbols, you can use the provided F<Symbol.*> files which list	3761	exported symbols, you can use the provided F<Symbol.*> files which list
2690	all public symbols, one per line:	3762	all public symbols, one per line:
2691		3763
2692	Symbols.ev for libev proper	3764	Symbols.ev for libev proper
2693	Symbols.event for the libevent emulation	3765	Symbols.event for the libevent emulation
2694		3766
2695	This can also be used to rename all public symbols to avoid clashes with	3767	This can also be used to rename all public symbols to avoid clashes with
2696	multiple versions of libev linked together (which is obviously bad in	3768	multiple versions of libev linked together (which is obviously bad in
2697	itself, but sometimes it is inconvinient to avoid this).	3769	itself, but sometimes it is inconvenient to avoid this).
2698		3770
2699	A sed command like this will create wrapper C<#define>'s that you need to	3771	A sed command like this will create wrapper C<#define>'s that you need to
2700	include before including F<ev.h>:	3772	include before including F<ev.h>:
2701		3773
2702	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3774	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2719	file.	3791	file.
2720		3792
2721	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3793	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2722	that everybody includes and which overrides some configure choices:	3794	that everybody includes and which overrides some configure choices:
2723		3795
2724	#define EV_MINIMAL 1	3796	#define EV_MINIMAL 1
2725	#define EV_USE_POLL 0	3797	#define EV_USE_POLL 0
2726	#define EV_MULTIPLICITY 0	3798	#define EV_MULTIPLICITY 0
2727	#define EV_PERIODIC_ENABLE 0	3799	#define EV_PERIODIC_ENABLE 0
2728	#define EV_STAT_ENABLE 0	3800	#define EV_STAT_ENABLE 0
2729	#define EV_FORK_ENABLE 0	3801	#define EV_FORK_ENABLE 0
2730	#define EV_CONFIG_H <config.h>	3802	#define EV_CONFIG_H <config.h>
2731	#define EV_MINPRI 0	3803	#define EV_MINPRI 0
2732	#define EV_MAXPRI 0	3804	#define EV_MAXPRI 0
2733		3805
2734	#include "ev++.h"	3806	#include "ev++.h"
2735		3807
2736	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3808	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2737		3809
2738	#include "ev_cpp.h"	3810	#include "ev_cpp.h"
2739	#include "ev.c"	3811	#include "ev.c"
2740		3812
		3813	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2741		3814
2742	=head1 COMPLEXITIES	3815	=head2 THREADS AND COROUTINES
2743		3816
2744	In this section the complexities of (many of) the algorithms used inside	3817	=head3 THREADS
2745	libev will be explained. For complexity discussions about backends see the
2746	documentation for C<ev_default_init>.
2747		3818
2748	All of the following are about amortised time: If an array needs to be	3819	All libev functions are reentrant and thread-safe unless explicitly
2749	extended, libev needs to realloc and move the whole array, but this	3820	documented otherwise, but libev implements no locking itself. This means
2750	happens asymptotically never with higher number of elements, so O(1) might	3821	that you can use as many loops as you want in parallel, as long as there
2751	mean it might do a lengthy realloc operation in rare cases, but on average	3822	are no concurrent calls into any libev function with the same loop
2752	it is much faster and asymptotically approaches constant time.	3823	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3824	of course): libev guarantees that different event loops share no data
		3825	structures that need any locking.
		3826
		3827	Or to put it differently: calls with different loop parameters can be done
		3828	concurrently from multiple threads, calls with the same loop parameter
		3829	must be done serially (but can be done from different threads, as long as
		3830	only one thread ever is inside a call at any point in time, e.g. by using
		3831	a mutex per loop).
		3832
		3833	Specifically to support threads (and signal handlers), libev implements
		3834	so-called C<ev_async> watchers, which allow some limited form of
		3835	concurrency on the same event loop, namely waking it up "from the
		3836	outside".
