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Revision 1.245 by root, Tue Jun 30 06:24:38 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
…		…
552	received events and started processing them. This timestamp does not	634	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	635	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	636	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).	637	event occurring (or more correctly, libev finding out about it).
556		638
		639	=item ev_now_update (loop)
		640
		641	Establishes the current time by querying the kernel, updating the time
		642	returned by C<ev_now ()> in the progress. This is a costly operation and
		643	is usually done automatically within C<ev_loop ()>.
		644
		645	This function is rarely useful, but when some event callback runs for a
		646	very long time without entering the event loop, updating libev's idea of
		647	the current time is a good idea.
		648
		649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
		676
557	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
558		678
559	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
560	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
561	events.	681	events.
…		…
563	If the flags argument is specified as C<0>, it will not return until	683	If the flags argument is specified as C<0>, it will not return until
564	either no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
565		685
566	Please note that an explicit C<ev_unloop> is usually better than	686	Please note that an explicit C<ev_unloop> is usually better than
567	relying on all watchers to be stopped when deciding when a program has	687	relying on all watchers to be stopped when deciding when a program has
568	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
569	automatically loops as long as it has to and no longer by virtue of	689	that automatically loops as long as it has to and no longer by virtue
570	relying on its watchers stopping correctly is a thing of beauty.	690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
571		692
572	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
573	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
574	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
575		697
576	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
577	neccessary) and will handle those and any outstanding ones. It will block	699	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	700	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	701	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	702	user-registered callback will be called), and will return after one
		703	iteration of the loop.
		704
		705	This is useful if you are waiting for some external event in conjunction
		706	with something not expressible using other libev watchers (i.e. "roll your
581	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
582	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
583		709
584	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
585		711
586	- Before the first iteration, call any pending watchers.	712	- Before the first iteration, call any pending watchers.
587	* If EVFLAG_FORKCHECK was used, check for a fork.	713	* If EVFLAG_FORKCHECK was used, check for a fork.
588	- If a fork was detected, queue and call all fork watchers.	714	- If a fork was detected (by any means), queue and call all fork watchers.
589	- Queue and call all prepare watchers.	715	- Queue and call all prepare watchers.
590	- If we have been forked, recreate the kernel state.	716	- If we have been forked, detach and recreate the kernel state
		717	as to not disturb the other process.
591	- Update the kernel state with all outstanding changes.	718	- Update the kernel state with all outstanding changes.
592	- Update the "event loop time".	719	- Update the "event loop time" (ev_now ()).
593	- Calculate for how long to sleep or block, if at all	720	- Calculate for how long to sleep or block, if at all
594	(active idle watchers, EVLOOP_NONBLOCK or not having	721	(active idle watchers, EVLOOP_NONBLOCK or not having
595	any active watchers at all will result in not sleeping).	722	any active watchers at all will result in not sleeping).
596	- Sleep if the I/O and timer collect interval say so.	723	- Sleep if the I/O and timer collect interval say so.
597	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
598	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
599	- Update the "event loop time" and do time jump handling.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
600	- Queue all outstanding timers.	727	- Queue all expired timers.
601	- Queue all outstanding periodics.	728	- Queue all expired periodics.
602	- If no events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
603	- Queue all check watchers.	730	- Queue all check watchers.
604	- Call all queued watchers in reverse order (i.e. check watchers first).	731	- Call all queued watchers in reverse order (i.e. check watchers first).
605	Signals and child watchers are implemented as I/O watchers, and will	732	Signals and child watchers are implemented as I/O watchers, and will
606	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	734	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
612	anymore.	739	anymore.
613		740
614	... queue jobs here, make sure they register event watchers as long	741	... 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..)	742	... as they still have work to do (even an idle watcher will do..)
616	ev_loop (my_loop, 0);	743	ev_loop (my_loop, 0);
617	... jobs done. yeah!	744	... jobs done or somebody called unloop. yeah!
618		745
619	=item ev_unloop (loop, how)	746	=item ev_unloop (loop, how)
620		747
621	Can be used to make a call to C<ev_loop> return early (but only after it	748	Can be used to make a call to C<ev_loop> return early (but only after it
622	has processed all outstanding events). The C<how> argument must be either	749	has processed all outstanding events). The C<how> argument must be either
623	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
624	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
625		752
626	This "unloop state" will be cleared when entering C<ev_loop> again.	753	This "unloop state" will be cleared when entering C<ev_loop> again.
627		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
628	=item ev_ref (loop)	757	=item ev_ref (loop)
629		758
630	=item ev_unref (loop)	759	=item ev_unref (loop)
631		760
632	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
633	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
634	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
635	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
636	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
637	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
638	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
639	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
640	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
641	libraries. Just remember to I<unref after start> and I<ref before stop>	773	third-party libraries. Just remember to I<unref after start> and I<ref
642	(but only if the watcher wasn't active before, or was active before,	774	before stop> (but only if the watcher wasn't active before, or was active
643	respectively).	775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
644		778
645	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
646	running when nothing else is active.	780	running when nothing else is active.
647		781
648	struct ev_signal exitsig;	782	ev_signal exitsig;
649	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
650	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
651	evf_unref (loop);	785	evf_unref (loop);
652		786
653	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
654		788
655	ev_ref (loop);	789	ev_ref (loop);
656	ev_signal_stop (loop, &exitsig);	790	ev_signal_stop (loop, &exitsig);
657		791
658	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	792	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
659		793
660	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	794	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
661		795
662	These advanced functions influence the time that libev will spend waiting	796	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	797	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.	798	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		799	latency.
665		800
666	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
667	allows libev to delay invocation of I/O and timer/periodic callbacks to	802	allows libev to delay invocation of I/O and timer/periodic callbacks
668	increase efficiency of loop iterations.	803	to increase efficiency of loop iterations (or to increase power-saving
		804	opportunities).
669		805
670	The background is that sometimes your program runs just fast enough to	806	The idea is that sometimes your program runs just fast enough to handle
671	handle one (or very few) event(s) per loop iteration. While this makes	807	one (or very few) event(s) per loop iteration. While this makes the
672	the program responsive, it also wastes a lot of CPU time to poll for new	808	program responsive, it also wastes a lot of CPU time to poll for new
673	events, especially with backends like C<select ()> which have a high	809	events, especially with backends like C<select ()> which have a high
674	overhead for the actual polling but can deliver many events at once.	810	overhead for the actual polling but can deliver many events at once.
675		811
676	By setting a higher I<io collect interval> you allow libev to spend more	812	By setting a higher I<io collect interval> you allow libev to spend more
677	time collecting I/O events, so you can handle more events per iteration,	813	time collecting I/O events, so you can handle more events per iteration,
678	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	814	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	815	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.	816	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		817	sleep time ensures that libev will not poll for I/O events more often then
		818	once per this interval, on average.
681		819
682	Likewise, by setting a higher I<timeout collect interval> you allow libev	820	Likewise, by setting a higher I<timeout collect interval> you allow libev
683	to spend more time collecting timeouts, at the expense of increased	821	to spend more time collecting timeouts, at the expense of increased
684	latency (the watcher callback will be called later). C<ev_io> watchers	822	latency/jitter/inexactness (the watcher callback will be called
685	will not be affected. Setting this to a non-null value will not introduce	823	later). C<ev_io> watchers will not be affected. Setting this to a non-null
686	any overhead in libev.	824	value will not introduce any overhead in libev.
687		825
688	Many (busy) programs can usually benefit by setting the io collect	826	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	827	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	828	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>,	829	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.	830	as this approaches the timing granularity of most systems. Note that if
		831	you do transactions with the outside world and you can't increase the
		832	parallelity, then this setting will limit your transaction rate (if you
		833	need to poll once per transaction and the I/O collect interval is 0.01,
		834	then you can't do more than 100 transations per second).
		835
		836	Setting the I<timeout collect interval> can improve the opportunity for
		837	saving power, as the program will "bundle" timer callback invocations that
		838	are "near" in time together, by delaying some, thus reducing the number of
		839	times the process sleeps and wakes up again. Another useful technique to
		840	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		841	they fire on, say, one-second boundaries only.
		842
		843	Example: we only need 0.1s timeout granularity, and we wish not to poll
		844	more often than 100 times per second:
		845
		846	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		847	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		848
		849	=item ev_loop_verify (loop)
		850
		851	This function only does something when C<EV_VERIFY> support has been
		852	compiled in, which is the default for non-minimal builds. It tries to go
		853	through all internal structures and checks them for validity. If anything
		854	is found to be inconsistent, it will print an error message to standard
		855	error and call C<abort ()>.
		856
		857	This can be used to catch bugs inside libev itself: under normal
		858	circumstances, this function will never abort as of course libev keeps its
		859	data structures consistent.
693		860
694	=back	861	=back
695		862
696		863
697	=head1 ANATOMY OF A WATCHER	864	=head1 ANATOMY OF A WATCHER
		865
		866	In the following description, uppercase C<TYPE> in names stands for the
		867	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		868	watchers and C<ev_io_start> for I/O watchers.
698		869
699	A watcher is a structure that you create and register to record your	870	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	871	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:	872	become readable, you would create an C<ev_io> watcher for that:
702		873
703	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	874	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
704	{	875	{
705	ev_io_stop (w);	876	ev_io_stop (w);
706	ev_unloop (loop, EVUNLOOP_ALL);	877	ev_unloop (loop, EVUNLOOP_ALL);
707	}	878	}
708		879
709	struct ev_loop *loop = ev_default_loop (0);	880	struct ev_loop *loop = ev_default_loop (0);
		881
710	struct ev_io stdin_watcher;	882	ev_io stdin_watcher;
		883
711	ev_init (&stdin_watcher, my_cb);	884	ev_init (&stdin_watcher, my_cb);
712	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	885	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
713	ev_io_start (loop, &stdin_watcher);	886	ev_io_start (loop, &stdin_watcher);
		887
714	ev_loop (loop, 0);	888	ev_loop (loop, 0);
715		889
716	As you can see, you are responsible for allocating the memory for your	890	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,	891	watcher structures (and it is I<usually> a bad idea to do this on the
718	although this can sometimes be quite valid).	892	stack).
		893
		894	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		895	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
719		896
720	Each watcher structure must be initialised by a call to C<ev_init	897	Each watcher structure must be initialised by a call to C<ev_init
721	(watcher *, callback)>, which expects a callback to be provided. This	898	(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	899	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	900	watchers, each time the event loop detects that the file descriptor given
724	is readable and/or writable).	901	is readable and/or writable).
725		902
726	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	903	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	904	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	905	is also a macro to combine initialisation and setting in one call: C<<
729	(watcher *, callback, ...) >>.	906	ev_TYPE_init (watcher *, callback, ...) >>.
730		907
731	To make the watcher actually watch out for events, you have to start it	908	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	909	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	910	*) >>), and you can stop watching for events at any time by calling the
734	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	911	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
735		912
736	As long as your watcher is active (has been started but not stopped) you	913	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	914	must not touch the values stored in it. Most specifically you must never
738	reinitialise it or call its C<set> macro.	915	reinitialise it or call its C<ev_TYPE_set> macro.
739		916
740	Each and every callback receives the event loop pointer as first, the	917	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	918	registered watcher structure as second, and a bitset of received events as
742	third argument.	919	third argument.
743		920
…		…
801		978
802	=item C<EV_ASYNC>	979	=item C<EV_ASYNC>
803		980
804	The given async watcher has been asynchronously notified (see C<ev_async>).	981	The given async watcher has been asynchronously notified (see C<ev_async>).
805		982
		983	=item C<EV_CUSTOM>
		984
		985	Not ever sent (or otherwise used) by libev itself, but can be freely used
		986	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		987
806	=item C<EV_ERROR>	988	=item C<EV_ERROR>
807		989
808	An unspecified error has occured, the watcher has been stopped. This might	990	An unspecified error has occurred, the watcher has been stopped. This might
809	happen because the watcher could not be properly started because libev	991	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	992	ran out of memory, a file descriptor was found to be closed or any other
		993	problem. Libev considers these application bugs.
		994
811	problem. You best act on it by reporting the problem and somehow coping	995	You best act on it by reporting the problem and somehow coping with the
812	with the watcher being stopped.	996	watcher being stopped. Note that well-written programs should not receive
		997	an error ever, so when your watcher receives it, this usually indicates a
		998	bug in your program.
813		999
814	Libev will usually signal a few "dummy" events together with an error,	1000	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	1001	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	1002	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	1003	the error from read() or write(). This will not work in multi-threaded
818	programs, though, so beware.	1004	programs, though, as the fd could already be closed and reused for another
		1005	thing, so beware.
819		1006
820	=back	1007	=back
821		1008
822	=head2 GENERIC WATCHER FUNCTIONS	1009	=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		1010
827	=over 4	1011	=over 4
828		1012
829	=item C<ev_init> (ev_TYPE *watcher, callback)	1013	=item C<ev_init> (ev_TYPE *watcher, callback)
830		1014
…		…
836	which rolls both calls into one.	1020	which rolls both calls into one.
837		1021
838	You can reinitialise a watcher at any time as long as it has been stopped	1022	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.	1023	(or never started) and there are no pending events outstanding.
840		1024
841	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1025	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
842	int revents)>.	1026	int revents)>.
		1027
		1028	Example: Initialise an C<ev_io> watcher in two steps.
		1029
		1030	ev_io w;
		1031	ev_init (&w, my_cb);
		1032	ev_io_set (&w, STDIN_FILENO, EV_READ);
843		1033
844	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1034	=item C<ev_TYPE_set> (ev_TYPE *, [args])
845		1035
846	This macro initialises the type-specific parts of a watcher. You need to	1036	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	1037	call C<ev_init> at least once before you call this macro, but you can
…		…
850	difference to the C<ev_init> macro).	1040	difference to the C<ev_init> macro).
851		1041
852	Although some watcher types do not have type-specific arguments	1042	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.	1043	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
854		1044
		1045	See C<ev_init>, above, for an example.
		1046
855	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1047	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
856		1048
857	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1049	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	1050	calls into a single call. This is the most convenient method to initialise
859	a watcher. The same limitations apply, of course.	1051	a watcher. The same limitations apply, of course.
		1052
		1053	Example: Initialise and set an C<ev_io> watcher in one step.
		1054
		1055	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
860		1056
861	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1057	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
862		1058
863	Starts (activates) the given watcher. Only active watchers will receive	1059	Starts (activates) the given watcher. Only active watchers will receive
864	events. If the watcher is already active nothing will happen.	1060	events. If the watcher is already active nothing will happen.
865		1061
		1062	Example: Start the C<ev_io> watcher that is being abused as example in this
		1063	whole section.
		1064
		1065	ev_io_start (EV_DEFAULT_UC, &w);
		1066
866	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1067	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
867		1068
868	Stops the given watcher again (if active) and clears the pending	1069	Stops the given watcher if active, and clears the pending status (whether
		1070	the watcher was active or not).
		1071
869	status. It is possible that stopped watchers are pending (for example,	1072	It is possible that stopped watchers are pending - for example,
870	non-repeating timers are being stopped when they become pending), but	1073	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	1074	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	1075	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.	1076	therefore a good idea to always call its C<ev_TYPE_stop> function.
874		1077
875	=item bool ev_is_active (ev_TYPE *watcher)	1078	=item bool ev_is_active (ev_TYPE *watcher)
876		1079
877	Returns a true value iff the watcher is active (i.e. it has been started	1080	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	1081	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>	1107	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
905	(default: C<-2>). Pending watchers with higher priority will be invoked	1108	(default: C<-2>). Pending watchers with higher priority will be invoked
906	before watchers with lower priority, but priority will not keep watchers	1109	before watchers with lower priority, but priority will not keep watchers
907	from being executed (except for C<ev_idle> watchers).	1110	from being executed (except for C<ev_idle> watchers).
908		1111
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	1112	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.	1113	you need to look at C<ev_idle> watchers, which provide this functionality.
916		1114
917	You I<must not> change the priority of a watcher as long as it is active or	1115	You I<must not> change the priority of a watcher as long as it is active or
918	pending.	1116	pending.
919		1117
		1118	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1119	fine, as long as you do not mind that the priority value you query might
		1120	or might not have been clamped to the valid range.
		1121
920	The default priority used by watchers when no priority has been set is	1122	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 :).	1123	always C<0>, which is supposed to not be too high and not be too low :).
922		1124
923	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1125	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	1126	priorities.
925	or might not have been adjusted to be within valid range.
926		1127
927	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1128	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
928		1129
929	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1130	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	1131	C<loop> nor C<revents> need to be valid as long as the watcher callback
931	can deal with that fact.	1132	can deal with that fact, as both are simply passed through to the
		1133	callback.
932		1134
933	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1135	=item int ev_clear_pending (loop, ev_TYPE *watcher)
934		1136
935	If the watcher is pending, this function returns clears its pending status	1137	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	1138	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>.	1139	watcher isn't pending it does nothing and returns C<0>.
938		1140
		1141	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1142	callback to be invoked, which can be accomplished with this function.
		1143
939	=back	1144	=back
940		1145
941		1146
942	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1147	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
943		1148
944	Each watcher has, by default, a member C<void *data> that you can change	1149	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	1150	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	1151	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	1152	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	1153	member, you can also "subclass" the watcher type and provide your own
949	data:	1154	data:
950		1155
951	struct my_io	1156	struct my_io
952	{	1157	{
953	struct ev_io io;	1158	ev_io io;
954	int otherfd;	1159	int otherfd;
955	void *somedata;	1160	void *somedata;
956	struct whatever *mostinteresting;	1161	struct whatever *mostinteresting;
957	}	1162	};
		1163
		1164	...
		1165	struct my_io w;
		1166	ev_io_init (&w.io, my_cb, fd, EV_READ);
958		1167
959	And since your callback will be called with a pointer to the watcher, you	1168	And since your callback will be called with a pointer to the watcher, you
960	can cast it back to your own type:	1169	can cast it back to your own type:
961		1170
962	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1171	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
963	{	1172	{
964	struct my_io *w = (struct my_io *)w_;	1173	struct my_io *w = (struct my_io *)w_;
965	...	1174	...
