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Revision 1.272 by root, Tue Nov 24 06:39:28 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
…		…
70	=head2 FEATURES	98	=head2 FEATURES
71		99
72	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
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	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
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	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
80	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
81	(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>).
82		111
83	It also is quite fast (see this	112	It also is quite fast (see this
84	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
85	for example).	114	for example).
86		115
87	=head2 CONVENTIONS	116	=head2 CONVENTIONS
88		117
89	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	122	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<ev_loop *>) will not have
		124	this argument.
95		125
96	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
97		127
98	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as some floatingpoint value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	135	throughout libev.
		136
		137	=head1 ERROR HANDLING
		138
		139	Libev knows three classes of errors: operating system errors, usage errors
		140	and internal errors (bugs).
		141
		142	When libev catches an operating system error it cannot handle (for example
		143	a system call indicating a condition libev cannot fix), it calls the callback
		144	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		145	abort. The default is to print a diagnostic message and to call C<abort
		146	()>.
		147
		148	When libev detects a usage error such as a negative timer interval, then
		149	it will print a diagnostic message and abort (via the C<assert> mechanism,
		150	so C<NDEBUG> will disable this checking): these are programming errors in
		151	the libev caller and need to be fixed there.
		152
		153	Libev also has a few internal error-checking C<assert>ions, and also has
		154	extensive consistency checking code. These do not trigger under normal
		155	circumstances, as they indicate either a bug in libev or worse.
		156
106		157
107	=head1 GLOBAL FUNCTIONS	158	=head1 GLOBAL FUNCTIONS
108		159
109	These functions can be called anytime, even before initialising the	160	These functions can be called anytime, even before initialising the
110	library in any way.	161	library in any way.
…		…
119		170
120	=item ev_sleep (ev_tstamp interval)	171	=item ev_sleep (ev_tstamp interval)
121		172
122	Sleep for the given interval: The current thread will be blocked until	173	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	174	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	175	this is a sub-second-resolution C<sleep ()>.
125		176
126	=item int ev_version_major ()	177	=item int ev_version_major ()
127		178
128	=item int ev_version_minor ()	179	=item int ev_version_minor ()
129		180
…		…
142	not a problem.	193	not a problem.
143		194
144	Example: Make sure we haven't accidentally been linked against the wrong	195	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	196	version.
146		197
147	assert (("libev version mismatch",	198	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
150		201
151	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
152		203
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	204	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	207	a description of the set values.
157		208
158	Example: make sure we have the epoll method, because yeah this is cool and	209	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	210	a must have and can we have a torrent of it please!!!11
160		211
161	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
163		214
164	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
165		216
166	Return the set of all backends compiled into this binary of libev and also	217	Return the set of all backends compiled into this binary of libev and also
167	recommended for this platform. This set is often smaller than the one	218	recommended for this platform. This set is often smaller than the one
168	returned by C<ev_supported_backends>, as for example kqueue is broken on	219	returned by C<ev_supported_backends>, as for example kqueue is broken on
169	most BSDs and will not be autodetected unless you explicitly request it	220	most BSDs and will not be auto-detected unless you explicitly request it
170	(assuming you know what you are doing). This is the set of backends that	221	(assuming you know what you are doing). This is the set of backends that
171	libev will probe for if you specify no backends explicitly.	222	libev will probe for if you specify no backends explicitly.
172		223
173	=item unsigned int ev_embeddable_backends ()	224	=item unsigned int ev_embeddable_backends ()
174		225
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	230	recommended ones.
180		231
181	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
182		233
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		235
185	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	238	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	239	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	240	or take some potentially destructive action.
190	function.	241
		242	Since some systems (at least OpenBSD and Darwin) fail to implement
		243	correct C<realloc> semantics, libev will use a wrapper around the system
		244	C<realloc> and C<free> functions by default.
191		245
192	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	247	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	248	or even to sleep a while and retry until some memory is available.
195		249
196	Example: Replace the libev allocator with one that waits a bit and then	250	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	251	retries (example requires a standards-compliant C<realloc>).
198		252
199	static void *	253	static void *
200	persistent_realloc (void *ptr, size_t size)	254	persistent_realloc (void *ptr, size_t size)
201	{	255	{
202	for (;;)	256	for (;;)
…		…
211	}	265	}
212		266
213	...	267	...
214	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
215		269
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		271
218	Set the callback function to call on a retryable syscall error (such	272	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	273	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	275	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	276	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	277	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	278	(such as abort).
225		279
226	Example: This is basically the same thing that libev does internally, too.	280	Example: This is basically the same thing that libev does internally, too.
…		…
237		291
238	=back	292	=back
239		293
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		295
242	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
243	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
244	events, and dynamically created loops which do not.	298	I<function>).
245		299
246	If you use threads, a common model is to run the default event loop	300	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	301	supports signals and child events, and dynamically created loops which do
248	create, you also create another event loop. Libev itself does no locking	302	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		303
253	=over 4	304	=over 4
254		305
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		307
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		312
262	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
263	function.	314	function.
264		315
		316	Note that this function is I<not> thread-safe, so if you want to use it
		317	from multiple threads, you have to lock (note also that this is unlikely,
		318	as loops cannot be shared easily between threads anyway).
		319
265	The default loop is the only loop that can handle C<ev_signal> and	320	The default loop is the only loop that can handle C<ev_signal> and
266	C<ev_child> watchers, and to do this, it always registers a handler	321	C<ev_child> watchers, and to do this, it always registers a handler
267	for C<SIGCHLD>. If this is a problem for your app you can either	322	for C<SIGCHLD>. If this is a problem for your application you can either
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	324	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
270	C<ev_default_init>.	325	C<ev_default_init>.
271		326
272	The flags argument can be used to specify special behaviour or specific	327	The flags argument can be used to specify special behaviour or specific
…		…
281	The default flags value. Use this if you have no clue (it's the right	336	The default flags value. Use this if you have no clue (it's the right
282	thing, believe me).	337	thing, believe me).
283		338
284	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
285		340
286	If this flag bit is ored into the flag value (or the program runs setuid	341	If this flag bit is or'ed into the flag value (or the program runs setuid
287	or setgid) then libev will I<not> look at the environment variable	342	or setgid) then libev will I<not> look at the environment variable
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	override the flags completely if it is found in the environment. This is	344	override the flags completely if it is found in the environment. This is
290	useful to try out specific backends to test their performance, or to work	345	useful to try out specific backends to test their performance, or to work
291	around bugs.	346	around bugs.
…		…
297	enabling this flag.	352	enabling this flag.
298		353
299	This works by calling C<getpid ()> on every iteration of the loop,	354	This works by calling C<getpid ()> on every iteration of the loop,
300	and thus this might slow down your event loop if you do a lot of loop	355	and thus this might slow down your event loop if you do a lot of loop
301	iterations and little real work, but is usually not noticeable (on my	356	iterations and little real work, but is usually not noticeable (on my
302	Linux system for example, C<getpid> is actually a simple 5-insn sequence	357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
303	without a syscall and thus I<very> fast, but my Linux system also has	358	without a system call and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
305		360
306	The big advantage of this flag is that you can forget about fork (and	361	The big advantage of this flag is that you can forget about fork (and
307	forget about forgetting to tell libev about forking) when you use this	362	forget about forgetting to tell libev about forking) when you use this
308	flag.	363	flag.
309		364
310	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
311	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
312		382
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		384
315	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
316	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
317	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
318	using this backend. It doesn't scale too well (O(highest_fd)), but its	388	using this backend. It doesn't scale too well (O(highest_fd)), but its
319	usually the fastest backend for a low number of (low-numbered :) fds.	389	usually the fastest backend for a low number of (low-numbered :) fds.
320		390
321	To get good performance out of this backend you need a high amount of	391	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	392	parallelism (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	393	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	394	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	395	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	396	readiness notifications you get per iteration.
		397
		398	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		399	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		400	C<exceptfds> set on that platform).
327		401
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	402	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		403
330	And this is your standard poll(2) backend. It's more complicated	404	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	405	than select, but handles sparse fds better and has no artificial
332	limit on the number of fds you can use (except it will slow down	406	limit on the number of fds you can use (except it will slow down
333	considerably with a lot of inactive fds). It scales similarly to select,	407	considerably with a lot of inactive fds). It scales similarly to select,
334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	408	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	409	performance tips.
336		410
		411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		413
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
338		418
339	For few fds, this backend is a bit little slower than poll and select,	419	For few fds, this backend is a bit little slower than poll and select,
340	but it scales phenomenally better. While poll and select usually scale	420	but it scales phenomenally better. While poll and select usually scale
341	like O(total_fds) where n is the total number of fds (or the highest fd),	421	like O(total_fds) where n is the total number of fds (or the highest fd),
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	422	epoll scales either O(1) or O(active_fds).
343	of shortcomings, such as silently dropping events in some hard-to-detect	423
344	cases and rewiring a syscall per fd change, no fork support and bad	424	The epoll mechanism deserves honorable mention as the most misdesigned
345	support for dup.	425	of the more advanced event mechanisms: mere annoyances include silently
		426	dropping file descriptors, requiring a system call per change per file
		427	descriptor (and unnecessary guessing of parameters), problems with dup and
		428	so on. The biggest issue is fork races, however - if a program forks then
		429	I<both> parent and child process have to recreate the epoll set, which can
		430	take considerable time (one syscall per file descriptor) and is of course
		431	hard to detect.
		432
		433	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		434	of course I<doesn't>, and epoll just loves to report events for totally
		435	I<different> file descriptors (even already closed ones, so one cannot
		436	even remove them from the set) than registered in the set (especially
		437	on SMP systems). Libev tries to counter these spurious notifications by
		438	employing an additional generation counter and comparing that against the
		439	events to filter out spurious ones, recreating the set when required.
346		440
347	While stopping, setting and starting an I/O watcher in the same iteration	441	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	442	will result in some caching, there is still a system call per such
349	(because the fd could point to a different file description now), so its	443	incident (because the same I<file descriptor> could point to a different
350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	444	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
351	very well if you register events for both fds.	445	file descriptors might not work very well if you register events for both
352		446	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		447
357	Best performance from this backend is achieved by not unregistering all	448	Best performance from this backend is achieved by not unregistering all
358	watchers for a file descriptor until it has been closed, if possible, i.e.	449	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	450	i.e. keep at least one watcher active per fd at all times. Stopping and
		451	starting a watcher (without re-setting it) also usually doesn't cause
		452	extra overhead. A fork can both result in spurious notifications as well
		453	as in libev having to destroy and recreate the epoll object, which can
		454	take considerable time and thus should be avoided.
360		455
		456	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		457	faster than epoll for maybe up to a hundred file descriptors, depending on
		458	the usage. So sad.
		459
361	While nominally embeddeble in other event loops, this feature is broken in	460	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	461	all kernel versions tested so far.
		462
		463	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		464	C<EVBACKEND_POLL>.
363		465
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	466	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		467
366	Kqueue deserves special mention, as at the time of this writing, it	468	Kqueue deserves special mention, as at the time of this writing, it
367	was broken on all BSDs except NetBSD (usually it doesn't work reliably	469	was broken on all BSDs except NetBSD (usually it doesn't work reliably
368	with anything but sockets and pipes, except on Darwin, where of course	470	with anything but sockets and pipes, except on Darwin, where of course
369	it's completely useless). For this reason it's not being "autodetected"	471	it's completely useless). Unlike epoll, however, whose brokenness
		472	is by design, these kqueue bugs can (and eventually will) be fixed
		473	without API changes to existing programs. For this reason it's not being
370	unless you explicitly specify it explicitly in the flags (i.e. using	474	"auto-detected" unless you explicitly specify it in the flags (i.e. using
371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	475	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
372	system like NetBSD.	476	system like NetBSD.
373		477
374	You still can embed kqueue into a normal poll or select backend and use it	478	You still can embed kqueue into a normal poll or select backend and use it
375	only for sockets (after having made sure that sockets work with kqueue on	479	only for sockets (after having made sure that sockets work with kqueue on
376	the target platform). See C<ev_embed> watchers for more info.	480	the target platform). See C<ev_embed> watchers for more info.
377		481
378	It scales in the same way as the epoll backend, but the interface to the	482	It scales in the same way as the epoll backend, but the interface to the
379	kernel is more efficient (which says nothing about its actual speed, of	483	kernel is more efficient (which says nothing about its actual speed, of
380	course). While stopping, setting and starting an I/O watcher does never	484	course). While stopping, setting and starting an I/O watcher does never
381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	485	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
382	two event changes per incident, support for C<fork ()> is very bad and it	486	two event changes per incident. Support for C<fork ()> is very bad (but
383	drops fds silently in similarly hard-to-detect cases.	487	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		488	cases
384		489
385	This backend usually performs well under most conditions.	490	This backend usually performs well under most conditions.
386		491
387	While nominally embeddable in other event loops, this doesn't work	492	While nominally embeddable in other event loops, this doesn't work
388	everywhere, so you might need to test for this. And since it is broken	493	everywhere, so you might need to test for this. And since it is broken
389	almost everywhere, you should only use it when you have a lot of sockets	494	almost everywhere, you should only use it when you have a lot of sockets
390	(for which it usually works), by embedding it into another event loop	495	(for which it usually works), by embedding it into another event loop
391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	496	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	497	also broken on OS X)) and, did I mention it, using it only for sockets.
		498
		499	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		500	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		501	C<NOTE_EOF>.
393		502
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	503	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		504
396	This is not implemented yet (and might never be, unless you send me an	505	This is not implemented yet (and might never be, unless you send me an
397	implementation). According to reports, C</dev/poll> only supports sockets	506	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	510	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		511
403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	512	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
404	it's really slow, but it still scales very well (O(active_fds)).	513	it's really slow, but it still scales very well (O(active_fds)).
405		514
406	Please note that solaris event ports can deliver a lot of spurious	515	Please note that Solaris event ports can deliver a lot of spurious
407	notifications, so you need to use non-blocking I/O or other means to avoid	516	notifications, so you need to use non-blocking I/O or other means to avoid
408	blocking when no data (or space) is available.	517	blocking when no data (or space) is available.
409		518
410	While this backend scales well, it requires one system call per active	519	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	520	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	521	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	522	might perform better.
414		523
415	On the positive side, ignoring the spurious readyness notifications, this	524	On the positive side, with the exception of the spurious readiness
416	backend actually performed to specification in all tests and is fully	525	notifications, this backend actually performed fully to specification
417	embeddable, which is a rare feat among the OS-specific backends.	526	in all tests and is fully embeddable, which is a rare feat among the
		527	OS-specific backends (I vastly prefer correctness over speed hacks).
		528
		529	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		530	C<EVBACKEND_POLL>.
418		531
419	=item C<EVBACKEND_ALL>	532	=item C<EVBACKEND_ALL>
420		533
421	Try all backends (even potentially broken ones that wouldn't be tried	534	Try all backends (even potentially broken ones that wouldn't be tried
422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	535	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
424		537
425	It is definitely not recommended to use this flag.	538	It is definitely not recommended to use this flag.
426		539
427	=back	540	=back
428		541
429	If one or more of these are ored into the flags value, then only these	542	If one or more of the backend flags are or'ed into the flags value,
430	backends will be tried (in the reverse order as listed here). If none are	543	then only these backends will be tried (in the reverse order as listed
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	544	here). If none are specified, all backends in C<ev_recommended_backends
		545	()> will be tried.
432		546
433	The most typical usage is like this:	547	Example: This is the most typical usage.
434		548
435	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437		551
438	Restrict libev to the select and poll backends, and do not allow	552	Example: Restrict libev to the select and poll backends, and do not allow
439	environment settings to be taken into account:	553	environment settings to be taken into account:
440		554
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	555	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442		556
443	Use whatever libev has to offer, but make sure that kqueue is used if	557	Example: Use whatever libev has to offer, but make sure that kqueue is
444	available (warning, breaks stuff, best use only with your own private	558	used if available (warning, breaks stuff, best use only with your own
445	event loop and only if you know the OS supports your types of fds):	559	private event loop and only if you know the OS supports your types of
		560	fds):
446		561
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	562	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448		563
449	=item struct ev_loop *ev_loop_new (unsigned int flags)	564	=item struct ev_loop *ev_loop_new (unsigned int flags)
450		565
451	Similar to C<ev_default_loop>, but always creates a new event loop that is	566	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot	567	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by	568	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).	569	undefined behaviour (or a failed assertion if assertions are enabled).
455		570
		571	Note that this function I<is> thread-safe, and the recommended way to use
		572	libev with threads is indeed to create one loop per thread, and using the
		573	default loop in the "main" or "initial" thread.
		574
456	Example: Try to create a event loop that uses epoll and nothing else.	575	Example: Try to create a event loop that uses epoll and nothing else.
457		576
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	577	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	578	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	579	fatal ("no epoll found here, maybe it hides under your chair");
461		580
462	=item ev_default_destroy ()	581	=item ev_default_destroy ()
463		582
464	Destroys the default loop again (frees all memory and kernel state	583	Destroys the default loop again (frees all memory and kernel state
465	etc.). None of the active event watchers will be stopped in the normal	584	etc.). None of the active event watchers will be stopped in the normal
466	sense, so e.g. C<ev_is_active> might still return true. It is your	585	sense, so e.g. C<ev_is_active> might still return true. It is your
467	responsibility to either stop all watchers cleanly yoursef I<before>	586	responsibility to either stop all watchers cleanly yourself I<before>
468	calling this function, or cope with the fact afterwards (which is usually	587	calling this function, or cope with the fact afterwards (which is usually
469	the easiest thing, you can just ignore the watchers and/or C<free ()> them	588	the easiest thing, you can just ignore the watchers and/or C<free ()> them
470	for example).	589	for example).
471		590
472	Note that certain global state, such as signal state, will not be freed by	591	Note that certain global state, such as signal state (and installed signal
473	this function, and related watchers (such as signal and child watchers)	592	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	593	as signal and child watchers) would need to be stopped manually.
475		594
476	In general it is not advisable to call this function except in the	595	In general it is not advisable to call this function except in the
477	rare occasion where you really need to free e.g. the signal handling	596	rare occasion where you really need to free e.g. the signal handling
478	pipe fds. If you need dynamically allocated loops it is better to use	597	pipe fds. If you need dynamically allocated loops it is better to use
479	C<ev_loop_new> and C<ev_loop_destroy>).	598	C<ev_loop_new> and C<ev_loop_destroy>.
480		599
481	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
482		601
483	Like C<ev_default_destroy>, but destroys an event loop created by an	602	Like C<ev_default_destroy>, but destroys an event loop created by an
484	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
…		…
504		623
505	=item ev_loop_fork (loop)	624	=item ev_loop_fork (loop)
506		625
507	Like C<ev_default_fork>, but acts on an event loop created by	626	Like C<ev_default_fork>, but acts on an event loop created by
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	627	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
509	after fork, and how you do this is entirely your own problem.	628	after fork that you want to re-use in the child, and how you do this is
		629	entirely your own problem.
		630
		631	=item int ev_is_default_loop (loop)
		632
		633	Returns true when the given loop is, in fact, the default loop, and false
		634	otherwise.
510		635
511	=item unsigned int ev_loop_count (loop)	636	=item unsigned int ev_loop_count (loop)
512		637
513	Returns the count of loop iterations for the loop, which is identical to	638	Returns the count of loop iterations for the loop, which is identical to
514	the number of times libev did poll for new events. It starts at C<0> and	639	the number of times libev did poll for new events. It starts at C<0> and
515	happily wraps around with enough iterations.	640	happily wraps around with enough iterations.
516		641
517	This value can sometimes be useful as a generation counter of sorts (it	642	This value can sometimes be useful as a generation counter of sorts (it
518	"ticks" the number of loop iterations), as it roughly corresponds with	643	"ticks" the number of loop iterations), as it roughly corresponds with
519	C<ev_prepare> and C<ev_check> calls.	644	C<ev_prepare> and C<ev_check> calls.
		645
		646	=item unsigned int ev_loop_depth (loop)
		647
		648	Returns the number of times C<ev_loop> was entered minus the number of
		649	times C<ev_loop> was exited, in other words, the recursion depth.
		650
		651	Outside C<ev_loop>, this number is zero. In a callback, this number is
		652	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		653	in which case it is higher.
		654
		655	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		656	etc.), doesn't count as exit.
520		657
521	=item unsigned int ev_backend (loop)	658	=item unsigned int ev_backend (loop)
522		659
523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	660	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
524	use.	661	use.
…		…
529	received events and started processing them. This timestamp does not	666	received events and started processing them. This timestamp does not
530	change as long as callbacks are being processed, and this is also the base	667	change as long as callbacks are being processed, and this is also the base
531	time used for relative timers. You can treat it as the timestamp of the	668	time used for relative timers. You can treat it as the timestamp of the
532	event occurring (or more correctly, libev finding out about it).	669	event occurring (or more correctly, libev finding out about it).
533		670
		671	=item ev_now_update (loop)
		672
		673	Establishes the current time by querying the kernel, updating the time
		674	returned by C<ev_now ()> in the progress. This is a costly operation and
		675	is usually done automatically within C<ev_loop ()>.
		676
		677	This function is rarely useful, but when some event callback runs for a
		678	very long time without entering the event loop, updating libev's idea of
		679	the current time is a good idea.
		680
		681	See also L<The special problem of time updates> in the C<ev_timer> section.
		682
		683	=item ev_suspend (loop)
		684
		685	=item ev_resume (loop)
		686
		687	These two functions suspend and resume a loop, for use when the loop is
		688	not used for a while and timeouts should not be processed.
		689
		690	A typical use case would be an interactive program such as a game: When
		691	the user presses C<^Z> to suspend the game and resumes it an hour later it
		692	would be best to handle timeouts as if no time had actually passed while
		693	the program was suspended. This can be achieved by calling C<ev_suspend>
		694	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		695	C<ev_resume> directly afterwards to resume timer processing.
		696
		697	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		698	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		699	will be rescheduled (that is, they will lose any events that would have
		700	occured while suspended).
		701
		702	After calling C<ev_suspend> you B<must not> call I<any> function on the
		703	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		704	without a previous call to C<ev_suspend>.
		705
		706	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		707	event loop time (see C<ev_now_update>).
		708
534	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
535		710
536	Finally, this is it, the event handler. This function usually is called	711	Finally, this is it, the event handler. This function usually is called
537	after you initialised all your watchers and you want to start handling	712	after you have initialised all your watchers and you want to start
538	events.	713	handling events.
539		714
540	If the flags argument is specified as C<0>, it will not return until	715	If the flags argument is specified as C<0>, it will not return until
541	either no event watchers are active anymore or C<ev_unloop> was called.	716	either no event watchers are active anymore or C<ev_unloop> was called.
542		717
543	Please note that an explicit C<ev_unloop> is usually better than	718	Please note that an explicit C<ev_unloop> is usually better than
544	relying on all watchers to be stopped when deciding when a program has	719	relying on all watchers to be stopped when deciding when a program has
545	finished (especially in interactive programs), but having a program that	720	finished (especially in interactive programs), but having a program
546	automatically loops as long as it has to and no longer by virtue of	721	that automatically loops as long as it has to and no longer by virtue
547	relying on its watchers stopping correctly is a thing of beauty.	722	of relying on its watchers stopping correctly, that is truly a thing of
		723	beauty.
548		724
549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	725	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
550	those events and any outstanding ones, but will not block your process in	726	those events and any already outstanding ones, but will not block your
551	case there are no events and will return after one iteration of the loop.	727	process in case there are no events and will return after one iteration of
		728	the loop.
552		729
553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	730	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
554	neccessary) and will handle those and any outstanding ones. It will block	731	necessary) and will handle those and any already outstanding ones. It
555	your process until at least one new event arrives, and will return after	732	will block your process until at least one new event arrives (which could
556	one iteration of the loop. This is useful if you are waiting for some	733	be an event internal to libev itself, so there is no guarantee that a
557	external event in conjunction with something not expressible using other	734	user-registered callback will be called), and will return after one
		735	iteration of the loop.
		736
		737	This is useful if you are waiting for some external event in conjunction
		738	with something not expressible using other libev watchers (i.e. "roll your
558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	739	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
559	usually a better approach for this kind of thing.	740	usually a better approach for this kind of thing.
560		741
561	Here are the gory details of what C<ev_loop> does:	742	Here are the gory details of what C<ev_loop> does:
562		743
563	- Before the first iteration, call any pending watchers.	744	- Before the first iteration, call any pending watchers.
564	* If EVFLAG_FORKCHECK was used, check for a fork.	745	* If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	746	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	747	- Queue and call all prepare watchers.
567	- If we have been forked, recreate the kernel state.	748	- If we have been forked, detach and recreate the kernel state
		749	as to not disturb the other process.
568	- Update the kernel state with all outstanding changes.	750	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	751	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	752	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	753	(active idle watchers, EVLOOP_NONBLOCK or not having
572	any active watchers at all will result in not sleeping).	754	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	755	- Sleep if the I/O and timer collect interval say so.
574	- Block the process, waiting for any events.	756	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	757	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	758	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	759	- Queue all expired timers.
578	- Queue all outstanding periodics.	760	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	761	- Unless any events are pending now, queue all idle watchers.
