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Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs.
Revision 1.312 by root, Thu Oct 21 15:14:49 2010 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#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_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_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_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_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_run (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	Familiarity 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<struct 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 (in practise
100	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
102	to the C<double> type in C, and when you need to do any calculations on	132	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as some floatingpoint value. Unlike the name	133	any calculations on it, you should treat it as some floating point value.
		134
104	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
		157
106		158
107	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
108		160
109	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
110	library in any way.	162	library in any way.
…		…
119		171
120	=item ev_sleep (ev_tstamp interval)	172	=item ev_sleep (ev_tstamp interval)
121		173
122	Sleep for the given interval: The current thread will be blocked until	174	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	175	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	176	this is a sub-second-resolution C<sleep ()>.
125		177
126	=item int ev_version_major ()	178	=item int ev_version_major ()
127		179
128	=item int ev_version_minor ()	180	=item int ev_version_minor ()
129		181
…		…
140	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	193	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	194	not a problem.
143		195
144	Example: Make sure we haven't accidentally been linked against the wrong	196	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	197	version (note, however, that this will not detect ABI mismatches :).
146		198
147	assert (("libev version mismatch",	199	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
150		202
151	=item unsigned int ev_supported_backends ()	203	=item unsigned int ev_supported_backends ()
152		204
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	205	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	206	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	208	a description of the set values.
157		209
158	Example: make sure we have the epoll method, because yeah this is cool and	210	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	211	a must have and can we have a torrent of it please!!!11
160		212
161	assert (("sorry, no epoll, no sex",	213	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	214	ev_supported_backends () & EVBACKEND_EPOLL));
163		215
164	=item unsigned int ev_recommended_backends ()	216	=item unsigned int ev_recommended_backends ()
165		217
166	Return the set of all backends compiled into this binary of libev and also	218	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	219	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	220	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	221	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	222	(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.	223	libev will probe for if you specify no backends explicitly.
172		224
173	=item unsigned int ev_embeddable_backends ()	225	=item unsigned int ev_embeddable_backends ()
174		226
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	231	recommended ones.
180		232
181	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
182		234
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		236
185	Sets the allocation function to use (the prototype is similar - the	237	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	238	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	239	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	240	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	241	or take some potentially destructive action.
190	function.	242
		243	Since some systems (at least OpenBSD and Darwin) fail to implement
		244	correct C<realloc> semantics, libev will use a wrapper around the system
		245	C<realloc> and C<free> functions by default.
191		246
192	You could override this function in high-availability programs to, say,	247	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,	248	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.	249	or even to sleep a while and retry until some memory is available.
195		250
196	Example: Replace the libev allocator with one that waits a bit and then	251	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	252	retries (example requires a standards-compliant C<realloc>).
198		253
199	static void *	254	static void *
200	persistent_realloc (void *ptr, size_t size)	255	persistent_realloc (void *ptr, size_t size)
201	{	256	{
202	for (;;)	257	for (;;)
…		…
211	}	266	}
212		267
213	...	268	...
214	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
215		270
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		272
218	Set the callback function to call on a retryable syscall error (such	273	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	274	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	275	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	276	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	277	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	278	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	279	(such as abort).
225		280
226	Example: This is basically the same thing that libev does internally, too.	281	Example: This is basically the same thing that libev does internally, too.
…		…
237		292
238	=back	293	=back
239		294
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		296
242	An event loop is described by a C<struct ev_loop *>. The library knows two	297	An event loop is described by a C<struct ev_loop *> (the C<struct> is
243	types of such loops, the I<default> loop, which supports signals and child	298	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	299	libev 3 had an C<ev_loop> function colliding with the struct name).
245		300
246	If you use threads, a common model is to run the default event loop	301	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	302	supports signals and child events, and dynamically created event loops
248	create, you also create another event loop. Libev itself does no locking	303	which do 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		304
253	=over 4	305	=over 4
254		306
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		308
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	312	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		313
262	If you don't know what event loop to use, use the one returned from this	314	If you don't know what event loop to use, use the one returned from this
263	function.	315	function.
264		316
		317	Note that this function is I<not> thread-safe, so if you want to use it
		318	from multiple threads, you have to lock (note also that this is unlikely,
		319	as loops cannot be shared easily between threads anyway).
		320
265	The default loop is the only loop that can handle C<ev_signal> and	321	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	322	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	323	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	324	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	325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
270	C<ev_default_init>.	326	C<ev_default_init>.
271		327
272	The flags argument can be used to specify special behaviour or specific	328	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	337	The default flags value. Use this if you have no clue (it's the right
282	thing, believe me).	338	thing, believe me).
283		339
284	=item C<EVFLAG_NOENV>	340	=item C<EVFLAG_NOENV>
285		341
286	If this flag bit is ored into the flag value (or the program runs setuid	342	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	343	or setgid) then libev will I<not> look at the environment variable
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	override the flags completely if it is found in the environment. This is	345	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	346	useful to try out specific backends to test their performance, or to work
291	around bugs.	347	around bugs.
292		348
293	=item C<EVFLAG_FORKCHECK>	349	=item C<EVFLAG_FORKCHECK>
294		350
295	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	351	Instead of calling C<ev_loop_fork> manually after a fork, you can also
296	a fork, you can also make libev check for a fork in each iteration by	352	make libev check for a fork in each iteration by enabling this flag.
297	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_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
312		387
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		389
315	This is your standard select(2) backend. Not I<completely> standard, as	390	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,	391	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	392	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	393	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.	394	usually the fastest backend for a low number of (low-numbered :) fds.
320		395
321	To get good performance out of this backend you need a high amount of	396	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	397	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	398	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	399	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	400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	401	readiness notifications you get per iteration.
		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
327		406
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		408
330	And this is your standard poll(2) backend. It's more complicated	409	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	410	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	411	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,	412	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	413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	414	performance tips.
336		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		418
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
338		423
339	For few fds, this backend is a bit little slower than poll and select,	424	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	425	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),	426	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	427	epoll scales either O(1) or O(active_fds).
343	of shortcomings, such as silently dropping events in some hard-to-detect	428
344	cases and rewiring a syscall per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
345	support for dup.	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required. Last
		445	not least, it also refuses to work with some file descriptors which work
		446	perfectly fine with C<select> (files, many character devices...).
346		447
347	While stopping, setting and starting an I/O watcher in the same iteration	448	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	449	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	450	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	451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
351	very well if you register events for both fds.	452	file descriptors might not work very well if you register events for both
352		453	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		454
357	Best performance from this backend is achieved by not unregistering all	455	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.	456	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	457	i.e. keep at least one watcher active per fd at all times. Stopping and
		458	starting a watcher (without re-setting it) also usually doesn't cause
		459	extra overhead. A fork can both result in spurious notifications as well
		460	as in libev having to destroy and recreate the epoll object, which can
		461	take considerable time and thus should be avoided.
360		462
		463	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		464	faster than epoll for maybe up to a hundred file descriptors, depending on
		465	the usage. So sad.
		466
361	While nominally embeddeble in other event loops, this feature is broken in	467	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	468	all kernel versions tested so far.
		469
		470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		471	C<EVBACKEND_POLL>.
363		472
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		474
366	Kqueue deserves special mention, as at the time of this writing, it	475	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	476	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	477	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"	478	it's completely useless). Unlike epoll, however, whose brokenness
		479	is by design, these kqueue bugs can (and eventually will) be fixed
		480	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	481	"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)	482	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
372	system like NetBSD.	483	system like NetBSD.
373		484
374	You still can embed kqueue into a normal poll or select backend and use it	485	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	486	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.	487	the target platform). See C<ev_embed> watchers for more info.
377		488
378	It scales in the same way as the epoll backend, but the interface to the	489	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	490	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	491	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	492	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	493	two event changes per incident. Support for C<fork ()> is very bad (but
383	drops fds silently in similarly hard-to-detect cases.	494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		495	cases
384		496
385	This backend usually performs well under most conditions.	497	This backend usually performs well under most conditions.
386		498
387	While nominally embeddable in other event loops, this doesn't work	499	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	500	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	501	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	502	(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	503	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	504	also broken on OS X)) and, did I mention it, using it only for sockets.
		505
		506	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		507	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		508	C<NOTE_EOF>.
393		509
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	510	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		511
396	This is not implemented yet (and might never be, unless you send me an	512	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	513	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		518
403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	519	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)).	520	it's really slow, but it still scales very well (O(active_fds)).
405		521
406	Please note that solaris event ports can deliver a lot of spurious	522	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	523	notifications, so you need to use non-blocking I/O or other means to avoid
408	blocking when no data (or space) is available.	524	blocking when no data (or space) is available.
409		525
410	While this backend scales well, it requires one system call per active	526	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	527	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	529	might perform better.
414		530
415	On the positive side, ignoring the spurious readyness notifications, this	531	On the positive side, with the exception of the spurious readiness
416	backend actually performed to specification in all tests and is fully	532	notifications, this backend actually performed fully to specification
417	embeddable, which is a rare feat among the OS-specific backends.	533	in all tests and is fully embeddable, which is a rare feat among the
		534	OS-specific backends (I vastly prefer correctness over speed hacks).
		535
		536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		537	C<EVBACKEND_POLL>.
418		538
419	=item C<EVBACKEND_ALL>	539	=item C<EVBACKEND_ALL>
420		540
421	Try all backends (even potentially broken ones that wouldn't be tried	541	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	542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
424		544
425	It is definitely not recommended to use this flag.	545	It is definitely not recommended to use this flag.
426		546
427	=back	547	=back
428		548
429	If one or more of these are ored into the flags value, then only these	549	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	550	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.	551	here). If none are specified, all backends in C<ev_recommended_backends
		552	()> will be tried.
432		553
433	The most typical usage is like this:	554	Example: This is the most typical usage.
434		555
435	if (!ev_default_loop (0))	556	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437		558
438	Restrict libev to the select and poll backends, and do not allow	559	Example: Restrict libev to the select and poll backends, and do not allow
439	environment settings to be taken into account:	560	environment settings to be taken into account:
440		561
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442		563
443	Use whatever libev has to offer, but make sure that kqueue is used if	564	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	565	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):	566	private event loop and only if you know the OS supports your types of
		567	fds):
446		568
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448		570
449	=item struct ev_loop *ev_loop_new (unsigned int flags)	571	=item struct ev_loop *ev_loop_new (unsigned int flags)
450		572
451	Similar to C<ev_default_loop>, but always creates a new event loop that is	573	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	574	always distinct from the default loop.
453	handle signal and child watchers, and attempts to do so will be greeted by	575
454	undefined behaviour (or a failed assertion if assertions are enabled).	576	Note that this function I<is> thread-safe, and one common way to use
		577	libev with threads is indeed to create one loop per thread, and using the
		578	default loop in the "main" or "initial" thread.
455		579
456	Example: Try to create a event loop that uses epoll and nothing else.	580	Example: Try to create a event loop that uses epoll and nothing else.
457		581
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	583	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	584	fatal ("no epoll found here, maybe it hides under your chair");
461		585
462	=item ev_default_destroy ()	586	=item ev_default_destroy ()
463		587
464	Destroys the default loop again (frees all memory and kernel state	588	Destroys the default loop (frees all memory and kernel state etc.). None
465	etc.). None of the active event watchers will be stopped in the normal	589	of the active event watchers will be stopped in the normal sense, so
466	sense, so e.g. C<ev_is_active> might still return true. It is your	590	e.g. C<ev_is_active> might still return true. It is your responsibility to
467	responsibility to either stop all watchers cleanly yoursef I<before>	591	either stop all watchers cleanly yourself I<before> calling this function,
468	calling this function, or cope with the fact afterwards (which is usually	592	or cope with the fact afterwards (which is usually the easiest thing, you
469	the easiest thing, you can just ignore the watchers and/or C<free ()> them	593	can just ignore the watchers and/or C<free ()> them for example).
470	for example).
471		594
472	Note that certain global state, such as signal state, will not be freed by	595	Note that certain global state, such as signal state (and installed signal
473	this function, and related watchers (such as signal and child watchers)	596	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	597	as signal and child watchers) would need to be stopped manually.
475		598
476	In general it is not advisable to call this function except in the	599	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	600	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	601	pipe fds. If you need dynamically allocated loops it is better to use
479	C<ev_loop_new> and C<ev_loop_destroy>).	602	C<ev_loop_new> and C<ev_loop_destroy>.
480		603
481	=item ev_loop_destroy (loop)	604	=item ev_loop_destroy (loop)
482		605
483	Like C<ev_default_destroy>, but destroys an event loop created by an	606	Like C<ev_default_destroy>, but destroys an event loop created by an
484	earlier call to C<ev_loop_new>.	607	earlier call to C<ev_loop_new>.
485		608
486	=item ev_default_fork ()	609	=item ev_default_fork ()
487		610
488	This function sets a flag that causes subsequent C<ev_loop> iterations	611	This function sets a flag that causes subsequent C<ev_run> iterations
489	to reinitialise the kernel state for backends that have one. Despite the	612	to reinitialise the kernel state for backends that have one. Despite the
490	name, you can call it anytime, but it makes most sense after forking, in	613	name, you can call it anytime, but it makes most sense after forking, in
491	the child process (or both child and parent, but that again makes little	614	the child process (or both child and parent, but that again makes little
492	sense). You I<must> call it in the child before using any of the libev	615	sense). You I<must> call it in the child before using any of the libev
493	functions, and it will only take effect at the next C<ev_loop> iteration.	616	functions, and it will only take effect at the next C<ev_run> iteration.
		617
		618	Again, you I<have> to call it on I<any> loop that you want to re-use after
		619	a fork, I<even if you do not plan to use the loop in the parent>. This is
		620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		621	during fork.
494		622
495	On the other hand, you only need to call this function in the child	623	On the other hand, you only need to call this function in the child
496	process if and only if you want to use the event library in the child. If	624	process if and only if you want to use the event loop in the child. If
497	you just fork+exec, you don't have to call it at all.	625	you just fork+exec or create a new loop in the child, you don't have to
		626	call it at all (in fact, C<epoll> is so badly broken that it makes a
		627	difference, but libev will usually detect this case on its own and do a
		628	costly reset of the backend).
498		629
499	The function itself is quite fast and it's usually not a problem to call	630	The function itself is quite fast and it's usually not a problem to call
500	it just in case after a fork. To make this easy, the function will fit in	631	it just in case after a fork. To make this easy, the function will fit in
501	quite nicely into a call to C<pthread_atfork>:	632	quite nicely into a call to C<pthread_atfork>:
502		633
…		…
504		635
505	=item ev_loop_fork (loop)	636	=item ev_loop_fork (loop)
506		637
507	Like C<ev_default_fork>, but acts on an event loop created by	638	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	639	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.	640	after fork that you want to re-use in the child, and how you keep track of
		641	them is entirely your own problem.
510		642
		643	=item int ev_is_default_loop (loop)
		644
		645	Returns true when the given loop is, in fact, the default loop, and false
		646	otherwise.
		647
511	=item unsigned int ev_loop_count (loop)	648	=item unsigned int ev_iteration (loop)
512		649
513	Returns the count of loop iterations for the loop, which is identical to	650	Returns the current iteration count for the event loop, which is identical
514	the number of times libev did poll for new events. It starts at C<0> and	651	to the number of times libev did poll for new events. It starts at C<0>
515	happily wraps around with enough iterations.	652	and happily wraps around with enough iterations.
516		653
517	This value can sometimes be useful as a generation counter of sorts (it	654	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	655	"ticks" the number of loop iterations), as it roughly corresponds with
519	C<ev_prepare> and C<ev_check> calls.	656	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		657	prepare and check phases.
		658
		659	=item unsigned int ev_depth (loop)
		660
		661	Returns the number of times C<ev_run> was entered minus the number of
		662	times C<ev_run> was exited, in other words, the recursion depth.
		663
		664	Outside C<ev_run>, this number is zero. In a callback, this number is
		665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		666	in which case it is higher.
		667
		668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		669	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		670	ungentleman-like behaviour unless it's really convenient.
520		671
521	=item unsigned int ev_backend (loop)	672	=item unsigned int ev_backend (loop)
522		673
523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
524	use.	675	use.
…		…
529	received events and started processing them. This timestamp does not	680	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	681	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	682	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).	683	event occurring (or more correctly, libev finding out about it).
533		684
		685	=item ev_now_update (loop)
		686
		687	Establishes the current time by querying the kernel, updating the time
		688	returned by C<ev_now ()> in the progress. This is a costly operation and
		689	is usually done automatically within C<ev_run ()>.
		690
		691	This function is rarely useful, but when some event callback runs for a
		692	very long time without entering the event loop, updating libev's idea of
		693	the current time is a good idea.
		694
		695	See also L<The special problem of time updates> in the C<ev_timer> section.
		696
		697	=item ev_suspend (loop)
		698
		699	=item ev_resume (loop)
		700
		701	These two functions suspend and resume an event loop, for use when the
		702	loop is not used for a while and timeouts should not be processed.
		703
		704	A typical use case would be an interactive program such as a game: When
		705	the user presses C<^Z> to suspend the game and resumes it an hour later it
		706	would be best to handle timeouts as if no time had actually passed while
		707	the program was suspended. This can be achieved by calling C<ev_suspend>
		708	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		709	C<ev_resume> directly afterwards to resume timer processing.
		710
		711	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		712	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		713	will be rescheduled (that is, they will lose any events that would have
		714	occurred while suspended).
		715
		716	After calling C<ev_suspend> you B<must not> call I<any> function on the
		717	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		718	without a previous call to C<ev_suspend>.
		719
		720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		721	event loop time (see C<ev_now_update>).
		722
534	=item ev_loop (loop, int flags)	723	=item ev_run (loop, int flags)
535		724
536	Finally, this is it, the event handler. This function usually is called	725	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	726	after you have initialised all your watchers and you want to start
538	events.	727	handling events. It will ask the operating system for any new events, call
		728	the watcher callbacks, an then repeat the whole process indefinitely: This
		729	is why event loops are called I<loops>.
539		730
540	If the flags argument is specified as C<0>, it will not return until	731	If the flags argument is specified as C<0>, it will keep handling events
541	either no event watchers are active anymore or C<ev_unloop> was called.	732	until either no event watchers are active anymore or C<ev_break> was
		733	called.
542		734
543	Please note that an explicit C<ev_unloop> is usually better than	735	Please note that an explicit C<ev_break> is usually better than
544	relying on all watchers to be stopped when deciding when a program has	736	relying on all watchers to be stopped when deciding when a program has
545	finished (especially in interactive programs), but having a program that	737	finished (especially in interactive programs), but having a program
546	automatically loops as long as it has to and no longer by virtue of	738	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.	739	of relying on its watchers stopping correctly, that is truly a thing of
		740	beauty.
548		741
549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
550	those events and any outstanding ones, but will not block your process in	743	those events and any already outstanding ones, but will not wait and
551	case there are no events and will return after one iteration of the loop.	744	block your process in case there are no events and will return after one
		745	iteration of the loop. This is sometimes useful to poll and handle new
		746	events while doing lengthy calculations, to keep the program responsive.
552		747
553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	748	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
554	neccessary) and will handle those and any outstanding ones. It will block	749	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	750	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	751	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	752	user-registered callback will be called), and will return after one
		753	iteration of the loop.
		754
		755	This is useful if you are waiting for some external event in conjunction
		756	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	757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
559	usually a better approach for this kind of thing.	758	usually a better approach for this kind of thing.
560		759
561	Here are the gory details of what C<ev_loop> does:	760	Here are the gory details of what C<ev_run> does:
562		761
		762	- Increment loop depth.
		763	- Reset the ev_break status.
563	- Before the first iteration, call any pending watchers.	764	- Before the first iteration, call any pending watchers.
		765	LOOP:
564	* If EVFLAG_FORKCHECK was used, check for a fork.	766	- If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	767	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	768	- Queue and call all prepare watchers.
		769	- If ev_break was called, goto FINISH.
567	- If we have been forked, recreate the kernel state.	770	- If we have been forked, detach and recreate the kernel state
		771	as to not disturb the other process.
568	- Update the kernel state with all outstanding changes.	772	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	773	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	774	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	775	(active idle watchers, EVRUN_NOWAIT or not having
572	any active watchers at all will result in not sleeping).	776	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	777	- Sleep if the I/O and timer collect interval say so.
		778	- Increment loop iteration counter.
574	- Block the process, waiting for any events.	779	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	780	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	781	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	782	- Queue all expired timers.
578	- Queue all outstanding periodics.	783	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	784	- Queue all idle watchers with priority higher than that of pending events.
580	- Queue all check watchers.	785	- Queue all check watchers.
581	- Call all queued watchers in reverse order (i.e. check watchers first).	786	- 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	787	Signals and child watchers are implemented as I/O watchers, and will
583	be handled here by queueing them when their watcher gets executed.	788	be handled here by queueing them when their watcher gets executed.
584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	789	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
585	were used, or there are no active watchers, return, otherwise	790	were used, or there are no active watchers, goto FINISH, otherwise
586	continue with step *.	791	continue with step LOOP.
		792	FINISH:
		793	- Reset the ev_break status iff it was EVBREAK_ONE.
		794	- Decrement the loop depth.
		795	- Return.
587		796
588	Example: Queue some jobs and then loop until no events are outstanding	797	Example: Queue some jobs and then loop until no events are outstanding
589	anymore.	798	anymore.
590		799
591	... queue jobs here, make sure they register event watchers as long	800	... 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..)	801	... as they still have work to do (even an idle watcher will do..)
593	ev_loop (my_loop, 0);	802	ev_run (my_loop, 0);
594	... jobs done. yeah!	803	... jobs done or somebody called unloop. yeah!
595		804
596	=item ev_unloop (loop, how)	805	=item ev_break (loop, how)
597		806
598	Can be used to make a call to C<ev_loop> return early (but only after it	807	Can be used to make a call to C<ev_run> return early (but only after it
599	has processed all outstanding events). The C<how> argument must be either	808	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	809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
602		811
603	This "unloop state" will be cleared when entering C<ev_loop> again.	812	This "unloop state" will be cleared when entering C<ev_run> again.
		813
		814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
604		815
605	=item ev_ref (loop)	816	=item ev_ref (loop)
606		817
607	=item ev_unref (loop)	818	=item ev_unref (loop)
608		819
609	Ref/unref can be used to add or remove a reference count on the event	820	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	821	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	822	count is nonzero, C<ev_run> will not return on its own.
612	a watcher you never unregister that should not keep C<ev_loop> from	823
613	returning, ev_unref() after starting, and ev_ref() before stopping it. For	824	This is useful when you have a watcher that you never intend to
		825	unregister, but that nevertheless should not keep C<ev_run> from
		826	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		827	before stopping it.
		828
614	example, libev itself uses this for its internal signal pipe: It is not	829	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	830	is not visible to the libev user and should not keep C<ev_run> from
616	no event watchers registered by it are active. It is also an excellent	831	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	832	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>	833	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,	834	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	835	before, respectively. Note also that libev might stop watchers itself
		836	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		837	in the callback).
621		838
622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	839	Example: Create a signal watcher, but keep it from keeping C<ev_run>
623	running when nothing else is active.	840	running when nothing else is active.
624		841
625	struct ev_signal exitsig;	842	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	843	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	844	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	845	evf_unref (loop);
629		846
630	Example: For some weird reason, unregister the above signal handler again.	847	Example: For some weird reason, unregister the above signal handler again.
631		848
632	ev_ref (loop);	849	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	850	ev_signal_stop (loop, &exitsig);
634		851
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	852	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		853
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	854	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		855
639	These advanced functions influence the time that libev will spend waiting	856	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	857	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.	858	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		859	latency.
642		860
643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	861	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	862	allows libev to delay invocation of I/O and timer/periodic callbacks
645	increase efficiency of loop iterations.	863	to increase efficiency of loop iterations (or to increase power-saving
		864	opportunities).
646		865
647	The background is that sometimes your program runs just fast enough to	866	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	867	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	868	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	869	events, especially with backends like C<select ()> which have a high
651	overhead for the actual polling but can deliver many events at once.	870	overhead for the actual polling but can deliver many events at once.
652		871
653	By setting a higher I<io collect interval> you allow libev to spend more	872	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,	873	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	874	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	875	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.	876	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		877	sleep time ensures that libev will not poll for I/O events more often then
		878	once per this interval, on average.
658		879
659	Likewise, by setting a higher I<timeout collect interval> you allow libev	880	Likewise, by setting a higher I<timeout collect interval> you allow libev
660	to spend more time collecting timeouts, at the expense of increased	881	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	882	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	883	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	884	value will not introduce any overhead in libev.
664		885
665	Many (busy) programs can usually benefit by setting the io collect	886	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	887	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	888	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>,	889	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.	890	as this approaches the timing granularity of most systems. Note that if
		891	you do transactions with the outside world and you can't increase the
		892	parallelity, then this setting will limit your transaction rate (if you
		893	need to poll once per transaction and the I/O collect interval is 0.01,
		894	then you can't do more than 100 transactions per second).
		895
		896	Setting the I<timeout collect interval> can improve the opportunity for
		897	saving power, as the program will "bundle" timer callback invocations that
		898	are "near" in time together, by delaying some, thus reducing the number of
		899	times the process sleeps and wakes up again. Another useful technique to
		900	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		901	they fire on, say, one-second boundaries only.
		902
		903	Example: we only need 0.1s timeout granularity, and we wish not to poll
		904	more often than 100 times per second:
		905
		906	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		907	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		908
		909	=item ev_invoke_pending (loop)
		910
		911	This call will simply invoke all pending watchers while resetting their
		912	pending state. Normally, C<ev_run> does this automatically when required,
		913	but when overriding the invoke callback this call comes handy.
		914
		915	=item int ev_pending_count (loop)
		916
		917	Returns the number of pending watchers - zero indicates that no watchers
		918	are pending.
		919
		920	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		921
		922	This overrides the invoke pending functionality of the loop: Instead of
		923	invoking all pending watchers when there are any, C<ev_run> will call
		924	this callback instead. This is useful, for example, when you want to
		925	invoke the actual watchers inside another context (another thread etc.).
		926
		927	If you want to reset the callback, use C<ev_invoke_pending> as new
		928	callback.
		929
		930	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		931
		932	Sometimes you want to share the same loop between multiple threads. This
		933	can be done relatively simply by putting mutex_lock/unlock calls around
		934	each call to a libev function.