966	}	1175	}
967		1176
968	More interesting and less C-conformant ways of casting your callback type	1177	More interesting and less C-conformant ways of casting your callback type
969	instead have been omitted.	1178	instead have been omitted.
970		1179
971	Another common scenario is having some data structure with multiple	1180	Another common scenario is to use some data structure with multiple
972	watchers:	1181	embedded watchers:
973		1182
974	struct my_biggy	1183	struct my_biggy
975	{	1184	{
976	int some_data;	1185	int some_data;
977	ev_timer t1;	1186	ev_timer t1;
978	ev_timer t2;	1187	ev_timer t2;
979	}	1188	}
980		1189
981	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1190	In this case getting the pointer to C<my_biggy> is a bit more
982	you need to use C<offsetof>:	1191	complicated: Either you store the address of your C<my_biggy> struct
		1192	in the C<data> member of the watcher (for woozies), or you need to use
		1193	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1194	programmers):
983		1195
984	#include <stddef.h>	1196	#include <stddef.h>
985		1197
986	static void	1198	static void
987	t1_cb (EV_P_ struct ev_timer *w, int revents)	1199	t1_cb (EV_P_ ev_timer *w, int revents)
988	{	1200	{
989	struct my_biggy big = (struct my_biggy *	1201	struct my_biggy big = (struct my_biggy *)
990	(((char *)w) - offsetof (struct my_biggy, t1));	1202	(((char *)w) - offsetof (struct my_biggy, t1));
991	}	1203	}
992		1204
993	static void	1205	static void
994	t2_cb (EV_P_ struct ev_timer *w, int revents)	1206	t2_cb (EV_P_ ev_timer *w, int revents)
995	{	1207	{
996	struct my_biggy big = (struct my_biggy *	1208	struct my_biggy big = (struct my_biggy *)
997	(((char *)w) - offsetof (struct my_biggy, t2));	1209	(((char *)w) - offsetof (struct my_biggy, t2));
998	}	1210	}
		1211
		1212	=head2 WATCHER PRIORITY MODELS
		1213
		1214	Many event loops support I<watcher priorities>, which are usually small
		1215	integers that influence the ordering of event callback invocation
		1216	between watchers in some way, all else being equal.
		1217
		1218	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1219	description for the more technical details such as the actual priority
		1220	range.
		1221
		1222	There are two common ways how these these priorities are being interpreted
		1223	by event loops:
		1224
		1225	In the more common lock-out model, higher priorities "lock out" invocation
		1226	of lower priority watchers, which means as long as higher priority
		1227	watchers receive events, lower priority watchers are not being invoked.
		1228
		1229	The less common only-for-ordering model uses priorities solely to order
		1230	callback invocation within a single event loop iteration: Higher priority
		1231	watchers are invoked before lower priority ones, but they all get invoked
		1232	before polling for new events.
		1233
		1234	Libev uses the second (only-for-ordering) model for all its watchers
		1235	except for idle watchers (which use the lock-out model).
		1236
		1237	The rationale behind this is that implementing the lock-out model for
		1238	watchers is not well supported by most kernel interfaces, and most event
		1239	libraries will just poll for the same events again and again as long as
		1240	their callbacks have not been executed, which is very inefficient in the
		1241	common case of one high-priority watcher locking out a mass of lower
		1242	priority ones.
		1243
		1244	Static (ordering) priorities are most useful when you have two or more
		1245	watchers handling the same resource: a typical usage example is having an
		1246	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1247	timeouts. Under load, data might be received while the program handles
		1248	other jobs, but since timers normally get invoked first, the timeout
		1249	handler will be executed before checking for data. In that case, giving
		1250	the timer a lower priority than the I/O watcher ensures that I/O will be
		1251	handled first even under adverse conditions (which is usually, but not
		1252	always, what you want).
		1253
		1254	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1255	will only be executed when no same or higher priority watchers have
		1256	received events, they can be used to implement the "lock-out" model when
		1257	required.
		1258
		1259	For example, to emulate how many other event libraries handle priorities,
		1260	you can associate an C<ev_idle> watcher to each such watcher, and in
		1261	the normal watcher callback, you just start the idle watcher. The real
		1262	processing is done in the idle watcher callback. This causes libev to
		1263	continously poll and process kernel event data for the watcher, but when
		1264	the lock-out case is known to be rare (which in turn is rare :), this is
		1265	workable.
		1266
		1267	Usually, however, the lock-out model implemented that way will perform
		1268	miserably under the type of load it was designed to handle. In that case,
		1269	it might be preferable to stop the real watcher before starting the
		1270	idle watcher, so the kernel will not have to process the event in case
		1271	the actual processing will be delayed for considerable time.
		1272
		1273	Here is an example of an I/O watcher that should run at a strictly lower
		1274	priority than the default, and which should only process data when no
		1275	other events are pending:
		1276
		1277	ev_idle idle; // actual processing watcher
		1278	ev_io io; // actual event watcher
		1279
		1280	static void
		1281	io_cb (EV_P_ ev_io *w, int revents)
		1282	{
		1283	// stop the I/O watcher, we received the event, but
		1284	// are not yet ready to handle it.
		1285	ev_io_stop (EV_A_ w);
		1286
		1287	// start the idle watcher to ahndle the actual event.
		1288	// it will not be executed as long as other watchers
		1289	// with the default priority are receiving events.
		1290	ev_idle_start (EV_A_ &idle);
		1291	}
		1292
		1293	static void
		1294	idle_cb (EV_P_ ev_idle *w, int revents)
		1295	{
		1296	// actual processing
		1297	read (STDIN_FILENO, ...);
		1298
		1299	// have to start the I/O watcher again, as
		1300	// we have handled the event
		1301	ev_io_start (EV_P_ &io);
		1302	}
		1303
		1304	// initialisation
		1305	ev_idle_init (&idle, idle_cb);
		1306	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1307	ev_io_start (EV_DEFAULT_ &io);
		1308
		1309	In the "real" world, it might also be beneficial to start a timer, so that
		1310	low-priority connections can not be locked out forever under load. This
		1311	enables your program to keep a lower latency for important connections
		1312	during short periods of high load, while not completely locking out less
		1313	important ones.
999		1314
1000		1315
1001	=head1 WATCHER TYPES	1316	=head1 WATCHER TYPES
1002		1317
1003	This section describes each watcher in detail, but will not repeat	1318	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	1342	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	1343	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	1344	descriptors to non-blocking mode is also usually a good idea (but not
1030	required if you know what you are doing).	1345	required if you know what you are doing).
1031		1346
1032	If you must do this, then force the use of a known-to-be-good backend	1347	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	1348	known-to-be-good backend (at the time of this writing, this includes only
1034	C<EVBACKEND_POLL>).	1349	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1350	descriptors for which non-blocking operation makes no sense (such as
		1351	files) - libev doesn't guarentee any specific behaviour in that case.
1035		1352
1036	Another thing you have to watch out for is that it is quite easy to	1353	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	1354	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	1355	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	1356	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	1357	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	1358	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	1359	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.	1360	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1044		1361
1045	If you cannot run the fd in non-blocking mode (for example you should not	1362	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	1363	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	1364	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	1365	interface such as poll (fortunately in our Xlib example, Xlib already
1049	its own, so its quite safe to use).	1366	does this on its own, so its quite safe to use). Some people additionally
		1367	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1368	indefinitely.
		1369
		1370	But really, best use non-blocking mode.
1050		1371
1051	=head3 The special problem of disappearing file descriptors	1372	=head3 The special problem of disappearing file descriptors
1052		1373
1053	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1374	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,	1375	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	1376	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	1377	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	1378	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	1379	registered with libev, there is no efficient way to see that this is, in
1059	fact, a different file descriptor.	1380	fact, a different file descriptor.
1060		1381
…		…
1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1412	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1092	C<EVBACKEND_POLL>.	1413	C<EVBACKEND_POLL>.
1093		1414
1094	=head3 The special problem of SIGPIPE	1415	=head3 The special problem of SIGPIPE
1095		1416
1096	While not really specific to libev, it is easy to forget about SIGPIPE:	1417	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	1418	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	1419	sent a SIGPIPE, which, by default, aborts your program. For most programs
1099	programs this is sensible behaviour, for daemons, this is usually	1420	this is sensible behaviour, for daemons, this is usually undesirable.
1100	undesirable.
1101		1421
1102	So when you encounter spurious, unexplained daemon exits, make sure you	1422	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	1423	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).	1424	somewhere, as that would have given you a big clue).
1105		1425
…		…
1111	=item ev_io_init (ev_io *, callback, int fd, int events)	1431	=item ev_io_init (ev_io *, callback, int fd, int events)
1112		1432
1113	=item ev_io_set (ev_io *, int fd, int events)	1433	=item ev_io_set (ev_io *, int fd, int events)
1114		1434
1115	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1435	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	1436	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.	1437	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1118		1438
1119	=item int fd [read-only]	1439	=item int fd [read-only]
1120		1440
1121	The file descriptor being watched.	1441	The file descriptor being watched.
1122		1442
…		…
1130		1450
1131	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1451	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	1452	readable, but only once. Since it is likely line-buffered, you could
1133	attempt to read a whole line in the callback.	1453	attempt to read a whole line in the callback.
1134		1454
1135	static void	1455	static void
1136	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1456	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1137	{	1457	{
1138	ev_io_stop (loop, w);	1458	ev_io_stop (loop, w);
1139	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1459	.. read from stdin here (or from w->fd) and handle any I/O errors
1140	}	1460	}
1141		1461
1142	...	1462	...
1143	struct ev_loop *loop = ev_default_init (0);	1463	struct ev_loop *loop = ev_default_init (0);
1144	struct ev_io stdin_readable;	1464	ev_io stdin_readable;
1145	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1465	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1146	ev_io_start (loop, &stdin_readable);	1466	ev_io_start (loop, &stdin_readable);
1147	ev_loop (loop, 0);	1467	ev_loop (loop, 0);
1148		1468
1149		1469
1150	=head2 C<ev_timer> - relative and optionally repeating timeouts	1470	=head2 C<ev_timer> - relative and optionally repeating timeouts
1151		1471
1152	Timer watchers are simple relative timers that generate an event after a	1472	Timer watchers are simple relative timers that generate an event after a
1153	given time, and optionally repeating in regular intervals after that.	1473	given time, and optionally repeating in regular intervals after that.
1154		1474
1155	The timers are based on real time, that is, if you register an event that	1475	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	1476	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	1477	year, it will still time out after (roughly) one hour. "Roughly" because
1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1478	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1159	monotonic clock option helps a lot here).	1479	monotonic clock option helps a lot here).
		1480
		1481	The callback is guaranteed to be invoked only I<after> its timeout has
		1482	passed (not I<at>, so on systems with very low-resolution clocks this
		1483	might introduce a small delay). If multiple timers become ready during the
		1484	same loop iteration then the ones with earlier time-out values are invoked
		1485	before ones with later time-out values (but this is no longer true when a
		1486	callback calls C<ev_loop> recursively).
		1487
		1488	=head3 Be smart about timeouts
		1489
		1490	Many real-world problems involve some kind of timeout, usually for error
		1491	recovery. A typical example is an HTTP request - if the other side hangs,
		1492	you want to raise some error after a while.
		1493
		1494	What follows are some ways to handle this problem, from obvious and
		1495	inefficient to smart and efficient.
		1496
		1497	In the following, a 60 second activity timeout is assumed - a timeout that
		1498	gets reset to 60 seconds each time there is activity (e.g. each time some
		1499	data or other life sign was received).
		1500
		1501	=over 4
		1502
		1503	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1504
		1505	This is the most obvious, but not the most simple way: In the beginning,
		1506	start the watcher:
		1507
		1508	ev_timer_init (timer, callback, 60., 0.);
		1509	ev_timer_start (loop, timer);
		1510
		1511	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1512	and start it again:
		1513
		1514	ev_timer_stop (loop, timer);
		1515	ev_timer_set (timer, 60., 0.);
		1516	ev_timer_start (loop, timer);
		1517
		1518	This is relatively simple to implement, but means that each time there is
		1519	some activity, libev will first have to remove the timer from its internal
		1520	data structure and then add it again. Libev tries to be fast, but it's
		1521	still not a constant-time operation.
		1522
		1523	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1524
		1525	This is the easiest way, and involves using C<ev_timer_again> instead of
		1526	C<ev_timer_start>.
		1527
		1528	To implement this, configure an C<ev_timer> with a C<repeat> value
		1529	of C<60> and then call C<ev_timer_again> at start and each time you
		1530	successfully read or write some data. If you go into an idle state where
		1531	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1532	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1533
		1534	That means you can ignore both the C<ev_timer_start> function and the
		1535	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1536	member and C<ev_timer_again>.
		1537
		1538	At start:
		1539
		1540	ev_init (timer, callback);
		1541	timer->repeat = 60.;
		1542	ev_timer_again (loop, timer);
		1543
		1544	Each time there is some activity:
		1545
		1546	ev_timer_again (loop, timer);
		1547
		1548	It is even possible to change the time-out on the fly, regardless of
		1549	whether the watcher is active or not:
		1550
		1551	timer->repeat = 30.;
		1552	ev_timer_again (loop, timer);
		1553
		1554	This is slightly more efficient then stopping/starting the timer each time
		1555	you want to modify its timeout value, as libev does not have to completely
		1556	remove and re-insert the timer from/into its internal data structure.
		1557
		1558	It is, however, even simpler than the "obvious" way to do it.
		1559
		1560	=item 3. Let the timer time out, but then re-arm it as required.
		1561
		1562	This method is more tricky, but usually most efficient: Most timeouts are
		1563	relatively long compared to the intervals between other activity - in
		1564	our example, within 60 seconds, there are usually many I/O events with
		1565	associated activity resets.
		1566
		1567	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1568	but remember the time of last activity, and check for a real timeout only
		1569	within the callback:
		1570
		1571	ev_tstamp last_activity; // time of last activity
		1572
		1573	static void
		1574	callback (EV_P_ ev_timer *w, int revents)
		1575	{
		1576	ev_tstamp now = ev_now (EV_A);
		1577	ev_tstamp timeout = last_activity + 60.;
		1578
		1579	// if last_activity + 60. is older than now, we did time out
		1580	if (timeout < now)
		1581	{
		1582	// timeout occured, take action
		1583	}
		1584	else
		1585	{
		1586	// callback was invoked, but there was some activity, re-arm
		1587	// the watcher to fire in last_activity + 60, which is
		1588	// guaranteed to be in the future, so "again" is positive:
		1589	w->repeat = timeout - now;
		1590	ev_timer_again (EV_A_ w);
		1591	}
		1592	}
		1593
		1594	To summarise the callback: first calculate the real timeout (defined
		1595	as "60 seconds after the last activity"), then check if that time has
		1596	been reached, which means something I<did>, in fact, time out. Otherwise
		1597	the callback was invoked too early (C<timeout> is in the future), so
		1598	re-schedule the timer to fire at that future time, to see if maybe we have
		1599	a timeout then.
		1600
		1601	Note how C<ev_timer_again> is used, taking advantage of the
		1602	C<ev_timer_again> optimisation when the timer is already running.
		1603
		1604	This scheme causes more callback invocations (about one every 60 seconds
		1605	minus half the average time between activity), but virtually no calls to
		1606	libev to change the timeout.
		1607
		1608	To start the timer, simply initialise the watcher and set C<last_activity>
		1609	to the current time (meaning we just have some activity :), then call the
		1610	callback, which will "do the right thing" and start the timer:
		1611
		1612	ev_init (timer, callback);
		1613	last_activity = ev_now (loop);
		1614	callback (loop, timer, EV_TIMEOUT);
		1615
		1616	And when there is some activity, simply store the current time in
		1617	C<last_activity>, no libev calls at all:
		1618
		1619	last_actiivty = ev_now (loop);
		1620
		1621	This technique is slightly more complex, but in most cases where the
		1622	time-out is unlikely to be triggered, much more efficient.
		1623
		1624	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1625	callback :) - just change the timeout and invoke the callback, which will
		1626	fix things for you.
		1627
		1628	=item 4. Wee, just use a double-linked list for your timeouts.
		1629
		1630	If there is not one request, but many thousands (millions...), all
		1631	employing some kind of timeout with the same timeout value, then one can
		1632	do even better:
		1633
		1634	When starting the timeout, calculate the timeout value and put the timeout
		1635	at the I<end> of the list.
		1636
		1637	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1638	the list is expected to fire (for example, using the technique #3).
		1639
		1640	When there is some activity, remove the timer from the list, recalculate
		1641	the timeout, append it to the end of the list again, and make sure to
		1642	update the C<ev_timer> if it was taken from the beginning of the list.
		1643
		1644	This way, one can manage an unlimited number of timeouts in O(1) time for
		1645	starting, stopping and updating the timers, at the expense of a major
		1646	complication, and having to use a constant timeout. The constant timeout
		1647	ensures that the list stays sorted.
		1648
		1649	=back
		1650
		1651	So which method the best?
		1652
		1653	Method #2 is a simple no-brain-required solution that is adequate in most
		1654	situations. Method #3 requires a bit more thinking, but handles many cases
		1655	better, and isn't very complicated either. In most case, choosing either
		1656	one is fine, with #3 being better in typical situations.
		1657
		1658	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1659	rather complicated, but extremely efficient, something that really pays
		1660	off after the first million or so of active timers, i.e. it's usually
		1661	overkill :)
		1662
		1663	=head3 The special problem of time updates
		1664
		1665	Establishing the current time is a costly operation (it usually takes at
		1666	least two system calls): EV therefore updates its idea of the current
		1667	time only before and after C<ev_loop> collects new events, which causes a
		1668	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1669	lots of events in one iteration.
1160		1670
1161	The relative timeouts are calculated relative to the C<ev_now ()>	1671	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	1672	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	1673	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	1674	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:	1675	timeout on the current time, use something like this to adjust for this:
1166		1676
1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1677	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1168		1678
1169	The callback is guarenteed to be invoked only when its timeout has passed,	1679	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	1680	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1171	order of execution is undefined.	1681	()>.
