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Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.319 by root, Fri Oct 22 10:09:12 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	=head1 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 occuring), 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
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 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	=head1 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	=head1 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 practice
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 such.	133	any calculations on it, you should treat it as some floating point value.
		134
		135	Unlike the name component C<stamp> might indicate, it is also used for
		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
104		158
105	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
106		160
107	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
108	library in any way.	162	library in any way.
…		…
111		165
112	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
113		167
114	Returns the current time as libev would use it. Please note that the	168	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	169	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	170	you actually want to know. Also interetsing is the combination of
		171	C<ev_update_now> and C<ev_now>.
		172
		173	=item ev_sleep (ev_tstamp interval)
		174
		175	Sleep for the given interval: The current thread will be blocked until
		176	either it is interrupted or the given time interval has passed. Basically
		177	this is a sub-second-resolution C<sleep ()>.
117		178
118	=item int ev_version_major ()	179	=item int ev_version_major ()
119		180
120	=item int ev_version_minor ()	181	=item int ev_version_minor ()
121		182
122	You can find out the major and minor version numbers of the library	183	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	184	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	185	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	186	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	187	version of the library your program was compiled against.
127		188
		189	These version numbers refer to the ABI version of the library, not the
		190	release version.
		191
128	Usually, it's a good idea to terminate if the major versions mismatch,	192	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	193	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	194	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	195	not a problem.
132		196
133	Example: Make sure we haven't accidentally been linked against the wrong	197	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	198	version (note, however, that this will not detect ABI mismatches :).
135		199
136	assert (("libev version mismatch",	200	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	201	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	202	&& ev_version_minor () >= EV_VERSION_MINOR));
139		203
140	=item unsigned int ev_supported_backends ()	204	=item unsigned int ev_supported_backends ()
141		205
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	206	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	207	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	209	a description of the set values.
146		210
147	Example: make sure we have the epoll method, because yeah this is cool and	211	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	212	a must have and can we have a torrent of it please!!!11
149		213
150	assert (("sorry, no epoll, no sex",	214	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	215	ev_supported_backends () & EVBACKEND_EPOLL));
152		216
153	=item unsigned int ev_recommended_backends ()	217	=item unsigned int ev_recommended_backends ()
154		218
155	Return the set of all backends compiled into this binary of libev and also	219	Return the set of all backends compiled into this binary of libev and
156	recommended for this platform. This set is often smaller than the one	220	also recommended for this platform, meaning it will work for most file
		221	descriptor types. This set is often smaller than the one returned by
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	222	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
158	most BSDs and will not be autodetected unless you explicitly request it	223	and will not be auto-detected unless you explicitly request it (assuming
159	(assuming you know what you are doing). This is the set of backends that	224	you know what you are doing). This is the set of backends that libev will
160	libev will probe for if you specify no backends explicitly.	225	probe for if you specify no backends explicitly.
161		226
162	=item unsigned int ev_embeddable_backends ()	227	=item unsigned int ev_embeddable_backends ()
163		228
164	Returns the set of backends that are embeddable in other event loops. This	229	Returns the set of backends that are embeddable in other event loops. This
165	is the theoretical, all-platform, value. To find which backends	230	value is platform-specific but can include backends not available on the
166	might be supported on the current system, you would need to look at	231	current system. To find which embeddable backends might be supported on
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	232	the current system, you would need to look at C<ev_embeddable_backends ()
168	recommended ones.	233	& ev_supported_backends ()>, likewise for recommended ones.
169		234
170	See the description of C<ev_embed> watchers for more info.	235	See the description of C<ev_embed> watchers for more info.
171		236
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	237	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		238
174	Sets the allocation function to use (the prototype is similar - the	239	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	240	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	241	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	242	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	243	or take some potentially destructive action.
179	function.	244
		245	Since some systems (at least OpenBSD and Darwin) fail to implement
		246	correct C<realloc> semantics, libev will use a wrapper around the system
		247	C<realloc> and C<free> functions by default.
180		248
181	You could override this function in high-availability programs to, say,	249	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	250	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	251	or even to sleep a while and retry until some memory is available.
184		252
185	Example: Replace the libev allocator with one that waits a bit and then	253	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	254	retries (example requires a standards-compliant C<realloc>).
187		255
188	static void *	256	static void *
189	persistent_realloc (void *ptr, size_t size)	257	persistent_realloc (void *ptr, size_t size)
190	{	258	{
191	for (;;)	259	for (;;)
…		…
200	}	268	}
201		269
202	...	270	...
203	ev_set_allocator (persistent_realloc);	271	ev_set_allocator (persistent_realloc);
204		272
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	273	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		274
207	Set the callback function to call on a retryable syscall error (such	275	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	276	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	277	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	278	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	279	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	280	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	281	(such as abort).
214		282
215	Example: This is basically the same thing that libev does internally, too.	283	Example: This is basically the same thing that libev does internally, too.
…		…
226		294
227	=back	295	=back
228		296
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	297	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		298
231	An event loop is described by a C<struct ev_loop *>. The library knows two	299	An event loop is described by a C<struct ev_loop *> (the C<struct> is
232	types of such loops, the I<default> loop, which supports signals and child	300	I<not> optional in this case unless libev 3 compatibility is disabled, as
233	events, and dynamically created loops which do not.	301	libev 3 had an C<ev_loop> function colliding with the struct name).
234		302
235	If you use threads, a common model is to run the default event loop	303	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	304	supports signals and child events, and dynamically created event loops
237	create, you also create another event loop. Libev itself does no locking	305	which do not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		306
242	=over 4	307	=over 4
243		308
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	309	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		310
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	314	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		315
251	If you don't know what event loop to use, use the one returned from this	316	If you don't know what event loop to use, use the one returned from this
252	function.	317	function.
253		318
		319	Note that this function is I<not> thread-safe, so if you want to use it
		320	from multiple threads, you have to lock (note also that this is unlikely,
		321	as loops cannot be shared easily between threads anyway).
		322
		323	The default loop is the only loop that can handle C<ev_signal> and
		324	C<ev_child> watchers, and to do this, it always registers a handler
		325	for C<SIGCHLD>. If this is a problem for your application you can either
		326	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		327	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		328	C<ev_default_init>.
		329
254	The flags argument can be used to specify special behaviour or specific	330	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	331	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		332
257	The following flags are supported:	333	The following flags are supported:
258		334
…		…
263	The default flags value. Use this if you have no clue (it's the right	339	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	340	thing, believe me).
265		341
266	=item C<EVFLAG_NOENV>	342	=item C<EVFLAG_NOENV>
267		343
268	If this flag bit is ored into the flag value (or the program runs setuid	344	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	345	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	346	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	347	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	348	useful to try out specific backends to test their performance, or to work
273	around bugs.	349	around bugs.
274		350
275	=item C<EVFLAG_FORKCHECK>	351	=item C<EVFLAG_FORKCHECK>
276		352
277	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	353	Instead of calling C<ev_loop_fork> manually after a fork, you can also
278	a fork, you can also make libev check for a fork in each iteration by	354	make libev check for a fork in each iteration by enabling this flag.
279	enabling this flag.
280		355
281	This works by calling C<getpid ()> on every iteration of the loop,	356	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	357	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	358	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	359	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	360	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	361	C<pthread_atfork> which is even faster).
287		362
288	The big advantage of this flag is that you can forget about fork (and	363	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	364	forget about forgetting to tell libev about forking) when you use this
290	flag.	365	flag.
291		366
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	367	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	368	environment variable.
		369
		370	=item C<EVFLAG_NOINOTIFY>
		371
		372	When this flag is specified, then libev will not attempt to use the
		373	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		374	testing, this flag can be useful to conserve inotify file descriptors, as
		375	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		376
		377	=item C<EVFLAG_SIGNALFD>
		378
		379	When this flag is specified, then libev will attempt to use the
		380	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		381	delivers signals synchronously, which makes it both faster and might make
		382	it possible to get the queued signal data. It can also simplify signal
		383	handling with threads, as long as you properly block signals in your
		384	threads that are not interested in handling them.
		385
		386	Signalfd will not be used by default as this changes your signal mask, and
		387	there are a lot of shoddy libraries and programs (glib's threadpool for
		388	example) that can't properly initialise their signal masks.
294		389
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	390	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		391
297	This is your standard select(2) backend. Not I<completely> standard, as	392	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	393	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	394	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	395	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	396	usually the fastest backend for a low number of (low-numbered :) fds.
		397
		398	To get good performance out of this backend you need a high amount of
		399	parallelism (most of the file descriptors should be busy). If you are
		400	writing a server, you should C<accept ()> in a loop to accept as many
		401	connections as possible during one iteration. You might also want to have
		402	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		403	readiness notifications you get per iteration.
		404
		405	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		406	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		407	C<exceptfds> set on that platform).
302		408
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	409	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		410
305	And this is your standard poll(2) backend. It's more complicated than	411	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	412	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	413	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	414	considerably with a lot of inactive fds). It scales similarly to select,
		415	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		416	performance tips.
		417
		418	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		419	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		420
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	421	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		422
		423	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		424	kernels).
		425
312	For few fds, this backend is a bit little slower than poll and select,	426	For few fds, this backend is a bit little slower than poll and select,
313	but it scales phenomenally better. While poll and select usually scale like	427	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	428	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	429	epoll scales either O(1) or O(active_fds).
316		430
		431	The epoll mechanism deserves honorable mention as the most misdesigned
		432	of the more advanced event mechanisms: mere annoyances include silently
		433	dropping file descriptors, requiring a system call per change per file
		434	descriptor (and unnecessary guessing of parameters), problems with dup and
		435	so on. The biggest issue is fork races, however - if a program forks then
		436	I<both> parent and child process have to recreate the epoll set, which can
		437	take considerable time (one syscall per file descriptor) and is of course
		438	hard to detect.
		439
		440	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		441	of course I<doesn't>, and epoll just loves to report events for totally
		442	I<different> file descriptors (even already closed ones, so one cannot
		443	even remove them from the set) than registered in the set (especially
		444	on SMP systems). Libev tries to counter these spurious notifications by
		445	employing an additional generation counter and comparing that against the
		446	events to filter out spurious ones, recreating the set when required. Last
		447	not least, it also refuses to work with some file descriptors which work
		448	perfectly fine with C<select> (files, many character devices...).
		449
317	While stopping and starting an I/O watcher in the same iteration will	450	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	451	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	452	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	453	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	454	file descriptors might not work very well if you register events for both
		455	file descriptors.
322		456
323	Please note that epoll sometimes generates spurious notifications, so you	457	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	458	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	459	i.e. keep at least one watcher active per fd at all times. Stopping and
		460	starting a watcher (without re-setting it) also usually doesn't cause
		461	extra overhead. A fork can both result in spurious notifications as well
		462	as in libev having to destroy and recreate the epoll object, which can
		463	take considerable time and thus should be avoided.
		464
		465	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		466	faster than epoll for maybe up to a hundred file descriptors, depending on
		467	the usage. So sad.
		468
		469	While nominally embeddable in other event loops, this feature is broken in
		470	all kernel versions tested so far.
		471
		472	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		473	C<EVBACKEND_POLL>.
326		474
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	475	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		476
329	Kqueue deserves special mention, as at the time of this writing, it	477	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	478	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	479	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	480	it's completely useless). Unlike epoll, however, whose brokenness
		481	is by design, these kqueue bugs can (and eventually will) be fixed
		482	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	483	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	484	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		485	system like NetBSD.
		486
		487	You still can embed kqueue into a normal poll or select backend and use it
		488	only for sockets (after having made sure that sockets work with kqueue on
		489	the target platform). See C<ev_embed> watchers for more info.
335		490
336	It scales in the same way as the epoll backend, but the interface to the	491	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	492	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	493	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	494	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	495	two event changes per incident. Support for C<fork ()> is very bad (but
		496	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		497	cases
		498
		499	This backend usually performs well under most conditions.
		500
		501	While nominally embeddable in other event loops, this doesn't work
		502	everywhere, so you might need to test for this. And since it is broken
		503	almost everywhere, you should only use it when you have a lot of sockets
		504	(for which it usually works), by embedding it into another event loop
		505	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		506	also broken on OS X)) and, did I mention it, using it only for sockets.
		507
		508	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		509	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		510	C<NOTE_EOF>.
341		511
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	512	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		513
344	This is not implemented yet (and might never be).	514	This is not implemented yet (and might never be, unless you send me an
		515	implementation). According to reports, C</dev/poll> only supports sockets
		516	and is not embeddable, which would limit the usefulness of this backend
		517	immensely.
345		518
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	519	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		520
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	521	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	522	it's really slow, but it still scales very well (O(active_fds)).
350		523
351	Please note that solaris ports can result in a lot of spurious	524	Please note that Solaris event ports can deliver a lot of spurious
352	notifications, so you need to use non-blocking I/O or other means to avoid	525	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	526	blocking when no data (or space) is available.
		527
		528	While this backend scales well, it requires one system call per active
		529	file descriptor per loop iteration. For small and medium numbers of file
		530	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		531	might perform better.
		532
		533	On the positive side, with the exception of the spurious readiness
		534	notifications, this backend actually performed fully to specification
		535	in all tests and is fully embeddable, which is a rare feat among the
		536	OS-specific backends (I vastly prefer correctness over speed hacks).
		537
		538	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		539	C<EVBACKEND_POLL>.
354		540
355	=item C<EVBACKEND_ALL>	541	=item C<EVBACKEND_ALL>
356		542
357	Try all backends (even potentially broken ones that wouldn't be tried	543	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	544	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	545	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		546
		547	It is definitely not recommended to use this flag.
		548
361	=back	549	=back
362		550
363	If one or more of these are ored into the flags value, then only these	551	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	552	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	553	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	554	()> will be tried.
367		555
368	The most typical usage is like this:	556	Example: This is the most typical usage.
369		557
370	if (!ev_default_loop (0))	558	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	559	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		560
373	Restrict libev to the select and poll backends, and do not allow	561	Example: Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:	562	environment settings to be taken into account:
375		563
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	564	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		565
378	Use whatever libev has to offer, but make sure that kqueue is used if	566	Example: Use whatever libev has to offer, but make sure that kqueue is
379	available (warning, breaks stuff, best use only with your own private	567	used if available (warning, breaks stuff, best use only with your own
380	event loop and only if you know the OS supports your types of fds):	568	private event loop and only if you know the OS supports your types of
		569	fds):
381		570
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	571	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		572
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	573	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		574
386	Similar to C<ev_default_loop>, but always creates a new event loop that is	575	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot	576	always distinct from the default loop.
388	handle signal and child watchers, and attempts to do so will be greeted by	577
389	undefined behaviour (or a failed assertion if assertions are enabled).	578	Note that this function I<is> thread-safe, and one common way to use
		579	libev with threads is indeed to create one loop per thread, and using the
		580	default loop in the "main" or "initial" thread.
390		581
391	Example: Try to create a event loop that uses epoll and nothing else.	582	Example: Try to create a event loop that uses epoll and nothing else.
392		583
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	584	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	585	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	586	fatal ("no epoll found here, maybe it hides under your chair");
396		587
397	=item ev_default_destroy ()	588	=item ev_default_destroy ()
398		589
399	Destroys the default loop again (frees all memory and kernel state	590	Destroys the default loop (frees all memory and kernel state etc.). None
400	etc.). None of the active event watchers will be stopped in the normal	591	of the active event watchers will be stopped in the normal sense, so
401	sense, so e.g. C<ev_is_active> might still return true. It is your	592	e.g. C<ev_is_active> might still return true. It is your responsibility to
402	responsibility to either stop all watchers cleanly yoursef I<before>	593	either stop all watchers cleanly yourself I<before> calling this function,
403	calling this function, or cope with the fact afterwards (which is usually	594	or cope with the fact afterwards (which is usually the easiest thing, you
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	595	can just ignore the watchers and/or C<free ()> them for example).
405	for example).	596
		597	Note that certain global state, such as signal state (and installed signal
		598	handlers), will not be freed by this function, and related watchers (such
		599	as signal and child watchers) would need to be stopped manually.
		600
		601	In general it is not advisable to call this function except in the
		602	rare occasion where you really need to free e.g. the signal handling
		603	pipe fds. If you need dynamically allocated loops it is better to use
		604	C<ev_loop_new> and C<ev_loop_destroy>.
406		605
407	=item ev_loop_destroy (loop)	606	=item ev_loop_destroy (loop)
408		607
409	Like C<ev_default_destroy>, but destroys an event loop created by an	608	Like C<ev_default_destroy>, but destroys an event loop created by an
410	earlier call to C<ev_loop_new>.	609	earlier call to C<ev_loop_new>.
411		610
412	=item ev_default_fork ()	611	=item ev_default_fork ()
413		612
		613	This function sets a flag that causes subsequent C<ev_run> iterations
414	This function reinitialises the kernel state for backends that have	614	to reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	615	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	616	the child process (or both child and parent, but that again makes little
417	again makes little sense).	617	sense). You I<must> call it in the child before using any of the libev
		618	functions, and it will only take effect at the next C<ev_run> iteration.
418		619
419	You I<must> call this function in the child process after forking if and	620	Again, you I<have> to call it on I<any> loop that you want to re-use after
420	only if you want to use the event library in both processes. If you just	621	a fork, I<even if you do not plan to use the loop in the parent>. This is
421	fork+exec, you don't have to call it.	622	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		623	during fork.
		624
		625	On the other hand, you only need to call this function in the child
		626	process if and only if you want to use the event loop in the child. If
		627	you just fork+exec or create a new loop in the child, you don't have to
		628	call it at all (in fact, C<epoll> is so badly broken that it makes a
		629	difference, but libev will usually detect this case on its own and do a
		630	costly reset of the backend).
422		631
423	The function itself is quite fast and it's usually not a problem to call	632	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	633	it just in case after a fork. To make this easy, the function will fit in
425	quite nicely into a call to C<pthread_atfork>:	634	quite nicely into a call to C<pthread_atfork>:
426		635
427	pthread_atfork (0, 0, ev_default_fork);	636	pthread_atfork (0, 0, ev_default_fork);
428		637
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	638	=item ev_loop_fork (loop)
434		639
435	Like C<ev_default_fork>, but acts on an event loop created by	640	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	641	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.	642	after fork that you want to re-use in the child, and how you keep track of
		643	them is entirely your own problem.
438		644
		645	=item int ev_is_default_loop (loop)
		646
		647	Returns true when the given loop is, in fact, the default loop, and false
		648	otherwise.
		649
439	=item unsigned int ev_loop_count (loop)	650	=item unsigned int ev_iteration (loop)
440		651
441	Returns the count of loop iterations for the loop, which is identical to	652	Returns the current iteration count for the event loop, which is identical
442	the number of times libev did poll for new events. It starts at C<0> and	653	to the number of times libev did poll for new events. It starts at C<0>
443	happily wraps around with enough iterations.	654	and happily wraps around with enough iterations.
444		655
445	This value can sometimes be useful as a generation counter of sorts (it	656	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	657	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	658	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		659	prepare and check phases.
		660
		661	=item unsigned int ev_depth (loop)
		662
		663	Returns the number of times C<ev_run> was entered minus the number of
		664	times C<ev_run> was exited, in other words, the recursion depth.
		665
		666	Outside C<ev_run>, this number is zero. In a callback, this number is
		667	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		668	in which case it is higher.
		669
		670	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		671	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		672	ungentleman-like behaviour unless it's really convenient.
448		673
449	=item unsigned int ev_backend (loop)	674	=item unsigned int ev_backend (loop)
450		675
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	676	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	677	use.
…		…
455		680
456	Returns the current "event loop time", which is the time the event loop	681	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	682	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	683	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	684	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	685	event occurring (or more correctly, libev finding out about it).
461		686
		687	=item ev_now_update (loop)
		688
		689	Establishes the current time by querying the kernel, updating the time
		690	returned by C<ev_now ()> in the progress. This is a costly operation and
		691	is usually done automatically within C<ev_run ()>.
		692
		693	This function is rarely useful, but when some event callback runs for a
		694	very long time without entering the event loop, updating libev's idea of
		695	the current time is a good idea.
		696
		697	See also L<The special problem of time updates> in the C<ev_timer> section.
		698
		699	=item ev_suspend (loop)
		700
		701	=item ev_resume (loop)
		702
		703	These two functions suspend and resume an event loop, for use when the
		704	loop is not used for a while and timeouts should not be processed.
		705
		706	A typical use case would be an interactive program such as a game: When
		707	the user presses C<^Z> to suspend the game and resumes it an hour later it
		708	would be best to handle timeouts as if no time had actually passed while
		709	the program was suspended. This can be achieved by calling C<ev_suspend>
		710	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		711	C<ev_resume> directly afterwards to resume timer processing.
		712
		713	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		714	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		715	will be rescheduled (that is, they will lose any events that would have
		716	occurred while suspended).
		717
		718	After calling C<ev_suspend> you B<must not> call I<any> function on the
		719	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		720	without a previous call to C<ev_suspend>.