		935
		936	However, C<ev_run> can run an indefinite time, so it is not feasible
		937	to wait for it to return. One way around this is to wake up the event
		938	loop via C<ev_break> and C<av_async_send>, another way is to set these
		939	I<release> and I<acquire> callbacks on the loop.
		940
		941	When set, then C<release> will be called just before the thread is
		942	suspended waiting for new events, and C<acquire> is called just
		943	afterwards.
		944
		945	Ideally, C<release> will just call your mutex_unlock function, and
		946	C<acquire> will just call the mutex_lock function again.
		947
		948	While event loop modifications are allowed between invocations of
		949	C<release> and C<acquire> (that's their only purpose after all), no
		950	modifications done will affect the event loop, i.e. adding watchers will
		951	have no effect on the set of file descriptors being watched, or the time
		952	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		953	to take note of any changes you made.
		954
		955	In theory, threads executing C<ev_run> will be async-cancel safe between
		956	invocations of C<release> and C<acquire>.
		957
		958	See also the locking example in the C<THREADS> section later in this
		959	document.
		960
		961	=item ev_set_userdata (loop, void *data)
		962
		963	=item ev_userdata (loop)
		964
		965	Set and retrieve a single C<void *> associated with a loop. When
		966	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		967	C<0.>
		968
		969	These two functions can be used to associate arbitrary data with a loop,
		970	and are intended solely for the C<invoke_pending_cb>, C<release> and
		971	C<acquire> callbacks described above, but of course can be (ab-)used for
		972	any other purpose as well.
		973
		974	=item ev_verify (loop)
		975
		976	This function only does something when C<EV_VERIFY> support has been
		977	compiled in, which is the default for non-minimal builds. It tries to go
		978	through all internal structures and checks them for validity. If anything
		979	is found to be inconsistent, it will print an error message to standard
		980	error and call C<abort ()>.
		981
		982	This can be used to catch bugs inside libev itself: under normal
		983	circumstances, this function will never abort as of course libev keeps its
		984	data structures consistent.
670		985
671	=back	986	=back
672		987
673		988
674	=head1 ANATOMY OF A WATCHER	989	=head1 ANATOMY OF A WATCHER
675		990
		991	In the following description, uppercase C<TYPE> in names stands for the
		992	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		993	watchers and C<ev_io_start> for I/O watchers.
		994
676	A watcher is a structure that you create and register to record your	995	A watcher is an opaque structure that you allocate and register to record
677	interest in some event. For instance, if you want to wait for STDIN to	996	your interest in some event. To make a concrete example, imagine you want
678	become readable, you would create an C<ev_io> watcher for that:	997	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		998	for that:
679		999
680	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1000	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
681	{	1001	{
682	ev_io_stop (w);	1002	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	1003	ev_break (loop, EVBREAK_ALL);
684	}	1004	}
685		1005
686	struct ev_loop *loop = ev_default_loop (0);	1006	struct ev_loop *loop = ev_default_loop (0);
		1007
687	struct ev_io stdin_watcher;	1008	ev_io stdin_watcher;
		1009
688	ev_init (&stdin_watcher, my_cb);	1010	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1011	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	1012	ev_io_start (loop, &stdin_watcher);
		1013
691	ev_loop (loop, 0);	1014	ev_run (loop, 0);
692		1015
693	As you can see, you are responsible for allocating the memory for your	1016	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,	1017	watcher structures (and it is I<usually> a bad idea to do this on the
695	although this can sometimes be quite valid).	1018	stack).
696		1019
		1020	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1021	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1022
697	Each watcher structure must be initialised by a call to C<ev_init	1023	Each watcher structure must be initialised by a call to C<ev_init (watcher
698	(watcher *, callback)>, which expects a callback to be provided. This	1024	*, callback)>, which expects a callback to be provided. This callback is
699	callback gets invoked each time the event occurs (or, in the case of io	1025	invoked each time the event occurs (or, in the case of I/O watchers, each
700	watchers, each time the event loop detects that the file descriptor given	1026	time the event loop detects that the file descriptor given is readable
701	is readable and/or writable).	1027	and/or writable).
702		1028
703	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1029	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	1030	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	1031	is also a macro to combine initialisation and setting in one call: C<<
706	(watcher *, callback, ...) >>.	1032	ev_TYPE_init (watcher *, callback, ...) >>.
707		1033
708	To make the watcher actually watch out for events, you have to start it	1034	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	1035	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	1036	*) >>), and you can stop watching for events at any time by calling the
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1037	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		1038
713	As long as your watcher is active (has been started but not stopped) you	1039	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	1040	must not touch the values stored in it. Most specifically you must never
715	reinitialise it or call its C<set> macro.	1041	reinitialise it or call its C<ev_TYPE_set> macro.
716		1042
717	Each and every callback receives the event loop pointer as first, the	1043	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	1044	registered watcher structure as second, and a bitset of received events as
719	third argument.	1045	third argument.
720		1046
…		…
729	=item C<EV_WRITE>	1055	=item C<EV_WRITE>
730		1056
731	The file descriptor in the C<ev_io> watcher has become readable and/or	1057	The file descriptor in the C<ev_io> watcher has become readable and/or
732	writable.	1058	writable.
733		1059
734	=item C<EV_TIMEOUT>	1060	=item C<EV_TIMER>
735		1061
736	The C<ev_timer> watcher has timed out.	1062	The C<ev_timer> watcher has timed out.
737		1063
738	=item C<EV_PERIODIC>	1064	=item C<EV_PERIODIC>
739		1065
…		…
757		1083
758	=item C<EV_PREPARE>	1084	=item C<EV_PREPARE>
759		1085
760	=item C<EV_CHECK>	1086	=item C<EV_CHECK>
761		1087
762	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1088	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
763	to gather new events, and all C<ev_check> watchers are invoked just after	1089	to gather new events, and all C<ev_check> watchers are invoked just after
764	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1090	C<ev_run> has gathered them, but before it invokes any callbacks for any
765	received events. Callbacks of both watcher types can start and stop as	1091	received events. Callbacks of both watcher types can start and stop as
766	many watchers as they want, and all of them will be taken into account	1092	many watchers as they want, and all of them will be taken into account
767	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1093	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
768	C<ev_loop> from blocking).	1094	C<ev_run> from blocking).
769		1095
770	=item C<EV_EMBED>	1096	=item C<EV_EMBED>
771		1097
772	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1098	The embedded event loop specified in the C<ev_embed> watcher needs attention.
773		1099
774	=item C<EV_FORK>	1100	=item C<EV_FORK>
775		1101
776	The event loop has been resumed in the child process after fork (see	1102	The event loop has been resumed in the child process after fork (see
777	C<ev_fork>).	1103	C<ev_fork>).
778		1104
		1105	=item C<EV_ASYNC>
		1106
		1107	The given async watcher has been asynchronously notified (see C<ev_async>).
		1108
		1109	=item C<EV_CUSTOM>
		1110
		1111	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1112	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1113
779	=item C<EV_ERROR>	1114	=item C<EV_ERROR>
780		1115
781	An unspecified error has occured, the watcher has been stopped. This might	1116	An unspecified error has occurred, the watcher has been stopped. This might
782	happen because the watcher could not be properly started because libev	1117	happen because the watcher could not be properly started because libev
783	ran out of memory, a file descriptor was found to be closed or any other	1118	ran out of memory, a file descriptor was found to be closed or any other
		1119	problem. Libev considers these application bugs.
		1120
784	problem. You best act on it by reporting the problem and somehow coping	1121	You best act on it by reporting the problem and somehow coping with the
785	with the watcher being stopped.	1122	watcher being stopped. Note that well-written programs should not receive
		1123	an error ever, so when your watcher receives it, this usually indicates a
		1124	bug in your program.
786		1125
787	Libev will usually signal a few "dummy" events together with an error,	1126	Libev will usually signal a few "dummy" events together with an error, for
788	for example it might indicate that a fd is readable or writable, and if	1127	example it might indicate that a fd is readable or writable, and if your
789	your callbacks is well-written it can just attempt the operation and cope	1128	callbacks is well-written it can just attempt the operation and cope with
790	with the error from read() or write(). This will not work in multithreaded	1129	the error from read() or write(). This will not work in multi-threaded
791	programs, though, so beware.	1130	programs, though, as the fd could already be closed and reused for another
		1131	thing, so beware.
792		1132
793	=back	1133	=back
794		1134
		1135	=head2 WATCHER STATES
		1136
		1137	There are various watcher states mentioned throughout this manual -
		1138	active, pending and so on. In this section these states and the rules to
		1139	transition between them will be described in more detail - and while these
		1140	rules might look complicated, they usually do "the right thing".
		1141
		1142	=over 4
		1143
		1144	=item initialiased
		1145
		1146	Before a watcher can be registered with the event looop it has to be
		1147	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1148	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1149
		1150	In this state it is simply some block of memory that is suitable for use
		1151	in an event loop. It can be moved around, freed, reused etc. at will.
		1152
		1153	=item started/running/active
		1154
		1155	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1156	property of the event loop, and is actively waiting for events. While in
		1157	this state it cannot be accessed (except in a few documented ways), moved,
		1158	freed or anything else - the only legal thing is to keep a pointer to it,
		1159	and call libev functions on it that are documented to work on active watchers.
		1160
		1161	=item pending
		1162
		1163	If a watcher is active and libev determines that an event it is interested
		1164	in has occurred (such as a timer expiring), it will become pending. It will
		1165	stay in this pending state until either it is stopped or its callback is
		1166	about to be invoked, so it is not normally pending inside the watcher
		1167	callback.
		1168
		1169	The watcher might or might not be active while it is pending (for example,
		1170	an expired non-repeating timer can be pending but no longer active). If it
		1171	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1172	but it is still property of the event loop at this time, so cannot be
		1173	moved, freed or reused. And if it is active the rules described in the
		1174	previous item still apply.
		1175
		1176	It is also possible to feed an event on a watcher that is not active (e.g.
		1177	via C<ev_feed_event>), in which case it becomes pending without being
		1178	active.
		1179
		1180	=item stopped
		1181
		1182	A watcher can be stopped implicitly by libev (in which case it might still
		1183	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1184	latter will clear any pending state the watcher might be in, regardless
		1185	of whether it was active or not, so stopping a watcher explicitly before
		1186	freeing it is often a good idea.
		1187
		1188	While stopped (and not pending) the watcher is essentially in the
		1189	initialised state, that is it can be reused, moved, modified in any way
		1190	you wish.
		1191
		1192	=back
		1193
795	=head2 GENERIC WATCHER FUNCTIONS	1194	=head2 GENERIC WATCHER FUNCTIONS
796
797	In the following description, C<TYPE> stands for the watcher type,
798	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
799		1195
800	=over 4	1196	=over 4
801		1197
802	=item C<ev_init> (ev_TYPE *watcher, callback)	1198	=item C<ev_init> (ev_TYPE *watcher, callback)
803		1199
…		…
809	which rolls both calls into one.	1205	which rolls both calls into one.
810		1206
811	You can reinitialise a watcher at any time as long as it has been stopped	1207	You can reinitialise a watcher at any time as long as it has been stopped
812	(or never started) and there are no pending events outstanding.	1208	(or never started) and there are no pending events outstanding.
813		1209
814	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1210	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
815	int revents)>.	1211	int revents)>.
816		1212
		1213	Example: Initialise an C<ev_io> watcher in two steps.
		1214
		1215	ev_io w;
		1216	ev_init (&w, my_cb);
		1217	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1218
817	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1219	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
818		1220
819	This macro initialises the type-specific parts of a watcher. You need to	1221	This macro initialises the type-specific parts of a watcher. You need to
820	call C<ev_init> at least once before you call this macro, but you can	1222	call C<ev_init> at least once before you call this macro, but you can
821	call C<ev_TYPE_set> any number of times. You must not, however, call this	1223	call C<ev_TYPE_set> any number of times. You must not, however, call this
822	macro on a watcher that is active (it can be pending, however, which is a	1224	macro on a watcher that is active (it can be pending, however, which is a
823	difference to the C<ev_init> macro).	1225	difference to the C<ev_init> macro).
824		1226
825	Although some watcher types do not have type-specific arguments	1227	Although some watcher types do not have type-specific arguments
826	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1228	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
827		1229
		1230	See C<ev_init>, above, for an example.
		1231
828	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1232	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
829		1233
830	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1234	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
831	calls into a single call. This is the most convinient method to initialise	1235	calls into a single call. This is the most convenient method to initialise
832	a watcher. The same limitations apply, of course.	1236	a watcher. The same limitations apply, of course.
833		1237
		1238	Example: Initialise and set an C<ev_io> watcher in one step.
		1239
		1240	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1241
834	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1242	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
835		1243
836	Starts (activates) the given watcher. Only active watchers will receive	1244	Starts (activates) the given watcher. Only active watchers will receive
837	events. If the watcher is already active nothing will happen.	1245	events. If the watcher is already active nothing will happen.
838		1246
		1247	Example: Start the C<ev_io> watcher that is being abused as example in this
		1248	whole section.
		1249
		1250	ev_io_start (EV_DEFAULT_UC, &w);
		1251
839	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1252	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
840		1253
841	Stops the given watcher again (if active) and clears the pending	1254	Stops the given watcher if active, and clears the pending status (whether
		1255	the watcher was active or not).
		1256
842	status. It is possible that stopped watchers are pending (for example,	1257	It is possible that stopped watchers are pending - for example,
843	non-repeating timers are being stopped when they become pending), but	1258	non-repeating timers are being stopped when they become pending - but
844	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1259	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
845	you want to free or reuse the memory used by the watcher it is therefore a	1260	pending. If you want to free or reuse the memory used by the watcher it is
846	good idea to always call its C<ev_TYPE_stop> function.	1261	therefore a good idea to always call its C<ev_TYPE_stop> function.
847		1262
848	=item bool ev_is_active (ev_TYPE *watcher)	1263	=item bool ev_is_active (ev_TYPE *watcher)
849		1264
850	Returns a true value iff the watcher is active (i.e. it has been started	1265	Returns a true value iff the watcher is active (i.e. it has been started
851	and not yet been stopped). As long as a watcher is active you must not modify	1266	and not yet been stopped). As long as a watcher is active you must not modify
…		…
867	=item ev_cb_set (ev_TYPE *watcher, callback)	1282	=item ev_cb_set (ev_TYPE *watcher, callback)
868		1283
869	Change the callback. You can change the callback at virtually any time	1284	Change the callback. You can change the callback at virtually any time
870	(modulo threads).	1285	(modulo threads).
871		1286
872	=item ev_set_priority (ev_TYPE *watcher, priority)	1287	=item ev_set_priority (ev_TYPE *watcher, int priority)
873		1288
874	=item int ev_priority (ev_TYPE *watcher)	1289	=item int ev_priority (ev_TYPE *watcher)
875		1290
876	Set and query the priority of the watcher. The priority is a small	1291	Set and query the priority of the watcher. The priority is a small
877	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1292	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
878	(default: C<-2>). Pending watchers with higher priority will be invoked	1293	(default: C<-2>). Pending watchers with higher priority will be invoked
879	before watchers with lower priority, but priority will not keep watchers	1294	before watchers with lower priority, but priority will not keep watchers
880	from being executed (except for C<ev_idle> watchers).	1295	from being executed (except for C<ev_idle> watchers).
881		1296
882	This means that priorities are I<only> used for ordering callback
883	invocation after new events have been received. This is useful, for
884	example, to reduce latency after idling, or more often, to bind two
885	watchers on the same event and make sure one is called first.
886
887	If you need to suppress invocation when higher priority events are pending	1297	If you need to suppress invocation when higher priority events are pending
888	you need to look at C<ev_idle> watchers, which provide this functionality.	1298	you need to look at C<ev_idle> watchers, which provide this functionality.
889		1299
890	You I<must not> change the priority of a watcher as long as it is active or	1300	You I<must not> change the priority of a watcher as long as it is active or
891	pending.	1301	pending.
892		1302
		1303	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1304	fine, as long as you do not mind that the priority value you query might
		1305	or might not have been clamped to the valid range.
		1306
893	The default priority used by watchers when no priority has been set is	1307	The default priority used by watchers when no priority has been set is
894	always C<0>, which is supposed to not be too high and not be too low :).	1308	always C<0>, which is supposed to not be too high and not be too low :).
895		1309
896	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1310	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
897	fine, as long as you do not mind that the priority value you query might	1311	priorities.
898	or might not have been adjusted to be within valid range.
899		1312
900	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1313	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
901		1314
902	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1315	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
903	C<loop> nor C<revents> need to be valid as long as the watcher callback	1316	C<loop> nor C<revents> need to be valid as long as the watcher callback
904	can deal with that fact.	1317	can deal with that fact, as both are simply passed through to the
		1318	callback.
905		1319
906	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1320	=item int ev_clear_pending (loop, ev_TYPE *watcher)
907		1321
908	If the watcher is pending, this function returns clears its pending status	1322	If the watcher is pending, this function clears its pending status and
909	and returns its C<revents> bitset (as if its callback was invoked). If the	1323	returns its C<revents> bitset (as if its callback was invoked). If the
910	watcher isn't pending it does nothing and returns C<0>.	1324	watcher isn't pending it does nothing and returns C<0>.
911		1325
		1326	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1327	callback to be invoked, which can be accomplished with this function.
		1328
		1329	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1330
		1331	Feeds the given event set into the event loop, as if the specified event
		1332	had happened for the specified watcher (which must be a pointer to an
		1333	initialised but not necessarily started event watcher). Obviously you must
		1334	not free the watcher as long as it has pending events.
		1335
		1336	Stopping the watcher, letting libev invoke it, or calling
		1337	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1338	not started in the first place.
		1339
		1340	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1341	functions that do not need a watcher.
		1342
912	=back	1343	=back
913		1344
914		1345
915	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1346	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
916		1347
917	Each watcher has, by default, a member C<void *data> that you can change	1348	Each watcher has, by default, a member C<void *data> that you can change
918	and read at any time, libev will completely ignore it. This can be used	1349	and read at any time: libev will completely ignore it. This can be used
919	to associate arbitrary data with your watcher. If you need more data and	1350	to associate arbitrary data with your watcher. If you need more data and
920	don't want to allocate memory and store a pointer to it in that data	1351	don't want to allocate memory and store a pointer to it in that data
921	member, you can also "subclass" the watcher type and provide your own	1352	member, you can also "subclass" the watcher type and provide your own
922	data:	1353	data:
923		1354
924	struct my_io	1355	struct my_io
925	{	1356	{
926	struct ev_io io;	1357	ev_io io;
927	int otherfd;	1358	int otherfd;
928	void *somedata;	1359	void *somedata;
929	struct whatever *mostinteresting;	1360	struct whatever *mostinteresting;
930	}	1361	};
		1362
		1363	...
		1364	struct my_io w;
		1365	ev_io_init (&w.io, my_cb, fd, EV_READ);
931		1366
932	And since your callback will be called with a pointer to the watcher, you	1367	And since your callback will be called with a pointer to the watcher, you
933	can cast it back to your own type:	1368	can cast it back to your own type:
934		1369
935	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1370	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
936	{	1371	{
937	struct my_io *w = (struct my_io *)w_;	1372	struct my_io *w = (struct my_io *)w_;
938	...	1373	...
939	}	1374	}
940		1375
941	More interesting and less C-conformant ways of casting your callback type	1376	More interesting and less C-conformant ways of casting your callback type
942	instead have been omitted.	1377	instead have been omitted.
943		1378
944	Another common scenario is having some data structure with multiple	1379	Another common scenario is to use some data structure with multiple
945	watchers:	1380	embedded watchers:
946		1381
947	struct my_biggy	1382	struct my_biggy
948	{	1383	{
949	int some_data;	1384	int some_data;
950	ev_timer t1;	1385	ev_timer t1;
951	ev_timer t2;	1386	ev_timer t2;
952	}	1387	}
953		1388
954	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1389	In this case getting the pointer to C<my_biggy> is a bit more
955	you need to use C<offsetof>:	1390	complicated: Either you store the address of your C<my_biggy> struct
		1391	in the C<data> member of the watcher (for woozies), or you need to use
		1392	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1393	programmers):
956		1394
957	#include <stddef.h>	1395	#include <stddef.h>
958		1396
959	static void	1397	static void
960	t1_cb (EV_P_ struct ev_timer *w, int revents)	1398	t1_cb (EV_P_ ev_timer *w, int revents)
961	{	1399	{
962	struct my_biggy big = (struct my_biggy *	1400	struct my_biggy big = (struct my_biggy *)
963	(((char *)w) - offsetof (struct my_biggy, t1));	1401	(((char *)w) - offsetof (struct my_biggy, t1));
964	}	1402	}
965		1403
966	static void	1404	static void
967	t2_cb (EV_P_ struct ev_timer *w, int revents)	1405	t2_cb (EV_P_ ev_timer *w, int revents)
968	{	1406	{
969	struct my_biggy big = (struct my_biggy *	1407	struct my_biggy big = (struct my_biggy *)
970	(((char *)w) - offsetof (struct my_biggy, t2));	1408	(((char *)w) - offsetof (struct my_biggy, t2));
971	}	1409	}
		1410
		1411	=head2 WATCHER PRIORITY MODELS
		1412
		1413	Many event loops support I<watcher priorities>, which are usually small
		1414	integers that influence the ordering of event callback invocation
		1415	between watchers in some way, all else being equal.
		1416
		1417	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1418	description for the more technical details such as the actual priority
		1419	range.
		1420
		1421	There are two common ways how these these priorities are being interpreted
		1422	by event loops:
		1423
		1424	In the more common lock-out model, higher priorities "lock out" invocation
		1425	of lower priority watchers, which means as long as higher priority
		1426	watchers receive events, lower priority watchers are not being invoked.
		1427
		1428	The less common only-for-ordering model uses priorities solely to order
		1429	callback invocation within a single event loop iteration: Higher priority
		1430	watchers are invoked before lower priority ones, but they all get invoked
		1431	before polling for new events.
		1432
		1433	Libev uses the second (only-for-ordering) model for all its watchers
		1434	except for idle watchers (which use the lock-out model).
		1435
		1436	The rationale behind this is that implementing the lock-out model for
		1437	watchers is not well supported by most kernel interfaces, and most event
		1438	libraries will just poll for the same events again and again as long as
		1439	their callbacks have not been executed, which is very inefficient in the
		1440	common case of one high-priority watcher locking out a mass of lower
		1441	priority ones.
		1442
		1443	Static (ordering) priorities are most useful when you have two or more
		1444	watchers handling the same resource: a typical usage example is having an
		1445	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1446	timeouts. Under load, data might be received while the program handles
		1447	other jobs, but since timers normally get invoked first, the timeout
		1448	handler will be executed before checking for data. In that case, giving
		1449	the timer a lower priority than the I/O watcher ensures that I/O will be
		1450	handled first even under adverse conditions (which is usually, but not
		1451	always, what you want).
		1452
		1453	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1454	will only be executed when no same or higher priority watchers have
		1455	received events, they can be used to implement the "lock-out" model when
		1456	required.
		1457
		1458	For example, to emulate how many other event libraries handle priorities,
		1459	you can associate an C<ev_idle> watcher to each such watcher, and in
		1460	the normal watcher callback, you just start the idle watcher. The real
		1461	processing is done in the idle watcher callback. This causes libev to
		1462	continuously poll and process kernel event data for the watcher, but when
		1463	the lock-out case is known to be rare (which in turn is rare :), this is
		1464	workable.
		1465
		1466	Usually, however, the lock-out model implemented that way will perform
		1467	miserably under the type of load it was designed to handle. In that case,
		1468	it might be preferable to stop the real watcher before starting the
		1469	idle watcher, so the kernel will not have to process the event in case
		1470	the actual processing will be delayed for considerable time.
		1471
		1472	Here is an example of an I/O watcher that should run at a strictly lower
		1473	priority than the default, and which should only process data when no
		1474	other events are pending:
		1475
		1476	ev_idle idle; // actual processing watcher
		1477	ev_io io; // actual event watcher
		1478
		1479	static void
		1480	io_cb (EV_P_ ev_io *w, int revents)
		1481	{
		1482	// stop the I/O watcher, we received the event, but
		1483	// are not yet ready to handle it.
		1484	ev_io_stop (EV_A_ w);
		1485
		1486	// start the idle watcher to handle the actual event.
		1487	// it will not be executed as long as other watchers
		1488	// with the default priority are receiving events.
		1489	ev_idle_start (EV_A_ &idle);
		1490	}
		1491
		1492	static void
		1493	idle_cb (EV_P_ ev_idle *w, int revents)
		1494	{
		1495	// actual processing
		1496	read (STDIN_FILENO, ...);
		1497
		1498	// have to start the I/O watcher again, as
		1499	// we have handled the event
		1500	ev_io_start (EV_P_ &io);
		1501	}
		1502
		1503	// initialisation
		1504	ev_idle_init (&idle, idle_cb);
		1505	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1506	ev_io_start (EV_DEFAULT_ &io);
		1507
		1508	In the "real" world, it might also be beneficial to start a timer, so that
		1509	low-priority connections can not be locked out forever under load. This
		1510	enables your program to keep a lower latency for important connections
		1511	during short periods of high load, while not completely locking out less
		1512	important ones.
972		1513
973		1514
974	=head1 WATCHER TYPES	1515	=head1 WATCHER TYPES
975		1516
976	This section describes each watcher in detail, but will not repeat	1517	This section describes each watcher in detail, but will not repeat
…		…
1000	In general you can register as many read and/or write event watchers per	1541	In general you can register as many read and/or write event watchers per
1001	fd as you want (as long as you don't confuse yourself). Setting all file	1542	fd as you want (as long as you don't confuse yourself). Setting all file
1002	descriptors to non-blocking mode is also usually a good idea (but not	1543	descriptors to non-blocking mode is also usually a good idea (but not
1003	required if you know what you are doing).	1544	required if you know what you are doing).
1004		1545
1005	If you must do this, then force the use of a known-to-be-good backend	1546	If you cannot use non-blocking mode, then force the use of a
1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1547	known-to-be-good backend (at the time of this writing, this includes only
1007	C<EVBACKEND_POLL>).	1548	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1549	descriptors for which non-blocking operation makes no sense (such as
		1550	files) - libev doesn't guarantee any specific behaviour in that case.
