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Revision 1.320 by root, Fri Oct 22 10:48:54 2010 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_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_break (EV_A_ EVBREAK_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_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_break (EV_A_ EVBREAK_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_run (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	Familiarity 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
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practice
115	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	132	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floatingpoint value. Unlike the name	133	any calculations on it, you should treat it as some floating point value.
		134
119	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
		157
121		158
122	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
123		160
124	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
125	library in any way.	162	library in any way.
…		…
128		165
129	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
130		167
131	Returns the current time as libev would use it. Please note that the	168	Returns the current time as libev would use it. Please note that the
132	C<ev_now> function is usually faster and also often returns the timestamp	169	C<ev_now> function is usually faster and also often returns the timestamp
133	you actually want to know.	170	you actually want to know. Also interetsing is the combination of
		171	C<ev_update_now> and C<ev_now>.
134		172
135	=item ev_sleep (ev_tstamp interval)	173	=item ev_sleep (ev_tstamp interval)
136		174
137	Sleep for the given interval: The current thread will be blocked until	175	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	176	either it is interrupted or the given time interval has passed. Basically
139	this is a subsecond-resolution C<sleep ()>.	177	this is a sub-second-resolution C<sleep ()>.
140		178
141	=item int ev_version_major ()	179	=item int ev_version_major ()
142		180
143	=item int ev_version_minor ()	181	=item int ev_version_minor ()
144		182
…		…
155	as this indicates an incompatible change. Minor versions are usually	193	as this indicates an incompatible change. Minor versions are usually
156	compatible to older versions, so a larger minor version alone is usually	194	compatible to older versions, so a larger minor version alone is usually
157	not a problem.	195	not a problem.
158		196
159	Example: Make sure we haven't accidentally been linked against the wrong	197	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	198	version (note, however, that this will not detect other ABI mismatches,
		199	such as LFS or reentrancy).
161		200
162	assert (("libev version mismatch",	201	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	202	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	203	&& ev_version_minor () >= EV_VERSION_MINOR));
165		204
166	=item unsigned int ev_supported_backends ()	205	=item unsigned int ev_supported_backends ()
167		206
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	207	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	208	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	210	a description of the set values.
172		211
173	Example: make sure we have the epoll method, because yeah this is cool and	212	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	213	a must have and can we have a torrent of it please!!!11
175		214
176	assert (("sorry, no epoll, no sex",	215	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	216	ev_supported_backends () & EVBACKEND_EPOLL));
178		217
179	=item unsigned int ev_recommended_backends ()	218	=item unsigned int ev_recommended_backends ()
180		219
181	Return the set of all backends compiled into this binary of libev and also	220	Return the set of all backends compiled into this binary of libev and
182	recommended for this platform. This set is often smaller than the one	221	also recommended for this platform, meaning it will work for most file
		222	descriptor types. This set is often smaller than the one returned by
183	returned by C<ev_supported_backends>, as for example kqueue is broken on	223	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
184	most BSDs and will not be autodetected unless you explicitly request it	224	and will not be auto-detected unless you explicitly request it (assuming
185	(assuming you know what you are doing). This is the set of backends that	225	you know what you are doing). This is the set of backends that libev will
186	libev will probe for if you specify no backends explicitly.	226	probe for if you specify no backends explicitly.
187		227
188	=item unsigned int ev_embeddable_backends ()	228	=item unsigned int ev_embeddable_backends ()
189		229
190	Returns the set of backends that are embeddable in other event loops. This	230	Returns the set of backends that are embeddable in other event loops. This
191	is the theoretical, all-platform, value. To find which backends	231	value is platform-specific but can include backends not available on the
192	might be supported on the current system, you would need to look at	232	current system. To find which embeddable backends might be supported on
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	233	the current system, you would need to look at C<ev_embeddable_backends ()
194	recommended ones.	234	& ev_supported_backends ()>, likewise for recommended ones.
195		235
196	See the description of C<ev_embed> watchers for more info.	236	See the description of C<ev_embed> watchers for more info.
197		237
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
199		239
200	Sets the allocation function to use (the prototype is similar - the	240	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	241	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	242	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	243	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
229	}	269	}
230		270
231	...	271	...
232	ev_set_allocator (persistent_realloc);	272	ev_set_allocator (persistent_realloc);
233		273
234	=item ev_set_syserr_cb (void (*cb)(const char *msg));	274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
235		275
236	Set the callback function to call on a retryable syscall error (such	276	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	277	as failed select, poll, epoll_wait). The message is a printable string
238	indicating the system call or subsystem causing the problem. If this	278	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	279	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	280	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	281	requested operation, or, if the condition doesn't go away, do bad stuff
242	(such as abort).	282	(such as abort).
243		283
244	Example: This is basically the same thing that libev does internally, too.	284	Example: This is basically the same thing that libev does internally, too.
…		…
255		295
256	=back	296	=back
257		297
258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	298	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
259		299
260	An event loop is described by a C<struct ev_loop *>. The library knows two	300	An event loop is described by a C<struct ev_loop *> (the C<struct> is
261	types of such loops, the I<default> loop, which supports signals and child	301	I<not> optional in this case unless libev 3 compatibility is disabled, as
262	events, and dynamically created loops which do not.	302	libev 3 had an C<ev_loop> function colliding with the struct name).
		303
		304	The library knows two types of such loops, the I<default> loop, which
		305	supports signals and child events, and dynamically created event loops
		306	which do not.
263		307
264	=over 4	308	=over 4
265		309
266	=item struct ev_loop *ev_default_loop (unsigned int flags)	310	=item struct ev_loop *ev_default_loop (unsigned int flags)
267		311
…		…
273	If you don't know what event loop to use, use the one returned from this	317	If you don't know what event loop to use, use the one returned from this
274	function.	318	function.
275		319
276	Note that this function is I<not> thread-safe, so if you want to use it	320	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,	321	from multiple threads, you have to lock (note also that this is unlikely,
278	as loops cannot bes hared easily between threads anyway).	322	as loops cannot be shared easily between threads anyway).
279		323
280	The default loop is the only loop that can handle C<ev_signal> and	324	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	325	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	326	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	327	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	328	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
285	C<ev_default_init>.	329	C<ev_default_init>.
286		330
287	The flags argument can be used to specify special behaviour or specific	331	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	340	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	341	thing, believe me).
298		342
299	=item C<EVFLAG_NOENV>	343	=item C<EVFLAG_NOENV>
300		344
301	If this flag bit is ored into the flag value (or the program runs setuid	345	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	346	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	347	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	348	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	349	useful to try out specific backends to test their performance, or to work
306	around bugs.	350	around bugs.
307		351
308	=item C<EVFLAG_FORKCHECK>	352	=item C<EVFLAG_FORKCHECK>
309		353
310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	354	Instead of calling C<ev_loop_fork> manually after a fork, you can also
311	a fork, you can also make libev check for a fork in each iteration by	355	make libev check for a fork in each iteration by enabling this flag.
312	enabling this flag.
313		356
314	This works by calling C<getpid ()> on every iteration of the loop,	357	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	358	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	359	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	360	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	361	without a system call and thus I<very> fast, but my GNU/Linux system also has
319	C<pthread_atfork> which is even faster).	362	C<pthread_atfork> which is even faster).
320		363
321	The big advantage of this flag is that you can forget about fork (and	364	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	365	forget about forgetting to tell libev about forking) when you use this
323	flag.	366	flag.
324		367
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	368	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	369	environment variable.
		370
		371	=item C<EVFLAG_NOINOTIFY>
		372
		373	When this flag is specified, then libev will not attempt to use the
		374	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		375	testing, this flag can be useful to conserve inotify file descriptors, as
		376	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		377
		378	=item C<EVFLAG_SIGNALFD>
		379
		380	When this flag is specified, then libev will attempt to use the
		381	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		382	delivers signals synchronously, which makes it both faster and might make
		383	it possible to get the queued signal data. It can also simplify signal
		384	handling with threads, as long as you properly block signals in your
		385	threads that are not interested in handling them.
		386
		387	Signalfd will not be used by default as this changes your signal mask, and
		388	there are a lot of shoddy libraries and programs (glib's threadpool for
		389	example) that can't properly initialise their signal masks.
327		390
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	391	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		392
330	This is your standard select(2) backend. Not I<completely> standard, as	393	This is your standard select(2) backend. Not I<completely> standard, as
331	libev tries to roll its own fd_set with no limits on the number of fds,	394	libev tries to roll its own fd_set with no limits on the number of fds,
332	but if that fails, expect a fairly low limit on the number of fds when	395	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	396	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.	397	usually the fastest backend for a low number of (low-numbered :) fds.
335		398
336	To get good performance out of this backend you need a high amount of	399	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	400	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	401	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	402	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	403	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readyness notifications you get per iteration.	404	readiness notifications you get per iteration.
		405
		406	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		407	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		408	C<exceptfds> set on that platform).
342		409
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	410	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		411
345	And this is your standard poll(2) backend. It's more complicated	412	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	413	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	414	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,	415	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	416	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	417	performance tips.
351		418
		419	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		420	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		421
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	422	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		423
		424	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		425	kernels).
353		426
354	For few fds, this backend is a bit little slower than poll and select,	427	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	428	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),	429	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	430	epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	431
359	cases and requiring a syscall per fd change, no fork support and bad	432	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	433	of the more advanced event mechanisms: mere annoyances include silently
		434	dropping file descriptors, requiring a system call per change per file
		435	descriptor (and unnecessary guessing of parameters), problems with dup and
		436	so on. The biggest issue is fork races, however - if a program forks then
		437	I<both> parent and child process have to recreate the epoll set, which can
		438	take considerable time (one syscall per file descriptor) and is of course
		439	hard to detect.
		440
		441	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		442	of course I<doesn't>, and epoll just loves to report events for totally
		443	I<different> file descriptors (even already closed ones, so one cannot
		444	even remove them from the set) than registered in the set (especially
		445	on SMP systems). Libev tries to counter these spurious notifications by
		446	employing an additional generation counter and comparing that against the
		447	events to filter out spurious ones, recreating the set when required. Last
		448	not least, it also refuses to work with some file descriptors which work
		449	perfectly fine with C<select> (files, many character devices...).
361		450
362	While stopping, setting and starting an I/O watcher in the same iteration	451	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	452	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	453	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	454	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	455	file descriptors might not work very well if you register events for both
367		456	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		457
372	Best performance from this backend is achieved by not unregistering all	458	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.	459	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	460	i.e. keep at least one watcher active per fd at all times. Stopping and
		461	starting a watcher (without re-setting it) also usually doesn't cause
		462	extra overhead. A fork can both result in spurious notifications as well
		463	as in libev having to destroy and recreate the epoll object, which can
		464	take considerable time and thus should be avoided.
375		465
		466	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		467	faster than epoll for maybe up to a hundred file descriptors, depending on
		468	the usage. So sad.
		469
376	While nominally embeddeble in other event loops, this feature is broken in	470	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	471	all kernel versions tested so far.
		472
		473	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		474	C<EVBACKEND_POLL>.
378		475
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	476	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		477
381	Kqueue deserves special mention, as at the time of this writing, it	478	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	479	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	480	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"	481	it's completely useless). Unlike epoll, however, whose brokenness
		482	is by design, these kqueue bugs can (and eventually will) be fixed
		483	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	484	"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)	485	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
387	system like NetBSD.	486	system like NetBSD.
388		487
389	You still can embed kqueue into a normal poll or select backend and use it	488	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	489	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.	490	the target platform). See C<ev_embed> watchers for more info.
392		491
393	It scales in the same way as the epoll backend, but the interface to the	492	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	493	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	494	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	495	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	496	two event changes per incident. Support for C<fork ()> is very bad (but
398	drops fds silently in similarly hard-to-detect cases.	497	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		498	cases
399		499
400	This backend usually performs well under most conditions.	500	This backend usually performs well under most conditions.
401		501
402	While nominally embeddable in other event loops, this doesn't work	502	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	503	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	504	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	505	(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	506	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	507	also broken on OS X)) and, did I mention it, using it only for sockets.
		508
		509	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		510	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		511	C<NOTE_EOF>.
408		512
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	513	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		514
411	This is not implemented yet (and might never be, unless you send me an	515	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	516	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	520	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		521
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	522	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)).	523	it's really slow, but it still scales very well (O(active_fds)).
420		524
421	Please note that solaris event ports can deliver a lot of spurious	525	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	526	notifications, so you need to use non-blocking I/O or other means to avoid
423	blocking when no data (or space) is available.	527	blocking when no data (or space) is available.
424		528
425	While this backend scales well, it requires one system call per active	529	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	530	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	531	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	532	might perform better.
429		533
430	On the positive side, ignoring the spurious readyness notifications, this	534	On the positive side, with the exception of the spurious readiness
431	backend actually performed to specification in all tests and is fully	535	notifications, this backend actually performed fully to specification
432	embeddable, which is a rare feat among the OS-specific backends.	536	in all tests and is fully embeddable, which is a rare feat among the
		537	OS-specific backends (I vastly prefer correctness over speed hacks).
		538
		539	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		540	C<EVBACKEND_POLL>.
433		541
434	=item C<EVBACKEND_ALL>	542	=item C<EVBACKEND_ALL>
435		543
436	Try all backends (even potentially broken ones that wouldn't be tried	544	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	545	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
439		547
440	It is definitely not recommended to use this flag.	548	It is definitely not recommended to use this flag.
441		549
442	=back	550	=back
443		551
444	If one or more of these are ored into the flags value, then only these	552	If one or more of the backend flags are or'ed into the flags value,
445	backends will be tried (in the reverse order as listed here). If none are	553	then only these backends will be tried (in the reverse order as listed
446	specified, all backends in C<ev_recommended_backends ()> will be tried.	554	here). If none are specified, all backends in C<ev_recommended_backends
		555	()> will be tried.
447		556
448	The most typical usage is like this:	557	Example: This is the most typical usage.
449		558
450	if (!ev_default_loop (0))	559	if (!ev_default_loop (0))
451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	560	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
452		561
453	Restrict libev to the select and poll backends, and do not allow	562	Example: Restrict libev to the select and poll backends, and do not allow
454	environment settings to be taken into account:	563	environment settings to be taken into account:
455		564
456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	565	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
457		566
458	Use whatever libev has to offer, but make sure that kqueue is used if	567	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	568	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):	569	private event loop and only if you know the OS supports your types of
		570	fds):
461		571
462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	572	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
463		573
464	=item struct ev_loop *ev_loop_new (unsigned int flags)	574	=item struct ev_loop *ev_loop_new (unsigned int flags)
465		575
466	Similar to C<ev_default_loop>, but always creates a new event loop that is	576	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	577	always distinct from the default loop.
468	handle signal and child watchers, and attempts to do so will be greeted by
469	undefined behaviour (or a failed assertion if assertions are enabled).
470		578
471	Note that this function I<is> thread-safe, and the recommended way to use	579	Note that this function I<is> thread-safe, and one common way to use
472	libev with threads is indeed to create one loop per thread, and using the	580	libev with threads is indeed to create one loop per thread, and using the
473	default loop in the "main" or "initial" thread.	581	default loop in the "main" or "initial" thread.
474		582
475	Example: Try to create a event loop that uses epoll and nothing else.	583	Example: Try to create a event loop that uses epoll and nothing else.
476		584
477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	585	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
478	if (!epoller)	586	if (!epoller)
479	fatal ("no epoll found here, maybe it hides under your chair");	587	fatal ("no epoll found here, maybe it hides under your chair");
480		588
481	=item ev_default_destroy ()	589	=item ev_default_destroy ()
482		590
483	Destroys the default loop again (frees all memory and kernel state	591	Destroys the default loop (frees all memory and kernel state etc.). None
484	etc.). None of the active event watchers will be stopped in the normal	592	of the active event watchers will be stopped in the normal sense, so
485	sense, so e.g. C<ev_is_active> might still return true. It is your	593	e.g. C<ev_is_active> might still return true. It is your responsibility to
486	responsibility to either stop all watchers cleanly yoursef I<before>	594	either stop all watchers cleanly yourself I<before> calling this function,
487	calling this function, or cope with the fact afterwards (which is usually	595	or cope with the fact afterwards (which is usually the easiest thing, you
488	the easiest thing, you can just ignore the watchers and/or C<free ()> them	596	can just ignore the watchers and/or C<free ()> them for example).
489	for example).
490		597
491	Note that certain global state, such as signal state, will not be freed by	598	Note that certain global state, such as signal state (and installed signal
492	this function, and related watchers (such as signal and child watchers)	599	handlers), will not be freed by this function, and related watchers (such
493	would need to be stopped manually.	600	as signal and child watchers) would need to be stopped manually.
494		601
495	In general it is not advisable to call this function except in the	602	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	603	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	604	pipe fds. If you need dynamically allocated loops it is better to use
498	C<ev_loop_new> and C<ev_loop_destroy>).	605	C<ev_loop_new> and C<ev_loop_destroy>.
499		606
500	=item ev_loop_destroy (loop)	607	=item ev_loop_destroy (loop)
501		608
502	Like C<ev_default_destroy>, but destroys an event loop created by an	609	Like C<ev_default_destroy>, but destroys an event loop created by an
503	earlier call to C<ev_loop_new>.	610	earlier call to C<ev_loop_new>.
504		611
505	=item ev_default_fork ()	612	=item ev_default_fork ()
506		613
507	This function sets a flag that causes subsequent C<ev_loop> iterations	614	This function sets a flag that causes subsequent C<ev_run> iterations
508	to reinitialise the kernel state for backends that have one. Despite the	615	to reinitialise the kernel state for backends that have one. Despite the
509	name, you can call it anytime, but it makes most sense after forking, in	616	name, you can call it anytime, but it makes most sense after forking, in
510	the child process (or both child and parent, but that again makes little	617	the child process (or both child and parent, but that again makes little
511	sense). You I<must> call it in the child before using any of the libev	618	sense). You I<must> call it in the child before using any of the libev
512	functions, and it will only take effect at the next C<ev_loop> iteration.	619	functions, and it will only take effect at the next C<ev_run> iteration.
		620
		621	Again, you I<have> to call it on I<any> loop that you want to re-use after
		622	a fork, I<even if you do not plan to use the loop in the parent>. This is
		623	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		624	during fork.
513		625
514	On the other hand, you only need to call this function in the child	626	On the other hand, you only need to call this function in the child
515	process if and only if you want to use the event library in the child. If	627	process if and only if you want to use the event loop in the child. If
516	you just fork+exec, you don't have to call it at all.	628	you just fork+exec or create a new loop in the child, you don't have to
		629	call it at all (in fact, C<epoll> is so badly broken that it makes a
		630	difference, but libev will usually detect this case on its own and do a
		631	costly reset of the backend).
517		632
518	The function itself is quite fast and it's usually not a problem to call	633	The function itself is quite fast and it's usually not a problem to call
519	it just in case after a fork. To make this easy, the function will fit in	634	it just in case after a fork. To make this easy, the function will fit in
520	quite nicely into a call to C<pthread_atfork>:	635	quite nicely into a call to C<pthread_atfork>:
521		636
…		…
523		638
524	=item ev_loop_fork (loop)	639	=item ev_loop_fork (loop)
525		640
526	Like C<ev_default_fork>, but acts on an event loop created by	641	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	642	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.	643	after fork that you want to re-use in the child, and how you keep track of
		644	them is entirely your own problem.
529		645
530	=item int ev_is_default_loop (loop)	646	=item int ev_is_default_loop (loop)
531		647
532	Returns true when the given loop actually is the default loop, false otherwise.	648	Returns true when the given loop is, in fact, the default loop, and false
		649	otherwise.
533		650
534	=item unsigned int ev_loop_count (loop)	651	=item unsigned int ev_iteration (loop)
535		652
536	Returns the count of loop iterations for the loop, which is identical to	653	Returns the current iteration count for the event loop, which is identical
537	the number of times libev did poll for new events. It starts at C<0> and	654	to the number of times libev did poll for new events. It starts at C<0>
538	happily wraps around with enough iterations.	655	and happily wraps around with enough iterations.
539		656
540	This value can sometimes be useful as a generation counter of sorts (it	657	This value can sometimes be useful as a generation counter of sorts (it
541	"ticks" the number of loop iterations), as it roughly corresponds with	658	"ticks" the number of loop iterations), as it roughly corresponds with
542	C<ev_prepare> and C<ev_check> calls.	659	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		660	prepare and check phases.
		661
		662	=item unsigned int ev_depth (loop)
		663
		664	Returns the number of times C<ev_run> was entered minus the number of
		665	times C<ev_run> was exited, in other words, the recursion depth.
		666
		667	Outside C<ev_run>, this number is zero. In a callback, this number is
		668	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		669	in which case it is higher.
		670
		671	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		672	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		673	ungentleman-like behaviour unless it's really convenient.
543		674
544	=item unsigned int ev_backend (loop)	675	=item unsigned int ev_backend (loop)
545		676
546	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	677	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
547	use.	678	use.
…		…
552	received events and started processing them. This timestamp does not	683	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	684	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	685	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).	686	event occurring (or more correctly, libev finding out about it).
556		687
		688	=item ev_now_update (loop)
		689
		690	Establishes the current time by querying the kernel, updating the time
		691	returned by C<ev_now ()> in the progress. This is a costly operation and
		692	is usually done automatically within C<ev_run ()>.
		693
		694	This function is rarely useful, but when some event callback runs for a
		695	very long time without entering the event loop, updating libev's idea of
		696	the current time is a good idea.
		697
		698	See also L<The special problem of time updates> in the C<ev_timer> section.
		699
		700	=item ev_suspend (loop)
		701
		702	=item ev_resume (loop)
		703
		704	These two functions suspend and resume an event loop, for use when the
		705	loop is not used for a while and timeouts should not be processed.
		706
		707	A typical use case would be an interactive program such as a game: When
		708	the user presses C<^Z> to suspend the game and resumes it an hour later it
		709	would be best to handle timeouts as if no time had actually passed while
		710	the program was suspended. This can be achieved by calling C<ev_suspend>
		711	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		712	C<ev_resume> directly afterwards to resume timer processing.
		713
		714	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		715	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		716	will be rescheduled (that is, they will lose any events that would have
		717	occurred while suspended).
		718
		719	After calling C<ev_suspend> you B<must not> call I<any> function on the
		720	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		721	without a previous call to C<ev_suspend>.
		722
		723	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		724	event loop time (see C<ev_now_update>).
		725
557	=item ev_loop (loop, int flags)	726	=item ev_run (loop, int flags)
558		727
559	Finally, this is it, the event handler. This function usually is called	728	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	729	after you have initialised all your watchers and you want to start
561	events.	730	handling events. It will ask the operating system for any new events, call
		731	the watcher callbacks, an then repeat the whole process indefinitely: This
		732	is why event loops are called I<loops>.
562		733
563	If the flags argument is specified as C<0>, it will not return until	734	If the flags argument is specified as C<0>, it will keep handling events
564	either no event watchers are active anymore or C<ev_unloop> was called.	735	until either no event watchers are active anymore or C<ev_break> was
		736	called.
565		737
566	Please note that an explicit C<ev_unloop> is usually better than	738	Please note that an explicit C<ev_break> is usually better than
567	relying on all watchers to be stopped when deciding when a program has	739	relying on all watchers to be stopped when deciding when a program has
568	finished (especially in interactive programs), but having a program that	740	finished (especially in interactive programs), but having a program
569	automatically loops as long as it has to and no longer by virtue of	741	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.	742	of relying on its watchers stopping correctly, that is truly a thing of
		743	beauty.
571		744
572	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	745	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
573	those events and any outstanding ones, but will not block your process in	746	those events and any already outstanding ones, but will not wait and
574	case there are no events and will return after one iteration of the loop.	747	block your process in case there are no events and will return after one
		748	iteration of the loop. This is sometimes useful to poll and handle new
		749	events while doing lengthy calculations, to keep the program responsive.
575		750
576	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	751	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
577	neccessary) and will handle those and any outstanding ones. It will block	752	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	753	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	754	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	755	user-registered callback will be called), and will return after one
		756	iteration of the loop.
		757
		758	This is useful if you are waiting for some external event in conjunction
		759	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	760	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
582	usually a better approach for this kind of thing.	761	usually a better approach for this kind of thing.
583		762
584	Here are the gory details of what C<ev_loop> does:	763	Here are the gory details of what C<ev_run> does:
585		764
		765	- Increment loop depth.
		766	- Reset the ev_break status.
586	- Before the first iteration, call any pending watchers.	767	- Before the first iteration, call any pending watchers.
		768	LOOP:
587	* If EVFLAG_FORKCHECK was used, check for a fork.	769	- If EVFLAG_FORKCHECK was used, check for a fork.
588	- If a fork was detected, queue and call all fork watchers.	770	- If a fork was detected (by any means), queue and call all fork watchers.
589	- Queue and call all prepare watchers.	771	- Queue and call all prepare watchers.
		772	- If ev_break was called, goto FINISH.
590	- If we have been forked, recreate the kernel state.	773	- If we have been forked, detach and recreate the kernel state
		774	as to not disturb the other process.
591	- Update the kernel state with all outstanding changes.	775	- Update the kernel state with all outstanding changes.
592	- Update the "event loop time".	776	- Update the "event loop time" (ev_now ()).