		721
		722	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		723	event loop time (see C<ev_now_update>).
		724
462	=item ev_loop (loop, int flags)	725	=item ev_run (loop, int flags)
463		726
464	Finally, this is it, the event handler. This function usually is called	727	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	728	after you have initialised all your watchers and you want to start
466	events.	729	handling events. It will ask the operating system for any new events, call
		730	the watcher callbacks, an then repeat the whole process indefinitely: This
		731	is why event loops are called I<loops>.
467		732
468	If the flags argument is specified as C<0>, it will not return until	733	If the flags argument is specified as C<0>, it will keep handling events
469	either no event watchers are active anymore or C<ev_unloop> was called.	734	until either no event watchers are active anymore or C<ev_break> was
		735	called.
470		736
471	Please note that an explicit C<ev_unloop> is usually better than	737	Please note that an explicit C<ev_break> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	738	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	739	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	740	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	741	of relying on its watchers stopping correctly, that is truly a thing of
		742	beauty.
476		743
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	744	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	745	those events and any already outstanding ones, but will not wait and
479	case there are no events and will return after one iteration of the loop.	746	block your process in case there are no events and will return after one
		747	iteration of the loop. This is sometimes useful to poll and handle new
		748	events while doing lengthy calculations, to keep the program responsive.
480		749
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	750	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	751	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	752	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	753	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	754	user-registered callback will be called), and will return after one
		755	iteration of the loop.
		756
		757	This is useful if you are waiting for some external event in conjunction
		758	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	759	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	760	usually a better approach for this kind of thing.
488		761
489	Here are the gory details of what C<ev_loop> does:	762	Here are the gory details of what C<ev_run> does:
490		763
491	* If there are no active watchers (reference count is zero), return.	764	- Increment loop depth.
492	- Queue prepare watchers and then call all outstanding watchers.	765	- Reset the ev_break status.
		766	- Before the first iteration, call any pending watchers.
		767	LOOP:
		768	- If EVFLAG_FORKCHECK was used, check for a fork.
		769	- If a fork was detected (by any means), queue and call all fork watchers.
		770	- Queue and call all prepare watchers.
		771	- If ev_break was called, goto FINISH.
493	- If we have been forked, recreate the kernel state.	772	- If we have been forked, detach and recreate the kernel state
		773	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	774	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	775	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	776	- Calculate for how long to sleep or block, if at all
		777	(active idle watchers, EVRUN_NOWAIT or not having
		778	any active watchers at all will result in not sleeping).
		779	- Sleep if the I/O and timer collect interval say so.
		780	- Increment loop iteration counter.
497	- Block the process, waiting for any events.	781	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	782	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	783	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	784	- Queue all expired timers.
501	- Queue all outstanding periodics.	785	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	786	- Queue all idle watchers with priority higher than that of pending events.
503	- Queue all check watchers.	787	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	788	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	789	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	790	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	791	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
508	were used, return, otherwise continue with step *.	792	were used, or there are no active watchers, goto FINISH, otherwise
		793	continue with step LOOP.
		794	FINISH:
		795	- Reset the ev_break status iff it was EVBREAK_ONE.
		796	- Decrement the loop depth.
		797	- Return.
509		798
510	Example: Queue some jobs and then loop until no events are outsanding	799	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	800	anymore.
512		801
513	... queue jobs here, make sure they register event watchers as long	802	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	803	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	804	ev_run (my_loop, 0);
516	... jobs done. yeah!	805	... jobs done or somebody called unloop. yeah!
517		806
518	=item ev_unloop (loop, how)	807	=item ev_break (loop, how)
519		808
520	Can be used to make a call to C<ev_loop> return early (but only after it	809	Can be used to make a call to C<ev_run> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	810	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	811	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	812	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		813
		814	This "unloop state" will be cleared when entering C<ev_run> again.
		815
		816	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
524		817
525	=item ev_ref (loop)	818	=item ev_ref (loop)
526		819
527	=item ev_unref (loop)	820	=item ev_unref (loop)
528		821
529	Ref/unref can be used to add or remove a reference count on the event	822	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	823	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	824	count is nonzero, C<ev_run> will not return on its own.
532	a watcher you never unregister that should not keep C<ev_loop> from	825
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	826	This is useful when you have a watcher that you never intend to
		827	unregister, but that nevertheless should not keep C<ev_run> from
		828	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		829	before stopping it.
		830
534	example, libev itself uses this for its internal signal pipe: It is not	831	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	832	is not visible to the libev user and should not keep C<ev_run> from
536	no event watchers registered by it are active. It is also an excellent	833	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	834	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	835	third-party libraries. Just remember to I<unref after start> and I<ref
		836	before stop> (but only if the watcher wasn't active before, or was active
		837	before, respectively. Note also that libev might stop watchers itself
		838	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		839	in the callback).
539		840
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	841	Example: Create a signal watcher, but keep it from keeping C<ev_run>
541	running when nothing else is active.	842	running when nothing else is active.
542		843
543	struct ev_signal exitsig;	844	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	845	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	846	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	847	evf_unref (loop);
547		848
548	Example: For some weird reason, unregister the above signal handler again.	849	Example: For some weird reason, unregister the above signal handler again.
549		850
550	ev_ref (loop);	851	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	852	ev_signal_stop (loop, &exitsig);
		853
		854	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		855
		856	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		857
		858	These advanced functions influence the time that libev will spend waiting
		859	for events. Both time intervals are by default C<0>, meaning that libev
		860	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		861	latency.
		862
		863	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		864	allows libev to delay invocation of I/O and timer/periodic callbacks
		865	to increase efficiency of loop iterations (or to increase power-saving
		866	opportunities).
		867
		868	The idea is that sometimes your program runs just fast enough to handle
		869	one (or very few) event(s) per loop iteration. While this makes the
		870	program responsive, it also wastes a lot of CPU time to poll for new
		871	events, especially with backends like C<select ()> which have a high
		872	overhead for the actual polling but can deliver many events at once.
		873
		874	By setting a higher I<io collect interval> you allow libev to spend more
		875	time collecting I/O events, so you can handle more events per iteration,
		876	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		877	C<ev_timer>) will be not affected. Setting this to a non-null value will
		878	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		879	sleep time ensures that libev will not poll for I/O events more often then
		880	once per this interval, on average.
		881
		882	Likewise, by setting a higher I<timeout collect interval> you allow libev
		883	to spend more time collecting timeouts, at the expense of increased
		884	latency/jitter/inexactness (the watcher callback will be called
		885	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		886	value will not introduce any overhead in libev.
		887
		888	Many (busy) programs can usually benefit by setting the I/O collect
		889	interval to a value near C<0.1> or so, which is often enough for
		890	interactive servers (of course not for games), likewise for timeouts. It
		891	usually doesn't make much sense to set it to a lower value than C<0.01>,
		892	as this approaches the timing granularity of most systems. Note that if
		893	you do transactions with the outside world and you can't increase the
		894	parallelity, then this setting will limit your transaction rate (if you
		895	need to poll once per transaction and the I/O collect interval is 0.01,
		896	then you can't do more than 100 transactions per second).
		897
		898	Setting the I<timeout collect interval> can improve the opportunity for
		899	saving power, as the program will "bundle" timer callback invocations that
		900	are "near" in time together, by delaying some, thus reducing the number of
		901	times the process sleeps and wakes up again. Another useful technique to
		902	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		903	they fire on, say, one-second boundaries only.
		904
		905	Example: we only need 0.1s timeout granularity, and we wish not to poll
		906	more often than 100 times per second:
		907
		908	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		909	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		910
		911	=item ev_invoke_pending (loop)
		912
		913	This call will simply invoke all pending watchers while resetting their
		914	pending state. Normally, C<ev_run> does this automatically when required,
		915	but when overriding the invoke callback this call comes handy. This
		916	function can be invoked from a watcher - this can be useful for example
		917	when you want to do some lengthy calculation and want to pass further
		918	event handling to another thread (you still have to make sure only one
		919	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		920
		921	=item int ev_pending_count (loop)
		922
		923	Returns the number of pending watchers - zero indicates that no watchers
		924	are pending.
		925
		926	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		927
		928	This overrides the invoke pending functionality of the loop: Instead of
		929	invoking all pending watchers when there are any, C<ev_run> will call
		930	this callback instead. This is useful, for example, when you want to
		931	invoke the actual watchers inside another context (another thread etc.).
		932
		933	If you want to reset the callback, use C<ev_invoke_pending> as new
		934	callback.
		935
		936	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		937
		938	Sometimes you want to share the same loop between multiple threads. This
		939	can be done relatively simply by putting mutex_lock/unlock calls around
		940	each call to a libev function.
		941
		942	However, C<ev_run> can run an indefinite time, so it is not feasible
		943	to wait for it to return. One way around this is to wake up the event
		944	loop via C<ev_break> and C<av_async_send>, another way is to set these
		945	I<release> and I<acquire> callbacks on the loop.
		946
		947	When set, then C<release> will be called just before the thread is
		948	suspended waiting for new events, and C<acquire> is called just
		949	afterwards.
		950
		951	Ideally, C<release> will just call your mutex_unlock function, and
		952	C<acquire> will just call the mutex_lock function again.
		953
		954	While event loop modifications are allowed between invocations of
		955	C<release> and C<acquire> (that's their only purpose after all), no
		956	modifications done will affect the event loop, i.e. adding watchers will
		957	have no effect on the set of file descriptors being watched, or the time
		958	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		959	to take note of any changes you made.
		960
		961	In theory, threads executing C<ev_run> will be async-cancel safe between
		962	invocations of C<release> and C<acquire>.
		963
		964	See also the locking example in the C<THREADS> section later in this
		965	document.
		966
		967	=item ev_set_userdata (loop, void *data)
		968
		969	=item ev_userdata (loop)
		970
		971	Set and retrieve a single C<void *> associated with a loop. When
		972	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		973	C<0.>
		974
		975	These two functions can be used to associate arbitrary data with a loop,
		976	and are intended solely for the C<invoke_pending_cb>, C<release> and
		977	C<acquire> callbacks described above, but of course can be (ab-)used for
		978	any other purpose as well.
		979
		980	=item ev_verify (loop)
		981
		982	This function only does something when C<EV_VERIFY> support has been
		983	compiled in, which is the default for non-minimal builds. It tries to go
		984	through all internal structures and checks them for validity. If anything
		985	is found to be inconsistent, it will print an error message to standard
		986	error and call C<abort ()>.
		987
		988	This can be used to catch bugs inside libev itself: under normal
		989	circumstances, this function will never abort as of course libev keeps its
		990	data structures consistent.
552		991
553	=back	992	=back
554		993
555		994
556	=head1 ANATOMY OF A WATCHER	995	=head1 ANATOMY OF A WATCHER
557		996
		997	In the following description, uppercase C<TYPE> in names stands for the
		998	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		999	watchers and C<ev_io_start> for I/O watchers.
		1000
558	A watcher is a structure that you create and register to record your	1001	A watcher is an opaque structure that you allocate and register to record
559	interest in some event. For instance, if you want to wait for STDIN to	1002	your interest in some event. To make a concrete example, imagine you want
560	become readable, you would create an C<ev_io> watcher for that:	1003	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1004	for that:
561		1005
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1006	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	1007	{
564	ev_io_stop (w);	1008	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	1009	ev_break (loop, EVBREAK_ALL);
566	}	1010	}
567		1011
568	struct ev_loop *loop = ev_default_loop (0);	1012	struct ev_loop *loop = ev_default_loop (0);
		1013
569	struct ev_io stdin_watcher;	1014	ev_io stdin_watcher;
		1015
570	ev_init (&stdin_watcher, my_cb);	1016	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1017	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	1018	ev_io_start (loop, &stdin_watcher);
		1019
573	ev_loop (loop, 0);	1020	ev_run (loop, 0);
574		1021
575	As you can see, you are responsible for allocating the memory for your	1022	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	1023	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	1024	stack).
578		1025
		1026	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1027	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1028
579	Each watcher structure must be initialised by a call to C<ev_init	1029	Each watcher structure must be initialised by a call to C<ev_init (watcher
580	(watcher *, callback)>, which expects a callback to be provided. This	1030	*, callback)>, which expects a callback to be provided. This callback is
581	callback gets invoked each time the event occurs (or, in the case of io	1031	invoked each time the event occurs (or, in the case of I/O watchers, each
582	watchers, each time the event loop detects that the file descriptor given	1032	time the event loop detects that the file descriptor given is readable
583	is readable and/or writable).	1033	and/or writable).
584		1034
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1035	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	1036	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	1037	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	1038	ev_TYPE_init (watcher *, callback, ...) >>.
589		1039
590	To make the watcher actually watch out for events, you have to start it	1040	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1041	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1042	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1043	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1044
595	As long as your watcher is active (has been started but not stopped) you	1045	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1046	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1047	reinitialise it or call its C<ev_TYPE_set> macro.
598		1048
599	Each and every callback receives the event loop pointer as first, the	1049	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1050	registered watcher structure as second, and a bitset of received events as
601	third argument.	1051	third argument.
602		1052
…		…
611	=item C<EV_WRITE>	1061	=item C<EV_WRITE>
612		1062
613	The file descriptor in the C<ev_io> watcher has become readable and/or	1063	The file descriptor in the C<ev_io> watcher has become readable and/or
614	writable.	1064	writable.
615		1065
616	=item C<EV_TIMEOUT>	1066	=item C<EV_TIMER>
617		1067
618	The C<ev_timer> watcher has timed out.	1068	The C<ev_timer> watcher has timed out.
619		1069
620	=item C<EV_PERIODIC>	1070	=item C<EV_PERIODIC>
621		1071
…		…
639		1089
640	=item C<EV_PREPARE>	1090	=item C<EV_PREPARE>
641		1091
642	=item C<EV_CHECK>	1092	=item C<EV_CHECK>
643		1093
644	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1094	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
645	to gather new events, and all C<ev_check> watchers are invoked just after	1095	to gather new events, and all C<ev_check> watchers are invoked just after
646	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1096	C<ev_run> has gathered them, but before it invokes any callbacks for any
647	received events. Callbacks of both watcher types can start and stop as	1097	received events. Callbacks of both watcher types can start and stop as
648	many watchers as they want, and all of them will be taken into account	1098	many watchers as they want, and all of them will be taken into account
649	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1099	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
650	C<ev_loop> from blocking).	1100	C<ev_run> from blocking).
651		1101
652	=item C<EV_EMBED>	1102	=item C<EV_EMBED>
653		1103
654	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1104	The embedded event loop specified in the C<ev_embed> watcher needs attention.
655		1105
656	=item C<EV_FORK>	1106	=item C<EV_FORK>
657		1107
658	The event loop has been resumed in the child process after fork (see	1108	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1109	C<ev_fork>).
660		1110
		1111	=item C<EV_ASYNC>
		1112
		1113	The given async watcher has been asynchronously notified (see C<ev_async>).
		1114
		1115	=item C<EV_CUSTOM>
		1116
		1117	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1118	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1119
661	=item C<EV_ERROR>	1120	=item C<EV_ERROR>
662		1121
663	An unspecified error has occured, the watcher has been stopped. This might	1122	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1123	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1124	ran out of memory, a file descriptor was found to be closed or any other
		1125	problem. Libev considers these application bugs.
		1126
666	problem. You best act on it by reporting the problem and somehow coping	1127	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1128	watcher being stopped. Note that well-written programs should not receive
		1129	an error ever, so when your watcher receives it, this usually indicates a
		1130	bug in your program.
668		1131
669	Libev will usually signal a few "dummy" events together with an error,	1132	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1133	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1134	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1135	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1136	programs, though, as the fd could already be closed and reused for another
		1137	thing, so beware.
674		1138
675	=back	1139	=back
676		1140
		1141	=head2 WATCHER STATES
		1142
		1143	There are various watcher states mentioned throughout this manual -
		1144	active, pending and so on. In this section these states and the rules to
		1145	transition between them will be described in more detail - and while these
		1146	rules might look complicated, they usually do "the right thing".
		1147
		1148	=over 4
		1149
		1150	=item initialiased
		1151
		1152	Before a watcher can be registered with the event looop it has to be
		1153	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1154	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1155
		1156	In this state it is simply some block of memory that is suitable for use
		1157	in an event loop. It can be moved around, freed, reused etc. at will.
		1158
		1159	=item started/running/active
		1160
		1161	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1162	property of the event loop, and is actively waiting for events. While in
		1163	this state it cannot be accessed (except in a few documented ways), moved,
		1164	freed or anything else - the only legal thing is to keep a pointer to it,
		1165	and call libev functions on it that are documented to work on active watchers.
		1166
		1167	=item pending
		1168
		1169	If a watcher is active and libev determines that an event it is interested
		1170	in has occurred (such as a timer expiring), it will become pending. It will
		1171	stay in this pending state until either it is stopped or its callback is
		1172	about to be invoked, so it is not normally pending inside the watcher
		1173	callback.
		1174
		1175	The watcher might or might not be active while it is pending (for example,
		1176	an expired non-repeating timer can be pending but no longer active). If it
		1177	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1178	but it is still property of the event loop at this time, so cannot be
		1179	moved, freed or reused. And if it is active the rules described in the
		1180	previous item still apply.
		1181
		1182	It is also possible to feed an event on a watcher that is not active (e.g.
		1183	via C<ev_feed_event>), in which case it becomes pending without being
		1184	active.
		1185
		1186	=item stopped
		1187
		1188	A watcher can be stopped implicitly by libev (in which case it might still
		1189	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1190	latter will clear any pending state the watcher might be in, regardless
		1191	of whether it was active or not, so stopping a watcher explicitly before
		1192	freeing it is often a good idea.
		1193
		1194	While stopped (and not pending) the watcher is essentially in the
		1195	initialised state, that is it can be reused, moved, modified in any way
		1196	you wish.
		1197
		1198	=back
		1199
677	=head2 GENERIC WATCHER FUNCTIONS	1200	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1201
682	=over 4	1202	=over 4
683		1203
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1204	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1205
…		…
691	which rolls both calls into one.	1211	which rolls both calls into one.
692		1212
693	You can reinitialise a watcher at any time as long as it has been stopped	1213	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1214	(or never started) and there are no pending events outstanding.
695		1215
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1216	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1217	int revents)>.
698		1218
		1219	Example: Initialise an C<ev_io> watcher in two steps.
		1220
		1221	ev_io w;
		1222	ev_init (&w, my_cb);
		1223	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1224
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1225	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
700		1226
701	This macro initialises the type-specific parts of a watcher. You need to	1227	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1228	call C<ev_init> at least once before you call this macro, but you can
703	call C<ev_TYPE_set> any number of times. You must not, however, call this	1229	call C<ev_TYPE_set> any number of times. You must not, however, call this
704	macro on a watcher that is active (it can be pending, however, which is a	1230	macro on a watcher that is active (it can be pending, however, which is a
705	difference to the C<ev_init> macro).	1231	difference to the C<ev_init> macro).
706		1232
707	Although some watcher types do not have type-specific arguments	1233	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1234	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1235
		1236	See C<ev_init>, above, for an example.
		1237
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1238	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1239
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1240	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1241	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1242	a watcher. The same limitations apply, of course.
715		1243
		1244	Example: Initialise and set an C<ev_io> watcher in one step.
		1245
		1246	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1247
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1248	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
717		1249
718	Starts (activates) the given watcher. Only active watchers will receive	1250	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1251	events. If the watcher is already active nothing will happen.
720		1252
		1253	Example: Start the C<ev_io> watcher that is being abused as example in this
		1254	whole section.
		1255
		1256	ev_io_start (EV_DEFAULT_UC, &w);
		1257
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1258	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
722		1259
723	Stops the given watcher again (if active) and clears the pending	1260	Stops the given watcher if active, and clears the pending status (whether
		1261	the watcher was active or not).
		1262
724	status. It is possible that stopped watchers are pending (for example,	1263	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1264	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1265	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1266	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1267	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1268
730	=item bool ev_is_active (ev_TYPE *watcher)	1269	=item bool ev_is_active (ev_TYPE *watcher)
731		1270
732	Returns a true value iff the watcher is active (i.e. it has been started	1271	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1272	and not yet been stopped). As long as a watcher is active you must not modify
…		…
749	=item ev_cb_set (ev_TYPE *watcher, callback)	1288	=item ev_cb_set (ev_TYPE *watcher, callback)
750		1289
751	Change the callback. You can change the callback at virtually any time	1290	Change the callback. You can change the callback at virtually any time
752	(modulo threads).	1291	(modulo threads).
753		1292
754	=item ev_set_priority (ev_TYPE *watcher, priority)	1293	=item ev_set_priority (ev_TYPE *watcher, int priority)
755		1294
756	=item int ev_priority (ev_TYPE *watcher)	1295	=item int ev_priority (ev_TYPE *watcher)
757		1296
758	Set and query the priority of the watcher. The priority is a small	1297	Set and query the priority of the watcher. The priority is a small
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1298	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1299	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1300	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1301	from being executed (except for C<ev_idle> watchers).
