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Revision 1.198 by root, Thu Oct 23 06:30:48 2008 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
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	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	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	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	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	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	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	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 *>)	108	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the C<double> type in C, and when you need to do any calculations on	117	to the C<double> type in C, and when you need to do any calculations on
51	it, you should treat it as such.	118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
52		141
53		142
54	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
55		144
56	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
…		…
62		151
63	Returns the current time as libev would use it. Please note that the	152	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	153	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	154	you actually want to know.
66		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
67	=item int ev_version_major ()	162	=item int ev_version_major ()
68		163
69	=item int ev_version_minor ()	164	=item int ev_version_minor ()
70		165
71	You can find out the major and minor version numbers of the library	166	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	167	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	168	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	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	170	version of the library your program was compiled against.
76		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
77	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	178	not a problem.
81		179
82	Example: make sure we haven't accidentally been linked against the wrong	180	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	181	version.
84		182
85	assert (("libev version mismatch",	183	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
88		186
89	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
90		188
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	192	a description of the set values.
95		193
96	Example: make sure we have the epoll method, because yeah this is cool and	194	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	195	a must have and can we have a torrent of it please!!!11
98		196
99	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
101		199
102	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
103		201
104	Return the set of all backends compiled into this binary of libev and also	202	Return the set of all backends compiled into this binary of libev and also
105	recommended for this platform. This set is often smaller than the one	203	recommended for this platform. This set is often smaller than the one
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	204	returned by C<ev_supported_backends>, as for example kqueue is broken on
107	most BSDs and will not be autodetected unless you explicitly request it	205	most BSDs and will not be auto-detected unless you explicitly request it
108	(assuming you know what you are doing). This is the set of backends that	206	(assuming you know what you are doing). This is the set of backends that
109	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
110		208
111	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
112		210
…		…
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
117	recommended ones.	215	recommended ones.
118		216
119	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
120		218
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
122		220
123	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	222	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	223	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	224	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
128		230
129	You could override this function in high-availability programs to, say,	231	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,	232	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.	233	or even to sleep a while and retry until some memory is available.
132		234
133	Example: replace the libev allocator with one that waits a bit and then	235	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	236	retries (example requires a standards-compliant C<realloc>).
135		237
136	static void *	238	static void *
137	persistent_realloc (void *ptr, long size)	239	persistent_realloc (void *ptr, size_t size)
138	{	240	{
139	for (;;)	241	for (;;)
140	{	242	{
141	void *newptr = realloc (ptr, size);	243	void *newptr = realloc (ptr, size);
142		244
…		…
148	}	250	}
149		251
150	...	252	...
151	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
152		254
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
154		256
155	Set the callback function to call on a retryable syscall error (such	257	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	258	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	259	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	260	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	261	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	262	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	263	(such as abort).
162		264
163	Example: do the same thing as libev does internally:	265	Example: This is basically the same thing that libev does internally, too.
164		266
165	static void	267	static void
166	fatal_error (const char *msg)	268	fatal_error (const char *msg)
167	{	269	{
168	perror (msg);	270	perror (msg);
…		…
174		276
175	=back	277	=back
176		278
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		280
179	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<ev_loop *>. The library knows two
180	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
181	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
182
183	If you use threads, a common model is to run the default event loop
184	in your main thread (or in a separate thread) and for each thread you
185	create, you also create another event loop. Libev itself does no locking
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		284
190	=over 4	285	=over 4
191		286
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		288
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		293
199	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
200	function.	295	function.
201		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
202	The flags argument can be used to specify special behaviour or specific	308	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>).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		310
205	The following flags are supported:	311	The following flags are supported:
206		312
…		…
211	The default flags value. Use this if you have no clue (it's the right	317	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	318	thing, believe me).
213		319
214	=item C<EVFLAG_NOENV>	320	=item C<EVFLAG_NOENV>
215		321
216	If this flag bit is ored into the flag value (or the program runs setuid	322	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	323	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	325	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	326	useful to try out specific backends to test their performance, or to work
221	around bugs.	327	around bugs.
222		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		350
225	This is your standard select(2) backend. Not I<completely> standard, as	351	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,	352	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	353	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	354	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	355	usually the fastest backend for a low number of (low-numbered :) fds.
		356
		357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
		363
		364	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		365	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		366	C<exceptfds> set on that platform).
230		367
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	368	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		369
233	And this is your standard poll(2) backend. It's more complicated than	370	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	371	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	372	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).	373	considerably with a lot of inactive fds). It scales similarly to select,
		374	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		375	performance tips.
		376
		377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		379
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	380	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		381
240	For few fds, this backend is a bit little slower than poll and select,	382	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	383	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	384	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	385	epoll scales either O(1) or O(active_fds). The epoll design has a number
		386	of shortcomings, such as silently dropping events in some hard-to-detect
		387	cases and requiring a system call per fd change, no fork support and bad
		388	support for dup.
244		389
245	While stopping and starting an I/O watcher in the same iteration will	390	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	391	will result in some caching, there is still a system call per such incident
247	(because the fd could point to a different file description now), so its	392	(because the fd could point to a different file description now), so its
248	best to avoid that. Also, dup()ed file descriptors might not work very	393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
249	well if you register events for both fds.	394	very well if you register events for both fds.
250		395
251	Please note that epoll sometimes generates spurious notifications, so you	396	Please note that epoll sometimes generates spurious notifications, so you
252	need to use non-blocking I/O or other means to avoid blocking when no data	397	need to use non-blocking I/O or other means to avoid blocking when no data
253	(or space) is available.	398	(or space) is available.
254		399
		400	Best performance from this backend is achieved by not unregistering all
		401	watchers for a file descriptor until it has been closed, if possible,
		402	i.e. keep at least one watcher active per fd at all times. Stopping and
		403	starting a watcher (without re-setting it) also usually doesn't cause
		404	extra overhead.
		405
		406	While nominally embeddable in other event loops, this feature is broken in
		407	all kernel versions tested so far.
		408
		409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		410	C<EVBACKEND_POLL>.
		411
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		413
257	Kqueue deserves special mention, as at the time of this writing, it	414	Kqueue deserves special mention, as at the time of this writing, it was
258	was broken on all BSDs except NetBSD (usually it doesn't work with	415	broken on all BSDs except NetBSD (usually it doesn't work reliably with
259	anything but sockets and pipes, except on Darwin, where of course its	416	anything but sockets and pipes, except on Darwin, where of course it's
260	completely useless). For this reason its not being "autodetected"	417	completely useless). For this reason it's not being "auto-detected" unless
261	unless you explicitly specify it explicitly in the flags (i.e. using	418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or
262	C<EVBACKEND_KQUEUE>).	419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.
		420
		421	You still can embed kqueue into a normal poll or select backend and use it
		422	only for sockets (after having made sure that sockets work with kqueue on
		423	the target platform). See C<ev_embed> watchers for more info.
263		424
264	It scales in the same way as the epoll backend, but the interface to the	425	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	426	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	427	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	428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	429	two event changes per incident. Support for C<fork ()> is very bad and it
		430	drops fds silently in similarly hard-to-detect cases.
		431
		432	This backend usually performs well under most conditions.
		433
		434	While nominally embeddable in other event loops, this doesn't work
		435	everywhere, so you might need to test for this. And since it is broken
		436	almost everywhere, you should only use it when you have a lot of sockets
		437	(for which it usually works), by embedding it into another event loop
		438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		439	using it only for sockets.
		440
		441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		443	C<NOTE_EOF>.
269		444
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	445	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		446
272	This is not implemented yet (and might never be).	447	This is not implemented yet (and might never be, unless you send me an
		448	implementation). According to reports, C</dev/poll> only supports sockets
		449	and is not embeddable, which would limit the usefulness of this backend
		450	immensely.
273		451
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	452	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		453
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	454	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)).	455	it's really slow, but it still scales very well (O(active_fds)).
278		456
279	Please note that solaris ports can result in a lot of spurious	457	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	458	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	459	blocking when no data (or space) is available.
		460
		461	While this backend scales well, it requires one system call per active
		462	file descriptor per loop iteration. For small and medium numbers of file
		463	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		464	might perform better.
		465
		466	On the positive side, with the exception of the spurious readiness
		467	notifications, this backend actually performed fully to specification
		468	in all tests and is fully embeddable, which is a rare feat among the
		469	OS-specific backends.
		470
		471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		472	C<EVBACKEND_POLL>.
282		473
283	=item C<EVBACKEND_ALL>	474	=item C<EVBACKEND_ALL>
284		475
285	Try all backends (even potentially broken ones that wouldn't be tried	476	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	477	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	478	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		479
		480	It is definitely not recommended to use this flag.
		481
289	=back	482	=back
290		483
291	If one or more of these are ored into the flags value, then only these	484	If one or more of these are or'ed into the flags value, then only these
292	backends will be tried (in the reverse order as given here). If none are	485	backends will be tried (in the reverse order as listed here). If none are
293	specified, most compiled-in backend will be tried, usually in reverse	486	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		487
296	The most typical usage is like this:	488	Example: This is the most typical usage.
297		489
298	if (!ev_default_loop (0))	490	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		492
301	Restrict libev to the select and poll backends, and do not allow	493	Example: Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	494	environment settings to be taken into account:
303		495
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	496	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		497
306	Use whatever libev has to offer, but make sure that kqueue is used if	498	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	499	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):	500	private event loop and only if you know the OS supports your types of
		501	fds):
309		502
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	503	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		504
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	505	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		506
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	507	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	508	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by	509	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).	510	undefined behaviour (or a failed assertion if assertions are enabled).
318		511
		512	Note that this function I<is> thread-safe, and the recommended way to use
		513	libev with threads is indeed to create one loop per thread, and using the
		514	default loop in the "main" or "initial" thread.
		515
319	Example: try to create a event loop that uses epoll and nothing else.	516	Example: Try to create a event loop that uses epoll and nothing else.
320		517
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	518	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	519	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	520	fatal ("no epoll found here, maybe it hides under your chair");
324		521
325	=item ev_default_destroy ()	522	=item ev_default_destroy ()
326		523
327	Destroys the default loop again (frees all memory and kernel state	524	Destroys the default loop again (frees all memory and kernel state
328	etc.). This stops all registered event watchers (by not touching them in	525	etc.). None of the active event watchers will be stopped in the normal
329	any way whatsoever, although you cannot rely on this :).	526	sense, so e.g. C<ev_is_active> might still return true. It is your
		527	responsibility to either stop all watchers cleanly yourself I<before>
		528	calling this function, or cope with the fact afterwards (which is usually
		529	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		530	for example).
		531
		532	Note that certain global state, such as signal state, will not be freed by
		533	this function, and related watchers (such as signal and child watchers)
		534	would need to be stopped manually.
		535
		536	In general it is not advisable to call this function except in the
		537	rare occasion where you really need to free e.g. the signal handling
		538	pipe fds. If you need dynamically allocated loops it is better to use
		539	C<ev_loop_new> and C<ev_loop_destroy>).
330		540
331	=item ev_loop_destroy (loop)	541	=item ev_loop_destroy (loop)
332		542
333	Like C<ev_default_destroy>, but destroys an event loop created by an	543	Like C<ev_default_destroy>, but destroys an event loop created by an
334	earlier call to C<ev_loop_new>.	544	earlier call to C<ev_loop_new>.
335		545
336	=item ev_default_fork ()	546	=item ev_default_fork ()
337		547
		548	This function sets a flag that causes subsequent C<ev_loop> iterations
338	This function reinitialises the kernel state for backends that have	549	to reinitialise the kernel state for backends that have one. Despite the
339	one. Despite the name, you can call it anytime, but it makes most sense	550	name, you can call it anytime, but it makes most sense after forking, in
340	after forking, in either the parent or child process (or both, but that	551	the child process (or both child and parent, but that again makes little
341	again makes little sense).	552	sense). You I<must> call it in the child before using any of the libev
		553	functions, and it will only take effect at the next C<ev_loop> iteration.
342		554
343	You I<must> call this function in the child process after forking if and	555	On the other hand, you only need to call this function in the child
344	only if you want to use the event library in both processes. If you just	556	process if and only if you want to use the event library in the child. If
345	fork+exec, you don't have to call it.	557	you just fork+exec, you don't have to call it at all.
346		558
347	The function itself is quite fast and it's usually not a problem to call	559	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	560	it just in case after a fork. To make this easy, the function will fit in
349	quite nicely into a call to C<pthread_atfork>:	561	quite nicely into a call to C<pthread_atfork>:
350		562
351	pthread_atfork (0, 0, ev_default_fork);	563	pthread_atfork (0, 0, ev_default_fork);
352		564
353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
354	without calling this function, so if you force one of those backends you
355	do not need to care.
356
357	=item ev_loop_fork (loop)	565	=item ev_loop_fork (loop)
358		566
359	Like C<ev_default_fork>, but acts on an event loop created by	567	Like C<ev_default_fork>, but acts on an event loop created by
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	568	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
361	after fork, and how you do this is entirely your own problem.	569	after fork that you want to re-use in the child, and how you do this is
		570	entirely your own problem.
		571
		572	=item int ev_is_default_loop (loop)
		573
		574	Returns true when the given loop is, in fact, the default loop, and false
		575	otherwise.
		576
		577	=item unsigned int ev_loop_count (loop)
		578
		579	Returns the count of loop iterations for the loop, which is identical to
		580	the number of times libev did poll for new events. It starts at C<0> and
		581	happily wraps around with enough iterations.
		582
		583	This value can sometimes be useful as a generation counter of sorts (it
		584	"ticks" the number of loop iterations), as it roughly corresponds with
		585	C<ev_prepare> and C<ev_check> calls.
362		586
363	=item unsigned int ev_backend (loop)	587	=item unsigned int ev_backend (loop)
364		588
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	590	use.
…		…
369		593
370	Returns the current "event loop time", which is the time the event loop	594	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	595	received events and started processing them. This timestamp does not
372	change as long as callbacks are being processed, and this is also the base	596	change as long as callbacks are being processed, and this is also the base
373	time used for relative timers. You can treat it as the timestamp of the	597	time used for relative timers. You can treat it as the timestamp of the
374	event occuring (or more correctly, libev finding out about it).	598	event occurring (or more correctly, libev finding out about it).
		599
		600	=item ev_now_update (loop)
		601
		602	Establishes the current time by querying the kernel, updating the time
		603	returned by C<ev_now ()> in the progress. This is a costly operation and
		604	is usually done automatically within C<ev_loop ()>.
		605
		606	This function is rarely useful, but when some event callback runs for a
		607	very long time without entering the event loop, updating libev's idea of
		608	the current time is a good idea.
		609
		610	See also "The special problem of time updates" in the C<ev_timer> section.
375		611
376	=item ev_loop (loop, int flags)	612	=item ev_loop (loop, int flags)
377		613
378	Finally, this is it, the event handler. This function usually is called	614	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	615	after you initialised all your watchers and you want to start handling
…		…
382	If the flags argument is specified as C<0>, it will not return until	618	If the flags argument is specified as C<0>, it will not return until
383	either no event watchers are active anymore or C<ev_unloop> was called.	619	either no event watchers are active anymore or C<ev_unloop> was called.
384		620
385	Please note that an explicit C<ev_unloop> is usually better than	621	Please note that an explicit C<ev_unloop> is usually better than
386	relying on all watchers to be stopped when deciding when a program has	622	relying on all watchers to be stopped when deciding when a program has
387	finished (especially in interactive programs), but having a program that	623	finished (especially in interactive programs), but having a program
388	automatically loops as long as it has to and no longer by virtue of	624	that automatically loops as long as it has to and no longer by virtue
389	relying on its watchers stopping correctly is a thing of beauty.	625	of relying on its watchers stopping correctly, that is truly a thing of
		626	beauty.
390		627
391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	628	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
392	those events and any outstanding ones, but will not block your process in	629	those events and any already outstanding ones, but will not block your
393	case there are no events and will return after one iteration of the loop.	630	process in case there are no events and will return after one iteration of
		631	the loop.
394		632
395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
396	neccessary) and will handle those and any outstanding ones. It will block	634	necessary) and will handle those and any already outstanding ones. It
397	your process until at least one new event arrives, and will return after	635	will block your process until at least one new event arrives (which could
398	one iteration of the loop. This is useful if you are waiting for some	636	be an event internal to libev itself, so there is no guarentee that a
399	external event in conjunction with something not expressible using other	637	user-registered callback will be called), and will return after one
		638	iteration of the loop.
		639
		640	This is useful if you are waiting for some external event in conjunction
		641	with something not expressible using other libev watchers (i.e. "roll your
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	642	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	643	usually a better approach for this kind of thing.
402		644
403	Here are the gory details of what C<ev_loop> does:	645	Here are the gory details of what C<ev_loop> does:
404		646
405	* If there are no active watchers (reference count is zero), return.	647	- Before the first iteration, call any pending watchers.
406	- Queue prepare watchers and then call all outstanding watchers.	648	* If EVFLAG_FORKCHECK was used, check for a fork.
		649	- If a fork was detected (by any means), queue and call all fork watchers.
		650	- Queue and call all prepare watchers.
407	- If we have been forked, recreate the kernel state.	651	- If we have been forked, detach and recreate the kernel state
		652	as to not disturb the other process.
408	- Update the kernel state with all outstanding changes.	653	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	654	- Update the "event loop time" (ev_now ()).