1172		1682
1173	=head3 Watcher-Specific Functions and Data Members	1683	=head3 Watcher-Specific Functions and Data Members
1174		1684
1175	=over 4	1685	=over 4
1176		1686
1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1687	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1178		1688
1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1689	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1180		1690
1181	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1691	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	1692	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	1693	reached. If it is positive, then the timer will automatically be
1184	later, again, and again, until stopped manually.	1694	configured to trigger again C<repeat> seconds later, again, and again,
		1695	until stopped manually.
1185		1696
1186	The timer itself will do a best-effort at avoiding drift, that is, if you	1697	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	1698	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	1699	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	1700	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.	1701	do stuff) the timer will not fire more than once per event loop iteration.
1191		1702
1192	=item ev_timer_again (loop, ev_timer *)	1703	=item ev_timer_again (loop, ev_timer *)
1193		1704
1194	This will act as if the timer timed out and restart it again if it is	1705	This will act as if the timer timed out and restart it again if it is
1195	repeating. The exact semantics are:	1706	repeating. The exact semantics are:
1196		1707
1197	If the timer is pending, its pending status is cleared.	1708	If the timer is pending, its pending status is cleared.
1198		1709
1199	If the timer is started but nonrepeating, stop it (as if it timed out).	1710	If the timer is started but non-repeating, stop it (as if it timed out).
1200		1711
1201	If the timer is repeating, either start it if necessary (with the	1712	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.	1713	C<repeat> value), or reset the running timer to the C<repeat> value.
1203		1714
1204	This sounds a bit complicated, but here is a useful and typical	1715	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	1716	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		1717
1229	=item ev_tstamp repeat [read-write]	1718	=item ev_tstamp repeat [read-write]
1230		1719
1231	The current C<repeat> value. Will be used each time the watcher times out	1720	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),	1721	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.	1722	which is also when any modifications are taken into account.
1234		1723
1235	=back	1724	=back
1236		1725
1237	=head3 Examples	1726	=head3 Examples
1238		1727
1239	Example: Create a timer that fires after 60 seconds.	1728	Example: Create a timer that fires after 60 seconds.
1240		1729
1241	static void	1730	static void
1242	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1731	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1243	{	1732	{
1244	.. one minute over, w is actually stopped right here	1733	.. one minute over, w is actually stopped right here
1245	}	1734	}
1246		1735
1247	struct ev_timer mytimer;	1736	ev_timer mytimer;
1248	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1737	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1249	ev_timer_start (loop, &mytimer);	1738	ev_timer_start (loop, &mytimer);
1250		1739
1251	Example: Create a timeout timer that times out after 10 seconds of	1740	Example: Create a timeout timer that times out after 10 seconds of
1252	inactivity.	1741	inactivity.
1253		1742
1254	static void	1743	static void
1255	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1744	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1256	{	1745	{
1257	.. ten seconds without any activity	1746	.. ten seconds without any activity
1258	}	1747	}
1259		1748
1260	struct ev_timer mytimer;	1749	ev_timer mytimer;
1261	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1750	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1262	ev_timer_again (&mytimer); /* start timer */	1751	ev_timer_again (&mytimer); /* start timer */
1263	ev_loop (loop, 0);	1752	ev_loop (loop, 0);
1264		1753
1265	// and in some piece of code that gets executed on any "activity":	1754	// and in some piece of code that gets executed on any "activity":
1266	// reset the timeout to start ticking again at 10 seconds	1755	// reset the timeout to start ticking again at 10 seconds
1267	ev_timer_again (&mytimer);	1756	ev_timer_again (&mytimer);
1268		1757
1269		1758
1270	=head2 C<ev_periodic> - to cron or not to cron?	1759	=head2 C<ev_periodic> - to cron or not to cron?
1271		1760
1272	Periodic watchers are also timers of a kind, but they are very versatile	1761	Periodic watchers are also timers of a kind, but they are very versatile
1273	(and unfortunately a bit complex).	1762	(and unfortunately a bit complex).
1274		1763
1275	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1764	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	1765	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	1766	(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 ()	1767	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	1768	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	1769	wrist-watch).
1281	roughly 10 seconds later).
1282		1770
1283	They can also be used to implement vastly more complex timers, such as	1771	You can tell a periodic watcher to trigger after some specific point
1284	triggering an event on each midnight, local time or other, complicated,	1772	in time: for example, if you tell a periodic watcher to trigger "in 10
1285	rules.	1773	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1774	not a delay) and then reset your system clock to January of the previous
		1775	year, then it will take a year or more to trigger the event (unlike an
		1776	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1777	it, as it uses a relative timeout).
1286		1778
		1779	C<ev_periodic> watchers can also be used to implement vastly more complex
		1780	timers, such as triggering an event on each "midnight, local time", or
		1781	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1782	those cannot react to time jumps.
		1783
1287	As with timers, the callback is guarenteed to be invoked only when the	1784	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	1785	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.	1786	timers become ready during the same loop iteration then the ones with
		1787	earlier time-out values are invoked before ones with later time-out values
		1788	(but this is no longer true when a callback calls C<ev_loop> recursively).
1290		1789
1291	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1292		1791
1293	=over 4	1792	=over 4
1294		1793
1295	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1794	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1296		1795
1297	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1796	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1298		1797
1299	Lots of arguments, lets sort it out... There are basically three modes of	1798	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:	1799	operation, and we will explain them from simplest to most complex:
1301		1800
1302	=over 4	1801	=over 4
1303		1802
1304	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1803	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1305		1804
1306	In this configuration the watcher triggers an event at the wallclock time	1805	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,	1806	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	1807	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.	1808	will be stopped and invoked when the system clock reaches or surpasses
		1809	this point in time.
1310		1810
1311	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1811	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1312		1812
1313	In this mode the watcher will always be scheduled to time out at the next	1813	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)	1814	C<offset + N * interval> time (for some integer N, which can also be
1315	and then repeat, regardless of any time jumps.	1815	negative) and then repeat, regardless of any time jumps. The C<offset>
		1816	argument is merely an offset into the C<interval> periods.
1316		1817
1317	This can be used to create timers that do not drift with respect to system	1818	This can be used to create timers that do not drift with respect to the
1318	time:	1819	system clock, for example, here is an C<ev_periodic> that triggers each
		1820	hour, on the hour (with respect to UTC):
1319		1821
1320	ev_periodic_set (&periodic, 0., 3600., 0);	1822	ev_periodic_set (&periodic, 0., 3600., 0);
1321		1823
1322	This doesn't mean there will always be 3600 seconds in between triggers,	1824	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	1825	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	1826	full hour (UTC), or more correctly, when the system time is evenly divisible
1325	by 3600.	1827	by 3600.
1326		1828
1327	Another way to think about it (for the mathematically inclined) is that	1829	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	1830	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.	1831	time where C<time = offset (mod interval)>, regardless of any time jumps.
1330		1832
1331	For numerical stability it is preferable that the C<at> value is near	1833	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	1834	C<ev_now ()> (the current time), but there is no range requirement for
1333	this value.	1835	this value, and in fact is often specified as zero.
1334		1836
		1837	Note also that there is an upper limit to how often a timer can fire (CPU
		1838	speed for example), so if C<interval> is very small then timing stability
		1839	will of course deteriorate. Libev itself tries to be exact to be about one
		1840	millisecond (if the OS supports it and the machine is fast enough).
		1841
1335	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1842	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1336		1843
1337	In this mode the values for C<interval> and C<at> are both being	1844	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	1845	ignored. Instead, each time the periodic watcher gets scheduled, the
1339	reschedule callback will be called with the watcher as first, and the	1846	reschedule callback will be called with the watcher as first, and the
1340	current time as second argument.	1847	current time as second argument.
1341		1848
1342	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1849	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,	1850	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	1851	allowed by documentation here>.
1345	starting an C<ev_prepare> watcher, which is legal).
1346		1852
		1853	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1854	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1855	only event loop modification you are allowed to do).
		1856
1347	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1857	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1348	ev_tstamp now)>, e.g.:	1858	*w, ev_tstamp now)>, e.g.:
1349		1859
		1860	static ev_tstamp
1350	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1861	my_rescheduler (ev_periodic *w, ev_tstamp now)
1351	{	1862	{
1352	return now + 60.;	1863	return now + 60.;
1353	}	1864	}
1354		1865
1355	It must return the next time to trigger, based on the passed time value	1866	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	1867	(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	1868	will usually be called just before the callback will be triggered, but
1358	might be called at other times, too.	1869	might be called at other times, too.
1359		1870
1360	NOTE: I<< This callback must always return a time that is later than the	1871	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.	1872	equal to the passed C<now> value >>.
1362		1873
1363	This can be used to create very complex timers, such as a timer that	1874	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	1875	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	1876	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	1877	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).	1878	reason I omitted it as an example).
1368		1879
1369	=back	1880	=back
…		…
1373	Simply stops and restarts the periodic watcher again. This is only useful	1884	Simply stops and restarts the periodic watcher again. This is only useful
1374	when you changed some parameters or the reschedule callback would return	1885	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	1886	a different time than the last time it was called (e.g. in a crond like
1376	program when the crontabs have changed).	1887	program when the crontabs have changed).
1377		1888
		1889	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1890
		1891	When active, returns the absolute time that the watcher is supposed
		1892	to trigger next. This is not the same as the C<offset> argument to
		1893	C<ev_periodic_set>, but indeed works even in interval and manual
		1894	rescheduling modes.
		1895
1378	=item ev_tstamp offset [read-write]	1896	=item ev_tstamp offset [read-write]
1379		1897
1380	When repeating, this contains the offset value, otherwise this is the	1898	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>).	1899	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1900	although libev might modify this value for better numerical stability).
1382		1901
1383	Can be modified any time, but changes only take effect when the periodic	1902	Can be modified any time, but changes only take effect when the periodic
1384	timer fires or C<ev_periodic_again> is being called.	1903	timer fires or C<ev_periodic_again> is being called.
1385		1904
1386	=item ev_tstamp interval [read-write]	1905	=item ev_tstamp interval [read-write]
1387		1906
1388	The current interval value. Can be modified any time, but changes only	1907	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	1908	take effect when the periodic timer fires or C<ev_periodic_again> is being
1390	called.	1909	called.
1391		1910
1392	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1911	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1393		1912
1394	The current reschedule callback, or C<0>, if this functionality is	1913	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	1914	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.	1915	the periodic timer fires or C<ev_periodic_again> is being called.
1397		1916
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	1917	=back
1404		1918
1405	=head3 Examples	1919	=head3 Examples
1406		1920
1407	Example: Call a callback every hour, or, more precisely, whenever the	1921	Example: Call a callback every hour, or, more precisely, whenever the
1408	system clock is divisible by 3600. The callback invocation times have	1922	system time is divisible by 3600. The callback invocation times have
1409	potentially a lot of jittering, but good long-term stability.	1923	potentially a lot of jitter, but good long-term stability.
1410		1924
1411	static void	1925	static void
1412	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1926	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1413	{	1927	{
1414	... its now a full hour (UTC, or TAI or whatever your clock follows)	1928	... its now a full hour (UTC, or TAI or whatever your clock follows)
1415	}	1929	}
1416		1930
1417	struct ev_periodic hourly_tick;	1931	ev_periodic hourly_tick;
1418	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1932	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1419	ev_periodic_start (loop, &hourly_tick);	1933	ev_periodic_start (loop, &hourly_tick);
1420		1934
1421	Example: The same as above, but use a reschedule callback to do it:	1935	Example: The same as above, but use a reschedule callback to do it:
1422		1936
1423	#include <math.h>	1937	#include <math.h>
1424		1938
1425	static ev_tstamp	1939	static ev_tstamp
1426	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1940	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1427	{	1941	{
1428	return fmod (now, 3600.) + 3600.;	1942	return now + (3600. - fmod (now, 3600.));
1429	}	1943	}
1430		1944
1431	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1945	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1432		1946
1433	Example: Call a callback every hour, starting now:	1947	Example: Call a callback every hour, starting now:
1434		1948
1435	struct ev_periodic hourly_tick;	1949	ev_periodic hourly_tick;
1436	ev_periodic_init (&hourly_tick, clock_cb,	1950	ev_periodic_init (&hourly_tick, clock_cb,
1437	fmod (ev_now (loop), 3600.), 3600., 0);	1951	fmod (ev_now (loop), 3600.), 3600., 0);
1438	ev_periodic_start (loop, &hourly_tick);	1952	ev_periodic_start (loop, &hourly_tick);
1439		1953
1440		1954
1441	=head2 C<ev_signal> - signal me when a signal gets signalled!	1955	=head2 C<ev_signal> - signal me when a signal gets signalled!
1442		1956
1443	Signal watchers will trigger an event when the process receives a specific	1957	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	1958	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	1959	will try it's best to deliver signals synchronously, i.e. as part of the
1446	normal event processing, like any other event.	1960	normal event processing, like any other event.
1447		1961
		1962	If you want signals asynchronously, just use C<sigaction> as you would
		1963	do without libev and forget about sharing the signal. You can even use
		1964	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1965
1448	You can configure as many watchers as you like per signal. Only when the	1966	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	1967	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	1968	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	1969	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	1970	the last signal watcher for a signal is stopped, libev will reset the
1453	SIG_DFL (regardless of what it was set to before).	1971	signal handler to SIG_DFL (regardless of what it was set to before).
1454		1972
1455	If possible and supported, libev will install its handlers with	1973	If possible and supported, libev will install its handlers with
1456	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	1974	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
1457	interrupted. If you have a problem with syscalls getting interrupted by	1975	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	1976	signals you can block all signals in an C<ev_check> watcher and unblock
1459	them in an C<ev_prepare> watcher.	1977	them in an C<ev_prepare> watcher.
1460		1978
1461	=head3 Watcher-Specific Functions and Data Members	1979	=head3 Watcher-Specific Functions and Data Members
1462		1980
…		…
1475		1993
1476	=back	1994	=back
1477		1995
1478	=head3 Examples	1996	=head3 Examples
1479		1997
1480	Example: Try to exit cleanly on SIGINT and SIGTERM.	1998	Example: Try to exit cleanly on SIGINT.
1481		1999
1482	static void	2000	static void
1483	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2001	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1484	{	2002	{
1485	ev_unloop (loop, EVUNLOOP_ALL);	2003	ev_unloop (loop, EVUNLOOP_ALL);
1486	}	2004	}
1487		2005
1488	struct ev_signal signal_watcher;	2006	ev_signal signal_watcher;
1489	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2007	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1490	ev_signal_start (loop, &sigint_cb);	2008	ev_signal_start (loop, &signal_watcher);
1491		2009
1492		2010
1493	=head2 C<ev_child> - watch out for process status changes	2011	=head2 C<ev_child> - watch out for process status changes
1494		2012
1495	Child watchers trigger when your process receives a SIGCHLD in response to	2013	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	2014	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	2015	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	2016	has been forked (which implies it might have already exited), as long
1499	loop isn't entered (or is continued from a watcher).	2017	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2018	forking and then immediately registering a watcher for the child is fine,
		2019	but forking and registering a watcher a few event loop iterations later or
		2020	in the next callback invocation is not.
1500		2021
1501	Only the default event loop is capable of handling signals, and therefore	2022	Only the default event loop is capable of handling signals, and therefore
1502	you can only rgeister child watchers in the default event loop.	2023	you can only register child watchers in the default event loop.
1503		2024
1504	=head3 Process Interaction	2025	=head3 Process Interaction
1505		2026
1506	Libev grabs C<SIGCHLD> as soon as the default event loop is	2027	Libev grabs C<SIGCHLD> as soon as the default event loop is
1507	initialised. This is necessary to guarantee proper behaviour even if	2028	initialised. This is necessary to guarantee proper behaviour even if
1508	the first child watcher is started after the child exits. The occurance	2029	the first child watcher is started after the child exits. The occurrence
1509	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2030	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1510	synchronously as part of the event loop processing. Libev always reaps all	2031	synchronously as part of the event loop processing. Libev always reaps all
1511	children, even ones not watched.	2032	children, even ones not watched.
1512		2033
1513	=head3 Overriding the Built-In Processing	2034	=head3 Overriding the Built-In Processing
…		…
1517	handler, you can override it easily by installing your own handler for	2038	handler, you can override it easily by installing your own handler for
1518	C<SIGCHLD> after initialising the default loop, and making sure the	2039	C<SIGCHLD> after initialising the default loop, and making sure the
1519	default loop never gets destroyed. You are encouraged, however, to use an	2040	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	2041	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.	2042	that, so other libev users can use C<ev_child> watchers freely.
		2043
		2044	=head3 Stopping the Child Watcher
		2045
		2046	Currently, the child watcher never gets stopped, even when the
		2047	child terminates, so normally one needs to stop the watcher in the
		2048	callback. Future versions of libev might stop the watcher automatically
		2049	when a child exit is detected.
1522		2050
1523	=head3 Watcher-Specific Functions and Data Members	2051	=head3 Watcher-Specific Functions and Data Members
1524		2052
1525	=over 4	2053	=over 4
1526		2054
…		…
1555	=head3 Examples	2083	=head3 Examples
1556		2084
1557	Example: C<fork()> a new process and install a child handler to wait for	2085	Example: C<fork()> a new process and install a child handler to wait for
1558	its completion.	2086	its completion.