		3837
		3838	If you want to know which design (one loop, locking, or multiple loops
		3839	without or something else still) is best for your problem, then I cannot
		3840	help you, but here is some generic advice:
2753		3841
2754	=over 4	3842	=over 4
2755		3843
2756	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3844	=item * most applications have a main thread: use the default libev loop
		3845	in that thread, or create a separate thread running only the default loop.
2757		3846
2758	This means that, when you have a watcher that triggers in one hour and	3847	This helps integrating other libraries or software modules that use libev
2759	there are 100 watchers that would trigger before that then inserting will	3848	themselves and don't care/know about threading.
2760	have to skip roughly seven (C<ld 100>) of these watchers.
2761		3849
2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3850	=item * one loop per thread is usually a good model.
2763		3851
2764	That means that changing a timer costs less than removing/adding them	3852	Doing this is almost never wrong, sometimes a better-performance model
2765	as only the relative motion in the event queue has to be paid for.	3853	exists, but it is always a good start.
2766		3854
2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3855	=item * other models exist, such as the leader/follower pattern, where one
		3856	loop is handed through multiple threads in a kind of round-robin fashion.
2768		3857
2769	These just add the watcher into an array or at the head of a list.	3858	Choosing a model is hard - look around, learn, know that usually you can do
		3859	better than you currently do :-)
2770		3860
2771	=item Stopping check/prepare/idle watchers: O(1)	3861	=item * often you need to talk to some other thread which blocks in the
		3862	event loop.
2772		3863
2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3864	C<ev_async> watchers can be used to wake them up from other threads safely
		3865	(or from signal contexts...).
2774		3866
2775	These watchers are stored in lists then need to be walked to find the	3867	An example use would be to communicate signals or other events that only
2776	correct watcher to remove. The lists are usually short (you don't usually	3868	work in the default loop by registering the signal watcher with the
2777	have many watchers waiting for the same fd or signal).	3869	default loop and triggering an C<ev_async> watcher from the default loop
2778		3870	watcher callback into the event loop interested in the signal.
2779	=item Finding the next timer in each loop iteration: O(1)
2780
2781	By virtue of using a binary heap, the next timer is always found at the
2782	beginning of the storage array.
2783
2784	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2785
2786	A change means an I/O watcher gets started or stopped, which requires
2787	libev to recalculate its status (and possibly tell the kernel, depending
2788	on backend and wether C<ev_io_set> was used).
2789
2790	=item Activating one watcher (putting it into the pending state): O(1)
2791
2792	=item Priority handling: O(number_of_priorities)
2793
2794	Priorities are implemented by allocating some space for each
2795	priority. When doing priority-based operations, libev usually has to
2796	linearly search all the priorities, but starting/stopping and activating
2797	watchers becomes O(1) w.r.t. prioritiy handling.
2798		3871
2799	=back	3872	=back
2800		3873
		3874	=head3 COROUTINES
2801		3875
2802	=head1 Win32 platform limitations and workarounds	3876	Libev is very accommodating to coroutines ("cooperative threads"):
		3877	libev fully supports nesting calls to its functions from different
		3878	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3879	different coroutines, and switch freely between both coroutines running the
		3880	loop, as long as you don't confuse yourself). The only exception is that
		3881	you must not do this from C<ev_periodic> reschedule callbacks.
		3882
		3883	Care has been taken to ensure that libev does not keep local state inside
		3884	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3885	they do not call any callbacks.
		3886
		3887	=head2 COMPILER WARNINGS
		3888
		3889	Depending on your compiler and compiler settings, you might get no or a
		3890	lot of warnings when compiling libev code. Some people are apparently
		3891	scared by this.
		3892
		3893	However, these are unavoidable for many reasons. For one, each compiler
		3894	has different warnings, and each user has different tastes regarding
		3895	warning options. "Warn-free" code therefore cannot be a goal except when
		3896	targeting a specific compiler and compiler-version.