410	- Calculate for how long to block.	655	- Calculate for how long to sleep or block, if at all
		656	(active idle watchers, EVLOOP_NONBLOCK or not having
		657	any active watchers at all will result in not sleeping).
		658	- Sleep if the I/O and timer collect interval say so.
411	- Block the process, waiting for any events.	659	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	660	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	661	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
414	- Queue all outstanding timers.	662	- Queue all expired timers.
415	- Queue all outstanding periodics.	663	- Queue all expired periodics.
416	- If no events are pending now, queue all idle watchers.	664	- Unless any events are pending now, queue all idle watchers.
417	- Queue all check watchers.	665	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	666	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	667	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	668	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	669	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
422	were used, return, otherwise continue with step *.	670	were used, or there are no active watchers, return, otherwise
		671	continue with step *.
423		672
424	Example: queue some jobs and then loop until no events are outsanding	673	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	674	anymore.
426		675
427	... queue jobs here, make sure they register event watchers as long	676	... queue jobs here, make sure they register event watchers as long
428	... as they still have work to do (even an idle watcher will do..)	677	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	678	ev_loop (my_loop, 0);
430	... jobs done. yeah!	679	... jobs done or somebody called unloop. yeah!
431		680
432	=item ev_unloop (loop, how)	681	=item ev_unloop (loop, how)
433		682
434	Can be used to make a call to C<ev_loop> return early (but only after it	683	Can be used to make a call to C<ev_loop> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	684	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
438		687
		688	This "unloop state" will be cleared when entering C<ev_loop> again.
		689
		690	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		691
439	=item ev_ref (loop)	692	=item ev_ref (loop)
440		693
441	=item ev_unref (loop)	694	=item ev_unref (loop)
442		695
443	Ref/unref can be used to add or remove a reference count on the event	696	Ref/unref can be used to add or remove a reference count on the event
444	loop: Every watcher keeps one reference, and as long as the reference	697	loop: Every watcher keeps one reference, and as long as the reference
445	count is nonzero, C<ev_loop> will not return on its own. If you have	698	count is nonzero, C<ev_loop> will not return on its own.
		699
446	a watcher you never unregister that should not keep C<ev_loop> from	700	If you have a watcher you never unregister that should not keep C<ev_loop>
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	701	from returning, call ev_unref() after starting, and ev_ref() before
		702	stopping it.
		703
448	example, libev itself uses this for its internal signal pipe: It is not	704	As an example, libev itself uses this for its internal signal pipe: It is
449	visible to the libev user and should not keep C<ev_loop> from exiting if	705	not visible to the libev user and should not keep C<ev_loop> from exiting
450	no event watchers registered by it are active. It is also an excellent	706	if no event watchers registered by it are active. It is also an excellent
451	way to do this for generic recurring timers or from within third-party	707	way to do this for generic recurring timers or from within third-party
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	708	libraries. Just remember to I<unref after start> and I<ref before stop>
		709	(but only if the watcher wasn't active before, or was active before,
		710	respectively).
453		711
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
455	running when nothing else is active.	713	running when nothing else is active.
456		714
457	struct dv_signal exitsig;	715	ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	716	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	717	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	718	evf_unref (loop);
461		719
462	Example: for some weird reason, unregister the above signal handler again.	720	Example: For some weird reason, unregister the above signal handler again.
463		721
464	ev_ref (myloop);	722	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	723	ev_signal_stop (loop, &exitsig);
		724
		725	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		726
		727	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		728
		729	These advanced functions influence the time that libev will spend waiting
		730	for events. Both time intervals are by default C<0>, meaning that libev
		731	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		732	latency.
		733
		734	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		735	allows libev to delay invocation of I/O and timer/periodic callbacks
		736	to increase efficiency of loop iterations (or to increase power-saving
		737	opportunities).
		738
		739	The idea is that sometimes your program runs just fast enough to handle
		740	one (or very few) event(s) per loop iteration. While this makes the
		741	program responsive, it also wastes a lot of CPU time to poll for new
		742	events, especially with backends like C<select ()> which have a high
		743	overhead for the actual polling but can deliver many events at once.
		744
		745	By setting a higher I<io collect interval> you allow libev to spend more
		746	time collecting I/O events, so you can handle more events per iteration,
		747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		748	C<ev_timer>) will be not affected. Setting this to a non-null value will
		749	introduce an additional C<ev_sleep ()> call into most loop iterations.
		750
		751	Likewise, by setting a higher I<timeout collect interval> you allow libev
		752	to spend more time collecting timeouts, at the expense of increased
		753	latency/jitter/inexactness (the watcher callback will be called
		754	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		755	value will not introduce any overhead in libev.
		756
		757	Many (busy) programs can usually benefit by setting the I/O collect
		758	interval to a value near C<0.1> or so, which is often enough for
		759	interactive servers (of course not for games), likewise for timeouts. It
		760	usually doesn't make much sense to set it to a lower value than C<0.01>,
		761	as this approaches the timing granularity of most systems.
		762
		763	Setting the I<timeout collect interval> can improve the opportunity for
		764	saving power, as the program will "bundle" timer callback invocations that
		765	are "near" in time together, by delaying some, thus reducing the number of
		766	times the process sleeps and wakes up again. Another useful technique to
		767	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		768	they fire on, say, one-second boundaries only.
		769
		770	=item ev_loop_verify (loop)
		771
		772	This function only does something when C<EV_VERIFY> support has been
		773	compiled in. which is the default for non-minimal builds. It tries to go
		774	through all internal structures and checks them for validity. If anything
		775	is found to be inconsistent, it will print an error message to standard
		776	error and call C<abort ()>.
		777
		778	This can be used to catch bugs inside libev itself: under normal
		779	circumstances, this function will never abort as of course libev keeps its
		780	data structures consistent.
466		781
467	=back	782	=back
		783
468		784
469	=head1 ANATOMY OF A WATCHER	785	=head1 ANATOMY OF A WATCHER
470		786
471	A watcher is a structure that you create and register to record your	787	A watcher is a structure that you create and register to record your
472	interest in some event. For instance, if you want to wait for STDIN to	788	interest in some event. For instance, if you want to wait for STDIN to
473	become readable, you would create an C<ev_io> watcher for that:	789	become readable, you would create an C<ev_io> watcher for that:
474		790
475	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	791	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
476	{	792	{
477	ev_io_stop (w);	793	ev_io_stop (w);
478	ev_unloop (loop, EVUNLOOP_ALL);	794	ev_unloop (loop, EVUNLOOP_ALL);
479	}	795	}
480		796
481	struct ev_loop *loop = ev_default_loop (0);	797	struct ev_loop *loop = ev_default_loop (0);
482	struct ev_io stdin_watcher;	798	ev_io stdin_watcher;
483	ev_init (&stdin_watcher, my_cb);	799	ev_init (&stdin_watcher, my_cb);
484	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
485	ev_io_start (loop, &stdin_watcher);	801	ev_io_start (loop, &stdin_watcher);
486	ev_loop (loop, 0);	802	ev_loop (loop, 0);
487		803
488	As you can see, you are responsible for allocating the memory for your	804	As you can see, you are responsible for allocating the memory for your
489	watcher structures (and it is usually a bad idea to do this on the stack,	805	watcher structures (and it is usually a bad idea to do this on the stack,
490	although this can sometimes be quite valid).	806	although this can sometimes be quite valid).
491		807
492	Each watcher structure must be initialised by a call to C<ev_init	808	Each watcher structure must be initialised by a call to C<ev_init
493	(watcher *, callback)>, which expects a callback to be provided. This	809	(watcher *, callback)>, which expects a callback to be provided. This
494	callback gets invoked each time the event occurs (or, in the case of io	810	callback gets invoked each time the event occurs (or, in the case of I/O
495	watchers, each time the event loop detects that the file descriptor given	811	watchers, each time the event loop detects that the file descriptor given
496	is readable and/or writable).	812	is readable and/or writable).
497		813
498	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
499	with arguments specific to this watcher type. There is also a macro	815	with arguments specific to this watcher type. There is also a macro
…		…
505	*) >>), and you can stop watching for events at any time by calling the	821	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
507		823
508	As long as your watcher is active (has been started but not stopped) you	824	As long as your watcher is active (has been started but not stopped) you
509	must not touch the values stored in it. Most specifically you must never	825	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	826	reinitialise it or call its C<set> macro.
511
512	You can check whether an event is active by calling the C<ev_is_active
513	(watcher *)> macro. To see whether an event is outstanding (but the
514	callback for it has not been called yet) you can use the C<ev_is_pending
515	(watcher *)> macro.
516		827
517	Each and every callback receives the event loop pointer as first, the	828	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	829	registered watcher structure as second, and a bitset of received events as
519	third argument.	830	third argument.
520		831
…		…
544	The signal specified in the C<ev_signal> watcher has been received by a thread.	855	The signal specified in the C<ev_signal> watcher has been received by a thread.
545		856
546	=item C<EV_CHILD>	857	=item C<EV_CHILD>
547		858
548	The pid specified in the C<ev_child> watcher has received a status change.	859	The pid specified in the C<ev_child> watcher has received a status change.
		860
		861	=item C<EV_STAT>
		862
		863	The path specified in the C<ev_stat> watcher changed its attributes somehow.
549		864
550	=item C<EV_IDLE>	865	=item C<EV_IDLE>
551		866
552	The C<ev_idle> watcher has determined that you have nothing better to do.	867	The C<ev_idle> watcher has determined that you have nothing better to do.
553		868
…		…
561	received events. Callbacks of both watcher types can start and stop as	876	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	877	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	878	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	879	C<ev_loop> from blocking).
565		880
		881	=item C<EV_EMBED>
		882
		883	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		884
		885	=item C<EV_FORK>
		886
		887	The event loop has been resumed in the child process after fork (see
		888	C<ev_fork>).
		889
		890	=item C<EV_ASYNC>
		891
		892	The given async watcher has been asynchronously notified (see C<ev_async>).
		893
566	=item C<EV_ERROR>	894	=item C<EV_ERROR>
567		895
568	An unspecified error has occured, the watcher has been stopped. This might	896	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	897	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	898	ran out of memory, a file descriptor was found to be closed or any other
		899	problem. Libev considers these application bugs.
		900
571	problem. You best act on it by reporting the problem and somehow coping	901	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	902	watcher being stopped. Note that well-written programs should not receive
		903	an error ever, so when your watcher receives it, this usually indicates a
		904	bug in your program.
573		905
574	Libev will usually signal a few "dummy" events together with an error,	906	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	907	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	908	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	909	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	910	programs, though, as the fd could already be closed and reused for another
		911	thing, so beware.
579		912
580	=back	913	=back
581		914
		915	=head2 GENERIC WATCHER FUNCTIONS
		916
		917	In the following description, C<TYPE> stands for the watcher type,
		918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		919
		920	=over 4
		921
		922	=item C<ev_init> (ev_TYPE *watcher, callback)
		923
		924	This macro initialises the generic portion of a watcher. The contents
		925	of the watcher object can be arbitrary (so C<malloc> will do). Only
		926	the generic parts of the watcher are initialised, you I<need> to call
		927	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		928	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		929	which rolls both calls into one.
		930
		931	You can reinitialise a watcher at any time as long as it has been stopped
		932	(or never started) and there are no pending events outstanding.
		933
		934	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		935	int revents)>.
		936
		937	Example: Initialise an C<ev_io> watcher in two steps.
		938
		939	ev_io w;
		940	ev_init (&w, my_cb);
		941	ev_io_set (&w, STDIN_FILENO, EV_READ);
		942
		943	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		944
		945	This macro initialises the type-specific parts of a watcher. You need to
		946	call C<ev_init> at least once before you call this macro, but you can
		947	call C<ev_TYPE_set> any number of times. You must not, however, call this
		948	macro on a watcher that is active (it can be pending, however, which is a
		949	difference to the C<ev_init> macro).
		950
		951	Although some watcher types do not have type-specific arguments
		952	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		953
		954	See C<ev_init>, above, for an example.
		955
		956	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		957
		958	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		959	calls into a single call. This is the most convenient method to initialise
		960	a watcher. The same limitations apply, of course.
		961
		962	Example: Initialise and set an C<ev_io> watcher in one step.
		963
		964	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		965
		966	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		967
		968	Starts (activates) the given watcher. Only active watchers will receive
		969	events. If the watcher is already active nothing will happen.
		970
		971	Example: Start the C<ev_io> watcher that is being abused as example in this
		972	whole section.
		973
		974	ev_io_start (EV_DEFAULT_UC, &w);
		975
		976	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		977
		978	Stops the given watcher if active, and clears the pending status (whether
		979	the watcher was active or not).
		980
		981	It is possible that stopped watchers are pending - for example,
		982	non-repeating timers are being stopped when they become pending - but
		983	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		984	pending. If you want to free or reuse the memory used by the watcher it is
		985	therefore a good idea to always call its C<ev_TYPE_stop> function.
		986
		987	=item bool ev_is_active (ev_TYPE *watcher)
		988
		989	Returns a true value iff the watcher is active (i.e. it has been started
		990	and not yet been stopped). As long as a watcher is active you must not modify
		991	it.
		992
		993	=item bool ev_is_pending (ev_TYPE *watcher)
		994
		995	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		996	events but its callback has not yet been invoked). As long as a watcher
		997	is pending (but not active) you must not call an init function on it (but
		998	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		999	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1000	it).
		1001
		1002	=item callback ev_cb (ev_TYPE *watcher)
		1003
		1004	Returns the callback currently set on the watcher.
		1005
		1006	=item ev_cb_set (ev_TYPE *watcher, callback)
		1007
		1008	Change the callback. You can change the callback at virtually any time
		1009	(modulo threads).
		1010
		1011	=item ev_set_priority (ev_TYPE *watcher, priority)
		1012
		1013	=item int ev_priority (ev_TYPE *watcher)
		1014
		1015	Set and query the priority of the watcher. The priority is a small
		1016	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1017	(default: C<-2>). Pending watchers with higher priority will be invoked
		1018	before watchers with lower priority, but priority will not keep watchers
		1019	from being executed (except for C<ev_idle> watchers).
		1020
		1021	This means that priorities are I<only> used for ordering callback
		1022	invocation after new events have been received. This is useful, for
		1023	example, to reduce latency after idling, or more often, to bind two
		1024	watchers on the same event and make sure one is called first.
		1025
		1026	If you need to suppress invocation when higher priority events are pending
		1027	you need to look at C<ev_idle> watchers, which provide this functionality.
		1028
		1029	You I<must not> change the priority of a watcher as long as it is active or
		1030	pending.
		1031
		1032	The default priority used by watchers when no priority has been set is
		1033	always C<0>, which is supposed to not be too high and not be too low :).
		1034
		1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1036	fine, as long as you do not mind that the priority value you query might
		1037	or might not have been adjusted to be within valid range.
		1038
		1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1040
		1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1042	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1043	can deal with that fact, as both are simply passed through to the
		1044	callback.
		1045
		1046	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1047
		1048	If the watcher is pending, this function clears its pending status and
		1049	returns its C<revents> bitset (as if its callback was invoked). If the
		1050	watcher isn't pending it does nothing and returns C<0>.
		1051
		1052	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1053	callback to be invoked, which can be accomplished with this function.
		1054
		1055	=back
		1056
		1057
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1058	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		1059
584	Each watcher has, by default, a member C<void *data> that you can change	1060	Each watcher has, by default, a member C<void *data> that you can change
585	and read at any time, libev will completely ignore it. This can be used	1061	and read at any time: libev will completely ignore it. This can be used
586	to associate arbitrary data with your watcher. If you need more data and	1062	to associate arbitrary data with your watcher. If you need more data and
587	don't want to allocate memory and store a pointer to it in that data	1063	don't want to allocate memory and store a pointer to it in that data
588	member, you can also "subclass" the watcher type and provide your own	1064	member, you can also "subclass" the watcher type and provide your own
589	data:	1065	data:
590		1066
591	struct my_io	1067	struct my_io
592	{	1068	{
593	struct ev_io io;	1069	ev_io io;
594	int otherfd;	1070	int otherfd;
595	void *somedata;	1071	void *somedata;
596	struct whatever *mostinteresting;	1072	struct whatever *mostinteresting;
597	}	1073	};
		1074
		1075	...
		1076	struct my_io w;
		1077	ev_io_init (&w.io, my_cb, fd, EV_READ);
598		1078
599	And since your callback will be called with a pointer to the watcher, you	1079	And since your callback will be called with a pointer to the watcher, you
600	can cast it back to your own type:	1080	can cast it back to your own type:
601		1081
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1082	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
603	{	1083	{
604	struct my_io *w = (struct my_io *)w_;	1084	struct my_io *w = (struct my_io *)w_;
605	...	1085	...
606	}	1086	}
607		1087
608	More interesting and less C-conformant ways of catsing your callback type	1088	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	1089	instead have been omitted.