593	- Calculate for how long to sleep or block, if at all	777	- Calculate for how long to sleep or block, if at all
594	(active idle watchers, EVLOOP_NONBLOCK or not having	778	(active idle watchers, EVRUN_NOWAIT or not having
595	any active watchers at all will result in not sleeping).	779	any active watchers at all will result in not sleeping).
596	- Sleep if the I/O and timer collect interval say so.	780	- Sleep if the I/O and timer collect interval say so.
		781	- Increment loop iteration counter.
597	- Block the process, waiting for any events.	782	- Block the process, waiting for any events.
598	- Queue all outstanding I/O (fd) events.	783	- Queue all outstanding I/O (fd) events.
599	- Update the "event loop time" and do time jump handling.	784	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
600	- Queue all outstanding timers.	785	- Queue all expired timers.
601	- Queue all outstanding periodics.	786	- Queue all expired periodics.
602	- If no events are pending now, queue all idle watchers.	787	- Queue all idle watchers with priority higher than that of pending events.
603	- Queue all check watchers.	788	- Queue all check watchers.
604	- Call all queued watchers in reverse order (i.e. check watchers first).	789	- 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	790	Signals and child watchers are implemented as I/O watchers, and will
606	be handled here by queueing them when their watcher gets executed.	791	be handled here by queueing them when their watcher gets executed.
607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	792	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
608	were used, or there are no active watchers, return, otherwise	793	were used, or there are no active watchers, goto FINISH, otherwise
609	continue with step *.	794	continue with step LOOP.
		795	FINISH:
		796	- Reset the ev_break status iff it was EVBREAK_ONE.
		797	- Decrement the loop depth.
		798	- Return.
610		799
611	Example: Queue some jobs and then loop until no events are outstanding	800	Example: Queue some jobs and then loop until no events are outstanding
612	anymore.	801	anymore.
613		802
614	... queue jobs here, make sure they register event watchers as long	803	... 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..)	804	... as they still have work to do (even an idle watcher will do..)
616	ev_loop (my_loop, 0);	805	ev_run (my_loop, 0);
617	... jobs done. yeah!	806	... jobs done or somebody called unloop. yeah!
618		807
619	=item ev_unloop (loop, how)	808	=item ev_break (loop, how)
620		809
621	Can be used to make a call to C<ev_loop> return early (but only after it	810	Can be used to make a call to C<ev_run> return early (but only after it
622	has processed all outstanding events). The C<how> argument must be either	811	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	812	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
624	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	813	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
625		814
626	This "unloop state" will be cleared when entering C<ev_loop> again.	815	This "unloop state" will be cleared when entering C<ev_run> again.
		816
		817	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
627		818
628	=item ev_ref (loop)	819	=item ev_ref (loop)
629		820
630	=item ev_unref (loop)	821	=item ev_unref (loop)
631		822
632	Ref/unref can be used to add or remove a reference count on the event	823	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	824	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	825	count is nonzero, C<ev_run> will not return on its own.
635	a watcher you never unregister that should not keep C<ev_loop> from	826
636	returning, ev_unref() after starting, and ev_ref() before stopping it. For	827	This is useful when you have a watcher that you never intend to
		828	unregister, but that nevertheless should not keep C<ev_run> from
		829	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		830	before stopping it.
		831
637	example, libev itself uses this for its internal signal pipe: It is not	832	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	833	is not visible to the libev user and should not keep C<ev_run> from
639	no event watchers registered by it are active. It is also an excellent	834	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	835	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>	836	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,	837	before stop> (but only if the watcher wasn't active before, or was active
643	respectively).	838	before, respectively. Note also that libev might stop watchers itself
		839	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		840	in the callback).
644		841
645	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	842	Example: Create a signal watcher, but keep it from keeping C<ev_run>
646	running when nothing else is active.	843	running when nothing else is active.
647		844
648	struct ev_signal exitsig;	845	ev_signal exitsig;
649	ev_signal_init (&exitsig, sig_cb, SIGINT);	846	ev_signal_init (&exitsig, sig_cb, SIGINT);
650	ev_signal_start (loop, &exitsig);	847	ev_signal_start (loop, &exitsig);
651	evf_unref (loop);	848	evf_unref (loop);
652		849
653	Example: For some weird reason, unregister the above signal handler again.	850	Example: For some weird reason, unregister the above signal handler again.
654		851
655	ev_ref (loop);	852	ev_ref (loop);
656	ev_signal_stop (loop, &exitsig);	853	ev_signal_stop (loop, &exitsig);
657		854
658	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	855	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
659		856
660	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	857	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
661		858
662	These advanced functions influence the time that libev will spend waiting	859	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	860	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.	861	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		862	latency.
665		863
666	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	864	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	865	allows libev to delay invocation of I/O and timer/periodic callbacks
668	increase efficiency of loop iterations.	866	to increase efficiency of loop iterations (or to increase power-saving
		867	opportunities).
669		868
670	The background is that sometimes your program runs just fast enough to	869	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	870	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	871	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	872	events, especially with backends like C<select ()> which have a high
674	overhead for the actual polling but can deliver many events at once.	873	overhead for the actual polling but can deliver many events at once.
675		874
676	By setting a higher I<io collect interval> you allow libev to spend more	875	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,	876	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	877	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	878	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.	879	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		880	sleep time ensures that libev will not poll for I/O events more often then
		881	once per this interval, on average.
681		882
682	Likewise, by setting a higher I<timeout collect interval> you allow libev	883	Likewise, by setting a higher I<timeout collect interval> you allow libev
683	to spend more time collecting timeouts, at the expense of increased	884	to spend more time collecting timeouts, at the expense of increased
684	latency (the watcher callback will be called later). C<ev_io> watchers	885	latency/jitter/inexactness (the watcher callback will be called
685	will not be affected. Setting this to a non-null value will not introduce	886	later). C<ev_io> watchers will not be affected. Setting this to a non-null
686	any overhead in libev.	887	value will not introduce any overhead in libev.
687		888
688	Many (busy) programs can usually benefit by setting the io collect	889	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	890	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	891	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>,	892	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.	893	as this approaches the timing granularity of most systems. Note that if
		894	you do transactions with the outside world and you can't increase the
		895	parallelity, then this setting will limit your transaction rate (if you
		896	need to poll once per transaction and the I/O collect interval is 0.01,
		897	then you can't do more than 100 transactions per second).
		898
		899	Setting the I<timeout collect interval> can improve the opportunity for
		900	saving power, as the program will "bundle" timer callback invocations that
		901	are "near" in time together, by delaying some, thus reducing the number of
		902	times the process sleeps and wakes up again. Another useful technique to
		903	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		904	they fire on, say, one-second boundaries only.
		905
		906	Example: we only need 0.1s timeout granularity, and we wish not to poll
		907	more often than 100 times per second:
		908
		909	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		910	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		911
		912	=item ev_invoke_pending (loop)
		913
		914	This call will simply invoke all pending watchers while resetting their
		915	pending state. Normally, C<ev_run> does this automatically when required,
		916	but when overriding the invoke callback this call comes handy. This
		917	function can be invoked from a watcher - this can be useful for example
		918	when you want to do some lengthy calculation and want to pass further
		919	event handling to another thread (you still have to make sure only one
		920	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		921
		922	=item int ev_pending_count (loop)
		923
		924	Returns the number of pending watchers - zero indicates that no watchers
		925	are pending.
		926
		927	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		928
		929	This overrides the invoke pending functionality of the loop: Instead of
		930	invoking all pending watchers when there are any, C<ev_run> will call
		931	this callback instead. This is useful, for example, when you want to
		932	invoke the actual watchers inside another context (another thread etc.).
		933
		934	If you want to reset the callback, use C<ev_invoke_pending> as new
		935	callback.
		936
		937	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		938
		939	Sometimes you want to share the same loop between multiple threads. This
		940	can be done relatively simply by putting mutex_lock/unlock calls around
		941	each call to a libev function.
		942
		943	However, C<ev_run> can run an indefinite time, so it is not feasible
		944	to wait for it to return. One way around this is to wake up the event
		945	loop via C<ev_break> and C<av_async_send>, another way is to set these
		946	I<release> and I<acquire> callbacks on the loop.
		947
		948	When set, then C<release> will be called just before the thread is
		949	suspended waiting for new events, and C<acquire> is called just
		950	afterwards.
		951
		952	Ideally, C<release> will just call your mutex_unlock function, and
		953	C<acquire> will just call the mutex_lock function again.
		954
		955	While event loop modifications are allowed between invocations of
		956	C<release> and C<acquire> (that's their only purpose after all), no
		957	modifications done will affect the event loop, i.e. adding watchers will
		958	have no effect on the set of file descriptors being watched, or the time
		959	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		960	to take note of any changes you made.
		961
		962	In theory, threads executing C<ev_run> will be async-cancel safe between
		963	invocations of C<release> and C<acquire>.
		964
		965	See also the locking example in the C<THREADS> section later in this
		966	document.
		967
		968	=item ev_set_userdata (loop, void *data)
		969
		970	=item ev_userdata (loop)
		971
		972	Set and retrieve a single C<void *> associated with a loop. When
		973	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		974	C<0.>
		975
		976	These two functions can be used to associate arbitrary data with a loop,
		977	and are intended solely for the C<invoke_pending_cb>, C<release> and
		978	C<acquire> callbacks described above, but of course can be (ab-)used for
		979	any other purpose as well.
		980
		981	=item ev_verify (loop)
		982
		983	This function only does something when C<EV_VERIFY> support has been
		984	compiled in, which is the default for non-minimal builds. It tries to go
		985	through all internal structures and checks them for validity. If anything
		986	is found to be inconsistent, it will print an error message to standard
		987	error and call C<abort ()>.
		988
		989	This can be used to catch bugs inside libev itself: under normal
		990	circumstances, this function will never abort as of course libev keeps its
		991	data structures consistent.
693		992
694	=back	993	=back
695		994
696		995
697	=head1 ANATOMY OF A WATCHER	996	=head1 ANATOMY OF A WATCHER
698		997
		998	In the following description, uppercase C<TYPE> in names stands for the
		999	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1000	watchers and C<ev_io_start> for I/O watchers.
		1001
699	A watcher is a structure that you create and register to record your	1002	A watcher is an opaque structure that you allocate and register to record
700	interest in some event. For instance, if you want to wait for STDIN to	1003	your interest in some event. To make a concrete example, imagine you want
701	become readable, you would create an C<ev_io> watcher for that:	1004	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1005	for that:
702		1006
703	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1007	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
704	{	1008	{
705	ev_io_stop (w);	1009	ev_io_stop (w);
706	ev_unloop (loop, EVUNLOOP_ALL);	1010	ev_break (loop, EVBREAK_ALL);
707	}	1011	}
708		1012
709	struct ev_loop *loop = ev_default_loop (0);	1013	struct ev_loop *loop = ev_default_loop (0);
		1014
710	struct ev_io stdin_watcher;	1015	ev_io stdin_watcher;
		1016
711	ev_init (&stdin_watcher, my_cb);	1017	ev_init (&stdin_watcher, my_cb);
712	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1018	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
713	ev_io_start (loop, &stdin_watcher);	1019	ev_io_start (loop, &stdin_watcher);
		1020
714	ev_loop (loop, 0);	1021	ev_run (loop, 0);
715		1022
716	As you can see, you are responsible for allocating the memory for your	1023	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,	1024	watcher structures (and it is I<usually> a bad idea to do this on the
718	although this can sometimes be quite valid).	1025	stack).
719		1026
		1027	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1028	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1029
720	Each watcher structure must be initialised by a call to C<ev_init	1030	Each watcher structure must be initialised by a call to C<ev_init (watcher
721	(watcher *, callback)>, which expects a callback to be provided. This	1031	*, callback)>, which expects a callback to be provided. This callback is
722	callback gets invoked each time the event occurs (or, in the case of io	1032	invoked each time the event occurs (or, in the case of I/O watchers, each
723	watchers, each time the event loop detects that the file descriptor given	1033	time the event loop detects that the file descriptor given is readable
724	is readable and/or writable).	1034	and/or writable).
725		1035
726	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1036	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	1037	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	1038	is also a macro to combine initialisation and setting in one call: C<<
729	(watcher *, callback, ...) >>.	1039	ev_TYPE_init (watcher *, callback, ...) >>.
730		1040
731	To make the watcher actually watch out for events, you have to start it	1041	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	1042	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	1043	*) >>), and you can stop watching for events at any time by calling the
734	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1044	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
735		1045
736	As long as your watcher is active (has been started but not stopped) you	1046	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	1047	must not touch the values stored in it. Most specifically you must never
738	reinitialise it or call its C<set> macro.	1048	reinitialise it or call its C<ev_TYPE_set> macro.
739		1049
740	Each and every callback receives the event loop pointer as first, the	1050	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	1051	registered watcher structure as second, and a bitset of received events as
742	third argument.	1052	third argument.
743		1053
…		…
752	=item C<EV_WRITE>	1062	=item C<EV_WRITE>
753		1063
754	The file descriptor in the C<ev_io> watcher has become readable and/or	1064	The file descriptor in the C<ev_io> watcher has become readable and/or
755	writable.	1065	writable.
756		1066
757	=item C<EV_TIMEOUT>	1067	=item C<EV_TIMER>
758		1068
759	The C<ev_timer> watcher has timed out.	1069	The C<ev_timer> watcher has timed out.
760		1070
761	=item C<EV_PERIODIC>	1071	=item C<EV_PERIODIC>
762		1072
…		…
780		1090
781	=item C<EV_PREPARE>	1091	=item C<EV_PREPARE>
782		1092
783	=item C<EV_CHECK>	1093	=item C<EV_CHECK>
784		1094
785	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1095	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
786	to gather new events, and all C<ev_check> watchers are invoked just after	1096	to gather new events, and all C<ev_check> watchers are invoked just after
787	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1097	C<ev_run> has gathered them, but before it invokes any callbacks for any
788	received events. Callbacks of both watcher types can start and stop as	1098	received events. Callbacks of both watcher types can start and stop as
789	many watchers as they want, and all of them will be taken into account	1099	many watchers as they want, and all of them will be taken into account
790	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1100	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
791	C<ev_loop> from blocking).	1101	C<ev_run> from blocking).
792		1102
793	=item C<EV_EMBED>	1103	=item C<EV_EMBED>
794		1104
795	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1105	The embedded event loop specified in the C<ev_embed> watcher needs attention.
796		1106
…		…
801		1111
802	=item C<EV_ASYNC>	1112	=item C<EV_ASYNC>
803		1113
804	The given async watcher has been asynchronously notified (see C<ev_async>).	1114	The given async watcher has been asynchronously notified (see C<ev_async>).
805		1115
		1116	=item C<EV_CUSTOM>
		1117
		1118	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1119	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1120
806	=item C<EV_ERROR>	1121	=item C<EV_ERROR>
807		1122
808	An unspecified error has occured, the watcher has been stopped. This might	1123	An unspecified error has occurred, the watcher has been stopped. This might
809	happen because the watcher could not be properly started because libev	1124	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	1125	ran out of memory, a file descriptor was found to be closed or any other
		1126	problem. Libev considers these application bugs.
		1127
811	problem. You best act on it by reporting the problem and somehow coping	1128	You best act on it by reporting the problem and somehow coping with the
812	with the watcher being stopped.	1129	watcher being stopped. Note that well-written programs should not receive
		1130	an error ever, so when your watcher receives it, this usually indicates a
		1131	bug in your program.
813		1132
814	Libev will usually signal a few "dummy" events together with an error,	1133	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	1134	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	1135	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	1136	the error from read() or write(). This will not work in multi-threaded
818	programs, though, so beware.	1137	programs, though, as the fd could already be closed and reused for another
		1138	thing, so beware.
819		1139
820	=back	1140	=back
821		1141
		1142	=head2 WATCHER STATES
		1143
		1144	There are various watcher states mentioned throughout this manual -
		1145	active, pending and so on. In this section these states and the rules to
		1146	transition between them will be described in more detail - and while these
		1147	rules might look complicated, they usually do "the right thing".
		1148
		1149	=over 4
		1150
		1151	=item initialiased
		1152
		1153	Before a watcher can be registered with the event looop it has to be
		1154	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1155	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1156
		1157	In this state it is simply some block of memory that is suitable for use
		1158	in an event loop. It can be moved around, freed, reused etc. at will.
		1159
		1160	=item started/running/active
		1161
		1162	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1163	property of the event loop, and is actively waiting for events. While in
		1164	this state it cannot be accessed (except in a few documented ways), moved,
		1165	freed or anything else - the only legal thing is to keep a pointer to it,
		1166	and call libev functions on it that are documented to work on active watchers.
		1167
		1168	=item pending
		1169
		1170	If a watcher is active and libev determines that an event it is interested
		1171	in has occurred (such as a timer expiring), it will become pending. It will
		1172	stay in this pending state until either it is stopped or its callback is
		1173	about to be invoked, so it is not normally pending inside the watcher
		1174	callback.
		1175
		1176	The watcher might or might not be active while it is pending (for example,
		1177	an expired non-repeating timer can be pending but no longer active). If it
		1178	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1179	but it is still property of the event loop at this time, so cannot be
		1180	moved, freed or reused. And if it is active the rules described in the
		1181	previous item still apply.
		1182
		1183	It is also possible to feed an event on a watcher that is not active (e.g.
		1184	via C<ev_feed_event>), in which case it becomes pending without being
		1185	active.
		1186
		1187	=item stopped
		1188
		1189	A watcher can be stopped implicitly by libev (in which case it might still
		1190	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1191	latter will clear any pending state the watcher might be in, regardless
		1192	of whether it was active or not, so stopping a watcher explicitly before
		1193	freeing it is often a good idea.
		1194
		1195	While stopped (and not pending) the watcher is essentially in the
		1196	initialised state, that is it can be reused, moved, modified in any way
		1197	you wish.
		1198
		1199	=back
		1200
822	=head2 GENERIC WATCHER FUNCTIONS	1201	=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		1202
827	=over 4	1203	=over 4
828		1204
829	=item C<ev_init> (ev_TYPE *watcher, callback)	1205	=item C<ev_init> (ev_TYPE *watcher, callback)
830		1206
…		…
836	which rolls both calls into one.	1212	which rolls both calls into one.
837		1213
838	You can reinitialise a watcher at any time as long as it has been stopped	1214	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.	1215	(or never started) and there are no pending events outstanding.
840		1216
841	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1217	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
842	int revents)>.	1218	int revents)>.
843		1219
		1220	Example: Initialise an C<ev_io> watcher in two steps.
		1221
		1222	ev_io w;
		1223	ev_init (&w, my_cb);
		1224	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1225
844	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1226	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
845		1227
846	This macro initialises the type-specific parts of a watcher. You need to	1228	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	1229	call C<ev_init> at least once before you call this macro, but you can
848	call C<ev_TYPE_set> any number of times. You must not, however, call this	1230	call C<ev_TYPE_set> any number of times. You must not, however, call this
849	macro on a watcher that is active (it can be pending, however, which is a	1231	macro on a watcher that is active (it can be pending, however, which is a
850	difference to the C<ev_init> macro).	1232	difference to the C<ev_init> macro).
851		1233
852	Although some watcher types do not have type-specific arguments	1234	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.	1235	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
854		1236
		1237	See C<ev_init>, above, for an example.
		1238
855	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1239	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
856		1240
857	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1241	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	1242	calls into a single call. This is the most convenient method to initialise
859	a watcher. The same limitations apply, of course.	1243	a watcher. The same limitations apply, of course.
860		1244
		1245	Example: Initialise and set an C<ev_io> watcher in one step.
		1246
		1247	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1248
861	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1249	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
862		1250
863	Starts (activates) the given watcher. Only active watchers will receive	1251	Starts (activates) the given watcher. Only active watchers will receive
864	events. If the watcher is already active nothing will happen.	1252	events. If the watcher is already active nothing will happen.
865		1253
		1254	Example: Start the C<ev_io> watcher that is being abused as example in this
		1255	whole section.
		1256
		1257	ev_io_start (EV_DEFAULT_UC, &w);
		1258
866	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1259	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
867		1260
868	Stops the given watcher again (if active) and clears the pending	1261	Stops the given watcher if active, and clears the pending status (whether
		1262	the watcher was active or not).
		1263
869	status. It is possible that stopped watchers are pending (for example,	1264	It is possible that stopped watchers are pending - for example,
870	non-repeating timers are being stopped when they become pending), but	1265	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	1266	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	1267	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.	1268	therefore a good idea to always call its C<ev_TYPE_stop> function.
874		1269
875	=item bool ev_is_active (ev_TYPE *watcher)	1270	=item bool ev_is_active (ev_TYPE *watcher)
876		1271
877	Returns a true value iff the watcher is active (i.e. it has been started	1272	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	1273	and not yet been stopped). As long as a watcher is active you must not modify
…		…
894	=item ev_cb_set (ev_TYPE *watcher, callback)	1289	=item ev_cb_set (ev_TYPE *watcher, callback)
895		1290
896	Change the callback. You can change the callback at virtually any time	1291	Change the callback. You can change the callback at virtually any time
897	(modulo threads).	1292	(modulo threads).
898		1293
899	=item ev_set_priority (ev_TYPE *watcher, priority)	1294	=item ev_set_priority (ev_TYPE *watcher, int priority)
900		1295
901	=item int ev_priority (ev_TYPE *watcher)	1296	=item int ev_priority (ev_TYPE *watcher)
902		1297
903	Set and query the priority of the watcher. The priority is a small	1298	Set and query the priority of the watcher. The priority is a small
904	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1299	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
905	(default: C<-2>). Pending watchers with higher priority will be invoked	1300	(default: C<-2>). Pending watchers with higher priority will be invoked
906	before watchers with lower priority, but priority will not keep watchers	1301	before watchers with lower priority, but priority will not keep watchers
907	from being executed (except for C<ev_idle> watchers).	1302	from being executed (except for C<ev_idle> watchers).
908		1303
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	1304	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.	1305	you need to look at C<ev_idle> watchers, which provide this functionality.
916		1306
917	You I<must not> change the priority of a watcher as long as it is active or	1307	You I<must not> change the priority of a watcher as long as it is active or
918	pending.	1308	pending.
919		1309
		1310	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1311	fine, as long as you do not mind that the priority value you query might
		1312	or might not have been clamped to the valid range.
		1313
920	The default priority used by watchers when no priority has been set is	1314	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 :).	1315	always C<0>, which is supposed to not be too high and not be too low :).
922		1316
923	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1317	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	1318	priorities.
925	or might not have been adjusted to be within valid range.
926		1319
927	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1320	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
928		1321
929	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1322	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	1323	C<loop> nor C<revents> need to be valid as long as the watcher callback
931	can deal with that fact.	1324	can deal with that fact, as both are simply passed through to the
		1325	callback.
932		1326
933	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1327	=item int ev_clear_pending (loop, ev_TYPE *watcher)
934		1328
935	If the watcher is pending, this function returns clears its pending status	1329	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	1330	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>.	1331	watcher isn't pending it does nothing and returns C<0>.
938		1332
		1333	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1334	callback to be invoked, which can be accomplished with this function.
		1335
		1336	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1337
		1338	Feeds the given event set into the event loop, as if the specified event
		1339	had happened for the specified watcher (which must be a pointer to an
		1340	initialised but not necessarily started event watcher). Obviously you must
		1341	not free the watcher as long as it has pending events.
		1342
		1343	Stopping the watcher, letting libev invoke it, or calling
		1344	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1345	not started in the first place.
		1346
		1347	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1348	functions that do not need a watcher.
		1349
939	=back	1350	=back
940		1351
941		1352
942	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1353	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
943		1354
944	Each watcher has, by default, a member C<void *data> that you can change	1355	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	1356	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	1357	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	1358	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	1359	member, you can also "subclass" the watcher type and provide your own
949	data:	1360	data:
950		1361
951	struct my_io	1362	struct my_io
952	{	1363	{
953	struct ev_io io;	1364	ev_io io;
954	int otherfd;	1365	int otherfd;
955	void *somedata;	1366	void *somedata;
956	struct whatever *mostinteresting;	1367	struct whatever *mostinteresting;
957	}	1368	};
		1369
		1370	...
		1371	struct my_io w;
		1372	ev_io_init (&w.io, my_cb, fd, EV_READ);
958		1373
959	And since your callback will be called with a pointer to the watcher, you	1374	And since your callback will be called with a pointer to the watcher, you
960	can cast it back to your own type:	1375	can cast it back to your own type:
961		1376
962	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1377	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
963	{	1378	{
964	struct my_io *w = (struct my_io *)w_;	1379	struct my_io *w = (struct my_io *)w_;
965	...	1380	...
966	}	1381	}
967		1382
968	More interesting and less C-conformant ways of casting your callback type	1383	More interesting and less C-conformant ways of casting your callback type
969	instead have been omitted.	1384	instead have been omitted.