1559		2087
1560	ev_child cw;	2088	ev_child cw;
1561		2089
1562	static void	2090	static void
1563	child_cb (EV_P_ struct ev_child *w, int revents)	2091	child_cb (EV_P_ ev_child *w, int revents)
1564	{	2092	{
1565	ev_child_stop (EV_A_ w);	2093	ev_child_stop (EV_A_ w);
1566	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2094	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1567	}	2095	}
1568		2096
1569	pid_t pid = fork ();	2097	pid_t pid = fork ();
1570		2098
1571	if (pid < 0)	2099	if (pid < 0)
1572	// error	2100	// error
1573	else if (pid == 0)	2101	else if (pid == 0)
1574	{	2102	{
1575	// the forked child executes here	2103	// the forked child executes here
1576	exit (1);	2104	exit (1);
1577	}	2105	}
1578	else	2106	else
1579	{	2107	{
1580	ev_child_init (&cw, child_cb, pid, 0);	2108	ev_child_init (&cw, child_cb, pid, 0);
1581	ev_child_start (EV_DEFAULT_ &cw);	2109	ev_child_start (EV_DEFAULT_ &cw);
1582	}	2110	}
1583		2111
1584		2112
1585	=head2 C<ev_stat> - did the file attributes just change?	2113	=head2 C<ev_stat> - did the file attributes just change?
1586		2114
1587	This watches a filesystem path for attribute changes. That is, it calls	2115	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	2116	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.	2117	and sees if it changed compared to the last time, invoking the callback if
		2118	it did.
1590		2119
1591	The path does not need to exist: changing from "path exists" to "path does	2120	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	2121	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	2122	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	2123	C<st_nlink> field being zero (which is otherwise always forced to be at
1595	the stat buffer having unspecified contents.	2124	least one) and all the other fields of the stat buffer having unspecified
		2125	contents.
1596		2126
1597	The path I<should> be absolute and I<must not> end in a slash. If it is	2127	The path I<must not> end in a slash or contain special components such as
		2128	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.	2129	your working directory changes, then the behaviour is undefined.
1599		2130
1600	Since there is no standard to do this, the portable implementation simply	2131	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	2132	portable implementation simply calls C<stat(2)> regularly on the path
1602	can specify a recommended polling interval for this case. If you specify	2133	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,	2134	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	2135	recommended!) then a I<suitable, unspecified default> value will be used
1605	five seconds, although this might change dynamically). Libev will also	2136	(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	2137	change dynamically). Libev will also impose a minimum interval which is
1607	usually overkill.	2138	currently around C<0.1>, but that's usually overkill.
1608		2139
1609	This watcher type is not meant for massive numbers of stat watchers,	2140	This watcher type is not meant for massive numbers of stat watchers,
1610	as even with OS-supported change notifications, this can be	2141	as even with OS-supported change notifications, this can be
1611	resource-intensive.	2142	resource-intensive.
1612		2143
1613	At the time of this writing, only the Linux inotify interface is	2144	At the time of this writing, the only OS-specific interface implemented
1614	implemented (implementing kqueue support is left as an exercise for the	2145	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	2146	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	2147	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		2148
1621	=head3 ABI Issues (Largefile Support)	2149	=head3 ABI Issues (Largefile Support)
1622		2150
1623	Libev by default (unless the user overrides this) uses the default	2151	Libev by default (unless the user overrides this) uses the default
1624	compilation environment, which means that on systems with optionally	2152	compilation environment, which means that on systems with large file
1625	disabled large file support, you get the 32 bit version of the stat	2153	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	2154	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	2155	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	2156	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	2157	obviously the case with any flags that change the ABI, but the problem is
1630	most noticably with ev_stat and largefile support.	2158	most noticeably displayed with ev_stat and large file support.
1631		2159
1632	=head3 Inotify	2160	The solution for this is to lobby your distribution maker to make large
		2161	file interfaces available by default (as e.g. FreeBSD does) and not
		2162	optional. Libev cannot simply switch on large file support because it has
		2163	to exchange stat structures with application programs compiled using the
		2164	default compilation environment.
1633		2165
		2166	=head3 Inotify and Kqueue
		2167
1634	When C<inotify (7)> support has been compiled into libev (generally only	2168	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	2169	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	2170	inotify descriptor will be created lazily when the first C<ev_stat>
1637	when the first C<ev_stat> watcher is being started.	2171	watcher is being started.
1638		2172
1639	Inotify presense does not change the semantics of C<ev_stat> watchers	2173	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	2174	except that changes might be detected earlier, and in some cases, to avoid
1641	making regular C<stat> calls. Even in the presense of inotify support	2175	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.	2176	there are many cases where libev has to resort to regular C<stat> polling,
		2177	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2178	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2179	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2180	xfs are fully working) libev usually gets away without polling.
1643		2181
1644	(There is no support for kqueue, as apparently it cannot be used to	2182	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	2183	implement this functionality, due to the requirement of having a file
1646	descriptor open on the object at all times).	2184	descriptor open on the object at all times, and detecting renames, unlinks
		2185	etc. is difficult.
		2186
		2187	=head3 C<stat ()> is a synchronous operation
		2188
		2189	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2190	the process. The exception are C<ev_stat> watchers - those call C<stat
		2191	()>, which is a synchronous operation.
		2192
		2193	For local paths, this usually doesn't matter: unless the system is very
		2194	busy or the intervals between stat's are large, a stat call will be fast,
		2195	as the path data is usually in memory already (except when starting the
		2196	watcher).
		2197
		2198	For networked file systems, calling C<stat ()> can block an indefinite
		2199	time due to network issues, and even under good conditions, a stat call
		2200	often takes multiple milliseconds.
		2201
		2202	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2203	paths, although this is fully supported by libev.
1647		2204
1648	=head3 The special problem of stat time resolution	2205	=head3 The special problem of stat time resolution
1649		2206
1650	The C<stat ()> syscall only supports full-second resolution portably, and	2207	The C<stat ()> system call only supports full-second resolution portably,
1651	even on systems where the resolution is higher, many filesystems still	2208	and even on systems where the resolution is higher, most file systems
1652	only support whole seconds.	2209	still only support whole seconds.
1653		2210
1654	That means that, if the time is the only thing that changes, you might	2211	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	2212	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	2213	calls your callback, which does something. When there is another update
1657	the same second, C<ev_stat> will be unable to detect it.	2214	within the same second, C<ev_stat> will be unable to detect unless the
		2215	stat data does change in other ways (e.g. file size).
1658		2216
1659	The solution to this is to delay acting on a change for a second (or till	2217	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>	2218	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>	2219	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	2220	ev_timer_again (loop, w)>).
1663	systems.	2221
		2222	The C<.02> offset is added to work around small timing inconsistencies
		2223	of some operating systems (where the second counter of the current time
		2224	might be be delayed. One such system is the Linux kernel, where a call to
		2225	C<gettimeofday> might return a timestamp with a full second later than
		2226	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2227	update file times then there will be a small window where the kernel uses
		2228	the previous second to update file times but libev might already execute
		2229	the timer callback).
1664		2230
1665	=head3 Watcher-Specific Functions and Data Members	2231	=head3 Watcher-Specific Functions and Data Members
1666		2232
1667	=over 4	2233	=over 4
1668		2234
…		…
1674	C<path>. The C<interval> is a hint on how quickly a change is expected to	2240	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	2241	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	2242	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.	2243	path for as long as the watcher is active.
1678		2244
1679	The callback will be receive C<EV_STAT> when a change was detected,	2245	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	2246	relative to the attributes at the time the watcher was started (or the
1681	last change was detected).	2247	last change was detected).
1682		2248
1683	=item ev_stat_stat (loop, ev_stat *)	2249	=item ev_stat_stat (loop, ev_stat *)
1684		2250
1685	Updates the stat buffer immediately with new values. If you change the	2251	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	2252	watched path in your callback, you could call this function to avoid
1687	detecting this change (while introducing a race condition). Can also be	2253	detecting this change (while introducing a race condition if you are not
1688	useful simply to find out the new values.	2254	the only one changing the path). Can also be useful simply to find out the
		2255	new values.
1689		2256
1690	=item ev_statdata attr [read-only]	2257	=item ev_statdata attr [read-only]
1691		2258
1692	The most-recently detected attributes of the file. Although the type is of	2259	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	2260	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	2261	suitable for your system, but you can only rely on the POSIX-standardised
		2262	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.	2263	some error while C<stat>ing the file.
1696		2264
1697	=item ev_statdata prev [read-only]	2265	=item ev_statdata prev [read-only]
1698		2266
1699	The previous attributes of the file. The callback gets invoked whenever	2267	The previous attributes of the file. The callback gets invoked whenever
1700	C<prev> != C<attr>.	2268	C<prev> != C<attr>, or, more precisely, one or more of these members
		2269	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2270	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1701		2271
1702	=item ev_tstamp interval [read-only]	2272	=item ev_tstamp interval [read-only]
1703		2273
1704	The specified interval.	2274	The specified interval.
1705		2275
1706	=item const char *path [read-only]	2276	=item const char *path [read-only]
1707		2277
1708	The filesystem path that is being watched.	2278	The file system path that is being watched.
1709		2279
1710	=back	2280	=back
1711		2281
1712	=head3 Examples	2282	=head3 Examples
1713		2283
1714	Example: Watch C</etc/passwd> for attribute changes.	2284	Example: Watch C</etc/passwd> for attribute changes.
1715		2285
1716	static void	2286	static void
1717	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2287	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1718	{	2288	{
1719	/* /etc/passwd changed in some way */	2289	/* /etc/passwd changed in some way */
1720	if (w->attr.st_nlink)	2290	if (w->attr.st_nlink)
1721	{	2291	{
1722	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2292	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1723	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2293	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1724	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2294	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1725	}	2295	}
1726	else	2296	else
1727	/* you shalt not abuse printf for puts */	2297	/* you shalt not abuse printf for puts */
1728	puts ("wow, /etc/passwd is not there, expect problems. "	2298	puts ("wow, /etc/passwd is not there, expect problems. "
1729	"if this is windows, they already arrived\n");	2299	"if this is windows, they already arrived\n");
1730	}	2300	}
1731		2301
1732	...	2302	...
1733	ev_stat passwd;	2303	ev_stat passwd;
1734		2304
1735	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2305	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1736	ev_stat_start (loop, &passwd);	2306	ev_stat_start (loop, &passwd);
1737		2307
1738	Example: Like above, but additionally use a one-second delay so we do not	2308	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	2309	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	2310	one might do the work both on C<ev_stat> callback invocation I<and> on
1741	C<ev_timer> callback invocation).	2311	C<ev_timer> callback invocation).
1742		2312
1743	static ev_stat passwd;	2313	static ev_stat passwd;
1744	static ev_timer timer;	2314	static ev_timer timer;
1745		2315
1746	static void	2316	static void
1747	timer_cb (EV_P_ ev_timer *w, int revents)	2317	timer_cb (EV_P_ ev_timer *w, int revents)
1748	{	2318	{
1749	ev_timer_stop (EV_A_ w);	2319	ev_timer_stop (EV_A_ w);
1750		2320
1751	/* now it's one second after the most recent passwd change */	2321	/* now it's one second after the most recent passwd change */
1752	}	2322	}
1753		2323
1754	static void	2324	static void
1755	stat_cb (EV_P_ ev_stat *w, int revents)	2325	stat_cb (EV_P_ ev_stat *w, int revents)
1756	{	2326	{
1757	/* reset the one-second timer */	2327	/* reset the one-second timer */
1758	ev_timer_again (EV_A_ &timer);	2328	ev_timer_again (EV_A_ &timer);
1759	}	2329	}
1760		2330
1761	...	2331	...
1762	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2332	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1763	ev_stat_start (loop, &passwd);	2333	ev_stat_start (loop, &passwd);
1764	ev_timer_init (&timer, timer_cb, 0., 1.01);	2334	ev_timer_init (&timer, timer_cb, 0., 1.02);
1765		2335
1766		2336
1767	=head2 C<ev_idle> - when you've got nothing better to do...	2337	=head2 C<ev_idle> - when you've got nothing better to do...
1768		2338
1769	Idle watchers trigger events when no other events of the same or higher	2339	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	2340	priority are pending (prepare, check and other idle watchers do not count
1771	count).	2341	as receiving "events").
1772		2342
1773	That is, as long as your process is busy handling sockets or timeouts	2343	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	2344	(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	2345	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	2346	are pending), the idle watchers are being called once per event loop
…		…
1787		2357
1788	=head3 Watcher-Specific Functions and Data Members	2358	=head3 Watcher-Specific Functions and Data Members
1789		2359
1790	=over 4	2360	=over 4
1791		2361
1792	=item ev_idle_init (ev_signal *, callback)	2362	=item ev_idle_init (ev_idle *, callback)
1793		2363
1794	Initialises and configures the idle watcher - it has no parameters of any	2364	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,	2365	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1796	believe me.	2366	believe me.
1797		2367
…		…
1800	=head3 Examples	2370	=head3 Examples
1801		2371
1802	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2372	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1803	callback, free it. Also, use no error checking, as usual.	2373	callback, free it. Also, use no error checking, as usual.
1804		2374
1805	static void	2375	static void
1806	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2376	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1807	{	2377	{
1808	free (w);	2378	free (w);
1809	// now do something you wanted to do when the program has	2379	// now do something you wanted to do when the program has
1810	// no longer anything immediate to do.	2380	// no longer anything immediate to do.
1811	}	2381	}
1812		2382
1813	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2383	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1814	ev_idle_init (idle_watcher, idle_cb);	2384	ev_idle_init (idle_watcher, idle_cb);
1815	ev_idle_start (loop, idle_cb);	2385	ev_idle_start (loop, idle_watcher);
1816		2386
1817		2387
1818	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2388	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1819		2389
1820	Prepare and check watchers are usually (but not always) used in tandem:	2390	Prepare and check watchers are usually (but not always) used in pairs:
1821	prepare watchers get invoked before the process blocks and check watchers	2391	prepare watchers get invoked before the process blocks and check watchers
1822	afterwards.	2392	afterwards.
1823		2393
1824	You I<must not> call C<ev_loop> or similar functions that enter	2394	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>	2395	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,	2398	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	2399	C<ev_check> so if you have one watcher of each kind they will always be
1830	called in pairs bracketing the blocking call.	2400	called in pairs bracketing the blocking call.
1831		2401
1832	Their main purpose is to integrate other event mechanisms into libev and	2402	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	2403	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	2404	variable changes, implement your own watchers, integrate net-snmp or a
1835	coroutine library and lots more. They are also occasionally useful if	2405	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,	2406	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>	2407	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1838	watcher).	2408	watcher).
1839		2409
1840	This is done by examining in each prepare call which file descriptors need	2410	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	2411	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	2412	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	2413	libraries provide exactly this functionality). Then, in the check watcher,
1844	any events that occured (by checking the pending status of all watchers	2414	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	2415	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,	2416	I/O and timer callbacks will never actually be called (but must be valid
1847	because you never know, you know?).	2417	nevertheless, because you never know, you know?).
1848		2418
1849	As another example, the Perl Coro module uses these hooks to integrate	2419	As another example, the Perl Coro module uses these hooks to integrate
1850	coroutines into libev programs, by yielding to other active coroutines	2420	coroutines into libev programs, by yielding to other active coroutines
1851	during each prepare and only letting the process block if no coroutines	2421	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	2422	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	2425	loop from blocking if lower-priority coroutines are active, thus mapping
1856	low-priority coroutines to idle/background tasks).	2426	low-priority coroutines to idle/background tasks).
1857		2427
1858	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2428	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	2429	priority, to ensure that they are being run before any other watchers
		2430	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2431
1860	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2432	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	2433	activate ("feed") events into libev. While libev fully supports this, they
1862	supports this, they will be called before other C<ev_check> watchers	2434	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	2435	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	2436	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	2437	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1866	coexist peacefully with others).	2438	others).
1867		2439
1868	=head3 Watcher-Specific Functions and Data Members	2440	=head3 Watcher-Specific Functions and Data Members
1869		2441
1870	=over 4	2442	=over 4
1871		2443
…		…
1873		2445
1874	=item ev_check_init (ev_check *, callback)	2446	=item ev_check_init (ev_check *, callback)
1875		2447
1876	Initialises and configures the prepare or check watcher - they have no	2448	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>	2449	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.	2450	macros, but using them is utterly, utterly, utterly and completely
		2451	pointless.
1879		2452
1880	=back	2453	=back
1881		2454
1882	=head3 Examples	2455	=head3 Examples
1883		2456
1884	There are a number of principal ways to embed other event loops or modules	2457	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	2458	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	2459	(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>	2460	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	2461	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1889	into the Glib event loop).	2462	Glib event loop).
1890		2463
1891	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2464	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	2465	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	2466	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	2467	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.	2468	the callbacks for the IO/timeout watchers might not have been called yet.
1896		2469
1897	static ev_io iow [nfd];	2470	static ev_io iow [nfd];
1898	static ev_timer tw;	2471	static ev_timer tw;
1899		2472
1900	static void	2473	static void
1901	io_cb (ev_loop *loop, ev_io *w, int revents)	2474	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1902	{	2475	{
1903	}	2476	}
1904		2477
1905	// create io watchers for each fd and a timer before blocking	2478	// create io watchers for each fd and a timer before blocking
1906	static void	2479	static void
1907	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2480	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1908	{	2481	{
1909	int timeout = 3600000;	2482	int timeout = 3600000;
1910	struct pollfd fds [nfd];	2483	struct pollfd fds [nfd];
1911	// actual code will need to loop here and realloc etc.	2484	// actual code will need to loop here and realloc etc.