		1090
		1091	Another common scenario is to use some data structure with multiple
		1092	embedded watchers:
		1093
		1094	struct my_biggy
		1095	{
		1096	int some_data;
		1097	ev_timer t1;
		1098	ev_timer t2;
		1099	}
		1100
		1101	In this case getting the pointer to C<my_biggy> is a bit more
		1102	complicated: Either you store the address of your C<my_biggy> struct
		1103	in the C<data> member of the watcher (for woozies), or you need to use
		1104	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1105	programmers):
		1106
		1107	#include <stddef.h>
		1108
		1109	static void
		1110	t1_cb (EV_P_ ev_timer *w, int revents)
		1111	{
		1112	struct my_biggy big = (struct my_biggy *
		1113	(((char *)w) - offsetof (struct my_biggy, t1));
		1114	}
		1115
		1116	static void
		1117	t2_cb (EV_P_ ev_timer *w, int revents)
		1118	{
		1119	struct my_biggy big = (struct my_biggy *
		1120	(((char *)w) - offsetof (struct my_biggy, t2));
		1121	}
610		1122
611		1123
612	=head1 WATCHER TYPES	1124	=head1 WATCHER TYPES
613		1125
614	This section describes each watcher in detail, but will not repeat	1126	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1127	information given in the last section. Any initialisation/set macros,
		1128	functions and members specific to the watcher type are explained.
616		1129
		1130	Members are additionally marked with either I<[read-only]>, meaning that,
		1131	while the watcher is active, you can look at the member and expect some
		1132	sensible content, but you must not modify it (you can modify it while the
		1133	watcher is stopped to your hearts content), or I<[read-write]>, which
		1134	means you can expect it to have some sensible content while the watcher
		1135	is active, but you can also modify it. Modifying it may not do something
		1136	sensible or take immediate effect (or do anything at all), but libev will
		1137	not crash or malfunction in any way.
617		1138
		1139
618	=head2 C<ev_io> - is this file descriptor readable or writable	1140	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1141
620	I/O watchers check whether a file descriptor is readable or writable	1142	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1143	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1144	would not block the process and writing would at least be able to write
623	condition persists. Remember you can stop the watcher if you don't want to	1145	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1146	receiving events as long as the condition persists. Remember you can stop
		1147	the watcher if you don't want to act on the event and neither want to
		1148	receive future events.
625		1149
626	In general you can register as many read and/or write event watchers per	1150	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1151	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1152	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1153	required if you know what you are doing).
630		1154
631	You have to be careful with dup'ed file descriptors, though. Some backends	1155	If you cannot use non-blocking mode, then force the use of a
632	(the linux epoll backend is a notable example) cannot handle dup'ed file	1156	known-to-be-good backend (at the time of this writing, this includes only
633	descriptors correctly if you register interest in two or more fds pointing	1157	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
634	to the same underlying file/socket etc. description (that is, they share
635	the same underlying "file open").
636		1158
637	If you must do this, then force the use of a known-to-be-good backend	1159	Another thing you have to watch out for is that it is quite easy to
638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1160	receive "spurious" readiness notifications, that is your callback might
		1161	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1162	because there is no data. Not only are some backends known to create a
		1163	lot of those (for example Solaris ports), it is very easy to get into
		1164	this situation even with a relatively standard program structure. Thus
		1165	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1166	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1167
		1168	If you cannot run the fd in non-blocking mode (for example you should
		1169	not play around with an Xlib connection), then you have to separately
		1170	re-test whether a file descriptor is really ready with a known-to-be good
		1171	interface such as poll (fortunately in our Xlib example, Xlib already
		1172	does this on its own, so its quite safe to use). Some people additionally
		1173	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1174	indefinitely.
		1175
		1176	But really, best use non-blocking mode.
		1177
		1178	=head3 The special problem of disappearing file descriptors
		1179
		1180	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1181	descriptor (either due to calling C<close> explicitly or any other means,
		1182	such as C<dup2>). The reason is that you register interest in some file
		1183	descriptor, but when it goes away, the operating system will silently drop
		1184	this interest. If another file descriptor with the same number then is
		1185	registered with libev, there is no efficient way to see that this is, in
		1186	fact, a different file descriptor.
		1187
		1188	To avoid having to explicitly tell libev about such cases, libev follows
		1189	the following policy: Each time C<ev_io_set> is being called, libev
		1190	will assume that this is potentially a new file descriptor, otherwise
		1191	it is assumed that the file descriptor stays the same. That means that
		1192	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1193	descriptor even if the file descriptor number itself did not change.
		1194
		1195	This is how one would do it normally anyway, the important point is that
		1196	the libev application should not optimise around libev but should leave
		1197	optimisations to libev.
		1198
		1199	=head3 The special problem of dup'ed file descriptors
		1200
		1201	Some backends (e.g. epoll), cannot register events for file descriptors,
		1202	but only events for the underlying file descriptions. That means when you
		1203	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1204	events for them, only one file descriptor might actually receive events.
		1205
		1206	There is no workaround possible except not registering events
		1207	for potentially C<dup ()>'ed file descriptors, or to resort to
		1208	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1209
		1210	=head3 The special problem of fork
		1211
		1212	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1213	useless behaviour. Libev fully supports fork, but needs to be told about
		1214	it in the child.
		1215
		1216	To support fork in your programs, you either have to call
		1217	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1218	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
639	C<EVBACKEND_POLL>).	1219	C<EVBACKEND_POLL>.
		1220
		1221	=head3 The special problem of SIGPIPE
		1222
		1223	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1224	when writing to a pipe whose other end has been closed, your program gets
		1225	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1226	this is sensible behaviour, for daemons, this is usually undesirable.
		1227
		1228	So when you encounter spurious, unexplained daemon exits, make sure you
		1229	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1230	somewhere, as that would have given you a big clue).
		1231
		1232
		1233	=head3 Watcher-Specific Functions
640		1234
641	=over 4	1235	=over 4
642		1236
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1237	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1238
645	=item ev_io_set (ev_io *, int fd, int events)	1239	=item ev_io_set (ev_io *, int fd, int events)
646		1240
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1241	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1242	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1243	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
650		1244
651	Please note that most of the more scalable backend mechanisms (for example	1245	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1246
653	for file descriptors, so you practically need to use non-blocking I/O (and	1247	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1248
655	interface before doing I/O (XLib can do this), or force the use of either	1249	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1250
657	problem. Also note that it is quite easy to have your callback invoked	1251	The events being watched.
658	when the readyness condition is no longer valid even when employing
659	typical ways of handling events, so its a good idea to use non-blocking
660	I/O unconditionally.
661		1252
662	=back	1253	=back
663		1254
		1255	=head3 Examples
		1256
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1257	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1258	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1259	attempt to read a whole line in the callback.
667		1260
668	static void	1261	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1262	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
670	{	1263	{
671	ev_io_stop (loop, w);	1264	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1265	.. read from stdin here (or from w->fd) and handle any I/O errors
673	}	1266	}
674		1267
675	...	1268	...
676	struct ev_loop *loop = ev_default_init (0);	1269	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1270	ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1271	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1272	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1273	ev_loop (loop, 0);
681		1274
682		1275
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1276	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1277
685	Timer watchers are simple relative timers that generate an event after a	1278	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1279	given time, and optionally repeating in regular intervals after that.
687		1280
688	The timers are based on real time, that is, if you register an event that	1281	The timers are based on real time, that is, if you register an event that
689	times out after an hour and you reset your system clock to last years	1282	times out after an hour and you reset your system clock to January last
690	time, it will still time out after (roughly) and hour. "Roughly" because	1283	year, it will still time out after (roughly) one hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1284	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1285	monotonic clock option helps a lot here).
		1286
		1287	The callback is guaranteed to be invoked only I<after> its timeout has
		1288	passed, but if multiple timers become ready during the same loop iteration
		1289	then order of execution is undefined.
		1290
		1291	=head3 Be smart about timeouts
		1292
		1293	Many real-world problems invole some kind of time-out, usually for error
		1294	recovery. A typical example is an HTTP request - if the other side hangs,
		1295	you want to raise some error after a while.
		1296
		1297	Here are some ways on how to handle this problem, from simple and
		1298	inefficient to very efficient.
		1299
		1300	In the following examples a 60 second activity timeout is assumed - a
		1301	timeout that gets reset to 60 seconds each time some data ("a lifesign")
		1302	was received.
		1303
		1304	=over 4
		1305
		1306	=item 1. Use a timer and stop, reinitialise, start it on activity.
		1307
		1308	This is the most obvious, but not the most simple way: In the beginning,
		1309	start the watcher:
		1310
		1311	ev_timer_init (timer, callback, 60., 0.);
		1312	ev_timer_start (loop, timer);
		1313
		1314	Then, each time there is some activity, C<ev_timer_stop> the timer,
		1315	initialise it again, and start it:
		1316
		1317	ev_timer_stop (loop, timer);
		1318	ev_timer_set (timer, 60., 0.);
		1319	ev_timer_start (loop, timer);
		1320
		1321	This is relatively simple to implement, but means that each time there
		1322	is some activity, libev will first have to remove the timer from it's
		1323	internal data strcuture and then add it again.
		1324
		1325	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1326
		1327	This is the easiest way, and involves using C<ev_timer_again> instead of
		1328	C<ev_timer_start>.
		1329
		1330	For this, configure an C<ev_timer> with a C<repeat> value of C<60> and
		1331	then call C<ev_timer_again> at start and each time you successfully read
		1332	or write some data. If you go into an idle state where you do not expect
		1333	data to travel on the socket, you can C<ev_timer_stop> the timer, and
		1334	C<ev_timer_again> will automatically restart it if need be.
		1335
		1336	That means you can ignore the C<after> value and C<ev_timer_start>
		1337	altogether and only ever use the C<repeat> value and C<ev_timer_again>.
		1338
		1339	At start:
		1340
		1341	ev_timer_init (timer, callback, 0., 60.);
		1342	ev_timer_again (loop, timer);
		1343
		1344	Each time you receive some data:
		1345
		1346	ev_timer_again (loop, timer);
		1347
		1348	It is even possible to change the time-out on the fly:
		1349
		1350	timer->repeat = 30.;
		1351	ev_timer_again (loop, timer);
		1352
		1353	This is slightly more efficient then stopping/starting the timer each time
		1354	you want to modify its timeout value, as libev does not have to completely
		1355	remove and re-insert the timer from/into it's internal data structure.
		1356
		1357	=item 3. Let the timer time out, but then re-arm it as required.
		1358
		1359	This method is more tricky, but usually most efficient: Most timeouts are
		1360	relatively long compared to the loop iteration time - in our example,
		1361	within 60 seconds, there are usually many I/O events with associated
		1362	activity resets.
		1363
		1364	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1365	but remember the time of last activity, and check for a real timeout only
		1366	within the callback:
		1367
		1368	ev_tstamp last_activity; // time of last activity
		1369
		1370	static void
		1371	callback (EV_P_ ev_timer *w, int revents)
		1372	{
		1373	ev_tstamp now = ev_now (EV_A);
		1374	ev_tstamp timeout = last_activity + 60.;
		1375
		1376	// if last_activity is older than now - timeout, we did time out
		1377	if (timeout < now)
		1378	{
		1379	// timeout occured, take action
		1380	}
		1381	else
		1382	{
		1383	// callback was invoked, but there was some activity, re-arm
		1384	// to fire in last_activity + 60.
		1385	w->again = timeout - now;
		1386	ev_timer_again (EV_A_ w);
		1387	}
		1388	}
		1389
		1390	To summarise the callback: first calculate the real time-out (defined as
		1391	"60 seconds after the last activity"), then check if that time has been
		1392	reached, which means there was a real timeout. Otherwise the callback was
		1393	invoked too early (timeout is in the future), so re-schedule the timer to
		1394	fire at that future time.
		1395
		1396	Note how C<ev_timer_again> is used, taking advantage of the
		1397	C<ev_timer_again> optimisation when the timer is already running.
		1398
		1399	This scheme causes more callback invocations (about one every 60 seconds),
		1400	but virtually no calls to libev to change the timeout.
		1401
		1402	To start the timer, simply intiialise the watcher and C<last_activity>,
		1403	then call the callback:
		1404
		1405	ev_timer_init (timer, callback);
		1406	last_activity = ev_now (loop);
		1407	callback (loop, timer, EV_TIMEOUT);
		1408
		1409	And when there is some activity, simply remember the time in
		1410	C<last_activity>:
		1411
		1412	last_actiivty = ev_now (loop);
		1413
		1414	This technique is slightly more complex, but in most cases where the
		1415	time-out is unlikely to be triggered, much more efficient.
		1416
		1417	=back
		1418
		1419	=head3 The special problem of time updates
		1420
		1421	Establishing the current time is a costly operation (it usually takes at
		1422	least two system calls): EV therefore updates its idea of the current
		1423	time only before and after C<ev_loop> collects new events, which causes a
		1424	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1425	lots of events in one iteration.
693		1426
694	The relative timeouts are calculated relative to the C<ev_now ()>	1427	The relative timeouts are calculated relative to the C<ev_now ()>
695	time. This is usually the right thing as this timestamp refers to the time	1428	time. This is usually the right thing as this timestamp refers to the time
696	of the event triggering whatever timeout you are modifying/starting. If	1429	of the event triggering whatever timeout you are modifying/starting. If
697	you suspect event processing to be delayed and you I<need> to base the timeout	1430	you suspect event processing to be delayed and you I<need> to base the
698	on the current time, use something like this to adjust for this:	1431	timeout on the current time, use something like this to adjust for this:
699		1432
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1433	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		1434
702	The callback is guarenteed to be invoked only when its timeout has passed,	1435	If the event loop is suspended for a long time, you can also force an
703	but if multiple timers become ready during the same loop iteration then	1436	update of the time returned by C<ev_now ()> by calling C<ev_now_update
704	order of execution is undefined.	1437	()>.
		1438
		1439	=head3 Watcher-Specific Functions and Data Members
705		1440
706	=over 4	1441	=over 4
707		1442
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1443	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1444
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1445	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		1446
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1447	Configure the timer to trigger after C<after> seconds. If C<repeat>
713	C<0.>, then it will automatically be stopped. If it is positive, then the	1448	is C<0.>, then it will automatically be stopped once the timeout is
714	timer will automatically be configured to trigger again C<repeat> seconds	1449	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	1450	configured to trigger again C<repeat> seconds later, again, and again,
		1451	until stopped manually.
716		1452
717	The timer itself will do a best-effort at avoiding drift, that is, if you	1453	The timer itself will do a best-effort at avoiding drift, that is, if
718	configure a timer to trigger every 10 seconds, then it will trigger at	1454	you configure a timer to trigger every 10 seconds, then it will normally
719	exactly 10 second intervals. If, however, your program cannot keep up with	1455	trigger at exactly 10 second intervals. If, however, your program cannot
720	the timer (because it takes longer than those 10 seconds to do stuff) the	1456	keep up with the timer (because it takes longer than those 10 seconds to
721	timer will not fire more than once per event loop iteration.	1457	do stuff) the timer will not fire more than once per event loop iteration.
722		1458
723	=item ev_timer_again (loop)	1459	=item ev_timer_again (loop, ev_timer *)
724		1460
725	This will act as if the timer timed out and restart it again if it is	1461	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1462	repeating. The exact semantics are:
727		1463
		1464	If the timer is pending, its pending status is cleared.
		1465
728	If the timer is started but nonrepeating, stop it.	1466	If the timer is started but non-repeating, stop it (as if it timed out).
729		1467
730	If the timer is repeating, either start it if necessary (with the repeat	1468	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1469	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1470
733	This sounds a bit complicated, but here is a useful and typical	1471	This sounds a bit complicated, see "Be smart about timeouts", above, for a
734	example: Imagine you have a tcp connection and you want a so-called idle	1472	usage example.
735	timeout, that is, you want to be called when there have been, say, 60	1473
736	seconds of inactivity on the socket. The easiest way to do this is to	1474	=item ev_tstamp repeat [read-write]
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1475
738	time you successfully read or write some data. If you go into an idle	1476	The current C<repeat> value. Will be used each time the watcher times out
739	state where you do not expect data to travel on the socket, you can stop	1477	or C<ev_timer_again> is called, and determines the next timeout (if any),
740	the timer, and again will automatically restart it if need be.	1478	which is also when any modifications are taken into account.
741		1479
742	=back	1480	=back
743		1481
		1482	=head3 Examples
		1483
744	Example: create a timer that fires after 60 seconds.	1484	Example: Create a timer that fires after 60 seconds.
745		1485
746	static void	1486	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1487	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
748	{	1488	{
749	.. one minute over, w is actually stopped right here	1489	.. one minute over, w is actually stopped right here
750	}	1490	}
751		1491
752	struct ev_timer mytimer;	1492	ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1493	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	1494	ev_timer_start (loop, &mytimer);
755		1495
756	Example: create a timeout timer that times out after 10 seconds of	1496	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	1497	inactivity.
758		1498
759	static void	1499	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1500	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
761	{	1501	{
762	.. ten seconds without any activity	1502	.. ten seconds without any activity
763	}	1503	}
764		1504
765	struct ev_timer mytimer;	1505	ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1506	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	1507	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	1508	ev_loop (loop, 0);
769		1509
770	// and in some piece of code that gets executed on any "activity":	1510	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	1511	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	1512	ev_timer_again (&mytimer);
773		1513
774		1514
775	=head2 C<ev_periodic> - to cron or not to cron	1515	=head2 C<ev_periodic> - to cron or not to cron?
776		1516
777	Periodic watchers are also timers of a kind, but they are very versatile	1517	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	1518	(and unfortunately a bit complex).