580	- Queue all check watchers.	762	- Queue all check watchers.
581	- Call all queued watchers in reverse order (i.e. check watchers first).	763	- Call all queued watchers in reverse order (i.e. check watchers first).
582	Signals and child watchers are implemented as I/O watchers, and will	764	Signals and child watchers are implemented as I/O watchers, and will
583	be handled here by queueing them when their watcher gets executed.	765	be handled here by queueing them when their watcher gets executed.
584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	766	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
589	anymore.	771	anymore.
590		772
591	... queue jobs here, make sure they register event watchers as long	773	... queue jobs here, make sure they register event watchers as long
592	... as they still have work to do (even an idle watcher will do..)	774	... as they still have work to do (even an idle watcher will do..)
593	ev_loop (my_loop, 0);	775	ev_loop (my_loop, 0);
594	... jobs done. yeah!	776	... jobs done or somebody called unloop. yeah!
595		777
596	=item ev_unloop (loop, how)	778	=item ev_unloop (loop, how)
597		779
598	Can be used to make a call to C<ev_loop> return early (but only after it	780	Can be used to make a call to C<ev_loop> return early (but only after it
599	has processed all outstanding events). The C<how> argument must be either	781	has processed all outstanding events). The C<how> argument must be either
600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	782	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	783	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
602		784
603	This "unloop state" will be cleared when entering C<ev_loop> again.	785	This "unloop state" will be cleared when entering C<ev_loop> again.
604		786
		787	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		788
605	=item ev_ref (loop)	789	=item ev_ref (loop)
606		790
607	=item ev_unref (loop)	791	=item ev_unref (loop)
608		792
609	Ref/unref can be used to add or remove a reference count on the event	793	Ref/unref can be used to add or remove a reference count on the event
610	loop: Every watcher keeps one reference, and as long as the reference	794	loop: Every watcher keeps one reference, and as long as the reference
611	count is nonzero, C<ev_loop> will not return on its own. If you have	795	count is nonzero, C<ev_loop> will not return on its own.
		796
612	a watcher you never unregister that should not keep C<ev_loop> from	797	If you have a watcher you never unregister that should not keep C<ev_loop>
613	returning, ev_unref() after starting, and ev_ref() before stopping it. For	798	from returning, call ev_unref() after starting, and ev_ref() before
		799	stopping it.
		800
614	example, libev itself uses this for its internal signal pipe: It is not	801	As an example, libev itself uses this for its internal signal pipe: It
615	visible to the libev user and should not keep C<ev_loop> from exiting if	802	is not visible to the libev user and should not keep C<ev_loop> from
616	no event watchers registered by it are active. It is also an excellent	803	exiting if no event watchers registered by it are active. It is also an
617	way to do this for generic recurring timers or from within third-party	804	excellent way to do this for generic recurring timers or from within
618	libraries. Just remember to I<unref after start> and I<ref before stop>	805	third-party libraries. Just remember to I<unref after start> and I<ref
619	(but only if the watcher wasn't active before, or was active before,	806	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	807	before, respectively. Note also that libev might stop watchers itself
		808	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		809	in the callback).
621		810
622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	811	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
623	running when nothing else is active.	812	running when nothing else is active.
624		813
625	struct ev_signal exitsig;	814	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	815	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	816	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	817	evf_unref (loop);
629		818
630	Example: For some weird reason, unregister the above signal handler again.	819	Example: For some weird reason, unregister the above signal handler again.
631		820
632	ev_ref (loop);	821	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	822	ev_signal_stop (loop, &exitsig);
634		823
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	824	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		825
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	826	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		827
639	These advanced functions influence the time that libev will spend waiting	828	These advanced functions influence the time that libev will spend waiting
640	for events. Both are by default C<0>, meaning that libev will try to	829	for events. Both time intervals are by default C<0>, meaning that libev
641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	830	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		831	latency.
642		832
643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	833	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
644	allows libev to delay invocation of I/O and timer/periodic callbacks to	834	allows libev to delay invocation of I/O and timer/periodic callbacks
645	increase efficiency of loop iterations.	835	to increase efficiency of loop iterations (or to increase power-saving
		836	opportunities).
646		837
647	The background is that sometimes your program runs just fast enough to	838	The idea is that sometimes your program runs just fast enough to handle
648	handle one (or very few) event(s) per loop iteration. While this makes	839	one (or very few) event(s) per loop iteration. While this makes the
649	the program responsive, it also wastes a lot of CPU time to poll for new	840	program responsive, it also wastes a lot of CPU time to poll for new
650	events, especially with backends like C<select ()> which have a high	841	events, especially with backends like C<select ()> which have a high
651	overhead for the actual polling but can deliver many events at once.	842	overhead for the actual polling but can deliver many events at once.
652		843
653	By setting a higher I<io collect interval> you allow libev to spend more	844	By setting a higher I<io collect interval> you allow libev to spend more
654	time collecting I/O events, so you can handle more events per iteration,	845	time collecting I/O events, so you can handle more events per iteration,
655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	846	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
656	C<ev_timer>) will be not affected. Setting this to a non-null value will	847	C<ev_timer>) will be not affected. Setting this to a non-null value will
657	introduce an additional C<ev_sleep ()> call into most loop iterations.	848	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		849	sleep time ensures that libev will not poll for I/O events more often then
		850	once per this interval, on average.
658		851
659	Likewise, by setting a higher I<timeout collect interval> you allow libev	852	Likewise, by setting a higher I<timeout collect interval> you allow libev
660	to spend more time collecting timeouts, at the expense of increased	853	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	854	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	855	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	856	value will not introduce any overhead in libev.
664		857
665	Many (busy) programs can usually benefit by setting the io collect	858	Many (busy) programs can usually benefit by setting the I/O collect
666	interval to a value near C<0.1> or so, which is often enough for	859	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	860	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	861	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches the timing granularity of most systems.	862	as this approaches the timing granularity of most systems. Note that if
		863	you do transactions with the outside world and you can't increase the
		864	parallelity, then this setting will limit your transaction rate (if you
		865	need to poll once per transaction and the I/O collect interval is 0.01,
		866	then you can't do more than 100 transations per second).
		867
		868	Setting the I<timeout collect interval> can improve the opportunity for
		869	saving power, as the program will "bundle" timer callback invocations that
		870	are "near" in time together, by delaying some, thus reducing the number of
		871	times the process sleeps and wakes up again. Another useful technique to
		872	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		873	they fire on, say, one-second boundaries only.
		874
		875	Example: we only need 0.1s timeout granularity, and we wish not to poll
		876	more often than 100 times per second:
		877
		878	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		879	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		880
		881	=item ev_invoke_pending (loop)
		882
		883	This call will simply invoke all pending watchers while resetting their
		884	pending state. Normally, C<ev_loop> does this automatically when required,
		885	but when overriding the invoke callback this call comes handy.
		886
		887	=item int ev_pending_count (loop)
		888
		889	Returns the number of pending watchers - zero indicates that no watchers
		890	are pending.
		891
		892	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		893
		894	This overrides the invoke pending functionality of the loop: Instead of
		895	invoking all pending watchers when there are any, C<ev_loop> will call
		896	this callback instead. This is useful, for example, when you want to
		897	invoke the actual watchers inside another context (another thread etc.).
		898
		899	If you want to reset the callback, use C<ev_invoke_pending> as new
		900	callback.
		901
		902	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		903
		904	Sometimes you want to share the same loop between multiple threads. This
		905	can be done relatively simply by putting mutex_lock/unlock calls around
		906	each call to a libev function.
		907
		908	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		909	wait for it to return. One way around this is to wake up the loop via
		910	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		911	and I<acquire> callbacks on the loop.
		912
		913	When set, then C<release> will be called just before the thread is
		914	suspended waiting for new events, and C<acquire> is called just
		915	afterwards.
		916
		917	Ideally, C<release> will just call your mutex_unlock function, and
		918	C<acquire> will just call the mutex_lock function again.
		919
		920	While event loop modifications are allowed between invocations of
		921	C<release> and C<acquire> (that's their only purpose after all), no
		922	modifications done will affect the event loop, i.e. adding watchers will
		923	have no effect on the set of file descriptors being watched, or the time
		924	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		925	to take note of any changes you made.
		926
		927	In theory, threads executing C<ev_loop> will be async-cancel safe between
		928	invocations of C<release> and C<acquire>.
		929
		930	See also the locking example in the C<THREADS> section later in this
		931	document.
		932
		933	=item ev_set_userdata (loop, void *data)
		934
		935	=item ev_userdata (loop)
		936
		937	Set and retrieve a single C<void *> associated with a loop. When
		938	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		939	C<0.>
		940
		941	These two functions can be used to associate arbitrary data with a loop,
		942	and are intended solely for the C<invoke_pending_cb>, C<release> and
		943	C<acquire> callbacks described above, but of course can be (ab-)used for
		944	any other purpose as well.
		945
		946	=item ev_loop_verify (loop)
		947
		948	This function only does something when C<EV_VERIFY> support has been
		949	compiled in, which is the default for non-minimal builds. It tries to go
		950	through all internal structures and checks them for validity. If anything
		951	is found to be inconsistent, it will print an error message to standard
		952	error and call C<abort ()>.
		953
		954	This can be used to catch bugs inside libev itself: under normal
		955	circumstances, this function will never abort as of course libev keeps its
		956	data structures consistent.
670		957
671	=back	958	=back
672		959
673		960
674	=head1 ANATOMY OF A WATCHER	961	=head1 ANATOMY OF A WATCHER
		962
		963	In the following description, uppercase C<TYPE> in names stands for the
		964	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		965	watchers and C<ev_io_start> for I/O watchers.
675		966
676	A watcher is a structure that you create and register to record your	967	A watcher is a structure that you create and register to record your
677	interest in some event. For instance, if you want to wait for STDIN to	968	interest in some event. For instance, if you want to wait for STDIN to
678	become readable, you would create an C<ev_io> watcher for that:	969	become readable, you would create an C<ev_io> watcher for that:
679		970
680	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	971	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
681	{	972	{
682	ev_io_stop (w);	973	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	974	ev_unloop (loop, EVUNLOOP_ALL);
684	}	975	}
685		976
686	struct ev_loop *loop = ev_default_loop (0);	977	struct ev_loop *loop = ev_default_loop (0);
		978
687	struct ev_io stdin_watcher;	979	ev_io stdin_watcher;
		980
688	ev_init (&stdin_watcher, my_cb);	981	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	982	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	983	ev_io_start (loop, &stdin_watcher);
		984
691	ev_loop (loop, 0);	985	ev_loop (loop, 0);
692		986
693	As you can see, you are responsible for allocating the memory for your	987	As you can see, you are responsible for allocating the memory for your
694	watcher structures (and it is usually a bad idea to do this on the stack,	988	watcher structures (and it is I<usually> a bad idea to do this on the
695	although this can sometimes be quite valid).	989	stack).
		990
		991	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		992	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
696		993
697	Each watcher structure must be initialised by a call to C<ev_init	994	Each watcher structure must be initialised by a call to C<ev_init
698	(watcher *, callback)>, which expects a callback to be provided. This	995	(watcher *, callback)>, which expects a callback to be provided. This
699	callback gets invoked each time the event occurs (or, in the case of io	996	callback gets invoked each time the event occurs (or, in the case of I/O
700	watchers, each time the event loop detects that the file descriptor given	997	watchers, each time the event loop detects that the file descriptor given
701	is readable and/or writable).	998	is readable and/or writable).
702		999
703	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1000	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
704	with arguments specific to this watcher type. There is also a macro	1001	macro to configure it, with arguments specific to the watcher type. There
705	to combine initialisation and setting in one call: C<< ev_<type>_init	1002	is also a macro to combine initialisation and setting in one call: C<<
706	(watcher *, callback, ...) >>.	1003	ev_TYPE_init (watcher *, callback, ...) >>.
707		1004
708	To make the watcher actually watch out for events, you have to start it	1005	To make the watcher actually watch out for events, you have to start it
709	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1006	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
710	*) >>), and you can stop watching for events at any time by calling the	1007	*) >>), and you can stop watching for events at any time by calling the
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1008	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		1009
713	As long as your watcher is active (has been started but not stopped) you	1010	As long as your watcher is active (has been started but not stopped) you
714	must not touch the values stored in it. Most specifically you must never	1011	must not touch the values stored in it. Most specifically you must never
715	reinitialise it or call its C<set> macro.	1012	reinitialise it or call its C<ev_TYPE_set> macro.
716		1013
717	Each and every callback receives the event loop pointer as first, the	1014	Each and every callback receives the event loop pointer as first, the
718	registered watcher structure as second, and a bitset of received events as	1015	registered watcher structure as second, and a bitset of received events as
719	third argument.	1016	third argument.
720		1017
…		…
778		1075
779	=item C<EV_ASYNC>	1076	=item C<EV_ASYNC>
780		1077
781	The given async watcher has been asynchronously notified (see C<ev_async>).	1078	The given async watcher has been asynchronously notified (see C<ev_async>).
782		1079
		1080	=item C<EV_CUSTOM>
		1081
		1082	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1083	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1084
783	=item C<EV_ERROR>	1085	=item C<EV_ERROR>
784		1086
785	An unspecified error has occured, the watcher has been stopped. This might	1087	An unspecified error has occurred, the watcher has been stopped. This might
786	happen because the watcher could not be properly started because libev	1088	happen because the watcher could not be properly started because libev
787	ran out of memory, a file descriptor was found to be closed or any other	1089	ran out of memory, a file descriptor was found to be closed or any other
		1090	problem. Libev considers these application bugs.
		1091
788	problem. You best act on it by reporting the problem and somehow coping	1092	You best act on it by reporting the problem and somehow coping with the
789	with the watcher being stopped.	1093	watcher being stopped. Note that well-written programs should not receive
		1094	an error ever, so when your watcher receives it, this usually indicates a
		1095	bug in your program.
790		1096
791	Libev will usually signal a few "dummy" events together with an error,	1097	Libev will usually signal a few "dummy" events together with an error, for
792	for example it might indicate that a fd is readable or writable, and if	1098	example it might indicate that a fd is readable or writable, and if your
793	your callbacks is well-written it can just attempt the operation and cope	1099	callbacks is well-written it can just attempt the operation and cope with
794	with the error from read() or write(). This will not work in multithreaded	1100	the error from read() or write(). This will not work in multi-threaded
795	programs, though, so beware.	1101	programs, though, as the fd could already be closed and reused for another
		1102	thing, so beware.
796		1103
797	=back	1104	=back
798		1105
799	=head2 GENERIC WATCHER FUNCTIONS	1106	=head2 GENERIC WATCHER FUNCTIONS
800
801	In the following description, C<TYPE> stands for the watcher type,
802	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
803		1107
804	=over 4	1108	=over 4
805		1109
806	=item C<ev_init> (ev_TYPE *watcher, callback)	1110	=item C<ev_init> (ev_TYPE *watcher, callback)
807		1111
…		…
813	which rolls both calls into one.	1117	which rolls both calls into one.
814		1118
815	You can reinitialise a watcher at any time as long as it has been stopped	1119	You can reinitialise a watcher at any time as long as it has been stopped
816	(or never started) and there are no pending events outstanding.	1120	(or never started) and there are no pending events outstanding.
817		1121
818	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1122	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
819	int revents)>.	1123	int revents)>.
		1124
		1125	Example: Initialise an C<ev_io> watcher in two steps.
		1126
		1127	ev_io w;
		1128	ev_init (&w, my_cb);
		1129	ev_io_set (&w, STDIN_FILENO, EV_READ);
820		1130
821	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1131	=item C<ev_TYPE_set> (ev_TYPE *, [args])
822		1132
823	This macro initialises the type-specific parts of a watcher. You need to	1133	This macro initialises the type-specific parts of a watcher. You need to
824	call C<ev_init> at least once before you call this macro, but you can	1134	call C<ev_init> at least once before you call this macro, but you can
…		…
827	difference to the C<ev_init> macro).	1137	difference to the C<ev_init> macro).
828		1138
829	Although some watcher types do not have type-specific arguments	1139	Although some watcher types do not have type-specific arguments
830	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1140	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
831		1141
		1142	See C<ev_init>, above, for an example.
		1143
832	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1144	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
833		1145
834	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1146	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
835	calls into a single call. This is the most convinient method to initialise	1147	calls into a single call. This is the most convenient method to initialise
836	a watcher. The same limitations apply, of course.	1148	a watcher. The same limitations apply, of course.
		1149
		1150	Example: Initialise and set an C<ev_io> watcher in one step.
		1151
		1152	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
837		1153
838	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1154	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
839		1155
840	Starts (activates) the given watcher. Only active watchers will receive	1156	Starts (activates) the given watcher. Only active watchers will receive
841	events. If the watcher is already active nothing will happen.	1157	events. If the watcher is already active nothing will happen.
842		1158
		1159	Example: Start the C<ev_io> watcher that is being abused as example in this
		1160	whole section.
		1161
		1162	ev_io_start (EV_DEFAULT_UC, &w);
		1163
843	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1164	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
844		1165
845	Stops the given watcher again (if active) and clears the pending	1166	Stops the given watcher if active, and clears the pending status (whether
		1167	the watcher was active or not).
		1168
846	status. It is possible that stopped watchers are pending (for example,	1169	It is possible that stopped watchers are pending - for example,
847	non-repeating timers are being stopped when they become pending), but	1170	non-repeating timers are being stopped when they become pending - but
848	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1171	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
849	you want to free or reuse the memory used by the watcher it is therefore a	1172	pending. If you want to free or reuse the memory used by the watcher it is
850	good idea to always call its C<ev_TYPE_stop> function.	1173	therefore a good idea to always call its C<ev_TYPE_stop> function.
851		1174
852	=item bool ev_is_active (ev_TYPE *watcher)	1175	=item bool ev_is_active (ev_TYPE *watcher)
853		1176
854	Returns a true value iff the watcher is active (i.e. it has been started	1177	Returns a true value iff the watcher is active (i.e. it has been started
855	and not yet been stopped). As long as a watcher is active you must not modify	1178	and not yet been stopped). As long as a watcher is active you must not modify
…		…
881	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1204	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
882	(default: C<-2>). Pending watchers with higher priority will be invoked	1205	(default: C<-2>). Pending watchers with higher priority will be invoked
883	before watchers with lower priority, but priority will not keep watchers	1206	before watchers with lower priority, but priority will not keep watchers
884	from being executed (except for C<ev_idle> watchers).	1207	from being executed (except for C<ev_idle> watchers).
885		1208
886	This means that priorities are I<only> used for ordering callback
887	invocation after new events have been received. This is useful, for
888	example, to reduce latency after idling, or more often, to bind two
889	watchers on the same event and make sure one is called first.
890
891	If you need to suppress invocation when higher priority events are pending	1209	If you need to suppress invocation when higher priority events are pending
892	you need to look at C<ev_idle> watchers, which provide this functionality.	1210	you need to look at C<ev_idle> watchers, which provide this functionality.
893		1211
894	You I<must not> change the priority of a watcher as long as it is active or	1212	You I<must not> change the priority of a watcher as long as it is active or
895	pending.	1213	pending.
896		1214
		1215	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1216	fine, as long as you do not mind that the priority value you query might
		1217	or might not have been clamped to the valid range.
		1218
897	The default priority used by watchers when no priority has been set is	1219	The default priority used by watchers when no priority has been set is
898	always C<0>, which is supposed to not be too high and not be too low :).	1220	always C<0>, which is supposed to not be too high and not be too low :).
899		1221
900	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1222	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
901	fine, as long as you do not mind that the priority value you query might	1223	priorities.
902	or might not have been adjusted to be within valid range.
903		1224
904	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1225	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
905		1226
906	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1227	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
907	C<loop> nor C<revents> need to be valid as long as the watcher callback	1228	C<loop> nor C<revents> need to be valid as long as the watcher callback
908	can deal with that fact.	1229	can deal with that fact, as both are simply passed through to the
		1230	callback.
909		1231
910	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1232	=item int ev_clear_pending (loop, ev_TYPE *watcher)
911		1233
912	If the watcher is pending, this function returns clears its pending status	1234	If the watcher is pending, this function clears its pending status and
913	and returns its C<revents> bitset (as if its callback was invoked). If the	1235	returns its C<revents> bitset (as if its callback was invoked). If the
914	watcher isn't pending it does nothing and returns C<0>.	1236	watcher isn't pending it does nothing and returns C<0>.
915		1237
		1238	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1239	callback to be invoked, which can be accomplished with this function.
		1240
916	=back	1241	=back
917		1242
918		1243
919	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1244	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
920		1245
921	Each watcher has, by default, a member C<void *data> that you can change	1246	Each watcher has, by default, a member C<void *data> that you can change
922	and read at any time, libev will completely ignore it. This can be used	1247	and read at any time: libev will completely ignore it. This can be used
923	to associate arbitrary data with your watcher. If you need more data and	1248	to associate arbitrary data with your watcher. If you need more data and
924	don't want to allocate memory and store a pointer to it in that data	1249	don't want to allocate memory and store a pointer to it in that data
925	member, you can also "subclass" the watcher type and provide your own	1250	member, you can also "subclass" the watcher type and provide your own
926	data:	1251	data:
927		1252
928	struct my_io	1253	struct my_io
929	{	1254	{
930	struct ev_io io;	1255	ev_io io;
931	int otherfd;	1256	int otherfd;
932	void *somedata;	1257	void *somedata;
933	struct whatever *mostinteresting;	1258	struct whatever *mostinteresting;
934	}	1259	};
		1260
		1261	...
		1262	struct my_io w;
		1263	ev_io_init (&w.io, my_cb, fd, EV_READ);
935		1264
936	And since your callback will be called with a pointer to the watcher, you	1265	And since your callback will be called with a pointer to the watcher, you
937	can cast it back to your own type:	1266	can cast it back to your own type:
938		1267
939	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1268	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
940	{	1269	{
941	struct my_io *w = (struct my_io *)w_;	1270	struct my_io *w = (struct my_io *)w_;
942	...	1271	...
943	}	1272	}
944		1273
945	More interesting and less C-conformant ways of casting your callback type	1274	More interesting and less C-conformant ways of casting your callback type
946	instead have been omitted.	1275	instead have been omitted.
947		1276
948	Another common scenario is having some data structure with multiple	1277	Another common scenario is to use some data structure with multiple
949	watchers:	1278	embedded watchers:
950		1279
951	struct my_biggy	1280	struct my_biggy
952	{	1281	{
953	int some_data;	1282	int some_data;
954	ev_timer t1;	1283	ev_timer t1;
955	ev_timer t2;	1284	ev_timer t2;
956	}	1285	}
957		1286
958	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1287	In this case getting the pointer to C<my_biggy> is a bit more
959	you need to use C<offsetof>:	1288	complicated: Either you store the address of your C<my_biggy> struct
		1289	in the C<data> member of the watcher (for woozies), or you need to use
		1290	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1291	programmers):
960		1292
961	#include <stddef.h>	1293	#include <stddef.h>
962		1294
963	static void	1295	static void
964	t1_cb (EV_P_ struct ev_timer *w, int revents)	1296	t1_cb (EV_P_ ev_timer *w, int revents)
965	{	1297	{
966	struct my_biggy big = (struct my_biggy *	1298	struct my_biggy big = (struct my_biggy *)
967	(((char *)w) - offsetof (struct my_biggy, t1));	1299	(((char *)w) - offsetof (struct my_biggy, t1));
968	}	1300	}
969		1301
970	static void	1302	static void
971	t2_cb (EV_P_ struct ev_timer *w, int revents)	1303	t2_cb (EV_P_ ev_timer *w, int revents)
972	{	1304	{
973	struct my_biggy big = (struct my_biggy *	1305	struct my_biggy big = (struct my_biggy *)
974	(((char *)w) - offsetof (struct my_biggy, t2));	1306	(((char *)w) - offsetof (struct my_biggy, t2));
975	}	1307	}
		1308
		1309	=head2 WATCHER PRIORITY MODELS
		1310
		1311	Many event loops support I<watcher priorities>, which are usually small
		1312	integers that influence the ordering of event callback invocation
		1313	between watchers in some way, all else being equal.
		1314
		1315	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1316	description for the more technical details such as the actual priority
		1317	range.
		1318
		1319	There are two common ways how these these priorities are being interpreted
		1320	by event loops:
		1321
		1322	In the more common lock-out model, higher priorities "lock out" invocation
		1323	of lower priority watchers, which means as long as higher priority
		1324	watchers receive events, lower priority watchers are not being invoked.
		1325
		1326	The less common only-for-ordering model uses priorities solely to order
		1327	callback invocation within a single event loop iteration: Higher priority
		1328	watchers are invoked before lower priority ones, but they all get invoked
		1329	before polling for new events.
		1330
		1331	Libev uses the second (only-for-ordering) model for all its watchers
		1332	except for idle watchers (which use the lock-out model).
		1333
		1334	The rationale behind this is that implementing the lock-out model for
		1335	watchers is not well supported by most kernel interfaces, and most event
		1336	libraries will just poll for the same events again and again as long as
		1337	their callbacks have not been executed, which is very inefficient in the
		1338	common case of one high-priority watcher locking out a mass of lower
		1339	priority ones.
