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Revision 1.321 by sf-exg, Fri Oct 22 10:50:24 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 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		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);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = ev_default_loop (0);
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_run (loop, 0);
		62
		63	// unloop was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		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
10		84
11	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
12	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
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	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
16	(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
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	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
20	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
21	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
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		105	timers (C<ev_timer>), absolute timers with customised rescheduling
		106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	107	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
		111
		112	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	114	for example).
33		115
34	=head1 CONVENTIONS	116	=head2 CONVENTIONS
35		117
36	Libev is very configurable. In this manual the default configuration	118	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	119	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	120	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	121	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	122	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	124	this argument.
43		125
44	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
45		127
46	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practice
48	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
49	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
50	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
51	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.
52		157
53		158
54	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
55		160
56	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
…		…
60		165
61	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
62		167
63	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
64	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
65	you actually want to know.	170	you actually want to know. Also interesting 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 ()>.
66		178
67	=item int ev_version_major ()	179	=item int ev_version_major ()
68		180
69	=item int ev_version_minor ()	181	=item int ev_version_minor ()
70		182
71	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
72	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
73	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
74	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
75	version of the library your program was compiled against.	187	version of the library your program was compiled against.
76		188
		189	These version numbers refer to the ABI version of the library, not the
		190	release version.
		191
77	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,
78	as this indicates an incompatible change. Minor versions are usually	193	as this indicates an incompatible change. Minor versions are usually
79	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
80	not a problem.	195	not a problem.
81		196
82	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
83	version:	198	version (note, however, that this will not detect other ABI mismatches,
		199	such as LFS or reentrancy).
84		200
85	assert (("libev version mismatch",	201	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	202	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	203	&& ev_version_minor () >= EV_VERSION_MINOR));
88		204
89	=item unsigned int ev_supported_backends ()	205	=item unsigned int ev_supported_backends ()
90		206
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	207	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	208	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	210	a description of the set values.
95		211
96	Example: make sure we have the epoll method, because yeah this is cool and	212	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	213	a must have and can we have a torrent of it please!!!11
98		214
99	assert (("sorry, no epoll, no sex",	215	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	216	ev_supported_backends () & EVBACKEND_EPOLL));
101		217
102	=item unsigned int ev_recommended_backends ()	218	=item unsigned int ev_recommended_backends ()
103		219
104	Return the set of all backends compiled into this binary of libev and also	220	Return the set of all backends compiled into this binary of libev and
105	recommended for this platform. This set is often smaller than the one	221	also recommended for this platform, meaning it will work for most file
		222	descriptor types. This set is often smaller than the one returned by
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	223	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
107	most BSDs and will not be autodetected unless you explicitly request it	224	and will not be auto-detected unless you explicitly request it (assuming
108	(assuming you know what you are doing). This is the set of backends that	225	you know what you are doing). This is the set of backends that libev will
109	libev will probe for if you specify no backends explicitly.	226	probe for if you specify no backends explicitly.
110		227
111	=item unsigned int ev_embeddable_backends ()	228	=item unsigned int ev_embeddable_backends ()
112		229
113	Returns the set of backends that are embeddable in other event loops. This	230	Returns the set of backends that are embeddable in other event loops. This
114	is the theoretical, all-platform, value. To find which backends	231	value is platform-specific but can include backends not available on the
115	might be supported on the current system, you would need to look at	232	current system. To find which embeddable backends might be supported on
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	233	the current system, you would need to look at C<ev_embeddable_backends ()
117	recommended ones.	234	& ev_supported_backends ()>, likewise for recommended ones.
118		235
119	See the description of C<ev_embed> watchers for more info.	236	See the description of C<ev_embed> watchers for more info.
120		237
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
122		239
123	Sets the allocation function to use (the prototype is similar to the	240	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	242	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	243	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	244	or take some potentially destructive action.
		245
		246	Since some systems (at least OpenBSD and Darwin) fail to implement
		247	correct C<realloc> semantics, libev will use a wrapper around the system
		248	C<realloc> and C<free> functions by default.
128		249
129	You could override this function in high-availability programs to, say,	250	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	251	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	252	or even to sleep a while and retry until some memory is available.
132		253
133	Example: replace the libev allocator with one that waits a bit and then	254	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	255	retries (example requires a standards-compliant C<realloc>).
135		256
136	static void *	257	static void *
137	persistent_realloc (void *ptr, long size)	258	persistent_realloc (void *ptr, size_t size)
138	{	259	{
139	for (;;)	260	for (;;)
140	{	261	{
141	void *newptr = realloc (ptr, size);	262	void *newptr = realloc (ptr, size);
142		263
…		…
148	}	269	}
149		270
150	...	271	...
151	ev_set_allocator (persistent_realloc);	272	ev_set_allocator (persistent_realloc);
152		273
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
154		275
155	Set the callback function to call on a retryable syscall error (such	276	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	277	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	278	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	279	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	280	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	281	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	282	(such as abort).
162		283
163	Example: do the same thing as libev does internally:	284	Example: This is basically the same thing that libev does internally, too.
164		285
165	static void	286	static void
166	fatal_error (const char *msg)	287	fatal_error (const char *msg)
167	{	288	{
168	perror (msg);	289	perror (msg);
…		…
174		295
175	=back	296	=back
176		297
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	298	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		299
179	An event loop is described by a C<struct ev_loop *>. The library knows two	300	An event loop is described by a C<struct ev_loop *> (the C<struct> is
180	types of such loops, the I<default> loop, which supports signals and child	301	I<not> optional in this case unless libev 3 compatibility is disabled, as
181	events, and dynamically created loops which do not.	302	libev 3 had an C<ev_loop> function colliding with the struct name).
182		303
183	If you use threads, a common model is to run the default event loop	304	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	305	supports signals and child events, and dynamically created event loops
185	create, you also create another event loop. Libev itself does no locking	306	which do not.
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		307
190	=over 4	308	=over 4
191		309
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	310	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		311
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	315	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		316
199	If you don't know what event loop to use, use the one returned from this	317	If you don't know what event loop to use, use the one returned from this
200	function.	318	function.
201		319
		320	Note that this function is I<not> thread-safe, so if you want to use it
		321	from multiple threads, you have to lock (note also that this is unlikely,
		322	as loops cannot be shared easily between threads anyway).
		323
		324	The default loop is the only loop that can handle C<ev_signal> and
		325	C<ev_child> watchers, and to do this, it always registers a handler
		326	for C<SIGCHLD>. If this is a problem for your application you can either
		327	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		328	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		329	C<ev_default_init>.
		330
202	The flags argument can be used to specify special behaviour or specific	331	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	332	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		333
205	The following flags are supported:	334	The following flags are supported:
206		335
…		…
211	The default flags value. Use this if you have no clue (it's the right	340	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	341	thing, believe me).
213		342
214	=item C<EVFLAG_NOENV>	343	=item C<EVFLAG_NOENV>
215		344
216	If this flag bit is ored into the flag value (or the program runs setuid	345	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	346	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	347	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	348	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	349	useful to try out specific backends to test their performance, or to work
221	around bugs.	350	around bugs.
222		351
		352	=item C<EVFLAG_FORKCHECK>
		353
		354	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		355	make libev check for a fork in each iteration by enabling this flag.
		356
		357	This works by calling C<getpid ()> on every iteration of the loop,
		358	and thus this might slow down your event loop if you do a lot of loop
		359	iterations and little real work, but is usually not noticeable (on my
		360	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		361	without a system call and thus I<very> fast, but my GNU/Linux system also has
		362	C<pthread_atfork> which is even faster).
		363
		364	The big advantage of this flag is that you can forget about fork (and
		365	forget about forgetting to tell libev about forking) when you use this
		366	flag.
		367
		368	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		369	environment variable.
		370
		371	=item C<EVFLAG_NOINOTIFY>
		372
		373	When this flag is specified, then libev will not attempt to use the
		374	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		375	testing, this flag can be useful to conserve inotify file descriptors, as
		376	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		377
		378	=item C<EVFLAG_SIGNALFD>
		379
		380	When this flag is specified, then libev will attempt to use the
		381	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		382	delivers signals synchronously, which makes it both faster and might make
		383	it possible to get the queued signal data. It can also simplify signal
		384	handling with threads, as long as you properly block signals in your
		385	threads that are not interested in handling them.
		386
		387	Signalfd will not be used by default as this changes your signal mask, and
		388	there are a lot of shoddy libraries and programs (glib's threadpool for
		389	example) that can't properly initialise their signal masks.
		390
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	391	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		392
225	This is your standard select(2) backend. Not I<completely> standard, as	393	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	394	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	395	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	396	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	397	usually the fastest backend for a low number of (low-numbered :) fds.
		398
		399	To get good performance out of this backend you need a high amount of
		400	parallelism (most of the file descriptors should be busy). If you are
		401	writing a server, you should C<accept ()> in a loop to accept as many
		402	connections as possible during one iteration. You might also want to have
		403	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		404	readiness notifications you get per iteration.
		405
		406	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		407	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		408	C<exceptfds> set on that platform).
230		409
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	410	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		411
233	And this is your standard poll(2) backend. It's more complicated than	412	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	413	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	414	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	415	considerably with a lot of inactive fds). It scales similarly to select,
		416	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		417	performance tips.
		418
		419	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		420	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		421
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	422	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		423
		424	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		425	kernels).
		426
240	For few fds, this backend is a bit little slower than poll and select,	427	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	428	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	429	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	430	epoll scales either O(1) or O(active_fds).
244		431
		432	The epoll mechanism deserves honorable mention as the most misdesigned
		433	of the more advanced event mechanisms: mere annoyances include silently
		434	dropping file descriptors, requiring a system call per change per file
		435	descriptor (and unnecessary guessing of parameters), problems with dup and
		436	so on. The biggest issue is fork races, however - if a program forks then
		437	I<both> parent and child process have to recreate the epoll set, which can
		438	take considerable time (one syscall per file descriptor) and is of course
		439	hard to detect.
		440
		441	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		442	of course I<doesn't>, and epoll just loves to report events for totally
		443	I<different> file descriptors (even already closed ones, so one cannot
		444	even remove them from the set) than registered in the set (especially
		445	on SMP systems). Libev tries to counter these spurious notifications by
		446	employing an additional generation counter and comparing that against the
		447	events to filter out spurious ones, recreating the set when required. Last
		448	not least, it also refuses to work with some file descriptors which work
		449	perfectly fine with C<select> (files, many character devices...).
		450
245	While stopping and starting an I/O watcher in the same iteration will	451	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	452	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	453	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	454	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	455	file descriptors might not work very well if you register events for both
		456	file descriptors.
250		457
251	Please note that epoll sometimes generates spurious notifications, so you	458	Best performance from this backend is achieved by not unregistering all
252	need to use non-blocking I/O or other means to avoid blocking when no data	459	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	460	i.e. keep at least one watcher active per fd at all times. Stopping and
		461	starting a watcher (without re-setting it) also usually doesn't cause
		462	extra overhead. A fork can both result in spurious notifications as well
		463	as in libev having to destroy and recreate the epoll object, which can
		464	take considerable time and thus should be avoided.
		465
		466	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		467	faster than epoll for maybe up to a hundred file descriptors, depending on
		468	the usage. So sad.
		469
		470	While nominally embeddable in other event loops, this feature is broken in
		471	all kernel versions tested so far.
		472
		473	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		474	C<EVBACKEND_POLL>.
254		475
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	476	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		477
257	Kqueue deserves special mention, as at the time of this writing, it	478	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	479	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	480	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	481	it's completely useless). Unlike epoll, however, whose brokenness
		482	is by design, these kqueue bugs can (and eventually will) be fixed
		483	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	484	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	485	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		486	system like NetBSD.
		487
		488	You still can embed kqueue into a normal poll or select backend and use it
		489	only for sockets (after having made sure that sockets work with kqueue on
		490	the target platform). See C<ev_embed> watchers for more info.
263		491
264	It scales in the same way as the epoll backend, but the interface to the	492	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	493	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	494	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	495	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	496	two event changes per incident. Support for C<fork ()> is very bad (but
		497	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		498	cases
		499
		500	This backend usually performs well under most conditions.
		501
		502	While nominally embeddable in other event loops, this doesn't work
		503	everywhere, so you might need to test for this. And since it is broken
		504	almost everywhere, you should only use it when you have a lot of sockets
		505	(for which it usually works), by embedding it into another event loop
		506	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		507	also broken on OS X)) and, did I mention it, using it only for sockets.
		508
		509	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		510	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		511	C<NOTE_EOF>.
269		512
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	513	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		514
272	This is not implemented yet (and might never be).	515	This is not implemented yet (and might never be, unless you send me an
		516	implementation). According to reports, C</dev/poll> only supports sockets
		517	and is not embeddable, which would limit the usefulness of this backend
		518	immensely.
273		519
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	520	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		521
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	522	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	523	it's really slow, but it still scales very well (O(active_fds)).
278		524
279	Please note that solaris ports can result in a lot of spurious	525	Please note that Solaris event ports can deliver a lot of spurious
280	notifications, so you need to use non-blocking I/O or other means to avoid	526	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	527	blocking when no data (or space) is available.
		528
		529	While this backend scales well, it requires one system call per active
		530	file descriptor per loop iteration. For small and medium numbers of file
		531	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		532	might perform better.
		533
		534	On the positive side, with the exception of the spurious readiness
		535	notifications, this backend actually performed fully to specification
		536	in all tests and is fully embeddable, which is a rare feat among the
		537	OS-specific backends (I vastly prefer correctness over speed hacks).
		538
		539	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		540	C<EVBACKEND_POLL>.
282		541
283	=item C<EVBACKEND_ALL>	542	=item C<EVBACKEND_ALL>
284		543
285	Try all backends (even potentially broken ones that wouldn't be tried	544	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	545	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	546	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		547
		548	It is definitely not recommended to use this flag.
		549
289	=back	550	=back
290		551
291	If one or more of these are ored into the flags value, then only these	552	If one or more of the backend flags are or'ed into the flags value,
292	backends will be tried (in the reverse order as given here). If none are	553	then only these backends will be tried (in the reverse order as listed
293	specified, most compiled-in backend will be tried, usually in reverse	554	here). If none are specified, all backends in C<ev_recommended_backends
294	order of their flag values :)	555	()> will be tried.
295		556
296	The most typical usage is like this:	557	Example: This is the most typical usage.
297		558
298	if (!ev_default_loop (0))	559	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	560	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		561
301	Restrict libev to the select and poll backends, and do not allow	562	Example: Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	563	environment settings to be taken into account:
303		564
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	565	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		566
306	Use whatever libev has to offer, but make sure that kqueue is used if	567	Example: Use whatever libev has to offer, but make sure that kqueue is
307	available (warning, breaks stuff, best use only with your own private	568	used if available (warning, breaks stuff, best use only with your own
308	event loop and only if you know the OS supports your types of fds):	569	private event loop and only if you know the OS supports your types of
		570	fds):
309		571
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	572	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		573
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	574	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		575
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	576	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot	577	always distinct from the default loop.
316	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).
318		578
		579	Note that this function I<is> thread-safe, and one common way to use
		580	libev with threads is indeed to create one loop per thread, and using the
		581	default loop in the "main" or "initial" thread.
		582
319	Example: try to create a event loop that uses epoll and nothing else.	583	Example: Try to create a event loop that uses epoll and nothing else.
320		584
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	585	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	586	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	587	fatal ("no epoll found here, maybe it hides under your chair");
324		588
325	=item ev_default_destroy ()	589	=item ev_default_destroy ()
326		590
327	Destroys the default loop again (frees all memory and kernel state	591	Destroys the default loop (frees all memory and kernel state etc.). None
328	etc.). None of the active event watchers will be stopped in the normal	592	of the active event watchers will be stopped in the normal sense, so
329	sense, so e.g. C<ev_is_active> might still return true. It is your	593	e.g. C<ev_is_active> might still return true. It is your responsibility to
330	responsibility to either stop all watchers cleanly yoursef I<before>	594	either stop all watchers cleanly yourself I<before> calling this function,
331	calling this function, or cope with the fact afterwards (which is usually	595	or cope with the fact afterwards (which is usually the easiest thing, you
332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	596	can just ignore the watchers and/or C<free ()> them for example).
333	for example).	597
		598	Note that certain global state, such as signal state (and installed signal
		599	handlers), will not be freed by this function, and related watchers (such
		600	as signal and child watchers) would need to be stopped manually.
		601
		602	In general it is not advisable to call this function except in the
		603	rare occasion where you really need to free e.g. the signal handling
		604	pipe fds. If you need dynamically allocated loops it is better to use
		605	C<ev_loop_new> and C<ev_loop_destroy>.
334		606
335	=item ev_loop_destroy (loop)	607	=item ev_loop_destroy (loop)
336		608
337	Like C<ev_default_destroy>, but destroys an event loop created by an	609	Like C<ev_default_destroy>, but destroys an event loop created by an
338	earlier call to C<ev_loop_new>.	610	earlier call to C<ev_loop_new>.
339		611
340	=item ev_default_fork ()	612	=item ev_default_fork ()
341		613
		614	This function sets a flag that causes subsequent C<ev_run> iterations
342	This function reinitialises the kernel state for backends that have	615	to reinitialise the kernel state for backends that have one. Despite the
343	one. Despite the name, you can call it anytime, but it makes most sense	616	name, you can call it anytime, but it makes most sense after forking, in
344	after forking, in either the parent or child process (or both, but that	617	the child process (or both child and parent, but that again makes little
345	again makes little sense).	618	sense). You I<must> call it in the child before using any of the libev
		619	functions, and it will only take effect at the next C<ev_run> iteration.
346		620
347	You I<must> call this function in the child process after forking if and	621	Again, you I<have> to call it on I<any> loop that you want to re-use after
348	only if you want to use the event library in both processes. If you just	622	a fork, I<even if you do not plan to use the loop in the parent>. This is
349	fork+exec, you don't have to call it.	623	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		624	during fork.
		625
		626	On the other hand, you only need to call this function in the child
		627	process if and only if you want to use the event loop in the child. If
		628	you just fork+exec or create a new loop in the child, you don't have to
		629	call it at all (in fact, C<epoll> is so badly broken that it makes a
		630	difference, but libev will usually detect this case on its own and do a
		631	costly reset of the backend).
350		632
351	The function itself is quite fast and it's usually not a problem to call	633	The function itself is quite fast and it's usually not a problem to call
352	it just in case after a fork. To make this easy, the function will fit in	634	it just in case after a fork. To make this easy, the function will fit in
353	quite nicely into a call to C<pthread_atfork>:	635	quite nicely into a call to C<pthread_atfork>:
354		636
355	pthread_atfork (0, 0, ev_default_fork);	637	pthread_atfork (0, 0, ev_default_fork);
356		638
357	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
358	without calling this function, so if you force one of those backends you
359	do not need to care.
360
361	=item ev_loop_fork (loop)	639	=item ev_loop_fork (loop)
362		640
363	Like C<ev_default_fork>, but acts on an event loop created by	641	Like C<ev_default_fork>, but acts on an event loop created by
364	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	642	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
365	after fork, and how you do this is entirely your own problem.	643	after fork that you want to re-use in the child, and how you keep track of
		644	them is entirely your own problem.
		645
		646	=item int ev_is_default_loop (loop)
		647
		648	Returns true when the given loop is, in fact, the default loop, and false
		649	otherwise.
		650
		651	=item unsigned int ev_iteration (loop)
		652
		653	Returns the current iteration count for the event loop, which is identical
		654	to the number of times libev did poll for new events. It starts at C<0>
		655	and happily wraps around with enough iterations.
		656
		657	This value can sometimes be useful as a generation counter of sorts (it
		658	"ticks" the number of loop iterations), as it roughly corresponds with
		659	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		660	prepare and check phases.
		661
		662	=item unsigned int ev_depth (loop)
		663
		664	Returns the number of times C<ev_run> was entered minus the number of
		665	times C<ev_run> was exited, in other words, the recursion depth.
		666
		667	Outside C<ev_run>, this number is zero. In a callback, this number is
		668	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		669	in which case it is higher.
		670
		671	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		672	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		673	ungentleman-like behaviour unless it's really convenient.
366		674
367	=item unsigned int ev_backend (loop)	675	=item unsigned int ev_backend (loop)
368		676
369	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	677	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
370	use.	678	use.
…		…
373		681
374	Returns the current "event loop time", which is the time the event loop	682	Returns the current "event loop time", which is the time the event loop
375	received events and started processing them. This timestamp does not	683	received events and started processing them. This timestamp does not
376	change as long as callbacks are being processed, and this is also the base	684	change as long as callbacks are being processed, and this is also the base
377	time used for relative timers. You can treat it as the timestamp of the	685	time used for relative timers. You can treat it as the timestamp of the
378	event occuring (or more correctly, libev finding out about it).	686	event occurring (or more correctly, libev finding out about it).
379		687
		688	=item ev_now_update (loop)
		689
		690	Establishes the current time by querying the kernel, updating the time
		691	returned by C<ev_now ()> in the progress. This is a costly operation and
		692	is usually done automatically within C<ev_run ()>.
		693
		694	This function is rarely useful, but when some event callback runs for a
		695	very long time without entering the event loop, updating libev's idea of
		696	the current time is a good idea.
		697
		698	See also L<The special problem of time updates> in the C<ev_timer> section.
		699
		700	=item ev_suspend (loop)
		701
		702	=item ev_resume (loop)
		703
		704	These two functions suspend and resume an event loop, for use when the
		705	loop is not used for a while and timeouts should not be processed.
		706
		707	A typical use case would be an interactive program such as a game: When
		708	the user presses C<^Z> to suspend the game and resumes it an hour later it
		709	would be best to handle timeouts as if no time had actually passed while
		710	the program was suspended. This can be achieved by calling C<ev_suspend>
		711	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		712	C<ev_resume> directly afterwards to resume timer processing.
		713
		714	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		715	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		716	will be rescheduled (that is, they will lose any events that would have
		717	occurred while suspended).
		718
		719	After calling C<ev_suspend> you B<must not> call I<any> function on the
		720	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		721	without a previous call to C<ev_suspend>.
		722
		723	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		724	event loop time (see C<ev_now_update>).
		725
380	=item ev_loop (loop, int flags)	726	=item ev_run (loop, int flags)
381		727
382	Finally, this is it, the event handler. This function usually is called	728	Finally, this is it, the event handler. This function usually is called
383	after you initialised all your watchers and you want to start handling	729	after you have initialised all your watchers and you want to start
384	events.	730	handling events. It will ask the operating system for any new events, call
		731	the watcher callbacks, an then repeat the whole process indefinitely: This
		732	is why event loops are called I<loops>.
385		733
386	If the flags argument is specified as C<0>, it will not return until	734	If the flags argument is specified as C<0>, it will keep handling events
387	either no event watchers are active anymore or C<ev_unloop> was called.	735	until either no event watchers are active anymore or C<ev_break> was
		736	called.
388		737
389	Please note that an explicit C<ev_unloop> is usually better than	738	Please note that an explicit C<ev_break> is usually better than
390	relying on all watchers to be stopped when deciding when a program has	739	relying on all watchers to be stopped when deciding when a program has
391	finished (especially in interactive programs), but having a program that	740	finished (especially in interactive programs), but having a program
392	automatically loops as long as it has to and no longer by virtue of	741	that automatically loops as long as it has to and no longer by virtue
393	relying on its watchers stopping correctly is a thing of beauty.	742	of relying on its watchers stopping correctly, that is truly a thing of
		743	beauty.
394		744
395	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	745	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
396	those events and any outstanding ones, but will not block your process in	746	those events and any already outstanding ones, but will not wait and
397	case there are no events and will return after one iteration of the loop.	747	block your process in case there are no events and will return after one
		748	iteration of the loop. This is sometimes useful to poll and handle new
		749	events while doing lengthy calculations, to keep the program responsive.
398		750
399	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	751	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
400	neccessary) and will handle those and any outstanding ones. It will block	752	necessary) and will handle those and any already outstanding ones. It
401	your process until at least one new event arrives, and will return after	753	will block your process until at least one new event arrives (which could
402	one iteration of the loop. This is useful if you are waiting for some	754	be an event internal to libev itself, so there is no guarantee that a
403	external event in conjunction with something not expressible using other	755	user-registered callback will be called), and will return after one
		756	iteration of the loop.
		757
		758	This is useful if you are waiting for some external event in conjunction
		759	with something not expressible using other libev watchers (i.e. "roll your
404	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	760	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
405	usually a better approach for this kind of thing.	761	usually a better approach for this kind of thing.
406		762
407	Here are the gory details of what C<ev_loop> does:	763	Here are the gory details of what C<ev_run> does:
408		764
409	* If there are no active watchers (reference count is zero), return.	765	- Increment loop depth.
410	- Queue prepare watchers and then call all outstanding watchers.	766	- Reset the ev_break status.
		767	- Before the first iteration, call any pending watchers.
		768	LOOP:
		769	- If EVFLAG_FORKCHECK was used, check for a fork.
		770	- If a fork was detected (by any means), queue and call all fork watchers.
		771	- Queue and call all prepare watchers.
		772	- If ev_break was called, goto FINISH.
411	- If we have been forked, recreate the kernel state.	773	- If we have been forked, detach and recreate the kernel state
		774	as to not disturb the other process.
412	- Update the kernel state with all outstanding changes.	775	- Update the kernel state with all outstanding changes.
413	- Update the "event loop time".	776	- Update the "event loop time" (ev_now ()).
414	- Calculate for how long to block.	777	- Calculate for how long to sleep or block, if at all
		778	(active idle watchers, EVRUN_NOWAIT or not having
		779	any active watchers at all will result in not sleeping).
		780	- Sleep if the I/O and timer collect interval say so.
		781	- Increment loop iteration counter.
415	- Block the process, waiting for any events.	782	- Block the process, waiting for any events.
416	- Queue all outstanding I/O (fd) events.	783	- Queue all outstanding I/O (fd) events.