779		1519
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1520	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
781	but on wallclock time (absolute time). You can tell a periodic watcher	1521	but on wall clock time (absolute time). You can tell a periodic watcher
782	to trigger "at" some specific point in time. For example, if you tell a	1522	to trigger after some specific point in time. For example, if you tell a
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1523	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
784	+ 10.>) and then reset your system clock to the last year, then it will	1524	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1525	clock to January of the previous year, then it will take more than year
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1526	to trigger the event (unlike an C<ev_timer>, which would still trigger
786	roughly 10 seconds later and of course not if you reset your system time	1527	roughly 10 seconds later as it uses a relative timeout).
787	again).
788		1528
789	They can also be used to implement vastly more complex timers, such as	1529	C<ev_periodic>s can also be used to implement vastly more complex timers,
790	triggering an event on eahc midnight, local time.	1530	such as triggering an event on each "midnight, local time", or other
		1531	complicated rules.
791		1532
792	As with timers, the callback is guarenteed to be invoked only when the	1533	As with timers, the callback is guaranteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	1534	time (C<at>) has passed, but if multiple periodic timers become ready
794	during the same loop iteration then order of execution is undefined.	1535	during the same loop iteration, then order of execution is undefined.
		1536
		1537	=head3 Watcher-Specific Functions and Data Members
795		1538
796	=over 4	1539	=over 4
797		1540
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1541	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
799		1542
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1543	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
801		1544
802	Lots of arguments, lets sort it out... There are basically three modes of	1545	Lots of arguments, lets sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	1546	operation, and we will explain them from simplest to most complex:
804		1547
805	=over 4	1548	=over 4
806		1549
807	=item * absolute timer (interval = reschedule_cb = 0)	1550	=item * absolute timer (at = time, interval = reschedule_cb = 0)
808		1551
809	In this configuration the watcher triggers an event at the wallclock time	1552	In this configuration the watcher triggers an event after the wall clock
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1553	time C<at> has passed. It will not repeat and will not adjust when a time
811	that is, if it is to be run at January 1st 2011 then it will run when the	1554	jump occurs, that is, if it is to be run at January 1st 2011 then it will
812	system time reaches or surpasses this time.	1555	only run when the system clock reaches or surpasses this time.
813		1556
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1557	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
815		1558
816	In this mode the watcher will always be scheduled to time out at the next	1559	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	1560	C<at + N * interval> time (for some integer N, which can also be negative)
818	of any time jumps.	1561	and then repeat, regardless of any time jumps.
819		1562
820	This can be used to create timers that do not drift with respect to system	1563	This can be used to create timers that do not drift with respect to the
821	time:	1564	system clock, for example, here is a C<ev_periodic> that triggers each
		1565	hour, on the hour:
822		1566
823	ev_periodic_set (&periodic, 0., 3600., 0);	1567	ev_periodic_set (&periodic, 0., 3600., 0);
824		1568
825	This doesn't mean there will always be 3600 seconds in between triggers,	1569	This doesn't mean there will always be 3600 seconds in between triggers,
826	but only that the the callback will be called when the system time shows a	1570	but only that the callback will be called when the system time shows a
827	full hour (UTC), or more correctly, when the system time is evenly divisible	1571	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	1572	by 3600.
829		1573
830	Another way to think about it (for the mathematically inclined) is that	1574	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	1575	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	1576	time where C<time = at (mod interval)>, regardless of any time jumps.
833		1577
		1578	For numerical stability it is preferable that the C<at> value is near
		1579	C<ev_now ()> (the current time), but there is no range requirement for
		1580	this value, and in fact is often specified as zero.
		1581
		1582	Note also that there is an upper limit to how often a timer can fire (CPU
		1583	speed for example), so if C<interval> is very small then timing stability
		1584	will of course deteriorate. Libev itself tries to be exact to be about one
		1585	millisecond (if the OS supports it and the machine is fast enough).
		1586
834	=item * manual reschedule mode (reschedule_cb = callback)	1587	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
835		1588
836	In this mode the values for C<interval> and C<at> are both being	1589	In this mode the values for C<interval> and C<at> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	1590	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	1591	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	1592	current time as second argument.
840		1593
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1594	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
842	ever, or make any event loop modifications>. If you need to stop it,	1595	ever, or make ANY event loop modifications whatsoever>.
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
844	starting a prepare watcher).
845		1596
		1597	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1598	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1599	only event loop modification you are allowed to do).
		1600
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1601	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
847	ev_tstamp now)>, e.g.:	1602	*w, ev_tstamp now)>, e.g.:
848		1603
		1604	static ev_tstamp
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1605	my_rescheduler (ev_periodic *w, ev_tstamp now)
850	{	1606	{
851	return now + 60.;	1607	return now + 60.;
852	}	1608	}
853		1609
854	It must return the next time to trigger, based on the passed time value	1610	It must return the next time to trigger, based on the passed time value
855	(that is, the lowest time value larger than to the second argument). It	1611	(that is, the lowest time value larger than to the second argument). It
856	will usually be called just before the callback will be triggered, but	1612	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	1613	might be called at other times, too.
858		1614
859	NOTE: I<< This callback must always return a time that is later than the	1615	NOTE: I<< This callback must always return a time that is higher than or
860	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1616	equal to the passed C<now> value >>.
861		1617
862	This can be used to create very complex timers, such as a timer that	1618	This can be used to create very complex timers, such as a timer that
863	triggers on each midnight, local time. To do this, you would calculate the	1619	triggers on "next midnight, local time". To do this, you would calculate the
864	next midnight after C<now> and return the timestamp value for this. How	1620	next midnight after C<now> and return the timestamp value for this. How
865	you do this is, again, up to you (but it is not trivial, which is the main	1621	you do this is, again, up to you (but it is not trivial, which is the main
866	reason I omitted it as an example).	1622	reason I omitted it as an example).
867		1623
868	=back	1624	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	1628	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	1629	when you changed some parameters or the reschedule callback would return
874	a different time than the last time it was called (e.g. in a crond like	1630	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	1631	program when the crontabs have changed).
876		1632
		1633	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1634
		1635	When active, returns the absolute time that the watcher is supposed to
		1636	trigger next.
		1637
		1638	=item ev_tstamp offset [read-write]
		1639
		1640	When repeating, this contains the offset value, otherwise this is the
		1641	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1642
		1643	Can be modified any time, but changes only take effect when the periodic
		1644	timer fires or C<ev_periodic_again> is being called.
		1645
		1646	=item ev_tstamp interval [read-write]
		1647
		1648	The current interval value. Can be modified any time, but changes only
		1649	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1650	called.
		1651
		1652	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1653
		1654	The current reschedule callback, or C<0>, if this functionality is
		1655	switched off. Can be changed any time, but changes only take effect when
		1656	the periodic timer fires or C<ev_periodic_again> is being called.
		1657
877	=back	1658	=back
878		1659
		1660	=head3 Examples
		1661
879	Example: call a callback every hour, or, more precisely, whenever the	1662	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	1663	system time is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	1664	potentially a lot of jitter, but good long-term stability.
882		1665
883	static void	1666	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1667	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
885	{	1668	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	1669	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	1670	}
888		1671
889	struct ev_periodic hourly_tick;	1672	ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1673	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	1674	ev_periodic_start (loop, &hourly_tick);
892		1675
893	Example: the same as above, but use a reschedule callback to do it:	1676	Example: The same as above, but use a reschedule callback to do it:
894		1677
895	#include <math.h>	1678	#include <math.h>
896		1679
897	static ev_tstamp	1680	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1681	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
899	{	1682	{
900	return fmod (now, 3600.) + 3600.;	1683	return now + (3600. - fmod (now, 3600.));
901	}	1684	}
902		1685
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1686	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		1687
905	Example: call a callback every hour, starting now:	1688	Example: Call a callback every hour, starting now:
906		1689
907	struct ev_periodic hourly_tick;	1690	ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	1691	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	1692	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	1693	ev_periodic_start (loop, &hourly_tick);
911		1694
912		1695
913	=head2 C<ev_signal> - signal me when a signal gets signalled	1696	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		1697
915	Signal watchers will trigger an event when the process receives a specific	1698	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	1699	signal one or more times. Even though signals are very asynchronous, libev
917	will try it's best to deliver signals synchronously, i.e. as part of the	1700	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	1701	normal event processing, like any other event.
919		1702
		1703	If you want signals asynchronously, just use C<sigaction> as you would
		1704	do without libev and forget about sharing the signal. You can even use
		1705	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1706
920	You can configure as many watchers as you like per signal. Only when the	1707	You can configure as many watchers as you like per signal. Only when the
921	first watcher gets started will libev actually register a signal watcher	1708	first watcher gets started will libev actually register a signal handler
922	with the kernel (thus it coexists with your own signal handlers as long	1709	with the kernel (thus it coexists with your own signal handlers as long as
923	as you don't register any with libev). Similarly, when the last signal	1710	you don't register any with libev for the same signal). Similarly, when
924	watcher for a signal is stopped libev will reset the signal handler to	1711	the last signal watcher for a signal is stopped, libev will reset the
925	SIG_DFL (regardless of what it was set to before).	1712	signal handler to SIG_DFL (regardless of what it was set to before).
		1713
		1714	If possible and supported, libev will install its handlers with
		1715	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1716	interrupted. If you have a problem with system calls getting interrupted by
		1717	signals you can block all signals in an C<ev_check> watcher and unblock
		1718	them in an C<ev_prepare> watcher.
		1719
		1720	=head3 Watcher-Specific Functions and Data Members
926		1721
927	=over 4	1722	=over 4
928		1723
929	=item ev_signal_init (ev_signal *, callback, int signum)	1724	=item ev_signal_init (ev_signal *, callback, int signum)
930		1725
931	=item ev_signal_set (ev_signal *, int signum)	1726	=item ev_signal_set (ev_signal *, int signum)
932		1727
933	Configures the watcher to trigger on the given signal number (usually one	1728	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	1729	of the C<SIGxxx> constants).
935		1730
		1731	=item int signum [read-only]
		1732
		1733	The signal the watcher watches out for.
		1734
936	=back	1735	=back
937		1736
		1737	=head3 Examples
938		1738
		1739	Example: Try to exit cleanly on SIGINT.
		1740
		1741	static void
		1742	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1743	{
		1744	ev_unloop (loop, EVUNLOOP_ALL);
		1745	}
		1746
		1747	ev_signal signal_watcher;
		1748	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1749	ev_signal_start (loop, &signal_watcher);
		1750
		1751
939	=head2 C<ev_child> - wait for pid status changes	1752	=head2 C<ev_child> - watch out for process status changes
940		1753
941	Child watchers trigger when your process receives a SIGCHLD in response to	1754	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	1755	some child status changes (most typically when a child of yours dies or
		1756	exits). It is permissible to install a child watcher I<after> the child
		1757	has been forked (which implies it might have already exited), as long
		1758	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1759	forking and then immediately registering a watcher for the child is fine,
		1760	but forking and registering a watcher a few event loop iterations later is
		1761	not.
		1762
		1763	Only the default event loop is capable of handling signals, and therefore
		1764	you can only register child watchers in the default event loop.
		1765
		1766	=head3 Process Interaction
		1767
		1768	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1769	initialised. This is necessary to guarantee proper behaviour even if
		1770	the first child watcher is started after the child exits. The occurrence
		1771	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1772	synchronously as part of the event loop processing. Libev always reaps all
		1773	children, even ones not watched.
		1774
		1775	=head3 Overriding the Built-In Processing
		1776
		1777	Libev offers no special support for overriding the built-in child
		1778	processing, but if your application collides with libev's default child
		1779	handler, you can override it easily by installing your own handler for
		1780	C<SIGCHLD> after initialising the default loop, and making sure the
		1781	default loop never gets destroyed. You are encouraged, however, to use an
		1782	event-based approach to child reaping and thus use libev's support for
		1783	that, so other libev users can use C<ev_child> watchers freely.
		1784
		1785	=head3 Stopping the Child Watcher
		1786
		1787	Currently, the child watcher never gets stopped, even when the
		1788	child terminates, so normally one needs to stop the watcher in the
		1789	callback. Future versions of libev might stop the watcher automatically
		1790	when a child exit is detected.
		1791
		1792	=head3 Watcher-Specific Functions and Data Members
943		1793
944	=over 4	1794	=over 4
945		1795
946	=item ev_child_init (ev_child *, callback, int pid)	1796	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		1797
948	=item ev_child_set (ev_child *, int pid)	1798	=item ev_child_set (ev_child *, int pid, int trace)
949		1799
950	Configures the watcher to wait for status changes of process C<pid> (or	1800	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	1801	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	1802	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	1803	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	1804	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	1805	process causing the status change. C<trace> must be either C<0> (only
		1806	activate the watcher when the process terminates) or C<1> (additionally
		1807	activate the watcher when the process is stopped or continued).
		1808
		1809	=item int pid [read-only]
		1810
		1811	The process id this watcher watches out for, or C<0>, meaning any process id.
		1812
		1813	=item int rpid [read-write]
		1814
		1815	The process id that detected a status change.
		1816
		1817	=item int rstatus [read-write]
		1818
		1819	The process exit/trace status caused by C<rpid> (see your systems
		1820	C<waitpid> and C<sys/wait.h> documentation for details).
956		1821
957	=back	1822	=back
958		1823
959	Example: try to exit cleanly on SIGINT and SIGTERM.	1824	=head3 Examples
960		1825
		1826	Example: C<fork()> a new process and install a child handler to wait for
		1827	its completion.
		1828
		1829	ev_child cw;
		1830
961	static void	1831	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1832	child_cb (EV_P_ ev_child *w, int revents)
963	{	1833	{
964	ev_unloop (loop, EVUNLOOP_ALL);	1834	ev_child_stop (EV_A_ w);
		1835	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	1836	}
966		1837
967	struct ev_signal signal_watcher;	1838	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		1839
		1840	if (pid < 0)
		1841	// error
		1842	else if (pid == 0)
		1843	{
		1844	// the forked child executes here
		1845	exit (1);
		1846	}
		1847	else
		1848	{
		1849	ev_child_init (&cw, child_cb, pid, 0);
		1850	ev_child_start (EV_DEFAULT_ &cw);
		1851	}
971		1852
		1853
		1854	=head2 C<ev_stat> - did the file attributes just change?
		1855
		1856	This watches a file system path for attribute changes. That is, it calls
		1857	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1858	compared to the last time, invoking the callback if it did.
		1859
		1860	The path does not need to exist: changing from "path exists" to "path does
		1861	not exist" is a status change like any other. The condition "path does
		1862	not exist" is signified by the C<st_nlink> field being zero (which is
		1863	otherwise always forced to be at least one) and all the other fields of
		1864	the stat buffer having unspecified contents.
		1865
		1866	The path I<should> be absolute and I<must not> end in a slash. If it is
		1867	relative and your working directory changes, the behaviour is undefined.
		1868
		1869	Since there is no standard kernel interface to do this, the portable
		1870	implementation simply calls C<stat (2)> regularly on the path to see if
		1871	it changed somehow. You can specify a recommended polling interval for
		1872	this case. If you specify a polling interval of C<0> (highly recommended!)
		1873	then a I<suitable, unspecified default> value will be used (which
		1874	you can expect to be around five seconds, although this might change
		1875	dynamically). Libev will also impose a minimum interval which is currently
		1876	around C<0.1>, but thats usually overkill.
		1877
		1878	This watcher type is not meant for massive numbers of stat watchers,
		1879	as even with OS-supported change notifications, this can be
		1880	resource-intensive.
		1881
		1882	At the time of this writing, the only OS-specific interface implemented
		1883	is the Linux inotify interface (implementing kqueue support is left as
		1884	an exercise for the reader. Note, however, that the author sees no way
		1885	of implementing C<ev_stat> semantics with kqueue).
		1886
		1887	=head3 ABI Issues (Largefile Support)
		1888
		1889	Libev by default (unless the user overrides this) uses the default
		1890	compilation environment, which means that on systems with large file
		1891	support disabled by default, you get the 32 bit version of the stat
		1892	structure. When using the library from programs that change the ABI to
		1893	use 64 bit file offsets the programs will fail. In that case you have to
		1894	compile libev with the same flags to get binary compatibility. This is
		1895	obviously the case with any flags that change the ABI, but the problem is
		1896	most noticeably disabled with ev_stat and large file support.
		1897
		1898	The solution for this is to lobby your distribution maker to make large
		1899	file interfaces available by default (as e.g. FreeBSD does) and not
		1900	optional. Libev cannot simply switch on large file support because it has
		1901	to exchange stat structures with application programs compiled using the
		1902	default compilation environment.
		1903
		1904	=head3 Inotify and Kqueue
		1905
		1906	When C<inotify (7)> support has been compiled into libev (generally
		1907	only available with Linux 2.6.25 or above due to bugs in earlier
		1908	implementations) and present at runtime, it will be used to speed up
		1909	change detection where possible. The inotify descriptor will be created
		1910	lazily when the first C<ev_stat> watcher is being started.
		1911
		1912	Inotify presence does not change the semantics of C<ev_stat> watchers
		1913	except that changes might be detected earlier, and in some cases, to avoid
		1914	making regular C<stat> calls. Even in the presence of inotify support
		1915	there are many cases where libev has to resort to regular C<stat> polling,
		1916	but as long as the path exists, libev usually gets away without polling.
