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Revision 1.148 by root, Thu Apr 24 01:42:11 2008 UTC vs.
Revision 1.256 by root, Tue Jul 14 20:31:21 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
28		30
29	// this causes all nested ev_loop's to stop iterating	31	// this causes all nested ev_loop's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
52		54
53	// initialise a timer watcher, then start it	55	// initialise a timer watcher, then start it
54	// simple non-repeating 5.5 second timeout	56	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
57		59
58	// now wait for events to arrive	60	// now wait for events to arrive
59	ev_loop (loop, 0);	61	ev_loop (loop, 0);
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
103	Libev is very configurable. In this manual the default (and most common)	117	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	118	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	119	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	120	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	121	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	123	this argument.
110		124
111	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
112		126
113	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floatingpoint value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
121		156
122	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
123		158
124	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
125	library in any way.	160	library in any way.
…		…
134		169
135	=item ev_sleep (ev_tstamp interval)	170	=item ev_sleep (ev_tstamp interval)
136		171
137	Sleep for the given interval: The current thread will be blocked until	172	Sleep for the given interval: The current thread will be blocked until
138	either it is interrupted or the given time interval has passed. Basically	173	either it is interrupted or the given time interval has passed. Basically
139	this is a subsecond-resolution C<sleep ()>.	174	this is a sub-second-resolution C<sleep ()>.
140		175
141	=item int ev_version_major ()	176	=item int ev_version_major ()
142		177
143	=item int ev_version_minor ()	178	=item int ev_version_minor ()
144		179
…		…
157	not a problem.	192	not a problem.
158		193
159	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	195	version.
161		196
162	assert (("libev version mismatch",	197	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
165		200
166	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
167		202
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	206	a description of the set values.
172		207
173	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
174	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
175		210
176	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
178		213
179	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
180		215
181	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
182	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
183	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
184	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
185	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
186	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
187		222
188	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
189		224
…		…
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
194	recommended ones.	229	recommended ones.
195		230
196	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
197		232
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
199		234
200	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	used to allocate and free memory (no surprises here). If it returns zero	237	used to allocate and free memory (no surprises here). If it returns zero
203	when memory needs to be allocated (C<size != 0>), the library might abort	238	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
229	}	264	}
230		265
231	...	266	...
232	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
233		268
234	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
235		270
236	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
237	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
238	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
239	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
240	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
241	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
242	(such as abort).	277	(such as abort).
243		278
244	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.
…		…
255		290
256	=back	291	=back
257		292
258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
259		294
260	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>
261	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>
262	events, and dynamically created loops which do not.	297	I<function>).
		298
		299	The library knows two types of such loops, the I<default> loop, which
		300	supports signals and child events, and dynamically created loops which do
		301	not.
263		302
264	=over 4	303	=over 4
265		304
266	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
267		306
…		…
273	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
274	function.	313	function.
275		314
276	Note that this function is I<not> thread-safe, so if you want to use it	315	Note that this function is I<not> thread-safe, so if you want to use it
277	from multiple threads, you have to lock (note also that this is unlikely,	316	from multiple threads, you have to lock (note also that this is unlikely,
278	as loops cannot bes hared easily between threads anyway).	317	as loops cannot be shared easily between threads anyway).
279		318
280	The default loop is the only loop that can handle C<ev_signal> and	319	The default loop is the only loop that can handle C<ev_signal> and
281	C<ev_child> watchers, and to do this, it always registers a handler	320	C<ev_child> watchers, and to do this, it always registers a handler
282	for C<SIGCHLD>. If this is a problem for your app you can either	321	for C<SIGCHLD>. If this is a problem for your application you can either
283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
285	C<ev_default_init>.	324	C<ev_default_init>.
286		325
287	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
…		…
296	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	336	thing, believe me).
298		337
299	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
300		339
301	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
302	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
305	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
306	around bugs.	345	around bugs.
…		…
313		352
314	This works by calling C<getpid ()> on every iteration of the loop,	353	This works by calling C<getpid ()> on every iteration of the loop,
315	and thus this might slow down your event loop if you do a lot of loop	354	and thus this might slow down your event loop if you do a lot of loop
316	iterations and little real work, but is usually not noticeable (on my	355	iterations and little real work, but is usually not noticeable (on my
317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
318	without a syscall and thus I<very> fast, but my GNU/Linux system also has	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
319	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
320		359
321	The big advantage of this flag is that you can forget about fork (and	360	The big advantage of this flag is that you can forget about fork (and
322	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
323	flag.	362	flag.
324		363
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	365	environment variable.
327		366
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		368
330	This is your standard select(2) backend. Not I<completely> standard, as	369	This is your standard select(2) backend. Not I<completely> standard, as
…		…
332	but if that fails, expect a fairly low limit on the number of fds when	371	but if that fails, expect a fairly low limit on the number of fds when
333	using this backend. It doesn't scale too well (O(highest_fd)), but its	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
334	usually the fastest backend for a low number of (low-numbered :) fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
335		374
336	To get good performance out of this backend you need a high amount of	375	To get good performance out of this backend you need a high amount of
337	parallelity (most of the file descriptors should be busy). If you are	376	parallelism (most of the file descriptors should be busy). If you are
338	writing a server, you should C<accept ()> in a loop to accept as many	377	writing a server, you should C<accept ()> in a loop to accept as many
339	connections as possible during one iteration. You might also want to have	378	connections as possible during one iteration. You might also want to have
340	a look at C<ev_set_io_collect_interval ()> to increase the amount of	379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readyness notifications you get per iteration.	380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
342		385
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		387
345	And this is your standard poll(2) backend. It's more complicated	388	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	389	than select, but handles sparse fds better and has no artificial
347	limit on the number of fds you can use (except it will slow down	390	limit on the number of fds you can use (except it will slow down
348	considerably with a lot of inactive fds). It scales similarly to select,	391	considerably with a lot of inactive fds). It scales similarly to select,
349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	393	performance tips.
351		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		397
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
353		399
354	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
355	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
356	like O(total_fds) where n is the total number of fds (or the highest fd),	402	like O(total_fds) where n is the total number of fds (or the highest fd),
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	403	epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	404
359	cases and requiring a syscall per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
361		421
362	While stopping, setting and starting an I/O watcher in the same iteration	422	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
364	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
367		427	file descriptors.
368	Please note that epoll sometimes generates spurious notifications, so you
369	need to use non-blocking I/O or other means to avoid blocking when no data
370	(or space) is available.
371		428
372	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
373	watchers for a file descriptor until it has been closed, if possible, i.e.	430	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
375		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
376	While nominally embeddeble in other event loops, this feature is broken in	441	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
378		446
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		448
381	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
382	was broken on all BSDs except NetBSD (usually it doesn't work reliably	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
383	with anything but sockets and pipes, except on Darwin, where of course	451	with anything but sockets and pipes, except on Darwin, where of course
384	it's completely useless). For this reason it's not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
385	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
387	system like NetBSD.	457	system like NetBSD.
388		458
389	You still can embed kqueue into a normal poll or select backend and use it	459	You still can embed kqueue into a normal poll or select backend and use it
390	only for sockets (after having made sure that sockets work with kqueue on	460	only for sockets (after having made sure that sockets work with kqueue on
391	the target platform). See C<ev_embed> watchers for more info.	461	the target platform). See C<ev_embed> watchers for more info.
392		462
393	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
394	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
395	course). While stopping, setting and starting an I/O watcher does never	465	course). While stopping, setting and starting an I/O watcher does never
396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
397	two event changes per incident, support for C<fork ()> is very bad and it	467	two event changes per incident. Support for C<fork ()> is very bad (but
398	drops fds silently in similarly hard-to-detect cases.	468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
399		470
400	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
401		472
402	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
403	everywhere, so you might need to test for this. And since it is broken	474	everywhere, so you might need to test for this. And since it is broken
404	almost everywhere, you should only use it when you have a lot of sockets	475	almost everywhere, you should only use it when you have a lot of sockets
405	(for which it usually works), by embedding it into another event loop	476	(for which it usually works), by embedding it into another event loop
406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
408		483
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		485
411	This is not implemented yet (and might never be, unless you send me an	486	This is not implemented yet (and might never be, unless you send me an
412	implementation). According to reports, C</dev/poll> only supports sockets	487	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		492
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
419	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
420		495
421	Please note that solaris event ports can deliver a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
422	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
423	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
424		499
425	While this backend scales well, it requires one system call per active	500	While this backend scales well, it requires one system call per active
426	file descriptor per loop iteration. For small and medium numbers of file	501	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	503	might perform better.
429		504
430	On the positive side, ignoring the spurious readyness notifications, this	505	On the positive side, with the exception of the spurious readiness
431	backend actually performed to specification in all tests and is fully	506	notifications, this backend actually performed fully to specification
432	embeddable, which is a rare feat among the OS-specific backends.	507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
433		512
434	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
435		514
436	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
439		518
440	It is definitely not recommended to use this flag.	519	It is definitely not recommended to use this flag.
441		520
442	=back	521	=back
443		522
444	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
445	backends will be tried (in the reverse order as listed here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
446	specified, all backends in C<ev_recommended_backends ()> will be tried.	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
447		526
448	The most typical usage is like this:	527	Example: This is the most typical usage.
449		528
450	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
452		531
453	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
454	environment settings to be taken into account:	533	environment settings to be taken into account:
455		534
456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
457		536
458	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
459	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
460	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
461		541
462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
463		543
464	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
465		545
466	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
…		…
472	libev with threads is indeed to create one loop per thread, and using the	552	libev with threads is indeed to create one loop per thread, and using the
473	default loop in the "main" or "initial" thread.	553	default loop in the "main" or "initial" thread.
474		554
475	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.
476		556
477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
478	if (!epoller)	558	if (!epoller)
479	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
480		560
481	=item ev_default_destroy ()	561	=item ev_default_destroy ()
482		562
483	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
484	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
485	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
486	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
487	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
488	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
489	for example).	569	for example).
490		570
491	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
492	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
493	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
494		574
495	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
496	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
497	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
498	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
523		603
524	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
525		605
526	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
527	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
528	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.
529		610
530	=item int ev_is_default_loop (loop)	611	=item int ev_is_default_loop (loop)
531		612
532	Returns true when the given loop actually is the default loop, false otherwise.	613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
533		615
534	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
535		617
536	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
537	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
538	happily wraps around with enough iterations.	620	happily wraps around with enough iterations.
539		621
540	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
541	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
542	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.
543		637
544	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
545		639
546	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
547	use.	641	use.
…		…
552	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
553	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
554	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
555	event occurring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
556		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
557	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
558		690
559	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
560	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
561	events.	693	events.
…		…
563	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
564	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.
565		697
566	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
567	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
568	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
569	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
570	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.
571		704
572	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
573	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
574	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.
575		709
576	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
577	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
578	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
579	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
580	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
581	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
582	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
583		721
584	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
585		723
586	- Before the first iteration, call any pending watchers.	724	- Before the first iteration, call any pending watchers.
587	* If EVFLAG_FORKCHECK was used, check for a fork.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
588	- 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.
589	- Queue and call all prepare watchers.	727	- Queue and call all prepare watchers.
590	- 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.
591	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
592	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
593	- Calculate for how long to sleep or block, if at all	732	- Calculate for how long to sleep or block, if at all
594	(active idle watchers, EVLOOP_NONBLOCK or not having	733	(active idle watchers, EVLOOP_NONBLOCK or not having
595	any active watchers at all will result in not sleeping).	734	any active watchers at all will result in not sleeping).
596	- Sleep if the I/O and timer collect interval say so.	735	- Sleep if the I/O and timer collect interval say so.
597	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
598	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
599	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
600	- Queue all outstanding timers.	739	- Queue all expired timers.
601	- Queue all outstanding periodics.	740	- Queue all expired periodics.
602	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
603	- Queue all check watchers.	742	- Queue all check watchers.
604	- 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).
605	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
606	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
607	- 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
…		…
612	anymore.	751	anymore.
613		752
614	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
615	... 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..)
616	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
617	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
618		757
619	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
620		759
621	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
622	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
623	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
624	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.
625		764
626	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.
627		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
628	=item ev_ref (loop)	769	=item ev_ref (loop)
629		770
630	=item ev_unref (loop)	771	=item ev_unref (loop)
631		772
632	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
633	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
634	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
635	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>
636	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
637	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
638	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
639	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
640	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
641	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
642	(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
643	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).
644		790
645	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>
646	running when nothing else is active.	792	running when nothing else is active.
647		793
648	struct ev_signal exitsig;	794	ev_signal exitsig;
649	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
650	ev_signal_start (loop, &exitsig);	796	ev_signal_start (loop, &exitsig);
651	evf_unref (loop);	797	evf_unref (loop);
652		798
653	Example: For some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
654		800
655	ev_ref (loop);	801	ev_ref (loop);
656	ev_signal_stop (loop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
657		803
658	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
659		805
660	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
661		807
662	These advanced functions influence the time that libev will spend waiting	808	These advanced functions influence the time that libev will spend waiting
663	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
664	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.
665		812
666	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>)
667	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
668	increase efficiency of loop iterations.	815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
669		817
670	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
671	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
672	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
673	events, especially with backends like C<select ()> which have a high	821	events, especially with backends like C<select ()> which have a high
674	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.
675		823
676	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
677	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,
678	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
679	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
680	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.
681		831
682	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
683	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
684	latency (the watcher callback will be called later). C<ev_io> watchers	834	latency/jitter/inexactness (the watcher callback will be called
685	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
686	any overhead in libev.	836	value will not introduce any overhead in libev.
687		837
688	Many (busy) programs can usually benefit by setting the io collect	838	Many (busy) programs can usually benefit by setting the I/O collect
689	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
690	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
691	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>,
692	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_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
		925
		926	=item ev_loop_verify (loop)
		927
		928	This function only does something when C<EV_VERIFY> support has been
		929	compiled in, which is the default for non-minimal builds. It tries to go
		930	through all internal structures and checks them for validity. If anything
		931	is found to be inconsistent, it will print an error message to standard
		932	error and call C<abort ()>.
		933
		934	This can be used to catch bugs inside libev itself: under normal
		935	circumstances, this function will never abort as of course libev keeps its
		936	data structures consistent.
693		937
694	=back	938	=back
695		939
696		940
697	=head1 ANATOMY OF A WATCHER	941	=head1 ANATOMY OF A WATCHER
		942
		943	In the following description, uppercase C<TYPE> in names stands for the
		944	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		945	watchers and C<ev_io_start> for I/O watchers.
698		946
699	A watcher is a structure that you create and register to record your	947	A watcher is a structure that you create and register to record your
700	interest in some event. For instance, if you want to wait for STDIN to	948	interest in some event. For instance, if you want to wait for STDIN to
701	become readable, you would create an C<ev_io> watcher for that:	949	become readable, you would create an C<ev_io> watcher for that:
702		950
703	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	951	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
704	{	952	{
705	ev_io_stop (w);	953	ev_io_stop (w);
706	ev_unloop (loop, EVUNLOOP_ALL);	954	ev_unloop (loop, EVUNLOOP_ALL);
707	}	955	}
708		956
709	struct ev_loop *loop = ev_default_loop (0);	957	struct ev_loop *loop = ev_default_loop (0);
		958
710	struct ev_io stdin_watcher;	959	ev_io stdin_watcher;
		960
711	ev_init (&stdin_watcher, my_cb);	961	ev_init (&stdin_watcher, my_cb);
712	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	962	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
713	ev_io_start (loop, &stdin_watcher);	963	ev_io_start (loop, &stdin_watcher);
		964
714	ev_loop (loop, 0);	965	ev_loop (loop, 0);
715		966
716	As you can see, you are responsible for allocating the memory for your	967	As you can see, you are responsible for allocating the memory for your
717	watcher structures (and it is usually a bad idea to do this on the stack,	968	watcher structures (and it is I<usually> a bad idea to do this on the
718	although this can sometimes be quite valid).	969	stack).
		970
		971	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		972	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
719		973
720	Each watcher structure must be initialised by a call to C<ev_init	974	Each watcher structure must be initialised by a call to C<ev_init
721	(watcher *, callback)>, which expects a callback to be provided. This	975	(watcher *, callback)>, which expects a callback to be provided. This
722	callback gets invoked each time the event occurs (or, in the case of io	976	callback gets invoked each time the event occurs (or, in the case of I/O
723	watchers, each time the event loop detects that the file descriptor given	977	watchers, each time the event loop detects that the file descriptor given
724	is readable and/or writable).	978	is readable and/or writable).
725		979
726	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	980	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
727	with arguments specific to this watcher type. There is also a macro	981	macro to configure it, with arguments specific to the watcher type. There
728	to combine initialisation and setting in one call: C<< ev_<type>_init	982	is also a macro to combine initialisation and setting in one call: C<<
729	(watcher *, callback, ...) >>.	983	ev_TYPE_init (watcher *, callback, ...) >>.
730		984
731	To make the watcher actually watch out for events, you have to start it	985	To make the watcher actually watch out for events, you have to start it
732	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	986	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
733	*) >>), and you can stop watching for events at any time by calling the	987	*) >>), and you can stop watching for events at any time by calling the
734	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	988	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
735		989
736	As long as your watcher is active (has been started but not stopped) you	990	As long as your watcher is active (has been started but not stopped) you
737	must not touch the values stored in it. Most specifically you must never	991	must not touch the values stored in it. Most specifically you must never
738	reinitialise it or call its C<set> macro.	992	reinitialise it or call its C<ev_TYPE_set> macro.
739		993
740	Each and every callback receives the event loop pointer as first, the	994	Each and every callback receives the event loop pointer as first, the
741	registered watcher structure as second, and a bitset of received events as	995	registered watcher structure as second, and a bitset of received events as
742	third argument.	996	third argument.
743		997
…		…
801		1055
802	=item C<EV_ASYNC>	1056	=item C<EV_ASYNC>
803		1057
804	The given async watcher has been asynchronously notified (see C<ev_async>).	1058	The given async watcher has been asynchronously notified (see C<ev_async>).
805		1059
		1060	=item C<EV_CUSTOM>
		1061
		1062	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1063	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1064
806	=item C<EV_ERROR>	1065	=item C<EV_ERROR>
807		1066
808	An unspecified error has occured, the watcher has been stopped. This might	1067	An unspecified error has occurred, the watcher has been stopped. This might
809	happen because the watcher could not be properly started because libev	1068	happen because the watcher could not be properly started because libev
810	ran out of memory, a file descriptor was found to be closed or any other	1069	ran out of memory, a file descriptor was found to be closed or any other
		1070	problem. Libev considers these application bugs.
		1071
811	problem. You best act on it by reporting the problem and somehow coping	1072	You best act on it by reporting the problem and somehow coping with the
812	with the watcher being stopped.	1073	watcher being stopped. Note that well-written programs should not receive
		1074	an error ever, so when your watcher receives it, this usually indicates a
		1075	bug in your program.
813		1076
814	Libev will usually signal a few "dummy" events together with an error,	1077	Libev will usually signal a few "dummy" events together with an error, for
815	for example it might indicate that a fd is readable or writable, and if	1078	example it might indicate that a fd is readable or writable, and if your
816	your callbacks is well-written it can just attempt the operation and cope	1079	callbacks is well-written it can just attempt the operation and cope with
817	with the error from read() or write(). This will not work in multithreaded	1080	the error from read() or write(). This will not work in multi-threaded
818	programs, though, so beware.	1081	programs, though, as the fd could already be closed and reused for another
		1082	thing, so beware.
819		1083
820	=back	1084	=back
821		1085
822	=head2 GENERIC WATCHER FUNCTIONS	1086	=head2 GENERIC WATCHER FUNCTIONS
823
824	In the following description, C<TYPE> stands for the watcher type,
825	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
826		1087
827	=over 4	1088	=over 4
828		1089
829	=item C<ev_init> (ev_TYPE *watcher, callback)	1090	=item C<ev_init> (ev_TYPE *watcher, callback)
830		1091
…		…
836	which rolls both calls into one.	1097	which rolls both calls into one.
837		1098
838	You can reinitialise a watcher at any time as long as it has been stopped	1099	You can reinitialise a watcher at any time as long as it has been stopped
839	(or never started) and there are no pending events outstanding.	1100	(or never started) and there are no pending events outstanding.
840		1101
841	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1102	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
842	int revents)>.	1103	int revents)>.
		1104
		1105	Example: Initialise an C<ev_io> watcher in two steps.
		1106
		1107	ev_io w;
		1108	ev_init (&w, my_cb);
		1109	ev_io_set (&w, STDIN_FILENO, EV_READ);
843		1110
844	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1111	=item C<ev_TYPE_set> (ev_TYPE *, [args])
845		1112
846	This macro initialises the type-specific parts of a watcher. You need to	1113	This macro initialises the type-specific parts of a watcher. You need to
847	call C<ev_init> at least once before you call this macro, but you can	1114	call C<ev_init> at least once before you call this macro, but you can
…		…
850	difference to the C<ev_init> macro).	1117	difference to the C<ev_init> macro).
851		1118
852	Although some watcher types do not have type-specific arguments	1119	Although some watcher types do not have type-specific arguments
853	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1120	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
854		1121
		1122	See C<ev_init>, above, for an example.
		1123
855	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1124	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
856		1125
857	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1126	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
858	calls into a single call. This is the most convinient method to initialise	1127	calls into a single call. This is the most convenient method to initialise
859	a watcher. The same limitations apply, of course.	1128	a watcher. The same limitations apply, of course.
		1129
		1130	Example: Initialise and set an C<ev_io> watcher in one step.
		1131
		1132	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
860		1133
861	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1134	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
862		1135
863	Starts (activates) the given watcher. Only active watchers will receive	1136	Starts (activates) the given watcher. Only active watchers will receive
864	events. If the watcher is already active nothing will happen.	1137	events. If the watcher is already active nothing will happen.
865		1138
		1139	Example: Start the C<ev_io> watcher that is being abused as example in this
		1140	whole section.
		1141
		1142	ev_io_start (EV_DEFAULT_UC, &w);
		1143
866	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1144	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
867		1145
868	Stops the given watcher again (if active) and clears the pending	1146	Stops the given watcher if active, and clears the pending status (whether
		1147	the watcher was active or not).