763		1302
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1303	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1304	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1305
772	You I<must not> change the priority of a watcher as long as it is active or	1306	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1307	pending.
774		1308
		1309	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1310	fine, as long as you do not mind that the priority value you query might
		1311	or might not have been clamped to the valid range.
		1312
775	The default priority used by watchers when no priority has been set is	1313	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1314	always C<0>, which is supposed to not be too high and not be too low :).
777		1315
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1316	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1317	priorities.
780	or might not have been adjusted to be within valid range.
781		1318
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1319	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1320
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1321	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1322	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1323	can deal with that fact, as both are simply passed through to the
		1324	callback.
787		1325
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1326	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1327
790	If the watcher is pending, this function returns clears its pending status	1328	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1329	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1330	watcher isn't pending it does nothing and returns C<0>.
793		1331
		1332	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1333	callback to be invoked, which can be accomplished with this function.
		1334
		1335	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1336
		1337	Feeds the given event set into the event loop, as if the specified event
		1338	had happened for the specified watcher (which must be a pointer to an
		1339	initialised but not necessarily started event watcher). Obviously you must
		1340	not free the watcher as long as it has pending events.
		1341
		1342	Stopping the watcher, letting libev invoke it, or calling
		1343	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1344	not started in the first place.
		1345
		1346	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1347	functions that do not need a watcher.
		1348
794	=back	1349	=back
795		1350
796		1351
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1352	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
798		1353
799	Each watcher has, by default, a member C<void *data> that you can change	1354	Each watcher has, by default, a member C<void *data> that you can change
800	and read at any time, libev will completely ignore it. This can be used	1355	and read at any time: libev will completely ignore it. This can be used
801	to associate arbitrary data with your watcher. If you need more data and	1356	to associate arbitrary data with your watcher. If you need more data and
802	don't want to allocate memory and store a pointer to it in that data	1357	don't want to allocate memory and store a pointer to it in that data
803	member, you can also "subclass" the watcher type and provide your own	1358	member, you can also "subclass" the watcher type and provide your own
804	data:	1359	data:
805		1360
806	struct my_io	1361	struct my_io
807	{	1362	{
808	struct ev_io io;	1363	ev_io io;
809	int otherfd;	1364	int otherfd;
810	void *somedata;	1365	void *somedata;
811	struct whatever *mostinteresting;	1366	struct whatever *mostinteresting;
812	}	1367	};
		1368
		1369	...
		1370	struct my_io w;
		1371	ev_io_init (&w.io, my_cb, fd, EV_READ);
813		1372
814	And since your callback will be called with a pointer to the watcher, you	1373	And since your callback will be called with a pointer to the watcher, you
815	can cast it back to your own type:	1374	can cast it back to your own type:
816		1375
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1376	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
818	{	1377	{
819	struct my_io *w = (struct my_io *)w_;	1378	struct my_io *w = (struct my_io *)w_;
820	...	1379	...
821	}	1380	}
822		1381
823	More interesting and less C-conformant ways of casting your callback type	1382	More interesting and less C-conformant ways of casting your callback type
824	instead have been omitted.	1383	instead have been omitted.
825		1384
826	Another common scenario is having some data structure with multiple	1385	Another common scenario is to use some data structure with multiple
827	watchers:	1386	embedded watchers:
828		1387
829	struct my_biggy	1388	struct my_biggy
830	{	1389	{
831	int some_data;	1390	int some_data;
832	ev_timer t1;	1391	ev_timer t1;
833	ev_timer t2;	1392	ev_timer t2;
834	}	1393	}
835		1394
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1395	In this case getting the pointer to C<my_biggy> is a bit more
837	you need to use C<offsetof>:	1396	complicated: Either you store the address of your C<my_biggy> struct
		1397	in the C<data> member of the watcher (for woozies), or you need to use
		1398	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1399	programmers):
838		1400
839	#include <stddef.h>	1401	#include <stddef.h>
840		1402
841	static void	1403	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1404	t1_cb (EV_P_ ev_timer *w, int revents)
843	{	1405	{
844	struct my_biggy big = (struct my_biggy *	1406	struct my_biggy big = (struct my_biggy *)
845	(((char *)w) - offsetof (struct my_biggy, t1));	1407	(((char *)w) - offsetof (struct my_biggy, t1));
846	}	1408	}
847		1409
848	static void	1410	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1411	t2_cb (EV_P_ ev_timer *w, int revents)
850	{	1412	{
851	struct my_biggy big = (struct my_biggy *	1413	struct my_biggy big = (struct my_biggy *)
852	(((char *)w) - offsetof (struct my_biggy, t2));	1414	(((char *)w) - offsetof (struct my_biggy, t2));
853	}	1415	}
		1416
		1417	=head2 WATCHER PRIORITY MODELS
		1418
		1419	Many event loops support I<watcher priorities>, which are usually small
		1420	integers that influence the ordering of event callback invocation
		1421	between watchers in some way, all else being equal.
		1422
		1423	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1424	description for the more technical details such as the actual priority
		1425	range.
		1426
		1427	There are two common ways how these these priorities are being interpreted
		1428	by event loops:
		1429
		1430	In the more common lock-out model, higher priorities "lock out" invocation
		1431	of lower priority watchers, which means as long as higher priority
		1432	watchers receive events, lower priority watchers are not being invoked.
		1433
		1434	The less common only-for-ordering model uses priorities solely to order
		1435	callback invocation within a single event loop iteration: Higher priority
		1436	watchers are invoked before lower priority ones, but they all get invoked
		1437	before polling for new events.
		1438
		1439	Libev uses the second (only-for-ordering) model for all its watchers
		1440	except for idle watchers (which use the lock-out model).
		1441
		1442	The rationale behind this is that implementing the lock-out model for
		1443	watchers is not well supported by most kernel interfaces, and most event
		1444	libraries will just poll for the same events again and again as long as
		1445	their callbacks have not been executed, which is very inefficient in the
		1446	common case of one high-priority watcher locking out a mass of lower
		1447	priority ones.
		1448
		1449	Static (ordering) priorities are most useful when you have two or more
		1450	watchers handling the same resource: a typical usage example is having an
		1451	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1452	timeouts. Under load, data might be received while the program handles
		1453	other jobs, but since timers normally get invoked first, the timeout
		1454	handler will be executed before checking for data. In that case, giving
		1455	the timer a lower priority than the I/O watcher ensures that I/O will be
		1456	handled first even under adverse conditions (which is usually, but not
		1457	always, what you want).
		1458
		1459	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1460	will only be executed when no same or higher priority watchers have
		1461	received events, they can be used to implement the "lock-out" model when
		1462	required.
		1463
		1464	For example, to emulate how many other event libraries handle priorities,
		1465	you can associate an C<ev_idle> watcher to each such watcher, and in
		1466	the normal watcher callback, you just start the idle watcher. The real
		1467	processing is done in the idle watcher callback. This causes libev to
		1468	continuously poll and process kernel event data for the watcher, but when
		1469	the lock-out case is known to be rare (which in turn is rare :), this is
		1470	workable.
		1471
		1472	Usually, however, the lock-out model implemented that way will perform
		1473	miserably under the type of load it was designed to handle. In that case,
		1474	it might be preferable to stop the real watcher before starting the
		1475	idle watcher, so the kernel will not have to process the event in case
		1476	the actual processing will be delayed for considerable time.
		1477
		1478	Here is an example of an I/O watcher that should run at a strictly lower
		1479	priority than the default, and which should only process data when no
		1480	other events are pending:
		1481
		1482	ev_idle idle; // actual processing watcher
		1483	ev_io io; // actual event watcher
		1484
		1485	static void
		1486	io_cb (EV_P_ ev_io *w, int revents)
		1487	{
		1488	// stop the I/O watcher, we received the event, but
		1489	// are not yet ready to handle it.
		1490	ev_io_stop (EV_A_ w);
		1491
		1492	// start the idle watcher to handle the actual event.
		1493	// it will not be executed as long as other watchers
		1494	// with the default priority are receiving events.
		1495	ev_idle_start (EV_A_ &idle);
		1496	}
		1497
		1498	static void
		1499	idle_cb (EV_P_ ev_idle *w, int revents)
		1500	{
		1501	// actual processing
		1502	read (STDIN_FILENO, ...);
		1503
		1504	// have to start the I/O watcher again, as
		1505	// we have handled the event
		1506	ev_io_start (EV_P_ &io);
		1507	}
		1508
		1509	// initialisation
		1510	ev_idle_init (&idle, idle_cb);
		1511	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1512	ev_io_start (EV_DEFAULT_ &io);
		1513
		1514	In the "real" world, it might also be beneficial to start a timer, so that
		1515	low-priority connections can not be locked out forever under load. This
		1516	enables your program to keep a lower latency for important connections
		1517	during short periods of high load, while not completely locking out less
		1518	important ones.
854		1519
855		1520
856	=head1 WATCHER TYPES	1521	=head1 WATCHER TYPES
857		1522
858	This section describes each watcher in detail, but will not repeat	1523	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1547	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1548	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1549	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1550	required if you know what you are doing).
886		1551
887	You have to be careful with dup'ed file descriptors, though. Some backends	1552	If you cannot use non-blocking mode, then force the use of a
888	(the linux epoll backend is a notable example) cannot handle dup'ed file	1553	known-to-be-good backend (at the time of this writing, this includes only
889	descriptors correctly if you register interest in two or more fds pointing	1554	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
890	to the same underlying file/socket/etc. description (that is, they share	1555	descriptors for which non-blocking operation makes no sense (such as
891	the same underlying "file open").	1556	files) - libev doesn't guarantee any specific behaviour in that case.
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896		1557
897	Another thing you have to watch out for is that it is quite easy to	1558	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1559	receive "spurious" readiness notifications, that is your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1560	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1561	because there is no data. Not only are some backends known to create a
901	lot of those (for example solaris ports), it is very easy to get into	1562	lot of those (for example Solaris ports), it is very easy to get into
902	this situation even with a relatively standard program structure. Thus	1563	this situation even with a relatively standard program structure. Thus
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1564	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1565	C<EAGAIN> is far preferable to a program hanging until some data arrives.
905		1566
906	If you cannot run the fd in non-blocking mode (for example you should not	1567	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1568	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1569	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1570	interface such as poll (fortunately in our Xlib example, Xlib already
910	its own, so its quite safe to use).	1571	does this on its own, so its quite safe to use). Some people additionally
		1572	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1573	indefinitely.
		1574
		1575	But really, best use non-blocking mode.
		1576
		1577	=head3 The special problem of disappearing file descriptors
		1578
		1579	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1580	descriptor (either due to calling C<close> explicitly or any other means,
		1581	such as C<dup2>). The reason is that you register interest in some file
		1582	descriptor, but when it goes away, the operating system will silently drop
		1583	this interest. If another file descriptor with the same number then is
		1584	registered with libev, there is no efficient way to see that this is, in
		1585	fact, a different file descriptor.
		1586
		1587	To avoid having to explicitly tell libev about such cases, libev follows
		1588	the following policy: Each time C<ev_io_set> is being called, libev
		1589	will assume that this is potentially a new file descriptor, otherwise
		1590	it is assumed that the file descriptor stays the same. That means that
		1591	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1592	descriptor even if the file descriptor number itself did not change.
		1593
		1594	This is how one would do it normally anyway, the important point is that
		1595	the libev application should not optimise around libev but should leave
		1596	optimisations to libev.
		1597
		1598	=head3 The special problem of dup'ed file descriptors
		1599
		1600	Some backends (e.g. epoll), cannot register events for file descriptors,
		1601	but only events for the underlying file descriptions. That means when you
		1602	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1603	events for them, only one file descriptor might actually receive events.
		1604
		1605	There is no workaround possible except not registering events
		1606	for potentially C<dup ()>'ed file descriptors, or to resort to
		1607	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1608
		1609	=head3 The special problem of fork
		1610
		1611	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1612	useless behaviour. Libev fully supports fork, but needs to be told about
		1613	it in the child.
		1614
		1615	To support fork in your programs, you either have to call
		1616	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1617	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1618	C<EVBACKEND_POLL>.
		1619
		1620	=head3 The special problem of SIGPIPE
		1621
		1622	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1623	when writing to a pipe whose other end has been closed, your program gets
		1624	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1625	this is sensible behaviour, for daemons, this is usually undesirable.
		1626
		1627	So when you encounter spurious, unexplained daemon exits, make sure you
		1628	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1629	somewhere, as that would have given you a big clue).
		1630
		1631	=head3 The special problem of accept()ing when you can't
		1632
		1633	Many implementations of the POSIX C<accept> function (for example,
		1634	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1635	connection from the pending queue in all error cases.
		1636
		1637	For example, larger servers often run out of file descriptors (because
		1638	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1639	rejecting the connection, leading to libev signalling readiness on
		1640	the next iteration again (the connection still exists after all), and
		1641	typically causing the program to loop at 100% CPU usage.
		1642
		1643	Unfortunately, the set of errors that cause this issue differs between
		1644	operating systems, there is usually little the app can do to remedy the
		1645	situation, and no known thread-safe method of removing the connection to
		1646	cope with overload is known (to me).
		1647
		1648	One of the easiest ways to handle this situation is to just ignore it
		1649	- when the program encounters an overload, it will just loop until the
		1650	situation is over. While this is a form of busy waiting, no OS offers an
		1651	event-based way to handle this situation, so it's the best one can do.
		1652
		1653	A better way to handle the situation is to log any errors other than
		1654	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1655	messages, and continue as usual, which at least gives the user an idea of
		1656	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1657	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1658	usage.
		1659
		1660	If your program is single-threaded, then you could also keep a dummy file
		1661	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1662	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1663	close that fd, and create a new dummy fd. This will gracefully refuse
		1664	clients under typical overload conditions.
		1665
		1666	The last way to handle it is to simply log the error and C<exit>, as
		1667	is often done with C<malloc> failures, but this results in an easy
		1668	opportunity for a DoS attack.
		1669
		1670	=head3 Watcher-Specific Functions
911		1671
912	=over 4	1672	=over 4
913		1673
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1674	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1675
916	=item ev_io_set (ev_io *, int fd, int events)	1676	=item ev_io_set (ev_io *, int fd, int events)
917		1677
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1678	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1679	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1680	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1681
922	=item int fd [read-only]	1682	=item int fd [read-only]
923		1683
924	The file descriptor being watched.	1684	The file descriptor being watched.
925		1685
926	=item int events [read-only]	1686	=item int events [read-only]
927		1687
928	The events being watched.	1688	The events being watched.
929		1689
930	=back	1690	=back
		1691
		1692	=head3 Examples
931		1693
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1694	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1695	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1696	attempt to read a whole line in the callback.
935		1697
936	static void	1698	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1699	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1700	{
939	ev_io_stop (loop, w);	1701	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1702	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1703	}
942		1704
943	...	1705	...
944	struct ev_loop *loop = ev_default_init (0);	1706	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1707	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1708	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1709	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1710	ev_run (loop, 0);
949		1711
950		1712
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1713	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1714
953	Timer watchers are simple relative timers that generate an event after a	1715	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1716	given time, and optionally repeating in regular intervals after that.
955		1717
956	The timers are based on real time, that is, if you register an event that	1718	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1719	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1720	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1721	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1722	monotonic clock option helps a lot here).
		1723
		1724	The callback is guaranteed to be invoked only I<after> its timeout has
		1725	passed (not I<at>, so on systems with very low-resolution clocks this
		1726	might introduce a small delay). If multiple timers become ready during the
		1727	same loop iteration then the ones with earlier time-out values are invoked
		1728	before ones of the same priority with later time-out values (but this is
		1729	no longer true when a callback calls C<ev_run> recursively).
		1730
		1731	=head3 Be smart about timeouts
		1732
		1733	Many real-world problems involve some kind of timeout, usually for error
		1734	recovery. A typical example is an HTTP request - if the other side hangs,
		1735	you want to raise some error after a while.
		1736
		1737	What follows are some ways to handle this problem, from obvious and
		1738	inefficient to smart and efficient.
		1739
		1740	In the following, a 60 second activity timeout is assumed - a timeout that
		1741	gets reset to 60 seconds each time there is activity (e.g. each time some
		1742	data or other life sign was received).
		1743
		1744	=over 4
		1745
		1746	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1747
		1748	This is the most obvious, but not the most simple way: In the beginning,
		1749	start the watcher:
		1750
		1751	ev_timer_init (timer, callback, 60., 0.);
		1752	ev_timer_start (loop, timer);
		1753
		1754	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1755	and start it again:
		1756
		1757	ev_timer_stop (loop, timer);
		1758	ev_timer_set (timer, 60., 0.);
		1759	ev_timer_start (loop, timer);
		1760
		1761	This is relatively simple to implement, but means that each time there is
		1762	some activity, libev will first have to remove the timer from its internal
		1763	data structure and then add it again. Libev tries to be fast, but it's
		1764	still not a constant-time operation.
		1765
		1766	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1767
		1768	This is the easiest way, and involves using C<ev_timer_again> instead of
		1769	C<ev_timer_start>.
		1770
		1771	To implement this, configure an C<ev_timer> with a C<repeat> value
		1772	of C<60> and then call C<ev_timer_again> at start and each time you
		1773	successfully read or write some data. If you go into an idle state where
		1774	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1775	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1776
		1777	That means you can ignore both the C<ev_timer_start> function and the
		1778	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1779	member and C<ev_timer_again>.
		1780
		1781	At start:
		1782
		1783	ev_init (timer, callback);
		1784	timer->repeat = 60.;
		1785	ev_timer_again (loop, timer);
		1786
		1787	Each time there is some activity:
		1788
		1789	ev_timer_again (loop, timer);
		1790
		1791	It is even possible to change the time-out on the fly, regardless of
		1792	whether the watcher is active or not:
		1793
		1794	timer->repeat = 30.;
		1795	ev_timer_again (loop, timer);
		1796
		1797	This is slightly more efficient then stopping/starting the timer each time
		1798	you want to modify its timeout value, as libev does not have to completely
		1799	remove and re-insert the timer from/into its internal data structure.
		1800
		1801	It is, however, even simpler than the "obvious" way to do it.
		1802
		1803	=item 3. Let the timer time out, but then re-arm it as required.
		1804
		1805	This method is more tricky, but usually most efficient: Most timeouts are
		1806	relatively long compared to the intervals between other activity - in
		1807	our example, within 60 seconds, there are usually many I/O events with
		1808	associated activity resets.
		1809
		1810	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1811	but remember the time of last activity, and check for a real timeout only
		1812	within the callback:
		1813
		1814	ev_tstamp last_activity; // time of last activity
		1815
		1816	static void
		1817	callback (EV_P_ ev_timer *w, int revents)
		1818	{
		1819	ev_tstamp now = ev_now (EV_A);
		1820	ev_tstamp timeout = last_activity + 60.;
		1821
		1822	// if last_activity + 60. is older than now, we did time out
		1823	if (timeout < now)
		1824	{
		1825	// timeout occurred, take action
		1826	}
		1827	else
		1828	{
		1829	// callback was invoked, but there was some activity, re-arm
		1830	// the watcher to fire in last_activity + 60, which is
		1831	// guaranteed to be in the future, so "again" is positive:
		1832	w->repeat = timeout - now;
		1833	ev_timer_again (EV_A_ w);
		1834	}
		1835	}
		1836
		1837	To summarise the callback: first calculate the real timeout (defined
		1838	as "60 seconds after the last activity"), then check if that time has
		1839	been reached, which means something I<did>, in fact, time out. Otherwise
		1840	the callback was invoked too early (C<timeout> is in the future), so
		1841	re-schedule the timer to fire at that future time, to see if maybe we have
		1842	a timeout then.
		1843
		1844	Note how C<ev_timer_again> is used, taking advantage of the
		1845	C<ev_timer_again> optimisation when the timer is already running.
		1846
		1847	This scheme causes more callback invocations (about one every 60 seconds
		1848	minus half the average time between activity), but virtually no calls to
		1849	libev to change the timeout.
		1850
		1851	To start the timer, simply initialise the watcher and set C<last_activity>
		1852	to the current time (meaning we just have some activity :), then call the
		1853	callback, which will "do the right thing" and start the timer:
		1854
		1855	ev_init (timer, callback);
		1856	last_activity = ev_now (loop);
		1857	callback (loop, timer, EV_TIMER);
		1858
		1859	And when there is some activity, simply store the current time in
		1860	C<last_activity>, no libev calls at all:
		1861
		1862	last_activity = ev_now (loop);
		1863
		1864	This technique is slightly more complex, but in most cases where the
		1865	time-out is unlikely to be triggered, much more efficient.
		1866
		1867	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1868	callback :) - just change the timeout and invoke the callback, which will
		1869	fix things for you.
		1870
		1871	=item 4. Wee, just use a double-linked list for your timeouts.
		1872
		1873	If there is not one request, but many thousands (millions...), all
		1874	employing some kind of timeout with the same timeout value, then one can
		1875	do even better:
		1876
		1877	When starting the timeout, calculate the timeout value and put the timeout
		1878	at the I<end> of the list.