970		1385
971	Another common scenario is having some data structure with multiple	1386	Another common scenario is to use some data structure with multiple
972	watchers:	1387	embedded watchers:
973		1388
974	struct my_biggy	1389	struct my_biggy
975	{	1390	{
976	int some_data;	1391	int some_data;
977	ev_timer t1;	1392	ev_timer t1;
978	ev_timer t2;	1393	ev_timer t2;
979	}	1394	}
980		1395
981	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1396	In this case getting the pointer to C<my_biggy> is a bit more
982	you need to use C<offsetof>:	1397	complicated: Either you store the address of your C<my_biggy> struct
		1398	in the C<data> member of the watcher (for woozies), or you need to use
		1399	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1400	programmers):
983		1401
984	#include <stddef.h>	1402	#include <stddef.h>
985		1403
986	static void	1404	static void
987	t1_cb (EV_P_ struct ev_timer *w, int revents)	1405	t1_cb (EV_P_ ev_timer *w, int revents)
988	{	1406	{
989	struct my_biggy big = (struct my_biggy *	1407	struct my_biggy big = (struct my_biggy *)
990	(((char *)w) - offsetof (struct my_biggy, t1));	1408	(((char *)w) - offsetof (struct my_biggy, t1));
991	}	1409	}
992		1410
993	static void	1411	static void
994	t2_cb (EV_P_ struct ev_timer *w, int revents)	1412	t2_cb (EV_P_ ev_timer *w, int revents)
995	{	1413	{
996	struct my_biggy big = (struct my_biggy *	1414	struct my_biggy big = (struct my_biggy *)
997	(((char *)w) - offsetof (struct my_biggy, t2));	1415	(((char *)w) - offsetof (struct my_biggy, t2));
998	}	1416	}
		1417
		1418	=head2 WATCHER PRIORITY MODELS
		1419
		1420	Many event loops support I<watcher priorities>, which are usually small
		1421	integers that influence the ordering of event callback invocation
		1422	between watchers in some way, all else being equal.
		1423
		1424	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1425	description for the more technical details such as the actual priority
		1426	range.
		1427
		1428	There are two common ways how these these priorities are being interpreted
		1429	by event loops:
		1430
		1431	In the more common lock-out model, higher priorities "lock out" invocation
		1432	of lower priority watchers, which means as long as higher priority
		1433	watchers receive events, lower priority watchers are not being invoked.
		1434
		1435	The less common only-for-ordering model uses priorities solely to order
		1436	callback invocation within a single event loop iteration: Higher priority
		1437	watchers are invoked before lower priority ones, but they all get invoked
		1438	before polling for new events.
		1439
		1440	Libev uses the second (only-for-ordering) model for all its watchers
		1441	except for idle watchers (which use the lock-out model).
		1442
		1443	The rationale behind this is that implementing the lock-out model for
		1444	watchers is not well supported by most kernel interfaces, and most event
		1445	libraries will just poll for the same events again and again as long as
		1446	their callbacks have not been executed, which is very inefficient in the
		1447	common case of one high-priority watcher locking out a mass of lower
		1448	priority ones.
		1449
		1450	Static (ordering) priorities are most useful when you have two or more
		1451	watchers handling the same resource: a typical usage example is having an
		1452	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1453	timeouts. Under load, data might be received while the program handles
		1454	other jobs, but since timers normally get invoked first, the timeout
		1455	handler will be executed before checking for data. In that case, giving
		1456	the timer a lower priority than the I/O watcher ensures that I/O will be
		1457	handled first even under adverse conditions (which is usually, but not
		1458	always, what you want).
		1459
		1460	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1461	will only be executed when no same or higher priority watchers have
		1462	received events, they can be used to implement the "lock-out" model when
		1463	required.
		1464
		1465	For example, to emulate how many other event libraries handle priorities,
		1466	you can associate an C<ev_idle> watcher to each such watcher, and in
		1467	the normal watcher callback, you just start the idle watcher. The real
		1468	processing is done in the idle watcher callback. This causes libev to
		1469	continuously poll and process kernel event data for the watcher, but when
		1470	the lock-out case is known to be rare (which in turn is rare :), this is
		1471	workable.
		1472
		1473	Usually, however, the lock-out model implemented that way will perform
		1474	miserably under the type of load it was designed to handle. In that case,
		1475	it might be preferable to stop the real watcher before starting the
		1476	idle watcher, so the kernel will not have to process the event in case
		1477	the actual processing will be delayed for considerable time.
		1478
		1479	Here is an example of an I/O watcher that should run at a strictly lower
		1480	priority than the default, and which should only process data when no
		1481	other events are pending:
		1482
		1483	ev_idle idle; // actual processing watcher
		1484	ev_io io; // actual event watcher
		1485
		1486	static void
		1487	io_cb (EV_P_ ev_io *w, int revents)
		1488	{
		1489	// stop the I/O watcher, we received the event, but
		1490	// are not yet ready to handle it.
		1491	ev_io_stop (EV_A_ w);
		1492
		1493	// start the idle watcher to handle the actual event.
		1494	// it will not be executed as long as other watchers
		1495	// with the default priority are receiving events.
		1496	ev_idle_start (EV_A_ &idle);
		1497	}
		1498
		1499	static void
		1500	idle_cb (EV_P_ ev_idle *w, int revents)
		1501	{
		1502	// actual processing
		1503	read (STDIN_FILENO, ...);
		1504
		1505	// have to start the I/O watcher again, as
		1506	// we have handled the event
		1507	ev_io_start (EV_P_ &io);
		1508	}
		1509
		1510	// initialisation
		1511	ev_idle_init (&idle, idle_cb);
		1512	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1513	ev_io_start (EV_DEFAULT_ &io);
		1514
		1515	In the "real" world, it might also be beneficial to start a timer, so that
		1516	low-priority connections can not be locked out forever under load. This
		1517	enables your program to keep a lower latency for important connections
		1518	during short periods of high load, while not completely locking out less
		1519	important ones.
999		1520
1000		1521
1001	=head1 WATCHER TYPES	1522	=head1 WATCHER TYPES
1002		1523
1003	This section describes each watcher in detail, but will not repeat	1524	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	1548	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	1549	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	1550	descriptors to non-blocking mode is also usually a good idea (but not
1030	required if you know what you are doing).	1551	required if you know what you are doing).
1031		1552
1032	If you must do this, then force the use of a known-to-be-good backend	1553	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	1554	known-to-be-good backend (at the time of this writing, this includes only
1034	C<EVBACKEND_POLL>).	1555	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1556	descriptors for which non-blocking operation makes no sense (such as
		1557	files) - libev doesn't guarantee any specific behaviour in that case.
1035		1558
1036	Another thing you have to watch out for is that it is quite easy to	1559	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	1560	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	1561	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	1562	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	1563	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	1564	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	1565	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.	1566	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1044		1567
1045	If you cannot run the fd in non-blocking mode (for example you should not	1568	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	1569	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	1570	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	1571	interface such as poll (fortunately in our Xlib example, Xlib already
1049	its own, so its quite safe to use).	1572	does this on its own, so its quite safe to use). Some people additionally
		1573	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1574	indefinitely.
		1575
		1576	But really, best use non-blocking mode.
1050		1577
1051	=head3 The special problem of disappearing file descriptors	1578	=head3 The special problem of disappearing file descriptors
1052		1579
1053	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1580	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,	1581	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	1582	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	1583	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	1584	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	1585	registered with libev, there is no efficient way to see that this is, in
1059	fact, a different file descriptor.	1586	fact, a different file descriptor.
1060		1587
…		…
1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1618	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1092	C<EVBACKEND_POLL>.	1619	C<EVBACKEND_POLL>.
1093		1620
1094	=head3 The special problem of SIGPIPE	1621	=head3 The special problem of SIGPIPE
1095		1622
1096	While not really specific to libev, it is easy to forget about SIGPIPE:	1623	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	1624	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	1625	sent a SIGPIPE, which, by default, aborts your program. For most programs
1099	programs this is sensible behaviour, for daemons, this is usually	1626	this is sensible behaviour, for daemons, this is usually undesirable.
1100	undesirable.
1101		1627
1102	So when you encounter spurious, unexplained daemon exits, make sure you	1628	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	1629	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).	1630	somewhere, as that would have given you a big clue).
1105		1631
		1632	=head3 The special problem of accept()ing when you can't
		1633
		1634	Many implementations of the POSIX C<accept> function (for example,
		1635	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1636	connection from the pending queue in all error cases.
		1637
		1638	For example, larger servers often run out of file descriptors (because
		1639	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1640	rejecting the connection, leading to libev signalling readiness on
		1641	the next iteration again (the connection still exists after all), and
		1642	typically causing the program to loop at 100% CPU usage.
		1643
		1644	Unfortunately, the set of errors that cause this issue differs between
		1645	operating systems, there is usually little the app can do to remedy the
		1646	situation, and no known thread-safe method of removing the connection to
		1647	cope with overload is known (to me).
		1648
		1649	One of the easiest ways to handle this situation is to just ignore it
		1650	- when the program encounters an overload, it will just loop until the
		1651	situation is over. While this is a form of busy waiting, no OS offers an
		1652	event-based way to handle this situation, so it's the best one can do.
		1653
		1654	A better way to handle the situation is to log any errors other than
		1655	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1656	messages, and continue as usual, which at least gives the user an idea of
		1657	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1658	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1659	usage.
		1660
		1661	If your program is single-threaded, then you could also keep a dummy file
		1662	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1663	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1664	close that fd, and create a new dummy fd. This will gracefully refuse
		1665	clients under typical overload conditions.
		1666
		1667	The last way to handle it is to simply log the error and C<exit>, as
		1668	is often done with C<malloc> failures, but this results in an easy
		1669	opportunity for a DoS attack.
1106		1670
1107	=head3 Watcher-Specific Functions	1671	=head3 Watcher-Specific Functions
1108		1672
1109	=over 4	1673	=over 4
1110		1674
1111	=item ev_io_init (ev_io *, callback, int fd, int events)	1675	=item ev_io_init (ev_io *, callback, int fd, int events)
1112		1676
1113	=item ev_io_set (ev_io *, int fd, int events)	1677	=item ev_io_set (ev_io *, int fd, int events)
1114		1678
1115	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1679	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	1680	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.	1681	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1118		1682
1119	=item int fd [read-only]	1683	=item int fd [read-only]
1120		1684
1121	The file descriptor being watched.	1685	The file descriptor being watched.
1122		1686
…		…
1130		1694
1131	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1695	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	1696	readable, but only once. Since it is likely line-buffered, you could
1133	attempt to read a whole line in the callback.	1697	attempt to read a whole line in the callback.
1134		1698
1135	static void	1699	static void
1136	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1700	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1137	{	1701	{
1138	ev_io_stop (loop, w);	1702	ev_io_stop (loop, w);
1139	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1703	.. read from stdin here (or from w->fd) and handle any I/O errors
1140	}	1704	}
1141		1705
1142	...	1706	...
1143	struct ev_loop *loop = ev_default_init (0);	1707	struct ev_loop *loop = ev_default_init (0);
1144	struct ev_io stdin_readable;	1708	ev_io stdin_readable;
1145	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1709	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1146	ev_io_start (loop, &stdin_readable);	1710	ev_io_start (loop, &stdin_readable);
1147	ev_loop (loop, 0);	1711	ev_run (loop, 0);
1148		1712
1149		1713
1150	=head2 C<ev_timer> - relative and optionally repeating timeouts	1714	=head2 C<ev_timer> - relative and optionally repeating timeouts
1151		1715
1152	Timer watchers are simple relative timers that generate an event after a	1716	Timer watchers are simple relative timers that generate an event after a
1153	given time, and optionally repeating in regular intervals after that.	1717	given time, and optionally repeating in regular intervals after that.
1154		1718
1155	The timers are based on real time, that is, if you register an event that	1719	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	1720	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	1721	year, it will still time out after (roughly) one hour. "Roughly" because
1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1722	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1159	monotonic clock option helps a lot here).	1723	monotonic clock option helps a lot here).
		1724
		1725	The callback is guaranteed to be invoked only I<after> its timeout has
		1726	passed (not I<at>, so on systems with very low-resolution clocks this
		1727	might introduce a small delay). If multiple timers become ready during the
		1728	same loop iteration then the ones with earlier time-out values are invoked
		1729	before ones of the same priority with later time-out values (but this is
		1730	no longer true when a callback calls C<ev_run> recursively).
		1731
		1732	=head3 Be smart about timeouts
		1733
		1734	Many real-world problems involve some kind of timeout, usually for error
		1735	recovery. A typical example is an HTTP request - if the other side hangs,
		1736	you want to raise some error after a while.
		1737
		1738	What follows are some ways to handle this problem, from obvious and
		1739	inefficient to smart and efficient.
		1740
		1741	In the following, a 60 second activity timeout is assumed - a timeout that
		1742	gets reset to 60 seconds each time there is activity (e.g. each time some
		1743	data or other life sign was received).
		1744
		1745	=over 4
		1746
		1747	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1748
		1749	This is the most obvious, but not the most simple way: In the beginning,
		1750	start the watcher:
		1751
		1752	ev_timer_init (timer, callback, 60., 0.);
		1753	ev_timer_start (loop, timer);
		1754
		1755	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1756	and start it again:
		1757
		1758	ev_timer_stop (loop, timer);
		1759	ev_timer_set (timer, 60., 0.);
		1760	ev_timer_start (loop, timer);
		1761
		1762	This is relatively simple to implement, but means that each time there is
		1763	some activity, libev will first have to remove the timer from its internal
		1764	data structure and then add it again. Libev tries to be fast, but it's
		1765	still not a constant-time operation.
		1766
		1767	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1768
		1769	This is the easiest way, and involves using C<ev_timer_again> instead of
		1770	C<ev_timer_start>.
		1771
		1772	To implement this, configure an C<ev_timer> with a C<repeat> value
		1773	of C<60> and then call C<ev_timer_again> at start and each time you
		1774	successfully read or write some data. If you go into an idle state where
		1775	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1776	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1777
		1778	That means you can ignore both the C<ev_timer_start> function and the
		1779	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1780	member and C<ev_timer_again>.
		1781
		1782	At start:
		1783
		1784	ev_init (timer, callback);
		1785	timer->repeat = 60.;
		1786	ev_timer_again (loop, timer);
		1787
		1788	Each time there is some activity:
		1789
		1790	ev_timer_again (loop, timer);
		1791
		1792	It is even possible to change the time-out on the fly, regardless of
		1793	whether the watcher is active or not:
		1794
		1795	timer->repeat = 30.;
		1796	ev_timer_again (loop, timer);
		1797
		1798	This is slightly more efficient then stopping/starting the timer each time
		1799	you want to modify its timeout value, as libev does not have to completely
		1800	remove and re-insert the timer from/into its internal data structure.
		1801
		1802	It is, however, even simpler than the "obvious" way to do it.
		1803
		1804	=item 3. Let the timer time out, but then re-arm it as required.
		1805
		1806	This method is more tricky, but usually most efficient: Most timeouts are
		1807	relatively long compared to the intervals between other activity - in
		1808	our example, within 60 seconds, there are usually many I/O events with
		1809	associated activity resets.
		1810
		1811	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1812	but remember the time of last activity, and check for a real timeout only
		1813	within the callback:
		1814
		1815	ev_tstamp last_activity; // time of last activity
		1816
		1817	static void
		1818	callback (EV_P_ ev_timer *w, int revents)
		1819	{
		1820	ev_tstamp now = ev_now (EV_A);
		1821	ev_tstamp timeout = last_activity + 60.;
		1822
		1823	// if last_activity + 60. is older than now, we did time out
		1824	if (timeout < now)
		1825	{
		1826	// timeout occurred, take action
		1827	}
		1828	else
		1829	{
		1830	// callback was invoked, but there was some activity, re-arm
		1831	// the watcher to fire in last_activity + 60, which is
		1832	// guaranteed to be in the future, so "again" is positive:
		1833	w->repeat = timeout - now;
		1834	ev_timer_again (EV_A_ w);
		1835	}
		1836	}
		1837
		1838	To summarise the callback: first calculate the real timeout (defined
		1839	as "60 seconds after the last activity"), then check if that time has
		1840	been reached, which means something I<did>, in fact, time out. Otherwise
		1841	the callback was invoked too early (C<timeout> is in the future), so
		1842	re-schedule the timer to fire at that future time, to see if maybe we have
		1843	a timeout then.
		1844
		1845	Note how C<ev_timer_again> is used, taking advantage of the
		1846	C<ev_timer_again> optimisation when the timer is already running.
		1847
		1848	This scheme causes more callback invocations (about one every 60 seconds
		1849	minus half the average time between activity), but virtually no calls to
		1850	libev to change the timeout.
		1851
		1852	To start the timer, simply initialise the watcher and set C<last_activity>
		1853	to the current time (meaning we just have some activity :), then call the
		1854	callback, which will "do the right thing" and start the timer:
		1855
		1856	ev_init (timer, callback);
		1857	last_activity = ev_now (loop);
		1858	callback (loop, timer, EV_TIMER);
		1859
		1860	And when there is some activity, simply store the current time in
		1861	C<last_activity>, no libev calls at all:
		1862
		1863	last_activity = ev_now (loop);
		1864
		1865	This technique is slightly more complex, but in most cases where the
		1866	time-out is unlikely to be triggered, much more efficient.
		1867
		1868	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1869	callback :) - just change the timeout and invoke the callback, which will
		1870	fix things for you.
		1871
		1872	=item 4. Wee, just use a double-linked list for your timeouts.
		1873
		1874	If there is not one request, but many thousands (millions...), all
		1875	employing some kind of timeout with the same timeout value, then one can
		1876	do even better:
		1877
		1878	When starting the timeout, calculate the timeout value and put the timeout
		1879	at the I<end> of the list.
		1880
		1881	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1882	the list is expected to fire (for example, using the technique #3).
		1883
		1884	When there is some activity, remove the timer from the list, recalculate
		1885	the timeout, append it to the end of the list again, and make sure to
		1886	update the C<ev_timer> if it was taken from the beginning of the list.
		1887
		1888	This way, one can manage an unlimited number of timeouts in O(1) time for
		1889	starting, stopping and updating the timers, at the expense of a major
		1890	complication, and having to use a constant timeout. The constant timeout
		1891	ensures that the list stays sorted.
		1892
		1893	=back
		1894
		1895	So which method the best?
		1896
		1897	Method #2 is a simple no-brain-required solution that is adequate in most
		1898	situations. Method #3 requires a bit more thinking, but handles many cases
		1899	better, and isn't very complicated either. In most case, choosing either
		1900	one is fine, with #3 being better in typical situations.
		1901
		1902	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1903	rather complicated, but extremely efficient, something that really pays
		1904	off after the first million or so of active timers, i.e. it's usually
		1905	overkill :)
		1906
		1907	=head3 The special problem of time updates
		1908
		1909	Establishing the current time is a costly operation (it usually takes at
		1910	least two system calls): EV therefore updates its idea of the current
		1911	time only before and after C<ev_run> collects new events, which causes a
		1912	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1913	lots of events in one iteration.
1160		1914
1161	The relative timeouts are calculated relative to the C<ev_now ()>	1915	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	1916	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	1917	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	1918	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:	1919	timeout on the current time, use something like this to adjust for this:
1166		1920
1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1921	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1168		1922
1169	The callback is guarenteed to be invoked only when its timeout has passed,	1923	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	1924	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1171	order of execution is undefined.	1925	()>.
		1926
		1927	=head3 The special problems of suspended animation
		1928
		1929	When you leave the server world it is quite customary to hit machines that
		1930	can suspend/hibernate - what happens to the clocks during such a suspend?
		1931
		1932	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1933	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1934	to run until the system is suspended, but they will not advance while the
		1935	system is suspended. That means, on resume, it will be as if the program
		1936	was frozen for a few seconds, but the suspend time will not be counted
		1937	towards C<ev_timer> when a monotonic clock source is used. The real time
		1938	clock advanced as expected, but if it is used as sole clocksource, then a
		1939	long suspend would be detected as a time jump by libev, and timers would
		1940	be adjusted accordingly.
		1941
		1942	I would not be surprised to see different behaviour in different between
		1943	operating systems, OS versions or even different hardware.
		1944
		1945	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1946	time jump in the monotonic clocks and the realtime clock. If the program
		1947	is suspended for a very long time, and monotonic clock sources are in use,
		1948	then you can expect C<ev_timer>s to expire as the full suspension time
		1949	will be counted towards the timers. When no monotonic clock source is in
		1950	use, then libev will again assume a timejump and adjust accordingly.
		1951
		1952	It might be beneficial for this latter case to call C<ev_suspend>
		1953	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1954	deterministic behaviour in this case (you can do nothing against
		1955	C<SIGSTOP>).
1172		1956
1173	=head3 Watcher-Specific Functions and Data Members	1957	=head3 Watcher-Specific Functions and Data Members
1174		1958
1175	=over 4	1959	=over 4
1176		1960
1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1961	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1178		1962
1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1963	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1180		1964
1181	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1965	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	1966	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	1967	reached. If it is positive, then the timer will automatically be
1184	later, again, and again, until stopped manually.	1968	configured to trigger again C<repeat> seconds later, again, and again,
		1969	until stopped manually.
1185		1970
1186	The timer itself will do a best-effort at avoiding drift, that is, if you	1971	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	1972	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	1973	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	1974	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.	1975	do stuff) the timer will not fire more than once per event loop iteration.
1191		1976
1192	=item ev_timer_again (loop, ev_timer *)	1977	=item ev_timer_again (loop, ev_timer *)
1193		1978
1194	This will act as if the timer timed out and restart it again if it is	1979	This will act as if the timer timed out and restart it again if it is
1195	repeating. The exact semantics are:	1980	repeating. The exact semantics are:
1196		1981
1197	If the timer is pending, its pending status is cleared.	1982	If the timer is pending, its pending status is cleared.
1198		1983
1199	If the timer is started but nonrepeating, stop it (as if it timed out).	1984	If the timer is started but non-repeating, stop it (as if it timed out).
1200		1985
1201	If the timer is repeating, either start it if necessary (with the	1986	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.	1987	C<repeat> value), or reset the running timer to the C<repeat> value.
1203		1988
1204	This sounds a bit complicated, but here is a useful and typical	1989	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	1990	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		1991
1214	That means you can ignore the C<after> value and C<ev_timer_start>	1992	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1215	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1216		1993
1217	ev_timer_init (timer, callback, 0., 5.);	1994	Returns the remaining time until a timer fires. If the timer is active,
1218	ev_timer_again (loop, timer);	1995	then this time is relative to the current event loop time, otherwise it's
1219	...	1996	the timeout value currently configured.
1220	timer->again = 17.;
1221	ev_timer_again (loop, timer);
1222	...
1223	timer->again = 10.;
1224	ev_timer_again (loop, timer);
1225		1997
1226	This is more slightly efficient then stopping/starting the timer each time	1998	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1227	you want to modify its timeout value.	1999	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2000	will return C<4>. When the timer expires and is restarted, it will return
		2001	roughly C<7> (likely slightly less as callback invocation takes some time,
		2002	too), and so on.
1228		2003
1229	=item ev_tstamp repeat [read-write]	2004	=item ev_tstamp repeat [read-write]
1230		2005
1231	The current C<repeat> value. Will be used each time the watcher times out	2006	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),	2007	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.	2008	which is also when any modifications are taken into account.
1234		2009
1235	=back	2010	=back
1236		2011
1237	=head3 Examples	2012	=head3 Examples
1238		2013
1239	Example: Create a timer that fires after 60 seconds.	2014	Example: Create a timer that fires after 60 seconds.
1240		2015
1241	static void	2016	static void
1242	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2017	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1243	{	2018	{
1244	.. one minute over, w is actually stopped right here	2019	.. one minute over, w is actually stopped right here
1245	}	2020	}
1246		2021
1247	struct ev_timer mytimer;	2022	ev_timer mytimer;
1248	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2023	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1249	ev_timer_start (loop, &mytimer);	2024	ev_timer_start (loop, &mytimer);
1250		2025
1251	Example: Create a timeout timer that times out after 10 seconds of	2026	Example: Create a timeout timer that times out after 10 seconds of
1252	inactivity.	2027	inactivity.
1253		2028
1254	static void	2029	static void
1255	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2030	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1256	{	2031	{
1257	.. ten seconds without any activity	2032	.. ten seconds without any activity
1258	}	2033	}
1259		2034
1260	struct ev_timer mytimer;	2035	ev_timer mytimer;
1261	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2036	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1262	ev_timer_again (&mytimer); /* start timer */	2037	ev_timer_again (&mytimer); /* start timer */
1263	ev_loop (loop, 0);	2038	ev_run (loop, 0);
1264		2039
1265	// and in some piece of code that gets executed on any "activity":	2040	// and in some piece of code that gets executed on any "activity":
1266	// reset the timeout to start ticking again at 10 seconds	2041	// reset the timeout to start ticking again at 10 seconds
1267	ev_timer_again (&mytimer);	2042	ev_timer_again (&mytimer);
1268		2043
1269		2044
1270	=head2 C<ev_periodic> - to cron or not to cron?	2045	=head2 C<ev_periodic> - to cron or not to cron?
1271		2046
1272	Periodic watchers are also timers of a kind, but they are very versatile	2047	Periodic watchers are also timers of a kind, but they are very versatile
1273	(and unfortunately a bit complex).	2048	(and unfortunately a bit complex).
1274		2049
1275	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2050	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	2051	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	2052	(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 ()	2053	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	2054	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	2055	wrist-watch).
1281	roughly 10 seconds later).