1912	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2485	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1913		2486
1914	/* the callback is illegal, but won't be called as we stop during check */	2487	/* the callback is illegal, but won't be called as we stop during check */
1915	ev_timer_init (&tw, 0, timeout * 1e-3);	2488	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1916	ev_timer_start (loop, &tw);	2489	ev_timer_start (loop, &tw);
1917		2490
1918	// create one ev_io per pollfd	2491	// create one ev_io per pollfd
1919	for (int i = 0; i < nfd; ++i)	2492	for (int i = 0; i < nfd; ++i)
1920	{	2493	{
1921	ev_io_init (iow + i, io_cb, fds [i].fd,	2494	ev_io_init (iow + i, io_cb, fds [i].fd,
1922	((fds [i].events & POLLIN ? EV_READ : 0)	2495	((fds [i].events & POLLIN ? EV_READ : 0)
1923	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2496	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1924		2497
1925	fds [i].revents = 0;	2498	fds [i].revents = 0;
1926	ev_io_start (loop, iow + i);	2499	ev_io_start (loop, iow + i);
1927	}	2500	}
1928	}	2501	}
1929		2502
1930	// stop all watchers after blocking	2503	// stop all watchers after blocking
1931	static void	2504	static void
1932	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2505	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1933	{	2506	{
1934	ev_timer_stop (loop, &tw);	2507	ev_timer_stop (loop, &tw);
1935		2508
1936	for (int i = 0; i < nfd; ++i)	2509	for (int i = 0; i < nfd; ++i)
1937	{	2510	{
1938	// set the relevant poll flags	2511	// set the relevant poll flags
1939	// could also call adns_processreadable etc. here	2512	// could also call adns_processreadable etc. here
1940	struct pollfd *fd = fds + i;	2513	struct pollfd *fd = fds + i;
1941	int revents = ev_clear_pending (iow + i);	2514	int revents = ev_clear_pending (iow + i);
1942	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2515	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1943	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2516	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1944		2517
1945	// now stop the watcher	2518	// now stop the watcher
1946	ev_io_stop (loop, iow + i);	2519	ev_io_stop (loop, iow + i);
1947	}	2520	}
1948		2521
1949	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2522	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1950	}	2523	}
1951		2524
1952	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2525	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.	2526	in the prepare watcher and would dispose of the check watcher.
1954		2527
1955	Method 3: If the module to be embedded supports explicit event	2528	Method 3: If the module to be embedded supports explicit event
1956	notification (adns does), you can also make use of the actual watcher	2529	notification (libadns does), you can also make use of the actual watcher
1957	callbacks, and only destroy/create the watchers in the prepare watcher.	2530	callbacks, and only destroy/create the watchers in the prepare watcher.
1958		2531
1959	static void	2532	static void
1960	timer_cb (EV_P_ ev_timer *w, int revents)	2533	timer_cb (EV_P_ ev_timer *w, int revents)
1961	{	2534	{
1962	adns_state ads = (adns_state)w->data;	2535	adns_state ads = (adns_state)w->data;
1963	update_now (EV_A);	2536	update_now (EV_A);
1964		2537
1965	adns_processtimeouts (ads, &tv_now);	2538	adns_processtimeouts (ads, &tv_now);
1966	}	2539	}
1967		2540
1968	static void	2541	static void
1969	io_cb (EV_P_ ev_io *w, int revents)	2542	io_cb (EV_P_ ev_io *w, int revents)
1970	{	2543	{
1971	adns_state ads = (adns_state)w->data;	2544	adns_state ads = (adns_state)w->data;
1972	update_now (EV_A);	2545	update_now (EV_A);
1973		2546
1974	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2547	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1975	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2548	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1976	}	2549	}
1977		2550
1978	// do not ever call adns_afterpoll	2551	// do not ever call adns_afterpoll
1979		2552
1980	Method 4: Do not use a prepare or check watcher because the module you	2553	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	2554	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	2555	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	2556	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1984	this.	2557	this approach, effectively embedding EV as a client into the horrible
		2558	libglib event loop.
1985		2559
1986	static gint	2560	static gint
1987	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2561	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1988	{	2562	{
1989	int got_events = 0;	2563	int got_events = 0;
1990		2564
1991	for (n = 0; n < nfds; ++n)	2565	for (n = 0; n < nfds; ++n)
1992	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2566	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1993		2567
1994	if (timeout >= 0)	2568	if (timeout >= 0)
1995	// create/start timer	2569	// create/start timer
1996		2570
1997	// poll	2571	// poll
1998	ev_loop (EV_A_ 0);	2572	ev_loop (EV_A_ 0);
1999		2573
2000	// stop timer again	2574	// stop timer again
2001	if (timeout >= 0)	2575	if (timeout >= 0)
2002	ev_timer_stop (EV_A_ &to);	2576	ev_timer_stop (EV_A_ &to);
2003		2577
2004	// stop io watchers again - their callbacks should have set	2578	// stop io watchers again - their callbacks should have set
2005	for (n = 0; n < nfds; ++n)	2579	for (n = 0; n < nfds; ++n)
2006	ev_io_stop (EV_A_ iow [n]);	2580	ev_io_stop (EV_A_ iow [n]);
2007		2581
2008	return got_events;	2582	return got_events;
2009	}	2583	}
2010		2584
2011		2585
2012	=head2 C<ev_embed> - when one backend isn't enough...	2586	=head2 C<ev_embed> - when one backend isn't enough...
2013		2587
2014	This is a rather advanced watcher type that lets you embed one event loop	2588	This is a rather advanced watcher type that lets you embed one event loop
…		…
2020	prioritise I/O.	2594	prioritise I/O.
2021		2595
2022	As an example for a bug workaround, the kqueue backend might only support	2596	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	2597	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	2598	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	2599	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	2600	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	2601	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.	2602	C<kevent>, but at least you can use both mechanisms for what they are
		2603	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2029		2604
2030	As for prioritising I/O: rarely you have the case where some fds have	2605	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	2606	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	2607	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	2608	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.	2609	the rest in a second one, and embed the second one in the first.
2035		2610
2036	As long as the watcher is active, the callback will be invoked every time	2611	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	2612	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	2613	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	2614	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	2615	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	2616	to give the embedded loop strictly lower priority for example).
2042	embedded loop sweep.
2043		2617
2044	As long as the watcher is started it will automatically handle events. The	2618	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	2619	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		2620
2049	Also, there have not currently been made special provisions for forking:	2621	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,	2622	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	2623	embedding loop forks. In other cases, the user is responsible for calling
2052	yourself.	2624	C<ev_loop_fork> on the embedded loop.
2053		2625
2054	Unfortunately, not all backends are embeddable, only the ones returned by	2626	Unfortunately, not all backends are embeddable: only the ones returned by
2055	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2627	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2056	portable one.	2628	portable one.
2057		2629
2058	So when you want to use this feature you will always have to be prepared	2630	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	2631	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	2632	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.	2633	create it, and if that fails, use the normal loop for everything.
2062		2634
		2635	=head3 C<ev_embed> and fork
		2636
		2637	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2638	automatically be applied to the embedded loop as well, so no special
		2639	fork handling is required in that case. When the watcher is not running,
		2640	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2641	as applicable.
		2642
2063	=head3 Watcher-Specific Functions and Data Members	2643	=head3 Watcher-Specific Functions and Data Members
2064		2644
2065	=over 4	2645	=over 4
2066		2646
2067	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2647	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2070		2650
2071	Configures the watcher to embed the given loop, which must be	2651	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	2652	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	2653	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,	2654	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).	2655	if you do not want that, you need to temporarily stop the embed watcher).
2076		2656
2077	=item ev_embed_sweep (loop, ev_embed *)	2657	=item ev_embed_sweep (loop, ev_embed *)
2078		2658
2079	Make a single, non-blocking sweep over the embedded loop. This works	2659	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	2660	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
2081	apropriate way for embedded loops.	2661	appropriate way for embedded loops.
2082		2662
2083	=item struct ev_loop *other [read-only]	2663	=item struct ev_loop *other [read-only]
2084		2664
2085	The embedded event loop.	2665	The embedded event loop.
2086		2666
…		…
2088		2668
2089	=head3 Examples	2669	=head3 Examples
2090		2670
2091	Example: Try to get an embeddable event loop and embed it into the default	2671	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	2672	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	2673	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	2674	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2095	used).	2675	used).
2096		2676
2097	struct ev_loop *loop_hi = ev_default_init (0);	2677	struct ev_loop *loop_hi = ev_default_init (0);
2098	struct ev_loop *loop_lo = 0;	2678	struct ev_loop *loop_lo = 0;
2099	struct ev_embed embed;	2679	ev_embed embed;
2100		2680
2101	// see if there is a chance of getting one that works	2681	// see if there is a chance of getting one that works
2102	// (remember that a flags value of 0 means autodetection)	2682	// (remember that a flags value of 0 means autodetection)
2103	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2683	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2104	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2684	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2105	: 0;	2685	: 0;
2106		2686
2107	// if we got one, then embed it, otherwise default to loop_hi	2687	// if we got one, then embed it, otherwise default to loop_hi
2108	if (loop_lo)	2688	if (loop_lo)
2109	{	2689	{
2110	ev_embed_init (&embed, 0, loop_lo);	2690	ev_embed_init (&embed, 0, loop_lo);
2111	ev_embed_start (loop_hi, &embed);	2691	ev_embed_start (loop_hi, &embed);
2112	}	2692	}
2113	else	2693	else
2114	loop_lo = loop_hi;	2694	loop_lo = loop_hi;
2115		2695
2116	Example: Check if kqueue is available but not recommended and create	2696	Example: Check if kqueue is available but not recommended and create
2117	a kqueue backend for use with sockets (which usually work with any	2697	a kqueue backend for use with sockets (which usually work with any
2118	kqueue implementation). Store the kqueue/socket-only event loop in	2698	kqueue implementation). Store the kqueue/socket-only event loop in
2119	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2699	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2120		2700
2121	struct ev_loop *loop = ev_default_init (0);	2701	struct ev_loop *loop = ev_default_init (0);
2122	struct ev_loop *loop_socket = 0;	2702	struct ev_loop *loop_socket = 0;
2123	struct ev_embed embed;	2703	ev_embed embed;
2124		2704
2125	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2705	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2126	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2706	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2127	{	2707	{
2128	ev_embed_init (&embed, 0, loop_socket);	2708	ev_embed_init (&embed, 0, loop_socket);
2129	ev_embed_start (loop, &embed);	2709	ev_embed_start (loop, &embed);
2130	}	2710	}
2131		2711
2132	if (!loop_socket)	2712	if (!loop_socket)
2133	loop_socket = loop;	2713	loop_socket = loop;
2134		2714
2135	// now use loop_socket for all sockets, and loop for everything else	2715	// now use loop_socket for all sockets, and loop for everything else
2136		2716
2137		2717
2138	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2718	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2139		2719
2140	Fork watchers are called when a C<fork ()> was detected (usually because	2720	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,	2723	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	2724	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	2725	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2146	handlers will be invoked, too, of course.	2726	handlers will be invoked, too, of course.
2147		2727
		2728	=head3 The special problem of life after fork - how is it possible?
		2729
		2730	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2731	up/change the process environment, followed by a call to C<exec()>. This
		2732	sequence should be handled by libev without any problems.
		2733
		2734	This changes when the application actually wants to do event handling
		2735	in the child, or both parent in child, in effect "continuing" after the
		2736	fork.
		2737
		2738	The default mode of operation (for libev, with application help to detect
		2739	forks) is to duplicate all the state in the child, as would be expected
		2740	when I<either> the parent I<or> the child process continues.
		2741
		2742	When both processes want to continue using libev, then this is usually the
		2743	wrong result. In that case, usually one process (typically the parent) is
		2744	supposed to continue with all watchers in place as before, while the other
		2745	process typically wants to start fresh, i.e. without any active watchers.
		2746
		2747	The cleanest and most efficient way to achieve that with libev is to
		2748	simply create a new event loop, which of course will be "empty", and
		2749	use that for new watchers. This has the advantage of not touching more
		2750	memory than necessary, and thus avoiding the copy-on-write, and the
		2751	disadvantage of having to use multiple event loops (which do not support
		2752	signal watchers).
		2753
		2754	When this is not possible, or you want to use the default loop for
		2755	other reasons, then in the process that wants to start "fresh", call
		2756	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2757	the default loop will "orphan" (not stop) all registered watchers, so you
		2758	have to be careful not to execute code that modifies those watchers. Note
		2759	also that in that case, you have to re-register any signal watchers.
		2760
2148	=head3 Watcher-Specific Functions and Data Members	2761	=head3 Watcher-Specific Functions and Data Members
2149		2762
2150	=over 4	2763	=over 4
2151		2764
2152	=item ev_fork_init (ev_signal *, callback)	2765	=item ev_fork_init (ev_signal *, callback)
…		…
2184	is that the author does not know of a simple (or any) algorithm for a	2797	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	2798	multiple-writer-single-reader queue that works in all cases and doesn't
2186	need elaborate support such as pthreads.	2799	need elaborate support such as pthreads.
2187		2800
2188	That means that if you want to queue data, you have to provide your own	2801	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	2802	queue. But at least I can tell you how to implement locking around your
2190	queue:	2803	queue:
2191		2804
2192	=over 4	2805	=over 4
2193		2806
2194	=item queueing from a signal handler context	2807	=item queueing from a signal handler context
2195		2808
2196	To implement race-free queueing, you simply add to the queue in the signal	2809	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	2810	handler but you block the signal handler in the watcher callback. Here is
2198	some fictitiuous SIGUSR1 handler:	2811	an example that does that for some fictitious SIGUSR1 handler:
2199		2812
2200	static ev_async mysig;	2813	static ev_async mysig;
2201		2814
2202	static void	2815	static void
2203	sigusr1_handler (void)	2816	sigusr1_handler (void)
…		…
2269	=over 4	2882	=over 4
2270		2883
2271	=item ev_async_init (ev_async *, callback)	2884	=item ev_async_init (ev_async *, callback)
2272		2885
2273	Initialises and configures the async watcher - it has no parameters of any	2886	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,	2887	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2275	believe me.	2888	trust me.
2276		2889
2277	=item ev_async_send (loop, ev_async *)	2890	=item ev_async_send (loop, ev_async *)
2278		2891
2279	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2892	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	2893	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	2894	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	2895	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2283	section below on what exactly this means).	2896	section below on what exactly this means).
2284		2897
		2898	Note that, as with other watchers in libev, multiple events might get
		2899	compressed into a single callback invocation (another way to look at this
		2900	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2901	reset when the event loop detects that).
		2902
2285	This call incurs the overhead of a syscall only once per loop iteration,	2903	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	2904	iteration, so while the overhead might be noticeable, it doesn't apply to
2287	calls to C<ev_async_send>.	2905	repeated calls to C<ev_async_send> for the same event loop.
2288		2906
2289	=item bool = ev_async_pending (ev_async *)	2907	=item bool = ev_async_pending (ev_async *)
2290		2908
2291	Returns a non-zero value when C<ev_async_send> has been called on the	2909	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	2910	watcher but the event has not yet been processed (or even noted) by the
2293	event loop.	2911	event loop.
2294		2912
2295	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2913	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,	2914	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	2915	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.	2916	quickly check whether invoking the loop might be a good idea.
2299		2917
2300	Not that this does I<not> check wether the watcher itself is pending, only	2918	Not that this does I<not> check whether the watcher itself is pending,
2301	wether it has been requested to make this watcher pending.	2919	only whether it has been requested to make this watcher pending: there
		2920	is a time window between the event loop checking and resetting the async
		2921	notification, and the callback being invoked.
2302		2922
2303	=back	2923	=back
2304		2924
2305		2925
2306	=head1 OTHER FUNCTIONS	2926	=head1 OTHER FUNCTIONS
…		…
2310	=over 4	2930	=over 4
2311		2931
2312	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2932	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2313		2933
2314	This function combines a simple timer and an I/O watcher, calls your	2934	This function combines a simple timer and an I/O watcher, calls your
2315	callback on whichever event happens first and automatically stop both	2935	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	2936	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	2937	or timeout without having to allocate/configure/start/stop/free one or
2318	more watchers yourself.	2938	more watchers yourself.
2319		2939
2320	If C<fd> is less than 0, then no I/O watcher will be started and events	2940	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	2941	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2322	C<events> set will be craeted and started.	2942	the given C<fd> and C<events> set will be created and started.
2323		2943
2324	If C<timeout> is less than 0, then no timeout watcher will be	2944	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	2945	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	2946	repeat = 0) will be started. C<0> is a valid timeout.
2327	dubious value.
2328		2947
2329	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2948	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	2949	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>	2950	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2332	value passed to C<ev_once>:	2951	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2952	a timeout and an io event at the same time - you probably should give io
		2953	events precedence.
2333		2954
		2955	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2956
2334	static void stdin_ready (int revents, void *arg)	2957	static void stdin_ready (int revents, void *arg)
2335	{	2958	{
2336	if (revents & EV_TIMEOUT)
2337	/* doh, nothing entered */;
2338	else if (revents & EV_READ)	2959	if (revents & EV_READ)
2339	/* stdin might have data for us, joy! */;	2960	/* stdin might have data for us, joy! */;
		2961	else if (revents & EV_TIMEOUT)
		2962	/* doh, nothing entered */;
2340	}	2963	}
2341		2964
2342	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2965	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2343		2966
2344	=item ev_feed_event (ev_loop *, watcher *, int revents)	2967	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2345		2968
2346	Feeds the given event set into the event loop, as if the specified event	2969	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	2970	had happened for the specified watcher (which must be a pointer to an
2348	initialised but not necessarily started event watcher).	2971	initialised but not necessarily started event watcher).
2349		2972
2350	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2973	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2351		2974
2352	Feed an event on the given fd, as if a file descriptor backend detected	2975	Feed an event on the given fd, as if a file descriptor backend detected
2353	the given events it.	2976	the given events it.
2354		2977
2355	=item ev_feed_signal_event (ev_loop *loop, int signum)	2978	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2356		2979
2357	Feed an event as if the given signal occured (C<loop> must be the default	2980	Feed an event as if the given signal occurred (C<loop> must be the default
2358	loop!).	2981	loop!).
2359		2982
2360	=back	2983	=back
2361		2984
2362		2985
…		…
2378		3001
2379	=item * Priorities are not currently supported. Initialising priorities	3002	=item * Priorities are not currently supported. Initialising priorities
2380	will fail and all watchers will have the same priority, even though there	3003	will fail and all watchers will have the same priority, even though there
2381	is an ev_pri field.	3004	is an ev_pri field.
2382		3005
		3006	=item * In libevent, the last base created gets the signals, in libev, the
		3007	first base created (== the default loop) gets the signals.
		3008
2383	=item * Other members are not supported.	3009	=item * Other members are not supported.
2384		3010
2385	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3011	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2386	to use the libev header file and library.	3012	to use the libev header file and library.