		1879
		1880	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1881	the list is expected to fire (for example, using the technique #3).
		1882
		1883	When there is some activity, remove the timer from the list, recalculate
		1884	the timeout, append it to the end of the list again, and make sure to
		1885	update the C<ev_timer> if it was taken from the beginning of the list.
		1886
		1887	This way, one can manage an unlimited number of timeouts in O(1) time for
		1888	starting, stopping and updating the timers, at the expense of a major
		1889	complication, and having to use a constant timeout. The constant timeout
		1890	ensures that the list stays sorted.
		1891
		1892	=back
		1893
		1894	So which method the best?
		1895
		1896	Method #2 is a simple no-brain-required solution that is adequate in most
		1897	situations. Method #3 requires a bit more thinking, but handles many cases
		1898	better, and isn't very complicated either. In most case, choosing either
		1899	one is fine, with #3 being better in typical situations.
		1900
		1901	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1902	rather complicated, but extremely efficient, something that really pays
		1903	off after the first million or so of active timers, i.e. it's usually
		1904	overkill :)
		1905
		1906	=head3 The special problem of time updates
		1907
		1908	Establishing the current time is a costly operation (it usually takes at
		1909	least two system calls): EV therefore updates its idea of the current
		1910	time only before and after C<ev_run> collects new events, which causes a
		1911	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1912	lots of events in one iteration.
961		1913
962	The relative timeouts are calculated relative to the C<ev_now ()>	1914	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	1915	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	1916	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	1917	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	1918	timeout on the current time, use something like this to adjust for this:
967		1919
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1920	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		1921
970	The callback is guarenteed to be invoked only when its timeout has passed,	1922	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	1923	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	1924	()>.
		1925
		1926	=head3 The special problems of suspended animation
		1927
		1928	When you leave the server world it is quite customary to hit machines that
		1929	can suspend/hibernate - what happens to the clocks during such a suspend?
		1930
		1931	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1932	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1933	to run until the system is suspended, but they will not advance while the
		1934	system is suspended. That means, on resume, it will be as if the program
		1935	was frozen for a few seconds, but the suspend time will not be counted
		1936	towards C<ev_timer> when a monotonic clock source is used. The real time
		1937	clock advanced as expected, but if it is used as sole clocksource, then a
		1938	long suspend would be detected as a time jump by libev, and timers would
		1939	be adjusted accordingly.
		1940
		1941	I would not be surprised to see different behaviour in different between
		1942	operating systems, OS versions or even different hardware.
		1943
		1944	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1945	time jump in the monotonic clocks and the realtime clock. If the program
		1946	is suspended for a very long time, and monotonic clock sources are in use,
		1947	then you can expect C<ev_timer>s to expire as the full suspension time
		1948	will be counted towards the timers. When no monotonic clock source is in
		1949	use, then libev will again assume a timejump and adjust accordingly.
		1950
		1951	It might be beneficial for this latter case to call C<ev_suspend>
		1952	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1953	deterministic behaviour in this case (you can do nothing against
		1954	C<SIGSTOP>).
		1955
		1956	=head3 Watcher-Specific Functions and Data Members
973		1957
974	=over 4	1958	=over 4
975		1959
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1960	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		1961
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1962	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		1963
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1964	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	1965	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	1966	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	1967	configured to trigger again C<repeat> seconds later, again, and again,
		1968	until stopped manually.
984		1969
985	The timer itself will do a best-effort at avoiding drift, that is, if you	1970	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	1971	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	1972	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	1973	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	1974	do stuff) the timer will not fire more than once per event loop iteration.
990		1975
991	=item ev_timer_again (loop)	1976	=item ev_timer_again (loop, ev_timer *)
992		1977
993	This will act as if the timer timed out and restart it again if it is	1978	This will act as if the timer timed out and restart it again if it is
994	repeating. The exact semantics are:	1979	repeating. The exact semantics are:
995		1980
996	If the timer is pending, its pending status is cleared.	1981	If the timer is pending, its pending status is cleared.
997		1982
998	If the timer is started but nonrepeating, stop it (as if it timed out).	1983	If the timer is started but non-repeating, stop it (as if it timed out).
999		1984
1000	If the timer is repeating, either start it if necessary (with the	1985	If the timer is repeating, either start it if necessary (with the
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	1986	C<repeat> value), or reset the running timer to the C<repeat> value.
1002		1987
1003	This sounds a bit complicated, but here is a useful and typical	1988	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1004	example: Imagine you have a tcp connection and you want a so-called idle	1989	usage example.
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012		1990
1013	That means you can ignore the C<after> value and C<ev_timer_start>	1991	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1015		1992
1016	ev_timer_init (timer, callback, 0., 5.);	1993	Returns the remaining time until a timer fires. If the timer is active,
1017	ev_timer_again (loop, timer);	1994	then this time is relative to the current event loop time, otherwise it's
1018	...	1995	the timeout value currently configured.
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024		1996
1025	This is more slightly efficient then stopping/starting the timer each time	1997	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1026	you want to modify its timeout value.	1998	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1999	will return C<4>. When the timer expires and is restarted, it will return
		2000	roughly C<7> (likely slightly less as callback invocation takes some time,
		2001	too), and so on.
1027		2002
1028	=item ev_tstamp repeat [read-write]	2003	=item ev_tstamp repeat [read-write]
1029		2004
1030	The current C<repeat> value. Will be used each time the watcher times out	2005	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	2006	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	2007	which is also when any modifications are taken into account.
1033		2008
1034	=back	2009	=back
1035		2010
		2011	=head3 Examples
		2012
1036	Example: Create a timer that fires after 60 seconds.	2013	Example: Create a timer that fires after 60 seconds.
1037		2014
1038	static void	2015	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2016	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	2017	{
1041	.. one minute over, w is actually stopped right here	2018	.. one minute over, w is actually stopped right here
1042	}	2019	}
1043		2020
1044	struct ev_timer mytimer;	2021	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2022	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	2023	ev_timer_start (loop, &mytimer);
1047		2024
1048	Example: Create a timeout timer that times out after 10 seconds of	2025	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	2026	inactivity.
1050		2027
1051	static void	2028	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2029	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	2030	{
1054	.. ten seconds without any activity	2031	.. ten seconds without any activity
1055	}	2032	}
1056		2033
1057	struct ev_timer mytimer;	2034	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2035	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	2036	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	2037	ev_run (loop, 0);
1061		2038
1062	// and in some piece of code that gets executed on any "activity":	2039	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	2040	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	2041	ev_timer_again (&mytimer);
1065		2042
1066		2043
1067	=head2 C<ev_periodic> - to cron or not to cron?	2044	=head2 C<ev_periodic> - to cron or not to cron?
1068		2045
1069	Periodic watchers are also timers of a kind, but they are very versatile	2046	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	2047	(and unfortunately a bit complex).
1071		2048
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2049	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	2050	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	2051	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2052	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	2053	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2054	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		2055
1081	They can also be used to implement vastly more complex timers, such as	2056	You can tell a periodic watcher to trigger after some specific point
		2057	in time: for example, if you tell a periodic watcher to trigger "in 10
		2058	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2059	not a delay) and then reset your system clock to January of the previous
		2060	year, then it will take a year or more to trigger the event (unlike an
		2061	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2062	it, as it uses a relative timeout).
		2063
		2064	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	2065	timers, such as triggering an event on each "midnight, local time", or
		2066	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2067	those cannot react to time jumps.
1083		2068
1084	As with timers, the callback is guarenteed to be invoked only when the	2069	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	2070	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	2071	timers become ready during the same loop iteration then the ones with
		2072	earlier time-out values are invoked before ones with later time-out values
		2073	(but this is no longer true when a callback calls C<ev_run> recursively).
		2074
		2075	=head3 Watcher-Specific Functions and Data Members
1087		2076
1088	=over 4	2077	=over 4
1089		2078
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2079	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		2080
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2081	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		2082
1094	Lots of arguments, lets sort it out... There are basically three modes of	2083	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	2084	operation, and we will explain them from simplest to most complex:
1096		2085
1097	=over 4	2086	=over 4
1098		2087
1099	=item * absolute timer (interval = reschedule_cb = 0)	2088	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		2089
1101	In this configuration the watcher triggers an event at the wallclock time	2090	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2091	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	2092	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	2093	will be stopped and invoked when the system clock reaches or surpasses
		2094	this point in time.
1105		2095
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2096	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		2097
1108	In this mode the watcher will always be scheduled to time out at the next	2098	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	2099	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	2100	negative) and then repeat, regardless of any time jumps. The C<offset>
		2101	argument is merely an offset into the C<interval> periods.
1111		2102
1112	This can be used to create timers that do not drift with respect to system	2103	This can be used to create timers that do not drift with respect to the
1113	time:	2104	system clock, for example, here is an C<ev_periodic> that triggers each
		2105	hour, on the hour (with respect to UTC):
1114		2106
1115	ev_periodic_set (&periodic, 0., 3600., 0);	2107	ev_periodic_set (&periodic, 0., 3600., 0);
1116		2108
1117	This doesn't mean there will always be 3600 seconds in between triggers,	2109	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	2110	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	2111	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	2112	by 3600.
1121		2113
1122	Another way to think about it (for the mathematically inclined) is that	2114	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	2115	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	2116	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		2117
		2118	For numerical stability it is preferable that the C<offset> value is near
		2119	C<ev_now ()> (the current time), but there is no range requirement for
		2120	this value, and in fact is often specified as zero.
		2121
		2122	Note also that there is an upper limit to how often a timer can fire (CPU
		2123	speed for example), so if C<interval> is very small then timing stability
		2124	will of course deteriorate. Libev itself tries to be exact to be about one
		2125	millisecond (if the OS supports it and the machine is fast enough).
		2126
1126	=item * manual reschedule mode (reschedule_cb = callback)	2127	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		2128
1128	In this mode the values for C<interval> and C<at> are both being	2129	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	2130	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	2131	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	2132	current time as second argument.
1132		2133
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2134	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	2135	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2136	allowed by documentation here>.
1136	starting a prepare watcher).
1137		2137
		2138	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2139	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2140	only event loop modification you are allowed to do).
		2141
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2142	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	2143	*w, ev_tstamp now)>, e.g.:
1140		2144
		2145	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2146	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	2147	{
1143	return now + 60.;	2148	return now + 60.;
1144	}	2149	}
1145		2150
1146	It must return the next time to trigger, based on the passed time value	2151	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	2152	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	2153	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	2154	might be called at other times, too.
1150		2155
1151	NOTE: I<< This callback must always return a time that is later than the	2156	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2157	equal to the passed C<now> value >>.
1153		2158
1154	This can be used to create very complex timers, such as a timer that	2159	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	2160	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	2161	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	2162	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	2163	reason I omitted it as an example).
1159		2164
1160	=back	2165	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	2169	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	2170	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	2171	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	2172	program when the crontabs have changed).
1168		2173
		2174	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2175
		2176	When active, returns the absolute time that the watcher is supposed
		2177	to trigger next. This is not the same as the C<offset> argument to
		2178	C<ev_periodic_set>, but indeed works even in interval and manual
		2179	rescheduling modes.
		2180
		2181	=item ev_tstamp offset [read-write]
		2182
		2183	When repeating, this contains the offset value, otherwise this is the
		2184	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2185	although libev might modify this value for better numerical stability).
		2186
		2187	Can be modified any time, but changes only take effect when the periodic
		2188	timer fires or C<ev_periodic_again> is being called.
		2189
1169	=item ev_tstamp interval [read-write]	2190	=item ev_tstamp interval [read-write]
1170		2191
1171	The current interval value. Can be modified any time, but changes only	2192	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	2193	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	2194	called.
1174		2195
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2196	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		2197
1177	The current reschedule callback, or C<0>, if this functionality is	2198	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	2199	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	2200	the periodic timer fires or C<ev_periodic_again> is being called.
1180		2201
1181	=back	2202	=back
1182		2203
		2204	=head3 Examples
		2205
1183	Example: Call a callback every hour, or, more precisely, whenever the	2206	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	2207	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	2208	potentially a lot of jitter, but good long-term stability.
1186		2209
1187	static void	2210	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2211	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1189	{	2212	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	2213	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	2214	}
1192		2215
1193	struct ev_periodic hourly_tick;	2216	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2217	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	2218	ev_periodic_start (loop, &hourly_tick);
1196		2219
1197	Example: The same as above, but use a reschedule callback to do it:	2220	Example: The same as above, but use a reschedule callback to do it:
1198		2221
1199	#include <math.h>	2222	#include <math.h>
1200		2223
1201	static ev_tstamp	2224	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2225	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	2226	{
1204	return fmod (now, 3600.) + 3600.;	2227	return now + (3600. - fmod (now, 3600.));
1205	}	2228	}
1206		2229
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2230	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		2231
1209	Example: Call a callback every hour, starting now:	2232	Example: Call a callback every hour, starting now:
1210		2233
1211	struct ev_periodic hourly_tick;	2234	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	2235	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	2236	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	2237	ev_periodic_start (loop, &hourly_tick);
1215		2238
1216		2239
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	2240	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		2241
1219	Signal watchers will trigger an event when the process receives a specific	2242	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	2243	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	2244	will try it's best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	2245	normal event processing, like any other event.
1223		2246
		2247	If you want signals to be delivered truly asynchronously, just use
		2248	C<sigaction> as you would do without libev and forget about sharing
		2249	the signal. You can even use C<ev_async> from a signal handler to
		2250	synchronously wake up an event loop.
		2251
1224	You can configure as many watchers as you like per signal. Only when the	2252	You can configure as many watchers as you like for the same signal, but
		2253	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2254	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2255	C<SIGINT> in both the default loop and another loop at the same time. At
		2256	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2257
1225	first watcher gets started will libev actually register a signal watcher	2258	When the first watcher gets started will libev actually register something
1226	with the kernel (thus it coexists with your own signal handlers as long	2259	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	2260	you don't register any with libev for the same signal).
1228	watcher for a signal is stopped libev will reset the signal handler to	2261
1229	SIG_DFL (regardless of what it was set to before).	2262	If possible and supported, libev will install its handlers with
		2263	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2264	not be unduly interrupted. If you have a problem with system calls getting
		2265	interrupted by signals you can block all signals in an C<ev_check> watcher
		2266	and unblock them in an C<ev_prepare> watcher.
		2267
		2268	=head3 The special problem of inheritance over fork/execve/pthread_create
		2269
		2270	Both the signal mask (C<sigprocmask>) and the signal disposition
		2271	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2272	stopping it again), that is, libev might or might not block the signal,
		2273	and might or might not set or restore the installed signal handler.
		2274
		2275	While this does not matter for the signal disposition (libev never
		2276	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2277	C<execve>), this matters for the signal mask: many programs do not expect
		2278	certain signals to be blocked.
		2279
		2280	This means that before calling C<exec> (from the child) you should reset
		2281	the signal mask to whatever "default" you expect (all clear is a good
		2282	choice usually).
		2283
		2284	The simplest way to ensure that the signal mask is reset in the child is
		2285	to install a fork handler with C<pthread_atfork> that resets it. That will
		2286	catch fork calls done by libraries (such as the libc) as well.
		2287
		2288	In current versions of libev, the signal will not be blocked indefinitely
		2289	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2290	the window of opportunity for problems, it will not go away, as libev
		2291	I<has> to modify the signal mask, at least temporarily.
		2292
		2293	So I can't stress this enough: I<If you do not reset your signal mask when
		2294	you expect it to be empty, you have a race condition in your code>. This
		2295	is not a libev-specific thing, this is true for most event libraries.
		2296
		2297	=head3 Watcher-Specific Functions and Data Members
1230		2298
1231	=over 4	2299	=over 4
1232		2300
1233	=item ev_signal_init (ev_signal *, callback, int signum)	2301	=item ev_signal_init (ev_signal *, callback, int signum)
1234		2302
…		…
1241		2309
1242	The signal the watcher watches out for.	2310	The signal the watcher watches out for.
1243		2311
1244	=back	2312	=back
1245		2313
		2314	=head3 Examples
		2315
		2316	Example: Try to exit cleanly on SIGINT.
		2317
		2318	static void
		2319	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2320	{
		2321	ev_break (loop, EVBREAK_ALL);
		2322	}
		2323
		2324	ev_signal signal_watcher;
		2325	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2326	ev_signal_start (loop, &signal_watcher);
		2327
1246		2328
1247	=head2 C<ev_child> - watch out for process status changes	2329	=head2 C<ev_child> - watch out for process status changes
1248		2330
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2331	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2332	some child status changes (most typically when a child of yours dies or
		2333	exits). It is permissible to install a child watcher I<after> the child
		2334	has been forked (which implies it might have already exited), as long
		2335	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2336	forking and then immediately registering a watcher for the child is fine,
		2337	but forking and registering a watcher a few event loop iterations later or
		2338	in the next callback invocation is not.
		2339
		2340	Only the default event loop is capable of handling signals, and therefore
		2341	you can only register child watchers in the default event loop.
		2342
		2343	Due to some design glitches inside libev, child watchers will always be
		2344	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2345	libev)
		2346
		2347	=head3 Process Interaction
		2348
		2349	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2350	initialised. This is necessary to guarantee proper behaviour even if the
		2351	first child watcher is started after the child exits. The occurrence
		2352	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2353	synchronously as part of the event loop processing. Libev always reaps all
		2354	children, even ones not watched.
		2355
		2356	=head3 Overriding the Built-In Processing
		2357
		2358	Libev offers no special support for overriding the built-in child
		2359	processing, but if your application collides with libev's default child
		2360	handler, you can override it easily by installing your own handler for
		2361	C<SIGCHLD> after initialising the default loop, and making sure the
		2362	default loop never gets destroyed. You are encouraged, however, to use an
		2363	event-based approach to child reaping and thus use libev's support for
		2364	that, so other libev users can use C<ev_child> watchers freely.
		2365
		2366	=head3 Stopping the Child Watcher
		2367
		2368	Currently, the child watcher never gets stopped, even when the
		2369	child terminates, so normally one needs to stop the watcher in the
		2370	callback. Future versions of libev might stop the watcher automatically
		2371	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2372	problem).
		2373
		2374	=head3 Watcher-Specific Functions and Data Members
1251		2375
1252	=over 4	2376	=over 4
1253		2377
1254	=item ev_child_init (ev_child *, callback, int pid)	2378	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2379
1256	=item ev_child_set (ev_child *, int pid)	2380	=item ev_child_set (ev_child *, int pid, int trace)
1257		2381
1258	Configures the watcher to wait for status changes of process C<pid> (or	2382	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2383	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2384	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2385	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2386	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2387	process causing the status change. C<trace> must be either C<0> (only
		2388	activate the watcher when the process terminates) or C<1> (additionally
		2389	activate the watcher when the process is stopped or continued).
1264		2390
1265	=item int pid [read-only]	2391	=item int pid [read-only]
1266		2392
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2393	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2394
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2401	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2402	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2403
1278	=back	2404	=back
1279		2405
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2406	=head3 Examples
1281		2407
		2408	Example: C<fork()> a new process and install a child handler to wait for
		2409	its completion.
		2410
		2411	ev_child cw;
		2412
1282	static void	2413	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2414	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2415	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2416	ev_child_stop (EV_A_ w);
		2417	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2418	}
1287		2419
1288	struct ev_signal signal_watcher;	2420	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2421
1290	ev_signal_start (loop, &sigint_cb);	2422	if (pid < 0)
		2423	// error
		2424	else if (pid == 0)
		2425	{
		2426	// the forked child executes here
		2427	exit (1);
		2428	}
		2429	else
		2430	{
		2431	ev_child_init (&cw, child_cb, pid, 0);
		2432	ev_child_start (EV_DEFAULT_ &cw);
		2433	}
1291		2434
1292		2435
1293	=head2 C<ev_stat> - did the file attributes just change?	2436	=head2 C<ev_stat> - did the file attributes just change?
1294		2437
1295	This watches a filesystem path for attribute changes. That is, it calls	2438	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2439	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2440	and sees if it changed compared to the last time, invoking the callback if
		2441	it did.
1298		2442
1299	The path does not need to exist: changing from "path exists" to "path does	2443	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2444	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2445	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2446	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2447	least one) and all the other fields of the stat buffer having unspecified
		2448	contents.
1304		2449
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2450	The path I<must not> end in a slash or contain special components such as
		2451	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2452	your working directory changes, then the behaviour is undefined.
1307		2453
1308	Since there is no standard to do this, the portable implementation simply	2454	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2455	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2456	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2457	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2458	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2459	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2460	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2461	currently around C<0.1>, but that's usually overkill.
1316		2462
1317	This watcher type is not meant for massive numbers of stat watchers,	2463	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2464	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2465	resource-intensive.