417	- Update the "event loop time" and do time jump handling.	784	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
418	- Queue all outstanding timers.	785	- Queue all expired timers.
419	- Queue all outstanding periodics.	786	- Queue all expired periodics.
420	- If no events are pending now, queue all idle watchers.	787	- Queue all idle watchers with priority higher than that of pending events.
421	- Queue all check watchers.	788	- Queue all check watchers.
422	- Call all queued watchers in reverse order (i.e. check watchers first).	789	- Call all queued watchers in reverse order (i.e. check watchers first).
423	Signals and child watchers are implemented as I/O watchers, and will	790	Signals and child watchers are implemented as I/O watchers, and will
424	be handled here by queueing them when their watcher gets executed.	791	be handled here by queueing them when their watcher gets executed.
425	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	792	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
426	were used, return, otherwise continue with step *.	793	were used, or there are no active watchers, goto FINISH, otherwise
		794	continue with step LOOP.
		795	FINISH:
		796	- Reset the ev_break status iff it was EVBREAK_ONE.
		797	- Decrement the loop depth.
		798	- Return.
427		799
428	Example: queue some jobs and then loop until no events are outsanding	800	Example: Queue some jobs and then loop until no events are outstanding
429	anymore.	801	anymore.
430		802
431	... queue jobs here, make sure they register event watchers as long	803	... queue jobs here, make sure they register event watchers as long
432	... as they still have work to do (even an idle watcher will do..)	804	... as they still have work to do (even an idle watcher will do..)
433	ev_loop (my_loop, 0);	805	ev_run (my_loop, 0);
434	... jobs done. yeah!	806	... jobs done or somebody called unloop. yeah!
435		807
436	=item ev_unloop (loop, how)	808	=item ev_break (loop, how)
437		809
438	Can be used to make a call to C<ev_loop> return early (but only after it	810	Can be used to make a call to C<ev_run> return early (but only after it
439	has processed all outstanding events). The C<how> argument must be either	811	has processed all outstanding events). The C<how> argument must be either
440	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	812	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
441	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	813	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		814
		815	This "unloop state" will be cleared when entering C<ev_run> again.
		816
		817	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
442		818
443	=item ev_ref (loop)	819	=item ev_ref (loop)
444		820
445	=item ev_unref (loop)	821	=item ev_unref (loop)
446		822
447	Ref/unref can be used to add or remove a reference count on the event	823	Ref/unref can be used to add or remove a reference count on the event
448	loop: Every watcher keeps one reference, and as long as the reference	824	loop: Every watcher keeps one reference, and as long as the reference
449	count is nonzero, C<ev_loop> will not return on its own. If you have	825	count is nonzero, C<ev_run> will not return on its own.
450	a watcher you never unregister that should not keep C<ev_loop> from	826
451	returning, ev_unref() after starting, and ev_ref() before stopping it. For	827	This is useful when you have a watcher that you never intend to
		828	unregister, but that nevertheless should not keep C<ev_run> from
		829	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		830	before stopping it.
		831
452	example, libev itself uses this for its internal signal pipe: It is not	832	As an example, libev itself uses this for its internal signal pipe: It
453	visible to the libev user and should not keep C<ev_loop> from exiting if	833	is not visible to the libev user and should not keep C<ev_run> from
454	no event watchers registered by it are active. It is also an excellent	834	exiting if no event watchers registered by it are active. It is also an
455	way to do this for generic recurring timers or from within third-party	835	excellent way to do this for generic recurring timers or from within
456	libraries. Just remember to I<unref after start> and I<ref before stop>.	836	third-party libraries. Just remember to I<unref after start> and I<ref
		837	before stop> (but only if the watcher wasn't active before, or was active
		838	before, respectively. Note also that libev might stop watchers itself
		839	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		840	in the callback).
457		841
458	Example: create a signal watcher, but keep it from keeping C<ev_loop>	842	Example: Create a signal watcher, but keep it from keeping C<ev_run>
459	running when nothing else is active.	843	running when nothing else is active.
460		844
461	struct dv_signal exitsig;	845	ev_signal exitsig;
462	ev_signal_init (&exitsig, sig_cb, SIGINT);	846	ev_signal_init (&exitsig, sig_cb, SIGINT);
463	ev_signal_start (myloop, &exitsig);	847	ev_signal_start (loop, &exitsig);
464	evf_unref (myloop);	848	evf_unref (loop);
465		849
466	Example: for some weird reason, unregister the above signal handler again.	850	Example: For some weird reason, unregister the above signal handler again.
467		851
468	ev_ref (myloop);	852	ev_ref (loop);
469	ev_signal_stop (myloop, &exitsig);	853	ev_signal_stop (loop, &exitsig);
		854
		855	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		856
		857	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		858
		859	These advanced functions influence the time that libev will spend waiting
		860	for events. Both time intervals are by default C<0>, meaning that libev
		861	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		862	latency.
		863
		864	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		865	allows libev to delay invocation of I/O and timer/periodic callbacks
		866	to increase efficiency of loop iterations (or to increase power-saving
		867	opportunities).
		868
		869	The idea is that sometimes your program runs just fast enough to handle
		870	one (or very few) event(s) per loop iteration. While this makes the
		871	program responsive, it also wastes a lot of CPU time to poll for new
		872	events, especially with backends like C<select ()> which have a high
		873	overhead for the actual polling but can deliver many events at once.
		874
		875	By setting a higher I<io collect interval> you allow libev to spend more
		876	time collecting I/O events, so you can handle more events per iteration,
		877	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		878	C<ev_timer>) will be not affected. Setting this to a non-null value will
		879	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		880	sleep time ensures that libev will not poll for I/O events more often then
		881	once per this interval, on average.
		882
		883	Likewise, by setting a higher I<timeout collect interval> you allow libev
		884	to spend more time collecting timeouts, at the expense of increased
		885	latency/jitter/inexactness (the watcher callback will be called
		886	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		887	value will not introduce any overhead in libev.
		888
		889	Many (busy) programs can usually benefit by setting the I/O collect
		890	interval to a value near C<0.1> or so, which is often enough for
		891	interactive servers (of course not for games), likewise for timeouts. It
		892	usually doesn't make much sense to set it to a lower value than C<0.01>,
		893	as this approaches the timing granularity of most systems. Note that if
		894	you do transactions with the outside world and you can't increase the
		895	parallelity, then this setting will limit your transaction rate (if you
		896	need to poll once per transaction and the I/O collect interval is 0.01,
		897	then you can't do more than 100 transactions per second).
		898
		899	Setting the I<timeout collect interval> can improve the opportunity for
		900	saving power, as the program will "bundle" timer callback invocations that
		901	are "near" in time together, by delaying some, thus reducing the number of
		902	times the process sleeps and wakes up again. Another useful technique to
		903	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		904	they fire on, say, one-second boundaries only.
		905
		906	Example: we only need 0.1s timeout granularity, and we wish not to poll
		907	more often than 100 times per second:
		908
		909	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		910	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		911
		912	=item ev_invoke_pending (loop)
		913
		914	This call will simply invoke all pending watchers while resetting their
		915	pending state. Normally, C<ev_run> does this automatically when required,
		916	but when overriding the invoke callback this call comes handy. This
		917	function can be invoked from a watcher - this can be useful for example
		918	when you want to do some lengthy calculation and want to pass further
		919	event handling to another thread (you still have to make sure only one
		920	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		921
		922	=item int ev_pending_count (loop)
		923
		924	Returns the number of pending watchers - zero indicates that no watchers
		925	are pending.
		926
		927	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		928
		929	This overrides the invoke pending functionality of the loop: Instead of
		930	invoking all pending watchers when there are any, C<ev_run> will call
		931	this callback instead. This is useful, for example, when you want to
		932	invoke the actual watchers inside another context (another thread etc.).
		933
		934	If you want to reset the callback, use C<ev_invoke_pending> as new
		935	callback.
		936
		937	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		938
		939	Sometimes you want to share the same loop between multiple threads. This
		940	can be done relatively simply by putting mutex_lock/unlock calls around
		941	each call to a libev function.
		942
		943	However, C<ev_run> can run an indefinite time, so it is not feasible
		944	to wait for it to return. One way around this is to wake up the event
		945	loop via C<ev_break> and C<av_async_send>, another way is to set these
		946	I<release> and I<acquire> callbacks on the loop.
		947
		948	When set, then C<release> will be called just before the thread is
		949	suspended waiting for new events, and C<acquire> is called just
		950	afterwards.
		951
		952	Ideally, C<release> will just call your mutex_unlock function, and
		953	C<acquire> will just call the mutex_lock function again.
		954
		955	While event loop modifications are allowed between invocations of
		956	C<release> and C<acquire> (that's their only purpose after all), no
		957	modifications done will affect the event loop, i.e. adding watchers will
		958	have no effect on the set of file descriptors being watched, or the time
		959	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		960	to take note of any changes you made.
		961
		962	In theory, threads executing C<ev_run> will be async-cancel safe between
		963	invocations of C<release> and C<acquire>.
		964
		965	See also the locking example in the C<THREADS> section later in this
		966	document.
		967
		968	=item ev_set_userdata (loop, void *data)
		969
		970	=item ev_userdata (loop)
		971
		972	Set and retrieve a single C<void *> associated with a loop. When
		973	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		974	C<0.>
		975
		976	These two functions can be used to associate arbitrary data with a loop,
		977	and are intended solely for the C<invoke_pending_cb>, C<release> and
		978	C<acquire> callbacks described above, but of course can be (ab-)used for
		979	any other purpose as well.
		980
		981	=item ev_verify (loop)
		982
		983	This function only does something when C<EV_VERIFY> support has been
		984	compiled in, which is the default for non-minimal builds. It tries to go
		985	through all internal structures and checks them for validity. If anything
		986	is found to be inconsistent, it will print an error message to standard
		987	error and call C<abort ()>.
		988
		989	This can be used to catch bugs inside libev itself: under normal
		990	circumstances, this function will never abort as of course libev keeps its
		991	data structures consistent.
470		992
471	=back	993	=back
472		994
473		995
474	=head1 ANATOMY OF A WATCHER	996	=head1 ANATOMY OF A WATCHER
475		997
		998	In the following description, uppercase C<TYPE> in names stands for the
		999	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1000	watchers and C<ev_io_start> for I/O watchers.
		1001
476	A watcher is a structure that you create and register to record your	1002	A watcher is an opaque structure that you allocate and register to record
477	interest in some event. For instance, if you want to wait for STDIN to	1003	your interest in some event. To make a concrete example, imagine you want
478	become readable, you would create an C<ev_io> watcher for that:	1004	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1005	for that:
479		1006
480	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1007	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
481	{	1008	{
482	ev_io_stop (w);	1009	ev_io_stop (w);
483	ev_unloop (loop, EVUNLOOP_ALL);	1010	ev_break (loop, EVBREAK_ALL);
484	}	1011	}
485		1012
486	struct ev_loop *loop = ev_default_loop (0);	1013	struct ev_loop *loop = ev_default_loop (0);
		1014
487	struct ev_io stdin_watcher;	1015	ev_io stdin_watcher;
		1016
488	ev_init (&stdin_watcher, my_cb);	1017	ev_init (&stdin_watcher, my_cb);
489	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1018	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
490	ev_io_start (loop, &stdin_watcher);	1019	ev_io_start (loop, &stdin_watcher);
		1020
491	ev_loop (loop, 0);	1021	ev_run (loop, 0);
492		1022
493	As you can see, you are responsible for allocating the memory for your	1023	As you can see, you are responsible for allocating the memory for your
494	watcher structures (and it is usually a bad idea to do this on the stack,	1024	watcher structures (and it is I<usually> a bad idea to do this on the
495	although this can sometimes be quite valid).	1025	stack).
496		1026
		1027	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1028	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1029
497	Each watcher structure must be initialised by a call to C<ev_init	1030	Each watcher structure must be initialised by a call to C<ev_init (watcher
498	(watcher *, callback)>, which expects a callback to be provided. This	1031	*, callback)>, which expects a callback to be provided. This callback is
499	callback gets invoked each time the event occurs (or, in the case of io	1032	invoked each time the event occurs (or, in the case of I/O watchers, each
500	watchers, each time the event loop detects that the file descriptor given	1033	time the event loop detects that the file descriptor given is readable
501	is readable and/or writable).	1034	and/or writable).
502		1035
503	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1036	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
504	with arguments specific to this watcher type. There is also a macro	1037	macro to configure it, with arguments specific to the watcher type. There
505	to combine initialisation and setting in one call: C<< ev_<type>_init	1038	is also a macro to combine initialisation and setting in one call: C<<
506	(watcher *, callback, ...) >>.	1039	ev_TYPE_init (watcher *, callback, ...) >>.
507		1040
508	To make the watcher actually watch out for events, you have to start it	1041	To make the watcher actually watch out for events, you have to start it
509	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1042	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
510	*) >>), and you can stop watching for events at any time by calling the	1043	*) >>), and you can stop watching for events at any time by calling the
511	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1044	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
512		1045
513	As long as your watcher is active (has been started but not stopped) you	1046	As long as your watcher is active (has been started but not stopped) you
514	must not touch the values stored in it. Most specifically you must never	1047	must not touch the values stored in it. Most specifically you must never
515	reinitialise it or call its C<set> macro.	1048	reinitialise it or call its C<ev_TYPE_set> macro.
516		1049
517	Each and every callback receives the event loop pointer as first, the	1050	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	1051	registered watcher structure as second, and a bitset of received events as
519	third argument.	1052	third argument.
520		1053
…		…
529	=item C<EV_WRITE>	1062	=item C<EV_WRITE>
530		1063
531	The file descriptor in the C<ev_io> watcher has become readable and/or	1064	The file descriptor in the C<ev_io> watcher has become readable and/or
532	writable.	1065	writable.
533		1066
534	=item C<EV_TIMEOUT>	1067	=item C<EV_TIMER>
535		1068
536	The C<ev_timer> watcher has timed out.	1069	The C<ev_timer> watcher has timed out.
537		1070
538	=item C<EV_PERIODIC>	1071	=item C<EV_PERIODIC>
539		1072
…		…
545		1078
546	=item C<EV_CHILD>	1079	=item C<EV_CHILD>
547		1080
548	The pid specified in the C<ev_child> watcher has received a status change.	1081	The pid specified in the C<ev_child> watcher has received a status change.
549		1082
		1083	=item C<EV_STAT>
		1084
		1085	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1086
550	=item C<EV_IDLE>	1087	=item C<EV_IDLE>
551		1088
552	The C<ev_idle> watcher has determined that you have nothing better to do.	1089	The C<ev_idle> watcher has determined that you have nothing better to do.
553		1090
554	=item C<EV_PREPARE>	1091	=item C<EV_PREPARE>
555		1092
556	=item C<EV_CHECK>	1093	=item C<EV_CHECK>
557		1094
558	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1095	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
559	to gather new events, and all C<ev_check> watchers are invoked just after	1096	to gather new events, and all C<ev_check> watchers are invoked just after
560	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1097	C<ev_run> has gathered them, but before it invokes any callbacks for any
561	received events. Callbacks of both watcher types can start and stop as	1098	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	1099	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1100	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	1101	C<ev_run> from blocking).
		1102
		1103	=item C<EV_EMBED>
		1104
		1105	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1106
		1107	=item C<EV_FORK>
		1108
		1109	The event loop has been resumed in the child process after fork (see
		1110	C<ev_fork>).
		1111
		1112	=item C<EV_ASYNC>
		1113
		1114	The given async watcher has been asynchronously notified (see C<ev_async>).
		1115
		1116	=item C<EV_CUSTOM>
		1117
		1118	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1119	by libev users to signal watchers (e.g. via C<ev_feed_event>).
565		1120
566	=item C<EV_ERROR>	1121	=item C<EV_ERROR>
567		1122
568	An unspecified error has occured, the watcher has been stopped. This might	1123	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	1124	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	1125	ran out of memory, a file descriptor was found to be closed or any other
		1126	problem. Libev considers these application bugs.
		1127
571	problem. You best act on it by reporting the problem and somehow coping	1128	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	1129	watcher being stopped. Note that well-written programs should not receive
		1130	an error ever, so when your watcher receives it, this usually indicates a
		1131	bug in your program.
573		1132
574	Libev will usually signal a few "dummy" events together with an error,	1133	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	1134	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	1135	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	1136	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	1137	programs, though, as the fd could already be closed and reused for another
		1138	thing, so beware.
579		1139
580	=back	1140	=back
581		1141
		1142	=head2 WATCHER STATES
		1143
		1144	There are various watcher states mentioned throughout this manual -
		1145	active, pending and so on. In this section these states and the rules to
		1146	transition between them will be described in more detail - and while these
		1147	rules might look complicated, they usually do "the right thing".
		1148
		1149	=over 4
		1150
		1151	=item initialiased
		1152
		1153	Before a watcher can be registered with the event looop it has to be
		1154	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1155	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1156
		1157	In this state it is simply some block of memory that is suitable for use
		1158	in an event loop. It can be moved around, freed, reused etc. at will.
		1159
		1160	=item started/running/active
		1161
		1162	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1163	property of the event loop, and is actively waiting for events. While in
		1164	this state it cannot be accessed (except in a few documented ways), moved,
		1165	freed or anything else - the only legal thing is to keep a pointer to it,
		1166	and call libev functions on it that are documented to work on active watchers.
		1167
		1168	=item pending
		1169
		1170	If a watcher is active and libev determines that an event it is interested
		1171	in has occurred (such as a timer expiring), it will become pending. It will
		1172	stay in this pending state until either it is stopped or its callback is
		1173	about to be invoked, so it is not normally pending inside the watcher
		1174	callback.
		1175
		1176	The watcher might or might not be active while it is pending (for example,
		1177	an expired non-repeating timer can be pending but no longer active). If it
		1178	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1179	but it is still property of the event loop at this time, so cannot be
		1180	moved, freed or reused. And if it is active the rules described in the
		1181	previous item still apply.
		1182
		1183	It is also possible to feed an event on a watcher that is not active (e.g.
		1184	via C<ev_feed_event>), in which case it becomes pending without being
		1185	active.
		1186
		1187	=item stopped
		1188
		1189	A watcher can be stopped implicitly by libev (in which case it might still
		1190	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1191	latter will clear any pending state the watcher might be in, regardless
		1192	of whether it was active or not, so stopping a watcher explicitly before
		1193	freeing it is often a good idea.
		1194
		1195	While stopped (and not pending) the watcher is essentially in the
		1196	initialised state, that is it can be reused, moved, modified in any way
		1197	you wish.
		1198
		1199	=back
		1200
582	=head2 GENERIC WATCHER FUNCTIONS	1201	=head2 GENERIC WATCHER FUNCTIONS
583
584	In the following description, C<TYPE> stands for the watcher type,
585	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
586		1202
587	=over 4	1203	=over 4
588		1204
589	=item C<ev_init> (ev_TYPE *watcher, callback)	1205	=item C<ev_init> (ev_TYPE *watcher, callback)
590		1206
…		…
596	which rolls both calls into one.	1212	which rolls both calls into one.
597		1213
598	You can reinitialise a watcher at any time as long as it has been stopped	1214	You can reinitialise a watcher at any time as long as it has been stopped
599	(or never started) and there are no pending events outstanding.	1215	(or never started) and there are no pending events outstanding.
600		1216
601	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1217	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
602	int revents)>.	1218	int revents)>.
603		1219
		1220	Example: Initialise an C<ev_io> watcher in two steps.
		1221
		1222	ev_io w;
		1223	ev_init (&w, my_cb);
		1224	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1225
604	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1226	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
605		1227
606	This macro initialises the type-specific parts of a watcher. You need to	1228	This macro initialises the type-specific parts of a watcher. You need to
607	call C<ev_init> at least once before you call this macro, but you can	1229	call C<ev_init> at least once before you call this macro, but you can
608	call C<ev_TYPE_set> any number of times. You must not, however, call this	1230	call C<ev_TYPE_set> any number of times. You must not, however, call this
609	macro on a watcher that is active (it can be pending, however, which is a	1231	macro on a watcher that is active (it can be pending, however, which is a
610	difference to the C<ev_init> macro).	1232	difference to the C<ev_init> macro).
611		1233
612	Although some watcher types do not have type-specific arguments	1234	Although some watcher types do not have type-specific arguments
613	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1235	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
614		1236
		1237	See C<ev_init>, above, for an example.
		1238
615	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1239	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
616		1240
617	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1241	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
618	calls into a single call. This is the most convinient method to initialise	1242	calls into a single call. This is the most convenient method to initialise
619	a watcher. The same limitations apply, of course.	1243	a watcher. The same limitations apply, of course.
620		1244
		1245	Example: Initialise and set an C<ev_io> watcher in one step.
		1246
		1247	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1248
621	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1249	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
622		1250
623	Starts (activates) the given watcher. Only active watchers will receive	1251	Starts (activates) the given watcher. Only active watchers will receive
624	events. If the watcher is already active nothing will happen.	1252	events. If the watcher is already active nothing will happen.
625		1253
		1254	Example: Start the C<ev_io> watcher that is being abused as example in this
		1255	whole section.
		1256
		1257	ev_io_start (EV_DEFAULT_UC, &w);
		1258
626	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1259	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
627		1260
628	Stops the given watcher again (if active) and clears the pending	1261	Stops the given watcher if active, and clears the pending status (whether
		1262	the watcher was active or not).
		1263
629	status. It is possible that stopped watchers are pending (for example,	1264	It is possible that stopped watchers are pending - for example,
630	non-repeating timers are being stopped when they become pending), but	1265	non-repeating timers are being stopped when they become pending - but
631	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1266	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
632	you want to free or reuse the memory used by the watcher it is therefore a	1267	pending. If you want to free or reuse the memory used by the watcher it is
633	good idea to always call its C<ev_TYPE_stop> function.	1268	therefore a good idea to always call its C<ev_TYPE_stop> function.
634		1269
635	=item bool ev_is_active (ev_TYPE *watcher)	1270	=item bool ev_is_active (ev_TYPE *watcher)
636		1271
637	Returns a true value iff the watcher is active (i.e. it has been started	1272	Returns a true value iff the watcher is active (i.e. it has been started
638	and not yet been stopped). As long as a watcher is active you must not modify	1273	and not yet been stopped). As long as a watcher is active you must not modify
…		…
641	=item bool ev_is_pending (ev_TYPE *watcher)	1276	=item bool ev_is_pending (ev_TYPE *watcher)
642		1277
643	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1278	Returns a true value iff the watcher is pending, (i.e. it has outstanding
644	events but its callback has not yet been invoked). As long as a watcher	1279	events but its callback has not yet been invoked). As long as a watcher
645	is pending (but not active) you must not call an init function on it (but	1280	is pending (but not active) you must not call an init function on it (but
646	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1281	C<ev_TYPE_set> is safe), you must not change its priority, and you must
647	libev (e.g. you cnanot C<free ()> it).	1282	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1283	it).
648		1284
649	=item callback = ev_cb (ev_TYPE *watcher)	1285	=item callback ev_cb (ev_TYPE *watcher)
650		1286
651	Returns the callback currently set on the watcher.	1287	Returns the callback currently set on the watcher.
652		1288
653	=item ev_cb_set (ev_TYPE *watcher, callback)	1289	=item ev_cb_set (ev_TYPE *watcher, callback)
654		1290
655	Change the callback. You can change the callback at virtually any time	1291	Change the callback. You can change the callback at virtually any time
656	(modulo threads).	1292	(modulo threads).
657		1293
		1294	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1295
		1296	=item int ev_priority (ev_TYPE *watcher)
		1297
		1298	Set and query the priority of the watcher. The priority is a small
		1299	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1300	(default: C<-2>). Pending watchers with higher priority will be invoked
		1301	before watchers with lower priority, but priority will not keep watchers
		1302	from being executed (except for C<ev_idle> watchers).
		1303
		1304	If you need to suppress invocation when higher priority events are pending
		1305	you need to look at C<ev_idle> watchers, which provide this functionality.
		1306
		1307	You I<must not> change the priority of a watcher as long as it is active or
		1308	pending.
		1309
		1310	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1311	fine, as long as you do not mind that the priority value you query might
		1312	or might not have been clamped to the valid range.
		1313
		1314	The default priority used by watchers when no priority has been set is
		1315	always C<0>, which is supposed to not be too high and not be too low :).
		1316
		1317	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1318	priorities.
		1319
		1320	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1321
		1322	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1323	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1324	can deal with that fact, as both are simply passed through to the
		1325	callback.
		1326
		1327	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1328
		1329	If the watcher is pending, this function clears its pending status and
		1330	returns its C<revents> bitset (as if its callback was invoked). If the
		1331	watcher isn't pending it does nothing and returns C<0>.
		1332
		1333	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1334	callback to be invoked, which can be accomplished with this function.
		1335
		1336	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1337
		1338	Feeds the given event set into the event loop, as if the specified event
		1339	had happened for the specified watcher (which must be a pointer to an
		1340	initialised but not necessarily started event watcher). Obviously you must
		1341	not free the watcher as long as it has pending events.
		1342
		1343	Stopping the watcher, letting libev invoke it, or calling
		1344	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1345	not started in the first place.
		1346
		1347	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1348	functions that do not need a watcher.
		1349
658	=back	1350	=back
659		1351
660		1352
661	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1353	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
662		1354
663	Each watcher has, by default, a member C<void *data> that you can change	1355	Each watcher has, by default, a member C<void *data> that you can change
664	and read at any time, libev will completely ignore it. This can be used	1356	and read at any time: libev will completely ignore it. This can be used
665	to associate arbitrary data with your watcher. If you need more data and	1357	to associate arbitrary data with your watcher. If you need more data and
666	don't want to allocate memory and store a pointer to it in that data	1358	don't want to allocate memory and store a pointer to it in that data
667	member, you can also "subclass" the watcher type and provide your own	1359	member, you can also "subclass" the watcher type and provide your own
668	data:	1360	data:
669		1361
670	struct my_io	1362	struct my_io
671	{	1363	{
672	struct ev_io io;	1364	ev_io io;
673	int otherfd;	1365	int otherfd;
674	void *somedata;	1366	void *somedata;
675	struct whatever *mostinteresting;	1367	struct whatever *mostinteresting;
676	}	1368	};
		1369
		1370	...