1282		2056
1283	They can also be used to implement vastly more complex timers, such as	2057	You can tell a periodic watcher to trigger after some specific point
1284	triggering an event on each midnight, local time or other, complicated,	2058	in time: for example, if you tell a periodic watcher to trigger "in 10
1285	rules.	2059	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2060	not a delay) and then reset your system clock to January of the previous
		2061	year, then it will take a year or more to trigger the event (unlike an
		2062	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2063	it, as it uses a relative timeout).
1286		2064
		2065	C<ev_periodic> watchers can also be used to implement vastly more complex
		2066	timers, such as triggering an event on each "midnight, local time", or
		2067	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2068	those cannot react to time jumps.
		2069
1287	As with timers, the callback is guarenteed to be invoked only when the	2070	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	2071	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.	2072	timers become ready during the same loop iteration then the ones with
		2073	earlier time-out values are invoked before ones with later time-out values
		2074	(but this is no longer true when a callback calls C<ev_run> recursively).
1290		2075
1291	=head3 Watcher-Specific Functions and Data Members	2076	=head3 Watcher-Specific Functions and Data Members
1292		2077
1293	=over 4	2078	=over 4
1294		2079
1295	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2080	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1296		2081
1297	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2082	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1298		2083
1299	Lots of arguments, lets sort it out... There are basically three modes of	2084	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:	2085	operation, and we will explain them from simplest to most complex:
1301		2086
1302	=over 4	2087	=over 4
1303		2088
1304	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2089	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1305		2090
1306	In this configuration the watcher triggers an event at the wallclock time	2091	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,	2092	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	2093	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.	2094	will be stopped and invoked when the system clock reaches or surpasses
		2095	this point in time.
1310		2096
1311	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2097	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1312		2098
1313	In this mode the watcher will always be scheduled to time out at the next	2099	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)	2100	C<offset + N * interval> time (for some integer N, which can also be
1315	and then repeat, regardless of any time jumps.	2101	negative) and then repeat, regardless of any time jumps. The C<offset>
		2102	argument is merely an offset into the C<interval> periods.
1316		2103
1317	This can be used to create timers that do not drift with respect to system	2104	This can be used to create timers that do not drift with respect to the
1318	time:	2105	system clock, for example, here is an C<ev_periodic> that triggers each
		2106	hour, on the hour (with respect to UTC):
1319		2107
1320	ev_periodic_set (&periodic, 0., 3600., 0);	2108	ev_periodic_set (&periodic, 0., 3600., 0);
1321		2109
1322	This doesn't mean there will always be 3600 seconds in between triggers,	2110	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	2111	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	2112	full hour (UTC), or more correctly, when the system time is evenly divisible
1325	by 3600.	2113	by 3600.
1326		2114
1327	Another way to think about it (for the mathematically inclined) is that	2115	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	2116	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.	2117	time where C<time = offset (mod interval)>, regardless of any time jumps.
1330		2118
1331	For numerical stability it is preferable that the C<at> value is near	2119	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	2120	C<ev_now ()> (the current time), but there is no range requirement for
1333	this value.	2121	this value, and in fact is often specified as zero.
1334		2122
		2123	Note also that there is an upper limit to how often a timer can fire (CPU
		2124	speed for example), so if C<interval> is very small then timing stability
		2125	will of course deteriorate. Libev itself tries to be exact to be about one
		2126	millisecond (if the OS supports it and the machine is fast enough).
		2127
1335	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2128	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1336		2129
1337	In this mode the values for C<interval> and C<at> are both being	2130	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	2131	ignored. Instead, each time the periodic watcher gets scheduled, the
1339	reschedule callback will be called with the watcher as first, and the	2132	reschedule callback will be called with the watcher as first, and the
1340	current time as second argument.	2133	current time as second argument.
1341		2134
1342	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2135	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,	2136	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	2137	allowed by documentation here>.
1345	starting an C<ev_prepare> watcher, which is legal).
1346		2138
		2139	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2140	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2141	only event loop modification you are allowed to do).
		2142
1347	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2143	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1348	ev_tstamp now)>, e.g.:	2144	*w, ev_tstamp now)>, e.g.:
1349		2145
		2146	static ev_tstamp
1350	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2147	my_rescheduler (ev_periodic *w, ev_tstamp now)
1351	{	2148	{
1352	return now + 60.;	2149	return now + 60.;
1353	}	2150	}
1354		2151
1355	It must return the next time to trigger, based on the passed time value	2152	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	2153	(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	2154	will usually be called just before the callback will be triggered, but
1358	might be called at other times, too.	2155	might be called at other times, too.
1359		2156
1360	NOTE: I<< This callback must always return a time that is later than the	2157	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.	2158	equal to the passed C<now> value >>.
1362		2159
1363	This can be used to create very complex timers, such as a timer that	2160	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	2161	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	2162	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	2163	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).	2164	reason I omitted it as an example).
1368		2165
1369	=back	2166	=back
…		…
1373	Simply stops and restarts the periodic watcher again. This is only useful	2170	Simply stops and restarts the periodic watcher again. This is only useful
1374	when you changed some parameters or the reschedule callback would return	2171	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	2172	a different time than the last time it was called (e.g. in a crond like
1376	program when the crontabs have changed).	2173	program when the crontabs have changed).
1377		2174
		2175	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2176
		2177	When active, returns the absolute time that the watcher is supposed
		2178	to trigger next. This is not the same as the C<offset> argument to
		2179	C<ev_periodic_set>, but indeed works even in interval and manual
		2180	rescheduling modes.
		2181
1378	=item ev_tstamp offset [read-write]	2182	=item ev_tstamp offset [read-write]
1379		2183
1380	When repeating, this contains the offset value, otherwise this is the	2184	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>).	2185	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2186	although libev might modify this value for better numerical stability).
1382		2187
1383	Can be modified any time, but changes only take effect when the periodic	2188	Can be modified any time, but changes only take effect when the periodic
1384	timer fires or C<ev_periodic_again> is being called.	2189	timer fires or C<ev_periodic_again> is being called.
1385		2190
1386	=item ev_tstamp interval [read-write]	2191	=item ev_tstamp interval [read-write]
1387		2192
1388	The current interval value. Can be modified any time, but changes only	2193	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	2194	take effect when the periodic timer fires or C<ev_periodic_again> is being
1390	called.	2195	called.
1391		2196
1392	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2197	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1393		2198
1394	The current reschedule callback, or C<0>, if this functionality is	2199	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	2200	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.	2201	the periodic timer fires or C<ev_periodic_again> is being called.
1397		2202
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	2203	=back
1404		2204
1405	=head3 Examples	2205	=head3 Examples
1406		2206
1407	Example: Call a callback every hour, or, more precisely, whenever the	2207	Example: Call a callback every hour, or, more precisely, whenever the
1408	system clock is divisible by 3600. The callback invocation times have	2208	system time is divisible by 3600. The callback invocation times have
1409	potentially a lot of jittering, but good long-term stability.	2209	potentially a lot of jitter, but good long-term stability.
1410		2210
1411	static void	2211	static void
1412	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2212	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1413	{	2213	{
1414	... its now a full hour (UTC, or TAI or whatever your clock follows)	2214	... its now a full hour (UTC, or TAI or whatever your clock follows)
1415	}	2215	}
1416		2216
1417	struct ev_periodic hourly_tick;	2217	ev_periodic hourly_tick;
1418	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2218	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1419	ev_periodic_start (loop, &hourly_tick);	2219	ev_periodic_start (loop, &hourly_tick);
1420		2220
1421	Example: The same as above, but use a reschedule callback to do it:	2221	Example: The same as above, but use a reschedule callback to do it:
1422		2222
1423	#include <math.h>	2223	#include <math.h>
1424		2224
1425	static ev_tstamp	2225	static ev_tstamp
1426	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2226	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1427	{	2227	{
1428	return fmod (now, 3600.) + 3600.;	2228	return now + (3600. - fmod (now, 3600.));
1429	}	2229	}
1430		2230
1431	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2231	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1432		2232
1433	Example: Call a callback every hour, starting now:	2233	Example: Call a callback every hour, starting now:
1434		2234
1435	struct ev_periodic hourly_tick;	2235	ev_periodic hourly_tick;
1436	ev_periodic_init (&hourly_tick, clock_cb,	2236	ev_periodic_init (&hourly_tick, clock_cb,
1437	fmod (ev_now (loop), 3600.), 3600., 0);	2237	fmod (ev_now (loop), 3600.), 3600., 0);
1438	ev_periodic_start (loop, &hourly_tick);	2238	ev_periodic_start (loop, &hourly_tick);
1439		2239
1440		2240
1441	=head2 C<ev_signal> - signal me when a signal gets signalled!	2241	=head2 C<ev_signal> - signal me when a signal gets signalled!
1442		2242
1443	Signal watchers will trigger an event when the process receives a specific	2243	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	2244	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	2245	will try it's best to deliver signals synchronously, i.e. as part of the
1446	normal event processing, like any other event.	2246	normal event processing, like any other event.
1447		2247
		2248	If you want signals to be delivered truly asynchronously, just use
		2249	C<sigaction> as you would do without libev and forget about sharing
		2250	the signal. You can even use C<ev_async> from a signal handler to
		2251	synchronously wake up an event loop.
		2252
1448	You can configure as many watchers as you like per signal. Only when the	2253	You can configure as many watchers as you like for the same signal, but
		2254	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2255	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2256	C<SIGINT> in both the default loop and another loop at the same time. At
		2257	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2258
1449	first watcher gets started will libev actually register a signal watcher	2259	When the first watcher gets started will libev actually register something
1450	with the kernel (thus it coexists with your own signal handlers as long	2260	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	2261	you don't register any with libev for the same signal).
1452	watcher for a signal is stopped libev will reset the signal handler to
1453	SIG_DFL (regardless of what it was set to before).
1454		2262
1455	If possible and supported, libev will install its handlers with	2263	If possible and supported, libev will install its handlers with
1456	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2264	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1457	interrupted. If you have a problem with syscalls getting interrupted by	2265	not be unduly interrupted. If you have a problem with system calls getting
1458	signals you can block all signals in an C<ev_check> watcher and unblock	2266	interrupted by signals you can block all signals in an C<ev_check> watcher
1459	them in an C<ev_prepare> watcher.	2267	and unblock them in an C<ev_prepare> watcher.
		2268
		2269	=head3 The special problem of inheritance over fork/execve/pthread_create
		2270
		2271	Both the signal mask (C<sigprocmask>) and the signal disposition
		2272	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2273	stopping it again), that is, libev might or might not block the signal,
		2274	and might or might not set or restore the installed signal handler.
		2275
		2276	While this does not matter for the signal disposition (libev never
		2277	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2278	C<execve>), this matters for the signal mask: many programs do not expect
		2279	certain signals to be blocked.
		2280
		2281	This means that before calling C<exec> (from the child) you should reset
		2282	the signal mask to whatever "default" you expect (all clear is a good
		2283	choice usually).
		2284
		2285	The simplest way to ensure that the signal mask is reset in the child is
		2286	to install a fork handler with C<pthread_atfork> that resets it. That will
		2287	catch fork calls done by libraries (such as the libc) as well.
		2288
		2289	In current versions of libev, the signal will not be blocked indefinitely
		2290	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2291	the window of opportunity for problems, it will not go away, as libev
		2292	I<has> to modify the signal mask, at least temporarily.
		2293
		2294	So I can't stress this enough: I<If you do not reset your signal mask when
		2295	you expect it to be empty, you have a race condition in your code>. This
		2296	is not a libev-specific thing, this is true for most event libraries.
1460		2297
1461	=head3 Watcher-Specific Functions and Data Members	2298	=head3 Watcher-Specific Functions and Data Members
1462		2299
1463	=over 4	2300	=over 4
1464		2301
…		…
1475		2312
1476	=back	2313	=back
1477		2314
1478	=head3 Examples	2315	=head3 Examples
1479		2316
1480	Example: Try to exit cleanly on SIGINT and SIGTERM.	2317	Example: Try to exit cleanly on SIGINT.
1481		2318
1482	static void	2319	static void
1483	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2320	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1484	{	2321	{
1485	ev_unloop (loop, EVUNLOOP_ALL);	2322	ev_break (loop, EVBREAK_ALL);
1486	}	2323	}
1487		2324
1488	struct ev_signal signal_watcher;	2325	ev_signal signal_watcher;
1489	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2326	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1490	ev_signal_start (loop, &sigint_cb);	2327	ev_signal_start (loop, &signal_watcher);
1491		2328
1492		2329
1493	=head2 C<ev_child> - watch out for process status changes	2330	=head2 C<ev_child> - watch out for process status changes
1494		2331
1495	Child watchers trigger when your process receives a SIGCHLD in response to	2332	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	2333	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	2334	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	2335	has been forked (which implies it might have already exited), as long
1499	loop isn't entered (or is continued from a watcher).	2336	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2337	forking and then immediately registering a watcher for the child is fine,
		2338	but forking and registering a watcher a few event loop iterations later or
		2339	in the next callback invocation is not.
1500		2340
1501	Only the default event loop is capable of handling signals, and therefore	2341	Only the default event loop is capable of handling signals, and therefore
1502	you can only rgeister child watchers in the default event loop.	2342	you can only register child watchers in the default event loop.
		2343
		2344	Due to some design glitches inside libev, child watchers will always be
		2345	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2346	libev)
1503		2347
1504	=head3 Process Interaction	2348	=head3 Process Interaction
1505		2349
1506	Libev grabs C<SIGCHLD> as soon as the default event loop is	2350	Libev grabs C<SIGCHLD> as soon as the default event loop is
1507	initialised. This is necessary to guarantee proper behaviour even if	2351	initialised. This is necessary to guarantee proper behaviour even if the
1508	the first child watcher is started after the child exits. The occurance	2352	first child watcher is started after the child exits. The occurrence
1509	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2353	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1510	synchronously as part of the event loop processing. Libev always reaps all	2354	synchronously as part of the event loop processing. Libev always reaps all
1511	children, even ones not watched.	2355	children, even ones not watched.
1512		2356
1513	=head3 Overriding the Built-In Processing	2357	=head3 Overriding the Built-In Processing
…		…
1517	handler, you can override it easily by installing your own handler for	2361	handler, you can override it easily by installing your own handler for
1518	C<SIGCHLD> after initialising the default loop, and making sure the	2362	C<SIGCHLD> after initialising the default loop, and making sure the
1519	default loop never gets destroyed. You are encouraged, however, to use an	2363	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	2364	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.	2365	that, so other libev users can use C<ev_child> watchers freely.
		2366
		2367	=head3 Stopping the Child Watcher
		2368
		2369	Currently, the child watcher never gets stopped, even when the
		2370	child terminates, so normally one needs to stop the watcher in the
		2371	callback. Future versions of libev might stop the watcher automatically
		2372	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2373	problem).
1522		2374
1523	=head3 Watcher-Specific Functions and Data Members	2375	=head3 Watcher-Specific Functions and Data Members
1524		2376
1525	=over 4	2377	=over 4
1526		2378
…		…
1555	=head3 Examples	2407	=head3 Examples
1556		2408
1557	Example: C<fork()> a new process and install a child handler to wait for	2409	Example: C<fork()> a new process and install a child handler to wait for
1558	its completion.	2410	its completion.
1559		2411
1560	ev_child cw;	2412	ev_child cw;
1561		2413
1562	static void	2414	static void
1563	child_cb (EV_P_ struct ev_child *w, int revents)	2415	child_cb (EV_P_ ev_child *w, int revents)
1564	{	2416	{
1565	ev_child_stop (EV_A_ w);	2417	ev_child_stop (EV_A_ w);
1566	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2418	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1567	}	2419	}
1568		2420
1569	pid_t pid = fork ();	2421	pid_t pid = fork ();
1570		2422
1571	if (pid < 0)	2423	if (pid < 0)
1572	// error	2424	// error
1573	else if (pid == 0)	2425	else if (pid == 0)
1574	{	2426	{
1575	// the forked child executes here	2427	// the forked child executes here
1576	exit (1);	2428	exit (1);
1577	}	2429	}
1578	else	2430	else
1579	{	2431	{
1580	ev_child_init (&cw, child_cb, pid, 0);	2432	ev_child_init (&cw, child_cb, pid, 0);
1581	ev_child_start (EV_DEFAULT_ &cw);	2433	ev_child_start (EV_DEFAULT_ &cw);
1582	}	2434	}
1583		2435
1584		2436
1585	=head2 C<ev_stat> - did the file attributes just change?	2437	=head2 C<ev_stat> - did the file attributes just change?
1586		2438
1587	This watches a filesystem path for attribute changes. That is, it calls	2439	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	2440	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.	2441	and sees if it changed compared to the last time, invoking the callback if
		2442	it did.
1590		2443
1591	The path does not need to exist: changing from "path exists" to "path does	2444	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	2445	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	2446	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	2447	C<st_nlink> field being zero (which is otherwise always forced to be at
1595	the stat buffer having unspecified contents.	2448	least one) and all the other fields of the stat buffer having unspecified
		2449	contents.
1596		2450
1597	The path I<should> be absolute and I<must not> end in a slash. If it is	2451	The path I<must not> end in a slash or contain special components such as
		2452	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.	2453	your working directory changes, then the behaviour is undefined.
1599		2454
1600	Since there is no standard to do this, the portable implementation simply	2455	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	2456	portable implementation simply calls C<stat(2)> regularly on the path
1602	can specify a recommended polling interval for this case. If you specify	2457	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,	2458	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	2459	recommended!) then a I<suitable, unspecified default> value will be used
1605	five seconds, although this might change dynamically). Libev will also	2460	(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	2461	change dynamically). Libev will also impose a minimum interval which is
1607	usually overkill.	2462	currently around C<0.1>, but that's usually overkill.
1608		2463
1609	This watcher type is not meant for massive numbers of stat watchers,	2464	This watcher type is not meant for massive numbers of stat watchers,
1610	as even with OS-supported change notifications, this can be	2465	as even with OS-supported change notifications, this can be
1611	resource-intensive.	2466	resource-intensive.
1612		2467
1613	At the time of this writing, only the Linux inotify interface is	2468	At the time of this writing, the only OS-specific interface implemented
1614	implemented (implementing kqueue support is left as an exercise for the	2469	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	2470	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	2471	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		2472
1621	=head3 ABI Issues (Largefile Support)	2473	=head3 ABI Issues (Largefile Support)
1622		2474
1623	Libev by default (unless the user overrides this) uses the default	2475	Libev by default (unless the user overrides this) uses the default
1624	compilation environment, which means that on systems with optionally	2476	compilation environment, which means that on systems with large file
1625	disabled large file support, you get the 32 bit version of the stat	2477	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	2478	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	2479	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	2480	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	2481	obviously the case with any flags that change the ABI, but the problem is
1630	most noticably with ev_stat and largefile support.	2482	most noticeably displayed with ev_stat and large file support.
1631		2483
1632	=head3 Inotify	2484	The solution for this is to lobby your distribution maker to make large
		2485	file interfaces available by default (as e.g. FreeBSD does) and not
		2486	optional. Libev cannot simply switch on large file support because it has
		2487	to exchange stat structures with application programs compiled using the
		2488	default compilation environment.
1633		2489
		2490	=head3 Inotify and Kqueue
		2491
1634	When C<inotify (7)> support has been compiled into libev (generally only	2492	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	2493	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	2494	inotify descriptor will be created lazily when the first C<ev_stat>
1637	when the first C<ev_stat> watcher is being started.	2495	watcher is being started.
1638		2496
1639	Inotify presence does not change the semantics of C<ev_stat> watchers	2497	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	2498	except that changes might be detected earlier, and in some cases, to avoid
1641	making regular C<stat> calls. Even in the presence of inotify support	2499	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.	2500	there are many cases where libev has to resort to regular C<stat> polling,
		2501	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2502	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2503	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2504	xfs are fully working) libev usually gets away without polling.
1643		2505
1644	(There is no support for kqueue, as apparently it cannot be used to	2506	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	2507	implement this functionality, due to the requirement of having a file
1646	descriptor open on the object at all times).	2508	descriptor open on the object at all times, and detecting renames, unlinks
		2509	etc. is difficult.
		2510
		2511	=head3 C<stat ()> is a synchronous operation
		2512
		2513	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2514	the process. The exception are C<ev_stat> watchers - those call C<stat
		2515	()>, which is a synchronous operation.
		2516
		2517	For local paths, this usually doesn't matter: unless the system is very
		2518	busy or the intervals between stat's are large, a stat call will be fast,
		2519	as the path data is usually in memory already (except when starting the
		2520	watcher).
		2521
		2522	For networked file systems, calling C<stat ()> can block an indefinite
		2523	time due to network issues, and even under good conditions, a stat call
		2524	often takes multiple milliseconds.
		2525
		2526	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2527	paths, although this is fully supported by libev.
1647		2528
1648	=head3 The special problem of stat time resolution	2529	=head3 The special problem of stat time resolution
1649		2530
1650	The C<stat ()> syscall only supports full-second resolution portably, and	2531	The C<stat ()> system call only supports full-second resolution portably,
1651	even on systems where the resolution is higher, many filesystems still	2532	and even on systems where the resolution is higher, most file systems
1652	only support whole seconds.	2533	still only support whole seconds.
1653		2534
1654	That means that, if the time is the only thing that changes, you might	2535	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	2536	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	2537	calls your callback, which does something. When there is another update
1657	the same second, C<ev_stat> will be unable to detect it.	2538	within the same second, C<ev_stat> will be unable to detect unless the
		2539	stat data does change in other ways (e.g. file size).
1658		2540
1659	The solution to this is to delay acting on a change for a second (or till	2541	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>	2542	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>	2543	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	2544	ev_timer_again (loop, w)>).
1663	systems.	2545
		2546	The C<.02> offset is added to work around small timing inconsistencies
		2547	of some operating systems (where the second counter of the current time
		2548	might be be delayed. One such system is the Linux kernel, where a call to
		2549	C<gettimeofday> might return a timestamp with a full second later than
		2550	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2551	update file times then there will be a small window where the kernel uses
		2552	the previous second to update file times but libev might already execute
		2553	the timer callback).
1664		2554
1665	=head3 Watcher-Specific Functions and Data Members	2555	=head3 Watcher-Specific Functions and Data Members
1666		2556
1667	=over 4	2557	=over 4
1668		2558
…		…
1674	C<path>. The C<interval> is a hint on how quickly a change is expected to	2564	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	2565	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	2566	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.	2567	path for as long as the watcher is active.
1678		2568
1679	The callback will be receive C<EV_STAT> when a change was detected,	2569	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	2570	relative to the attributes at the time the watcher was started (or the
1681	last change was detected).	2571	last change was detected).
1682		2572
1683	=item ev_stat_stat (loop, ev_stat *)	2573	=item ev_stat_stat (loop, ev_stat *)
1684		2574
1685	Updates the stat buffer immediately with new values. If you change the	2575	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	2576	watched path in your callback, you could call this function to avoid
1687	detecting this change (while introducing a race condition). Can also be	2577	detecting this change (while introducing a race condition if you are not
1688	useful simply to find out the new values.	2578	the only one changing the path). Can also be useful simply to find out the
		2579	new values.
1689		2580
1690	=item ev_statdata attr [read-only]	2581	=item ev_statdata attr [read-only]
1691		2582
1692	The most-recently detected attributes of the file. Although the type is of	2583	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	2584	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	2585	suitable for your system, but you can only rely on the POSIX-standardised
		2586	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.	2587	some error while C<stat>ing the file.
1696		2588
1697	=item ev_statdata prev [read-only]	2589	=item ev_statdata prev [read-only]
1698		2590
1699	The previous attributes of the file. The callback gets invoked whenever	2591	The previous attributes of the file. The callback gets invoked whenever
1700	C<prev> != C<attr>.	2592	C<prev> != C<attr>, or, more precisely, one or more of these members
		2593	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2594	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1701		2595
1702	=item ev_tstamp interval [read-only]	2596	=item ev_tstamp interval [read-only]
1703		2597
1704	The specified interval.	2598	The specified interval.
1705		2599
1706	=item const char *path [read-only]	2600	=item const char *path [read-only]
1707		2601
1708	The filesystem path that is being watched.	2602	The file system path that is being watched.
1709		2603
1710	=back	2604	=back
1711		2605
1712	=head3 Examples	2606	=head3 Examples
1713		2607
1714	Example: Watch C</etc/passwd> for attribute changes.	2608	Example: Watch C</etc/passwd> for attribute changes.
1715		2609
1716	static void	2610	static void
1717	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2611	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1718	{	2612	{
1719	/* /etc/passwd changed in some way */	2613	/* /etc/passwd changed in some way */
1720	if (w->attr.st_nlink)	2614	if (w->attr.st_nlink)
1721	{	2615	{
1722	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2616	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1723	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2617	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1724	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2618	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1725	}	2619	}
1726	else	2620	else
1727	/* you shalt not abuse printf for puts */	2621	/* you shalt not abuse printf for puts */
1728	puts ("wow, /etc/passwd is not there, expect problems. "	2622	puts ("wow, /etc/passwd is not there, expect problems. "
1729	"if this is windows, they already arrived\n");	2623	"if this is windows, they already arrived\n");
1730	}	2624	}
1731		2625
1732	...	2626	...