1008		1551
1009	Another thing you have to watch out for is that it is quite easy to	1552	Another thing you have to watch out for is that it is quite easy to
1010	receive "spurious" readyness notifications, that is your callback might	1553	receive "spurious" readiness notifications, that is your callback might
1011	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1554	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1012	because there is no data. Not only are some backends known to create a	1555	because there is no data. Not only are some backends known to create a
1013	lot of those (for example solaris ports), it is very easy to get into	1556	lot of those (for example Solaris ports), it is very easy to get into
1014	this situation even with a relatively standard program structure. Thus	1557	this situation even with a relatively standard program structure. Thus
1015	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1558	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1016	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1559	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1017		1560
1018	If you cannot run the fd in non-blocking mode (for example you should not	1561	If you cannot run the fd in non-blocking mode (for example you should
1019	play around with an Xlib connection), then you have to seperately re-test	1562	not play around with an Xlib connection), then you have to separately
1020	whether a file descriptor is really ready with a known-to-be good interface	1563	re-test whether a file descriptor is really ready with a known-to-be good
1021	such as poll (fortunately in our Xlib example, Xlib already does this on	1564	interface such as poll (fortunately in our Xlib example, Xlib already
1022	its own, so its quite safe to use).	1565	does this on its own, so its quite safe to use). Some people additionally
		1566	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1567	indefinitely.
		1568
		1569	But really, best use non-blocking mode.
1023		1570
1024	=head3 The special problem of disappearing file descriptors	1571	=head3 The special problem of disappearing file descriptors
1025		1572
1026	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1573	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1027	descriptor (either by calling C<close> explicitly or by any other means,	1574	descriptor (either due to calling C<close> explicitly or any other means,
1028	such as C<dup>). The reason is that you register interest in some file	1575	such as C<dup2>). The reason is that you register interest in some file
1029	descriptor, but when it goes away, the operating system will silently drop	1576	descriptor, but when it goes away, the operating system will silently drop
1030	this interest. If another file descriptor with the same number then is	1577	this interest. If another file descriptor with the same number then is
1031	registered with libev, there is no efficient way to see that this is, in	1578	registered with libev, there is no efficient way to see that this is, in
1032	fact, a different file descriptor.	1579	fact, a different file descriptor.
1033		1580
…		…
1062	To support fork in your programs, you either have to call	1609	To support fork in your programs, you either have to call
1063	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1610	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1611	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1065	C<EVBACKEND_POLL>.	1612	C<EVBACKEND_POLL>.
1066		1613
		1614	=head3 The special problem of SIGPIPE
		1615
		1616	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1617	when writing to a pipe whose other end has been closed, your program gets
		1618	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1619	this is sensible behaviour, for daemons, this is usually undesirable.
		1620
		1621	So when you encounter spurious, unexplained daemon exits, make sure you
		1622	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1623	somewhere, as that would have given you a big clue).
		1624
		1625	=head3 The special problem of accept()ing when you can't
		1626
		1627	Many implementations of the POSIX C<accept> function (for example,
		1628	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1629	connection from the pending queue in all error cases.
		1630
		1631	For example, larger servers often run out of file descriptors (because
		1632	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1633	rejecting the connection, leading to libev signalling readiness on
		1634	the next iteration again (the connection still exists after all), and
		1635	typically causing the program to loop at 100% CPU usage.
		1636
		1637	Unfortunately, the set of errors that cause this issue differs between
		1638	operating systems, there is usually little the app can do to remedy the
		1639	situation, and no known thread-safe method of removing the connection to
		1640	cope with overload is known (to me).
		1641
		1642	One of the easiest ways to handle this situation is to just ignore it
		1643	- when the program encounters an overload, it will just loop until the
		1644	situation is over. While this is a form of busy waiting, no OS offers an
		1645	event-based way to handle this situation, so it's the best one can do.
		1646
		1647	A better way to handle the situation is to log any errors other than
		1648	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1649	messages, and continue as usual, which at least gives the user an idea of
		1650	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1651	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1652	usage.
		1653
		1654	If your program is single-threaded, then you could also keep a dummy file
		1655	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1656	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1657	close that fd, and create a new dummy fd. This will gracefully refuse
		1658	clients under typical overload conditions.
		1659
		1660	The last way to handle it is to simply log the error and C<exit>, as
		1661	is often done with C<malloc> failures, but this results in an easy
		1662	opportunity for a DoS attack.
1067		1663
1068	=head3 Watcher-Specific Functions	1664	=head3 Watcher-Specific Functions
1069		1665
1070	=over 4	1666	=over 4
1071		1667
1072	=item ev_io_init (ev_io *, callback, int fd, int events)	1668	=item ev_io_init (ev_io *, callback, int fd, int events)
1073		1669
1074	=item ev_io_set (ev_io *, int fd, int events)	1670	=item ev_io_set (ev_io *, int fd, int events)
1075		1671
1076	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1672	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1077	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1673	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1078	C<EV_READ | EV_WRITE> to receive the given events.	1674	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1079		1675
1080	=item int fd [read-only]	1676	=item int fd [read-only]
1081		1677
1082	The file descriptor being watched.	1678	The file descriptor being watched.
1083		1679
…		…
1091		1687
1092	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1688	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1093	readable, but only once. Since it is likely line-buffered, you could	1689	readable, but only once. Since it is likely line-buffered, you could
1094	attempt to read a whole line in the callback.	1690	attempt to read a whole line in the callback.
1095		1691
1096	static void	1692	static void
1097	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1693	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1098	{	1694	{
1099	ev_io_stop (loop, w);	1695	ev_io_stop (loop, w);
1100	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1696	.. read from stdin here (or from w->fd) and handle any I/O errors
1101	}	1697	}
1102		1698
1103	...	1699	...
1104	struct ev_loop *loop = ev_default_init (0);	1700	struct ev_loop *loop = ev_default_init (0);
1105	struct ev_io stdin_readable;	1701	ev_io stdin_readable;
1106	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1702	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1107	ev_io_start (loop, &stdin_readable);	1703	ev_io_start (loop, &stdin_readable);
1108	ev_loop (loop, 0);	1704	ev_run (loop, 0);
1109		1705
1110		1706
1111	=head2 C<ev_timer> - relative and optionally repeating timeouts	1707	=head2 C<ev_timer> - relative and optionally repeating timeouts
1112		1708
1113	Timer watchers are simple relative timers that generate an event after a	1709	Timer watchers are simple relative timers that generate an event after a
1114	given time, and optionally repeating in regular intervals after that.	1710	given time, and optionally repeating in regular intervals after that.
1115		1711
1116	The timers are based on real time, that is, if you register an event that	1712	The timers are based on real time, that is, if you register an event that
1117	times out after an hour and you reset your system clock to last years	1713	times out after an hour and you reset your system clock to January last
1118	time, it will still time out after (roughly) and hour. "Roughly" because	1714	year, it will still time out after (roughly) one hour. "Roughly" because
1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1715	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1120	monotonic clock option helps a lot here).	1716	monotonic clock option helps a lot here).
		1717
		1718	The callback is guaranteed to be invoked only I<after> its timeout has
		1719	passed (not I<at>, so on systems with very low-resolution clocks this
		1720	might introduce a small delay). If multiple timers become ready during the
		1721	same loop iteration then the ones with earlier time-out values are invoked
		1722	before ones of the same priority with later time-out values (but this is
		1723	no longer true when a callback calls C<ev_run> recursively).
		1724
		1725	=head3 Be smart about timeouts
		1726
		1727	Many real-world problems involve some kind of timeout, usually for error
		1728	recovery. A typical example is an HTTP request - if the other side hangs,
		1729	you want to raise some error after a while.
		1730
		1731	What follows are some ways to handle this problem, from obvious and
		1732	inefficient to smart and efficient.
		1733
		1734	In the following, a 60 second activity timeout is assumed - a timeout that
		1735	gets reset to 60 seconds each time there is activity (e.g. each time some
		1736	data or other life sign was received).
		1737
		1738	=over 4
		1739
		1740	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1741
		1742	This is the most obvious, but not the most simple way: In the beginning,
		1743	start the watcher:
		1744
		1745	ev_timer_init (timer, callback, 60., 0.);
		1746	ev_timer_start (loop, timer);
		1747
		1748	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1749	and start it again:
		1750
		1751	ev_timer_stop (loop, timer);
		1752	ev_timer_set (timer, 60., 0.);
		1753	ev_timer_start (loop, timer);
		1754
		1755	This is relatively simple to implement, but means that each time there is
		1756	some activity, libev will first have to remove the timer from its internal
		1757	data structure and then add it again. Libev tries to be fast, but it's
		1758	still not a constant-time operation.
		1759
		1760	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1761
		1762	This is the easiest way, and involves using C<ev_timer_again> instead of
		1763	C<ev_timer_start>.
		1764
		1765	To implement this, configure an C<ev_timer> with a C<repeat> value
		1766	of C<60> and then call C<ev_timer_again> at start and each time you
		1767	successfully read or write some data. If you go into an idle state where
		1768	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1769	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1770
		1771	That means you can ignore both the C<ev_timer_start> function and the
		1772	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1773	member and C<ev_timer_again>.
		1774
		1775	At start:
		1776
		1777	ev_init (timer, callback);
		1778	timer->repeat = 60.;
		1779	ev_timer_again (loop, timer);
		1780
		1781	Each time there is some activity:
		1782
		1783	ev_timer_again (loop, timer);
		1784
		1785	It is even possible to change the time-out on the fly, regardless of
		1786	whether the watcher is active or not:
		1787
		1788	timer->repeat = 30.;
		1789	ev_timer_again (loop, timer);
		1790
		1791	This is slightly more efficient then stopping/starting the timer each time
		1792	you want to modify its timeout value, as libev does not have to completely
		1793	remove and re-insert the timer from/into its internal data structure.
		1794
		1795	It is, however, even simpler than the "obvious" way to do it.
		1796
		1797	=item 3. Let the timer time out, but then re-arm it as required.
		1798
		1799	This method is more tricky, but usually most efficient: Most timeouts are
		1800	relatively long compared to the intervals between other activity - in
		1801	our example, within 60 seconds, there are usually many I/O events with
		1802	associated activity resets.
		1803
		1804	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1805	but remember the time of last activity, and check for a real timeout only
		1806	within the callback:
		1807
		1808	ev_tstamp last_activity; // time of last activity
		1809
		1810	static void
		1811	callback (EV_P_ ev_timer *w, int revents)
		1812	{
		1813	ev_tstamp now = ev_now (EV_A);
		1814	ev_tstamp timeout = last_activity + 60.;
		1815
		1816	// if last_activity + 60. is older than now, we did time out
		1817	if (timeout < now)
		1818	{
		1819	// timeout occurred, take action
		1820	}
		1821	else
		1822	{
		1823	// callback was invoked, but there was some activity, re-arm
		1824	// the watcher to fire in last_activity + 60, which is
		1825	// guaranteed to be in the future, so "again" is positive:
		1826	w->repeat = timeout - now;
		1827	ev_timer_again (EV_A_ w);
		1828	}
		1829	}
		1830
		1831	To summarise the callback: first calculate the real timeout (defined
		1832	as "60 seconds after the last activity"), then check if that time has
		1833	been reached, which means something I<did>, in fact, time out. Otherwise
		1834	the callback was invoked too early (C<timeout> is in the future), so
		1835	re-schedule the timer to fire at that future time, to see if maybe we have
		1836	a timeout then.
		1837
		1838	Note how C<ev_timer_again> is used, taking advantage of the
		1839	C<ev_timer_again> optimisation when the timer is already running.
		1840
		1841	This scheme causes more callback invocations (about one every 60 seconds
		1842	minus half the average time between activity), but virtually no calls to
		1843	libev to change the timeout.
		1844
		1845	To start the timer, simply initialise the watcher and set C<last_activity>
		1846	to the current time (meaning we just have some activity :), then call the
		1847	callback, which will "do the right thing" and start the timer:
		1848
		1849	ev_init (timer, callback);
		1850	last_activity = ev_now (loop);
		1851	callback (loop, timer, EV_TIMER);
		1852
		1853	And when there is some activity, simply store the current time in
		1854	C<last_activity>, no libev calls at all:
		1855
		1856	last_activity = ev_now (loop);
		1857
		1858	This technique is slightly more complex, but in most cases where the
		1859	time-out is unlikely to be triggered, much more efficient.
		1860
		1861	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1862	callback :) - just change the timeout and invoke the callback, which will
		1863	fix things for you.
		1864
		1865	=item 4. Wee, just use a double-linked list for your timeouts.
		1866
		1867	If there is not one request, but many thousands (millions...), all
		1868	employing some kind of timeout with the same timeout value, then one can
		1869	do even better:
		1870
		1871	When starting the timeout, calculate the timeout value and put the timeout
		1872	at the I<end> of the list.
		1873
		1874	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1875	the list is expected to fire (for example, using the technique #3).
		1876
		1877	When there is some activity, remove the timer from the list, recalculate
		1878	the timeout, append it to the end of the list again, and make sure to
		1879	update the C<ev_timer> if it was taken from the beginning of the list.
		1880
		1881	This way, one can manage an unlimited number of timeouts in O(1) time for
		1882	starting, stopping and updating the timers, at the expense of a major
		1883	complication, and having to use a constant timeout. The constant timeout
		1884	ensures that the list stays sorted.
		1885
		1886	=back
		1887
		1888	So which method the best?
		1889
		1890	Method #2 is a simple no-brain-required solution that is adequate in most
		1891	situations. Method #3 requires a bit more thinking, but handles many cases
		1892	better, and isn't very complicated either. In most case, choosing either
		1893	one is fine, with #3 being better in typical situations.
		1894
		1895	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1896	rather complicated, but extremely efficient, something that really pays
		1897	off after the first million or so of active timers, i.e. it's usually
		1898	overkill :)
		1899
		1900	=head3 The special problem of time updates
		1901
		1902	Establishing the current time is a costly operation (it usually takes at
		1903	least two system calls): EV therefore updates its idea of the current
		1904	time only before and after C<ev_run> collects new events, which causes a
		1905	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1906	lots of events in one iteration.
1121		1907
1122	The relative timeouts are calculated relative to the C<ev_now ()>	1908	The relative timeouts are calculated relative to the C<ev_now ()>
1123	time. This is usually the right thing as this timestamp refers to the time	1909	time. This is usually the right thing as this timestamp refers to the time
1124	of the event triggering whatever timeout you are modifying/starting. If	1910	of the event triggering whatever timeout you are modifying/starting. If
1125	you suspect event processing to be delayed and you I<need> to base the timeout	1911	you suspect event processing to be delayed and you I<need> to base the
1126	on the current time, use something like this to adjust for this:	1912	timeout on the current time, use something like this to adjust for this:
1127		1913
1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1914	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1129		1915
1130	The callback is guarenteed to be invoked only when its timeout has passed,	1916	If the event loop is suspended for a long time, you can also force an
1131	but if multiple timers become ready during the same loop iteration then	1917	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1132	order of execution is undefined.	1918	()>.
		1919
		1920	=head3 The special problems of suspended animation
		1921
		1922	When you leave the server world it is quite customary to hit machines that
		1923	can suspend/hibernate - what happens to the clocks during such a suspend?
		1924
		1925	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1926	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1927	to run until the system is suspended, but they will not advance while the
		1928	system is suspended. That means, on resume, it will be as if the program
		1929	was frozen for a few seconds, but the suspend time will not be counted
		1930	towards C<ev_timer> when a monotonic clock source is used. The real time
		1931	clock advanced as expected, but if it is used as sole clocksource, then a
		1932	long suspend would be detected as a time jump by libev, and timers would
		1933	be adjusted accordingly.
		1934
		1935	I would not be surprised to see different behaviour in different between
		1936	operating systems, OS versions or even different hardware.
		1937
		1938	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1939	time jump in the monotonic clocks and the realtime clock. If the program
		1940	is suspended for a very long time, and monotonic clock sources are in use,
		1941	then you can expect C<ev_timer>s to expire as the full suspension time
		1942	will be counted towards the timers. When no monotonic clock source is in
		1943	use, then libev will again assume a timejump and adjust accordingly.
		1944
		1945	It might be beneficial for this latter case to call C<ev_suspend>
		1946	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1947	deterministic behaviour in this case (you can do nothing against
		1948	C<SIGSTOP>).
1133		1949
1134	=head3 Watcher-Specific Functions and Data Members	1950	=head3 Watcher-Specific Functions and Data Members
1135		1951
1136	=over 4	1952	=over 4
1137		1953
1138	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1954	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1139		1955
1140	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1956	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1141		1957
1142	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1958	Configure the timer to trigger after C<after> seconds. If C<repeat>
1143	C<0.>, then it will automatically be stopped. If it is positive, then the	1959	is C<0.>, then it will automatically be stopped once the timeout is
1144	timer will automatically be configured to trigger again C<repeat> seconds	1960	reached. If it is positive, then the timer will automatically be
1145	later, again, and again, until stopped manually.	1961	configured to trigger again C<repeat> seconds later, again, and again,
		1962	until stopped manually.
1146		1963
1147	The timer itself will do a best-effort at avoiding drift, that is, if you	1964	The timer itself will do a best-effort at avoiding drift, that is, if
1148	configure a timer to trigger every 10 seconds, then it will trigger at	1965	you configure a timer to trigger every 10 seconds, then it will normally
1149	exactly 10 second intervals. If, however, your program cannot keep up with	1966	trigger at exactly 10 second intervals. If, however, your program cannot
1150	the timer (because it takes longer than those 10 seconds to do stuff) the	1967	keep up with the timer (because it takes longer than those 10 seconds to
1151	timer will not fire more than once per event loop iteration.	1968	do stuff) the timer will not fire more than once per event loop iteration.
1152		1969
1153	=item ev_timer_again (loop)	1970	=item ev_timer_again (loop, ev_timer *)
1154		1971
1155	This will act as if the timer timed out and restart it again if it is	1972	This will act as if the timer timed out and restart it again if it is
1156	repeating. The exact semantics are:	1973	repeating. The exact semantics are:
1157		1974
1158	If the timer is pending, its pending status is cleared.	1975	If the timer is pending, its pending status is cleared.
1159		1976
1160	If the timer is started but nonrepeating, stop it (as if it timed out).	1977	If the timer is started but non-repeating, stop it (as if it timed out).
1161		1978
1162	If the timer is repeating, either start it if necessary (with the	1979	If the timer is repeating, either start it if necessary (with the
1163	C<repeat> value), or reset the running timer to the C<repeat> value.	1980	C<repeat> value), or reset the running timer to the C<repeat> value.
1164		1981
1165	This sounds a bit complicated, but here is a useful and typical	1982	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1166	example: Imagine you have a tcp connection and you want a so-called idle	1983	usage example.
1167	timeout, that is, you want to be called when there have been, say, 60
1168	seconds of inactivity on the socket. The easiest way to do this is to
1169	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1170	C<ev_timer_again> each time you successfully read or write some data. If
1171	you go into an idle state where you do not expect data to travel on the
1172	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1173	automatically restart it if need be.
1174		1984
1175	That means you can ignore the C<after> value and C<ev_timer_start>	1985	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1176	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1177		1986
1178	ev_timer_init (timer, callback, 0., 5.);	1987	Returns the remaining time until a timer fires. If the timer is active,
1179	ev_timer_again (loop, timer);	1988	then this time is relative to the current event loop time, otherwise it's
1180	...	1989	the timeout value currently configured.
1181	timer->again = 17.;
1182	ev_timer_again (loop, timer);
1183	...
1184	timer->again = 10.;
1185	ev_timer_again (loop, timer);
1186		1990
1187	This is more slightly efficient then stopping/starting the timer each time	1991	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1188	you want to modify its timeout value.	1992	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1993	will return C<4>. When the timer expires and is restarted, it will return
		1994	roughly C<7> (likely slightly less as callback invocation takes some time,
		1995	too), and so on.
1189		1996
1190	=item ev_tstamp repeat [read-write]	1997	=item ev_tstamp repeat [read-write]
1191		1998
1192	The current C<repeat> value. Will be used each time the watcher times out	1999	The current C<repeat> value. Will be used each time the watcher times out
1193	or C<ev_timer_again> is called and determines the next timeout (if any),	2000	or C<ev_timer_again> is called, and determines the next timeout (if any),
1194	which is also when any modifications are taken into account.	2001	which is also when any modifications are taken into account.
1195		2002
1196	=back	2003	=back
1197		2004
1198	=head3 Examples	2005	=head3 Examples
1199		2006
1200	Example: Create a timer that fires after 60 seconds.	2007	Example: Create a timer that fires after 60 seconds.
1201		2008
1202	static void	2009	static void
1203	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2010	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1204	{	2011	{
1205	.. one minute over, w is actually stopped right here	2012	.. one minute over, w is actually stopped right here
1206	}	2013	}
1207		2014
1208	struct ev_timer mytimer;	2015	ev_timer mytimer;
1209	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2016	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1210	ev_timer_start (loop, &mytimer);	2017	ev_timer_start (loop, &mytimer);
1211		2018
1212	Example: Create a timeout timer that times out after 10 seconds of	2019	Example: Create a timeout timer that times out after 10 seconds of
1213	inactivity.	2020	inactivity.
1214		2021
1215	static void	2022	static void
1216	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2023	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1217	{	2024	{
1218	.. ten seconds without any activity	2025	.. ten seconds without any activity
1219	}	2026	}
1220		2027
1221	struct ev_timer mytimer;	2028	ev_timer mytimer;
1222	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2029	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1223	ev_timer_again (&mytimer); /* start timer */	2030	ev_timer_again (&mytimer); /* start timer */
1224	ev_loop (loop, 0);	2031	ev_run (loop, 0);
1225		2032
1226	// and in some piece of code that gets executed on any "activity":	2033	// and in some piece of code that gets executed on any "activity":
1227	// reset the timeout to start ticking again at 10 seconds	2034	// reset the timeout to start ticking again at 10 seconds
1228	ev_timer_again (&mytimer);	2035	ev_timer_again (&mytimer);
1229		2036
1230		2037
1231	=head2 C<ev_periodic> - to cron or not to cron?	2038	=head2 C<ev_periodic> - to cron or not to cron?
1232		2039
1233	Periodic watchers are also timers of a kind, but they are very versatile	2040	Periodic watchers are also timers of a kind, but they are very versatile
1234	(and unfortunately a bit complex).	2041	(and unfortunately a bit complex).
1235		2042
1236	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2043	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1237	but on wallclock time (absolute time). You can tell a periodic watcher	2044	relative time, the physical time that passes) but on wall clock time
1238	to trigger "at" some specific point in time. For example, if you tell a	2045	(absolute time, the thing you can read on your calender or clock). The
1239	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2046	difference is that wall clock time can run faster or slower than real
1240	+ 10.>) and then reset your system clock to the last year, then it will	2047	time, and time jumps are not uncommon (e.g. when you adjust your
1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2048	wrist-watch).
1242	roughly 10 seconds later).
1243		2049
1244	They can also be used to implement vastly more complex timers, such as	2050	You can tell a periodic watcher to trigger after some specific point
1245	triggering an event on each midnight, local time or other, complicated,	2051	in time: for example, if you tell a periodic watcher to trigger "in 10
1246	rules.	2052	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2053	not a delay) and then reset your system clock to January of the previous
		2054	year, then it will take a year or more to trigger the event (unlike an
		2055	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2056	it, as it uses a relative timeout).
1247		2057
		2058	C<ev_periodic> watchers can also be used to implement vastly more complex
		2059	timers, such as triggering an event on each "midnight, local time", or
		2060	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2061	those cannot react to time jumps.
		2062
1248	As with timers, the callback is guarenteed to be invoked only when the	2063	As with timers, the callback is guaranteed to be invoked only when the
1249	time (C<at>) has been passed, but if multiple periodic timers become ready	2064	point in time where it is supposed to trigger has passed. If multiple
1250	during the same loop iteration then order of execution is undefined.	2065	timers become ready during the same loop iteration then the ones with
		2066	earlier time-out values are invoked before ones with later time-out values
		2067	(but this is no longer true when a callback calls C<ev_run> recursively).
1251		2068
1252	=head3 Watcher-Specific Functions and Data Members	2069	=head3 Watcher-Specific Functions and Data Members
1253		2070
1254	=over 4	2071	=over 4
1255		2072
1256	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2073	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1257		2074
1258	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2075	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1259		2076
1260	Lots of arguments, lets sort it out... There are basically three modes of	2077	Lots of arguments, let's sort it out... There are basically three modes of
1261	operation, and we will explain them from simplest to complex:	2078	operation, and we will explain them from simplest to most complex:
1262		2079
1263	=over 4	2080	=over 4
1264		2081
1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2082	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1266		2083
1267	In this configuration the watcher triggers an event at the wallclock time	2084	In this configuration the watcher triggers an event after the wall clock
1268	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2085	time C<offset> has passed. It will not repeat and will not adjust when a
1269	that is, if it is to be run at January 1st 2011 then it will run when the	2086	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1270	system time reaches or surpasses this time.	2087	will be stopped and invoked when the system clock reaches or surpasses
		2088	this point in time.
1271		2089
1272	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2090	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1273		2091
1274	In this mode the watcher will always be scheduled to time out at the next	2092	In this mode the watcher will always be scheduled to time out at the next
1275	C<at + N * interval> time (for some integer N, which can also be negative)	2093	C<offset + N * interval> time (for some integer N, which can also be
1276	and then repeat, regardless of any time jumps.	2094	negative) and then repeat, regardless of any time jumps. The C<offset>
		2095	argument is merely an offset into the C<interval> periods.
1277		2096
1278	This can be used to create timers that do not drift with respect to system	2097	This can be used to create timers that do not drift with respect to the
1279	time:	2098	system clock, for example, here is an C<ev_periodic> that triggers each
		2099	hour, on the hour (with respect to UTC):
1280		2100
1281	ev_periodic_set (&periodic, 0., 3600., 0);	2101	ev_periodic_set (&periodic, 0., 3600., 0);
1282		2102
1283	This doesn't mean there will always be 3600 seconds in between triggers,	2103	This doesn't mean there will always be 3600 seconds in between triggers,
1284	but only that the the callback will be called when the system time shows a	2104	but only that the callback will be called when the system time shows a
1285	full hour (UTC), or more correctly, when the system time is evenly divisible	2105	full hour (UTC), or more correctly, when the system time is evenly divisible
1286	by 3600.	2106	by 3600.
1287		2107
1288	Another way to think about it (for the mathematically inclined) is that	2108	Another way to think about it (for the mathematically inclined) is that
1289	C<ev_periodic> will try to run the callback in this mode at the next possible	2109	C<ev_periodic> will try to run the callback in this mode at the next possible
1290	time where C<time = at (mod interval)>, regardless of any time jumps.	2110	time where C<time = offset (mod interval)>, regardless of any time jumps.