		1340
		1341	Static (ordering) priorities are most useful when you have two or more
		1342	watchers handling the same resource: a typical usage example is having an
		1343	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1344	timeouts. Under load, data might be received while the program handles
		1345	other jobs, but since timers normally get invoked first, the timeout
		1346	handler will be executed before checking for data. In that case, giving
		1347	the timer a lower priority than the I/O watcher ensures that I/O will be
		1348	handled first even under adverse conditions (which is usually, but not
		1349	always, what you want).
		1350
		1351	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1352	will only be executed when no same or higher priority watchers have
		1353	received events, they can be used to implement the "lock-out" model when
		1354	required.
		1355
		1356	For example, to emulate how many other event libraries handle priorities,
		1357	you can associate an C<ev_idle> watcher to each such watcher, and in
		1358	the normal watcher callback, you just start the idle watcher. The real
		1359	processing is done in the idle watcher callback. This causes libev to
		1360	continously poll and process kernel event data for the watcher, but when
		1361	the lock-out case is known to be rare (which in turn is rare :), this is
		1362	workable.
		1363
		1364	Usually, however, the lock-out model implemented that way will perform
		1365	miserably under the type of load it was designed to handle. In that case,
		1366	it might be preferable to stop the real watcher before starting the
		1367	idle watcher, so the kernel will not have to process the event in case
		1368	the actual processing will be delayed for considerable time.
		1369
		1370	Here is an example of an I/O watcher that should run at a strictly lower
		1371	priority than the default, and which should only process data when no
		1372	other events are pending:
		1373
		1374	ev_idle idle; // actual processing watcher
		1375	ev_io io; // actual event watcher
		1376
		1377	static void
		1378	io_cb (EV_P_ ev_io *w, int revents)
		1379	{
		1380	// stop the I/O watcher, we received the event, but
		1381	// are not yet ready to handle it.
		1382	ev_io_stop (EV_A_ w);
		1383
		1384	// start the idle watcher to ahndle the actual event.
		1385	// it will not be executed as long as other watchers
		1386	// with the default priority are receiving events.
		1387	ev_idle_start (EV_A_ &idle);
		1388	}
		1389
		1390	static void
		1391	idle_cb (EV_P_ ev_idle *w, int revents)
		1392	{
		1393	// actual processing
		1394	read (STDIN_FILENO, ...);
		1395
		1396	// have to start the I/O watcher again, as
		1397	// we have handled the event
		1398	ev_io_start (EV_P_ &io);
		1399	}
		1400
		1401	// initialisation
		1402	ev_idle_init (&idle, idle_cb);
		1403	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1404	ev_io_start (EV_DEFAULT_ &io);
		1405
		1406	In the "real" world, it might also be beneficial to start a timer, so that
		1407	low-priority connections can not be locked out forever under load. This
		1408	enables your program to keep a lower latency for important connections
		1409	during short periods of high load, while not completely locking out less
		1410	important ones.
976		1411
977		1412
978	=head1 WATCHER TYPES	1413	=head1 WATCHER TYPES
979		1414
980	This section describes each watcher in detail, but will not repeat	1415	This section describes each watcher in detail, but will not repeat
…		…
1004	In general you can register as many read and/or write event watchers per	1439	In general you can register as many read and/or write event watchers per
1005	fd as you want (as long as you don't confuse yourself). Setting all file	1440	fd as you want (as long as you don't confuse yourself). Setting all file
1006	descriptors to non-blocking mode is also usually a good idea (but not	1441	descriptors to non-blocking mode is also usually a good idea (but not
1007	required if you know what you are doing).	1442	required if you know what you are doing).
1008		1443
1009	If you must do this, then force the use of a known-to-be-good backend	1444	If you cannot use non-blocking mode, then force the use of a
1010	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1445	known-to-be-good backend (at the time of this writing, this includes only
1011	C<EVBACKEND_POLL>).	1446	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1447	descriptors for which non-blocking operation makes no sense (such as
		1448	files) - libev doesn't guarentee any specific behaviour in that case.
1012		1449
1013	Another thing you have to watch out for is that it is quite easy to	1450	Another thing you have to watch out for is that it is quite easy to
1014	receive "spurious" readyness notifications, that is your callback might	1451	receive "spurious" readiness notifications, that is your callback might
1015	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1452	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1016	because there is no data. Not only are some backends known to create a	1453	because there is no data. Not only are some backends known to create a
1017	lot of those (for example solaris ports), it is very easy to get into	1454	lot of those (for example Solaris ports), it is very easy to get into
1018	this situation even with a relatively standard program structure. Thus	1455	this situation even with a relatively standard program structure. Thus
1019	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1456	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1020	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1457	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1021		1458
1022	If you cannot run the fd in non-blocking mode (for example you should not	1459	If you cannot run the fd in non-blocking mode (for example you should
1023	play around with an Xlib connection), then you have to seperately re-test	1460	not play around with an Xlib connection), then you have to separately
1024	whether a file descriptor is really ready with a known-to-be good interface	1461	re-test whether a file descriptor is really ready with a known-to-be good
1025	such as poll (fortunately in our Xlib example, Xlib already does this on	1462	interface such as poll (fortunately in our Xlib example, Xlib already
1026	its own, so its quite safe to use).	1463	does this on its own, so its quite safe to use). Some people additionally
		1464	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1465	indefinitely.
		1466
		1467	But really, best use non-blocking mode.
1027		1468
1028	=head3 The special problem of disappearing file descriptors	1469	=head3 The special problem of disappearing file descriptors
1029		1470
1030	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1471	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1031	descriptor (either by calling C<close> explicitly or by any other means,	1472	descriptor (either due to calling C<close> explicitly or any other means,
1032	such as C<dup>). The reason is that you register interest in some file	1473	such as C<dup2>). The reason is that you register interest in some file
1033	descriptor, but when it goes away, the operating system will silently drop	1474	descriptor, but when it goes away, the operating system will silently drop
1034	this interest. If another file descriptor with the same number then is	1475	this interest. If another file descriptor with the same number then is
1035	registered with libev, there is no efficient way to see that this is, in	1476	registered with libev, there is no efficient way to see that this is, in
1036	fact, a different file descriptor.	1477	fact, a different file descriptor.
1037		1478
…		…
1066	To support fork in your programs, you either have to call	1507	To support fork in your programs, you either have to call
1067	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1508	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1068	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1509	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1069	C<EVBACKEND_POLL>.	1510	C<EVBACKEND_POLL>.
1070		1511
		1512	=head3 The special problem of SIGPIPE
		1513
		1514	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1515	when writing to a pipe whose other end has been closed, your program gets
		1516	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1517	this is sensible behaviour, for daemons, this is usually undesirable.
		1518
		1519	So when you encounter spurious, unexplained daemon exits, make sure you
		1520	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1521	somewhere, as that would have given you a big clue).
		1522
1071		1523
1072	=head3 Watcher-Specific Functions	1524	=head3 Watcher-Specific Functions
1073		1525
1074	=over 4	1526	=over 4
1075		1527
1076	=item ev_io_init (ev_io *, callback, int fd, int events)	1528	=item ev_io_init (ev_io *, callback, int fd, int events)
1077		1529
1078	=item ev_io_set (ev_io *, int fd, int events)	1530	=item ev_io_set (ev_io *, int fd, int events)
1079		1531
1080	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1532	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1081	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1533	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1082	C<EV_READ | EV_WRITE> to receive the given events.	1534	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1083		1535
1084	=item int fd [read-only]	1536	=item int fd [read-only]
1085		1537
1086	The file descriptor being watched.	1538	The file descriptor being watched.
1087		1539
…		…
1095		1547
1096	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1548	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1097	readable, but only once. Since it is likely line-buffered, you could	1549	readable, but only once. Since it is likely line-buffered, you could
1098	attempt to read a whole line in the callback.	1550	attempt to read a whole line in the callback.
1099		1551
1100	static void	1552	static void
1101	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1553	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1102	{	1554	{
1103	ev_io_stop (loop, w);	1555	ev_io_stop (loop, w);
1104	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1556	.. read from stdin here (or from w->fd) and handle any I/O errors
1105	}	1557	}
1106		1558
1107	...	1559	...
1108	struct ev_loop *loop = ev_default_init (0);	1560	struct ev_loop *loop = ev_default_init (0);
1109	struct ev_io stdin_readable;	1561	ev_io stdin_readable;
1110	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1562	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1111	ev_io_start (loop, &stdin_readable);	1563	ev_io_start (loop, &stdin_readable);
1112	ev_loop (loop, 0);	1564	ev_loop (loop, 0);
1113		1565
1114		1566
1115	=head2 C<ev_timer> - relative and optionally repeating timeouts	1567	=head2 C<ev_timer> - relative and optionally repeating timeouts
1116		1568
1117	Timer watchers are simple relative timers that generate an event after a	1569	Timer watchers are simple relative timers that generate an event after a
1118	given time, and optionally repeating in regular intervals after that.	1570	given time, and optionally repeating in regular intervals after that.
1119		1571
1120	The timers are based on real time, that is, if you register an event that	1572	The timers are based on real time, that is, if you register an event that
1121	times out after an hour and you reset your system clock to last years	1573	times out after an hour and you reset your system clock to January last
1122	time, it will still time out after (roughly) and hour. "Roughly" because	1574	year, it will still time out after (roughly) one hour. "Roughly" because
1123	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1575	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1124	monotonic clock option helps a lot here).	1576	monotonic clock option helps a lot here).
		1577
		1578	The callback is guaranteed to be invoked only I<after> its timeout has
		1579	passed (not I<at>, so on systems with very low-resolution clocks this
		1580	might introduce a small delay). If multiple timers become ready during the
		1581	same loop iteration then the ones with earlier time-out values are invoked
		1582	before ones of the same priority with later time-out values (but this is
		1583	no longer true when a callback calls C<ev_loop> recursively).
		1584
		1585	=head3 Be smart about timeouts
		1586
		1587	Many real-world problems involve some kind of timeout, usually for error
		1588	recovery. A typical example is an HTTP request - if the other side hangs,
		1589	you want to raise some error after a while.
		1590
		1591	What follows are some ways to handle this problem, from obvious and
		1592	inefficient to smart and efficient.
		1593
		1594	In the following, a 60 second activity timeout is assumed - a timeout that
		1595	gets reset to 60 seconds each time there is activity (e.g. each time some
		1596	data or other life sign was received).
		1597
		1598	=over 4
		1599
		1600	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1601
		1602	This is the most obvious, but not the most simple way: In the beginning,
		1603	start the watcher:
		1604
		1605	ev_timer_init (timer, callback, 60., 0.);
		1606	ev_timer_start (loop, timer);
		1607
		1608	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1609	and start it again:
		1610
		1611	ev_timer_stop (loop, timer);
		1612	ev_timer_set (timer, 60., 0.);
		1613	ev_timer_start (loop, timer);
		1614
		1615	This is relatively simple to implement, but means that each time there is
		1616	some activity, libev will first have to remove the timer from its internal
		1617	data structure and then add it again. Libev tries to be fast, but it's
		1618	still not a constant-time operation.
		1619
		1620	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1621
		1622	This is the easiest way, and involves using C<ev_timer_again> instead of
		1623	C<ev_timer_start>.
		1624
		1625	To implement this, configure an C<ev_timer> with a C<repeat> value
		1626	of C<60> and then call C<ev_timer_again> at start and each time you
		1627	successfully read or write some data. If you go into an idle state where
		1628	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1629	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1630
		1631	That means you can ignore both the C<ev_timer_start> function and the
		1632	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1633	member and C<ev_timer_again>.
		1634
		1635	At start:
		1636
		1637	ev_init (timer, callback);
		1638	timer->repeat = 60.;
		1639	ev_timer_again (loop, timer);
		1640
		1641	Each time there is some activity:
		1642
		1643	ev_timer_again (loop, timer);
		1644
		1645	It is even possible to change the time-out on the fly, regardless of
		1646	whether the watcher is active or not:
		1647
		1648	timer->repeat = 30.;
		1649	ev_timer_again (loop, timer);
		1650
		1651	This is slightly more efficient then stopping/starting the timer each time
		1652	you want to modify its timeout value, as libev does not have to completely
		1653	remove and re-insert the timer from/into its internal data structure.
		1654
		1655	It is, however, even simpler than the "obvious" way to do it.
		1656
		1657	=item 3. Let the timer time out, but then re-arm it as required.
		1658
		1659	This method is more tricky, but usually most efficient: Most timeouts are
		1660	relatively long compared to the intervals between other activity - in
		1661	our example, within 60 seconds, there are usually many I/O events with
		1662	associated activity resets.
		1663
		1664	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1665	but remember the time of last activity, and check for a real timeout only
		1666	within the callback:
		1667
		1668	ev_tstamp last_activity; // time of last activity
		1669
		1670	static void
		1671	callback (EV_P_ ev_timer *w, int revents)
		1672	{
		1673	ev_tstamp now = ev_now (EV_A);
		1674	ev_tstamp timeout = last_activity + 60.;
		1675
		1676	// if last_activity + 60. is older than now, we did time out
		1677	if (timeout < now)
		1678	{
		1679	// timeout occured, take action
		1680	}
		1681	else
		1682	{
		1683	// callback was invoked, but there was some activity, re-arm
		1684	// the watcher to fire in last_activity + 60, which is
		1685	// guaranteed to be in the future, so "again" is positive:
		1686	w->repeat = timeout - now;
		1687	ev_timer_again (EV_A_ w);
		1688	}
		1689	}
		1690
		1691	To summarise the callback: first calculate the real timeout (defined
		1692	as "60 seconds after the last activity"), then check if that time has
		1693	been reached, which means something I<did>, in fact, time out. Otherwise
		1694	the callback was invoked too early (C<timeout> is in the future), so
		1695	re-schedule the timer to fire at that future time, to see if maybe we have
		1696	a timeout then.
		1697
		1698	Note how C<ev_timer_again> is used, taking advantage of the
		1699	C<ev_timer_again> optimisation when the timer is already running.
		1700
		1701	This scheme causes more callback invocations (about one every 60 seconds
		1702	minus half the average time between activity), but virtually no calls to
		1703	libev to change the timeout.
		1704
		1705	To start the timer, simply initialise the watcher and set C<last_activity>
		1706	to the current time (meaning we just have some activity :), then call the
		1707	callback, which will "do the right thing" and start the timer:
		1708
		1709	ev_init (timer, callback);
		1710	last_activity = ev_now (loop);
		1711	callback (loop, timer, EV_TIMEOUT);
		1712
		1713	And when there is some activity, simply store the current time in
		1714	C<last_activity>, no libev calls at all:
		1715
		1716	last_actiivty = ev_now (loop);
		1717
		1718	This technique is slightly more complex, but in most cases where the
		1719	time-out is unlikely to be triggered, much more efficient.
		1720
		1721	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1722	callback :) - just change the timeout and invoke the callback, which will
		1723	fix things for you.
		1724
		1725	=item 4. Wee, just use a double-linked list for your timeouts.
		1726
		1727	If there is not one request, but many thousands (millions...), all
		1728	employing some kind of timeout with the same timeout value, then one can
		1729	do even better:
		1730
		1731	When starting the timeout, calculate the timeout value and put the timeout
		1732	at the I<end> of the list.
		1733
		1734	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1735	the list is expected to fire (for example, using the technique #3).
		1736
		1737	When there is some activity, remove the timer from the list, recalculate
		1738	the timeout, append it to the end of the list again, and make sure to
		1739	update the C<ev_timer> if it was taken from the beginning of the list.
		1740
		1741	This way, one can manage an unlimited number of timeouts in O(1) time for
		1742	starting, stopping and updating the timers, at the expense of a major
		1743	complication, and having to use a constant timeout. The constant timeout
		1744	ensures that the list stays sorted.
		1745
		1746	=back
		1747
		1748	So which method the best?
		1749
		1750	Method #2 is a simple no-brain-required solution that is adequate in most
		1751	situations. Method #3 requires a bit more thinking, but handles many cases
		1752	better, and isn't very complicated either. In most case, choosing either
		1753	one is fine, with #3 being better in typical situations.
		1754
		1755	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1756	rather complicated, but extremely efficient, something that really pays
		1757	off after the first million or so of active timers, i.e. it's usually
		1758	overkill :)
		1759
		1760	=head3 The special problem of time updates
		1761
		1762	Establishing the current time is a costly operation (it usually takes at
		1763	least two system calls): EV therefore updates its idea of the current
		1764	time only before and after C<ev_loop> collects new events, which causes a
		1765	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1766	lots of events in one iteration.
1125		1767
1126	The relative timeouts are calculated relative to the C<ev_now ()>	1768	The relative timeouts are calculated relative to the C<ev_now ()>
1127	time. This is usually the right thing as this timestamp refers to the time	1769	time. This is usually the right thing as this timestamp refers to the time
1128	of the event triggering whatever timeout you are modifying/starting. If	1770	of the event triggering whatever timeout you are modifying/starting. If
1129	you suspect event processing to be delayed and you I<need> to base the timeout	1771	you suspect event processing to be delayed and you I<need> to base the
1130	on the current time, use something like this to adjust for this:	1772	timeout on the current time, use something like this to adjust for this:
1131		1773
1132	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1774	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1133		1775
1134	The callback is guarenteed to be invoked only when its timeout has passed,	1776	If the event loop is suspended for a long time, you can also force an
1135	but if multiple timers become ready during the same loop iteration then	1777	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1136	order of execution is undefined.	1778	()>.
		1779
		1780	=head3 The special problems of suspended animation
		1781
		1782	When you leave the server world it is quite customary to hit machines that
		1783	can suspend/hibernate - what happens to the clocks during such a suspend?
		1784
		1785	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1786	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1787	to run until the system is suspended, but they will not advance while the
		1788	system is suspended. That means, on resume, it will be as if the program
		1789	was frozen for a few seconds, but the suspend time will not be counted
		1790	towards C<ev_timer> when a monotonic clock source is used. The real time
		1791	clock advanced as expected, but if it is used as sole clocksource, then a
		1792	long suspend would be detected as a time jump by libev, and timers would
		1793	be adjusted accordingly.
		1794
		1795	I would not be surprised to see different behaviour in different between
		1796	operating systems, OS versions or even different hardware.
		1797
		1798	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1799	time jump in the monotonic clocks and the realtime clock. If the program
		1800	is suspended for a very long time, and monotonic clock sources are in use,
		1801	then you can expect C<ev_timer>s to expire as the full suspension time
		1802	will be counted towards the timers. When no monotonic clock source is in
		1803	use, then libev will again assume a timejump and adjust accordingly.
		1804
		1805	It might be beneficial for this latter case to call C<ev_suspend>
		1806	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1807	deterministic behaviour in this case (you can do nothing against
		1808	C<SIGSTOP>).
1137		1809
1138	=head3 Watcher-Specific Functions and Data Members	1810	=head3 Watcher-Specific Functions and Data Members
1139		1811
1140	=over 4	1812	=over 4
1141		1813
1142	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1814	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1143		1815
1144	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1816	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1145		1817
1146	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1818	Configure the timer to trigger after C<after> seconds. If C<repeat>
1147	C<0.>, then it will automatically be stopped. If it is positive, then the	1819	is C<0.>, then it will automatically be stopped once the timeout is
1148	timer will automatically be configured to trigger again C<repeat> seconds	1820	reached. If it is positive, then the timer will automatically be
1149	later, again, and again, until stopped manually.	1821	configured to trigger again C<repeat> seconds later, again, and again,
		1822	until stopped manually.
1150		1823
1151	The timer itself will do a best-effort at avoiding drift, that is, if you	1824	The timer itself will do a best-effort at avoiding drift, that is, if
1152	configure a timer to trigger every 10 seconds, then it will trigger at	1825	you configure a timer to trigger every 10 seconds, then it will normally
1153	exactly 10 second intervals. If, however, your program cannot keep up with	1826	trigger at exactly 10 second intervals. If, however, your program cannot
1154	the timer (because it takes longer than those 10 seconds to do stuff) the	1827	keep up with the timer (because it takes longer than those 10 seconds to
1155	timer will not fire more than once per event loop iteration.	1828	do stuff) the timer will not fire more than once per event loop iteration.
1156		1829
1157	=item ev_timer_again (loop)	1830	=item ev_timer_again (loop, ev_timer *)
1158		1831
1159	This will act as if the timer timed out and restart it again if it is	1832	This will act as if the timer timed out and restart it again if it is
1160	repeating. The exact semantics are:	1833	repeating. The exact semantics are:
1161		1834
1162	If the timer is pending, its pending status is cleared.	1835	If the timer is pending, its pending status is cleared.
1163		1836
1164	If the timer is started but nonrepeating, stop it (as if it timed out).	1837	If the timer is started but non-repeating, stop it (as if it timed out).
1165		1838
1166	If the timer is repeating, either start it if necessary (with the	1839	If the timer is repeating, either start it if necessary (with the
1167	C<repeat> value), or reset the running timer to the C<repeat> value.	1840	C<repeat> value), or reset the running timer to the C<repeat> value.
1168		1841
1169	This sounds a bit complicated, but here is a useful and typical	1842	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1170	example: Imagine you have a tcp connection and you want a so-called idle	1843	usage example.
1171	timeout, that is, you want to be called when there have been, say, 60
1172	seconds of inactivity on the socket. The easiest way to do this is to
1173	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1174	C<ev_timer_again> each time you successfully read or write some data. If
1175	you go into an idle state where you do not expect data to travel on the
1176	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1177	automatically restart it if need be.
1178		1844
1179	That means you can ignore the C<after> value and C<ev_timer_start>	1845	=item ev_timer_remaining (loop, ev_timer *)
1180	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1181		1846
1182	ev_timer_init (timer, callback, 0., 5.);	1847	Returns the remaining time until a timer fires. If the timer is active,
1183	ev_timer_again (loop, timer);	1848	then this time is relative to the current event loop time, otherwise it's
1184	...	1849	the timeout value currently configured.
1185	timer->again = 17.;
1186	ev_timer_again (loop, timer);
1187	...
1188	timer->again = 10.;
1189	ev_timer_again (loop, timer);
1190		1850
1191	This is more slightly efficient then stopping/starting the timer each time	1851	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1192	you want to modify its timeout value.	1852	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1853	will return C<4>. When the timer expires and is restarted, it will return
		1854	roughly C<7> (likely slightly less as callback invocation takes some time,
		1855	too), and so on.
1193		1856
1194	=item ev_tstamp repeat [read-write]	1857	=item ev_tstamp repeat [read-write]
1195		1858
1196	The current C<repeat> value. Will be used each time the watcher times out	1859	The current C<repeat> value. Will be used each time the watcher times out
1197	or C<ev_timer_again> is called and determines the next timeout (if any),	1860	or C<ev_timer_again> is called, and determines the next timeout (if any),
1198	which is also when any modifications are taken into account.	1861	which is also when any modifications are taken into account.
1199		1862
1200	=back	1863	=back
1201		1864
1202	=head3 Examples	1865	=head3 Examples
1203		1866
1204	Example: Create a timer that fires after 60 seconds.	1867	Example: Create a timer that fires after 60 seconds.
1205		1868
1206	static void	1869	static void
1207	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1870	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1208	{	1871	{
1209	.. one minute over, w is actually stopped right here	1872	.. one minute over, w is actually stopped right here
1210	}	1873	}
1211		1874
1212	struct ev_timer mytimer;	1875	ev_timer mytimer;
1213	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1876	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1214	ev_timer_start (loop, &mytimer);	1877	ev_timer_start (loop, &mytimer);
1215		1878
1216	Example: Create a timeout timer that times out after 10 seconds of	1879	Example: Create a timeout timer that times out after 10 seconds of
1217	inactivity.	1880	inactivity.
1218		1881
1219	static void	1882	static void
1220	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1883	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1221	{	1884	{
1222	.. ten seconds without any activity	1885	.. ten seconds without any activity
1223	}	1886	}
1224		1887
1225	struct ev_timer mytimer;	1888	ev_timer mytimer;
1226	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1889	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1227	ev_timer_again (&mytimer); /* start timer */	1890	ev_timer_again (&mytimer); /* start timer */
1228	ev_loop (loop, 0);	1891	ev_loop (loop, 0);
1229		1892
1230	// and in some piece of code that gets executed on any "activity":	1893	// and in some piece of code that gets executed on any "activity":
1231	// reset the timeout to start ticking again at 10 seconds	1894	// reset the timeout to start ticking again at 10 seconds
1232	ev_timer_again (&mytimer);	1895	ev_timer_again (&mytimer);
1233		1896
1234		1897
1235	=head2 C<ev_periodic> - to cron or not to cron?	1898	=head2 C<ev_periodic> - to cron or not to cron?
1236		1899
1237	Periodic watchers are also timers of a kind, but they are very versatile	1900	Periodic watchers are also timers of a kind, but they are very versatile
1238	(and unfortunately a bit complex).	1901	(and unfortunately a bit complex).