		3897
		3898	Another reason is that some compiler warnings require elaborate
		3899	workarounds, or other changes to the code that make it less clear and less
		3900	maintainable.
		3901
		3902	And of course, some compiler warnings are just plain stupid, or simply
		3903	wrong (because they don't actually warn about the condition their message
		3904	seems to warn about). For example, certain older gcc versions had some
		3905	warnings that resulted an extreme number of false positives. These have
		3906	been fixed, but some people still insist on making code warn-free with
		3907	such buggy versions.
		3908
		3909	While libev is written to generate as few warnings as possible,
		3910	"warn-free" code is not a goal, and it is recommended not to build libev
		3911	with any compiler warnings enabled unless you are prepared to cope with
		3912	them (e.g. by ignoring them). Remember that warnings are just that:
		3913	warnings, not errors, or proof of bugs.
		3914
		3915
		3916	=head2 VALGRIND
		3917
		3918	Valgrind has a special section here because it is a popular tool that is
		3919	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3920
		3921	If you think you found a bug (memory leak, uninitialised data access etc.)
		3922	in libev, then check twice: If valgrind reports something like:
		3923
		3924	==2274== definitely lost: 0 bytes in 0 blocks.
		3925	==2274== possibly lost: 0 bytes in 0 blocks.
		3926	==2274== still reachable: 256 bytes in 1 blocks.
		3927
		3928	Then there is no memory leak, just as memory accounted to global variables
		3929	is not a memleak - the memory is still being referenced, and didn't leak.
		3930
		3931	Similarly, under some circumstances, valgrind might report kernel bugs
		3932	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3933	although an acceptable workaround has been found here), or it might be
		3934	confused.
		3935
		3936	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3937	make it into some kind of religion.
		3938
		3939	If you are unsure about something, feel free to contact the mailing list
		3940	with the full valgrind report and an explanation on why you think this
		3941	is a bug in libev (best check the archives, too :). However, don't be
		3942	annoyed when you get a brisk "this is no bug" answer and take the chance
		3943	of learning how to interpret valgrind properly.
		3944
		3945	If you need, for some reason, empty reports from valgrind for your project
		3946	I suggest using suppression lists.
		3947
		3948
		3949	=head1 PORTABILITY NOTES
		3950
		3951	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
2803		3952
2804	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3953	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2805	requires, and its I/O model is fundamentally incompatible with the POSIX	3954	requires, and its I/O model is fundamentally incompatible with the POSIX
2806	model. Libev still offers limited functionality on this platform in	3955	model. Libev still offers limited functionality on this platform in
2807	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3956	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2808	descriptors. This only applies when using Win32 natively, not when using	3957	descriptors. This only applies when using Win32 natively, not when using
2809	e.g. cygwin.	3958	e.g. cygwin.
2810		3959
		3960	Lifting these limitations would basically require the full
		3961	re-implementation of the I/O system. If you are into these kinds of
		3962	things, then note that glib does exactly that for you in a very portable
		3963	way (note also that glib is the slowest event library known to man).
		3964
2811	There is no supported compilation method available on windows except	3965	There is no supported compilation method available on windows except
2812	embedding it into other applications.	3966	embedding it into other applications.
2813		3967
		3968	Sensible signal handling is officially unsupported by Microsoft - libev
		3969	tries its best, but under most conditions, signals will simply not work.
		3970
		3971	Not a libev limitation but worth mentioning: windows apparently doesn't
		3972	accept large writes: instead of resulting in a partial write, windows will
		3973	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3974	so make sure you only write small amounts into your sockets (less than a
		3975	megabyte seems safe, but this apparently depends on the amount of memory
		3976	available).