1291		2111
1292	For numerical stability it is preferable that the C<at> value is near	2112	For numerical stability it is preferable that the C<offset> value is near
1293	C<ev_now ()> (the current time), but there is no range requirement for	2113	C<ev_now ()> (the current time), but there is no range requirement for
1294	this value.	2114	this value, and in fact is often specified as zero.
1295		2115
		2116	Note also that there is an upper limit to how often a timer can fire (CPU
		2117	speed for example), so if C<interval> is very small then timing stability
		2118	will of course deteriorate. Libev itself tries to be exact to be about one
		2119	millisecond (if the OS supports it and the machine is fast enough).
		2120
1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2121	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1297		2122
1298	In this mode the values for C<interval> and C<at> are both being	2123	In this mode the values for C<interval> and C<offset> are both being
1299	ignored. Instead, each time the periodic watcher gets scheduled, the	2124	ignored. Instead, each time the periodic watcher gets scheduled, the
1300	reschedule callback will be called with the watcher as first, and the	2125	reschedule callback will be called with the watcher as first, and the
1301	current time as second argument.	2126	current time as second argument.
1302		2127
1303	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2128	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1304	ever, or make any event loop modifications>. If you need to stop it,	2129	or make ANY other event loop modifications whatsoever, unless explicitly
1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2130	allowed by documentation here>.
1306	starting an C<ev_prepare> watcher, which is legal).
1307		2131
		2132	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2133	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2134	only event loop modification you are allowed to do).
		2135
1308	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2136	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1309	ev_tstamp now)>, e.g.:	2137	*w, ev_tstamp now)>, e.g.:
1310		2138
		2139	static ev_tstamp
1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2140	my_rescheduler (ev_periodic *w, ev_tstamp now)
1312	{	2141	{
1313	return now + 60.;	2142	return now + 60.;
1314	}	2143	}
1315		2144
1316	It must return the next time to trigger, based on the passed time value	2145	It must return the next time to trigger, based on the passed time value
1317	(that is, the lowest time value larger than to the second argument). It	2146	(that is, the lowest time value larger than to the second argument). It
1318	will usually be called just before the callback will be triggered, but	2147	will usually be called just before the callback will be triggered, but
1319	might be called at other times, too.	2148	might be called at other times, too.
1320		2149
1321	NOTE: I<< This callback must always return a time that is later than the	2150	NOTE: I<< This callback must always return a time that is higher than or
1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2151	equal to the passed C<now> value >>.
1323		2152
1324	This can be used to create very complex timers, such as a timer that	2153	This can be used to create very complex timers, such as a timer that
1325	triggers on each midnight, local time. To do this, you would calculate the	2154	triggers on "next midnight, local time". To do this, you would calculate the
1326	next midnight after C<now> and return the timestamp value for this. How	2155	next midnight after C<now> and return the timestamp value for this. How
1327	you do this is, again, up to you (but it is not trivial, which is the main	2156	you do this is, again, up to you (but it is not trivial, which is the main
1328	reason I omitted it as an example).	2157	reason I omitted it as an example).
1329		2158
1330	=back	2159	=back
…		…
1334	Simply stops and restarts the periodic watcher again. This is only useful	2163	Simply stops and restarts the periodic watcher again. This is only useful
1335	when you changed some parameters or the reschedule callback would return	2164	when you changed some parameters or the reschedule callback would return
1336	a different time than the last time it was called (e.g. in a crond like	2165	a different time than the last time it was called (e.g. in a crond like
1337	program when the crontabs have changed).	2166	program when the crontabs have changed).
1338		2167
		2168	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2169
		2170	When active, returns the absolute time that the watcher is supposed
		2171	to trigger next. This is not the same as the C<offset> argument to
		2172	C<ev_periodic_set>, but indeed works even in interval and manual
		2173	rescheduling modes.
		2174
1339	=item ev_tstamp offset [read-write]	2175	=item ev_tstamp offset [read-write]
1340		2176
1341	When repeating, this contains the offset value, otherwise this is the	2177	When repeating, this contains the offset value, otherwise this is the
1342	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2178	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2179	although libev might modify this value for better numerical stability).
1343		2180
1344	Can be modified any time, but changes only take effect when the periodic	2181	Can be modified any time, but changes only take effect when the periodic
1345	timer fires or C<ev_periodic_again> is being called.	2182	timer fires or C<ev_periodic_again> is being called.
1346		2183
1347	=item ev_tstamp interval [read-write]	2184	=item ev_tstamp interval [read-write]
1348		2185
1349	The current interval value. Can be modified any time, but changes only	2186	The current interval value. Can be modified any time, but changes only
1350	take effect when the periodic timer fires or C<ev_periodic_again> is being	2187	take effect when the periodic timer fires or C<ev_periodic_again> is being
1351	called.	2188	called.
1352		2189
1353	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2190	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1354		2191
1355	The current reschedule callback, or C<0>, if this functionality is	2192	The current reschedule callback, or C<0>, if this functionality is
1356	switched off. Can be changed any time, but changes only take effect when	2193	switched off. Can be changed any time, but changes only take effect when
1357	the periodic timer fires or C<ev_periodic_again> is being called.	2194	the periodic timer fires or C<ev_periodic_again> is being called.
1358		2195
1359	=item ev_tstamp at [read-only]
1360
1361	When active, contains the absolute time that the watcher is supposed to
1362	trigger next.
1363
1364	=back	2196	=back
1365		2197
1366	=head3 Examples	2198	=head3 Examples
1367		2199
1368	Example: Call a callback every hour, or, more precisely, whenever the	2200	Example: Call a callback every hour, or, more precisely, whenever the
1369	system clock is divisible by 3600. The callback invocation times have	2201	system time is divisible by 3600. The callback invocation times have
1370	potentially a lot of jittering, but good long-term stability.	2202	potentially a lot of jitter, but good long-term stability.
1371		2203
1372	static void	2204	static void
1373	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2205	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1374	{	2206	{
1375	... its now a full hour (UTC, or TAI or whatever your clock follows)	2207	... its now a full hour (UTC, or TAI or whatever your clock follows)
1376	}	2208	}
1377		2209
1378	struct ev_periodic hourly_tick;	2210	ev_periodic hourly_tick;
1379	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2211	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1380	ev_periodic_start (loop, &hourly_tick);	2212	ev_periodic_start (loop, &hourly_tick);
1381		2213
1382	Example: The same as above, but use a reschedule callback to do it:	2214	Example: The same as above, but use a reschedule callback to do it:
1383		2215
1384	#include <math.h>	2216	#include <math.h>
1385		2217
1386	static ev_tstamp	2218	static ev_tstamp
1387	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2219	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1388	{	2220	{
1389	return fmod (now, 3600.) + 3600.;	2221	return now + (3600. - fmod (now, 3600.));
1390	}	2222	}
1391		2223
1392	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2224	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1393		2225
1394	Example: Call a callback every hour, starting now:	2226	Example: Call a callback every hour, starting now:
1395		2227
1396	struct ev_periodic hourly_tick;	2228	ev_periodic hourly_tick;
1397	ev_periodic_init (&hourly_tick, clock_cb,	2229	ev_periodic_init (&hourly_tick, clock_cb,
1398	fmod (ev_now (loop), 3600.), 3600., 0);	2230	fmod (ev_now (loop), 3600.), 3600., 0);
1399	ev_periodic_start (loop, &hourly_tick);	2231	ev_periodic_start (loop, &hourly_tick);
1400		2232
1401		2233
1402	=head2 C<ev_signal> - signal me when a signal gets signalled!	2234	=head2 C<ev_signal> - signal me when a signal gets signalled!
1403		2235
1404	Signal watchers will trigger an event when the process receives a specific	2236	Signal watchers will trigger an event when the process receives a specific
1405	signal one or more times. Even though signals are very asynchronous, libev	2237	signal one or more times. Even though signals are very asynchronous, libev
1406	will try it's best to deliver signals synchronously, i.e. as part of the	2238	will try it's best to deliver signals synchronously, i.e. as part of the
1407	normal event processing, like any other event.	2239	normal event processing, like any other event.
1408		2240
		2241	If you want signals to be delivered truly asynchronously, just use
		2242	C<sigaction> as you would do without libev and forget about sharing
		2243	the signal. You can even use C<ev_async> from a signal handler to
		2244	synchronously wake up an event loop.
		2245
1409	You can configure as many watchers as you like per signal. Only when the	2246	You can configure as many watchers as you like for the same signal, but
		2247	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2248	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2249	C<SIGINT> in both the default loop and another loop at the same time. At
		2250	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2251
1410	first watcher gets started will libev actually register a signal watcher	2252	When the first watcher gets started will libev actually register something
1411	with the kernel (thus it coexists with your own signal handlers as long	2253	with the kernel (thus it coexists with your own signal handlers as long as
1412	as you don't register any with libev). Similarly, when the last signal	2254	you don't register any with libev for the same signal).
1413	watcher for a signal is stopped libev will reset the signal handler to	2255
1414	SIG_DFL (regardless of what it was set to before).	2256	If possible and supported, libev will install its handlers with
		2257	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2258	not be unduly interrupted. If you have a problem with system calls getting
		2259	interrupted by signals you can block all signals in an C<ev_check> watcher
		2260	and unblock them in an C<ev_prepare> watcher.
		2261
		2262	=head3 The special problem of inheritance over fork/execve/pthread_create
		2263
		2264	Both the signal mask (C<sigprocmask>) and the signal disposition
		2265	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2266	stopping it again), that is, libev might or might not block the signal,
		2267	and might or might not set or restore the installed signal handler.
		2268
		2269	While this does not matter for the signal disposition (libev never
		2270	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2271	C<execve>), this matters for the signal mask: many programs do not expect
		2272	certain signals to be blocked.
		2273
		2274	This means that before calling C<exec> (from the child) you should reset
		2275	the signal mask to whatever "default" you expect (all clear is a good
		2276	choice usually).
		2277
		2278	The simplest way to ensure that the signal mask is reset in the child is
		2279	to install a fork handler with C<pthread_atfork> that resets it. That will
		2280	catch fork calls done by libraries (such as the libc) as well.
		2281
		2282	In current versions of libev, the signal will not be blocked indefinitely
		2283	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2284	the window of opportunity for problems, it will not go away, as libev
		2285	I<has> to modify the signal mask, at least temporarily.
		2286
		2287	So I can't stress this enough: I<If you do not reset your signal mask when
		2288	you expect it to be empty, you have a race condition in your code>. This
		2289	is not a libev-specific thing, this is true for most event libraries.
1415		2290
1416	=head3 Watcher-Specific Functions and Data Members	2291	=head3 Watcher-Specific Functions and Data Members
1417		2292
1418	=over 4	2293	=over 4
1419		2294
…		…
1428		2303
1429	The signal the watcher watches out for.	2304	The signal the watcher watches out for.
1430		2305
1431	=back	2306	=back
1432		2307
		2308	=head3 Examples
		2309
		2310	Example: Try to exit cleanly on SIGINT.
		2311
		2312	static void
		2313	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2314	{
		2315	ev_break (loop, EVBREAK_ALL);
		2316	}
		2317
		2318	ev_signal signal_watcher;
		2319	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2320	ev_signal_start (loop, &signal_watcher);
		2321
1433		2322
1434	=head2 C<ev_child> - watch out for process status changes	2323	=head2 C<ev_child> - watch out for process status changes
1435		2324
1436	Child watchers trigger when your process receives a SIGCHLD in response to	2325	Child watchers trigger when your process receives a SIGCHLD in response to
1437	some child status changes (most typically when a child of yours dies).	2326	some child status changes (most typically when a child of yours dies or
		2327	exits). It is permissible to install a child watcher I<after> the child
		2328	has been forked (which implies it might have already exited), as long
		2329	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2330	forking and then immediately registering a watcher for the child is fine,
		2331	but forking and registering a watcher a few event loop iterations later or
		2332	in the next callback invocation is not.
		2333
		2334	Only the default event loop is capable of handling signals, and therefore
		2335	you can only register child watchers in the default event loop.
		2336
		2337	Due to some design glitches inside libev, child watchers will always be
		2338	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2339	libev)
		2340
		2341	=head3 Process Interaction
		2342
		2343	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2344	initialised. This is necessary to guarantee proper behaviour even if the
		2345	first child watcher is started after the child exits. The occurrence
		2346	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2347	synchronously as part of the event loop processing. Libev always reaps all
		2348	children, even ones not watched.
		2349
		2350	=head3 Overriding the Built-In Processing
		2351
		2352	Libev offers no special support for overriding the built-in child
		2353	processing, but if your application collides with libev's default child
		2354	handler, you can override it easily by installing your own handler for
		2355	C<SIGCHLD> after initialising the default loop, and making sure the
		2356	default loop never gets destroyed. You are encouraged, however, to use an
		2357	event-based approach to child reaping and thus use libev's support for
		2358	that, so other libev users can use C<ev_child> watchers freely.
		2359
		2360	=head3 Stopping the Child Watcher
		2361
		2362	Currently, the child watcher never gets stopped, even when the
		2363	child terminates, so normally one needs to stop the watcher in the
		2364	callback. Future versions of libev might stop the watcher automatically
		2365	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2366	problem).
1438		2367
1439	=head3 Watcher-Specific Functions and Data Members	2368	=head3 Watcher-Specific Functions and Data Members
1440		2369
1441	=over 4	2370	=over 4
1442		2371
…		…
1468		2397
1469	=back	2398	=back
1470		2399
1471	=head3 Examples	2400	=head3 Examples
1472		2401
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	2402	Example: C<fork()> a new process and install a child handler to wait for
		2403	its completion.
1474		2404
		2405	ev_child cw;
		2406
1475	static void	2407	static void
1476	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2408	child_cb (EV_P_ ev_child *w, int revents)
1477	{	2409	{
1478	ev_unloop (loop, EVUNLOOP_ALL);	2410	ev_child_stop (EV_A_ w);
		2411	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1479	}	2412	}
1480		2413
1481	struct ev_signal signal_watcher;	2414	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2415
1483	ev_signal_start (loop, &sigint_cb);	2416	if (pid < 0)
		2417	// error
		2418	else if (pid == 0)
		2419	{
		2420	// the forked child executes here
		2421	exit (1);
		2422	}
		2423	else
		2424	{
		2425	ev_child_init (&cw, child_cb, pid, 0);
		2426	ev_child_start (EV_DEFAULT_ &cw);
		2427	}
1484		2428
1485		2429
1486	=head2 C<ev_stat> - did the file attributes just change?	2430	=head2 C<ev_stat> - did the file attributes just change?
1487		2431
1488	This watches a filesystem path for attribute changes. That is, it calls	2432	This watches a file system path for attribute changes. That is, it calls
1489	C<stat> regularly (or when the OS says it changed) and sees if it changed	2433	C<stat> on that path in regular intervals (or when the OS says it changed)
1490	compared to the last time, invoking the callback if it did.	2434	and sees if it changed compared to the last time, invoking the callback if
		2435	it did.
1491		2436
1492	The path does not need to exist: changing from "path exists" to "path does	2437	The path does not need to exist: changing from "path exists" to "path does
1493	not exist" is a status change like any other. The condition "path does	2438	not exist" is a status change like any other. The condition "path does not
1494	not exist" is signified by the C<st_nlink> field being zero (which is	2439	exist" (or more correctly "path cannot be stat'ed") is signified by the
1495	otherwise always forced to be at least one) and all the other fields of	2440	C<st_nlink> field being zero (which is otherwise always forced to be at
1496	the stat buffer having unspecified contents.	2441	least one) and all the other fields of the stat buffer having unspecified
		2442	contents.
1497		2443
1498	The path I<should> be absolute and I<must not> end in a slash. If it is	2444	The path I<must not> end in a slash or contain special components such as
		2445	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1499	relative and your working directory changes, the behaviour is undefined.	2446	your working directory changes, then the behaviour is undefined.
1500		2447
1501	Since there is no standard to do this, the portable implementation simply	2448	Since there is no portable change notification interface available, the
1502	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2449	portable implementation simply calls C<stat(2)> regularly on the path
1503	can specify a recommended polling interval for this case. If you specify	2450	to see if it changed somehow. You can specify a recommended polling
1504	a polling interval of C<0> (highly recommended!) then a I<suitable,	2451	interval for this case. If you specify a polling interval of C<0> (highly
1505	unspecified default> value will be used (which you can expect to be around	2452	recommended!) then a I<suitable, unspecified default> value will be used
1506	five seconds, although this might change dynamically). Libev will also	2453	(which you can expect to be around five seconds, although this might
1507	impose a minimum interval which is currently around C<0.1>, but thats	2454	change dynamically). Libev will also impose a minimum interval which is
1508	usually overkill.	2455	currently around C<0.1>, but that's usually overkill.
1509		2456
1510	This watcher type is not meant for massive numbers of stat watchers,	2457	This watcher type is not meant for massive numbers of stat watchers,
1511	as even with OS-supported change notifications, this can be	2458	as even with OS-supported change notifications, this can be
1512	resource-intensive.	2459	resource-intensive.
1513		2460
1514	At the time of this writing, only the Linux inotify interface is	2461	At the time of this writing, the only OS-specific interface implemented
1515	implemented (implementing kqueue support is left as an exercise for the	2462	is the Linux inotify interface (implementing kqueue support is left as an
1516	reader). Inotify will be used to give hints only and should not change the	2463	exercise for the reader. Note, however, that the author sees no way of
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2464	implementing C<ev_stat> semantics with kqueue, except as a hint).
1518	to fall back to regular polling again even with inotify, but changes are
1519	usually detected immediately, and if the file exists there will be no
1520	polling.
1521		2465
1522	=head3 Inotify	2466	=head3 ABI Issues (Largefile Support)
1523		2467
		2468	Libev by default (unless the user overrides this) uses the default
		2469	compilation environment, which means that on systems with large file
		2470	support disabled by default, you get the 32 bit version of the stat
		2471	structure. When using the library from programs that change the ABI to
		2472	use 64 bit file offsets the programs will fail. In that case you have to
		2473	compile libev with the same flags to get binary compatibility. This is
		2474	obviously the case with any flags that change the ABI, but the problem is
		2475	most noticeably displayed with ev_stat and large file support.
		2476
		2477	The solution for this is to lobby your distribution maker to make large
		2478	file interfaces available by default (as e.g. FreeBSD does) and not
		2479	optional. Libev cannot simply switch on large file support because it has
		2480	to exchange stat structures with application programs compiled using the
		2481	default compilation environment.
		2482
		2483	=head3 Inotify and Kqueue
		2484
1524	When C<inotify (7)> support has been compiled into libev (generally only	2485	When C<inotify (7)> support has been compiled into libev and present at
1525	available on Linux) and present at runtime, it will be used to speed up	2486	runtime, it will be used to speed up change detection where possible. The
1526	change detection where possible. The inotify descriptor will be created lazily	2487	inotify descriptor will be created lazily when the first C<ev_stat>
1527	when the first C<ev_stat> watcher is being started.	2488	watcher is being started.
1528		2489
1529	Inotify presense does not change the semantics of C<ev_stat> watchers	2490	Inotify presence does not change the semantics of C<ev_stat> watchers
1530	except that changes might be detected earlier, and in some cases, to avoid	2491	except that changes might be detected earlier, and in some cases, to avoid
1531	making regular C<stat> calls. Even in the presense of inotify support	2492	making regular C<stat> calls. Even in the presence of inotify support
1532	there are many cases where libev has to resort to regular C<stat> polling.	2493	there are many cases where libev has to resort to regular C<stat> polling,
		2494	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2495	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2496	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2497	xfs are fully working) libev usually gets away without polling.
1533		2498
1534	(There is no support for kqueue, as apparently it cannot be used to	2499	There is no support for kqueue, as apparently it cannot be used to
1535	implement this functionality, due to the requirement of having a file	2500	implement this functionality, due to the requirement of having a file
1536	descriptor open on the object at all times).	2501	descriptor open on the object at all times, and detecting renames, unlinks
		2502	etc. is difficult.
		2503
		2504	=head3 C<stat ()> is a synchronous operation
		2505
		2506	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2507	the process. The exception are C<ev_stat> watchers - those call C<stat
		2508	()>, which is a synchronous operation.
		2509
		2510	For local paths, this usually doesn't matter: unless the system is very
		2511	busy or the intervals between stat's are large, a stat call will be fast,
		2512	as the path data is usually in memory already (except when starting the
		2513	watcher).
		2514
		2515	For networked file systems, calling C<stat ()> can block an indefinite
		2516	time due to network issues, and even under good conditions, a stat call
		2517	often takes multiple milliseconds.
		2518
		2519	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2520	paths, although this is fully supported by libev.
1537		2521
1538	=head3 The special problem of stat time resolution	2522	=head3 The special problem of stat time resolution
1539		2523
1540	The C<stat ()> syscall only supports full-second resolution portably, and	2524	The C<stat ()> system call only supports full-second resolution portably,
1541	even on systems where the resolution is higher, many filesystems still	2525	and even on systems where the resolution is higher, most file systems
1542	only support whole seconds.	2526	still only support whole seconds.
1543		2527
1544	That means that, if the time is the only thing that changes, you might	2528	That means that, if the time is the only thing that changes, you can
1545	miss updates: on the first update, C<ev_stat> detects a change and calls	2529	easily miss updates: on the first update, C<ev_stat> detects a change and
1546	your callback, which does something. When there is another update within	2530	calls your callback, which does something. When there is another update
1547	the same second, C<ev_stat> will be unable to detect it.	2531	within the same second, C<ev_stat> will be unable to detect unless the
		2532	stat data does change in other ways (e.g. file size).
1548		2533
1549	The solution to this is to delay acting on a change for a second (or till	2534	The solution to this is to delay acting on a change for slightly more
1550	the next second boundary), using a roughly one-second delay C<ev_timer>	2535	than a second (or till slightly after the next full second boundary), using
1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2536	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1552	is added to work around small timing inconsistencies of some operating	2537	ev_timer_again (loop, w)>).
1553	systems.	2538
		2539	The C<.02> offset is added to work around small timing inconsistencies
		2540	of some operating systems (where the second counter of the current time
		2541	might be be delayed. One such system is the Linux kernel, where a call to
		2542	C<gettimeofday> might return a timestamp with a full second later than
		2543	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2544	update file times then there will be a small window where the kernel uses
		2545	the previous second to update file times but libev might already execute
		2546	the timer callback).
1554		2547
1555	=head3 Watcher-Specific Functions and Data Members	2548	=head3 Watcher-Specific Functions and Data Members
1556		2549
1557	=over 4	2550	=over 4
1558		2551
…		…
1564	C<path>. The C<interval> is a hint on how quickly a change is expected to	2557	C<path>. The C<interval> is a hint on how quickly a change is expected to
1565	be detected and should normally be specified as C<0> to let libev choose	2558	be detected and should normally be specified as C<0> to let libev choose
1566	a suitable value. The memory pointed to by C<path> must point to the same	2559	a suitable value. The memory pointed to by C<path> must point to the same
1567	path for as long as the watcher is active.	2560	path for as long as the watcher is active.
1568		2561
1569	The callback will be receive C<EV_STAT> when a change was detected,	2562	The callback will receive an C<EV_STAT> event when a change was detected,
1570	relative to the attributes at the time the watcher was started (or the	2563	relative to the attributes at the time the watcher was started (or the
1571	last change was detected).	2564	last change was detected).
1572		2565
1573	=item ev_stat_stat (ev_stat *)	2566	=item ev_stat_stat (loop, ev_stat *)
1574		2567
1575	Updates the stat buffer immediately with new values. If you change the	2568	Updates the stat buffer immediately with new values. If you change the
1576	watched path in your callback, you could call this fucntion to avoid	2569	watched path in your callback, you could call this function to avoid
1577	detecting this change (while introducing a race condition). Can also be	2570	detecting this change (while introducing a race condition if you are not
1578	useful simply to find out the new values.	2571	the only one changing the path). Can also be useful simply to find out the
		2572	new values.
1579		2573
1580	=item ev_statdata attr [read-only]	2574	=item ev_statdata attr [read-only]
1581		2575
1582	The most-recently detected attributes of the file. Although the type is of	2576	The most-recently detected attributes of the file. Although the type is
1583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2577	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1584	suitable for your system. If the C<st_nlink> member is C<0>, then there	2578	suitable for your system, but you can only rely on the POSIX-standardised
		2579	members to be present. If the C<st_nlink> member is C<0>, then there was
1585	was some error while C<stat>ing the file.	2580	some error while C<stat>ing the file.
1586		2581
1587	=item ev_statdata prev [read-only]	2582	=item ev_statdata prev [read-only]
1588		2583
1589	The previous attributes of the file. The callback gets invoked whenever	2584	The previous attributes of the file. The callback gets invoked whenever
1590	C<prev> != C<attr>.	2585	C<prev> != C<attr>, or, more precisely, one or more of these members
		2586	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2587	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1591		2588
1592	=item ev_tstamp interval [read-only]	2589	=item ev_tstamp interval [read-only]
1593		2590
1594	The specified interval.	2591	The specified interval.
1595		2592
1596	=item const char *path [read-only]	2593	=item const char *path [read-only]
1597		2594
1598	The filesystem path that is being watched.	2595	The file system path that is being watched.
1599		2596
1600	=back	2597	=back
1601		2598
1602	=head3 Examples	2599	=head3 Examples
1603		2600
1604	Example: Watch C</etc/passwd> for attribute changes.	2601	Example: Watch C</etc/passwd> for attribute changes.
1605		2602
1606	static void	2603	static void
1607	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2604	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1608	{	2605	{
1609	/* /etc/passwd changed in some way */	2606	/* /etc/passwd changed in some way */
1610	if (w->attr.st_nlink)	2607	if (w->attr.st_nlink)
1611	{	2608	{
1612	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2609	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1613	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2610	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1614	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2611	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1615	}	2612	}
1616	else	2613	else
1617	/* you shalt not abuse printf for puts */	2614	/* you shalt not abuse printf for puts */
1618	puts ("wow, /etc/passwd is not there, expect problems. "	2615	puts ("wow, /etc/passwd is not there, expect problems. "
1619	"if this is windows, they already arrived\n");	2616	"if this is windows, they already arrived\n");
1620	}	2617	}
1621		2618
1622	...	2619	...