		1148
869	status. It is possible that stopped watchers are pending (for example,	1149	It is possible that stopped watchers are pending - for example,
870	non-repeating timers are being stopped when they become pending), but	1150	non-repeating timers are being stopped when they become pending - but
871	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1151	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
872	you want to free or reuse the memory used by the watcher it is therefore a	1152	pending. If you want to free or reuse the memory used by the watcher it is
873	good idea to always call its C<ev_TYPE_stop> function.	1153	therefore a good idea to always call its C<ev_TYPE_stop> function.
874		1154
875	=item bool ev_is_active (ev_TYPE *watcher)	1155	=item bool ev_is_active (ev_TYPE *watcher)
876		1156
877	Returns a true value iff the watcher is active (i.e. it has been started	1157	Returns a true value iff the watcher is active (i.e. it has been started
878	and not yet been stopped). As long as a watcher is active you must not modify	1158	and not yet been stopped). As long as a watcher is active you must not modify
…		…
904	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1184	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
905	(default: C<-2>). Pending watchers with higher priority will be invoked	1185	(default: C<-2>). Pending watchers with higher priority will be invoked
906	before watchers with lower priority, but priority will not keep watchers	1186	before watchers with lower priority, but priority will not keep watchers
907	from being executed (except for C<ev_idle> watchers).	1187	from being executed (except for C<ev_idle> watchers).
908		1188
909	This means that priorities are I<only> used for ordering callback
910	invocation after new events have been received. This is useful, for
911	example, to reduce latency after idling, or more often, to bind two
912	watchers on the same event and make sure one is called first.
913
914	If you need to suppress invocation when higher priority events are pending	1189	If you need to suppress invocation when higher priority events are pending
915	you need to look at C<ev_idle> watchers, which provide this functionality.	1190	you need to look at C<ev_idle> watchers, which provide this functionality.
916		1191
917	You I<must not> change the priority of a watcher as long as it is active or	1192	You I<must not> change the priority of a watcher as long as it is active or
918	pending.	1193	pending.
919		1194
		1195	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1196	fine, as long as you do not mind that the priority value you query might
		1197	or might not have been clamped to the valid range.
		1198
920	The default priority used by watchers when no priority has been set is	1199	The default priority used by watchers when no priority has been set is
921	always C<0>, which is supposed to not be too high and not be too low :).	1200	always C<0>, which is supposed to not be too high and not be too low :).
922		1201
923	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1202	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
924	fine, as long as you do not mind that the priority value you query might	1203	priorities.
925	or might not have been adjusted to be within valid range.
926		1204
927	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
928		1206
929	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1207	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
930	C<loop> nor C<revents> need to be valid as long as the watcher callback	1208	C<loop> nor C<revents> need to be valid as long as the watcher callback
931	can deal with that fact.	1209	can deal with that fact, as both are simply passed through to the
		1210	callback.
932		1211
933	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1212	=item int ev_clear_pending (loop, ev_TYPE *watcher)
934		1213
935	If the watcher is pending, this function returns clears its pending status	1214	If the watcher is pending, this function clears its pending status and
936	and returns its C<revents> bitset (as if its callback was invoked). If the	1215	returns its C<revents> bitset (as if its callback was invoked). If the
937	watcher isn't pending it does nothing and returns C<0>.	1216	watcher isn't pending it does nothing and returns C<0>.
938		1217
		1218	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1219	callback to be invoked, which can be accomplished with this function.
		1220
939	=back	1221	=back
940		1222
941		1223
942	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1224	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
943		1225
944	Each watcher has, by default, a member C<void *data> that you can change	1226	Each watcher has, by default, a member C<void *data> that you can change
945	and read at any time, libev will completely ignore it. This can be used	1227	and read at any time: libev will completely ignore it. This can be used
946	to associate arbitrary data with your watcher. If you need more data and	1228	to associate arbitrary data with your watcher. If you need more data and
947	don't want to allocate memory and store a pointer to it in that data	1229	don't want to allocate memory and store a pointer to it in that data
948	member, you can also "subclass" the watcher type and provide your own	1230	member, you can also "subclass" the watcher type and provide your own
949	data:	1231	data:
950		1232
951	struct my_io	1233	struct my_io
952	{	1234	{
953	struct ev_io io;	1235	ev_io io;
954	int otherfd;	1236	int otherfd;
955	void *somedata;	1237	void *somedata;
956	struct whatever *mostinteresting;	1238	struct whatever *mostinteresting;
957	}	1239	};
		1240
		1241	...
		1242	struct my_io w;
		1243	ev_io_init (&w.io, my_cb, fd, EV_READ);
958		1244
959	And since your callback will be called with a pointer to the watcher, you	1245	And since your callback will be called with a pointer to the watcher, you
960	can cast it back to your own type:	1246	can cast it back to your own type:
961		1247
962	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1248	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
963	{	1249	{
964	struct my_io *w = (struct my_io *)w_;	1250	struct my_io *w = (struct my_io *)w_;
965	...	1251	...
966	}	1252	}
967		1253
968	More interesting and less C-conformant ways of casting your callback type	1254	More interesting and less C-conformant ways of casting your callback type
969	instead have been omitted.	1255	instead have been omitted.
970		1256
971	Another common scenario is having some data structure with multiple	1257	Another common scenario is to use some data structure with multiple
972	watchers:	1258	embedded watchers:
973		1259
974	struct my_biggy	1260	struct my_biggy
975	{	1261	{
976	int some_data;	1262	int some_data;
977	ev_timer t1;	1263	ev_timer t1;
978	ev_timer t2;	1264	ev_timer t2;
979	}	1265	}
980		1266
981	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1267	In this case getting the pointer to C<my_biggy> is a bit more
982	you need to use C<offsetof>:	1268	complicated: Either you store the address of your C<my_biggy> struct
		1269	in the C<data> member of the watcher (for woozies), or you need to use
		1270	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1271	programmers):
983		1272
984	#include <stddef.h>	1273	#include <stddef.h>
985		1274
986	static void	1275	static void
987	t1_cb (EV_P_ struct ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
988	{	1277	{
989	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
990	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
991	}	1280	}
992		1281
993	static void	1282	static void
994	t2_cb (EV_P_ struct ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
995	{	1284	{
996	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
997	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
998	}	1287	}
		1288
		1289	=head2 WATCHER PRIORITY MODELS
		1290
		1291	Many event loops support I<watcher priorities>, which are usually small
		1292	integers that influence the ordering of event callback invocation
		1293	between watchers in some way, all else being equal.
		1294
		1295	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1296	description for the more technical details such as the actual priority
		1297	range.
		1298
		1299	There are two common ways how these these priorities are being interpreted
		1300	by event loops:
		1301
		1302	In the more common lock-out model, higher priorities "lock out" invocation
		1303	of lower priority watchers, which means as long as higher priority
		1304	watchers receive events, lower priority watchers are not being invoked.
		1305
		1306	The less common only-for-ordering model uses priorities solely to order
		1307	callback invocation within a single event loop iteration: Higher priority
		1308	watchers are invoked before lower priority ones, but they all get invoked
		1309	before polling for new events.
		1310
		1311	Libev uses the second (only-for-ordering) model for all its watchers
		1312	except for idle watchers (which use the lock-out model).
		1313
		1314	The rationale behind this is that implementing the lock-out model for
		1315	watchers is not well supported by most kernel interfaces, and most event
		1316	libraries will just poll for the same events again and again as long as
		1317	their callbacks have not been executed, which is very inefficient in the
		1318	common case of one high-priority watcher locking out a mass of lower
		1319	priority ones.
		1320
		1321	Static (ordering) priorities are most useful when you have two or more
		1322	watchers handling the same resource: a typical usage example is having an
		1323	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1324	timeouts. Under load, data might be received while the program handles
		1325	other jobs, but since timers normally get invoked first, the timeout
		1326	handler will be executed before checking for data. In that case, giving
		1327	the timer a lower priority than the I/O watcher ensures that I/O will be
		1328	handled first even under adverse conditions (which is usually, but not
		1329	always, what you want).
		1330
		1331	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1332	will only be executed when no same or higher priority watchers have
		1333	received events, they can be used to implement the "lock-out" model when
		1334	required.
		1335
		1336	For example, to emulate how many other event libraries handle priorities,
		1337	you can associate an C<ev_idle> watcher to each such watcher, and in
		1338	the normal watcher callback, you just start the idle watcher. The real
		1339	processing is done in the idle watcher callback. This causes libev to
		1340	continously poll and process kernel event data for the watcher, but when
		1341	the lock-out case is known to be rare (which in turn is rare :), this is
		1342	workable.
		1343
		1344	Usually, however, the lock-out model implemented that way will perform
		1345	miserably under the type of load it was designed to handle. In that case,
		1346	it might be preferable to stop the real watcher before starting the
		1347	idle watcher, so the kernel will not have to process the event in case
		1348	the actual processing will be delayed for considerable time.
		1349
		1350	Here is an example of an I/O watcher that should run at a strictly lower
		1351	priority than the default, and which should only process data when no
		1352	other events are pending:
		1353
		1354	ev_idle idle; // actual processing watcher
		1355	ev_io io; // actual event watcher
		1356
		1357	static void
		1358	io_cb (EV_P_ ev_io *w, int revents)
		1359	{
		1360	// stop the I/O watcher, we received the event, but
		1361	// are not yet ready to handle it.
		1362	ev_io_stop (EV_A_ w);
		1363
		1364	// start the idle watcher to ahndle the actual event.
		1365	// it will not be executed as long as other watchers
		1366	// with the default priority are receiving events.
		1367	ev_idle_start (EV_A_ &idle);
		1368	}
		1369
		1370	static void
		1371	idle_cb (EV_P_ ev_idle *w, int revents)
		1372	{
		1373	// actual processing
		1374	read (STDIN_FILENO, ...);
		1375
		1376	// have to start the I/O watcher again, as
		1377	// we have handled the event
		1378	ev_io_start (EV_P_ &io);
		1379	}
		1380
		1381	// initialisation
		1382	ev_idle_init (&idle, idle_cb);
		1383	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1384	ev_io_start (EV_DEFAULT_ &io);
		1385
		1386	In the "real" world, it might also be beneficial to start a timer, so that
		1387	low-priority connections can not be locked out forever under load. This
		1388	enables your program to keep a lower latency for important connections
		1389	during short periods of high load, while not completely locking out less
		1390	important ones.
999		1391
1000		1392
1001	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
1002		1394
1003	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
…		…
1027	In general you can register as many read and/or write event watchers per	1419	In general you can register as many read and/or write event watchers per
1028	fd as you want (as long as you don't confuse yourself). Setting all file	1420	fd as you want (as long as you don't confuse yourself). Setting all file
1029	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
1030	required if you know what you are doing).	1422	required if you know what you are doing).
1031		1423
1032	If you must do this, then force the use of a known-to-be-good backend	1424	If you cannot use non-blocking mode, then force the use of a
1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1425	known-to-be-good backend (at the time of this writing, this includes only
1034	C<EVBACKEND_POLL>).	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1427	descriptors for which non-blocking operation makes no sense (such as
		1428	files) - libev doesn't guarentee any specific behaviour in that case.
1035		1429
1036	Another thing you have to watch out for is that it is quite easy to	1430	Another thing you have to watch out for is that it is quite easy to
1037	receive "spurious" readyness notifications, that is your callback might	1431	receive "spurious" readiness notifications, that is your callback might
1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1432	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1039	because there is no data. Not only are some backends known to create a	1433	because there is no data. Not only are some backends known to create a
1040	lot of those (for example solaris ports), it is very easy to get into	1434	lot of those (for example Solaris ports), it is very easy to get into
1041	this situation even with a relatively standard program structure. Thus	1435	this situation even with a relatively standard program structure. Thus
1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1436	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1043	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1437	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1044		1438
1045	If you cannot run the fd in non-blocking mode (for example you should not	1439	If you cannot run the fd in non-blocking mode (for example you should
1046	play around with an Xlib connection), then you have to seperately re-test	1440	not play around with an Xlib connection), then you have to separately
1047	whether a file descriptor is really ready with a known-to-be good interface	1441	re-test whether a file descriptor is really ready with a known-to-be good
1048	such as poll (fortunately in our Xlib example, Xlib already does this on	1442	interface such as poll (fortunately in our Xlib example, Xlib already
1049	its own, so its quite safe to use).	1443	does this on its own, so its quite safe to use). Some people additionally
		1444	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1445	indefinitely.
		1446
		1447	But really, best use non-blocking mode.
1050		1448
1051	=head3 The special problem of disappearing file descriptors	1449	=head3 The special problem of disappearing file descriptors
1052		1450
1053	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1451	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1054	descriptor (either by calling C<close> explicitly or by any other means,	1452	descriptor (either due to calling C<close> explicitly or any other means,
1055	such as C<dup>). The reason is that you register interest in some file	1453	such as C<dup2>). The reason is that you register interest in some file
1056	descriptor, but when it goes away, the operating system will silently drop	1454	descriptor, but when it goes away, the operating system will silently drop
1057	this interest. If another file descriptor with the same number then is	1455	this interest. If another file descriptor with the same number then is
1058	registered with libev, there is no efficient way to see that this is, in	1456	registered with libev, there is no efficient way to see that this is, in
1059	fact, a different file descriptor.	1457	fact, a different file descriptor.
1060		1458
…		…
1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1489	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1092	C<EVBACKEND_POLL>.	1490	C<EVBACKEND_POLL>.
1093		1491
1094	=head3 The special problem of SIGPIPE	1492	=head3 The special problem of SIGPIPE
1095		1493
1096	While not really specific to libev, it is easy to forget about SIGPIPE:	1494	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1097	when reading from a pipe whose other end has been closed, your program	1495	when writing to a pipe whose other end has been closed, your program gets
1098	gets send a SIGPIPE, which, by default, aborts your program. For most	1496	sent a SIGPIPE, which, by default, aborts your program. For most programs
1099	programs this is sensible behaviour, for daemons, this is usually	1497	this is sensible behaviour, for daemons, this is usually undesirable.
1100	undesirable.
1101		1498
1102	So when you encounter spurious, unexplained daemon exits, make sure you	1499	So when you encounter spurious, unexplained daemon exits, make sure you
1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1500	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1104	somewhere, as that would have given you a big clue).	1501	somewhere, as that would have given you a big clue).
1105		1502
…		…
1111	=item ev_io_init (ev_io *, callback, int fd, int events)	1508	=item ev_io_init (ev_io *, callback, int fd, int events)
1112		1509
1113	=item ev_io_set (ev_io *, int fd, int events)	1510	=item ev_io_set (ev_io *, int fd, int events)
1114		1511
1115	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1512	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1116	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1513	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1117	C<EV_READ | EV_WRITE> to receive the given events.	1514	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1118		1515
1119	=item int fd [read-only]	1516	=item int fd [read-only]
1120		1517
1121	The file descriptor being watched.	1518	The file descriptor being watched.
1122		1519
…		…
1130		1527
1131	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1528	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1132	readable, but only once. Since it is likely line-buffered, you could	1529	readable, but only once. Since it is likely line-buffered, you could
1133	attempt to read a whole line in the callback.	1530	attempt to read a whole line in the callback.
1134		1531
1135	static void	1532	static void
1136	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1533	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1137	{	1534	{
1138	ev_io_stop (loop, w);	1535	ev_io_stop (loop, w);
1139	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1536	.. read from stdin here (or from w->fd) and handle any I/O errors
1140	}	1537	}
1141		1538
1142	...	1539	...
1143	struct ev_loop *loop = ev_default_init (0);	1540	struct ev_loop *loop = ev_default_init (0);
1144	struct ev_io stdin_readable;	1541	ev_io stdin_readable;
1145	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1542	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1146	ev_io_start (loop, &stdin_readable);	1543	ev_io_start (loop, &stdin_readable);
1147	ev_loop (loop, 0);	1544	ev_loop (loop, 0);
1148		1545
1149		1546
1150	=head2 C<ev_timer> - relative and optionally repeating timeouts	1547	=head2 C<ev_timer> - relative and optionally repeating timeouts
1151		1548
1152	Timer watchers are simple relative timers that generate an event after a	1549	Timer watchers are simple relative timers that generate an event after a
1153	given time, and optionally repeating in regular intervals after that.	1550	given time, and optionally repeating in regular intervals after that.
1154		1551
1155	The timers are based on real time, that is, if you register an event that	1552	The timers are based on real time, that is, if you register an event that
1156	times out after an hour and you reset your system clock to last years	1553	times out after an hour and you reset your system clock to January last
1157	time, it will still time out after (roughly) and hour. "Roughly" because	1554	year, it will still time out after (roughly) one hour. "Roughly" because
1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1159	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
		1557
		1558	The callback is guaranteed to be invoked only I<after> its timeout has
		1559	passed (not I<at>, so on systems with very low-resolution clocks this
		1560	might introduce a small delay). If multiple timers become ready during the
		1561	same loop iteration then the ones with earlier time-out values are invoked
		1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
		1564
		1565	=head3 Be smart about timeouts
		1566
		1567	Many real-world problems involve some kind of timeout, usually for error
		1568	recovery. A typical example is an HTTP request - if the other side hangs,
		1569	you want to raise some error after a while.
		1570
		1571	What follows are some ways to handle this problem, from obvious and
		1572	inefficient to smart and efficient.
		1573
		1574	In the following, a 60 second activity timeout is assumed - a timeout that
		1575	gets reset to 60 seconds each time there is activity (e.g. each time some
		1576	data or other life sign was received).
		1577
		1578	=over 4
		1579
		1580	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1581
		1582	This is the most obvious, but not the most simple way: In the beginning,
		1583	start the watcher:
		1584
		1585	ev_timer_init (timer, callback, 60., 0.);
		1586	ev_timer_start (loop, timer);
		1587
		1588	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1589	and start it again:
		1590
		1591	ev_timer_stop (loop, timer);
		1592	ev_timer_set (timer, 60., 0.);
		1593	ev_timer_start (loop, timer);
		1594
		1595	This is relatively simple to implement, but means that each time there is
		1596	some activity, libev will first have to remove the timer from its internal
		1597	data structure and then add it again. Libev tries to be fast, but it's
		1598	still not a constant-time operation.
		1599
		1600	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1601
		1602	This is the easiest way, and involves using C<ev_timer_again> instead of
		1603	C<ev_timer_start>.
		1604
		1605	To implement this, configure an C<ev_timer> with a C<repeat> value
		1606	of C<60> and then call C<ev_timer_again> at start and each time you
		1607	successfully read or write some data. If you go into an idle state where
		1608	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1609	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1610
		1611	That means you can ignore both the C<ev_timer_start> function and the
		1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1613	member and C<ev_timer_again>.
		1614
		1615	At start:
		1616
		1617	ev_init (timer, callback);
		1618	timer->repeat = 60.;
		1619	ev_timer_again (loop, timer);
		1620
		1621	Each time there is some activity:
		1622
		1623	ev_timer_again (loop, timer);
		1624
		1625	It is even possible to change the time-out on the fly, regardless of
		1626	whether the watcher is active or not:
		1627
		1628	timer->repeat = 30.;
		1629	ev_timer_again (loop, timer);
		1630
		1631	This is slightly more efficient then stopping/starting the timer each time
		1632	you want to modify its timeout value, as libev does not have to completely
		1633	remove and re-insert the timer from/into its internal data structure.
		1634
		1635	It is, however, even simpler than the "obvious" way to do it.
		1636
		1637	=item 3. Let the timer time out, but then re-arm it as required.
		1638
		1639	This method is more tricky, but usually most efficient: Most timeouts are
		1640	relatively long compared to the intervals between other activity - in
		1641	our example, within 60 seconds, there are usually many I/O events with
		1642	associated activity resets.
		1643
		1644	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1645	but remember the time of last activity, and check for a real timeout only
		1646	within the callback:
		1647
		1648	ev_tstamp last_activity; // time of last activity
		1649
		1650	static void
		1651	callback (EV_P_ ev_timer *w, int revents)
		1652	{
		1653	ev_tstamp now = ev_now (EV_A);
		1654	ev_tstamp timeout = last_activity + 60.;
		1655
		1656	// if last_activity + 60. is older than now, we did time out
		1657	if (timeout < now)
		1658	{
		1659	// timeout occured, take action
		1660	}
		1661	else
		1662	{
		1663	// callback was invoked, but there was some activity, re-arm
		1664	// the watcher to fire in last_activity + 60, which is
		1665	// guaranteed to be in the future, so "again" is positive:
		1666	w->repeat = timeout - now;
		1667	ev_timer_again (EV_A_ w);
		1668	}
		1669	}
		1670
		1671	To summarise the callback: first calculate the real timeout (defined
		1672	as "60 seconds after the last activity"), then check if that time has
		1673	been reached, which means something I<did>, in fact, time out. Otherwise
		1674	the callback was invoked too early (C<timeout> is in the future), so
		1675	re-schedule the timer to fire at that future time, to see if maybe we have
		1676	a timeout then.
		1677
		1678	Note how C<ev_timer_again> is used, taking advantage of the
		1679	C<ev_timer_again> optimisation when the timer is already running.
		1680
		1681	This scheme causes more callback invocations (about one every 60 seconds
		1682	minus half the average time between activity), but virtually no calls to
		1683	libev to change the timeout.
		1684
		1685	To start the timer, simply initialise the watcher and set C<last_activity>
		1686	to the current time (meaning we just have some activity :), then call the
		1687	callback, which will "do the right thing" and start the timer:
		1688
		1689	ev_init (timer, callback);
		1690	last_activity = ev_now (loop);
		1691	callback (loop, timer, EV_TIMEOUT);
		1692
		1693	And when there is some activity, simply store the current time in
		1694	C<last_activity>, no libev calls at all:
		1695
		1696	last_actiivty = ev_now (loop);
		1697
		1698	This technique is slightly more complex, but in most cases where the
		1699	time-out is unlikely to be triggered, much more efficient.
		1700
		1701	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1702	callback :) - just change the timeout and invoke the callback, which will
		1703	fix things for you.
		1704
		1705	=item 4. Wee, just use a double-linked list for your timeouts.