		1371	struct my_io w;
		1372	ev_io_init (&w.io, my_cb, fd, EV_READ);
677		1373
678	And since your callback will be called with a pointer to the watcher, you	1374	And since your callback will be called with a pointer to the watcher, you
679	can cast it back to your own type:	1375	can cast it back to your own type:
680		1376
681	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1377	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
682	{	1378	{
683	struct my_io *w = (struct my_io *)w_;	1379	struct my_io *w = (struct my_io *)w_;
684	...	1380	...
685	}	1381	}
686		1382
687	More interesting and less C-conformant ways of catsing your callback type	1383	More interesting and less C-conformant ways of casting your callback type
688	have been omitted....	1384	instead have been omitted.
		1385
		1386	Another common scenario is to use some data structure with multiple
		1387	embedded watchers:
		1388
		1389	struct my_biggy
		1390	{
		1391	int some_data;
		1392	ev_timer t1;
		1393	ev_timer t2;
		1394	}
		1395
		1396	In this case getting the pointer to C<my_biggy> is a bit more
		1397	complicated: Either you store the address of your C<my_biggy> struct
		1398	in the C<data> member of the watcher (for woozies), or you need to use
		1399	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1400	programmers):
		1401
		1402	#include <stddef.h>
		1403
		1404	static void
		1405	t1_cb (EV_P_ ev_timer *w, int revents)
		1406	{
		1407	struct my_biggy big = (struct my_biggy *)
		1408	(((char *)w) - offsetof (struct my_biggy, t1));
		1409	}
		1410
		1411	static void
		1412	t2_cb (EV_P_ ev_timer *w, int revents)
		1413	{
		1414	struct my_biggy big = (struct my_biggy *)
		1415	(((char *)w) - offsetof (struct my_biggy, t2));
		1416	}
		1417
		1418	=head2 WATCHER PRIORITY MODELS
		1419
		1420	Many event loops support I<watcher priorities>, which are usually small
		1421	integers that influence the ordering of event callback invocation
		1422	between watchers in some way, all else being equal.
		1423
		1424	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1425	description for the more technical details such as the actual priority
		1426	range.
		1427
		1428	There are two common ways how these these priorities are being interpreted
		1429	by event loops:
		1430
		1431	In the more common lock-out model, higher priorities "lock out" invocation
		1432	of lower priority watchers, which means as long as higher priority
		1433	watchers receive events, lower priority watchers are not being invoked.
		1434
		1435	The less common only-for-ordering model uses priorities solely to order
		1436	callback invocation within a single event loop iteration: Higher priority
		1437	watchers are invoked before lower priority ones, but they all get invoked
		1438	before polling for new events.
		1439
		1440	Libev uses the second (only-for-ordering) model for all its watchers
		1441	except for idle watchers (which use the lock-out model).
		1442
		1443	The rationale behind this is that implementing the lock-out model for
		1444	watchers is not well supported by most kernel interfaces, and most event
		1445	libraries will just poll for the same events again and again as long as
		1446	their callbacks have not been executed, which is very inefficient in the
		1447	common case of one high-priority watcher locking out a mass of lower
		1448	priority ones.
		1449
		1450	Static (ordering) priorities are most useful when you have two or more
		1451	watchers handling the same resource: a typical usage example is having an
		1452	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1453	timeouts. Under load, data might be received while the program handles
		1454	other jobs, but since timers normally get invoked first, the timeout
		1455	handler will be executed before checking for data. In that case, giving
		1456	the timer a lower priority than the I/O watcher ensures that I/O will be
		1457	handled first even under adverse conditions (which is usually, but not
		1458	always, what you want).
		1459
		1460	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1461	will only be executed when no same or higher priority watchers have
		1462	received events, they can be used to implement the "lock-out" model when
		1463	required.
		1464
		1465	For example, to emulate how many other event libraries handle priorities,
		1466	you can associate an C<ev_idle> watcher to each such watcher, and in
		1467	the normal watcher callback, you just start the idle watcher. The real
		1468	processing is done in the idle watcher callback. This causes libev to
		1469	continuously poll and process kernel event data for the watcher, but when
		1470	the lock-out case is known to be rare (which in turn is rare :), this is
		1471	workable.
		1472
		1473	Usually, however, the lock-out model implemented that way will perform
		1474	miserably under the type of load it was designed to handle. In that case,
		1475	it might be preferable to stop the real watcher before starting the
		1476	idle watcher, so the kernel will not have to process the event in case
		1477	the actual processing will be delayed for considerable time.
		1478
		1479	Here is an example of an I/O watcher that should run at a strictly lower
		1480	priority than the default, and which should only process data when no
		1481	other events are pending:
		1482
		1483	ev_idle idle; // actual processing watcher
		1484	ev_io io; // actual event watcher
		1485
		1486	static void
		1487	io_cb (EV_P_ ev_io *w, int revents)
		1488	{
		1489	// stop the I/O watcher, we received the event, but
		1490	// are not yet ready to handle it.
		1491	ev_io_stop (EV_A_ w);
		1492
		1493	// start the idle watcher to handle the actual event.
		1494	// it will not be executed as long as other watchers
		1495	// with the default priority are receiving events.
		1496	ev_idle_start (EV_A_ &idle);
		1497	}
		1498
		1499	static void
		1500	idle_cb (EV_P_ ev_idle *w, int revents)
		1501	{
		1502	// actual processing
		1503	read (STDIN_FILENO, ...);
		1504
		1505	// have to start the I/O watcher again, as
		1506	// we have handled the event
		1507	ev_io_start (EV_P_ &io);
		1508	}
		1509
		1510	// initialisation
		1511	ev_idle_init (&idle, idle_cb);
		1512	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1513	ev_io_start (EV_DEFAULT_ &io);
		1514
		1515	In the "real" world, it might also be beneficial to start a timer, so that
		1516	low-priority connections can not be locked out forever under load. This
		1517	enables your program to keep a lower latency for important connections
		1518	during short periods of high load, while not completely locking out less
		1519	important ones.
689		1520
690		1521
691	=head1 WATCHER TYPES	1522	=head1 WATCHER TYPES
692		1523
693	This section describes each watcher in detail, but will not repeat	1524	This section describes each watcher in detail, but will not repeat
694	information given in the last section.	1525	information given in the last section. Any initialisation/set macros,
		1526	functions and members specific to the watcher type are explained.
		1527
		1528	Members are additionally marked with either I<[read-only]>, meaning that,
		1529	while the watcher is active, you can look at the member and expect some
		1530	sensible content, but you must not modify it (you can modify it while the
		1531	watcher is stopped to your hearts content), or I<[read-write]>, which
		1532	means you can expect it to have some sensible content while the watcher
		1533	is active, but you can also modify it. Modifying it may not do something
		1534	sensible or take immediate effect (or do anything at all), but libev will
		1535	not crash or malfunction in any way.
695		1536
696		1537
697	=head2 C<ev_io> - is this file descriptor readable or writable?	1538	=head2 C<ev_io> - is this file descriptor readable or writable?
698		1539
699	I/O watchers check whether a file descriptor is readable or writable	1540	I/O watchers check whether a file descriptor is readable or writable
…		…
707	In general you can register as many read and/or write event watchers per	1548	In general you can register as many read and/or write event watchers per
708	fd as you want (as long as you don't confuse yourself). Setting all file	1549	fd as you want (as long as you don't confuse yourself). Setting all file
709	descriptors to non-blocking mode is also usually a good idea (but not	1550	descriptors to non-blocking mode is also usually a good idea (but not
710	required if you know what you are doing).	1551	required if you know what you are doing).
711		1552
712	You have to be careful with dup'ed file descriptors, though. Some backends	1553	If you cannot use non-blocking mode, then force the use of a
713	(the linux epoll backend is a notable example) cannot handle dup'ed file	1554	known-to-be-good backend (at the time of this writing, this includes only
714	descriptors correctly if you register interest in two or more fds pointing	1555	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
715	to the same underlying file/socket/etc. description (that is, they share	1556	descriptors for which non-blocking operation makes no sense (such as
716	the same underlying "file open").	1557	files) - libev doesn't guarantee any specific behaviour in that case.
717
718	If you must do this, then force the use of a known-to-be-good backend
719	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
720	C<EVBACKEND_POLL>).
721		1558
722	Another thing you have to watch out for is that it is quite easy to	1559	Another thing you have to watch out for is that it is quite easy to
723	receive "spurious" readyness notifications, that is your callback might	1560	receive "spurious" readiness notifications, that is your callback might
724	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
725	because there is no data. Not only are some backends known to create a	1562	because there is no data. Not only are some backends known to create a
726	lot of those (for example solaris ports), it is very easy to get into	1563	lot of those (for example Solaris ports), it is very easy to get into
727	this situation even with a relatively standard program structure. Thus	1564	this situation even with a relatively standard program structure. Thus
728	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1565	it is best to always use non-blocking I/O: An extra C<read>(2) returning
729	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1566	C<EAGAIN> is far preferable to a program hanging until some data arrives.
730		1567
731	If you cannot run the fd in non-blocking mode (for example you should not	1568	If you cannot run the fd in non-blocking mode (for example you should
732	play around with an Xlib connection), then you have to seperately re-test	1569	not play around with an Xlib connection), then you have to separately
733	wether a file descriptor is really ready with a known-to-be good interface	1570	re-test whether a file descriptor is really ready with a known-to-be good
734	such as poll (fortunately in our Xlib example, Xlib already does this on	1571	interface such as poll (fortunately in our Xlib example, Xlib already
735	its own, so its quite safe to use).	1572	does this on its own, so its quite safe to use). Some people additionally
		1573	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1574	indefinitely.
		1575
		1576	But really, best use non-blocking mode.
		1577
		1578	=head3 The special problem of disappearing file descriptors
		1579
		1580	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1581	descriptor (either due to calling C<close> explicitly or any other means,
		1582	such as C<dup2>). The reason is that you register interest in some file
		1583	descriptor, but when it goes away, the operating system will silently drop
		1584	this interest. If another file descriptor with the same number then is
		1585	registered with libev, there is no efficient way to see that this is, in
		1586	fact, a different file descriptor.
		1587
		1588	To avoid having to explicitly tell libev about such cases, libev follows
		1589	the following policy: Each time C<ev_io_set> is being called, libev
		1590	will assume that this is potentially a new file descriptor, otherwise
		1591	it is assumed that the file descriptor stays the same. That means that
		1592	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1593	descriptor even if the file descriptor number itself did not change.
		1594
		1595	This is how one would do it normally anyway, the important point is that
		1596	the libev application should not optimise around libev but should leave
		1597	optimisations to libev.
		1598
		1599	=head3 The special problem of dup'ed file descriptors
		1600
		1601	Some backends (e.g. epoll), cannot register events for file descriptors,
		1602	but only events for the underlying file descriptions. That means when you
		1603	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1604	events for them, only one file descriptor might actually receive events.
		1605
		1606	There is no workaround possible except not registering events
		1607	for potentially C<dup ()>'ed file descriptors, or to resort to
		1608	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1609
		1610	=head3 The special problem of fork
		1611
		1612	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1613	useless behaviour. Libev fully supports fork, but needs to be told about
		1614	it in the child.
		1615
		1616	To support fork in your programs, you either have to call
		1617	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1618	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1619	C<EVBACKEND_POLL>.
		1620
		1621	=head3 The special problem of SIGPIPE
		1622
		1623	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1624	when writing to a pipe whose other end has been closed, your program gets
		1625	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1626	this is sensible behaviour, for daemons, this is usually undesirable.
		1627
		1628	So when you encounter spurious, unexplained daemon exits, make sure you
		1629	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1630	somewhere, as that would have given you a big clue).
		1631
		1632	=head3 The special problem of accept()ing when you can't
		1633
		1634	Many implementations of the POSIX C<accept> function (for example,
		1635	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1636	connection from the pending queue in all error cases.
		1637
		1638	For example, larger servers often run out of file descriptors (because
		1639	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1640	rejecting the connection, leading to libev signalling readiness on
		1641	the next iteration again (the connection still exists after all), and
		1642	typically causing the program to loop at 100% CPU usage.
		1643
		1644	Unfortunately, the set of errors that cause this issue differs between
		1645	operating systems, there is usually little the app can do to remedy the
		1646	situation, and no known thread-safe method of removing the connection to
		1647	cope with overload is known (to me).
		1648
		1649	One of the easiest ways to handle this situation is to just ignore it
		1650	- when the program encounters an overload, it will just loop until the
		1651	situation is over. While this is a form of busy waiting, no OS offers an
		1652	event-based way to handle this situation, so it's the best one can do.
		1653
		1654	A better way to handle the situation is to log any errors other than
		1655	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1656	messages, and continue as usual, which at least gives the user an idea of
		1657	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1658	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1659	usage.
		1660
		1661	If your program is single-threaded, then you could also keep a dummy file
		1662	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1663	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1664	close that fd, and create a new dummy fd. This will gracefully refuse
		1665	clients under typical overload conditions.
		1666
		1667	The last way to handle it is to simply log the error and C<exit>, as
		1668	is often done with C<malloc> failures, but this results in an easy
		1669	opportunity for a DoS attack.
		1670
		1671	=head3 Watcher-Specific Functions
736		1672
737	=over 4	1673	=over 4
738		1674
739	=item ev_io_init (ev_io *, callback, int fd, int events)	1675	=item ev_io_init (ev_io *, callback, int fd, int events)
740		1676
741	=item ev_io_set (ev_io *, int fd, int events)	1677	=item ev_io_set (ev_io *, int fd, int events)
742		1678
743	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1679	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
744	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1680	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
745	C<EV_READ | EV_WRITE> to receive the given events.	1681	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1682
		1683	=item int fd [read-only]
		1684
		1685	The file descriptor being watched.
		1686
		1687	=item int events [read-only]
		1688
		1689	The events being watched.
746		1690
747	=back	1691	=back
748		1692
		1693	=head3 Examples
		1694
749	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1695	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
750	readable, but only once. Since it is likely line-buffered, you could	1696	readable, but only once. Since it is likely line-buffered, you could
751	attempt to read a whole line in the callback:	1697	attempt to read a whole line in the callback.
752		1698
753	static void	1699	static void
754	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1700	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
755	{	1701	{
756	ev_io_stop (loop, w);	1702	ev_io_stop (loop, w);
757	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1703	.. read from stdin here (or from w->fd) and handle any I/O errors
758	}	1704	}
759		1705
760	...	1706	...
761	struct ev_loop *loop = ev_default_init (0);	1707	struct ev_loop *loop = ev_default_init (0);
762	struct ev_io stdin_readable;	1708	ev_io stdin_readable;
763	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1709	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
764	ev_io_start (loop, &stdin_readable);	1710	ev_io_start (loop, &stdin_readable);
765	ev_loop (loop, 0);	1711	ev_run (loop, 0);
766		1712
767		1713
768	=head2 C<ev_timer> - relative and optionally repeating timeouts	1714	=head2 C<ev_timer> - relative and optionally repeating timeouts
769		1715
770	Timer watchers are simple relative timers that generate an event after a	1716	Timer watchers are simple relative timers that generate an event after a
771	given time, and optionally repeating in regular intervals after that.	1717	given time, and optionally repeating in regular intervals after that.
772		1718
773	The timers are based on real time, that is, if you register an event that	1719	The timers are based on real time, that is, if you register an event that
774	times out after an hour and you reset your system clock to last years	1720	times out after an hour and you reset your system clock to January last
775	time, it will still time out after (roughly) and hour. "Roughly" because	1721	year, it will still time out after (roughly) one hour. "Roughly" because
776	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1722	detecting time jumps is hard, and some inaccuracies are unavoidable (the
777	monotonic clock option helps a lot here).	1723	monotonic clock option helps a lot here).
		1724
		1725	The callback is guaranteed to be invoked only I<after> its timeout has
		1726	passed (not I<at>, so on systems with very low-resolution clocks this
		1727	might introduce a small delay). If multiple timers become ready during the
		1728	same loop iteration then the ones with earlier time-out values are invoked
		1729	before ones of the same priority with later time-out values (but this is
		1730	no longer true when a callback calls C<ev_run> recursively).
		1731
		1732	=head3 Be smart about timeouts
		1733
		1734	Many real-world problems involve some kind of timeout, usually for error
		1735	recovery. A typical example is an HTTP request - if the other side hangs,
		1736	you want to raise some error after a while.
		1737
		1738	What follows are some ways to handle this problem, from obvious and
		1739	inefficient to smart and efficient.
		1740
		1741	In the following, a 60 second activity timeout is assumed - a timeout that
		1742	gets reset to 60 seconds each time there is activity (e.g. each time some
		1743	data or other life sign was received).
		1744
		1745	=over 4
		1746
		1747	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1748
		1749	This is the most obvious, but not the most simple way: In the beginning,
		1750	start the watcher:
		1751
		1752	ev_timer_init (timer, callback, 60., 0.);
		1753	ev_timer_start (loop, timer);
		1754
		1755	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1756	and start it again:
		1757
		1758	ev_timer_stop (loop, timer);
		1759	ev_timer_set (timer, 60., 0.);
		1760	ev_timer_start (loop, timer);
		1761
		1762	This is relatively simple to implement, but means that each time there is
		1763	some activity, libev will first have to remove the timer from its internal
		1764	data structure and then add it again. Libev tries to be fast, but it's
		1765	still not a constant-time operation.
		1766
		1767	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1768
		1769	This is the easiest way, and involves using C<ev_timer_again> instead of
		1770	C<ev_timer_start>.
		1771
		1772	To implement this, configure an C<ev_timer> with a C<repeat> value
		1773	of C<60> and then call C<ev_timer_again> at start and each time you
		1774	successfully read or write some data. If you go into an idle state where
		1775	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1776	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1777
		1778	That means you can ignore both the C<ev_timer_start> function and the
		1779	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1780	member and C<ev_timer_again>.
		1781
		1782	At start:
		1783
		1784	ev_init (timer, callback);
		1785	timer->repeat = 60.;
		1786	ev_timer_again (loop, timer);
		1787
		1788	Each time there is some activity:
		1789
		1790	ev_timer_again (loop, timer);
		1791
		1792	It is even possible to change the time-out on the fly, regardless of
		1793	whether the watcher is active or not:
		1794
		1795	timer->repeat = 30.;
		1796	ev_timer_again (loop, timer);
		1797
		1798	This is slightly more efficient then stopping/starting the timer each time
		1799	you want to modify its timeout value, as libev does not have to completely
		1800	remove and re-insert the timer from/into its internal data structure.
		1801
		1802	It is, however, even simpler than the "obvious" way to do it.
		1803
		1804	=item 3. Let the timer time out, but then re-arm it as required.
		1805
		1806	This method is more tricky, but usually most efficient: Most timeouts are
		1807	relatively long compared to the intervals between other activity - in
		1808	our example, within 60 seconds, there are usually many I/O events with
		1809	associated activity resets.
		1810
		1811	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1812	but remember the time of last activity, and check for a real timeout only
		1813	within the callback:
		1814
		1815	ev_tstamp last_activity; // time of last activity
		1816
		1817	static void
		1818	callback (EV_P_ ev_timer *w, int revents)
		1819	{
		1820	ev_tstamp now = ev_now (EV_A);
		1821	ev_tstamp timeout = last_activity + 60.;
		1822
		1823	// if last_activity + 60. is older than now, we did time out
		1824	if (timeout < now)
		1825	{
		1826	// timeout occurred, take action
		1827	}
		1828	else
		1829	{
		1830	// callback was invoked, but there was some activity, re-arm
		1831	// the watcher to fire in last_activity + 60, which is
		1832	// guaranteed to be in the future, so "again" is positive:
		1833	w->repeat = timeout - now;
		1834	ev_timer_again (EV_A_ w);
		1835	}
		1836	}
		1837
		1838	To summarise the callback: first calculate the real timeout (defined
		1839	as "60 seconds after the last activity"), then check if that time has
		1840	been reached, which means something I<did>, in fact, time out. Otherwise
		1841	the callback was invoked too early (C<timeout> is in the future), so
		1842	re-schedule the timer to fire at that future time, to see if maybe we have
		1843	a timeout then.
		1844
		1845	Note how C<ev_timer_again> is used, taking advantage of the
		1846	C<ev_timer_again> optimisation when the timer is already running.
		1847
		1848	This scheme causes more callback invocations (about one every 60 seconds
		1849	minus half the average time between activity), but virtually no calls to
		1850	libev to change the timeout.
		1851
		1852	To start the timer, simply initialise the watcher and set C<last_activity>
		1853	to the current time (meaning we just have some activity :), then call the
		1854	callback, which will "do the right thing" and start the timer:
		1855
		1856	ev_init (timer, callback);
		1857	last_activity = ev_now (loop);
		1858	callback (loop, timer, EV_TIMER);
		1859
		1860	And when there is some activity, simply store the current time in
		1861	C<last_activity>, no libev calls at all:
		1862
		1863	last_activity = ev_now (loop);
		1864
		1865	This technique is slightly more complex, but in most cases where the
		1866	time-out is unlikely to be triggered, much more efficient.
		1867
		1868	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1869	callback :) - just change the timeout and invoke the callback, which will
		1870	fix things for you.
		1871
		1872	=item 4. Wee, just use a double-linked list for your timeouts.
		1873
		1874	If there is not one request, but many thousands (millions...), all
		1875	employing some kind of timeout with the same timeout value, then one can
		1876	do even better:
		1877
		1878	When starting the timeout, calculate the timeout value and put the timeout
		1879	at the I<end> of the list.
		1880
		1881	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1882	the list is expected to fire (for example, using the technique #3).
		1883
		1884	When there is some activity, remove the timer from the list, recalculate
		1885	the timeout, append it to the end of the list again, and make sure to
		1886	update the C<ev_timer> if it was taken from the beginning of the list.
		1887
		1888	This way, one can manage an unlimited number of timeouts in O(1) time for
		1889	starting, stopping and updating the timers, at the expense of a major
		1890	complication, and having to use a constant timeout. The constant timeout
		1891	ensures that the list stays sorted.
		1892
		1893	=back
		1894
		1895	So which method the best?
		1896
		1897	Method #2 is a simple no-brain-required solution that is adequate in most
		1898	situations. Method #3 requires a bit more thinking, but handles many cases
		1899	better, and isn't very complicated either. In most case, choosing either
		1900	one is fine, with #3 being better in typical situations.
		1901
		1902	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1903	rather complicated, but extremely efficient, something that really pays
		1904	off after the first million or so of active timers, i.e. it's usually
		1905	overkill :)
		1906
		1907	=head3 The special problem of time updates
		1908
		1909	Establishing the current time is a costly operation (it usually takes at
		1910	least two system calls): EV therefore updates its idea of the current
		1911	time only before and after C<ev_run> collects new events, which causes a
		1912	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1913	lots of events in one iteration.
778		1914
779	The relative timeouts are calculated relative to the C<ev_now ()>	1915	The relative timeouts are calculated relative to the C<ev_now ()>
780	time. This is usually the right thing as this timestamp refers to the time	1916	time. This is usually the right thing as this timestamp refers to the time
781	of the event triggering whatever timeout you are modifying/starting. If	1917	of the event triggering whatever timeout you are modifying/starting. If
782	you suspect event processing to be delayed and you I<need> to base the timeout	1918	you suspect event processing to be delayed and you I<need> to base the
783	on the current time, use something like this to adjust for this:	1919	timeout on the current time, use something like this to adjust for this:
784		1920
785	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1921	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
786		1922
787	The callback is guarenteed to be invoked only when its timeout has passed,	1923	If the event loop is suspended for a long time, you can also force an
788	but if multiple timers become ready during the same loop iteration then	1924	update of the time returned by C<ev_now ()> by calling C<ev_now_update
789	order of execution is undefined.	1925	()>.
		1926
		1927	=head3 The special problems of suspended animation
		1928
		1929	When you leave the server world it is quite customary to hit machines that
		1930	can suspend/hibernate - what happens to the clocks during such a suspend?
		1931
		1932	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1933	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1934	to run until the system is suspended, but they will not advance while the
		1935	system is suspended. That means, on resume, it will be as if the program
		1936	was frozen for a few seconds, but the suspend time will not be counted
		1937	towards C<ev_timer> when a monotonic clock source is used. The real time
		1938	clock advanced as expected, but if it is used as sole clocksource, then a
		1939	long suspend would be detected as a time jump by libev, and timers would
		1940	be adjusted accordingly.
		1941
		1942	I would not be surprised to see different behaviour in different between
		1943	operating systems, OS versions or even different hardware.
		1944
		1945	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1946	time jump in the monotonic clocks and the realtime clock. If the program
		1947	is suspended for a very long time, and monotonic clock sources are in use,
		1948	then you can expect C<ev_timer>s to expire as the full suspension time
		1949	will be counted towards the timers. When no monotonic clock source is in
		1950	use, then libev will again assume a timejump and adjust accordingly.
		1951
		1952	It might be beneficial for this latter case to call C<ev_suspend>
		1953	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1954	deterministic behaviour in this case (you can do nothing against
		1955	C<SIGSTOP>).
		1956
		1957	=head3 Watcher-Specific Functions and Data Members
790		1958
791	=over 4	1959	=over 4
792		1960
793	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1961	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
794		1962
795	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1963	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
796		1964
797	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1965	Configure the timer to trigger after C<after> seconds. If C<repeat>
798	C<0.>, then it will automatically be stopped. If it is positive, then the	1966	is C<0.>, then it will automatically be stopped once the timeout is
799	timer will automatically be configured to trigger again C<repeat> seconds	1967	reached. If it is positive, then the timer will automatically be
800	later, again, and again, until stopped manually.	1968	configured to trigger again C<repeat> seconds later, again, and again,
		1969	until stopped manually.