1733	ev_stat passwd;	2627	ev_stat passwd;
1734		2628
1735	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2629	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1736	ev_stat_start (loop, &passwd);	2630	ev_stat_start (loop, &passwd);
1737		2631
1738	Example: Like above, but additionally use a one-second delay so we do not	2632	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	2633	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	2634	one might do the work both on C<ev_stat> callback invocation I<and> on
1741	C<ev_timer> callback invocation).	2635	C<ev_timer> callback invocation).
1742		2636
1743	static ev_stat passwd;	2637	static ev_stat passwd;
1744	static ev_timer timer;	2638	static ev_timer timer;
1745		2639
1746	static void	2640	static void
1747	timer_cb (EV_P_ ev_timer *w, int revents)	2641	timer_cb (EV_P_ ev_timer *w, int revents)
1748	{	2642	{
1749	ev_timer_stop (EV_A_ w);	2643	ev_timer_stop (EV_A_ w);
1750		2644
1751	/* now it's one second after the most recent passwd change */	2645	/* now it's one second after the most recent passwd change */
1752	}	2646	}
1753		2647
1754	static void	2648	static void
1755	stat_cb (EV_P_ ev_stat *w, int revents)	2649	stat_cb (EV_P_ ev_stat *w, int revents)
1756	{	2650	{
1757	/* reset the one-second timer */	2651	/* reset the one-second timer */
1758	ev_timer_again (EV_A_ &timer);	2652	ev_timer_again (EV_A_ &timer);
1759	}	2653	}
1760		2654
1761	...	2655	...
1762	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1763	ev_stat_start (loop, &passwd);	2657	ev_stat_start (loop, &passwd);
1764	ev_timer_init (&timer, timer_cb, 0., 1.01);	2658	ev_timer_init (&timer, timer_cb, 0., 1.02);
1765		2659
1766		2660
1767	=head2 C<ev_idle> - when you've got nothing better to do...	2661	=head2 C<ev_idle> - when you've got nothing better to do...
1768		2662
1769	Idle watchers trigger events when no other events of the same or higher	2663	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	2664	priority are pending (prepare, check and other idle watchers do not count
1771	count).	2665	as receiving "events").
1772		2666
1773	That is, as long as your process is busy handling sockets or timeouts	2667	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	2668	(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	2669	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	2670	are pending), the idle watchers are being called once per event loop
…		…
1787		2681
1788	=head3 Watcher-Specific Functions and Data Members	2682	=head3 Watcher-Specific Functions and Data Members
1789		2683
1790	=over 4	2684	=over 4
1791		2685
1792	=item ev_idle_init (ev_signal *, callback)	2686	=item ev_idle_init (ev_idle *, callback)
1793		2687
1794	Initialises and configures the idle watcher - it has no parameters of any	2688	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,	2689	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1796	believe me.	2690	believe me.
1797		2691
…		…
1800	=head3 Examples	2694	=head3 Examples
1801		2695
1802	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2696	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1803	callback, free it. Also, use no error checking, as usual.	2697	callback, free it. Also, use no error checking, as usual.
1804		2698
1805	static void	2699	static void
1806	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2700	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1807	{	2701	{
1808	free (w);	2702	free (w);
1809	// now do something you wanted to do when the program has	2703	// now do something you wanted to do when the program has
1810	// no longer anything immediate to do.	2704	// no longer anything immediate to do.
1811	}	2705	}
1812		2706
1813	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2707	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1814	ev_idle_init (idle_watcher, idle_cb);	2708	ev_idle_init (idle_watcher, idle_cb);
1815	ev_idle_start (loop, idle_cb);	2709	ev_idle_start (loop, idle_watcher);
1816		2710
1817		2711
1818	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1819		2713
1820	Prepare and check watchers are usually (but not always) used in tandem:	2714	Prepare and check watchers are usually (but not always) used in pairs:
1821	prepare watchers get invoked before the process blocks and check watchers	2715	prepare watchers get invoked before the process blocks and check watchers
1822	afterwards.	2716	afterwards.
1823		2717
1824	You I<must not> call C<ev_loop> or similar functions that enter	2718	You I<must not> call C<ev_run> or similar functions that enter
1825	the current event loop from either C<ev_prepare> or C<ev_check>	2719	the current event loop from either C<ev_prepare> or C<ev_check>
1826	watchers. Other loops than the current one are fine, however. The	2720	watchers. Other loops than the current one are fine, however. The
1827	rationale behind this is that you do not need to check for recursion in	2721	rationale behind this is that you do not need to check for recursion in
1828	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2722	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	2723	C<ev_check> so if you have one watcher of each kind they will always be
1830	called in pairs bracketing the blocking call.	2724	called in pairs bracketing the blocking call.
1831		2725
1832	Their main purpose is to integrate other event mechanisms into libev and	2726	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	2727	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	2728	variable changes, implement your own watchers, integrate net-snmp or a
1835	coroutine library and lots more. They are also occasionally useful if	2729	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,	2730	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>	2731	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1838	watcher).	2732	watcher).
1839		2733
1840	This is done by examining in each prepare call which file descriptors need	2734	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	2735	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	2736	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	2737	libraries provide exactly this functionality). Then, in the check watcher,
1844	any events that occured (by checking the pending status of all watchers	2738	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	2739	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,	2740	I/O and timer callbacks will never actually be called (but must be valid
1847	because you never know, you know?).	2741	nevertheless, because you never know, you know?).
1848		2742
1849	As another example, the Perl Coro module uses these hooks to integrate	2743	As another example, the Perl Coro module uses these hooks to integrate
1850	coroutines into libev programs, by yielding to other active coroutines	2744	coroutines into libev programs, by yielding to other active coroutines
1851	during each prepare and only letting the process block if no coroutines	2745	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	2746	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	2749	loop from blocking if lower-priority coroutines are active, thus mapping
1856	low-priority coroutines to idle/background tasks).	2750	low-priority coroutines to idle/background tasks).
1857		2751
1858	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2752	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	2753	priority, to ensure that they are being run before any other watchers
		2754	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2755
1860	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2756	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	2757	activate ("feed") events into libev. While libev fully supports this, they
1862	supports this, they will be called before other C<ev_check> watchers	2758	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	2759	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	2760	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	2761	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1866	coexist peacefully with others).	2762	others).
1867		2763
1868	=head3 Watcher-Specific Functions and Data Members	2764	=head3 Watcher-Specific Functions and Data Members
1869		2765
1870	=over 4	2766	=over 4
1871		2767
…		…
1873		2769
1874	=item ev_check_init (ev_check *, callback)	2770	=item ev_check_init (ev_check *, callback)
1875		2771
1876	Initialises and configures the prepare or check watcher - they have no	2772	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>	2773	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.	2774	macros, but using them is utterly, utterly, utterly and completely
		2775	pointless.
1879		2776
1880	=back	2777	=back
1881		2778
1882	=head3 Examples	2779	=head3 Examples
1883		2780
1884	There are a number of principal ways to embed other event loops or modules	2781	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	2782	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	2783	(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>	2784	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	2785	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1889	into the Glib event loop).	2786	Glib event loop).
1890		2787
1891	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2788	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	2789	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	2790	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	2791	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.	2792	the callbacks for the IO/timeout watchers might not have been called yet.
1896		2793
1897	static ev_io iow [nfd];	2794	static ev_io iow [nfd];
1898	static ev_timer tw;	2795	static ev_timer tw;
1899		2796
1900	static void	2797	static void
1901	io_cb (ev_loop *loop, ev_io *w, int revents)	2798	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1902	{	2799	{
1903	}	2800	}
1904		2801
1905	// create io watchers for each fd and a timer before blocking	2802	// create io watchers for each fd and a timer before blocking
1906	static void	2803	static void
1907	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2804	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1908	{	2805	{
1909	int timeout = 3600000;	2806	int timeout = 3600000;
1910	struct pollfd fds [nfd];	2807	struct pollfd fds [nfd];
1911	// actual code will need to loop here and realloc etc.	2808	// actual code will need to loop here and realloc etc.
1912	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2809	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1913		2810
1914	/* the callback is illegal, but won't be called as we stop during check */	2811	/* the callback is illegal, but won't be called as we stop during check */
1915	ev_timer_init (&tw, 0, timeout * 1e-3);	2812	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1916	ev_timer_start (loop, &tw);	2813	ev_timer_start (loop, &tw);
1917		2814
1918	// create one ev_io per pollfd	2815	// create one ev_io per pollfd
1919	for (int i = 0; i < nfd; ++i)	2816	for (int i = 0; i < nfd; ++i)
1920	{	2817	{
1921	ev_io_init (iow + i, io_cb, fds [i].fd,	2818	ev_io_init (iow + i, io_cb, fds [i].fd,
1922	((fds [i].events & POLLIN ? EV_READ : 0)	2819	((fds [i].events & POLLIN ? EV_READ : 0)
1923	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2820	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1924		2821
1925	fds [i].revents = 0;	2822	fds [i].revents = 0;
1926	ev_io_start (loop, iow + i);	2823	ev_io_start (loop, iow + i);
1927	}	2824	}
1928	}	2825	}
1929		2826
1930	// stop all watchers after blocking	2827	// stop all watchers after blocking
1931	static void	2828	static void
1932	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2829	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1933	{	2830	{
1934	ev_timer_stop (loop, &tw);	2831	ev_timer_stop (loop, &tw);
1935		2832
1936	for (int i = 0; i < nfd; ++i)	2833	for (int i = 0; i < nfd; ++i)
1937	{	2834	{
1938	// set the relevant poll flags	2835	// set the relevant poll flags
1939	// could also call adns_processreadable etc. here	2836	// could also call adns_processreadable etc. here
1940	struct pollfd *fd = fds + i;	2837	struct pollfd *fd = fds + i;
1941	int revents = ev_clear_pending (iow + i);	2838	int revents = ev_clear_pending (iow + i);
1942	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2839	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1943	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2840	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1944		2841
1945	// now stop the watcher	2842	// now stop the watcher
1946	ev_io_stop (loop, iow + i);	2843	ev_io_stop (loop, iow + i);
1947	}	2844	}
1948		2845
1949	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2846	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1950	}	2847	}
1951		2848
1952	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2849	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.	2850	in the prepare watcher and would dispose of the check watcher.
1954		2851
1955	Method 3: If the module to be embedded supports explicit event	2852	Method 3: If the module to be embedded supports explicit event
1956	notification (adns does), you can also make use of the actual watcher	2853	notification (libadns does), you can also make use of the actual watcher
1957	callbacks, and only destroy/create the watchers in the prepare watcher.	2854	callbacks, and only destroy/create the watchers in the prepare watcher.
1958		2855
1959	static void	2856	static void
1960	timer_cb (EV_P_ ev_timer *w, int revents)	2857	timer_cb (EV_P_ ev_timer *w, int revents)
1961	{	2858	{
1962	adns_state ads = (adns_state)w->data;	2859	adns_state ads = (adns_state)w->data;
1963	update_now (EV_A);	2860	update_now (EV_A);
1964		2861
1965	adns_processtimeouts (ads, &tv_now);	2862	adns_processtimeouts (ads, &tv_now);
1966	}	2863	}
1967		2864
1968	static void	2865	static void
1969	io_cb (EV_P_ ev_io *w, int revents)	2866	io_cb (EV_P_ ev_io *w, int revents)
1970	{	2867	{
1971	adns_state ads = (adns_state)w->data;	2868	adns_state ads = (adns_state)w->data;
1972	update_now (EV_A);	2869	update_now (EV_A);
1973		2870
1974	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2871	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1975	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2872	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1976	}	2873	}
1977		2874
1978	// do not ever call adns_afterpoll	2875	// do not ever call adns_afterpoll
1979		2876
1980	Method 4: Do not use a prepare or check watcher because the module you	2877	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	2878	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	2879	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	2880	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1984	this.	2881	this approach, effectively embedding EV as a client into the horrible
		2882	libglib event loop.
1985		2883
1986	static gint	2884	static gint
1987	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2885	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1988	{	2886	{
1989	int got_events = 0;	2887	int got_events = 0;
1990		2888
1991	for (n = 0; n < nfds; ++n)	2889	for (n = 0; n < nfds; ++n)
1992	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2890	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1993		2891
1994	if (timeout >= 0)	2892	if (timeout >= 0)
1995	// create/start timer	2893	// create/start timer
1996		2894
1997	// poll	2895	// poll
1998	ev_loop (EV_A_ 0);	2896	ev_run (EV_A_ 0);
1999		2897
2000	// stop timer again	2898	// stop timer again
2001	if (timeout >= 0)	2899	if (timeout >= 0)
2002	ev_timer_stop (EV_A_ &to);	2900	ev_timer_stop (EV_A_ &to);
2003		2901
2004	// stop io watchers again - their callbacks should have set	2902	// stop io watchers again - their callbacks should have set
2005	for (n = 0; n < nfds; ++n)	2903	for (n = 0; n < nfds; ++n)
2006	ev_io_stop (EV_A_ iow [n]);	2904	ev_io_stop (EV_A_ iow [n]);
2007		2905
2008	return got_events;	2906	return got_events;
2009	}	2907	}
2010		2908
2011		2909
2012	=head2 C<ev_embed> - when one backend isn't enough...	2910	=head2 C<ev_embed> - when one backend isn't enough...
2013		2911
2014	This is a rather advanced watcher type that lets you embed one event loop	2912	This is a rather advanced watcher type that lets you embed one event loop
…		…
2020	prioritise I/O.	2918	prioritise I/O.
2021		2919
2022	As an example for a bug workaround, the kqueue backend might only support	2920	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	2921	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	2922	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	2923	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	2924	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	2925	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.	2926	C<kevent>, but at least you can use both mechanisms for what they are
		2927	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2029		2928
2030	As for prioritising I/O: rarely you have the case where some fds have	2929	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	2930	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	2931	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	2932	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.	2933	the rest in a second one, and embed the second one in the first.
2035		2934
2036	As long as the watcher is active, the callback will be invoked every time	2935	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	2936	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	2937	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	2938	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	2939	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	2940	to give the embedded loop strictly lower priority for example).
2042	embedded loop sweep.
2043		2941
2044	As long as the watcher is started it will automatically handle events. The	2942	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	2943	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		2944
2049	Also, there have not currently been made special provisions for forking:	2945	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,	2946	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	2947	embedding loop forks. In other cases, the user is responsible for calling
2052	yourself.	2948	C<ev_loop_fork> on the embedded loop.
2053		2949
2054	Unfortunately, not all backends are embeddable, only the ones returned by	2950	Unfortunately, not all backends are embeddable: only the ones returned by
2055	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2951	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2056	portable one.	2952	portable one.
2057		2953
2058	So when you want to use this feature you will always have to be prepared	2954	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	2955	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	2956	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.	2957	create it, and if that fails, use the normal loop for everything.
2062		2958
		2959	=head3 C<ev_embed> and fork
		2960
		2961	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2962	automatically be applied to the embedded loop as well, so no special
		2963	fork handling is required in that case. When the watcher is not running,
		2964	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2965	as applicable.
		2966
2063	=head3 Watcher-Specific Functions and Data Members	2967	=head3 Watcher-Specific Functions and Data Members
2064		2968
2065	=over 4	2969	=over 4
2066		2970
2067	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2971	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2070		2974
2071	Configures the watcher to embed the given loop, which must be	2975	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	2976	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	2977	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,	2978	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).	2979	if you do not want that, you need to temporarily stop the embed watcher).
2076		2980
2077	=item ev_embed_sweep (loop, ev_embed *)	2981	=item ev_embed_sweep (loop, ev_embed *)
2078		2982
2079	Make a single, non-blocking sweep over the embedded loop. This works	2983	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	2984	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2081	apropriate way for embedded loops.	2985	appropriate way for embedded loops.
2082		2986
2083	=item struct ev_loop *other [read-only]	2987	=item struct ev_loop *other [read-only]
2084		2988
2085	The embedded event loop.	2989	The embedded event loop.
2086		2990
…		…
2088		2992
2089	=head3 Examples	2993	=head3 Examples
2090		2994
2091	Example: Try to get an embeddable event loop and embed it into the default	2995	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	2996	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	2997	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	2998	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2095	used).	2999	used).
2096		3000
2097	struct ev_loop *loop_hi = ev_default_init (0);	3001	struct ev_loop *loop_hi = ev_default_init (0);
2098	struct ev_loop *loop_lo = 0;	3002	struct ev_loop *loop_lo = 0;
2099	struct ev_embed embed;	3003	ev_embed embed;
2100		3004
2101	// see if there is a chance of getting one that works	3005	// see if there is a chance of getting one that works
2102	// (remember that a flags value of 0 means autodetection)	3006	// (remember that a flags value of 0 means autodetection)
2103	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3007	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2104	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3008	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2105	: 0;	3009	: 0;
2106		3010
2107	// if we got one, then embed it, otherwise default to loop_hi	3011	// if we got one, then embed it, otherwise default to loop_hi
2108	if (loop_lo)	3012	if (loop_lo)
2109	{	3013	{
2110	ev_embed_init (&embed, 0, loop_lo);	3014	ev_embed_init (&embed, 0, loop_lo);
2111	ev_embed_start (loop_hi, &embed);	3015	ev_embed_start (loop_hi, &embed);
2112	}	3016	}
2113	else	3017	else
2114	loop_lo = loop_hi;	3018	loop_lo = loop_hi;
2115		3019
2116	Example: Check if kqueue is available but not recommended and create	3020	Example: Check if kqueue is available but not recommended and create
2117	a kqueue backend for use with sockets (which usually work with any	3021	a kqueue backend for use with sockets (which usually work with any
2118	kqueue implementation). Store the kqueue/socket-only event loop in	3022	kqueue implementation). Store the kqueue/socket-only event loop in
2119	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3023	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2120		3024
2121	struct ev_loop *loop = ev_default_init (0);	3025	struct ev_loop *loop = ev_default_init (0);
2122	struct ev_loop *loop_socket = 0;	3026	struct ev_loop *loop_socket = 0;
2123	struct ev_embed embed;	3027	ev_embed embed;
2124		3028
2125	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3029	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2126	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3030	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2127	{	3031	{
2128	ev_embed_init (&embed, 0, loop_socket);	3032	ev_embed_init (&embed, 0, loop_socket);
2129	ev_embed_start (loop, &embed);	3033	ev_embed_start (loop, &embed);
2130	}	3034	}
2131		3035
2132	if (!loop_socket)	3036	if (!loop_socket)
2133	loop_socket = loop;	3037	loop_socket = loop;
2134		3038
2135	// now use loop_socket for all sockets, and loop for everything else	3039	// now use loop_socket for all sockets, and loop for everything else
2136		3040
2137		3041
2138	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3042	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2139		3043
2140	Fork watchers are called when a C<fork ()> was detected (usually because	3044	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,	3047	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	3048	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	3049	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2146	handlers will be invoked, too, of course.	3050	handlers will be invoked, too, of course.
2147		3051
		3052	=head3 The special problem of life after fork - how is it possible?
		3053
		3054	Most uses of C<fork()> consist of forking, then some simple calls to set
		3055	up/change the process environment, followed by a call to C<exec()>. This
		3056	sequence should be handled by libev without any problems.
		3057
		3058	This changes when the application actually wants to do event handling
		3059	in the child, or both parent in child, in effect "continuing" after the
		3060	fork.
		3061
		3062	The default mode of operation (for libev, with application help to detect
		3063	forks) is to duplicate all the state in the child, as would be expected
		3064	when I<either> the parent I<or> the child process continues.
		3065
		3066	When both processes want to continue using libev, then this is usually the
		3067	wrong result. In that case, usually one process (typically the parent) is
		3068	supposed to continue with all watchers in place as before, while the other
		3069	process typically wants to start fresh, i.e. without any active watchers.
		3070
		3071	The cleanest and most efficient way to achieve that with libev is to
		3072	simply create a new event loop, which of course will be "empty", and
		3073	use that for new watchers. This has the advantage of not touching more
		3074	memory than necessary, and thus avoiding the copy-on-write, and the
		3075	disadvantage of having to use multiple event loops (which do not support
		3076	signal watchers).
		3077
		3078	When this is not possible, or you want to use the default loop for
		3079	other reasons, then in the process that wants to start "fresh", call
		3080	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		3081	the default loop will "orphan" (not stop) all registered watchers, so you
		3082	have to be careful not to execute code that modifies those watchers. Note
		3083	also that in that case, you have to re-register any signal watchers.
		3084
2148	=head3 Watcher-Specific Functions and Data Members	3085	=head3 Watcher-Specific Functions and Data Members
2149		3086
2150	=over 4	3087	=over 4
2151		3088
2152	=item ev_fork_init (ev_signal *, callback)	3089	=item ev_fork_init (ev_signal *, callback)
…		…
2156	believe me.	3093	believe me.
2157		3094
2158	=back	3095	=back
2159		3096
2160		3097
2161	=head2 C<ev_async> - how to wake up another event loop	3098	=head2 C<ev_async> - how to wake up an event loop
2162		3099
2163	In general, you cannot use an C<ev_loop> from multiple threads or other	3100	In general, you cannot use an C<ev_run> from multiple threads or other
2164	asynchronous sources such as signal handlers (as opposed to multiple event	3101	asynchronous sources such as signal handlers (as opposed to multiple event
2165	loops - those are of course safe to use in different threads).	3102	loops - those are of course safe to use in different threads).
2166		3103
2167	Sometimes, however, you need to wake up another event loop you do not	3104	Sometimes, however, you need to wake up an event loop you do not control,
2168	control, for example because it belongs to another thread. This is what	3105	for example because it belongs to another thread. This is what C<ev_async>
2169	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3106	watchers do: as long as the C<ev_async> watcher is active, you can signal
2170	can signal it by calling C<ev_async_send>, which is thread- and signal	3107	it by calling C<ev_async_send>, which is thread- and signal safe.
2171	safe.
2172		3108
2173	This functionality is very similar to C<ev_signal> watchers, as signals,	3109	This functionality is very similar to C<ev_signal> watchers, as signals,
2174	too, are asynchronous in nature, and signals, too, will be compressed	3110	too, are asynchronous in nature, and signals, too, will be compressed
2175	(i.e. the number of callback invocations may be less than the number of	3111	(i.e. the number of callback invocations may be less than the number of
2176	C<ev_async_sent> calls).	3112	C<ev_async_sent> calls).
…		…
2181	=head3 Queueing	3117	=head3 Queueing
2182		3118
2183	C<ev_async> does not support queueing of data in any way. The reason	3119	C<ev_async> does not support queueing of data in any way. The reason
2184	is that the author does not know of a simple (or any) algorithm for a	3120	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	3121	multiple-writer-single-reader queue that works in all cases and doesn't
2186	need elaborate support such as pthreads.	3122	need elaborate support such as pthreads or unportable memory access
		3123	semantics.
2187		3124
2188	That means that if you want to queue data, you have to provide your own	3125	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	3126	queue. But at least I can tell you how to implement locking around your
2190	queue:	3127	queue:
2191		3128
2192	=over 4	3129	=over 4
2193		3130
2194	=item queueing from a signal handler context	3131	=item queueing from a signal handler context
2195		3132
2196	To implement race-free queueing, you simply add to the queue in the signal	3133	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	3134	handler but you block the signal handler in the watcher callback. Here is
2198	some fictitiuous SIGUSR1 handler:	3135	an example that does that for some fictitious SIGUSR1 handler:
2199		3136
2200	static ev_async mysig;	3137	static ev_async mysig;
2201		3138
2202	static void	3139	static void
2203	sigusr1_handler (void)	3140	sigusr1_handler (void)
…		…
2269	=over 4	3206	=over 4
2270		3207
2271	=item ev_async_init (ev_async *, callback)	3208	=item ev_async_init (ev_async *, callback)
2272		3209
2273	Initialises and configures the async watcher - it has no parameters of any	3210	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,	3211	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2275	believe me.	3212	trust me.
2276		3213
2277	=item ev_async_send (loop, ev_async *)	3214	=item ev_async_send (loop, ev_async *)
2278		3215
2279	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3216	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	3217	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	3218	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	3219	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2283	section below on what exactly this means).	3220	section below on what exactly this means).
2284		3221
		3222	Note that, as with other watchers in libev, multiple events might get
		3223	compressed into a single callback invocation (another way to look at this
		3224	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3225	reset when the event loop detects that).
		3226
2285	This call incurs the overhead of a syscall only once per loop iteration,	3227	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	3228	iteration, so while the overhead might be noticeable, it doesn't apply to
2287	calls to C<ev_async_send>.	3229	repeated calls to C<ev_async_send> for the same event loop.
2288		3230
2289	=item bool = ev_async_pending (ev_async *)	3231	=item bool = ev_async_pending (ev_async *)
2290		3232
2291	Returns a non-zero value when C<ev_async_send> has been called on the	3233	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	3234	watcher but the event has not yet been processed (or even noted) by the
2293	event loop.	3235	event loop.
2294		3236
2295	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3237	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,	3238	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	3239	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.	3240	quickly check whether invoking the loop might be a good idea.
2299		3241
2300	Not that this does I<not> check wether the watcher itself is pending, only	3242	Not that this does I<not> check whether the watcher itself is pending,
2301	wether it has been requested to make this watcher pending.	3243	only whether it has been requested to make this watcher pending: there
		3244	is a time window between the event loop checking and resetting the async
		3245	notification, and the callback being invoked.