		1917
		1918	There is no support for kqueue, as apparently it cannot be used to
		1919	implement this functionality, due to the requirement of having a file
		1920	descriptor open on the object at all times, and detecting renames, unlinks
		1921	etc. is difficult.
		1922
		1923	=head3 The special problem of stat time resolution
		1924
		1925	The C<stat ()> system call only supports full-second resolution portably, and
		1926	even on systems where the resolution is higher, most file systems still
		1927	only support whole seconds.
		1928
		1929	That means that, if the time is the only thing that changes, you can
		1930	easily miss updates: on the first update, C<ev_stat> detects a change and
		1931	calls your callback, which does something. When there is another update
		1932	within the same second, C<ev_stat> will be unable to detect unless the
		1933	stat data does change in other ways (e.g. file size).
		1934
		1935	The solution to this is to delay acting on a change for slightly more
		1936	than a second (or till slightly after the next full second boundary), using
		1937	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1938	ev_timer_again (loop, w)>).
		1939
		1940	The C<.02> offset is added to work around small timing inconsistencies
		1941	of some operating systems (where the second counter of the current time
		1942	might be be delayed. One such system is the Linux kernel, where a call to
		1943	C<gettimeofday> might return a timestamp with a full second later than
		1944	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1945	update file times then there will be a small window where the kernel uses
		1946	the previous second to update file times but libev might already execute
		1947	the timer callback).
		1948
		1949	=head3 Watcher-Specific Functions and Data Members
		1950
		1951	=over 4
		1952
		1953	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1954
		1955	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1956
		1957	Configures the watcher to wait for status changes of the given
		1958	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1959	be detected and should normally be specified as C<0> to let libev choose
		1960	a suitable value. The memory pointed to by C<path> must point to the same
		1961	path for as long as the watcher is active.
		1962
		1963	The callback will receive an C<EV_STAT> event when a change was detected,
		1964	relative to the attributes at the time the watcher was started (or the
		1965	last change was detected).
		1966
		1967	=item ev_stat_stat (loop, ev_stat *)
		1968
		1969	Updates the stat buffer immediately with new values. If you change the
		1970	watched path in your callback, you could call this function to avoid
		1971	detecting this change (while introducing a race condition if you are not
		1972	the only one changing the path). Can also be useful simply to find out the
		1973	new values.
		1974
		1975	=item ev_statdata attr [read-only]
		1976
		1977	The most-recently detected attributes of the file. Although the type is
		1978	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1979	suitable for your system, but you can only rely on the POSIX-standardised
		1980	members to be present. If the C<st_nlink> member is C<0>, then there was
		1981	some error while C<stat>ing the file.
		1982
		1983	=item ev_statdata prev [read-only]
		1984
		1985	The previous attributes of the file. The callback gets invoked whenever
		1986	C<prev> != C<attr>, or, more precisely, one or more of these members
		1987	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1988	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1989
		1990	=item ev_tstamp interval [read-only]
		1991
		1992	The specified interval.
		1993
		1994	=item const char *path [read-only]
		1995
		1996	The file system path that is being watched.
		1997
		1998	=back
		1999
		2000	=head3 Examples
		2001
		2002	Example: Watch C</etc/passwd> for attribute changes.
		2003
		2004	static void
		2005	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2006	{
		2007	/* /etc/passwd changed in some way */
		2008	if (w->attr.st_nlink)
		2009	{
		2010	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2011	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2012	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2013	}
		2014	else
		2015	/* you shalt not abuse printf for puts */
		2016	puts ("wow, /etc/passwd is not there, expect problems. "
		2017	"if this is windows, they already arrived\n");
		2018	}
		2019
		2020	...
		2021	ev_stat passwd;
		2022
		2023	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2024	ev_stat_start (loop, &passwd);
		2025
		2026	Example: Like above, but additionally use a one-second delay so we do not
		2027	miss updates (however, frequent updates will delay processing, too, so
		2028	one might do the work both on C<ev_stat> callback invocation I<and> on
		2029	C<ev_timer> callback invocation).
		2030
		2031	static ev_stat passwd;
		2032	static ev_timer timer;
		2033
		2034	static void
		2035	timer_cb (EV_P_ ev_timer *w, int revents)
		2036	{
		2037	ev_timer_stop (EV_A_ w);
		2038
		2039	/* now it's one second after the most recent passwd change */
		2040	}
		2041
		2042	static void
		2043	stat_cb (EV_P_ ev_stat *w, int revents)
		2044	{
		2045	/* reset the one-second timer */
		2046	ev_timer_again (EV_A_ &timer);
		2047	}
		2048
		2049	...
		2050	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2051	ev_stat_start (loop, &passwd);
		2052	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2053
		2054
972	=head2 C<ev_idle> - when you've got nothing better to do	2055	=head2 C<ev_idle> - when you've got nothing better to do...
973		2056
974	Idle watchers trigger events when there are no other events are pending	2057	Idle watchers trigger events when no other events of the same or higher
975	(prepare, check and other idle watchers do not count). That is, as long	2058	priority are pending (prepare, check and other idle watchers do not count
976	as your process is busy handling sockets or timeouts (or even signals,	2059	as receiving "events").
977	imagine) it will not be triggered. But when your process is idle all idle	2060
978	watchers are being called again and again, once per event loop iteration -	2061	That is, as long as your process is busy handling sockets or timeouts
		2062	(or even signals, imagine) of the same or higher priority it will not be
		2063	triggered. But when your process is idle (or only lower-priority watchers
		2064	are pending), the idle watchers are being called once per event loop
979	until stopped, that is, or your process receives more events and becomes	2065	iteration - until stopped, that is, or your process receives more events
980	busy.	2066	and becomes busy again with higher priority stuff.
981		2067
982	The most noteworthy effect is that as long as any idle watchers are	2068	The most noteworthy effect is that as long as any idle watchers are
983	active, the process will not block when waiting for new events.	2069	active, the process will not block when waiting for new events.
984		2070
985	Apart from keeping your process non-blocking (which is a useful	2071	Apart from keeping your process non-blocking (which is a useful
986	effect on its own sometimes), idle watchers are a good place to do	2072	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	2073	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	2074	event loop has handled all outstanding events.
989		2075
		2076	=head3 Watcher-Specific Functions and Data Members
		2077
990	=over 4	2078	=over 4
991		2079
992	=item ev_idle_init (ev_signal *, callback)	2080	=item ev_idle_init (ev_signal *, callback)
993		2081
994	Initialises and configures the idle watcher - it has no parameters of any	2082	Initialises and configures the idle watcher - it has no parameters of any
995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2083	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	2084	believe me.
997		2085
998	=back	2086	=back
999		2087
		2088	=head3 Examples
		2089
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	2090	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	2091	callback, free it. Also, use no error checking, as usual.
1002		2092
1003	static void	2093	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2094	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1005	{	2095	{
1006	free (w);	2096	free (w);
1007	// now do something you wanted to do when the program has	2097	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	2098	// no longer anything immediate to do.
1009	}	2099	}
1010		2100
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2101	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	2102	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	2103	ev_idle_start (loop, idle_cb);
1014		2104
1015		2105
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2106	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		2107
1018	Prepare and check watchers are usually (but not always) used in tandem:	2108	Prepare and check watchers are usually (but not always) used in pairs:
1019	prepare watchers get invoked before the process blocks and check watchers	2109	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	2110	afterwards.
1021		2111
		2112	You I<must not> call C<ev_loop> or similar functions that enter
		2113	the current event loop from either C<ev_prepare> or C<ev_check>
		2114	watchers. Other loops than the current one are fine, however. The
		2115	rationale behind this is that you do not need to check for recursion in
		2116	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2117	C<ev_check> so if you have one watcher of each kind they will always be
		2118	called in pairs bracketing the blocking call.
		2119
1022	Their main purpose is to integrate other event mechanisms into libev and	2120	Their main purpose is to integrate other event mechanisms into libev and
1023	their use is somewhat advanced. This could be used, for example, to track	2121	their use is somewhat advanced. They could be used, for example, to track
1024	variable changes, implement your own watchers, integrate net-snmp or a	2122	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	2123	coroutine library and lots more. They are also occasionally useful if
		2124	you cache some data and want to flush it before blocking (for example,
		2125	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2126	watcher).
1026		2127
1027	This is done by examining in each prepare call which file descriptors need	2128	This is done by examining in each prepare call which file descriptors
1028	to be watched by the other library, registering C<ev_io> watchers for	2129	need to be watched by the other library, registering C<ev_io> watchers
1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2130	for them and starting an C<ev_timer> watcher for any timeouts (many
1030	provide just this functionality). Then, in the check watcher you check for	2131	libraries provide exactly this functionality). Then, in the check watcher,
1031	any events that occured (by checking the pending status of all watchers	2132	you check for any events that occurred (by checking the pending status
1032	and stopping them) and call back into the library. The I/O and timer	2133	of all watchers and stopping them) and call back into the library. The
1033	callbacks will never actually be called (but must be valid nevertheless,	2134	I/O and timer callbacks will never actually be called (but must be valid
1034	because you never know, you know?).	2135	nevertheless, because you never know, you know?).
1035		2136
1036	As another example, the Perl Coro module uses these hooks to integrate	2137	As another example, the Perl Coro module uses these hooks to integrate
1037	coroutines into libev programs, by yielding to other active coroutines	2138	coroutines into libev programs, by yielding to other active coroutines
1038	during each prepare and only letting the process block if no coroutines	2139	during each prepare and only letting the process block if no coroutines
1039	are ready to run (it's actually more complicated: it only runs coroutines	2140	are ready to run (it's actually more complicated: it only runs coroutines
1040	with priority higher than or equal to the event loop and one coroutine	2141	with priority higher than or equal to the event loop and one coroutine
1041	of lower priority, but only once, using idle watchers to keep the event	2142	of lower priority, but only once, using idle watchers to keep the event
1042	loop from blocking if lower-priority coroutines are active, thus mapping	2143	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	2144	low-priority coroutines to idle/background tasks).
1044		2145
		2146	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2147	priority, to ensure that they are being run before any other watchers
		2148	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2149
		2150	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2151	activate ("feed") events into libev. While libev fully supports this, they
		2152	might get executed before other C<ev_check> watchers did their job. As
		2153	C<ev_check> watchers are often used to embed other (non-libev) event
		2154	loops those other event loops might be in an unusable state until their
		2155	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2156	others).
		2157
		2158	=head3 Watcher-Specific Functions and Data Members
		2159
1045	=over 4	2160	=over 4
1046		2161
1047	=item ev_prepare_init (ev_prepare *, callback)	2162	=item ev_prepare_init (ev_prepare *, callback)
1048		2163
1049	=item ev_check_init (ev_check *, callback)	2164	=item ev_check_init (ev_check *, callback)
1050		2165
1051	Initialises and configures the prepare or check watcher - they have no	2166	Initialises and configures the prepare or check watcher - they have no
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2167	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1053	macros, but using them is utterly, utterly and completely pointless.	2168	macros, but using them is utterly, utterly, utterly and completely
		2169	pointless.
1054		2170
1055	=back	2171	=back
1056		2172
1057	Example: *TODO*.	2173	=head3 Examples
1058		2174
		2175	There are a number of principal ways to embed other event loops or modules
		2176	into libev. Here are some ideas on how to include libadns into libev
		2177	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2178	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2179	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2180	Glib event loop).
1059		2181
		2182	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2183	and in a check watcher, destroy them and call into libadns. What follows
		2184	is pseudo-code only of course. This requires you to either use a low
		2185	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2186	the callbacks for the IO/timeout watchers might not have been called yet.
		2187
		2188	static ev_io iow [nfd];
		2189	static ev_timer tw;
		2190
		2191	static void
		2192	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2193	{
		2194	}
		2195
		2196	// create io watchers for each fd and a timer before blocking
		2197	static void
		2198	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2199	{
		2200	int timeout = 3600000;
		2201	struct pollfd fds [nfd];
		2202	// actual code will need to loop here and realloc etc.
		2203	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2204
		2205	/* the callback is illegal, but won't be called as we stop during check */
		2206	ev_timer_init (&tw, 0, timeout * 1e-3);
		2207	ev_timer_start (loop, &tw);
		2208
		2209	// create one ev_io per pollfd
		2210	for (int i = 0; i < nfd; ++i)
		2211	{
		2212	ev_io_init (iow + i, io_cb, fds [i].fd,
		2213	((fds [i].events & POLLIN ? EV_READ : 0)
		2214	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2215
		2216	fds [i].revents = 0;
		2217	ev_io_start (loop, iow + i);
		2218	}
		2219	}
		2220
		2221	// stop all watchers after blocking
		2222	static void
		2223	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2224	{
		2225	ev_timer_stop (loop, &tw);
		2226
		2227	for (int i = 0; i < nfd; ++i)
		2228	{
		2229	// set the relevant poll flags
		2230	// could also call adns_processreadable etc. here
		2231	struct pollfd *fd = fds + i;
		2232	int revents = ev_clear_pending (iow + i);
		2233	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2234	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2235
		2236	// now stop the watcher
		2237	ev_io_stop (loop, iow + i);
		2238	}
		2239
		2240	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2241	}
		2242
		2243	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2244	in the prepare watcher and would dispose of the check watcher.
		2245
		2246	Method 3: If the module to be embedded supports explicit event
		2247	notification (libadns does), you can also make use of the actual watcher
		2248	callbacks, and only destroy/create the watchers in the prepare watcher.
		2249
		2250	static void
		2251	timer_cb (EV_P_ ev_timer *w, int revents)
		2252	{
		2253	adns_state ads = (adns_state)w->data;
		2254	update_now (EV_A);
		2255
		2256	adns_processtimeouts (ads, &tv_now);
		2257	}
		2258
		2259	static void
		2260	io_cb (EV_P_ ev_io *w, int revents)
		2261	{
		2262	adns_state ads = (adns_state)w->data;
		2263	update_now (EV_A);
		2264
		2265	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2266	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2267	}
		2268
		2269	// do not ever call adns_afterpoll
		2270
		2271	Method 4: Do not use a prepare or check watcher because the module you
		2272	want to embed is not flexible enough to support it. Instead, you can
		2273	override their poll function. The drawback with this solution is that the
		2274	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2275	this approach, effectively embedding EV as a client into the horrible
		2276	libglib event loop.
		2277
		2278	static gint
		2279	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2280	{
		2281	int got_events = 0;
		2282
		2283	for (n = 0; n < nfds; ++n)
		2284	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2285
		2286	if (timeout >= 0)
		2287	// create/start timer
		2288
		2289	// poll
		2290	ev_loop (EV_A_ 0);
		2291
		2292	// stop timer again
		2293	if (timeout >= 0)
		2294	ev_timer_stop (EV_A_ &to);
		2295
		2296	// stop io watchers again - their callbacks should have set
		2297	for (n = 0; n < nfds; ++n)
		2298	ev_io_stop (EV_A_ iow [n]);
		2299
		2300	return got_events;
		2301	}
		2302
		2303
1060	=head2 C<ev_embed> - when one backend isn't enough	2304	=head2 C<ev_embed> - when one backend isn't enough...
1061		2305
1062	This is a rather advanced watcher type that lets you embed one event loop	2306	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	2307	into another (currently only C<ev_io> events are supported in the embedded
		2308	loop, other types of watchers might be handled in a delayed or incorrect
		2309	fashion and must not be used).
1064		2310
1065	There are primarily two reasons you would want that: work around bugs and	2311	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2312	prioritise I/O.
1067		2313
1068	As an example for a bug workaround, the kqueue backend might only support	2314	As an example for a bug workaround, the kqueue backend might only support
1069	sockets on some platform, so it is unusable as generic backend, but you	2315	sockets on some platform, so it is unusable as generic backend, but you
1070	still want to make use of it because you have many sockets and it scales	2316	still want to make use of it because you have many sockets and it scales
1071	so nicely. In this case, you would create a kqueue-based loop and embed it	2317	so nicely. In this case, you would create a kqueue-based loop and embed
1072	into your default loop (which might use e.g. poll). Overall operation will	2318	it into your default loop (which might use e.g. poll). Overall operation
1073	be a bit slower because first libev has to poll and then call kevent, but	2319	will be a bit slower because first libev has to call C<poll> and then
1074	at least you can use both at what they are best.	2320	C<kevent>, but at least you can use both mechanisms for what they are
		2321	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1075		2322
1076	As for prioritising I/O: rarely you have the case where some fds have	2323	As for prioritising I/O: under rare circumstances you have the case where
1077	to be watched and handled very quickly (with low latency), and even	2324	some fds have to be watched and handled very quickly (with low latency),
1078	priorities and idle watchers might have too much overhead. In this case	2325	and even priorities and idle watchers might have too much overhead. In
1079	you would put all the high priority stuff in one loop and all the rest in	2326	this case you would put all the high priority stuff in one loop and all
1080	a second one, and embed the second one in the first.	2327	the rest in a second one, and embed the second one in the first.
		2328
		2329	As long as the watcher is active, the callback will be invoked every time
		2330	there might be events pending in the embedded loop. The callback must then
		2331	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2332	their callbacks (you could also start an idle watcher to give the embedded
		2333	loop strictly lower priority for example). You can also set the callback
		2334	to C<0>, in which case the embed watcher will automatically execute the
		2335	embedded loop sweep.