801		1970
802	The timer itself will do a best-effort at avoiding drift, that is, if you	1971	The timer itself will do a best-effort at avoiding drift, that is, if
803	configure a timer to trigger every 10 seconds, then it will trigger at	1972	you configure a timer to trigger every 10 seconds, then it will normally
804	exactly 10 second intervals. If, however, your program cannot keep up with	1973	trigger at exactly 10 second intervals. If, however, your program cannot
805	the timer (because it takes longer than those 10 seconds to do stuff) the	1974	keep up with the timer (because it takes longer than those 10 seconds to
806	timer will not fire more than once per event loop iteration.	1975	do stuff) the timer will not fire more than once per event loop iteration.
807		1976
808	=item ev_timer_again (loop)	1977	=item ev_timer_again (loop, ev_timer *)
809		1978
810	This will act as if the timer timed out and restart it again if it is	1979	This will act as if the timer timed out and restart it again if it is
811	repeating. The exact semantics are:	1980	repeating. The exact semantics are:
812		1981
		1982	If the timer is pending, its pending status is cleared.
		1983
813	If the timer is started but nonrepeating, stop it.	1984	If the timer is started but non-repeating, stop it (as if it timed out).
814		1985
815	If the timer is repeating, either start it if necessary (with the repeat	1986	If the timer is repeating, either start it if necessary (with the
816	value), or reset the running timer to the repeat value.	1987	C<repeat> value), or reset the running timer to the C<repeat> value.
817		1988
818	This sounds a bit complicated, but here is a useful and typical	1989	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
819	example: Imagine you have a tcp connection and you want a so-called idle	1990	usage example.
820	timeout, that is, you want to be called when there have been, say, 60	1991
821	seconds of inactivity on the socket. The easiest way to do this is to	1992	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
822	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1993
823	time you successfully read or write some data. If you go into an idle	1994	Returns the remaining time until a timer fires. If the timer is active,
824	state where you do not expect data to travel on the socket, you can stop	1995	then this time is relative to the current event loop time, otherwise it's
825	the timer, and again will automatically restart it if need be.	1996	the timeout value currently configured.
		1997
		1998	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1999	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2000	will return C<4>. When the timer expires and is restarted, it will return
		2001	roughly C<7> (likely slightly less as callback invocation takes some time,
		2002	too), and so on.
		2003
		2004	=item ev_tstamp repeat [read-write]
		2005
		2006	The current C<repeat> value. Will be used each time the watcher times out
		2007	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2008	which is also when any modifications are taken into account.
826		2009
827	=back	2010	=back
828		2011
		2012	=head3 Examples
		2013
829	Example: create a timer that fires after 60 seconds.	2014	Example: Create a timer that fires after 60 seconds.
830		2015
831	static void	2016	static void
832	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2017	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
833	{	2018	{
834	.. one minute over, w is actually stopped right here	2019	.. one minute over, w is actually stopped right here
835	}	2020	}
836		2021
837	struct ev_timer mytimer;	2022	ev_timer mytimer;
838	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2023	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
839	ev_timer_start (loop, &mytimer);	2024	ev_timer_start (loop, &mytimer);
840		2025
841	Example: create a timeout timer that times out after 10 seconds of	2026	Example: Create a timeout timer that times out after 10 seconds of
842	inactivity.	2027	inactivity.
843		2028
844	static void	2029	static void
845	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2030	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
846	{	2031	{
847	.. ten seconds without any activity	2032	.. ten seconds without any activity
848	}	2033	}
849		2034
850	struct ev_timer mytimer;	2035	ev_timer mytimer;
851	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2036	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
852	ev_timer_again (&mytimer); /* start timer */	2037	ev_timer_again (&mytimer); /* start timer */
853	ev_loop (loop, 0);	2038	ev_run (loop, 0);
854		2039
855	// and in some piece of code that gets executed on any "activity":	2040	// and in some piece of code that gets executed on any "activity":
856	// reset the timeout to start ticking again at 10 seconds	2041	// reset the timeout to start ticking again at 10 seconds
857	ev_timer_again (&mytimer);	2042	ev_timer_again (&mytimer);
858		2043
859		2044
860	=head2 C<ev_periodic> - to cron or not to cron?	2045	=head2 C<ev_periodic> - to cron or not to cron?
861		2046
862	Periodic watchers are also timers of a kind, but they are very versatile	2047	Periodic watchers are also timers of a kind, but they are very versatile
863	(and unfortunately a bit complex).	2048	(and unfortunately a bit complex).
864		2049
865	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2050	Unlike C<ev_timer>, periodic watchers are not based on real time (or
866	but on wallclock time (absolute time). You can tell a periodic watcher	2051	relative time, the physical time that passes) but on wall clock time
867	to trigger "at" some specific point in time. For example, if you tell a	2052	(absolute time, the thing you can read on your calender or clock). The
868	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2053	difference is that wall clock time can run faster or slower than real
869	+ 10.>) and then reset your system clock to the last year, then it will	2054	time, and time jumps are not uncommon (e.g. when you adjust your
870	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2055	wrist-watch).
871	roughly 10 seconds later and of course not if you reset your system time
872	again).
873		2056
874	They can also be used to implement vastly more complex timers, such as	2057	You can tell a periodic watcher to trigger after some specific point
		2058	in time: for example, if you tell a periodic watcher to trigger "in 10
		2059	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2060	not a delay) and then reset your system clock to January of the previous
		2061	year, then it will take a year or more to trigger the event (unlike an
		2062	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2063	it, as it uses a relative timeout).
		2064
		2065	C<ev_periodic> watchers can also be used to implement vastly more complex
875	triggering an event on eahc midnight, local time.	2066	timers, such as triggering an event on each "midnight, local time", or
		2067	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2068	those cannot react to time jumps.
876		2069
877	As with timers, the callback is guarenteed to be invoked only when the	2070	As with timers, the callback is guaranteed to be invoked only when the
878	time (C<at>) has been passed, but if multiple periodic timers become ready	2071	point in time where it is supposed to trigger has passed. If multiple
879	during the same loop iteration then order of execution is undefined.	2072	timers become ready during the same loop iteration then the ones with
		2073	earlier time-out values are invoked before ones with later time-out values
		2074	(but this is no longer true when a callback calls C<ev_run> recursively).
		2075
		2076	=head3 Watcher-Specific Functions and Data Members
880		2077
881	=over 4	2078	=over 4
882		2079
883	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2080	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
884		2081
885	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2082	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
886		2083
887	Lots of arguments, lets sort it out... There are basically three modes of	2084	Lots of arguments, let's sort it out... There are basically three modes of
888	operation, and we will explain them from simplest to complex:	2085	operation, and we will explain them from simplest to most complex:
889		2086
890	=over 4	2087	=over 4
891		2088
892	=item * absolute timer (interval = reschedule_cb = 0)	2089	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
893		2090
894	In this configuration the watcher triggers an event at the wallclock time	2091	In this configuration the watcher triggers an event after the wall clock
895	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2092	time C<offset> has passed. It will not repeat and will not adjust when a
896	that is, if it is to be run at January 1st 2011 then it will run when the	2093	time jump occurs, that is, if it is to be run at January 1st 2011 then it
897	system time reaches or surpasses this time.	2094	will be stopped and invoked when the system clock reaches or surpasses
		2095	this point in time.
898		2096
899	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2097	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
900		2098
901	In this mode the watcher will always be scheduled to time out at the next	2099	In this mode the watcher will always be scheduled to time out at the next
902	C<at + N * interval> time (for some integer N) and then repeat, regardless	2100	C<offset + N * interval> time (for some integer N, which can also be
903	of any time jumps.	2101	negative) and then repeat, regardless of any time jumps. The C<offset>
		2102	argument is merely an offset into the C<interval> periods.
904		2103
905	This can be used to create timers that do not drift with respect to system	2104	This can be used to create timers that do not drift with respect to the
906	time:	2105	system clock, for example, here is an C<ev_periodic> that triggers each
		2106	hour, on the hour (with respect to UTC):
907		2107
908	ev_periodic_set (&periodic, 0., 3600., 0);	2108	ev_periodic_set (&periodic, 0., 3600., 0);
909		2109
910	This doesn't mean there will always be 3600 seconds in between triggers,	2110	This doesn't mean there will always be 3600 seconds in between triggers,
911	but only that the the callback will be called when the system time shows a	2111	but only that the callback will be called when the system time shows a
912	full hour (UTC), or more correctly, when the system time is evenly divisible	2112	full hour (UTC), or more correctly, when the system time is evenly divisible
913	by 3600.	2113	by 3600.
914		2114
915	Another way to think about it (for the mathematically inclined) is that	2115	Another way to think about it (for the mathematically inclined) is that
916	C<ev_periodic> will try to run the callback in this mode at the next possible	2116	C<ev_periodic> will try to run the callback in this mode at the next possible
917	time where C<time = at (mod interval)>, regardless of any time jumps.	2117	time where C<time = offset (mod interval)>, regardless of any time jumps.
918		2118
		2119	For numerical stability it is preferable that the C<offset> value is near
		2120	C<ev_now ()> (the current time), but there is no range requirement for
		2121	this value, and in fact is often specified as zero.
		2122
		2123	Note also that there is an upper limit to how often a timer can fire (CPU
		2124	speed for example), so if C<interval> is very small then timing stability
		2125	will of course deteriorate. Libev itself tries to be exact to be about one
		2126	millisecond (if the OS supports it and the machine is fast enough).
		2127
919	=item * manual reschedule mode (reschedule_cb = callback)	2128	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
920		2129
921	In this mode the values for C<interval> and C<at> are both being	2130	In this mode the values for C<interval> and C<offset> are both being
922	ignored. Instead, each time the periodic watcher gets scheduled, the	2131	ignored. Instead, each time the periodic watcher gets scheduled, the
923	reschedule callback will be called with the watcher as first, and the	2132	reschedule callback will be called with the watcher as first, and the
924	current time as second argument.	2133	current time as second argument.
925		2134
926	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2135	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
927	ever, or make any event loop modifications>. If you need to stop it,	2136	or make ANY other event loop modifications whatsoever, unless explicitly
928	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2137	allowed by documentation here>.
929	starting a prepare watcher).
930		2138
		2139	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2140	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2141	only event loop modification you are allowed to do).
		2142
931	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2143	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
932	ev_tstamp now)>, e.g.:	2144	*w, ev_tstamp now)>, e.g.:
933		2145
		2146	static ev_tstamp
934	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2147	my_rescheduler (ev_periodic *w, ev_tstamp now)
935	{	2148	{
936	return now + 60.;	2149	return now + 60.;
937	}	2150	}
938		2151
939	It must return the next time to trigger, based on the passed time value	2152	It must return the next time to trigger, based on the passed time value
940	(that is, the lowest time value larger than to the second argument). It	2153	(that is, the lowest time value larger than to the second argument). It
941	will usually be called just before the callback will be triggered, but	2154	will usually be called just before the callback will be triggered, but
942	might be called at other times, too.	2155	might be called at other times, too.
943		2156
944	NOTE: I<< This callback must always return a time that is later than the	2157	NOTE: I<< This callback must always return a time that is higher than or
945	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2158	equal to the passed C<now> value >>.
946		2159
947	This can be used to create very complex timers, such as a timer that	2160	This can be used to create very complex timers, such as a timer that
948	triggers on each midnight, local time. To do this, you would calculate the	2161	triggers on "next midnight, local time". To do this, you would calculate the
949	next midnight after C<now> and return the timestamp value for this. How	2162	next midnight after C<now> and return the timestamp value for this. How
950	you do this is, again, up to you (but it is not trivial, which is the main	2163	you do this is, again, up to you (but it is not trivial, which is the main
951	reason I omitted it as an example).	2164	reason I omitted it as an example).
952		2165
953	=back	2166	=back
…		…
957	Simply stops and restarts the periodic watcher again. This is only useful	2170	Simply stops and restarts the periodic watcher again. This is only useful
958	when you changed some parameters or the reschedule callback would return	2171	when you changed some parameters or the reschedule callback would return
959	a different time than the last time it was called (e.g. in a crond like	2172	a different time than the last time it was called (e.g. in a crond like
960	program when the crontabs have changed).	2173	program when the crontabs have changed).
961		2174
		2175	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2176
		2177	When active, returns the absolute time that the watcher is supposed
		2178	to trigger next. This is not the same as the C<offset> argument to
		2179	C<ev_periodic_set>, but indeed works even in interval and manual
		2180	rescheduling modes.
		2181
		2182	=item ev_tstamp offset [read-write]
		2183
		2184	When repeating, this contains the offset value, otherwise this is the
		2185	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2186	although libev might modify this value for better numerical stability).
		2187
		2188	Can be modified any time, but changes only take effect when the periodic
		2189	timer fires or C<ev_periodic_again> is being called.
		2190
		2191	=item ev_tstamp interval [read-write]
		2192
		2193	The current interval value. Can be modified any time, but changes only
		2194	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2195	called.
		2196
		2197	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2198
		2199	The current reschedule callback, or C<0>, if this functionality is
		2200	switched off. Can be changed any time, but changes only take effect when
		2201	the periodic timer fires or C<ev_periodic_again> is being called.
		2202
962	=back	2203	=back
963		2204
		2205	=head3 Examples
		2206
964	Example: call a callback every hour, or, more precisely, whenever the	2207	Example: Call a callback every hour, or, more precisely, whenever the
965	system clock is divisible by 3600. The callback invocation times have	2208	system time is divisible by 3600. The callback invocation times have
966	potentially a lot of jittering, but good long-term stability.	2209	potentially a lot of jitter, but good long-term stability.
967		2210
968	static void	2211	static void
969	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2212	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
970	{	2213	{
971	... its now a full hour (UTC, or TAI or whatever your clock follows)	2214	... its now a full hour (UTC, or TAI or whatever your clock follows)
972	}	2215	}
973		2216
974	struct ev_periodic hourly_tick;	2217	ev_periodic hourly_tick;
975	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2218	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
976	ev_periodic_start (loop, &hourly_tick);	2219	ev_periodic_start (loop, &hourly_tick);
977		2220
978	Example: the same as above, but use a reschedule callback to do it:	2221	Example: The same as above, but use a reschedule callback to do it:
979		2222
980	#include <math.h>	2223	#include <math.h>
981		2224
982	static ev_tstamp	2225	static ev_tstamp
983	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2226	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
984	{	2227	{
985	return fmod (now, 3600.) + 3600.;	2228	return now + (3600. - fmod (now, 3600.));
986	}	2229	}
987		2230
988	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2231	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
989		2232
990	Example: call a callback every hour, starting now:	2233	Example: Call a callback every hour, starting now:
991		2234
992	struct ev_periodic hourly_tick;	2235	ev_periodic hourly_tick;
993	ev_periodic_init (&hourly_tick, clock_cb,	2236	ev_periodic_init (&hourly_tick, clock_cb,
994	fmod (ev_now (loop), 3600.), 3600., 0);	2237	fmod (ev_now (loop), 3600.), 3600., 0);
995	ev_periodic_start (loop, &hourly_tick);	2238	ev_periodic_start (loop, &hourly_tick);
996		2239
997		2240
998	=head2 C<ev_signal> - signal me when a signal gets signalled!	2241	=head2 C<ev_signal> - signal me when a signal gets signalled!
999		2242
1000	Signal watchers will trigger an event when the process receives a specific	2243	Signal watchers will trigger an event when the process receives a specific
1001	signal one or more times. Even though signals are very asynchronous, libev	2244	signal one or more times. Even though signals are very asynchronous, libev
1002	will try it's best to deliver signals synchronously, i.e. as part of the	2245	will try it's best to deliver signals synchronously, i.e. as part of the
1003	normal event processing, like any other event.	2246	normal event processing, like any other event.
1004		2247
		2248	If you want signals to be delivered truly asynchronously, just use
		2249	C<sigaction> as you would do without libev and forget about sharing
		2250	the signal. You can even use C<ev_async> from a signal handler to
		2251	synchronously wake up an event loop.
		2252
1005	You can configure as many watchers as you like per signal. Only when the	2253	You can configure as many watchers as you like for the same signal, but
		2254	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2255	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2256	C<SIGINT> in both the default loop and another loop at the same time. At
		2257	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2258
1006	first watcher gets started will libev actually register a signal watcher	2259	When the first watcher gets started will libev actually register something
1007	with the kernel (thus it coexists with your own signal handlers as long	2260	with the kernel (thus it coexists with your own signal handlers as long as
1008	as you don't register any with libev). Similarly, when the last signal	2261	you don't register any with libev for the same signal).
1009	watcher for a signal is stopped libev will reset the signal handler to	2262
1010	SIG_DFL (regardless of what it was set to before).	2263	If possible and supported, libev will install its handlers with
		2264	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2265	not be unduly interrupted. If you have a problem with system calls getting
		2266	interrupted by signals you can block all signals in an C<ev_check> watcher
		2267	and unblock them in an C<ev_prepare> watcher.
		2268
		2269	=head3 The special problem of inheritance over fork/execve/pthread_create
		2270
		2271	Both the signal mask (C<sigprocmask>) and the signal disposition
		2272	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2273	stopping it again), that is, libev might or might not block the signal,
		2274	and might or might not set or restore the installed signal handler.
		2275
		2276	While this does not matter for the signal disposition (libev never
		2277	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2278	C<execve>), this matters for the signal mask: many programs do not expect
		2279	certain signals to be blocked.
		2280
		2281	This means that before calling C<exec> (from the child) you should reset
		2282	the signal mask to whatever "default" you expect (all clear is a good
		2283	choice usually).
		2284
		2285	The simplest way to ensure that the signal mask is reset in the child is
		2286	to install a fork handler with C<pthread_atfork> that resets it. That will
		2287	catch fork calls done by libraries (such as the libc) as well.
		2288
		2289	In current versions of libev, the signal will not be blocked indefinitely
		2290	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2291	the window of opportunity for problems, it will not go away, as libev
		2292	I<has> to modify the signal mask, at least temporarily.
		2293
		2294	So I can't stress this enough: I<If you do not reset your signal mask when
		2295	you expect it to be empty, you have a race condition in your code>. This
		2296	is not a libev-specific thing, this is true for most event libraries.
		2297
		2298	=head3 Watcher-Specific Functions and Data Members
1011		2299
1012	=over 4	2300	=over 4
1013		2301
1014	=item ev_signal_init (ev_signal *, callback, int signum)	2302	=item ev_signal_init (ev_signal *, callback, int signum)
1015		2303
1016	=item ev_signal_set (ev_signal *, int signum)	2304	=item ev_signal_set (ev_signal *, int signum)
1017		2305
1018	Configures the watcher to trigger on the given signal number (usually one	2306	Configures the watcher to trigger on the given signal number (usually one
1019	of the C<SIGxxx> constants).	2307	of the C<SIGxxx> constants).
1020		2308
		2309	=item int signum [read-only]
		2310
		2311	The signal the watcher watches out for.
		2312
1021	=back	2313	=back
1022		2314
		2315	=head3 Examples
		2316
		2317	Example: Try to exit cleanly on SIGINT.
		2318
		2319	static void
		2320	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2321	{
		2322	ev_break (loop, EVBREAK_ALL);
		2323	}
		2324
		2325	ev_signal signal_watcher;
		2326	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2327	ev_signal_start (loop, &signal_watcher);
		2328
1023		2329
1024	=head2 C<ev_child> - watch out for process status changes	2330	=head2 C<ev_child> - watch out for process status changes
1025		2331
1026	Child watchers trigger when your process receives a SIGCHLD in response to	2332	Child watchers trigger when your process receives a SIGCHLD in response to
1027	some child status changes (most typically when a child of yours dies).	2333	some child status changes (most typically when a child of yours dies or
		2334	exits). It is permissible to install a child watcher I<after> the child
		2335	has been forked (which implies it might have already exited), as long
		2336	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2337	forking and then immediately registering a watcher for the child is fine,
		2338	but forking and registering a watcher a few event loop iterations later or
		2339	in the next callback invocation is not.
		2340
		2341	Only the default event loop is capable of handling signals, and therefore
		2342	you can only register child watchers in the default event loop.
		2343
		2344	Due to some design glitches inside libev, child watchers will always be
		2345	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2346	libev)
		2347
		2348	=head3 Process Interaction
		2349
		2350	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2351	initialised. This is necessary to guarantee proper behaviour even if the
		2352	first child watcher is started after the child exits. The occurrence
		2353	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2354	synchronously as part of the event loop processing. Libev always reaps all
		2355	children, even ones not watched.
		2356
		2357	=head3 Overriding the Built-In Processing
		2358
		2359	Libev offers no special support for overriding the built-in child
		2360	processing, but if your application collides with libev's default child
		2361	handler, you can override it easily by installing your own handler for
		2362	C<SIGCHLD> after initialising the default loop, and making sure the
		2363	default loop never gets destroyed. You are encouraged, however, to use an
		2364	event-based approach to child reaping and thus use libev's support for
		2365	that, so other libev users can use C<ev_child> watchers freely.
		2366
		2367	=head3 Stopping the Child Watcher
		2368
		2369	Currently, the child watcher never gets stopped, even when the
		2370	child terminates, so normally one needs to stop the watcher in the
		2371	callback. Future versions of libev might stop the watcher automatically
		2372	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2373	problem).
		2374
		2375	=head3 Watcher-Specific Functions and Data Members
1028		2376
1029	=over 4	2377	=over 4
1030		2378
1031	=item ev_child_init (ev_child *, callback, int pid)	2379	=item ev_child_init (ev_child *, callback, int pid, int trace)
1032		2380
1033	=item ev_child_set (ev_child *, int pid)	2381	=item ev_child_set (ev_child *, int pid, int trace)
1034		2382
1035	Configures the watcher to wait for status changes of process C<pid> (or	2383	Configures the watcher to wait for status changes of process C<pid> (or
1036	I<any> process if C<pid> is specified as C<0>). The callback can look	2384	I<any> process if C<pid> is specified as C<0>). The callback can look
1037	at the C<rstatus> member of the C<ev_child> watcher structure to see	2385	at the C<rstatus> member of the C<ev_child> watcher structure to see
1038	the status word (use the macros from C<sys/wait.h> and see your systems	2386	the status word (use the macros from C<sys/wait.h> and see your systems
1039	C<waitpid> documentation). The C<rpid> member contains the pid of the	2387	C<waitpid> documentation). The C<rpid> member contains the pid of the
1040	process causing the status change.	2388	process causing the status change. C<trace> must be either C<0> (only
		2389	activate the watcher when the process terminates) or C<1> (additionally
		2390	activate the watcher when the process is stopped or continued).
		2391
		2392	=item int pid [read-only]
		2393
		2394	The process id this watcher watches out for, or C<0>, meaning any process id.
		2395
		2396	=item int rpid [read-write]
		2397
		2398	The process id that detected a status change.
		2399
		2400	=item int rstatus [read-write]
		2401
		2402	The process exit/trace status caused by C<rpid> (see your systems
		2403	C<waitpid> and C<sys/wait.h> documentation for details).
1041		2404
1042	=back	2405	=back
1043		2406
1044	Example: try to exit cleanly on SIGINT and SIGTERM.	2407	=head3 Examples
1045		2408
		2409	Example: C<fork()> a new process and install a child handler to wait for
		2410	its completion.
		2411
		2412	ev_child cw;
		2413
1046	static void	2414	static void
1047	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2415	child_cb (EV_P_ ev_child *w, int revents)
1048	{	2416	{
1049	ev_unloop (loop, EVUNLOOP_ALL);	2417	ev_child_stop (EV_A_ w);
		2418	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1050	}	2419	}
1051		2420
1052	struct ev_signal signal_watcher;	2421	pid_t pid = fork ();
1053	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2422
1054	ev_signal_start (loop, &sigint_cb);	2423	if (pid < 0)
		2424	// error
		2425	else if (pid == 0)
		2426	{
		2427	// the forked child executes here
		2428	exit (1);
		2429	}
		2430	else
		2431	{
		2432	ev_child_init (&cw, child_cb, pid, 0);
		2433	ev_child_start (EV_DEFAULT_ &cw);
		2434	}
		2435
		2436
		2437	=head2 C<ev_stat> - did the file attributes just change?
		2438
		2439	This watches a file system path for attribute changes. That is, it calls
		2440	C<stat> on that path in regular intervals (or when the OS says it changed)
		2441	and sees if it changed compared to the last time, invoking the callback if
		2442	it did.
		2443
		2444	The path does not need to exist: changing from "path exists" to "path does
		2445	not exist" is a status change like any other. The condition "path does not
		2446	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2447	C<st_nlink> field being zero (which is otherwise always forced to be at
		2448	least one) and all the other fields of the stat buffer having unspecified
		2449	contents.
		2450
		2451	The path I<must not> end in a slash or contain special components such as
		2452	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2453	your working directory changes, then the behaviour is undefined.
		2454
		2455	Since there is no portable change notification interface available, the
		2456	portable implementation simply calls C<stat(2)> regularly on the path
		2457	to see if it changed somehow. You can specify a recommended polling
		2458	interval for this case. If you specify a polling interval of C<0> (highly
		2459	recommended!) then a I<suitable, unspecified default> value will be used
		2460	(which you can expect to be around five seconds, although this might
		2461	change dynamically). Libev will also impose a minimum interval which is
		2462	currently around C<0.1>, but that's usually overkill.
		2463
		2464	This watcher type is not meant for massive numbers of stat watchers,
		2465	as even with OS-supported change notifications, this can be
		2466	resource-intensive.
		2467
		2468	At the time of this writing, the only OS-specific interface implemented
		2469	is the Linux inotify interface (implementing kqueue support is left as an
		2470	exercise for the reader. Note, however, that the author sees no way of
		2471	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2472
		2473	=head3 ABI Issues (Largefile Support)
		2474
		2475	Libev by default (unless the user overrides this) uses the default
		2476	compilation environment, which means that on systems with large file
		2477	support disabled by default, you get the 32 bit version of the stat
		2478	structure. When using the library from programs that change the ABI to
		2479	use 64 bit file offsets the programs will fail. In that case you have to
		2480	compile libev with the same flags to get binary compatibility. This is
		2481	obviously the case with any flags that change the ABI, but the problem is
		2482	most noticeably displayed with ev_stat and large file support.