		1706
		1707	If there is not one request, but many thousands (millions...), all
		1708	employing some kind of timeout with the same timeout value, then one can
		1709	do even better:
		1710
		1711	When starting the timeout, calculate the timeout value and put the timeout
		1712	at the I<end> of the list.
		1713
		1714	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1715	the list is expected to fire (for example, using the technique #3).
		1716
		1717	When there is some activity, remove the timer from the list, recalculate
		1718	the timeout, append it to the end of the list again, and make sure to
		1719	update the C<ev_timer> if it was taken from the beginning of the list.
		1720
		1721	This way, one can manage an unlimited number of timeouts in O(1) time for
		1722	starting, stopping and updating the timers, at the expense of a major
		1723	complication, and having to use a constant timeout. The constant timeout
		1724	ensures that the list stays sorted.
		1725
		1726	=back
		1727
		1728	So which method the best?
		1729
		1730	Method #2 is a simple no-brain-required solution that is adequate in most
		1731	situations. Method #3 requires a bit more thinking, but handles many cases
		1732	better, and isn't very complicated either. In most case, choosing either
		1733	one is fine, with #3 being better in typical situations.
		1734
		1735	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1736	rather complicated, but extremely efficient, something that really pays
		1737	off after the first million or so of active timers, i.e. it's usually
		1738	overkill :)
		1739
		1740	=head3 The special problem of time updates
		1741
		1742	Establishing the current time is a costly operation (it usually takes at
		1743	least two system calls): EV therefore updates its idea of the current
		1744	time only before and after C<ev_loop> collects new events, which causes a
		1745	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1746	lots of events in one iteration.
1160		1747
1161	The relative timeouts are calculated relative to the C<ev_now ()>	1748	The relative timeouts are calculated relative to the C<ev_now ()>
1162	time. This is usually the right thing as this timestamp refers to the time	1749	time. This is usually the right thing as this timestamp refers to the time
1163	of the event triggering whatever timeout you are modifying/starting. If	1750	of the event triggering whatever timeout you are modifying/starting. If
1164	you suspect event processing to be delayed and you I<need> to base the timeout	1751	you suspect event processing to be delayed and you I<need> to base the
1165	on the current time, use something like this to adjust for this:	1752	timeout on the current time, use something like this to adjust for this:
1166		1753
1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1754	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1168		1755
1169	The callback is guarenteed to be invoked only when its timeout has passed,	1756	If the event loop is suspended for a long time, you can also force an
1170	but if multiple timers become ready during the same loop iteration then	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1171	order of execution is undefined.	1758	()>.
1172		1759
1173	=head3 Watcher-Specific Functions and Data Members	1760	=head3 Watcher-Specific Functions and Data Members
1174		1761
1175	=over 4	1762	=over 4
1176		1763
1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1764	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1178		1765
1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1766	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1180		1767
1181	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1768	Configure the timer to trigger after C<after> seconds. If C<repeat>
1182	C<0.>, then it will automatically be stopped. If it is positive, then the	1769	is C<0.>, then it will automatically be stopped once the timeout is
1183	timer will automatically be configured to trigger again C<repeat> seconds	1770	reached. If it is positive, then the timer will automatically be
1184	later, again, and again, until stopped manually.	1771	configured to trigger again C<repeat> seconds later, again, and again,
		1772	until stopped manually.
1185		1773
1186	The timer itself will do a best-effort at avoiding drift, that is, if you	1774	The timer itself will do a best-effort at avoiding drift, that is, if
1187	configure a timer to trigger every 10 seconds, then it will trigger at	1775	you configure a timer to trigger every 10 seconds, then it will normally
1188	exactly 10 second intervals. If, however, your program cannot keep up with	1776	trigger at exactly 10 second intervals. If, however, your program cannot
1189	the timer (because it takes longer than those 10 seconds to do stuff) the	1777	keep up with the timer (because it takes longer than those 10 seconds to
1190	timer will not fire more than once per event loop iteration.	1778	do stuff) the timer will not fire more than once per event loop iteration.
1191		1779
1192	=item ev_timer_again (loop, ev_timer *)	1780	=item ev_timer_again (loop, ev_timer *)
1193		1781
1194	This will act as if the timer timed out and restart it again if it is	1782	This will act as if the timer timed out and restart it again if it is
1195	repeating. The exact semantics are:	1783	repeating. The exact semantics are:
1196		1784
1197	If the timer is pending, its pending status is cleared.	1785	If the timer is pending, its pending status is cleared.
1198		1786
1199	If the timer is started but nonrepeating, stop it (as if it timed out).	1787	If the timer is started but non-repeating, stop it (as if it timed out).
1200		1788
1201	If the timer is repeating, either start it if necessary (with the	1789	If the timer is repeating, either start it if necessary (with the
1202	C<repeat> value), or reset the running timer to the C<repeat> value.	1790	C<repeat> value), or reset the running timer to the C<repeat> value.
1203		1791
1204	This sounds a bit complicated, but here is a useful and typical	1792	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1205	example: Imagine you have a tcp connection and you want a so-called idle	1793	usage example.
1206	timeout, that is, you want to be called when there have been, say, 60
1207	seconds of inactivity on the socket. The easiest way to do this is to
1208	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1209	C<ev_timer_again> each time you successfully read or write some data. If
1210	you go into an idle state where you do not expect data to travel on the
1211	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1212	automatically restart it if need be.
1213
1214	That means you can ignore the C<after> value and C<ev_timer_start>
1215	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1216
1217	ev_timer_init (timer, callback, 0., 5.);
1218	ev_timer_again (loop, timer);
1219	...
1220	timer->again = 17.;
1221	ev_timer_again (loop, timer);
1222	...
1223	timer->again = 10.;
1224	ev_timer_again (loop, timer);
1225
1226	This is more slightly efficient then stopping/starting the timer each time
1227	you want to modify its timeout value.
1228		1794
1229	=item ev_tstamp repeat [read-write]	1795	=item ev_tstamp repeat [read-write]
1230		1796
1231	The current C<repeat> value. Will be used each time the watcher times out	1797	The current C<repeat> value. Will be used each time the watcher times out
1232	or C<ev_timer_again> is called and determines the next timeout (if any),	1798	or C<ev_timer_again> is called, and determines the next timeout (if any),
1233	which is also when any modifications are taken into account.	1799	which is also when any modifications are taken into account.
1234		1800
1235	=back	1801	=back
1236		1802
1237	=head3 Examples	1803	=head3 Examples
1238		1804
1239	Example: Create a timer that fires after 60 seconds.	1805	Example: Create a timer that fires after 60 seconds.
1240		1806
1241	static void	1807	static void
1242	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1808	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1243	{	1809	{
1244	.. one minute over, w is actually stopped right here	1810	.. one minute over, w is actually stopped right here
1245	}	1811	}
1246		1812
1247	struct ev_timer mytimer;	1813	ev_timer mytimer;
1248	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1814	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1249	ev_timer_start (loop, &mytimer);	1815	ev_timer_start (loop, &mytimer);
1250		1816
1251	Example: Create a timeout timer that times out after 10 seconds of	1817	Example: Create a timeout timer that times out after 10 seconds of
1252	inactivity.	1818	inactivity.
1253		1819
1254	static void	1820	static void
1255	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1821	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1256	{	1822	{
1257	.. ten seconds without any activity	1823	.. ten seconds without any activity
1258	}	1824	}
1259		1825
1260	struct ev_timer mytimer;	1826	ev_timer mytimer;
1261	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1827	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1262	ev_timer_again (&mytimer); /* start timer */	1828	ev_timer_again (&mytimer); /* start timer */
1263	ev_loop (loop, 0);	1829	ev_loop (loop, 0);
1264		1830
1265	// and in some piece of code that gets executed on any "activity":	1831	// and in some piece of code that gets executed on any "activity":
1266	// reset the timeout to start ticking again at 10 seconds	1832	// reset the timeout to start ticking again at 10 seconds
1267	ev_timer_again (&mytimer);	1833	ev_timer_again (&mytimer);
1268		1834
1269		1835
1270	=head2 C<ev_periodic> - to cron or not to cron?	1836	=head2 C<ev_periodic> - to cron or not to cron?
1271		1837
1272	Periodic watchers are also timers of a kind, but they are very versatile	1838	Periodic watchers are also timers of a kind, but they are very versatile
1273	(and unfortunately a bit complex).	1839	(and unfortunately a bit complex).
1274		1840
1275	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1841	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1276	but on wallclock time (absolute time). You can tell a periodic watcher	1842	relative time, the physical time that passes) but on wall clock time
1277	to trigger "at" some specific point in time. For example, if you tell a	1843	(absolute time, the thing you can read on your calender or clock). The
1278	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1844	difference is that wall clock time can run faster or slower than real
1279	+ 10.>) and then reset your system clock to the last year, then it will	1845	time, and time jumps are not uncommon (e.g. when you adjust your
1280	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1846	wrist-watch).
1281	roughly 10 seconds later).
1282		1847
1283	They can also be used to implement vastly more complex timers, such as	1848	You can tell a periodic watcher to trigger after some specific point
1284	triggering an event on each midnight, local time or other, complicated,	1849	in time: for example, if you tell a periodic watcher to trigger "in 10
1285	rules.	1850	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1851	not a delay) and then reset your system clock to January of the previous
		1852	year, then it will take a year or more to trigger the event (unlike an
		1853	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1854	it, as it uses a relative timeout).
1286		1855
		1856	C<ev_periodic> watchers can also be used to implement vastly more complex
		1857	timers, such as triggering an event on each "midnight, local time", or
		1858	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1859	those cannot react to time jumps.
		1860
1287	As with timers, the callback is guarenteed to be invoked only when the	1861	As with timers, the callback is guaranteed to be invoked only when the
1288	time (C<at>) has been passed, but if multiple periodic timers become ready	1862	point in time where it is supposed to trigger has passed. If multiple
1289	during the same loop iteration then order of execution is undefined.	1863	timers become ready during the same loop iteration then the ones with
		1864	earlier time-out values are invoked before ones with later time-out values
		1865	(but this is no longer true when a callback calls C<ev_loop> recursively).
1290		1866
1291	=head3 Watcher-Specific Functions and Data Members	1867	=head3 Watcher-Specific Functions and Data Members
1292		1868
1293	=over 4	1869	=over 4
1294		1870
1295	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1871	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1296		1872
1297	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1873	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1298		1874
1299	Lots of arguments, lets sort it out... There are basically three modes of	1875	Lots of arguments, let's sort it out... There are basically three modes of
1300	operation, and we will explain them from simplest to complex:	1876	operation, and we will explain them from simplest to most complex:
1301		1877
1302	=over 4	1878	=over 4
1303		1879
1304	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1880	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1305		1881
1306	In this configuration the watcher triggers an event at the wallclock time	1882	In this configuration the watcher triggers an event after the wall clock
1307	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1883	time C<offset> has passed. It will not repeat and will not adjust when a
1308	that is, if it is to be run at January 1st 2011 then it will run when the	1884	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1309	system time reaches or surpasses this time.	1885	will be stopped and invoked when the system clock reaches or surpasses
		1886	this point in time.
1310		1887
1311	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1888	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1312		1889
1313	In this mode the watcher will always be scheduled to time out at the next	1890	In this mode the watcher will always be scheduled to time out at the next
1314	C<at + N * interval> time (for some integer N, which can also be negative)	1891	C<offset + N * interval> time (for some integer N, which can also be
1315	and then repeat, regardless of any time jumps.	1892	negative) and then repeat, regardless of any time jumps. The C<offset>
		1893	argument is merely an offset into the C<interval> periods.
1316		1894
1317	This can be used to create timers that do not drift with respect to system	1895	This can be used to create timers that do not drift with respect to the
1318	time:	1896	system clock, for example, here is an C<ev_periodic> that triggers each
		1897	hour, on the hour (with respect to UTC):
1319		1898
1320	ev_periodic_set (&periodic, 0., 3600., 0);	1899	ev_periodic_set (&periodic, 0., 3600., 0);
1321		1900
1322	This doesn't mean there will always be 3600 seconds in between triggers,	1901	This doesn't mean there will always be 3600 seconds in between triggers,
1323	but only that the the callback will be called when the system time shows a	1902	but only that the callback will be called when the system time shows a
1324	full hour (UTC), or more correctly, when the system time is evenly divisible	1903	full hour (UTC), or more correctly, when the system time is evenly divisible
1325	by 3600.	1904	by 3600.
1326		1905
1327	Another way to think about it (for the mathematically inclined) is that	1906	Another way to think about it (for the mathematically inclined) is that
1328	C<ev_periodic> will try to run the callback in this mode at the next possible	1907	C<ev_periodic> will try to run the callback in this mode at the next possible
1329	time where C<time = at (mod interval)>, regardless of any time jumps.	1908	time where C<time = offset (mod interval)>, regardless of any time jumps.
1330		1909
1331	For numerical stability it is preferable that the C<at> value is near	1910	For numerical stability it is preferable that the C<offset> value is near
1332	C<ev_now ()> (the current time), but there is no range requirement for	1911	C<ev_now ()> (the current time), but there is no range requirement for
1333	this value.	1912	this value, and in fact is often specified as zero.
1334		1913
		1914	Note also that there is an upper limit to how often a timer can fire (CPU
		1915	speed for example), so if C<interval> is very small then timing stability
		1916	will of course deteriorate. Libev itself tries to be exact to be about one
		1917	millisecond (if the OS supports it and the machine is fast enough).
		1918
1335	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1919	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1336		1920
1337	In this mode the values for C<interval> and C<at> are both being	1921	In this mode the values for C<interval> and C<offset> are both being
1338	ignored. Instead, each time the periodic watcher gets scheduled, the	1922	ignored. Instead, each time the periodic watcher gets scheduled, the
1339	reschedule callback will be called with the watcher as first, and the	1923	reschedule callback will be called with the watcher as first, and the
1340	current time as second argument.	1924	current time as second argument.
1341		1925
1342	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1926	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1343	ever, or make any event loop modifications>. If you need to stop it,	1927	or make ANY other event loop modifications whatsoever, unless explicitly
1344	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1928	allowed by documentation here>.
1345	starting an C<ev_prepare> watcher, which is legal).
1346		1929
		1930	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1931	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1932	only event loop modification you are allowed to do).
		1933
1347	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1934	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1348	ev_tstamp now)>, e.g.:	1935	*w, ev_tstamp now)>, e.g.:
1349		1936
		1937	static ev_tstamp
1350	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1938	my_rescheduler (ev_periodic *w, ev_tstamp now)
1351	{	1939	{
1352	return now + 60.;	1940	return now + 60.;
1353	}	1941	}
1354		1942
1355	It must return the next time to trigger, based on the passed time value	1943	It must return the next time to trigger, based on the passed time value
1356	(that is, the lowest time value larger than to the second argument). It	1944	(that is, the lowest time value larger than to the second argument). It
1357	will usually be called just before the callback will be triggered, but	1945	will usually be called just before the callback will be triggered, but
1358	might be called at other times, too.	1946	might be called at other times, too.
1359		1947
1360	NOTE: I<< This callback must always return a time that is later than the	1948	NOTE: I<< This callback must always return a time that is higher than or
1361	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1949	equal to the passed C<now> value >>.
1362		1950
1363	This can be used to create very complex timers, such as a timer that	1951	This can be used to create very complex timers, such as a timer that
1364	triggers on each midnight, local time. To do this, you would calculate the	1952	triggers on "next midnight, local time". To do this, you would calculate the
1365	next midnight after C<now> and return the timestamp value for this. How	1953	next midnight after C<now> and return the timestamp value for this. How
1366	you do this is, again, up to you (but it is not trivial, which is the main	1954	you do this is, again, up to you (but it is not trivial, which is the main
1367	reason I omitted it as an example).	1955	reason I omitted it as an example).
1368		1956
1369	=back	1957	=back
…		…
1373	Simply stops and restarts the periodic watcher again. This is only useful	1961	Simply stops and restarts the periodic watcher again. This is only useful
1374	when you changed some parameters or the reschedule callback would return	1962	when you changed some parameters or the reschedule callback would return
1375	a different time than the last time it was called (e.g. in a crond like	1963	a different time than the last time it was called (e.g. in a crond like
1376	program when the crontabs have changed).	1964	program when the crontabs have changed).
1377		1965
		1966	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1967
		1968	When active, returns the absolute time that the watcher is supposed
		1969	to trigger next. This is not the same as the C<offset> argument to
		1970	C<ev_periodic_set>, but indeed works even in interval and manual
		1971	rescheduling modes.
		1972
1378	=item ev_tstamp offset [read-write]	1973	=item ev_tstamp offset [read-write]
1379		1974
1380	When repeating, this contains the offset value, otherwise this is the	1975	When repeating, this contains the offset value, otherwise this is the
1381	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1976	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1977	although libev might modify this value for better numerical stability).
1382		1978
1383	Can be modified any time, but changes only take effect when the periodic	1979	Can be modified any time, but changes only take effect when the periodic
1384	timer fires or C<ev_periodic_again> is being called.	1980	timer fires or C<ev_periodic_again> is being called.
1385		1981
1386	=item ev_tstamp interval [read-write]	1982	=item ev_tstamp interval [read-write]
1387		1983
1388	The current interval value. Can be modified any time, but changes only	1984	The current interval value. Can be modified any time, but changes only
1389	take effect when the periodic timer fires or C<ev_periodic_again> is being	1985	take effect when the periodic timer fires or C<ev_periodic_again> is being
1390	called.	1986	called.
1391		1987
1392	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1988	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1393		1989
1394	The current reschedule callback, or C<0>, if this functionality is	1990	The current reschedule callback, or C<0>, if this functionality is
1395	switched off. Can be changed any time, but changes only take effect when	1991	switched off. Can be changed any time, but changes only take effect when
1396	the periodic timer fires or C<ev_periodic_again> is being called.	1992	the periodic timer fires or C<ev_periodic_again> is being called.
1397		1993
1398	=item ev_tstamp at [read-only]
1399
1400	When active, contains the absolute time that the watcher is supposed to
1401	trigger next.
1402
1403	=back	1994	=back
1404		1995
1405	=head3 Examples	1996	=head3 Examples
1406		1997
1407	Example: Call a callback every hour, or, more precisely, whenever the	1998	Example: Call a callback every hour, or, more precisely, whenever the
1408	system clock is divisible by 3600. The callback invocation times have	1999	system time is divisible by 3600. The callback invocation times have
1409	potentially a lot of jittering, but good long-term stability.	2000	potentially a lot of jitter, but good long-term stability.
1410		2001
1411	static void	2002	static void
1412	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2003	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1413	{	2004	{
1414	... its now a full hour (UTC, or TAI or whatever your clock follows)	2005	... its now a full hour (UTC, or TAI or whatever your clock follows)
1415	}	2006	}
1416		2007
1417	struct ev_periodic hourly_tick;	2008	ev_periodic hourly_tick;
1418	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2009	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1419	ev_periodic_start (loop, &hourly_tick);	2010	ev_periodic_start (loop, &hourly_tick);
1420		2011
1421	Example: The same as above, but use a reschedule callback to do it:	2012	Example: The same as above, but use a reschedule callback to do it:
1422		2013
1423	#include <math.h>	2014	#include <math.h>
1424		2015
1425	static ev_tstamp	2016	static ev_tstamp
1426	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2017	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1427	{	2018	{
1428	return fmod (now, 3600.) + 3600.;	2019	return now + (3600. - fmod (now, 3600.));
1429	}	2020	}
1430		2021
1431	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2022	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1432		2023
1433	Example: Call a callback every hour, starting now:	2024	Example: Call a callback every hour, starting now:
1434		2025
1435	struct ev_periodic hourly_tick;	2026	ev_periodic hourly_tick;
1436	ev_periodic_init (&hourly_tick, clock_cb,	2027	ev_periodic_init (&hourly_tick, clock_cb,
1437	fmod (ev_now (loop), 3600.), 3600., 0);	2028	fmod (ev_now (loop), 3600.), 3600., 0);
1438	ev_periodic_start (loop, &hourly_tick);	2029	ev_periodic_start (loop, &hourly_tick);
1439		2030
1440		2031
1441	=head2 C<ev_signal> - signal me when a signal gets signalled!	2032	=head2 C<ev_signal> - signal me when a signal gets signalled!
1442		2033
1443	Signal watchers will trigger an event when the process receives a specific	2034	Signal watchers will trigger an event when the process receives a specific
1444	signal one or more times. Even though signals are very asynchronous, libev	2035	signal one or more times. Even though signals are very asynchronous, libev
1445	will try it's best to deliver signals synchronously, i.e. as part of the	2036	will try it's best to deliver signals synchronously, i.e. as part of the
1446	normal event processing, like any other event.	2037	normal event processing, like any other event.
1447		2038
		2039	If you want signals asynchronously, just use C<sigaction> as you would
		2040	do without libev and forget about sharing the signal. You can even use
		2041	C<ev_async> from a signal handler to synchronously wake up an event loop.
		2042
1448	You can configure as many watchers as you like per signal. Only when the	2043	You can configure as many watchers as you like per signal. Only when the
1449	first watcher gets started will libev actually register a signal watcher	2044	first watcher gets started will libev actually register a signal handler
1450	with the kernel (thus it coexists with your own signal handlers as long	2045	with the kernel (thus it coexists with your own signal handlers as long as
1451	as you don't register any with libev). Similarly, when the last signal	2046	you don't register any with libev for the same signal). Similarly, when
1452	watcher for a signal is stopped libev will reset the signal handler to	2047	the last signal watcher for a signal is stopped, libev will reset the
1453	SIG_DFL (regardless of what it was set to before).	2048	signal handler to SIG_DFL (regardless of what it was set to before).
1454		2049
1455	If possible and supported, libev will install its handlers with	2050	If possible and supported, libev will install its handlers with
1456	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2051	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
1457	interrupted. If you have a problem with syscalls getting interrupted by	2052	interrupted. If you have a problem with system calls getting interrupted by
1458	signals you can block all signals in an C<ev_check> watcher and unblock	2053	signals you can block all signals in an C<ev_check> watcher and unblock
1459	them in an C<ev_prepare> watcher.	2054	them in an C<ev_prepare> watcher.