		3977
2814	Due to the many, low, and arbitrary limits on the win32 platform and the	3978	Due to the many, low, and arbitrary limits on the win32 platform and
2815	abysmal performance of winsockets, using a large number of sockets is not	3979	the abysmal performance of winsockets, using a large number of sockets
2816	recommended (and not reasonable). If your program needs to use more than	3980	is not recommended (and not reasonable). If your program needs to use
2817	a hundred or so sockets, then likely it needs to use a totally different	3981	more than a hundred or so sockets, then likely it needs to use a totally
2818	implementation for windows, as libev offers the POSIX model, which cannot	3982	different implementation for windows, as libev offers the POSIX readiness
2819	be implemented efficiently on windows (microsoft monopoly games).	3983	notification model, which cannot be implemented efficiently on windows
		3984	(due to Microsoft monopoly games).
		3985
		3986	A typical way to use libev under windows is to embed it (see the embedding
		3987	section for details) and use the following F<evwrap.h> header file instead
		3988	of F<ev.h>:
		3989
		3990	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3991	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3992
		3993	#include "ev.h"
		3994
		3995	And compile the following F<evwrap.c> file into your project (make sure
		3996	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3997
		3998	#include "evwrap.h"
		3999	#include "ev.c"
2820		4000
2821	=over 4	4001	=over 4
2822		4002
2823	=item The winsocket select function	4003	=item The winsocket select function
2824		4004
2825	The winsocket C<select> function doesn't follow POSIX in that it requires	4005	The winsocket C<select> function doesn't follow POSIX in that it
2826	socket I<handles> and not socket I<file descriptors>. This makes select	4006	requires socket I<handles> and not socket I<file descriptors> (it is
2827	very inefficient, and also requires a mapping from file descriptors	4007	also extremely buggy). This makes select very inefficient, and also
2828	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4008	requires a mapping from file descriptors to socket handles (the Microsoft
2829	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4009	C runtime provides the function C<_open_osfhandle> for this). See the
2830	symbols for more info.	4010	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4011	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2831		4012
2832	The configuration for a "naked" win32 using the microsoft runtime	4013	The configuration for a "naked" win32 using the Microsoft runtime
2833	libraries and raw winsocket select is:	4014	libraries and raw winsocket select is:
2834		4015
2835	#define EV_USE_SELECT 1	4016	#define EV_USE_SELECT 1
2836	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4017	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2837		4018
2838	Note that winsockets handling of fd sets is O(n), so you can easily get a	4019	Note that winsockets handling of fd sets is O(n), so you can easily get a
2839	complexity in the O(n²) range when using win32.	4020	complexity in the O(n²) range when using win32.
2840		4021
2841	=item Limited number of file descriptors	4022	=item Limited number of file descriptors
2842		4023
2843	Windows has numerous arbitrary (and low) limits on things. Early versions	4024	Windows has numerous arbitrary (and low) limits on things.
2844	of winsocket's select only supported waiting for a max. of C<64> handles	4025
		4026	Early versions of winsocket's select only supported waiting for a maximum
2845	(probably owning to the fact that all windows kernels can only wait for	4027	of C<64> handles (probably owning to the fact that all windows kernels
2846	C<64> things at the same time internally; microsoft recommends spawning a	4028	can only wait for C<64> things at the same time internally; Microsoft
2847	chain of threads and wait for 63 handles and the previous thread in each).	4029	recommends spawning a chain of threads and wait for 63 handles and the
		4030	previous thread in each. Sounds great!).
2848		4031
2849	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4032	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2850	to some high number (e.g. C<2048>) before compiling the winsocket select	4033	to some high number (e.g. C<2048>) before compiling the winsocket select
2851	call (which might be in libev or elsewhere, for example, perl does its own	4034	call (which might be in libev or elsewhere, for example, perl and many
2852	select emulation on windows).	4035	other interpreters do their own select emulation on windows).
2853		4036
2854	Another limit is the number of file descriptors in the microsoft runtime	4037	Another limit is the number of file descriptors in the Microsoft runtime
2855	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4038	libraries, which by default is C<64> (there must be a hidden I<64>
2856	or something like this inside microsoft). You can increase this by calling	4039	fetish or something like this inside Microsoft). You can increase this
2857	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4040	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2858	arbitrary limit), but is broken in many versions of the microsoft runtime	4041	(another arbitrary limit), but is broken in many versions of the Microsoft
2859	libraries.