1623	ev_stat passwd;	2620	ev_stat passwd;
1624		2621
1625	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2622	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1626	ev_stat_start (loop, &passwd);	2623	ev_stat_start (loop, &passwd);
1627		2624
1628	Example: Like above, but additionally use a one-second delay so we do not	2625	Example: Like above, but additionally use a one-second delay so we do not
1629	miss updates (however, frequent updates will delay processing, too, so	2626	miss updates (however, frequent updates will delay processing, too, so
1630	one might do the work both on C<ev_stat> callback invocation I<and> on	2627	one might do the work both on C<ev_stat> callback invocation I<and> on
1631	C<ev_timer> callback invocation).	2628	C<ev_timer> callback invocation).
1632		2629
1633	static ev_stat passwd;	2630	static ev_stat passwd;
1634	static ev_timer timer;	2631	static ev_timer timer;
1635		2632
1636	static void	2633	static void
1637	timer_cb (EV_P_ ev_timer *w, int revents)	2634	timer_cb (EV_P_ ev_timer *w, int revents)
1638	{	2635	{
1639	ev_timer_stop (EV_A_ w);	2636	ev_timer_stop (EV_A_ w);
1640		2637
1641	/* now it's one second after the most recent passwd change */	2638	/* now it's one second after the most recent passwd change */
1642	}	2639	}
1643		2640
1644	static void	2641	static void
1645	stat_cb (EV_P_ ev_stat *w, int revents)	2642	stat_cb (EV_P_ ev_stat *w, int revents)
1646	{	2643	{
1647	/* reset the one-second timer */	2644	/* reset the one-second timer */
1648	ev_timer_again (EV_A_ &timer);	2645	ev_timer_again (EV_A_ &timer);
1649	}	2646	}
1650		2647
1651	...	2648	...
1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2649	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1653	ev_stat_start (loop, &passwd);	2650	ev_stat_start (loop, &passwd);
1654	ev_timer_init (&timer, timer_cb, 0., 1.01);	2651	ev_timer_init (&timer, timer_cb, 0., 1.02);
1655		2652
1656		2653
1657	=head2 C<ev_idle> - when you've got nothing better to do...	2654	=head2 C<ev_idle> - when you've got nothing better to do...
1658		2655
1659	Idle watchers trigger events when no other events of the same or higher	2656	Idle watchers trigger events when no other events of the same or higher
1660	priority are pending (prepare, check and other idle watchers do not	2657	priority are pending (prepare, check and other idle watchers do not count
1661	count).	2658	as receiving "events").
1662		2659
1663	That is, as long as your process is busy handling sockets or timeouts	2660	That is, as long as your process is busy handling sockets or timeouts
1664	(or even signals, imagine) of the same or higher priority it will not be	2661	(or even signals, imagine) of the same or higher priority it will not be
1665	triggered. But when your process is idle (or only lower-priority watchers	2662	triggered. But when your process is idle (or only lower-priority watchers
1666	are pending), the idle watchers are being called once per event loop	2663	are pending), the idle watchers are being called once per event loop
…		…
1677		2674
1678	=head3 Watcher-Specific Functions and Data Members	2675	=head3 Watcher-Specific Functions and Data Members
1679		2676
1680	=over 4	2677	=over 4
1681		2678
1682	=item ev_idle_init (ev_signal *, callback)	2679	=item ev_idle_init (ev_idle *, callback)
1683		2680
1684	Initialises and configures the idle watcher - it has no parameters of any	2681	Initialises and configures the idle watcher - it has no parameters of any
1685	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2682	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1686	believe me.	2683	believe me.
1687		2684
…		…
1690	=head3 Examples	2687	=head3 Examples
1691		2688
1692	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2689	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1693	callback, free it. Also, use no error checking, as usual.	2690	callback, free it. Also, use no error checking, as usual.
1694		2691
1695	static void	2692	static void
1696	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2693	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1697	{	2694	{
1698	free (w);	2695	free (w);
1699	// now do something you wanted to do when the program has	2696	// now do something you wanted to do when the program has
1700	// no longer anything immediate to do.	2697	// no longer anything immediate to do.
1701	}	2698	}
1702		2699
1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2700	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1704	ev_idle_init (idle_watcher, idle_cb);	2701	ev_idle_init (idle_watcher, idle_cb);
1705	ev_idle_start (loop, idle_cb);	2702	ev_idle_start (loop, idle_watcher);
1706		2703
1707		2704
1708	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2705	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1709		2706
1710	Prepare and check watchers are usually (but not always) used in tandem:	2707	Prepare and check watchers are usually (but not always) used in pairs:
1711	prepare watchers get invoked before the process blocks and check watchers	2708	prepare watchers get invoked before the process blocks and check watchers
1712	afterwards.	2709	afterwards.
1713		2710
1714	You I<must not> call C<ev_loop> or similar functions that enter	2711	You I<must not> call C<ev_run> or similar functions that enter
1715	the current event loop from either C<ev_prepare> or C<ev_check>	2712	the current event loop from either C<ev_prepare> or C<ev_check>
1716	watchers. Other loops than the current one are fine, however. The	2713	watchers. Other loops than the current one are fine, however. The
1717	rationale behind this is that you do not need to check for recursion in	2714	rationale behind this is that you do not need to check for recursion in
1718	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2715	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1719	C<ev_check> so if you have one watcher of each kind they will always be	2716	C<ev_check> so if you have one watcher of each kind they will always be
1720	called in pairs bracketing the blocking call.	2717	called in pairs bracketing the blocking call.
1721		2718
1722	Their main purpose is to integrate other event mechanisms into libev and	2719	Their main purpose is to integrate other event mechanisms into libev and
1723	their use is somewhat advanced. This could be used, for example, to track	2720	their use is somewhat advanced. They could be used, for example, to track
1724	variable changes, implement your own watchers, integrate net-snmp or a	2721	variable changes, implement your own watchers, integrate net-snmp or a
1725	coroutine library and lots more. They are also occasionally useful if	2722	coroutine library and lots more. They are also occasionally useful if
1726	you cache some data and want to flush it before blocking (for example,	2723	you cache some data and want to flush it before blocking (for example,
1727	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2724	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1728	watcher).	2725	watcher).
1729		2726
1730	This is done by examining in each prepare call which file descriptors need	2727	This is done by examining in each prepare call which file descriptors
1731	to be watched by the other library, registering C<ev_io> watchers for	2728	need to be watched by the other library, registering C<ev_io> watchers
1732	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2729	for them and starting an C<ev_timer> watcher for any timeouts (many
1733	provide just this functionality). Then, in the check watcher you check for	2730	libraries provide exactly this functionality). Then, in the check watcher,
1734	any events that occured (by checking the pending status of all watchers	2731	you check for any events that occurred (by checking the pending status
1735	and stopping them) and call back into the library. The I/O and timer	2732	of all watchers and stopping them) and call back into the library. The
1736	callbacks will never actually be called (but must be valid nevertheless,	2733	I/O and timer callbacks will never actually be called (but must be valid
1737	because you never know, you know?).	2734	nevertheless, because you never know, you know?).
1738		2735
1739	As another example, the Perl Coro module uses these hooks to integrate	2736	As another example, the Perl Coro module uses these hooks to integrate
1740	coroutines into libev programs, by yielding to other active coroutines	2737	coroutines into libev programs, by yielding to other active coroutines
1741	during each prepare and only letting the process block if no coroutines	2738	during each prepare and only letting the process block if no coroutines
1742	are ready to run (it's actually more complicated: it only runs coroutines	2739	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1745	loop from blocking if lower-priority coroutines are active, thus mapping	2742	loop from blocking if lower-priority coroutines are active, thus mapping
1746	low-priority coroutines to idle/background tasks).	2743	low-priority coroutines to idle/background tasks).
1747		2744
1748	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2745	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1749	priority, to ensure that they are being run before any other watchers	2746	priority, to ensure that they are being run before any other watchers
		2747	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2748
1750	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2749	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1751	too) should not activate ("feed") events into libev. While libev fully	2750	activate ("feed") events into libev. While libev fully supports this, they
1752	supports this, they will be called before other C<ev_check> watchers	2751	might get executed before other C<ev_check> watchers did their job. As
1753	did their job. As C<ev_check> watchers are often used to embed other	2752	C<ev_check> watchers are often used to embed other (non-libev) event
1754	(non-libev) event loops those other event loops might be in an unusable	2753	loops those other event loops might be in an unusable state until their
1755	state until their C<ev_check> watcher ran (always remind yourself to	2754	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1756	coexist peacefully with others).	2755	others).
1757		2756
1758	=head3 Watcher-Specific Functions and Data Members	2757	=head3 Watcher-Specific Functions and Data Members
1759		2758
1760	=over 4	2759	=over 4
1761		2760
…		…
1763		2762
1764	=item ev_check_init (ev_check *, callback)	2763	=item ev_check_init (ev_check *, callback)
1765		2764
1766	Initialises and configures the prepare or check watcher - they have no	2765	Initialises and configures the prepare or check watcher - they have no
1767	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2766	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1768	macros, but using them is utterly, utterly and completely pointless.	2767	macros, but using them is utterly, utterly, utterly and completely
		2768	pointless.
1769		2769
1770	=back	2770	=back
1771		2771
1772	=head3 Examples	2772	=head3 Examples
1773		2773
1774	There are a number of principal ways to embed other event loops or modules	2774	There are a number of principal ways to embed other event loops or modules
1775	into libev. Here are some ideas on how to include libadns into libev	2775	into libev. Here are some ideas on how to include libadns into libev
1776	(there is a Perl module named C<EV::ADNS> that does this, which you could	2776	(there is a Perl module named C<EV::ADNS> that does this, which you could
1777	use for an actually working example. Another Perl module named C<EV::Glib>	2777	use as a working example. Another Perl module named C<EV::Glib> embeds a
1778	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2778	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1779	into the Glib event loop).	2779	Glib event loop).
1780		2780
1781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1782	and in a check watcher, destroy them and call into libadns. What follows	2782	and in a check watcher, destroy them and call into libadns. What follows
1783	is pseudo-code only of course. This requires you to either use a low	2783	is pseudo-code only of course. This requires you to either use a low
1784	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2784	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1785	the callbacks for the IO/timeout watchers might not have been called yet.	2785	the callbacks for the IO/timeout watchers might not have been called yet.
1786		2786
1787	static ev_io iow [nfd];	2787	static ev_io iow [nfd];
1788	static ev_timer tw;	2788	static ev_timer tw;
1789		2789
1790	static void	2790	static void
1791	io_cb (ev_loop *loop, ev_io *w, int revents)	2791	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1792	{	2792	{
1793	}	2793	}
1794		2794
1795	// create io watchers for each fd and a timer before blocking	2795	// create io watchers for each fd and a timer before blocking
1796	static void	2796	static void
1797	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2797	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1798	{	2798	{
1799	int timeout = 3600000;	2799	int timeout = 3600000;
1800	struct pollfd fds [nfd];	2800	struct pollfd fds [nfd];
1801	// actual code will need to loop here and realloc etc.	2801	// actual code will need to loop here and realloc etc.
1802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1803		2803
1804	/* the callback is illegal, but won't be called as we stop during check */	2804	/* the callback is illegal, but won't be called as we stop during check */
1805	ev_timer_init (&tw, 0, timeout * 1e-3);	2805	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1806	ev_timer_start (loop, &tw);	2806	ev_timer_start (loop, &tw);
1807		2807
1808	// create one ev_io per pollfd	2808	// create one ev_io per pollfd
1809	for (int i = 0; i < nfd; ++i)	2809	for (int i = 0; i < nfd; ++i)
1810	{	2810	{
1811	ev_io_init (iow + i, io_cb, fds [i].fd,	2811	ev_io_init (iow + i, io_cb, fds [i].fd,
1812	((fds [i].events & POLLIN ? EV_READ : 0)	2812	((fds [i].events & POLLIN ? EV_READ : 0)
1813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1814		2814
1815	fds [i].revents = 0;	2815	fds [i].revents = 0;
1816	ev_io_start (loop, iow + i);	2816	ev_io_start (loop, iow + i);
1817	}	2817	}
1818	}	2818	}
1819		2819
1820	// stop all watchers after blocking	2820	// stop all watchers after blocking
1821	static void	2821	static void
1822	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2822	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1823	{	2823	{
1824	ev_timer_stop (loop, &tw);	2824	ev_timer_stop (loop, &tw);
1825		2825
1826	for (int i = 0; i < nfd; ++i)	2826	for (int i = 0; i < nfd; ++i)
1827	{	2827	{
1828	// set the relevant poll flags	2828	// set the relevant poll flags
1829	// could also call adns_processreadable etc. here	2829	// could also call adns_processreadable etc. here
1830	struct pollfd *fd = fds + i;	2830	struct pollfd *fd = fds + i;
1831	int revents = ev_clear_pending (iow + i);	2831	int revents = ev_clear_pending (iow + i);
1832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1834		2834
1835	// now stop the watcher	2835	// now stop the watcher
1836	ev_io_stop (loop, iow + i);	2836	ev_io_stop (loop, iow + i);
1837	}	2837	}
1838		2838
1839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1840	}	2840	}
1841		2841
1842	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2842	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1843	in the prepare watcher and would dispose of the check watcher.	2843	in the prepare watcher and would dispose of the check watcher.
1844		2844
1845	Method 3: If the module to be embedded supports explicit event	2845	Method 3: If the module to be embedded supports explicit event
1846	notification (adns does), you can also make use of the actual watcher	2846	notification (libadns does), you can also make use of the actual watcher
1847	callbacks, and only destroy/create the watchers in the prepare watcher.	2847	callbacks, and only destroy/create the watchers in the prepare watcher.
1848		2848
1849	static void	2849	static void
1850	timer_cb (EV_P_ ev_timer *w, int revents)	2850	timer_cb (EV_P_ ev_timer *w, int revents)
1851	{	2851	{
1852	adns_state ads = (adns_state)w->data;	2852	adns_state ads = (adns_state)w->data;
1853	update_now (EV_A);	2853	update_now (EV_A);
1854		2854
1855	adns_processtimeouts (ads, &tv_now);	2855	adns_processtimeouts (ads, &tv_now);
1856	}	2856	}
1857		2857
1858	static void	2858	static void
1859	io_cb (EV_P_ ev_io *w, int revents)	2859	io_cb (EV_P_ ev_io *w, int revents)
1860	{	2860	{
1861	adns_state ads = (adns_state)w->data;	2861	adns_state ads = (adns_state)w->data;
1862	update_now (EV_A);	2862	update_now (EV_A);
1863		2863
1864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1866	}	2866	}
1867		2867
1868	// do not ever call adns_afterpoll	2868	// do not ever call adns_afterpoll
1869		2869
1870	Method 4: Do not use a prepare or check watcher because the module you	2870	Method 4: Do not use a prepare or check watcher because the module you
1871	want to embed is too inflexible to support it. Instead, youc na override	2871	want to embed is not flexible enough to support it. Instead, you can
1872	their poll function. The drawback with this solution is that the main	2872	override their poll function. The drawback with this solution is that the
1873	loop is now no longer controllable by EV. The C<Glib::EV> module does	2873	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1874	this.	2874	this approach, effectively embedding EV as a client into the horrible
		2875	libglib event loop.
1875		2876
1876	static gint	2877	static gint
1877	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2878	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1878	{	2879	{
1879	int got_events = 0;	2880	int got_events = 0;
1880		2881
1881	for (n = 0; n < nfds; ++n)	2882	for (n = 0; n < nfds; ++n)
1882	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2883	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1883		2884
1884	if (timeout >= 0)	2885	if (timeout >= 0)
1885	// create/start timer	2886	// create/start timer
1886		2887
1887	// poll	2888	// poll
1888	ev_loop (EV_A_ 0);	2889	ev_run (EV_A_ 0);
1889		2890
1890	// stop timer again	2891	// stop timer again
1891	if (timeout >= 0)	2892	if (timeout >= 0)
1892	ev_timer_stop (EV_A_ &to);	2893	ev_timer_stop (EV_A_ &to);
1893		2894
1894	// stop io watchers again - their callbacks should have set	2895	// stop io watchers again - their callbacks should have set
1895	for (n = 0; n < nfds; ++n)	2896	for (n = 0; n < nfds; ++n)
1896	ev_io_stop (EV_A_ iow [n]);	2897	ev_io_stop (EV_A_ iow [n]);
1897		2898
1898	return got_events;	2899	return got_events;
1899	}	2900	}
1900		2901
1901		2902
1902	=head2 C<ev_embed> - when one backend isn't enough...	2903	=head2 C<ev_embed> - when one backend isn't enough...
1903		2904
1904	This is a rather advanced watcher type that lets you embed one event loop	2905	This is a rather advanced watcher type that lets you embed one event loop
…		…
1910	prioritise I/O.	2911	prioritise I/O.
1911		2912
1912	As an example for a bug workaround, the kqueue backend might only support	2913	As an example for a bug workaround, the kqueue backend might only support
1913	sockets on some platform, so it is unusable as generic backend, but you	2914	sockets on some platform, so it is unusable as generic backend, but you
1914	still want to make use of it because you have many sockets and it scales	2915	still want to make use of it because you have many sockets and it scales
1915	so nicely. In this case, you would create a kqueue-based loop and embed it	2916	so nicely. In this case, you would create a kqueue-based loop and embed
1916	into your default loop (which might use e.g. poll). Overall operation will	2917	it into your default loop (which might use e.g. poll). Overall operation
1917	be a bit slower because first libev has to poll and then call kevent, but	2918	will be a bit slower because first libev has to call C<poll> and then
1918	at least you can use both at what they are best.	2919	C<kevent>, but at least you can use both mechanisms for what they are
		2920	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1919		2921
1920	As for prioritising I/O: rarely you have the case where some fds have	2922	As for prioritising I/O: under rare circumstances you have the case where
1921	to be watched and handled very quickly (with low latency), and even	2923	some fds have to be watched and handled very quickly (with low latency),
1922	priorities and idle watchers might have too much overhead. In this case	2924	and even priorities and idle watchers might have too much overhead. In
1923	you would put all the high priority stuff in one loop and all the rest in	2925	this case you would put all the high priority stuff in one loop and all
1924	a second one, and embed the second one in the first.	2926	the rest in a second one, and embed the second one in the first.
1925		2927
1926	As long as the watcher is active, the callback will be invoked every time	2928	As long as the watcher is active, the callback will be invoked every
1927	there might be events pending in the embedded loop. The callback must then	2929	time there might be events pending in the embedded loop. The callback
1928	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2930	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1929	their callbacks (you could also start an idle watcher to give the embedded	2931	sweep and invoke their callbacks (the callback doesn't need to invoke the
1930	loop strictly lower priority for example). You can also set the callback	2932	C<ev_embed_sweep> function directly, it could also start an idle watcher
1931	to C<0>, in which case the embed watcher will automatically execute the	2933	to give the embedded loop strictly lower priority for example).
1932	embedded loop sweep.
1933		2934
1934	As long as the watcher is started it will automatically handle events. The	2935	You can also set the callback to C<0>, in which case the embed watcher
1935	callback will be invoked whenever some events have been handled. You can	2936	will automatically execute the embedded loop sweep whenever necessary.
1936	set the callback to C<0> to avoid having to specify one if you are not
1937	interested in that.
1938		2937
1939	Also, there have not currently been made special provisions for forking:	2938	Fork detection will be handled transparently while the C<ev_embed> watcher
1940	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2939	is active, i.e., the embedded loop will automatically be forked when the
1941	but you will also have to stop and restart any C<ev_embed> watchers	2940	embedding loop forks. In other cases, the user is responsible for calling
1942	yourself.	2941	C<ev_loop_fork> on the embedded loop.
1943		2942
1944	Unfortunately, not all backends are embeddable, only the ones returned by	2943	Unfortunately, not all backends are embeddable: only the ones returned by
1945	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2944	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1946	portable one.	2945	portable one.
1947		2946
1948	So when you want to use this feature you will always have to be prepared	2947	So when you want to use this feature you will always have to be prepared
1949	that you cannot get an embeddable loop. The recommended way to get around	2948	that you cannot get an embeddable loop. The recommended way to get around
1950	this is to have a separate variables for your embeddable loop, try to	2949	this is to have a separate variables for your embeddable loop, try to
1951	create it, and if that fails, use the normal loop for everything.	2950	create it, and if that fails, use the normal loop for everything.
1952		2951
		2952	=head3 C<ev_embed> and fork
		2953
		2954	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2955	automatically be applied to the embedded loop as well, so no special
		2956	fork handling is required in that case. When the watcher is not running,
		2957	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2958	as applicable.
		2959
1953	=head3 Watcher-Specific Functions and Data Members	2960	=head3 Watcher-Specific Functions and Data Members
1954		2961
1955	=over 4	2962	=over 4
1956		2963
1957	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2964	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1960		2967
1961	Configures the watcher to embed the given loop, which must be	2968	Configures the watcher to embed the given loop, which must be
1962	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2969	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1963	invoked automatically, otherwise it is the responsibility of the callback	2970	invoked automatically, otherwise it is the responsibility of the callback
1964	to invoke it (it will continue to be called until the sweep has been done,	2971	to invoke it (it will continue to be called until the sweep has been done,
1965	if you do not want thta, you need to temporarily stop the embed watcher).	2972	if you do not want that, you need to temporarily stop the embed watcher).
1966		2973
1967	=item ev_embed_sweep (loop, ev_embed *)	2974	=item ev_embed_sweep (loop, ev_embed *)
1968		2975
1969	Make a single, non-blocking sweep over the embedded loop. This works	2976	Make a single, non-blocking sweep over the embedded loop. This works
1970	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2977	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1971	apropriate way for embedded loops.	2978	appropriate way for embedded loops.
1972		2979
1973	=item struct ev_loop *other [read-only]	2980	=item struct ev_loop *other [read-only]
1974		2981
1975	The embedded event loop.	2982	The embedded event loop.
1976		2983
…		…
1978		2985
1979	=head3 Examples	2986	=head3 Examples
1980		2987
1981	Example: Try to get an embeddable event loop and embed it into the default	2988	Example: Try to get an embeddable event loop and embed it into the default
1982	event loop. If that is not possible, use the default loop. The default	2989	event loop. If that is not possible, use the default loop. The default
1983	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2990	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1984	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2991	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1985	used).	2992	used).
1986		2993
1987	struct ev_loop *loop_hi = ev_default_init (0);	2994	struct ev_loop *loop_hi = ev_default_init (0);
1988	struct ev_loop *loop_lo = 0;	2995	struct ev_loop *loop_lo = 0;
1989	struct ev_embed embed;	2996	ev_embed embed;
1990		2997
1991	// see if there is a chance of getting one that works	2998	// see if there is a chance of getting one that works
1992	// (remember that a flags value of 0 means autodetection)	2999	// (remember that a flags value of 0 means autodetection)
1993	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3000	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1994	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3001	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1995	: 0;	3002	: 0;
1996		3003
1997	// if we got one, then embed it, otherwise default to loop_hi	3004	// if we got one, then embed it, otherwise default to loop_hi
1998	if (loop_lo)	3005	if (loop_lo)
1999	{	3006	{
2000	ev_embed_init (&embed, 0, loop_lo);	3007	ev_embed_init (&embed, 0, loop_lo);
2001	ev_embed_start (loop_hi, &embed);	3008	ev_embed_start (loop_hi, &embed);
2002	}	3009	}
2003	else	3010	else
2004	loop_lo = loop_hi;	3011	loop_lo = loop_hi;
2005		3012
2006	Example: Check if kqueue is available but not recommended and create	3013	Example: Check if kqueue is available but not recommended and create
2007	a kqueue backend for use with sockets (which usually work with any	3014	a kqueue backend for use with sockets (which usually work with any
2008	kqueue implementation). Store the kqueue/socket-only event loop in	3015	kqueue implementation). Store the kqueue/socket-only event loop in
2009	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3016	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2010		3017
2011	struct ev_loop *loop = ev_default_init (0);	3018	struct ev_loop *loop = ev_default_init (0);
2012	struct ev_loop *loop_socket = 0;	3019	struct ev_loop *loop_socket = 0;
2013	struct ev_embed embed;	3020	ev_embed embed;
2014		3021
2015	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3022	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2016	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3023	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2017	{	3024	{
2018	ev_embed_init (&embed, 0, loop_socket);	3025	ev_embed_init (&embed, 0, loop_socket);
2019	ev_embed_start (loop, &embed);	3026	ev_embed_start (loop, &embed);
2020	}	3027	}
2021		3028
2022	if (!loop_socket)	3029	if (!loop_socket)
2023	loop_socket = loop;	3030	loop_socket = loop;
2024		3031
2025	// now use loop_socket for all sockets, and loop for everything else	3032	// now use loop_socket for all sockets, and loop for everything else
2026		3033
2027		3034
2028	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3035	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2029		3036
2030	Fork watchers are called when a C<fork ()> was detected (usually because	3037	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2033	event loop blocks next and before C<ev_check> watchers are being called,	3040	event loop blocks next and before C<ev_check> watchers are being called,
2034	and only in the child after the fork. If whoever good citizen calling	3041	and only in the child after the fork. If whoever good citizen calling
2035	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3042	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2036	handlers will be invoked, too, of course.	3043	handlers will be invoked, too, of course.
2037		3044
		3045	=head3 The special problem of life after fork - how is it possible?
		3046
		3047	Most uses of C<fork()> consist of forking, then some simple calls to set
		3048	up/change the process environment, followed by a call to C<exec()>. This
		3049	sequence should be handled by libev without any problems.
		3050
		3051	This changes when the application actually wants to do event handling
		3052	in the child, or both parent in child, in effect "continuing" after the
		3053	fork.
		3054
		3055	The default mode of operation (for libev, with application help to detect
		3056	forks) is to duplicate all the state in the child, as would be expected
		3057	when I<either> the parent I<or> the child process continues.
		3058
		3059	When both processes want to continue using libev, then this is usually the
		3060	wrong result. In that case, usually one process (typically the parent) is
		3061	supposed to continue with all watchers in place as before, while the other
		3062	process typically wants to start fresh, i.e. without any active watchers.
		3063
		3064	The cleanest and most efficient way to achieve that with libev is to
		3065	simply create a new event loop, which of course will be "empty", and
		3066	use that for new watchers. This has the advantage of not touching more
		3067	memory than necessary, and thus avoiding the copy-on-write, and the
		3068	disadvantage of having to use multiple event loops (which do not support
		3069	signal watchers).
		3070
		3071	When this is not possible, or you want to use the default loop for
		3072	other reasons, then in the process that wants to start "fresh", call
		3073	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		3074	the default loop will "orphan" (not stop) all registered watchers, so you
		3075	have to be careful not to execute code that modifies those watchers. Note
		3076	also that in that case, you have to re-register any signal watchers.