1081		2336
1082	As long as the watcher is started it will automatically handle events. The	2337	As long as the watcher is started it will automatically handle events. The
1083	callback will be invoked whenever some events have been handled. You can	2338	callback will be invoked whenever some events have been handled. You can
1084	set the callback to C<0> to avoid having to specify one if you are not	2339	set the callback to C<0> to avoid having to specify one if you are not
1085	interested in that.	2340	interested in that.
1086		2341
1087	Also, there have not currently been made special provisions for forking:	2342	Also, there have not currently been made special provisions for forking:
1088	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2343	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1089	but you will also have to stop and restart any C<ev_embed> watchers	2344	but you will also have to stop and restart any C<ev_embed> watchers
1090	yourself.	2345	yourself - but you can use a fork watcher to handle this automatically,
		2346	and future versions of libev might do just that.
1091		2347
1092	Unfortunately, not all backends are embeddable, only the ones returned by	2348	Unfortunately, not all backends are embeddable: only the ones returned by
1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2349	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1094	portable one.	2350	portable one.
1095		2351
1096	So when you want to use this feature you will always have to be prepared	2352	So when you want to use this feature you will always have to be prepared
1097	that you cannot get an embeddable loop. The recommended way to get around	2353	that you cannot get an embeddable loop. The recommended way to get around
1098	this is to have a separate variables for your embeddable loop, try to	2354	this is to have a separate variables for your embeddable loop, try to
1099	create it, and if that fails, use the normal loop for everything:	2355	create it, and if that fails, use the normal loop for everything.
1100		2356
1101	struct ev_loop *loop_hi = ev_default_init (0);	2357	=head3 C<ev_embed> and fork
1102	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;
1104
1105	// see if there is a chance of getting one that works
1106	// (remember that a flags value of 0 means autodetection)
1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1109	: 0;
1110		2358
1111	// if we got one, then embed it, otherwise default to loop_hi	2359	While the C<ev_embed> watcher is running, forks in the embedding loop will
1112	if (loop_lo)	2360	automatically be applied to the embedded loop as well, so no special
1113	{	2361	fork handling is required in that case. When the watcher is not running,
1114	ev_embed_init (&embed, 0, loop_lo);	2362	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1115	ev_embed_start (loop_hi, &embed);	2363	as applicable.
1116	}	2364
1117	else	2365	=head3 Watcher-Specific Functions and Data Members
1118	loop_lo = loop_hi;
1119		2366
1120	=over 4	2367	=over 4
1121		2368
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2369	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		2370
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2371	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		2372
1126	Configures the watcher to embed the given loop, which must be embeddable.	2373	Configures the watcher to embed the given loop, which must be
		2374	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2375	invoked automatically, otherwise it is the responsibility of the callback
		2376	to invoke it (it will continue to be called until the sweep has been done,
		2377	if you do not want that, you need to temporarily stop the embed watcher).
		2378
		2379	=item ev_embed_sweep (loop, ev_embed *)
		2380
		2381	Make a single, non-blocking sweep over the embedded loop. This works
		2382	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2383	appropriate way for embedded loops.
		2384
		2385	=item struct ev_loop *other [read-only]
		2386
		2387	The embedded event loop.
1127		2388
1128	=back	2389	=back
1129		2390
		2391	=head3 Examples
		2392
		2393	Example: Try to get an embeddable event loop and embed it into the default
		2394	event loop. If that is not possible, use the default loop. The default
		2395	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2396	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2397	used).
		2398
		2399	struct ev_loop *loop_hi = ev_default_init (0);
		2400	struct ev_loop *loop_lo = 0;
		2401	ev_embed embed;
		2402
		2403	// see if there is a chance of getting one that works
		2404	// (remember that a flags value of 0 means autodetection)
		2405	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2406	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2407	: 0;
		2408
		2409	// if we got one, then embed it, otherwise default to loop_hi
		2410	if (loop_lo)
		2411	{
		2412	ev_embed_init (&embed, 0, loop_lo);
		2413	ev_embed_start (loop_hi, &embed);
		2414	}
		2415	else
		2416	loop_lo = loop_hi;
		2417
		2418	Example: Check if kqueue is available but not recommended and create
		2419	a kqueue backend for use with sockets (which usually work with any
		2420	kqueue implementation). Store the kqueue/socket-only event loop in
		2421	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2422
		2423	struct ev_loop *loop = ev_default_init (0);
		2424	struct ev_loop *loop_socket = 0;
		2425	ev_embed embed;
		2426
		2427	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2428	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2429	{
		2430	ev_embed_init (&embed, 0, loop_socket);
		2431	ev_embed_start (loop, &embed);
		2432	}
		2433
		2434	if (!loop_socket)
		2435	loop_socket = loop;
		2436
		2437	// now use loop_socket for all sockets, and loop for everything else
		2438
		2439
		2440	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2441
		2442	Fork watchers are called when a C<fork ()> was detected (usually because
		2443	whoever is a good citizen cared to tell libev about it by calling
		2444	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2445	event loop blocks next and before C<ev_check> watchers are being called,
		2446	and only in the child after the fork. If whoever good citizen calling
		2447	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2448	handlers will be invoked, too, of course.
		2449
		2450	=head3 Watcher-Specific Functions and Data Members
		2451
		2452	=over 4
		2453
		2454	=item ev_fork_init (ev_signal *, callback)
		2455
		2456	Initialises and configures the fork watcher - it has no parameters of any
		2457	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2458	believe me.
		2459
		2460	=back
		2461
		2462
		2463	=head2 C<ev_async> - how to wake up another event loop
		2464
		2465	In general, you cannot use an C<ev_loop> from multiple threads or other
		2466	asynchronous sources such as signal handlers (as opposed to multiple event
		2467	loops - those are of course safe to use in different threads).
		2468
		2469	Sometimes, however, you need to wake up another event loop you do not
		2470	control, for example because it belongs to another thread. This is what
		2471	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2472	can signal it by calling C<ev_async_send>, which is thread- and signal
		2473	safe.
		2474
		2475	This functionality is very similar to C<ev_signal> watchers, as signals,
		2476	too, are asynchronous in nature, and signals, too, will be compressed
		2477	(i.e. the number of callback invocations may be less than the number of
		2478	C<ev_async_sent> calls).
		2479
		2480	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2481	just the default loop.
		2482
		2483	=head3 Queueing
		2484
		2485	C<ev_async> does not support queueing of data in any way. The reason
		2486	is that the author does not know of a simple (or any) algorithm for a
		2487	multiple-writer-single-reader queue that works in all cases and doesn't
		2488	need elaborate support such as pthreads.
		2489
		2490	That means that if you want to queue data, you have to provide your own
		2491	queue. But at least I can tell you how to implement locking around your
		2492	queue:
		2493
		2494	=over 4
		2495
		2496	=item queueing from a signal handler context
		2497
		2498	To implement race-free queueing, you simply add to the queue in the signal
		2499	handler but you block the signal handler in the watcher callback. Here is
		2500	an example that does that for some fictitious SIGUSR1 handler:
		2501
		2502	static ev_async mysig;
		2503
		2504	static void
		2505	sigusr1_handler (void)
		2506	{
		2507	sometype data;
		2508
		2509	// no locking etc.
		2510	queue_put (data);
		2511	ev_async_send (EV_DEFAULT_ &mysig);
		2512	}
		2513
		2514	static void
		2515	mysig_cb (EV_P_ ev_async *w, int revents)
		2516	{
		2517	sometype data;
		2518	sigset_t block, prev;
		2519
		2520	sigemptyset (&block);
		2521	sigaddset (&block, SIGUSR1);
		2522	sigprocmask (SIG_BLOCK, &block, &prev);
		2523
		2524	while (queue_get (&data))
		2525	process (data);
		2526
		2527	if (sigismember (&prev, SIGUSR1)
		2528	sigprocmask (SIG_UNBLOCK, &block, 0);
		2529	}
		2530
		2531	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2532	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2533	either...).
		2534
		2535	=item queueing from a thread context
		2536
		2537	The strategy for threads is different, as you cannot (easily) block
		2538	threads but you can easily preempt them, so to queue safely you need to
		2539	employ a traditional mutex lock, such as in this pthread example:
		2540
		2541	static ev_async mysig;
		2542	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2543
		2544	static void
		2545	otherthread (void)
		2546	{
		2547	// only need to lock the actual queueing operation
		2548	pthread_mutex_lock (&mymutex);
		2549	queue_put (data);
		2550	pthread_mutex_unlock (&mymutex);
		2551
		2552	ev_async_send (EV_DEFAULT_ &mysig);
		2553	}
		2554
		2555	static void
		2556	mysig_cb (EV_P_ ev_async *w, int revents)
		2557	{
		2558	pthread_mutex_lock (&mymutex);
		2559
		2560	while (queue_get (&data))
		2561	process (data);
		2562
		2563	pthread_mutex_unlock (&mymutex);
		2564	}
		2565
		2566	=back
		2567
		2568
		2569	=head3 Watcher-Specific Functions and Data Members
		2570
		2571	=over 4
		2572
		2573	=item ev_async_init (ev_async *, callback)
		2574
		2575	Initialises and configures the async watcher - it has no parameters of any
		2576	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2577	trust me.
		2578
		2579	=item ev_async_send (loop, ev_async *)
		2580
		2581	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2582	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2583	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2584	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2585	section below on what exactly this means).
		2586
		2587	This call incurs the overhead of a system call only once per loop iteration,
		2588	so while the overhead might be noticeable, it doesn't apply to repeated
		2589	calls to C<ev_async_send>.
		2590
		2591	=item bool = ev_async_pending (ev_async *)
		2592
		2593	Returns a non-zero value when C<ev_async_send> has been called on the
		2594	watcher but the event has not yet been processed (or even noted) by the
		2595	event loop.
		2596
		2597	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2598	the loop iterates next and checks for the watcher to have become active,
		2599	it will reset the flag again. C<ev_async_pending> can be used to very
		2600	quickly check whether invoking the loop might be a good idea.
		2601
		2602	Not that this does I<not> check whether the watcher itself is pending, only
		2603	whether it has been requested to make this watcher pending.
		2604
		2605	=back
		2606
1130		2607
1131	=head1 OTHER FUNCTIONS	2608	=head1 OTHER FUNCTIONS
1132		2609
1133	There are some other functions of possible interest. Described. Here. Now.	2610	There are some other functions of possible interest. Described. Here. Now.
1134		2611
1135	=over 4	2612	=over 4
1136		2613
1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2614	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1138		2615
1139	This function combines a simple timer and an I/O watcher, calls your	2616	This function combines a simple timer and an I/O watcher, calls your
1140	callback on whichever event happens first and automatically stop both	2617	callback on whichever event happens first and automatically stops both
1141	watchers. This is useful if you want to wait for a single event on an fd	2618	watchers. This is useful if you want to wait for a single event on an fd
1142	or timeout without having to allocate/configure/start/stop/free one or	2619	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	2620	more watchers yourself.
1144		2621
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	2622	If C<fd> is less than 0, then no I/O watcher will be started and the
1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2623	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1147	C<events> set will be craeted and started.	2624	the given C<fd> and C<events> set will be created and started.
1148		2625
1149	If C<timeout> is less than 0, then no timeout watcher will be	2626	If C<timeout> is less than 0, then no timeout watcher will be
1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2627	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2628	repeat = 0) will be started. C<0> is a valid timeout.
1152	dubious value.
1153		2629
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2630	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1155	passed an C<revents> set like normal event callbacks (a combination of	2631	passed an C<revents> set like normal event callbacks (a combination of
1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2632	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1157	value passed to C<ev_once>:	2633	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2634	a timeout and an io event at the same time - you probably should give io
		2635	events precedence.
1158		2636
		2637	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2638
1159	static void stdin_ready (int revents, void *arg)	2639	static void stdin_ready (int revents, void *arg)
1160	{	2640	{
1161	if (revents & EV_TIMEOUT)
1162	/* doh, nothing entered */;
1163	else if (revents & EV_READ)	2641	if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;	2642	/* stdin might have data for us, joy! */;
		2643	else if (revents & EV_TIMEOUT)
		2644	/* doh, nothing entered */;
1165	}	2645	}
1166		2646
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2647	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168		2648
1169	=item ev_feed_event (loop, watcher, int events)	2649	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1170		2650
1171	Feeds the given event set into the event loop, as if the specified event	2651	Feeds the given event set into the event loop, as if the specified event
1172	had happened for the specified watcher (which must be a pointer to an	2652	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).	2653	initialised but not necessarily started event watcher).
1174		2654
1175	=item ev_feed_fd_event (loop, int fd, int revents)	2655	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1176		2656
1177	Feed an event on the given fd, as if a file descriptor backend detected	2657	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	2658	the given events it.
1179		2659
1180	=item ev_feed_signal_event (loop, int signum)	2660	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1181		2661
1182	Feed an event as if the given signal occured (loop must be the default loop!).	2662	Feed an event as if the given signal occurred (C<loop> must be the default
		2663	loop!).
1183		2664
1184	=back	2665	=back
1185		2666
1186		2667
1187	=head1 LIBEVENT EMULATION	2668	=head1 LIBEVENT EMULATION
…		…
1202		2683
1203	=item * Priorities are not currently supported. Initialising priorities	2684	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	2685	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	2686	is an ev_pri field.
1206		2687
		2688	=item * In libevent, the last base created gets the signals, in libev, the
		2689	first base created (== the default loop) gets the signals.
		2690
1207	=item * Other members are not supported.	2691	=item * Other members are not supported.
1208		2692
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2693	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	2694	to use the libev header file and library.
1211		2695
1212	=back	2696	=back
1213		2697
1214	=head1 C++ SUPPORT	2698	=head1 C++ SUPPORT
1215		2699
1216	TBD.	2700	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2701	you to use some convenience methods to start/stop watchers and also change
		2702	the callback model to a model using method callbacks on objects.
		2703
		2704	To use it,
		2705
		2706	#include <ev++.h>
		2707
		2708	This automatically includes F<ev.h> and puts all of its definitions (many
		2709	of them macros) into the global namespace. All C++ specific things are
		2710	put into the C<ev> namespace. It should support all the same embedding
		2711	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2712
		2713	Care has been taken to keep the overhead low. The only data member the C++
		2714	classes add (compared to plain C-style watchers) is the event loop pointer
		2715	that the watcher is associated with (or no additional members at all if
		2716	you disable C<EV_MULTIPLICITY> when embedding libev).
		2717
		2718	Currently, functions, and static and non-static member functions can be
		2719	used as callbacks. Other types should be easy to add as long as they only
		2720	need one additional pointer for context. If you need support for other
		2721	types of functors please contact the author (preferably after implementing
		2722	it).
		2723
		2724	Here is a list of things available in the C<ev> namespace:
		2725
		2726	=over 4
		2727
		2728	=item C<ev::READ>, C<ev::WRITE> etc.
		2729
		2730	These are just enum values with the same values as the C<EV_READ> etc.
		2731	macros from F<ev.h>.
		2732
		2733	=item C<ev::tstamp>, C<ev::now>
		2734
		2735	Aliases to the same types/functions as with the C<ev_> prefix.
		2736
		2737	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2738
		2739	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2740	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2741	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2742	defines by many implementations.
		2743
		2744	All of those classes have these methods:
		2745
		2746	=over 4
		2747
		2748	=item ev::TYPE::TYPE ()
		2749
		2750	=item ev::TYPE::TYPE (struct ev_loop *)
		2751
		2752	=item ev::TYPE::~TYPE
		2753
		2754	The constructor (optionally) takes an event loop to associate the watcher
		2755	with. If it is omitted, it will use C<EV_DEFAULT>.
		2756
		2757	The constructor calls C<ev_init> for you, which means you have to call the
		2758	C<set> method before starting it.
		2759
		2760	It will not set a callback, however: You have to call the templated C<set>
		2761	method to set a callback before you can start the watcher.
		2762
		2763	(The reason why you have to use a method is a limitation in C++ which does
		2764	not allow explicit template arguments for constructors).
		2765
		2766	The destructor automatically stops the watcher if it is active.
		2767
		2768	=item w->set<class, &class::method> (object *)
		2769
		2770	This method sets the callback method to call. The method has to have a
		2771	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2772	first argument and the C<revents> as second. The object must be given as
		2773	parameter and is stored in the C<data> member of the watcher.
		2774
		2775	This method synthesizes efficient thunking code to call your method from
		2776	the C callback that libev requires. If your compiler can inline your
		2777	callback (i.e. it is visible to it at the place of the C<set> call and
		2778	your compiler is good :), then the method will be fully inlined into the
		2779	thunking function, making it as fast as a direct C callback.
		2780
		2781	Example: simple class declaration and watcher initialisation
		2782
		2783	struct myclass
		2784	{
		2785	void io_cb (ev::io &w, int revents) { }
		2786	}
		2787
		2788	myclass obj;
		2789	ev::io iow;
		2790	iow.set <myclass, &myclass::io_cb> (&obj);
		2791
		2792	=item w->set<function> (void *data = 0)
		2793
		2794	Also sets a callback, but uses a static method or plain function as
		2795	callback. The optional C<data> argument will be stored in the watcher's
		2796	C<data> member and is free for you to use.
		2797
		2798	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2799
		2800	See the method-C<set> above for more details.
		2801
		2802	Example: Use a plain function as callback.
		2803
		2804	static void io_cb (ev::io &w, int revents) { }
		2805	iow.set <io_cb> ();
		2806
		2807	=item w->set (struct ev_loop *)
		2808
		2809	Associates a different C<struct ev_loop> with this watcher. You can only
		2810	do this when the watcher is inactive (and not pending either).