1320		2466
1321	At the time of this writing, only the Linux inotify interface is	2467	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2468	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2469	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2470	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2471
1326	usually detected immediately, and if the file exists there will be no	2472	=head3 ABI Issues (Largefile Support)
1327	polling.	2473
		2474	Libev by default (unless the user overrides this) uses the default
		2475	compilation environment, which means that on systems with large file
		2476	support disabled by default, you get the 32 bit version of the stat
		2477	structure. When using the library from programs that change the ABI to
		2478	use 64 bit file offsets the programs will fail. In that case you have to
		2479	compile libev with the same flags to get binary compatibility. This is
		2480	obviously the case with any flags that change the ABI, but the problem is
		2481	most noticeably displayed with ev_stat and large file support.
		2482
		2483	The solution for this is to lobby your distribution maker to make large
		2484	file interfaces available by default (as e.g. FreeBSD does) and not
		2485	optional. Libev cannot simply switch on large file support because it has
		2486	to exchange stat structures with application programs compiled using the
		2487	default compilation environment.
		2488
		2489	=head3 Inotify and Kqueue
		2490
		2491	When C<inotify (7)> support has been compiled into libev and present at
		2492	runtime, it will be used to speed up change detection where possible. The
		2493	inotify descriptor will be created lazily when the first C<ev_stat>
		2494	watcher is being started.
		2495
		2496	Inotify presence does not change the semantics of C<ev_stat> watchers
		2497	except that changes might be detected earlier, and in some cases, to avoid
		2498	making regular C<stat> calls. Even in the presence of inotify support
		2499	there are many cases where libev has to resort to regular C<stat> polling,
		2500	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2501	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2502	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2503	xfs are fully working) libev usually gets away without polling.
		2504
		2505	There is no support for kqueue, as apparently it cannot be used to
		2506	implement this functionality, due to the requirement of having a file
		2507	descriptor open on the object at all times, and detecting renames, unlinks
		2508	etc. is difficult.
		2509
		2510	=head3 C<stat ()> is a synchronous operation
		2511
		2512	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2513	the process. The exception are C<ev_stat> watchers - those call C<stat
		2514	()>, which is a synchronous operation.
		2515
		2516	For local paths, this usually doesn't matter: unless the system is very
		2517	busy or the intervals between stat's are large, a stat call will be fast,
		2518	as the path data is usually in memory already (except when starting the
		2519	watcher).
		2520
		2521	For networked file systems, calling C<stat ()> can block an indefinite
		2522	time due to network issues, and even under good conditions, a stat call
		2523	often takes multiple milliseconds.
		2524
		2525	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2526	paths, although this is fully supported by libev.
		2527
		2528	=head3 The special problem of stat time resolution
		2529
		2530	The C<stat ()> system call only supports full-second resolution portably,
		2531	and even on systems where the resolution is higher, most file systems
		2532	still only support whole seconds.
		2533
		2534	That means that, if the time is the only thing that changes, you can
		2535	easily miss updates: on the first update, C<ev_stat> detects a change and
		2536	calls your callback, which does something. When there is another update
		2537	within the same second, C<ev_stat> will be unable to detect unless the
		2538	stat data does change in other ways (e.g. file size).
		2539
		2540	The solution to this is to delay acting on a change for slightly more
		2541	than a second (or till slightly after the next full second boundary), using
		2542	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2543	ev_timer_again (loop, w)>).
		2544
		2545	The C<.02> offset is added to work around small timing inconsistencies
		2546	of some operating systems (where the second counter of the current time
		2547	might be be delayed. One such system is the Linux kernel, where a call to
		2548	C<gettimeofday> might return a timestamp with a full second later than
		2549	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2550	update file times then there will be a small window where the kernel uses
		2551	the previous second to update file times but libev might already execute
		2552	the timer callback).
		2553
		2554	=head3 Watcher-Specific Functions and Data Members
1328		2555
1329	=over 4	2556	=over 4
1330		2557
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2558	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2559
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2563	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2564	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2565	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2566	path for as long as the watcher is active.
1340		2567
1341	The callback will be receive C<EV_STAT> when a change was detected,	2568	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2569	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2570	last change was detected).
1344		2571
1345	=item ev_stat_stat (ev_stat *)	2572	=item ev_stat_stat (loop, ev_stat *)
1346		2573
1347	Updates the stat buffer immediately with new values. If you change the	2574	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2575	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2576	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2577	the only one changing the path). Can also be useful simply to find out the
		2578	new values.
1351		2579
1352	=item ev_statdata attr [read-only]	2580	=item ev_statdata attr [read-only]
1353		2581
1354	The most-recently detected attributes of the file. Although the type is of	2582	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2584	suitable for your system, but you can only rely on the POSIX-standardised
		2585	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2586	some error while C<stat>ing the file.
1358		2587
1359	=item ev_statdata prev [read-only]	2588	=item ev_statdata prev [read-only]
1360		2589
1361	The previous attributes of the file. The callback gets invoked whenever	2590	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2591	C<prev> != C<attr>, or, more precisely, one or more of these members
		2592	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2593	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2594
1364	=item ev_tstamp interval [read-only]	2595	=item ev_tstamp interval [read-only]
1365		2596
1366	The specified interval.	2597	The specified interval.
1367		2598
1368	=item const char *path [read-only]	2599	=item const char *path [read-only]
1369		2600
1370	The filesystem path that is being watched.	2601	The file system path that is being watched.
1371		2602
1372	=back	2603	=back
1373		2604
		2605	=head3 Examples
		2606
1374	Example: Watch C</etc/passwd> for attribute changes.	2607	Example: Watch C</etc/passwd> for attribute changes.
1375		2608
1376	static void	2609	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2610	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2611	{
1379	/* /etc/passwd changed in some way */	2612	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2613	if (w->attr.st_nlink)
1381	{	2614	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2615	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2616	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2617	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2618	}
1386	else	2619	else
1387	/* you shalt not abuse printf for puts */	2620	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2621	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2622	"if this is windows, they already arrived\n");
1390	}	2623	}
1391		2624
1392	...	2625	...
1393	ev_stat passwd;	2626	ev_stat passwd;
1394		2627
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2628	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2629	ev_stat_start (loop, &passwd);
		2630
		2631	Example: Like above, but additionally use a one-second delay so we do not
		2632	miss updates (however, frequent updates will delay processing, too, so
		2633	one might do the work both on C<ev_stat> callback invocation I<and> on
		2634	C<ev_timer> callback invocation).
		2635
		2636	static ev_stat passwd;
		2637	static ev_timer timer;
		2638
		2639	static void
		2640	timer_cb (EV_P_ ev_timer *w, int revents)
		2641	{
		2642	ev_timer_stop (EV_A_ w);
		2643
		2644	/* now it's one second after the most recent passwd change */
		2645	}
		2646
		2647	static void
		2648	stat_cb (EV_P_ ev_stat *w, int revents)
		2649	{
		2650	/* reset the one-second timer */
		2651	ev_timer_again (EV_A_ &timer);
		2652	}
		2653
		2654	...
		2655	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2656	ev_stat_start (loop, &passwd);
		2657	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2658
1398		2659
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2660	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2661
1401	Idle watchers trigger events when no other events of the same or higher	2662	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2663	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2664	as receiving "events").
1404		2665
1405	That is, as long as your process is busy handling sockets or timeouts	2666	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2667	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2668	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2669	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2676	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2677	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2678	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2679	event loop has handled all outstanding events.
1419		2680
		2681	=head3 Watcher-Specific Functions and Data Members
		2682
1420	=over 4	2683	=over 4
1421		2684
1422	=item ev_idle_init (ev_signal *, callback)	2685	=item ev_idle_init (ev_idle *, callback)
1423		2686
1424	Initialises and configures the idle watcher - it has no parameters of any	2687	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2688	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2689	believe me.
1427		2690
1428	=back	2691	=back
1429		2692
		2693	=head3 Examples
		2694
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2695	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2696	callback, free it. Also, use no error checking, as usual.
1432		2697
1433	static void	2698	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2699	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2700	{
1436	free (w);	2701	free (w);
1437	// now do something you wanted to do when the program has	2702	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2703	// no longer anything immediate to do.
1439	}	2704	}
1440		2705
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2706	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2707	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2708	ev_idle_start (loop, idle_watcher);
1444		2709
1445		2710
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2711	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2712
1448	Prepare and check watchers are usually (but not always) used in tandem:	2713	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2714	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2715	afterwards.
1451		2716
1452	You I<must not> call C<ev_loop> or similar functions that enter	2717	You I<must not> call C<ev_run> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2718	the current event loop from either C<ev_prepare> or C<ev_check>
1454	watchers. Other loops than the current one are fine, however. The	2719	watchers. Other loops than the current one are fine, however. The
1455	rationale behind this is that you do not need to check for recursion in	2720	rationale behind this is that you do not need to check for recursion in
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2721	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2722	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2723	called in pairs bracketing the blocking call.
1459		2724
1460	Their main purpose is to integrate other event mechanisms into libev and	2725	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2726	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2727	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2728	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2729	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2730	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2731	watcher).
1467		2732
1468	This is done by examining in each prepare call which file descriptors need	2733	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2734	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2735	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2736	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2737	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2738	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2739	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2740	nevertheless, because you never know, you know?).
1476		2741
1477	As another example, the Perl Coro module uses these hooks to integrate	2742	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2743	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2744	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2745	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2746	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2747	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2748	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2749	low-priority coroutines to idle/background tasks).
1485		2750
		2751	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2752	priority, to ensure that they are being run before any other watchers
		2753	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2754
		2755	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2756	activate ("feed") events into libev. While libev fully supports this, they
		2757	might get executed before other C<ev_check> watchers did their job. As
		2758	C<ev_check> watchers are often used to embed other (non-libev) event
		2759	loops those other event loops might be in an unusable state until their
		2760	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2761	others).
		2762
		2763	=head3 Watcher-Specific Functions and Data Members
		2764
1486	=over 4	2765	=over 4
1487		2766
1488	=item ev_prepare_init (ev_prepare *, callback)	2767	=item ev_prepare_init (ev_prepare *, callback)
1489		2768
1490	=item ev_check_init (ev_check *, callback)	2769	=item ev_check_init (ev_check *, callback)
1491		2770
1492	Initialises and configures the prepare or check watcher - they have no	2771	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2772	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2773	macros, but using them is utterly, utterly, utterly and completely
		2774	pointless.
1495		2775
1496	=back	2776	=back
1497		2777
1498	Example: To include a library such as adns, you would add IO watchers	2778	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	2779
		2780	There are a number of principal ways to embed other event loops or modules
		2781	into libev. Here are some ideas on how to include libadns into libev
		2782	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2783	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2784	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2785	Glib event loop).
		2786
		2787	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	2788	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	2789	is pseudo-code only of course. This requires you to either use a low
		2790	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2791	the callbacks for the IO/timeout watchers might not have been called yet.
1502		2792
1503	static ev_io iow [nfd];	2793	static ev_io iow [nfd];
1504	static ev_timer tw;	2794	static ev_timer tw;
1505		2795
1506	static void	2796	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	2797	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	2798	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	2799	}
1515		2800
1516	// create io watchers for each fd and a timer before blocking	2801	// create io watchers for each fd and a timer before blocking
1517	static void	2802	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2803	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	2804	{
1520	int timeout = 3600000;	2805	int timeout = 3600000;
1521	struct pollfd fds [nfd];	2806	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	2807	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2808	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		2809
1525	/* the callback is illegal, but won't be called as we stop during check */	2810	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	2811	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1527	ev_timer_start (loop, &tw);	2812	ev_timer_start (loop, &tw);
1528		2813
1529	// create on ev_io per pollfd	2814	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	2815	for (int i = 0; i < nfd; ++i)
1531	{	2816	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	2817	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	2818	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2819	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		2820
1536	fds [i].revents = 0;	2821	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	2822	ev_io_start (loop, iow + i);
1539	}	2823	}
1540	}	2824	}
1541		2825
1542	// stop all watchers after blocking	2826	// stop all watchers after blocking
1543	static void	2827	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2828	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	2829	{
1546	ev_timer_stop (loop, &tw);	2830	ev_timer_stop (loop, &tw);
1547		2831
1548	for (int i = 0; i < nfd; ++i)	2832	for (int i = 0; i < nfd; ++i)
		2833	{
		2834	// set the relevant poll flags
		2835	// could also call adns_processreadable etc. here
		2836	struct pollfd *fd = fds + i;
		2837	int revents = ev_clear_pending (iow + i);
		2838	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2839	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2840
		2841	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	2842	ev_io_stop (loop, iow + i);
		2843	}
1550		2844
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2845	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	2846	}
		2847
		2848	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2849	in the prepare watcher and would dispose of the check watcher.
		2850
		2851	Method 3: If the module to be embedded supports explicit event
		2852	notification (libadns does), you can also make use of the actual watcher
		2853	callbacks, and only destroy/create the watchers in the prepare watcher.
		2854
		2855	static void
		2856	timer_cb (EV_P_ ev_timer *w, int revents)
		2857	{
		2858	adns_state ads = (adns_state)w->data;
		2859	update_now (EV_A);
		2860
		2861	adns_processtimeouts (ads, &tv_now);
		2862	}
		2863
		2864	static void
		2865	io_cb (EV_P_ ev_io *w, int revents)
		2866	{
		2867	adns_state ads = (adns_state)w->data;
		2868	update_now (EV_A);
		2869
		2870	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2871	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2872	}
		2873
		2874	// do not ever call adns_afterpoll
		2875
		2876	Method 4: Do not use a prepare or check watcher because the module you
		2877	want to embed is not flexible enough to support it. Instead, you can
		2878	override their poll function. The drawback with this solution is that the
		2879	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2880	this approach, effectively embedding EV as a client into the horrible
		2881	libglib event loop.
		2882
		2883	static gint
		2884	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2885	{
		2886	int got_events = 0;
		2887
		2888	for (n = 0; n < nfds; ++n)
		2889	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2890
		2891	if (timeout >= 0)
		2892	// create/start timer
		2893
		2894	// poll
		2895	ev_run (EV_A_ 0);
		2896
		2897	// stop timer again
		2898	if (timeout >= 0)
		2899	ev_timer_stop (EV_A_ &to);
		2900
		2901	// stop io watchers again - their callbacks should have set
		2902	for (n = 0; n < nfds; ++n)
		2903	ev_io_stop (EV_A_ iow [n]);
		2904
		2905	return got_events;
		2906	}
1553		2907
1554		2908
1555	=head2 C<ev_embed> - when one backend isn't enough...	2909	=head2 C<ev_embed> - when one backend isn't enough...
1556		2910
1557	This is a rather advanced watcher type that lets you embed one event loop	2911	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	2917	prioritise I/O.
1564		2918
1565	As an example for a bug workaround, the kqueue backend might only support	2919	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	2920	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	2921	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	2922	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	2923	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	2924	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	2925	C<kevent>, but at least you can use both mechanisms for what they are
		2926	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		2927
1573	As for prioritising I/O: rarely you have the case where some fds have	2928	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	2929	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	2930	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	2931	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	2932	the rest in a second one, and embed the second one in the first.
1578		2933
1579	As long as the watcher is active, the callback will be invoked every time	2934	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	2935	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2936	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	2937	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	2938	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	2939	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		2940
1587	As long as the watcher is started it will automatically handle events. The	2941	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	2942	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		2943
1592	Also, there have not currently been made special provisions for forking:	2944	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2945	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	2946	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	2947	C<ev_loop_fork> on the embedded loop.
1596		2948
1597	Unfortunately, not all backends are embeddable, only the ones returned by	2949	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2950	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	2951	portable one.
1600		2952
1601	So when you want to use this feature you will always have to be prepared	2953	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	2954	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	2955	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	2956	create it, and if that fails, use the normal loop for everything.
1605		2957
1606	struct ev_loop *loop_hi = ev_default_init (0);	2958	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		2959
1616	// if we got one, then embed it, otherwise default to loop_hi	2960	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	2961	automatically be applied to the embedded loop as well, so no special
1618	{	2962	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	2963	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	2964	as applicable.
1621	}	2965
1622	else	2966	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		2967
1625	=over 4	2968	=over 4
1626		2969
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2970	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		2971
…		…
1630		2973
1631	Configures the watcher to embed the given loop, which must be	2974	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2975	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	2976	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	2977	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	2978	if you do not want that, you need to temporarily stop the embed watcher).
1636		2979
1637	=item ev_embed_sweep (loop, ev_embed *)	2980	=item ev_embed_sweep (loop, ev_embed *)
1638		2981
1639	Make a single, non-blocking sweep over the embedded loop. This works	2982	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2983	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1641	apropriate way for embedded loops.	2984	appropriate way for embedded loops.
1642		2985
1643	=item struct ev_loop *loop [read-only]	2986	=item struct ev_loop *other [read-only]
1644		2987
1645	The embedded event loop.	2988	The embedded event loop.
1646		2989
1647	=back	2990	=back
		2991
		2992	=head3 Examples
		2993
		2994	Example: Try to get an embeddable event loop and embed it into the default
		2995	event loop. If that is not possible, use the default loop. The default
		2996	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2997	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2998	used).
		2999
		3000	struct ev_loop *loop_hi = ev_default_init (0);
		3001	struct ev_loop *loop_lo = 0;
		3002	ev_embed embed;
		3003
		3004	// see if there is a chance of getting one that works
		3005	// (remember that a flags value of 0 means autodetection)
		3006	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3007	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3008	: 0;
		3009
		3010	// if we got one, then embed it, otherwise default to loop_hi
		3011	if (loop_lo)
		3012	{
		3013	ev_embed_init (&embed, 0, loop_lo);
		3014	ev_embed_start (loop_hi, &embed);
		3015	}
		3016	else
		3017	loop_lo = loop_hi;
		3018
		3019	Example: Check if kqueue is available but not recommended and create
		3020	a kqueue backend for use with sockets (which usually work with any
		3021	kqueue implementation). Store the kqueue/socket-only event loop in
		3022	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3023
		3024	struct ev_loop *loop = ev_default_init (0);
		3025	struct ev_loop *loop_socket = 0;
		3026	ev_embed embed;
		3027
		3028	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3029	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3030	{
		3031	ev_embed_init (&embed, 0, loop_socket);
		3032	ev_embed_start (loop, &embed);
		3033	}
		3034
		3035	if (!loop_socket)
		3036	loop_socket = loop;
		3037
		3038	// now use loop_socket for all sockets, and loop for everything else
1648		3039
1649		3040
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3041	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		3042
1652	Fork watchers are called when a C<fork ()> was detected (usually because	3043	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1655	event loop blocks next and before C<ev_check> watchers are being called,	3046	event loop blocks next and before C<ev_check> watchers are being called,
1656	and only in the child after the fork. If whoever good citizen calling	3047	and only in the child after the fork. If whoever good citizen calling
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3048	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1658	handlers will be invoked, too, of course.	3049	handlers will be invoked, too, of course.
1659		3050
		3051	=head3 The special problem of life after fork - how is it possible?
		3052
		3053	Most uses of C<fork()> consist of forking, then some simple calls to set
		3054	up/change the process environment, followed by a call to C<exec()>. This
		3055	sequence should be handled by libev without any problems.
		3056
		3057	This changes when the application actually wants to do event handling
		3058	in the child, or both parent in child, in effect "continuing" after the
		3059	fork.
		3060
		3061	The default mode of operation (for libev, with application help to detect
		3062	forks) is to duplicate all the state in the child, as would be expected
		3063	when I<either> the parent I<or> the child process continues.
		3064
		3065	When both processes want to continue using libev, then this is usually the
		3066	wrong result. In that case, usually one process (typically the parent) is
		3067	supposed to continue with all watchers in place as before, while the other
		3068	process typically wants to start fresh, i.e. without any active watchers.
		3069
		3070	The cleanest and most efficient way to achieve that with libev is to
		3071	simply create a new event loop, which of course will be "empty", and
		3072	use that for new watchers. This has the advantage of not touching more
		3073	memory than necessary, and thus avoiding the copy-on-write, and the
		3074	disadvantage of having to use multiple event loops (which do not support
		3075	signal watchers).
		3076
		3077	When this is not possible, or you want to use the default loop for
		3078	other reasons, then in the process that wants to start "fresh", call
		3079	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		3080	the default loop will "orphan" (not stop) all registered watchers, so you
		3081	have to be careful not to execute code that modifies those watchers. Note
		3082	also that in that case, you have to re-register any signal watchers.
		3083
		3084	=head3 Watcher-Specific Functions and Data Members
		3085
1660	=over 4	3086	=over 4
1661		3087
1662	=item ev_fork_init (ev_signal *, callback)	3088	=item ev_fork_init (ev_signal *, callback)
1663		3089
1664	Initialises and configures the fork watcher - it has no parameters of any	3090	Initialises and configures the fork watcher - it has no parameters of any
…		…
1666	believe me.	3092	believe me.
1667		3093
1668	=back	3094	=back
1669		3095
1670		3096
		3097	=head2 C<ev_async> - how to wake up an event loop
		3098
		3099	In general, you cannot use an C<ev_run> from multiple threads or other
		3100	asynchronous sources such as signal handlers (as opposed to multiple event
		3101	loops - those are of course safe to use in different threads).