		3077
2038	=head3 Watcher-Specific Functions and Data Members	3078	=head3 Watcher-Specific Functions and Data Members
2039		3079
2040	=over 4	3080	=over 4
2041		3081
2042	=item ev_fork_init (ev_signal *, callback)	3082	=item ev_fork_init (ev_signal *, callback)
…		…
2046	believe me.	3086	believe me.
2047		3087
2048	=back	3088	=back
2049		3089
2050		3090
		3091	=head2 C<ev_async> - how to wake up an event loop
		3092
		3093	In general, you cannot use an C<ev_run> from multiple threads or other
		3094	asynchronous sources such as signal handlers (as opposed to multiple event
		3095	loops - those are of course safe to use in different threads).
		3096
		3097	Sometimes, however, you need to wake up an event loop you do not control,
		3098	for example because it belongs to another thread. This is what C<ev_async>
		3099	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3100	it by calling C<ev_async_send>, which is thread- and signal safe.
		3101
		3102	This functionality is very similar to C<ev_signal> watchers, as signals,
		3103	too, are asynchronous in nature, and signals, too, will be compressed
		3104	(i.e. the number of callback invocations may be less than the number of
		3105	C<ev_async_sent> calls).
		3106
		3107	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3108	just the default loop.
		3109
		3110	=head3 Queueing
		3111
		3112	C<ev_async> does not support queueing of data in any way. The reason
		3113	is that the author does not know of a simple (or any) algorithm for a
		3114	multiple-writer-single-reader queue that works in all cases and doesn't
		3115	need elaborate support such as pthreads or unportable memory access
		3116	semantics.
		3117
		3118	That means that if you want to queue data, you have to provide your own
		3119	queue. But at least I can tell you how to implement locking around your
		3120	queue:
		3121
		3122	=over 4
		3123
		3124	=item queueing from a signal handler context
		3125
		3126	To implement race-free queueing, you simply add to the queue in the signal
		3127	handler but you block the signal handler in the watcher callback. Here is
		3128	an example that does that for some fictitious SIGUSR1 handler:
		3129
		3130	static ev_async mysig;
		3131
		3132	static void
		3133	sigusr1_handler (void)
		3134	{
		3135	sometype data;
		3136
		3137	// no locking etc.
		3138	queue_put (data);
		3139	ev_async_send (EV_DEFAULT_ &mysig);
		3140	}
		3141
		3142	static void
		3143	mysig_cb (EV_P_ ev_async *w, int revents)
		3144	{
		3145	sometype data;
		3146	sigset_t block, prev;
		3147
		3148	sigemptyset (&block);
		3149	sigaddset (&block, SIGUSR1);
		3150	sigprocmask (SIG_BLOCK, &block, &prev);
		3151
		3152	while (queue_get (&data))
		3153	process (data);
		3154
		3155	if (sigismember (&prev, SIGUSR1)
		3156	sigprocmask (SIG_UNBLOCK, &block, 0);
		3157	}
		3158
		3159	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3160	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3161	either...).
		3162
		3163	=item queueing from a thread context
		3164
		3165	The strategy for threads is different, as you cannot (easily) block
		3166	threads but you can easily preempt them, so to queue safely you need to
		3167	employ a traditional mutex lock, such as in this pthread example:
		3168
		3169	static ev_async mysig;
		3170	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3171
		3172	static void
		3173	otherthread (void)
		3174	{
		3175	// only need to lock the actual queueing operation
		3176	pthread_mutex_lock (&mymutex);
		3177	queue_put (data);
		3178	pthread_mutex_unlock (&mymutex);
		3179
		3180	ev_async_send (EV_DEFAULT_ &mysig);
		3181	}
		3182
		3183	static void
		3184	mysig_cb (EV_P_ ev_async *w, int revents)
		3185	{
		3186	pthread_mutex_lock (&mymutex);
		3187
		3188	while (queue_get (&data))
		3189	process (data);
		3190
		3191	pthread_mutex_unlock (&mymutex);
		3192	}
		3193
		3194	=back
		3195
		3196
		3197	=head3 Watcher-Specific Functions and Data Members
		3198
		3199	=over 4
		3200
		3201	=item ev_async_init (ev_async *, callback)
		3202
		3203	Initialises and configures the async watcher - it has no parameters of any
		3204	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3205	trust me.
		3206
		3207	=item ev_async_send (loop, ev_async *)
		3208
		3209	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3210	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3211	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3212	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3213	section below on what exactly this means).
		3214
		3215	Note that, as with other watchers in libev, multiple events might get
		3216	compressed into a single callback invocation (another way to look at this
		3217	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3218	reset when the event loop detects that).
		3219
		3220	This call incurs the overhead of a system call only once per event loop
		3221	iteration, so while the overhead might be noticeable, it doesn't apply to
		3222	repeated calls to C<ev_async_send> for the same event loop.
		3223
		3224	=item bool = ev_async_pending (ev_async *)
		3225
		3226	Returns a non-zero value when C<ev_async_send> has been called on the
		3227	watcher but the event has not yet been processed (or even noted) by the
		3228	event loop.
		3229
		3230	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3231	the loop iterates next and checks for the watcher to have become active,
		3232	it will reset the flag again. C<ev_async_pending> can be used to very
		3233	quickly check whether invoking the loop might be a good idea.
		3234
		3235	Not that this does I<not> check whether the watcher itself is pending,
		3236	only whether it has been requested to make this watcher pending: there
		3237	is a time window between the event loop checking and resetting the async
		3238	notification, and the callback being invoked.
		3239
		3240	=back
		3241
		3242
2051	=head1 OTHER FUNCTIONS	3243	=head1 OTHER FUNCTIONS
2052		3244
2053	There are some other functions of possible interest. Described. Here. Now.	3245	There are some other functions of possible interest. Described. Here. Now.
2054		3246
2055	=over 4	3247	=over 4
2056		3248
2057	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3249	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2058		3250
2059	This function combines a simple timer and an I/O watcher, calls your	3251	This function combines a simple timer and an I/O watcher, calls your
2060	callback on whichever event happens first and automatically stop both	3252	callback on whichever event happens first and automatically stops both
2061	watchers. This is useful if you want to wait for a single event on an fd	3253	watchers. This is useful if you want to wait for a single event on an fd
2062	or timeout without having to allocate/configure/start/stop/free one or	3254	or timeout without having to allocate/configure/start/stop/free one or
2063	more watchers yourself.	3255	more watchers yourself.
2064		3256
2065	If C<fd> is less than 0, then no I/O watcher will be started and events	3257	If C<fd> is less than 0, then no I/O watcher will be started and the
2066	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3258	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2067	C<events> set will be craeted and started.	3259	the given C<fd> and C<events> set will be created and started.
2068		3260
2069	If C<timeout> is less than 0, then no timeout watcher will be	3261	If C<timeout> is less than 0, then no timeout watcher will be
2070	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3262	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2071	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3263	repeat = 0) will be started. C<0> is a valid timeout.
2072	dubious value.
2073		3264
2074	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3265	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2075	passed an C<revents> set like normal event callbacks (a combination of	3266	passed an C<revents> set like normal event callbacks (a combination of
2076	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3267	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2077	value passed to C<ev_once>:	3268	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3269	a timeout and an io event at the same time - you probably should give io
		3270	events precedence.
2078		3271
		3272	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3273
2079	static void stdin_ready (int revents, void *arg)	3274	static void stdin_ready (int revents, void *arg)
2080	{	3275	{
2081	if (revents & EV_TIMEOUT)
2082	/* doh, nothing entered */;
2083	else if (revents & EV_READ)	3276	if (revents & EV_READ)
2084	/* stdin might have data for us, joy! */;	3277	/* stdin might have data for us, joy! */;
		3278	else if (revents & EV_TIMER)
		3279	/* doh, nothing entered */;
2085	}	3280	}
2086		3281
2087	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3282	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2088		3283
2089	=item ev_feed_event (ev_loop *, watcher *, int revents)
2090
2091	Feeds the given event set into the event loop, as if the specified event
2092	had happened for the specified watcher (which must be a pointer to an
2093	initialised but not necessarily started event watcher).
2094
2095	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3284	=item ev_feed_fd_event (loop, int fd, int revents)
2096		3285
2097	Feed an event on the given fd, as if a file descriptor backend detected	3286	Feed an event on the given fd, as if a file descriptor backend detected
2098	the given events it.	3287	the given events it.
2099		3288
2100	=item ev_feed_signal_event (ev_loop *loop, int signum)	3289	=item ev_feed_signal_event (loop, int signum)
2101		3290
2102	Feed an event as if the given signal occured (C<loop> must be the default	3291	Feed an event as if the given signal occurred (C<loop> must be the default
2103	loop!).	3292	loop!).
2104		3293
2105	=back	3294	=back
2106		3295
2107		3296
…		…
2123		3312
2124	=item * Priorities are not currently supported. Initialising priorities	3313	=item * Priorities are not currently supported. Initialising priorities
2125	will fail and all watchers will have the same priority, even though there	3314	will fail and all watchers will have the same priority, even though there
2126	is an ev_pri field.	3315	is an ev_pri field.
2127		3316
		3317	=item * In libevent, the last base created gets the signals, in libev, the
		3318	first base created (== the default loop) gets the signals.
		3319
2128	=item * Other members are not supported.	3320	=item * Other members are not supported.
2129		3321
2130	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3322	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2131	to use the libev header file and library.	3323	to use the libev header file and library.
2132		3324
2133	=back	3325	=back
2134		3326
2135	=head1 C++ SUPPORT	3327	=head1 C++ SUPPORT
2136		3328
2137	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3329	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2138	you to use some convinience methods to start/stop watchers and also change	3330	you to use some convenience methods to start/stop watchers and also change
2139	the callback model to a model using method callbacks on objects.	3331	the callback model to a model using method callbacks on objects.
2140		3332
2141	To use it,	3333	To use it,
2142		3334
2143	#include <ev++.h>	3335	#include <ev++.h>
2144		3336
2145	This automatically includes F<ev.h> and puts all of its definitions (many	3337	This automatically includes F<ev.h> and puts all of its definitions (many
2146	of them macros) into the global namespace. All C++ specific things are	3338	of them macros) into the global namespace. All C++ specific things are
2147	put into the C<ev> namespace. It should support all the same embedding	3339	put into the C<ev> namespace. It should support all the same embedding
2148	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3340	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2182		3374
2183	=over 4	3375	=over 4
2184		3376
2185	=item ev::TYPE::TYPE ()	3377	=item ev::TYPE::TYPE ()
2186		3378
2187	=item ev::TYPE::TYPE (struct ev_loop *)	3379	=item ev::TYPE::TYPE (loop)
2188		3380
2189	=item ev::TYPE::~TYPE	3381	=item ev::TYPE::~TYPE
2190		3382
2191	The constructor (optionally) takes an event loop to associate the watcher	3383	The constructor (optionally) takes an event loop to associate the watcher
2192	with. If it is omitted, it will use C<EV_DEFAULT>.	3384	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2215	your compiler is good :), then the method will be fully inlined into the	3407	your compiler is good :), then the method will be fully inlined into the
2216	thunking function, making it as fast as a direct C callback.	3408	thunking function, making it as fast as a direct C callback.
2217		3409
2218	Example: simple class declaration and watcher initialisation	3410	Example: simple class declaration and watcher initialisation
2219		3411
2220	struct myclass	3412	struct myclass
2221	{	3413	{
2222	void io_cb (ev::io &w, int revents) { }	3414	void io_cb (ev::io &w, int revents) { }
2223	}	3415	}
2224		3416
2225	myclass obj;	3417	myclass obj;
2226	ev::io iow;	3418	ev::io iow;
2227	iow.set <myclass, &myclass::io_cb> (&obj);	3419	iow.set <myclass, &myclass::io_cb> (&obj);
		3420
		3421	=item w->set (object *)
		3422
		3423	This is a variation of a method callback - leaving out the method to call
		3424	will default the method to C<operator ()>, which makes it possible to use
		3425	functor objects without having to manually specify the C<operator ()> all
		3426	the time. Incidentally, you can then also leave out the template argument
		3427	list.
		3428
		3429	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3430	int revents)>.
		3431
		3432	See the method-C<set> above for more details.
		3433
		3434	Example: use a functor object as callback.
		3435
		3436	struct myfunctor
		3437	{
		3438	void operator() (ev::io &w, int revents)
		3439	{
		3440	...
		3441	}
		3442	}
		3443
		3444	myfunctor f;
		3445
		3446	ev::io w;
		3447	w.set (&f);
2228		3448
2229	=item w->set<function> (void *data = 0)	3449	=item w->set<function> (void *data = 0)
2230		3450
2231	Also sets a callback, but uses a static method or plain function as	3451	Also sets a callback, but uses a static method or plain function as
2232	callback. The optional C<data> argument will be stored in the watcher's	3452	callback. The optional C<data> argument will be stored in the watcher's
…		…
2234		3454
2235	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3455	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2236		3456
2237	See the method-C<set> above for more details.	3457	See the method-C<set> above for more details.
2238		3458
2239	Example:	3459	Example: Use a plain function as callback.
2240		3460
2241	static void io_cb (ev::io &w, int revents) { }	3461	static void io_cb (ev::io &w, int revents) { }
2242	iow.set <io_cb> ();	3462	iow.set <io_cb> ();
2243		3463
2244	=item w->set (struct ev_loop *)	3464	=item w->set (loop)
2245		3465
2246	Associates a different C<struct ev_loop> with this watcher. You can only	3466	Associates a different C<struct ev_loop> with this watcher. You can only
2247	do this when the watcher is inactive (and not pending either).	3467	do this when the watcher is inactive (and not pending either).
2248		3468
2249	=item w->set ([args])	3469	=item w->set ([arguments])
2250		3470
2251	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3471	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2252	called at least once. Unlike the C counterpart, an active watcher gets	3472	method or a suitable start method must be called at least once. Unlike the
2253	automatically stopped and restarted when reconfiguring it with this	3473	C counterpart, an active watcher gets automatically stopped and restarted
2254	method.	3474	when reconfiguring it with this method.
2255		3475
2256	=item w->start ()	3476	=item w->start ()
2257		3477
2258	Starts the watcher. Note that there is no C<loop> argument, as the	3478	Starts the watcher. Note that there is no C<loop> argument, as the
2259	constructor already stores the event loop.	3479	constructor already stores the event loop.
2260		3480
		3481	=item w->start ([arguments])
		3482
		3483	Instead of calling C<set> and C<start> methods separately, it is often
		3484	convenient to wrap them in one call. Uses the same type of arguments as
		3485	the configure C<set> method of the watcher.
		3486
2261	=item w->stop ()	3487	=item w->stop ()
2262		3488
2263	Stops the watcher if it is active. Again, no C<loop> argument.	3489	Stops the watcher if it is active. Again, no C<loop> argument.
2264		3490
2265	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3491	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2277		3503
2278	=back	3504	=back
2279		3505
2280	=back	3506	=back
2281		3507
2282	Example: Define a class with an IO and idle watcher, start one of them in	3508	Example: Define a class with two I/O and idle watchers, start the I/O
2283	the constructor.	3509	watchers in the constructor.
2284		3510
2285	class myclass	3511	class myclass
2286	{	3512	{
2287	ev::io io; void io_cb (ev::io &w, int revents);	3513	ev::io io ; void io_cb (ev::io &w, int revents);
		3514	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2288	ev:idle idle void idle_cb (ev::idle &w, int revents);	3515	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2289		3516
2290	myclass (int fd)	3517	myclass (int fd)
2291	{	3518	{
2292	io .set <myclass, &myclass::io_cb > (this);	3519	io .set <myclass, &myclass::io_cb > (this);
		3520	io2 .set <myclass, &myclass::io2_cb > (this);
2293	idle.set <myclass, &myclass::idle_cb> (this);	3521	idle.set <myclass, &myclass::idle_cb> (this);
2294		3522
2295	io.start (fd, ev::READ);	3523	io.set (fd, ev::WRITE); // configure the watcher
		3524	io.start (); // start it whenever convenient
		3525
		3526	io2.start (fd, ev::READ); // set + start in one call
2296	}	3527	}
2297	};	3528	};
		3529
		3530
		3531	=head1 OTHER LANGUAGE BINDINGS
		3532
		3533	Libev does not offer other language bindings itself, but bindings for a
		3534	number of languages exist in the form of third-party packages. If you know
		3535	any interesting language binding in addition to the ones listed here, drop
		3536	me a note.
		3537
		3538	=over 4
		3539
		3540	=item Perl
		3541
		3542	The EV module implements the full libev API and is actually used to test
		3543	libev. EV is developed together with libev. Apart from the EV core module,
		3544	there are additional modules that implement libev-compatible interfaces
		3545	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3546	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3547	and C<EV::Glib>).
		3548
		3549	It can be found and installed via CPAN, its homepage is at
		3550	L<http://software.schmorp.de/pkg/EV>.
		3551
		3552	=item Python
		3553
		3554	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3555	seems to be quite complete and well-documented.
		3556
		3557	=item Ruby
		3558
		3559	Tony Arcieri has written a ruby extension that offers access to a subset
		3560	of the libev API and adds file handle abstractions, asynchronous DNS and
		3561	more on top of it. It can be found via gem servers. Its homepage is at
		3562	L<http://rev.rubyforge.org/>.
		3563
		3564	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3565	makes rev work even on mingw.
		3566
		3567	=item Haskell
		3568
		3569	A haskell binding to libev is available at
		3570	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3571
		3572	=item D
		3573
		3574	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3575	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3576
		3577	=item Ocaml
		3578
		3579	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3580	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3581
		3582	=item Lua
		3583
		3584	Brian Maher has written a partial interface to libev for lua (at the
		3585	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3586	L<http://github.com/brimworks/lua-ev>.
		3587
		3588	=back
2298		3589
2299		3590
2300	=head1 MACRO MAGIC	3591	=head1 MACRO MAGIC
2301		3592
2302	Libev can be compiled with a variety of options, the most fundamantal	3593	Libev can be compiled with a variety of options, the most fundamental
2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3594	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2304	functions and callbacks have an initial C<struct ev_loop *> argument.	3595	functions and callbacks have an initial C<struct ev_loop *> argument.
2305		3596
2306	To make it easier to write programs that cope with either variant, the	3597	To make it easier to write programs that cope with either variant, the
2307	following macros are defined:	3598	following macros are defined:
…		…
2312		3603
2313	This provides the loop I<argument> for functions, if one is required ("ev	3604	This provides the loop I<argument> for functions, if one is required ("ev
2314	loop argument"). The C<EV_A> form is used when this is the sole argument,	3605	loop argument"). The C<EV_A> form is used when this is the sole argument,
2315	C<EV_A_> is used when other arguments are following. Example:	3606	C<EV_A_> is used when other arguments are following. Example:
2316		3607
2317	ev_unref (EV_A);	3608	ev_unref (EV_A);
2318	ev_timer_add (EV_A_ watcher);	3609	ev_timer_add (EV_A_ watcher);
2319	ev_loop (EV_A_ 0);	3610	ev_run (EV_A_ 0);
2320		3611
2321	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3612	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2322	which is often provided by the following macro.	3613	which is often provided by the following macro.
2323		3614
2324	=item C<EV_P>, C<EV_P_>	3615	=item C<EV_P>, C<EV_P_>
2325		3616
2326	This provides the loop I<parameter> for functions, if one is required ("ev	3617	This provides the loop I<parameter> for functions, if one is required ("ev
2327	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3618	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2328	C<EV_P_> is used when other parameters are following. Example:	3619	C<EV_P_> is used when other parameters are following. Example:
2329		3620
2330	// this is how ev_unref is being declared	3621	// this is how ev_unref is being declared
2331	static void ev_unref (EV_P);	3622	static void ev_unref (EV_P);
2332		3623
2333	// this is how you can declare your typical callback	3624	// this is how you can declare your typical callback
2334	static void cb (EV_P_ ev_timer *w, int revents)	3625	static void cb (EV_P_ ev_timer *w, int revents)
2335		3626
2336	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3627	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2337	suitable for use with C<EV_A>.	3628	suitable for use with C<EV_A>.
2338		3629
2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3630	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2340		3631
2341	Similar to the other two macros, this gives you the value of the default	3632	Similar to the other two macros, this gives you the value of the default
2342	loop, if multiple loops are supported ("ev loop default").	3633	loop, if multiple loops are supported ("ev loop default").
		3634
		3635	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3636
		3637	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3638	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3639	is undefined when the default loop has not been initialised by a previous
		3640	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3641
		3642	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3643	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2343		3644
2344	=back	3645	=back
2345		3646
2346	Example: Declare and initialise a check watcher, utilising the above	3647	Example: Declare and initialise a check watcher, utilising the above
2347	macros so it will work regardless of whether multiple loops are supported	3648	macros so it will work regardless of whether multiple loops are supported
2348	or not.	3649	or not.
2349		3650
2350	static void	3651	static void
2351	check_cb (EV_P_ ev_timer *w, int revents)	3652	check_cb (EV_P_ ev_timer *w, int revents)
2352	{	3653	{
2353	ev_check_stop (EV_A_ w);	3654	ev_check_stop (EV_A_ w);
2354	}	3655	}
2355		3656
2356	ev_check check;	3657	ev_check check;
2357	ev_check_init (&check, check_cb);	3658	ev_check_init (&check, check_cb);
2358	ev_check_start (EV_DEFAULT_ &check);	3659	ev_check_start (EV_DEFAULT_ &check);
2359	ev_loop (EV_DEFAULT_ 0);	3660	ev_run (EV_DEFAULT_ 0);
2360		3661
2361	=head1 EMBEDDING	3662	=head1 EMBEDDING
2362		3663
2363	Libev can (and often is) directly embedded into host	3664	Libev can (and often is) directly embedded into host
2364	applications. Examples of applications that embed it include the Deliantra	3665	applications. Examples of applications that embed it include the Deliantra
…		…
2371	libev somewhere in your source tree).	3672	libev somewhere in your source tree).
2372		3673
2373	=head2 FILESETS	3674	=head2 FILESETS
2374		3675
2375	Depending on what features you need you need to include one or more sets of files	3676	Depending on what features you need you need to include one or more sets of files
2376	in your app.	3677	in your application.
2377		3678
2378	=head3 CORE EVENT LOOP	3679	=head3 CORE EVENT LOOP
2379		3680
2380	To include only the libev core (all the C<ev_*> functions), with manual	3681	To include only the libev core (all the C<ev_*> functions), with manual
2381	configuration (no autoconf):	3682	configuration (no autoconf):
2382		3683
2383	#define EV_STANDALONE 1	3684	#define EV_STANDALONE 1
2384	#include "ev.c"	3685	#include "ev.c"
2385		3686
2386	This will automatically include F<ev.h>, too, and should be done in a	3687	This will automatically include F<ev.h>, too, and should be done in a
2387	single C source file only to provide the function implementations. To use	3688	single C source file only to provide the function implementations. To use
2388	it, do the same for F<ev.h> in all files wishing to use this API (best	3689	it, do the same for F<ev.h> in all files wishing to use this API (best
2389	done by writing a wrapper around F<ev.h> that you can include instead and	3690	done by writing a wrapper around F<ev.h> that you can include instead and
2390	where you can put other configuration options):	3691	where you can put other configuration options):
2391		3692
2392	#define EV_STANDALONE 1	3693	#define EV_STANDALONE 1
2393	#include "ev.h"	3694	#include "ev.h"
2394		3695
2395	Both header files and implementation files can be compiled with a C++	3696	Both header files and implementation files can be compiled with a C++
2396	compiler (at least, thats a stated goal, and breakage will be treated	3697	compiler (at least, that's a stated goal, and breakage will be treated
2397	as a bug).	3698	as a bug).
2398		3699
2399	You need the following files in your source tree, or in a directory	3700	You need the following files in your source tree, or in a directory
2400	in your include path (e.g. in libev/ when using -Ilibev):	3701	in your include path (e.g. in libev/ when using -Ilibev):
2401		3702
2402	ev.h	3703	ev.h
2403	ev.c	3704	ev.c
2404	ev_vars.h	3705	ev_vars.h
2405	ev_wrap.h	3706	ev_wrap.h
2406		3707
2407	ev_win32.c required on win32 platforms only	3708	ev_win32.c required on win32 platforms only
2408		3709
2409	ev_select.c only when select backend is enabled (which is enabled by default)	3710	ev_select.c only when select backend is enabled (which is enabled by default)
2410	ev_poll.c only when poll backend is enabled (disabled by default)	3711	ev_poll.c only when poll backend is enabled (disabled by default)
2411	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3712	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2412	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3713	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2413	ev_port.c only when the solaris port backend is enabled (disabled by default)	3714	ev_port.c only when the solaris port backend is enabled (disabled by default)
2414		3715
2415	F<ev.c> includes the backend files directly when enabled, so you only need	3716	F<ev.c> includes the backend files directly when enabled, so you only need
2416	to compile this single file.	3717	to compile this single file.
2417		3718
2418	=head3 LIBEVENT COMPATIBILITY API	3719	=head3 LIBEVENT COMPATIBILITY API
2419		3720
2420	To include the libevent compatibility API, also include:	3721	To include the libevent compatibility API, also include:
2421		3722
2422	#include "event.c"	3723	#include "event.c"
2423		3724
2424	in the file including F<ev.c>, and:	3725	in the file including F<ev.c>, and:
2425		3726
2426	#include "event.h"	3727	#include "event.h"
2427		3728
2428	in the files that want to use the libevent API. This also includes F<ev.h>.	3729	in the files that want to use the libevent API. This also includes F<ev.h>.
2429		3730
2430	You need the following additional files for this:	3731	You need the following additional files for this:
2431		3732
2432	event.h	3733	event.h
2433	event.c	3734	event.c
2434		3735
2435	=head3 AUTOCONF SUPPORT	3736	=head3 AUTOCONF SUPPORT
2436		3737
2437	Instead of using C<EV_STANDALONE=1> and providing your config in	3738	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2438	whatever way you want, you can also C<m4_include([libev.m4])> in your	3739	whatever way you want, you can also C<m4_include([libev.m4])> in your
2439	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3740	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2440	include F<config.h> and configure itself accordingly.	3741	include F<config.h> and configure itself accordingly.