2387		3013
2388	=back	3014	=back
2389		3015
2390	=head1 C++ SUPPORT	3016	=head1 C++ SUPPORT
2391		3017
2392	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3018	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2393	you to use some convinience methods to start/stop watchers and also change	3019	you to use some convenience methods to start/stop watchers and also change
2394	the callback model to a model using method callbacks on objects.	3020	the callback model to a model using method callbacks on objects.
2395		3021
2396	To use it,	3022	To use it,
2397		3023
2398	#include <ev++.h>	3024	#include <ev++.h>
2399		3025
2400	This automatically includes F<ev.h> and puts all of its definitions (many	3026	This automatically includes F<ev.h> and puts all of its definitions (many
2401	of them macros) into the global namespace. All C++ specific things are	3027	of them macros) into the global namespace. All C++ specific things are
2402	put into the C<ev> namespace. It should support all the same embedding	3028	put into the C<ev> namespace. It should support all the same embedding
2403	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3029	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2470	your compiler is good :), then the method will be fully inlined into the	3096	your compiler is good :), then the method will be fully inlined into the
2471	thunking function, making it as fast as a direct C callback.	3097	thunking function, making it as fast as a direct C callback.
2472		3098
2473	Example: simple class declaration and watcher initialisation	3099	Example: simple class declaration and watcher initialisation
2474		3100
2475	struct myclass	3101	struct myclass
2476	{	3102	{
2477	void io_cb (ev::io &w, int revents) { }	3103	void io_cb (ev::io &w, int revents) { }
2478	}	3104	}
2479		3105
2480	myclass obj;	3106	myclass obj;
2481	ev::io iow;	3107	ev::io iow;
2482	iow.set <myclass, &myclass::io_cb> (&obj);	3108	iow.set <myclass, &myclass::io_cb> (&obj);
		3109
		3110	=item w->set (object *)
		3111
		3112	This is an B<experimental> feature that might go away in a future version.
		3113
		3114	This is a variation of a method callback - leaving out the method to call
		3115	will default the method to C<operator ()>, which makes it possible to use
		3116	functor objects without having to manually specify the C<operator ()> all
		3117	the time. Incidentally, you can then also leave out the template argument
		3118	list.
		3119
		3120	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3121	int revents)>.
		3122
		3123	See the method-C<set> above for more details.
		3124
		3125	Example: use a functor object as callback.
		3126
		3127	struct myfunctor
		3128	{
		3129	void operator() (ev::io &w, int revents)
		3130	{
		3131	...
		3132	}
		3133	}
		3134
		3135	myfunctor f;
		3136
		3137	ev::io w;
		3138	w.set (&f);
2483		3139
2484	=item w->set<function> (void *data = 0)	3140	=item w->set<function> (void *data = 0)
2485		3141
2486	Also sets a callback, but uses a static method or plain function as	3142	Also sets a callback, but uses a static method or plain function as
2487	callback. The optional C<data> argument will be stored in the watcher's	3143	callback. The optional C<data> argument will be stored in the watcher's
…		…
2489		3145
2490	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3146	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2491		3147
2492	See the method-C<set> above for more details.	3148	See the method-C<set> above for more details.
2493		3149
2494	Example:	3150	Example: Use a plain function as callback.
2495		3151
2496	static void io_cb (ev::io &w, int revents) { }	3152	static void io_cb (ev::io &w, int revents) { }
2497	iow.set <io_cb> ();	3153	iow.set <io_cb> ();
2498		3154
2499	=item w->set (struct ev_loop *)	3155	=item w->set (struct ev_loop *)
2500		3156
2501	Associates a different C<struct ev_loop> with this watcher. You can only	3157	Associates a different C<struct ev_loop> with this watcher. You can only
2502	do this when the watcher is inactive (and not pending either).	3158	do this when the watcher is inactive (and not pending either).
2503		3159
2504	=item w->set ([args])	3160	=item w->set ([arguments])
2505		3161
2506	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3162	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2507	called at least once. Unlike the C counterpart, an active watcher gets	3163	called at least once. Unlike the C counterpart, an active watcher gets
2508	automatically stopped and restarted when reconfiguring it with this	3164	automatically stopped and restarted when reconfiguring it with this
2509	method.	3165	method.
2510		3166
2511	=item w->start ()	3167	=item w->start ()
…		…
2535	=back	3191	=back
2536		3192
2537	Example: Define a class with an IO and idle watcher, start one of them in	3193	Example: Define a class with an IO and idle watcher, start one of them in
2538	the constructor.	3194	the constructor.
2539		3195
2540	class myclass	3196	class myclass
2541	{	3197	{
2542	ev::io io; void io_cb (ev::io &w, int revents);	3198	ev::io io ; void io_cb (ev::io &w, int revents);
2543	ev:idle idle void idle_cb (ev::idle &w, int revents);	3199	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2544		3200
2545	myclass (int fd)	3201	myclass (int fd)
2546	{	3202	{
2547	io .set <myclass, &myclass::io_cb > (this);	3203	io .set <myclass, &myclass::io_cb > (this);
2548	idle.set <myclass, &myclass::idle_cb> (this);	3204	idle.set <myclass, &myclass::idle_cb> (this);
2549		3205
2550	io.start (fd, ev::READ);	3206	io.start (fd, ev::READ);
2551	}	3207	}
2552	};	3208	};
2553		3209
2554		3210
2555	=head1 OTHER LANGUAGE BINDINGS	3211	=head1 OTHER LANGUAGE BINDINGS
2556		3212
2557	Libev does not offer other language bindings itself, but bindings for a	3213	Libev does not offer other language bindings itself, but bindings for a
2558	numbe rof languages exist in the form of third-party packages. If you know	3214	number of languages exist in the form of third-party packages. If you know
2559	any interesting language binding in addition to the ones listed here, drop	3215	any interesting language binding in addition to the ones listed here, drop
2560	me a note.	3216	me a note.
2561		3217
2562	=over 4	3218	=over 4
2563		3219
2564	=item Perl	3220	=item Perl
2565		3221
2566	The EV module implements the full libev API and is actually used to test	3222	The EV module implements the full libev API and is actually used to test
2567	libev. EV is developed together with libev. Apart from the EV core module,	3223	libev. EV is developed together with libev. Apart from the EV core module,
2568	there are additional modules that implement libev-compatible interfaces	3224	there are additional modules that implement libev-compatible interfaces
2569	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3225	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2570	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3226	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3227	and C<EV::Glib>).
2571		3228
2572	It can be found and installed via CPAN, its homepage is found at	3229	It can be found and installed via CPAN, its homepage is at
2573	L<http://software.schmorp.de/pkg/EV>.	3230	L<http://software.schmorp.de/pkg/EV>.
2574		3231
		3232	=item Python
		3233
		3234	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3235	seems to be quite complete and well-documented.
		3236
2575	=item Ruby	3237	=item Ruby
2576		3238
2577	Tony Arcieri has written a ruby extension that offers access to a subset	3239	Tony Arcieri has written a ruby extension that offers access to a subset
2578	of the libev API and adds filehandle abstractions, asynchronous DNS and	3240	of the libev API and adds file handle abstractions, asynchronous DNS and
2579	more on top of it. It can be found via gem servers. Its homepage is at	3241	more on top of it. It can be found via gem servers. Its homepage is at
2580	L<http://rev.rubyforge.org/>.	3242	L<http://rev.rubyforge.org/>.
2581		3243
		3244	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3245	makes rev work even on mingw.
		3246
		3247	=item Haskell
		3248
		3249	A haskell binding to libev is available at
		3250	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3251
2582	=item D	3252	=item D
2583		3253
2584	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3254	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2585	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3255	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3256
		3257	=item Ocaml
		3258
		3259	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3260	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2586		3261
2587	=back	3262	=back
2588		3263
2589		3264
2590	=head1 MACRO MAGIC	3265	=head1 MACRO MAGIC
2591		3266
2592	Libev can be compiled with a variety of options, the most fundamantal	3267	Libev can be compiled with a variety of options, the most fundamental
2593	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3268	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2594	functions and callbacks have an initial C<struct ev_loop *> argument.	3269	functions and callbacks have an initial C<struct ev_loop *> argument.
2595		3270
2596	To make it easier to write programs that cope with either variant, the	3271	To make it easier to write programs that cope with either variant, the
2597	following macros are defined:	3272	following macros are defined:
…		…
2602		3277
2603	This provides the loop I<argument> for functions, if one is required ("ev	3278	This provides the loop I<argument> for functions, if one is required ("ev
2604	loop argument"). The C<EV_A> form is used when this is the sole argument,	3279	loop argument"). The C<EV_A> form is used when this is the sole argument,
2605	C<EV_A_> is used when other arguments are following. Example:	3280	C<EV_A_> is used when other arguments are following. Example:
2606		3281
2607	ev_unref (EV_A);	3282	ev_unref (EV_A);
2608	ev_timer_add (EV_A_ watcher);	3283	ev_timer_add (EV_A_ watcher);
2609	ev_loop (EV_A_ 0);	3284	ev_loop (EV_A_ 0);
2610		3285
2611	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3286	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2612	which is often provided by the following macro.	3287	which is often provided by the following macro.
2613		3288
2614	=item C<EV_P>, C<EV_P_>	3289	=item C<EV_P>, C<EV_P_>
2615		3290
2616	This provides the loop I<parameter> for functions, if one is required ("ev	3291	This provides the loop I<parameter> for functions, if one is required ("ev
2617	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3292	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2618	C<EV_P_> is used when other parameters are following. Example:	3293	C<EV_P_> is used when other parameters are following. Example:
2619		3294
2620	// this is how ev_unref is being declared	3295	// this is how ev_unref is being declared
2621	static void ev_unref (EV_P);	3296	static void ev_unref (EV_P);
2622		3297
2623	// this is how you can declare your typical callback	3298	// this is how you can declare your typical callback
2624	static void cb (EV_P_ ev_timer *w, int revents)	3299	static void cb (EV_P_ ev_timer *w, int revents)
2625		3300
2626	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3301	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2627	suitable for use with C<EV_A>.	3302	suitable for use with C<EV_A>.
2628		3303
2629	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3304	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
…		…
2645		3320
2646	Example: Declare and initialise a check watcher, utilising the above	3321	Example: Declare and initialise a check watcher, utilising the above
2647	macros so it will work regardless of whether multiple loops are supported	3322	macros so it will work regardless of whether multiple loops are supported
2648	or not.	3323	or not.
2649		3324
2650	static void	3325	static void
2651	check_cb (EV_P_ ev_timer *w, int revents)	3326	check_cb (EV_P_ ev_timer *w, int revents)
2652	{	3327	{
2653	ev_check_stop (EV_A_ w);	3328	ev_check_stop (EV_A_ w);
2654	}	3329	}
2655		3330
2656	ev_check check;	3331	ev_check check;
2657	ev_check_init (&check, check_cb);	3332	ev_check_init (&check, check_cb);
2658	ev_check_start (EV_DEFAULT_ &check);	3333	ev_check_start (EV_DEFAULT_ &check);
2659	ev_loop (EV_DEFAULT_ 0);	3334	ev_loop (EV_DEFAULT_ 0);
2660		3335
2661	=head1 EMBEDDING	3336	=head1 EMBEDDING
2662		3337
2663	Libev can (and often is) directly embedded into host	3338	Libev can (and often is) directly embedded into host
2664	applications. Examples of applications that embed it include the Deliantra	3339	applications. Examples of applications that embed it include the Deliantra
…		…
2671	libev somewhere in your source tree).	3346	libev somewhere in your source tree).
2672		3347
2673	=head2 FILESETS	3348	=head2 FILESETS
2674		3349
2675	Depending on what features you need you need to include one or more sets of files	3350	Depending on what features you need you need to include one or more sets of files
2676	in your app.	3351	in your application.
2677		3352
2678	=head3 CORE EVENT LOOP	3353	=head3 CORE EVENT LOOP
2679		3354
2680	To include only the libev core (all the C<ev_*> functions), with manual	3355	To include only the libev core (all the C<ev_*> functions), with manual
2681	configuration (no autoconf):	3356	configuration (no autoconf):
2682		3357
2683	#define EV_STANDALONE 1	3358	#define EV_STANDALONE 1
2684	#include "ev.c"	3359	#include "ev.c"
2685		3360
2686	This will automatically include F<ev.h>, too, and should be done in a	3361	This will automatically include F<ev.h>, too, and should be done in a
2687	single C source file only to provide the function implementations. To use	3362	single C source file only to provide the function implementations. To use
2688	it, do the same for F<ev.h> in all files wishing to use this API (best	3363	it, do the same for F<ev.h> in all files wishing to use this API (best
2689	done by writing a wrapper around F<ev.h> that you can include instead and	3364	done by writing a wrapper around F<ev.h> that you can include instead and
2690	where you can put other configuration options):	3365	where you can put other configuration options):
2691		3366
2692	#define EV_STANDALONE 1	3367	#define EV_STANDALONE 1
2693	#include "ev.h"	3368	#include "ev.h"
2694		3369
2695	Both header files and implementation files can be compiled with a C++	3370	Both header files and implementation files can be compiled with a C++
2696	compiler (at least, thats a stated goal, and breakage will be treated	3371	compiler (at least, that's a stated goal, and breakage will be treated
2697	as a bug).	3372	as a bug).
2698		3373
2699	You need the following files in your source tree, or in a directory	3374	You need the following files in your source tree, or in a directory
2700	in your include path (e.g. in libev/ when using -Ilibev):	3375	in your include path (e.g. in libev/ when using -Ilibev):
2701		3376
2702	ev.h	3377	ev.h
2703	ev.c	3378	ev.c
2704	ev_vars.h	3379	ev_vars.h
2705	ev_wrap.h	3380	ev_wrap.h
2706		3381
2707	ev_win32.c required on win32 platforms only	3382	ev_win32.c required on win32 platforms only
2708		3383
2709	ev_select.c only when select backend is enabled (which is enabled by default)	3384	ev_select.c only when select backend is enabled (which is enabled by default)
2710	ev_poll.c only when poll backend is enabled (disabled by default)	3385	ev_poll.c only when poll backend is enabled (disabled by default)
2711	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3386	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2712	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3387	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2713	ev_port.c only when the solaris port backend is enabled (disabled by default)	3388	ev_port.c only when the solaris port backend is enabled (disabled by default)
2714		3389
2715	F<ev.c> includes the backend files directly when enabled, so you only need	3390	F<ev.c> includes the backend files directly when enabled, so you only need
2716	to compile this single file.	3391	to compile this single file.
2717		3392
2718	=head3 LIBEVENT COMPATIBILITY API	3393	=head3 LIBEVENT COMPATIBILITY API
2719		3394
2720	To include the libevent compatibility API, also include:	3395	To include the libevent compatibility API, also include:
2721		3396
2722	#include "event.c"	3397	#include "event.c"
2723		3398
2724	in the file including F<ev.c>, and:	3399	in the file including F<ev.c>, and:
2725		3400
2726	#include "event.h"	3401	#include "event.h"
2727		3402
2728	in the files that want to use the libevent API. This also includes F<ev.h>.	3403	in the files that want to use the libevent API. This also includes F<ev.h>.
2729		3404
2730	You need the following additional files for this:	3405	You need the following additional files for this:
2731		3406
2732	event.h	3407	event.h
2733	event.c	3408	event.c
2734		3409
2735	=head3 AUTOCONF SUPPORT	3410	=head3 AUTOCONF SUPPORT
2736		3411
2737	Instead of using C<EV_STANDALONE=1> and providing your config in	3412	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2738	whatever way you want, you can also C<m4_include([libev.m4])> in your	3413	whatever way you want, you can also C<m4_include([libev.m4])> in your
2739	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3414	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2740	include F<config.h> and configure itself accordingly.	3415	include F<config.h> and configure itself accordingly.
2741		3416
2742	For this of course you need the m4 file:	3417	For this of course you need the m4 file:
2743		3418
2744	libev.m4	3419	libev.m4
2745		3420
2746	=head2 PREPROCESSOR SYMBOLS/MACROS	3421	=head2 PREPROCESSOR SYMBOLS/MACROS
2747		3422
2748	Libev can be configured via a variety of preprocessor symbols you have to	3423	Libev can be configured via a variety of preprocessor symbols you have to
2749	define before including any of its files. The default in the absense of	3424	define before including any of its files. The default in the absence of
2750	autoconf is noted for every option.	3425	autoconf is documented for every option.
2751		3426
2752	=over 4	3427	=over 4
2753		3428
2754	=item EV_STANDALONE	3429	=item EV_STANDALONE
2755		3430
…		…
2757	keeps libev from including F<config.h>, and it also defines dummy	3432	keeps libev from including F<config.h>, and it also defines dummy
2758	implementations for some libevent functions (such as logging, which is not	3433	implementations for some libevent functions (such as logging, which is not
2759	supported). It will also not define any of the structs usually found in	3434	supported). It will also not define any of the structs usually found in
2760	F<event.h> that are not directly supported by the libev core alone.	3435	F<event.h> that are not directly supported by the libev core alone.
2761		3436
		3437	In stanbdalone mode, libev will still try to automatically deduce the
		3438	configuration, but has to be more conservative.
		3439
2762	=item EV_USE_MONOTONIC	3440	=item EV_USE_MONOTONIC
2763		3441
2764	If defined to be C<1>, libev will try to detect the availability of the	3442	If defined to be C<1>, libev will try to detect the availability of the
2765	monotonic clock option at both compiletime and runtime. Otherwise no use	3443	monotonic clock option at both compile time and runtime. Otherwise no
2766	of the monotonic clock option will be attempted. If you enable this, you	3444	use of the monotonic clock option will be attempted. If you enable this,
2767	usually have to link against librt or something similar. Enabling it when	3445	you usually have to link against librt or something similar. Enabling it
2768	the functionality isn't available is safe, though, although you have	3446	when the functionality isn't available is safe, though, although you have
2769	to make sure you link against any libraries where the C<clock_gettime>	3447	to make sure you link against any libraries where the C<clock_gettime>
2770	function is hiding in (often F<-lrt>).	3448	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2771		3449
2772	=item EV_USE_REALTIME	3450	=item EV_USE_REALTIME
2773		3451
2774	If defined to be C<1>, libev will try to detect the availability of the	3452	If defined to be C<1>, libev will try to detect the availability of the
2775	realtime clock option at compiletime (and assume its availability at	3453	real-time clock option at compile time (and assume its availability
2776	runtime if successful). Otherwise no use of the realtime clock option will	3454	at runtime if successful). Otherwise no use of the real-time clock
2777	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3455	option will be attempted. This effectively replaces C<gettimeofday>
2778	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3456	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2779	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3457	correctness. See the note about libraries in the description of
		3458	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3459	C<EV_USE_CLOCK_SYSCALL>.