2302		3246
2303	=back	3247	=back
2304		3248
2305		3249
2306	=head1 OTHER FUNCTIONS	3250	=head1 OTHER FUNCTIONS
…		…
2310	=over 4	3254	=over 4
2311		3255
2312	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3256	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2313		3257
2314	This function combines a simple timer and an I/O watcher, calls your	3258	This function combines a simple timer and an I/O watcher, calls your
2315	callback on whichever event happens first and automatically stop both	3259	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	3260	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	3261	or timeout without having to allocate/configure/start/stop/free one or
2318	more watchers yourself.	3262	more watchers yourself.
2319		3263
2320	If C<fd> is less than 0, then no I/O watcher will be started and events	3264	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	3265	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2322	C<events> set will be craeted and started.	3266	the given C<fd> and C<events> set will be created and started.
2323		3267
2324	If C<timeout> is less than 0, then no timeout watcher will be	3268	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	3269	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	3270	repeat = 0) will be started. C<0> is a valid timeout.
2327	dubious value.
2328		3271
2329	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3272	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2330	passed an C<revents> set like normal event callbacks (a combination of	3273	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>	3274	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2332	value passed to C<ev_once>:	3275	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3276	a timeout and an io event at the same time - you probably should give io
		3277	events precedence.
2333		3278
		3279	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3280
2334	static void stdin_ready (int revents, void *arg)	3281	static void stdin_ready (int revents, void *arg)
2335	{	3282	{
2336	if (revents & EV_TIMEOUT)
2337	/* doh, nothing entered */;
2338	else if (revents & EV_READ)	3283	if (revents & EV_READ)
2339	/* stdin might have data for us, joy! */;	3284	/* stdin might have data for us, joy! */;
		3285	else if (revents & EV_TIMER)
		3286	/* doh, nothing entered */;
2340	}	3287	}
2341		3288
2342	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3289	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2343		3290
2344	=item ev_feed_event (ev_loop *, watcher *, int revents)
2345
2346	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
2348	initialised but not necessarily started event watcher).
2349
2350	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3291	=item ev_feed_fd_event (loop, int fd, int revents)
2351		3292
2352	Feed an event on the given fd, as if a file descriptor backend detected	3293	Feed an event on the given fd, as if a file descriptor backend detected
2353	the given events it.	3294	the given events it.
2354		3295
2355	=item ev_feed_signal_event (ev_loop *loop, int signum)	3296	=item ev_feed_signal_event (loop, int signum)
2356		3297
2357	Feed an event as if the given signal occured (C<loop> must be the default	3298	Feed an event as if the given signal occurred (C<loop> must be the default
2358	loop!).	3299	loop!).
2359		3300
2360	=back	3301	=back
2361		3302
2362		3303
…		…
2391	=back	3332	=back
2392		3333
2393	=head1 C++ SUPPORT	3334	=head1 C++ SUPPORT
2394		3335
2395	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3336	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2396	you to use some convinience methods to start/stop watchers and also change	3337	you to use some convenience methods to start/stop watchers and also change
2397	the callback model to a model using method callbacks on objects.	3338	the callback model to a model using method callbacks on objects.
2398		3339
2399	To use it,	3340	To use it,
2400		3341
2401	#include <ev++.h>	3342	#include <ev++.h>
2402		3343
2403	This automatically includes F<ev.h> and puts all of its definitions (many	3344	This automatically includes F<ev.h> and puts all of its definitions (many
2404	of them macros) into the global namespace. All C++ specific things are	3345	of them macros) into the global namespace. All C++ specific things are
2405	put into the C<ev> namespace. It should support all the same embedding	3346	put into the C<ev> namespace. It should support all the same embedding
2406	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3347	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2440		3381
2441	=over 4	3382	=over 4
2442		3383
2443	=item ev::TYPE::TYPE ()	3384	=item ev::TYPE::TYPE ()
2444		3385
2445	=item ev::TYPE::TYPE (struct ev_loop *)	3386	=item ev::TYPE::TYPE (loop)
2446		3387
2447	=item ev::TYPE::~TYPE	3388	=item ev::TYPE::~TYPE
2448		3389
2449	The constructor (optionally) takes an event loop to associate the watcher	3390	The constructor (optionally) takes an event loop to associate the watcher
2450	with. If it is omitted, it will use C<EV_DEFAULT>.	3391	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2473	your compiler is good :), then the method will be fully inlined into the	3414	your compiler is good :), then the method will be fully inlined into the
2474	thunking function, making it as fast as a direct C callback.	3415	thunking function, making it as fast as a direct C callback.
2475		3416
2476	Example: simple class declaration and watcher initialisation	3417	Example: simple class declaration and watcher initialisation
2477		3418
2478	struct myclass	3419	struct myclass
2479	{	3420	{
2480	void io_cb (ev::io &w, int revents) { }	3421	void io_cb (ev::io &w, int revents) { }
2481	}	3422	}
2482		3423
2483	myclass obj;	3424	myclass obj;
2484	ev::io iow;	3425	ev::io iow;
2485	iow.set <myclass, &myclass::io_cb> (&obj);	3426	iow.set <myclass, &myclass::io_cb> (&obj);
		3427
		3428	=item w->set (object *)
		3429
		3430	This is a variation of a method callback - leaving out the method to call
		3431	will default the method to C<operator ()>, which makes it possible to use
		3432	functor objects without having to manually specify the C<operator ()> all
		3433	the time. Incidentally, you can then also leave out the template argument
		3434	list.
		3435
		3436	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3437	int revents)>.
		3438
		3439	See the method-C<set> above for more details.
		3440
		3441	Example: use a functor object as callback.
		3442
		3443	struct myfunctor
		3444	{
		3445	void operator() (ev::io &w, int revents)
		3446	{
		3447	...
		3448	}
		3449	}
		3450
		3451	myfunctor f;
		3452
		3453	ev::io w;
		3454	w.set (&f);
2486		3455
2487	=item w->set<function> (void *data = 0)	3456	=item w->set<function> (void *data = 0)
2488		3457
2489	Also sets a callback, but uses a static method or plain function as	3458	Also sets a callback, but uses a static method or plain function as
2490	callback. The optional C<data> argument will be stored in the watcher's	3459	callback. The optional C<data> argument will be stored in the watcher's
…		…
2492		3461
2493	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3462	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2494		3463
2495	See the method-C<set> above for more details.	3464	See the method-C<set> above for more details.
2496		3465
2497	Example:	3466	Example: Use a plain function as callback.
2498		3467
2499	static void io_cb (ev::io &w, int revents) { }	3468	static void io_cb (ev::io &w, int revents) { }
2500	iow.set <io_cb> ();	3469	iow.set <io_cb> ();
2501		3470
2502	=item w->set (struct ev_loop *)	3471	=item w->set (loop)
2503		3472
2504	Associates a different C<struct ev_loop> with this watcher. You can only	3473	Associates a different C<struct ev_loop> with this watcher. You can only
2505	do this when the watcher is inactive (and not pending either).	3474	do this when the watcher is inactive (and not pending either).
2506		3475
2507	=item w->set ([args])	3476	=item w->set ([arguments])
2508		3477
2509	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3478	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2510	called at least once. Unlike the C counterpart, an active watcher gets	3479	method or a suitable start method must be called at least once. Unlike the
2511	automatically stopped and restarted when reconfiguring it with this	3480	C counterpart, an active watcher gets automatically stopped and restarted
2512	method.	3481	when reconfiguring it with this method.
2513		3482
2514	=item w->start ()	3483	=item w->start ()
2515		3484
2516	Starts the watcher. Note that there is no C<loop> argument, as the	3485	Starts the watcher. Note that there is no C<loop> argument, as the
2517	constructor already stores the event loop.	3486	constructor already stores the event loop.
2518		3487
		3488	=item w->start ([arguments])
		3489
		3490	Instead of calling C<set> and C<start> methods separately, it is often
		3491	convenient to wrap them in one call. Uses the same type of arguments as
		3492	the configure C<set> method of the watcher.
		3493
2519	=item w->stop ()	3494	=item w->stop ()
2520		3495
2521	Stops the watcher if it is active. Again, no C<loop> argument.	3496	Stops the watcher if it is active. Again, no C<loop> argument.
2522		3497
2523	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3498	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2535		3510
2536	=back	3511	=back
2537		3512
2538	=back	3513	=back
2539		3514
2540	Example: Define a class with an IO and idle watcher, start one of them in	3515	Example: Define a class with two I/O and idle watchers, start the I/O
2541	the constructor.	3516	watchers in the constructor.
2542		3517
2543	class myclass	3518	class myclass
2544	{	3519	{
2545	ev::io io; void io_cb (ev::io &w, int revents);	3520	ev::io io ; void io_cb (ev::io &w, int revents);
		3521	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2546	ev:idle idle void idle_cb (ev::idle &w, int revents);	3522	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2547		3523
2548	myclass (int fd)	3524	myclass (int fd)
2549	{	3525	{
2550	io .set <myclass, &myclass::io_cb > (this);	3526	io .set <myclass, &myclass::io_cb > (this);
		3527	io2 .set <myclass, &myclass::io2_cb > (this);
2551	idle.set <myclass, &myclass::idle_cb> (this);	3528	idle.set <myclass, &myclass::idle_cb> (this);
2552		3529
2553	io.start (fd, ev::READ);	3530	io.set (fd, ev::WRITE); // configure the watcher
		3531	io.start (); // start it whenever convenient
		3532
		3533	io2.start (fd, ev::READ); // set + start in one call
2554	}	3534	}
2555	};	3535	};
2556		3536
2557		3537
2558	=head1 OTHER LANGUAGE BINDINGS	3538	=head1 OTHER LANGUAGE BINDINGS
2559		3539
2560	Libev does not offer other language bindings itself, but bindings for a	3540	Libev does not offer other language bindings itself, but bindings for a
2561	numbe rof languages exist in the form of third-party packages. If you know	3541	number of languages exist in the form of third-party packages. If you know
2562	any interesting language binding in addition to the ones listed here, drop	3542	any interesting language binding in addition to the ones listed here, drop
2563	me a note.	3543	me a note.
2564		3544
2565	=over 4	3545	=over 4
2566		3546
2567	=item Perl	3547	=item Perl
2568		3548
2569	The EV module implements the full libev API and is actually used to test	3549	The EV module implements the full libev API and is actually used to test
2570	libev. EV is developed together with libev. Apart from the EV core module,	3550	libev. EV is developed together with libev. Apart from the EV core module,
2571	there are additional modules that implement libev-compatible interfaces	3551	there are additional modules that implement libev-compatible interfaces
2572	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3552	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2573	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3553	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3554	and C<EV::Glib>).
2574		3555
2575	It can be found and installed via CPAN, its homepage is found at	3556	It can be found and installed via CPAN, its homepage is at
2576	L<http://software.schmorp.de/pkg/EV>.	3557	L<http://software.schmorp.de/pkg/EV>.
2577		3558
		3559	=item Python
		3560
		3561	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3562	seems to be quite complete and well-documented.
		3563
2578	=item Ruby	3564	=item Ruby
2579		3565
2580	Tony Arcieri has written a ruby extension that offers access to a subset	3566	Tony Arcieri has written a ruby extension that offers access to a subset
2581	of the libev API and adds filehandle abstractions, asynchronous DNS and	3567	of the libev API and adds file handle abstractions, asynchronous DNS and
2582	more on top of it. It can be found via gem servers. Its homepage is at	3568	more on top of it. It can be found via gem servers. Its homepage is at
2583	L<http://rev.rubyforge.org/>.	3569	L<http://rev.rubyforge.org/>.
2584		3570
		3571	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3572	makes rev work even on mingw.
		3573
		3574	=item Haskell
		3575
		3576	A haskell binding to libev is available at
		3577	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3578
2585	=item D	3579	=item D
2586		3580
2587	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3581	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2588	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3582	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3583
		3584	=item Ocaml
		3585
		3586	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3587	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3588
		3589	=item Lua
		3590
		3591	Brian Maher has written a partial interface to libev for lua (at the
		3592	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3593	L<http://github.com/brimworks/lua-ev>.
2589		3594
2590	=back	3595	=back
2591		3596
2592		3597
2593	=head1 MACRO MAGIC	3598	=head1 MACRO MAGIC
2594		3599
2595	Libev can be compiled with a variety of options, the most fundamantal	3600	Libev can be compiled with a variety of options, the most fundamental
2596	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3601	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2597	functions and callbacks have an initial C<struct ev_loop *> argument.	3602	functions and callbacks have an initial C<struct ev_loop *> argument.
2598		3603
2599	To make it easier to write programs that cope with either variant, the	3604	To make it easier to write programs that cope with either variant, the
2600	following macros are defined:	3605	following macros are defined:
…		…
2605		3610
2606	This provides the loop I<argument> for functions, if one is required ("ev	3611	This provides the loop I<argument> for functions, if one is required ("ev
2607	loop argument"). The C<EV_A> form is used when this is the sole argument,	3612	loop argument"). The C<EV_A> form is used when this is the sole argument,
2608	C<EV_A_> is used when other arguments are following. Example:	3613	C<EV_A_> is used when other arguments are following. Example:
2609		3614
2610	ev_unref (EV_A);	3615	ev_unref (EV_A);
2611	ev_timer_add (EV_A_ watcher);	3616	ev_timer_add (EV_A_ watcher);
2612	ev_loop (EV_A_ 0);	3617	ev_run (EV_A_ 0);
2613		3618
2614	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3619	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2615	which is often provided by the following macro.	3620	which is often provided by the following macro.
2616		3621
2617	=item C<EV_P>, C<EV_P_>	3622	=item C<EV_P>, C<EV_P_>
2618		3623
2619	This provides the loop I<parameter> for functions, if one is required ("ev	3624	This provides the loop I<parameter> for functions, if one is required ("ev
2620	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3625	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2621	C<EV_P_> is used when other parameters are following. Example:	3626	C<EV_P_> is used when other parameters are following. Example:
2622		3627
2623	// this is how ev_unref is being declared	3628	// this is how ev_unref is being declared
2624	static void ev_unref (EV_P);	3629	static void ev_unref (EV_P);
2625		3630
2626	// this is how you can declare your typical callback	3631	// this is how you can declare your typical callback
2627	static void cb (EV_P_ ev_timer *w, int revents)	3632	static void cb (EV_P_ ev_timer *w, int revents)
2628		3633
2629	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3634	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2630	suitable for use with C<EV_A>.	3635	suitable for use with C<EV_A>.
2631		3636
2632	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3637	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
…		…
2648		3653
2649	Example: Declare and initialise a check watcher, utilising the above	3654	Example: Declare and initialise a check watcher, utilising the above
2650	macros so it will work regardless of whether multiple loops are supported	3655	macros so it will work regardless of whether multiple loops are supported
2651	or not.	3656	or not.
2652		3657
2653	static void	3658	static void
2654	check_cb (EV_P_ ev_timer *w, int revents)	3659	check_cb (EV_P_ ev_timer *w, int revents)
2655	{	3660	{
2656	ev_check_stop (EV_A_ w);	3661	ev_check_stop (EV_A_ w);
2657	}	3662	}
2658		3663
2659	ev_check check;	3664	ev_check check;
2660	ev_check_init (&check, check_cb);	3665	ev_check_init (&check, check_cb);
2661	ev_check_start (EV_DEFAULT_ &check);	3666	ev_check_start (EV_DEFAULT_ &check);
2662	ev_loop (EV_DEFAULT_ 0);	3667	ev_run (EV_DEFAULT_ 0);
2663		3668
2664	=head1 EMBEDDING	3669	=head1 EMBEDDING
2665		3670
2666	Libev can (and often is) directly embedded into host	3671	Libev can (and often is) directly embedded into host
2667	applications. Examples of applications that embed it include the Deliantra	3672	applications. Examples of applications that embed it include the Deliantra
…		…
2674	libev somewhere in your source tree).	3679	libev somewhere in your source tree).
2675		3680
2676	=head2 FILESETS	3681	=head2 FILESETS
2677		3682
2678	Depending on what features you need you need to include one or more sets of files	3683	Depending on what features you need you need to include one or more sets of files
2679	in your app.	3684	in your application.
2680		3685
2681	=head3 CORE EVENT LOOP	3686	=head3 CORE EVENT LOOP
2682		3687
2683	To include only the libev core (all the C<ev_*> functions), with manual	3688	To include only the libev core (all the C<ev_*> functions), with manual
2684	configuration (no autoconf):	3689	configuration (no autoconf):
2685		3690
2686	#define EV_STANDALONE 1	3691	#define EV_STANDALONE 1
2687	#include "ev.c"	3692	#include "ev.c"
2688		3693
2689	This will automatically include F<ev.h>, too, and should be done in a	3694	This will automatically include F<ev.h>, too, and should be done in a
2690	single C source file only to provide the function implementations. To use	3695	single C source file only to provide the function implementations. To use
2691	it, do the same for F<ev.h> in all files wishing to use this API (best	3696	it, do the same for F<ev.h> in all files wishing to use this API (best
2692	done by writing a wrapper around F<ev.h> that you can include instead and	3697	done by writing a wrapper around F<ev.h> that you can include instead and
2693	where you can put other configuration options):	3698	where you can put other configuration options):
2694		3699
2695	#define EV_STANDALONE 1	3700	#define EV_STANDALONE 1
2696	#include "ev.h"	3701	#include "ev.h"
2697		3702
2698	Both header files and implementation files can be compiled with a C++	3703	Both header files and implementation files can be compiled with a C++
2699	compiler (at least, thats a stated goal, and breakage will be treated	3704	compiler (at least, that's a stated goal, and breakage will be treated
2700	as a bug).	3705	as a bug).
2701		3706
2702	You need the following files in your source tree, or in a directory	3707	You need the following files in your source tree, or in a directory
2703	in your include path (e.g. in libev/ when using -Ilibev):	3708	in your include path (e.g. in libev/ when using -Ilibev):
2704		3709
2705	ev.h	3710	ev.h
2706	ev.c	3711	ev.c
2707	ev_vars.h	3712	ev_vars.h
2708	ev_wrap.h	3713	ev_wrap.h
2709		3714
2710	ev_win32.c required on win32 platforms only	3715	ev_win32.c required on win32 platforms only
2711		3716
2712	ev_select.c only when select backend is enabled (which is enabled by default)	3717	ev_select.c only when select backend is enabled (which is enabled by default)
2713	ev_poll.c only when poll backend is enabled (disabled by default)	3718	ev_poll.c only when poll backend is enabled (disabled by default)
2714	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3719	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2715	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3720	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2716	ev_port.c only when the solaris port backend is enabled (disabled by default)	3721	ev_port.c only when the solaris port backend is enabled (disabled by default)
2717		3722
2718	F<ev.c> includes the backend files directly when enabled, so you only need	3723	F<ev.c> includes the backend files directly when enabled, so you only need
2719	to compile this single file.	3724	to compile this single file.
2720		3725
2721	=head3 LIBEVENT COMPATIBILITY API	3726	=head3 LIBEVENT COMPATIBILITY API
2722		3727
2723	To include the libevent compatibility API, also include:	3728	To include the libevent compatibility API, also include:
2724		3729
2725	#include "event.c"	3730	#include "event.c"
2726		3731
2727	in the file including F<ev.c>, and:	3732	in the file including F<ev.c>, and:
2728		3733
2729	#include "event.h"	3734	#include "event.h"
2730		3735
2731	in the files that want to use the libevent API. This also includes F<ev.h>.	3736	in the files that want to use the libevent API. This also includes F<ev.h>.
2732		3737
2733	You need the following additional files for this:	3738	You need the following additional files for this:
2734		3739
2735	event.h	3740	event.h
2736	event.c	3741	event.c
2737		3742
2738	=head3 AUTOCONF SUPPORT	3743	=head3 AUTOCONF SUPPORT
2739		3744
2740	Instead of using C<EV_STANDALONE=1> and providing your config in	3745	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2741	whatever way you want, you can also C<m4_include([libev.m4])> in your	3746	whatever way you want, you can also C<m4_include([libev.m4])> in your
2742	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3747	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2743	include F<config.h> and configure itself accordingly.	3748	include F<config.h> and configure itself accordingly.
2744		3749
2745	For this of course you need the m4 file:	3750	For this of course you need the m4 file:
2746		3751
2747	libev.m4	3752	libev.m4
2748		3753
2749	=head2 PREPROCESSOR SYMBOLS/MACROS	3754	=head2 PREPROCESSOR SYMBOLS/MACROS
2750		3755
2751	Libev can be configured via a variety of preprocessor symbols you have to	3756	Libev can be configured via a variety of preprocessor symbols you have to
2752	define before including any of its files. The default in the absense of	3757	define before including (or compiling) any of its files. The default in
2753	autoconf is noted for every option.	3758	the absence of autoconf is documented for every option.
		3759
		3760	Symbols marked with "(h)" do not change the ABI, and can have different
		3761	values when compiling libev vs. including F<ev.h>, so it is permissible
		3762	to redefine them before including F<ev.h> without breaking compatibility
		3763	to a compiled library. All other symbols change the ABI, which means all
		3764	users of libev and the libev code itself must be compiled with compatible
		3765	settings.
2754		3766
2755	=over 4	3767	=over 4
2756		3768
		3769	=item EV_COMPAT3 (h)
		3770
		3771	Backwards compatibility is a major concern for libev. This is why this
		3772	release of libev comes with wrappers for the functions and symbols that
		3773	have been renamed between libev version 3 and 4.
		3774
		3775	You can disable these wrappers (to test compatibility with future
		3776	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3777	sources. This has the additional advantage that you can drop the C<struct>
		3778	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3779	typedef in that case.
		3780
		3781	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3782	and in some even more future version the compatibility code will be
		3783	removed completely.
		3784
2757	=item EV_STANDALONE	3785	=item EV_STANDALONE (h)
2758		3786
2759	Must always be C<1> if you do not use autoconf configuration, which	3787	Must always be C<1> if you do not use autoconf configuration, which
2760	keeps libev from including F<config.h>, and it also defines dummy	3788	keeps libev from including F<config.h>, and it also defines dummy
2761	implementations for some libevent functions (such as logging, which is not	3789	implementations for some libevent functions (such as logging, which is not
2762	supported). It will also not define any of the structs usually found in	3790	supported). It will also not define any of the structs usually found in
2763	F<event.h> that are not directly supported by the libev core alone.	3791	F<event.h> that are not directly supported by the libev core alone.
2764		3792
		3793	In standalone mode, libev will still try to automatically deduce the
		3794	configuration, but has to be more conservative.
		3795
2765	=item EV_USE_MONOTONIC	3796	=item EV_USE_MONOTONIC
2766		3797
2767	If defined to be C<1>, libev will try to detect the availability of the	3798	If defined to be C<1>, libev will try to detect the availability of the
2768	monotonic clock option at both compiletime and runtime. Otherwise no use	3799	monotonic clock option at both compile time and runtime. Otherwise no
2769	of the monotonic clock option will be attempted. If you enable this, you	3800	use of the monotonic clock option will be attempted. If you enable this,
2770	usually have to link against librt or something similar. Enabling it when	3801	you usually have to link against librt or something similar. Enabling it
2771	the functionality isn't available is safe, though, although you have	3802	when the functionality isn't available is safe, though, although you have
2772	to make sure you link against any libraries where the C<clock_gettime>	3803	to make sure you link against any libraries where the C<clock_gettime>
2773	function is hiding in (often F<-lrt>).	3804	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2774		3805
2775	=item EV_USE_REALTIME	3806	=item EV_USE_REALTIME
2776		3807
2777	If defined to be C<1>, libev will try to detect the availability of the	3808	If defined to be C<1>, libev will try to detect the availability of the
2778	realtime clock option at compiletime (and assume its availability at	3809	real-time clock option at compile time (and assume its availability
2779	runtime if successful). Otherwise no use of the realtime clock option will	3810	at runtime if successful). Otherwise no use of the real-time clock
2780	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3811	option will be attempted. This effectively replaces C<gettimeofday>
2781	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3812	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2782	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3813	correctness. See the note about libraries in the description of
		3814	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3815	C<EV_USE_CLOCK_SYSCALL>.
		3816
		3817	=item EV_USE_CLOCK_SYSCALL
		3818
		3819	If defined to be C<1>, libev will try to use a direct syscall instead
		3820	of calling the system-provided C<clock_gettime> function. This option
		3821	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3822	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3823	programs needlessly. Using a direct syscall is slightly slower (in
		3824	theory), because no optimised vdso implementation can be used, but avoids
		3825	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3826	higher, as it simplifies linking (no need for C<-lrt>).
2783		3827
2784	=item EV_USE_NANOSLEEP	3828	=item EV_USE_NANOSLEEP
2785		3829
2786	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3830	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2787	and will use it for delays. Otherwise it will use C<select ()>.	3831	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2795	2.7 or newer, otherwise disabled.	3839	2.7 or newer, otherwise disabled.
2796		3840
2797	=item EV_USE_SELECT	3841	=item EV_USE_SELECT
2798		3842
2799	If undefined or defined to be C<1>, libev will compile in support for the	3843	If undefined or defined to be C<1>, libev will compile in support for the
2800	C<select>(2) backend. No attempt at autodetection will be done: if no	3844	C<select>(2) backend. No attempt at auto-detection will be done: if no
2801	other method takes over, select will be it. Otherwise the select backend	3845	other method takes over, select will be it. Otherwise the select backend
2802	will not be compiled in.	3846	will not be compiled in.