1239		1902
1240	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1903	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1241	but on wallclock time (absolute time). You can tell a periodic watcher	1904	relative time, the physical time that passes) but on wall clock time
1242	to trigger "at" some specific point in time. For example, if you tell a	1905	(absolute time, the thing you can read on your calender or clock). The
1243	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1906	difference is that wall clock time can run faster or slower than real
1244	+ 10.>) and then reset your system clock to the last year, then it will	1907	time, and time jumps are not uncommon (e.g. when you adjust your
1245	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1908	wrist-watch).
1246	roughly 10 seconds later).
1247		1909
1248	They can also be used to implement vastly more complex timers, such as	1910	You can tell a periodic watcher to trigger after some specific point
1249	triggering an event on each midnight, local time or other, complicated,	1911	in time: for example, if you tell a periodic watcher to trigger "in 10
1250	rules.	1912	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1913	not a delay) and then reset your system clock to January of the previous
		1914	year, then it will take a year or more to trigger the event (unlike an
		1915	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1916	it, as it uses a relative timeout).
1251		1917
		1918	C<ev_periodic> watchers can also be used to implement vastly more complex
		1919	timers, such as triggering an event on each "midnight, local time", or
		1920	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1921	those cannot react to time jumps.
		1922
1252	As with timers, the callback is guarenteed to be invoked only when the	1923	As with timers, the callback is guaranteed to be invoked only when the
1253	time (C<at>) has been passed, but if multiple periodic timers become ready	1924	point in time where it is supposed to trigger has passed. If multiple
1254	during the same loop iteration then order of execution is undefined.	1925	timers become ready during the same loop iteration then the ones with
		1926	earlier time-out values are invoked before ones with later time-out values
		1927	(but this is no longer true when a callback calls C<ev_loop> recursively).
1255		1928
1256	=head3 Watcher-Specific Functions and Data Members	1929	=head3 Watcher-Specific Functions and Data Members
1257		1930
1258	=over 4	1931	=over 4
1259		1932
1260	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1933	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1261		1934
1262	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1935	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1263		1936
1264	Lots of arguments, lets sort it out... There are basically three modes of	1937	Lots of arguments, let's sort it out... There are basically three modes of
1265	operation, and we will explain them from simplest to complex:	1938	operation, and we will explain them from simplest to most complex:
1266		1939
1267	=over 4	1940	=over 4
1268		1941
1269	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1942	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1270		1943
1271	In this configuration the watcher triggers an event at the wallclock time	1944	In this configuration the watcher triggers an event after the wall clock
1272	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1945	time C<offset> has passed. It will not repeat and will not adjust when a
1273	that is, if it is to be run at January 1st 2011 then it will run when the	1946	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1274	system time reaches or surpasses this time.	1947	will be stopped and invoked when the system clock reaches or surpasses
		1948	this point in time.
1275		1949
1276	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1950	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1277		1951
1278	In this mode the watcher will always be scheduled to time out at the next	1952	In this mode the watcher will always be scheduled to time out at the next
1279	C<at + N * interval> time (for some integer N, which can also be negative)	1953	C<offset + N * interval> time (for some integer N, which can also be
1280	and then repeat, regardless of any time jumps.	1954	negative) and then repeat, regardless of any time jumps. The C<offset>
		1955	argument is merely an offset into the C<interval> periods.
1281		1956
1282	This can be used to create timers that do not drift with respect to system	1957	This can be used to create timers that do not drift with respect to the
1283	time:	1958	system clock, for example, here is an C<ev_periodic> that triggers each
		1959	hour, on the hour (with respect to UTC):
1284		1960
1285	ev_periodic_set (&periodic, 0., 3600., 0);	1961	ev_periodic_set (&periodic, 0., 3600., 0);
1286		1962
1287	This doesn't mean there will always be 3600 seconds in between triggers,	1963	This doesn't mean there will always be 3600 seconds in between triggers,
1288	but only that the the callback will be called when the system time shows a	1964	but only that the callback will be called when the system time shows a
1289	full hour (UTC), or more correctly, when the system time is evenly divisible	1965	full hour (UTC), or more correctly, when the system time is evenly divisible
1290	by 3600.	1966	by 3600.
1291		1967
1292	Another way to think about it (for the mathematically inclined) is that	1968	Another way to think about it (for the mathematically inclined) is that
1293	C<ev_periodic> will try to run the callback in this mode at the next possible	1969	C<ev_periodic> will try to run the callback in this mode at the next possible
1294	time where C<time = at (mod interval)>, regardless of any time jumps.	1970	time where C<time = offset (mod interval)>, regardless of any time jumps.
1295		1971
1296	For numerical stability it is preferable that the C<at> value is near	1972	For numerical stability it is preferable that the C<offset> value is near
1297	C<ev_now ()> (the current time), but there is no range requirement for	1973	C<ev_now ()> (the current time), but there is no range requirement for
1298	this value.	1974	this value, and in fact is often specified as zero.
1299		1975
		1976	Note also that there is an upper limit to how often a timer can fire (CPU
		1977	speed for example), so if C<interval> is very small then timing stability
		1978	will of course deteriorate. Libev itself tries to be exact to be about one
		1979	millisecond (if the OS supports it and the machine is fast enough).
		1980
1300	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1981	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1301		1982
1302	In this mode the values for C<interval> and C<at> are both being	1983	In this mode the values for C<interval> and C<offset> are both being
1303	ignored. Instead, each time the periodic watcher gets scheduled, the	1984	ignored. Instead, each time the periodic watcher gets scheduled, the
1304	reschedule callback will be called with the watcher as first, and the	1985	reschedule callback will be called with the watcher as first, and the
1305	current time as second argument.	1986	current time as second argument.
1306		1987
1307	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1988	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1308	ever, or make any event loop modifications>. If you need to stop it,	1989	or make ANY other event loop modifications whatsoever, unless explicitly
1309	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1990	allowed by documentation here>.
1310	starting an C<ev_prepare> watcher, which is legal).
1311		1991
		1992	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1993	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1994	only event loop modification you are allowed to do).
		1995
1312	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1996	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1313	ev_tstamp now)>, e.g.:	1997	*w, ev_tstamp now)>, e.g.:
1314		1998
		1999	static ev_tstamp
1315	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2000	my_rescheduler (ev_periodic *w, ev_tstamp now)
1316	{	2001	{
1317	return now + 60.;	2002	return now + 60.;
1318	}	2003	}
1319		2004
1320	It must return the next time to trigger, based on the passed time value	2005	It must return the next time to trigger, based on the passed time value
1321	(that is, the lowest time value larger than to the second argument). It	2006	(that is, the lowest time value larger than to the second argument). It
1322	will usually be called just before the callback will be triggered, but	2007	will usually be called just before the callback will be triggered, but
1323	might be called at other times, too.	2008	might be called at other times, too.
1324		2009
1325	NOTE: I<< This callback must always return a time that is later than the	2010	NOTE: I<< This callback must always return a time that is higher than or
1326	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2011	equal to the passed C<now> value >>.
1327		2012
1328	This can be used to create very complex timers, such as a timer that	2013	This can be used to create very complex timers, such as a timer that
1329	triggers on each midnight, local time. To do this, you would calculate the	2014	triggers on "next midnight, local time". To do this, you would calculate the
1330	next midnight after C<now> and return the timestamp value for this. How	2015	next midnight after C<now> and return the timestamp value for this. How
1331	you do this is, again, up to you (but it is not trivial, which is the main	2016	you do this is, again, up to you (but it is not trivial, which is the main
1332	reason I omitted it as an example).	2017	reason I omitted it as an example).
1333		2018
1334	=back	2019	=back
…		…
1338	Simply stops and restarts the periodic watcher again. This is only useful	2023	Simply stops and restarts the periodic watcher again. This is only useful
1339	when you changed some parameters or the reschedule callback would return	2024	when you changed some parameters or the reschedule callback would return
1340	a different time than the last time it was called (e.g. in a crond like	2025	a different time than the last time it was called (e.g. in a crond like
1341	program when the crontabs have changed).	2026	program when the crontabs have changed).
1342		2027
		2028	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2029
		2030	When active, returns the absolute time that the watcher is supposed
		2031	to trigger next. This is not the same as the C<offset> argument to
		2032	C<ev_periodic_set>, but indeed works even in interval and manual
		2033	rescheduling modes.
		2034
1343	=item ev_tstamp offset [read-write]	2035	=item ev_tstamp offset [read-write]
1344		2036
1345	When repeating, this contains the offset value, otherwise this is the	2037	When repeating, this contains the offset value, otherwise this is the
1346	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2038	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2039	although libev might modify this value for better numerical stability).
1347		2040
1348	Can be modified any time, but changes only take effect when the periodic	2041	Can be modified any time, but changes only take effect when the periodic
1349	timer fires or C<ev_periodic_again> is being called.	2042	timer fires or C<ev_periodic_again> is being called.
1350		2043
1351	=item ev_tstamp interval [read-write]	2044	=item ev_tstamp interval [read-write]
1352		2045
1353	The current interval value. Can be modified any time, but changes only	2046	The current interval value. Can be modified any time, but changes only
1354	take effect when the periodic timer fires or C<ev_periodic_again> is being	2047	take effect when the periodic timer fires or C<ev_periodic_again> is being
1355	called.	2048	called.
1356		2049
1357	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2050	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1358		2051
1359	The current reschedule callback, or C<0>, if this functionality is	2052	The current reschedule callback, or C<0>, if this functionality is
1360	switched off. Can be changed any time, but changes only take effect when	2053	switched off. Can be changed any time, but changes only take effect when
1361	the periodic timer fires or C<ev_periodic_again> is being called.	2054	the periodic timer fires or C<ev_periodic_again> is being called.
1362		2055
1363	=item ev_tstamp at [read-only]
1364
1365	When active, contains the absolute time that the watcher is supposed to
1366	trigger next.
1367
1368	=back	2056	=back
1369		2057
1370	=head3 Examples	2058	=head3 Examples
1371		2059
1372	Example: Call a callback every hour, or, more precisely, whenever the	2060	Example: Call a callback every hour, or, more precisely, whenever the
1373	system clock is divisible by 3600. The callback invocation times have	2061	system time is divisible by 3600. The callback invocation times have
1374	potentially a lot of jittering, but good long-term stability.	2062	potentially a lot of jitter, but good long-term stability.
1375		2063
1376	static void	2064	static void
1377	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2065	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1378	{	2066	{
1379	... its now a full hour (UTC, or TAI or whatever your clock follows)	2067	... its now a full hour (UTC, or TAI or whatever your clock follows)
1380	}	2068	}
1381		2069
1382	struct ev_periodic hourly_tick;	2070	ev_periodic hourly_tick;
1383	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2071	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1384	ev_periodic_start (loop, &hourly_tick);	2072	ev_periodic_start (loop, &hourly_tick);
1385		2073
1386	Example: The same as above, but use a reschedule callback to do it:	2074	Example: The same as above, but use a reschedule callback to do it:
1387		2075
1388	#include <math.h>	2076	#include <math.h>
1389		2077
1390	static ev_tstamp	2078	static ev_tstamp
1391	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2079	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1392	{	2080	{
1393	return fmod (now, 3600.) + 3600.;	2081	return now + (3600. - fmod (now, 3600.));
1394	}	2082	}
1395		2083
1396	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2084	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1397		2085
1398	Example: Call a callback every hour, starting now:	2086	Example: Call a callback every hour, starting now:
1399		2087
1400	struct ev_periodic hourly_tick;	2088	ev_periodic hourly_tick;
1401	ev_periodic_init (&hourly_tick, clock_cb,	2089	ev_periodic_init (&hourly_tick, clock_cb,
1402	fmod (ev_now (loop), 3600.), 3600., 0);	2090	fmod (ev_now (loop), 3600.), 3600., 0);
1403	ev_periodic_start (loop, &hourly_tick);	2091	ev_periodic_start (loop, &hourly_tick);
1404		2092
1405		2093
1406	=head2 C<ev_signal> - signal me when a signal gets signalled!	2094	=head2 C<ev_signal> - signal me when a signal gets signalled!
1407		2095
1408	Signal watchers will trigger an event when the process receives a specific	2096	Signal watchers will trigger an event when the process receives a specific
1409	signal one or more times. Even though signals are very asynchronous, libev	2097	signal one or more times. Even though signals are very asynchronous, libev
1410	will try it's best to deliver signals synchronously, i.e. as part of the	2098	will try it's best to deliver signals synchronously, i.e. as part of the
1411	normal event processing, like any other event.	2099	normal event processing, like any other event.
1412		2100
		2101	If you want signals to be delivered truly asynchronously, just use
		2102	C<sigaction> as you would do without libev and forget about sharing
		2103	the signal. You can even use C<ev_async> from a signal handler to
		2104	synchronously wake up an event loop.
		2105
1413	You can configure as many watchers as you like per signal. Only when the	2106	You can configure as many watchers as you like for the same signal, but
		2107	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2108	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2109	C<SIGINT> in both the default loop and another loop at the same time. At
		2110	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2111
1414	first watcher gets started will libev actually register a signal watcher	2112	When the first watcher gets started will libev actually register something
1415	with the kernel (thus it coexists with your own signal handlers as long	2113	with the kernel (thus it coexists with your own signal handlers as long as
1416	as you don't register any with libev). Similarly, when the last signal	2114	you don't register any with libev for the same signal).
1417	watcher for a signal is stopped libev will reset the signal handler to	2115
1418	SIG_DFL (regardless of what it was set to before).	2116	If possible and supported, libev will install its handlers with
		2117	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2118	not be unduly interrupted. If you have a problem with system calls getting
		2119	interrupted by signals you can block all signals in an C<ev_check> watcher
		2120	and unblock them in an C<ev_prepare> watcher.
		2121
		2122	=head3 The special problem of inheritance over execve
		2123
		2124	Both the signal mask (C<sigprocmask>) and the signal disposition
		2125	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2126	stopping it again), that is, libev might or might not block the signal,
		2127	and might or might not set or restore the installed signal handler.
		2128
		2129	While this does not matter for the signal disposition (libev never
		2130	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2131	C<execve>), this matters for the signal mask: many programs do not expect
		2132	certain signals to be blocked.
		2133
		2134	This means that before calling C<exec> (from the child) you should reset
		2135	the signal mask to whatever "default" you expect (all clear is a good
		2136	choice usually).
		2137
		2138	The simplest way to ensure that the signal mask is reset in the child is
		2139	to install a fork handler with C<pthread_atfork> that resets it. That will
		2140	catch fork calls done by libraries (such as the libc) as well.
		2141
		2142	In current versions of libev, you can also ensure that the signal mask is
		2143	not blocking any signals (except temporarily, so thread users watch out)
		2144	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2145	is not guaranteed for future versions, however.
1419		2146
1420	=head3 Watcher-Specific Functions and Data Members	2147	=head3 Watcher-Specific Functions and Data Members
1421		2148
1422	=over 4	2149	=over 4
1423		2150
…		…
1432		2159
1433	The signal the watcher watches out for.	2160	The signal the watcher watches out for.
1434		2161
1435	=back	2162	=back
1436		2163
		2164	=head3 Examples
		2165
		2166	Example: Try to exit cleanly on SIGINT.
		2167
		2168	static void
		2169	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2170	{
		2171	ev_unloop (loop, EVUNLOOP_ALL);
		2172	}
		2173
		2174	ev_signal signal_watcher;
		2175	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2176	ev_signal_start (loop, &signal_watcher);
		2177
1437		2178
1438	=head2 C<ev_child> - watch out for process status changes	2179	=head2 C<ev_child> - watch out for process status changes
1439		2180
1440	Child watchers trigger when your process receives a SIGCHLD in response to	2181	Child watchers trigger when your process receives a SIGCHLD in response to
1441	some child status changes (most typically when a child of yours dies).	2182	some child status changes (most typically when a child of yours dies or
		2183	exits). It is permissible to install a child watcher I<after> the child
		2184	has been forked (which implies it might have already exited), as long
		2185	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2186	forking and then immediately registering a watcher for the child is fine,
		2187	but forking and registering a watcher a few event loop iterations later or
		2188	in the next callback invocation is not.
		2189
		2190	Only the default event loop is capable of handling signals, and therefore
		2191	you can only register child watchers in the default event loop.
		2192
		2193	Due to some design glitches inside libev, child watchers will always be
		2194	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2195	libev)
		2196
		2197	=head3 Process Interaction
		2198
		2199	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2200	initialised. This is necessary to guarantee proper behaviour even if the
		2201	first child watcher is started after the child exits. The occurrence
		2202	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2203	synchronously as part of the event loop processing. Libev always reaps all
		2204	children, even ones not watched.
		2205
		2206	=head3 Overriding the Built-In Processing
		2207
		2208	Libev offers no special support for overriding the built-in child
		2209	processing, but if your application collides with libev's default child
		2210	handler, you can override it easily by installing your own handler for
		2211	C<SIGCHLD> after initialising the default loop, and making sure the
		2212	default loop never gets destroyed. You are encouraged, however, to use an
		2213	event-based approach to child reaping and thus use libev's support for
		2214	that, so other libev users can use C<ev_child> watchers freely.
		2215
		2216	=head3 Stopping the Child Watcher
		2217
		2218	Currently, the child watcher never gets stopped, even when the
		2219	child terminates, so normally one needs to stop the watcher in the
		2220	callback. Future versions of libev might stop the watcher automatically
		2221	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2222	problem).
1442		2223
1443	=head3 Watcher-Specific Functions and Data Members	2224	=head3 Watcher-Specific Functions and Data Members
1444		2225
1445	=over 4	2226	=over 4
1446		2227
…		…
1472		2253
1473	=back	2254	=back
1474		2255
1475	=head3 Examples	2256	=head3 Examples
1476		2257
1477	Example: Try to exit cleanly on SIGINT and SIGTERM.	2258	Example: C<fork()> a new process and install a child handler to wait for
		2259	its completion.
1478		2260
		2261	ev_child cw;
		2262
1479	static void	2263	static void
1480	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2264	child_cb (EV_P_ ev_child *w, int revents)
1481	{	2265	{
1482	ev_unloop (loop, EVUNLOOP_ALL);	2266	ev_child_stop (EV_A_ w);
		2267	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1483	}	2268	}
1484		2269
1485	struct ev_signal signal_watcher;	2270	pid_t pid = fork ();
1486	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2271
1487	ev_signal_start (loop, &sigint_cb);	2272	if (pid < 0)
		2273	// error
		2274	else if (pid == 0)
		2275	{
		2276	// the forked child executes here
		2277	exit (1);
		2278	}
		2279	else
		2280	{
		2281	ev_child_init (&cw, child_cb, pid, 0);
		2282	ev_child_start (EV_DEFAULT_ &cw);
		2283	}
1488		2284
1489		2285
1490	=head2 C<ev_stat> - did the file attributes just change?	2286	=head2 C<ev_stat> - did the file attributes just change?
1491		2287
1492	This watches a filesystem path for attribute changes. That is, it calls	2288	This watches a file system path for attribute changes. That is, it calls
1493	C<stat> regularly (or when the OS says it changed) and sees if it changed	2289	C<stat> on that path in regular intervals (or when the OS says it changed)
1494	compared to the last time, invoking the callback if it did.	2290	and sees if it changed compared to the last time, invoking the callback if
		2291	it did.
1495		2292
1496	The path does not need to exist: changing from "path exists" to "path does	2293	The path does not need to exist: changing from "path exists" to "path does
1497	not exist" is a status change like any other. The condition "path does	2294	not exist" is a status change like any other. The condition "path does not
1498	not exist" is signified by the C<st_nlink> field being zero (which is	2295	exist" (or more correctly "path cannot be stat'ed") is signified by the
1499	otherwise always forced to be at least one) and all the other fields of	2296	C<st_nlink> field being zero (which is otherwise always forced to be at
1500	the stat buffer having unspecified contents.	2297	least one) and all the other fields of the stat buffer having unspecified
		2298	contents.
1501		2299
1502	The path I<should> be absolute and I<must not> end in a slash. If it is	2300	The path I<must not> end in a slash or contain special components such as
		2301	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1503	relative and your working directory changes, the behaviour is undefined.	2302	your working directory changes, then the behaviour is undefined.
1504		2303
1505	Since there is no standard to do this, the portable implementation simply	2304	Since there is no portable change notification interface available, the
1506	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2305	portable implementation simply calls C<stat(2)> regularly on the path
1507	can specify a recommended polling interval for this case. If you specify	2306	to see if it changed somehow. You can specify a recommended polling
1508	a polling interval of C<0> (highly recommended!) then a I<suitable,	2307	interval for this case. If you specify a polling interval of C<0> (highly
1509	unspecified default> value will be used (which you can expect to be around	2308	recommended!) then a I<suitable, unspecified default> value will be used
1510	five seconds, although this might change dynamically). Libev will also	2309	(which you can expect to be around five seconds, although this might
1511	impose a minimum interval which is currently around C<0.1>, but thats	2310	change dynamically). Libev will also impose a minimum interval which is
1512	usually overkill.	2311	currently around C<0.1>, but that's usually overkill.
1513		2312
1514	This watcher type is not meant for massive numbers of stat watchers,	2313	This watcher type is not meant for massive numbers of stat watchers,
1515	as even with OS-supported change notifications, this can be	2314	as even with OS-supported change notifications, this can be
1516	resource-intensive.	2315	resource-intensive.
1517		2316
1518	At the time of this writing, only the Linux inotify interface is	2317	At the time of this writing, the only OS-specific interface implemented
1519	implemented (implementing kqueue support is left as an exercise for the	2318	is the Linux inotify interface (implementing kqueue support is left as an
1520	reader). Inotify will be used to give hints only and should not change the	2319	exercise for the reader. Note, however, that the author sees no way of
1521	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2320	implementing C<ev_stat> semantics with kqueue, except as a hint).
1522	to fall back to regular polling again even with inotify, but changes are
1523	usually detected immediately, and if the file exists there will be no
1524	polling.
1525		2321
1526	=head3 Inotify	2322	=head3 ABI Issues (Largefile Support)
1527		2323
		2324	Libev by default (unless the user overrides this) uses the default
		2325	compilation environment, which means that on systems with large file
		2326	support disabled by default, you get the 32 bit version of the stat
		2327	structure. When using the library from programs that change the ABI to
		2328	use 64 bit file offsets the programs will fail. In that case you have to
		2329	compile libev with the same flags to get binary compatibility. This is
		2330	obviously the case with any flags that change the ABI, but the problem is
		2331	most noticeably displayed with ev_stat and large file support.
		2332
		2333	The solution for this is to lobby your distribution maker to make large
		2334	file interfaces available by default (as e.g. FreeBSD does) and not
		2335	optional. Libev cannot simply switch on large file support because it has
		2336	to exchange stat structures with application programs compiled using the
		2337	default compilation environment.
		2338
		2339	=head3 Inotify and Kqueue
		2340
1528	When C<inotify (7)> support has been compiled into libev (generally only	2341	When C<inotify (7)> support has been compiled into libev and present at
1529	available on Linux) and present at runtime, it will be used to speed up	2342	runtime, it will be used to speed up change detection where possible. The
1530	change detection where possible. The inotify descriptor will be created lazily	2343	inotify descriptor will be created lazily when the first C<ev_stat>
1531	when the first C<ev_stat> watcher is being started.	2344	watcher is being started.
1532		2345
1533	Inotify presense does not change the semantics of C<ev_stat> watchers	2346	Inotify presence does not change the semantics of C<ev_stat> watchers
1534	except that changes might be detected earlier, and in some cases, to avoid	2347	except that changes might be detected earlier, and in some cases, to avoid
1535	making regular C<stat> calls. Even in the presense of inotify support	2348	making regular C<stat> calls. Even in the presence of inotify support
1536	there are many cases where libev has to resort to regular C<stat> polling.	2349	there are many cases where libev has to resort to regular C<stat> polling,
		2350	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2351	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2352	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2353	xfs are fully working) libev usually gets away without polling.
1537		2354
1538	(There is no support for kqueue, as apparently it cannot be used to	2355	There is no support for kqueue, as apparently it cannot be used to
1539	implement this functionality, due to the requirement of having a file	2356	implement this functionality, due to the requirement of having a file
1540	descriptor open on the object at all times).	2357	descriptor open on the object at all times, and detecting renames, unlinks
		2358	etc. is difficult.
		2359
		2360	=head3 C<stat ()> is a synchronous operation
		2361
		2362	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2363	the process. The exception are C<ev_stat> watchers - those call C<stat
		2364	()>, which is a synchronous operation.
		2365
		2366	For local paths, this usually doesn't matter: unless the system is very
		2367	busy or the intervals between stat's are large, a stat call will be fast,
		2368	as the path data is usually in memory already (except when starting the
		2369	watcher).
		2370
		2371	For networked file systems, calling C<stat ()> can block an indefinite
		2372	time due to network issues, and even under good conditions, a stat call
		2373	often takes multiple milliseconds.
		2374
		2375	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2376	paths, although this is fully supported by libev.
1541		2377
1542	=head3 The special problem of stat time resolution	2378	=head3 The special problem of stat time resolution
1543		2379
1544	The C<stat ()> syscall only supports full-second resolution portably, and	2380	The C<stat ()> system call only supports full-second resolution portably,
1545	even on systems where the resolution is higher, many filesystems still	2381	and even on systems where the resolution is higher, most file systems
1546	only support whole seconds.	2382	still only support whole seconds.