		3460
		3461	=item EV_USE_CLOCK_SYSCALL
		3462
		3463	If defined to be C<1>, libev will try to use a direct syscall instead
		3464	of calling the system-provided C<clock_gettime> function. This option
		3465	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3466	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3467	programs needlessly. Using a direct syscall is slightly slower (in
		3468	theory), because no optimised vdso implementation can be used, but avoids
		3469	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3470	higher, as it simplifies linking (no need for C<-lrt>).
2780		3471
2781	=item EV_USE_NANOSLEEP	3472	=item EV_USE_NANOSLEEP
2782		3473
2783	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3474	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2784	and will use it for delays. Otherwise it will use C<select ()>.	3475	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2792	2.7 or newer, otherwise disabled.	3483	2.7 or newer, otherwise disabled.
2793		3484
2794	=item EV_USE_SELECT	3485	=item EV_USE_SELECT
2795		3486
2796	If undefined or defined to be C<1>, libev will compile in support for the	3487	If undefined or defined to be C<1>, libev will compile in support for the
2797	C<select>(2) backend. No attempt at autodetection will be done: if no	3488	C<select>(2) backend. No attempt at auto-detection will be done: if no
2798	other method takes over, select will be it. Otherwise the select backend	3489	other method takes over, select will be it. Otherwise the select backend
2799	will not be compiled in.	3490	will not be compiled in.
2800		3491
2801	=item EV_SELECT_USE_FD_SET	3492	=item EV_SELECT_USE_FD_SET
2802		3493
2803	If defined to C<1>, then the select backend will use the system C<fd_set>	3494	If defined to C<1>, then the select backend will use the system C<fd_set>
2804	structure. This is useful if libev doesn't compile due to a missing	3495	structure. This is useful if libev doesn't compile due to a missing
2805	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3496	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2806	exotic systems. This usually limits the range of file descriptors to some	3497	on exotic systems. This usually limits the range of file descriptors to
2807	low limit such as 1024 or might have other limitations (winsocket only	3498	some low limit such as 1024 or might have other limitations (winsocket
2808	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3499	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2809	influence the size of the C<fd_set> used.	3500	configures the maximum size of the C<fd_set>.
2810		3501
2811	=item EV_SELECT_IS_WINSOCKET	3502	=item EV_SELECT_IS_WINSOCKET
2812		3503
2813	When defined to C<1>, the select backend will assume that	3504	When defined to C<1>, the select backend will assume that
2814	select/socket/connect etc. don't understand file descriptors but	3505	select/socket/connect etc. don't understand file descriptors but
…		…
2859	otherwise another method will be used as fallback. This is the preferred	3550	otherwise another method will be used as fallback. This is the preferred
2860	backend for Solaris 10 systems.	3551	backend for Solaris 10 systems.
2861		3552
2862	=item EV_USE_DEVPOLL	3553	=item EV_USE_DEVPOLL
2863		3554
2864	reserved for future expansion, works like the USE symbols above.	3555	Reserved for future expansion, works like the USE symbols above.
2865		3556
2866	=item EV_USE_INOTIFY	3557	=item EV_USE_INOTIFY
2867		3558
2868	If defined to be C<1>, libev will compile in support for the Linux inotify	3559	If defined to be C<1>, libev will compile in support for the Linux inotify
2869	interface to speed up C<ev_stat> watchers. Its actual availability will	3560	interface to speed up C<ev_stat> watchers. Its actual availability will
…		…
2876	access is atomic with respect to other threads or signal contexts. No such	3567	access is atomic with respect to other threads or signal contexts. No such
2877	type is easily found in the C language, so you can provide your own type	3568	type is easily found in the C language, so you can provide your own type
2878	that you know is safe for your purposes. It is used both for signal handler "locking"	3569	that you know is safe for your purposes. It is used both for signal handler "locking"
2879	as well as for signal and thread safety in C<ev_async> watchers.	3570	as well as for signal and thread safety in C<ev_async> watchers.
2880		3571
2881	In the absense of this define, libev will use C<sig_atomic_t volatile>	3572	In the absence of this define, libev will use C<sig_atomic_t volatile>
2882	(from F<signal.h>), which is usually good enough on most platforms.	3573	(from F<signal.h>), which is usually good enough on most platforms.
2883		3574
2884	=item EV_H	3575	=item EV_H
2885		3576
2886	The name of the F<ev.h> header file used to include it. The default if	3577	The name of the F<ev.h> header file used to include it. The default if
…		…
2925	When doing priority-based operations, libev usually has to linearly search	3616	When doing priority-based operations, libev usually has to linearly search
2926	all the priorities, so having many of them (hundreds) uses a lot of space	3617	all the priorities, so having many of them (hundreds) uses a lot of space
2927	and time, so using the defaults of five priorities (-2 .. +2) is usually	3618	and time, so using the defaults of five priorities (-2 .. +2) is usually
2928	fine.	3619	fine.
2929		3620
2930	If your embedding app does not need any priorities, defining these both to	3621	If your embedding application does not need any priorities, defining these
2931	C<0> will save some memory and cpu.	3622	both to C<0> will save some memory and CPU.
2932		3623
2933	=item EV_PERIODIC_ENABLE	3624	=item EV_PERIODIC_ENABLE
2934		3625
2935	If undefined or defined to be C<1>, then periodic timers are supported. If	3626	If undefined or defined to be C<1>, then periodic timers are supported. If
2936	defined to be C<0>, then they are not. Disabling them saves a few kB of	3627	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2943	code.	3634	code.
2944		3635
2945	=item EV_EMBED_ENABLE	3636	=item EV_EMBED_ENABLE
2946		3637
2947	If undefined or defined to be C<1>, then embed watchers are supported. If	3638	If undefined or defined to be C<1>, then embed watchers are supported. If
2948	defined to be C<0>, then they are not.	3639	defined to be C<0>, then they are not. Embed watchers rely on most other
		3640	watcher types, which therefore must not be disabled.
2949		3641
2950	=item EV_STAT_ENABLE	3642	=item EV_STAT_ENABLE
2951		3643
2952	If undefined or defined to be C<1>, then stat watchers are supported. If	3644	If undefined or defined to be C<1>, then stat watchers are supported. If
2953	defined to be C<0>, then they are not.	3645	defined to be C<0>, then they are not.
…		…
2963	defined to be C<0>, then they are not.	3655	defined to be C<0>, then they are not.
2964		3656
2965	=item EV_MINIMAL	3657	=item EV_MINIMAL
2966		3658
2967	If you need to shave off some kilobytes of code at the expense of some	3659	If you need to shave off some kilobytes of code at the expense of some
2968	speed, define this symbol to C<1>. Currently only used for gcc to override	3660	speed, define this symbol to C<1>. Currently this is used to override some
2969	some inlining decisions, saves roughly 30% codesize of amd64.	3661	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3662	much smaller 2-heap for timer management over the default 4-heap.
2970		3663
2971	=item EV_PID_HASHSIZE	3664	=item EV_PID_HASHSIZE
2972		3665
2973	C<ev_child> watchers use a small hash table to distribute workload by	3666	C<ev_child> watchers use a small hash table to distribute workload by
2974	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3667	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2981	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3674	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2982	usually more than enough. If you need to manage thousands of C<ev_stat>	3675	usually more than enough. If you need to manage thousands of C<ev_stat>
2983	watchers you might want to increase this value (I<must> be a power of	3676	watchers you might want to increase this value (I<must> be a power of
2984	two).	3677	two).
2985		3678
		3679	=item EV_USE_4HEAP
		3680
		3681	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3682	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3683	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3684	faster performance with many (thousands) of watchers.
		3685
		3686	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3687	(disabled).
		3688
		3689	=item EV_HEAP_CACHE_AT
		3690
		3691	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3692	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3693	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3694	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3695	but avoids random read accesses on heap changes. This improves performance
		3696	noticeably with many (hundreds) of watchers.
		3697
		3698	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3699	(disabled).
		3700
		3701	=item EV_VERIFY
		3702
		3703	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3704	be done: If set to C<0>, no internal verification code will be compiled
		3705	in. If set to C<1>, then verification code will be compiled in, but not
		3706	called. If set to C<2>, then the internal verification code will be
		3707	called once per loop, which can slow down libev. If set to C<3>, then the
		3708	verification code will be called very frequently, which will slow down
		3709	libev considerably.
		3710
		3711	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3712	C<0>.
		3713
2986	=item EV_COMMON	3714	=item EV_COMMON
2987		3715
2988	By default, all watchers have a C<void *data> member. By redefining	3716	By default, all watchers have a C<void *data> member. By redefining
2989	this macro to a something else you can include more and other types of	3717	this macro to a something else you can include more and other types of
2990	members. You have to define it each time you include one of the files,	3718	members. You have to define it each time you include one of the files,
2991	though, and it must be identical each time.	3719	though, and it must be identical each time.
2992		3720
2993	For example, the perl EV module uses something like this:	3721	For example, the perl EV module uses something like this:
2994		3722
2995	#define EV_COMMON \	3723	#define EV_COMMON \
2996	SV *self; /* contains this struct */ \	3724	SV *self; /* contains this struct */ \
2997	SV *cb_sv, *fh /* note no trailing ";" */	3725	SV *cb_sv, *fh /* note no trailing ";" */
2998		3726
2999	=item EV_CB_DECLARE (type)	3727	=item EV_CB_DECLARE (type)
3000		3728
3001	=item EV_CB_INVOKE (watcher, revents)	3729	=item EV_CB_INVOKE (watcher, revents)
3002		3730
…		…
3007	definition and a statement, respectively. See the F<ev.h> header file for	3735	definition and a statement, respectively. See the F<ev.h> header file for
3008	their default definitions. One possible use for overriding these is to	3736	their default definitions. One possible use for overriding these is to
3009	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3737	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3010	method calls instead of plain function calls in C++.	3738	method calls instead of plain function calls in C++.
3011		3739
		3740	=back
		3741
3012	=head2 EXPORTED API SYMBOLS	3742	=head2 EXPORTED API SYMBOLS
3013		3743
3014	If you need to re-export the API (e.g. via a dll) and you need a list of	3744	If you need to re-export the API (e.g. via a DLL) and you need a list of
3015	exported symbols, you can use the provided F<Symbol.*> files which list	3745	exported symbols, you can use the provided F<Symbol.*> files which list
3016	all public symbols, one per line:	3746	all public symbols, one per line:
3017		3747
3018	Symbols.ev for libev proper	3748	Symbols.ev for libev proper
3019	Symbols.event for the libevent emulation	3749	Symbols.event for the libevent emulation
3020		3750
3021	This can also be used to rename all public symbols to avoid clashes with	3751	This can also be used to rename all public symbols to avoid clashes with
3022	multiple versions of libev linked together (which is obviously bad in	3752	multiple versions of libev linked together (which is obviously bad in
3023	itself, but sometimes it is inconvinient to avoid this).	3753	itself, but sometimes it is inconvenient to avoid this).
3024		3754
3025	A sed command like this will create wrapper C<#define>'s that you need to	3755	A sed command like this will create wrapper C<#define>'s that you need to
3026	include before including F<ev.h>:	3756	include before including F<ev.h>:
3027		3757
3028	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3758	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
3045	file.	3775	file.
3046		3776
3047	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3777	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3048	that everybody includes and which overrides some configure choices:	3778	that everybody includes and which overrides some configure choices:
3049		3779
3050	#define EV_MINIMAL 1	3780	#define EV_MINIMAL 1
3051	#define EV_USE_POLL 0	3781	#define EV_USE_POLL 0
3052	#define EV_MULTIPLICITY 0	3782	#define EV_MULTIPLICITY 0
3053	#define EV_PERIODIC_ENABLE 0	3783	#define EV_PERIODIC_ENABLE 0
3054	#define EV_STAT_ENABLE 0	3784	#define EV_STAT_ENABLE 0
3055	#define EV_FORK_ENABLE 0	3785	#define EV_FORK_ENABLE 0
3056	#define EV_CONFIG_H <config.h>	3786	#define EV_CONFIG_H <config.h>
3057	#define EV_MINPRI 0	3787	#define EV_MINPRI 0
3058	#define EV_MAXPRI 0	3788	#define EV_MAXPRI 0
3059		3789
3060	#include "ev++.h"	3790	#include "ev++.h"
3061		3791
3062	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3792	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3063		3793
3064	#include "ev_cpp.h"	3794	#include "ev_cpp.h"
3065	#include "ev.c"	3795	#include "ev.c"
3066		3796
		3797	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3067		3798
3068	=head1 THREADS AND COROUTINES	3799	=head2 THREADS AND COROUTINES
3069		3800
3070	=head2 THREADS	3801	=head3 THREADS
3071		3802
3072	Libev itself is completely threadsafe, but it uses no locking. This	3803	All libev functions are reentrant and thread-safe unless explicitly
		3804	documented otherwise, but libev implements no locking itself. This means
3073	means that you can use as many loops as you want in parallel, as long as	3805	that you can use as many loops as you want in parallel, as long as there
3074	only one thread ever calls into one libev function with the same loop	3806	are no concurrent calls into any libev function with the same loop
3075	parameter.	3807	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3808	of course): libev guarantees that different event loops share no data
		3809	structures that need any locking.
3076		3810
3077	Or put differently: calls with different loop parameters can be done in	3811	Or to put it differently: calls with different loop parameters can be done
3078	parallel from multiple threads, calls with the same loop parameter must be	3812	concurrently from multiple threads, calls with the same loop parameter
3079	done serially (but can be done from different threads, as long as only one	3813	must be done serially (but can be done from different threads, as long as
3080	thread ever is inside a call at any point in time, e.g. by using a mutex	3814	only one thread ever is inside a call at any point in time, e.g. by using
3081	per loop).	3815	a mutex per loop).
3082		3816
3083	If you want to know which design is best for your problem, then I cannot	3817	Specifically to support threads (and signal handlers), libev implements
		3818	so-called C<ev_async> watchers, which allow some limited form of
		3819	concurrency on the same event loop, namely waking it up "from the
		3820	outside".
		3821
		3822	If you want to know which design (one loop, locking, or multiple loops
		3823	without or something else still) is best for your problem, then I cannot
3084	help you but by giving some generic advice:	3824	help you, but here is some generic advice:
3085		3825
3086	=over 4	3826	=over 4
3087		3827
3088	=item * most applications have a main thread: use the default libev loop	3828	=item * most applications have a main thread: use the default libev loop
3089	in that thread, or create a seperate thread running only the default loop.	3829	in that thread, or create a separate thread running only the default loop.
3090		3830
3091	This helps integrating other libraries or software modules that use libev	3831	This helps integrating other libraries or software modules that use libev
3092	themselves and don't care/know about threading.	3832	themselves and don't care/know about threading.
3093		3833
3094	=item * one loop per thread is usually a good model.	3834	=item * one loop per thread is usually a good model.
3095		3835
3096	Doing this is almost never wrong, sometimes a better-performance model	3836	Doing this is almost never wrong, sometimes a better-performance model
3097	exists, but it is always a good start.	3837	exists, but it is always a good start.
3098		3838
3099	=item * other models exist, such as the leader/follower pattern, where one	3839	=item * other models exist, such as the leader/follower pattern, where one
3100	loop is handed through multiple threads in a kind of round-robbin fashion.	3840	loop is handed through multiple threads in a kind of round-robin fashion.
3101		3841
3102	Chosing a model is hard - look around, learn, know that usually you cna do	3842	Choosing a model is hard - look around, learn, know that usually you can do
3103	better than you currently do :-)	3843	better than you currently do :-)
3104		3844
3105	=item * often you need to talk to some other thread which blocks in the	3845	=item * often you need to talk to some other thread which blocks in the
		3846	event loop.
		3847
3106	event loop - C<ev_async> watchers can be used to wake them up from other	3848	C<ev_async> watchers can be used to wake them up from other threads safely
3107	threads safely (or from signal contexts...).	3849	(or from signal contexts...).
		3850
		3851	An example use would be to communicate signals or other events that only
		3852	work in the default loop by registering the signal watcher with the
		3853	default loop and triggering an C<ev_async> watcher from the default loop
		3854	watcher callback into the event loop interested in the signal.
3108		3855
3109	=back	3856	=back
3110		3857
3111	=head2 COROUTINES	3858	=head3 COROUTINES
3112		3859
3113	Libev is much more accomodating to coroutines ("cooperative threads"):	3860	Libev is very accommodating to coroutines ("cooperative threads"):
3114	libev fully supports nesting calls to it's functions from different	3861	libev fully supports nesting calls to its functions from different
3115	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3862	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3116	different coroutines and switch freely between both coroutines running the	3863	different coroutines, and switch freely between both coroutines running the
3117	loop, as long as you don't confuse yourself). The only exception is that	3864	loop, as long as you don't confuse yourself). The only exception is that
3118	you must not do this from C<ev_periodic> reschedule callbacks.	3865	you must not do this from C<ev_periodic> reschedule callbacks.
3119		3866
3120	Care has been invested into making sure that libev does not keep local	3867	Care has been taken to ensure that libev does not keep local state inside
3121	state inside C<ev_loop>, and other calls do not usually allow coroutine	3868	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3122	switches.	3869	they do not call any callbacks.