1460		2055
1461	=head3 Watcher-Specific Functions and Data Members	2056	=head3 Watcher-Specific Functions and Data Members
1462		2057
…		…
1475		2070
1476	=back	2071	=back
1477		2072
1478	=head3 Examples	2073	=head3 Examples
1479		2074
1480	Example: Try to exit cleanly on SIGINT and SIGTERM.	2075	Example: Try to exit cleanly on SIGINT.
1481		2076
1482	static void	2077	static void
1483	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2078	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1484	{	2079	{
1485	ev_unloop (loop, EVUNLOOP_ALL);	2080	ev_unloop (loop, EVUNLOOP_ALL);
1486	}	2081	}
1487		2082
1488	struct ev_signal signal_watcher;	2083	ev_signal signal_watcher;
1489	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2084	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1490	ev_signal_start (loop, &sigint_cb);	2085	ev_signal_start (loop, &signal_watcher);
1491		2086
1492		2087
1493	=head2 C<ev_child> - watch out for process status changes	2088	=head2 C<ev_child> - watch out for process status changes
1494		2089
1495	Child watchers trigger when your process receives a SIGCHLD in response to	2090	Child watchers trigger when your process receives a SIGCHLD in response to
1496	some child status changes (most typically when a child of yours dies). It	2091	some child status changes (most typically when a child of yours dies or
1497	is permissible to install a child watcher I<after> the child has been	2092	exits). It is permissible to install a child watcher I<after> the child
1498	forked (which implies it might have already exited), as long as the event	2093	has been forked (which implies it might have already exited), as long
1499	loop isn't entered (or is continued from a watcher).	2094	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2095	forking and then immediately registering a watcher for the child is fine,
		2096	but forking and registering a watcher a few event loop iterations later or
		2097	in the next callback invocation is not.
1500		2098
1501	Only the default event loop is capable of handling signals, and therefore	2099	Only the default event loop is capable of handling signals, and therefore
1502	you can only rgeister child watchers in the default event loop.	2100	you can only register child watchers in the default event loop.
		2101
		2102	Due to some design glitches inside libev, child watchers will always be
		2103	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2104	libev)
1503		2105
1504	=head3 Process Interaction	2106	=head3 Process Interaction
1505		2107
1506	Libev grabs C<SIGCHLD> as soon as the default event loop is	2108	Libev grabs C<SIGCHLD> as soon as the default event loop is
1507	initialised. This is necessary to guarantee proper behaviour even if	2109	initialised. This is necessary to guarantee proper behaviour even if
1508	the first child watcher is started after the child exits. The occurance	2110	the first child watcher is started after the child exits. The occurrence
1509	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2111	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1510	synchronously as part of the event loop processing. Libev always reaps all	2112	synchronously as part of the event loop processing. Libev always reaps all
1511	children, even ones not watched.	2113	children, even ones not watched.
1512		2114
1513	=head3 Overriding the Built-In Processing	2115	=head3 Overriding the Built-In Processing
…		…
1517	handler, you can override it easily by installing your own handler for	2119	handler, you can override it easily by installing your own handler for
1518	C<SIGCHLD> after initialising the default loop, and making sure the	2120	C<SIGCHLD> after initialising the default loop, and making sure the
1519	default loop never gets destroyed. You are encouraged, however, to use an	2121	default loop never gets destroyed. You are encouraged, however, to use an
1520	event-based approach to child reaping and thus use libev's support for	2122	event-based approach to child reaping and thus use libev's support for
1521	that, so other libev users can use C<ev_child> watchers freely.	2123	that, so other libev users can use C<ev_child> watchers freely.
		2124
		2125	=head3 Stopping the Child Watcher
		2126
		2127	Currently, the child watcher never gets stopped, even when the
		2128	child terminates, so normally one needs to stop the watcher in the
		2129	callback. Future versions of libev might stop the watcher automatically
		2130	when a child exit is detected.
1522		2131
1523	=head3 Watcher-Specific Functions and Data Members	2132	=head3 Watcher-Specific Functions and Data Members
1524		2133
1525	=over 4	2134	=over 4
1526		2135
…		…
1555	=head3 Examples	2164	=head3 Examples
1556		2165
1557	Example: C<fork()> a new process and install a child handler to wait for	2166	Example: C<fork()> a new process and install a child handler to wait for
1558	its completion.	2167	its completion.
1559		2168
1560	ev_child cw;	2169	ev_child cw;
1561		2170
1562	static void	2171	static void
1563	child_cb (EV_P_ struct ev_child *w, int revents)	2172	child_cb (EV_P_ ev_child *w, int revents)
1564	{	2173	{
1565	ev_child_stop (EV_A_ w);	2174	ev_child_stop (EV_A_ w);
1566	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2175	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1567	}	2176	}
1568		2177
1569	pid_t pid = fork ();	2178	pid_t pid = fork ();
1570		2179
1571	if (pid < 0)	2180	if (pid < 0)
1572	// error	2181	// error
1573	else if (pid == 0)	2182	else if (pid == 0)
1574	{	2183	{
1575	// the forked child executes here	2184	// the forked child executes here
1576	exit (1);	2185	exit (1);
1577	}	2186	}
1578	else	2187	else
1579	{	2188	{
1580	ev_child_init (&cw, child_cb, pid, 0);	2189	ev_child_init (&cw, child_cb, pid, 0);
1581	ev_child_start (EV_DEFAULT_ &cw);	2190	ev_child_start (EV_DEFAULT_ &cw);
1582	}	2191	}
1583		2192
1584		2193
1585	=head2 C<ev_stat> - did the file attributes just change?	2194	=head2 C<ev_stat> - did the file attributes just change?
1586		2195
1587	This watches a filesystem path for attribute changes. That is, it calls	2196	This watches a file system path for attribute changes. That is, it calls
1588	C<stat> regularly (or when the OS says it changed) and sees if it changed	2197	C<stat> on that path in regular intervals (or when the OS says it changed)
1589	compared to the last time, invoking the callback if it did.	2198	and sees if it changed compared to the last time, invoking the callback if
		2199	it did.
1590		2200
1591	The path does not need to exist: changing from "path exists" to "path does	2201	The path does not need to exist: changing from "path exists" to "path does
1592	not exist" is a status change like any other. The condition "path does	2202	not exist" is a status change like any other. The condition "path does not
1593	not exist" is signified by the C<st_nlink> field being zero (which is	2203	exist" (or more correctly "path cannot be stat'ed") is signified by the
1594	otherwise always forced to be at least one) and all the other fields of	2204	C<st_nlink> field being zero (which is otherwise always forced to be at
1595	the stat buffer having unspecified contents.	2205	least one) and all the other fields of the stat buffer having unspecified
		2206	contents.
1596		2207
1597	The path I<should> be absolute and I<must not> end in a slash. If it is	2208	The path I<must not> end in a slash or contain special components such as
		2209	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1598	relative and your working directory changes, the behaviour is undefined.	2210	your working directory changes, then the behaviour is undefined.
1599		2211
1600	Since there is no standard to do this, the portable implementation simply	2212	Since there is no portable change notification interface available, the
1601	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2213	portable implementation simply calls C<stat(2)> regularly on the path
1602	can specify a recommended polling interval for this case. If you specify	2214	to see if it changed somehow. You can specify a recommended polling
1603	a polling interval of C<0> (highly recommended!) then a I<suitable,	2215	interval for this case. If you specify a polling interval of C<0> (highly
1604	unspecified default> value will be used (which you can expect to be around	2216	recommended!) then a I<suitable, unspecified default> value will be used
1605	five seconds, although this might change dynamically). Libev will also	2217	(which you can expect to be around five seconds, although this might
1606	impose a minimum interval which is currently around C<0.1>, but thats	2218	change dynamically). Libev will also impose a minimum interval which is
1607	usually overkill.	2219	currently around C<0.1>, but that's usually overkill.
1608		2220
1609	This watcher type is not meant for massive numbers of stat watchers,	2221	This watcher type is not meant for massive numbers of stat watchers,
1610	as even with OS-supported change notifications, this can be	2222	as even with OS-supported change notifications, this can be
1611	resource-intensive.	2223	resource-intensive.
1612		2224
1613	At the time of this writing, only the Linux inotify interface is	2225	At the time of this writing, the only OS-specific interface implemented
1614	implemented (implementing kqueue support is left as an exercise for the	2226	is the Linux inotify interface (implementing kqueue support is left as an
1615	reader). Inotify will be used to give hints only and should not change the	2227	exercise for the reader. Note, however, that the author sees no way of
1616	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2228	implementing C<ev_stat> semantics with kqueue, except as a hint).
1617	to fall back to regular polling again even with inotify, but changes are
1618	usually detected immediately, and if the file exists there will be no
1619	polling.
1620		2229
1621	=head3 ABI Issues (Largefile Support)	2230	=head3 ABI Issues (Largefile Support)
1622		2231
1623	Libev by default (unless the user overrides this) uses the default	2232	Libev by default (unless the user overrides this) uses the default
1624	compilation environment, which means that on systems with optionally	2233	compilation environment, which means that on systems with large file
1625	disabled large file support, you get the 32 bit version of the stat	2234	support disabled by default, you get the 32 bit version of the stat
1626	structure. When using the library from programs that change the ABI to	2235	structure. When using the library from programs that change the ABI to
1627	use 64 bit file offsets the programs will fail. In that case you have to	2236	use 64 bit file offsets the programs will fail. In that case you have to
1628	compile libev with the same flags to get binary compatibility. This is	2237	compile libev with the same flags to get binary compatibility. This is
1629	obviously the case with any flags that change the ABI, but the problem is	2238	obviously the case with any flags that change the ABI, but the problem is
1630	most noticably with ev_stat and largefile support.	2239	most noticeably displayed with ev_stat and large file support.
1631		2240
1632	=head3 Inotify	2241	The solution for this is to lobby your distribution maker to make large
		2242	file interfaces available by default (as e.g. FreeBSD does) and not
		2243	optional. Libev cannot simply switch on large file support because it has
		2244	to exchange stat structures with application programs compiled using the
		2245	default compilation environment.
1633		2246
		2247	=head3 Inotify and Kqueue
		2248
1634	When C<inotify (7)> support has been compiled into libev (generally only	2249	When C<inotify (7)> support has been compiled into libev and present at
1635	available on Linux) and present at runtime, it will be used to speed up	2250	runtime, it will be used to speed up change detection where possible. The
1636	change detection where possible. The inotify descriptor will be created lazily	2251	inotify descriptor will be created lazily when the first C<ev_stat>
1637	when the first C<ev_stat> watcher is being started.	2252	watcher is being started.
1638		2253
1639	Inotify presence does not change the semantics of C<ev_stat> watchers	2254	Inotify presence does not change the semantics of C<ev_stat> watchers
1640	except that changes might be detected earlier, and in some cases, to avoid	2255	except that changes might be detected earlier, and in some cases, to avoid
1641	making regular C<stat> calls. Even in the presence of inotify support	2256	making regular C<stat> calls. Even in the presence of inotify support
1642	there are many cases where libev has to resort to regular C<stat> polling.	2257	there are many cases where libev has to resort to regular C<stat> polling,
		2258	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2259	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2260	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2261	xfs are fully working) libev usually gets away without polling.
1643		2262
1644	(There is no support for kqueue, as apparently it cannot be used to	2263	There is no support for kqueue, as apparently it cannot be used to
1645	implement this functionality, due to the requirement of having a file	2264	implement this functionality, due to the requirement of having a file
1646	descriptor open on the object at all times).	2265	descriptor open on the object at all times, and detecting renames, unlinks
		2266	etc. is difficult.
		2267
		2268	=head3 C<stat ()> is a synchronous operation
		2269
		2270	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2271	the process. The exception are C<ev_stat> watchers - those call C<stat
		2272	()>, which is a synchronous operation.
		2273
		2274	For local paths, this usually doesn't matter: unless the system is very
		2275	busy or the intervals between stat's are large, a stat call will be fast,
		2276	as the path data is usually in memory already (except when starting the
		2277	watcher).
		2278
		2279	For networked file systems, calling C<stat ()> can block an indefinite
		2280	time due to network issues, and even under good conditions, a stat call
		2281	often takes multiple milliseconds.
		2282
		2283	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2284	paths, although this is fully supported by libev.
1647		2285
1648	=head3 The special problem of stat time resolution	2286	=head3 The special problem of stat time resolution
1649		2287
1650	The C<stat ()> syscall only supports full-second resolution portably, and	2288	The C<stat ()> system call only supports full-second resolution portably,
1651	even on systems where the resolution is higher, many filesystems still	2289	and even on systems where the resolution is higher, most file systems
1652	only support whole seconds.	2290	still only support whole seconds.
1653		2291
1654	That means that, if the time is the only thing that changes, you might	2292	That means that, if the time is the only thing that changes, you can
1655	miss updates: on the first update, C<ev_stat> detects a change and calls	2293	easily miss updates: on the first update, C<ev_stat> detects a change and
1656	your callback, which does something. When there is another update within	2294	calls your callback, which does something. When there is another update
1657	the same second, C<ev_stat> will be unable to detect it.	2295	within the same second, C<ev_stat> will be unable to detect unless the
		2296	stat data does change in other ways (e.g. file size).
1658		2297
1659	The solution to this is to delay acting on a change for a second (or till	2298	The solution to this is to delay acting on a change for slightly more
1660	the next second boundary), using a roughly one-second delay C<ev_timer>	2299	than a second (or till slightly after the next full second boundary), using
1661	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2300	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1662	is added to work around small timing inconsistencies of some operating	2301	ev_timer_again (loop, w)>).
1663	systems.	2302
		2303	The C<.02> offset is added to work around small timing inconsistencies
		2304	of some operating systems (where the second counter of the current time
		2305	might be be delayed. One such system is the Linux kernel, where a call to
		2306	C<gettimeofday> might return a timestamp with a full second later than
		2307	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2308	update file times then there will be a small window where the kernel uses
		2309	the previous second to update file times but libev might already execute
		2310	the timer callback).
1664		2311
1665	=head3 Watcher-Specific Functions and Data Members	2312	=head3 Watcher-Specific Functions and Data Members
1666		2313
1667	=over 4	2314	=over 4
1668		2315
…		…
1674	C<path>. The C<interval> is a hint on how quickly a change is expected to	2321	C<path>. The C<interval> is a hint on how quickly a change is expected to
1675	be detected and should normally be specified as C<0> to let libev choose	2322	be detected and should normally be specified as C<0> to let libev choose
1676	a suitable value. The memory pointed to by C<path> must point to the same	2323	a suitable value. The memory pointed to by C<path> must point to the same
1677	path for as long as the watcher is active.	2324	path for as long as the watcher is active.
1678		2325
1679	The callback will be receive C<EV_STAT> when a change was detected,	2326	The callback will receive an C<EV_STAT> event when a change was detected,
1680	relative to the attributes at the time the watcher was started (or the	2327	relative to the attributes at the time the watcher was started (or the
1681	last change was detected).	2328	last change was detected).
1682		2329
1683	=item ev_stat_stat (loop, ev_stat *)	2330	=item ev_stat_stat (loop, ev_stat *)
1684		2331
1685	Updates the stat buffer immediately with new values. If you change the	2332	Updates the stat buffer immediately with new values. If you change the
1686	watched path in your callback, you could call this fucntion to avoid	2333	watched path in your callback, you could call this function to avoid
1687	detecting this change (while introducing a race condition). Can also be	2334	detecting this change (while introducing a race condition if you are not
1688	useful simply to find out the new values.	2335	the only one changing the path). Can also be useful simply to find out the
		2336	new values.
1689		2337
1690	=item ev_statdata attr [read-only]	2338	=item ev_statdata attr [read-only]
1691		2339
1692	The most-recently detected attributes of the file. Although the type is of	2340	The most-recently detected attributes of the file. Although the type is
1693	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2341	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1694	suitable for your system. If the C<st_nlink> member is C<0>, then there	2342	suitable for your system, but you can only rely on the POSIX-standardised
		2343	members to be present. If the C<st_nlink> member is C<0>, then there was
1695	was some error while C<stat>ing the file.	2344	some error while C<stat>ing the file.
1696		2345
1697	=item ev_statdata prev [read-only]	2346	=item ev_statdata prev [read-only]
1698		2347
1699	The previous attributes of the file. The callback gets invoked whenever	2348	The previous attributes of the file. The callback gets invoked whenever
1700	C<prev> != C<attr>.	2349	C<prev> != C<attr>, or, more precisely, one or more of these members
		2350	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2351	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1701		2352
1702	=item ev_tstamp interval [read-only]	2353	=item ev_tstamp interval [read-only]
1703		2354
1704	The specified interval.	2355	The specified interval.
1705		2356
1706	=item const char *path [read-only]	2357	=item const char *path [read-only]
1707		2358
1708	The filesystem path that is being watched.	2359	The file system path that is being watched.
1709		2360
1710	=back	2361	=back
1711		2362
1712	=head3 Examples	2363	=head3 Examples
1713		2364
1714	Example: Watch C</etc/passwd> for attribute changes.	2365	Example: Watch C</etc/passwd> for attribute changes.
1715		2366
1716	static void	2367	static void
1717	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2368	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1718	{	2369	{
1719	/* /etc/passwd changed in some way */	2370	/* /etc/passwd changed in some way */
1720	if (w->attr.st_nlink)	2371	if (w->attr.st_nlink)
1721	{	2372	{
1722	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2373	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1723	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2374	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1724	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2375	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1725	}	2376	}
1726	else	2377	else
1727	/* you shalt not abuse printf for puts */	2378	/* you shalt not abuse printf for puts */
1728	puts ("wow, /etc/passwd is not there, expect problems. "	2379	puts ("wow, /etc/passwd is not there, expect problems. "
1729	"if this is windows, they already arrived\n");	2380	"if this is windows, they already arrived\n");
1730	}	2381	}
1731		2382
1732	...	2383	...
1733	ev_stat passwd;	2384	ev_stat passwd;
1734		2385
1735	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2386	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1736	ev_stat_start (loop, &passwd);	2387	ev_stat_start (loop, &passwd);
1737		2388
1738	Example: Like above, but additionally use a one-second delay so we do not	2389	Example: Like above, but additionally use a one-second delay so we do not
1739	miss updates (however, frequent updates will delay processing, too, so	2390	miss updates (however, frequent updates will delay processing, too, so
1740	one might do the work both on C<ev_stat> callback invocation I<and> on	2391	one might do the work both on C<ev_stat> callback invocation I<and> on
1741	C<ev_timer> callback invocation).	2392	C<ev_timer> callback invocation).
1742		2393
1743	static ev_stat passwd;	2394	static ev_stat passwd;
1744	static ev_timer timer;	2395	static ev_timer timer;
1745		2396
1746	static void	2397	static void
1747	timer_cb (EV_P_ ev_timer *w, int revents)	2398	timer_cb (EV_P_ ev_timer *w, int revents)
1748	{	2399	{
1749	ev_timer_stop (EV_A_ w);	2400	ev_timer_stop (EV_A_ w);
1750		2401
1751	/* now it's one second after the most recent passwd change */	2402	/* now it's one second after the most recent passwd change */
1752	}	2403	}
1753		2404
1754	static void	2405	static void
1755	stat_cb (EV_P_ ev_stat *w, int revents)	2406	stat_cb (EV_P_ ev_stat *w, int revents)
1756	{	2407	{
1757	/* reset the one-second timer */	2408	/* reset the one-second timer */
1758	ev_timer_again (EV_A_ &timer);	2409	ev_timer_again (EV_A_ &timer);
1759	}	2410	}
1760		2411
1761	...	2412	...
1762	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2413	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1763	ev_stat_start (loop, &passwd);	2414	ev_stat_start (loop, &passwd);
1764	ev_timer_init (&timer, timer_cb, 0., 1.01);	2415	ev_timer_init (&timer, timer_cb, 0., 1.02);
1765		2416
1766		2417
1767	=head2 C<ev_idle> - when you've got nothing better to do...	2418	=head2 C<ev_idle> - when you've got nothing better to do...
1768		2419
1769	Idle watchers trigger events when no other events of the same or higher	2420	Idle watchers trigger events when no other events of the same or higher
1770	priority are pending (prepare, check and other idle watchers do not	2421	priority are pending (prepare, check and other idle watchers do not count
1771	count).	2422	as receiving "events").
1772		2423
1773	That is, as long as your process is busy handling sockets or timeouts	2424	That is, as long as your process is busy handling sockets or timeouts
1774	(or even signals, imagine) of the same or higher priority it will not be	2425	(or even signals, imagine) of the same or higher priority it will not be
1775	triggered. But when your process is idle (or only lower-priority watchers	2426	triggered. But when your process is idle (or only lower-priority watchers
1776	are pending), the idle watchers are being called once per event loop	2427	are pending), the idle watchers are being called once per event loop
…		…
1787		2438
1788	=head3 Watcher-Specific Functions and Data Members	2439	=head3 Watcher-Specific Functions and Data Members
1789		2440
1790	=over 4	2441	=over 4
1791		2442
1792	=item ev_idle_init (ev_signal *, callback)	2443	=item ev_idle_init (ev_idle *, callback)
1793		2444
1794	Initialises and configures the idle watcher - it has no parameters of any	2445	Initialises and configures the idle watcher - it has no parameters of any
1795	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2446	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1796	believe me.	2447	believe me.
1797		2448
…		…
1800	=head3 Examples	2451	=head3 Examples
1801		2452
1802	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2453	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1803	callback, free it. Also, use no error checking, as usual.	2454	callback, free it. Also, use no error checking, as usual.
1804		2455
1805	static void	2456	static void
1806	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2457	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1807	{	2458	{
1808	free (w);	2459	free (w);
1809	// now do something you wanted to do when the program has	2460	// now do something you wanted to do when the program has
1810	// no longer anything immediate to do.	2461	// no longer anything immediate to do.
1811	}	2462	}
1812		2463
1813	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2464	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1814	ev_idle_init (idle_watcher, idle_cb);	2465	ev_idle_init (idle_watcher, idle_cb);
1815	ev_idle_start (loop, idle_cb);	2466	ev_idle_start (loop, idle_watcher);
1816		2467
1817		2468
1818	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2469	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1819		2470
1820	Prepare and check watchers are usually (but not always) used in tandem:	2471	Prepare and check watchers are usually (but not always) used in pairs:
1821	prepare watchers get invoked before the process blocks and check watchers	2472	prepare watchers get invoked before the process blocks and check watchers
1822	afterwards.	2473	afterwards.