		3102
		3103	Sometimes, however, you need to wake up an event loop you do not control,
		3104	for example because it belongs to another thread. This is what C<ev_async>
		3105	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3106	it by calling C<ev_async_send>, which is thread- and signal safe.
		3107
		3108	This functionality is very similar to C<ev_signal> watchers, as signals,
		3109	too, are asynchronous in nature, and signals, too, will be compressed
		3110	(i.e. the number of callback invocations may be less than the number of
		3111	C<ev_async_sent> calls).
		3112
		3113	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3114	just the default loop.
		3115
		3116	=head3 Queueing
		3117
		3118	C<ev_async> does not support queueing of data in any way. The reason
		3119	is that the author does not know of a simple (or any) algorithm for a
		3120	multiple-writer-single-reader queue that works in all cases and doesn't
		3121	need elaborate support such as pthreads or unportable memory access
		3122	semantics.
		3123
		3124	That means that if you want to queue data, you have to provide your own
		3125	queue. But at least I can tell you how to implement locking around your
		3126	queue:
		3127
		3128	=over 4
		3129
		3130	=item queueing from a signal handler context
		3131
		3132	To implement race-free queueing, you simply add to the queue in the signal
		3133	handler but you block the signal handler in the watcher callback. Here is
		3134	an example that does that for some fictitious SIGUSR1 handler:
		3135
		3136	static ev_async mysig;
		3137
		3138	static void
		3139	sigusr1_handler (void)
		3140	{
		3141	sometype data;
		3142
		3143	// no locking etc.
		3144	queue_put (data);
		3145	ev_async_send (EV_DEFAULT_ &mysig);
		3146	}
		3147
		3148	static void
		3149	mysig_cb (EV_P_ ev_async *w, int revents)
		3150	{
		3151	sometype data;
		3152	sigset_t block, prev;
		3153
		3154	sigemptyset (&block);
		3155	sigaddset (&block, SIGUSR1);
		3156	sigprocmask (SIG_BLOCK, &block, &prev);
		3157
		3158	while (queue_get (&data))
		3159	process (data);
		3160
		3161	if (sigismember (&prev, SIGUSR1)
		3162	sigprocmask (SIG_UNBLOCK, &block, 0);
		3163	}
		3164
		3165	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3166	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3167	either...).
		3168
		3169	=item queueing from a thread context
		3170
		3171	The strategy for threads is different, as you cannot (easily) block
		3172	threads but you can easily preempt them, so to queue safely you need to
		3173	employ a traditional mutex lock, such as in this pthread example:
		3174
		3175	static ev_async mysig;
		3176	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3177
		3178	static void
		3179	otherthread (void)
		3180	{
		3181	// only need to lock the actual queueing operation
		3182	pthread_mutex_lock (&mymutex);
		3183	queue_put (data);
		3184	pthread_mutex_unlock (&mymutex);
		3185
		3186	ev_async_send (EV_DEFAULT_ &mysig);
		3187	}
		3188
		3189	static void
		3190	mysig_cb (EV_P_ ev_async *w, int revents)
		3191	{
		3192	pthread_mutex_lock (&mymutex);
		3193
		3194	while (queue_get (&data))
		3195	process (data);
		3196
		3197	pthread_mutex_unlock (&mymutex);
		3198	}
		3199
		3200	=back
		3201
		3202
		3203	=head3 Watcher-Specific Functions and Data Members
		3204
		3205	=over 4
		3206
		3207	=item ev_async_init (ev_async *, callback)
		3208
		3209	Initialises and configures the async watcher - it has no parameters of any
		3210	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3211	trust me.
		3212
		3213	=item ev_async_send (loop, ev_async *)
		3214
		3215	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3216	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3217	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3218	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3219	section below on what exactly this means).
		3220
		3221	Note that, as with other watchers in libev, multiple events might get
		3222	compressed into a single callback invocation (another way to look at this
		3223	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3224	reset when the event loop detects that).
		3225
		3226	This call incurs the overhead of a system call only once per event loop
		3227	iteration, so while the overhead might be noticeable, it doesn't apply to
		3228	repeated calls to C<ev_async_send> for the same event loop.
		3229
		3230	=item bool = ev_async_pending (ev_async *)
		3231
		3232	Returns a non-zero value when C<ev_async_send> has been called on the
		3233	watcher but the event has not yet been processed (or even noted) by the
		3234	event loop.
		3235
		3236	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3237	the loop iterates next and checks for the watcher to have become active,
		3238	it will reset the flag again. C<ev_async_pending> can be used to very
		3239	quickly check whether invoking the loop might be a good idea.
		3240
		3241	Not that this does I<not> check whether the watcher itself is pending,
		3242	only whether it has been requested to make this watcher pending: there
		3243	is a time window between the event loop checking and resetting the async
		3244	notification, and the callback being invoked.
		3245
		3246	=back
		3247
		3248
1671	=head1 OTHER FUNCTIONS	3249	=head1 OTHER FUNCTIONS
1672		3250
1673	There are some other functions of possible interest. Described. Here. Now.	3251	There are some other functions of possible interest. Described. Here. Now.
1674		3252
1675	=over 4	3253	=over 4
1676		3254
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3255	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1678		3256
1679	This function combines a simple timer and an I/O watcher, calls your	3257	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	3258	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	3259	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	3260	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	3261	more watchers yourself.
1684		3262
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	3263	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3264	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	3265	the given C<fd> and C<events> set will be created and started.
1688		3266
1689	If C<timeout> is less than 0, then no timeout watcher will be	3267	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3268	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3269	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		3270
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3271	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1695	passed an C<revents> set like normal event callbacks (a combination of	3272	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3273	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1697	value passed to C<ev_once>:	3274	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3275	a timeout and an io event at the same time - you probably should give io
		3276	events precedence.
1698		3277
		3278	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3279
1699	static void stdin_ready (int revents, void *arg)	3280	static void stdin_ready (int revents, void *arg)
1700	{	3281	{
1701	if (revents & EV_TIMEOUT)
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)	3282	if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;	3283	/* stdin might have data for us, joy! */;
		3284	else if (revents & EV_TIMER)
		3285	/* doh, nothing entered */;
1705	}	3286	}
1706		3287
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3288	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1708		3289
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)
1710
1711	Feeds the given event set into the event loop, as if the specified event
1712	had happened for the specified watcher (which must be a pointer to an
1713	initialised but not necessarily started event watcher).
1714
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3290	=item ev_feed_fd_event (loop, int fd, int revents)
1716		3291
1717	Feed an event on the given fd, as if a file descriptor backend detected	3292	Feed an event on the given fd, as if a file descriptor backend detected
1718	the given events it.	3293	the given events it.
1719		3294
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	3295	=item ev_feed_signal_event (loop, int signum)
1721		3296
1722	Feed an event as if the given signal occured (C<loop> must be the default	3297	Feed an event as if the given signal occurred (C<loop> must be the default
1723	loop!).	3298	loop!).
1724		3299
1725	=back	3300	=back
1726		3301
1727		3302
…		…
1743		3318
1744	=item * Priorities are not currently supported. Initialising priorities	3319	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	3320	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	3321	is an ev_pri field.
1747		3322
		3323	=item * In libevent, the last base created gets the signals, in libev, the
		3324	first base created (== the default loop) gets the signals.
		3325
1748	=item * Other members are not supported.	3326	=item * Other members are not supported.
1749		3327
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3328	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	3329	to use the libev header file and library.
1752		3330
1753	=back	3331	=back
1754		3332
1755	=head1 C++ SUPPORT	3333	=head1 C++ SUPPORT
1756		3334
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3335	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	3336	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	3337	the callback model to a model using method callbacks on objects.
1760		3338
1761	To use it,	3339	To use it,
1762		3340
1763	#include <ev++.h>	3341	#include <ev++.h>
1764		3342
1765	This automatically includes F<ev.h> and puts all of its definitions (many	3343	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	3344	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	3345	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3346	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1802		3380
1803	=over 4	3381	=over 4
1804		3382
1805	=item ev::TYPE::TYPE ()	3383	=item ev::TYPE::TYPE ()
1806		3384
1807	=item ev::TYPE::TYPE (struct ev_loop *)	3385	=item ev::TYPE::TYPE (loop)
1808		3386
1809	=item ev::TYPE::~TYPE	3387	=item ev::TYPE::~TYPE
1810		3388
1811	The constructor (optionally) takes an event loop to associate the watcher	3389	The constructor (optionally) takes an event loop to associate the watcher
1812	with. If it is omitted, it will use C<EV_DEFAULT>.	3390	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	3413	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	3414	thunking function, making it as fast as a direct C callback.
1837		3415
1838	Example: simple class declaration and watcher initialisation	3416	Example: simple class declaration and watcher initialisation
1839		3417
1840	struct myclass	3418	struct myclass
1841	{	3419	{
1842	void io_cb (ev::io &w, int revents) { }	3420	void io_cb (ev::io &w, int revents) { }
1843	}	3421	}
1844		3422
1845	myclass obj;	3423	myclass obj;
1846	ev::io iow;	3424	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	3425	iow.set <myclass, &myclass::io_cb> (&obj);
1848		3426
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	3427	=item w->set (object *)
		3428
		3429	This is a variation of a method callback - leaving out the method to call
		3430	will default the method to C<operator ()>, which makes it possible to use
		3431	functor objects without having to manually specify the C<operator ()> all
		3432	the time. Incidentally, you can then also leave out the template argument
		3433	list.
		3434
		3435	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3436	int revents)>.
		3437
		3438	See the method-C<set> above for more details.
		3439
		3440	Example: use a functor object as callback.
		3441
		3442	struct myfunctor
		3443	{
		3444	void operator() (ev::io &w, int revents)
		3445	{
		3446	...
		3447	}
		3448	}
		3449
		3450	myfunctor f;
		3451
		3452	ev::io w;
		3453	w.set (&f);
		3454
		3455	=item w->set<function> (void *data = 0)
1850		3456
1851	Also sets a callback, but uses a static method or plain function as	3457	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	3458	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	3459	C<data> member and is free for you to use.
1854		3460
		3461	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3462
1855	See the method-C<set> above for more details.	3463	See the method-C<set> above for more details.
1856		3464
		3465	Example: Use a plain function as callback.
		3466
		3467	static void io_cb (ev::io &w, int revents) { }
		3468	iow.set <io_cb> ();
		3469
1857	=item w->set (struct ev_loop *)	3470	=item w->set (loop)
1858		3471
1859	Associates a different C<struct ev_loop> with this watcher. You can only	3472	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	3473	do this when the watcher is inactive (and not pending either).
1861		3474
1862	=item w->set ([args])	3475	=item w->set ([arguments])
1863		3476
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3477	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
1865	called at least once. Unlike the C counterpart, an active watcher gets	3478	method or a suitable start method must be called at least once. Unlike the
1866	automatically stopped and restarted when reconfiguring it with this	3479	C counterpart, an active watcher gets automatically stopped and restarted
1867	method.	3480	when reconfiguring it with this method.
1868		3481
1869	=item w->start ()	3482	=item w->start ()
1870		3483
1871	Starts the watcher. Note that there is no C<loop> argument, as the	3484	Starts the watcher. Note that there is no C<loop> argument, as the
1872	constructor already stores the event loop.	3485	constructor already stores the event loop.
1873		3486
		3487	=item w->start ([arguments])
		3488
		3489	Instead of calling C<set> and C<start> methods separately, it is often
		3490	convenient to wrap them in one call. Uses the same type of arguments as
		3491	the configure C<set> method of the watcher.
		3492
1874	=item w->stop ()	3493	=item w->stop ()
1875		3494
1876	Stops the watcher if it is active. Again, no C<loop> argument.	3495	Stops the watcher if it is active. Again, no C<loop> argument.
1877		3496
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	3497	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		3498
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3499	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	3500	C<ev_TYPE_again> function.
1882		3501
1883	=item w->sweep () C<ev::embed> only	3502	=item w->sweep () (C<ev::embed> only)
1884		3503
1885	Invokes C<ev_embed_sweep>.	3504	Invokes C<ev_embed_sweep>.
1886		3505
1887	=item w->update () C<ev::stat> only	3506	=item w->update () (C<ev::stat> only)
1888		3507
1889	Invokes C<ev_stat_stat>.	3508	Invokes C<ev_stat_stat>.
1890		3509
1891	=back	3510	=back
1892		3511
1893	=back	3512	=back
1894		3513
1895	Example: Define a class with an IO and idle watcher, start one of them in	3514	Example: Define a class with two I/O and idle watchers, start the I/O
1896	the constructor.	3515	watchers in the constructor.
1897		3516
1898	class myclass	3517	class myclass
1899	{	3518	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	3519	ev::io io ; void io_cb (ev::io &w, int revents);
		3520	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	3521	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		3522
1903	myclass ();	3523	myclass (int fd)
1904	}	3524	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	3525	io .set <myclass, &myclass::io_cb > (this);
		3526	io2 .set <myclass, &myclass::io2_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	3527	idle.set <myclass, &myclass::idle_cb> (this);
1910		3528
1911	io.start (fd, ev::READ);	3529	io.set (fd, ev::WRITE); // configure the watcher
		3530	io.start (); // start it whenever convenient
		3531
		3532	io2.start (fd, ev::READ); // set + start in one call
		3533	}
1912	}	3534	};
		3535
		3536
		3537	=head1 OTHER LANGUAGE BINDINGS
		3538
		3539	Libev does not offer other language bindings itself, but bindings for a
		3540	number of languages exist in the form of third-party packages. If you know
		3541	any interesting language binding in addition to the ones listed here, drop
		3542	me a note.
		3543
		3544	=over 4
		3545
		3546	=item Perl
		3547
		3548	The EV module implements the full libev API and is actually used to test
		3549	libev. EV is developed together with libev. Apart from the EV core module,
		3550	there are additional modules that implement libev-compatible interfaces
		3551	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3552	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3553	and C<EV::Glib>).
		3554
		3555	It can be found and installed via CPAN, its homepage is at
		3556	L<http://software.schmorp.de/pkg/EV>.
		3557
		3558	=item Python
		3559
		3560	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3561	seems to be quite complete and well-documented.
		3562
		3563	=item Ruby
		3564
		3565	Tony Arcieri has written a ruby extension that offers access to a subset
		3566	of the libev API and adds file handle abstractions, asynchronous DNS and
		3567	more on top of it. It can be found via gem servers. Its homepage is at
		3568	L<http://rev.rubyforge.org/>.
		3569
		3570	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3571	makes rev work even on mingw.
		3572
		3573	=item Haskell
		3574
		3575	A haskell binding to libev is available at
		3576	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3577
		3578	=item D
		3579
		3580	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3581	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3582
		3583	=item Ocaml
		3584
		3585	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3586	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3587
		3588	=item Lua
		3589
		3590	Brian Maher has written a partial interface to libev for lua (at the
		3591	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3592	L<http://github.com/brimworks/lua-ev>.
		3593
		3594	=back
1913		3595
1914		3596
1915	=head1 MACRO MAGIC	3597	=head1 MACRO MAGIC
1916		3598
1917	Libev can be compiled with a variety of options, the most fundemantal is	3599	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3600	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	3601	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		3602
1921	To make it easier to write programs that cope with either variant, the	3603	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	3604	following macros are defined:
1923		3605
1924	=over 4	3606	=over 4
…		…
1927		3609
1928	This provides the loop I<argument> for functions, if one is required ("ev	3610	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	3611	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	3612	C<EV_A_> is used when other arguments are following. Example:
1931		3613
1932	ev_unref (EV_A);	3614	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	3615	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	3616	ev_run (EV_A_ 0);
1935		3617
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3618	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	3619	which is often provided by the following macro.
1938		3620
1939	=item C<EV_P>, C<EV_P_>	3621	=item C<EV_P>, C<EV_P_>
1940		3622
1941	This provides the loop I<parameter> for functions, if one is required ("ev	3623	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3624	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	3625	C<EV_P_> is used when other parameters are following. Example:
1944		3626
1945	// this is how ev_unref is being declared	3627	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	3628	static void ev_unref (EV_P);
1947		3629
1948	// this is how you can declare your typical callback	3630	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	3631	static void cb (EV_P_ ev_timer *w, int revents)
1950		3632
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3633	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	3634	suitable for use with C<EV_A>.
1953		3635
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3636	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		3637
1956	Similar to the other two macros, this gives you the value of the default	3638	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	3639	loop, if multiple loops are supported ("ev loop default").
		3640
		3641	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3642
		3643	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3644	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3645	is undefined when the default loop has not been initialised by a previous
		3646	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3647
		3648	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3649	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		3650
1959	=back	3651	=back
1960		3652
1961	Example: Declare and initialise a check watcher, utilising the above	3653	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	3654	macros so it will work regardless of whether multiple loops are supported
1963	or not.	3655	or not.
1964		3656
1965	static void	3657	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	3658	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	3659	{
1968	ev_check_stop (EV_A_ w);	3660	ev_check_stop (EV_A_ w);
1969	}	3661	}
1970		3662
1971	ev_check check;	3663	ev_check check;
1972	ev_check_init (&check, check_cb);	3664	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	3665	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	3666	ev_run (EV_DEFAULT_ 0);
1975		3667
1976	=head1 EMBEDDING	3668	=head1 EMBEDDING
1977		3669
1978	Libev can (and often is) directly embedded into host	3670	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	3671	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3672	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	3673	and rxvt-unicode.
1982		3674
1983	The goal is to enable you to just copy the neecssary files into your	3675	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	3676	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	3677	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	3678	libev somewhere in your source tree).
1987		3679
1988	=head2 FILESETS	3680	=head2 FILESETS
1989		3681
1990	Depending on what features you need you need to include one or more sets of files	3682	Depending on what features you need you need to include one or more sets of files
1991	in your app.	3683	in your application.
1992		3684
1993	=head3 CORE EVENT LOOP	3685	=head3 CORE EVENT LOOP
1994		3686
1995	To include only the libev core (all the C<ev_*> functions), with manual	3687	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	3688	configuration (no autoconf):
1997		3689
1998	#define EV_STANDALONE 1	3690	#define EV_STANDALONE 1
1999	#include "ev.c"	3691	#include "ev.c"
2000		3692
2001	This will automatically include F<ev.h>, too, and should be done in a	3693	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	3694	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	3695	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	3696	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	3697	where you can put other configuration options):
2006		3698
2007	#define EV_STANDALONE 1	3699	#define EV_STANDALONE 1
2008	#include "ev.h"	3700	#include "ev.h"
2009		3701
2010	Both header files and implementation files can be compiled with a C++	3702	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	3703	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	3704	as a bug).
2013		3705
2014	You need the following files in your source tree, or in a directory	3706	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	3707	in your include path (e.g. in libev/ when using -Ilibev):
2016		3708
2017	ev.h	3709	ev.h
2018	ev.c	3710	ev.c
2019	ev_vars.h	3711	ev_vars.h
2020	ev_wrap.h	3712	ev_wrap.h
2021		3713
2022	ev_win32.c required on win32 platforms only	3714	ev_win32.c required on win32 platforms only
2023		3715
2024	ev_select.c only when select backend is enabled (which is enabled by default)	3716	ev_select.c only when select backend is enabled (which is enabled by default)
2025	ev_poll.c only when poll backend is enabled (disabled by default)	3717	ev_poll.c only when poll backend is enabled (disabled by default)
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3718	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3719	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	3720	ev_port.c only when the solaris port backend is enabled (disabled by default)
2029		3721
2030	F<ev.c> includes the backend files directly when enabled, so you only need	3722	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	3723	to compile this single file.
2032		3724
2033	=head3 LIBEVENT COMPATIBILITY API	3725	=head3 LIBEVENT COMPATIBILITY API
2034		3726
2035	To include the libevent compatibility API, also include:	3727	To include the libevent compatibility API, also include:
2036		3728
2037	#include "event.c"	3729	#include "event.c"
2038		3730
2039	in the file including F<ev.c>, and:	3731	in the file including F<ev.c>, and:
2040		3732
2041	#include "event.h"	3733	#include "event.h"
2042		3734
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	3735	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		3736
2045	You need the following additional files for this:	3737	You need the following additional files for this:
2046		3738
2047	event.h	3739	event.h
2048	event.c	3740	event.c
2049		3741
2050	=head3 AUTOCONF SUPPORT	3742	=head3 AUTOCONF SUPPORT
2051		3743
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	3744	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	3745	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3746	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	3747	include F<config.h> and configure itself accordingly.
2056		3748
2057	For this of course you need the m4 file:	3749	For this of course you need the m4 file:
2058		3750
2059	libev.m4	3751	libev.m4
2060		3752
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	3753	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		3754
2063	Libev can be configured via a variety of preprocessor symbols you have to define	3755	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	3756	define before including (or compiling) any of its files. The default in
2065	and only include the select backend.	3757	the absence of autoconf is documented for every option.