2860
2861	This might get you to about C<512> or C<2048> sockets (depending on	4042	runtime libraries. This might get you to about C<512> or C<2048> sockets
2862	windows version and/or the phase of the moon). To get more, you need to	4043	(depending on windows version and/or the phase of the moon). To get more,
2863	wrap all I/O functions and provide your own fd management, but the cost of	4044	you need to wrap all I/O functions and provide your own fd management, but
2864	calling select (O(n²)) will likely make this unworkable.	4045	the cost of calling select (O(n²)) will likely make this unworkable.
2865		4046
2866	=back	4047	=back
2867		4048
		4049	=head2 PORTABILITY REQUIREMENTS
		4050
		4051	In addition to a working ISO-C implementation and of course the
		4052	backend-specific APIs, libev relies on a few additional extensions:
		4053
		4054	=over 4
		4055
		4056	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4057	calling conventions regardless of C<ev_watcher_type *>.
		4058
		4059	Libev assumes not only that all watcher pointers have the same internal
		4060	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4061	assumes that the same (machine) code can be used to call any watcher
		4062	callback: The watcher callbacks have different type signatures, but libev
		4063	calls them using an C<ev_watcher *> internally.
		4064
		4065	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4066
		4067	The type C<sig_atomic_t volatile> (or whatever is defined as
		4068	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4069	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4070	believed to be sufficiently portable.
		4071
		4072	=item C<sigprocmask> must work in a threaded environment
		4073
		4074	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4075	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4076	pthread implementations will either allow C<sigprocmask> in the "main
		4077	thread" or will block signals process-wide, both behaviours would
		4078	be compatible with libev. Interaction between C<sigprocmask> and
		4079	C<pthread_sigmask> could complicate things, however.
		4080
		4081	The most portable way to handle signals is to block signals in all threads
		4082	except the initial one, and run the default loop in the initial thread as
		4083	well.
		4084
		4085	=item C<long> must be large enough for common memory allocation sizes
		4086
		4087	To improve portability and simplify its API, libev uses C<long> internally
		4088	instead of C<size_t> when allocating its data structures. On non-POSIX
		4089	systems (Microsoft...) this might be unexpectedly low, but is still at
		4090	least 31 bits everywhere, which is enough for hundreds of millions of
		4091	watchers.
		4092
		4093	=item C<double> must hold a time value in seconds with enough accuracy
		4094
		4095	The type C<double> is used to represent timestamps. It is required to
		4096	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4097	enough for at least into the year 4000. This requirement is fulfilled by
		4098	implementations implementing IEEE 754, which is basically all existing
		4099	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4100	2200.
		4101
		4102	=back
		4103
		4104	If you know of other additional requirements drop me a note.
		4105
		4106
		4107	=head1 ALGORITHMIC COMPLEXITIES
		4108
		4109	In this section the complexities of (many of) the algorithms used inside
		4110	libev will be documented. For complexity discussions about backends see
		4111	the documentation for C<ev_default_init>.
		4112
		4113	All of the following are about amortised time: If an array needs to be
		4114	extended, libev needs to realloc and move the whole array, but this
		4115	happens asymptotically rarer with higher number of elements, so O(1) might
		4116	mean that libev does a lengthy realloc operation in rare cases, but on
		4117	average it is much faster and asymptotically approaches constant time.
		4118
		4119	=over 4
		4120
		4121	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4122
		4123	This means that, when you have a watcher that triggers in one hour and
		4124	there are 100 watchers that would trigger before that, then inserting will
		4125	have to skip roughly seven (C<ld 100>) of these watchers.
		4126
		4127	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4128
		4129	That means that changing a timer costs less than removing/adding them,
		4130	as only the relative motion in the event queue has to be paid for.