2441		3742
2442	For this of course you need the m4 file:	3743	For this of course you need the m4 file:
2443		3744
2444	libev.m4	3745	libev.m4
2445		3746
2446	=head2 PREPROCESSOR SYMBOLS/MACROS	3747	=head2 PREPROCESSOR SYMBOLS/MACROS
2447		3748
2448	Libev can be configured via a variety of preprocessor symbols you have to define	3749	Libev can be configured via a variety of preprocessor symbols you have to
2449	before including any of its files. The default is not to build for multiplicity	3750	define before including (or compiling) any of its files. The default in
2450	and only include the select backend.	3751	the absence of autoconf is documented for every option.
		3752
		3753	Symbols marked with "(h)" do not change the ABI, and can have different
		3754	values when compiling libev vs. including F<ev.h>, so it is permissible
		3755	to redefine them before including F<ev.h> without breaking compatibility
		3756	to a compiled library. All other symbols change the ABI, which means all
		3757	users of libev and the libev code itself must be compiled with compatible
		3758	settings.
2451		3759
2452	=over 4	3760	=over 4
2453		3761
		3762	=item EV_COMPAT3 (h)
		3763
		3764	Backwards compatibility is a major concern for libev. This is why this
		3765	release of libev comes with wrappers for the functions and symbols that
		3766	have been renamed between libev version 3 and 4.
		3767
		3768	You can disable these wrappers (to test compatibility with future
		3769	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3770	sources. This has the additional advantage that you can drop the C<struct>
		3771	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3772	typedef in that case.
		3773
		3774	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3775	and in some even more future version the compatibility code will be
		3776	removed completely.
		3777
2454	=item EV_STANDALONE	3778	=item EV_STANDALONE (h)
2455		3779
2456	Must always be C<1> if you do not use autoconf configuration, which	3780	Must always be C<1> if you do not use autoconf configuration, which
2457	keeps libev from including F<config.h>, and it also defines dummy	3781	keeps libev from including F<config.h>, and it also defines dummy
2458	implementations for some libevent functions (such as logging, which is not	3782	implementations for some libevent functions (such as logging, which is not
2459	supported). It will also not define any of the structs usually found in	3783	supported). It will also not define any of the structs usually found in
2460	F<event.h> that are not directly supported by the libev core alone.	3784	F<event.h> that are not directly supported by the libev core alone.
2461		3785
		3786	In standalone mode, libev will still try to automatically deduce the
		3787	configuration, but has to be more conservative.
		3788
2462	=item EV_USE_MONOTONIC	3789	=item EV_USE_MONOTONIC
2463		3790
2464	If defined to be C<1>, libev will try to detect the availability of the	3791	If defined to be C<1>, libev will try to detect the availability of the
2465	monotonic clock option at both compiletime and runtime. Otherwise no use	3792	monotonic clock option at both compile time and runtime. Otherwise no
2466	of the monotonic clock option will be attempted. If you enable this, you	3793	use of the monotonic clock option will be attempted. If you enable this,
2467	usually have to link against librt or something similar. Enabling it when	3794	you usually have to link against librt or something similar. Enabling it
2468	the functionality isn't available is safe, though, although you have	3795	when the functionality isn't available is safe, though, although you have
2469	to make sure you link against any libraries where the C<clock_gettime>	3796	to make sure you link against any libraries where the C<clock_gettime>
2470	function is hiding in (often F<-lrt>).	3797	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2471		3798
2472	=item EV_USE_REALTIME	3799	=item EV_USE_REALTIME
2473		3800
2474	If defined to be C<1>, libev will try to detect the availability of the	3801	If defined to be C<1>, libev will try to detect the availability of the
2475	realtime clock option at compiletime (and assume its availability at	3802	real-time clock option at compile time (and assume its availability
2476	runtime if successful). Otherwise no use of the realtime clock option will	3803	at runtime if successful). Otherwise no use of the real-time clock
2477	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3804	option will be attempted. This effectively replaces C<gettimeofday>
2478	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3805	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2479	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3806	correctness. See the note about libraries in the description of
		3807	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3808	C<EV_USE_CLOCK_SYSCALL>.
		3809
		3810	=item EV_USE_CLOCK_SYSCALL
		3811
		3812	If defined to be C<1>, libev will try to use a direct syscall instead
		3813	of calling the system-provided C<clock_gettime> function. This option
		3814	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3815	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3816	programs needlessly. Using a direct syscall is slightly slower (in
		3817	theory), because no optimised vdso implementation can be used, but avoids
		3818	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3819	higher, as it simplifies linking (no need for C<-lrt>).
2480		3820
2481	=item EV_USE_NANOSLEEP	3821	=item EV_USE_NANOSLEEP
2482		3822
2483	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3823	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2484	and will use it for delays. Otherwise it will use C<select ()>.	3824	and will use it for delays. Otherwise it will use C<select ()>.
2485		3825
		3826	=item EV_USE_EVENTFD
		3827
		3828	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3829	available and will probe for kernel support at runtime. This will improve
		3830	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3831	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3832	2.7 or newer, otherwise disabled.
		3833
2486	=item EV_USE_SELECT	3834	=item EV_USE_SELECT
2487		3835
2488	If undefined or defined to be C<1>, libev will compile in support for the	3836	If undefined or defined to be C<1>, libev will compile in support for the
2489	C<select>(2) backend. No attempt at autodetection will be done: if no	3837	C<select>(2) backend. No attempt at auto-detection will be done: if no
2490	other method takes over, select will be it. Otherwise the select backend	3838	other method takes over, select will be it. Otherwise the select backend
2491	will not be compiled in.	3839	will not be compiled in.
2492		3840
2493	=item EV_SELECT_USE_FD_SET	3841	=item EV_SELECT_USE_FD_SET
2494		3842
2495	If defined to C<1>, then the select backend will use the system C<fd_set>	3843	If defined to C<1>, then the select backend will use the system C<fd_set>
2496	structure. This is useful if libev doesn't compile due to a missing	3844	structure. This is useful if libev doesn't compile due to a missing
2497	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3845	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2498	exotic systems. This usually limits the range of file descriptors to some	3846	on exotic systems. This usually limits the range of file descriptors to
2499	low limit such as 1024 or might have other limitations (winsocket only	3847	some low limit such as 1024 or might have other limitations (winsocket
2500	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3848	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2501	influence the size of the C<fd_set> used.	3849	configures the maximum size of the C<fd_set>.
2502		3850
2503	=item EV_SELECT_IS_WINSOCKET	3851	=item EV_SELECT_IS_WINSOCKET
2504		3852
2505	When defined to C<1>, the select backend will assume that	3853	When defined to C<1>, the select backend will assume that
2506	select/socket/connect etc. don't understand file descriptors but	3854	select/socket/connect etc. don't understand file descriptors but
…		…
2508	be used is the winsock select). This means that it will call	3856	be used is the winsock select). This means that it will call
2509	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3857	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2510	it is assumed that all these functions actually work on fds, even	3858	it is assumed that all these functions actually work on fds, even
2511	on win32. Should not be defined on non-win32 platforms.	3859	on win32. Should not be defined on non-win32 platforms.
2512		3860
2513	=item EV_FD_TO_WIN32_HANDLE	3861	=item EV_FD_TO_WIN32_HANDLE(fd)
2514		3862
2515	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3863	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2516	file descriptors to socket handles. When not defining this symbol (the	3864	file descriptors to socket handles. When not defining this symbol (the
2517	default), then libev will call C<_get_osfhandle>, which is usually	3865	default), then libev will call C<_get_osfhandle>, which is usually
2518	correct. In some cases, programs use their own file descriptor management,	3866	correct. In some cases, programs use their own file descriptor management,
2519	in which case they can provide this function to map fds to socket handles.	3867	in which case they can provide this function to map fds to socket handles.
2520		3868
		3869	=item EV_WIN32_HANDLE_TO_FD(handle)
		3870
		3871	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3872	using the standard C<_open_osfhandle> function. For programs implementing
		3873	their own fd to handle mapping, overwriting this function makes it easier
		3874	to do so. This can be done by defining this macro to an appropriate value.
		3875
		3876	=item EV_WIN32_CLOSE_FD(fd)
		3877
		3878	If programs implement their own fd to handle mapping on win32, then this
		3879	macro can be used to override the C<close> function, useful to unregister
		3880	file descriptors again. Note that the replacement function has to close
		3881	the underlying OS handle.
		3882
2521	=item EV_USE_POLL	3883	=item EV_USE_POLL
2522		3884
2523	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3885	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2524	backend. Otherwise it will be enabled on non-win32 platforms. It	3886	backend. Otherwise it will be enabled on non-win32 platforms. It
2525	takes precedence over select.	3887	takes precedence over select.
2526		3888
2527	=item EV_USE_EPOLL	3889	=item EV_USE_EPOLL
2528		3890
2529	If defined to be C<1>, libev will compile in support for the Linux	3891	If defined to be C<1>, libev will compile in support for the Linux
2530	C<epoll>(7) backend. Its availability will be detected at runtime,	3892	C<epoll>(7) backend. Its availability will be detected at runtime,
2531	otherwise another method will be used as fallback. This is the	3893	otherwise another method will be used as fallback. This is the preferred
2532	preferred backend for GNU/Linux systems.	3894	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3895	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2533		3896
2534	=item EV_USE_KQUEUE	3897	=item EV_USE_KQUEUE
2535		3898
2536	If defined to be C<1>, libev will compile in support for the BSD style	3899	If defined to be C<1>, libev will compile in support for the BSD style
2537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3900	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2550	otherwise another method will be used as fallback. This is the preferred	3913	otherwise another method will be used as fallback. This is the preferred
2551	backend for Solaris 10 systems.	3914	backend for Solaris 10 systems.
2552		3915
2553	=item EV_USE_DEVPOLL	3916	=item EV_USE_DEVPOLL
2554		3917
2555	reserved for future expansion, works like the USE symbols above.	3918	Reserved for future expansion, works like the USE symbols above.
2556		3919
2557	=item EV_USE_INOTIFY	3920	=item EV_USE_INOTIFY
2558		3921
2559	If defined to be C<1>, libev will compile in support for the Linux inotify	3922	If defined to be C<1>, libev will compile in support for the Linux inotify
2560	interface to speed up C<ev_stat> watchers. Its actual availability will	3923	interface to speed up C<ev_stat> watchers. Its actual availability will
2561	be detected at runtime.	3924	be detected at runtime. If undefined, it will be enabled if the headers
		3925	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2562		3926
		3927	=item EV_ATOMIC_T
		3928
		3929	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3930	access is atomic with respect to other threads or signal contexts. No such
		3931	type is easily found in the C language, so you can provide your own type
		3932	that you know is safe for your purposes. It is used both for signal handler "locking"
		3933	as well as for signal and thread safety in C<ev_async> watchers.
		3934
		3935	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3936	(from F<signal.h>), which is usually good enough on most platforms.
		3937
2563	=item EV_H	3938	=item EV_H (h)
2564		3939
2565	The name of the F<ev.h> header file used to include it. The default if	3940	The name of the F<ev.h> header file used to include it. The default if
2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3941	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2567	used to virtually rename the F<ev.h> header file in case of conflicts.	3942	used to virtually rename the F<ev.h> header file in case of conflicts.
2568		3943
2569	=item EV_CONFIG_H	3944	=item EV_CONFIG_H (h)
2570		3945
2571	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3946	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2572	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3947	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2573	C<EV_H>, above.	3948	C<EV_H>, above.
2574		3949
2575	=item EV_EVENT_H	3950	=item EV_EVENT_H (h)
2576		3951
2577	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3952	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2578	of how the F<event.h> header can be found, the default is C<"event.h">.	3953	of how the F<event.h> header can be found, the default is C<"event.h">.
2579		3954
2580	=item EV_PROTOTYPES	3955	=item EV_PROTOTYPES (h)
2581		3956
2582	If defined to be C<0>, then F<ev.h> will not define any function	3957	If defined to be C<0>, then F<ev.h> will not define any function
2583	prototypes, but still define all the structs and other symbols. This is	3958	prototypes, but still define all the structs and other symbols. This is
2584	occasionally useful if you want to provide your own wrapper functions	3959	occasionally useful if you want to provide your own wrapper functions
2585	around libev functions.	3960	around libev functions.
…		…
2604	When doing priority-based operations, libev usually has to linearly search	3979	When doing priority-based operations, libev usually has to linearly search
2605	all the priorities, so having many of them (hundreds) uses a lot of space	3980	all the priorities, so having many of them (hundreds) uses a lot of space
2606	and time, so using the defaults of five priorities (-2 .. +2) is usually	3981	and time, so using the defaults of five priorities (-2 .. +2) is usually
2607	fine.	3982	fine.
2608		3983
2609	If your embedding app does not need any priorities, defining these both to	3984	If your embedding application does not need any priorities, defining these
2610	C<0> will save some memory and cpu.	3985	both to C<0> will save some memory and CPU.
2611		3986
2612	=item EV_PERIODIC_ENABLE	3987	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3988	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3989	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2613		3990
2614	If undefined or defined to be C<1>, then periodic timers are supported. If	3991	If undefined or defined to be C<1> (and the platform supports it), then
2615	defined to be C<0>, then they are not. Disabling them saves a few kB of	3992	the respective watcher type is supported. If defined to be C<0>, then it
2616	code.	3993	is not. Disabling watcher types mainly saves code size.
2617		3994
2618	=item EV_IDLE_ENABLE	3995	=item EV_FEATURES
2619
2620	If undefined or defined to be C<1>, then idle watchers are supported. If
2621	defined to be C<0>, then they are not. Disabling them saves a few kB of
2622	code.
2623
2624	=item EV_EMBED_ENABLE
2625
2626	If undefined or defined to be C<1>, then embed watchers are supported. If
2627	defined to be C<0>, then they are not.
2628
2629	=item EV_STAT_ENABLE
2630
2631	If undefined or defined to be C<1>, then stat watchers are supported. If
2632	defined to be C<0>, then they are not.
2633
2634	=item EV_FORK_ENABLE
2635
2636	If undefined or defined to be C<1>, then fork watchers are supported. If
2637	defined to be C<0>, then they are not.
2638
2639	=item EV_MINIMAL
2640		3996
2641	If you need to shave off some kilobytes of code at the expense of some	3997	If you need to shave off some kilobytes of code at the expense of some
2642	speed, define this symbol to C<1>. Currently only used for gcc to override	3998	speed (but with the full API), you can define this symbol to request
2643	some inlining decisions, saves roughly 30% codesize of amd64.	3999	certain subsets of functionality. The default is to enable all features
		4000	that can be enabled on the platform.
		4001
		4002	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4003	with some broad features you want) and then selectively re-enable
		4004	additional parts you want, for example if you want everything minimal,
		4005	but multiple event loop support, async and child watchers and the poll
		4006	backend, use this:
		4007
		4008	#define EV_FEATURES 0
		4009	#define EV_MULTIPLICITY 1
		4010	#define EV_USE_POLL 1
		4011	#define EV_CHILD_ENABLE 1
		4012	#define EV_ASYNC_ENABLE 1
		4013
		4014	The actual value is a bitset, it can be a combination of the following
		4015	values:
		4016
		4017	=over 4
		4018
		4019	=item C<1> - faster/larger code
		4020
		4021	Use larger code to speed up some operations.
		4022
		4023	Currently this is used to override some inlining decisions (enlarging the
		4024	code size by roughly 30% on amd64).
		4025
		4026	When optimising for size, use of compiler flags such as C<-Os> with
		4027	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4028	assertions.
		4029
		4030	=item C<2> - faster/larger data structures
		4031
		4032	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4033	hash table sizes and so on. This will usually further increase code size
		4034	and can additionally have an effect on the size of data structures at
		4035	runtime.
		4036
		4037	=item C<4> - full API configuration
		4038
		4039	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4040	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4041
		4042	=item C<8> - full API
		4043
		4044	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4045	details on which parts of the API are still available without this
		4046	feature, and do not complain if this subset changes over time.
		4047
		4048	=item C<16> - enable all optional watcher types
		4049
		4050	Enables all optional watcher types. If you want to selectively enable
		4051	only some watcher types other than I/O and timers (e.g. prepare,
		4052	embed, async, child...) you can enable them manually by defining
		4053	C<EV_watchertype_ENABLE> to C<1> instead.
		4054
		4055	=item C<32> - enable all backends
		4056
		4057	This enables all backends - without this feature, you need to enable at
		4058	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4059
		4060	=item C<64> - enable OS-specific "helper" APIs
		4061
		4062	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4063	default.
		4064
		4065	=back
		4066
		4067	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4068	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4069	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4070	watchers, timers and monotonic clock support.
		4071
		4072	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4073	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4074	your program might be left out as well - a binary starting a timer and an
		4075	I/O watcher then might come out at only 5Kb.
		4076
		4077	=item EV_AVOID_STDIO
		4078
		4079	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4080	functions (printf, scanf, perror etc.). This will increase the code size
		4081	somewhat, but if your program doesn't otherwise depend on stdio and your
		4082	libc allows it, this avoids linking in the stdio library which is quite
		4083	big.
		4084
		4085	Note that error messages might become less precise when this option is
		4086	enabled.
		4087
		4088	=item EV_NSIG
		4089
		4090	The highest supported signal number, +1 (or, the number of
		4091	signals): Normally, libev tries to deduce the maximum number of signals
		4092	automatically, but sometimes this fails, in which case it can be
		4093	specified. Also, using a lower number than detected (C<32> should be
		4094	good for about any system in existence) can save some memory, as libev
		4095	statically allocates some 12-24 bytes per signal number.
2644		4096
2645	=item EV_PID_HASHSIZE	4097	=item EV_PID_HASHSIZE
2646		4098
2647	C<ev_child> watchers use a small hash table to distribute workload by	4099	C<ev_child> watchers use a small hash table to distribute workload by
2648	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4100	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2649	than enough. If you need to manage thousands of children you might want to	4101	usually more than enough. If you need to manage thousands of children you
2650	increase this value (I<must> be a power of two).	4102	might want to increase this value (I<must> be a power of two).
2651		4103
2652	=item EV_INOTIFY_HASHSIZE	4104	=item EV_INOTIFY_HASHSIZE
2653		4105
2654	C<ev_stat> watchers use a small hash table to distribute workload by	4106	C<ev_stat> watchers use a small hash table to distribute workload by
2655	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4107	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2656	usually more than enough. If you need to manage thousands of C<ev_stat>	4108	disabled), usually more than enough. If you need to manage thousands of
2657	watchers you might want to increase this value (I<must> be a power of	4109	C<ev_stat> watchers you might want to increase this value (I<must> be a
2658	two).	4110	power of two).
		4111
		4112	=item EV_USE_4HEAP
		4113
		4114	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4115	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4116	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4117	faster performance with many (thousands) of watchers.
		4118
		4119	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4120	will be C<0>.
		4121
		4122	=item EV_HEAP_CACHE_AT
		4123
		4124	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4125	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4126	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4127	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4128	but avoids random read accesses on heap changes. This improves performance
		4129	noticeably with many (hundreds) of watchers.
		4130
		4131	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4132	will be C<0>.
		4133
		4134	=item EV_VERIFY
		4135
		4136	Controls how much internal verification (see C<ev_verify ()>) will
		4137	be done: If set to C<0>, no internal verification code will be compiled
		4138	in. If set to C<1>, then verification code will be compiled in, but not
		4139	called. If set to C<2>, then the internal verification code will be
		4140	called once per loop, which can slow down libev. If set to C<3>, then the
		4141	verification code will be called very frequently, which will slow down
		4142	libev considerably.
		4143
		4144	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4145	will be C<0>.
2659		4146
2660	=item EV_COMMON	4147	=item EV_COMMON
2661		4148
2662	By default, all watchers have a C<void *data> member. By redefining	4149	By default, all watchers have a C<void *data> member. By redefining
2663	this macro to a something else you can include more and other types of	4150	this macro to something else you can include more and other types of
2664	members. You have to define it each time you include one of the files,	4151	members. You have to define it each time you include one of the files,
2665	though, and it must be identical each time.	4152	though, and it must be identical each time.
2666		4153
2667	For example, the perl EV module uses something like this:	4154	For example, the perl EV module uses something like this:
2668		4155
2669	#define EV_COMMON \	4156	#define EV_COMMON \
2670	SV *self; /* contains this struct */ \	4157	SV *self; /* contains this struct */ \
2671	SV *cb_sv, *fh /* note no trailing ";" */	4158	SV *cb_sv, *fh /* note no trailing ";" */
2672		4159
2673	=item EV_CB_DECLARE (type)	4160	=item EV_CB_DECLARE (type)
2674		4161
2675	=item EV_CB_INVOKE (watcher, revents)	4162	=item EV_CB_INVOKE (watcher, revents)
2676		4163
…		…
2681	definition and a statement, respectively. See the F<ev.h> header file for	4168	definition and a statement, respectively. See the F<ev.h> header file for
2682	their default definitions. One possible use for overriding these is to	4169	their default definitions. One possible use for overriding these is to
2683	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4170	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2684	method calls instead of plain function calls in C++.	4171	method calls instead of plain function calls in C++.
2685		4172
		4173	=back
		4174
2686	=head2 EXPORTED API SYMBOLS	4175	=head2 EXPORTED API SYMBOLS
2687		4176
2688	If you need to re-export the API (e.g. via a dll) and you need a list of	4177	If you need to re-export the API (e.g. via a DLL) and you need a list of
2689	exported symbols, you can use the provided F<Symbol.*> files which list	4178	exported symbols, you can use the provided F<Symbol.*> files which list
2690	all public symbols, one per line:	4179	all public symbols, one per line:
2691		4180
2692	Symbols.ev for libev proper	4181	Symbols.ev for libev proper
2693	Symbols.event for the libevent emulation	4182	Symbols.event for the libevent emulation
2694		4183
2695	This can also be used to rename all public symbols to avoid clashes with	4184	This can also be used to rename all public symbols to avoid clashes with
2696	multiple versions of libev linked together (which is obviously bad in	4185	multiple versions of libev linked together (which is obviously bad in
2697	itself, but sometimes it is inconvinient to avoid this).	4186	itself, but sometimes it is inconvenient to avoid this).
2698		4187
2699	A sed command like this will create wrapper C<#define>'s that you need to	4188	A sed command like this will create wrapper C<#define>'s that you need to
2700	include before including F<ev.h>:	4189	include before including F<ev.h>:
2701		4190
2702	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4191	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2719	file.	4208	file.
2720		4209
2721	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4210	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2722	that everybody includes and which overrides some configure choices:	4211	that everybody includes and which overrides some configure choices:
2723		4212
2724	#define EV_MINIMAL 1	4213	#define EV_FEATURES 8
2725	#define EV_USE_POLL 0	4214	#define EV_USE_SELECT 1
2726	#define EV_MULTIPLICITY 0
2727	#define EV_PERIODIC_ENABLE 0	4215	#define EV_PREPARE_ENABLE 1
		4216	#define EV_IDLE_ENABLE 1
2728	#define EV_STAT_ENABLE 0	4217	#define EV_SIGNAL_ENABLE 1
2729	#define EV_FORK_ENABLE 0	4218	#define EV_CHILD_ENABLE 1
		4219	#define EV_USE_STDEXCEPT 0
2730	#define EV_CONFIG_H <config.h>	4220	#define EV_CONFIG_H <config.h>
2731	#define EV_MINPRI 0
2732	#define EV_MAXPRI 0
2733		4221
2734	#include "ev++.h"	4222	#include "ev++.h"
2735		4223
2736	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4224	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2737		4225
2738	#include "ev_cpp.h"	4226	#include "ev_cpp.h"
2739	#include "ev.c"	4227	#include "ev.c"
2740		4228
		4229	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2741		4230
2742	=head1 COMPLEXITIES	4231	=head2 THREADS AND COROUTINES
2743		4232
2744	In this section the complexities of (many of) the algorithms used inside	4233	=head3 THREADS
2745	libev will be explained. For complexity discussions about backends see the
2746	documentation for C<ev_default_init>.
2747		4234
2748	All of the following are about amortised time: If an array needs to be	4235	All libev functions are reentrant and thread-safe unless explicitly
2749	extended, libev needs to realloc and move the whole array, but this	4236	documented otherwise, but libev implements no locking itself. This means
2750	happens asymptotically never with higher number of elements, so O(1) might	4237	that you can use as many loops as you want in parallel, as long as there
2751	mean it might do a lengthy realloc operation in rare cases, but on average	4238	are no concurrent calls into any libev function with the same loop
2752	it is much faster and asymptotically approaches constant time.	4239	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4240	of course): libev guarantees that different event loops share no data
		4241	structures that need any locking.
		4242
		4243	Or to put it differently: calls with different loop parameters can be done
		4244	concurrently from multiple threads, calls with the same loop parameter
		4245	must be done serially (but can be done from different threads, as long as
		4246	only one thread ever is inside a call at any point in time, e.g. by using
		4247	a mutex per loop).
		4248
		4249	Specifically to support threads (and signal handlers), libev implements
		4250	so-called C<ev_async> watchers, which allow some limited form of
		4251	concurrency on the same event loop, namely waking it up "from the
		4252	outside".
		4253
		4254	If you want to know which design (one loop, locking, or multiple loops
		4255	without or something else still) is best for your problem, then I cannot
		4256	help you, but here is some generic advice:
2753		4257
2754	=over 4	4258	=over 4
2755		4259
2756	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4260	=item * most applications have a main thread: use the default libev loop
		4261	in that thread, or create a separate thread running only the default loop.
2757		4262
2758	This means that, when you have a watcher that triggers in one hour and	4263	This helps integrating other libraries or software modules that use libev
2759	there are 100 watchers that would trigger before that then inserting will	4264	themselves and don't care/know about threading.
2760	have to skip roughly seven (C<ld 100>) of these watchers.
2761		4265
2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4266	=item * one loop per thread is usually a good model.
2763		4267
2764	That means that changing a timer costs less than removing/adding them	4268	Doing this is almost never wrong, sometimes a better-performance model
2765	as only the relative motion in the event queue has to be paid for.	4269	exists, but it is always a good start.
2766		4270
2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4271	=item * other models exist, such as the leader/follower pattern, where one
		4272	loop is handed through multiple threads in a kind of round-robin fashion.
2768		4273
2769	These just add the watcher into an array or at the head of a list.	4274	Choosing a model is hard - look around, learn, know that usually you can do
		4275	better than you currently do :-)
2770		4276
2771	=item Stopping check/prepare/idle watchers: O(1)	4277	=item * often you need to talk to some other thread which blocks in the
		4278	event loop.
2772		4279
2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4280	C<ev_async> watchers can be used to wake them up from other threads safely
		4281	(or from signal contexts...).