1823		2474
1824	You I<must not> call C<ev_loop> or similar functions that enter	2475	You I<must not> call C<ev_loop> or similar functions that enter
1825	the current event loop from either C<ev_prepare> or C<ev_check>	2476	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1828	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2479	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1829	C<ev_check> so if you have one watcher of each kind they will always be	2480	C<ev_check> so if you have one watcher of each kind they will always be
1830	called in pairs bracketing the blocking call.	2481	called in pairs bracketing the blocking call.
1831		2482
1832	Their main purpose is to integrate other event mechanisms into libev and	2483	Their main purpose is to integrate other event mechanisms into libev and
1833	their use is somewhat advanced. This could be used, for example, to track	2484	their use is somewhat advanced. They could be used, for example, to track
1834	variable changes, implement your own watchers, integrate net-snmp or a	2485	variable changes, implement your own watchers, integrate net-snmp or a
1835	coroutine library and lots more. They are also occasionally useful if	2486	coroutine library and lots more. They are also occasionally useful if
1836	you cache some data and want to flush it before blocking (for example,	2487	you cache some data and want to flush it before blocking (for example,
1837	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2488	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1838	watcher).	2489	watcher).
1839		2490
1840	This is done by examining in each prepare call which file descriptors need	2491	This is done by examining in each prepare call which file descriptors
1841	to be watched by the other library, registering C<ev_io> watchers for	2492	need to be watched by the other library, registering C<ev_io> watchers
1842	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2493	for them and starting an C<ev_timer> watcher for any timeouts (many
1843	provide just this functionality). Then, in the check watcher you check for	2494	libraries provide exactly this functionality). Then, in the check watcher,
1844	any events that occured (by checking the pending status of all watchers	2495	you check for any events that occurred (by checking the pending status
1845	and stopping them) and call back into the library. The I/O and timer	2496	of all watchers and stopping them) and call back into the library. The
1846	callbacks will never actually be called (but must be valid nevertheless,	2497	I/O and timer callbacks will never actually be called (but must be valid
1847	because you never know, you know?).	2498	nevertheless, because you never know, you know?).
1848		2499
1849	As another example, the Perl Coro module uses these hooks to integrate	2500	As another example, the Perl Coro module uses these hooks to integrate
1850	coroutines into libev programs, by yielding to other active coroutines	2501	coroutines into libev programs, by yielding to other active coroutines
1851	during each prepare and only letting the process block if no coroutines	2502	during each prepare and only letting the process block if no coroutines
1852	are ready to run (it's actually more complicated: it only runs coroutines	2503	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1855	loop from blocking if lower-priority coroutines are active, thus mapping	2506	loop from blocking if lower-priority coroutines are active, thus mapping
1856	low-priority coroutines to idle/background tasks).	2507	low-priority coroutines to idle/background tasks).
1857		2508
1858	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2509	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1859	priority, to ensure that they are being run before any other watchers	2510	priority, to ensure that they are being run before any other watchers
		2511	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2512
1860	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2513	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1861	too) should not activate ("feed") events into libev. While libev fully	2514	activate ("feed") events into libev. While libev fully supports this, they
1862	supports this, they will be called before other C<ev_check> watchers	2515	might get executed before other C<ev_check> watchers did their job. As
1863	did their job. As C<ev_check> watchers are often used to embed other	2516	C<ev_check> watchers are often used to embed other (non-libev) event
1864	(non-libev) event loops those other event loops might be in an unusable	2517	loops those other event loops might be in an unusable state until their
1865	state until their C<ev_check> watcher ran (always remind yourself to	2518	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1866	coexist peacefully with others).	2519	others).
1867		2520
1868	=head3 Watcher-Specific Functions and Data Members	2521	=head3 Watcher-Specific Functions and Data Members
1869		2522
1870	=over 4	2523	=over 4
1871		2524
…		…
1873		2526
1874	=item ev_check_init (ev_check *, callback)	2527	=item ev_check_init (ev_check *, callback)
1875		2528
1876	Initialises and configures the prepare or check watcher - they have no	2529	Initialises and configures the prepare or check watcher - they have no
1877	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2530	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1878	macros, but using them is utterly, utterly and completely pointless.	2531	macros, but using them is utterly, utterly, utterly and completely
		2532	pointless.
1879		2533
1880	=back	2534	=back
1881		2535
1882	=head3 Examples	2536	=head3 Examples
1883		2537
1884	There are a number of principal ways to embed other event loops or modules	2538	There are a number of principal ways to embed other event loops or modules
1885	into libev. Here are some ideas on how to include libadns into libev	2539	into libev. Here are some ideas on how to include libadns into libev
1886	(there is a Perl module named C<EV::ADNS> that does this, which you could	2540	(there is a Perl module named C<EV::ADNS> that does this, which you could
1887	use for an actually working example. Another Perl module named C<EV::Glib>	2541	use as a working example. Another Perl module named C<EV::Glib> embeds a
1888	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2542	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1889	into the Glib event loop).	2543	Glib event loop).
1890		2544
1891	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2545	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1892	and in a check watcher, destroy them and call into libadns. What follows	2546	and in a check watcher, destroy them and call into libadns. What follows
1893	is pseudo-code only of course. This requires you to either use a low	2547	is pseudo-code only of course. This requires you to either use a low
1894	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2548	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1895	the callbacks for the IO/timeout watchers might not have been called yet.	2549	the callbacks for the IO/timeout watchers might not have been called yet.
1896		2550
1897	static ev_io iow [nfd];	2551	static ev_io iow [nfd];
1898	static ev_timer tw;	2552	static ev_timer tw;
1899		2553
1900	static void	2554	static void
1901	io_cb (ev_loop *loop, ev_io *w, int revents)	2555	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1902	{	2556	{
1903	}	2557	}
1904		2558
1905	// create io watchers for each fd and a timer before blocking	2559	// create io watchers for each fd and a timer before blocking
1906	static void	2560	static void
1907	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2561	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1908	{	2562	{
1909	int timeout = 3600000;	2563	int timeout = 3600000;
1910	struct pollfd fds [nfd];	2564	struct pollfd fds [nfd];
1911	// actual code will need to loop here and realloc etc.	2565	// actual code will need to loop here and realloc etc.
1912	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2566	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1913		2567
1914	/* the callback is illegal, but won't be called as we stop during check */	2568	/* the callback is illegal, but won't be called as we stop during check */
1915	ev_timer_init (&tw, 0, timeout * 1e-3);	2569	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1916	ev_timer_start (loop, &tw);	2570	ev_timer_start (loop, &tw);
1917		2571
1918	// create one ev_io per pollfd	2572	// create one ev_io per pollfd
1919	for (int i = 0; i < nfd; ++i)	2573	for (int i = 0; i < nfd; ++i)
1920	{	2574	{
1921	ev_io_init (iow + i, io_cb, fds [i].fd,	2575	ev_io_init (iow + i, io_cb, fds [i].fd,
1922	((fds [i].events & POLLIN ? EV_READ : 0)	2576	((fds [i].events & POLLIN ? EV_READ : 0)
1923	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2577	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1924		2578
1925	fds [i].revents = 0;	2579	fds [i].revents = 0;
1926	ev_io_start (loop, iow + i);	2580	ev_io_start (loop, iow + i);
1927	}	2581	}
1928	}	2582	}
1929		2583
1930	// stop all watchers after blocking	2584	// stop all watchers after blocking
1931	static void	2585	static void
1932	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2586	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1933	{	2587	{
1934	ev_timer_stop (loop, &tw);	2588	ev_timer_stop (loop, &tw);
1935		2589
1936	for (int i = 0; i < nfd; ++i)	2590	for (int i = 0; i < nfd; ++i)
1937	{	2591	{
1938	// set the relevant poll flags	2592	// set the relevant poll flags
1939	// could also call adns_processreadable etc. here	2593	// could also call adns_processreadable etc. here
1940	struct pollfd *fd = fds + i;	2594	struct pollfd *fd = fds + i;
1941	int revents = ev_clear_pending (iow + i);	2595	int revents = ev_clear_pending (iow + i);
1942	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2596	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1943	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2597	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1944		2598
1945	// now stop the watcher	2599	// now stop the watcher
1946	ev_io_stop (loop, iow + i);	2600	ev_io_stop (loop, iow + i);
1947	}	2601	}
1948		2602
1949	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2603	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1950	}	2604	}
1951		2605
1952	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2606	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1953	in the prepare watcher and would dispose of the check watcher.	2607	in the prepare watcher and would dispose of the check watcher.
1954		2608
1955	Method 3: If the module to be embedded supports explicit event	2609	Method 3: If the module to be embedded supports explicit event
1956	notification (adns does), you can also make use of the actual watcher	2610	notification (libadns does), you can also make use of the actual watcher
1957	callbacks, and only destroy/create the watchers in the prepare watcher.	2611	callbacks, and only destroy/create the watchers in the prepare watcher.
1958		2612
1959	static void	2613	static void
1960	timer_cb (EV_P_ ev_timer *w, int revents)	2614	timer_cb (EV_P_ ev_timer *w, int revents)
1961	{	2615	{
1962	adns_state ads = (adns_state)w->data;	2616	adns_state ads = (adns_state)w->data;
1963	update_now (EV_A);	2617	update_now (EV_A);
1964		2618
1965	adns_processtimeouts (ads, &tv_now);	2619	adns_processtimeouts (ads, &tv_now);
1966	}	2620	}
1967		2621
1968	static void	2622	static void
1969	io_cb (EV_P_ ev_io *w, int revents)	2623	io_cb (EV_P_ ev_io *w, int revents)
1970	{	2624	{
1971	adns_state ads = (adns_state)w->data;	2625	adns_state ads = (adns_state)w->data;
1972	update_now (EV_A);	2626	update_now (EV_A);
1973		2627
1974	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2628	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1975	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2629	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1976	}	2630	}
1977		2631
1978	// do not ever call adns_afterpoll	2632	// do not ever call adns_afterpoll
1979		2633
1980	Method 4: Do not use a prepare or check watcher because the module you	2634	Method 4: Do not use a prepare or check watcher because the module you
1981	want to embed is too inflexible to support it. Instead, youc na override	2635	want to embed is not flexible enough to support it. Instead, you can
1982	their poll function. The drawback with this solution is that the main	2636	override their poll function. The drawback with this solution is that the
1983	loop is now no longer controllable by EV. The C<Glib::EV> module does	2637	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1984	this.	2638	this approach, effectively embedding EV as a client into the horrible
		2639	libglib event loop.
1985		2640
1986	static gint	2641	static gint
1987	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2642	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1988	{	2643	{
1989	int got_events = 0;	2644	int got_events = 0;
1990		2645
1991	for (n = 0; n < nfds; ++n)	2646	for (n = 0; n < nfds; ++n)
1992	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2647	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1993		2648
1994	if (timeout >= 0)	2649	if (timeout >= 0)
1995	// create/start timer	2650	// create/start timer
1996		2651
1997	// poll	2652	// poll
1998	ev_loop (EV_A_ 0);	2653	ev_loop (EV_A_ 0);
1999		2654
2000	// stop timer again	2655	// stop timer again
2001	if (timeout >= 0)	2656	if (timeout >= 0)
2002	ev_timer_stop (EV_A_ &to);	2657	ev_timer_stop (EV_A_ &to);
2003		2658
2004	// stop io watchers again - their callbacks should have set	2659	// stop io watchers again - their callbacks should have set
2005	for (n = 0; n < nfds; ++n)	2660	for (n = 0; n < nfds; ++n)
2006	ev_io_stop (EV_A_ iow [n]);	2661	ev_io_stop (EV_A_ iow [n]);
2007		2662
2008	return got_events;	2663	return got_events;
2009	}	2664	}
2010		2665
2011		2666
2012	=head2 C<ev_embed> - when one backend isn't enough...	2667	=head2 C<ev_embed> - when one backend isn't enough...
2013		2668
2014	This is a rather advanced watcher type that lets you embed one event loop	2669	This is a rather advanced watcher type that lets you embed one event loop
…		…
2020	prioritise I/O.	2675	prioritise I/O.
2021		2676
2022	As an example for a bug workaround, the kqueue backend might only support	2677	As an example for a bug workaround, the kqueue backend might only support
2023	sockets on some platform, so it is unusable as generic backend, but you	2678	sockets on some platform, so it is unusable as generic backend, but you
2024	still want to make use of it because you have many sockets and it scales	2679	still want to make use of it because you have many sockets and it scales
2025	so nicely. In this case, you would create a kqueue-based loop and embed it	2680	so nicely. In this case, you would create a kqueue-based loop and embed
2026	into your default loop (which might use e.g. poll). Overall operation will	2681	it into your default loop (which might use e.g. poll). Overall operation
2027	be a bit slower because first libev has to poll and then call kevent, but	2682	will be a bit slower because first libev has to call C<poll> and then
2028	at least you can use both at what they are best.	2683	C<kevent>, but at least you can use both mechanisms for what they are
		2684	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2029		2685
2030	As for prioritising I/O: rarely you have the case where some fds have	2686	As for prioritising I/O: under rare circumstances you have the case where
2031	to be watched and handled very quickly (with low latency), and even	2687	some fds have to be watched and handled very quickly (with low latency),
2032	priorities and idle watchers might have too much overhead. In this case	2688	and even priorities and idle watchers might have too much overhead. In
2033	you would put all the high priority stuff in one loop and all the rest in	2689	this case you would put all the high priority stuff in one loop and all
2034	a second one, and embed the second one in the first.	2690	the rest in a second one, and embed the second one in the first.
2035		2691
2036	As long as the watcher is active, the callback will be invoked every time	2692	As long as the watcher is active, the callback will be invoked every
2037	there might be events pending in the embedded loop. The callback must then	2693	time there might be events pending in the embedded loop. The callback
2038	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2694	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2039	their callbacks (you could also start an idle watcher to give the embedded	2695	sweep and invoke their callbacks (the callback doesn't need to invoke the
2040	loop strictly lower priority for example). You can also set the callback	2696	C<ev_embed_sweep> function directly, it could also start an idle watcher
2041	to C<0>, in which case the embed watcher will automatically execute the	2697	to give the embedded loop strictly lower priority for example).
2042	embedded loop sweep.
2043		2698
2044	As long as the watcher is started it will automatically handle events. The	2699	You can also set the callback to C<0>, in which case the embed watcher
2045	callback will be invoked whenever some events have been handled. You can	2700	will automatically execute the embedded loop sweep whenever necessary.
2046	set the callback to C<0> to avoid having to specify one if you are not
2047	interested in that.
2048		2701
2049	Also, there have not currently been made special provisions for forking:	2702	Fork detection will be handled transparently while the C<ev_embed> watcher
2050	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2703	is active, i.e., the embedded loop will automatically be forked when the
2051	but you will also have to stop and restart any C<ev_embed> watchers	2704	embedding loop forks. In other cases, the user is responsible for calling
2052	yourself.	2705	C<ev_loop_fork> on the embedded loop.
2053		2706
2054	Unfortunately, not all backends are embeddable, only the ones returned by	2707	Unfortunately, not all backends are embeddable: only the ones returned by
2055	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2708	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2056	portable one.	2709	portable one.
2057		2710
2058	So when you want to use this feature you will always have to be prepared	2711	So when you want to use this feature you will always have to be prepared
2059	that you cannot get an embeddable loop. The recommended way to get around	2712	that you cannot get an embeddable loop. The recommended way to get around
2060	this is to have a separate variables for your embeddable loop, try to	2713	this is to have a separate variables for your embeddable loop, try to
2061	create it, and if that fails, use the normal loop for everything.	2714	create it, and if that fails, use the normal loop for everything.
2062		2715
		2716	=head3 C<ev_embed> and fork
		2717
		2718	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2719	automatically be applied to the embedded loop as well, so no special
		2720	fork handling is required in that case. When the watcher is not running,
		2721	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2722	as applicable.
		2723
2063	=head3 Watcher-Specific Functions and Data Members	2724	=head3 Watcher-Specific Functions and Data Members
2064		2725
2065	=over 4	2726	=over 4
2066		2727
2067	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2728	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2070		2731
2071	Configures the watcher to embed the given loop, which must be	2732	Configures the watcher to embed the given loop, which must be
2072	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2733	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2073	invoked automatically, otherwise it is the responsibility of the callback	2734	invoked automatically, otherwise it is the responsibility of the callback
2074	to invoke it (it will continue to be called until the sweep has been done,	2735	to invoke it (it will continue to be called until the sweep has been done,
2075	if you do not want thta, you need to temporarily stop the embed watcher).	2736	if you do not want that, you need to temporarily stop the embed watcher).
2076		2737
2077	=item ev_embed_sweep (loop, ev_embed *)	2738	=item ev_embed_sweep (loop, ev_embed *)
2078		2739
2079	Make a single, non-blocking sweep over the embedded loop. This works	2740	Make a single, non-blocking sweep over the embedded loop. This works
2080	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2741	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
2081	apropriate way for embedded loops.	2742	appropriate way for embedded loops.
2082		2743
2083	=item struct ev_loop *other [read-only]	2744	=item struct ev_loop *other [read-only]
2084		2745
2085	The embedded event loop.	2746	The embedded event loop.
2086		2747
…		…
2088		2749
2089	=head3 Examples	2750	=head3 Examples
2090		2751
2091	Example: Try to get an embeddable event loop and embed it into the default	2752	Example: Try to get an embeddable event loop and embed it into the default
2092	event loop. If that is not possible, use the default loop. The default	2753	event loop. If that is not possible, use the default loop. The default
2093	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2754	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2094	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2755	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2095	used).	2756	used).
2096		2757
2097	struct ev_loop *loop_hi = ev_default_init (0);	2758	struct ev_loop *loop_hi = ev_default_init (0);
2098	struct ev_loop *loop_lo = 0;	2759	struct ev_loop *loop_lo = 0;
2099	struct ev_embed embed;	2760	ev_embed embed;
2100		2761
2101	// see if there is a chance of getting one that works	2762	// see if there is a chance of getting one that works
2102	// (remember that a flags value of 0 means autodetection)	2763	// (remember that a flags value of 0 means autodetection)
2103	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2764	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2104	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2765	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2105	: 0;	2766	: 0;
2106		2767
2107	// if we got one, then embed it, otherwise default to loop_hi	2768	// if we got one, then embed it, otherwise default to loop_hi
2108	if (loop_lo)	2769	if (loop_lo)
2109	{	2770	{
2110	ev_embed_init (&embed, 0, loop_lo);	2771	ev_embed_init (&embed, 0, loop_lo);
2111	ev_embed_start (loop_hi, &embed);	2772	ev_embed_start (loop_hi, &embed);
2112	}	2773	}
2113	else	2774	else
2114	loop_lo = loop_hi;	2775	loop_lo = loop_hi;
2115		2776
2116	Example: Check if kqueue is available but not recommended and create	2777	Example: Check if kqueue is available but not recommended and create
2117	a kqueue backend for use with sockets (which usually work with any	2778	a kqueue backend for use with sockets (which usually work with any
2118	kqueue implementation). Store the kqueue/socket-only event loop in	2779	kqueue implementation). Store the kqueue/socket-only event loop in
2119	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2780	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2120		2781
2121	struct ev_loop *loop = ev_default_init (0);	2782	struct ev_loop *loop = ev_default_init (0);
2122	struct ev_loop *loop_socket = 0;	2783	struct ev_loop *loop_socket = 0;
2123	struct ev_embed embed;	2784	ev_embed embed;
2124		2785
2125	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2786	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2126	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2787	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2127	{	2788	{
2128	ev_embed_init (&embed, 0, loop_socket);	2789	ev_embed_init (&embed, 0, loop_socket);
2129	ev_embed_start (loop, &embed);	2790	ev_embed_start (loop, &embed);
2130	}	2791	}
2131		2792
2132	if (!loop_socket)	2793	if (!loop_socket)
2133	loop_socket = loop;	2794	loop_socket = loop;
2134		2795
2135	// now use loop_socket for all sockets, and loop for everything else	2796	// now use loop_socket for all sockets, and loop for everything else
2136		2797
2137		2798
2138	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2799	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2139		2800
2140	Fork watchers are called when a C<fork ()> was detected (usually because	2801	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2143	event loop blocks next and before C<ev_check> watchers are being called,	2804	event loop blocks next and before C<ev_check> watchers are being called,
2144	and only in the child after the fork. If whoever good citizen calling	2805	and only in the child after the fork. If whoever good citizen calling
2145	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2806	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2146	handlers will be invoked, too, of course.	2807	handlers will be invoked, too, of course.
2147		2808
		2809	=head3 The special problem of life after fork - how is it possible?
		2810
		2811	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2812	up/change the process environment, followed by a call to C<exec()>. This
		2813	sequence should be handled by libev without any problems.
		2814
		2815	This changes when the application actually wants to do event handling
		2816	in the child, or both parent in child, in effect "continuing" after the
		2817	fork.
		2818
		2819	The default mode of operation (for libev, with application help to detect
		2820	forks) is to duplicate all the state in the child, as would be expected
		2821	when I<either> the parent I<or> the child process continues.
		2822
		2823	When both processes want to continue using libev, then this is usually the
		2824	wrong result. In that case, usually one process (typically the parent) is
		2825	supposed to continue with all watchers in place as before, while the other
		2826	process typically wants to start fresh, i.e. without any active watchers.
		2827
		2828	The cleanest and most efficient way to achieve that with libev is to
		2829	simply create a new event loop, which of course will be "empty", and
		2830	use that for new watchers. This has the advantage of not touching more
		2831	memory than necessary, and thus avoiding the copy-on-write, and the
		2832	disadvantage of having to use multiple event loops (which do not support
		2833	signal watchers).
		2834
		2835	When this is not possible, or you want to use the default loop for
		2836	other reasons, then in the process that wants to start "fresh", call
		2837	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2838	the default loop will "orphan" (not stop) all registered watchers, so you
		2839	have to be careful not to execute code that modifies those watchers. Note
		2840	also that in that case, you have to re-register any signal watchers.