		2483
		2484	The solution for this is to lobby your distribution maker to make large
		2485	file interfaces available by default (as e.g. FreeBSD does) and not
		2486	optional. Libev cannot simply switch on large file support because it has
		2487	to exchange stat structures with application programs compiled using the
		2488	default compilation environment.
		2489
		2490	=head3 Inotify and Kqueue
		2491
		2492	When C<inotify (7)> support has been compiled into libev and present at
		2493	runtime, it will be used to speed up change detection where possible. The
		2494	inotify descriptor will be created lazily when the first C<ev_stat>
		2495	watcher is being started.
		2496
		2497	Inotify presence does not change the semantics of C<ev_stat> watchers
		2498	except that changes might be detected earlier, and in some cases, to avoid
		2499	making regular C<stat> calls. Even in the presence of inotify support
		2500	there are many cases where libev has to resort to regular C<stat> polling,
		2501	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2502	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2503	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2504	xfs are fully working) libev usually gets away without polling.
		2505
		2506	There is no support for kqueue, as apparently it cannot be used to
		2507	implement this functionality, due to the requirement of having a file
		2508	descriptor open on the object at all times, and detecting renames, unlinks
		2509	etc. is difficult.
		2510
		2511	=head3 C<stat ()> is a synchronous operation
		2512
		2513	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2514	the process. The exception are C<ev_stat> watchers - those call C<stat
		2515	()>, which is a synchronous operation.
		2516
		2517	For local paths, this usually doesn't matter: unless the system is very
		2518	busy or the intervals between stat's are large, a stat call will be fast,
		2519	as the path data is usually in memory already (except when starting the
		2520	watcher).
		2521
		2522	For networked file systems, calling C<stat ()> can block an indefinite
		2523	time due to network issues, and even under good conditions, a stat call
		2524	often takes multiple milliseconds.
		2525
		2526	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2527	paths, although this is fully supported by libev.
		2528
		2529	=head3 The special problem of stat time resolution
		2530
		2531	The C<stat ()> system call only supports full-second resolution portably,
		2532	and even on systems where the resolution is higher, most file systems
		2533	still only support whole seconds.
		2534
		2535	That means that, if the time is the only thing that changes, you can
		2536	easily miss updates: on the first update, C<ev_stat> detects a change and
		2537	calls your callback, which does something. When there is another update
		2538	within the same second, C<ev_stat> will be unable to detect unless the
		2539	stat data does change in other ways (e.g. file size).
		2540
		2541	The solution to this is to delay acting on a change for slightly more
		2542	than a second (or till slightly after the next full second boundary), using
		2543	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2544	ev_timer_again (loop, w)>).
		2545
		2546	The C<.02> offset is added to work around small timing inconsistencies
		2547	of some operating systems (where the second counter of the current time
		2548	might be be delayed. One such system is the Linux kernel, where a call to
		2549	C<gettimeofday> might return a timestamp with a full second later than
		2550	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2551	update file times then there will be a small window where the kernel uses
		2552	the previous second to update file times but libev might already execute
		2553	the timer callback).
		2554
		2555	=head3 Watcher-Specific Functions and Data Members
		2556
		2557	=over 4
		2558
		2559	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2560
		2561	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2562
		2563	Configures the watcher to wait for status changes of the given
		2564	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2565	be detected and should normally be specified as C<0> to let libev choose
		2566	a suitable value. The memory pointed to by C<path> must point to the same
		2567	path for as long as the watcher is active.
		2568
		2569	The callback will receive an C<EV_STAT> event when a change was detected,
		2570	relative to the attributes at the time the watcher was started (or the
		2571	last change was detected).
		2572
		2573	=item ev_stat_stat (loop, ev_stat *)
		2574
		2575	Updates the stat buffer immediately with new values. If you change the
		2576	watched path in your callback, you could call this function to avoid
		2577	detecting this change (while introducing a race condition if you are not
		2578	the only one changing the path). Can also be useful simply to find out the
		2579	new values.
		2580
		2581	=item ev_statdata attr [read-only]
		2582
		2583	The most-recently detected attributes of the file. Although the type is
		2584	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2585	suitable for your system, but you can only rely on the POSIX-standardised
		2586	members to be present. If the C<st_nlink> member is C<0>, then there was
		2587	some error while C<stat>ing the file.
		2588
		2589	=item ev_statdata prev [read-only]
		2590
		2591	The previous attributes of the file. The callback gets invoked whenever
		2592	C<prev> != C<attr>, or, more precisely, one or more of these members
		2593	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2594	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2595
		2596	=item ev_tstamp interval [read-only]
		2597
		2598	The specified interval.
		2599
		2600	=item const char *path [read-only]
		2601
		2602	The file system path that is being watched.
		2603
		2604	=back
		2605
		2606	=head3 Examples
		2607
		2608	Example: Watch C</etc/passwd> for attribute changes.
		2609
		2610	static void
		2611	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2612	{
		2613	/* /etc/passwd changed in some way */
		2614	if (w->attr.st_nlink)
		2615	{
		2616	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2617	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2618	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2619	}
		2620	else
		2621	/* you shalt not abuse printf for puts */
		2622	puts ("wow, /etc/passwd is not there, expect problems. "
		2623	"if this is windows, they already arrived\n");
		2624	}
		2625
		2626	...
		2627	ev_stat passwd;
		2628
		2629	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2630	ev_stat_start (loop, &passwd);
		2631
		2632	Example: Like above, but additionally use a one-second delay so we do not
		2633	miss updates (however, frequent updates will delay processing, too, so
		2634	one might do the work both on C<ev_stat> callback invocation I<and> on
		2635	C<ev_timer> callback invocation).
		2636
		2637	static ev_stat passwd;
		2638	static ev_timer timer;
		2639
		2640	static void
		2641	timer_cb (EV_P_ ev_timer *w, int revents)
		2642	{
		2643	ev_timer_stop (EV_A_ w);
		2644
		2645	/* now it's one second after the most recent passwd change */
		2646	}
		2647
		2648	static void
		2649	stat_cb (EV_P_ ev_stat *w, int revents)
		2650	{
		2651	/* reset the one-second timer */
		2652	ev_timer_again (EV_A_ &timer);
		2653	}
		2654
		2655	...
		2656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2657	ev_stat_start (loop, &passwd);
		2658	ev_timer_init (&timer, timer_cb, 0., 1.02);
1055		2659
1056		2660
1057	=head2 C<ev_idle> - when you've got nothing better to do...	2661	=head2 C<ev_idle> - when you've got nothing better to do...
1058		2662
1059	Idle watchers trigger events when there are no other events are pending	2663	Idle watchers trigger events when no other events of the same or higher
1060	(prepare, check and other idle watchers do not count). That is, as long	2664	priority are pending (prepare, check and other idle watchers do not count
1061	as your process is busy handling sockets or timeouts (or even signals,	2665	as receiving "events").
1062	imagine) it will not be triggered. But when your process is idle all idle	2666
1063	watchers are being called again and again, once per event loop iteration -	2667	That is, as long as your process is busy handling sockets or timeouts
		2668	(or even signals, imagine) of the same or higher priority it will not be
		2669	triggered. But when your process is idle (or only lower-priority watchers
		2670	are pending), the idle watchers are being called once per event loop
1064	until stopped, that is, or your process receives more events and becomes	2671	iteration - until stopped, that is, or your process receives more events
1065	busy.	2672	and becomes busy again with higher priority stuff.
1066		2673
1067	The most noteworthy effect is that as long as any idle watchers are	2674	The most noteworthy effect is that as long as any idle watchers are
1068	active, the process will not block when waiting for new events.	2675	active, the process will not block when waiting for new events.
1069		2676
1070	Apart from keeping your process non-blocking (which is a useful	2677	Apart from keeping your process non-blocking (which is a useful
1071	effect on its own sometimes), idle watchers are a good place to do	2678	effect on its own sometimes), idle watchers are a good place to do
1072	"pseudo-background processing", or delay processing stuff to after the	2679	"pseudo-background processing", or delay processing stuff to after the
1073	event loop has handled all outstanding events.	2680	event loop has handled all outstanding events.
1074		2681
		2682	=head3 Watcher-Specific Functions and Data Members
		2683
1075	=over 4	2684	=over 4
1076		2685
1077	=item ev_idle_init (ev_signal *, callback)	2686	=item ev_idle_init (ev_idle *, callback)
1078		2687
1079	Initialises and configures the idle watcher - it has no parameters of any	2688	Initialises and configures the idle watcher - it has no parameters of any
1080	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2689	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1081	believe me.	2690	believe me.
1082		2691
1083	=back	2692	=back
1084		2693
		2694	=head3 Examples
		2695
1085	Example: dynamically allocate an C<ev_idle>, start it, and in the	2696	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1086	callback, free it. Alos, use no error checking, as usual.	2697	callback, free it. Also, use no error checking, as usual.
1087		2698
1088	static void	2699	static void
1089	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2700	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1090	{	2701	{
1091	free (w);	2702	free (w);
1092	// now do something you wanted to do when the program has	2703	// now do something you wanted to do when the program has
1093	// no longer asnything immediate to do.	2704	// no longer anything immediate to do.
1094	}	2705	}
1095		2706
1096	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2707	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1097	ev_idle_init (idle_watcher, idle_cb);	2708	ev_idle_init (idle_watcher, idle_cb);
1098	ev_idle_start (loop, idle_cb);	2709	ev_idle_start (loop, idle_watcher);
1099		2710
1100		2711
1101	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1102		2713
1103	Prepare and check watchers are usually (but not always) used in tandem:	2714	Prepare and check watchers are usually (but not always) used in pairs:
1104	prepare watchers get invoked before the process blocks and check watchers	2715	prepare watchers get invoked before the process blocks and check watchers
1105	afterwards.	2716	afterwards.
1106		2717
1107	You I<must not> call C<ev_loop> or similar functions that enter	2718	You I<must not> call C<ev_run> or similar functions that enter
1108	the current event loop from either C<ev_prepare> or C<ev_check>	2719	the current event loop from either C<ev_prepare> or C<ev_check>
1109	watchers. Other loops than the current one are fine, however. The	2720	watchers. Other loops than the current one are fine, however. The
1110	rationale behind this is that you do not need to check for recursion in	2721	rationale behind this is that you do not need to check for recursion in
1111	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1112	C<ev_check> so if you have one watcher of each kind they will always be	2723	C<ev_check> so if you have one watcher of each kind they will always be
1113	called in pairs bracketing the blocking call.	2724	called in pairs bracketing the blocking call.
1114		2725
1115	Their main purpose is to integrate other event mechanisms into libev and	2726	Their main purpose is to integrate other event mechanisms into libev and
1116	their use is somewhat advanced. This could be used, for example, to track	2727	their use is somewhat advanced. They could be used, for example, to track
1117	variable changes, implement your own watchers, integrate net-snmp or a	2728	variable changes, implement your own watchers, integrate net-snmp or a
1118	coroutine library and lots more. They are also occasionally useful if	2729	coroutine library and lots more. They are also occasionally useful if
1119	you cache some data and want to flush it before blocking (for example,	2730	you cache some data and want to flush it before blocking (for example,
1120	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2731	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1121	watcher).	2732	watcher).
1122		2733
1123	This is done by examining in each prepare call which file descriptors need	2734	This is done by examining in each prepare call which file descriptors
1124	to be watched by the other library, registering C<ev_io> watchers for	2735	need to be watched by the other library, registering C<ev_io> watchers
1125	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2736	for them and starting an C<ev_timer> watcher for any timeouts (many
1126	provide just this functionality). Then, in the check watcher you check for	2737	libraries provide exactly this functionality). Then, in the check watcher,
1127	any events that occured (by checking the pending status of all watchers	2738	you check for any events that occurred (by checking the pending status
1128	and stopping them) and call back into the library. The I/O and timer	2739	of all watchers and stopping them) and call back into the library. The
1129	callbacks will never actually be called (but must be valid nevertheless,	2740	I/O and timer callbacks will never actually be called (but must be valid
1130	because you never know, you know?).	2741	nevertheless, because you never know, you know?).
1131		2742
1132	As another example, the Perl Coro module uses these hooks to integrate	2743	As another example, the Perl Coro module uses these hooks to integrate
1133	coroutines into libev programs, by yielding to other active coroutines	2744	coroutines into libev programs, by yielding to other active coroutines
1134	during each prepare and only letting the process block if no coroutines	2745	during each prepare and only letting the process block if no coroutines
1135	are ready to run (it's actually more complicated: it only runs coroutines	2746	are ready to run (it's actually more complicated: it only runs coroutines
1136	with priority higher than or equal to the event loop and one coroutine	2747	with priority higher than or equal to the event loop and one coroutine
1137	of lower priority, but only once, using idle watchers to keep the event	2748	of lower priority, but only once, using idle watchers to keep the event
1138	loop from blocking if lower-priority coroutines are active, thus mapping	2749	loop from blocking if lower-priority coroutines are active, thus mapping
1139	low-priority coroutines to idle/background tasks).	2750	low-priority coroutines to idle/background tasks).
1140		2751
		2752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2753	priority, to ensure that they are being run before any other watchers
		2754	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2755
		2756	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2757	activate ("feed") events into libev. While libev fully supports this, they
		2758	might get executed before other C<ev_check> watchers did their job. As
		2759	C<ev_check> watchers are often used to embed other (non-libev) event
		2760	loops those other event loops might be in an unusable state until their
		2761	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2762	others).
		2763
		2764	=head3 Watcher-Specific Functions and Data Members
		2765
1141	=over 4	2766	=over 4
1142		2767
1143	=item ev_prepare_init (ev_prepare *, callback)	2768	=item ev_prepare_init (ev_prepare *, callback)
1144		2769
1145	=item ev_check_init (ev_check *, callback)	2770	=item ev_check_init (ev_check *, callback)
1146		2771
1147	Initialises and configures the prepare or check watcher - they have no	2772	Initialises and configures the prepare or check watcher - they have no
1148	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2773	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1149	macros, but using them is utterly, utterly and completely pointless.	2774	macros, but using them is utterly, utterly, utterly and completely
		2775	pointless.
1150		2776
1151	=back	2777	=back
1152		2778
1153	Example: To include a library such as adns, you would add IO watchers	2779	=head3 Examples
1154	and a timeout watcher in a prepare handler, as required by libadns, and	2780
		2781	There are a number of principal ways to embed other event loops or modules
		2782	into libev. Here are some ideas on how to include libadns into libev
		2783	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2784	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2785	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2786	Glib event loop).
		2787
		2788	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1155	in a check watcher, destroy them and call into libadns. What follows is	2789	and in a check watcher, destroy them and call into libadns. What follows
1156	pseudo-code only of course:	2790	is pseudo-code only of course. This requires you to either use a low
		2791	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2792	the callbacks for the IO/timeout watchers might not have been called yet.
1157		2793
1158	static ev_io iow [nfd];	2794	static ev_io iow [nfd];
1159	static ev_timer tw;	2795	static ev_timer tw;
1160		2796
1161	static void	2797	static void
1162	io_cb (ev_loop *loop, ev_io *w, int revents)	2798	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1163	{	2799	{
1164	// set the relevant poll flags
1165	// could also call adns_processreadable etc. here
1166	struct pollfd *fd = (struct pollfd *)w->data;
1167	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1168	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1169	}	2800	}
1170		2801
1171	// create io watchers for each fd and a timer before blocking	2802	// create io watchers for each fd and a timer before blocking
1172	static void	2803	static void
1173	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2804	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1174	{	2805	{
1175	int timeout = 3600000;truct pollfd fds [nfd];	2806	int timeout = 3600000;
		2807	struct pollfd fds [nfd];
1176	// actual code will need to loop here and realloc etc.	2808	// actual code will need to loop here and realloc etc.
1177	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2809	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1178		2810
1179	/* the callback is illegal, but won't be called as we stop during check */	2811	/* the callback is illegal, but won't be called as we stop during check */
1180	ev_timer_init (&tw, 0, timeout * 1e-3);	2812	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1181	ev_timer_start (loop, &tw);	2813	ev_timer_start (loop, &tw);
1182		2814
1183	// create on ev_io per pollfd	2815	// create one ev_io per pollfd
1184	for (int i = 0; i < nfd; ++i)	2816	for (int i = 0; i < nfd; ++i)
1185	{	2817	{
1186	ev_io_init (iow + i, io_cb, fds [i].fd,	2818	ev_io_init (iow + i, io_cb, fds [i].fd,
1187	((fds [i].events & POLLIN ? EV_READ : 0)	2819	((fds [i].events & POLLIN ? EV_READ : 0)
1188	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2820	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1189		2821
1190	fds [i].revents = 0;	2822	fds [i].revents = 0;
1191	iow [i].data = fds + i;
1192	ev_io_start (loop, iow + i);	2823	ev_io_start (loop, iow + i);
1193	}	2824	}
1194	}	2825	}
1195		2826
1196	// stop all watchers after blocking	2827	// stop all watchers after blocking
1197	static void	2828	static void
1198	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2829	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1199	{	2830	{
1200	ev_timer_stop (loop, &tw);	2831	ev_timer_stop (loop, &tw);
1201		2832
1202	for (int i = 0; i < nfd; ++i)	2833	for (int i = 0; i < nfd; ++i)
		2834	{
		2835	// set the relevant poll flags
		2836	// could also call adns_processreadable etc. here
		2837	struct pollfd *fd = fds + i;
		2838	int revents = ev_clear_pending (iow + i);
		2839	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2840	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2841
		2842	// now stop the watcher
1203	ev_io_stop (loop, iow + i);	2843	ev_io_stop (loop, iow + i);
		2844	}
1204		2845
1205	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2846	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1206	}	2847	}
		2848
		2849	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2850	in the prepare watcher and would dispose of the check watcher.
		2851
		2852	Method 3: If the module to be embedded supports explicit event
		2853	notification (libadns does), you can also make use of the actual watcher
		2854	callbacks, and only destroy/create the watchers in the prepare watcher.
		2855
		2856	static void
		2857	timer_cb (EV_P_ ev_timer *w, int revents)
		2858	{
		2859	adns_state ads = (adns_state)w->data;
		2860	update_now (EV_A);
		2861
		2862	adns_processtimeouts (ads, &tv_now);
		2863	}
		2864
		2865	static void
		2866	io_cb (EV_P_ ev_io *w, int revents)
		2867	{
		2868	adns_state ads = (adns_state)w->data;
		2869	update_now (EV_A);
		2870
		2871	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2872	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2873	}
		2874
		2875	// do not ever call adns_afterpoll
		2876
		2877	Method 4: Do not use a prepare or check watcher because the module you
		2878	want to embed is not flexible enough to support it. Instead, you can
		2879	override their poll function. The drawback with this solution is that the
		2880	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2881	this approach, effectively embedding EV as a client into the horrible
		2882	libglib event loop.
		2883
		2884	static gint
		2885	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2886	{
		2887	int got_events = 0;
		2888
		2889	for (n = 0; n < nfds; ++n)
		2890	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2891
		2892	if (timeout >= 0)
		2893	// create/start timer
		2894
		2895	// poll
		2896	ev_run (EV_A_ 0);
		2897
		2898	// stop timer again
		2899	if (timeout >= 0)
		2900	ev_timer_stop (EV_A_ &to);
		2901
		2902	// stop io watchers again - their callbacks should have set
		2903	for (n = 0; n < nfds; ++n)
		2904	ev_io_stop (EV_A_ iow [n]);
		2905
		2906	return got_events;
		2907	}
1207		2908
1208		2909
1209	=head2 C<ev_embed> - when one backend isn't enough...	2910	=head2 C<ev_embed> - when one backend isn't enough...
1210		2911
1211	This is a rather advanced watcher type that lets you embed one event loop	2912	This is a rather advanced watcher type that lets you embed one event loop
…		…
1217	prioritise I/O.	2918	prioritise I/O.
1218		2919
1219	As an example for a bug workaround, the kqueue backend might only support	2920	As an example for a bug workaround, the kqueue backend might only support
1220	sockets on some platform, so it is unusable as generic backend, but you	2921	sockets on some platform, so it is unusable as generic backend, but you
1221	still want to make use of it because you have many sockets and it scales	2922	still want to make use of it because you have many sockets and it scales
1222	so nicely. In this case, you would create a kqueue-based loop and embed it	2923	so nicely. In this case, you would create a kqueue-based loop and embed
1223	into your default loop (which might use e.g. poll). Overall operation will	2924	it into your default loop (which might use e.g. poll). Overall operation
1224	be a bit slower because first libev has to poll and then call kevent, but	2925	will be a bit slower because first libev has to call C<poll> and then
1225	at least you can use both at what they are best.	2926	C<kevent>, but at least you can use both mechanisms for what they are
		2927	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1226		2928
1227	As for prioritising I/O: rarely you have the case where some fds have	2929	As for prioritising I/O: under rare circumstances you have the case where
1228	to be watched and handled very quickly (with low latency), and even	2930	some fds have to be watched and handled very quickly (with low latency),
1229	priorities and idle watchers might have too much overhead. In this case	2931	and even priorities and idle watchers might have too much overhead. In
1230	you would put all the high priority stuff in one loop and all the rest in	2932	this case you would put all the high priority stuff in one loop and all
1231	a second one, and embed the second one in the first.	2933	the rest in a second one, and embed the second one in the first.
1232		2934
1233	As long as the watcher is active, the callback will be invoked every time	2935	As long as the watcher is active, the callback will be invoked every
1234	there might be events pending in the embedded loop. The callback must then	2936	time there might be events pending in the embedded loop. The callback
1235	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2937	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1236	their callbacks (you could also start an idle watcher to give the embedded	2938	sweep and invoke their callbacks (the callback doesn't need to invoke the
1237	loop strictly lower priority for example). You can also set the callback	2939	C<ev_embed_sweep> function directly, it could also start an idle watcher
1238	to C<0>, in which case the embed watcher will automatically execute the	2940	to give the embedded loop strictly lower priority for example).
1239	embedded loop sweep.
1240		2941
1241	As long as the watcher is started it will automatically handle events. The	2942	You can also set the callback to C<0>, in which case the embed watcher
1242	callback will be invoked whenever some events have been handled. You can	2943	will automatically execute the embedded loop sweep whenever necessary.
1243	set the callback to C<0> to avoid having to specify one if you are not
1244	interested in that.
1245		2944
1246	Also, there have not currently been made special provisions for forking:	2945	Fork detection will be handled transparently while the C<ev_embed> watcher
1247	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2946	is active, i.e., the embedded loop will automatically be forked when the
1248	but you will also have to stop and restart any C<ev_embed> watchers	2947	embedding loop forks. In other cases, the user is responsible for calling
1249	yourself.	2948	C<ev_loop_fork> on the embedded loop.
1250		2949
1251	Unfortunately, not all backends are embeddable, only the ones returned by	2950	Unfortunately, not all backends are embeddable: only the ones returned by
1252	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2951	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1253	portable one.	2952	portable one.
1254		2953
1255	So when you want to use this feature you will always have to be prepared	2954	So when you want to use this feature you will always have to be prepared
1256	that you cannot get an embeddable loop. The recommended way to get around	2955	that you cannot get an embeddable loop. The recommended way to get around
1257	this is to have a separate variables for your embeddable loop, try to	2956	this is to have a separate variables for your embeddable loop, try to
1258	create it, and if that fails, use the normal loop for everything:	2957	create it, and if that fails, use the normal loop for everything.
1259		2958
1260	struct ev_loop *loop_hi = ev_default_init (0);	2959	=head3 C<ev_embed> and fork
1261	struct ev_loop *loop_lo = 0;
1262	struct ev_embed embed;
1263
1264	// see if there is a chance of getting one that works
1265	// (remember that a flags value of 0 means autodetection)
1266	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1267	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1268	: 0;
1269		2960
1270	// if we got one, then embed it, otherwise default to loop_hi	2961	While the C<ev_embed> watcher is running, forks in the embedding loop will
1271	if (loop_lo)	2962	automatically be applied to the embedded loop as well, so no special
1272	{	2963	fork handling is required in that case. When the watcher is not running,
1273	ev_embed_init (&embed, 0, loop_lo);	2964	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1274	ev_embed_start (loop_hi, &embed);	2965	as applicable.
1275	}	2966
1276	else	2967	=head3 Watcher-Specific Functions and Data Members
1277	loop_lo = loop_hi;
1278		2968
1279	=over 4	2969	=over 4
1280		2970
1281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2971	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1282		2972
…		…
1284		2974
1285	Configures the watcher to embed the given loop, which must be	2975	Configures the watcher to embed the given loop, which must be
1286	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2976	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1287	invoked automatically, otherwise it is the responsibility of the callback	2977	invoked automatically, otherwise it is the responsibility of the callback
1288	to invoke it (it will continue to be called until the sweep has been done,	2978	to invoke it (it will continue to be called until the sweep has been done,
1289	if you do not want thta, you need to temporarily stop the embed watcher).	2979	if you do not want that, you need to temporarily stop the embed watcher).
1290		2980
1291	=item ev_embed_sweep (loop, ev_embed *)	2981	=item ev_embed_sweep (loop, ev_embed *)
1292		2982
1293	Make a single, non-blocking sweep over the embedded loop. This works	2983	Make a single, non-blocking sweep over the embedded loop. This works
1294	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2984	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1295	apropriate way for embedded loops.	2985	appropriate way for embedded loops.
		2986
		2987	=item struct ev_loop *other [read-only]
		2988
		2989	The embedded event loop.
1296		2990
1297	=back	2991	=back
1298		2992
		2993	=head3 Examples
		2994
		2995	Example: Try to get an embeddable event loop and embed it into the default
		2996	event loop. If that is not possible, use the default loop. The default
		2997	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2998	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2999	used).