1547		2383
1548	That means that, if the time is the only thing that changes, you might	2384	That means that, if the time is the only thing that changes, you can
1549	miss updates: on the first update, C<ev_stat> detects a change and calls	2385	easily miss updates: on the first update, C<ev_stat> detects a change and
1550	your callback, which does something. When there is another update within	2386	calls your callback, which does something. When there is another update
1551	the same second, C<ev_stat> will be unable to detect it.	2387	within the same second, C<ev_stat> will be unable to detect unless the
		2388	stat data does change in other ways (e.g. file size).
1552		2389
1553	The solution to this is to delay acting on a change for a second (or till	2390	The solution to this is to delay acting on a change for slightly more
1554	the next second boundary), using a roughly one-second delay C<ev_timer>	2391	than a second (or till slightly after the next full second boundary), using
1555	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2392	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1556	is added to work around small timing inconsistencies of some operating	2393	ev_timer_again (loop, w)>).
1557	systems.	2394
		2395	The C<.02> offset is added to work around small timing inconsistencies
		2396	of some operating systems (where the second counter of the current time
		2397	might be be delayed. One such system is the Linux kernel, where a call to
		2398	C<gettimeofday> might return a timestamp with a full second later than
		2399	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2400	update file times then there will be a small window where the kernel uses
		2401	the previous second to update file times but libev might already execute
		2402	the timer callback).
1558		2403
1559	=head3 Watcher-Specific Functions and Data Members	2404	=head3 Watcher-Specific Functions and Data Members
1560		2405
1561	=over 4	2406	=over 4
1562		2407
…		…
1568	C<path>. The C<interval> is a hint on how quickly a change is expected to	2413	C<path>. The C<interval> is a hint on how quickly a change is expected to
1569	be detected and should normally be specified as C<0> to let libev choose	2414	be detected and should normally be specified as C<0> to let libev choose
1570	a suitable value. The memory pointed to by C<path> must point to the same	2415	a suitable value. The memory pointed to by C<path> must point to the same
1571	path for as long as the watcher is active.	2416	path for as long as the watcher is active.
1572		2417
1573	The callback will be receive C<EV_STAT> when a change was detected,	2418	The callback will receive an C<EV_STAT> event when a change was detected,
1574	relative to the attributes at the time the watcher was started (or the	2419	relative to the attributes at the time the watcher was started (or the
1575	last change was detected).	2420	last change was detected).
1576		2421
1577	=item ev_stat_stat (ev_stat *)	2422	=item ev_stat_stat (loop, ev_stat *)
1578		2423
1579	Updates the stat buffer immediately with new values. If you change the	2424	Updates the stat buffer immediately with new values. If you change the
1580	watched path in your callback, you could call this fucntion to avoid	2425	watched path in your callback, you could call this function to avoid
1581	detecting this change (while introducing a race condition). Can also be	2426	detecting this change (while introducing a race condition if you are not
1582	useful simply to find out the new values.	2427	the only one changing the path). Can also be useful simply to find out the
		2428	new values.
1583		2429
1584	=item ev_statdata attr [read-only]	2430	=item ev_statdata attr [read-only]
1585		2431
1586	The most-recently detected attributes of the file. Although the type is of	2432	The most-recently detected attributes of the file. Although the type is
1587	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2433	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1588	suitable for your system. If the C<st_nlink> member is C<0>, then there	2434	suitable for your system, but you can only rely on the POSIX-standardised
		2435	members to be present. If the C<st_nlink> member is C<0>, then there was
1589	was some error while C<stat>ing the file.	2436	some error while C<stat>ing the file.
1590		2437
1591	=item ev_statdata prev [read-only]	2438	=item ev_statdata prev [read-only]
1592		2439
1593	The previous attributes of the file. The callback gets invoked whenever	2440	The previous attributes of the file. The callback gets invoked whenever
1594	C<prev> != C<attr>.	2441	C<prev> != C<attr>, or, more precisely, one or more of these members
		2442	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2443	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1595		2444
1596	=item ev_tstamp interval [read-only]	2445	=item ev_tstamp interval [read-only]
1597		2446
1598	The specified interval.	2447	The specified interval.
1599		2448
1600	=item const char *path [read-only]	2449	=item const char *path [read-only]
1601		2450
1602	The filesystem path that is being watched.	2451	The file system path that is being watched.
1603		2452
1604	=back	2453	=back
1605		2454
1606	=head3 Examples	2455	=head3 Examples
1607		2456
1608	Example: Watch C</etc/passwd> for attribute changes.	2457	Example: Watch C</etc/passwd> for attribute changes.
1609		2458
1610	static void	2459	static void
1611	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2460	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1612	{	2461	{
1613	/* /etc/passwd changed in some way */	2462	/* /etc/passwd changed in some way */
1614	if (w->attr.st_nlink)	2463	if (w->attr.st_nlink)
1615	{	2464	{
1616	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2465	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1617	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2466	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1618	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2467	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1619	}	2468	}
1620	else	2469	else
1621	/* you shalt not abuse printf for puts */	2470	/* you shalt not abuse printf for puts */
1622	puts ("wow, /etc/passwd is not there, expect problems. "	2471	puts ("wow, /etc/passwd is not there, expect problems. "
1623	"if this is windows, they already arrived\n");	2472	"if this is windows, they already arrived\n");
1624	}	2473	}
1625		2474
1626	...	2475	...
1627	ev_stat passwd;	2476	ev_stat passwd;
1628		2477
1629	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2478	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1630	ev_stat_start (loop, &passwd);	2479	ev_stat_start (loop, &passwd);
1631		2480
1632	Example: Like above, but additionally use a one-second delay so we do not	2481	Example: Like above, but additionally use a one-second delay so we do not
1633	miss updates (however, frequent updates will delay processing, too, so	2482	miss updates (however, frequent updates will delay processing, too, so
1634	one might do the work both on C<ev_stat> callback invocation I<and> on	2483	one might do the work both on C<ev_stat> callback invocation I<and> on
1635	C<ev_timer> callback invocation).	2484	C<ev_timer> callback invocation).
1636		2485
1637	static ev_stat passwd;	2486	static ev_stat passwd;
1638	static ev_timer timer;	2487	static ev_timer timer;
1639		2488
1640	static void	2489	static void
1641	timer_cb (EV_P_ ev_timer *w, int revents)	2490	timer_cb (EV_P_ ev_timer *w, int revents)
1642	{	2491	{
1643	ev_timer_stop (EV_A_ w);	2492	ev_timer_stop (EV_A_ w);
1644		2493
1645	/* now it's one second after the most recent passwd change */	2494	/* now it's one second after the most recent passwd change */
1646	}	2495	}
1647		2496
1648	static void	2497	static void
1649	stat_cb (EV_P_ ev_stat *w, int revents)	2498	stat_cb (EV_P_ ev_stat *w, int revents)
1650	{	2499	{
1651	/* reset the one-second timer */	2500	/* reset the one-second timer */
1652	ev_timer_again (EV_A_ &timer);	2501	ev_timer_again (EV_A_ &timer);
1653	}	2502	}
1654		2503
1655	...	2504	...
1656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2505	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1657	ev_stat_start (loop, &passwd);	2506	ev_stat_start (loop, &passwd);
1658	ev_timer_init (&timer, timer_cb, 0., 1.01);	2507	ev_timer_init (&timer, timer_cb, 0., 1.02);
1659		2508
1660		2509
1661	=head2 C<ev_idle> - when you've got nothing better to do...	2510	=head2 C<ev_idle> - when you've got nothing better to do...
1662		2511
1663	Idle watchers trigger events when no other events of the same or higher	2512	Idle watchers trigger events when no other events of the same or higher
1664	priority are pending (prepare, check and other idle watchers do not	2513	priority are pending (prepare, check and other idle watchers do not count
1665	count).	2514	as receiving "events").
1666		2515
1667	That is, as long as your process is busy handling sockets or timeouts	2516	That is, as long as your process is busy handling sockets or timeouts
1668	(or even signals, imagine) of the same or higher priority it will not be	2517	(or even signals, imagine) of the same or higher priority it will not be
1669	triggered. But when your process is idle (or only lower-priority watchers	2518	triggered. But when your process is idle (or only lower-priority watchers
1670	are pending), the idle watchers are being called once per event loop	2519	are pending), the idle watchers are being called once per event loop
…		…
1681		2530
1682	=head3 Watcher-Specific Functions and Data Members	2531	=head3 Watcher-Specific Functions and Data Members
1683		2532
1684	=over 4	2533	=over 4
1685		2534
1686	=item ev_idle_init (ev_signal *, callback)	2535	=item ev_idle_init (ev_idle *, callback)
1687		2536
1688	Initialises and configures the idle watcher - it has no parameters of any	2537	Initialises and configures the idle watcher - it has no parameters of any
1689	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2538	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1690	believe me.	2539	believe me.
1691		2540
…		…
1694	=head3 Examples	2543	=head3 Examples
1695		2544
1696	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2545	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1697	callback, free it. Also, use no error checking, as usual.	2546	callback, free it. Also, use no error checking, as usual.
1698		2547
1699	static void	2548	static void
1700	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2549	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1701	{	2550	{
1702	free (w);	2551	free (w);
1703	// now do something you wanted to do when the program has	2552	// now do something you wanted to do when the program has
1704	// no longer anything immediate to do.	2553	// no longer anything immediate to do.
1705	}	2554	}
1706		2555
1707	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2556	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1708	ev_idle_init (idle_watcher, idle_cb);	2557	ev_idle_init (idle_watcher, idle_cb);
1709	ev_idle_start (loop, idle_cb);	2558	ev_idle_start (loop, idle_watcher);
1710		2559
1711		2560
1712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2561	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1713		2562
1714	Prepare and check watchers are usually (but not always) used in tandem:	2563	Prepare and check watchers are usually (but not always) used in pairs:
1715	prepare watchers get invoked before the process blocks and check watchers	2564	prepare watchers get invoked before the process blocks and check watchers
1716	afterwards.	2565	afterwards.
1717		2566
1718	You I<must not> call C<ev_loop> or similar functions that enter	2567	You I<must not> call C<ev_loop> or similar functions that enter
1719	the current event loop from either C<ev_prepare> or C<ev_check>	2568	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2571	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1723	C<ev_check> so if you have one watcher of each kind they will always be	2572	C<ev_check> so if you have one watcher of each kind they will always be
1724	called in pairs bracketing the blocking call.	2573	called in pairs bracketing the blocking call.
1725		2574
1726	Their main purpose is to integrate other event mechanisms into libev and	2575	Their main purpose is to integrate other event mechanisms into libev and
1727	their use is somewhat advanced. This could be used, for example, to track	2576	their use is somewhat advanced. They could be used, for example, to track
1728	variable changes, implement your own watchers, integrate net-snmp or a	2577	variable changes, implement your own watchers, integrate net-snmp or a
1729	coroutine library and lots more. They are also occasionally useful if	2578	coroutine library and lots more. They are also occasionally useful if
1730	you cache some data and want to flush it before blocking (for example,	2579	you cache some data and want to flush it before blocking (for example,
1731	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2580	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1732	watcher).	2581	watcher).
1733		2582
1734	This is done by examining in each prepare call which file descriptors need	2583	This is done by examining in each prepare call which file descriptors
1735	to be watched by the other library, registering C<ev_io> watchers for	2584	need to be watched by the other library, registering C<ev_io> watchers
1736	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2585	for them and starting an C<ev_timer> watcher for any timeouts (many
1737	provide just this functionality). Then, in the check watcher you check for	2586	libraries provide exactly this functionality). Then, in the check watcher,
1738	any events that occured (by checking the pending status of all watchers	2587	you check for any events that occurred (by checking the pending status
1739	and stopping them) and call back into the library. The I/O and timer	2588	of all watchers and stopping them) and call back into the library. The
1740	callbacks will never actually be called (but must be valid nevertheless,	2589	I/O and timer callbacks will never actually be called (but must be valid
1741	because you never know, you know?).	2590	nevertheless, because you never know, you know?).
1742		2591
1743	As another example, the Perl Coro module uses these hooks to integrate	2592	As another example, the Perl Coro module uses these hooks to integrate
1744	coroutines into libev programs, by yielding to other active coroutines	2593	coroutines into libev programs, by yielding to other active coroutines
1745	during each prepare and only letting the process block if no coroutines	2594	during each prepare and only letting the process block if no coroutines
1746	are ready to run (it's actually more complicated: it only runs coroutines	2595	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1749	loop from blocking if lower-priority coroutines are active, thus mapping	2598	loop from blocking if lower-priority coroutines are active, thus mapping
1750	low-priority coroutines to idle/background tasks).	2599	low-priority coroutines to idle/background tasks).
1751		2600
1752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2601	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1753	priority, to ensure that they are being run before any other watchers	2602	priority, to ensure that they are being run before any other watchers
		2603	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2604
1754	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2605	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1755	too) should not activate ("feed") events into libev. While libev fully	2606	activate ("feed") events into libev. While libev fully supports this, they
1756	supports this, they will be called before other C<ev_check> watchers	2607	might get executed before other C<ev_check> watchers did their job. As
1757	did their job. As C<ev_check> watchers are often used to embed other	2608	C<ev_check> watchers are often used to embed other (non-libev) event
1758	(non-libev) event loops those other event loops might be in an unusable	2609	loops those other event loops might be in an unusable state until their
1759	state until their C<ev_check> watcher ran (always remind yourself to	2610	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1760	coexist peacefully with others).	2611	others).
1761		2612
1762	=head3 Watcher-Specific Functions and Data Members	2613	=head3 Watcher-Specific Functions and Data Members
1763		2614
1764	=over 4	2615	=over 4
1765		2616
…		…
1767		2618
1768	=item ev_check_init (ev_check *, callback)	2619	=item ev_check_init (ev_check *, callback)
1769		2620
1770	Initialises and configures the prepare or check watcher - they have no	2621	Initialises and configures the prepare or check watcher - they have no
1771	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2622	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1772	macros, but using them is utterly, utterly and completely pointless.	2623	macros, but using them is utterly, utterly, utterly and completely
		2624	pointless.
1773		2625
1774	=back	2626	=back
1775		2627
1776	=head3 Examples	2628	=head3 Examples
1777		2629
1778	There are a number of principal ways to embed other event loops or modules	2630	There are a number of principal ways to embed other event loops or modules
1779	into libev. Here are some ideas on how to include libadns into libev	2631	into libev. Here are some ideas on how to include libadns into libev
1780	(there is a Perl module named C<EV::ADNS> that does this, which you could	2632	(there is a Perl module named C<EV::ADNS> that does this, which you could
1781	use for an actually working example. Another Perl module named C<EV::Glib>	2633	use as a working example. Another Perl module named C<EV::Glib> embeds a
1782	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2634	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1783	into the Glib event loop).	2635	Glib event loop).
1784		2636
1785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2637	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1786	and in a check watcher, destroy them and call into libadns. What follows	2638	and in a check watcher, destroy them and call into libadns. What follows
1787	is pseudo-code only of course. This requires you to either use a low	2639	is pseudo-code only of course. This requires you to either use a low
1788	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2640	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1789	the callbacks for the IO/timeout watchers might not have been called yet.	2641	the callbacks for the IO/timeout watchers might not have been called yet.
1790		2642
1791	static ev_io iow [nfd];	2643	static ev_io iow [nfd];
1792	static ev_timer tw;	2644	static ev_timer tw;
1793		2645
1794	static void	2646	static void
1795	io_cb (ev_loop *loop, ev_io *w, int revents)	2647	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1796	{	2648	{
1797	}	2649	}
1798		2650
1799	// create io watchers for each fd and a timer before blocking	2651	// create io watchers for each fd and a timer before blocking
1800	static void	2652	static void
1801	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2653	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1802	{	2654	{
1803	int timeout = 3600000;	2655	int timeout = 3600000;
1804	struct pollfd fds [nfd];	2656	struct pollfd fds [nfd];
1805	// actual code will need to loop here and realloc etc.	2657	// actual code will need to loop here and realloc etc.
1806	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2658	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1807		2659
1808	/* the callback is illegal, but won't be called as we stop during check */	2660	/* the callback is illegal, but won't be called as we stop during check */
1809	ev_timer_init (&tw, 0, timeout * 1e-3);	2661	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1810	ev_timer_start (loop, &tw);	2662	ev_timer_start (loop, &tw);
1811		2663
1812	// create one ev_io per pollfd	2664	// create one ev_io per pollfd
1813	for (int i = 0; i < nfd; ++i)	2665	for (int i = 0; i < nfd; ++i)
1814	{	2666	{
1815	ev_io_init (iow + i, io_cb, fds [i].fd,	2667	ev_io_init (iow + i, io_cb, fds [i].fd,
1816	((fds [i].events & POLLIN ? EV_READ : 0)	2668	((fds [i].events & POLLIN ? EV_READ : 0)
1817	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2669	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1818		2670
1819	fds [i].revents = 0;	2671	fds [i].revents = 0;
1820	ev_io_start (loop, iow + i);	2672	ev_io_start (loop, iow + i);
1821	}	2673	}
1822	}	2674	}
1823		2675
1824	// stop all watchers after blocking	2676	// stop all watchers after blocking
1825	static void	2677	static void
1826	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2678	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1827	{	2679	{
1828	ev_timer_stop (loop, &tw);	2680	ev_timer_stop (loop, &tw);
1829		2681
1830	for (int i = 0; i < nfd; ++i)	2682	for (int i = 0; i < nfd; ++i)
1831	{	2683	{
1832	// set the relevant poll flags	2684	// set the relevant poll flags
1833	// could also call adns_processreadable etc. here	2685	// could also call adns_processreadable etc. here
1834	struct pollfd *fd = fds + i;	2686	struct pollfd *fd = fds + i;
1835	int revents = ev_clear_pending (iow + i);	2687	int revents = ev_clear_pending (iow + i);
1836	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2688	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1837	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2689	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1838		2690
1839	// now stop the watcher	2691	// now stop the watcher
1840	ev_io_stop (loop, iow + i);	2692	ev_io_stop (loop, iow + i);
1841	}	2693	}
1842		2694
1843	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2695	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1844	}	2696	}
1845		2697
1846	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2698	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1847	in the prepare watcher and would dispose of the check watcher.	2699	in the prepare watcher and would dispose of the check watcher.
1848		2700
1849	Method 3: If the module to be embedded supports explicit event	2701	Method 3: If the module to be embedded supports explicit event
1850	notification (adns does), you can also make use of the actual watcher	2702	notification (libadns does), you can also make use of the actual watcher
1851	callbacks, and only destroy/create the watchers in the prepare watcher.	2703	callbacks, and only destroy/create the watchers in the prepare watcher.
1852		2704
1853	static void	2705	static void
1854	timer_cb (EV_P_ ev_timer *w, int revents)	2706	timer_cb (EV_P_ ev_timer *w, int revents)
1855	{	2707	{
1856	adns_state ads = (adns_state)w->data;	2708	adns_state ads = (adns_state)w->data;
1857	update_now (EV_A);	2709	update_now (EV_A);
1858		2710
1859	adns_processtimeouts (ads, &tv_now);	2711	adns_processtimeouts (ads, &tv_now);
1860	}	2712	}
1861		2713
1862	static void	2714	static void
1863	io_cb (EV_P_ ev_io *w, int revents)	2715	io_cb (EV_P_ ev_io *w, int revents)
1864	{	2716	{
1865	adns_state ads = (adns_state)w->data;	2717	adns_state ads = (adns_state)w->data;
1866	update_now (EV_A);	2718	update_now (EV_A);
1867		2719
1868	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2720	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1869	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2721	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1870	}	2722	}
1871		2723
1872	// do not ever call adns_afterpoll	2724	// do not ever call adns_afterpoll
1873		2725
1874	Method 4: Do not use a prepare or check watcher because the module you	2726	Method 4: Do not use a prepare or check watcher because the module you
1875	want to embed is too inflexible to support it. Instead, youc na override	2727	want to embed is not flexible enough to support it. Instead, you can
1876	their poll function. The drawback with this solution is that the main	2728	override their poll function. The drawback with this solution is that the
1877	loop is now no longer controllable by EV. The C<Glib::EV> module does	2729	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1878	this.	2730	this approach, effectively embedding EV as a client into the horrible
		2731	libglib event loop.
1879		2732
1880	static gint	2733	static gint
1881	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2734	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1882	{	2735	{
1883	int got_events = 0;	2736	int got_events = 0;
1884		2737
1885	for (n = 0; n < nfds; ++n)	2738	for (n = 0; n < nfds; ++n)
1886	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2739	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1887		2740
1888	if (timeout >= 0)	2741	if (timeout >= 0)
1889	// create/start timer	2742	// create/start timer
1890		2743
1891	// poll	2744	// poll
1892	ev_loop (EV_A_ 0);	2745	ev_loop (EV_A_ 0);
1893		2746
1894	// stop timer again	2747	// stop timer again
1895	if (timeout >= 0)	2748	if (timeout >= 0)
1896	ev_timer_stop (EV_A_ &to);	2749	ev_timer_stop (EV_A_ &to);
1897		2750
1898	// stop io watchers again - their callbacks should have set	2751	// stop io watchers again - their callbacks should have set
1899	for (n = 0; n < nfds; ++n)	2752	for (n = 0; n < nfds; ++n)
1900	ev_io_stop (EV_A_ iow [n]);	2753	ev_io_stop (EV_A_ iow [n]);
1901		2754
1902	return got_events;	2755	return got_events;
1903	}	2756	}
1904		2757
1905		2758
1906	=head2 C<ev_embed> - when one backend isn't enough...	2759	=head2 C<ev_embed> - when one backend isn't enough...
1907		2760
1908	This is a rather advanced watcher type that lets you embed one event loop	2761	This is a rather advanced watcher type that lets you embed one event loop
…		…
1914	prioritise I/O.	2767	prioritise I/O.
1915		2768
1916	As an example for a bug workaround, the kqueue backend might only support	2769	As an example for a bug workaround, the kqueue backend might only support
1917	sockets on some platform, so it is unusable as generic backend, but you	2770	sockets on some platform, so it is unusable as generic backend, but you
1918	still want to make use of it because you have many sockets and it scales	2771	still want to make use of it because you have many sockets and it scales
1919	so nicely. In this case, you would create a kqueue-based loop and embed it	2772	so nicely. In this case, you would create a kqueue-based loop and embed
1920	into your default loop (which might use e.g. poll). Overall operation will	2773	it into your default loop (which might use e.g. poll). Overall operation
1921	be a bit slower because first libev has to poll and then call kevent, but	2774	will be a bit slower because first libev has to call C<poll> and then
1922	at least you can use both at what they are best.	2775	C<kevent>, but at least you can use both mechanisms for what they are
		2776	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1923		2777
1924	As for prioritising I/O: rarely you have the case where some fds have	2778	As for prioritising I/O: under rare circumstances you have the case where
1925	to be watched and handled very quickly (with low latency), and even	2779	some fds have to be watched and handled very quickly (with low latency),
1926	priorities and idle watchers might have too much overhead. In this case	2780	and even priorities and idle watchers might have too much overhead. In
1927	you would put all the high priority stuff in one loop and all the rest in	2781	this case you would put all the high priority stuff in one loop and all
1928	a second one, and embed the second one in the first.	2782	the rest in a second one, and embed the second one in the first.
1929		2783
1930	As long as the watcher is active, the callback will be invoked every time	2784	As long as the watcher is active, the callback will be invoked every
1931	there might be events pending in the embedded loop. The callback must then	2785	time there might be events pending in the embedded loop. The callback
1932	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2786	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1933	their callbacks (you could also start an idle watcher to give the embedded	2787	sweep and invoke their callbacks (the callback doesn't need to invoke the
1934	loop strictly lower priority for example). You can also set the callback	2788	C<ev_embed_sweep> function directly, it could also start an idle watcher
1935	to C<0>, in which case the embed watcher will automatically execute the	2789	to give the embedded loop strictly lower priority for example).
1936	embedded loop sweep.
1937		2790
1938	As long as the watcher is started it will automatically handle events. The	2791	You can also set the callback to C<0>, in which case the embed watcher
1939	callback will be invoked whenever some events have been handled. You can	2792	will automatically execute the embedded loop sweep whenever necessary.
1940	set the callback to C<0> to avoid having to specify one if you are not
1941	interested in that.
1942		2793
1943	Also, there have not currently been made special provisions for forking:	2794	Fork detection will be handled transparently while the C<ev_embed> watcher
1944	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2795	is active, i.e., the embedded loop will automatically be forked when the
1945	but you will also have to stop and restart any C<ev_embed> watchers	2796	embedding loop forks. In other cases, the user is responsible for calling
1946	yourself.	2797	C<ev_loop_fork> on the embedded loop.
1947		2798
1948	Unfortunately, not all backends are embeddable, only the ones returned by	2799	Unfortunately, not all backends are embeddable: only the ones returned by
1949	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2800	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1950	portable one.	2801	portable one.