		2841
2148	=head3 Watcher-Specific Functions and Data Members	2842	=head3 Watcher-Specific Functions and Data Members
2149		2843
2150	=over 4	2844	=over 4
2151		2845
2152	=item ev_fork_init (ev_signal *, callback)	2846	=item ev_fork_init (ev_signal *, callback)
…		…
2184	is that the author does not know of a simple (or any) algorithm for a	2878	is that the author does not know of a simple (or any) algorithm for a
2185	multiple-writer-single-reader queue that works in all cases and doesn't	2879	multiple-writer-single-reader queue that works in all cases and doesn't
2186	need elaborate support such as pthreads.	2880	need elaborate support such as pthreads.
2187		2881
2188	That means that if you want to queue data, you have to provide your own	2882	That means that if you want to queue data, you have to provide your own
2189	queue. But at least I can tell you would implement locking around your	2883	queue. But at least I can tell you how to implement locking around your
2190	queue:	2884	queue:
2191		2885
2192	=over 4	2886	=over 4
2193		2887
2194	=item queueing from a signal handler context	2888	=item queueing from a signal handler context
2195		2889
2196	To implement race-free queueing, you simply add to the queue in the signal	2890	To implement race-free queueing, you simply add to the queue in the signal
2197	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2891	handler but you block the signal handler in the watcher callback. Here is
2198	some fictitiuous SIGUSR1 handler:	2892	an example that does that for some fictitious SIGUSR1 handler:
2199		2893
2200	static ev_async mysig;	2894	static ev_async mysig;
2201		2895
2202	static void	2896	static void
2203	sigusr1_handler (void)	2897	sigusr1_handler (void)
…		…
2269	=over 4	2963	=over 4
2270		2964
2271	=item ev_async_init (ev_async *, callback)	2965	=item ev_async_init (ev_async *, callback)
2272		2966
2273	Initialises and configures the async watcher - it has no parameters of any	2967	Initialises and configures the async watcher - it has no parameters of any
2274	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2968	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2275	believe me.	2969	trust me.
2276		2970
2277	=item ev_async_send (loop, ev_async *)	2971	=item ev_async_send (loop, ev_async *)
2278		2972
2279	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2973	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2280	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2974	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2281	C<ev_feed_event>, this call is safe to do in other threads, signal or	2975	C<ev_feed_event>, this call is safe to do from other threads, signal or
2282	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	2976	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2283	section below on what exactly this means).	2977	section below on what exactly this means).
2284		2978
		2979	Note that, as with other watchers in libev, multiple events might get
		2980	compressed into a single callback invocation (another way to look at this
		2981	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2982	reset when the event loop detects that).
		2983
2285	This call incurs the overhead of a syscall only once per loop iteration,	2984	This call incurs the overhead of a system call only once per event loop
2286	so while the overhead might be noticable, it doesn't apply to repeated	2985	iteration, so while the overhead might be noticeable, it doesn't apply to
2287	calls to C<ev_async_send>.	2986	repeated calls to C<ev_async_send> for the same event loop.
2288		2987
2289	=item bool = ev_async_pending (ev_async *)	2988	=item bool = ev_async_pending (ev_async *)
2290		2989
2291	Returns a non-zero value when C<ev_async_send> has been called on the	2990	Returns a non-zero value when C<ev_async_send> has been called on the
2292	watcher but the event has not yet been processed (or even noted) by the	2991	watcher but the event has not yet been processed (or even noted) by the
2293	event loop.	2992	event loop.
2294		2993
2295	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2994	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2296	the loop iterates next and checks for the watcher to have become active,	2995	the loop iterates next and checks for the watcher to have become active,
2297	it will reset the flag again. C<ev_async_pending> can be used to very	2996	it will reset the flag again. C<ev_async_pending> can be used to very
2298	quickly check wether invoking the loop might be a good idea.	2997	quickly check whether invoking the loop might be a good idea.
2299		2998
2300	Not that this does I<not> check wether the watcher itself is pending, only	2999	Not that this does I<not> check whether the watcher itself is pending,
2301	wether it has been requested to make this watcher pending.	3000	only whether it has been requested to make this watcher pending: there
		3001	is a time window between the event loop checking and resetting the async
		3002	notification, and the callback being invoked.
2302		3003
2303	=back	3004	=back
2304		3005
2305		3006
2306	=head1 OTHER FUNCTIONS	3007	=head1 OTHER FUNCTIONS
…		…
2310	=over 4	3011	=over 4
2311		3012
2312	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3013	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2313		3014
2314	This function combines a simple timer and an I/O watcher, calls your	3015	This function combines a simple timer and an I/O watcher, calls your
2315	callback on whichever event happens first and automatically stop both	3016	callback on whichever event happens first and automatically stops both
2316	watchers. This is useful if you want to wait for a single event on an fd	3017	watchers. This is useful if you want to wait for a single event on an fd
2317	or timeout without having to allocate/configure/start/stop/free one or	3018	or timeout without having to allocate/configure/start/stop/free one or
2318	more watchers yourself.	3019	more watchers yourself.
2319		3020
2320	If C<fd> is less than 0, then no I/O watcher will be started and events	3021	If C<fd> is less than 0, then no I/O watcher will be started and the
2321	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3022	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2322	C<events> set will be craeted and started.	3023	the given C<fd> and C<events> set will be created and started.
2323		3024
2324	If C<timeout> is less than 0, then no timeout watcher will be	3025	If C<timeout> is less than 0, then no timeout watcher will be
2325	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3026	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2326	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3027	repeat = 0) will be started. C<0> is a valid timeout.
2327	dubious value.
2328		3028
2329	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3029	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2330	passed an C<revents> set like normal event callbacks (a combination of	3030	passed an C<revents> set like normal event callbacks (a combination of
2331	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3031	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2332	value passed to C<ev_once>:	3032	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3033	a timeout and an io event at the same time - you probably should give io
		3034	events precedence.
2333		3035
		3036	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3037
2334	static void stdin_ready (int revents, void *arg)	3038	static void stdin_ready (int revents, void *arg)
2335	{	3039	{
2336	if (revents & EV_TIMEOUT)
2337	/* doh, nothing entered */;
2338	else if (revents & EV_READ)	3040	if (revents & EV_READ)
2339	/* stdin might have data for us, joy! */;	3041	/* stdin might have data for us, joy! */;
		3042	else if (revents & EV_TIMEOUT)
		3043	/* doh, nothing entered */;
2340	}	3044	}
2341		3045
2342	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3046	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2343		3047
2344	=item ev_feed_event (ev_loop *, watcher *, int revents)	3048	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2345		3049
2346	Feeds the given event set into the event loop, as if the specified event	3050	Feeds the given event set into the event loop, as if the specified event
2347	had happened for the specified watcher (which must be a pointer to an	3051	had happened for the specified watcher (which must be a pointer to an
2348	initialised but not necessarily started event watcher).	3052	initialised but not necessarily started event watcher).
2349		3053
2350	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3054	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2351		3055
2352	Feed an event on the given fd, as if a file descriptor backend detected	3056	Feed an event on the given fd, as if a file descriptor backend detected
2353	the given events it.	3057	the given events it.
2354		3058
2355	=item ev_feed_signal_event (ev_loop *loop, int signum)	3059	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2356		3060
2357	Feed an event as if the given signal occured (C<loop> must be the default	3061	Feed an event as if the given signal occurred (C<loop> must be the default
2358	loop!).	3062	loop!).
2359		3063
2360	=back	3064	=back
2361		3065
2362		3066
…		…
2391	=back	3095	=back
2392		3096
2393	=head1 C++ SUPPORT	3097	=head1 C++ SUPPORT
2394		3098
2395	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3099	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2396	you to use some convinience methods to start/stop watchers and also change	3100	you to use some convenience methods to start/stop watchers and also change
2397	the callback model to a model using method callbacks on objects.	3101	the callback model to a model using method callbacks on objects.
2398		3102
2399	To use it,	3103	To use it,
2400		3104
2401	#include <ev++.h>	3105	#include <ev++.h>
2402		3106
2403	This automatically includes F<ev.h> and puts all of its definitions (many	3107	This automatically includes F<ev.h> and puts all of its definitions (many
2404	of them macros) into the global namespace. All C++ specific things are	3108	of them macros) into the global namespace. All C++ specific things are
2405	put into the C<ev> namespace. It should support all the same embedding	3109	put into the C<ev> namespace. It should support all the same embedding
2406	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3110	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2473	your compiler is good :), then the method will be fully inlined into the	3177	your compiler is good :), then the method will be fully inlined into the
2474	thunking function, making it as fast as a direct C callback.	3178	thunking function, making it as fast as a direct C callback.
2475		3179
2476	Example: simple class declaration and watcher initialisation	3180	Example: simple class declaration and watcher initialisation
2477		3181
2478	struct myclass	3182	struct myclass
2479	{	3183	{
2480	void io_cb (ev::io &w, int revents) { }	3184	void io_cb (ev::io &w, int revents) { }
2481	}	3185	}
2482		3186
2483	myclass obj;	3187	myclass obj;
2484	ev::io iow;	3188	ev::io iow;
2485	iow.set <myclass, &myclass::io_cb> (&obj);	3189	iow.set <myclass, &myclass::io_cb> (&obj);
		3190
		3191	=item w->set (object *)
		3192
		3193	This is an B<experimental> feature that might go away in a future version.
		3194
		3195	This is a variation of a method callback - leaving out the method to call
		3196	will default the method to C<operator ()>, which makes it possible to use
		3197	functor objects without having to manually specify the C<operator ()> all
		3198	the time. Incidentally, you can then also leave out the template argument
		3199	list.
		3200
		3201	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3202	int revents)>.
		3203
		3204	See the method-C<set> above for more details.
		3205
		3206	Example: use a functor object as callback.
		3207
		3208	struct myfunctor
		3209	{
		3210	void operator() (ev::io &w, int revents)
		3211	{
		3212	...
		3213	}
		3214	}
		3215
		3216	myfunctor f;
		3217
		3218	ev::io w;
		3219	w.set (&f);
2486		3220
2487	=item w->set<function> (void *data = 0)	3221	=item w->set<function> (void *data = 0)
2488		3222
2489	Also sets a callback, but uses a static method or plain function as	3223	Also sets a callback, but uses a static method or plain function as
2490	callback. The optional C<data> argument will be stored in the watcher's	3224	callback. The optional C<data> argument will be stored in the watcher's
…		…
2492		3226
2493	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3227	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2494		3228
2495	See the method-C<set> above for more details.	3229	See the method-C<set> above for more details.
2496		3230
2497	Example:	3231	Example: Use a plain function as callback.
2498		3232
2499	static void io_cb (ev::io &w, int revents) { }	3233	static void io_cb (ev::io &w, int revents) { }
2500	iow.set <io_cb> ();	3234	iow.set <io_cb> ();
2501		3235
2502	=item w->set (struct ev_loop *)	3236	=item w->set (struct ev_loop *)
2503		3237
2504	Associates a different C<struct ev_loop> with this watcher. You can only	3238	Associates a different C<struct ev_loop> with this watcher. You can only
2505	do this when the watcher is inactive (and not pending either).	3239	do this when the watcher is inactive (and not pending either).
2506		3240
2507	=item w->set ([args])	3241	=item w->set ([arguments])
2508		3242
2509	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3243	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2510	called at least once. Unlike the C counterpart, an active watcher gets	3244	called at least once. Unlike the C counterpart, an active watcher gets
2511	automatically stopped and restarted when reconfiguring it with this	3245	automatically stopped and restarted when reconfiguring it with this
2512	method.	3246	method.
2513		3247
2514	=item w->start ()	3248	=item w->start ()
…		…
2538	=back	3272	=back
2539		3273
2540	Example: Define a class with an IO and idle watcher, start one of them in	3274	Example: Define a class with an IO and idle watcher, start one of them in
2541	the constructor.	3275	the constructor.
2542		3276
2543	class myclass	3277	class myclass
2544	{	3278	{
2545	ev::io io; void io_cb (ev::io &w, int revents);	3279	ev::io io ; void io_cb (ev::io &w, int revents);
2546	ev:idle idle void idle_cb (ev::idle &w, int revents);	3280	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2547		3281
2548	myclass (int fd)	3282	myclass (int fd)
2549	{	3283	{
2550	io .set <myclass, &myclass::io_cb > (this);	3284	io .set <myclass, &myclass::io_cb > (this);
2551	idle.set <myclass, &myclass::idle_cb> (this);	3285	idle.set <myclass, &myclass::idle_cb> (this);
2552		3286
2553	io.start (fd, ev::READ);	3287	io.start (fd, ev::READ);
2554	}	3288	}
2555	};	3289	};
2556		3290
2557		3291
2558	=head1 OTHER LANGUAGE BINDINGS	3292	=head1 OTHER LANGUAGE BINDINGS
2559		3293
2560	Libev does not offer other language bindings itself, but bindings for a	3294	Libev does not offer other language bindings itself, but bindings for a
2561	numbe rof languages exist in the form of third-party packages. If you know	3295	number of languages exist in the form of third-party packages. If you know
2562	any interesting language binding in addition to the ones listed here, drop	3296	any interesting language binding in addition to the ones listed here, drop
2563	me a note.	3297	me a note.
2564		3298
2565	=over 4	3299	=over 4
2566		3300
2567	=item Perl	3301	=item Perl
2568		3302
2569	The EV module implements the full libev API and is actually used to test	3303	The EV module implements the full libev API and is actually used to test
2570	libev. EV is developed together with libev. Apart from the EV core module,	3304	libev. EV is developed together with libev. Apart from the EV core module,
2571	there are additional modules that implement libev-compatible interfaces	3305	there are additional modules that implement libev-compatible interfaces
2572	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3306	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2573	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3307	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3308	and C<EV::Glib>).
2574		3309
2575	It can be found and installed via CPAN, its homepage is found at	3310	It can be found and installed via CPAN, its homepage is at
2576	L<http://software.schmorp.de/pkg/EV>.	3311	L<http://software.schmorp.de/pkg/EV>.
2577		3312
		3313	=item Python
		3314
		3315	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3316	seems to be quite complete and well-documented.
		3317
2578	=item Ruby	3318	=item Ruby
2579		3319
2580	Tony Arcieri has written a ruby extension that offers access to a subset	3320	Tony Arcieri has written a ruby extension that offers access to a subset
2581	of the libev API and adds filehandle abstractions, asynchronous DNS and	3321	of the libev API and adds file handle abstractions, asynchronous DNS and
2582	more on top of it. It can be found via gem servers. Its homepage is at	3322	more on top of it. It can be found via gem servers. Its homepage is at
2583	L<http://rev.rubyforge.org/>.	3323	L<http://rev.rubyforge.org/>.
2584		3324
		3325	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3326	makes rev work even on mingw.
		3327
		3328	=item Haskell
		3329
		3330	A haskell binding to libev is available at
		3331	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3332
2585	=item D	3333	=item D
2586		3334
2587	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3335	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2588	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3336	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3337
		3338	=item Ocaml
		3339
		3340	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3341	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2589		3342
2590	=back	3343	=back
2591		3344
2592		3345
2593	=head1 MACRO MAGIC	3346	=head1 MACRO MAGIC
2594		3347
2595	Libev can be compiled with a variety of options, the most fundamantal	3348	Libev can be compiled with a variety of options, the most fundamental
2596	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3349	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2597	functions and callbacks have an initial C<struct ev_loop *> argument.	3350	functions and callbacks have an initial C<struct ev_loop *> argument.
2598		3351
2599	To make it easier to write programs that cope with either variant, the	3352	To make it easier to write programs that cope with either variant, the
2600	following macros are defined:	3353	following macros are defined:
…		…
2605		3358
2606	This provides the loop I<argument> for functions, if one is required ("ev	3359	This provides the loop I<argument> for functions, if one is required ("ev
2607	loop argument"). The C<EV_A> form is used when this is the sole argument,	3360	loop argument"). The C<EV_A> form is used when this is the sole argument,
2608	C<EV_A_> is used when other arguments are following. Example:	3361	C<EV_A_> is used when other arguments are following. Example:
2609		3362
2610	ev_unref (EV_A);	3363	ev_unref (EV_A);
2611	ev_timer_add (EV_A_ watcher);	3364	ev_timer_add (EV_A_ watcher);
2612	ev_loop (EV_A_ 0);	3365	ev_loop (EV_A_ 0);
2613		3366
2614	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3367	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2615	which is often provided by the following macro.	3368	which is often provided by the following macro.
2616		3369
2617	=item C<EV_P>, C<EV_P_>	3370	=item C<EV_P>, C<EV_P_>
2618		3371
2619	This provides the loop I<parameter> for functions, if one is required ("ev	3372	This provides the loop I<parameter> for functions, if one is required ("ev
2620	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3373	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2621	C<EV_P_> is used when other parameters are following. Example:	3374	C<EV_P_> is used when other parameters are following. Example:
2622		3375
2623	// this is how ev_unref is being declared	3376	// this is how ev_unref is being declared
2624	static void ev_unref (EV_P);	3377	static void ev_unref (EV_P);
2625		3378
2626	// this is how you can declare your typical callback	3379	// this is how you can declare your typical callback
2627	static void cb (EV_P_ ev_timer *w, int revents)	3380	static void cb (EV_P_ ev_timer *w, int revents)
2628		3381
2629	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3382	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2630	suitable for use with C<EV_A>.	3383	suitable for use with C<EV_A>.
2631		3384
2632	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3385	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
…		…
2648		3401
2649	Example: Declare and initialise a check watcher, utilising the above	3402	Example: Declare and initialise a check watcher, utilising the above
2650	macros so it will work regardless of whether multiple loops are supported	3403	macros so it will work regardless of whether multiple loops are supported
2651	or not.	3404	or not.
2652		3405
2653	static void	3406	static void
2654	check_cb (EV_P_ ev_timer *w, int revents)	3407	check_cb (EV_P_ ev_timer *w, int revents)
2655	{	3408	{
2656	ev_check_stop (EV_A_ w);	3409	ev_check_stop (EV_A_ w);
2657	}	3410	}
2658		3411
2659	ev_check check;	3412	ev_check check;
2660	ev_check_init (&check, check_cb);	3413	ev_check_init (&check, check_cb);
2661	ev_check_start (EV_DEFAULT_ &check);	3414	ev_check_start (EV_DEFAULT_ &check);
2662	ev_loop (EV_DEFAULT_ 0);	3415	ev_loop (EV_DEFAULT_ 0);
2663		3416
2664	=head1 EMBEDDING	3417	=head1 EMBEDDING
2665		3418
2666	Libev can (and often is) directly embedded into host	3419	Libev can (and often is) directly embedded into host
2667	applications. Examples of applications that embed it include the Deliantra	3420	applications. Examples of applications that embed it include the Deliantra
…		…
2674	libev somewhere in your source tree).	3427	libev somewhere in your source tree).
2675		3428
2676	=head2 FILESETS	3429	=head2 FILESETS
2677		3430
2678	Depending on what features you need you need to include one or more sets of files	3431	Depending on what features you need you need to include one or more sets of files
2679	in your app.	3432	in your application.
2680		3433
2681	=head3 CORE EVENT LOOP	3434	=head3 CORE EVENT LOOP
2682		3435
2683	To include only the libev core (all the C<ev_*> functions), with manual	3436	To include only the libev core (all the C<ev_*> functions), with manual
2684	configuration (no autoconf):	3437	configuration (no autoconf):
2685		3438
2686	#define EV_STANDALONE 1	3439	#define EV_STANDALONE 1
2687	#include "ev.c"	3440	#include "ev.c"
2688		3441
2689	This will automatically include F<ev.h>, too, and should be done in a	3442	This will automatically include F<ev.h>, too, and should be done in a
2690	single C source file only to provide the function implementations. To use	3443	single C source file only to provide the function implementations. To use
2691	it, do the same for F<ev.h> in all files wishing to use this API (best	3444	it, do the same for F<ev.h> in all files wishing to use this API (best
2692	done by writing a wrapper around F<ev.h> that you can include instead and	3445	done by writing a wrapper around F<ev.h> that you can include instead and
2693	where you can put other configuration options):	3446	where you can put other configuration options):
2694		3447
2695	#define EV_STANDALONE 1	3448	#define EV_STANDALONE 1
2696	#include "ev.h"	3449	#include "ev.h"
2697		3450
2698	Both header files and implementation files can be compiled with a C++	3451	Both header files and implementation files can be compiled with a C++
2699	compiler (at least, thats a stated goal, and breakage will be treated	3452	compiler (at least, that's a stated goal, and breakage will be treated
2700	as a bug).	3453	as a bug).
2701		3454
2702	You need the following files in your source tree, or in a directory	3455	You need the following files in your source tree, or in a directory
2703	in your include path (e.g. in libev/ when using -Ilibev):	3456	in your include path (e.g. in libev/ when using -Ilibev):
2704		3457
2705	ev.h	3458	ev.h
2706	ev.c	3459	ev.c
2707	ev_vars.h	3460	ev_vars.h
2708	ev_wrap.h	3461	ev_wrap.h
2709		3462
2710	ev_win32.c required on win32 platforms only	3463	ev_win32.c required on win32 platforms only
2711		3464
2712	ev_select.c only when select backend is enabled (which is enabled by default)	3465	ev_select.c only when select backend is enabled (which is enabled by default)
2713	ev_poll.c only when poll backend is enabled (disabled by default)	3466	ev_poll.c only when poll backend is enabled (disabled by default)
2714	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3467	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2715	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3468	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2716	ev_port.c only when the solaris port backend is enabled (disabled by default)	3469	ev_port.c only when the solaris port backend is enabled (disabled by default)
2717		3470
2718	F<ev.c> includes the backend files directly when enabled, so you only need	3471	F<ev.c> includes the backend files directly when enabled, so you only need
2719	to compile this single file.	3472	to compile this single file.
2720		3473
2721	=head3 LIBEVENT COMPATIBILITY API	3474	=head3 LIBEVENT COMPATIBILITY API
2722		3475
2723	To include the libevent compatibility API, also include:	3476	To include the libevent compatibility API, also include:
2724		3477
2725	#include "event.c"	3478	#include "event.c"
2726		3479
2727	in the file including F<ev.c>, and:	3480	in the file including F<ev.c>, and:
2728		3481
2729	#include "event.h"	3482	#include "event.h"
2730		3483
2731	in the files that want to use the libevent API. This also includes F<ev.h>.	3484	in the files that want to use the libevent API. This also includes F<ev.h>.