		3000
		3001	struct ev_loop *loop_hi = ev_default_init (0);
		3002	struct ev_loop *loop_lo = 0;
		3003	ev_embed embed;
		3004
		3005	// see if there is a chance of getting one that works
		3006	// (remember that a flags value of 0 means autodetection)
		3007	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3008	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3009	: 0;
		3010
		3011	// if we got one, then embed it, otherwise default to loop_hi
		3012	if (loop_lo)
		3013	{
		3014	ev_embed_init (&embed, 0, loop_lo);
		3015	ev_embed_start (loop_hi, &embed);
		3016	}
		3017	else
		3018	loop_lo = loop_hi;
		3019
		3020	Example: Check if kqueue is available but not recommended and create
		3021	a kqueue backend for use with sockets (which usually work with any
		3022	kqueue implementation). Store the kqueue/socket-only event loop in
		3023	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3024
		3025	struct ev_loop *loop = ev_default_init (0);
		3026	struct ev_loop *loop_socket = 0;
		3027	ev_embed embed;
		3028
		3029	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3030	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3031	{
		3032	ev_embed_init (&embed, 0, loop_socket);
		3033	ev_embed_start (loop, &embed);
		3034	}
		3035
		3036	if (!loop_socket)
		3037	loop_socket = loop;
		3038
		3039	// now use loop_socket for all sockets, and loop for everything else
		3040
		3041
		3042	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3043
		3044	Fork watchers are called when a C<fork ()> was detected (usually because
		3045	whoever is a good citizen cared to tell libev about it by calling
		3046	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3047	event loop blocks next and before C<ev_check> watchers are being called,
		3048	and only in the child after the fork. If whoever good citizen calling
		3049	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3050	handlers will be invoked, too, of course.
		3051
		3052	=head3 The special problem of life after fork - how is it possible?
		3053
		3054	Most uses of C<fork()> consist of forking, then some simple calls to set
		3055	up/change the process environment, followed by a call to C<exec()>. This
		3056	sequence should be handled by libev without any problems.
		3057
		3058	This changes when the application actually wants to do event handling
		3059	in the child, or both parent in child, in effect "continuing" after the
		3060	fork.
		3061
		3062	The default mode of operation (for libev, with application help to detect
		3063	forks) is to duplicate all the state in the child, as would be expected
		3064	when I<either> the parent I<or> the child process continues.
		3065
		3066	When both processes want to continue using libev, then this is usually the
		3067	wrong result. In that case, usually one process (typically the parent) is
		3068	supposed to continue with all watchers in place as before, while the other
		3069	process typically wants to start fresh, i.e. without any active watchers.
		3070
		3071	The cleanest and most efficient way to achieve that with libev is to
		3072	simply create a new event loop, which of course will be "empty", and
		3073	use that for new watchers. This has the advantage of not touching more
		3074	memory than necessary, and thus avoiding the copy-on-write, and the
		3075	disadvantage of having to use multiple event loops (which do not support
		3076	signal watchers).
		3077
		3078	When this is not possible, or you want to use the default loop for
		3079	other reasons, then in the process that wants to start "fresh", call
		3080	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		3081	the default loop will "orphan" (not stop) all registered watchers, so you
		3082	have to be careful not to execute code that modifies those watchers. Note
		3083	also that in that case, you have to re-register any signal watchers.
		3084
		3085	=head3 Watcher-Specific Functions and Data Members
		3086
		3087	=over 4
		3088
		3089	=item ev_fork_init (ev_signal *, callback)
		3090
		3091	Initialises and configures the fork watcher - it has no parameters of any
		3092	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3093	believe me.
		3094
		3095	=back
		3096
		3097
		3098	=head2 C<ev_async> - how to wake up an event loop
		3099
		3100	In general, you cannot use an C<ev_run> from multiple threads or other
		3101	asynchronous sources such as signal handlers (as opposed to multiple event
		3102	loops - those are of course safe to use in different threads).
		3103
		3104	Sometimes, however, you need to wake up an event loop you do not control,
		3105	for example because it belongs to another thread. This is what C<ev_async>
		3106	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3107	it by calling C<ev_async_send>, which is thread- and signal safe.
		3108
		3109	This functionality is very similar to C<ev_signal> watchers, as signals,
		3110	too, are asynchronous in nature, and signals, too, will be compressed
		3111	(i.e. the number of callback invocations may be less than the number of
		3112	C<ev_async_sent> calls).
		3113
		3114	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3115	just the default loop.
		3116
		3117	=head3 Queueing
		3118
		3119	C<ev_async> does not support queueing of data in any way. The reason
		3120	is that the author does not know of a simple (or any) algorithm for a
		3121	multiple-writer-single-reader queue that works in all cases and doesn't
		3122	need elaborate support such as pthreads or unportable memory access
		3123	semantics.
		3124
		3125	That means that if you want to queue data, you have to provide your own
		3126	queue. But at least I can tell you how to implement locking around your
		3127	queue:
		3128
		3129	=over 4
		3130
		3131	=item queueing from a signal handler context
		3132
		3133	To implement race-free queueing, you simply add to the queue in the signal
		3134	handler but you block the signal handler in the watcher callback. Here is
		3135	an example that does that for some fictitious SIGUSR1 handler:
		3136
		3137	static ev_async mysig;
		3138
		3139	static void
		3140	sigusr1_handler (void)
		3141	{
		3142	sometype data;
		3143
		3144	// no locking etc.
		3145	queue_put (data);
		3146	ev_async_send (EV_DEFAULT_ &mysig);
		3147	}
		3148
		3149	static void
		3150	mysig_cb (EV_P_ ev_async *w, int revents)
		3151	{
		3152	sometype data;
		3153	sigset_t block, prev;
		3154
		3155	sigemptyset (&block);
		3156	sigaddset (&block, SIGUSR1);
		3157	sigprocmask (SIG_BLOCK, &block, &prev);
		3158
		3159	while (queue_get (&data))
		3160	process (data);
		3161
		3162	if (sigismember (&prev, SIGUSR1)
		3163	sigprocmask (SIG_UNBLOCK, &block, 0);
		3164	}
		3165
		3166	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3167	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3168	either...).
		3169
		3170	=item queueing from a thread context
		3171
		3172	The strategy for threads is different, as you cannot (easily) block
		3173	threads but you can easily preempt them, so to queue safely you need to
		3174	employ a traditional mutex lock, such as in this pthread example:
		3175
		3176	static ev_async mysig;
		3177	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3178
		3179	static void
		3180	otherthread (void)
		3181	{
		3182	// only need to lock the actual queueing operation
		3183	pthread_mutex_lock (&mymutex);
		3184	queue_put (data);
		3185	pthread_mutex_unlock (&mymutex);
		3186
		3187	ev_async_send (EV_DEFAULT_ &mysig);
		3188	}
		3189
		3190	static void
		3191	mysig_cb (EV_P_ ev_async *w, int revents)
		3192	{
		3193	pthread_mutex_lock (&mymutex);
		3194
		3195	while (queue_get (&data))
		3196	process (data);
		3197
		3198	pthread_mutex_unlock (&mymutex);
		3199	}
		3200
		3201	=back
		3202
		3203
		3204	=head3 Watcher-Specific Functions and Data Members
		3205
		3206	=over 4
		3207
		3208	=item ev_async_init (ev_async *, callback)
		3209
		3210	Initialises and configures the async watcher - it has no parameters of any
		3211	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3212	trust me.
		3213
		3214	=item ev_async_send (loop, ev_async *)
		3215
		3216	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3217	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3218	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3219	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3220	section below on what exactly this means).
		3221
		3222	Note that, as with other watchers in libev, multiple events might get
		3223	compressed into a single callback invocation (another way to look at this
		3224	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3225	reset when the event loop detects that).
		3226
		3227	This call incurs the overhead of a system call only once per event loop
		3228	iteration, so while the overhead might be noticeable, it doesn't apply to
		3229	repeated calls to C<ev_async_send> for the same event loop.
		3230
		3231	=item bool = ev_async_pending (ev_async *)
		3232
		3233	Returns a non-zero value when C<ev_async_send> has been called on the
		3234	watcher but the event has not yet been processed (or even noted) by the
		3235	event loop.
		3236
		3237	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3238	the loop iterates next and checks for the watcher to have become active,
		3239	it will reset the flag again. C<ev_async_pending> can be used to very
		3240	quickly check whether invoking the loop might be a good idea.
		3241
		3242	Not that this does I<not> check whether the watcher itself is pending,
		3243	only whether it has been requested to make this watcher pending: there
		3244	is a time window between the event loop checking and resetting the async
		3245	notification, and the callback being invoked.
		3246
		3247	=back
		3248
1299		3249
1300	=head1 OTHER FUNCTIONS	3250	=head1 OTHER FUNCTIONS
1301		3251
1302	There are some other functions of possible interest. Described. Here. Now.	3252	There are some other functions of possible interest. Described. Here. Now.
1303		3253
1304	=over 4	3254	=over 4
1305		3255
1306	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3256	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1307		3257
1308	This function combines a simple timer and an I/O watcher, calls your	3258	This function combines a simple timer and an I/O watcher, calls your
1309	callback on whichever event happens first and automatically stop both	3259	callback on whichever event happens first and automatically stops both
1310	watchers. This is useful if you want to wait for a single event on an fd	3260	watchers. This is useful if you want to wait for a single event on an fd
1311	or timeout without having to allocate/configure/start/stop/free one or	3261	or timeout without having to allocate/configure/start/stop/free one or
1312	more watchers yourself.	3262	more watchers yourself.
1313		3263
1314	If C<fd> is less than 0, then no I/O watcher will be started and events	3264	If C<fd> is less than 0, then no I/O watcher will be started and the
1315	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3265	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1316	C<events> set will be craeted and started.	3266	the given C<fd> and C<events> set will be created and started.
1317		3267
1318	If C<timeout> is less than 0, then no timeout watcher will be	3268	If C<timeout> is less than 0, then no timeout watcher will be
1319	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3269	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1320	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3270	repeat = 0) will be started. C<0> is a valid timeout.
1321	dubious value.
1322		3271
1323	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3272	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1324	passed an C<revents> set like normal event callbacks (a combination of	3273	passed an C<revents> set like normal event callbacks (a combination of
1325	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3274	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1326	value passed to C<ev_once>:	3275	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3276	a timeout and an io event at the same time - you probably should give io
		3277	events precedence.
1327		3278
		3279	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3280
1328	static void stdin_ready (int revents, void *arg)	3281	static void stdin_ready (int revents, void *arg)
1329	{	3282	{
1330	if (revents & EV_TIMEOUT)
1331	/* doh, nothing entered */;
1332	else if (revents & EV_READ)	3283	if (revents & EV_READ)
1333	/* stdin might have data for us, joy! */;	3284	/* stdin might have data for us, joy! */;
		3285	else if (revents & EV_TIMER)
		3286	/* doh, nothing entered */;
1334	}	3287	}
1335		3288
1336	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3289	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1337		3290
1338	=item ev_feed_event (ev_loop *, watcher *, int revents)
1339
1340	Feeds the given event set into the event loop, as if the specified event
1341	had happened for the specified watcher (which must be a pointer to an
1342	initialised but not necessarily started event watcher).
1343
1344	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3291	=item ev_feed_fd_event (loop, int fd, int revents)
1345		3292
1346	Feed an event on the given fd, as if a file descriptor backend detected	3293	Feed an event on the given fd, as if a file descriptor backend detected
1347	the given events it.	3294	the given events it.
1348		3295
1349	=item ev_feed_signal_event (ev_loop *loop, int signum)	3296	=item ev_feed_signal_event (loop, int signum)
1350		3297
1351	Feed an event as if the given signal occured (C<loop> must be the default	3298	Feed an event as if the given signal occurred (C<loop> must be the default
1352	loop!).	3299	loop!).
1353		3300
1354	=back	3301	=back
1355		3302
1356		3303
…		…
1372		3319
1373	=item * Priorities are not currently supported. Initialising priorities	3320	=item * Priorities are not currently supported. Initialising priorities
1374	will fail and all watchers will have the same priority, even though there	3321	will fail and all watchers will have the same priority, even though there
1375	is an ev_pri field.	3322	is an ev_pri field.
1376		3323
		3324	=item * In libevent, the last base created gets the signals, in libev, the
		3325	first base created (== the default loop) gets the signals.
		3326
1377	=item * Other members are not supported.	3327	=item * Other members are not supported.
1378		3328
1379	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3329	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1380	to use the libev header file and library.	3330	to use the libev header file and library.
1381		3331
1382	=back	3332	=back
1383		3333
1384	=head1 C++ SUPPORT	3334	=head1 C++ SUPPORT
1385		3335
1386	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3336	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1387	you to use some convinience methods to start/stop watchers and also change	3337	you to use some convenience methods to start/stop watchers and also change
1388	the callback model to a model using method callbacks on objects.	3338	the callback model to a model using method callbacks on objects.
1389		3339
1390	To use it,	3340	To use it,
1391		3341
1392	#include <ev++.h>	3342	#include <ev++.h>
1393		3343
1394	(it is not installed by default). This automatically includes F<ev.h>	3344	This automatically includes F<ev.h> and puts all of its definitions (many
1395	and puts all of its definitions (many of them macros) into the global	3345	of them macros) into the global namespace. All C++ specific things are
1396	namespace. All C++ specific things are put into the C<ev> namespace.	3346	put into the C<ev> namespace. It should support all the same embedding
		3347	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1397		3348
1398	It should support all the same embedding options as F<ev.h>, most notably	3349	Care has been taken to keep the overhead low. The only data member the C++
1399	C<EV_MULTIPLICITY>.	3350	classes add (compared to plain C-style watchers) is the event loop pointer
		3351	that the watcher is associated with (or no additional members at all if
		3352	you disable C<EV_MULTIPLICITY> when embedding libev).
		3353
		3354	Currently, functions, and static and non-static member functions can be
		3355	used as callbacks. Other types should be easy to add as long as they only
		3356	need one additional pointer for context. If you need support for other
		3357	types of functors please contact the author (preferably after implementing
		3358	it).
1400		3359
1401	Here is a list of things available in the C<ev> namespace:	3360	Here is a list of things available in the C<ev> namespace:
1402		3361
1403	=over 4	3362	=over 4
1404		3363
…		…
1420		3379
1421	All of those classes have these methods:	3380	All of those classes have these methods:
1422		3381
1423	=over 4	3382	=over 4
1424		3383
1425	=item ev::TYPE::TYPE (object *, object::method *)	3384	=item ev::TYPE::TYPE ()
1426		3385
1427	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3386	=item ev::TYPE::TYPE (loop)
1428		3387
1429	=item ev::TYPE::~TYPE	3388	=item ev::TYPE::~TYPE
1430		3389
1431	The constructor takes a pointer to an object and a method pointer to	3390	The constructor (optionally) takes an event loop to associate the watcher
1432	the event handler callback to call in this class. The constructor calls	3391	with. If it is omitted, it will use C<EV_DEFAULT>.
1433	C<ev_init> for you, which means you have to call the C<set> method	3392
1434	before starting it. If you do not specify a loop then the constructor	3393	The constructor calls C<ev_init> for you, which means you have to call the
1435	automatically associates the default loop with this watcher.	3394	C<set> method before starting it.
		3395
		3396	It will not set a callback, however: You have to call the templated C<set>
		3397	method to set a callback before you can start the watcher.
		3398
		3399	(The reason why you have to use a method is a limitation in C++ which does
		3400	not allow explicit template arguments for constructors).
1436		3401
1437	The destructor automatically stops the watcher if it is active.	3402	The destructor automatically stops the watcher if it is active.
1438		3403
		3404	=item w->set<class, &class::method> (object *)
		3405
		3406	This method sets the callback method to call. The method has to have a
		3407	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3408	first argument and the C<revents> as second. The object must be given as
		3409	parameter and is stored in the C<data> member of the watcher.
		3410
		3411	This method synthesizes efficient thunking code to call your method from
		3412	the C callback that libev requires. If your compiler can inline your
		3413	callback (i.e. it is visible to it at the place of the C<set> call and
		3414	your compiler is good :), then the method will be fully inlined into the
		3415	thunking function, making it as fast as a direct C callback.
		3416
		3417	Example: simple class declaration and watcher initialisation
		3418
		3419	struct myclass
		3420	{
		3421	void io_cb (ev::io &w, int revents) { }
		3422	}
		3423
		3424	myclass obj;
		3425	ev::io iow;
		3426	iow.set <myclass, &myclass::io_cb> (&obj);
		3427
		3428	=item w->set (object *)
		3429
		3430	This is a variation of a method callback - leaving out the method to call
		3431	will default the method to C<operator ()>, which makes it possible to use
		3432	functor objects without having to manually specify the C<operator ()> all
		3433	the time. Incidentally, you can then also leave out the template argument
		3434	list.
		3435
		3436	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3437	int revents)>.
		3438
		3439	See the method-C<set> above for more details.
		3440
		3441	Example: use a functor object as callback.
		3442
		3443	struct myfunctor
		3444	{
		3445	void operator() (ev::io &w, int revents)
		3446	{
		3447	...
		3448	}
		3449	}
		3450
		3451	myfunctor f;
		3452
		3453	ev::io w;
		3454	w.set (&f);
		3455
		3456	=item w->set<function> (void *data = 0)
		3457
		3458	Also sets a callback, but uses a static method or plain function as
		3459	callback. The optional C<data> argument will be stored in the watcher's
		3460	C<data> member and is free for you to use.
		3461
		3462	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3463
		3464	See the method-C<set> above for more details.
		3465
		3466	Example: Use a plain function as callback.
		3467
		3468	static void io_cb (ev::io &w, int revents) { }
		3469	iow.set <io_cb> ();
		3470
1439	=item w->set (struct ev_loop *)	3471	=item w->set (loop)
1440		3472
1441	Associates a different C<struct ev_loop> with this watcher. You can only	3473	Associates a different C<struct ev_loop> with this watcher. You can only
1442	do this when the watcher is inactive (and not pending either).	3474	do this when the watcher is inactive (and not pending either).
1443		3475
1444	=item w->set ([args])	3476	=item w->set ([arguments])
1445		3477
1446	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3478	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
1447	called at least once. Unlike the C counterpart, an active watcher gets	3479	method or a suitable start method must be called at least once. Unlike the
1448	automatically stopped and restarted.	3480	C counterpart, an active watcher gets automatically stopped and restarted
		3481	when reconfiguring it with this method.
1449		3482
1450	=item w->start ()	3483	=item w->start ()
1451		3484
1452	Starts the watcher. Note that there is no C<loop> argument as the	3485	Starts the watcher. Note that there is no C<loop> argument, as the
1453	constructor already takes the loop.	3486	constructor already stores the event loop.
		3487
		3488	=item w->start ([arguments])
		3489
		3490	Instead of calling C<set> and C<start> methods separately, it is often
		3491	convenient to wrap them in one call. Uses the same type of arguments as
		3492	the configure C<set> method of the watcher.
1454		3493
1455	=item w->stop ()	3494	=item w->stop ()
1456		3495
1457	Stops the watcher if it is active. Again, no C<loop> argument.	3496	Stops the watcher if it is active. Again, no C<loop> argument.
1458		3497
1459	=item w->again () C<ev::timer>, C<ev::periodic> only	3498	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1460		3499
1461	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3500	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1462	C<ev_TYPE_again> function.	3501	C<ev_TYPE_again> function.
1463		3502
1464	=item w->sweep () C<ev::embed> only	3503	=item w->sweep () (C<ev::embed> only)
1465		3504
1466	Invokes C<ev_embed_sweep>.	3505	Invokes C<ev_embed_sweep>.
1467		3506
		3507	=item w->update () (C<ev::stat> only)
		3508
		3509	Invokes C<ev_stat_stat>.
		3510
1468	=back	3511	=back
1469		3512
1470	=back	3513	=back
1471		3514
1472	Example: Define a class with an IO and idle watcher, start one of them in	3515	Example: Define a class with two I/O and idle watchers, start the I/O
1473	the constructor.	3516	watchers in the constructor.
1474		3517
1475	class myclass	3518	class myclass
1476	{	3519	{
1477	ev_io io; void io_cb (ev::io &w, int revents);	3520	ev::io io ; void io_cb (ev::io &w, int revents);
		3521	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1478	ev_idle idle void idle_cb (ev::idle &w, int revents);	3522	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1479		3523
1480	myclass ();	3524	myclass (int fd)
		3525	{
		3526	io .set <myclass, &myclass::io_cb > (this);
		3527	io2 .set <myclass, &myclass::io2_cb > (this);
		3528	idle.set <myclass, &myclass::idle_cb> (this);
		3529
		3530	io.set (fd, ev::WRITE); // configure the watcher
		3531	io.start (); // start it whenever convenient
		3532
		3533	io2.start (fd, ev::READ); // set + start in one call
		3534	}
1481	}	3535	};
1482		3536
1483	myclass::myclass (int fd)	3537
1484	: io (this, &myclass::io_cb),	3538	=head1 OTHER LANGUAGE BINDINGS
1485	idle (this, &myclass::idle_cb)	3539
		3540	Libev does not offer other language bindings itself, but bindings for a
		3541	number of languages exist in the form of third-party packages. If you know
		3542	any interesting language binding in addition to the ones listed here, drop
		3543	me a note.
		3544
		3545	=over 4
		3546
		3547	=item Perl
		3548
		3549	The EV module implements the full libev API and is actually used to test
		3550	libev. EV is developed together with libev. Apart from the EV core module,
		3551	there are additional modules that implement libev-compatible interfaces
		3552	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3553	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3554	and C<EV::Glib>).
		3555
		3556	It can be found and installed via CPAN, its homepage is at
		3557	L<http://software.schmorp.de/pkg/EV>.
		3558
		3559	=item Python
		3560
		3561	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3562	seems to be quite complete and well-documented.
		3563
		3564	=item Ruby
		3565
		3566	Tony Arcieri has written a ruby extension that offers access to a subset
		3567	of the libev API and adds file handle abstractions, asynchronous DNS and
		3568	more on top of it. It can be found via gem servers. Its homepage is at
		3569	L<http://rev.rubyforge.org/>.
		3570
		3571	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3572	makes rev work even on mingw.
		3573
		3574	=item Haskell
		3575
		3576	A haskell binding to libev is available at
		3577	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3578
		3579	=item D
		3580
		3581	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3582	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3583
		3584	=item Ocaml
		3585
		3586	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3587	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3588
		3589	=item Lua
		3590
		3591	Brian Maher has written a partial interface to libev for lua (at the
		3592	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3593	L<http://github.com/brimworks/lua-ev>.
		3594
		3595	=back
		3596
		3597
		3598	=head1 MACRO MAGIC
		3599
		3600	Libev can be compiled with a variety of options, the most fundamental
		3601	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3602	functions and callbacks have an initial C<struct ev_loop *> argument.
		3603
		3604	To make it easier to write programs that cope with either variant, the
		3605	following macros are defined:
		3606
		3607	=over 4
		3608
		3609	=item C<EV_A>, C<EV_A_>
		3610
		3611	This provides the loop I<argument> for functions, if one is required ("ev
		3612	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3613	C<EV_A_> is used when other arguments are following. Example:
		3614
		3615	ev_unref (EV_A);
		3616	ev_timer_add (EV_A_ watcher);
		3617	ev_run (EV_A_ 0);
		3618
		3619	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3620	which is often provided by the following macro.
		3621
		3622	=item C<EV_P>, C<EV_P_>
		3623
		3624	This provides the loop I<parameter> for functions, if one is required ("ev
		3625	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3626	C<EV_P_> is used when other parameters are following. Example:
		3627
		3628	// this is how ev_unref is being declared
		3629	static void ev_unref (EV_P);
		3630
		3631	// this is how you can declare your typical callback
		3632	static void cb (EV_P_ ev_timer *w, int revents)
		3633
		3634	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3635	suitable for use with C<EV_A>.
		3636
		3637	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3638
		3639	Similar to the other two macros, this gives you the value of the default
		3640	loop, if multiple loops are supported ("ev loop default").
		3641
		3642	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3643
		3644	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3645	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3646	is undefined when the default loop has not been initialised by a previous
		3647	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3648
		3649	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3650	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3651
		3652	=back
		3653
		3654	Example: Declare and initialise a check watcher, utilising the above
		3655	macros so it will work regardless of whether multiple loops are supported
		3656	or not.
		3657
		3658	static void
		3659	check_cb (EV_P_ ev_timer *w, int revents)
1486	{	3660	{
1487	io.start (fd, ev::READ);	3661	ev_check_stop (EV_A_ w);
1488	}	3662	}
		3663
		3664	ev_check check;
		3665	ev_check_init (&check, check_cb);
		3666	ev_check_start (EV_DEFAULT_ &check);
		3667	ev_run (EV_DEFAULT_ 0);
1489		3668
1490	=head1 EMBEDDING	3669	=head1 EMBEDDING
1491		3670
1492	Libev can (and often is) directly embedded into host	3671	Libev can (and often is) directly embedded into host
1493	applications. Examples of applications that embed it include the Deliantra	3672	applications. Examples of applications that embed it include the Deliantra
1494	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3673	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1495	and rxvt-unicode.	3674	and rxvt-unicode.
1496		3675
1497	The goal is to enable you to just copy the neecssary files into your	3676	The goal is to enable you to just copy the necessary files into your
1498	source directory without having to change even a single line in them, so	3677	source directory without having to change even a single line in them, so
1499	you can easily upgrade by simply copying (or having a checked-out copy of	3678	you can easily upgrade by simply copying (or having a checked-out copy of
1500	libev somewhere in your source tree).	3679	libev somewhere in your source tree).
1501		3680
1502	=head2 FILESETS	3681	=head2 FILESETS
1503		3682
1504	Depending on what features you need you need to include one or more sets of files	3683	Depending on what features you need you need to include one or more sets of files
1505	in your app.	3684	in your application.