1951		2802
1952	So when you want to use this feature you will always have to be prepared	2803	So when you want to use this feature you will always have to be prepared
1953	that you cannot get an embeddable loop. The recommended way to get around	2804	that you cannot get an embeddable loop. The recommended way to get around
1954	this is to have a separate variables for your embeddable loop, try to	2805	this is to have a separate variables for your embeddable loop, try to
1955	create it, and if that fails, use the normal loop for everything.	2806	create it, and if that fails, use the normal loop for everything.
1956		2807
		2808	=head3 C<ev_embed> and fork
		2809
		2810	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2811	automatically be applied to the embedded loop as well, so no special
		2812	fork handling is required in that case. When the watcher is not running,
		2813	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2814	as applicable.
		2815
1957	=head3 Watcher-Specific Functions and Data Members	2816	=head3 Watcher-Specific Functions and Data Members
1958		2817
1959	=over 4	2818	=over 4
1960		2819
1961	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2820	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1964		2823
1965	Configures the watcher to embed the given loop, which must be	2824	Configures the watcher to embed the given loop, which must be
1966	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2825	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1967	invoked automatically, otherwise it is the responsibility of the callback	2826	invoked automatically, otherwise it is the responsibility of the callback
1968	to invoke it (it will continue to be called until the sweep has been done,	2827	to invoke it (it will continue to be called until the sweep has been done,
1969	if you do not want thta, you need to temporarily stop the embed watcher).	2828	if you do not want that, you need to temporarily stop the embed watcher).
1970		2829
1971	=item ev_embed_sweep (loop, ev_embed *)	2830	=item ev_embed_sweep (loop, ev_embed *)
1972		2831
1973	Make a single, non-blocking sweep over the embedded loop. This works	2832	Make a single, non-blocking sweep over the embedded loop. This works
1974	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2833	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1975	apropriate way for embedded loops.	2834	appropriate way for embedded loops.
1976		2835
1977	=item struct ev_loop *other [read-only]	2836	=item struct ev_loop *other [read-only]
1978		2837
1979	The embedded event loop.	2838	The embedded event loop.
1980		2839
…		…
1982		2841
1983	=head3 Examples	2842	=head3 Examples
1984		2843
1985	Example: Try to get an embeddable event loop and embed it into the default	2844	Example: Try to get an embeddable event loop and embed it into the default
1986	event loop. If that is not possible, use the default loop. The default	2845	event loop. If that is not possible, use the default loop. The default
1987	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2846	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1988	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2847	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1989	used).	2848	used).
1990		2849
1991	struct ev_loop *loop_hi = ev_default_init (0);	2850	struct ev_loop *loop_hi = ev_default_init (0);
1992	struct ev_loop *loop_lo = 0;	2851	struct ev_loop *loop_lo = 0;
1993	struct ev_embed embed;	2852	ev_embed embed;
1994		2853
1995	// see if there is a chance of getting one that works	2854	// see if there is a chance of getting one that works
1996	// (remember that a flags value of 0 means autodetection)	2855	// (remember that a flags value of 0 means autodetection)
1997	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2856	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1998	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2857	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1999	: 0;	2858	: 0;
2000		2859
2001	// if we got one, then embed it, otherwise default to loop_hi	2860	// if we got one, then embed it, otherwise default to loop_hi
2002	if (loop_lo)	2861	if (loop_lo)
2003	{	2862	{
2004	ev_embed_init (&embed, 0, loop_lo);	2863	ev_embed_init (&embed, 0, loop_lo);
2005	ev_embed_start (loop_hi, &embed);	2864	ev_embed_start (loop_hi, &embed);
2006	}	2865	}
2007	else	2866	else
2008	loop_lo = loop_hi;	2867	loop_lo = loop_hi;
2009		2868
2010	Example: Check if kqueue is available but not recommended and create	2869	Example: Check if kqueue is available but not recommended and create
2011	a kqueue backend for use with sockets (which usually work with any	2870	a kqueue backend for use with sockets (which usually work with any
2012	kqueue implementation). Store the kqueue/socket-only event loop in	2871	kqueue implementation). Store the kqueue/socket-only event loop in
2013	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2872	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2014		2873
2015	struct ev_loop *loop = ev_default_init (0);	2874	struct ev_loop *loop = ev_default_init (0);
2016	struct ev_loop *loop_socket = 0;	2875	struct ev_loop *loop_socket = 0;
2017	struct ev_embed embed;	2876	ev_embed embed;
2018		2877
2019	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2878	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2020	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2879	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2021	{	2880	{
2022	ev_embed_init (&embed, 0, loop_socket);	2881	ev_embed_init (&embed, 0, loop_socket);
2023	ev_embed_start (loop, &embed);	2882	ev_embed_start (loop, &embed);
2024	}	2883	}
2025		2884
2026	if (!loop_socket)	2885	if (!loop_socket)
2027	loop_socket = loop;	2886	loop_socket = loop;
2028		2887
2029	// now use loop_socket for all sockets, and loop for everything else	2888	// now use loop_socket for all sockets, and loop for everything else
2030		2889
2031		2890
2032	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2891	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2033		2892
2034	Fork watchers are called when a C<fork ()> was detected (usually because	2893	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2037	event loop blocks next and before C<ev_check> watchers are being called,	2896	event loop blocks next and before C<ev_check> watchers are being called,
2038	and only in the child after the fork. If whoever good citizen calling	2897	and only in the child after the fork. If whoever good citizen calling
2039	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2898	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2040	handlers will be invoked, too, of course.	2899	handlers will be invoked, too, of course.
2041		2900
		2901	=head3 The special problem of life after fork - how is it possible?
		2902
		2903	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2904	up/change the process environment, followed by a call to C<exec()>. This
		2905	sequence should be handled by libev without any problems.
		2906
		2907	This changes when the application actually wants to do event handling
		2908	in the child, or both parent in child, in effect "continuing" after the
		2909	fork.
		2910
		2911	The default mode of operation (for libev, with application help to detect
		2912	forks) is to duplicate all the state in the child, as would be expected
		2913	when I<either> the parent I<or> the child process continues.
		2914
		2915	When both processes want to continue using libev, then this is usually the
		2916	wrong result. In that case, usually one process (typically the parent) is
		2917	supposed to continue with all watchers in place as before, while the other
		2918	process typically wants to start fresh, i.e. without any active watchers.
		2919
		2920	The cleanest and most efficient way to achieve that with libev is to
		2921	simply create a new event loop, which of course will be "empty", and
		2922	use that for new watchers. This has the advantage of not touching more
		2923	memory than necessary, and thus avoiding the copy-on-write, and the
		2924	disadvantage of having to use multiple event loops (which do not support
		2925	signal watchers).
		2926
		2927	When this is not possible, or you want to use the default loop for
		2928	other reasons, then in the process that wants to start "fresh", call
		2929	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2930	the default loop will "orphan" (not stop) all registered watchers, so you
		2931	have to be careful not to execute code that modifies those watchers. Note
		2932	also that in that case, you have to re-register any signal watchers.
		2933
2042	=head3 Watcher-Specific Functions and Data Members	2934	=head3 Watcher-Specific Functions and Data Members
2043		2935
2044	=over 4	2936	=over 4
2045		2937
2046	=item ev_fork_init (ev_signal *, callback)	2938	=item ev_fork_init (ev_signal *, callback)
…		…
2078	is that the author does not know of a simple (or any) algorithm for a	2970	is that the author does not know of a simple (or any) algorithm for a
2079	multiple-writer-single-reader queue that works in all cases and doesn't	2971	multiple-writer-single-reader queue that works in all cases and doesn't
2080	need elaborate support such as pthreads.	2972	need elaborate support such as pthreads.
2081		2973
2082	That means that if you want to queue data, you have to provide your own	2974	That means that if you want to queue data, you have to provide your own
2083	queue. But at least I can tell you would implement locking around your	2975	queue. But at least I can tell you how to implement locking around your
2084	queue:	2976	queue:
2085		2977
2086	=over 4	2978	=over 4
2087		2979
2088	=item queueing from a signal handler context	2980	=item queueing from a signal handler context
2089		2981
2090	To implement race-free queueing, you simply add to the queue in the signal	2982	To implement race-free queueing, you simply add to the queue in the signal
2091	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2983	handler but you block the signal handler in the watcher callback. Here is
2092	some fictitiuous SIGUSR1 handler:	2984	an example that does that for some fictitious SIGUSR1 handler:
2093		2985
2094	static ev_async mysig;	2986	static ev_async mysig;
2095		2987
2096	static void	2988	static void
2097	sigusr1_handler (void)	2989	sigusr1_handler (void)
2098	{	2990	{
2099	sometype data;	2991	sometype data;
2100		2992
2101	// no locking etc.	2993	// no locking etc.
2102	queue_put (data);	2994	queue_put (data);
2103	ev_async_send (DEFAULT_ &mysig);	2995	ev_async_send (EV_DEFAULT_ &mysig);
2104	}	2996	}
2105		2997
2106	static void	2998	static void
2107	mysig_cb (EV_P_ ev_async *w, int revents)	2999	mysig_cb (EV_P_ ev_async *w, int revents)
2108	{	3000	{
…		…
2139	// only need to lock the actual queueing operation	3031	// only need to lock the actual queueing operation
2140	pthread_mutex_lock (&mymutex);	3032	pthread_mutex_lock (&mymutex);
2141	queue_put (data);	3033	queue_put (data);
2142	pthread_mutex_unlock (&mymutex);	3034	pthread_mutex_unlock (&mymutex);
2143		3035
2144	ev_async_send (DEFAULT_ &mysig);	3036	ev_async_send (EV_DEFAULT_ &mysig);
2145	}	3037	}
2146		3038
2147	static void	3039	static void
2148	mysig_cb (EV_P_ ev_async *w, int revents)	3040	mysig_cb (EV_P_ ev_async *w, int revents)
2149	{	3041	{
…		…
2163	=over 4	3055	=over 4
2164		3056
2165	=item ev_async_init (ev_async *, callback)	3057	=item ev_async_init (ev_async *, callback)
2166		3058
2167	Initialises and configures the async watcher - it has no parameters of any	3059	Initialises and configures the async watcher - it has no parameters of any
2168	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3060	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2169	believe me.	3061	trust me.
2170		3062
2171	=item ev_async_send (loop, ev_async *)	3063	=item ev_async_send (loop, ev_async *)
2172		3064
2173	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3065	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2174	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3066	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2175	C<ev_feed_event>, this call is safe to do in other threads, signal or	3067	C<ev_feed_event>, this call is safe to do from other threads, signal or
2176	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3068	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2177	section below on what exactly this means).	3069	section below on what exactly this means).
2178		3070
		3071	Note that, as with other watchers in libev, multiple events might get
		3072	compressed into a single callback invocation (another way to look at this
		3073	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3074	reset when the event loop detects that).
		3075
2179	This call incurs the overhead of a syscall only once per loop iteration,	3076	This call incurs the overhead of a system call only once per event loop
2180	so while the overhead might be noticable, it doesn't apply to repeated	3077	iteration, so while the overhead might be noticeable, it doesn't apply to
2181	calls to C<ev_async_send>.	3078	repeated calls to C<ev_async_send> for the same event loop.
		3079
		3080	=item bool = ev_async_pending (ev_async *)
		3081
		3082	Returns a non-zero value when C<ev_async_send> has been called on the
		3083	watcher but the event has not yet been processed (or even noted) by the
		3084	event loop.
		3085
		3086	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3087	the loop iterates next and checks for the watcher to have become active,
		3088	it will reset the flag again. C<ev_async_pending> can be used to very
		3089	quickly check whether invoking the loop might be a good idea.
		3090
		3091	Not that this does I<not> check whether the watcher itself is pending,
		3092	only whether it has been requested to make this watcher pending: there
		3093	is a time window between the event loop checking and resetting the async
		3094	notification, and the callback being invoked.
2182		3095
2183	=back	3096	=back
2184		3097
2185		3098
2186	=head1 OTHER FUNCTIONS	3099	=head1 OTHER FUNCTIONS
…		…
2190	=over 4	3103	=over 4
2191		3104
2192	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3105	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2193		3106
2194	This function combines a simple timer and an I/O watcher, calls your	3107	This function combines a simple timer and an I/O watcher, calls your
2195	callback on whichever event happens first and automatically stop both	3108	callback on whichever event happens first and automatically stops both
2196	watchers. This is useful if you want to wait for a single event on an fd	3109	watchers. This is useful if you want to wait for a single event on an fd
2197	or timeout without having to allocate/configure/start/stop/free one or	3110	or timeout without having to allocate/configure/start/stop/free one or
2198	more watchers yourself.	3111	more watchers yourself.
2199		3112
2200	If C<fd> is less than 0, then no I/O watcher will be started and events	3113	If C<fd> is less than 0, then no I/O watcher will be started and the
2201	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3114	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2202	C<events> set will be craeted and started.	3115	the given C<fd> and C<events> set will be created and started.
2203		3116
2204	If C<timeout> is less than 0, then no timeout watcher will be	3117	If C<timeout> is less than 0, then no timeout watcher will be
2205	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3118	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2206	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3119	repeat = 0) will be started. C<0> is a valid timeout.
2207	dubious value.
2208		3120
2209	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3121	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2210	passed an C<revents> set like normal event callbacks (a combination of	3122	passed an C<revents> set like normal event callbacks (a combination of
2211	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3123	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2212	value passed to C<ev_once>:	3124	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3125	a timeout and an io event at the same time - you probably should give io
		3126	events precedence.
2213		3127
		3128	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3129
2214	static void stdin_ready (int revents, void *arg)	3130	static void stdin_ready (int revents, void *arg)
2215	{	3131	{
2216	if (revents & EV_TIMEOUT)
2217	/* doh, nothing entered */;
2218	else if (revents & EV_READ)	3132	if (revents & EV_READ)
2219	/* stdin might have data for us, joy! */;	3133	/* stdin might have data for us, joy! */;
		3134	else if (revents & EV_TIMEOUT)
		3135	/* doh, nothing entered */;
2220	}	3136	}
2221		3137
2222	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3138	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2223		3139
2224	=item ev_feed_event (ev_loop *, watcher *, int revents)	3140	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2225		3141
2226	Feeds the given event set into the event loop, as if the specified event	3142	Feeds the given event set into the event loop, as if the specified event
2227	had happened for the specified watcher (which must be a pointer to an	3143	had happened for the specified watcher (which must be a pointer to an
2228	initialised but not necessarily started event watcher).	3144	initialised but not necessarily started event watcher).
2229		3145
2230	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3146	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2231		3147
2232	Feed an event on the given fd, as if a file descriptor backend detected	3148	Feed an event on the given fd, as if a file descriptor backend detected
2233	the given events it.	3149	the given events it.
2234		3150
2235	=item ev_feed_signal_event (ev_loop *loop, int signum)	3151	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2236		3152
2237	Feed an event as if the given signal occured (C<loop> must be the default	3153	Feed an event as if the given signal occurred (C<loop> must be the default
2238	loop!).	3154	loop!).
2239		3155
2240	=back	3156	=back
2241		3157
2242		3158
…		…
2258		3174
2259	=item * Priorities are not currently supported. Initialising priorities	3175	=item * Priorities are not currently supported. Initialising priorities
2260	will fail and all watchers will have the same priority, even though there	3176	will fail and all watchers will have the same priority, even though there
2261	is an ev_pri field.	3177	is an ev_pri field.
2262		3178
		3179	=item * In libevent, the last base created gets the signals, in libev, the
		3180	first base created (== the default loop) gets the signals.
		3181
2263	=item * Other members are not supported.	3182	=item * Other members are not supported.
2264		3183
2265	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3184	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2266	to use the libev header file and library.	3185	to use the libev header file and library.
2267		3186
2268	=back	3187	=back
2269		3188
2270	=head1 C++ SUPPORT	3189	=head1 C++ SUPPORT
2271		3190
2272	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3191	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2273	you to use some convinience methods to start/stop watchers and also change	3192	you to use some convenience methods to start/stop watchers and also change
2274	the callback model to a model using method callbacks on objects.	3193	the callback model to a model using method callbacks on objects.
2275		3194
2276	To use it,	3195	To use it,
2277		3196
2278	#include <ev++.h>	3197	#include <ev++.h>
2279		3198
2280	This automatically includes F<ev.h> and puts all of its definitions (many	3199	This automatically includes F<ev.h> and puts all of its definitions (many
2281	of them macros) into the global namespace. All C++ specific things are	3200	of them macros) into the global namespace. All C++ specific things are
2282	put into the C<ev> namespace. It should support all the same embedding	3201	put into the C<ev> namespace. It should support all the same embedding
2283	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3202	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2350	your compiler is good :), then the method will be fully inlined into the	3269	your compiler is good :), then the method will be fully inlined into the
2351	thunking function, making it as fast as a direct C callback.	3270	thunking function, making it as fast as a direct C callback.
2352		3271
2353	Example: simple class declaration and watcher initialisation	3272	Example: simple class declaration and watcher initialisation
2354		3273
2355	struct myclass	3274	struct myclass
2356	{	3275	{
2357	void io_cb (ev::io &w, int revents) { }	3276	void io_cb (ev::io &w, int revents) { }
2358	}	3277	}
2359		3278
2360	myclass obj;	3279	myclass obj;
2361	ev::io iow;	3280	ev::io iow;
2362	iow.set <myclass, &myclass::io_cb> (&obj);	3281	iow.set <myclass, &myclass::io_cb> (&obj);
		3282
		3283	=item w->set (object *)
		3284
		3285	This is an B<experimental> feature that might go away in a future version.
		3286
		3287	This is a variation of a method callback - leaving out the method to call
		3288	will default the method to C<operator ()>, which makes it possible to use
		3289	functor objects without having to manually specify the C<operator ()> all
		3290	the time. Incidentally, you can then also leave out the template argument
		3291	list.
		3292
		3293	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3294	int revents)>.
		3295
		3296	See the method-C<set> above for more details.
		3297
		3298	Example: use a functor object as callback.
		3299
		3300	struct myfunctor
		3301	{
		3302	void operator() (ev::io &w, int revents)
		3303	{
		3304	...
		3305	}
		3306	}
		3307
		3308	myfunctor f;
		3309
		3310	ev::io w;
		3311	w.set (&f);
2363		3312
2364	=item w->set<function> (void *data = 0)	3313	=item w->set<function> (void *data = 0)
2365		3314
2366	Also sets a callback, but uses a static method or plain function as	3315	Also sets a callback, but uses a static method or plain function as
2367	callback. The optional C<data> argument will be stored in the watcher's	3316	callback. The optional C<data> argument will be stored in the watcher's
…		…
2369		3318
2370	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3319	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2371		3320
2372	See the method-C<set> above for more details.	3321	See the method-C<set> above for more details.
2373		3322
2374	Example:	3323	Example: Use a plain function as callback.
2375		3324
2376	static void io_cb (ev::io &w, int revents) { }	3325	static void io_cb (ev::io &w, int revents) { }
2377	iow.set <io_cb> ();	3326	iow.set <io_cb> ();
2378		3327
2379	=item w->set (struct ev_loop *)	3328	=item w->set (struct ev_loop *)
2380		3329
2381	Associates a different C<struct ev_loop> with this watcher. You can only	3330	Associates a different C<struct ev_loop> with this watcher. You can only
2382	do this when the watcher is inactive (and not pending either).	3331	do this when the watcher is inactive (and not pending either).
2383		3332
2384	=item w->set ([args])	3333	=item w->set ([arguments])
2385		3334
2386	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3335	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2387	called at least once. Unlike the C counterpart, an active watcher gets	3336	called at least once. Unlike the C counterpart, an active watcher gets
2388	automatically stopped and restarted when reconfiguring it with this	3337	automatically stopped and restarted when reconfiguring it with this
2389	method.	3338	method.
2390		3339
2391	=item w->start ()	3340	=item w->start ()
…		…
2415	=back	3364	=back
2416		3365
2417	Example: Define a class with an IO and idle watcher, start one of them in	3366	Example: Define a class with an IO and idle watcher, start one of them in
2418	the constructor.	3367	the constructor.
2419		3368
2420	class myclass	3369	class myclass
2421	{	3370	{
2422	ev::io io; void io_cb (ev::io &w, int revents);	3371	ev::io io ; void io_cb (ev::io &w, int revents);
2423	ev:idle idle void idle_cb (ev::idle &w, int revents);	3372	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2424		3373
2425	myclass (int fd)	3374	myclass (int fd)
2426	{	3375	{
2427	io .set <myclass, &myclass::io_cb > (this);	3376	io .set <myclass, &myclass::io_cb > (this);
2428	idle.set <myclass, &myclass::idle_cb> (this);	3377	idle.set <myclass, &myclass::idle_cb> (this);
2429		3378
2430	io.start (fd, ev::READ);	3379	io.start (fd, ev::READ);
2431	}	3380	}
2432	};	3381	};
		3382
		3383
		3384	=head1 OTHER LANGUAGE BINDINGS
		3385
		3386	Libev does not offer other language bindings itself, but bindings for a
		3387	number of languages exist in the form of third-party packages. If you know
		3388	any interesting language binding in addition to the ones listed here, drop
		3389	me a note.
		3390
		3391	=over 4
		3392
		3393	=item Perl
		3394
		3395	The EV module implements the full libev API and is actually used to test
		3396	libev. EV is developed together with libev. Apart from the EV core module,
		3397	there are additional modules that implement libev-compatible interfaces
		3398	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3399	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3400	and C<EV::Glib>).
		3401
		3402	It can be found and installed via CPAN, its homepage is at
		3403	L<http://software.schmorp.de/pkg/EV>.
		3404
		3405	=item Python
		3406
		3407	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3408	seems to be quite complete and well-documented.
		3409
		3410	=item Ruby
		3411
		3412	Tony Arcieri has written a ruby extension that offers access to a subset
		3413	of the libev API and adds file handle abstractions, asynchronous DNS and
		3414	more on top of it. It can be found via gem servers. Its homepage is at
		3415	L<http://rev.rubyforge.org/>.
		3416
		3417	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3418	makes rev work even on mingw.
		3419
		3420	=item Haskell
		3421
		3422	A haskell binding to libev is available at
		3423	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3424
		3425	=item D
		3426
		3427	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3428	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3429
		3430	=item Ocaml
		3431
		3432	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3433	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3434
		3435	=item Lua
		3436
		3437	Brian Maher has written a partial interface to libev
		3438	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3439	L<http://github.com/brimworks/lua-ev>.
		3440
		3441	=back
2433		3442
2434		3443
2435	=head1 MACRO MAGIC	3444	=head1 MACRO MAGIC
2436		3445
2437	Libev can be compiled with a variety of options, the most fundamantal	3446	Libev can be compiled with a variety of options, the most fundamental
2438	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3447	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2439	functions and callbacks have an initial C<struct ev_loop *> argument.	3448	functions and callbacks have an initial C<struct ev_loop *> argument.
2440		3449
2441	To make it easier to write programs that cope with either variant, the	3450	To make it easier to write programs that cope with either variant, the
2442	following macros are defined:	3451	following macros are defined:
…		…
2447		3456
2448	This provides the loop I<argument> for functions, if one is required ("ev	3457	This provides the loop I<argument> for functions, if one is required ("ev
2449	loop argument"). The C<EV_A> form is used when this is the sole argument,	3458	loop argument"). The C<EV_A> form is used when this is the sole argument,
2450	C<EV_A_> is used when other arguments are following. Example:	3459	C<EV_A_> is used when other arguments are following. Example:
2451		3460
2452	ev_unref (EV_A);	3461	ev_unref (EV_A);
2453	ev_timer_add (EV_A_ watcher);	3462	ev_timer_add (EV_A_ watcher);
2454	ev_loop (EV_A_ 0);	3463	ev_loop (EV_A_ 0);
2455		3464
2456	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3465	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2457	which is often provided by the following macro.	3466	which is often provided by the following macro.
2458		3467
2459	=item C<EV_P>, C<EV_P_>	3468	=item C<EV_P>, C<EV_P_>
2460		3469
2461	This provides the loop I<parameter> for functions, if one is required ("ev	3470	This provides the loop I<parameter> for functions, if one is required ("ev
2462	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3471	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2463	C<EV_P_> is used when other parameters are following. Example:	3472	C<EV_P_> is used when other parameters are following. Example:
2464		3473
2465	// this is how ev_unref is being declared	3474	// this is how ev_unref is being declared
2466	static void ev_unref (EV_P);	3475	static void ev_unref (EV_P);
2467		3476
2468	// this is how you can declare your typical callback	3477	// this is how you can declare your typical callback
2469	static void cb (EV_P_ ev_timer *w, int revents)	3478	static void cb (EV_P_ ev_timer *w, int revents)
2470		3479
2471	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3480	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2472	suitable for use with C<EV_A>.	3481	suitable for use with C<EV_A>.
2473		3482
2474	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3483	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2475		3484
2476	Similar to the other two macros, this gives you the value of the default	3485	Similar to the other two macros, this gives you the value of the default
2477	loop, if multiple loops are supported ("ev loop default").	3486	loop, if multiple loops are supported ("ev loop default").