3123		3870
		3871	=head2 COMPILER WARNINGS
3124		3872
3125	=head1 COMPLEXITIES	3873	Depending on your compiler and compiler settings, you might get no or a
		3874	lot of warnings when compiling libev code. Some people are apparently
		3875	scared by this.
3126		3876
3127	In this section the complexities of (many of) the algorithms used inside	3877	However, these are unavoidable for many reasons. For one, each compiler
3128	libev will be explained. For complexity discussions about backends see the	3878	has different warnings, and each user has different tastes regarding
3129	documentation for C<ev_default_init>.	3879	warning options. "Warn-free" code therefore cannot be a goal except when
		3880	targeting a specific compiler and compiler-version.
3130		3881
3131	All of the following are about amortised time: If an array needs to be	3882	Another reason is that some compiler warnings require elaborate
3132	extended, libev needs to realloc and move the whole array, but this	3883	workarounds, or other changes to the code that make it less clear and less
3133	happens asymptotically never with higher number of elements, so O(1) might	3884	maintainable.
3134	mean it might do a lengthy realloc operation in rare cases, but on average
3135	it is much faster and asymptotically approaches constant time.
3136		3885
3137	=over 4	3886	And of course, some compiler warnings are just plain stupid, or simply
		3887	wrong (because they don't actually warn about the condition their message
		3888	seems to warn about). For example, certain older gcc versions had some
		3889	warnings that resulted an extreme number of false positives. These have
		3890	been fixed, but some people still insist on making code warn-free with
		3891	such buggy versions.
3138		3892
3139	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3893	While libev is written to generate as few warnings as possible,
		3894	"warn-free" code is not a goal, and it is recommended not to build libev
		3895	with any compiler warnings enabled unless you are prepared to cope with
		3896	them (e.g. by ignoring them). Remember that warnings are just that:
		3897	warnings, not errors, or proof of bugs.
3140		3898
3141	This means that, when you have a watcher that triggers in one hour and
3142	there are 100 watchers that would trigger before that then inserting will
3143	have to skip roughly seven (C<ld 100>) of these watchers.
3144		3899
3145	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3900	=head2 VALGRIND
3146		3901
3147	That means that changing a timer costs less than removing/adding them	3902	Valgrind has a special section here because it is a popular tool that is
3148	as only the relative motion in the event queue has to be paid for.	3903	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3149		3904
3150	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3905	If you think you found a bug (memory leak, uninitialised data access etc.)
		3906	in libev, then check twice: If valgrind reports something like:
3151		3907
3152	These just add the watcher into an array or at the head of a list.	3908	==2274== definitely lost: 0 bytes in 0 blocks.
		3909	==2274== possibly lost: 0 bytes in 0 blocks.
		3910	==2274== still reachable: 256 bytes in 1 blocks.
3153		3911
3154	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3912	Then there is no memory leak, just as memory accounted to global variables
		3913	is not a memleak - the memory is still being referenced, and didn't leak.
3155		3914
3156	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3915	Similarly, under some circumstances, valgrind might report kernel bugs
		3916	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3917	although an acceptable workaround has been found here), or it might be
		3918	confused.
3157		3919
3158	These watchers are stored in lists then need to be walked to find the	3920	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3159	correct watcher to remove. The lists are usually short (you don't usually	3921	make it into some kind of religion.
3160	have many watchers waiting for the same fd or signal).
3161		3922
3162	=item Finding the next timer in each loop iteration: O(1)	3923	If you are unsure about something, feel free to contact the mailing list
		3924	with the full valgrind report and an explanation on why you think this
		3925	is a bug in libev (best check the archives, too :). However, don't be
		3926	annoyed when you get a brisk "this is no bug" answer and take the chance
		3927	of learning how to interpret valgrind properly.
3163		3928
3164	By virtue of using a binary heap, the next timer is always found at the	3929	If you need, for some reason, empty reports from valgrind for your project
3165	beginning of the storage array.	3930	I suggest using suppression lists.
3166		3931
3167	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3168		3932
3169	A change means an I/O watcher gets started or stopped, which requires	3933	=head1 PORTABILITY NOTES
3170	libev to recalculate its status (and possibly tell the kernel, depending
3171	on backend and wether C<ev_io_set> was used).
3172		3934
3173	=item Activating one watcher (putting it into the pending state): O(1)	3935	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3174
3175	=item Priority handling: O(number_of_priorities)
3176
3177	Priorities are implemented by allocating some space for each
3178	priority. When doing priority-based operations, libev usually has to
3179	linearly search all the priorities, but starting/stopping and activating
3180	watchers becomes O(1) w.r.t. priority handling.
3181
3182	=item Sending an ev_async: O(1)
3183
3184	=item Processing ev_async_send: O(number_of_async_watchers)
3185
3186	=item Processing signals: O(max_signal_number)
3187
3188	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3189	calls in the current loop iteration. Checking for async and signal events
3190	involves iterating over all running async watchers or all signal numbers.
3191
3192	=back
3193
3194
3195	=head1 Win32 platform limitations and workarounds
3196		3936
3197	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3937	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3198	requires, and its I/O model is fundamentally incompatible with the POSIX	3938	requires, and its I/O model is fundamentally incompatible with the POSIX
3199	model. Libev still offers limited functionality on this platform in	3939	model. Libev still offers limited functionality on this platform in
3200	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3940	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3201	descriptors. This only applies when using Win32 natively, not when using	3941	descriptors. This only applies when using Win32 natively, not when using
3202	e.g. cygwin.	3942	e.g. cygwin.
3203		3943
		3944	Lifting these limitations would basically require the full
		3945	re-implementation of the I/O system. If you are into these kinds of
		3946	things, then note that glib does exactly that for you in a very portable
		3947	way (note also that glib is the slowest event library known to man).
		3948
3204	There is no supported compilation method available on windows except	3949	There is no supported compilation method available on windows except
3205	embedding it into other applications.	3950	embedding it into other applications.
3206		3951
		3952	Sensible signal handling is officially unsupported by Microsoft - libev
		3953	tries its best, but under most conditions, signals will simply not work.
		3954
		3955	Not a libev limitation but worth mentioning: windows apparently doesn't
		3956	accept large writes: instead of resulting in a partial write, windows will
		3957	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3958	so make sure you only write small amounts into your sockets (less than a
		3959	megabyte seems safe, but this apparently depends on the amount of memory
		3960	available).
		3961
3207	Due to the many, low, and arbitrary limits on the win32 platform and the	3962	Due to the many, low, and arbitrary limits on the win32 platform and
3208	abysmal performance of winsockets, using a large number of sockets is not	3963	the abysmal performance of winsockets, using a large number of sockets
3209	recommended (and not reasonable). If your program needs to use more than	3964	is not recommended (and not reasonable). If your program needs to use
3210	a hundred or so sockets, then likely it needs to use a totally different	3965	more than a hundred or so sockets, then likely it needs to use a totally
3211	implementation for windows, as libev offers the POSIX model, which cannot	3966	different implementation for windows, as libev offers the POSIX readiness
3212	be implemented efficiently on windows (microsoft monopoly games).	3967	notification model, which cannot be implemented efficiently on windows
		3968	(due to Microsoft monopoly games).
		3969
		3970	A typical way to use libev under windows is to embed it (see the embedding
		3971	section for details) and use the following F<evwrap.h> header file instead
		3972	of F<ev.h>:
		3973
		3974	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3975	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3976
		3977	#include "ev.h"
		3978
		3979	And compile the following F<evwrap.c> file into your project (make sure
		3980	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3981
		3982	#include "evwrap.h"
		3983	#include "ev.c"
3213		3984
3214	=over 4	3985	=over 4
3215		3986
3216	=item The winsocket select function	3987	=item The winsocket select function
3217		3988
3218	The winsocket C<select> function doesn't follow POSIX in that it requires	3989	The winsocket C<select> function doesn't follow POSIX in that it
3219	socket I<handles> and not socket I<file descriptors>. This makes select	3990	requires socket I<handles> and not socket I<file descriptors> (it is
3220	very inefficient, and also requires a mapping from file descriptors	3991	also extremely buggy). This makes select very inefficient, and also
3221	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	3992	requires a mapping from file descriptors to socket handles (the Microsoft
3222	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	3993	C runtime provides the function C<_open_osfhandle> for this). See the
3223	symbols for more info.	3994	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3995	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3224		3996
3225	The configuration for a "naked" win32 using the microsoft runtime	3997	The configuration for a "naked" win32 using the Microsoft runtime
3226	libraries and raw winsocket select is:	3998	libraries and raw winsocket select is:
3227		3999
3228	#define EV_USE_SELECT 1	4000	#define EV_USE_SELECT 1
3229	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4001	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3230		4002
3231	Note that winsockets handling of fd sets is O(n), so you can easily get a	4003	Note that winsockets handling of fd sets is O(n), so you can easily get a
3232	complexity in the O(n²) range when using win32.	4004	complexity in the O(n²) range when using win32.
3233		4005
3234	=item Limited number of file descriptors	4006	=item Limited number of file descriptors
3235		4007
3236	Windows has numerous arbitrary (and low) limits on things. Early versions	4008	Windows has numerous arbitrary (and low) limits on things.
3237	of winsocket's select only supported waiting for a max. of C<64> handles	4009
		4010	Early versions of winsocket's select only supported waiting for a maximum
3238	(probably owning to the fact that all windows kernels can only wait for	4011	of C<64> handles (probably owning to the fact that all windows kernels
3239	C<64> things at the same time internally; microsoft recommends spawning a	4012	can only wait for C<64> things at the same time internally; Microsoft
3240	chain of threads and wait for 63 handles and the previous thread in each).	4013	recommends spawning a chain of threads and wait for 63 handles and the
		4014	previous thread in each. Sounds great!).
3241		4015
3242	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4016	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3243	to some high number (e.g. C<2048>) before compiling the winsocket select	4017	to some high number (e.g. C<2048>) before compiling the winsocket select
3244	call (which might be in libev or elsewhere, for example, perl does its own	4018	call (which might be in libev or elsewhere, for example, perl and many
3245	select emulation on windows).	4019	other interpreters do their own select emulation on windows).
3246		4020
3247	Another limit is the number of file descriptors in the microsoft runtime	4021	Another limit is the number of file descriptors in the Microsoft runtime
3248	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4022	libraries, which by default is C<64> (there must be a hidden I<64>
3249	or something like this inside microsoft). You can increase this by calling	4023	fetish or something like this inside Microsoft). You can increase this
3250	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4024	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3251	arbitrary limit), but is broken in many versions of the microsoft runtime	4025	(another arbitrary limit), but is broken in many versions of the Microsoft
3252	libraries.
3253
3254	This might get you to about C<512> or C<2048> sockets (depending on	4026	runtime libraries. This might get you to about C<512> or C<2048> sockets
3255	windows version and/or the phase of the moon). To get more, you need to	4027	(depending on windows version and/or the phase of the moon). To get more,
3256	wrap all I/O functions and provide your own fd management, but the cost of	4028	you need to wrap all I/O functions and provide your own fd management, but
3257	calling select (O(n²)) will likely make this unworkable.	4029	the cost of calling select (O(n²)) will likely make this unworkable.
3258		4030
3259	=back	4031	=back
3260		4032
		4033	=head2 PORTABILITY REQUIREMENTS
		4034
		4035	In addition to a working ISO-C implementation and of course the
		4036	backend-specific APIs, libev relies on a few additional extensions:
		4037
		4038	=over 4
		4039
		4040	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4041	calling conventions regardless of C<ev_watcher_type *>.
		4042
		4043	Libev assumes not only that all watcher pointers have the same internal
		4044	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4045	assumes that the same (machine) code can be used to call any watcher
		4046	callback: The watcher callbacks have different type signatures, but libev
		4047	calls them using an C<ev_watcher *> internally.
		4048
		4049	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4050
		4051	The type C<sig_atomic_t volatile> (or whatever is defined as
		4052	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4053	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4054	believed to be sufficiently portable.
		4055
		4056	=item C<sigprocmask> must work in a threaded environment
		4057
		4058	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4059	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4060	pthread implementations will either allow C<sigprocmask> in the "main
		4061	thread" or will block signals process-wide, both behaviours would
		4062	be compatible with libev. Interaction between C<sigprocmask> and
		4063	C<pthread_sigmask> could complicate things, however.
		4064
		4065	The most portable way to handle signals is to block signals in all threads
		4066	except the initial one, and run the default loop in the initial thread as
		4067	well.
		4068
		4069	=item C<long> must be large enough for common memory allocation sizes
		4070
		4071	To improve portability and simplify its API, libev uses C<long> internally
		4072	instead of C<size_t> when allocating its data structures. On non-POSIX
		4073	systems (Microsoft...) this might be unexpectedly low, but is still at
		4074	least 31 bits everywhere, which is enough for hundreds of millions of
		4075	watchers.
		4076
		4077	=item C<double> must hold a time value in seconds with enough accuracy
		4078
		4079	The type C<double> is used to represent timestamps. It is required to
		4080	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4081	enough for at least into the year 4000. This requirement is fulfilled by
		4082	implementations implementing IEEE 754 (basically all existing ones).
		4083
		4084	=back
		4085
		4086	If you know of other additional requirements drop me a note.
		4087
		4088
		4089	=head1 ALGORITHMIC COMPLEXITIES
		4090
		4091	In this section the complexities of (many of) the algorithms used inside
		4092	libev will be documented. For complexity discussions about backends see
		4093	the documentation for C<ev_default_init>.
		4094
		4095	All of the following are about amortised time: If an array needs to be
		4096	extended, libev needs to realloc and move the whole array, but this
		4097	happens asymptotically rarer with higher number of elements, so O(1) might
		4098	mean that libev does a lengthy realloc operation in rare cases, but on
		4099	average it is much faster and asymptotically approaches constant time.
		4100
		4101	=over 4
		4102
		4103	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4104
		4105	This means that, when you have a watcher that triggers in one hour and
		4106	there are 100 watchers that would trigger before that, then inserting will
		4107	have to skip roughly seven (C<ld 100>) of these watchers.
		4108
		4109	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4110
		4111	That means that changing a timer costs less than removing/adding them,
		4112	as only the relative motion in the event queue has to be paid for.
		4113
		4114	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4115
		4116	These just add the watcher into an array or at the head of a list.
		4117
		4118	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4119
		4120	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4121
		4122	These watchers are stored in lists, so they need to be walked to find the
		4123	correct watcher to remove. The lists are usually short (you don't usually
		4124	have many watchers waiting for the same fd or signal: one is typical, two
		4125	is rare).
		4126
		4127	=item Finding the next timer in each loop iteration: O(1)
		4128
		4129	By virtue of using a binary or 4-heap, the next timer is always found at a
		4130	fixed position in the storage array.
		4131
		4132	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4133
		4134	A change means an I/O watcher gets started or stopped, which requires
		4135	libev to recalculate its status (and possibly tell the kernel, depending
		4136	on backend and whether C<ev_io_set> was used).
		4137
		4138	=item Activating one watcher (putting it into the pending state): O(1)
		4139
		4140	=item Priority handling: O(number_of_priorities)
		4141
		4142	Priorities are implemented by allocating some space for each
		4143	priority. When doing priority-based operations, libev usually has to
		4144	linearly search all the priorities, but starting/stopping and activating
		4145	watchers becomes O(1) with respect to priority handling.
		4146
		4147	=item Sending an ev_async: O(1)
		4148
		4149	=item Processing ev_async_send: O(number_of_async_watchers)
		4150
		4151	=item Processing signals: O(max_signal_number)
		4152
		4153	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4154	calls in the current loop iteration. Checking for async and signal events
		4155	involves iterating over all running async watchers or all signal numbers.
		4156
		4157	=back
		4158
		4159
		4160	=head1 GLOSSARY
		4161
		4162	=over 4
		4163
		4164	=item active
		4165
		4166	A watcher is active as long as it has been started (has been attached to
		4167	an event loop) but not yet stopped (disassociated from the event loop).
		4168
		4169	=item application
		4170
		4171	In this document, an application is whatever is using libev.
		4172
		4173	=item callback
		4174
		4175	The address of a function that is called when some event has been
		4176	detected. Callbacks are being passed the event loop, the watcher that
		4177	received the event, and the actual event bitset.
		4178
		4179	=item callback invocation
		4180
		4181	The act of calling the callback associated with a watcher.
		4182
		4183	=item event
		4184
		4185	A change of state of some external event, such as data now being available
		4186	for reading on a file descriptor, time having passed or simply not having
		4187	any other events happening anymore.
		4188
		4189	In libev, events are represented as single bits (such as C<EV_READ> or
		4190	C<EV_TIMEOUT>).
		4191
		4192	=item event library
		4193
		4194	A software package implementing an event model and loop.
		4195
		4196	=item event loop
		4197
		4198	An entity that handles and processes external events and converts them
		4199	into callback invocations.
		4200
		4201	=item event model
		4202
		4203	The model used to describe how an event loop handles and processes
		4204	watchers and events.
		4205
		4206	=item pending
		4207
		4208	A watcher is pending as soon as the corresponding event has been detected,
		4209	and stops being pending as soon as the watcher will be invoked or its
		4210	pending status is explicitly cleared by the application.
		4211
		4212	A watcher can be pending, but not active. Stopping a watcher also clears
		4213	its pending status.
		4214
		4215	=item real time
		4216
		4217	The physical time that is observed. It is apparently strictly monotonic :)
		4218
		4219	=item wall-clock time
		4220
		4221	The time and date as shown on clocks. Unlike real time, it can actually
		4222	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4223	clock.
		4224
		4225	=item watcher
		4226
		4227	A data structure that describes interest in certain events. Watchers need
		4228	to be started (attached to an event loop) before they can receive events.
		4229
		4230	=item watcher invocation
		4231
		4232	The act of calling the callback associated with a watcher.
		4233
		4234	=back
3261		4235
3262	=head1 AUTHOR	4236	=head1 AUTHOR
3263		4237
3264	Marc Lehmann <libev@schmorp.de>.	4238	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3265		4239

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