		2811
		2812	=item w->set ([arguments])
		2813
		2814	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2815	called at least once. Unlike the C counterpart, an active watcher gets
		2816	automatically stopped and restarted when reconfiguring it with this
		2817	method.
		2818
		2819	=item w->start ()
		2820
		2821	Starts the watcher. Note that there is no C<loop> argument, as the
		2822	constructor already stores the event loop.
		2823
		2824	=item w->stop ()
		2825
		2826	Stops the watcher if it is active. Again, no C<loop> argument.
		2827
		2828	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2829
		2830	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2831	C<ev_TYPE_again> function.
		2832
		2833	=item w->sweep () (C<ev::embed> only)
		2834
		2835	Invokes C<ev_embed_sweep>.
		2836
		2837	=item w->update () (C<ev::stat> only)
		2838
		2839	Invokes C<ev_stat_stat>.
		2840
		2841	=back
		2842
		2843	=back
		2844
		2845	Example: Define a class with an IO and idle watcher, start one of them in
		2846	the constructor.
		2847
		2848	class myclass
		2849	{
		2850	ev::io io ; void io_cb (ev::io &w, int revents);
		2851	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2852
		2853	myclass (int fd)
		2854	{
		2855	io .set <myclass, &myclass::io_cb > (this);
		2856	idle.set <myclass, &myclass::idle_cb> (this);
		2857
		2858	io.start (fd, ev::READ);
		2859	}
		2860	};
		2861
		2862
		2863	=head1 OTHER LANGUAGE BINDINGS
		2864
		2865	Libev does not offer other language bindings itself, but bindings for a
		2866	number of languages exist in the form of third-party packages. If you know
		2867	any interesting language binding in addition to the ones listed here, drop
		2868	me a note.
		2869
		2870	=over 4
		2871
		2872	=item Perl
		2873
		2874	The EV module implements the full libev API and is actually used to test
		2875	libev. EV is developed together with libev. Apart from the EV core module,
		2876	there are additional modules that implement libev-compatible interfaces
		2877	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2878	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2879	and C<EV::Glib>).
		2880
		2881	It can be found and installed via CPAN, its homepage is at
		2882	L<http://software.schmorp.de/pkg/EV>.
		2883
		2884	=item Python
		2885
		2886	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2887	seems to be quite complete and well-documented. Note, however, that the
		2888	patch they require for libev is outright dangerous as it breaks the ABI
		2889	for everybody else, and therefore, should never be applied in an installed
		2890	libev (if python requires an incompatible ABI then it needs to embed
		2891	libev).
		2892
		2893	=item Ruby
		2894
		2895	Tony Arcieri has written a ruby extension that offers access to a subset
		2896	of the libev API and adds file handle abstractions, asynchronous DNS and
		2897	more on top of it. It can be found via gem servers. Its homepage is at
		2898	L<http://rev.rubyforge.org/>.
		2899
		2900	=item D
		2901
		2902	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2903	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2904
		2905	=back
		2906
		2907
		2908	=head1 MACRO MAGIC
		2909
		2910	Libev can be compiled with a variety of options, the most fundamental
		2911	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2912	functions and callbacks have an initial C<struct ev_loop *> argument.
		2913
		2914	To make it easier to write programs that cope with either variant, the
		2915	following macros are defined:
		2916
		2917	=over 4
		2918
		2919	=item C<EV_A>, C<EV_A_>
		2920
		2921	This provides the loop I<argument> for functions, if one is required ("ev
		2922	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2923	C<EV_A_> is used when other arguments are following. Example:
		2924
		2925	ev_unref (EV_A);
		2926	ev_timer_add (EV_A_ watcher);
		2927	ev_loop (EV_A_ 0);
		2928
		2929	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2930	which is often provided by the following macro.
		2931
		2932	=item C<EV_P>, C<EV_P_>
		2933
		2934	This provides the loop I<parameter> for functions, if one is required ("ev
		2935	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2936	C<EV_P_> is used when other parameters are following. Example:
		2937
		2938	// this is how ev_unref is being declared
		2939	static void ev_unref (EV_P);
		2940
		2941	// this is how you can declare your typical callback
		2942	static void cb (EV_P_ ev_timer *w, int revents)
		2943
		2944	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2945	suitable for use with C<EV_A>.
		2946
		2947	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2948
		2949	Similar to the other two macros, this gives you the value of the default
		2950	loop, if multiple loops are supported ("ev loop default").
		2951
		2952	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2953
		2954	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2955	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2956	is undefined when the default loop has not been initialised by a previous
		2957	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2958
		2959	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2960	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2961
		2962	=back
		2963
		2964	Example: Declare and initialise a check watcher, utilising the above
		2965	macros so it will work regardless of whether multiple loops are supported
		2966	or not.
		2967
		2968	static void
		2969	check_cb (EV_P_ ev_timer *w, int revents)
		2970	{
		2971	ev_check_stop (EV_A_ w);
		2972	}
		2973
		2974	ev_check check;
		2975	ev_check_init (&check, check_cb);
		2976	ev_check_start (EV_DEFAULT_ &check);
		2977	ev_loop (EV_DEFAULT_ 0);
		2978
		2979	=head1 EMBEDDING
		2980
		2981	Libev can (and often is) directly embedded into host
		2982	applications. Examples of applications that embed it include the Deliantra
		2983	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2984	and rxvt-unicode.
		2985
		2986	The goal is to enable you to just copy the necessary files into your
		2987	source directory without having to change even a single line in them, so
		2988	you can easily upgrade by simply copying (or having a checked-out copy of
		2989	libev somewhere in your source tree).
		2990
		2991	=head2 FILESETS
		2992
		2993	Depending on what features you need you need to include one or more sets of files
		2994	in your application.
		2995
		2996	=head3 CORE EVENT LOOP
		2997
		2998	To include only the libev core (all the C<ev_*> functions), with manual
		2999	configuration (no autoconf):
		3000
		3001	#define EV_STANDALONE 1
		3002	#include "ev.c"
		3003
		3004	This will automatically include F<ev.h>, too, and should be done in a
		3005	single C source file only to provide the function implementations. To use
		3006	it, do the same for F<ev.h> in all files wishing to use this API (best
		3007	done by writing a wrapper around F<ev.h> that you can include instead and
		3008	where you can put other configuration options):
		3009
		3010	#define EV_STANDALONE 1
		3011	#include "ev.h"
		3012
		3013	Both header files and implementation files can be compiled with a C++
		3014	compiler (at least, thats a stated goal, and breakage will be treated
		3015	as a bug).
		3016
		3017	You need the following files in your source tree, or in a directory
		3018	in your include path (e.g. in libev/ when using -Ilibev):
		3019
		3020	ev.h
		3021	ev.c
		3022	ev_vars.h
		3023	ev_wrap.h
		3024
		3025	ev_win32.c required on win32 platforms only
		3026
		3027	ev_select.c only when select backend is enabled (which is enabled by default)
		3028	ev_poll.c only when poll backend is enabled (disabled by default)
		3029	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3030	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3031	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3032
		3033	F<ev.c> includes the backend files directly when enabled, so you only need
		3034	to compile this single file.
		3035
		3036	=head3 LIBEVENT COMPATIBILITY API
		3037
		3038	To include the libevent compatibility API, also include:
		3039
		3040	#include "event.c"
		3041
		3042	in the file including F<ev.c>, and:
		3043
		3044	#include "event.h"
		3045
		3046	in the files that want to use the libevent API. This also includes F<ev.h>.
		3047
		3048	You need the following additional files for this:
		3049
		3050	event.h
		3051	event.c
		3052
		3053	=head3 AUTOCONF SUPPORT
		3054
		3055	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3056	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3057	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3058	include F<config.h> and configure itself accordingly.
		3059
		3060	For this of course you need the m4 file:
		3061
		3062	libev.m4
		3063
		3064	=head2 PREPROCESSOR SYMBOLS/MACROS
		3065
		3066	Libev can be configured via a variety of preprocessor symbols you have to
		3067	define before including any of its files. The default in the absence of
		3068	autoconf is documented for every option.
		3069
		3070	=over 4
		3071
		3072	=item EV_STANDALONE
		3073
		3074	Must always be C<1> if you do not use autoconf configuration, which
		3075	keeps libev from including F<config.h>, and it also defines dummy
		3076	implementations for some libevent functions (such as logging, which is not
		3077	supported). It will also not define any of the structs usually found in
		3078	F<event.h> that are not directly supported by the libev core alone.
		3079
		3080	=item EV_USE_MONOTONIC
		3081
		3082	If defined to be C<1>, libev will try to detect the availability of the
		3083	monotonic clock option at both compile time and runtime. Otherwise no use
		3084	of the monotonic clock option will be attempted. If you enable this, you
		3085	usually have to link against librt or something similar. Enabling it when
		3086	the functionality isn't available is safe, though, although you have
		3087	to make sure you link against any libraries where the C<clock_gettime>
		3088	function is hiding in (often F<-lrt>).
		3089
		3090	=item EV_USE_REALTIME
		3091
		3092	If defined to be C<1>, libev will try to detect the availability of the
		3093	real-time clock option at compile time (and assume its availability at
		3094	runtime if successful). Otherwise no use of the real-time clock option will
		3095	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		3096	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		3097	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3098
		3099	=item EV_USE_NANOSLEEP
		3100
		3101	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3102	and will use it for delays. Otherwise it will use C<select ()>.
		3103
		3104	=item EV_USE_EVENTFD
		3105
		3106	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3107	available and will probe for kernel support at runtime. This will improve
		3108	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3109	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3110	2.7 or newer, otherwise disabled.
		3111
		3112	=item EV_USE_SELECT
		3113
		3114	If undefined or defined to be C<1>, libev will compile in support for the
		3115	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3116	other method takes over, select will be it. Otherwise the select backend
		3117	will not be compiled in.
		3118
		3119	=item EV_SELECT_USE_FD_SET
		3120
		3121	If defined to C<1>, then the select backend will use the system C<fd_set>
		3122	structure. This is useful if libev doesn't compile due to a missing
		3123	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3124	exotic systems. This usually limits the range of file descriptors to some
		3125	low limit such as 1024 or might have other limitations (winsocket only
		3126	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3127	influence the size of the C<fd_set> used.
		3128
		3129	=item EV_SELECT_IS_WINSOCKET
		3130
		3131	When defined to C<1>, the select backend will assume that
		3132	select/socket/connect etc. don't understand file descriptors but
		3133	wants osf handles on win32 (this is the case when the select to
		3134	be used is the winsock select). This means that it will call
		3135	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3136	it is assumed that all these functions actually work on fds, even
		3137	on win32. Should not be defined on non-win32 platforms.
		3138
		3139	=item EV_FD_TO_WIN32_HANDLE
		3140
		3141	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3142	file descriptors to socket handles. When not defining this symbol (the
		3143	default), then libev will call C<_get_osfhandle>, which is usually
		3144	correct. In some cases, programs use their own file descriptor management,
		3145	in which case they can provide this function to map fds to socket handles.
		3146
		3147	=item EV_USE_POLL
		3148
		3149	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3150	backend. Otherwise it will be enabled on non-win32 platforms. It
		3151	takes precedence over select.
		3152
		3153	=item EV_USE_EPOLL
		3154
		3155	If defined to be C<1>, libev will compile in support for the Linux
		3156	C<epoll>(7) backend. Its availability will be detected at runtime,
		3157	otherwise another method will be used as fallback. This is the preferred
		3158	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3159	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3160
		3161	=item EV_USE_KQUEUE
		3162
		3163	If defined to be C<1>, libev will compile in support for the BSD style
		3164	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3165	otherwise another method will be used as fallback. This is the preferred
		3166	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3167	supports some types of fds correctly (the only platform we found that
		3168	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3169	not be used unless explicitly requested. The best way to use it is to find
		3170	out whether kqueue supports your type of fd properly and use an embedded
		3171	kqueue loop.
		3172
		3173	=item EV_USE_PORT
		3174
		3175	If defined to be C<1>, libev will compile in support for the Solaris
		3176	10 port style backend. Its availability will be detected at runtime,
		3177	otherwise another method will be used as fallback. This is the preferred
		3178	backend for Solaris 10 systems.
		3179
		3180	=item EV_USE_DEVPOLL
		3181
		3182	Reserved for future expansion, works like the USE symbols above.
		3183
		3184	=item EV_USE_INOTIFY
		3185
		3186	If defined to be C<1>, libev will compile in support for the Linux inotify
		3187	interface to speed up C<ev_stat> watchers. Its actual availability will
		3188	be detected at runtime. If undefined, it will be enabled if the headers
		3189	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3190
		3191	=item EV_ATOMIC_T
		3192
		3193	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3194	access is atomic with respect to other threads or signal contexts. No such
		3195	type is easily found in the C language, so you can provide your own type
		3196	that you know is safe for your purposes. It is used both for signal handler "locking"
		3197	as well as for signal and thread safety in C<ev_async> watchers.
		3198
		3199	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3200	(from F<signal.h>), which is usually good enough on most platforms.
		3201
		3202	=item EV_H
		3203
		3204	The name of the F<ev.h> header file used to include it. The default if
		3205	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3206	used to virtually rename the F<ev.h> header file in case of conflicts.
		3207
		3208	=item EV_CONFIG_H
		3209
		3210	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3211	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3212	C<EV_H>, above.
		3213
		3214	=item EV_EVENT_H
		3215
		3216	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3217	of how the F<event.h> header can be found, the default is C<"event.h">.
		3218
		3219	=item EV_PROTOTYPES
		3220
		3221	If defined to be C<0>, then F<ev.h> will not define any function
		3222	prototypes, but still define all the structs and other symbols. This is
		3223	occasionally useful if you want to provide your own wrapper functions
		3224	around libev functions.
		3225
		3226	=item EV_MULTIPLICITY
		3227
		3228	If undefined or defined to C<1>, then all event-loop-specific functions
		3229	will have the C<struct ev_loop *> as first argument, and you can create
		3230	additional independent event loops. Otherwise there will be no support
		3231	for multiple event loops and there is no first event loop pointer
		3232	argument. Instead, all functions act on the single default loop.
		3233
		3234	=item EV_MINPRI
		3235
		3236	=item EV_MAXPRI
		3237
		3238	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3239	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3240	provide for more priorities by overriding those symbols (usually defined
		3241	to be C<-2> and C<2>, respectively).
		3242
		3243	When doing priority-based operations, libev usually has to linearly search
		3244	all the priorities, so having many of them (hundreds) uses a lot of space
		3245	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3246	fine.
		3247
		3248	If your embedding application does not need any priorities, defining these
		3249	both to C<0> will save some memory and CPU.
		3250
		3251	=item EV_PERIODIC_ENABLE
		3252
		3253	If undefined or defined to be C<1>, then periodic timers are supported. If
		3254	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3255	code.
		3256
		3257	=item EV_IDLE_ENABLE
		3258
		3259	If undefined or defined to be C<1>, then idle watchers are supported. If
		3260	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3261	code.
		3262
		3263	=item EV_EMBED_ENABLE
		3264
		3265	If undefined or defined to be C<1>, then embed watchers are supported. If
		3266	defined to be C<0>, then they are not. Embed watchers rely on most other
		3267	watcher types, which therefore must not be disabled.
		3268
		3269	=item EV_STAT_ENABLE
		3270
		3271	If undefined or defined to be C<1>, then stat watchers are supported. If
		3272	defined to be C<0>, then they are not.
		3273
		3274	=item EV_FORK_ENABLE
		3275
		3276	If undefined or defined to be C<1>, then fork watchers are supported. If
		3277	defined to be C<0>, then they are not.
		3278
		3279	=item EV_ASYNC_ENABLE
		3280
		3281	If undefined or defined to be C<1>, then async watchers are supported. If
		3282	defined to be C<0>, then they are not.
		3283
		3284	=item EV_MINIMAL
		3285
		3286	If you need to shave off some kilobytes of code at the expense of some
		3287	speed, define this symbol to C<1>. Currently this is used to override some
		3288	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3289	much smaller 2-heap for timer management over the default 4-heap.
		3290
		3291	=item EV_PID_HASHSIZE
		3292
		3293	C<ev_child> watchers use a small hash table to distribute workload by
		3294	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3295	than enough. If you need to manage thousands of children you might want to
		3296	increase this value (I<must> be a power of two).
		3297
		3298	=item EV_INOTIFY_HASHSIZE
		3299
		3300	C<ev_stat> watchers use a small hash table to distribute workload by
		3301	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3302	usually more than enough. If you need to manage thousands of C<ev_stat>
		3303	watchers you might want to increase this value (I<must> be a power of
		3304	two).
		3305
		3306	=item EV_USE_4HEAP
		3307
		3308	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3309	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3310	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3311	faster performance with many (thousands) of watchers.
		3312
		3313	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3314	(disabled).
		3315
		3316	=item EV_HEAP_CACHE_AT
		3317
		3318	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3319	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3320	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3321	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3322	but avoids random read accesses on heap changes. This improves performance
		3323	noticeably with many (hundreds) of watchers.