2732		3485
2733	You need the following additional files for this:	3486	You need the following additional files for this:
2734		3487
2735	event.h	3488	event.h
2736	event.c	3489	event.c
2737		3490
2738	=head3 AUTOCONF SUPPORT	3491	=head3 AUTOCONF SUPPORT
2739		3492
2740	Instead of using C<EV_STANDALONE=1> and providing your config in	3493	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2741	whatever way you want, you can also C<m4_include([libev.m4])> in your	3494	whatever way you want, you can also C<m4_include([libev.m4])> in your
2742	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3495	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2743	include F<config.h> and configure itself accordingly.	3496	include F<config.h> and configure itself accordingly.
2744		3497
2745	For this of course you need the m4 file:	3498	For this of course you need the m4 file:
2746		3499
2747	libev.m4	3500	libev.m4
2748		3501
2749	=head2 PREPROCESSOR SYMBOLS/MACROS	3502	=head2 PREPROCESSOR SYMBOLS/MACROS
2750		3503
2751	Libev can be configured via a variety of preprocessor symbols you have to	3504	Libev can be configured via a variety of preprocessor symbols you have to
2752	define before including any of its files. The default in the absense of	3505	define before including any of its files. The default in the absence of
2753	autoconf is noted for every option.	3506	autoconf is documented for every option.
2754		3507
2755	=over 4	3508	=over 4
2756		3509
2757	=item EV_STANDALONE	3510	=item EV_STANDALONE
2758		3511
…		…
2760	keeps libev from including F<config.h>, and it also defines dummy	3513	keeps libev from including F<config.h>, and it also defines dummy
2761	implementations for some libevent functions (such as logging, which is not	3514	implementations for some libevent functions (such as logging, which is not
2762	supported). It will also not define any of the structs usually found in	3515	supported). It will also not define any of the structs usually found in
2763	F<event.h> that are not directly supported by the libev core alone.	3516	F<event.h> that are not directly supported by the libev core alone.
2764		3517
		3518	In stanbdalone mode, libev will still try to automatically deduce the
		3519	configuration, but has to be more conservative.
		3520
2765	=item EV_USE_MONOTONIC	3521	=item EV_USE_MONOTONIC
2766		3522
2767	If defined to be C<1>, libev will try to detect the availability of the	3523	If defined to be C<1>, libev will try to detect the availability of the
2768	monotonic clock option at both compiletime and runtime. Otherwise no use	3524	monotonic clock option at both compile time and runtime. Otherwise no
2769	of the monotonic clock option will be attempted. If you enable this, you	3525	use of the monotonic clock option will be attempted. If you enable this,
2770	usually have to link against librt or something similar. Enabling it when	3526	you usually have to link against librt or something similar. Enabling it
2771	the functionality isn't available is safe, though, although you have	3527	when the functionality isn't available is safe, though, although you have
2772	to make sure you link against any libraries where the C<clock_gettime>	3528	to make sure you link against any libraries where the C<clock_gettime>
2773	function is hiding in (often F<-lrt>).	3529	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2774		3530
2775	=item EV_USE_REALTIME	3531	=item EV_USE_REALTIME
2776		3532
2777	If defined to be C<1>, libev will try to detect the availability of the	3533	If defined to be C<1>, libev will try to detect the availability of the
2778	realtime clock option at compiletime (and assume its availability at	3534	real-time clock option at compile time (and assume its availability
2779	runtime if successful). Otherwise no use of the realtime clock option will	3535	at runtime if successful). Otherwise no use of the real-time clock
2780	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3536	option will be attempted. This effectively replaces C<gettimeofday>
2781	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3537	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2782	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3538	correctness. See the note about libraries in the description of
		3539	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3540	C<EV_USE_CLOCK_SYSCALL>.
		3541
		3542	=item EV_USE_CLOCK_SYSCALL
		3543
		3544	If defined to be C<1>, libev will try to use a direct syscall instead
		3545	of calling the system-provided C<clock_gettime> function. This option
		3546	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3547	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3548	programs needlessly. Using a direct syscall is slightly slower (in
		3549	theory), because no optimised vdso implementation can be used, but avoids
		3550	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3551	higher, as it simplifies linking (no need for C<-lrt>).
2783		3552
2784	=item EV_USE_NANOSLEEP	3553	=item EV_USE_NANOSLEEP
2785		3554
2786	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3555	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2787	and will use it for delays. Otherwise it will use C<select ()>.	3556	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2795	2.7 or newer, otherwise disabled.	3564	2.7 or newer, otherwise disabled.
2796		3565
2797	=item EV_USE_SELECT	3566	=item EV_USE_SELECT
2798		3567
2799	If undefined or defined to be C<1>, libev will compile in support for the	3568	If undefined or defined to be C<1>, libev will compile in support for the
2800	C<select>(2) backend. No attempt at autodetection will be done: if no	3569	C<select>(2) backend. No attempt at auto-detection will be done: if no
2801	other method takes over, select will be it. Otherwise the select backend	3570	other method takes over, select will be it. Otherwise the select backend
2802	will not be compiled in.	3571	will not be compiled in.
2803		3572
2804	=item EV_SELECT_USE_FD_SET	3573	=item EV_SELECT_USE_FD_SET
2805		3574
2806	If defined to C<1>, then the select backend will use the system C<fd_set>	3575	If defined to C<1>, then the select backend will use the system C<fd_set>
2807	structure. This is useful if libev doesn't compile due to a missing	3576	structure. This is useful if libev doesn't compile due to a missing
2808	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3577	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2809	exotic systems. This usually limits the range of file descriptors to some	3578	on exotic systems. This usually limits the range of file descriptors to
2810	low limit such as 1024 or might have other limitations (winsocket only	3579	some low limit such as 1024 or might have other limitations (winsocket
2811	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3580	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2812	influence the size of the C<fd_set> used.	3581	configures the maximum size of the C<fd_set>.
2813		3582
2814	=item EV_SELECT_IS_WINSOCKET	3583	=item EV_SELECT_IS_WINSOCKET
2815		3584
2816	When defined to C<1>, the select backend will assume that	3585	When defined to C<1>, the select backend will assume that
2817	select/socket/connect etc. don't understand file descriptors but	3586	select/socket/connect etc. don't understand file descriptors but
…		…
2862	otherwise another method will be used as fallback. This is the preferred	3631	otherwise another method will be used as fallback. This is the preferred
2863	backend for Solaris 10 systems.	3632	backend for Solaris 10 systems.
2864		3633
2865	=item EV_USE_DEVPOLL	3634	=item EV_USE_DEVPOLL
2866		3635
2867	reserved for future expansion, works like the USE symbols above.	3636	Reserved for future expansion, works like the USE symbols above.
2868		3637
2869	=item EV_USE_INOTIFY	3638	=item EV_USE_INOTIFY
2870		3639
2871	If defined to be C<1>, libev will compile in support for the Linux inotify	3640	If defined to be C<1>, libev will compile in support for the Linux inotify
2872	interface to speed up C<ev_stat> watchers. Its actual availability will	3641	interface to speed up C<ev_stat> watchers. Its actual availability will
…		…
2879	access is atomic with respect to other threads or signal contexts. No such	3648	access is atomic with respect to other threads or signal contexts. No such
2880	type is easily found in the C language, so you can provide your own type	3649	type is easily found in the C language, so you can provide your own type
2881	that you know is safe for your purposes. It is used both for signal handler "locking"	3650	that you know is safe for your purposes. It is used both for signal handler "locking"
2882	as well as for signal and thread safety in C<ev_async> watchers.	3651	as well as for signal and thread safety in C<ev_async> watchers.
2883		3652
2884	In the absense of this define, libev will use C<sig_atomic_t volatile>	3653	In the absence of this define, libev will use C<sig_atomic_t volatile>
2885	(from F<signal.h>), which is usually good enough on most platforms.	3654	(from F<signal.h>), which is usually good enough on most platforms.
2886		3655
2887	=item EV_H	3656	=item EV_H
2888		3657
2889	The name of the F<ev.h> header file used to include it. The default if	3658	The name of the F<ev.h> header file used to include it. The default if
…		…
2928	When doing priority-based operations, libev usually has to linearly search	3697	When doing priority-based operations, libev usually has to linearly search
2929	all the priorities, so having many of them (hundreds) uses a lot of space	3698	all the priorities, so having many of them (hundreds) uses a lot of space
2930	and time, so using the defaults of five priorities (-2 .. +2) is usually	3699	and time, so using the defaults of five priorities (-2 .. +2) is usually
2931	fine.	3700	fine.
2932		3701
2933	If your embedding app does not need any priorities, defining these both to	3702	If your embedding application does not need any priorities, defining these
2934	C<0> will save some memory and cpu.	3703	both to C<0> will save some memory and CPU.
2935		3704
2936	=item EV_PERIODIC_ENABLE	3705	=item EV_PERIODIC_ENABLE
2937		3706
2938	If undefined or defined to be C<1>, then periodic timers are supported. If	3707	If undefined or defined to be C<1>, then periodic timers are supported. If
2939	defined to be C<0>, then they are not. Disabling them saves a few kB of	3708	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2946	code.	3715	code.
2947		3716
2948	=item EV_EMBED_ENABLE	3717	=item EV_EMBED_ENABLE
2949		3718
2950	If undefined or defined to be C<1>, then embed watchers are supported. If	3719	If undefined or defined to be C<1>, then embed watchers are supported. If
2951	defined to be C<0>, then they are not.	3720	defined to be C<0>, then they are not. Embed watchers rely on most other
		3721	watcher types, which therefore must not be disabled.
2952		3722
2953	=item EV_STAT_ENABLE	3723	=item EV_STAT_ENABLE
2954		3724
2955	If undefined or defined to be C<1>, then stat watchers are supported. If	3725	If undefined or defined to be C<1>, then stat watchers are supported. If
2956	defined to be C<0>, then they are not.	3726	defined to be C<0>, then they are not.
…		…
2966	defined to be C<0>, then they are not.	3736	defined to be C<0>, then they are not.
2967		3737
2968	=item EV_MINIMAL	3738	=item EV_MINIMAL
2969		3739
2970	If you need to shave off some kilobytes of code at the expense of some	3740	If you need to shave off some kilobytes of code at the expense of some
2971	speed, define this symbol to C<1>. Currently only used for gcc to override	3741	speed (but with the full API), define this symbol to C<1>. Currently this
2972	some inlining decisions, saves roughly 30% codesize of amd64.	3742	is used to override some inlining decisions, saves roughly 30% code size
		3743	on amd64. It also selects a much smaller 2-heap for timer management over
		3744	the default 4-heap.
		3745
		3746	You can save even more by disabling watcher types you do not need
		3747	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3748	(C<-DNDEBUG>) will usually reduce code size a lot.
		3749
		3750	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3751	provide a bare-bones event library. See C<ev.h> for details on what parts
		3752	of the API are still available, and do not complain if this subset changes
		3753	over time.
2973		3754
2974	=item EV_PID_HASHSIZE	3755	=item EV_PID_HASHSIZE
2975		3756
2976	C<ev_child> watchers use a small hash table to distribute workload by	3757	C<ev_child> watchers use a small hash table to distribute workload by
2977	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3758	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2984	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3765	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2985	usually more than enough. If you need to manage thousands of C<ev_stat>	3766	usually more than enough. If you need to manage thousands of C<ev_stat>
2986	watchers you might want to increase this value (I<must> be a power of	3767	watchers you might want to increase this value (I<must> be a power of
2987	two).	3768	two).
2988		3769
		3770	=item EV_USE_4HEAP
		3771
		3772	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3773	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3774	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3775	faster performance with many (thousands) of watchers.
		3776
		3777	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3778	(disabled).
		3779
		3780	=item EV_HEAP_CACHE_AT
		3781
		3782	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3783	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3784	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3785	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3786	but avoids random read accesses on heap changes. This improves performance
		3787	noticeably with many (hundreds) of watchers.
		3788
		3789	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3790	(disabled).
		3791
		3792	=item EV_VERIFY
		3793
		3794	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3795	be done: If set to C<0>, no internal verification code will be compiled
		3796	in. If set to C<1>, then verification code will be compiled in, but not
		3797	called. If set to C<2>, then the internal verification code will be
		3798	called once per loop, which can slow down libev. If set to C<3>, then the
		3799	verification code will be called very frequently, which will slow down
		3800	libev considerably.
		3801
		3802	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3803	C<0>.
		3804
2989	=item EV_COMMON	3805	=item EV_COMMON
2990		3806
2991	By default, all watchers have a C<void *data> member. By redefining	3807	By default, all watchers have a C<void *data> member. By redefining
2992	this macro to a something else you can include more and other types of	3808	this macro to a something else you can include more and other types of
2993	members. You have to define it each time you include one of the files,	3809	members. You have to define it each time you include one of the files,
2994	though, and it must be identical each time.	3810	though, and it must be identical each time.
2995		3811
2996	For example, the perl EV module uses something like this:	3812	For example, the perl EV module uses something like this:
2997		3813
2998	#define EV_COMMON \	3814	#define EV_COMMON \
2999	SV *self; /* contains this struct */ \	3815	SV *self; /* contains this struct */ \
3000	SV *cb_sv, *fh /* note no trailing ";" */	3816	SV *cb_sv, *fh /* note no trailing ";" */
3001		3817
3002	=item EV_CB_DECLARE (type)	3818	=item EV_CB_DECLARE (type)
3003		3819
3004	=item EV_CB_INVOKE (watcher, revents)	3820	=item EV_CB_INVOKE (watcher, revents)
3005		3821
…		…
3010	definition and a statement, respectively. See the F<ev.h> header file for	3826	definition and a statement, respectively. See the F<ev.h> header file for
3011	their default definitions. One possible use for overriding these is to	3827	their default definitions. One possible use for overriding these is to
3012	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3828	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3013	method calls instead of plain function calls in C++.	3829	method calls instead of plain function calls in C++.
3014		3830
		3831	=back
		3832
3015	=head2 EXPORTED API SYMBOLS	3833	=head2 EXPORTED API SYMBOLS
3016		3834
3017	If you need to re-export the API (e.g. via a dll) and you need a list of	3835	If you need to re-export the API (e.g. via a DLL) and you need a list of
3018	exported symbols, you can use the provided F<Symbol.*> files which list	3836	exported symbols, you can use the provided F<Symbol.*> files which list
3019	all public symbols, one per line:	3837	all public symbols, one per line:
3020		3838
3021	Symbols.ev for libev proper	3839	Symbols.ev for libev proper
3022	Symbols.event for the libevent emulation	3840	Symbols.event for the libevent emulation
3023		3841
3024	This can also be used to rename all public symbols to avoid clashes with	3842	This can also be used to rename all public symbols to avoid clashes with
3025	multiple versions of libev linked together (which is obviously bad in	3843	multiple versions of libev linked together (which is obviously bad in
3026	itself, but sometimes it is inconvinient to avoid this).	3844	itself, but sometimes it is inconvenient to avoid this).
3027		3845
3028	A sed command like this will create wrapper C<#define>'s that you need to	3846	A sed command like this will create wrapper C<#define>'s that you need to
3029	include before including F<ev.h>:	3847	include before including F<ev.h>:
3030		3848
3031	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3849	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
3048	file.	3866	file.
3049		3867
3050	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3868	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3051	that everybody includes and which overrides some configure choices:	3869	that everybody includes and which overrides some configure choices:
3052		3870
3053	#define EV_MINIMAL 1	3871	#define EV_MINIMAL 1
3054	#define EV_USE_POLL 0	3872	#define EV_USE_POLL 0
3055	#define EV_MULTIPLICITY 0	3873	#define EV_MULTIPLICITY 0
3056	#define EV_PERIODIC_ENABLE 0	3874	#define EV_PERIODIC_ENABLE 0
3057	#define EV_STAT_ENABLE 0	3875	#define EV_STAT_ENABLE 0
3058	#define EV_FORK_ENABLE 0	3876	#define EV_FORK_ENABLE 0
3059	#define EV_CONFIG_H <config.h>	3877	#define EV_CONFIG_H <config.h>
3060	#define EV_MINPRI 0	3878	#define EV_MINPRI 0
3061	#define EV_MAXPRI 0	3879	#define EV_MAXPRI 0
3062		3880
3063	#include "ev++.h"	3881	#include "ev++.h"
3064		3882
3065	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3883	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3066		3884
3067	#include "ev_cpp.h"	3885	#include "ev_cpp.h"
3068	#include "ev.c"	3886	#include "ev.c"
3069		3887
		3888	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3070		3889
3071	=head1 THREADS AND COROUTINES	3890	=head2 THREADS AND COROUTINES
3072		3891
3073	=head2 THREADS	3892	=head3 THREADS
3074		3893
3075	Libev itself is completely threadsafe, but it uses no locking. This	3894	All libev functions are reentrant and thread-safe unless explicitly
		3895	documented otherwise, but libev implements no locking itself. This means
3076	means that you can use as many loops as you want in parallel, as long as	3896	that you can use as many loops as you want in parallel, as long as there
3077	only one thread ever calls into one libev function with the same loop	3897	are no concurrent calls into any libev function with the same loop
3078	parameter.	3898	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3899	of course): libev guarantees that different event loops share no data
		3900	structures that need any locking.
3079		3901
3080	Or put differently: calls with different loop parameters can be done in	3902	Or to put it differently: calls with different loop parameters can be done
3081	parallel from multiple threads, calls with the same loop parameter must be	3903	concurrently from multiple threads, calls with the same loop parameter
3082	done serially (but can be done from different threads, as long as only one	3904	must be done serially (but can be done from different threads, as long as
3083	thread ever is inside a call at any point in time, e.g. by using a mutex	3905	only one thread ever is inside a call at any point in time, e.g. by using
3084	per loop).	3906	a mutex per loop).
3085		3907
3086	If you want to know which design is best for your problem, then I cannot	3908	Specifically to support threads (and signal handlers), libev implements
		3909	so-called C<ev_async> watchers, which allow some limited form of
		3910	concurrency on the same event loop, namely waking it up "from the
		3911	outside".
		3912
		3913	If you want to know which design (one loop, locking, or multiple loops
		3914	without or something else still) is best for your problem, then I cannot
3087	help you but by giving some generic advice:	3915	help you, but here is some generic advice:
3088		3916
3089	=over 4	3917	=over 4
3090		3918
3091	=item * most applications have a main thread: use the default libev loop	3919	=item * most applications have a main thread: use the default libev loop
3092	in that thread, or create a seperate thread running only the default loop.	3920	in that thread, or create a separate thread running only the default loop.
3093		3921
3094	This helps integrating other libraries or software modules that use libev	3922	This helps integrating other libraries or software modules that use libev
3095	themselves and don't care/know about threading.	3923	themselves and don't care/know about threading.
3096		3924
3097	=item * one loop per thread is usually a good model.	3925	=item * one loop per thread is usually a good model.
3098		3926
3099	Doing this is almost never wrong, sometimes a better-performance model	3927	Doing this is almost never wrong, sometimes a better-performance model
3100	exists, but it is always a good start.	3928	exists, but it is always a good start.
3101		3929
3102	=item * other models exist, such as the leader/follower pattern, where one	3930	=item * other models exist, such as the leader/follower pattern, where one
3103	loop is handed through multiple threads in a kind of round-robbin fashion.	3931	loop is handed through multiple threads in a kind of round-robin fashion.
3104		3932
3105	Chosing a model is hard - look around, learn, know that usually you cna do	3933	Choosing a model is hard - look around, learn, know that usually you can do
3106	better than you currently do :-)	3934	better than you currently do :-)
3107		3935
3108	=item * often you need to talk to some other thread which blocks in the	3936	=item * often you need to talk to some other thread which blocks in the
		3937	event loop.
		3938
3109	event loop - C<ev_async> watchers can be used to wake them up from other	3939	C<ev_async> watchers can be used to wake them up from other threads safely
3110	threads safely (or from signal contexts...).	3940	(or from signal contexts...).
		3941
		3942	An example use would be to communicate signals or other events that only
		3943	work in the default loop by registering the signal watcher with the
		3944	default loop and triggering an C<ev_async> watcher from the default loop
		3945	watcher callback into the event loop interested in the signal.
3111		3946
3112	=back	3947	=back
3113		3948
		3949	=head4 THREAD LOCKING EXAMPLE
		3950
		3951	Here is a fictitious example of how to run an event loop in a different
		3952	thread than where callbacks are being invoked and watchers are
		3953	created/added/removed.
		3954
		3955	For a real-world example, see the C<EV::Loop::Async> perl module,
		3956	which uses exactly this technique (which is suited for many high-level
		3957	languages).
		3958
		3959	The example uses a pthread mutex to protect the loop data, a condition
		3960	variable to wait for callback invocations, an async watcher to notify the
		3961	event loop thread and an unspecified mechanism to wake up the main thread.
		3962
		3963	First, you need to associate some data with the event loop:
		3964
		3965	typedef struct {
		3966	mutex_t lock; /* global loop lock */
		3967	ev_async async_w;
		3968	thread_t tid;
		3969	cond_t invoke_cv;
		3970	} userdata;
		3971
		3972	void prepare_loop (EV_P)
		3973	{
		3974	// for simplicity, we use a static userdata struct.
		3975	static userdata u;
		3976
		3977	ev_async_init (&u->async_w, async_cb);
		3978	ev_async_start (EV_A_ &u->async_w);
		3979
		3980	pthread_mutex_init (&u->lock, 0);
		3981	pthread_cond_init (&u->invoke_cv, 0);
		3982
		3983	// now associate this with the loop
		3984	ev_set_userdata (EV_A_ u);
		3985	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3986	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3987
		3988	// then create the thread running ev_loop
		3989	pthread_create (&u->tid, 0, l_run, EV_A);
		3990	}
		3991
		3992	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3993	solely to wake up the event loop so it takes notice of any new watchers
		3994	that might have been added:
		3995
		3996	static void
		3997	async_cb (EV_P_ ev_async *w, int revents)
		3998	{
		3999	// just used for the side effects
		4000	}
		4001
		4002	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4003	protecting the loop data, respectively.