		3487
		3488	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3489
		3490	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3491	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3492	is undefined when the default loop has not been initialised by a previous
		3493	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3494
		3495	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3496	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2478		3497
2479	=back	3498	=back
2480		3499
2481	Example: Declare and initialise a check watcher, utilising the above	3500	Example: Declare and initialise a check watcher, utilising the above
2482	macros so it will work regardless of whether multiple loops are supported	3501	macros so it will work regardless of whether multiple loops are supported
2483	or not.	3502	or not.
2484		3503
2485	static void	3504	static void
2486	check_cb (EV_P_ ev_timer *w, int revents)	3505	check_cb (EV_P_ ev_timer *w, int revents)
2487	{	3506	{
2488	ev_check_stop (EV_A_ w);	3507	ev_check_stop (EV_A_ w);
2489	}	3508	}
2490		3509
2491	ev_check check;	3510	ev_check check;
2492	ev_check_init (&check, check_cb);	3511	ev_check_init (&check, check_cb);
2493	ev_check_start (EV_DEFAULT_ &check);	3512	ev_check_start (EV_DEFAULT_ &check);
2494	ev_loop (EV_DEFAULT_ 0);	3513	ev_loop (EV_DEFAULT_ 0);
2495		3514
2496	=head1 EMBEDDING	3515	=head1 EMBEDDING
2497		3516
2498	Libev can (and often is) directly embedded into host	3517	Libev can (and often is) directly embedded into host
2499	applications. Examples of applications that embed it include the Deliantra	3518	applications. Examples of applications that embed it include the Deliantra
…		…
2506	libev somewhere in your source tree).	3525	libev somewhere in your source tree).
2507		3526
2508	=head2 FILESETS	3527	=head2 FILESETS
2509		3528
2510	Depending on what features you need you need to include one or more sets of files	3529	Depending on what features you need you need to include one or more sets of files
2511	in your app.	3530	in your application.
2512		3531
2513	=head3 CORE EVENT LOOP	3532	=head3 CORE EVENT LOOP
2514		3533
2515	To include only the libev core (all the C<ev_*> functions), with manual	3534	To include only the libev core (all the C<ev_*> functions), with manual
2516	configuration (no autoconf):	3535	configuration (no autoconf):
2517		3536
2518	#define EV_STANDALONE 1	3537	#define EV_STANDALONE 1
2519	#include "ev.c"	3538	#include "ev.c"
2520		3539
2521	This will automatically include F<ev.h>, too, and should be done in a	3540	This will automatically include F<ev.h>, too, and should be done in a
2522	single C source file only to provide the function implementations. To use	3541	single C source file only to provide the function implementations. To use
2523	it, do the same for F<ev.h> in all files wishing to use this API (best	3542	it, do the same for F<ev.h> in all files wishing to use this API (best
2524	done by writing a wrapper around F<ev.h> that you can include instead and	3543	done by writing a wrapper around F<ev.h> that you can include instead and
2525	where you can put other configuration options):	3544	where you can put other configuration options):
2526		3545
2527	#define EV_STANDALONE 1	3546	#define EV_STANDALONE 1
2528	#include "ev.h"	3547	#include "ev.h"
2529		3548
2530	Both header files and implementation files can be compiled with a C++	3549	Both header files and implementation files can be compiled with a C++
2531	compiler (at least, thats a stated goal, and breakage will be treated	3550	compiler (at least, that's a stated goal, and breakage will be treated
2532	as a bug).	3551	as a bug).
2533		3552
2534	You need the following files in your source tree, or in a directory	3553	You need the following files in your source tree, or in a directory
2535	in your include path (e.g. in libev/ when using -Ilibev):	3554	in your include path (e.g. in libev/ when using -Ilibev):
2536		3555
2537	ev.h	3556	ev.h
2538	ev.c	3557	ev.c
2539	ev_vars.h	3558	ev_vars.h
2540	ev_wrap.h	3559	ev_wrap.h
2541		3560
2542	ev_win32.c required on win32 platforms only	3561	ev_win32.c required on win32 platforms only
2543		3562
2544	ev_select.c only when select backend is enabled (which is enabled by default)	3563	ev_select.c only when select backend is enabled (which is enabled by default)
2545	ev_poll.c only when poll backend is enabled (disabled by default)	3564	ev_poll.c only when poll backend is enabled (disabled by default)
2546	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3565	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2547	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3566	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2548	ev_port.c only when the solaris port backend is enabled (disabled by default)	3567	ev_port.c only when the solaris port backend is enabled (disabled by default)
2549		3568
2550	F<ev.c> includes the backend files directly when enabled, so you only need	3569	F<ev.c> includes the backend files directly when enabled, so you only need
2551	to compile this single file.	3570	to compile this single file.
2552		3571
2553	=head3 LIBEVENT COMPATIBILITY API	3572	=head3 LIBEVENT COMPATIBILITY API
2554		3573
2555	To include the libevent compatibility API, also include:	3574	To include the libevent compatibility API, also include:
2556		3575
2557	#include "event.c"	3576	#include "event.c"
2558		3577
2559	in the file including F<ev.c>, and:	3578	in the file including F<ev.c>, and:
2560		3579
2561	#include "event.h"	3580	#include "event.h"
2562		3581
2563	in the files that want to use the libevent API. This also includes F<ev.h>.	3582	in the files that want to use the libevent API. This also includes F<ev.h>.
2564		3583
2565	You need the following additional files for this:	3584	You need the following additional files for this:
2566		3585
2567	event.h	3586	event.h
2568	event.c	3587	event.c
2569		3588
2570	=head3 AUTOCONF SUPPORT	3589	=head3 AUTOCONF SUPPORT
2571		3590
2572	Instead of using C<EV_STANDALONE=1> and providing your config in	3591	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2573	whatever way you want, you can also C<m4_include([libev.m4])> in your	3592	whatever way you want, you can also C<m4_include([libev.m4])> in your
2574	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3593	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2575	include F<config.h> and configure itself accordingly.	3594	include F<config.h> and configure itself accordingly.
2576		3595
2577	For this of course you need the m4 file:	3596	For this of course you need the m4 file:
2578		3597
2579	libev.m4	3598	libev.m4
2580		3599
2581	=head2 PREPROCESSOR SYMBOLS/MACROS	3600	=head2 PREPROCESSOR SYMBOLS/MACROS
2582		3601
2583	Libev can be configured via a variety of preprocessor symbols you have to define	3602	Libev can be configured via a variety of preprocessor symbols you have to
2584	before including any of its files. The default is not to build for multiplicity	3603	define before including any of its files. The default in the absence of
2585	and only include the select backend.	3604	autoconf is documented for every option.
2586		3605
2587	=over 4	3606	=over 4
2588		3607
2589	=item EV_STANDALONE	3608	=item EV_STANDALONE
2590		3609
…		…
2592	keeps libev from including F<config.h>, and it also defines dummy	3611	keeps libev from including F<config.h>, and it also defines dummy
2593	implementations for some libevent functions (such as logging, which is not	3612	implementations for some libevent functions (such as logging, which is not
2594	supported). It will also not define any of the structs usually found in	3613	supported). It will also not define any of the structs usually found in
2595	F<event.h> that are not directly supported by the libev core alone.	3614	F<event.h> that are not directly supported by the libev core alone.
2596		3615
		3616	In standalone mode, libev will still try to automatically deduce the
		3617	configuration, but has to be more conservative.
		3618
2597	=item EV_USE_MONOTONIC	3619	=item EV_USE_MONOTONIC
2598		3620
2599	If defined to be C<1>, libev will try to detect the availability of the	3621	If defined to be C<1>, libev will try to detect the availability of the
2600	monotonic clock option at both compiletime and runtime. Otherwise no use	3622	monotonic clock option at both compile time and runtime. Otherwise no
2601	of the monotonic clock option will be attempted. If you enable this, you	3623	use of the monotonic clock option will be attempted. If you enable this,
2602	usually have to link against librt or something similar. Enabling it when	3624	you usually have to link against librt or something similar. Enabling it
2603	the functionality isn't available is safe, though, although you have	3625	when the functionality isn't available is safe, though, although you have
2604	to make sure you link against any libraries where the C<clock_gettime>	3626	to make sure you link against any libraries where the C<clock_gettime>
2605	function is hiding in (often F<-lrt>).	3627	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2606		3628
2607	=item EV_USE_REALTIME	3629	=item EV_USE_REALTIME
2608		3630
2609	If defined to be C<1>, libev will try to detect the availability of the	3631	If defined to be C<1>, libev will try to detect the availability of the
2610	realtime clock option at compiletime (and assume its availability at	3632	real-time clock option at compile time (and assume its availability
2611	runtime if successful). Otherwise no use of the realtime clock option will	3633	at runtime if successful). Otherwise no use of the real-time clock
2612	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3634	option will be attempted. This effectively replaces C<gettimeofday>
2613	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3635	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2614	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3636	correctness. See the note about libraries in the description of
		3637	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3638	C<EV_USE_CLOCK_SYSCALL>.
		3639
		3640	=item EV_USE_CLOCK_SYSCALL
		3641
		3642	If defined to be C<1>, libev will try to use a direct syscall instead
		3643	of calling the system-provided C<clock_gettime> function. This option
		3644	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3645	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3646	programs needlessly. Using a direct syscall is slightly slower (in
		3647	theory), because no optimised vdso implementation can be used, but avoids
		3648	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3649	higher, as it simplifies linking (no need for C<-lrt>).
2615		3650
2616	=item EV_USE_NANOSLEEP	3651	=item EV_USE_NANOSLEEP
2617		3652
2618	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3653	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2619	and will use it for delays. Otherwise it will use C<select ()>.	3654	and will use it for delays. Otherwise it will use C<select ()>.
2620		3655
		3656	=item EV_USE_EVENTFD
		3657
		3658	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3659	available and will probe for kernel support at runtime. This will improve
		3660	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3661	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3662	2.7 or newer, otherwise disabled.
		3663
2621	=item EV_USE_SELECT	3664	=item EV_USE_SELECT
2622		3665
2623	If undefined or defined to be C<1>, libev will compile in support for the	3666	If undefined or defined to be C<1>, libev will compile in support for the
2624	C<select>(2) backend. No attempt at autodetection will be done: if no	3667	C<select>(2) backend. No attempt at auto-detection will be done: if no
2625	other method takes over, select will be it. Otherwise the select backend	3668	other method takes over, select will be it. Otherwise the select backend
2626	will not be compiled in.	3669	will not be compiled in.
2627		3670
2628	=item EV_SELECT_USE_FD_SET	3671	=item EV_SELECT_USE_FD_SET
2629		3672
2630	If defined to C<1>, then the select backend will use the system C<fd_set>	3673	If defined to C<1>, then the select backend will use the system C<fd_set>
2631	structure. This is useful if libev doesn't compile due to a missing	3674	structure. This is useful if libev doesn't compile due to a missing
2632	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3675	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2633	exotic systems. This usually limits the range of file descriptors to some	3676	on exotic systems. This usually limits the range of file descriptors to
2634	low limit such as 1024 or might have other limitations (winsocket only	3677	some low limit such as 1024 or might have other limitations (winsocket
2635	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3678	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2636	influence the size of the C<fd_set> used.	3679	configures the maximum size of the C<fd_set>.
2637		3680
2638	=item EV_SELECT_IS_WINSOCKET	3681	=item EV_SELECT_IS_WINSOCKET
2639		3682
2640	When defined to C<1>, the select backend will assume that	3683	When defined to C<1>, the select backend will assume that
2641	select/socket/connect etc. don't understand file descriptors but	3684	select/socket/connect etc. don't understand file descriptors but
…		…
2643	be used is the winsock select). This means that it will call	3686	be used is the winsock select). This means that it will call
2644	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3687	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2645	it is assumed that all these functions actually work on fds, even	3688	it is assumed that all these functions actually work on fds, even
2646	on win32. Should not be defined on non-win32 platforms.	3689	on win32. Should not be defined on non-win32 platforms.
2647		3690
2648	=item EV_FD_TO_WIN32_HANDLE	3691	=item EV_FD_TO_WIN32_HANDLE(fd)
2649		3692
2650	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3693	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2651	file descriptors to socket handles. When not defining this symbol (the	3694	file descriptors to socket handles. When not defining this symbol (the
2652	default), then libev will call C<_get_osfhandle>, which is usually	3695	default), then libev will call C<_get_osfhandle>, which is usually
2653	correct. In some cases, programs use their own file descriptor management,	3696	correct. In some cases, programs use their own file descriptor management,
2654	in which case they can provide this function to map fds to socket handles.	3697	in which case they can provide this function to map fds to socket handles.
2655		3698
		3699	=item EV_WIN32_HANDLE_TO_FD(handle)
		3700
		3701	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3702	using the standard C<_open_osfhandle> function. For programs implementing
		3703	their own fd to handle mapping, overwriting this function makes it easier
		3704	to do so. This can be done by defining this macro to an appropriate value.
		3705
		3706	=item EV_WIN32_CLOSE_FD(fd)
		3707
		3708	If programs implement their own fd to handle mapping on win32, then this
		3709	macro can be used to override the C<close> function, useful to unregister
		3710	file descriptors again. Note that the replacement function has to close
		3711	the underlying OS handle.
		3712
2656	=item EV_USE_POLL	3713	=item EV_USE_POLL
2657		3714
2658	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3715	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2659	backend. Otherwise it will be enabled on non-win32 platforms. It	3716	backend. Otherwise it will be enabled on non-win32 platforms. It
2660	takes precedence over select.	3717	takes precedence over select.
2661		3718
2662	=item EV_USE_EPOLL	3719	=item EV_USE_EPOLL
2663		3720
2664	If defined to be C<1>, libev will compile in support for the Linux	3721	If defined to be C<1>, libev will compile in support for the Linux
2665	C<epoll>(7) backend. Its availability will be detected at runtime,	3722	C<epoll>(7) backend. Its availability will be detected at runtime,
2666	otherwise another method will be used as fallback. This is the	3723	otherwise another method will be used as fallback. This is the preferred
2667	preferred backend for GNU/Linux systems.	3724	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3725	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2668		3726
2669	=item EV_USE_KQUEUE	3727	=item EV_USE_KQUEUE
2670		3728
2671	If defined to be C<1>, libev will compile in support for the BSD style	3729	If defined to be C<1>, libev will compile in support for the BSD style
2672	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3730	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2685	otherwise another method will be used as fallback. This is the preferred	3743	otherwise another method will be used as fallback. This is the preferred
2686	backend for Solaris 10 systems.	3744	backend for Solaris 10 systems.
2687		3745
2688	=item EV_USE_DEVPOLL	3746	=item EV_USE_DEVPOLL
2689		3747
2690	reserved for future expansion, works like the USE symbols above.	3748	Reserved for future expansion, works like the USE symbols above.
2691		3749
2692	=item EV_USE_INOTIFY	3750	=item EV_USE_INOTIFY
2693		3751
2694	If defined to be C<1>, libev will compile in support for the Linux inotify	3752	If defined to be C<1>, libev will compile in support for the Linux inotify
2695	interface to speed up C<ev_stat> watchers. Its actual availability will	3753	interface to speed up C<ev_stat> watchers. Its actual availability will
2696	be detected at runtime.	3754	be detected at runtime. If undefined, it will be enabled if the headers
		3755	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2697		3756
2698	=item EV_ATOMIC_T	3757	=item EV_ATOMIC_T
2699		3758
2700	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	3759	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2701	access is atomic with respect to other threads or signal contexts. No such	3760	access is atomic with respect to other threads or signal contexts. No such
2702	type is easily found in the C language, so you can provide your own type	3761	type is easily found in the C language, so you can provide your own type
2703	that you know is safe for your purposes. It is used both for signal handler "locking"	3762	that you know is safe for your purposes. It is used both for signal handler "locking"
2704	as well as for signal and thread safety in C<ev_async> watchers.	3763	as well as for signal and thread safety in C<ev_async> watchers.
2705		3764
2706	In the absense of this define, libev will use C<sig_atomic_t volatile>	3765	In the absence of this define, libev will use C<sig_atomic_t volatile>
2707	(from F<signal.h>), which is usually good enough on most platforms.	3766	(from F<signal.h>), which is usually good enough on most platforms.
2708		3767
2709	=item EV_H	3768	=item EV_H
2710		3769
2711	The name of the F<ev.h> header file used to include it. The default if	3770	The name of the F<ev.h> header file used to include it. The default if
…		…
2750	When doing priority-based operations, libev usually has to linearly search	3809	When doing priority-based operations, libev usually has to linearly search
2751	all the priorities, so having many of them (hundreds) uses a lot of space	3810	all the priorities, so having many of them (hundreds) uses a lot of space
2752	and time, so using the defaults of five priorities (-2 .. +2) is usually	3811	and time, so using the defaults of five priorities (-2 .. +2) is usually
2753	fine.	3812	fine.
2754		3813
2755	If your embedding app does not need any priorities, defining these both to	3814	If your embedding application does not need any priorities, defining these
2756	C<0> will save some memory and cpu.	3815	both to C<0> will save some memory and CPU.
2757		3816
2758	=item EV_PERIODIC_ENABLE	3817	=item EV_PERIODIC_ENABLE
2759		3818
2760	If undefined or defined to be C<1>, then periodic timers are supported. If	3819	If undefined or defined to be C<1>, then periodic timers are supported. If
2761	defined to be C<0>, then they are not. Disabling them saves a few kB of	3820	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2768	code.	3827	code.
2769		3828
2770	=item EV_EMBED_ENABLE	3829	=item EV_EMBED_ENABLE
2771		3830
2772	If undefined or defined to be C<1>, then embed watchers are supported. If	3831	If undefined or defined to be C<1>, then embed watchers are supported. If
2773	defined to be C<0>, then they are not.	3832	defined to be C<0>, then they are not. Embed watchers rely on most other
		3833	watcher types, which therefore must not be disabled.
2774		3834
2775	=item EV_STAT_ENABLE	3835	=item EV_STAT_ENABLE
2776		3836
2777	If undefined or defined to be C<1>, then stat watchers are supported. If	3837	If undefined or defined to be C<1>, then stat watchers are supported. If
2778	defined to be C<0>, then they are not.	3838	defined to be C<0>, then they are not.
…		…
2788	defined to be C<0>, then they are not.	3848	defined to be C<0>, then they are not.
2789		3849
2790	=item EV_MINIMAL	3850	=item EV_MINIMAL
2791		3851
2792	If you need to shave off some kilobytes of code at the expense of some	3852	If you need to shave off some kilobytes of code at the expense of some
2793	speed, define this symbol to C<1>. Currently only used for gcc to override	3853	speed (but with the full API), define this symbol to C<1>. Currently this
2794	some inlining decisions, saves roughly 30% codesize of amd64.	3854	is used to override some inlining decisions, saves roughly 30% code size
		3855	on amd64. It also selects a much smaller 2-heap for timer management over
		3856	the default 4-heap.
		3857
		3858	You can save even more by disabling watcher types you do not need
		3859	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3860	(C<-DNDEBUG>) will usually reduce code size a lot.
		3861
		3862	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3863	provide a bare-bones event library. See C<ev.h> for details on what parts
		3864	of the API are still available, and do not complain if this subset changes
		3865	over time.
		3866
		3867	=item EV_NSIG
		3868
		3869	The highest supported signal number, +1 (or, the number of
		3870	signals): Normally, libev tries to deduce the maximum number of signals
		3871	automatically, but sometimes this fails, in which case it can be
		3872	specified. Also, using a lower number than detected (C<32> should be
		3873	good for about any system in existance) can save some memory, as libev
		3874	statically allocates some 12-24 bytes per signal number.
2795		3875
2796	=item EV_PID_HASHSIZE	3876	=item EV_PID_HASHSIZE
2797		3877
2798	C<ev_child> watchers use a small hash table to distribute workload by	3878	C<ev_child> watchers use a small hash table to distribute workload by
2799	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3879	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2806	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3886	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2807	usually more than enough. If you need to manage thousands of C<ev_stat>	3887	usually more than enough. If you need to manage thousands of C<ev_stat>
2808	watchers you might want to increase this value (I<must> be a power of	3888	watchers you might want to increase this value (I<must> be a power of
2809	two).	3889	two).
2810		3890
		3891	=item EV_USE_4HEAP
		3892
		3893	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3894	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3895	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3896	faster performance with many (thousands) of watchers.
		3897
		3898	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3899	(disabled).
		3900
		3901	=item EV_HEAP_CACHE_AT
		3902
		3903	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3904	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3905	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3906	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3907	but avoids random read accesses on heap changes. This improves performance
		3908	noticeably with many (hundreds) of watchers.
		3909
		3910	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3911	(disabled).
		3912
		3913	=item EV_VERIFY
		3914
		3915	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3916	be done: If set to C<0>, no internal verification code will be compiled
		3917	in. If set to C<1>, then verification code will be compiled in, but not
		3918	called. If set to C<2>, then the internal verification code will be
		3919	called once per loop, which can slow down libev. If set to C<3>, then the
		3920	verification code will be called very frequently, which will slow down
		3921	libev considerably.
		3922
		3923	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3924	C<0>.
		3925
2811	=item EV_COMMON	3926	=item EV_COMMON
2812		3927
2813	By default, all watchers have a C<void *data> member. By redefining	3928	By default, all watchers have a C<void *data> member. By redefining
2814	this macro to a something else you can include more and other types of	3929	this macro to a something else you can include more and other types of
2815	members. You have to define it each time you include one of the files,	3930	members. You have to define it each time you include one of the files,
2816	though, and it must be identical each time.	3931	though, and it must be identical each time.
2817		3932
2818	For example, the perl EV module uses something like this:	3933	For example, the perl EV module uses something like this:
2819		3934
2820	#define EV_COMMON \	3935	#define EV_COMMON \
2821	SV *self; /* contains this struct */ \	3936	SV *self; /* contains this struct */ \
2822	SV *cb_sv, *fh /* note no trailing ";" */	3937	SV *cb_sv, *fh /* note no trailing ";" */
2823		3938
2824	=item EV_CB_DECLARE (type)	3939	=item EV_CB_DECLARE (type)
2825		3940
2826	=item EV_CB_INVOKE (watcher, revents)	3941	=item EV_CB_INVOKE (watcher, revents)
2827		3942
…		…
2832	definition and a statement, respectively. See the F<ev.h> header file for	3947	definition and a statement, respectively. See the F<ev.h> header file for
2833	their default definitions. One possible use for overriding these is to	3948	their default definitions. One possible use for overriding these is to
2834	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3949	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2835	method calls instead of plain function calls in C++.	3950	method calls instead of plain function calls in C++.
2836		3951
		3952	=back
		3953
2837	=head2 EXPORTED API SYMBOLS	3954	=head2 EXPORTED API SYMBOLS
2838		3955
2839	If you need to re-export the API (e.g. via a dll) and you need a list of	3956	If you need to re-export the API (e.g. via a DLL) and you need a list of
2840	exported symbols, you can use the provided F<Symbol.*> files which list	3957	exported symbols, you can use the provided F<Symbol.*> files which list
2841	all public symbols, one per line:	3958	all public symbols, one per line:
2842		3959
2843	Symbols.ev for libev proper	3960	Symbols.ev for libev proper
2844	Symbols.event for the libevent emulation	3961	Symbols.event for the libevent emulation
2845		3962
2846	This can also be used to rename all public symbols to avoid clashes with	3963	This can also be used to rename all public symbols to avoid clashes with
2847	multiple versions of libev linked together (which is obviously bad in	3964	multiple versions of libev linked together (which is obviously bad in
2848	itself, but sometimes it is inconvinient to avoid this).	3965	itself, but sometimes it is inconvenient to avoid this).
2849		3966
2850	A sed command like this will create wrapper C<#define>'s that you need to	3967	A sed command like this will create wrapper C<#define>'s that you need to
2851	include before including F<ev.h>:	3968	include before including F<ev.h>:
2852		3969
2853	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3970	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2870	file.	3987	file.
2871		3988
2872	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3989	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2873	that everybody includes and which overrides some configure choices:	3990	that everybody includes and which overrides some configure choices:
2874		3991
2875	#define EV_MINIMAL 1	3992	#define EV_MINIMAL 1
2876	#define EV_USE_POLL 0	3993	#define EV_USE_POLL 0
2877	#define EV_MULTIPLICITY 0	3994	#define EV_MULTIPLICITY 0
2878	#define EV_PERIODIC_ENABLE 0	3995	#define EV_PERIODIC_ENABLE 0
2879	#define EV_STAT_ENABLE 0	3996	#define EV_STAT_ENABLE 0
2880	#define EV_FORK_ENABLE 0	3997	#define EV_FORK_ENABLE 0
2881	#define EV_CONFIG_H <config.h>	3998	#define EV_CONFIG_H <config.h>
2882	#define EV_MINPRI 0	3999	#define EV_MINPRI 0
2883	#define EV_MAXPRI 0	4000	#define EV_MAXPRI 0
2884		4001
2885	#include "ev++.h"	4002	#include "ev++.h"
2886		4003
2887	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4004	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2888		4005
2889	#include "ev_cpp.h"	4006	#include "ev_cpp.h"
2890	#include "ev.c"	4007	#include "ev.c"
2891		4008
		4009	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2892		4010
2893	=head1 COMPLEXITIES	4011	=head2 THREADS AND COROUTINES
2894		4012
2895	In this section the complexities of (many of) the algorithms used inside	4013	=head3 THREADS
2896	libev will be explained. For complexity discussions about backends see the
2897	documentation for C<ev_default_init>.