		4131
		4132	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4133
		4134	These just add the watcher into an array or at the head of a list.
		4135
		4136	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4137
		4138	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4139
		4140	These watchers are stored in lists, so they need to be walked to find the
		4141	correct watcher to remove. The lists are usually short (you don't usually
		4142	have many watchers waiting for the same fd or signal: one is typical, two
		4143	is rare).
		4144
		4145	=item Finding the next timer in each loop iteration: O(1)
		4146
		4147	By virtue of using a binary or 4-heap, the next timer is always found at a
		4148	fixed position in the storage array.
		4149
		4150	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4151
		4152	A change means an I/O watcher gets started or stopped, which requires
		4153	libev to recalculate its status (and possibly tell the kernel, depending
		4154	on backend and whether C<ev_io_set> was used).
		4155
		4156	=item Activating one watcher (putting it into the pending state): O(1)
		4157
		4158	=item Priority handling: O(number_of_priorities)
		4159
		4160	Priorities are implemented by allocating some space for each
		4161	priority. When doing priority-based operations, libev usually has to
		4162	linearly search all the priorities, but starting/stopping and activating
		4163	watchers becomes O(1) with respect to priority handling.
		4164
		4165	=item Sending an ev_async: O(1)
		4166
		4167	=item Processing ev_async_send: O(number_of_async_watchers)
		4168
		4169	=item Processing signals: O(max_signal_number)
		4170
		4171	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4172	calls in the current loop iteration. Checking for async and signal events
		4173	involves iterating over all running async watchers or all signal numbers.
		4174
		4175	=back
		4176
		4177
		4178	=head1 GLOSSARY
		4179
		4180	=over 4
		4181
		4182	=item active
		4183
		4184	A watcher is active as long as it has been started (has been attached to
		4185	an event loop) but not yet stopped (disassociated from the event loop).
		4186
		4187	=item application
		4188
		4189	In this document, an application is whatever is using libev.
		4190
		4191	=item callback
		4192
		4193	The address of a function that is called when some event has been
		4194	detected. Callbacks are being passed the event loop, the watcher that
		4195	received the event, and the actual event bitset.
		4196
		4197	=item callback invocation
		4198
		4199	The act of calling the callback associated with a watcher.
		4200
		4201	=item event
		4202
		4203	A change of state of some external event, such as data now being available
		4204	for reading on a file descriptor, time having passed or simply not having
		4205	any other events happening anymore.
		4206
		4207	In libev, events are represented as single bits (such as C<EV_READ> or
		4208	C<EV_TIMEOUT>).
		4209
		4210	=item event library
		4211
		4212	A software package implementing an event model and loop.
		4213
		4214	=item event loop
		4215
		4216	An entity that handles and processes external events and converts them
		4217	into callback invocations.
		4218
		4219	=item event model
		4220
		4221	The model used to describe how an event loop handles and processes
		4222	watchers and events.
		4223
		4224	=item pending
		4225
		4226	A watcher is pending as soon as the corresponding event has been detected,
		4227	and stops being pending as soon as the watcher will be invoked or its
		4228	pending status is explicitly cleared by the application.
		4229
		4230	A watcher can be pending, but not active. Stopping a watcher also clears
		4231	its pending status.
		4232
		4233	=item real time
		4234
		4235	The physical time that is observed. It is apparently strictly monotonic :)
		4236
		4237	=item wall-clock time
		4238
		4239	The time and date as shown on clocks. Unlike real time, it can actually
		4240	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4241	clock.
		4242
		4243	=item watcher
		4244
		4245	A data structure that describes interest in certain events. Watchers need
		4246	to be started (attached to an event loop) before they can receive events.
		4247
		4248	=item watcher invocation
		4249
		4250	The act of calling the callback associated with a watcher.
		4251
		4252	=back
2868		4253
2869	=head1 AUTHOR	4254	=head1 AUTHOR
2870		4255
2871	Marc Lehmann <libev@schmorp.de>.	4256	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2872		4257

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