		4004
		4005	static void
		4006	l_release (EV_P)
		4007	{
		4008	userdata *u = ev_userdata (EV_A);
		4009	pthread_mutex_unlock (&u->lock);
		4010	}
		4011
		4012	static void
		4013	l_acquire (EV_P)
		4014	{
		4015	userdata *u = ev_userdata (EV_A);
		4016	pthread_mutex_lock (&u->lock);
		4017	}
		4018
		4019	The event loop thread first acquires the mutex, and then jumps straight
		4020	into C<ev_loop>:
		4021
		4022	void *
		4023	l_run (void *thr_arg)
		4024	{
		4025	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4026
		4027	l_acquire (EV_A);
		4028	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4029	ev_loop (EV_A_ 0);
		4030	l_release (EV_A);
		4031
		4032	return 0;
		4033	}
		4034
		4035	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4036	signal the main thread via some unspecified mechanism (signals? pipe
		4037	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4038	have been called (in a while loop because a) spurious wakeups are possible
		4039	and b) skipping inter-thread-communication when there are no pending
		4040	watchers is very beneficial):
		4041
		4042	static void
		4043	l_invoke (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046
		4047	while (ev_pending_count (EV_A))
		4048	{
		4049	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4050	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4051	}
		4052	}
		4053
		4054	Now, whenever the main thread gets told to invoke pending watchers, it
		4055	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4056	thread to continue:
		4057
		4058	static void
		4059	real_invoke_pending (EV_P)
		4060	{
		4061	userdata *u = ev_userdata (EV_A);
		4062
		4063	pthread_mutex_lock (&u->lock);
		4064	ev_invoke_pending (EV_A);
		4065	pthread_cond_signal (&u->invoke_cv);
		4066	pthread_mutex_unlock (&u->lock);
		4067	}
		4068
		4069	Whenever you want to start/stop a watcher or do other modifications to an
		4070	event loop, you will now have to lock:
		4071
		4072	ev_timer timeout_watcher;
		4073	userdata *u = ev_userdata (EV_A);
		4074
		4075	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4076
		4077	pthread_mutex_lock (&u->lock);
		4078	ev_timer_start (EV_A_ &timeout_watcher);
		4079	ev_async_send (EV_A_ &u->async_w);
		4080	pthread_mutex_unlock (&u->lock);
		4081
		4082	Note that sending the C<ev_async> watcher is required because otherwise
		4083	an event loop currently blocking in the kernel will have no knowledge
		4084	about the newly added timer. By waking up the loop it will pick up any new
		4085	watchers in the next event loop iteration.
		4086
3114	=head2 COROUTINES	4087	=head3 COROUTINES
3115		4088
3116	Libev is much more accomodating to coroutines ("cooperative threads"):	4089	Libev is very accommodating to coroutines ("cooperative threads"):
3117	libev fully supports nesting calls to it's functions from different	4090	libev fully supports nesting calls to its functions from different
3118	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4091	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3119	different coroutines and switch freely between both coroutines running the	4092	different coroutines, and switch freely between both coroutines running
3120	loop, as long as you don't confuse yourself). The only exception is that	4093	the loop, as long as you don't confuse yourself). The only exception is
3121	you must not do this from C<ev_periodic> reschedule callbacks.	4094	that you must not do this from C<ev_periodic> reschedule callbacks.
3122		4095
3123	Care has been invested into making sure that libev does not keep local	4096	Care has been taken to ensure that libev does not keep local state inside
3124	state inside C<ev_loop>, and other calls do not usually allow coroutine	4097	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3125	switches.	4098	they do not call any callbacks.
3126		4099
		4100	=head2 COMPILER WARNINGS
3127		4101
3128	=head1 COMPLEXITIES	4102	Depending on your compiler and compiler settings, you might get no or a
		4103	lot of warnings when compiling libev code. Some people are apparently
		4104	scared by this.
3129		4105
3130	In this section the complexities of (many of) the algorithms used inside	4106	However, these are unavoidable for many reasons. For one, each compiler
3131	libev will be explained. For complexity discussions about backends see the	4107	has different warnings, and each user has different tastes regarding
3132	documentation for C<ev_default_init>.	4108	warning options. "Warn-free" code therefore cannot be a goal except when
		4109	targeting a specific compiler and compiler-version.
3133		4110
3134	All of the following are about amortised time: If an array needs to be	4111	Another reason is that some compiler warnings require elaborate
3135	extended, libev needs to realloc and move the whole array, but this	4112	workarounds, or other changes to the code that make it less clear and less
3136	happens asymptotically never with higher number of elements, so O(1) might	4113	maintainable.
3137	mean it might do a lengthy realloc operation in rare cases, but on average
3138	it is much faster and asymptotically approaches constant time.
3139		4114
3140	=over 4	4115	And of course, some compiler warnings are just plain stupid, or simply
		4116	wrong (because they don't actually warn about the condition their message
		4117	seems to warn about). For example, certain older gcc versions had some
		4118	warnings that resulted an extreme number of false positives. These have
		4119	been fixed, but some people still insist on making code warn-free with
		4120	such buggy versions.
3141		4121
3142	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4122	While libev is written to generate as few warnings as possible,
		4123	"warn-free" code is not a goal, and it is recommended not to build libev
		4124	with any compiler warnings enabled unless you are prepared to cope with
		4125	them (e.g. by ignoring them). Remember that warnings are just that:
		4126	warnings, not errors, or proof of bugs.
3143		4127
3144	This means that, when you have a watcher that triggers in one hour and
3145	there are 100 watchers that would trigger before that then inserting will
3146	have to skip roughly seven (C<ld 100>) of these watchers.
3147		4128
3148	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4129	=head2 VALGRIND
3149		4130
3150	That means that changing a timer costs less than removing/adding them	4131	Valgrind has a special section here because it is a popular tool that is
3151	as only the relative motion in the event queue has to be paid for.	4132	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3152		4133
3153	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4134	If you think you found a bug (memory leak, uninitialised data access etc.)
		4135	in libev, then check twice: If valgrind reports something like:
3154		4136
3155	These just add the watcher into an array or at the head of a list.	4137	==2274== definitely lost: 0 bytes in 0 blocks.
		4138	==2274== possibly lost: 0 bytes in 0 blocks.
		4139	==2274== still reachable: 256 bytes in 1 blocks.
3156		4140
3157	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4141	Then there is no memory leak, just as memory accounted to global variables
		4142	is not a memleak - the memory is still being referenced, and didn't leak.
3158		4143
3159	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4144	Similarly, under some circumstances, valgrind might report kernel bugs
		4145	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4146	although an acceptable workaround has been found here), or it might be
		4147	confused.
3160		4148
3161	These watchers are stored in lists then need to be walked to find the	4149	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3162	correct watcher to remove. The lists are usually short (you don't usually	4150	make it into some kind of religion.
3163	have many watchers waiting for the same fd or signal).
3164		4151
3165	=item Finding the next timer in each loop iteration: O(1)	4152	If you are unsure about something, feel free to contact the mailing list
		4153	with the full valgrind report and an explanation on why you think this
		4154	is a bug in libev (best check the archives, too :). However, don't be
		4155	annoyed when you get a brisk "this is no bug" answer and take the chance
		4156	of learning how to interpret valgrind properly.
3166		4157
3167	By virtue of using a binary heap, the next timer is always found at the	4158	If you need, for some reason, empty reports from valgrind for your project
3168	beginning of the storage array.	4159	I suggest using suppression lists.
3169		4160
3170	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3171		4161
3172	A change means an I/O watcher gets started or stopped, which requires	4162	=head1 PORTABILITY NOTES
3173	libev to recalculate its status (and possibly tell the kernel, depending
3174	on backend and wether C<ev_io_set> was used).
3175		4163
3176	=item Activating one watcher (putting it into the pending state): O(1)	4164	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3177
3178	=item Priority handling: O(number_of_priorities)
3179
3180	Priorities are implemented by allocating some space for each
3181	priority. When doing priority-based operations, libev usually has to
3182	linearly search all the priorities, but starting/stopping and activating
3183	watchers becomes O(1) w.r.t. priority handling.
3184
3185	=item Sending an ev_async: O(1)
3186
3187	=item Processing ev_async_send: O(number_of_async_watchers)
3188
3189	=item Processing signals: O(max_signal_number)
3190
3191	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3192	calls in the current loop iteration. Checking for async and signal events
3193	involves iterating over all running async watchers or all signal numbers.
3194
3195	=back
3196
3197
3198	=head1 Win32 platform limitations and workarounds
3199		4165
3200	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4166	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3201	requires, and its I/O model is fundamentally incompatible with the POSIX	4167	requires, and its I/O model is fundamentally incompatible with the POSIX
3202	model. Libev still offers limited functionality on this platform in	4168	model. Libev still offers limited functionality on this platform in
3203	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4169	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3204	descriptors. This only applies when using Win32 natively, not when using	4170	descriptors. This only applies when using Win32 natively, not when using
3205	e.g. cygwin.	4171	e.g. cygwin.
3206		4172
		4173	Lifting these limitations would basically require the full
		4174	re-implementation of the I/O system. If you are into these kinds of
		4175	things, then note that glib does exactly that for you in a very portable
		4176	way (note also that glib is the slowest event library known to man).
		4177
3207	There is no supported compilation method available on windows except	4178	There is no supported compilation method available on windows except
3208	embedding it into other applications.	4179	embedding it into other applications.
3209		4180
		4181	Sensible signal handling is officially unsupported by Microsoft - libev
		4182	tries its best, but under most conditions, signals will simply not work.
		4183
		4184	Not a libev limitation but worth mentioning: windows apparently doesn't
		4185	accept large writes: instead of resulting in a partial write, windows will
		4186	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4187	so make sure you only write small amounts into your sockets (less than a
		4188	megabyte seems safe, but this apparently depends on the amount of memory
		4189	available).
		4190
3210	Due to the many, low, and arbitrary limits on the win32 platform and the	4191	Due to the many, low, and arbitrary limits on the win32 platform and
3211	abysmal performance of winsockets, using a large number of sockets is not	4192	the abysmal performance of winsockets, using a large number of sockets
3212	recommended (and not reasonable). If your program needs to use more than	4193	is not recommended (and not reasonable). If your program needs to use
3213	a hundred or so sockets, then likely it needs to use a totally different	4194	more than a hundred or so sockets, then likely it needs to use a totally
3214	implementation for windows, as libev offers the POSIX model, which cannot	4195	different implementation for windows, as libev offers the POSIX readiness
3215	be implemented efficiently on windows (microsoft monopoly games).	4196	notification model, which cannot be implemented efficiently on windows
		4197	(due to Microsoft monopoly games).
		4198
		4199	A typical way to use libev under windows is to embed it (see the embedding
		4200	section for details) and use the following F<evwrap.h> header file instead
		4201	of F<ev.h>:
		4202
		4203	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4204	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4205
		4206	#include "ev.h"
		4207
		4208	And compile the following F<evwrap.c> file into your project (make sure
		4209	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4210
		4211	#include "evwrap.h"
		4212	#include "ev.c"
3216		4213
3217	=over 4	4214	=over 4
3218		4215
3219	=item The winsocket select function	4216	=item The winsocket select function
3220		4217
3221	The winsocket C<select> function doesn't follow POSIX in that it requires	4218	The winsocket C<select> function doesn't follow POSIX in that it
3222	socket I<handles> and not socket I<file descriptors>. This makes select	4219	requires socket I<handles> and not socket I<file descriptors> (it is
3223	very inefficient, and also requires a mapping from file descriptors	4220	also extremely buggy). This makes select very inefficient, and also
3224	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4221	requires a mapping from file descriptors to socket handles (the Microsoft
3225	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4222	C runtime provides the function C<_open_osfhandle> for this). See the
3226	symbols for more info.	4223	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4224	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3227		4225
3228	The configuration for a "naked" win32 using the microsoft runtime	4226	The configuration for a "naked" win32 using the Microsoft runtime
3229	libraries and raw winsocket select is:	4227	libraries and raw winsocket select is:
3230		4228
3231	#define EV_USE_SELECT 1	4229	#define EV_USE_SELECT 1
3232	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4230	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3233		4231
3234	Note that winsockets handling of fd sets is O(n), so you can easily get a	4232	Note that winsockets handling of fd sets is O(n), so you can easily get a
3235	complexity in the O(n²) range when using win32.	4233	complexity in the O(n²) range when using win32.
3236		4234
3237	=item Limited number of file descriptors	4235	=item Limited number of file descriptors
3238		4236
3239	Windows has numerous arbitrary (and low) limits on things. Early versions	4237	Windows has numerous arbitrary (and low) limits on things.
3240	of winsocket's select only supported waiting for a max. of C<64> handles	4238
		4239	Early versions of winsocket's select only supported waiting for a maximum
3241	(probably owning to the fact that all windows kernels can only wait for	4240	of C<64> handles (probably owning to the fact that all windows kernels
3242	C<64> things at the same time internally; microsoft recommends spawning a	4241	can only wait for C<64> things at the same time internally; Microsoft
3243	chain of threads and wait for 63 handles and the previous thread in each).	4242	recommends spawning a chain of threads and wait for 63 handles and the
		4243	previous thread in each. Sounds great!).
3244		4244
3245	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4245	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3246	to some high number (e.g. C<2048>) before compiling the winsocket select	4246	to some high number (e.g. C<2048>) before compiling the winsocket select
3247	call (which might be in libev or elsewhere, for example, perl does its own	4247	call (which might be in libev or elsewhere, for example, perl and many
3248	select emulation on windows).	4248	other interpreters do their own select emulation on windows).
3249		4249
3250	Another limit is the number of file descriptors in the microsoft runtime	4250	Another limit is the number of file descriptors in the Microsoft runtime
3251	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4251	libraries, which by default is C<64> (there must be a hidden I<64>
3252	or something like this inside microsoft). You can increase this by calling	4252	fetish or something like this inside Microsoft). You can increase this
3253	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4253	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3254	arbitrary limit), but is broken in many versions of the microsoft runtime	4254	(another arbitrary limit), but is broken in many versions of the Microsoft
3255	libraries.
3256
3257	This might get you to about C<512> or C<2048> sockets (depending on	4255	runtime libraries. This might get you to about C<512> or C<2048> sockets
3258	windows version and/or the phase of the moon). To get more, you need to	4256	(depending on windows version and/or the phase of the moon). To get more,
3259	wrap all I/O functions and provide your own fd management, but the cost of	4257	you need to wrap all I/O functions and provide your own fd management, but
3260	calling select (O(n²)) will likely make this unworkable.	4258	the cost of calling select (O(n²)) will likely make this unworkable.
3261		4259
3262	=back	4260	=back
3263		4261
3264
3265	=head1 PORTABILITY REQUIREMENTS	4262	=head2 PORTABILITY REQUIREMENTS
3266		4263
3267	In addition to a working ISO-C implementation, libev relies on a few	4264	In addition to a working ISO-C implementation and of course the
3268	additional extensions:	4265	backend-specific APIs, libev relies on a few additional extensions:
3269		4266
3270	=over 4	4267	=over 4
3271		4268
		4269	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4270	calling conventions regardless of C<ev_watcher_type *>.
		4271
		4272	Libev assumes not only that all watcher pointers have the same internal
		4273	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4274	assumes that the same (machine) code can be used to call any watcher
		4275	callback: The watcher callbacks have different type signatures, but libev
		4276	calls them using an C<ev_watcher *> internally.
		4277
3272	=item C<sig_atomic_t volatile> must be thread-atomic as well	4278	=item C<sig_atomic_t volatile> must be thread-atomic as well
3273		4279
3274	The type C<sig_atomic_t volatile> (or whatever is defined as	4280	The type C<sig_atomic_t volatile> (or whatever is defined as
3275	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4281	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3276	threads. This is not part of the specification for C<sig_atomic_t>, but is	4282	threads. This is not part of the specification for C<sig_atomic_t>, but is
3277	believed to be sufficiently portable.	4283	believed to be sufficiently portable.
3278		4284
3279	=item C<sigprocmask> must work in a threaded environment	4285	=item C<sigprocmask> must work in a threaded environment
3280		4286
…		…
3287		4293
3288	The most portable way to handle signals is to block signals in all threads	4294	The most portable way to handle signals is to block signals in all threads
3289	except the initial one, and run the default loop in the initial thread as	4295	except the initial one, and run the default loop in the initial thread as
3290	well.	4296	well.
3291		4297
		4298	=item C<long> must be large enough for common memory allocation sizes
		4299
		4300	To improve portability and simplify its API, libev uses C<long> internally
		4301	instead of C<size_t> when allocating its data structures. On non-POSIX
		4302	systems (Microsoft...) this might be unexpectedly low, but is still at
		4303	least 31 bits everywhere, which is enough for hundreds of millions of
		4304	watchers.
		4305
		4306	=item C<double> must hold a time value in seconds with enough accuracy
		4307
		4308	The type C<double> is used to represent timestamps. It is required to
		4309	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4310	enough for at least into the year 4000. This requirement is fulfilled by
		4311	implementations implementing IEEE 754, which is basically all existing
		4312	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4313	2200.
		4314
3292	=back	4315	=back
3293		4316
3294	If you know of other additional requirements drop me a note.	4317	If you know of other additional requirements drop me a note.
3295		4318
3296		4319
		4320	=head1 ALGORITHMIC COMPLEXITIES
		4321
		4322	In this section the complexities of (many of) the algorithms used inside
		4323	libev will be documented. For complexity discussions about backends see
		4324	the documentation for C<ev_default_init>.
		4325
		4326	All of the following are about amortised time: If an array needs to be
		4327	extended, libev needs to realloc and move the whole array, but this
		4328	happens asymptotically rarer with higher number of elements, so O(1) might
		4329	mean that libev does a lengthy realloc operation in rare cases, but on
		4330	average it is much faster and asymptotically approaches constant time.
		4331
		4332	=over 4
		4333
		4334	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4335
		4336	This means that, when you have a watcher that triggers in one hour and
		4337	there are 100 watchers that would trigger before that, then inserting will
		4338	have to skip roughly seven (C<ld 100>) of these watchers.
		4339
		4340	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4341
		4342	That means that changing a timer costs less than removing/adding them,
		4343	as only the relative motion in the event queue has to be paid for.
		4344
		4345	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4346
		4347	These just add the watcher into an array or at the head of a list.
		4348
		4349	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4350
		4351	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4352
		4353	These watchers are stored in lists, so they need to be walked to find the
		4354	correct watcher to remove. The lists are usually short (you don't usually
		4355	have many watchers waiting for the same fd or signal: one is typical, two
		4356	is rare).
		4357
		4358	=item Finding the next timer in each loop iteration: O(1)
		4359
		4360	By virtue of using a binary or 4-heap, the next timer is always found at a
		4361	fixed position in the storage array.
		4362
		4363	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4364
		4365	A change means an I/O watcher gets started or stopped, which requires
		4366	libev to recalculate its status (and possibly tell the kernel, depending
		4367	on backend and whether C<ev_io_set> was used).
		4368
		4369	=item Activating one watcher (putting it into the pending state): O(1)
		4370
		4371	=item Priority handling: O(number_of_priorities)
		4372
		4373	Priorities are implemented by allocating some space for each
		4374	priority. When doing priority-based operations, libev usually has to
		4375	linearly search all the priorities, but starting/stopping and activating
		4376	watchers becomes O(1) with respect to priority handling.
		4377
		4378	=item Sending an ev_async: O(1)
		4379
		4380	=item Processing ev_async_send: O(number_of_async_watchers)
		4381
		4382	=item Processing signals: O(max_signal_number)
		4383
		4384	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4385	calls in the current loop iteration. Checking for async and signal events
		4386	involves iterating over all running async watchers or all signal numbers.
		4387
		4388	=back
		4389
		4390
		4391	=head1 GLOSSARY
		4392
		4393	=over 4
		4394
		4395	=item active
		4396
		4397	A watcher is active as long as it has been started (has been attached to
		4398	an event loop) but not yet stopped (disassociated from the event loop).
		4399
		4400	=item application
		4401
		4402	In this document, an application is whatever is using libev.
		4403
		4404	=item callback
		4405
		4406	The address of a function that is called when some event has been
		4407	detected. Callbacks are being passed the event loop, the watcher that
		4408	received the event, and the actual event bitset.
		4409
		4410	=item callback invocation
		4411
		4412	The act of calling the callback associated with a watcher.
		4413
		4414	=item event
		4415
		4416	A change of state of some external event, such as data now being available
		4417	for reading on a file descriptor, time having passed or simply not having
		4418	any other events happening anymore.
		4419
		4420	In libev, events are represented as single bits (such as C<EV_READ> or
		4421	C<EV_TIMEOUT>).
		4422
		4423	=item event library
		4424
		4425	A software package implementing an event model and loop.
		4426
		4427	=item event loop
		4428
		4429	An entity that handles and processes external events and converts them
		4430	into callback invocations.
		4431
		4432	=item event model
		4433
		4434	The model used to describe how an event loop handles and processes
		4435	watchers and events.
		4436
		4437	=item pending
		4438
		4439	A watcher is pending as soon as the corresponding event has been detected,
		4440	and stops being pending as soon as the watcher will be invoked or its
		4441	pending status is explicitly cleared by the application.
		4442
		4443	A watcher can be pending, but not active. Stopping a watcher also clears
		4444	its pending status.
		4445
		4446	=item real time
		4447
		4448	The physical time that is observed. It is apparently strictly monotonic :)
		4449
		4450	=item wall-clock time
		4451
		4452	The time and date as shown on clocks. Unlike real time, it can actually
		4453	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4454	clock.
		4455
		4456	=item watcher
		4457
		4458	A data structure that describes interest in certain events. Watchers need
		4459	to be started (attached to an event loop) before they can receive events.
		4460
		4461	=item watcher invocation
		4462
		4463	The act of calling the callback associated with a watcher.
		4464
		4465	=back
		4466
3297	=head1 AUTHOR	4467	=head1 AUTHOR
3298		4468
3299	Marc Lehmann <libev@schmorp.de>.	4469	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3300		4470

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