2803		3847
2804	=item EV_SELECT_USE_FD_SET	3848	=item EV_SELECT_USE_FD_SET
2805		3849
2806	If defined to C<1>, then the select backend will use the system C<fd_set>	3850	If defined to C<1>, then the select backend will use the system C<fd_set>
2807	structure. This is useful if libev doesn't compile due to a missing	3851	structure. This is useful if libev doesn't compile due to a missing
2808	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3852	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2809	exotic systems. This usually limits the range of file descriptors to some	3853	on exotic systems. This usually limits the range of file descriptors to
2810	low limit such as 1024 or might have other limitations (winsocket only	3854	some low limit such as 1024 or might have other limitations (winsocket
2811	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3855	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2812	influence the size of the C<fd_set> used.	3856	configures the maximum size of the C<fd_set>.
2813		3857
2814	=item EV_SELECT_IS_WINSOCKET	3858	=item EV_SELECT_IS_WINSOCKET
2815		3859
2816	When defined to C<1>, the select backend will assume that	3860	When defined to C<1>, the select backend will assume that
2817	select/socket/connect etc. don't understand file descriptors but	3861	select/socket/connect etc. don't understand file descriptors but
…		…
2819	be used is the winsock select). This means that it will call	3863	be used is the winsock select). This means that it will call
2820	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3864	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2821	it is assumed that all these functions actually work on fds, even	3865	it is assumed that all these functions actually work on fds, even
2822	on win32. Should not be defined on non-win32 platforms.	3866	on win32. Should not be defined on non-win32 platforms.
2823		3867
2824	=item EV_FD_TO_WIN32_HANDLE	3868	=item EV_FD_TO_WIN32_HANDLE(fd)
2825		3869
2826	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3870	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2827	file descriptors to socket handles. When not defining this symbol (the	3871	file descriptors to socket handles. When not defining this symbol (the
2828	default), then libev will call C<_get_osfhandle>, which is usually	3872	default), then libev will call C<_get_osfhandle>, which is usually
2829	correct. In some cases, programs use their own file descriptor management,	3873	correct. In some cases, programs use their own file descriptor management,
2830	in which case they can provide this function to map fds to socket handles.	3874	in which case they can provide this function to map fds to socket handles.
		3875
		3876	=item EV_WIN32_HANDLE_TO_FD(handle)
		3877
		3878	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3879	using the standard C<_open_osfhandle> function. For programs implementing
		3880	their own fd to handle mapping, overwriting this function makes it easier
		3881	to do so. This can be done by defining this macro to an appropriate value.
		3882
		3883	=item EV_WIN32_CLOSE_FD(fd)
		3884
		3885	If programs implement their own fd to handle mapping on win32, then this
		3886	macro can be used to override the C<close> function, useful to unregister
		3887	file descriptors again. Note that the replacement function has to close
		3888	the underlying OS handle.
2831		3889
2832	=item EV_USE_POLL	3890	=item EV_USE_POLL
2833		3891
2834	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3892	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2835	backend. Otherwise it will be enabled on non-win32 platforms. It	3893	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2862	otherwise another method will be used as fallback. This is the preferred	3920	otherwise another method will be used as fallback. This is the preferred
2863	backend for Solaris 10 systems.	3921	backend for Solaris 10 systems.
2864		3922
2865	=item EV_USE_DEVPOLL	3923	=item EV_USE_DEVPOLL
2866		3924
2867	reserved for future expansion, works like the USE symbols above.	3925	Reserved for future expansion, works like the USE symbols above.
2868		3926
2869	=item EV_USE_INOTIFY	3927	=item EV_USE_INOTIFY
2870		3928
2871	If defined to be C<1>, libev will compile in support for the Linux inotify	3929	If defined to be C<1>, libev will compile in support for the Linux inotify
2872	interface to speed up C<ev_stat> watchers. Its actual availability will	3930	interface to speed up C<ev_stat> watchers. Its actual availability will
…		…
2879	access is atomic with respect to other threads or signal contexts. No such	3937	access is atomic with respect to other threads or signal contexts. No such
2880	type is easily found in the C language, so you can provide your own type	3938	type is easily found in the C language, so you can provide your own type
2881	that you know is safe for your purposes. It is used both for signal handler "locking"	3939	that you know is safe for your purposes. It is used both for signal handler "locking"
2882	as well as for signal and thread safety in C<ev_async> watchers.	3940	as well as for signal and thread safety in C<ev_async> watchers.
2883		3941
2884	In the absense of this define, libev will use C<sig_atomic_t volatile>	3942	In the absence of this define, libev will use C<sig_atomic_t volatile>
2885	(from F<signal.h>), which is usually good enough on most platforms.	3943	(from F<signal.h>), which is usually good enough on most platforms.
2886		3944
2887	=item EV_H	3945	=item EV_H (h)
2888		3946
2889	The name of the F<ev.h> header file used to include it. The default if	3947	The name of the F<ev.h> header file used to include it. The default if
2890	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3948	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2891	used to virtually rename the F<ev.h> header file in case of conflicts.	3949	used to virtually rename the F<ev.h> header file in case of conflicts.
2892		3950
2893	=item EV_CONFIG_H	3951	=item EV_CONFIG_H (h)
2894		3952
2895	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3953	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2896	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3954	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2897	C<EV_H>, above.	3955	C<EV_H>, above.
2898		3956
2899	=item EV_EVENT_H	3957	=item EV_EVENT_H (h)
2900		3958
2901	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3959	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2902	of how the F<event.h> header can be found, the default is C<"event.h">.	3960	of how the F<event.h> header can be found, the default is C<"event.h">.
2903		3961
2904	=item EV_PROTOTYPES	3962	=item EV_PROTOTYPES (h)
2905		3963
2906	If defined to be C<0>, then F<ev.h> will not define any function	3964	If defined to be C<0>, then F<ev.h> will not define any function
2907	prototypes, but still define all the structs and other symbols. This is	3965	prototypes, but still define all the structs and other symbols. This is
2908	occasionally useful if you want to provide your own wrapper functions	3966	occasionally useful if you want to provide your own wrapper functions
2909	around libev functions.	3967	around libev functions.
…		…
2928	When doing priority-based operations, libev usually has to linearly search	3986	When doing priority-based operations, libev usually has to linearly search
2929	all the priorities, so having many of them (hundreds) uses a lot of space	3987	all the priorities, so having many of them (hundreds) uses a lot of space
2930	and time, so using the defaults of five priorities (-2 .. +2) is usually	3988	and time, so using the defaults of five priorities (-2 .. +2) is usually
2931	fine.	3989	fine.
2932		3990
2933	If your embedding app does not need any priorities, defining these both to	3991	If your embedding application does not need any priorities, defining these
2934	C<0> will save some memory and cpu.	3992	both to C<0> will save some memory and CPU.
2935		3993
2936	=item EV_PERIODIC_ENABLE	3994	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3995	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3996	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2937		3997
2938	If undefined or defined to be C<1>, then periodic timers are supported. If	3998	If undefined or defined to be C<1> (and the platform supports it), then
2939	defined to be C<0>, then they are not. Disabling them saves a few kB of	3999	the respective watcher type is supported. If defined to be C<0>, then it
2940	code.	4000	is not. Disabling watcher types mainly saves code size.
2941		4001
2942	=item EV_IDLE_ENABLE	4002	=item EV_FEATURES
2943
2944	If undefined or defined to be C<1>, then idle watchers are supported. If
2945	defined to be C<0>, then they are not. Disabling them saves a few kB of
2946	code.
2947
2948	=item EV_EMBED_ENABLE
2949
2950	If undefined or defined to be C<1>, then embed watchers are supported. If
2951	defined to be C<0>, then they are not.
2952
2953	=item EV_STAT_ENABLE
2954
2955	If undefined or defined to be C<1>, then stat watchers are supported. If
2956	defined to be C<0>, then they are not.
2957
2958	=item EV_FORK_ENABLE
2959
2960	If undefined or defined to be C<1>, then fork watchers are supported. If
2961	defined to be C<0>, then they are not.
2962
2963	=item EV_ASYNC_ENABLE
2964
2965	If undefined or defined to be C<1>, then async watchers are supported. If
2966	defined to be C<0>, then they are not.
2967
2968	=item EV_MINIMAL
2969		4003
2970	If you need to shave off some kilobytes of code at the expense of some	4004	If you need to shave off some kilobytes of code at the expense of some
2971	speed, define this symbol to C<1>. Currently only used for gcc to override	4005	speed (but with the full API), you can define this symbol to request
2972	some inlining decisions, saves roughly 30% codesize of amd64.	4006	certain subsets of functionality. The default is to enable all features
		4007	that can be enabled on the platform.
		4008
		4009	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4010	with some broad features you want) and then selectively re-enable
		4011	additional parts you want, for example if you want everything minimal,
		4012	but multiple event loop support, async and child watchers and the poll
		4013	backend, use this:
		4014
		4015	#define EV_FEATURES 0
		4016	#define EV_MULTIPLICITY 1
		4017	#define EV_USE_POLL 1
		4018	#define EV_CHILD_ENABLE 1
		4019	#define EV_ASYNC_ENABLE 1
		4020
		4021	The actual value is a bitset, it can be a combination of the following
		4022	values:
		4023
		4024	=over 4
		4025
		4026	=item C<1> - faster/larger code
		4027
		4028	Use larger code to speed up some operations.
		4029
		4030	Currently this is used to override some inlining decisions (enlarging the
		4031	code size by roughly 30% on amd64).
		4032
		4033	When optimising for size, use of compiler flags such as C<-Os> with
		4034	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4035	assertions.
		4036
		4037	=item C<2> - faster/larger data structures
		4038
		4039	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4040	hash table sizes and so on. This will usually further increase code size
		4041	and can additionally have an effect on the size of data structures at
		4042	runtime.
		4043
		4044	=item C<4> - full API configuration
		4045
		4046	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4047	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4048
		4049	=item C<8> - full API
		4050
		4051	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4052	details on which parts of the API are still available without this
		4053	feature, and do not complain if this subset changes over time.
		4054
		4055	=item C<16> - enable all optional watcher types
		4056
		4057	Enables all optional watcher types. If you want to selectively enable
		4058	only some watcher types other than I/O and timers (e.g. prepare,
		4059	embed, async, child...) you can enable them manually by defining
		4060	C<EV_watchertype_ENABLE> to C<1> instead.
		4061
		4062	=item C<32> - enable all backends
		4063
		4064	This enables all backends - without this feature, you need to enable at
		4065	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4066
		4067	=item C<64> - enable OS-specific "helper" APIs
		4068
		4069	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4070	default.
		4071
		4072	=back
		4073
		4074	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4075	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4076	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4077	watchers, timers and monotonic clock support.
		4078
		4079	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4080	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4081	your program might be left out as well - a binary starting a timer and an
		4082	I/O watcher then might come out at only 5Kb.
		4083
		4084	=item EV_AVOID_STDIO
		4085
		4086	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4087	functions (printf, scanf, perror etc.). This will increase the code size
		4088	somewhat, but if your program doesn't otherwise depend on stdio and your
		4089	libc allows it, this avoids linking in the stdio library which is quite
		4090	big.
		4091
		4092	Note that error messages might become less precise when this option is
		4093	enabled.
		4094
		4095	=item EV_NSIG
		4096
		4097	The highest supported signal number, +1 (or, the number of
		4098	signals): Normally, libev tries to deduce the maximum number of signals
		4099	automatically, but sometimes this fails, in which case it can be
		4100	specified. Also, using a lower number than detected (C<32> should be
		4101	good for about any system in existence) can save some memory, as libev
		4102	statically allocates some 12-24 bytes per signal number.
2973		4103
2974	=item EV_PID_HASHSIZE	4104	=item EV_PID_HASHSIZE
2975		4105
2976	C<ev_child> watchers use a small hash table to distribute workload by	4106	C<ev_child> watchers use a small hash table to distribute workload by
2977	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4107	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2978	than enough. If you need to manage thousands of children you might want to	4108	usually more than enough. If you need to manage thousands of children you
2979	increase this value (I<must> be a power of two).	4109	might want to increase this value (I<must> be a power of two).
2980		4110
2981	=item EV_INOTIFY_HASHSIZE	4111	=item EV_INOTIFY_HASHSIZE
2982		4112
2983	C<ev_stat> watchers use a small hash table to distribute workload by	4113	C<ev_stat> watchers use a small hash table to distribute workload by
2984	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4114	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2985	usually more than enough. If you need to manage thousands of C<ev_stat>	4115	disabled), usually more than enough. If you need to manage thousands of
2986	watchers you might want to increase this value (I<must> be a power of	4116	C<ev_stat> watchers you might want to increase this value (I<must> be a
2987	two).	4117	power of two).
		4118
		4119	=item EV_USE_4HEAP
		4120
		4121	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4122	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4123	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4124	faster performance with many (thousands) of watchers.
		4125
		4126	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4127	will be C<0>.
		4128
		4129	=item EV_HEAP_CACHE_AT
		4130
		4131	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4132	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4133	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4134	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4135	but avoids random read accesses on heap changes. This improves performance
		4136	noticeably with many (hundreds) of watchers.
		4137
		4138	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4139	will be C<0>.
		4140
		4141	=item EV_VERIFY
		4142
		4143	Controls how much internal verification (see C<ev_verify ()>) will
		4144	be done: If set to C<0>, no internal verification code will be compiled
		4145	in. If set to C<1>, then verification code will be compiled in, but not
		4146	called. If set to C<2>, then the internal verification code will be
		4147	called once per loop, which can slow down libev. If set to C<3>, then the
		4148	verification code will be called very frequently, which will slow down
		4149	libev considerably.
		4150
		4151	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4152	will be C<0>.
2988		4153
2989	=item EV_COMMON	4154	=item EV_COMMON
2990		4155
2991	By default, all watchers have a C<void *data> member. By redefining	4156	By default, all watchers have a C<void *data> member. By redefining
2992	this macro to a something else you can include more and other types of	4157	this macro to something else you can include more and other types of
2993	members. You have to define it each time you include one of the files,	4158	members. You have to define it each time you include one of the files,
2994	though, and it must be identical each time.	4159	though, and it must be identical each time.
2995		4160
2996	For example, the perl EV module uses something like this:	4161	For example, the perl EV module uses something like this:
2997		4162
2998	#define EV_COMMON \	4163	#define EV_COMMON \
2999	SV *self; /* contains this struct */ \	4164	SV *self; /* contains this struct */ \
3000	SV *cb_sv, *fh /* note no trailing ";" */	4165	SV *cb_sv, *fh /* note no trailing ";" */
3001		4166
3002	=item EV_CB_DECLARE (type)	4167	=item EV_CB_DECLARE (type)
3003		4168
3004	=item EV_CB_INVOKE (watcher, revents)	4169	=item EV_CB_INVOKE (watcher, revents)
3005		4170
…		…
3010	definition and a statement, respectively. See the F<ev.h> header file for	4175	definition and a statement, respectively. See the F<ev.h> header file for
3011	their default definitions. One possible use for overriding these is to	4176	their default definitions. One possible use for overriding these is to
3012	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4177	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3013	method calls instead of plain function calls in C++.	4178	method calls instead of plain function calls in C++.
3014		4179
		4180	=back
		4181
3015	=head2 EXPORTED API SYMBOLS	4182	=head2 EXPORTED API SYMBOLS
3016		4183
3017	If you need to re-export the API (e.g. via a dll) and you need a list of	4184	If you need to re-export the API (e.g. via a DLL) and you need a list of
3018	exported symbols, you can use the provided F<Symbol.*> files which list	4185	exported symbols, you can use the provided F<Symbol.*> files which list
3019	all public symbols, one per line:	4186	all public symbols, one per line:
3020		4187
3021	Symbols.ev for libev proper	4188	Symbols.ev for libev proper
3022	Symbols.event for the libevent emulation	4189	Symbols.event for the libevent emulation
3023		4190
3024	This can also be used to rename all public symbols to avoid clashes with	4191	This can also be used to rename all public symbols to avoid clashes with
3025	multiple versions of libev linked together (which is obviously bad in	4192	multiple versions of libev linked together (which is obviously bad in
3026	itself, but sometimes it is inconvinient to avoid this).	4193	itself, but sometimes it is inconvenient to avoid this).
3027		4194
3028	A sed command like this will create wrapper C<#define>'s that you need to	4195	A sed command like this will create wrapper C<#define>'s that you need to
3029	include before including F<ev.h>:	4196	include before including F<ev.h>:
3030		4197
3031	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4198	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
3048	file.	4215	file.
3049		4216
3050	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4217	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3051	that everybody includes and which overrides some configure choices:	4218	that everybody includes and which overrides some configure choices:
3052		4219
3053	#define EV_MINIMAL 1	4220	#define EV_FEATURES 8
3054	#define EV_USE_POLL 0	4221	#define EV_USE_SELECT 1
3055	#define EV_MULTIPLICITY 0
3056	#define EV_PERIODIC_ENABLE 0	4222	#define EV_PREPARE_ENABLE 1
		4223	#define EV_IDLE_ENABLE 1
3057	#define EV_STAT_ENABLE 0	4224	#define EV_SIGNAL_ENABLE 1
3058	#define EV_FORK_ENABLE 0	4225	#define EV_CHILD_ENABLE 1
		4226	#define EV_USE_STDEXCEPT 0
3059	#define EV_CONFIG_H <config.h>	4227	#define EV_CONFIG_H <config.h>
3060	#define EV_MINPRI 0
3061	#define EV_MAXPRI 0
3062		4228
3063	#include "ev++.h"	4229	#include "ev++.h"
3064		4230
3065	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4231	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3066		4232
3067	#include "ev_cpp.h"	4233	#include "ev_cpp.h"
3068	#include "ev.c"	4234	#include "ev.c"
3069		4235
		4236	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3070		4237
3071	=head1 THREADS AND COROUTINES	4238	=head2 THREADS AND COROUTINES
3072		4239
3073	=head2 THREADS	4240	=head3 THREADS
3074		4241
3075	Libev itself is completely threadsafe, but it uses no locking. This	4242	All libev functions are reentrant and thread-safe unless explicitly
		4243	documented otherwise, but libev implements no locking itself. This means
3076	means that you can use as many loops as you want in parallel, as long as	4244	that you can use as many loops as you want in parallel, as long as there
3077	only one thread ever calls into one libev function with the same loop	4245	are no concurrent calls into any libev function with the same loop
3078	parameter.	4246	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4247	of course): libev guarantees that different event loops share no data
		4248	structures that need any locking.
3079		4249
3080	Or put differently: calls with different loop parameters can be done in	4250	Or to put it differently: calls with different loop parameters can be done
3081	parallel from multiple threads, calls with the same loop parameter must be	4251	concurrently from multiple threads, calls with the same loop parameter
3082	done serially (but can be done from different threads, as long as only one	4252	must be done serially (but can be done from different threads, as long as
3083	thread ever is inside a call at any point in time, e.g. by using a mutex	4253	only one thread ever is inside a call at any point in time, e.g. by using
3084	per loop).	4254	a mutex per loop).
3085		4255
3086	If you want to know which design is best for your problem, then I cannot	4256	Specifically to support threads (and signal handlers), libev implements
		4257	so-called C<ev_async> watchers, which allow some limited form of
		4258	concurrency on the same event loop, namely waking it up "from the
		4259	outside".
		4260
		4261	If you want to know which design (one loop, locking, or multiple loops
		4262	without or something else still) is best for your problem, then I cannot
3087	help you but by giving some generic advice:	4263	help you, but here is some generic advice:
3088		4264
3089	=over 4	4265	=over 4
3090		4266
3091	=item * most applications have a main thread: use the default libev loop	4267	=item * most applications have a main thread: use the default libev loop
3092	in that thread, or create a seperate thread running only the default loop.	4268	in that thread, or create a separate thread running only the default loop.
3093		4269
3094	This helps integrating other libraries or software modules that use libev	4270	This helps integrating other libraries or software modules that use libev
3095	themselves and don't care/know about threading.	4271	themselves and don't care/know about threading.
3096		4272
3097	=item * one loop per thread is usually a good model.	4273	=item * one loop per thread is usually a good model.
3098		4274
3099	Doing this is almost never wrong, sometimes a better-performance model	4275	Doing this is almost never wrong, sometimes a better-performance model
3100	exists, but it is always a good start.	4276	exists, but it is always a good start.
3101		4277
3102	=item * other models exist, such as the leader/follower pattern, where one	4278	=item * other models exist, such as the leader/follower pattern, where one
3103	loop is handed through multiple threads in a kind of round-robbin fashion.	4279	loop is handed through multiple threads in a kind of round-robin fashion.
3104		4280
3105	Chosing a model is hard - look around, learn, know that usually you cna do	4281	Choosing a model is hard - look around, learn, know that usually you can do
3106	better than you currently do :-)	4282	better than you currently do :-)
3107		4283
3108	=item * often you need to talk to some other thread which blocks in the	4284	=item * often you need to talk to some other thread which blocks in the
		4285	event loop.
		4286
3109	event loop - C<ev_async> watchers can be used to wake them up from other	4287	C<ev_async> watchers can be used to wake them up from other threads safely
3110	threads safely (or from signal contexts...).	4288	(or from signal contexts...).
		4289
		4290	An example use would be to communicate signals or other events that only
		4291	work in the default loop by registering the signal watcher with the
		4292	default loop and triggering an C<ev_async> watcher from the default loop
		4293	watcher callback into the event loop interested in the signal.
3111		4294
3112	=back	4295	=back
3113		4296
		4297	=head4 THREAD LOCKING EXAMPLE
		4298
		4299	Here is a fictitious example of how to run an event loop in a different
		4300	thread than where callbacks are being invoked and watchers are
		4301	created/added/removed.
		4302
		4303	For a real-world example, see the C<EV::Loop::Async> perl module,
		4304	which uses exactly this technique (which is suited for many high-level
		4305	languages).
		4306
		4307	The example uses a pthread mutex to protect the loop data, a condition
		4308	variable to wait for callback invocations, an async watcher to notify the
		4309	event loop thread and an unspecified mechanism to wake up the main thread.
		4310
		4311	First, you need to associate some data with the event loop:
		4312
		4313	typedef struct {
		4314	mutex_t lock; /* global loop lock */
		4315	ev_async async_w;
		4316	thread_t tid;
		4317	cond_t invoke_cv;
		4318	} userdata;
		4319
		4320	void prepare_loop (EV_P)
		4321	{
		4322	// for simplicity, we use a static userdata struct.
		4323	static userdata u;
		4324
		4325	ev_async_init (&u->async_w, async_cb);
		4326	ev_async_start (EV_A_ &u->async_w);
		4327
		4328	pthread_mutex_init (&u->lock, 0);
		4329	pthread_cond_init (&u->invoke_cv, 0);
		4330
		4331	// now associate this with the loop
		4332	ev_set_userdata (EV_A_ u);
		4333	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4334	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4335
		4336	// then create the thread running ev_loop
		4337	pthread_create (&u->tid, 0, l_run, EV_A);
		4338	}
		4339
		4340	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4341	solely to wake up the event loop so it takes notice of any new watchers
		4342	that might have been added:
		4343
		4344	static void
		4345	async_cb (EV_P_ ev_async *w, int revents)
		4346	{
		4347	// just used for the side effects
		4348	}
		4349
		4350	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4351	protecting the loop data, respectively.
		4352
		4353	static void
		4354	l_release (EV_P)
		4355	{
		4356	userdata *u = ev_userdata (EV_A);
		4357	pthread_mutex_unlock (&u->lock);
		4358	}
		4359
		4360	static void
		4361	l_acquire (EV_P)
		4362	{
		4363	userdata *u = ev_userdata (EV_A);
		4364	pthread_mutex_lock (&u->lock);
		4365	}
		4366
		4367	The event loop thread first acquires the mutex, and then jumps straight
		4368	into C<ev_run>:
		4369
		4370	void *
		4371	l_run (void *thr_arg)
		4372	{
		4373	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4374
		4375	l_acquire (EV_A);
		4376	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4377	ev_run (EV_A_ 0);
		4378	l_release (EV_A);
		4379
		4380	return 0;
		4381	}
		4382
		4383	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4384	signal the main thread via some unspecified mechanism (signals? pipe
		4385	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4386	have been called (in a while loop because a) spurious wakeups are possible
		4387	and b) skipping inter-thread-communication when there are no pending
		4388	watchers is very beneficial):
		4389
		4390	static void
		4391	l_invoke (EV_P)
		4392	{
		4393	userdata *u = ev_userdata (EV_A);
		4394
		4395	while (ev_pending_count (EV_A))
		4396	{
		4397	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4398	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4399	}
		4400	}
		4401
		4402	Now, whenever the main thread gets told to invoke pending watchers, it
		4403	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4404	thread to continue:
		4405
		4406	static void
		4407	real_invoke_pending (EV_P)
		4408	{
		4409	userdata *u = ev_userdata (EV_A);
		4410
		4411	pthread_mutex_lock (&u->lock);
		4412	ev_invoke_pending (EV_A);
		4413	pthread_cond_signal (&u->invoke_cv);
		4414	pthread_mutex_unlock (&u->lock);
		4415	}
		4416
		4417	Whenever you want to start/stop a watcher or do other modifications to an
		4418	event loop, you will now have to lock:
		4419
		4420	ev_timer timeout_watcher;
		4421	userdata *u = ev_userdata (EV_A);
		4422
		4423	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4424
		4425	pthread_mutex_lock (&u->lock);
		4426	ev_timer_start (EV_A_ &timeout_watcher);
		4427	ev_async_send (EV_A_ &u->async_w);
		4428	pthread_mutex_unlock (&u->lock);
		4429
		4430	Note that sending the C<ev_async> watcher is required because otherwise
		4431	an event loop currently blocking in the kernel will have no knowledge
		4432	about the newly added timer. By waking up the loop it will pick up any new
		4433	watchers in the next event loop iteration.