2898		4014
2899	All of the following are about amortised time: If an array needs to be	4015	All libev functions are reentrant and thread-safe unless explicitly
2900	extended, libev needs to realloc and move the whole array, but this	4016	documented otherwise, but libev implements no locking itself. This means
2901	happens asymptotically never with higher number of elements, so O(1) might	4017	that you can use as many loops as you want in parallel, as long as there
2902	mean it might do a lengthy realloc operation in rare cases, but on average	4018	are no concurrent calls into any libev function with the same loop
2903	it is much faster and asymptotically approaches constant time.	4019	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4020	of course): libev guarantees that different event loops share no data
		4021	structures that need any locking.
		4022
		4023	Or to put it differently: calls with different loop parameters can be done
		4024	concurrently from multiple threads, calls with the same loop parameter
		4025	must be done serially (but can be done from different threads, as long as
		4026	only one thread ever is inside a call at any point in time, e.g. by using
		4027	a mutex per loop).
		4028
		4029	Specifically to support threads (and signal handlers), libev implements
		4030	so-called C<ev_async> watchers, which allow some limited form of
		4031	concurrency on the same event loop, namely waking it up "from the
		4032	outside".
		4033
		4034	If you want to know which design (one loop, locking, or multiple loops
		4035	without or something else still) is best for your problem, then I cannot
		4036	help you, but here is some generic advice:
2904		4037
2905	=over 4	4038	=over 4
2906		4039
2907	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4040	=item * most applications have a main thread: use the default libev loop
		4041	in that thread, or create a separate thread running only the default loop.
2908		4042
2909	This means that, when you have a watcher that triggers in one hour and	4043	This helps integrating other libraries or software modules that use libev
2910	there are 100 watchers that would trigger before that then inserting will	4044	themselves and don't care/know about threading.
2911	have to skip roughly seven (C<ld 100>) of these watchers.
2912		4045
2913	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4046	=item * one loop per thread is usually a good model.
2914		4047
2915	That means that changing a timer costs less than removing/adding them	4048	Doing this is almost never wrong, sometimes a better-performance model
2916	as only the relative motion in the event queue has to be paid for.	4049	exists, but it is always a good start.
2917		4050
2918	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4051	=item * other models exist, such as the leader/follower pattern, where one
		4052	loop is handed through multiple threads in a kind of round-robin fashion.
2919		4053
2920	These just add the watcher into an array or at the head of a list.	4054	Choosing a model is hard - look around, learn, know that usually you can do
		4055	better than you currently do :-)
2921		4056
2922	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4057	=item * often you need to talk to some other thread which blocks in the
		4058	event loop.
2923		4059
2924	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4060	C<ev_async> watchers can be used to wake them up from other threads safely
		4061	(or from signal contexts...).
2925		4062
2926	These watchers are stored in lists then need to be walked to find the	4063	An example use would be to communicate signals or other events that only
2927	correct watcher to remove. The lists are usually short (you don't usually	4064	work in the default loop by registering the signal watcher with the
2928	have many watchers waiting for the same fd or signal).	4065	default loop and triggering an C<ev_async> watcher from the default loop
2929		4066	watcher callback into the event loop interested in the signal.
2930	=item Finding the next timer in each loop iteration: O(1)
2931
2932	By virtue of using a binary heap, the next timer is always found at the
2933	beginning of the storage array.
2934
2935	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2936
2937	A change means an I/O watcher gets started or stopped, which requires
2938	libev to recalculate its status (and possibly tell the kernel, depending
2939	on backend and wether C<ev_io_set> was used).
2940
2941	=item Activating one watcher (putting it into the pending state): O(1)
2942
2943	=item Priority handling: O(number_of_priorities)
2944
2945	Priorities are implemented by allocating some space for each
2946	priority. When doing priority-based operations, libev usually has to
2947	linearly search all the priorities, but starting/stopping and activating
2948	watchers becomes O(1) w.r.t. priority handling.
2949
2950	=item Sending an ev_async: O(1)
2951
2952	=item Processing ev_async_send: O(number_of_async_watchers)
2953
2954	=item Processing signals: O(max_signal_number)
2955
2956	Sending involves a syscall I<iff> there were no other C<ev_async_send>
2957	calls in the current loop iteration. Checking for async and signal events
2958	involves iterating over all running async watchers or all signal numbers.
2959		4067
2960	=back	4068	=back
2961		4069
		4070	=head4 THREAD LOCKING EXAMPLE
2962		4071
2963	=head1 Win32 platform limitations and workarounds	4072	Here is a fictitious example of how to run an event loop in a different
		4073	thread than where callbacks are being invoked and watchers are
		4074	created/added/removed.
		4075
		4076	For a real-world example, see the C<EV::Loop::Async> perl module,
		4077	which uses exactly this technique (which is suited for many high-level
		4078	languages).
		4079
		4080	The example uses a pthread mutex to protect the loop data, a condition
		4081	variable to wait for callback invocations, an async watcher to notify the
		4082	event loop thread and an unspecified mechanism to wake up the main thread.
		4083
		4084	First, you need to associate some data with the event loop:
		4085
		4086	typedef struct {
		4087	mutex_t lock; /* global loop lock */
		4088	ev_async async_w;
		4089	thread_t tid;
		4090	cond_t invoke_cv;
		4091	} userdata;
		4092
		4093	void prepare_loop (EV_P)
		4094	{
		4095	// for simplicity, we use a static userdata struct.
		4096	static userdata u;
		4097
		4098	ev_async_init (&u->async_w, async_cb);
		4099	ev_async_start (EV_A_ &u->async_w);
		4100
		4101	pthread_mutex_init (&u->lock, 0);
		4102	pthread_cond_init (&u->invoke_cv, 0);
		4103
		4104	// now associate this with the loop
		4105	ev_set_userdata (EV_A_ u);
		4106	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4107	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4108
		4109	// then create the thread running ev_loop
		4110	pthread_create (&u->tid, 0, l_run, EV_A);
		4111	}
		4112
		4113	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4114	solely to wake up the event loop so it takes notice of any new watchers
		4115	that might have been added:
		4116
		4117	static void
		4118	async_cb (EV_P_ ev_async *w, int revents)
		4119	{
		4120	// just used for the side effects
		4121	}
		4122
		4123	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4124	protecting the loop data, respectively.
		4125
		4126	static void
		4127	l_release (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130	pthread_mutex_unlock (&u->lock);
		4131	}
		4132
		4133	static void
		4134	l_acquire (EV_P)
		4135	{
		4136	userdata *u = ev_userdata (EV_A);
		4137	pthread_mutex_lock (&u->lock);
		4138	}
		4139
		4140	The event loop thread first acquires the mutex, and then jumps straight
		4141	into C<ev_loop>:
		4142
		4143	void *
		4144	l_run (void *thr_arg)
		4145	{
		4146	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4147
		4148	l_acquire (EV_A);
		4149	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4150	ev_loop (EV_A_ 0);
		4151	l_release (EV_A);
		4152
		4153	return 0;
		4154	}
		4155
		4156	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4157	signal the main thread via some unspecified mechanism (signals? pipe
		4158	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4159	have been called (in a while loop because a) spurious wakeups are possible
		4160	and b) skipping inter-thread-communication when there are no pending
		4161	watchers is very beneficial):
		4162
		4163	static void
		4164	l_invoke (EV_P)
		4165	{
		4166	userdata *u = ev_userdata (EV_A);
		4167
		4168	while (ev_pending_count (EV_A))
		4169	{
		4170	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4171	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4172	}
		4173	}
		4174
		4175	Now, whenever the main thread gets told to invoke pending watchers, it
		4176	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4177	thread to continue:
		4178
		4179	static void
		4180	real_invoke_pending (EV_P)
		4181	{
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	pthread_mutex_lock (&u->lock);
		4185	ev_invoke_pending (EV_A);
		4186	pthread_cond_signal (&u->invoke_cv);
		4187	pthread_mutex_unlock (&u->lock);
		4188	}
		4189
		4190	Whenever you want to start/stop a watcher or do other modifications to an
		4191	event loop, you will now have to lock:
		4192
		4193	ev_timer timeout_watcher;
		4194	userdata *u = ev_userdata (EV_A);
		4195
		4196	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4197
		4198	pthread_mutex_lock (&u->lock);
		4199	ev_timer_start (EV_A_ &timeout_watcher);
		4200	ev_async_send (EV_A_ &u->async_w);
		4201	pthread_mutex_unlock (&u->lock);
		4202
		4203	Note that sending the C<ev_async> watcher is required because otherwise
		4204	an event loop currently blocking in the kernel will have no knowledge
		4205	about the newly added timer. By waking up the loop it will pick up any new
		4206	watchers in the next event loop iteration.
		4207
		4208	=head3 COROUTINES
		4209
		4210	Libev is very accommodating to coroutines ("cooperative threads"):
		4211	libev fully supports nesting calls to its functions from different
		4212	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4213	different coroutines, and switch freely between both coroutines running
		4214	the loop, as long as you don't confuse yourself). The only exception is
		4215	that you must not do this from C<ev_periodic> reschedule callbacks.
		4216
		4217	Care has been taken to ensure that libev does not keep local state inside
		4218	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4219	they do not call any callbacks.
		4220
		4221	=head2 COMPILER WARNINGS
		4222
		4223	Depending on your compiler and compiler settings, you might get no or a
		4224	lot of warnings when compiling libev code. Some people are apparently
		4225	scared by this.
		4226
		4227	However, these are unavoidable for many reasons. For one, each compiler
		4228	has different warnings, and each user has different tastes regarding
		4229	warning options. "Warn-free" code therefore cannot be a goal except when
		4230	targeting a specific compiler and compiler-version.
		4231
		4232	Another reason is that some compiler warnings require elaborate
		4233	workarounds, or other changes to the code that make it less clear and less
		4234	maintainable.
		4235
		4236	And of course, some compiler warnings are just plain stupid, or simply
		4237	wrong (because they don't actually warn about the condition their message
		4238	seems to warn about). For example, certain older gcc versions had some
		4239	warnings that resulted an extreme number of false positives. These have
		4240	been fixed, but some people still insist on making code warn-free with
		4241	such buggy versions.
		4242
		4243	While libev is written to generate as few warnings as possible,
		4244	"warn-free" code is not a goal, and it is recommended not to build libev
		4245	with any compiler warnings enabled unless you are prepared to cope with
		4246	them (e.g. by ignoring them). Remember that warnings are just that:
		4247	warnings, not errors, or proof of bugs.
		4248
		4249
		4250	=head2 VALGRIND
		4251
		4252	Valgrind has a special section here because it is a popular tool that is
		4253	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4254
		4255	If you think you found a bug (memory leak, uninitialised data access etc.)
		4256	in libev, then check twice: If valgrind reports something like:
		4257
		4258	==2274== definitely lost: 0 bytes in 0 blocks.
		4259	==2274== possibly lost: 0 bytes in 0 blocks.
		4260	==2274== still reachable: 256 bytes in 1 blocks.
		4261
		4262	Then there is no memory leak, just as memory accounted to global variables
		4263	is not a memleak - the memory is still being referenced, and didn't leak.
		4264
		4265	Similarly, under some circumstances, valgrind might report kernel bugs
		4266	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4267	although an acceptable workaround has been found here), or it might be
		4268	confused.
		4269
		4270	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4271	make it into some kind of religion.
		4272
		4273	If you are unsure about something, feel free to contact the mailing list
		4274	with the full valgrind report and an explanation on why you think this
		4275	is a bug in libev (best check the archives, too :). However, don't be
		4276	annoyed when you get a brisk "this is no bug" answer and take the chance
		4277	of learning how to interpret valgrind properly.
		4278
		4279	If you need, for some reason, empty reports from valgrind for your project
		4280	I suggest using suppression lists.
		4281
		4282
		4283	=head1 PORTABILITY NOTES
		4284
		4285	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
2964		4286
2965	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4287	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2966	requires, and its I/O model is fundamentally incompatible with the POSIX	4288	requires, and its I/O model is fundamentally incompatible with the POSIX
2967	model. Libev still offers limited functionality on this platform in	4289	model. Libev still offers limited functionality on this platform in
2968	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4290	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2969	descriptors. This only applies when using Win32 natively, not when using	4291	descriptors. This only applies when using Win32 natively, not when using
2970	e.g. cygwin.	4292	e.g. cygwin.
2971		4293
		4294	Lifting these limitations would basically require the full
		4295	re-implementation of the I/O system. If you are into these kinds of
		4296	things, then note that glib does exactly that for you in a very portable
		4297	way (note also that glib is the slowest event library known to man).
		4298
2972	There is no supported compilation method available on windows except	4299	There is no supported compilation method available on windows except
2973	embedding it into other applications.	4300	embedding it into other applications.
2974		4301
		4302	Sensible signal handling is officially unsupported by Microsoft - libev
		4303	tries its best, but under most conditions, signals will simply not work.
		4304
		4305	Not a libev limitation but worth mentioning: windows apparently doesn't
		4306	accept large writes: instead of resulting in a partial write, windows will
		4307	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4308	so make sure you only write small amounts into your sockets (less than a
		4309	megabyte seems safe, but this apparently depends on the amount of memory
		4310	available).
		4311
2975	Due to the many, low, and arbitrary limits on the win32 platform and the	4312	Due to the many, low, and arbitrary limits on the win32 platform and
2976	abysmal performance of winsockets, using a large number of sockets is not	4313	the abysmal performance of winsockets, using a large number of sockets
2977	recommended (and not reasonable). If your program needs to use more than	4314	is not recommended (and not reasonable). If your program needs to use
2978	a hundred or so sockets, then likely it needs to use a totally different	4315	more than a hundred or so sockets, then likely it needs to use a totally
2979	implementation for windows, as libev offers the POSIX model, which cannot	4316	different implementation for windows, as libev offers the POSIX readiness
2980	be implemented efficiently on windows (microsoft monopoly games).	4317	notification model, which cannot be implemented efficiently on windows
		4318	(due to Microsoft monopoly games).
		4319
		4320	A typical way to use libev under windows is to embed it (see the embedding
		4321	section for details) and use the following F<evwrap.h> header file instead
		4322	of F<ev.h>:
		4323
		4324	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4325	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4326
		4327	#include "ev.h"
		4328
		4329	And compile the following F<evwrap.c> file into your project (make sure
		4330	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4331
		4332	#include "evwrap.h"
		4333	#include "ev.c"
2981		4334
2982	=over 4	4335	=over 4
2983		4336
2984	=item The winsocket select function	4337	=item The winsocket select function
2985		4338
2986	The winsocket C<select> function doesn't follow POSIX in that it requires	4339	The winsocket C<select> function doesn't follow POSIX in that it
2987	socket I<handles> and not socket I<file descriptors>. This makes select	4340	requires socket I<handles> and not socket I<file descriptors> (it is
2988	very inefficient, and also requires a mapping from file descriptors	4341	also extremely buggy). This makes select very inefficient, and also
2989	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4342	requires a mapping from file descriptors to socket handles (the Microsoft
2990	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4343	C runtime provides the function C<_open_osfhandle> for this). See the
2991	symbols for more info.	4344	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4345	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2992		4346
2993	The configuration for a "naked" win32 using the microsoft runtime	4347	The configuration for a "naked" win32 using the Microsoft runtime
2994	libraries and raw winsocket select is:	4348	libraries and raw winsocket select is:
2995		4349
2996	#define EV_USE_SELECT 1	4350	#define EV_USE_SELECT 1
2997	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4351	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2998		4352
2999	Note that winsockets handling of fd sets is O(n), so you can easily get a	4353	Note that winsockets handling of fd sets is O(n), so you can easily get a
3000	complexity in the O(n²) range when using win32.	4354	complexity in the O(n²) range when using win32.
3001		4355
3002	=item Limited number of file descriptors	4356	=item Limited number of file descriptors
3003		4357
3004	Windows has numerous arbitrary (and low) limits on things. Early versions	4358	Windows has numerous arbitrary (and low) limits on things.
3005	of winsocket's select only supported waiting for a max. of C<64> handles	4359
		4360	Early versions of winsocket's select only supported waiting for a maximum
3006	(probably owning to the fact that all windows kernels can only wait for	4361	of C<64> handles (probably owning to the fact that all windows kernels
3007	C<64> things at the same time internally; microsoft recommends spawning a	4362	can only wait for C<64> things at the same time internally; Microsoft
3008	chain of threads and wait for 63 handles and the previous thread in each).	4363	recommends spawning a chain of threads and wait for 63 handles and the
		4364	previous thread in each. Sounds great!).
3009		4365
3010	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4366	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3011	to some high number (e.g. C<2048>) before compiling the winsocket select	4367	to some high number (e.g. C<2048>) before compiling the winsocket select
3012	call (which might be in libev or elsewhere, for example, perl does its own	4368	call (which might be in libev or elsewhere, for example, perl and many
3013	select emulation on windows).	4369	other interpreters do their own select emulation on windows).
3014		4370
3015	Another limit is the number of file descriptors in the microsoft runtime	4371	Another limit is the number of file descriptors in the Microsoft runtime
3016	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4372	libraries, which by default is C<64> (there must be a hidden I<64>
3017	or something like this inside microsoft). You can increase this by calling	4373	fetish or something like this inside Microsoft). You can increase this
3018	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4374	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3019	arbitrary limit), but is broken in many versions of the microsoft runtime	4375	(another arbitrary limit), but is broken in many versions of the Microsoft
3020	libraries.
3021
3022	This might get you to about C<512> or C<2048> sockets (depending on	4376	runtime libraries. This might get you to about C<512> or C<2048> sockets
3023	windows version and/or the phase of the moon). To get more, you need to	4377	(depending on windows version and/or the phase of the moon). To get more,
3024	wrap all I/O functions and provide your own fd management, but the cost of	4378	you need to wrap all I/O functions and provide your own fd management, but
3025	calling select (O(n²)) will likely make this unworkable.	4379	the cost of calling select (O(n²)) will likely make this unworkable.
3026		4380
3027	=back	4381	=back
3028		4382
		4383	=head2 PORTABILITY REQUIREMENTS
		4384
		4385	In addition to a working ISO-C implementation and of course the
		4386	backend-specific APIs, libev relies on a few additional extensions:
		4387
		4388	=over 4
		4389
		4390	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4391	calling conventions regardless of C<ev_watcher_type *>.
		4392
		4393	Libev assumes not only that all watcher pointers have the same internal
		4394	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4395	assumes that the same (machine) code can be used to call any watcher
		4396	callback: The watcher callbacks have different type signatures, but libev
		4397	calls them using an C<ev_watcher *> internally.
		4398
		4399	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4400
		4401	The type C<sig_atomic_t volatile> (or whatever is defined as
		4402	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4403	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4404	believed to be sufficiently portable.
		4405
		4406	=item C<sigprocmask> must work in a threaded environment
		4407
		4408	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4409	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4410	pthread implementations will either allow C<sigprocmask> in the "main
		4411	thread" or will block signals process-wide, both behaviours would
		4412	be compatible with libev. Interaction between C<sigprocmask> and
		4413	C<pthread_sigmask> could complicate things, however.
		4414
		4415	The most portable way to handle signals is to block signals in all threads
		4416	except the initial one, and run the default loop in the initial thread as
		4417	well.
		4418
		4419	=item C<long> must be large enough for common memory allocation sizes
		4420
		4421	To improve portability and simplify its API, libev uses C<long> internally
		4422	instead of C<size_t> when allocating its data structures. On non-POSIX
		4423	systems (Microsoft...) this might be unexpectedly low, but is still at
		4424	least 31 bits everywhere, which is enough for hundreds of millions of
		4425	watchers.
		4426
		4427	=item C<double> must hold a time value in seconds with enough accuracy
		4428
		4429	The type C<double> is used to represent timestamps. It is required to
		4430	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4431	enough for at least into the year 4000. This requirement is fulfilled by
		4432	implementations implementing IEEE 754, which is basically all existing
		4433	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4434	2200.
		4435
		4436	=back
		4437
		4438	If you know of other additional requirements drop me a note.
		4439
		4440
		4441	=head1 ALGORITHMIC COMPLEXITIES
		4442
		4443	In this section the complexities of (many of) the algorithms used inside
		4444	libev will be documented. For complexity discussions about backends see
		4445	the documentation for C<ev_default_init>.
		4446
		4447	All of the following are about amortised time: If an array needs to be
		4448	extended, libev needs to realloc and move the whole array, but this
		4449	happens asymptotically rarer with higher number of elements, so O(1) might
		4450	mean that libev does a lengthy realloc operation in rare cases, but on
		4451	average it is much faster and asymptotically approaches constant time.
		4452
		4453	=over 4
		4454
		4455	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4456
		4457	This means that, when you have a watcher that triggers in one hour and
		4458	there are 100 watchers that would trigger before that, then inserting will
		4459	have to skip roughly seven (C<ld 100>) of these watchers.
		4460
		4461	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4462
		4463	That means that changing a timer costs less than removing/adding them,
		4464	as only the relative motion in the event queue has to be paid for.
		4465
		4466	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4467
		4468	These just add the watcher into an array or at the head of a list.
		4469
		4470	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4471
		4472	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4473
		4474	These watchers are stored in lists, so they need to be walked to find the
		4475	correct watcher to remove. The lists are usually short (you don't usually
		4476	have many watchers waiting for the same fd or signal: one is typical, two
		4477	is rare).
		4478
		4479	=item Finding the next timer in each loop iteration: O(1)
		4480
		4481	By virtue of using a binary or 4-heap, the next timer is always found at a
		4482	fixed position in the storage array.
		4483
		4484	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4485
		4486	A change means an I/O watcher gets started or stopped, which requires
		4487	libev to recalculate its status (and possibly tell the kernel, depending
		4488	on backend and whether C<ev_io_set> was used).
		4489
		4490	=item Activating one watcher (putting it into the pending state): O(1)
		4491
		4492	=item Priority handling: O(number_of_priorities)
		4493
		4494	Priorities are implemented by allocating some space for each
		4495	priority. When doing priority-based operations, libev usually has to
		4496	linearly search all the priorities, but starting/stopping and activating
		4497	watchers becomes O(1) with respect to priority handling.
		4498
		4499	=item Sending an ev_async: O(1)
		4500
		4501	=item Processing ev_async_send: O(number_of_async_watchers)
		4502
		4503	=item Processing signals: O(max_signal_number)
		4504
		4505	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4506	calls in the current loop iteration. Checking for async and signal events
		4507	involves iterating over all running async watchers or all signal numbers.
		4508
		4509	=back
		4510
		4511
		4512	=head1 GLOSSARY
		4513
		4514	=over 4
		4515
		4516	=item active
		4517
		4518	A watcher is active as long as it has been started (has been attached to
		4519	an event loop) but not yet stopped (disassociated from the event loop).
		4520
		4521	=item application
		4522
		4523	In this document, an application is whatever is using libev.
		4524
		4525	=item callback
		4526
		4527	The address of a function that is called when some event has been
		4528	detected. Callbacks are being passed the event loop, the watcher that
		4529	received the event, and the actual event bitset.
		4530
		4531	=item callback invocation
		4532
		4533	The act of calling the callback associated with a watcher.
		4534
		4535	=item event
		4536
		4537	A change of state of some external event, such as data now being available
		4538	for reading on a file descriptor, time having passed or simply not having
		4539	any other events happening anymore.
		4540
		4541	In libev, events are represented as single bits (such as C<EV_READ> or
		4542	C<EV_TIMEOUT>).
		4543
		4544	=item event library
		4545
		4546	A software package implementing an event model and loop.
		4547
		4548	=item event loop
		4549
		4550	An entity that handles and processes external events and converts them
		4551	into callback invocations.
		4552
		4553	=item event model
		4554
		4555	The model used to describe how an event loop handles and processes
		4556	watchers and events.
		4557
		4558	=item pending
		4559
		4560	A watcher is pending as soon as the corresponding event has been detected,
		4561	and stops being pending as soon as the watcher will be invoked or its
		4562	pending status is explicitly cleared by the application.
		4563
		4564	A watcher can be pending, but not active. Stopping a watcher also clears
		4565	its pending status.
		4566
		4567	=item real time
		4568
		4569	The physical time that is observed. It is apparently strictly monotonic :)
		4570
		4571	=item wall-clock time
		4572
		4573	The time and date as shown on clocks. Unlike real time, it can actually
		4574	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4575	clock.
		4576
		4577	=item watcher
		4578
		4579	A data structure that describes interest in certain events. Watchers need
		4580	to be started (attached to an event loop) before they can receive events.
		4581
		4582	=item watcher invocation
		4583
		4584	The act of calling the callback associated with a watcher.
		4585
		4586	=back
3029		4587
3030	=head1 AUTHOR	4588	=head1 AUTHOR
3031		4589
3032	Marc Lehmann <libev@schmorp.de>.	4590	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3033		4591

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