1506		3685
1507	=head3 CORE EVENT LOOP	3686	=head3 CORE EVENT LOOP
1508		3687
1509	To include only the libev core (all the C<ev_*> functions), with manual	3688	To include only the libev core (all the C<ev_*> functions), with manual
1510	configuration (no autoconf):	3689	configuration (no autoconf):
1511		3690
1512	#define EV_STANDALONE 1	3691	#define EV_STANDALONE 1
1513	#include "ev.c"	3692	#include "ev.c"
1514		3693
1515	This will automatically include F<ev.h>, too, and should be done in a	3694	This will automatically include F<ev.h>, too, and should be done in a
1516	single C source file only to provide the function implementations. To use	3695	single C source file only to provide the function implementations. To use
1517	it, do the same for F<ev.h> in all files wishing to use this API (best	3696	it, do the same for F<ev.h> in all files wishing to use this API (best
1518	done by writing a wrapper around F<ev.h> that you can include instead and	3697	done by writing a wrapper around F<ev.h> that you can include instead and
1519	where you can put other configuration options):	3698	where you can put other configuration options):
1520		3699
1521	#define EV_STANDALONE 1	3700	#define EV_STANDALONE 1
1522	#include "ev.h"	3701	#include "ev.h"
1523		3702
1524	Both header files and implementation files can be compiled with a C++	3703	Both header files and implementation files can be compiled with a C++
1525	compiler (at least, thats a stated goal, and breakage will be treated	3704	compiler (at least, that's a stated goal, and breakage will be treated
1526	as a bug).	3705	as a bug).
1527		3706
1528	You need the following files in your source tree, or in a directory	3707	You need the following files in your source tree, or in a directory
1529	in your include path (e.g. in libev/ when using -Ilibev):	3708	in your include path (e.g. in libev/ when using -Ilibev):
1530		3709
1531	ev.h	3710	ev.h
1532	ev.c	3711	ev.c
1533	ev_vars.h	3712	ev_vars.h
1534	ev_wrap.h	3713	ev_wrap.h
1535		3714
1536	ev_win32.c required on win32 platforms only	3715	ev_win32.c required on win32 platforms only
1537		3716
1538	ev_select.c only when select backend is enabled (which is by default)	3717	ev_select.c only when select backend is enabled (which is enabled by default)
1539	ev_poll.c only when poll backend is enabled (disabled by default)	3718	ev_poll.c only when poll backend is enabled (disabled by default)
1540	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3719	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1541	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3720	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1542	ev_port.c only when the solaris port backend is enabled (disabled by default)	3721	ev_port.c only when the solaris port backend is enabled (disabled by default)
1543		3722
1544	F<ev.c> includes the backend files directly when enabled, so you only need	3723	F<ev.c> includes the backend files directly when enabled, so you only need
1545	to compile this single file.	3724	to compile this single file.
1546		3725
1547	=head3 LIBEVENT COMPATIBILITY API	3726	=head3 LIBEVENT COMPATIBILITY API
1548		3727
1549	To include the libevent compatibility API, also include:	3728	To include the libevent compatibility API, also include:
1550		3729
1551	#include "event.c"	3730	#include "event.c"
1552		3731
1553	in the file including F<ev.c>, and:	3732	in the file including F<ev.c>, and:
1554		3733
1555	#include "event.h"	3734	#include "event.h"
1556		3735
1557	in the files that want to use the libevent API. This also includes F<ev.h>.	3736	in the files that want to use the libevent API. This also includes F<ev.h>.
1558		3737
1559	You need the following additional files for this:	3738	You need the following additional files for this:
1560		3739
1561	event.h	3740	event.h
1562	event.c	3741	event.c
1563		3742
1564	=head3 AUTOCONF SUPPORT	3743	=head3 AUTOCONF SUPPORT
1565		3744
1566	Instead of using C<EV_STANDALONE=1> and providing your config in	3745	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1567	whatever way you want, you can also C<m4_include([libev.m4])> in your	3746	whatever way you want, you can also C<m4_include([libev.m4])> in your
1568	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3747	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1569	include F<config.h> and configure itself accordingly.	3748	include F<config.h> and configure itself accordingly.
1570		3749
1571	For this of course you need the m4 file:	3750	For this of course you need the m4 file:
1572		3751
1573	libev.m4	3752	libev.m4
1574		3753
1575	=head2 PREPROCESSOR SYMBOLS/MACROS	3754	=head2 PREPROCESSOR SYMBOLS/MACROS
1576		3755
1577	Libev can be configured via a variety of preprocessor symbols you have to define	3756	Libev can be configured via a variety of preprocessor symbols you have to
1578	before including any of its files. The default is not to build for multiplicity	3757	define before including (or compiling) any of its files. The default in
1579	and only include the select backend.	3758	the absence of autoconf is documented for every option.
		3759
		3760	Symbols marked with "(h)" do not change the ABI, and can have different
		3761	values when compiling libev vs. including F<ev.h>, so it is permissible
		3762	to redefine them before including F<ev.h> without breaking compatibility
		3763	to a compiled library. All other symbols change the ABI, which means all
		3764	users of libev and the libev code itself must be compiled with compatible
		3765	settings.
1580		3766
1581	=over 4	3767	=over 4
1582		3768
		3769	=item EV_COMPAT3 (h)
		3770
		3771	Backwards compatibility is a major concern for libev. This is why this
		3772	release of libev comes with wrappers for the functions and symbols that
		3773	have been renamed between libev version 3 and 4.
		3774
		3775	You can disable these wrappers (to test compatibility with future
		3776	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3777	sources. This has the additional advantage that you can drop the C<struct>
		3778	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3779	typedef in that case.
		3780
		3781	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3782	and in some even more future version the compatibility code will be
		3783	removed completely.
		3784
1583	=item EV_STANDALONE	3785	=item EV_STANDALONE (h)
1584		3786
1585	Must always be C<1> if you do not use autoconf configuration, which	3787	Must always be C<1> if you do not use autoconf configuration, which
1586	keeps libev from including F<config.h>, and it also defines dummy	3788	keeps libev from including F<config.h>, and it also defines dummy
1587	implementations for some libevent functions (such as logging, which is not	3789	implementations for some libevent functions (such as logging, which is not
1588	supported). It will also not define any of the structs usually found in	3790	supported). It will also not define any of the structs usually found in
1589	F<event.h> that are not directly supported by the libev core alone.	3791	F<event.h> that are not directly supported by the libev core alone.
1590		3792
		3793	In standalone mode, libev will still try to automatically deduce the
		3794	configuration, but has to be more conservative.
		3795
1591	=item EV_USE_MONOTONIC	3796	=item EV_USE_MONOTONIC
1592		3797
1593	If defined to be C<1>, libev will try to detect the availability of the	3798	If defined to be C<1>, libev will try to detect the availability of the
1594	monotonic clock option at both compiletime and runtime. Otherwise no use	3799	monotonic clock option at both compile time and runtime. Otherwise no
1595	of the monotonic clock option will be attempted. If you enable this, you	3800	use of the monotonic clock option will be attempted. If you enable this,
1596	usually have to link against librt or something similar. Enabling it when	3801	you usually have to link against librt or something similar. Enabling it
1597	the functionality isn't available is safe, though, althoguh you have	3802	when the functionality isn't available is safe, though, although you have
1598	to make sure you link against any libraries where the C<clock_gettime>	3803	to make sure you link against any libraries where the C<clock_gettime>
1599	function is hiding in (often F<-lrt>).	3804	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1600		3805
1601	=item EV_USE_REALTIME	3806	=item EV_USE_REALTIME
1602		3807
1603	If defined to be C<1>, libev will try to detect the availability of the	3808	If defined to be C<1>, libev will try to detect the availability of the
1604	realtime clock option at compiletime (and assume its availability at	3809	real-time clock option at compile time (and assume its availability
1605	runtime if successful). Otherwise no use of the realtime clock option will	3810	at runtime if successful). Otherwise no use of the real-time clock
1606	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3811	option will be attempted. This effectively replaces C<gettimeofday>
1607	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3812	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1608	in the description of C<EV_USE_MONOTONIC>, though.	3813	correctness. See the note about libraries in the description of
		3814	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3815	C<EV_USE_CLOCK_SYSCALL>.
		3816
		3817	=item EV_USE_CLOCK_SYSCALL
		3818
		3819	If defined to be C<1>, libev will try to use a direct syscall instead
		3820	of calling the system-provided C<clock_gettime> function. This option
		3821	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3822	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3823	programs needlessly. Using a direct syscall is slightly slower (in
		3824	theory), because no optimised vdso implementation can be used, but avoids
		3825	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3826	higher, as it simplifies linking (no need for C<-lrt>).
		3827
		3828	=item EV_USE_NANOSLEEP
		3829
		3830	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3831	and will use it for delays. Otherwise it will use C<select ()>.
		3832
		3833	=item EV_USE_EVENTFD
		3834
		3835	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3836	available and will probe for kernel support at runtime. This will improve
		3837	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3838	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3839	2.7 or newer, otherwise disabled.
1609		3840
1610	=item EV_USE_SELECT	3841	=item EV_USE_SELECT
1611		3842
1612	If undefined or defined to be C<1>, libev will compile in support for the	3843	If undefined or defined to be C<1>, libev will compile in support for the
1613	C<select>(2) backend. No attempt at autodetection will be done: if no	3844	C<select>(2) backend. No attempt at auto-detection will be done: if no
1614	other method takes over, select will be it. Otherwise the select backend	3845	other method takes over, select will be it. Otherwise the select backend
1615	will not be compiled in.	3846	will not be compiled in.
1616		3847
1617	=item EV_SELECT_USE_FD_SET	3848	=item EV_SELECT_USE_FD_SET
1618		3849
1619	If defined to C<1>, then the select backend will use the system C<fd_set>	3850	If defined to C<1>, then the select backend will use the system C<fd_set>
1620	structure. This is useful if libev doesn't compile due to a missing	3851	structure. This is useful if libev doesn't compile due to a missing
1621	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3852	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1622	exotic systems. This usually limits the range of file descriptors to some	3853	on exotic systems. This usually limits the range of file descriptors to
1623	low limit such as 1024 or might have other limitations (winsocket only	3854	some low limit such as 1024 or might have other limitations (winsocket
1624	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3855	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1625	influence the size of the C<fd_set> used.	3856	configures the maximum size of the C<fd_set>.
1626		3857
1627	=item EV_SELECT_IS_WINSOCKET	3858	=item EV_SELECT_IS_WINSOCKET
1628		3859
1629	When defined to C<1>, the select backend will assume that	3860	When defined to C<1>, the select backend will assume that
1630	select/socket/connect etc. don't understand file descriptors but	3861	select/socket/connect etc. don't understand file descriptors but
…		…
1632	be used is the winsock select). This means that it will call	3863	be used is the winsock select). This means that it will call
1633	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3864	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1634	it is assumed that all these functions actually work on fds, even	3865	it is assumed that all these functions actually work on fds, even
1635	on win32. Should not be defined on non-win32 platforms.	3866	on win32. Should not be defined on non-win32 platforms.
1636		3867
		3868	=item EV_FD_TO_WIN32_HANDLE(fd)
		3869
		3870	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3871	file descriptors to socket handles. When not defining this symbol (the
		3872	default), then libev will call C<_get_osfhandle>, which is usually
		3873	correct. In some cases, programs use their own file descriptor management,
		3874	in which case they can provide this function to map fds to socket handles.
		3875
		3876	=item EV_WIN32_HANDLE_TO_FD(handle)
		3877
		3878	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3879	using the standard C<_open_osfhandle> function. For programs implementing
		3880	their own fd to handle mapping, overwriting this function makes it easier
		3881	to do so. This can be done by defining this macro to an appropriate value.
		3882
		3883	=item EV_WIN32_CLOSE_FD(fd)
		3884
		3885	If programs implement their own fd to handle mapping on win32, then this
		3886	macro can be used to override the C<close> function, useful to unregister
		3887	file descriptors again. Note that the replacement function has to close
		3888	the underlying OS handle.
		3889
1637	=item EV_USE_POLL	3890	=item EV_USE_POLL
1638		3891
1639	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3892	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1640	backend. Otherwise it will be enabled on non-win32 platforms. It	3893	backend. Otherwise it will be enabled on non-win32 platforms. It
1641	takes precedence over select.	3894	takes precedence over select.
1642		3895
1643	=item EV_USE_EPOLL	3896	=item EV_USE_EPOLL
1644		3897
1645	If defined to be C<1>, libev will compile in support for the Linux	3898	If defined to be C<1>, libev will compile in support for the Linux
1646	C<epoll>(7) backend. Its availability will be detected at runtime,	3899	C<epoll>(7) backend. Its availability will be detected at runtime,
1647	otherwise another method will be used as fallback. This is the	3900	otherwise another method will be used as fallback. This is the preferred
1648	preferred backend for GNU/Linux systems.	3901	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3902	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1649		3903
1650	=item EV_USE_KQUEUE	3904	=item EV_USE_KQUEUE
1651		3905
1652	If defined to be C<1>, libev will compile in support for the BSD style	3906	If defined to be C<1>, libev will compile in support for the BSD style
1653	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3907	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
1666	otherwise another method will be used as fallback. This is the preferred	3920	otherwise another method will be used as fallback. This is the preferred
1667	backend for Solaris 10 systems.	3921	backend for Solaris 10 systems.
1668		3922
1669	=item EV_USE_DEVPOLL	3923	=item EV_USE_DEVPOLL
1670		3924
1671	reserved for future expansion, works like the USE symbols above.	3925	Reserved for future expansion, works like the USE symbols above.
1672		3926
		3927	=item EV_USE_INOTIFY
		3928
		3929	If defined to be C<1>, libev will compile in support for the Linux inotify
		3930	interface to speed up C<ev_stat> watchers. Its actual availability will
		3931	be detected at runtime. If undefined, it will be enabled if the headers
		3932	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3933
		3934	=item EV_ATOMIC_T
		3935
		3936	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3937	access is atomic with respect to other threads or signal contexts. No such
		3938	type is easily found in the C language, so you can provide your own type
		3939	that you know is safe for your purposes. It is used both for signal handler "locking"
		3940	as well as for signal and thread safety in C<ev_async> watchers.
		3941
		3942	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3943	(from F<signal.h>), which is usually good enough on most platforms.
		3944
1673	=item EV_H	3945	=item EV_H (h)
1674		3946
1675	The name of the F<ev.h> header file used to include it. The default if	3947	The name of the F<ev.h> header file used to include it. The default if
1676	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3948	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1677	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3949	used to virtually rename the F<ev.h> header file in case of conflicts.
1678		3950
1679	=item EV_CONFIG_H	3951	=item EV_CONFIG_H (h)
1680		3952
1681	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3953	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1682	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3954	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1683	C<EV_H>, above.	3955	C<EV_H>, above.
1684		3956
1685	=item EV_EVENT_H	3957	=item EV_EVENT_H (h)
1686		3958
1687	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3959	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
1688	of how the F<event.h> header can be found.	3960	of how the F<event.h> header can be found, the default is C<"event.h">.
1689		3961
1690	=item EV_PROTOTYPES	3962	=item EV_PROTOTYPES (h)
1691		3963
1692	If defined to be C<0>, then F<ev.h> will not define any function	3964	If defined to be C<0>, then F<ev.h> will not define any function
1693	prototypes, but still define all the structs and other symbols. This is	3965	prototypes, but still define all the structs and other symbols. This is
1694	occasionally useful if you want to provide your own wrapper functions	3966	occasionally useful if you want to provide your own wrapper functions
1695	around libev functions.	3967	around libev functions.
…		…
1700	will have the C<struct ev_loop *> as first argument, and you can create	3972	will have the C<struct ev_loop *> as first argument, and you can create
1701	additional independent event loops. Otherwise there will be no support	3973	additional independent event loops. Otherwise there will be no support
1702	for multiple event loops and there is no first event loop pointer	3974	for multiple event loops and there is no first event loop pointer
1703	argument. Instead, all functions act on the single default loop.	3975	argument. Instead, all functions act on the single default loop.
1704		3976
1705	=item EV_PERIODICS	3977	=item EV_MINPRI
1706		3978
1707	If undefined or defined to be C<1>, then periodic timers are supported,	3979	=item EV_MAXPRI
1708	otherwise not. This saves a few kb of code.	3980
		3981	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3982	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3983	provide for more priorities by overriding those symbols (usually defined
		3984	to be C<-2> and C<2>, respectively).
		3985
		3986	When doing priority-based operations, libev usually has to linearly search
		3987	all the priorities, so having many of them (hundreds) uses a lot of space
		3988	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3989	fine.
		3990
		3991	If your embedding application does not need any priorities, defining these
		3992	both to C<0> will save some memory and CPU.
		3993
		3994	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3995	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3996	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		3997
		3998	If undefined or defined to be C<1> (and the platform supports it), then
		3999	the respective watcher type is supported. If defined to be C<0>, then it
		4000	is not. Disabling watcher types mainly saves code size.
		4001
		4002	=item EV_FEATURES
		4003
		4004	If you need to shave off some kilobytes of code at the expense of some
		4005	speed (but with the full API), you can define this symbol to request
		4006	certain subsets of functionality. The default is to enable all features
		4007	that can be enabled on the platform.
		4008
		4009	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4010	with some broad features you want) and then selectively re-enable
		4011	additional parts you want, for example if you want everything minimal,
		4012	but multiple event loop support, async and child watchers and the poll
		4013	backend, use this:
		4014
		4015	#define EV_FEATURES 0
		4016	#define EV_MULTIPLICITY 1
		4017	#define EV_USE_POLL 1
		4018	#define EV_CHILD_ENABLE 1
		4019	#define EV_ASYNC_ENABLE 1
		4020
		4021	The actual value is a bitset, it can be a combination of the following
		4022	values:
		4023
		4024	=over 4
		4025
		4026	=item C<1> - faster/larger code
		4027
		4028	Use larger code to speed up some operations.
		4029
		4030	Currently this is used to override some inlining decisions (enlarging the
		4031	code size by roughly 30% on amd64).
		4032
		4033	When optimising for size, use of compiler flags such as C<-Os> with
		4034	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4035	assertions.
		4036
		4037	=item C<2> - faster/larger data structures
		4038
		4039	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4040	hash table sizes and so on. This will usually further increase code size
		4041	and can additionally have an effect on the size of data structures at
		4042	runtime.
		4043
		4044	=item C<4> - full API configuration
		4045
		4046	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4047	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4048
		4049	=item C<8> - full API
		4050
		4051	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4052	details on which parts of the API are still available without this
		4053	feature, and do not complain if this subset changes over time.
		4054
		4055	=item C<16> - enable all optional watcher types
		4056
		4057	Enables all optional watcher types. If you want to selectively enable
		4058	only some watcher types other than I/O and timers (e.g. prepare,
		4059	embed, async, child...) you can enable them manually by defining
		4060	C<EV_watchertype_ENABLE> to C<1> instead.
		4061
		4062	=item C<32> - enable all backends
		4063
		4064	This enables all backends - without this feature, you need to enable at
		4065	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4066
		4067	=item C<64> - enable OS-specific "helper" APIs
		4068
		4069	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4070	default.
		4071
		4072	=back
		4073
		4074	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4075	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4076	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4077	watchers, timers and monotonic clock support.
		4078
		4079	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4080	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4081	your program might be left out as well - a binary starting a timer and an
		4082	I/O watcher then might come out at only 5Kb.
		4083
		4084	=item EV_AVOID_STDIO
		4085
		4086	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4087	functions (printf, scanf, perror etc.). This will increase the code size
		4088	somewhat, but if your program doesn't otherwise depend on stdio and your
		4089	libc allows it, this avoids linking in the stdio library which is quite
		4090	big.
		4091
		4092	Note that error messages might become less precise when this option is
		4093	enabled.
		4094
		4095	=item EV_NSIG
		4096
		4097	The highest supported signal number, +1 (or, the number of
		4098	signals): Normally, libev tries to deduce the maximum number of signals
		4099	automatically, but sometimes this fails, in which case it can be
		4100	specified. Also, using a lower number than detected (C<32> should be
		4101	good for about any system in existence) can save some memory, as libev
		4102	statically allocates some 12-24 bytes per signal number.
		4103
		4104	=item EV_PID_HASHSIZE
		4105
		4106	C<ev_child> watchers use a small hash table to distribute workload by
		4107	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4108	usually more than enough. If you need to manage thousands of children you
		4109	might want to increase this value (I<must> be a power of two).
		4110
		4111	=item EV_INOTIFY_HASHSIZE
		4112
		4113	C<ev_stat> watchers use a small hash table to distribute workload by
		4114	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4115	disabled), usually more than enough. If you need to manage thousands of
		4116	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4117	power of two).
		4118
		4119	=item EV_USE_4HEAP
		4120
		4121	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4122	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4123	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4124	faster performance with many (thousands) of watchers.
		4125
		4126	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4127	will be C<0>.
		4128
		4129	=item EV_HEAP_CACHE_AT
		4130
		4131	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4132	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4133	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4134	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4135	but avoids random read accesses on heap changes. This improves performance
		4136	noticeably with many (hundreds) of watchers.
		4137
		4138	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4139	will be C<0>.
		4140
		4141	=item EV_VERIFY
		4142
		4143	Controls how much internal verification (see C<ev_verify ()>) will
		4144	be done: If set to C<0>, no internal verification code will be compiled
		4145	in. If set to C<1>, then verification code will be compiled in, but not
		4146	called. If set to C<2>, then the internal verification code will be
		4147	called once per loop, which can slow down libev. If set to C<3>, then the
		4148	verification code will be called very frequently, which will slow down
		4149	libev considerably.
		4150
		4151	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4152	will be C<0>.
1709		4153
1710	=item EV_COMMON	4154	=item EV_COMMON
1711		4155
1712	By default, all watchers have a C<void *data> member. By redefining	4156	By default, all watchers have a C<void *data> member. By redefining
1713	this macro to a something else you can include more and other types of	4157	this macro to something else you can include more and other types of
1714	members. You have to define it each time you include one of the files,	4158	members. You have to define it each time you include one of the files,
1715	though, and it must be identical each time.	4159	though, and it must be identical each time.
1716		4160
1717	For example, the perl EV module uses something like this:	4161	For example, the perl EV module uses something like this:
1718		4162
1719	#define EV_COMMON \	4163	#define EV_COMMON \
1720	SV *self; /* contains this struct */ \	4164	SV *self; /* contains this struct */ \
1721	SV *cb_sv, *fh /* note no trailing ";" */	4165	SV *cb_sv, *fh /* note no trailing ";" */
1722		4166
1723	=item EV_CB_DECLARE (type)	4167	=item EV_CB_DECLARE (type)
1724		4168
1725	=item EV_CB_INVOKE (watcher, revents)	4169	=item EV_CB_INVOKE (watcher, revents)
1726		4170
1727	=item ev_set_cb (ev, cb)	4171	=item ev_set_cb (ev, cb)
1728		4172
1729	Can be used to change the callback member declaration in each watcher,	4173	Can be used to change the callback member declaration in each watcher,
1730	and the way callbacks are invoked and set. Must expand to a struct member	4174	and the way callbacks are invoked and set. Must expand to a struct member
1731	definition and a statement, respectively. See the F<ev.v> header file for	4175	definition and a statement, respectively. See the F<ev.h> header file for
1732	their default definitions. One possible use for overriding these is to	4176	their default definitions. One possible use for overriding these is to
1733	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4177	avoid the C<struct ev_loop *> as first argument in all cases, or to use
1734	method calls instead of plain function calls in C++.	4178	method calls instead of plain function calls in C++.
		4179
		4180	=back
		4181
		4182	=head2 EXPORTED API SYMBOLS
		4183
		4184	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4185	exported symbols, you can use the provided F<Symbol.*> files which list
		4186	all public symbols, one per line:
		4187
		4188	Symbols.ev for libev proper
		4189	Symbols.event for the libevent emulation
		4190
		4191	This can also be used to rename all public symbols to avoid clashes with
		4192	multiple versions of libev linked together (which is obviously bad in
		4193	itself, but sometimes it is inconvenient to avoid this).
		4194
		4195	A sed command like this will create wrapper C<#define>'s that you need to
		4196	include before including F<ev.h>:
		4197
		4198	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4199
		4200	This would create a file F<wrap.h> which essentially looks like this:
		4201
		4202	#define ev_backend myprefix_ev_backend
		4203	#define ev_check_start myprefix_ev_check_start
		4204	#define ev_check_stop myprefix_ev_check_stop
		4205	...
1735		4206
1736	=head2 EXAMPLES	4207	=head2 EXAMPLES
1737		4208
1738	For a real-world example of a program the includes libev	4209	For a real-world example of a program the includes libev
1739	verbatim, you can have a look at the EV perl module	4210	verbatim, you can have a look at the EV perl module
…		…
1742	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	4213	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
1743	will be compiled. It is pretty complex because it provides its own header	4214	will be compiled. It is pretty complex because it provides its own header
1744	file.	4215	file.
1745		4216
1746	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4217	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
1747	that everybody includes and which overrides some autoconf choices:	4218	that everybody includes and which overrides some configure choices:
1748		4219
		4220	#define EV_FEATURES 8
		4221	#define EV_USE_SELECT 1
		4222	#define EV_PREPARE_ENABLE 1
		4223	#define EV_IDLE_ENABLE 1
		4224	#define EV_SIGNAL_ENABLE 1
		4225	#define EV_CHILD_ENABLE 1
1749	#define EV_USE_POLL 0	4226	#define EV_USE_STDEXCEPT 0
1750	#define EV_MULTIPLICITY 0
1751	#define EV_PERIODICS 0
1752	#define EV_CONFIG_H <config.h>	4227	#define EV_CONFIG_H <config.h>
1753		4228
1754	#include "ev++.h"	4229	#include "ev++.h"
1755		4230
1756	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4231	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
1757		4232
1758	#include "ev_cpp.h"	4233	#include "ev_cpp.h"
1759	#include "ev.c"	4234	#include "ev.c"
1760		4235
		4236	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
1761		4237
		4238	=head2 THREADS AND COROUTINES
		4239
		4240	=head3 THREADS
		4241
		4242	All libev functions are reentrant and thread-safe unless explicitly
		4243	documented otherwise, but libev implements no locking itself. This means
		4244	that you can use as many loops as you want in parallel, as long as there
		4245	are no concurrent calls into any libev function with the same loop
		4246	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4247	of course): libev guarantees that different event loops share no data
		4248	structures that need any locking.