		3758
		3759	Symbols marked with "(h)" do not change the ABI, and can have different
		3760	values when compiling libev vs. including F<ev.h>, so it is permissible
		3761	to redefine them before including F<ev.h> without breaking compatibility
		3762	to a compiled library. All other symbols change the ABI, which means all
		3763	users of libev and the libev code itself must be compiled with compatible
		3764	settings.
2066		3765
2067	=over 4	3766	=over 4
2068		3767
		3768	=item EV_COMPAT3 (h)
		3769
		3770	Backwards compatibility is a major concern for libev. This is why this
		3771	release of libev comes with wrappers for the functions and symbols that
		3772	have been renamed between libev version 3 and 4.
		3773
		3774	You can disable these wrappers (to test compatibility with future
		3775	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3776	sources. This has the additional advantage that you can drop the C<struct>
		3777	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3778	typedef in that case.
		3779
		3780	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3781	and in some even more future version the compatibility code will be
		3782	removed completely.
		3783
2069	=item EV_STANDALONE	3784	=item EV_STANDALONE (h)
2070		3785
2071	Must always be C<1> if you do not use autoconf configuration, which	3786	Must always be C<1> if you do not use autoconf configuration, which
2072	keeps libev from including F<config.h>, and it also defines dummy	3787	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	3788	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	3789	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	3790	F<event.h> that are not directly supported by the libev core alone.
2076		3791
		3792	In standalone mode, libev will still try to automatically deduce the
		3793	configuration, but has to be more conservative.
		3794
2077	=item EV_USE_MONOTONIC	3795	=item EV_USE_MONOTONIC
2078		3796
2079	If defined to be C<1>, libev will try to detect the availability of the	3797	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	3798	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	3799	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	3800	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	3801	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	3802	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	3803	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		3804
2087	=item EV_USE_REALTIME	3805	=item EV_USE_REALTIME
2088		3806
2089	If defined to be C<1>, libev will try to detect the availability of the	3807	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	3808	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	3809	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3810	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3811	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	3812	correctness. See the note about libraries in the description of
		3813	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3814	C<EV_USE_CLOCK_SYSCALL>.
		3815
		3816	=item EV_USE_CLOCK_SYSCALL
		3817
		3818	If defined to be C<1>, libev will try to use a direct syscall instead
		3819	of calling the system-provided C<clock_gettime> function. This option
		3820	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3821	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3822	programs needlessly. Using a direct syscall is slightly slower (in
		3823	theory), because no optimised vdso implementation can be used, but avoids
		3824	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3825	higher, as it simplifies linking (no need for C<-lrt>).
		3826
		3827	=item EV_USE_NANOSLEEP
		3828
		3829	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3830	and will use it for delays. Otherwise it will use C<select ()>.
		3831
		3832	=item EV_USE_EVENTFD
		3833
		3834	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3835	available and will probe for kernel support at runtime. This will improve
		3836	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3837	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3838	2.7 or newer, otherwise disabled.
2095		3839
2096	=item EV_USE_SELECT	3840	=item EV_USE_SELECT
2097		3841
2098	If undefined or defined to be C<1>, libev will compile in support for the	3842	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	3843	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	3844	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	3845	will not be compiled in.
2102		3846
2103	=item EV_SELECT_USE_FD_SET	3847	=item EV_SELECT_USE_FD_SET
2104		3848
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	3849	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	3850	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3851	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	3852	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	3853	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3854	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	3855	configures the maximum size of the C<fd_set>.
2112		3856
2113	=item EV_SELECT_IS_WINSOCKET	3857	=item EV_SELECT_IS_WINSOCKET
2114		3858
2115	When defined to C<1>, the select backend will assume that	3859	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	3860	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	3862	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3863	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	3864	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	3865	on win32. Should not be defined on non-win32 platforms.
2122		3866
		3867	=item EV_FD_TO_WIN32_HANDLE(fd)
		3868
		3869	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3870	file descriptors to socket handles. When not defining this symbol (the
		3871	default), then libev will call C<_get_osfhandle>, which is usually
		3872	correct. In some cases, programs use their own file descriptor management,
		3873	in which case they can provide this function to map fds to socket handles.
		3874
		3875	=item EV_WIN32_HANDLE_TO_FD(handle)
		3876
		3877	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3878	using the standard C<_open_osfhandle> function. For programs implementing
		3879	their own fd to handle mapping, overwriting this function makes it easier
		3880	to do so. This can be done by defining this macro to an appropriate value.
		3881
		3882	=item EV_WIN32_CLOSE_FD(fd)
		3883
		3884	If programs implement their own fd to handle mapping on win32, then this
		3885	macro can be used to override the C<close> function, useful to unregister
		3886	file descriptors again. Note that the replacement function has to close
		3887	the underlying OS handle.
		3888
2123	=item EV_USE_POLL	3889	=item EV_USE_POLL
2124		3890
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3891	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	3892	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	3893	takes precedence over select.
2128		3894
2129	=item EV_USE_EPOLL	3895	=item EV_USE_EPOLL
2130		3896
2131	If defined to be C<1>, libev will compile in support for the Linux	3897	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	3898	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	3899	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	3900	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3901	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2135		3902
2136	=item EV_USE_KQUEUE	3903	=item EV_USE_KQUEUE
2137		3904
2138	If defined to be C<1>, libev will compile in support for the BSD style	3905	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3906	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	3919	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	3920	backend for Solaris 10 systems.
2154		3921
2155	=item EV_USE_DEVPOLL	3922	=item EV_USE_DEVPOLL
2156		3923
2157	reserved for future expansion, works like the USE symbols above.	3924	Reserved for future expansion, works like the USE symbols above.
2158		3925
2159	=item EV_USE_INOTIFY	3926	=item EV_USE_INOTIFY
2160		3927
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	3928	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	3929	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	3930	be detected at runtime. If undefined, it will be enabled if the headers
		3931	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2164		3932
		3933	=item EV_ATOMIC_T
		3934
		3935	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3936	access is atomic with respect to other threads or signal contexts. No such
		3937	type is easily found in the C language, so you can provide your own type
		3938	that you know is safe for your purposes. It is used both for signal handler "locking"
		3939	as well as for signal and thread safety in C<ev_async> watchers.
		3940
		3941	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3942	(from F<signal.h>), which is usually good enough on most platforms.
		3943
2165	=item EV_H	3944	=item EV_H (h)
2166		3945
2167	The name of the F<ev.h> header file used to include it. The default if	3946	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3947	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3948	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		3949
2171	=item EV_CONFIG_H	3950	=item EV_CONFIG_H (h)
2172		3951
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3952	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3953	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	3954	C<EV_H>, above.
2176		3955
2177	=item EV_EVENT_H	3956	=item EV_EVENT_H (h)
2178		3957
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3958	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	3959	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		3960
2182	=item EV_PROTOTYPES	3961	=item EV_PROTOTYPES (h)
2183		3962
2184	If defined to be C<0>, then F<ev.h> will not define any function	3963	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	3964	prototypes, but still define all the structs and other symbols. This is
2186	occasionally useful if you want to provide your own wrapper functions	3965	occasionally useful if you want to provide your own wrapper functions
2187	around libev functions.	3966	around libev functions.
…		…
2206	When doing priority-based operations, libev usually has to linearly search	3985	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	3986	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	3987	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	3988	fine.
2210		3989
2211	If your embedding app does not need any priorities, defining these both to	3990	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	3991	both to C<0> will save some memory and CPU.
2213		3992
2214	=item EV_PERIODIC_ENABLE	3993	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3994	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3995	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2215		3996
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	3997	If undefined or defined to be C<1> (and the platform supports it), then
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	3998	the respective watcher type is supported. If defined to be C<0>, then it
2218	code.	3999	is not. Disabling watcher types mainly saves code size.
2219		4000
2220	=item EV_IDLE_ENABLE	4001	=item EV_FEATURES
2221
2222	If undefined or defined to be C<1>, then idle watchers are supported. If
2223	defined to be C<0>, then they are not. Disabling them saves a few kB of
2224	code.
2225
2226	=item EV_EMBED_ENABLE
2227
2228	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.
2230
2231	=item EV_STAT_ENABLE
2232
2233	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.
2235
2236	=item EV_FORK_ENABLE
2237
2238	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.
2240
2241	=item EV_MINIMAL
2242		4002
2243	If you need to shave off some kilobytes of code at the expense of some	4003	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	4004	speed (but with the full API), you can define this symbol to request
2245	some inlining decisions, saves roughly 30% codesize of amd64.	4005	certain subsets of functionality. The default is to enable all features
		4006	that can be enabled on the platform.
		4007
		4008	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4009	with some broad features you want) and then selectively re-enable
		4010	additional parts you want, for example if you want everything minimal,
		4011	but multiple event loop support, async and child watchers and the poll
		4012	backend, use this:
		4013
		4014	#define EV_FEATURES 0
		4015	#define EV_MULTIPLICITY 1
		4016	#define EV_USE_POLL 1
		4017	#define EV_CHILD_ENABLE 1
		4018	#define EV_ASYNC_ENABLE 1
		4019
		4020	The actual value is a bitset, it can be a combination of the following
		4021	values:
		4022
		4023	=over 4
		4024
		4025	=item C<1> - faster/larger code
		4026
		4027	Use larger code to speed up some operations.
		4028
		4029	Currently this is used to override some inlining decisions (enlarging the
		4030	code size by roughly 30% on amd64).
		4031
		4032	When optimising for size, use of compiler flags such as C<-Os> with
		4033	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4034	assertions.
		4035
		4036	=item C<2> - faster/larger data structures
		4037
		4038	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4039	hash table sizes and so on. This will usually further increase code size
		4040	and can additionally have an effect on the size of data structures at
		4041	runtime.
		4042
		4043	=item C<4> - full API configuration
		4044
		4045	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4046	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4047
		4048	=item C<8> - full API
		4049
		4050	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4051	details on which parts of the API are still available without this
		4052	feature, and do not complain if this subset changes over time.
		4053
		4054	=item C<16> - enable all optional watcher types
		4055
		4056	Enables all optional watcher types. If you want to selectively enable
		4057	only some watcher types other than I/O and timers (e.g. prepare,
		4058	embed, async, child...) you can enable them manually by defining
		4059	C<EV_watchertype_ENABLE> to C<1> instead.
		4060
		4061	=item C<32> - enable all backends
		4062
		4063	This enables all backends - without this feature, you need to enable at
		4064	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4065
		4066	=item C<64> - enable OS-specific "helper" APIs
		4067
		4068	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4069	default.
		4070
		4071	=back
		4072
		4073	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4074	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4075	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4076	watchers, timers and monotonic clock support.
		4077
		4078	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4079	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4080	your program might be left out as well - a binary starting a timer and an
		4081	I/O watcher then might come out at only 5Kb.
		4082
		4083	=item EV_AVOID_STDIO
		4084
		4085	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4086	functions (printf, scanf, perror etc.). This will increase the code size
		4087	somewhat, but if your program doesn't otherwise depend on stdio and your
		4088	libc allows it, this avoids linking in the stdio library which is quite
		4089	big.
		4090
		4091	Note that error messages might become less precise when this option is
		4092	enabled.
		4093
		4094	=item EV_NSIG
		4095
		4096	The highest supported signal number, +1 (or, the number of
		4097	signals): Normally, libev tries to deduce the maximum number of signals
		4098	automatically, but sometimes this fails, in which case it can be
		4099	specified. Also, using a lower number than detected (C<32> should be
		4100	good for about any system in existence) can save some memory, as libev
		4101	statically allocates some 12-24 bytes per signal number.
2246		4102
2247	=item EV_PID_HASHSIZE	4103	=item EV_PID_HASHSIZE
2248		4104
2249	C<ev_child> watchers use a small hash table to distribute workload by	4105	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4106	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2251	than enough. If you need to manage thousands of children you might want to	4107	usually more than enough. If you need to manage thousands of children you
2252	increase this value (I<must> be a power of two).	4108	might want to increase this value (I<must> be a power of two).
2253		4109
2254	=item EV_INOTIFY_HASHSIZE	4110	=item EV_INOTIFY_HASHSIZE
2255		4111
2256	C<ev_staz> watchers use a small hash table to distribute workload by	4112	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4113	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	4114	disabled), usually more than enough. If you need to manage thousands of
2259	watchers you might want to increase this value (I<must> be a power of	4115	C<ev_stat> watchers you might want to increase this value (I<must> be a
2260	two).	4116	power of two).
		4117
		4118	=item EV_USE_4HEAP
		4119
		4120	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4121	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4122	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4123	faster performance with many (thousands) of watchers.
		4124
		4125	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4126	will be C<0>.
		4127
		4128	=item EV_HEAP_CACHE_AT
		4129
		4130	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4131	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4132	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4133	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4134	but avoids random read accesses on heap changes. This improves performance
		4135	noticeably with many (hundreds) of watchers.
		4136
		4137	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4138	will be C<0>.
		4139
		4140	=item EV_VERIFY
		4141
		4142	Controls how much internal verification (see C<ev_verify ()>) will
		4143	be done: If set to C<0>, no internal verification code will be compiled
		4144	in. If set to C<1>, then verification code will be compiled in, but not
		4145	called. If set to C<2>, then the internal verification code will be
		4146	called once per loop, which can slow down libev. If set to C<3>, then the
		4147	verification code will be called very frequently, which will slow down
		4148	libev considerably.
		4149
		4150	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4151	will be C<0>.
2261		4152
2262	=item EV_COMMON	4153	=item EV_COMMON
2263		4154
2264	By default, all watchers have a C<void *data> member. By redefining	4155	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	4156	this macro to something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	4157	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	4158	though, and it must be identical each time.
2268		4159
2269	For example, the perl EV module uses something like this:	4160	For example, the perl EV module uses something like this:
2270		4161
2271	#define EV_COMMON \	4162	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	4163	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	4164	SV *cb_sv, *fh /* note no trailing ";" */
2274		4165
2275	=item EV_CB_DECLARE (type)	4166	=item EV_CB_DECLARE (type)
2276		4167
2277	=item EV_CB_INVOKE (watcher, revents)	4168	=item EV_CB_INVOKE (watcher, revents)
2278		4169
2279	=item ev_set_cb (ev, cb)	4170	=item ev_set_cb (ev, cb)
2280		4171
2281	Can be used to change the callback member declaration in each watcher,	4172	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	4173	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	4174	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	4175	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4176	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	4177	method calls instead of plain function calls in C++.
		4178
		4179	=back
		4180
		4181	=head2 EXPORTED API SYMBOLS
		4182
		4183	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4184	exported symbols, you can use the provided F<Symbol.*> files which list
		4185	all public symbols, one per line:
		4186
		4187	Symbols.ev for libev proper
		4188	Symbols.event for the libevent emulation
		4189
		4190	This can also be used to rename all public symbols to avoid clashes with
		4191	multiple versions of libev linked together (which is obviously bad in
		4192	itself, but sometimes it is inconvenient to avoid this).
		4193
		4194	A sed command like this will create wrapper C<#define>'s that you need to
		4195	include before including F<ev.h>:
		4196
		4197	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4198
		4199	This would create a file F<wrap.h> which essentially looks like this:
		4200
		4201	#define ev_backend myprefix_ev_backend
		4202	#define ev_check_start myprefix_ev_check_start
		4203	#define ev_check_stop myprefix_ev_check_stop
		4204	...
2287		4205
2288	=head2 EXAMPLES	4206	=head2 EXAMPLES
2289		4207
2290	For a real-world example of a program the includes libev	4208	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	4209	verbatim, you can have a look at the EV perl module
…		…
2296	file.	4214	file.
2297		4215
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4216	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	4217	that everybody includes and which overrides some configure choices:
2300		4218
2301	#define EV_MINIMAL 1	4219	#define EV_FEATURES 8
2302	#define EV_USE_POLL 0	4220	#define EV_USE_SELECT 1
2303	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	4221	#define EV_PREPARE_ENABLE 1
		4222	#define EV_IDLE_ENABLE 1
2305	#define EV_STAT_ENABLE 0	4223	#define EV_SIGNAL_ENABLE 1
2306	#define EV_FORK_ENABLE 0	4224	#define EV_CHILD_ENABLE 1
		4225	#define EV_USE_STDEXCEPT 0
2307	#define EV_CONFIG_H <config.h>	4226	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0
2310		4227
2311	#include "ev++.h"	4228	#include "ev++.h"
2312		4229
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4230	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		4231
2315	#include "ev_cpp.h"	4232	#include "ev_cpp.h"
2316	#include "ev.c"	4233	#include "ev.c"
2317		4234
		4235	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2318		4236
		4237	=head2 THREADS AND COROUTINES
		4238
		4239	=head3 THREADS
		4240
		4241	All libev functions are reentrant and thread-safe unless explicitly
		4242	documented otherwise, but libev implements no locking itself. This means
		4243	that you can use as many loops as you want in parallel, as long as there
		4244	are no concurrent calls into any libev function with the same loop
		4245	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4246	of course): libev guarantees that different event loops share no data
		4247	structures that need any locking.
		4248
		4249	Or to put it differently: calls with different loop parameters can be done
		4250	concurrently from multiple threads, calls with the same loop parameter
		4251	must be done serially (but can be done from different threads, as long as
		4252	only one thread ever is inside a call at any point in time, e.g. by using
		4253	a mutex per loop).
		4254
		4255	Specifically to support threads (and signal handlers), libev implements
		4256	so-called C<ev_async> watchers, which allow some limited form of
		4257	concurrency on the same event loop, namely waking it up "from the
		4258	outside".
		4259
		4260	If you want to know which design (one loop, locking, or multiple loops
		4261	without or something else still) is best for your problem, then I cannot
		4262	help you, but here is some generic advice:
		4263
		4264	=over 4
		4265
		4266	=item * most applications have a main thread: use the default libev loop
		4267	in that thread, or create a separate thread running only the default loop.
		4268
		4269	This helps integrating other libraries or software modules that use libev
		4270	themselves and don't care/know about threading.
		4271
		4272	=item * one loop per thread is usually a good model.
		4273
		4274	Doing this is almost never wrong, sometimes a better-performance model
		4275	exists, but it is always a good start.
		4276
		4277	=item * other models exist, such as the leader/follower pattern, where one
		4278	loop is handed through multiple threads in a kind of round-robin fashion.
		4279
		4280	Choosing a model is hard - look around, learn, know that usually you can do
		4281	better than you currently do :-)
		4282
		4283	=item * often you need to talk to some other thread which blocks in the
		4284	event loop.
		4285
		4286	C<ev_async> watchers can be used to wake them up from other threads safely
		4287	(or from signal contexts...).
		4288
		4289	An example use would be to communicate signals or other events that only
		4290	work in the default loop by registering the signal watcher with the
		4291	default loop and triggering an C<ev_async> watcher from the default loop
		4292	watcher callback into the event loop interested in the signal.
		4293
		4294	=back
		4295
		4296	=head4 THREAD LOCKING EXAMPLE
		4297
		4298	Here is a fictitious example of how to run an event loop in a different
		4299	thread than where callbacks are being invoked and watchers are
		4300	created/added/removed.
		4301
		4302	For a real-world example, see the C<EV::Loop::Async> perl module,
		4303	which uses exactly this technique (which is suited for many high-level
		4304	languages).
		4305
		4306	The example uses a pthread mutex to protect the loop data, a condition
		4307	variable to wait for callback invocations, an async watcher to notify the
		4308	event loop thread and an unspecified mechanism to wake up the main thread.
		4309
		4310	First, you need to associate some data with the event loop:
		4311
		4312	typedef struct {
		4313	mutex_t lock; /* global loop lock */
		4314	ev_async async_w;
		4315	thread_t tid;
		4316	cond_t invoke_cv;
		4317	} userdata;
		4318
		4319	void prepare_loop (EV_P)
		4320	{
		4321	// for simplicity, we use a static userdata struct.
		4322	static userdata u;
		4323
		4324	ev_async_init (&u->async_w, async_cb);
		4325	ev_async_start (EV_A_ &u->async_w);
		4326
		4327	pthread_mutex_init (&u->lock, 0);
		4328	pthread_cond_init (&u->invoke_cv, 0);
		4329
		4330	// now associate this with the loop
		4331	ev_set_userdata (EV_A_ u);
		4332	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4333	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4334
		4335	// then create the thread running ev_loop
		4336	pthread_create (&u->tid, 0, l_run, EV_A);
		4337	}
		4338
		4339	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4340	solely to wake up the event loop so it takes notice of any new watchers
		4341	that might have been added:
		4342
		4343	static void
		4344	async_cb (EV_P_ ev_async *w, int revents)
		4345	{
		4346	// just used for the side effects
		4347	}
		4348
		4349	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4350	protecting the loop data, respectively.