2774		4282
2775	These watchers are stored in lists then need to be walked to find the	4283	An example use would be to communicate signals or other events that only
2776	correct watcher to remove. The lists are usually short (you don't usually	4284	work in the default loop by registering the signal watcher with the
2777	have many watchers waiting for the same fd or signal).	4285	default loop and triggering an C<ev_async> watcher from the default loop
2778		4286	watcher callback into the event loop interested in the signal.
2779	=item Finding the next timer in each loop iteration: O(1)
2780
2781	By virtue of using a binary heap, the next timer is always found at the
2782	beginning of the storage array.
2783
2784	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2785
2786	A change means an I/O watcher gets started or stopped, which requires
2787	libev to recalculate its status (and possibly tell the kernel, depending
2788	on backend and wether C<ev_io_set> was used).
2789
2790	=item Activating one watcher (putting it into the pending state): O(1)
2791
2792	=item Priority handling: O(number_of_priorities)
2793
2794	Priorities are implemented by allocating some space for each
2795	priority. When doing priority-based operations, libev usually has to
2796	linearly search all the priorities, but starting/stopping and activating
2797	watchers becomes O(1) w.r.t. prioritiy handling.
2798		4287
2799	=back	4288	=back
2800		4289
		4290	=head4 THREAD LOCKING EXAMPLE
2801		4291
2802	=head1 Win32 platform limitations and workarounds	4292	Here is a fictitious example of how to run an event loop in a different
		4293	thread than where callbacks are being invoked and watchers are
		4294	created/added/removed.
		4295
		4296	For a real-world example, see the C<EV::Loop::Async> perl module,
		4297	which uses exactly this technique (which is suited for many high-level
		4298	languages).
		4299
		4300	The example uses a pthread mutex to protect the loop data, a condition
		4301	variable to wait for callback invocations, an async watcher to notify the
		4302	event loop thread and an unspecified mechanism to wake up the main thread.
		4303
		4304	First, you need to associate some data with the event loop:
		4305
		4306	typedef struct {
		4307	mutex_t lock; /* global loop lock */
		4308	ev_async async_w;
		4309	thread_t tid;
		4310	cond_t invoke_cv;
		4311	} userdata;
		4312
		4313	void prepare_loop (EV_P)
		4314	{
		4315	// for simplicity, we use a static userdata struct.
		4316	static userdata u;
		4317
		4318	ev_async_init (&u->async_w, async_cb);
		4319	ev_async_start (EV_A_ &u->async_w);
		4320
		4321	pthread_mutex_init (&u->lock, 0);
		4322	pthread_cond_init (&u->invoke_cv, 0);
		4323
		4324	// now associate this with the loop
		4325	ev_set_userdata (EV_A_ u);
		4326	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4327	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4328
		4329	// then create the thread running ev_loop
		4330	pthread_create (&u->tid, 0, l_run, EV_A);
		4331	}
		4332
		4333	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4334	solely to wake up the event loop so it takes notice of any new watchers
		4335	that might have been added:
		4336
		4337	static void
		4338	async_cb (EV_P_ ev_async *w, int revents)
		4339	{
		4340	// just used for the side effects
		4341	}
		4342
		4343	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4344	protecting the loop data, respectively.
		4345
		4346	static void
		4347	l_release (EV_P)
		4348	{
		4349	userdata *u = ev_userdata (EV_A);
		4350	pthread_mutex_unlock (&u->lock);
		4351	}
		4352
		4353	static void
		4354	l_acquire (EV_P)
		4355	{
		4356	userdata *u = ev_userdata (EV_A);
		4357	pthread_mutex_lock (&u->lock);
		4358	}
		4359
		4360	The event loop thread first acquires the mutex, and then jumps straight
		4361	into C<ev_run>:
		4362
		4363	void *
		4364	l_run (void *thr_arg)
		4365	{
		4366	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4367
		4368	l_acquire (EV_A);
		4369	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4370	ev_run (EV_A_ 0);
		4371	l_release (EV_A);
		4372
		4373	return 0;
		4374	}
		4375
		4376	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4377	signal the main thread via some unspecified mechanism (signals? pipe
		4378	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4379	have been called (in a while loop because a) spurious wakeups are possible
		4380	and b) skipping inter-thread-communication when there are no pending
		4381	watchers is very beneficial):
		4382
		4383	static void
		4384	l_invoke (EV_P)
		4385	{
		4386	userdata *u = ev_userdata (EV_A);
		4387
		4388	while (ev_pending_count (EV_A))
		4389	{
		4390	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4391	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4392	}
		4393	}
		4394
		4395	Now, whenever the main thread gets told to invoke pending watchers, it
		4396	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4397	thread to continue:
		4398
		4399	static void
		4400	real_invoke_pending (EV_P)
		4401	{
		4402	userdata *u = ev_userdata (EV_A);
		4403
		4404	pthread_mutex_lock (&u->lock);
		4405	ev_invoke_pending (EV_A);
		4406	pthread_cond_signal (&u->invoke_cv);
		4407	pthread_mutex_unlock (&u->lock);
		4408	}
		4409
		4410	Whenever you want to start/stop a watcher or do other modifications to an
		4411	event loop, you will now have to lock:
		4412
		4413	ev_timer timeout_watcher;
		4414	userdata *u = ev_userdata (EV_A);
		4415
		4416	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4417
		4418	pthread_mutex_lock (&u->lock);
		4419	ev_timer_start (EV_A_ &timeout_watcher);
		4420	ev_async_send (EV_A_ &u->async_w);
		4421	pthread_mutex_unlock (&u->lock);
		4422
		4423	Note that sending the C<ev_async> watcher is required because otherwise
		4424	an event loop currently blocking in the kernel will have no knowledge
		4425	about the newly added timer. By waking up the loop it will pick up any new
		4426	watchers in the next event loop iteration.
		4427
		4428	=head3 COROUTINES
		4429
		4430	Libev is very accommodating to coroutines ("cooperative threads"):
		4431	libev fully supports nesting calls to its functions from different
		4432	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4433	different coroutines, and switch freely between both coroutines running
		4434	the loop, as long as you don't confuse yourself). The only exception is
		4435	that you must not do this from C<ev_periodic> reschedule callbacks.
		4436
		4437	Care has been taken to ensure that libev does not keep local state inside
		4438	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4439	they do not call any callbacks.
		4440
		4441	=head2 COMPILER WARNINGS
		4442
		4443	Depending on your compiler and compiler settings, you might get no or a
		4444	lot of warnings when compiling libev code. Some people are apparently
		4445	scared by this.
		4446
		4447	However, these are unavoidable for many reasons. For one, each compiler
		4448	has different warnings, and each user has different tastes regarding
		4449	warning options. "Warn-free" code therefore cannot be a goal except when
		4450	targeting a specific compiler and compiler-version.
		4451
		4452	Another reason is that some compiler warnings require elaborate
		4453	workarounds, or other changes to the code that make it less clear and less
		4454	maintainable.
		4455
		4456	And of course, some compiler warnings are just plain stupid, or simply
		4457	wrong (because they don't actually warn about the condition their message
		4458	seems to warn about). For example, certain older gcc versions had some
		4459	warnings that resulted in an extreme number of false positives. These have
		4460	been fixed, but some people still insist on making code warn-free with
		4461	such buggy versions.
		4462
		4463	While libev is written to generate as few warnings as possible,
		4464	"warn-free" code is not a goal, and it is recommended not to build libev
		4465	with any compiler warnings enabled unless you are prepared to cope with
		4466	them (e.g. by ignoring them). Remember that warnings are just that:
		4467	warnings, not errors, or proof of bugs.
		4468
		4469
		4470	=head2 VALGRIND
		4471
		4472	Valgrind has a special section here because it is a popular tool that is
		4473	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4474
		4475	If you think you found a bug (memory leak, uninitialised data access etc.)
		4476	in libev, then check twice: If valgrind reports something like:
		4477
		4478	==2274== definitely lost: 0 bytes in 0 blocks.
		4479	==2274== possibly lost: 0 bytes in 0 blocks.
		4480	==2274== still reachable: 256 bytes in 1 blocks.
		4481
		4482	Then there is no memory leak, just as memory accounted to global variables
		4483	is not a memleak - the memory is still being referenced, and didn't leak.
		4484
		4485	Similarly, under some circumstances, valgrind might report kernel bugs
		4486	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4487	although an acceptable workaround has been found here), or it might be
		4488	confused.
		4489
		4490	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4491	make it into some kind of religion.
		4492
		4493	If you are unsure about something, feel free to contact the mailing list
		4494	with the full valgrind report and an explanation on why you think this
		4495	is a bug in libev (best check the archives, too :). However, don't be
		4496	annoyed when you get a brisk "this is no bug" answer and take the chance
		4497	of learning how to interpret valgrind properly.
		4498
		4499	If you need, for some reason, empty reports from valgrind for your project
		4500	I suggest using suppression lists.
		4501
		4502
		4503	=head1 PORTABILITY NOTES
		4504
		4505	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4506
		4507	GNU/Linux is the only common platform that supports 64 bit file/large file
		4508	interfaces but I<disables> them by default.
		4509
		4510	That means that libev compiled in the default environment doesn't support
		4511	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4512
		4513	Unfortunately, many programs try to work around this GNU/Linux issue
		4514	by enabling the large file API, which makes them incompatible with the
		4515	standard libev compiled for their system.
		4516
		4517	Likewise, libev cannot enable the large file API itself as this would
		4518	suddenly make it incompatible to the default compile time environment,
		4519	i.e. all programs not using special compile switches.
		4520
		4521	=head2 OS/X AND DARWIN BUGS
		4522
		4523	The whole thing is a bug if you ask me - basically any system interface
		4524	you touch is broken, whether it is locales, poll, kqueue or even the
		4525	OpenGL drivers.
		4526
		4527	=head3 C<kqueue> is buggy
		4528
		4529	The kqueue syscall is broken in all known versions - most versions support
		4530	only sockets, many support pipes.
		4531
		4532	Libev tries to work around this by not using C<kqueue> by default on
		4533	this rotten platform, but of course you can still ask for it when creating
		4534	a loop.
		4535
		4536	=head3 C<poll> is buggy
		4537
		4538	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4539	implementation by something calling C<kqueue> internally around the 10.5.6
		4540	release, so now C<kqueue> I<and> C<poll> are broken.
		4541
		4542	Libev tries to work around this by not using C<poll> by default on
		4543	this rotten platform, but of course you can still ask for it when creating
		4544	a loop.
		4545
		4546	=head3 C<select> is buggy
		4547
		4548	All that's left is C<select>, and of course Apple found a way to fuck this
		4549	one up as well: On OS/X, C<select> actively limits the number of file
		4550	descriptors you can pass in to 1024 - your program suddenly crashes when
		4551	you use more.
		4552
		4553	There is an undocumented "workaround" for this - defining
		4554	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4555	work on OS/X.
		4556
		4557	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4558
		4559	=head3 C<errno> reentrancy
		4560
		4561	The default compile environment on Solaris is unfortunately so
		4562	thread-unsafe that you can't even use components/libraries compiled
		4563	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,
		4564	isn't defined by default.
		4565
		4566	If you want to use libev in threaded environments you have to make sure
		4567	it's compiled with C<_REENTRANT> defined.
		4568
		4569	=head3 Event port backend
		4570
		4571	The scalable event interface for Solaris is called "event ports". Unfortunately,
		4572	this mechanism is very buggy. If you run into high CPU usage, your program
		4573	freezes or you get a large number of spurious wakeups, make sure you have
		4574	all the relevant and latest kernel patches applied. No, I don't know which
		4575	ones, but there are multiple ones.
		4576
		4577	If you can't get it to work, you can try running the program by setting
		4578	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4579	C<select> backends.
		4580
		4581	=head2 AIX POLL BUG
		4582
		4583	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4584	this by trying to avoid the poll backend altogether (i.e. it's not even
		4585	compiled in), which normally isn't a big problem as C<select> works fine
		4586	with large bitsets, and AIX is dead anyway.
		4587
		4588	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4589
		4590	=head3 General issues
2803		4591
2804	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4592	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2805	requires, and its I/O model is fundamentally incompatible with the POSIX	4593	requires, and its I/O model is fundamentally incompatible with the POSIX
2806	model. Libev still offers limited functionality on this platform in	4594	model. Libev still offers limited functionality on this platform in
2807	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4595	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2808	descriptors. This only applies when using Win32 natively, not when using	4596	descriptors. This only applies when using Win32 natively, not when using
2809	e.g. cygwin.	4597	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4598	as every compielr comes with a slightly differently broken/incompatible
		4599	environment.
		4600
		4601	Lifting these limitations would basically require the full
		4602	re-implementation of the I/O system. If you are into this kind of thing,
		4603	then note that glib does exactly that for you in a very portable way (note
		4604	also that glib is the slowest event library known to man).
2810		4605
2811	There is no supported compilation method available on windows except	4606	There is no supported compilation method available on windows except
2812	embedding it into other applications.	4607	embedding it into other applications.
2813		4608
		4609	Sensible signal handling is officially unsupported by Microsoft - libev
		4610	tries its best, but under most conditions, signals will simply not work.
		4611
		4612	Not a libev limitation but worth mentioning: windows apparently doesn't
		4613	accept large writes: instead of resulting in a partial write, windows will
		4614	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4615	so make sure you only write small amounts into your sockets (less than a
		4616	megabyte seems safe, but this apparently depends on the amount of memory
		4617	available).
		4618
2814	Due to the many, low, and arbitrary limits on the win32 platform and the	4619	Due to the many, low, and arbitrary limits on the win32 platform and
2815	abysmal performance of winsockets, using a large number of sockets is not	4620	the abysmal performance of winsockets, using a large number of sockets
2816	recommended (and not reasonable). If your program needs to use more than	4621	is not recommended (and not reasonable). If your program needs to use
2817	a hundred or so sockets, then likely it needs to use a totally different	4622	more than a hundred or so sockets, then likely it needs to use a totally
2818	implementation for windows, as libev offers the POSIX model, which cannot	4623	different implementation for windows, as libev offers the POSIX readiness
2819	be implemented efficiently on windows (microsoft monopoly games).	4624	notification model, which cannot be implemented efficiently on windows
		4625	(due to Microsoft monopoly games).
2820		4626
2821	=over 4	4627	A typical way to use libev under windows is to embed it (see the embedding
		4628	section for details) and use the following F<evwrap.h> header file instead
		4629	of F<ev.h>:
2822		4630
		4631	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4632	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4633
		4634	#include "ev.h"
		4635
		4636	And compile the following F<evwrap.c> file into your project (make sure
		4637	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4638
		4639	#include "evwrap.h"
		4640	#include "ev.c"
		4641
2823	=item The winsocket select function	4642	=head3 The winsocket C<select> function
2824		4643
2825	The winsocket C<select> function doesn't follow POSIX in that it requires	4644	The winsocket C<select> function doesn't follow POSIX in that it
2826	socket I<handles> and not socket I<file descriptors>. This makes select	4645	requires socket I<handles> and not socket I<file descriptors> (it is
2827	very inefficient, and also requires a mapping from file descriptors	4646	also extremely buggy). This makes select very inefficient, and also
2828	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4647	requires a mapping from file descriptors to socket handles (the Microsoft
2829	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4648	C runtime provides the function C<_open_osfhandle> for this). See the
2830	symbols for more info.	4649	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4650	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2831		4651
2832	The configuration for a "naked" win32 using the microsoft runtime	4652	The configuration for a "naked" win32 using the Microsoft runtime
2833	libraries and raw winsocket select is:	4653	libraries and raw winsocket select is:
2834		4654
2835	#define EV_USE_SELECT 1	4655	#define EV_USE_SELECT 1
2836	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4656	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2837		4657
2838	Note that winsockets handling of fd sets is O(n), so you can easily get a	4658	Note that winsockets handling of fd sets is O(n), so you can easily get a
2839	complexity in the O(n²) range when using win32.	4659	complexity in the O(n²) range when using win32.
2840		4660
2841	=item Limited number of file descriptors	4661	=head3 Limited number of file descriptors
2842		4662
2843	Windows has numerous arbitrary (and low) limits on things. Early versions	4663	Windows has numerous arbitrary (and low) limits on things.
2844	of winsocket's select only supported waiting for a max. of C<64> handles	4664
		4665	Early versions of winsocket's select only supported waiting for a maximum
2845	(probably owning to the fact that all windows kernels can only wait for	4666	of C<64> handles (probably owning to the fact that all windows kernels
2846	C<64> things at the same time internally; microsoft recommends spawning a	4667	can only wait for C<64> things at the same time internally; Microsoft
2847	chain of threads and wait for 63 handles and the previous thread in each).	4668	recommends spawning a chain of threads and wait for 63 handles and the
		4669	previous thread in each. Sounds great!).
2848		4670
2849	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4671	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2850	to some high number (e.g. C<2048>) before compiling the winsocket select	4672	to some high number (e.g. C<2048>) before compiling the winsocket select
2851	call (which might be in libev or elsewhere, for example, perl does its own	4673	call (which might be in libev or elsewhere, for example, perl and many
2852	select emulation on windows).	4674	other interpreters do their own select emulation on windows).
2853		4675
2854	Another limit is the number of file descriptors in the microsoft runtime	4676	Another limit is the number of file descriptors in the Microsoft runtime
2855	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4677	libraries, which by default is C<64> (there must be a hidden I<64>
2856	or something like this inside microsoft). You can increase this by calling	4678	fetish or something like this inside Microsoft). You can increase this
2857	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4679	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2858	arbitrary limit), but is broken in many versions of the microsoft runtime	4680	(another arbitrary limit), but is broken in many versions of the Microsoft
2859	libraries.
2860
2861	This might get you to about C<512> or C<2048> sockets (depending on	4681	runtime libraries. This might get you to about C<512> or C<2048> sockets
2862	windows version and/or the phase of the moon). To get more, you need to	4682	(depending on windows version and/or the phase of the moon). To get more,
2863	wrap all I/O functions and provide your own fd management, but the cost of	4683	you need to wrap all I/O functions and provide your own fd management, but
2864	calling select (O(n²)) will likely make this unworkable.	4684	the cost of calling select (O(n²)) will likely make this unworkable.
		4685
		4686	=head2 PORTABILITY REQUIREMENTS
		4687
		4688	In addition to a working ISO-C implementation and of course the
		4689	backend-specific APIs, libev relies on a few additional extensions:
		4690
		4691	=over 4
		4692
		4693	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4694	calling conventions regardless of C<ev_watcher_type *>.
		4695
		4696	Libev assumes not only that all watcher pointers have the same internal
		4697	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4698	assumes that the same (machine) code can be used to call any watcher
		4699	callback: The watcher callbacks have different type signatures, but libev
		4700	calls them using an C<ev_watcher *> internally.
		4701
		4702	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4703
		4704	The type C<sig_atomic_t volatile> (or whatever is defined as
		4705	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4706	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4707	believed to be sufficiently portable.
		4708
		4709	=item C<sigprocmask> must work in a threaded environment
		4710
		4711	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4712	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4713	pthread implementations will either allow C<sigprocmask> in the "main
		4714	thread" or will block signals process-wide, both behaviours would
		4715	be compatible with libev. Interaction between C<sigprocmask> and
		4716	C<pthread_sigmask> could complicate things, however.
		4717
		4718	The most portable way to handle signals is to block signals in all threads
		4719	except the initial one, and run the default loop in the initial thread as
		4720	well.
		4721
		4722	=item C<long> must be large enough for common memory allocation sizes
		4723
		4724	To improve portability and simplify its API, libev uses C<long> internally
		4725	instead of C<size_t> when allocating its data structures. On non-POSIX
		4726	systems (Microsoft...) this might be unexpectedly low, but is still at
		4727	least 31 bits everywhere, which is enough for hundreds of millions of
		4728	watchers.
		4729
		4730	=item C<double> must hold a time value in seconds with enough accuracy
		4731
		4732	The type C<double> is used to represent timestamps. It is required to
		4733	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4734	good enough for at least into the year 4000 with millisecond accuracy
		4735	(the design goal for libev). This requirement is overfulfilled by
		4736	implementations using IEEE 754, which is basically all existing ones. With
		4737	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
2865		4738
2866	=back	4739	=back
2867		4740
		4741	If you know of other additional requirements drop me a note.
		4742
		4743
		4744	=head1 ALGORITHMIC COMPLEXITIES
		4745
		4746	In this section the complexities of (many of) the algorithms used inside
		4747	libev will be documented. For complexity discussions about backends see
		4748	the documentation for C<ev_default_init>.
		4749
		4750	All of the following are about amortised time: If an array needs to be
		4751	extended, libev needs to realloc and move the whole array, but this
		4752	happens asymptotically rarer with higher number of elements, so O(1) might
		4753	mean that libev does a lengthy realloc operation in rare cases, but on
		4754	average it is much faster and asymptotically approaches constant time.
		4755
		4756	=over 4
		4757
		4758	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4759
		4760	This means that, when you have a watcher that triggers in one hour and
		4761	there are 100 watchers that would trigger before that, then inserting will
		4762	have to skip roughly seven (C<ld 100>) of these watchers.
		4763
		4764	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4765
		4766	That means that changing a timer costs less than removing/adding them,
		4767	as only the relative motion in the event queue has to be paid for.
		4768
		4769	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4770
		4771	These just add the watcher into an array or at the head of a list.
		4772
		4773	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4774
		4775	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4776
		4777	These watchers are stored in lists, so they need to be walked to find the
		4778	correct watcher to remove. The lists are usually short (you don't usually
		4779	have many watchers waiting for the same fd or signal: one is typical, two
		4780	is rare).
		4781
		4782	=item Finding the next timer in each loop iteration: O(1)
		4783
		4784	By virtue of using a binary or 4-heap, the next timer is always found at a
		4785	fixed position in the storage array.
		4786
		4787	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4788
		4789	A change means an I/O watcher gets started or stopped, which requires
		4790	libev to recalculate its status (and possibly tell the kernel, depending
		4791	on backend and whether C<ev_io_set> was used).
		4792
		4793	=item Activating one watcher (putting it into the pending state): O(1)
		4794
		4795	=item Priority handling: O(number_of_priorities)
		4796
		4797	Priorities are implemented by allocating some space for each
		4798	priority. When doing priority-based operations, libev usually has to
		4799	linearly search all the priorities, but starting/stopping and activating
		4800	watchers becomes O(1) with respect to priority handling.
		4801
		4802	=item Sending an ev_async: O(1)
		4803
		4804	=item Processing ev_async_send: O(number_of_async_watchers)
		4805
		4806	=item Processing signals: O(max_signal_number)
		4807
		4808	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4809	calls in the current loop iteration. Checking for async and signal events
		4810	involves iterating over all running async watchers or all signal numbers.
		4811
		4812	=back
		4813
		4814
		4815	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4816
		4817	The major version 4 introduced some minor incompatible changes to the API.
		4818
		4819	At the moment, the C<ev.h> header file tries to implement superficial
		4820	compatibility, so most programs should still compile. Those might be
		4821	removed in later versions of libev, so better update early than late.
		4822
		4823	=over 4
		4824
		4825	=item function/symbol renames
		4826
		4827	A number of functions and symbols have been renamed:
		4828
		4829	ev_loop => ev_run
		4830	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4831	EVLOOP_ONESHOT => EVRUN_ONCE
		4832
		4833	ev_unloop => ev_break
		4834	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4835	EVUNLOOP_ONE => EVBREAK_ONE
		4836	EVUNLOOP_ALL => EVBREAK_ALL
		4837
		4838	EV_TIMEOUT => EV_TIMER
		4839
		4840	ev_loop_count => ev_iteration
		4841	ev_loop_depth => ev_depth
		4842	ev_loop_verify => ev_verify
		4843
		4844	Most functions working on C<struct ev_loop> objects don't have an
		4845	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4846	associated constants have been renamed to not collide with the C<struct
		4847	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4848	as all other watcher types. Note that C<ev_loop_fork> is still called
		4849	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4850	typedef.
		4851
		4852	=item C<EV_COMPAT3> backwards compatibility mechanism
		4853
		4854	The backward compatibility mechanism can be controlled by
		4855	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4856	section.
		4857
		4858	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4859
		4860	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4861	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4862	and work, but the library code will of course be larger.
		4863
		4864	=back
		4865
		4866
		4867	=head1 GLOSSARY
		4868
		4869	=over 4
		4870
		4871	=item active
		4872
		4873	A watcher is active as long as it has been started (has been attached to
		4874	an event loop) but not yet stopped (disassociated from the event loop).
		4875
		4876	=item application
		4877
		4878	In this document, an application is whatever is using libev.
		4879
		4880	=item callback
		4881
		4882	The address of a function that is called when some event has been
		4883	detected. Callbacks are being passed the event loop, the watcher that
		4884	received the event, and the actual event bitset.
		4885
		4886	=item callback invocation
		4887
		4888	The act of calling the callback associated with a watcher.
		4889
		4890	=item event
		4891
		4892	A change of state of some external event, such as data now being available
		4893	for reading on a file descriptor, time having passed or simply not having
		4894	any other events happening anymore.
		4895
		4896	In libev, events are represented as single bits (such as C<EV_READ> or
		4897	C<EV_TIMER>).
		4898
		4899	=item event library
		4900
		4901	A software package implementing an event model and loop.
		4902
		4903	=item event loop
		4904
		4905	An entity that handles and processes external events and converts them
		4906	into callback invocations.
		4907
		4908	=item event model
		4909
		4910	The model used to describe how an event loop handles and processes
		4911	watchers and events.
		4912
		4913	=item pending
		4914
		4915	A watcher is pending as soon as the corresponding event has been detected,
		4916	and stops being pending as soon as the watcher will be invoked or its
		4917	pending status is explicitly cleared by the application.
		4918
		4919	A watcher can be pending, but not active. Stopping a watcher also clears
		4920	its pending status.
		4921
		4922	=item real time
		4923
		4924	The physical time that is observed. It is apparently strictly monotonic :)
		4925
		4926	=item wall-clock time
		4927
		4928	The time and date as shown on clocks. Unlike real time, it can actually
		4929	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4930	clock.
		4931
		4932	=item watcher
		4933
		4934	A data structure that describes interest in certain events. Watchers need
		4935	to be started (attached to an event loop) before they can receive events.
		4936
		4937	=item watcher invocation
		4938
		4939	The act of calling the callback associated with a watcher.
		4940
		4941	=back
2868		4942
2869	=head1 AUTHOR	4943	=head1 AUTHOR
2870		4944
2871	Marc Lehmann <libev@schmorp.de>.	4945	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2872		4946

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