		4249
		4250	Or to put it differently: calls with different loop parameters can be done
		4251	concurrently from multiple threads, calls with the same loop parameter
		4252	must be done serially (but can be done from different threads, as long as
		4253	only one thread ever is inside a call at any point in time, e.g. by using
		4254	a mutex per loop).
		4255
		4256	Specifically to support threads (and signal handlers), libev implements
		4257	so-called C<ev_async> watchers, which allow some limited form of
		4258	concurrency on the same event loop, namely waking it up "from the
		4259	outside".
		4260
		4261	If you want to know which design (one loop, locking, or multiple loops
		4262	without or something else still) is best for your problem, then I cannot
		4263	help you, but here is some generic advice:
		4264
		4265	=over 4
		4266
		4267	=item * most applications have a main thread: use the default libev loop
		4268	in that thread, or create a separate thread running only the default loop.
		4269
		4270	This helps integrating other libraries or software modules that use libev
		4271	themselves and don't care/know about threading.
		4272
		4273	=item * one loop per thread is usually a good model.
		4274
		4275	Doing this is almost never wrong, sometimes a better-performance model
		4276	exists, but it is always a good start.
		4277
		4278	=item * other models exist, such as the leader/follower pattern, where one
		4279	loop is handed through multiple threads in a kind of round-robin fashion.
		4280
		4281	Choosing a model is hard - look around, learn, know that usually you can do
		4282	better than you currently do :-)
		4283
		4284	=item * often you need to talk to some other thread which blocks in the
		4285	event loop.
		4286
		4287	C<ev_async> watchers can be used to wake them up from other threads safely
		4288	(or from signal contexts...).
		4289
		4290	An example use would be to communicate signals or other events that only
		4291	work in the default loop by registering the signal watcher with the
		4292	default loop and triggering an C<ev_async> watcher from the default loop
		4293	watcher callback into the event loop interested in the signal.
		4294
		4295	=back
		4296
		4297	=head4 THREAD LOCKING EXAMPLE
		4298
		4299	Here is a fictitious example of how to run an event loop in a different
		4300	thread than where callbacks are being invoked and watchers are
		4301	created/added/removed.
		4302
		4303	For a real-world example, see the C<EV::Loop::Async> perl module,
		4304	which uses exactly this technique (which is suited for many high-level
		4305	languages).
		4306
		4307	The example uses a pthread mutex to protect the loop data, a condition
		4308	variable to wait for callback invocations, an async watcher to notify the
		4309	event loop thread and an unspecified mechanism to wake up the main thread.
		4310
		4311	First, you need to associate some data with the event loop:
		4312
		4313	typedef struct {
		4314	mutex_t lock; /* global loop lock */
		4315	ev_async async_w;
		4316	thread_t tid;
		4317	cond_t invoke_cv;
		4318	} userdata;
		4319
		4320	void prepare_loop (EV_P)
		4321	{
		4322	// for simplicity, we use a static userdata struct.
		4323	static userdata u;
		4324
		4325	ev_async_init (&u->async_w, async_cb);
		4326	ev_async_start (EV_A_ &u->async_w);
		4327
		4328	pthread_mutex_init (&u->lock, 0);
		4329	pthread_cond_init (&u->invoke_cv, 0);
		4330
		4331	// now associate this with the loop
		4332	ev_set_userdata (EV_A_ u);
		4333	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4334	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4335
		4336	// then create the thread running ev_loop
		4337	pthread_create (&u->tid, 0, l_run, EV_A);
		4338	}
		4339
		4340	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4341	solely to wake up the event loop so it takes notice of any new watchers
		4342	that might have been added:
		4343
		4344	static void
		4345	async_cb (EV_P_ ev_async *w, int revents)
		4346	{
		4347	// just used for the side effects
		4348	}
		4349
		4350	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4351	protecting the loop data, respectively.
		4352
		4353	static void
		4354	l_release (EV_P)
		4355	{
		4356	userdata *u = ev_userdata (EV_A);
		4357	pthread_mutex_unlock (&u->lock);
		4358	}
		4359
		4360	static void
		4361	l_acquire (EV_P)
		4362	{
		4363	userdata *u = ev_userdata (EV_A);
		4364	pthread_mutex_lock (&u->lock);
		4365	}
		4366
		4367	The event loop thread first acquires the mutex, and then jumps straight
		4368	into C<ev_run>:
		4369
		4370	void *
		4371	l_run (void *thr_arg)
		4372	{
		4373	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4374
		4375	l_acquire (EV_A);
		4376	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4377	ev_run (EV_A_ 0);
		4378	l_release (EV_A);
		4379
		4380	return 0;
		4381	}
		4382
		4383	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4384	signal the main thread via some unspecified mechanism (signals? pipe
		4385	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4386	have been called (in a while loop because a) spurious wakeups are possible
		4387	and b) skipping inter-thread-communication when there are no pending
		4388	watchers is very beneficial):
		4389
		4390	static void
		4391	l_invoke (EV_P)
		4392	{
		4393	userdata *u = ev_userdata (EV_A);
		4394
		4395	while (ev_pending_count (EV_A))
		4396	{
		4397	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4398	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4399	}
		4400	}
		4401
		4402	Now, whenever the main thread gets told to invoke pending watchers, it
		4403	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4404	thread to continue:
		4405
		4406	static void
		4407	real_invoke_pending (EV_P)
		4408	{
		4409	userdata *u = ev_userdata (EV_A);
		4410
		4411	pthread_mutex_lock (&u->lock);
		4412	ev_invoke_pending (EV_A);
		4413	pthread_cond_signal (&u->invoke_cv);
		4414	pthread_mutex_unlock (&u->lock);
		4415	}
		4416
		4417	Whenever you want to start/stop a watcher or do other modifications to an
		4418	event loop, you will now have to lock:
		4419
		4420	ev_timer timeout_watcher;
		4421	userdata *u = ev_userdata (EV_A);
		4422
		4423	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4424
		4425	pthread_mutex_lock (&u->lock);
		4426	ev_timer_start (EV_A_ &timeout_watcher);
		4427	ev_async_send (EV_A_ &u->async_w);
		4428	pthread_mutex_unlock (&u->lock);
		4429
		4430	Note that sending the C<ev_async> watcher is required because otherwise
		4431	an event loop currently blocking in the kernel will have no knowledge
		4432	about the newly added timer. By waking up the loop it will pick up any new
		4433	watchers in the next event loop iteration.
		4434
		4435	=head3 COROUTINES
		4436
		4437	Libev is very accommodating to coroutines ("cooperative threads"):
		4438	libev fully supports nesting calls to its functions from different
		4439	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4440	different coroutines, and switch freely between both coroutines running
		4441	the loop, as long as you don't confuse yourself). The only exception is
		4442	that you must not do this from C<ev_periodic> reschedule callbacks.
		4443
		4444	Care has been taken to ensure that libev does not keep local state inside
		4445	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4446	they do not call any callbacks.
		4447
		4448	=head2 COMPILER WARNINGS
		4449
		4450	Depending on your compiler and compiler settings, you might get no or a
		4451	lot of warnings when compiling libev code. Some people are apparently
		4452	scared by this.
		4453
		4454	However, these are unavoidable for many reasons. For one, each compiler
		4455	has different warnings, and each user has different tastes regarding
		4456	warning options. "Warn-free" code therefore cannot be a goal except when
		4457	targeting a specific compiler and compiler-version.
		4458
		4459	Another reason is that some compiler warnings require elaborate
		4460	workarounds, or other changes to the code that make it less clear and less
		4461	maintainable.
		4462
		4463	And of course, some compiler warnings are just plain stupid, or simply
		4464	wrong (because they don't actually warn about the condition their message
		4465	seems to warn about). For example, certain older gcc versions had some
		4466	warnings that resulted in an extreme number of false positives. These have
		4467	been fixed, but some people still insist on making code warn-free with
		4468	such buggy versions.
		4469
		4470	While libev is written to generate as few warnings as possible,
		4471	"warn-free" code is not a goal, and it is recommended not to build libev
		4472	with any compiler warnings enabled unless you are prepared to cope with
		4473	them (e.g. by ignoring them). Remember that warnings are just that:
		4474	warnings, not errors, or proof of bugs.
		4475
		4476
		4477	=head2 VALGRIND
		4478
		4479	Valgrind has a special section here because it is a popular tool that is
		4480	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4481
		4482	If you think you found a bug (memory leak, uninitialised data access etc.)
		4483	in libev, then check twice: If valgrind reports something like:
		4484
		4485	==2274== definitely lost: 0 bytes in 0 blocks.
		4486	==2274== possibly lost: 0 bytes in 0 blocks.
		4487	==2274== still reachable: 256 bytes in 1 blocks.
		4488
		4489	Then there is no memory leak, just as memory accounted to global variables
		4490	is not a memleak - the memory is still being referenced, and didn't leak.
		4491
		4492	Similarly, under some circumstances, valgrind might report kernel bugs
		4493	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4494	although an acceptable workaround has been found here), or it might be
		4495	confused.
		4496
		4497	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4498	make it into some kind of religion.
		4499
		4500	If you are unsure about something, feel free to contact the mailing list
		4501	with the full valgrind report and an explanation on why you think this
		4502	is a bug in libev (best check the archives, too :). However, don't be
		4503	annoyed when you get a brisk "this is no bug" answer and take the chance
		4504	of learning how to interpret valgrind properly.
		4505
		4506	If you need, for some reason, empty reports from valgrind for your project
		4507	I suggest using suppression lists.
		4508
		4509
		4510	=head1 PORTABILITY NOTES
		4511
		4512	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4513
		4514	GNU/Linux is the only common platform that supports 64 bit file/large file
		4515	interfaces but I<disables> them by default.
		4516
		4517	That means that libev compiled in the default environment doesn't support
		4518	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4519
		4520	Unfortunately, many programs try to work around this GNU/Linux issue
		4521	by enabling the large file API, which makes them incompatible with the
		4522	standard libev compiled for their system.
		4523
		4524	Likewise, libev cannot enable the large file API itself as this would
		4525	suddenly make it incompatible to the default compile time environment,
		4526	i.e. all programs not using special compile switches.
		4527
		4528	=head2 OS/X AND DARWIN BUGS
		4529
		4530	The whole thing is a bug if you ask me - basically any system interface
		4531	you touch is broken, whether it is locales, poll, kqueue or even the
		4532	OpenGL drivers.
		4533
		4534	=head3 C<kqueue> is buggy
		4535
		4536	The kqueue syscall is broken in all known versions - most versions support
		4537	only sockets, many support pipes.
		4538
		4539	Libev tries to work around this by not using C<kqueue> by default on this
		4540	rotten platform, but of course you can still ask for it when creating a
		4541	loop - embedding a socket-only kqueue loop into a select-based one is
		4542	probably going to work well.
		4543
		4544	=head3 C<poll> is buggy
		4545
		4546	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4547	implementation by something calling C<kqueue> internally around the 10.5.6
		4548	release, so now C<kqueue> I<and> C<poll> are broken.
		4549
		4550	Libev tries to work around this by not using C<poll> by default on
		4551	this rotten platform, but of course you can still ask for it when creating
		4552	a loop.
		4553
		4554	=head3 C<select> is buggy
		4555
		4556	All that's left is C<select>, and of course Apple found a way to fuck this
		4557	one up as well: On OS/X, C<select> actively limits the number of file
		4558	descriptors you can pass in to 1024 - your program suddenly crashes when
		4559	you use more.
		4560
		4561	There is an undocumented "workaround" for this - defining
		4562	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4563	work on OS/X.
		4564
		4565	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4566
		4567	=head3 C<errno> reentrancy
		4568
		4569	The default compile environment on Solaris is unfortunately so
		4570	thread-unsafe that you can't even use components/libraries compiled
		4571	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4572	defined by default. A valid, if stupid, implementation choice.
		4573
		4574	If you want to use libev in threaded environments you have to make sure
		4575	it's compiled with C<_REENTRANT> defined.
		4576
		4577	=head3 Event port backend
		4578
		4579	The scalable event interface for Solaris is called "event
		4580	ports". Unfortunately, this mechanism is very buggy in all major
		4581	releases. If you run into high CPU usage, your program freezes or you get
		4582	a large number of spurious wakeups, make sure you have all the relevant
		4583	and latest kernel patches applied. No, I don't know which ones, but there
		4584	are multiple ones to apply, and afterwards, event ports actually work
		4585	great.
		4586
		4587	If you can't get it to work, you can try running the program by setting
		4588	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4589	C<select> backends.
		4590
		4591	=head2 AIX POLL BUG
		4592
		4593	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4594	this by trying to avoid the poll backend altogether (i.e. it's not even
		4595	compiled in), which normally isn't a big problem as C<select> works fine
		4596	with large bitsets on AIX, and AIX is dead anyway.
		4597
		4598	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4599
		4600	=head3 General issues
		4601
		4602	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4603	requires, and its I/O model is fundamentally incompatible with the POSIX
		4604	model. Libev still offers limited functionality on this platform in
		4605	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4606	descriptors. This only applies when using Win32 natively, not when using
		4607	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4608	as every compielr comes with a slightly differently broken/incompatible
		4609	environment.
		4610
		4611	Lifting these limitations would basically require the full
		4612	re-implementation of the I/O system. If you are into this kind of thing,
		4613	then note that glib does exactly that for you in a very portable way (note
		4614	also that glib is the slowest event library known to man).
		4615
		4616	There is no supported compilation method available on windows except
		4617	embedding it into other applications.
		4618
		4619	Sensible signal handling is officially unsupported by Microsoft - libev
		4620	tries its best, but under most conditions, signals will simply not work.
		4621
		4622	Not a libev limitation but worth mentioning: windows apparently doesn't
		4623	accept large writes: instead of resulting in a partial write, windows will
		4624	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4625	so make sure you only write small amounts into your sockets (less than a
		4626	megabyte seems safe, but this apparently depends on the amount of memory
		4627	available).
		4628
		4629	Due to the many, low, and arbitrary limits on the win32 platform and
		4630	the abysmal performance of winsockets, using a large number of sockets
		4631	is not recommended (and not reasonable). If your program needs to use
		4632	more than a hundred or so sockets, then likely it needs to use a totally
		4633	different implementation for windows, as libev offers the POSIX readiness
		4634	notification model, which cannot be implemented efficiently on windows
		4635	(due to Microsoft monopoly games).
		4636
		4637	A typical way to use libev under windows is to embed it (see the embedding
		4638	section for details) and use the following F<evwrap.h> header file instead
		4639	of F<ev.h>:
		4640
		4641	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4642	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4643
		4644	#include "ev.h"
		4645
		4646	And compile the following F<evwrap.c> file into your project (make sure
		4647	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4648
		4649	#include "evwrap.h"
		4650	#include "ev.c"
		4651
		4652	=head3 The winsocket C<select> function
		4653
		4654	The winsocket C<select> function doesn't follow POSIX in that it
		4655	requires socket I<handles> and not socket I<file descriptors> (it is
		4656	also extremely buggy). This makes select very inefficient, and also
		4657	requires a mapping from file descriptors to socket handles (the Microsoft
		4658	C runtime provides the function C<_open_osfhandle> for this). See the
		4659	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4660	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4661
		4662	The configuration for a "naked" win32 using the Microsoft runtime
		4663	libraries and raw winsocket select is:
		4664
		4665	#define EV_USE_SELECT 1
		4666	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4667
		4668	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4669	complexity in the O(n²) range when using win32.
		4670
		4671	=head3 Limited number of file descriptors
		4672
		4673	Windows has numerous arbitrary (and low) limits on things.
		4674
		4675	Early versions of winsocket's select only supported waiting for a maximum
		4676	of C<64> handles (probably owning to the fact that all windows kernels
		4677	can only wait for C<64> things at the same time internally; Microsoft
		4678	recommends spawning a chain of threads and wait for 63 handles and the
		4679	previous thread in each. Sounds great!).
		4680
		4681	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4682	to some high number (e.g. C<2048>) before compiling the winsocket select
		4683	call (which might be in libev or elsewhere, for example, perl and many
		4684	other interpreters do their own select emulation on windows).
		4685
		4686	Another limit is the number of file descriptors in the Microsoft runtime
		4687	libraries, which by default is C<64> (there must be a hidden I<64>
		4688	fetish or something like this inside Microsoft). You can increase this
		4689	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4690	(another arbitrary limit), but is broken in many versions of the Microsoft
		4691	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4692	(depending on windows version and/or the phase of the moon). To get more,
		4693	you need to wrap all I/O functions and provide your own fd management, but
		4694	the cost of calling select (O(n²)) will likely make this unworkable.
		4695
		4696	=head2 PORTABILITY REQUIREMENTS
		4697
		4698	In addition to a working ISO-C implementation and of course the
		4699	backend-specific APIs, libev relies on a few additional extensions:
		4700
		4701	=over 4
		4702
		4703	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4704	calling conventions regardless of C<ev_watcher_type *>.
		4705
		4706	Libev assumes not only that all watcher pointers have the same internal
		4707	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4708	assumes that the same (machine) code can be used to call any watcher
		4709	callback: The watcher callbacks have different type signatures, but libev
		4710	calls them using an C<ev_watcher *> internally.
		4711
		4712	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4713
		4714	The type C<sig_atomic_t volatile> (or whatever is defined as
		4715	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4716	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4717	believed to be sufficiently portable.
		4718
		4719	=item C<sigprocmask> must work in a threaded environment
		4720
		4721	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4722	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4723	pthread implementations will either allow C<sigprocmask> in the "main
		4724	thread" or will block signals process-wide, both behaviours would
		4725	be compatible with libev. Interaction between C<sigprocmask> and
		4726	C<pthread_sigmask> could complicate things, however.
		4727
		4728	The most portable way to handle signals is to block signals in all threads
		4729	except the initial one, and run the default loop in the initial thread as
		4730	well.
		4731
		4732	=item C<long> must be large enough for common memory allocation sizes
		4733
		4734	To improve portability and simplify its API, libev uses C<long> internally
		4735	instead of C<size_t> when allocating its data structures. On non-POSIX
		4736	systems (Microsoft...) this might be unexpectedly low, but is still at
		4737	least 31 bits everywhere, which is enough for hundreds of millions of
		4738	watchers.
		4739
		4740	=item C<double> must hold a time value in seconds with enough accuracy
		4741
		4742	The type C<double> is used to represent timestamps. It is required to
		4743	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4744	good enough for at least into the year 4000 with millisecond accuracy
		4745	(the design goal for libev). This requirement is overfulfilled by
		4746	implementations using IEEE 754, which is basically all existing ones. With
		4747	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4748
		4749	=back
		4750
		4751	If you know of other additional requirements drop me a note.
		4752
		4753
1762	=head1 COMPLEXITIES	4754	=head1 ALGORITHMIC COMPLEXITIES
1763		4755
1764	In this section the complexities of (many of) the algorithms used inside	4756	In this section the complexities of (many of) the algorithms used inside
1765	libev will be explained. For complexity discussions about backends see the	4757	libev will be documented. For complexity discussions about backends see
1766	documentation for C<ev_default_init>.	4758	the documentation for C<ev_default_init>.
		4759
		4760	All of the following are about amortised time: If an array needs to be
		4761	extended, libev needs to realloc and move the whole array, but this
		4762	happens asymptotically rarer with higher number of elements, so O(1) might
		4763	mean that libev does a lengthy realloc operation in rare cases, but on
		4764	average it is much faster and asymptotically approaches constant time.
1767		4765
1768	=over 4	4766	=over 4
1769		4767
1770	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4768	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
1771		4769
		4770	This means that, when you have a watcher that triggers in one hour and
		4771	there are 100 watchers that would trigger before that, then inserting will
		4772	have to skip roughly seven (C<ld 100>) of these watchers.
		4773
1772	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4774	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
1773		4775
		4776	That means that changing a timer costs less than removing/adding them,
		4777	as only the relative motion in the event queue has to be paid for.
		4778
1774	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4779	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
1775		4780
		4781	These just add the watcher into an array or at the head of a list.
		4782
1776	=item Stopping check/prepare/idle watchers: O(1)	4783	=item Stopping check/prepare/idle/fork/async watchers: O(1)
1777		4784
1778	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	4785	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
1779		4786
		4787	These watchers are stored in lists, so they need to be walked to find the
		4788	correct watcher to remove. The lists are usually short (you don't usually
		4789	have many watchers waiting for the same fd or signal: one is typical, two
		4790	is rare).
		4791
1780	=item Finding the next timer per loop iteration: O(1)	4792	=item Finding the next timer in each loop iteration: O(1)
		4793
		4794	By virtue of using a binary or 4-heap, the next timer is always found at a
		4795	fixed position in the storage array.
1781		4796
1782	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4797	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
1783		4798
1784	=item Activating one watcher: O(1)	4799	A change means an I/O watcher gets started or stopped, which requires
		4800	libev to recalculate its status (and possibly tell the kernel, depending
		4801	on backend and whether C<ev_io_set> was used).
		4802
		4803	=item Activating one watcher (putting it into the pending state): O(1)
		4804
		4805	=item Priority handling: O(number_of_priorities)
		4806
		4807	Priorities are implemented by allocating some space for each
		4808	priority. When doing priority-based operations, libev usually has to
		4809	linearly search all the priorities, but starting/stopping and activating
		4810	watchers becomes O(1) with respect to priority handling.
		4811
		4812	=item Sending an ev_async: O(1)
		4813
		4814	=item Processing ev_async_send: O(number_of_async_watchers)
		4815
		4816	=item Processing signals: O(max_signal_number)
		4817
		4818	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4819	calls in the current loop iteration. Checking for async and signal events
		4820	involves iterating over all running async watchers or all signal numbers.
1785		4821
1786	=back	4822	=back
1787		4823
1788		4824
		4825	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4826
		4827	The major version 4 introduced some minor incompatible changes to the API.
		4828
		4829	At the moment, the C<ev.h> header file tries to implement superficial
		4830	compatibility, so most programs should still compile. Those might be
		4831	removed in later versions of libev, so better update early than late.
		4832
		4833	=over 4
		4834
		4835	=item function/symbol renames
		4836
		4837	A number of functions and symbols have been renamed:
		4838
		4839	ev_loop => ev_run
		4840	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4841	EVLOOP_ONESHOT => EVRUN_ONCE
		4842
		4843	ev_unloop => ev_break
		4844	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4845	EVUNLOOP_ONE => EVBREAK_ONE
		4846	EVUNLOOP_ALL => EVBREAK_ALL
		4847
		4848	EV_TIMEOUT => EV_TIMER
		4849
		4850	ev_loop_count => ev_iteration
		4851	ev_loop_depth => ev_depth
		4852	ev_loop_verify => ev_verify
		4853
		4854	Most functions working on C<struct ev_loop> objects don't have an
		4855	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4856	associated constants have been renamed to not collide with the C<struct
		4857	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4858	as all other watcher types. Note that C<ev_loop_fork> is still called
		4859	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4860	typedef.
		4861
		4862	=item C<EV_COMPAT3> backwards compatibility mechanism
		4863
		4864	The backward compatibility mechanism can be controlled by
		4865	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4866	section.
		4867
		4868	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4869
		4870	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4871	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4872	and work, but the library code will of course be larger.
		4873
		4874	=back
		4875
		4876
		4877	=head1 GLOSSARY
		4878
		4879	=over 4
		4880
		4881	=item active
		4882
		4883	A watcher is active as long as it has been started and not yet stopped.
		4884	See L<WATCHER STATES> for details.
		4885
		4886	=item application
		4887
		4888	In this document, an application is whatever is using libev.
		4889
		4890	=item backend
		4891
		4892	The part of the code dealing with the operating system interfaces.
		4893
		4894	=item callback
		4895
		4896	The address of a function that is called when some event has been
		4897	detected. Callbacks are being passed the event loop, the watcher that
		4898	received the event, and the actual event bitset.
		4899
		4900	=item callback/watcher invocation
		4901
		4902	The act of calling the callback associated with a watcher.
		4903
		4904	=item event
		4905
		4906	A change of state of some external event, such as data now being available
		4907	for reading on a file descriptor, time having passed or simply not having
		4908	any other events happening anymore.
		4909
		4910	In libev, events are represented as single bits (such as C<EV_READ> or
		4911	C<EV_TIMER>).
		4912
		4913	=item event library
		4914
		4915	A software package implementing an event model and loop.
		4916
		4917	=item event loop
		4918
		4919	An entity that handles and processes external events and converts them
		4920	into callback invocations.
		4921
		4922	=item event model
		4923
		4924	The model used to describe how an event loop handles and processes
		4925	watchers and events.
		4926
		4927	=item pending
		4928
		4929	A watcher is pending as soon as the corresponding event has been
		4930	detected. See L<WATCHER STATES> for details.
		4931
		4932	=item real time
		4933
		4934	The physical time that is observed. It is apparently strictly monotonic :)
		4935
		4936	=item wall-clock time
		4937
		4938	The time and date as shown on clocks. Unlike real time, it can actually
		4939	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4940	clock.
		4941
		4942	=item watcher
		4943
		4944	A data structure that describes interest in certain events. Watchers need
		4945	to be started (attached to an event loop) before they can receive events.
		4946
		4947	=back
		4948
1789	=head1 AUTHOR	4949	=head1 AUTHOR
1790		4950
1791	Marc Lehmann <libev@schmorp.de>.	4951	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
1792		4952

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