		4434
3114	=head2 COROUTINES	4435	=head3 COROUTINES
3115		4436
3116	Libev is much more accomodating to coroutines ("cooperative threads"):	4437	Libev is very accommodating to coroutines ("cooperative threads"):
3117	libev fully supports nesting calls to it's functions from different	4438	libev fully supports nesting calls to its functions from different
3118	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4439	coroutines (e.g. you can call C<ev_run> on the same loop from two
3119	different coroutines and switch freely between both coroutines running the	4440	different coroutines, and switch freely between both coroutines running
3120	loop, as long as you don't confuse yourself). The only exception is that	4441	the loop, as long as you don't confuse yourself). The only exception is
3121	you must not do this from C<ev_periodic> reschedule callbacks.	4442	that you must not do this from C<ev_periodic> reschedule callbacks.
3122		4443
3123	Care has been invested into making sure that libev does not keep local	4444	Care has been taken to ensure that libev does not keep local state inside
3124	state inside C<ev_loop>, and other calls do not usually allow coroutine	4445	C<ev_run>, and other calls do not usually allow for coroutine switches as
3125	switches.	4446	they do not call any callbacks.
3126		4447
		4448	=head2 COMPILER WARNINGS
3127		4449
3128	=head1 COMPLEXITIES	4450	Depending on your compiler and compiler settings, you might get no or a
		4451	lot of warnings when compiling libev code. Some people are apparently
		4452	scared by this.
3129		4453
3130	In this section the complexities of (many of) the algorithms used inside	4454	However, these are unavoidable for many reasons. For one, each compiler
3131	libev will be explained. For complexity discussions about backends see the	4455	has different warnings, and each user has different tastes regarding
3132	documentation for C<ev_default_init>.	4456	warning options. "Warn-free" code therefore cannot be a goal except when
		4457	targeting a specific compiler and compiler-version.
3133		4458
3134	All of the following are about amortised time: If an array needs to be	4459	Another reason is that some compiler warnings require elaborate
3135	extended, libev needs to realloc and move the whole array, but this	4460	workarounds, or other changes to the code that make it less clear and less
3136	happens asymptotically never with higher number of elements, so O(1) might	4461	maintainable.
3137	mean it might do a lengthy realloc operation in rare cases, but on average
3138	it is much faster and asymptotically approaches constant time.
3139		4462
3140	=over 4	4463	And of course, some compiler warnings are just plain stupid, or simply
		4464	wrong (because they don't actually warn about the condition their message
		4465	seems to warn about). For example, certain older gcc versions had some
		4466	warnings that resulted in an extreme number of false positives. These have
		4467	been fixed, but some people still insist on making code warn-free with
		4468	such buggy versions.
3141		4469
3142	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4470	While libev is written to generate as few warnings as possible,
		4471	"warn-free" code is not a goal, and it is recommended not to build libev
		4472	with any compiler warnings enabled unless you are prepared to cope with
		4473	them (e.g. by ignoring them). Remember that warnings are just that:
		4474	warnings, not errors, or proof of bugs.
3143		4475
3144	This means that, when you have a watcher that triggers in one hour and
3145	there are 100 watchers that would trigger before that then inserting will
3146	have to skip roughly seven (C<ld 100>) of these watchers.
3147		4476
3148	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4477	=head2 VALGRIND
3149		4478
3150	That means that changing a timer costs less than removing/adding them	4479	Valgrind has a special section here because it is a popular tool that is
3151	as only the relative motion in the event queue has to be paid for.	4480	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3152		4481
3153	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4482	If you think you found a bug (memory leak, uninitialised data access etc.)
		4483	in libev, then check twice: If valgrind reports something like:
3154		4484
3155	These just add the watcher into an array or at the head of a list.	4485	==2274== definitely lost: 0 bytes in 0 blocks.
		4486	==2274== possibly lost: 0 bytes in 0 blocks.
		4487	==2274== still reachable: 256 bytes in 1 blocks.
3156		4488
3157	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4489	Then there is no memory leak, just as memory accounted to global variables
		4490	is not a memleak - the memory is still being referenced, and didn't leak.
3158		4491
3159	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4492	Similarly, under some circumstances, valgrind might report kernel bugs
		4493	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4494	although an acceptable workaround has been found here), or it might be
		4495	confused.
3160		4496
3161	These watchers are stored in lists then need to be walked to find the	4497	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3162	correct watcher to remove. The lists are usually short (you don't usually	4498	make it into some kind of religion.
3163	have many watchers waiting for the same fd or signal).
3164		4499
3165	=item Finding the next timer in each loop iteration: O(1)	4500	If you are unsure about something, feel free to contact the mailing list
		4501	with the full valgrind report and an explanation on why you think this
		4502	is a bug in libev (best check the archives, too :). However, don't be
		4503	annoyed when you get a brisk "this is no bug" answer and take the chance
		4504	of learning how to interpret valgrind properly.
3166		4505
3167	By virtue of using a binary heap, the next timer is always found at the	4506	If you need, for some reason, empty reports from valgrind for your project
3168	beginning of the storage array.	4507	I suggest using suppression lists.
3169		4508
3170	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3171		4509
3172	A change means an I/O watcher gets started or stopped, which requires	4510	=head1 PORTABILITY NOTES
3173	libev to recalculate its status (and possibly tell the kernel, depending
3174	on backend and wether C<ev_io_set> was used).
3175		4511
3176	=item Activating one watcher (putting it into the pending state): O(1)	4512	=head2 GNU/LINUX 32 BIT LIMITATIONS
3177		4513
3178	=item Priority handling: O(number_of_priorities)	4514	GNU/Linux is the only common platform that supports 64 bit file/large file
		4515	interfaces but I<disables> them by default.
3179		4516
3180	Priorities are implemented by allocating some space for each	4517	That means that libev compiled in the default environment doesn't support
3181	priority. When doing priority-based operations, libev usually has to	4518	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3182	linearly search all the priorities, but starting/stopping and activating
3183	watchers becomes O(1) w.r.t. priority handling.
3184		4519
3185	=item Sending an ev_async: O(1)	4520	Unfortunately, many programs try to work around this GNU/Linux issue
		4521	by enabling the large file API, which makes them incompatible with the
		4522	standard libev compiled for their system.
3186		4523
3187	=item Processing ev_async_send: O(number_of_async_watchers)	4524	Likewise, libev cannot enable the large file API itself as this would
		4525	suddenly make it incompatible to the default compile time environment,
		4526	i.e. all programs not using special compile switches.
3188		4527
3189	=item Processing signals: O(max_signal_number)	4528	=head2 OS/X AND DARWIN BUGS
3190		4529
3191	Sending involves a syscall I<iff> there were no other C<ev_async_send>	4530	The whole thing is a bug if you ask me - basically any system interface
3192	calls in the current loop iteration. Checking for async and signal events	4531	you touch is broken, whether it is locales, poll, kqueue or even the
3193	involves iterating over all running async watchers or all signal numbers.	4532	OpenGL drivers.
3194		4533
3195	=back	4534	=head3 C<kqueue> is buggy
3196		4535
		4536	The kqueue syscall is broken in all known versions - most versions support
		4537	only sockets, many support pipes.
3197		4538
3198	=head1 Win32 platform limitations and workarounds	4539	Libev tries to work around this by not using C<kqueue> by default on this
		4540	rotten platform, but of course you can still ask for it when creating a
		4541	loop - embedding a socket-only kqueue loop into a select-based one is
		4542	probably going to work well.
		4543
		4544	=head3 C<poll> is buggy
		4545
		4546	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4547	implementation by something calling C<kqueue> internally around the 10.5.6
		4548	release, so now C<kqueue> I<and> C<poll> are broken.
		4549
		4550	Libev tries to work around this by not using C<poll> by default on
		4551	this rotten platform, but of course you can still ask for it when creating
		4552	a loop.
		4553
		4554	=head3 C<select> is buggy
		4555
		4556	All that's left is C<select>, and of course Apple found a way to fuck this
		4557	one up as well: On OS/X, C<select> actively limits the number of file
		4558	descriptors you can pass in to 1024 - your program suddenly crashes when
		4559	you use more.
		4560
		4561	There is an undocumented "workaround" for this - defining
		4562	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4563	work on OS/X.
		4564
		4565	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4566
		4567	=head3 C<errno> reentrancy
		4568
		4569	The default compile environment on Solaris is unfortunately so
		4570	thread-unsafe that you can't even use components/libraries compiled
		4571	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4572	defined by default. A valid, if stupid, implementation choice.
		4573
		4574	If you want to use libev in threaded environments you have to make sure
		4575	it's compiled with C<_REENTRANT> defined.
		4576
		4577	=head3 Event port backend
		4578
		4579	The scalable event interface for Solaris is called "event
		4580	ports". Unfortunately, this mechanism is very buggy in all major
		4581	releases. If you run into high CPU usage, your program freezes or you get
		4582	a large number of spurious wakeups, make sure you have all the relevant
		4583	and latest kernel patches applied. No, I don't know which ones, but there
		4584	are multiple ones to apply, and afterwards, event ports actually work
		4585	great.
		4586
		4587	If you can't get it to work, you can try running the program by setting
		4588	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4589	C<select> backends.
		4590
		4591	=head2 AIX POLL BUG
		4592
		4593	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4594	this by trying to avoid the poll backend altogether (i.e. it's not even
		4595	compiled in), which normally isn't a big problem as C<select> works fine
		4596	with large bitsets on AIX, and AIX is dead anyway.
		4597
		4598	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4599
		4600	=head3 General issues
3199		4601
3200	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4602	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3201	requires, and its I/O model is fundamentally incompatible with the POSIX	4603	requires, and its I/O model is fundamentally incompatible with the POSIX
3202	model. Libev still offers limited functionality on this platform in	4604	model. Libev still offers limited functionality on this platform in
3203	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4605	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3204	descriptors. This only applies when using Win32 natively, not when using	4606	descriptors. This only applies when using Win32 natively, not when using
3205	e.g. cygwin.	4607	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4608	as every compielr comes with a slightly differently broken/incompatible
		4609	environment.
		4610
		4611	Lifting these limitations would basically require the full
		4612	re-implementation of the I/O system. If you are into this kind of thing,
		4613	then note that glib does exactly that for you in a very portable way (note
		4614	also that glib is the slowest event library known to man).
3206		4615
3207	There is no supported compilation method available on windows except	4616	There is no supported compilation method available on windows except
3208	embedding it into other applications.	4617	embedding it into other applications.
3209		4618
		4619	Sensible signal handling is officially unsupported by Microsoft - libev
		4620	tries its best, but under most conditions, signals will simply not work.
		4621
		4622	Not a libev limitation but worth mentioning: windows apparently doesn't
		4623	accept large writes: instead of resulting in a partial write, windows will
		4624	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4625	so make sure you only write small amounts into your sockets (less than a
		4626	megabyte seems safe, but this apparently depends on the amount of memory
		4627	available).
		4628
3210	Due to the many, low, and arbitrary limits on the win32 platform and the	4629	Due to the many, low, and arbitrary limits on the win32 platform and
3211	abysmal performance of winsockets, using a large number of sockets is not	4630	the abysmal performance of winsockets, using a large number of sockets
3212	recommended (and not reasonable). If your program needs to use more than	4631	is not recommended (and not reasonable). If your program needs to use
3213	a hundred or so sockets, then likely it needs to use a totally different	4632	more than a hundred or so sockets, then likely it needs to use a totally
3214	implementation for windows, as libev offers the POSIX model, which cannot	4633	different implementation for windows, as libev offers the POSIX readiness
3215	be implemented efficiently on windows (microsoft monopoly games).	4634	notification model, which cannot be implemented efficiently on windows
		4635	(due to Microsoft monopoly games).
3216		4636
3217	=over 4	4637	A typical way to use libev under windows is to embed it (see the embedding
		4638	section for details) and use the following F<evwrap.h> header file instead
		4639	of F<ev.h>:
3218		4640
		4641	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4642	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4643
		4644	#include "ev.h"
		4645
		4646	And compile the following F<evwrap.c> file into your project (make sure
		4647	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4648
		4649	#include "evwrap.h"
		4650	#include "ev.c"
		4651
3219	=item The winsocket select function	4652	=head3 The winsocket C<select> function
3220		4653
3221	The winsocket C<select> function doesn't follow POSIX in that it requires	4654	The winsocket C<select> function doesn't follow POSIX in that it
3222	socket I<handles> and not socket I<file descriptors>. This makes select	4655	requires socket I<handles> and not socket I<file descriptors> (it is
3223	very inefficient, and also requires a mapping from file descriptors	4656	also extremely buggy). This makes select very inefficient, and also
3224	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4657	requires a mapping from file descriptors to socket handles (the Microsoft
3225	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4658	C runtime provides the function C<_open_osfhandle> for this). See the
3226	symbols for more info.	4659	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4660	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3227		4661
3228	The configuration for a "naked" win32 using the microsoft runtime	4662	The configuration for a "naked" win32 using the Microsoft runtime
3229	libraries and raw winsocket select is:	4663	libraries and raw winsocket select is:
3230		4664
3231	#define EV_USE_SELECT 1	4665	#define EV_USE_SELECT 1
3232	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4666	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3233		4667
3234	Note that winsockets handling of fd sets is O(n), so you can easily get a	4668	Note that winsockets handling of fd sets is O(n), so you can easily get a
3235	complexity in the O(n²) range when using win32.	4669	complexity in the O(n²) range when using win32.
3236		4670
3237	=item Limited number of file descriptors	4671	=head3 Limited number of file descriptors
3238		4672
3239	Windows has numerous arbitrary (and low) limits on things. Early versions	4673	Windows has numerous arbitrary (and low) limits on things.
3240	of winsocket's select only supported waiting for a max. of C<64> handles	4674
		4675	Early versions of winsocket's select only supported waiting for a maximum
3241	(probably owning to the fact that all windows kernels can only wait for	4676	of C<64> handles (probably owning to the fact that all windows kernels
3242	C<64> things at the same time internally; microsoft recommends spawning a	4677	can only wait for C<64> things at the same time internally; Microsoft
3243	chain of threads and wait for 63 handles and the previous thread in each).	4678	recommends spawning a chain of threads and wait for 63 handles and the
		4679	previous thread in each. Sounds great!).
3244		4680
3245	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4681	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3246	to some high number (e.g. C<2048>) before compiling the winsocket select	4682	to some high number (e.g. C<2048>) before compiling the winsocket select
3247	call (which might be in libev or elsewhere, for example, perl does its own	4683	call (which might be in libev or elsewhere, for example, perl and many
3248	select emulation on windows).	4684	other interpreters do their own select emulation on windows).
3249		4685
3250	Another limit is the number of file descriptors in the microsoft runtime	4686	Another limit is the number of file descriptors in the Microsoft runtime
3251	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4687	libraries, which by default is C<64> (there must be a hidden I<64>
3252	or something like this inside microsoft). You can increase this by calling	4688	fetish or something like this inside Microsoft). You can increase this
3253	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4689	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3254	arbitrary limit), but is broken in many versions of the microsoft runtime	4690	(another arbitrary limit), but is broken in many versions of the Microsoft
3255	libraries.
3256
3257	This might get you to about C<512> or C<2048> sockets (depending on	4691	runtime libraries. This might get you to about C<512> or C<2048> sockets
3258	windows version and/or the phase of the moon). To get more, you need to	4692	(depending on windows version and/or the phase of the moon). To get more,
3259	wrap all I/O functions and provide your own fd management, but the cost of	4693	you need to wrap all I/O functions and provide your own fd management, but
3260	calling select (O(n²)) will likely make this unworkable.	4694	the cost of calling select (O(n²)) will likely make this unworkable.
3261		4695
3262	=back
3263
3264
3265	=head1 PORTABILITY REQUIREMENTS	4696	=head2 PORTABILITY REQUIREMENTS
3266		4697
3267	In addition to a working ISO-C implementation, libev relies on a few	4698	In addition to a working ISO-C implementation and of course the
3268	additional extensions:	4699	backend-specific APIs, libev relies on a few additional extensions:
3269		4700
3270	=over 4	4701	=over 4
3271		4702
		4703	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4704	calling conventions regardless of C<ev_watcher_type *>.
		4705
		4706	Libev assumes not only that all watcher pointers have the same internal
		4707	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4708	assumes that the same (machine) code can be used to call any watcher
		4709	callback: The watcher callbacks have different type signatures, but libev
		4710	calls them using an C<ev_watcher *> internally.
		4711
3272	=item C<sig_atomic_t volatile> must be thread-atomic as well	4712	=item C<sig_atomic_t volatile> must be thread-atomic as well
3273		4713
3274	The type C<sig_atomic_t volatile> (or whatever is defined as	4714	The type C<sig_atomic_t volatile> (or whatever is defined as
3275	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4715	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3276	threads. This is not part of the specification for C<sig_atomic_t>, but is	4716	threads. This is not part of the specification for C<sig_atomic_t>, but is
3277	believed to be sufficiently portable.	4717	believed to be sufficiently portable.
3278		4718
3279	=item C<sigprocmask> must work in a threaded environment	4719	=item C<sigprocmask> must work in a threaded environment
3280		4720
…		…
3287		4727
3288	The most portable way to handle signals is to block signals in all threads	4728	The most portable way to handle signals is to block signals in all threads
3289	except the initial one, and run the default loop in the initial thread as	4729	except the initial one, and run the default loop in the initial thread as
3290	well.	4730	well.
3291		4731
		4732	=item C<long> must be large enough for common memory allocation sizes
		4733
		4734	To improve portability and simplify its API, libev uses C<long> internally
		4735	instead of C<size_t> when allocating its data structures. On non-POSIX
		4736	systems (Microsoft...) this might be unexpectedly low, but is still at
		4737	least 31 bits everywhere, which is enough for hundreds of millions of
		4738	watchers.
		4739
		4740	=item C<double> must hold a time value in seconds with enough accuracy
		4741
		4742	The type C<double> is used to represent timestamps. It is required to
		4743	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4744	good enough for at least into the year 4000 with millisecond accuracy
		4745	(the design goal for libev). This requirement is overfulfilled by
		4746	implementations using IEEE 754, which is basically all existing ones. With
		4747	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4748
3292	=back	4749	=back
3293		4750
3294	If you know of other additional requirements drop me a note.	4751	If you know of other additional requirements drop me a note.
3295		4752
3296		4753
		4754	=head1 ALGORITHMIC COMPLEXITIES
		4755
		4756	In this section the complexities of (many of) the algorithms used inside
		4757	libev will be documented. For complexity discussions about backends see
		4758	the documentation for C<ev_default_init>.
		4759
		4760	All of the following are about amortised time: If an array needs to be
		4761	extended, libev needs to realloc and move the whole array, but this
		4762	happens asymptotically rarer with higher number of elements, so O(1) might
		4763	mean that libev does a lengthy realloc operation in rare cases, but on
		4764	average it is much faster and asymptotically approaches constant time.
		4765
		4766	=over 4
		4767
		4768	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4769
		4770	This means that, when you have a watcher that triggers in one hour and
		4771	there are 100 watchers that would trigger before that, then inserting will
		4772	have to skip roughly seven (C<ld 100>) of these watchers.
		4773
		4774	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4775
		4776	That means that changing a timer costs less than removing/adding them,
		4777	as only the relative motion in the event queue has to be paid for.
		4778
		4779	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4780
		4781	These just add the watcher into an array or at the head of a list.
		4782
		4783	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4784
		4785	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4786
		4787	These watchers are stored in lists, so they need to be walked to find the
		4788	correct watcher to remove. The lists are usually short (you don't usually
		4789	have many watchers waiting for the same fd or signal: one is typical, two
		4790	is rare).
		4791
		4792	=item Finding the next timer in each loop iteration: O(1)
		4793
		4794	By virtue of using a binary or 4-heap, the next timer is always found at a
		4795	fixed position in the storage array.
		4796
		4797	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4798
		4799	A change means an I/O watcher gets started or stopped, which requires
		4800	libev to recalculate its status (and possibly tell the kernel, depending
		4801	on backend and whether C<ev_io_set> was used).
		4802
		4803	=item Activating one watcher (putting it into the pending state): O(1)
		4804
		4805	=item Priority handling: O(number_of_priorities)
		4806
		4807	Priorities are implemented by allocating some space for each
		4808	priority. When doing priority-based operations, libev usually has to
		4809	linearly search all the priorities, but starting/stopping and activating
		4810	watchers becomes O(1) with respect to priority handling.
		4811
		4812	=item Sending an ev_async: O(1)
		4813
		4814	=item Processing ev_async_send: O(number_of_async_watchers)
		4815
		4816	=item Processing signals: O(max_signal_number)
		4817
		4818	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4819	calls in the current loop iteration. Checking for async and signal events
		4820	involves iterating over all running async watchers or all signal numbers.
		4821
		4822	=back
		4823
		4824
		4825	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4826
		4827	The major version 4 introduced some minor incompatible changes to the API.
		4828
		4829	At the moment, the C<ev.h> header file tries to implement superficial
		4830	compatibility, so most programs should still compile. Those might be
		4831	removed in later versions of libev, so better update early than late.
		4832
		4833	=over 4
		4834
		4835	=item function/symbol renames
		4836
		4837	A number of functions and symbols have been renamed:
		4838
		4839	ev_loop => ev_run
		4840	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4841	EVLOOP_ONESHOT => EVRUN_ONCE
		4842
		4843	ev_unloop => ev_break
		4844	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4845	EVUNLOOP_ONE => EVBREAK_ONE
		4846	EVUNLOOP_ALL => EVBREAK_ALL
		4847
		4848	EV_TIMEOUT => EV_TIMER
		4849
		4850	ev_loop_count => ev_iteration
		4851	ev_loop_depth => ev_depth
		4852	ev_loop_verify => ev_verify
		4853
		4854	Most functions working on C<struct ev_loop> objects don't have an
		4855	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4856	associated constants have been renamed to not collide with the C<struct
		4857	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4858	as all other watcher types. Note that C<ev_loop_fork> is still called
		4859	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4860	typedef.
		4861
		4862	=item C<EV_COMPAT3> backwards compatibility mechanism
		4863
		4864	The backward compatibility mechanism can be controlled by
		4865	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4866	section.
		4867
		4868	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4869
		4870	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4871	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4872	and work, but the library code will of course be larger.
		4873
		4874	=back
		4875
		4876
		4877	=head1 GLOSSARY
		4878
		4879	=over 4
		4880
		4881	=item active
		4882
		4883	A watcher is active as long as it has been started and not yet stopped.
		4884	See L<WATCHER STATES> for details.
		4885
		4886	=item application
		4887
		4888	In this document, an application is whatever is using libev.
		4889
		4890	=item backend
		4891
		4892	The part of the code dealing with the operating system interfaces.
		4893
		4894	=item callback
		4895
		4896	The address of a function that is called when some event has been
		4897	detected. Callbacks are being passed the event loop, the watcher that
		4898	received the event, and the actual event bitset.
		4899
		4900	=item callback/watcher invocation
		4901
		4902	The act of calling the callback associated with a watcher.
		4903
		4904	=item event
		4905
		4906	A change of state of some external event, such as data now being available
		4907	for reading on a file descriptor, time having passed or simply not having
		4908	any other events happening anymore.
		4909
		4910	In libev, events are represented as single bits (such as C<EV_READ> or
		4911	C<EV_TIMER>).
		4912
		4913	=item event library
		4914
		4915	A software package implementing an event model and loop.
		4916
		4917	=item event loop
		4918
		4919	An entity that handles and processes external events and converts them
		4920	into callback invocations.
		4921
		4922	=item event model
		4923
		4924	The model used to describe how an event loop handles and processes
		4925	watchers and events.
		4926
		4927	=item pending
		4928
		4929	A watcher is pending as soon as the corresponding event has been
		4930	detected. See L<WATCHER STATES> for details.
		4931
		4932	=item real time
		4933
		4934	The physical time that is observed. It is apparently strictly monotonic :)
		4935
		4936	=item wall-clock time
		4937
		4938	The time and date as shown on clocks. Unlike real time, it can actually
		4939	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4940	clock.
		4941
		4942	=item watcher
		4943
		4944	A data structure that describes interest in certain events. Watchers need
		4945	to be started (attached to an event loop) before they can receive events.
		4946
		4947	=back
		4948
3297	=head1 AUTHOR	4949	=head1 AUTHOR
3298		4950
3299	Marc Lehmann <libev@schmorp.de>.	4951	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3300		4952

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