		3324
		3325	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3326	(disabled).
		3327
		3328	=item EV_VERIFY
		3329
		3330	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3331	be done: If set to C<0>, no internal verification code will be compiled
		3332	in. If set to C<1>, then verification code will be compiled in, but not
		3333	called. If set to C<2>, then the internal verification code will be
		3334	called once per loop, which can slow down libev. If set to C<3>, then the
		3335	verification code will be called very frequently, which will slow down
		3336	libev considerably.
		3337
		3338	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3339	C<0>.
		3340
		3341	=item EV_COMMON
		3342
		3343	By default, all watchers have a C<void *data> member. By redefining
		3344	this macro to a something else you can include more and other types of
		3345	members. You have to define it each time you include one of the files,
		3346	though, and it must be identical each time.
		3347
		3348	For example, the perl EV module uses something like this:
		3349
		3350	#define EV_COMMON \
		3351	SV *self; /* contains this struct */ \
		3352	SV *cb_sv, *fh /* note no trailing ";" */
		3353
		3354	=item EV_CB_DECLARE (type)
		3355
		3356	=item EV_CB_INVOKE (watcher, revents)
		3357
		3358	=item ev_set_cb (ev, cb)
		3359
		3360	Can be used to change the callback member declaration in each watcher,
		3361	and the way callbacks are invoked and set. Must expand to a struct member
		3362	definition and a statement, respectively. See the F<ev.h> header file for
		3363	their default definitions. One possible use for overriding these is to
		3364	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3365	method calls instead of plain function calls in C++.
		3366
		3367	=back
		3368
		3369	=head2 EXPORTED API SYMBOLS
		3370
		3371	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3372	exported symbols, you can use the provided F<Symbol.*> files which list
		3373	all public symbols, one per line:
		3374
		3375	Symbols.ev for libev proper
		3376	Symbols.event for the libevent emulation
		3377
		3378	This can also be used to rename all public symbols to avoid clashes with
		3379	multiple versions of libev linked together (which is obviously bad in
		3380	itself, but sometimes it is inconvenient to avoid this).
		3381
		3382	A sed command like this will create wrapper C<#define>'s that you need to
		3383	include before including F<ev.h>:
		3384
		3385	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3386
		3387	This would create a file F<wrap.h> which essentially looks like this:
		3388
		3389	#define ev_backend myprefix_ev_backend
		3390	#define ev_check_start myprefix_ev_check_start
		3391	#define ev_check_stop myprefix_ev_check_stop
		3392	...
		3393
		3394	=head2 EXAMPLES
		3395
		3396	For a real-world example of a program the includes libev
		3397	verbatim, you can have a look at the EV perl module
		3398	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3399	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3400	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3401	will be compiled. It is pretty complex because it provides its own header
		3402	file.
		3403
		3404	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3405	that everybody includes and which overrides some configure choices:
		3406
		3407	#define EV_MINIMAL 1
		3408	#define EV_USE_POLL 0
		3409	#define EV_MULTIPLICITY 0
		3410	#define EV_PERIODIC_ENABLE 0
		3411	#define EV_STAT_ENABLE 0
		3412	#define EV_FORK_ENABLE 0
		3413	#define EV_CONFIG_H <config.h>
		3414	#define EV_MINPRI 0
		3415	#define EV_MAXPRI 0
		3416
		3417	#include "ev++.h"
		3418
		3419	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3420
		3421	#include "ev_cpp.h"
		3422	#include "ev.c"
		3423
		3424	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3425
		3426	=head2 THREADS AND COROUTINES
		3427
		3428	=head3 THREADS
		3429
		3430	All libev functions are reentrant and thread-safe unless explicitly
		3431	documented otherwise, but libev implements no locking itself. This means
		3432	that you can use as many loops as you want in parallel, as long as there
		3433	are no concurrent calls into any libev function with the same loop
		3434	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3435	of course): libev guarantees that different event loops share no data
		3436	structures that need any locking.
		3437
		3438	Or to put it differently: calls with different loop parameters can be done
		3439	concurrently from multiple threads, calls with the same loop parameter
		3440	must be done serially (but can be done from different threads, as long as
		3441	only one thread ever is inside a call at any point in time, e.g. by using
		3442	a mutex per loop).
		3443
		3444	Specifically to support threads (and signal handlers), libev implements
		3445	so-called C<ev_async> watchers, which allow some limited form of
		3446	concurrency on the same event loop, namely waking it up "from the
		3447	outside".
		3448
		3449	If you want to know which design (one loop, locking, or multiple loops
		3450	without or something else still) is best for your problem, then I cannot
		3451	help you, but here is some generic advice:
		3452
		3453	=over 4
		3454
		3455	=item * most applications have a main thread: use the default libev loop
		3456	in that thread, or create a separate thread running only the default loop.
		3457
		3458	This helps integrating other libraries or software modules that use libev
		3459	themselves and don't care/know about threading.
		3460
		3461	=item * one loop per thread is usually a good model.
		3462
		3463	Doing this is almost never wrong, sometimes a better-performance model
		3464	exists, but it is always a good start.
		3465
		3466	=item * other models exist, such as the leader/follower pattern, where one
		3467	loop is handed through multiple threads in a kind of round-robin fashion.
		3468
		3469	Choosing a model is hard - look around, learn, know that usually you can do
		3470	better than you currently do :-)
		3471
		3472	=item * often you need to talk to some other thread which blocks in the
		3473	event loop.
		3474
		3475	C<ev_async> watchers can be used to wake them up from other threads safely
		3476	(or from signal contexts...).
		3477
		3478	An example use would be to communicate signals or other events that only
		3479	work in the default loop by registering the signal watcher with the
		3480	default loop and triggering an C<ev_async> watcher from the default loop
		3481	watcher callback into the event loop interested in the signal.
		3482
		3483	=back
		3484
		3485	=head3 COROUTINES
		3486
		3487	Libev is very accommodating to coroutines ("cooperative threads"):
		3488	libev fully supports nesting calls to its functions from different
		3489	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3490	different coroutines, and switch freely between both coroutines running the
		3491	loop, as long as you don't confuse yourself). The only exception is that
		3492	you must not do this from C<ev_periodic> reschedule callbacks.
		3493
		3494	Care has been taken to ensure that libev does not keep local state inside
		3495	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3496	they do not clal any callbacks.
		3497
		3498	=head2 COMPILER WARNINGS
		3499
		3500	Depending on your compiler and compiler settings, you might get no or a
		3501	lot of warnings when compiling libev code. Some people are apparently
		3502	scared by this.
		3503
		3504	However, these are unavoidable for many reasons. For one, each compiler
		3505	has different warnings, and each user has different tastes regarding
		3506	warning options. "Warn-free" code therefore cannot be a goal except when
		3507	targeting a specific compiler and compiler-version.
		3508
		3509	Another reason is that some compiler warnings require elaborate
		3510	workarounds, or other changes to the code that make it less clear and less
		3511	maintainable.
		3512
		3513	And of course, some compiler warnings are just plain stupid, or simply
		3514	wrong (because they don't actually warn about the condition their message
		3515	seems to warn about). For example, certain older gcc versions had some
		3516	warnings that resulted an extreme number of false positives. These have
		3517	been fixed, but some people still insist on making code warn-free with
		3518	such buggy versions.
		3519
		3520	While libev is written to generate as few warnings as possible,
		3521	"warn-free" code is not a goal, and it is recommended not to build libev
		3522	with any compiler warnings enabled unless you are prepared to cope with
		3523	them (e.g. by ignoring them). Remember that warnings are just that:
		3524	warnings, not errors, or proof of bugs.
		3525
		3526
		3527	=head2 VALGRIND
		3528
		3529	Valgrind has a special section here because it is a popular tool that is
		3530	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3531
		3532	If you think you found a bug (memory leak, uninitialised data access etc.)
		3533	in libev, then check twice: If valgrind reports something like:
		3534
		3535	==2274== definitely lost: 0 bytes in 0 blocks.
		3536	==2274== possibly lost: 0 bytes in 0 blocks.
		3537	==2274== still reachable: 256 bytes in 1 blocks.
		3538
		3539	Then there is no memory leak, just as memory accounted to global variables
		3540	is not a memleak - the memory is still being refernced, and didn't leak.
		3541
		3542	Similarly, under some circumstances, valgrind might report kernel bugs
		3543	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3544	although an acceptable workaround has been found here), or it might be
		3545	confused.
		3546
		3547	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3548	make it into some kind of religion.
		3549
		3550	If you are unsure about something, feel free to contact the mailing list
		3551	with the full valgrind report and an explanation on why you think this
		3552	is a bug in libev (best check the archives, too :). However, don't be
		3553	annoyed when you get a brisk "this is no bug" answer and take the chance
		3554	of learning how to interpret valgrind properly.
		3555
		3556	If you need, for some reason, empty reports from valgrind for your project
		3557	I suggest using suppression lists.
		3558
		3559
		3560	=head1 PORTABILITY NOTES
		3561
		3562	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3563
		3564	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3565	requires, and its I/O model is fundamentally incompatible with the POSIX
		3566	model. Libev still offers limited functionality on this platform in
		3567	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3568	descriptors. This only applies when using Win32 natively, not when using
		3569	e.g. cygwin.
		3570
		3571	Lifting these limitations would basically require the full
		3572	re-implementation of the I/O system. If you are into these kinds of
		3573	things, then note that glib does exactly that for you in a very portable
		3574	way (note also that glib is the slowest event library known to man).
		3575
		3576	There is no supported compilation method available on windows except
		3577	embedding it into other applications.
		3578
		3579	Not a libev limitation but worth mentioning: windows apparently doesn't
		3580	accept large writes: instead of resulting in a partial write, windows will
		3581	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3582	so make sure you only write small amounts into your sockets (less than a
		3583	megabyte seems safe, but this apparently depends on the amount of memory
		3584	available).
		3585
		3586	Due to the many, low, and arbitrary limits on the win32 platform and
		3587	the abysmal performance of winsockets, using a large number of sockets
		3588	is not recommended (and not reasonable). If your program needs to use
		3589	more than a hundred or so sockets, then likely it needs to use a totally
		3590	different implementation for windows, as libev offers the POSIX readiness
		3591	notification model, which cannot be implemented efficiently on windows
		3592	(Microsoft monopoly games).
		3593
		3594	A typical way to use libev under windows is to embed it (see the embedding
		3595	section for details) and use the following F<evwrap.h> header file instead
		3596	of F<ev.h>:
		3597
		3598	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3599	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3600
		3601	#include "ev.h"
		3602
		3603	And compile the following F<evwrap.c> file into your project (make sure
		3604	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3605
		3606	#include "evwrap.h"
		3607	#include "ev.c"
		3608
		3609	=over 4
		3610
		3611	=item The winsocket select function
		3612
		3613	The winsocket C<select> function doesn't follow POSIX in that it
		3614	requires socket I<handles> and not socket I<file descriptors> (it is
		3615	also extremely buggy). This makes select very inefficient, and also
		3616	requires a mapping from file descriptors to socket handles (the Microsoft
		3617	C runtime provides the function C<_open_osfhandle> for this). See the
		3618	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3619	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3620
		3621	The configuration for a "naked" win32 using the Microsoft runtime
		3622	libraries and raw winsocket select is:
		3623
		3624	#define EV_USE_SELECT 1
		3625	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3626
		3627	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3628	complexity in the O(n²) range when using win32.
		3629
		3630	=item Limited number of file descriptors
		3631
		3632	Windows has numerous arbitrary (and low) limits on things.
		3633
		3634	Early versions of winsocket's select only supported waiting for a maximum
		3635	of C<64> handles (probably owning to the fact that all windows kernels
		3636	can only wait for C<64> things at the same time internally; Microsoft
		3637	recommends spawning a chain of threads and wait for 63 handles and the
		3638	previous thread in each. Great).
		3639
		3640	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3641	to some high number (e.g. C<2048>) before compiling the winsocket select
		3642	call (which might be in libev or elsewhere, for example, perl does its own
		3643	select emulation on windows).
		3644
		3645	Another limit is the number of file descriptors in the Microsoft runtime
		3646	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3647	or something like this inside Microsoft). You can increase this by calling
		3648	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3649	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3650	libraries.
		3651
		3652	This might get you to about C<512> or C<2048> sockets (depending on
		3653	windows version and/or the phase of the moon). To get more, you need to
		3654	wrap all I/O functions and provide your own fd management, but the cost of
		3655	calling select (O(n²)) will likely make this unworkable.
		3656
		3657	=back
		3658
		3659	=head2 PORTABILITY REQUIREMENTS
		3660
		3661	In addition to a working ISO-C implementation and of course the
		3662	backend-specific APIs, libev relies on a few additional extensions:
		3663
		3664	=over 4
		3665
		3666	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3667	calling conventions regardless of C<ev_watcher_type *>.
		3668
		3669	Libev assumes not only that all watcher pointers have the same internal
		3670	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3671	assumes that the same (machine) code can be used to call any watcher
		3672	callback: The watcher callbacks have different type signatures, but libev
		3673	calls them using an C<ev_watcher *> internally.
		3674
		3675	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3676
		3677	The type C<sig_atomic_t volatile> (or whatever is defined as
		3678	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3679	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3680	believed to be sufficiently portable.
		3681
		3682	=item C<sigprocmask> must work in a threaded environment
		3683
		3684	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3685	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3686	pthread implementations will either allow C<sigprocmask> in the "main
		3687	thread" or will block signals process-wide, both behaviours would
		3688	be compatible with libev. Interaction between C<sigprocmask> and
		3689	C<pthread_sigmask> could complicate things, however.
		3690
		3691	The most portable way to handle signals is to block signals in all threads
		3692	except the initial one, and run the default loop in the initial thread as
		3693	well.
		3694
		3695	=item C<long> must be large enough for common memory allocation sizes
		3696
		3697	To improve portability and simplify its API, libev uses C<long> internally
		3698	instead of C<size_t> when allocating its data structures. On non-POSIX
		3699	systems (Microsoft...) this might be unexpectedly low, but is still at
		3700	least 31 bits everywhere, which is enough for hundreds of millions of
		3701	watchers.
		3702
		3703	=item C<double> must hold a time value in seconds with enough accuracy
		3704
		3705	The type C<double> is used to represent timestamps. It is required to
		3706	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3707	enough for at least into the year 4000. This requirement is fulfilled by
		3708	implementations implementing IEEE 754 (basically all existing ones).
		3709
		3710	=back
		3711
		3712	If you know of other additional requirements drop me a note.
		3713
		3714
		3715	=head1 ALGORITHMIC COMPLEXITIES
		3716
		3717	In this section the complexities of (many of) the algorithms used inside
		3718	libev will be documented. For complexity discussions about backends see
		3719	the documentation for C<ev_default_init>.
		3720
		3721	All of the following are about amortised time: If an array needs to be
		3722	extended, libev needs to realloc and move the whole array, but this
		3723	happens asymptotically rarer with higher number of elements, so O(1) might
		3724	mean that libev does a lengthy realloc operation in rare cases, but on
		3725	average it is much faster and asymptotically approaches constant time.
		3726
		3727	=over 4
		3728
		3729	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3730
		3731	This means that, when you have a watcher that triggers in one hour and
		3732	there are 100 watchers that would trigger before that, then inserting will
		3733	have to skip roughly seven (C<ld 100>) of these watchers.
		3734
		3735	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3736
		3737	That means that changing a timer costs less than removing/adding them,
		3738	as only the relative motion in the event queue has to be paid for.
		3739
		3740	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3741
		3742	These just add the watcher into an array or at the head of a list.
		3743
		3744	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3745
		3746	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3747
		3748	These watchers are stored in lists, so they need to be walked to find the
		3749	correct watcher to remove. The lists are usually short (you don't usually
		3750	have many watchers waiting for the same fd or signal: one is typical, two
		3751	is rare).
		3752
		3753	=item Finding the next timer in each loop iteration: O(1)
		3754
		3755	By virtue of using a binary or 4-heap, the next timer is always found at a
		3756	fixed position in the storage array.
		3757
		3758	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3759
		3760	A change means an I/O watcher gets started or stopped, which requires
		3761	libev to recalculate its status (and possibly tell the kernel, depending
		3762	on backend and whether C<ev_io_set> was used).
		3763
		3764	=item Activating one watcher (putting it into the pending state): O(1)
		3765
		3766	=item Priority handling: O(number_of_priorities)
		3767
		3768	Priorities are implemented by allocating some space for each
		3769	priority. When doing priority-based operations, libev usually has to
		3770	linearly search all the priorities, but starting/stopping and activating
		3771	watchers becomes O(1) with respect to priority handling.
		3772
		3773	=item Sending an ev_async: O(1)
		3774
		3775	=item Processing ev_async_send: O(number_of_async_watchers)
		3776
		3777	=item Processing signals: O(max_signal_number)
		3778
		3779	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3780	calls in the current loop iteration. Checking for async and signal events
		3781	involves iterating over all running async watchers or all signal numbers.
		3782
		3783	=back
		3784
1217		3785
1218	=head1 AUTHOR	3786	=head1 AUTHOR
1219		3787
1220	Marc Lehmann <libev@schmorp.de>.	3788	Marc Lehmann <libev@schmorp.de>.
1221		3789

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