		4351
		4352	static void
		4353	l_release (EV_P)
		4354	{
		4355	userdata *u = ev_userdata (EV_A);
		4356	pthread_mutex_unlock (&u->lock);
		4357	}
		4358
		4359	static void
		4360	l_acquire (EV_P)
		4361	{
		4362	userdata *u = ev_userdata (EV_A);
		4363	pthread_mutex_lock (&u->lock);
		4364	}
		4365
		4366	The event loop thread first acquires the mutex, and then jumps straight
		4367	into C<ev_run>:
		4368
		4369	void *
		4370	l_run (void *thr_arg)
		4371	{
		4372	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4373
		4374	l_acquire (EV_A);
		4375	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4376	ev_run (EV_A_ 0);
		4377	l_release (EV_A);
		4378
		4379	return 0;
		4380	}
		4381
		4382	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4383	signal the main thread via some unspecified mechanism (signals? pipe
		4384	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4385	have been called (in a while loop because a) spurious wakeups are possible
		4386	and b) skipping inter-thread-communication when there are no pending
		4387	watchers is very beneficial):
		4388
		4389	static void
		4390	l_invoke (EV_P)
		4391	{
		4392	userdata *u = ev_userdata (EV_A);
		4393
		4394	while (ev_pending_count (EV_A))
		4395	{
		4396	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4397	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4398	}
		4399	}
		4400
		4401	Now, whenever the main thread gets told to invoke pending watchers, it
		4402	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4403	thread to continue:
		4404
		4405	static void
		4406	real_invoke_pending (EV_P)
		4407	{
		4408	userdata *u = ev_userdata (EV_A);
		4409
		4410	pthread_mutex_lock (&u->lock);
		4411	ev_invoke_pending (EV_A);
		4412	pthread_cond_signal (&u->invoke_cv);
		4413	pthread_mutex_unlock (&u->lock);
		4414	}
		4415
		4416	Whenever you want to start/stop a watcher or do other modifications to an
		4417	event loop, you will now have to lock:
		4418
		4419	ev_timer timeout_watcher;
		4420	userdata *u = ev_userdata (EV_A);
		4421
		4422	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4423
		4424	pthread_mutex_lock (&u->lock);
		4425	ev_timer_start (EV_A_ &timeout_watcher);
		4426	ev_async_send (EV_A_ &u->async_w);
		4427	pthread_mutex_unlock (&u->lock);
		4428
		4429	Note that sending the C<ev_async> watcher is required because otherwise
		4430	an event loop currently blocking in the kernel will have no knowledge
		4431	about the newly added timer. By waking up the loop it will pick up any new
		4432	watchers in the next event loop iteration.
		4433
		4434	=head3 COROUTINES
		4435
		4436	Libev is very accommodating to coroutines ("cooperative threads"):
		4437	libev fully supports nesting calls to its functions from different
		4438	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4439	different coroutines, and switch freely between both coroutines running
		4440	the loop, as long as you don't confuse yourself). The only exception is
		4441	that you must not do this from C<ev_periodic> reschedule callbacks.
		4442
		4443	Care has been taken to ensure that libev does not keep local state inside
		4444	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4445	they do not call any callbacks.
		4446
		4447	=head2 COMPILER WARNINGS
		4448
		4449	Depending on your compiler and compiler settings, you might get no or a
		4450	lot of warnings when compiling libev code. Some people are apparently
		4451	scared by this.
		4452
		4453	However, these are unavoidable for many reasons. For one, each compiler
		4454	has different warnings, and each user has different tastes regarding
		4455	warning options. "Warn-free" code therefore cannot be a goal except when
		4456	targeting a specific compiler and compiler-version.
		4457
		4458	Another reason is that some compiler warnings require elaborate
		4459	workarounds, or other changes to the code that make it less clear and less
		4460	maintainable.
		4461
		4462	And of course, some compiler warnings are just plain stupid, or simply
		4463	wrong (because they don't actually warn about the condition their message
		4464	seems to warn about). For example, certain older gcc versions had some
		4465	warnings that resulted in an extreme number of false positives. These have
		4466	been fixed, but some people still insist on making code warn-free with
		4467	such buggy versions.
		4468
		4469	While libev is written to generate as few warnings as possible,
		4470	"warn-free" code is not a goal, and it is recommended not to build libev
		4471	with any compiler warnings enabled unless you are prepared to cope with
		4472	them (e.g. by ignoring them). Remember that warnings are just that:
		4473	warnings, not errors, or proof of bugs.
		4474
		4475
		4476	=head2 VALGRIND
		4477
		4478	Valgrind has a special section here because it is a popular tool that is
		4479	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4480
		4481	If you think you found a bug (memory leak, uninitialised data access etc.)
		4482	in libev, then check twice: If valgrind reports something like:
		4483
		4484	==2274== definitely lost: 0 bytes in 0 blocks.
		4485	==2274== possibly lost: 0 bytes in 0 blocks.
		4486	==2274== still reachable: 256 bytes in 1 blocks.
		4487
		4488	Then there is no memory leak, just as memory accounted to global variables
		4489	is not a memleak - the memory is still being referenced, and didn't leak.
		4490
		4491	Similarly, under some circumstances, valgrind might report kernel bugs
		4492	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4493	although an acceptable workaround has been found here), or it might be
		4494	confused.
		4495
		4496	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4497	make it into some kind of religion.
		4498
		4499	If you are unsure about something, feel free to contact the mailing list
		4500	with the full valgrind report and an explanation on why you think this
		4501	is a bug in libev (best check the archives, too :). However, don't be
		4502	annoyed when you get a brisk "this is no bug" answer and take the chance
		4503	of learning how to interpret valgrind properly.
		4504
		4505	If you need, for some reason, empty reports from valgrind for your project
		4506	I suggest using suppression lists.
		4507
		4508
		4509	=head1 PORTABILITY NOTES
		4510
		4511	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4512
		4513	GNU/Linux is the only common platform that supports 64 bit file/large file
		4514	interfaces but I<disables> them by default.
		4515
		4516	That means that libev compiled in the default environment doesn't support
		4517	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4518
		4519	Unfortunately, many programs try to work around this GNU/Linux issue
		4520	by enabling the large file API, which makes them incompatible with the
		4521	standard libev compiled for their system.
		4522
		4523	Likewise, libev cannot enable the large file API itself as this would
		4524	suddenly make it incompatible to the default compile time environment,
		4525	i.e. all programs not using special compile switches.
		4526
		4527	=head2 OS/X AND DARWIN BUGS
		4528
		4529	The whole thing is a bug if you ask me - basically any system interface
		4530	you touch is broken, whether it is locales, poll, kqueue or even the
		4531	OpenGL drivers.
		4532
		4533	=head3 C<kqueue> is buggy
		4534
		4535	The kqueue syscall is broken in all known versions - most versions support
		4536	only sockets, many support pipes.
		4537
		4538	Libev tries to work around this by not using C<kqueue> by default on this
		4539	rotten platform, but of course you can still ask for it when creating a
		4540	loop - embedding a socket-only kqueue loop into a select-based one is
		4541	probably going to work well.
		4542
		4543	=head3 C<poll> is buggy
		4544
		4545	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4546	implementation by something calling C<kqueue> internally around the 10.5.6
		4547	release, so now C<kqueue> I<and> C<poll> are broken.
		4548
		4549	Libev tries to work around this by not using C<poll> by default on
		4550	this rotten platform, but of course you can still ask for it when creating
		4551	a loop.
		4552
		4553	=head3 C<select> is buggy
		4554
		4555	All that's left is C<select>, and of course Apple found a way to fuck this
		4556	one up as well: On OS/X, C<select> actively limits the number of file
		4557	descriptors you can pass in to 1024 - your program suddenly crashes when
		4558	you use more.
		4559
		4560	There is an undocumented "workaround" for this - defining
		4561	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4562	work on OS/X.
		4563
		4564	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4565
		4566	=head3 C<errno> reentrancy
		4567
		4568	The default compile environment on Solaris is unfortunately so
		4569	thread-unsafe that you can't even use components/libraries compiled
		4570	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4571	defined by default. A valid, if stupid, implementation choice.
		4572
		4573	If you want to use libev in threaded environments you have to make sure
		4574	it's compiled with C<_REENTRANT> defined.
		4575
		4576	=head3 Event port backend
		4577
		4578	The scalable event interface for Solaris is called "event
		4579	ports". Unfortunately, this mechanism is very buggy in all major
		4580	releases. If you run into high CPU usage, your program freezes or you get
		4581	a large number of spurious wakeups, make sure you have all the relevant
		4582	and latest kernel patches applied. No, I don't know which ones, but there
		4583	are multiple ones to apply, and afterwards, event ports actually work
		4584	great.
		4585
		4586	If you can't get it to work, you can try running the program by setting
		4587	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4588	C<select> backends.
		4589
		4590	=head2 AIX POLL BUG
		4591
		4592	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4593	this by trying to avoid the poll backend altogether (i.e. it's not even
		4594	compiled in), which normally isn't a big problem as C<select> works fine
		4595	with large bitsets on AIX, and AIX is dead anyway.
		4596
		4597	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4598
		4599	=head3 General issues
		4600
		4601	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4602	requires, and its I/O model is fundamentally incompatible with the POSIX
		4603	model. Libev still offers limited functionality on this platform in
		4604	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4605	descriptors. This only applies when using Win32 natively, not when using
		4606	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4607	as every compielr comes with a slightly differently broken/incompatible
		4608	environment.
		4609
		4610	Lifting these limitations would basically require the full
		4611	re-implementation of the I/O system. If you are into this kind of thing,
		4612	then note that glib does exactly that for you in a very portable way (note
		4613	also that glib is the slowest event library known to man).
		4614
		4615	There is no supported compilation method available on windows except
		4616	embedding it into other applications.
		4617
		4618	Sensible signal handling is officially unsupported by Microsoft - libev
		4619	tries its best, but under most conditions, signals will simply not work.
		4620
		4621	Not a libev limitation but worth mentioning: windows apparently doesn't
		4622	accept large writes: instead of resulting in a partial write, windows will
		4623	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4624	so make sure you only write small amounts into your sockets (less than a
		4625	megabyte seems safe, but this apparently depends on the amount of memory
		4626	available).
		4627
		4628	Due to the many, low, and arbitrary limits on the win32 platform and
		4629	the abysmal performance of winsockets, using a large number of sockets
		4630	is not recommended (and not reasonable). If your program needs to use
		4631	more than a hundred or so sockets, then likely it needs to use a totally
		4632	different implementation for windows, as libev offers the POSIX readiness
		4633	notification model, which cannot be implemented efficiently on windows
		4634	(due to Microsoft monopoly games).
		4635
		4636	A typical way to use libev under windows is to embed it (see the embedding
		4637	section for details) and use the following F<evwrap.h> header file instead
		4638	of F<ev.h>:
		4639
		4640	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4641	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4642
		4643	#include "ev.h"
		4644
		4645	And compile the following F<evwrap.c> file into your project (make sure
		4646	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4647
		4648	#include "evwrap.h"
		4649	#include "ev.c"
		4650
		4651	=head3 The winsocket C<select> function
		4652
		4653	The winsocket C<select> function doesn't follow POSIX in that it
		4654	requires socket I<handles> and not socket I<file descriptors> (it is
		4655	also extremely buggy). This makes select very inefficient, and also
		4656	requires a mapping from file descriptors to socket handles (the Microsoft
		4657	C runtime provides the function C<_open_osfhandle> for this). See the
		4658	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4659	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4660
		4661	The configuration for a "naked" win32 using the Microsoft runtime
		4662	libraries and raw winsocket select is:
		4663
		4664	#define EV_USE_SELECT 1
		4665	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4666
		4667	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4668	complexity in the O(n²) range when using win32.
		4669
		4670	=head3 Limited number of file descriptors
		4671
		4672	Windows has numerous arbitrary (and low) limits on things.
		4673
		4674	Early versions of winsocket's select only supported waiting for a maximum
		4675	of C<64> handles (probably owning to the fact that all windows kernels
		4676	can only wait for C<64> things at the same time internally; Microsoft
		4677	recommends spawning a chain of threads and wait for 63 handles and the
		4678	previous thread in each. Sounds great!).
		4679
		4680	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4681	to some high number (e.g. C<2048>) before compiling the winsocket select
		4682	call (which might be in libev or elsewhere, for example, perl and many
		4683	other interpreters do their own select emulation on windows).
		4684
		4685	Another limit is the number of file descriptors in the Microsoft runtime
		4686	libraries, which by default is C<64> (there must be a hidden I<64>
		4687	fetish or something like this inside Microsoft). You can increase this
		4688	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4689	(another arbitrary limit), but is broken in many versions of the Microsoft
		4690	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4691	(depending on windows version and/or the phase of the moon). To get more,
		4692	you need to wrap all I/O functions and provide your own fd management, but
		4693	the cost of calling select (O(n²)) will likely make this unworkable.
		4694
		4695	=head2 PORTABILITY REQUIREMENTS
		4696
		4697	In addition to a working ISO-C implementation and of course the
		4698	backend-specific APIs, libev relies on a few additional extensions:
		4699
		4700	=over 4
		4701
		4702	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4703	calling conventions regardless of C<ev_watcher_type *>.
		4704
		4705	Libev assumes not only that all watcher pointers have the same internal
		4706	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4707	assumes that the same (machine) code can be used to call any watcher
		4708	callback: The watcher callbacks have different type signatures, but libev
		4709	calls them using an C<ev_watcher *> internally.
		4710
		4711	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4712
		4713	The type C<sig_atomic_t volatile> (or whatever is defined as
		4714	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4715	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4716	believed to be sufficiently portable.
		4717
		4718	=item C<sigprocmask> must work in a threaded environment
		4719
		4720	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4721	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4722	pthread implementations will either allow C<sigprocmask> in the "main
		4723	thread" or will block signals process-wide, both behaviours would
		4724	be compatible with libev. Interaction between C<sigprocmask> and
		4725	C<pthread_sigmask> could complicate things, however.
		4726
		4727	The most portable way to handle signals is to block signals in all threads
		4728	except the initial one, and run the default loop in the initial thread as
		4729	well.
		4730
		4731	=item C<long> must be large enough for common memory allocation sizes
		4732
		4733	To improve portability and simplify its API, libev uses C<long> internally
		4734	instead of C<size_t> when allocating its data structures. On non-POSIX
		4735	systems (Microsoft...) this might be unexpectedly low, but is still at
		4736	least 31 bits everywhere, which is enough for hundreds of millions of
		4737	watchers.
		4738
		4739	=item C<double> must hold a time value in seconds with enough accuracy
		4740
		4741	The type C<double> is used to represent timestamps. It is required to
		4742	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4743	good enough for at least into the year 4000 with millisecond accuracy
		4744	(the design goal for libev). This requirement is overfulfilled by
		4745	implementations using IEEE 754, which is basically all existing ones. With
		4746	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4747
		4748	=back
		4749
		4750	If you know of other additional requirements drop me a note.
		4751
		4752
2319	=head1 COMPLEXITIES	4753	=head1 ALGORITHMIC COMPLEXITIES
2320		4754
2321	In this section the complexities of (many of) the algorithms used inside	4755	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	4756	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	4757	the documentation for C<ev_default_init>.
2324		4758
2325	All of the following are about amortised time: If an array needs to be	4759	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	4760	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	4761	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	4762	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	4763	average it is much faster and asymptotically approaches constant time.
2330		4764
2331	=over 4	4765	=over 4
2332		4766
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4767	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		4768
2335	This means that, when you have a watcher that triggers in one hour and	4769	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	4770	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	4771	have to skip roughly seven (C<ld 100>) of these watchers.
2338		4772
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4773	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		4774
2341	That means that for changing a timer costs less than removing/adding them	4775	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	4776	as only the relative motion in the event queue has to be paid for.
2343		4777
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4778	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		4779
2346	These just add the watcher into an array or at the head of a list.	4780	These just add the watcher into an array or at the head of a list.
		4781
2347	=item Stopping check/prepare/idle watchers: O(1)	4782	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		4783
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4784	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		4785
2351	These watchers are stored in lists then need to be walked to find the	4786	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	4787	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	4788	have many watchers waiting for the same fd or signal: one is typical, two
		4789	is rare).
2354		4790
2355	=item Finding the next timer per loop iteration: O(1)	4791	=item Finding the next timer in each loop iteration: O(1)
		4792
		4793	By virtue of using a binary or 4-heap, the next timer is always found at a
		4794	fixed position in the storage array.
2356		4795
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4796	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		4797
2359	A change means an I/O watcher gets started or stopped, which requires	4798	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	4799	libev to recalculate its status (and possibly tell the kernel, depending
		4800	on backend and whether C<ev_io_set> was used).
2361		4801
2362	=item Activating one watcher: O(1)	4802	=item Activating one watcher (putting it into the pending state): O(1)
2363		4803
2364	=item Priority handling: O(number_of_priorities)	4804	=item Priority handling: O(number_of_priorities)
2365		4805
2366	Priorities are implemented by allocating some space for each	4806	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	4807	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	4808	linearly search all the priorities, but starting/stopping and activating
		4809	watchers becomes O(1) with respect to priority handling.
		4810
		4811	=item Sending an ev_async: O(1)
		4812
		4813	=item Processing ev_async_send: O(number_of_async_watchers)
		4814
		4815	=item Processing signals: O(max_signal_number)
		4816
		4817	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4818	calls in the current loop iteration. Checking for async and signal events
		4819	involves iterating over all running async watchers or all signal numbers.
2369		4820
2370	=back	4821	=back
2371		4822
2372		4823
		4824	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4825
		4826	The major version 4 introduced some minor incompatible changes to the API.
		4827
		4828	At the moment, the C<ev.h> header file tries to implement superficial
		4829	compatibility, so most programs should still compile. Those might be
		4830	removed in later versions of libev, so better update early than late.
		4831
		4832	=over 4
		4833
		4834	=item function/symbol renames
		4835
		4836	A number of functions and symbols have been renamed:
		4837
		4838	ev_loop => ev_run
		4839	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4840	EVLOOP_ONESHOT => EVRUN_ONCE
		4841
		4842	ev_unloop => ev_break
		4843	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4844	EVUNLOOP_ONE => EVBREAK_ONE
		4845	EVUNLOOP_ALL => EVBREAK_ALL
		4846
		4847	EV_TIMEOUT => EV_TIMER
		4848
		4849	ev_loop_count => ev_iteration
		4850	ev_loop_depth => ev_depth
		4851	ev_loop_verify => ev_verify
		4852
		4853	Most functions working on C<struct ev_loop> objects don't have an
		4854	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4855	associated constants have been renamed to not collide with the C<struct
		4856	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4857	as all other watcher types. Note that C<ev_loop_fork> is still called
		4858	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4859	typedef.
		4860
		4861	=item C<EV_COMPAT3> backwards compatibility mechanism
		4862
		4863	The backward compatibility mechanism can be controlled by
		4864	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4865	section.
		4866
		4867	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4868
		4869	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4870	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4871	and work, but the library code will of course be larger.
		4872
		4873	=back
		4874
		4875
		4876	=head1 GLOSSARY
		4877
		4878	=over 4
		4879
		4880	=item active
		4881
		4882	A watcher is active as long as it has been started and not yet stopped.
		4883	See L<WATCHER STATES> for details.
		4884
		4885	=item application
		4886
		4887	In this document, an application is whatever is using libev.
		4888
		4889	=item backend
		4890
		4891	The part of the code dealing with the operating system interfaces.
		4892
		4893	=item callback
		4894
		4895	The address of a function that is called when some event has been
		4896	detected. Callbacks are being passed the event loop, the watcher that
		4897	received the event, and the actual event bitset.
		4898
		4899	=item callback/watcher invocation
		4900
		4901	The act of calling the callback associated with a watcher.
		4902
		4903	=item event
		4904
		4905	A change of state of some external event, such as data now being available
		4906	for reading on a file descriptor, time having passed or simply not having
		4907	any other events happening anymore.
		4908
		4909	In libev, events are represented as single bits (such as C<EV_READ> or
		4910	C<EV_TIMER>).
		4911
		4912	=item event library
		4913
		4914	A software package implementing an event model and loop.
		4915
		4916	=item event loop
		4917
		4918	An entity that handles and processes external events and converts them
		4919	into callback invocations.
		4920
		4921	=item event model
		4922
		4923	The model used to describe how an event loop handles and processes
		4924	watchers and events.
		4925
		4926	=item pending
		4927
		4928	A watcher is pending as soon as the corresponding event has been
		4929	detected. See L<WATCHER STATES> for details.
		4930
		4931	=item real time
		4932
		4933	The physical time that is observed. It is apparently strictly monotonic :)
		4934
		4935	=item wall-clock time
		4936
		4937	The time and date as shown on clocks. Unlike real time, it can actually
		4938	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4939	clock.
		4940
		4941	=item watcher
		4942
		4943	A data structure that describes interest in certain events. Watchers need
		4944	to be started (attached to an event loop) before they can receive events.
		4945
		4946	=back
		4947
2373	=head1 AUTHOR	4948	=head1 AUTHOR
2374		4949
2375	Marc Lehmann <libev@schmorp.de>.	4950	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2376		4951

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